Waste Minimization and Cost Reduction for the Process Industries

WASTE MINIMIZATION AND COST REDUCTION FOR THE PROCESS INDUSTRIES

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WASTE MINIMIZATION AND COST REDUCTION FOR THE PROCESS INDUSTRIES

Paul N. Cheremisinoff, P.E., D.E.E. Professor New Jersey Institute of Technology

NOYES PUBLICATIONS Park Ridge, New Jersey, U S A .

Copyright 0 1995 by Paul N. Cheremisinoff No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without permission in writing from the Publisher. Library of Congress Catalog Card Number: 95-4917 ISBN: 0-8155-1388-7 Printed in the United States Published in the United States of America by Noyes Publications Mill Road, Park Ridge, New Jersey 07656 10 9 8 7 6 5 4 3 2 1

Library of Congress Cataloging-in-Publication Data Cheremisinoff, Paul N. Waste minimization and cost reduction for the process industries / by Paul N. Cheremisinoff. an. p. Includes index. ISBN 0-8155-1388-7 1. Chemical industry--Waste disposal. 2. Waste minimization. I. Title. TD899.C5C49 1995 660'.28--dcU) 95-4917

CIP

ABOUT THE AUTHOR Paul N. Cheremisinoff, P.E. has been involved for more than 45 years with industry and academia. Experienced in research, design and consulting for a wide range of government and industrial organizations. He is author and co-author of numerous papers and books on the environment, energy, and resources and is a licensed professional engineer, member of Sigma Xi and Tau Beta Pi, and a Diplomate of the American Academy of Environmental Engineers.

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The purpose of this book is to provide a base of information and analysis to assist in implementation of the policy of reducing and/or minimizing hazardous waste generation in manufacturing and more specifically in the process industries. What is the significance of reducing the generation of all process wastes? This book examines the technical nature of waste reduction and the extent to which waste reduction can likely be implemented. Also explored is the extent to which technology itself as well as information and resources are a barrier to waste reduction? In what ways are waste reduction decisions dependent on specific circumstances? Can the amount of feasible waste reduction be estimated? Auditing of manufacturing and unit operations and processes are particularly significant and useful in the chemical process industries (food, pharmaceuticals, chemicals, fertilizer, petrochemicals, etc.) since it is estimated that these industries account for more than half of the hazardous wastes generated. This book presents a compilation of complete information on potential sources of waste loss or generation through technical inspection. Also presented are calculation methods for determining air/waste/solid wastes material balances, informational requirements and waste reduction analysis. This book is an outgrowth from the author's assignment by the United Nations Economic and Social Commission for Asia and the Pacific on waste auditing and reduction. As a result of concern over hazardous waste issues in the Southeast Asia region a project on industrial auditing and waste minimization was initiated. Materials, views, references were collected, some of which are described here. The data and information covers many appropriate industries as case specific studies and examples. The reader should find the book useful in the areas of auditing and waste minimization. It is replete with useful information as well as specific case histories which should make it a practical tool for the user. Paul N. Cheremisinoff vii

NOTICE To the best of our knowledge the information in this publication is accurate; however, the Publisher does not assume any responsibility or liability for the accuracy or completeness of, or consequences arising from, such information. This book is intended for informational purposes only. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the Publisher. Final determination of the suitability of any information or product for use contemplated by any user, and the manner of that use, is the sole responsibility of the user. We recommend that anyone intending to rely on any recommendation of materials or procedures mentioned in this publication should satisfy himself as to such suitability, and that he can meet all applicable safety and health standards.

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CONTENTS

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1 WASTE REDUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Definitions Used in This Book . . . . . . . . . . . . . . . . . . . . 2 Waste Reduction Approaches . . . . . . . . . . . . . . . . . . . . . 7 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Prevention and Control . . . . . . . . . . . . . . . . . . . . . . . . . 10 Waste Reduction? What Is It? . . . . . . . . . . . . . . . . . . . 11 Definitions of Waste Reduction and Similar Terms . . . . . 11 Recycling ................................. 12 International Dimensions . . . . . . . . . . . . . . . . . . . . . . . . 14 Waste Reduction Methods ....................... 14 Broad Approaches to Waste Reduction . . . . . . . . . . . . . . 15 15 Process Recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . Technology and Equipment Changes . . . . . . . . . . . . . . . 16 Process Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Effect on Products . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 Waste Reduction Methods Selection and Practice . . . . . . 17 Waste Reduction Examples . . . . . . . . . . . . . . . . . . . . . . 19 Organic Solvents Replacement . . . . . . . . . . . . . . . . . . . 19 Solvent Recovery from Processes . . . . . . . . . . . . . . . . . 20 Mechanical Processes ......................... 20 21 Vapor Loss Prevention . . . . . . . . . . . . . . . . . . . . . . . . 21 Process Water Use Reduction . . . . . . . . . . . . . . . . . . . . 22 Limits of Applicability . . . . . . . . . . . . . . . . . . . . . . . . Waste Reduction Decisions . . . . . . . . . . . . . . . . . . . . . . . 22 The Waste Reduction Audit . . . . . . . . . . . . . . . . . . . . . 23 Hazardous Substances Identification . . . . . . . . . . . . . . . 23 Source(s) of Hazardous Substance(s) . . . . . . . . . . . . . . . 24 Waste Reduction Priorities ...................... 24 Technically and Economically Feasible Waste 24 Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Contents Waste Reduction Alternatives to Waste Management 25 Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Waste Reduction Incentives . . . . . . . . . . . . . . . . . . . . . Industrial Process Characteristics . . . . . . . . . . . . . . . . . 25 Technology and Information . . . . . . . . . . . . . . . . . . . . . 28 Worker Training . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 Waste Reduction Economics . . . . . . . . . . . . . . . . . . . . 30 Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 How Much Waste Reduction ..................... 31 Waste Reduction Technology Availability . . . . . . . . . . . 32 Competition from Waste Management . . . . . . . . . . . . . . 33 Waste Reduction Data . . . . . . . . . . . . . . . . . . . . . . . . . . 34 Information Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Waste Reduction Audit . . . . . . . . . . . . . . . . . . . . . . . . 35 Identification of Hazardous Substances . . . . . . . . . . . . . 36 Identification of the Source(s) of Hazardous Substances and Wastes . . . . . . . . . . . . . . . . . . . . . . . 36 Priorities for Waste Reduction . . . . . . . . . . . . . . . . . . . 37 Technically and Economically Feasible Reduction . . . . . . 37 Waste Reduction and Waste Management Options . . . . . 38 Waste Reduction Measures . . . . . . . . . . . . . . . . . . . . . 38 Waste Costs Charges . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Waste Reduction Information . . . . . . . . . . . . . . . . . . . . . 40 Waste Reduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Measure Waste Reduction . . . . . . . . . . . . . . . . . . . . . . . 42 Hazardous Waste Reduction ..................... 44 International Perspective . . . . . . . . . . . . . . . . . . . . . . . . 49 50 Multilateral Organizations . . . . . . . . . . . . . . . . . . . . . .

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2 AUDITING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Environmental Factors and Audit Summary Checklist Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Audit Team . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . An Important Tool . . . . . . . . . . . . . . . . . . . . . . . . . . . Importance of the Audit . . . . . . . . . . . . . . . . . . . . . . . . Developing Resources . . . . . . . . . . . . . . . . . . . . . . . . . Audit Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Protocols and Questionnaires . . . . . . . . . . . . . . . . . . . . Field Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

52 . . 53 55 57 58 59 59 60 61 63 64 65

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Working Papers and Recordkeeping . . . . . . . . . . . . . . . 67 Evaluation of Findings and Exit Interviews . . . . . . . . . . 68 70 Audit Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3 WASTE MINIMIZATION DATMNFORMATION REQUIREMENTS-A GENERAL APPROACH FOR MANUFACTURING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 Getting Started-Step 1 . . . . . . . . . . . . . . . . . . . . . . . . . 73 List Process Steps and Identify Wasteful Streams . . . . . . 76 Analyzing Process Steps-Preparing Process Flow 76 Charts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 Material and Energy Balances Assign Costs to Waste Streams . . . . . . . . . . . . . . . . . . 80 Process to Identify Causes . . . . . . . . . . . . . . . . . . . . . . 81 Poor Housekeeping . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Operational and Maintenance Negligence . . . . . . . . . . . . 81 Poor Raw Material Quality . . . . . . . . . . . . . . . . . . . . . 83 Poor Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 Managerial Cases. Inadequately Trained Personnel . . . . . 83 Employee Demotivation . . . . . . . . . . . . . . . . . . . . . . . 83 84 Developing Opportunities . . . . . . . . . . . . . . . . . . . . . . Workable Waste Minimization Selection . . . . . . . . . . . . 84 Technical Feasibility . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Economic Viability . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 Environmental Aspects . . . . . . . . . . . . . . . . . . . . . . . . . 88 Implementation Solutions . . . . . . . . . . . . . . . . . . . . . . . . 88 Monitor and Evaluate Results . . . . . . . . . . . . . . . . . . . . 89 Audit StudieMummary Section . . . . . . . . . . . . . . . . . . 90 Objective . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 90 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Post-Audit Activities . . . . . . . . . . . . . . . . . . . . . . . . . Problems Encountered During the Audit . . . . . . . . . . . . 91 91 Aspects Covered . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Status of Pollution Control . . . . . . . . . . . . . . . . . . . . . . 91 Performance Study . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 Reports of Audit Studies . . . . . . . . . . . . . . . . . . . . . . . 92 Housekeepinflaste Reduction Practices for Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 Suggested Housekeeping Measures . . . . . . . . . . . . . . . . 93 Identification Required of Water Pollution Sources for Waste ReductiodMinimization Potentials . . . . . . . 96

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Contents

. . 104 Data to be Determined . . . . . . . . . . . . . . . . . . . . . . . . . 104 Sources of Wastes/Releases . . . . . . . . . . . . . . . . . . . . . . 104 Overview of Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 106 Definitions of Major Approaches . . . . . . . . . . . . . . . . . 108 Observations on the Use of Data . . . . . . . . . . . . . . . . . 109 Approach to Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 111 Fugitive Air Emissions . . . . . . . . . . . . . . . . . . . . . . . Point Source Air Emission . . . . . . . . . . . . . . . . . . . . . 111 Releases to Wastewater . . . . . . . . . . . . . . . . . . . . . . . 112 Release in Solids. Slurries. and Nonaqueous Liquids . . . 112 Estimating Releases to Air . . . . . . . . . . . . . . . . . . . . . . 113 Sources of Release to Air and Release Estimation Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 113 Process Vents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 Estimating Releases in Wastewater . . . . . . . . . . . . . . . . 126 Sources of Wastewater and Methods for its Disposal . . . 126 Direct Discharge to Surface Waters . . . . . . . . . . . . . . . 127 Discharge to Sewers . . . . . . . . . . . . . . . . . . . . . . . . . 127 128 Underground Injection . . . . . . . . . . . . . . . . . . . . . . . . Surface Impoundments . . . . . . . . . . . . . . . . . . . . . . . 128 Land Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 Calculating Releases in Wastewater . . . . . . . . . . . . . . . 128 Direct Measurement . . . . . . . . . . . . . . . . . . . . . . . . . 129 Releases Based on Total Annual Volume and Average 129 Measured Concentration ..................... Sources and Disposal Methods for Solid. Slurry and Nonaqueous Liquid Wastes . . . . . . . . . . . . . . . . . . . . 138 Landfilling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Land Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 Underground Injection . . . . . . . . . . . . . . . . . . . . . . . . 139 Surface Impoundments . . . . . . . . . . . . . . . . . . . . . . . 139 Methods for Calculating Releases in Solid. Slurry and Nonaqueous Liquid Wastes . . . . . . . . . . . . . . . . 140

4 ESTIMATING RELEASES TO THE ENVIRONMENT

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5 WASTE QUESTIONNAIRES-WATER

CONTROL CHECKLIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Model Questionnaires . . . . . . . . . . . . . . . . . . . . . . . . . Water Pollution Control Audit Questionnaire . . . . . . . . Air Pollution Control Questionnaire . . . . . . . . . . . . . .

146 147 147 149

Contents Solid and Hazardous Waste Questionnaire . . . . . . . . . . Environmentally Safe Layout for Manufacturing Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Guidelines to Minimize Material Losses and Wastes . . . How to Reduce Raw Material Losses . . . . . . . . . . . . . How to Reduce Water Usage and Wastewater Generation in Process Streams . . . . . . . . . . . . . . . . How to Reduce Emissions .....................

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6 ANALYSIS OF PROCESS CHEMISTRY EXAMPLE PROCESSES . . . . . . . . . . . . . . . . . . . . . . . . . Draft Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Post Audit Activities . . . . . . . . . . . . . . . . . . . . . . . . . Evaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acetic Acid by Methanol Carbonylation . . . . . . . . . . . . Industry Description . . . . . . . . . . . . . . . . . . . . . . . . . Methanol Carbonylation Process Description . . . . . . . . Monsanto Process . . . . . . . . . . . . . . . . . . . . . . . . . . . BASF Process (Reppe Process) . . . . . . . . . . . . . . . . . . Process Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . Analysis of the Monsanto Methanol Carbonylation Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Process Waste Streams . . . . . . . . . . . . . . . . . . . . . . . Acetaldehyde by Liquid-Phase Ethylene Oxidation . . . . Process Descriptions for Oxidizing Ethylene to Acetaldehyde . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . One-Stage Process .......................... Two-Stage Process . . . . . . . . . . . . . . . . . . . . . . . . . . Process Comparison . . . . . . . . . . . . . . . . . . . . . . . . . Process Chemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . Analysis of the Wacker-Hoechst Process for the Oxidation of Ethylene to Acetaldehyde . . . . . . . . . . . Process Waste Discharges . . . . . . . . . . . . . . . . . . . . . Single-Stage Process Waste Streams . . . . . . . . . . . . . . Two-Stage Process Waste Streams . . . . . . . . . . . . . . .

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7 INDUSTRY PROFILIGFERTILIZERS . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Manufacturing Processes . . . . . . . . . . . . . . . . . . . . . . . Gasification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shift Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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156 158 158 159 160 162 165 165 165 167 167 167 167 173 173 177 184 185 188 189 192 194 194 201 214 214 218 222 222 224 224 228

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Contents Carbon Dioxide Recovery and Gas Purification . . . . . . 228 229 Urea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ammonium Sulphate . . . . . . . . . . . . . . . . . . . . . . . . . 231 234 Ammonium Chloride . . . . . . . . . . . . . . . . . . . . . . . . . Calcium Ammonium Nitrate (CAN) . . . . . . . . . . . . . . 234 234 Nitric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulphuric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 Phosphoric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . 238 Single Super Phosphate (SSP) . . . . . . . . . . . . . . . . . . 242 Triple Superphosphate (TSP) . . . . . . . . . . . . . . . . . . . 242 Diammonium Phosphate (DAP) . . . . . . . . . . . . . . . . . 242 246 Nitrophosphate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ammonium Phosphate Sulphate . . . . . . . . . . . . . . . . . 248 248 Urea Ammonium Phosphate . . . . . . . . . . . . . . . . . . . . NPK Complex Fertilizer . . . . . . . . . . . . . . . . . . . . . . 248 Raw Water Supply and Treatment . . . . . . . . . . . . . . . . 253 253 Demineralization (DM) . . . . . . . . . . . . . . . . . . . . . . . Steam and Power Generation . . . . . . . . . . . . . . . . . . . 254 254 Material Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . Effluent Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . 254 Generation of Impurities and Pollutants . . . . . . . . . . . . 255 255 Ammonia Plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Steam Reformation Process . . . . . . . . . . . . . . . . . . . . 256 UreaPlant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257 Ammonium Sulphate . . . . . . . . . . . . . . . . . . . . . . . . . Ammonium Chloride . . . . . . . . . . . . . . . . . . . . . . . . . 257 Calcium Ammonium Nitrate (CAN) . . . . . . . . . . . . . . 258 Nitric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Sulphuric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 258 Phosphoric Acid . . . . . . . . . . . . . . . . . . . . . . . . . . . . Single Super Phosphate (SSP) . . . . . . . . . . . . . . . . . . 259 259 Triple Super Phosphate . . . . . . . . . . . . . . . . . . . . . . . Diammonium Phosphate (DAP) . . . . . . . . . . . . . . . . . 259 260 Nitrophosphate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ammonium Phosphate Sulphate (APS) . . . . . . . . . . . . 260 Urea Ammonium Phosphate (UAP) . . . . . . . . . . . . . . . 260 NPK Complex Fertilizer . . . . . . . . . . . . . . . . . . . . . . 261 261 Demineralization of Water . . . . . . . . . . . . . . . . . . . . . Steam and Power Generation . . . . . . . . . . . . . . . . . . . 261 261 Cooling Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Accidental Spills . . . . . . . . . . . . . . . . . . . . . . . . . . . 262

Contents

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Pollutant Pararnete-Effects . . . . . . . . . . . . . . . . . . . 262 264 Wastewater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Solid Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269 Abatement of Pollution . . . . . . . . . . . . . . . . . . . . . . . . 269 Segregation of Process Effluent . . . . . . . . . . . . . . . . . 270 Segregation of Cooling Water . . . . . . . . . . . . . . . . . . 270 Monitoring of Effluents ....................... 271 Carbon Slurry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 Cyanide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 Process Condensate . . . . . . . . . . . . . . . . . . . . . . . . . . 271 Arsenical Waste . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 271 Purge Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271 Vacuum Condensate ......................... 272 Captive Storage Tank . . . . . . . . . . . . . . . . . . . . . . . . Prilling Tower Dedusting System . . . . . . . . . . . . . . . . 272 Urea Dust Scrubber . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Urea Solution Recycle . . . . . . . . . . . . . . . . . . . . . . . . 275 275 Ammonium Salt Plants . . . . . . . . . . . . . . . . . . . . . . . Nitric Acid Plant Emission . . . . . . . . . . . . . . . . . . . . 275 Sulphuric Acid Plant Emission . . . . . . . . . . . . . . . . . . 278 Hydrofluosilicic Acid Recovery . . . . . . . . . . . . . . . . . 278 Dedusting During the Rock Phosphate Grinding . . . . . . . 280 280 Fume Scrubber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 Gypsum Conveying System . . . . . . . . . . . . . . . . . . . . Scrubber Water Recycle . . . . . . . . . . . . . . . . . . . . . . . 280 Emission Control in DAP Plant . . . . . . . . . . . . . . . . . 280 Nitrophosphate, Ammonium Phosphate Sulphate, Urea Ammonium Phosphate and NPK Complex Fertilizer Plants Effluent Control . . . . . . . . . . . . . . . 281 Dust Emission and Oil Pollution During Raw Material Handling . . . . . . . . . . . . . . . . . . . . . . . . . 281 Raw Water Treatment Plant Sludge . . . . . . . . . . . . . . . 281 Demineralization Plant Effluents . . . . . . . . . . . . . . . . . 281 Boiler House Flue Gas . . . . . . . . . . . . . . . . . . . . . . . 281 Oil Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281 Cooling Tower Blowdown Water . . . . . . . . . . . . . . . . 281 Evaluation of Process Treatment of Effluent . . . . . . . . . 282 282 Evaluation of Effluent . . . . . . . . . . . . . . . . . . . . . . . . Assessment from Design Figures . . . . . . . . . . . . . . . . 282 Assessment from Actual Measurements . . . . . . . . . . . . 282

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Contents Experience of Other Operating Plants . . . . . . . . . . . . . 283 283 Disposal of Effluent . . . . . . . . . . . . . . . . . . . . . . . . . Study of the Receiving Water . . . . . . . . . . . . . . . . . . . 284 Disposal to Lagoon for Irrigation . . . . . . . . . . . . . . . . 284

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8 TREATMENT OF EFFLUENT FERTILIZER INDUSTRY 285 EXAMPLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nitrogenous Pollutants ......................... 285 Ammoniacal Nitrogen 286 Air Stripping of Ammonia . . . . . . . . . . . . . . . . . . . . . 286 Steam Stripping . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 Ion Exchange Process . . . . . . . . . . . . . . . . . . . . . . . . 291 Recovery of Ammonia with Disposal of Water . . . . . . . 291 Recovery of Ammonia and Water . . . . . . . . . . . . . . . . 295 Biological Nitrification and Denitrification . . . . . . . . . . 297 Biological Nitrification . . . . . . . . . . . . . . . . . . . . . . . 299 300 Biological Denitrification . . . . . . . . . . . . . . . . . . . . . . Biological Nitrification and Denitrification . . . . . . . . . . 301 Algal Uptake . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 Organic Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 Oxidized Nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 Other Constituents . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 Arsenic. Monoethanolamine (MEA). Methanol and Vanadium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 Arsenic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 Monoethanolamine ( M U ) and Methanol . . . . . . . . . . . 307 Vanadium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 Cyanide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 Sulphide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 Fluoride and Phosphate . . . . . . . . . . . . . . . . . . . . . . . 312 Oil and Grease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 Chromate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315 Total Dissolved Solids ( T D S ) . . . . . . . . . . . . . . . . . . . 317 Suspended Solids . . . . . . . . . . . . . . . . . . . . . . . . . . . 317 Acid and Alkali . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320 Biochemical Oxygen Demand (BOD) . . . . . . . . . . . . . 320 Recovery, Reuse and Recycle in the Process . . . . . . . . . 320 Conservation of Water . . . . . . . . . . . . . . . . . . . . . . . . 320 Recoveries from Wastes and Byproducts . . . . . . . . . . . 322 Housekeeping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323

Contents

xvii

Separation Technologies for Removal of Organic and Pesticidal Chemicals from Wastewater . . . . . . . . 324

INDEX

........................................

325

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CHAFTER 1 WASTE REDUCTION Waste reduction is an economically sensible response to what many people see as a hazardous waste crisis. Several thousand pounds of hazardous waste are generated annually for every person in the world. Many thousands of people have lost their drinking water because of contamination by toxic waste. Across the world there are thousands of sites contaminated by hazardous waste that require billions of dollars for cleanup. An increasing number of lawsuits are being brought by people who claim to have suffered adverse health effects from living near toxic waste sites. Also the number of lawsuits being instituted by governments is mounting rapidly. Suits claim that certain waste generators have not complied with regulations and that generators who have used waste management facilities must pay for cleanups. More significant is the fact that such processes are inefficent and more expensive than they should be. Waste reduction and waste auditing is critical to the prevention of future hazardous waste problems. By reducing the generation of waste, materials can be used more efficiently and achieve more certain protection for health and the environment. At the same time, industry can lower waste management and regulatory compliance costs, liabilities, and risks. Although there are many environmental and economic benefits to waste reduction, over 99 percent of environmental spending is devoted to controlling pollution after waste is generated. Less than 1percent is spent to reduce the generation of waste. Since many hazardous substances are not as yet regulated, annual expenditures, in all likelihood, will continue to increase in light of risks and liabilities involved and irregardless of regulation changes. 1

2

Waste Minimization

Reducing waste to prevent pollution from being generated at its source is now a practical way to complement costly pollution control as well as being economically desirable in many cases. Because of sporadic and uneven enforcement, the current regulatory system weakens the incentive to reduce waste. Waste reduction, no matter how far it is taken, cannot eliminate all wastes, but it can help to lower costs for environmental protection as economics continue to expand. Figures 1through 4 show typical audit data requirements that preceed any waste reduction program.

Definitions Used in This Book Waste Reduction: In-plant practices that reduce, avoid, or eliminate the generation of hazardous waste so as to reduce risks to health and environment and improve productivity. Actions taken away from the waste generating activity, including waste recycling or treatment of wastes after they are generated, are not considered waste reduction. Also, an action that merely concentrates the hazardous content of a waste to reduce waste volume or dilutes it to reduce degree of hazard is not considered waste reduction. This definition is meant to be consistent with the goal of preventing the generation of waste at its source rather than controlling, treating, or managing waste after its generation. Hazardous Waste: All nonproduct or product hazardous outputs from an industrial operation into all environmental media, even though they may be within permitted limits. This is broader than the legal definition of hazardous solid waste. Hazardous refers to harm to human health or the environment and is broader than the term "toxic." For example, wastes that are hazardous because of their corrosivity, flammability, explosiveness, or infectiousness are not normally considered toxic. Waste Audit: The inventory and information gathering aspect to determine how much; composition and other data which defines waste reduction and hazardous waste. Current pollution control methods often do little more than move waste around. For example: air and water pollution control devices typically generate solid, hazardous waste that goes to landfills and too often leaches from there into groundwater. Many hazardous wastes, such as most toxic air emissions, and permissible emissions legally sanction the generation of some wastes. Establishing a comprehensive, multimedia approach to reducing wastes going into the air, land, and water is essential.

Waste Reduction -~PRE-AUDIT

ACTIVITIES

3

fSYNTHESIS: .INTERVIEWS WITH CROSS SECTION OF STAFF .VERIFICATION OF RECORDS OF THE COMPANY .FIELD INSPECTION

MATERIAL BALANCE:

OBTAI,N PRELIMINARY INFORMATONS THROUGH QUESTONNAIRE SURVEY

REVIEW AND IDENTIFY MAIN AREAS OF CONSIDERATKIN

.DETERMINE PROCESS INPUTS, RECORD WASTE USAGE AND OF RECYCLE/REUSE .DETERMINE PROCESS OUTPUTS QUANTIFY PRODUCTS/BYPRODUCTS, ACCOUNT FOR WASTE WATER. EMltSIONS AND SOLID/HAZ. WASTE .INCORPORATE DATA ON PROCESS FLOW SHEETS, OERIVE HATERIAL BALANCE AND WATER BALANCE

PREPARE AUDIT TEAM

c3

ORGANISE RESOURCES

c3

DEVELOP VISIT PROGRAMM

c9

4LLOCATE S P E C M ’ASK TO TEAM MEMBERS

.EVALUATE THE‘ TECHNICAL AND ATTITUDINAC CAPABILITIES OF STAFF .FORMULATE RECOMMENDATIONS FOR THE BEST PRACTICA6LE WASTE MANAGEMENT

G WASTE FLOW:

L3

.EVALUATE PERFORMANCE 6 ADEaAC’I JF THE WASTE TREATMENT FAClLlTlE .IDfNTFY THE PROBLEMS RELATE0 T WASTE GENERATION, TREATMNT AND DISPOSAL .SEGREGATE WASTE ANO IDENTIFY WASTE REDUCTION MEASURES

.IDENTIFY WASTE FLOW LINES .OBTAIN DETAILS OF PRETREATMENT AN0 FINAL TREATMENT .OBTAIN DETAILS OF OISPOSAL

MONITORING L ANALYSIS: .DESIGN MONITORING NETWORK FOR SAMPLING WASTEWATER, SOLID WASTE, PERFORMANCE STUDY OF TREATMEYT FACILITIES AND THE RECEVING ENVIRONMENT I IDENTIFY PARAMETERS FOR ANALYSIS ,DETERMINE TYPE AND FREQUENCY OF SAMPLING ,ANALYSE SAMPLES

G

CONCLUDING SESSION: ,DRAFT REPORT PREPARATION ,PRESENTATION OF ORAFT REPORT AN0 DISCUSStON WITH THE MANAGEMENT

Figure 1-1: Environment audit procedure.

FINAL REPORT PREPARATKW WITH RECDMMENDATl&

ACTON PLANS WITH

M

FRAME FOR MPLEMENTATlON

FOLLOW-UP

4

Waste Minimization

Consent to surveying

I

Assessment criteria

inhabitants

Views

review

I

1 prefedural governor

I

4

Figure 1-2: A flow of the environmental impact assessment process (in the case of a thermal power plant project).

I

pollution control measures

I Fuel measures

Facility measures

I emissions

(>

Control of

Use of good quality fuels combustion methods

emissions

.... ....................................................

Use of LNG Direct combustion of crude oil Use of light oil Use of good quality coal Use of low-sulfur fuel oil

Flue gas recirculation Two-stage combustion Low-NOx burner Installation of flue gas denitrificationfacilities

Figure 1-3: An outline of air pollution control measures.

Operational measures

-7 Thoroughgoing combustion control, monitoring of pollution sources, etc.

6

Waste Minimization

r---+GAsEOUS

EMISSIONS

I I

I

I

RAW MATERIALS

I

CATALYST

)

>

WATER /AIR

PRODUCT

PLANT PROCESS

BY PRODUCTS

OR UNIT OPERATION

POWER

>

r

1

Recycle

I I

I--

CATALYST

-> RECOVERY FROM WASTE j WASTEWATER

I

I L--I

I

REUSABLE WASTE IN ANOTHER OPERATION

LIQUID WASTES FOR STORAGE AND I OR O F F SITE DISPOSAL +SOLID WASTES FOR STORAGE AND I OR OFF SITE DISPOSAL

Figure 1-4: A typical unit operation material balance.

Waste Reduction

7

There is no common definition of waste reduction. There are few or no data on the extent of industrial waste reduction. Waste reduction is usually measured and the information that is collected on waste generation is generally not useful for waste reduction. If waste reduction is defined to include waste treatment, companies will naturally pay more attention to treatment, which is a familiar activity, than to the reduction of waste. Problems of definition and lack of information should be addressed and ongoing waste reduction efforts should be documented by auditing even if decisions to reduce waste remain at the discretion of individuals. Despite some claims to the contrary, advantage is not taken of all effective waste reduction opportunities that are available. Reducing waste involves more than buying a black box, reading the directions, and plugging it in. Even a simple step toward waste reduction can seem difficult with few technical resources and no obvious place to go for guidance. Reducing waste in an industrial process requires intimate knowledge of all aspects of that specific production process, in contrast to waste treatment, which is essentially an add on to the end of the process. There are also clear pressures to reduce waste tomorrow, rather than today. The attention and resources given to required pollution control activities limit the amount of thought, time, and money that industry can devote to waste reduction. Some, however, have verified the fact that waste reduction pays for itself quickly, especially when compared to the time needed to comply with regulations, obtain regulatory permits, or site waste management facilities. Some are even beginning to sell new products and services that help others to reduce waste. Waste reduction succeeds when it is part of the everyday consciousness of those involved with production-where the waste reduction opportunities are-rather than when it is a job only of those responsible for complying with environmental regulations. A few people with end-of-pipe, pollution control jobs are not in a position to reduce waste by themselves; such efforts must involve upstream workers, facilities and management.

Waste Reduction Approaches There are five approaches that industry can take to reduce hazardous waste including: 0 0

change the raw materials of production, change production technology and equipment,

8

Waste Minimization 0 0

0

improve production operations and procedures, recycle waste within the plant, and design or reformulate end-products.

Opportunities that exist for common processes and wastes are: 0

0

0

0

using mechanical techniques rather than toxic organic solvents to clean metal surfaces, using water-based raw materials instead of materials based on organic solvents, and changing plant practices to generate less hazardous wastewater improve housekeeping and materials handling procedures.

So far regulators have not required waste reduction. The impact on industry, particularly on troubled manufacturing sectors, could be substantial. Alternatively, we could move to an economically sensible environmental protection strategy based on both pollution control (waste management) and pollution prevention (waste reduction) with auditing providing leadership and assistance. The first need is policy development, education, and oversight. Also, there is a need for innovative engineering and management. Opportunities are embedded in every part of the industrial production system. There is no way to predetermine the amount of waste reduction possible; its technical and economic feasibility depend on the characteristics, circumstances, and goals of specific waste generators. Success in reducing waste depends on the ability of organizations to modernize, innovate, and cut costs, increasing profits and reducing long-term liabilities. Waste reduction could be used as a measure of performance as energy efficiency and productivity often are possible legislative actions that could clarify the definition of waste reduction, spur better collection of information on waste reduction, and encourage more attention to the subject.

BACKGROUND Environmental protection efforts emphasize control and cleanup of pollution by hazardous substances after they are generated and no longer serve a productive function. Virtually, all industries, whether high technology or other generate hazardous waste. The cost of controlling that

Waste Reduction

9

waste totals many billions of dollars annually. Usually, hazardous industrial wastes are not destroyed by pollution control methods, but they are put into the land, water, or air where they disperse and migrate. The result is that pollution control for one environmental medium can mean that waste is transferred to another medium or elsewhere. As the costs of administering environmental programs and the costs of compliance has grown the economic and environmental benefits of reducing the generation of hazardous waste at the source have become more compelling. But it is exactly these requirements and costs of complying with them that both encourage some waste reduction and make it difficult for industry to give waste reduction the priority and resources it deserves for near-term wide-scale implementation. Although current costs for pollution control serve as an indirect incentive for waste reduction, it is not certain that: 0 0

0

an incentive exists for everybody; all or most waste generators have the technical and economic resources to respond to that incentive; the incentive is consistently supported by regulatory actions.

In practice, waste reduction is frequently subordinated to pollution control, even though reducing waste can be the most effective way to prevent environmental risk. Domination of pollution control over waste reduction is not new; occurring over many years and it will not be reversed overnight. Waste reduction is the preferred anti-pollution method; but actions often send a different-or ambiguous-message to waste generators. Regulations are not the sole determinants of how much waste is reduced. Frequently, inadequate information makes it difficult for waste generators to assess the benefits of a one-time, nearer investment for waste reduction against repeated spending and ongoing liabilities over the long term for waste management. Pollution control measures are more familiar and thus more certain. Uncertainty also arises because waste reduction, as a measure of materials productivity, is subordinated to other measures of the efficiency of industrial operations, such as labor productivity and energy consumption. Waste reduction results which saves money for industry and protects the environment, is being implemented in an uneven and largely undocumented fashion. Assessing the economics of waste reduction poses problems.

10

Waste Minimization

OBJECTIVES The purpose of this book is to provide a base of information and analysis to assist in awaiting implementation of the policy of reducing the generation of hazardous waste. To explore the context for concern about waste reduction. What is the significance of reducing the generation of all hazardous industrial waste rather than only those regulated as solid, hazardous waste? Why is waste reduction important? An initial task in this was to adopt precise definitions of hazardous waste and waste reduction already given. To examine the technical-nature of waste reduction and the extent to which waste reduction is likely to be implemented. To what extent is technology itself rather than information and resources a barrier to waste reduction? In what ways are waste reduction decisions dependent on specific circumstances? Can the amount of feasible waste reduction be estimated? How much can research increase? To analyze directly or indirectly industrial waste reduction.

PREVENTION AND CONTROL Pollution controls solve no problem; they only alter the problem, shifting it from one form to another, contrary to this immutable law of nature: the form of matter may be changed, but matter does not disappear. What emerges is a paradox, it takes resources to remove pollution; pollution removal generates residue; it takes more resources to dispose of this residue and disposal of residue produces pollution. Reduction-applied to a broad universe of emissions, discharges, and wastes-is the best means of achieving pollution prevention. Developing a complementary environmental protection strategy, based on waste reduction, represents a major shift in thinking. We now have an entrenched pollution control culture, this shift would be a substantial change for industry and government. Waste reduction is implemented, pollution control regulations will always be needed for wastes that cannot be or have not yet been reduced. Emphasis on pollution control and the viewpoint that substantial waste reduction is a long-term goal, not a realizable short-term strategy, hinders the alternatives for waste generators. One inhibiting factor is concern about risking product quality by changing processes solely for the purpose of reducing waste. Waste reduction is an obvious way to offset the economic and environmental costs of managing increasing

Waste Reduction

11

amounts of wastes. Waste reduction also addresses concerns about the economic inefficiency of increasing pollution control regulations; that is, spending more and more for smaller increments in environmental protection. Environmental benefits, shows that the development and implementation of pollution control regulations takes considerable effort, time, and money. Steadily increasing environmental regulations have resulted in a growth in environmental spending. There are many factors that determine the extent of spending to protect the environment, including how much waste is generated, exactly what the law calls for, and how these regulations are enforced. Solutions present for reducing spending on the environment are: government can change regulations-for by redefining hazardous waste, or by cutting regulations and/or limiting enforcement-or generators can reduce wastes. The latter approach is more desirable; waste reduction has already demonstrated to have the capability-for some waste generators-of turning the spending down as regulations continue to increase. Decreasing environmental spending nationwide through waste reduction can occur only if regulations were to establish the primacy of waste reduction that is, of pollution prevention over waste management. From the generator's perspective, waste reduction is an alternative that reduces the costs of compliance and reduces the potential for enormous costs of later litigation. From the government's viewpoint, waste reduction does not sacrifice the integrity or environmental protection goals of pollution control regulations. From a manufacturer's viewpoint it can reduce costs.

Waste Reduction? What Is It? Waste reduction means different things to different people. Waste reduction is not a trivial pursuit, the definition of affects the design, implementation, and effectiveness of actions.

Definitions of Waste Reduction and Similar Terms Terms used to describe preferred methods of dealing with hazardous waste include: 0 0 0 0

waste waste waste waste

reduction prevention minimization avoidance

12

Waste Minimization 0 0 0

waste abatement waste elimination source reductions

Definitions include pollution control activities as well as pollution prevention activities. Among these are: 0 0 0 0

out-of-process recycling; off-site recycling; on-site or off-site treatment, such as incineration; and weight or volume reduction with a corresponding increase in concentration of hazardous content.

The distinction between preventing waste from being generated and controlling waste after it is generated is blurred when pollution control actions are included in the definition of waste reduction and similar terms. The most serious problems is that any definition included in waste management, including waste treatment and recycling away from the production site, diverts attention away from the goal of waste reduction. Waste reduction refers to in-plant practices that reduce, avoid, or eliminate the generation of hazardous waste so as to re duce risks to health and environment. The focus, therefore, is on what occurs at the source of generation. The goal of waste reduction is to alter practice and to design future processes and operations in a way that will reduce the degree of hazard of waste and the amount to be managed, controlled, and regulated.

Recycling Recycling is not considered waste reduction if waste exits a process, exists as a separate entity, involving significant handling, and transportation from the waste generating location to another site for reuse, or to an off-site recycling facility or waste exchange. This distinction does not mean that such waste management is unacceptable, or improper. Recycling is a preferred waste management alternative. Hazardous waste refers to all nonproduct hazardous outputs from an industrial operation into all environmental media, even though they may be within permitted or licensed limits. Ways to promote waste reduction: Conduct a waste reduction audit to provide information about: 0

types, amounts, and levels of hazard of wastes generated;

Waste Reduction 0 0 0

13

sources of hazard of wastes generated; sources of those wastes within the production operation; and feasible reduction techniques for those wastes.

Revise accounting methods so that both short and long-term costs of managing wastes, including liabilities, are charged to the departments and individuals responsible for the processes and operations that generate the waste. Involve all employees in waste reduction planning and implementation. Waste reduction must be seen as the responsibility of all workers and managers involved in production rather than just the responsibility of those who deal with pollution control and compliance. Motivate employees and focus attention on waste reduction by setting goals and rewarding employees' suggestions that lead to successful waste-reduction. Special education and training can help all types of employees identify waste reduction opportunities at all levels of operation and production. Transfer knowledge throughout the company so that waste reducing techniques implemented in one part of the company can benefit all divisions and plants. This is particularly important in large companies. Newsletters and company meetings can be helpful tools for disseminating information about waste reduction opportunities. Seek technical assistance from outside sources. This may be particularly useful for smaller companies with limited technical resources. Sources of outside assistance include professional consultants. Interests and actions to be considered include: 0

0

0

0

plans and commitments for waste reduction as a condition for obtaining pollution liability insurance; financial institutions may use waste reduction plans and performance as criteria to judge merits of borrowers; they view investments for waste reduction in the same way as they view traditional investments for expansion and modernization, then waste reduction efforts will be aided; some environmental organizations and public interest groups are now making waste reduction a priority issue, and its importance in trying to influence government and industry decisions and programs; and various organizations offer seminars, short courses, and conferences, which bring attention to waste reduction, and transfer technical information to people in industry.

Waste Minimization

14

It is evident that they are destined to play a role in stimulating industrial waste reduction.

INTERNATIONAL DIMENSIONS Other nations also have come to the conclusion that waste reduction is important. The degree of interest in waste reduction among governments in developing as well as industrialized nations is increasing. The United Kingdom, for example, has decided to concentrate its efforts on ensuring adequate waste management, while Japan has concentrated on promoting reuse or recycling technologies. Other governments are just beginning to take action. Canada until recently left waste reduction up to its Provinces. A serious effort was seen by the author in a mission to India and other southeast Asian countries. Most European governments such as France, the Federal Republic of Germany, Sweden, Norway, Denmark, The Netherlands, and Austria have exercised more leadership in waste reduction and have devoted more money to waste reduction than others. While the development of governmental programs to promote waste reduction dates from the early 1980s in West European countries, they have been supporting the concept of low- and non-waste technologies or clean technologies since the 1970s. Differences in definitions for hazardous waste and waste reduction also hampers comparisons.

WASTE REDUCTION METHODS Waste reduction is likely to have other consequences; which may be just as significant. Worker productivity may increase as a result of a particular waste reduction action; while product quality might decrease as a result of another action. There are costs, benefits, and site-specific constraints to waste reduction which cannot be totally predicted. The feasibility of waste reduction is in the entire production system within which it takes place. Waste reduction activities are very open-ended and very difficult to assess comprehensively. Certain activities often related to technology use and assessment and are not easily undertaken for waste reduction. Included are: 0 0

forecasting, how much waste reduction is feasible; suggesting how government might require companies to achieve

Waste Reduction

15

a given level of waste reduction. How much waste reduction is achievable depends on how much attention is given to it and on the amount of waste reduction technology available. Success in reducing waste starts with human factors and requires an examination of opportunities.

BROAD APPROACHES TO WASTE REDUCTION Developing the technical approaches to waste reduction is important because the range is so large. Approaches that are applicable to almost all industrial operations are cited.

Process Recycling Potential wastes, or its components, can be returned for reuse within existing operations. Recycling is a means of waste reduction and an integral part of production operations. An example of waste reduction by in-process recycling is countercurrent rinsing and recycling of caustic soda from bottling and packaging operations. This reduces the amount of caustic soda discharged in wastewater by altering the rinsing process washing to permit recycling of the caustic soda. Original technology included by rinsing the bottles in water baths that were discharged after use. The waste reducing technology replaces these baths with a stream of running water. Caustic gradually concentrates in the rinse water until it is efficient and cost-effective in the concentration sufficiently to allow recycling back into the process. The technology reduces both the volume and the amount of hazardous waste generated, per unit product. Major limitations to in-process recycling include: 0

0

0 0 0

differences between recycled and virgin materials and the inability to use waste that may be different than the raw materials, fluctuating market prices for virgin raw materials, continuous vs. batch processes, amounts that are too small to justify, and the process needs in some cases to perform costly steps to separate components before some of the waste can be recycled.

Waste Minimization

16

In process recycling does not require substantial testing and development or capital investment, in many cases waste reduction by this option is related to pollution control, which in part explains its wide use. Technology and Equipment Changes

Changes in the basic technology and equipment of production, including modernization, modification, or better control of process equipment may result in reduction of waste. Reduction may also come about through major changes in technology (such as a different way of making a chemical or refining a metal-bearing ore may reduce waste). Major changes may often require capital investment which may be easier to make when redesigning an entire process a new plant or operation rather than as modification to a part of an operating system. Equipment and technology changes do not necessarily require a major process overhaul. Operations in the Plant

Plant management or better housekeeping can reduce waste. Operation changes can include: 0

a

improvements in plant operations such as better maintenance; better handling of materials to reduce fugitive emissions, leaks or spills; changes in methods of equipment cleaning to avoid use of hazardous materials; monitoring of process equipment for corrosion, and leaks; automation of processing; separation of waste streams to facilitate in process recycling, and segregation covers on tanks and other actions to lessen vapor losses; more use of instrumentation to detect and prevent releases of wastes.

Floating roofs on tanks of volatile solvents, greatly reducing waste emissions is an example. Process Changes

Raw material changes either to different materials such as water instead of organic solvents or materials with different specifications such

Waste Reduction

17

as lower levels of contaminants may reduce waste. For example replace the solvent 1-1-1 trichloroethane with a water soluble cleaner for degreasing applications. Replace an organic solvent used to prepare coated tablets with a water-based solvent and also different spray equipment. Process input changes may be used to reduce wastes in mining such as nontoxic reagents substituted for cyanide in the processing reagents can, and by using reagents less toxic than caustic and ammonia such as lime. Changing raw materials can be associated with making changes in process technology and equipment, or in the composition of products. Vendors may suggest changes in raw materials. When the waste generators are their own raw materials suppliers, waste reduction can be facilitated. Waste reduction through changes in process inputs such as substitution of water-based solvents for organic solvent-based compounds. Reducing or eliminating fire hazards, to eliminate ignitable hazardous waste holding areas and to eliminate hazardous waste disposal costs. Such raw materials substitution requires some equipment changes and retraining of employees to work with the water-based technology and drying techniques. The change also requires suppliers to develop a full range of water-based materials that did not exist.

Effect on Products Design, composition, or specifications changes of end products that allow changes in manufacturing or in use of raw materials can directly lead to waste reduction such as using a material instead of a metal alloy in manufacture, can eliminate a specific containing hazardous waste. Such an approach can be difficult because of constraints imposed on the product by customers, by performance specifications. Implementation may require significant changes in the production technology or the raw materials. This is the most difficult waste reduction approach cited this far.

Waste Reduction Methods Selection and Practice Recycling and plant operation changes are add-ons and similar to end-of-pipe techniques that achieve conventional pollution control goals. Such actions can be part of production but do not tend to involve major changes in process technology or equipment. Recycling and plant operation changes are also often the least

18

Waste Minimization

expensive, rarely requiring large capital investment and typically bringing immediate returns. Although recycling can be costly to set up, the benefits of using recycled material are certain and easy to compute. Using a recycled material instead of a virgin material can be calculated out in a straightforward manner, such as by making trial runs with the recycled material to determine processing parameters and product quality. Such approaches are simple for engineers to identlfy and relatively easy to implement. Also they are unlikely to disrupt plant operations and risk product quality and, therefore, require little attention since these approaches are so simple, they may not be tracked. Because they are easy to implement, they are difficult to document and unlikely to be emphasized. Changing plant operations and in-process recycling usually poses little risk because neither the product nor processes are affected significantly. Changing process technology, raw materials, and end products may require intensive technical factors that may pose possible risks for product quality and customer acceptance, and may call for significant capital investment. Effectiveness of these changes in terms of waste reduction may not be easily predictable. Most engineers do not have either the training, expertise or authority to implement such actions. As interest or pressure for waste reduction increases, the obvious, simple, cheap, and quickly implemented ways of achieving this will be exhausted. Capital that must be invested to achieve further waste reduction will increase and certainty about the return on investments may decrease. Additional waste reduction efforts increasingly require changing the process fundamentals and product design. Such more complex measures depend on knowledge of specific details of technology and operations. Experimentation and implementation must be effected and reliance on outside experts may be necessary. Combination of greater resource requirements and greater uncertainty in payoff become barriers to further waste reduction eventually. When this point has been reached may be a matter of opinion. To go further may require more time, money, and investment in waste reduction. Information about technical data may be difficult. To overcome investment-uncertainty and pursue the most effective means of waste reduction, strong motivation is needed either from management or from outside government assistance and consultants. In some sense, the evolution fiom simple and cheap, to complex and costly means to achieve waste reduction may be happening in the Nation as a whole. This is a speculative statement because not every industrial

Waste Reduction

19

plant is starting waste reduction at the same time or proceeding at the same pace. However, because we have had a voluntary approach to waste reduction, industrial efforts probably have concentrated on the easiest approaches to waste reduction, although some fitms have progressed further. Many firms may not have had enough time yet to implement fully even the easiest forms of waste reduction, much less to consider or examine more costly approaches. Government policies and programs have not yet paid much attention to waste reduction, information and technology transfer are in early stages, and many industries are still just beginning to undertake waste reduction as an end in itself. Nor has waste reduction become a major issue for the public. This state of affairs underlines an important fact: waste reduction's subordinate position to pollution control and to the more traditional imperatives of the production system has resulted in suboptimal levels of waste reduction.

WASTE REDUCTION EXAMPLES A wide range of industries have become involved in waste reduction. However, the distribution should not be taken as demonstration of waste reduction activity or lack thereof in any particular industry. Some examples deal with waste heat and with nonhazardous wastes.

Organic Solvents Replacement There are successful examples of cost cutting and hazardous waste problems by changing from materials that contain organic solvents to ones based with water. There are also examples of changes from pure organic solvents to water-based agents. This competes with in-process recycling of organic solvents, which is also applicable and on the rise. The substitution approach is a more specific example of waste reduction. Material substitution eliminates (not just reduces) a particular waste stream and also eliminates other problems, such as contamination from leaking underground storage tanks and worker exposure to the primary solvent. Problems with product quality may result, such as development necessary before water-based products are similar to the solvent-based products they replaced. Organic solvents include: methanol, hexane, toluene, methylene chloride, Freons, xylene, chloroform, isopropanol, acetonitrile, trichloroethylene, and other compounds. Organic solvents continue to be considered essential or preferable in certain applications. There are many waste reduction opportunities requiring development

20

Waste Minimization

work for major or minor changes in plant process opportunities. Organic solvents can also be replaced by materials other than water for waste reduction. An example is replacing some organic solvents with inexpensive inorganic acids and bases. This and other changes reduce generation of chemical wastes. Solvent Recovery from Processes

Solvent recovery is a form of waste reduction. In-process solvent recovery is widely used as an alternative to solvent replacement to reduce waste generation. It is attractive, like end-of-pipe pollution control, since it requires little change in existing processes. There is widespread commercial availability of solvent recovery equipment which is another attraction. Availability of equipment suitable for small operations, especially batch operations, make in-process recovery of solvents economically preferable to raw materials substitution. Commercially available solvent recovery equipment include:

0

0

Carbon adsorption of solvent, removal of the solvent by steam, and separation of the solvent for reuse in the operation. Carbon must be regenerated, two or more units are required to keep the operations continuous. Chloric acid formation from chlorinated solvents, carbon bed plugging by particulates, and buildup of certain volatile organics on the carbon and corrosion can be a problem. Distillation and condensation can be used to separate and recover solvent from other liquids. Removal efficiency can be very high using this process and can be used for solvent mixtures as well as single solvents. Dissolving the solvent in another material such as scrubbing. Solvents must be then recovered from the resulting solution, through distillation but efficiency of removal is often not high using this method.

Mechanical Processes

Should liquids be used to transfer or remove material, it may be feasible to accomplish this by mechanical means. For example, metal beads can replace caustic solution for dirt removal on metal parts. Some types of plating can be accomplished mechanically rather than by traditional electroplating methods. Paint can be removed by impingement with plastic or metal beads rather than using solvents. Alternate sources

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21

of energy can replace liquid chemicals.

Vapor Loss Prevention Hazardous air emissions can be prevented by simple techniques while realizing cost savings on raw materials. Fugitive emissions, are an example. It is simple to design equipment that will do the job. Floating roofs on open tanks of volatile materials are an example. Other techniques include: condensers in or near operations to recover vapors as liquids, which can be reused; increasing the height of vapor degreaser tanks to increase the distance between the vapor and tank top, and using automatic tank covers to close between degreasing operations. Another approach is to convert from batch to continuous process.

Process Water Use Reduction Large volumes of hazardous aqueous waste result from the use of water to transfer heat and materials, especially in cleaning of equipment for batch processes. Such wastes are usually very dilute solutions with low concentrations of hazardous substance-and often not practical to remove and reuse them. Aqueous waste if put through a water treatment plant typically creates sludge or releases hazardous air emissions. Water is usually so cheap and costs of managing dilute aqueous wastes have been so low that it is has been widely used with no thought of the hazardous waste consequences. There many opportunities to cut down on waste created by process water contamination. Water used strictly for the removal of heat as a heat transfer medium for heat pump or refrigeration systems based on coolants circulation in a closed-loop can be used instead. Cooling water problems include chemicals that are added to lessen bacterial growth, and slime buildup on cooling coils. Such agents may contain chromium which eventually renders water hazardous. In many operations water is used as a solvent. Organic solvents can be so much more powerful that reductions in water use of two or three orders of magnitude may be possible. Higher initial costs can be more than offset if the organic solvents are recovered and recycled. Recycling can also ease removal and possible reuse of dissolved materials. As the cost of managing wastewater increases, the use of organic solvents might become more attractive. A major industrial use of water is as a medium for chemical precipitation. Result is wastewater that may contain dissolved hazardous

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Waste Minimization

inorganic salts.Precipitation for product recovery might be replaced by separation techniques such as physical treatments. Large quantities of water are used for cleaning, a good example of reduction is to replace high-volume water streams for cleaning tanks, equipment and products with systems that use lesser amounts. Pressurized water or drip tanks to collect chemicals rather than a water tank; counterflowing multiple rinse tanks; and squeegees to remove residues are alternate approaches. Flow restrictors will inhibit. Schedule batch processing to maximize back-to-back production of products, minimizing washdowns. Water sometimes can be directly recycled into production systems or can be economically treated to recover valuable components, as metals, oils, for return back to the process. There is a vast array of technologies to separate and remove valuable substances from wastewater. Included are membrane technologies such as electrodialysis, reverse osmosis, ultrafiltration, liquid membranes; adsorption using a variety of materials such as activated carbon; bubble and foam separation. One or more of these techniques might be applicable to a particular waste stream and should be reviewed. An important aspect of recovering contaminants is that many technologies allow the use of closed-loop systems in which process water is recycled rather than passed through the system once only. Such approaches are attractive because they drastically cut water consumption and can eliminate the generation of large amounts of sludge in water treatment plants.

Limits of Applicability A limitation of waste reduction is that generic opportunities are often not recognized.

WASTE REDUCTION DECISIONS There is no standard method by which to make decisions about waste reduction. Waste reduction is carried out, as troublesome or costly specific action is undertaken to reduce or eliminate generation. Wastes can be reduced by process improvements in which waste reduction is only a secondary consideration. As waste reduction gains prominence, systematic audits will be developed to guide comprehensive waste reduction programs.

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The Waste Reduction Audit Waste reduction audits are somewhat different from environmental audits. Environmental audits are actually compliance audits; internal reviews of operations to meet environmental requirements. Waste reduction audits are systematic, periodic internal reviews of processes and operations designed to identify and provide information about opportunities to reduce wastes. Audits provide a useful tool for undertaking systematic, comprehensive waste reduction. For more information on environmental auditing the reader is referred to "Environmental Auditing" published by Noyes Publications in 1993 by P. Cheremisinoff. This is a comprehensive examination of the auditing process. The waste reduction audit has the advantage of increasing consciousness of the need for waste reduction and can stimulate workers to think about methods of reducing waste and help shift thinking away from pollution control syndromes. Comprehensiveness of waste reduction audits and the types of actions that emerge from them also depend on the way terms are defined. How is waste reduction defined? The audit may or may not review waste in all environmental media, focus on reduction of waste at the source, and measure reduction on a product output basis. Waste reduction audits are relatively new, and take a variety of forms. Consulting firms have begun marketing waste reduction auditing.

Hazardous Substances Identification Identification of hazardous wastes may be made by a number of techniques. A very gross analysis of the contents of their wastes are commonly made by some small businesses which may not have people, money, or knowledge on how to conduct analyses and collect data. This review may be no more than a realization that an organization is wasting a great deal of resources. Focus in such cases is on quantities of particular waste materials. Systematically conduct chemical analyses of all wastes over a given time is especially important in batch processes where wastes vary, to obtain more exact data regarding both chemical composition and amounts of waste. Difficulty is in identifying and measuring all wastes, including fugitive emissions, leaks, and spills. Mass balances on hazardous substances include calculations, subtracting the amount of a hazardous substance going into product from the amount purchased as raw material, and taking into account reaction

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Waste Minimization

processes and products. Calculate how much of the substance is generated as waste. Accounting for all of the waste streams, emissions, leaks, and spills in the operations requires a great deal of time and resources, and such procedures are necessary only when an action is required on a particular substance of concern. Updating mass balance information on even one hazardous substance in a plant can be a big job.

Source(s) of Hazardous Substance(s) Identifying the process source of the waste for a specific product is necessary. Without knowing which process is generating the wastes one cannot know what actions are required to reduce wastes. Such information may take time and resources, and may be made more difficult by accounting methods used. If waste management costs are routinely charged to some general environmental operation, then the connection between waste and production process and product may not be easily identified.

Waste Reduction Priorities Which types of waste are target for reduction and points in which processes? This can be an independent, external decision directed for example, by consultants. Recognition that a waste is environmentally hazardous also plays an important role in waste reduction decisions. Evaluation of costs of waste generation and management and the savings from waste reduction, waste generation should be measured on production output. Not putting costs and savings on a product basis could lead to poor business decisions. What appears to be a relatively small waste management cost for a waste may be otherwise it assessed in relation to a small profit margin.

Technically and Economically Feasible Waste Reduction After a waste is targeted for reduction, the problem of choosing one or more feasible waste reduction techniques is the conclusion. Different techniques will offer varying levels of effectiveness at costs and at differing levels of risk. If there is no reason to reduce one waste rather than another, one may decide to take action first on wastes that are the easiest and less costly to reduce and postpone the more difficult waste reduction for later.

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Waste Reduction Alternatives to Waste Management Options After attractive waste reduction alternatives have been identified, they still require proof. Waste management is the known, safe option providing clear results for an investment and creates little disruption and risk to process operations. Waste reduction is the newer approach that has the potential for effects including interference in process operations and product quality. Waste reduction may be perceived as economically risky by decisionmakers. Both the benefits and costs of waste reduction must be documented to make informed decisions about whether to take further waste reduction steps. Obtaining data on waste generation is the way to evaluate the technical and economic success or failure of waste reduction efforts.

Waste Reduction Incentives Proven technologies do not guarantee these technologies will be used. Factors that affect the ability and willingness to implement waste reduction measures include: 0 0 0

0

0 0

nature of the company's industrial processes, size and structure of the company, technology and data available, attitudes and opinions about process operations, economics of waste reduction, government regulations.

