Water Treatment Residuals Management for Small Systems

Transcription

1 Water Treatment Residuals Management for Small Systems Subject Area: Water Resources and Environmental Sustainability

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3 Water Treatment Residuals Management for Small Systems

4 About the Water Research Foundation The Water Research Foundation (formerly Awwa Research Foundation or AwwaRF) is a membersupported, international, 501(c)3 nonprofit organization that sponsors research to enable water utilities, public health agencies, and other professionals to provide safe and affordable drinking water to consumers. The Foundation s mission is to advance the science of water to improve the quality of life. To achieve this mission, the Foundation sponsors studies on all aspects of drinking water, including resources, treatment, distribution, and health effects. Funding for research is provided primarily by subscription payments from close to 1,000 water utilities, consulting firms, and manufacturers in North America and abroad. Additional funding comes from collaborative partnerships with other national and international organizations and the U.S. federal government, allowing for resources to be leveraged, expertise to be shared, and broadbased knowledge to be developed and disseminated. From its headquarters in Denver, Colorado, the Foundation s staff directs and supports the efforts of more than 800 volunteers who serve on the board of trustees and various committees. These volunteers represent many facets of the water industry, and contribute their expertise to select and monitor research studies that benefit the entire drinking water community. The results of research are disseminated through a number of channels, including reports, the Web site, Webcasts, conferences, and periodicals. For its subscribers, the Foundation serves as a cooperative program in which water suppliers unite to pool their resources. By applying Foundation research findings, these water suppliers can save substantial costs and stay on the leading edge of drinking water science and technology. Since its inception, AwwaRF has supplied the water community with more than $460 million in applied research value. More information about the Foundation and how to become a subscriber is available on the Web at

5 Water Treatment Residuals Management for Small Systems Prepared by: Nancy E. McTigue and David A. Cornwell, Ph.D., P.E. BCEE EE&T, Inc. 712 Gum Rock Court Newport News, VA Jointly sponsored by: Water Research Foundation 6666 W. Quincy Ave Denver, Colorado and U.S. Enviromental Protection Agency Washington, D.C. Published by: Distributed by:

6 DISCLAIMER This study was jointly funded by the Water Research Foundation (the Foundation) and the U.S. Environmental Protection Agency (USEPA) under Cooperative Agreement No. X The Foundation and USEPA assume no responsibility for the content of the research study reported in this publication or for the opinions or statements of fact expressed in the report. The mention of trade names for commercial products does not represent or imply the approval of the Foundation or USEPA. This report is presented solely for informational purposes. Copyright 2009 by Water Research Foundation ALL RIGHTS RESERVED. No part of this publication may be copied, reproduced or otherwise utilized without permission. ISBN Printed in the U.S.A.

7 CONTENTS LIST OF TABLES... ix LIST OF FIGURES... xi FOREWORD... xiii ACKNOWLEDGMENTS... xv EXECUTIVE SUMMARY... xvii CHAPTER 1: INTRODUCTION...1 How to Use this Manual...2 CHAPTER 2: WHAT KIND OF RESIDUALS ARE PRODUCED?...3 What Residuals are Produced...3 Coagulation Waste Streams...7 Softening Waste Streams...9 Ion Exchange and Media Adsorption Residuals...10 Membrane and Reverse Osmosis Residuals...11 Iron and Manganese Oxidation Residuals...12 CHAPTER 3: QUANTITIES AND CHARACTERISTICS...13 Coagulant Solids...13 Lime Residuals...18 Manganese and Iron Removal Residuals...19 Ion Exchange and Media Adsorption Residuals...19 Spent Filter Backwash Water...21 Membrane Residuals...22 Spent GAC and Filtration Media...23 Precoat Filtration Residuals...23 Slow Sand Filtration Residuals...23 Residuals Characteristics...24 Physical Properties...24 Characteristics of Predominately Liquid Sludge...26 Characteristics of Predominately Solid Sludge...27 Chemical Characteristics...27 CHAPTER 4: REGULATIONS...29 Clean Water Act...29 Discharge to Sewers (Pretreatment Program)...30 Direct Discharge to Receiving Stream (NPDES Program)...31 Filter Backwash and Recycling Rule (FBRR)...31 Safe Drinking Water Act...32 Underground Injection...32 v

8 On-Site Dewatering...33 Resource Conservation and Recovery Act of Solids Disposal in a Municipal Solid Waste Landfill...34 Solids Disposal in a Hazardous Waste Landfill...34 Land Application of Liquid Residuals...36 The Atomic Energy Act of 1954, As Amended...36 Disposal of Residuals Containing Radioactivity...36 Department of Transportation (DOT) Regulations (49 CFR 171 to 180)...37 Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA)...38 CHAPTER 5: THICKENING AND DEWATERING...39 Pumps and Piping...40 Equalization...41 Gravity Thickening...42 Thickening Tanks...42 Plate Settlers...43 Conditioning...43 Non-Mechanical Dewatering...43 Sand Drying Beds Description...45 Solar Drying Bed or Evaporation Ponds...46 Dewatering Lagoons...46 Freeze-Thaw Beds...47 Mechanical Dewatering...48 Centrifuges...49 Pressure Filter Press...51 Belt Filter Press...51 Vacuum Filter...53 CHAPTER 6: SPECIAL WASTES...55 Arsenic...55 Regulations...57 Processes...58 Residuals Quantities and Characteristics...64 Treatment of Arsenic Containing Liquid Residuals...66 Handling of Solids From Arsenic Removal...70 Radioactivity...70 Residuals Production...70 Characterization...74 Regulations...75 State TENORM Regulations...76 Ultimate Disposal Options...78 Mixed Waste...81 CHAPTER 7: LANDFILL...83 Nonhazardous Landfills...83 vi

