Implementation of Arsenic Treatment Systems Part 1. Process Selection

AWWA

Research Foundation

Implementation of Arsenic Treatment Systems Part 1. Process Selection

Subject Area: Water Treatment

Implementation of Arsenic Treatment Systems Part 1. Process Selection

The mission of the Awwa Research Foundation is to advance the science of water to improve the quality of life. Funded primarily through annual subscription payments from over 1,000 utili ties, consulting firms, and manufacturers in North America and abroad, AwwaRF sponsors research on all aspects of drinking water, including supply and resources, treatment, monitoring and analysis, distribution, management, and health effects. From its headquarters in Denver, Colorado, the AwwaRF staff directs and supports the efforts of over 500 volunteers, who are the heart of the research program. These volunteers, serving on various boards and committees, use their expertise to select and monitor research studies to ben efit the entire drinking water community. Research findings are disseminated through a number of technology transfer activities, includ ing research reports, conferences, videotape summaries, and periodicals.

Implementation of Arsenic Treatment Systems Part 1. Process Selection_____ Prepared by: Zaid Chowdhury and Sunil Kommineni Malcolm Pirnie, Inc. 432 N. 44th Street, Suite 400 Phoenix, AZ 85008 Ramesh Narasimhan and John Brereton Narasimhan Consulting Services Inc. 3150 N. 24th Street, Suite D-104 Phoenix, AZ 85016 Gary Amy and Shahnawaz Sinha University of Colorado at Boulder ECOT 441 Boulder, CO 80309 Jointly sponsored by: Awwa Research Foundation 6666 West Quincy Avenue Denver, CO 80235-3098 and United States Environmental Protection Agency 1200 Pennsylvania Avenue, NW Washington, DC 20460-0003 Published by the Awwa Research Foundation and American Water Works Association

Disclaimer This study was jointly funded by the Awwa Research Foundation (AwwaRF) and the U.S. Environmental Protection Agency (USEPA) under Cooperative Agreement No. CR827268-01. AwwaRF and USEPA assume no responsibility for the content of the research study reported in this publication or 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 or endorsement of AwwaRF or USEPA. This report is presented solely for informational purposes.

Library of Congress Cataloging-in-Publication Data has been applied for;

Copyright 2002 by Awwa Research Foundation and American Water Works Association Printed in the U.S.A.

ISBN 1-58321-236-1

Printed on recycled paper

CONTENTS LIST OF TABLES.......................................................................................................................xiii LIST OF FIGURES....................................................................................................................... xv FOREWORD .............................................................................................................................xvii ACKNOWLEDGMENTS ...........................................................................................................xix EXECUTIVE SUMMARY..........................................................................................................xxi CHAPTER 1: BACKGROUND AND INTRODUCTION........................................................... 1 Background......................................................................................................................... 1 Regulatory Update................................................................................................... 1 Compliance Status................................................................................................... 2 Introduction......................................................................................................................... 3 Project Objectives................................................................................................... 3 Proven Arsenic Treatment Technologies................................................................ 5 Emerging Arsenic Treatment Technologies............................................................ 9 CHAPTER 2: TREATMENT TECHNOLOGIES AND WATER QUALITY CONSIDERATIONS........................................................................................................ 13 Arsenic Chemistry............................................................................................................. 13 Ion Exchange..................................................................................................................... 15 Water Quality Considerations............................................................................... 19 Regeneration.......................................................................................................... 22 Residuals Handling............................................................................................... 22 Adsorptive Processes......................................................................................................... 22 Water Quality Considerations............................................................................... 25 Regeneration..........................................................................................................29 Residuals Handling for On-Site AA Regeneration Systems................................. 29 Throwaway AA..................................................................................................... 30 Granular Ferric Hydroxide.................................................................................... 30 Precipitative Processes...................................................................................................... 36

Conventional Treatment........................................................................................36 Iron and Aluminum Coagulation........................................................................... 38 Water Quality Impacts.......................................................................................... 39 Residuals Handling............................................................................................... 40 Enhanced Softening............................................................................................... 42 Oxidation/Filtration Processes.............................................................................. 44 Greensand Filtration Systems................................................................................ 45 Iron Removal Plants.............................................................................................. 46 Residuals Handling (for Oxidation/Filtration Systems)........................................ 48 Membrane Processes......................................................................................................... 48 Coagulation-Assisted Microfiltration.................................................................... 49 Water Quality Considerations............................................................................... 50 Residuals Handling............................................................................................... 51 Nanofiltration and Reverse Osmosis..................................................................... 52 Water Quality Considerations............................................................................... 53 Residuals Handling............................................................................................... 55 Partial Stream Treatment................................................................................................... 56 Point of Entry vs. Wellhead Treatment............................................................................. 57 CHAPTER 3: RESIDUALS HANDLING AND DISPOSAL..................................................... 59 Residuals Handling Options.............................................................................................. 59 Ion Exchange......................................................................................................... 59 Adsorptive Processes............................................................................................. 60 Precipitative Processes.......................................................................................... 61 Membrane Processes............................................................................................. 62 Dewatering Considerations .................................................................................. 62 Hazard Potential of Arsenic Residuals.............................................................................. 63 Computing Arsenic Residuals Volumes and Characteristics............................................ 66 Ion Exchange.........................................................................................................67 Adsorptive Processes............................................................................................. 71 Precipitative Processes..........................................................................................77

VI

Membrane Processes.............................................................................................78 CHAPTER 4: SELECTION AND INTEGRATION OF ARSENIC REMOVALTECHNOLOGIES......................................................................................... 81 Decision Tree Tool for Systems with Existing Treatment................................................ 82 Decision Trees for Existing Treatment Systems................................................... 82 Surface Water - Existing Conventional Treatment............................................... 83 Surface Water - Existing Direct Filtration............................................................ 86 Groundwater/Surface Water - Existing Precipitative Softening........................... 88 Groundwater/Surface Water - Existing Iron Removal Process (Oxidation/Filtration)................................................................................ 90 Groundwater/Surface Water - Existing Iron and Manganese Removal Process (Manganese Greensand Filtration)............................................................ 90 Groundwater- No Existing Treatment................................................................... 93 Spreadsheet Decision Tree Tool for Systems with No Existing Treatment...................... 96 Applicable Treatment and Residuals Handling/Disposal Trains.......................... 96 Decision Analysis Tool Overview........................................................................ 98 Mandatory Inputs..................................................................................................99 Residuals Estimations........................................................................................... 99 Costs Calculations...............................................................................................100 Other Computations............................................................................................ 100 Critical Decision Drivers and Technology Feasibility Evaluation...................... 100 Qualitative Decision Drivers and Ranking of Feasible Alternatives.................. 102 Summary Output of the Most Preferred Alternatives......................................... 103 Qualitative Guidance on Innovative Technologies......................................................... 103 CHAPTERS: COSTS................................................................................................................ 105 Introduction..................................................................................................................... 105 Treatment Unit Costs.......................................................................................... 105 Residuals Handling and Disposal Unit Costs...................................................... 107 Treatment Cost Assumptions.......................................................................................... 108

Vll

Enhanced Coagulation/Filtration......................................................................... 108 Enhanced Lime Softening................................................................................... 113 Direct Filtration to Conventional Filtration........................................................ 114 Throwaway Activated Alumina.......................................................................... 114 Granular Ferric Hydroxide.................................................................................. 115 Conventional Activated Alumina........................................................................ 116 Ion Exchange....................................................................................................... 118 Coagulation-Assisted Microfiltration.................................................................. 119 Nanofiltration/Reverse Osmosis......................................................................... 119 Electrodialysis Reversal...................................................................................... 120 Iron/Manganese Removal................................................................................... 120 Residuals Handling and Disposal Cost Assumptions..................................................... 120 Residuals Handling Alternatives......................................................................... 121 Residuals Disposal Alternatives.......................................................................... 123 Pre-Oxidation Cost.......................................................................................................... 126 Land Cost........................................................................................................................ 127 CHAPTER 6: UTILITY CASE STUDY SUMMARIES .......................................................... 129 City of Phoenix, Arizona................................................................................................. 129 Background......................................................................................................... 129 Operational Characteristics................................................................................. 131 Evaluation of Treatment Technologies for Well #280........................................ 134 Systemwide Evaluation of Treatment Technologies........................................... 136 Blending Options................................................................................................. 136 Summary............................................................................................................. 137 City of Tucson, Arizona.................................................................................................. 138 Background......................................................................................................... 138 Operational Characteristics................................................................................. 138 Evaluation of Treatment Technologies Using Spreadsheet Tool........................ 139 Summary............................................................................................................. 140 City of Scottsdale, Arizona............................................................................................. 141

Vlll

Background...................................................................................................-.. 141 Operational Characteristics................................................................................. 142 Evaluation of Treatment Technologies Using Spreadsheet Tool........................ 143 Summary............................................................................................................. 144 Metropolitan Water District, Tucson, Arizona................................................................ 145 Background......................................................................................................... 145 Alternative Source Waters .................................................................................. 145 Evaluation of Treatment Technologies Using Spreadsheet Tool........................ 146 Summary............................................................................................................. 147 Water System A (Anonymous), Arizona........................................................................ 148 Background......................................................................................................... 148 Operational Characteristics................................................................................. 150 Evaluation of Treatment Technologies for Location A2, Well# 4...................... 150 Systemwide Evaluation of Treatment Technologies........................................... 152 Summary............................................................................................................. 154 Water System B (Anonymous), Arizona......................................................................... 154 Background......................................................................................................... 154 Operational Characteristics................................................................................. 156 Evaluation of Treatment Technologies Using Spreadsheet Tool........................ 156 Systemwide Evaluation of Treatment Technologies........................................... 158 Summary............................................................................................................. 158 Los Angeles Department of Water and Power, California.............................................. 159 Background......................................................................................................... 159 Operational Characteristics................................................................................. 160 Evaluation of Treatment Technologies Using Spreadsheet Tool........................ 161 Summary............................................................................................................. 162 South Tahoe Public Utility District, Nevada................................................................... 162 Background......................................................................................................... 162 Operational Characteristics................................................................................. 163 Evaluation of Treatment Technologies Using Spreadsheet Tool........................ 164 Systemwide Evaluation of Treatment Technologies........................................... 166

IX

Blending Options.................................................................................................168 Summary............................................................................................................. 169 East Valley Water System, Douglas County, Nevada.................................................... 169 Background......................................................................................................... 169 Operational Characteristics................................................................................. 170 Evaluation of Treatment Technologies Using Spreadsheet Tool........................ 171 Summary............................................................................................................. 173 Stagecoach Improvement District, Nevada..................................................................... 173 Background......................................................................................................... 173 Operational Characteristics.................................................................................174 Evaluation of Treatment Technologies Using Spreadsheet Tool........................ 175 Summary.............................................................................................................178 Carson City Water, Nevada............................................................................................. 179 Background.........................................................................................................179 Operational Characteristics.................................................................................181 Evaluation of Treatment Technologies for Well# 4............................................181 Systemwide Evaluation of Treatment Technologies........................................... 183 Blending Options.................................................................................................183 Summary.............................................................................................................186 Town of Bremen, Indiana................................................................................................ 186 Background.........................................................................................................186 Operational Characteristics.................................................................................187 Evaluation of Treatment Technologies Using Spreadsheet Tool........................ 188 Summary.............................................................................................................188 Water System C (Anonymous), Arizona......................................................................... 189 Background.........................................................................................................189 Operational Characteristics................................................................................. 189 Evaluation of Treatment Technologies Using Spreadsheet Tool........................ 189 Summary............................................................................................................. 191 Other Participating Utilities ............................................................................................ 191

CHAPTER 7: CONSIDERATIONS FOR INNOVATIVE TECHNOLOGIES........................ 193 Introduction..................................................................................................................... 193 Magnetic Ion-Exchange (MIEX ) Resin.....................................................193 Hydrous Iron Oxide Particles (fflOPs)............................................................... 194 Sand Ballasted Coagulation Sedimentation (Actiflo )...................................... 194 Immersed Membrane Technologies With Innovative Adsorbents...................... 195 Bench-Scale Testing....................................................................................................... 195 Evaluation of MIEX and HIOPs Arsenic Removal Capability........................ 195 Evaluation of Coagulants and Coagulation Processes for Arsenic Removal..... 198 Arsenic Removal With a Membrane System Coupled With MIEX and fflOPs........................................................................ 199 Results............................................................................................................................. 199 Evaluation of MIEX and HIOPs Arsenic Removal Capability in Synthetic Milli-Q Water...................................................................... 199 Evaluation of MEEX and HIOPs Arsenic Removal Capability in Synthetic Natural Water...................................................................... 200 Evaluation of Coagulants and Coagulation Processes for Arsenic Removal...... 203 Arsenic Removal by Immersed Membrane System Combined with MIEX and fflOPs.......................................................................... 204 Conclusions.....................................................................................................................206 CHAPTER 8: RECOMMENDATIONS FOR UTILITIES....................................................... 207 APPENDIX A: SPREADSHEET TOOL TABLES................................................................... 211 APPENDIXB: QUESTIONNAIRE..........................................................................................225 APPENDIX C: UNIT COST EQUATIONS.............................................................................. 235 APPENDIX D: INNOVATIVE TECHNOLOGIES.................................................................. 257 APPENDIX E: ARSENIC DECISION eTREE TOOL MANUAL........................................... 341 REFERENCES............................................................................................................................ 351 ABBREVIATIONS..................................................................................................................... 361 CONVERSION TABLE.............................................................................................................367

XI

TABLES 1.1.

Arsenic compliance monitoring methods and their detection limits................................... 3

2.1

Forms of arsenic in water.................................................................................................. 15

2.2

Physical properties of GFH media.................................................................................... 32

2.3

Arsenic removal with iron coagulation............................................................................. 41

3.1

Types of residuals generated from arsenic removal processes ......................................... 65

3.2

Arsenic treatment residuals characteristics....................................................................... 67

4.1

Qualitative assessment of selected innovative technologies........................................... 104

5.1

Summary of AA and GFH design parameters ......................................................\......... 116

5.2

Bed volumes versus influent arsenic concentration for activated alumina with and without pH adjustment.............................................................................................. 118

6.1

City of Phoenix water quality data summary.................................................................. 132

6.2

Costs for feasible technologies for well #280................................................................. 135

6.3

Technology ranking and annualized Cost....................................................................... 136

6.4

Summary of most preferred treatment option costs........................................................ 137

6.5.

Arsenic removal options for impacted POEs for City of Tucson, AZ............................ 140

6.6.

Arsenic removal options for impacted POEs for City of Scottsdale, AZ ....................... 144

6.7.

Arsenic removal options for impacted POEs for Metropolitan Water, AZ.................... 147

6.8.

Water quality data for Water System A, AZ...................................................................149

6.9.

Costs for feasible technologies for Well #4.................................................................... 151

6.10

Top three technologies selected using decision tree spreadsheet.................................... 152

6.11

Systemwide arsenic treatment summary......................................................................... 152

6.12

Summary of costs for preferred treatment technology.................................................... 154

6.13

Well flows and water quality for affected wells (if MCL = 10 ug/L)............................. 155

6.14


6.15

Treatment technology ranking, annualized cost and land requirement........................... 157

6.16


6.17

Water quality data for impacted active wells at South Tahoe Public Utility District (assuming a MCL of 10 ug/L)..................................................................... 164

6.18

Costs for feasible technologies for Airport Well............................................................ 166

Xlll

6.19

Treatment technology ranking, annualized cost and land requirement........................... 166

6.20


6.21


6.22

Treatment costs for blending wells ................................................................................. 169

6.23

Characteristics of new combined POE............................................................................ 170

6.24

Feasible technologies for arsenic removal...................................................................... 172

6.25

Treatment technology ranking and annualized cost for combined POE......................... 172

6.26

Arsenic treatment summary ............................................................................................ 172

6.27

Well flows and water quality for affected wells (if MCL = 10 ug/L)............................. 174

6.28

Feasible technologies for arsenic removal at Churchill Downs Well............................. 176

6.29

Treatment technology ranking and annualized cost for Churchill Downs Well............. 176

6.30

Feasible technologies for arsenic removal at CHR N/S combined POE......................... 177

6.31

Treatment technology ranking and annualized cost for the CHR N/S Combined POE.. 177

6.32

Systemwide summary of costs for most preferred technology....................................... 178

6.33

Well flows and arsenic levels for the Carson City System............................................. 180

6.34

Distribution system water quality summary.................................................................... 180

6.35


6.36

Top three technologies selected using decision tree spreadsheet.................................... 182

6.37


6.38


6.39

Possible blending scenarios............................................................................................. 185

6.40

Summary of treatment options for wells operated by Water System C.......................... 190

7.1

Raw water quality of Los Angeles Aqueduct Filtration Plant, CA................................. 196

7.2

Raw water quality of City of Phoenix, AZ...................................................................... 197

7.3

Summary of batch absorption experiments conducted with MIEX , EHOPs, and AA in Milli-Q water......................................................................................................... 200

7.4

Summary of batch absorption experiments conducted with MEEX , HIOPs, and AA on LADWP water...................................................................................................... 201

7.5

Summary of batch absorption experiments conducted with MIEX , HIOPs, and AA on City of Phoenix water........................................................................................... 202

XIV

FIGURES 2.1.

Speciation versus pH diagram for As(V) and As(ni)....................................................... 16

2.2.

Ion exchange treatment process schematic....................................................................... 18

2.3.

Arsenic peaking in IX columns ........................................................................................ 20

2.4.

IX residuals handling schematic ....................................................................................... 23

2.5.

Activated alumina treatment process schematic ............................................................... 25

2.6.

Impact of silica breakthrough on arsenic removal ........................................................... 27

2.7.

Regenerative AA residuals handling schematic................................................................29

2.8.

Process schematic of conventional treatment of surface water......................................... 37

2.9

Effect of coagulation pH on arsenic removal bench-scale test results from Verde River Water, Phoenix, AZ........................................................................................... 39

2.10

Process schematic for conventional coagulation-filtration and enhanced coagulation filtration system with residuals handling ....................................................................42

2.11

Residuals handling options from coagulation and lime softening processes.................... 43

2.12

Process schematic of iron removal process....................................................................... 47

2.13

Process schematic of manganese removal by greensand filtration................................... 47

2.14

CMF process schematic .................................................................................................... 50

2.15

CMF residuals handling schematic................................................................................... 52

2.16

NF/RO/EDR residuals handling schematic....................................................................... 56

2.17

Partial stream treatment schematic.................................................................................... 57

4.1.

Chart outlining when the decision trees will be used and when the spreadsheet tool has to be used.............................................................................................................. 83

4.2.

Arsenic decision tree for surface water treatment plants with conventional treatment as existing treatment.................................................................................................... 85

4.3.

Arsenic decision tree for surface water treatment plants with direct filtration as the existing treatment........................................................................................................ 87

4.4.

Arsenic decision tree for surface or groundwater treatment plants with precipitative softening as the existing treatment.............................................................................. 89

4.5.

Arsenic decision tree for surface or groundwater treatment plants with iron removal system using oxidation-filtration as the existing treatment......................................... 91

XV

4.6.

Arsenic decision tree for surface or groundwater treatment plants with ironmanganese removal using greensand filtration as the existing treatment................... 92

4.7.

Arsenic decision tree for groundwater treatment plants with disinfection alone as the existing treatment........................................................................................................95

5.1.

Ion exchange with evaporation pond and non-hazardous landfill................................... 109

5.2.

Ion exchange with chemical precipitation and non-hazardous landfill........................... 110

5.3.

Ion exchange with indirect discharge and non-hazardous landfill.................................. Ill

5.4

Coagulation-assisted microfiltration with mechanical dewatering and non-hazardous landfill.......................................................................................................................112

5.5.

Nanofiltration or reverse osmosis or electrodialysis reversal with indirect discharge.... 113

6.1.

Average and 90th percentile arsenic concentrations in the City of Phoenix.................... 133

7.1

Absorptive capacity of MIEX, fflOPs, AA, Al*3, and Fe+3 for LADWP water spiked with arsenic to 100 ug/L concentration..................................................................... 202

7.2

Arsenic removal from LADWP (spiked with 100 u,g/L of arsenic) water by alum in conventional and Actiflo processes........................................................................... 203

7.3

Arsenic removal from LADWP (spiked with 100 ug/L of arsenic) water by ferric chloride in conventional and Actiflo modes ............................................................. 204

7.4

Plot showing the arsenic levels in the membrane feed and product water from test conducted with LADWP water spiked with 100 ug/L of arsenic............................. 205

7.5

Plot showing the arsenic levels in the membrane feed and product water from test conducted with the City of Phoenix, AZ water spiked with 100 ug/L of arsenic..... 205

XVI

FOREWORD The Awwa 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 working 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 Applications, 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 manufacturers 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.

XVll

The true benefits are realized when the results are implemented at the utility level. foundation's trustees are pleased to offer this publication as a contribution toward that end.

Edmund G. Archuleta. P.E.

James F. Manwaring, P.E.

Chair, Board of Trustees

Executive Director

Awwa Research Foundation

Awwa Research Foundation

XVlll

The

ACKNOWLEDGMENTS The authors would like to acknowledge the generous financial support of AWWARF and USEPA without which this study would not have been possible. The development of this work has been overseen from the beginning by an enthusiastic Project Officer and experienced Project Advisory Committee (PAC) whose guidance, expertise and suggestions were of valuable assistance. The project team would like to thank the following Project Officer and the PAC members for their kind support and guidance: Project Officer:

Dr. Kenan Ozekin, AWWARF, Denver, CO

PAC Members:

Mr. Thomas Sorg, USEPA, Cincinnati, OH Mr. Peter Hillis, North West Water Limited, UK Mr. Dennis Peyton, City of Fresno, Fresno, CA Mr. Greg Mathews, New Jersey Water, NJ

Several utility members across the U.S. participated in this project by attending workshops, supplying with their utility information for case study development, reviewing the decision tree tool and providing valuable comments from time to time.

The authors would like to

acknowledge the support of the following water utility participants: Dr. Laxman Devkota, City of Phoenix, AZ Mr. Walid Alsamadi, City of Phoenix, AZ Mr. Chris Hill, Metropolitan Water Improvement District, AZ Mr. Brian Biesemeyer, Citizens Water Resources, AZ Mr. Gene Michael, City of Glendale, AZ Mr. William Suchodoloski, City of Tucson Water Department, AZ Mr. Thomas Jefferson, City of Tucson Water Department, AZ Ms. Michelle De Haan, City of Scottsdale, AZ Mr. Michael Block, Metropolitan Water Improvement District, AZ Ms. Sheila Bowen, Community Water Company Green Valley, AZ Mr. Pankaj Parekh, Los Angeles Department of Water and Power (LADWP), CA Mr. Gary Stolarik, LADWP, CA Mr. Don Christie, LADWP, CA

XIX

Mr. Robert Little, City of Fresno, CA Ms. Zahra Panahi, City of Riverside, CA Mr. John Moreno, City of Oxnard, CA Mr. Jeff Hershman, City of Oxnard, CA Mr. Curtis Horton, Carson City Utilities, NV Mr. Edward James, Carson City Utilities, NV Mr. Charles Lawson, Stage Coach General Improvement District, NV Mr. Marlin Cook, Stage Coach General Improvement District, NV Mr. Rick Hydrick, South Tahoe Utility District, NV Mr. John Thiel, South Tahoe Utility District, NV Mr. Carl Ruschmeyer, Douglas County, NV Mr. Robert Leible, Indiana-American Water Company in Kokomo, IN Mr. Bruno Trimboli, Mishawaka Water Department, IN Ms. Connie Cummings, Mishawaka Water Department, IN Dr. Art Umble, Elkhart Public Works Department, IN and Mr. David Turngate, South Bend Water Works, IN The authors would like to acknowledge the support and services provide by the other team members including: Ms. Catherine Pallota, Malcolm Pirnie, Inc. Ms. Melissa Moran, Malcolm Pirnie, Inc. Ms. Patricia Hausser, Malcolm Pirnie, Inc. and Mr. Manish Kumar, NCS Engineering Finally, the authors would like to acknowledge Mr. Mike McPhee of EE&T for providing some of the residual handling schematics that are shown in Chapter 2.