Such factors may serve as constraints or incentives for waste reduction and vary even between different plants. It must be recognized that decisionmaking procedures vary greatly and invite exceptions. A wide variety of other considerations may also shape decisions. Change represents risk. The inclination is not to make changes unless there is some reason to do so. Resources are likely to be concentrated on the obvious threats to survival rather than on making changes for waste reduction. The burden is on proponents of waste reduction to justify change. If the case for waste reduction is not made, waste reduction will not happen.

Industrial Process Characteristics The most important factor is the ability to reduce generation of hazardous waste. There are more opportunities for waste reduction in

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Waste Minimization

some industries and some processes than in others. Features of industrial processes that can be identified affecting probability that waste reduction opportunities will be available are included in the following discussion. (See Table 1.) The frequency with which operations and/or processes must be redesigned is important. Some manufacturers are under pressure to put out new products. Most product changes require some operations change; frequent product reformulation makes a company conscious of its daily operations and of opportunities to reduce waste without risking the new product design. Relationships between product reformulation and process change is more complex. Product reformulation may not require process changes. Some product changes involve a different process, such as those that require completely different materials. Some of these alterations may eliminate one hazardous waste, but produce a new one. Despite opportunities for waste reduction, it is unrealistic to expect to redesign products or processes except under pressure from the marketplace or when impelled in order to comply with government regulations. Redesign of product or a process is expensive and risky. When the market for product expands, requiring additional plant facilities, process change becomes more feasible. Some firms have set up new production lines for chemicals in high demand as an example in the chemicals industry. In industries such as petroleum refining and commodity chemicals, where there is little call for product or process change, opportunities for waste reduction may be limited. In mature industries, intense competition may stimulate the use of new but proven processes permitting a better quality and less expensive product. Textile and steel industries are cases in point. Even in mature industries with little potential for process and product change, opportunities for operational changes and in-process recycling may be there and may offer benefits beyond waste reduction. They may not be pursued because of limited resources and other pressing needs that have a higher priority. An industry characteristic affecting waste reduction opportunities has to do with the product quality. Market demands of very high quality may provide fewer opportunities for substitution or in-process recycling. Operations in such plants may also produce large quantities of substandard products because of quality demands. High-quality products generally carry both high costs and profits, making such industries less sensitive to waste management costs and reducing incentives for waste reduction.

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Table 1 Potential for Waste Reduction Type Example Industries Mature process technology high volume product

Rubber Petroleum Commodity chemicals Paper products Lumber

Stringent product specifications or high product quality demands for high costhigh profit products

Pharmaceuticals Weapons Robotics

Frequently changing, high-tech products for industrial use

Electronic components Medical equipment

Job shop processing of many different industrial products

Electroplating Printing Foundries Machine Shops

Changing production technology for commodity goods

Steelmaking Nonferrous metals Textiles

Large-scale manufacture of consumer goods

Automobiles Appliances Consumer electronics Paints

It may be difficult as well to find less-hazardous or nonhazardous raw materials for the manufacture of some products. Water-based paints are being used in many applications since they eliminate the need for solvents which then become hazardous wastes. Such paints may be adequate for many household appliances, but not adequate for highperformance machinery. Another aspect of product quality that may influence the ability to m o d e processes is the degree to which manufacturing processes are dictated by product specifications. Opportunities exist at the design stage for the manufacturer to incorporate less waste-intensive features into the

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Waste Minimization

process. However, the procedure to modify specifications may be so slow that even if a contractor discovers less waste-intensive methods for manufacturing products of equal quality, he will not be able to implement them within the time of his contract. Hindrances to the use of new waste reduction techniques also arise from the fact that many types of equipment stay in production for years. Rigid specifications also raise the question of what level of quality is really necessary. Review of performance levels at the front end of the product-design process might eliminate need for some hazardous materials. The barriers that specifications place on waste reduction efforts reviewing this problem is part of waste minimization. People involved in decision making differs from one company to another. Small firms are likely to make informal decisions, relying on their own professional judgment and experience since they are unlikely to have the resources for extensive assessments of alternatives. In large corporations decisions are made or approved by many people of varied knowledge and background who are often only vaguely familiar with the technology involved. The need to convince nontechnical managers that waste reduction measures are desirable and be financially justified requires quantifiable, economic analysis. Large businesses are therefore likely to make waste reduction or other environmental decisions more slowly when conducting assessments of waste reduction options. A problem in large companies is that environmental engineers are often assigned to the end of the process where they manage the wastes produced, and it is usually they who are given responsibility for waste reduction in spite of the fact that they have little contact with design and research at the front end. Plant process and operations people may also limit contact with those responsible for major process and product changes. Among larger companies structure affects decisions made. Some companies are very decentralized. Plant managers can make major process and operations decisions without corporate approval. In other cases, headquarters governs the day-to-day running of plants.

TECHNOLOGY AND INFORMATION Industry type and company size affect what new technology and information will be available. In some industries a great deal more information about waste reduction techniques and technologies has been developed than in others. Size, and industry/process type affect whether

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a company can develop information and technology in-house when it is not available elsewhere. The alternative is using consultants. Techniques and technologies that have been successfully demonstrated and used elsewhere are always welcomed. There are more proven measures for some types of processes than for others. A number of consultants offer equipment and services for waste reduction. Sellers of waste reduction services are or were waste generators who have successfully developed procedures and are profitably selling expertise to others. Development and marketing of transferable technology occurs widely. Proprietary concerns frequently inhibit this kind of technology transfer, particularly when firms compete directly. This is often the case in industries where there are only a few producers. Commodity chemicals, for example, has always been a very competitive industry. However, larger producers are likely to have their own expertise to develop technologies in-house. Dissemination of waste reduction technologies is more complex than transferring established pollution control technologies. End-of-pipe control usually requires a limited set of solutions, often involving installation of off-the-shelf equipment. Waste reduction, on the other hand, may involve diverse techniques applied at the front end to processes, equipment or operations. A relatively small number of reduction techniques are generic enough to be transferred with simple off-the-shelf prescriptions. When available, this may only have the capability of reducing a limited number of wastes, and may not be the wastes that occur in the highest volume or are the most hazardous. An obstacle to waste reduction in smaller companies is that they purchase much of their technology and raw materials from larger companies. Small firms trying to avoid or reduce hazardous waste generation need information about the contents of raw materials from suppliers. Instead of listing. the chemicals in the raw materials, labels may state that: contents are proprietary. Unless they know what is going into their processes, users cannot screen inputs for hazardous constituents that may later appear in their wastes or products.

Worker Training It is essential to educate those who operate processes about practices which create less waste. These may include simple things such as not leaving faucets running and avoiding spillage. Larger companies have already put together videotapes aimed at educating all levels of people about the importance of reducing waste. Opinion outside the company

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Waste Minimization

may also influence waste decisions made within the company. Public opinion is important. Waste reduction can be an opportunity to portray a more positive image of a company for the public. Some firms are committed to new hazardous waste management facilities and waste reduction.

Waste Reduction Economics Economics is the driving force for most business decisions, and waste reduction is no exception. Assessment of costs and benefits can act as incentive or a constraint on waste reduction depending on circumstances. If waste management costs are high and it is found that it can institute significant waste reduction measures with relatively low costs, saving on waste management expenditures, one will be inclined to reduce waste. If waste management costs are low relative to total costs or if costs are not immediately born by that operation, one may decide not to disrupt or risk processes, or operations, and products with waste reduction. The outside consultant analyst generally does not attempt to estimate economic consequences of such disruptions and risks and for this reason costs of waste reduction may be perceived in a more positive light than is justified. Rising costs of waste management and associated liabilities for waste disposal are the primary considerations for waste reduction. Such considerations are critical to industries in which waste management costs are a high proportion of operating costs or profits. Electroplating, steelmaking, commodity chemicals, and companies that have already experienced substantial penalties for past waste management practices are examples. Liabilities may be speculative and may be discounted in terms of present dollar value, or may be given less importance because of the belief that changes in government policy may reduce them. Accounting procedures may influence the probability that waste reduction measures will compete successfully. Return on investment calculations and the extent to which the way in which waste management costs are incorporated into investment calculations will influence the amount of capital investment, and the kinds of waste reduction measures likely to be made. Most operations have a single budget for environmental programs and this includes waste reduction. Such operations of waste reduction must compete with waste management and compliance programs for attention. Waste management options are often difficult to compete with when in implementing them it is painfully clear, that they will be threatened with

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citations for noncompliance with pollution control regulations. Waste management presents a clearer, surer investment option in the eyes of most generators who see off-the-shelf pollution control equipment and operations changes as proven. Waste reduction options are newer, methods unproven, and the results unpredictable. Uncertainty about the costs of implementing waste reduction measures is critical to decisionmakers who want reliable figures on waste management savings, labor, capital and operating costs, as well as on the costs or savings in raw materials from the waste reduction. Changes at the front end of an operation tend to have ripple effects throughout, and quantlfying these effects and costs or savings can be extremely difficult. Isolating waste reduction may result in smaller benefits, while seeing it as part of a broader effort in production. There are ways to make waste reduction appear more or less attractive economically. Regulations

Despite widespread noncompliance and complaints about ineffectiveness, environmental regulations influence ways businesses make decisions regarding waste. Regulations may be of both types; they may directly require that business take action or they may affect the environment in which businesses make decisions. Both of these hit directly at the financial calculations which determine waste-related decisions. Responses to government requirements for environmental action vary with the size and structure of the company, as well as with more intangible factors such as management and corporate attitudes. Environmental regulations may have handicapped waste reduction in several ways. Existing elaborate framework of pollution control laws has become the center of environmental protection. Control laws are established and enforceable.

HOW MUCH WASTE REDUCTION? Because of the large number of targets for waste reduction and many ways to achieve it, and lack of data, it is impossible to forecast levels of waste reduction. No matter how much waste reduction has been accomplished, unless the potential amount is known, there is uncertainty about the effort. The degree of unrealized waste reduction potential is a definition of the problem. The higher the potential, the stronger the case for doing something. Effective waste treatment is also an option and it

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Waste Minimization

may not always be advisable to reduce wastes in a specific case. A point of diminishing returns for waste reduction may happen somewhere along the line. Further waste reduction may or may not make environmental or economic sense, but this cannot be known unless the possibility of waste reduction is examined thoroughly. If economical factors are excluded, estimates for technically and economically feasible amounts of waste avoidance and reduction in the future are uncertain since: 9

There are too many industrial processes and wastes--to examine in detail. 9 Waste generation and reduction are plant- and process-specific, but the limited waste generation data available are aggregated over numerous processes and over a diversity of plants and companies. 9 It is not known how much waste was and is now being generated; therefore, reduction is difficult to document. 9 It is difficult to predict what changes in production technology and products will occur in the broad range of industry for reasons unrelated to waste. Such changes can substantially change the nature/quantity of waste, or both. 9 Some wastes are legally sanctioned and continued implementation of environmental programs will create more waste. 9 Regulatory, enforcement, and judicial actions that affect the economic feasibility and need for waste reduction may occur. Because of the range of technical approaches, the best any analyst will be able to do is to make estimates for the techniques that are easiest to use.

Waste Reduction Technology Availability Waste reduction is affected by the extent to which information and products are diffused and are available. For the most part, we are in the early stages of transferring waste reduction technology. Comprehensive or efficient transfer of technology and information is required. Because waste reduction technology is evolving from simpler to more complex, process-specific techniques, it will become more difficult to transfer. In-process recycling and plant operations add-on techniques, currently utilized, are the simplest to transfer across industries. Another type of waste reduction also readily transferable; the

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substitution of certain raw materials to common manufacturing operations. An example previously cited is the replacement of solvents with waterbased formulas essentially eliminating generation of spent solvents in this manner. Companies that manufacture products used by other companies as raw materials can increasingly commercialize new products with waste reduction advantages for sale to industry.

Competition from Waste Management The degree of which waste technologies are implemented in the future will depend strongly on alternative waste management methods. Different approaches to waste reduction may compete with each other, and the competition between waste reduction and waste management approach will persist. Waste minimization is defined to mean reducing the amount of waste that is land disposed. Lack of data and imprecise forecasts contribute to the ideal that environmental protection means only better waste management. It is better to treat wastes to render them permanently harmless rather than to use any form of land disposal. It is still better to avoid or reduce the generation of hazardous waste, if it is technically and economically feasible. Waste management activity will pose some environmental risks and require regulation. It is because waste management has been inexpensive that there has seemed to be little point in cutting costs by not generating wastes to start with. For some time to come, waste reduction, particularly by more costly methods, will face competition from waste treatment and disposal technologies. Waste management will remain a viable alternative for the foreseeable future. For most cases it is impossible to reach zero waste generation because of technical feasibility. It is not possible to accurately estimate future waste reduction in terms of the maximum technologically possible. The technical possibilities for waste reduction are rapidly changing. Estimates are likely to be low. Industry is unlikely to be able to assess the full range of waste reduction techniques---possible---in the near term and long run. While the technological potential for waste reduction is substantial, it is quantifiable only in approximate terms, in both industries and waste types. The conclusion that there are many opportunities for waste reduction in the future rests on evidence that industry has not been sufficiently motivated or has not had enough time to do more than get started, and has only begun to exploit the possibilities.

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Waste Minimization

WASTE REDUCTION DATA One of the obstacles to waste reduction analysis is scarcity of numerical data. In devdoping waste reduction policy, one should have data from many industries on current waste generation, waste reduction accomplished so far, and estimates of possible future waste reduction. Such data would help to decide if action is needed, what kinds of actions might be taken, and what kinds of wastes or which industries might be targeted for action. Few such data exists and that that does, for example, waste generation data, is collected in such a way that it reveals little or nothing about waste reduction. Current waste generation data is inadequate since the majority of waste generation estimates arc only for regulated wastes. It does not include emissions into other media; or releases of nonregulated hazardous wastes. Annual waste generation estimates vary widely and must be viewed as uncertain because they arc based on sampling and modeling. Virtually all existing estimates of waste generation are estimates of mass, weight or vohme only; no attempt is made to estimate the degree of hazard of the waste. Knowing that a company has reduced the vohme or mass of its wastes tells nothing about true waste reduction because no information is given about the hazardous content before and after. Many hazardous waste streams are made up principally of nonhazardous substances or materials of little or no value, often water, and contain only a small amount of hazardous or recoverable material. Sludges frequently contain a substantial amount of water and other nonhazardous materials and simple dcwatcring of wastes can produce large vohme decreases with no actual decrease in the hazardous substance content of the waste. Waste generation figures are not typically correlated to production. Many companies and some entire industries recorded less waste generation in the early 1980s than in previous years, but industrial production was down during that period. It is impossible to tell how much reduction in waste generation occurred because of reduced production, and how much resulted from implementation of actual wastereducing measures. Generation data as now collected is not useful for assessing potential or achieved waste reduction. End-of-pipe generation data does reveal enough on what is going on inside the plant to differentiate between changes due to waste reduction and those caused by changes in production levels, product mix, or even waste treatment methods, all of

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which may affect the composition and mass of a waste stream. Assessing waste reduction requires fundamentally different sorts of data and information than have been required for traditional pollution control environmental programs. Waste reduction is a form of production process or operations improvement. It requires actions at the front end of the process, rather than at the end of the pipe where current pollution control programs focus. Planning, implementing, and assessing waste reduction are activities that require the same kinds of production information that would be required for any other production improvement. They also require data about the amount of hazardous waste generated per unit of production output, as well as data on costs and savings of the waste reduction actions. Often types of information when reducing waste is not collected. This is not the type of information currently being collected, a fact which has important implications for the development of waste reduction.

INFORMATION NEEDS Almost all information relevant to waste reduction must come from industry. Government can affect the kinds of information industry collects through new regulations and it can also affect the format of collection, periodicity of data, but the fact remains that information must be collected by industry. Waste Reduction Audit A waste reduction audit can provide the information needed to reduce wastes. Many do not conduct formal audits prior to instituting waste reduction measures. Waste reduction largely remains a byproduct of other process improvements or is on an ad hoe basis to address one waste that presents immediate problems. However, as the concept of comprehensive and systematic waste reduction is better understood and more effectively implemented, audits will become more common because they provide analytic support for waste reduction decisions. Even when taking ad hoe actions, however, companies usually try to pull together s o m e of the information and data discussed below that make it possible to plan and carry out waste reduction in an effective manner. The steps that a company might go through in conducting a waste reduction audit are discussed. Following is an overview of information generated by the audit and the subjects covered more detail in subsequent chapters.

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Waste Minimization

Identification of Hazardous Substances One must identify the amounts and kinds of wastes they generate before anything, can be done about reducing them. This analysis is at different levels of detail and the level of detail of the information required will vary accordingly. One may choose to or may have to make only rough estimates of the kinds and amounts of wastes generated. If only a limited level of waste reduction effort is planned or is possible, gross analysis may be sufficient. Better data on chemical composition and quantities of wastes can be generated, at greater expense, by systematically conducting chemical analyses of waste streams over time an specially important factor in conducting analyses of batch processes where waste streams are not constant. This method of waste identification is common in industry since many companies already collect chemical analysis data on wastes to help them with waste management. The drawback to this method is that in practice all waste streams that must be analyzed, including fugitive emissions, leaks, and spills cannot be identified. The most complete and reliable measure of quantities of specific substances released into the environment is obtained from mass balance calculations. By subtracting the amount of a hazardous substance going out as product from the amount brought into the plant or process, one can calculate the total amount that appears as waste and can then attempt to account for this amount through waste stream measurements. Such calculations may contain uncertainties, and accounting for all of a substance in a process is usually time-consuming and expensive. Mass balance calculations are done routinely in some industries, but frequently they are not sufficiently sensitive for waste reduction purposes.

Identification of the Source(s) of Hazardous Substances and Wastes Without knowing exactly which processes are generating specific wastes, one cannot know how to reduce those wastes. Information at this stage may also be collected at varying levels of detail. One can informally link identified wastes with the process(es) or operation(s) already known to produce them without collecting more information, or may attempt to trace hazardous substances back to where waste generation is occurring. An effective way to do this is to conduct process level mass balance calculations for hazardous substances, and then search processes for points of waste generation or emission until all waste has been accounted for.

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Tracing every hazardous substance back through the process and accounting for all wastes and emissions is an overwhelmingly task. Usually an attempt to identify waste sources for only some wastes is made. Due to limited resources it may reasonably be decided that one can identify enough waste reduction opportunities without seeking exhaustive information about all wastes and waste sources.

Priorities for Waste Reduction Priorities for waste reduction actions may be influenced by: 9 9 9 9

existing regulations affecting particular types of hazardous wastes, need to conserve costly raw materials, ease and expense of implementing waste reduction for particular substances adverse health effects and degree of hazard of different wastes.

One of these factors may override all others. Regulations may promote some waste reduction action for a particular substance, in which case information on the others may be of passing interest only.

Technically and Economically Feasible Reduction Decide which wastes to target, then decide on the best way to accomplish reduction. Needed is information about process engineering and materials, costs of waste reduction approaches and savings possible from use, risks involved in changes, and internal investment conditions. Process engineering and materials information for target processes is often provided by in-house personnel but, in some instances, waste reduction information from other plants, trade associations or technical assistance programs---may be useful. Technical assistance in the form of a consultant brought onsite, may be useful. Cost and savings information on waste reduction approaches includes anticipated effects on the costs of capital, labor, raw materials, and waste management. Potential side effects on production operations and product quality can also be important and assessed. Estimates of these figures are difficult to make because waste reducing measures are front-end process modifications and may have effects on other parts of the operation that are difficult to predict. Information needed about risks involved in waste reduction actions include the cost of disrupting operations and possible

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costs associated with changes in product quality. Information needs for waste reduction needs are summarized in Table 2.

Waste Reduction and Waste Management Options Waste reduction must be shown to be economically preferable to more traditional waste control methods if they are to be attractive. Information that will be required to compare waste reduction measures with the alternative of waste management includes data about the technical and economics of the waste reduction action as well as current waste management costs. Economic assessment of waste reduction versus management must include some information, about the potentially high costs associated with waste management liability.

Waste Reduction Measures In order to plan future waste reduction intelligently, companies must find out how successful their past and current efforts are. They must know how waste reduction measures have altered the composition and amount of their wastes and what the costs and savings have been. They must also compare actual costs and savings with the estimates that were made in the planning stage to understand how good their planning has been. Information needed includes: 9

9

Information on all postreduction waste streams, including their composition, amounts, and fate, to measure reduction and to show to what extent wastes have just been shifted from one environmental medium to another; costs and savings, including information about unanticipated inconveniences and unforeseen benefits of waste reduction;

Table 2: Information Needs for Waste Reduction Waste Reduction Action

Type of Information Needed

Identify hazardous substances of concern in wastes or emissions Identify source(s) of the hazardous substance(s) of concern

Kinds of hazardous wastes generated (Type W) Amounts of those wastes generated (Type W) (continued)

Waste Reduction

39

Table 2: (continued) Waste Reduction Action

Type of Information Needed

Set priorities for actions

Above, plus process engineering and chemistry (Type T) Above, plus process engineering affecting wastes generated (Type R) Health effects and degree of hazard posed by different wastes

(Type H)

Analyze and select technically and economically feasible reduction techniques

Ease and expense of implementing waste reduction for any substance (see below) Above, but more specific process engineering and chemistry information (Type T) Potential costs/savings of the waste reduction action (Type E) General economic situation of the company (Type E) Market information about the affected product9s) and estimates of any effects waste reduction may have on the product (Type

E) Compare economics of waste reduction with waste management alternatives Evaluate waste reduction progress and success

Above, plus current waste management costs including potential liabilities (Type E) Above, plus waste stream contents

(Type w) Actual waste reduction costs/savings (Type E) Glitches, inconveniences, and unforeseen benefits to waste reduction activities (Type T)

Key: Type W - Waste stream data Type P - Production information Type E - Economic information

Type T - Technology information Type R - Regulatory information Type H - Health and environmental effects information

Source: Office of Technology Assessment 1986.

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Waste Minimization

Waste Costs Charges Each production process should be charged with the ultimate costs of managing the wastes generated. Neglect exerts a bias against waste reduction. Waste management costs, such as the costs of running on-site treatment, storage, and disposal facility may be a separate budget item. When costs are externalized engineers have little incentive to reduce wastes. Production decisions may be made in favor of more wasteintensive methods which are not cost-effective since waste management costs have not been fully factored into the decision. Only when companies counting information on waste costs is developed at the process and operations level can cost-effective decisions and the full economic benefits of waste reduction be shown.

WASTE REDUCTION I N F O R M A T I O N Each plant operation requires many different kinds of information if it is going to be effective in reducing the generation of waste. These are: 9

Waste stream data. Data to identify the chemical composition of a waste stream and the amount of each hazardous substance present and relate chemical contents to different processes and points within processes. 9 Production information on types and amounts of inputs and outputs measured over time and proportions of inputs which end up as hazardous wastes or react to produce hazardous wastes. 9 Economic information costs and savings of waste reduction measures; waste management costs, including liability costs; and information on the general economic situation of the company, available capital, labor costs, production costs. 9 Technology information on the chemistry and engineering of processes and on possible waste-reducing changes. 9 Regulatory requirements that affect operations or that affect proposed waste-reducing changes in those operations. 9 Health and environmental effects and degree of hazard information on hazardous substances. Included is information about degree of risk, comprising a wide range of data about concentrations of substances, disposal methods, and the environmental characteristics of the areas in which wastes are generated, handled, transported, and disposed.

Waste Reduction

41

Second, the kinds of information which weigh most heavily in industry decisions about waste reduction tend to be those that are operation-specific, such as economic production, and waste data. Health and degree of hazard information is usually less important in industry's decisions about waste reduction. Information that most directly affects industrial waste reduction efforts, particularly economic information about production, waste management costs, and liabilities, is confidential. Existing data systems do not come close to satisfying many criteria or shed much light on any of the basic questions about the waste reduction situation. Part of the reason for this is in the way in which we currently collect information about hazardous wastes, and the complexity of gathering waste reduction information itself is also responsible. Waste Reduction

Data developed for pollution control do not provide any basis for a hazardous waste reduction program. Information provides few insights into waste reduction and no sense of how much waste reduction might be possible. Inadequacies of data for waste reduction stem from existing pollution control programs which are ; not multimedia in nature, address only a limited number of hazardous substances, and address a different set of substances in each environmental medium. The data collected is not usually substance-specific but covers some conglomerate waste, only a portion of which may be hazardous. The following features limit the applicability of data to waste reduction analyses: 9 9

9

While a large amount of data is available on wastes, very little is available on the processes that generate the wastes. What production and process information exists is protected as confidential business information which limits access to this data by the public, and also for any purpose other than that for which it was explicitly collected. Much of this data is not available to waste minimization people. Little uniformity in collection method or time period in existing data. Much of the most useful data for waste reduction has been collected only on an ad hoc basis, often as part of a contractor's study to support action on some single substance or small group of substances. Much data is extrapolated from a sampling of representative plants. Samples and techniques

42

Waste Minimization are not the same among industry categories and are not the same over time. 9 Most information concerns emissions that are dispersed into only one environmental medium. 9 Different amounts, kinds, and qualities of data have been collected for different hazardous substances depending on the kinds of regulatory actions that have been applied. 9 Very little, if any, information exists for the many hazardous substances that are not regulated. 9 Existing data are not very accessible. Most often is in hard copy and often scattered.

M E A S U R E W A S T E REDUCTION How much waste is currently being generated, and how that is being reduced or increased over time should be answerable with data on waste generation. Waste reduction may be disguised in waste generation by changes in production, changes in the amount of nonhazardous constituents in waste streams, regulatory changes, and cross-media shifts. E x isting waste generation data are not useful for answering waste reduction questions because: they deal only with some fraction of hazardous wastes, often only with wastes regulated under a single statute (wastes); they are mass or volume estimates only; and they are not correlated to production. Most hazardous wastes are complex mixtures of hazardous and nonhazardous constituents. Often water is the largest component of raw waste streams that contain only small amounts of hazardous substances. Volume reduction measurements by themselves reveal nothing about the hazardous portion of any waste stream. Concentration of hazardous substances alone is not waste reduction. Similarly, waste generation depends on production; trends in data not correlated to production may indicate a rise or fall in waste generation attributable only to an increase or decrease in capacity utilization of a plant or operation. Reduction in one waste stream does not necessarily mean that total emissions of a substance have been reduced; most operations have several points of emission for any given substance and discharge wastes into more than one environmental medium. Simply charting trends in waste generation data as it is now collected does not adequately measurement waste reduction. What is adequate? The only meaningful measure of waste reduction is the total amount of

Waste Reduction

43

ardous waste generated per unit of production. This compensates for production, volume, and multimedia limitations of data in existence. Such measurement requires a large amount of very detailed process and substance-specific waste information collected based on a production output basis. There are many reasons why collecting this amount and type of data is impractical, but understanding what data is required to assess waste reduction illustrates some of the uncertainties incurred by using imperfect and misleading data. Waste Reduction Data Must Be Correlated to Production--Waste generation varies directly with capacity utilization, everything else remains the same; it is important to know whether waste amounts are rising and falling because more or less product is being manufactured, or because waste reduction measures are being implemented. Waste generation figures not correlated to production can mask waste reduction. Waste reduction as the business is growing, may be implemented. Waste volumes may appear to be going up while waste per unit product, the true measure of waste reduction, is actually going down. It may be to the advantage of companies to measure waste generation on a per unit product, the true measure of waste reduction. It may be to the advantage of companies to measure waste generation on a per unit product basis. Waste Reduction Information Must be Substance-Specific--It is the only way to overcome the volume measurement problem and the media shifting. When waste streams are complex mixtures of hazardous and nonhazardous substances, volume measurements do not give the amount of hazardous substances in the waste, or the amount of any given hazardous substance. Fugitive air emissions, leaks, and spills can contain substantial amounts of hazardous materials and would almost certainly not be accounted for in such a system. It is usually possible to calculate the amount of a specific substance appearing as waste in a process. One subtracts the amount of the substance in the product from the amount of the substance in the raw material; the difference is waste. Then, how much of that substance must be accounted for in all waste streams and emissions. A mass balance calculation for specific substances keeps nonhazardous constituents from diluting the usefulness of hazardous waste data. An accounting of all emissions throughout the process results in finding previously unknown sources of waste which may aid in planning waste reduction. Mass balance calculations are not always easy to conduct or reliable. There is uncertainty in input and output measurements. If inputs and outputs are large relative to the difference between them, the uncertainties

44

Waste Minimization

may be larger than the amount of waste. Such types of calculations may reveal little or nothing about small quantities of highly hazardous wastes. Process chemistry can create additional practical difficulties in calculating mass balances. Waste Reduction Data Must Be Process-Specific--Mass balance calculations at the plant level with a high degree of sensitivity and accuracy is difficult. Processes, reactions, and transformations are usually so complex that good data cannot be collected except at the smallest production level--the process or unit operation. It might be possible in some cases to conduct a very rough mass balance on a hazardous substance at the plant level by figuring the difference between input and product output and assuming the rest is waste, without trying to track that waste. Doing this over time, one might get a rough sense of the amount of waste reduction. The uncertainties in this calculation are almost always large and may not reveal much about small amounts of highly hazardous waste. An important impact on waste reduction decisions are economic factors---costs, liabilities, need to increase productivity and improve product quality, and regulatory requirements are rated important. Obstacles to waste reduction efforts are economic factors--dollar value of benefits from waste reduction and the costs of carrying it out--were rated significant barriers by all respondents. Among waste reduction activities implemented, in-process recycling is ranked first. Changes in equipment or technology ranked second, and improvements in housekeeping and general operations changes third. The least used action is making changes in the final product(s). The following is an overview questionnaire that might be found useful for users of this book. HAZARDOUS WASTE REDUCTION 1. a) b) c) d) e)

Check off one of the following that most closely describes your situation: ~ I am a technical person (science or engineering background) involved in plant operations I am a technical person in mid-level management I am a technical person at the corporate rather than plant operations level I am a non-technical person at the corporate level other.

Waste Reduction .

b) c) .

a) b) c) 4.

a) b) 0

0

45

With regard to your company's efforts to avoid generating waste: I make decisions leading to actions I make recommendations to others for decisions other. My operation is best characterized as: small or medium sized company large company with corporate technical resources on which to draw other. My company does primarily: chief products or outputs are: Principal activity is in (location) in which there is, as far as you know (check off as many as apply): no waste reduction program a technical assistance program for waste reduction an information transfer program for waste reduction some type(s) of tax on hazardous waste some type of awards program for waste reduction some other governmental effort concerning waste reduction, Consider the following statements concerning factors that may aleady have affected the extent of your waste avoidance efforts and give each statement one of the following evaluations: usually true in your operation occasionally true in your operation rarely true in your operation capital costs of major waste avoidance efforts can not now be justified in economic terms in comparison to other capital projects in the company government environmental regulations accomplish enough, and lead to whatever attention we can give to dealing with hazardous waste issues we don't have enough technical information on what to do for waste avoidance or the resources to get more information management hasn't given waste avoidance a high priority technical staff is too small or preoccupied with other more important jobs to give attention to waste avoidance

46

Waste Minimization physical nature or age of our operation does not allow us to increase our waste avoidance efforts rising costs of managing our wastes have made increasing waste avoidance efforts a high priority the difficulty of using land disposal for our hazardous waste has been important to waste avoidance in our operation public awareness and attention to wastes, emissions, discharges, accidental releases to the environment have not been relevant to our decision-making about waste avoidance.

.

a) b) c)

0

91p

Have programs affected your waste avoidance efforts? yes b) no If yes, please indicate briefly what program(s) were If yes, do you believe that the effort was a form of subsidy or aid for your waste avoidance efforts without which your effort would have been less? yes no

Have your waste avoidance efforts been held back because you lack enough detailed information on: yes no a) the nature (e.g. degree of hazard) of your hazwastes b) the costs of managing specific waste c) the costs of carrying out waste avoidance d) the dollar value of benefits (other than avoiding waste management costs) In planning your waste avoidance actions and targeting waste streams are you more likely to focus on the weight or volume of waste rather than the specific threat or level of hazard of the waste? yes no

10. If yes, has lack of information on degree of hazard of your waste(s) been a problem? yes no 11. Of the waste avoidance activities which you have implemented to date, rank the following five broad approaches in terms of their importance (1 - the most successful approach): changes in process equipment or technology improvements in "housekeeping" or general operations changes in raw materials used in operations

Waste Reduction

47

in-process recycling/recovery changes in the final product(s) produced 12. When speaking of waste reduction most people focus on solid, hazardous waste associated with regulation. Consider the following other types of hazardous waste and indicate the level of attention your company is giving to reducing them. Use the following: 1 - much attention, action already or specific plans; 2 - a little attention; 3 - no attention at present; x - not a relevant waste a) routine toxic air emissions b) accidental toxic air emissions c) unregulated discharges of hazardous materials to surface waters d) regulated discharges to surface waters e) discharges of hazardous materials to sewers 13. Rate the following circumstances with regard to their direct or indirect impact on your waste avoidance decisions and activities to date (1 -- most important)" an interest in improving public and consumer perceptions of the company overall need to reduce costs, increase productivity, or improve product(s) actual and perceived regulatory demands, costs, and liabilities 14. Consider the following eight potential types of programs and, assuming that they would be done well, evaluate potential impact on your waste avoidance effort by giving each one of the following: 1 - would have a major positive impact; 2 - would have a small but positive impact; 3 - would not be a significant factor technical information on specific waste avoidance approaches is made available free to you free technical assistance especially designed for your operation to help develop your waste avoidance effort is made available to you some type of tax credit or advantage is made available to you for capital spending on waste avoidance

48

Waste Minimization a specific requirement mandated for a certain amount of waste reduction over a specified time as compared to some base year of waste generation awards are given annually for outstanding waste reduction efforts grants made for whatever programs they want to use to enhance industrial waste avoidance efforts through regulatory programs and enforcement, the use of land disposal is greatly reduced and all waste m a n agement costs increase still more waste generators face increasingly greater burdens to pay for cleanups of toxic waste sites either offsite or onsite

15. Overall, with regard to waste avoidance, if you had your way would you want to: leave things just the way they are now or take some further action to assist industry to carry out more waste avoidance activities? 16. Will your future waste avoidance activities be limited to a significant extent by your uncertainties about environmental regulations and their enforcement? yes no 17. What might be a successful waste avoidance effort by a company may be misleading as to its environmental or economic benefits. Do you agree? yes no 18. If yes, could you briefly explain why you agree: 19. Future waste avoidance efforts, rank the following five broad approaches as to their expected importance (1 - most important): changes in process equipment or technology improvements in "housekeeping" or general operations changes in raw materials used in operations in-process recycling/recovery changes in the final product produced 20. Which of the following is most correct waste avoidance in our company will either have no effect on our total employment or might increase it or waste avoidance in our company will reduce employment.

Waste Reduction

49

21. There is interest in adopting some type of requirement to conduct an inventory of hazardous waste generation by industry. Would such regular reporting by industry of all of its toxic chemical generation stimulate more waste avoidance? yes no 22. Evaluate the potential for waste avoidance in your industry in the following two situations: a) Using best available technology, how much (by weight) of the hazardous waste (all types in all type of environmental media) generated by your operation could have been avoided? less than 25% 25% to 50% 50% to 75% b) Using best available future technology, how much (by weight) of the hazardous waste (all types in all types of environmental media) generated by your operation could have been avoided? less than 25% 25% to 50% 50% to 75%

INTERNATIONAL PERSPECTIVE The actions of other national governments in the area of waste reduction may be of interest to American policy makers for two reasons. First, the choices made by other countries can serve as policy models The varied experience of countries actively promoting waste reduction and those attempting to deal with waste problems in other ways can help Americans understand the range of policies available to them and, over time, the results of those policies. Second, expertise gained by other nations with longer experience in waste reduction can present a challenge. Many Western European governments have actively encouraged waste reduction for many years. To the extent that their lead in waste reduction results in more efficient processes and increased productivity among European industries, U.S. firms in similar industrial sectors may be placed in an inferior competitive position. In addition, to the extent that a profitable worldwide market for waste reducing technologies and techniques opens up, U.S. firms may find it difficult to sell their waste reduction technologies to industrial operations here and overseas if Europeans are offering a wider variety of better techniques, tested over a longer period of time.

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Waste Minimization

Multilateral Organizations Some of the earliest initiatives in waste reduction came from international organizations. The United Nations sponsored the first International Conference on Non-Waste Technology in Paris in 1976. In 1979 the ECE adopted a detailed "Declaration on Lowland Non-Waste Technology and Reutilization and Recycling of Wastes." In this document recommended action on both the national and international levels to develop and promote low- and non-waste technologies. Activities resulting from this declaration have included: 9 publication of a four-volume compendium on low- and nonwaste technologies in 1982, listing over 80 examples of successful pollution prevention efforts by European industrial firms; (United Nations Economic Commission for Europe, Declaration on Low- and Non-Waste Technology and R e utilization and Recycling of Wastes (Geneva, Switzerland: November 1979). 9 publication of a compendium of lectures by experts in low- and non-waste technology in 1983; 9 holding a European Seminar on Clean Technologies at the Hague in 1980; 9 setting up a Working Party on Low- and NonWaste Technology and Reutilization and Recycling of Wastes which has met annually since 1980; and 9 setting up an Environmental Fund for demonstration of innovative technologies that are broadly applicable to reducing pollution. A sum of 6.5 million in European Currency Units (about 6.1 million U.S. dollars) was set aside for this purpose in 1985. The Organization for Economic Cooperation and Development (OECD) has taken a stand in favor of waste reduction although no promotional activities have been taken. An OECD conference in 1985 on transborder movements of hazardous waste concluded that the first basic principle for the management of waste is: "to prevent and reduce, so far as possible, the generation of wastes, to limit their hazardous character and to try to improve production processes." Recycling and proper treatment of wastes are included in the second principle. OECD further recommended that member countries make sure that: "adequate measures are taken for preventing or reducing the generation of hazardous wastes

Waste Reduction ..."

51

in new investment or development projects. European industry has also espoused the concept of waste reduction. In its recently published "Summary of Principles of Industrial Waste Management," the European Council of Chemical Manufacturers' Federations headed its list of principles with: . . . waste reduction: Take all economically and technically justifiable measures to minimize generation of waste through process optimization or redesign.

CHAPTER

2

AUDITING

Auditing is an umbrella term used to describe the procedure which systematically and objectively reviews a given situation. This meaning can be very broad and there are many different types of audits. Virtually every situation and every type of operation can be audited. The nature of an audit is such that it can be tailored to meet a specific need. Nonetheless, there are some similarities and recurrent themes to group types of audits. While the reasons for initiating an audit program may vary, the benefits realized almost always include improved regulatory compliance, an increased awareness of environmental conditions, programs, improved relations with both regulatory agency and the public, a reduction in risks and potential liabilities, increased management efficiency, reduction of wastes. Due to the nature of the information that an audit can provide, and the importance placed on the results, common sense dictates that careful consideration and planning precede the actual performance of the audit, rather than being performed in a nonchalant manner. Preplanning makes sense since substantial expenditures of capital, time, and potential liabilities may be associated with these audits. Deficiencies of audits are most commonly due to an improper or unclear scope, or an inadequate auditing team. In order to keep the costs as minimal as possible, it is essential for the scope of the audit to be defined as early as possible. Audits may result in questionable results that are irreversible or, at best, difficult to refute. Therefore, the audit process chosen must be considered carefully in order to insure the required expertise to deliver the scope of work. This book provides a guide of environmental auditing, and describes those elements to be evaluated in auditing and to a review of observations 52

Auditing

53

to be included during the actual audit as well and is focused on waste minimization and reduction for its goals. The contents are focused on waste reduction for the process industries. The intention is providing the reader with some insight into the reasons behind auditing, and the individual components that are required for a successful audit. The reader will have a fuller understanding of the capabilities, as well as the limitations of an audit, and the audit may yield the maximum value possible. Also provided are specific examples for waste reduction and minimization. The following checklist provides some of the considerations critical for site location and factors. It must be remembered that no two locations, businesses or industries are identical. Each auditor will view this checklist differently and may want to modify it to suit specific requirements.

E N V I R O N M E N T A L FACTORS AND AUDIT SUMMARY CHECKLIST Historic Data D Location, name and types of industry D Past and present ownership D Past and present uses D Regulatory history D Regulatory permits D Products D Raw materials Considerations Based on Anticipated Change in the Environment D Discharges - gaseous - liquid - solid wastes; what are the ecological considerations? D Existing area ecological relationships (use available background data and augment as necessary) D Control measures to minimize environmental effects D Terrestrial and aquatic areas D Physical tolerance levels - ambient air quality standards - water quality standards- noise level standards - glare and/or lighting standards i--! Nutrients D Detrimental and beneficial development 17 Buffer zones and green belts

54

Waste Minimization

Water Supply D Water needs - process - cooling - potable - fire protection D Water availability - public water supply - private water supply ground water surface water D Ground water geological potential D Water characteristics - chemical - bacteriological - corrosiveness D Water distribution - amount available - pressure - variations proximity to site - size of lines D Cost of water supply - extension of existing service - d e velopment of new supply -extension of existing service - d e velopment of new supply - cost per 1,000 gallons D Water treatment requirements - process - cooling - boiler feedwater - potable other D Special considerations - restriction on use - future supplies compatibility for use in process. Wastewater Disposal D Sewerage systems - stormwater - cooling water - process w a s t e water D Anticipated mode of occurrence, flow and characteristics of plant wastewater discharge D Proposed pollution loadings D Toxic materials present D Variations in wastewater treatability D Inplant control measures D Onsite wastewater treatment and disposal possibilities D Existing stream quality D Water uses to be protected D Stream quality standards D Wastewater effluents standards D State regulatory agencies concerned D Stream flow characteristics, design critical flow D Development of treatment design parameters D Availability of a public sewerage system D Pretreatment requirements if discharged to public sewers D Sewer service charges and surcharges for industrial wastewaters D Onsite underground disposal system - p e r c o l a t i o n rates D Scavenger hauling of liquid wastes D Emergency operation - e l e c t r i c power dependability D Performance reliability requirements

Auditing Air D D D D

D D D

55

Pollution Control Considerations Regional airshed standards Air pollution standards Local air pollution enforcement regulations and ordinances Meteorological conditions - wind direction and velocity variability, inversion frequency intensity and height, and other microclimatology factors Proximity to population/employment centers Local topography Effect other area industrial emissions may have on the quality of plan environment or on allowable emission rates

Solid Waste Disposal D State and local regulations D Disposal facilities available - incineration - sanitary landfill other D Local contract pickup and disposal - municipal control competition between haulers D Costs of solid waste disposal D Dependability - lifetime of disposal facilities - probability of flooding D Onsite disposal - incineration - landfill D Responsibility - public collector - private collector - other disposal D Special handling and disposal practices required for industrial wastes In-Plant Operations D General Housekeeping D Ventilation adequacy D Worker training adequacy D Labeling, placarding, drum/package identification D Raw material and product storage D Safety D Noise levels

OVERVIEW Environmental audits are an unbiased evaluation of a site, operation or facility to determine whether real or potential threats of environmental

56

Waste Minimization

contamination exist and a basis for waste minimization or reduction possibilities. Involved is prioritizing those areas at a site or facility where contaminants are generated so that a plan for prevention and remediation may be developed and implemented. Several types of environmental or process audits are possible. Audits are differentiated by their respective goals and may use different approaches to accomplish goals. Audits discussed and emphasized here are for the purpose of waste reduction and minimization from manufacturing. Such enterprises typically include manufacturing facilities, laboratories, commercial and mining facilities, etc. There are also regulatory or enforcement audits. These can be similar to the more routine inspections performed by regulatory personnel or can be performed by independent groups. Audits are requested when an agency or management believes that general deficiencies exist at a site. Audits often identify waste sources and result in ideas to implement waste-minimization and toxicity reduction through recycling, reclamation or material substitution. It is prudent to perform an internal due diligence audit before developing a waste reduction plan to address the complete facility and project the program's ramifications. The internal due diligence audit accomplishes one or more of the following tasks: determines compliance status, evaluates environmental management practices and facilities and identifies risks and liabilities, including those attributable to past as well as present practices, monitors operations in general, determines waste sources and the fate of materials during processing. There are two types of internal due diligence audits: comprehensive and focused. Comprehensive audits address all aspects of environmental, health and safety and practices for processes relevant to a given facility. The audit is performed to evaluate compliance with requirements and how well a facility meets best management practices. The duration of a comprehensive audit varies according to the facility size, complexity and the number of members comprising the audit team. A comprehensive audit may go on simultaneously in different areas of the facility. The auditing team is composed of independently functioning groups; that is, one group addresses aspects relating to air discharges while another group may work with those individuals responsible for wastewater treatment or hazardous waste management at the facility as well as processing. A comprehensive audit can take between 1 to 5 days and is staffed with a team of 1 to 10 professionals. If the facility is complex, the auditors should meet each day to review what has been found. Interaction of team members while on site helps to ensure the accuracy,

Auditing

57

thoroughness, and consistency of the audit. A detailed process study may take considerably longer depending on how much detail the study requires. Focused audits are more targeted and involve less time and fewer auditors than the comprehensive audit. Focused audits may be called into play after a facility incident, a change in process, a change in regulation, to study an operation or process or as a follow up to areas that were targeted for revisions after a comprehensive audit. Because focused audits require less manpower, time and costs, they may be performed more frequently and preferable to repeating a comprehensive audit. The results of the focused audits, however, must be included in the support documentation provided to audit teams performing future comprehensive audits. The Audit Team An important component of a successful audit is the selection of the audit team. The team members must be impartial in their review of the facility's status. Frequently, the most knowledgeable individual for a given area is the manager or supervisor of that area. If the audit team member is such an individual, negative or deficient areas within his own area of responsibility must be accurately and impartially reported. Organization, company or internal personnel may be part of the audit team, as long as they can function independent of the entity being audited. Often corporate staff conduct the audit, or the team is a combination of corporate professionals and those stationed at other facilities in the organization. Outside consultants and specialists may serve as audit team members as long as they fully understand the audit purpose and protocols. Consultants may be requested to conduct the audit in its entirety. If a sampling or testing program is to be implemented as a part of the audit, laboratories and testing should be elected well in advance and used. Outside audit teams or team members should be used if the facility is too small to staff a team, facility personnel are too busy to perform the audit or are not qualified, management prefers an independent or more objective assessment, perceived anonymity by facility employees to independent auditors is desired, and that multiple facilities may be compared for management. Professionals from a variety of disciplines may be effective audit team members. Most commonly, audit professionals are environmental engineers, environmental chemists, chemical engineers, civil engineers,

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Waste Minimization

hydrogeologists, industrial hygienists, geotechnical engineers, safety engineers, atmosphere scientists, health physicists, environmental control managers. An auditor's experience and expertise may be more important than his educational background. For example, an environmental engineer experienced only in industrial wastewater treatment would be inappropriate for the air pollution control survey. Hydrogeologists are qualified to evaluate the adequacy of groundwater monitoring programs or corrective actions at land-disposal facilities, but in most cases they are not trained to assess spill-prevention control facilities and plans. It is important that auditors know the regulations they will be dealing with in the audit. It is necessary for members of the audit team to have a primary and secondary expertise. This allows for more interaction among audit team members and a more conclusive end product. Additionally, such an audit team may divide work assignments if necessary. A clear definition of the audit's purpose should be provided to the audit team and those individuals who are required to respond to the demands of the team. Similarly, each member of the audit team must have a clear understanding of his role in the audit. Audit results and copies of all applicable assessments such as laboratory results, permits, reports from internal or external consultants, relevant standard operating procedures and training files must be filled and maintained and be available for review, distribution or both. If not available, facility personnel must know where any missing information may be obtained. Guidance in this area of information retrieval and organization is often provided by a questionnaire. This questionnaire should be given to facility personnel before the onsite phase of the audit begins, with sufficient lead time to answer the questions and prepare the document files. As the audit progresses, cross-checks need to be in place to ensure accuracy, consistency and thoroughness. Examples of such cross-checks include reconciling waste disposal records with annual reports to regulatory agencies and comparing hazardous material purchase records with waste disposal records. The Report

When an audit is complete, an audit report is prepared. This report should be concise and candid. It needs to address, in detail, the areas of deficiency rather than the areas of good performance. Areas that are efficient may serve as a reference to help remediate deficient areas.

Auditing

59

Recommendations in the audit report might include: 9 9 9 9

No action Physical plant upgrades Improved sampling Revisions to standard operating procedures

Additional study to determine the extent and impact of questionable areas that cannot readily be determined from the audit may also be recommended. The reader is referred to other sections of this Workbook for more details and specific examples.

An Important Tool Auditing is an important tool which really has just evolved during the recent past. Environmental auditing began in the early to mid-1970's when a few companies began establishing internal programs to verify their compliance with the ever growing number of laws and regulations which had a direct affect on the operations. Today, organizations have developed formal audit requirements which can be used in achieving an organization's most important goals and objectives to upper management, as well as being a guide to higher efficiency and profits as well as waste reduction and minimization. When one hears the word audit, what usually first comes to mind is the accounting firm which prepares a firm's year-end annual report stating its financial position. However, auditing, in the most common sense, is a methodical examination, involving tests, analyses, and confirmations of procedures and practices which lead to verification of practices. As a result, programs have been developed to monitor and "audit" the performance of activities. This results in environmental auditing becoming a powerful tool to help determine status and performance of operating facilities and processes. There are various other terms which are used to describe these programs. Audit is the most common; however, review, surveillance, survey, appraisal, and assessment are used interchangeably. Some firms deliberately do not use the word audit because of requests of legal or financial staff. Others use audit in order to lend credibility and meaning to their program.

Importance of the Audit Audits are important for some very specific reasons. Audits determine

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Waste Minimization

and document the status of operations. Management wants assurance that facilities are operating in accordance with efficiency. The presence of an audit program simply means that management views environmental protection and waste minimization as important and necessary. Further, wanted are assurances that an organization is being directed as a good citizen, and which is also controlling costs. Thus, auditing can serve to assure that no unforeseen material risks have been identified and will limit exposure to liability and can assure efficient operations. Audits help to improve the performance at operating facilities and increase overall awareness throughout the company as well as potentially improve operations. If workers at a production or manufacturing site are kept informed of the various requirements affecting their specific operations or job, that plant will have a better chance of maintaining compliance. Also, if a plant is routinely audited, workers will become more aware of their operations and individual actions which ultimately leads to an increase in overall environmental awareness and improved plant operating performance. Audits also help to ensure that the systems designed to detect and manage problems are operating as designed. These systems are established in order to ensure compliance and efficiency. Specifically, the system includes: a written statement of plant-level controls specifying minimum standards, methods for collecting data which will then be measured against these standards, and a reporting system which indicates areas of smooth operation and areas of problems. Simply stated, the control system provides a structure against which to audit. While the audit is like a snapshot at a given time, the management and control system is constantly generating data and providing reports on the plant's and company's performance. The more the audit can help strengthen this system, the better the ability to meet management's need for reassurance.

Developing Resources An area in which audits can help in a company's planning effort is to serve as a basis for developing resources. Audits can be useful in optimizing resources and minimizing wastes, as roles and responsibilities of personnel, and planning for capital expenditures. In addition to determining compliance at a given facility, audits are useful to identify current and anticipated costs, suggesting ways of reducing these costs, and identify potential long-term savings. Audit programs that focus on resource optimization tend to center on costs savings. For instance, this type of audit program may help to define

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facility personnel roles for specific disciplines and the responsibilities necessary for carrying out these roles. It can define gaps in job responsibilities, where no responsibilities have been assigned, or where assignments have not been communicated effectively. Conversely, such programs can identify efficient and cost-effective ways of achieving compliance. Examples of this are installation of more efficient/less cosily control equipment, and potentially reducing current requirements. These are just a few of the major ways audits can help to develop and optimize an organization's resources as well as maximum productivity, use of materials and minimizing wastes. In summary, the benefits of auditing are as broad and diverse as the reasons for which companies develop auditing programs. Simply, companies with established audit policies feel strongly that the benefits are substantial. This is resulting in an increase in the number of auditing programs and requirements for them. Environmental and process auditing can be defined as a systematic, documented, periodic, and objective review by regulated entities, of facility operations and practices related to meeting requirements. Audits can be designed to accomplish any or all of the following: verify compliance with environmental requirements; evaluate the effectiveness of management systems already in place; or assess risks from materials practices, and processing operations.

Audit Types The actual definition of an audit is more closely related to the purpose for which it is intended. Although nearly any operation, process or product that occurs at a facility can be audited, the purpose of auditing for our purposes is for effecting waste minimization and reductions. Broadly defined, an audit is an objective review. The purpose of this review is to determine, as well as to identify, all of the sources, actual and potential, which are the cause of, or may result in, environmental or waste problems. Properly conducted, the audit will serve such purposes, that is, to assess the potential for, or effect of, operations and to ultimately recommend future courses of action. When conducted at an active facility, auditing can be defined as a means by which the effectiveness of the existing management programs can be evaluated and, as necessary modified if possible. The term "auditing" has become somewhat of a blanket term which may not have the same meaning for all who use it. Each audit which will be conducted is unique with the ultimate result structured by the ultimate

62

Waste Minimization

reason for conducting the audit. There are various terms which represent various degrees of insight into the audit. The terms are often used interchangeably and methodologies associated with these terms are used in environmental investigations. An environmental or process inventory identifies and lists what materials are present on a site and in what quantities. Dependent on the size and complexity of the facility, this may be a simple or complicated task. This type of inventory may be conducted on either a specific operation or for the entire facility. Inspection defines that activity which encompasses a visual walk through inspection of the facility or property to identify the operations and materials which are present, as well as how and where they are used. This inspection may include basic sampling and analysis of unknown materials to supplement the visual observations made during the inspection. The term audit represents that activity which encompasses a broader view of the facility than those previously defined. The results of this audit will serve to determine and separate the suspected, actual, and potential conditions associated with the facility or operation. The audit may be extended further in an assessment. An assessment evaluates any actual or potential impacts determined through the terms described above. The more one becomes familiar with this process, the more it becomes apparent that none of these terms are well defined. Instead, they are all lumped together under the umbrella of "auditing". This work essentially encompasses all terms and conditions. The scope of these activities can be tailored to the needs of the individual situation and can result in an undertaking which can range from the very simple to the quite complex. Although each audit is unique, it essentially consists of three (3) phases. These phases are not necessarily mutually exclusive, rather, as with the terms previously identified, there is some overlap inherent in their description. A Phase I audit consists of the identification of whether or not contamination exists by means of a general site survey, a historical property evaluation, and a file check as to variable information. The Phase II audit expands on this idea through the characterization of the types and sources of contamination as well as the delineation of their extent, by means of a detailed survey and a historical evaluation, sampling and records research. Phase II audit includes a detailed assessment which will serve to attempt to isolate the components and services

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63

of the contamination or waste generation. Phase IIl will include recommendations and possible answers to questions raised in Phase I and Phase II. Phases I and II may involve materials testing, as well as a review of records. The actual scope of the audit, as well as the boundary between each of the phases, is essentially based on a decision whether it is to be terminated, to use the information gained to refine the data or to seek more detail or data and information before making a decision. These phases are not necessarily distinct nor are they mutually exclusive.

Objectives An audit should accomplish the following: the identification of problems in the process, the delineation and quantification of the potential extent of risks, and the information and recommendations which can result in informed decision making alternatives. Again, the results of the audit will be a function of its initial scope and ultimate goals. While the ultimate goal is often times a written report to supply to the persons involved, other long and short term goals may be involved. Whether or not these are actual intended goals at the onset of the procedure, the completion of a properly conducted audit will achieve the following results: 9

At the time of the audit, the onsite conditions and operations will be accurately determined and documented. 9 The audit may serve to identify any toxic or hazardous components with a potential for release, as well as to identify potential pathways for exposure, and the inherent hazards associated with some or all of the materials located onsite. 9 Dependent on the scope of the audit, the site conditions may be compared to established regulatory and or operating requirements and assessed for compliance. 9 The audit can be used to assess procedures, policies, and guidelines related to hazardous waste management as related to the current management scheme, and may serve to evaluate future environmental management plans, to assess potential exposures and areas of liability, associated with past and current site activities. 9 Determine operating conditions, by products, generation of wastes.

64

Waste Minimization Make recommendations or develop, remedial action plans to reduce or eliminate the risks as well as improve operations.

Objectives which are mentioned above are achieved through a series of steps which may vary a great deal, but which essentially consist of the following. These steps may include a file search and a review pertinent regulatory and technical records, followed by an on-site inspection, interviews on site, corporate and plant management, and the preparation of a report. The scope of this report will vary and there is no standard, except possibly for the simplest case. Each report will be site specific and commensurate with the need or desire for information to support decisions. Because any site may change hands and the conditions are constantly evolving, an audit report becomes an input for further studies, and can also be a legal record of a facility at any one time, that is, the time at which the audit was conducted. Regardless of the degree of effort and the amount of time and capital invested, it is essential to remember that there is no assurance that the audit can uncover all conditions at the site. It is therefore important that the final report clearly states and describes both the procedures which were used in conducting the audit, a factual description of the facility and the information available as it existed at the time of the audit, as well as the presence of all existing liabilities. An audit is a snapshot in time. The value of the analysis is that it helps uncover and document conditions and serves as a basis of response and actions for implementation. Given all these limitations and restrictions, one may question why an audit is performed. The answer is directly related to the purpose for which the audit is performed in the first place.