9 Municipal Solid Waste Landfills...83 Monofill...84 Hazardous Waste Landfill...85 What Data Would be Required to Dispose of Material in a Hazardous Waste Facility?...86 Low Level Radioactive Waste Landfill (LLRW)...86 What Data Will be Needed for Disposal at a LLRW Landfill?...87 CHAPTER 8: LAND APPLICATION AND BENEFICIAL USES...89 Background...89 What Type of Data are Needed to Use Land Application?...91 Beneficial Uses...93 Regulatory Evaluation...94 Residuals Characterization...94 User Requirements...97 Preliminary Economic Analysis...97 Noneconomic Analysis...98 Contract Haulers...98 CHAPTER 9: SEWER AND DIRECT DISCHARGE...99 Discharge by Connection to a POTW...99 What Kind of Data will a POTW Require?...99 Equalization Direct Discharge to Surface Water CHAPTER 10: UNDERGROUND INJECTION CONTROL WELLS Background What are the Requirements for UIC Well Disposal? Feasibility What Data are Needed to be Able to Use This Option? CHAPTER 11: SUMMARY APPENDIX A: STATE, REGIONAL, FEDERAL AND TRIBAL CONTACTS APPENDIX B: TCLP CONTAMINANTS AND REGULATORY LEVELS REFERENCES ABBREVIATIONS vii

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11 TABLES 1.1 Water system categories Small system regulatory summary Regulated contaminant list (partial) and possible removal technologies Residual type by treatment technology Examples of estimated sludge production Range of cake solid concentrations obtainable Summary of residuals and management methods for arsenic treatment technologies Summary of example residuals quantity from arsenic processes Arsenic residuals sample characterization Concentration of arsenic in residuals Summary of treatment results for removing arsenic from liquid arsenic waste Radionuclides MCLs Summary of treatment technologies for removal of naturally occurring radionuclides in water SPARRC elements Disposal requirements of certain states Common disposal considerations for residuals containing radioactivity Operating low level radioactive waste landfills Important residuals quality parameters for land applying coagulant residuals Recommended cumulative metal limits for cropland Physical test parameters useful for beneficial use Chemical test parameters useful for residuals beneficial use...96 ix

12 9.1 Parameters of importance to a POTW Example in-stream water quality guidelines and standards x

13 FIGURES 2.1 Major residual streams commonly generated by coagulation water treatment plants Waste producing processes in softening plants Schematic of ion exchange process with upflow regeneration Quantity of dry alum solids produced under different conditions Volume of alum sludge produced under different conditions Quantity of dry ferric solids produced under different conditions Volume of ferric sludge produced under different conditions Example of annual sludge production variation by month Estimated of quantity of adsorption media required at different flows and contact time Decision tree for the disposal of liquid (non-solid) residuals Decision tree for the disposal of solids residuals Federal regulations governing the disposal of residuals Hazardous waste determination decision tree Sludge handling options Nonmechanical dewatering Solids dewatered by two different nonmechanical processes drying beds and freeze-thaw Example centrifuge system Schematic of skid mounted centrifuge system Andritz belt filter press Waco, Texas, USA Schematic of ion exchange process with regeneration for arsenic removal Schematic of membrane process for arsenic removal...59 xi

14 6.3 Schematic of AA adsorption process with regeneration for arsenic removal Schematic of oxidation-filtration iron and manganese removal process for arsenic removal Schematic of iron and manganese (greensand) filtration process for arsenic removal Arsenic residuals treatment options Arsenic residuals handling and disposal decision tree Decision Tree 1: Solids residuals disposal containing radioactivity Decision Tree 2: Liquid residuals disposal containing radioactivity Decision Tree 3: Liquid residuals disposal intermediate processing Typical municipal solids waste landfill Schematic of hazardous waste landfill after closure...86 xii

15 FOREWORD The Water Research Foundation is a nonprofit corporation that is dedicated to the implementation of a research effort to help utilities respond to regulatory requirements and traditional high-priority concerns of the industry. The research agenda is developed through a process of consultation with subscribers and drinking water professionals. Under the umbrella of a Strategic Research Plan, the Research Advisory Council prioritizes the suggested projects based upon current and future needs, applicability, and past work; the recommendations are forwarded to the Board of Trustees for final selection. The Foundation also sponsors research projects through the unsolicited proposal process; the Collaborative Research, Research Application, and Tailored Collaboration programs; and various joint research efforts with organizations such as the U.S. Environmental Protection Agency, the U.S. Bureau of Reclamation, and the Association of California Water Agencies. This publication is a result of one of these sponsored studies, and it is hoped that its findings will be applied in communities throughout the world. The following report serves not only as a means of communicating the results of the water industry s centralized research program but also as a tool to enlist the further support of the nonmember utilities and individuals. Projects are managed closely from their inception to the final report by the Foundation s staff and large cadre of volunteers who willingly contribute their time and expertise. The Foundation serves a planning and management function and awards contracts to other institutions such as water utilities, universities, and engineering firms. The funding for this research effort comes primarily from the Subscription Program, through which water utilities subscribe to the research program and make an annual payment proportionate to the volume of water they deliver and consultants and manufactures subscribe based on their annual billings. The program offers a cost-effective and fair method for funding research in the public interest. A broad spectrum of water supply issues is addressed by the Foundation s research agenda: resources, treatment, and operations, distribution and storage, water quality and analysis, toxicology, economics, and management. The ultimate purpose of the coordinated effort is to assist water suppliers to provide the highest possible quality of water economically and reliably. The true benefits are realized when the results are implemented at the utility level. The Foundation s trustees are pleased to offer this publication as a contribution toward that end. David E. Rager Chair, Board of Trustees Water Research Foundation Robert C. Renner, P.E. Executive Director Water Research Foundation xiii