XX

EXECUTIVE SUMMARY INTRODUCTION Arsenic is ubiquitous in nature and is often found in drinking water sources including ground water and surface waters. High levels of arsenic ingestion through consumption of drinking water have been found to have various health implications.

Some studies also associated

presence of low levels of arsenic in drinking water with cancer of skin and bladder. Consequently, the U.S. Environmental Protection Agency (USEPA) has lowered the enforceable maximum contaminant level (MCL) for arsenic from 50 /ig/L to 10 /ig/L. All community water systems (CWS) and non-transient, non-community water systems (NTNCWS) will be required to comply with the new rule by January 2006. Since only a few utilities in the U.S. use source waters with arsenic concentrations above the old MCL of 50 /ig/L, arsenic removal has not been a consideration in the design of the existing treatment plants.

Some existing treatment facilities may incidentally accomplish arsenic

removal, but, in many instances, the imposition of the more stringent MCL (10 jig/L) may require implementation of new treatment practices or significant modifications to the existing treatment schemes. These changes in treatment practices can result in secondary impacts on the finished water quality, generate residuals that need appropriate handling and disposal, and increase the costs for treatment. This research effort was aimed at developing guidance for assisting the large and small water utilities by providing preliminary cost information and decision making for these changes and by providing some understanding of the issues related to the implementation of the new rule. STUDY OBJECTIVES The original objectives of the study were to: Systematically evaluate the impact of integrating arsenic treatment technologies with existing treatment trains

XXI

Identify the issues and cost associated with the treatment plant integration of each technology Develop decision trees regarding influent water quality (pH, sulfate, arsenic, etc.) existing treatment, waste disposal limitations and other factors that will influence assembly of a treatment train. The final product of the study will be a step-by-step procedure that utilities can use to decide which arsenic treatment technology is best for them, the issues and associated costs with retrofitting the technology in an existing treatment train and the techniques to deal with them. This work focuses on providing guidance (in the form of a written report and interactive tools) to the water utilities with respect to the selection of arsenic treatment and residuals handling/disposal alternatives. This guidance will include: Optimization methods for systems that have an existing treatment in-place, Impact of other compounds on performance of various arsenic removal technologies, and Secondary impacts of the arsenic treatment processes. A secondary goal of the study was to develop interactive, web-based decision tree tools for screening and selecting preferred optimization methods (for systems with existing treatment) and arsenic removal technologies (for systems with no treatment in-place). These interactive decision tree tools were developed with data from a large sample of participating utilities across the nation. The costs for arsenic treatment can vary significantly depending on the technology selected, water quality and local issues. The decision analysis tool can also calculate conceptual level costs for installation and operation of treatment and residuals handling systems. Case study summary reports of the participating utilities are presented (in Chapter 6) to serve as an example for other utilities that will be addressing arsenic removal in their source waters. ARSENIC TREATMENT TECHNOLOGIES There are several treatment technologies that are available for arsenic removal from drinking water. Mechanistically, these technologies can be broadly classified as, (1) ion exchange, (2) adsorption, (3) precipitation, and (4) membrane processes. Most of these treatment processes

XXll

work more efficiently to remove arsenate [As(V)j compared to arsenite [As(IQ)]. Therefore, a pre-oxidation step with addition of chlorine or other oxidant is often an integral part of an arsenic removal process. In addition to the proven technologies, many proprietary and innovative processes, which utilize some of the above technologies with certain modifications, are also available. Examples of innovative processes include, sand-ballasted coagulation sedimentation, fluidized-bed microsand oxidation-adsorption and coagulation-assisted ceramic media filtration. Synopsis discussion of the innovative technologies is presented in Chapter 7 and the detailed discussion is shown in Appendix D. Ion Exchange - Ion exchange (DC) using strong base anionic resins is another proven technology for arsenic removal. The strong base anionic resins are available in two forms, hydroxide or chloride form. When water is passed through a column containing the IX resin, either chlorides or hydroxides are exchanged for arsenic and other anions in the water. The concentration of sulfate in the feed water determines the capacity for arsenic exchange by the IX process. Adsorptive Processes - Adsorption is a physico-chemical process wherein the ions in the raw water are adsorbed to a solid substrate. There are several alumina (e.g., activated alumina [AA]) and iron (e.g., granular ferric hydroxide [GFH]) based adsorbents that are effective for arsenic removal. Precipitative Processes - The precipitative processes include coagulation-filtration (CF) and lime softening (LS). When a coagulant such as ferric chloride is added to water it hydrolyzes to form ferric hydroxide floe. Arsenate co-precipitates or adsorbs to the surface of the floe and gets removed during sedimentation or filtration. Membranes - Through size exclusion, nanofiltration (NF) and reverse osmosis (RO) processes can remove both dissolved As(V) and As(in). Low-pressure membranes such as microfiltration (MF) and ultrafiltration (UF) can also be employed for arsenic removal if assisted by a coagulation step.

xxm

Innovative Technologies - There are several technologies that are emerging as promising technologies for arsenic removal. Unfortunately, there is very little historical information available on these emerging technologies. Therefore, to better understand some of the promising innovative technologies, bench-scale tests were conducted and the results of these tests are discussed in Chapter 7. The innovative technologies that are discussed in Chapter 7 include: Magnetic ion-exchange (MIEX ) resins Hydrous iron oxide particles (HIOPs) Sand-ballasted coagulation sedimentation (Actiflo process) Immersed membranes in combination with adsorbents WATER QUALITY CONSIDERATIONS Chapter 2 presents an overview of the predominant arsenic removal treatment technologies, arsenic chemistry and the related water quality considerations and residuals handling issues. With respect to arsenic chemistry and treatment efficiency, the major consideration is the valence state of arsenic. Due to the differences in the ionic charge of the arsenite [As(IH)] and arsenate [As(V)] particles in the pH 6-9 range, the neutrally charged arsenite compound (HsAsOs) is difficult to remove when compared to the negatively charged As(V) compounds, HAsCV2 and HÂsCV. The key water quality observations for each technology are summarized below: Ion Exchange - Sulfate is preferentially removed to all other anions in anion exchange systems; as sulfate levels increase, IX becomes decreasingly cost effective due to shortened run lengths. Although no arsenic-specific IX resin is known to exist, standard resins are capable of arsenic removal. Nitrates above 5 mg/L will impact IX systems as chromatographic peaking could occur. A moderate pH drop can be expected during the beginning of an IX run as bicarbonate alkalinity is removed. Adsorptive Processes - With an EBCT of 5 minutes and at a pH of 6.0, between 10,000 and 25,000 bed volumes (BVs) (30 to 90 days of continuous operation) can be treated prior to AA media exhaustion, depending on interference from other parameters and arsenic concentrations in

XXIV

the feed. Water quality considerations include chloride, pH, silica and fluoride. Most AA type processes may not operate optimally without pH adjustment. Precipitative Processes - In addition to removing colloids and suspended solids, addition of coagulants such as ferric chloride, ferric sulfate, and aluminum sulfate can also remove natural organic matter (NOM), certain inorganics and trace metals, including arsenic, in drinking waters. At optimal pH levels less than or equal to 7, greater than 80% removal of arsenic can be achieved with enhanced coagulation, or addition of elevated levels of coagulant beyond what is required for turbidity removal. At pH levels above 9, the effectiveness of iron and aluminum coagulants on arsenic removal is reduced, due to less efficient floe and precipitate formation. Silica is expected to reduce arsenic removal in the pH 7-9 range. As the coagulation pH level is lowered, the silica interference is reduced. Arsenite and arsenate can be removed effectively (at rates of 75 to 100 %) at higher pH levels (>10.5) during the softening process with pH optimization and addition of elevated quantities of lime, or addition of iron coagulant during the process. Where oxidizing filters are present for iron and manganese removal, they can also be used for removing arsenic concurrently if the process is optimized. Arsenic removal rates of greater than 80% can be achieved in oxidizing filters depending on operating pH, natural iron levels, and amount of coagulant added. This process is enhanced when more natural iron is present in the water. Membranes - Membranes such as RO, NF and UF/MF (with pretreatment using a coagulant) have been proven as an effective arsenic removal technology in previous bench and pilot studies. Considerations in UF/MF membrane performance include NOM levels, pH and silica. For NF/RO membranes, performance considerations include arsenic speciation and ionic charge, pH, NOM content of raw water, and presence of other inorganics such as calcium, magnesium, barium, strontium, sulfate, chloride and carbonate (potential foulants) and colloidal matter. Biological fouling has also been observed in NF/RO membranes.

XXV

Partial Stream Treatment - A discussion on partial treatment as a potential cost savings option is included in Chapter 2. Under this scenario, a portion of the flow is treated while the remaining flow is bypassed and blended back with the treated flow to ensure the desired arsenic level is achieved. Point of Entry versus Wellhead Treatment - Several factors related to combined treatment at a common point of entry into the distribution system versus wellhead treatment are also discussed in Chapter 2. Factors to be considered when making this decision include land availability, the number of impacted wells, the arsenic levels and flow rates in the impacted wells, the need for treatment required to comply with other regulations, and the proximity of the wells to one another. RESIDUALS HANDLING AND DISPOSAL In the above-discussed treatment processes, arsenic removal occurs either by transfer of arsenic from water to a solid phase (as in AA or enhanced coagulation) or by concentration of arsenic in another liquid phase (as in the brine for DC or membranes). Therefore, each of the technologies that are discussed above produce residuals, which could possibly be characterized as hazardous materials requiring special handling and disposal. Arsenic residuals exhibit two of the four characteristics, corrosivity and toxicity, which can result in classification of a solid waste as a hazardous waste. Arsenic bearing wastes are considered hazardous when the arsenic concentration exceeds the toxicity characteristic (TC) limit of 5.0 mg/L. For liquid wastes with less than 0.5 percent solids, the 5 mg/L criterion is applied to the dissolved arsenic. For wastes with greater than 0.5 percent solids (including sludges), the limit is applied on the leachate derived by Toxicity Characteristic Leaching Procedure (TCLP) test performed on the solid residuals. According to Resource Conservation and Recovery Act (RCRA), a material becomes waste when its no longer used in the treatment process. As such, spent regenerant solutions generated by treatment processes like AA and DC may be classified as a waste when they are no longer

XXVI

used in the treatment process. When this waste solution has an arsenic concentration greater than 5 mg/L, it will be defined as hazardous waste. The precipitation of arsenic by such methods as ferric chloride addition constitutes the treatment of a hazardous waste. Under RCRA, on-site treatment of hazardous wastes to render them non-hazardous will require a treatment, storage, and disposal facility (TSDF) permit.

Compliance with all RCRA record keeping, facility

construction, contingency plan, personnel training and maintenance requirements will also apply. This presents a challenging scenario for the typical drinking water facility due to the liability and public perception issues associated with treatment of hazardous wastes on site. Another option for utilities that generate hazardous wastes is off-site disposal that will also require RCRA compliance including, obtaining an USEPA ID number, preparing a waste manifest and complying with the Department of Transportation requirements. The off-site disposal option may be cost-prohibitive in most instances and environmentally unacceptable. Therefore, the primary arsenic removal processes that minimize or eliminate the generation of hazardous wastes are preferred from a practical implementation standpoint. Residuals handling and disposal largely depend on treatment technology in use and the nature (quantity and quality) of the residuals generated. Liquid wastes produced from the regeneration of DC or AA processes are likely to be characterized as hazardous unless a precipitation process is also included in the treatment process to bind the soluble arsenic into an insoluble precipitate. Solid wastes generated from coagulation process or the exhausted adsorption media are expected to be characterized as non-hazardous materials and could be sent to landfills.

Details of

characteristics of residuals generated by each treatment technology and some preferred options for handling the residuals are presented in Chapter 3. Waste management regulations across Europe and around the world are not consistent from country to country. For example, in Germany, waste disposal is regulated by State law and not by Federal law.

To classify waste as "nontoxic" with regard to arsenic, an elution test

concentration must not exceed 0.1 mg/L. In this test, 10 grams of waste (e.g., spent adsorbent) is suspended in 1 L deionized water at pH 7, shaken for 24 hours, and the solids allowed to settle. The supernatant is then sampled and analyzed for arsenic concentration.

XXVll

COSTS The capital and operational and maintenance cost curves were developed in such a way that costs may be calculated for any targeted effluent arsenic concentration to enable cost determinations for any potential arsenic MCL. Unit cost curves were revised from previously published cost curves for the following four surface water and ten groundwater treatment alternatives: > Surface water treatment alternatives Enhanced coagulation/filtration; Enhanced lime softening; Conversion of direct filtration to conventional filtration; and Coagulation-assisted microfiltration > Groundwater treatment alternatives Ion exchange with evaporation pond (for liquid waste streams) and non-hazardous landfill (for solid residuals); Ion exchange with chemical precipitation and non-hazardous landfill; Ion exchange with indirect discharge and non-hazardous landfill; Conventional activated alumina with evaporation pond and non-hazardous landfill; Conventional activated alumina with indirect discharge and non-hazardous landfill; Throwaway/disposable activated alumina Coagulation-assisted microfiltration with mechanical dewatering and non-hazardous landfill; Coagulation-assisted microfiltration with indirect discharge of backwash and rinse waters; Nanofiltration/reverse osmosis with indirect discharge for brine or reject stream; and Electrodialysis reversal with indirect discharge for brine or reject stream. The surface water treatment plants with enhanced coagulation/filtration, enhanced lime softening or direct filtration are assumed to have the necessary resources in-place to handle any additional residuals that may be generated from optimizing the existing treatment to achieve the necessary

XXVlll

arsenic removal. Therefore, unit cost curves were only developed for residuals handling for groundwater systems. Cost curves were also developed for pre-oxidation with chlorine for application to systems that may have arsenite [As(m)] and that do not have an existing oxidation step. Cost for land acquisition is estimated for each technology based on the local land value ($/acre) and the amount of land required for treatment and residuals handling. The land required is estimated based on the footprints developed for each technology for different system sizes.

ARSENIC DECISION TREES Decision Trees For Existing Treatment Systems

The water-quality based decision trees were developed to assist utilities in selecting and integrating arsenic treatment processes where existing treatment facilities are present. The decision trees were developed for the following typical scenarios: 1) Surface water - existing conventional treatment process 2) Surface Water - existing direct filtration process 3) Groundwater/surface water - existing precipitative softening process 4) Groundwater/surface water - existing iron removal process (oxidation-filtration) 5) Groundwater/surface water- existing iron and manganese removal process (manganese greensand filtration) 6) Groundwater - with disinfection alone (no other existing treatment process) The typical decision analysis process that is used in these flow charts includes: 1) determining the arsenic species in the raw water and the need for pre-oxidation 2) evaluating process optimization methods, first on a bench or pilot-scale level, then on a full-scale level 3) optimizing treatment by addition of pre-oxidants, switching to a different coagulant, increasing the coagulant dose, decreasing the coagulation pH and polymer addition 4) monitoring the finished water obtained as a result of the optimization process to determine which treatment scenario is most effective, considering arsenic, other water quality goals, residuals generation, costs, and operational factors, and secondary effects;

XXIX

5) considering polishing treatment if the optimization processes do not achieve sufficient arsenic removal rates; and 6) evaluating waste handling and disposal requirements throughout the decision making process. The decision trees also considered innovative technologies. Where necessary, the decision trees suggest innovative technologies. Discussion of some of the suggested innovative technologies is provided in Chapter 7. The project team developed an interactive program outlining the abovediscussed optimization routines for achieving the necessary arsenic removal in systems with treatment in-place. This program is available for use on the AWWARF web site at the following location: http://www.awwarf.com/ArsenicTool/ArsenicTree/index.cfm Decision Tree Tool For No Existing Treatment Systems

The project team developed, a web-based, interactive decision tree tool to screen and select preferred arsenic removal technologies for the impacted points-of-entries that do not have an existing treatment (other than disinfection alone) in place. This tool is equipped with information on fifteen different treatment-residuals handling/disposal alternatives for surface water and groundwater systems. This e-tool will seek system information such as flows, raw water quality, residuals handling preferences and site constraints and based on the information entered, the tool will estimate the qualities/quantities of residuals that would be generated, land required for installing new treatment systems and also outputs planning-level costs for each treatment technology. The tool identifies and ranks the feasible technologies based on qualitative decision drivers like ease of implementation, public acceptance and labor required. With this tool, the user can analyze various "what if scenarios to evaluate alternative ways to address the arsenic removal from their impacted point-of-entries. This tool was developed and demonstrated with input from about 20 utilities across the nation that participated in the AWWARF project. The interactive decision tree tool is presently available at the following location: http://www.awwarf.com/ArsenicTool/WHITree/index.cfm

XXX

Instructions for using the web tool are available at the above location under the "help" and "about" files that can be accessed by clicking on the so labeled buttons on the home page. The web tool has forms to input the impacted points-of-entries system information and based on the inputs it generates output forms containing information on residuals quantities and characteristics, water quality considerations, treatment costs and the most applicable technologies for that point-of-entry. UTILITY CASE STUDIES Case study summaries for the participating utilities were prepared using the decision tree tools. These summaries are available under Chapter 6. These case study summaries were prepared for a targeted finished water arsenic concentration of 8 jtig/L (80% of the anticipated MCL of 10 /ig/L). Initially, the water system information was obtained through questionnaires (shown in Appendix B) that were mailed to the utility representatives.

Subsequently, the case study

discussions were developed with ample contributions from the water utility representatives during their participation at the workshops (conducted in Phoenix, Arizona, Los Angeles, California; Reno, Nevada; and Mishawaka, Indiana) and from subsequent communications. These case studies are included to demonstrate the process of evaluating treatment strategies using the decision-tree spreadsheet tool. The case studies represent a wide range of system sizes, existing treatment processes, source water characteristics, and arsenic contamination. For a majority of groundwater systems that are considering wellhead treatment, throwaway adsorption process (e.g., throwaway activated alumina or granular ferric hydroxide) could be the lowest, lifecycle cost option. INNOVATIVE TECHNOLOGIES Innovative adsorbents (MEEX , HIOPs), coupled adsorbent-membrane systems, and alternative coagulation/flocculation process were all effective in removing arsenic from water. In natural water samples, arsenic capacities for the adsorptive media followed the trend HIOPs > MTF.X > AA. The adsorptive capacities of HIOPs, MIEX , and AA were greater in synthetic water than in natural water. This difference is attributed to the presence of anions competing with arsenic

XXXI

for adsorption sites in natural water samples.

Greater arsenic removal was obtained with

conventional coagulation than with adsorption onto MIEX , HIOPs, and AA. Similar arsenic removal levels were obtained with conventional and sand-ballasted coagulation sedimentation (Actiflo ) processes. The addition of HIOPs or MIEX to the low-pressure membrane feed water resulted in greater arsenic removal compared to when no adsorbents were added to the membrane feed waters. RECOMMENDATIONS TO UTILITIES A decision tree based approach will serve as an initial step for a utility in "narrowing the field" of feasible arsenic treatment alternatives. This approach will eliminate the need to conduct extensive tests of several potential treatment alternatives. By using the decision tree tools the small and large water utilities can assess realistic arsenic removal options based on water quality conditions and the need to achieve multiple treatment objectives. Two interactive decision tree programs were developed as part of this project. One of the programs provides guidance for optimization process for systems with treatment in-place. The second program will help isolate feasible and promising treatment technologies at locations where there is no treatment (other than disinfection) in-place. Both these interactive programs are made available at the AWWARF web page at the following location: http://www.awwarf.com/ArsenicTool/ArsenicTree/index.cfm Impacted water utilities can use the interactive tools along with this report to understand some of the primary and secondary issues associated with the proposed arsenic regulation. This report has chapters on water quality, residuals handling, costs and integration issues that are part of implementing arsenic removal treatment processes. Utilities are expected to keep up to date with the emerging technologies and use the tool as a guide and not as the final answer. The technologies that are suggested by the tools have to be bench, pilot and full-scale tested prior to implementation.

XXXll

CHAPTER 1 BACKGROUND AND INTRODUCTION 1.1.

Background

1.1.1. Regulatory Update

In 1993, the World Health Organization (WHO) recommended a provisional guideline value of 10 micrograms/liter Oig/L) or 0.01 milligrams/liter (mg/L) for total arsenic.

The current

standards for arsenic in potable water in Australia, European Union, Canada and Japan are respectively 7 ug/L, 10 j^g/L, 25 /ig/L and 50 fJig/L. The WHO guideline for arsenic is based on a calculation estimating an additional lifetime risk of six skin cancers per 10,000 people. The European Union adopted this limit of 10 /ig/L in January 1999. Australia has set its guideline of 7 fjig/L based on the WHO's recommended maximum tolerable intake of arsenic from all sources of 2 jKg/kg body weight per day. Canada's interim, maximum acceptable concentration of 25 jig/L is based on available practical treatment technology and an estimated additional skin cancer risk of 9.0 x 10"4. This interim risk will be periodically reviewed contingent on technology developments and additional health risk data. Under the 1986 amendments to the Safe Drinking Water Act (SDWA), Congress directed USEPA to publish Maximum Contaminant Level Goals (MCLGs) and promulgate National Primary Drinking Water Regulations (NPDWRs) for 83 contaminants, including arsenic. Epidemiological evidence on the toxicity of inorganic arsenic suggests that the current maximum contaminant level (MCL) may not be sufficiently protective. On January 22nd, 2001, USEPA established a non-enforceable MCLG of zero and an enforceable MCL of 0.01 mg/L for arsenic (Federal Register, 2001). According to the published rule, all community water systems (CWS) and non-transient, non-community water systems (NTNCWS) must comply with the new MCL by January 2006. This deadline is based on USEPA having granted all affected systems five years from promulgation to comply, which includes the Safe Drinking Water Act minimum of three years plus two additional years when capital improvements are required.