Protocols and Questionnaires Most environmental audit programs use some form of written guidance during the on-site audit. Some audits use checklists or outlines. Others use detailed guidelines and comprehensive procedures to audit against those requirements. An audit questionnaire is used to allow the auditor to accomplish the objective of the audit. This serves as a guide in collecting information and a record of audit procedures completed. The completed questionnaire provides a record of reason of any changes or deviations from the plan or procedures. A good inquiry lists the procedures to be followed during the audit to gather evidence about the facility's practices. This can be very useful in establishing a consistency into the audit, especially where

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65

rotating audit teams are used. An environmental audit should not be a rigid checklist where no deviation is allowed. It is a guidance tool used by audit team members to conduct an effective, quality survey. While many various formats for audits can be used, there are certain basic elements which are common to most. A description of the objectives should be included. Judgement must be used in understanding the program goals and any limits that are expected to be adhered to in deviating from the company's audit procedures. The audit survey questions should be prepared as early in advance of the total program since it provides the foundation of individual audits. It is important to not only outline the various topics to be covered but also the depth of review for each subject/topic to be covered. Each functional area such as water pollution control, air pollution control, etc. should be developed. Checklists can be modified for each individual audit. Examples of audit checklists for various program areas are given elsewhere in this book. When developing your audit, there are a number of steps that should be taken. First, the scope of the audit must be established. Various functional areas (air, water, hazardous waste, process, etc.) and the topics within each function area must be defined. Differentiation between offsite and on-site activities must be made and a list of audit topics should be constructed. Field Work There are five basic steps to carry out the on-site activities of the audit. The first step is to develop an understanding of a facility's internal system. Information obtained directly from plant personnel, discussions with managers or key staff is useful in obtaining information regarding policies, procedures, practices, and controls. A working understanding of how the facility intends to manage activities that can affect performance is the goal here. Once the facility's internal controls are understood, the next step of the audit process is to evaluate the strength of the design of those controls. Some of the factors that lead to satisfactory control include: 9 9 9 9 9

Clearly defined responsibilities Adequate system of authorizations Division of duties Trained and experienced personnel Documentation

66

Waste Minimization 9 Protective Measures 9 Internal Verification

These require significant judgement by the auditor since there really are not any widely used standards in this area. After the facility's internal controls have been evaluated, the next step is to gather evidence to identify and substantiate findings in accordance with audit objectives. Evidence is the information that forms the basis for the audit opinion. There are three basic types of evidence gathered in an audit: physical, documentary, and circumstantial. Physical evidence relates to something the auditor can see or touch. Examples of this would be stack monitoring equipment, analysis of effluents, analysis of materials, etc. Documentary evidence is something that can be visible in a paper trail. A good example of this would be manifests, shipping records, inventories which allows a review of past waste shipments. Limitations are that manifests do not tell the auditor about shipments not recorded. Also, these documents can be changed while preparing for an audit. Circumstantial evidence is useful in developing an overall impression of a facility during an audit. General housekeeping, neat files and records, qualified personnel, and attitudes of operators and foremen are examples of this form of evidence. It should be mentioned that internal control systems can include both engineered and managed controls. As a result, functional tests may be performed to verify either system, installed equipment or both. Ideally, one would like to use both these testing efforts; however, given staffing and resource constraints, everything cannot typically be verified. After the gathering of evidence, the field work is significantly completed. Evaluating and reporting findings are sometimes partially completed on-site. During the on-site audit, each member of the audit team performs various procedures to determine the status of the facility. While there are various ways of collecting date, the three basic methods are: inquiry, observation, and testing. The most important and frequently used method is probably inquiry. The auditor will ask plant personnel questions by use of questionnaires (formal) or through discussion (informal). Collection of data through inquiry usually provides satisfactory answers to unclear items found in records. However, one must consider factors such as the level of knowledge of persons questioned, the objectivity of the questioned party, and the logic and reasonableness of the response.

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67

Often, observation is one of the more reliable sources of evidence.,This is true especially where specific operations are material to performance and desirable to be observed. The method solely proves physical existence, not if the system or equipment is working properly. Verification activities or testing can be used to increase confidence in the evidence and internal controls. Evidence is usually developed which leads to a conclusion by testing or sampling a portion of a whole collection of items. Samples selected can be judgmental or systematic. A few methods are commonly used. Block sampling looks at certain segments of records or areas of a facility. For example, if files were arranged alphabetically, one or more blocks (i.e., all the P's) could be selected for inspection. Random sampling selects items by chance. If it is done correctly, each item or record in the population has an equal chance of being selected. Stratification sampling arranges and selects items for review based on the auditor's judgement of risk. Thus, higher risk areas receive greater review and testing. Regardless of which sampling method is used, judgement must be used to evaluate the strength of the internal controls and to interpret the significance of the results obtained from testing.

Working Papers and Recordkeeping Working papers are the documentation of the work performed, techniques used, and conclusions reached during an audit. Working papers document the information gathered and substantiate the conclusions reached about areas of investigation. Audit working papers consist of three basic elements: a description of the management systems in place for managing various aspects of compliance, a description of the specific audit methods or actions taken to complete each step of the protocol, and a summary of the findings, observations, and conclusions reached. When describing the internal systems in place, sketches can be used to describe the facility's systems in the working papers. Flow charts are excellent since they can be used to trace, document, highlight and evaluate the events and steps in any work process or procedure. Working papers should also describe the process used to gather information about a specific step, the information and facts collected, and the sources of information. The auditor should clearly identify the rationale for the tests to be performed, the sample selected, the results of the tests and observations made. As an example, if the procedure calls for a review of all water discharge sources, the action taken could be a

68

Waste Minimization

review of all facility plans, a discussion with the facility engineer, a tour with the manager, documentation of all water discharges noted, and comparison of noted sources with reviewed plans. In order to prove that the audit followed the proper procedure or modified procedures as required to conduct the survey, the working papers should provide enough detail about the testing rationale used and the resulting evidence for each item investigated. Working papers should include description to the sample, an explanation of the rationale, and a table showing the results of the comparison. It is important to take a few minutes at the end of the day during an audit to list tentative conclusions reached and items or areas that require further attention. Often because of time constraints and pressure, it may not be possible to perform these important tasks. The process of summarizing and drawing conclusions involves a review of the audit activities undertaken, the results achieved, and the notation recorded in each auditor's working papers. The results of this review are then noted in the working papers. Interim summaries and conclusions should be clearly labeled/identified. Also, it is important to refer to these lists later in the audit to check off open-ended items resolved and to modify/confirm tentative conclusions so that the final working papers represent a consistent package. In connection with the use of working papers, it is important to understand any other implications that come into play. Since working papers are an important record and represent proof of the audit, if questions arise at a later date, they may be needed to support the findings in the report. Working papers must be complete, easy to understand, and accurate since conclusions may be challenged, complete working papers will provide a strong basis for defense of the work.

Evaluation of Findings and Exit Interviews Two important tasks in any auditing program are the evaluation of audit findings and the reporting to facility management at the conclusion of the audit. Evaluating findings is one area that is often overlooked usually because of time constraints. After the field work has been completed, the auditors must determine how best to organize the findings in order to be reported to the appropriate level of management. During this step, the findings and observations of each auditor should be evaluated and ultimate disposition determined. The auditors should inform facility staff of any deficiencies as they are observed. This is important for a smooth, effective program. Communication of potential problems

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69

and deficiencies should be an ongoing process between audits and plant staff. Depending on the severity of problems encountered, most items may require the attention of the facility manager. Others require reporting to higher levels of management. Preparing the audit findings is an important step which takes a lot of time. After the field work, each auditor should develop a list of his own findings and determine if enough evidence is present to substantiate the findings. The auditor should be comfortable in the event he is challenged, so he can prove his case. Once these lists are established, the auditors must plan what they will say in the exit interview and how to say it. The first formal reporting usually occurs at the exit interview with an oral report to site management. The report should be carefully planned and prepared for. Usually, a handwritten summary of the findings is used to provide a basis for the oral report and to document what the auditors told facility management. Findings are noted with working paper page references. A copy of this write-up is normally left with the facility as a record of the exit interview. The audit team leader and members should be prepared to discuss each exception and the evidence found with facility management. The team should listen to all comments provided by the facility, take such comments under consideration, and not move on to a new subject until facility personnel fully understand the exception. Any recommendations by the audit team should be included as a part of the exit interview and oral report. Some audit teams prepare action plans on-site. These plans discuss what corrective action facility management should take to improve their environmental management systems. Facility personnel also assist in developing this plan since it will be implemented by them. Action plans should be as specific and workable as possible and identify accountable individuals. Schedules and milestones should also be established and procedures necessary to carry out the work identified. It is also common practice to acknowledge the good practices of the facility during the exit interview either orally or formally in the audit report. The audit team leader should schedule the exit interview far in advance so that key facility personnel can be present. This can usually be determined after the field work is completed. The exit interview is a meeting held at the conclusion of the audit with the audit team, facility manager, and other key personnel responsible for processing, operational or environmental activities. Exit interviews are important to the overall effectiveness of the audit. Sufficient time should

70

Waste Minimization

be provided to discuss all exceptions noted during the audit. It is a good time to enhance relations between the audit team and plant personnel. There are three basic parts to an exit interview. First, the stage should be set. The audit team should get the attention of facility personnel by acknowledging their cooperation throughout the audit, state that all findings have been discussed with facility personnel, and showing a willingness to discuss all issues in as much detail as necessary. It is important to begin the interview by making some positive comments about the facility's programs. It is also useful to explain that because of the nature of the audit, most of the discussion during the interview tends to focus on the negative noncompliance. Next, the findings and observations should be discussed. Each exception should be discussed, including why it is a finding and the evidence found. Recommendations or action plans are also presented at this time. Each deficiency must be clearly explained so that everyone has a common view of the facts. Comments made by facility personnel should also be noted. Finally, at the end of the interview, the audit team leader should explain the reporting process and the facility's role in that process. Included would be how the report is prepared, contents, when and to whom it will be issued, and procedures for the facility providing comments. Facility personnel should be fully aware of what will be included in the report before it is issued. The audit team should also describe any action required such as responding to the report or developing action plans. Communication should be encouraged between facility personnel and the audit team if questions arise.

Audit Reports The general focus of the audit report is to provide management information, initiate corrective action, and provide documentation of the audit and its findings. However, the audit report must also consider other concerns inherent to audit reporting such as disclosure requirements, and confidentiality issues. These concerns must be addressed to avoid undue liability. In conducting an auditing program, confidentiality concerns should not inhibit the performance of an audit. It may be wise to take certain steps to maximize protection of confidentiality. When preparing the audit report, it is important to report the facts clearly, concisely, and accurately. Every statement should be based on sound evidence. The report should not stress individuals or bring attention to the mistakes of any individual.

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The guidelines to follow when writing the report: First, use short familiar words, not big words. The point here is that too many big words make it more difficult for the reader. Secondly, make sure the sentences are not exceedingly long. Long sentences could feed the readers too many ideas at once, compromising the overall understanding. Finally, the report must be complete and accurate. This means placing findings in proper perspective and defining any terms not familiar to the reader. The content of the audit report should be broken down into three distinct sections: 9 The first element is background. In this section, the objective of the report and the audit should be discussed. The scope of the audit, where it was conducted, when, and who performed it should also be discussed. The particular methods that were used, i.e., physical survey, records review, interviews, tests, etc. must also be addressed. 9 A second key element in the report is the findings of the audit and corresponding relevance. This is the auditors listing of exceptions and opinions, usually and interpretation is provided to help the reader understand what is required and an explanation of the facts or evidence found. 9 A third key element is the findings related to the process or facility. This section includes findings, a list of exceptions, and recommendations. Each exception should be clearly defined and a way of correcting deficiencies suggested with any further recommendations. Figure 2-1 shows the basic steps in an environmental audit.

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Waste Minimization

POST AU()IT ACTIVITIES

ACt IVI1 II-S AT SITE

PPIE AUDIT ACTIVITIES

ISSUE DRAFT REPORT

STEP 1 ' Identify and Understand Menagemenl

SELECT AND SCHEDULE FACILITY TO AUDIT

Control Systems 9Correded Closing Report

9 Based on- Seledion Cdteda

--Ip

9Review Background information

Priorities 9 Assigned

9Determine Distribution List 9Distribute Drift Report

9Opening Meeting 9O~ientationTour of Facility

9Mow Time for Corredions

9Review Audit P 88 9Con6rm Understanding d Internal Controls

SELECT AUDIT TEAM MEMBERS

T

STEP 2' Assess Management Control Systems 9Confirm their AvaH=bility

ISSUE FINAL REPORT

9Make Travel and Lodging Arrangements 9Assign Audit Responsibilities

9Idenl/tyStrengthsind Weaknessof InternalControls 9Adipl Audit Plan and Resource Allocation

9Cctreeled Draft Report"

9Define Testing and Verification Strategies ......

9Distribute FiNd Report. 9~ Requirement for ,action Plan

I

9Determine Action Plan Preparation Deadline . . . . .

STEP 3" Gather Audit Evidence 9Apply Testing and Verification Strategies

CONTACT FACILITY AND PLAN AUDIT

9Coiled Data 9Ensure Protocol Steps are Completed 9Review aft Findings and Observations

9Discuss Audit Programr~ 9Obtain Background Information 9Adnerister (if necessary) Questionnaire. 9Derwx~Scope 9 Determ~e Applicable Requirements

9Ensure that all Findings are Factual 9Conduct Further Testing if Required

9Oetermine Resource Needs

9Based on Audit Findings in Final Report

I

9 No(e Priority Tol~s 9Modify or Adapt Protocols

ACTION PLAN PREPARATION AND IMPLEMENTATION

STEP 4 Evaluate Audit Findings

,,

9Develop Complete List of Findings 9AssembleWorking Papers and Documents L

'k"

9Integrate and Summarize Findings 9Prepare Report for Closing Meeting

Y FOLLOW-UP ACTION,PLAN J

,

I

T

STEP 4: ReportF ~

. to F a a ~

9Present Findings at Closing Meeting 9Discuss Findings with Plant Personnel

Figure 2 - 1 : Basic steps of an environmental audit.

CHAPTER 3 WASTE MINIMIZATION DATA/INFORMATION REQUIREMENTS ---A G E N E R A L A P P R O A C H F O R M A N U F A C T U R I N G - - It is essential that a methodical step-by-step approach is adopted to bring the various groups together and ensure the implementation of any waste minimization program. The approach should be flexible enough to adapt itself to unexpected circumstances. Such an approach also ensures the exploitation of maximum waste minimization opportunities. A typical approach which has been tried and tested in several situations is discussed here.

G E T H N G STARTED---STEP 1 A waste minimization team is essential for coordinating the program to get the various measures implemented and to bear overall responsibility. The team should comprise personnel from operating, design engineering, management personnel. Depending on the need, external experts can also be included. General information regarding the unit, and record is shown in Worksheet 1. A pulp and paper mill is used as a case example here. It must be remembered that each audit study is unique and industry or plant specific. Waste minimization activities require several documents and information. If these are not available, they will have to be generated and updated. The checklist given in Worksheet 2 would help in assessing the level of information available. 73

74

Waste Minimization

WORKSHEET 1 General Information Name of the Company" Waste Minimization Team: Name

A.

Designation

Major Raw Materials Consumption i) FIBROUSMATERIAL a) Wheatstraw b) Elephantgrass c) Bagasse d) Others ii)

CHEMICALS a) Causticsoda b) Hypo c) Others

B~

Energy Consumption a) Electricalenergy b) Fuel for boilers c) Others

C~

Water Consumption Production INSTALLED CAPACITY Pulp-making Paper-making ACTUAL PRODUCTION Pulp Paper Bleached Unbleached

D.

Eo

F.

Type of Effluent Treatment Primary Secondary No treatment Any Other Relevant Information

T/yr T/yr T/yr T/yr T/yr T/yr T/yr kWh/yr T/yr

T/day T/day T/yr T/yr T/yr

*

WORKSHEET 2 Available Information Information

Availability

Remarks

Process flow diagram Material balance Energy Balance Water Balance Plant layout Waste analysis Emission records Production log sheets Maintenance log sheets Any other information

I

I

l

76

Waste Minimization

LIST PROCESS STEPS AND IDENTIFY WASTEFUL STREAMS During the first study, the team should identify input and output streams. Major and obvious waste generating areas should be marked as shown in Worksheet 3. Labelling the waste streams with respect to their physical state (solid, liquid or gaseous) is a subsequent help at the waste quantification stage. If possible, the reasons for the generation of wastes should also be identified and recorded. Examples shown in Worksheet 3 is for a specific paper making operation. In a pulp and paper mill, for example, poor housekeeping alone may contribute a significant amount of waste. This often neglected area can be the simplest and most attractive starting point to effect waste minimization. While conducting the first shop-floor study, the waste minimization team should pay special attention to areas with poor housekeeping. Worksheet 4 could be used to record the housekeeping status in each section. Some commonly encountered housekeeping shortcomings are indicated in it. Many more can be elaborated under "others." It would now be possible and desirable to record some basic cost data. At this stage, it would suffice to obtain the cost of direct input materials (purchase cost) which would be easily available from purchase and store records. A sample Worksheet 5A for the pulp mill section is shown. Similar worksheets can easily be worked out for other plant sections, by replacing the first column in Worksheet 5A with the appropriate input materials for each section. A list of commonly used input materials in other sections is given below; this could be appropriately amended if necessary. 9

Raw

material preparation:

rag, jute, waste paper, steam,

electricity. 9

Stock preparation: Alum, rosin, high gum, talc/soapstone, dye,

9

Paper machine: Kerosene, electricity, steam, water.

steam, electricity.

ANALYZING PROCESS STEPS---PREPARING PROCESS FLOW CHARTS The preparation of a detailed and correct process flow diagram is the first key step in the entire analysis and forms the basis for compilation of the material and energy balance.

Waste Minimization Data/Information Requirements WORKSHEET 3 Process Flow Diagram Indicating Waste Streams Inputs Agro residue

Water ~

Process Steps >

> Wet cleaning wastewater (I)

I I

I . ..

>

Waste Streams

preparation -" '

(,screening rejects/pith} t ~

> Others > Leakages, spills, floor wash (I)

Caustic Cooking aids

> Pulp wash Pulping section

Water

> Bleach wash > Screening rejects (s) > centricleaner

Steam

> Rejects (I) > Decker filtorate (I)

Additives

> Others

Dyes

> Others Fillers ~ >

!

l ~

Stock preparation

> Excess wire pit water

>

(I)

Bioaids Paper machine

Steam Water

(I) > Floor wash (I)

Kerosene Alum

> Spills (additives/dyes)

>

.

]-

> Centricleaner reject (I) > Saveall excess water > Couch decker lilterate > Others > DG Set flue gas (g)

Utilities

> Boiler flue gas (g). > Boiler ash (s) > Hypo section sludge (s) > Other wastes

77

78

Waste Minimization WORKSItEET 4 Housekeeping Status 9 Paper Mill Example Lapses in ltousekeeping

Sections Raw material preparation (RM)

RM spillage from conveyor/screens Dust spillage from screens Others

Pulp mill section

RM/Pulp spillage during digester loading/unloading D Leakage/spillage of caustic/hypo, etc D Spillage of screen rejects and its interference with product stream D Loss of fiber due to defective wiremesh of potcher drums/bleacher drums/pulp deckers, etc. D Other

Stock preparation

Spillage of additives specially gums and dyes due to improper handling Overflow of pulp from chest due to high level Splashing of pulp from chest due to low level Others

Paper machine

Open water hoses Overflow from fan pump pit/wire pit Overflow of tray water Others

WORKSHEET 5A Input Materials Cost: Pulp Mill Section Chemicals Pulping chemicals Bleaching chemicals Steam Electricity Water

Cost/Ton

Annual Consumption

Consumption/ Ton of Paper

Waste Minimization Data/Information Requirements

79

Flow charts are diagrammatic/schematic representations of production, created with the purpose of labelling process steps and the sources of waste streams and emissions. A flow chart should list and, if possible, characterize input and output streams. Special care needs to be taken to identify recycle streams. Free or cheap inputs for water, air, sand, etc., should be particularly highlighted as these often end up being a major cause of waste. Materials which are used occasionally and/or which do not appear in output streams should be highlighted. It is not necessary to cover the entire plant under this step. One may select just one section to begin with, one which may have the maximum waste minimization potential. Such focused attention simplifies tasks and avoids confusion.

MATERIAL AND ENERGY BAIANCES The second important step is to draw a material/energy balance of the selected unit or section. Material and energy balances are important for any waste minimization program, as they make it possible to identify and quantify previously unknown losses or emissions. These balances are also useful for monitoring the advances made in a prevention program and evaluating its costs and benefits. While it is not possible to lay down comprehensive guidelines for establishing material balances, certain points might be useful. 9

It is better to first draw up the overall material balance across each major section: raw material preparation processing. 9 When splitting up the total system, simple subsystems should be chosen. Suggested subsystems for these four major sections are:

Raw material preparation D D (21 D I"i D D D

Cleaning Dewatering (in case of wet cleaning) Cooking (hydro pulping in case of waste paper) Washing Refining Screening Centricleaning Bleaching

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Waste Minimization

Stock preparation section V! Blending Process section l-'l Centricleaning r-1 Dewatering U] Drying The following measurement guidelines could be useful to avoid pitfalls while preparing the material balance: 9 9

9

The measurements should be carried out on a per-day basis. The values could then be expressed in per pound or ton produced. Wherever required, these can be extrapolated to a per-year basis, keeping a note of variations in raw material, quality etc, to determine annual figures for a feasibility analysis. All measurements of raw material should be converted to dry basis. This would simplify calculations due to variations in moisture content.

Component Balance It may be useful to evolve the component balance from the overall and section-wise material and energy balance. The most useful c o m ponent balances are: 9 9

Total solid balance Water balance

These balances give a direct indication of the efficiency of utilization of fibrous raw material, chemicals and water. They give the relative importance of different waste streams in terms of quantum of loss, and would therefore, enable priorization of various streams for developing waste minimization measures.

Assign Costs To Waste Streams In order to establish profit enhancement potential of waste streams, a basic requirement is to assign costs to them. These costs essentially reflect the monetary loss due to waste. Apparently, a waste stream does not appear to have any quantifiable cost attachable except where direct raw material product loss is associated with it, for example, fiber content in the wastewater of a pulp and paper plant, unused dye loss in waste

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81

liquor, caustic loss in pulp wash water, etc. However, a deeper analysis would show several direct and indirect cost components associated with the waste stream. A list of possible cost components is given below. 9 9 9 9 9 9 9 9

Cost of raw materials in waste Cost of product in waste Cost of steam and electricity consumed in processing the waste Cost of treatment of waste to comply with regulatory r e quirements Cost of waste transportation Cost of waste disposal Cost of maintaining required work environment Cost due to waste excess and its handling and pumping r e quirements

The above, and others, if present, should be worked out for each waste stream/emission and finally as the total cost per unit of waste.

Process to identity Causes The process can be reviewed in the context of most cost intensive wastes. Through the material and energy balances developed, a cost analysis should be carded out to locate and pinpoint the causes of waste generation. These causes would subsequently become the tools for evolving waste minimization or reduction measures. There could be a wide variety of causes for waste generation ranging from simple lapses in housekeeping to complex technical reasons as indicated below:

Poor Housekeeping 9 9 9 9 9 9 9

Leaking taps/valves/flanges Continuous running of hose pipes Excess water and or raw material use Overflowing tanks Spillage of raw material from worn-out transfer belts Contamination due to spillage of raw material Spillage of chemicals.

Operational and Maintenance Negligence 9 9

Sub-optimal conditions---improper temperature control Low bath ratios

82

Waste Minimization WORKSHEET 6A RAW MATERIALS: Item .

.

PRODUCTS: Quantity

.

.

.

.

.

.

Quantity

Item

.

. . . . .

.

.

.

.

.

.

.

.

.

. . . . .

.

.

.

.

.

.

.

.

.

. . . . .

AUXILIARY MATERIALS:

SOLID WASTE'

Item 1. Catalysts 2. Lubricant

Item

Quantity .... ....

Quantity

. . . . .

PROCESS

. . . .

. . . . .

. . . . .

WASTE WATER: WATER CONSUMPTION: Item 1. Showers 2. Washing 3. Dilution 4. Cleaning

Item 1. Process 2. Condensate 3. Cooling 4. Overflow 5. Cleaning

Quantity .... .... .... ....

Qty Contaminant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . .

AIR EMISSIONS: Item

Qty

Contaminant

. . . . .

. . . . .

WORKSHEET 6B Energy Balance STEAM Quality 1. 2. 3.

PRODUCTS Item Heat Content 1. 2. 3.

Quantity

PROCESS ELECTRICITY Quantity FUEL CONSUMPTION Item Quantity 1. Coal 2. Oil 3. Agroresidues 4.

ENERGY LOSSES Item Heat Content 1. 2.

Qty

ety

WASTE WATER Item Heat Content Qty 1. Process 2. Condensate 3. Cooling

Waste Minimization Data/Information Requirements 9 9 9 9 9 9 9 9

9

83

Suboptimal loading of reactors Wearing out/absence of insulation on reactors, steam pipes, condensate pipes, etc Improper maintenance of steam traps Worn out wire mesh, resulting in leakage/loss of materials Unnecessary running of refiners, resulting in overrefining Improper maintenance Low and uncontrolled pressure of water in nozzles and cleaning showers Continuance of worn-out press rolls with uneven surface, resulting in increased press picking and consequent production loss Improper maintenance of condensate removal system from steam dryers.

Poor Raw Material Quality 9 9 9

Use of dirty and degraded raw materials Use of low grade chemicals Improper storage of raw material.

Poor layout 9 9 9 9

Unplarmed/ad hoc expansion Improper collection and handling Location of equipment. Improper routing of steam pipes resulting in unnecessary pressure drop.

Managerial Cases, Inadequately Trained Personnel 9 9 9 9 9

Increased dependence on casual contract labor Lack of a formalized training system Lack of training facilities High turnover of senior technical personnel Understaffing at the technical personnel level hence work overpressure

Employee Demotivation 9 9

Lack of appreciation Absence of reward/punishment policies

84

Waste Minimization 9 Emphasis only on production not on people 9 Lack of commitment and attention by top management

Developing Opportunities Having identified and assigned causes to waste generation, Waste Minimization measures can be determined. Summarizing waste streams as shown in Worksheet 7 would help in making a quick qualitative estimate of the possibilities of waste minimization. WORKSHEET 7 Summary and Waste Streams and Possibilities of_Waste Minimization Section

Waste Stream

Possibility of

Recycling

Source reduction

Housekeeping

Input Material Change

Better Process Control

Equipment Modification

Technical Change

Onsite Reuse/ Recycle

Creation of Byproduct

In this step, techniques like brain-storming and group discussions can be used to determine all the possible options. Finding the potential options depends on the knowledge and creativity of team members. The range of waste minimization measures could also be of help in developing specific opportunities. Some other sources of help in developing waste minimization opportunities could be" 9 Other personnel from similar plants elsewhere 9 Associations of task groups 9 Outside consultants

Workable Waste Minimization Selection The options developed are subsequently examined to assess theft technical-economic feasibility. The weeding-out process should be simple, fast and straightforward and is often only qualitative. There should not be any ambiguity or bias. Objectives should be to avoid the

Waste Minimization Data/Information Requirements

85

unnecessary effort of undertaking detailed feasibility analyses of opportunities which are impractical or non-feasible. Worksheet 8 would help in identifying and listing which waste minimization opportunities: 9 can be implemented straightaway without any feasibility analysis (obvious measures); 9 require further detailed feasibility analysis; and 9 can be rejected. Note that you only have to stick to the appropriate category, and that no detailed analysis is required at this stage. .

,

WORKSHEET 8 Selecting Workable Waste Minimization Opportuniti..es

Waste Minimization Opportunity

Category

Direct Implementable

Requires Further A na lysis ..

Reject

Raw material section Pulping section Stock preparation Pa~r-making section

The selection of a waste minimization solution for implementation requires that it should not only be techno-economically viable but also environmentally desirable. The short listed opportunities selected above which require further detailed analysis should be studied from the following perspectives.

T E C H N I C A L FEASIBILITY The technical evaluation determines whether a proposed waste minimization option will work for a specific application. The evaluation often begins with an examination of the impact of the proposed measure on process, product, production rate, safety, etc. In case there is significant deviation from the present process practices, laboratory testing and trial runs might be required to assess the technical feasibility. A typical checklist for technical evaluation is provided in Worksheet 9. The measures which are technically not feasible due to nonavailability of technology, equipment, space or any other reason should

86

Waste Minimization

be listed separately for future studies by technical personnel. Technically feasible measures should next be subjected to an economic analysis. WORKSHEET 9 Technical Feasibility Analysis A. Technical Requirement Component

Requirement--Yes/No

Indigenous Availability

1. Hardware

Equipment Instrumentation Technology 2. Space 3. Manpower 4. Shut down

B. Technical Impact Impact

Area

Positive

Negative

Production capacity Product quality Energy Conservation Steam Electrical Chemical Consumption Safety

Maintenance Operational

Flexibility Others

Economic Viability Economic viability often becomes the key parameter for the management to accept or reject the proposed waste minimization measure. For a smooth take-off, it is essential that the first few waste minimization measures to be reported to management are economically attractive. Such a strategy helps in creating more interest and commitment. The economic analysis can be conducted using a variety of methods, for example, the payback period method, internal rate of return method, net present value method, etc. For low-investment, short-duration measures with attractive

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economic viability, the simplest---the pay back period method--is usually good enough. A typical worksheet (Worksheet 10) which would help in working out techno-economic viability is given. It may have to be modified to suit the different options, but care should be taken to keep it as simple and transparent as possible. Even measures which are not economically viable should not be dropped out. It could be possible that some of these options might have a significant impact on the environment and may, therefore, warrant implementation even if they are economically unattractive.

WORKSHEET I0 Economic Viability Analysis Name/Description of the Waste Minimization Measure Investment

Savings

Hardware Pumps Piping Civil Circulation tank Holding tank Equipment (specify) Land requirement Others Total

Energy Steam Electrical Chemicals Caustic Bleaching chemicals Additives Fiber Raw material Manpower Due to increased production Reduced environmental costs Treatment cost Waste transport cost Waste disposal cost Others

Annual Operating Cost Interest (15-1 8%) Depreciation Maintenance (2-4 %) Manpower Skilled Unskilled Energy Steam Electricity Chemicals Cost due to shutdown Others Total

Total Net Savings = (Savings--Operating cost) PAYBACK = (Investment/Net Savings) x 12 = ...Months

88

Waste Minimization

ENVIRONMENTAL ASPECTS The options for waste minimization must be assessed with respect to their impact on the environment. In many cases, the environmental advantage is obvious: there is a net reduction in the toxicity and/or quantity of waste. Other effects could be changes in treatability of the waste, changes in applicability of environmental regulations. In the initial stages, environmental aspects may not appear to be as compelling as the economic aspects. However, it should be realized that environmental aspects may be the most important consideration, irrespective of the economic viability.

IMPLEMENTATION SOLUTIONS Following the technical, economical and environmental assessment, waste minimization measures may be selected for implementation. Understandably, the most attractive ones would be those with the greatest financial benefits, provided technical feasibility is favorable. However, in a growing number of cases, especially when active pressure groups are present, environmental factors can take priority. In cases where a large number of waste minimization measures have been developed, it could be confusing to decide and allocate priority to them with respect to implementation. It would help in rating and prioritizing the measures for implementation. It would also be useful in determining the resources required (finances, manpower, time, etc.) and in evolving an implementation plan. A certain amount of subjectivity is intentionally introduced to enable the team to grade the measures even if they fall in the same category during the feasibility analysis. It would be desirable to document the work done so far. Apart from becoming a reference document for seeking approvals and in implementation, the document would also be useful in obtaining finances from external institutions, reporting status to other agencies and establishing base levels for performance evaluation review. The selected solutions should next be taken up for implementation. A large number of solutions can be implemented as soon as they are identified (leakages sealed, taps closed, idle running stopped, etc); several others, though, might require a systematic plan of implementation. The waste minimization team needs to prepare itself as well as other concerned groups to take up the job of implementation. The preparation

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would include seeking financial approvals, obtaining concurrence from concerned departments, establishing linkages in case of multi-department solutions, etc. These tasks require, in addition to the technical aspects, a careful handling of the concerned persons to ensure their support and cooperation throughout implementation. Good liaison, awareness and information dissemination assist implementation. Checklists of tasks involved, agencies/departments to be approached, contacts need, etc. provide useful help. The reader is referred to other sections of this book for further details. Implementing waste minimization solutions is analogous to any other industrial modification and does not require elaboration here. The tasks comprise layout and drawing preparation, equipment fabrication/procurement, transportation to site, installation and commissioning. Whenever required, simultaneous training of manpower should be undertaken, for an excellent measure may fail miserably if not backed by adequately trained people. To the extent possible, the implementation team should be aware of the job and its purpose, as several useful suggestions have often emerged from the implementation crew. WORKSHEET 11 Environmental Aspects Analysis Name/Description of the Waste Minimization Measure ,

Medium .

.

Parameter .

.

.

AIR

Particulates Gaseous Others

WATER

BOD COD TS Others

LAND

Solid Waste Organic Inorganic

..

Impact on Environment .

.

Qualitative .

.

Quantitative

MONITOR AND EVALUATE RESULTS Finally, the solutions implemented need to be monitored for performance evaluation. The results obtained should be matched with those estimated/worked out during technical evaluation and causes for deviation, if present, should be established. Shortcomings should be

90

Waste Minimization

specifically highlighted and taken care of. A comprehensive report should be prepared to inform management. Concerned personnel should be made aware of the results. Implementation is considered to be over only after successful commissioning and sustained stable performance over a reasonable length of time. The biggest challenge in waste minimization in small scale industry lies in sustaining a program. The euphoria of a waste minimization program soon dies out and the situation returns to where it started. The zeal and tempo of the waste minimization team also tends to wane. Often, it is the top management which is responsible for such tragic ends. Backing out on commitments, predominance of production at any cost, absence of rewards and appreciation for performers, and shifting priorities are some of the commonly encountered reasons which need to be checked and avoided. The monitoring and review of the implemented measures should be so presented that the desire to minimize waste is encouraged. Efforts should be made to integrate waste minimization with the normal planning process of the company. The involvement of as large a number of employees as possible and rewarding the deserving is a sure key to longterm sustenance. In a nutshell, a philosophy of minimizing waste must be developed within the organization. This implies that waste minimization should become an integrated part of the organization's activities. Successful waste minimization programs have been founded on this philosophy.

AUDIT STUDIES

SUMMARY SECTION

Objective Although, the purpose for which such audit studies are done has been dealt with in detail, the broad objective of conducting such studies involves identification of waste reduction possibilities and that may be used as a demonstration for beginning effective controls in other similar industrial activities.

Methodology Audit team members are first of all identified in respect of each of the units studied.

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91

Post-Audit Activities The activities that follows visits to the site mainly include (i) preparation of the final report, and (ii) development and follow-ups for implementation of a corrective action program.

Problems Encountered During the Audit Problems which the audit team may face are likely to vary from facility to facility. However, what could be generally expected and need attention, are: 9 The prior history of the site. 9 The age of the relevant equipment. 9 Lack of records related to the relevant equipment. 9 The attitude of the concerned personnel onsite towards such audit studies. 9 Problems as well as responses of the concerned management for implementation the corrective measures.

Aspects Covered Although there are common aspects which vary little from industry to industry or category to category, the aspects which should be covered during the studies are as follows:

Status of Pollution Control Information collection on the following: 9 9 9 9 9 9 9 9 9 9

Products and capacity, Consent conditions (air & water), Raw material consumption; Water consumption (Process, cooling, boiler feed, gardening etc. separately); Fuel and power consumption (sulphur content of fuel); Chemicals (including catalysts) used in the manufacturing process/treatment systems; Manufacturing process(es) with flow diagram; Inplant measures to minimize pollution including recovery and recycling; Lay-out plan showing collection system for effluent, storm water, sewage, position of stacks etc.; Details of effluent treatment plant;

92

Waste Minimization 9 Details on air pollution control systems; 9 Solid waste generation (type, quantity and disposal) 9 Hazardous waste/sludge generation, storage, treatment disposal; and 9 Receiving body of water (name, flow and quality data)

and

Waste stream identification and measurement of their flow and characteristics also for the combined streams going into drains for separate disposal; Monitoring of ground water quality near effluent storage and land disposal site; Monitoring of receiving water quality before and after discharge of effluent. Stack emissions: 9 Details of stacks with respect to height and diameter, arrangement for monitoring of emission such as port hole and platform. 9 Stack emission-monitoring. Monitoring of fugitive emissions, wherever necessary, measurement of relevant parameters for air quality at boundary limit of the industry. Monitoring of ambient air quality with respect to concerned parameters which are relevant to the industry, and Analysis of sludge and solid waste in case of leachable and toxic constituents.

Performance Study Performance studies of the effluent treatment systems provide for individual sections within the complex with respect to influent and effluent characteristics and also observation of operating parameters which are relevant. Performance study of combined effluent treatment system for each unit process for relevant parameters including measurement of operating parameters, measurement of flow and collection of details on design criteria. Performance study of air pollution control system in specific cases by conducting emission measurements before and after control device(s) for the relevant parameters.

Reports of Audit Studies Auditing reports for each of the units studied are prepared by the respective task teams. The reports can be quite elaborate. A format was

Waste Minimization Data/Information Requirements

93

therefore developed and provided a brief report, typically for units studied in a uniform manner for a systematic presentation.

Housekeeping/Waste Reduction Practices for Manufacturing General housekeeping in many plants can be far from satisfactory. Good housekeeping is, in fact, the first step in any waste minimization program. The expenditure is small and the savings are immediate with a very attractive pay back period usually less than a year. A well kept operation has tremendous psychological impact on the employees and helps in building the right attitude for waste minimization. Other side benefits like better working conditions, reduced risks and hazards etc. further motivates the employees. Housekeeping related waste minimization measures are mostly unit specific and can be easily identified through a careful inspection of the production sections. A range of such measures found in some plants albeit to varying degree, are given below. The technical requirements are usually minimal and have therefore not been discussed in detail. The economics (expenditure and savings) is operation dependent and it is difficult to give a general range. The measures given should be taken as a guideline and specific measures should than be evolved from case to case.

Suggested Housekeeping Measures 9

9 9 9 9 9 9 9

Installation of appropriate chutes to collect screening rejects. The collected rejects should be handled and disposed with minimum spillage. Repair of raw material conveyor to prevent spillage of raw material and contamination of cooked pulp. Modification of loading chutes to prevent the spillage of raw material. Covering of all vibratory screens and chemical dosing tanks by proper lids to prevent spills. Provision of dykes in dumping areas to contain and channelize the flow of black liquor into drain. Installation of spring actuated self closing valves in all water hose pipes to minimize water wastage. Avoidance of spillage of lime sludge in Hypo section by proper containment, handling and disposal. Proper collection and storage system for dedusting rejects to contain its spillage.

94

Waste Minimization 9

Provision of appropriate discharge system for unloading cooked pulp in potchers (in cases where pulp is directly discharged in potcher) to avoid spillage/ splashing of pulp and black liquor. 9 Control of leakages and spillages in handling and preparation of chemicals and additives. 9 Avoidance of pump gland leakages through proper pump maintenance. 9 Timely repair/sealing of water and steam leakages from pipes, valves, flanges. The following is a detailed review checklist of housekeeping measure that should be accounted for in any waste minimization program: 9 An efficient and environmentally safe layout takes care of the material loss, cost of collection, disposal, recycle and treatment which are parts of the process itself, and the plant facility. 9 This layout postulates that efficiency is a factor for designing any equipment, reaction vessel, material transfer arrangement, storage tank and support service to operate the production system. 9 All places of storage of solid and liquid materials are to be diked without drains. Any spillage should be wiped out and not be washed out. 9 Each vessel should have its own catchpit to collect spills. 9 Each pump must be mounted on its own catchpit; a suction line of the pump should be connected to empty the pit, periodically, regularly or continuously. 9 As losses of material take place during charging of the reaction vessels, discharging of product and dripping of outlet valves, and as materials may be either solid or solid slurry or liquid, care needs to be exercised to prevent the losses, if necessary by changing the charging / discharging and transfer devices. 9 In order to collect spills from a particular vessel before the spilled materials get a chance for contamination with spills from another vessel, the two vessels must be installed at sufficient distance so that intercontamination cannot take place. The extra distance or "non-contaminating distance" is to be provided for recycle or collection of materials.

Waste Minimization Data/Information Requirements

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9 Flange joints should be avoided wherever avoidable or if used, adequately maintained and properly gasketed. 9 Corrosion-prone areas and construction materials liable to atmospheric and process induced corrosion should be given special attention for finding better replacement material and stricter preventive maintenance frequency. 9 Exhaust ducts and fan outlets are sources of pollution, and loss of material if the thrown out air is contaminated with materials. These may be treated before being vented. Any vapor line should be connected with either a recovery system or an absorption/adsorption system. 9 The engineering for the operation of pressurized systems and the established practice for preventive maintenance are consistent with the protection of the environment as well as an efficient process that minimizes wastes. These systems are fitted with pressure relief valves, and in many cases with rupture discs. A past practice is to allow the released materials to the atmosphere. To be environmentally safe these lines should to be connected to recovery / adsorption / absorption arrangements. The rupturing of safety discs is accompanied with sudden release at high pressure; the design of the recovery arrangement of the released materials should be befitting the sudden emerging conditions of high temperatures/pressures/volumes. 9 New units should be built with floors with expanded metals, slotted angles, steel grills, steel grates, prefabricated industrial floor gratings and the like which will make floor washing redundant. 9 If plant layout demands that vessels be installed in upper floors, arrangements should be simultaneously made for spill avoidance / collection. Vulnerable points of leakage should be taken special care of. This is necessary not only for pollution control and materials recovery but also for the safety of the plant personnel working on the lower floors. 9 Storage tanks of raw materials for supply to the production vessels, should be installed on a separate structure located just outside main plant buildings, with arrangements for holding spills and overflows. Level alarms should be installed where possible; where the same is not feasible because of the nature of the liquid, two overflow pipes at two different levels to the tank should be fitted.

96

Waste Minimization 9 Plant management should evolve policy and procedure for washing equipment, where a particular equipment is used for the manufacture of different products. Dry scraping of equipment surface followed by mopping with wet cloth should be carried out before hosing operation. This reduces quantity of contaminants and wastewater volume. 9 All channels should be fitted with wastewater measuring devices, half barrier for the separation of floating immiscible liquid and built-in separation / sedimentation basins for withholding settleable particulate matters. This provision may be treated as compulsory for wastewater channels in the immediate vicinity of units generating wastewater. 9 All water usages that do not come in contact with chemicals should have no opportunity to mix with process water. Uncontaminated water should have separate outlets from the plant and if recycle is not possible, should be drained out through separate channels, without any chance of getting contaminated. This is known as segregation of streams. 9 Proposed layouts recognizes the solid waste generated in a process of manufacture and must find a place within the plant premises. It will be stored on land /lagoon which will be lined with compatible geo-textile material to prevent infiltration of soft. 9 The detoxification operation is to be carried out outside the main production plant, and provision has to be kept for the same. 9 Storm water drains should be segregated from process water drains. The former may be used for the removal of cooling water and non-process water. (Source: adapted from: Minimal National Standards - Pesticide manufacturing and formulation industry, COINDS/15/1985-86, Central Pollution Control Board, Delhi, India.)

IDENTIFICATION REQUIRED OF WATER POLLUTION SOURCES FOR WASTE REDUCTION/MINIMIZATION POTENTIALS The following is a checklist of potential sources which may be candidates for waste reduction.

Waste Minimization Data/Information Requirements

97

CHECKLIST D D D D D D D D D D D D

D D D D

Name of Industry/Company/Facility/Process Address Telephone Number Telex Number Distance between plant and factory township Distance between plant and nearest railway station Name of the person with designation responsible for pollution control Total employees Township population Finished products with production capacity per day Intermediate products with production capacity per day Raw material requirements per day Utilities D Electricity requirement - Supplied from D Captive power plant, if any - Generation capacity D Steam generation - Quantity and pressure - Fuel requirement per day - Sulphur content of fuel D Water requirement m3/hr. - Supplied from Capital Investment of main plant Capital Investment of Pollution Control Operating cost of Pollution Control System Annual turnover (last financial year). WATER

Raw

D D D D D

Water

Source Arrangement for drawing Total water requirement Storage capacity and size Total water consumption break-up Process water Make-up water of different cooling towers Other uses in the process

98

Waste Minimization

D D D

9 Demineralized Water Boiler feed for steam generation Boiler feed for waste Heat Boilers Boiler feed for power house Fire water Sanitary water Raw water use Cost of raw water Analysis of raw water (range)

Raw Water Treatment Plant D

D

D D D

Capacity of clarifier Whether softening uses lime Coagulants/polyelectrolytes used Filtration system Whether prechlorination is followed Whether post chlorination is done for the entire quantity of water Storage capacity of filtered water Filter back wash water Frequency Quantity How is clarifier sludge disposed How filter back wash water is disposed Analysis of treated water after filtration (Range)

Cooling Water D Once-through or recirculating type D Number of cooling towers and the following details of each cooling tower D Servicing plant D Recirculation rate D Make up D Blow down D Concentration factor I"1 Temperature drop I"1 Conditioning chemicals inhibitors biocides

Waste Minimization Data/Information Requirements

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17 Holding capacity of basin and loop 1"-! Contamination of cooling water by leakage in the process contaminants concentration of contaminants in cooling water mg/1. E! Circulating water analysis of all the cooling towers (range) !"1 Side stream filters are provided which water is used for filter back-wash frequency quantity Analysis -particularly suspended solid content of discharged back-wash water (range) Demineralized Water

Capacity of demineralized plant I"! Streams !"1 Units cation anion mixed bed condensate polishing 13 Process water/raw water requirement i"1 Condensate polished, m3/hr I"1 Acid used with daily requirement I"! Alkali used with daily requirement !-'! Usual frequency of regeneration !"1 Effluents during each regeneration Acidic effluent, m 3 Alkaline effluent, m 3 i"1 Analysis of the effluent--pH and acidity/alkalinity, etc. C] Whether neutralization system is provided in the plant O Any use of the wastewater of demineralization plant i-'! Filter back-wash water frequency quantity analysis - suspended solid which water is used for back-wash? Individual Plant Data I-! Raw material requirement

100

Waste Minimization D Raw material analysis I-I Production capacity per day

D Usual production per day D Process of manufacture with drawings I-'! Liquid effluents source with drawings frequency temperature pressure at the source point flow m3/hr analysis (actual) routing with drawings D Emissions source with drawings frequency temperature quantity discharge point elevation - m internal diameter- mm composition design figure actual figure Liquid

Effluent

D D D D

Recycle and reuse of effluent or treated effluent if any (with drawing) Quantity Analysis of effluent Treatment of effluent routing of effluent to treatment plant (shown in the plot plan of the plant) are any effluents are routed by the storm water drain process of treatment (with drawing) analysis of effluent before and after each treatment unit efficiency of treatment unit design actual frequency of analysis done for control of units how the treated effluents are discharged (by pipe, channel or drain) where the treated effluents are discharged

Waste Minimization Data/Information Requirements

D

D

D D D

101

if there are ponds for collection of treated/untreated effluents, indicate the capacities and sizes of ponds with detention time available Any irrigation use of the effluents quantity m3/hr frequency analysis (range) Final effluent which finds out of the factory premises quantity m3/hr analysis (range) frequency of analysis Any complaints about the effluents by local people Disposal pipe line and pumping system, if any details of pipe line with material of construction. Are plant and municipal sewage treated process of treatment analysis before and after treatment quantity treated EMISSION AND AMBIENT AIR

D Does the plant possesses emission and ambient air monitoring equipment? D Are emissions and ambient air monitored, if so, analyse figures D Any use of emissions D Any complaints from local people SOLID WASTES D El D D D

What are the solid wastes Quantity per day How they are disposed Any reuse of solid wastes, if so, what are these Any complaints from local people RECEIVING WATER

D D D D

Receiving water analysis before and after disposal of effluent If river, usual maximum and minimum flow Receiving water uses Fish kill and complaints by local people, if any

102

Waste Minimization SEEPAGE PROBLEMS !"1 Any problem of seepage of effluent into the ground water 1"7 Any investigation done about it 1"! Any complaint received PROPOSED SCHEME FOR POLLUTION CONTROL

If the industry has already decided to execute some pollution control systems Details of the scheme (with drawing) Time schedule for execution Cost involved UTILITIES In the utilities section, the steam boiler is the major source of waste generation. It generates solid, liquid and and gaseous wastes. Quite often, the role of boiler department is limited to supplying steam at the desired pressure and in desired quantities. The efficiency of steam generation is rarely taken seriously, resulting in increased waste generation and also higher energy losses. The waste minimization measures described pertain mainly to boiler efficiency improvement.

WASTE Waste Minimization Measure Use of soft water as feed water

MINIMIZATION

MEASURES

Anticipated Benefits O Reduced scaling of boiler tubes and thus lower tube failures O Increased boiler efficiency and capacity O Re4uced blow-down heat loss O Reduced boiler maintenance O Reduce blow-down requirements

IN THE

UTILITIES

Technical Requirements Equipment: O Water softening plant

SECTION:

Environmental Impact

Comments

Reduced air

The additional cost of

pollution

regeneration chcmicab and manpower requirement is very

Technology: n Indigenously available

low as compared to savings. The mm of

soR water has a beneficial effect on boiler life

Manpower: [3 Skilled manpower is required Insulation of feed water tank and condensate recovery tank

O Increase gram generating capacity O Reduced fuel requirement

Equipment: [3 Insulation material

pollution

Proper insulation of steam pipelines

0 Reduced steam pressure and temperature drop 0 Reduced heat loss from steam pipelines 0 Bettor cooking due to availability of higher steam pressure

Equipment: O Insulation material

Marginal reduction in air pollution

The measure is easily

Regular maintenance of DG set

O Reduction in specific fuel consumption by 5-10%

Process: O Preventive maintenance

Reduced air pollution from DG set

Preventive maintenance plan has to be prepared and adhered to

Reduced air

The measure is easily implementablr

implementable

Waste Minimization Data/Information Requirements

103

WASTE MINIMIZATION MEASURES IN THE UTILITIES SECTION: (continued) Waste Minimization Measure Installation of maximum demand (MD) controller

Anticipated Benefits 0 Enables avoidance of penalties levied due to exceeding the contracted power demand

Technical Requirements Equipment: [] MD controller

Environmental Impact

Comments

No direct impact

The option is applicable to units with lower contract demand limits. The savings would depend on the number of times the MD exceeds contract demand

Technology: [] Indigenously available

Provision of fuel (rice husk) lead control mechanism in boiler

0 Enables boiler operation at maximum capacity and efficiency by ensuring uniform fuel firing

Equipment: [] Feed controller Technology: [] Available indigenously

Reduced air pollution Reduction ash generation

Simple and easy to implement

Supply of make-up water in condensate tank

0 Reduces steam loclfing of condensatr feed pump [] Reduces flash steam loss from condensate tank

Equipment: [] Piping

Marginal impact

Simple and easy to implement

Combustion optimization in boilers

0 Reduced fuel requirement due to reduce.d stack and unburnt loss in ash

Manpower: r'l Requires training of boiler operators to optimize combustion

Reduced air pollution

The measure requires improvement in operational practices

Use of fluidized bed boiler

0 Improvement in borer efficiency by 10-15% over that of fixed grate boilers 0 Better steam pressure

Reduced air pollution Reduced ash generation

The measure is more attractive for new mills going in for expansion and requiring additional steam generation capacity

Avoidance of condensate and steam leakages

0 Reduced heat loss 0 Reduced make,-up water requirement

Equipment: I=1 Fluidized bed boiler Technology: 1"1 Indigenously available Manpower: [] Skilled operator required Nil

No significant impact

The measure requires timely repair and maintenance

Rationalization of steam and condensate lines

0 Reduced temperature and pressure drop

No significant impact

Special care needs to be taken to avoid unnecessary bends and submergence of condensate fine in water

Equipment: I"1 Pipelines

CHAPTER 4 ESTIMATING

RELEASES TO THE ENVIRONMENT

Described in this section are the data that a facility should determine, and a discussion of information that is necessary for the facility to generate the data required. Also presented are calculation methods for estimating such releases.

DATA TO BE DETERMINED The following releases of the chemicals should determined: 9 air from fugitive or nonpoint sources 9 air from stack or point sources 9 water directly discharged to a receiving stream 9 wastes that are injected underground 9 land on site (including landfills, surface impoundments, landspreading) 9 water discharged to sewers 9 other wastes transferred offsite for treatment or disposal.

or

Quantities found and reported should reflect the amounts of chemicals released after any onsite treatment and specific to the chemical, metal, or chemical category. These quantities do not reflect the total quantity of waste or constituents of the waste. SOURCES OF WASTES/RELEASES All sources of wastes should be considered in estimating releases of a chemical from the facility. Sources include but are not limited to the following. 104

Estimating Releases to the Environment

105

Fugitive air sources 9 Volatilization from open vessels, waste-treatment facilities, spills, and/or shipping containers 9 Leaks from pumps, valves, and/or flanges 9 Building ventilation systems Stack or point air sources 9 Vents from reactors and other process vessels 9 Storage tank vents 9 Stacks or vents from pollution control devices, incinerators, etc. Water sources 9 Process steps 9 Pollution control devices 9 Washings from vessels, containers, etc. 9 Storm water Solids, slurries, and nonaqueous liquid sources 9 Filter cakes, and/or filter media 9 Distillation fractions 9 Pollution control wastes such as baghouse particulates, absorber sludges, spent activated carbon, and/or wastewater treatment sludge 9 Spent catalysts 9 Vessel or tank residues (if not included under water sources) 9 Spills and sweepings 9 Off-specification product 9 Spent solvents 9 Byproducts Accidental or nonroutine releases should also account for in the release totals, and not listed separately. The quantities that are to be reported should be the total of the releases from the various individual release points of waste streams for each medium (i.e., air, water, and land). For example, fugitive air emissions estimated separately for leaks, open vessels, and spills would be added and reported as fugitive or nonpoint air emissions. So that consideration of all the possible points/sources of release is ensured prior to making release estimates, it will be useful to prepare or refer to simplified flow diagrams for those processes involving the listed chemical; for example, for a polymerization process that uses a specific chemical, a schematic of the major pieces of equipment in which the

106

Waste Minimization

polymerization is carried out, the associated storage vessels, and the treatment steps for wastes containing the solvent would be helpful in assessing possible release points/sources. If the chemical is made or used in multiple processes, the quantities to be reported are the total releases for all processes; a flow diagram for each process is also helpful.

O V E R V I E W OF ANALYSIS The level of detail of the analysis and the level of effort required depend on your specific circumstances. Before data needs are described and before methods are outlined for estimating quantities, it should be noted that many, if notmost processors and users will have only limited data on a given chemical. Further, if monitoring data are available for that release, simple multiplication of the concentration of the chemical in the waste by the volume of the waste released may yield an acceptable estimate. The following are examples of this simple solution: 9 A furniture maker uses a listed solvent in coating furniture. The solvent evaporates in a drying area, from which it is ducted to a discharge stack and is then released into the air without treatment. In this case, the release estimate would simply be the amount of solvent present in the coating(s) purchased (adjusted for any inventory change). This value would be noted under point source emissions to air or as a process loss. 9 A food processor uses an aqueous cleaning solution that contains a nonvolatile component to wash down food processing equipment. In this case, the quantity of cleaning solution used multiplied by the concentration of the nonvolatile component in the cleaning solution would be used as an estimate of the release, say to a sewer (assuming that it does not undergo treatment prior to discharge). 9 The manufacture of a chemical compound in solution generates a solid filter cake that is land-filled on site. The filter cake contains a chemical. The release of the chemical would be estimated by multiplying the concentration of that chemical in the filter cake by the quantity of the filter cake landfilled. 9 A processor of copper-containing compounds has measured the concentration of copper in wastewater. The copper concentration times the daily volume of wastewater times the

Estimating Releases to the Environment

107

number of days on which discharge occurs yields the release estimate. In all of the above situations, readily available data on the volume of the chemical manufactured, processed, or used and data from the measurement of the concentration of the chemical in the waste were all that was needed to estimate a release or loss. Of course, careful scrutiny of the process(es) at the facility is necessary to ensure that no sources are overlooked. For example, discarded containers of unused coating or water used to wash a filter press may be additional sources in the first and third examples, respectively. The task is somewhat more complicated when, for example, there are several waste streams, treatment is used, or wastewater is discharged but the chemical in the wastewater has not been measured. The following are examples of slightly more complex situations: 9 A paint formulator incorporates a pigment into coatings. The formulator has determined that there are two sources of release for the pigment: 1) fine solids emitted to air from a milling step, and 2) solvent cleaning wastes that are sent to an off-site location for incineration. In this case, total release would be equal to the amount of pigment used (purchases adjusted for inventory changes) minus the amount of pigment sold in the product (the concentration of the pigment in the coating multiplied by the weight of coating solid). Because two wastes are involved, it is necessary to apportion the total release between them. It is unlikely that "fugitive" solids to air will have been measured; therefore, the best approach may be to estimate the amount of cleaning waste (perhaps based on the known volume of the waste shipped offsite, the concentration of coating in the waste, and the concentration of the pigment in the coating). The release quantity in cleaning wastes can be calculated from these estimates and could then be subtracted from the total release estimate to yield the fugitive air emissions. 9 The processor of copper-containing compounds, discussed earlier, precipitates solids from wastewater generated by the process. In addition to the discharge mentioned previously, some precipitate is shipped to a waste broker. This additional copper release may be estimated by multiplying the volume of waste shipped by the concentration of copper in the waste.

108

Waste Minimization The type of disposal (transfer to a waste broker) would be indicated. Treatment efficiency may be calculated by dividing the amount of copper in solids by the total amount of copper (the amount of copper in solids plus the amount in the treated water). The resulting fraction would be multiplied by 100 to obtain a percentage reduction of copper in water resulting from the treatment (precipitation step). The concentration of copper in the influent would simply be the total copper in the two "releases" divided by the wastewater volume. Alternatively, copper concentration in influent water may have been measured.