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17 ACKNOWLEDGMENTS The authors would like to thank Dr. Kenan Ozekin, the Water Research Foundation Project Manager and the members of the Project Advisory Committee, including Jennifer Moller, Ground Water and Drinking Water Office, US Environmental Protection Agency, Washington, D.C.; Jerry W. Gibbs, P.E., Park City Municipal Corporation, Park City, UT; Jerry Biberstine, National Rural Water Association, Denver, CO. The authors also thank the group of experts who provided insight and guidance for this project. They include Joy Barrett, Ph.D., Rural Community Assistance Partnership (RCAP), Boulder, CO; Bill Hogrewe, Ph.D., P.E., Rural Community Assistance Corporation, Boulder, CO; Christopher A. Impellitteri, Ph.D., National Risk Management Research Laboratory, US Environmental Protection Agency, Cincinnati, OH; Cynthia Klevens, New Hampshire Department of Environmental Services, Concord, NH; Pat Kline, American Water Works Association, Denver, CO; Stephen Roy, New Hampshire Department of Environmental Services, Concord, NH; John Scheltens, City of Hot Springs, SD; Robert Wichser, Rivanna Water and Sewer Authority, Charlottesville, VA; Mel Aust, Hidden Valley Lake Community Services District, Hidden Valley Lake, CA. xv

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19 EXECUTIVE SUMMARY This document was prepared to aid small system owners, consultants and regulators better understand the issues and constraints involved with the treating and disposal of residuals created by water treatment systems. The document is designed to provide information on processes utilized by small systems. In this publication, small systems are systems that serve 10,000 or fewer customers. This document contains the information and methodology that small system personnel need to make informed decisions about their residuals. The Water Research Foundation previously published Water Treatment Residuals Engineering (2006), a comprehensive guidance manual on this topic. This work is based on that previous report, but is focused on processes utilized by small systems. Water systems serving a small number of customers generally need to comply with the same regulatory requirements as do larger systems, but they rarely have the resources to research all the different options available to provide safe and affordable drinking water. This is particularly true for systems that need to change treatment to comply with a new regulation, and in doing so, produce a new type of residual. All water treatment processes produce some type of waste product. It is important for water system owners to dispose of this material in an affordable manner that meets all regulations. When a water system needs to install a new treatment process, handling and disposal of the waste material, or residuals is often the most costly and complicated step of the new treatment process, but unfortunately it is a step that is often ignored until the new process is in place. This document first presents information on how to determine the type, the amount and the characteristics of residuals produced by water treatment processes (Chapters 2, and 3.) Then, regulatory constraints for handling and disposal of residuals are described (Chapter 4.) Chapter 5 describes how residual material can be conveyed and also various means of dewatering the residuals. Arsenic and radioactivity-bearing residuals are discussed in depth in Chapter 6. Finally, Chapters 7 through 10 describe the various methods available for the ultimate disposal of water treatment residuals. TYPES OF RESIDUALS Water treatment processes are utilized to remove contaminants from water or to alter the contaminant properties in order to produce a potable water. All water treatment processes that remove contaminants produce a waste by-product. That by-product may be liquid, solid, a mixture of the two, or a gaseous vapor. These water treatment plant wastes are referred to as residuals. The names of individual waste streams are generally a function of how the residual is produced. There are five general types of water treatment processes that produce residuals. The first is produced at those plants that coagulate and oxidize a surface water to remove particles (both organic and inorganic) and dissolved contaminants such as color, organic carbon, iron, manganese, and occasionally trace metals. These coagulation plants produce two major residuals, sedimentation (or clarifier) sludge and spent filter backwash water (SFBW). The second type of treatment plants are those that practice chemical softening for the removal of calcium and magnesium. These plants may also remove trace metals, radioactivity, xvii

20 and particles if surface water is being treated. These plants also produce a clarifier sludge and spent filter backwash water. Ion exchange processes as their name implies are used to remove cation or anion contaminants such as calcium and magnesium, arsenic, nitrate, and barium. These processes produce a brine residual as well as spent rinse water. There are also adsorption processes that may produce similar types of residuals. Some adsorption processes use throw away media such that the residual produced is the spent adsorption material. Adsorption media may also need to be backwashed so that a spent backwash water is produced. The fourth general category of treatment is when membranes are used to remove particulates or dissolved solids. In this case a concentrate is produced which consists of concentrated levels of the raw water contaminants that the membrane has rejected as well as any additives that may have been used prior to membrane treatment. Finally, gaseous residuals are produced by air stripping processes that release vapor to the atmosphere. These releases are primarily volatile organic compounds and radon. QUANTITIES AND CHARACTERISTICS The amount of material generated by a water treatment process is the first piece of information needed in order to plan for its treatment and disposal. Chapter 3 presents equations, graphs and measurement techniques that system personnel can use to estimate the quantity of residuals produced by different technologies. Also presented is a description of the methodology used to determine if a material is a solid or a liquid, and the testing USEPA requires to be used to determine if a material is hazardous. REGULATIONS Of particular importance to the disposal of residuals are the following federal regulations: Clean Water Act Resource Conservation and Recovery Act Safe Drinking Water Act Filter Backwash and Recycling Rule Atomic Energy Act Hazardous Materials Transportation Act How these laws affect residuals disposal is discussed in Chapter 4. SPECIAL WASTES Residuals from water treatment processes designed to remove arsenic and radioactive material pose special challenges to utilities. Not only can they contain high levels of the contaminant the treatment system has targeted, but they can also contain high levels of any contaminant that is present in the raw water. High levels of contaminants in residuals can result in the material being categorized as hazardous or radioactive. In that situation, the material has to be disposed of in specialized landfills, which is typically quite expensive. Chapter 6 discusses these residuals. xviii

