United States
Environmental Protection
Agency
Office of
Drinking Water
Cincinnati, OH 45268
Center for
Research Information
Cincinnati, OH 45288
Technology Transfer
EPA/625/4-89/023
Technologies for
Upgrading Existing or
Designing New Drinking
Water Treatment
Facilities
Treatment
Sedimentation
Activated Carbon
Ion Exchange
Disinfection
Options
Coagulation
Filtration
Aeration
Reverse Osmosis
Other...
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EPA/625/4-89/023
March 1990
Technologies for Upgrading Existing or
Designing New Drinking Water
Treatment Facilities
Office of Drinking Water
Center for Environmental Research Information
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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Notice
This report has been reviewed by the U.S. Environmental Protection Agency and approved for
publication. Mention of trade names or commercial products does not constitute endorsement or
recommendation for use.
11
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Contents
Notice u
Tables ..... ix
Figures ........... xii
Acknowledgments xiii
Chapter 1. Introduction 1
Chapter 2. Selecting and Evaluating Treatment Processes 3
2.1 Overview of Federal Drinking Water Regulations 3
2.2 Selecting Treatment Technologies 5
2.3 Overview of Available Treatment Alternatives 7
2.3.1 Filtration 7
2.3.2 Disinfection 9
2.3.3 Organic Contaminant Removal 11
2.3.4 Inorganic Contaminant Removal and Control 12
2.4 Final Process Selection and Design 14
Chapter 3. Prefiltration Treatment Elements 17
3.1 Modifying Chemical Feed 18
3.1.1 Chemical Type , 18
3.1.2 Chemical Dosage Management 19
3.1.3 Chemical Application Methods and Considerations 21
3.2 Modifying or Adding Rapid Coagulant Mixing 22
3.3 Improving Flocculation 25
3.3.1 Improving Mixing 25
3.3.2 Improving Flocculator Inlet and Outlet Conditions 26
3.3.3 Improving Basin Circulation with Baffles 27
3.4 Improving Sedimentation 27
3.4.1 Horizontal Flow Sedimentation Basins 29
3.4.2 Upflow Solids Contact Clarifiers 30
Chapter 4. Filtration Technologies 33
4.1 Modifying Filtration Systems 33
4.1.1 General Effectiveness of Filtration Systems 34
4.1.2 Filtration System Improvements 34
4.1.3 System Design Checklist 37
4.2 Direct Filtration 37
4.2.1 Process Description 37
4.2.2 System Performance 38
4.3 Slow Sand Filtration , 38
4.3.1 System Design Considerations 39
4.3.2 Operation and Maintenance 39
4.3.3 System Performance 41
4.3.4 System Costs 41
4.4 Package Plant Filtration 41
4.4.1 Selecting a Package Plant System 42
4.4.2 System Description and Design Considerations 42
4.4.3 Operation and Maintenance 43
111
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4.4.4 System Performance 44
4.4.5 System Costs 44
4.5 Diatomaceous Earth Filtration 44
4.5.1 System Design 46
4.5.2 Operation and Maintenance 46
4.5.3 System Performance 47
4.5.4 System Costs 47
4.6 Other Filtration Systems 48
4.6.1 Membrane Filtration '..-.' 48
4.6.2 Cartridge Filtration 51
4.7 Selecting the Appropriate Filtration Treatment System 52
4.7.1 Steps in an Evaluation 52
4.7.2 Needfor Pilot Studies 53
4.7.3 Flocculation and Sedimentation Studies 53
4.7.4 Filtration Studies 53
Chapter 5. Disinfection and Disinfection By-Products 57
5.1 The Objectives of Disinfection 57
5.1.1 CT Values 58
5.2 Disinfection By-Products 59
5.2.1 The Chemistry of Oxidation 60
5.2.2 The Presence of Disinfection By-Products in Drinking Water 61
5.2.3 Strategies for Controlling Disinfection By-Products 61
5.3 Comparing Disinfectants 63
5.3.1 Chlorine 63
5.3.2 Chlorine Dioxide 63
5.3.3 Monochloramine 63
5.3.4 Ozone 64
5.3.5 Ultraviolet Radiation 65
5.3.6 Advanced Oxidation Processes 65
5.4 Primary Disinfection Technologies 65
5.4.1 Chlorine 66
5.4.2 Ozone 72
5.4.3 Chlorine Dioxide 81
5.4.4 Ultraviolet Radiation 87
5.5 Secondary Disinfectants 92
5.5.1 Chloramination 92
Chapter 6. Treatments of Organic Contaminants 97
6.1 Pretreatment for Natural Organic Contaminant Removal 97
6.1.1 Coagulant Pretreatment 99
6.1.2 Oxidation Pretreatment 100
6.2 Granular Activated Carbon 100
6.2.1 Process Design Considerations 101
6.2.2 Tests for Deriving Carbon Usage and Other Design Criteria 104
6.2.3 Least Cost Design Criteria 104
6.2.4 Facility Design Criteria 105
6T2.5 Operation and Maintenance 105
5.2.6 System Performance 106
6.2.7 System Costs 106
6.3 Packed Column Aeration 109
6.3.1 System Design Considerations 112
6.3.2 Pilot Testing PCA 112
IV
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6.3.3 VOC Emission Control 113
6.3.4 Operation and Maintenance , 115
6.3.5 System Performance 115
6.3.6 SystemCosts ,.. 115
6.4 Powdered Activated Carbon Plus Conventional Treatment ,.. 118
6.4.1 PAC Application,Techniques 118
6.4.2 System Design Considerations 119
6.4.3 System Performance 120
6.5 Diffused Aeration 120
6.5.1 System Design Considerations 121
6.5.2 System Performance 121
6.6 Multiple Tray Aeration 121
6.6.1 SystemDesign , 121
6.6.2 System Performance 121
6.7 Emerging Applications of Treatment Technologies for Organic Contaminants 121
6.7.1 Oxidation Including Ozone 122
6.7.2 Reverse Osmosis 124
6.7.3 Mechanical Aeration 124
6.7.4 CatenaryGrid .... 124
6.7.5 Higee Aeration 124
6.7.6 Resins 125
Chapter 7. Treatments for Inorganic Contaminants 131
7.1 Techniques for Controlling Corrosion 131
7.1.1 The Problem of Corrosion 132
7.1.2 Diagnosing and Evaluating the Problem 133
7.1.3 Corrosion Controls 135
7.2 Treatment Technologies for Controlling Inorganic Contaminants,
Including Radionuclides 139
7.2.1 Removing Radionuclides in Drinking Water 141
7.2.2 Conventional Treatment: Coagulation and Lime Softening 141
7.2.3 Reverse Osmosis 144
7.2.4 Ion Exchange 148
7.2.5 Activated Alumina 149
Chapter 8. Current and Emerging Research 153
8.1 Current Research on Disinfection By-Products 153
8.1.1 Identifying and Controlling Chlorination By-Products 153
8.1.2 Identifying Ozone By-Products 153
8.2 Treatment of Organic and Inorganic Contaminants 153
8.2.1 Granular Activated Carbon Systems 155
8.2.2 Ozone Oxidation Systems 157
8.2.3 Ultraviolet Treatment '... 157
8.2.4 Reverse Osmosis 157
8.2.5 Ultrafiltration 157
8.2.6 Packed Tower Aeration . 157
8.2.7 Conventional Treatment , 158
8.2.8 Ion Exchange 158
8.2.9 Technologies for Removing Radionuclides 158
8.2.10 Secondary Sources of Pollution 159
8.2.11 Small Systems Technologies ..... 159
8-3 Mandatory Disinfection 159
8.3.1 Treatment/Distribution Microbiology 159
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8.3.2 Bacterial Detection/Monitoring 160
8.4 Prohibition of Lead Materials 160
8.5 Systems and Cost Modeling Studies 160
8.6 Future Directions 161
Chapter 9. References 163
Appendix A Experience Modifying Existing Filtration Systems 169
A.I Upgrading Existing Treatment Facilities 169
A.I.I Horizontal Flow Basin Example 169
A.I.2 Upflow Solids Contact Clarifier Example 170
A.1.3 Sacramento, California 170
A. 1.4 Erie County, New York 170
A.I.5 Corvallis, Oregon 171
A.I.6 Novato, California 172
A.2 Slow Sand Filter Systems 173
A.2.1 Idaho State '.'.'. 173
A.2.2 New York State 173
A.2.3 Mclndoe Falls, Vermont 174
A.2.4 Village of 100 Mile House, British Columbia, Canada 175
A.3 Package Plants 175
A.3.1 Conventional Package Plants 175
A.3.2 Adsorption Clarifier Package Plants 176
A.4 Diatomaceous Earth Filters 180
A.4.1 Colorado State University Study 180
A.4.2 Mclndoe Falls, Vermont 180
A.5 Selecting a Filtration System 180
A.5.1 Lake County, California 180
Appendix B Case Histories of Emerging Disinfection Technologies 185
B.I Ozone Case Histories 185
B.I.I Primary Disinfection with Ozone: North Andover, Massachusetts ... 185
B.1.2 Preozonation for THM Control: Kennewick, Washington 186
B.2 UV Radiation Case Histories 188
B.2.1 Ultraviolet Radiation for Primary Disinfection: Fort Benton, Montana 188
B.3 Chlorine Dioxide Case Histories 188
B.3.1 Predisinfection for THM Control: Evansville, Indiana 188
B.3.2 Primary and Secondary Disinfection with Chlorine Dioxide:
Hamilton, Ohio 189
B.3.3 Preoxidation with Chlorine Dioxide, Postchlorination with Chlorine
Dioxide and Chloramine: Galveston, Texas 191
B.4 Chloramine Case Histories 192
B.4.1 Prechlorination, Postchloramination: Bloomington, Indiana 192
B.4.2 Prechlorine Dioxide, Prechlorination, and Postchloramination:
Philadelphia, Pennsylvania 192
Appendix C. Experience with Treatment Technologies for Organic Contaminants 195
C.I Experience with Granular Activated Carbon 195
C.I.I GAG for VOC Removal: Washington, New Jersey 195
C.I.2 GAG for Contaminant Control: Cincinnati, Ohio 195
C.1.3 EPA Health Advisory Example 196
C.2 Experience with PTA: Scottsdale, Arizona 196
C.3 Experience with PAC 197
VI
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Appendix D. Experience with Treatment Technologies for Inorganic Contaminants 203
D.I Corrosion Control 203
D.I.I Controlling Lead: Seattle, Washington 203
D.1.2 Controlling Lead with pH Adjustment: Boston, Massachusetts 203
D.2 Coagulation to Control Barium: Illinois 204
D.3 Reverse Osmosis: Sarasota, Florida 204
D.4 Ion Exchange: McFarland, California 205
D.5 Activated Alumina: Gila Bend, Arizona 206
Appendix E Summary of Corrosion Indices 209
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Tables
2-1 Contaminants Required to be Regulated Under the SDWA Amendments of 1986 4
2-2. Final MCLGs and MCLs for VOCs 5
2-3. Monitoring for Unregulated VOCs 5
2-4. Proposed MCLGs and MCLs for SOCs and lOCs 6
2-5! Proposed SMCLs 6
2-6 Overview of Water Treatment Technologies 8
2-7. Typical Influent Characteristics and Capacities for Filtration Technologies 10
2-8. Removal Capacities of Seven Filter Options .< 10
2-9. Advantages and Disadvantages of Five Disinfectants 11
2-10. Disinfectant Production Considerations 11
2-ll! Desired Points of Disinfectant Application 11
2-12. Disinfectant Application Considerations 12
2-13. Treatment Technology Removal Effectiveness Reported
for Organic Contaminants (percent) 13
2-14. Operational Conditions for Organic Treatments 14
2-15 Corrosion Control Considerations ; , 14
2-16. Most Probable Treatment Application for Inorganic Treatments 14
2-17! Removal Effectiveness for Nine Processes by Inorganic Contaminant 15
2-18. Advantages and Disadvantages of Inorganic Contaminant 16
3-1. Summary of Conventional Treatment Operating Issues, 17
3-2. Chemical Costs for Conventional Treatment 18
3-3. Estimated Costs for Supplementing Surface Water Treatment
by Adding Alum Feed Facilities 23
3-4. Estimated Costs for Supplementing Surface Water Treatment
by Adding Polymer Feed Facilities 23
3-5. Estimated Costs for Supplementing Surface Water Treatment
by Adding Sodium Hydroxide Feed Facilities 23
3-6 Estimated Costs for Supplementing Surface Water Treatment
by Adding Sulfuric Acid Feed Facilities 24
3-7. Typical Rapid Mixer Contact Times and Velocity Gradients 24
3-B. Estimated Costs for Supplementing Surface Water Treatment
by Adding Rapid Mix 25
3-9. Estimated Costs for Supplementing Surface Water Treatment
by Adding Flocculation 28
3-10. Horizontal Flow Basins Loading Rates 30
3-11 Upflow Clarifier Loading Rates for Cold Water 31
3-12. Estimated Costs for Supplementing Surface Water Treatment
by Adding Tube Settling Modules 32
4-1. Generalized Capability of Filtration Systems To Accommodate
Raw Water Quality Conditions 35
4-2 Removal Efficiencies OfGiardia Lamblia By Water Treatment Processes 35
4-3 Removal Efficiencies Of Viruses By Water Treatment Processes 35
4-4. Estimated Costs For Supplementing Surface Water Treatment
By Slow Sand Filtration ;.. : 42
4-5. Summary Of Results Of Adsorption Clarification Package Plants 46
4-6. Estimated Costs for Supplementing Surface Water Treatment
by Complete Treatment Package Plants 146
4-7. Estimated Costs for Supplementing Surface Water Treatment
by Direct Filtration Using Diatomaceous Earth 48
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4-8. Estimated Costs for Supplementing Surface Water Treatment
by Package Membrane Filtration Plants 52
5-1. CT Values for Achieving 90 Percent Inactivation ofGiardia Lamblia ,.. 58
5-2. CT Values for Achieving 99.9 Percent Inactivation of Giardia Lambliaa '.'.'.'.'.'.'.'.'.'.[ 59
5-3. CT Values for Achieving Inactivation of Viruses at pH 6 Through 9 '.'.'.'.'. 59
5-4. Oxidation Potentials of Water Treatment Oxidants 60
5-5. Occurrence of Chlorinated Disinfection By-Products at 10 Water Utilities ............... 61
5-6. Summary of Health Effects Associated with Chlorination By-Products '.'.'.'.'.' 61
5-7. Disinfectants and Disinfectant By-Products Listed in the First
Drinking Water Priority List gg
5-8. Capital Costs for Gas Chlorination 70
5-9. Capital Costs for Gas Chlorination yg
5-10. Capital Costs for Liquid Chlorinators 71
5-11. Operation and Maintenance Cost Summary for Sodium Hypochlorite Solution Feed 72
5-12. Costs of Ozonation Equipment for Small Water Supply Systems: Supplier A '.'.'.'. 80
5-13. Costs of Ozonation Equipment for Small Water Supply Systems: Supplier B '.', 81
5-14. Operating and Maintenance Costs for Small Ozone Systems 82
5-15. Costs of Chlorine Dioxide Generating Equipment 90
5-16. Operation and Maintenance Cost Summary for Chlorine Dioxide
Generating and Feed Systems 90
5-17. Construction Costs for Ultraviolet Light Disinfection 94
5-18. Operation and Maintenance Costs for Ultraviolet Light Disinfection 94
5-19. Chemical Costs for Generating Monochloramine for 2,500 GPD
Water Treatment Plant 95
6-1. Performance Summary for Five Organic Technologies ! 98
6-2. Readily and Poorly Adsorbed Organics 101
6-3. Summary of Carbon Usage Rates 103
6-4. Cost for 95 Percent Removal of Several Organics and Radon
Using GAG Adsorption 109
6-5. Henry's Law Constants for Nine Organic Chemicals HI
6-6. Typical Air Stripping Design Parameters for Removal of 13 Commonly
Occurring Volatile Organic Chemicals Hg
6-7. Examples of Removal Efficiencies for PTA Systems H9
6-8. Cost for 99 Percent Removal of Several VOCs and Radon
Using Packed Tower Aeration : 12Q
6-9. Typical Performance of Conventional Treatment Processes without and with PAC 121
6-10. Typical Performance of Diffused Aeration 123
6-11. Design Parameters for Peroxide-Ozone Treatment Plant and
Assumptions for Cost Comparisons 12g
6-12. Comparison of Annual Treatment Costs for Removal of PCE and TCE
from Ground Water 12g
6-13. Typical Performance of Ozonation Process :............ 126
6-14. Typical Performance of Reverse Osmosis Process 127
7-1. Factors Affecting the Corrosivity of Drinking Water \ 132
7-2. Galvanic Series - Order of Electrochemical Activity of
Common Metals Used in Water Distribution Systems 133
7-3. Typical Customer Complaints Due to Corrosion 134
7-4. Percentage of Test Sites with Lead in Drinking Water
Greater than 20 ug/L at Low pH '. 134
7-5. Percentage of Test Sites with Lead in Drinking Water
Greater than 20 ug/L at Medium pH , 135
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7-6. Percentage of Test Sites with Lead in Drinking Water
Greater than 20 ug/L at High pH .
7-7. Corrosion Properties of Frequently Used Materials in Water Distribution Systems
7-8. Pipe Wall Linings ................. ......................
7-9. Water Storage Tank Linings and Coatings
7-10. Removal Effectiveness for Eight Processes by Inorganic Contaminant ..... .
7-11. Most Effective Treatment Methods for Removal of Inorganic Contaminants
7-12. Advantages and Disadvantages of Inorganic Contaminant Removal Processes
7-13. Treatment Technologies for Removing Radionuclides .......... .
7-14. Radionuclide Process Treatment Costs
7-15. Costs for Removing Radon from Drinking Water by Packed Tower Aeration
7-16. Costs of Radon Treatment at the Plant Scale (200 GPD) for GAC Versus Aeration
7-17. Removal Efficiency Potential of Alum Versus Ferric Chloride
7-18. Removals Possible with Lime Softening ....................... .
8-1. Common Chlorination By-Products .......
8-2. Treatment Technologies Evaluated by the Drinking Water Research Division
8-3. Chemicals for Which Carbon Usage Rates are Being Developed ....... .
A-l. Characteristics of Slow Sand Filter Installations in New York
A-2. Filter Ripening Data - Summary ...............
A-3. Water Treatment Facilities Surveyed in Field Study
A-4. Treatment Process Characteristics ........................ : ----
A-5. Plant Turbidity Values (NTU) ........................
A-6. Operating Data -Greenfield, IA ---- . ............ .....
A-7. Operating Data - Lewisburg, WV ........
A-8. Operating Data -Philomath, OR ..... .'. ... ........... . . . .
A-9. Operating Data -Harrisburg, PA
A-10. Operating Data -Red Lodge, MT ..........................
A-ll. Clear Lake Water Quality Analysis ...... . . .............
A-12. Clear Lake Water Quality at DWR Sampling Station No. 1 at Lakeport
B-l. Design Criteria for Kennewick Water Treatment Plant Preozonation Facilities
B-2. Summary of THM Data at Bloomington, Indiana,
with Free Chlorination, August 16, 1984 ....................
B-3. Summary of THM Data at Bloomington, Indiana,
withPostchloramination, August 26, 1984 ................
C-l. Profile of System used in EPA Health Advisory ...................... .
C-2. Influent Characterization for System Used in EPA Health Advisory
D-l. Metropolitan District Commission Water Quality Data .....
D-2. Design Criteria of Reverse Osmosis Equipment ..... . ......................
D-3. Pre- and Posttreatment Reverse Osmosis Processes .........................
D-4. Chemical Analyses of Sarasota County Reverse Osmosis Systems
D-5. Reverse Osmosis Treatment System Costs
D-6. Ion Exchange Cost Components for McFarland, California ($1983)
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144
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156
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192
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200
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207
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Figures
3-1. Simplified diagram of streaming current detector
3-2. In-line jet injection mixer
3-3. Coagulant diffuser
3-4. Divided flocculation basin
3-5. Typical tube settler installation in rectangular basin
3-6. Radial solids contact clarifier with tube settlers
4-1. Relationship between cyst removal and filtered water turbidity
4-2. Cutaway view of typical rapid sand filter
4-3. Flow diagram of typical direct filtration system
4-4. Flow diagram of in-line direct filtration system
4-5. Flow diagram of modified direct filtration system
4-6. Typical unhoused slow sand filter installation
4-7. Typical housed slow sand filter installation
4-8. Flow diagram of a package plant
4-9. Adsorption clarifier package plant
4-10. Operating cycles of package plant
4-11. Typical pressure diatomaceous earth filtration system
4-12. Flow diagram of membrane filtration system
4-13. Skid-mounted membrane filtration assembly
4-14. Tube settling test module
4-15. Pilot filter schematic
5-1. Distribution of hypochlorous acid and hypochlorite ions in water at different
pH values and temperatures of 0ฐC and 20ฐC
5-2. Graphical representation of the breakpoint chlorination reaction
5-3. Solution feed-gas chlorination system
5-4. Low pressure air feed-gas treatment schematic for ozone generation
5-5. High pressure air feed-gas treatment schematic for ozone generation
5-6. Typical ozone generating configuration for a Corona discharge cell
5-7. Two-compartment ozone contactor with porous diffusers
5-8. Schematic diagram of an automatic feed, automatic flow-proportional
chlorine dioxide system: Generation from chlorine and sodium chlorite.
5-9. Manual feed equipment arrangement for generating chlorine dioxide
from sodium hypochlorite solution and mineral acid
5-10. Schematic of CIFEC chlorine dioxide generating system
5-11. Schematic of manual chlorine dioxide system
5-12. Proportions of mono- and dichloramines in water with equimolar
concentrations of chlorine and ammonia
6-1. Effectof carbon cost on facility cost
6-2. Steady-state adsorption/decay curve for radon
6-3. Effectof contaminant on carbon life
6-4. Effect of compound on carbon life
6-5. Application of Freundlich Isotherm Relationship
6-6. Adsorption isotherms for several organic compounds found
in ground-water supplies
6-7. Diagram of pilot column test system
. 20
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. 30
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6-8. Diagram of dynamic mini-column adsorption system 107
6-9. GAG treatment options 108
6-10. Wavefront within GAC contactor 1ฐ8
6-11. GAC facility cost components 11ฐ
6-12. Cost comparison of carbon regeneration/replacement options HI
6-13. Packed tower aeration system. H3
6-14. Distributor types 114
6-15. Effect of compound on packed-column design Ho
6-16. Packing height vs. removal efficiency for trichloroethylene 116
6-17. Schematic of pilot aeration column.
6-18. Schematic of catalytic incineration process
6-19. Vapor-phase carbon system for treatment of aeration exhaust air 119
6-20. Schematic of the Roberts-Haberer process 12ฐ
6-21. Schematic of PAC adsorption process 122
6-22. Schematic of a plant-scale diffused aeration process 122
6-23. Home diffused aeration system 123
6-24. Schematic of a redwood slat tray aerator 125
6-25. Schematic of mechanical aeration process 127
6-26. Catenary grid system ^28
6-27. Schematic of Higee system I29
7-1. Solubility of lead as a function of pH and carbonate 137
7-2. Lime softening treatment system 145
7-3. Schematic of a reverse osmosis system 146
7-4. Two types of reverse osmosis membranes. 147
7-5. Ion exchange treatment system 149
7-6. Activated alumina systems: Operating mode flow schematics 150
8-1. Pilot plant schematic for disinfection by-product control 155
A-l. Flow diagram of the pilot filtration equipment I71
A-2. Giordia cysts in the raw water 176
A-3. Average raw andfiltered water turbidity 17?
C-l. GAC treatment plant schematic Vannatta Street Station. 196
C-2. Cincinnati treatment train with addition of GAC I97
C-3. Typical TOG reduction curve during pilot study i98
C-4. Regeneration system schematic 1"
C-5. Schematic diagram of a Scottsdale packed column. 201
Xlll
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Acknowledgments
* >~i o o "-C>-****t3 * ' ^ " *^* J.i*iป.j.xig TT dUCJ. j. J.CdUilJLCil,lj JL' ClClllUXCS.
of these workshops were sponsored by local sections of the American Water Works Association
(AWWA) and others by the Association of State Drinking Water Administrators (ASDWA) Other
sponsors included the United States Environmental Protection Agency's (EPA) Offices of Drinking
Water and Research and Development and Regions.
Overall management of the workshop series and preparation of this document was provided by Dr
James E. Smith, Jr., of EPA's Center for Environmental Research Information. He was assisted in
providing technical direction by representatives of ASDWA, the local AWWA Sections, EPA Regional
Personnel, John Trax and Ken Hay of EPA's Office of Drinking Water, and Walter Feige and other
members of EPA's Drinking Water Research Division.
Unless otherwise noted, the technical material in this document was taken from handout materials
^Presentations Provided bv the following speakers in the workshops: Dr. Robert M. Clark Director
of EPA 8 Drinking Water Research Division, Cincinnati, Ohio; John F. Dyksen, Director Department
of Water Supply, Village of Ridgewood, New Jersey; Sigurd Hansen, HDR, Inc., Cameron Park
California; Dr. Gary S. Logsdon, Chief of EPA's Microbiological Treatment Branch, Cincinnati Ohio-
Dr. Rip G. Rice, Rice International Consulting Enterprises, Ashton, Maryland; and Dr. Edward
Singley, James Montgomery Consulting Engineers, Gainesville, Florida. Appreciation is also
expressed to those individuals around the country who participated in panels and presented case
histories of their treatment experiences.
Organization and presentation of the material, technical writing, and editorial work was provided by
Lynn Knight, John Reinhardt, and Susan Richmond of Eastern Research Group, Inc., Arlington,
Massachusetts. Appreciation is expressed to those individuals in EPA's Offices of Drinking Water and
Research and Development who assisted in reviewing drafts of this publication; especially Peter Cook
Ronnie Levin, Michael Schock, and Tom Sorg. The workshop presenters are acknowledged for their
assistance in reviewing materials, especially John Dyksen who provided overall technical review.
In addition, EPA gratefully acknowledges the assistance of:
Kalyan Ramen, Environmental Engineer, Malcolm Pirnie, Inc.
Ross Hymen and Paul Anderson, Massachusetts Dept. of Environmental
Quality Engineering.
Tom Boshar, Lally Associates
Dr. Carl Nebel, PCI Ozone Corporation
Fred Zinnbauer, Aquionics, Inc.
Gary Swanson, Robert Peccia Associates
xiv
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Chapter 1
Introduction
This document discusses drinking water treatment
technologies that address contaminants and
contaminant categories regulated under the Safe
Drinking Water Act (SDWA - 42 U.S.C. 300f, et seq.)
and its 1986 amendments. The information was
distilled from materials used in a series of workshops
conducted from 1987 through 1989 in locations
throughout the United States. The workshops were
sponsored by the Offices of Drinking Water (ODW)
and Research and Development (ORD) of the United
States Environmental Protection Agency (EPA), and
the Association of State Drinking Water
Administrators (ASDWA).
The 1986 statutory provisions of the SDWA
amendments bring a large number of previously
unregulated or minimally regulated water systems
under significant regulatory control. This document
covers both established and emerging technologies
needed to comply with these new regulations.
Descriptions of each technology include an overview
of the process, performance, design considerations,
operating and maintenance aspects, costs, and
experiences. This information is meant to assist
public water system engineers, operators, and
decision-makers faced with the many new regulatory
requirements in selecting methods of compliance.
Chapter 2 is an overview of the selection process and
the potential technological solutions for each
contaminant or contaminant category. This chapter
serves as a guide to subsequent chapters that discuss
each treatment technology in more detail. It includes
many tables that compare relevant information
between technologies. Case histories illustrating
experience with each technology are provided in
appendices.
Chapter 3 covers prefiltration elements of a water
treatment system, including rapid mixing, chemical
dosage, coagulation, flocculation, and sedimentation.
While these elements usually precede filtration, they
may be found with other treatment technologies as
well. These elements impact the performance of
subsequent components in the treatment train,
which are described in Chapters 4 through 7.
Chapter 4 describes filtration technologies that
address removal'of turbidity and microbial
contamination. Technologies covered include
conventional, direct, slow sand, diatomaceous earth,
membrane, and cartridge filtration systems.
Chapter 5 reports on the five major disinfection
technologies: chlorine, ozone, ultraviolet (UV)
radiation, chlorine dioxide, and chloramines. The
problem of disinfection by-products and strategies for
their control are also addressed.
Chapters 6 and 7 describe technologies that address
organic and inorganic contamination, respectively.
Treatment technologies for organics removal include
granular activated carbon, packed column aeration,
powdered activated carbon, diffused aeration,
multiple tray aeration, oxidation, mechanical
aeration, catenary grid aeration, Higee aeration, and
membrane filtration. Treatment technologies for
inorganics removal include corrosion control, reverse
osmosis, ion exchange, activated alumina, aeration,
and powdered activated carbon.
Chapter 8 reviews the recent research activities of
EPA's Drinking Water Research Division.
Finally, Chapter 9 lists the references used in the
entire document.
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Chapter 2
Selecting and Evaluating Treatment Processes
This chapter serves as a guide to the entire document.
It begins in Section 2.1 with a brief summary of the
statutory and regulatory framework that applies to
public drinking water systems. The new statutory
and regulatory provisions drive the treatment
objectives for drinking water. Identifying these
objectives and selecting treatment alternatives are
discussed in Section 2.2. Section 2.3 summarizes the
various technological alternatives available to water
utilities for complying with the new regulatory
provisions. Section 2.4 discusses the final selection
process.
2.1 Overview of Federal Drinking Water
Regulations
This overview provides a general context for
discussing the available treatment technologies
presented in this document. It is not intended as a
substitute for the Code of Federal Regulations that
describes each provision's many regulatory
specifications, variances, and exceptions.
The 1986 amendments significantly strengthen and
expand the 1974 Safe Drinking Water Act (SDWA).
A major focus of the amendments is establishing a
strict schedule for promulgating drinking water
regulations that use numerical standards, referred to
as Maximum Contaminant Levels (MCLs), or
treatment technique requirements for 83
contaminants (see Table 2-1). Prior to the 1986
amendments, only 22 MCLs had been set. In addition,
EPA must regulate 25 additional contaminants every
3 years beginning in 1991.
The regulatory provisions derived from the 1986
amendments use the following terms to describe
controls for water contaminants:
Maximum Contaminant Levels (MCLs): These
are the maximum permissible levels of
contaminants delivered to a user of public water
supplies.
Maximum Contaminant Level Goals (MCLG):
These are nonenforceable limits that indicate the
level of the contaminant that does not cause any
known or anticipated adverse effect on human
health. They were formerly termed Recom-
mended Maximum Contaminant levels (RMCLs).
Secondary Maximum Contaminant Levels
(SMCLs): These are nonenforceable goals for
preserving the aesthetic qualities of drinking
water.
The amendments authorize EPA to set treatment
technique requirements in lieu of MCLs when it is
not economically or technically feasible for water
suppliers to determine the level of contaminants. In
addition, the amendments require EPA to set best
available technology (BAT) for purposes of complying
with National Primary Drinking Water Regulations.
For instance, the statute lists granular activated
carbon (GAG) as BAT for synthetic organic chemical
(SOC) removal. For purposes of complying with the
regulations, any other technology, treatment
technique, or control strategy selected to remove
SOCs must be as effective as GAC. BAT is also set for
purposes of issuing variances under Section 1415.
In addition to the quantitative provisions noted
above, there are several far-reaching provisions on
monitoring, filtration, disinfection, and use of lead
materials included in the 1986 Amendments to the
SOW A, as follows:
Monitoring: The amendments instruct EPA to
promulgate regulations requiring monitoring of
certain unregulated contaminants. The
monitoring schedule is varied based on the
number of persons served by the system, the
-------
Tablo 2-1. Contaminants Required to be Regulated Under
the SDWA Amendments of 1986
Votatlta Organic Chemicals
Tnchtoroethytene
Tetrachtoroethylene
Carbon tetrachloride
1,1,1 -Trichloroethane
1,2-Dtchtoroethane
Vinyl chloride
Methytene chloride
Microbiology and Turbidity
Total coliformsa
Turbidity*
Giardia lamblla
Inorganics
Arsenic*
Barium4
Cadmium8
Chromium11
Load*
Mercury*
Nitrate*
Selenium*
Silver*
Fluoride*
Aluminum
Antimony
Synthetic Organlcs
Endrin*
Lmdane*
Methoxychtor*
Toxaphene8
2,4-D*
2,4,5-TP*
Aldicarb
Chtordane
Oalapon
Diquat
Entfcthall
Glyphosate
Carbofuran
Alachor
Epichtorohydrin
Toloene
Adipates
2.3,7.8-Chtortnated dibenzo
furans (Dkwin)
Radlonucltdes
Radium 226 and 228*
Beta particle and photon
radioactivity*
Uranium
Regulated prior to 1986 amendments to SDWA.
Source: U.S. EPA Fact Sheet; February 1989.
source of the supply, and the contaminants likely
to be found.
ป Filtration: EPA was required to specify criteria
under which filtration is required for surface
Benzene
Chlorobenzene
Dichlorobenzene
Trichlorobenzene
1,1 -Dichloroethylene
trans-1,2 Dichloroethylene
cis-1,2-Dichloroethylene
Viruses
Standard plate count
Legionella
Molybdenum
Asbestos
Sulfate
Copper
Vanadium
Sodium
Nickel
Zinc
Thallium
Beryllium
Cyanide
1,1,2-Trichloroethane
Vydate
Simazine
PAHs
PCBs
Atrazine
Phthalates
Acrylamide
Dibromochloropropane (DBCP)
1,2-Dichloropropane
Pentachlorophenol
Ptehloram
Dinoseb
Ethylene dibromide (EDB)
Dibromomethane
Xylene
Hexachlorocyclopentadiene
Total trihalomethanes3
Gross alpha particle activity3
Radon
water sources and procedures for States to
determine which systems must filter.
Disinfection: All public water supplies will be
required to disinfect their water.
Lead: The amendments prohibit the use of
solders and fluxes containing more than 0.2
percent lead and pipes and pipe fittings
containing more than 8 percent lead.
The three primary entities involved with the
regulatory effort for the 1986 amendments are:
U.S. EPA, with the primary roles of national
primary and secondary drinking water
regulations, designating BATs, and overseeing
State programs and enforcement.
States, with the primary responsibility of
implementation, program administration, and
enforcement.
Utilities, which will have to increase monitoring,
install new treatment processes, and increase
public awareness of contamination problems.
These are very simplified descriptions of each role.
The statute and regulations require significant
interplay between the three groups.
The regulatory effort is divided into the following five
phases:
Phase I: Volatile organic compounds
Phase II: Synthetic organic compounds,
inorganic compounds, and unreg-
ulated contaminant monitoring
Phase HI: Radionuclide contaminants
Phase IV: Disinfectant and oxidant by-products
Phase V: Inorganic compounds and synthetic
organic compounds
On July 8,1987, EPA promulgated final regulations
for eight VOCs and fluoride. The final MCLGs and
MCLs for the VOCs are shown in Table 2-2. The
regulations published July 8,1987, also include
monitoring requirements for 51 unregulated
contaminants, which are shown in Table 2-3.
In May 1989, EPA issued proposed regulations for 30
SOCs and 8 inorganic chemicals (lOCs), which are
listed in Table 2-4. For two contaminants, epichloro-
hydrin and acrylamide, EPA proposed a treatment
technique in lieu of an MCL and monitoring
-------
Table 2-2. Final MCLGs and MCLs for VOCs
Final MCLG3 Final MCL
(mg/L) (mg/L)
Table 2-3. Monitoring for Unregulated VOCs
Trichloroethylene
Carbon tetrachloride
Vinyl chloride
1 ,2-Dichloroethane
Benzene
para-Dichlorobenzene
1,1-Dichloroethylene
1,1,1 -Trichloroethane
zero
zero
zero
zero
zero
0.075
0.007
0.2
0.005
0.005
0.002
0.005
0.005
0.075
0.007
0.2
Final MCLGs were published Nov. 13, 1985. The MCLG and
MCL for p-dichlorobenzene were reproposed at zero and 0.005
mg/L on April 17, 1987; comment was requested on levels of
0.075 mg/L and 0.075 mg/L, respectively.
Source: U.S. EPA Fact Sheet; February 1989.
requirements. The proposal also established nine
new secondary MCLs, which are listed in Table 2-5.
In June 1988, EPA issued proposed regulations to
define MCLs and MCLGs for lead and copper. The
MCLG proposed for lead is zero, and 1.3 mg/L for
copper. The proposed MCLs applicable to water
entering the distribution system were 0.005 mg/L for
lead and 1.3 mg/L for copper. EPA also was
considering MCLs and/or action levels for lead and
copper and other related water quality parameters at
the consumers' tap. These proposed regulations are in
various stages of finalization.
On June 29,1989, the Surface Water Treatment Rule
(SWTR) and the Coliform Rule were promulgated.
According to the SWTR, all public water systems
using surface water or ground water under direct
influence of surface water, must disinfect and may be
required to filter if certain source water quality
requirements and site-specific conditions are not met.
The MCLGs established in the rule are:
Giardia lamblia - 0
Viruses - 0
Legionella - 0
No MCLGs were set for turbidity and heterotrophic
plate count. Treatment requirements also were
established in lieu of MCLs for Giardia, viruses,
HPC, Legionella, and turbidity. Treatment must
reliably achieve at least 99.9 percent
removal/inactivation of Giardia lamblia cysts and
99.99 percent removal/inactivation of viruses.
The Coliform Rule requires all public water systems
to meet the coliform MCL and monitor total coliform
with frequencies depending on population served,
and requires small systems to conduct a sanitary
survey. To comply with the coliform MCL, no more
than 50 percent of all total coliform samples per
month can be total coliform-positive.
Required for All Systems-
Chloroform
Bromodichloromethane
Chlorodibrornomethane
Bromoform
trans-1,2-Dichloroethylene
Chlorobenzene
m-Dichlorobenzene
Dichloromethane
cis-1,2-Dichloroethylene
o-Dichlorobenzene
Dibromomethane
1,1 -Dichloropropane
Tetrachloroethylene
Toluene
p-Xylene
o-Xylene
m-Xylene
1,1-Dichloroethane
Required for Vulnerable
Systems Only:
1,2-Dibromo-3-chloropropane
(DBCP)
Ethylenedibromide (EDB)
At Each State's Discretion:
1,2,4-Trimethylbenzene
1,2,4-Trichlorobenzene
1,2,3-Trichlorobenzene
n-Propylbenzene
n-Butylbenzene
Naphthalene
Hexachlorobutadiene
1,2-Dichloropropane
1,1,2,2-Tetrachloroethane
Ethylbenzene
1,3-Dichloropropane
Styrene
Chloromethane
Bromomethane
1,2,3-Trichloropropane
1,1,1,2-Tetrachloroethane
Chloroethane
1,1,2-Trichloroethane
2,2-Dichloropropane
o-Chlorotoluene
p-Chlorotoluene
Bromobenzene
1,3-Dichloropropane
Ethylene dibromide
1,2-Dibromo-3-chloropropane
1,3,5-Trimethylbenzene
p-lsopropyltoluene
Isopropylbenzene
tert-butylbenzene
sec-butylbenzene
Fluorotrichloromethane
Dichlorodifluoromethane
Bromochloromethane
Source: U.S. EPA Fact Sheet; February 1989.
2.2 Selecting Treatment Technologies
Defining treatment objectives and selecting control
technologies involve eight basic considerations:
Effluent requirements
Influent characteristics
Existing system configuration
Cost
Operating requirements
Pretreatment and posttreatment components
Waste management
Future needs of the service area
-------
TabI0 2-4. Proposed MCLGs and MCLs for SOCs and
IOCS
Contaminant
Acrytemkte
Alachtor
Aldicarb
Aldicarb suIfoxSde
Aldicarb sulfone
Atraaina
Carbofuran
Chlordane
ois-1,2-
Dtehtoroelhylene
Dibromochloropropane
(DBCP)
1,2-Dichloropropan8
o-Oichlorobenzeno
2,4-D
Ethylanedibfomide
(EDB)
Epichtorphydrin
Ethylbenzene
Heptachtor
Hoptachlor epoxide
Lindana
Melhoxychtor
Monochlorobonzone
PCBs (as
dacachlorobiphenyl)
Pontachtorophenol
Styrana*5
Tetrachloroethytene
Toluene
2,4,S-TP2,4,5-TP
Toxaphene
trans-1,2-
Djchtoroethylene
Xylonos (total)
IOC
Asbestos
Barium
Cadmium
Chromium
Mercury
Nitrate (as nitrogen)
Nitrite (as nitrogen)
Selenium
Existing
NPDWRa
(mg/L)
-
-
-
_
_
_
-
-
-
_
_
0.1
-
-
-
-
-
0.004
0.1
-
-
~*
0.01
0.005
*~
-
1.0
0.010
0.05
0.002
10.0
0.01
ซ NPDWR = National Primary Drinking
Proposed
MCLG
(mg/L)
zero
zero
0.01
0.01
0.04
0.003
0.04
zero
0.07
zero
zero
0.6
0.07
zero
zero
0.7
zero
zero
0.0002
0.4
0.1
zero
0.2
zero/O.I
zero
2.0
0.05
zero
0.1
10.0
7F/Ld
5.0
0.005
0.1
0.002
10.0
1.0
0.05
Proposed
MCL
(mg/L)
TTb
0.002
0.01
0.01
0.04
0.003
0.04
0.002
0.07
0.0002
0.005
0.6
0.07
0.00005
TTb
0.7
0.0004
0.0002
0.0002
0.4
0.1
0.005
0.2
0.005/0.1
0.005
2.0
0.05
0.005
0.1
10.0
7F/Ld
5.0
0.005
0.1
0.002
10.0
1.0
0.05
Water Regulations.
bTT ป Treatment Technique.
C CO A r\rt"ปl"W>eซO RjtOf t* r\( f\ 4 msv/t l\f\r*r\r\ tin n n.rm m /*** nA.
-------
automation, also increases as influent consistency
decreases. Other important operating considerations
include:
Energy requirements
Chemical availability and consumption rate
Instrumentation and automation
Preventative maintenance
Noise
Esthetics
Backup/Redundant systems
Startup phase requirements before full removal
capacity is achieved
Cleaning and backwashing requirements
Pretreatment and Posttreatment Processes
All water treatment technologies perform differently
with different pretreatment and posttreatment
processes. The compatibility of all the processes in
the treatment train is key to achieving individual
treatment goals. For instance, a lower pH is desirable
for maximum efficiency of chlorine disinfection;
however, lower pH accelerates corrosion of the water
distribution system. For successful implementation
of a treatment technology, all elements of the train
must interact efficiently and effectively.
Waste Management
Waste management is a concern associated with the
removal of contaminants in drinking water. Most
treatment processes concentrate contaminants,
sometimes hazardous, into residuals that requires
special handling. Such wastes are in the form of
solutions, gases, sludges, and solids. Extensive
regulations cover the management of these wastes,
particularly those classified as hazardous.
Future Service Area Needs
The last major factor in selecting a treatment
technology is the future of the service and supply
areas. Population and economic forecasts of the
service area are the basic tools for evaluating future
demands, Examination and analyses of the
watershed(s) of present and potential water supplies
are important to determine the vulnerability of
supplies to anthropogenic and natural threats.
2.3 Overview of Available Treatment
Alternatives
This section provides an overview of the available
treatment technologies associated with all categories
of treatment objectives. Summary data are presented
for each technology and alternatives are compared on
the basis of:
Performance
Suitability to treatment plant size
Degree of acceptance
Conditions required for effective operation
Operating and maintenance requirements
Compatibility with other treatment processes
Table 2-6 lists the treatment options associated with
each of five categories of treatment objectives:
filtration, disinfection, organic and inorganic
contaminant removal, and corrosion control. The
table indicates four levels of treatment technology
acceptance: experimental, emerging, established,
and BAT. Experimental technologies have shown
promise in some applications, but have not been
extensively tested. Emerging technologies have
proven themselves in the laboratory, but not in the
field. Established treatments are commonly used in
the water industry. BAT is a regulatory designation
that indicates the level of contaminant removal
achievable through specification of a technology or a
technology equivalent, rather than an MCL.
Detailed discussions of all technologies are provided
in Sections 3 through 7, as follows:
ซ Prefiltration and filtration for treatment of
primarily turbidity and color - Chapters 3 and 4.
Disinfection for treatment of pathogenic
organisms, including Giardia cysts, bacteria, and
viruses - Chapter 5.
Organic contaminant removal, including volatile
organic chemicals and other synthetic organic
chemicals - Chapter 6.
ซ Inorganic contaminant removal, including
products of distribution system corrosion and
radioactive contaminants - Chapter 7.
2.3.1 Filtration
The three basic regulatory requirements associated
with filtration systems are control of turbidity, color,
and biological contamination (Giardia cysts, enteric
viruses, and coliform bacteria). Other key consid-
erations in selecting a filtration system include:
Frequency of the cleaning cycle
Chemical requirements
* Operational complexity
Sludge volume and toxicity
Each of these factors is site specific. In addition,
climate will determine whether it is necessary to
house the filter operation, which in some cases is
prohibitively expensive.
In most conventional filtration systems, mixing,
flocculation, and sedimentation processes typically
precede actual filtration. While these pretreatment
elements are always found in conventional filtration
-------
Table 2-6. Overview of Water Treatment Technologies
Treatment Requirements Under the New
Regulations
Technological Options
to Meet Regulatory
Requirements
Stage of Size
Acceptability Suitability
Comments
Filtration of surface water supplies to control
turbidity and microbial contamination
Conventional filtration
Direct filtration
Slow sand filtration
Package plant filtration
Diatomaceous earth
filtration
Membrane filtration
Cartridge filtration
Established All Most common; adaptable for
adding other processes
Established All Lower cost alternative to
conventional filtration
Established Especially Operationally simple; low cost, but
small, but all requires large land areas
sizes
Established Mostly small Compact; variety of process
combinations available
Established Mostly small Limited applicability; potentially
expensive for small systems
Emerging Mostly small Experimental, expensive
Emerging Small Experimental, expensive
Disinfection of all pubfe water supplies
Chlorine
Chlorine dioxide
Monochloramine
Ozone
Ultraviolet radiation
Advanced oxidation
(ozone plus H2Oa and
ozone plus ultraviolet
radiation)
Established All
Established All
Established All
Established All
Established All
Emerging All
Most widely used method;
concerns about health effects of
by-products
Relatively new to the United .
States; concerns about inorganic
by-products
Secondary disinfectant only; some
by-product concerns
Very effective and requires a
secondary disinfectant
Simple, no established harmful by-
products and requires secondary
disinfectant
Not much information concerning
disinfection aspects of this process
Organic contamination control, including 50
specific compounds
Granular activated BAT All
carbon
Packed column aeration BAT All
Powdered activated
carbon
Diffused aeration
Multiple tray aeration
Oxidation
Reverse osmosis
Mechanical aeration
Catenary grid
Higee aeration
Established Large
Established All
Established All
Experimental All
Emerging Small to
medium
Experimental All
Experimental All
Experimental Small
Highly effective; potential waste
disposal issues
Highly effective for volatile
compounds; potential air
emissions issues
Requires conventional treatment
process train for application
Variable removal effectiveness
Variable removal effectiveness
By-products concerns
Variable removal effectiveness;
expensive
Mostly for wastewater treatment;
high energy requirements, easy to
operate
Performance data are scarce;
potential air emissions issues
Compact, high energy
requirements; potential air
emissions issues
(Continued)
-------
Table 2-6. (Continued)
Treatment Requirements Under the New
Regulations
Technological Options
to Meet Regulatory
Requirements
Stage of Size
Acceptability Suitability
Comments
Resins
Ultrafiltration
Experimental Small
Emerging Small
Data scarce
Primarily for turbidity; data for
organics removal are scarce
Inorganic contamination control, including 36
specific inorganic contaminants, and 5
radioactive contaminants
Reverse osmosis
Ion exchange
Activated alumina
Granular activated
carbon
Corrosion controls pH control
Corrosion Inhibitors
Established
Established
Established
Experimental
Established
Established
Small to
medium
Small to
medium
Small
Small
All
All
Highly effective; expensive;
potential waste disposal issues
Highly effective; expensive;
potential waste disposal issues
Highly effective; expensive;
potential waste disposal issues
Experimental for radionuclide
removal; potential waste disposal
issues
Potential to conflict with other-
treatments
Variable effectiveness depending
on type of inhibitor
Source: Derived from tables and text included in Chapters 3 through 7.
systemsj^iey are also sometimes found in
nonconventional systems. In addition to the three
prefiltration steps, additives, such as chemicals for
pH adjustment, coagulants, coagulant aids, and
polymers, are commonly used in conjunction with
filtration. All of these elements affect the
performance of the filter system. These effects are
discussed in detail in Chapter 3.
The seven filtration options reviewed in this
document include:
Conventional filtration
Direct filtration
Slow sand filtration
Package plant filtration
Diatomaceous earth filtration
Membrane filtration (reverse osmosis)
Cartridge filtration
The performance of each filter type depends on the
quality of the influent and proper design and
operation. The range of influent characteristics for
which various filters are effective is provided in
Table 2-7.
Conventional filtration, with rapid mix, flocculation,
and sedimentation, is clearly the most versatile in its
effectiveness in treating variable influents.
Coagulation/filtration systems are more difficult to
operate compared to slow sand or diatomaceous earth
filters because they involve adjusting water
chemistry for proper coagulation. Slow sand,
diatomaceous earth, membrane, and cartridge
filtration units do not have a coagulation step. The
complexity of operating a package filtration plant
varies with the manufacturer and model. Package
plants, slow sand, membrane, and cartridge filtration
are most applicable to small systems.
The removal capacities for Giardia cysts and viruses
of the seven filter systems are presented in Table
2-8.
2.3.2 Disinfection
The recently promulgated SWTR requires water
treatment systems to inactivate 99.9 percent of
Giardia cysts and 99.99 percent of enteric viruses.
Disinfection systems alone, or in conjunction with
filtration systems, can meet these requirements. At
the same time, regulations regarding disinfection by-
products in the finished water must be met.
Currently, total trihalomethanes are the only
disinfection by-products regulated by EPA; however,
new disinfection by-product regulations are
anticipated.
Primary disinfectants are those used for the
inactivation of Giardia cysts, viruses, and bacterial
contaminants, while secondary disinfectants
suppress biological regeneration in the distribution
system. Common primary disinfectants are chlorine,
chlorine dioxide, ozone, and UV radiation. Most are
suitable for both ground water and surface water. An
exception is UV radiation, which is only suitable for
ground water because it is not effective against
-------
Table 2-7, Typical Influent Characteristics and Capacities for Filtration Technologies
Coliform Count Typical Capacity
Filtration Options
Conventional
Direct
Slow sand
Package Plant
Diatomaceous earth
Membrane
Cartridge
Turbidity (NTUs)
No restrictions
<14
<5
Color (in color units)
<75
<40
<10
(per 100 mL)
< 20,000
<500
<800
[depends on processes utilized ]
<5
<1
<2
<5
[fouling index of
NA
<50
<10]
NA
(MOD)
> All sizes
> All sizes
<15
<6
<100
<0.5
<1.0
NA ป not available.
1 MOD - 0.044 rriVsec
Source: See tables and text in Chapters 3 and 4.
Table 2-8. Removal Capacities of Seven Filter Options
(percent removal)
Filtration Options
Conventional
Direct
Stow sand
Package plant
Diatomaceous earth
Membrane
Cartridge
Achievable
Giardia Cyst
Levels
99.9
99.9
99.99
varies with
99.99
100
>99
Achievable Virus
Levels
99.0
99.0
99.9999
manufacturer
> 99.95
Very low
Little data available
Source: See tables and text in Chapters 3 and 4.
Giardia cysts. Secondary disinfectants include
chlorine, chlorine dioxide, and chloramines.
Disinfection effectiveness is measured in terms of the
residual concentration and length of contact time
necessary to achieve the desired inactivations. Four
chemical disinfectants listed in descending order of
their effectiveness are ozone, chlorine dioxide,
chlorine, and chloramines. The effectiveness of a
particular disinfectant is also influenced by water
quality, temperature, and pH. Lower disinfectant
dosages may be used when:
There is filtration or oxidation prior to the
disinfection step.
The water temperature is high.
The dosage of chlorine required for effective
disinfection is reduced as the pH of the water is
reduced. A qualitative summary of the advantages
and disadvantages of the five disinfectants is
provided in Table 2-9.
Some disinfectants are unstable and, therefore, have
to be generated on site. Production considerations for
the five disinfectants are contained in Table 2-10.
The table also provides the number and type of
alternative production methods.
The preferred application point for the various
disinfectants are described in Table 2-11. Table 2-12
compares basic operational considerations, pH,
presence of by-products, operational simplicity, and
maintenance required.
One of the most important considerations in
assessing disinfectants is balancing inactivation or
biocidal effectiveness with by-product production.
The by-products of greatest current concern are
trihalomethanes and other halogenated organic
compounds; chlorine has the greatest potential for
generating harmful by-products. The amount of these
by-products produced by chlorine is affected by:
Chlorine dosage
Types and concentrations of organic material in
the influent
Influent temperature
Influent pH
Contact time for free chlorine
Nature of residual (free chlorine vs. combined
chlorine)
Presence of bromide ion
If chlorine produces an unsatisfactory level of by-
products, then other disinfectants are potential
alternatives. Chlorine dioxide is effective, but the
total levels of chlorine dioxide and its
oxidation/reduction products may limit its
applicability. Ozone and UV radiation are very
effective primary disinfectants, but require the use of
secondary disinfectants. Ozone will produce harmful
halogenated by-products with influent containing
bromide ions. It will also produce harmful oxidation
products in the presence of certain synthetic organics
such as heptachlor. Chlorine dioxide and
monochloramines are effective secondary
disinfectants, but require careful dosage and
application management to avoid producing harmful
by-products in finished water. (Chapter 5 contains a
more complete discussion of disinfection by-products
and strategies for their control.)
10
-------
Table 2-9. Advantages and Disadvantages of Five Disinfectants
Disinfectant
Advantages
Disadvantages
Chlorine
Ozone
Ultraviolet radiation
Chlorine dioxide
Chloramines
Effective. Widely used. Variety of possible application
points. Inexpensive. Appropriate as both primary and
secondary disinfectant.
Very effective. Minimal harmful by-products identified to
date. Enhances slow sand and GAG filters. Provides
oxidation and disinfection in the same step.
Very effective for viruses and bacteria. Readily '
available. No harmful residuals. Simple operation and
maintenance. ,
Effective. Relatively low cost. Generally does not
produce THMS.
Mildly effective for bacteria. Long-lasting residual.
Generally does not produce THMS.
Harmful halogenated by-products. Potential conflict with
corrosion control pH levels, when used as a secondary,
disinfectant
Requires secondary disinfectant. Relatively high cost.
More complex operations because it must be generated
on-site.
Inappropriate for water with Giardia cysts, high
suspended solids, high color, high turbidity, or soluble
organics. Requires a secondary disinfectant.
Some harmful by-products. Low dosages currently
recommended by U.S. EPA may make it ineffective.'
Must be generated on-site.
Some harmful by-products, Toxic effects for kidney
dialysis patients. Only recommended as a secondary
disinfectant. Ineffective against viruses and cysts.
Source: See tables and text in Chapter 5.
Table 2-10. Disinfectant Production Considerations
Chlorine Mono- Ultraviolet
Chlorine Dioxide chloramine Ozone Radiation
Table 2-11. Desired Points of Disinfectant Application3 .
Chemically Yes Yes
stable
On-site No Yes
production
required
Number of NA 3a
alternative
on-site
generation
techniques
Yes No NA
Yes Yes Yes
2*> 3ฐ NA
^Including:
1. Treating sodium chlorite solution with chlorine gas
2. Treating sodium chlorite solution with sodium
hypochlorite and mineral acid
3. Treating sodium chlorite solution with mineral acid
^Including:
1. Adding ammonia to a water and chlorine solution
2. Adding chlorine to a water and ammonia solution
clncluding:
1. Ambient air
2. Pure oxygen
3. Oxygen-enriched air
NA = not applicable.
Source: See text and tables in Chapter 5.
2.3.3 Organic Contaminant Removal
The 1986 Amendments to the SDWA require the
establishment of new MCLs for many organic
contaminants, including disinfection by-products.
The regulations designate BATs as well as MCLs for
organic contaminants. The July 1987 regulations
specify packed column aeration (PCA) and GAG as
the BAT for seven of the eight VOCs. PCA is BAT for
vinyl chloride, the eighth VOC. Water utilities with
these contaminants will have to provide removals at
least equivalent to those achieved by the designated
BATs.
Chlorine
Ozone
Ultraviolet radiation
Chlorine dioxide
Monochtoramines
Towards the end of the water treatment
process to minimize JHM formation and
provide secondary disinfection
Prior to the rapid mixing step in all treat-,
ment processes, except GAG and conven-
tional treatment processes; prior to filtra-
tion for GAG; post-sedimentation for con-
ventional treatment. In addition, sufficient
time for biodegradation of the oxidation
products of the ozonation of organic com-
pounds is recommended priorto
secondary disinfection. '
Towards the end of the water treatment
process to minimize presence of other
contaminants that interfere with this
disinfectant
Prior to filtration; to assure low levels of
CI02, CI02-, and CI03, treat with GAG after
disinfection.
Best applied towards the end of the
process as a secondary disinfectant
a In general, disinfectant dosages will be lessened by placing the
point of application towards the end of the water treatment process
because of the lower levels of contaminants that would interfere
with efficient disinfection. However, water plants with short
detention times in clear wells and with nearby first customers may
be required to move their point of disinfection upstream to attain
the appropriate CT value under the Surface Water Treatment
Rule.
Source: See text and tables in Chapter 5.
The removal capabilities of selected treatment
technologies for several organic contaminants and
contaminant classes are provided in Table 2-13. The
first listed treatment, coagulation/filtration is widely
used primarily for turbidity and microbial
contaminant control, but can be somewhat effective
in removing certain organic compounds. GAG and
PCA are designated as BAT for many of the organic
chemicals and are much more effective. Costs for
either technology vary depending on the contaminant
11
-------
Table 2-12. Disinfectant Application Considerations
Mono-
CIOa chloramine O3
UV
Optimum
water pH
By-products
present
Operational
simplicity
Maintenance
required
7
Yes
Yes
Low
6-9
Yes
No
Low
7-8
Yes
No
Low
6
Yes
No"
High
N/A
No
Yes
High
"Operationally simplified with an automated system.
NA " not applicable.
Source: See text and tables in Chapter 5.
removed and whether waste management is a
potential issue. Powdered activated carbon (PAC),
the fourth treatment listed in the table, is only suited
for application to conventional systems with rapid
mix, flocculation, sedimentation, and filtration
components. PAC also addresses some taste and odor
problems. This form of activated carbon is especially
suitable for seasonal organic contaminant problems
since it can be added as needed. In some instances,
however, such high dosages of PAC are required to
achieve organic removal that waste management
becomes a problem.
All other listed treatments, including the different
aeration configurations, are less established. The
aeration treatments, developed for specific
applications, are generally equal to or less effective
than PCA, but have higher energy requirements. For
some, controlling biological growth in the systems is
a problem. The remaining treatments, besides the
aeration technologies, all tend to be very effective in
removing contaminants, but their application to
specific organics is still experimental. The
efficiencies of all treatments depend on the type and
concentration of the contaminants. While
pretreatment is not always required, it can increase
the effectiveness of some of the treatments. Table 2-
14 illustrates the variation in operating conditions
for these treatments.
2.3.4 Inorganic Contaminant Removal and
Control
Inorganic contaminant treatments are categorized as
prevention strategies or removal technologies.
Corrosion controls prevent or minimize the presence
of corrosion products (inorganic contaminants) at the
point of use. Removal technologies treat source water
that is contaminated with metals or radionuclides.
2.3.4,1 Corrosion Controls
Corrosion controls address the two primary aspects of
corrosion:
Water quality characteristics
Materials subject to corrosion
The two most significant water quality
characteristics that influence corrosion are pH and
carbonate/bicarbonate alkalinity. Components of the
distribution system subject to corrosion include pipes,
valves, meters, plumbing, solder, and flux. The
longer the contact time between the water and
corrodible materials in the distribution system, the
higher the concentration of dissolved metals in the
drinking water.
The four general types of corrosion controls are:
Adjustments to water pH
Addition of corrosion inhibitors to the water to
form protective coatings over the potentially
corrodible metal
Electronic cathodic protection
Applied coatings and linings
The most commonly used corrosion control is pH
adjustment because it is inexpensive and easily
applied. Table 2-15 compares corrosion controls.
Corrosion controls involving pH adjustment may
conflict with ideal pH conditions for disinfection and
control of disinfection by-products. The treatment
methods selected for both treatment objectives should
be carefully coordinated to avoid diminishing the
effectiveness of either process.
2.3.4.2 Inorganic Contaminant Removal
There are 10 treatment processes for addressing the
many inorganic contaminants, including
radionuclides. Most treatment processes are effective
for only a specific set of contaminants under certain
circumstances. Fortunately, all of the inorganic
contaminants do not often occur simultaneously. The
most appropriate applications for each treatment
process are shown in Table 2-16. This table
distinguishes between ground water and surface
water by the generally higher concentrations of
suspended solids in most surface water. Table 2-17
provides removal efficiencies for specific
contaminants with the same treatments. For radon
removal, which is not included in the table, aeration
is highly effective.
The most important factors affecting inorganic
contaminant removal are:
Contaminant type and valence
Influent contaminant concentration
Influent levels of dissolved solids and pH
Desired effluent concentration
12
-------
Table 2-13. Treatment Technology Removal Effectiveness Reported for Organic Contaminants (percent)
Coagulation/
Contaminant Filtration
Acrylamide
Alachlor
Aldicarb
Benzene
Carbofuran
Carbon, tetrachloride
Chlordane
Chlorobenzene
2,4-D
1 ,2-Dichloroethane
1 ,2-Dichloropropane
Dibromochloropropane
Dichlorobenzene
o-Dichlorobenzene
p-Dichlorobenzene
1,1-Dichloroethylene
cis-1 ,2-Dichloroethylene
trans-1 ,2-
Dichloroethylene
Epichlorohydrin
Ethylbenzene
Ethylene dibromide
Heptachlor
Heptachlor epoxide
High molecular weight
hydrocarbons (gasoline,
dyes, amines, humics)
Lindane
Methoxychlor
Monochlorobenzene
Natural organic material
RGBs
Phenol and
chlorophenols
Pentachlorophenol
Styrene
Tetrachloroethylene
Trichloroethylene
Trichloroethane
1,1,1 -Trichloroethane
Toluene
2,4,5-TP
Toxaphene
Vinyl chloride
Xylenes
5
0-49
NA
0-29
54-79
0-29
NA
0-29
0-29
0-29
0-29
0-29
NA
0-29
0-29
0-29
0-29
0-29
NA
0-29
0-29
64
NA
NA
0-29
NA
NA
P
NA
NA
NA
0-29
NA
0-29
NA
0-29
0-29
63
0-29
0-29
0-29
GAG
NA
70-100
NA
70-100
,70-100
70-100
70-100
70-100
70-100
70-100
70-100
70-100
70-100
70-100
70-100
70-100
70-100
70-100
NA
70-100
, 70-100
70-100
NA
. W
70-100
70-100
NA
P
70-100
: W
70-100
NA
70-100
70-100
70-100
70-100
70-100
70-100
70-100
1 70-100
70-100
PGA
0-29
70-100
0-29
70-100
0-29
70-100
0-29
70-100
70-100
70-100
70-100
30-69
NA
70-100
70-100
70-100
70-100
70-100
0-29
70-100
70-100
70-100
NA
NA
0-29
NA
NA
NA
70-100
NA
0
NA
NA
70-100
NA
70-100
70-100
NA
70-100
70-100
70-100
PAC
13
36-100
NA
NA
45-75
0-25
NA
NA
69-100
NA
NA
NA
NA
38-95
NA
NA
NA
NA
NA
33-99
NA ,
53-97
NA
NA
82-97
NA
14-99
P
NA
NA
NA
NA
NA
NA
NA
40-65
0-67
82-99
40-99
NA
60-99
Diffused
Aeration
NA
NA
NA
NA
11-20
NA
NA
NA
NA
42-77
12-79
NA
NA
14-72
NA
97
32-85
37-96
NA
24-89
NA
NA .
NA
NA
NA
NA
14-85
NA
NA
NA
NA
NA
73-95
53-95
NA
58-90
22-89
NA
NA
NA
18-89
Oxidation3
NA
70-100
NA
70-100
70-100
0-29
NA
30-69
W
0-29
0-29
0-29
NA
30-88-
30-69
70-100
:70-100
70-100
0-29
70-100
,0-29
70-100
26
NA
0-100
NA
86-98
' W
NA
W
70-100
70-100
W
30-69
NA
0-29
70-100
30-69
NA
70-100
70-100
Reverse
Osmosis
0-97
70-100
94-99
0-29 '
70-100
70-100
NA
70-100
0-65
15-70
10-100
NA
NA
30-69
0-10
NA
0-30
0-30
NA
0-30 .
37-100
NA
NA
NA
50-75
>90
50-100
P
,95 '
NA
NA
NA
70-90
0-100
NA
15-100
NA
NA
NA
NA
10-85
W = well removed.
P = poorly removed.
NA = not available.
aThe specifics of the oxidation processes effective in removing each contaminant are provided in Chapter 6.
Note: Little or no specific performance data were available for: . ,
1. Multiple Tray Aeration
2. Catenary Aeration
3. Higee Aeration
4. Resins
5. Ultrafiltration
6. Mechanical Aeration
Source: See text and tables in Chapter 6.
13
-------
Table 2-14. Operational Conditions for Organic
Treatments
Level of
Operational Skill
Technology Required
Coagulation/
Filtration
GAC
PCA
PAC
Diffused
aeration
Multiple tray
aeration
Oxidation
Reverse
osmosis
Mechanical
aeration
Catenary grid
Higee
aeration
Rosins
Ulirafiltralion
High
Medium
Low
Low
Low
Low
High
High
Low
Low
Low
Medium
Medium
Level of
Maintenance
Required
High
Low
Low
Medium
Low
Low
High
High
Low
Low
Medium
Medium
High
Energy
Require-
ments
Low
Low
Varies
Low
Varies
Low
Varies
High
Low
High
High
Low
Medium
Source: See text and tables in Chapter 6.
Table 2-15. Corrosion Control
Corrosion Controls
Water Treatment
pH adjustment
Inorganic
phosphates
Silicates
Cathodic
Protection
Coatings and
Unings
Amount of
System
Covered by
the Control
Total
Total
Total
Partial
Partial
Considerations
Completely
Agreeable
with
Consumers
Yes
Usually
Yes
Yes
Yes
Optimum
Level of
Additive in
the Water
>8.0pH
Varies
2-12 mg/L
NA
NA
Table 2-16. Most Probable Treatment Application for
Inorganic Treatments
Most Probable Application
NA ซ not applicable.
Source: See tables and text in Chapter 7.
The first three factors are site specific. Table 2-18
summarizes the advantages and disadvantages of
each of the treatment mechanisms.
2.4 Final Process Selection and Design
When modifying an existing or designing a new
treatment system, consideration must be given to all
the regulations impacting the system. For surface
water, regulations regarding microbiological,
disinfection by-product, and lead contaminants are
most likely to impact the treatment system. For
ground-water systems, regulations regarding organic
Treatment
Conventional with
coagulation
Lime softening
Ion exchange: cation
an ion
Reverse osmosis
Powdered activated
carbon
Granular activated
carbon
Activated alumina
Source Water
Surface
Surface (hard)
Ground water
Ground water
Ground water
Ground water
Surface water
Surface water
Ground water
Ground water
Contaminants
Ag, As, Cd, Cr, or
Pb
As V, Cd, Cr III, F,
orPb
Ba or Ra
Ba or Ra
NO3, Se
All
Organic Hg from
spills
Organic Hg
Organic Hg
As, F, or Se
Source: See tables and text in Chapter 7.
chemicals (particularly VOCs), radon, lead, and
disinfection will have the most impact.
Balancing the processes selected for microbiological
control, disinfection by-product removal, and lead
control will be important for both surface and
ground-water treatment. One water quality
parameter that affects all three processes is pH. A
low pH is desirable for disinfection, disinfection by-
product removal, and minimizing by-product
formation in the distribution system. However,
minimizing lead corrosion in the distribution system
requires a higher pH. One option to meet all
conditions involves use of a corrosion inhibitor, thus
permitting a lower pH in the finished water for
disinfection and by-product control.
For ground-water supplies, process selection should
consider treatments capable of controlling a number
of contaminants. For example, PCA can remove both
VOCs and radon. It also removes carbon dioxide from
the water, which raises the pH to levels desirable for
lead corrosion control. As another example, oxidation
techniques, such as ozone, may oxidize organic
chemicals as well as provide disinfection. Also,
reverse osmosis might be considered when both
organic and inorganic chemical contaminants are
present in the raw water. Use of one treatment
technique to meet multiple regulatory requirements
will help reduce operating complexity and costs.
Evaluation of potential treatment technologies
proceeds from literature searches to bench-scale or
field tests. Sludge volume and composition are also
important considerations in the final design
selection. Construction costs for the final alternatives
are used to select the appropriate option before
developing the final design.
14
-------
Table 2-17. Removal Effectiveness for Nine Processes by Inorganic Contaminant
"c
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Table 2-17. R
Treatment
2 i i x . x xxii i
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X X X XI X2'l-"-i
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X 2 I XX X2-J2 5
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2 I I 22IIXI I
1 1 1 1 1 -I 1 1 1 1
X X 2 IX I 1 1 _i 1
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|g -5.1 "5 1 S| ffl ง 'S S"ง ^> 5>
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X 2 _i =' CO
15
-------
Tabla 2-18. Advantages and Disadvantages of Inorganic
Contaminant Removal Processes
Precipitation and Coprecipitation Used in Coagulation/Filtration
Advantages
Low cost for high volume
Often improved by high ionic strength
Reliable process well suited to automatic control
D sadvantages
Stotehiometrte chemical additions required
High-water-content sludge must be disposed of
Parts-per-billion effluent contaminant levels may require two-
stage precipitation
Not readily applied to small, intermittent flows
Coprecipitation efficiency depends on initial contaminant
concentration and surface area of primary floe
ton Exchange
Advantages
Operates on demand
Relatively insensitive to flow variations
Essentially zero level of effluent contamination possible
Large variety of specific resins available
Beneficial selectivity reversal commonly occurs upon
regeneration
Disadvantages
Potential for chromatographic effluent peaking
Spent regenerant must be disposed of
Variable effluent quality with respect to background ions
Usually not feasible at high levels of total dissolved solids
Activated Alumina
Advantages
Operates on demand
Insensitive to flow and total dissolved solids background
Low effluent contaminant level possible
Highly selective for fluoride and arsenic
Disadvantages
Both acid and base are required for regeneration
Media tend to dissolve, producing fine particles
* Slow adsorption kinetics
Spent regenerant must be disposed of
Membranes (Reverse Osmosis and Electrodialysis)
Advantages
All contaminant ions and most dissolved non-ions are
removed
Relatively insensitive to flow and total dissolved solids
level
Low effluent concentration possible
In reverse osmosis, bacteria and particles are removed
as well
Disadvantages
High capital and operating costs
High level of pretreatment required
Membranes are prone to fouling
Reject stream is 20-90% of feed flow
Source: Clifford (1986).
The chapters that follow elaborate on each group of
treatment techniques. Filtration technologies are
discussed in Chapters 3 and 4, disinfection in
Chapter 5, organic contaminant treatments in
Chapter 6, and technologies that control corrosion
and remove inorganic compounds and radionuclides
in Chapter 7.
16
-------
Chapter 3
Prefiltration Treatment Elements
Conventional treatment is the most widely used train
of processes to control microbial and turbidity levels
in surface supplied drinking water. The precise order
and composition of conventional treatment elements
are not invariably the same, but commonly include
chemical feed, rapid mix, flocculation, sedimentation,
filtration, and disinfection.
The performance of a filtration technology is greatly
impacted by the processes that precede it.
Prefiltration elements, including chemical feed,
rapid mix, flocculation, and sedimentation may need
upgrading to improve overall system performance or
accommodate system expansions. This chapter
presents typical problems and recommended
solutions associated with prefiltration processes.
It is often necessary to modify existing conventional
treatment plants due to changes in population,
financial constraints, raw water quality, and
regulatory atmosphere. These changes may upgrade
the present system to:
Improve the water quality
Increase plant capacity
Improve reliability
Reduce maintenance
Reduce costs
Upgrading conventional treatment plants can effect
significant improvements. For example, upgrading
can increase the capacity of most soundly constructed
plants by 100 to 200 percent, provided traditional
design parameters were used in the original plant
installation.
Any of the five basic components of conventional
treatment can be upgraded, alone or in combination.
A deficiency, or a set of deficiencies, in one or more
components of conventional treatment will typically
prompt an evaluation of the potential for upgrading.
Table 3-1 summarizes the causes of potential
Table 3-1. Summary of Conventional Treatment Operating
Issues
Treatment
Element
Potential Causes of Problems
Chemical feed -Choice of chemical(s)
-Choice of chemical dose and pH
-Control of chemical addition; performance
of chemical pumping equipment
-Maintenance of chemical feed lines
-Flexibility in feed system to allow for
changing the point of addition, adding
chemicals at more than one point, etc.
-Sequence of adding different chemicals
-Degree of dilution of chemicals before injection
Rapid mix -Type of rapid mix; in-line versus mechanical mix
-Number of rapid mixers
-Method of chemical addition
-Mixing speed/detention time
Flocculation -Optimum detention time
-Optimum mixing intensity
-Number of stages
r-Adequate baffling to approximate plug flow
conditions
Sedimentation -Surface loading rates
-Short circuiting due to wind, temperature,
density differences, inlet and outlet design
-Amount and rate of accumulation of sludge
-Sludge removal
Filtration -Filter rate and rate control
-Hydraulics
-Chemical pretreatment of water reaching the
filter
-Inadequate backwashing
deficiencies for each treatment element. Techniques
for upgrading fall into five basic categories, according
to treatment element:
ซ Modifying chemical treatment or dosage
Modifying or adding rapid coagulant mixing
Improving flocculation
Improving sedimentation
Modifying filtration processes
17
-------
The remainder of this chapter discusses the first four
categories of modification. The last category,
modifying filtration processes, is discussed in
Chapter 4.
3.1 Modifying Chemical Feed
Proper chemical feed is critical to optimal
performance of flocculation, sedimentation,
filtration, and disinfection systems. The three basic
aspects of chemical feed systems are chemical type,
dosage management, and method of chemical
application. This chapter addresses these topics and
the costs associated with modifying chemical feed
systems.
3.1.1 Chemical Type
The three types of chemicals usually applied to the
raw water at the beginning of the conventional
treatment train are coagulants, coagulant aids, and
pH control substances. Some polymer coagulants are
used to coat filters during backwash cycles to
increase their effectiveness. However, this
application is discussed in the chapter on filtration.
Coagulants
Coagulants are chemicals used to remove turbidity
and organic substances from raw water by
precipitation. Coagulation also removes bacteria,
algae, color, iron oxide, magnesium oxide, calcium
carbonate, and clay. Coagulation's effectiveness in
removing humic acids is important because humic
acids combine with chlorine to form trihalomethanes.
Coagulants act by overcoming the charges of
suspended particles thus allowing larger particle
groupings to form. They are introduced during the
initial stage of water treatment just before the rapid
mixing step. Coagulants are effective by themselves
and in conjunction with coagulant aids and pH
modifiers. The two most common coagulant types are
metallic salts and polymers; the most common
metallic salt coagulants are aluminum sulfate (alum)
and ferric chloride.
The selection of a particular coagulant depends on
frho roflllirorl loxrol rv^offio/ปfivonocc A oton^arH iar foef
Table 3-2. Chemical Costs for Conventional Treatment
/&4 QOC\
($1300)
Chemical
Alum (dry)
Alum (liquid)
Lime (quick)
Lim6 (hydrated)
Ferric chloride
Ferrous sulfate
Ferric sulfate
Soda ash
Sodium hydroxide
Chlorine
Sodium hypochlorite
Liquid carbon dioxide
Sodium
hexametaphosphate
Zinc orthophosphate
Ammonia, aqua
Ammonia, anhydrous
Sulfuric acid
Hydrochloric acid
Activated carbon
powdered
Activated carbon
granular
Activated alumina
Potassium
permanganate
Sodium bisulfate
(anhydrous)
Sodium silicate
Sodium chloride
Polyelectrolyte
Diatomaceous earth
Magnesium
Sodium chlorite
Sodium hydroxide
76%
Sodium bicarbonate
Calcium hypochlorite
Small (<1 MOD)
Systems, $/ton
$ 500
300
100
150
cnn
OOO
277
200
250
595
500
190
350
1,160
1,520
230
410
140
171
950
1,900
1,694
2,800
909
400
105
1,500
680
650
3,200
590
490
2,700
Large ( > 1 MGD)
Systems, $/ton
$ 250
125
75
100
275
250
155
200
316
300
150
100
1,100
1,000
200 .
350
100
166
800
1,600
1,156
2,500
673
200
85
1,000
310
582
2,800
316
380
1,540
Is the recommended method to determine the relative
effectiveness of various coagulants for a particular
raw water supply. Jar test procedures are described
later in this chapter. If different coagulants are
equally effective, then the factors that should be
considered are cost; availability; overall safety; and
ease of storage, handling, and application. Metallic
salts, for example, are much less expensive than
polymers, as shown in Table 3-2, which lists a variety
of chemical costs.
Alum is the most widely used coagulant because of its
availability, low cost, ease of use, and ease of storage.
1 MGD = 0.044 m3/sec
Ferric chloride, other metallic salts, and polymers
are less widely used. Alum's performance, however,
is greatly affected by the pH of the influent. The
recommended dosage of alum ranges from 5 to 150
mg/L, but the problem of sludge disposal increases
with higher alum dosages.
Due to health concerns about aluminum, some water
utilities are considering switching to ferric chloride.
Although ferric chloride is not always as effective as
18
-------
alum in reducing trihalomethane formation potential
(THMFP) and total organic carbon (TOO, it is more
effective than alum for water with high dissolved
color, low turbidity, and a moderate pH.
Polymers are effective coagulants, coagulant aids,
and filter aids. They consist of chains of monomers
and are classified according to their charge or lack of
charge. A polymer with a charge is an ionized
polymer, or a polyelectrolyte. If a polymer has a
positive charge, it is cationic; if it has a negative
charge, it is anionic; and if it has no charge, it is non-
ionic.
Cationic polymers are effective for coagulating
negatively charged clay particles, while anionic
polymers are not very effective for this purpose.
Anionic polymers are generally more effective for
removing certain positively charged colloids and
when used in conjunction with alum or other metallic
coagulants. Nonionic polymers are effective filter
aids. Polymers are not effective for coagulating some
organic colors. Polymer selection requires frequent
use of the standard jar test to adjust and compensate
for seasonal changes in the influent characteristics.
In applications where polymers are effective, dosages
are generally lower than alum dosages for the same
effect. Typical polymer dosages range from 1.5 to 10
mg/L. Consequently, polymer coagulants produce
less residual sludge than alum. To avoid large sludge
volumes, there is a trend towards replacing alum
with either cationic polymers, cationic polymers plus
alum, or sodium aluminate. The use of cationic
polymers instead of alum is most applicable to raw
water with turbidity of less than 5 NTU and where
direct filtration is feasible.
Coagulant Aids
Coagulant aids are added to the influent after or
simultaneously with the primary coagulant to
improve particle capture during flocculation, poor
flocculation basin performance.clarification,
efficiency, and retention in filters of the coagulated
particles that agglomerate (floe). Coagulant aids,
through formation of faster settling floe, will improve
the sedimentation process and reduce turbidity
loadings on filters, thus potentially extending filter
operating cycles. Nonionic and anionic polymers are
used as coagulant aids. Nonionic polymers
strengthen floe.
Coagulant aid dosages are stated in terms of their
ratio to the amount of alum added to the influent.
Dosages are determined by raw water characteristics
and operational factors. The ratio of alum to polymer
dosages ranges from 100:1 to 50:1. Again, standard
jar tests are required to determine precise coagulant
aid dosage.
pH and Alkalinity Controls
The optimum pH range makes metallic coagulants
insoluble and improves the strength of the fioc, and
stronger floe enhances turbidity removal through
sedimentation and filtration. The water must contain
sufficient alkalinity for aluminum or iron floe
formation. When pH is too low, adding soda ash, lime,
sodium hydroxide, or sodium bicarbonate will
increase the water's pH and alkalinity. Without
sufficient alkalinity, the coagulation process will not
proceed to completion. Very low pH levels will also
lead to high aluminum ion residual in the finished
water, which is undesirable.