Calculations are more complicated when a volatile material is made or used and air emissions must be estimated for leaks, vents, etc., or when no data are available on water releases and the water comes from several points in the process. 9

9

The manufacture of a solvent uses a continuous process that involves a reactor, distillation columns, pumps, compressors, miles of piping, and hundreds of fittings as well as associated storage tanks and pollution control devices. Generally, the air release points will not have been monitored, and no "emission factor (s)" for the process as a whole are available. Estimates of air releases must then be based on the other calculation techniques. Other calculation techniques are presented in the section on calculating air releases. The manufacture of a chemical or product may generate wastewater. This wastewater is separated for treatment prior to discharge. Additional wastewaters arising from product washings and pollution control equipment can be combined in a central treatment system. The amount of chemical released can be estimated by considering the losses from each part of the process and then using mass balances and engineering calculations. Obviously, the larger the number of sources, the more difficult it will be to estimate the total release.

DEFINITIONS OF M A J O R A P P R O A C H E S The preceding examples illustrated four basic approaches to estimating releases after release points have been identified. These approaches are defined here.

Estimating Releases to the Environment

109

9

Calculations based on measured concentrations of the chemical in a waste stream and the volume/flow rate of that stream. 9 Mass balance around entire processes or pieces of process equipment. The amount of a chemical leaving a vessel equals the amount entering. If input and output or product streams are known (based on measured values), a waste stream can be calculated as the difference between input and product. Any accumulation/ depletion of the chemical in the equipment such as by reaction, must also be accounted for. 9 Emission factors, which (usually) express releases as a ratio of amount released to process or equipment throughput. Emissions factors, which are commonly used for air emissions, are based on the average measured emissions at several facilities in the same industry. In many cases these may be available from references in the technical literature. 9 Engineering calculations and/or judgment based on physical/chemical properties and relationships such as the ideal gas law. A single release estimate may involve the use of more than one of these estimation techniques; for example, when a mass balance is used to estimate the amount of wastewater leaving a process, and water solubility is used to calculate the maximum amount of chemical in that wastewater. Estimates may be based on analogy. The emission factor approach relies heavily on determination that the process is analogous to the process for which data were used to derive the factor. The use of any published data (for example, on the effectiveness of wastewater treatment for a chemical or on the releases from a papermaking plant) implies that the treatment schemes of processes are analogous to those used. Extreme caution should be used in the application of an analogy, especially from one facility to another. OBSERVATIONS ON T H E USE OF DATA You may be able to estimate a release in several ways based on the various sets of data that are available. If this is the case, you will have to make a decision as to which estimate to report based on the expected accuracy of each. Assuming that equally valid and equally accurate data are available for each of the preceding approaches, the following should be noted.

110

Waste Minimization Data on the actual released waste will generally provide a better estimate than data on the waste before treatment (to which a treatment efficiency must be applied). Data on the aggregate stream are preferable to data on the several streams that make up the aggregate. Data on the specific chemical are preferable to data on an analogue. Data on the chemical for a specific process are preferable to published data on similar processes. In fact, data on the treatment efficiency for a close analogue chemical treated at a specific facility will probably provide a better estimate than published data on the actual chemical, as operating conditions vary greatly from plant to plant. It may be easier to make a good chemical analogy based on physical/chemical properties than to make a process analogy.

Data, for example, on the concentration of a chemical in wastewater, may be available as a range of measured values. In this case, the average value of all measurements can be used for data specific to the facility as it operated in the reporting period, unless it can be demonstrated that some data points can be disregarded. If operating conditions varied during the time frame, such as the chemical was used periodically, or new equipment was installed at midyear, releases should be estimated for each set of conditions, such as three months during which the chemical was used, 9 months during which it was not, and these values should be added. Representative data taken during the reporting period should be used. You should, however, consider whether including data from previous years might improve the estimate because few samples are taken each year. With regard to published data on other processes, the average for facilities/equipment/operating conditions most closely analogous to the one in question should be used.

A P P R O A C H TO USE Selection of the best approach to estimating releases depends on the circumstances at your facility. Available information on a process may be the single most important factor in determining how to proceed. Provided are some general guidelines on the most effective approach(es), assuming

Estimating Releases to the Environment

111

that information is available to complete the analysis. It is organized according to type of release. There may be more than one approach.

Fugitive Air Emissions Measurement data on fugitive air emissions will rarely be available. Furthermore, the fugitive emissions from most single sources is small compared with the total volume of chemical handled; therefore, inaccuracies in measurements of input and output can totally mask the magnitude of the release if mass balance is attempted (an exception is the example of all solvent volatilized after application of a coating). For this reason, the use of emission factors is a major method for estimating fugitive air emissions. This approach requires the following: 9 A published factor (usually reported as pounds emitted per pound of chemical processed or pounds emitted per piece of equipment, such as a valve). 9 The amount of chemical handled at a facility and/or a count of the valves, pumps, etc., for which emission factors are available. Specific emission factors are available for only a few processes as a whole, and these process-specific factors can only be applied to processes that are very similar to the one for which the factor was developed. Volatilization equations can also be used for open vessels or for spills. This approach, however, requires that the vapor pressure of the chemical at the appropriate temperature, its molecular weight, and the open surface are known or estimated.

Point Source Air Emission Point-source air emissions releases are much more likely to have been measured (as compared with fugitive air emissions). This permits calculations based on available data on the concentration and flow rate of the emission. For example, multiplication of the measured benzene concentration by the measured flow rate of air through a vent yields the quantity of benzene being released. Unavailability of analytical techniques for determining airborne concentration of many of the chemicals limits this approach. When this is the case, total hydrocarbon analysis can be used to set up upper limits to the estimate.

112

Waste Minimization

Emission factors specific to some point sources such as the reactor vent for ethylene dichloride production are available and should be used if monitoring data are not available. When these approaches are not possible, estimates for point sources must be based on mass balance calculations or on engineering calculations, design data, etc. Point sources such as storage tanks will usually require a calculation based on physical properties of the chemical, the throughput, and the configuration of the storage tank.

Releases to Wastewater Frequently, wastewater discharges have been monitored. If this is the case, release can be calculated directly. In fact, your discharge data may contain sufficient information to support any needed calculations such as concentration of the chemical in the discharge and the wastewater flow rate. Multiplication of the measured concentration by the measured flow will yield an estimate of the release. When monitoring data for the chemical are not available at your facility, the following approaches may be applicable (in approximate order of preference): 9

Identifying individual process points that contribute to water discharge, performing a mass balance calculation around each to determine individual releases, and then totaling them. 9 Conducting a mass balance around the process as a Whole. For example, input of dye equals output on dyed fabric plus output in wastewater (individual sources of that water need not be estimated). This approach is most appropriate if the only release of the chemical is through a wastewater stream. 9 Using discharge data on the chemical from similar facilities.

Release in Solids, Slurries, and Nonaqueous Liquids Some of these wastes may be hazardous. Frequently, however, the concentration of individual chemicals that make up a waste will not have been measured. In this case, the concentration of the chemical will have to be determined, either by measurement or by an estimation method based on mass balance, engineering calculations, etc. For nonhazardous wastes in this category, the volume or total weight of the waste should be readily derivable from shipping records, a count of waste containers, etc. Again, the important factor to determine is the concentration of chemical of concern. Unfortunately, there are no solid

Estimating Releases to the Environment

113

waste emission factors and little published data on concentrations of chemicals in such wastes. When monitoring data are not available for a waste, mass balance and engineering calculation approaches will be necessary.

ESTIMATING RELEASES TO AIR Air emissions can originate from a wide variety of sources and therefore are usually not centrally collected before being discharged; as a consequence, each source or category of sources must be evaluated individually to determine the amount released. Often, releases to air are reduced by the use of air pollution control devices, and the effectiveness of the control devices must be accounted for in the calculation of the release estimate. This section provides various methods for estimating releases to air and for determining the efficiency of pollution control devices. Tables are provided pertaining to releases and efficiency of the pollution control devices.

SOURCES OF RELEASE TO AIR AND RELEASE E S T I M A T I O N METHODS Releases to air from industrial processes can be broadly categorized as follows: point sources, such as stacks and vents, and fugitive sources, which are not contained or ducked into the atmosphere. Whether a source is considered a point or fugitive source depends on whether the release is contained in a duct or stack before it enters the atmosphere. An accompanying table lists common air emission sources that should be considered when estimating releases. Examples illustrate the emission estimation methods for air emission sources. The examples presented are for purposes of illustration only; they are not meant to predict actual releases.

Process Vents In general, process vents are the main air exhaust devices in a manufacturing or processing operation functioning under normal conditions; however, emergency venting devices on unit operations, such as relief valves, are also grouped under process vents. The methods that can be used to estimate releases to air from a process vent are discussed

114

Waste Minimization

here; they include measurement, mass balance, emission factors, engineering calculations, or a combination of these methods. Several examples are given to illustrate the basic principles of each technique. Measurement Measurement is the most straightforward means of estimating releases. The pollutant concentration and flow rate from a process vent during typical operating conditions, if available, can be used to calculate releases. Total releases are based on the plant operating schedule.

SOURCE CATEGORIF_~ FOR COMMON RELEASES TO AIR

(1) Process Vents

(2) Secondary Sources

o)

(4)

Fugitive Sources

Handing, Storage, and Loading

Reactors

Pond evaporation

Flanges/connectors

Breathing losses

Distillation system

Cooling tower evaporation

Valves

Loading/unloading

Vacuum systems

Wastewater treatment facilities

Pump seal

Line venting

Baghouses or precipitators

Compressor seals

Packaging/container loading

Combustion stacks

Open-ended lines

Blow molding

Pressure relief devices (e.g, rupture disks)

Spray drying Curing/drying

Lab hoods

Scrubbers/absorbers

Process sampling

Centrifuges

Equipment inspection

Extrusion operations

Equipment cleaning

Pressure safety valves

Equipment maintenance

Manual ventings

Blowing out pipelines Storage piles

Note: Process vents are usually point sources. Secondary sources are usually not contained and are considered fugitive sources. Storage tank emissions are considered as point sources; other loading and unloading releases could be categorized as either point or fugitive sources, depending on whether the releases are ducted.

Estimating Releases to the Environment

115

Example 1: Use of a Mass Balance to Estimate Air Emissions From a Process Vent:

Step 1: Draw a diagram, label all streams, and list input and output values. Consider a unit process that uses Chemical X to produce a product. In a year, 10,000 lb of Chemical X is used to produce 24,000 lb of a product containing 25% of Chemical X by weight. The input consists of 8000 lb of purchased Chemical X and 2000 lb that is collected from recycling. This process generates 5 tons or 10,000 lb of solid waste containing 15% (1500 lb) of Chemical X. The only other unit process stream is a process vent, which emits an unknown amount of Chemical X to the atmosphere. The following presents a schematic of this hypothetical unit process.

l~

MASS BALANCE BOUO ft ARY

PROCESS I VENT

I

x

1

J INI'uI ~J U~wIr j_ i ..... { " -I_PR~ ESS. I ' [I RECYCLE 1 1- WASTE

J

I jI

,

PRODUCT ,

,

,,-.-

r

Hypothetical unit process using Chemical X Step 2: Set up equations with input streams equal to output streams. Considering the quantities of Chemical X in all streams that enter or leave the process, the amount of Chemical X that is lost through the process vent on an annual basis can be estimated as follows: Input Output

= =

Input

=

Amount purchased (8000 lb) Product (24,000 lb x 25%) + waste (10,000 lb x 15%) + process vent loss (unknown) Output

8000 lb Chemical x = 6000 lb + 1500 lb + process vent loss Process vent loss = 8000 - 6000 - 1500 = 500 lb Chemical x per yr

116

Waste Minimization

Example 2: Use of an Emission Factor to Estimate Toxic Air Emissions From a Process Vent Step 1" Assemble emission factor information from literature. Hydrofluoric acid is being produced by reacting fluospar with sulfuric acid. The emission factor given from the literature is 50 pounds of fluoride per ton of acid product. The plant produced 55,000 tons of acid in the past year. Step 2: Calculate releases In the absence of more accurate information, the uncontrolled fluoride emissions from the process would be calculated as follows: 50,000 tons 50 lb • - 2,750,000 lb per year year ton Based on information, the use of a water scrubber to control releases would reduce emissions to 0.2 lb of fluoride per ton of acid. Emissions after control would thus be: 55,000 tons • 0.2 lb = 11,000 lb per year year ton Example 3: Use of Emission Factors to Determine Specific Chemical Air Emissions: Step 1: Air emissions from the blast furnace of a primary lead smelting facility are controlled by a fabric filter system. In the literature, an emission factor for uncontrolled releases of particulate is given as 361 lb per ton of lead produced. A particulate removal efficiency range of 95 to 99% is provided for fabric filter control devices used for primary lead smelting operations. Step 2: Calculate particulate releases. Assuming the fabric filter system is 97% efficient, the particulate emission factor is reduced to (1.00 -0.97) •

361 lb particulate _ 10.83 lb particulate per ton of lead ton lead produced

Thus, an annual production of 31,500 tons of lead will result in the emission of 341,000 lb or particulate (10.83 x 31,500).

Estimating Releases to the Environment

117

Step 3: Calculate specific chemical releases. A typical chemical composition for particulate matter sampled downstream of a fabric filter controlling emissions from a primary lead smelting blast furnace is given. Based on this information, annual emissions of individual toxic compounds can be calculated by multiplying the respective chemical composition by the total particulate of 341,000 lb/yr. The specific compounds found according to this data source, their respective percentages of the total particulate matter, and their resultant annual emissions are summarized below. Compound

Chromium Nickel Copper Zinc Cadmium Lead

Percentage of Particulate 0.02 0.06 0.35 15.2 23.1 30.7

Annual emissions, ib

63 189 1,197 50,400 78,750 103,950

Example 4: Use of Engineering Calculations to Estimate Toxic Air Emissions from a Process Vent Step 1: Assemble process composition information A process vessel containing 5 wt % A, 15 wt % B, and 80 wt % C is vented to the atmosphere. The discharge rate through the vent has been measured at 5 ft3 per minute at 70~ The process tank is in service 200 days per year. At 32~ 1 lb-mole occupies 359 ft3. Step 2: Calculate composition of vented gas. Assuming equilibrium between air and liquid in the tank, the emissions of A are calculated as follows: wt.%A MWA XAL = mole fraction A wt. % A + wt. % B + wt. % C MW A MW B MW c where MW = molecular weight of compound PA = XAL po where pO = vapors pressure of A at ambient temperature PA/Pr = fraction of gas in air phase, XA6

118

Waste Minimization

Step 3" Calculate annual release To calculate the annual release, the following factors must be multiplied: h x 200 operating days X ^ ~ X 5fta x 60 min x ----24 h day yr rain. x lb mole (32"F + 460)0R x (MW) lb 359 ft3 (70*F + 460)*R lb-mole -- pounds of chemical A emitted per year

Example 5: Use of Engineering Calculations to Estimate Toxic Air Emissions From a Process Vent: Step 1: Assemble process composition information. A process vessel containing 5 wt % A, 15 wt % B, and 80 wt % C is vented to the atmosphere. The discharge rate through the vent has been measured at 5 ft3 per minute at 70~ The process tank is in service 2000 days per year. At 32~ 1 lb-mole occupies 359 ~ . Step 2: Calculate composition of vented gas. Assuming equilibrium between air and liquid in the tank, the emissions of A are calculated as follows: wt. % A MW^ XAL - mole fraction^ -wt. % A + wt. % B + wt. % C MW^ MW b MWc/ where MW = molecular weight of compound PA = XAL po where po = vapor pressure of at ambient temperature PA/PT = fraction of gas in air phase, XAo Step 3: Calculate annual release. To calculate the annual release, the following factors must be multiplied: X^GX 5fta x 60 min x ~ 2 4h x 200 operating days h day yr min. x lb mole (32"F + 460) ~ x (MW) lb 359 ft3 (/0*F + 460)*R lb-mole - pounds of chemical A emitted per year

Estimating Releases to the Environment

119

Step: 4 Set up mass balance around entire process. An overall mass balance around the entire process can be used to solve for X:

t o.7~

(! 9z) I (PCE Emissions) .... ~__ ~[Solvent IIb _ ~ Oegre4ser Recovery (Fresh P C [ ) I O.ZZ (i 9t) JI (Spent PC[)

J

II

-

[

,

L

. .

.

-

-

t

J L

I

_ . ,

X (accrclcd PCE) ,J.J

.....

Input Fresh PCE 1 1 X

,...,

= = = = =

,...,..

~

0.0SS + 0.0s

( Honrtcover~b|e PCE')

I

I-~--Overa i I Hass j Balance 80undtry

Line

Output emissions + nonrecoverable PCE 0.78 ( 1 + X) + 0.055 + 0.055X 0.78 + 0.78 + 0.055 + 0.055X 0.2 lb of PCE recycled per pound of fresh PCE used

Step 5" The PCE emitted per lb of fresh PCE can then be calculated. PCE emissions = = =

0.78 (1 + X) 0.78 (1 + 0.20) 0.94 lb per pound of fresh PCE

Total annual emissions of PCE would be 0.94 times the total amount of fresh PCE consumed annually.

Example 6: Use of an Emission Factor to Estimate Air Emissions From Material Storage: Step 1: Assemble tank and product data. The following calculations are for a 10,000-gallon, white, fixed-roof tank that holds, 1,1,1-trichloroethane at an average temperature of 60~ The tank is 10 feet in diameter and 17 feet high. On the average, the tank is half full and has a throughput of 2000 gallons per month, or 24,000 gallons per year. The average diurnal (day and night) temperature change is 20~ Ambient pressure is I atmosphere or 14.7 psi. Chemical handbook data show that 1,1,1-trichloroethane has a molecular weight of 133 and a vapor pressure of 1.6 psi at 60~ The vapor pressure may be

120

Waste Minimization

estimated by plotting temperature against vapor pressures obtained from handbooks and selecting the pressure at the given temperature. Step 2: Insert values into equations and calculate releases. Breathing losses (pounds/year) 0.0226

(factor)

x 133

(molecular weight)

x 1.6 1 4 . 7 - 1.6

(vapor pressure ratio)

x 10 ~'73

(tank diameter)

x 8.5 ~

(half-full)

x (20) 0.5

(diurnal temperature change)

xl

(paint factor for white)

x 0.51

(adjustment for small tanks)

xl

(product factor)

= 262 pounds/year Working losses are estimated by use of the following Equation.

CALCULATE LOADING LOSSES FOR VOLATILE ORGANIC LIQUIDS"

L L = 12.46 SPM T ~-

release in pounds/1000 gal of liquids loaded

P

=

liquid vapor pressure, psia

M

.R

molecular weight

T

_~

liquid temperature (~ + 460)

S

__.

saturation factor depending on carrier and mode of operation as shown below.

L

Estimating Releases to the Environment

121

Cargo carrier

Mode of operation

S factor

Tank trucks and tank cars

Submerged loading of a clean cargo tank

0.50

Splash loading of a clean cargo tank

1.45

Submerging loading: normal dedicated service

0.60

Splash loading: dedicated vapor balance service

1.45

Splash loading: dedicated vapor balance service

1.00

Submerged loading: ships

0.2

Submerged loading" barges

0.5

Marine vessels

EPA Publication AP-42, Section 4.4

Working losses (pounds/year) 2.4 x 10 -s (factor) x 133

(molecular weight)

x 1.6

(vapor pressure)

x 10,000

(tank capacity)

x

(turnovers per year)

24,000 gal used 10,000 gal capacity

xl

(turnover factor)

xl

(product factor)

= 123 pounds/year Total losses = 262 + 123 = 385 lb per year

122

Waste Minimization

The density of 1,1,1-trichloroethane is 11.2 pounds per gallon. Annual throughput is 24,000 gallons or 269,000 pounds. The calculated annual release is 385 pounds. A mass balance could not determine a 385 pound loss in 269,000 pounds handled. Consequently, the use of emission factors is an appropriate method for estimating tank releases. If the storage tank in the preceding example contained a mixture of materials A and B, the air releases could be calculated in a similar manner given the mole fractions of the components in the liquid phase (XAL and XBL) and the vapor pressure of the pure components (WA and ~). The molecular weight and vapor pressure used in the calculation of breathing and working losses would be calculated as:

Molecular weight - Mv - (MA) X

PA

AL §

P, j

XL/

X

LP:'J

O

True vapor pressure = P, = (PA) (XAL) + (PB) (XBL)

Example 7: Use of Measurement Data to Estimate Potential Toxic Air Emissions From Uncaptured Process Releases: Step 1: Determine basis for estimating releases and assemble necessary data. Employee exposure to benzene should not exceed 1 ppm as an 8-hour time-weighted average. A plant has an alarm system that responds to 0.2 ppm benzene and a ventilation system that exhausts 20,000 acfm of room air at 70*F. If the alarm has not sounded during the course of the year and the plant operates 24 hours per day, 330 days per year, a conservative estimation of benzene fugitive releases could be performed as follows. Step 2: Calculate releases. Benzene releases per year would be calculated as follows:

20,000 ft3 • 60 minutes x 24 hr x 330 days x 0.2 ft3 benzene _ 1900 ft3 minute hour day year 106 ft3 air

Estimating Releases to the Environment The density of benzene vapor is 0.2 would be less than: 1900 ft 3 benzene

x

year

0.2 lb

lb/ft 3,

123

and the annual release

= 380 lb of benzene per year

ft3

This value thus serves as an upper limit of potential releases.

TECItNIQUES Catalytic I ncineration"

.

FOR

CONTROLLING

Thermal Incineration" .

SELECTED

Boilers/process heaters" . .

AIR POLLUTANTS . Flares"

Absorption Acetaldehydec

Acmlein

Butadiene 9

Acetaldehyde

Acrylonitrile

Acrylonitrile

Cumenc

Acrolein

Acrylonitrilc

Benzene

Aniline

Ethylbenzene/styrene

Acrylic acid

Acrylic acid Allyl chloride

Acrylic acid

Butadieneb

Benzene

Ethylene oxide

Acryionitrilr

Cumene

Benzyi chloridec

Formaldehyde

AUyl chloride

Aniline

Ethylene dichloride

Butadieneb

Phenol

Butadieme'~

Benzene

Ethylene oxide

Epichlorohydrin

Propylene oxide

Chloromethanes~

Benzyl chloridec

Phenol

Ethylene dichloride

Chlomprene

Butadienca

Formaldehyde

Cumene

Carbon tetrachloridc

Methyl chloroform

Ethylbenzene/styrene

Chlorobenzene

Perchloroethylene/ trichloroethylene

Ethylene oxide

Chloroprcne

Polychlorinated bipheyls

Formaldehyde Methyl methacrylatc

Epichlorhydrin Ethylbcnzcne/styrene

Toluene

Propylene oxide

Ethylene dichloride

Toluene diisocyanate

Ethylene oxide

Vinylidene chloride

Methyl chloroform Perchloroethylene/ trichloroethylene Phenol Phosgene Propylene/oxide vinylidene chloride Xylene

9Combustion techniques. b Refers to 1.3 butadiene. c Possible control technique. d Chlorometlumes include methylene chloride, chloroform, and carbon te.trachloride.

TECHNIOUI Adsorption Acrylonitrile Aniline

Benzene :arbon wrachloridd perchlorocthylcne Chlorobcnzcne Chloroform Ethylcne dichloridc Muhyl chloroform Mclhyl rncthacrylatc Mcthyl rncchacrylale Mcthylcne chloride Phenol Naphthalac Phosgene Styrene Toluene Toluene diisocyanate Trichlorcahylcne Vinyl chloride Vinylidene chloride Vinyl chloride Xylene

~

Fabric Filters

Condensation Acetaldehyde Acrylic acid Acrylonirrile Ally1 chloride Aniline Bcnzcnc B a y 1 chloride" Butadienc Carbon tetrachloride Chlorobenzcnc Chloromcthancs' Chloropmc Ethylbwucndstyme Ethylene dichloridc Elhylcne dichloride uhylcnc oxide Formaldehyde Mcthyl chloroform Mcthyl mcthacrylatc PerchloroechylcnJ trichlotoahylene PhUlOl Toluene Toluene diisooyuutc Viylidenc chloridc Xylene

II

FOR CONTROLLING SELECTED AIR F LLUTANTS

Cadmium Chromium

Copper Nickel

' Combustion techniques. Refcrs to 1.3 butadicne.

' Possible w n m l tcchniquc. Chloromcthancs include rncthykne chloride, chloroform, and carbon tetrachloride.

Wet Scrubbing Cadmium Chlorobcnzene Chromium Nickel khenc diisocyanatc

Electrostatic Precipitators Cadmium Chromium Copper Nickel

Cyclone Cadmium

Copper Nickel

Ij

I

I i !,I

Estimating Releases to the Environment

125

Thermal incineration ,,,

[

...

-

Catalytic incineration Carbon adsorption

"

,

l

.~

.,

T

Absorption

T_.,~O-T

~

T---="T

. . . .

,_

Condensation

T---~ ~ ~, 2o

~o

~ so

I I(~

= 2~

t :)oo

I sr

Inlet Concentration,

~. I.(>~ VOC

~-.~~ ~ ~ z.(x>o 2.r

~

I s.o,:x3

I ~o.o(~

, 2o.~

(ppmv)

Percent reduction ranges for add-on control devices. Represents maximum achievable reduction for the corresponding inlet concentration.

M.$ N.I N.$ tt N

Ve~luti Prellure DrolD 1;^ HtOl

70 ._~ r 0

, ~

, ~

,. o.,

, =,. , , , . , o., ~,o.,o,,.~

.

, =.~

, =.~

--_ ,o

SIZE OF PARTICALES (AERODYNAMIC MEAN DIA.) (MICRONS)

Venturi scrubber collection efficiencies

,~

126

Waste Minimization

E S T I M A T I N G RELEASES IN W A S T E W A T E R At most facilities, wastewater from individual process sources is centrally collected and discharged from one point. This greatly simplifies the task of estimating releases of toxic materials to water because it decreases to one or a few the number of discharge streams for which releases must be estimated. Nevertheless, in some situations it may be necessary to estimate releases in wastewater from individual sources. A facility that discharges or has the potential to discharge water containing toxic and/or hazardous wastes usually requires measurements of the water volume and analyses of some generalized wastewater parameters such as biological oxygen demand (BOD) and total suspended solids (TSS). Occasionally, releases which require analyses. In these instances, releases can be calculated by straightforward multiplication of the volume of wastewater released by the concentration of the chemical released. The wastewater may or may not be treated before its discharge to minimize releases. The following subsections present some of the various sources of wastewater and methods of wastewater disposal. Also discussed are methods for calculating releases of compounds in wastewater and estimating efficiencies of wastewater treatment devices.

SOURCES OF W A S T E W A T E R AND M E T H O D S F O R ITS DISPOSAL Releases of toxic chemicals can originate from a variety of wastewater sources. Some of the more common sources and process that generate wastewater is given. Unlike air emissions, wastewater from individual sources in a facility are usually centrally collected and combined for discharge at one or a few points. Methods of wastewater disposal are presented and discussed briefly in the following sections.

T Y P I C A L W A S T E W A T E R SOURCES Untreated process wastewater Miscellaneous untreated wastewater - equipment wash-down, steam jet condensate, cooling water (continued)

Estimating Releases to the Environment

127

Decantates or filtrates Cleaning wastes Steam stripping wastes Acid leaching solutions Spent plating, stripping or cleaning baths Spent scrubber, absorber, or quench liquid Off-spec, discarded products or feedstock Distillation side cuts Cyclone or centrifuge wastes Spills, leaks, vessel overflows

METHODS OF WASTEWATER DISPOSAL Direct discharge to surface waters Discharge to a publicly owned treatment works Underground injection Surface impoundments Land treatment

Direct Discharge to Surface Waters Many facilities discharge wastewater directly to nearby bodies of water. Monitoring of the wastewater discharge flow and the concentrations of various constituents within the wastewater, usually generalized constituents such as BOD and TSS, may be available. Monitoring may not usually be required for most individual chemicals or compounds. When such monitoring is required, wastewater flow rate and concentration data collected can be used to calculate wastewater releases directly.

Discharge to Sewers Many facilities discharge their wastewater to sewers. In some cases, a sewer may require pretreatment of wastewater and/or monitoring of the

128

Waste Minimization

flow rate and the concentration of various constituents. If monitoring of a chemical or compound subject is made, releases of that chemical or compound in the wastewater can be calculated by multiplying the reported concentration by the flow rate.

Underground Injection In some situations, wastewater containing hazardous and/or toxic wastes may be injected beneath the earth's surface in location where it is unlikely to contaminate ground water. Injection operations are usually controlled by special procedures that require maintaining records of the volumes and analyses of the wastes injected. From this information, quantities of chemicals and/or compounds that are disposed of in this manner can be directly calculated.

Surface Impoundments A surface impoundment is a natural topographic depression, man-made excavation, or diked area formed primarily of earthen materials (although it may be lined with man-made materials), which is designed to hold an accumulation of liquid wastes or wastes containing free liquids. Examples of surface impoundments are holding, storage, settling, and elevation pits, ponds, and lagoons. If the pit, pond, or lagoon is intended for storage or holding without discharge, it is considered to be a surface impoundment. This information can be used for direct calculation of the quantity of a listed chemical and/or compound disposed of in this manner. This disposal method is often considered as a release to land; however, chemicals in the impoundment may be released to air by volatilization, collected as sludge and removed, or biodegraded. Any releases from the impoundment should be accounted for in release totals to air, water, land, or offsite disposal.

Land Treatment Land treatment is a disposal method in which wastewater is applied onto or incorporated into soil. This information can be used to calculate the quantity of a listed chemical and/or compound disposed of in this manner. Chemicals and/or compounds in the wastewater are released to the soil or to air (by volatilization).

Calculating Releases in Wastewater Quantities of chemicals and/or compounds released to the environment in wastewater can be calculated by summing the releases from

Estimating Releases to the Environment

129

individual operations or by determining releases from a central wastewater discharge point (if available). The latter method is preferred because it involves the direct measurement or estimation of the flow of the discharge stream, and the concentrations of chemicals and/or compounds it contains. The following subsections describe the use of direct measurement, mass balance, release data from other facilities in the industry, and engineering calculations to estimate releases of listed chemicals and/or compounds in wastewater. In some instances, information from other facilities in the industry can be applied to estimate releases in wastewater. Direct Measurement

Direct measurement can be used to calculate releases in wastewater, individual processes or from a central discharge point. This method is used by multiplying the wastewater flow rate by the concentration of the chemical or compound of concern. The following two items describe direct measurement of wastewater releases based on average measured values and multiple measured values, respectively. Releases Based on Total Annual Volume and Average Measured Concentration

If a wastewater stream has a relatively constant daily flow rate and the measured concentrations of chemicals and/or compounds in the stream do not vary greatly or are well characterized, average values for flow rate and concentration can be used to calculate releases. Example 1: Use of Direct Measurement to Estimate Toxic Wastewater Emissions:

Step 1: Gather process information and monitoring data. A stream containing an average acetaldehyde concentration of 500 milligrams per liter is sent to an onsite treatment system at a rate of 5 gal/min. The stream leaving the treatment system at 5 gal/min contains 25 milligrams of acetaldehyde per liter. If the plant operates 24 hours per day, 330 days per year, the quantity of acetaldehyde entering and leaving the treatment system can be calculated, assuming no net loss of water or acetaldehyde by evaporation to air. Also, the treatment system efficiency can be calculated.

130

Waste Minimization

Step 2: Calculate the quantity of acetaldehyde entering and leaving the system. Volume - 5 gal x 60min x 24 h x 330 days = 2.38 milliongal min hour day year year Into system:

2.38 milgal x year

5 0 0 m g x 3.78 liters x 1 lb = 93301b liter gallon 453,000 mg year

From system: 2.38 milgal • year

25 mg • 3.78 liters • 1 lb = 4961b liter gallon 453,000 mg year

Step 3: Calculate treatment system efficiency. Treatment system efficiency: 9930 - 496 x 100 =95% 9930 Example 2: Use of Direct Measurement to Estimate Toxic Wastewater Emissions:

Step 1: Gather wastewater flow and concentration. This leather tanning facility requires daily monitoring of wastewater flow volume and biweekly analysis of a daily composite sample of this discharge for total chromium. The total chromium analytical results for the year are presented below. Step 2: Calculate releases for those days in which a chromium analysis was performed. The total chromium releases (in pounds per day) to water for a given day at this facility are calculated by multiplying the daily flow (in million gallons per day) by the total chromium concentration (in micrograms per liter) times a conversion factor (8.34 x 10-3)

Estimating Releases to the Environment

Discharge flow rate 10~ gal/day

Total chromium, /zg/liter

0.415 0.394 0.417 0.440 0.364 0.340 0.457 0.424 0.463 0.414 0.476 0.431 0.369 0.392 0.323 0.302 0.358 0.322 0.330 0.322 0.408 0.442 0.442 0.356 0.390 0.423 0.487

918 700 815 683 787 840 865 643 958 681 680 627 807 729 964 722 566 510 630 630 652 649 649 695 758 658 970

131

Releases, lb/day 3.2 2.3 2.8 2.5 2.4 2.4 3.3 2.3 3.7 2.4 2.7 2.3 2.5 2.4 2.6 1.8 1.7 1.4 1.7 1.7 2.2 2.4 2.4 2.1 2.5 2.3 3.9

Average

2.44

Step 3: Calculate annual releases. Based on an average daily release of 2.44 lb over the year and 250 days of discharge during the year, the yearly total chromium discharged water is: 2.44 lb x 250 days = 610 lb per year day year

132

Waste Minimization

Example 3: Use of Direct Measurement to Estimate Toxic Wastewater Emissions:

Step 1: Gather analytical results and determine average value. The results of 10 copper analyses are express in micrograms per liter: 6 10

<5 <5

<5 <5 <5 <5

<5 <5

The average concentration is: 1(6) + (10) § 1(8) + 7(5/2) _ 4.2 micrograms 10 liter = 4.2 x 10-6 grams per liter Step 2: Determine annual releases. For an annual flow of 37.8 million liters (million gallons), the average discharge would be 4.2 x 1 0 -6 liters/year = 159 grams/year or 0.35 lb/year. Example 4: Use of a Mass Balance to Estimate Toxic Wastewater Emissions

Step 1: Gather purchasing and inventory data. A plant buys 10,000 gal (37,900 liters) per year of a water-based cleaner that contains 0.5 lb/gal (60 g/liter) of 1,1,1-tri-chloroethane as an emulsion. No material is recovered and year-beginning and year-ending inventories are both 1000 gallons. Step 2: Calculate annual releases. Assume all trichloroethane is discharged into the plant wastewater and none evaporates into the air.

Annual emissions = 10,000 gal x 0/5 lb = 5000 lb year gallon year If the plant wastewater undergoes treatment before discharge, releases would equal 5000 lb/year multiplied by [1 minus the treatment efficiency] for trichloroethane.

Estimating Releases to the Environment

133

Example 5: Use of a Mass Balance to Estimate Toxic Wastewater Releases Step 1: Gather production data. A plant processes 220,000 lb per year of scrap containing an average of 12% silver. The plant recovers 26,000 lb of 100% silver metal. Step 2: Calculate annual releases. Emissions = Material I n - Material Recovered 220,000 lb scrap x

0.12 lb silver = 26,400 lb silver lb scrap

26,400 lb silver in scrap - 26,000 lb silver = 400 lb discharged yearly Again, any treatment of plant wastewater would result in a release adjusted for the treatment removal efficiency for silver.

Example 6: Use of Engineering Calculations to Estimate Toxic Wastewater Emissions Step 1: Diagram process. In the production of ethylene dichloride (EDC) by the oxygen process (oxychlorination), a decanter is used to separate EDC from 1-120 formed during the reaction step. The decanted H20 stream is then discharged to a sewer along with wastewater from the entire facility. Step 2: Make engineering assumptions to estimate chemical concentration in process streams. To estimate the quantity of EDC emitted to the sewer from this particular operation, the following engineering calculations will be used to develop a mass balance around the decanter: Engineering calculation: The reaction stoichiometry dictates that equal molar portions of EDC and water are contained in the stream entering the decanter (Stream No. 1). As such, the composition of Stream No. 1 is known. 1 mole EDC = 97 grams; I mole 1-120 = 18 grams 1 mole EDC + 1 mole 1-120 = 115 grams EDC weight percentage = 99 grams x 100 = 86% 100

134

Waste Minimization Engineering calculation: The solubility of EDC in water is 0.869 gram per 100 grams. Assuming equilibrium in the decanter, this solubility represents the concentration of EDC in the wastewater stream (Stream No. 2). Also, the solubility of water in EDC is 0.160 gram per 100 grams. This solubility represents the concentration of H20 in the EDC product stream (Stream No. 3).

Step 3" Perform mass balance around the process. This facility is known to produce 185,000 Mg/year (megagrams per year) of EDC. By combining this with the engineering calculations above, the following mass balance can be performed. Stream

No. 1

Equal-molar ratio of HP20 and EDC w h i c h yields 86% EDC and 14% H20

S t r e a m No.

2

S t r e a m No.

(waste)

3

(product) DECANTER

Wastewater cont a i n i n g EDC at 0.869 g/lO0 g r a m s of water, w h i c h

equals a weight of

percentage of O. 869.

185,000 Mg/yr EDC plus of of H20. The collection of H20 contains 0.160 g of w a t e r p e r I00 g of EDC, which equals a weight percentage of an u n k n o w n quality

0.16.

Mass Balance: Total: Stream No. 1 (Mg/yr) = Stream No. 2 (Mg/yr) + Stream No 3 (Mg/yr) From the EDC production rate, it is known that: Stream No. 3 = 185,000 Mg EDC/yr + X Mg H20/yr The quantity of H20 in Stream No. 3 is determined by using the solubility of H20 in EDC:

Estimating Releases to the Environment

X -

0.160 gram H20 100 grams EDC = 296 x

X

135

185,000 Mg EDC x 104 grams EDC year 1 mg EDC

106 grams H20

296 Mg H20

year

year

Stream No. 3 -

185,296 Mg year

The total mass balance can be written as: Equation A: Stream No. 1 (Mg/yr) = Stream No. 2 (Mg/yr) + 185,296 (Mg/yr) EDC: Equation B: (0.86) Stream No. 1 = (0.00869) Stream No. 2 + 185,000 EqB

EqA

0.86 - (0.00869) Stream No. 2 + 185,000 (Mg/yr) Stream No. 2 + 185,296 (Mg/yr)

Solving for Stream No. 2 = 30,125 Mg/yr Step 4: Calculate total annual releases. Therefore EDC emissions to the wastewater equal (30,125 Mg/yr) x (0.00869) = 262 Mg/yr 262 Mg/yr x 10 3 Kg/Mg x 2.2 lb/Kg - 576,400 lb/year

UNIT O P E R A T I O N S AND T R E A T M E N T PROCESSES USED TO T R E A T W A S T E W A T E R

Chemical oxidation Alkaline chlorination Ozone Electrochemical Other chemical oxidation (specify) (continued)

136

Waste Minimization

Chemical precipitation (pH adjustment, flocculation, and settling) Lime Sodium hydroxide Soda ash Sulfide Other precipitation Chemical reduction Sodium bisulfite Sulfur dioxide Ferrous sulfate Other reduction

Complexed metals treatment High pH precipitation Other complexed metals treatment Emulsion Thermal Chemical Other emulsion breaking Adsorption Carbon adsorption Ion exchange Resin adsorption Other adsorption Stripping Air stripping Steam stripping

UNIT OPERATIONS AND TREATMENT PROCESSES USED TO TREAT WASTEWATER Filtration Diatomaceous earth Sand Multimedia Other filtration (specify)

(continued)

Estimating Releases to the Environment

137

Air flotation Dissolved air flotation Other air flotation (specify)

Oil skimming (gravity separation) Gravity separation Coalescing plate separation Other oil skimming (specify)

Aerobic biological treatment Activated sludge Rotating biological contactor Trickling filter Waste stabilization pond Nitrification Other aerobic treatment (specify)

Anaerobic biological treatment Anaerobic digestion Dentrification Other anaerobic treatment (specify)

Recovery of metals Activated carbon (for metals recovery) Electrodialysis (for metals recovery) Electrolytic metal recovery Ion exchange (for metals recovery) Reverse osmosis (for metals recovery) Solvent extraction (for metals recovery) Ultrafiltration (for metals recovery) Other metals recovery (specify)

ESTIMATING RELEASES IN SOLID, SLURRY, AND NONAQUEOUS LIQUID WASTES The terms solid, slurry, and nonaqueous liquid refer to those wastes which are not gaseous waste or wastewater. Where a waste is a mature of water and organic liquid, it is considered a wastewater unless the organic content exceeds 50% Slurries containing water should be reported as solids if they contain appreciable amounts of settleable or dissolved solids such that the viscosity or density of the waste is considerably

138

Waste Minimization

different from that of process wastewater. Throughout this book, "solids/slurry waste" refers to all solid, slurry, and nonaqueous liquid wastes. Solids/slurry wastes originate from a wide variety of sources. Based on the physical and chemical characteristics of a particular solid waste, it can be treated and disposed of either individually by source or mixed with other wastes from a facility. Treatment and disposal can take place on site or at an approved off-site facility. For a number of toxic chemicals, generation, storage, transportation, treatment, and disposal of wastes are subject to regulations. Sources and disposal methods for solids/slurry wastes are presented, along with associated release estimation techniques. Treatment methods and efficiencies are also discussed.

SOURCES AND DISPOSAL METHODS FOR SOLID, SLURRY AND NONAQUEOUS LIQUID WASTES Some generalized sources are presented of solid/slurry wastes, and the following subsections describe disposal methods for these wastes. Quantities of the chemicals disposed of by these methods have the potential of being calculated directly from the information available. Incineration is not discussed as a disposal method. Sometimes, solids, slurry wastes are discharged in wastewater (either to an onsite wastewater treatment facility or a sewer). In this instance, these wastes would be reported as part of the releases to water after accounting for any onsite removal.

Landfilling Typically, the ultimate disposal method for solid wastes has been landfilling. Any waste generating free liquids must be disposed of in some other fashion besides landfilling. For onsite landfills, volatilization of toxic chemicals from the landfill must be accounted for as a separate emission to air.

Land Treatment Land treatment is a disposal method in which waste is applied onto or incorporated into soft. This disposal method is considered a release to land, but volatilization of toxic chemicals into air from this source must be accounted for.

Estimating Releases to the Environment

139

Underground Injection Analogous to underground injection of wastewater, "pumpable" solid/flurry wastes containing hazardous and/or toxic chemicals may be injected beneath the earth's surface, where they are unlikely to contaminate ground water.

Surface Impoundments A surface impoundment is a natural topographic depression, man-made excavation, or diked area formed primarily of earthen materials (although some may be lined with man-made materials), which is designed to hold an accumulation of liquid wastes or wastes containing free liquids. Examples of surface impoundments are holding, storage, settling, and elevation pits; ponds; and lagoons. If the pit, pond, or lagoon is intended for storage or holding without discharge, it is considered to be a surface impoundment used as final disposal method. This disposal method is considered a release to land; however, chemicals in the impoundment may be released to air by volatilization, collected as sludge and removed, or biodegraded.

SOME SOLID, SLURRY, AND NONAQUEOUS WASTESTREAM SOURCES Spent solvents Heavy e n d s - distillation residues Heavy ends - miscellaneous Light ends - condensable Steam stripping wastes Acid leaching solutions Spent plating, stripping, or cleaning baths Off-spec, discarded products or feedstock Distillation side cuts Residue in containers, liners, drums, cans, cleaning rags, gloves Spills, leaks, vessel overflows Precipitates or filtration residues Spent activated carbon or other adsorber Spent ion-exchange resins (continued)

140

Waste Minimization Spent catalyst Scrap metal Solid scrap from finishing or trimming operations Untreated solid waste Equipment cleaning sludge (tank bottoms, heat exchangers) Oven residue Wastewater treatment sludges - biological Wastewater treatment sludges - other Treated organics Treated solids Oily waste from treated wastewater

METHODS FOR CALCULATING RELEASES IN SOLID, SLURRY AND NONAQUEOUS LIQUID WASTES Combination of direct measurement, mass balance, and engineering calculations may be used to estimate environmental releases of listed chemicals from the disposal of solid/slurry wastes. A general compilation of emission factors for these wastes is not available. However, some emission factors may be found in trade journals and the literature for specific industries. The quantity of solid waste generated can be estimated from shipping invoices if the waste is sent offsite. Quantities can also be estimated by keeping track of the drums or tanks filled with waste prior to disposal. Specific constituents in the waste may be available from chemical analyses performed to determine the hazardous nature.

UNIT OPERATIONS AND TREATMENT PROCESSES USED TO TREAT SOLID, SLURRY, AND NONAQUEOUS WASTES Incineration/thermal treatment Liquid injection incineration Rotary kiln incineration Fluidized bed incineration Multiple hearth chamber incineration Pyrolytic destruction Other incineration/thermal treatment (specify)

(continued)

Estimating Releases to the Environment

141

Reuse as fuel Cement kiln Aggregate kiln Asphalt kiln Other kiln (specify) Blast furnace Sulfur recovery furnace Smelting, melting, and refining furnace Coke oven Other furnace (specify) Industrial boiler Utility boiler Other reuse as fuel unit (specify) Fuel blending Solidification Cement-based processes Pozzolanic processes Asphaltic processes Thermoplastic techniques Organic polymer techniques Macro-encapsulation Other solidification (specify) Recovery of solvents and other organic chemicals Fractionation Batch still distillation Solvent extraction Thin film evaporation Other solvent recovery (specify) Recovery of metals Activated carbon (for metals recovery) Electrodialysis (for metals recovery) Electrolytic metal recovery Ion exchange (for metals recovery) Reverse osmosis (for metals recovery) Solvent extraction (for metals recovery) Ultrafiltration (for metals recovery) Other metals recovery (specify)

(continued)

142

Waste Minimization

Dewatering operations Gravity thickening Vacuum filtration Pressure filtration (belt, plate and frame, leaf) Centrifuge Other dewatering (specify)

Example 1: Use of Direct Measurement Solid/Slurry Releases

to

Estimate

Toxic

Spent degreasing sludges are disposed of by shipping to an off-site waste treatment facility. The specific release of methylene chloride can be estimated as follows: Step 1" Gather information from inventory. The quantity of waste identified as hazardous waste is recorded as 50,000 gallons per year. The receiver of this waste has analyzed each shipment and determined that the methylene chloride content averages 10 percent by weight. Step 2: Calculate annual releases. The methylene chloride release (to off-site disposal) iscalculated by multiplying the volume shipped by its density (8.5 lb/gal determined by weighing a known volume of waste) and by the weight percent of methylene chloride. 50,000gal x 8.5 lb x 10% • year gallon

1 __ 42,5001b 100 year

Example 2: Use of Direct Measurement to Estimate Toxic Solid/Slurry Releases Step 1: Gather information on quantity and concentration of solids/slurry waste. During the year, an electroplater shipped 7500 gallons of solution as a hazardous waste treatment, storage, and disposal (TSD) facility. The electroplater's analyses showed that the wastes contained an average of 87.4 grams of cyanide per liter of solution before treatment.

Estimating Releases to the Environment

143

Step 2: Calculate annual releases. Cyanide shipped to TSD facility: 7500 gal

•

(3.785 liters] g-~lo-n )

•

[87.4 grams] 5467 lb liter ) = 2,480,000 grams or year

Example 3: Use of a Combination of Measurement, Mass Balance, and an Engineering Calculation to Estimate Toxic Solid/Slurry Releases Step 1: Gather process and analytical information. A tannery utilizes a filter press to dewater raw sludge from its wastewater treatment plant. The dewatered sludge is disposed of in an on-site landfill. Liquid filtrate from the filtering operation is recirculated to the wastewater treatment process. Several analyses for chromium have been made on the dewatered sludge, yielding an average value of 100 mg total Cr/Kg sludge chromium. The quantity of dewatered sludge disposed multiplied by this concentration will yield the quantity of chromium releases to land from this source. To calculate the quantity of dewatered sludge sent to the landfill, an engineering estimate and mass balance will be used. Moisture measurements of the raw and dewatered sludge show that these streams contain an average of 95 and 93 and 53% H20 by weight, respectively. RAW SLUDGE 95% H 0 5% SOLIDS

-[

-1

FILTER

.......

PRESS

[

~- FILTRATE

!

-loo%

H20

D E W A T E R E D SLUDGE 53% H 0 47% S~LIDS

Step 2: Make an engineering assumption to estimate the quantity of filtrate from the filter process. It is known that the filter press has a filtration area of 100 ft2 and operates an average of 10 hours per day, 5 days per week, and 50 weeks per year. When designing the filter press, a filtration rate of 10 gal/h per ft 2 of filtration area was used. With this information, the total amount of filtrate produced by the filter press can be estimated.

144

Waste Minimization

100 ft2 •

10 gal filtrate • hr ft2

5 days x 50 weeks x 8.34 lb week year gal

10 hr day

20.85

•

10 6

lb filtrate

year Step 3: Perform a mass balance around the process. A mass balance can then be performed around the filter press to find the quantity of dewatered sludge produced per year. Total mass balance: (raw sludge) = (dewatered sludge) + (filtrate) Eq. 1: Raw sludge = dewatered sludge + 20.85 x

lb year

10 6

Solids mass balance: Eq. 2: (0.05)(raw sludge) = (0.47)(dewatered sludge) (0.4,7) (dewatered sludge) Eq.____~2:0.05 Eq. 1 (dewatered sludge) + 20.85 • 106 lb/yr dewatered sludge = 2.482 x

106 lb year

Step 4: Calculate annual releases. To calculate the amount of chromium discharged to l a n d : 100 mg _ 100 mg _ 100 lb 10 6 lb kg 106 mg i

10 6

100 lb Cr 2.482 x 106 lb dewatered sludge lb x dewateredsludge year 248.2 lb Cr year

Example 4: Use of an Engineering Calculation to Estimate Toxic Solid and Slurry Releases: Step 1: Gather process information. A semiconductor production facility uses 1,1,1,-trichloroethane (1,1,1-TCE) to degrease semiconductors. The solvent is pumped into

Estimating Releases to the Environment

145

degreasing units from 55-gallon steel drums when needed. The empty drums are sent to an offsite drum cleaning facility for reclamation. Step 2: Use an engineering estimate of the quantity of residue left in each drum. To estimate the quantity of 1,1,1-trichloroethane sent to the drum cleaning facility as residue in the drums. Results from experimentation on residue quantities left in drums and tanks when emptied. Results are presented as the mass percent of the vessel capacity, and are categorized based on unloading method, vessel material, and bulk fluid material properties (i.e., viscosity and surface tension). In this example, steel drums were pumped empty; of the four materials tested, 1,1,1-trichloroethane most resembles kerosene. As such, it can be estimated that each empty drum contains approximately 2.5 percent of the 1,1,1-trichlorethane in the drum. Step 3: Calculate annual releases. The yearly quantity of solvent sent to the drum reclaimer would be estimated as follows based on the use of 1.3249 as the specific gravity of 1,1,1,-trichloroethane relative to 1-120 at 1.00. 100 drums x 55 gal solvent x 8.34 lb H20 x 1 "3249 lb solvent year drum gallon lb H20 0.025 lb residue - 1519 lb of solvent residue per year Ib solvent

CHAPTER

5

WASTE QUESTIONNAIRES WATER CONTROL CHECKLIST

This questionnaire is intended as a guide for designing and conducting facility audits. It is intended to be used in conjunction with other data and may require additions, revisions, or modifications in order to meet particular requirements. Yes

Which of the following activities are conducted? D Treated wastewater is discharged to surface waters. Untreated process wastewater is discharged to surface waters. D - Surface run-off D - Discharges to sewers D On-site disposal F! Have there been charges in the process or facility. Facility expansion, modification, or shut D - Production increase, modification, or decrease D - Process modification D - Quantity and type of pollutants D _ Changes in water quality parameter for receiving waters D Does the facility have a separate storm sewer system ? D 146

No

N/A

D

D

D D D i'-i

D D D D

l-i

D

!"1 D D

D D r-i

D

I"!

D

D

Waste Questionnaires--Waste Control Checklist Yes

D D D D D

No

147 N/A

Are any of the following wastewaters discharged into a separate storm sewer? - Process wastewater D 1"1 D Storm water from raw materials storage, process areas, pollution contaminated softs etc. D !"-1 D Sanitary wastewaters D 13 D Have samples been obtained and analyzed for pollutants of concern? D !"1 D Using the process flow diagrams and facility layout, locate and note all points of emissions. Where possible, list pollutants in emissions. Record location of all emission control and monitoring facilities. Sources of emissions not included above (e.g., fugitive dust and process losses). Location and type of activity of the facility's neighbors (e.g., industrial, residential, and institutional).

Document in flow chart or descriptive form the following: D Air pollution control systems and procedures D Continuous monitoring D Periodic monitoring and sampling programs and procedures D Procedures for record keeping and reporting D Testing and analytical procedures D Information handling and documentation procedures List aU active, pending and operating akbome emissions, during the ~period under review. MODEL QUESTIONNAIRES WATER POLLUTION CONTROL AUDIT QUESTIONNAIRE This audit questionnaire is intended as a guide for conducting facility audits. It may require additions, revisions, or modifications in order to meet the needs of your particular objectives, industrial setting, or other circumstances. Facility Name Date(s) Team Members Participating Prepared By: Reviewed By:

148

Waste Minimization

From data of the facility or process review the following checklists: D Manufacturing process flow diagrams and descriptions D Facility layout including sewer diagrams and wastewater treatment system flow diagrams D Applicable corporate policies, procedures, and standards D Facility policies and procedures D Spill control plans D Quality assurance and reliability testing program for wastewater analyses Familiarize yourself with responses. To increase your understanding of the facility's responses appropriate inquiries should be made. During the audit, tour the facility following manufacturing processes. D Determine process flow diagram, sewer diagram and facility layout are accurate with observations. D Inspection should show that all discharges are conveyed to a point source location. D Based on observation, note any locations where it appears that process drainage leaves the facility site. D A review sewer and process flow diagrams and observations, determine if separate storm sewers convey process wastewaters or storm water run-off contaminated by contact with raw material wastes or pollutant-contaminated areas. D All flow rate measurements and water sampling and monitoring devices should be specified on permits. D Prepare conclusions in narrative form. D Utilizing flow diagram, facility layout maps, sewer diagrams, etc., identify and locate all storage and handling facilities. D Record location and capacity of all tanks and determine if based on capacity an oil spill plan is required. D Location of materials requiring dikes and determine if tank separation and diking requirements are adequate. D Record location of liquid transfer equipment used in loading and unloading as well as well as all spill monitoring and control equipment. D Location where spillage might create a problems results in leakage to receiving waters. Document in flow chart or, description following: D Water pollution control systems and procedures D Monitoring and sampling programs and procedures

Waste Questionnaires--Waste Control Checklist

149

V! Procedures for record keeping and reporting D Testing and analytical procedures D Information handling and documentation for (b) through (d) above Develop a flow chart or other description showing process and responsibilities for water pollution control activities such as sampling, analysis, record maintenance, and regulatory reporting. Based on information developed and an understanding of the system, confirm the operation of the data collection and reporting system. For data collection, with facility personnel, observe the procedure for sample collection, analysis, and data recording. Document the maintenance and calibration programs for composite sampling, effluent flow measuring, in-place monitoring and recording devices, and control equipment. D Provisions for crosschecking or verification by independent analysis. D Assess appropriateness of maintenance and calibration programs. D Analytical techniques utilized and maintenance of laboratory instruments is routinely performed.

AIR POLLUTION CONTROL QUESTIONNAIRE This questionnaire is intended as a guide for conducting facility audits. It may require additions, revisions, or modifications in order to meet the needs of your particular objectives, industrial setting, or other circumstances. Facility Name: Team Members Participating Prepared By:

Date(s) Reviewed By:

From data of the facility or process review the following checklist: D Manufacturing process flow diagrams and descriptions including control devices D Facility layout, including location of all stationary sources D Emission inventory D Regulations---federal, state, and local (including attainmentnonattainment status for each pollutant) D Any outstanding court orders--variances, compliance orders, administrative orders, etc. D Applicable corporate policies, procedures, and standards D Facility policies and procedures

150 D D D

Waste Minimization Operating manuals for air pollution control systems Air pollution alert and emergency plans Operating and construction or modification planned or intended

Familiarize yourself with facility responses. To increase your understanding of the facility's responses, appropriate inquiries should be made. During the audit, tour the facility following manufacturing processes and facility layout of stationary sources. D Confirm all identified emission sources Yes

9 Are permits in effect for all required emission sources? 9 Has there been any construction and/or m o d ification of the stationary sources within the time limits of the survey. 9 Does the facility maintain records indicating the occurrence and duration of any malfunctions during start-up, operation, or shutdown? 9 Is a written report of excess emissions kept? 9 Any continuous monitoring systems? 9 Has the facility conducted any performance tests of air pollution control systems? 9 Are permanent files maintained at the facility for the following? Emission monitoring - Ambient air monitoring - Calibration checks of monitoring devices - Measurements for determining performance Records of maintenance of monitoring devices At least two years following the dates of execution of calibration, monitoring, etc. 9 Facility compliance with emission standards for the following at all emission sources Suspended particulates - Sulfur dioxide

No

N/A

I-I

D

D

D

D

D

D D I-I

D D D

D D D

CI

D

D

CI D D D

D D D D

D D D D

D

D

D

D

D

D

D D

D D

D D

Waste Questionnaires--Waste Control Checklist

- Carbon monoxide - Photochemical oxidants - Hydrocarbons - Nitrogen dioxide - Hydrogen sulfide - Excursions on emission limits occurred Does the facility have odorous emissions that result in complaints? Are fugitive dust emissions a problem?