21 DEWATERING AND ULTIMATE DISPOSAL Chapters are included that describe the various methods available to dewater residuals and to dispose of the resulting material. Descriptions, design parameters and expected results of nonmechanical dewatering practices are described in Chapter 5. An introduction to mechanical dewatering devices is also included. Water treatment residuals can be disposed of by means of: Landfill Land Application Beneficial Reuse Sewer or Direct Discharge Underground Injection Control wells Each of these methods requires compliance with regulations and restrictions. These are described in Chapters 7 through 10. Finally, since many states have authority to control the ultimate disposal of residuals, all of the state contacts in the drinking water, UIC and radiation programs are included in Appendix A. xix

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23 CHAPTER 1 INTRODUCTION Nearly all water treatment processes produce some type of waste product. It is important for water system owners to dispose of this material in an affordable manner that meets all regulations. When a water system needs to install a new treatment process, the handling and disposal of the waste material, or residuals is often the most costly and complicated step of the new treatment process, but unfortunately it is a step that is often ignored until the new process is in place. This document was prepared to aid small system owners, consultants and regulators better understand the issues and constraints involved with the treating and disposal of the byproducts water treatment systems create when they treat their water. It is aimed at small systems, which, in this publication, are systems that serve 10,000 or fewer customers. The size of a water treatment utility is usually classified by USEPA according to the number of customers it serves. Table 1.1, adapted from USEPA s Office of Ground Water shows the range of water production flows that would be expected at plants serving the populations shown. In order to estimate the amount of residuals produced by a water plant the amount of water treated the flow- is needed. This document is meant to assist those systems serving fewer than 10,000 people. From Table 1.1, it can be seen that systems serving 10,000 or fewer people will typically produce 1.5 mgd or less. USEPA estimates that there are about 48,000 of these systems, serving a population of 52.4 million, which is about 18 percent of the U.S. population. There are also more than 20,000 nontransient, noncommunity water systems (NTNCWSs) and nearly 100,000 TNCWSs, or transient noncommunity water systems (USEPA 1999). Most systems serving fewer than 10,000 customers use groundwater as a source. Water systems serving a small number of customers need to comply with the same regulatory requirements as do larger systems, but they rarely have the resources to research all the different options available to provide safe and affordable drinking water. This is particularly true for systems that need to change treatment to comply with a new regulation, and in doing so, produce a new type of residual. Category Table 1.1 Water system categories Median Average flow Population range population* (mgd) Flow range (mgd) , ,001 3,300 1, ,301 10,000 5, Source: Adapted from DPRA 1993 *Calculated from FRDS database 7/96 1

24 These small systems differ from their larger counterparts in terms of ownership, resources and complexity. The intent of this document is to assist small system personnel in evaluating residuals processes in terms of complexity and regulatory requirements in a way that is meaningful to a small system. It is not meant as a guide to the selection of a new water treatment process, but it does provide the information needed to understand what is involved in the handling and disposal of the by-products of existing and new processes. Because of the expense that may be involved with disposal of certain types of wastes that exceed regulatory limits, the most cost-effective treatment may be a compromise between treatment optimization and maintaining the characteristics of the waste stream below specified levels (Idaho DEQ 2007). Much information on small systems and on residual treatment is readily available from the Water Research Foundation, the USEPA, AWWA, and the National Rural Water Association as well as from state regulatory agencies. For more information on small system issues, go to HOW TO USE THIS MANUAL The intent of this manual is to highlight the information applicable to small systems from existing sources and to direct users to these existing sources. It s intended to allow the user to determine the residuals impact of treatment choices and so choose the system that makes the most sense in terms of residuals disposal and water quality. It is also meant to demonstrate that solids are much easier to dispose of than liquid residuals, and that is also a good practice to avoid the production of a material that could be considered hazardous or radioactive. The document is organized as follows: Chapter 1 Introduction Chapter 2 What kind of residuals do water treatment processes produce? Chapter 3 Quantities and Characteristics Chapter 4 What are the regulations that govern the disposal and handling of these residuals? Chapter 5 Thickening and Dewatering Chapter 6 Special Wastes Chapter 7 Landfill Chapter 8 Land Application and Beneficial Uses Chapter 9 Sewer and Direct Discharge Chapter 10 Underground Injection Chapter 11 Summary Appendix A is very important in the planning of any residuals project. It contains all of the State contacts in the drinking water, UIC and radiation programs. 2