When the pH level is too high due to factors such as
algae and aquatic plant activity, adding acid is
necessary. Typical acids used for this application are
sulfuric acid and hydrochloric acid.
3.1.2 Chemical Dosage Management
Coagulant dosage management is a universal
problem that is critical for achieving low turbidities
in any plant, both well equipped and poorly equipped.
Too little coagulant will result in excessive turbidity;
too much coagulant could also result in excessive
turbidity and wasted coagulant. Coagulant aid and
pH control dosages are determined using jar test
procedures.
While coagulant type is largely determined by
influent characteristics, coagulant dosage is chiefly
determined by effluent testing. The tests are
performed either in a batch reactor or on a continuous
basis. Batch tests provide indications of proper
coagulant dosage selection at a single point in the
influent stream, but continuous tests are preferable
because they can be used to constantly monitor the
coagulation process and adjust operations. The three
basic tests are the jar test, particle charge
observation technique, and pilot filters. Turbidity
monitoring provides an indication of coagulation
effectiveness.
Jar Tests
The most common technique, the standard jar test,
involves laboratory tests of samples, the results of
which are extrapolated to full-scale operations.
Different coagulant dosages are applied to influent
samples, with each dosage level in a different jar. For
prescribed periods of time, the resultant turbidity
levels are observed to derive the optimal dosage.
Jar tests are simple, but certain aspects require
attention. Because jar tests are not very accurate for
low turbidity water, coagulant dosages for influent
turbidities less than 5 NTU are difficult to ascertain
with only jar test results based on settled water
turbidity. In such cases, it may be appropriate to
19
-------
filter settled water through filter paper before
measuring turbidity. Careful attention is necessary
to ensure that the jar test water temperature is the
same as that of the plant influent. In addition, jar
tests are inappropriate for establishing expected
performance of direct filtration plants because the
sedimentation process simulated in the jar test is not
part of a direct filtration system.
Zeta Potential Observation Procedures
The zeta potential observation technique is a batch
test method that measures particle charge with
electrodes. However, it can be adapted to a
continuous test method using a streaming current
detector (SCD), which provides a continuous
indication of particle charge.
The particle charge test relates electrode output to
the zeta potential, a measure of the electrical
potential between the water and the counter ions
surrounding the colloid particles. Colloids are
usually negatively charged and resist coagulation.
Different colloids require different coagulants to
adjust this zeta potential and thus enhance their
removal from the water stream. Zeta potential after ,
coagulation ranges from +5 to -10 mini volts (mv).
Organic colloids require near 0 zeta potentials for
coagulation, while clay colloids require negative zeta
potentials. Particle charge observation tests are
calibrated with jar tests or filtrate monitoring.
The results of an SCD, which continuously measures
indicators of zeta potential, can be used to continually
control the chemical feed pumps. Streaming current
detectors provide information on coagulant dose more
rapidly than jar tests.1 Therefore, they enable oper-
ators to optimize chemical doses and cut chemical
costs, especially in systems with variable influent
quality. Use of an SCD improves plant operations,
but is not a substitute for an effective operator.
Figure 3-1 is a schematic diagram of an SCD.
The matching of the zeta potential with specific plant
output must be carefully observed because, while
there is a high correlation between zeta potential and
finished water quality, there is no causal
relationship. The lack of careful scrutiny of the
relationship between particle charge observation test
results and plant effluent will lead to false
conclusions about the finished water's clarity. Bench-
scale particle charge tests are best suited for water
with small annual variations in quality and are also
useful in research. They are not practical for plant
operations, because they require a high level of skill
and patience to perform and interpret the results.,
Synchronous
Motor
I I] Loose Fitting Piston"*6fv
' ^Insulating Plastic
Cutaway of Cell Body and
Pump Bore of Insulating Plastic
Synchronous
Rectifier
1 For a thorough discussion of SCDs, see Steven K. Dertel and
Christine M. KIngery; November 1988; "An Evaluation of
Streaming Current Detectors," American Water Works Association;
Denver, Colorado.
Figure 3-1. Simplified diagram of streaming current
detector.
Pilot Filters
Pilot filters measure the water quality on a
continuous basis. They provide an accurate and
direct measure of the expected plant effluent
turbidity, avoiding the intermediate step of
extrapolating lab tests to predict plant-scale
performance. Pilot filters determine the adequacy of
the coagulant dosage and are used with manual or
automated coagulant adjustment mechanisms. Their
accuracy in monitoring effluent turbidity can achieve
significant cost savings through improved efficiency
of coagulant usage. Pilot filters have the advantage of
providing indications of floe strength and filter
headless rate. This information is useful for filter
management and minimizing backwash water.
In general, pilot filters are used to determine whether
an applied coagulant dosage is adequate to produce
acceptable quality water from the plant filters. A
small sample of water, taken immediately after the
addition of coagulants, is processed through a small
(usually an 11.43-cm [4.5-in] inside diameter
plexiglass column) pilot filter. The turbidity of the
pilot filter is monitored continuously, and the
information provides advance warning of improper
coagulant dosages, which may lead to excessively
high turbidity levels from the plant filter. Improper
coagulant dosages can be detected with pilot filters
within 10 to 15 minutes of coagulant application.
Floe breakthrough in the pilot filter can contribute to
effluent turbidities and interfere with accurate
coagulant dosage determination. To prevent floe
20
-------
breakthrough, excessive doses of polymer filter aids
are applied to pilot filter influent.
Automated coagulant control systems can be used
with the pilot filter systems. Some units are equipped
with plant flow pace meters to account for flow
variation. Override controls can also be placed
throughout the system.
Turbidity Monitoring
Turbidity is a measure of suspended particles.
Monitoring filtered water turbidity is important
because it reflects the effectiveness of the coagulation
process. In addition, turbidity monitoring is:
Required of all surface water systems by the
recently passed Surface Water Treatment Rule
Related to probable level of potentially
pathogenic organisms in the finished water
Reflective of the overall treatment effectiveness
A primary aesthetic indicator of the finished
water quality
The current availability of inexpensive and accurate
turbidimeters makes monitoring the turbidity of
finished water very cost effective. Continuous
monitoring of each filter unit is especially useful for
optimizing the quality of effluent blended from
different filters.
Particle counting is another method of measuring
turbidity that provides a profile description of the
particle sizes. Particles as small as 1 micron can be
measured by this method, but since many particles
are less than a micron in size, the method is of limited
applicability. However, particle counting is very
useful for pilot plants and research applications,
especially for asbestiform fiber detection.
3.1.3 Chemical Application Methods and
Considerations
The following discussion covers the equipment and
methods used to apply treatment chemicals,
including operation and maintenance considerations.
The following four chemical feed systems are
reviewed: liquid alum, polymer, sodium hydroxide,
and sulfuric acid.
Chemical feed system options change as plants
increase in size. Plants with a capacity of 0.12 m3/sec
(2.5 MOD) or greater generally are able to justify
bulk purchases and storage of chemical stock and
install the requisite storage and handling equipment.
Special storage facilities for chemicals are also
usually needed for larger plants. For example, liquid
alum is available from 15,140-L (4,000-gal) tank
trucks for larger plants, while smaller plants often
use dry bagged chemicals that are mixed with water
to produce desired treatment-strength solutions.
The point of application of any chemical will have a
great impact on its effectiveness. Chemicals are
added at seven basic points in the water treatment
process:
To raw water before rapid mixing
During rapid mixing
Before flocculation
Before sedimentation
Before filtration
After filtration
Prior to filter backwash
The optimal application point depends on site-specific
factors. The best situation is to have the capability to
add chemicals at several points, so that the plant
operator can perform tests to determine the ideal
application point.
Most chemical feed systems commonly include
several basic elements such as mixing tanks, mixers,
and metering p,umps. In the chemical feed process,
operators manually add chemicals either wet or dry,
in specific concentrations to the mixing tank. A
metering pump ensures accurate feeding of known
concentrations of coagulants, polymers, coagulant
aids, or pH adjustment chemicals into the water
stream.
Liquid Alum Feed
Specialized liquid alum feed systems become
appropriate for plants larger than about 0.12 m3/sec
(2.5 MOD). Design elements for these facilities
include:
Storage facilities for a 15-day supply
(recommended)
Fiberglass reinforced or polyethylene tanks
Indoor uncovered tanks for smaller systems
Outdoor, covered, and heated tanks for larger
systems, because crystallization occurs at under
10ฐC (50ฐF)
Polymer Feed
In plants of less than about 0.12 m3/sec (2.5 MGD),
polymer application can be performed using a basic
chemical feed system. In small plants, a polymer feed
may include two tanks of equal size, a mixer, and a
metering pump. One tank is used for mixing and one
for storage of the polymer feed solution. The polymer
mixing tank is elevated above the storage tank to
permit gravity feed of the polymer solution.
Optionally, a single tank suitable for water
treatment operations can be interrupted to prepare
the polymer solutions. A preparation of 0.25 percent
21
-------
stock polymer solution is generally used for all plant
sizes.
Plants greater than 0.12 m3/sec (2.5 MGD) generally
require two tanks of equal size and a mixer, but, in
addition, require a dry chemical storage hopper and a
dry chemical feeder.
Sodium Hydroxide Feed
Plants less than about 0.12 m3/sec (2.5 MGD) are able
to use basic chemical feed systems to apply sodium
hydroxide solution prepared from up to 90.72 kg (200
lb)/day of dry sodium hydroxide. These plants
require:
Piping and valves to convey water for mixing
98.9 percent pure dry sodium hydroxide
A volumetric feeder for mixing
Two mixing tanks because of the slow mixing
rate necessary to accommodate the high heat of
the process
Application of the sodium hydroxide in a 10
percent solution
A dual headed metered pump to deliver the
sodium hydroxide solution to the point of
application
Plants greater than 0.12 m3/sec (2.5 MGD) are
designed to use liquid sodium hydroxide, which
requires equipment over and above the basic feed
system. Plants using liquid sodium hydroxide feed a
premixed 50 percent solution containing 6.38 pounds
of sodium hydroxide per gallon. To store a 15-day
supply of this stock solution, plants need fiberglass
reinforced or steel tanks. The sodium hydroxide must
be kept indoors or stored in heated tanks to avoid
crystallization of the solution that occurs at or below
12.2ฐC (54ฐF).
Sulfuric Add Feed
Sulfuric acid feed systems are designed to directly
apply a 93 percent solution to the water through a
metering system that includes standby metering
pumps.
Most plants will purchase acid in bulk, which must
be stored in fiberglass reinforced tanks. Only very
small plants will use sulfuric acid delivered in drums
that will require indoor storage facilities. All plants
should have storage capacity for a 15-day supply.
Capital and operating and maintenance costs for
alum, polymer, sodium hydroxide, and sulfuric acid
feed systems are presented in Tables 3-3 through 3-6.
3.2 Modifying or Adding Rapid
Coagulant Mixing
Rapid mixing is generally the first stage of the
treatment process. This step is essential for quick and
complete dispersion and mixing of the coagulant; the
absence of complete mixing could result in excessive
effluent turbidity. While some plants only have one
rapid mixer to add coagulants, other plants have
multiple rapid mixers to achieve optimum
performance.
Increasing the plant flow rates often necessitates
improvements to existing rapid mixing facilities to
ensure complete and thorough mixing of coagulants
with incoming water. Effective rapid mixing also can
reduce coagulant dosage requirements.
Improvements to rapid mixing involve adjusting both
the means of mixing the coagulant with the influent
and the coagulant's point of application. Refinements
to the rapid mixing process usually result in
significant improvements to the finished water. The
savings in coagulant usage justify the low capital cost
of the improvements.
Rapid mixer effectiveness is usually gauged by
contact time and the velocity gradient imparted to
the water stream. Contact time refers to the
detention time of the water in the rapid mixer. The
velocity gradient is the difference in water speeds in
the rapid mixing chamber (where water with the
highest speed is in proximity to the mixing device
and the slowest water is near the chamber wall).
Velocity gradient is related to the amount of energy
imparted to the water during mixing.
Complete coagulant dispersion is accomplished in
very little time and with a wide range of velocity
gradients. The reaction times for coagulation range
from microseconds up to 30 seconds, and the velocity
gradients of various mixers range from 700 to 5,000
sec-1. Table 3-7 presents contact times and velocity
gradients for four types of rapid mixers.
The contact time required for successful coagulation
depends on which of the two primary coagulation
processes - adsorption or sweep-floe (enmeshment) - is
necessary for the particular raw. Adsorption takes
place very quickly; sweep-floe coagulation takes
longer. In adsorption, if polymers are not formed
during the application process, then coagulation can
occur in microseconds. If polymers are formed,
coagulation will still take less than a second. Sweep
floe, a process that is triggered by large doses of alum,
ferric chloride, and other precipitative coagulants,
takes from 1 to 7 seconds to complete.
The types of devices used for rapid mixing include
mechanical mixers, static mixers, jet injection
mixers, and coagulant diffusers. Table 3-8 presents
22
-------
Table 3-3. Estimated Costs for Supplementing Surface Water Treatment by Adding Alum Feed facilities (10
mg/i) ($1978)
Category
1
2
3
4
5
6
7
a
9
10
11
12
Plant Capacity,
MOD
0.026
0.068
0.166
0.50
2.50
5.85
11.59
22.86
39.68
109.90
404
1,275
Average Flow,
MOD
0.013
0.45
0.13
0.40
1.30
3.25
6.75
11.50
20.00
55.50
205
650
Capital Cost,
$1,000
12.2
15.9
20.3
28.0
40.7
47.1
58.1
70.4
81.6
128
250
575
Operation and Maintenance Costs
$1,000/yr
2.3
2.6
5.4
7.7
4.1
7.9
14.9
24.4
41.3
112
402
1,245
0/1 ,000 gal
47.8
16.0
11.5
5.3
0.9
0.7
0.6
0.6
0.6
0.55
0.54
0.52
Total Cost,
0/1 ,000 gal
87.1
26.2
16.5
7.5
1.9
1.1
0.9
0.8
0.7
0.63
0.58
0.55
Source: U.S. EPA (1979).
Table 3-4. Estimated Costs for Supplementing Surface Water Treatment by Adding Polymer Feed Facilities
(0.3 mg/l) ($1978)
Category
1
2
3
4
5
6
7
8
9
10
11
12
Plant Capacity,
MOD
0.026
0.068
0.166
0.50
2.50
5.85
11.59
22.86
39.68
109.90
404
1,275
Average Flow,
MOD
0.013
0.045
0.13
0.40
1.30
3.25
6.75
1 1 .50
20.00
55.50
205
650
Capital Cost,
$1,000
2.8
3.3
3.8
4.6
66.1
66.7
68.8
72.7
78.6
107.2
159.9
227.3
Operation and
$1,000/yra
1.3
1.4
3.5
3.7
5.8
6.8
8.4
10.7
14.6
31.1
100 '
299
Maintenance Costs
0/1,000 gal
28.3
8.6
7.3
2.5
1.2
0.6
0.3
0.2
0.2
0.2
>' 0.1
0.1
Total Cost,
0/1 ,000 gal
35.3
11.0
8.2
2.9
2.9
1.2
0.7
0.5
0.3
0.2
0.2
0.1
^Polymer cost for Categories 1 through 4 is 750/lb, and for Categories 5 through 12 it is $1,000/ton
Source: U.S. EPA (1979).
Table 3-5. Estimated Costs for Supplementing Surface Water Treatment by Adding Sodium Hydroxide
Facilities ($1978)
Operation and Maintenance Costs Total Cost,
Category
1
2
3
4
5
6
7
8
9
10
11
12
MGD
0.026
0.068
0.166
0.50
2.50
5.85
11.59
22.86
39.68
109.90
404
1 ,275
MGD
0.013
0.045
0.13
0.40
1.30
3.25
6.75
11.50
20.00
55.50
205
650
$1,000
2.4
2.7
3.3
5.4
33.3
36.9
43.0
56.3
76.4
159
353
697
$1,000/yra
1.2
1.4
3.3
6.2
8.8
18.4
35.8
59.4
101
275
1,015
3,210
0/1 ,000 gal
24.3
8.8
7.6
4.2
1.8
1.6
1.4
1.4
1.4
1.4
1.4
1.4
0/1,000 gal
30.2
10.7
8.4 '
4.7
2.7
1.9
1.6
1.6
1.5
1.4
1.4
1.4
a Costs include storage and feed facilities to add NaOH at a concentration of 10 mg/L. Dry sodium hydroxide is used for
Categories 1 through 4, while a liquid solution is used for bulk delivery for Categories 5 through 12.
Source: U.S. EPA (1979).
23
-------
Table 3-6. Estimated Costs for Supplementing Surface Water Treatment by Adding Sulfuric Acid Feed
Facilities ($1978)
Category
1
2
3
4
5
6
7
8
g
10
11
12
Plant Capacity,
MGD
0.026
0.068
0.166
0.50
2.50
5.85
11.59
22.86
39.68
109.90
404
1,275
Average Flow,
MGD
0.013
0.045
0.13
0.40
1.30
3.25
6.75
11.50
20.00
55.50
205
650
Capital Cost,
$1,000
2.8
3.2
4.0
5.7
21.6
25.6
29.7
37.9
49.9
86.9
210.3
431.0
Operation and Maintenance Costs
$1 ,000/yra
0.9
1.3
3.2
5.6
2.4
3.6
5.8
8.8
14.1
36.3
128.3
404.7
0/1 ,000 gal
20.0
7.6
6.7
3.9
0.5
0.3
0.2
0.2
0.2
0.2
0.2
0.2
Total Cost,
0/1 ,000 gal
27.0
9.9
7.6
4.3
1.0
0.6
0.4
0.3
0.3
0.2
0.2
0.2
ซ Costs include storage (15 days), feed, and metering facilities for delivering concentrated acid directly from storage to
application point. Categories 1 through 6 include delivery in drums, stored indoors. Categories 7 through 12 include
delivery and outdoor storage in FRP tanks. Application rate is 2.5 mg/L.
Source: U.S. EPA (1979).
> bulk
Table 3-7. Typical Rapid Mixer Contact Times and
Velocity Gradients
Mixer Type
Mechanical mixers
In-line mechanical
and static blenders
In-line jet irpclors
Hydraulic mixers
Typical Contact
Time Range
(in seconds)
10-30
0.5
0.5
2
Typical Velocity
Gradients
(in sec-1)
700-1,000
3,000-5,000
1 ,000-2,000
800
Source: Williams and Culp (1986).
the estimated capital and operating costs associated
with adding rapid mixing.
Mechanical Mixers
The most common mixing devices are mechanical
mixing tanks, also termed completely mixed or back-
mixed units. They use turbines or impellers to mix
coagulant with water. The three advantages of
mechanical mixers are that they (1) are effective, (2)
impart little headloss (headloss being loss of pressure
or the reduction of the water velocity within the
plant), and (3) are unaffected by the volume of water
and flow variations.
A variable speed drive can alter mixer speeds to
achieve different velocity gradients. Lower velocity
gradients are used following the application of
polyelectrolyte coagulant aids. Labor is required for
daily jar testing operations and routine inspections,
as well as annual inspections, cleaning, tank
drainage, and oil changes.
In-LJne Static Mixers
In-line static mixers consist of a series of baffle
elements placed in a pipe section to impart
alternating changes in flow direction and intense
mixing action as water flows through the device.
Headloss ranging from 0.3 to 1.8 m (1 to 6 ft) occurs as
the flow passes through the static mixer. Static
mixers achieve virtually instantaneous mixing, are
relatively maintenance free, and are less expensive
than other rapid mixing processes. The only
disadvantage of in-line static mixers is that mixing
intensity depends upon the plant's water flow rate.
As rates decrease, the mixing intensity slows.
In-Line Mechanical Blenders
In-line mechanical blenders provide rapid mixing of
treatment chemicals with water flowing in a pipeline
under pressure. These devices consist of a housed
propeller driven by an electrical motor. They have
the advantage over static mixers of imparting
considerably less headloss and not being affected by
change in flow. In addition, in-line blenders offer the
following advantages:
Virtually instantaneous mixing with a minimum
of short-circuiting
Minimal headlosses
Less expense than more conventional rapid mix
units
Jet Injection Blending
Jet injection mixers, a type of in-line blender, are
used for attaining nearly instantaneous dispersion of
coagulant with raw water, usually at larger
treatment plants. Jet injectors can avoid the
backmixing inefficiencies of turbine or impeller
mixers, and the recommended detention times are
24
-------
Table 3-8. Estimated Costs for Supplementing Surface Water Treatment by Adding Rapid Mix ($1978)
Category
1
2
3
4
5
6
7
8
9
10
11
12
Plant Capacity,
MOD
0.026
0.068
0.166
0.50
2.50
5.85
11.59
22.86
39.68
109.90
404
1,275
Average Flow,
MOD
0.013
0.045
0.133
0.40
1.30
3.25
6.75
11.50
20.00
55.50
205
650
Capital Cost,
$1,000
13.2
17.5
22.5
30.9
47.7
63.7
88.2
139
218
587
2,100
6,670
Operation and Maintenance Costs
$1,000/yr
2.8
2.9
7.0
7.9
13.3
22.4
38.2
69.2
116
313
1,130
3,540
0/1 ,000 gal
58.6
17.6
14.7
5.4
2.8
1.9
1.6
1.6
1.6
1.5
1.5
1.5
Total Cost,
0/1 ,000 gal
91.3
30.1
20.3
7.9
4.0
2.5
2.0
2.0
1.9
1.9
1.8
1.8
Source: U.S. EPA (1979).
shorter than for mechanical mixers. The primary
disadvantages are that the orifices in the injection
pipe tend to become plugged and the mixing intensity
cannot be varied. Figure 3-2 illustrates a jet injection
mixer.
Coagulant Diffusers
Coagulant diffusers are also used to improve the
rapid mixing process. Figure 3-3 is a schematic
diagram of a coagulant diffuser. Coagulant diffusers
are similar to jet-injection mixers in design, except
that jet injectors are usually used in a pipe setting
and coagulant diffusers are typically used in basin
settings. Coagulant diffusers are designed to apply
the coagulant at the point of maximum turbulence.
In some plants, multiple application points spaced
uniformly across the flow cross section permit rapid
and thorough contact of chemical solution with the
entire incoming water flow. This rapid and uniform
dispersion of coagulant prevents its hydrolysis, which
is a common problem in systems with single
application points. Where turbulence in incoming
channels or pipelines provides good mixing, the
simple addition of a coagulant diffuser could improve
coagulation and lead to improved filtered water
quality.
3.3 Improving Flocculation
Flocculation usually follows the rapid mixing process
in conventional treatment plants. Flocculation is a
time-dependent process that directly affects
clarification efficiency by providing multiple
opportunities for particles suspended in water to
collide through gentle and prolonged agitation. The
process takes place in a basin equipped with a mixer
that provides agitation. This agitation must be
thorough enough to encourage interparticle contact,
but gentle enough to prevent disintegration of
existing flocculated particles.
Effective flocculation is important for the successful
operation of the sedimentation process. Expanding
plant capacity will require flocculation improvement
to maintain plant performance. For example, a
doubling of plant capacity resulting from a change in
filter media from rapid sand to mixed- or dual-media
can increase flow capacity from 1.34 to 2.7 L/sec/m2 (2
to 4 GPM/sq ft). The increased flow will cut the
flocculation detention time in half, thereby
preventing completion of the flocculation process,
and reducing sedimentation effectiveness.
Three basic methods of improving the flocculation
process are:
Installing new mixing equipment to improve
agitation
ซ Improving inlet and outlet conditions to
minimize destabilizing turbulence ,
ซ Adding baffling to reduce basin short-circuiting
3.3.1 Improving Mixing
Different mixing equipment can improve turbulence
patterns in the basin to maximize the formation of
flocculated particles and minimize the destruction of
previously formed floe. There are several types of
mixers used for flocculation, with the mechanical
mixer being the most common. Mechanical mixers for
flocculation basins are differentiated by overall
design and type of agitator.
The most important goal in flocculatpr design is the
efficient removal of floe during sedimentation and
filtration. Many flocculator units, especially low-
energy mixers, tend to maximize floe size rather than
floe density, which affects the speed with which floe
25
-------
Vertical Turbine Pump
Liquid Alum Feed Point
Raw Water
To Floccu-
lation Basin
Figure 3-2. In-line Jet Injection mixer.
settles. High-energy mixers create smaller and
denser floe which settles faster and occupies less
volume in the filter bed than the larger floe created
by low-energy mixers.
Paddle, walking-beam, and flat blade turbine mixers
are known as low-energy mechanical mixers. The
paddle or reel mixer operates with low tip speeds of 2
to 15 revolutions per minute (rpm) to prevent floe
destruction. The flat blade turbine typically operates
at 10 to 15 rpm. Flat blade turbines can produce
excessively high velocity gradients of over 45 rpm.
Axial flow propellers or turbines, known as high-
energy mechanical flocculators, typically operate at
150 to 1,500 rpm with no limit on blade tip speed.
Axial flow propellers are favored in some situations
because they produce uniform turbulence and are
simple to install and maintain.
Careful evaluation is needed to determine whether a
plant should change to high-energy flocculators.
Sometimes, higher energy gradients can be achieved
through modifying paddle-style units by adding more
paddles or installing a new higher speed mechanical
drive.
3.3.2
72 in Influent Pipe
Improving Fioccuiator Inlet and Outlet
Conditions
The desired detention time (i.e., residence time)
determines the size and occasionally the design
configuration of the flocculation basin. The basin's
internal design then determines detention time
effectiveness. The design of the basin inlet, outlet,
and internal circulation patterns all affect floe
formation and destruction.
Typical detention times range from 15 to 45 minutes.
These are influenced by the influent water
conditions, type of coagulant used, and requirements
of downstream processes. Cold, low turbidity water
could require 30 minutes of detention, while the same
water undergoing direct filtration at higher
temperatures could require only 15 minutes of
detention. In small plants with high efficiency
volumetric mixing, 10 to 15 minutes of detention
might be acceptable.
If water passes through the flocculation basin in
much less than the volumetric residence time, the
influent stream is said to have "short-circuited." To
achieve effective flocculation and minimize short-
circuiting, designers must pay particular attention to
inlets, outlets, and internal baffling. Inlet and outlet
turbulence is the major source of destructive energy
26
-------
:.-.
.
*
*
*:
r
h
r
U
^. Coagulant
Feed Line
T4 in Cres Pipe
14 in
Cr
ฃT '( T I
-L
I
1
Coagulant
Diffuser
* *.
* tt
*
*
*
Multijet
Slide
Gate
[
Coagulant
Source
Water
Flow
Front View
Section View
Figure 3-3. Coagulant diffuser.
in the flocculation basin contributing to short-
circuiting.
Effective baffle, inlet, and outlet design reduces
short-circuit problems. Improvements that are often
overlooked can include:
Adding inlet diffusers to improve the uniformity
of the distribution of incoming water
Enlarging connecting conduits to reduce floe-
disrupting turbulence
Adding a secondary entry baffle across the inlet
to the floceulation basin to impart increased
headloss for uniform water entry
Improving inlet and outlet conditions will reduce
basin turbulence and thus lessen floe breakup,
increase detention times, and allow more efficient
coagulant usage.
3.3.3 Improving Basin Circulation with
Baffles
Flocculation basins can be baffled to direct the
movement of the water through the basin. Baffling,
usually near the basin entrances and exits, can
improve basin circulation and achieve more uniform
flocculation. Baffles, commonly made of wood,
plastic, concrete, or steel are either "over-under" or
"around-the-end" in design. "Over-under" designs
direct water flow either over or under the baffle,
while "around-the-end" designs direct the water
around either end of the baffle. Baffles should be
designed to direct the water flow such that the
velocity gradients are less than those produced in the
flocculation process but greater than those in the flow
moving laterally across the inlets. An example of a
basin divided with baffling is illustrated in Figure
3-4.
Estimated costs for adding flocculation are presented
in Table 3-9.
3.4 Improving Sedimentation
Sedimentation is the step in conventional water
treatment systems that follows flocculation and
precedes filtration. Its purpose is to enhance the
filtration process by removing particulates.
Sedimentation requires that the water flow through
the basin at a slow enough velocity to permit the
particles to settle to the bottom before the water exits
the basin. The equipment required for this process
includes a settling basin of either rectangular,
27
-------
Perforated
Entrance
Baffle
3.65m (12ft)
3.42m (11.25 ft)
H ^ +\
4.57m
(15ft)
Apply 0.25 mg/L
Product B (985 N)
tSteWISg
Typical
with
Top
Wood Well
Port in
of Wall
Typical Wood Well
with Port in
Bottom
Typical Baffle Would be the
Same Elevation as the
Port Extending 1.22m
(4 ft) into the Compartment
Figure 3-4. Divided flocculation basin.
Table 3-9. Estimated Costs for Supplementing Surface Water Treatment by Adding Flocculation ($1978)
Category
1
2
3
4
5
6
7
8
9
10
11
12 ,
Plant Capacity,
MGD
0.026
0.068
0.166
0.50
2.50
5.85
11.59
22.86
39.68
109.90
404
1,275
Average Flow,
MGD
0.013
0.045
0.133
0.40
1.30
3.25
6.75
11.50
20.00
55.50
205
650
Capital Cost,
$1,000
10
18
34
73
217
325
418
587
840
1,830
6,060
19,200
Operation and Maintenance Costs
$1,000/yr
1.0
1.1
2.3
2.7
3.8
5.6
8.7
14.5
22.9
53.9
182
569
0/1 ,000 gal
21.7
6.9
4.9
1.8
0.8
0.5
0.4
0.4
0.3
0.3
0.2
0.2
Total Cost,
0/1 ,000 gal
45.2
20.1
13.3
7.7
6.2
3.7
2.3
2.0
1.7
1.3
1.2
1.2
Source: U.S. EPA (1979).
square, or circular configuration. The basin includes
provisions for inlet and outlet structures, and a
sludge collection system. In addition, sedimentation
systems are optionally equipped with tube or plate
settlers to improve performance.
Improvements in other elements of the treatment
process often require modification of the settling
basins to maintain effluent water quality. Typical
system improvements that necessitate sedimentation
modification involve expanded flow rates, resulting
28
-------
in decreased detention times and increased
clarification rates.
Problems with settling basins that might require
modification include:
Poor entry and/or exit conditions
Destructive basin turbulence
Excessive clarification rate
Inadequate sludge collection and removal
Settling basin inlets are often responsible for
creating turbulence that results in breaking floe. One
way to avoid such destructive turbulence is to
eliminate conduits and pipes between flocculation
and settling basins by conducting both flocculation
and sedimentation in one basin separated by
perforated baffles. Baffles will minimize the breaking
of floe and evenly distribute the flocculated water to
the settling basin to maximize settling efficiency.
Improperly designed outlets are often responsible for
sedimentation basin short-circuiting. One method of
reducing short-circuiting in rectangular basins is to
use finger launders extending inward from the exit
wall in a uniform pattern. Finger launders are small
troughs with V-notch weir openings that collect
water uniformly over a large area of the basin. Weir
loading rates ranging from 126.2 to 252.3 m3/day/m
(10,000 to 20,000 gpd/ft) of weir length are optimal.
For circular or radial flow basins, clarified water is
collected in a continuous peripheral weir trough.
These collection troughs should be designed with the
same loading rate as weir troughs used in
rectangular basins.
Tube or plate settlers are often added to settling
basins to improve their efficiency, especially if flows
are to be increased beyond original design conditions.
This established technology is widely used to reduce
floe carryover in existing basins. Tube settlers can be
installed in most conventionally designed settling
basins and, in many cases, result in twice the basin's
original settling capacity. Also, the use of tube and
plate settlers in new plant construction minimizes
settling basin costs by minimizing the basin size
necessary to attain a desired level of treatment. Tube
settlers can also be used with vacuum sludge removal
systems.
Tube settlers typically use 0.6 to 0.9 m (2 to 3 ft) long
tubes or plates placed from 5.1 to 10.2 cm (2 to 4 in)
apart and installed over part or all of a basin. They
are generally designed to accept flow rates ranging
from 0.68 to 2.04 L/see/nv* (1 to 3 GPM/ft2). The
shallow settling depths and the large surface area
provided by tube settlers permit effective
clarification at detention times of several minutes
versus several hours in conventional sedimentation
basins.
There are several different types of commonly used
tube settling basin designs. The two most common
choices are horizontal flow basins (either rectangular
or circular) and upflow solids contact clarifiers.
Either design uses tube settling modules or plates to
apply the principles of shallow depth sedimentation,
permitting operation at higher clarification rates
than conventional clarifiers.
The major by-product of sedimentation is a volume of
sludge, which must be removed on a continuous
basis. Sludge collection systems are either manual or
automated. Automated mechanical sludge collection
equipment is suitable for larger plants to attain
continuous and complete sludge removal.
3.4.1 Horizontal Flow Sedimentation Basins
As the name implies, the water generally follows a
horizontal flow path in this type of basin. Water is
introduced at one end of the basin and suspended
particles settle to the bottom as the water moves
through to the exit. The particular basin
configuration will affect the design requirements for
installing tube or plate settlers to improve
performance or increase capacity.
The terms overflow rate, clarification rate, and
loading rate all refer to the amount of water that can
be adequately processed by sedimentation (i.e., the
velocity of water through the tubes expressed in
GPM/sq ft). The clarification rate at which tubes or
plate settlers can be operated depends on the type of
clarifier and water characteristics, including
temperature and the desired effluent quality. For
example, the tube clarification rate must be reduced
when influent turbidity increases or water
temperature decreases. The specific relationships
between tube loading rates and influent and effluent
turbidity for cold and warm water are presented in
Table 3-10.
The preferred location for tube modules in horizontal
flow basins is away from areas of possible turbulence
such as basin entrances. For example, in a horizontal
basin, often as much as one third of the basin length
at the inlet end may be left uncovered by the tubes so
that it may be used as a "stilling" zone, where water
turbulence is diminished in preparation for
sedimentation. This is permissible in most basins
because the required number of tube settlers will
cover only a portion of the basin. Tube modules are
usually placed at least 0.6 m (2 ft) below the surface
in standard depth (3 to 3.9 m [10 to 13 ft]) settling
basins. They can be submerged as much as 1.2 m (4
ft) for deeper basins (4.8 to 6 m [16 to 20 ft]). In all
cases sufficient clearance must be maintained
beneath the tube settling module for movement of
sludge collection equipment.
29
-------
Table 3-10. Horizontal Flow Basins Loading Rates
Overflow Rate, Based
on Total Clarifier Area
(GPM/ftZ)
For water temper-
atures 40 ฐF or less:
2.0
2.0
2.0
2.0
For water tempera-
tures 50ฐF or above:
2.0
2.0
2.0
3.0
2.0
2.0
Overflow Rate, Probable
Raw Portion of Basin Effluent
Water Covered by Tubes Turbidity,
Turbidity (GPM/ftZ) NTU
0-100
0-100
100-1,000
100-1,000
0-100
0-100
0-100
0-100
100-1,000
100-1,000
2.5
3.0
2.5
3.0
2.5
3.0
4.0
3.5
2.5
3.0
1-5
3-7
3-7
5-10
1-3
1-5
3-7
1-5
1-5
3-7
1 0PM - 0.06308 L/sec; 1
ฐC ป ("F - 32) X .556.
0.0929 m2;
Figure 3-5 shows a typical tube settler installation in
a rectangular basin illustrating the arrangement of
tube settling modules and the utilization of collection
troughs in the covered area to ensure uniform flow
collection. In radial flow basins (see Figure 3-6), the
required quantity of modules can be placed in a ring
around the basin periphery, leaving an inner-ring
open area between the modules and the center well to
dissipate inlet turbulence.
3.4.2 Upflow Solids Contact Clarifiers
The design of upflow solids contact clarifiers is based
upon maintenance of a layer or blanket of flocculated
material through which water flows in a vertical
direction in the clarifier. The purpose of the layer,
known as a sludge blanket, is to entrap slowly
settling small particles and achieve a high level of
clarification. The sludge blanket is maintained at a
certain level and concentration by the controlled
removal of sludge. The precise height is determined
by the clarification rate. When the flow is increased,
the clarification rate is greater and the level of the
blanket rises.
In solids contact clarifiers, the clarification efficiency
of tube settlers depends upon both the clarification
rate and the concentration of floe in the sludge
blanket. The allowable loading rate or velocity of flow
through tube settlers is dependent upon:
Average settling velocity of the floe layer or
sludge blanket
Ability of the clarifier to concentrate solids
Ability of the sludge removal system to maintain
an equilibrium solids concentration; if the sludge
is not removed quickly enough, then the solids
layer will pass through the tubes and into the
effluent
Temperature of the water
Influent Zone
Effluent
Collection Zone
rr
J L
] C
New Baffle
Existing Launders
\r~
New Launders
Tube Supports
Figure 3-5. Typical tube settler installation in rectangular basin.
Tube Modules
30
-------
Variable Speed
Recirculation Pump
Collector Drive
Flocculation and
Secondary Reaction Zone
Sludge Collector
" Sludge Wasting Sump
Sludge Slowdown
Sectional Elevation
Figure 3-6. Radial solids contact clarifier with tube settlers.
Recommended loading rates for upflow clarifiers are
provided in Table 3-11.
Table 3-1 1 . Upflow Clarifier Loading Rates for Cold Water
Overflow Rate, Based Overflow Rate, Portion Probable Ef-
on Total Clarifier Area of Basin Covered by fluent Turbid-
(GPM/ft2) Tubes (GPM/ft2) ity, NTU
For water temperatures
40ฐF or less:
1.5
1.5
1.5
2.0
2.0
For water temperatures
50 ฐF or above:
2.0
2.0
2.0
2.5
"2.5
2.0
3.0
4.0
2.0
3.0
2.0
3.0
4.0
2.5
3.0
1-3
1-5
3-7
1-5
3-7
1-3
1-5
3-7
3-7 ,
5-10
1 GPM = 0.06308 L/sec; 1 ft2 = 0.0929 m2;
ฐC = (ฐF - 32) x .556.
Expansion of the capacity of this type of clarifier is
limited by its ability to remove solids from the
system. Generally, the maximum expansion from
original design capacities is limited to 50 to 100
percent.
Tube module placement is governed by the same
general rule as that for horizontal flow basins; that
is, tube modules are best located away from influent
turbulence. In terms of placement depth and general
proximity, the recommendations regarding distance
from the inlet and depth from the surface are also the
same. Lastly, collection launders should be placed at
3- to 4.5-m (10- to 15-ft) intervals to ensure uniform
collection of flow over the area covered by the tube
settling modules.
Estimates of the costs of adding tube modules to
conventional water systems are provided in Table 3-
12. These costs include modules, supports, anchor
braces, transition baffles, effluent launders^nd
installation.
31
-------
Table 3-12. Estimated Costs for Supplementing Surface
Water Treatment by Adding Tube Settling
Modules ($1978)
Cate-
gory
1
2
3
4
5
6
7
a
g
10
11
12
Costs
baffle,
i MGD
Source:
Plant
Capacity,
MGD
0.026
0.068
0.166
0.50
2.50
5.85
11.59
22.86
39.68
109.90
404
1,275
Average
Flow, MGD
0.013
0.045
0.133
0.40
1.30
3.25
6.75
11.50
20.00
55.50
205
650
Capital Cost,
$1,000a
1.1
2.3
3.9
8.2
25.2
46.8
92.0
163.0
250
684
2,500
7,850
include modules, supports and anchor brackets,
effluent launders, and installation.
- 0.044 m3/sec; 1,000 gallon = 3.785 m3
U.S. EPA (1979).
Total Cost,
0/1 ,000 gal
2.7
1.6
0.9
0.7
0.6
0.5
0.4
0.4
0.4
0.4
0.4
0.4
transition
32
-------
Chapter 4
Filtration Technologies
This section describes several available filtration
technologies ranging from commonly used
conventional systems to new and emerging
technologies. Filtration is one of the most important
elements in traditional water treatment systems and
also plays an important role in controlling some
organic contaminants.
The filtration process itself may need upgrading due
to expansions or the need to meet stricter effluent
quality limits. Section 4.1 addresses typical concerns
and describes beneficial modifications. Many water
supply systems will have to add filtration to comply
with the 1986 Safe Drinking Water Act (SDWA)
Amendments and the resultant Surface Water
Treatment Rule. Sections 4.2 through 4.6 provide
overviews of the following filtration technologies:
Conventional treatment and direct filtration
Direct filtration (gravity and pressure filters)
Slow sand filtration
Package plants
Diatomaceous earth filtration
Membrane filters
Cartridge filters
Conventional treatment and direct filtration (Section
4.2) are the most widely used systems. Slow sand
filters (Section 4.3), package plants (Section 4.4), and
diatomaceous earth filtration (Section 4.5) are
considered newer technologies, but have broad
applicability. While slow sand filters have been used
for many decades, they do not have an established
record of performance with a large number of water
systems in this country. Membrane and cartridge
filtration systems (Section 4.6) are considered
emerging technologies because they show promise
but have not generally been used for treatment of
drinking water. Package plants, slow sand, diatoma-
ceous earth, membrane, and cartridge filters are
considered best suited for small systems (less than
0.44 m3/sec [10 MOD]).
The sections describing filtration technologies
provide information on each type of system covering
the following aspects:
Process description
System design'
Operation and maintenance
System performance
ซ System costs
The last subsection, Section 4.8, provides some
guidance in selecting the appropriate filtration
technology for particular applications. Appendix A
includes descriptions of experiences with the various
filtration technologies.
4.1 Modifying Filtration Systems
Filtration is usually the final step in conventional
treatment trains, although disinfection frequently
follows filtration. This section addresses
improvements that can be made to plants that use
rapid sand, mixed-media, or dual-media filters.
Filtration systems are regarded as effective for
removal of turbidity and microbial contaminants.
Microbial contaminants of special concern include
coliform bacteria, Giardia lamblia, enterovirus, and
Legionella.
The Surface Water Treatment Rule (SWTR) requires
that filters achieve turbidities of less than 0.5 NTU
in 95 percent of the finished water samples, and
never exceed 5 NTU. Turbidity is a measure of
suspended particles, which can include organic
solids, viruses, bacteria, and other substances.
Turbidity particles range in size from less than 1
micron to 100 microns.
33
-------
4.1.1 General Effectiveness of Filtration
Systems
The effectiveness of filtration systems is determined
by their ability to remove microorganisms, turbidity,
and color. Color is imparted to water supplies by
organic material and can be removed by chemical
coagulation. Once the color is coagulated and
combined with the floe particles, color removal can be
related to turbidity removal. The measurement and
control of microbes and turbidity are distinct
procedures. The effectiveness of filter systems in
removing microbial contaminants, however, is
heavily related to influent turbidity. The general
rule of thumb is to minimize turbidity to maximize
microbial removal.
The filtration systems discussed in this document are
appropriate for raw water with varying
characteristics. Table 4-1 contains the recommended
upper limits for several influent variables, including
coliform bacteria, turbidity, and color, for four
filtration technologies. Conventional treatment is
clearly the most accommodating of the filtration
systems in the table because it includes flocculation
and sedimentation, which reduce turbidity before the
water is actually processed by the filter.
Diatomaceous earth filtration systems, which include
little pretreatment, require high-quality influent.
Giardia lamblia is of particular concern in drinking
water supplies because it forms a cyst that cannot be
effectively killed by traditional chlorine disinfection.
Effective removal can be attained only by filtration.
Conversely, viral and bacterial pathogens are
relatively easy to destroy with disinfection.
Figure 4-1 is a graph of the relationship between
filter effluent turbidity and cyst removal efficiency
after filtration. The graph clearly shows that filtered
water with very low levels of turbidity, ranging
below 0.1 NTU, contained almost no cysts (DeWalle
et al., 1984). The four filtration systems shown in
Table 4-2 are very effective in removing Giardia; the
only exception is direct filtration without
coagulation, which does not effectively reduce
turbidity. If water supplies containing Giardia are
not effectively coagulated, the cysts will pass through
the entire treatment process, including the filters.
The viral removal efficiencies of four filter
technologies found to be very effective are shown in
Table 4-3. Of these processes, direct filtration
provides the poorest removal of viruses, ranging from
90 to 99 percent.
4.1.2 Filtration System Improvements
Improving filtration systems can increase plant
capacity and improve effluent quality. Increasing the
capacity and effectiveness of rapid sand filters,
originally designed to operate at 1.36 L/sec/m2 (2
GPM/sq ft), is usually achieved by either changing
the filter media to dual- or mixed-media or replacing
the top layer of sand with anthracite coal (also
termed "capping" the filter). With these
modifications, filter rates often can be increased to
2.7 to 3.4 L/sec/m2 (4 to 5 GPM/sq ft), doubling plant
capacity and producing higher quality effluent.
A thorough hydraulic study is required to determine
the feasibility of improving a filtration system. For
example, if a plant is going to be expanded,
sedimentation basins and interprocess transfer
systems have to be evaluated in terms of their ability
to accommodate the increased flow from larger
filters. Assessing the maximum carrying capacities
for all components of the system is a prerequisite to
evaluating the expansion potential of a treatment
plant. Field testing of the entire system is the
preferred method for conducting hydraulic
evaluations.
If a hydraulic evaluation reveals that it is feasible to
increase plant capacity, a specific evaluation of filter
modification is appropriate. Such an evaluation will
include consideration of filter box design, underdrain
type, surface wash system, air scour system, flow-
limiting devices and piping, filtration rate controls,
filter aid application, and backwash additives. Figure
4-2 illustrates the basic components of a sand filter
system that need to be evaluated.
Filter Boxes
Filter boxes, the structures that contain the filter
media, should be examined first to see if they can
accommodate a filter that will operate at higher
flows. Most rapid sand filters are easily converted to
higher volume dual- or mixed-media filters.
Backwash rates, the primary operational
consideration, are about the same for these two filter
types.
When flow capacities are increased using either dual-
or mixed-media filters, wash troughs and certain
filter cleaning technologies will require specific
consideration. Filter wash troughs, structures at the
top of filter boxes that collect waste backwash water
during filter cleaning, may need to be deepened to
prevent loss of the lighter anthracite coal media.
Wash troughs that are shallow and wide and spaced
closely together can create overly high rise velocities
that wash out anthracite coal during backwash. If
filter troughs cover more than half the area of the
filter box, narrower and deeper troughs covering less
surface area may be needed to prevent excessive coal
loss during filter backwashing.
34
-------
Table 4-1. Generalized Capability of Filtration Systems To Accommodate Raw Water Quality Conditions
Recommended Upper Limits For Influent
Treatment Technology
Conventional treatment
- with no predisinfection
Direct Filtration
Slow Sand Filtration
Diatomaceous Earth Filtration
Total Conforms, #71 00 mL
< 20,000
< 5,000
<500
<800
<50
Turbidity, NTU
No Restrictions
No Restrictions
<7-l4
<10
<5
Color, CU
75
75
<40
<5
<5
1.0
0.5
i
&
jo
0.1
0.05
0.01
40
50
90
100
60 70 80
Cyst Removal - %
Figure 4-1. Relationship between cyst removal and filtered
water turbidity.
Table 4-2.
Unit Process
Removal Efficiencies Of Giarctia Lamblia By
Water Treatment Processes
Percent
Removal
Rapid Filtration with Coagulation, sedimentation
Direct Filtration
- with coagulation
- without coagulation
- with flocculation
Diatomaceous Earth Filtration
Slow Sand Filtration
96.9-99.9
95.9-99.9
10-70
95-99
99-99.99a
98-100b
a Aided by coagulation.
b Fully-ripened filter.
Table 4-3. Removal Efficiencies Of Viruses By Water
Treatment Processes
Percent
Unit Process Removal
Slow Sand Filtration 99.9999
Diatomaceous Earth Filtration (with filter aid) >99.95a
Direct Filtration 90-99
Conventional Treatment "
a No viruses recovered.
L/ndercfra/ns
The condition of the underdrain gravel, the coarse
layer underneath the filter media, is difficult to
assess in a filter evaluation. Removing filter media
and visually inspecting the condition of the
underdrain is the only reliable method of
ascertaining whether it is satisfactory. However,
indirect indications of underdrain failure include
boils incurred during the backwash process or an
uneven mounding of the filter surface. As a general
practice, underdrain gravel is removed and replaced
with new material along with the filter media.
Frequently, the existing backwash water
distribution system, which commonly consists of pipe
laterals, is also replaced at the same time.
Surface Wash Systems
Surface wash systems are used to scour the upper
layers of the filter during or prior to backwashing.
These systems are more important for dual- and
mixed-media filters than for sand filters. Surface
washers prevent the formation of "mud-balls," which
form within the filter media, most frequently at the
sand-coal interface. Also, surface washers improve
the process of cleaning dual- and mixed-media filters
when polyelectrolytes are added, a practice used at
filter How rates of 2.7 to 4.1 L/sec/m2 (4 to 6 GPM/sq
ft) to control floe breakthrough.
Surface wash systems may be designed with one or
two rotary arms. The single-rotary-arm systems
position the arm at the filter surface. The two-arm
system has one arm on the surface and one arm
within the filter bed at the sand and coal interface in
35
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Filter Tank
Cast
Figure 4-2. Cutaway view of typical rapid sand filter.
a dv al media filter. The arms deliver a high velocity
stream of water that violently agitates the filter
media as it turns.
Air Scour Systems
Air scour systems can be used to clean rapid sand or
dual-media filters, eliminating the need for surface
wash systems. They require specially designed wash
water distribution systems and generally do not use a
coarse grade gravel support layer, because the violent
mixing action caused by introducing air beneath a
filter would upset a graded gravel underdrain system
and destroy the filter bed. Instead, specially designed
nozzles with retaining screens placed on a false floor
in the filter box under the filter media are commonly
used. The air introduced beneath either dual- or
mixed-media filters destratifies the media. To return
a destratified filter to service involves backwashing
at 10.2 L/sec/m2 (15 GPM/sq ft) to reclassify the filter
media.
Piping and Controls
Filter effluent piping and filter flow rate controllers
may be too small to accommodate expansion of a
current system. Backwash water supply and waste
piping in rapid sand filter plants, however, generally
have adequate capacity for expansions. Design
changes may be necessary to accommodate other
modifications that diminish the already limited
available space in filter pipe galleries. For instance,
cast iron piping and gate valves can be replaced by
more compact fabricated steel piping and less bulky
butterfly valves.
Method of Filter Rate Control
There are two methods for controlling filter rates:
constant rate filtration and variable declining rate
filtration. Constant rate filtration is the most
common method. While constant rate filters have
provisions to control both the influent and effluent
flow of each filter, variable declining control systems
do not use filter rate-of-flow controllers and have a
common filter effluent collection flume or pipe. In
variable declining rate filtration, filtration rate
declines as headloss builds up during the filtering
process. In plants designed with multiple filters,
filter influent flow frequently is directed
automatically to another cleaner filter.
36
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Variable declining rate filtration can be used where
the capacity of an existing rapid sand filter is to be
increased. Its major advantages over traditional
constant rate filtration methods are its relatively low
cost and its elimination of rate-of-flow controllers
which require maintenance. Also, the filters are
never operated at negative heads with this type of
control, thus eliminating the potential for air
binding. The major limitation is that the filtration
rate of individual filters is uncontrolled at the
beginning of a filter cycle.
Filtration Aid Application
Filtration aids prevent premature turbidity
breakthrough by controlling floe penetration into the
filter. Chemically, they are usually nonionic
polyelectrolytes, and are very useful in maximizing
the performance of high-rate filters and systems with
cold influent water. These aids should be applied in
systems that upgrade from sand to dual- or mixed-
media filters. An optimal dosage of filtration aid
minimizes the effluent turbidity until the filter
achieves its maximum headloss. Typical filtration
aid dosages are from 0.02 to 0.1 mg/L.
Addition of Polymer to Backwash
The addition of polymers to the backwash water can
reduce the initial turbidity peaks during filter
ripening following backwash and extend filter
operation before breakthrough occurs. Polymer
enhances the ability of the filter to retain turbidity
particles. Adding polymer also improves the settling
and thickening rate of the backwash solids. In
addition, savings in backwash water can be achieved
by precoating filters with polymer.
Polymer should be added during the first 5 to 7
minutes of the 10- to 15-minute backwash period.
Polymer additions ranging from 0.1 to 0.15 mg/L
have reduced the initial turbidity breakthrough by
one half.
4.1.3 System Design Checklist
The following steps are recommended to maximize
the efficiency of any filter modification:
Use pilot test data to select filter size and
medium; however, if pilot test data are not
available, use data from analogous applications.
Provide for the addition of disinfectant directly to
filter influent.
Pro vide for the addition of polyelectrolytes
directly to filter influent for dual- or mixed-media
filters.
Provide for the continuous monitoring and
recording of turbidity from each filter.
Provide for the continuous monitoring and
recording of flow and headloss from each filter.
Provide for the housing of filter controls and pipe
galleries.
Use color-coded filter piping.
Provide for the easy removal of pumps and valves
for maintenance.
Equip each filter with a filter-to-waste cycle for
unsatisfactory water.
Provide for filter cleansing with either surface
wash or air scouring.
Equip with an automatic filter backwash system.
ป Select backwash rate based on filter media and
expected wash water temperatures.
Select backwash supply storage capacity to
accommodate a minimum of two filter
backwashes.
Provide backup capacity to the largest single
pump for backwashing and surface washing.
Equip pressure filters with pressure and vacuum
release valves.
Equip backwash supply lines with air release
valves.
Appendix A presents briefcase histories of plant
upgrades, discussing some of those steps in more
detail.
4.2 Direct Filtration
Direct filtration systems are similar to conventional
systems, but omit sedimentation. This section
describes direct filtration technology.
4.2.1 Process Description
Direct filtration is an established technology that
was developed because dual- and mixed-media filters
are able to effectively process higher influent
turbidities without the use of sedimentation. The
direct filtration process is expected to be more widely
used on water supplies that, up until now, only
performed chlorination.
Direct filtration is only applicable for systems with
high-quality and seasonally consistent influent
supplies. The influent generally should have
turbidity of less than 5 to 10 NTU and color of less
than 20 to 30 units.
Direct filtration consists of several combinations of
treatment processes. It always includes coagulation
and filtration, and sometimes includes flocculation or
a contact basin after coagulation addition. Typical
coagulant dosages range from less than 1 to 30 mg/L.
Cationic polymers often successfully coagulate water
supplies and assist direct filtration. Nonionic
polymers sometimes are added to the filtration step to
increase filter efficiency. A flow diagram of a typical
direct filtration system is shown in Figure 4-3.
In-line direct filtration, the simplest version of direct
filtration, is commonly used in pressure filtration
37
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Coagulants
Influent
Figure 4-3. Flow diagram of typical direct filtration system.
systems (see Figure 4-4). In this process, chemical
coagulant application and mixing are followed by
addition of a nonionic polymer aid and filtration.
There is no separate flocculation step. This treatment
is effective and commonly used in the removal of iron
and manganese from ground water when
accompanied by appropriate coagulant doses. In-line
direct filtration, however, is only applicable for
surface waters with seasonal average turbidities of
less than 2 to 3 NTU and free of contamination by
wastewater sources (when permitted by regulatory
agencies).
r
Coagulants
Rapid Mix
30 sec-2 mm
Detention
r
f
w
ruonic roiymer
Nitration Aid
Dual or Mixed
Media Filter
4-5 GPM/ft2
Influent
Figure 4-4. Row diagram of in-line direct filtration system.
Another version of a direct filtration system is the
"modified" system, which substitutes a contact basin
for the flocculation basin found in the typical direct
filtration process. Figure 4-5 is a flow diagram of
modified direct filtration. The 1-hour detention
contact basin serves primarily to condition the floe
prior to filtration. Contact basins also provide
pretreatment by decreasing turbidity peaks in the
influent, providing silt and sand removal, and
allowing for more equal distribution of coagulant.
4.2.2 System Performance
Direct filtration units can perform effectively within
the following general influent parameters:
ซ Less than 500 total coliforms per 100 mL
Less than 14 NTU of turbidity
ฎ Less than 40 color units
While the direct filtration process is able to operate
satisfactorily with influent turbidities as high as 14
NTU, optimally, influent turbidity should be less
than 5 NTU. Effective direct filtration performance
ranges from 90 to 99 percent and from 10 to 99.99
percent for virus and Giardia removal, respectively.
The wide variation in direct filtration's Giardia
removal efficiencies is due to the wide range of
available system configurations. The most effective
direct filtration configurations for Giardia removal
must include coagulation.
Flocculation
15-30 min
Dual or Mixed
Media Filter
4-5 GPM/fta
4.3 Slow Sand Filtration
Slow sand filtration systems have a long history,
having been used without disinfection at least since
the 1850s in London, England. Slow sand filters were
also commonly used in the United States in smaller
facilities. Rapid sand filters have replaced many of
them to accommodate the increase in water demand;
consequently, slow sand filters are now not very
common. According to the Surface Water Treatment
Rule under the SDWA, many small systems could
meet their regulatory filtration obligations with the
simple slow sand filters. With the requirement for
the multiple barrier disinfection approach in water
treatment, slow sand filters are almost always
accompanied by disinfection. Because slow sand
filters with disinfection have not been used
extensively, they are classified as "new" technology
in the current literature.
Slow sand filters are similar to single media rapid
rate filters (conventional systems) except that they:
Are 50 to 100 times slower than normal filtration
rates
Use biological processes, which may enhance
chemical/physical removal processes
Require a ripening period before operation
Use smaller pores between sand (i.e., smaller
sand particles)
Do not require backwashing
Have longer run times between cleanings
Slow sand filters are most attractive for smaller
systems with high quality raw water. Specifically,
water which comes from a protected surface water
supply, has previously received only chlorination as a
treatment, contains less than 10 NTU, and has no
color problems is the most suitable for slow sand
filtration. While their operational simplicity makes
them very suitable for small plants, slow sand filters
are also applicable for medium to large plants.
The advantages of slow sand filtration include its
simplicity and reliability, low cost, and ability to
achieve greater than 99.9 percent Giardia cyst
removal. In addition, these systems do not require
continuous turbidity monitoring since they are
applied to water supplies with relatively low
turbidity.
Slow sand filters have several limitations, however.
Due to a low filtration rate, these filters require
38
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Influent
Figure 4-5. Flow diagram of modified direct filtration system.
relatively extensive land area. Without pretreatment
(particularly coagulation), limitations exist on the
quality of raw water that is suitable for treatment
using slow sand filtration. Also because pretreatment
is minimal or nonexistent at slow sand filter plants,
other contaminants such as synthetic organic
chemicals, disinfection by-product precursors, or
inorganic chemicals are not readily removed.
Systems with raw water containing high color or
algae content are probably not appropriate for slow
sand filtration, because these contaminants are not
removed by slow sand filtration and the raw water
will likely contain precursors for chlorination by-
products.
4.3.1 System Design Considerations
Slow sand filters require influent that does not
exceed the following parameters:
Turbidity of < 10 or up to 20 NTU depending on
other operating characteristics
Color of less than 30 units as prescribed by the
Ten State Standards
Algae of less than 5 mg per cubic meter of
chlorophyll A
These are maximum limits, not typical operational
parameters. Design flow rates range from 0.94 to 9.35
m3/m2 (1 to 10 million gallons per acre)per day, with
the usual range from 2.8 to 5.6 m3/m2 (3 to 6 million
gallons per acre)per day. Slow sand filters require
sand with particle sizes ranging in effective
diameters from 0.25 to 0.35 mm, with a uniformity
coefficient of 2 to 3. A higher uniformity coefficient is
acceptable for filters with pilot test verifications of
the performance.
Typical underdrains for slow sand filters are made
from split tile with laterals placed in coarse stone.
These drains routinely discharge to a tile or concrete
main drain. Recently constructed slow sand systems
are equipped with perforated polyvinyl chloride pipe
as laterals. Manually adjusted weirs, outlets, and
valves are adequate for these systems. Inlet
structures may be located at the end or side of the
filter.
Slow sand filters perform poorly during the first 1 to
2 days of operation, called the "ripening period." The
ripening period is the time required by the filter after
1 hr Contact
Basin
te
t
Dual or Mixed
Media Filter
4-5 GPM/ft2
- Nonionic Polymer
Filtration Aid
a cleaning cycle to become a functioning biological
filter. Although Giardia removal is not usually
affected by the ripening period, the overall poor water
quality during this period requires provision of a
filter-to-waste cycle.
These filters require continuous operation under
submerged conditions, ranging in depth from 0.9 to
1.5 m (3 to 5 ft). Hydraulic filter outlet controls keep
the filters submerged at all times. The difference
between the level of water in the collection gallery
and the level of water above the filter media is called
the headloss through the media. The initial headless
is about 0.06 m (0.2 ft). Maximum headloss should be
less than the submerged depth of 1.2 to 1.5 m (4 to 5
ft) to avoid air binding and the uneven flow of water
through the filter medium. The buildup of the
maximum headloss is slow, taking up to 6 months.
Redundant, or stand-by, systems are required to
accommodate the extended cleaning periods
associated with slow sand systems.
In climates subject to below freezing temperatures,
slow sand filters usually must be housed. Unhoused
filters in harsh climates develop an ice layer that
prevents cleaning during the winter months.
Uncovered slow sand filters will operate effectively,
however, if influent turbidities are low enough to
permit the filter to operate through the winter
months without cleaning. An illustration of an
unhoused system is provided in Figure 4-6; Figure 4-
7 shows an example of a housed system.
Because of filter housing costs, slow sand filters are
most appropriate for small systems. Due to this
expense, large systems can usually only utilize slow
sand filters when they are located in moderate
climates and therefore do not require housing. The
slow sand filter in Salem, Oregon, is an example of a
large system that is able to use unhoused slow sand
filters because of climate.
4.3.2 Operation and Maintenance
The primary operational consideration for a slow
sand filtration system is maintaining a clean filter.
Cleaning becomes necessary when headloss reaches
about 1.2 m (4 ft). The normal length of time between
cleanings ranges from 20 to 90 days, but will vary
depending on raw water quality, sand size, and
39
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Slow Sand Filter
Effluent Flow
Control Structure
Clean/veil
Raw
Water axt
Filter Bed
Berm
ฃ- ^
-V Supernatant Water /
Sand Filter Bed
Support Gravel
Perforated Drain Pipe
To Sewer or Raw
Water Source
Control Valve
Filtered Water for Backfilling
Backfill
Pump
Figure 4-6. Typical unhoused slow sand filter installation.
Slow Sand Filter
Raw Water
Effluent Flow
Control Structure
Vent
Clean/veil
Supernatant
Water Drain
Filtered
Water for
Backfilling
Sand Filter Bed-
Support Gravel
Drain Tile
Flow Meter
Control Valve
To Sewer or
Raw Water Source
Pump to
Filters for
Back Filling
Figure 4-7. Typical housed slow sand filter installation.
filtration rate. Filters should be cleaned every 1 to 2
months.
Cleaning involves manually scraping off the top 2.5
to 5 cm (1 to 2 in) of the filter media. The removed
sand is either discarded or treated separately. Most
small systems use manual cleaning techniques, but
very large systems may use mechanical scrapers.
A number of precautions must be observed in regard
to cleaning operations. Cleaning filters necessitates
removing the filter from service, after which a
ripening period is required to bring the filter back
into operation. Operators must minimize
40
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intermittent operation by coordinating maintenance
tasks. While cleaning, operators should take care to
avoid disturbing the filter bed during backwashing,
shock chlorination (if practiced), and raking the
surface of the filter bed. Scouring and subsequent
erosion of the filter media from refilling after
cleaning must also be avoided. Gradual filling from
the bottom of the filter during the startup phase
partially addresses this problem. Excessive drying of
the filter beds also should be avoided during
cleanings. During the postcleaning ripening period,
filtered water should be directed to waste. Operators
should periodically remove algae from the filter and,
to accommodate seasonal changes, reduce filtration
rates during the winter months.
If sand depth drops below 61 cm (24 in), new sand
needs to be added. Bed depths of only 30.5 to 50.8 cm
(12 to 20 in) have had poor performance records.
Replacing sand, however, is not considered a normal
operational or maintenance task because with
careful cleaning, resanding may be necessary only
once every 10 years.
In addition to the above maintenance considerations,
slow sand filters require daily inspection, control
valve adjustment, and turbidity monitoring. The
filter housing structure, if present, also requires
routine maintenance.
4.3.3 System Performance
Slow sand filtration units perform best within the
following general influent parameters:
Less than 800 total coliforms per 100 mL
Less than 10 NTU of turbidity
Less than 5 color units
Effective slow sand filtration performance, with
respect to virus and Giardia removal, ranges from 91
to 99.9999 percent and 100 percent, respectively.
4.3.4 System Costs
Slow sand filter cost data are presented in Table 4-4.
Smaller plants are typically designed with cast-in-
place concrete structures with wood or concrete slab
covers. The piping is either cast iron or steel and
below grade. Flow meters are used to monitor the
output for each filter. A below-grade concrete clear-
well is another cost element included in Table 4-4.
Larger plants, on the other hand, use uncovered
earthen berm structures. These on-grade plastic
membrane-lined structures have all below-grade
piping, and some plants use above-grade steel tanks.
Flow meters are also used for each filter in the
effluent control structure.
The process energy requirements of slow sand filters
are negligible assuming they have gravity-fed source
water. The housing structure energy requirements
include heating, lighting, and ventilation, and are
directly related to the size of the structure.
Maintenance supply requirements are also negligible
since the filters are assumed to operate virtually
unattended. Replacement sand is not included
because it is needed so infrequently.
4.4 Package Plant Filtration
Package plants are categorized as "new" treatment
technology. They are not altogether different
processes from other treatments mentioned in this
section, although several models contain treatment
elements that are innovative, such as adsorptive
clarifiers. The primary distinction, however, between
package plants and custom-designed plants is that
package plants are built in a factory, skid mounted,
and transported virtually assembled to the operation
site.
Package plants are designed to effectively remove
turbidity and bacteria from surface water with
generally consistent low-to-moderate turbidity
levels. While package plants can treat influent
streams with highly variable characteristics, they
would require more skilled operators and closer
attention.
There are about 650 to 700 package plants operating
in the United States with capacities ranging from
27.3 m3/day to 0.18 nvVsec (7,200 GPD to 4 MGD).
Many are built to conventional design standards.
Others, using tube settlers, have reduced size and
larger capacities. More recently, package plants have
been built with efficient and compact adsorptive
clarifiers. Package plants with adsorptive clarifiers
have capacities ranging from 54.5 m3/day to 0.26
m3/sec (14,400 GPD to 6 MGD).
The four major advantages of package plants are
their compact size, cost effectiveness, relative ease of
operation, and design for unattended operation.
Typically, these types of filtration plants are used to
treat small community water supplies and for a
variety of special applications, including:
Emergency supplies
Recreational areas
State parks
Construction sites
Ski areas
Military installations
Other areas not served by municipal supplies
Package plants can differ widely with regard to
design criteria, and operating and maintenance
considerations.
41
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Table 4-4. Estimated Costs For Supplementing Surface Water Treatment By Slow Sand Filtration ($1978)
Plant Capacity,
Category MGD
1 0.026
2 0.068
3 0.166
4 0.5
5 2.5
6 5.85
7 11.59
Average Flow,
MGD
0.013
0.045
0.133
0.40
1.30
3.25
6.75
Capital Cost,
$1,000
145
273
508
603
1,213
2,573
4,782
Operation and Maintenance Costs
$1 ,000/yra
0.8
1.6
5.1
9.0
20.5
38.0
62.3
0/1 ,000 gal
17.9
9.9
10.5
6.2
4.3
3.2
2.5
Total Cost,
0/1 ,000 gal
377.8
205.1
133.4
54.7
34.3
28.7
25.3
rป sl?w *fd f!lters ** c'earwe" storaae. Sand filters in Categories 1 through 3 are constructed of concrete and are
covered. Sand filters in Categories 4 through 7 are constructed of membrane-lined earthern berms and are uncovered
1 MGD - 0.044 m3/s; 1,000 gal = 3.78 m*.
Source: U.S. EPA (1979).
4.4.1 Selecting a Package Plant System
Package plant systems are most appropriate for plant
sizes ranging from 94.6 to 22,710 m3/day (25,000 to
6,000,000 GPD). Common treatment elements in a
package plant are chemical coagulation, flocculation,
settling, and filtration.
Some package plant manufacturers have used new
treatment technologies to improve their product's
performance, for example, tube settlers, adsqrptive
clarifiers, and high flow rate mixed- or dual-media
filters. Package plants employing innovative
technologies sometimes encounter regulatory
barriers, because many existing State design
standards recognize only conventional treatment
processes.
Influent water quality is the most important
consideration in determining the suitability of a
package plant application. Complete influent water
quality records should be examined to establish
turbidity levels, seasonal temperature fluctuations,
and color level expectations. Both high turbidity and
color may require coagulant dosages beyond many
package plant design specifications. In cases of
consistently high levels of turbidity and color, the
package plant capacity must be down-rated or a
larger model selected. Where turbidity exceeds 100 to
200 NTU, presedimentation may be required as a
pretreatment. Pilot tests may be necessary to select a
package plant for more innovative designs using high
flow rates and shorter detention time unit processes.
4.4.2 System Description and Design
Considerations
The three basic types of package plant filter systems
areconventional package plants, tube-type clarifi-
cation package plants, and adsorption clarifier
package plants.
Conventional Package Plants
Conventional package plants are manufactured by
several firms to a variety of specifications. As their
name indicates, they contain the conventional
processes of coagulation, flocculation, sedimentation,
and filtration. Typical design standards for these
units are:
20- to 30-minute flocculation detention time
2-hour sedimentation detention time
Rapid sand filters rated at 1.34 L/sec/m2 (2
GPM/ft2)
Tube-Type Clarifier Package Plants
A flow diagram of a tube-type clarifier package plant
is illustrated in Figure 4-8. This type of plant has two
versions with different capacity ranges; one version
can treat from 0.63 to 6.3 L/sec (10 to 100 GPM) and
the other, equipped with dual units, can treat from
12.6 to 88.3 L/sec (200 to 1,400 GPM).
In these package systems, the disinfectant, primary
coagulant, and polyelectrolyte coagulant aid are
added before the influent enters the flash mixer.
After the flash mixer, the water enters the
flocculation chamber where mechanical mixers
gently agitate the water for 10 to 20 minutes
depending on the flow.
The flocculated water then enters the tube settlers,
which consist of many 2.5-cm (1-in) deep, 99-cm (39-
in) long split-hexagonal-shaped passageways. The
large surface area of the many 2.5-cm (1-in) deep tube
settlers achieves an effective clarification overflow
rate of less than 6.1 m3/day/m2 (150 GPD/ft2).
Adequate clarification is attained with less than 15-
minute detention times.
The clarified water then enters a gravity flow mixed-
media filter. A constant filtration rate is maintained
42
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Effluent
Connection
Clear Water
and
Backwash
Storage
To Service""""^
Backwash
Connection
Figure 4-8. Flow diagram of a package plant.
by a low-head filter effluent pump discharging
through a float operated, level control valve. After a
preset headloss is reached, backwashing of the filter
is initiated automatically. A manual backwash cycle
can be initiated any time (if desired). Settled sludge
from the tube settlers is flushed during the
backwashing cycle. Combining backwashing and
tube settler flushing simplifies operations and
reduces operator skill requirements.
Adsorption Clarifier Package Plant
The adsorption clarifier package plant is a new
concept developed in the early 1980s. It uses an
upflow filter with low density plastic bead media
(called the adsorption clarifier) followed by a mixed-
media filter to complete the water treatment. The
adsorption clarifier replaces the flocculation and the
sedimentation basins, combining flocculation and
sedimentation into one step. A typical example is
contained in Figure 4-9.
While passing through the adsorption media, the
coagulant and water are mixed, contact flocculated,
and clarified. The mixing intensity, as measured by
the mean temporal velocity, ranges from 150 to 300
per second. Flocculation is accomplished through
turbulence as the water passes through the
adsorption media. In addition, flocculation is
enhanced by contact between the flocculated
materials and the floe-coated media. Turbidity is
reduced through adsorption of the coagulated and
flocculated solids onto the adsorption media and the
previously adsorbed materials. The adsorption
clarifier can achieve 95 percent or greater removal at
6.8 L/sec/m2 (10 GPM/ft2). This highly efficient
clarification method results in extremely compact
designs.
Adsorption clarifiers are cleaned by a combination of
air scouring followed by water flushing. The air
scouring starts the cleaning process for the plastic
media used in the clarifier. Adsorption clarifier
cleaning is initiated more frequently than filter
backwashing because more solids are removed by the
clarifier. The clarifier cleaning process is
automatically initiated either by a timer or a
pressure switch that continuously monitors headloss
across the adsorption media.
The air introduced under the adsorption media
causes a vigorous scrubbing action. The scrubbing
action dislodges solids, which are washed away by
the flow of the incoming water. Flushing is generally
timed to occur between every fourth and eighth hour.
Complete cleaning of the adsorption media is not
desired because performance is enhanced by some
residual solids. Diagrams illustrating the various
cycles of an adsorption clarifier package plant are
contained in Figure 4-10.
4.4.3 Operation and Maintenance
Package plant operation is simplified by automated
features, and maintenance requirements are well
documented in manuals. However, the operator needs
to be well acquainted with water treatment
principles and the plant manual, and should have
attended a comprehensive training session. ,
Common automated devices found in package plants
are effluent turbidimeters and chemical feed
controls. The effluent turbidimeters and fail-safe
controls are built into many plants to ensure that the
finished water does not exceed set turbidity levels.
Automated chemical feed systems are especially
appropriate for plants without full-time operators or
with highly variable influent characteristics.
Typical plant operator and maintenance manuals
contain operating principles, methods of establishing
proper chemical dosages, operating instructions, and
troubleshooting guides.
Periodic visits by the manufacturer to make
adjustments to the plant and inspect the equipment
43
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Surface Wash Valve
Backwash
Pump
Filter Underdrain
Influent
Control Panel
Aquaritrolฎ
Mixed Media Filter
Adsorption Clarifier
Air Scour
Distribution i
Figure 4-9. Adsorption clarifier package plant (courtesy of Microfloc products).
operations and performance are recommended. The
first visit should be no more than 6 months after
initial operation; the next should follow in another 6
months. Subsequently, annual visits should be
sufficient.
4.4.4 System Performance
According to extensive manufacturer evaluations,
system performance, in general, is improving
because of better equipment, more highly skilled
operators, and greater surveillance by regulators.
Table 4-5 contains summaries of evaluations at three
plants in Oregon. All finished water reported in the
table had less than 0.53 NTU turbidity.
4.4.5 System Costs
Table 4-6 presents capital, operating, and
maintenance costs for package plants. Costs range
from $0.14 to $2.50/m3 ($0.52 to $9.44/1,000 gal).
4.5 Diatomaceous Earth Filtration
Diatomaceous earth filtration, also known as precoat
or diatomite filtration, relies on a layer of
diatomaceous earth about 0.3-cm (1/8-in) thick placed
on a septum or filter element. The septums may be
placed in pressure vessels or operated under a
vacuum in open vessels. A schematic diagram of a
typical pressure system is shown in Figure 4-11.
Diatomaceous earth filters are effective in removing
cysts, algae, and asbestos. For water supplies with
low amounts of suspended solids, they have lower
initial costs than conventional rapid sand filtration
systems. Diatomaceous earth filters are especially
effective against Giardia cysts.
The difficulties in maintaining a perfect film of
diatomaceous earth as the filtering layer have
discouraged wide usage of diatomaceous earth filters
for potable water treatment, except in favorable
circumstances (i.e., waters with low turbidity and low
bacterial counts). Consequently, while this
technology has been used extensively in specialized
applications, such as swimming pools, it is a "new"
technology for water supply treatment.
Diatomaceous earth filter plants have been chosen
for projects with limited initial capital, and for
emergency or standby capacity to service large
seasonal increases in demand. Since these systems
are most suitable for applications where influent is
low in turbidity and bacterial counts, water supplies
presently receiving just chlorination may consider
using diatomaceous earth to meet the filtration
requirements of the SWTR.l
1 "Ten State Standards" refers to the publication: Recommended
Standards for Water Works: Policies for the Review and
Approval of Plans and Specifications for Public Water
Supplies, 1982, by Committee of the Great Lakes/Upper
Mississippi River Board of Sanitary Engineers, published by Health
Education Service, P.O. Box 7283, Albany, New York 12224.
44
-------
Operating
Water Level
Media
Retainer
Air
Inlet'
Influent
\J
Filtration Mode
Filter Effluent
Flush Cycle
Water Level
Media
Retainer
Waste
Air
Inlet
Influent
Collection Trough
L ฐ ' ' al'
-|.' Adsorption', :*l.
ป' V: ' 1 Media: ;,.""J'
f>- Ex'panded for .1
P ซ' Cleaning *. Jป
A '..''... .-.. . . .
tp w 4- Air afid0Water-'i"
'-^nQ-'- flow',:"1 J
\J
Media
Retainer"
Waste and
Overflow
Connection
Air
Inlet
Influent
Backwash
Inlet
Adsorption Clarifier Flush Cycle,
Filter
Effluent
Wash Cycle
Water Level
Surface Wash
Inlet
"1 1 i
Collection Trough
"-.- >'
"(* Adsorption 4
" V''.. Media; '; o-'S
-------
Table 4-5. Summary Of Results Of Adsorption Clarification Package Plants
Location
Corvalis, OR
Rainier, OR
Newport, OR
Rates, GP
Adsorption
Clarifier
5 (12.2)
10 (24.4)
8 (19.5)
10 (24.4)
15 (36.6)
20 (48.8)
10 (24.4)
15 (36.6)
20 (48.8)
M/ft2 (mm)
Mixed-Media
9 (22.0)
10 (24.4)
7(17.1)
5 (12.2)
5 (12.2)
5 (12.2)
5 (12.2)
7.5 (18.3)
10 (24.4)
Water Temp.,
ฐF (ฐC)
68 (20)
68 (20)
57 (14)
41 (5)
41 (5)
41 (5)
45(7)
45(7)
45(7)
Color Units
0
0
0
30
30
30
8
8
9
Influent
100
46
103
9.3
8.2
8.1
19
15
9
Turbidity, NTU
. .
Aosorption
Clarifier
Effluent
8
10
21
1.4
1.6
1.7
4.3
3.7
3.8
Mixed-Media
Effluent
0.27
0.52
0.30
0.24
0.22
0.20
0.13
0.11
0.23
1 GPM/ftZ - 0.679 L/sec/m2-
Source: Mtoroftow Products Group.
Tablo 4-6. Estimated Costs for Supplementing Surface Water Treatment by Complete Treatment Package
Plants ($1978)
Plant Capacity,
Category MOD
1
2
3
4
5
6
0.026
0.068
0.166
0.50
2.50
5.85
Average Flow,
MGD
0.013
0.045
0.13
0.40
1.30
3.25
Capital Cost,
$1,000
278
295
428
773
1,770
2,952
Operation and Maintenance Costs
$l,000/yra
12.2
15.9
42.4
75.1
137
274
(f/1,000 gal
255.2
87.5
89.2
51.4
29.0
23.1
Total Cost,
0/1 ,000 gal
944.5
277.4
195.1
113.6
72.8
52.4
ซ Processes include chemical feed (alum, soda ash, and polymer); complete treatment package plant (flocculation, tube
settling, and mixed media filtration); backwash storage/clearwell basins; and sludge dewatering lagoons. A separate
pumping station is used to transmit unthickened sludge to the sludge dewatering lagoons in Categories 5 and 6. Sludge
pumping is included in the cost of the package plant in Categories 1 through 4.
1 MGD * 0.044 m3/sec; 1,000 gallons = 3.78 m3
Source: U.S. EPA (1979).
4.5.1 System Design
The majority of the minimum design criteria in the
Ten State Standards for diatomaceous earth systems
meet the SWTR. However, two design criteria in
addition to the Ten State Standards are necessary to
meet current regulations:
1. The minimum amount of filter precoat should be
1 kg/m2 (0.2 Ib/ft2) to enhance Giardia cyst
removal.
2. The minimum thickness of the precoat should be
increased from 0.3- to 0.5-cm (1/8- to 1/5-inch)
(found to be more important than the size
graduation of the diatomaceous earth), also to
enhance Giardia cyst removal.
An additional recommendation is to use coagulant
(alum or a suitable polymer) to coat the body feed to
improve removal rates for viruses, bacteria, and
turbidity. Adding these chemicals to the coating does
not improve Giardia removal rates.
4.5.2 Operation and Maintenance
Operating a diatomaceous earth filter requires:
Preparation of filter body feed (diatomaceous
earth) and precoat
Verification of proper dosages
Periodic backwashing
Disposal of spent filter cake
Periodic inspection of filter septum for
cleanliness and damage
Verification of the effluent quality
A common operating difficulty is maintaining a
complete and uniform thickness of diatomaceous
earth on the filter septum.