151

Yes

No

N/A

D D 1"-I 1"i D D

D D D D D D

1"-1 I-i D E! F'I D

D D

D D

D D

From data of the facility or process review the following checklist: D Facility layout D Process flow diagrams D Descriptions of known points of solid and hazardous waste generation D Applicable corporate policies, procedures, and standards D Facility policies and procedures D Instructional procedures for solid and hazardous waste handling and disposal D On-site systems for handling, treating, storage, and disposal of solid and hazardous wastes D Off-site systems for handling, treating, storage, transportation, and disposal of solid and hazardous wastes Review the Solid and Hazardous Waste Questionnaire. Familiarize yourself with facility resources. Make inquiries as desired to increase your understanding of the responses.

SOLID AND HAZARDOUS WASTE QUESTIONNAIRE This questionnaire is intended as a guide for conducting facility audits. It may require additions, revisions, or modifications in order to meet the needs of your particular audit, industrial setting, or other circumstances. Facility Name: Team Members Participating

Prepared By:

Date(s):

Reviewed By:

152

Waste Minimization

Document in flow chart or description form, the following showing responsibilities for action and record keeping for solid and hazardous wastes: D Responsibility for classifying wastes D Labeling D Storage D Shipping D Sampling D Maintaining records D Other action and record keeping activities, if any During the audit, tour the facility, following the process flow diagram, for the purpose of D Determining points at which solid and hazardous wastes are generated, insuring that all points are accounted for D Inspecting collection, handling, and storage facilities D Inspecting all treatment facilities D Inspecting active disposal areas at the plant site D Inspecting inactive disposal sites El Inspecting labeling, handling, storage, etc Waste generation should be determined as follows: D Determine if points identified on the drawings actually exist and if unidentified points are found. D Verify those wastes that have been tested to establish if they can be subject to waste reduction. D Determine at what point waste quantities are measured and labeled and document responsibility. D Are wastes sent directly to on-site or off-site treatment or disposal facilities, or do they go into storage. D Determine what quantities of contaminated waste are generated. Are special arrangements for handling and disposal of these wastes needed? On-site treatment and disposal, note on facility layout D Identify what is currently and has historically (during the period under review) been treated. D Treatment or disposal methods used: incineration, other thermal treatment, landfill, land treatment, physical chemical treatment, biological treatment, or underground injection. D Identify ultimate disposal of any residues

Waste Questionnaires--Waste Control Checklist

153

Obtain operating records of all methods identified. Inspect the records and document the information recorded for the period under review D Do the records contain quantities and types of solid and hazardous wastes treated. D Disposal methods and disposal locations of any residues. D On-site disposal into or on land or underground On-Site storage D Observations on layout, housekeeping, and containment. D Instructions for labeling and dating wastes received into storage. D Inspect labels and dates on a cross-section of wastes in storage. Document agreement between inventory records and wastes in storage. El Flow records from the time of receipt of waste at storage site until removal. D Do labels retain their integrity during handling and storage. Off-site disposal D Record names and addresses of all off-site contractors, including any type of disposal. D Document waste shipment by inspection. D Are shipping containers properly marked and labeled? D Determine that operations at all off-site disposal locations have been inspected within last two years by company personnel. D Prepare detailed list of audit findings.

SOLID AND HAZARDOUS WASTE QUESTIONNAIRE This audit questionnaire is intended as a guide for conducting facility audits. It is intended to be used in conjunction with an audit. This questionnaire may require additions, revisions, or modifications in order to meet the needs of your particular audit objectives, industrial setting, or other special circumstances. Confirmation of facility data Has the facility characterized all solid wastes generated to determine which are hazardous Does the facility produce any wastes classified as hazardous?

Yes

No

N/A

D

D

D

D

D

D

154

Waste Minimization Yes

-

Ignitable Corrosive Reactive Toxic Other (explain) Does the plant treat, store, or dispose of hazardous wastes on site? Does the facility have a written waste analysis plan? Does the facility accept wastes from other facilities for storage, treatment, ordisposal?

N o

N / A

D I-I D D D

D D D D D

II D D D D

["1

D

D

I-1

D

D

D

D

D

Are solid and hazardous wastes treated at the facility site by any of the following methods? Incineration I"i D 1"1 Other thermal treatment 1"i !"! F! Landfill 17 I"i I'-! Land treatment, for example, land farming I'-I El i"! Physical or chemical treatment i"! 121 D Biological treatment rl I] i-1 - Underground injection D i"1 !-'1 Does the facility accumulate or store wastes by any of the following? Pries Wl !-'1 !"! Surface impoundments I"1 1-'! !"! Drums D I-'I 13 - Tanks D D D Other containers D D D

Are hazardous waste containers in the following Labeled (waste type and date of accumulation) Compatible with wastes Closed Are storage areas inspected regularly for leaks, corrosion, or other deterioration? Does the facility maintain a record of the identity and location of all stored wastes?

condition? El D D

i-1 F'I !"i

D I"i I'-I

!"1

El

!"1

I'-!

D

I"i

Waste Questionnaires--Waste Control Checklist Y e s

-

-

-

-

-

-

Is the storage area covered, diked, etc.? Written inspection schedule available? Does the facility have a record keeping and reporting system? For all waste management operations Accumulation/storage Treatment Disposal Does the facility monitor its storage, treatment, and/or disposal facilities? Groundwater monitoring Has the plan been prepared by hydrologists? Does the plan include specification and number of wells? Does the plan include analysis of samples (frequency and constituents)? Is leachate monitoring required? Are hazardous wastes transported offsite? Are hazardous wastes transported by any of the following? Company vehicles Transporter vehicles Common carriers

Does the facility utilize off-site facilities for the or disposal of hazardous wastes? Off-site facilities for treatment - Off-site facilities for storage - Off-site facilities for disposal Have the facility's solid and hazardous waste programs been reviewed by an outside source in the past three years? -

N o

155 N/A

D D

D D

D D

D

D

D

D D D

D D D

D D D

D

D

I-'I

D

D

D

D

I'I

r1

D I"I

D D

I-I D

D

D

El

D D D

I'-I D D

D I-I El

treatment, storage, D D D

D D D

D I'-I El

D

D

D

-

156

Waste Minimization

E N V I R O N M E N T A L L Y SAFE LAYOUT F O R M A N U F A C T U R I N G UNITS 9 An environmentally safe layout plan takes care of material loss, cost of collection, disposal, recycle, and treatment which are parts of the process itself and consequently of the layout arrangement. 9

This layout code postulates that environment protection is a factor for designing any equipment, reaction vessel material transfer arrangement, storage tank and service support to operate the production system.

9 All places of storage of solid and liquid materials are to be diked without drains. Any spillage is to be wiped out and cannot be washed out. 9

Each vessel should have its own catchpit to collect spills.

9

Each pump must be mounted on its own catchpit, a suction line of the pump should be connected to empty the pit periodically or regularly or continuously.

9 As losses of materials take place during charging of the reaction vessels discharging of produce and dripping of outlet valves, and as materials may be either solid or solid slurry or liquid care needs to be exercised to prevent the losses if necessary by changing the charging/discharging and transfer devices. 9

In order to collect spills from a particular vessel before the spilled materials get a chance of contamination with spills from another nearby vessel the two vessels must be installed at sufficient distance so that inter-contamination cannot take place. The extra distance noncontaminating distance is to be provided for recycle of materials.

9

Flange joints should be avoided wherever avoidable.

9

9

Corrosion-prone atmospheric and special attention stricter preventive

areas and construction materials liable to process induced corrosion should be given for finding better replacement material and maintenance frequency.

Exhaust ducts and fan outlets are sources of pollution if the thrown out air is contaminated with pollutants. These may be treated before vented. Any vapor line should be connected with either a recovery system or an absorption system.

Waste Questionnaires--Waste Control Checklist

157

9 Engineering for the operation of pressurized systems and the established practice for preventive maintenance are consistent with the protection of the environment. These systems are fitted with pressure release valves, and in many cases with rupturable discs. The present practice is to allow the released materials to the atmosphere. To be environmentally safe, these lines ought to be connected to recovery/adsorption arrangements. The rupturing of safety discs is accompanied with sudden release of high pressure; the design of the recovery arrangement of the released materials should be befitting the sudden emerging conditions of high temperatures/pressure/volumes. 9 New units will build floors with expanded metals, slotted angles, steel grills, steel grates, prefabricated industrial floor gratings, and the like which will make floor washing redundant. 9

If the plant layout demands that vessels should be installed in upper floors, arrangements should be simultaneously made for spill avoidance/collection. Vulnerable points of leakage should be taken special care of. This is necessary not only for pollution control but also for the safety of plant personnel working in lower floors.

9 Storage tanks of raw materials for supply to the production vessels, should be installed on a separate structure located just outside the main plant building, with arrangement for holding spills and overflow. Level alarms should be installed where possible; where the same is not feasible because of the nature of the liquid, two overflow pipes at two different levels of the tank should be fitted. 9

Plant management should evolve its own code for washing equipment, where a particular equipment is used for the manufacture of different products. Dry scraping of equipment surfaces followed by moping with wet cloth should be carried out before hosing operations. This will reduce the quantity of contaminants and wastewater volume.

9 All channels to be fitted with wastewater measuring devices, half barrier for the separation floating immiscible liquid, and in-built separation/sedimentation basins for withholding settleable particulate matters. This provision may be treated as compulsory for wastewater channels in the immediate vicinity of wastewater generating units.

158

Waste Minimization All water usages that do not come in contact with chemicals, should have no opportunity to mix with process water. Uncontaminated water should have separate outlets from the plant and if recycle is not possible, should be drained out through separate channels, without any change of getting contaminated.

This proposed layout recognizes the solid waste generated in the process of manufacture must find a place within the factory premises. It will be stored on land/lagoon which will be lined with compatible geotextile materials. The detoxification operation should be carried out outside the main production plant, and provision has to be kept for the same. Storm water drains should be segregated from process water drains. The former may be used for the removal of cooling water and nonprocess water.

GUIDELINES TO MINIMIZE MATERIAL LOSSES AND WASTES HOW TO REDUCE RAW MATERIAL LOSSES Keep only an appropriate inventory of raw materials to ensure minimum material handling losses, evaporation losses etc. Adopt mechanical handling of materials with proper monitoring facilities so as to dose only the predetermined quantities as per norms prescribed. Plant layout should be propedy made so as to minimize transfer distance of materials between storage and process or between unit operations. There is a risk of cross-contamination due to usage of same storage tanks for different materials depending on the batch product. Separate storages are to be provided. Separate process lines for separate products or separate equipment for each unit operation can minimize losses due to residues left in the equipment which are usually washed out. Storage tanks should be provided with proper dip arrangements for exhausts/vents, and insulation provided so as to reduce evaporation losses. Enclosed and covered material storage areas. Keep them secured and reduce losses due to carry over by wind and rain.

Waste Questionnaires--Waste Control Checklist

159

9

Enclosures should be made to collect spills and overflows of m a terials at the material transfer and sampling points. These, if collected properly, can be recycled.

9

Regular maintenance should be taken to check flange leaks, breaks/cracks, pump failures etc.

9

Raw material purity should be ensured. Viscous raw materials lead to losses due to residues in drums. Raw materials should be easy to handle. Good house-keeping practices should be followed.

9

Norms for performance of various process operations to be fixed so that the material usages are minimized and hence the material losses.

H O W TO REDUCE WATER USAGE AND W A S T E W A T E R GENERATION IN PROCESS STREAMS Quantities required for each operation should be determined and water usage regulated strictly. Reduced water usage reduces wastewater. Good house-keeping practices reduces water usage. Spills of materials should be restricted to enclosures constructed for this purpose. The floor washings can then be minimized and at times totally avoided. Wastewater may be stored and reused. The storage costs may be lower than waste treatment and disposal costs. Storm water drains should be kept separate and provisions should be made to collect only the rainfall of the first few hours which carries contaminants. This can be subsequently treated and disposed. The scrubbing of gaseous emissions with a suitable chemical can yield a useful by-product. The discharges thus can be avoided by recycle or recovery of useful by-products. The wastewater is usually treated up to the secondary treatment level to conform to the required standards. By providing tertiary treatment by dual media filtration, chlorination, activated carbon filtration etc. wastewater can be reused for floor wash, gardening, toilets etc.

160

Waste Minimization

HOW TO REDUCE EMISSIONS

The process operations where emissions arise, should be provided with control equipment. Condensers can collect certain emissions which can be entirely reused. The transfer of materials should be done through closed operations. The areas where fugitive emissions arise and can be avoided should be enclosed and the air exhausted through induced draft, and passed through control equipment before venting off. The enclosed area should be provided with at least three air replacements per minute. Evaporation losses from storage tanks should be checked by proper insulation and putting the vents in suitable dip columns. Loading and unloading of materials from tankers leads to huge quantities of emissions. ~'i~ne material-transfers should be done through pil~s/holes keeping the outlet of the tanker and the inlet of the receiving tank covered. While loading the tanker, if the tanker inlet cannot be covered, a hood can be provided over the inlet, and emissions collected through a ducting system and further controlled.

R A W WATER

v P R O C E S S WATER

S E R V I C E WATER

P O T A B L E WATER

LOSS I N EVAPORATION AN0 WINDAGE LOSS

I I 11

9,

I

Figure 5-1: Mass balance of water consumption and effluent generation in industries.

I

FIRE

I

2 (P

a

I

g

I

s

I

MISC.

0,

2

CHAPTER 6 ANALYSIS OF PROCESS CHEMISTRY EXAMPLE PROCESSES

Chemicals manufacturing involves both physical and chemical conditions. The physical conditions are those associated with operating conditions such as high temperature and pressure. The chemical conditions are those associated with the process streams, which may contain flammable, toxic and/or highly reactive materials. Organic chemical reactions are not usually clean, that is, there are usually a number of competing side reactions in addition to the desired reaction, and a number of intermediate compounds are often formed along the reaction pathway to the final product. Some of these by products or intermediates may themselves be undesirable, or may warrant recovery because of potential values or for environmental reasons. Therefore, is important to know what these compounds are to properly evaluate them with the manufacturing process and see if they can be reduced for waste minimization purposes. It is for these reasons that the example processes given were chosen. One way of obtaining this information is through a comprehensive analysis of the process stream. This approach is generally only available to the manufacturers who, for proprietary reasons, may not want to reveal the information. In addition, analysis may reveal only those species that are suspected as being present. Further, the analysis is limited to the sensitivity of the analytical technique employed, which might not be sufficient to detect critical trace components. Another approach is to develop the information from a consideration of the reaction chemistry and a knowledge of feedstock impurities. Consideration of the reaction chemistry, as presented is the approach taken in this section. 162

Analysis of Process Chemistry Example Processes

163

Generated wastes associated with chemical manufacturing processes can be categorized into chemical losses and equipment losses. Chemical losses are related to the physical and chemical properties of the substances present in the process stream. The most important properties with respect to chemical substance are its flammability, explosiveness, toxicity, corrosivity, vapor pressure, solubility etc. Equipment losses are related to such factors as construction materials, equipment age, maintenance, reliability of instrumentation, controls, and human error. Equipment losses include, for example, the release of a material from a valve that was opened by mistake, leaks from pipe flanges or pump seals, and the failure of process vessels due to corrosion or excess pressures. Equipment hazards are site-specific, they cannot be analyzed in detail without reference to a specific plant. This discussion is limited to those hazards associated with the substances present in process and effluent streams. This section provides specific industry and process background, process descriptions, and chemicals that may be released as typical examples. These substances can effect the overall efficiency of a process and be the source of wastes. In addition to industry background information and a description of the process, a discussion is given of the process streams. Process waste discharges are also described. It is intended that these processes may act as examples for waste reduction projects. However, it must be pointed out that each individual manufacturing operation is case specific. The activities at a site include deriving material balance, identifying waste flow lines, monitoring of characteristics, evaluating performance of system, assessing environmental quality, holding discussions with the management and finally preparing the draft report. Interviews should be carried out with various cross-sections of the staff engaged in production, laboratory/quality control, environmental management, etc. so as to understand different operations. Manufacturing process surveys should be made to be familiar with layout of the plant and process operations, and to understand possible impact on the surrounding environment, and losses of materials. The entire manufacturing process of each product should be drawn into a process flow sheet representing various unit operations as blocks. A unit operation is a process where materials are input, a function occurs and materials are output mostly in a different form, state or composition. Typical process flow diagrams are given in this section. This process includes the unit operations, adduct formation, and purification. Typical

164

Waste Minimization

unit operation with inputs of raw materials, catalyst, water/air, power and recycled material and outputs of products and by-products, wastewater, emissions, solid waste and reusable waste in operations are schematicaUy shown. The quantities of inputs and outputs at each unit operation should be worked out for the entire process and data incorporated in the process flow sheet. Discussions with the staff, perusal of the records of the plant and process and the survey will help in arriving at these flow sheets. From these flow sheets, data sheets incorporating the raw material requirement, water consumption, wastewater and solid waste generation, and gaseous emissions should be worked out for each product manufactured. The water balance sheet which shows areas of water usage and wastewater generation and their quantities. From the material balance, the sources and quantities of generation of wastewater, gaseous emissions and solid waste should be identified. The waste pretreatment, final treatment and disposal path should be identified. The production staff should be consulted as these people are likely to know about waste discharge points and about unplanned waste generations such as spills, leaks, washings, etc. Also, visits to the process plants may disclose many other discharge points due to overflows, spills and other material handling practices which are not accounted and recorded. The quantities and sources should be accordingly finalized and a waste flow sheet prepared. The characteristics of the wastes as generated from the sources are important to understand its use for recycle, recovery or treatment. Also, the performance of treatment facilities are to be monitored so as to check their efficiencies and to modify or install additional equipment/facility, if necessary. The surrounding environment -groundwater, stream, soft, surrounding land u s e s - residential, agricultural etc., and ambient air quality should be monitored to determine the impact due to the industry. With the above objectives, sampling points should be identified and monitoring network established. Parameters to be analyzed should be determined from the material balances of the wastes generated. Frequency of sampling should be fixed so as to cover hourly and daily variations and should also cover at least one full cycle of operations. Multiple sets of data can result in more realistic results. Samples collected should be of grab type where characteristics do not vary significantly and of composite type where characteristics fluctuate. Grab sampling means collection of sample in one pick while composite sampling requires collection of sample continuously or at predetermined

Analysis of Process Chemistry Example Processes

165

frequency (1-hr, 2-hr. etc) and compositing it in proportion to the flow rate observed at each sampling time. The method of analysis of samples should be done as per standard procedure and by trained analysts. The entire plant should be inspected thoroughly. The aspects of site layout, material handling and storage, drainage system, safety aspects, lapses/negligence in operations and attitude of operators in process and waste treatment facilities, handling of scrap and wastes, usage of sign boards, instruction, color codes etc. should be observed. The attitude and technical capability of various staff including senior management should be observed as it is very critical in achieving the goal of a safer environment. The training requirements can be assessed based on these observations.

Draft Report After completing the above-mentioned activities including determining material balance, identifying waste flow, monitoring and analysis of various samples and field observations, a draft report should be prepared with findings and possible recommendations. The draft report should be presented before the senior management and various points should be thoroughly discussed. The management should put forward their views. The participation of the management and their acceptance of various observations and recommendations makes the task of implementation meaningful.

Post Audit Activities The requirement of various raw materials according to the mass balance of the chemical equation involved in the manufacture of a product is called the stoichiometric requirement. A comparison of these requirements with those actually used in the industry gives an indication of excess usage of various raw materials. These excesses may be presumed to be finding their way to the air, water and soil thus causing pollution. Hence, it is important to reduce these excesses. The unit operation should be checked up to determine the cause of excess usage of the materials and accordingly modifications made. Norms should then be fixed for performance of each of the unit operations, for wastes generated from each of these unit operations.

Evaluation Performance of various operations should be evaluated based on the analysis reports and diagnosed. From the individual streams of

166

Waste Minimization

wastewater, recyclable and recoverable materials should be identified and provisions made for the same. All avoidable wastes should be completely controlled. The wastes if possible should be segregated based on the characteristics, such as inorganic, organic, acidic, alkaline, easily biodegradable, not easily biodegradable and toxic streams; and pretreatment units viz. oil separator, neutralization, detoxification etc. should be provided, wherever required, at the source so as to minimize the cost of final treatment or recovery. Wastewaters of similar nature should be combined and common treatment facilities provided. This would be efficient and economical. Many times, It is observed that inorganic wastes and non-biodegradable wastes are treated in biological treatment plants which on the contrary render biological treatment ineffective. Toxic wastes should be detoxified before treating in the biological treatment plant. Highly toxic wastes may be isolated and incinerated. The rate of wastewater flow and polluted loads to the effluent treatment plant should be properly regulated to present offshock loads to micro-organisms. The designed criteria and the actual operating conditions of various treatment units should be compared and norms fixed for the operation of these units. Similarly, the problems related to gaseous emission and solid waste generation may be identified. Recommendations for the best practicable waste management systems should be formulated. Guidelines for environmentally safe layouts are given and reduction of raw material losses, and wastewater and gaseous emissions are given elsewhere in this book. To oversee the implementation of the measures discussed and the overall management, there should be a peer group review comprising members from production, quality control/laboratory, and waste treatment divisions, the top management, and an environmental specialist. Various aspects discussed above should be compiled and a final report prepared along with recommendations. The final report may be sent to top management for comments in order to make further modifications. The recommendations include measures for best practicable management. If the cost burden, or the annualized capital cost of the control measures and their operating cost, for the implementation of all the recommendations is high, and the investment not feasible for the industry, then these recommendations should be implemented in phases. Priorities should be fixed and action plans with a time-frame should be formulated. Follow-up actions should be taken to check the progress of implementation of the recommendations.

Analysis of Process Chemistry Example Processes

167

ACETIC ACID BY METHANOL CARBONYIATION Industry Description Acetic acid is used in the manufacture of synthetic fibers and resins and as a solvent in polyester fiber production. Acetic anhydride is derived from acetic acid and used to manufacture cellulose acetate fiber and plastics. Vinyl acetate, used in the production of polyvinyl acetate, for safety glass interlayers, surface coatings and fibers, is also derived from acetic acid. There are three major commercial acetic acid manufacturing processes: 1. oxidation of acetaldehyde, 2. oxidation of paraffin hydrocarbons (primarily butanes), and 3. methanol carbonylation. Availability of methanol and carbon monoxide favor the methanol carbonylation process as presented here. Two methanol carbonylation processes have been commercialized: 1. The Reppe process, commercialized by Badische Anilin- and Soda Fabrik AG (BASF), is a high-pressure, cobalt-catalyzed liquid-phase process operated at about 650 atm pressure and 250~ 2. The Monsanto process is a low-pressure, rhodium-catalyzed liquid-phase process operated at about 30 arm pressure and 175~

Methanol Carbonylation Process Description Monsanto Process Figure 6-1 is a schematic diagram illustrating the process flow. Carbon monoxide is bubbled through a liquid reaction medium in a reactor maintained at about 175~ and 30 atm pressure. The reaction medium consists of methanol, acetic acid, methyl acetate, methyl iodide, hydrogen iodide, water and a rhodium iodocarbonyl catalyst complex. Recycle streams from downstream processing that contain methanol, acetic acid, methyl acetate, methyl iodide, hydrogen iodide, water and catalyst are also fed continuously to the reactor along with makeup catalyst as required.

CO t o Flare or r e c y c l e

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DISTILLATION T F N N

Figure 6-1: Methanol carbonylation-Monsanto

process.

Product Flnlshlnp

Analysis of Process Chemistry Example Processes

169

The methanol carbonylation reaction is represented by CH 3

OH + CO

~

CH 3

COOH

Thus, at least one mole of carbon monoxide is required per mole of alcohol; however, an excess of carbon monoxide is generally used in the manufacturing process. Gases from the reactor (stream 3) are cooled. Condensables are separated from the carbon monoxide and inerts in a high-pressure separator. The condensed material (stream 5) is then passed into a lowpressure separator from which it is recycled back to the reactor. Gases from the low-pressure separator (stream 8), consisting primarily of carbon monoxide, methyl iodide, of methanol and methyl acetate, are mixed with the gases from the high-pressure separator (stream 6) and the combined stream (stream 9) is scrubbed with methanol to remove the organics from the gas before it is discharged. The effluent gas (stream 11) either may be recycled, burned or discharged to the atmosphere, depending on its quality. The methanol from the scrubber (stream 12), containing the organics removed from the gas stream, is fed to the reactor. Liquid from the reactor (stream 13) is passed through a distillation train to recover catalyst for recycle and to dry and purify the product acetic acid. A number of distillation schemes have been reported in the literature for recovery of acetic acid from the reaction medium. The scheme illustrated in Figure 6-1 is based on patented processes for purifying acetic acid manufactured according to the Monsanto process and on descriptions of the Monsanto process published in the technical literature. The illustrated purification process proceeds as follows. Liquid from the reactor (stream 13) enters the lower half of a multiple-tray distillation column operating at or above atmospheric pressure. The hydriodic acid present in the feed stream is concentrated in the acetic acid solution in the bottom of the column. This stream (stream 15) is recycled back to the reactor. Carbon monoxide, water, methyl iodide and some entrained hydriodic acid comprise the overhead stream (stream 14) from the column. This stream passes through a condenser and a phase separator. The uncondensed gas from the phase separator (stream 19) is directed to the methanol scrubber. The condensate separates into two phases: a water phasecontaining some organics (stream 16), and an organic phase (primarily methyl iodide) containing some water (stream 17). The organic phase is recycled to the reactor (stream 18). Part of the

170

Waste Minimization

water phase is used as reflux in the distillation column and the excess is recycled to the reactor (stream 19). A solution of acetic acid in water containing some iodide, catalyst and by-products is withdrawn from the middle of the column (stream 20) and introduced into the top section of a second multiple-tray distillation column operating at or above atmospheric pressure. In this column, water and remaining inerts are withdrawn overhead (stream 21) and passed through a phase separator from which the gas (stream 25) is directed to the methanol scrubber. A portion of the condensate (mostly water) is returned as reflux (stream 26) to the column and the excess (stream 40) is recycled to the reactor. To avoid accumulation of water in the system, it is necessary to discard a portion of the water separated in the column. However, it is desirable to reclaim the methyl iodide in the overhead stream for the reaction. According to a patent, it is possible to remove a stream of water substantially free of methyl iodide as a sidestream from the column and thus accomplish the desired removal of excess water from the system without discarding a significant portion of the methyl iodide. This stream (stream 24) can be discarded (stream 24a) or processed in a stripper to recover any entrained organics, as shown in Figure 1. Residual hydriodic acid in the feed stream to the column concentrates at a location near the middle of the distillation column. By continually withdrawing the solution containing the hydriodic acid from the middle of the distillation column, virtually all the hydriodic acid is removed from the column. This solution (stream 23) can be recycled directly to the reactor or, alternatively, recycled to the lower half of the previous distillation column, where it will be concentrated and removed with the bottoms stream of that column. The column bottoms (stream 22) are dry acetic acid that may contain some catalyst as an impurity. Depending on the purity of acetic acid desired, further processing may be necessary, as shown in Figure 6-1. Acetic acid product can be withdrawn from the drying column without further processing; however, to minimize product contamination with catalyst, acetic acid vapor is withdrawn from the bottom of the column and passed through a condenser from which it is pumped to storage. Liquid acetic acid containing residual catalyst is periodically withdrawn from the bottom of the column and recycled to the reactor. If further purification of the acetic acid is desired, the bottoms from the column (stream 22) are pumped to another distillation column, where the acetic acid is removed as an overhead product (stream 34) and any "heavy" by-products, such as propionic acid, are removed from the

Analysis of Process Chemistry Example Processes

171

bottoms (stream 32) and incinerated. The acetic acid overhead product may be further purified to remove remaining impurities, and the "pure" acetic acid is removed as a sidedraw product (stream 39) from near the bottom of the column. An alternative acetic acid purification scheme uses azeotropic distillation to remove the water from the acetic acid. However, this purification scheme was eliminated in the Monsanto process in favor of the method described above. Azeotropic distillation is used by the plants manufacturing acetic acid by the BASF process. Table 6-1 identifies the major constituents of the numbered process streams in Figure 6-1. It is likely that each of the internal process streams will contain some amount of every chemical initially present in the reactor. However, in the purification process the chemicals initially present in the reactor are separated so that each chemical is concentrated in some streams and substantially eliminated from other streams. Impurities may be present in the raw materials, methanol and carbon monoxide used in the process. The quantity and nature of these impurities depend on the method of manufacture and on the source of the material. These impurities may be inert and pass through the reactor unchanged, or they may react within the system to form additional product and/or by-products. Table 6-1: Stream No.

Methanol Carbonylation Process Stream Components

Phase

Major Components

1 2 3

Gas Liquid Gas

4

Liquid and gas Liquid Gas Liquid Gas Gas

Carbon monoxide Methanol, water Carbon monoxide, methyl iodide, methanol, methyl acetate, acetic acid Carbon monoxide, acetic acid, methyl iodide, methanol, methyl acetate Methyl iodide, methanol, methyl acetate, acetic acid Carbon monoxide Methyl iodide, methanol, methyl acetate, acetic acid Methyl iodide, methanol, methyl acetate, acetic acid Carbon monoxide, methyl iodide, methanol, methyl acetate, acetic acid Carbon monoxide, methyl iodide, methanol, methyl acetate, acetic acid

5 6 7 8 9 10

Gas

(continued)

172

Waste Minimization

Table 6-1: (continued) Slream No.

Pha~

Major Components

!1 12 13

Gas Liquid Liquid

14

Gas

15

Liquid

16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43

Liquid Liquid Liquid Gas Liquid Gas Liquid Liquid Liquid Gas Liquid Gas Liquid Liquid Gas Gas I,iquid Gas Liquid Gas Liquid Gas Liquid Liquid Liquid Liquid Gas Liquid

44

Liquid

Carbon monoxide, methanol Methanol, methyl iodide, methyl acetate, acetic acid Methyl acetate, methyl iodide, methanol, water, acetic acid, hydriodic acid, rhodium catalyst complex Methyl acetate, methyl iodide, methanol, carbon monoxide, water Acetic acid, water, hydriodic acid, rhodium catalyst complex Water, acetic acid, methyl acetate, methyl iodide Methyl iodide, water, methyl acetate, acetic acid Water, acetic acid, methyl acetate, methyl iodide Carbon monoxide, methyl iodide Acetic acid, water, hydriodic acid, methyl iodide Water, acetic acid, methyl iodide Acetic acid Water, hydriodic acid, acetic acid Water, acetic acid Water, acetic acid Water, acetic acid, methyl iodide Water, acetic acid Acetic acid Water, acetic acid Water Acetic acid Propionic acid Acetic acid Acetic acid Water, acetic acid Acetic acid Water, acetic acid Water, acetic acid Acetic acid Water, hydriodic acid, acetic acid, methyl iodide Water, hydriodic acid, acetic acid, methyl iodide Carbon monoxide, methyl iodide, water, acetic acid Acetic acid, catalyst complex, water, methyl iodide, hydriodic acid, methyl acetate Rhodium catalyst complex, hydriodic acid

Analysis of Process Chemistry Example Processes

173

Depending on the source, carbon monoxide may contain hydrogen, carbon dioxide, methane, nitrogen, noble gases, water and/or paraffinic. The presence of inerts in the carbon monoxide requires that the process operating pressure be raised to maintain the desired partial pressure of the carbon monoxide in the reactor. Methanol may contain dimethyl ether, acetone, acetic acid, aUyl alcohol, methyl formate, and other alcohols, aldehydes, ketones and acids. Under the reaction conditions, dimethyl ether forms methanol and thus does not contribute to the formation of numerous other compounds and polymers. Methanol of up to 99-9% purity is commercially available and thus the formation of undesirable by-products can be minimized.

BASF Process (Reppe Process) The process flow diagram of the BASF process is almost identical to that of the Monsanto process. As stated previously, the main differences between the two processes are the operating temperature and pressure and the type of catalyst used. Both processes use an iodide promoter. A number of intermediates and by-products are formed in the presence of the cobalt catalyst that either are not formed or are formed in only negligible quantities in the rhodium catalyzed process. Byproducts and intermediates that have been identified in the cobaltcatalyzed process include ethanol, acetaldehyde, propionic acid, propionaldehyde, butyraldehyde, butanol, dimethyl ether, methyl formate, formic acid, hydrogen, methane, carbon dioxide and water. The presence of impurities in the carbon monoxide as well as in the methanol used for the process will result in an increase in the quantity of by-products formed in the BASF process.

Process Chemistry The reaction of the methanol with carbon monoxide is represented by CH3OH

+

CO

"i- CH3COH

II

(1)

0

methanol

carbon monoxide

acetic acid

As is the case for many chemical reactions, the reaction does not proceed directly from raw materials to product, but involves a number of intermediate steps and reaction products that ultimately result in final product formation. In addition, a number of reactions other than

174

Waste Minimization

carbonylation can occur in the system simultaneously with the carbonylation reaction. In the Monsanto methanol carbonylation process, the catalyst is a rhodium compound and the promoter is an iodide compound. It is believed that in the reaction medium the catalyst is a rhodiumiodocarbonyl compound. However, the rhodium may be initially charged to the system in the form of rhodium metal, rhodium halide, rhodium oxide, an organorhodium compound, a coordination compound of rhodium or other rhodium-containing compound. The promoter charged to the reactor may be an aqueous solution of hydriodic acid, methyl iodide, hydrated calcium iodide, pure iodine, or any of a number of other organic or inorganic iodine compounds. The catalyst and promoter are soluble in the reaction medium and thus the reaction is homogeneous. The rhodium-catalyzed carbonylation reaction is believed to proceed as described below. Methanol is rapidly converted to methyl iodide CH3OH + HI

:- CH3I + H20

(2)

The methyl iodide combines with the rhodium complex by oxidative addition to form an alkyl-rhodium compound: CHal + Rh complex

_ -slow

CH3

(3) Rh complex

I I

Reaction 3 proceeds slowly and is the rate-determining step for the overall reaction. All preceding and subsequent steps proceed rapidly. Carbon monoxide initially reacts with the rhodium to form a rhodium carbonyl complex (Equation 4). The carbon monoxide subsequently is inserted into the rhodium alkyl bond to form an acyl rhodium complex, while another CO molecule is simultaneously or subsequently reinserted into the rhodium complex to reform rhodium carbonyl (Equations 5 and

6). CH3

CH 3

I Rh complex + CO

I ,

,,

Rh complex 9CO

I

I

I

I

(4)

Analysis of Process Chemistry Example Processes CH 3

175

CH 3

I Rh complex 9CO

C=0

I

I

I

Rh complex

(5)

I I

CH 3

CH3

I

I

C=0

C=0

(6)

+CO Rh complex

Rh complex 9CO

!

!

I

I

The final step in the reaction sequence involves reaction of the acyl rhodium complex to yield acetic acid and the original rhodium complex. It is believed that this step involves the reductive elimination of acetyl iodide from the rhodium complex (Equation 7)accompanied by immediate hydrolysis of the acetyl iodide to produce acetic acid (Equation 8). CH 3

i C=0

I

-- CH3C- I + rhodium carbonyl complex

(7)

I!

Rh complex ~ CO

O

I 1

CH31CI - I + H 2 0

"CH3 C - O H + H I

II

ii

O

o

(8)

Other reactions that may proceed simultaneously in the reaction medium include:

176

Waste Minimization

CHaOH + CHa~OH

CHaO~CH3

H20

aceticacid

methyl acetate

water

CHaOH methanol

CHaOCH3 dirnethyl ether

H20 water

CH 30~CH 3

HI hydriodic acid

(9) methanol

2

CH3I

+ CH3~OH

methyl iodide

acetic acid

methyl acetate

CHa[~OH

CH 3-O-CH

O acetic acid

methyl formate

H20 water

CO2 carbon dioxide

(10)

(11)

CO carbon monoxide 4 CO

: CH4 methane

2H20 water

carbon monoxide

(12)

H2 hydrogen

3 CO2 carbon dioxide

(13)

(14)

CH3CH2C-OH

CH 30CCH3

(15)

I!

O methyl acetate

propionic acid CH3~H

H20

hydrogen

acetaldehyde

water

H2 hydrogen

:

H=O

CH3C-OH

H2

acetic acid CHaOH methanol

=

(16)

CH4 methane

water

(17)

Analysis of Process Chemistry Example Processes

177

The above equations represent the various reactions that could occur, and are not necessarily representative of the reaction paths or of the intermediate compounds that may be formed as the reactions proceed. It is reported that methyl formate, acetaldehyde and propionic acid are essentially absent from the rhodium-catalyzed process. The rhodiumcatalyzed system is characterized by high specificity for the carbonylation reaction and apparently does not promote hydrogenation to any measurable degree. Therefore, Reactions 16 and 17 do not occur in this system even when the carbon monoxide contains hydrogen as an impurity. This is in contrast to the cobalt-based (BASF) process, in which hydrogenation reactions do occur and lead to reduced yields of these compo acetic acid. In addition to the by-products that can be formed from the main feed-stock materials, additional products can be formed from the reaction of impurities in the feedstock streams. If the methanol feedstock contains higher-molecular-weight alcohols, acids and/or esters, the reaction medium will also contain the higher-molecular-weight alcohols, acids and esters. The rhodium will also catalyze the carbonylation of the higher-molecular-weight alcohols and esters. These, in turn, can react with each other and with the initial feed ingredients to form yet highermolecular-weight homologs and polymers. The rhodium-catalyzed process reaction rate was found to be independent of methanol concentration or of carbon monoxide partial pressure i.e., zero-order in both methanol concentration and carbon monoxide concentration. The reaction rate is, however, directly proportional (first order)to both the rhodium and iodide concentrations. By contrast, the cobalt-catalyzed process is first order with respect to methanol concentration, second order with respect to carbon monoxide concentration, first order with respect to iodine concentration and of variable order with respect to the cobalt concentration. Thus, it appears that two different reaction mechanisms are involved in the two processes and they are not directly comparable with respect to stream compositions or to the potential hazards associated with the processes.

Analysis of the Monsanto Methanol Carbonylation Process The chemistry of the Monsanto methanol carbonylation process has been described and the chemical compounds likely to be found in the process streams have been identified. The physical properties and ratings of these compounds are presented in Table 6-2.

Table 6-2: Physical Properties and Hazard Ratings of Chemicals Present in Methanol Carbonylation Process Streams CornDoundlFormula

Parameter Molecular Weight Melting Point, OC Boiling Point, OC Specific Gravity of Liquid @ 2OoC relative to water at 4OC Vapor Density (air = 1) Heat of combustion, kcal/mole Heat of formation, kcal/mole Heat of vaporization, @ boiling point, cal/g Autoignition temperature, OC Flammable limits in air, % by volume Upper Lower Flash point, OC closed cup NFPA Hazard Rating: Health: flammability: reactivity Toxicity Rating (Sax, 1975) Inhalation: acute local; acute systemic Dow Material Factor

Methanol CH30H 32.04 -97.8 64.7 0,792 1.1 -173.65 -57.036

Carbon Monoxide

co

28.01 -207 -192 0.97 -67.64 -26.416

Acetic Acid CH3COOH

Methyl Acetate CH3COOCH3

Methyl Iodide

60.05 16.7 118.1

74.08 -98.7 57.1

141.95 -64.4 42.4

1.049 2.08 -209.4 -1 16.2

0.924 2.8 -381.2 N/Aa

2.279 4.9 -194.7 N/Aa

CH31

262.8 385

1443.6 609

96.8 462

104.4 454

46.6 -

36 6.7 11.1

74 12.5 -

19.9 4 39

16 3.1 -10

-

1;3;0

2 ;4 ;O

2;2;1

1;3;0

-

19

0 ;3 4.3

2;Ub 5.6

u ;2

u ;3

8.6

8.5

-

Table 6-2: (continued)

Compound/Formula

Parameter Molecular Weight Melting Point, OC Boiling Point, OC Specific Gravity of Liquid @ 2OoC relative to water at 4OC Vapor Density (air = 1) Heat of Combustion, kcal/mole Heat of Formation, k c d m o l e Heat of Vaporization,@ boiling point, cal/g Au toignition temperature, O C Flammable Limits in Air, % by volume Upper Lower Flash Point, OC closed cup NFPA Hazard Rating: Health: flammability ;reactivity Toxicity Rating (Sax, 1975) lnhalation: acute local; acute systemic Dow Material Factor

Dimethyl Ether (CH3)20

Ethanol CH3CH2 OH

Acetaldehyde CH3CHO

46.07 -138.5 -2 3.7

46.07 -112 78.4

44.05 -123.5 20.2

1.6 -347.6 -43.06

0.789 1.6 -326.68 -66.35

0.783 @ 18OC 1.5 -278.77 -39.72

-365.03 -121.7

350

204.26 363

136.17 175

98.81 465

207.2

27 3.4

-

19 3.3 13

60 4 -37.8

12.1 2.9 52

17 2.6 -30

2 ;4 ;1

0;3;0

2 ;4 ;2

2;2;0

2;3;1

U2

u ;2 11.5

3 ;2 10.5

u ;u

2 ;2 13.6

12.4

Propionic Acid Propionaldehyde CH~CHZCOOH CH3CH2CHO

74.08 -22 141.1 0.992

-

8.9

58.08 -8 1 49.5 0.807 2.0 -434.1 -49.15

-

CI

cx,

Table 6-2: (continued)

0

*E

Compound/Formula Butyraldehyde Parameter

CH3(CHz)zCHO

Molecular Weight 72.1 Melting Point, OC -9 9 Boiling Point, O C 75.7 Specific Gravity of Liquid @ 2OoC relative to water at 4OC 0.8 17 Vapor Density (air = 1) 2 .5 Heat of Combusion, kcal/mole -597.08 Heat of Formation, kcal/mole 52.4 Heat of Vaporization, @ boiling point, calk Autoignition temperaturc, O C 218 Flammable Limits in Air, % by volume 12.5 Upper Lower 1.9 Flash Point, OC closed cup -22 NFPA Hazard Rating: Health: flammability ;reactivity 2 ;3 ;1 Toxicity Rating (Sax,1975) Inhalation: acute local; acute systemic 12 Dow Material Factor 13.9

(D

Methyl Fonnate

Acetone

Hydrogen

CH300CH

CHjCOCH3

HZ

74.12 -79.9 117

60.05 -99.8 32

58.08 -94.6

2.016 -259.1 -252.7

0.810 2.6 -639.53 -79.61

0.914 2.1 -234.1 -95.26

0.792 2 .o -437.92 -59.32

112.35

134.74 465

Butanol CH,(CH,),CH20H

141.26 343

449

565

0.1 -68.31 74 -

5 00

11.2 1.4 29

23 4.5 -18.9

1;3;0

2;4P

130

0;4;0

U2

u;3

14.3

6.9

22 12.3

0 ;I 51.6

13 2.1 -20

75 4

z5'

3: 0

Table 6-2: (continued) Compound/Formula

Parameter Molecular Weight Melting Point, OC Boiling Point, OC Specific Gravity of Liquid @ 2OoC relative to water at 4OC Vapor Density (air = 1) Heat of Combusion, kcal/mole Heat of Formation, kcal/mole Heat of Vaporization, @ boiling point, cayg

Autoignition temperature, OC Flammable Limits in Air, $6 by volume upper Lower Flash Point, O C closed cup NFPA Hazard Rating: Health: flammability; reactivity Toxicity Rating (Sax, 1975) Inhalation: acute local; acute systemic Dow Material Factor a NA = Not available. b~ = Unknown

Methane CH4

Hydriodic Acid HI

Formic Acid HCOOH

16.04 -182.6 -161.4

127.93 -50.8 -35.5

46.03 8.6 100.8

0.6 -212.19 -17.889 5 31

4.43 6.27

Decomposes -

1.220 1.6 -60.86 -91.8 119.93 5 39

15 5

57 18 69

1;4P

3;2$

0;l 21.5

u ;3 -

u ;2 2.5

a

Table 6-3: Hazard Rating of Process Streams stream No.

1 2 3 4 5

Approximate Temperature Phase Gas Liquid Gas Liquid and gas Liquid

6 7

Gas Liquid

8

Gas

9

Gas

10

Gas

11 12

Gas Liquid

13

Liquid

14

Gas

15

Liquid

16 17 18

Liquid Liquid Liquid

Major Components Carbon monoxide Methanol, water Carbon monoxide, methyl iodide, methanol, methyl acetate, acetic acid Carbon monoxide, acetic acid, methyl iodide methanol, methyl acetate Methyl iodide, methanol, methyl acetate, acetate, acetic acid Carbon monoxide Methyl iodide, methanol, methyl acetate, acetic acid Methyl iodide, methanol, methyl acetate, acetic acid Carbon monoxide, methyl iodide, methanol, methyl acetate, acetic acid Carbon monoxide, methyl iodide, methanol, methyl acetate, acetic acid Carbon monoxide, methanol Methanol, methyl iodide, methyl acetate, acetic acid Methyl acetate, methyl iodide, methanol, water, acetic acid, hydriodic acid, rhodium catalyst complex Methyl acetate, methyl iodide, methanol, carbon monoxide, water Acetic acid, water, hydriodic acid, rhodium catalyst complex Water, acetic acid, methyl acetate, methyl iodide Methyl iodide, water, methyl acetate, acetic acid Water, acetic acid, methyl acetate, methyl iodide

CL

00 N

Relative Pressure

Flammability

Toxic

Chemical Burn

HUud

Hazard

Risk

Ambient Ambient

Ha La

H

H

H

Ma

No No

175

H

M

H

No

10

H

L

M

Yes

10

L

M

10

H H

H

H

Yes No

10

L

L

M

Yes

10

L

L

M

No

10

L

H

H

No

25 Ambient

L L

H H

H H

No No

Ambient

L

H

M

Yes

175

L

L

H

Yes

100

L

L

H

Yes

120

L L L L

L L L L

H H H H

Yes Yes Yes Yes

("a

K 5:

E.E

2. 0

30

30 30

3

Table 6-3: (continued) Approximate Temperature

stream

No.

Phase

Major Components

19 20 21 22 23 24,24a 25 26 27 28 29 30 31 32 33 34 35 36 31 38 39 40 41 42

Gas Liquid Gas Liquid Liquid Liquid Gas Liquid Gas Liquid Liquid Gas Gas Liquid Gas Liquid Gas Liquid Gas Liquid Liquid Liquid Liquid Gas

43

Liquid

Carbon monoxide. methvl iodide Acetic acid, water, hydriodic acid, methyl iodide Water, acetic acid, methyl iodide Acetic acid Water, hydriodic acid, acetic acid Water, acetic acid Water, acetic acid Water, acetic acid, methyl iodide Water, acetic acid Acetic acid Water, acetic acid Water Acetic acid Propionic acid Acetic acid Acetic acid Water, acetic acid Acetic acid Water, acetic acid Water, acetic acid Acetic acid Water, hydriodic acid, acetic acid, methyl iodide Water, hydriodic acid, acetic acid, methyl iodide Carbon monoxide, methyl iodide, water, acetic acid Acetic acid, rhodium catalyst complex, water, methyl iodide, hydriodic acid, methyl acetate Rhodium catalyst complex, hydriodic acid I

.

("0

Relative Pressure

Liquid

H a d

Hazard H

L M

M

L L

M

L

M

M M

L L L L L L L L

L

L L

30 100 Ambient

Toxic

M

30 110 110 155 110 110 30 30 100 120 30 30 120 140 30 30 110 120 30 30 120 30 100

H

L

L L

L

M

Chemical Burn

Risk Yes Yes Yes Yes Yes Yes

Yes Yes

L

L

M

M M

L

L L M M

L

L

L

M M M L

M

M

M

M

M M

L

L L

M

Yes Yes Yes Yes Yes

L

M

H

Yes

L L

H H

Yes Yes

L L L L L L

H H a L = Low; M = Moderate; H = High. High pressure is approximately 30 atm. Lower pressure is 1-4 atm. 44

Flammability

M

Yes Yes Yes No Yes

L

Yes

L

Yes Yes Yes

L

M M L

a

z c)

CD

m m

Yes

CI

00

w

184

Waste Minimization

The chemical compounds present in the process are all flammable and/or toxic to varying degrees. Because of variations in the type and quantity of chemicals present in different process streams, the hazard posed by the accidental release of material varies from stream to stream within the process. Hazards posed by the materials present in each of the process streams is evaluated and presented in Table 6-3. The streams were rated in terms of low, moderate or high flammability and toxicity. Streams that can cause tissue bums were also identified. Factors considered in rating the flammability and toxicity include: 9 9 9 9 9 9

the components of the stream, the volume of the stream, the relative quantity of each component in the stream, stream phase (gas or liquid), stream pressure, and stream temperature.

In general, a high-volume stream is more hazardous and prone to losses than a low-volume stream; a gas is considered to be more loss prone than a liquid in the plant; a gas is more easily ignited than a liquid and, therefore, is considered to be more of a flammable hazard; hightemperature liquid streams are considered to be more loss prone than low-temperature streams because of theft greater volatility; high-pressure liquid streams are also more loss prone than low-pressure streams because they evaporate rapidly when suddenly released into a lowerpressure environment. Although not considered in the loss analysis, some streams may pose a lesser loss because of their physical and chemical properties. An additional loss potential may be posed by corrosiveness of the process streams. Process equipment is constructed of Hastelloy, Teflon, and other materials resistant to the corrosive effects of the organic acids and acid halides present in the process streams. However, if these corrosive streams were accidentally released to the environment, they might come in contact with equipment that is not resistant to their corrosive effects. This other process equipment may be damaged or weakened to the point that they might release their contents.

Process Waste Streams There are three points of waste discharge from the methanol carbonylation process"

Analysis of Process Chemistry Example Processes

185

9 a gaseous discharge from the methanol scrubber, 9 a wastewater discharge from the drying column, and 9 an organic liquid discharge from the product recovery column. Figure 6-2 illustrates the handling of the gaseous discharge originating from the reactor and from the distillation column vents. The gaseous discharge from the reactor is primarily unreacted carbon monoxide along with some inerts such as carbon dioxide, methane, and hydrogen, and entrained organics such as acetic acid and methyl iodide. The gas stream is cooled to about 10~ to condense a major portion of the organics from the stream for recycle to the reactor. The noncondensable gases and residual organic vapors are combined with the gaseous emissions from the distillation column vents and scrubbed with fresh methanol to remove the residual organics in the stream. The methanol from the scrubber is used as the feed to the reactor. T h e gaseous stream issuing from the scrubber is comprised primarily of carbon monoxide, inerts and methanol and can be disposed of in a combustion device, such as a flare or recycled to the reactor. The primary contaminant of the wastewater stream is acetic acid. Stream 24 contains as much as 50% acetic acid, which may represent as much as 5% of the acetic acid produced by the process. Therefore, it may be worthwhile to try and recover the acid in a water stripper (illustrated as optional in Figure 6-3). Acetic acid is relatively innocuous to aquatic life, except when present in an amount sufficient to raise the acidity of the water. As it is biodegradable, its presence can contribute to a lowering of the oxygen content of a waterway. Its biodegradability makes it amenable to biological treatment processes for removal from the wastewater stream. The third waste stream is composed of high-molecular-weight byproducts formed in the reaction. It is easily destroyed by combustion, e.g., incineration. ACETALDEHYDE BY LIQUID-PHASE ETHYLENE OXIDATION Acetaldehyde is used primarily as an intermediate for the production of other organic chemicals, the major derivatives being acetic acid, acetic anhydride, n-butanol and 2-ethylhexanol. Other products derived from acetaldehyde are pentaerythritol, trimethylol propane, pyridines, peracetic acid, crotonaldehyde, chloral, 1,3-butylene glycol, lactic acid, glyoxal and alkylamines.

2

+

vater out

I High Pressure Separator

Condenser High

9

refrigerated water i n

Pressure

rp;5

L

C

‘A

-- ::

entrained organics inerts t o Flare or recycle

’

8

I IT

Zone

6

I

G

Low Pressure

Separator I G 42 L 12 L+7

175OC

I

I 13

v Combined D i s t i l l a t i o n Column Vent Streams

Reactor Product

Legend L

G

-

liquid phase gas phase

Figure 6-2: Methanol carbonylation-Monsanto process. Gaseous emission handling.

+

19

Combined D i s Z l l l a t l o n C Colum Li q u i d Recycle

srrr-

to

15

I7

R..CtOI

+ T O Reacror

I

LECEND

I

1

18

40 41

Light Ends S.p.r.tl0" COluM

Figure 6-3: Methanol carbonylation-Monsanto

Orylng COlUnm

Product Recovery

Product

COlUml

COlUml

Flnlshlnp

process. Distillation train showing waste discharge points.

188

Waste Minimization

Acetic acid, for example, is now more economically made from methanol and carbon monoxide in locations where methane is available to produce the methanol. Propylene based processes have replaced acetaldehyde-based processes for the production of n-butanol and 2ethylhexanol. Four commercial processes for the manufacture of acetic acid are: 9 hydration of 9 vapor-phase 9 vapor-phase and 9 liquid-phase

acetylene, partial oxidation or dehydration of ethyl alcohol, oxidation of butane, propane or mixtures thereof, oxidation of ethylene.

The liquid-phase oxidation of the ethylene process was commercialized in 1960 and is a principal commercial production method for acetaldehyde.

PROCESS DESCRIPTIONS

FOR OXIDIZING ETHYLENE

TO

ACETALDEHYDE The direct oxidation of ethylene to acetaldehyde can be affected by means of liquid-phase homogeneous catalysis. The commercial process is carried out in two ways: 9

A one-stage process is used in which ethylene oxidation and

catalyst regeneration take place simultaneously in the same reactor, with oxygen used for catalyst oxidation. 9 A two-stage process is used in which ethylene oxidation takes place in one reactor and the catalyst is oxidized by air in a second reactor. The process is based on the oxidation of ethylene by aqueous palladium chloride to form acetaldehyde, palladium metal and hydrogen chloride: C2H4 + PdCI2 + 1-120 ~

CH3CHO + Pd~ + 2HC1

Cupric chloride is used as the second component of the catalyst system to reoxidize the palladium metal to palladium chloride: 2 CuC12 + Pd~ --# PdC12 + 2 CuCI

Analysis of Process Chemistry Example Processes

189

The cuprous chloride thus formed is, in turn, reoxidized by oxygen to cupric chloride" 2 CuC1 + 1/2 02 + 2 HCI --,

CuC12 + 1-120

The continuous regeneration of the palladium chloride permits its use in relatively low concentrations. Details of the two process variations are presented below.

One-Stage Process The one-stage process for liquid-phase oxidation of ethylene to acetaldehyde is illustrated in Figure 6-4. Ethylene gas (stream 2), oxygen (stream 1) and a recycle gas stream (stream 31) are continuously fed to a reactor vessel containing an aqueous solution of palladium chloride and copper chloride. The reactor is operated at 120~176 and 3 atm pressure. The exit stream from the reactor (stream 3) flows into a gasliquid separator operated near atmospheric pressure. The liquid stream from the separator (stream 4) is split into two streams; one stream (stream 6) is recycled to the reactor and the second stream (stream 5) is passed to a regenerator, where it is mixed with air or oxygen and heated with steam to about 170~ to decompose copper oxalate and other organics prior to being returned to the reactor. The gas stream from the separator (stream 11) that contains the product, acetaldehyde, is sent to a quench scrubber, where it is cooled and scrubbed with water to condense the acetaldehyde and other condensables. The noncondensable gases (stream 12) consisting of unreacted ethylene, oxygen and inerts exit from the top of the scrubber. A portion of the stream (stream 13) is purged to a flare to control the accumulation of inerts in the system, and the remainder (stream 14) is recycled to the reactor. The condensed stream (stream 16), containing about 9% acetaldehyde by weight, is split into two streams: one stream (stream 17) is recycled to the scrubber, while the second stream (stream 18) is heated and fed to a light ends distillation column where dissolved gases and low boiling substances (primarily alkyl chlorides) are removed overhead (stream 19). The bottoms (stream 20) from the light end distillation column are fed to the product recovery column where acetaldehyde is removed as an overhead stream (stream 22) and a by-product stream (stream 27) of crotonaldehyde is removed as a side product from the middle of the column. Water contaminated with residual organics (stream 29) is removed from the bottom of the column and disposed of through a wastewater treatment system. The product recovery column is illustrated as operating at atmospheric pressure.

Light ends to Flare

L1

I n e r t Gas P u r g e to F l a r e

A

Water

1 I

I I

Sever Oxygen

-

16

QUENCH SCRUBBER

HEAT EXCHANGER

Steam 20

1

k - j l d e h y 20 de

LIGHT ENDS DISTILUTION C O L N

Figure 6-4: Single-stage process for manufacturing acetaldehyde from ethylene.

to Disposal

Steam

PRODUCT UECOVERY

coLlPIN

Analysis of Process Chemistry Example Processes

191

Because of the low boiling temperature of acetaldehyde, refrigerated water would have to be used in the overhead condenser. An inert gas blanket would have to be maintained in the reflux drum to minimize the risk of air coming in contact with the acetaldehyde. Alternatively, the column could be operated under 2-5 atm pressure. Table 6-4 identifies the major constituents of the numbered process streams in Figure 6-4.