25 CHAPTER 2 WHAT KIND OF RESIDUALS ARE PRODUCED? Water treatment processes remove contaminants from water or alter the contaminant properties in order to produce potable water. All water treatment processes that remove contaminants produce a waste by-product. That by-product may be liquid, solid, a mixture of the two, or a gaseous vapor. These water treatment plant wastes are referred to as residuals. Small systems are looking at adding different types of treatment to meet new regulatory requirements as shown in Table 2.1. Although this manual isn t meant to help in the decision process involved with choosing treatment technologies themselves, Table 2.2 shows the types of treatments that USEPA has indicated can be used to meet those new regulations. This chapter discusses the types of residuals produced by these treatments. To find out more about strategies for compliance with regulations for small systems, go to: and To start assessing the disposal options available for treatment residuals, a system operator must know: Whether the residuals produced are solids or liquids Some information on the chemical and physical quality of the material How much of this material is produced This chapter and the next help answer those questions. WHAT RESIDUALS ARE PRODUCED? Table 2.3 shows the residuals produced by the treatment processes USEPA has determined to be the Best Available Technologies (BAT) or Small System Compliance Technologies (SSCT) for regulated contaminants. BATs can be implemented by any utility for compliance, but the SSCT can only be used by utilities serving <10,000 customers. As shown in these tables, each process can produce a number of waste streams, all of which have unique handling and disposal requirements. Each type of process and the waste streams resulting from its use is briefly described in this chapter. There are six general types of water treatment processes that produce residuals: Common Waste Products from Water Treatment Clarifier/Sedimentation sludge Spent filter backwash water Spent rinse water/cleaning solution Brine Spent adsorption material Concentrate Gas 3

26 Table 2.1 Small system regulatory summary Regulation Summary What systems are affected? Microbiological (National Primary Drinking Water Regulations (NPDWR) Volatile Organic Chemicals (NPDWR) Coliform MCL MCLs* All types and sizes All CWSs and NTNCWSs Radionuclides MCLs* All types and sizes Radon MCLs* All types and sizes Inorganic Chemicals (NPDWR) MCLs* All CWSs and NTNCWSs; transient systems exempt except for nitrates, nitrites Total Coliform Rule No more than 5% of samples positive for coliform; distribution system sampling Surface Water Treatment Rule 3 Log (99.9%) removal of Giardia, 4 Log (99.9%) virus inactivation filtration treatment specified All types and sizes All surface water and groundwater under the direct influence of surface water Lead and Copper Rule Distribution system action levels All CWSs and NTNCWSs Arsenic MCLs* All CWSs and NTNCWSs Groundwater Rule Long Term 1 Enhanced Surface Water Treatment Rule Filter Backwash Rule Appropriate use of disinfectants, multibarrier approach All systems using groundwater as source 2 Log removal (99%) of Cryptosporidium, 0.2 NTU for Turbidity, TOC H reductions for precursor removal Recycling filter backwash with treatment All surface water and groundwater under the direct influence of surface water All conventional (flocculation/coagulation/sedimentation) and direct filtration systems State 1 Disinfectants/Disinfection By- Total Trihalomethane MCL reduced to CWSs and NTNCWSs that use a Products Rule (D/DBP) 0.08 mg/l; 5 Haloacetic acids total of mg/l; chlorite MCL 1.0 mg/l; bromate mg/l MCL; maximum residual disinfectant levels set at 4.0 mg/l as Cl 2 and 0.8 mg/l as ClO 2. chemical disinfectant Long Term 2 Enhanced Surface Enacted together to balance microbial All types and sizes Water Rule and Stage 2 D/DBP Rules and disinfectant by-product formation; Possible lowering of current MCLs and distribution system requirements Contaminant Candidate List (CCL) Possible new MCLs All types and sizes Source: USEPA 2003a *For MCL information, please visit: H Total Organic Carbon 4

27 Table 2.2 Regulated contaminant list (partial) and possible removal technologies Microbial Contaminants and Turbidity Turbidity (suspended material) Filtration Coliform Bacteria, Viruses, Cryptosporidium oocysts and Giardia cysts Radioactivity Turbidity reduction by filtration as noted above followed by disinfection Beta particle and photon activity Mixed bed ion exchange, reverse osmosis Gross Alpha Particle activity Radium 226 and Radium 228 Radon Uranium Treatment method depends on the specific radionuclide (e.g. radium, radon, or uranium) Cation ion exchange, reverse osmosis Activated carbon Health-Related Inorganic Contaminants Antimony Arsenic (+3) Arsenic (+5) Organic Arsenic complexes Asbestos Barium Beryllium Cadmium Chromium (+3) Anion ion exchange, activated alumina, microfiltration, reverse osmosis Microfiltration, reverse osmosis Reverse osmosis Iron based media, anion ion exchange, activated alumina, reverse osmosis Activated carbon Organic Chromium Complexes Activated carbon Copper, Nickel Fluoride Lead Mercury (+2) Mercury (HgCl 3-1) Organic Mercury Complexes Nitrate and Nitrite Selenium (+4) Selenium (+6) Sulfate Submicron filtration, reverse osmosis Cation ion exchange, reverse osmosis Submicron filtration and carbon, activated alumina, cation ion exchange, reverse osmosis Submicron filtration, cation ion exchange, reverse osmosis Cation ion exchange, reverse osmosis Cation ion exchange, reverse osmosis Activated alumina, reverse osmosis Cation ion exchange, submicron filtration and carbon, reverse osmosis Cation ion exchange, submicron filtration and carbon, reverse osmosis Anion ion exchange, reverse osmosis Activated carbon Anion ion exchange, reverse osmosis, biological treatment Submicron filtration and carbon, anion ion exchange, activated alumina, reverse osmosis Anion ion exchange, activated alumina, reverse osmosis Anion ion exchange, activated alumina, reverse osmosis (continued) 5