In some cases, alum precoatingof the diatomaceous
earth can improve performance. Typical alum doses
range from 1 to 2 percent by weight (1 to 2 kg/100 kg
of diatomaceous earth applied). Typical precoats of
diatomaceous earth of 0.49 to 0.98 kg/m2 (0.1 to 0.2
lb/ffc2) are applied to prepare the filter. These filters
also require a continuous supplemental body feed of
diatomite because the filter is subject to cracking. If
46
-------
Filtrate
Raw
Water
Source
Precoat
Drain
Line
To
Drain
Filter
Feed
Pump
Backwash
Drain Line
Figure 4-11. Typical pressure diatomaceous earth filtration system.
the filter has no body feed, there will be rapid
increases in headless due to buildup on the surface of
the filter cake. Body feed rates must be adjusted for
effective turbidity removal. Diatomaceous earth
filters do not need a filter-to-waste cycle, because of
the precoating process.
Regular cleaning will maintain up to 95 percent of
the filter septum area available for filtration after
100 filter runs. The filter cake drops off the septum
during an interruption in flow, such as occurs during
cleaning. During operating interruptions, clean
diatomaceous earth and filter water should be used to
recoat the filter to reduce the potential for passage of
pathogens. .
Filter runs typically range from 2 to 4 days. The rate
of the body feed and the diatomite media size are
critical in determining the filter run length. Shorter
filter runs will minimize filtered water odor and taste
problems stemming from the decomposition of
organic matter trapped in the filter.
Vacuum diatomaceous earth filters are a variation of
this technology that offer the advantages of visibility
during backwashing and of not requiring pressure
vessels. Their primary disadvantage is that they run
an increased risk of the release of gases in the filter
cake that shorten filter runs.
4.5.3 System Performance
Diatomaceous earth filtration units perform well on
waters with low influent turbidity and bacteria
levels. Effective removals of viruses and Giardia
range up to 99.95 percent and from 99 to 99.99
percent, respectively.
Some researchers have found that diatomaceous
earth filters, with added operational steps, are
effective in removing polioviruses. The additional
steps include coating the filter surface with filter aid
or mixing the filter influent with a cationic polymer.
The limited research found:
No viruses were detected in 11 effluent samples
from a 12-hour run of a filter coated with 1 mg of
cationic polymer per gram of diatomaceous earth.
Only 1 of 12 effluent samples contained viruses
during the operation of another filter coated with
1 mg of cationic polymer per gram of
diatomaceous earth.
ป No viruses were detected in the effluent in 12
samples from another 12-hour run of an uncoated
filter, and the influent was mixed with 0.14 mg of
cationic polymer per liter of water.
4.5.4 System Costs
Costs for diatomaceous earth filters are provided in
Table 4-7. Costs range from $0.09 to $1.78/m3 ($0.35
to $6.73/1,000 gal) depending on plant size.
47
-------
Table 4-7. Estimated Costs for Supplementing Surface Water Treatment by Direct Filtration Using
Diatomaceous Earth ($1978)
Plant Capacity,
Category MGD
1
2
3
4
5
6
7
8
9
10
0.026
0.068
0.166
0.50
2.50
5.85
11.59
22.86
39.68
109.90
Average Flow,
MGD
0.013
0.045
0.130
0.40
1.30
3.25
6.75
11.50
20.00
55.50
Capital Cost,
$1,000
221
285
374
570
1,573
2,538
4,433
10,713
15,982
37,733
Operation and Maintenance Costs
$1,000/yra
6.0
8.0
20.0
30.4
128
214
369
762
1,165
2,730
0/1 ,000 gal
127.0
43.7
42.2
20.8
27.0
18.0
15.0
18.1
16.0
13.5
Total Cost,
0/1 ,000 gal
672.9
227.2
134.7
66.6
66.0
43.1
36.1
48.1
41.7
35.4
ซ Processes include pressure diatomaceous earth filtration units, diatomaceous earth feed equipment; filtered water storage
clearwell; and sludge dewatering lagoons. A separate administration, lab, and maintenance building is included in
Categories 5 through 10. Sludge pumps are included in the package facilities used in Categories 1 through 4, but separate
sludge pumping stations are included in Categories 5 through 10. Categories 8 through 10 include sludge holding tanks,
sludge dewatering with filter presses, and hauling of dewatered solids to landfill disposal.
1 MGD - 0.044 m3/sec; 1,000 gallons = 3.78 m3
Source: U.S. EPA (1979).
4.6 Other Filtration Systems
This section covers the "emerging technologies" of
membrane and cartridge filtration. Since there are
limited operational data concerning these
technologies, pilot and case studies assume more
importance.
4.6.1 Membrane Filtration
Membrane filtration, also known as ultrafiltration, is
extremely compact and does not require coagulation.
Membrane filters use hollow fiber membranes to
remove undissolved, suspended, and emulsified
solids. The membranes are typically able to exclude
all particles greater than 0.2 microns from the water
stream.
Membrane filters are typically used for specialized
applications that require highly purified water, and
often serve as:
Pretreatment processes for reverse osmosis
Pretreatment to remove colloidal silica from
boiler feed water
Treatment for drinking water supplies with
influent turbidities of 1NTU or less, and fouling
indexes of less than 10
Typically, ground water and surface water of high
clarity have fouling indexes of less than 10. Fouling
of the hollow fibers by turbidity is the major problem
preventing widespread application of this technology.
Traditional membrane filters introduce feed water to
the inside of the hollow fiber membrane, with the
permeate or filtrate emerging on the outside of the
membrane. State-of-the-art membrane filters are
designed to pass influent to either the inside or
outside of the membrane. The hollow fiber
membranes are contained in a pressure vessel or
cartridge and operate over a pressure range of 10 to
100 psi. Contaminants collect on the end of the hollow
fiber and are discharged to waste by reversing the
water flow. A sample membrane system is shown in
Figure 4-12.
Periodic backflushing and occasional chemical
cleaning is necessary to maintain the membrane
fibers. Treatment of the flush water containing solids
requires separate coagulation and clarification. The
clarified flush water is either recycled or discharged
after treatment. The sludge collected from this type of
system is typically dried and disposed of in a landfill.
Customarily, 90 percent of the feed water is collected
as permeate; the other 10 percent is discharged along
with the contaminants. These filters can be designed
to exclude particles larger than 0.01 um. Unlike
reverse osmosis, this process does not exclude
inorganic salts and electrolytes. Hollow fiber filters
with the finest membranes remove bacteria, Giardia,
and some viruses.
The hollow fiber membranes vary in size and porosity
and in their corresponding effectiveness, yet all
membrane filter fibers are sensitive to influent
concentrations of suspended and colloidal solids.
Specifically, the flux level (the volume of permeate
produced per unit area of membrane filter per day)
and the flux stability are affected by:
Quality of the influent
Filter cycle duration
Quality of the backwashing water
In general, influent water with a fouling index of less
than 10 will permit filter cycles of 8 hours with a 10
48
-------
Filtered Water
Raw Water
Clarified
Recycle
Discharge
-M-
Hollow Fiber Membranes
Membrane
Cartridge
Chemical
Coagulant
1
Membrane
Cleaning
Solution to
Sewer
Air Inlet for
Backwashing
Sludge
Backflush
Wastewater
Backflush
Clarifier
Figure 4-12. Flow diagram of membrane filtration system.
49
-------
percent reduction in flux. In between backflushes, a
high degree of the original fiber porosity can be
retained with fast forward flushes of the influent,
which can then be routed to waste. After two to three
fast forward flushes, a full backflush is required to
restore the initial flux level.
Application Considerations
Membrane filtration is an attractive option for small
systems because of its small size and automated
operation. Because it is best suited for small systems,
many typical membrane systems are skid-mounted
units. The diagram in Figure 4-13 illustrates this
type of membrane system, and includes the following
elements:
Hollow membranes in cartridges
Automatic and manual valves for backwashing
and unit isolation
Plow meters
Pressure gauges
Integral supply pump
Control panel
Three other necessary components of membrane
systems are (1) a separate supply pump and
interconnecting piping for plants with multiple filter
units, (2) storage tanks and chemical feed pumps for
membrane cleaning solutions, and (3) filtered water
storage with chlorination capacity.
System Performance
System performance data for membrane filter
systems include data on Giardia, coliform, and
turbidity removal. The following results were from
tests conducted at Colorado State University's
Department of Pathology.
One test evaluated Giardia removal effectiveness for
one manufacturer's hollow membrane unit. The 0.2
um membrane filters were found to be 100 percent
effective in removing Giardia cysts at influent
concentrations of 1,100 cysts per liter. In addition,
researchers found that the unit's "radial pulse"
cleaning mechanism was effective in preventing
membrane fouling and caused no reductions in
Giardia cyst removal.
Coliform removal was evaluated for a manufacturer's
hollow membrane unit. This evaluation used water
seeded vtlkhEscherichia coli bacteria ranging from 20
to 30 million organisms per 100 mL. During a 130-
minute test run, the effluent contained less than 1
coliform bacteria per 100 mL. No membrane
breakthrough was experienced during three test
runs.
Turbidity removal was also evaluated by Colorado
State University. Prior to development of
intermittent, air-assisted membrane cleaning,
membrane filters would experience rapid loss of flux
or flow rates at medium or high turbidity levels. The
"radial pulse" system permits cleaning units without
such reductions in flux rates. The test results of this
system found that:
Turbidity up to 30 NTU created from the
introduction of bentonite clay were reduced to 0.2
NTU.
Actual field tests with 190 NTU influent
turbidity resulted in effluent with 0.6 NTU.
Tests with effluent ranging from 2.4 to 3.0 NTU
resulted in effluent of 0.25 to 0.57 NTU.
Operation and Maintenance
Effective cleaning is essential for the successful
operation of a membrane filter system. It is achieved
by backflushing and chemically cleaning the hollow
fibers to prevent fouling. Chlorine is sometimes
added to the backflush to destroy bacteria.
Backflushing and chemical cleaning restore the
original porosity and flux rates; permitting the filter
to operate indefinitely.
Chemical cleaning is routinely done only once a
week, unless there are unusually high levels of
suspended solids in the influent. The cleaning
solution is a mixture of caustic-based detergent and
hydrogen peroxide disinfectant. Membranes of water
systems with iron in their influent may require
cleaning with hydrochloric acid. Methods for disposal
of the spent cleaning solutions must comply with all
applicable regulations.
One manufacturer lias developed the self-cleaning
"radial pulse" system. This cleaning innovation
periodically injects gas under high pressure into the
center of the hollow fibers. The specially designed
membrane expands as the gas passes through, thus
removing materials fouling the membrane. Radial
pulse cleaning prolongs the effectiveness of the
membrane and thus extends the time between
chemical cleanings.
Another manufacturer has developed a self-cleaning
hollow-fiber membrane filter system that uses a flow
of water from the outside to the inside of the fibers to
clean the membranes. A water stream is tangentially
introduced outside of the fiber. The filter system then
collects filtrate in the interior of the fiber, and the
rejected stream of concentrate is either recycled or
discharged. Continuous recycling permits extremely
high filtered water recovery rates of up to 99 percent.
This system uses a more porous fiber than the more
traditional inside-to-outside design that is only about
70 percent porous with a 0.2 um nominal pore size.
The higher porosity of these membranes allow for
50
-------
Non-Corrosive Piping System
Chemical Resistant Membranes
Clean in Place System
Stainless Steel
Skid Mounted
Frame
Microprocessor Controls for
Radial Pulse, CIP System, and
Membrane Integrity Check
Stainless Steel
Centrifugal Pumps
Prefiltration and Pretreatment System
When Required
Figure 4-13. Skid-mounted membrane filtration assembly.
treatment of influent with higher suspended solids
concentrations. These filters will meet turbidity
standards, exclude all Giardia cysts, and remove
coliform and other bacteria, but will not remove
viruses.
System Costs
Cost data for membrane filter units for small systems
are contained in Table 4-8. The total costs range from
$0.37/m3 for the largest systems to $1.21/m3 for the
smallest systems ($1.38 to $4.56/1,000 gal).
Potential Problems
The primary application concerns with membrane
filters are membrane failure and organics removal
effectiveness. Pilot testing is needed to qualify each
application, because of the lack of experience with the
process. Membrane failure is a major concern because
the membrane is the only barrier between potentially
pathogenic microbial contaminants and the finished
water. Most other treatment systems have multiple
barriers to pathogenic breakthrough. To guard
against this potential problem, some membrane
systems include features that trigger an operational
shutdown or activate an alarm. One manufacturer
includes a manual or automatic device to verify the
integrity of each membrane.
The second concern is that membrane filters may not
be effective in removing certain organic components.
Larger membranes of about 0.2 urn will not
effectively remove organic materials contributing
color. Smaller inside-to-outside membranes of about
0.1 um will remove smaller particles, but when
influent contains organic materials that contribute to
color, such as humic or fulvic acids, supplemental
treatments may be necessary.
Pilot testing of membrane systems is generally
necessary to establish design criteria and operating
parameters. The paucity of available data
necessitates pilot testing. The only known membrane
filter used for water supply treatment is in Keystone,
Colorado. Most membrane experience has been in the
medical and electronic fields where tap water is
treated for special high purity applications.
4.6.2 Cartridge Filtration
Cartridge filters are considered an emerging
technology suitable for removing microbes and
turbidity in small systems. These filters are
mechanically simple but manually operated, so they
could be expensive to operate. They also require low
turbidity influent. Cartridge filters use ceramic or
polypropylene microporous filter elements that are
packed into pressurized housings. They operate by
the physical process of straining the water through
porous membranes and can exclude particles down to
0.2 um. The pore sizes that are suitable for producing
potable water range from 0.2 to 1.0 um. The ease of
operation and maintenance of cartridge filters makes
them very attractive for small systems.
51
-------
Table 4-8. Estimated Costs for Supplementing Surface Water Treatment by Package Membrane Filtration
Plants ($1978)
Category
1
2
3
4
Plant Capacity,
MGD
0.026
0.068
0.166
0.50
Average Flow,
MGD
0.013
0.045
0.130
0.40
Capital Cost,
$1,000
142
269
503
1,144
Operation and Maintenance Costs
$1,000/yra 0/1 ,000 gal
5.0 105.2
9.8 53.7
26.0 54.7
67.7 46.4
Total Cost,
0/1,000 gal
455.6
226.8
179.2
138.4
ป Processes include a complete package membrane filtration unit, clean/veil storage, and sludge dewatering lagoons with
liquid sludge hauling.
1 MGD = 0.044 m3/sec; 1,000 gallons = 3.78 m*
Source: U.S. EPA (1979).
One manufacturer uses single microporous ceramic
filter elements packaged together in a cartridge
housing with flow capacities of up to 1.5 L/sec (24
GPM). This filter has pore sizes as small as 0.2 um
and is suitable for influent with moderate levels of
turbidity, algae, and microbial contaminants. The
clean filter pressure drop is about 3.2 kg/cm2 (45 psi),
while the pressure drop during cleaning reaches
about 6.2 kg/cm2 (88 psi).
Application Considerations
Roughing filters, for pretreatment prior to cartridge
filtration, are sometimes necessary to remove larger
suspended solids and prevent the rapid fouling of the
cartridges. Roughing filters can be rapid sand filters,
multimedia filters, or fine mesh screens.
Prechlorination is recommended to prevent surface-
fouling microbial growth on the cartridge filters and
reduce microbial pass-through. Except for chlorine,
no chemical additions are necessary ./There is a lack
of data concerning the effectiveness oif cartridge
filters for viral removal.
Operation and Maintenance
These systems are operationally simple, apart from
cleaning and membrane replacement. There is no
need for skilled personnel; personnel are necessary
only for general maintenance. Ceramic membranes
may be cleaned and used for repeated filter cycles.
Polypropylene cartridges become fouled relatively
quickly and must be replaced with new units.
In one manufacturer's unit, cleaning the ceramic
cartridge filters entails cleaning each vertical filter
element with a hand-operated hydraulically driven
brush that fits over the element. Some
manufacturers use disposable polypropylene filter
elements in multi-cartridge stainless steel housing to
avoid the cleaning procedures. This type of unit is
available with capacities ranging from 0.13 to 45.4
L/sec (2 to 720 GPM). The primary disadvantage of
the disposable polypropylene membrane is that it can
only be cleaned once before disposal. Manufacturers'
guidelines state that these filters have service
periods ranging from 5 to 20 days with influent
turbidities of 2 NTU or less, depending on the pore
size of the filter. Another manufacturer incorporates
particles of silver into the ceramic filters to prevent
bacterial growth.
4.7 Selecting the Appropriate Filtration
Treatment System
This section discusses considerations in selecting an
appropriate filtration technology. First, it discusses
the steps involved in selecting any filtration system.
Next, it discusses the role and objectives of pilot
studies, flocculation and sedimentation studies, and
filtration studies in selecting the specific operating
characteristics for selected filtration technologies.
4.7.1 Steps in an Evaluation
The first step in selecting a new water treatment
technology is to review all raw water quality data to
establish the requirements for the potential
alternatives. Next, a list of alternative technologies
should be compiled. The considered alternatives must
be able, in theory or as proven under similar
conditions, to solve the problems identified with the
current filtration system. Once the potential
alternatives are selected, one must determine the
necessity of pilot or bench-scale tests. If the desired
performance of one or more of the alternatives is in
doubt, testing is appropriate. (Testing is always
useful if time and budget allow.) Otherwise,
literature surveys, bench-scale studies, or pilot test
results can be used to derive performance
characteristics and design considerations for each
alternative. For small systems, the alternatives for a
particular application may include slow sand filters,
package plants, diatomaceous earth filtration, or
membrane filters.
Following this initial selection, the basic process
concerns for the various alternatives should be
identified, including the following:
Turbidity removal performance
Color removal performance
Giardia removal performance
Cleaning cycle frequency
Necessary chemicals
52
-------
Chemical dosages
Requisite operational skill
Applicable regulatory standards
Necessary sludge management
In the next stage, conceptual designs and
preliminary layouts for selected alternatives are
prepared. Also, construction costs for the alternatives
should be developed. One should compare all
alternatives for reliability, simplicity, flexibility, and
ease of implementation, to select the appropriate
application. Finally, one can proceed with the final
design.
4.7.2 Need for Pilot Studies
A pilot study is a broad term used for small-scale
testing of either complete water treatment processes
or merely individual processes. Pilot studies are used
to evaluate alternate treatment options and
operating techniques. Pilot tests can be relatively
short or very long in duration. For example, time
requirements for pilot tests of rapid filtration are
about 2 weeks; for slow sand filtration, 2 to 4 months;
and for corrosion inhibitors, up to 6 months. These
tests maybe continuous or intermittent. The longer,
more involved tests are more expensive. To avoid
unnecessary costs, pilot tests should have clearly
delineated objectives to prevent including extraneous
evaluations. Yet they should be performed long
enough to encounter the full range of raw water
conditions and process design parameters.
Simple jar tests are usually sufficient to evaluate
procedures for traditional coagulation, flocculation,
sedimentation, and filtration processes. However,
new or innovative technologies usually require the
more extensive pilot tests.
Pilot tests have been endorsed by field experts for
many years to assess precise design specifications,
operational recommendations, and chemical
applications procedures. In addition, pilot tests are
required for some technologies to adjust individual
processes to specific local water conditions. Pilot tests
are also used to identify unforeseen design and
operating problems, demonstrate operation to
regulatory authorities, and develop better
information concerning capital and operating costs.
Pilot studies may also be a prerequisite to obtaining
conditional regulatory approval. They are especially
needed for new and emerging technologies and for
accepted technologies with innovative elements, such
as tube settlers or mixed-media filters.
Pilot studies are important to ensure the suitability
of a small-scale prototypical plant for a particular
application. This is especially true for raw water with
difficult treatment aspects or poor quality, such as
highly polluted water with high concentrations of
organics, iron, manganese, and algae. Pilot tests are
also particularly necessary for plants that use new
short-detention and high-rate processes or where
direct filtration is being considered.
4.7.3 Flocculation and Sedimentation
Studies
Full-scale flocculation and sedimentation studies are
necessary because it is difficult to extrapolate the
performance of pilot-scale flocculation and
sedimentation tanks to full-scale plants. Since
flocculator efficiency is directly related to volume,
smaller floeculators perform more efficiently than
their full-scale-counterparts. Consequently, pilot
flocculation studies do not provide results applicable
to full-scale facilities.
Traditional sedimentation basins present even
greater extrapolation problems. Since small-scale
versions cannot duplicate the process of traditional
basins, which are generally 2.7 to 4.5 m (9 to 15 ft)
deep, full-scale sedimentation studies are also
necessary. However, tube settlers can be evaluated
on a pilot scale. Figure 4-14 shows a sample test
module for a settling tube. These pilot-scale units can
be suspended from existing basin walls or collection
launders and operated at various flow rates.
4.7.4 Filtration Studies
Filtration studies can successfully employ pilot tests.
They are necessary for plants considering direct
filtration and very useful for plants with unusual raw
water characteristics. One of the problems that can
be identified and evaluated with pilot tests is the
presence of diatoms (filter clogging algae) that do not
show up as high turbidity, yet can clog filters.
Another such problem involves the presence of paper
fiber, a common situation for water intakes below
paper plant effluent outfalls. These fibers also may
not show up as high turbidity but present filter
clogging problems. Filtration pilot tests establish
whether the presence of paper fiber or diatoms will
cause problems.
Side-by-side pilot filters will provide useful
comparisons of different filter media designs being
considered for a particular application. A schematic
of a pilot filter is shown in Figure 4-15. Each of the
three filters can be operated at the same flow rate and
is designed to maintain a constant flow as headloss
increases. Pilot filters also include provisions to
measure headloss. Measurements of the filtered
water turbidity and filter headloss are two of the
most useful results of side-by-side pilot tests to
predict filtration efficiency and filter run length.
Pilot tests are especially recommended when high-
rate clarification/filtration processes are being
considered. When such systems have short contact
times, a significant risk of poor performance is
53
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Discharge
2 ft 6 in
Flow Control Valve -
Sample Pump
Discharge Pipe
Support Bracket
ffil
Flow Indicator
Perforated Collection Pipe
Corrugated Fiberglass
Side Panels
4 RO in
Figure 4-14. Tube settling test module.
present if a maladjustment of the system occurs. Due
to the small permissible margin of error, pilot tests of
actual site conditions are necessary to supplement
system designs with extensive operational and pilot
test histories.
Tube Settling Module
54
-------
Mixer Coagulant
Flash Mix,
Constant
Level Tank
_._.-
;;r:
n
in:
->
vivai
ul_.
-_..
L
Overflow to Dra
...Jvrl
Differential
Pressure Gage
Surface
Wash
Backwash
Pressure
Regulator
Figure 4-15. Pilot filter schematic.
55
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-------
Chapter 5
Disinfection and Disinfection By-Products
Disinfection is a process that kills or inactivates
pathogenic microorganisms that occur in drinking
water supplies. Water treatment plants employ both
primary and secondary disinfection. Primary
disinfection achieves the desired level of
microorganism kill or inactivation. Secondary
disinfection ensures a stable residual concentration
of disinfectant in the finished water to prevent
microbial growth in the distribution system.
Chlorine, ozone, chlorine dioxide, and ultraviolet
(UV) radiation are the major primary disinfectants;
chlorine and monochloramine are the major
secondary disinfectants. Some disinfectants can be
used for both processes.
The 1986 Amendments to the Safe Drinking Water
Act (SDWA) require all public water suppliers to
disinfect drinking water. In addition, inorganic and
organic chemicals will be regulated by means of
Maximum Contaminant Levels (MCLs). Since some
disinfectants can produce chemical by-products, the
dual objective of disinfection is to provide the
required level of organism destruction while
remaining within the MCLs for by-products set by
EPA.
Chlorine has been the most widely used disinfectant
in the United States; however, it produces
trihalomethanes (THMs) and other halogenated
organic compounds in drinking water. Because of
this, water suppliers are beginning to utilize other
disinfectants, such as ozone, chlorine dioxide, and
monochloramine, or combinations of disinfectants,
such as ozone followed by chlorine. Research on the
potential by-products associated with these other
disinfectants and combinations of disinfectants is
ongoing.
This chapter discusses the various disinfection
technologies used today as well as the issues relating
to disinfection by-products. Section 5.1 discusses the
objectives of disinfection and Section 5.2, the problem
of disinfection by-products and strategies for their
control. The advantages and disadvantages of the
major disinfectants are discussed in Section 5.3.
Sections 5.4 and 5.5 provide an overview of primary
and secondary disinfection technologies. Appendix B
provides ease histories of water treatment plants
using various disinfection technologies.
5.1 The Objectives of Disinfection
According to the Amendments to the SDWA, all
public water suppliers, including those that rely on
ground water, will have to disinfect drinking water
before distribution. To assure compliance with all
applicable regulations (both current and
anticipated), the specific objectives of disinfection are
to:
Assure 99.9 percent (3 log) and 99.99 percent (4
log) inactivation of Giardia lamblia cysts and
enteric viruses, respectively
Assure control of other harmful microorganisms
Not impart toxieity to the disinfected water
Minimize the formation of undesirable
disinfection by-products
ซ Meet the Maximum Contaminant Levels (MCLs)
for the disinfectants used and by-products that
may form
Disinfection alone, or a combination of disinfection
and filtration, can achieve the minimum mandatory
removals and/or inactivations of 99.9 percent Giardia
cysts and 99.99 percent enteric viruses. Primary
disinfection systems that use ozone, chlorine, or
chlorine dioxide can achieve greater than the above-
stated inactivation of enteric viruses when 99.9
percent inactivation ofGiardia cysts is attained.
Therefore, achieving sufficient Giardia cyst
inaetivation can assure adequate inactivation of both
types of organisms. This is not the case, however,
when using chloramination because it is such a poor
virucide. Pilot-scale tests must be conducted by the
57
-------
utility to assure both inactivations are achieved
when relying on chloramination as a primary
disinfectant.
Conventional treatment, which includes coagulation,
flocculation, sedimentation, and filtration, along
with disinfection, can achieve 99.9 percent
inactivation of Giardia cysts and 99.99 inactivation
of enteric viruses when properly designed and
operated. Direct filtration, slow sand filtration, and
diatomaceous earth filtration systems, each
combined with disinfection, have also achieved these
reductions.
Ground-water systems that apply disinfection to
comply with regulations may have to add filtration if
they contain iron and manganese. Insoluble oxides
form when chlorine, chlorine dioxide, or ozone are
added to these systems; thus, filters would be needed
for their removal. In addition, both ozonation and
chlorination may cause flocculation of dissolved
organics, thus increasing turbidity and necessitating
filtration. The presence of such insolubles will
require the use of secondary disinfection after
filtration as well.
5.1.1 CT Values
"CT values" indicate the effectiveness of
disinfectants in achieving primary disinfection. They
describe the attainable degree of disinfection as the
product of the disinfectant residual concentration (in
mg/L) and the contact time (in minutes). For
chlorine, chlorine dioxide, or monochloramine, the
contact time can be the time required for the water to
move from the point at which the disinfectant is
applied to the point it reaches the first customer (at
peak flow). This is the total time the water is exposed
to the chlorinous residual before being used. Ozone,
however, has a short half-life in water; therefore, the
contact time is considered the time water is exposed
to a continuous ozone residual during the water
treatment process only.
The Final Surface Water Treatment Rule (SWTR)
(U.S. EPA, 1989b) states:
Systems may measure "C" (in mg/L) at different
points along the treatment train, and may use
this value, with the corresponding "T" (in
minutes), to calculate the total percent
inactivation. In determining the total percent
inactivation, the system may calculate the CT at
each point where "C" was measured and compare
this with the CTg9.9 value (the CT value
necessary to achieve 99.9 percent inactivation of
Giardia cysts) in the rule for specified conditions
(pH, temperature, and residual disinfectant
concentration). Each calculated CT value (CTcaic)
must be divided by the CTgg.g value found in the
SWTR tables to determine the inactivation ratio.
If the sum of the inactivation ratios, or
:aCTcaic/CT99.9
at each point prior to the first customer where CT
was calculated is equal to or greater than 1.0, i.e.,
there was a total of at least 99.9 percent
inactivation of Giardia lamblia, the system is in
compliance with the performance requirement of
the SWTR.
The final Guidance Manual for the SWTR is expected
to recommend that systems determine contact time
based on the time it takes water with 10 percent of an
approximate tracer concentration (Tin) to appear at
the sampling site at peak hourly flow. For ground
water not under direct influence of surface water, CT
is determined in the same manner using enteric
viruses or an acceptable viral surrogate as the
determinant microorganism, since Giardia cysts will
not be present.
Table 5-1 presents the CT values required to attain 1-
log reductions of Giardia cysts, for four disinfectants.
As shown, lower temperatures require higher CT
values; with chlorine, an increase in pH also
increases necessary CT values. If more than one
disinfectant is used, the percent inactivation
achieved by each is additive and can be included in
calculating the total CT value.
Table 5-1. CT Values for Achieving 90 Percent Inactivation
of Giardia Lamblia
Temperature
Disinfectant
Free
Chlorine8
(2 mg/L)
Ozone
Chlorine
dioxide
pH
6
7
8
9
6-9
6-9
Ch!oraminesb 6-9
(preformed)
ฃ1ฐC
55
79
115
167
0.97
21
1,270
5ฐC
39
55
81
118
0.63
8.7
735
10ฐC
29
41
61
88
0.48
7.7
615
15ฐC
19
28
41
59
0.32
6.3
500
20ฐC
15
21
30
44
0.24
5
370
25ฐC
10
14
20
29
0.16
3.7
250
a CT values will vary depending on concentration of free chlorine.
Values indicated are for 2.0 mg/L of free chlorine. CT values for
different free chlorine concentrations are specified in tables in the
Guidance Manual.
b To obtain 99.99 percent inactivation of enteric viruses with
preformed chloramines requires CT values > 5,000 at
temperatures of 0.5, 5,10, and 15ฐC.
Source: U.S. EPA (1989a).
When direct filtration is included in the water
treatment process, disinfection credit can be taken by
the filtration step for a 2-log inactivation of Giardia
cysts and a 1-log inactivation of viruses. This means
that the primary disinfectant must provide an
additional 1-log inactivation of Giardia cysts and 3-
log inactivation of viruses. In the specific instance of
58
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a conventional treatment process that includes
coagulation, fiocculation, sedimentation, and
filtration, an inactivation credit of 2.5 logs for
Giardia cysts and 2 logs for viruses may be taken.
This means that the primary disinfectant must
provide an additional 0.5 log inactivation of Giardia
cysts but a 2-log inactivation of viruses.
If a water supply system does not use filtration, the
99.9 percent inactivation of Giardia and 99.99
percent inactivation of enteric viruses must be
achieved by the primary disinfecting agents alone.
Table 5-2 presents CT values for the four
disinfectants for achieving 99.9 percent reductions of
Giardia cysts. Table 5-3 presents the CT values for
virus inactivation. Although ground-water
disinfection regulations have not been finalized,
these values will probably apply to systems treating
ground water determined by the State not to be under
direct influence of surface water.
Table 5-2. CT Values for Achieving 99.9 Percent
Inactivation of Giard/'a Lamblia3
Table 5-3. CT Values for Achieving Inactivation of Viruses
at pH 6 Through 9
Temperature
Disinfectant
Free
Chlorine15
(2 mg/L)
Ozone
Chlorine
dioxide
Chloraminesc
(preformed)
pH
6
7
8
9
6-9
6-9
6-9
<1ฐC
165
236
346
500
2.9
63
3,800
5ฐC
116
165
243
353
1.9
26
2,200
10ฐC
87
124
182
265
1.4
23
1,850
15ฐC
58
83
122
177
0.95
19
1,500
20ฐC
44
62
91
132
0.72
15
1,100
25CC
29
41
61
88
0.48
11
750
a These CT values for free chlorine, chlorine dioxide, and ozone will
guarantee greater than 99.99 percent inactivation of enteric viruses.
b CT values will vary depending on concentration of free chlorine.
Values indicated are for 2.0 mg/L of free chlorine. CT values for
different free chlorine concentrations are specified in tables in the
Guidance Manual (U.S. EPA, I989a).
ฐ To obtain 99.99 percent inactivation of enteric viruses with
preformed chloramines requires CT values > 5,000 at
temperatures of 0.5, 5,10, and 15ฐC.
Source: U.S. EPA (1989a).
In the final SWTR (U.S. EPA, 1989b), the CT values
for ozone have been lowered to levels such that the
CT values required to provide 0.5-log inactivation of
Giardia cysts at the higher water temperatures are
below those required to provide 2 or 3 logs of
inactivation of enteric viruses. Consequently, the 2-
or 3-log virus inactivation CT requirement becomes
the pacing parameter for the amount of additional
primary disinfection to be provided by ozone during
conventional treatment, rather than the 0.5-log
inactivation of Giardia cysts.
5.2 Disinfection By-Products
Disinfection by-products are formed by two basic
mechanisms: (1) reduction, oxidation, or
Log
Inac-
tivatior
Free
Chlorine3
Ozoneb
Chlorine
dioxide0
Chlor-
aminesd
2
3
4
2
3
4
2
3
4
2
3
4
Temperature
1 0.5ฐC
6
9 ,
12
0.9
1.4
1.8
8.4
25.6
50.1
1,243
2,063
2,883
5ฐC
4
6
8
0.6
0.9
1.2
5.6
17.1
33.4
857
1,423
1,988
10ฐC
3
4
6
0.5
0.8
1.0
4.2
12.8
25.1
643
1,067
1,491
15ฐC
2
3
4
0.3
0.5
0.6
2.8
8.6
16.7
428
712
994
20ฐC
1
2
3
0.25
0.4
0.5
2.1
6.4
12.5
321
534
746
25 ฐC
1
1
2
0.15
0.25
0.3
-
-
-
214
356
497
a Data adapted from Sobsey (I988a) for inactivation of Hepatitis A
Virus (HAV) at pH = 6, 7, 8, 9, and 10 and at 5ฐC. CT values
include a safety factor of 3.
b Data adapted from Roy et al. (1982) for inactivation of poliovirus at
pH 7.2 and 5ฐC. CT values include a safety factor of 3.
c CT values for chlorine dioxide are based on laboratory studies at
pH 6.0 and 5ฐC (Sobsey, 1988a). CT values include a safety
factor of 3.
d Data from Sobsey (I988a) for inactivation of HAV for pH = 8.0,
5ฐC, and assumed to apply to pH in the range of 6.0 to 10.0.
These CT values apply only for systems using combined chlorine
where chlgrine is added prior to ammonia in the treatment
sequence. CT values given here should not be used for estimating
the adequacy of disinfection in systems applying preformed
chloramines, or applying ammonia ahead of chlorine.
Source: U.S. EPA (19893).
disproportionation of the disinfecting agent and (2)
reaction of oxidation by the disinfectant with
materials already in the water. Reduction, oxidation,
or disproportionation can occur when the disinfecting
agent is added to water. Three examples of this
reaction are the formation of chlorite and chlorate
ions associated with chlorine dioxide, the formation
of dissolved oxygen associated with ozone, and the
formation of chloride ions associated with chlorine.
Oxidation of humic acids (in the water from organic
materials) produces aldehydes, ketones, alcohols, and
carboxylic acids upon the addition of ozone, chlorine,
chlorine dioxide, or potassium permanganate.
Halogenation of organic materials can occur in the
presence of free chlorine to produce trihalomethanes
and other halogenated organics. Chlorine can also
form organic chloramines by reacting with nitrogen-
containing organic compounds (amino acids and
proteins). In addition, monochloramine can produce
organic chloramines in the presence of
organonitrogen compounds.
If bromide ion is present in the untreated water, it
may be oxidized by ozone or chlorine (but apparently
not by chlorine dioxide or chloramine) to form
hypobromous acid, which in turn can brominate
organic materials. Bromine-containing
59
-------
trihalomethanes, for example, are known to form in
this manner.
By-products are also produced when oxidants, like
ozone or chlorine, are used for oxidation purposes
other than disinfection. For instance, breakpoint
chlorination is sometimes used early in the water
treatment process to remove ammonia. In the
presence of organic compounds considered
precursors, the same by-products that are formed
during chlorine disinfection are also formed in this
oxidation step.
As another example, ozone is used as an oxidant to
improve turbidity, color, taste, odor, or
microflocculation; or to oxidize organic compounds,
iron, or manganese. The addition of ozone early in the
treatment process as an oxidant may produce the
same by-products as when added later in an ozone
disinfection process. Potassium permanganate, also
used as an early oxidant, can produce oxidation by-
products as well. The maximum concentration of by-
products is usually produced when oxidants are used
at the point in the treatment process where the
concentration of organics capable of being oxidized is
greatest and/or when large amounts of oxidizing
agents are employed for long contact times.
Even when oxidants are used in the treatment
process for purposes other than disinfection, some
degree of disinfection occurs. In some cases,
especially in treatment processes involving ozone,
chlorine dioxide, and chlorine under lower pH
conditions, the primary disinfection requirement
may be satisfied during the preoxidation procedure
(prior to filtration).
Since oxidation is so important in determining
disinfection by-products, a brief description of the
chemistry of oxidation is provided in Section 5.2.1.
This is followed in Section 5.2.2 by a short overview of
the occurrence and nature of disinfection by-
products. Lastly, Section 5.2.3 discusses the
strategies for controlling disinfection by-products.
5.2.1 The Chemistry of Oxidation
The measure of an agent's ability to oxidize organic
material is its oxidation potential (measured in volts
of electrical energy). Oxidation potential indicates
the degree of chemical transformation to be expected
when using various oxidants. It gauges the ease with
which a substance loses electrons and is converted to
a higher state of oxidation. For example, if substance
A has a higher oxidation potential than substance B,
substance B theoretically can be oxidized by
substance A. Conversely, a particular substance
cannot oxidize another with a higher oxidation
potential. For example, ozone and chlorine can
oxidize bromide ions to hypobromous acid, but
chlorine dioxide cannot. The oxidation potentials of
common oxidants and disinfectants associated with
water treatment are listed in Table 5-4.
Table 5-4.
Oxidation Potentials of Water Treatment
Oxidants
Species
Hydroxyl free radical
Ozone3
Hydrogen peroxide
Permanganate ion
Hypochlorous acida
Chlorine3
Hypobromous acid3
Bromine3
Hypoidous acid
Chlorine dioxide3
Iodine3
Oxygen
Oxidation Potential (Volts)
(OH)-
03
H2O2
MnO4
HOCI
CI2
HOBr
Br2
HOI
CI02(aq)
la
C-2
2.80
2.07
1.76
1.68
1.49
1.36
1.33
1.07
0.99
0.95
0.54
0.40
3Excellent disinfecting agents.
An agent's effectiveness as a disinfectant is not
always related to its effectiveness as an oxidant. For
example, whereas ozone is both a powerful oxidant
and disinfectant, hydrogen peroxide and potassium
permanganate are powerful oxidants but poor
disinfectants. Chlorine dioxide and iodine are weak
oxidants but strong disinfectants.
Oxidation potential does not indicate the relative
speed of oxidation nor how complete the oxidation
reactions will be. Complete oxidation converts a
specific organic compound to carbon dioxide and
water. Oxidation reactions that take place during
water treatment are rarely complete; therefore,
partially oxidized organic compounds, such as
aldehydes, ketones, acids, and alcohols, normally are
produced during the relatively short reaction periods.
The behavior of a disinfectant as an oxidant will also
depend on the particular organic compounds in the
water supply. The level of total organic carbon (TOG)
and the total organic halogen formation potential
(TOXFP), when chlorine is used, indicate the
likelihood that undesirable halogenated by-products
will be formed. Simply monitoring the reduction in
concentration of a particular organic compound,
however, is insufficient to indicate how completely
oxidation reactions are taking place. Unless a
compound is totally oxidized to carbon dioxide and
water, the TOC level may not change; therefore, the
concentrations of oxidation products must also be
measured. The TOXFP and the nonvolatile TOXFP,
referred to as the nonpurgeable TOXFP (NPTOXFP),
indicate the potential for halogenated by-products to
be formed from a specific raw water source.
60
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5.2.2 The Presence of Disinfection By-
products in Drinking Water
EPA has recently surveyed 10 operating water
utilities for the presence of 22 halogenated
disinfection by-products in chlorine-treated water
(Stevens et al., 1987). Table 5-5 presents the
frequency and range of concentrations of those by-
products of greatest concern. Table 5-6 summarizes
the current knowledge of health effects of selected
chlorination by-products. EPA is currently studying
the by-products associated with ozonation. To date,
however, extensive studies of by-products of
treatment with ozone, chloramination, and chlorine
dioxide have not been conducted.
Table 5-5. Occurrence of Chlorinated Disinfection By-
products at 10 Water Utilities3
Number of Range of Values
Compound Locations ug/U
High Confidence
Chloroform 1 0 of 1 0 2.6 to 594
Bromodichloromethane 10 of 10 2.6 to 77
Chtorodibromomethane 10 of 10 0.1 to 31
Bromoform 6 of 10 0.1 to 2.7
Dichloroacetonitrile 10 of 10 0.2 to 9.5
Dibromoacetonitrile 3 of 7 0.4 to 1.2
Bromochloroacetonitrile 7 of 7 0.2 to 4.0
Chloropicrin 8 of 10 0.2 to 5.6
Low Confidence
Chloroacetic acid 6 of 1 0 < 1 0
Dichloroacetic acid 1 0 of 1 0 < 1 0 to > 1 00
Trichloroacetic acid 6 of 10 10 to 100
Trichloroacetaldehyde 10 of 10 10 to 100
(as chloral hydrate)
1,1,1 -Trichloropropanone 1 0 of 1 0 1 0 to 1 00
2-Chlorophenol 0 of 10
2,4-Dichlorophenol Oof 10
2,4,6-Trichlorophenol Oof 10
Qualitative Only
1,1-Dichloropropanone Oof 8
1 ,1 -Dichloro-2-butanone 0 of 8
3,3-Dichloro-2-butanone 1 of 8
1,1,1 -Trichloro-2-butanone 0 of 8
Cyanogen chloride 1 of 7
Dichloroacetaldehyde 0 of 10
Table 5-6. Summary of Health Effects Associated with
Chlorination By-Products
Toxicological
Chemical Class Example Effects
Trihalomethanes Chloroform C, H, RT
Dichlorobromomethane H, RT
Dibromochloromethane H, RT
Bromoform H, RT
Haloacetonitriles Chloroacetonitrile G, D
Dichloroacetonitrile M, G, D
Trichloroacetonitrile G, D
Bromochloroacetonitrile M, G, D
Dibromoacetonitrile G, D
Haloacid derivatives Dichloroacetic acid MD, C, N, OL, A
Trichloroacetic acid HPP
Chlorophenols 2-Chlorophenol F, TP
2,4-Dichlorophenol F, TP
2,4,6-Trichlorophenol C
Chlorinated ketones 1,1-Dichloropropanone M
1,1,1- M
Trichloropropanone
1,1,3,3- M
Tetrachloropropanone
Chlorinated furanones MX M, Cl
Chlorinated aldehydes 2-Chloroacetaldehyde G
Key to Toxicological Effects:
C = Carcinogenic N = Neurotoxic
H = Hepatotoxic OL = Ocular Lesions
RT = Renal Toxic A = Aspermatogenesis
G = Genotoxic HPP = Hepatic Peroxisome Proliferation
D = Developmental F = Fetotoxic
M = Mutagenic TP = Tumor Promoter
MD = Metabolic Cl =ป Clastogenic
Disturbance
Source: Akin et al. (1987).
5.2.3 Strategies for Controlling Disinfection
By-Products
The formation of halogenated by-products is affected
by a number of factors, including the concentration
and types of organic materials present when chlorine
is added, the dosage of chlorine, the temperature and
pH of the water, and the reaction time. EPA has
identified three strategies for controlling formation
of halogenated materials during chlorination:
1 . Remove the by-products after they are formed.
2. Use alternate disinfectants that do not produce
undesirable by-products.
In the first two groups, contaminants are grouped according to
whether current knowledge of health effects indicates a high or low
confidence that adverse health effects exist; in the third group,
current knowledge of health effects is only qualitative to date.
Source: Stevens et al. (1987).
3. Reduce the concentration of organics in the water
before oxidation or chlorination to minimize the
formation of by-products.
61
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The first approach, removing the by-products after
they are formed, can be difficult and costly. Section 6
discusses the treatment technologies available for
organic contaminant removal. The second approach,
using alternative disinfectants, is often the most cost-
effective. The third approach, reducing the
concentrations of organic precursors before adding
chlorine or other oxidants, will provide the highest
quality finished water.
Using Alternative Disinfectants
The second approach, using other than chlorine for
disinfection, is sound if the replacements do not
produce undesirable by-products of their own and if
they perform equally as both primary and secondary
disinfectants. Cost is also a consideration.
Alternative disinfectants currently being considered
by water treatment specialists are chlorine dioxide,
monochloramine, UV radiation, and ozone. Both
ozone and UV radiation do not provide stable
residuals for the distribution system and, therefore,
cannot be used as substitute disinfectants by
themselves.1
Although extensive studies of ozone by-products have
not yet been conducted, many immediate oxidation
products of naturally occurring organic materials
have been identified repeatedly. For the most part,
these by-products are organic aldehydes, acids, and
ke tones. Oxidation of raw water containing bromide
ion will produce hypobromous acid, which can
brominate organic precursors.
Since ozone is employed only for primary
disinfection, a chlorinated compound (chlorine or
chloramine) must be added for secondary disinfection
following ozonation, i.e., to provide a residual for the
distribution system. Consequently, the "secondary"
by-products, those formed by the reaction of chlorine
or chloramine with the primary by-products of
ozonation, become a concern to water treatment
specialists. Although some studies have examined
by-products produced by two-step oxidation
sequences of this type, no compounds have yet been
reported that are not produced by one of the two
oxidation processes acting alone.
For example, preozonation may affect the yields of
THMs formed by subsequent chlorination. Usually
these THM yields are lowered by preozonation, but in
some cases, usually with high ozone dosages or at
high pH values, they can be enhanced. The yield of
10zone has been shown to be an effective secondary disinfectant in
a study of European and Canadian applications. However, four
conditions must be met simultaneously, which were found to coexist
only rarely. The conditions are: (1) water temperatures must be
cool to stow bfotogicai regrowths, (2) water must be free of iron and
ammonia, (3) total organic carbon values must be less than 1 mg/L,
and (4) residence time in the distribution system must be less than
12 hours (Miller at a)., 1978).
chloropicrin (nitrotrichloro-methane) can be
enhanced if chlorination is preceded by ozonation.
Chloramine is known to react with acetaldehyde to
produce acetonitrile under drinking water treatment
conditions. This and other nitriles might be expected
to be produced upon direct chloramination of
ozonated waters containing aldehydes.
Chlorine dioxide is effective as a primary and
secondary disinfectant, but some chlorite ion is
produced. (See Section 5.5.1. for a discussion of the
chemistry of chlorine dioxide.) The use of chlorine
dioxide has been associated with hematological
effects in laboratory animals, which may result from
the production of chlorite and chlorate ions.
Neurological effects have also been identified. Due to
these concerns, EPA currently recommends
maximum total oxidant levels (total chlorine dioxide
plus chlorite ion plus chlorate ion) in finished water
of 1 mg/L. Thus, chlorine dioxide normally can be
used as a primary disinfectant only in very clean
waters, requiring low dosages of no more than 1.2 to
1.4 mg/L.
If a strong chemical reducing agent is added
somewhere in the treatment process after chlorine
dioxide primary disinfection, then chlorine dioxide
and chlorite ions can be reduced to chloride ion. This
would leave only traces of chlorate ion in the water.
This chemical reduction technique will allow much
higher chlorine dioxide dosages to be applied for
oxidation and/or primary disinfection than the 1.2 to
1.4 mg/L currently recommended
At present, granular activated carbon (GAC) or
sulfur dioxide are known to chemically reduce
chlorine dioxide and chlorite ion (but not chlorate
ion) to the innocuous chloride ion. This approach to
the application of chlorine dioxide will be discussed
in more detail in Section 5.4.3.2.
The remaining alternative, monochloramine, is a
weak disinfectant. The very high CT values required
to inactivate 99.9 percent Giardia and 99.99 percent
enteric viruses make monochloramine impractical
for use as a primary disinfectant. Therefore,
monochloramine should only be considered as a
secondary disinfectant.
Minimizing Precursor Concentrations
The third approach for controlling disinfection by-
products is to reduce the concentration of organic
materials before adding chlorine or any oxidant. This
approach will minimize the formation of by-products.
Another option is to use an oxidant that does not
contain chlorine, such as ozone, potassium
permanganate, or hydrogen peroxide, before or
during rapid mix and/or filtration to partially oxidize
organics. This will improve the flocculation and
filtration processes that follow. However, if the water
62
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contains substantial amounts of bromide ion,
brominated organics may be produced.
Because all disinfectants and oxidants produce some
types of by-products, the most efficient approach to
lowering organic by-product precursors is to optimize
physical process treatment steps before adding
oxidants. For example, if alum is used as the
coagulant, it should be recognized that the optimum
pH is about 6.5. In addition, coagulant dosage should
be tested to maximize removal of organics.
It is important to note that extensive oxidation
converts natural organic materials (and some SOCs)
into simpler oxidation products (aldehydes, acids,
ketones, etc.), which are much more biodegradable
than the initial organic materials. Consequently, a
biological treatment step following oxidation can
mineralize the oxidized materials, removing them
from solution, thus avoiding the incorporation of
these by-products into the finished water.
Examples of effective biological treatment steps are
filtration, specifically through sand; dual media
filters; GAC/sand filters (GAC on top of sand); and
postfiltration GAC adsorbers. The biological
efficiencies of these types of filters increase in the
order listed. To allow biological filtration, it is critical
that no residual disinfectant be present in solution.
Otherwise, microbial activity present in the filter
media will be eliminated or at least adversely
affected.
5.3 Comparing Disinfectants
This section summarizes the advantages and
disadvantages of the various disinfectants. Since
most disinfectants also function as oxidizing agents,
both oxidizing and disinfecting properties must be
considered when selecting a disinfecting agent. The
important characteristics of chlorine, chlorine
dioxide, monochloramine, ozone, and UV radiation
are described in Sections 5.3.1 through 5.3.5. Section
5.3.6 describes advanced oxidation processes that use
combinations of ozone with UV radiation or hydrogen
peroxide/Sections 5.4 and 5.5 describe the
technologies used to apply each disinfectant.
5.3.1 Chlorine
Chlorine is an excellent disinfectant and oxidant, and
is also a good chlorinating agent. It provides a stable
residual for the distribution system if the water is
free of chlorine-demanding ammonia and organic
materials. Since chlorine can produce THMs and
other halogenated (TOX) and nonhalogenated
organic compounds, the use of chlorine should be
minimized, particularly when THM and TOX
precursors are present. Some of the nonhalogenated
oxidation products of chlorination of humic and fulvic
acids are identical to those produced by potassium
permanganate, ozone, and chlorine dioxide.
5.3.2 Chlorine Dioxide
Chlorine dioxide is an excellent disinfectant, but is
not as strong an oxidant as free chlorine. Because it is
unstable, it must be generated on site. In its pure
state, chlorine dioxide does not produce THMs in the
presence of organic materials. Some procedures for
synthesizing chlorine dioxide (e.g., sodium chlorite
and elemental chlorine procedures) use excess
chlorine, which can produce THMs. Using less excess
chlorine in these procedures will lower the resulting
THM concentrations. Generating chlorine dioxide
with mineral acid and sodium chlorite solution
avoids the presence of excess free chlorine.
Chlorine dioxide treatment of organic pollutants
generally produces nonchlorinated oxidation
products and some chlorinated oxidation products,
but in smaller quantities than chlorine. Chlorine
dioxide does hot oxidize bromide ion to hypobromous
acid, as do ozone and chlorine, apparently because of
its low oxidation potential.
During oxidation and disinfection reactions, as much
as 90-95 percent of the chlorine dioxide reverts back
to chlorite ion, which, along with chlorate ion, has
been associated with undesirable health effects. EPA
currently recommends that finished water supplies
contain a maximum total of 1 mg/L combined chlorite
and chlorate ions, and chlorine dioxide.
5.3.3 Monochloramine
Monochloramine is a weak cysticidal disinfectant
and a poorer virucide. Therefore, the contact times
and concentrations required for adequate primary
disinfection are much longer and higher than with
chlorine, chlorine dioxide, or ozone. When mono-
chloramine is generated, dichloramine can be
present. Water containing chloramines can be fatal
to individuals on kidney dialysis, so local hospitals
and treatment centers must be warned against using
water containing chloramines for these patients.
Monochloramine is also a weak oxidant, and its slow
dissociation in water to free chlorine produces traces
of halogenated organic materials. Monochloramine is
not recommended as a primary disinfectant because
its inactivation ofGiardia cysts is slow and it is a
poor viricide.
Monochloramine may be produced in three ways: (1)
adding ammonia to water containing chlorine, (2)
adding chlorine to water containing ammonia, and
(3) using a preformed solution of monochloramine.
Each technique is discussed in more detail in Section
5.5.2.
63
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Adding ammonia to water treated with chlorine
(Method 1) will form THMs and other by-products
associated with chlorination during the chlorine
contact time used for disinfection or oxidation
purposes. In this case, the benefit from using an
alternative disinfectant to chlorine is negated.
Adding ammonia will arrest THM generation,
however, and the THM level will remain as produced
from the initial chlorination contact time.
Adding chlorine to water already treated with
ammonia (Method 2), assuming proper mixing, will
produce insignificant concentrations of free chlorine
and, consequently, lower concentrations of
halogenated materials. However, disinfection is less
effective because the weak disinfectant
monochloramine is performing the disinfection
function, rather than free chlorine.
This problem is exacerbated if organic nitrogen
materials are already in the water. They react with
free chlorine and chloramines to form organic
chloramines, and all organic chloramines are even
weaker disinfectants than monochloramine.
Available field analytical methods do not distinguish
between inorganic monochloramine and organic
chloramines in water. A utility with raw water
containing organic nitrogen materials that adds
ammonia and then chlorine to produce
monochloramine for primary disinfection may
seriously overestimate the degree of disinfection
attained.
Using a preformed monochloramine solution (Method
3), creates the same problem of producing less
effective organic chloramines, if organo-nitrogen
compounds are present.
5.3.4 Ozone
Ozone is the strongest disinfectant and oxidizing
agent available for water treatment; however, it is an
unstable gas and must be generated on site. In
addition, it is only partially soluble in water, so
efficient contact with the water must be established
and excess ozone from the contactor must be handled
properly. Section 5.4.2 discusses the specifics of ozone
generation and contacting methods. Ozone cannot be
used as a secondary disinfectant because it is unable
to maintain an adequate residual in water for more
than a short period of time.
Although the capital costs of ozonation systems are
high, their operating costs are moderate. Because of
its high oxidation potential, ozone requires short
contact times and dosages for disinfection and
pxidative purposes. As a microflocculation aid, ozone
is added during or before the rapid mix step and its
usage is followed by coagulation and direct or
conventional filtration. Higher dosages are used to
oxidize undesirable inorganic materials, such as iron,
manganese, sulfide, nitrite, and arsenic; or to treat
organic materials responsible for tastes, odors, color,
and THM precursors.
Ozone does not directly produce any halogenated
organic materials, but if bromide ion is present in the
raw water, it may do so indirectly. Ozone converts
bromide ion to hypobromous acid, which can then
form brominated organic materials. The primary by-
products of ozonation are oxygen-containing
derivatives of the original organic materials, mostly
aldehydes, ketones, alcohols, and carboxylic acids.
Ozone, however, produces toxic oxidation products
from a few organic compounds. For example, the
pesticide heptachlor forms high yields of heptachlor
epoxide upon ozonation. Therefore, when selecting
ozone for oxidation and/or disinfection purposes, one
must know the specific compounds present in the raw
water so as to provide the appropriate downstream
treatment to cope with by-products. Researchers are
continuing to study ozonation by-products and their
potential health effects.
Even when ozone is used to oxidize rather than
disinfect, primary disinfection is attained
simultaneously provided contact times and dissolved
ozone concentrations are appropriate. Consequently,
both oxidation and primary disinfection objectives
can be satisfied with ozone prior to filtration, after
which only secondary disinfection is needed.
There are two cases in which this one-step
oxidation/disinfection with ozone is not feasible: (1)
when high concentrations of iron or manganese are
in the raw water, and (2) when ozone is used for
turbidity control. In both cases, measurement of the
degree of disinfection (dissolved ozone
concentrations) is impractical. When iron or
manganese are in the water, ozonation precipitates
dark insoluble oxides that interfere with the
measurement of dissolved ozone. When ozone is used
for turbidity control, such low dosages of ozone are
used that a measurable concentration of dissolved
ozone may never be attained. In these two cases,
ozone oxidation and disinfection must occur
separately.
After being partially oxidized by ozone, organic
materials become more biodegradable and, therefore,
more easily mineralized during biological filtration.
Preozonation of water fed to slow sand filters
increases the ease of biodegradation of organic
materials and enhances biological removal of organic
materials during GAG filtration. The adsorptive
efficiency of the GAG is extended because it only has
to adsorb the organics unchanged by ozone, while the
partially oxidized organics are biologically converted
to carbon dioxide and water.
Primary disinfection (or oxidation) with ozone
produces a significant amount of assimilable organic
64
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carbon (AOC) comprised of readily biodegradable
aldehydes, acids, ketones, and alcohols. Many of
these are also precursors of THMs and TOX
compounds. Consequently, if ozone disinfection is
immediately followed by chlorination, higher levels
of THMs and TOX compounds may be produced than
without ozonation.
5.3.5 Ultraviolet Radiation
UV radiation (254 nm) disinfection of bacteria and
viruses has several important advantages: (1) it is
readily available; (2) it produces no toxic residuals;
(3) required contact times are relatively short; and (4)
the equipment is easy to operate and maintain,
although maintenance must be performed on a
regular basis to prevent fouling of certain
components. Section 5.4.3. discusses the specifics of
UV radiation equipment operation and maintenance.
UV radiation disinfection is inappropriate for:
Inactivation of Giardia lamblia cysts
Water containing high suspended solids
concentrations, color, and turbidity
Water with high concentrations of soluble
organic matter that can react with or absorb the
UV radiation, thus reducing the disinfectant's
performance
Since UV radiation is ineffective against Giardia
cysts, but effective against viruses and bacteria, it is
a good candidate for disinfecting ground water not
directly influenced by surface water. If the amount of
radiation received by a target organism is not a lethal
dose, however, reconstitution of the organism and
reinfection of the water can occur.
Since UV radiation disinfection provides no
disinfecting residual, a secondary disinfectant is
needed. Very little oxidation of organic materials
occurs with typical UV radiation systems used for
drinking water disinfection; consequently if
oxidation is required (for iron, manganese, sulfide,
nitrate, etc.), a strong oxidizing agent may be
necessary and can serve as a primary disinfectant as
well. However, higher energy intensities and lower
UV wavelengths (184.9 nm) can produce oxidation
reactions.
UV bulbs that produce radiation at 184.9 nm
generate some quantities of ozone which, in turn, can
provide some oxidation of organic materials. The
combination of UV radiation and ozone produces the
hydroxyl free radical, which is a more powerful
oxidizing agent than is ozone itself (see Section 5.3.6,
Advanced Oxidation Processes).
The 184.9 wavelength radiation is not as effective for
UV disinfection as the 254 nm wavelength, except by
the amount of ozone generated, which will provide
some CT value. '
5.3.6 Advanced Oxidation Processes
Ozone used in combination with UV radiation or
hydrogen peroxide can adequately disinfect and, at
the same time, oxidize many refractory organic
compounds such as halogenated organics present in
raw water. Although contact times for ozone
disinfection are relatively short, they are quite long
for oxidizing organic compounds. This combination
process accelerates the oxidation reactions.
Advanced oxidation processes involve combining
ozonation with UV radiation (UV254 bulbs
submerged in the ozone contactor) with hydrogen
peroxide (added prior to ozonation) or simply by
conducting the ozonation process at elevated pH
levels (between 8 and 10). Under any of these
conditions, ozone decomposes to produce the hydroxyl
free radical, which has an oxidation potential of 2.80
V compared with 2.07 V for molecular ozone.
However, hydroxyl free radicals have very short half-
lives, on the order of microseconds, compared with
much longer half-lives for the ozone molecule.
Many organic compounds that normally are stable
under direct reaction with the ozone molecule can be
oxidized rapidly by the hydroxyl free radical.
Chlorinated solvents such as trichloroethylene (TCB)
and tetrachloroethylene (PCE) can be destroyed
rapidly and cost effectively by hydroxyl free radicals
(Glaze et al.,1988; Aieta et al., 1988)r
5.4 Primary Disinfection Technologies
Primary disinfection is a key step in the water
treatment process. Typically, this step occurs either
just before or just after filtration in a conventional
surface water treatment plant. Chlorine dioxide can
be used for primary disinfection. However, the
maximum recommended residual for chlorine dioxide
and its decomposition products (chlorite and chlorate
ions) may limit the use of this chemical as a primary
disinfectant, except in cases of very clean waters
and/or short distribution systems that need only a
small amount of disinfectant. Monochloramine
cannot achieve the required inactivations of Giardia
cysts and enteric viruses within reasonable contact
times, and, therefore, is not appropriate for primary
disinfection.
For surface water treatment, chlorine and ozone are
the predominant candidates. For ground water (not
directly influenced by surface water), chlorine, ozone,
and UV radiation are potential primary
disinfectants. Chlorine dioxide appears to be a good
primary disinfection candidate for both types of
waters, provided that a means of reducing chlorine
65
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dioxide and chlorate ions is used (e.g., GAG or some
strong chemical reducing agent).
Because chlorine produces undesirable by-products
regulated by EPA, its use for pretreatment or
primary disinfection must be carefully scrutinized. It
is anticipated that EPA will lower the current MCL
for THMs (100 /g/L), making chlorine use more
difficult. In addition, regulation of some of the other
halogenated by-products of chlorination listed in
Table 5-7 may place even greater restrictions on
chlorine use.
Tabto 5-7. Disinfectants and Disinfectant By-Products
Listed In the First Drinking Water Priority List
(DWPL)
Disinfectants:
Chkxine
Hypochlorite ion
Chlorine dioxide
Chlorite ton
Chlorate ton
Chtoramino
Ammonia
Hatoacetonitriles:
Bromochtoroacetonitrile
Dtchloroacetonitrile
Dibromoace'.omtrile
Triehtoroacetonilrile
Tftnafometnanea:
Chloroform
Bromoform
BromocRchloromethane
Dtohlorobromomethane
Hatogenated Acids, Alcohols, Aldehydes, Ketones, and Other Nitrites
Others:
Chbropterin (trichtoronitromethane)
Cyanogen chloride
Ozona by-products
The four primary disinfection technologies, chlorine,
chlorine dioxide, ozone, and UV radiation, will be
discussed in Sections 5.4.1 through 5.4.4. Since most
of the utilities that are affected by the Surface Water
Treatment and upcoming Ground-Water Disinfection
Treatment Rules serve less than 10,000 persons, this
discussion will emphasize smaller utilities.
5.4.1 Chlorine
Chlorine is the most common primary and secondary
disinfectant used in the United States. It is available
as a gas, solid, or aqueous solution. Chlorine gas is
used most frequently, especially by large utilities,
because of its lower cost. Chlorine in its solid form is
calcium hypochlorite (Ca[OCl]a); the liquid form is
available as sodium hypochlorite (NaOCl) solution.
Section 5.4.1.1 describes the chlorination process,
including the physical and chemical factors affecting
its efficiency and applicability to specific sites. The
equipment, chemical, and operating and
maintenance considerations relevant to the three
physical forms of chlorine are discussed in Sections
5.4.1.2 through 5.4.1.4.
5.4.1.1 Process Description
Chlorine undergoes chemical reactions when added
to water, and the resulting compounds inactivate or
kill undesirable microorganisms. Chlorine gas will
form hydrochloric and hypochlorous acids according
to the following reaction:
C12
chlorine
H2O
water
HC1
hydro-
chloric
acid
+ HOC1
hypo-
chlorous
acid
The hypochlorous acid reacts further depending on
the pH of the solution. The higher the pH, the more it
will react, as shown below:
HOC1
hypochlorous
acid
(OC1) + H+
hypochlorite hydrogen
ion
on
The concentration of hydrogen ions in the water
determines the pH; the more hydrogen ions present,
the lower the pH. At neutral pH (pH = 7.0), almost
80 percent of the chlorine is in its most effective
disinfecting form, hypochlorous acid; the remainder
exists in the less effective disinfecting form,
hypochlorite ion. Increasing pH reduces the total
disinfecting strength of the solution because it causes
an increasing amount of hypochlorous acid to form
more hypochlorite ion. At pH 8.0, for example, nearly
80 percent of the chlorine is present as the
hypochlorite ion.
Table 5-2, presented earlier, gives CT values for
inactivation of Giardia lamblia cysts with free
chlorine (2.0 mg/L). At any given concentration of
chlorine, the CT values increase rapidly as the pH
rises above 7.0. This Is also true at each temperature
listed. Figure 5-1 shows the relationship between pH
and the concentration of hypochlorous acid. Effective
pH control is essential to achieve a desired level of
disinfection for systems relying upon chlorination.
When sodium hypochlorite (liquid) or calcium
hypochlorite (solid) is used for chlorination, the
resulting chemical reactions produce alkaline (basic)
compounds as follows:
The resulting hydroxides increase the pH of the
water, thereby lowering the concentration of
hypochlorous acid and diminishing disinfection
66
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NaOCl
sodium
hypo-
chlorite
Ca(OCl)2
calcium
hypo-
chlorite
100
H20
water
H20
water
HOC1 + NaOH
hydro- sodium
chlorous hydroxide
acid
-> 2HOC1 + CaOH
hypo- calcium
chlorous
acid
hydroxide
100
Figure 5-1. Distribution of hypochlorous acid and
hypochlorite ions in water at different pH values
and temperatures of 0ฐC and 20CC.
efficiencies. Therefore, the ability to adjust and
control pH is critical when using the hypochlorite
forms of chlorine.
Hypochlorous acid, a strong disinfecting agent, is one
of the most powerful oxidizing agents, and an
effective chlorinating agent. In addition to acting on
target organisms, it reacts with many substances in
water, as evidenced by the production of THMs and
other halogenated compounds associated with
chlorination. Chlorine also produces considerable
quantities of nonhalogenated organic oxidation
products, e.g., aldehydes, acids, and ketones.
Adequate chlorine concentration will achieve
effective disinfection of currently regulated
microorganisms. Since chlorine will react with many
substances in the water, the "chlorine demand" of
these other substances must be satisfied before an
excess of free chlorine is available for disinfection.
Thus, the amount of chlorine necessary to effectively
disinfect must be greater than the chlorine demand of
the water.
The "available chlorine residual" is the amount of
chlorine that remains available for disinfection after
the chlorine demand is satisfied. This is quantified by
an approximate analytical testing procedure. The
residual may be either a free available residual, a
combined available residual, or a combination of the
two. Free available chlorine refers to the total
concentration of hypochlorous acid and hypochlorite
ions. Combined available chlorine is the total
concentration of mono- and dichloramines, plus
nitrogen trichloride and organic nitrogen chlorine-
containing compounds. (See discussion of
chloramines in Section 5.5.2.)
Because of the many complex reactions that take
place, the relationship between the amount of
chlorine added and the available residual does not
become linear until a certain minimum amount of
chlorine has been added. In other words, increasing
the amount of chlorine does not result in a
proportional increase in the available residual until
that "chlorine breakpoint" is reached.
A series of chemical reactions causes the breakpoint
phenomenon. Water may contain small amounts of
reduced substances such as sulfides and ferrous iron,
as well as organic materials, organic nitrogen
materials (amino acids and proteins), and some
ammonia, all of which exert a chlorine demand. The
initial amount of chlorine added is taken up by
reactions with these contaminating substances,
leaving no free available chlorine. After the chlorine
demands of the reduced substances have been
satisfied, the hypochlorous acid will begin to react
with ammonia, organic nitrogen materials, and some
of the organics present to yield chloramines, oxidized
organics and chlorinated organic compounds. Next,
the addition of more chlorine may induce the
hypochlorous acid to oxidize or chlorinate some of the
same materials it has just created. At this point, a
decrease in the amount of residual (combined
residual) is observed. When these oxidation reactions
are complete, the breakpoint is reached, and adding
more chlorine finally increases the available chlorine
measured.
Figure 5-2 shows a "chlorine breakpoint curve," with
the amount of chlorine shown on the horizontal scale
and the amount of available chlorine shown on the
vertical scale. According to the curve, the chlorine
residual will not appear until 3 mg/L of chlorine is
added. After this point, additional chlorine will result
in an increase in residual. However, at about 6 mg/L,
67
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Chlorine Residual,
mg/L
Immediate
Demand
H2S,
Fe**, etc.
Chlorine and
Ammonia or similar
compounds
Free Residuals
Figure 5-2. Graphical representation of the breakpoint ohlorination reaction. The straight line at the left shows that chlorine
11 <= ^ Molof PrฐPฐrtlonal to dosage in pure water. When impurities are present, they exert a chlorine demand.
U.o. crf\ (19oo).
further additions of chlorine actually bring about a
decrease in residual until the breakpoint is reached
(8 mg/L in this diagram). After breakpoint is
achieved, additional chlorine finally results in a
proportional accumulation of residual free available
chlorine.
Actual reactions are considerably more complex than
described above because of the time and
concentration dependencies of these processes. For
these reasons, a breakpoint curve is difficult to
recreate and predict; thus, individual tests must be
run seasonally, and the data plotted to define the
breakpoint for each water supply.
Factors Affecting the Efficiency of Chlorine
Disinfection
Chlorine in its free state (HOC1 + [OC1]-) is an
effective disinfectant and inactivates most
microorganisms in a matter of minutes. However,
effective disinfection with chlorine requires careful
attention to the following factors:
Free available chlorine concentration. The
concentration must be high enough to always be
detectable at the farthest points in the
distribution system to effect both primary and
secondary disinfection.
68
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pH. The pH should be maintained as close to 7.0
as is practical or consistent with other water
quality aspects. This is necessary to maintain as
much of the chlorine residual as possible in the
hypochlorous acid form. New EPA regulatory
initiatives, however, are encouraging utilities to
adjust the pH of their product water to 8.0 in
order to minimize corrosion effects (U.S. EPA,
1988a). This higher pH will necessitate higher
doses of chlorine to attain primary disinfection.
Contact time. Contact time must be long enough
to achieve the desired degree of microbial
inactivation (i.e., attain the CT value that applies
to the concentration of chlorine and the pH and
water temperature).
Mixing. The chlorine contactor should either
contain sufficient baffling to eliminate the
possibility of short-circuiting or an external
mixing device should be added.
Temperature also affects the disinfection rate; the
higher the temperature, the faster the rate of
disinfection. Consequently, at higher temperatures,
the CT values become lower.
The choice of chlorination system - gas, solid, or
liquid - depends on a number of site-specific factors
including:
Availability of chlorine source chemical
Capital cost of the chlorination system
Operation and maintenance costs of the
equipment
Chemical costs
Location of the facility
Operator skills
Safety considerations
Local regulations regarding the storage of
chlorine gas
Each chlorination method provides the same
disinfecting power on a pound for pound basis of
available chlorine at the same pH. The choice of
method depends primarily on the availability of each
chemical and the construction and annual operating
costs for the different systems.
5.4.1.2 Disinfection with Chlorine Gas
Elemental chlorine is a toxic, yellow-green gas at
standard temperatures and pressures. It is supplied
as a liquid in high-strength high-pressure steel
cylinders, and vaporizes rapidly when released. As
the liquid evaporates, its temperature falls and slows
evaporation rate, necessitating use of a container
manifold or vaporizer.
Chlorine gas can be supplied in cylinders with
capacities of 45.4 to 907.2 kg (100 to 2,000 Ib), or in
tank cars. The quantities required by small water
systems can be purchased from local chemical or
swimming pool chemical suppliers.
There are two basic types of gas chlorinators: (1)
pressure-operated direct gas feed units and (2)
vacuum operated solution-feed units. Direct gas feed
units supply pressurized chlorine gas to the water
and are used only when electrical power is
unavailable or the water pressure differentials are
insufficient to operate a solution feed unit. The
solution feed units mix the gas with a side stream of
water to form a solution of hypochlorous acid and
hypochlorite ion, which then is mixed with the main
stream. These units operate on a vacuum-controlled
basis, automatically shutting off if the side stream
flow is interrupted. The solution feed system is safer
to operate and, therefore, is preferred by most
operators. Figure 5-3 shows a solution feed system.
Equipment Costs
Table 5-8 presents a range of equipment costs for one
basic and five increasingly complex solution feed gas
chlorination systems. The basic system includes
equipment to handle two 68-kg (150-lb) chlorine
cylinders, two cylinder-mounted chlorine gas
regulators, an automatic changeover valve, and a
chlorine gas flow and rate valve ejector (with system
backup).
The most sophisticated system includes the basic
system plus two scales, a gas mask, a diffuser
corporation cock (to allow connection under water
line pressure), a flow-pacing chlorine addition
system, a flow meter, a booster pump and piping, and
a chlorine leak detector.
The costs are based on a small water treatment
system sized to treat water volumes up to at least
0.044 m3/sec (1 MGD). They include equipment,
installation, safety enclosure, contractor's overhead
and profit, and a 10 percent engineering fee. In May
1980 dollars, the least expensive gaseous
chlorination system costs were about $9,350. The
most sophisticated gaseous chlorination system with
all the options added cost $16,050.
Operating and Maintenance Costs
For small solution-feed systems treating from 9.5
m3/day to 0.044 m3/sec (2,500 GPD to 1 MGD),
operating and maintenance costs for gas chlorination
systems ar'e approximately the same. About 1,630
kWh each year is required to run the booster pump
and approximately 2,560 kWh annually is required
for the building housing the system, assuming a 58.1-
m2 (625 ft2) building. Maintenance materials for
miscellaneous repair of valves, electrical switches,
and other equipment cost about $40/yr. Labor
69
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To Vent
Lead
Chlorine Gaskel
Cylinder
Valve
Vacuum Seal
Yoke
Clamp
. Rate Valve
Outlet Connection
Vent Valve
Rate Indicator
Regulating
Diaphragm
Assembly
Vacuum Line
Chlorine Cylinder
Ejector and
Check Valve
Assembly
Water Supply
Chlorine
Solution
Figure 5-3. Solution feed-gas chlorinatlon system.
Source: Capital Controls Co., Inc.
Table 5-8. Capital Costs for Gas Chlorinationa ($1980)
Equipment Costs for a System Producing 100 Lb/Day
or Less
System
Basic System15 $ 1,373
Complex System 8,579
Installation 1,157
Safety Enclosure 3,500
Contractor's Overhead and Profit (20%) 1,869
Engineering Fees (10%) 934
Total Capita) Cost
Baste System $ 9,343
Complex System $16,049
* May 1980 quotes (three vendors).
*> Basic system includes two 150-lb chlorine cylinders, two cylinder-
mounted regulators, automatic changeover valve, chlorine gas flow
rate valve, and ejector (system with backup).
1 to - 0.4536 kg
Source: U.S. EPA (1983).
requirements of 1/2 hr/day (or 183 hr/yr) cover daily
checks on equipment.
Table 5-9 estimates total annual operating and
maintenance costs of $2,163 for a solution feed gas
chlorination system. The estimate assumes energy
costs of $0.07/kWh and labor costs of $10/hr, which
were the prevailing rates in 1982.
Chemical Costs
The cost of chlorine for a system can be estimated
using the following formula:
C12 dosage (mg/L X water treated (L/day) X Cl2cost($flb)
1,000 (mg/g) X 454(g/lb)
= Cl2cost($/day)
Table 5-9. Capital Costs for Gas Chlorlnationa ($1980)
Item Requirements Costs in $
Electrical Energy
Process
Building
Subtotal
Maintenance Materials
Labor
Total Annual O&M Cost
1,630kWh/yr
2.560 kWh/vr
4,l90kWh/yr
183 h/yr
114.10
179.20
293.30a
40.00
1,830b
2,163
a Assumes $0.07/kWh.
b Assumes $10/hour labor cost.
Source: U.S. EPA (1983).
In the New York metropolitan area (1989), a 68-kg
(150-lb) cylinder of chlorine costs about $1.65/kg
($0.75/lb). Applying the above equation, assuming a
dosage of 5 mg/L, gaseous chlorine would cost $30/yr
for a 9.5 m3/day (2,500-GPD) plant and $ll,400/yr for
a 0.044 m3/sec (1-MGD) plant.
70
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5.4.1.3 Disinfection with Sodium Hypochlorite
Solution
Sodium hypochlorite solution is usually supplied
commercially in concentrations of 5 and 15 percent
chlorine. It is easier to handle than gaseous chlorine
or calcium hypochlorite. Metered chlorinators deliver
the solution directly into the water.
Sodium hypochlorite solutions lose their disinfecting
(oxidizing) power during storage, and thus should be
stored in a cool, dark, dry area. No more than a 1-
month supply of the chemical should be purchased at
one time to prevent loss of available chlorine. The
material is supplied in glass or plastic bottles,
carboys, or lined drums ranging in size from 1.89 to
208.2 L (0.5 to 55 gal). Bulk shipment by tank truck
is also a common form of transport.
Sodium hypochlorite solution is more costly per
pound of available chlorine and does not contain the
high concentrations of chlorine available from
chlorine gas. However, the handling and storage
costs are lower than for chlorine gas.
An onsite generation technique for hypochlorite
solutions recently has been developed. This system
consists of a two-cell unit, in which a brine solution
(salt in water) is electrolyzed, producing a solution of
hypochlorous acid in one cell and a solution of caustic
(sodium hydroxide) in the other, according to the
following equation:
Na+
sodium
chloride
2H2O
water
HOC1 +
hypochlorous
acid
NaOH
sodium
, hydroxide
e-
electron
H2
hydrogen
Using onsite generation avoids the purchase and
storage of large volumes of chlorine gas or
hypochlorite solutions, but there are significant
disadvantages. The generation process produces
hydrogen, which poses fire and explosion hazards,
and sodium hydroxide, which is a caustic solution
that requires proper disposal. Also, the cost per pound
of available chlorine is typically much higher for
onsite generation (e.g., $0.66 to $0.77/kg [$0.30 to
$0.35/lb] for onsite generation compared to $0.18 to
$0.33/kg [$0.08 to $0.15/lb] for chlorine gas).
However, certain site-specific considerations may
make onsite generation a preferred disinfection
technique.
Equipment Costs
Table 5-10 presents estimated capital costs for
sodium hypochlorite chlorination systems. This table
provides estimates for basic and complex systems,
both electrically and hydraulically activated. The
basic liquid hypochlorination systems include two
metering pumps (one serving as a standby), a
solution tank, diffuser, and appropriate quantities of
tubing. The more complex system adds a diffuser
corporation cock, antisiphon backflow preventer, a
safety housing enclosure, a flow pacing system, and a
flow meter and signal.
Table 5-10. Capital Costs for Liquid Chlorinatorsa ($1980)
Electrically
Activated
Hydraulically
Activated
Equipment Cost (basic systeriib)
Installation
Site Work
Contractor's Overhead & Profit
(20%)
Engineering Fees
Add Ons:
Alternate #1: add diffuser .
corporation cock and antisiphon
backflow preventer
Alternate #2: add safety enclosure
(housing)
Alternate #3: add flow pacing
existing signal
Alternate #4: add flow meter
signal, 8 in. or less
Total Capital Cost
Basic System
Most Sophisticated
$ 1,800
500
250
729
364
165
6,930
$ 3,643
$10,738
i 2,266
1,000
250
1,004
503
231
6,930
1,485
1,452
$ 5,023
$15,121
a May 1980 quotes (two vendors).
b Basic System includes two metering pumps (one standby), tubing,
solution tank, and diffuser.
Source: U.S. EPA (1983).
Total capital costs for an electrically activated system
range from $3,643 for the basic system to $10,738 for
the most sophisticated system. The comparable range
for the hydraulically activated systems is $5,023 to
$15,121.
Operating and Maintenance Costs
As with solution-feed gas chlorinators, operating and
maintenance costs for systems in the 9.5 m3/day to
0.044 m3/sec (2,500 GPD to 1 MGD) size range are
roughly the same. The annual estimated energy
requirements for the diaphragm metering pump and
the housing structure, assumed to be 58.1 m2 (625
ft2), are 570 kWh and 2,560 kWh, respectively.
Maintenance materials for minor component repairs
are about $20 each year. Approximately 1 hour of
labor is required each day to mix the sodium
hypochlorite solution and check equipment.