Table 6-4: Stream Components of One-Stage Process for Oxidation of Ethylene to Acetaldehyde Stream No. 1 2 3 4,5,6 7

Phase Gas Gas Gas and liquid Liquid

9 10 11

Liquid and gas Liquid and gas Gas Gas Gas

12,13,14

Gas

15,16,17,18

Liquid

19 20

Gas

8

Liquid

21 22 23,24,25 26 27 28 29

Gas Liquid Vapor Liquid Gas Liquid

30

Liquid

31

Gas

32

Liquid

Gas

Major Components Oxygen Ethylene Acetaldehyde, ethylene, oxygen, carbon dioxide, water, catalyst components Palladium chloride, copper chloride, hydrochloric acid, water Palladium chloride, copper chloride, copper oxalate, hydrochloric acid, water, carbon dioxide Palladium chloride, copper chloride, hydrochloric acid, copper oxalate, water, carbon dioxide Oxygen or air Water Ethylene, oxygen, carbon dioxide, water, acetaldehyde Ethylene, oxygen, carbon dioxide, water vapor, some organics Water, acetaldehyde, alkyl chlorides, oxygenated organics Alkyl chlorides (methyl and ethyl chloride) Acetaldehyde, crotonaldehyde, chlorinated aldehydes, water Water Acetaldehyde Acetaldehyde, nitrogen Acetaldehyde, water Crotonaldehyde Water Water, chlorinated aldehydes, other oxygenated and chlorinated organic compounds Water, hydrochloric acid, palladium chloride, copper chloride Ethylene, oxygen, carbon dioxide, water vapor, some organics Water

192

Waste Minimization

Two-stage Process The two-stage process for the liquid-phase oxidation of ethylene to acetaldehyde is illustrated in Figure 6-5. Ethylene (stream 1) is continuously fed to a tubular plug flow reactor where it mixes with an aqueous stream (stream 41) containing palladium chloride and copper chloride salts in solution at a pressure of about 9 atm and a temperature of 130~ The ethylene is almost completely reacted by the time the reactant mixture leaves the tubular reactor. The exit stream from the reactor (stream 2) enters a flash tower maintained at approximately atmospheric pressure. In the flash tower, adiabatic flash evaporation of water and acetaldehyde occurs and removes the heat of the reaction. The overhead from the flash tower (stream 11) is processed in a crude distillation column. The bottoms from the flash tower (stream 4) are recycled to a second tubular reactor where they are mixed with air (stream 5) to oxidize the cuprous salts to cupric salts. The reoxidized salt solution enters a phase separator from which the unreacted oxygen, inerts and some organics exit overhead (stream 6). The exit gases are passed through a scrubber prior to discharge (stream 25). The liquid salt solution from the phase separator (stream 7) is split into two streams, one stream (stream 40) is recycled to the reactor and the second stream (stream 8) is passed through a heater and regenerator where copper oxalate and other nonvolatile by-products are decomposed at 170~ The regenerated stream (stream 10) is directed to the flash tower where it is combined with the reactor exit stream and the liquid and gas phases are separated. Water separated from the stream entering the crude distillation column is removed as bottoms (stream 12) from the column. Part of the water (stream 15) is used as a scrubber medium in the process gas scrubbers and the remainder (stream 14) is recycled to the process through the flash tower. The overhead stream from the crude distillation column (stream 16) flows to a condenser and reflux drum from which noncondensables (stream 20) are vented to a scrubber. A portion of the condensed stream is used as reflux (stream 18) and the remainder (stream 19) enters a surge drum from which it is pumped (stream 26) to a light ends distillation column. In the light ends distillation column, low-boiling impurities, primarily chlorinated alkanes, are removed as overhead (stream 27). The bottoms (stream 31) from the light ends distillation column are distilled in a product recovery column to recover acetaldehyde as an overhead product (stream 34). Chlorinated aldehydes are removed as a sidestream (stream 35) from the columns and residual water (stream 36) is removed from the bottom of the column.

Light Elldm to

Flare

LIQIT

PRODLKT REWMRY

DISTILUTION WLLWN

CoLunn

)Lm ENDS

Figure 6-5: Two-stage process for manufacturing acetaldehyde from ethylene.

194

Waste Minimization

As in the one-stage process, the product recovery column is illustrated as operating at atmospheric pressure, thus requiring refrigerated condenser water and inert gas blanketing of the reflux drum. The column could also be operated under 2-5 atm pressure. Table 6 - 4 identifies the major constituents of the numbered process streams in Figure 6-4.

Process Comparison The ethylene purity can be lower for the two-stage process than for the one-stage process. This is because of the need to recycle ethylene in the one-stage process. The recycle stream must be purged to minimize the buildup of inerts. The purge stream contains some ethylene. If the ethylene purity were low, the volume of the purge stream would be greater and, consequently, more ethylene would be lost with the purge stream. The use of a lower-purity ethylene in the two-stage process could, however, increase by-product formation. Both processes use the same amount of catalyst for makeup; however, the two-stage process produces more chlorinated by-products and, consequently, requires more hydrochloric acid makeup than the one-stage process.

PROCESS CHEMISTRY The Wacker process for production of acetaldehyde by the direct liquid-phase oxidation of ethylene is based on three chemical reactions: CzH4 + PdC12 + H20 ---* CH3CHO + ethylene palladium water chloride

Pd ~

2 HC1

acetaldehyde palladium hydrogen chloride

Pd*

+ 2 CuCI 2 ""

palladium

cupric chloride

PdCI 2

(1)

2 CuCI J

2CuCI+

2HCI

cuprous chloride

hydrogen chloride

+

p a l l a d i u m cuprous chloride chloride 8902 ~ oxygen

~

(,2)

2 CuCI2 + 1-120 cupric chloride

water

(3)

The first reaction alone is sufficient to produce acetaldehyde. H o w ever, this reaction would not make a viable commercial process because

Analysis of Process Chemistry Example Processes

195

stoichiometric amounts of palladium chloride are needed. Reactions (2) and (3) provide the means for making the process commercially feasible. The metallic palladium is reoxidized to palladium chloride, which can be reused for Reaction (1). Because direct oxidation of metallic palladium with oxygen is a slow process, a more efficient oxidant such as cupric chloride is used. Any material with a redox potential higher than that of palladium chloride can theoretically be used, e.g., FeCI3. Cupric chloride is used commercially because it is easily regenerated from the cuprous form and also because it is inexpensive. Equations (1), (2), and (3) represent overall reactions. As is the case for many chemical reactions, a number of intermediate reaction steps are involved and intermediate products are formed. In addition, a number of reactions other than the desired reactions may take place. The sequence of steps in the formation of acetaldehyde according to Equation (1) is as follows: .

In an aqueous solution of palladium chloride, ethylene forms a metal-organic n-complex with the palladium chloride in accordance with the following reaction: [PdC14]2- + C2H4 ," [n--C2H4PdCIa]- + CI-

.

The palladium ethylene n-complex is subsequently hydrolyzed to form an aquo-complex while losing another chloride ion: a--C24PdCI 3- + H20 ,~ a--C2H4PdC12H20 + C1-

0

(4)

(5)

The aquo-complex then dissociates to a hydroxo-complex and a hydrogen ion: n---C2H4PdCI2H20 + 1-120 ,~ [n---C2H4PdCI2OH ]- + H30

(6)

There is a difference of opinion about the next step in the reaction sequence. It is generally agreed that the monohydroxo-bis-chloroethylene palladium complex should be a cis isomer to facilitate interaction between the hydroxo-ligand and the olefin. It is believed that a trans monohydroxo-bis chloroethylene complex is formed by Reaction (6) and that three additional steps are required for isomerization of the trans isomer to the cis isomer: 1~ A

water molecule replaces a cis-chloro ligand of the monohydroxo-bis-chloroethylelae complex to form d chlorohydroxo-aquo complex:

196

Waste Minimization H

I

H - ("

Pd I1 --(7

CI

I

- 0tt

+ Ci

I

(7)

H20

t!

H

trans monohydroxo-bischloroethylene

chloro-hydroxo-aquo

complex

complex

The chloro-hydroxo-aquo dihydroxo complex:

complex

H

dissociates

to form

H

H-~

~1 [[

I

Pd

+ H20

01t

I

0

C!

H -

I

~

H - C

[H -~

Pd

-OH

I

+ H20

H20

I

t

~d - OH

[[

#

a

OH

H - C

I

H

1

+ H3 O+

(8)

H

3. The trans-hydroxo ligand is replaced by a chloro ligand:

n H- C' ]l [[

["-C C' t

= Pd - O

I OH

H-V

+ H30 + + CI- #

[[ ~

H-~

H

Pd - C

I OH

(9) + 2H20

H

The cis and transisomers may exist in equilibrium and that it is meaningless to speak of the intermediate equilibrium steps postulated above. The next step in the reaction sequence involves rearrangement of the n-ethylene complex to a o-complex, in which the ethylene is inserted into the hydroxopalladium bond: H

/

H- ~

[

CI

,' ,1

II---- Pd - c

H- 7 !

H

-

OH

+ H~O-----

(10) o- I -~-~,d-.~W H

H

CI

Analysis of Process Chemistry Example Processes

197

The manner in which the o-complex is converted into products is the subject of continuing discussion. The o-bonded complex decomposes directly through a 1,2-hydride shift, which is facilitated by formation of a palladium hydride complex intermediate. In this scheme, a 13-positioned hydroxide from the ethyl molecule forms a bond with the palladium and a ~r-bonded vinyl alcohol palladium hydride complex forms H

I

H

I

HO-

H

CI

-

C - C - Pd - H 2 H

I

I

H

CI

H - C

ol I _------~

H

[[ H

CI

" Pd - H 2

\

C

CI

i

]

O1

(11)

OH The n-bonded complex then rearranges to form an a-hydroxyethyl palladium complex, which decomposes to products: H

I

I

I/ ._c .C,o[-i.

I I

H - C

H

= Pd - " 2

II ~

1

I

~"

~

H - .C -

J

c1I

-Pd OH

- H2

(12)

CI

OH H

H

IH - c I- c I |

|

H

OH

CI

-

- PI, - . ~ o

I

1

H

a_._: . - c - Ic -

I

CI

H

I

o,~,o§

(13)

H

It has been suggested that following Reaction (12), a carbonium or ion or oxonium ion and palladium metal are cleaved from the a-hydroxyethyl palladium complex" H

I

[CH3~HPdCI2H20]-

~ CH 3 ~

OH

- H20 + + Pd~ + 2CI-

(14)

OH It

I

CH3V OH

9 !-!20 + ~

CH3CHO+H3

O+

(15)

198

Waste Minimization

In a third proposed mechanism, there is no palladium hydride complex as an intermediate step. The palladium does, however, assist in the transfer of a 15-positioned hydrogen to the carbon that is bonded to the palladium: [ H O C H 2 C H 2 PdCI2 H 2 0 ]

[CH3~HPdC12H20 ] -

(16)

OH Its use in place of copper chloride would reduce or eliminate the formation of the chlorinated compounds but it has a high toxic rating, causing irritation at vapor concentrations of 0.5. Quinone is also toxic to fish. [CH 3

HPdC12tt20]

_ ~

-~ C H 3 C H O

+Pd ~ + 2 CI-+

H 3O +

(17)

OH

If the hydroxyethyl palladium complex cleaves before hydride transfer takes place, a hydroxyethyl carbonium ion is formed that can react with chloride ions present in solution to form ethylene chlorohydrin (2chloroethanol), a by-product that is produced in the Wacker process. Copper chloride is required to promote the formation of ethylene chlorohydrin. In addition to the by-products that can be formed from the main feedstock materials, additional products can be formed from the reaction of impurities in the feedstock stream. The presence of a large excess of cupric chloride is believed to modify the reaction path for acetaldehyde production because palladium metal precipitation does not occur under those conditions. Suggested is that a copper chloride, palladium olefin complex is involved that breaks down without the formation of palladium metal: 3-

culIcI 3

I

CI

I

13Cu II _ C I - P d ] HO

(18) CH2 ~ - = ~

= CH3CHO+H

§ + PdCi 2 + 2culcI3 2-

CH 2

The reaction medium also contains copper chloride salts to reoxidize the metallic palladium formed in the main reaction back to palladium chloride (Equation 2). The copper chloride is subsequently regenerated by

Analysis of Process Chemistry Example Processes

199

oxygen (Equation 3). In the one-stage process, all the reactions occur in the same reactor. In the two-stage process, the copper chloride is regenerated in a vessel separate from that in which the ethylene oxidation occurs. The concentrations of copper (II) and copper (I), and chloride ions and their effect on the reactions that occur in the process are interrelated. This results in some difference in the composition of the reaction medium for the two processes. The degree of oxidation is represented by the ratio of concentration of copper (II) to the total copper concentration. The reaction is carried out at conditions that give high reaction rates and avoid precipitation of cuprous chloride, palladium chloride and copper oxychloride. In the one-stage process, the rate of cupric chloride reduction to cuprous chloride is equal to the rate of cuprous chloride oxidation to cupric chloride. The ratio of copper (II) to total copper (oxidation degree) is maintained at a level sufficient to avoid palladium precipitation. The solution is maintained between 0.5 and 3 pH, with hydrochloric acid to provide sufficient chloride ion to maintain the copper (I)mainly in the form of CuCI 2- complex, which is soluble, and to provide a hydrogen ion concentration that will prevent copper oxychloride precipitation. In the two-stage process, a higher concentration of copper and chloride is maintained than in the single-stage process. The composition of the reaction medium is controlled to avoid precipitation of cuprous chloride, palladium and copper oxychloride. The steps involved in oxidation of the palladium and the cuprous chloride are summarized as follows" Pd~ + 2 CuC12 + 4 CI- ,~ PdCI42- + 2 CuC12-

(19)

CuC12- + 02 ,~ C1CuO + Cl-

(20)

ClCuO 2 + 1-t30+ --~ CuC1§ + H O 2 + 1-t20

(21)

CuCIf + H O f

-~ CuCI 2 + HO 2-

(22)

HO=- + 1-130+ ,~ 1420 = + 1420

(23)

2 CuCl 2 + 1-1202 ,, 2 CuCI 2 + 2 HO-

(24)

In addition to performing its primary function of regenerating the palladium salt for the reaction, copper chloride promotes the formation of

200

Waste Minimization

chlorinated by-products. Chlorinated by-products derived from ethylene include chlorohydrin, chloroethanol, methyl chloride, ethyl chloride, vinyl chloride and chloroacetaldehyde. Propylene forms monochloro- and dichloro-acetone. Butane reacts to form 3,3-dichlorobutanone and 3chlorobutanone. Methylethylketone reacts to form 3-chloro-2-butanone. These compounds are not formed when an oxidant such as benzoquinone is used. Other side products that have been identified are acetic acid, oxalic acid, crotonaldehyde and chlorocrotonaldehyde. Acetic acid and oxalic acid react with copper to form copper acetate and copper oxalate, respectively. A typical ethylene specification is given in Table 6-5. Although impurities in the ethylene are present in relatively small quantities, they can participate in reactions that lead to the formation of by-products.

Table 6-5: Typical Specification of Polymer-Grade Ethylene Component

Specification

Ethylene Methane and ethane Propylene and higher-molecular weight organics CO2 CO 02 H2 H20 Acetylene Sulfur Oxygenated organics Ammonia and amines Organic halides

99.9 mole % (min) 0.1 mol % (max) 30 ppm (vol) 20 ppm (vol) 5 ppm (vol) 5 ppm (wt) 5 ppm (wt) 5 ppm (wt) 10 ppm (wt) 5 ppm (wt) 10 ppm (wt) 10 ppm (wt) 10 ppm (wt

The reaction mechanism of higher-molecular-weight olefins is similar to that of ethylene. In an aqueous solution of a palladium salt, they form carbonyl compounds having the same carbon skeleton as the original olefin. Terminal olefins produce mixtures of ketones and

Analyais of Process Chemistry Example Processes

201

aldehydes. Internal olefins yield ketones. Acetone and propionaldehyde are produced from propylene. 1-Butane forms a mixture of methyl ethyl ketone and butyraldehyde; 2-butane forms methyl ethyl ketone. More of the higher-molecular-weight derivatives may be produced than would be expected form the concentration of impurities in the ethylene because palladium (II) salts also catalyze the dimerization of ethylene to butane. Saturated aliphatic hydrocarbons as well as compounds such as benzene and toluene are inert in this process and act only as diluents. Acetylene forms a complex with palladium chloride in aqueous solution. Among the products that result from decomposition of the complex are acrolein and formaldehyde. Carbon monoxide is oxidized to carbon dioxide in aqueous solutions of palladium chloride. Carbonyl complexes are intermediates in the reaction of the palladium chloride salt solution with carbon monoxide: [PdCOCI2] 2 + 2 H2^O

-'* Pd + CO2 + 2 HC1

(25)

Ethyl vinyl sulfone may be formed from ethylene, sulfur dioxide and palladium chloride in aqueous solutions. Although of interest, details of the evidence for the reaction sequence presented above and for the formation of the various compounds mentioned are deemed to be beyond the scope here. They have been discussed to illustrate the complexity of some determination for waste potentials by reactions in chemical processing.

Analysis of the Wacker-Hoechst Process for the Oxidation of Ethylene to Acetaldehyde In the section entitled Process Chemistry, the chemistry of the Wacker-Hoechst process for the oxidation of ethylene to acetaldehyde was described and the chemical compounds likely to be found in the process streams identified. The physical properties and hazard ratings of a number of these compounds are presented in Table 6-6. The chemical compounds present in the process have a wide range or properties. Because of variations in the type and quantity of chemicals present in different process streams, the losses of material possible vary from stream to stream within the process. The losses posed by the materials present in each of the process streams can be evaluated. Evaluation is presented in Tables 6-7 and 6-8. The streams were rated in terms of low, moderate or high flammability and toxicity.

Table 6-6: Physical Properties and Hazard Ratings of Chemicals Present in Process Streams for Production of Acetaldehyde by Liquid-Phase Oxidation of Ethylene

N

8$

Compound/Formula

Parameter Molecular Weight Melting Point, OC Boiling Point, OC Specific Gravity of Liquid @ 2OoC relative to water at 4OC Vapor Density (air = 1) Heat of Combustion, kcal/mole Heat of Formation, k d m o l e Heat of Vaporization @ boiling point CaYg Autoignition temperature, OC Flammable Limits in Air, % by volume Upper Lower Flash Point, OC closed cup NFPA Hazard Rating: Health: flammability; reactivity Toxicity Rating (Sax, 1975) Inhalation: acute local; acute systemic Dow Material Factor

Copper Acetate Cu(CzH302)2H20 199.65 115 Decomposes at 24OOC

-

Acetone CH3COCH3

Acetic Acid CHSCOOH

Carbon Dioxide

co2

Hydrochloric Acid HCI

58.08 -94.6 56.48 0.792

60.05 16.7 118.1 1.0492

44.01 -57.1 -78.2 -

36.47 -1 14.3 -84.8 1.25 -

-

2.00 -437.92 -59.32

2.08 -209.4 -116.2

1.53 3 36 .O

-

134.14 465

96.8 462

132.4 None

103.12 None

-

19 4 39

-

-

-

-

13 2.1 -20

None

None

-

1;3$

22;l

-

3 ;O;O

Not rated

2 ;2 12.3

2;ua 5.6

0;l -

u ;3

-

39.8 liquid 22.06 vapor

-

g 5:

E.E

Table 6-6: (continued)

Compound/Formula Oxalic Acid Parameter

COOHCOOH.2 H2O

Acetaldehyde CHBCHO

p-Benzoquinone CbH402

Butyraldehyde CH3(CH2 12CHO(normal)

EL

3

L.

Molecular Weight Melting Point, OC Boiling Point, OC Specific Gravity of Liquid @ 2OoC relative to water at 4OC Vapor Density (air = 1) Heat of Combustion, kcal/mole Heat of Formation, kcal/mole Heat of Vaporization @ boiling point, cal/g Au toignition temperature, O C Flammable Limits in Air, % by volume Upper Lower Flash Point, OC closed cup NFPA Hazard Rating: Health ;flammabilit y ;reactivity Toxicity Rating (Sax,1975) Inhalation: acute local; acute systemic Dow Material Factor

126.1 101 150 (sublime) 1.65

-

60.1 195.36 0.17 cal/g for sublimation Decomposes

Nonfiie 1 ;1 ;O

Fire 2 ;1 ;O 3 ;3 0.8

108.1 115.7

72.1 -99 75.7

44.05 -123.5 20.2

Sublimes

0.783 @ 18OC 1.5 -278.77 -39.72

1.32 3.7 656.6 -46.4

0.817 2.5 -597.08 52.4

136.17

-

104.4

175

560

218

60

-

4

-

-31.8

38-93

12.5 1.9 -22

2;42

12;l

2;3;1

32 10.5

u ;3 10.9

12 13.9

v1

a 7 0

!s

Table 6 - 6 (continued)

P

e

Compound/Fomula

Parameter Molecular Weight Melting Point, OC Boiling Point, OC Specific Gravity of Liquid @ 2OoC realtive to water at 4 ' ~ Vapor Density (air = 1) Heat of Combustion, kcal/mole Heat of Formation, kcal/mole Heat of Vaporization @ boiling point, cal/g Autoignition temperature, OC Flammable Limits in Air, % by volume Upper Lower Flash Point, OC closed cup NFPA Hazard Rating: Health; flammability; reactivity Toxicity Rating (SaxJ975) Inhalation: acute local; acute systemic Dow Material Factor

Chloroacetone CH 3COCHz Cl 92.5 3 -44.5 119 1.15

-

-

2-chlomcrotonaldehyde CHjCHCClCHO 104.54

141 1.14 (density of solid)b

-

-

-

(Ethylene Chlorohydrin) 2-Chloroethanol CH2ClCH20H

D

2 CD

z

chloroform ma3

80.52 -69 128.8 1.197

119.39 -6 3.5 61.7 1.483

2.78

4.12 89.2 21.43

123 425

59.0 -

15.9 4.9

-

-

-

60

None

Not rated

-

32;O

2;o;o

-

u;3

u;3 1;3

-

3;3

-

-

-

-

-

Bi!I 5' 3

Table 6-6: (continued)

Compound/Formula

Parameter Moleculax Weight

Melting Point, O C Boiling Point, O C Specific Gravity of Liquid @ 2OoC relative to water at 4OC Vapor Density (air = 1) Heat of Combustion, kcal/mole Heat of Formation, kcal/mole Heat of Vaporization @boilingpoint aug Autoignition temperature, OC Flammable Limits in Air, % by volume Upper Lower Flash Point, O C closed cup NFPA Hazard Rating: Health; flammability; reactivity Toxicity Rating (Sax, 1975) Inhalation: acute local; acute systemic Dow Material Factor

Cuprous Chloride (I) CuCl 98.99 430 149C

Cuprous Chloride (11) cuc12 134.44 620 Decomposes @ 993

Ethyl Chloride CH3CHzCI

Methyl Chloride CHjCl

Copper Oxalate CuC04. 1/2 HzO

64.52 -1 39 12.3

50.49 -97.7 -23.1

160.57

g c

w

E . rA

-

s

-

8 rA

Y

0

-

-

-31.4

-48.83

-

-

90.55 523

101.30 637

-

-

-

17.2 10.7
-

R

-

Fl

-

0.9214 2.22 316.7 31.6 liquid 25.1 vapor

0.920 1.78 164.2 -19.58

-

-

-

-

-

15.4 3.8 -50.4

-

-

2;4$

2 ;4 ;O

-

-

Not rated

-

U;2 8.2

1 ;3 5.8

1;2

-

-

0

K

&.

3

F

E (D

7 CD

r A rA

8 N

t?

Table 6-6: (continued)

Parameter Molecular Weight Melting Point, OC Boiling Point, OC Specific Gravity of Liquid @ 2OoC relative to water at 4OC Vapor Density (air = 1) Heat of Combustion, kcallmole Heat of Formation, kcal/mole Heat of Vaporization @boiling point, cavg

Autoignition temperature, O C Flammable Limits in Air, % by volume Upper Lower Flash Point, OC closed cup NFPA Hazard Rating: Health; flammability; reactivity Toxicity Rating (Sax, 1975) Inhalation: acute local; acute systemic Dow Material Factor

Compound/Formula MonochloroEthylene acetaldehyde CHzCH2 CzH3OCl

Crotonaldehyde CH3CHCHCHO

Dichloromethane CH2CIz

70.09 -76 102

84.94 -96.7 39.8

28.05 -169.4 -103.9

0.9 2.41 542.1 40.6

1.326 2.93 144.47 28.83

-

-

0.98 316.20

-

-

-

123 232

78.18 667

115.39 548

-

-

-

-

-

-

78.5 -

Copper Oxychloride c U a 2 * 3 CuO.4 H2O

445.13 14OOC (-3 H2O) -

=5

-

15.5 2.1 13

66.4 15.5 None

32 3.1 -1 37

3;32

2;l;O

1;42

Not rated

-

3 ;u 13.9

u ;3

0 ;2 25.1

Not rated

1 ;2

3.0

-

-

z kEl

Table 6-6: (continued) Cornpound/Fonnula Palladium

Chloride Oxygen Parameter

02

Molecular Weight Melting Point, OC Boiling Point, OC Specific Gravity of Liquid @ 2OoC relative to water at 4OC Vapor Density (air = 1) Heat of Combustion, kcal/mole Heat of Formation, k d / m o l e

32.00 -218.4 -183.0 1.429 at O°C

Heat of Vaporization @ boiling point, =l/g Autoignition temperature, OC Flammable Limits in Air, % by volume Upper Lower Flash Point, OC closed cup NFPA Hazard Rating: Health; flammability ;reactivity Toxicity Rating (Sax,1975) Inhalation: acute local; acute systemic Dow Material Factor a U = Unknown.

bAt 23OC.

At 18OC.

Palladium Pd

P d a 2 . 2 H2O or PdCl2

106.4 213.35 or 177.35 1552 Decomposes a t 500 3140 12.02 (density 4.0' (density of solid) of solid)

-

-

0

0

Carbon Tetrachloride

ca4 153.84 -22.6

-

76.8 1.594

-

5.28 37.3 33.8 liquid 25.9 vapor

-

50.9 -

46.41 None

8

L

2. a 8

w w

n

K

&.

None 3;O;O

None

-

3;O;O

Low toxicity No rating -

Same as Pd

-

0;3 0.4

z0 m 0 Lj

B w

4

Table 6-7: Hazard Rating of Process Streams, One-Stage Process Approximate Temperature Stream No. 1 2 3

Phase Gas Gas Gas and liquid

4S,6

Liquid

7

Liquid and gas

8

Liquid and

9 10 11

Gas Gas Gas

12,13,14

Gas

lS,l6,17,18

Liquid

Major Components Oxygen Ethylene Acetaldehyde, ethylene, oxygen, carbon dioxide, water, catalyst components Palladium chloride, copper chloride copper oxalate, hydrochloric acid, water Palladium chloride, copper chloride carbon dioxide, hydrochloric acid, water Palladium chloride, copper chloride copper oxalate, hydrochloric acid, water, carbon dioxide Oxygen or air Water Ethylene, oxygen, carbon dioxide water, acetaldehyde Ethylene, oxygen, carbon dioxide water, acetaldehyde, alkyl chlorides Water, acetaldehyde, alkyl chloride chlorinated and oxygenated byproducts

Relative Pressure

Flammability Hazard

Toxic Hazard

2s

Ma

25 125

M

La Ha H

L L H

("0

M

Chemical Burn

Risk L L H

@ P,

%

z

E: k' P,

g. 5

100

170

170

25 180 100 1s

1s

Table 6-7: (continued)

Stream No.

Major Components

phase

18a

Liquid

19 20

Gas Liquid

21 22 23,24,25 26 21 28 29

Gas Gas Liquid Vapor Liquid Gas Liquid

30

Liquid

31

Gas

32

Liquid

Water, acetaldehyde, alkyl chlorides chlorinated and oxygenated byproducts A k y l chlorides Acetaldehyde, crotonaldehyde, chlorinated aldehydes, water Water Acetaldehyde Acetaldehyde Acetaldehyde, nitrogen Crotonaldehyde, water Water Water, chlorinated aldehydes, oxygenated and chlorinatcd organics Water, hydrogen chloride, palladium chloride, copper chloride Ethylene, oxygen, carbon dioxide, water vapor, organics Water

-

Chemical

Approximate Temperature ("C)

Relative Pressure

Flammability Hazard

Toxic Hazard

Burn Risk

k

90

L

M

H

L

g. &

1s 110

L

L

M M

180 110

M L L L L M L

25

M

L

15

M

H

15

L

L

180 21

I5 15

102

a L = Low;M = Moderate; H High, Moderate pressure = 3-10 atm. Low pressure = 1-3 atm.

L H

L

L L L L L L

M

H

H M H

L

L

B

B&. (D

M

E

F

N 0 W

Table 6-8: Hazard Rating of Process Streams, Two-Stage Process CD

Approximate Temperature Stream No.

Phve

1 2

Gas Liquid

3

Liquid

4

Liquid

5

6

Gas Gas

7.8

Liquid

9

Liquid

10

Liquid and gas

Mljor Components Ethylene Acetaldehyde, palladium chloride, hydrogen chloride, water, chlorinated organics, acetic acid Acetaldehyde, palladium chloride, copper chloride, acetic acid, water, chlorinated organics Palladium chloride, copper chloride, hydrogen chloride, water Air Acetaldehyde, water, carbon dioxide, oxygen, nitrogen Palladium chloride, copper chloride, copper oxalate, hydrogen chloride, water Palladium chloride, copper chloride, copper oxalate, hydrogen chloride, water Palladium chloride, copper chloride, hydrogen chloride, water, carbon dioxide

("C)

Relative Pressure

Chemical Burn

Flammability Hazard

Toxic Hazard La H

L H

Risk

25 130

Ma

M

Ha H

150

L

H

H

H

100

L

L

M

H

25 130

M L

L L

L L

L L

130

M

L

M

H

170

M

L

M

H

170

M

L

M

H

z 5: E. E5' El

Table 6-8: (continued)

Approximate Temperature Stream No.

Phase

11

Gas

12 13,14,1S 16

Liquid Liquid Gas

17,18,19

Liquid

20 22 23,24 25 26

Gas Liquid Gas Liquid Gas Liquid

26a

Liquid

27 28,29

Gas Liquid Gas

21

30

Major Components Acetaldehyde, acetic acid, chlorinated organic compounds, carbon dioxide, water Water, organics Water, organics Acetaldehyde, acetic acid, water, chlorinated organics Acetaldehyde, acetic acid, water, chlorinated organics Acetaldehyde, alkyl chlorides, water Acetaldehyde, water Acetaldehyde, water Acetaldehyde, water Nitrogen, water, carbon dioxide Acetaldehyde, water, chlorinated ornanics Acetaldehyde, water, chlorinated organics Alkyl chlorides, water Alkyl chlorides, water Alkyl chlorides, water

("0

Relative Pressure

Flammability Htuud

Toxic Hazard

Chemical Burn

Risk

100

L

M

H

M

110 15 50

L L

L

L

L

M

L L H

M

30

L

H

H

L

30

L

L

L

M

L

15

20

L L

M L M

H

20 15 30

L

L L H

M M H

L L L L

80

L

H

H

L

20

L

L

L L

L M

M L M

L

15

IS

L

L

L

L

L L

Table 6-8: (continued)

Stream No.

Phase

31

Liquid

32 33,34 35 36

Gas Liquid Liquid Liquid

37

Liquid

38 39

Gas Liquid

40.41

Liquid

Major Components Acetaldehyde, acetic acid, chlorinated aldehydes, water Acetaldehyde Acetaldehyde Chlorinated aldehydes Water, chlorinated aldehydes, acetic acid Water, chlorinated aldehydes, acetic acid Water Palladium chloride, copper chloride, hydrogen chloride, water Palladium chloride, copper chloride, copper oxalate, hydrogen chloride, water

Approximate Temperature ("C)

Relative Pressure

Flammability tiozvd

Toxic

Chemical Burn

Hazard

Risk

110

L

H

H

L

21 15

L

L

H H L L

H H H M

L L L L

40

L

L

M

L

180 30

M M

L L

L M

L H

130

M

L

M

H

85 110

a L = Low; M = Moderate; H = High. Moderate pressure = 3-10atrn. Low pressure = 1-3 atm.

L L

Analysis of Process Chemistry Example Processes

213

Factors considered in rating: 9 9 9 9 9 9

the components of the stream, the volume of the stream, the relative quantity of each component in the stream, stream phase (gas or liquid), stream pressure, and stream temperature.

In general, a high-volume stream is more loss prone than a lowvolume stream; a gas is considered to be more loss prone than a liquid, high temperature streams are considered to be more loss prone than lowtemperature streams because of their greater volatility; high-pressure liquid streams are also more loss prone than low-pressure streams because they evaporate rapidly when suddenly released into a lowerpressure reactor, tank or environment. Although not considered in loss analysis, some streams may pose a lesser loss potential than is indicated by their physical and chemical properties. Losses may be posed by the corrosiveness of the process streams. The corrosive properties of the catalyst solution are such as to require the use of titanium or bricklined equipment. Acetaldehyde decomposes rubber products on contact; it also oxidizes readily to acetic acid. If the corrosive streams were accidentally released to the environment, they might come in contact with equipment that is not resistant to their corrosive effects. These other pieces of process equipment could be damaged or weakened to the point of releasing their contents to the environment. Acetaldehyde is volatile, has a low flash point and oxidizes readily in air forming unstable peroxides that may explode spontaneously. Nitrogen blanketing is used in vessels containing acetaldehyde where there is the possibility that air could otherwise come in contact with the acetaldehyde, such as in storage tanks and distillation columns. Acetaldehyde is also easily polymerized. Acetaldehyde is an irritant and an anesthetic. At high concentrations it can cause respiratory paralysis. In normal industrial operations, if reasonable precautions are taken, acetaldehyde is safe to handle. Acetaldehyde is miscible with water and degrades rapidly. The catalyst solution is corrosive. Hydrogen chloride fumes are irritating to the respiratory system. The copper salt presents a potential hazard if it enters a waterway. Aquatic organisms may concentrate copper in their systems to the point where the organism becomes unfit for human

214

Waste Minimization

consumption. The oxygenated and chlorinated by-products of the process are also toxic to varying degrees. The chlorinated by-products pose a potential hazard in the event of a fire because phosgene may be produced when they are exposed to the heat of the fire. Phosgene is rapidly fatal at 50 ppm concentration after even short exposure. Ethylene chlorohydrin (2-chloroethanol) is a narcotic poison. At concentrations above 2 ppm it can damage internal organs and the nervous system and lead to death. It permeates rubber, and fatal amounts of ethylene chlorohydrin can be adsorbed through the skin. In the process, ethylene chlorohydrin is normally formed in amounts of less than 1%; however, at high concentrations of cupric chloride (up to 3 mole/e), the formation of ethylene chlorohydrin becomes the predominant reaction. The chlorinated compounds also pose a potential hazard because they degrade more slowly than a nonchlorinated hydrocarbon with the same structural skeleton. Thus, in the event of an accidental release, they would tend to persist in the environment. Quinone has been mentioned in the literature as a possible substitute for copper chloride in the process and as a possible additive to promote the dissolution of oxygen into the catalyst solution. However, there was no indication in the literature that it is used.

Process Waste Discharges The manufacture of acetaldehyde by the aqueous liquid-phase oxidation of ethylene produces the following types of waste streams: 9 9 9 9

inert process gases contaminated with organics, unrecoverable volatile organic by-products, unrecoverable liquid organic by-products, and process contact wastewater contaminated with organic and inorganic process chemicals.

The principal difference in the waste streams from the two process variations is in the contaminant concentrations.

Single-Stage Process Waste Streams Figure 6-6 illustrates the handling of the gaseous emissions from the single-stage process for manufacturing acetaldehyde from ethylene.

-

Sw. COI(PkESS0p

C u e o u s Emission

Figure 6 - 6 Gaseous emission points in the single-stage process for manufacturing acetaldehyde from ethylene.

216

Waste Minimization

The reactor exit stream (stream 3) containing acetaldehyde, catalyst solution and unreacted ethylene gas, oxygen and inerts is depressurized in a gas-liquid separator from which the acetaldehyde and unreacted ethylene, oxygen and inerts pass overhead in the form of a gas (stream 11). The gas stream flows into a scrubber where the acetaldehyde is removed from the gas with water. The unreacted ethylene, oxygen and inerts are not soluble and flow out the top of the scrubber for recycle to the reactor. To avoid the accumulation of inerts in the system, a portion of the recycle stream is continuously purged (stream 13). This stream contains primarily ethylene, oxygen, carbon dioxide and nitrogen and is most readily disposed of in a combustion device such as a flare. The crude acetaldehyde solution in the bottom of the scrubber is fed to a distillation column to remove alkyl chlorides, formed as by-products of the reaction, and dissolved ethylene and inerts (stream 19). The alkyl chlorides are not produced in quantities sufficient to make their recovery worthwhile and must be disposed of. This stream can be flared; however, hydrogen chloride will be formed on flaring and may create a problem, depending on the gas volumes involved. Table 6-9 gives reported emission factors for the single-stage process. If the product recovery column operates at atmospheric solution pressure, the column vent (stream 26) may release acetaldehyde vapors along with inerts during process operation.

Table 6-9 Emission Factors for Single-Stage Process for Acetaldehyde from Ethylene Stream Source

Stream Number

Quench Scrubber

13

Light Ends Distillation of Column

19

Stream Component

Emission Factor (kg/metric ton acetaldehyde)

Ethane Ethylene Acetaldehyde Methane Methyl chloride

2.2 27.4 Trace Trace Trace

Methyl chloride Acetaldehyde

8.7 Trace

Figure 6-7 illustrates the wastewater and organic liquid waste discharges from the process.

I n e r t Gas Purge to Flare

r------1

111

12

Light ends to Flare

CONDENSER

@I+

REFLUX

-y

l y u c t

Storage

to Disposal Steam

-

SUL COWRESSOR

L i q u i d Uasca

Figure 6-7: Liquid waste discharge points in the single-stage process for manufacturing acetaldehyde from ethylene.

218

Waste Minimization

The wastewater results from the use of a water scrubber to remove the product acetaldehyde from the reactor gases. The wastewater is removed from the bottom of the product recovery column (stream 29) and is contaminated primarily with acetic acid and chlorinated acetaldehydes. Wastewater flowrate factors have been reported as ranging between 0.3 and 0.75 kg water/kg acetaldehyde produced. The pollutant loading is dependent on the efficiency of the product recovery column for acetaldehyde recovery and on the control of by-product formation in the reactor. The wastewater stream may be sufficiently dilute to be amenable to biological degradation. Palladium and copper salts, as well as sulfate and oil contaminants, have also been found in wastewater effluents from the process. It is probably reasonable to assume that the consumption of palladium chloride in the process is due to losses of these compounds to the wastewater. Palladium chloride and copper chloride consumption in the process averages, respectively, 0.9 and 120 g/ton of acetaldehyde produced. A side stream (stream 27), containing primarily crotonaldehyde, is also removed from the product recovery column. This stream is sufficiently concentrated to be amenable to disposal by incineration. Deep well injection of liquid wastes is also practiced.

Two-Stage Process Waste Streams Figure 6-6 illustrates the handling of the gaseous emissions from the two-stage process for manufacturing acetaldehyde from ethylene. The reactor exit stream (stream 2) contains dissolved gases and inerts that are present in the ethylene and in the catalyst solution. Additionally, carbon dioxide is generated in the catalyst regenerator where oxalates are decomposed. The inerts and noncondensable gases from the reactor and catalyst regenerator are released from the vent on the reflux drum of the crude distillation tower (stream 20). This vent stream is passed through a water scrubber to recover entrained acetaldehyde and unreacted ethylene. The noncondensables pass through the scrubber vent (stream 22) and may be flared or incinerated to destroy any residual hydrocarbons. A second gas stream originates at the catalyst oxidizer where air is used to oxidize the spent catalyst solution. The nitrogen fraction of the air separates from the oxidized catalyst solution in the gas-liquid separator (stream 6) and passes through a water scrubber for removal of entrained organics. The scrubber exit stream (stream 25) contains more than 99% nitrogen and can be used to fulfill requirements for an inert gas such as for blanketing of process vessels and the acetaldehyde storage tank.

Analysis of Process Chemistry Example Processes

219

The alkyl chloride by-products (primarily methyl and ethyl chloride) are removed from the crude product stream in the light ends distillation column. This stream (stream 30) is treated in the same manner as the equivalent stream in the one-stage process, i.e., by flaring. The product recovery column, if operated at atmospheric pressure, is vented through the reflux drum (stream 42). This vent may release acetaldehyde vapors along with inerts when the column is in operation. Figure 6-7 illustrates the wastewater and organic liquid waste discharges from the process. The liquid organic waste discharge from the two-stage process is primarily chlorinated acetaldehyde, removed as a side stream (stream 35) from the product recovery column. This stream is amenable to disposal by incineration, although hydrogen chloride formed during incineration may pose a problem. Recovery of monochloroacetaldehyde from this stream may be economically feasible. The wastewater is discharged as bottoms from the product recovery column (stream 36). It is used to preheat the crude acetaldehyde entering the light ends distillation column prior to disposal. The stream is more concentrated in acetic acid and chlorinated aldehydes than the equivalent stream from the one-stage process because less process contact water is used. The stream is not amenable to biological treatment without dilution or pretreatment because of the high concentration of chlorinated compounds. Pretreatment schemes suggested in the literature for decomposing the halogenated compounds include (1) addition of ammonia, ammonium salts or amines and heating above 60~ under 10 atm pressure for a minimum of 5 minutes; (2) addition of caustic calcium hydroxide followed by heating; and (3) heating at moderate temperatures and pressures using aqueous solutions of cupric salts. As for the one-stage process, the wastewater also contains copper and palladium salts as a result of catalyst losses during process operation. Catalyst losses for the two-stage process have been reported to be the same as for the one-stage process.

C2H4 and l w molecular welght alkyl chlorides to flare

I FUSH

CRUDE

TOWER

DISTILLATION TOWER

CAS SCRUBBERS

Steam

36

” 1 k M N C E R DISTILLATIONCOLUMN

Y

wLu)QI

SEWER

Figure 6-8: Gaseous emission points in the two-stage process for manufacturing acetaldehyde from ethylene.

Light Ends LO Flare

BIGtl

PPESSURE ZONE ( 9 am.)

Figure 6-9: Liquid waste discharge points in the two-stage process for manufacturing acetaldehyde from ethylene.

CHAPTER 7

INDUSTRY PROFILE--FERTILIZERS

INTRODUCTION Chemical fertilizers are compounds containing high concentration of nutrients required for plant growth. Apart from the three main constituent elements, carbon, oxygen and hydrogen, plants require substantial quantity of nutrients. These nutrients are classified as primary nutrients, secondary nutrients, and micronutrients. The elements responsible for providing these nutrients are listed in Table 7-1. Generally fertilizer industry is engaged in the production of primary plant nutrients suitable for application in the soft. In nitrogenous fertilizers, nitrogen is present as ammoniacal nitrogen such as ammonium sulphate, ammonium chloride; nitrate nitrogen such as calcium ammonium nitrate in which both ammoniacal and nitrate nitrogen are present, and amide nitrogen such as urea. In phosphatic fertilizers, phosphate is present as available phosphate such as single super phosphate (SSP), triple super phosphate (TSP). The requirement of potassium can be met with muriate (potassium chloride) and sulphate of potash. Based on the type of the nutrient present, fertilizers are usually grouped. When only one nutrient is present in the fertilizer, it is termed as straight fertilizer whereas when more than one nutrient is present the fertilizer is termed as complex or mixed fertilizer. Nitrogenous straight fertilizer: 9 9 9 9

Urea Ammonium sulphate Ammonium chloride Calcium ammonium nitrate (CAN) 222

Industry Profile---Fertilizers

223

TABLE 7-1 ELEMENTS NECESSARY FOR PLANT GROWTH Primary nutrients

Secondary nutrients

Micro nutrients

Nitrogen

Calcium

Boron

Phosphorus

Magnesium

Chlorine

Potassium

Sulphur

Copper Iron Manganese Molybdenum Zinc

Phosphatic straight fertilizer: 9 9

Single super phosphate (SSP) Triplesuperphosphate (TSP)

Complex and mixed fertilizers: 9 Ammonium phosphate (DAP) 9 Nitrophosphate (NP) 9 Different blends of NPK fertilizers Since fertilizer is related to food production, the growth of the fertilizer industry is evident and desired by all concerned. The manufacture of fertilizer, however, is associated with the pollution of the environment and historically consisted of low efficiency operations. Increased fertilizer production can mean more and more pollutant generation and releases to the environment. For effective control in the fertilizer industry, it is imperative to ascertain proper control measures. This chapter provides detailed information on the manufacturing process, generation of pollutants, toxic effect of pollutants, control mcasures--inplant and end of process, present status of control measures and also, the recommendations for implementation as well as waste reduction potential.

224

Waste Minimization

MANUFACTURING PROCESSES Ammonia~Ammonia is produced by the reaction of hydrogen with nitrogen in the three to one (3"1) volume ratio: 3 H2 + N2 ---~ 2 NH3 The raw material source of nitrogen is atmospheric air. Hydrogen is obtained from a variety of sources such as water, cokeoven gas, naphtha, fuel oil, coal, natural gas etc. The manufacturing process involves four successive steps: 9 9 9 9

gasification shift conversion carbon dioxide recovery and gas purification ammonia synthesis

The selection of gasification process mainly depend on raw material as indicated in Table 7-2. TABLE 7-2 FEEDSTOCK AND RELATED GASIFICATION PROCESS Feedstock

Gasification process

Water

Hydrogen off-gas from electrolysis

Cokeoven Gas

Partial oxidation or reformation

Naphtha

Partial oxidation or reformation

Fuel Oil

Partial oxidation

Coal

Partial oxidation

Natural Gas

Reformation

Gasification Electrolysis: The electrolytic process consists of passing direct current through a dilute aqueous solution of caustic soda. This decomposes water according to the following equation: 2H20--~ 2H 2 + O 2

Industry Profile---Fertilizers

225

Hydrogen produced using this process is pure. It is mixed with nitrogen obtained from an air separation plant to prepare a synthesis gas mixture. Partial oxidation: Feedstock fuel oil essentially follows a partial oxidation route. Coal gasification is also a partial oxidation process. Naphtha and cokeoven gas, on the other hand, may adopt either partial oxidation or steam reformation process for gasification. In the partial oxidation process oxygen or oxygen enriched air and steam are preheated separately and injected into a refractory lined chamber. The partial oxidation is carried out between 1000 ~ and 1500~ temperature and at pressure up to 80 atmospheres. Hydrocarbons are not completely oxidized. Some quantity of uncombusted carbon as soot remains in the gas mixture. The gas is freed from carbon by scrubbing with water. This gas is desulfurized and sent to the shift conversion unit. Air separation unit is an integral part of the partial oxidation process for supply of oxygen and nitrogen. A flow diagram of ammonia production partial oxidation process is given in Figure 7-1. Coal gasification: Dried powdered coal is fed to the bunker attached to the individual burner and required quantities of oxygen and steam are introduced through the mixing screw into the gasifier where gasification reactions take place at around 1500~ Heat is recovered by passing the product gas through a waste heat boiler and subsequently a washer cooler. Steam Reformation: In the steam reformation process, first step is removal of sulphur from the feedstock. The natural gas or vaporized naphtha is sent to the desulfurizer where in the presence of catalyst, sulfur is removed. The desulfurized feed is mixed with steam and led to the primary reformer filled with nickel catalyst. The reaction being endothermic, external heating of the reformer tubes is necessary. The partially reformed gas flows to the secondary reformer. Here some quantity of preheated air is mixed with the gas to get the stoichiometric quantity of nitrogen gas in the synthesis gas mixture. The mixture of partially reformed gas, steam and air passes through a bed of nickel catalyst. Heat is recovered from the gas by generating high pressure steam in the waste heat boilers. The exit gas after cooling in heat exchangers is sent to the shift conversion units. In Figure 7-2 a flow diagram for ammonia production by steam reformation process is provided.

I FLUE GAS

NAPHTHA/ FUEL PIC

0

STEAM

PARTIAL OXIDATION

A

Ah

EMISSION

-

I

8Oi:ER

BLOWDOWN

r

CARBON AND CYANIDE REMOVAL

-

AIR

>

OlR SEPARATION UNIT

FLUE GAS

SHIFT CONVERSION

I ,

11

CO2 REMOVAL

LIQUIG NITRGGE N WASH

AMMbNIA SY NT HE 515

OILY EFiLUENT SOLUTION LOSS

Figure 7-1: Ammonia production by partial oxidation process.

m

1

BLOWCEWN

_*-

-

PURGE GAS

r

CARBON WASTEWATER

0

CARBON DlOXlOE

N N

+

AMMONIA

-

r

FLUE GAS A

'

STEAM

1

>

A

- - --1-11

PRIMARY SECONDARY REFORMER -+ REFORMER ~~

C 02 REMOVAL

SHIFT CONVERSION

HETHANATION

ABSORBENT SOLUTION LOSS

BOILER BLOWDOWN

PROCESS

j

AMMONIA SYNTHESIS

?f

'

A

OILY EFFLUENT

V BOUE R

eLowDowN PURGE GAS

L

-. \

Figure 7-2: Ammonia production by steam reformation process.

A~~~~~~

*

228

Waste Minimization

Shift Conversion

The constituents of the gas leaving secondary reformer are mostly Hz, CO and CO 2. The carbon monoxide content of gas is converted into carbon dioxide and hydrogen by passing over activated iron oxide catalyst in presence of steam, thus generating further hydrogen by water-gas shift reaction: CO+H20~

H2 + C 0 2

This shift reaction is carried out in two stages" high temperature (HT) and low temperature (LT) shift reaction. The carbon monoxide con-tent of the gas is reduced to around 0.2 % and the constituents of the gas are mostly CO2, H 2 and N 2. Carbon Dioxide Recovery and Gas Purification

Carbon dioxide is obtained in the mixed state with hydrogen and is recovered and removed by absorption. The carbon dioxide absorption processes and typical constituents of absorbent solution are given in Table 7-3. The carbon dioxide is later recovered by desorption and usually used in the urea manufacturing process and in the preparation of ammonium carbonate solution needed for the manufacture of ammonium sulphate by the Merseberg process. TABLE 7-3 CARBON DIOXIDE ABSORPTION PROCESSES AND TYPICAL ABSORBENT SOLUTION Process

Constituents of absorbent solution

Vetrocoke

Potassium Carbonate (20 per cent) and arsenic trioxide (15 per cent)

Benfield

Potassium Carbonate (30 per cent) Diethanolamine (3 per cent) and arsenic trioxide (0.3 to 0.9 per cent)

Monoethanolamine (MEA)

MEA (15-20 per cent)

Rectisol

Methanol

Catacarb

Potassium carbonate, Diethanoiamine and Vanadium Pentoxide

Glycine

Potassium carbonate and glycine

Industry Profile---Fertilizers

229

Small amounts of CO and CO 2 remaining in the gas as impurity are removed by methanation by passing the hot gas through nickel based catalyst to convert CO and CO 2 into Methane (CH4) and water: CO + 3H 2 "* CH 4 + a 2 0

CO 2 + 4H 2 --* CH4 + 2H20 In the plants where partial oxidation process is practiced, liquid nitrogen is available from an air separation unit. In these plants the impurities CO, CO2, methane, argon etc. are removed by liquid nitrogen wash instead of methanation. Ammonia synthesis: Ammonia synthesis is carried out at elevated temperature and pressure of the order of 500~ and 270 to 350 atmosphere respectively by passing hydrogen and nitrogen mixture (1:3 volume ratio) over an activated iron oxide catalyst in converters. Since at these operating conditions the conversion of hydrogen and nitrogen to ammonia is of the order of 10-20%, the reaction gas needs to be cooled to condense and separate ammonia. The residual gas is recompressed and mixed with fresh make up gas and recycled to the ammonia converter. The ammonia product is stored either in large spheres at a pressure of 20 atmosphere under ambient temperature or in large atmospheric tanks at a temperature of-33~ Urea Urea is manufactured by the reaction of ammonia and carbon dioxide to form ammonium carbamate first. Ammonium carbamate is then dehydrated to form urea: 2 NH 3 + CO 2 ~

NI-I4 COO NH2

NH4COO NH 2 --* NH 2 CO NH2+ H20

The carbon dioxide-ammonia reaction to form urea, ammonium carbamate and water takes place in a reaction vessel at a pressure 160-200 atmosphere and temperature 170~176 Unreacted ammonia and carbon dioxide are also present along with ammonium carbamate and urea in the reactor exit stream. The pressure of the exit stream is let down in stages in decomposers. The urea formed remains in the solution while the ammonia and carbon dioxide evolved, are recovered from the decomposers and recycled in the reaction vessel. The urea solution thus obtained is concentrated to 99.8% in vacuum evaporators and finally prilled in priUing tower. A schematic flow diagram for the urea production process is given in Figure 7-3.

A

r

RECYCLE

RECOVERY

SILO

A

A

STRIPPING CARBON OlDXlDE

REACTOR

AND DECOHPOSI~ON

Figure 7-3: Urea production process.

7

-

Y EVAPORATION

PRlLLl NG

BAGGING

-

h UREA

Industry Profile---Fertilizers

231

Ammonium Sulphate The following processes describe the production of ammonium sulphate.

Direct neutralization Ammonia is directly neutralized with sulphuric acid to produce ammonium sulphate. 2NH 2 + H2SO4 ~ (NH4)2SO4 The neutralizer, evaporator and the crystallizer are interconnected so that the heat released during neutralization is utilized to evaporate water in the ammonium sulphate slurry. These units operate under partial vacuum. The salt is separated by centrifugation and the mother liquor is recycled. The wet salt passes through rotary drier and cooler to obtain the product. The flow diagram for ammonium sulphate production by direct neutralization process is given in Figure 7-4.

Merseberg Process In this process, first carbon dioxide is absorbed in ammonia solution to obtain ammonium carbonate solution. Ammonium carbonate solution is then reacted with gypsum (CaSO4, 2H20) to produce ammonium sulphate and calcium carbonate. 2NH4OH + CO2 ~ (NH4)2 CO3 + H20 CaSO4, 2H20 + (NH4)2 CO3 ~ (NH4)2 SO4 + CaCO a + 2H20 Calcium carbonate is removed by filtration. The ammonium sulphate solution is evaporated under vacuum, crystallized, centrifuged and dried. The byproduct gypsum of the phosphoric acid plant may be used as a raw material for the production of ammonium sulphate by the above process. The production process is shown in Figure 7-5.

Ammonium Sulphate from Cokeoven Byproduct Ammonia Cokeoven gas contains about one per cent ammonia by volume. This gas is cooled and passed into saturators containing weak sulphuric acid. Ammonium sulphate crystals formed in the saturator are recovered, centrifuged, washed and dried to obtain ammonium sulphate salt.

SULPHURIC ACID AMMONIA AIR

’

EVAPORATOR CRYSTALLISER

*

CENTRIFUGE

MOTHER LIQUOR

9

DRIER 6 COOLER

I

Figure 7-4: Ammonium sulfate production by direct neutralization process.

-

5 AMMO N l UM SULPHATE

EMISSION

EMISSION

4

h

AMMihllA CABON UOXlOE

.

'

. CARBONATION TOWER

REACTION TANK

--L

FILTRATION

A

-

EVAPORATION

d

AMMONIUM SULPHATE CRYSTAL SEPARATION

---L

DRYING h COOLING ~

AMMONIU; SULPHATE

Y

s a

GYPSUM

4

9 GYPSUM WASHIN6

V WASH ~

E

R

SPL-SE

CHAL. JLURRY

Figure 7-5: Ammonium sulfate product by Merseberg process.

CONDENSATE

234

Waste Minimization

Ammonium Chloride The modified Solvey process is used for production of ammonium chloride. In this process, sea salt is first washed with saturated m a g nesium salts. The purified salt is then pulverized and mixed with a m monia. Ammoniated brine is reacted with carbon dioxide in a series of carbonation towers to form sodium bicarbonate and ammonium chloride. NaCI + NH 2 + CO 2 + H20 --~ NaHCO 3 + NI-I4C1 Sodium bicarbonate crystals out and is separated by filtration while ammonium chloride remains in the filtrate. Ammonium chloride solution thus obtained is cooled to subzero temperature and pure sodium chloride salt is added for crystallization of ammonium chloride. Ammonium chloride crystals are separated by centrifugation and the brine is recirculated to the carbonation tower. The ammonium chloride crystals are dried in rotary driers to obtain the product. The process of manufacture of ammonium chloride is shown in Figure 7-6.

Calcium Ammonium Nitrate (CAN) First, ammonium nitrate solution is prepared by reacting preheated ammonia with nitric acid in a neutralizer. The heat of reaction is utilized for evaporation and 80-83% ammonium nitrate solution is obtained. This concentrated solution is further concentrated to obtain 92-94% solution in a vacuum concentrator. Concentrated ammonium nitrate solution is then sprayed into the granulator along with a regulated quantity of limestone powder and the recycle fines from the screens. The hot granules are dried in a rotary drier by hot air, screened and cooled in coolers to obtain the product. The process of manufacture is given in Figure 7-7. Nitric Acid Nitric acid is produced by oxidation of ammonia. The liquid ammonia is evaporated, superheated and sent with compressed air to a convertor, containing platinum and rhodium catalyst. In the convertor ammonia is converted into nitric oxide which is then converted into nitrogen dioxide in the oxidation vessel with the help of secondary air. The process water absorbs nitrogen dioxide to form nitric acid in the absorption column. 4 NH 3 + 702 ~ 4 NO z + 6 H20 4NO 2+2H20 +O 2~4HNO

3

In the fertilizer industry normally 53-55% nitric acid is produced. The flow diagram for nitric acid production is given in Figure 7-8.