28 Health-Related Organic Compounds Table 2.2 (Continued) Use activated carbon or aeration to remove the following contaminants Adipates Benzene Carbon Tetrachloride Dibromochloropropane Dichlorobenzene (O-, m-, p-) 1,2-Dichloroethane 1,1-Dichloroethene Cis- and trans-1,2-dichloroethene 1,2-Dichloropropane Ethylbenzene Ethylene Dibromide Hexachlorocyclopentadiene Monochlorobenzene Styrene Use activated carbon to remove the following contaminants Alachor Aldicarb Aldicarb Sulfone Aldicarb Sulfoxide Atrazine Benzo(a)anthracene (PAH) Benzo(a)pyrene (PAH) Benzo(b)fluoranthene (PAH) Benzo(k)fluoranthene (PAH) Butyl benzyl phthlate (PAH) Carbofuran Source: USEPA 2003a Treatment Spent resins/media Chlordane Chrysene (PAH) 2,4-D Dalapon Di (2-ethylhexyl) adipate Dibenz (a,h)anthracene (PAH) Glyphosate Heptachlor Epoxide Hexachlorobenzene Indeno (1,2,3-c,d) Pyrene (PAH) Table 2.3 Residual type by treatment technology Solid Spent membranes Sludge Brine Types of residuals Spent backwash water Coagulation/ Filtration Τ Τ Τ Lime softening Τ Τ Τ Tetrachloroethylene Toluene 1,2,4-Trichlorobenzene 1,1,1-Trichloroethane 1,1,2-Trichloroethane Trichloroethylene Trihalomethanes Lindane Methoxychlor Oxamyl Pentachlorophenol Picloram Polychlorinated Biphenyls Simazine 2,3,7,8-TCDD (dioxin) Toxaphene 2,4,5-TP (Silvex) Rinse water Ion exchange Τ Τ Τ Τ Adsorption Τ Τ Τ Τ Liquid Acid neutralization water Concentrate Membranes Τ Τ Τ Aeration! Gaseous release Reverse osmosis Τ Τ Iron based media Τ Τ Biological treatment Green sand filtration Τ Τ Τ Activated alumina Τ Τ Τ Τ Τ Source: Adapted from USEPA 2005a Τ 6

29 Coagulation/filtration Lime softening Ion exchange Adsorption Membranes Aeration The first general category of residuals is produced at those plants that coagulate and oxidize a surface water to remove particles (both organic and inorganic) and dissolved contaminants such as color, organic carbon, iron, manganese, and occasionally trace metals. These coagulation plants produce two major residuals, sedimentation (or clarifier) sludge and spent filter backwash water (SFBW). They can also produce spent filtration media, although this is produced only once in several years. The second type of treatment plants are those that practice softening for the removal of calcium and magnesium by using lime or sodium hydroxide addition. These plants may also remove trace metals, radioactivity, and particles if a surface water is being treated. These plants also produce a clarifier sludge and spent filter backwash water, and spent filtration media. Ion exchange processes as their name implies are used to remove cation or anion contaminants such as calcium and magnesium, arsenic, nitrate and barium. These processes produce a brine residual as well as spent rinse water, spent media and often, spent filter backwash water. Adsorption processes can produce residuals similar to those produced by ion exchange if the material is regenerated. Many adsorption processes can use throw away media such that the residual produced is the spent adsorption material. Adsorption media may also need to be backwashed and so a spent backwash water is produced. The fifth general category of treatment is when membranes are used to remove particles or dissolved solids. In this case a concentrate is produced that consists of concentrated levels of the raw water contaminants that the membrane has rejected as well as any additives that may have been used prior to membrane treatment. Cleaning solutions and the spent membranes are also considered to be residuals. Finally, gaseous residuals are produced by air stripping processes that release vapor to the atmosphere. These releases that can be of concern are primarily volatile organic compounds and radon. COAGULATION WASTE STREAMS Coagulation of surface waters is by far the most commonly used water treatment technology. It is historically used to remove turbidity and reduce biological activity of the source water. Recently, it has been shown to be effective at removing raw water arsenic. Figure 2.1 shows a schematic of a conventional coagulation treatment process showing the typical waste products. Some water plants also have a pre-sedimentation step. This is generally used only when the raw water source is high in settleable solids. Smaller systems often utilize package filtration plants that incorporate coagulation/sedimentation with filtration. The residuals produced in these package plants are the same as discussed here. 7

30 Raw Rapid Mix Flocculation Basin M M M Sedimentation Basin Filters Process Residuals Streams Sedimentation Basin Sludge Spent Filter Backwash Water Filtered Water Secondary Residual Streams Thickener/Lagoon Thickener Supernatant Residuals Treatment Processes often Combined Thickened Sludge SFBW Clarified Stream SFBW Clarifier SFBW Settled Solids M Equalization Basin Recycle Sewer Stream Discharge Dewatering Residuals Streams Recycle Sewer Stream Discharge Liquid Stream Mechanical/ Non-Mechanical Dewatering Dewatered Solids or Sludge Cake Recycle Sewer Stream Discharge Thickener Sewer Other Source: Cornwell 2006 Figure 2.1 Major residual streams commonly generated by coagulation water treatment plants The coagulation process itself generates most of the waste solids. Generally a metal salt (aluminum or iron) is added as the primary coagulant. In addition to the coagulant other solids producing chemicals such as powdered activated carbon, polymer, clay, lime, or activated silica may be used. These added chemicals will produce waste solids. They are usually removed, along with the solids in the raw water, in a sedimentation tank or clarifier. These residuals are referred to as sedimentation or clarifier sludge. They are more specifically referred to by the type of coagulant used. For example, alum sludge is the residual produced from the use of an aluminum based coagulant and iron sludge is the residual produced by the use of an iron based coagulant. When dissolved air flotation is used as the clarification step, the residuals are referred to as float. In areas with very good raw water quality, the clarification step is occasionally omitted and the solids are removed by filtration only. This process, commonly known as direct filtration, is usually used for water with low turbidity and is one that requires low levels of coagulant. It is also used in arsenic removal coagulation filtration processes. The residuals can be further treated on site resulting in additional residuals streams. A thickener treating clarifier sludge or clarifier sludge plus SFBW produces thickened sludge (which could be thickened alum or iron sludge) and thickener supernatant. A thickener that only treats SFBW will produce SFBW settled solids. A dewatering device will produce a sludge cake (also called dewatered solids) as well as a liquid stream. The liquid stream is referred to by the type of dewatering used such as filtrate, decant, centrate, and pressate. 8