71
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Table 5-11 summarizes total annual operating and
Table 5-11. Operation and Maintenance Cost Summary
for Sodium Hypochlorite Solution Feed
($1982)
Item
Electrical Energy
Process
Building
Subtotal
Maintenance Materials
Labor
Total Annual O&M Cost
Requirements
570 kWh/yr
2.560 kWh/vr
3.130 kWh/yr
365 h/yr
Costs in $
39.90
179.20
219.10a
20.00
3,65Qb
3,889
ซ Assumes $0.07/kWh.
b Assumes $lO/hour labor cost
Source: U.S. EPA (1983).
maintenance costs for the sodium hypochlorite
solution feed system. The total of $3,889/yr is based
on the same energy and labor cost assumptions of
$0.07/kWh and $10/hr as were used for the gas
chlorination system.
Chemical Costs
Typically, sodium hypochlorite is available as a 15
percent (by weight) solution. Four-tenths of a kg (0.9
Ib) of sodium hypochlorite solution is equivalent in
oxidation potential to 0.45 kg (1 Ib) of gaseous
chlorine, and its cost is about 3 times that of gaseous
chlorine. These ratios for the two forms of chlorine
can be used in conjunction with the formula provided
in Section 5.4.1.2 to estimate the cost of the solution.
For example, a small water utility treating 9.5
m3/day (2,500 GPD) with a dosage requirement of 5
mg/L of chlorine requires 242.2 L (64 gal)/yr of the 15
percent solution. If the cost of the solution was
?0.13/L ($0.50/gal) (as it was in the
Baltimore/Washington, D.C. area in 1987), the
annual chemical cost would be $32.00. A 0.044 m3/sec
(1-MGD) plant using the same chlorine dosage would
require 400 times the chemical volume and would
spend $12,800 annually.
5.4.1.4 Disinfection with Solid Calcium
Hypochlorite
Calcium hypochlorite is a white solid that can be
purchased in granular, powdered, or tablet form. It
contains 65 percent available chlorine and is readily
soluble in water. The chemical is available in 0.9-,
2.3-, 3.6-, and 15.9-kg (2-, 5-, 8-, and 35-lb) cans and
362.9-kg (800-lb) drums, which are usually
resealable. Calcium hypochlorite is a corrosive
material with a strong odor and requires proper
handling.
When packaged, calcium hypochlorite is very stable;
therefore, an annual supply can be purchased in a
single procurement. However, it is hygroscopic
(readily absorbs moisture), and reacts slowly with
atmospheric moisture to form chlorine gas.
Therefore, shipping containers must be emptied
completely or carefully resealed. Bulk handling
systems cannot be used.
Typically, the entire contents of a calcium
hypochlorite container are emptied into a mixing
tank where they are readily and completely dissolved
in water. The resulting corrosive solution is stored in
and fed from a stock solution vessel constructed of
corrosion-resistant materials such as plastic,
ceramic, glass, or rubber lined steel. Solutions of 1 or
2 percent available chlorine can be delivered by a
diaphragm-type, chemical feed/metering pump.
Equipment, Operating, and Maintenance
Costs
Equipment, operating, and maintenance costs for
calcium hypochlorite solution feed systems are
similar to those for sodium hypochlorite feed systems.
The equipment needed to mix the solution and inject
it into the water being treated is the same.
Chemical Costs
A 9.5 m3/day (2,500-GPD) treatment plant using a 5
mg/L dosage of chlorine needs 0.104 Ib chlorine/day.
Because solid calcium hypochlorite contains 65
percent available chlorine, 15.95 kg (0.16 lb)/day is
required.
In 1987 (in the Baltimore/Washington D.C. area), 1
kg of calcium hypochlorite cost $2.09 ($0.95/lb). For a
9.5 m3/day (2,500-GPD) facility, 26.5 kg (58.4 Ib)
costing $55.48 is needed for 1 year. A 0.044 m3/sec (1-
MGD) facility, using 400 times that amount of
chlorine, would spend $22,192 annually.
5.4.2 Ozone
While ozone is widely used for disinfection and
oxidation in other parts of the world, it is relatively
new in the United States. The process of ozone
disinfection, including its chemistry, is discussed in
Section 5.4.2.1. Section 5.4.2.2, system design
considerations, covers issues related to the essential
components of an ozone treatment system. Lastly,
Section 5.4.2.3 reviews the costs of ozone system
equipment, installation, housing, and operation and
maintenance.
5.4.2.1 Process Description
Ozone (63) is a powerful oxidizing agent, second only
to elemental fluorine among readily available
chemical supplies. Because it is such a strong
oxidant, ozone is also a powerful disinfectant. Unlike
chlorine, ozone does not react with water to produce a
72
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disinfecting species. Instead, when exposed to a
neutral or alkaline environment (pH above 6), UV
light, or hydrogen peroxide, it decomposes in water to
more reactive hydroxyl free radicals as shown in the
equation below:
03 + H20 > 02
ozone water oxygen
2(OH)
hydroxyl
radicals
This reaction is accelerated at pH values above 8.
In water, ozone reacts as the ozone molecule, the
hydroxyl free radical, or as a mixture of both. For
primary disinfection, CT values for ozone (shown in
Tables 5-1 and 5-2) have been developed for
molecular ozone, not for hydroxyl free radicals. These
free radical species are more effective oxidizing
agents than molecular ozone. However, they have
extremely short half-lives (microseconds) and
consequently may not be good disinfectants.2
Since ozone is unstable at ambient temperatures and
pressures, it must be generated onsite and used
quickly. Ozone is generated by applying energy to
oxygen (pure oxygen or dried air). A high-energy
electrical field causes oxygen to dissociate according
to the equation below:
02
oxygen
electrons
2[0]
oxygen
"fragments"
These oxygen "fragments" are highly reactive and
combine rapidly with molecular oxygen to form the
triatomic molecule, ozone:
2[O]
oxygen
"fragments"
2O2
oxygen
2O3
ozone
The overall reaction that produces ozone is the sum of
the above reactions:
3O2
oxygen
e-
energy
2O3
ozone
2 Very recent data (Wolfe et al., 1989) show that hydroxyl free
residuals produced by the combination of ozone with hydrogen
peroxide have the ability to inactivate Giardia cysts and enteric
viruses rapidly.
This reaction is reversible; once formed, ozone
decomposes to oxygen. This reverse reaction occurs
quite rapidly above 35ฐC. Because the reactions that
convert oxygen to ozone also produce a considerable
amount of heat, ozone generators have cooling
components to minimize ozone losses by thermal
decomposition.
Ozone has a characteristic odor that is detectable
even at low concentrations (0.01 to 0.02 ppm by
volume). Higher levels may cause olfactory and other
reaction fatigue, and much higher levels are acutely
toxic in some instances. The longer the exposure to
ozone, the less noticeable the odor.
Ozone is only slightly soluble in water, about 2 to 10
times more soluble than oxygen, depending on the
temperature and its concentration as it enters the
ozone contactor. The higher the concentration of
ozone generated, the more soluble it is in water.
Increasing pressure in the ozone contactor system
also increases its solubility. Ozone's half-life in water
ranges from 8 minutes to 14 hours, depending on the
level of ozone-demanding contaminants in the water.
5.4.2.2 System Design Considerations
The five major elements of an ozonation system are:
Air preparation or oxygen feed
Electrical power supply
Ozone generation
Ozone contacting
Ozone contactor exhaust gas destruction
Air Preparation
Ambient air should be dried to a maximum dew point
of-65ฐC before use in the ozonation system. Using air
with a higher dew point will produce less ozone, cause
slow fouling of the ozone production (dielectric) tubes,
and cause increased corrosion in the ozone generator
unit and downstream equipment. These last two
factors result in increased maintenance and
downtime of the equipment.
Air feed systems can dry ambient air or use pure
oxygen. Using pure oxygen has certain advantages
that have to be weighed against its added expense.
Most suppliers of large-scale ozone equipment
consider it cost effective to use ambient air for ozone
systems having less than 1,587.6 kg/day (3,500
Ib/day) generating capacity. Above this production
rate, pure oxygen appears to be more cost effective.
Systems that dry ambient air consist of desiccant
dryers, commonly used in conjunction with
compression and refrigerant dryers for generating
large and moderate quantities of ozone. Very small
systems (up to 0.044 m3/sec [1 MOD]) can use air
drying systems with just two desiccant dryers (no
compression or refrigerant drying). These systems
73
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use silica gel, activated alumina, or molecular sieves
to dry air to the necessary dew point (-65ฐC).
Ambient^air feed systems used for ozone generation
are classified by low, medium, or high operating
pressure. The most common type is a system that
operates at medium pressures ranging from 0.7 to
1.05 kg/cm2 (10 to 15 psig). High-pressure systems
operate at pressures ranging from 4.9 to 7.03 kg/cm2
(70 to 100 psig) and reduce the pressure prior to the
ozone generator. Low- and high-pressure systems are
typically used in small- to medium-sized
applications. Medium- and high-pressure systems
may be used in conjunction with most ozone
generators and with most contacting systems. Low-
pressure systems operate at subatmospheric
pressures, usually created by a submerged turbine or
other contactors producing a partial vacuum
throughout the air preparation and ozone generation
system. Creation of this vacuum results in ambient
air being drawn into the ozonation system.
The decision to use a high-, medium-, or low-pressure
air preparation system often is based on a qualitative
evaluation of potential maintenance requirements,
as well as an evaluation of capital and operating
costs. High-pressure air pretreatment equipment
generally has higher air compressor maintenance
requirements, lower desiccant dryer maintenance
requirements, and lower capital costs.
At small- to medium-sized installations, the lower
capital costs may offset the additional maintenance
required for the air compressors and associated
equipment, such as filters for the oil-type
compressors. Typical low- and high-pressure feed gas
pretreatment systems are shown in Figures 5-4 and
6-5. Figure 5-4 is also representative of a medium-
pressure system, but may require a pressure
reducing valve upstream from the ozone generator.
For many applications, pure oxygen is a more
attractive ozone feed gas than air for the following
reasons:
It has a higher production density (more ozone
produced per unit area of dielectric).
* It requires lower energy consumption (energy
supplied per unit area of dielectric).
* Essentially double the amount of ozone can be
generated per unit time from oxygen than from
air (for the same power expenditure); this means
that ozone generation and contacting equipment
can be halved in size when using oxygen, to
generate and contact the same amount of ozone.
Smaller gas volumes are handled using oxygen,
rather than air, for the same ozone output; thus,
costs for ancillary equipment are lower with
oxygen feed gas than with air.
If used in a once-through system, gas recovery
and pretreatment equipment are eliminated.
Ozone transfer efficiencies are higher due to the
higher concentration of ozone generated.
However, the economic implications of these
advantages must be weighed against the capital
expenditure required for onsite oxygen production or
operating costs associated with purchase of liquid
oxygen produced off site.
Oxygen can be purchased as a gas (pure or mixed
with nitrogen) or as a liquid (at -183ฐC or below).
Normally the purity of the available oxygen gas is
quite adequate, and no particular pretreatment is
required. Its purity always should be better than 95
percent, and its dew point consistently lower than
-60ฐC. When liquid oxygen is the oxygen source, it is
converted to the gas phase in an evaporator, and then
sent directly to the ozone generator. Purchasing
oxygen as a gas or liquid is only practical for small- to
medium-sized systems. Liquid oxygen can be added to
dried air to produce oxygen-enriched air (as at the
Tailfer plant serving Brussels, Belgium). A
membrane separation method that also produces
oxygen-enriched air is being developed.
There are currently two methods for producing
oxygen on site for ozone generation; pressure swing
adsorption of oxygen from air and cryogenic
production (liquefaction of air followed by fractional
distillative separation of oxygen from nitrogen).
Systems for the production of oxygen on site contain
many of the same elements as air preparation
systems discussed above, since the gas stream must
be clean and dry in order to successfully generate
ozone. Gaseous oxygen produced on site by pressure
swing adsorption typically is 93 to 95 percent pure,
while liquid oxygen produced cryogenically generally
is 99.5 percent pure. In most plants utilizing on site
production of ozone, a backup liquid oxygen storage
system is included.
At smaller plants, oxygen can be separated from
ambient air by pressure swing adsorption using
molecular sieves. During the high-pressure phase,
nitrogen is adsorbed by the sieves and oxygen exits
the system as product gas. When the pressure is
reduced, the nitrogen desorbs and is removed from
the vessel by purge gas. Precautions should be taken
to avoid contamination of the oxygen prepared by this
procedure with hydrocarbons, which are present as
oils associated with the pressurized equipment.
Pressure swing adsorption systems for producing
oxygen are manufactured to produce from 90.7 to
27,216 kg/day (200 to 60,000 Ib/day) of oxygen. This
production range would supply ozone for water
treatment systems at 6 percent concentration in
oxygen, for an applied ozone dosage of 4 mg/L and
74
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! After-Cooler |
Heat-Reactivated
Dessicant Dryers
To Ozone Generator
Figure 5-4. Low pressure air feed-gas treatment schematic for ozone generation.
Source: U.S. EPA (1986b).
To Ozone Generator
production of water at the rates of about 0.018 m3/sec
to about 5.26 m3/sec (0.4 MOD to about 120 MOD).
For cryogenic oxygen production, low temperature
refrigeration is used to liquefy the air, followed by
column distillation to separate oxygen from nitrogen.
Cryogenic systems are operationally sophisticated,
and operating and maintenance expertise is required.
Production of oxygen by the cryogenic technique is
more capital intensive than by pressure swing
adsorption, but generally operation and maintenance
costs are lower. For oxygen requirements of 18,144 to
18,144,000 kg/day (20 to 20,000 tons/day), cryogenic
separation systems are quite practical. This would
exclude their use for small water treatment plants.
The Los Angeles Aqueduct Filtration Plant, which is
26.28m3/sec (600 MGD) is using a 3,628.8-kg/day
(8,000-lb/day) ozone system, with cryogenically
produced oxygen as a feed gas.-
Reuse or recycling of the oxygen-rich contactor
offgases is possible, and requires removal of moisture
and possible ammonia, carbon dioxide, and nitrogen
before returning the gas to the generator:
Electrical Power Supply
The voltage or frequency supplied to the ozone ,
generator is varied to control the amount and rate of
ozone produced. Varying the power requires
specialized supply equipment that should be designed
for and purchased from the ozone generator
manufacturer.
75
-------
Pre-Compressor Filter
Pre-Compressor Filter
After-Cooler
After-Cooler
Heat-Reactivated
Desiccant Dryers
To Ozone Generator
Figure 5*5. High pressure air feed-gas treatment schematic for ozone generation.
Source: U.S. EPA (I986b).
To Ozone Generator
Ozone generators use high voltages (> 10,000 V) or
high-frequency electrical current (up to 2,000 Hz),
necessitating special electrical design considerations.
Electrical wires have to be properly insulated; high
voltage transformers must be kept in a cool
environment; and transformers should be protected
from ozone contamination, which can occur from
small ozone leaks. The frequency and voltage
transformers must be high quality units designed
specifically for ozone service. The ozone generator
supplier should be responsible for designing and
supplying the electrical subsystems.
Ozone Generators
Ozone used for water treatment is usually generated
using a corona discharge cell.3 The discharge cell
consists of two electrodes separated by a discharge
gap and a dielectric material, across which high
voltage potentials are maintained. Oxygen-enriched
air, pure oxygen, or air that has been dried and cooled
flows between the electrodes and produces ozone.
More recent designs use medium and high
frequencies, rather than high voltages and low
frequencies, to generate ozone.
3 This technique produces concentrations of ozone sufficiently
high (above 1 percent by weight) to solubilize enough ozone
and to attain the requisite CT values necessary to guarantee
disinfection of Giardia cysts. Ozone also can be generated by
UV radiation techniques, but only at maximum concentrations
of 0.25 percent by weight. At such low gas concentrations, it is
not possible to solubilize sufficient ozone to guarantee
disinfection of Giarda cysts.
76
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Figure 5-6 depicts the essential components of a
corona discharge ozone generator. Either ambient
air, oxygen-enriched air, or pure oxygen is fed to the
generator. If ambient air is used, the generator
produces dry, cool air containing 1 to 3.5 percent
ozone (by weight), which can be mixed with water.
When pure oxygen is used, the concentration of ozone
produced is approximately double that produced with
ambient air (up to 8 to 9 percent by weight).
The most common commercially available ozone
generators are:
Horizontal tube, one electrode water cooled
Vertical tube, one electrode water cooled
Vertical tube, both electrodes cooled (water and
oil cooled)
Plate, water or air cooled
The operating conditions of these generators can be
subdivided into low frequency (60 Hz), high voltage
(> 20,000 V); medium frequency (600 Hz), medium
voltage (< 20,000 V); and high frequency (> 1,000
Hz), low voltage (< 10,000 V).
Currently, low frequency, high voltage units are
most common, but recent improvements in electronic
circuitry make higher frequency, lower voltage units
more desirable.
Operating an ozone generator at 60 to 70 percent of
its maximum production rate is most cost effective.
Therefore, if the treatment plant normally requires
45.36 kg/day (100 Ib/day) of ozone and 68.04 kg/day
(150 Ib/day) during peak periods, it is wise to
purchase three generators, each designed for 27.22
kg/day (60 Ib/day) and operate all three at about 65
percent capacity for normal production. This
arrangement will satisfy peak demands and one
generator will be on hand during off-peak periods for
standby or maintenance.
Ozone Contacting
Ozone can be generated under positive or negative air
pressure. If generated under positive pressure, the
contactor most commonly used is a two-chamber
porous plate diffuser, with a 4.8-m (16-ffc) water
column. With this method, the ozone-containing air
exits the ozone generator at approximately 1.05
kg/cm2 (15 psig) and passes through porous diffusers
at the base of the column. Fine bubbles containing
ozone and air (or oxygen) rise slowly through the
column, the mass of ozone is transferred (dissolves),
and oxidation and/or disinfection takes place. The
4.8-m (16-fb) height maximizes the amount of ozone
transferred from the bubbles as they rise in this type
of porous diffuser contactor.
Other types of positive pressure ozone contactors
include packed columns, static mixers, and high
speed agitators. An atomizer that sprays water
through small orifices into an ozone-containing
atmosphere also can be used.
When ozone is generated under negative pressure,
vacuum action draws the ozone mixture from the
generators, providing contact as the gas mixes with
the flowing water as with a submerged turbine.
Other common methods of creating negative pressure
use injectors or Venturi-type nozzles. These systems
pump water past a small orifice (injector) or through
a Venturi nozzle, thus creating negative pressure.
The diffuser and packed tower contactors require no
energy above that required to generate ozone at 1.05
Heat
/.. I
02
Discharge Gap
-*o3
Dielectric
Electrode
< I
Heat
Figure 5-6. Typical ozone generating configuration for a Corona discharge cell.
77
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kg/cm2 (15 psig). The high speed agitators, static
mixers, and all the negative pressure contactors
require additional energy.
Ozone reactions are very fast to destroy or inactivate
microorganisms; oxidize iron, manganese, sulfide
and nitrite ions, and some organics; and lower
turbidity levels. However, ozone oxidizes organic
compounds such as humic and fulvic materials, as
well as many pesticides and volatile organic
compounds, quite slowly compared to these other
solutes.
For disinfection, the initial dose of ozone is used to
satisfy the ozone demand of the water. Once this
demand is satisfied, a specific ozone concentration
must be maintained for a specific period of time for
disinfection. These two stages of ozonation are
usually conducted in two different contacting
chambers (see Figure 5-7). Approximately two-thirds
of the total ozone required is added to the first
chamber where the ozone demand of the water is met
and the dissolved ozone reaches a residual level
(typically 0.4 mg/L). The remaining ozone is applied
in the second chamber, where it maintains the
residual ozone concentration for the necessary
contact time with water to attain the required CT
value.
When ozone is added to water, its dissolved residual
is not stable. Not only will ozone react with many
contaminants in water supplies, but its half-life in
water is fairly short, on the order of minutes, due to
decomposition back to oxygen. At the higher pH
ranges (above 8), decomposition of molecular ozone
into reactive intermediates (including the hydroxyl
free radical) is accelerated. Consequently, it is not
possible to monitor the residual ozone concentration
at any single point in the treatment train and expect
a single concentration level to hold steady from the
point of gas/liquid mixing throughout the ozone
treatment subsystem.
Therefore, it is important when using ozone for
primary disinfection to monitor for dissolved ozone at
a minimum of two points. In the event that two ozone
contact chambers are utilized, the dissolved residual
ozone can be monitored at the outlets of the, two
chambers. The average of these two numbers can be
used as the "C" for calculation of CT values.
Absolute measurement of ozone contact time ("T") is
not simple, because the objective of adding ozone to
water involves maximizing the mixing of a partially
soluble gas with the liquid. The more complete the
contacting, the shorter the actual residence time for
the water in the contacting chamber. As a result, the
more completely the gas and liquid media are mixed,
the less the hydraulic residence time can be used as
the value for "T". Only when water flowing through
an ozone contacting system approaches plug flow does
the actual ozone contact time approach the hydraulic
residence time.
The greater the number of ozone contact chambers
that can be connected in series, the closer the water
flow will approach plug flow. In such cases, the TIQ
(time for 10 percent of an added tracer to pass
through the ozone contacting system) will approach
50 percent of the hydraulic detention time for water
passed through the ozone contacting system.
Recently published studies of the 26.28 m3/sec (600-
MGD) Los Angeles Aqueduct Filtration Plant and of
the design of the 5.26 m3/sec (120-MGD) Tucson
water treatment plant have confirmed that the actual
hydraulic residence time (Tio) is approximately 50
percent of the theoretical hydraulic residence time.
Destruction of Excess Ozone from Ozone
Contactor Exhaust Gases
The ozone in exhaust gases from the contacting unit
must be destroyed or removed by recycling prior to
venting. The current Occupational Safety and Health
Administration standard for exposure of workers
during an 8-hour work day is a maximum ozone
concentration of 0.0002 g/m3 (0.1 ppm by volume
time-weighted average). Typical concentrations in
contactor exhaust gases are greater than 1 g/m3 (500
ppm by volume).
The four primary methods of destroying excess ozone
are thermal destruction (heating the gases to 300ฐ to
350ฐC for 3 seconds), thermal/catalytic destruction,
and catalytic destruction (with metal catalysts or
metal oxides). Moist granular activated carbon is
used extensively at European plants treating less
than 0.088 m3/sec (2 MGD) and for swimming pools
using ozone.
When ozone is generated from air, destroying ozone
in exhaust gases is more cost effective than
recirculating the gases through the air preparation
system and ozone generator. When ozone is generated
from pure oxygen, destroying the ozone and
discharging the excess oxygen can be more cost
effective than destroying the excess ozone, and drying
and recycling the excess oxygen. A number of "once-
through" oxygen feed systems have been installed
throughout the world since 1980 to generate ozone.
The largest of these is at the 26.28 m3/sec (600-MGD)
Los Angeles plant, which has been operating in this
manner since 1987.
Other System Design Considerations
Ozonation system components that directly contact
ozone-containing gas should be constructed of
corrosion-resistant material, such as reinforced
concrete for the contactors, stainless steel for the
78
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Contact
Chamber
Off-Gas
Ozone-Rich
Air
I ' I
Ozonated
Water
Flow Meter (Typical)
Valve (Typical)
Figure 5-7. Two-compartment ozone contactor with porous diffusers.
piping, and Teflon for gaskets. Piping for dry service
should be 304-L stainless steel, while piping for wet
service should be 316-L stainless steel.
Proper monitors and controllers should be supplied
with the ozone system, including:
Gas pressure and temperature monitors at key
points in the air preparation system. Simple
pressure gauges and mercury thermometers are
adequate.
Continuous monitors/controllers for the dew
point to determine the moisture content of the
dried feed gas to the ozone generator. The
monitors should sound an alarm and shut down
the generator when high dew points are
indicated. Equipment to calibrate the dew point
monitor should be provided as well.
Inlet/discharge temperature monitors for the
ozone generator coolant media (water and/or oil,
or air), and a means of determining whether
coolant is actually flowing through the generator.
An automatic system shutdown should be
provided if coolant flow is interrupted or if its
discharge pressure exceeds specified limits.
Flow rate, temperature, and pressure monitors,
and an ozone concentration monitor for the gas
discharged from the ozone generator to determine
the ozone production rate.
Power input monitor for the ozone generator.
5.4.2.3 Costs of Ozonation Systems
The discussion of ozone system costs is divided into
four sections covering equipment, installation,
housing, and operating and maintenance costs.
Equipment Costs
Ozonation equipment to be purchased includes: air
preparation equipment (drying and cooling), an ozone
generator, an ozone contactor, an ozone destruction
unit, and instrumentation and controls. Because of
the many differences in air pretreatment methods,
ozone contacting, contactor exhaust gas handling,
monitoring, and other operational parameters,
equipment costs presented in this section are general
guidelines only.
For generating large quantities of ozone, 45.36
kg/day (100 Ib/day) and higher, air preparation,
ozone generation, and contacting equipment costs
run approximately $2,866/kg ($l,300/lb) of ozone
generation capacity per day. This figure does not
include ozone destruction, instrumentation, control,
building, and installation costs.
79
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For smaller quantities of ozone, costs are higher per
kilogram, but vary significantly from site to site. For
plants serving less than 10,000 persons per day, 1.4 to
9.5 kg (3 to 21 Ib/day), all items can be assembled into
a. single skid mounted unit.
Small ozonation systems can use diffuser contactors,
which are generally constructed of polyvinyl chloride
(P VC) pipe standing on end, or fiberglass reinforced
plastic (FRP) tanks. Tables 5-12 and 5-13 list
Table 5-12. Costs of Ozonation Equipment for Small Water
Supply Systems: Supplier A ($1982)
Size of Treatment Plant
500.000 GPP 350,000 GPP 180,000 GPD
Maximum
dosage of
ozone
(mg/L)at
poakftow
Daily ozone
requirement
(to)
Contact
chamber
diameter*
(ft)
Equipment
Costs
Atr prepare- $31,500 $25,000 $25,000 $22,000 $22,000 $19,500
ton and
ozone gen-
eration unit
535353
21 14 14 7 7 5
665544
Contact
chamber
with
diffusors
Monitoring
Instrumen-
tation"
Ozone
Destruction
Unit
Total
Equipment
Costs
Power
Require-
ment (kWh)
11,500 11,500 10,200 10,200 9,900 9,900
15,000 15.000 15,000 15,000 15,000 15,000
6,700 5,000 5,000 4,200 4,200 4,200
(10 cfm) (7 cfm) (7 cfm) (3 cfm) (3 cfm) (3 cfm)
$64,700 $56,500 $55,200 $51,400 $51,100 $48,600
13.3 10.1 10.1 5.0 5.0 3.65
ป14 It high, (our compartments, four diffusers, Derakane fiberglass
reinforced plastic.
b Includes monitors for ozone in generator product, ozone in ambient
plant air, ozone dissolved in water, and dew point monitor in air
preparation unit
1 tb - 0.4536 kg;
1 ft ซ 0.3048 meters;
1 GPD - 0.003785 m3/day.
Source: U.S. EPA (1983).
equipment cost estimates obtained from two
ozonation system suppliers in 1982 for small water
supply systems. Equipment costs are higher at
higher dosages for a given flow rate.
Ozone Supplier A provides four monitors with the
system: dew point in the air preparation unit, ozone
output of the generator, ozone in the plant ambient
air (incase of leaks), and dissolved ozone residual in
the water. All are optional (but recommended) for
optimum performance and minimal labor and
downtime.
Ozone Supplier B provided estimates for two types of
air preparation equipment. One type operates at high
pressures (5.6 to 8.4 kg/cm2 [80 to 120 psig]), the
other at low pressures (0.56 to 0.84 kg/cm2 [8 to 12
psig]). The high-pressure units have lower capital
costs, but require more energy for their operation.
Supplier B offers two types of devices to monitor
ozone output from the generator. The automatic, in-
line continuous reading monitor costs $4,000; the
nonautomatic monitor, which requires wet chemistry
calculations to determine ozone output, costs $2,000.
Installation Costs
Costs to install ozonation equipment include labor
and material for piping and electrical wiring. Piping
can be extensive - transporting water to and from the
ozone generators (if they are water-cooled) and the
contactor, transporting ozone-containing air to the
contactor chamber, and transporting contactor off-
gases to and from the ozone destruction unit.
The ozonation equipment suppliers estimate that for
units producing up to 13.6 kg/day (30 Ib/day) of ozone,
installation costs average from $9,705 to $16,175 for
Supplier A and $12,750 to $21,250 for Supplier B.
Housing Costs
Installation of the power supply, air preparation,
ozone generation, and turbine contacting operations
require an area of approximately 3 by 5.1 m (10 by 17
ft). Diffuser contacting units are quite large and high
(5.4 m [18 ft]), and are typically installed outside
existing buildings or in the basement of buildings
constructed for the other ozonation equipment. A
Butler building with the above dimensions can be
constructed for about $6,000.
Operating and Maintenance Costs
Operating costs for ozonation systems vary
depending on:
Oxygen use or air preparation method - high or
low pressure, or subatmospheric pressure
desiccant systems with or without an air chiller
Generator cooling method - air or water cooled. In
northern climates, water at the plant is generally
cold enough to be used as a coolant all year:
Southern climates must refrigerate cooling water
80
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Table 5-13. Costs of Ozonation Equipment for Small Water Supply Systems: Supplier B ($1982)
Size of Treatment Plant
Maximum ozone
dosage (mg/L), at
peak flow
0.1 MGD
3
0.2 MGD
3
0.3 MGD
3
0.4 MGD
3
0.5 MGD
3
Daily ozone
requirement (Ib/day)
Equipment Costs
6
12
14
Pressure
Lowb High0
Pressure Pressure Pressure Pressure
Lowb High0 Lowb High0 Lowb High0 Lowb High0
Air preparation and
ozone generator8
Power requirements
(kWh/lb of 03
generated)
Ozone contractor with
diffusers
Ozone generation
monitor
Chamber exhaust
monitor
Dew point monitor
Total Equipment
Costs
$17,500
10.5 20
$8,500
4,000
2,200
3,500
$35,700
$33,200 $30,200
10.5 13.5
$12,000
4,000
2,200
3,500
$52,900 $49,900
$38,500 $35,000
10.5 13.5
$16,000
4,000
2,200
3,500
$62,200 $59,200
$43,000 $40,000
10.5 13.5
$21,000
4,000
2,200
3,500
$71,700 $68,700
$49,800 $46,800
10.5 13.5
$29,000
4,000
2,200
3,500
$86,500 $83,500
a Includes air preparation, ozone generation, ozone destruction, and system controls.
b Air preparation unit includes air filters or separators, compressor delivering air at 8 to 12 psig to a refrigerative cooler and a dual tower
ฐ Same as low-pressure air preparation system, except compressor delivers air at 80 to 120 psig. High-pressure system takes less space and
requires less maintenance, but requires more energy.
d $4,000 instrument is an automatic, continuous reading in-line monitor. A substitute is a $2,000 instrument that is not automatic and utilizes
wet chemistry.
1 pound = 0.4536 kilograms; 1 MGD = 0.044 m3/sec.
Source: U.S. EPA, 1983.
most of the year. Medium frequency generators
require increased cooling.
ป Contacting method - diffuser contactors do not
require electrical energy as do the more compact
turbine diffusers.
Ozone dosage required
Contactor exhaust gas handling - thermal,
catalytic, or GAG destruction systems.
Maintenance costs include periodic cleaning, repair,
and replacement of equipment parts. For example,
air preparation systems contain air prefilters that
must be replaced frequently, and tube-type ozone
generators normally are shut down for annual tube
cleaning and other general maintenance. Tube
cleaning can require several days of labor, depending
on the number and size of ozone generators in the
system. Tubes, which can be broken during cleaning
or deteriorate after years of operation at high
voltages (or more rapidly if the air is improperly
treated), must be replaced periodically.
Labor requirements, other than for periodic
generator cleaning, include annual maintenance of
the contacting basins and day-to-day operation of the
generating equipment (average 0.5 hour/day).
Table 5-14 summarizes operating and maintenance
costs for equipment from ozone Suppliers A and B.
This table also includes building heating costs
(assumed to be the same up to a 0.22 m3/sec [0.5-
MGD] plant). There are no chemical costs related to
ozone generation, except for periodic changing of
desiccant in air preparation systems (normally after
5 years of use).
5.4.3 Chlorine Dioxide
Chlorine dioxide is an unstable gas, explosive in air
in concentrations above 10 percent by volume
(corresponding to solution concentrations of about 12
g/L). Because of its instability, chlorine dioxide is
always generated on site, in aqueous solution, and
used shortly after its preparation. Solutions up to 5
g/L can be stored for up to 7 days. As long as care is
taken to keep chlorine dioxide in solution and long-
time storage of solution is avoided, there is no
81
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Table 5-14. Operating and Maintenance Costs for Small Ozone Systems3 ($1982)
Electrical Energy (kWh/yr)
Water Flow Rate (mgd)
Supplier A
0.18
0.35
0.50
Supplier B (High-Pressure Air Preparation)
0.10
0.20
0.30
0.40
0.50
Building
6,570
6,570
6,570
6,570
6,570
6,570
6,570
6,570
Process
6,661
12,775
51,611
21,900
29,565
34,493
59,130
68,985
Total
13,231
19,345
58,181
28,470
36,135
41,063
65,700
75,555
Energy I
Costsb
$926
1,354
4,073
$1,993
2,529
2,874
4,599
5,289
Maintenance Labor
Material (hr/yr)
$120
200
300
$120
120
200
250
300
250
250
250
250
250
250
250
250
Labor
Cosf
$2,500
2,500
2,500
$2,500
2,500
2,500
2,500
2,500
Total Cost
($/yr)
$3,546
4,054
6,873
$4,613
5,149
5,574
7,349
8,089
* Assumes 3 mg/L ozone dosage.
b Assumes 0.07/kWh.
c Assumes 10/hour.
1 mgd = 0.044 m3/sec
Source: U.S. EPA (1983).
explosion hazard. Chlorine dioxide is readily soluble
in water, but decomposes in sunlight.
Chlorine dioxide is a more powerful biocide than
chlorine but has a lower oxidation potential. When
prepared in the absence of excess free chlorine, it does
not produce THMs or other chlorinated organic by-
products of concern. Additionally, oxidation of
bromide ion to hypobromous acid does not occur
except when free chlorine is present. However, some
chlorine dioxide generation methods do create
conditions of excess free chlorine in which by-
products are produced if their precursors are present.
Excess free chlorine can also slowly produce chlorite
and chlorate ions by disproportionation under pH
conditions below 2 or above 11. (These conditions are
not usually found in treating drinking water.)
Health effects studies have shown hematological
effects in laboratory animals as a result of exposures
to chlorate and chlorite ions (Abdel-Rahman et al.,
1980). For this reason, EPA currently advises that
the total concentration of chlorine dioxide and its
decomposition products (chlorite and chlorate ions)
be maintained at or below 1 mg/L, which is
equivalent to a maximum applied dosage of 1.2 to 1.4
mg/L.
Gaseous chlorine dioxide has a strong, disagreeable
odor, similar to that of chlorine gas, and is toxic to
humans when inhaled. Its odor is detectable above
concentrations of 0.1 ppm.
Chlorine dioxide can be used to preoxidize phenolic
compounds and separate iron and manganese from
some organic complexes that are stable to
chlorination. Distribution system residuals of
dissolved chlorine dioxide can be longer-lasting than
those of chlorine because chlorine dioxide does not
react with ammonia or form chlorinated organic
materials. Depending on the types and quantities of
organic materials present, periodic tastes and odors
can be produced by chlorine dioxide (Routt, 1989).
Section 5.4.3.1 describes the generation of chlorine
dioxide. Section 5.4.3.2 explains how excess chlorine
dioxide and chlorite ion can be removed from
solution.and Section 5.4.3.3 discusses system design
considerations. Lastly, Section 5.4.3.4 discusses
system costs.
5.4.3.1 Process Description
For drinking water treatment, chlorine dioxide is
generated from solutions of sodium chlorite
(NaClO-2), which is usually purchased as a 25 percent
aqueous solution or as a solid (80 percent sodium
chlorite). Historically, chlorine dioxide has been
produced by treating sodium chlorite with either
chlorine gas, sodium hypochlorite solution and
mineral acid, or mineral acid alone. In all three cases,
the appropriate aqueous solutions of reactants are
metered into and mixed in a chlorine dioxide reactor,
which is a cylinder containing flow distributing
packings, such as Raschig rings, glass beads, or
hollow glass cylinders. Residence time of the
solutions in a properly sized reactor is only a few
seconds. The resulting yellow solution is pumped
directly into the water to be treated.
In this manner, chlorine dioxide solutions are
generated as the material is required and used
immediately. Reactor operations are automated with
appropriate metering and instrumentation that
controls the addition of chlorine dioxide according to
the flow rate of the water being treated.
82
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The three historical techniques for generating
chlorine dioxide are discussed in detail by U.S. EPA
(1983). However, some of these procedures can result
in excess free chlorine being present. Free chlorine
can oxidize chlorine dioxide to form chlorate ions,
which are difficult to remove from solution.
Consequently, the current recommended approach to
chlorine dioxide generation is to maximize its yield
while minimizing the presence of free chlorine (thus
minimizing the formation of chlorate ion).
Slootmaekers et al. (1989) discusses generation
techniques to meet these objectives.
For water disinfection, chlorine dioxide can be
generated using several reaction schemes, such as
the reaction of aqueous hypochlorous acid with
dissolved chlorite ion:
2NaCl02 + HOC1
> NaCl + NaOH + 2C1O2
[1]
Chlorine dioxide also can be generated by the
reaction of solid sodium chlorite in solution with
mineral acid, with chlorine or with hypochlorous
acid. The reaction for chlorine and/or hypochlorous
acid with chlorite ion is:
2C1O2- + Cl2(g) [2a]
>2ClO2(g) + 2C1
2C1O2- + HOC1 [2b]
>2C102(g) + Cl- + (OH)
These reactions involve the formation of the
unsymmetrical intermediate, Cl2O2:
C12 + C102 > [C1202] + Cl- [3]
At high concentrations of both reactants, the
intermediate is formed very rapidly. Elemental
chlorine formed by Equation [4] is recycled by means
of Equation [3]. Thus, primarily chlorine dioxide is
produced as a result:
2[C12O2]
2C1O2
C12
or
[C12O2J + C1O2 ------ > 2C1O2
Cl
[4]
[5]
On the other hand, at low initial reactant
concentrations, or in the presence of excess
hypochlorous acid, primarily chlorate ion is formed,
due to the following reactions:
[C1202] + H20
> cio3- + cr
2H+
and
[C12O2] + HOC1
> C1C-3- +
Cl- + H+
[6]
[7]
Thus, high concentrations of excess chlorite ion favor
the second order reactions (Equations 4 and 5), and
chlorine dioxide is formed. At low concentrations,
the second order disproportionation process becomes
unimportant, and reactions 6 and 7 produce chlorate
ion rather than chlorine dioxide. The reasons for the
production of chlorate ion are related to the presence
of high concentrations of free chlorine and the rapid
formation of the C12O2 intermediate, which, in turn,
reacts with the excess hypochlorous acid to form the
unwanted chlorate ion.
The stoichiometry of the undesirable reactions which
forms chlorate ion is:
C12O2- 4- HOC1
> cio3- + cr
C1O2- + C12
----- > C1C-3- +
+ H2O
2C1- +
2H+
[8]
[9]
Therefore, the most effective way to minimize
chlorate ion formation is to avoid conditions that
result in low reaction rates (e.g., high pH values
and/or low initial reactant concentrations, and the
presence of free hypochlorous acid). Clearly, the
reaction forming chlorate ion (Equation 6) will be
more troublesome in dilute solutions. On the other
hand, whenever treatment by chlorine dioxide (which
forms chlorite ion in the process) is followed by the
addition of free chlorine (HOC1 with a pH of 5 to 8),
the unwanted chlorate ion will also be formed.
5.4.3.2 Establishing a Chlorine Dioxide
Residual
Laboratory studies have shown that about 70 percent,
of the chlorine dioxide added to drinking water is
converted to chlorite ion (Singer, 1986). Therefore,
1.2 to 1.4 mg/L chlorine dioxide is the maximum
practical dosage to meet the currently recommended
maximum total oxidant residual of 1 mg/L. However,
Slootmaekers et al. (1989) reports that nearly all of
the chlorine dioxide ion added as a primary
oxidant/disinfectant is converted to chlorite ion.
Because of differences in the nature of water
constituents that exert demand for chlorine dioxide,
this ratio should be individually determined for each
water supply.
83
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Recent studies (Pinsky and Coletti, 1988) have shown
that when water containing 1 to 5 mg/L of chlorine
dioxide is passed through a GAC column (with 6-
minute EBCT), the residual chlorine dioxide and
chlorite ions are chemically reduced to innocuous
chloride ions. This implies that as long as GAC with
sufficient EBCT is used after primary disinfection or
oxidation with chlorine dioxide, the currently
recommended maximum levels for chlorine dioxide,
chlorite, and chlorate are achievable regardless of the
dosages of chlorine dioxide used.
More recently, Howe et al. (1989) have confirmed the
reduction of chlorine dioxide and chlorite ion on
passage through GAC. GAC does not, however,
remove chlorate ion. These researchers showed that
breakthrough of chlorite ion occurred after
approximately 94 and 100 days of passage through
GAC columns having 7.5 and 15 minute EBCT,
respectively. Thus, the capacity for GAC removing
chlorite ions in these studies was between 14 and 15
mg of chlorite ion per gram of GAC.
These data indicate that if GAC is to be installed for
postfiltration adsorption of organics, chlorine dioxide
can be employed as a primary disinfectant
some where ahead of the GAC. However, if
postfiltration GAC adsorption is installed only to
remove chlorine dioxide and chlorite ion, the costs
will be very high (because of the postfiltration GAC
installation and 90-110 days reactivation needed for
breakthrough of chlorite ion).
Slootmaekers et al. (1989) have shown that it is
technologically feasible to reduce chlorine dioxide
and chlorite ions to chloride ion with sulfur dioxide.
Once oxidant demand has been satisfied with
chlorine dioxide, excess sulfur dioxide/sulfite ion can
be added to the treated water to remove residual
chlorine dioxide and chlorite ion. This would be
followed by the addition of free chlorine to remove the
excess residual sulfur dioxide/sulfite ion.
The stoichiometry of the reaction is consistent with
the equation:
cio2
cr
This corresponds to a stoichiometry of two moles of
SOgS- consumed for every mole of C102- reduced.
Over a range of conditions studied by Slootmaekers et
al. (1989), at room temperature, the stoichiometry
deviated by less than 5% from the value shown in the
equation. Furthermore, the stoichiometry appears to
be independent of temperature in the 5ฐ to 30ฐC
range.
However, at pH 8 and above and in the presence of
air, the overall stoichiometry appears to deviate from
that shown by the above equation, probably due to an
increase in the rate of the competing sulfite
ion/oxygen reaction. Thus, less acid solutions (e.g., in
the pH 5.5 to 6 range) favor the rapid reduction of
chlorite ion and minimize the loss of sulfite ion from
the competing sulfite ion/oxygen reaction.
Thus, Slootmaekers et al. (1989) have established
that the sulfur dioxide/sulfite ion - chlorite ion
reaction is greater than 95 percent effective.
Furthermore, with a 10-fold excess of sulfur
dioxide/sulfite ion and with chlorite ion at the 0.5 to 7
mg/L level, the removal of chlorite ion is complete in
less than one minute at pH 5 and below, and
completed in 15 minutes or less at pH 6.5. This
means that sulfur dioxide/sulfite ion can be used to
reduce the level of chlorite ion by-product in drinking
water to below the 0.1 mg/L without great difficulty.
However, the rate of reductive conversion of chlorine
dioxide and chlorite ion to chloride ion decreases with
increasing pH as illustrated by the following data:
Beginning Chloride
pH Ion Cone. (mg/L)
5.0
5.5
5.5
6.5
6.5
7.5
7.5
8.5
0.5
0.5
1.0
1.0
1.Q
1.0
1.0
1.0
Beginning Sulfite
Ion Cone. (mg/L)
5.0
5.0
10.0
10.0
20.0
10.0
100.0
. 100.0
Time required for
99% removal of
chlorite ion
0.34 minutes
4.4 minutes
1.1 minutes
15.2 minutes
3.8 minutes
15.6 hours
9.4 minutes
3.2 days
In practice, if all of the chlorite ion is not removed in
the time allotted, three choices are available to the
treatment plant operator:
Increase the amount of sulfur dioxide/sulfite ion
used in the removal process: doubling the
amount will remove the chlorite ion four times
faster since the rate is second order in the
concentration of sulfur dioxide/sulfite ion.
Decrease the pH: every decrease of pH by one
unit increases the rate of chlorite removal by at
least a factor of ten.
Increase the length of time for removal: the rate
of removal is logarithmic in time, since the
removal of chlorite ion is first order in the
concentration of chlorite ion.
The ability to remove chlorite ion by-product allows
considerably higher chlorine dioxide concentrations
to be used (easily up to 6 to 8 mg/L), eliminating the
84
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need for a combination of chlorine dioxide and free
chlorine, the most common sources of chlorate ion.
It is important to note that chlorate ion is not
chemically reduced by sulfur dioxide/sulfite ion
under the conditions studied by Slootmaekers et al.
(1989). The calculated half-life for the removal of
mg/L levels of chlorate ion with excess sulfur
dioxide/sulfite ion is in excess of many months.
Chlorate ion in the finished water can arise from one
of two possible sources:
Improperly tuned older chlorine dioxide
generators.
As a by-product during the chlorine dioxide
oxidation/disinfection step, especially when free
chlorine is used concomitantly.
5.4.3.3 Chlorine Dioxide System Design
Considerations
Several types of generation equipment are available.
Each supplier provides recipes for preparing and
metering the solutions to the reactor to produce a
known and constant chlorine dioxide concentration.
For smaller systems treating less than 0.022 m3/sec
(0.5 MGD), the chlorine dioxide dosages required are
very low. In these cases, the generating units may be
operated intermittently, collecting chlorine dioxide
solution in an enclosed holding tank from which a
metered flow can be delivered later. Intermittent
operation is recommended over continuous operation
because the mixing of reactant solutions is less
efficient in the reactor at consistently low flow rates;
thus, the conversion of chlorite ion to chlorine dioxide
will be less efficient. Selected generation systems are
briefly discussed below.
Gaseous Chlorine Systems
The most common chlorine dioxide generation
process uses chlorine gas and sodium chlorite (U.S.
EPA, 1983). This process is convenient when
chlorine gas was previously used for primary
disinfection at the plant. Figure 5-8 is a schematic
diagram of such a system.
Sodium Hypochlorite and Mineral Acid
Systems
A manual feed system that produces chlorine dioxide
using sodium hypochlorite solution with sodium
chlorite and strong mineral acid is illustrated in
Figure 5-9.This process is well suited to most small
treatment systems. The operator can adjust solution
strength for each reactant so that feed pumps of equal
capacities can be used. The chlorine dioxide
production and addition rates are paced according to
the flow rate of the water and/or the secondary
disinfectant demand.
Sodium chlorite is available either as a solid (80
percent active sodium chlorite) in 90.72-kilogram
(200-pound) drums or as a solution (25 percent active
sodium chlorite, 31.25 percent solids in 208.2-liter
[55 gallon] drums). If not used directly from the
drum, sodium chlorite solution is stored in
polyethylene or fiberglass tanks and transferred by
means of PVC, rubber, or Tygon tubing systems.
Diaphragm pumps with PVC components are used to
transfer the sodium chlorite solution. Provision must
be made for immediate washdown of any chemical
spills; this precaution is generic to all chlorine
dioxide generating systems.
The CIFEC System for Generating Chlorine
Dioxide
The CIFEC System was developed in France and is
currently used by several treatment plants in the
United States. Figure 5-10 is a schematic diagram of
this system, which produces chlorine dioxide from
chlorine gas. This system produces high yields of
chlorine dioxide under conditions of minimal excess
free chlorine.
In the CIFEC system, chlorine gas is injected into
continuously circulating water, referred to as an
"enrichment loop." This method produces much
higher concentrations of dissolved chlorine
(hypochlorous acid) than those achieved in a system
using a single injection point. The hypochlorous acid
solution (pH below 4) is pumped into the reactor
along with a sodium chlorite solution. Since the pH
of the hypochlorous acid solution is below 4, more
chlorite ions are converted to chlorine dioxide than in
other chlorine gas systems that operate in higher pH
ranges. In addition, chlorine dioxide is produced with
little free chlorine.
Rio Linda Chlorine Dioxide Generator
Rio Linda Chemical Co., Inc. manufactures a unique
chlorine dioxide generator. In this system, shown
schematically in Figure 5-11, chlorine dioxide is
generated by the addition of chlorine gas to a sodium
chlorite solution, as in other systems. The novel
aspect of this generator is that chlorine gas is mixed
with concentrated sodium chlorite solution just
before the reactor. The vacuum action from the water
flowing through an eductor into the reactor brings
the two solutions together. Since there is no need for
a pump, the system is more compact.
This system can be operated manually or
automatically. Additionally, the system can be
designed to mix in solutions of hydrochloric acid,
hypochlorite and sodium chlorite just before the
chlorine dioxide reactor. Generator efficiencies with
85
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excess chlorine are claimed to approach greater than
98 percent conversion of the sodium chlorite into
chlorine dioxide, with minimal production of chlorate
ion at an effluent pH between 6.5 and 7. Production
rates of these generators can range from a few pounds
up to 2,721.6 kilograms (6,000 pounds) per day.
Summary of Commercial Chlorine Dioxide
Generators
In many older chlorine dioxide generators,
hydrochloric acid is fed into the chlorine solution
before reaction with the sodium chlorite. The acid
shifts the chlorine solution equilibria in favor of
molecular chlorine (Slootmaekers et al., 1989). (The
hypochlorous acid dissociation and the chlorine
hydrolysis equilibrium are shown in the equations
below.)
HOC1 > (OCl)'
+ H2O
+ H*
> HOC1
HC1-
The acid must be carefully controlled so that the pH
of the chlorine dioxide solution is maintained
between 2 and 3. Higher or lower pH values result in
decreased yields. Yields of more than 90 percent
have been reported from a properly pH-adjusted
system (Aieta & Berg, 1986), with approximately 7
percent excess chlorine remaining in solution (where
excess chlorine is defined as the amount of unreacted
chlorine remaining in the chlorine dioxide generator
effluent).
High yields of chlorine dioxide, with low levels of free
chlorine in solution, can be produced using a chlorine
solution with a concentration greater than 4 g/L.
This chlorine concentration is near the upper
operating limit of commercial chlorine ejectors.
Since these ejectors operate at constant water flow
rates, the yield of this method of generation is
dependent upon the production rate, with lower
production rates resulting in lower yields. This type
of generator normally operates on an intermittent
basis to maintain a high yield when less than
maximum production capacity is required.
The most recent development in chlorine dioxide
generator technology is a system that uses the
reaction of chlorine with a concentrated sodium
chlorite solution under vacuum (Aieta & Berg, 1986;
Aieta & Roberts, 1986). The chlorine dioxide is
removed from the reaction chamber by a gas ejector,
which is very similar to the common chlorine gas
vacuum feed system. This technique of generation
produces chlorine dioxide solutions with yields in
excess of 95 percent. The chlorine dioxide
concentration is 200 to 1,000 mg/L and contains less
than 5 percent excess chlorine with minimum
formation of chlorate ion. However, in this context, it
should be noted that almost all older chlorine dioxide
generators now in use in water treatment plants
throughout the United States continue to produce
some chlorate ion, unless they are very carefully
tuned and properly monitored. A well-tuned
generator may produce as little as 1 to 2 percent
chlorate ion (Slootmaekers et al., 1989).
5.4.3.4 Costs of Chlorine Dioxide Disinfection
The costs of chlorine dioxide systems are presented in
three categories: equipment, operating and
maintenance, and chemical costs.
Equipment Costs
Quotes from two suppliers of chlorine dioxide
generation equipment were obtained in 1982 (see
Table 5-15). Supplier A's recirculating loop system
(CIFEC) is the highest priced unit at $34,000. It
operates with a special recirculating pump designed
to handle hypochlorous acid below pH 4, plus a
sodium chlorite solution pump and all necessary
instrumentation to allow automatic operation. There
are shutdown provisions in the event of interruptions
in water flow.
The next lowest in price is the system from Supplier
B that generates chlorine dioxide from 33 percent
hydrochloric acid, 12 percent sodium hypochlorite,
and 25 percent sodium chlorite solution. This wall-
mounted unit costs $25,000 (installed), and includes
three solution pumps, a water flow rate detector, and
switches to shut down the unit if the water flow stops.
For chlorine dioxide volumes sufficient to treat flows
in communities with populations of 5,000 and 2,500,
this unit is capable of continuous operation, with no
loss in conversion efficiency of chlorite ion to chlorine
dioxide. However, to supply the needs of systems
serving as few as 25 persons, the unit must be
operated intermittently, with chlorine dioxide
solution being stored in a holding tank for later
metering into the water.
Supplier C provides two types of chlorine dioxide
generators for small water supply systems. One uses
acid/sodium chlorite; the other uses chlorine gas and
sodium chlorite. These units cost $3,600 wall-
mounted, and $4,320 for a floor-mounted cabinet. The
single size unit offered by this supplier is designed to
generate up to 63.5 kg/day (140 Ib/day). In order to
produce 3.63 kg/day (8 Ib/day) or less, a small water
utility must install a holding tank and operate the
generator intermittently.
The chlorine gas/sodium chlorite generator of
Supplier C requires a gas chlorinator to feed chlorine
gas. Therefore, in new plants considering this type of
equipment, the cost of a chlorinator must be added to
the cost of the chlorine dioxide generator. In existing
plants currently using gas chlorination, the
86
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Water Flow Metei
G - Gage
Chlorine
Orifice
Positioner
Chlorine Dioxide
Generating Tower
Point of
_L Application
Injector Water Supply
Figure 5-8. Schematic diagram of an automatic feed, automatic flow-proportional chlorine dioxide system: Generation from
chlorine and sodium chlorite.
Source: Capital Controls Co., Inc.
chlorinator already is in place, and therefore would
not represent additional equipment cost.
The purchaser of chlorine dioxide generating systems
should consider the inclusion of additional equipment
to allow automatic operation, such as microprocessor-
controlled electronic valve systems, ratio-
proportioning and flow-paced systems, and remote
start and feed capabilities. In addition, alarm
facilities for operating parameters such as low
feed/production ratios, low yields, shut-offs for
chlorine dioxide in air, low reactant feed for chlorine
gas or sodium chlorite solution, high or low vacuum,
and low water flows or pressures are advisable
options.
Operating and Maintenance Costs
In general, operating and maintenance costs for
generating chlorine dioxide are independent of the
quantities generated. Table 5-16 summarizes these
costs on an annual basis. Maintenance material costs
are for minor equipment repair only. Labor required
for preparation of solutions and periodic maintenance
of the equipment is estimated to be 1 hour/day, or 365
hours/year. Total annual operating and maintenance
costs of $4,124/year are estimated.
Chemical Costs
At a production rate of only 3.6 kg/day (8 Ib/day)
(maximum for a 0.044 m3/sec [1-MGD] water
treatment plant at a 1 mg/L applied chlorine dioxide
dose), chemical costs are not as significant as
pumping costs. Chemical costs in 1982 were as
follows:
Gaseous chlorine $1.04/kg ($0.47/lb)
Sodium chlorite
$3.42 to $3.64 ($1.55 to
$1.6571b) (100 percent
solids)
Hydrochloric acid $0.22/kg ($0.10/lb)
Sodium hypochlorite $0.25/L ($0.93/gal) (15
percent solution)
5.4.4 Ultraviolet Radiation
UV radiation is an effective bactericide and virucide,
but an ineffective cysticide. Consequently, it is
recommended as a primary disinfectant only for
ground waters not directly influenced by surface
waters (where there is no risk ofGiardia cyst
contamination). UV radiation (254 nm wavelength)
penetrates the cell wall and is absorbed by the
cellular nucleic acids. Radiation absorption prevents
87
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CIO2
Chlorine Dioxide
Generating Tower
Point of
Application
o
Dual-Head
Diaphragm Pump
Q
i
*
]
Sulfuric Acid
Rgure 5-9. Manual feed equipment arrangement for generating chlorine dioxide from sodium hypochlorite solution and
mineral acid.
Source: U.S. EPA (1983).
replication, thus killing the cell. Since UV radiation
is not a chemical agent, it produces no toxic residual.
Major advantages of UV radiation are its simplicity,
lack of impact on the environment and aquatic life,
and minimal space requirements. In addition,
required contact times are seconds rather than
minutes. The equipment is simple to operate and
maintain if the apparatus is cleaned properly on a
regular basis.
Section 5.4.4.1 describes the process of disinfection
with UV radiation. System design considerations,
including lamp designs, are provided in Section
5.4.4.2. Operating and maintenance considerations
are discussed in Section 5.4.4.3 and costs of UV
systems are described in Section 5.4.4.4.
5.4.4.1 Process Description
UV radiation disinfection uses a special lamp to
transfer electromagnetic energy to the target
organism cells. The most efficient and widely used
device is the mercury arc lamp. It is popular because
approximately 85 percent of its energy output is of
the 253.7 nm wavelength, within the optimum
germicidal range of 250 to 270 nm. The lamps are
long thin tubes. When an electric arc is struck
through mercury vapor, the energy discharge
generated by the mercury excitation results in the
emission of UV radiation. This radiation then
destroys the cell's genetic material and the cell dies.
The effectiveness of radiation is a direct function of
the energy dose absorbed by the organism, measured
as the product of the lamp's intensity and the time of
exposure. Intensity is the rate at which photons are
delivered to the target. The intensity in a reactor is
governed not only by the power of the lamp, but also
by the placement of the lamps relative to the water,
and by the presence of energy sinks that consume UV
radiation. Water with suspended solids, color,
turbidity, and soluble organic matter can react with
or absorb the UV radiation, reducing the disinfection
performance. Therefore, water with high
concentrations of these substances may receive
inadequate disinfection.
The radiation dose absorbed by the water is the
water's UV demand, which is analogous to chlorine
demand and is quantified as the absorption of UV
energy (wavelength of 253.7 nm) in a given depth of
water. The measurement is most commonly
expressed by the UV absorbance coefficient alpha:
alpha = 2.3 absorbance units(a.u.)/cm
In addition to intensity and UV demand of the water,
the exposure time also affects the energy dosage that
the target organisms absorb. Exposure time is
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Chlorinator
Vacuum Line of Chlorine
Ejector with Check Valve Assembly
ij=O C1O2 Exit
Jt
Sodium Chlorite Metering Pump
Chlorine Cylinder
Recirculating Pump
Flow Meter
Electric Valve
Make-Up
Water Supply
Figure 5-10. Schematic of CIFEC chlorine dioxide generating system.
Source: CIFEC, Inc., Paris, France.
Chlorine Dioxide Solution
to Process
Chlorine Dioxide
Reaction Column
Chlorine
Rotameter
Figure 5-11. Schematic of manual chlorine dioxide system.
Source: Rio Linda Chemical Co., Sacramento, California
89
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Tabls 5-15. Costs of Chlorine Dioxide Generating Equipment $1982
Vendor System Type
Production
Capacity Space
(Ib/day) Requirements3
Reactants
Unit Cost
($)
Supplier A Recirculating loop 1-10 2 x 3 x 6 feet
(CIFEC)
Supplier B Wall-mounted unit 4 3.5 x 4 x 1.5
feet
Supplier C Floor-mounted unit 14-140 4x3x1.5
6.5 inches
Supplier C Wall-mounted unit 14-140 37.5 x 27 x
6.5 inches
Supplier C Floor-mounted unit 14-140 4 x 3 x 1.5
feet
Supplier C Wall-mounted unit 14-140 37.5 x 27 x
6.5 inches
Chlorine gas, sodium chlorite solution 34,000
Hydrochloric acid, sodium hypochlorite, and 25,000
sodium chlorite solutions
Chlorine gas and sodium chlorite solution 4,300b
Chlorine gas and sodium chlorite solution 3,600b
Hydrochloric acid and sodium chlorite solution 4,300
Hydrochloric acid and sodium chlorite solution 3,600
Spaca requirements for solution tanks are not included.
b Costs for a chlorinator are not included in these estimates.
1 Ib - 0.4536 kg; 1 ft - 0.3 m; 1 inch = 2.54 cm.
Source: U.S. EPA (1983).
Table 5-16. Operation and Maintenance Cost Summary
for Chlorine Dioxide Generating and Feed
Systems
Item
Electrical Energy
Metering pumps and
mixers
Building
Subtotal
Maintenance Materials
Labor
Total Annual O&M Cost
Requirements
1,240 kWh/yr
4,100 kWh/vr
5,340 kWh/yr
365 h/yr
Annual Costs
($)
86.80
287.00
373.803
100.00
3,650b
4,124
ซ Assumes S0.07/kWh.
b Assumes $10/hour labor cost
Source: U.S. EPA (1983).
controlled by the residence time of the water in the
reactor. Continually maintaining the required
residence time is not always possible, but the system
design should maximize plug-flow operation.
If the energy dosage is not sufficient to destroy the
target organisms' DNA macromolecules, disinfection
is not effective. Photoenzymatic repair occurs if the
genetic material is only damaged during irradiation.
This repair mechanism, called photoreactivation,
occurs with exposure to light from the sun or most
incandescent and fluorescent lights (wavelengths
between 300 and 500 nm). Photoreactivation does not
occur with all bacterial species and is difficult to
predict.
To prevent photoreactivation, the rule of thumb is to
increase the dosage necessary to meet required
reductions in organism levels (U.S. EPA, 1986b). For
example, if the disinfection criteria require a 3-log
reduction of microorganism concentrations, the UV
radiation system should be designed to provide a 4-
log reduction.
5.4.4.2 UV Disinfection System Design
Considerations
The basic design considerations for a UV system are:
Satisfying the U V demand of the water
Maximizing the use of UV energy delivered by
the lamps
Maintaining the conditions that encourage plug
flow
UV lamps are usually submerged in the water,
perpendicular or parallel to the water flow.
Submerged lamps are inserted into a quartz sleeve to
minimize the water's fouling effects. The further the
distance between the water and the lamp, the weaker
the radiation dosage delivered because the energy
dissipates or becomes dilute as the space it occupies
increases in volume. The UV demand of other
contaminants in the water also consumes radiation.
Specific design parameters to consider are:
1. Residence Time Distribution (RTD) - This
describes the detention time of the water in the
reactor and should be determined for several flow
conditions.
2. Plug Flow - The ability to maintain plug flow in
the reactor is influenced by the inlet and exit
designs. Disturbances at the inlet and exit planes
of the lamp battery should be minimized and
90
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necessary changes in the flow direction should be
made outside the lamp battery.
3. Dispersion Number - A key goal is to minimize
the dispersion number, d (cm2/s). As a design
goal, d should be between 0.02 and 0.05. This
number represents a plug-flow reactor with low
to moderate dispersion. This value is attained by
increasing the product of the velocity (cm/s) of
and distance traveled (cm) by the water as it
flows through the reactor while under direct
exposure to UV radiation. However, extended
lengths and higher velocities cause higher head
losses; therefore, adjusting the dispersion
number may be necessary to meet specific
criteria for both full-scale modules or pilot units.
Head loss is determined over a wide velocity
range and excludes entrance and exit losses.
4. Effective Volume- The inlet and outlet designs
should achieve equivalent water velocities at all
points entering and exiting the lamp battery.
This maximizes the lamp battery use and
improves cost effectiveness. Stilling walls
(perforated baffles) and weirs in the reactor
design assist in controlling water velocities.
UV Lamp Designs
Lamps used in UV disinfection systems typically
have arc lengths of approximately 0.8 and 1.5 m (2.5
and 4.9 ft) and full lengths of 0.9 and 1.6 m (3 and 5.3
ft), respectively. The arc length describes the active,
light-emitting portion of the lamp. Lamp diameters
typically are 1.52 and 2.0 cm (0.6 and 0.8 in). A sleeve
made of fused quartz or another material that is
highly transparent to UV light, such as Vycor,
protects lamps that are submerged. Nonsubmerged
lamps are placed near the wall of the water conduit,
which is made of a UV light-translucent material.
Factors Affecting the Design of the UV
Disinfection System
Initial microorganism density, suspended solids (or
turbidity), UV demand of the water at the
disinfection point, and water flow rate all affect the
size and performance of the U V disinfection system.
The performance of a UV disinfection unit relates
directly to the initial density of the indicator
organisms. The higher the initial density, the greater
the dosage of radiation required. For this reason,
microorganism density should be continually
monitored. Turbidity directly affects the performance
of the UV disinfection system as well. Particulates
suspended in water block the UV radiation, thereby
protecting bacteria and hindering disinfection. The
U V demand of the water affects the radiation
intensity in the reactor and, thus, affects the system
size and the lamp placement that achieves the
desired performance.
Water flow rate is another key factor in determining
system size. Both the hydraulic load to the plant and
the design of the processes preceding disinfection
affect flow. The size of the UV system, however,
should be based on peak flow rates and projected
flows for the plant's design year rather than on
average flows, which are used to predict operating
and maintenance requirements.
5.4.4.3 UV System Operating and Maintenance
Considerations
This chapter discusses operation and maintenance of
UV lamps and reactor care. The intensity of radiation
in the reactor depends on the lamp output and the
reactor cleanliness. Therefore, monitoring lamp
intensity and properly maintaining the reactor are
essential to reliable system performance.
Operation and Maintenance of UV Lamps
Lamp output is influenced by lamp temperature,
voltage potential across the lamp, and age of the
lamp. Lamp temperature cannot be controlled in
submerged lamp systems. In other systems, however,
lamp temperatures are controlled by regulating
ambient air temperatures using cooling fans or
recirculating the heat generated by the lamp ballasts
for warming.
Adjusting the voltage will vary the lamp output.
Decreasing the voltage reduces current to the lamp
and, therefore, lamp output. Voltage regulators
improve system efficiency by reducing voltage and
"dimming" lamps to conserve power during periods of
low UV demand. Lamp intensity cannot be reduced to
levels below 50 percent, however, without causing
the lamps to flicker and eventually turn off.
Factors affecting deterioration of performance and
aging of UV lamps include electrode failure; mercury
plating or blackening in the lamp's glass tube; and
tube solarization, which results in reduced energy
transmission through the glass. These factors can
reduce lamp output by 40 to 60 percent.
U V lamps used for disinfection are typically hot
cathode lamps, which deteriorate progressively with
each startup. Life expectancy is determined by the
number of times the lamp is started. The lamp life
cited by most manufacturers is 7,500 hours, based on
a burning cycle of 8 hours; that is, the lamp will last
7,500 hours assuming it is restarted every 8 hours.
The average UV output after 7,500 hours is
estimated to be 70 percent of the lamp output at 100
hours.
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Monitoring Lamp Intensity
Lamp intensity should be measured to monitor lamp
condition and determine the need for maintenance.
The monitoring procedure compares current lamp
intensity to the intensity of new lamps. The operator
first measures the intensity, at a fixed distance, of
three to five new lamps that have burned for about
100 hours (the first 100 hours is considered a "burn-
in" period). The average of these values is the
benchmark from which to measure the relative
output of the lamps. Each lamp is tagged so that it
can be monitored individually.
A similar procedure is used to monitor the
transmittance of a quartz sleeve. First, the intensity
of a single lamp is measured with and without a new,
clean quartz sleeve. Similar measurements are taken
of the quartz unit in use and compared to the
transmittance of the new quartz. Before being tested,
the quartz is cleaned to assure that maximum
transmittance is restored.
Operation and Maintenance of the Reactor
The most important operating factor for the UV
reactor is the cleanliness of the surfaces through
which radiation must pass. Surface fouling can result
in inadequate performance, so a strict maintenance
schedule is recommended.
An operator determines the need for reactor
cleansing by draining and visually inspecting the
surfaces. Open reactor systems are easily inspected.
Systems with sealed vessels are inspected through
portholes or manways in the reactor shell. Surfaces of
submerged quartz systems become coated with an
inorganic scale, very much like boiler scale. This is a
particular problem in areas with hard water.
Additionally, the inside surface of the quartz and the
outer surfaces of the Teflon tubes eventually develop
a grimy dust layer, primarily from airborne dirt and
water vapor.
Fouling of the reactor's internal surfaces also is
indicated by reduced performance and intensity
measured by in-line probes. While these provide some
indication of fouling, operators must still visually
inspect the surfaces.
The fouled surfaces of lamps and quartz sleeves are
cleaned manually with a mild soap solution and then
swabbed with a rag soaked in isopropyl alcohol. The
transmittance of the lamps and sleeves is measured
after cleaning and those that have inadequate
measurements are replaced. An inventory allows the
plant operator to trace operation of individual
components. Quartz sleeves should last between 4
and 7 years, but this varies by site.
In Teflon systems, the lamps are on removable racks
and should be cleaned and monitored in the same
manner as the quartz systems. The Teflon tubes
should also be cleaned with mild soap and swabbed
with alcohol. Each tube should be monitored for
transmittance, just as with the quartz sleeves.
Monitoring may not be as straightforward because of
the limited accessibility to the tubes and problems in
obtaining direct measurements with a U V
radiometer/detector.
5.4.4.4 Costs of UV Radiation Systems
Table 5-17 summarizes construction costs developed
for single and multiple UV lamp disinfecting units
ranging in water throughput capacity from 54.5 to
4,251.3 m3/day (14,400 to 1,123,200 gal/day). UV
generating units are quite compact; for example, the
4,251.3 m3/day (1,123,400 gal/day) unit occupies an
area less than 2.2 m2 (24 ft2). Costs listed in Table 5-
17 include UV unit equipment costs, and the related
piping, electrical, installation, and equipment
housing costs.
Operating and maintenance costs are shown in Table
5-18 for the same size plants as in Table 5-17. Costs
assume continuous 24 hour/day operation, with only
occasional shutdown to clean cells and replace worn
out UV lamps. These costs include process energy for
the mercury lamps and building energy for heating,
lighting, and ventilating.
Maintenance materials costs are related to
replacement of the UV lamps, which may be required
about every 8 months if operated continuously. Labor
requirements include occasional cleaning of the
quartz sleeves surrounding the mercury vapor lamps,
and periodic replacement of the weak UV bulbs.
5.5 Secondary Disinfectants
Secondary disinfectants provide an essential residual
that prevents regrowth in the distribution system.
Although chlorine is the most widely used secondary
disinfectant, chlorine dioxide and monochloramine
are appropriate as well. As secondary disinfectants,
chlorine and chlorine dioxide are handled in the same
manner as for primary disinfectants. (See Sections
5.4.1. and 5.4.3 for information on the process and
equipment). Section 5.5.1. discusses the use of
monochloramine as a secondary disinfectant.
5.5.1 Chloramination
Chloramine is recommended as a secondary
disinfectant because it is ineffective as a virucide,
and is only marginally effective against Giardia
cysts. It is formed from the combination of ammonia
and chlorine (hypochlorite or hypochlorous acid). The
chemical is generated on site, usually by injecting
ammonia gas or adding an ammonium sulfate
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solution to chlorinated water, or by adding chlorine to
water containing ammonia. Ammonia gas can be
purchased as an anhydrous liquid in cylinders for
small water treatment systems; ammonium sulfate
can be purchased as a powder in bags.
Section 5.5.1.1 describes the chloramination process.
Sections 5.5.1.2 through 5.5.1.4 discuss establishing
a chloramine residual, system design considerations,
and chloramination systems costs, respectively.
5.5.1.1 Process Description
When water, chlorine, and ammonia are combined,
three different species of chloramine compounds can
be generated:
NH3
HOC1
ammonia hypochlorous
acid
H2O
water
NH2C1
mono-
chlpr-
amine
NH2C1 + HOC1
H2O
NHC12 + HOC1 ----- > H2O
NHC12
dichloramine
I- NC13
nitrogen
trichloride
The mix of species produced depends on the ratio of
chlorine to ammonia and the pH of the water. In the
pH range of 7 to 8 with a chlorine-to-ammonia ratio
(by weight) of 3 to 1, monochloramine is the principal
product. At higher chlorine-to-ammonia ratios or at
lower pH values (5 to 7), some dichloramine will be
formed. If the pH drops below 5, some nitrogen
trichloride (often erroneously called "trichloramine")
may be formed. Nitrogen trichloride formation
should be avoided because it imparts undesirable
taste and odor to the water.
Figure 5-12 shows the relative percentages of
monochloramine and dichloramine produced as the
pH changes, for different weight ratios of chlorine to
ammonia. At a pH value of about 5.7, approximately
equal amounts of mono- and dichloramines are
present in solution.
Care should be taken not to exceed chlorine-to-
ammonia ratios of 5 to 1. This is the "breakpoint"
curve above which all ammonia is removed,
chloramines are absent, and free residual chlorine is
present.
5.5. 1.2 Establishing a Chloramine Residual
Establishing a chloramine residual involves a period
of mixing the chlorine and ammonia with the water,
followed by a short holding time to allow the
reactions to take place. Usually, chloramine-forming
reactions are at least 99 percent complete within a
few minutes.
The National Academy of Sciences (NAS)
recommends adding ammonia to chlorinated water
rather than adding chlorine to water containing
ammonia. The recommended process produces a
residual of free chlorine above that required to
oxidize nitrogen (particularly the organic nitrogen
compounds), Organic nitrogen compounds will
compete successfully with ammonia-nitrogen for
chlorine, forming organic chloramines, which are
weaker disinfectants than monochloramine. Normal
field analytical techniques cannot distinguish
between inorganic and organic chloramines. Thus,
formation of inorganic chloramines in the presence of
organic nitrogen compounds can seriously overstate
the actual capability of the chloramine system to
provide secondary disinfection.
5.5.1.3 Chloramination System Design
Considerations
Ammonia is available as an anhydrous gas (NHg), a
29 percent aqueous solution (aqua ammonia), or as
ammonium sulfate powder ([NH4]2SO4). Gaseous
ammonia is supplied in 68-kg (150-lb) cylinders, aqua
ammonia in 208.2-L (55-gal) drums, and ammonium
sulfate in 45.4-kg (100-lb) bags (98 percent pure, 25
percent available ammonia).
Ammonia gas is injected into treated water using
systems and equipment similar to those used for
chlorine gas. Aqua ammonia is handled using
systems similar to those used for sodium
hypochlorite. This form of ammonia is basic and has a
strong odor, but is not corrosive. For ammonium
sulfate powder, a 25 to 30 percent solution is prepared
in a plastic or fiberglass container and added to the
water by means of a chemical metering pump.
Equipment similar to that used for handling calcium
hypochlorite can be used for this process. Solutions of
ammonium sulfate are stable, but acidic, and,
therefore, corrosive to some metals. Materials that
withstand dilute sulfuric acid will also withstand the
corrosion effects of dilute ammonium sulfate
solutions.
5.5.1.4 Costs for Chloramination
Generation of chloramines requires the same
equipment as chlorination (gaseous or aqueous
hypochlorination), plus equipment for adding
ammonia (gaseous or aqueous). Costs for chlorination
equipment and for its operation and maintenance
were presented earlier (Section 5.4.1). This section
presents the chemical costs for generating
chloramine from ammonia and chlorine gas.
In the Baltimore/Washington, D.C., area during
1983, costs for cylinders of liquid ammonia were
93
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Table 5-17. Construction Costs for Ultraviolet Light Disinfection ($1978)
Plant Capacity (GPP)
Cost Category
Excavation and
sitework
Manufactured
equipment
Concrete
Labor
Pipe and valves
Electrical and
instrumentation
Housing
Subtotal
Miscellaneous and
contingency
Total
1 QPD * 0,003785
14,400
$60
800
250
110
60
430
1,500
3,210
470
$3,680
nvVday
28,800
$60
1,125
250
170
150
430
1,500
3,885
560
$4,445
187,200
$60
4,485
250
250
350
430
1,500
7,225
1,010
$8,335
374,400
$60
8,685
250
300
450
430
1,500
11,675
1,580
$13,255
748,800
$80
17,365
280
400
750
480
1,800
21,155
2,830
$24,085
1,123,200
$110
26,050
300
500
1,000
480
2,000
30,440
4,060
$34,500
Source: U.S. EPA (1979).
$0.88/kg($0.40/lb), $1.54/kg ($0.70/lb) for drums of
contained ammonia in 28 percent solution, and
$1.12/kg ($0.51/lb) for bags of solid ammonium
sulfate.
Chemical costs were derived for a 9.46 m3/day (2,500-
gal/day) water treatment plant using a maximum
dose of 2.5 mg/L monochloramine (the maximum
level currently recommended by EPA). These costs
are presented in Table 5-19. Chemical costs for both
chlorine gas and the ammonia-based chemical range
from $14.75 to $24.55 annually, depending on which
ammonia source chemical is used. Anhydrous
ammonia is the least expensive, while ammonia
sulfate is the most expensive.
The direction of EPA's regulatory initiative under
the SDWA Amendments of 1986 is to reduce the
levels of secondary disinfectants in treated water. For
example, the newly promulgated Surface Water
Treatment Rule (EPA, 1989b) requires that a
minimum of 0.2 mg/L of secondary disinfectant be
present as the treated water enters the distribution
system. This level does not have to be maintained in
the distribution system, as long as heterotrophic
plate counts remain below 500/mL. Consequently,
the costs for chloramination can be lower than the
costs presented here.
Table 5-18. Operating and Maintenance Costs for Ultraviolet Light Disinfection ($1978)
Water Flow
Rate (QPO)
14,400
28,800
187,200
374,400
748,800
1,123,200
tiec
Building
10,260
10,260
10,260
10,260
12,310
13,340
tncai tnergy (k
Process
440
800
5,260
10,510
21,020
31,540
:wn/yr)
Total
10,700
11,140
15,520
20,770
33,330
44,880
Energy
Costs8
$749
780
1,086
1,454
2,333
3,142
Maintenance
Material ($/yr)
$100
140
600
1,120
2,250
3,300
Labor (hr/yr)
24
24
24
30
36
42
Labor
Costb
$240
240
240
300
360
420
Total Cost
($/yr)
$1,089
1,160
1,926
2,874
4,943
6,862
ซ Assumes 0.07/kWh.
b Assumes 10/hour.
1 QPD - 0.003785 m3/day
Source: U.S. EPA (1979).
94
-------
1.
Table 5-19. Chemical Costs for Generating Monoohloramine
for 2,500 GPD Water Treatment Plant ($1983)
Source Chemicals
Anhydrous ammonia
and chlorine gas
Aqua ammonia
and chlorine gas
Ammonia sulfate
and chlorine gas
Amount
Needed (Ib/yr)
6.2
26.1
6.2
26.1
24.1
26.1
Unit Cost ($/lb)
0.40
0.47
Total
0.70
0.47
Total
0.51
0.47
Total
Annual
Cost ($)
2.48
12.27
14.75
4.35
12.27
16.62
12.29
12.27
24.55
1 Ib = 0.4536 kg; 1 GPD = 0.003785 m3/day.
Figure 5-12. Proportions of mono- and dichloramines in
water with equimolar concentrations of chlorine
and ammonia.
Source: National Academy of Sciences (1980).
95
-------
-------
Chapter 6
Treatment of Organic Contaminants
Treatment of organic contaminants in drinking
water depends on the nature of the contaminants
targeted for removal. The two largest categories of
organic contaminants are synthetic organic
compounds (SOCs) and natural organic materials
(NOMs). Of special interest are SOCs and NOMs
having significant potential health effects, including
volatile organic compounds (VOCs), aromatic
hydrocarbons, halogenated aromatic hydrocarbons
(including polychlorinated biphenols [PCBs]),
polynuclear aromatics, halogenated nonaromatics,
hydrocarbons, and organic pesticides.
Natural organic material found in raw water is in a
dissolved or particulate phase; most SOCs are in this
dissolved phase. The particulate phase NOM can be
removed using sedimentation and filtration
processes. To enhance NOM removal, pretreatment
processes preceding sedimentation and filtration can
be optimized to convert as much of the dissolved
NOM as possible to particulate NOM. Section 6.1
contains a discussion of these enhancements.
Twelve treatment technologies are discussed in three
general categories of applicability. The first category,
discussed in Sections 6.2 and 6.3, covers the most
frequently used technologies, which include granular
activated carbon (GAC) and packed tower aeration
(PTA), also referred to as packed column aeration
(PCA). GAC and PTA are classified as best available
treatment (BAT) technologies for removal of VOCs
under the U.S. EPA regulations promulgated in July
1987.