Later, within 60 days of promulgation, the new Administration put a hold on the regulation and decided to review the scientific and financial basis. The review included seeking comments from the National Academy of Sciences on the newest arsenic health effects science and convening the National Drinking Water Advisory Council to review the relevant economic issues. USEPA completed the review and decided to retain 10 fig/L as the MCL and this will be effective from January 2006. 1.1.2. Compliance Status

According to the published rule, beginning in January 2004, all CWS and NTNCWSs must monitor for arsenic at each entry point to the distribution system. After the effective date of the rule, systems will determine compliance based on analytical results obtained at each sampling point. If any sampling point is in violation of the MCL, the system is in violation. For systems monitoring more than once a year, compliance with the MCL is determined by a running annual average at each sampling point. For systems monitoring annually or less frequently whose sample result exceeds the MCL must revert to quarterly sampling the next quarter. Systems triggered into increased monitoring will not be considered in violation of the MCL until they have completed one year of quarterly sampling. If any sample result will cause the running annual average to exceed the MCL at any sampling point (i.e., the measured result is greater than four times the MCL), the system is out of compliance with the MCL immediately. Systems may not monitor more frequently than specified by the State to determine compliance unless they have applied to and obtained approval from the State. If a system does not collect all required samples when compliance is based on a running annual average of quarterly samples, compliance will be based on a running annual average of the samples collected. If a sample result is less than the method detection limit then zero should be used to calculate the annual average. States have the discretion to delete results of obvious sampling or analytic errors. Sample collection and handling requirements are detailed in the Federal Registry 40 CFR Parts 9, 141 and 142 (2001).

USEPA approved the following four analytical methods for determining compliance with the new arsenic MCL: 1. Inductively Coupled Plasma Mass Spectroscopy (ICP-MS), USEPA Method 200.8 2. Stabilized Temperature Platform Graphite Furnace Atomic Absorption (STP-GFAA), USEPA Method 200.9 3. Graphite Furnace Atomic Absorption (GFAA), Standard Methods 3113B 4. Gaseous Hydride Atomic Absorption (GHAA), Standard Methods 3114B USEPA withdrew the two methods that use Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) because their detection limits are too high to reliably determine compliance at the new MCL. Table 1.1 has the method references, method detection limits (MDLs) and estimated costs for some commonly used arsenic analytical techniques. Table 1.1 Arsenic compliance monitoring methods and their detection limits Arsenic analytical

Reference

method

1.2.

Detection limit

Estimated analysis cost

0*g/L)

($/sample)

ICP-MS

USEPA 200.8

1.4

$10415

STP-GFAA

USEPA 200.9

0.5

$15450

GFAA

Standard Methods 31 13B

1.0

$15450

GHAA

Standard Methods 3 1 14B

0.5

$15450

Introduction

1.2.1. Project Objectives

Since only a few utilities in the US use source waters with arsenic concentrations above the current MCL of 50 ptg/L, arsenic removal has not been a consideration in the design of the existing treatment plants. Some existing treatment facilities may incidentally accomplish arsenic removal, but, in many instances, the imposition of a stringent MCL (3 to 20 pig/L) may require

implementation of new treatment practices or significant modifications to the existing treatment schemes. This study was aimed at providing assistance to water utilities (both large and small sized systems) in recognizing and quantifying the secondary impacts of these changes in the treatment practices. The specific goals of the study were to: > Provide guidance to the water utilities with regards to the selection of arsenic treatment and residuals handling/disposal alternatives.

This guidance includes optimization

methods for systems that have an existing treatment in-place, impact of presence of other compounds on arsenic removal technologies performance, secondary impacts of the arsenic treatment technologies on the finished water quality, associated waste handling and disposal issues and conceptual costs. The guidance developed in this study are summarized in this report. > Develop interactive, web-based decision tree tools for screening and selecting preferred optimization methods (for systems with existing treatment) or arsenic removal technologies (for systems with no treatment in-place).

An user-friendly, interactive

decision tree was developed based on the information gathered from literature survey, bench-scale study results on innovative technologies, and best professional judgment of the team and project advisory committee members. > Develop and demonstrate the interactive decision tree tools using data from a large sample of participating utilities across the nation. Case study summary reports are presented in this report to serve as examples for other utilities that will be addressing arsenic removal in their source waters. With the interactive decision tree tools, the users are able to analyze various "what if scenarios to evaluate alternative ways to address the arsenic treatment issue at their site. The web-based tools seek system information such as flows, raw water quality, site constraints and residuals handling preferences and based on the system information entered, the tool estimates the types of residuals that will be generated, land required and planning-level costs for each technology. The tool also addresses the impact of qualitative decision drivers like ease of implementation and public acceptance in selecting the feasible treatment alternatives.

A decision tree based approach serves as an initial step for a utility in "narrowing the field" of feasible arsenic treatment alternatives. This approach eliminates the need to conduct extensive tests of several potential treatment alternatives. Chapter 5 has more details on how decision tree tools enable surface and ground water utilities to assess realistic arsenic removal options based on water quality conditions and the need to achieve multiple treatment objectives. 7.2.2. Proven Arsenic Treatment Technologies

Several treatment technologies are getting attention with respect to arsenic removal from drinking water. Mechanistically, these technologies can be broadly classified as: 1. Ion exchange 2. Adsorption 3. Precipitation and 4. Membrane Processes Most of the arsenic treatment processes work more efficiently to remove arsenate [As(V)] compared to arsenite [As(HI)]. Therefore, a pre-oxidation step with addition of chlorine or other oxidants is often an integral part of an arsenic removal process. In addition to the proven technologies, many companies are selling or actively pursuing the development of proprietary and innovative processes, which utilize some of the above technologies with certain modifications. Examples of such processes include, sand-ballasted coagulation sedimentation fluidized-bed microsand oxidation-adsorption and coagulation-assisted ceramic media filtration (Chowdhury et al, 2001, Kommineni et al., 2001 and Sinha et al., 2001). Detailed description of the established and emerging processes for arsenic removal are presented in Chapter 2.

1.2.2.1. Ion Exchange

Ion exchange (IX) using strong base anionic resins is another proven technology for arsenic removal. The strong base anionic resins are available in two forms, hydroxide or chloride form. When water is passed through a column containing the DC resin, either chlorides or hydroxides are exchanged for arsenic and other anions in the water. The concentration of sulfate in the feed water determines the achievable run length for the IX process. The number of bed volumes (a bed volume is the volume of the resin available for treatment) of water that can be processed by IX decreases with increasing sulfate concentrations (Clifford, 1999). The chloride form resins are regenerated using sodium chloride salt solution while the hydroxide form resins are regenerated using the sodium hydroxide caustic solution. The spent regenerant solutions will contain elevated concentrations of sulfate, nitrate and arsenic. The spent regenerant solution can be re-used (with chemical conditioning, an innovative process) or discarded (as in conventional IX). Pilot-scale studies are being conducted to evaluate two innovative versions of ion exchange process, namely, the advanced ion exchange operation (AIXO) and indefinite brine recycling (IBR) (Perry et al, 2000, Kwan et al, 2001(a) and Kwan et al, 2001(b)). 1.2.2.2. Adsorptive Processes

Adsorption is a physico-chemical process wherein the ions in the raw water are adsorbed to a solid substrate. There are several alumina (e.g., AA) and iron (e.g., GFH) based adsorbents that are effective for arsenic removal.

When water with arsenic is passed through a column

containing the adsorbent media the arsenic adsorbs to the oxidized alumina or iron surface. When the adsorption media becomes saturated with arsenic it requires either replacement or regeneration. The volume of water treated by a unit volume of the adsorbent media, before saturation, is a key performance parameter for adsorption technologies. AA is a common name given to types of high surface area aluminum oxides (A12O3). Conventional AA is regenerated on-site using caustic solution. GFH is a weakly crystalline Pferric oxyhydroxide (FeOOH), produced by conditioning compacted iron hydroxide slurry (Jekel and Seith, 2000). The chemical composition of GFH is 52 to 57 percent of FeOOH and 43 to 48

percent of water (Jekel and Seith, 2000). To achieve longer ran lengths before saturation, the pH of the raw water for the conventional AA systems may have to be lowered, to pH of 6 or lower. The key feature of the throwaway adsorbents (like throwaway AA or GFH) is that they can treat a larger volume of water before saturation, without either a pH adjustment or the need to regenerate on-site. A number of proprietary, disposable adsorbents for arsenic removal are being evaluated in several pilot-scale studies (Norton et al., 2001). High concentrations of silica can decrease the sorption capacity for arsenic by the alumina and iron based adsorbents (Norton et al., 2001). Lowering the pH of the feed water can reduce silica interference. Disposal issues and secondary effects with adsorption treatment processes are also very important. The disposal of spent regenerant and spent media must be included in design of the adsorption process. Secondary effects including the lowered pH and increased IDS of the finished water must be give due consideration in the case of utilities that face corrosion control or water quality issues. 1.2.2.3. Precipitative Processes

The precipitative processes include coagulation-filtration (GF) and lime softening (LS). When a coagulant like ferric chloride is added to water it hydrolyzes to form ferric hydroxide floe. Arsenate co-precipitates or adsorbs to the surface of the floe and gets removed during sedimentation or filtration. In CF and LS systems, adding ferric, alum, or lime to the raw water forms floe particles. Many surface water treatment plants already use some sort of coagulation process, which may have to be optimized if the finished water arsenic concentrations are above the MCL. This optimization may include switching of coagulants (ferric is better than alum for arsenic removal) or lowering the pH for coagulation. Co-occurring solutes such as sulfate, calcium or silica may compete for the surface binding sites on the coagulant floe and reduce the adsorption of less prominent contaminants such as arsenic. Greensand filtration is an oxidation filtration process that has demonstrated effectiveness for the removal of arsenic. Greensand is a zeolite filtration material that contains glauconite, a green, lay-like material that is iron-rich and exhibits ion-exchange properties. Greensand is processed

with manganese sulfide or manganese sulfate and potassium permanganate in alternative steps to produce a black precipitate of manganese dioxide on the granules. Greensand can be operated as a rapid sand filter, and includes a regeneration step (New Mexico State University, 1999). Greensand filtration is similar to conventional filtration except the use of greensand instead of sand or anthracite and the fact that it can be configured as a pressure filter. Greensand acts as an oxidizer, ion exchanger, and absorber. Greensand filtration has the capacity to absorb water that contains iron, manganese, and arsenic. EPA considers greensand filtration to be an emerging alternative technology for the removal of arsenic from drinking water. In arsenic treatment, the manganese in the greensand oxidizes AsQH) to As(V). As(V) is exchanged for the reduced manganese and absorbed to the media. Once its oxidation and absorption capacity has been exhausted the manganese component of the greensand is regenerated using potassium permanganate (New Mexico State University, 1999 and EPA, 2000b). 1.2.2.4. Membrane Processes

Through size exclusion, nanofiltration (NF) and reverse osmosis (RO) processes can remove both dissolved As(V) and As(m) (Brandhuber et al., 1998). Although, the NF/RO treatment demonstrated good short-term rejection of As(V) in single-element test, the long-term rejection rate in a production-configured array was found to be problematic (AWWARF, 2000). In longterm studies with spiral wound NF elements, the arsenic removals steadily declined from approximately 75% to 11% over a 60-day test period (AWWARF, 2000). Arsenic removal by NF/RO treatment depends to some degree on operating parameters, membrane properties and arsenic speciation. Adjustment of raw water pH may be required to prevent membrane fouling. Fouling will results in loss of membrane productivity with time. NF and RO processes may also require extensive pretreatment to remove foulants and sealants. Also, the volume of rejected concentrate/brine can be substantial, between 15 to 20 percent of the influent flow. Water utilities should be willing to accept an additional 15 to 20 percent water loss to implement NF/RO treatment.

Low-pressure membranes such as microflltration (MF) and ultrafiltration (UF) can also be employed for arsenic removal if assisted by a coagulation step. Coagulation is an effective treatment technique for arsenic removal whereas MF or UF alone are not. Coagulation-assisted microfiltration (CMF) or coagulation-assisted ultrafiltration (CUF) use low-pressure membrane filtration rather than conventional filtration and have the advantages of providing a more effective microbial barrier, retaining smaller floe, and providing increased capacity in a smaller area. MF or UF, coupled with low dose (2-10 mg/L) of ferric chloride pre-treatment was demonstrated as technically feasible method for arsenic removal from a groundwaters possessing natural arsenic concentrations between 14-18 /ig/L (AWWARF, 2000 and Kommineni et al., 2001). Not all membranes are compatible with all coagulants, which may prevent the MF/UF and coagulation processes from being combined. In some cases, in-line coagulation may be possible, and in other cases, the coagulant may need to be settled before being filtered. 1.2.3. Emerging Arsenic Treatment Technologies

Several innovative treatment technologies, such as sand ballasted coagulation sedimentation, fiuidized-bed in-situ oxidation adsorption, coagulation-assisted ceramic media filtration and immersed membranes with innovative carrier particles are being tested at the bench and pilotscale studies. Some of these emerging technologies were evaluated with bench-scale testing and some other are currently being studied at two sites in Arizona (Tucson and Scottsdale) as part of the arsenic technology demonstration project (AWWARF project 2661). 1.2.3.1. Sand Ballasted Coagulation Sedimentation

Sand ballasted coagulation sedimentation process consists of a unique combination of microsand, ferric chloride and polymer that results in a dense, arsenic-adsorbing floe. This process utilizes existing coagulants (e.g., FeCls or FeSCU) with micro-sand (a ballast) and polymer (cationic or anionic based on affectivity) to improve coagulation. Micro-sand and polymers are added to provide additional particles (or as 'seed') to enhance floe formation and to promote enmeshment for more settleable floe and to reduce coagulant dose. With this process, relatively lower coagulant dosages may be required to achieve the necessary arsenic removal (Chowdhury et al.,

2001). Package plants of sand ballasted coagulation sedimentation are available for installation at wellhead sites.

1.2.2.2. Fluidized-Bed In-Situ Oxidation Adsorption

Fluidized-bed in-situ oxidation adsorption is a new technology developed for the removal of dissolved contaminants such as arsenic.

The key mechanisms of this process consist of

adsorption and oxidation of Fe(n) on the surface of a fluidized inert material such as microsand. In this process, arsenic in the liquid phase is adsorbed/co-precipitated on a continuously generated oxide surface (Chowdhury et al., 2001). 1.2.2.3. Coagulation-Assisted Ceramic Media Filtration

Coagulation-assisted ceramic media filtration is a two-step process consisting of coagulant addition followed by filtration through a ceramic media filter. Filtration using the ceramic media depends on physical straining and adsorption as primary removal mechanisms. Just like CMF, this process also requires chemical pre-treatment and periodic backwashing of the filter media. In this process, the filter loading rates as high as 10 gallons per minute per square foot can be achieved (Kommineni et al., 2001). 1.2.2.4. Immersed Membranes with Innovative Carrier Panicles

Immersed MF or UF membranes can be used along with innovative carrier particles (such as hydrous iron oxide particles [HIOPs] and magnetic ion exchange beads [MIEX]) for arsenic removal. In immersed membrane technology, filtration is achieved by immersing the membrane modules directly in the raw water process tank and by drawing water through the membrane surface under a slight vacuum.

In these systems, the water flows from outside into the

membrane core and therefore they are referred to as 'outside-in' hollow-fiber membrane processes. In this process, the HIOPs or MIEX particles that are added to the feed water tank adsorb arsenic and these arsenic-adsorbed particles are large enough to be rejected by the immersed MF/UF membrane (Sinha et al., 2001). 10

The emerging technologies discussed above were considered, when applicable, in the development of the decision trees. Chapter 7 provides guidance on the water quality impact on some of these innovative technologies. Detailed bench-scale test methods and results on the innovative technologies are summarized in Appendix D. Bench, pilot and full-scale testing is recommended prior to implementing the innovative technologies. Each of the technologies that are discussed above produce residuals, which could possibly be characterized as hazardous materials requiring special handling and disposal. Residuals handling and disposal largely depend on treatment technology in use and the nature (quantity and quality) of the residuals generated. Liquid wastes produced from the regeneration of DC or AA processes are likely to be characterized as hazardous unless a precipitation process is also included in the treatment process to bind the soluble arsenic into an insoluble precipitate.

Solid wastes

generated from coagulation process or the exhausted adsorption media are expected to be characterized as non-hazardous materials and could be sent to landfills. Details of residuals characteristics are presented under Chapter 3.

11

CHAPTER 2 TREATMENT TECHNOLOGIES AND WATER QUALITY CONSIDERATIONS This section presents an overview of the predominant arsenic removal treatment technologies, and the related water quality considerations and residuals handling issues. This background information is provided to assist with using the decision analysis spreadsheet tool and the decision tree flow charts for selecting the appropriate treatment technologies for arsenic removal. The complex residuals handling and disposal issues are presented along with operations and maintenance (O&M) and process considerations to help prioritize and assess feasibility and implementation issues.

2.1. Arsenic Chemistry Arsenic has an atomic number of 33 and an atomic weight of 75. In its natural or zero valence state, elemental arsenic is gray and metallic in appearance and brittle. Due to atmospheric exposure, the metal loses its luster, forming arsenic trioxide (AsaOs). Zero valence arsenic begins to vaporize noticeably at +100 C and sublimes when heated to about 615 C (1135 F). Arsenic is rarely found in nature as the element, however, it is usually combined with sulfur, oxygen, chlorine, sodium and/or other metals.

Sodium arsenate (Na2HAsO4> and sodium

arsenite (NaAsOa) are also common naturally occurring arsenic compounds. Elemental arsenic has a zero valence state and is insoluble; arsenic in AsOs"3 has a -3 valence state and is soluble; arsenic in NaAsOa has a +3 valence state and is very soluble.

Arsenic can exhibit four valence

states, +5, +3, 0, and occasionally -3, as in arsine. The +3 and +5 valence states are the most common, particularly in inorganic compounds. Solid arsenic compounds frequently contain arsenic as an anionic radical such as arsenate, AsCV3 or arsenite, AsOs"3 (e.g., HkAsCV1). arsenate [As(V)] and arsenite [As(IH)] salts are soluble in water (CRC Handbook, 1991). In addition to the oxidation state, the size fraction of the arsenic particles in a water supply is also an important consideration in treatment technology selection.

Paniculate arsenic, the

fraction greater than 0.45 micron in size, can be removed by physical separation processes such

13

as granular media filters, MF, and UF, without chemical pretreatment. Paniculate arsenic can also plug adsorption and chemical exchange media, resulting in more frequent backwashing. Dissolved arsenic, the fraction less than 0.45 microns, generally requires adsorption, chemical exchange, pressure driven membranes, or precipitative processes for efficient removal. In most groundwaters, where iron and manganese do not co-occur with arsenic, dissolved arsenic is expected to be the dominant form. Where paniculate iron and manganese are present, paniculate arsenic may also be present. However, the size fraction of arsenic is very site specific and these assumptions are broad in nature and should be verified on a site-specific basis. As part of the source water characterization process, size fractionation should be performed in addition to arsenic speciation, when performing an arsenic evaluation for a drinking water system. Size fractionation is included in most commercially available arsenic speciation field test kits. Arsenic can be present in the dissolved state as either As (HI) in anaerobic/anoxic (reduced) systems and as As (V) in aerobic (oxidized) systems. In typical drinking water pH ranges of 6 to 9, the predominant arsenite species is neutral in charge (HsAsOs) while arsenate species are present as H2As(V and HAsCV 2. The pKai, pKaa and pKas for arsenic acid are 2.2, 7.0 and 11.0 (Wagner et al., 1982). Table 2.1 contains a summary of the forms of arsenic typically present in water (Clifford and Zhang, 1994). Figure 2.1 provides a graphical representation of redox potential versus pH for arsenic. Figure 2.1 shows the speciation of As(V) as a function of pH (top chart) and the speciation of As(III) as a function of pH (bottom chart) (Clifford and Zhang, 1994). Arsenic compounds can also be sorbed to oxide surfaces (paniculate iron and manganese). Although both organic and inorganic forms of arsenic have been detected, organic species (methylated arsenic) are generally not present in drinking water compared with inorganic arsenic (Anderson and Bruland, 1991). In oxygenated waters, As(V) is dominant, existing in anionic forms of either HaAsCV or HAsC>42~ over the pH range typically encountered in water treatment. Under anoxic conditions, As(m) is stable, with nonionic (H3AsO3) and anionic (H2AsO3~) species dominant below and above pH 9.2, respectively.

14

Table 2.1 Forms of arsenic in water

Nature

Organic

Inorganic As(V)

pH ranges where compound is predominant

Compound

Monomethylarsonic acid (CH3H2As03)

varies

Dimethylarsinic acid [(CH3)2HAisO2]

varies

H3AsO4

9.2

Due to the differences in ionic charge of the arsenate and arsenite particles in the pH 6 to 9 range, the neutrally charged arsenite compound (H3AsO3) is difficult to remove when compared to the divalent (HAsO4"2) and monovalent arsenate anions (H2AsO4~). The negative charges on the arsenate compounds make arsenic easy to remove by adsorptive, co-precipitative, and chemical exchange processes. 2.2. Ion Exchange IX can achieve more than 90% removal for As(V). Strong base anion (SBA) exchange resin is so strongly basic that it is useful as an ion exchanger over the entire pH range from 1 to 13. Arsenic removal is accomplished by using either hydroxide or chloride form SBA resins. The resins are generally made from polystyrene products. Reactions for arsenic removal with SBA resins are shown below (Clifford, 1999):

15

3

CO

IX)

•ai

§

&.

h-*«

V-*

3

10

8

ro o (5o 6S i.

Log Concentration

N> o

I II

oa'

D) (0 CD

T3 (D Q. (D (0

^

s

Icr

q

I

T3

to

_i

o

00

O)

Log Concentration

Hydroxide SB A Resin:

2ResinOH+H2AsO4 -» Resin2H2AsO4 + 2OH"

where, OH"

=

hydroxyl anion

HaAsO^

=

monovalent arsenic anion

Resin

=

surface of resin bead

Chloride SB A Resin:

2ResinCl + HAsO42" -> Resin2HAsO4 + 2C1~

where, Resin

=

positively charged anion exchange resin

Cl"

=

chloride anion

HAsC>42~

=

divalent arsenic anion

The arsenic forms a chemical compound with DC resin. Either chlorides or hydroxides are exchanged for arsenic and other anions in the water. The particle size of the IX resin is 500 to 600 microns. The IX column is operated until sulfate breakthrough (where influent and effluent levels are similar) occurs. SB A resins can be regenerated in the chloride or hydroxide mode for arsenic removal. For economic and chemical handling reasons, the chloride mode is preferred since regeneration is performed using salt brine instead of caustic solution. The selectivity of IX resin for removal of anions is as follows (Clifford, 1999): SO42" > HAsO42' > CO32 & NO3 > Cr > H2As(V > HCO3" > > Si(OH)4, H3AsO3 where, SO42"

=

sulfate anion

HAsO42~

=

divalent arsenic anion

CO32~

=

carbonate anion

HCO3~

=

bicarbonate anion

NO3"

=

nitrate anion

Si(OH)4

=

silica hydroxide anion

H3AsO3

=

neutral arsenate ion

17

Because the sulfate concentration is several magnitudes higher than the arsenic concentration in the ground water, it is the most important factor in determining how many bed volumes (BVs) of water can be treated before regeneration is required. Water recovery rates and the residuals quantities are also directly related to sulfate levels, due to variations in column run length. Many previous studies have indicated that the volume of a contactor should be based on an empty-bed contact time (EBCT) of 1.5 minutes. Unlike AA or iron oxide media, increased arsenic exchange capacity (on mass arsenic removal per mass resin) is not present at higher EBCTs. EX contactors are placed in parallel with the flow split equally between the columns, as shown in Figure 2.2.