31 The second major residual produced by coagulation/filtration is from the batch process of backwashing the filters, spent filter backwash water (SFBW). This waste stream is produced at very high flow rates for short periods of time. Another waste product that is occasionally produced in a coagulation-based plant is spent filtration media and spent granular activated carbon (GAC). GAC is sometimes used in the filters or post-filtration. When its use is for taste and odor removal, the carbon is disposed of after its capacity is exhausted. When its use is for continuous low-level organics removal it is often returned to the vendor for regeneration. SOFTENING WASTE STREAMS Wastes produced by softening plants represent the second major waste product produced by the water industry. Fortunately, these wastes are generally more easily dewatered than are coagulant wastes, although the presence of some trace inorganics can make their proper disposal difficult. There are many variations of the softening process. Chemical addition, flow processes, and the subsequent waste quantities and characteristics are all dependent on raw water hardness and alkalinity, and the desired finished water quality. Softening is accomplished either by chemical precipitation of the calcium and magnesium or by the use of ion exchange resins. The former, traditionally called lime/soda ash softening is by far the most widely used softening process by larger facilities and ion exchange is common for small systems and as a home softener. In the lime method, lime is added for the removal of carbonate hardness, supplemented with the use of soda ash for non-carbonate hardness removal if required. From the standpoint of sludge economics, it is desirable to leave as much magnesium hardness in the water as considered acceptable. The less magnesium in the sludge, the easier it is to dewater. Figure 2.2 is a simplified softening plant schematic. Several variations and complications of Figure 2.2 are used to obtain the desired water quality and minimize costs. In softening plants there are usually two waste streams produced: the lime sludge from the clarifier and the spent filter backwash water. Some plants will add a polymer or metal salt to aid in the removal of fine precipitates or color or turbidity present in the original water. From a sludge viewpoint, the addition of metal salts should be held to a minimum as the presence of metal hydroxides could significantly increase sludge treatment costs. The use of polymers and slurry recirculation can help minimize the use of these coagulants. As with coagulation plants, spent filter backwash water is produced at high flow rates for short periods of time. Chemical Additions Oxidant Lime Soda Ash Coagulant Coagulant Aid Coagulant Coagulant Aid Coagulant CO2 Oxidant Filter Aid Fluoride Corrosion Control Oxidant M M M M Raw Water Clarifier Filtration Rapid Mix Reaction Zone Recarbonation Softening Residual Streams Source: Cornwell 2006 Lime Sludge Figure 2.2 Waste producing processes in softening plants Spent Filter Backwash Water 9

32 ION EXCHANGE AND MEDIA ADSORPTION RESIDUALS Removal of trace inorganic substances such as arsenic, barium, cadmium, chromium, fluoride, lead, nitrate, selenium, silver, radium and uranium by ion exchange (IX) or adsorption is becoming widely used by small systems. Ion exchange (IX) involves the selective removal of charged inorganic species from water using an ion-specific resin. Removal of hardness by IX has been used for many years by small systems. Resins can be categorized as anion exchange or cation exchange resins. Anion exchange resins selectively remove anionic species such as nitrate (NO - 3 ) and fluoride (F - ). Anion exchange resins are often regenerated with sodium hydroxide or sodium chloride solutions, which replace the anions removed from the water with hydroxide (OH - ) or chloride (Cl - ) ions, respectively. Cation exchange resins are used to remove undesired cations from water and exchange them for protons (H + ), sodium ions (Na + ) or potassium ions (K + ). Anion exchange is a USEPA identified best available technology (BAT) for arsenic removal. Arsenic ions are exchanged for chloride ions. Ion exchange has also been used historically to soften water. In water softening by ion exchange the water containing the hardness is passed through a column containing the ion exchange material. The hardness in the water exchanges with an ion (usually sodium) from the ion exchange resin. When used for softening the exchange results in essentially 100 percent removal of the hardness from the water until the exchange capacity of the ion exchange material is reached. When the ion exchange resin becomes saturated, breakthrough occurs because the hardness is no longer removed. At this point the ion exchange material is regenerated. During regeneration, the hardness is removed from the material by passing water containing a large amount of sodium chloride (NaCl) through the column. The process is shown in Figure 2.3. This spent regenerant or brine is the residual stream that requires disposal. It contains the excess or left over NaCl, and the ions removed. Ocean brine disposal is sometimes practiced as well as discharge to municipal wastewater systems, or to receiving streams. Two additional waste streams are also produced in conjunction with ion exchange. Prior to the use of the regenerant, the column is usually backwashed in an upflow mode to remove any suspended material. After regeneration the column is rinsed, which will produce a waste stream also high in dissolved solids. Adsorption, particularly with a media created specifically for a particular contaminant removal is widely used by small systems because of the ease of operation. For example, many iron based media developed specifically to remove arsenic from groundwaters are now being used by small systems. The residuals produced by adsorption are the spent media as well as the rinse or spent filter backwash water. Adsorption media can be regenerated like an ion exchange media or the spent media can be replaced without regeneration. Operationally, adsorption is very similar to ion exchange and the residuals produced are very similar when the media is regenerated. One notable difference, however is that certain media have been developed for specific contaminants and cannot be regenerated, or are not regenerated. This avoids the production of a waste regenerate solution, but adds the operating cost of media disposal and replacement. In this case, the media is disposed of after break-through occurs. 10