GAC and PTA have different removal efficiencies for
different organic compounds. PTA is only effective for
VOC removal. Treatment technologies frequently are
chosen based on potential removal efficiencies for a
specific organic contaminant. However, if a decision
is based only on cost, then PTA is often chosen for
VOCs because of its lower cost. Sometimes, both
technologies are necessary to remove a particular
combination of organic compounds. In these cases,
the resultant total costs are not always additive;
installing both systems may result in some cost
savings.
The second category discussed includes treatment
processes that have some record of performance, but
are not as widely applicable as GAC or PTA to be
classified as BAT. These treatments include
powdered activated carbon (PAC) in a conventional
treatment process train, covered in Section 6.4;
diffused aeration, covered in Section 6.5; and
multiple tray aeration, covered in Section 6.6.
The final category, discussed in Section 6.7, consists
of technologies that are emerging from the laboratory
and pilot-level stages as promising alternatives for
the near future. This category embraces a number of
candidates including oxidation (ozone,
ozone/ultraviolet radiation, and ozone/hydrogen
peroxide), reverse osmosis, mechanical aeration,
catenary grid aeration, Higee aeration, resins, and
oxidation followed by a biological filtration step.
Appendix C describes case experiences with GAC,
PTA, and PAC.
There are so many organic compounds that
performance data concerning each technology's
removal ability for every organic compound are not
available. Table 6-1 contains a partial matrix of five
of the above technologies and their removal
efficiencies for 33 compounds.
6.1 Pretreatment for Natural Organic
Contaminant Removal
Water treatment processes used prior to
sedimentation and filtration may be designed to
enhance NOM removal. The most important of these
is the coagulation process, which is used primarily for
controlling turbidity and is routinely applied to
surface water. While the portion of organic
97
-------
Table 6-1. Performance Summary for Five Organic Technologies
Removal Efficiency"
Organic Compounds
Granular
Activated Carbon
Adsorption
Filtrasorb 40Qb
Packed Reverse Ozone
Column Osmosis Thin Oxidation Conventional
Aeration Film Composite (2-6 mg/l) Treatment
Volatile Organic Contaminants
Alkanes
Carbon tetrachloride
1,2-Dichtoroethane
1,1,1 -Trichloroethane
1,2-Dichtoropropane
Ethytene dibromide
Dibromochloropropane
Alkenes
Vinyl chloride
Styrene
1,1 -Dichloroethylene
c/s-1,2-Dichloroethylene
trans-1,2-Dichloroethylene
Trichloroethylene
AromaOcs
Benzene
Toluene
Xylenes
Ethylbenzene
Chtorobenzene
o-Dichlorobenzene
p-Dichlorobenzene
Pesticides
NA
f +
+ -t-
+ +
NA
NA
NA
NA
NA
0
NA
0
NA
NA
NA
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Pantachtorophenol
2.4-D
Alachlor
AWicarb
Carbofuran
Lindane
Toxaphene
Heptachlor
Chtordane
2,4,5-TP
Methoxyehtor
Other
Acrylamide
Eptehlorohydrin
PCBs
+ + o
+ +
+ + + +
NA 0
+ + 0
+ + 0
+ 4- + +
+ + + +
+ + 0
+ + NA
+ + NA
NA 0
NA 0
n- -n-
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
+ +
+
+ +
NA
0
NA
+ +c
NA
+
NA
NA
0
NA
NA
0
0
NA
o
0
o
NA
NA
NA
NA
NA
NA
NA
* ++ ป Excellent 70-100%
+ s Average 30-69%
0 *> Poor 0-29%
NA - Data not available or compound has not been tested by EPA Drinking Water Research Division.
"> Excellent removal category for carbon indicates compound has been demonstrated to ba adsorbable onto GAC, in
full- or pilot-scale applications, or in the laboratory with characteristics suggesting GAC can be a cost-effective
technology.
0 Ozone oxidation of heptachlor produces a high yield of heptachlor epoxide, which is not suitable for further oxidation.
contamination removed by effective coagulation is
generally small, in conjunction with other
treatments, coagulation can significantly add to a
plant's removal effectiveness.
In general, coagulation is most effective in removing
organic contaminants that are hydrophobic, acidic,
and high in molecular weight. While coagulation
commonly removes less than half of the organic
content of the water, it tends to remove contaminants
that are not removed by GAC. These contaminants
include color, some trihalomethane (THM)
precursors, hydrophobic SOCs, and toxic metals.
Oxidation is another pretreatment step that can have
a pronounced effect upon the removal of organic
98
-------
contaminants. Ozone or other advanced oxidation
processes employed before filtration drastically
change the chemical structure of many organic
contaminants.
Section 6.1.1 focuses on how adjusting the coagulant
type, coagulant dosage, coagulant aid application
procedures, pH, and point of coagulant addition can
improve organic contaminant removal. Section 6.1.2
describes the use of oxidation pretreatments to
enhance organics removal.
6.1.1 Coagulant Pretreatment
All coagulants will remove some organic
contamination, especially contaminants associated
with macromolecules. However, different coagulants
with equivalent turbidity removal efficiencies may
have different organic contaminant affinities.
Coagulants should be chosen by matching their
particular affinities to the specific organic
contaminants of concern.
Metallic salt coagulants, most commonly alum and
ferric chloride, are more effective thancationic
polymers in removing lower molecular weight
organic compounds with acidic functional groups
(such as carbonyl or carboxyl groups). Newer metallic
salt coagulants, such as polyaluminum chloride and
polymeric iron chloride, are also effective at
removing organics. Polymer coagulants are effective
in enhancing the removal of NOMs, such as humic
and color compounds.
Determining the optimal dosage of coagulant for
treatment of organic contaminants parallels the
derivation of the optimal conditions for turbidity
removal. The first step is to fully characterize the
plant influent using laboratory jar tests and pH
assessments. Care should be taken to avoid errors in
performing the laboratory tests. One common
laboratory mistake is to overlook the adsorption of
organic contaminants onto glass and filter paper. In
addition, laboratory procedures should take into
account contaminant volatilization. Under optimum
circumstances, laboratory tests should be followed by
full-scale plant tests. See Section 4.1 for a more
complete discussion on determining optimum
coagulant dosages.
Coagulant Dosage
The most effective method of applying coagulants
depends on the characteristics of the raw water. For
raw water with low pH (about 5 to 6 for alum),
containing high and homogeneous concentrations of
NOM, organic contaminant removal is characterized
by a sharp increase in removal effectiveness around a
specific coagulant dosage. For raw water with high
pH, containing low and heterogenous concentrations
of NOM, the removal pattern is characterized by a
gradual increase in removal effectiveness with
increasing coagulant dosage that asymptotically
approaches maximum removal.
Overdosage is possible with the first pattern of
removal, but not with the second. The second pattern
is typical for surface waters with moderate to high
turbidity and alkalinity. SOC removal tends to follow
the second pattern of removal.
Coagulant Aid Application Procedures
Coagulant aids include substances that improve the
nature of the flocculated particles, and reduce
turbidity. Among these substances are acids, bases,
anionic and cationic organic polymers, activated
silica, and bentonite clay. Except for acids and bases,
the mere presence of coagulant aids has not been
found to dramatically affect organic contaminant
removal. However, the order of application of
coagulant aids has been found to have a significant
impact.
Chemical application procedures are subject to many
confounding site specific conditions. In addition, few
published data exist regarding optimum chemical
application strategies. However, the following four
recommendations were derived from assumptions
concerning removal mechanisms for anionic
contaminants:
Add acids before metal-salt coagulants to lower
the pH toward an optimal level and promote the
production of positively charged ions.
Add bases after metal-salt coagulants to
maintain the lower optimal pH levels and avoid
encrustation of the mixer or injection nozzle.
Add clay and PAC before metal-salt coagulants to
allow adsorption of NOMs and SOCs before clay
and PAC coagulation.
Add polymers, especially anionic polymers, after
metal-salt coagulants.
pH
The optimal pH for the removal of NOM with alum is
frequently between 5 and 6, but can be higher with
iron salts. While SOC removal is clearly associated
with pH, the optimal pH level varies with each SOC.
Experience thus far indicates that negatively
charged SOCs generally are removed most easily in
water with a pH of 5 to 7. Furthermore, positively
charged SOCs are most easily removed in water with
a pH between 7 and 8.5, but more data are required to
confirm this finding.
Point of Coagulation Application
The point at which coagulants are added can
significantly affect the final level of organic
contaminants. Oxidation typically is used for
99
-------
disinfection purposes, yet it also reduces organic
contaminant levels. Oxidation that precedes the
coagulation improves its effectiveness by removing
turbidity and changing the nature of the organic
contaminants. However, when chlorine
disinfection/pretreatment is used, it is better to add
the coagulant first to reduce the level of organic
contamination that can form halogenated by-
products during chlorination. This is not as much of a
concern with preoxidation using ozone or chlorine
dioxide, where halogenated by-products are not as
much of a problem.
6.1.2 Oxidation Pretreatmenl
Several pxidants are available for treating organics
in drinking water, including ozone, chlorine, chlorine
dioxide, permanganate, hydrogen peroxide and
ultraviolet radiation. Organic compounds can be
completely oxidized into carbon dioxide and water, or
partially oxidized into intermediate reaction
products. Complete oxidation is not always possible
because the intermediate products formed may be
more resistant to further oxidation than the original
organic chemical. Pretreatment with an oxidant may
convert dissolved organic material to particulate
matter, thereby enhancing removal by sedimentation
and filtration. In addition, oxidation of many SOCs
may be accomplished during pretreatment.
Because of the concern for halogenated disinfection
by-products, the use of nonchlorinous oxidants may
be preferred in the early stages of water treatment. In
such cases, the nonchlorinous oxidants do not
produce halogenated by-products, except in those
waters containing substantial amounts of bromide
ion. Some waters, when treated with a preoxidant,
have been shown to produce more chlorinated by-
products because oxidation of the organics in the raw
water produces precursors to by-product materials.
Recently, studies have been conducted to investigate
the use of advanced oxidation processes (AOPs)
where several oxidants are used in combination (e.g.,
ozone and hydrogen peroxide, ozone and ultraviolet
radiation, ultraviolet radiation and hydrogen
peroxide). These processes involve the generation of
the hydroxyl radical in sufficient quantities to impact
treatment. AOPs may achieve treatment at a lower
cost than conventional oxidation. The use of AOPs
has been applied to the removal of SOCs and also
NOMs.
6.2 Granular Activated Carbon
Activated carbon is used for water treatment either
as a granular adsorption medium or as a powder
added to the water like a coagulant, which later
settles out in sedimentation basins or clarifiers.
Granular activated carbon (GAG), the more common
method for removing organic contaminants, is
discussed in this section. Powdered activated carbon
(PAC) is covered in Section 6.4.
Granular activated carbon unit; Smyrna, OE.
Activated carbon works on the principle of
adsorption. Dissolved contaminants (adsorbate) are
transferred from the water solution to the
microporous surface of the carbon particles
(adsorbent). Activated carbon's large internal
surface area and porosity are the primary reasons for
its excellent adsorption capabilities. One gram of
activated carbon has a surface area equivalent to that
of a football field.
The adsorption process is primarily a physical
process that can be reversed relatively easily. The
ease of reversing adsorption is another key factor in
activated carbon's usefulness because it facilitates
the recycling or reuse of the carbon.
Contaminant characteristics greatly affect GAC's
adsorption ability. GAC has an affinity for
contaminants that are:
ซ Branch-chained, rather than straight-chained
High in molecular weight
Low solubility
100
-------
Nonpolar
Present in higher concentrations
GAC's affinity for larger molecular weight
compounds is illustrated by its reduced effectiveness
when preceded by ozonation. Ozonation breaks down
contaminants and thus can reduce GAC's ability to
adsorb them. Table 6-2 lists readily and poorly
adsorbed contaminants.
Table 6-2. Readily and Poorly Adsorbed Organics
Readily Adsorbed Organics
Aromatic solvents (benzene, toluene, nitrobenzenes)
Chlorinated aromatics (PCBs, chlorobenzenes,
chloronaphthalene)
Phenol and chlorophenols
Polynuclear aromatics (acenapthene, benzopyrenes)
Pesticides and herbicides (DDT, aldrin, chlordane, heptachlor)
Chlorinated nonaromatics (carbon tetrachloride, chloroalkyl
ethers)
High molecular weight hydrocarbons (dyes, gasoline, amines,
humics)
Poorly Adsorbed Organics
Alcohols
Low molecular weight ketones, acids, and aldehydes
Sugars and starches
Very high molecular weight or colloidal organics
Low molecular weight aliphatics _-
The outer surfaces of macropores on GAC particles
are large enough to house colonies of bacteria that
feed on biodegradable organics as they pass in and
out of the macropores. Consequently, considerable
mineralization of organic material occurs after a few
weeks of operating unused GAC. Ozonation and other
advanced oxidation (ozone/hydrogen peroxide or
ozone/ultraviolet radiation) convert organic
contaminants into more readily biodegradable
materials.
Raw water characteristics also affect GAC's
adsorption ability. The most important characteristic
is the presence of competing contaminants or
dissolved solids which can adversely affect
adsorption.
Process, least cost, and facility design considerations
are covered in Sections 6.2.1,6.2.3, and 6.2.4,
respectively. Section 6.2.2 contains a discussion of
tests for deriving the optimum activated carbon
usage rates for different applications. The last four
sections cover operation and maintenance (6.2.5),
system performance (6.2.6), and system costs (6.2.7).
6.2.1 Process Design Considerations
Key process design considerations include:
GAC type
Surface loading rate of the GAC filter
Empty bed contact time (EBCT)
Contaminant.type and concentration
Contaminant competition
Carbon depth and usage
GAC Type
Various types of GAC are available for removing
organics from drinking water. The most frequently
used carbon in U.S. treatment plants is coal-based
carbon because of its hardness, adsorption capacity,
and availability. Some peat and lignite carbons have
been used. Several sizes of carbon are available, and
the size selected for a particular application is based
on backwash and headless characteristics, rate of
adsorption, and cost. Headloss is lessened with the
larger carbons, while the rate of adsorption is
increased with the smaller carbons. The relationship
of carbon cost and total production cost for a wide
range of reactivation frequencies is shown on Figure
6-1.
a = Carbon Cost $l.00/lb
b = Carbon Cost $0.80/lb
c = Carbon Cost $0.60/lb
2 46 8 10
Reactivation Frequency, Months
12
Figure 6-1. Effect of carbon cost on facility cost.
Surface Loading Rate
The surface loading rate of the GAC filter is related
to an individual plant's design capacity. Surface
loading rate is the amount of water passing through a
one square foot area of the activated carbon filter bed
per unit of time, and it typically ranges from 2 to 10
GPM/sqft.
Empty Bed Contact Time
Contact between the influent and GAC is the
primary factor in determining the size and capital
101
-------
cost of a GAG treatment system. The empty bed
contact time (EBCT), the time required for water to
pass through the empty column or bed (absent of
GAG), is determined by the following equation:
EBCT (min) = GAG (m3)/flow rate (m3/min)
While most EBCTs range from 5 to 30 minutes,
EBCTs of less than 7.5 minutes have been ineffective.
Typical effective EBCTs are around 10 to 15 minutes
and 10-minute EBCTs are typical for removal of most
organic compounds. GAG is effective in removing
radon with 180- to 200-minute EBCTs (Lowry and
Brandown). However, these long EBCTs are only
practical for point-of-use applications, not for many
community systems.
Contaminant Type and Concentration
GAC's removal efficiency varies for different organic
compounds. To date, removal tests for only a fraction
of the myriad of organic compounds have been
conducted using GAG technology. Table 6-1
(presented earlier) shows examples of GAC's removal
ability.
Contaminants in the water can occupy GAG
adsorption sites, whether they are targeted for
removal or not. Therefore, the presence of other
contaminants may interfere with the removal of the
contaminants of concern. A profile of all
contaminants in the water will help predict the
design specifications required to achieve mandatory
effluent levels for regulated contaminants.
Radon requires an extremely long EBCT, ranging
from 100 to 200 minutes; therefore, only small
amounts of radon are adsorbed during typical GAC
operations for organic contaminants. In addition,
radon decays continuously during the removal
process (Lowry and Brandown). Consequently, the
small amount of radon adsorbed during a typical
organic contaminant EBCT also decays during its
residency in the GAC, thus the carbon is renewed on
a continual basis, as shown in Figure 6-2. Section
7.3.1 contains a more detailed discussion of radon
removal.
Carbon Depth and Usage
Carbon depth is related to the amount of carbon
necessary to achieve a desired EBCT and filter life
with a specific level of contamination. Typical carbon
depth reaches 3 to 9 m (10 to 30 ft).
Carbon usage, expressed in grams of carbon per cubic
meter (pounds of carbon per 1,000 gallons) of treated
water, largely determines the system's operating
expenses. The carbon is considered to be exhausted
when the effluent organic concentration approaches
the influent organic concentration, at which time
regeneration becomes necessary. Determining when
regeneration is necessary, however, is a site-specific
decision. It may be necessary either when
contamination is detected in the finished water or
when the level of contamination exceeds the
regulated level.
Typical carbon usage ranges from 6 to 120 g/m3 (0.05
to 1.0 lb/1,000 gal) of treated water, although SOCs
are removed with carbon usage rates as low as 1.2
g/m3 (0.01 lb/1,000 gal) of treated water (O'Brien et
al., 1981). Table 6-3 provides carbon usage rates for
the removal of eight organic compounds.
Carbon usage varies with the type of contamination.
VOCs utilize the most carbon, and quickly shorten
the carbon's useful life as an adsorption medium.
Pesticides generally use less carbon than VOCs,
however, their demands on carbon usage vary. Of the
organics listed in Table 6-3, chlorinated aromatic
organic compounds use the least amount of carbon.
VOC carbon usage rates typically translate into
carbon replacement intervals of 3 to 6 months, while
other organic compounds require carbon replacement
rates of from 1 to 2 years depending on contaminant
concentrations. Pretreatment can significantly
extend carbon's longevity. For example, PTA
preceding GAC removes a large portion of VOCs. In
addition, oxidation can lower the amount of
adsorbable organics by converting some organics into
materials that are biochemically mineralized during
passage through the GAC.
In addition to the specific type of organic
contamination present, an influent's dissolved
organic carbon (DOC) level can increase GAC usage.
DOC is especially a problem for surface water
supplies. Pretreatment of surface water with
coagulation and filtration reduces the burden of
turbidity and DOC and thus extends GAC's
longevity.
The relationship between carbon longevity, influent
concentrations, and effluent contamination levels for
the contaminant trichloroethylene is illustrated in
Figure 6-3. For this example, the EBCT is 10
minutes. To achieve an effluent concentration of 1
ug/L from an influent with 100 ug/L, the carbon life is
estimated at 130 days. To allow a greater effluent
concentration of 10 ug/L from an influent of 100 ug/L,
the life of the carbon is extended to about 180 days.
Figure 6-4 compares carbon longevity in the removal
of three different organic compounds. The curves, for
each compound, illustrate the correlation between
influent concentrations and the useful life of the
carbon filter. The curves assume an EBCT of 10
minutes and an effluent concentration of 10 ug/L. At
influent concentrations of 200 ug/L, the carbon life
ranges from about 1 month for 1,1,1-trichloroethane
102
-------
Influent/Effluent,
100 ,-
75
50
25
10
Typical GAG
Breakthrough Curve for
Non-Decaying Adsorbate
. Typical Steady-State
Adsorption/Decay of
Radon on GAG
_L
, i
I i i .. I . i i i I i i i i I i i i i I
15 20 25
Time, days
30
35
40
Figure 6-2. Steady-state adsorption/decay curve for radon.
Table 6-3. Summary of Carbon Usage Rates
Contaminant
Concentration
Influent Effluent (lb/1 ,000 gal)a
Volatile Organic Compounds
(VOCs)
Tetrachloroethylene (PCE)
Trichloroethylene (TCE)
Trichloroethane (TCA)
Pesticides
Chlordane
Dibromochloropropane
(DBCP)
Aldicarb
Chlorinated Aromatics
Dichlorobenzene
PCB(Aroclorl016)
100
100
100
100
100
100
100
100
2
2
2
1
1
1
2
2
0.08
0.16
0.96
0.012
0.016
0.02
0.01
0.015
*1 lb/1 ,000 gal = 120g/m3
Carbon Life, Compound: Trichloroethylene
DaVs EBCT = 10 min
200
Effluent Concentration
501ปg/L
lOUg/L
_L
i i I L
_L
I 1
1
0 100 200 300 400 500 600 700 800 900 1,000
Influent Concentration, ug/L
Figure 6-3. Effect of contaminant on carbon life.
103
-------
removal to over 1 year for tetrachloroethylene
removal.
Carbon Life,
Days
Effluent Concentration = pg/L
EBCT = 10 min
Tetrachloroethylene
0 100 200 300 400 500 600 700 800 900 1,000
Influent Concentration, pg/L
Figure 6-4. Effect of compound on carbon life.
6.2.2 Tests for Deriving Carbon Usage and
Other Design Criteria
Carbon usage rates are derived from three standard
laboratory and field tests: isotherm, dynamic column,
and mini-column tests. The test results are critical in
deriving and evaluating GAG process design
parameters. Isotherm and mini-column tests are
laboratory tests, and the dynamic column test is a
field method that determines carbon usage.
The isotherm test is the simplest and least costly of
the three methods. It evaluates the impact of pH,
temperature, and the presence of other contaminants
on adsorption. It can also compare the effectiveness of
different carbon types. Isotherms are derived by
mixing a measured weight of pulverized carbon in
water with a known concentration of contamination.
Following a specific contact time, the contaminant
concentration of the mixture is measured.
The isotherm test is based on the Freundlich
Isotherm Relationship:
x/m =
where:
x/m =
k =
c =
1/n =
equilibrium capacity (mg of contaminant
per gram of carbon)
capacity at 1 mg/L of contaminant
concentration
contaminant effluent concentration in
mg/L
exponent
The Freundlich Isotherm Relationship yields
isotherms for each contaminant, with residual
contaminant concentrations in the effluent graphed
against the ratio of contaminant adsorbed per gram
of carbon. Figure 6-6 shows graphs of six isotherms
(Dobbs and Cohen, 1980). Isotherm tests are quick
and cost about one to three thousand dollars. Many
contaminants' isotherms are available from existing
literature, l
In contrast to isotherm tests, dynamic column field
tests can take 6 to 10 months and cost tens of
thousands of dollars. These pilot tests are used to
model full-scale facility design parameters. The
seven most useful design parameters in this test are:
Type of GAG
Different EBCTs
Carbon bed depths
Hydraulic loadings
Number of vessels
Carbon exhaustion rates, life, and regeneration
cycle length
Contaminant loading rates
Typical dynamic pilot column tests use GAC columns
that are about 5 feet deep with 4-inch internal
diameters (see Figure 6-7).
The mini-column laboratory test is between the
isotherm and dynamic column tests in accuracy and
complexity. The cost is about the same as the cost for
an isotherm test. This test is used to determine the
feasibility of using GAC, establish preliminary
design criteria, and approximate cost. Test
procedures involve pumping raw water through a
short column of GAC about 70 mm deep. A schematic
diagram of a mini-column test is shown in Figure 6-8.
6.2.3 Least Cost Design Criteria
To derive the optimal design criteria for an effective
GAC system, the design must consider EBCT, carbon
usage, and column configuration. EBCT has greatest
impact on capital costs, while carbon usage has the
greatest impact on operating costs. The first step in
determining the most cost-effective EBCT and carbon
usage rates is to examine the breakthrough curves
for the organic compounds contaminating the
influent. The breakthrough curves indicate how long
a GAC filter can produce a desired effluent
concentration for an organic contaminant.
The next step is to calculate the carbon usage (CU)
rate with the following formula:
Figure 6-6 shows an application of this equation in
making carbon usage estimates.
1 Data for several compounds are contained in: Carbon Adsorption
Isotherms for Toxic Organics, EPA-600/8-80-023, April 1980.
104
-------
cu =
Mass of Carbon
Volume of Water Treated through Breakthrough
Carbon usage is then plotted against EBCT to select
the optimal combination.
Column configuration is the next important factor to
consider in determining the length of the carbon
regeneration period. Parallel column configurations
require carbon replacement or regeneration when a
filter breakthrough occurs, while a series column
configuration allows replacement to take place at the
point of carbon exhaustion. Carbon exhaustion occurs
when the saturated carbon can no longer hold
contamination. Series configuration extends the
operating period between regeneration cycles.
Selection of the appropriate system involves a
tradeoff between capital and operating costs. Parallel
systems require fewer contactors, and their
associated capital expense. Series configuration has a
longer carbon regeneration cycle with lower
operating costs.
6.2.4 Facility Design Criteria
The three major components of a GAC system are the
carbon contactor, carbon transfer system (which
moves the carbon in and out of the contactors), and
carbon regeneration system (see Figure 6-9).
The two important operational characteristics of
contactors are flow direction (upflow or downflow)
and water feed mode (gravity or pressure). Upflow
and downflow carbon contactors are used in either
series or parallel column configuration. Pressure
contactors usually cause a minimum pressure drop of
10 psi.
Upflow contactors are used for contact periods of up to
2 hours (U.S. EPA, 1973). The upflow design permits
suspended solids to pass through without excessive
drops in pressure/These extended contact periods are
used to remove suspended solids and organic
compounds. The disadvantage of upflow contactors is
that they sometimes carry fine carbon particles into
their effluent. Upflow designs are more typical of
wastewater treatment plants than drinking water
treatment facilities. Downflow contactors typically
are used for contact periods of 30 minutes or less, and
are able to remove only a small amount of suspended
solids during backwashing.
Pressure-fed contactors are used for systems with
capacities between 0.04 and 0.44 m3/sec (1 and 10
MOD); packaged plants using pressure-fed contactors
are rarely over 0.04 m3/sec (1 MGD). The pressure-
fed contactor operates with higher head loss levels
than the gravity-fed contactor. In the pressure-fed
contactor, pumps move the water from the well to the
contactors and into the distribution system. Existing
pump systems usually are adequate to maintain
pressures in the distribution systems.
Gravity-fed contactors typically are used for systems
with greater than 0.44 m3/sec (10 MGD) capacity. By
using common wall construction, they are able to
reduce costs. Gravity-fed GAC systems are
constructed either by modifying existing gravity-fed
sand filters or by using new concrete contactors.
The foremost consideration in carbon transfer system
design is minimizing carbon loss due to abrasion. The
hydraulics of the slurry system, system velocities,
and construction materials all affect carbon abrasion.
Carbon regeneration can take place either on site or
off site, or the carbon may be used on a disposable
basis, depending on the system size. Systems with
carbon exhaustion rates between 226.8 and 907.2 kg
(500 and 2,000 lb)/day will generally use offsite
regeneration, which is routinely performed on a
contract basis. Systems exhausting over 907.2 kg
(2,000 Ib) carbon/day may consider onsite
regeneration, which involves heating the carbon to
destroy the organics. To avoid unnecessary energy
costs, de watering of the carbon is required. Systems
using less than 226.8 kg (500 lb)/day generally
dispose of their carbon, rather than regenerate it.
Both carbon replacement and regeneration produce
wastes. Disposing of carbon with contaminants
classified as hazardous waste will dramatically
increase disposal costs. Carbon regeneration
operations must meet all applicable air quality
regulations. Gas emissions from these operations are
sometimes categorized as significant point sources.
6.2.5 Operation and Maintenance
Several operational and maintenance factors affect
the performance of GAC units, including those
involving the nature of the influent, dynamics of the
GAC process, and management of the resultant
wastes. These factors require consistent and careful
monitoring. ,
A significant drop in influent contaminant
concentration will cause a GAC filter to desorb, or
slough off, the contaminant, because GAC is an
equilibrium process (McKinnon and Dyksen, 1982).
Another operational problem related to influent
characteristics is the competition among
contaminants for adsorption sites. Adsorbed
contaminants are displaced by other contaminants
with which GAC has greater affinities. As a result,
water with frequently changing quality
characteristics will produce effluent with .
unpredictable levels of contamination.
Bacterial growth on the carbon may be one potential
problem. However, the nature and implications of
105
-------
Isotherm equation:
x/m = KG""
where:
! |/n
Kซ 28 fmfl).,,, (L) {From i-othorm
(gm) (mg) ป
l/n ป 0.62 (From isotherm data)
(Cj) ป TCE influent concentration ป
(C0) s TCE effluent concentration =
5F 3 Safety Factor = 0.75
Rearranging:
Carbon U~nnn - Ci - Co ~ g
(lb/1,000 gal) Km)wnbF
(100- 5) ug
L
28 ( 100)ฐ62
(1,000)
data)
100 ug/L
5 ug/L
1 34 "W ซ-)
J (1,000 gal) (mg)
x 1 mq
1 .000 uq x
X 0.75
8.34 Ib x L
(1,000 gal) mg
= O.16lb/I000gal
Note: llb/1,000gal = I20g/m3
Figure 6-5. Application of Freundlich Isotherm Relationship.
100,0
10.0
1.0
0.1
0.0001 0.001 0.01 0.1
Residual Concentration, ug/L
1.0
Numbers in parentheses indicate the molecular weight of the
compound.
Figure 6-5. Adsorption Isotherms for several organic
compounds found In ground-water supplies.
this growth are not clearly defined and require
further study. Excessive bacterial growth could cause
clogging and higher bacterial counts in the effluent.
However, it is also possible that such growth
improves GAC's removal efficiencies through
biodegradation.
Another potential problem is the disruption of the
adsorption zone procession through a GAC contactor.
This zone of saturated GAC typically moves in a
wave formation through the carbon depth, as shown
in Figure 6-10. If the wave of used GAC is
interrupted, then the contactor may experience
premature breakthrough. Changes in influent
composition and concentration^ well as the method
and frequency of filter backwashing all can affect the
movement of the wavefront.
The final operational issue concerns the proper
management of GAC wastes. Wastes from carbon
regeneration and backwashing sometimes require
treatment prior to disposal.
6.2.6 System Performance
GAC effectively removes most organic compounds
from drinking water. GAC's precise removal
effectiveness for a large number of organic
compounds is unknown because of the multitude of
organic compounds in existence. Table 6-1 presents
removal efficiencies for 33 compounds.
GAC is not effective in removing vinyl chloride from
water. In addition, the long EBCT required for radon
removal makes it infeasible at the treatment plant
scale. However, at the residential scale GAC systems
are cost-effective for radon removal.
6.2.7 System Costs
The cost of removing many organic compounds with
GAC is well within the range of general costs for
delivering treated drinking water. Within the United
States, that cost generally ranges from $0.26 to
$0.40/m3 ($1.00 to $1.50/1,000 gal) (1989 dollars) of
treated water. Most regulated organic contaminants
are managed with GAC systems having carbon bed
lives of at least 3 months and EBCTs of 15 minutes.
106
-------
Feed Pretreatmenf
Tank*
1
'
\
Carbon
Feed
. tank
r
i
Sample
Taps ~
x~>^-*vs^K
1 1
* Pretreatment tanks optional depending on
suspended solids concentration in feed.
j
-%
. 2
:
i
i
,
-*
-
Ca
i
rbon Columns . .
T
i
?
'
i
*
^
.
Product
Water
Backwash
Water
Figure 6-7. Diagram of pilot column test system.
#12 Neoprene Stopper
300 ml Stainless Steel
Pulsation Dampener Cylinder
3/8" OD X 1/4" ID 316
Grade Stainless Steel Tubing
Chemical Metering
Pump 250 psi Max.
Varispeed
Glass Sample
Reservoir
1/4" OD x 1/8" ID
Teflon Tubing
Pressure Gage (0-200 psi)
Swagelock SS Fittings
Mini Carbon Column
1/4" OD x. 1/8" ID
Stainless Steel
Teflon Dispensing
Line
EPA:Approved VOC
Vial (15 or 40 ml)
Figure 6-8. Diagram of dynamic mini-column adsorption system.
107
-------
Contaminated Well
GAC
To Distribution
System
Gravity GAG
Contactor
GAC
To Distribution
System
Figure 6-9. GAC treatment options.
Influent
Wavefront
Pressure GAC Contactor
systems to $0.26 to $0.79/m3 ($1.00 to $3.00/1,000
gal) for small water systems (less than 0.04 m3/sec or
1 MOD).
The most costly organic contaminants to remove are
VOCs, followed by chlorinated aromatic compounds.
In general, the least expensive contaminants to
remove with GAC are pesticides. Table 6-4 shows the
costs of removing alachlor (a pesticide), TCE (a VOC),
and radon using GAC. The costs for alachlor removal
may be considered representative of the costs for
removing typical pesticides using GAC. The costs for
TCE removal are representative of the costs for
removing the typical VOCs found in ground water.
As shown in the table, the costs for radon removal are
extremely high, probably precluding the use of GAC
for radon removal. Also shown in Table 6-4 are the
approximate costs per home per year for installing
GAC for removal of any one of the organic chemicals.
GAC Contactor
Figure 6-10. Wavefront within GAC contactor.
Water systems with GAC units having these
operational characteristics cost from $0.03 to
$0.04/m.3 ($0.10 to $0.15/1,000 gal) for very large
The three fundamental cost components of a GAC
system are contactors, GAC, and piping. Carbon
storage and carbon transport facilities are also
necessary cost components. In addition, there are
many site-specific cost elements to consider
including:
108
-------
Table 6-4. Cost for 95 Percent Removal of Several Organics and Radon Using GAC Adsorption ($1989)
Costs by System Size
System Capacity (MGD)
Average Daily Flow (MGD)
Population Served
0.1
0.032
500
0.5
0.22
1,500
1.0
0.4
3,000
10.0
4.32
22,000
50.0
22.65
100,000
Alachlor
Capital Cost
Annual O&M Cost
Total Cost ($/l,000 gal)a."
Cost/Home/Year0
Trichloroethylene
Capital Cost
Annual O&M Cost
Total Cost ($71,000 gal)
Cost/Home/Year
Radon
69,000
8,500
1.41
100
138,000
19,100
0.44
70
190,000
26,500
0.33
50
1,500,000
117,000
0.19
40
5,600,000
329,000
0.12
30
106,000
16,000
2.44
170
212,000
38,200
0.80
125
318,000
54,100
0.50
90
2,200,000
265,000
0.30
70
10,100,000
930,000
0.25
60
Capital Cost
Annual O&M Cost
Total Cost ($/i, 000 gal)
Cost/Home/Year
445,000
106,000
13.55
950
1,300,000
318,000
6.00
900
2,100,000
530,000
5.30
800
d
d
d
d
d
d
d
d
a Total cost is calculated based on amortizing the capital cost over 20 years at 10 percent interest rate, adding the annual
O&M cost, and dividing by the total annual flow.
b 1,000 gallons = 3.78 m3.
o Cost per home per year is calculated based on total cost per year divided by the number of homes served using 3.0
people per home.
d These costs were not calculated because they are too high for practical municipal application.
Raw water holding tank (for ground-water
systems)
Restaged well pump to address excessive
pressure drops caused by the contactors
o Contactor housing, required in cold climates
Chemical feed equipment
Clear well storage tank and pumps
ซ Backwash storage tank
The capital costs increase directly with system size.
Consequently, the capital costs can be derived from
the estimated EBCT, a direct measure of system size
because of its relationship with the carbon contactor.
The predominant elements of capital costs, as well as
operating and maintenance costs, are shown in
Figure 6-11.
The two primary capital cost considerations are (1)
construction type and (2) carbon and reactivation
strategy. Steel pressurized GAC units are most
economical for small systems, generally less than
0.44 m3/sec(10 MGD), while concrete gravity-fed
systems are more appropriate for larger systems.
The carbon and reactivation system, including either
onsite or offsite carbon reactivation, compose nearly
half of the GAC system costs. Infrared carbon
reactivation systems are cost effective for smaller
systems, and fluid bed reactivation systems are
suited for plants using more than 1,360,800 kg
(3,000,000 Ib) of carbon annually. Multiple hearth
reactivation systems are more expensive than either
infrared or fluid bed systems. Figure 6-12 compares
the costs of carbon replacement and two methods of
carbon regeneration for several carbon consumption
rates.
Operating costs do not correlate strongly with system
size, but are dependent on carbon usage rates, which
rely on the nature of the contaminants in the
influent. Other operating and maintenance cost
components are carbon type, labor, fuel, steam,
power, maintenance, and laboratory analysis.
6.3 Packed Column Aeration
Aeration, also called air-stripping, mixes water with
air to volatilize contaminants. The volatilized
contaminants are either released directly to the
atmosphere or are treated and then released.
Aeration is used primarily to remove VOCs.
109
-------
Capital Cost
Srteworketc. (15%)
Carbon Transfer and
Storage (5%)
Carbon Contactor (50%)
Carbon Regeneration (30%)
O&M Cost
Power (10%)
Labor (10%)
Maintenance Material (5%)
Carbon Regeneration (75%)
Figure 6-11. GAC facility cost components.
The aeration process is based on the principles of
mass transfer from liquids to gases. This transfer is
expressed in the following equation:
M = (Kl) (a) (P)
where:
M = the mass of the substance transferred from
water to air expressed in lb/hr/ft3
Kl = the coefficient of mass transfer expressed in
Ib/hr/ft2
a = the effective area in ft2
P = the concentration difference or driving force
(The driving force is the difference between
conditions in the aeration unit and
equilibrium conditions for the substance
between gas and liquid phases.)
110
-------
120
100
S 80
H
o
j5 60
c
>
0.0000001 ?b
0.004"
0.01ป
0.059"
0.081"
Note: Constants estimated at about 20 ฐC.
a AWWA Research Foundation and KIWA (1983).
t>U.S. EPA (1988D).
underneath the medium in the tower or column. A
typical PTA unit is shown in Figure 6-13.
The major process elements of PTA are the column
(or tower), packing medium, blower, booster pump,
and instrumentation. Columns can be constructed
from fiberglass-reinforced plastic, aluminum,
stainless steel, or concrete. Within the column are
mist eliminators to prevent water from escaping in
the vents, packing material, support grids for the
packing material, and liquid distributors to separate
the influent into many smaller streams. The four
primary designs for liquid distributors are orifice
plate (see Figure 6-14), trough-type distributor (see
Figure 6-14), orifice headers, and spray nozzles.
Adding PTA to an existing plan will require (1)
changes in the staging of the well pumps and (2)
repumping treated water to the distribution system.
Housing the tower usually is not necessary because
the water temperature remains fairly constant
throughout the PTA-treatment process.
Consequently, water rarely freezes during the
process.
PTA systems vary: in some, water cascading over
spillways imparts the necessary turbulence; in
others, several layers of slats mix the water with air.
Innovations in PTA are reflected in the newest
additions to the latter type of aeration system.
Emerging aeration techniques include the catenary
grid and Higee systems which are discussed in
Sections 6.7.4 and 6.7.5.
The rest of this section profiles aeration technology
including design considerations (Section 6.3.1),
operation and maintenance (Section 6.3.4), system
performance (Section 6.3.5), and system costs
111
-------
Fiberglass-reinforced plastic packed column with two carbon
vapor phase treatment units; Battle Creek, Ml.
(Section 6.3.6). In addition, this section reviews pilot
testing of PTA systems (Section 6.3.2) and managing
of VOC emissions from aeration (Section 6.3.3).
6.3.1 System Design Considerations
Aeration provides a fixed percentage of contaminant
removal regardless of influent concentration. To
compensate for uncertainty, aeration systems can be
designed to incorporate safety factors of two or three
times the expected influent contaminant
concentrations to ensure compliance with regulatory
standards.
Aeration system performance is affected primarily by
column size and airflow. Increases in airflow and
column height improve removal efficiencies. Typical
design parameters are provided for 13 common VOCs
in Table 6-6. Design considerations include:
Type of organic contaminant(s)
Concentration of contaminant(s)
Type of packing material
Height of packing material
ซ Air-to-water ratio
Water loading rate
Water temperature
Different contaminants require different designs to
accommodate the particular degrees of volatility and,
thus, affinities for aeration. Packing materials are
designed to simultaneously provide a low pressure
drop across the material and maximum air-water
contact area. They typically are made from plastic or
ceramic, and come in the following forms: super
intalox, Tellerettes, Tri-packs, pall rings, berl
saddles, and Raschig rings. The desired contaminant
removal level and air-to-water ratio determines the
packing material height. The selected column height
and design of air intake louvers must comply with
local zoning regulations concerning structural height
and noise nuisance. These zoning regulations are the
most basic site-specific considerations.
The air-to-water ratio in a column is a function of the
water temperature and the desired level of
contaminant removal. This ratio determines the size
of the system's blower, which is the primary
component of operating costs for PTA systems. Air-to-
water ratios typically range from 30:1 to 100:1. The
water loading rate, the amount of water passing
through the column, routinely ranges from 16 9 to
20.4 L/sec/m2 (25 to 30 GPM/ft2). The column
diameter specification is derived to accommodate the
desired water loading on the column.
All of these factors affect aeration's removal
efficiency. Figure 6-15 illustrates the dramatically
different removal rates achieved by the same packed
material depth for three different contaminants. PTA
removal effectiveness usually increases as water
temperature increases. The decrease in column
height required to achieve the same level of
contaminant removal as the water temperature
increases is shown in Figure 6-16. In most cases,
heating influent is not cost effective, but in
temporary situations of low flow, it has been used
effectively.
Pretreatment to remove iron, solids, and biological
growth may be necessary to prevent clogging of the
packing material and, thus, the entire system.
Posttreatment also may be necessary to reduce
corrosive properties that develop in the water due to
the increased presence of dissolved oxygen during the
aeration process. One solution is the use of a
corrosion inhibitor.
6.3.2 Pilot Testing PGA
Figure 6-17 is a schematic diagram of a typical pilot
column. Pilot columns are used to test various water
loading rates, airflow rates, air-to-water ratios, and
packing materials. Typically, 8 to 12 pilot column
runs are used to test various combinations of design
factors. A test run lasts for about 30 minutes to
112
-------
To Atmosphere
Packed
Column
Spray
Header
Plastic
Media
High Service
Vertical
Turbine Pumps
Blower
Assembly
1
Finished Water
to System
*
Clearwell
Well
Figure 6-13. Packed tower aeration system.
achieve steady state. Influent and effluent samples
are collected for each test run.
The following precautions should be taken to ensure
accurate pilot test results:
Carefully place packing material into the column
to avoid channeling and vacant pockets.
Level the pilot column to avoid channeling and
wall effects.
Select representative performance points for
sampling.
Collect and analyze duplicate samples to check
results.
Verify laboratory results.
6.3.3 VOC Emission Control
To meet air emission regulations, PTA exhaust gas
may require treatment. VOC emissions for PTA units
are calculated with the following formula:
six
Emission rate (in Ib/hour) = (C1-C2)*(V)*(5/1Q7)
where:
Cl =
C2 =
V =
Influent concentration of the VOC expressed
in ug/L
Effluent concentration of the VOC expressed
in ug/L
Water flow rate in GPM
The emission rate must be evaluated in the context of
applicable air quality regulations and other site-
specific factors. These factors include proximity to
human habitation, treatment plant worker exposure,
local air quality, and local meteorological conditions.
Air emission regulations are expressed either in
terms of permissible emission rates (Ib/day or Ib/hr)
or projected ground level concentrations (mg/m3). If
the plant's emission rate is unacceptable, then
column or plant process design may be changed to
bring the plant into compliance.
113
-------
Orifice - Type Distributor
Trough - Type Distributor
Figure 6-14. Distributor types.
Modifying PTA plants to dilute emissions to an
acceptable level is the least costly method of
achieving compliance with air regulations. Such
plant modifications include increases in tower
height, airflow rate, and exhaust gas velocity. If these
steps are insufficient to achieve compliance, then a
vapor phase treatment component may be required.
The four methods used for vapor phase treatment of
VOC emissions are (1) thermal destruction, (2)
catalytic incineration, (3) ozone destruction, and (4)
carbon adsorption. The first three methods are not
used extensively. Thermal destruction is effective but
very expensive because of the high energy
requirements. Catalytic incineration, depicted in
Figure 6-18, lowers the energy requirements of the
thermal destruction process. However, catalytic
incineration is not used widely because it is not
effective in eliminating low levels of chlorinated
organic compounds. To date, ozone destruction used
in conjunction with ultra violet radiation has only
been evaluated on a pilot scale.
Carbon adsorption for control of VOC off-gases from
PTA is accomplished with a vapor phase GAC unit.
Currently, GAC is the most frequently used approach
to controlling these VOC emissions. Figure 6-19
shows a schematic diagram of a typical gas phase
unit. The heating element eliminates humidity,
which competes with organic compounds for the
available GAC. The specifications of a gas phase unit
depend on individual PTA system requirements,
114
-------
6.3.5 System Performance
Orifice-type distributor plate for a packed column aerator.
including air-to-water ratio, influent concentration of
the VOC, and acceptable level of VOC emissions.
Carbon usage for gas phase control of VOCs from
aeration units is less than equivalent VOC controls
for the liquid phase GAG units. In addition, since gas
phase adsorption kinetics are faster than liquid
phase kinetics, the carbon bed size is reduced. Carbon
exhaustion is estimated either by using a mass
balance approach or monitoring with gas
chromatography or mass spectrometry.
6.3.4 Operation and Maintenance
Typically, packed columns are operated
automatically. Daily visits assure that all equipment
is running satisfactorily. Maintenance requirements
generally involve several hours per month to service
pump and blower motors and to replace air filters on
he blowers, if necessary. Some packed column
installations have reported operational difficulties
from the plugging of the packing material and
inadequate liquid distribution. However, most
installations report no unusual operational
problemsthe blowers, if necessary. Some packed
column installations have reported operational
difficulties from the plugging of the packing material
and inadequate liquid distribution. However, most
installations report no unusual operational problems.
PTA is an effective and practical removal process for
several organic compounds applicable to water
treatment plants of all sizes. It is typically used for
systems drawing ground water. Larger plants using
PTA for radon removal have the added task of
properly managing the associated air emissions.
PTA effectively removes from drinking water most
compounds with high Henry's Law constants, which
includes most VOCs. PTA is the BAT for vinyl
chloride, which has an extremely high Henry's Law
constant; GAG and PTA are BAT for other regulated
VOCs. Table 6-7 lists examples of aeration's removal
effectiveness for trichloroethylene, vinyl chloride,
VOCs, and aldicarb.
6.3.6 System Costs
The cost of removing many organic compounds with
PTA, by itself, is well within the range of the cost of
delivering treated drinking water in the United
States, which typically costs from $0.26 to $0.40/m3
($1.00 to $1.50/1,000 gal of water). The cost of
controlling air emissions from PTA units
significantly increases total system costs.
Table 6-8 presents estimated costs of removing 95
percent of several VOCs and radon using PTA. As the
table indicates, costs in terms of cents per 1,000 gal of
treated water drop significantly as system size
increases. Of the VOCs listed in the table, the most
expensive VOC to remove with PTA is
dibromochloropropane; the least expensive is vinyl
chloride. Both vinyl chloride and radon are removed
equally as well using PTA, therefore the costs for
removing these contaminants are similar.
Approximate costs per home per year are presented
in the table for each of the contaminants.
The capital cost elements for PTA systems include
the tower or column, internal column parts, packing
material, blower(s), clearwell, booster pump(s), and
any associated piping. Site-specific costs may include
a raw water holding tank, restaged well pump,
blower building, chemical facility, noise control
installation, and air emission control.
The cost of vapor phase controls to manage air
emissions from PTA operations can strongly
influence plant design and total costs. EPA research
indicates that adding a vapor phase carbon
adsorption unit will double the costs of PTA. Carbon
adsorption units have significant capital and
operation and maintenance cost components,
including costs for carbon contactors, initial
activated carbon material, gas heaters, and
installation.
115
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Table 6-6. Typical Air Stripping Design Parameters for Removal of 13 Commonly Occurring Volatile
Organic Chemicals3
Compound
Triditofoethylene
Tetrachtoroethylerte
Carbon tetrachloride
1 ,1 ,1 -Trichtoroethane
1 ,2-Dichloroethylene
Dtehtorome thane
C/S-1,2-
Dtchloroethylene
Vinyl chloride
Benzene
Toluene
m-Xylene
Chtorobenzene
1 ,2-Dichlorobenzene
Henry's Law
Constant
0.116
0.295
0.556
0.172
0.023
0.048
0.093
265.000
0.106
0.117
0.093
0.069
0.090 ,
Air-to-Water Ratio
29.9
11.8
6.2
20.1
150.6
71.59
37.10
0.013C
32.69
29.62
37.26
50.29
38.67
Air Stripper Height
(feet)b
38.03 38.03
43.77
44.88
40.06
33.47
28.61
34.88
59.58
36.25
39.04
40.49
37.60
. 40.45
Diameter of Packed
Column (feet)
8.10
5.97
4.95
7.07
14.89
11.12
8.73
1.90
8.37
8.07
18.34
22.74
8.86
ซ Water flow rate - 2.16 MGD (8.17 ml/day), inlet water concentration - 100.0
air-stripper temperature - 50 ฐF (10ฐC), air-stripper packing pressure drop
packing - 3-inch plastic saddles
b i ft - 0.3 m.
ฐ Theoretical calculation based on the extremely high Henry's Law constant.
Source: Crittenden et al. (1988).
water treatment objective - 1.0 ng/L,
50.0 (N/m2)/m packing, air- stripper
100
80
60
40
20
Chloroform
1,2-Dichloroethane
95 Percent Removal
Temperature: 55ฐ F
TCE
0 20:1 40:1 60:1 80:1 100:1 120:1
A:W Ratio
Figure 6-15. Effect of compound on packed-column design.
Packing Height, ft
35 -
30 -
50 75
90
95 97.5 99
99.5 99.8
Removal Efficiency, %
Figure 6-16. Packing height vs. removal efficiency for
trichloroethylene.
116
-------
Effluent Air
From Raw
Water
Source
Raw Water Sample Tap
Water Distribution Plate
Packing Media
Intermediate Sample Tap (Typ.)
Support Plate (Typ.)
Connecting Flange (Typ.)
Tower Support Table
120 Volts Single Phase
15 Amps Blower
Air Flow Metering Valve
Pressure Gage
4,
Effluent Water Sample Tap ฃ7
9 I
Influent Air
Effluent Water to Drain
Figure 6-17. Schematic of pilot aeration column.
117
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Recirc.
damper or
Secondary
Heat
Exchanger
Filter/Mixer
s\ A Secondary
Air Addition
Figure 6-18. Schematic of catalytic incineration process.
6.4 Powdered Activated Carbon Plus
Conventional Treatment
The PAC process is based on the same principles of
adsorption as GAG. However, PAC is not a granular
filter medium; rather it is a powder added directly to
the water at one or more points during the treatment
process. Typically, PAC can be added during
coagulation, flocculation, sedimentation, and
filtration. The addition of PAC:
Improves the organic removal effectiveness of
conventional treatment processes
Addresses short-term and emergency problems
with conventional treatment systems
Acts as a coagulant aid
Removes taste and odor
PAC is also an attractive treatment technology
because it is less expensive than GAG in addressing
seasonal problems, is easily started and stopped,
creates no headless, does not encourage microbial
growth, and has relatively small capital
requirements.
The chief disadvantage of this process is that some
contaminants require large dosages of PAC for
removal. Another disadvantage is that PAC is
suitable only for conventional treatment systems.
PAC also requires specific system hydraulics, space,
and sludge-handling practices. PAC has proven
ineffective in removing natural organic matter, due
to the competition from other contaminants for
surface adsorption and the limited contact time
between the water and PAC. In addition, PAC
adsorption is not amenable to basin-mixed flow
reactions (as opposed to column-mixed flow
reactions).
The rest of this section discusses PAC application
techniques, including the Roberts-Haberer process
and the fluidized-bed adsorber (Section 6.4.1), design
considerations (Section 6.4.2), and system
performance (Section 6.4.3).
6.4.1 PAC Application Techniques
Two potential techniques for improving PAC's
effectiveness for organic contaminant removal are
the Roberts-Haberer process and the fluidized-bed
PAC adsorber.
Roberts-Haberer PAC Process
The Roberts-Haberer process uses an upflow filter
composed of foamed polystyrene beads having a
specific gravity of less than 0.1. Figure 6-20 shows a
simplified diagram of the three-phased process.
During the conditioning phase, water recirculates
through the filter media to allow the PAC to adhere.
During filtration, the media act as a combination
upflow filter and activated carbon adsorber. When
the PAC is exhausted, it is released to the drain
through the backwashing process. The Roberts-
Haberer process used with coagulation is especially
effective with low turbidity influent or combined
with the sedimentation process. It can also provide
flocculation for a system.
The reported advantages of the Roberts-Haberer
process include:
118
-------
Treated Air
Contaminated Air
L
Heating Element
Blower
Blower
> I
Treated Water
Figure 6-19. Vapor-phase carbon system for treatment of aeration exhaust air.
Table 6-7. Examples of Removal Efficiencies for PTA
Systems
TCE
A full-scale redwood slate tray aeration plant with a 3.8
MGD capacity at an air-to-water ratio of 30:1 achieved
50 to 60 percent reductions from initial TCE influent
concentrations of 8;3 to 39.5 yg/L.
A full-scale multiple tray aeration unit with a 6 MGD
capacity achieved 50 percent reductions from initial TCE
influent concentrations of 150 ng/L.
A full-scale packed tower aeration column plant using
ground water at an air-to-water ratio of 25:1 achieved 97
to 99 percent reductions from initial TCE influent
concentrations ranging from 1,500 to 2,000 pg/L.
Vinyl Chloride
A pilot packed tower aerator, with 9ฐC influent, achieved
up to 99.27 percent removal of vinyl chloride.
A spray tower aeration unit removed vinyl chloride from
ground water with VOC concentrations of 100 to 200
Aldicarb
VOCs
An in-well aeration unit with an air-lift pump achieved 97
percent removal of vinyl chloride. .
Aeration was found to be ineffective in reducing levels of
aldicarb because of its low Henry's Law constant.
A four-stage aeration design with four shower heads and
a pressure drop of 10 psi achieved 99.9 percent VOC
removal.
Reduced PAC use because of the increased
contact time
Quicker adsorption and increased utilization of
carbon, relative to the GAG process, due to the
small size of the carbon particles
Decreased carbon use relative to the GAC process
Increased SOC removal if used after coagulation,
due to the removal of high molecular weight
substances by coagulation
Improved filtration efficiency by removing THM
precursors prior to filtration and allowing
prefiltration chlorination, which reduces the
microbial presence on the filter
Minimal bacterial growth because of the
frequency of backwashes
Increased ability to accommodate multiple
objective water treatments
Eased recovery or modification of PAC
application
Fluidized-Bed PAC Adsorber
This experimental method processes water through
flocculated carbon, which extends the contact period.
The strength of the flocculated carbon particles
increases the carbon's longevity for treatment
purposes. Floe strength must be balanced with
particle breakup, which increases carbon surface
area and, therefore, adsorption of contaminants.
Because fluidized-bed PAC adsorbers are relatively
new, more research is required for a full evaluation.
6.4.2 System Design Considerations
The primary design considerations for instituting
PAC are dosage, contact time, and points of
application. Dosages commonly are less than 100
mg/L but can range as high as 300 mg/L, and the
minimum contact time is usually 0.25 hour. PAC
points of application customarily are (1) before the
rapid mix process, (2) after rapid mixing but before
flocculation, or (3) after flocculation and before
119
-------
Table 6-8. Cost Tor 99 Percent Removal of Several VOCs and Radon Using Packed Tower Aeration ($1989)
Costs by System Size
System Capacity (MGD)
Average Daily Flow (MGD)
Population Served
Dibromochloropropane
Capital Cost
Annual O&M Cost
Total Cost (S/1,000 galja.b
Cost/Home/Yearฐ
Trichloroethylene
Capital Cost
Annual O&M Cost
Total Cost ($/1 ,000 gal)
Cost/Home/Year
Vlnyl,'ChtoridelRadon
Capital Cost
Annual O&M Cost
Total Cost ($/l,000 gal)
Cost/Home/Year
0.1
0.032
500
106,000
4,500
1.90
175
85,000
2,700
1.10
75
54,000
1,600
0.70
50
0.5
0.22
1,500
420,000
25,000
0.90
165
210,000
10,800
0.45
70
148,000
6,800
0.30
45
1.0
0.4
3,000
636,000
50,000
0.85
160
318,000
21,200
0.40
65
210,000
16,700
0.25
40
10.0
4.32
22,000
5,700,000
460,000
0.60
155
2,100,000
201,000
0.30
60
1,484,000
106,000
0.20 .
35
50.0
22.65
100,000
5,600,000
329,000
0.12
30
10,100,000
930,000
0.25
60
5,830,000
477,000
0.15
30
ป Total cost is calculated based on amortizing the capital cost over 20 years at 10
O&M cost, and dividing by the total annual flow.
b 1,000 gallons = 3.78 m?.
c Cost per home per year is calculated based on total cost per year divided by the
people per home.
percent interest rate, adding the annual
number of homes served using 3.0
Conditioning
Filtration
Backwash
PAC
Figure 6*20. Schematic of the Roberts-Haberer process.
sedimentation. Figure 6-21 is a schematic diagram of
PAC usage.
6.4.3 System Performance
Adding PAC to conventional treatment systems can
greatly improve their performance in removing
certain organic chemicals. Table 6-9 compares
removal efficiencies of the conventional treatment
process with and without PAC for 15 organic
compounds, including two VOCs and 13 SOCs.
6.5 Diffused Aeration
The diffused aeration system bubbles air through a
contact chamber for aeration; the diffuser is usually
located near the bottom of the chamber. The air
introduced through the diffuser, usually under
pressure, produces fine bubbles that impart water-air
120
-------
mixing turbulence as they rise through the chamber.
Diffused aeration units are designed to serve either
point-of-use or plant situations. Figure 6-22 depicts a
plant-scale system. Figure 6-23 shows a home-scale
aeration system.
Table 6-9. Typical Performance of Conventional
Treatment Processes without and with PAC
Compound
VOCs
Carbon tetrachloride
1,1,1-Trichloroethane
SOCs
Acrylamide
Alachlor
Carbofuran
o-Dichlorobenzene
2.4-O
Ethylbenzene
Heptachlor
Lindane
Monochlorobenzene
Toluene
2,4,5-TP
Toxaphene
Xylenes
Conven-
tional
Treatment
without
PAC
Percent
Removal
_a
_a
5
<50
54-79
_a
0-3
-a
64
10-20
_a
-a
63
_a
a
Conventional Treatment
with PAC
Dosage
(mg/L)
9.6-30.0
7
8
4-34
9-25
8-27
11-306
8-27
11-97
2-34
8-27
8-27
1.5-17.0
1-44
8-27
Percent
Removal
0-25
40-65
13
36-100
45-75
38-95
69-100
33->99
53-97
82-97
14->99
0-67
82-99
40-99
60->99
a Information not available.
Source: Miltner and Frank (1985).
The main advantage of diffused aeration systems is
that they can be created from existing structures,
such as storage tanks. This type of aeration, however,
is less effective than PCA and is generally used only
in systems with adaptable existing structures.
6.5.1 System Design Considerations
The critical process design considerations for diffused
aeration units are:
Diffuser type and air bubble size
Chamber depth: 1.5 to 3 m (5 to 10 ft)
Air-to-water ratio: 5:1 to 15:1
Detention time: 10 to 15 minutes
Chamber hydraulics
One of the most important diffuser design
considerations is the air introduction method and the
resultant bubble size. Air diffusers use porous plates
or tubes, or perforated pipes placed along the bottom
or sides of the chamber. Chamber hydraulics affect
the uniformity with which the aeration process takes
place and, therefore, the completeness of removal.
Baffling that achieves plug flow conditions followed
by mixing is the general method of assuring proper
chamber hydraulics.
6.5.2 System Performance
Table 6-10 presents removal effectiveness data of
diffused aeration for five VOCs and nine SOCs. The
removal rates, ranging from 11 to 95 percent, are
based on diffused aeration units with air-to-water
ratios of 5:1 to 15:1 and contact times of 10 to 15
minutes.
6.6 Multiple Tray Aeration
Multiple tray aeration directs water through a series
of trays made of slats, perforations, or wire mesh. Air
is introduced from underneath the trays, either with
or without added pressure. Figure 6-24 is a diagram
of a redwood slat tray aerator.
Multiple tray aeration units have less surface area
susceptible to clogging from iron and manganese
precipitation than PTA. However, this type of
aeration is not as effective as PTA and can experience
clogging problems, in addition to biological growth
and corrosion problems. Multiple tray aeration units
are generally available as package systems.
6.6.1 System Design
The principal design considerations for multiple tray
aeration are tray type, tray height, pressurized or
unpressurized air flow, and air-to-water ratio. Trays
are usually made from wood or plastic and range in
stack height from 3.6 to 4.8 m (12 to 16 ft).
Pressurized air flow is used to increase the air-to-
water ratio, with the typical ratio being 30:1.
6.6.2 System Performance
Slat tray aeration with an air-to-water ratio of 30:1
and a tray height of 3.6 to 4.8 m (12 to 16 ft) has
achieved 30 to 90 percent reductions of
trichloroethylene and 20 to 85 percent reductions of
tetrachloroethylene.
6.7 Emerging Applications of Treatment
Technologies for Organic
Contaminants
This section discusses seven emerging water
treatment technologies that hold promise of
becoming BATs for removing organic contamination,
including:
121
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Chemicals - Powdered Activated Carbon
Disinfectant
Rapid Mix Flocculation
Figure 6-21. Schematic of PAC adsorption process.
Air Supply
X
Diffuser Grid
Sedimentation
Filtration
Influent
Effluent
Figure 6-22. Schematic of a plant-scale diffused aeration
process.
* Oxidation including ozone and advanced
oxidation processes
Reverse osmosis
Mechanical aeration
Catenary grid aeration
Higee aeration
Resins
All of these technologies require extensive laboratory
and field testing before becoming BATs.
6.7.1 Oxidation Including Ozone
Oxidation is usually accomplished with either
chlorine, chlorine dioxide, ozone, or potassium
permanganate. Complete oxidation reactions also
destroy organic contaminants. Incomplete oxidation
reactions, however, produce by-products, most of
which are biodegradable and some of which may pose
health risks.
Chlorination, the most widely used disinfection, is
used routinely for oxidation (e.g., breakpoint
chlorination). Unfortunately, THMs and other
halogenated by-products are known to be formed
during chlorination. Other oxidation agents and
processes that do not pose this problem are being
studied as agents to reduce levels of halogenated
organic contaminants.
Ozone is widely used in Europe and is gaining
substantial interest in the United States. A 600-
MGD direct filtration plant in Los Angeles,
California, is employing preozonation to enhance
turbidity removal and filter longevity. Three
advanced oxidation processes for treating organic
contamination are currently being tested: (1) ozone
with high pH levels, (2) ozone with hydrogen
peroxide, and (3) ozone with ultraviolet radiation.
Each of these processes forms the hydroxyl free
radical, which has an oxidation potential about 30
percent higher than molecular ozone. These processes
combine organic compound removal with
disinfection, and taste and odor control.
Ozone with High pH Levels
Ozone, at low pH levels (less than 7), reacts primarily
as the QS molecule by selective and sometimes
relatively slow reactions. Ozone at elevated pH
(above 8) rapidly decomposes into hydroxyl free
radicals, which react very quickly. Many organic
compounds that are slow to oxidize with ozone,
oxidize rapidly with hydroxyl free radicals.
The alkalinity of the water is a key parameter in
advanced oxidation processes. This is because
bicarbonate and carbonate ions are excellent
scavengers for free radicals. Consequently, advanced
oxidation processes are incompatible with highly
alkaline water. In addition, carbonate ions are 20 to
30 times more effective in scavenging for hydroxyl
free radicals than bicarbonate ions. Therefore,
ozonation at high pH should be conducted below 10.3
at which level all bicarbonate ions convert to
carbonate ions.
Ozone with Hydrogen Peroxide (the Peroxide
Process)
The combination of ozone with hydrogen peroxide
much more effectively reduces levels of
trichloroethylene (TCE) and tetrachloroethylene
(PCE) than ozone alone. Table 6-11 shows design
criteria and assumptions for a full-scale
ozone/hydrogen peroxide plant.
A significant advantage of the peroxide process over
GAC and PTA is the absence of vapor controls
122
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Pump/Level
Control Box
Air-Stripped Radon to
Outside Vent
Aeration
Tank
Raw Water from
Radon Generator
To Metered
Household
Water Use
Hydropneumatic Tank
Air Compressor
or Pump
Figure 6-23. Home diffused aeration system
Table 6-10. Typical Performance of Diffused Aeration
Compound % Removal
VOCs
Trichloroethylene
Tetrachloroethylene
1,2-Dichloroethane
1,1-Dichloroethylene
1,1,1 -Trichloroethane
SOCs
Carbofuran
1,2-DichIoropropane
cis-1,2-Dichloroethylene
trans-\ ,2-Dichloroethylene
o-Dichlorobenzene
Ethylbenzene
Monochlorobenzene
Toluene
Xylenes
53-95
73-95
42-77
97
58-90
11-20
12-79
32-85
37-96
14-72
24-89
14-85
22-89
18-89
Source: Miltner and Frank (1985).
because the contaminants are destroyed, not merely
removed from the water. Table 6-12 compares annual
costs for four system types: aeration, aeration with
gas-phase GAC, liquid-phase GAG, and an advanced
oxidation process.
Ozone/Ultraviolet
In ozone/ultraviolet (UV) treatment, ozone catalyzed
by UV oxidizes organic substances. This process
breaks down the saturated bonds of the contaminant
molecules. Typical contact time is 0.25 hours. Table
6-13 presents system removal efficiencies with 0.25-
hour contact times and varying ozone dosages for 13
SOCs. A major advantage of this system is that it
does not produce any THMs. These systems also do
not require waste disposal because the contaminants
are destroyed.
There is some concern about the completeness of the
ozone/UV oxidation process and the intermediate
breakdown products. If oxidation is incomplete, some
of the compounds produced in the intermediate
reactions may still be available to form THMs. The
influent contaminant profile also affects the
performance of these systems. However, if oxidation
is followed by a biological filtration step, particularly
GAC on sand or GAC adsorber, these oxidation
products are mineralized into carbon dioxide and
123
-------
Multiple tray aeraton Norwalk, CT.
water. Consequently, THM formation potential and
TOX formation potential are lowered.
6.7.2 Reverse Osmosis
Reverse osmosis is a proven technology for the
removal of inorganic compounds. The process is fully
described in Section 7.3.3. Reverse osmosis also is
effective in removing THM humic and fulvic acid
precursors, pesticides, and microbiological
contaminants (viruses, bacteria, and protozoa). This
treatment has been shown to remove VOCs with low
molecular weights. Table 6-14 presents performance
data for reverse osmosis units operating at about 200
psi for 7 VOCs and 16 SOCs.
6.7.3 Mechanical Aeration
Mechanical aeration systems use surface or
subsurface mechanical stirring mechanisms to create
turbulence to mix air with the water. These systems
effectively remove VOCs but are generally used for
wastewater treatment systems. Surface and
subsurface aerator designs are shown in Figure 6-25
(Roberts and Dandliker, 1982).
Mechanical aeration units consume large amounts of
space because they demand long detention times for
effective treatment. As a result, they often require
open-air designs, which may freeze in very cold
climates. These units also have high energy
requirements. Mechanical aeration systems,
however, are easy to operate and are less susceptible
to clogging from biological growth than PTA.
6.7.4 Catenary Grid
Catenary grid systems are a variation of the PTA
process. The catenary grid directs water through a
series of parabolic wire screens mounted within the
column, above which turbulence is created. The
screens mix the air and water in the same way as the
packing materials in PTA systems. Figure 6-26
depicts a sample unit.
These systems can achieve VOC removal rates
comparable to PTA systems. Catenary grid units
require more airflow and, thus, have higher energy
requirements than PTA systems. They also have
shorter aeration columns with smaller diameters.
Their more compact design lowers their capital cost
relative to PTA.
Catenary grid systems, however, have limitations.
Limited data are available concerning this system's
removal effectiveness for a wide variety of organic
compounds. Also, the procedure for scaling systems
up from pilot plants to full-scale operations is not
fully developed.
The principal design considerations for catenary grid
systems are air-to-water ratio, number of screens,
and hydraulic loading rate. Removal efficiency
improves with increases in air-to-water ratios and
increasing number of screens in the column.
6.7.5 Higee Aeration
Higee aeration systems are another variation of the
PTA process. These systems pump water into the
center of a spinning disc of packing material to
achieve the necessary air and water mix (Glitsch,
Inc.). By design, the packing material has a large
surface area per unit volume. Air is pumped
countercurrently toward the center from the outside
of the spinning disc. Simultaneously, water flows
from the center of the disc and mixes with the air (see
Figure 6-27).
Higee units require less packing material than PTA
units to attain equivalent removal efficiencies. They
require smaller air volumes and can process high
water flows in a compact space. The Higee unit's
compact size permits its application within
constrained spaces and heights. Current Higee
systems are best suited for temporary applications of
less than 1 year with capacities up to 6.3 L/sec (100
124
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Inlet
Chamber
Distributor
Nipples
Staggered
Slat Trays
Air Inlet
Water
Inlet;
Blower
^ ) Air
/^ X Outlet
Baffles
Air Stacks
Air Seal
Water
Outlet
Figure 6-24. Schematic of a redwood slat tray aerator.
GPM). Few data are available concerning the organic
compound removal efficiencies of Higee systems.
6.7.6 Resins
In this process, synthetic resins are used in place of
GAC to remove organic compounds by adsorption.
Their performance varies with resin type, EBCT, and
regeneration frequency.
The advantages of resins include shorter EBCT
requirements and longer operational life, relative to
GAC. Also, resins can be regenerated on site with
steam. However, wastewater from this process can be
difficult to manage properly because of its high
concentrations of hazardous constituents (Ruggiero
and Ausubel, 1982).
Resins are more costly than GAC, costing up to
$0.02/g ($10/lb), compared to less than $0.01/g
($0.80/lb)forGAC.
125
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Tablo 6-11. Design Parameters for Peroxide-
Ozone Treatment Plant and
Assumptions for Cost Comparisons
Parameter Value
Table 6-12. Comparison of Annual Treatment Costs for
Removal of PCE and TCE from Ground Water
Plant flow-GPM
TCE concentration - u,g/L
PCE concentration - yg/L
Reaction tank capacity - gal
Hydraulic detention time - min
Reaction tank stages - number
Ozone dosage - mg/L
Ozone generator capacity - Ib/day
Peroxide dosage - mg/L
Peroxide storage - gal at 50 percent
concentration
2,000
200
20
6,000
3
1
4
100
2
1,000
Assumptions
The treatment plant is to be built for one well with a capacity of
2,000 GPM (126 Us).
The TCE concentration of the ground water being pumped
remains constant for 10 years. At the end of this time, all
the TCE has been extracted and the treatment plant is no
longer needed.
The rate of Interest remains at 8 percent for 10 years.
The capital cost of the aqueous-phase GAC treatment plant
is $1.3 million.
The capital cost of the air-stripping treatment plant alone is
$325.000.
The capital cost of the treatment plant for air stripping plus
gas-phase GAC adsorption is $725,000.
The annual operating cost of each system is the power
requirement plus one quarter of a person-year for
maintenance.
The cost of power is $1.08/lb.
The cost of hydrogen peroxide is $1.08/lb.
1 pound ป 453.6 grams
1 gallon - 3.785 liters
Source: Aieta et a). (I988a).
Cost Type
Capital cost (annual-
ized, 10 years, 8%)
Operating and
maintenance costs
GAC replacement
costs
Total annualized
costs
Dollar cost per 1,000
gallons (based on
2,000-gallon flow)
Aeration
48,400
30,200
NA
78,600
(0.075)
Aeration
with Gas-
Phase
GAC
Adsorption
108,000
78,300
105,100
291,400
(0.277)
Liquid
Phase
GAC
Adsorption
192,500
13,900
210,400
416,800
(0.397)
Peroxide
Ozone
Advanced
Oxidation
Process
35,000
63,900
NA
98,900
(0.094)
NA = not available.
1,000 gallons = 3.78 m3
Source: Aieta etal. (1988).
Table 6-13. Typical Performance of Ozonation Process
Compound Dosage (mg/L) Percent Removal
SOCs
Carbofuran
1 ,2-Dichloropropane
c/s-1,2
Dichloroethylene
frans-1 ,2
Dichloroethylene
o-Dichlorobenzene
Ethylene dibromide
Ethylbenzene
Heptachlor
Heptachlor epoxide
Lindane
Monochlorobenzene
Toluene
Xylenes
9
0.9-6.0
2-10
0.9-6.0
9
0.9-6.0
1.5-9.0
17
17
0.4-150.0
0.4-6.0
1.5-12.0
1.5-12.0
100
8-22
87-93
100
88
8-9
47-95
100a
26
0-100
86-98
49-98
54-98
a Oxidation of heptachlor produces heptachlor epoxide, which is
relatively stable to further oxidation.
Source: Miltner and Frank (1985).
126
-------
Drive
Table 6-14. Typical Performance of Reverse Osmosis
Process
Compound
YOCs
1 ,2-Dichloraethane
1 ,i,l -Trichloroethane
Carbon tetrachloride
Trichloroethylene
Tetraehloroethylene
Benzene
p-Dichlorobenzene
SOCs
Acrylamide
Aldicarb
Alachlor
Carbofuran
1 ,2-Dichloropropane
c;'s-1 ,2-Dichloroethylene
frans-1 ,2-Dichloroethylene
2,4-D
o-Dichlorobenzene
Ethylbenzene
Ethylene Dibromide
Lindane
Methoxychlor
Monochlorobenzene
RGBs
Xylenes
Percent Removal
15-70
15-100
95
0-75
70-90
2-18
0-10
0-97
94-99
100
86-99
10-90
0-30
0-30
1-65
65
30
37-84
50-75
>90
50-100
95
10-85
Mechanical Surface Aerator
Drive O
, Compressor
t
Turbine *-G-*
Sparger 5
sฐ
!- -i '-
I Air
r
ป
i
Submerged Turbine Aerator
Source: Roberts and Dandliker (1982).
Figure 6-25. Schematic of mechanical aeration process.
Source: Miltner and Frank (1985).
127
-------
Demister
Water Inlet
Ruidized Zone
Treated Water
Sample Collector
Manometer for
Air Ftowrate Measurement
Raw Water
Rotameter
Raw Water
Sample Tap
Treated Water
Sample Tap
Water Flow
Metering Valve
Treated Water to Drain -
Figure 6-26. Catenary grid system.
128
-------
Pilot catenary grid aerator unit.
Air In
XT
Blower
Ground Water
Filter
Exhaust Air
ป V
n
-f~
Higee
Product Water
Pump
Figure 6-27. Schematic of Higee system.
129
-------
-------
Chapter 7
Treatments for Inorganic Contaminants
This chapter describes the technologies available for
removing inorganic contaminants from drinking
water. Inorganic contaminants tend to come from
natural sources and, therefore, are more predictable
in behavior and composition than organic
contaminants that come from manmade sources.
Inorganic contaminants are classified as cationic,
anionic, or neutral and occur as atoms, ions, or
molecules. The two most significant properties
affecting the removal of inorganic contaminants from
water are valence and solubility in water.
The most common treatments for inorganic
contaminants are:
Precipitation
Coprecipitation
Adsorption
Ion exchange
Membrane separation by reverse osmosis or
electrodialysis
A combination of two or more of the above five
technologies
Other treatments for removing inorganic
contaminants include:
Distillation
Evaporation
Oxidation/Reduction
Air stripping
Biological treatment
EPA has specified best available technologies (BAT)
for three inorganic contaminants, including:
Corrosion control for lead
ป Ion exchange or reverse osmosis for nitrate
Ion exchange and reverse osmosis for radium
It is expected that aeration will be designated as BAT
for radon. Corrosion control targets lead as a
corrosion by-product. Lead, when found in source
water, requires conventional or other treatment such
as reverse osmosis and ion exchange.
Twelve inorganic contaminants are presently
regulated under SDWA: lead, radium, nitrate,
arsenic, selenium, barium, fluoride, cadmium,
chromium (total), mercury, silver, and strontium-90.
Lead is not typically found in source water, but
rather at the consumer's tap as a result of corrosion of
the plumbing or distribution system. The other
contaminants are found regionally for a variety of
reasons. Radionuclides are of particular concern
because few utilities currently test for other than
radium and EPA has found them to be more
prevalent than previously determined.
This chapter presents two distinct approaches to
water treatment for inorganic contamination: (1)
preventing inorganic contamination of finished
water and/or (2) removing inorganic contaminants
from raw water. Section 7.1 discusses corrosion
control, the primary method for minimizing
inorganic contamination of finished water. The major
focus of this subsection is lead. Section 7.2 describes
treatment options for removing inorganic
contaminants from raw water. Appendix D provides
case histories on corrosion control and treatment
methods to remove inorganics.
7.1 Techniques for Controlling
Corrosion
Lead is found in drinking water chiefly because the
metals used in water distribution systems, home
plumbing, and appliances, such as water coolers,
corrode. These metals generally are not found in
significant amounts in source waters, but rather at
the final point of use. Zinc, copper, and iron also are
commonly present in water as corrosion products.
Cadmium has been found in water systems with new
galvanized pipe. Lead and cadmium are toxic at low
131
-------
concentrations; copper and zinc are toxic only at
much higher levels. Because ofits ubiquity and
toxicity, lead is the corrosion product of most concern.
Cadmium also has significant health implications,
but it is not as widespread in drinking water as lead.
Lead levels in drinking water are minimized with
corrosion controls. The current lead MCL applies to
finished water from a treatment plant. New lead
regulations may include an MCL at the consumer's
tap. While corrosion is recognized as a critical factor
for proper management of any water system, the lack
of a standard measure of corrosion has thwarted
development of uniform controls.
7.1.1 The Problem of Corrosion
Corrosion occurs because metals tend to oxidize when
in contact with potable water and form stable solids
on metal surfaces. All metals in contact with water
will corrode to some extent. Corrosion has
implications for health, costs, and aesthetics.
Drinking water contaminated with metals adversely
affects human health. Corrosion reduces the useful
life of water distribution systems and household
plumbing, and is thus responsible for higher costs
due to problems with:
* Pumping caused by narrowed pipe diameters
resulting from corrosion deposits
* Pumping and water production caused by
corrosion holes, which reduce water pressure and
increase the amount of finished water required to
deliver a gallon of water to the point of
consumption
Water damage caused by corrosion-related pipe
failures
Replacement frequency of hot water heaters,
radiators, valves, pipes, and meters
* Customer complaints of color, staining, and taste
problems
ป Repairs for pipe leaks and breaks
Lastly, corrosion can produce conditions that promote
microorganisms that cause disagreeable tastes,
odors, slimes, and further corrosion.
All water is corrosive to some degree, but water that
is acidic will have faster corrosion rates. Many
naturally occurring acidic waters are also soft. Soft
water is generally defined as water with less than
100 mg/L of calcium as calcium carbonate (CaCOa);
acidic water has a pH of less than 7.0.
The degree of corrosion is determined primarily by
the characteristics of the metal and water, and the
nature and duration of the contact between the two.
Table 7-1 summarizes the factors affecting drinking
water corrosivity. Water treatment processes can
change water quality characteristics that
significantly affect the water's corrosion potential.
For example, pH is lowered with the use of
coagulants or disinfectants. Other treatment
processes affect water chemistry parameters such as
disinfectant residual, hardness, and alkalinity.
Table 7-1. Factors Affecting the Corrosivity of Drinking
Water
Factor Effect on Corrosivity
Low pHs generally accelerate corrosion.
Dissolved oxygen in water induces active corrosion,
particularly of ferrous and copper materials.
The presence of free chlorine in water promotes
corrosion of ferrous metals and copper.
There is insufficient alkalinity to limit corrosion
activity.
A molar ratio of strong mineral acids much above 0.5
results in conditions favorable to pitting corrosion
(mostly in iron and copper pipe).
PH
Dissolved
oxygen
Free chlorine
residual
Low
buffering
capacity
High
halogen and
sulfate-
alkalinity
ratio
Total
dissolved
solids
Calcium
Higher concentrations of dissolved salts increase
conductivity and may increase corrosiveness.
Conductivity measurements may be used to estimate
total dissolved solids.
Calcium can reduce corrosion by forming protective
films with dissolved carbonate, particularly with steel,
iron, or galvanized pipe.
Tannins Tannins may form protective organic films over
metals.
Flow rates Turbulence at high flow rates allows oxygen to reach
the surface more easily, removes protective films,
and causes higher corrosion rates.
Metal ions Certain ions, such as copper, can aggravate
corrosion of downstream materials. For example,
copper ions may increase the corrosion of galvanized
pipe.
Temperature High temperature increases corrosion reaction rates.
Rates High temperature also lowers the solubility of calcium
carbonate, magnesium silicates, and calcium sulfate
and thus may cause scale formation in hot-water
heaters and pipes.