FROM WELL

RESIDUALS HANDLING SYSTEM

9

STRAINER

SPENT REGENERAN BACKWASH & RINSE STREAMS

REGENERANT (NaCI) RINSE BACKWASH SUPPLY

STORAGE TANK

TO DISTRIBUTION SYSTEM

Figure 2.2. Ion exchange treatment process schematic

18

2.2.7. Water Quality Considerations

Several water quality parameters will impact the performance of the IX process and conversely, the IX process will affect water quality, as discussed below: Sulfate Interference. Moderate levels of sulfate impact IX processes as the run length is reduced as IX columns preferentially remove sulfate over arsenic (Kwan el al., 2001). Previous research indicates that the number of BVs treated before regeneration decreases from 1500 (at 25 milligrams per liter [mg/L] sulfate) to 700 BV (at 50 mg/L sulfate), and further decreases to 300 (at 100 mg/L sulfate) (Clifford, 1999). The BV is the cubic feet (or cubic meters) of water treated divided by the cubic feet (or cubic meters) of resin that is available for the water to pass through for treatment. Although this relationship will not be exactly the same for all waters, it does provide a general indication of the impact of sulfates with respect to EX treatment processes. Based on this information the following ranges of sulfate levels were used to assess the impacts on an EX process: • Moderate impact on treatment at influent sulfate concentrations less than 25 mg/L • Significant impact with reduction in bed volumes treated at influent sulfate concentrations between 25 and 150 mg/L • Extreme impacts on treatment, process should not be considered at sulfate concentrations greater than 150 mg/L Arsenic Peaking. As sulfate accumulates on an EX resin, the less preferred anions will be released from the column (nitrate, arsenic, bicarbonates, etc.) potentially increasing the effluent concentrations of these less preferred anions when compared to the influent concentrations. If the column run is not terminated when sulfate breakthrough occurs, arsenic peaking (higher effluent arsenic concentrations when compared to the influent) could occur and the integrity of the EX system could be threatened (Kwan et al., 2001a). This effect can be minimized with multiple parallel columns and regenerating columns at proper intervals. An example of arsenic breakthrough and peaking in an EX column is shown in Figure 2.3.

19

Nitrate Interference. Although arsenic is preferred over nitrates by SBA exchange resins, nitrate is also removed by IX resins along with arsenic. Nitrate peaking is a phenomenon where nitrate that is removed by the IX column at the beginning and during the middle of a run is released at the end of the run because the sulfate is preferred by the resin over nitrate (sulfate displaces accumulated nitrate as the number of available exchange sites diminishes). While there is excess exchange capacity in the earlier stages of the column run, peaking can produce effluent nitrate concentrations of two to four times the influent concentration. This poses a significant threat to the integrity of IX effluent. Placement of multiple columns in parallel is required to dampen the effects of peaking in any single column. By placing a minimum of three columns in parallel and staggering the run start times, the effects of peaking can be minimized (NCS, 2001). Even with three columns in parallel, nitrate peaks in excess of the maximum contaminant level of 10 mg/L can occur when the influent levels exceed 5 mg/L and three parallel columns are present. This would occur assuming a nitrate peak of four times the influent occurs in one column and influent and effluent levels are equal in the other two columns, as shown in the following mass balance (NCS, 2001):

12/28/1999

12/29/1999

12/30/1999

• Influent SO4 • IX Effluent Arsenic

12/31/1999

01/01/2000

--•IX Effluent Sulfate •A- Influent Arsenic

Figure 2.3. Arsenic peaking in DC columns 20

[NOs]3 columns combined

=

([NOsJcolumn 1 + [NOsJcolumn 2 + [NO3] Column 3) ^ 3

If 1

=

[NO3]column2

=

[NO3]influent, and

[NO3]column3

=

4 X [NO3]influent

Then: [NO3] 5 columns combined =

([NO3 ] influent + 4 X [NO3]infiuent + [NO3]infiuent) -r 3

[NO3] 3 columns combined =

nitrate concentration in blended flow from 3

where, columns [NO3]coiumn i

=

effluent nitrate concentration at column 1

[NO3]coiumn 2

=


[NO3]coiumn 3

=


=

IX influent nitrate concentration

Setting the left side of the equation equal to 10 mg/L results in an influent nitrate level of 5 mg/L, conditions under which nitrate peaking would be significant enough to pose concerns with compliance with the MCL. Therefore, nitrate levels greater than 5 mg/L will likely pose a threat to the integrity of an IX system and use of IX where nitrate levels exceed 5 mg/L should be limited. Changes in pH. Since bicarbonate is removed by an IX exchange column, a pH drop of 0.5 to 1 unit can be expected through an EX column, particularly at the beginning of a run. To minimize this impact multiple parallel columns or post pH adjustment with bicarbonate or caustic soda addition is required. 2.2.2. Regeneration

DC for arsenic removal would utilize a chloride based resin operated and regenerated in a down flow mode. Sodium chloride solution (brine) with a strength of 1 to 5 molar (M), or 58,000 to

21

292,000 mg/L, is generally used to regenerate the resin. Recycling brine could minimize the use of salt, the volume of waste solids generated, and the volume of waste brine that must be handled. However, recycling brine would also increase hazard potential of waste streams and will likely generate hazardous wastes, as discussed under Section 3.1 of Chapter 3. For this reason, brine recycle is not considered in this project. For low sulfate waters ( 10.8. The exact pH for optimized CaCO3 and Mg(OH)2 precipitation may differ slightly from this due to calcium and magnesium interactions with other solutes (Benefteld and Morgan, 1999). Units in a typical lime-soda ash softening process include rapid mix, flocculation, and sedimentation. More commonly, the process is combined into a solids contact unit where rapid

42

mix, flocculation, and sedimentation occur in a single unit. A typical schematic of lime softening and enhanced lime softening treatment system with residuals handling is shown in Figure 2.11 (McPhee, 2001). Softening can also be used to remove other metals, inorganics and radionuclides. Arsenate can be removed effectively (75 to 100%) with the process at pH levels > 10.5. The mechanisms for removal include coprecipitation, occlusion, and adsorption with the calcium and magnesium precipitates (Edwards, 1998). In addition to these two precipitates, Fe(OH)3 formed by the precipitation of soluble iron naturally present in treatment plant influent or by the addition of iron coagulant during softening is a controlling factor in arsenate removal.

The primary

mechanism for removal of arsenic is thought to be co-precipitation with the Mg(OH)2. Calcium carbonate precipitation typically will remove only a small amount of arsenate. A study of fullscale lime softening facilities showed arsenic removal efficiencies at plants precipitating only calcite was between 0 and 10%, whereas soluble arsenate removal at plants precipitating calcite and magnesium hydroxide or iron was between 60 and 80% (AwwaRF, 2000). Sorg et al. (1978) showed lime softening processes to achieve > 90% removal of As5+ at pH 11.0 in a study of treatment technologies for removal of inorganics. CONVENTIONAL FILTRATION

CHEMICAL

- . —. — . J

• Fed, • POLYMER • pH ADJUSTMENT

SOLIDS TO LANDFILL LIQUID TO POTW

Figure 2.11. Process schematic for lime softening and enhanced lime softening treatment system with residuals handling.

43

As with coagulation, lime softening will not be used specifically for arsenic removal, but softening facilities treating water with elevated arsenic levels can optimize their existing processes to meet multiple water quality goals without additional polishing treatments. AwwaRF, 2000 presented a hierarchy for existing lime softening plants to optimize arsenic removal. Optimization includes oxidation of any arsenite present to arsenate, addition of small amount of iron (< 5 mg/L) to increase arsenic removal at plants precipitating only calcium carbonate, and increasing the pH to precipitate magnesium hydroxide which strongly sorbs arsenate. Residuals produced from lime softening processes include sedimentation basin blow down and filter backwash. The quantity of residuals produced is a function of the amount of hardness removed. The quantity of residuals produced is typically much greater than the quantity of residuals produced from coagulation facilities because of the large amounts of lime used in softening. Typical quantities of solids produced can be in the range of 1,000 to 8,000 Ib of solids per million gallons of water treated, depending on the hardness of the water. The arsenic concentration in the residuals will be much lower than in coagulation WTP residuals because of the greater quantity of softening residuals produced (AwwaRF, 2000).

2.4.3. Oxidation/Filtration Processes

When it is necessary to meet multiple water quality goals, processes that are considered for arsenic removal include oxidizing filters (manganese greensand) and iron removal systems (aeration-pre-oxidation) followed by filtration. Oxidizing filters are commonly used for the removal of iron, manganese, and hydrogen sulfide, primarily from groundwaters.

Typical

oxidizing filtration processes include aeration followed by granular media filtration (pressure or gravity configuration), chemical addition, and use of pre-oxidants such as ozone or chlorine dioxide followed by filtration.

During the oxidation process, soluble forms of iron and

manganese are oxidized to insoluble forms either prior to or during filtration. In groundwaters, the most common oxidants are air, chlorine, and potassium permanganate for iron and manganese treatment. Where microbial concerns exist, ozone and chloride dioxide may also be used. Schematics of typical oxidizing filtration process are shown in Figures 2.12 and 2.13 (iron removal with aeration, and manganese removal with KMnO4 and greensand filtration).

44

2.4.3.1. Greensand Filtration Systems

The predominant mineral in greensand is glauconite, a green colored material. Glauconite grains are processed with manganese sulfide or manganese sulfate and potassium permanganate in alternating steps to produce a black precipitate of manganese dioxide on the granules (Subramanian et al., 1997). It is used as a filter media, and the filters are operated similar to a conventional filter except for a regeneration step. Regeneration is typically performed using potassium permanganate. Oxidation is carried out at adsorption sites on the filter media; natural zeolite or manganese greensand can be used as the oxidizing media if treated with a permanganate solution. The treated material develops a coating of manganese dioxide that has a large adsorption capacity for both iron and manganese.

Field studies of existing installations indicate that manganese

greensand filters remove over 80% of arsenic in drinking water when iron is not present (Magyar, 1992). Arsenic Removal Performance. A full-scale arsenic removal study using greensand concluded that 95% removal rates of arsenic were possible at a treatment plant in Kelliher, Saskatchewan. The village of Kelliher had developed a new well that produced an average of 54 ug/L of arsenic during the test period (Magyar, 1992). Extensive arsenic removal pilot studies were conducted in New Mexico using the Greensand filtration process (Subramanian et al., 1997). Sulfate was not a significant competing anion when iron was not present. Arsenite was expected to have the same removal as arsenate. The strong oxidizing capacity of the manganese dioxide coating on the manganese greensand filter media oxidizes the arsenite to arsenate. A contact time of 15 minutes was adequate in the 30-inch deep bed with a 2 gpm/ft2 filtration rate. The reaction was complete only after the media had been pre-treated with dilute nitric acid. More than 400 bed volumes of water were treated without even a slight breakthrough.

45

2.4.3.2. Iron Removal Plants

Iron removal systems, particularly for groundwater, are common in the Midwest for oxidizing soluble ferrous compounds into insoluble ferric precipitates. Iron removal systems are typically used for aesthetic reasons associated with particulates and "red water". Iron removal facilities may be utilized where raw water iron concentrations exceed 1 mg/L, although lower levels can also pose problems. This process can also be optimized for arsenic removal as iron precipitates will also remove arsenic. The amount of natural iron required for arsenic removal has been speculated to be in the range of ten parts iron per part arsenic (10:1) to 20:1 although no firm evidence exists to support this theory. According to a recent EPA study, iron removal plants can remove between 75% and 85% (with influent arsenic concentrations of 20 to 50 ug/L) of influent arsenic without optimization (Field, Chen, and Wang, 2000). In several of the case studies investigated in this project, existing iron removal plants achieved arsenic removals ranging from 60 to 80%. Enhanced arsenic removals (95%) were achieved at the Kokomo Treatment Plant, Indiana by adding ferric chloride to the iron-manganese removal process. Typical schematics of iron and manganese removal plants are shown in Figures 2.12 and 2.13 respectively (Fields et al., 2000).

46

Filtration Vessel

Reaction Vessels

uuu ., Recycle Supernatant Water

Concrete Vat

Finished Water To Clear Well

Backwash Water Filter Press /

Sludge Holding \ Tank

Filter Cake to Municipal Landfill Sludge

Figure 2.12. Process schematic of iron removal process

Raw Water from Groundwater Aeration Wells

Sedimentation

(2)

Filtration (Greensand)

Softening i> Finished Water

Approximately 2/3 of Flow Treated Using Zeolite Softening

Supenatant Water and Wastewater Discharged to Sanitary Sewer

• Sludge Sent to Drying Beds, Then to Local Farm Fields

Figure 2.13. Process schematic of manganese removal by greensand filtration

47

The type of filtration process and media used can impact the performance of an iron removal plant with respect to arsenic removal. Several manufacturers supply proprietary high rate filter media for iron removal in a pressure filtration system (without sedimentation). Use of additional coagulants or pH adjustment for enhanced arsenic removal may be limited in these systems, as the filter loading rates would be significantly impacted. Polymers maybe required to enhance the filtration performance. Use of conventional filter media (dual media, or deep bed anthracite) for iron removal may provide more flexibility in arsenic removal as these filters can tolerate higher influent solids loadings and the pH of these systems can be optimized as well. If sedimentation is provided, the capacity for arsenic removal is significantly increased due to the additional flexibility to elevate the coagulant dose (similar to a conventional process). 2.4.3.3. Residuals Handling (for Oxidation/Filtration Systems)

Residuals handling facilities for oxidation/filtration processes are similar to those used for CMF or direct filtration. Two residuals treatment options are most commonly used: 1. Equalization, thickening, and dewatering - The spent backwash is equalized and then sent to a thickener, after which the thickener underflow is dewatered, either using a mechanical device such as a filter press or solar drying beds. The supernatant from the thickener is recycled through the main treatment process. 2. Settling lagoon or pond and dewatering - The spent backwash is delivered to a settling pond where the solids are accumulated at the bottom of the pond under quiescent conditions. The lagoons are loaded multiple times until the solids depth is between two and four feet. At this point the lagoon is taken out of service and the solids are solar dried. The decant from the lagoon is recycled through the main treatment plant. 2. In some instances, particularly for smaller plants, sewer or off-site disposal of the waste wash water or settled solids from backwash clarification may be possible. 2.5. Membrane Processes Membranes have been proven as an effective arsenic removal technology in previous bench and pilot studies (AwwaRF, 2000; NCS, 2001; Kommineni et al, 2001, Sinha et al, 2001). Membranes that can remove arsenic with FeCl3 pretreatment include MF and UF. Very little arsenic removal would occur in MF and UF systems without pretreatment since most arsenic in 48

groundwater systems is in the dissolved form (AwwaRF, 2000). In UF systems, the amount of coagulant that can be fed is limited due to the small pore size of the membrane (8,000-10,000 Daltons). Elevated levels of coagulant will foul the membrane quickly. Additionally, MF is a more proven technology for arsenic removal. For these reasons, UF is less preferred for arsenic treatment. NF and RO systems are able to remove dissolved arsenic without FeCls pretreatment. Pressure requirements are higher and water recovery rates are lower for RO when compared to NF. CMF, NF and RO are discussed in more detail in the following sections. Electric voltage driven membranes that can remove arsenic include electrodialysis (ED) and electrodialysis reversal (EDR) systems. 2.5.7.

Coagulation-Assisted Microfiltration

Coagulants, such as aluminum sulfate or ferric chloride/sulfate, neutralize the surface charge of particles in water and allow the particles to form larger floe particles. These floes settle more readily and can be easily removed by conventional filters and microfilters. The negatively charged arsenate compounds (HaAsO^ and HAsO^2) adsorb to the floe particles. As with most arsenic removal technologies, water that contains a significant amount of As(ni) would require pre-oxidation to As(V) to achieve better removal rates. A modification of the conventional coagulation/filtration treatment is iron coagulation followed by MF, referred to as CMF. This treatment is sensitive to the dose of iron, mixing energy, detention time, and pH. Pilot studies in Phoenix, Arizona; Albuquerque, New Mexico; Tucson, Arizona and Billings, Montana have indicated that arsenic removal rates in excess of 80 percent can be achieved with ferric chloride dosages of 2 to 10 mg/L (as FeCls) at pH levels of 7.5 to 8.5 (NCS, 2001 and Kommineni et al., 2001). Higher removal rates may require pH adjustment to 6 to 6.5 or more contact time between coagulant and water. The presence of silica may impact performance as the silica particles compete with arsenic for sites on the iron precipitate. Silica may also cause fouling of membranes. This requires periodic cleaning with citric acid. A high mixing intensity, or "G", value of 1000 sec"1 and a minimum contact time of 10 to 20 seconds is needed to disperse the chemical and form floe that will adsorb arsenic. 49

Effective arsenic removal from groundwater has been accomplished with a membrane flux rate of 80 to 120 gallons per square foot per day (gfd) with an operating pressure of approximately 20 pounds per square inch (psi) (NCS, 2001). Manufacturers recommend a flux rate of 50 to 65 gfd for CMF operation. The actual flux rate will be governed by the water quality of the raw water. The CMF process is illustrated schematically in Figure 2.14. The MF units are backwashed (using an air scour process) on a periodic basis to remove accumulated ferric hydroxide solids from the membranes. Backwashing occurs every 20 to 30 minutes. The water recovery rate for the CMF process ranges between 90 and 95 percent. 2.5.1.1. Water Quality Considerations

Raw water quality parameters can have a significant impact on the performance of CMF for arsenic removal. The important parameters include arsenic species, NOM levels, and presence of silica. As with most technologies As(V) species (arsenate) are more easily removed by coagulation than As(ni) species. At normal pH ranges (pH = 7), arsenite exists in the neutral form that does not adsorb as well as As(V) on a coagulant floe.

FERRIC CHLORIDE FEED SYSTEM

J

)

CONTACT CHAMBER

MIXER

WELL

SPENT BACKWASH (DISCHARGED TO SEWER OR TREATED ON-SITE)

Figure 2.14. CMF process schematic

50

Higher NOM levels could cause interference in arsenic removal when low levels of coagulant are used as NOM contributes to coagulant demand. In the pH range 4 to 7, the organics do not have a significant effect as compared to at pH 9.0 (Bering and Elimelech, 1996). As(DI) removal is more impacted by NOM levels than As(V) removal. The presence of calcium was observed to offset the effect of organics in the same study. Silica has not directly been correlated to the decline in performance of coagulation microflltration. However pilot studies at Phoenix have shown that high levels of silica might impact arsenic removal and cause fouling of the membrane. In recent studies, silica has been shown to impact the performance of coagulants for arsenic removal at higher pH levels by adsorbing onto the coagulant floe (Meng et al., 2000). It is known that silica can interact with Fe (IE) to form soluble polymers and highly dispersed colloids as pH decreases. In earlier studies it had been shown these are not removed by filtration (Her, 1979; Robinson et al., 1992). These soluble polymers and colloids might be the reason for the excessive fouling found during the pilot tests, particularly at lower pH values. Presence of chlorine in the raw water for CMF processes is not expected to cause deterioration of the membranes as the membrane materials for microflltration membranes are resistant to chlorine.

2.5.1.2. Residuals Handling

The backwash waste stream for CMF will not be classified as a hazardous waste because the arsenic is present in particulate form, not dissolved (this is discussed in more detail in Chapter 3). Residuals generally cannot be discharged directly to the sewer if the total arsenic concentration is in excess of the threshold based local limits (TBLL) for arsenic. If sewer disposal is not viable, residuals handling requirements for CMF systems would include a clarifier or plate settler, solar drying basin or mechanical device for underflow solids dewatering, and a waste citric acid holding tank for membrane cleaning solution. Decant from the plate settler will be sent to the sewer or recycled through the CMF unit, or an evaporative lagoon. Dewatered sludge will be disposed in a non-hazardous waste landfill. The waste membrane cleaning solution stream will be disposed off-site as either a hazardous waste (based on pH) or a non-hazardous waste (if neutralization is feasible). A schematic illustrating the residuals handling for CMF is shown in Figure 2.15.

51

MICROFILTRAT10N MEMBRANES

RAW WATER SOURCE

CHEMICAL COAGULANT MICROFILTER BACKWASH BATCH CLARIFICATION AND THICKENING

LIQUID SUPERNATANT DISPOSAL: • POTW • DIRECT DISCHARGE • RECYCLE

CHEMICAL —— • CONDITIONING; SOLIDS TO MECHANICAL OR NON-MECHANICAL OEWATER1NG SYSTEM

• FeCb • POLYMER • pH ADJUSTMENT

SOLIDS DISPOSAL: • LANDFILL

LIQUID STREAM • POTW

Figure 2.15. CMF residuals handling schematic 2.5.2. Nanofiltradon and Reverse Osmosis

NF and RO are pressure-driven processes where feedwater enters one or more pressurized modules containing membranes. Membranes are permeable to water but not to substances that are removed. All membrane processes separate feed water into two streams, the product and the concentrate. The concentrate stream contains the substances removed from the feed water after being rejected by the membrane barrier. NF/RO membranes have been developed that have retention capabilities of molecular weight between 100 and 1000 Daltons. NF is not as fine a filtration process as RO, but it utilizes a lower operating pressure to separate reject from permeate. Since a molecular weight of 100 equates to a large molecule of about 1 nanometer, these membranes are called NF membranes. Applied pressure requirements for NF are generally less than for RO. Ion-selectivity is a significant feature of NF. Smaller monovalent anions (e.g., chlorides) are able to pass through

52

the membrane, while salts with polyvalent anions (e.g., sulfates, calcium, magnesium) and some larger monovalent ions are retained. RO rejects both monovalent and polyvalent ions. The RO rejection for monovalent and polyvalent ions is above 90%. NF and RO are used for treating surface waters to remove natural organic matter (NOM) such as humic and fulvic acids in order to prevent the formation of unwanted disinfection by-products (e.g., trihalomethanes). Dissolved arsenic particles are typically in the range of 200 to 400 Daltons. NF, unlike RO, is affected by the charge of the particles being rejected. Particles with higher charges are more likely to be rejected than others (HAsO42~ is more likely to be rejected than H2AsO4"). Manufacturers' data for NF/RO membranes indicate that operating pressures range between 100 and 400 psi and arsenic rejection rates are between 60 and 80 percent per stage. Previous testing has indicated that NF/RO membranes would achieve greater than 90% arsenic rejection (AwwaRF, 2000). A three-stage array could potentially remove over 85% of influent dissolved arsenic, depending on site-specific conditions. Water recovery rates would range between 80 and 90 percent. It should be noted that the impacts of long-term operations on membrane fouling have not been well investigated in previous studies. The most common types of membranes used in NF/RO are comprised of cellulose acetate or polyamide. Thin film composite polyamide membranes have a uniform pore size, are chemically resistant and pH tolerant, but are sensitive to chlorine. Cellulose di- and triacetate-blend polymer membranes have a low fouling potential and are chlorine-tolerant. 2.5.2.1. Water Quality Considerations

Water quality impacts on NF/RO membrane performance include arsenic speciation and ionic charge, raw water pH, NOM content of raw water, presence of inorganics and presence of colloidal matter. For tighter RO membranes, the arsenic charge does not have a major impact on the rejection. However for loose NF membranes where electrostatic repulsion at the membrane surface is also a major component in rejection, arsenic charge has a major effect. As(IH) species

53

are neutral and are not very well rejected by negatively charged NF membranes while negatively charged As(V) species show good removal by NF membranes. The pH effects on arsenic rejection are not significant for RO membranes where arsenic removal is mostly by size exclusion. For NF membranes where arsenic removal by electrostatic repulsion is significant pH effects are important. It was found that at neutral pH, anionic arsenic(V) species (arsenate) was rejected to a substantial degree by the negatively charged NF membranes (AwwaRF, 2000; Hering and Elimelech, 1996). At this pH, As (V) is in the form of HAsO42" and EkAsCV. However, under more acidic conditions, when the As(V) is in the form of IÂsCV and H3AsO4 (neutral), the arsenic rejection was reduced. For the As (HI) species, the rejection was low at a neutral pH (as present in neutral H3AsO3 form) but at a pH of 10.8 (predominant species being H2AsO3" and HAsO32~), the rejection increased substantially. It can be concluded that arsenic rejections for both species would decrease with decreasing pH values for membranes where electrostatic rejection is predominant. Presence of NOM has also been seen to effect arsenic removal. Increased rejections have been observed for arsenic in high NOM waters but increases in NOM can cause fouling of the membrane surface necessitating frequent membrane chemical cleaning (Braghetta et al., 1997). The raw water characteristics have a major impact on NOM fouling of NF membranes. Increase in ionic strength, decrease of solution pH and presence of divalent cations increase the rate of NOM fouling of NF membranes (Hong and Elimelich, 1997). The presence of inorganic ions like calcium, magnesium, barium, strontium, sulfate, chloride and carbonate can lead to inorganic scaling on the membrane surface if present in amounts exceeding their saturation potential. A point to be considered here is that in multistage systems, typically employed in NF/RO systems, these ions can be concentrated to levels as much as four times higher than in raw water.