I

I

CARBON DIOXIDE

CYCLONE

OlST IL LAT D N

1

DISTILLER WASTE

A M MONlA

SALT

SALT PURIFICATION

--+

AMMONIATION

-+

CARBON AllON

FILTRATION

M

SODIUM BICARBONATE CALCINATION

SODIUM CARBONAT<

7,

I

/

4

CdMPRESSOR OILY WATER 4

PaMP SEAL WATER

’

-

NHLCI CRYSTALLISATION - - - - c C E N T m F u C A T l o N

Figure 7 - 6 Ammonium chloride production-modified Solvey process.

DRY”G

AMMONIUM

CHLORIDE

LIMESTONE

LIMESTONE GRINDING

CONDENSER

NITRIC-

EVAPORATOR

VACUUM CONCENTRATOR

-

LIMESTONE POWDER MIXER

-

GRANULATOR j

Figure 7-7: Calcium ammonium nitrate (CAN) production process.

DRIER

SCREEN ---5 COOLER

A

CALCIUMAMMONIUM

f

BOILER BLOWOOWN

Figure 7-8: Nitric acid production process.

COOLING W A E R BLOWOOYIN

238

Waste Minimization

Sulphuric Acid Sulphuric acid is produced from sulphur. Sulphur dioxide is first obtained by the burning of the molten sulphur in presence of air. Sulphur dioxide is then converted to sulphur trioxide in presence of vanadium pentoxide catalyst. The sulphur trioxide thus obtained is absorbed in recycling concentrated sulphuric acid in an absorption tower. The plants installed earlier and the smaller units of sulphuric acid plants use a single absorption process which has conversion efficiency of 96-98%. New large sulphuric acid production plants now-a-days utilize double conversion double absorption (DCDA) process. DCDA process can realize above 99% conversion efficiency. The manufacturing process for sulphuric acid by the single absorption process and DCDA process are shown in Figure 7-9 and Figure 7-10 respectively.

Phosphoric Acid Phosphoric acid is produced by the wet process using rock phosphate. The production.of phosphoric acid is made using the following steps:

Rock phosphate grinding~In the grinding mill the rock phosphate is ground to a level of fine powder. Acidulation---Finely ground rock phosphate and sulphuric acid is mixed in a digester at a temperature around 70 to 80~ to form phosphoric acid and gypsum. Caa,o(PO4)6F2 + 10 HzSO4 + 20 1-120 --} 10(CaSO4 2H20) + 6HaPO4 + 2HF

Separation of Gypsum Gypsum formed, is separated from phosphoric acid by filtration in the pan filters.

Washing of Gypsum Gypsum is washed to make it free from phosphoric acid and is disposed as gypsum slurry or gypsum cake.

Concentration of Phosphoric Acid Dilute phosphoric acid is recycled to the digester. The concentrated portion of acid is further concentrated by direct heating using steam in vacuum evaporator. The concentrated acid thus obtained is of 52-54% P205. Figure 7-11 shows the manufacturing process for phosphoric acid.

SULPMlR

SULPHUR FURNACE

4 WASTE HEAT

BOILER

U CONVERSION

--C

ABSORPTION

--+ AUO COOLIN6 -&2

0 CIRCULATION SULPHUR,C lANK ACID

7,

Figure 7-9: Production of sulfuric acid-single absorption process.

--

N

P 0

T

r

SULPHUR

SULPHUR FURNACE

IR WYING

-

---.+

WASTE HEAT8OILER

-

CONVERSION

V

BLOWOOWN

Figure 7-10: Sulfuric acid production-DCDA

AOSORPTION

process.

HEAT 4 EXCHANGER

INTERSTAGE ABSORPTION

-

V

ACID COOLING h CIRCULATING

.

6

SULPHURIC ACID

MAKE UP WATER

1 DUST

EMISSION

V

FUME SCRUBBER

COLLECTOR

TI

I

ROCK PHOSPHATE SULPHURIC ACID

*

GRINOING

-

I ACIDULATION

CONCENTRATION

I

I

GYPSUM REPULPING 4 FILTRATION

Figure 7-11: Phosphoric acid production process.

WATER

AGIO

242

Waste Minimization

Single Super Phosphate (SSP) Ground rock phosphate (90% passing through 100 mesh sieve) is mixed with sulphuric acid (55 to 75%) in a specially designed mixer which discharges the product to a wide belt conveyor. The reaction is completed in the belt conveyor: Caxo(PO4)6 F2 + 7 H2SO4 --* 3 Ca (H2 PO4)2 + 7 CaSO4 + 2HF The reacted mass is then sent to a curing shed where the product is stored for 3 to 4 weeks for curing and drying. The cured product is dried, milled and screened to obtain the product SSP. Where granulation is practiced, the cured SSP is granulated in the presence of steam. The manufacturing process is given in Figure 7-12. Triple Superphosphate (TSP) As in the case of SSP, the rock phosphate is ground to a fine mesh and reacted with concentrated phosphoric acid (52 to 54% P205) ill a cone mixer: Caxo (PO4)6 F2 + 14H3PO4 -~ 10 Ca (H2PO4)2 + 2HF It is then fed to a continuous den and piled for curing. After curing, the material is sized and used as a fertilizer. The material can also be granulated, if desired. In the granulation process, a lower concentration of phosphoric acid (40-45% P2Os) is used. A slurry of rock phosphate and phosphoric acid is made. Chemical reactions proceed towards completion in the fluid state. After I to 2 hours mixing period, the slurry is distributed over dry TSP material. The distribution is done in a rotary drum where granules are formed. The granules are dried, screened and cooled. The over and undersize granules are recycled in the rotary drum. The sequence of manufacturing of TSP without granulation and with granulation processes are given i n Figure 7-13 and Figure 7-14 respectively.

Diammonium Phosphate (DAP) DAP is manufactured by reacting ammonia with phosphoric acid: 2 NH 3 + HaPO4 --~ (NH4)2 HPO4

DUST

EMISSION

€MI SlON

r WAT E R

SCRUBBER

I

+

I

E!F LUENT

Figure 7-12: Single super phosphate (SSP) production process.

i

+ DUST

EMISSION

EMISSION

DEDUSTINC

I

ROCK PHOSPHATE

GRINDING

WATER

PHOSPHORIC ACID

( 5 2 - 5 4 % 905)

SCRUBBER

I{

MIXER

;

1 B E L T DEN

TRIPLE SUPER P H O S P H A T E

v

EFF'LUENl

Figure 7-13: Triple super phosphate (TSP) production process without granulation.

A WATER

4

I\

Figure 7-14: Granulated triple super phosphate (TSP) production process. N

R

246

Waste Minimization

Ammonia, either gaseous or liquid, and phosphoric acid of 40-54% PzOs are used for the reaction. The preliminary neutralization is carried out in a preneutralizer and then the slurry containing a mixture of DAP and MAP (monoammonium phosphate) is sent to the granulator where it is further ammoniated to get the desired mole ratio of ammonia/phosphoric acid. Any unreacted ammonia gas is then scrubbed with weak phosphoric acid and returned to the preneutralizer. The granulator discharge is then dried and screened. Dried undersize granules are separated and recycled in the process. Product size granules are cooled to obtain DAP product. The production process for DAP is shown in Figure 7-15.

Nitrophosphate The term nitrophosphate covers the range of fertilizers containing nutrients nitrogen and phosphorus (sometimes along with potassium) obtained from nitric acid acidulation of rock phosphate. The main raw materials required for the production of nitrophosphates are nitric acid, rock phosphate and ammonia. A few processes are available for the production of nitrophosphates but the process generally adopted with the steps followed in the manufacturing process are: 9 9 9 9 9 9 9

digestion crystallization of calcium nitrate calcium nitrate separation neutralization of mother liquor calcium nitrate conversion and recycle evaporation priUing

Digestion: Ground rock phosphate is digested with 54% HNO 3 in reactors, where the following reaction takes place: Ca~0(PO4)6 F2 + 20HNO a --* 6H3PO4 + 10Ca (NO3)2 + 2HF

Crystallization: The undesirable calcium nitrate is removed as calcium nitrate tetrahydrate by cooling the acidulated mass. Calcium nitrate separation: Calcium nitrate tetrahyrate crystals are separated by filtration or centrifugation. Neutralization of mother liquor: The mother liquor is neutralized with ammonia in the neutralizer. Due to heat of reaction, considerable quantity of water is vaporized during neutralization.

DUST

EMISSION

b

t

7

1

SCRUBBER

I

OEOUSTING

b

V

PRENEUTRALISER

I

GRANULATION

DRIER

Figure 7-15: Diammonium phosphate (DAP) production process.

I

I

1

SCREEN I

IAMMANIUW DpHOSPHAfE

248

Waste Minimization

Calcium nitrate conversion: The separated calcium nitrate crystals are taken to the reactor and reacted with ammonia and carbon dioxide to form ammonium nitrate and calcium carbonate. Chalk is separated by filtration and the mother liquor after concentration is taken to the neutralizer. Evaporation: The neutralized mother liquor augmented with ammonium nitrate is evaporated where the moisture content is reduced to around 0.5%. Prilling: The nitrophosphate melt from the evaporator is finaUy priUed in prilling tower. The production process of nitrophosphate fertilizer is given in Figure 7-16.

Ammonium Phosphate Sulphate: Ammonium phosphate sulphate is produced by neutralization of a mixture of sulphuric acid and phosphoric acid by ammonia and granulating the resultant slurry. Alternatively, it may also be produced by addition of ammonium sulphate to phosphoric acid and then ammoniating the mixture. Sometimes, urea addition is effected to obtain high nitrogen product. The mixture is dried, screened and cooled to obtain the product ammonium phosphate sulphate. The manufacturing process is given in Figure 7-- 17.

Urea Ammonium Phosphate Ammonia and phosphoric acid in the required proportions are neutralized in the reactor. The resulting ammonium phosphate slurry is taken to the granulator. In the granulator, urea is added. Sand or dolomite may be added as filler depending upon the grade required. The granulator discharge is then dried, screened and cooled. The product of undesired size is recycled in the granulator. Dust and fumes are scrubbed with phosphoric acid solution and recycled in the reactor. The production process is given in Figure 7-18.

NPK Complex Fertilizer Various grades of NPK complex fertilizers can be produced adopting the same process route. The common process involves metering of ammonia and phosphoric acid in required proportions to the preneutralizer and transferring the resulting slurry to the granulator. During granulation the nitrogen content of the product is increased as per required by addition of ammonia and urea as necessary.

OUST

OUST

EMISSION

t OEOUSTING

oun

A

SCRUBBER

OEOUSTING

4

Y % NITRIC ACIO

ous:

EMISSION

4

A

A

: REACTPH NITRo-PHOSPHATE

ROO( PHOSPHATE

5 a CALCIUM NITRATE CONVERSION

I

1

7 0

FILTRATION

c

CHALK

Y

EFFLUENT

Figure 7-16: Nitrophosphate production process.

v

0

k’

N P \o

1

WATER

OEOUSTING

SCRUBBER

A

4

4

SULF'HURlC ACID PHOSPHORIC ACID

a

V

* NEUTRALISATION

BRANULATION

- - DRYING

Figure 7-17: Ammonium phosphate sulfate production process.

SCREENING

1

COOLING

t;::::,","s u ~ p

HATE

L.

EMMISSION

t SCR U88 E R

I " !

t CYCLONE

Ii

t

t AMMONIA

REACTOR

d

GRANULATOR.

%

t DRYING

UREA

Figure 7-18: Urea ammonium phosphate production process.

- t

SCREENING

E? a

UREA '

AMMONIUM PHOSPHATE-

8 3

252

Waste Minimization

Potash and suitable filler are also added to obtain the correct product formulation. The granulator discharge is then dried, screened, cooled and coated with coating agent to improve, the storage properties. The manufacturing process is shown in Figure 7-19. oG

,oo.~

r

,

y

*

O

S

ao

.

.

.

.

.

.

/

.

~2o

6 O,

1.0

i

I Z

40 ~ (1)

-

~

J

-6O

t.. -9

+.3" -17 Z

4-* C

~

u

ca.

80

~ r

....

_

6

8

tO

~2

pH- Figure 7-19: Distribution of NH 2 and NH4+ ion on different pH and temperature. Apart from the main production plants, the fertilizer industry needs some additional facilities which are supplied by the following auxiliary plants: 9 raw water supply and treatment 9 demineralization (DM)

Industry Profile--Fertilizers 9 9 9

253

steam generation (SG) and power generation material handling effluent treatment

Raw Water Supply and Treatment The fertilizer industry consumes considerable quantity of water in production. The main requirements are for: 9 9 9 9

cooling tower makeup feed to the demineralization (DM) plant process and fire needs sanitary supply

Usually one of the main factors of site selection is the availability of a required quantity of water. Generally raw water is drawn from rivers, streams, canals, lakes, reservoirs. Ground water is also used by many industries. In some cases municipalities supply clarified water. In most cases sufficient storage facility in a reservoir is provided inside the factory area or adjacent to the factory to cope with any unexpected shortfall of water. Raw water treatment plant is installed mainly for the clarification of water. In some cases, partial softening is also carried out in the raw water treatment plant. The treatment chemicals are usually alum-lime and disinfection is carried out by chlorination. In most cases, clarifier outlet water after filtration in rapid sand filters is supplied for process use. The sanitary water is essentially filtered and chlorinated before supply.

Demineralization (DM) Demineralized water is required particularly for boiler feed purposes. In case where the total dissolved solids (TDS) of the raw water is very high, demineralized (DM) water is used for the cooling tower make-up water. In one variation, DM water is used as the make-up water for the urea plant direct cooling tower (CT). This is because a small quantity of the circulating water is recycled in the process. DM plant consists of cation and anion exchange units followed by a mixed bed unit. Usually, cation exchange units are regenerated by sulphuric acid. A few industries use hydrochloric acid for regeneration. The anion exchange units are regenerated by sodium hydroxide. In some plants, where weak base anion exchangers are also installed, the regeneration is carried out by ammonium hydroxide. Generally, the mixed bed unit regeneration is effected by use of sulphuric acid and sodium hydroxide.

254

Waste Minimization

In some industries condensate polishing units are provided particularly for the removal of heavy metals present in the condensate. These units are provided with cation exchange units.

Steam and Power Generation The industry consumes considerable quantity of steam of different pressures. In general, in the older industries, power may be available from public utilities. In cases due to inadequate and irregular power supply, industries have installed power plants of their own for captive use. These captive power plants are integral parts of many facilities. The fuel for the steam generation plants and power plants varies widely depending mainly on availability. Coal, fuel oil, natural gas etc. are normally used. In some of the plant sections, e.g., steam reformation, waste heat is recovered and high pressure steam is generated. Steam and power generation plants use boiler feed water obtained from DM plant. Such requirements have been discussed earlier in this book.

Material Handling Material handling involves: 9 raw material unloading, storage and transfer to the processing plants 9 finished product bagging, storage, loading and supply to distribution ends

Effluent Treatment Effluent treatment plant is an important facility. The treatment system may consist of a number of control or removal units, for example: 9 9 9 9 9 9 9 9 9 9

air stripper, steam stripper biological treatment system cyanide removal chromate removal vanadium removal neutralization fluoride and phosphate removal oil and grease removal ion exchanger for treatment clarifiers and settlers etc.

Industry Profile--Fertilizers

255

The treated effluent disposal system also forms a part of the effluent treatment plant and may offer waste minimization and recovery potentials.

GENERATION OF IMPURITIES AND POLLUTANTS During the manufacture of fertilizers, various impurities and pollutants are generated and released in the liquid effluent, gaseous emissions and solid wastes. The origin of these are usually due to: 9 9 9 9 9 9 9 9 9

raw materials intermediate product product chemicals used in the process side reaction in process cooling water blowdown boiler blowdown demineralization plant regeneration raw water and effluent treatment system.

The sources from where the impurities find their way out of different plant sections and the types of the pollutants generated, are described plantwise in the examples. In the flow diagrams of the manufacturing processes, locations of the source points of the pollutants are indicated. Ammonia Plant

P a r t i a l oxidation process--In the partial oxidation process the carbon in the hydrocarbon feedstock is not completely combusted. Unbumt carbon as soot is generated. In most plants, inplant provisions are incorporated for recycle of as much as 80% of the carbon generated. The rest of the 20% of carbon produced must be disposed of. Further, cyanides are formed due to a side reaction during gasification. Both carbon and cyanide come out in the wash water. Inplant systems are usually provided for removal of the major quantity of cyanide in the stripper where the stripping is done by steam and acidic gases. However, a part of the stripper bottom effluent contains some residual cyanide and is subject to discharge if not further treated. In the case of fuel oil feedstock the effluent discharged contains suspended carbon, sulphide, formate, ammonia and metals like vanadium, nickel, iron etc. along with cyanide. Where the fuel oil feedstock contains

256

Waste Minimization

high sulphur (e.g., containing sulphur 3 to 4%), a sulphur recovery plant can be incorporated for recovery of sulphur. Where coal is used as feedstock, a considerable quantity of flyash is discharged in the wash water of the gasification section. This wash water also contains a small quantity of cyanide. Steam Reformation Process Process Condensate:In the steam reformation process excess steam greater than the stoichiometric requirement is supplied to the primary reformer. When the gas is cooled, excess steam condenses out and forms process condensate. The process condensate thus generated contains ammonia, methanol and some organics. In newer plants, built-in systems are provided for removal of the major quantity of ammonia by stripping. This makes the condensate fit for use as boiler feed water with or without polishing. However, when the contaminants in the condensate are high, the condensate is unfit for use as boiler feed water and is discharged as effluent after proper treatment. In the carbon dioxide recovery section, though the absorption towers are operated in dosed circuit, some absorbent chemicals find their way out in the cooler condensate, sludge formed in the process, and leakage and spillage from the system. The type of pollutant depends on the absorbent used. Oil bearing effluent originates from the pump and compressor sections. Emissions: Flue gas from heaters are discharged from the stack. Purge gas from ammonia synthesis section is burnt in the steam reformers of the ammonia plants. Urea Plant Vacuum Condensate: Urea solution formed remains associated with ammonium carbamate, ammonium carbonate, ammonia and carbon dioxide. After recovery of ammonia and carbon dioxide, this solution is concentrated in vacuum concentrators. During evaporation, vapors condense to form contaminated condensate. This condensate contains urea, ammonia and carbon dioxide. This is the main source of pollution from the urea plant. In the modem urea plants a built-in facility thermal urea hydrolyser stripper is provided whereby major quantity of contaminants such as urea and ammonia are removed from the condensate and recycled in the process. This system appreciably improves the quantity of the condensate.

Industry Profile--Fertilizers

257

Another effluent stream generates from the carbon dioxide compression section which mainly contains oil. The ammonia and carbamate solution plunger pump leakage also forms an effluent stream which contains ammonia, urea and oil. Emissions: The inert gases are discharged after recovery of ammonia by condensation. Urea Dust: Significant quantity of urea dust is discharged from the prilling tower. Generally, induced draft prilling towers generate higher quantities of dust than the natural draft towers. Therefore, the modem trend is towards installation of natural draft towers. Urea dust also originates from the urea, silo and bagging plant. Solid Waste: Solid urea spillage takes place in and around the prilling tower.

Ammonium Sulphate Liquid effluent: In the direct neutralization process, the main effluent is the condensate generated from the vacuum concentration section. This condensate mainly contain ammonia and ammonium sulphate. The other effluent may arise due to leakage, spillage, washings, etc. Ammonium sulphate manufactured by adopting the Merseberg process also produces ammonia and ammonium sulphate bearing condensate from the vacuum evaporation section. In addition to this, considerable quantity of the wastewater originates, containing ammonia, ammonium sulphate and suspended matter from the reaction and filtration section due to spillage and leakage, washing etc. of the equipment. Emissions: Emission of ammonium sulphate dust takes place f r o m the drying cooling, storage and bagging sections. Solid Wastes: In the Merseberg process, considerable quantity of chalk is produced as byproduct. This chalk contains small amount of ammonium sulphate, gypsum, silica etc. as impurities. Ammonium Chloride Liquid effluent: There are two main effluent streams in the production of ammonium chloride. One is ammonia bearing effluent from the vacuum pump seal water of the carbonation tower. The other is distillation tower bottom wastewater containing high quantity of calcium chloride with a small quantity of ammonia. Small quantities of wastewater are generated from the carbon dioxide compressor house, which contains oil. Since brine is used as a raw material for the production of

258

Waste Minimization

ammonium chloride, considerable quantity of sodium chloride wastewater is discharged from various sources due to spillage, leakage, washings etc. Emissions: The main source of emission is the exit air containing ammonia from the drying section.

Calcium Ammonium Nitrate (CAN) Liquid Effluent: Condensates containing ammonia and ammonium nitrate are generated during the neutralization and vacuum concentration of ammonium nitrate solution. Emissions: Ammonia emissions take place from the neutralization section. Dust emissions originate from lime stone grinding, granulation, drying, screening and cooling operations. Nitric acid Liquid Effluent: There is no significant generation of liquid effluent during the production of nitric acid. Small quantities of boiler blowdown water is discharged continuously/intermittently from the waste heat boilers. Small quantities of acidic wastewaters is generated during the spillage, leakage and washing of the plants. Emission: Tail gas mainly containing oxides of nitrogen (NOx) is released continuously from the absorption tower stack. Sulphuric Acid Liquid Effluent: The source of liquid effluents are waste heat boiler blowdown water and the acidic water containing sulphufic acid due to spillage, leakage and washing of the plant equipment. Emissions: The off gas from the absorption tower stack contains sulphur dioxide, sulphur trioxide (SO3) and acid mist and is continuously discharged. Phosphoric Acid Liquid Effluent: Fluorine compounds present in the rock phosphate are released during acidulation and filtration operations. These emissions contain mainly silicon-tetra-fluoride (SiF4) and hydrofluoric acid (HF). These emissions are usually scrubbed with water. The recycle scrubber water purge forms an effluent stream containing suspended solids, fluoride, phosphate etc. The other effluent stream is the hydrofluosilicic

Industry Profile--Fertilizers

259

acid containing condensate generated from the vacuum concentration section. The gypsum pond overflow forms another stream of effluent which contains suspended solids, fluoride and phosphate. Emissions: Considerable quantity of rock phosphate dust is emitted from the rock handling and grinding section. The emission from the fume scrubber contains mainly residual fluoride compounds and is released continuously. Solid Waste: Byproduct gypsum is produced during phosphoric acid production. Two methods are followed for conveyance of gypsum from the filtration section. One is as gypsum slurry in water and pumping to the gypsum pond, and the other is solid transportation of gypsum using a conveyor belt.

Single Super Phosphate (SSP) Liquid Effluent: Off gases from plant equipment are scrubbed with water and recycled. The purge of this recycled water forms an effluent stream containing suspended solids, fluoride, phosphate, etc. Emissions: Emission of dust takes place from the rock phosphate handling and grinding section. Fumes of fluoride compounds originate from the acidulation of the rock phosphate. During the curing of the product, considerable quantities of dust and fluoride compounds are released. Triple Super Phosphate (TSP)

Liquid Effluent: During the manufacture of TSP, fumes and dust originate from various plant sections. These are scrubbed using water. The purge water of the scrubber forms an effluent stream but, in most cased, this purge water is reused in the process. Emissions: Rock phosphate dust originates from rock handling and grinding operations. Where granulation is practiced, TSP dust originates from drying, sizing and cooling operations. Fumes originate from scrubber exit emissions. These emissions contain dust and fluoride compounds. Fumes of fluoride compounds also originate from the TSP curing section. Diammonium Phosphate (DAP) Liquid Effluent: The fumes and the dusts originate from different

260

Waste Minimization

unit operations. These are usually scrubbed with dilute phosphoric acid and the acid is reused in the process. As such, under normal operation of the plant, no liquid effluent is expected from this plant. Emissions: Fumes of ammonia and small quantity of fluoride compounds originate from the neutralization and granulation operation. These fumes are scrubbed with dilute phosphoric acid and the gases containing residual contaminants like dust, ammonia, fluoride etc. are discharged through a stack. Emission of dust takes place in the drying, screening and cooling sections, These dusts are also scrubbed with dilute phosphoric acid and let out through the stack.

Nitrophosphate Liquid Effluent: The main liquid effluent is from the scrubbers meant for emission control. The scrubber liquor purge forms an effluent stream which contains ammonia, nitrate, phosphate and suspended solids. The other effluent stream originates due to spillage, leakage etc. which also contains ammonia, nitrate, phosphate and suspended solids. Emissions: Rock phosphate dust originates from the grinding mill. Dust and oxides of nitrogen (NOx) originate from the reaction vessels. Fumes originate from calcium nitrate conversion, crystallization, filtration/centrifugation, neutralization and evaporation sections. Nitrophosphate dust comes out from prilling tower and product cooling section.

Ammonium Phosphate Sulphate (APS) Liquid Effluent: Under normal operation of the plant, no effluent is expected from this plant. However, leakage, washing of the plant equipment etc. may develop at times and form an effluent stream. Emissions: Emission of ammonia takes place from the neutralization section. Dusts originate from granulation, drying, screening and cooling operations. Urea Ammonium Phosphate (UAP) Liquid Effluent: No liquid effluent is expected under the normal operation of the plant. However, at times the leakage and washing of the plant equipment may generate and form an effluent stream. Emissions: Emission of ammonia takes place from reaction and granulation sections. Dust originates from granulator, drier, screen, and cooler.

Industry Profile--Fertilizers

261

NPK Complex Fertilizer Liquid Effluent: Under normal operation, no liquid effluent is generated in this plant. Emissions: Emission of fumes mainly containing ammonia takes place from neutralization and granulation operations. Fertilizer dust originates from drying, screening and cooling operations. Raw Material: Raw material handling, storage, transportation and preparation cause pollution and losses. Solid raw material causes dust emission in unloading, storage and grinding operations. On the other hand, the liquid raw materials, e.g., naphtha, fuel oil etc. are the source of oil pollution due to spillage and leakage while unloading, storage and supplying the process. Raw Water Treatment: During the clarification of raw water, sludges are formed which require disposal. Dust emission takes place from the lime handling and lime slurry preparation section ~ Demineralization of Water Liquid Effluent: Acidic wastewater originates during the regeneration of cation exchange unit. Alkaline wastewater originates during the regeneration of the anion exchange unit. Steam and Power Generation Liquid Effluent: Boiler blowdown water containing high total dissolved solid (TDS) and conditioning chemicals like hydrazine/sodium sulphite, sodium phosphate are discharged continuously or intermittently. Emissions: Flue gas from the boiler house is discharged through the stack. The contaminants depend on the type of fuel used. In the case of solid fuels such as coal, particulate matter, and sulphur dioxide, oxides of nitrogen etc. remain present in the flue gas. Liquid or gaseous fuel, on the other hand, does not discharge particulate matter. Solid Waste: In case coal is used as fuel, a considerable quantity of coal ash originates. The ash is usually discharged to ash ponds as ash slurry. Cooling Water Considerable quantities of cooling water are required in the production process of fertilizers. The cooling water system may be (a) once through type or (b) recirculation type. In a once through type, the entire

262

Waste Minimization

water after cooling service, is discharged to the source of intake water. The once through cooling system is adopted where an abundant quantity of water is available e.g. sea water. During the circulation of water, some contamination may be picked up by the water due to leakage or by direct cooling of the process material. A recirculation type cooling water system requires blowdown to maintain the concentration factor of the circulation water. Recirculating cooling water needs conditioning by addition of inhibitors and biocides. Consequently cooling water blowdown also contains inhibitors and biocides. In some plants, chromate-phosphate or chromate-phosphate-zinc, inhibitor system is adopted. The recirculating cooling water also picks up contaminants from the process due to occasional leakages in the coolers, or direct cooling of process material. The cooling water blowdown may contain pollutants like inhibitors, biocides and process materials.

Accidental Spills Accidental spills of process solution represent one of the most severe pollution hazards. Though many accidental discharges go unobserved and are small in volume, they need to be given special attention. However, it is almost impossible to prevent every potential accident due to spills from occurring. There are some measures that may be adopted to control such occurrences:

9 The usual source points are to be clearly identified 9 Allow only knowledgeable personnel to operate the valves which may cause spills. 9 Install indicator or warning systems for leaks and spills wherever possible. 9 Provide a diversion facility for all accidental spills to a holding tank for detention. 9 Establish a regular predictive and preventive maintenance program of all process equipment which may result leaks and spills.

POLLUTANT PARAMETERS.--EFFECTS In a fertilizer manufacturing facility, several pollutants are generated. These pollutants remain distributed in the wastewater, emission and solid wastes.

Industry Profile--Fertilizers Wastewater

Nitrogenous pollutants Ammoniacal Nitrogen Free ammonia Ammonium salts Oxidized Nitrogen Nitrite nitrogen Nitrate nitrogen Organic nitrogen Urea Arsenic Monocthonolaminc (MEA) Methanol Vanadium Cyanide Sulphide Fluoride Phosphate Oil and grease Chromate Total dissolved solid (TDS) Suspended solid (SS) Acid and Alkali Biochemical Oxygen Demand (BOD) Emissions

Oxides of sulphur (SOx) Sulphur dioxide (SOz) Sulphur trioxide (SOs) Hydrogen sulphide Oxides of nitrogen (NOx) Nitrogen dioxide (NOz) Nitric oxide (NO) Ammonia Fluoride compounds Hydrofluoric acid (HF) Silicon tetra-fluoride (SiF4) Hydrocyanic acid (HCN) Carbon monoxide (CO) Suspended particulate matter Acid mist

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Solid Wastes

-

Carbon Ash Chalk Gypsum Arsenic sludge Chromium sludge - Sludges from treatment of effluent and water The effects of discharge of these wastes to the environment can cause varied adverse conditions which mainly depend on the nature and the quantity of discharge of pollutants. The deleterious effects of some of the pollutants relevant to the fertilizer industry are indicated below. Wastewater A m m o n i a c a l Nitrogen: Nitrogenous pollutants may be present in the liquid effluent as ammoniacal nitrogen, oxidized nitrogen or organic nitrogen. Ammoniacal nitrogen may be present as free ammonia or ammonium salt. The relative distribution of which is dependant on the pH and temperature of the effluent water. For determination of the distribution of free ammonia and ammonium ion, curves are given in Figure 7-19. It can be seen from the curves that ammonia exists in its non-ionized state at high pH levels and is toxic in this state. As the pH of the effluent water is lowered, the content of ionized ammonia increases with a consequent decrease in non-ionized ammonia, and the toxicity of ammoniacal nitrogen gradually decreases. The ammonium salts are less toxic than free ammonia which exists in non-ionic form. Free ammonia is considered toxic to fish above the level of i .5 mg/s Ammonia in presence of dissolved oxygen is converted into nitrate by nitrifying bacteria present in the water system. This causes depletion of the dissolved oxygen in the water. Sometimes under depressed dissolved oxygen conditions a substantial quantity of nitrites may also remain in the water which may need further quantity of oxygen for transforming it to nitrate. Such condition is undesirable as the nitrites are also toxic. Ammonia and ammonium salts are nutrients to the plants and may contribute to explosive algal bloom. This may promote eutrophication in the receiving waters. Oxidized Nitrogen: Nitrites and nitrates are usually termed oxidized nitrogen. Nitrites are not usually present in the fertilizer factory effluent in considerable quantity. In most cases nitrites are oxidized to nitrates

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from with the dissolved oxygen present in the water. The presence of nitrates in water cause various harmful effects. Excess nitrates cause irritation to the mucous lining of the gastrointestinal tracts and the bladder. Such symptom may be observed by the drinking of one liter of water containing 500 rag//? nitrates. It is also considered that a nitrate level above 50 mg/~? may cause infant methemoglobinemia, a disease characterized by certain specific changes in blood and cyanosis. Organic Nitrogen: The source of organic nitrogen is urea. Urea as such is not considered as a pollutant. But urea may decompose into ammonia and carbon dioxide due to biochemical hydrolysis under certain conditions. Ammonia thus released may cause pollution as indicated earlier under ammoniacal nitrogen. Arsenic: Arsenic is a cumulative poison with long term chronic effects on both aquatic organisms and on mammalian species. It is moderately toxic to plants. Arsenic trioxide (As2Os) at the range of 1.96 to 40 mg//? was found to be hannfial to fish and other aquatic life. Severe human poisoning can result from a 100 mg concentration, and 130 mg may prove fatal. Arsenic can accumulate in the body faster than it is excreted and may build up to a toxic level from small amounts taken periodically through the lungs and intestinal walls from air, water and food. Although a very low concentration of arsenates may stimulate plant growth, the presence of excessive soluble arsenic in irrigation waters may reduce the yield of crops. The main effect appears in the destruction of chlorophyll in foliage. The arsenic limit in drinking water (ISI) is 0.05 mg/~? as As. Monoethonalamine (MEA): The amines exert biochemical oxygen demand (BOD) and consequently cause depletion of dissolved oxygen from the water. At higher concentration, MEA is toxic to fish and other living organism. Methanol: Methanol also exerts biochemical oxygen demand (BOD). It is toxic for human consumption. A small amount of methanol may lead to blindness and a dose of 10 ml. may cause death. Aquatic life has more tolerance to methanol. Vanadium: Vanadium compounds are toxic to man and lower animals. The reported lethal dose of vanadium pentoxide (VzOs) for man is 30 mg. Depending on the species of fish and the vanadium compound, the toxicity to fish varies between 4.8 and 55 mg/e. Cyanide: Cyanides and hydrocyanic acid (HCN) are poisons. These are highly toxic to most forms of life. It is reported that fish are killed on long exposure to waters containing 0.1 mg//? cyanide, and 0.3 mg//?

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concentration is sufficient to kill microorganisms. Cyanides and HCN gas when inhaled, combine in the tissues with the enzymes associated with oxidation. They thereby render the oxygen unavailable to the tissues and cause death. Acceptable daily intake of HCN has been established at 0.5 mg/kg, of body weight of man. The limit of cyanide in drinking water (ISI) is fixed at 0.05 mg/~? as CN. Sulphides: Sulphides are considered to be toxic substances. This is mainly because upon interaction with acidic material or acids, the sulphides liberate hydrogen sulphide (H2S) which is a highly toxic gas. Fluoride: Excessive fluoride in water causes mottled teeth and fluorosis. Studies conducted lead to the generalization that for children and adults, water containing less than 0.9 to 1.0 mg/~? and 3 to 4 mg/~? fluoride respectively is not likely to cause any deleterious effect on teeth. At the same time, it is also reported that maintaining 0.8 to 1.5 mg of fluoride ion in drinking water aids in reduction of dental decay, especially among children. Fluorides in high quantity are toxic to human. Doses of 250 to 450 mg. may cause severe symptoms which may even cause death. Chronic fluoride poisoning of livestock has been observed in areas where water contained 10 to 15 mg/~? fluoride. Data for fresh water indicate that fluorides are toxic to fish at concentration higher than 1.5 mg/~?. High concentration of fluoride may cause damage to citrus plants and some other agricultural products. The desirable limit of fluoride in drinking water s between 0.6 and 1.2 rag//? as F. Phosphate: Phosphates present in the fertilizer factory effluent are not considered injurious to health, fish life and plants. However, its presence in the receiving waters may promote the growth of algae when other nutrients are also available. This may result in eutrophication causing the water to be unsuitable for various uses. Oil and Grease: Oil and grease may cause depletion of dissolved oxygen in the water system. Floating oil reduces reaeration of the water surface and interferes in the photosynthetic activity of the aquatic plants. Oils and emulsions adhere to the gills of fish causing respiration difficulty. The deposition of oil sludge at the bottom sediments of may cause benthic growths, thus interrupting the aquatic food chain. Chromate: The chromium may be present in water as chromium salts and as chromates. The toxicity of chromium salts are comparatively less than the chromates. Chromates when inhaled in large doses may have corrosive effects on the intestinal tract and may cause inflammation of kidneys. The level of chromates that can be tolerated by man is considered to be very low. The maximum permissible chromate level in

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drinking water is 0.05 mg/g as Cr 6§ Total Dissolved Solids (TDS): High dissolved solids reduces palatability and therefore is not acceptable for human consumption. The water containing high dissolved solids is unsuitable for irrigation purposes. Suspended Solids (SS): Solids in suspension in water is aesthetically displeasing. Suspended solids when settling cover the bottom of the water body and destroy the bottom flora and fauna. Suspended solids increase the turbidity of water, reduce the light penetration in the water causing diminished photosynthetic activity for aquatic plants. Turbidity also interferes with the water clarification process. Biochemical Oxygen Demand (BOD): BOD is a measure of biodegradable organic pollution. It would cause depletion of the dissolved oxygen concentration in the water body. Inadequate dissolved oxygen in the water source contributes an unfavorable environment for fish and other aquatic life. The absence of dissolved oxygen also develops anaerobic conditions in the water sources, which may give rise to unpleasant odors and be unsuitable for domestic water supplies. Acid and Alkali: Acid lowers pH while alkali increases pH. The neutral pH is 7.0. Waters with pH below 6.0 is corrosive to water system, water distribution lines and household plumbing fixtures. This may also cause a sour taste. On the other hand, as the pH increases above 8.0, the effect of chlorine on bacterial pollution is weakened, and also free ammonia is liberated if ammonium salt is present. The extreme pH conditions or rapid change in pH may result in killing of aquatic life.

Emissions Oxides of Sulphur (SO~): Oxides of sulphur arc known to cause widespread injury to man and vegetation. Sulphur Dioxide (SO:): Sulphur dioxide causes irritation and inflammation of eyes. Concentration of 6 to 12 ppm causes immediate irritation to throat. It mainly affects the upper respiratory tract and the bronchi. 400 to 500 ppm is considered dangerous for life. Concentration of less than 1 ppm SO2 may cause injury to plant foliage. Sulphur Trioxide (SPa): It is highly irritant and very toxic, if inhaled. When it comes in contact with moisture, sulphuric acid is formed, which is corrosive and results in various hazards. Hydrogen Sulphide (HzS): Hydrogen sulphide has an offensive odor. The low concentration of H2S causes irritation to eyes. Higher concentration results in headache, dizziness, excitement, diarrhoea etc. It has a paralytic action on the nervous system. Exposure to 800-1,000 ppm of

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1-12S may be fatal. It has also a damaging effects on plants and crops. Oxides of Nitrogen (NO~): The oxides of nitrogen are mostly NO, NO 2 or N204. Both NO and NO 2 can produce smog by photochemical reaction in the atmosphere. When NO~ is inhaled it reacts with oxygen in the respiratory system forming nitric and nitrous acid. These acids are an irritant and cause conjection of throat and bronchi of lungs. The acids are neutralized by alkali present in tissues with the formation of nitrates and nitrites which may affect the health adversely. Because of its solubility in water, NO~ is little irritating to mucous membranes and upper respiratory tracts. This may result in unnoticed inhaling of more NO~ without taking precaution. Concentration of 100150 ppm is dangerous for short exposures of 30-60 minutes while 200700 ppm may be fatal. Continual exposure to low concentrations of NO~ may cause chronic irritation of the respiratory tract with cough, headache, loss of appetite, dyspepsia, corrosion of teeth etc. High concentration of NO~ causes defoliation in plants. Ammonia (NH3): Ammonia is irritating to eyes, mucous membrane and respiratory tract. It may cause conjunctivitis, swelling of eye lids, coughing, vomiting etc. It has a repelling odor. Higher concentrations of ammonia in air damages plants. Fluorine Compounds: Acute effects resulting from exposure to fluorine compounds are due to hydrofluoric acid (HF) which is highly irritating and very toxic when inhaled. It is corrosive and irritating to skin and mucous membranes. Concentration of 50-250 ppm is dangerous for health even for a short period. The fluorides may cause calcification of ligaments and mottling of teeth. Hydrofluoric acid and fluorides are responsible for plant damages. The injury of plants takes place by gradual accumulation especially on the leaves and fruits of the plants. Hydrocyanic Acid (HCN): Small concentrations of hydrocyanic acid if inhaled, causes headache, dizziness, feeling of suffocation, nausea, etc. Exposure to concentration of 100-200 ppm hydrocyanic acid for a period of 0-60 minutes may cause death. Carbon Monoxide (CO): Carbon monoxide inhalation at a low concentration causes headache, dizziness, shortness of breath, mental confusion etc. Exposure to 1000-2000 ppm is dangerous to health. Particulate Matter: Particulate matter is a hazard because they can be toxic themselves or they may be a carrier of toxic material as an adsorbent. Further it may cause physical interference in the cleaning mechanism provided in the respirator tracts. Particulate matter may cause a wide range of damage to the material and environment. In plants,

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photosynthetic activity is restricted by particulate matter deposits on the surface of the leaves. A d d Mist: Acid mist causes coughing and irritation of the mucous membranes of the eyes and upper respiratory tract. It causes damage to foliage by causing spots on the upper surface of leaves. Solid Waste Carbon: Carbon as such is not harmful. But carbon is usually discharged as slurry in association with small quantity of cyanide. Consequently toxicity due to cyanide may develop. When discharged to a water body, it may form a mat both on the surface and bottom of the water body which prevents photosynthetic activity and destroys the fish food. Ash" Coal ash generated from steam raising and power plants does not contain pollutants. But the ash originating from coal gasification process contains some cyanide which may turn to be toxic. Ash slurry when discharged to a water body covers the bottom and causes the fish food to be unavailable and may cause pollution due to heavy metals. Chalk (Calcium Carbonate): Chalk is a harmless compound. But chalk is usually discharged along with a small quantity of ammonia, ammonium sulphate, or ammonium nitrate which may cause problems when discharged to a water body. It also deposits on the bottom of water resources with attendant problems. Gypsum: Gypsum slurry invariably contains fluorine and phosphorous compounds which may result in toxicity, particularly due to the presence of fluorine in the water body or ground water depending on the mode of disposal. Arsenic Sludge: Arsenic sludge is highly toxic. C h r o m i u m Sludge: Chromium sludge may contain in addition to trivalent chromium compounds, some hexavalent chromium compounds. Sludges from Treatment of Effluent and Water- The sludge originating from the effluent and water treatment sections may be inorganic sludge or organic sludge. Organic sludge is harmful for discharging into a water body as it takes up dissolved oxygen from water by a degradation process. On the other hand, inorganic sludge may create problems due to deposition on the bottom of the water body.

A B A T E M E N T OF P O L L U T I O N The approaches that are generally followed in abatement of pollution are shown below:

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Waste Minimization 9 incorporation of in-plant pollution control system 9 end of process treatment for removal of pollutants from effluents 9 recovery, reuse and recycle in the process 9 house keeping

The in-plant pollution control measures are very significant particularly in the case of the fertilizer industry. This relates to elimination/reduction of volume and strength of effluent by incorporation of suitable pollution control systems in the plant itself. This limits the pollutants in the plant and stops/minimizes release to the outside of the plant. Some of the effluent treatment problems can be handle effectively where adequate in-plant measures are adopted and implemented. The main process for production of fertilizer cannot be changed for elimination and reducing pollution. But some modifications in the process or inclusion of some additional units are always possible to accommodate the reduction of wastes or pollution. Similarly, use of toxic chemicals in the plant should be avoided wherever possible. Some of the significant approaches which can be adopted as in-plant control measures, are indicated below.

Segregation of Process Effluent Segregation of process effluents and their routing is very important from the point of view of abatement of pollution. In many cases process effluents are combined together in the in-plant drainage system before leaving the plant. This practice causes hindrance in treatment of the effluent downstream. In some other cases, the process effluents are diluted using cooling water or other process water. This practice increases the volume of the process effluent rendering if difficult to treat in the effluent treatment plant. Process effluents having the same characteristics may be joined together wherever considered necessary. This may be done after thorough assessment of the situation. The factory sewage effluents are to be collected and routed separately. The storm water drains must remain separate and not mix with process or sanitary effluents.

Segregation of Cooling Water The cooling water circuit must remain separate, and the entire quantity of water is to be returned to the cooling tower basin in case of recirculating cooling systems, or be discharged separately in case of once-through cooling water systems. The in-plant system requires that

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no cooling water drainage takes place in the plant area.

Monitoring of Effluents In-plant suitable systems need to be provided for measurement of flow, and sampling is required for assessment of the quantity and composition of effluent streams.

Carbon Slurry The carbon slurry generated in the partial oxidation process is a nuisance and a hazardous substance. A good and dependable in-plant recycle system for carbon should be provided.

Cyanide Major quantities of cyanides originating with carbon slurry can be stripped out by an in-plant cyanide stripper using steam and acidic gases.

Process Condensate The process condensate is a source of ammoniacal effluent. A builtin facility can be installed for steam stripping of ammonia followed by polishing in the ion-exchange unit. The treated condensate can be used as boiler-feed water.

Arsenical Waste In the carbon dioxide recovery section various types of absorbent solutions can be used. In one of the absorption processes, arsenical solution and sludge find their way out of the various of operations and cause pollution problems due to arsenic. The problem of arsenic pollution can be prevented by use of some other suitable absorbent solution.

Purge Gas In-plant purge gas recovery units can be provided, and residual gases may be burnt as fuel in the reformer.

Vacuum Condensate After reactions, the urea solution remains in association with ammonia and carbon dioxide. This solution is concentrated under reduced pressure. The condensate generated during concentration contains

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significant quantities of urea, ammonia and carbon dioxide. An in-plant thermal urea hydrolyser stripper can be installed for recovery of ammonia, and also for ammonia present in urea. A modem urea hydrolyser stripper can deliver condensate of high purity which can be used as boiler feed water. The recovered ammonia pays back the investment within a few years. Figure 7-21 shows the flow diagram of a thermal urea hydrolyser with ammonia recovery.

Captive Storage T a n k During shut down or for maintenance sometimes it becomes necessary to drain the urea-ammonia solution of the reactor and the loop. Normally some tanks are provided for collection of urea-ammonia solution during draining. Serious problem arises when repeated tripping of the plants take place due to some or other reasons, necessitating draining of the urea-ammonia solution. To cope with such emergency situations additional in-plant captive tanks will provide some flexibility to the operational staff for control of pollution. Some extra capacity in the thermal hydrolyser stripper may also help in such situations.

Prilling Tower Dedusting System Earlier prilling towers may be installed with an induced draft system. Consequently the urea dust emission was appreciably high. The modem prilling towers use a natural draft system whereby the urea dust emission is reduced. For further lowering the urea dust content in the prilling tower exit air, wet systems can be incorporated. An illustration of the system is given in Figure 7-21. In this system the outgoing air stream containing urea dust is allowed to pass through a water spray chamber equipped with spray nozzles and filter type mist eliminator made of stainless steel. Water is sprayed from the top through a distribution system and collected at the bottom water sump. From the sump, urea laden water is recirculated to the header of the spray nozzles. When the urea solution attains 15-20% strength, it is taken to the urea solution tank for reuse in the process. The make-up water for the dedusting system may be the clean effluent of urea plant e.g. hydrolyzer stripper outlet effluent.

Urea Dust Scrubber During conveying, storing and bagging of product urea, considerable quantities of urea dust remain present in the environment of such operations. These urea dusts are extracted and scrubbed with water.

UREA AMMON IA EFFLUENT

STEAM

STRIPPER

-

UREA HYOROLYSER

STRIPPER

-

Figure 7-20: Thermal urea hydrolyser system with ammonia recovery.

*TREATED

EFFLUENT

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EXHAUST

FILTER PAD SPRAY NOZZLES

TT

UREA SOLUTION RECIRCULATING PUMP

PRILLING TOWERAIR

I0 RECOVERY TANK

HYGR6~.YSER 'OUTLET WA'rER AS ~ MAKE-Lk ~ WATER

Figure 7-21: Urea dedusting system in prilling tower.

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The scrubber liquor is recirculated. When the solution attains about 15% strength, the urea solution is taken to the urea solution tank for use in the process. The in-plant scrubber system keeps the working environment clean and simultaneously recovers urea.

Urea Solution Recycle Another in-plant process is available for reduction of pollution urea with a simultaneous increase in production. The urea solution collected in the urea solution is concentrated to a suitable limit by addition of the urea spillage in and around the prilling tower. This eliminates the disposal problem of spillage urea. In this tank, comparatively high concentration of urea solution which is drained during the emergency draining of the equipment, overflow of vessels, leakages etc., can be fed for recycle to the process. The urea solution thus collected in the urea solution tank is filtered, further concentrated by indirect steam heating if required and then reused in the process. The system is shown in Figure 7-22.

Ammonium Salt Plants Many suitable systems can be developed and incorporated as in-plant systems to recycle and reuse most of the waste waters of these plants. These systems need to be considered on a case to case basis after examining the specific plant operation.

Nitric Acid Plant Emission In-plant control systems are necessary for control of the discharge of oxides of nitrogen (NO,.). A few processes are available for NO~ control. In the extended absorption process the tail gas leaving the original absorption tower, is fed to the additional absorption tower where more contact time is provided. The extended absorption step is carried out by cooling the absorption reaction with cooling water. In another absorption process the NO~ is reduced by scrubbing with chilled water. Caustic soda solution can also be used for scrubbing purposes. This process yields sodium nitrite/sodium nitrate solution. The catalytic abatement system (Figure 7-23) employs a reaction between the tail gas and the fuel gas supplied from an external source. The fuel gases used are natural gas, methane, hydrogen, purge gas of ammonia plant etc. The catalyst contains palladium or platinum. The tail gas from the absorber are heated, mixed with fuel gas and passed over the catalyst bed. In the first reaction nitrogen dioxide (NOz) is converted into nitric oxide (NO) rapidly.

.1I FILTER WASH WATER

Figure 7-22: Spillage urea recycle system.

+I

I UREA CONCENTRATION ANK’

TO PROCES!

OFF GAS

x CATALYTIC REDUCTION UNIT

T A I I

7I

WATER WATER

f h C

r

COMPRESSOR COMPRESSOR

WASTE HEAT BOILER

~

u -

E

B

-- +

BOILER BLOW OOWN

Figure 7-23: Tail gas catalytic reduction system. N

4 4

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Waste Minimization

In the next reaction NO is converted into nitrogen gas. The latter reaction proceeds slowly. When this reaction is complete total abatement is achieved. The gas NO 2 is reddish brown and the gas NO is colorless. This sometimes misleads the visual observer regarding the status of the reaction. The performance of the system can only be evaluated after monitoring the emissions.

Sulphuric Acid Plant Emission Sulphuric acid production plants need an in-plant control system for reduction of emissions of oxides of sulphur (SO~). For the small capacity plants, the lime absorption process, sodium sulphite/bisulphite process, or ammonia absorption process may be adopted. In the fertilizer industries where ammonia and ammonium sulphate are produced, ammonia absorption process has the edge over the other processes. In this process sulphur dioxide (SO2) emission is absorbed in ammonia solution. The resultant solution containing ammonium sulphite/bisulphite is neutralized with sulphuric acid to form ammonium sulphate and SO2 gas. The recovered SO 2 can be bottled and sold or can be recycled in the sulphuric acid plant which will boost acid production. The ammonium sulphate solution can be fed to the evaporation section of the ammonium sulphate production plant. In the comparatively larger capacity sulphuric acid plants, the double conversion double absorption (DCDA) system can be effectively incorporated. This system has double advantages and reduces SO 2 emission with the simultaneous increase in acid production. In fact, there is a cost pay back within a few years. The feature which makes this process different from the single absorption process is the addition of a second absorption tower. The second tower is installed at a point intermediate between the first and the final SO2 to SO3 catalytic conversion steps. Utilization of this second absorption tower permits the achievement of greater SO 2 conversion to SO3 and this significantly reduces the quantity of SO 2 in the plant emission. The plants with a DCDA system can realize about 99% efficiency. Figure 7-24 illustrates the process flow of a typical sulphuric acid plant after incorporation of a DCDA system. In the DCDA system, an acid mist control system can be incorporated by use of electrostatic precipitators, glass fiber filters or Teflon packed gas cleaners.

Hydrofluosilicic Acid Recovery During the vacuum concentration of dilute phosphoric acid, the condensate obtained is almost pure hydrofluosilic acid.

FEE0 STREAM

WASTE HEAT BOILER

n

-FINAL HEAT EXCHANGER

MIST ELLMINATOR ,-ECOK)MISER

t+l

? l

I Figure 7-24: Process flow of typical sulphuric acid plant after incorporation of DCDA system.

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Waste Minimization

It is possible to attain a concentration of hydrofluosilicic acid of 15 to 20% by recycle of the condensate. Segregation of this wastewater helps in lowering the load of fluoride compounds in the effluent of the phosphoric acid plant. This segregated hydrofluosilicic acid solution may be used for fluoridation of drinking water and for recovery of fluoride chemicals.

Dedusting During the Rock Phosphate Grinding It is necessary to provide bag filters or a wet dedusting system in the rock phosphate handling grinding and conveying section for reduction of dust emissions. The scrubber water may have a provision for recycle after treatment.

Fume Scrubber The fluoride emission from the phosphoric acid plant needs to be controlled effectively for controlling fluoride. For this purpose, as inplant measure, double wet scrubbing system is necessary. These scrubbers may be operated in series. Provision needs to be provided for the recycle of the scrubber water after treatment. The efficiency of fluoride removal may be improved by use of a mildly alkaline medium in the scrubber.

Gypsum Conveying System The byproduct gypsum can be disposed of as solid material from the plant. For this purpose, if desired a gypsum conveyor belt can be provided as in-plant measure.

Scrubber Water Recycle The wet scrubbers of SSP and TSP plants can be built in such a way, that scrubber waters with or without treatment can be recycled.

Emission Control in DAP Plant Adequate in-plant measures need to be provided for all emissions by incorporating a dilute phosphoric acid scrubbing system. The resulting phosphoric acid along with the scrubbed material is used in the reactor as feed material.

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Nitrophosphate, Ammonium Phosphate Sulphate, Urea Ammonium Phosphate and NPK Complex Fertilizer Plants Effluent Control The in-plant control system for these plants involve reuse of the wastewater discharged from plant sections and emission control systems. Appropriate recycle arrangements can be attempted after examining the system.

Dust Emission and Oil Pollution During Raw Material Handling The raw material handling section requires particulate matter emission control systems, and oil interceptors. Suitable arresting systems for these pollutants are required to be provided as an in-plant control measure.

Raw Water Treatment Plant Sludge The in-plant control system for sludges from the raw water treatment plant (section 4.20) is a drying bed for sludges discharged from the clarifiers.

Demineralization Plant Effluents The in-plant control system involves a separate segregation and storage system for acidic and alkaline effluents. The idea is to reuse these acidic and alkaline solutions in effluent treatment systems wherever necessary.

Boiler House Flue Gas Wherever solid fuels are used, particulate matter needs to be controlled by use of electrostatic precipitators. The control of sulphur dioxide is made by raising the stack height as per the emission regulations. Oil Traps In the various plant sections oil is discharged from such sources as compressors, pumps, equipment etc. These oily waters need complete segregation and a suitable system for controlling the oil.

Cooling Tower Blowdown Water Built-in facilities in the plant need to be provided for cooling water blowdown and its conveyance to the appropriate location.

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Evaluation of Process Treatment of Effluent End of process treatment of effluent actually means the treatment of effluent when it leaves the operating plant boundary limit. Before deciding the type, pattern and degree of end of process treatment required, it is necessary to have information on the following aspects of the effluent: 9 nature of the effluent ascertained after evaluation 9 standard for the effluent to be conformed

Evaluation of Effluent The evaluation of the effluent of an industry is an important activity in the abatement of pollution. The evaluation covers: 9 identification of the source and location of discharge of effluent. 9 condition of effluent discharged e.g. temperature and pressure of the effluent pipe size and material frequency of discharge etc. 9 effluent flow rate e.g. maximum, minimum and average. 9 composition of effluent e.g. maximum, minimum and average content of pollutants with deviations due to malfunctioning of plant operation. 9 relevant production plant condition (start-up/shut down optimum production, low production, sustain run etc.) when the flow and characteristic are assessed. 9 assessment of the effluent by calculation based on the design figures of the plant and by actual monitoring of the effluents.

Assessment from Design Figures The process designer of the production plant provides detailed information regarding the source, flow and composition of effluents which are expected to be discharged from various sections. When the pollution aspect of a new proposed plant has to be assessed then one has to depend on the data supplied by the designer of the plant. In most of the plants, this information provides reasonable idea about the effluents, and the pollution abatement system can be designed based on the data provided by the designer. However, the experiences of operating plants using the same production process may also be considered while assessing the effluent, and designing a dependable effluent treatment plant.

Assessment from Actual Measurements In case of operating plants the assessment of the effluent is to be

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made by performing actual measurements. First, the identification of the actual source points of the effluent streams are made. This follows marking of the locations in the process flow sheet and in the layout drawing. Then the detailed information regarding the source point is collected and recorded. The flow is to be measured over a 24 hr period for several days under various plant operational conditions, and data for maximum, minimum, average flow rate and composition are established. Installation of flow meters with continuous recording arrangements is useful. In cases where the volume of effluent is less and the flow measuring device could not be installed, the effluent may be allowed to flow into a holding tank or pond and the volume recorded after a lapse of time. When recording the flow measurement, the sample of the effluent is collected. Sometimes composite samples are collected to obtain representative values. This involves collection of hourly samples proportionate to the flow of the effluent. Automatic proportionate samplers are available for this purpose. However, this may not be suitable for installation in some of the source points of the effluents. Wherever automatic proportionate sampling is not practicable, manual methods for approximating proportionate sample collection may be used. The collected composition sample is reduced in volume and taken to the laboratory for analysis. It is imperative that during the measurement of the flow and sampling of the effluent, the plant operating conditions are recorded. The analysis of effluents gives the compositionof the effluent under the average flow conditions of the effluent. Further, it may be necessary to draw grab samples at some regular intervals to establish the upper and lower limits of the pollutants in the effluent. All these figures, including the temperature, pressure, pipe size, frequency of discharge of the effluent are properly tabulated to understand the nature and condition of the effluent.