Source: Adapted from Williams (1986).
The type of corrosion products present depends on the
metals composing the solder, pipes, valves, meters,
and faucets in distribution and plumbing systems.
The most common metals used are steel, iron,
galvanized steel, copper, lead, brass, and bronze.
Zinc, cadmium, and some lead are present in
galvanized coatings. The most frequent sources of
lead are brass faucets, meters, pipe solder, and
valves. Lead is no longer generally used for pipes, but
in older cities service connections between houses
and water mains still contain lead pipe. Many cities
have initiated lead service line replacement
programs to address this source.
While lead pipes have long been recognized as
hazardous, lead-based solder was used in the United
132
-------
States until it was banned in the 1986 SDWA
Amendments. This ban prohibits the use of solder
containing lead and the associated high lead levels
often found in newly constructed homes and in new
plumbing in existing homes. Precise estimates of lead
levels in drinking water resulting from lead-based
solders and fluxes vary. This stems from the
difficulty in consistently measuring lead levels from
the tap, especially if there is a brass faucet, which
contributes to lead levels as well. The method of
solder application affects the amount of lead
imparted to the water. Improper application, which is
difficult to determine in retrospect, allows solder to
flow on to the inner portion of the pipe, thus
increasing its area of contact with the water.
7.1.2 Diagnosing and Evaluating the Problem
There are dozens of types of corrosion, but the two
broad categories of particular concern in water
treatment are uniform and nonuniform corrosion.
Nonuniform corrosion shortens the useful life of pipes
and plumbing more quickly than uniform corrosion,
and is thus more of a problem for water systems. The
five most common types of nonuniform corrosion to
affect water systems are:
Galvanic - Occurs when two different metals are
joined together; the more electrochemically
active of the joined metals will corrode. (See
Table 7-2 for relative activity of various metals
and Section 7.1.3.1 for discussion of this
characteristic.)
Table 7-2. Galvanic Series - Order of Electrochemical
Activity of Common Metals Used in Water
Distribution Systems
Metal Activity
Zinc
Mild steel
Cast iron
Lead
Brass
Copper
Stainless steel
More Active
Less Active
Source: U.S. EPA (1984).
Pitting - Occurs as uneven pits or holes in the
pipe surface, which are undetectable until the
pipe fails. Pitting is usually caused by pockets of
corrosion initiated by tiny imperfections,
scratches, or surface deposits in the pipe.
Crevice - Occurs locally around gaskets, lap
joints, rivets, and surface deposits. It is caused by
changes in acidity, oxygen concentrations,
dissolved ions, and the absence of corrosion
inhibitors.
e Erosion - Occurs due to the removal of protective
coatings through high water velocities,
turbulence, sudden changes in flow direction, and
abrasive action of suspended solids or gases.
Biological - Occurs in mechanical crevices or
accumulations of corroded materials due to the
interaction between the metal and bacteria,
algae, or fungi.
Most lead corrosion problems are diagnosed
indirectly. Risk factors that indicate potentially high
lead levels at the tap are:
The water distribution system or structure's
plumbing is made of lead.
The structure's plumbing has solder containing
lead.
The structure is less than 5 years old.
The tap water is soft and acidic.
The water stays in the plumbing for 6 or more
hours.
The structure's electrical system is grounded to
the plumbing system.
The presence of any of these factors justifies further
investigation.
One direct method of measuring lead corrosivity of
water is to sample standing water from the
consumer's tap. In addition, consumer complaints,
corrosion indices, sampling and chemical analysis,
pipe scale examination, and measurement of the
corrosion rate over time are all proxies for corrosion
contaminants.
7.1.2.1 Consumer Complaints
Many times a consumer complaint is the first
indication of a corrosion problem. Table 7-3 lists the
most common complaints and their causes. In
investigating the extent of the corrosion, complaints
can be plotted on a map of a water service area. Then
investigators can examine the construction materials
used in the water distribution system and in the
plumbing of the complaint areas. Random sample
surveys are commonly used to confirm the extent of
the corrosion problems flagged by these complaints.
7.1.2.2 Corrosion Indices
Corrosion related to calcium carbonate deposition can
be estimated using indices derived from common
water quality measures. The Langelier Saturation
Index (LSI) is the most commonly used and is equal to
the water pH minus the saturation pH. The
saturation pH refers to the pH at the water's calcium
carbonate saturation point, the point where calcium
133
-------
Table 7-3. Typical Customer Complaints Due to Corrosion
Customer Complaint Possible Cause
Rod water or reddish-brown
staining of fixtures and laundry
Bluish stains on fixtures
Black water
Foul taste and/or odors
Loss of pressure
Lack of hot water
Short service life of household
plumbing
Corrosion of iron pipes or
presence of natural iron in raw
water
Corrosion of copper lines
Sulfide corrosion of copper or
iron lines or precipitations of
natural manganese
By-products from microbial
activity
Excessive scaling, tubercle
build-up from pitting corrosion,
leak in system from pitting or
other type of corrosion
Buildup of mineral deposits in
hot water system (can be
reduced by setting thermostats
to under 60ฐC [140ฐF])
Rapid deterioration of pipes
from pitting or other types of
corrosion
Source: Adapted from U.S. EPA (1984).
carbonate is neither deposited nor dissolved. Calcium
carbonate may precipitate and form a protective
layer on metals. The saturation pH is related to the
water's calcium ion concentration, alkalinity,
temperature, pH, and presence of other dissolved
solids, such as chlorides and sulfates.
The Aggressive Index (AI) is a simplification of the
LSI that only approximates the solubility of calcium
carbonate and may not be useful. The Ryznar
Stability Index (RSI), also a modification of the LSI,
uses visual inspections. McCauley's Driving Force
Index (DPI) estimates the amount of calcium
carbonate that will precipitate based on the same
factors as the LSI.
Riddick's Corrosion Index (CI) is distinct from the
LSI. Its empirical equation incorporates different
factors to predict corrosion, such as dissolved oxygen,
chloride ion, noncarbonate hardness, and silica.
Appendix E provides the equations, descriptions of
test parameters, and interpretations of each index.
7.1.2.3 Sampling and Chemical Analysis
Corrosion can also be assessed by conducting a
chemical sampling program. Water with a low pH
(less than 6) is more corrosive. Temperature and total
dissolved solids can be important indicators of
corrosivity, although this varies case by case.
Proper sampling and analysis methods are essential
to obtain accurate and meaningful test results.
Determining whether lead is from a service pipe or
internal plumbing requires sampling at multiple
locations or getting accurate and precise samples
representing water in prolonged contact with the
suspected section of pipe (e.g., service line, soldered
joints). Experiments show that sample volume also
affects the amount of lead detected in tap water.
Other critical sampling elements include sampling
location, amount of water in each sample, flow rate of
sample, and the contact time of the water with the
metal. The amount of time the water remains in the
pipes significantly affects lead levels. Also, the time
of day is a critical factor in accurately assessing
sampling results. Early morning sample results will
reflect water that has been held in the pipes
overnight, while evening water samples may assess
water intermittently drawn by daily activities.
The age of the pipe solder has been shown to affect
lead levels in water. One study found that 4 to 5
weeks after an application of lead-based solder, lead
levels declined by 93 percent from initial
measurements. The effects of solder age and the
length of time the water stands in the pipes are
illustrated in Table 7-4, Table 7-5, and Table 7-6 for
low, medium, and high water pH levels, respectively.
Table 7-4. Percentage of Test Sites with Lead in Drinking
Water Greater than 20 pg/L at Low pH (6.4 and
less)
Age of
Test
Site
(Years)
0-1
1-2
2-3
3-4
4-5
6-7
9-10
15-16
20 and
older
First
Draw
100%
100
86
100
86
78
71
57
86
10
Sec
100%
71
86
86
57
44
29
14
27
20
Sec
100%
86
57
100
29
33
14
14
29
30
Sec
100%
57
57
71
43
33
14
14
0
45
Sec
100%
57
43
71
43
11
14
14
14
60
Sec
86%
29
43
71
43
11
14
14
0
90
Sec
86%
43
43
29
14
11
0
14
14
120
Sec
88%
14
29
29
0
0
0
14
0
7.1.2.4 Scale or Pipe Surface Examination
Pipe scale and the inner surface of pipes can be
examined by optical or microscopic observation, x-
rays, wet chemical analysis, and Raman and infrared
spectroscopy. Obviously the most practical and
economic method is simple observation. The other
methods require expensive equipment and highly
skilled personnel. Even simple observation, however,
requires taking sections of pipe out of service.
Chemical examinations can determine the
composition of pipe scale, such as the proportion of
calcium carbonate present that shields pipes from
dissolved oxygen and thus reduces corrosion.
134
-------
Table 7-5. Percentage of Test Sites with Lead in Drinking
Water Greater than 20 pg/L at Medium pH
(7.0-7.4)
A nr\ f\f
Age 01
Test
Site
(Years)
0-1
1-2
2-3
3-4
4-5
6-7
9-10
15-16
20 and
older
First
Draw
100%
80
40
50
30
10
20
40
20
Table 7-6.
A /.*-ป rvt
Age OT
Test
Site
(Years)
0-1
1-2
2-3
3-4
4-5
6-7
9-10
15-16
on anrl
ฃ.\J Ol W
older
First
Draw
10
Sec
90%
60
20
20
10
0
0
20
0
20
Sec
90%
30
10
20
10
0
0
20
0
30
Sec
60%
10
10
30
0
0
0
10
0
Percentage of Test
Water Greater than
(8.0 and
10
Sec
100% 100%
67
30
25
30
20
10
33
20
22
10
0
10
0
0
22
o
45
Sec
30%
20
10
20
10
0
0
0
10
60
Sec
20%
0
0
30
0
0
0
0
0
Sites with Lead
20 ng/L at High
90
Sec
10%
10
0
30
0
0
0
0
0
120
Sec
10%
0
0
20
0
0
0
0
0
in Drinking
pH
Greater)
20
Sec
60%
11
10
0
0
0
10
11
0
30
Sec
45
Sec
10% 20%
11
0
0
0
0
0
11
0
11
0
0
0
0
0
0
0
60
Sec
10%
0
0
0
0
0
10
0
0
90
Sec
20%
11
0
0
0
0
0
0
0
120
Sec
0%
0
0
13
0
0
10
0
0
flat coupons are commonly placed in the middle of a
pipe in the system. The coupons are weighed before
and after they are put in place and the recorded
weight loss is translated into a uniform corrosion rate
with the following formula:
534 X W
Rate of Corrosion (MPY) =
D X A X J.
where:
W = weight loss in mg
D = density of the specimen in g/cm3
A = surface area of the specimen in sq in
T = exposure time in hours
This method can be used to monitor corrosion
progress over time or to spot check the corrosion rate.
The loop system weight-loss method is similar to the
flat coupon method, except that it uses actual sections
of pipe in the system instead of flat coupons. Loop
system corrosion rates are usually determined by
analyzing corrosion over a period of time.
Electrochemical rate measurement requires
expensive and sophisticated equipment beyond the
means of most smaller systems. In this method, two
or three electrodes are placed in the corrosive
environment, and instrumentation measures the
corrosion rate in MPY.
7.1.3 Corrosion Controls
If any of the tests described above reveal
unacceptably high levels of lead, then immediate
measures should be taken to minimize human
exposure until a long-term action plan is developed,
approved, and implemented. Some short-term
measures for water consumers are:
Chemical analyses and microscope assistance then
should be used to augment these findings.
7.1.2.5 Rate Measurements
The corrosion rate is usually expressed in thousands
of an inch (mils) per year (MPY). The three methods
for calculating this rate are:
Coupon weight-loss
Loop system concentration increase
Electrochemical rate measurement
The first two methods are much less expensive than
the third.
The coupon weight-loss method uses flat metal pieces
or test sections of pipes called coupons or inserts. The
Running the water for 1 to 3 minutes before each
use
Using only cold tap water for drinking or cooking
Using a home-scale reverse osmosis unit or other
treatment process, in extreme cases
Using bottled water
Longer term solutions fall into six categories:
Distribution and plumbing system design
considerations
Water quality modification
Corrosion inhibitors
Coatings and linings
Use of only nonlead based solder for construction
and repairs
Replacement of lead pipes
135
-------
7.1.3.1 Distribution and Plumbing System
Design Considerations
Many distribution and plumbing system design
considerations will reduce corrosion. For example,
water distribution systems designed to operate with
lower flow rates will have reduced turbulence and
decreased erosion of protective layers. Other
measures that minimize corrosion include:
Using only lead-free pipes, fittings, and
components
Selecting appropriate system shape and
geometry
Avoiding sharp turns and elbows
Avoiding dead ends and stagnant areas
Eliminating shielded areas
Providing adequate drainage
Selecting appropriate metal thickness
Using welded ends, instead of rivets
Reducing mechanical stresses
Avoiding uneven heat distribution
Providing adequate insulation
Providing easy access for inspection,
maintenance, and replacement
* Eliminating the grounding of electrical circuits
to the system
To implement these measures effectively, local
plumbing codes may need to be modified.
Distribution system designers should base their
materials selection criteria on system water
characteristics. For example, water with low pH
levels and high dissolved oxygen levels corrodes
metals quickly. Concrete may be more appropriate
than metal in this case because, although concrete
dissolves under lowpH conditions, the rise in
dissolved calcium in the water is not objectionable
and since concrete pipes are thick they have a longer
lifetime. Table 7-7 presents the corrosion properties
of common distribution system materials.
Metal electrochemical activity is the measure of a
metal's tendency to oxidize. When placed together,
metals with different activities create galvanic
corrosion cells. Therefore, if different metals must be
placed together, minimizing the differences in their
activity will lessen corrosion. Galvanic corrosion is
also avoided by placing dielectric insulating
couplings between the dissimilar metals.
While many corrosion control programs address the
lead content of pipes, solder, and other plumbing
components, they do not target lead-bearing
plumbing fixtures, such as brass faucets or valves.
Changing the composition of solder used in plumbing
is considered the most important factor in any lead
corrosion control strategy. In the past, solder used in
plumbing has been 50 percent tin and 50 percent
Table 7-7. Corrosion Properties of Frequently Used
Materials in Water Distribution Systems
Distribution
Material
Copper,
iron
Lead
Corrosion Resistance
Good overall corrosion
resistance; subject to
corrosive attack from high
velocities, soft water, chlor-
ine, dissolved oxygen, and
low pH
Corrodes in water with low
pH and high alkalinities
Associated Potential
Contaminants
Copper and possibly zinc,
tin, arsenic, cadmium, and
lead from associated pipes
and solder
Lead (can be well above
MCLa), arsenic, and
Mild steel Subject to uniform
corrosion; affected
primarily by high dissolved
oxygen levels
Cast or Can be subject to surface
ductile iron erosion by aggressive
(unlined) waters
Galvanized Subject to galvanic corro-
iron sion of zinc by aggressive
waters; corrosion is
accelerated by contact
with copper
materials;corrosion is
accelerated at higher
temperatures as in hot-
water systems
Asbestos- Good corrosion resistance;
cement immune to electrolysis;
aggressive waters can
leach calcium from cement
Plastic Resistant to corrosion
Brass Fairly good; subject to
dezincification depending
on the water quality and
alloy
cadmium
Iron, resulting in turbidity
and red-water complaints
Iron, resulting in turbidity
and red-water complaints
Zinc and iron; cadmium
and lead (impurities in
galvanizing process may
exceed primary MCLs)
Asbestos fibers
Lead, copper, zinc,
arsenic
aMCL .= Maximum contaminant level.
Source: Adapted from U.S. EPA (1984).
lead. Alternative lead-free solders are available at a
higher cost.
Two alternative solders are made from 95 percent tin
and 5 percent antimony or silver. The 1984 costs per
gram of standard lead-; antimony-; and silver-based
solders were $9.92, $17.64, and $44.09, respectively
($4.50, $8.00, and $2G.OO/lb, respectively). Plumbers
estimate that plumbing in an average residence
requires less than 1 Ib of solder, which makes solder
costs relatively insignificant. However, these
alternative solders do not perform exactly the same
as lead-based solder. For instance, both silver-tin and
antimony-tin solders are more difficult to work with
than lead solder because of higher and more narrow
melting ranges.
7.1.3.2Water Quality Modifications
Measures that change water quality to reduce
corrosion contamination, especially lead corrosion,
include pH and alkalinity adjustment, lime-soda
136
-------
softening, and adjustment of dissolved oxygen levels,
although altering oxygen levels is not a common
method of control. Any corrosion adjustment program
should include a monitoring component that enables
dosage modification in response to changing water
characteristics over time.
pH Adjustment
Frequently corrosion is mistakenly associated merely
with water acidity. The pH level plays a central role
in determining the corrosion rate and is relatively
inexpensive to control. Generally, water pH less than
6.5 is associated with uniform corrosion, while pHs
between 6.5 and 8.0 can be associated with pitting
corrosion. Systems using only pH to control corrosion
should maintain their water above 9.0 pH to reduce
the availability of hydrogen ions as electron
acceptors. However, pH is not the only factor in the
corrosion equation; carbonate and alkalinity levels
may affect corrosion as well.
By adjusting pH, alkalinity, and calcium levels,
operators can promote the precipitation of a
protective calcium carbonate (scale) coating onto the
metal surface of plumbing. While these protective
coatings build up over time, they are disturbed by:
ซ Water turbulence due to high velocities and flow
rates
Stagnation of water causing prolonged periods of
contact
Variations in the control of velocities, flow rates,
and stagnation
Calcium carbonate scaling occurs when water is
oversaturated with calcium carbonate. Below the
saturation point, calcium carbonate will redissolve
and at saturation, calcium carbonate is neither
precipitated nor dissolved. The saturation point of
any particular water source depends on the
concentration of calcium ions, alkalinity,
temperature, and pH, and the presence of other
dissolved materials, such as phosphates, sulfates,
chlorides, sulfides, and some trace metals. A coating
is usually attained through simple pH control, given
adequate concentrations of alkalinity and carbonate.
Adding lime or alkaline substances also promotes the
formation of calcium carbonate scale in most
systems. The Langelier or CCAP Indices are useful
for initiating this corrosion inhibiting strategy
because they estimate calcium carbonate saturation.
Further pH and/or carbonate and/or calcium
adjustments may be required to reach equilibrium, as
established by system monitoring.
Lime Softening
Lime softening, which is sometimes known as linie-
soda softening when soda ash is required in addition
to lime, affects lead's solubility by changing the
water's pH and carbonate levels. Increasing pH levels
reduces the presence of hydrogen ions and increases .
the presence of hydroxide ions. Hydroxide ions
decrease lead solubility by promoting the formation
of solid basic lead carbonates that passivate the
surface of the pipe. Similarly, elevating carbonate to
a certain level increases the presence of carbonate
ions, which, in turn, boost the presence of basic lead
carbonate or lead carbonate. However, continuing to
increase carbonate levels at a pH above about 7.5 will
increase lead solubility (see Figure 7-1). If carbonate
levels are the only other factors under consideration,
then the optimal pH range to avoid lead corrosion is
between 9.0 and 10.0.
200
150 -
8
.a
a.
100
Figure 7-1. Solubility of lead as a function of pH and
carbonate.
Source: Adapted from Schook and Wagner (1985).
Usually water carbonate levels are directly related to
water alkalinity because alkalinity refers to the
water's ability to neutralize acids and the most
common base is dissolved inorganic carbon
(carbonate species). At drinking water treatment
plants, neutralization is performed primarily with
calcium and sodium hydroxides, although carbonates
may also be added. Carbon dioxide and water form
bicarbonate as the pH increases; when the pH
reaches 10.3, the carbonic species is expressed as
carbonate. Coordinating pH level with alkalinity
supplementation may reduce lead corrosion.
Optimum alkalinity levels are 30 to 60 mg/L as
calcium carbonate (CaCOa).
Adjustment of both pH and alkalinity using lime-
soda softening is an effective method for controlling
lead corrosion. However, optimum water quality for
corrosion control may not coincide with optimum
hardness reduction. Water hardness is due mostly to
137
-------
the presence of calcium and magnesium ions. Lime-
soda softening reduces the presence of these ions by
adding hydrated lime (Ca(OH)2), caustic soda
(NaOH), or soda ash (sodium carbonate) under
certain water quality conditions. This technique has
been used to address water hardness, rather than
corrosion. Comprehensive water treatment, however,
must balance water hardness, carbonate, and
alkalinity, as well as corrosive potential.
In addition, pH levels that are well suited for
corrosion control may not be optimum for other water
treatment processes, such as coagulation or
disinfection. To avoid this type of conflict, the pH
level should be adjusted for corrosion control
immediately prior to water distribution, but after the
other water treatment requirements have been
satisfied.
Oxygen Levels
The other major water quality factor affecting
corrosion is the presence of excessive dissolved
oxygen. Dissolved oxygen increases water's corrosive
activity by providing a potent electron acceptor. The
optimum level of dissolved oxygen for corrosion
control is 0.5 to 2.0 ppm. However, removing oxygen
from water is not practical because of cost. The most
reasonable strategy is to minimize the presence of
oxygen.
Minimizing dissolved oxygen levels is effective for
ground-water supplies. Ground water is sometimes
aerated prior to treatment to address high levels of
iron, hydrogen sulfide, and carbon dioxide. This
aeration step eliminates free carbon dioxide, which,
in turn, reduces the amount of lime necessary in
lime-soda softening or for pH control; however,
aeration increases corrosion by increasing dissolved
oxygen. Consequently, excluding the aeration step
and increasing lime softening can effectively reduce
unnecessary and potentially counterproductive high
oxygen concentrations.
Oxygen requirements are also reduced by extending
the detention periods for treated water in reservoirs.
Longer detention times allow the oxidation of
hydrogen sulfide and organic carbon at the water
surface. In addition, correct sizing of the water pumps
used in the treatment plant minimizes the
introduction of air during pumping.
Other Modifications
The potential of other substances to affect lead's
solubility has been investigated. Tests show that
adding sulfate, chlorine, and nitrate to water has
little impact on lead solubility and, thus, corrosion.
However, chlorine lowers pH, and chloramines (as
opposed to free chlorine) have been shown to increase
the solubility of lead-based solder. A few studies
indicate that some natural organic compounds
increase lead solubility; however, others have shown
that tannins reduce corrosion by forming protective
coatings on the metal surface.
7.1.3.3 Corrosion Inhibitors
Corrosion inhibitors form, or cause to form, protective
coatings on pipes that reduce corrosion, but may not
totally arrest it. The success of any corrosion
inhibitor hinges on the treatment plant operator's
ability to:
Apply double and triple ultimate dosages of
inhibitor during initial applications to build a
base protective coat to prevent pitting. Typical
initial coatings take several weeks to form.
Maintain continuous and sufficiently high
inhibitor dosages to prevent redissolving.
Attain a steady water flow over all the system's
metal surfaces for a continuous application of the
inhibitor onto all exposed surfaces in the system.
There are several hundred commercially available
corrosion inhibitors. Among the most common for
potable water supply stems are:
Inorganic phosphates
Sodium silicates
Mixtures of phosphates and silicates
These corrosion inhibitors can be applied with
normal chemical feed systems.
Inorganic Phosphates
Inorganic phosphate corrosion inhibitors include
polyphosphates, orthophosphates, glassy phosphates,
and bimetallic phosphates. Zinc, added in conjunction
with polyphosphates or orthophosphates, also helps
inhibit corrosion in some cases. Phosphates can
inhibit excessive calcium carbonate scale formation,
form a protective coating with the pipe metal, or
prevent aesthetically objectionable corrosion by-
products. Water characteristics that affect the
efficiency of phosphate corrosion inhibition include:
Flow velocity
Phosphate concentration
Temperature
pH
Calcium
Carbonate levels
The effectiveness of potential phosphate inhibitors
should be confirmed by laboratory and field tests.
Glassy phosphates, such as sodium
hexametaphosphate, effectively reduce iron corrosion
at dosages of 20 to 40 mg/L. At lower dosages, this
glassy phosphate may merely mask corrosion by
138
-------
eliminating the red color associated with iron
corrosion. Under some circumstances, adding zinc in
dosages of about 2 mg/L improves phosphate's
corrosion control. Zinc phosphate also has been used
effectively to inhibit corrosion.
Some studies show that orthophosphate is an
effective lead corrosion inhibitor within specific
ranges of carbonate and hydrogen ion concentrations.
Polyphosphates have not been shown to be more
effective than simple orthophosphates, and adding
zinc sulfate has not improved polyphosphates'
performance. In addition, polyphosphates can
increase lead solubility in the absence of
orthophosphate.
Silicates
Sodium silicates have been used for over 50 years to
inhibit corrosion, yet the process by which they form
a protective layer is not completely understood. The
effectiveness of sodium silicates depends on pH and
carbonate concentration. Sodium silicates are
particularly effective for systems with high water
velocities, low hardness, low alkalinity, and pH of
less than 8.4. Typical coating maintenance dosages of
sodium silicates range from 2 to 12 mg/L. They offer
advantages in hot-water systems because of their
chemical stability, as contrasted with many
phosphates.
While silicates are hypothesized to inhibit lead
corrosion, little data has been gathered to evaluate
this theory.
7.1.3.4Cathodic Protection
Cathodic protection is an electrical method of
inhibiting corrosion. However, this expensive
corrosion control method is not practical or effective
for protecting entire water systems. It is used
primarily to protect water storage tanks when a
minimum metal surface area is exposed.
Metallic corrosion occurs when contact between a
metal and an electrically conductive solution
produces a flow of electrons (or current) from the
metal to the solution. The electrons given up by the
metal cause the metal to corrode rather than remain
in its pure metallic form. Cathodic protection
overcomes this current with an external power .
source. The electrons provided by the external power
source prevent the metal from losing electrons,
forcing it to be a cathode. This reaction allows the
metal to remain in its less stable metallic form.
Cathodic protection is accomplished either by
inserting electrodes into the metal to induce an
external current or by placing a sacrificial galvanic
anode in the current system. The sacrificial anode
then corrodes in place of the protected metal.
Galvanizing is a form of cathodie protection.
7.1.3.5 Coatings and Linings
Mechanically applied coatings and linings differ for t
pipes and water storage tanks. They usually are
applied prior to installation, although some pipes can
be lined after installation. While coal-tar products for
pipes and tanks have been widely used for linings,
they are under regulatory scrutiny due to the
presence of polynuclear aromatic hydrocarbons in
their composition.
The most common pipe linings are coal-tar enamels,
epoxy paints, cement mortar, and polyethylene.
Table 7-8 summarizes the advantages and
disadvantages of these four primary pipe coatings -
and linings.
The most common types of water storage tank
coatings and linings include coalปtar paints and
enamels, vinyls, and epoxy. Eleven of these coatings
and linings are described in Table 7-9.
7.2 Treatment Technologies f or.
Controlling Inorganic Contaminants,
Including Radionuclides
Inorganic contamination of raw drinking water
supplies occurs from a wide variety of sources,
Contaminants include metal ions, nitrate, fluoride,
and radioactive substances; the most common
contaminants are fluoride, arsenic, and nitrate.
Contaminants that pose significant problems on a
regional basis are selenium, barium, and radium-
226. Inorganic contaminants are grouped as either
naturally occurring or anthropogenic (resulting from
human activities). Many naturally occurring
inorganics, such as fluoride, arsenic, selenium, and
radium-226, are commonly found in ground-water
sources. Anthropogenic contaminants are usually
found in surface water supplies. For example,
nitrates and nitrites are a problem in agricultural
areas or areas without sanitary sewer systems.
Contaminant type, valence, and solubility determine
the most appropriate removal mechanism. Each
removal technology uses a distinct mechanism or
series of mechanisms to remove inorganic
contaminants. Valence is particularly important to
the removal efficiency of lime softening and
coagulation. The primary factors in selecting an
inorganic removal technology are:
Contaminant type(s) and valence(s) .
Influent contaminant concentrations, because
many technologies remove fixed percentages of
contamination
Desired effluent contaminant concentrations
139
-------
Table 7-8.
Material
Pipe Wall Linings
Use
Advantages
Disadvantages
Hoi applied Lining for steel pipes (used in 50 to
coal-tar enamel 80% of pipes in distribution
systems)
Epoxy Lining for steel and ductile iron
pipes (can be applied in the field or
in a foundry)
Cement mortar Standard lining for ductile iron
pipes, sometimes used in steel or
cast-iron pipes
Long service life (> 50 years)
Good erosion resistance to silt or sand
Resistant to biological attachment
Smooth surface results in reduced
pumping costs
Formulated from components approved
by the Food and Drug Administration
Relatively inexpensive
Easy to apply (can be applied in place or
in pipe manufacturing process)
Calcium hydroxide release may protect
uncoated metal at pipe joints
Need to reapply to welded areas
Extreme heat may cause cracking
Extreme cold may cause brittleness
May cause an increase in trace
organics in water
Relatively expensive
Less resistant to abrasion than
coal-tar enamel
Service life < 15 years
Rigidity of lining may lead to
cracking or sloughing
Thickness of coating reduces
cross-sectional area of pipe and
reduces carrying capacity
Polyethylene Lining used in ductile iron and steel
pipe (applied at foundry)
Long service life (50 years)
Good erosion resistance to abrasives (silt
and sand)
Good resistance to bacterial corrosion
Smooth surface results in reduced
pumping costs
Relatively expensive
Source: U.S. EPA (1984).
Table 7-9. Water Storage Tank Linings and Coatings
Material
Comments
Hot applied coal-tar enamel
Coal-tar paints
Coal-tar epoxy paints
Coal-tar emulsion paint
Vinyl
Epoxy
Hot and cold wax coatings
Metallic-sprayed zinc coating
Zinc-rich paints
Chlorinated rubber paints
Asphalt-based linings
Most common coal-tar based coating used in water tanks; tends to sag or ripple when applied above
the waterline when tank walls are heated.
Most commonly used to reline existing water tanks; those paints containing xylene and naphtha solvents
give the water an unpleasant taste and odor and should be used only above the waterline.
Other coal tar paints containing no solvent bases can be used below the waterline but should not be
exposed to sunlight or ice; service life of 5 to 10 years.
Less resistant to abrasion than coal tar enamel; can cause taste and odor problems in the water;
service life of about 20 years.
Good adhesive characteristics, odorless, and resists sunlight degradation but not as watertight as other
coal-tar paints, which limits use below waterline.
Nonreactive; hard, smooth surface; service life (about 20 years) is reduced by soft water conditions.
Forms hard, smooth surface; low water permeability; good adhesive characteristics if properly
formulated and applied.
Applied directly over rust or old paint, short service life (about 5 years).
Relatively expensive process that requires special skills and equipment, good rust inhibition, and service
life of up to 50 years.
Hard surface; resistant to rust and abrasion; relatively expensive.
Used when controlling fumes from application of other linings is difficult, or where their use is specified.
Use is generally limited to relining existing asphalt-lined tanks.
Source: U.S. EPA (1984).
Influent levels of dissolved solids and pH
Pretreatment requirements, such as filtration
required before reverse osmosis or ion exchange
treatments
System size, because of the significant savings
from economies of scale for most technologies
Water flow variability; for example, the
coagulation process may not respond readily to
flow fluctuations, while ion exchange, reverse
osmosis, and activated alumina are relatively
unaffected by changes in flow
Cost
Sludge management
140
-------
Adaptability of existing facilities
Clearly, no single treatment is perfectly suited for all
inorganic contaminants. Possible treatment
technologies include conventional treatment with
coagulation, lime softening, cation exchange, anion
exchange, reverse osmosis and electrodialysis, PAC,
GAG, and activated alumina. Table 7-10 presents the
principal applications and removal efficiencies of the
eight treatment technologies for inorganics.
Many inorganic treatment decisions are based on the
need to reduce the levels of a single contaminant.
However, to treat more than one contaminant,
multiple treatments in series or a membrane
treatment unit, such as reverse osmosis, is most
appropriate. Reverse osmosis and electrodialysis are
effective for most contaminants; however, their low
tolerance for turbidity makes them inappropriate
without preliminary treatment for most surface
water. The removal effectiveness of the other seven
treatments in Table 7-10 varies from poor to
excellent, depending on the contaminant. The
removal percentages provided in the table are
approximations that apply to favorable water quality
conditions.
The actual performance of a removal technology
depends on the selection factors listed above. Table 7-
11 presents a summary of the most effective
treatments for 11 common inorganic contaminants.
The assumptions in the table include consideration of
treatment costs. Table 7-12 summarizes advantages
and disadvantages of each treatment technology.
Section 7.2.1 discusses radionuclide contamination.
Radionuclides present different health risks and
require different analytical evaluation techniques
than other inorganic contaminants, but are removed
by many of the same technologies that are effective
for inorganic and organic contaminants. Sections
7.2.2 through 7.2.5 review the five treatment
technologies designated primarily for inorganic
contamination.
7.2.1 Removing Radionuclides in Drinking
Water
Radionuclides are radioactive atoms that are
characterized by the number of protons and neutrons
in their nucleus and their energy content. The
number that appears with a radionuclide's chemical
abbreviation relates to this nuclear composition. The
most common radionuclides in drinking water are
radium, uranium, and radon.
Many methods are used to measure radionuclides'
levels in drinking water. Atoms emit three types of
nuclear radiation: alpha, beta, and gamma radiation.
The average estimated costs for analyzing these
radiation types range from $25 to $100 per sample.
Many of the techniques for removing radionuclides
are the same as those for inorganic and organic
contaminant removal. Table 7-13 lists the effective
treatment processes for radionuclides. The radium
and uranium removal processes can achieve up to 96
and 99 percent removal, respectively. GAC and
aeration are effective for removing radon. (Complete
discussions of GAC and aeration are provided in
Sections 6.2 and 6.3.)
7.2.1.1 Costs
EPA has developed preliminary cost estimates for
removing radionuclides (see Table 7-14). The costs for
aeration are based on experience from two system
sizes, those serving 100 to 500 persons and those
serving 100,000 persons. Lower costs for larger
systems reflect economies of scale for the aeration
process.
Tables 7-15 and 7-16 present the costs of removing
radon from drinking water. Table 7-15 compares cost
data for removing radon with aeration for three plant
sizes and Table 7-16 compares packed column
aeration and GAC for managing three different
levels of radon in effluent. The costs of removing
radon from tap water vary with the radon
contamination level and the removal method.
Aeration is more expensive and effective than GAC
for contaminant levels of 30,000 pCi/L. However,
GAC is more expensive and effective at higher radon
concentrations of 150,000 pCi/L.
7.2.2 Conventional Treatment: Coagulation
and Lime Softening
Coagulation and lime softening are traditionally
used to control turbidity, hardness, tastes, and odors,
but also are effective in removing some inorganic
contaminants. Section 4.1 describes the conventional
water treatment processes in common practice at
many water utilities. However, employing these
processes to remove specific inorganic contaminants
is relatively new.
Coagulation, discussed in Section 7.2.2.1, is effective
in removing most metal ions or eolloidally dispersed
compounds, but is ineffective in removing nitrate,
nitrite, radium, barium, and sulfate. Lime softening,
discussed in Section 7.2.2.2, increases water pH,
which precipitates the polyvalent cations and anions
of calcium, magnesium, carbonate, and phosphate;
however, lime softening is ineffective for nitrate
removal. ,
Typically, higher dosages of coagulants are required
for effective inorganics removal than for removal of
turbidity, color, or hardness. For example, typical
141
-------
Table 7-10. Removal Effectiveness for Eight Processes by Inorganic Contaminant
Contaminant
Treatment
Conventional treatment
Lime softening
Reverse osmosis
Cation exchange
Anion exchange
Activated alumina
Powdered activated
carbon
Granular activated
carbon
Ag
H
-
H
-
-
-
L
_
As As'"
M
M
M
L
-
H
- _
_ _
Asv
H
H
H
-
-
-
_
_
Ba
L
H
H
H
M
L
L
L
Cd
H
H
H
H
M
L
M
M
Cr CH"
H
H
H
H
M
-
L
L
Or*
H
L
-
L
H
-
_
F
L
M
H
L
-
H
L
L
Hg Hg(0)
M
L
H
-
_ _
_ _
M
H
Hqd)
M
M
_
-
_
_
M
H
NO-,
L
L
M
L
H
_
L
L
Ph
H
H
H
H
M
_
Ra
L
H
H
H
M
L
L
L
Rp
_
_
H
L
H
H
Selv Sevl
M L
M L
_
_ _
_
_
H - High - >80% removal.
M - Medium - 20-80% removal.
L ซ Low ป 20% removal.
- indicates no data were provided.
Table 7-11. Most
Contaminant
Effective Treatment Methods for Removal of Inorganic Contaminants
Most Effective Treatment Methods
Arsenic
Barium
Cadmium
Chromium
Fluoride
Lead
Mercury
Nitrate
Radium
Selenium
Silver
As V-iron coagulation, pH 6-8; alum coagulation, pH 6-7; excess lime softening; activated alumina, pH 5-6
As Ill-oxidation treatment of As III to As V; use same treatment list for As V
Lime softening, pH 11; ion exchange softening
Iron coagulation, above pH 8; lime softening; excess lime softening
Cr Ill-iron coagulation, pH 6-9; alum coagulation, pH 7-9; excess lime softening
Cr-ferrous sulfate coagulation, pH 7-9.5
Ion exchange with activated alumina or bone char
Iron coagulation, pH 6-9; alum coagulation, pH 6-9; lime or excess lime softening
Inorganic-ferric sulfate coagulation, pH 7-8; granular activated carbon
Organic-granular activated carbon
Ion exchange with anion resin
Lime softening; ion exchange with cation resin
Se IV-fem'c sulfate coagulation, pH 6-7; ion exchange with anion resin or activated alumina; reverse osmosis
Se IV-ion exchange with anion resin or activated alumina; reverse osmosis
Ferric sulfate coagulation. pH 7-9; alum coagulation, pH 6-8; lime or excess lime softening
Source: Sorg (1980).
alum dosages for turbidity control range from 5 to 40
mg/L, while the dosage for arsenic removal is about
100 mg/L. Higher dosages increase costs and create
more sludge.
7.2.2.1 Coagulation
The coagulation processes that remove turbidity as
well as inorganic contaminants include adsorption
and precipitation. Coagulation with iron or
aluminum salts also removes trace anions of
selenium, arsenic, and fluoride through
coprecipitation or sorption onto flocculated particles.
Coagulation is more effective in removing
polyvalent, as opposed to monovalent, cations and
anions. The effectiveness of coagulation also depends
on influent turbidity and/or color levels, the quality
of the flocculated particles produced, and the amount
of turbidity or color removed.
Table 7-17 presents potential removal efficiencies
using alum and ferric salts as coagulants. The
optimum pH level varies depending on the target
inorganic substance and the coagulant used. The
table provides the most suitable pH level for
removing each inorganic substance, when available.
As indicated, iron salts are more effective over a
wider range of pH levels than alum. Ferric salts are
effective at pH levels between 4.0 and 12.0, while
alum is generally effective at pH 5.5 to 8.0.
142
-------
Table 7-12. Advantages and Disadvantages of Inorganic
Contaminant Removal Processes
Table 7-13. Treatment Technologies for Removing
Radionuclides
Precipitation and Coprecipitation Used in
Coagulation/Conventional
Advantages
Low cost for high volume
Often improved by high ionic strength
Reliable process well suited to automatic control
Disad antages
Stoichiometric chemical additions required
High-water-content sludge disposal
Part-per-billion effluent contaminant levels may require
two-stage precipitation
Not readily applied to small or intermittent flows
Coprecipitation efficiency depends on initial contaminant
concentration and surface area of primary floe
Ion Exchange
Advantages
Operates on demand
Relatively insensitive to flow variations
Essentially zero level of effluent contamination possible
Large variety of specific resins available
Beneficial selectivity reversal commonly occurs upon
regeneration
Disadvantages
Potential for chromatographic effluent peaking
Spent regenerant disposal
Variable effluent quality with respect to background ions
Usually not feasible at high levels of total dissolved solids
Activated Alumina
Advantages
Operates on demand
Insensitive to flow and total dissolved solids background
Low effluent contaminant level possible
Highly selective for fluoride and arsenic
Disadvantages
Both acid and base are required for regeneration
Medium tend to dissolve, producing fine particles
Slow adsorption kinetics
Spent regenerant disposal
Membranes (Reverse Osmosis and Bectrodialysis)
Advantages
Disadvantages
All contaminant ions and most dissolved non-ions are
removed
Relatively insensitive to flow and total dissolved solids
level
Low effluent concentration possible
Bacteria and particles are removed
High capital and operating costs
High level of pretreatment required
Membranes are prone to fouling
Reject stream is 20 to 90% of feed flow
Source: Clifford (1986).
Adjusting the pH and using coagulant aids can
optimize inorganic compound removal. Coagulant
aids may reduce the higher doses of coagulant needed
for inorganic contaminant removal. Optimal dosages
Reported
Approximate
Process
Treatment Radio- Efficiency
Technology nuclide (percent)
Comments
Conventional
treatment
with
coagulation-
filtration
Lime
softening
Ra
U
Ra
U
Ion exchange Ra
U
Adsorption
Aeration
Reverse
osmosis
Ra
Rn
Rn
Ra
U
< 25 High pH and Mg required
18-98 High pH (10 +) and high
dosages of ferric chloride
or alum only accomplished
in lab studies with
diatomaceous earth
filtration
75-96 Best choice for large plants
43-92 Plant-scale results
80 Plant-scale results
85-90 pH 10.6-11.5
99 High pH, high Mg
95 + Best choice for small plants;
99 cation exchangers
99 Brine disposal problem
Anion exchangers; largely
experimental but some full-
scale plants on line
90 + Adsorption on any solids;
85-90 experimental
62-99 Sand adsorption;
experimental
GAC adsorption
20-96 Depends on process
93 + Depends on process
87-96 Plant-scale data
87-98 Based on eight plants
95 + High-volume brine solution
95 + for disposal
High-volume brine solution
for disposal
Table 7-14. Radionuclide Process Treatment Costs
Range of Costs of Removal
Process (dollars/1,000 gallons
Process of water)
Coagulation/Filtration3 0.07 to 6.28b
Lime softening3 0.1 Ob
Aeration 0.10to0.75c
Ion exchange (cationic) 0.30 to 0.80C
Ion and manganese treatment 0.30 to 1,10ฐ
Lime softening (new) 0.50b
Ion exchange (anionic) 1.60 to 2.10b
Reverse osmosis l.60to3.2Qc
1,000 gallons = 3.78 m3
3 Adding to an existing facility.
b 1982 dollars.
c 1987 dollars.
for coagulants, coagulant aids, and pH adjusters may
be derived using jar tests and pilot studies.
143
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Table 7-15.
Costs for Removing Radon from Drinking
Water by Packed Tower Aeration
(99% Removal)
Population Served
3,300- 75,000-
100-500 10,000 100,000
Total capital cost ($1,000)
Operations and maintenance cost
($1,000 per year)
Cost (cents/1,000 gallons)
67 250 2,200
1.2 15 230
75
14
1,000 gallons ซ 3.78
Tabla 7-16. Costs of Radon Treatment at the Plant Scale
(200 GPD) for GAG Versus Aeration
Operating
, , Effluent Concentrations Capital Costs Costs in
^contra (pCi/L) in Dollars Dollars
lions (pCi/L) la
15,000 1,350-3,300
llป I II I
750 430-760 900 20
II
60
30,000
2,700-6,600 1,500 430-760 900 20 80
150,000
I - GAC process.
bll > Aeration process.
1,200 67.500 1,500 1,000 40 80
Section 7.1.3.2 for discussion of the effect of lime
softening on corrosion.) The pH is an important
design consideration for inorganic contaminant
removal using lime softening because it affects:
Contaminant species (soluble or insoluble)
Coagulant form
Type of flocculated particle formed
Higher dosages of lime create higher pH levels,
which, in turn, increase precipitation of inorganic
contaminants and adsorption of both organic and
inorganic species. The harder the water, the more
effective the lime softening process is in removing
inorganic contaminants. This happens because the
softening process depends on the enmeshment of ions
within the flocculated particles or adsorption on the
surface of precipitates.
Table 7-18 presents the removal efficiency of lime for
seven inorganic contaminants. Lime softening is
effective for cadmium, lead, silver, fluoride, and
cation removal in general. It also effectively removes
arsenic(V), barium, and chromium(III) at the specific
pH levels shown in the table. Lime-soda softening is
generally ineffective in removing nitrate,
selenium(VI), mercury(O), or chromium(IV).
Tabla 7-17.
Removal Efficiency Potential of Alum Versus
Ferric Chloride
Table 7-18. Removals Possible with Lime Softening
Inorganic Contaminant pH Percent Removal
Inorganic
Contaminant
Ag (pH < 8.0)
Ag (pH ป 8.0)
AsV
As V (pH <
7.5)
AS V (pH ซ
7.5)
CxMpH
S8.0)
Qd(pH
^8.5)
Cr (III)
Cr III (pH =
10.5)
Cr VI (using
Fell)
Hg
Pb
Removal
Alum Coagulant
90%
-
-
90%
-
-
70%
90%
-
-
70%
90%
Efficiency
Iron Coagulant
-
70%
90%
-
90%
-
-
-
90%
90%
-
-
7.2.2.2 L/me Softening
Lime softening is a reliable and established
treatment for "hard" water and corrosion control, and
also removes some inorganic contaminants. (See
As(V)
As(V)
As (III)
Cd
Cr (III)
Pb
Ag
Ba
10.0-10.5
>10.8
>10.5
NA
>10.5
NA
NA
9.5-10.8
70
90
70
90
70-90
90
70
NA = Not available.
Figure 7-2 shows a typical lime-soda softening
process. Characteristic elements of such a system
include raw water pumps, lime and soda ash addition
facilities, sedimentation, recarbonation, filtration,
disinfection, storage, and distribution. The
recarbonation step is designed to lower the pH to the
point of calcium carbonate saturation after the lime
has had its effect in the sedimentation basin.
7.2.3 Reverse Ostmosis
Reverse osmosis is an expensive process that uses a
semipermeable membrane to remove contaminants
from solution. Water with different contaminant
concentration is placed on each side of the membrane.
The water is directed through the membrane by
hydrostatic pressure to the side with the lower
concentration of contaminants. Since the membrane
permits only water, and not dissolved ions, to pass
144
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Chemicals
Disinfectant
Rapid Mix
Flocculation
Sedimentation
Recarbonation Filtration
Figure 7-2. Lime softening treatment system.
through its pores, contaminants are left behind in a
brine solution. These membranes are available with
a variety of pore sizes and characteristics.
Electrodialysis is a process that also uses
membranes. However, in this process direct electrical
current is used to attract the ions to one side of the
treatment chamber.
The membranes adjacent to the influent stream are
charged either positively or negatively, and this
charge attracts counter-ions toward the membrane.
The membranes are designed so as to allow either
positively or negatively charged ions to pass through
the membrane, thus they move from the product
water stream through a membrane to the two reject
water streams.
The three essential elements of the system are (1) a
source of pressurized water, (2) a direct current power
supply, and (3) a pair of selective membranes. The
average ion removal varies from 25 to 60 percent per
stage. Multistage units can increase the efficiency of
removal. Many membrane pairs are "stacked" in the
treatment vessel.
Fouling of the membranes may limit the amount of
water treated before cleaning is required. Fouling is
caused when membrane pores are clogged by salt
precipitation or by physical obstruction of suspended
particulates. Particulates, suspended in water, can be
removed in pretreatment but salts that exceed their
solubility product at the membrane surface must be
controlled chemically by pH reduction (to reduce
carbonate concentration) or chelation of metal ions
(by use of phosphate, for example). A recent
innovation has been the occasional reversal of the
charge on the membranes, a process called
electrodialysis reversal (EDR). This helps to flush the
attached ions from the membrane surface, thus
extending the time between cleanings.
Reverse osmosis is a compact system that is well
suited for treating water with high levels of inorganic
substances, organic substances, or total dissolved
solids. It has effectively treated water with total
dissolved solids as high as seawater, at 8,600 mg/L.
While reverse osmosis is a proven technology for
removing inorganic substances, it has also removed
the following effectively:
9 Radium
* THM precursors including humic and fulvic acids
Pesticides
Microbiological contaminants (viruses, bacteria,
and protozoa)
Reverse osmosis systems are particularly effective in
series. Water passing through multiple units can
achieve near zero effluent contaminant
concentrations.
Reverse osmosis is also suitable for small systems
with a high degree of seasonal fluctuation in water
demand. Reverse osmosis systems are relatively
insensitive to changes in flow and operate
immediately, without any minimum break-in period.
Their operational simplicity and minimal labor
requirements make them suitable for small system
applications. One disadvantage of reverse osmosis
units is high operating and capital costs. Managing
the wastewater (brine solution) is also a potential
problem.
7.2.3.1 Design Considerations
Typical reverse osmosis units include raw water
pumps, pretreatment, membranes, disinfection,
storage, and distribution elements. Figure 7-3 is a
schematic diagram of a reverse osmosis system.
These units are able to process virtually any desired
quantity or quality of water by configuring units
sequentially to reprocess waste brine from the earlier
stages of the process. The principal design
considerations for reverse osmosis units are:
Operating pressure
Membrane type and pore size
Pretreatment requirements
e Product conversion rate (the ratio of the influent
recovered as waste brine water to the finished
water)
145
-------
Generator Set
High Service Pumps
Brine to
Percolation
Pond
Product to Degasifier
and Reservoir
Cleaning
Solution
Sodium Silicate Feed
Figure 7-3. Schematic of a reverse osmosis system.
Operating Pressure
Typical operating pressures range from 5.3 to higher
than 24.6 kg/cm2 (75 to higher than 350 psi). Reverse
osmosis systems rated at less than 17.6 kg/cm2 (250
psi) are classified as low-pressure units, while those
operating above 24.6 kg/cm2 (350 psi) are classified
as high-pressure units. High water pressure can lead
to noise, vibration, and corrosion problems, but, in
general, these systems are more effective. Recently
developed models, however, are able to perform well
at low pressures.
Membrane Type
Two distinct membrane designs for reverse osmosis
are illustrated in Figure 7-4. The spiral-wound unit
clogs less frequently when processing influent with
high solids content. The hollow-fiber membrane,
however, has much greater surface area per unit of
space than the spiral-wound design. The hollow-fiber
unit has about 3,280 m2 of membrane surface/m3 of
membrane module (1,000 sq ft/cu ft of membrane
module), as compared to about 328 m2 (100 sq ft) for
the spiral-wound unit.
Until the 1970s, membranes were made almost '
exclusively of cellulose acetate. Now membranes are
also made from aromatic polyamide and thin-filmed
polymer composites. Different membrane materials
will have distinct characteristics, such as hydraulic
resistance, pH range, temperature range, chlorine
tolerance, and biodegradation tolerance.
Pretreatment Requirements
Assessing pretreatment requirements requires
careful consideration of the following factors:
Influent suspended solid concentration
Ionic size of the contaminants
Membrane type
Other influent characteristics such as contaminant
concentration, water temperature, and presence of
competing ions are also important. Some systems
with poor quality influent require extensive
pretreatment.
Pretreatment is most commonly used to prevent
fouling of the membrane during operation. Fouling is
also caused by biological growth during periods of
disuse. Typical pretreatment for reverse osmosis
includes particle removal by filtration, and
sequestering hardness ions by precipitates and pH
control to prevent clogging.
A major problem with reverse osmosis units is proper
management of the waste water quantity and quality.
The percentage of treated water recovered from these
systems typically ranges from 50 to 90 percent of the
influent. Systems that produce reject water ranging
146
-------
Feed
(Raw Water)
A ^ Filtrate
(Treated Water)
Filtrate
^
Courtesy of Millipore Corporation
Process Flow Through Spiral-Wound Reverse Osmosis Unit
Casing
Treated
Water
L
Hollow Fiber
Feed
(Raw Water)
Hollow-Fiber Reverse Osmosis Unit
Figure 7-4. Two types of reverse osmosis membranes.
147
-------
as high as 90 percent of the feed water are generally
uneconomical.
Ratio of Reject Water to Finished Water
The ratio of reject water, or "brine," to finished water
depends on several factors primarily ionic charge and
ionic size. The higher the ionic charge and the larger
the ionic size of the contaminant, the more easily the
ion is removed and the more finished water is
recovered relative to the amount of brine. The ionic
charge for some contaminants depends on pH. The
quality of the brine depends on the influent quality
and requires site-specific assessments to develop
environmentally sound waste management.
7.2.3.2 System Performance
Reverse osmosis can remove essentially all inorganic
contaminants from water effectively. It removes over
70 percent of the following: arsenic(III), arsenic(V),
barium, cadmium, chromium(III), chromium(VI),
fluoride, lead, mercury, nitrite, selenium(IV),
selenium(VI), and silver. Properly operated reverse
osmosis units will attain 96 percent removal rates,
while similarly operated lime-soda softening
operations will attain from 75 to 96 percent removal.
Comparative ion exchange units achieve between 81
and 97 percent removal.
7.2.3.3 System Costs
The predominant disadvantage of reverse osmosis is
its high cost. Operating costs range from $0.79 to
$1.59/m3 ($3 to $6/1,000 gal) of treated water for a
reverse osmosis plant of less than 0.04 m3/sec (1
MGD). For plants with larger capacities and lower
operating pressures, costs may be potentially
competitive with other processes. Capital costs are
usually high, especially if there is a need for
pretreatment. In general, capital costs range from
$264 to $528/m3 ($1 to $2/gal) of capacity.
7.2.4 Ion Exchange
Ion exchange units are used to remove any ionic
substance from water, but are used predominantly to
remove hardness and nitrate from ground water.
Typical ion exchange units consist of prefiltration,
ion exchange, disinfection, storage, and distribution
elements (see Figure 7-5).
Inorganics removal is accomplished through
adsorption of contaminant ions onto a resin exchange
medium. As the name implies, one ion is substituted
for another on the charged surface of the medium,
which is a resin, usually a synthetic plastic. This
resin surface is designed as either cationic or anionic.
The exchange medium is saturated with the
exchangeable ion before treatment operations.
During ion exchange, the contaminant ions replace
the regenerant ions because they are preferred by the
exchange medium. After the exchange medium
reaches equilibrium with the contaminant ions, the
medium is regenerated with a suitable solution,
which then resaturates the medium with the
appropriate ions. Because of the required "down
time," the shortest economical regeneration cycles
are once per day. Ion exchange waste is highly
concentrated and requires careful disposal,
analogous to reverse osmosis reject streams.
The porous exchange medium is covered with tiny
holes, which clog when significant levels of
suspended solids are in the influent stream.
Consequently, filtration may be a necessary
pretreatment for ion exchange units. Ion exchange
units are also sensitive to the presence of competing
ions. For example, influent with high levels of
hardness will effectively compete with other cations
for sites on the exchange medium.
The resin exchange capacity is expressed in terms of
weight per unit volume of the resin. The calculation
of the breakthrough time for an ion exchange unit
requires knowledge of the resin exchange capacity,
the influent contaminant concentration, and the
desired effluent quality.
The ion exchange process, like reverse osmosis, is
relatively insensitive to flow rate and virtually fully
operational upon process initiation. Each resin, of the
many available from suppliers, is effective in
removing specific contaminants. In addition, ion
exchange is able to achieve very low contaminant
concentrations in finished water.
The primary disadvantage of ion exchange concerns
effluent peaking. Effluent peaking occurs when
contaminant ions compete with other ions for
exchange medium sites, resulting in unacceptable
levels (peaks) of contamination in the effluent. It is
most common with poorly adsorbed contaminants,
such as nitrate. Effluent peaking necessitates more
frequent regeneration of the exchange medium.
In addition, ion exchangers that use sodium chloride
to saturate the exchange medium may experience
problems with sodium residual in the finished water.
Sodium is used because of its low cost, but high
sodium residual is unacceptable for individuals with
salt-restricted diets. This problem may be avoided by
using other saturant materials, such as potassium
chloride.
7.2.4.1 System Performance
Ion exchange effectively removes greater than 90
percent of barium, cadmium, chromium(HI), silver,
and radium using cationic resins as the exchange
medium. In addition, it achieves greater than 90
148
-------
Salt Loading
I
Overflow
Brine
Tank
Brine
Potable
Water
to
Brine
System
Pressure Tank
L
Vessel 1
Blending Valves
Treated Water
Raw Water
L
\ essel 2
Distribution
System
L
Vessel 3
rT
Backwash
Nitrate
Analysis
Waste to
Disposal
~j Alarm and
Shutdown
Well Supply
Conductivity
Monitor
Figure 7-5. Ion exchange treatment system.
Ion exchange facility for nitrate removal; McFarland, CA.
percent removal of nitrites, selenium, arsenic(V),
chromium(VI), and nitrate using anionic resins.
While it is effective for all of the contaminants listed
above, ion exchange is especially well suited to
remove barium, radium, nitrate, and selenium.
7.2.5 Activated Alumina
Activated alumina, a commercially available ion
exchange medium, is primarily used for fluoride
removal from ground water. The activated alumina
process is an ion exchange process that consists of the
following six basic elements: raw water pumps,
pretreatment, activated alumina contact,
disinfection, storage, and distribution. Figure 7-6
shows schematic diagrams of the four-phase
operational process.
Before processing, the activated alumina medium is
saturated with hydroxyl ions from a strong sodium
hydroxide solution. During the removal process,
activated alumina exchanges the hydroxyl ions for
fluoride anions. When the medium becomes
saturated, the activated alumina must be
regenerated with sodium hydroxide. This increases
the pH level of the water in the treatment unit to a
point where buffer solutions of 3 percent sulfuric acid
149
-------
Raw Water
Acid -
Treated Water
r
n
Treatment Unit
Treatment and
Downflow Rinse
Raw Water
t,
ent Unit
i
^
T
Waste
Backwash and
Upflow Rinse
Raw Water
Raw Water
Caustic
Waste
Upflow
Regeneration
Treatment Unit
>
Caustic
Waste
Downflow
Regeneration
Figure 7-6. Activated alumina systems: Operating mode flow schematics
are required for neutralization, after the water leaves
the exchange unit.
While activated alumina requires pretreatment for
suspended solids, it can tolerate high levels of total
dissolved solids. As with other ion exchange
processes, the activated alumina process is sensitive
to competing ions. It is also sensitive to pH. Optimum
removal efficiency for fluoride occurs below a pH of
8.2.
While activated alumina effectively removes several
contaminants, it requires the handling of potentially
hazardous strongly acidic and basic solutions. The
process of heating the sodium hydroxide solution to
maintain it as a liquid in cold climates is particularly
hazardous.
Activated alumina's costs are also higher than ion
exchange costs. The loss of activated alumina to the
sodium hydroxide solution during processing can
range up to 20 percent annually. In addition, waste
management may also increase costs because of the
high contaminant and aluminum concentrations in
the waste stream, as well as the high pH.
150
-------
7.2.5.1 System Performance
Activated alumina is operational immediately
because of its relative insensitivity to flow rates. It
effectively removes over 90 percent of arsenic(V),
fluoride, and selenium(IV); removes 70 percent of
selenium(VI); and also effectively removes iron. It is
ineffective for barium, cadmium, and radium
removal, since these contaminants occur primarily as
cations.
151
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-------
Chapter 8
Current and Emerging Research
This chapter describes the activities of EPA's
Drinking Water Research Division (DWRD),
highlighting the division's recent research efforts
and future directions. The impetus for the majority of
DWRD's research is to provide technical support for
the Agency as it implements the SDWA and its
amendments. At present, there are four aspects of the
regulatory process influencing current areas of
research:
1. Development of Final Surface Water and the
anticipated Ground-Water Treatment Rules,
which will require disinfection and, in the case of
surface waters, filtration of drinking water in
communities serving more than 25 persons.
2. The requirement that EPA set Maximum
Contaminant Levels (MCLs) for listed
contaminants, e.g., volatile organic compounds
(VOCs), synthetic organic compounds (SOCs),
inorganics, radionuclides, microbiological
contaminants, and turbidity according to the
timetable specified in the 1986 Amendments to
the SDWA.
3. The requirement that every 3 years EPA publish
a Drinking Water Priority List of contaminants
known or anticipated to occur in public drinking
water systems and pose a human health risk; and
subsequently regulate at least 25 of the
contaminants listed according to the schedule set
in the act. The first list of 44 contaminants was
already published and, therefore, 25 of those
contaminants listed must be regulated by
January 1990.
4. The Disinfection By-Products Rule, whose
proposal is anticipated along with the Ground-
Water Treatment Rule in 1991, will regulate
disinfection by-products that have been, and are
still being, identified.
In pursuit of these regulatory milestones, research
has focused on identifying contaminants that will be
regulated and evaluating the removal potential of
available technologies. This research includes
identifying and characterizing disinfection by-
products associated with chlorination and the use of
ozone. Also in support of the rules, DWRD is studying
various methods of meeting mandatory disinfection
requirements; investigating factors affecting the
occurrence of lead in drinking water; and evaluating
methods of controlling corrosion, exposure of
consumers to disinfection by-products, and microbial
contamination in distribution systems.
In addition to its research activities, DWRD provides
technical assistance to State agencies, EPA regional
offices, water utilities, and professional
organizations. DWRD also supplies information and
provides consultation on the technical aspects of
drinking water treatment systems.
8.1 Current Research on Disinfection
By-Products
The SDWA and Amendments of 1986 require most
public water supplies to disinfect drinking water
before distribution (U.S. EPA, 1986a). In the past,
chlorine has been the most widely used disinfectant,
and while its effectiveness in controlling pathogens is
proven, unhealthful chemical by-products have been
identified.
Research on these by-products is a very important
area of investigation for EPA. A disinfection by-
product work group was formed to coordinate
research efforts between the EPA Office of Research
and Development (ORD) and Office of Drinking
Water (ODW). Research efforts are focused on
identifying and characterizing the by-products of
chlorine disinfection, and evaluating treatment
techniques that will control by-product generation.
Since a promising strategy for control is to use ozone
153
-------
as an alternate disinfectant, EPA is also researching
the by-products and other issues associated with
ozone disinfection.
8.1.1 Identifying and Controlling
Chlorination By-Products
DWRD has been conducting experiments, mostly in
the laboratory, to develop methods of identifying by-
products associated with the use of chlorine as a
disinfectant. In close association with the Technical
Support Division of ODW, DWRD is isolating the
various by-products that have been identified in field
studies (Stevens et al., 1987).
To date, six compounds (or in some cases groups of
compounds) have been identified:
Trihalomethanes (4 compounds)
Dihaloacetonitriles (3 compounds)
Chloroacetic acids (3 compounds)
Chloral hydrate
Chloropicrin
1,1,1-Tr ichloropropanone
These by-products comprise 30 to 60 percent of the
total organic halogen (TOX) in drinking water. The
levels of common chlorination by-products found in
drinking water are presented in Table 8-1 (Stevens et
al., 1987).
Table 8-1. Common Chlorination By-Products
General Compound
Identification
Trihatometnanes
DihatoacQtonitriles
Chloroacetic acids
Chforal hydrate
Chkxoptcrin
1,1,1-Trichtoro-
propanona
Number of
Individual
Compounds
4
3
3
Nominal
<10
X
X
X
X
Concentration (pg/l)
10-100 >100
X
X X
X
Source: Stevens et al. (1987).
Methods of controlling chlorine disinfection by-
products are being studied by DWRD in an onsite
pilot plant (Stevens et al., 1989). (Figure 8-1 is a
schematic of the pilot plant.) The pilot plant was
constructed with two channels: the first was
represented by the experiment control; the second
was used to test the effects of changing the point of
chlorination on the production of by-products.
Through experimentation, it was found that moving
chlorination to a point just before filtration
minimized the production of total trihalomethanes
(TTHMs) while maintaining microbiological quality.
The assimilable organic carbon of the finished water,
which is a measure of the biological quality, was also
found to be reduced. Therefore, the overall quality of
the water improved under this scenario.
Although the individual concentrations of the
disinfection by-products (DBFs) vary with pH,
temperature, and chlorine concentration, pilot
studies have shown that the removal of TTHM
precursor seems to remove the formation potential for
the other individual DBFs. This finding confirms
earlier studies and opens up the possibility of
precursor removal as an effective means of
controlling chlorinated DBF (Lykins et al., 1988a).
An alternative to chlorine is the use of chloramines
or chlorine dioxide for minimized DBF. Studies have
shown that these approaches can be effective in
maintaining microbiological integrity and
minimizing by-product formation (Singer, 1988).
This issue and the associated technologies will
become extremely important if the THM standard is
ultimately lowered.
8.1.2 Identifying Ozone By-Products
The DWRD is studying several issues related to
using ozone as an alternate disinfectant to chlorine.
The broadest issue concerns the identification of by-
products formed by ozone reacting with naturally
occurring organics in drinking water (Glaze, 1986).
The health effects of these by-products are being
characterized and compared to the health effects of
by-products of chlorination. Also being investigated
is the effect of ozone on the precursors of chlorine by-
products, an issue if chlorine is used as a secondary
disinfectant.
Other research related to ozone as a disinfectant
covers its ability to destroy contaminants and its
effects on the formation of bromide ion or other
brominated organics when bromide ion is present.
Some substances formed through the oxidation of
bromide ion are known to be harmful to humans.
8.2 Treatment of Organic and Inorganic
Contaminants
The SDWA amendments accelerated the schedule for
setting MCLs for contaminants in drinking water.
Contaminant limits are set according to the removal
potential of existing technologies that can be
obtained at a reasonable cost. Traditionally, EPA set
contaminant limits by studying treatment
techniques for each chemical individually. Since
there is such a large number of chemicals to be
considered for regulation, and the deadlines for
promulgating MCLs are quite stringent, EPA is
studying the effectiveness of various technologies in
removing groups of contaminants using bench- and
pilot-scale experiments. Table 8-2 lists the
technologies that have been and are being evaluated
by DWRD (Clark et al., 1988b; Feige et al., 1987).
154
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(Phage)
(Sewage)
Floe
-
Settle -
I 2
Chlorine
Alum
(Acid)
Alum
(Chlorine)
Floe
-
Settle
K2H
Figure 8-1. Pilot plant schematic for disinfection by-product control.
Table 8-2. Treatment Technologies Evaluated by the
Drinking Water Research Divisfon
Contaminant Proven
(or Effective Proven
Contaminant in Field Effective in
Classes) Tests Pilot Tests
Being Evaluated as
Promising Technologies
Volatile Carbon
organic adsorption,
compounds packed
tower and
diffused
aeration
Synthetic Carbon
organic adsorption
compounds
Nitrates Ion Reverse
exchange osmosis
Ozone oxidation, reverse
osmosis, ultraviolet treatment
Conventional treatment with
powdered activated carbon,
ozone oxidation,, reverse
osmosis, ultraviolet treatment
Radium
Radon
Uranium
Reverse
osmosis,
ion
exchange
Carbon
adsorption
Ion Reverse
exchange osmosis
Aeration
-
Source: Clark et al. (I988b); Feige et al. (1987).
Granular Activated Carbon (GAG), ozone oxidation,
reverse osmosis, ultraviolet (UV) treatment,
ultrafiltration, packed tower aeration, and
conventional treatment are being studied as methods
of controlling organic compounds, including certain
disinfection by-products. Ion exchange, reverse
osmosis, aeration, and carbon adsorption are being
tested for their ability to remove inorganic
compounds, including radionuclides. In addition,
technologies for controlling secondary sources of
pollution from treatment processes are being
investigated. This section summarizes the relevant
research projects.
8.2.1 Granular Activated Carbon Systems
GAG is the legal feasible technology for treating
SOCs. DWRD is currently developing data on the
effectiveness of GAG for removing a variety of
organic chemicals.
One measure of effectiveness is the carbon usage rate
for each chemical. This indicator describes the ability
of each compound to be adsorbed by the carbon in the
treatment system. It also describes how quickly the
carbon bed will be exhausted (adsorption surfaces of
the carbon granules will be used) and, therefore,
dictates the size of the GAG system needed for
optimal operation. EPA is currently developing
carbon usage rate data for the 45 chemicals listed in
Table 8-3 (Clark et al., 1989a). Carbon usage rates
are established by laboratory or field experiments.
8.2.1.1 Establishing Carbon Usage Rates
A mathematical model that uses isotherm results to
simulate full-scale carbon adsorption treatment
systems is being used (Speth and Miltner, 1989).
Pilot testing is a common first step in designing a
full-scale treatment system and much data are
available correlating pilot-scale test results to actual
full-scale operating parameters. Therefore, engineers
155
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Table 8-3. Chemicals for Which Carbon Usage Rates are
Being Developed
2,4-D
Sitvex
LirxJane
Methoxychtor
Toxaphene
Chtordane
HeptacWor
Heplachlor opoxide
PCS(s)
Pentachfcxophenol
Alachlor
Carbofuran
AkJicarb
Aldtearb sulfone
AkJicarb sulfoxide
Ten-Butyl methyl ether
Mefdachtor
Tetrachtoroethorte
1,3,5-Trtchlorobenzene
Bromobenzsne
Dibromomethane
2,2-Dichloropropane
1,1,1,2-TetrachIoroethane
2,4,5-Trichtorophenoxy acetic acid
Endrin
Phthalate{s)
Adipato(s)
PAH(s)
HaxacWorocyctopentadiene
Diacamba
Slmazine
Atrazine
Diquat
Endothalf
Plctoram
Dalapon
Dinoseb
Glyphosate
Oxamyl
N,N-Ethylene-thiourea
Metribuzin
Hexachlorobenzene
c/s-1,3-dichloropropene
o-chlorotoluene
1,1-Dichloroethane
1,1 -Dichloropropene
1.1,2,2-Tetrachloroethane
EDB
DBCP
1,2-Dtohloropropane
c/s-1,2-Dichloroethylene
trans-1,2-Dichloroethylene
Chloro benzene
o-Dichlorobenzene
Toluene
Styrene
Ethyl benzene
o-Xylene
m-Xylene
p-Xylene
Cyanazine
1,1,2-Trichloroethane
Isophorone
Trifluralin
Methylene chloride
frar/s-1,3-Dichloropropene
p-Chlorotoluene
1,3-Dichloropropane
2,4-Dinitrotoluene
1,2,3-Trichloropropane
conducting pilot tests have sufficient data to
confidently predict full-scale operations. There is not,
however, much information on how well computer
models will predict full-scale operations.
DWRD has evaluated microcolumn modeling
techniques, focusing on verifying the results of
available computer models. DWRD conducted
microcolumn tests and used existing models to
estimate carbon usage rates and other design
parameters for a full-scale operation. The modeled
results were then compared to isotherm model
predictions and to actual results obtained in the field.
The investigations concluded that microcolumn
predictions offered no particular advantage over
isotherm predictions (Speth and Miltner, 1989). Some
computer models also contain a component that
estimates the cost of various sized full-scale systems
(Adams et al., 1989). Several of these models are in
the process of being validated by DWRD.
8.2.1.2 Field Tests of Granular Activated
Carbon Systems
DWRD has conducted extensive field studies on the
potential of GAG to remove organic contaminants
from surface water. It was found that carbon
adsorption is an effective means of removing both
volatile and synthetic organic compounds. Field
testing sites included Jefferson Parish, Louisiana;
Cincinnati, Ohio; Manchester, New Hampshire;
Evansville, Indiana; Miami, Florida; Huntington,
West Virginia; Beaver Falls, Pennsylvania; and
Passaic, New Jersey (Lykins et al., 1984).
More recent studies of GAG systems have focused on
organics removal from ground water at three sites:
Suffolk County, New York; San Joaquin Valley,
California; and Wausau, Wisconsin. A brief
description of these ground-water treatment studies
follows (Clark et al., 1988b).
The purpose of the Suffolk County project was to
study the removal of organic compounds, pesticides,
and nitrates under low-flow situations (simulating
residential usage). GAG in combination with an ion-
exchange system, and a reverse osmosis system were
operated in parallel at this test site. Data on
treatment effectiveness and system costs were
collected and analyzed to assist in the design and
testing of large public water supply systems. These
results will be especially useful to operators of water
treatment systems in farming communities where
pesticides, nitrates, and other organics are a common
problem.
The field study in the San Joaquin Valley examined
point-of-use GAG units servicing small treatment
systems and private wells of homeowners and
farmers. The purpose of the project was to develop
cost-effective design and operating guidelines for
small GAC systems that are capable of removing
pesticides (including dibromochloropropane) from
drinking water supplies.
The third site, Wausau, has ground water with high
levels of contaminants from a nearby Superfund site.
Air stripping was studied as a companion technology
to GAC at this site. Modeling techniques were used to
predict full-scale design criteria, and the modeled
estimates were verified with actual cost and
performance data obtained from GAC contractors.
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8.2.2 Ozone Oxidation Systems
Ozone oxidation as a method of removing VOCs was
studied in DWRD's in-house pilot plant facilities
(Fronk, 1987a). To date, tests on 29 VOCs in distilled
and ground water revealed that ozone is effective in
removing aromatic compounds, alkenes, and certain
pesticides. It is not effective, however, in removing
alkanes.
Research showed that removal of some alkanes was
enhanced by increasing pH. Also, increasing the
dosage of ozone improves removal of alkenes and
aromatics. For most compounds, the composition of
the water (the background matrix) did not
significantly affect the removal efficiencies of ozone.
In general, it was found that, when treated with
ozone, VOCs behaved similarly in aqueous solutions
as in the gaseous or liquid phases, as the literature
concluded.
In order to further evaluate the effectiveness of using
ozone to oxidize VOCs, DWRD funded a cooperative
agreement with the Los Angeles Department of
Water and Power (LADWP) (Glaze and Kang, 1988).
The oxidation of TCE and PCE by ozone and
modification of the traditional ozone treatment with
the addition of hydrogen peroxide were studied at the
bench scale. Results from this project were very
promising and indicate that the kinetics of the
H2O2/O3 process warrants further research.
8.2.3 Ultraviolet Treatment
Ultraviolet light in combination with ozone may also
be an effective means of controlling organic
compounds. DWRD is conducting a study with the
Los Angeles Water and Power Company to determine
whether these two technologies can successfully treat
organics in ground water (Glaze and Kang, 1988).
The goal of this treatment technique is to oxidize
undesirable chemicals into carbon dioxide and water,
thus eliminating the need to control off-gases, which
are a problem with other oxidation processes.
8.2.4 Reverse Osmosis
DWRD is conducting experiments at the bench and
pilot scale to evaluate the potential for controlling
volatile and synthetic organic compounds using
reverse osmosis. Some field tests have been conducted
as well. Preliminary results indicate that, for ground-
water treatment systems, certain membranes are
very effective in removing a wide range of organic
chemicals (Fronk, 1987b).
Reverse osmosis has been proven as an effective
treatment technology for radium. Several years ago,
EPA conducted field studies in cooperation with
Sarasota County, Florida (Sorg et al., 1980). Six
different types of reverse osmosis systems varying in
size from 3 m3/day to 0.044 m3/sec (800 GPD to 1
MGD) were operated in eight locations. Both hollow
fiber and spiral wound cellulose acetate membranes
were tested. The results of the study indicate that 82
to 96 percent of radium-226 was removed from all
systems, thus meeting the EPA MCL of 5 pCi/L.
Reverse osmosis systems have also been tested for
removing nitrate. In Suffolk County, where research
on removing organic compounds from ground water
has been ongoing, seven different commercially
available membranes were tested for nitrate removal
(Lykins and Baier, 1985). Removals obtained ranged
from 75 to 95 percent. Polyamide membranes were
efficient in reducing nitrate and SOCs.
A field study in Charlotte Harbor, Florida, tested
reverse osmosis under conditions of high pressure
(18.6 to 25.2 kg/cm2 [265 to 359 psig]) (Huxstep,
1981). Removal of nitrate and other inorganic
contaminants added to the ground-water influent
were monitored. The investigation showed that a
high pressure system could obtain better removals of
all substances monitored. For nitrate, the high-
pressure system attained an 80 percent removal as
opposed to the low-pressure system, which attained 6
to 24 percent removal.
8.2.5 Ultrafiltration
Ultrafiltration is being studied as a method of
reducing production of TTHMs in small water
treatment systems (Taylor et al., 1987). This study
involved treating two ground-water systems that
contained large amounts of natural organic
contaminants that act as TTHM precursors. Both
produced more than 400 g/L TTHMs when treated
with conventional systems. A low-pressure
membrane system to reduce precursors to TTHMs
was tested in a pilot plant. During pilot plant tests,
the Ultrafiltration system produced finished water
that easily met the TTHM MCL (100 g/L). Since the
tests were successful and the costs of the system were
considered reasonable, more extensive testing of this
technology is under way.
8.2.6 Packed Tower Aeration
Three field studies were recently completed to study
packed tower aeration (PTA) techniques, which have
proven effective in removing VOC. In Wausau,
Wisconsin, and Baldwin Park, California, research
focused on the effectiveness of PTA in removing
VOCs from ground water (Clark et al., 1989a). Off-
gas control technologies were tested at both sites as
well (Crittenden et al., 1988; Lang et al., 1987). In
Wausau, it was found that air stripping was effective
in removing compounds that normally are expected
to be difficult to remove (compounds have lower
Henry's Law constants) by air stripping.
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At the third site, Brewster, New York, a pilot-scale
project evaluating air stripping techniques was
completed. Results were used to develop models that
consulting engineers could use to estimate costs and
performance of full-scale aeration systems (Wallman
and Cummins, 1986).
8.2.7 Conventional Treatment
Although conventional treatment is not very
effective in removing organic contaminants, field
studies were conducted to test the effectiveness of
adding powdered activated carbon (PAC) to water
prior to conventional treatment (Miltner et al., 1989).
These tests were conducted in Tiffin, Ohio, where
river water containing seasonally high levels of
pesticides from area farms was a problem. The
technique was found to effectively remove SOCs.
8.2.8 ton Exchange
Ion exchange has been studied as a means of
removing nitrate and uranium. In field tests, anion
exchange has proven effective in removing nitrates.
A demonstration nitrate removal plant operated
automatically in McFarland, California, for over 3
years (Lauch and Outer, 1986; Outer, 1982). The
plant has a capacity of 0.044 m3/sec (1 MOD) and
consists of three anion exchange vessels designed to
reduce nitrate-N levels to below 10 mg/L (the current
MCL and State standard in California). In this plant,
part of the influent stream bypassed the treatment
vessels and was blended with the treated water
before leaving the plant. The blended water meets
the required limits for nitrate and, in addition, meets
EPA's Secondary Regulations (40 CFR Part 143) for
chloride (250 mg/L) and sulfate (250 mg/L).
Laboratory-, pilot-, and (small) full-scale tests have
been conducted to examine the effectiveness of anion
exchange in removing uranium (Reid et al., 1985). In
the laboratory, more than 9,000 bed volumes were
treated before breakthrough was observed on a
ground water containing 300 ug/L uranium was
passed through the anion exchange resin. In the field,
twelve 0.007-m3 (0.25-ffc3) anion exchange systems
were installed at 10 sites (in New Mexico, Colorado,
and Arizona) where uranium levels in the ground
water exceeded 20 ug/L. The field results actually
showed better removals than the laboratory tests;
some systems had treated over 50,000 bed volumes of
water when they were finally shut down.
A small 0.63-L/sec (10-GPM) full-scale anion
exchange system has been shown to be very effective
in removing 95 to 98 percent of 47 to 90 ug/L of
uranium from a water supply serving a school in
Jefferson County, Colorado (Jelinek and Sorg, 1988).
The system is regenerated with salt about once every
2 to 3 months and the brine disposed at a school
district owned wastewater treatment plant.
Ion exchange systems, using both weak and strong
acid resins in the hydrogen form, have been studied
as a means of controlling radium from ground water
(Clifford et al., 1988). Both types of resins are capable
of removing radium to below the MCL of 5 pCi/L.
However, both systems require the pH of treated
water to be adjusted by either air stripping or the
combination of air stripping and caustic addition.
EPA has also sponsored tests on the removal of
radium with the DOW Chemical Company's Radium-
Selective Complexer (RSC), a synthetic resin with a
high affinity for radium. Field tests have shown the
RSC to remove radium from more than 50,000 bed
volumes of treated water. However, because the RSC
cannot be regenerated, it must be disposed when its
capacity for radium is reached. For this reason,
studies have been conducted to examine its efficiency
for removing radium from the brine waste of a cation
exchange system. A field study in Colorado showed
the RSC to be very effective for concentrating the
radium from the brine of an ion exchange system for
over 2 years. When its capacity is reached, this
material will be disposed at a low radioactive waste
disposal site.
Recent EPA studies in Illinois have also shown that
activated alumina modified with barium sulfate has
a removal capability similar to the RSC. Plain
activated alumina also removed radium but its
capacity was about a fifth of the modified alumina.
The advantage of the plain alumina was that it could
be regenerated whereas the modified alumina could
not.