Pretreatment strategies such as addition of antiscalant and pH

adjustment should be considered if the inorganic ion concentrations are high. Inorganic scale is difficult to clean and causes a rapid decline in production during operation.

54

Another inorganic component of concern is silica. Silica is known to polymerize at high concentrations. Silica polymerization can cause what is called "blinding" of the membrane by forming a layer of difficult to remove scale. Colloidal fouling had been observed in NF and RO membranes and studied using model colloids (kaolinite). It was found that colloids cause a rapid flux decline during operation and the rate of flux decline increases as the ionic strength increases. The rejection also decreases as the membrane fouling increases (AwwaRF, 2000). Biological fouling has also been observed in NF/RO membranes. Membrane material like cellulose acetate and cellulose triacetate provide a very favorable substrate for microbial growth. These microbes cause flux decline by forming a biofilm on the membrane surface. The fouling biofilm has been described as an organic film composed of live and dead microorganisms embedded in a polymer matrix of their own, consisting of excreted polysaccharides (Ridgway, 1987). The sensitivity of the NF/RO membranes to chlorine varies and in general the water needs to be dechlorinated before sending it to the membrane. Polyamide TFC membranes are very sensitive to chlorine levels in the water while cellulose acetate membranes are more resistant. 2.5.2.2. Residuals Handling

NF/RO residuals could potentially be disposed directly to the sanitary sewer without further treatment where raw water arsenic levels are below 15 ug/L and TDS levels were not excessive (42~ > 50 mg/L and NOs" > 5 mg/L as N), DC becomes infeasible because of high sulfate interference and nitrate peaking. In DC treatment, arsenic peaking is typically followed by nitrate peaking and they are both initiated by sulfate. By placing a minimum of three columns in parallel and staggering the run start times, the effects of peaking can be

93

minimized. Even with three columns in parallel, nitrate peaks in excess of the MCL of 10 mg/L of N can occur when the influent nitrate levels exceed 5 mg/L as N (NCS, 2001). For waters with high sulfate and nitrate concentrations, AA should be considered with regeneration. If nitrates and sulfates are not in high concentration then DC should be considered with either sewer discharge or evaporation ponds. If hazardous waste generation is acceptable and brine can be disposed of then DC with regeneration is the preferred technology. For the AA with regeneration system to be considered, brine disposal to evaporation ponds or sewer must be feasible and handling of hazardous AA regenerant must be acceptable. If not, then throwaway AA, GFH and modified AA (innovative technology) should be considered. If pH of raw water is above 7.5 then use of these media with pH adjustment should be considered. If pH is below 7.5 then use of media with and without pH adjustment should be considered. If column run lengths to full exhaustion with a total system EBCT of 10 minutes (2, 5-minute contactors) with the throwaway media is higher than 6 months (under intermittent conditions) then compliance with a 10 ug/L standard for arsenic is anticipated. If column run lengths are less than six months then membrane technologies should be considered. First CMF should be considered. If residual handling requirements are not met with CMF, then NF or ROshould be considered. The water loss estimated for NF/RO technologies is about 15% and brine disposal is generally a significant issue. If brine disposal is possible and 15% water loss is acceptable then compliance with a 10 |ig/L standard for arsenic using NF/RO is expected. If both CMF and NF/RO are found to be infeasible then throwaway media should be re-evaluated with shortened run lengths. The spreadsheet tool can be utilized to assess many of the feasibility issues discussed above. It provides estimates of land area for lagoons, column run lengths, residuals characteristics, and water loss rates.

94

Disinfection AKHIB {For Waters Wtth No Iron Or Manganese ftofaloms)

j Consider activated alumina j | with regeneration

Yes I Can ion exchange ' esiduals be discharge directly to sewer?

TYes Can activated alumina residuals be discharged directly to sewer

Is average relative humidity tess than 75% and annual net evaporation positive?

Consider activated alumina with sewer discharge of residuals

Yes

No average relative humidity less than 75% and annual net evaporation positive?

i quality or brine i handling problems? ! (hazardous waste j generation and handling)

Yes Consider activated alumina with evaporation ponds for residuals disposal

Are there any significant water quality or spent regenerant handing problems? (hazardous waste generation and handling)

No Anticipated compliance with ! the arsenic regulation

,

Evaluate use of throwaway 1 adsorbent media with ana ! without pH adjustment j

Evaluate coagulation-assisted mlcrofiltration

No

i ; Are residual handling 1 1 requirements met?

:———r-N5—

No i Anticipated compliance with the arsenic |____regulation___

Are column run lengths a minimum of 6 months at full breakthrough?

pi]

Yes Anticipated compliance with the arsenic regulation

Stop

Consider membrane treatment with nape-filtration, reverse osmosis or electrodiarvsis reversal Yes

Anticipated compliance with the arsenic regulation

Is 15% water loss acceptable I and can brine be disposed of? Evaluate use of throwaway adsorption media with and twithout pH adjustment ; Consider using throwaway adsorbents with shortened

run lengths

Yes

: Evaluate use of throwaway •j adsorption media with pH adjustment

i Anticipated compliance 1 with the arsenic regulation

i

Figure 4.7. Arsenic decision tree for groundwater treatment plants with disinfection alone (with no iron/manganese problems) as the existing treatment

95

4.2. Spreadsheet Decision Tree Tool for Systems with No Existing Treatment The spreadsheet decision tree tool guides the user through the process of selecting an arsenic removal technology for an impacted point-of-entry (POE). This spreadsheet analytical tool will seek user input of water quality, flows, site constraints and residuals handling preferences. Based on the inputs entered by the user, the spreadsheet tool will identify and rank some preferred treatment alternatives. The spreadsheet tool will also provide characteristics (qualities and quantities) of residuals and conceptual capital and operational costs for each treatment technology. Prior to running the spreadsheet tool the user is recommended to read the following discussion. 4.2.1. Applicable Treatment and Residuals Handling/Disposal Trains

The spreadsheet tool evaluates the applicability of four surface water and ten groundwater treatment and residuals handling/disposal trains for arsenic removal at any given point-of-entry (POE).

Only the established treatment and residuals handling/disposal processes were

considered in developing this decision tree tool.

Due to the limited amount of process,

operational and cost information being available on innovative and vendor-specific, patented (e.g., sand ballasted coagulation, magnetized IX beads and hydrous iron oxide particles) treatment processes, they were not included in this decision tree tool. Although GFH is an innovative process, it has been recently established as an effective arsenic removal process in the US in several studies conducted at City of Tucson, City of Scottsdale and City of Phoenix in Arizona.

The web version of the spreadsheet tool has the cost equations for GFH and

throwaway AA. The four surface water treatment trains that the decision tree tool evaluates include: • Enhanced coagulation/filtration [ECF] • Enhanced lime softening [ELS] • Conversion of direct filtration to conventional filtration [DF -^ CF] • Coagulation-assisted microfiltration [CMF]

96

For all the surface water treatment trains, additional land was assumed to be available at the POE; no additional cost was included to acquire land. Except for CMF, for all the other surface water treatment trains, the existing facilities at the WTP were assumed to be capable of handling the additional residuals that were generated. The eleven groundwater treatment and residuals disposal trains consist of: • Throwaway activated alumina with and without pH adjustment [TAA] • Granular ferric hydroxide with and without pH adjustment [GFH] • Regenerable activated alumina (with and without pH adjustment) with evaporation pond (for liquid waste handling) and non-hazardous landfill (for solid waste disposal) [AAEPNH] • Regenerable activated alumina (with and without pH adjustment) with indirect discharge (liquid waste to sewer) and non-hazardous landfill (for solid waste disposal) [AA-ID] • Ion exchange with evaporation pond (for liquid waste handling) and non-hazardous landfill (for solid waste disposal) [EX-EPNH] • Ion exchange with chemical precipitation (for liquid waste handling) and non-hazardous landfill (for solid waste disposal) [IX-CPNH] • Ion exchange with indirect discharge (liquid waste to sewer) and non-hazardous landfill (for solid waste disposal) [IX-ID] • Coagulation-assisted microfiltration with mechanical dewatering (for liquid waste handling) and non-hazardous landfill (for sludge disposal) [CMF-MDNH] • Coagulation-assisted microfiltration with indirect discharge of backwash [CMF-ID] • Nanofiltration or reverse osmosis with indirect discharge of brine [NF/RO-ID] • Electrodialysis reversal with indirect discharge of brine [EDR-ID] The spreadsheet tool does not have equations or cost curves to compute the costs for iron/manganese treatment processes. The understanding for this is that all the utilities that currently have an iron/manganese problem will have a treatment system that can be enhanced (as suggested in the decision tree charts, Figures 4.5 and 4.6) to achieve the necessary arsenic removal. The enhancements/modifications to iron/manganese removal systems will be fairly minor and will also be a function of what is currently in-place (which would be case specific). 97

So, no costs were developed for building or operating an iron/manganese removal system that could also achieve arsenic removal. 4.2.2. Decision Analysis Tool Overview

The manual for the interactive, web version of the spreadsheet tool is in Appendix E. The spreadsheet decision tree tool has 12 worksheets that are labeled: Summary, POE 1 (point-ofentry 1), POE 2, POE 3, POE 4, POE 5, POE 6, POE 7, POE 8, POE 9, POE 10 and Backup of Table A. 10. Enable the macros when you open the spreadsheet decision tree tool file. Open the worksheet POE 1 by clicking on it. When you open POE 1 you will observe several tables. Shown in Appendix A are the samples of these tables. Table A.I is the input table. Enter the flows, water quality and system information in the highlighted (dark yellow) cells of Table A.I. To guide the user with the inputs, example values are currently shown in these cells. The type of entry (value or yes/no flag) is indicated in the column to the right of the highlighted column. Based on these inputs the spreadsheet will estimate the residuals (Table A.2), land requirements (Table A.4), percent water loss (Table A.4) and costs (Table A.5). Based on the values entered in the input block (Table A.I) the spreadsheet identifies and lists the feasible technologies with no additional land purchase (Table A.7) and with additional land purchase (Table A.8). The user does not have to enter any values in Tables A.2 through A.8 since the spreadsheet automatically computes these based on the system inputs of Table A.I. Shown in Tables A.9 and A. 10 are the qualitative decision drivers that are used in ranking the feasible technologies. Table A. 10 has the suggested ranking values. The values in Table A. 10 are based on the best professional judgment of the team that developed this tool. The user is recommended to read the following discussion on the decision tree tool before modifying the suggested values for qualitative drivers shown in Table A. 10. Tables A. 11 and A. 12 summarize the three highest scoring treatment alternatives for the impacted POE. Tables A. 11 and A. 12 of each POE are summarized in the "summary worksheet". The user can print the summary tables from the summary worksheet. If the system has more than 10 POEs then the user is recommended to make copies of the POE 1 worksheet or the entire spreadsheet file itself.

98

The spreadsheet decision tree analysis consists of twelve tables as shown in the POE 1 worksheet: • Input block (Table A.I) • Residuals quantities and characteristics (Table A. 2) • Applicable flow ranges for cost curves (Table A.3) • Split-stream treatment flows and land required computations (Table A.4) • Treatment/residuals handling capital and operational costs (Table A.5) • Water quality observations (Table A.6) • Feasible technologies for no additional land purchase (Table A.7) • Feasible technologies for additional land purchase (Table A. 8) • Qualitative decision drivers ranks for feasible technologies (Table A.9) • Suggested ranking table (Table A. 10) • Summary table of feasible technologies for no additional land purchase • (Table A.I 1) • Summary table of feasible technologies for additional land purchase (Table A. 12) 4.2.3. Mandatory Inputs

Table A.I has the basic inputs necessary to start the decision tree analysis. The inputs sought in Table A.I include the type of source water, the average (long-term) and maximum flows, influent and target arsenic concentrations, other water quality parameters (e.g., nitrate, sulfate concentrations), land availability, acceptable water loss, willingness to handle residuals, possibility of discharging liquid wastes to the sewer and amortization interest rates/period. The type of input, whether it is a value or a flag (yes/no), is identified in the column to right side of the highlighted column. 4.2.4. Residuals Estimations

Based on the inputs entered in Table A.I, the spreadsheet computes the qualities and quantities of residuals that are generated by the various arsenic removal processes like AA and DC. These residuals characteristics are summarized in Table A.2. Most arsenic removal processes transfer 99

arsenic from one (water) phase to another (solid/liquid) phase. Therefore, arsenic treatment processes generate either liquid or solid wastes containing elevated levels of arsenic that require special handling and disposal techniques. The characteristics of residuals that are summarized in Table A.2 must be given due consideration while selecting an arsenic removal technology. 4.2.5. Costs Calculations

The spreadsheet tool is equipped with a Visual Basic macro that contains unit cost curves for estimating the capital and operational costs for pre-oxidation, treatment and residuals handling/disposal. The maximum and average flow ranges that the cost curves are appli cable are shown in Table A.3. Pre-oxidation costs are added to the total costs only when there is no chlorine addition at the POE. The itemized capital and operational costs for treatment and residuals handling/disposal for each technology are shown in Table A.5. The costs shown in Table A.5 are corrected to the current time using the engineering news records cost indices. 4.2.6. Other Computations

Shown in Table A.4 are the split-stream treatment design and average flows, if the user chooses to do a blending of the arsenic treated water with the raw water to achieve the necessary targeted arsenic concentration. Also, shown in Table A.4 are the values for land required (for treatment and residuals handling) and percent additional water loss for each technology. Table A.6 gives a summary of types of waste streams that would be generated, suggested residuals handling practices and water quality comments. The water quality comments warn the user of possible interferences to the treatment process from the presence of other constituents such as silica or sulfate in the raw water. These warnings are also based on the data entered by the user in Table

4.2.7. Critical Decision Drivers and Technology Feasibility Evaluation

The feasibility criteria used for selecting the various treatment trains are shown in Tables A.7 and A.8. The feasibility criteria include (1) source water type (ground or surface water), (2)

100

arsenic removal achievable compared to the required, (3) land availability for purchase or otherwise, (4) willingness to handle possible hazardous waste, (5) acceptable additional percent water loss, (6) local regulations with respect to sewer discharge, (7) raw water quality and (8) flow limits. If a particular treatment process meets a criterion then the spreadsheet assigns a binary value of "1" and if it does not meet the criterion then it assigns a value of "0" for that particular criterion. For a treatment process to be feasible it should meet a/1 of the above criteria. As mentioned earlier, only some processes were assumed to be applicable for surface waters and certain others were considered to be feasible for well head treatment and this is evaluated under the source water feasibility criteria. The arsenic removal required is based on the influent arsenic and the target arsenic. The program calculates the percent arsenic removal achievable for each technology based on the finished water arsenic concentrations. The spreadsheet has some default values for the finished water arsenic concentrations and also lets the user to input alternative finished water arsenic concentrations as shown in Table A.4. Then, the spreadsheet compares the achievable arsenic removal to the required arsenic removal and assigns a value of "1" (feasible) to those technologies that have higher achievable removals compared to the required. The spreadsheet uses the default values for finished water arsenic concentrations only when there are no user-assigned values in the highlighted cells of Table A.4. Land is another critical decision driver. Table A.7 identifies the technologies that are feasible with the land that is currently available at the site and with no additional land purchase. Alternatively, at some sites, it may be possible to purchase some land and the technologies that would become feasible under additional land purchase are listed under Table A. 8.

For

technologies under Table A. 8 cost for purchasing the additional land is added to the treatment cost. If a utility does not want to handle potentially hazardous (liquid/solid) wastes generated by a process at a particular POE then the waste criterion will assign a value "0" (infeasible) to those treatment technologies that produce those wastes. Some treatment processes such as NF/RO can result in large (10-15 percent) quantities of water loss. The water losses assumed for each treatment process are shown in Table A.4. If the acceptable percent water loss is greater than the estimated water loss for the technology then that

101

particular process is considered to be feasible. Similarly, the discharge of the liquid wastes to the sewer is dependent on the local discharge limits and regulations.

The quantities and

characteristics of the residuals generated by each treatment process are shown in Table A.2. Based on the results shown in Table A.2 and the local discharge limits the user can decide and enter whether they could discharge the liquid waste to a publicly-owned wastewater sewer or some alternative brine streams. The water quality criterion is used to evaluate the presence of sulfates that could interfere with DC process. The spreadsheet tool assumes DC to be a feasible technology only if the raw water has sulfate concentration less than 150 mg/L. The flow limits criteria are used to verify that the split-stream treatment design/average flows are within the limits of cost curves. The flow ranges over which the cost curves are applicable are shown in Table A. 3. 4.2.8. Qualitative Decision Drivers and Ranking of Feasible Alternatives

Based on the inputs given in Table A.I, the decision tree tool will isolate the technologies that are feasible in Tables A.7 and A.8. Then the spreadsheet ranks the feasible technologies based on the qualitative drivers that are identified in Table A.9. The qualitative drivers are assigned certain weightage factors that are shown in red in the highlighted cells of the last row of Table A.9. The spreadsheet computes a weighted-average score based on the rank and the weightage factor. The weightage factors can be altered by the user based on the site-specific conditions. For example, the user can choose to assign a higher weightage value to public acceptance driver (for a POE that is located in a domestic neighborhood) by entering a higher value in the row titled "weights". The values for the qualitative decision drivers of Table A.9 were automated to read directly from Table A. 10, the suggested ranking table. The values in Table A. 10 were developed from the researchers experience and input from the utility workshop participants. The cost decision driver of Table A.9 automatically assigns values based on the annualized total cost for treatment and residuals handling/disposal. For example, if a POE has 8 groundwater treatment technologies that are feasible and among the 8 feasible alternatives, if DC with indirect discharge and non-

102

hazardous landfill (DC-ID) is the least costing technology then it would be assigned the highest rank of 8.

Table A.9 has been automated to list the default ranks of only the feasible

technologies. Similarly, the ranking for other qualitative drivers was also automated to read as proportions of the values listed in the suggested ranking table and the total number of feasible alternatives. The user has the option to change the default values of Table A. 10. By modifying the scores of Table A. 10, the user will automatically overrule the default ranks and that will in turn change the scores of Table A.9. A back-up copy of Table A. 10 is provided in a separate worksheet just in case the user wants to revert back to the default values. 4.2.9. Summary Output of the Most Preferred Alternatives

Tables A. 11 and A. 12 summarize the three most preferred alternatives (based on the score) for no land purchase and for additional land purchase.

This spreadsheet analysis has to be

performed independently for each impacted POE. The summary tables from each POE are then summarized under the "summary" worksheet. Based on the treatment alternatives recommended for each POE the utility can decide upon a system-wide alternative or POE-specific alternatives. The summary tables also include the scores, annualized total cost and additional land required.

4.3. Qualitative Guidance on Innovative Technologies Table 4.1 outlines a qualitative comparison of several innovative technologies targeting arsenic removal. In making these comparisons it was assumed that the existing process would be conventional coagulation treatment (as the "starting point") and process modifications were being considered to the existing treatment to enhance its ability to remove arsenic. Optimizing coagulation for arsenic removal using MIEX®, HIOPS, Actiflo™, immersed membranes used in conjunction with an innovative adsorbent (i.e. MIEX® or HIOPS), and GFH are the alternatives that are presented in the table. Several criteria were assessed for each process modification in terms of the qualitative impact relative to the other options. Systems with favorable, neutral and negative impact were designated by +, 0 and ~, respectively. For example, it was estimated that optimizing existing coagulation for arsenic removal would be the cheapest (favorable, +) with

103

respect to the total cost (capital plus O&M) alternative, and that immersed membranes with innovative adsorbents would be one of the most expensive (negative, -) alternatives compared to the other innovative alternatives. Water quality considerations for some of the innovative technologies are discussed in Chapter 7.

Extensive bench, pilot, full-scale testing is

recommended prior to considering innovative treatment alternatives. Table 4.1 Qualitative assessment of selected innovative technologies Optimized conventional coagulation Cost (Capital and O&M)

Technology MIEX®

fflOPs

0

0

Actiflo™

Immersed membranes withMffiX® or fflOPs

0

Residuals Handling and Disposal Size of Footprint

0 0

0

0

0

Ease of Operation Ease of Implementation Safety Public Acceptance Labor Required + Favorable impact;

0 0 0 Neutral impact;

104

0

GFH

0 Negative impact

0

CHAPTERS UNIT COST ASSUMPTIONS 5.1.

Introduction

Providing conceptual level costs for treatment and residuals handling is one of the key objectives of this study. Towards this goal, unit cost curves were developed for all treatment and residuals handling options that were discussed in Chapters 2, 3 and 4.

This chapter presents the

assumptions used in developing these unit cost curves. The actual cost equations are shown in Appendix C. Tables C.I, C.2, C.3, C.4 and C.5 have respectively the cost equations for treatment capital, treatment operations and maintenance (O&M), residuals handling capital, residuals handling O&M and pre-oxidation capital/O&M. Knowing the assumptions that went into development of the cost equations will enable the reader to understand the conceptual-level costs that are being outputted by the interactive, spreadsheet tool. 5.1.1. Treatment Unit Costs

The unit cost curves for the various arsenic treatment technologies (except for NF) were developed using the Water/Wastewater Cost model (Gulp et al., 1994), the Water model (Gulp et a/., 1984) and the Very Small Systems Best Available Technology Cost Document (Malcolm Pirnie, 1993). The Water/Wastewater Cost model was used in developing the costs for large systems with design flows ranging between 10 and 200 mgd. The Water model was used for developing the cost curves for systems with design flows between 0.27 and 1 mgd. The Very Small Systems document was used for system sizes between 0.015 and 0.100 mgd. Costs for flows in the intermediate regions (0.10 to 0.27 and 1 to 10 mgd) were estimated using linear interpolation techniques. At least four data points were generated for each of the flow segments (0.015 to 0.10, 0.27 to 1.0 and 10 to 200 mgd) and best-fit equations were derived to allow cost determination as a function of flow. In the transition zones (0.10 to 0.27 mgd, 1 to 10 mgd), cost estimates were based on

105

linear regressions between the last data point of the previous region and the first data point of the following region. All three models required the inputting of flows to calculate the capital and O&M costs. Additional user-specified variables such as design factors, unit costs and cost indices were also inputted to the models.