33 Raw Water Source Pre-Filter Ion Exchange Column Spent Backwash/Rinse Ion Exchange Resin Spent Regenerant (Brine) [To Waste Disposal] Backwash/Rinse Product/Treated Water Regenerant Regeneration Streams Source: SAIC 2000 Figure 2.3 Schematic of ion exchange process with upflow regeneration MEMBRANE AND REVERSE OSMOSIS RESIDUALS Membranes can be used to remove a variety of contaminants. The size of contaminant removed depends upon the type of membrane selected and its associated pore size. As membrane systems are increasingly used for water utility applications, the management of their residuals has become a growing challenge. Membrane technology uses a driving force (e.g., electrical, pressure/vacuum, etc.) to separate contaminants from the water. Pressure-driven membranes include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). Electrically-driven membranes include electrodialysis (ED) and its variant electrodialysis reversal (EDR). Whereas MF and UF membranes are designed for particle removal and use low-pressure, NF, RO, and ED/EDR are designed for desalination and softening. MF and UF processes are low pressure membranes that primarily remove particles. They are used commonly by small systems to treat relatively clean groundwaters, springs and streams for pathogen removal. They are also used in the coagulation microfiltration process for arsenic removal. The particles build up on the membranes and are backwashed off to clean the membrane. This membrane backwash residual contains the particles that were removed from the source water. Occasionally a coagulant or PAC is added to the raw water prior to the membrane and that will also be in the membrane backwash. These residuals are referred to as membrane backwash. High pressure membranes such as RO and NF primarily remove dissolved ions. These membranes produce a fairly continuous residual that contains the concentrated ions that the membrane rejects. The waste streams are referred to as concentrate and occasionally brine. 11

34 Cleaning solutions are used in membrane operations. Those residuals reflect the chemicals used in the cleaning process, so the resulting chemical cleaning waste includes some remaining active chemical ingredient, as well as dissolved organic materials, suspended solids, and salts from chemical reactions between the chemicals and foulants (AWWA 2003). Chlorine residuals in concentrates and cleaning wastes may range from 1 mg/l to 1,000 mg/l as Cl 2, and ph may be acidic (ph<6) or basic (ph>9) depending on the chemicals used. When surfactants are employed they may cause foaming when the spent cleaning solution is discharged. IRON AND MANGANESE OXIDATIONS RESIDUALS Iron and manganese are often removed by oxidation followed by filtration. Oxidation is achieved through the addition of air, chlorine, or permanganate followed by granular media filtration. Other inorganic contaminants, most notably arsenic (as arsenate) are also removed by this process. The insoluble form of the contaminant is deposited on the media. When the filters are backwashed, SFBW is generated and this liquid plus suspended solids waste contains the contaminants. Greensand filtration, with the addition of potassium permanganate also removes a variety of contaminants including iron, manganese and in some cases arsenic. Again, the waste generated by this process is through backwashing of the filter, spent filter backwash water (SFBW). 12

35 CHAPTER 3 QUANTITIES AND CHARACTERISTICS The amount of material generated by a water treatment process is an important piece of information needed in order to plan for its treatment and disposal. In this chapter, methods to estimate quantities of different types of residuals will be described. Characteristics of the material will also be discussed. COAGULANT SOLIDS Coagulant solids are produced from coagulation/filtration, softening and some iron and manganese removal processes (oxidation/filtration.) The quantity of solid/liquid wastes (which are commonly referred to as sludge) generated from water treatment plants depends upon the raw water quality, the type and dosage of chemicals used, and the efficiency of the treatment process. One of the most difficult tasks facing the utility or engineer in planning and designing a residuals treatment process is determining the amount of waste to be handled. The waste quantity is usually determined as an annual average for a given design year and is a function of flow projections. As important as average production values is information on seasonal and monthly variations. It is not unusual for order of magnitude differences in sludge production to exist for different months of the year. Sludge volumes from sedimentation basins tend to be 0.1 to 3 percent of the raw water flow with one national survey finding an average of 0.6 percent. (AWWA 1999) There are three methods used to determine sludge quantities. None are completely accurate. Those methods are: calculations, coagulant mass balance analysis, and field determination. Here, an explanation of how to use calculations to estimate the quantity of coagulant sludge will be shown, as this is the most useful method for small systems. Further information on mass balance calculations and field measurements can be found in Cornwell, The amount of alum (or iron) sludge generated can be calculated fairly closely by considering the reactions of alum or iron in the coagulation process. When alum is added to water as aluminum sulfate, the reaction results in the production of a solid species of aluminum hydroxide. The resulting aluminum hydroxide species (or coagulant sludge) is such that 1 mg/l of alum as dry weight product added to water will produce approximately 0.44 mg/l of inorganic aluminum solids. Suspended solids present in the raw water produce an equivalent weight of sludge solids since they are non-reactive. It can be assumed that other additives such as polymer and powdered activated carbon produce sludge on a one to one basis. The amount of sludge produced in an alum coagulation plant for the removal of turbidity is then: S = 8.34 Q (0.44 Al + SS + A) (3.1) 13