The application of preformed manganese dioxide floe
for radium removal was studied at the same field site
in Illinois and this process (adsorption)showed
promising results (Patel and Clifford, 1989). Feeding
of 1 to 2 mg/L of manganese oxide as manganese in a
contact tank before a multimedia filter showed 80 to
95 percent removal of radium (12 pCi/L) from the
ground water. Cost estimates of this process indicate
that it should be competitive with ion exchange
treatment.
8.2.9 Technologies for Removing
Radionuclides
DWRD has funded a project to study several
treatment techniques for removing radon gas from
drinking water (Kinner et al., 1987a). Packed tower
aeration, diffused bubble aeration, and GAC have
been evaluated at a field site in New Hampshire.
Both the packed tower and the diffused bubble
aeration systems were very efficient at removing
radon (90 to 99 percent). The GAC system flow rate
and influent radon concentration above design
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loadings were attributed to the lower removals by the
GAC. This same study also investigated the removal
of radon by several low cost technologies associated
with storage. The simple techniques consisted of
spraying the water into a storage tank, simple
aeration (bubble) in the bottom of the storage tank,
and the combination of these methods (Kinner et al.,
1987b). These methods showed removals ranging
from 50 percent by free fall of the water into the tank
to around 90 percent with the combination of free fall
and bubble aeration.
8.2.10 Secondary Sources of Pollution
Drinking water treatment technologies are designed
to remove pollutants from water. Once removed,
however, the pollutants can create a secondary source
problem. Research on GAC systems treating surface
water found that dioxins were formed as by-products
of the reactivation process (Lykins et al., 1988a).
Afterburners were installed and operated at 1315.6ฐC
(2,400ฐF) to eliminate these toxic gases.
Harmful compounds in air stripping of waste gases
can also be a problem. The field studies of air
stripping technologies at Baldwin Park, California,
and Wausau, Wisconsin, included testing of gas-
phase carbon adsorption techniques to remove
synthetic and volatile organic compounds from waste
gases (Lang et al., 1987; Hand et al., 1986). At
Baldwin Park a higher waste gas stack is also being
used to increase dispersion of waste gases.
8.2.11 Small Systems Technologies
Small systems account for most of the MCL violations
under the Safe Drinking Water Act. DWRD has
conducted and is continuing to conduct studies of
technology that is specifically designed to solve small
system problems. A recently completed study
demonstrated the feasibility of using point-of-entry
devices for controlling arsenic and fluoride in a
municipally sound treatment system (Rogers, in
press).
8.3 Mandatory Disinfection
The proposed Surface Water Treatment Rule will
require communities whose water supply comes from
surface water or is influenced by surface water (e.g.,
ground water that is stored in open reservoirs) and
supplies more than 25 persons to filter and disinfect
drinking water before distribution. Upon
promulgation of the final rule, all affected suppliers
must comply within 3 years. The Ground Water
Treatment Rule, anticipated in 1991, is expected to
apply similar requirements to ground-water drinking
sources.
Historically, efficacy of disinfection has been
measured by testing for the presence of coliform
bacteria. The new regulations, however, specify
requirements to control and regulate levels of
Giardia, viruses, Legionella, and heterotrophic
bacteria. In view of these requirements, research
(extramural and in-house) is being conducted on
methods to achieve adequate disinfection of the
specified microorganisms. Inactivation studies using
chlorine and chloramine have been completed on
particle-associated coliforms, and on inactivation of
three coliphages using chlorine, chlorine dioxide and
monochloramine (Berman et al., 1988; Berman and
Sullivan, 1988). Disinfection studies on inactivation
of hepatitis A virus and model viruses in water are
ongoing; as are studies on inactivation of Giardia
(Ohio State University) using chlorine, chlorine
dioxide, and chloramine; and Cryptosporidium
(University of Arizona) using chlorine and
chloramines (Sobsey et al., 1988). Results of these
investigations will provide contact time (CT) values
for the various organisms and disinfectants based on
temperature, pH, and disinfectant dosage (Hoff, 1986;
Clark et al., 1989b). An in-house project will examine
the influence of strain variations in Giardia lamblia
on disinfection inactivation.
A study is being conducted on the inactivation of
viruses and Giardia using chlorine and chloramines
in a flow-through treatment plant (John Hopkins
University).
The use of alternative disinfectants, such as ozone
applied as a preoxidant, has been shown to increase
the level of readily assimilable organic carbon (AOC)
in treated water. The trend toward the use of ozone
and alternative disinfectants to control THM
formation in the United States may result in
increased problems of bacterial regrowth, and
possible coliform MCL compliance during water
storage and distribution. Investigations are under
way to examine AOC levels in treated drinking water
and the relationship between microbial regrowth
(coliforms) and AOC, and a recently completed
project examined modifications of a procedure
developed in the Netherlands to determine AOC
levels in drinking water (Kaplan and Bott, 1989).
Control of Legionella pneumophilia in drinking water
treatment through prevention of the Legionella/free-
living amoebae association is also being examined.
8.3.1 Treatment/Distribution Microbiology
Examination of factors involved in microbial water
quality have been addressed in other completed
studies. Point-of-use or point-of-entry water
treatment may have possible applications where
central treatment is not feasible for various reasons.
Microbiological studies of point-of-entry treatment
devices, used primarily for aesthetic purposes (taste
and odor removal) have shown that the GAC
cartridge devices become bacterial generators,
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regardless of whether they contain silver as a
bacteriostatic agent (Reasoner et al., 1987a,b).
The use of phosphate corrosion control additives on
bacterial growth was examined to determine the role
of added phosphate on coliform occurrence problems
(Rosenzweig, 1987). GAG fines were shown to be a
means by which particle-associated bacteria,
including coliforms, can pass from treatment into the
distribution system (McFeters et al., 1987). Particle-
associated coliforms have also been shown to be less
susceptible to disinfection than those that are not
particle-associated.
8.3.2 Bacterial Detection/Monitoring
A variety of studies, completed and ongoing, have
examined various aspects of the bacteriological
quality of drinking water. Studies of detection
methods for bacteria in potable water, and for
monitoring coliform bacteria in potable water include
the development and evaluation of a composite
sampling protocol for coliforms in treated and
distribution water, comparison of media for
recovering total coliforms, detection of Klebsiellain
water systems, the presence-absence coliform test for
monitor-drinking water quality, a radiometric
method for detection of fecal coliforms in water, and
occurrence of pigmented bacteria in treated and
distributed drinking water. An overview that
summarizes much of drinking water microbiology
research during the past decade is available
(Reasoner, 1988).
8.4 Prohibition of Lead Materials
The amendments to SDWA prohibit the use of lead in
pipes, pipe spider, or any other apparatus that comes
in contact with drinking water. On August 18,1988,
the Office of Drinking Water published in the
Federal Register a proposed new regulation for
controlling lead and copper in drinking water (U.S.
EPA, 1988a). This document has drawn a
considerable response, and a lot of work and
manpower is being devoted to technical issues
surrounding this legislation. On October 31,1988,
the Lead Contamination Control Act (LCCA) was
enacted as an amendment to SDWA (Pub. Law 92-
339). The LCCA added Section 1464, which requires
EPA to publish and distribute to the States a
guidance document and testing protocol to assist
schools in determining the source of lead
contamination in school drinking water.
The Drinking Water Research Division has funded a
major study in Long Island on the impact of lead and
other metallic solders on water quality. Ninety test
sites were selected to provide ten sites in each of nine
age groups ranging from new construction to
construction more than 20 years old. During the
study, the pH was adjusted to three levels. The
results of this study indicated that leaching of lead
into drinking water is greatly affected by pH and the
age of a home. The leaching was the highest for new
homes using low pH water. Furthermore, first draw
samples after overnight detention times had the
highest amounts of lead. A project report will
summarize the results of the study.
In-house research includes studying lead
contamination from kitchen faucets and in water
coolers. Of the 12 faucets used in this study, the tree
cast brass faucets contributed significant amounts of
lead to the drinking water. Traces of lead were
obtained from the other metallic faucets and a plastic
faucet was lead free. The results of this study were
presented at the Water Quality Technology
Conference in November 1988, and have been
accepted for publication in the July 1989, issue of the
Journal of the American Water Works Association
(Gardels and Sorg, 1989).
Twenty-two water coolers supplied by the U.S. Navy
and two from a Portland, Maine, School District were
used in the lead studies. Several coolers contributed
lead to the drinking water in amounts considerably
above the present standard. At the end of the
leaching period, the reservoirs were cut open and
several had lead-lined tanks. The results of this study
appeared in the April 10,1989, Federal Register
entitled "Drinking Water Coolers that Are Not Lead
Free" (U.S. EPA, 1989c). This document and the one
entitled "Lead Contamination in School Drinking
Water Supplies" were issued pursuant to the Lead
Contamination Control Act (U.S. EPA, 1989d). Some
chemical analyses and x-ray diffraction examina-
tions of internal deposits were performed on two of
the reservoirs. The results will be presented as part of
a review of lead corrosion research at the AWWA
Annual Conference in June 1989.
Initiation of new in-house research into the effect of
orthophosphate on lead solubility under different
water qualities, determination of corrosion products
and inhibitor films in lead pipes from field sites,
integrating new data into corrosion models, and the
effect of water softening on corrosivity towards lead
and copper is planned. DWRD is also participating in
a study to gather baseline data and look at the impact
of municipal softening on water corrosivity in
Oakwood, Ohio, where there are still many lead
service lines.
8.5 Systems and Cost Modeling Studies
The DWRD has been modeling the deterioration of
water quality in distribution systems. Subsequent to
water leaving the treatment plant, conditions in the
distribution system sometimes lead to the
introduction of contaminants to the water or to the
occurrence of other types of water quality decline.
The research in this area is focused on computer
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modeling to predict and assist in alleviating
distribution system problems (Clark et al., 1988c,d).
In addition to field and laboratory research, DWRD is
developing a computer model that will predict water
quality based on the known characteristics of the
distribution system. For example, TTHM levels can
be projected throughout the distribution system
based on the time of travel and the mixing of water
from various sources (Eilers and Clark, 1988).
Other modeling efforts include a project being
conducted in cooperation with French scientists
investigating the effects of hydraulics on the
propagation of contaminants in distribution systems.
Case studies have been conducted to develop models
that analyze distribution system characteristics and
identify factors that contribute to the potential for
water main breaks (Clark et al., 1988a). Some models
estimate costs of repairs and other system
renovations.
DWRD has conducted cost modeling for many years.
Cost data have been collected from design studies and
merged with performance data to develop cost and
performance models. These models are very useful in
estimating the behavior of full-scale systems (Adams
etal.,1989).
8.6 Future Directions
As the Safe Drinking Water Act matures, areas of
major research will be to complete activities in the
areas mentioned to this point. In addition, increasing
emphasis will be placed in the following areas:
Use of ozone as a disinfectant and oxidant!
Particular emphasis will be placed on the
formation and control of disinfection by-products
and the maintenance of microbiological integrity
of distribution systems.
Effects of the use of corrosion inhibitors as a
means of controlling lead leaching from
household plumbing.
Characterization and treatment of residuals from
drinking water unit processes.
Development of increasingly sophisticated cost
and performance models.
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Chapter 9
References
Abdel-Rahman, M.S., D. Couri, and J.D. Jones. 1980
Chlorine dioxide metabolism in rats. J. Environ.
Pathol. andToxicol. 3:421-430.
Adams, J.Q., andR.M. Clark. 1989. Cost estimates
for GAG treatment systems. JAWWA. 81(l):35-42.
January.
Adams, J.Q., R.M. Clark, and R.J. Miltner. 1989.
Controlling organics with GAC: a cost and
performance analysis. JAWWA. 81(4):132-140. April.
Aieta, E.M., and J.D. Berg. 1986. A review of chlorine
dioxide in drinking water treatment. J. Am. Water
Works Assoc. 78:62-72.
Aieta, E.M., K.M. Reagan, J.S. Lang, L. McReynolds,
J.-W. Kang, and W.H. Glaze. 1988. Advanced
oxidation processes for treating ground water
contaminated with TCE and PCE: pilot-scale
evaluations. JAWWA. 80(5):64-72. May.
Aieta, E.M., and P.V. Roberts. 1986. Application of
mass-transfer theory to the kinetics of a fast gas-
liquid reaction: chlorine hydrolysis. Environ. Sci.
Technol. 20:44-50.
Akin, E. et al. 1987. The U.S. EPA Office of Research
and Development Health Research Program on
Drinking Water Disinfectants and their By-Products.
Issue paper prepared for a Science Advisory Board
Program Review.
American Water Works Association. 1973. Water
Chlorination Principles and Practice. AWWA
Publication No. M20, p. 12.
American Water Works Association Research
Foundation and KIWA. 1983. Occurrence and
removal of volatile organic chemicals from drinking
water.
Augenstein, H.W. 1974. Use of chlorine dioxide to
disinfect water supplies. J. Am. Water Works Assoc.
66:716-717.
Berman, D., E.W. Rice, and J.C. Hoff. 1988.
Inactivation of particle-associated coliforms by
chlorine and monochloramine. Appl. Environ.
Microbiol. 54(2):507-512.
Berman, D. andR. Sullivan. 1988. Inactivation of
three coliiphages by chlorine, chlorine dioxide, and
monochloramine at 5ฐC. Project Report WERL-C1-
0807. EPA/2-88/039. U.S. EPA Risk Reduction
Engineering Laboratory. Cincinnati, OH.
Bryck, J., B. Walker, and G. Mills. 1987. Giardia
removal by slow sand filtration - pilot to full scale.
Paper presented at the AWWA National Conference.
June.
Chrobak, R.S., D.L. Kelleher, and I.H. Suffet. 1985.
Full-scale GAC adsorption performance compared to
pilot plant predictions. Paper presented at the 1985
Annual Conference of the American Water Works
Association, Washington, DC. June 27.
Clark, R.M., R.J. Miltner, C.A. Fronk, andT.F.
Speth. 1989a. Unit process research for removing
VOCs from drinking water: an overview in
significance and treatment of volatile organic
compounds in water supplies. Lewis Publishers, Inc.,
Chelsea, Michigan.
Clark, R.M., E.J. Read, and J.C. Hoff. 1989b.
Analysis of inactivation of Giardia lamblia by
chlorine. Journal of Environ. Eng. ASCE. 115(1):80-
90. February.
Clark, R.M., R.G. Eilers, and J.A. Goodrich. 1988a.
Distribution system: cost of repair and replacement.
In: Proceedings of the Conference on Pipeline
Infrastructure, ASCE, Boston, MA. June 6-7.
163
-------
Clark, R.M., C.A. Fronk, and B.W. Lykins, Jr. 1988b.
Removing organic contaminants from ground water.
Environ. Sci. Tech. 22(10):1126-1130.
Clark, R.M., W.M. Grayman, and R.M. Males. 1988c.
Contaminant propagation in distribution systems. J.
of Environ. Eng. ASCE. 114(4):929-943.
Clark, R.M., W.M. Grayman, R.M. Males, and J.A.
Coyle. 1988d. Modeling contaminant propagation in
drinking water distribution systems. Aqua. No. 3, pp
137-151.
Clifford, D., W. Jijjeswaropu, and S. Subramonian.
1988. Evaluating various absorbents and membranes
for removing radium from ground water. JAWWA.
80(7):94.
Clifford, D., S. Subramonian, andT. Sorg. 1986.
Removing dissolved inorganic contaminants from
water. Environ. Sci. and Tech. 20(11):1072-1080.
November.
Cline, G.C., T. J. Lane, and M. Saldamando. 1985.
Packed column aeration for trichlorethylene removal
at Scottsdale, Arizona. Paper presented at the 1985
Annual Conference of the AWWA held in
Washington, DC. June.
Collins, F. and C. Y. Shieh. 1971. More water from the
same plant. The American City. p. 96. October.
Conley, W.R. and S.P. Hansen. 1987. Trident pilot
study: Lakeport, California. Unpublished Report.
HDR Engineering. March.
Crittenden, J.C., R.D. Cartright, B. Rick, S.R. Tang,
and D. Perram. 1988. Using GAG to remove VOCs
from air stripper off-gas. JAWWA. 80(5):64-72.
Cryer, E.T. 1986. Preozonation at Kennewick,
Washington, Case history. Paper presented at Intl.
Ozone Assoc. Workshop on Drinking Water
Treatment with Ozone, Perrysburg, OH, April.
Gulp, R.L. 1976. Increasing water treatment capacity
with minimum additions. Public Works. August.
DeMarco, J. 1983. Experiences in operating a full-
scale granular activated carbon system with on-site
reactivation. In: I.H. Suffet and M. J. McGuire (ed.),
Treatment of Water by Granular Activated Carbon.
Advances in Chemistry Series, American Chemical
Society Books.
DeWalle, F.B., J. Engeset, and W. Lawrence. 1984.
Removal o(Giardia tamblia cysts by drinking water
plants. Report No. EPA/600/S2-84-069, U.S. EPA,
MERL, Cincinnati, OH. May.
Dobbs, R.A. and J.M. Cohen. 1980. Carbon adsorption
isotherms for toxic organics. Report No. EPA 600/8-
80-023. Office of Research and Development, MERL,
Cincinnati, OH.
Dyksen, J.E., K. Raman, R.F. Raczko, and R.M.
Clark. 1987. GAG treatment costs - minimizing
them. Paper presented at the AWWA Annual
Conference, Kansas City, MO. June 14-18.
Eilers, R.G. and R.M. Clark. 1988. Flow separation
conditions at pipe walls of water distribution mains.
In: Proceedings of the AWWA Annual Conference,
Orlando, FL. June 19-23. pp. 1619-1624.
Feige, W.A., R.M. Clark, B.W. Lykins, Jr., and C.A.
Fronk. 1987. Treatment of water from contaminated
wells. In: Rural Groundwater Contamination. Lewis
Publishers, Inc.
Fronk, C.A. 1987a. Destruction of volatile organic
contaminants in drinking water by ozone treatment.
Ozone Science and Engineering. 9(3):265-287.
Fronk, C.A. 1987b. Removal of low molecular weight
organic contaminants from drinking water using
reverse osmosis membranes. In: Proceedings of the
AWWA Annual Conference, Kansas City,
MO/Denver, CO.
Gardels, M.C. and J.J. Sorg. 1989. A laboratory study
of lead leaching from, drinking water faucets.
JAWWA. July.
Glaze, W.H. 1986. Reaction products of ozone: a
review. Environ. Hlth Persp. Vol. 69, p. 151.
Glaze, W.H. and J.-W. Kang. 1988. Advanced
oxidation processes for treating ground water
contaminated with TCE and PCE: laboratory studies
JAWWA. 80(5):57-63. May.
Glaze, W.H., J.-W. Kang, and M. Aieta. 1987. Ozone-
Hydrogen peroxide systems for control of organics in
municipal water supplies. In: D. W. Smith and G.R.
Finch (eds), Proc. Second Intl. Conf. on the Role of
Ozone in Water and Wastewater Treatment.
TekTran International Ltd., Kitchener, Ontario,
Canada, pp. 233-244.
Glitsch, Inc. P.O. Box 660053. Dallas, TX.
Guter, Gerald A. 1982. Removal of nitrate for
contaminated water supplies for public use. Final
Report. Project Summary. Report No. EPA/600/S2-
82-042. Cincinnati, O'H.
Hand, D.W., J.C. Crittenden, J.L. Gerbin, and B.W.
Lykins, Jr. 1986. Design and evaluation of an air
stripping tower for removing VOCs from ground
water. JAWWA. 78(9):87-97.
164
-------
Hansen, S.P. 1987. Adsorption clarifier pilot study
evaluation. Unpublished Report. Lake Arrowhead
Community Services District, September.
Hoff, J.C. 1986. Inactivation of microbial agents by
chemical disinfectants. Report No. EPA/600/2-86-
067. Risk Reduction Engineering Laboratory, U.S.
EPA, Cincinnati, OH.
Howe, E.W., E.M. Aieta, S. Liang, and M.J. McGuire.
1989. Removal of chlorite residuals with granular
activated carbon: a case study. Presented at
International Chlorine Dioxide Symposium, Denver,
CO (Washington, DC: Chemical Manufacturers
Association).
High-tech water on the green fields of Iowa. 1985.
Water Engineering and Management. January.
Huxstep, Martin R. 1981. Inorganic contaminant
removal from drinking water by reverse osmosis.
Project Summary. Report No. EPA/600/S2-81-115.
WERL, Cincinnati, OH. ?
Jelinek, R.T. and T.J. Sorg. 1988. Operating a full-
scale ion exchange system for uranium. JAWWA.
8(7):79. July.
Kaplan, L.A. and T.L. Bott. 1989. Nutrients for
bacterial growth in drinking water: bioassay
evaluation. Report No. EPA/600/2-89/030. Risk
Reduction Engineering Laboratory. U.S. EPA.
Cincinnati, OH.
Kinner, N.E., C.E. Lassard, andG.S. Schell. 1987a.
Low cost/low technology aeration techniques for
removing radon from drinking water. Report No.
EPA/600/M-87/031. U.S. EPA.
Kinner, N.E., C.E. Lassard, and G.S. Schell. 1987b.
Radon removal from small community public water
supplies using granular activated carbon and low
technology/low cost techniques. In: Proceedings of the
AWWA Seminar on Radionuclides in Drinking
Water, Kansas City, MO.
Lang, J.S., A.R. Trussel, M.D. Umphries, and C.H.
Tate. 1987. Gas adsorption of air stripping emissions.
In: Proceedings of AWWA Seminar on Treatment
Processes for the Control of Synthetic Organic
Chemicals, Kansas City, MO.
Lange, K.P., R. T. Rice, and W. Hemphill. 1985.
Integration of contact clarifier and filtration
processes, Microfloc Product. Paper presented at the
1985 Rocky Mountain AWWA/WPCA Conference,
Albuquerque, NM.
Lange, K.P., W.D. Bellamy, and D.W. Hindricks.
1984. Filtration of Giardia cysts and other
substances. Vol. 1: Diatomaceous Earth Filtration.
Report No. EPA/600/2-84-114. U.S. Environmental
Protection Agency, MERL, Cincinnati, OH. June.
NTIS: PB-84-212703.
Lauch, R.P. and G.A. Guter. 1986. Ion exchange for
the removal of nitrate from well water. JAWWA.
78(5):83-88.
Letterman, R.D. andT.R. Cullen, Jr. 1985. Slow sand
filtration maintenance costs and effects on water
quality. Report No. EPA/600/2-85-056. U.S.
Environmental Protection Agency, Cincinnati, OH.
May. NTIS: PB-85-199669/AS.
Lin, S.D. 1989. Proposed lead rules add chores, costs
to utility burden. Water Engineering and
Management, pp. 35-47. February.
Lowry, J.D. and J.E. Brandown. Removal of radon
from ground water supplies using granular activated
carbon or diffused aeration. University of Maine,
Department of Civil Engineering, Orono, ME.
Lykins, B.W., Jr., R.M. Clark, and J.Q. Adams.
1988a. Granular activated carbon for controlling
THMs. JAWWA. pp. 85-92. May.
Lykins, B.W., Jr., R.M. Clark, and D.H. Cleverly.
1988b. Polychlorinated dioxin and furan discharge
during carbon reactivation. Journal of Environ. Eng.
ASCE. 114(2):300-316. April.
Lykins, B.W., Jr. and M.H. Griese. 1986. Using
chlorine dioxide for trihalomethane control. J. Am.
Water Works Assoc. 78:88-93.
Lykins, B.W., Jr. and J.A. Baier. 1985. Removal of
agricultural contaminants from ground water. In:
Proceedings of the AWWA Conference, pp. 1151-
1164.
Lykins, B.W., Jr., E.E. Geldreich, J.Q. Adams, J.C.
Ireland, and R.M. Clark. 1984. Granular activated
carbon for removing nontrihalomethane organics
from drinking water. Report No. EPA/600/S2-84-165.
McFeters, G.A., A.K. Camper, M.W. LeChevallier,
S.C. Broadway, and D.G. Davies. 1987. Bacteria
attached to granular activated carbon in drinking
water. Environmental Research Brief. Report No.
EPA/600/M-87/003. Risk Reduction Engineering
Laboratory, U.S. EPA, Cincinnati, OH.
McKeon, W.R., J.J. Muldowney and B.S. Aptowicz.
1986. The evolution of a modified strategy to reduce
trihalomethane formation. In: Proc. Annual Meeting,
Am. Water Works Assoc., Denver, CO. pp. 967-997.
McKinnon, R.J. and J.E. Dyksen. 1982. Aeration plus
carbon adsorption remove organics from Rockaway
Township (NJ) ground water supply. Paper presented
165
-------
at the 1982 Annual Convention of the American
Society of Civil Engineers, New Orleans, LA. October
25-27.
Miller, G.W., R.G. Rice, C.M. Robson, R.L. Scullin,
W. Kuhn and H. Wolf. 1978. An assessment of ozone
and chlorine dioxide technologies for treatment of
municipal water supplies. EPA Report No.
EPA/600/2-78-147.
Miltner, R.J. and C.A. Fronk. 1985. Treatment of
synthetic organic contaminants for Phase II
Regulations. Internal Report. DWRD, U.S. EPA.
December.
Miltner, R.J., T.F. Speth, and C.A. Fronk. 1989.
Treatment of seasonal pesticides in surface waters.
JAWWA. 81(l):43-52. January.
Morand, J.M. and M.J. Young. 1983. Performance
characteristics of package water treatment plants.
Project summary. Report No. EPA/600/S2-82-101,
Municipal Environmental Research Laboratory,
Cincinnati, OH. March.
Morse, D. 1988. Lead: taking it from the tap. Civil
Engineering, pp. 71-73.
Myers, G.L., A. Thompson, D.M. Owen and J.M.
Baker. 1986. Control of trihalomethanes and taste
and odor at Galveston County Water Authority. In:
Proc. Annual Meeting Am. Water Works Assoc.,
Denver, CO, 1986, pp. 1667-1675.
National Academy of Sciences. 1980. Drinking Water
and Health. Vol. 1, Chapter 2. Washington, D.C.,
National Academy Press.
O'Brien, R.P., D.M. Jordan, and W.R. Musser. 1981.
Trace organics removal from contaminated ground
waters with granular activated carbon. Calgon
Corporation, Pittsburg, PA. Paper presented at the
National American Chemical Society Meeting, -
Atlanta, GA. March 29 - April 3.
Patel, R. and D. Clifford. 1989. Radium removal from
water by manganese dioxide adsorption and
diatomaceous earth filtration. Draft Report. U S
EPA.
Pinsky, D.E. and V.F. Coletti. 1988. Rehabilitating a
New England water treatment plant. J. New
England Water Works Assoc., pp. 132-157. June.
Pyper, G.R. 1985. Slow sand filter and package
treatment plant evaluation operating costs and
removal of bacteria, Giardia, and trihalomethanes
.Report No. EPA/600/2-85-052. U.S. Environmental
Protection Agency, Cincinnati, OH. April.
Randtke, S. 1988. Organic contaminant removal by
coagulation and related processes. JAWWA.
80(5):40-56. May.
Reasoner, D. J. 1988. Drinking water microbiology
research in the United States: an overview of the past
decade. Water Sci. Technol. 20(11/12):101107.
Reasoner, D.J., J.C. Blannon, E.E. Geldreich, and
J.A. Barnick. 1987a. Microbiological studies of
activated carbon point-of-use systems: an interim
report. Report No. EPA/600/2-88/004. Risk Reduction
Engineering Laboratory, U.S. EPA, Cincinnati, OH.
Reasoner, D.J., J.C. Blannon, and E.E. Geldreich.
1987b. Microbiological characteristics of third-faucet
point-of-use devices. JAWWA. 79(10):60-66.
Reid, George N., P. Lassovszky, and S. Hathaway.
1985. Treatment, waste management and cost for
removal of radioactivity from drinking water. Health
Physics. 48(5):671-694.
Roberts, P.V. and P. Dandliker. 1982. Mass transfer
of volatile organic contaminants during surface
aeration. Paper presented at the 1982 Annual
Conference of the AWWA, Miami Beach, FL. May.
Rogers, K.R. in press. Arsenic and fluoride removal
from drinking water at San Ysidro, N.M. Risk
Reduction Engineering Laboratory, Office of
Research and Development, U.S. EPA, Cincinnati,
OH.
Rosenzweig, W.D. 1987. Influence of phosphate
corrosion control compounds on bacterial growth.
Report No. EPA/600/2-87/045. Risk Reduction
Engineering Laboratory, U.S. EPA, Cincinnati, OH.
Routt, J.C. 1989. Chlorine dioxide trihalomethane
control and distribution system odor problem: a
utility's 5-year experience. Paper presented at the
AWWA Annual Meeting, Los Angeles, CA. June.
Roy, D., R.S. Englebrecht, and E.S.K. Chian. 1982.
Comparative inactivation of six enteroviruses by
ozone. JAWWA. 74(12):660-664.
Ruggiero, D.D. and R. Ausubel. 1982. Removal of
organic contaminants from drinking water supply at
Glen Cove, New York, Phase II. Report No.
EPA/600/2-82/027, U.S. EPA. March.
Ruggiero, D.D. and R. Ausubel. 1980. Removal of
organic contaminants from drinking water supply at
Glen Cove, New York, Phase I. Report No. EPA600/2-
80-198.
166
-------
Schock, M.R. 1980. Response of lead solubility to
dissolved carbonate in drinking water. JAWWA. Vol.
72, p. 695.
Schock, M.R. and I. Wagner. 1985. Corrosion and
solubility of lead in drinking water: Internal
corrosion of water distribution systems. AWWA
Research Foundation/DVGW.
Sequeira, J.A., L. Harry, S.P. Hansen, and R.L. Culp.
1983. Pilot filtration tests at the American River
water treatment plant. Public Works. 114:1:36.
Singer, P.S. 1988. Alternative oxidant and
disinfectant treatment strategies for controlling
trihalomethane formation. Report No. EPA/600/S2-
88/044, Water Engineering Research Laboratory,
Cincinnati, Ohio. October.
Singer, P.S. 1986. THM control using alternate
oxidant and disinfectant strategies: an evaluation.
In: Proc. 1986 Annual Conference, Am. Water Works
Assoc. Denver, CO. pp. 999-1017.
Slootmaekers, B., S. Tachiyashiki, D. Wood, and G.
Gordon. 1989. The removal of chlorite ion and
chlorate ion from drinking water. Presented at
International Chlorine Dioxide Symposium, Denver,
CO, November (Washington, DC: Chemical
Manufacturers Association).
Sobsey, M.D., T. Fugi, and P.A. Shields. 1988.
Inactivation of hepatitis A virus and model viruses in
water by free chlorine and monochloramine. In:
Proceedings of International Conference on Water
and Wastewater, Microbiology, Newport Beach,
California. 2(64):l-7-
Sobsey, M.D. 1988a. Detection and chlorine
disinfection of hepatitus A in water. CR-813-024,
EPA Quarterly Report/December 1988.
Sorg, T. J. 1979. Treatment technology to meet the
interim primary drinking water regulations for
inorganics, Part IV: chromium and mercury.
JAWWA. pp. 454-466. August.
Sorg, T. J. 1978. Treatment technology to meet the
interim primary drinking water regulations for
inorganics, Part I: nitrite and fluoride. JAWWA.pp.
105-112. February.
Sorg, T. J. and G. Logsdon. 1980. Treatment
technology to meet the interim primary drinking
water regulations for inorganics, Part V: barium and
radionuclides. JAWWA. pp. 411-422. July.
Sorg, T.J. and G. Logsdon. 1978. Treatment
technology to meet the interim primary drinking
water regulations for inorganics, Part If: arsenic antf
selenium. JAWWA. p. 379-393. July.
Sorg, T.J., R. Forbes, and D. Chambers. 1980.
Removal of radiu-226 from Sarasota County,
Florida's drinking water by reverse osmosis.
JAWWA. pp. 230-237. April.
Sorg, T.J., M. Csanady, and G. Logsdon. 1978.
Treatment technology to meet the interim primary
drinking water regulations for inorganics, Part III:
cadmium, lead, and silver. JAWWA. pp. 680-691.
December.
Speth, T.A. and R.J. Miltner. 1989. Effect of
preloading on the scale-up of GAG microcolumns.
JAWWA. 81(4): 141-148. April.
Stevens, A.A., L.A. Moore, and R.J. Miltner. 1989:
Formation and control of nontrihalomethane by-
products. In: Proceedings of the AWWA Water
Quality Technology Conference, St. Louis, Missouri.
Stevens, A.A., L.A. Moore, C.J. Slocum, B.L. Smith,
D.R. Seeger, and J.C. Ireland. 1987. By-products of
chlorination at ten operating utilities. In:
Proceedings of the Sixth Conference on Water
Chlorination: Environmental Impact and Health
Effects. Oak Ridge Associated Universities, Oak
Ridge, Tennessee. May 3-8.
Tanner, S. 1988. Evaluation of Slow Sand Filters in
Northern Idaho. Idaho Division of Environmental
Quality. May 9.
Taylor, J.S., D.M. Thompson, J.K. Carswell. 1987.
Applying membrane processes to ground water
sources for THM control. JAWWA. 79(8):72-82.
U.S. EPA. 1989. National Primary and Secondary
Drinking Water Regulations. Proposed Rule. Fed.
Reg. 54(97):22064. May 22.
U.S. EPA. 1989a. Guidance manual for compliance
with the filtration and disinfection requirements for
public water systems using surface water sources.
Draft. Science and Technology Branch, Office of
Drinking Water, U.S. EPA, Washington, DC,
October.
U.S. EPA, 1989b. Drinking water; national primary
drinking water regulations; filtration, disinfection,
turbidity, Giardia lamblia, viruses, Legionella, and
heterotrophic bacteria. Final Rule. Fed. Reg.
54(124):27485-27541. June 29.
U.S. EPA. 1989e. Drinking water coolers that are not
lead free. Proposed List and Request for Comments,
Fed. Reg. 54(67):14320-14322. April 10.
167
-------
U.S. EPA. 1989d. Lead contamination in school
drinking water supplies. Guidance Document and
Testing Protocol. Notice of Availability and Request
for Comments. Fed. Reg. 54(67):14316-14318. April
10.
U.S. EPA. 1988a. Drinking water regulations:
Maximum Contaminant Level Goals and Natural
Primary Drinking Water Regulations for lead and
copper. Proposed Rule. Fed. Reg. 53(160):31516.
August 18.
U.S. EPA. 1988b. Technologies and costs for the
removal of synthetic organic chemicals from potable
water supplies. Draft. U.S. EPA, Office of Drinking
Water, Washington, DC. September.
U.S. EPA. 1988c. Drinking water; substitution of
contaminants and drinking water priority list of
additional substances which may require regulation
under the Safe Drinking Water Act. Federal Register
53(14):1891-1902.
U.S. EPA. 1987. Technologies and costs for the
removal of microbiological contaminants from
potable water supplies. Draft. Office of Drinking
Water, Criteria and Standards Branch.
U.S. EPA. 1986a. Safe Drinking Water Act 1986
Amendments. Report No. EPA/570/9-86-002. Office
of Drinking Water. August.
U.S. EPA. 1986b. Design manual: municipal
wastewater disinfection. Report No. EPA/625/1-
86/021 (October 1986). U.S. EPA, Office of Research
and Development, Water Engineering Research
Laboratory, Center for Environmental Research
Information, Cincinnati, OH 45268.
U.S. EPA. 1984. Corrosion manual for internal
corrosion of water distribution systems. Report No.
EPA/570/9-84-001. Office of Drinking Water. April.
U.S. EPA. 1983. Microorganism removal for small
water systems. Report No. EPA/570/9-83-012. U.S.
EPA, Office of Drinking Water, Washington, D.C.
June.
U.S. EPA. 1979. Estimating water treatment costs.
Volumes 1-4. Report No. EPA/600/2-79-162a.
Municipal Environmental Research Laboratory,
Office of Research and Development, U.S. EPA,
Cincinnati, OH. August.
U.S. EPA. 1973. Process design manual for carbon
adsorption. Technology Transfer. October.
Wallman, H. and M.C. Cummins. 1986. Design scale-
up suitability for air stripping columns. Report No.
EPA/600/S2-86-009. U.S. EPA, Drinking Water
Research Division, Cincinnati, OH.
Westerhoff, G. P. 1971. Experiences with higher
filtration rates. JAWWA. 63:6:376.
Westerhoff, G.P. and R. Miller. 1985. Design of the
nation's first major GAC facility for drinking water
treatment at Cincinnati, Ohio. Paper presented at
the 1985 Annual Conference of the AWWA held in
Washington, DC. June.
Williams, R.B. and G.L. Culp. 1986. Handbook of
Public Water Systems. New York, New York, Van
Nostrand Reinhold Company.
Wolfe, R.L., M.H. Stewart, K.N. Scott and M.J.
Mcguire. 1989. Inactivation ofGiardia muris and
indicator organisms seeded in surface water supplies
by peroxone and ozone. Env. Sci. Technol. 23(6):744-
745.
168
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Appendix A
Experience Modifying Existing Filtration Systems
This Appendix provides brief case histories of
modifications resulting in plant expansions (Section
A.I) and installation of different filtration systems,
including slow sand (Section A. 2), package plant
(Section A.3), and diatomaceous earth (Section A.4)
filters. Experience selecting a filtration system is
provided in Section A. 5.
A.1 Upgrading Existing Treatment
Facilities
A. 1.1 Horizontal Flow Basin Example
This example involved a modification of existing
facilities. The plant equipment includes a
rectangular sedimentation basin and rapid sand
filters with a capacity of 0.18 m3/sec (4 MOD). The
basin is 9 meters (30 ft) wide, 40.5 meters (133 ft)
long, and averages 4.5 meters (15 ft) in depth. The
design surface overflow rate is 40.7 m3/day/m2 (1,000
GPD/sq ft). The sedimentation basin has a single
overflow weir across the outlet end. Sedimentation is
preceded by mechanical flocculation with a 40-
minute detention period. Coagulant aids are added
during periods of high turbidity and low water
temperature conditions. Influent water
characteristics include a maximum turbidity ranging
from 25 to 30 NTU and a temperature rarely below
10ฐC (50ฐF).
The plan was to expand the plant capacity from 0.18
to 0.35 m3/sec (4 to 8 MOD). At a 0.35 nvVsec (8-
MGD) capacity, the sedimentation basin overflow
rate is 81.5 nvVday/m2 (2,000 GPD/sq ft) or 0.95
L/sec/m2 (1.4 GPM/sq ft). This basin overflow rate,
coupled with the plant's influent turbidity, are the
primary factors used to derive the appropriate
overflow rate for the tube modules. According to the
recommended overflow rates for systems with
influent temperatures generally over 10ฐC (50ฐF), an
overflow rate of 2.04 L/sec/m2 (3 GPM/sq ft) is
acceptable for the basin area covered by the tube
settlers when preceding either dual- or mixed-media
filters.
The area of the basin covered by tube modules was
calculated using the allowable tube capacity to
achieve the desired overflow rate. The two-step
calculation is based on acceptable plant capacity and
tube rate parameters:
1. Quantity
oftubes=
(area)
capacity, GPM
allowable tube rate, GPM/sq ft
_ 8 MGD X 700 GPM/MGD
3 GPM/sq ft
= 1,870 ft2 or 173.
2. Area = length X width
1,870 = length X 30 ft
length = 1,870/30 = 62.5 ft or 19m
The tube lengths were rounded off to the nearest 10 ft
to permit use of standard tube module dimensions.
The tube modules were installed in an area extending
from the outlet end of the basin to an isolation baffle
wall separating the tube modules from the area of
inlet turbulence. Three new effluent launders
extending from the exit end wall were required to
ensure uniform flow through the tube modules. The
launders were installed at 3-m (10-ft) intervals. The
tube modules were submerged 1.2 m (4 ft) because of
the 4.8-m (16-ft) depth of the basin.
169
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A.1.2 Upflow Solids Contact Clarifier
Example
This example also involves the modification of
existing facilities. The plant has two 3.9-m2 (42-sq ft)
upflow clarifiers of 189.2 L/sec (3,000 GPM),each
with peripheral collection launders. The total surface
area of each clarifier is 163.5 m2 (1,760 sq ft). The
influent center well consumes 18.6 m2 (200 sq ft) of
settling area.
Peak flows reach 1.3 L/sec/m2 (1.92 GPM/sq ft), which
is high enough to impede clarifier performance,
especially at colder temperatures. Influent turbidity
ranges from 30 to 70 NTU. Influent temperature
rarely falls below 10ฐC (50ฐF).
The plan is to increase the capacity of each clarifier to
252.3 L/sec (4,000 GPM). At this flow, the clarifica-
tion rate based on the available overflow rate
allowable for tube settlers would be 1.77 L/sec/m2 (2.6
GPM/sq ft). This rate is within the recommended
limits for the expected influent turbidity levels and
could be achieved by totally covering the basin with
tubes. Total coverage of each basin is the simplest
solution because of the ease of supporting the tube
modules. This would result in 144.9 m2 (1,560 sq ft) of
tubes, with radial launders added to provide equal
flow distribution. At the 1.77 L/sec/m2 (2.6-GPM/sq
ft) clarifier overflow rate, the probable effluent
turbidity would fall within 3 to 7 NTU. An effluent
with this turbidity level is acceptable for filtration
with dual-or mixed-media filters.
A.1.3 Sacramento, California (Sequeira
et al., 1983)
This case involves upgrading the capacity of a
municipal plant from 2.6 to 4.4 m3/sec (60 to 101
MGD). This plant, built in 1963, uses the American
River as its water source. Originally the plant
provided for 25 minutes of flocculation followed by
115 minutes of sedimentation detention. The
expansion reduced flocculation detention to 14
minutes and sedimentation time to 65 minutes.
Filter flow rates increased from 2.0 to 3.6 L/sec/m2
(3.0 to 5.3 GPM/sq ft) at the expanded flow.
The feasibility study found that a change in filtration
media alone from rapid sand to either dual or mixed
media, would compensate for higher turbidities
anticipated from the increased plant flow rate. It was
concluded that the modification could be
accomplished without structural changes.
Extensive pilot tests of various filter media were
conducted fromFebruary to May, 1982, to determine
the optimal filter medium in terms of efficiency and
economics. The tests involved four types of filter
media; each pilot filter was monitored for turbidity
and headloss.
Figure A-l shows the pilot filtration equipment
setup. Influent came either directly from the river or
after coagulation, flocculation, and sedimentation in
the plant. Pilot filter influent turbidities ranged from
3 to 33 NTU and pilot filter rates were set at 3.4,4.4,
and 6.8 L/sec/m2 (5,6.5, and 10 GPM/sq ft). Alum
dosages ranged from 12 to 21 mg/L and polymer
dosages ranged from 0 to 0.3 mg/L. The City of
Sacramento allows only 0.1 NTU of turbidity in
finished water, so the pilot tests were terminated
when turbidity levels achieved that figure. Both
mixed- and dual-media filters performed well at all
filter test flow rates, but mixed-media filters were
more reliable in achieving the desired turbidity goal.
The recommendations from the pilot test data
endorsed both dual- and mixed-media filters. A
polyelectrolyte preparation and feed system were also
recommended. During qualifying tests of the new
filters, the plant produced effluent turbidities of less
than 0.1 NTU (generally between 0.06 and 0.08
NTU).
A.1.4 Erie County, New York (Westerhoff,
1971)
This case involves upgrading a 1.93 m3/sec (44 MGD)
plant to 2.63 m3/sec (60 MGD). The Erie County
Water Authority built this plant in 1961 using Lake
Erie as its water source. The steps of the plant
treatment train are:
Aeration
Chemical addition
Rapid mixing
Flocculation and sedimentation
Filtration
Chlorination
The Authority decided to add six new mixed-media
filters to the existing four rapid sand filters as the
first stage of facility expansion. The decision to use
mixed-media filters for the expansion was based on a
year-long study in which 48 parallel filters were
tested. Sand filters were tested at a flow rate of 1.36
L/sec/m2 (2 GPM/sq ft), while mixed-media filters
were tested at rates of 1.36 to 6.79 L/sec/m2 (2 to 10
GPM/sq ft). Tests were terminated at headlosses of
2.4 m (8 ft). Test influent turbidities ranged from 2 to
4 NTU, clarifier overflows ranged from 25.5 to 38.3
m3/day/m2 (625 to 940 GPD/sq ft), and alum dosages
ranged from 14 to 16 mg/L.
The test results indicated that:
Sand filter effluent turbidity was 0.10 NTU or
less for greater than 80 percent of the time.
170
-------
Plant Filter Influent Water
(Following Alum Addition, Mixing,
Flocculation, and Settling)
NOTE:
Fine Filter Media Depth is'24
Inches Throughout
,1
i
f' s
Pilot Filter / ~ \ Influent
/ N
Tri-Mixed 1- Tri-Mixed
Media No. 1 Media No. 2
1
t
\
Sand
X
V J
t-
r
l r
,'
Multipoint Turbidity
r
Water
Dual-Mixed
Media
t
1
>
r
f
Anthracite-
Capped
Sand
t
t
i
r
Recorder
Figure A-1. Flow diagram of the pilot filtration equipment.
Mixed-media filter effluent turbidity was 0.10
NTU or less for greater than 88 percent of the
time.
Mixed-media filters produced consistently less
turbid finished water at flow rates of 1.36 to 6.79
L/see/m2 (2 to 10 GPM/sq ft) than did sand filters
at flow rates of just 1.36 L/sec/m2 (2 GPM/sq ft).
Mixed-media filters had lower microscopic counts
of particulate matter at flow rates of up to 4.1
L/sec/m2 (6 GPM/sq ft) than did sand filters at
1.36 L/sec/m2 (2 GPM/sq ft).
Mixed-media filters at flow rates of 3.4 L/sec/m2
(5 GPM/sq ft) had an average run length of 29
hours.
Mixed-media filters at flow rates of 4.1 L/sec/m2
(6 GPM/sq ft) had an average run length of 20
hours.
Mixed-media filters at flow rates of from 3.4 to
4.1 L/sec/m2 (5 to 6 GPM/sq ft) used
proportionately less wash water than sand filters
at a flow rate of 1.36 L/sec/m2 (2 GPM/sq ft).
The finished water goals for this modified plant,
using mixed-media filters at a rate of 4.1 L/sec/m2 (6
GPM/sq ft), include:
Average turbidity of less than 0.1 NTU
Pilot Filters
Effluent Rate of Flow Controllers
and Meters
Turbidimeters
ซ Maximum turbidity of less than 0.5 NTU
Average total microscopic count of less than 200
su/mL
Maximum total microscopic count of less than
3QOsu/mL
Less than 1 unit of color
Less than detectable odor
Less than 0.05 mg/L of aluminum
* Less than O.Q5 mg/L of if on
A.1,5 Corvallis, Oregon (Collins and
Shleh, 1971)
This case involved upgrading an 0.35 m3/sec (8 MGD)
plant to 0.92 m3/sec (21 MGD). This municipal plant,
which uses water from the Willamette River, was
planned in phases of four MGD subunits, with the
first phase built in 1949. The second phase was built
in 1961, but the third and fourth were never built.
Instead, the 0.35 m3/see (8 MGD) plant was expanded
with nonstructural modifications during the early
1970s. Willamette River water has turbidity ranging
from 15 to 30 NTU, with surges to 1,000 NTU. The
original facility included flpcculation and
sedimentation basins, with two rapid sand filters per
set of flocculation and sedimentation basins. ,
The expansion involved the replacement of the sand
media with mixed media in the filters. It also added
shallow-depth sedimentation using.tube settlers and
171
-------
coagulation control techniques. Typical chemical
dosages used to treat the raw water include:
20 to 40 mg/L of alum
10 to 20 mg/L of lime
2 mg/L of chlorine
0.1 to 0.2 mg/L of polymer as coagulant aid
5 to 10 mg/L of activated carbon for taste and odor
control
Almost all treatment plant piping was enlarged to
accept the expanded flows. Settling tubes covering 60
percent of the 325.2 m2 (3,500 sq ft) rectangular
sedimentation basins were positioned at the
discharge end of the basins. The tube modules were
supported on a simple "I" beam extended across the
basin width. New effluent weirs and launders were
also installed to ensure proper flow distribution. The
overflow rate in the settling basin with tubes was 2.8
L/sec/m2 (4.2 GPM/sq ft) compared to 0.71 L/sec/m2
(1.05 GPM/sq ft) prior to the tube installation.
Experience has proved that the modified plant, at
full-scale operation, consistently produced water
with less than 0.2 NTU turbidity. Also, filter run
lengths have increased from 40 to 65 hours due to the
improved turbidity removal achieved by tube
settling. The filtration rate is now 5.1 L/sec/m2 (7.5
GPM/sq ft). The plant uses a pilot filter to establish
coagulant dosages and has turbidimeters on each
filter to continuously monitor effluent turbidity. The
increased filter cycle length reduced operating costs
through backwash water savings.
The cost of this expansion in 1969 was $430,000. In
contrast, the original expansion plan of constructing
new flocculation, sedimentation, and filter units to
0.7 m3/sec (16 MGD) capacity was estimated at
$650,000, in 1969 dollars. The nonstructural
expansion included:
New 0.22 m3/sec (5-MGD) reservoir
New high service pump station
A cross-town 40.6-cm (16-in) transmission pipe to
the new reservoir
219 L/sec (5 MGD) larger capacity than the
original expansion
In addition, the expansion resulted in improved
finished water quality.
A.1.6 Novato, California (Gulp, 1976)
This case involved the expansion of a North Marin
County Water District plant from a capacity of 0.16 to
0,27 m3/sec (3.75 to 6.2 MGD) during 1973 and 1974,
without major additions to the plant.
Stafford Lake is the District's water source. The
turbidity ranges from 2 to 35 NTU, with the usual
turbidity between 10 and 20 NTU. Stafford Lake's
coliform MPN values range from 5 to 72,400 per 100
mL and its color ranges from 25 to 50 units. Although
the existing system could manage the high raw water
turbidity and coliform count, the system had a
clarification problem when the water exhibited low
turbidity and high color. Also, high plankton
populations caused taste and odor problems. The
plankton and other biological contaminants
significantly shortened filter run length.
The characteristics of the existing treatment system
included:
* Disinfection with chlorine and coagulation with
alum in a downflow hydraulic mixing chamber
Flocculation, with additions of recirculated
sludge and lime, followed by clarification
Additions of activated carbon immediately prior
to rapid sand filtration
Dechlorination through the addition of sulfur
dioxide in the filtered water clearwell
Elevated water storage for backwashing
Discharge of backwash water to a recovery pond
and recycling to the plant influent for
reprocessing
Spraying of flocculated sludge on land for
disposal
The expansion required three major changes:
1. Modifying the clarifier by adding settling tubes
2. Changing the filter media from sand to mixed
media
3. Installing a coagulant control center and
turbidity monitoring unit
These changes are discussed below.
Settling tube modules were added to the annular
outer settling compartment of the circular clarifier.
As a general rule the addition of settling tubes
permits processing two to four times as much water
with no loss in clarification effectiveness. However,
due to the presence of light alum floe, it was decided
to increase capacity to only 263 from 164 L/sec (6.0
from 3.75 MGD). This change increased the surface
overflow rate on the clarifier from 1.03 to 1.7 L/sec/m2
(1.52 to 2.5 GPM/sq ft) and decreased the detention
time from 1.3 to 0.8 hours. The weir loading increased
from 1.47 to 2.3 L/sec/m2 (7 to 11 GPM/ft).
In addition, capacities of certain plant equipment
were increased to aiccommodate the increased plant
flows. In addition to expanded pump capacities,
pipelines, meters, chemical feeders and valves, and
controls were modified to accommodate the increased
plant capacity. The simple hydraulic mixing chamber
was equipped with a vertical mechanical rapid mixer.
Provisions were made to add polymer to aid
172
-------
flocculation. Also, a system to store and feed sodium
hydroxide solution for pH control replaced the lime
system.
The filter bottoms were replaced along with
replacement of sand media with mixed media. The
mixed-media filter was supported by graded silica
gravel with an upper layer of coarse garnet gravel.
Gate valves were replaced with butterfly valves.
A coagulant control center and turbidity monitoring
equipment were installed to ensure compliance with
the California Department of Health Services
standard of 0.5 NTU.
The changes resulted in achieving a 107 L/sec (2.45
MGD) increase in capacity at a cost of $337,445, in
1974 prices. The expansion took only 8 months to
complete. The plant has performed efficiently and
reliably at the maximum design capacity,
consistently achieving less than 0.15 NTU turbidity
levels and effective bacteriological removal.
A.2 Slow Sand Filter Systems
A.2.1 Idaho State (Tanner, 1988)
In a joint 1-year project in cooperation with Idaho
State, the EPA and University of Washington's
Department of Environmental Health focused on
three typical slow sand filter plants. In the course of
this study, 13 additional slow sand filter plants were
surveyed, and the following plant performance data
were collected:
Turbidity
Total and fecal coliform removal
Giardia samples
Microscopic particle evaluation
Temperature
In addition, the study collected and examined the
following operating data:
Filtration rates
Sand depth
Effective sand size
Cleaning method and frequency
Problems
From the results of the study, the researchers
concluded that:
Slow sand filters are very effective and reliable, if
they are properly designed, operated, and
maintained.
Slow sand filter performance is not reliably
determined through examination of turbidity and
coliform removal.
Microscopic particulate analysis (MPA) can be a
good indicator of slow sand filter performance.
The easiest method of projecting slow sand
performance is to examine design and
operational specifications.
Raw water quality can have a large impact on
slow sand performance.
Slow sand filters can have significant operational
problems.
This study made the following recommendations in
considering the slow sand filter option:
Use pilot filters to guide design and construction.
Use experienced design professionals.
Use multiple beds for the filters.
Use properly educated operators.
Reduce filtration rates during winter.
Include proper watershed management in
operation and maintenance procedures.
The researchers also recommended the use of routine
sanitary surveys, which would include monitoring
influent water quality, operating factors, and plant
performance. Specifically, water quality should be
monitored as to water source, watershed
management and status, turbidity, and temperature.
Operating factors monitored should include filtration
rates, cleaning procedures, and bypassing. Finally,
monitoring plant performance should include the
recording of turbidity, cleaning frequencies, and
freezing frequencies.
A.2.2 New York State (Letterman and Cullen,
1985)
A recent study of seven slow sand filter plants in New
York State examined the effects of cleaning
procedures on the effluent water quality. The water
quality parameters examined included turbidity,
total particle count, standard plate count, and total
coliforms. Characteristics studied at the seven plants
included average operating flow, design filtration
rate, average operating filtration rate, filter sand
uniformity coefficient, and effective sand size (see
Table A-l).
The operational data from these plants are contained
in Table A-2. Even during the ripening periods, all
but one plant achieved effluent turbidities of less
than 0.43 NTU. The one plant that exceeded 0.43
NTU had submicron particle size turbidity, which is
ineffectively controlled with slow sand filtration. All
seven plants performed well in removing particles
greater than 2 um. The removal rate for particles
ranging from 2 to 60 um was from 90 to 99.8 percent.
173
-------
Table A-1. Characteristics of Slow Sand Filter Installations in New York
Slow Sand Filtration
Average Operating Flow Design Filtration
Location Rate (MGD) Rate (mgad)
Auburn
Geneva
Hamilton
llton
Newark
Ogdensburg
Waverty
6.0
2.5
-0.3
1.5
2.0
3.6
1.2
2.83
4.9
-
-
4.1
5.1
4.1
Average Operating
Filtration Rate Fllter Sand
(mgad)
3.6
4.9
1.0
4.1-4.6
4.1
4.6
4.1
Uniformity Coefficient
2.4
1.9
2.4
2.2
1.7
1.7
2.4
Effective Size (mm)
0.45
0.37
0.27
0.37
0.35
0.35
0.15
1 MOD - 0.044 m3/sec; 1 MGAD = 0.935 m3/m2/day
Source: Letterman and Cullen (1985).
Total plate count removals varied widely from 0 to 50
percent.
A.2.3 Mclndoe Falls, Vermont (Pyper, 1985)
This was a 2-year study of a municipal slow sand
filter plant with two 37.2-m2 (400-sq ft) filters, sand
depth of 106.7 cm (42 in), effective silica sand size of
0.33 mm, and a design filtration rate of 1.92
m3/m2/day (2.05 mgad).
The raw water was obtained from two shallow spring-
fed ponds with several beaver dams and lodges.
Influent water turbidity ranged from 0.4 to 4.6 NTU,
with a seasonal average of 2.1 NTU. The study
examined the removal of turbidity, bacteria,
coliforms, and Giardia cysts.
The evaluation of this slow sand filter plant revealed
the following:
Effluent turbidity of less than 1 NTU was
achieved 99.19 percent of the time.
Effluent turbidity of less than 1 NTU was
achieved 99.68 percent of the time, after the first
100 days of operation.
Effluent turbidity of less than 0.2 NTU was
achieved 72 percent of the time (during this time
influent turbidity was 1.45 NTU or less).
Influent total coliform count was reduced from
1,300 per 100 mL or less to 10 per 100 mL or less,
86 percent of the time.
Tablo A-2. Filter Ripening Data - Summary
Type of
Operation
Location Visit'
Auburn
Auburn
Auburn
Geneva
Hamilton
Itton
Newark
Newark
Ofldensburg
Ogdensburg
Waverty
(D
0)
(D
(1)
(D
(1)
(D
(2)
(3)
0)
0)
Date of
Site Visit
Jul83
Jut 83
Ju)84
Jut 83
May 84
Jul 83
Aug 83
Jan 84
Aug 83
Feb84
Jun84
Raw Water
Turbidity
During Site
Visit (NTU)
1.2-2.0
1.2-2.0
2.0-2.8
-
1.0-1.5
2.0-4.0
1.2-3.5
0.6-2.7
0.3-0.6
1.0-1.2
6.0-11.0
Filter Turbidity Approximately 5 Hours
Water Tern- After Filter Startup (NTU) Evidence of Ac
perature Dur-
ing Site Visit
~19ฐC
~19ฐC
~18ฐC
-
~12ฐC
~23ฐC
~13ฐC
~4ฐC
~15ฐC
~2ฐC
~15ฐC
Scraped/Re-
sanded Filter
0.43
0.28
0.22
-
0.28
0.30
0.35
0.41
0.12
0.22
2.3
Ripening ol
Control Filter^ Period
0.27
0.27
0.23
-
None
0.40
0.35
0.12
0.10
0.24
1.6
Yes
None
None
-
None
Minimal
(particle
count only)
None
Yes
None
None
Yes
(proximate Length
f Ripening Period
(days)
0.25
-
-
-
-
0.5
-
2
-
-
10
ซ(1) Scraping operation.
(2) Resanding operation.
(3) Scraping combined with resanding.
b Control filter - Filter on-line at least 1 month, except Ogdensburg where the filter was on-line 1 week.
Source: Letterman and Cullen (1985).
174
-------
Influent occurrences of high total coliforms
(spikes) and plate count bacteria were removed in
water temperatures of from 5 to 10ฐC.
Biological removal efficiencies were lower at
temperatures of less than 5ฐC, especially from 0
to 1ฐC; for example:
- Giardia removal efficiency was lowered to
93.7 percent in one test.
- At 1ฐC total coliform count removal was
reduced from 98 to 43 percent and the
standard plate count bacterial removal was
reduced from 98 to 80 percent over a 9-day
monitoring period.
Influent standard plate counts of 500 per mL
were reduced to 10 per mL or less, 94 percent of
the time.
Influent total coliform counts were reduced from
440 organisms per 100 mL to 4 per mL.
Influent heterotrophic organisms were reduced
from 520 organisms per 100 mL to 15 organisms
per 100 mL, based on the standard plate count.
Influent Giardia levels were reduced by 99.98
percent under warm water conditions.
Influent Giardia levels were reduced by 99.36 to
99.91 percent in water temperatures of less than
7ฐC.
A.2.4 Village of 100 Mile House, British
Columbia, Canada (Bryck et al.,
1987)
This example concerns a water supply operation that
only chlorinated their water before distribution to a
2,000 person service area. Giardia in the raw water
intake from beavers and muskrats upstream became
a concern. In 1984,the village decided to construct a
slow sand filter system to augment their chlorination
operation after Giardia occurrences in 1981,1982,
and 1983. The new plant included the following
components:
Surface water intake
Raw and treated water pumping station
Chlorine equipment
Contact tank
Clear well
Three slow sand filter beds
The three filters used filter media derived from local
sand that was washed, dried, and sieved. The
resultant effective sand size for their filter media
ranged between 0.2 and 0.3 mm, with an average of
0.25 mm. The sand media uniformity coefficient
ranged between 3.3 and 3.8, with an average of 3.5.
Each of the filter cells are 43 m (141 ft) long, 6 m (20
ft) wide, 3.75 to 3.9 m (12.5 to 13 ft) deep, and have a
total surface area of 262 m2 (2,820 ft2). The design
filter rate is 0.11 L/sec/m2 (0.16 GPM/ft2). All three
filters are operated to the accepted maximum unit
flow of 2,422.4 m3/day (640,000 GPD) per filter for a
total of 7,255.8 nvVday (1,917,000 GPD). To protect
against freezing, the filters are covered with precast
panels. Filter walls have rigid insulation and are also
insulated with backfilled soil.
The performance results of the new plant are
presented in Figures A-2 and A-3. Influent sample
Giardia cyst counts for the period of November 1985
through November 1986 are contained in Figure A-2.
No cysts were detected in the effluent during that
period. Influent and effluent sample turbidity data
are contained in Figure A-3. Effluent turbidity
ranged from 0.15 to 3.5 NTU,and was lower both
when influent turbidities were lower and after the
filter ripened.
Operating cycles for the filters ranged from 52 to 215
days, with the longer filter cycles occurring in the
winter and spring months. Increased loadings of
algae during late spring and summer months
contributed to shorter filter cycles during those
periods.
The construction cost of the new plant, in 1984
Canadian dollars, was $780,000. The average annual
operating costs were $20,700, including costs for
chlorination; energy requirements; media
replacement; cleaning; and labor for daily inspection,
which consumed from 0.5 to 1.0 hours. Cleaning
required 16 person hours per filter and cost about
$225 per cleaning. The total operating cost was
estimated to be $0.25/m3 ($0.96/1,000 gal).
A.3 Package Plants
A.3.1 Conventional Package Plants (Morand
and Matthew, 1983)
The EPA surveyed the effectiveness of six
conventional package plants, most of which were
built during the 1970s. The results of this survey
were published in March 1983. The plants were
chosen for study because they operated throughout
the year, used surface water as their source, and
served small populations. Profiles of the six plants
are contained in Table A-3; treatment processes are
described in Table A-4. Design capacities ranged
from 545.0 to 3,028.0 m3/day (144,000 to 800,000
GPD) and average daily flows ranged from 45.4 to
1,249.0 m3/day (12,000 to 330,000 GPD).
175
-------
Village of 100 Mile House
500
400
Number 3ฐฐ
of Cysts
200
100
0
oi
i
I
P
^ ^ H H
8 p ^K555p
a7-Nov-85 21-Jan-86 20-Mar-86 29-Apr-86 21-Jul-86
26-Aug-86 03-Nov-86
Figuro A-2. Glardla cysts In the raw water.
The survey examined samples for turbidity, total
coliforms, and chlorine residuals through the
collection of grab samples from the influent, effluent,
and distribution systems. Influent and effluent
turbidities are shown in Table A-5. Plants C, T, and
W consistently met the 1NTU standard, while plants
P, V, and M met the 1 NTU standard less than half
the time. This discrepancy in the latter plants was
due to:
* Inadequate design detention time
ป Inadequately trained operators
* Inadequate time allocated for the operation
* Periods of high influent turbidities for plants V
andM
After the appropriate adjustments were made to the
equipment and operations, plants P, V, and M met
the 1 NTU standard.
Time (Months)
A.3.2 Adsorption Clarifier Package Plants
This section contains descriptions of six facilities that
have used adsorption clarifier package plants. The
plant profiles and effluent data are from facilities in
Lake Arrowhead, California; Greenfield, Iowa;
Lewisburg, Virginia; Philomath, Oregon;
Harrisburg, Pennsylvania; and Red Lodge, Montana.
Lake Arrowhead, California (Hansen, 1987)
This case history involves a pilot study where
Giardio cysts were introduced into a water supply to
test the removal effectiveness of an adsorption
clarifier. The adsorption clarification/filtration pilot
plant had a 1.26 L/sec (20-GPM) capacity. The
concentration of Giarrfia introduced to the raw water
was 2,100 cysts per liter. The results of the pilot test
revealed that filtration removed 100 percent of the
cysts. Plant effluent turbidity ranged from 0.05 to
176
-------
Village of 100 Mile House
5-
4-
_ 3-
Jg
2 -
1 -
0 -
04-N
A
I i " i i i . i
ov-85 1 1 -Feb-86
Date
D Raw Water
Figure A-3. Average raw and filtered water turbidity.
Table A-3. Water Treatment Facilities Surveyed in Field
rH ^ ^
ill uu. Lu
*\-e-/ \^ \ /Ja-e~\ /~e~\
\ \ P \/ ii
^^A/^-^v^.
V
T 1 1 T | | | J 1 1 I 1 | 1 1 1 1
04-Jun-86 29-Sep-86
(months)
+ Filtered Water
Study
Manufacturer Design Flow Population Served/ Average Volume per Group Type of Distribution
Site Model, Year Rate GPM (L/s) No. of Meters Day, GPM (mt/d) Served Pipe Used Source
W Neptune Microfloc 200(12.6) 1,500/552
AQ-40, 1973
T Neptune Microfloc 200(12.6) 1,000/360
AQ-40, 1973 :
V Neptune Microfloc 200(12.6) /423
AQ-40, 1976
M Neptune Microfloc 560(35.3) /1.680
AQ-112, 1972
P Neptune Microfloc 100(6.31) /411
Water Boy, 1972
C Permulti 200(12.6) State park
Permajet, 1971
aPSD = Public Service District.
Source: Morand and Matthew (1 983).
110,000(0.42) City PVC Surface
impoundment
78,000(0.30) City PVC, cast iron, Surface
asbestos cement impoundment
72,000 (0.27) PSDa PVC River
330,000(1.25) PSD PVC River
82,000(0.31) PSD PVC Surface
impoundment
57,000 (0.22) State park Asbestos cement River
177
-------
Table A-4. Treatment Process Characteristics
Rapid Mix
Flocculation
Sedimentation
Filtration
Site
W
T
V
M
P
C
Prechemtea)
Addition
C1, alum,
soda ash
Cl.alum,
soda ash,
poly
C1, alum,
soda ash,
poly
C1, alum,
soda ash,
poly
C1 , alum,
soda ash,
carbon
(summer)
C1, alum,
soda ash,
poly
Type
In pipe
In pipe
In pipe
Chamber
Chamber
not used
In pipe
Detention
Time
(sec) Type
3 Paddle
3 Paddle
3 Paddle
30 Paddle
Paddle
Detention
Time
(min)
12.8
12.8
14
10
10
Upflow solids contact
rise rate -
1 GPM/H2
Loading
Type (GPM/ft2)
Tubes 1 00
Tubes 100
Tubes 100
Tubes 100
Tubes 150
2 hr detention time
Media
Mixed
anthracite,
silica sand,
garnet sand,
Mixed
anthracite,
silica sand,
garnet sand,
Mixed
anthracite,
silica sand,
garnet sand,
Mixed
anthracite,
silica sand,
garnet sand,
Mixed
anthracite,
silica sand,
garnet sand,
Silica Sand,
18 in.
9 in.
3 in.
18 in.
9 in.
3 in.
18 in.
9 in.
3 in.
18 in.
9 in.
3 in.
18 in.
9 in.
3 in.
24 in.
Rate
(GPM/ft2) Notes
5 Polymer
added before
tubes
5 Post-soda
ash
5 Post-sodium
hexameta-
phosphate
5
5
2 Soda ash
added before
filtration
GPM/ft2 - 0.679 L/sec/m2; 1 inch * 2.54 cm
Source: Morand and Matthew (1983).
0.06 NTU. Clarified effluent contained cysts when
effluent turbidity ranged up to 0.3 to 0.4 NTU.
Greenfield, Iowa (WEM, 1985)
This case history presents operating performance
data from a 0.044 m3/sec (1.0 MGD) plant between
July and December 1984. The plant's influent comes
from Lake Greenfield which contains turbidity, taste,
color, and iron contaminants. At the Greenfield
plant, powdered activated carbon is added to control
odor and taste problems. Table A-6 presents the
operating data for the plant. Pilot test turbidities
were similar to those from regular operational
experience, typically ranging from 0.3 to 0.5 NTU.
Alum dosages in the full-scale plant range from 7 to
20 mg/L, which are slightly lower than those
established in pilot tests.
Lewisburg, West Virginia (Lange et a/., 1985)
This case involves a 0.087 m3/sec (2-MGD) plant that
has operated since December 1983. Three months of
records on turbidity removal are contained in Table
A-7. The clarifier generally achieved 90 percent
turbidity removal. While turbidity ranged as high as
50 NTU in May 1985, the plant was able to produce
effluent with turbidities of less than 0.5 NTU at all
times.
Philomath, Oregon (Lange et at., 1985)
A 0.044 m3/sec (1.0-MGD) plant utilizing an
adsorption clarification unit began operation in
February 1986. Seven months of turbidity data and
chemical feed data are contained in Table A-8.
Influent turbidity ranged from 3.02 NTU to 26.7
NTU in February 1986. The system performed
effectively with filter effluent turbidity ranging from
0.17 to 0.26 NTU. Net water production did not fall
below 88 percent during this period.
Harrisburg, Pennsylvania (Lange et a/., 1985)
This example involves an existing plant that was
built in 1964 without sufficient clarifying capacity.
The original plant contained a circular upflow sludge
blanket clarifier and stored backwash gravity filters.
The system was operated in the direct filtration mode
at 2.7 L/sec/m2 (4 GPM/sq ft) because clarification
capacity was inadequate.
Three adsorption clarifier packaged units were added
to expand the plant to 0.394 m3/sec (9 MGD) with
each adsorption clarifier operating at between 6.79
and 10.19 L/sec/m2 (10 and 15 GPM/sq ft). Three
months of turbidity and chemical feed records are
found in Table A-9. Overall turbidity removal ranged
from 70 to 90 percent. The length of filter runs
doubled from 13 to 26 hours with the addition of the
178
-------
Table A-5. Turbidity Values (NTU)
Plant C Plant W
Plant T
Plant V
Plant M
PlantP
Raw
8.5
6.2
1.2
1.6
2.2
4.0
12.6
5.2
2.2
.2
Clean/veil
Effluent Raw
0.3
0.2 5.0
0.3 4.2
0.1 19.0
0.1 9.2
0.1 11.5
0.7 12.0
0.2 11.0
0.2 29.7
1.9
Clearwell
Effluent
0.9
0.3
0.4
0.8
2.0
0.3
0.2
0.3
0.9
Raw
10.0
8.0
6.0
3.2
3.2
3.2
5.8
10.4
3.4
12.8
Clearwell
Effluent
1.9
0.2
0.4
1.1
0.2
0.2
0.2
3.2
0.7
0.2
Clearwell
Raw Effluent
4.0
12.0
_a
35.0
42.0a
10.00
90.0a
28.0a
19.0a
13.0a
8.0a
6.0a
> 100.03
60.03
24.0
13.0
2.7
1.2
3.3
1.8
2.8
9.6
1.5
2.0
2.4
8.5
5.4
0.3
0.8
0.3
0.3
0.5
0.5
1.2
0.3
1.2
1.0
0.5
Raw
-
39.0
40.0
27.0
6.0
3.8
73.0
3.6a
3.8
47.03
70.03
25.03
> 100.03
> 100.03
8.53
4.3
4.03
9.6a
19.1
64.0
8.2
Clearwell
Effluent Raw
0.2 12.0
3.8 4.4
2.6
2.4 3.5
1.2 2.0
0.1 1.2
11.0 15.6
0.1 3.1
0.3 177
1.2 6.0
16.0
3.4
55.0
31.0
2.2
0.4
1.0
1.9
1.1
6.9
1.0
Clearwell
Effluent
0.8
2.4
7.0
1.5
0.1
0.5
9.7
2.2
0.5
aAveraged values for day.
Source: Morand and Matthew (1983).
Table A-6.
Month
Operating Data - Greenfield, IA
Turbidity, NTU
Raw
Clarifier
Filter
Iron, mg/L
Raw
Filter
Chemical Feed, mg/L
Alum
Polymer
Chlorine
Jul, 1984
Mean 5.9
Range 2.5-13.0
0.51
0.32-0.70
0.13
0.08-0.22
0.03
0.01-0.07
15.5
11.1-19.6
0.32
0.28-0.37
7.0
6.0-8.7
Aug. 1984
Mean 3.9
Range 2.5-6.0
1.26
0.46
0.39-0.62
0.18
0.07-0.32
0.03
0.0-0.04
12.2
8.9-23.9
0.32
0.16-0.48
3.9
2.3-5.6
Sep. 1984
Mean 4.4
Range 3.6-5.3
0.39
0.36-0.60
0.14
0.10-0.24
0.02
0.01-0.03
0.02
8.4
6.9-12.9
0.35
0.32-0.37
7.8
7.4-8.1
Oct,1984 Mean 6.3 2.3 0.40 0.21
Range 4.0-8.2 1.8-2.9 0.26-0.56 0.14-0.29
0.20
0.13-0.26
o.Ts""
5.9
3.7-7.4
"I!
Nov. 1984
~DeO984~
Mean 6.4 2.3 0.33 0.20 0.01 13.1
Range 4.2-13.0 2.0-2.5 0.17-0.47 0.14-0.33 0.01-0.02 7.3-22.3
Mean
Range
2.8
1.8-7.5
1.7
1.6-2.0
0.35
0.27-0.48
0.11
0.02-0.17
0.01
0.00-0.03
10.2
8.3-14.6
0.22
0.17-0.25
2.5
2.1-2.8
adsorption clarifiers, in spite of the 20 to 30 percent
increase in flow.
Red Lodge, Montana (Lange et a/., 1985)
This case involves installing a new 0.061 m3/sec (1.4-
MGD) plant starting up in January 1984. Prior to
construction, the water was only chlorinated because
of its high quality. Because the raw water turbidity is
so low, the plant is equipped with a bentonite feed
system to assist in the treatment of the plant's
typically cold, low turbidity (less than 1 NTU)
influent. Bentonite is added to the influent before the
alum and polymer feed points. The treatment goal is
to produce effluent with less than 0.1 NTU turbidity
to guard against Giardia breakthrough. As Table A-
179
-------
Table A-7. Operating Data - Lewisburg, wv
Turbidity, NTU
Month
Dec, 1984
May, 1985
Jun, 1985
Mean
Range
Mean
Range
Mean
Range
Clarifier
Influent
5.0
1.8-18
9.6
2.0-5.0
1.7
0,70-5.0
Clarifier
Effluent
1.2
0.6-2.5
1.0
0.4-6.0
0.60
0.1-1.1
Filter Effluent
0.16
0.10-0.20
0.18
0.10-0.50
0.16
0.10-0.50
Table A-8.
Operating Data - Philomath, OR
(Monthly Average Values)
Turbidity, NTU
Month
Fob,
1986
Mar,
1986
Apr,
1986
May,
1986
Jun,
1986
Juf,
1886
Aug,
1986
Raw
26.7
6.50
6.27
5.82
4.25
3.43
3.02
Clarifier
3.40
1.67
1.49
1.45
1.21
_
-
Filter
_
0.17
0.20
0.23
0.14
0.22
0.26
Chemical Feed, mg/L
Alum Soda Ash
15.5 21.2
11.4 4.5
_ _
11.7 1.2
11.3 4.8
10.0 5.7
16.6
Polymer
0.29
0.08
_
0.08
0.07
0.07
0.07
Net
Produc-
tion3
_
91%
90%
88%
93%
93%
93%
Net production is the percentage of raw water that was turned into
finished water.
10 indicates, the plant achieved its turbidity goal for
the entire 6-month period over which data were
collected. It should be noted that the turbidity of the
clarifier effluent is sometimes higher than that of the
raw water influent due to occasional carryover of
alum-coagulated bentonite particulates.
A.4 Dlatomaceous Earth Filters
A.4.1 Colorado State University Study
(Lange et al., 1984)
The study examined Giardia inactivation in addition
to removal of turbidity, total coliform bacteria,
standard plate count bacteria, and particles. Eight
operational parameters evaluated for their influence
on removal effectiveness were:
Seven grades of diatomaceous earth
Hydraulic loading rates of 0.68,1.36, and 2.72
L/sec/m2 (1,2, and 4 GPM/ft2)
Influent temperatures, ranging from 5 to 19ฐC
Influent concentrations of bacteria, ranging from
100 to 10,000 per 100 mL
Influent concentrations of Giardia cysts, ranging
from 50 to 5,000 cysts per liter
Filter headless rates
Filter run times
Alum coating of the diatomaceous earth
The results of the study indicated that Giardia
removal exceeded 99 percent for all grades of
diatomaceous earth at filter hydraulic loadings of
0.68 to 2.72 L/sec/m2 (1.0 to 4.0 GPM/sq ft), and at all
study temperatures.
In addition, the grade of diatomaceous earth affected
the removal rates of other contaminants. The
coarsest grade of material achieved removal of 99.9
percent of the Giardia, 95 percent of the cyst-sized
particles, 20 to 35 percent of the coliform bacteria, 40
to 70 percent of the heterotrophic bacteria, and 12 to
16 percent of the turbidity. The finest grade of
diatomaceous earth achieved the removal of 99.9
percent of the bacteria and 98 percent of the
turbidity.
A.4.2 Mclndoe Falls, Vermont (Pyper, 1985)
This case involves an evaluation of the parallel
operation of a diatomaceous earth and a slow sand
filter. The diatoma.ceous earth filter rate ranged from
0.68 to 1.22 L/sec/m.2 (1.0 to 1.8 GPM/sq ft), using a
0.63 to 1.26 L/sec/r.n2 (10 to 20 GPM) pressure unit.
The pressure diatomaceous earth filters dependably
removed 99.97 percent of the Giardia cysts and 86
percent of the coliforms. They also achieved 80
percent standard plate count bacteria removal in 70
percent of the samples. The average influent
contained 271 total bacteria count per 100 mL and 30
standard plate count bacteria per mL. The average
effluent contained 38 total bacteria count per 100 mL
and 6 standard plate count bacteria per mL.
A.5 Selecting a Filtration System
A.5.1 Lake County, California (Conley and
Hansen, 1987)
This case study concerns the process of selecting a
centralized new treatment facility for an area that
was previously served by individual supplies. Clear
Lake, the source of raw water, experiences severe
seasonal taste and odor problems caused by blue-
green algae blooms (Microcystis and Anabaena).
Clear Lake is classified as eutrophic. The taste and
odor problems typically start in May and finish in
November with lake water taste and threshold odor
numbers (TON) ranging as high as 10 during this
period. Clear Lake's turbidity ranges from 3 to 90
NTU. Clear Lake has excellent mineral qualities, as
180
-------
Table A-9.
Month
Jul, 1985
Aug, 1985
Sep, 1985
Operating Data - Harrisburg, PA
Turbidity, NTU
Mean
Range
Mean
Range
Mean
Range
Raw
8.1
5.7-15.1
8.6
4.8-14.3
9.3
5.9-37
Clarifier
1.36
0.60-3.4
0.94
0.7-1.5
1.2
0.5-4.9
Filter
0.17
0.13-0.32
0.18
0.13-0.25
0.18
0.09-0.34
Chemical
Alum
NA
11
8.1-13.4
9
4.9-18.7
Feed mg/L
Polymer
NA
0.12
0.10-0.15
0.07
0-0.31
Clarifier Rate
GPM/ft2
NA
14
13
11.7-14.9
GPM/ft2 = 0.679 L/sec/m2
NA = not available
Table A-10.
Month
Jan, 1985
Feb. 1985
Mar, 1985
Apr, 1985
May, 1985
Jun, 1985
Operating Data - Red
Mean
Range
Mean
Range
Mean
Range
Mean
Range
Mean
Range
Mean
Range
Raw
0.20
0.15-0.33
0.19
0.16-0.21
0.20
0.18-0.22
1.1
0.22-1.6
2.1
0.16-4.5
3.5
1.5-6.2
Lodge, MT
Turbidity, NTU
Clarifier
0.29
0.21-0.35
0.28
0.22-0.39
0.29
0.25-0.32
0.49
0.27-1.1
0.41
0.16-0.80
0.41
0.21-0.75
Chemical Feed
Filter
0.04
0.03-0.05
0.05
0.30-0.07
0.05
0.03-0.06
0.08
0.04-0.14
0.07
0.03-0.14
0.07
0.04-0.18
Alum
2.5
1.4-3.5
2.3
1.4-3.6
3.0
1.9-3.9
5.0
2.3-7.1
7.3
3.6-13.4
10.4
7.4-12.8
Polymer
0.48
0.48-0.48
0.48
0.48-0.48
0.48
0.48-0.48
0.60
0.48-0.75
0.48
0.48-0.48
0.60
0.48-0.75
mg/L Water Temperature
Bentonite
0.93
0.93-0.93
0.93
0.93-0.93
0.93
0.93-0.93
0
0
0
ฐF
36
34-38
34
33-38
36
35-37
40
38-43
44
43-47
45
43-49
ฐC = (ฐF - 32) x 5/9
shown in Table A-ll, but the lake water requires
turbidity removal, taste control, and odor control.