Where necessary, vendors and equipment

manufacturers were contacted to assess the accuracy of the cost models, and costs were modified to reflect the input from these sources. The capital and O&M cost curves were based on blending scenarios and developed in such a way that costs may be calculated for any target effluent arsenic concentration. This will enable cost determinations for any potential arsenic MCL. The portions of flow that have to be processed by the various treatment technologies were calculated based on the achievable finished water arsenic concentrations which were assumed to be: • 2.0 jig/L for enhanced softening, AA and GFH; •

1.0 /ig/L for enhanced coagulation, CMF, NF/RO and EDR; and

• 0.5 /tg/L for EX A Technology Design Panel formed through EPA recommended some modifications to the costs generated by the above-mentioned models.

These modifications were incorporated in the

development of the unit cost curves. Detailed discussions of the panel recommendations are available in Guide for Implementing Phase I Water Treatment Upgrade (EPA, 1998a) and Water Treatment Costs Development (Phase I): Road Map to Cost Comparisons (EPA, 1998b). Capital costs include process costs (i.e., manufactured equipment, concrete, steel, instrumentation and control, piping/valving and housing), construction costs (i.e., sitework, excavation, subsurface considerations, standby power, land, contingencies, interest), and engineering costs (contractor overhead and profit, engineering fees, legal, fiscal and administrative fees including permitting). However, the capital costs do not include costs for retrofitting, piloting, additional storage space and redundancy.

106

Capital and O&M cost equations for various treatment alternatives are listed in Tables Cl and C2 of Appendix C. The assumptions that were made in preparing these cost equations are summarized in Section 5.2. 5.1.2. Residuals Handling and Disposal Unit Costs

No cost curves were developed for residuals handling and disposal by surface water technologies, except for plants that may have to retrofit the CMF process. The existing surface water treatment plants (with enhanced coagulation/filtration, enhanced lime softening or direct filtration) are assumed to have the necessary resources in-place to handle any additional residuals that may be generated from optimizing the treatment to achieve the necessary arsenic removal. For groundwater treatment technologies, the residuals handling and disposal cost curves were generated using the Small Water System Byproducts Treatment and Disposal Cost Document (DPRA, 1993a) and Water System Byproducts Treatment and Disposal Cost Document (DPRA, 1993b). As discussed in Chapter 3, the residuals generated from each treatment technology can be handled in several different ways. The residuals handling and disposal alternatives assumed for each treatment technology are summarized below: • Ion exchange -

Evaporation pond (for liquid waste streams) and non-hazardous landfill (for solid residuals) ([IX-EPNH], Figure 5.1)

-

Chemical precipitation and non-hazardous landfill ([DC-CPNH], Figure 5.2)

-

Indirect discharge and non-hazardous landfill ([DC-ID], Figure 5.3)

• Regenerable activated alumina - Evaporation pond and non-hazardous landfill (AA-EPNH) -

Indirect or POTW discharge and non-hazardous landfill (AA-ID)

• Throwaway activated alumina (TAA) -

Non-hazardous landfilling of spent media

• Granular ferric hydroxide (GFH) -

Non-hazardous landfilling of spent media

• Coagulation-assisted microfiltration

107

-

Mechanical dewatering and non-hazardous landfill ([CMF-MDNH], Figure 5.4)

-

Indirect or POTW discharge for backwash, reject and rinse waters (CMF-DD)

• Nanofiltration or Reverse Osmosis -

Indirect or POTW discharge for brine or reject stream (NF-ED or RO-ID) (Figure 5.5)

• Electrodialysis reversal -

Indirect or POTW discharge for brine or reject stream (EDR-ID) (Figure 5.5)

Illustrated in Figures 5.1 through 5.5 are decision trees for residuals handling and disposal for EX-EPNH, K-CPNH, AA-EPNH, CMF-MDNH and NF/EDR/RO-ID.

Descriptions of the

various unit processes that make up these trees are presented in Chapter 3. Cost equations for residuals handling and disposal alternatives are presented in Tables C3 and C4 of Appendix C. The assumptions that were made in developing these cost equations are discussed in Section 5.3.

5.2.

Treatment Cost Assumptions

5.2.1. Enhanced Coagulation/Filtration

Enhanced

coagulation/filtration

(ECF)

involves

modifications

to

the

conventional

coagulation/filtration process to achieve the necessary arsenic removal. These modifications could involve increasing of coagulant dose or lowering the coagulation pH or both.

For

developing the cost equations, it was assumed that conventional treatment can achieve about 50 percent arsenic removal prior to enhancement.

It was also assumed that the increase in

operational and maintenance costs would result from increased material and power costs and not from additional labor. The ECF costs were developed based on the following conceptual facilities and operational parameters: • Additional ferric chloride dose of 10 mg/L; • Additional feed system for increased ferric chloride dose; • Additional lime dose of 10 mg/L for pH adjustment; and • Additional feed system for increased lime dose.

108

Ion Exchange Holding Tank and Thickener

Rinse Water

Brine

1

Indirect Discharge

Decant Brine

J Thickened Solids Holding Tank Legend: Handling Method | Disposal Method

I SolarBedsDrying I

I

Non-Hazardous Landfill

Figure 5.1. Ion exchange with evaporation pond and non-hazardous landfill

109

S

\

1 Evaporation

\

Ponds

Ion Exchange Indirect Discharge Rinse Water

n Brine

Precipitation Tank

L ;±r

Decant Brine

Precipitated Solids Holding Tank • i

Legend: I

Handling Method

|

Disposal Method

I


Figure 5.2. Ion exchange with chemical precipitation and non-hazardous landfill

110

Spent Resin

Ion Exchange

Rinse & Brine Waters ____

Equalization Tank

_______

1

r_____

_______

Resin Storage

I

Non-Hazardous Landfill POTW Discharge

Legend: Handling Method

|

Disposal Method

I

Figure 5.3. Ion exchange with indirect discharge and non-hazardous landfill

ill

Overflow Cleaning Solution

Coagulation-Assisted Microfiltration

Neutralization Tank

Inclined Plate Settler

Backwash

i

Thickened Solids

Indirect Discharge

I

Legend:

Holding Tank ^/

Mechanical Dewater I

I Handling Method | I

Disposal Method


I

Figure 5.4. Coagulation-assisted microfiltration with mechanical dewatering and non-hazardous landfill

112

Nanofiltration/ Reverse Osmosis/ Electrodialysis Reversal Reject/Brine

.

Equalization Tank

•

Legend: Handling Method | Disposal Method

Indirect Discharge

I

Figure 5.5. Nanofiltration or reverse osmosis or electrodialysis reversal with indirect discharge

5.2.2. Enhanced Lime Softening

Enhanced lime softening (ELS) involves modifications to the lime softening process to achieve higher arsenic removals. These modifications may consist of either increasing the lime dosage or the soda ash dosage. It may also be necessary to adjust the pH of the treated water by recarbonation. Similar to conventional treatment, for purposes of estimating the costs, it was assumed that an existing lime softening plant could achieve 50 percent arsenic removal prior to

113

enhancement or modifications. The ELS costs were developed based on the following design criteria: • Additional lime dose of 50 mg/L; • Additional feed system for increased lime dose; • Additional re-carbonation at 35 mg/L of carbon dioxide (liquid); and • Additional feed system for increased carbon dioxide dose. 5.2.3. Direct Filtration to Conventional Filtration

To address the conversion of direct filtration systems to conventional filtration (DF -> CF), unit cost curves were developed for addition of sedimentation basins with modified coagulation. The DF-^CF costs were developed based on the following design criteria: > conventional sedimentation units at loading rates of 1000 gpd/ft2 would be used instead of high rate settling processes; and > an additional dose of 20 mg/L ferric chloride to supplement the existing 5 mg/L dose level, considered typical of direct filtration plants. 5. 2.4. Throwaway Activated Alumina

The Water and Water/Wastewater cost models provide process descriptions and cost estimates for fluoride removal using AA, softening via ion exchange, and organic removal using granular activated carbon; these technologies are comparable to the AA and GFH processes assumed for arsenic removal. However, due to fundamental differences between the cost models and the process assumptions for arsenic removal, it was determined that the cost models were unsuitable for direct estimation of AA and GFH costs. The costs for AA and GFH were developed by obtaining quotations for significant process items (e.g., pressure vessels, strainers, charging devices, media and so on) from vendors or suppliers, these costs were utilized as appropriate. Some information from the cost models was used to support the development of multipliers applied to the equipment and media quotes. For both AA and GFH systems, the process train was assumed to consist of two vessels in series with a third standby vessel, which is used for substituting for the exhausted vessel as necessary.

114

The first vessel in the series is referred to as the roughing vessel, the second vessel is the polishing vessel. The roughing vessel will reach exhaustion initially, after which the polishing vessel becomes the roughing vessel and the standby vessel becomes the polishing vessel. The spent media in the initial roughing vessel is replaced with virgin media. This "merry-go-round" approach has been described elsewhere for use in ion exchange systems (Clifford, 1999). Capital cost estimates include all the components necessary for the three vessel system. The redundant vessel was also assumed to contain new media at the time of starting the treatment system. Where necessary, for large systems, more than one train was assumed. Both AA and GFH were assumed to operate on a media throw away basis at all pH conditions. Table 5.1 shows some of the assumptions used to estimate the vessel size, media volume required, and costs for AA and GFH treatment. 5.2.5. Granular Ferric Hydroxide

In addition to what was described above, the following design parameters were assumed in developing the costs for GFH treatment. These design criteria are based on the operational data of existing plants in Germany and England. • Separate capital and O&M cost curves were developed for systems with and without pH adjustment. • The achievable bed volumes for source waters with pH adjustment (to pH 6.5) and without pH adjustment (at ambient pH of the water) were assumed to be 110,000 and 75,000, respectively. Achievable bed volumes are the typical run lengths expected at the given pH prior to unacceptable breakthrough. These bed volumes were assumed based on the information that was available from the GFH treatment plants in Europe that were being operated with EBCTs between 3-10 minutes. • Other design recommendations include (GEH Wasserchemie, 2001; Jekel, 2001, Selvin, 2000): -

Media bed depth of 2 to 5 feet

-

Bed approach velocity of 5 to 8 gal/min-ft2

-

Particle size of 0.32 to 2 mm

-

Tolerable headless of 1 psi/ft 115

Table 5.1 Summary of AA and GFH design parameters Design parameter /operating condition

AA

GFH

Empty bed contact time (EBCT)

5 minutes/vessel; 10 minutes/train (higher EBCTs were assumed at 5200 BV to achieve 90 day periods between exhaustion)

2.5 minutes/vessel; 5 minutes/train

Target hydraulic lading rate

6 gpm/ft2 (lower loading rates were assumed at 5200 B V)

6 gpm/ft2

47 lbs/ft3

75 lbs/ft3

Minimum bed depth

3 feet/vessel, 6 feet/train


Maximum bed depth



12 feet

12 feet

1.5 times the media depth + 1.5 feet for support sand and/or internals

1.5 times the media depth + 1.5 feet for support sand and/or internals

Operations at natural pH 8-8.3

5,200 bed volumes assumed prior to media exhaustion


Operations at natural pH 7-8



Reduced pH operations

15,400 and 23,100 bed volumes assumed prior to media exhaustion at optimal pH of 6.0


AA bulk density

Maximum vessel diameter Media expansion + freeboard

5.2. 6. Conventional Activated Alumina

The number of bed volumes achievable for AA is strongly dependent on the influent arsenic (EPA, 2000(a)) and pH (Simms and Azizian, 1997; Norton et al, 2001). Higher influent arsenic concentrations and higher pH result in lower bed volumes for AA. For the decision tree tool, 116

cost equations were developed factoring in these effects of pH and influent arsenic concentrations. Summarized in Table 5.2 are the assumptions that were made with respect to the achievable bed volumes for varying influent arsenic concentrations, with and without pH adjustment (to pH between 5.5 and 6.0). The AA costs were developed based on the following conceptual facilities and operational parameters:

• Regeneration is performed when arsenic breakthrough occurs; • Approximately 1.5% of the AA media is replaced per regeneration; • Regeneration frequencies as shown in Table 5.2; • Regenerant consists of 10 Ib of NaOH per cubic foot of the media used; • Regenerant is acidified by KbSCU addition to precipitate residual aluminum and desorbed arsenic; • Regeneration cycle consists of 35 minutes of regeneration at a loading rate of 2.5 gpm/ft2 followed by a 30 minute rinse at 5 gpm/ft2; and • Backwashing will be performed periodically (when headloss increases to 10 psi) for 10 minutes at 8-9 gpm/ft2.

The following assumptions were made for AA systems with pH adjustment:

• Optimum treatment pH is between 5.5 and 6.0; • H2SO4 dose of 70 mg/L is assumed to obtain the optimum treatment pH; and • NaOH dose of 50 mg/L is assumed for increasing the pH after arsenic removal.

117

Table 5.2 Bed volumes versus influent arsenic concentration for activated alumina with and without pH adjustment Influent arsenic

Number of bed volumes achievable

concentration

WithpH

Without pH

0*g/P

adjustment

adjustment

5 to 15

50,000

3,000

15 to 35

25,000

7,000

>35

10,000

16,500

5.2.7. Ion Exchange

As discussed in Chapters 2 and 3, the sulfate concentrations in the influent water significantly affect the capacity of the ion exchange (IX) resin with respect to arsenic removal. Therefore, for IX treatment, cost curves were developed for two levels of sulfate occurrence: (1) less than 20 mg/L and (2) between 20 and 50 mg/L. If the raw water sulfate concentrations exceed 50 mg/L, then EX treatment was assumed to be infeasible from a cost perspective. The EX costs were developed based on the following conceptual facilities and operational parameters: • Achievable bed volumes were based on sulfate concentrations; • Raw water pH of 6.5 to 9.0. No pH adjustment was considered; •

Anion exchange resin replacement of 25% per year;

• Regeneration is performed when breakthrough occurs; • Empty-bed contact time (EBCT) of 2.5 minutes; •

Resin cost of $125/ft3;

• Regenerant dose of 5 Ib NaCl/ft3 of resin; • Bed expansion during regeneration is 50%; • Regeneration cycle consists of 10 minutes backwashing at a loading rate of 2.5 gpm/ft2 and 10 minutes regeneration at 0.5 gpm/ft2, followed by a 20-minute rinse; and •

Addition of NaaCOs to account for bicarbonate loss during treatment.

118

5.2.8. Coagulation-Assisted Microfiltration

Coagulation can be used in combination with low-pressure membrane processes, like MF, to aid in removing dissolved constituents that normally would not be removed by the membrane process. Coagulation is an effective treatment technique for arsenic removal whereas MF alone is not. CMF uses MF in place of a conventional gravity filter. The CMF process includes coagulation, flocculation, sedimentation and MF.

Costs for the coagulation portion were

estimated using the cost models mentioned in Section 5.1.1. The MF costs were developed based on vendor quotes and case studies (EPA, 2000 (a)) for industry standard specifications. The following design criteria were used in developing the costs for coagulation portion for small 0ess than 1 mgd) systems: • Package plant with filtration rate of 5 gpm/ft2; and • FeCl3 dose of 25 mg/L. For systems with flow rates greater than 1 mgd, following assumptions were made for estimating the costs of the coagulation portion: • FeCl3 dose of 25 mg/L; • Rapid mix for 1 minute; • Flocculation for 20 minutes; and • Sedimentation at 1,000 gallons per day/ft2 in rectangular basins. 5.2.9. Nanofiltration/Reverse Osmosis

NF/RO treatment costs were developed based on a survey consisting of some softening plants (Bergman, 1996). No specific design criteria were used in developing the cost equations, other than the data published by Bergman, 1996. The published survey included 11 existing plants and 5 under-construction plants. The largest plant surveyed was of 14 mgd capacity. All plants surveyed were using groundwater as the source water. The costs presented in the survey were 119

corrected independently for decrease (approximately by 50%) in the membrane element price that has occurred in the recent years. Bergman's costs included HaSC^ and NaOH addition for pre- and post-filtration pH adjustment. They also include anti-sealant addition for scale control. Survey costs were adjusted for an equivalent raw water temperature of 20 °C. Brine disposal costs were accounted for separately and were not included under the treatment costs. 5.2.70. Electrodialysis Reversal

Installation and operational costs for EDR were assumed to be similar to NF/RO. Therefore, no separate cost equations were developed for EDR. 5.2.11. Iron/Manganese Removal

As mentioned in Chapter 4, no cost equations were developed for iron/manganese treatment systems. The reason for this was that any utility that currently has an iron/manganese problem will have some sort of a treatment system that can be enhanced (as suggested in the decision tree charts, Figures 4.5 and 4.6) to achieve the necessary arsenic removal. These costs for these enhancements or modifications to the existing iron/manganese removal system are expected to be minor. 5.3.

Residuals Handling and Disposal Cost Assumptions

Each of the treatment technologies discussed above will produce residuals, either solid or liquid streams, containing elevated concentrations of arsenic. The selection of residuals handling and disposal alternatives is a function of a number of factors including the treatment technology employed, capital and operations costs, and amount and characteristics of the waste generated. The various residuals handling and disposal alternatives for which cost curves were developed and included in the decision tree are briefly discussed in this section.

120

5.3. 1. Residuals Handling Alternatives 5.3.1.1.

Mechanical Dewatering

Mechanical dewatering (MD) processes include centrifuges, vacuum-assisted dewatering beds, belt filter presses, and plate and frame filter presses. Such processes generally have high capital, as well as high O&M costs, compared to similar capacity non-mechanical dewatering processes (e.g., storage lagoons). Due to the high costs, MD processes are generally not suitable for application with small water systems. Mechanical and non-mechanical dewatering devices are generally not applicable to NF or RO systems due to the high volume, high TDS waste produced. Filter presses and centrifuges have been used in the water industry for the past several years. Filter presses have been successfully applied to both lime softening and coagulation/filtration process sludges. Filter presses require little land, have high capital costs, and are labor intensive. Centrifugation is a continuous process requiring minimal time to achieve the optimal coagulation/filtration. Centrifuges have low land requirements and high capital costs. They are more labor intensive than non-mechanical alternatives, but less labor intensive than filter presses. The MD costs were developed based on the following conceptual facilities and operational parameters: • Filters presses are effective for sludge flow rates greater than 100 gal/day. • Polymer feed systems consists of a polymer storage tank, a polymer pump, a polymer/sludge contact tank and a 20-30 minute holding tank. • A positive displacement pump delivers sludge to the filter press. • The filter press operates on a batch basis. The filtrate collects in a filtrate holding tank prior to being pumped to the head of the treatment plant. • In the smaller systems, filter cake collects in a small, wheeled container that is emptied into a larger solids bin as necessary. • In the larger systems, the filter cake drops into roll-off bins located beneath the filter press. • Accumulated solids require disposal on a periodic basis. 121

5.3. 1.2.

Evaporation Ponds and Drying Beds

Evaporation ponds (EPs) and drying beds are non-mechanical dewatering technologies whereby favorable climatic conditions are used to dewater waste brines generated by treatment processes such as reverse osmosis and ion exchange. Ponds and drying beds are not generally suitable for lime softening or coagulation/filtration process sludges.

Evaporation is an extremely land

intensive handling option requiring shallow basins with large surface areas which can be an important consideration in densely populated regions. Evaporation ponds and drying beds have few operation and maintenance requirements but are only feasible in regions with high temperatures, low humidity, and low precipitation. Using EPs to treat hazardous liquid wastes (wastes with total dissolved arsenic concentration of 5 mg/L or greater) may not be an acceptable alternative due to high costs. The EP costs were developed based on the following conceptual facilities and operational parameters: • Waste brines flow from the treatment plant to the EP by gravity or by the pressure from the treatment system via 1,250-4,000 ft of 4-8 inch diameter PVC piping. Pipes are laid 4 ft below grade. • The EP can be used to evaporate the non-hazardous (with total arsenic concentration < 5 mg/L) AA or DC wastes. The influent solids concentration ranges from 1.5 to 3.5% by weight. • The pond is designed for a geographical region with a net annual evaporation rate of at least 45 inches/year. • The pond is constructed with a synthetic membrane liner and a geotextile support fabric; 1 ft of sand is placed on top of the liner. • Piping from the treatment process is sized to discharge the waste brines to the ponds as they are generated. The treatment process is assumed to run 8 to 16 hrs/day. • The EPs are sized with sufficient surface area to evaporate the average daily flow. The pond depth is 2 ft; this depth provides solids storage volume and accommodates peak flows.

122

5.3.1.3.

Chemical Precipitation

This option is only applicable to IX brine stream. In chemical precipitation (CP), the spent brine from the IX will be sent to a retention tank where it will be dosed with ferric chloride. Then, the precipitated ferric hydroxide will be settled in the brine basin and the supernatant will be pumped and taken to disposal (POTW or for re-use). The solids ferric hydroxide will be pumped to a clarifier. The thickened solids will then be pumped to a recessed plate and frame filter press for dewatering. The dewatered solids will then be disposed of to a non-hazardous landfill after passing the TCLP test. The CP costs were developed based on the following conceptual facilities and operational parameters: • Mixing and holding tanks for ferric chloride solution, a precipitation tank, a clarifier, agitators and pumps; • The precipitation tank has a 30-min retention time and a 5 percent over-design; • The clarifier or settling tank has a 1- to 2-hour retention time; • The waste brine flows to the CP system under pressure from the ion exchange system; • The CP equipment is located in the water treatment building; and • The sludge volume generated by CP is 2 percent of the influent brine volume. 5.3.2. Residuals Disposal Alternatives 5.3.2.1.

Direct Discharge

Direct discharge to a surface water is becoming a less feasible method of disposal for water treatment residuals. This method may be used to dispose of some nanofiltration brine streams. Direct discharge of lime softening or coagulation/filtration sludges to a surface water is not a likely disposal alternative because the typical solid concentration of these (lime softening and coagulation/filtration sludges) exceed the usual National Pollutant Discharge Elimination System (NPDES) limit of 30 mg/L. Direct discharge of ion exchange or activated alumina residuals to

123

receiving surface waters is also an unlikely disposal alternative due to high arsenic concentration and high salt content. Direct discharge was not used as a residuals disposal alternative in the decision tree and therefore no cost equations were developed. 5.3.2.2.