Experience of Other Operating Plants If possible, the data and other relevant information on the effluents of plants operating elsewhere adopting a similar process, the same feedstock, and finished products, are collected in order to compare and identify the deviations, if any. The experience of the existing operating plants provides dependable guidance in assessment of effluents.

Disposal of Effluent The fertilizer industry consumes huge quantities of water for processing. The water is usually supplied from a nearby fiver, lake etc., or

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Waste Minimization

drawn from groundwater reservoirs. An appreciable part of the intake water is converted into wastewater after use. The effluents generated, after treatment must meet the relevant specifications laid down by regulations depending on the receiving body of water. In some cases, the effluents after treatment are collected in lagoons and partly used for irrigation. As the fertilizer industries require large volume of a fresh water supply, most of the large fertilizer plants are usually located near a river for easy availability of a sufficient quantity of water. In such cases, the effluents also find their way to the same river from where the water supply was taken. Normally, the intake jackwell is located at the upstream of the effluent disposal point to avoid contamination by the effluents. It is very important to properly locate the effluent discharge point.

Study of the Receiving Water In view of the above, it is necessary to carry out a survey of the river water, particularly in respect to its quality and quantity when planning a new facility near a river for the discharge of effluents. Operating plants where effluents are disposed in the river also require a quality survey of the river water in order to determine the status of the river. Similar studies in the similar line are also required for the effluents discharged to other receptors. In this case, the regulations for protection of the environmen need to be considered. The condition of the receiving water source directs the degree of the reduction of the pollutants in the effluent.

Disposal to Lagoon for Irrigation Since the supply of irrigation water is not required throughout the year at the same rate, it is necessary to construct a large lagoon for holding treated effluent water particularly for rainy days when the agricultural fields may not require the same quantity of irrigation water. Further, if the treated effluent is desired to be used as irrigation water, it must meet the specifications of irrigation water. When a lagoon system is considered for the disposal of treated effluent, it is imperative to construct well organized and defined reservoirs. The problem of seepage with consequent ground water pollution prevention should also be taken into consideration for disposal in a lagoon and subsequent use as irrigation water. The standards of the effluent, receiving water and irrigation water imposed by the authorities play a deciding role regarding the degree of treatment of the effluent necessary at the end of the process.

CHAPTER 8 TREATMENT OF EFFLUENT FERTILIZER INDUSTRY EXAMPLE

Salient features of some of effluent treatment systems are discussed in the following sections for general guidance. A few processes which are still under research and development or in the pilot plant stage and have future prospects for commercial exploitation are also included for general information and adoption if considered workable. The methods of treatment are provided with schematic flow diagrams. The industry is free to choose from them according to their need and examine in-depth regarding their efficiency, practicability of adoption, and all other relevant aspects before deciding implementation. However, this may require updating with the inclusion of developments based on the availability of new treatment technology. This subject is treated separately in this chapter since it has wider applications for other process industries.

NITROGENOUS POLLUTANTS Nitrogenous compounds may be present in the fertilizer factory liquid effluent as: 9 ammoniacal nitrogen, e.g. ammonia, ammonium ammonium chloride, etc. 9 organic nitrogen, e.g. urea 9 oxidized nitrogen, e.g. nitrate and nitrite

sulphate,

The total Kjeldahl Nitrogen (TKN) value provides the combine values of ammoniacal nitrogen and organic nitrogen, but not oxidized nitrogen. In ammonium nitrate both ammoniacal nitrogen and oxidized nitrogen are 285

286

Waste Minimization

present, whereas in urea ammonium phosphate, the nitrogen is present both as organic nitrogen and ammoniacal nitrogen. The forms of nitrogen indicated above may be present individually or in mixture of two or three in the effluent.

AMMONIACAL NITROGEN The main pollutant in the nitrogenous fertilizer manufacture is ammoniacal nitrogen. Therefore, the treatment of effluent for removal/ recovery/recycle of ammoniacal nitrogen is essential in almost all nitrogenous and complex fertilizer plants. Many processes have been studied for exploring the treatment of wastewaters containing ammoniacal nitrogen. Of these, a few processes are of commercial importance and may be adopted for treatment. In some of these, full or part of the ammoniacal nitrogen can be recovered and utilized, whereas in the other processes, the ammoniacal nitrogen present in the effluent is removed or destroyed. The available processes of practical importance can be broadly divided into two main categories: Physico-chemical processes which involves stripping of ammonia of effluent by air or steam and ion exchange process. Biological processes which includes nitrification followed by denitrification of ammonia and algal uptake of ammoniacal nitrogen. Some other methods of treatment which have less practical importance are: 9 9 9 9

chlorination electrodialysis reverse osmosis distillation etc.

Processes having practical applications are given below. Air Stripping of Ammonia The stripping of dissolved ammoniacal nitrogen present in liquid effluent by use of air is a recent process and adopted in a few fertilizer plants.

Treatment of Effluent Fertilizer Industry Example

287

Ammonium ion (NH4 +) ill water exists in equilibrium with ammonia (NH3) and hydrogen ion (H+): NI-I-I-4+ vt N H 3 + I-I+

The above equation shows that ammoniacal nitrogen may remain present in effluent as NH4§ ion, or as NH 3, or as the combination of NH4+ ion or NH 3, depending on the pH of the effluent water. When the pH is lower than 7.0 the concentration of ammonium ion progressively increases which means that ammoniacal nitrogen is mainly present as ammonium salt, e.g., ammonium sulphate, ammonium nitrate etc. On the other hand, when the pH of the effluent is increased, the above equilibrium shifts towards the right and consequently the concentration of ammonia (NH3) progressively increases. The Figure 8-1 illustrates the distribution of ammonium ion (NH4) and ammonia (NH3) under different pH and temperature conditions. The air stripping process for reduction of ammoniacal nitrogen takes advantage of dissolved ammonia (NH3) in the effluent at a high pH condition for stripping by use of air. It may be observed from Figure 8-1, at pH 10.0 and 20~ temperature of the effluent, about 80% of the ammoniacal nitrogen of the effluent is in the form of ammonia (NH3), while at pH 11.0 and 20~ of water above 90% of total ammoniacal nitrogen is in the state of ammonia (NH3). In an actual process, the effluent containing ammoniacal nitrogen is collected in a tank and the pH of the effluent is raised above 10.5 by addition of alkali. The selection of the type of alkali is important. When lime is used for raising pH, a calcium carbonate (CaCO3) sludge is formed which requires a clarification unit and also sludge disposal system. The problem of clarification and sludge disposal may be eliminated by use of caustic soda (NaOH) for raising pH of the effluent. It may also be possible to raise the pH of the effluent by use of D.M. plant alkaline wastewater. After raising the pH of the effluent, it is pumped to the top of cooling tower type packed tower and distributed to cover the full surface of the packings. The effluent moves down the tower against the flow of air. The ammonia stripping towers usually adopt induced draft with a cross flow air circulation system. However, counter flow air circulation with forced draft system may also be followed. During the fail, the water strikes the packings and droplets are formed due to splashing on the fills. The process continues with continuous fall throughout the height of the fill, and the air flow drives out the dissolved ammonia (NH3) from the effluent thereby lowering the ammonia content of the effluent. The efficiency of ammonia removal depends on factors

288

Waste Minimization

such as pH, temperature, concentration of ammonia, contact time, effluent/air ratio etc. The significant operational sequences are: 9 9 9

raising the pH of the wastewater formation and reformation of droplet in the stripping tower providing air water contact and droplet agitation by circulation of large quantities of air through the tower.

,//,,

100

/ 0------

,o..

ff

4O

'1

t~ "1" Z 40

~

6

0

,'*-

+.1" :3::: Z

c: G,I

.,-, u

2

G,p (3.

I00 6

8

10

~2

pH Figure 8-1: Distribution of NH 3 and NH4§ ion on different pH and temperature.

Treatment of Effluent Fertilizer Industry Example

289

For attaining higher efficiency, the effluent of the tower may be recirculated or two stripping towers may be operated in series. Ammonia removal efficiency can also be increased by raising the temperature of the influent to the tower. If satisfactory design and operational parameters are maintained in air stripper system around 90% of the ammoniacal nitrogen can be removed. In Figure 8-1 and Figure 8-2 cross flow and counter flow types of stripping tower respectively are illustrated. The treatment scheme using lime/caustic soda is shown in Figure 8-3. With air stripping of ammonia it is not advantageous to recover ammonia from the effluent, but the process is suitable for removal of ammonia at any concentration level. The capital and operational cost is also low. The main disadvantage of this process is that the ammonia in the wastewater is transferred to the surrounding atmosphere. But due to the use of a high volume of air in stripping, the concentration of ammonia in the ambient air usually remains low depending on the quantity of ammonia removed. When lime is used for raising pH, sometimes scaling problem due to precipitation of calcium carbonate occurs. This requires periodical cleaning of the tower and the associated equipment. AfR OUTLET

/

FAN

i

AMMONIACAL EFFLUENT

, i " "/'/

' ;t

i /

-7 ,j

FILL

AIR INLE T

ORIF T ELIMINATOR

////

I--

Figure 8-2: Air stripper---cross flow type.

r

T R EARED EFFLUENT

290

Waste Minimization AIR

O U T L E T

FAN--

C; AMMONIACAL

( - - - - - - - 0RIFT ELIMINATOR

~-~__

EFFLUENT

~ ~ ' r ' - - - - r - - - - i : z

_

( - - - - FILL

.

,

f / ff~--.

~L

-

AIR INLET

/ / f

! COLLECIION 8ASIN-'-~

-

L 'If----

~-~'- TR EAr E 0 E F F L U EN T

Figure 8-3: Air stripper---counter current type. Steam Stripping The steam stripping of ammonia for its removal and recovery is a well established process and has been practiced in most of the byproduct cokeovens for recovery of ammonia for a long time. The principle of the process is that ammonia present as ammonium hydroxide, carbonate, bicarbonate etc. dissociates into ammonia at high temperature. When the ammonia is present in the effluent as sulphate, chloride etc., it is necessary to raise the pH of the effluent by addition of alkali, e.g., lime or caustic soda, to obtain dissociation of ammonium ion for efficient stripping of ammonia by steam. In an actual process, the pH of the effluent is raised wherever necessary, then pumped at the top of the stripping tower. The effluent obtains primary heating from the exchange of heat from the outgoing condensate from the stripper bottom. The low pressure steam enters the tower from the bottom. The tower is usually packed with ceramic rings. The ammonia vapor coming out of the stripper is diluted with air through a venturi arrangement when recovery

Treatment of Effluent Fertilizer Industry Example

291

of ammonia is not practiced. With recovery of ammonia, it is directly converted into ammonium salt by passing through a saturator containing acid, or condensed to produce ammoniacal liquor. Where there is an ammonium sulphate production plant, the weak ammonium sulphate solution obtained from the saturator is fed to the evaporators. Also, a continuous weak ammonia solution may be recycled in the process or used in other plant sections where available. Where lime is used for raising pH of the effluent, an additional clarification unit is necessary. Therefore, it is preferable to use caustic soda (NaOH) to raise pH. The concentration of ammonia in the condensate can be increased by incorporation of a rectification column. In general, steam stripping is suitable for a low volume of effluent containing high concentration of ammoniacal nitrogen. Where the bottom liquor is proposed to be recycled in the process or as boiler feed water, raising of pH using alkali should be avoided. Under proper operating conditions, it is possible to remove 95 to 9 9 % o f ammonia from the effluent by a steam stripping process. Schematic flow diagram of ammonia removal/recovery system using steam stripping process is shown in Figure 8-5. Another schematic diagram of steam/air stripping system with recovery and removal of ammonia is illustrated in Figure 8-6.

Ion Exchange Process Ion exchange can be utilized for the treatment of ammoniacal effluents, but the effluent should not contain any undesirable contaminants that can cause fouling of the exchange material, and contaminate the recovered ammonium salt solution making it unsuitable for use. This process may be adopted for: 9 recovery of ammonia with disposal of the effluent after neutralization. 9 recovery of both ammonia and water suitable for use as boiler feed water.

Recovery of Ammonia with Disposal of Water The effluent water containing ammoniacal nitrogen is first treated for removal of contaminants such as oils, organics, free chlorine, suspended solids etc., if present. Next the effluent is taken to a cation exchange unit. The cation exchange resins take up the ammoniacal nitrogen from the effluent and the water is released from the bottom of the unit. On exhaustion the unit is regenerated using sulphuric/nitric acid.

0

LIME

- xL , I

I

*

TREATEC EFFLUENT

AIR STRIPPER

CL A RI F I E R

L

;I

.

.

+

SLUDGE

"r ,*T-yy

SATURATOR

CONOENSEA

AMMONIACAL

EFFLUENT 1

@

SULPHATE

AMMONIA

RECOVERY

HEAT EXCHANGER

1

CAUSTIC SOOA

Figure 8-5: Ammonia removaVrecovery by stream stripper.

TREATED

EF'FLUEN

VCNT

,

.

SATURATOR

AMMONIUM

& AMMONIA

CONDENSER

RECOVERY

q

AMMONIACAL CONOEHSATE

ST IPPER

-ED

LIME OTHER AMMONIACAL EFFLUENT

SULP HATE

, ,

12

MIXING TANK

v CLARIFIER

Figure 8-6: Steam-air stripper system for removalhecovery of ammonia.

-

EFFLUENT

Treatment of Effluent Fertilizer Industry Example

295

During regeneration ammonium salt solution is produced. The regeneration technique is designed for minimum regenerant use to obtain maximum concentration of ammonium salt in the product solution. The fractionated elution technique is generally employed to obtain the fraction which is highest in ammonium salt content and lowest in free acidity. This portion of the salt is taken out for further use in the plants where ammonium sulphate/ammonium nitrate salts are produced. The fraction which contains low ammonium salt and high acid is further augmented with acid solution and used for regeneration in the next cycle. The exit effluent after removal of ammoniacal nitrogen is taken to the neutralization pit and disposed of after neutralization. The process may be represented as below: 9 During effluent pass through the cation exchange column

NH4N031

+ RH

.

.> RNH~

(NH4)2 SO4

I HN03 H2S04

9 During regeneration of the cation exchange column RNH4 +

HNO31

.,.> RH +

H2S04

Note: R stands for resin

I NH4NO3 (NH4)2S04

Ammonium salt product solution

The above process is illustrated in Figure 8-7.

Recovery of Ammonia and Water When recovery of water is envisaged in addition to the recovery of ammonia, an anion exchange unit is incorporated after the cation exchanger unit. In this process, ammonium salt contaminated water after pretreatment first flows through a bed of strongly acidic cation exchange resin operating in the hydrogen form. The ammonium ion combines with the cation resin while the hydrogen ion combines with the nitrate/sulphate radical to form nitric/sulphuric acid. The acidic water discharged from the cation exchange unit then enters the anion exchange unit containing anion exchange resin in the base from where the acidic ions are absorbed. The effluent water from the anion exchange unit is very low in ammonium salt content and other constituents and may be reused in the process as make up water in the boiler feed water treatment plant at a suitable point or may be used in the boilers after polishing in the polishing units.

V AMMONIACAL EFFLUEKI

FILTER

CATION EXCHANGER

1

\

F

AMMONIUM

MUTRALl 5 A TI ON I

SETTLING

SALT

TREATED

SLUTDGE Figure 8-7: Recovery of ammonia as ammonium salt solution by ion exchange process.

SOLUTION

E F F L U E NT

Treatment of Effluent Fertilizer Industry Example

297

The anion exchange resins are regenerated with ammonium hydroxide to form ammonium sulphate or ammonium nitrate solution. In this case also the fraction of elution containing higher concentration of salt solution is separated out and the fraction containing very low concentration of salt is further fortified with ammonium hydroxide for regeneration of anion exchange resin in the next cycle of regeneration The first stage equations in the cation exchange unit were already indicated earlier, the second stage may be represented as follows: During effluent pass through the anion exchange resin after the cation exchange column ROH

>

+ H20

H2SO4

H2SO4

9 During regeneration of the anion exchange column with ammonium hydroxide RNO3 NH4NO3

]

+ NH4OH

......

>

ROH

H2SO4J

+

[

(NH4)2SO4

Ammonium salt product solution The solution of ammonium sulphate or ammonium nitrate from the regeneration of both the cation and anion exchange columns is combined and sent to the salt plant for evaporation and production of ammonium sulphate or ammonium nitrate fertilizer material along with the existing facilities of the plant. It may be noted that the soluble contaminants in the waste water will also find their way into the product fertilizer thus produced. The process is illustrated in Figure 8-8. This process is applicable for any concentration of ammonia or ammonium salt in the effluent. Strength of the salt solution can be made between 15 and 20%. The acid consumption is slightly higher than the stoichiometric requirement.

Biological Nitrification and Denitrification The biological nitrification and denitrification process can reduce ammoniacal nitrogen content of the effluent to a very low limit. The process basically consists of oxidizing all the ammoniacal nitrogen to nitrate nitrogen (nitrification) and subsequent reduction of nitrate nitrogen into nitrogen gas (denitrification) which is released to the atmosphere.

AMMONIA

ACIC

AMMWACA~ EFFLUENT

*

FILTER

-

V

CATION EXCHANGER

-

I

OEGASSER

I __*I

Y ANION EXCHANGER

BOILER FEED WATER

1

t

V

Y

Figure 8-8: Recovery of ammonia as ammonium salt solution with recovery of water.

\

AMMONIUM SkLl SOLUTION

.

Treatment of Effluent Fertilizer Industry Example

299

The process may be illustrated as: Organic carbon

Ammoniacal N it roge n

Aeration .......... > N it rifying Organism

Nitrate N it r o g e n

Denitrification ................... > Den it rifyi n g organism

N2 + C O 2

Biological Nitrification This is an aerobic process in which a specialized group of chemoautotrophic bacteria such as nitrosomonas, nitrosospira, nitroeystis, nitrosogloes convert ammoniacal nitrogen into nitrite nitrogen and finally to the nitrate nitrogen form. These nitrifying organisms can use carbon dioxide from air as their source of carbon for synthesizing their cell material and obtain energy for the process by oxidizing ammoniacal nitrogen. The biological nitrification may be represented as follows: First Step: Second Step:

NH4§ + 1.502 --* N O r + 2H § + H20

(1)

NO2- + 0.5 02 ---, NO 3-

(2)

Overall Reaction: NI-14§ + 202 ~ N O 3- + 2H § + H20

(3)

Equation (3) shows that for oxidizing one part of ammoniacal nitrogen, about 4.5 parts of oxygen is required. This requirement of oxygen must be supplied in the aeration tank for proper nitrification. The efficiency of nitrate conversion depends on many factors. The optimum pH for nitrification is 7.0 to 8.5, optimum temperature is 20~176 dissolved oxygen level in nitrification tank is 2.0 mg/s or higher and the detention time may vary between 3 and 10 hrs. or more depending on the other variables including the bacterial population. The nitrification process is associated with the destruction of alkalinity. One part of ammoniacal nitrogen destroys about 7.2 parts of alkalinity. Therefore when nitrification proceeds, the pH of the effluent in the nitrification tank falls. In order to maintain the pH at the optimum level it is a common practice to supplement additional alkalinity. Similar supplementation may be required for other bacterial nutrients like phosphate, potassium, iron etc. if these are not originally adequately present in the waste water. The nitrification step may be carried out in tank, pond, lagoon, trickling filter etc.

300

Waste Minimization

Biological Denitrification Biological denitrification is an anaerobic process wherein the nitrite and the nitrate ions fulfil the role normally played by oxygen in aerobic respiration. In this process, nitrite and nitrate ions are reduced to nitrogen gas. The ability to bring about denitrification is characteristic of a wide variety of common facultative bacteria including the general pseudomenas, achromobacltor and bacillas. As these organisms can only utilize organic carbon as their carbon source, a supplemental nonnitrogenous readily oxidizable soluble organic compound must be added to the nitrified effluent prior to its entry into the denitrification system. The organic carbon source is usually sewage effluent, organic waste or methanol. The denitrifying organisms cause the nitrates and organic carbon to be broken down into nitrogen and carbon dioxide gas. The requirement for organic carbon may be assessed from the following denitrification reactions using methanol as organic carbon source: First Step: 6NO 3- + 2CH3OH ~ 2CO 2 + 4H20 + 6NO 2-

(4)

6NO 2- + 6H § + 3CHaOH ~ 3CO 2 + 3N 2 + 9H20

(5)

Second Step:

Overall Reaction" 6NO 3- + 6H § + 5CH3OH ---, 5CO 2 + 3N 2 + 151-120

(6)

Thus, 1.9 part of methanol is theoretically required for denitrification of one part of nitrate nitrogen. However, the actual requirement of methanol is much higher than the theoretical value. This is because dissolved oxygen present in the nitrification reaction also reacts with methanol and further some excess of methanol is required to be maintained for effective and continuous denitrification. The basic requirements for denitrification step may be summarized as under: 9 9 9 9 9

dissolved oxygen concentration less than 0.5 mg/g in the denitrification tank. preferable pH range 6.5 to 7.5 temperature range 30 ~ to 35~ addition of biodegradable organic carbon at a proper amount in the denitrification tank detention time varies widely, depending on the other variables, including the bacterial population in the denitrification tank.

Treatment of Effluent Fertilizer Industry Example

301

Biological Nitrification and Denitrification Since the conditions necessary for nitrification and denitrification are different, these two processes are to be separated into two distinct systems. In a continuous nitrification-denitrification system, the ammoniacal nitrogen containing waste water flows first to the nitrification system provided with surface aerators and a sludge recirculation system. The settled water from the nitrification unit flows to the denitrification system where an appropriate quantity of organic carbon is added. This unit is also provided with a separate sludge recirculation system. The settled water of the denitrification unit is aerated, clarified and disposed of. For the initial start up of the plant the organisms responsible for both nitrification and denitrification arc cultured separatc!y in different culture tanks and supplied to units for development of the microorganisms. It is important to note that since the nitrification/denitrification process depends on living organisms, it is necessary to see that the influcnt to the plant does not fluctuate widely in composition, and also toxic chemicals which may harm the growth of the microorganism are not allowed to enter the system. When properly designed and operated, this system may remove 95 to 99% of ammoniacal nitrogen. In Figure 8-9 a schematic flow diagram showing biological nitrification followed by denitrification is given. In the above figure, nitrate removal in a biological denitrification unit is also shown. In general, the fertilizer factory effluents do not contain sufficient BOD for the dcnitrification process. The factory sewage effluent also does not contain appreciable quantity of BOD. Therefore, in case denitrification is desired by adopting the above process, some organic material, e.g., methanol, molasses, township sewage effluent containing high BOD which can provide the required amount of BOD for denitrffication needs to be imported to the factory area. This limitation makes the process unacceptable and unsuitable for application in the fertilizer industry. Moreover, it may be noted here that nitrite and nitrate nitrogen is more harmful than ammoniacal nitrogen. This aspect infers that adoption of biological nitrification process without incorporating complete denitrification system is undesirable and should be avoided. However, in cases where both nitrification followed by complete denitrification can be adopted, this process may be followed.

V

AMWNIACAL EFFLUENT

.b

u

i

NITRIFICAT~ON

3

NITRATE EFFLUENT

7ORGANIC

.

-

CARBON (SEWAGE/

M E THANGL)

-COffiUtANT/POLYEL€ClROLY

1E

>

OkiNITRIFICATION

\I

V

v

~

AERATOR CLARIFIER

A TR E A T E D E FFLIJENT

Figure 8-9: Biological nitrification and denitrification.

Treatment of Effluent Fertilizer Industry Example

303

Algal Uptake Algae while growing in the ponds take up nutrients from waste water for their cell synthesis. The major nutrient extracted by algae for synthesis of cell mass is ammoniacal nitrogen. The growth of algae and cell division mainly depend on the photosynthetic activity and also the availability of the nutrients. Therefore, this carbon requirement of algae must be supplied by carbon dioxide. The source of carbon dioxide may be obtained by diffusion of dilute carbon dioxide gas into the culture media or using some biogradable organic matter e.g. sewage effluent. For optimum growth of algae, the culture pond should be exposed to sunlight so that light penetrates without obstruction into the algae culture pond for optimum photosynthesis. The process is similar to the oxidation pond system with the exception that the growth rate of algae is higher with consequent high removal of ammoniacal nitrogen from the culture media, i.e., effluent. In actual process, oxidation pond-like shallow ponds are used for the treatment of the effluent. In most cases, this treatment is adopted as a secondary or tertiary treatment. Usually a collection and equalization pond is used at the front end of the shallow algae culture pond. The water flows to the pond having a suitable detention time for removal of ammoniacal nitrogen by algae. Under suitable conditions of depth of the pond, concentration of algae and ammoniacal nitrogen in the pond, good sunlight, adequate carbon dioxide supply etc. the uptake of ammoniacal nitrogen is quite appreciable. The algae thus produced is harvested and used as cattle feed or organic manure. Oxidized nitrogen and urea nitrogen bearing effluents may also be treated adopting this process. It is also possible to develop a fish pond at the rear end of the algae culture pond where the algal mass can be used as fish food. Figure 8-10 illustrates the removal system of ammoniacal/urea/nitrate nitrogen by algae culture.

ORGANIC NITROGEN The source of organic nitrogen in the fertilizer factory effluent is urea. The physico-chemical process for removal of urea by thermal urea hydrolysis is explained earlier along with the in-plant measures. In the end of process treatment, urea can be removed by the biological hydrolysis process. The effluent-containing urea nitrogen is subjected to bio-hydrolysis in presence of enzyme urease secreted by bacteria usually found in soft, compost, sewage, etc.

w

B

SUNLIGHT

NUTRIENT

AMMONIACAL / UREAINITRATE

CARBON OIOXIOE/ORGANIC CARBON(SEWAGE)

AL.GAE

CULTURE

-ALGA

TREATED EFFLUENT

POND

E

Figure 8-10: Removal system of ammoniacal/urea/nitrate nitrogen by algae culture.

Treatment of Effluent Fertilizer Industry Example

305

The dilute urea solution is hydrolysed by the above bacteria in presence of biodegradable organic carbon into ammonia and carbon dioxide: N H 2 C O N H 2 + 2H20 --~ ( N H 4 ) 2 C O 3 ~

2 N H 3 + CO 2 H 2 0

The process can be carried out under both aerobic and anaerobic conditions. As the hydrolysis continues, the pH of the effluent increases and the effluent is taken to the air stripper for air stripping. After stripping of ammonia the effluent is recycled to the hydrolysis tank. A part of the effluent is continuously discharged from the air stripper. The residual ammonia may be treated in another air stripper in series or may be treated for nitrification followed by denitrification if the situation permits. The system of urea hydrolysis is illustrated in Figure 8-11.

OXIDIZED NITROGEN In the fertilizer factory effluent insignificant quantities of nitrite nitrogen remain. As such, no treatment for removal of nitrite is normally required. However, nitrate nitrogen released in the effluent requires control. The control system should be at the source of origination of nitrate bearing effluent as mentioned earlier in in-plant measures. The methods for removal of nitrate nitrogen from the effluent are limited and can be treated by adoption of 9 ion exchange process 9 biological denitrification process The details of these processes were discussed earlier. The best approach for the control of nitrate nitrogen is to adopt a manufacturing process which does not release nitrate nitrogen requiring treatment at the end of the process. The other approach is to segregate and reuse the nitrate bearing effluent in the other production plants if possible. O T H E R CONSTITUENTS

Arsenic, Monoethanolamine (MEA), Methanol and Vanadium Depending on the type of the carbon dioxide absorption process adopted, arsenic, MEA, methanol or vanadium arise in the effluent.

AMMONIA

t

SEWAGE

Y UREA EFFLUENT

'

UREA HYDROLYSIS

AIR STRIPPER

c

, SLUOGE RECIRCULATION

/

RECYCLE

I t

EFFLUENT

Figure 8-11: Biological urea hydrolysis system.

Treatment of Effluent Fertilizer Industry Example

307

Arsenic Where the Vetrocoke process is used, the major constituent of the absorption solution is arsenic. Normally, adequate arrangements are provided in the plant so that arsenic does not find its way out in the effluent. But in actual operation, due to leakage in the pumps, flanges, joints, filter wash etc., and also from spillages some arsenical solution originates and is discharged. This arsenic solution is collected, filtered, concentrated and again filtered through active carbon filters and recycled in the process. In case the quality of the arsenic solution is not suitable for recycle, the collected solution is evaporated to dryness by indirect steam heating and the solids are packed in concrete drums, sealed properly and buried underground or disposed into deep sea far away from the coastline. The sludges and the deposits of the filters are also disposed of in the similar manner stated above. The schematic flow of arsenical solution recycle and disposal system is illustrated in Figure 8-12. Monoethanolamine (MEA) and Methanol Normally the quantity of MEA or methanol which is left in the effluent is quite low and does not pose a pollution problem. These constituents can exert some small variation in the BOD of the final effluent. Wherever a denitrification process is adopted, this waste may be utilized for supply of organic carbon. Under normal operating conditions of the plants, usually no specific treatment is necessary for MEA and methanol. Vanadium The quantity of vanadium discharged from the carbon dioxide absorption system is quite low and as such no specific treatment is usually required. However, the quantity of vanadium discharged in the grey water from the Texaco gasification process using fuel oil as feedstock, is usually high. This effluent requires removal of vanadium. Vanadium, in such cases, can be removed by precipitation with ferrous sulphate: V205 + FeSO 4 + H20 ~ Fe (VO3)2 4" H2SO4

In the above reaction one part of vanadium requires about 2.75 parts of ferrous sulphate (FeSO4.7HzO). However, the actual requirement of ferrous sulphate is much higher.

308

Waste Minimization

TO

PROCESS PARAOET ~

I COLt ARSENICAL WATER ECTIOtlSUMi

l

9 LSOLUTION RECOVERYIANK

t-

RECYCLE

RIECYCI.E

f\

~

-,

ARSENICAL SOL'~O W A S T E

Figure 8-12: Arsenical solution recycle and disposal system. The treatment process involves addition of ferrous sulphate with pH adjustment around 8.0 by adding acid/alkali. A detention time of about 0.5 hour is provided for reaction. The vanadium removal efficiency is around 98%. The flow scheme of the system is shown in Figure 8-13.

I

ACIWALKILI

1

I

R E A C T I O N TANK

J

3 3.

i B L

CLARIFIER

TREATEO E F F L U E N T

k'

E

SLUDGE

Figure 8-13: Vanadium removal system. w

310

Waste Minimization

Cyanide As earlier stated cyanides originate from the feedstock gasification process. The cyanide bearing effluents are treated by the alkaline chlorination method. In this process, cyanides are ultimately converted into carbon dioxide and nitrogen gas. Cyanides initially form cyanogen chloride when treated with chlorine: NaCN + CI2 ~ CNCI + NaCI One part of cyanide requires 2.73 parts chlorine in the above reaction. In presence of caustic soda, sodium cyanate is formed from cyanogen chloride: CNC1 + 2NaOH --* NaCNO + H20 + NaC1 One part of chlorine applied, requires 1.13 parts of caustic soda. The sodium cyanate formed in the above reaction is less toxic. However, if complete degradation of cyanides are desired, sodium cyanate thus formed is further oxidized with chlorine: 2NaCNO + 4NaOH + 3C12 --* 2CO 2 + 6NaCI + N 2 + 2H20 The above reaction requires 4.09 parts of chlorine and 3.08 parts of sodium hydroxide for one part of cyanide. The total amount of theoretical chlorine requirement is 6.82 parts per part of cyanide. But, in actual plant operation the chlorine requirement is higher than the theoretical value. In order to have simplified operation and control, a single vessel can be used for complete cyanide removal. The pH is maintained at about 8.5 by dosing caustic soda and chlorine. With proper mixing and adequate detention time it is possible to obtain very high efficiency of cyanide removal. It is always preferable to adopt the complete cyanide degradation process for control of cyanide pollution. A schematic flow diagram of twin unit cyanide removal system prefixed with an in-plant cyanide stripper is shown in Figure 8-14.

Sulphide In effluents, sulphides may be present as dissolved hydrogen sulphide (H2S) gas or as sulphides, or both may be present depending on the pH of the effluent water. When pH is high it is present as sulphide. On the other hand, when pH is low, it is present as dissolved hydrogen sulphide gas.

HYDROCfANIC 4Ctlc

CYANIOE EFFLUENT

PI

I

I

[wi

0 m

COMPLETE OXIDATION

>

TREAEEO EFFLUENT

Figure 8-14: Vanadium removal system.

312

Waste Minimization

Normally, in the fertilizer factory effluent, the quantity and the concentration of sulphide is usually very low. As such, in most of the cases specific treatment for sulphides is not necessary. Where cyanides are present with sulphides, the chlorination treatment for removal of cyanides will also destroy sulphides. The dissolved hydrogen sulphide may be removed by aeration or by stripping using acidic gases, like carbon dioxide.

Fluoride and Phosphate Fluorides and phosphates originate in the effluent during the manufacture of phosphatic fertilizers. The main sources are the scrubber liquors from various unit operations involving scrubbing of off-gases, washing, gypsum pond water etc. In the effluent, fluorides are present as fluosilicic acid with small amounts of sodium/potassium fluosilicates and hydrofluoric acid. Phosphorus is present as phosphoric acid with small amounts of calcium phosphates. The process of removal of fluorides and phosphates involves a twostage operation. In the first stage, chalk or powdered lime stone is used whereas in the second stage, only lime is used. It is also possible to use only lime for both the stages. In the latter case, it is called double lime treatment. The two stage operation is necessary to bring down the levels of fluorides and phosphates to very low values. In the first stage, the effluent is treated with chalk or finely ground calcium carbonate (CaCOa) at pH around 3.0 with continuous agitation. In this stage of treatment, most of the fluorides and silica are precipitated as calcium fluoride and silica while most of the phosphates still remain in solution as monocalcium phosphate. H2SiF 6 + 3

CaCO 3 ~

2H3PO 4 +

3 CaF 2

+ SiO 2 +

3CO 2 + 1-120

CaCO3 --~ Ca(H2PO4)2 + 1-12O + CO 2

The actual requirement of calcium carbonate (CaCO3) is 3.0 to 3.5 parts for each part of fluoride (F) and 0.6 to 0.7 parts for each part of phosphate (PO4). The effluent after the first stage reaction is allowed to settle in a settler or a pond and after separation of suspended precipitates, is taken for the second stage treatment with lime to raise the pH to around 8.5. In the second stage for an efficient reaction, agitation is provided. In this reaction with calcium hydroxide, the residual fluorides and phosphates of the first stage reaction are converted into insoluble calcium fluoride and calcium hydroxy apatite respectively according to the following reactions:

Treatment of Effluent Fertilizer Industry Example

313

H2SiF6 + 3Ca(OH)2 ~ 3 CaF 2 + SiO 2 + 4H20 3Ca(H2PO4) 2 t 7Ca(OH)2 ~ 2Cas OH(PO4)3 + 121-120 In the above reactions, under the actual operational condition the requirement of calcium hydroxide, Ca(OH)2, is 2.1 to 2.3 parts per part of fluoride (F)and 1.0 to 1.1 parts per part of phosphate (PO4). The precipitates formed are settled in clarifier or in pond and the clear overflow water is discharged or recycled in the process for scrubbing further quantities of fluorides and phosphates. The clarity of the effluent can be improved by using coagulant alum and, polyelectrolyte. This arrangement reduces fluoride concentration further in the effluent. The reduction of fluoride and phosphate content of the effluent depend upon proper mixing of the chemicals with the effluent, detention time provided, the pH conditions etc. In this two stage treatment, it is possible to attain fluoride concentration below 10 mg//? as F, and phosphate concentration below 5 mg//? as P. The byproduct chalk produced during the ammonium sulphate production by the Merseberg process may also be used for the first stage reaction. When byproduct chalk is used, it should contain very low levels of ammonium sulphate. The schematic flow diagram of fluoride and phosphate removal system is shown in Figure 8-15. Oil and Grease

The main sources of oil in the fertilizer factory effluent are from the oil unloading, storage and pumping sections. The other source is from the pumps and compressors bay. In general, the proportion of emulsified oil is low with respect to the total quantity of the oil present in the effluent. Therefore, under normal conditions emulsion breaking by treatment is not necessary. These oils and greases are almost insoluble in water. Being lighter than water, oil and grease float on the surface of the water. For the removal of oil and grease, usually mechanical gravity type oil separators are used. These gravity separators are provided with a suitable type of oil skimmer and the skimmed oil is recovered, reconditioned and reused. In a well designed mechanical gravity type oil separator, it is possible to bring down the oil level of the effluent to around 50 mg//?. When a greater degree of oil removal is desired a separate unit containing porous coke or active carbon is placed in series with the gravity oil separator. This adsorption system provides a very high efficiency of oil separation.

CHALK/ LIME

SETTLING ALUM/ POLYELECTROLYTE

*

T R E A T E D EFFLUENT SE TTLlNC

11

V

fL"OI3E

Figure 8-15: Fluoride-phosphate removal system.

Treatment of Effluent Fertilizer Industry Example

315

In some cases, it may be necessary to incorporate an emulsion breaking unit to take care of the oil emulsion. The emulsion breaking systems are similar to the clarifiers where coagulants e.g. alum, ferrous sulphate, ferric chloride etc. with or without lime addition is followed. In some cases, bentonite is used as coagulant aid. In recent years, varieties of polyelectrolytes and other patented chemicals are available for emulsion breaking and coagulation. In this system, the oils which float on the clarifiers are skimmed out and the recovered oil is collected from the bottom sump. The technology of dissolved air flotation systems can be adopted for the removal of oils from the effluent. Figure 8-16 illustrates the oil removal system.

Chromate Where chromate chemicals are used as inhibitors in the cooling water conditioning, chromate bearing waste water originates from cooling tower blowdown. The basic principle of chromate removal is reduction of hexavalent chromium to trivalent form followed by precipitation of chromium as chromium hydroxide. The cooling water blowdown which contains chromate is collected in a tank and the pH of the water is lowered to the range of 2 to 4 by adding sulphuric acid. After lowering the pH, the chromate reduction is carried out by use of any of the chemicals ferrous sulphate, sodium sulphite, sodium metabisulphite or sulphur dioxide (SO2) gas. Since ferrous sulphate is cheap and easily available, it is widely used for reduction of chromate: Na2Cr207 + 6FeSO4 + 7H2SO4 ~ Cr2(SO4)3 + 3Fe2 (SO4)3 + 7H20 + Na2SO4 When sulphur dioxide gas is used for reduction of chromate the following reaction occurs: Na2Cr20 7 + 3SO 2 + H2SO4 ~ Cr2(SO4) 3 + H20 + Na2SO 4 In the above reaction one part of chromate (CrO4) requires 7.2 parts of FeSO4.7H20 or 0.83 parts of SO 2 gas by weight. After reduction, lime is added to the effluent for precipitation of chromium and iron, in case ferrous sulphate is used: Cr2 (SO4)3

+

3Ca(OH)2 --* 2Cr(OH)3 + 3CaSO 4

Fe2(SO4) 3 + 3Ca(OI-I)2 --. 2Fe(OH)3 + 3CaSO 4

EFFLUENT FROM OIL HANDLINF~SECTION

1

I

= h

SKIMMED OIL c

SLUDGE

Figure 8-16: Oil removal system.

Treatment of Effluent Fertilizer Industry Example

317

The process is carried out in a twin vessel----one for lowering the pH and reduction, and the other is for the precipitation. The system is followed by a clarifier or settler for removal of suspended solids. The process is indicated in Figure 8-17. In a recent process, iron electrodes are used for reduction of chromate and can be used for the removal of hexavalent chromium.

Total Dissolved Solids (TDS) Usually in the fertilizer factory effluent, the total dissolved solids (TDS) do not exceed the normal prescribed limits, suitable for irrigation purposes. But in some specific cases particularly when the TDS of raw water is very high, the TDS of the effluent is also high. There is no economic convenient method for lowering the TDS content of the effluent water. In practice, the higher TDS-containing effluents are segregated and solar evaporated to dryness and disposed of as solid wastes.

Suspended Solids Suspended solids originate from various sources: 9 9 9 9 9 9

raw water clarification ash flurry carbon slurry chalk slurry gypsum slurry precipitation and neutralization reactions in the effluent treatment plant etc.

The raw water treatment plant sludge is removed in the sludge drying bed. Ash, carbon, chalk, gypsum slurry are settled in well designed settlers. The precipitates originating from precipitation and neutralization reactions in the effluent treatment plant can be settled in settlers or in clarifiers. When the particle size of the suspended solids in the above mentioned effluents are comparatively lower in diameter, then clarification requires addition of coagulants and/or polyelectrolytes. In general, suspended solids of the fertilizer industry are of inorganic solids. Therefore, they do not cause oxygen demand when discharged into receiving waters. Only in case of a biological treatment system, organic sludges may develop which can be separated in sludge drying beds. The flow diagram for suspended solids removal system is provided in Figure 8-18.

FERROUS SULPHATE /SODIUM SULPHITE

ACIOIACIDIC EFFLUENT

CHROHATE REDUCTION

PR E C I P l r A T I O N

SETTLING

Figure 8-17: Chromate-removal system.

EFFLUENT

EFFLUENT CONTAININ6 EASILY SETTLEABLE SOLlOS

COAGULANT/POLYEECCTROLYTE

EFFLUWl CONTNNNG SUSPENDED SCLIGS REQUlRlNG COAGULAlION FLASH MIXER L

I SLUDGE ORYINS BED/ THICKNER/ FILTER

SLUDGE

Figure 8-18: Suspended solid removal system.

320

Waste Minimization

Acid and Alkali Generally the acids and alkaline effluents are mutually neutralized with final pH adjustment by lime/soda ash or acid. Otherwise, acidic and alkaline effluents are separately neutralized by use of lime/soda ash and acid respectively. In the process of neutralization proper mixing of effluents with the chemicals is very important and this is usually effected by proper mixing with the use of agitators or by recirculation of the effluents particularly when lime is used for neutralization. It is necessary to incorporate a settler or a clarifier for removal of suspended solids, in case precipitation takes place during neutralization. The acidic and alkaline effluents, depending on the quality, may be utilized in the effluent treatment system. In such cases, it is necessary to segregate them in the collection system of the effluent. In the effluent treatment system where pH lowering is necessary, acidic effluents may be dosed. On the other hand if pH raising is desired, alkaline effluent addition serves the purpose. The neutralization system is represented in Figure 8-19.

Biochemical Oxygen Demand (BOD) The fertilizer industry effluent usually contains low BOD. As such, no specific treatment is required for removal of BOD under normal operational conditions. But the sewage effluent, i.e., wastewater from toilets and other sanitary facilities in the factory area contain some quantity of BOD and suspended solid. The volume of this effluent is usually low. Any of the conventional sewage treatment system may be adopted for treatment of this effluent, e.g., aeration processes, oxidation ponds etc. The sewage effluent may find use in the biological treatment units of the effluent treatment plant for supplementation of the BOD requirement. In such cases no separate treatment for sewage effluent is required.

RECOVERY, REUSE AND RECYCLE IN THE PROCESS

Conservation of Water Conservation of water means reduction in the consumption of water by the industry which in turn effects reduction in the volume of the effluent. Proper management of a water system and economy in the use of the water, result in savings for reduced consumption of water, and also for effluent treatment cost due to reduced volume of effluent.

,I

ALKALINE EFFLUENT

I

b5I N EUTRAUSATION

EFFLUENl SETTLING

FUMP RECIRCULATION

c

SLU06E

Figure 8-19: Neutralization system for acidic and alkaline effluent.

322

Waste Minimization

In order to identify the points from where water conservation may be made, it is necessary to conduct an elaborate survey of the complete water supply and consumption. The examination of the material balance of water will indicate the possible areas which may be studied further with the aim to reduce the consumption of water. Some of the common areas from where the consumption of water may be reduced/eliminated are discussed below: 9 The consumption of cooling water may be reduced considerably by use of recirculating type cooling water system instead of once through cooling water system. Increase in the concentration factor of the recirculation system also reduces the blowdown quantity from the cooling tower. 9 The cooling water blowdown and the effluent water after treatment may find use for preparation of ash slurry. 9 The waste waters of the phosphoric acid plant can be recycled after treatment for use in the scrubbers, washing of gypsum and preparation of gypsum slurry. Treated effluent water can be used for preparation of the chalk slurry in the manufacture of ammonium sulphate. 9 In the effluent treatment plant, treated effluent can be used for preparation of lime slurry and chemical solutions. 9 The bottom water of the sludge drying bed of clarifier sludge may be recycled in the plant. 9 The condensates of the process plants after removal of the contaminants can be used as boiler feed water. 9 Drycleaning of the process equipment and the floor of the plants will reduce unnecessary wastewater generation. 9 General awareness regarding water consumption also minimize the wastage of water.

Recoveries from Wastes and Byproducts The oil spillage during unloading, storage and transportation may be separated by a gravity separation method and reconditioned for reuse in the process, or as fuel. The coal ash may be recovered and processed for making roads building material etc. The carbon obtained from the partial oxidation process may be further processed to obtain commercial grade carbon black suitable for use in printing ink, rubber, battery and other industries.

Treatment of Effluent Fertilizer Industry Example

323

When substantial quantity of ammonia remains present in the wastewater, this may be recovered by steam stripping or by ion exchange processes. The byproduct gypsum obtained from the phosphoric acid manufacture can be used as raw material for the production of ammonium sulphate. The gypsum may also find use in the manufacture of plaster board, building material etc. The other uses of gypsum are in the reclamation of alkaline soil and in the manufacture of cement. The byproduct chalk of the ammonium sulphate manufacture using gypsum can be used in the manufacture of cement. This may also find use in neutralization of the acidic waste waters and treatment of fluoridephosphate bearing effluents. During the vacuum concentration of dilute phosphoric acid, it is possible to segregate the condensate which mainly contains hydrofluosilicic acid. The concentration of hydrofiuosilicic acid may be raised by recirculation to 15 to 20% solution. This hydrofluosilicic acid solution may be used as raw material for the manufacture of fluoride chemicals, e.g., sodium fluoride, aluminum fluoride, cryolite etc. The hydrofluosilicic acid thus obtained may also be used for fluoridation of potable water supply. Where the raw water source is groundwater with high hardness, softening of the water is practiced by lime treatment. In such cases, sludge of the softening unit is predominantly calcium carbonate (CaCO3). The sludge may be dried in sludge drying beds and calcined to obtain quicklime for softening the groundwater again and again, or any other suitable purpose.

HOUSE KEEPING Good house keeping is important for abatement of pollution. The control measures for accidental spills have already been dealt with previously. Other aspects in good house keeping involve: 9 9 9

Replacement of the faulty equipment, instruments etc. Incorporation of newly developed/modified systems for pollution control wherever possible. Regular monitoring of the water circuit and effluents and recording them systematically so that the status of pollution vis-a-vis wastage of product material is readily available for evaluation.

324

Waste Minimization 9 Updating of the drawings related to pollution control and of the effluents. 9 Sustained operation of the effluent treatment plant. This relates to maintenance and ready stock of chemicals needs for effluent treatment. 9 Regular maintenance of the pollution control equipment, considering their status equivalent to that of production plants.

SEPARATION TECHNOLOGIES FOR REMOVAL OF ORGANIC AND PESTICIDAL CHEMICALS FROM WASTEWATER The following unit operations have been grouped here for removal and recovery of organic and pesticidal chemicals from wastewater: 1. Absorption 2. Adsorption including bubble adsorption 3. Centrifugation 4. Clathration 5. Coagulation 6. Coalescence 7. Condensation 8. Cyclonic Action 9. Desorption 10. Dialysis 11. Diffusion Process 12. Electro-phoresis 13. Evaporation 14. Extraction 15. Filtration 16. Flash Expansion 17. Flotation 18. Foam Fractionation 19. Gravity Settling 20. Impingement 21. Membrane Permeation 22. Precipitation 23. Reverse Osmosis 24. Scrubbing 25. Stripping 26. Ultra-filtration

INDEX

ammonium phosphate sulphate 248, 260 ammonium salt plants 275 ammonium sulphate 222, 231, 257 anaerobic biological treatment 137 analyzing process steps 76 approaches to waste reduction 15 aqueous waste 21 arsenic 265, 305, 307 arsenic sludge 269 arsenical solution recycle 308 arsenical waste 271 ash 269 audit data 2 audit procedure 3 audit questionnaire 147 audit reports 70 audit studies 90 audit summary 53 audit team 57, 69 audit types 61 auditing 1, 52

A absorption processes 228 accidental spills 262 accounting 13, 30 acetaldehyde 167, 185, 213 acetic acid 167 acidulation 238 actuation production 74 add-on control devices 125 adsorption 136 aerobic biological treatment 137 air emissions 21, 115 air flotation 137 air pollution control 55 air pollution control questionnaire 149 air separation 225 air stripper 289 air stripping of ammonia 286 algal uptake 303 ambient air 101 ammonia 224, 268 ammonia plant 255 ammonia production 226 ammonia recovery 273 ammonia removal 292 ammoniacal nitrogen 264, 286 ammonium chloride 222, 234, 257

B

biochemical oxygen demand 267, 320 biological nitrification 297, 299 325

326

Waste Minimization

biological processes 137, 286 blowdown water 281 boiler flue gas 281 C calcium ammonium nitrate 222, 234, 236, 258 calcium nitrate separation 246 calculating releases in wastewater 128 captive storage tank 272 carbon 269 carbon adsorption 20 carbon dioxide recovery 228 carbon monoxide 268 carbon slurry 271 carboxylation 167 chalk 269 checklist 97 chemical air emissions 116 chemical analyses 23 chemical fertilizers 222 chemical oxidation 135 chemical precipitation 21, 136 chemical reduction 136 chemicals manufacturing 162 chemoautotrophic bacteria 299 chromate 266, 315 chromate removal 318 chromium 21 chromium sludge 269 cleaning 22 cokeoven byproduct ammonia 231 cokeoven gas 231 coal gasification 225 collection efficiencies 125 commodity chemicals 26 complexed metals 136 component balance 80

comprehensive audits 56 concentration of phosphoric acid 238 condensation 20 conservation of water 320 control methods 2 cooling tower 281 cooling water 21, 98, 261, 270 copper 107 corrosion 95 costs 30, 80 crystallization 246 cyanide 265, 271, 310 D data 109 DCDA process 240 dedusting 280 definitions of waste reduction 11 demineralization 253, 261, 281 demineralized water 99 denitrification 297 design 17 detoxification operation 96 developing resources 60 dewatering operations 142 diammonium phosphate 242, 247, 259 digestion 246 direct discharge to surface waters 127 direct measurement 129, 142 discharge to sewers 127 discharging of product 94 dissolving the solvent 20 distillation 20 dust emission 281

Index E economic information 40 economic viability 86 effluent generation 161 effluent treatment 253 electrolysis 224 emission control 280 emissions 256 employee demotivation 83 emulsion 136 energy balances 79 energy consumption 74 engineering calculations 117, 133 environmental aspects analysis 89 environmental organizations 13 equipment changes 16 estimating releases 137 ethylene oxidation 185 evaluation of findings 68 exhaust ducts 95 exit interview 68, 69

facility audits 146 fan outlets 95 feasible reduction 37 feedstock impurities 162 fertilizers 222 field work 65 filtration 136 financial institutions 13 fire hazards 17 flange joints 95 floating roofs on tanks 16 flow charts 79 fluoride 266, 312 fluorine compounds 268 food production 223

327

fugitive air emissions 111 fugitive air sources 105 fugitive emissions 21 fume scrubber 280 G gas purification 228 gaseous emission 215 gasification 224 gasification process 224 generation of impurities 255 gravity separation 137 gypsum 238, 269 gypsum conveying system 280 H

hazard rating 178, 210 hazardous substances identification 23 hazardous waste 2 health and environmental effects 40 heat pump 21 heat transfer medium 21 historic data 53 housekeeping 76, 81, 93, 323 housekeeping status 78 hydrocyanic acid 268 hydrofluosilicic acid recovery 278 hydrogen sulphide 267

identification of hazardous substances 23, 36 identification of source(s) 36 impact assessment 4 implementation solutions 88 in-plant operations 55

328

Waste Minimization

incineration 140 information needs 28, 35, 38 installed capacity 74 internal controls 65 international dimensions 14 international perspective 49 investment-uncertainty 18 ion exchange 291 K Kjeldahl nitrogen 285 L land treatment 128, 138 landfilling 138 lawsuits 1 layout 83 layout manufacturing units 156 lime caustic soda 292 liquid-phase oxidation 188 liquid effluent 100 liquid sources 105 loading losses 120 M maintenance negligence 81 major approaches 108 management options 25, 38, 83 mass balance 23, 115, 132, 161 material balance 6 material costs 78 material handling 253 material storage 119 material substitution 17, 19 measure waste reduction 42 measuring devices 157 mechanical processes 8, 20 Merseberg process 231, 233

methanol 167, 265, 305, 307 methanol carboxylation 167 minimization data 73 mixed fertilizers 223 model questionnaires 147 monitoring of effluents 271 monoethanolamine 265, 305, 307 Monsanto process 167 multilateral organization 50 N neutralization 246, 321 nitric acid 234, 258 nitric acid plant emission 275 nitric acid production 237 nitrification 297 nitrogenous pollutants 285 nitrogenous straight fertilizer 222 nitrophosphate 223, 246, 260 nitrophosphate production 249 nonaqueous liquids 112 nonaqueous wastestream sources 139 nonroutine-releases 105 NPK complex fertilizer 248, 261 O oil and grease 266, 313 oil pollution 281 oil removal 316 oil skimming 137 oil spillage 322 oil traps 281 operations in the plant 16 organic nitrogen 265, 303 organic solvents replacement 19

Index oxides of nitrogen 268 oxides of sulphur 267 oxidized nitrogen 264, 305 oxidizing ethylene 188 P paint 20, 107 paper machine 76 paper mill 76, 78 paraffin hydrocarbons 167 partial oxidation 226, 255 particulate matter 268 performance study 92 pesticidal chemicals 324 petroleum refining 26 Phase I audit 62 Phase II audit 62 phosphate 266, 312 phosphatic fertilizers 222 phosphoric acid 238, 241, 258 plant data 99 plant growth 223 plant layout 95, 157 plant management 157 plant practices 8, 12 plant sludge 281 point air sources 105, 111 pollutant parameters 262 pollution control 5, 10, 91 polymer-grade ethylene 200 post audit activities 165 potential for waste reduction 27 pressurized systems 95, 157 prevention and control 10 prilling tower 274 prilling tower dedusting system 272 priorities for waste reduction 37

329

process audits 56 process changes 16 process characteristics 25 process chemistry 162 process condensate 256, 271 process flow charts 76 process flow diagram 77 process inputs 17 process recycling 15 process source 24 process stream components 159, 171 process vents 113 process waste streams 184, 214 process water use 21 product quality 26 production information 40 production of sulfuric acid 239 profit enhancement 80 protocols 64 purge gas 271 Q questionnaires

64

R

raw material changes 16, 17 raw material consumptioh 74 raw material handling 281 raw material losses 158 raw material preparation 76, 79 raw material quality 83 raw water 97, 253 raw water treatment 98 reaction chemistry 162 receiving water 101 recoveries from wastes 322 recovery of ammonia 291, 295 recovery of metals 137, 141 recovery of solvents 141

330

Waste Minimization

reduction 10 reduction alternatives 25 reduction audit 35 reduction data 34, 40 reduction decisions 22 reduction economics 30 reduction incentives 25 reduction methods 14, 38 reduction priorities 24 reduction techniques 24 reformation process 225 refrigeration systems 21 regulations 31, 40 release estimation 113 release in solids 112 releases to air 113 releases to the environment 104 releases to wastewater 112 Reppe process 173 reuse as fuel 141 rock phosphate grinding 238, 280 S sampling 164 scrubber water recycle 280 seepage problems 102 segregation of cooling water 270 segregation of process effluent 270 separation technologies 324 single absorption process 239 single super phosphate 259 sludges 269 solid waste disposal 55 solid wastes 101 solidification 141 solvent recovery 20

Solvey process 235 source categories 114 sources of wastes 104 sources of wastewater 126 sources(s) of hazardous substances(s) 24 specifications changes 17 spills 94, 262 steam and power generation 253, 261 steam reformation 225, 227, 256 steam stripping 290, 294 steps of an environmental audit 72 stock preparation 76 storage tanks 95, 157 storm water drains 96 stripping 136, 286 substitution approach 19 sulphide 266, 310 sulphur dioxide 267 sulphur trioxide 267 sulphuric acid 238, 258 sulphuric acid emission 278 super phosphate 222 surface impoundments 128, 139 suspended solid removal 319 suspended solids 267, 317 T tail gas catalytic reduction 277 technical feasibility 85 technology availability 32 technology information 40 thermal treatment 140 thermal urea hydrolyser 273 total dissolved solids 267, 317 toxic air emissions 117

Index transfer knowledge 13 treatment processes 135 triple super phosphate 242, 259

Venturi scrubber 125 volatile organic liquids

331

120

W U uncaptured process releases 122 underground injection 128, 139 unit operation 6, 135 urea 222, 229 urea ammonium phosphate 248, 260 urea dedusting 2 74 urea dust 257, 272 urea hydrolysis 306 urea production 230 urea recycle 276 urea solution recycle 275 utilities 102 V vacuum concentration 278 vacuum condensate 256, 271 vanadium 265, 305, 307 vanadium removal 311 vapor loss prevention 21

Wacker process 194 Wacker-Hoechst process 201 washing of gypsum 238 waste audit 2 waste flow sheet 164 waste management 33 waste minimization 73 waste questionnaire 146, 151 waste reduction 2, 44 waste reduction approaches 7, 19 waste reduction audit 23 waste stream data 40 wastewater 22, 126, 264 wastewater disposal 54, 127 water consumption 74, 161 water control checklist 146 water pollution 96, 147 water supply 54, 105 water usages 96 water-based raw materials 8 worker training 29 worksheet 73

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