Several other jurisdictions in addition to Lake
County use Clear Lake for a water supply.
Consequently, there were data available from other
operations using the same influent. One of these
neighboring jurisdictions, the City of Lakeport,
installed a plant equipped with both ozone and
activated carbon, which effectively manages the odor
and taste problems.
A feasibility study recommended a complete
treatment system rated at 0.088m3/sec (2 MGD) with
preozonation, chemical coagulation, pH control,
floeculation, sedimentation, filtration, and
postfiltration. A suitable package plant was selected
as the most cost-effective choice.
The selected package plant required pilot tests for
establishing process feasibility and design criteria.
Four utilities were contacted with regard to their
experiences before pilot testing commenced. The
utilities reported that taste and odor had been
increasingly troublesome, and they described rising
Table A-11. Clear Lake Water Quality Analysis
Concentrations, mg/L
Mineral Constituents
Calcium
Magnesium
Sodium
Potassium
Bicarbonate
Sulfate
Chloride
Nitrate
Fluoride
Boron
Silica
Hardness
Turbidity
High
30
21
14
2.8
212
35
10
11
0.4
1.2
34
158
90T(Ja
Low
17
9.8
4
0.1
96
5.1
3.2
0.0
0.0
0.1
0.7
78
3TU
Median
23
15
10
2.0
145
9
6
1.6
0.1
0.7
14
115
15 TU
^Turbidity Units
floe problems due to air bubbles introduced by algae.
In addition, algae blooms had interfered with the
clarification process. Water quality data from
181
-------
January 1977 to November 1980 for a sampling
station on Clear Lake is summarized in Table A-12.
The odor and taste problems had been successfully
treated by the other utilities with potassium
permanganate and powdered activated carbon.
However, the two utilities using ozone received the
fewest complaints. Also, some utilities had recently
installed postfilter granular activated carbon
contactors.
As a result of reviewing the existing data, Lake
County decided to install adsorption clarifiers as a
prefiltration step. The adsorption clarifier uses an
upflow design with a buoyant medium to assist the
clarification process.
The manufacturer was requested to perform the pilot
tests. The two primary test objectives were to:
Measure turbidity removal capabilities
Determine the effectiveness of adding potassium
permanganate or powdered activated carbon
prior to clarification to remove trihalomethane
(THM) precursors, taste substances, and odor
substances
If the pilot tests were successful, the utility would be
able to avoid the expensive option of using ozone
treatment to control taste and odor.
The tests were performed during September and
October of 1986 and verified by a design consultant.
There were no major algae blooms during the test
period.
The pilot test report indicated that the new plant
could remove a high percentage of turbidity.
Furthermore, low concentrations of potassium
permanganate could be used to control taste and odor
substances. In addition, the powdered activated
carbon assisted in the removal of THM precursors.
The report indicated that the adsorption clarifiers
were effective at dosages of up to 25 mg/L, with no
filter breakthroughs or short filter cycles.
Based on the pilot test results, an adsorption clarifier
package plant and chemical feed system were
recommended. The adsorption clarifier will have a
design loading of 6.79 L/sec/m2 (10 GPM/sq ft), a
filtration rate of 3.4 L/sec/m2 (5 GPM/sq ft), and a tri-
mixed filter media. The chemical feed system will use
the following chemical dosages:
1 to 2 mg/L of ozone
10 to 20 mg/L of alum
0.2 to 1.0 mg/L of potassium permanganate
1 to 10 mg/L of cationic polymer
10 to 20 mg/L of powdered activated carbon
0.1 to 0.5 mg/L of nonionic polymer
20 to 40 mg/L of sodium hydroxide
182
-------
Table A-12. Clear Lake Water Quality at DWR Sampling Station No. 1 at Lakeport
Date Turbidity Sp. Cond. DO Sodium Alkalinity Chloride Nitrates
Sampled (NTU) (uMHOS/cm) pH (mg/L) (mg/L) (CaCO3) (mg/L) (mg/L)
1/7/77
2/3/77
3/10/77
4/7/77
5/5/77
6/16/77
7/14/77
8/11/77
9/22/77
10/14/77
11/4/77
12/9/77
1/6/78
2/10/78
3/9/78
4/6/78
5/11/78
6/8/78
7/13/78
8/10/78
9/14/78
10/5/78
1 1/9/78
12/7/78
1/5/79
2/16/79
3/15/79
4/5/79
5/10/79
6/8/79
7/12/79
8/10/79
9/7/79
10/4/79
11/8/79
12/7/79
1/11/80
2/6/80
3/6/80
4/10/80
5/8/80
6/6/80
7/11/80
8/22/80
9/18/80
10/15/80
11/13/80
21
9
25
18
14
35
14
7
60
50
33
36
67
49
20
13
6
3
3
7
18
12
22
20
21
18
12
20
8
5
6
4
13
17
28
19
28
17
3
19
3
6
5
5
12
9
13
307
308
308
316
321
337
346
302
364
385
373
366
193
197
216
223
227
225
238
258
271
275
290
294
299
255
281
260
259
284
291
304
311
320
299
299
260
245
228
235
236
246
263
268
280
185
256
8.3
8.1
7.7
8.1
8.0
7.8
8.0
8.0
8.2
8.1
8.3
8.2
7.3
7.6
7.6
7.6
8.2
8.2
8.1
7.8
7.8
8.4
7.5
7.7
7.8
7.7
7.2
8.1
8.2
7.8
8.1
8.0
8.1
8.6
7.7
7.5
8.3
7.9
7.7
7.7
8.1
8.1
8.1
7.9
8.3
8.3
8.4
9.9 13 142 6.8 0.25
11.8 13 144 7.0 0.14
9.2 12 144 6.6 0.12
7.7 12 147 6.4 0.69
9.1 14 156 6.5 0.01
4.5 14 154 7.9 0.05
5.0 14 160 8.8
4.3 16 138 9.6 0.04
2.6 17 165 8.8 0.05
3.6 17 170 10 0.01
5.7 16 174 7.7 0.14
6.8 16 169 8.5 0.17
9.7
10.0
9.1
9.1
10.4
6.9
8.1
5.9
7.0
10.6
4.3
9.5
10.4 13 138 8.1
10.4
6.7
10.2
9.9
7.0
7.0 12 130 6.0
5.8
5.3 13 143 6.0
7.0
8.5
7.1
10.2
10.3
9.8
9.6
8.8
8.5
7.7 10
6.7
4.8
7.1
9.1
Ortho Po4
(mg/L)
0.05
0.00
0.01
0.00
0.00
0.00
0.09
0.08
0.03
0.02
0.02
0.08
N.D.
183
-------
-------
Appendix B
Case Histories of Emerging Disinfection
Technologies
Several case histories of water supply systems that
have used disinfectants other than chlorine are
presented in this appendix. The descriptions of each
case include the modifications in disinfection/oxida-
tion techniques necessary to (1) attain the desired
degree of disinfection while minimizing the
formation of disinfection by-products; and (2) cope
with other common problems such as taste, odor,
color, and algae.
The case histories cover ozone, ultraviolet radiation,
chlorine dioxide, and chloramine. Section B.I
presents case histories involving the use of ozone as a
primary disinfectant and as a preoxidant for lowering
THM levels. Section B.2 illustrates the use of
ultraviolet radiation as a primary disinfectant for
surface water followed by chlorination. Three case
studies involving the uses of chlorine dioxide as a
preoxidant for THM control, as a primary and
secondary disinfectant, and in combination with
chloramines to lower THM production are presented
in Section B.3. Lastly, chloramine case histories are
presented in Section B.4.
B.1 Ozone Case Histories
B.1.1 Primary Disinfection with Ozone: North
Andover, Massachusetts
Under normal circumstances, total coliforms in
North Andover's raw water supply, Lake
Cochichewick, are between 50 and 500 per 100 mL
and turbidity is between 1 and 2 NTU. However, in
early 1986,18 cases of Giardiasis were reported.
Residents were instructed to boil tap water for at
least 5 minutes before use, while public health
officials sought to locate and correct the problem.
The raw water was found to contain Giardia cysts in
samples taken in April 1986. In addition to the
concern that residential septic systems were affecting
the water supply, local officials found that the lake's
watershed had a large muskrat population.
At the time of the Giardiasis outbreak, treatment of
North Andover water included chlorination without
filtration. Two pumping stations distributed the
water through the piping system, each station
handling 0.12 to 0.13m3/sec (2.5 to 3 MGD). Over the
years, the distribution pipes have formed substantial
biofilm and scale, due to high humic concentrations
in the water.
Increased chlorination overcame the immediate
Giardia problem, but subsequent descaling of the
distribution pipes released coliform organisms to the
water. The State Department of Environmental
Quality Engineering (DEQE) had to continue the
"boil water" notice. In addition, THM levels rose to
above 200/p.g/L due to the increased chlorination, and
residents began complaining about the strong
chlorine concentrations. Thus, ozone was
investigated as an alternative primary disinfectant.
Interim Solution
In October 1986, ozonation systems, rented from an
equipment supplier, began operating at both Lake
Cochichewick pumping stations. One system had a
22.7-kg/day (50-lb/day) ozone generating capacity
and the second had a 68.04-kg/day (150-lb/day)
capacity. When the efficacy of ozonation was proven,
the town purchased and installed two 68.04-kg/day
(150-lb/day) ozonation systems, one at each pumping
station. At four points in the distribution system,
chlorine was added to provide a residual disinfectant.
These two ozonation systems were installed as a stop-
gap measure to control Giardia cysts until a proposed
$10.5 million 0.53 m3/sec (12-MGD) plant was
designed and constructed. The new plant, to be on
line in 1991, will provide complete treatment,
185
-------
including ozonation, filtration, and postfiltration
GAG adsorption with residual chlorination.
The State Department of Environmental Quality
Engineering (DEQE) provided emergency funding of
$2.5 million for installing the interim ozonation
systems, connecting pipelines to the three
neighboring communities, relining pipes with
cement, and replacing water mains. Annual rental
fees for the two ozonation systems were
approximately $90,000. The two 68.04-kg/day (150
Ib/day) ozonation systems were purchased for
$325,000 (total). This price included the air
preparation systems, ozone generators, diffuser
contactors, and ozone destruction equipment; plus the
appropriate instrumentation, including a residual
ozone monitor for the outlet of the contact chamber.
Each of the purchased contacting chambers is 3 m (10
ft) wide, 6 m (20 ft) long, and 4.8 m (16 ft) deep. The
contactors have five baffled sections to which equal
amounts of ozone are applied. Plug flow is
maintained throughout the ozone contactors. Applied
ozone dosages are 5 mg/L and the dissolved ozone
concentration at the outlet of each contact chamber is
between 0.9 and 1.0 mg/L. For design purposes, the
average ozone concentration in each contactor was
assumed to be 0.5 mg/L. Total residence time of water
in the contactors is 10 minutes during the summer at
full pumping rate. During the winter, when pumping
rates are reduced by 50 percent, the residence time is
20 minutes.
Water temperatures of the lake vary from about 5ฐC
(41ฐF) in winter to just under 20ฐC (68ฐF) during the
summer. Therefore, the appropriate CT values for
99.9 percent inactivation ofGiardiaJamblia range
from 1.9 to 0.72 mg/L-min. During the summer, the
period when the shortest contact time is experienced,
at an average dissolved ozone concentration of 0.5
mg/L, a TIO contact time of 5 minutes (50 percent of
the peak-flow hydraulic detention time) would attain
a CT value of 2.5 mg/L-min, which is more than
adequate. During winter (Tio = 10 min), the CT will
be 5 mg/L-min.
The Results
After approximately 90 days of ozone treatment, the
State DEQE unconditionally lifted the "boil water"
order, which had been in effect for 9 months. Both
Giardia cysts and coliform organisms were
eliminated from the North Andover water supply.
In addition to the microorganism control, several
other benefits resulted from use of ozonation. Prior to
the outbreak problem, THM values ranged from 8 to
120 pg/L. Since ozonation, measured THM levels
range from 1.1 to 2 pg/L. In addition, the color of the
treated water has improved significantly (65 to 95
percent lower) and taste and odor of the finished
water greatly improved.
Permanent Solution
The planned 0.53 m3/sec (12-MGD) treatment plant
will include ozonation, filtration, and postfiltration
GAC adsorption, followed by secondary disinfection.
Preozonation will be applied before rapid mix and
filtration. After dual media filtration, GAC
adsorption is incorporated, followed by chlorination
for secondary disinfection. In addition to providing
additional removal of contaminants, the GAC step
will allow mineralisation of much of the
biodegradable organic fractions of the water.
B.1.2 Preozonation for THM Control:
Kennewick, Washington (Cryer, 1986)
Prior to 1977, the City of Kennewick drew its water
supply from a system of five Ranney collectors located
in the Columbia River. The water was chlorinated
before distribution. When installed, this system was
capable of producing approximately 0.876 m3/sec (20
MGD); however, its output deteriorated to about
0.657 m3/sec (15 MGD) by 1977. By 1978, peak water
demand reached the capacity of the system. It was
determined that direct utilization of the Columbia
River would be the only long-term reliable water
source.
Since the raw water would be drawn directly from the
river, additional treatment was necessary to
maintain finished water quality. A pilot plant study
was undertaken to test alternative water treatment
processing steps. This study included the use of
preozonation and conventional postfiltration GAC
adsorption, in addition to conventional and direct
filtration procedures.
Average values of the raw water quality parameters
of the Columbia River are:
TTHM -1 ug/L
TTHM Formation Potential -136 ug/L (7 days
chlorine contact time)
TOC - 2.4 mg/L
No. Particles - 11,650/mL
Particle Volume -160,700 nL/L
Turbidity-1.7 NTU
In the pilot study, the preozonation and
coagulation/filtration steps each provided
approximately 30 percent reduction in TTHM
formation potential (TTHMFP) levels and 10 percent
reduction in TOC levels. The combined processes
gave approximately 60 percent reduction in levels of
TTHMFP and 20 percent reduction in TOC levels.
The preozonation, coagulation, and filtration steps
combined were determined to be operationally
equivalent to activated carbon adsorption for the
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removal of THM precursors; the process was also
determined to be the most cost-effective method of
treating organics in the Columbia River water
supply.
Solution
A 1.314-m3/sec (30-MGD) water treatment plant was
constructed in four stages, adding 0.329m3/sec (7.5
MOD) capacity in each stage. The new plant includes
preozonation, flash mix, coagulation, flocculation,
filtration, and postchlorination. Design criteria for
the preozonation facilities are given in Table B-l.
Table B-1. Design Criteria for Kennewick Water
Treatment Plant Preozonation Facilities
Design Criteria
Hem
Units
Initial
Ultimate
Plant Capacity
Ozone Contact
Basins
No. of basins
Detention time at
design flow
Basin dimensions r
inside
Average water depth
Basin volume
Total basin volume
Chemical Feed Rate
(max. dosage at
design flow)
Chemical Feeders
Chemical Storage
Capacity
Number of Ozone
Generators
MOD
cfs
GPM
mm
ft
ft
gal
Ib/day
Ib/day
7.5
11.6
5,200
4
10
14 x 8
16
1,792
13,400
7,168
250
2 X 125
250
2
30.0
46.41
20,800
16
10
14 X 8
16
1,792
13,400
28,672
1,000
3 X 250
2 X 125
1,000
1 pound = 0.4536 kilograms; 1 MGD = 0.044 m3/sec;
1 GPM = 0.063 L/sec; 1 foot = 0.3 meters; 1 ft3 = 0.0283
m3.
At the point of application, ozone dosages averaged
1.5 mg/L and peaked at 4.0 mg/L. The contactors
provide 10 minutes of detention time. Raw water
total coliform levels are consistently less than 50 per
100 mL. Raw water turbidities range from 1.5 to 2.0
NTU.
The new 0.329-m3/sec (7.5-MGD) direct filtration
treatment plant operates from May through October,
when system demand exceeds the capacity of the
Ranney collector system. The collector system is still
used because it operates at lower cost than the new
treatment plant. Generally, the service area
customers have been satisfied with the quality of
water provided. Judging from the limited number of
complaints, the treated river water has a higher
customer acceptance than the water from the Ranney
collector. Water quality from the collector system is
not very different from the raw water from the
Columbia River.
THM analyses indicate that the treated water from
the new plant has average TTHM concentrations of
approximately 14 ug/L, while the water from the
Ranney collector averages approximately 107 ug/L
TTHM.
Applied Ozone Dosages
Applied ozone dosage rates have ranged from 1.7 to
2.5 mg/L. Until 1983, ozone residual levels at the
contactor outlet were maintained at approximately
0.5 mg/L. In 1983, the city installed a dissolved ozone
analyzer to control the ozone dosage, which has
lowered the dissolved ozone residual concentrations
to 0.1 mg/L, thus saving ozone, and still controlling
biological growth in the filters and basins prior to
chlorination.
Assuming an ozone concentration of 0.1 mg/L is
present throughout the 10-minute hydraulic contact
time (Tin - 5 min), a CT value of 0.5 mg/L-min is
obtained. Since the treatment process includes
filtration, which provides a 2-log reduction of Giardia
cysts, only 1 additional log reduction is required to
meet the disinfection requirements of the Surface
Water Treatment Rule. The CT value attained by
ozonation (0.5 mg/L-min) is less than the 1-log
reduction requirement at 5ฐC (0.63 mg/L-min) but
provides at least 80 percent of the required
disinfection. In addition, the 60-minute chlorine
contact time (at pH 8.0) for secondary disinfection,
provides an additional 36 percent of the required
disinfection. Consequently, the combined disinfection
with ozone and free chlorine provides at least 116
percent of the primary disinfection required by the
Surface Water Treatment Rule.
System Operation
Operationally, the ozone generation equipment has
performed very well. The compressors have required
only preventive maintenance. The ozone generators
required the replacement of only three burned out
tubes during the first 6 years of operation. The major
maintenance problem appears to be tube fouling
caused by excessive moisture in the feed gas. This
situation was caused by two factors. First, after
several years of operation, the refrigerant air dryer
unit had developed a small leak, which reduced the
effectiveness of the air preparation system. Second,
the absorptive medium in the desiccant drier should
have been replaced when its regeneration capacity
was reduced to 40 percent of its original capacity.
Cleaning of dielectric tubes has become an annual
maintenance procedure.
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The only other significant operational problem
concerned the ozone contactors. Excess foaming and
scum production can occur during spring and late
summer, primarily caused by algae destruction. This
problem was remedied by installing surface
skimmers and froth spray equipment. In addition,
the stainless steel tubes holding the ceramic diffusers
corrode after about 2 to 3 years of use, and must be
checked and occasionally replaced when the diffusers
are cleaned.
System Costs
Ozone generation efficiency has averaged
approximately 35.3 to 37.5 kWh/kg (16 to 17 kWh/lb)
of ozone produced. Based on qualitative observation,
the addition of ozone prior to flocculation and
filtration results in a 10 percent reduction in the
amount of flocculants. In 1987, the treatment plant
was producing finished water at a cost of
approximately $3.73/1,000 m3 ($14.10/mil gal).
B.2 UV Radiation Case Histories
B.2.1 Ultraviolet Radiation for Primary
Disinfection: Fort Benton, Montana
The city of Fort Benton, Montana, obtains drinking
water from the Missouri River. The then current
filtration plant (20 to 30 years old) was in need of
upgrading. Rather than building a new filtration
plant, the city built a new 0.088m3/sec (2-MGD)
treatment plant in 1987. Water is drawn through
Ranney collectors installed 6 to 7.5 m (20 to 25 ft)
below the river bed, a system that allows the river
bed to naturally filter the raw water. Turbidities of
water entering the treatment plant average 0.08
NTU. No Giardia cysts have been found in the water
from the Ranney collectors.
The water is treated with U V radiation for primary
disinfection, then chlorinated for secondary
disinfection. An applied chlorine dosage of only about
1 mg/L is necessary. The entire water treatment
system is housed in a 2.97-m2 (32-sq ft) building.
The UV disinfection system consists of six irradiation
chambers, two control cabinets with alarms, chart
recorders, relays, hour-run meters, lamp and power
on-lights, six thermostats, electrical door interlocks,
mimic diagrams, and six UV intensity monitors
measuring total U V output. Each irradiation
chamber contains one 2.5-kW mercury vapor,
medium-pressure arc tube, generating UV radiation
at 253.7 nm.
The initial UV dosage is 41,000 uW sec/cm2 at
maximum water flow 104 L/sec (1,650 gal/min)
through each irradiation unit. Expected arc tube life
is 4,500 operating hours, providing a minimum UV
dosage of 25,000 uW sec/cm2. These conditions are
designed to reduce concentrations of Escherichia coli
organisms by a minimum of 5 logs (105 reduction).
The system is equipped with a telemetry control
system and fully automated backup system. Each
bank of three irradiation chambers has two units on
line at all times, with the third unit serving as
backup. In the event that the UV intensity drops
below acceptable limits (20,000 uW sec/cm2) in any of
the chambers, the automatic butterfly valve will
close, stopping flow through the chamber; at that
time, the automatic butterfly valve on the standby
unit will open. The alarm system also is activated if
UV intensity drops below acceptable limits in any of
the chambers. The UV alarm system is interfaced
with the automatic dialer and alarm system.
In 1987, total equipment costs for the six-unit UV
irradiation system with butterfly valves was $74,587.
EPA's latest Draft Guidance Manual for compliance
with disinfection requirements (EPA, 1989a)
contains "CT Values" for inactivation of viruses by
UV radiation independent of temperature:
Log Virus Inactivation
CT Values by UV
(mW-sec/cm2)
2.0
3.0
21
36
For the UV facility at Ft. Benton, the initial UV
dosage of 41 mW-sec/cm2 provides well in excess of 3
logs inactivation of viruses. However, after 4,500
hours of UV tube operation, the anticipated decrease
in UV dosage (to 25 inW-sec/cm2) will provide only 2
logs of viral inactivation.
B.3 Chlorine Dioxide Case Histories
B.3.1 Predisinfection for THM Control:
Evansville, Indiana (Lykins and Griese,
1986)
In order to comply with the November 1979
Amendments to the National Interim Primary
Drinking Water Regulations, the Evansville Water
and Sewer Utility had to reduce THM levels in
drinking water. At the time, raw water was
chlorinated, treated with alum prior to primary
settling, treated with lime to raise the pH to 8, passed
through secondary settling, fluoridated, filtered
through rapid sand, and finally postchlorinated.
These processes were conductedin two 1.31-m3/sec
(30-MGD) treatment trains. THM levels exceeded the
THM standard of 100 ug/L. Prechlorination doses
averaged 6 mg/L and distribution system residence
time averaged 3 days.
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Pilot Plant Study
With EPA's assistance, research evaluating the use
of chlorine dioxide as an alternate disinfectant was
initiated in a 6.3-L/sec (100-gal/min) pilot plant. One
train of the adjacent full-scale treatment plant served
as the control for the pilot plant study.
In the first phase of the study, chlorine dioxide was
substituted for postchlorination. The water treated
with chlorine dioxide was stored 3 days to simulate
the distribution system residence time. TTHM
concentrations were much lower using chlorine
dioxide postdisinfection, 1.2 ug/L (1.9 mg/L residual)
as compared with 141 ug/L (2.5 mg/L residual) using
chlorine postdisinfection.
Predisinfection with chlorine dioxide to maintain a
residual through the pilot plant did not increase the
THM concentration and provided adequate
disinfection. The chlorine dioxide residual decreased
from 4 to 0.3 mg/L through the pilot plant.
In the second phase of the study, the pilot plant
procedures were evaluated throughout the year to
determine the extent of seasonal effects. In this
phase, predisinfection with chlorine dioxide (1.1
mg/L average applied dosage) reduced the amount of
THMs formed during postchlorination by
approximately 60 percent. The idea of postdisinfec-
ting with chlorine dioxide was abandoned because of
the difficulty in maintaining an adequate residual in
the distribution system while meeting the current
EPA recommendation for total oxidant concentra-
tions from chlorine dioxide (1 mg/L maximum). The
average chlorine residual concentration in the
clear well was 2.1 mg/L.
Plant Modifications
Based on data obtained from the pilot plant study,
changing the primary disinfectant from chlorine to
chlorine dioxide was judged to be the most effective,
lowest cost procedure for meeting the THM standard.
A separate building was constructed to house the
chlorine dioxide generator and two 907.2-kg (1-ton)
cylinders of chlorine. The installation is capable of
generating 6.46 kg (14.24 Ib) of chlorine dioxide per
hour, which can be divided in any proportion between
the two halves of the treatment plant. Gaseous
chlorine and 25 percent sodium chlorite solution are
delivered to the chlorine dioxide reactor under partial
vacuum generated by an eductor. Both reagent flows
are controlled by flow rate meters, and the system is
designed to shut down if the eductor water supply
fails or if chemical feed lines break.
Operating Experience
During the first 5 months of use, various chlorine
dioxide dosages were used to determine the optimum
dosage for maximum reductions in THMs and the
portion of the total dosage that would appear as an
oxidant residual in the finished water. A general
review of system operations was conducted at the
same time.
During this period, operators encountered only one
major problem. The concentrated disinfectant
oxidized the brass corporation cocks used to connect
the PVC chlorine dioxide feed lines to the water
influent piping. This oxidation and subsequent
leaking of chlorine dioxide solution temporarily
disrupted operations. The problem was resolved by
sliding a section of PVC pipe through new
corporation cocks into the main stream of the raw
water lines. This modification permitted the PVC
piping to serve as an inductor, while preventing
direct contact of the brass corporation cocks with
concentrated chlorine dioxide solution.
Since the implementation of the new chlorine dioxide
system, total oxidant levels from chlorine dioxide
have been maintained consistently below the 1.0
mg/L recommended by EPA. With an average applied
chlorine dioxide pretreatment dosage of 1.2 mg/L,
total oxidant concentrations in the finished water
have averaged 0.5 mg/L. These data show that
approximately 42 percent of the chlorine dioxide
dosage remains as total oxidant. In addition, the new
system maintains TTHM levels in the distribution
system between 50 and 80 ug/L.
B.3.2 Primary and Secondary Disinfection
with Chlorine Dioxide: Hamilton, Ohio
(Augenstein, 1974; Miller et al., 1978;
U.S. EPA, 1983)
In 1956, a 0.657-m3/sec (15-MGD) lime-softening
ground water treatment plant began operating in
Hamilton, Ohio (18 wells, 60-m [200-ft] deep).
Chlorine was used as the sole disinfectant when the
plant opened. Because of customer complaints of
chlorinous tastes and odors, however, chlorine
dioxide was tested and then substituted for chlorine
in 1972 as a primary and secondary disinfectant.
Hamilton's treatment process now includes aeration,
lime addition, flash mixing, sedimentation,
recarbonation (with food-grade carbon dioxide),
filtration, fluoridation (sodium silicofluoride),
chlorine dioxide for primary and secondary
disinfection, and clearwell storage. Raw water
turbidities are below 1 NTU, and raw water total
coliforms are less than 1 per 100 mL.
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Generation of Chlorine Dioxide
Chlorine dioxide is generated by mixing 37 percent
aqueous sodium chlorite and aqueous chlorine in a
ratio of 1:1 by weight, 0.24 g of each reagent/m3 of
water to be disinfected (2 Ib of each reagent/mil gal
water). This provides an applied chlorine dioxide
dosage of 0.25 mg/L. The residual leaving the
clearwell is approximately 0.15 mg/L, and is 0.10
mg/L at the extremities of the distribution system.
The generation system consists of one plant-
fabricated reactor vessel for chlorine dioxide
production, one peristaltic pump for sodium chlorite
solution, and two chlorinators (one serves as a
standby). Aqueous sodium chlorite solution (37
percent) is delivered in 90.72-kg (200-lb) drums.
Chlorine gas is delivered to the site in 68-kg (150-lb)
cylinders, and two 68 kg (150-lb) liquid chlorine
cylinders are positioned next to the chlorinators. The
weight of the cylinder contents is measured by a
scale. Switching over from one cylinder to the other is
conducted manually. PVC tubing connects the
chlorinator and chlorine dioxide reactor vessel; heavy
Tygon tubing transports the sodium chlorite solution
from the drum to a small plastic day-tank and the
reactor. After about 1 month, the Tygon tubing loses
its rigidity and must be replaced. The semi-
transparent day-tank allows visual inspection of the
sodium chlorite level, thus enabling the operator to
maintain an acceptable suction head on the
peristaltic pump.
The chlorine dioxide reactor vessel is constructed of
Schedule 80 PVC piping, 45.72 cm (18 in) high and
approximately 15.24 cm (6 in) in diameter. The vessel
is filled with PVC rings, 2.5 cm (1 in) in diameter.
The chamber is opaque except for the sight glass
mounted in-line on the discharge piping. A white
card is positioned behind the sight glass for better
observation of the chlorine dioxide color.
Other Benefits of the Chlorine Dioxide System
Prior to the installation of the chlorine dioxide
system, customers complained about brown iron
stains on laundry articles. The switch to chlorine
dioxide treatment loosened the brown slimes from the
mains. The distribution system was flushed, and
shortly thereafter the staining problems were
resolved. Plant personnel attributed the source of the
problem to crenothrix and leptothrix bacteria (iron
bacteria) that had been present in the extremities of
the distribution system before chlorine dioxide was
introduced.
Coste of Chlorine Dioxide
In 1977, the costs of chlorine dioxide disinfection for
Hamilton were about 3.60/capita/year. Total
chemical costs averaged $0.05/m3 ($0.19/1,000 gal),
chlorine dioxide accounting for only a fraction of the
total. The operating and maintenance costs were less
than $50 annually. The plant-fabricated reactor,
piping, hardware, and installation, which was
performed by plant personnel, cost roughly $400 in
1977. The peristaltic pump for sodium chlorite
solution cost less than $200. The two chlorinators,
each worth $600, were already on line at the plant.
Implications of the SWTR CT Values for
Hamilton
Although the Hamilton raw water is ground water,
and therefore probably will not be subject to the
requirements of the Surface Water Treatment Rule,
it is interesting to consider the effects if such
disinfection requirements as listed in the latest EPA
Guidance Manual (U.S. EPA, 1989a) were to be
levied on this water supply system.
Chlorine dioxide is added to the Hamilton water in
applied doses of 0.25 mg/L as it enters the clearwell.
The water temperature is about 20ฐC (68ฐF) year
round, and the pH is 9.4 to 9.5. Hamilton's first
customer is located about 0.5 miles from the plant.
Thus there is very little contact time in the
distribution system.
The plant filters efficiently, and therefore only 1-log
additional inactivation ofGiardia cysts and 2-logs
inactivation of viruses need to be provided by the
chlorine dioxide. The latest EPA Guidance Manual
shows that at 15ฐC (59ฐF) CT values of 5 mg/L-min
and 2.8 mg/L-min will provide the required degrees of
disinfection for Giardia cysts and viruses,
respectively.
The Hamilton clearwell holds 1,892,500 L (500,000
gal). During periods of high water use, water is
produced at the rate of 0.83 m3/sec (19 MGD). In
periods of low water use, only 0.35 m3/sec (8 MGD)
are produced. Thus the contact time in the Hamilton
clearwell ranges from 30 to 90 minutes, at the high
and low production rates, respectively. Assuming
that the average concentration of chlorine dioxide in
the clearwell is 0.2 mg/L, then the CT values
provided are 6 and 18 mg/L-min, respectively.
Thus the current disinfection conditions using
chlorine dioxide meet the CT requirements for both
Giardia cysts and viruses.
Secondary Disinfection with Chlorine Dioxide
at Hamilton
The recently promulgated Surface Water Treatment
Rule requires that a minimum secondary
disinfectant concentration of 0.20 mg/L be present as
the water enters the distribution system or that the
HPC level be less than 500 mL in the distribution
system. Since Hamilton's chlorine dioxide
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concentration entering the distribution system is
0.15 mg/L, the city will either have to increase this
residual to 0.20 mg/L or rely on HPC analyses to
comply.
B.3.3 Preoxidation with Chlorine Dioxide,
Postchlorination with Chlorine Dioxide
and Chloramine: Galveston, Texas
(Myers etal., 1986)
The Galveston County Water Authority (GCWA)
owns and operates an 18-MGD water treatment plant
in Texas City, Texas. In 1986, the plant produced
0.526 m3/sec (12 MGD) from the Brazos River. Raw
water had high color; variable turbidities (68 to 111
NTU); high organic content; high iron (2.7 to 3.8
mg/L); and seasonally high algae content, sometimes
reaching levels of 5,000 blue-green algae per mL.
Total THM formation potentials for Brazos River
water between September 1983 and April 1984
ranged from 400 to 650 ug/L. Finished water THM
concentrations during the same period ranged from
180 to 350 ug/L. During periods of intermittent raw
water algae blooms and associated high organic
carbon contents, numerous taste and odor complaints
were received. These problems prompted an
investigation of alternative disinfectants.
The original treatment process included the addition
of cationic polymers for primary coagulation, lime for
pH adjustment, prechlorination for taste and odor
control, and ferric sulfate as a flocculent aid prior to
upflow reactors and clarifiers, which provided
flocculation and sedimentation. Dual media
filtration, chlorine disinfection (2.4 to 5.0 mg/L total
available chlorine residual), and fluoridation
followed.
Pilot Study
Chloramines and chloride dioxide were selected for
further study and pilot plant testing. Several
preoxidation/postdisinfection combinations involving
chlorine, chloramine, and chlorine dioxide were
studied. The studies indicated that preoxidation with
chlorine dioxide and postdisinfection with chlorine
dioxide in combination with either chlorine or
chloramines provided effective taste and odor control,
maintained an active disinfectant residual, and
minimized THM formation (to a level of about 68
ug/L). A brief summary of the results obtained from
the combinations studied follows:
Chlorine/chlorine - Finished water exhibited
intermittent algae-related tastes and odors; THM
levels were in excess of Federal standards;
bacterial quality was excellent.
Chloraminefchloramine - Chlorine-to-ammonia
weight ratios of 3:1 and 7:1 were used. With the
3:1 ratio, THM levels were lowered to about 60
ug/L, but bacterial counts for coliforms indicated
an inadequate residual in the distribution
system. The experiments were repeated using a
7:1 chlorine-to-ammonia ratio. Acceptable
bacterial quality was achieved, but numerous
taste and odor complaints were received during
this period.
Chlorine dioxide/chlorine - Chlorine dioxide was
installed in May 1984, using a generator with a
conversion efficiency (chlorite ion to chlorine
dioxide) of approximately 80 percent. After
preoxidation, the clarified water showed no
traces of THMs. No taste and odor complaints
were received, despite very high raw water algae
counts (up to 5,000 blue-green algae/mL).
However, finished water THM levels sometimes
persisted above 100 ug/L. In November 1984, a
chlorine dioxide generator with a greater than 98
percent conversion efficiency was installed. THM
levels averaged 102 ug/L, and no taste and odor
complaints were received.
Chlorine dioxide/chlorine dioxide - Chlorine
dioxide for preoxidation and postdisinfection was
tested in March 1985. The Texas Department of
Health required that a maximum chlorine
dioxide residual of 1.0 mg/L be maintained and
that finished water quality be monitored
throughout.the distribution system. During the
test period, finished water THM concentrations
averaged 60 ug/L and turbidities were the lowest
of any of the alternative disinfectant scenarios.
Bacterial counts generally were excellent, but
intermittent elevated counts were noted at the
clear well and at two locations 3.2 and 8 km (2 and
5 mi) from the plant. Additionally, bacterial
counts displayed a shift from orange to yellow-
staining gram negative (-) rods to white-staining
gram positive (+) rods, similar to slime-forming
Bacillus sp.
Chlorine dioxide/chlorine and chlorine dioxide -
The above test was repeated, adding chlorine in
conjunction with chlorine dioxide. Excellent
bacterial quality was obtained with plate counts
at or below the 500 colonies per 100 mL for all
monitoring locations. The shift in bacterial
species distribution continued as the plate counts
decreased, so that over 95 percent of all colonies
examined were either yellow gram negative rods
or white gram positive rods. THM levels of the
finished water rose to an average of 81 ug/L.
Chlorine dioxide/'chloramine and chlorine dioxide
- These tests were conducted in December 1985.
THM levels of the finished water averaged 68
ug/L, and the bacterial quality remained
excellent. No coliforms were found in the
clearwell or in the distribution system and
bacterial counts had ranged from < 1 to 30
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colonies per 100 mL. Of those colonies identified,
over 95 percent were white-staining, gram
positive Bacillus sp. with less than 1 percent
belonging to the orange-staining gram negative
type.
Chlorine dioxide preoxidation has proved an
excellent algicide and biocide. The effectiveness of
chlorine dioxide in removing algae in flocculation
and sedimentation has resulted in a decrease in filter
fouling and improved finished water turbidities.
Odors experienced at the flocculating clarifiers, and
taste and odor complaints were reduced.
Bacterial counts, using the membrane filter method
for coliforms, have greatly improved as well. With
the new system, all bacterial counts obtained from
samples collected at the distribution point have been
below 30 colonies per 100 mL, and all but two
samples have been below 10 colonies per 100 mL.
Samples from the distribution system are continually
below the guideline of 500 colonies per mL, and often
are below 5 colonies per 100 mL. These counts
indicate an adequate and stable residual.
B.4 Chloramine Case Histories
B.4.1 Prechlorination, Postchloramination:
Bloomington, Indiana (Singer, 1986)
Bloomington obtains raw water from a lake with
TOG levels of 4 to 6 mg/L. The water is treated with
alum coagulation, flocculation, sedimentation, and
filtration through pressure filters. Prior to
September 1984, chlorine was applied to the raw
water and just before the pressure filters. Average
chlorine dosages were 1.8 and 1.0 mg/L at each point,
respectively. According to quarterly compliance
monitoring reports, average TTHM concentrations
were exceeding the 100 ug/L limit a majority of the
time.
In September 1984, the Bloomington water utility
changed from post chlorination to postchloramina-
tion. Before the pressure filters, an average 0.54
mg/L of ammonia was applied along with 1.5 mg/L of
chlorine. The desired residual chlorine concentration
leaving the plant of 1.0 mg/L of free chlorine was
changed to 1.5 mg/L of combined chlorine. After the
change, quarterly THM levels ranged from 24 to 57
Table B-2 summarizes THM and TOX (total organic
halide) data for samples collected at points in the
treatment train when chlorine was used for both pre-
and posttreatment. The data show that TOX levels
increase with TTHM levels. Table B-3 summarizes
similar data after postchloramination was instituted.
These data show that although the TTHM formation
ceases after the addition of ammonia, the production
of TOX continues, but at a greatly reduced rate.
Thus, as MCLs for halogenated organic materials
other than THMs are promulgated, utilities using
postchloramination should plan to determine the
makeup of their TOX fraction,
Table B-2. Summary of THM Data at Bloomington, Indiana,
with Free Chlorination, August 16,1984
Chlorine Residual Toe
Sampling Point (mg/L) (mq/L)
Raw water
Settled water
Filtered water
Dist. system #1
Dist. system #2
-
0.25
1.0
1.8
0.65
4.3
3.6
2.4
-
-
Tthm Tox
(ug/L) (ug/L)
1
48
81
110
151
23
127
205
291
363
Source: Singer (1986).
Table B-3. Summary of THM Data at Bloomington, Indiana,
with Postchloramination, August 26,1984
Sampling Point
Raw water
Settled water
Filtered water
Dist. system #1
Dist. system #2
Chlorine Residual
(mg/L)
-
Trace, free
1 .2 combined
1 .0 combined
0.9 combined
Toe
(mg/L)
4.1
2.8
2.8
-
-
Tthm
(H9/L)
0
53
55
52
57
Tox
(ug/L)
17
94
91
115
116
Source: Singer (1986).
Since switching to postchloramination, the utility
has experienced no adverse effects in operations or in
finished water quality. According to distribution
system monitoring records, the microbiological
quality of the water has been maintained.
B.4.2 Prechlorine Dioxide, Prechlorination,
and Postchloramination: Philadelphia,
Pennsylvania (McKeon et al., 1986)
The Baxter Water Treatment Plant, a 12.35-m3/sec
(282-MGD) conventional treatment plant built in
1960, supplies drinking water from the Delaware
River to a population of over 800,000. Chemicals used
in treatment include chlorine, ferric chloride or
ferrous sulfate, lime, .fluoride, and ammonia.
Powdered activated carbon is used on demand for
control of taste and odor, and chloride dioxide is used
for control of THMs, tastes, and odors. The chlorine
dioxide system was left over from the previous water
treatment plant on that site. In the 1950s, it was used
to oxidize phenolic compounds found in the
watershed, which have since been eliminated.
Prior to 1976, the Baxter plant practiced breakpoint
chlorination at the raw water basin and maintained
192
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free chlorine in the distribution system. A total of 96
hours of free chlorine contact time was typically
achieved.
In 1978, analyses of THMs showed peak
concentrations above 300 ug/L with an annual
average of 140 ug/L. In light of these results, the
Philadelphia Water Department began to reevaluate
its disinfection strategies. Factors that affected the
selection of an alternative included THM, bacterial,
taste, odor, algae, and corrosion control; residual
duration; and economics.
Process Modifications
Modifications were implemented between 1976 and
1983. Chloraminationof the finished water was
introduced in 1976 to reduce free chlorine contact
times and THM levels. Ammonia was added to
convert free chlorine to monochloramine. The
monochloramine reduced contact time from 96 to 24
hours, provided a stable residual in the distribution
system, improved the organoleptic properties of the
water, and reduced the corrosion rates associated
with the use of free chlorine. Adequate disinfection
was assured by maintaining a free chlorine residual
of 2 to 3 mg/L throughout the plant treatment
process. THM formation potential within the
treatment process was reduced by 40 percent (from
231 to 174 ug/L with the 96-hour contact time) under
summer conditions.
Between 1976 and 1979, the addition of chlorine at
the raw water basin inlet was gradually phased down
from 7.19 g (60 Ib) in 1975 to between 2.4 and 3.6 g
chlorine/m3 (20 to 30 Ib/mil gal) in 1979. While algae
blooms, taste, and odor problems were controlled,
THM levels were still too high (200 g/L in the
summer, and 140 ug/L annual average).
In early 1980, routine use of chlorine at the raw
water intake basin was abandoned. In its place,
chlorine dioxide was added in dosages between 0.5
and 1.0 mg/L. Free chlorine contact times were
reduced to 5 hours. Summertime THM values were
reduced from 200 ug/L to 140 ug/L. This treatment
was sufficient to control taste and odor problems from
algae at all times except during the spring algae
bloom. For that period of time, breakpoint
chlorination of the intake water and/or 12 to 24 g
powdered activated carbon/m3 (IQO to 200 Vofro.il gal)
were added to eliminate vegetative tastes and odors.
In the fall of 1980, a chlorine application point was
installed in the "applied to filters" channel which
allowed for increased flexibility in the use of chlorine.
Free chlorine contact time was reduced from 5 hours
to 1. Chlorine was added at the rapid mix to barely
achieve breakpoint and provide a residual, which
dissipated within a few minutes. Chloramines were
carried across the flocculation and sedimentation
basins. Sufficient chlorine was then added at the new
application point to achieve a free chlorine residual of
1.5 to 2.0 mg/L. This residual was converted to
chloramines 1 hour later as the water left the filter
building.
This treatment regimen gave adequate control of
taste and odor, again, except during spring algae
blooms, which forced a reversion back to free chlorine
at the intake. THM levels, with only 1 hour of free
chlorine contact time, resulted in summer values
averaging 100 ug/L with an annual average of 60
ug/L.
In November 1982, a 10-minute chlorine contact time
was tested. Results indicated that satisfactory
disinfection could be achieved with only chloramines
carried through the flocculation/sedimentation
basins when the water temperature was below 15.6ฐC
(60ฐF). This strategy was initiated on a plant scale in
December 1982. Adequate disinfection was achieved,
but periodic taste and odor problems persisted,
especially after storms. Average annual THM levels
were reduced from 60 to 50 ug/L.
The 10-minute chlorine contact time trial was
terminated in December 1983, because the
disinfection scheme did not adequately address taste
and odor problems. The treatment regimen returned
to a 1-hour free chlorine contact time.
Costs
Over the 10-year period, a 70 percent reduction in
THM concentrations was realized. In 1978,
disinfection cost $1.32/1,000 m3 ($5.01/mil gal); in
1986, the cost was $1.46 ($5.52) (1977 dollars). Cost
increases were minimized because the reduced
chlorine contact times resulted in less evaporative
losses of chlorine, which netted a 20 percent decrease
in the amount of chlorine needed.
Future Considerations
The near-term goal of the Philadelphia Water
Department is to reduce the annual average TOM
concentrations to below 50 ug/L, a 15 percent
reduction from 1986 levels. This can be achieved at
minimum expenditure by installing a pH adjustment
point at posttreatment. The existing treatment
scheme calls for raising the raw water pH to 8.4
during rapid mix and carrying this high pH through
the distribution system for corrosion protection.
Addition of a pH adjustment point at posttreatment
will allow a pH of 7.5 to be used through the
flocculation/sedimentation basins and filters, moving
adjustment to a 8.4 pH to just after chloramination.
Plant-scale trials of this strategy yielded a 20 percent
reduction in THM formation (to about 40 ug/L).
193
-------
If the THM MCL is reduced to below 50 ug/L, ozone
and/or GAC become the likely alternatives at the
Baxter plant. Extensive laboratory and pilot plant
evaluations have developed conceptual full-scale
plant designs incorporating these two treatment
techniques.
Estimated annual amortized capital and operating
costs for ozone at the Baxter plant are estimated to be
about $13.21/1,000 m3 ($50/mil gal). The associated
costs for GAC postfiltration (15-minute EBCT) with a
75-day regeneration frequency would be about
$56/1,000 m3 ($212/mil gal). This design
configuration (ozone plus postfiltration GAC) is
capable of producing THM concentrations of less than
10 ug/L.
194
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Appendix C
Experience with Treatment Technologies for
Organic Contaminants
This appendix is a collection of field experiences with
organics treatment technologies. Section C.I includes
descriptions of GAC systems in use, C.2 describes
packed tower aerators, and C.3 describes powdered
activated carbon.
C.1 Experience with Granular Activated
Carbon
C. 1.1 GAC for VOC Removal: Washington,
New Jersey (Chrobak et al., 1985)
A well with a 0.04 m3/sec (0.8-MGD) capacity in this
community was contaminated with four VOCs. The
VOC levels fluctuated throughout the well's 9-hour
daily operating cycle according to the following
concentration ranges:
Tetrachloroethylene (PCE): 50 to 500 ug/L
Trichloroethylene (TCE): 1 to 10 ug/L
1,1,1-Trichloroethane: 1 to 20 ug/L
Carbon tetrachloride: 1 to 5 ug/L
The town selected a GAC system with two downflow
pressure contactors in parallel. The filters have 2.1-m
(7-ft) diameters, 3-m (10-ft) carbon depths, hydraulic
loadings of 4.8 L/sec/m2 (7.1 GPM/ft2), and EBCTs of
10.5 minutes. Filter backwashing is performed once a
month due to solids in the influent. Wash water is
filtered with sand media and recycled. Figure C-l
shows a schematic diagram of the plant.
Carbon usage rates for meeting the PCE standard
averaged about 10.8 g GAC/m3 (90 Ib/mil gal) of
treated water. Meeting the 1,1,1-trichloroethane
standard required carbon usage rates of 25.2 g
GAC/m3 (210 Ib/mil gal) of treated water. GAC
consumption for the two compounds before
breakthrough (any contamination of the effluent, as
opposed to effluent concentrations over the regulated
standards) was about 12 and 32.4 g/m3 (100 and 270
Ib/mil gal) for PCE and 1,1,1-trichloroethane,
respectively.
The capital cost for the system was $508,500 in 1981
dollars, while the operating costs have been about
$15,000 annually based on 9 hours of operation per
day.
C.1.2 GAC for Contaminant Control:
Cincinnati, Ohio (DeMarco, 1983)
(Westerhoff and Miller, 1985)
This case involves a 9.6-m3/sec (220-MGD) plant that
uses Ohio River water. The proposed addition of GAC
to the original process train is shown in Figure C-2.
Figure C-3 shows TOC removal during a GAC pilot
study conducted at the plant. The chief goals of
adding GAC to this plant were to (1) reduce TOC in
the effluent to less than 1.0 mg/L, (2) maximize the
use of existing plant facilities, (3) maximize the
flexibility to accommodate future requirements, and
(4) keep costs reasonable.
The primary design elements for the addition were a
postfiltration GAC adsorption unit that used
downflow deep-bed contactors, post-GAC
chlorination, and onsite carbon regeneration using a
fluidized-bed furnace. In addition, the design was
intended to keep carbon losses to a minimum.
The addition of the GAC process resulted in the
following system capacities:
7.7 m3/sec (175 MGD) maximum daily plant flow
rate
5.4 m3/sec (124 MGD) average daily average
plant flow rate
15-minute EBCT- 3-m (10-ft) GAC bed depth
3-meter (10-foot) GAC bed depth
24,494.4 kg/day (54,000 Ib/day) average carbon
usage
195
-------
Wastewater Recycle
Filtered Water to
Distribution System
Figure C-1. GAC treatment plant schematic Vannatta Street Station.
41,731.2 kg/day (92,000 Ib/day) peak carbon
usage rate
The carbon transportation system employed for
regeneration uses schedule 10 316L stainless steel
pipe and maintains water velocities of 91.4 to 152.4
cm/sec (3 to 5 ft/sec). The layout design required that
pipe bends in the transportation system have
minimum radii to allow the free flow of the carbon
and minimize abrasion. As a result, pipe bends for
7.6-cm (3-in) diameter pipe used 60.96 cm (24-in)
minimum radii, 10.16-cm (4-in) pipe used 91.4-cm
(36-in) radii, and 20.32-cm (8-in) pipe used 121.9-cm
(48-in) radii. Figure C-4 shows the regeneration
system.
The capital cost of adding the GAC system was $57.7
million (1988 dollars). This included the GAC
contactors, regeneration equipment, intermediate
pumping equipment, outside piping, and
modifications to the existing plant. The operating
and maintenance costs are estimated to average $3 to
$4 million annually, including costs for labor, power,
natural gas, and replacement carbon. These
combined costs resulted in a 30 to 40 percent increase
in the consumers' average annual water charge from
?80 to about $110 per year.
C.1.3 EPA Health Advisory Example
This case involves a system serving 30,000 persons.
The plant had a capacity of 0.22 m3/sec (5.1 MGD), an
average demand of 0.13 m3/sec (3.0 MGD), and peak
demands of 0.18 m3/sec (4.2 MGD). Table C-1
presents a profile of this 1957 system.
The influent for the system is characterized in Table
C-2. The presence of vinyl chloride required use of
PTA because GAC is ineffective for that compound.
However, GAC was also needed to remove
trichloroethylene and aldicarb.
Costs for three technological alternatives were
developed. The alternatives included GAC and PTA
individually and GAC and PTA together. PTA proved
to be almost one fourth as expensive as GAC.
However, combining the two treatments proved less
expensive than adding both treatments separately.
C.2 Experience with PTA: Scottsdale,
Arizona (Clirie et al., 1985)
The only application of the PTA system described in
this appendix is located in Scottsdale, Arizona. In the
Scottsdale system, PTA was added to a system with
24 wells and the combined capacity of 1.75 m3/sec (40
MGD). Two of the wells were contaminated with TCE
at levels of 18 to 200 ug/L and 5 to 43 ug/L,
respectively.
Both PTA and GAC were considered as potential
treatment solutions; PTA was chosen for its cost
effectiveness. For this application, GAC was
estimated to cost from $0.04 to $0.10/m3 ($0.17 to
$0.38/1,000 gal), while PTA was estimated to cost
only $0.02/m3 ($0.07/1,000 gal).
196
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Presetting
Basin
Presetting
Basin
Lamella
Settler
Pumping
Stations
East
Chemical
Building
Rocculation/
Sedimentation
Basins
Filters
Clearwell
Distribution System
Figure C-2. Cincinnati treatment train with addition of GAC.
The PTA unit was designed to manage a 75.7 L/sec
(1,200 GPM) flow rate with 3.6 m (12 ft) of packing
material, a 50:1 air-to-water ratio, and a column
diameter of 3 m (10 ft). Figure C-5 is a schematic
diagram of this facility.
The PTA achieved over 98 percent reductions from
the initial influent levels, producing effluent levels of
TCE ranging from 0.5 to 1.2 ug/L. The system's
capital cost was $300,000, and its operation and
maintenance costs average $25,000 annually.
C.3 Experience with PAC
Currently only pilot-scale units operate in the United
States. There are, however, full-scale Roberts-
Haberer units operating in Africa and Europe,
including a 0.42 m3/sec (9.5-MGD) plant in
Wiesbaden, West Germany, that has operated since
1970.
In Newport News, Virginia, a Roberts-Haberer pilot
plant reduced TOC by 90 percent during initial
operations. Within a 24-hour period, TOC removal
decreased to only 20 percent. During that same
period, this unit significantly reduced THM
precursors.
In Shreveport, Louisiana, a Roberts-Haberer unit
was used as a roughing filter to reduce THM
formation potential. The unit succeeded in reducing
THM formation potential from about 265 ug/L by 7 to
197
-------
Concen
ng/L
4000
3500
3000
2500
2000
1500
1000
500
tratton
\
--
**"*^
~~r~
/
/
/
^-
\
-^
\
/
X
/
^
^
\
TO(
^.i '
V
DRe
^
s
move
~~
\
d
Infli
/
/
ent
/
f
\
y
\
Cor
\
"
itactc
^
rEff
\
^
^V
uent
V
\
\
\
^~>
X
f
/
ฐ 20 40 60 80 100
Time, Days
/
Flgura C-3. Typical TOC reduction curve during pilot study.
31 pg/L with PAC dosage of 26 to 29 mg/L. This
operation, however, did not use the optimum PAC
dosage.
198
-------
Dewatered
Spent Carbon
Regeneration
Furnace
Recycle
Dried Spent
Carbon
Figure C-4. Regeneration system schematic.
Dryer Off-Gas
Furnace
Off-Gas
To Scrubbers
and Stack
1
Recuperator
Afterburner
199
-------
Table C-1. Profits of System used in EPA Health Advisory
Source:
* Three wells approximately 500 feet deep
Capacity of each well is 1.8 million gallons per day
Screened between 400 to 500 feet with gravel pack
18-inch steel casing from 0 to 400 feet
Portland cement grout from 0 to 200 feet
All wells are pumped to a common manifold that flows to
the water treatment plant
* Soil profile: 0 to 100 feet, sandy soil; 100 to 400 feet,
sand clay mixture; 400 to 500 feet, wet sand and gravel;
500 feet, bedrock
Storage:3.5 million gallons
Treatment: Iron removal using chlorine oxidation, alum
coagulation, sedimentation, and rapid pressure
sand filtration; disinfection (chlorine), fluoridation,
and corrosion control (lime and metallic
phosphates) are also practiced.
Constructed:! 957
Mechanical Structural Condition: Excellent
1 foot - 0.3048 meters.
11nch - 2.54 centimeters.
1 galton ซ 3.785 liters.
Tablo C-2. Influent Characterization for System Used in
EPA Health Advisory
Well #1
Well #2
Well #3
Parameter Raw Treated Raw Treated Raw Treated
Iron(moA) 3.0 o.os
PH 6.0 7.8
Alkalinity (mgfL) 10 no
Vinyl chloride 40 20
2.2 0.05
5.9 7.8
14 110
20
Trichforoethytene 50 RQ
(WL)
AWtcarb (total) 30 30
(yglL)
Total organic 3.0 1 o
carbon (mg/L)
14
30
30
2.1
60
30
1.0
2.0 0.05
6.2 7.8
12 110
6 20
100 60
30 30
1.0 1.0
200
-------
Treated Water
to Reservoir
Figure C-5. Schematic diagram of a Scottsdale packed column.
201
-------
-------
Appendix D
Experience with Treatment Technologies for
Inorganic Contaminants
This appendix describes a number of field
experiences with inorganics treatment technologies.
Section D.I covers two cases of corrosion control;
Section D.2, the use of coagulants; Section D.3,
reverse osmosis; Section D.4, ion exchange; and
Section D.5, activated alumina.
D.1 Corrosion Control
D.1.1 Controlling Lead: Seattle, Washington
Seattle, Washington, has instituted a successful
corrosion control program. The program has a
component that assists residents in materials
selection, in addition to a water treatment
modification program. The city encourages the use of
plastic piping, types K and L copper piping, and
solder with less than 0.2 percent lead. In addition, the
city requires dielectric insulators to mitigate
corrosion from joining dissimilar metals.
D.1.2 Controlling Lead with pH Adjustment:
Boston, Massachusetts
A1975 survey found significant levels of lead in tap
water supplied to Boston residents by the
Metropolitan District Commission (MDC). The
protected watersheds of the MDC's main water
sources precluded contamination of the raw water.
Instead, the lead contamination came from a
combination of corrosive water and extensive use of
lead in service lines and plumbing. The corrosive
water was characterized as acidic and low in
hardness and alkalinity. Table D-l presents water
quality characteristics for the MDC's raw and
finished water. Prior to discovery of the lead problem,
the finished water underwent only chlorination and
ammoniation treatments, as shown in the column for
"raw water."
The MDC, in conjunction with U.S. EPA, developed a
water monitoring program to ascertain the optimal
Table D-1. Metropolitan District Commission Water Quality
Data
Parameters
Hardness (as CaCO3)
Alkalinity (as CaCO3)
Total Dissolved Solids
Calcium
Sodium
Sulfate
Chloride
Specific conductance
(micromhos)
pH (units)
Copper
Iron
Zinc
Lead
Shan 4
(Southborough,
MA)
Raw Water
12
8
37
3.2
5.5
<15
<10
59
6.7
<0.02
<0.10
<0.02
< 0.005
Norumbega
Reservoir
(Weston, MA)
Finished Water
12
12
46
3.4
9.7
<15
<10
78
8.5
<0.02
<0.10
<0.02
< 0.005
Note: All values in mg/L unless otherwise specified.
Source: U.S. EPA (1984).
solution for corrosion control. The monitoring
program was also designed to measure progress in
reducing corrosion with the chosen solution. The
MDC selected two treatment alternatives.
The first treatment, plan adding zinc
orthophosphate, was implemented from June
through December 1976. While reductions in lead
contamination were attained, levels were still above
theMCL.
The second treatment plan data shown in the second
column in Table D-l, which proved more successful,
consisted of adding sodium hydroxide to adjust the
pH. During 1979, pH levels dropped below 8.0 and
then were increased to the target level of 9.0. Lead
203
-------
levels in the water rose and then dropped with the
resumption of the higher pH level. The pH increase
also reduced copper contamination levels, but had
little effect on iron corrosion.
The treatment consisted of applying a dosage of 14
mg/L of a 50 percent sodium hydroxide solution to
about 13.18 m3/sec(301 MGD). This dosage, in 1981,
cost $2.54/1,000 m3 ($9.64/mil gal of treated water).
Chemical costs for that year were $900,000 and
operation and maintenance costs were $161,000.
D.2 Coagulation to Control Barium:
Illinois
This case involves a conventional treatment plant in
northeastern Illinois with high barium
concentrations in its source groundwater. Barium
concentrations in the plant's influent ranged between
0.4 and 8.5 mg/L; the MCL for barium is 1 mg/L.
Contamination was found in small areas of the water
utility's watershed and the contaminated water was
drawn through Cambrian/Ordovician soils. No
barium contamination occurred in wells with sulfate
levels greater than 50 mg/L, because of the low
solubility of barium sulfate.
Plant operators conducted many jar tests to evaluate
alternative chemical additives to address the barium
contamination. Influent samples with 7.4- mg/L
levels of barium were used. The tested additives and
their operational purposes include:
Alum as a coagulant-precipitant
Ferrous sulfate as a coagulant-precipitant
Calcium hydroxide as a preeipitant-pH adjuster
Sulfuric acid as a pH adjuster-precipitant
Hydrochloric acid as a pH adjuster
Sodium hydroxide as a pH adjuster
Potassium hydroxide as a pH adjuster
Calcium sulfate (gypsum) as a precipitant
Commercial gypsum as a precipitant
Sodium bisulfate as a precipitant
Anionic polymer as aflocculent-filter aid
Diatomaceous earth as a filter precoat
The laboratory jar tests determined that the most
effective additive was calcium sulfate. Optimum
dosages ranged between 75 and 175 mg/L with a pH
of 11.0. A 0.066-m3/sec (1.5 MGD) pilot plant
provided precipitation, direct filtration, and polymer
additions for a variety of barium concentrations,
which confirmed the laboratory approximation.
At full-scale operation, the plant uses dosages of 100
mg/L of gypsum and 0.25 mg/L of polymer to achieve
a 91 percent reduction in barium from 6 mg/L to 0.5
mg/L. The plant's filter operates at 1.0 L/sec/m2 (1.5
GPM/ft2) at a pH level of 11.0.
Total capital costs were $2,366,000 (1980 dollars) to
address the barium contamination. The costs to
address the barium contamination covered 10 capital
components, including aerator, rapid mix tank,
flocculation basin, gravity filter, recarbonation
system, transfer pumps, potassium hydroxide
system, gypsum system, polymer system, and
appurtenances. Total construction costs were
$1,068,100. Annual operating and maintenance costs
were $155,900.
D.3 Reverse Osmosis: Sarasota, Florida
This case involves a study of eight existing ground-
water supplies in Sarasota County, Florida. Water
treatment plants ranged in capacity up to 3.03
m3/day to 0.044 m3/r,ec (from 800 to 1 MGD) and
served five mobile home/trailer parks, one school, and
two communities. The study was performed
cooperatively by U.S. EPA's Division of Water
Supply Research and the Sarasota County Board of
Health between January and June 1977.
The influent for the eight plants was naturally
contaminated with concentrations of radium-226
ranging from 3.4 to 20.2 pCi/L due to the presence of
phosphatic limestone. In addition, many supplies had
high levels of total dissolved solids.
Design parameters for the eight treatment plants are
summarized in Table D-2. These plants added reverse
osmosis units with either hollow-fiber or spiral-
wound membrane designs from six different
manufacturers. Their pretreatment processes
included cartridge filtration, pH adjustment, and ion
sequestration. Posttreatment processes included pH
adjustment, degassification, and chlorination. Table
D-3 lists the pre- and posttreatment processes for
each plant.
All eight plants achieved compliance with the 5 pCi/L
standard for radium-226, with operating pressures
ranging from 14.1 to 29.9 kg/cm.2 (200 to 425 psi).
Finished or product water consisted of 28 to 54
percent of the influent volume, and finished water
concentrations ranged from 0.14 to 2.0 pCi/L. Waste
or reject brine water contained from 7.8 to 37.8 pCi/L
of radium-226.
Table D-4 presents chemical analyses for the eight
plants. The table contains analyses of the raw water
and product water collected after at least 1 hour of
operation. Analytical data were examined at several
different points during operation to assess the effect
of operating duration on removal efficiency.
Although the eight systems attained 76 percent
efficiency upon initiation of operation, two systems
examined attained peak operational efficiency after
about 5 minutes of operation.
204
-------
Table D-2. ' Design Criteria of Reverse
Product Water
Design Capacity
Popula- GPD
System tion kL/day x 103
Venice 15,000 3,800 1,000
Sorrento 1,300 780 200
Shores
Spanish 800 265 70
Lakes MHP
Bay Lakes 340 150 40
Estates
MHP
Kings Gate 800 115 30
TP
Sarasota 135 19 5
Bay MHP
Bay Front 39 6 1.6
TP
Nokomis 800 3 0.8
school
Osmosis Equipmc
Reverse
Osmosis System
Manufacturer
Polymetrics,
Santa Clara, CA
Permutit,
Paramus, NJ
Universal Oil
Products (UOP),
San Diego, CA
Publication
Techniques,
Avon-by-
the-Sea, NJ
Purification
Techniques,
Avon-by-
the-Sea, NJ
Polymetrics,
Santa Clara, CA
Continental
Water
Conditioning,
El Paso, TX
Basic Tech-
nologies, West
Palm Beach, FL
snt
i Recovery
hra^p Pumos Ooeratina Pressure Percent
Type kw
Hollow 4,900
fibers
Spiral 1,470
woundb
Spiral 490
woundb
Hollow 290
fiber3
Hollow 390
fiber3
Hollow 50
fiber3
Hollow 7
fiber3
Spiral 5
wound0
hp kPa
500 2,800
150 2,900
50 2,800
30 2,800
40 2,800
5 2,800
3/4 1,400
1/2 1,400
psi Stages Design Actual
400 2 50 54
425 1 75 39
400 2 66 31
400 2 55 NA
400 2 70 NA
400 1 50 50
200 1 28 28
' ' " , -
200 T 35 NA
3DuPont, Wilmington, Delaware.
^Universal Oil Products (UOP), San Diego, California.
"Basic Technologies, West Palm Beach, Florida.
NA = not available.
1,000 gallon - 3.78 m3
1 psi = 0.0703 kg/cm2
Source: Sorg (1980a).
The operating costs for these units ranged from $0.16
to $0.41/m3 ($0.60 to $1.54/1,000 gal) of treated water
(see Table D-5). These costs include chemicals,
electrical power, filter cartridge replacement, and
labor. However, these data are not complete or
comparable because they were derived from
interviews with operators and owners, and do not
necessarily use the same basis for each cost element.
D.4 Ion Exchange: McFarland, California
This case involves a 0.044 m3/sec (1-MGD) plant with
four ground-water wells contaminated with nitrates
from agricultural application of fertilizers and
manure. Influent concentrations of nitrate ranged
from 6.8 to 22.1 mg/L and averaged 16 mg/L.
To address this contamination problem, ion exchange
units were selected for wellhead application because
they are effective and easy to operate. The treatment
process included:
Anion exchange with A-101-D, Duolite resin
Sodium chloride regeneration with slow rinse
and declassification
Aerated lagoons and spray irrigation for brine
waste treatment
The ion exchange units used three reaction basins,
each measuring 1.8 m (6 ft) in diameter and 3 m (10
ft) in height. The standard operational height of the
reaction basin is only 0.9 m (3 ft), with operational
maximums of 1,5 m (5 ft). According to system
design, one of the basins undergoes regeneration,
while the other two operate. The plant uses a 2.5-
minute EBCT; the treated water flow rate was 15.77
L/sec (250 GPM) with surface loading rates of 6.13
L/sec/m2 (9.03 GPM/ft2). Treated water was blended
with raw water in a 7-to-3 ratio.
The regeneration process used a 6 percent sodium
chloride brine. Regeneration involved quick rinse,
slow rinse, and resin reclassification procedures that
required 981 kg (2,162 Ib) of salt daily during periods
of continuous operation. The process produced
saturated brine at a rate of 2.27 L/sec (36 GPM) and
diluted brine at 12 L/sec (190.5 GPM). Brine was
discharged to a municipal wastewater treatment
plant, where it was diluted by the other waste
streams and then placed in aeration lagoons. This
205
-------
TaWe D-3. Pro- and Posttreatment Reverse Osmosis Processes
Pre treatment
Posttreatment
System
Venice
Sorrento
Chnrna
OflOfBS
Spanish
Lakes MHP
Bay Lakes
Ce)ซ]tfevป
CobbUKJd
MHP
Kings Gate
TP
Sarasota
Bay MHP
Bay Front
TP
Nokoonis
school
pH Adjustment Sequestering
Chemical Agent Filters um
H2S04
H2S04
H2S04
H2S04
H2S04
HCI
None
C02
Na3(P03)6
Na3(P03)6
Na3(P03)6
Na3(P03)6
Na3(P03)3
Na3(P03)B
poly-stabilizer
A-5
None
5
10
25
10
10
5
10
5
Degassification pH Adjustment
or Aeration Chemical
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
a
Na3CO3
None
None
None
None
None
None
Chlorin-
ation
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Blending Raw and
Treated Water
a
75%
reverse osmosis
No
84%
reverse osmosis
Mo
No
55%
reverse osmosis
No
Reject Water
Disposal Method
Creek
Bay
Pond
Storm sewer
Ditch
Subsurface
drainfield
Subsurface
drainfield
Subsurface
drainfield
* Blooded with lime-softened water in approximate ratio of 2 parts lime-softened water to 1 part reverse osmosis water
Sourco: Sorg (1980a).
aerated solution was spray- irrigated onto animal
feed crops and cotton.
The treated water had nitrate levels of 2 to 5 mg/L.
The blended finished water nitrate levels ranged
from 6 to 10 mg/L with a 7 mg/L average.
The total construction costs for the ion exchange
units were $354,638 in 1983 dollars. The operating
and maintenance costs totaled $0.03/m3 (12.8
cents/1,000 gal) of treated water. Table D-6 shows the
components of both types of costs. These costs include
the annual loss of 20 percent of the resin.
D.5 Activated Alumina: Gila Bend,
Arizona
This case involves a ground-water supply with
undesirable levels of fluoride ranging from 4 to 6
mg/L, with a 5 mg/L average. The plant, with an
average capacity of 37.8 L/sec (600 GPM) and a
maximum capacity of 56.77 L/sec (900 GPM), was
equipped with the following elements to manage the
fluoride contamination:
* Activated alumina: Alcoa activated alumina,
grade P-l, -28 to +48 mesh
Caustic regeneration
ป Acid neutralization
* Evaporation pond for regenerant waste
treatment
The treatment process produces 90 percent treated
finished water and 10 percent waste water. The
finished water averages 0.7 mg/L of fluoride, with a
maximum of 1.4 mg/L.
The alumina medium was placed in two vessels 3 m
(10 ft) in diameter and height. The alumina takes up
1.5 m (5 ft) of vessel height, and expands about 50
percent of its original height during backwash
operations. Approximately 15 em (6 in) of basin
freeboard is provided. The water's superficial
residency time is 5 minutes. The maximum
operational flow rate in the basins is 4.75 L/sec/m2 (7
GPM/ft2), while the backwash rate is 7.47 L/sec/m2
(11 GPM/ft2).
For every 13.2 to 15.1 thousand cubic meters (3.5 to 4
million gallons) of water treated, a 10-hour
regeneration cycle is required. Annual losses of
alumina due to regeneration range from 10 to 12
percent. Regeneration of the alumina medium is
accomplished with a 1 percent solution of sodium
hydroxide. The 1 percent solution flows through the
basins at a maximum rate of 1.70 L/sec/m2 (2.5
GPM/ft2), with a detention time of 24 minutes. The
regeneration process uses 757 L (200 gal) of sodium
hydroxide solution/lb fluoride removed.
The caustic water from the regeneration process
requires a 0.04 percent solution of sulfuric acid for
neutralization. The acid solution is derived by
diluting a bulk 93 percent acid solution. (The
neutralization process flow rate is 4.75 L/sec/m.2 [7
GPM/ft2] at most.) The goal of the neutralization <
process is to produce acceptable pH levels from 6.5 to
8.5 for disposal. The backwash and neutralization
rinse water wastes are discharged to the sewer. The
206
-------
Table D-4. Chemical Analyses of Sarasota County Reverse Osmosis Systems
Spanish Lakes MHP Water
Bay Lakes Estates
MHP Water Kings Gate TP Water
Parameter3
TDS
Specific conductance-uS
Turbidity - NTU
Color - color units
pH - pH units
Alkalinity (as CaCO,)
Hardness (as CaCO3)
Calcium
Magnesium
Chloride
Sulfate
Sodium
Lithium
Silica
Arsenic
Selenium
Fluoride
Radium-226 -
pCi/Lฑ2ฎป
Table D-4. Continued
Raw
2,532
2,525
0.9
a
7.3
114
1,620
385
153
105
1,460
48
0.07
8.4
0.021
0.019
2.0
3.2
ฑ0.07
Product
113 1
196 1
0.12
3
6.0
20
68 1
15.1
6.6
13
59
8.6
<0.01
<1.0
< 0.005
< 0.005
0.4
0.14
ฑ0.02
Raw
,620
,822
0.45
5
7.5
144
,020
244
90
85
840
51
0.02
12.9
0.01
0.014
0.7
15.74
ฑ0.26
Sorrento Shores Water
Parameter3
TDS
Specific conductance-pS
Turbidity - NTU
Color - color units
pH - pH units
Alkalinity (as CaCO,)
Hardness (as CaCO3)
Calcium
Magnesium
Chloride
Sulfate
Sodium
Lithium
Silica
Arsenic
Selenium
Fluoride
Radium-226, -
pCi/Lฑ2>b
Raw
3,373
3,900
1.5
6
7.15
114
1,980
488
171
520
1,880
258
0.12
7.6
0.095
0.025
2.2
4.59
ฑ0.08
Product
404
406
0.06
3
5.25
8
70
16.9
5.7
95
42
45
<0.01
1.9
0.008
< 0.005
0.8
0.21
ฑ0.02
Reject
5,330
5,505
0.4
5
5.1
6
3,100
780
263
690
2,800
366
0.26
11.1
0.190
0.035
2.8
7.86
ฑ0.11
Product
256 1
385 1
0.15
4
6.35
30
134
32.2
12.6
27
118
21.3
<0.01
2.8
< 0.005
< 0.005
0.3
2.01
ฑ0.04
Defective Membranes
(3/77)
Raw
,194
,401
0.23
8
7.55
164
750
214
56.4
71
580
40
<0.01
9.2
0.008
0.01
0.5
11.41
ฑ0.15
Product
496
630
0.11
4
7.3
68
286
75.0
21.4
32
210
19
<0.01
4.9
< 0.005
< 0.005
0.3
3.97
ฑ0.06
Venice Water
Raw
2,412
2,781
0.75
5
7.25
110
1,425
326
144
300
1,200
140
0.04
7.2
0.015
0.015
2.2
3.37
ฑ0.08
Product
129
216
0.09
3
5.9
20
44
9.4
4.5
33
43
25.4
<0.01
<1.0
< 0.005
< 0.005
0.8
0.26
ฑ0.02
Reject
5,238
5,040
0.4
6
5.45
14
3,050
700
313
500
2,800
249
0.36
16.8
0.025
0.045
4.0
7.84
ฑ0.09
New Membranes
(3/78)
Raw
1,327
1,580
0.24
10
8.0
176
865
222
63.8
66
670
39
<0.01
12.7
0.03
0.017
0.4
10.49
ฑ0.11
Bay
Raw
895
1,215
0.54
50 -
7.45
294
570
171
28.2
95
240
59
<0.01
8.1
0.008
< 0.005
0.4
12.10
ฑ0.19
Product
158
255
0.11
4
6.1
1.0
98
23.0
6.59
14
80
7.5
<0.01
3.2
< 0.005
< 0.005
0.2
1.18
ฑ0.03
Reject
3,380
3,224
0.70
25
6.7
24
2,130
570
153
135
2,000
91
.11
30.6
0.075
0.03
0.7
20.48
ฑ0.02
Front Water
Product
66
123
0.1 i
3
6.75
36
32
, 9.4
1.6
<10
10
13
<0.01
<1
< 0.005
< 0.005
0.1
0.62
ฑ0.03
Reject
1,578
1,967
0.50
70
7.5
540
980
292
47.5
150
480
100
<0.01
14.8
0.016
0.018
0.5
19.38
ฑ0.2
3AII units are reported as mg/L except as noted.
b ฑ 26 represents instrument counting error of Ra-226 analysis.
Source: Sorg (I980a).
207
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Tabto D-5. Reverse Osmosis Treatment System Costs
Capital Estimated Operating
System
Venice
Sorrento Shores
Spanish Lakes
Bay Lakes Estates
MHP
Kings Gale MPH
Sarasota Bay MPH
Bay Front TP
Nokomis school
Year
Con-
structed
1975
1975
1974
1973
1974
1975
1976
1976
Cost3
$/1,000
gal
1,000
250
150
25
30
14
11.2
5.5
$/kL
0.16
0.29
0.41
0.33
C
0.32
0.28
C
Costb
$/1,000
gal
0.60
1.08
1.54
1.06
c
1.22
1.06
C
"Capital costs include reverse osmosis units and pumps, pre- and
post- treatment equipment, filters, flushing equipment, booster pumps,
and shatter.
^Operating costs include chemicals, power (0.4/kwhr), filled cartridge
replacement, and labor. Excluded were amortization costs and
membrane replacement Blending was not taken into account.
^Insufficient data.
1,000 gallons = 3.78 ntf
Source: Sorg (I380a).
Table D-S. Ion Exchange Cost Components for McFarland,
California ($1983)
Construction Costs Components in (expressed in$):
Ion exchange unit vessels 111,741
Onsite Construction 81,154
Resin 56,610
Engineering 46,388
Brine tank 18,700
Other 40.045
Total 354,638
Operation and Maintenance Costs Components (expressed in
cents/1,000 gallons):
Salt 3.4
Rosin replacement 3.2
Power 2.2
Normal operating and maintenance 1.9
Operating labor 1.3
MisceNeneous 0.8
Total 12.8
1,000 gallons - 3.78 rrfl
regenerant waste is discharged to a lined evaporation
pond which is 73 m (240 ft) by 134 m (440 ft) by 2.7 m
(9ft).
The construction costs for the unit totaled $285,000
in 1978 dollars, and included treatment facility, well,
1,892,500-L (500,000-gal) steel tank, evaporation
pond, booster pumps, standby generator, and
chlorination facilities. The plant's operating costs
were 7.1 to 7.4 cents/m3 (27 to 28 cents/1,000 gal) of
treated water. These costs included salaries, power,
chemicals, and media replacement.
208
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Appendix E
Summary of Corrosion Indices
Index
Equation
Parameters
Meaning
Langelier
Saturation Index
(LSI)
LSI = pH- pHs
Total alkalinity, mg/L as.CaCO3
, Calcium, mg/L as CaCO3
Hardness.'.mg/L as CaCO3
Total dissolved solids, mg/L
Onsite pH
Onsite temperature
LSI > 0 = Water is super-
saturated; tends to precipitate
CaCO3
LSI = 0 = Water is saturated (in
equilibrium); CaCO3 scale is neither
dissolved nor deposited . '
LSI < 0 = Water is under-
saturated; tends to dissolve solid
CaCO3
Aggressive Index
(Al) (for use with
asbestos cement)
Al = pH + log [(A)(H)J
Total alkalinity, mg/L as CaCO3
Hardness^mg/L as CaCO3
Onsite pH'
Al < 10 = Very aggressive .
Al = 10 -12 = Moderately
aggressive
Al > 12 = Nonaggressive
Ryznar Stability
Index (RSI)
RSI = 2pHs - pH
Total alkalinity, mg/L as CaCO3
Calcium, mg/L as CaCO3
Hardness, mg/L as CaCO3
Total dissolved solids, mg/L
Onsite pH
Onsite temperature
RSI < 6.5 = Water is super-
saturated; tends to precipitate
CaCO3
6.5 < RSI < 7.0 = Water is
saturated (in equilibrium); CaCO3
scale is neither dissolved nor
deposited . /
RSI > 7.0 = Water is under-
saturated; tends to dissolve solid
CaCO3
Riddick's
Corrosion Index
(Cl)
112
Hardness - AIK
+ Cl' + 2N\ x
f 10~] f DO * 2 I
I S/02 I I Sa * DO J
Driving Force
Index (DPI)
CaCO3
Ca*+(ppm) x
= (ppm)
Kso x 1010
CO2, mg/L
Hardness, mg/L as CaCO3
Alkalinity, mg/L as CaCO3
Cl', mg/L
N, mg/L
DO, mg/L
Saturation DO3 (value for
oxygen saturation), mg/L
Calcium, mg/L as CaCO3
CO3 " = mg/L as CaCO3
Kso = solubility product of
CaCOo
Cl = 0-5 Scale forming
,6-25 Noncorrosive
26-50 Moderately corrosive
51-75 Corrosive
76-100 Very corrosive
101 + Extremely corrosive
DPI > 1 = Water super-
saturated; tends to precipitate
DPI = 1 = Water saturated (in
equilibrium); CaCO3 scale is
neither dissolved nor deposited
DPI < 1 = Water under-
saturated; tends to dissolve
CaCO3
aDO = dissolved oxygen
Source: U.S. EPA (1984).
*U.S. GOVERNMENT PRINTING OFFICE: 1992-6'ปe-OOV'il8't6
209
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