Indirect or POTWDischarge

Indirect or public-owned treatment works (POTW) discharge is a commonly used method of disposal for filter backwash and membrane brine waste streams. Coagulation/filtration and lime softening sludges have also been successfully disposed of in this manner. The primary cost associated with POTW discharge is the wastewater treatment cost for the residuals. Additional costs associated with POTW discharge may include lift stations, additional piping for access to the sewer system, or other surcharges to accommodate the increased demands on the POTW. POTW discharge is an inappropriate disposal option for coagulation/filtration and lime softening systems because the effluent arsenic concentration exceeds the range of threshold based local limits (TBLL) of 50 fig/L to 1,000 /ig/L identified by most industrial protection programs (EPA 2000c; McPhee et al., 2000). It is unlikely that AA or IX residuals could be discharged to a sanitary sewer for treatment at a POTW because the concentration of the brine waste system far exceeds the typical TBLL of 50 /ig/L to 1,000 /ig/L. The costs for POTW discharge were developed based on the following conceptual facilities and operational parameters: • The conveyance line connecting the water treatment system to the sewer system is about 1,000 feet; • The flow through the conveyance line occurs by gravity or under pressure from the treatment process to the sewer line; • Pipe of 2-inch minimum diameter to prevent clogging. Pipe diameter ranges from 2 to 24 inches; • PVC or reinforced concrete piping is used; and • An equalization basin or storage lagoon is provided upstream of the conveyance system.

124

5.3.2.3.

Non-Hazardous or Sanitary Landfill Disposal

Two forms of sanitary landfill are commonly used for disposal of water treatment by-products: monofills and commercial non-hazardous (NH) waste landfills. Monofills accept only one type of waste, for example, fly ash or water treatment sludges. In some parts of the country, decreasing landfill availability, rising costs, and increasing regulations are making landfill disposal more expensive. Costs associated with the development of monofills are generally less than that of a sanitary landfill. Commercial NH landfills accept a mix of residential and industrial wastes. Sanitary landfills are regulated by both state and federal regulations. Sanitary landfill sludges have to meet the toxicity characteristic leaching procedure (TCLP) limits. The current TCLP limit for arsenic is 5 mg/L, which is 100 times the current MCL of 50 pig/L. If the MCL is lowered in the future, the TCLP value will be lowered accordingly. For example, if the MCL were to be lowered to 5 jiig/L then the TCLP would be lowered to 500 /ig/L. As a result, water treatment residuals containing arsenic may meet current sanitary landfill disposal criteria, but may not under a future regulatory framework. The capital components for a NH landfill include land clearing, landfill excavation, composite (clay and synthetic liner), leachate collection system, groundwater monitoring system, equipment storage and maintenance buildings, visual screening bqrm, bulldozer, truck and inspection, testing and quality assurance.

The O&M components include labor and supervision,

maintenance and materials, intermediate cover, groundwater monitoring, leachate collection and treatment and utilities. The costs for NH landfills were developed based on the following conceptual facilities and operational parameters: • The landfill has a 20-year operating life; • The landfill is a combination fill; • The landfill has double liners (two feet of clay and a 30 mil high-density polyethylene liner), one foot of sand with leachate collection system and a geotextile fabric on one foot of native soil fill; • The intermediate cover consists of slope and earthfill soils;

125

A groundwater monitoring system is installed and is sampled semi-annually;

•

• The final cover consists of one foot of native soil fill, a geotextile support fabric, a 30 mil poly vinyl chloride liner, one foot of sand with drain tiles, a geotextile filter fabric and 1.5 feet of topsoil; and • The post-closure care period is 30 years. 5.3.2.4.

Hazardous Waste Landfill Disposal

Water treatment residuals containing arsenic which fail the TCLP test for toxicity must be disposed of in designated and licensed hazardous waste landfill. Hazardous waste landfills are regulated by the Federal government under the authority of RCRA or by the individual states that received authorization under RCRA. The primary factor that affects the disposal of arsenic containing residuals in a hazardous landfill is the presence of free liquids. If any water treatment sludge contains free liquids, usually determined by the Paint Filter Liquids Test (SW-846, Method 9095), it is not suitable for landfilling.

Sludges containing free liquids must be

stabilized or treated by another method to remove free liquids prior to disposal. Hazardous landfills have extensive monitoring and operational requirements that cause the cost of this method to be much greater than that of a typical sanitary landfill. Since, hazardous waste landfill disposal will only be used as a last resort if the waste fails the TCLP test, no cost equations were developed for this option. 5.4.

Pre-Oxidation Cost

As discussed in Chapter 2, arsenate, As(V) is more readily removed than arsenite, As(in) by most arsenic treatment technologies. Therefore, if the source water arsenic is in As(ni) form then pre-treatment with chlorine or other oxidant addition is often an integral part of an arsenic removal process. Costs for pre-oxidation with chlorine addition were developed for a dosage of 5 mg/L. For small systems (less than 1 mgd), chlorine was assumed to be added in a liquid form and for large systems (greater than 10 mgd) chlorine was assumed to be added in a gaseous form. Linear regressions were used to estimate the costs in the transition region of 1 to 10 mgd. In the

126

decision tree, costs for chlorine oxidation are only added if the raw water has As(in) and if there are no alternative oxidation or disinfection practices in-place.

5.5.

Land Cost

In the decision tree, cost for land acquisition is estimated for each technology based on the local land value ($/acre) and the amount of land required for treatment and residuals handling. The land required is estimated based on the footprints developed for each technology for different system sizes. These footprints were based on preliminary design layouts developed by the project team for other arsenic projects. The land required equations were developed based on the following criteria: • Minimum area of 30' x 30' (0.02 acres) for IX and AA facilities (without regeneration) for a 0.02 mgd facility. The footprint size is increased based on plant flow, as indicated below: -

60' x 60' (0.08 acres) for a 0.5 mgd facility

-

100' x 100' (0.22 acres) for 1 mgd facility

-

160' x 160' (0.59 acres) for a 10 mgd facility

-

0.59 acres for each 10 mgd addition to the facility beyond 10 mgd

• A 25% addition to the footprint was made for more mechanically complex processes such as CMF, EDR and NF. • Existing conventional, direct filtration, and softening facilities will not need additional land to implement process changes identified in the decision tree and spreadsheet. • Land requirements for brine evaporation were computed using the annual brine volume (computed from the spreadsheet) and an average net evaporation rate of 45-inches per year.

127

CHAPTER 6 UTILITY CASE STUDY SUMMARIES The following case study summaries for the participating utilities were prepared using the decision tree tools that were discussed under Chapter 4. These case study summaries were prepared for a targeted finished water arsenic concentration of 8 /ig/L (80% of the anticipated MCL of 10 /ig/L). Initially, the water system information was obtained through questionnaires (shown in Appendix B) that were mailed to the utility representatives. Subsequently, the case study discussions were developed with ample contributions from the water utility representatives during their participation at the workshops (conducted in Phoenix, Arizona; Los Angeles, California; Reno, Nevada; and Mishawaka, Indiana) and from subsequent communications. These case studies are included to demonstrate the process of evaluating treatment strategies using the decision tree spreadsheet tool. The case studies represent a wide range of system sizes, existing treatment processes, source water characteristics, and arsenic contamination. It should be noted that an earlier version of the decision tree spreadsheet tool was used in developing these case studies.

It should be noted that at locations where TAA is applicable, GFH is also

applicable. When the case study summaries were being developed there was no cost information available for arsenic removal by GFH. Therefore, GFH was not included in the spreadsheet tool under the possible list of technologies. The current, interactive, web version of the spreadsheet tool has the updated cost equations for GFH, TAA, ECF, ELS, DF-»CF, CMF and IX.

6.1.

City of Phoenix, Arizona

6.1.1. Background Q

The City of Phoenix provides treated drinking water to approximately 1,200,000 retail and 200,000 wholesale customers. In 2000, the average day water production was around 300 MGD. This amounts to an average water use of 210 gallons per capita per day (gpcd). The maximum

129

day water demands have historically been around 1.6 times the annual average demand (340 gpcd). To meet this demand, a combination of the following water sources is utilized: •

Surface water from the Salt River Project (SRP) canal system, which consists of runoff, snowmelt, and springs from the Salt and Verde Rivers. The Verde River typically has arsenic concentrations between 10 and 20 ptg/L. Four WTPs, namely the Verde, Val Vista, Squaw Peak, and Deer Valley, use conventional processes (chemical addition [alum, polymers, sulfuric acid], coagulation, sedimentation, and filtration) to treat the SRP supply. These WTPs are located in the eastern and central portions of the City's service area. Raw water 90th percentile arsenic levels at these WTPs range between 7 and 14 jig/L. Finished water 90th percentile arsenic levels range between 3 and 9 /ttg/L. Previous testing conducted by the City indicated that enhanced coagulation, with approximately twice the normal alum dose, would be required to consistently meet a lower arsenic standard. The added operational costs associated with elevated alum addition for enhanced coagulation are approximately $1,000,000 annually for elevated alum addition.

•

Surface water from the Central Arizona Project (CAP) canal, which delivers Colorado River water to the Union Hills WTP, a direct filtration facility. This WTP serves the northern portion of the City with finished water arsenic concentrations typically below 3 Aig/L. The Lake Pleasant WTP is planned in the near future and the type of process is currently being developed. No impact is anticipated for this source.

•

Groundwater from 44 wells with a combined production capacity of 88 mgd. This includes currently active wells and wells that will be on-line within the next year. Of the 44 wells, 16 are grouped into three distinct well fields while the remaining 28 are distributed wells. For the Verde and Deer Valley well fields, blending with treated surface water appears to be the most feasible means of complying with arsenic levels of 10 /ig/L. No impact exists on the Ahwatukee well field at an MCL of 10 fig/L.

During normal rainfall periods, over 95% of the water supply is provided by treating surface water at the five surface WTPs. During periods of drought in the watershed(s), the wells are utilized to meet system demands.

130

With the exception of the Verde, Deer Valley and Ahwatukee well fields, the wells are scattered throughout the distribution system. Of the 28 remaining distributed well sites, 22 are impacted by an arsenic MCL of 10 /ig/L, as shown in Table 6.1. Blending with nearby low-level arsenic sources could not easily be implemented at these 22 sites without constructing lengthy new pipelines. Development of treatment costs in this case study assume that individual wellhead treatment would be required to comply with a reduced arsenic standard at these sites. Centralized facilities are cost-effective and practical only where the wells pump into the same pressure zone and are in close proximity to one another (within approximately two miles of the central facility to be cost effective). There are no alternate source waters available and significant hydraulic restrictions exist in the system. There are concerns regarding corrosion in the distribution system, and DBF concerns at the surface WTPs. A recent master planning and pilot testing study has been completed for the Arsenic Rule. Significant bench, pilot, and full-scale testing have been carried out. The City of Phoenix is not willing to consider hazardous waste generating treatment systems, subject to RCRA regulations. Currently, there is a 100 /ig/L limit on arsenic levels in residuals disposal to the sewer. Limited land is available for modifications or expansion (90%As(V)

Increasing

adsorption

(min)

removal

pH on

(g/L)

As(V) removal

HCO3'

SO42' (SiO4)' PO43'

MIEX®

5-10

0.5

Removal J,

HIOPs

10-20

1.9

Removal J,

1

J.

~

Activated

2-10

0.5

Removal J,

1

I

n.a.

Alumina (4) decreased arsenic adsorption (=) no significant change in arsenic adsorption n.a., information not available to comment

7.3.2. Evaluation 0/MffiX® and HIOPs Arsenic Removal Capability in Synthetic Natural Water Tables 7.4 and 7.5, and Figure 7.1 present the results of batch adsorption experiments conducted with natural water samples. MIEX®, HIOPs, and AA were effective in removing arsenic from water, however, their adsorption capacities were significantly lower in natural water than in synthetic water. This was probably due to the presence of other anions competing with arsenic for adsorption sites in the natural water samples. Unlike the observations in the experiments conducted on synthetic water, HIOPs exhibited the largest arsenic removal capacity from natural water. Adsorptive capacities followed the general trend: HIOPs > MIEX® > AA. Adsorption was observed to be pH dependent. For the MIEX® resin the adsorption of arsenic increased as 200

pH increased (the opposite of what was observed in synthetic water), and the optimal pH range for adsorption was found to be between 6.0 and 7.5. For HIOPs, the arsenic removal decreased as the pH was increased, and the optimal pH range for adsorption was between 6.0 and 7.5. For MEX® resin, the presence of sulfate and silicate anions resulted in reduced arsenic removal while phosphate addition did not have a significant effect. Table 7.4 Summary of batch adsorption experiments conducted with MCEX®, HIOPs, and AA on LADWP water

Adsorbing

Dose for

Effect of

media

>90% As(V)

increasing pH

removal (g/L)

on As(V) removal

MIEX®

1.0

Removal!

Effect of anions on As(V) adsorption

SO42"

(SiO^"4

PO43

11

=

=

=

J.

n.a.

n.a.

n.a.

Optimal pH Range is 7 - 8 HIOPs

0.4

Removal], Optimal pH Range is 6-7.5

AA

5.0

n.a.

(|) decreased arsenic adsorption (=) no significant change in arsenic adsorption n.a., information not available to comment

201

Table 7.5 Summary of batch adsorption experiments conducted with MIEX®, HIOPs, and AA on City of Phoenix water Adsorbing media

Dose for >90% As(V) removal (g/L)

MIEX®

1.0

HIOPs

0.8 2.5*

AA

(J,) decreased arsenic adsorption (=) no significant change in arsenic adsorption (*) dose for 60% arsenic removal

A MLEX (LADWP-at 7.5) •HIOPs (LADWP-at 7.5) XAA (LADWP-at 7.5) XA1+3 (LADWP) O Fe+3 (LADWP)

0.0 -I

-1.0-2.0 < o

-3.0-4.0 -

00

2

-5-0 -4.0

-3.0

-1.0 -2.0 Log Ceq (mg/L of Arsenic)

0.0

1.0

Figure 7.1. Adsorptive capacity of MIEX, HIOPs, AA, AT3, and Fe+3 for LADWP water spiked with arsenic to 100 u.g/L concentration

202

7.3.3. Evaluation of Coagulants and Coagulation Processes for Arsenic Removal

The results of conventional coagulation experiments for arsenic removal are illustrated in Figure 7.1. Conventional coagulation with both ferric chloride and alum was effective in removing arsenic from solution. On a molecular metal weight basis (Fe3+ and A13+), ferric chloride and alum removed similar amounts of arsenic.

Greater arsenic removal was obtained with

conventional coagulation than with adsorption onto MIEX®, HIOPs, and AA. Figures 7.2 and 7.3 illustrate arsenic removal obtained using conventional and Actiflo™ processes in combination with alum and ferric chloride. Li all cases, the removal levels obtained with both processes were similar. The pH of solution strongly affected arsenic removal. As illustrated in Figures 7.2 and 7.3, alum effectively removed arsenic at pH greater than 6, while ferric chloride was effective at pH 5 or greater.

Conventional-Ahun - © - Actiflo-Alum A pH-Conventional O pH-Actiflo

0

20

Figure 7.2. Arsenic removal from LADWP (spiked with 100 ng/L of arsenic) water by alum in conventional and Actiflo processes

203

j 8.0 - 7.0 -6.0 _

Conventional-FeC13 - © - ActifloêClS A pH-Conventional O pH-Actiflo

CD

cr MIEX® > AA.

•

The adsorptive capacities of HIOPs, MIEX®, and AA were observed to be greater in synthetic water than in natural water. This difference can be attributed to the presence of anions competing with arsenic for adsorption sites in natural water samples.

•

Greater arsenic removal was obtained with conventional coagulation than with adsorption onto MEEX®, HIOPs, and AA.

•

Similar arsenic removal levels were obtained with conventional and Actiflo™ coagulation processes.

•

The addition of HIOPs or MEX® to the membrane immersion tank improved overall arsenic removal compared to the membrane alone.

206

CHAPTERS RECOMMENDATIONS FOR UTILITIES Compliance with the current arsenic standard of 50 pig/L has not been a significant challenge to water treatment practices because of low level occurrence in most source waters; however, the anticipated lowering of this standard by the USEPA to a level less than 20 u,g/L is causing significant concerns among the water purveyors of this country.

The selection of arsenic

treatment technologies is a complex process and must consider a multi-faceted water quality considerations as well as the issues related to residuals handling and disposal. In this study, decision trees were developed to assist utilities with treatment technology selection and to understand the various issues and costs associated with treatment process integration. Two interactive decision tree programs were developed as part of this project. One of the programs provides guidance for optimization process for systems with treatment in-place. The second program, based on a spreadsheet application, is designed to isolate feasible and promising treatment technologies at locations where there is no treatment (other than disinfection) in-place. These interactive, web tools for arsenic treatment selection and optimization are available at the AWWARF web site at the following web location: http://www.awwarf.com/ArsenicTool/ArsenicTree/index.cfm Decision trees developed for systems with existing treatment include conventional treatment, direct filtration, precipitative softening, and iron/manganese removal.

The program first

recommends users to consider process optimization methods with bench, pilot and full-scale testing such as addition of a pre-oxidant, adjusting pH, or using a more effective coagulant. If the finished water still contains unacceptable levels of arsenic, the program recommends consideration of facility improvements (e.g., addition of polymers, alternative filter media, and addition of new filters) or installation of an arsenic polishing treatment (e.g., post filter activated alumina adsorption). Considerations for other water quality goals (corrosion, DBFs, primary disinfection, etc.) and waste handling and disposal requirements are also weighed into the process of making a treatment process modification. 207

For utilities with no treatment-in-place or only disinfectant application in-place, the guidance in this document leads the reader through the decision tree which considers proven treatment technologies and is primarily water quality driven, however, it does evaluate the least cost options initially. Utilities have to input information such as flows, raw water quality, residuals handling preferences and site constraints for each impacted point-of-entry into the spreadsheet tool in order to process the information and develop guidance for a process selection. The program generates planning level estimates of residuals quality/quantity, land requirements, and treatment costs for each technology. The tool will identify and rank feasible technologies based on qualitative drivers such as ease of implementation, public acceptance and labor required. Smaller systems with less operator experience and fewer economical resources will likely choose technologies which require less chemical addition such as disposable adsorptive media (e.g., AA or GFH) processes. For many small utilities, disposable media may present the least cost option for their system. Choosing an adsorptive media process with no regeneration eliminates the need for the utility to handle hazardous chemicals that are used in regeneration and also eliminates complicated requirements for disposal of the spent regenerant. Secondary effects such as pH reduction that result in higher TDS in the finished water must be considered in cases where the utilities face corrosion control or other water quality issues. Also, systems with high levels of co-occurring contaminants such as fluoride, silica, phosphate and chloride must consider the possible interferences of these ions with the adsorption processes. Larger systems with better operator experiences and greater resources are more likely to install or modify relatively more complex treatment systems which could include the use of hazardous chemicals for altering water quality during treatment (e.g., pH reduction to achieve greater adsorption capacity) or in the regeneration of spent media. These systems are also more likely to invent in technologies such as CMF and be prepared to deal with residuals from this type of treatment process. They are typically more adequately staffed to handle operational-intensive processes such as enhanced coagulation, iron removal and enhanced lime softening. As with smaller systems, the larger utilities will have to consider the impact of co-occurring contaminants such as silica on the arsenic treatment efficiency.

208

Impacted water utilities can use the interactive tools along with this report to understand some of the primary and secondary issues associated with the proposed arsenic regulation. Utilities with existing treatment and utilities with no treatment-in-place can use the flow charts and spreadsheet as preliminary decision making tools to determine which technologies would be more appropriate for their specific situations.

Once the preferred technologies have been

identified using these tools, the utilities can then focus their attention on bench- and pilot-scale testing of these processes before a final technology is chosen. This saves the utility the costs of assessing multiple treatment technologies by eliminating inappropriate technologies at the outset. As discussed in Chapter 7 new and innovative processes and adsorptive media are currently being developed which may prove more efficient than current technologies. Therefore utilities, especially those using adsorptive media, need to keep up to date with emerging technologies and use these tools as a general guide and not a final answer. This report includes discussions on water quality, residuals handling, costs and integration issues that are part of the overall implementation processes. Case study summaries of some impacted utilities are also provided as examples to help other utilities addressing similar issues. While this report and the accompanying tools cover the process selection and integration issues, the second report (Implementation of Arsenic Treatment Systems: Part 2, Design and Operational Considerations) provides guidelines on the design and operational issues associated with the integration of arsenic removal technologies.

209

APPENDIX A SPREADSHEET TOOL TABLES

Following are the tables that were part of the original spreadsheet tool. The interactive web tool has similar tables in a different format.

211

Table A. 1 Input table Input Block lsttesoun»waiteragrouiidwater(CF

0.01-430

0.003-270

streams that actually

AA. IX. NF. EDR__________0.01-430_____0.003-270______require treatment.

214

Table A.4 Land required computations (partial table)

Short Nolens

*

Treatment (acres)

^ \^ . (acres)

"«*"***••*«

(acres)

Required (acres)

ECF

0.00

0.00

0.00

0.00

ELS

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

CMF

0.00

0.00

0.00

0.00

TAA

025

0.00

0.25

0.00

AA-EPNH

0.25

0.43

0.68

0.43

AAHD _._„_„_„_._._._ft25._.___.____2-00___________Pi25._._._._._.jO.OO_ IX-EPNH IX-CPNH

025 0.25

1.03 0.25

1.28

1.03

0.50

0.25

JX_-ID _________„.»._._. JO-25._____._._.i-?°_._._._____0;25._._._._._.£-00. CMF-MDNH

0.31

0.50

0.81

0.56

.CMjP-tjD__________._. JO-21._._._.__.J2.-9°_._______P;31.__.«._._.£•?§. NF-ID

0.31

0.00

0.31

0.08

EDR-ID_______________0.31____________0.00___________0.31____________0.06

215

Table A.5 Capital and O&M cost computations (partial table) Treatment/Residuals Handlina Capital and Operational Costs Short Notations

Treatment Capital Cost ($)

Land Cost (J)

Disposal Capital Cost ($)

Pro-Ox Capital Cost CF

UquIoVSotid Uquid/Solid

CMF

UquloVSolid

TAA AA-EPNH

Water Quality Comments

Waste Stream Type Chemicals Handling & Storage Required

Membrane cleaning solutions, ferric chloride and caustic.

None

Sutturic acid and caustic.

UquloVSolid

Sulfuric acid and caustic.

Silica can Interfere with the coagulation process.

.AA;!P. _ . ___ .uqujAsofld_ .sjjifiirJfasitsnisaHUs-. _ . _ . _ . _ . ___ . _ . _ . _ . ___ ._.-. ___ . _ . IX-EPNH

Liquid/Solid

Salt, ferric chloride & caustic

IX-CPNH

Liquid/Solid

Salt, ferric chloride ft caustic

UquiaVSdld

Membrane cleaning solutions, ferric chloride and caustic.

.DM2. CMF-MDNH

Silica can interfere with the coagulation process.

JCMESJ. _ _ _ __ _ _ _ Liquid/Solid. . _ J^^myjje^tt^sftjfimJmjcMfMeaiviawfS: . __ . ___ . SSSlSt. i2ftSHS-vSS! SS -effl9H!?&n£lSSSS: . NF-1D

Uquid

Acid and cleaning solutions

EOR-ID

LJauid

Oeanina e

Higher pHs can increase membrane fouling.

217

Table A.7 Technologies feasible for no additional land purchase (partial table)

Feasible Technologies For No Additional Land Purchase Short Notations

Source Water

Percent Water toss

Sewer Discharge

Water Quality

Lower Design Flow Limit

Upper Design Flow Limit

Lower Average Flow Limit

1

1

1

ECF

0

1

1

ELS

0

1

DF->CF

0

1

1 1

1 1 1

1 1 1

CMF

0

1

1

1

1

i 1 i 1

1 1

1 1

i 1

1

1

!

1

1

1

1

1 1 1 i i 1

1

1

1

j

LA-ID

1

1

1 1 1

IX-EPNH

1

1

1

IX-CPNH

1

1

1

DC-ID

1

1

CMF-MDNH

1

1

1 1 1

TAA

1

1

AA-EPNH

1

1

ICMF-ID

1

NF-ID

1

0

EDR-ID

1

0

1 1

1 _._._.!. __ ._._._ i i i i

218

1 1

1

_._

1

1

1

1

_._ J

1

1

1

1

Table A.8 Technologies feasible for additional land purchase (partial table)

Feasible Technologies For Additional Land Purchase Short Notations

Overall Score

Land

Technology Feasibility

ECF

1

Not Feasible

ELS

1

Not Feasible

ELS

DF->CF

1

Not Feasible

DF->CF

CMF

1

Not Feasible

CMF

TAA

1

Feasible

69.6

$216,573

TAA

0.00

AA-EPNH

1

Feasible

45.9

$327,589

AA-EPNH

0.43

$322,650

AA-ID

0.00

$414,757

IX-EPNH

1.03

IX-CPNH

0.25

Short Notations

ECF

AA-ID

1

Feasible

50.5

IX-EPNH

1

Feasible

28.1

IX-CPNH

1

Feasible

34.1

$268,824

IX-ID

1

Feasible

43.0

$243,392

IX-ID

0.00

$356,266

CMF-MDNH

0.56

$276^72

CMF-ID

0.06

CMF-MDNH

1

Feasible

57.8

CMF-ID

1

Feasible

61.2

NF-ID

1

Not Feasible

NF-ID

EDR-ID

1

Not Feasible

EDR-ID

Count f or QW

8.0

Count for SW

0.0

219

Table A.9 Qualitative decision drivers scores for feasible technologies (partial table) Qualitative Decision Drivers Ranks For Feasible Technologies Short Notations

EOF

CostDrtver

$216373 $327389

8.0 5.3

Labor Required

Process Reliability

8.0

8.0

48

83

6.4

Z4

8.0

2.4

._._.*•'>

32

._._._8.p_._._._ 32

6"16""

Not Feasible

ELS

Not Feasible

DF->CF

Not Feasible

CMF

Not Feasible

TAA

Feasible Feasible

AA-EPNH

Annualized Total Cost ($/yr)

IX-EPNH

Feasible

$414,757

4.2

5.6

1.6

IX-CPNH

Feasible

$268324

6.4

40

03

_._._.&? CMF-MDNH

Feasible

Give a high score il

1.6 03

—3-2

.._._. If———..

$276372

Not Feasible NF-ID EDB-ID________Not Feasible

Give a low score If

.._._§£._._._

6.4___ ._

._.._ip_.._.._.._.io..._.._.._.._. .ip.. _H)ghoost_ _ _

Cumbersome to operate

Labor Intensive

Complex process

Automated and Simple and widely Easy to operate requires less manual Low cost______and maintain____maintenance___demonstrated process

220

More moving parts

Sturdy process

Table A. 10 Default ranks for qualitative decision drivers (partial table)

Treatment Technology Train

^^ costumier

Ease of hnplei i IBI tuition

Labor Required

Process Reliabmty

Positive System Ne gadve System V Vater Quality Water Quality Irnpscts Impacts

Mechanical Reliability

Surface Water Technologies •4".

ECF

• •'• *

ELS

,

DF->CF CMF

" ••

4

'

. - ' 4

'••

•• '•

.' ;

•:•--; ' 2 1 •*•• •

- :V- 2 :;- '-' " . i •' • •

"'- '3 .

3

••'. 3

. 3.

3

' '•" 3-

-' '-'

. •

.•'

.

-1

1

2 :

2

2

2 2

.

2

4

4

Groundwater Technologies

TAA —— ._._._. _AA.-ID

...10.

10

Automated for each case- * study

8'

-'

"5

IX-EPNH

7

IX-CPNH

• 5-

..-

'.

•- -'

.

1

..

'•*• •-.'••

' 4 ' 4

IX-ID

1

7

4

CMF-MDNH

9

6

8

:;

••••8 '

: . '2 1 -4

2;

5

•'

2

.

2

2

2

10

8

CMF4D

6

6

8

7

10

NF-ID EOFHD

2 3

9 8

2 1

6 6

8

221

- .'

.-'*-•'

.

" • \8 ' 5-

8

'•'

9 • ' '

.

•>~; ..-.V

3

10 •-•

4;

10

. 10

4 ; •• ••' ' -.2"'

-' '

•

• •" - 3 . '.•* .'

i

a

.._§_._.10 10

Table A. 11 Feasible technologies summary table for no additional land purchase

Feasible Technologies For No Additional Land Purchase Promising Treatments

Score

Jechno| '

An"ual|z^ ™al Cost ($/yr)

SW Selection 1 Selection 2 _Se!ectipn_3___._._._._._._._._._._._._._._ _ GW

_._

Selection 1

TAA

69.6

$216,573

Selection 2

A A-ID

50.5

$322,650

Selection 3

IX-ID________43.0_______ $243,392

222

Table A. 12 Feasible technologies summary table for additional land purchase

Feasible Technologies For Additional Land Purchase__________________ _ . . _ Prom,s,ng Treatments

_ . . Technology

_ Score

____

Annualized Total Cost($/yr) __

Additional Land Required (acre)

sw Selection 1 Selection 2 Selection 3 GW Selection 1

TAA

69.6

$216,573

0.00

Selection 2

CMF-ID

61.2

$276,872

0.06

Selection 3

CMF-MDNH

57.8

$356,266

0.56

223

APPENDIX B QUESTIONNAIRE 1.

Are you a member of the American Water Works Association (AWWA)? D Yes D No If not, do you plan on becoming a member in the near future?

2.

The current MCL for arsenic is 50 ug/L. The proposed MCL for arsenic would likely be between 5 and 10 ug/L. Do you anticipate any impact due to this lowering of the arsenic MCL? D Yes D No What percentage of your source waters would be impacted by an arsenic MCL of 5 ug/L?

What percentage of your source waters would be impacted by an arsenic MCL of 10

3.

Describe your source waters: D Groundwater only D Surface water only D Combined groundwater and surface water For combined water source, what are the proportions of ground and surface waters?

If groundwater is one of the source waters, how many active wells do you have?

If surface water is one of the source waters, how many surface water treatment plants do you have?

225

To what size population do you distribute potable water? Please pick one of the following categories of people served or specify the number of people served. D 25 to 100 D 101 to 500 D 501 to 1,000 D 1,001 to 3,000 D 3,301 to 10,000 D 10,001 to 50,000 D 50,001 to 100,000 D 100,001 to 1,000,000 D Greater than 1,000,000

What are your system wide design and operating flow rates? Design flow rate: Operational flow rate:

mgd (million gallons per day) mgd

What are your average and peak system demands? Average system demand: Peak system demand:

mgd mgd

If surface water is one of your source waters, h'st the design and average flows for each surface water treatment plant. Treatment Plant Name

Average Flow (mgd)

226

Design Flow (mgd)

If groundwater is one of your source waters, identify and list the average, maximum and minimum flows for each wellfield system? Wellfield

Average Flow (mgd or gpm)

Minimum Flow (mgd or gpm)

Maximum Flow (mgd or gpm)

Are there any significant hydraulic restrictions associated with moving the water within the distribution system, i.e., between the different zones?

Describe your existing treatment system. Groundwater

Surface water

Disinfection Alone - Number of Sites: Precipitative Softening - Number of Sites: Iron/Manganese Removal - Number of Sites: Other treatments (please describe) - Number of Sites:

Conventional Treatment - Number of Sites: Direct Filtration - Number of Sites: Precipitative Softening - Number of Sites: Enhanced Coagulation - Number of Sites: Enhanced Softening - Number of Sites: Other treatments (please describe) - Number of Sites:

227

Combined water Conventional Treatment - Number of Sites: Direct Filtration - Number of Sites: Precipitative Softening - Number of Sites: Enhanced Coagulation - Number of Sites: Enhanced Softening - Number of Sites: Other treatments (please describe) - Number of Sites:

10.

What is the average arsenic concentration in the "impacted" source waters? If you have more than one source water please check multiple alternatives and identify the source water type next to it. > < 3 ug/L- Number of Sites: > between 3 and 5 ug/L - Number of Sites: > between 5 and 10 ng/L - Number of Sites: > between 10 and 20 ug/L - Number of Sites: > between 20 and 30 ug/L - Number of Sites: > between 30 and 50 (ig/L - Number of Sites: > 50 ug/L - Number of Sites:

11.

Do the existing treatment processes listed under Question 9 achieve any arsenic removal? If so, what are the finished or treated water arsenic concentrations? If you do not have this information please mention "NA" (not available). Please list the processes and the arsenic removals achieved in the same order as shown under Question 9.

12.

Is the utility currently addressing any process optimizations to enhance the water quality for arsenic or other regulatory (e.g., Stage-2 DBFs) compliance? Please state any completed or planned activities.

13.

For surface water treatment plant(s), can you draw a simple line schematic indicating coagulant dosages and other design criteria? Alternatively, you may attach process schematics of your plant(s).

228

If groundwater is a source water, please attach or draw a simple sketch of your pumping well and wellhead treatment process. Also, please provide a simple map of your system indicating locations of wells and treatment plants. 14.

Describe your source water quality. If you have more than four source water types please copy this page and list them separately. If you do not have the information on a particular parameter just say NA (not available). Parameters

Source Water - 1

Treatment Plant/ Wellfield System Name Arsenic, |jg/L Sulfate, mg/L Nitrate, mg/L Silica, mg/L Iron, mg/L Manganese, mg/L Chloride, mg/L Fluoride, mg/L Selenium, mg/L Hardness, mg/L as CaCO3 Alkalinity, mg/L as CaCOs PH Total dissolved solids in mg/L (or specific conductance in uS/cm) Total organic carbon content, mg/L

229

Source Water - 2 Source Water - 3

15.

Are there any regional source water protection programs in-place?

16.

What fraction of the total water capacity has arsenic at concentrations >3 ug/L? D 50%

17.

Are there any alternative source waters that could be used in place of the waters containing arsenic at concentrations greater than 3 ug/L? D Yes D No If yes, please describe.

18.

If you have any treatment systems in-place, what are your current residuals handling and disposal practices? Residuals handling D D D D

Residuals disposal D D

None Mechanical dewatering (e.g., filter press, centrifuges) Non-mechanical dewatering (e.g., evaporation ponds) Storage lagoons Other (please specify)

None Direct discharge to a natural water body Indirect or POTW discharge Dewatered sludge land application 230

D D D

19.

Non-hazardous or sanitary landfill disposal Hazardous waste landfill disposal Other (please specify)

Are there any limitations or local ordinances pertaining to residuals handling and disposal especially to the sewer system (pre-treatment limits for arsenic and TDS): Yes D No D If yes, please describe ordinances/limitations.

20.

all

the relevant residuals

handling

and disposal

Are you willing to consider treatment systems that can generate hazardous wastes which are subject to RCRA regulations for treatment, storage and disposal? Yes D

n

NO

21.

Describe temperature and relative humidity conditions? What are the average rates of evaporation and precipitation?

22.

Is land available for modifications or for future expansions (1-2 acres per site)? Yes D No D Is land available for purchasing? Yes D No D

231

If additional land is available for purchasing, what is the approximate cost ($/acre) of land?

23.

What are the primary and secondary disinfectants currently employed? Primary disinfectant : Secondary disinfectant

24.

Does the utility have or anticipate any Disinfection By-Product (DBF) problems? DBFs include Trihalomethanes (THMs) and Haloacetic Acids (HAAS). The regulated total THMs include chloroform, bromodichloromethane, dibromochloromethane and bromoform. HAAS is the sum of mono-, di- and tri-chloro acetic acids and mono- and di-bromo acetic acids.

25.

Are there any existing/anticipated corrosion problems within the treatment plant or in the distribution system?

Please identify any corrosion control measures such as chemical additions that are inplace? What is the finished water quality?

26.

Does the existing treatment process have provisions for any of the following: D D D

27.

Chlorine addition Ozone addition Permanganate addition

Has the utility performed or participated in any of the following: D Yes > Bench/pilot-scale testing for arsenic treatment D Yes > Other AWWARF or EPA arsenic projects D Yes > Any paper study addressing arsenic rule 232

D No D No D No

Any water resources study on arsenic occurrence Master plan for arsenic rule

D Yes D Yes

D No D No

28.

How would you like the research team to handle the utility information supplied? D Use the information for developing the decision tree and publish it with proper utility identification in the AWWARF final report D Use the information for developing the decision tree and publish it under a coded (to hide the utility name) identification in the AWWARF final report D Just use the information for developing the decision tree and not publish it in any written report(s)

29.

Certain treatment technologies may generate large quantities of unusable water. For example, nanofiltration membrane treatment at 85% recovery will generate 15% of brine water. What percentage water loss is acceptable? D Operational and implementation ease

LJ

> System-wide applicability

LJ

> Capital and O&M costs > Water loss

EH

> On-site and off-site safety

LJ

> Space and land requirements

LJ

> Impact on other existing/anticipated regulations

LJ

> Public acceptance

LJ

> Upgradability

LJ

233

APPENDIX C UNIT COST EQUATIONS

235

Table Cl Treatment capital cost equations Applicable Flow Range Cost Equation Technology (mgd)* Description ($) < 0.007 Not Available Throw-away activated 0.007 - 0.1 1004700(01*) + 34122 alumina with pH 0.1-1.0 -258750(DF)2 + 828060(DF) + 53949 adjustment 1.0 - 76 490160(DF) + 199180 (to pH 6) > 76 Not Available < 0.007 Not Available Throw-away activated 0.007 - 0.1 336040(DF) + 5301.1 alumina without pH 0.1 -1.0 110260(DF)2 + 183100(DF) + 8180.9 adjustment (ambient pH 7-8) 1.0 - 76 229940(DF) + 8805.3 > 76 Not Available

Conventional activated alumina

< 0.01

Not Available

0.01 - 0.1 0.1 - 0.27

4345438(DF)2 + 219335(DF) + 43863 7296957(DF) - 620445

0.27 -1.0 1.0 -10.0

175443(DF)2 + 1301173(DF) + 985627 278721(DF) + 2183522

10.0 - 430.0 33(DF)2 + 399034(DF) + 977094 > 430 Not Available

< 0.01 0.01 -1 Ion exchange (for two sulfate levels) 1 -100 > 100

Not Available 860837(DF) + 50219 for < 20 mg/L influent SO4 860837(DF) + 50219 for 20-50 mg/L influent SO4 156852(DF) + 418584 for < 20 mg/L influent SO4 156852(DF) + 418584 for 20-50 mg/L influent SO4 Not Available

(Continued)

236

Tabled (Continued) Treatment capital cost equations

Technology Description

Nanofiltration

Applicable Flow Range (mgd)*

Cost Equation ($)__

< 0.01

Not Available

0.01 - 0.1 0.1 - 0.27

17043869(DF)2 + 215457(DF) + 13673 2048323(DF) - 35175

0.27 -10.0 1764499(DF)° 8049 10.0 - 430.01268854(DF) - 1799954 > 430 Not Available < 0.01 0.01 - 0.1 Electrodialysis reversal 0.1 - 0.27

Not Available 17043869(DF)2 + 215457(DF) + 13673 2048323(DF) - 35175

0.27 -10.0 1764499(DF)08049 10.0 - 430.0 1268854(DF) -1799954 > 430 Not Available 76

-23.5(DF)2 + 8039.5(DF) + 242270 Not Available

< 0.01

Not Available

0.01 -1.0 1.0 -10.0

-37858(DF)2 + 58725(DF) + 8045.8 116550(DF) - 88241

10.0 - 76 > 76

-147.8(DF)2 + 31625(DF) + 516200 Not Available (Continued)

237

Table Cl (Continued) Treatment capital cost equations


Applicable Flow Range (mgd)* 100

< 0.01 Conversion of direct 0.01-1.0 filtration to 1-10 conventional treatment 10-76 > 76

Cost Equation ($) Not Available 6000000(DF) + 286870 2000000(DF) + 1000000 1000000(DF) + 2000000 855589(DF) + 8000000 Not Available

Not Available 261340(DF)2 + 480390(DF) + 6925.2 176240(DF) + 150170 -24.3(DF)2 + 118730(DF) +• 553910 Not Available

< 0.007 Not Available Granular ferric Q 007 _ Q 1 85874o(DF)2 + 393910(DF) + 24558 hydroxide -> without pH adjustment ** ~ ™ -192670(DF)2 + 704020(DF) - 413.7 (ambient pH 7-8.5) 1-0-76 465940(DF) + 88624 > 76 Not Available < 0.007 Not Available Granular ferric 0.007-0.1 726600(DF) + 28290 hydroxide with pH 0.1 -1.0 477350(DF) + 100370 adjustment 1.0-76 483440(DF) + 128600 (topH6.S) > 76 Not Available *mgd - Million gallons per day *DF - Design/maximum capacity flow in mgd

238

Table C2 Treatment O&M cost equations



< 0.0015 __ Throw-away activated 0.0015- 0.025 alumina with 0.025-0.41 pH adjustment 0.41-38 >38 Throw-away < 0.0015 activated Q.0015-0.025 alumina without pH 0.025-0.41 adjustment 0.41-38 (ambient >38 pH7-8) < 0.003

Conventional 0.003-0.03 activated 0.03 - 0.09 alumina (3000 o 09 - 0 36 ' bed volumes) '

Cost Equation

($/yr)

Not Available 513720(AFt) +8737.3 157260(AF)2 + 390850(AF) + 11533 450360(AF) + 13481 Not Available Not Available 336040(AF) + 5301.1 110260(AF)2 + 183100(AF) + 8180.9 229940(AF) + 8805.3 Not Available Not Available -1623215(AF)2 + 493975(AF) + 14084 379880(AF) + 16061

U.JO - 4.D

-7495(AF)2 + 91816(AF) + 40890 90418(AF)+40422

4.5 - 270 >270

-5.02(AF)2 + 86399(AF) + 58611 Not Available

< 0.003

Not Available

Conventional 0.003-0.03 activated 0.03 - 0.09 alumina (7000 o 09 - 0 36 bed volumes)

-1527071(AF)2 + 472723(AF) + 13738 310666(AF) + 17294

U.3O - 4.5

-141178(AF)2 + 90167(AF) + 36362 54712(AF)+ 47288

4.5 - 270 >270

-2.4(AF)2 + 58931(AF) + 28350 Not Available (Continued)

239

Table C2 (Continued) Treatment O&M cost equations Technology Description

Applicable Flow Range (mgd)* < 0.003

Conventional 0.003-0.03 0.03 - 0.09 activated alumina (16500 Q 09 - 0 36 bed volumes) Q'36 _ 4J 4.5 - 270 >270 Ion exchange 100

Ion exchange 100

Nanofiltration

< 0.003 0.003 - 0.03

0.03 - 5.0 5.0 - 270 >270

Cost Equation

($/yr)

Not Available -1415947(AF)2 + 448159(AF) + 13338 264372(AF) + 17675 -18686(AF)2 + 88917(AF) + 32902 42678(AF) + 47126 -1.2(AF)2 + 49346(AF) + 17146 Not Available Not Available 53599(AF) + 6533.5 74627(AF) + 14596 Not Available

Not Available 857579(AF) + 50063 156436(AF) + 415250 Not Available

Not Available 740927(AF) + 328 409950.9(AF)05065 183312(AF) + 444404.5 Not Available (Continued)

240



< 0.003 Electrodialysis 0.003 - 0.03 reversal 0.03 - 5.0 5.0 - 270 >270 < 0.003 Enhanced coagulation/ 0.003 - 0.36 0.36 - 4.5 filtration 4.5 - 38 > 38 < 0.003 Enhanced lime 0.003 - 0.36 softening 0.36 - 4.5 4.5 - 38 >38 < 0.003 0.003 - 0.05

Coagulation assisted microfiltration 0.8-3.5 3.5-100 >100

Cost Equation ($/yr) Not Available 740927(AF) + 328 409950.9(AF)05065 183312(AF) +444404.5 Not Available Not Available 3584(AF)2 + 9173.2(AF) + 351.5 10609(AF) + 236 -0.9(AF)2 + 8153.9(AF) + 2126.9 Not Available Not Available -461.7(AF)2 + 27501(AF) + 234.4 30270(AF) + 791.6 27198(AF) + 9748.5 Not Available Not Available 1000000(AF) + 14172 522365(AF) + 71030 282914(AF) + 229014 150013(AF) + 767802 Not Available (Continued)

241



Conversion of < 0-003 direct filtration 0.003-0.18 to conventional Q jg_Q gg treatment 0.68-36

Cost Equation ($/yr)

Not Available 1959.4(AF)2 + 13194(AF) + 432.2 35914(AF) + 2090.7 -3.2(AF)2 + 10198(AF) + 17712

>38

Not Available

< 0.003

Not Available

Conventional 0.003-0.03 0.03 - 0.09 activated alumina (10000 Q Q270


< 0.003

Not Available

Conventional 0.003-0.03 0.03 - 0.09 activated alumina (25000 Q 09 - 0 36 ' bed volumes) U.Jo - 4.J 4.5 - 270 >270

-1352455(AF)2 + 434124(AF) + 13110 246419(AF) + 17629 -19648(AF)2 + 87994(AF) + 31399 37787(AF) +46927 -0.96(AF)2 + 45327(AF) + 13015 Not Available (Continued)

242


Conventional activated alumina (50000 bed volumes)


Cost Equation

($/yr)

< 0.003

Not Available

0.003-0.03 0.03 - 0.09 Q 09 - 0 36 Q36 _ 45

-1110631(AF)2 + 380671(AF) + 12240 266461(AF) + 14731 -21008(AF)2 + 88142(AF) + 30204 35056(AF)+ 46592

4.5 - 270 >270


< 0.0015 0.0015-0.025 _ „-_ n „ °-025-°-41 0.41-38 > 38

Not Available 231200(AF) + 5471.1 208190(AF) + 8232.9 212550(AF) + 8231.3 Not Available

< 0.0015 Granular ferric 0.0015-0.025 hydroxide with pH adjustment 0.025-0.41 (topH6.5) 0.41-38 >38

Not Available 242430(AF) + 8609.5 266990(AF) + 4761.8 235070(AF) + 1535.8 Not Available

Granular ferric hydroxide without pH adjustment (ambient pH 7-8.5)

*mgd - Million gallons per day f AF - Average flow in mgd

243

Table C3 Residuals handling/disposal capital cost equations Applicable Flow Range Technology (mgd)* Description Ion exchange ( < 25 mg/L sulfate) 430

Cost Equation ___($)

Not Available -448669(DFf)2 + 1721917(DF) + 20860 1500994(DF) - 26091 1623875(DF) -137376 Not Available