United States
Environmental
Protection Agency
Office of Water
(4607)
EPA815-R-99-012
May 1999
Enhanced Coagulation and
Enhanced Precipitative
Softening Guidance Manual
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DISCLAIMER
This manual provides public water systems and drinking water primacy agencies with guidance for
complying with the enhanced coagulation and enhanced precipitative softening treatment technique
contained in the Stage 1 Disinfectants and Disinfection Byproducts Rule (DBPR).
This document is EPA guidance only. It does not establish or affect legal rights or obligation. EPA
decisions in any particular case will be made applying the laws and regulation on the basis of specific
facts when permits are issued or regulations promulgated.
Mention of trade names or commercial products does not constitute an EPA endorsement or
recommendation for use.
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ACKNOWLEDGMENTS
The Environmental Protection Agency gratefully acknowledges the assistance of the
members of the Microbial and Disinfection Byproducts Federal Advisory Committee and
Technical Work Group for their comments and suggestions to improve this document.
EPA also wishes to thank the representatives of drinking water utilities, researchers, and
the American Water Works Association for their review and comment. In particular, the
Agency would like to recognize the following individuals for their contributions:
Stuart Krasner, Metropolitan Water District of Southern California
Sarah Clark, City of Austin
Mike Hotaling, City of Newport News
R. Scott Summers, University of Colorado
Dan Schechter, American Waterworks Service Company, Inc.
Tim Soward, International Consultants, Inc.
David Jorgenson, International Consultants, Inc.
Zaid Chowdhury, Malcolm Pirnie, Inc.
Anne Jack, Malcolm Pirnie, Inc.
Dan Fraser, The Cadmus Group, Inc.
Thomas Grubbs, EPA
Steve Allgeier, EPA
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Table of Contents
Page
EXECUTIVE SUMMARY ES-1
1.0 DISINFECTION BYPRODUCT RULE OVERVIEW
1.1 Introduction 1-1
1.2 General Requirements 1-1
1.2.1 Treatment Techniques 1-1
1.2.2 Compliance Schedule 1-2
1.2.3 Maximum Contaminant Levels 1-3
1.2.4 Maximum Residual Disinfectant Levels 1-5
1.3 Analytical Requirements 1-6
1.4 Reporting Requirements 1-6
1.5 Compliance 1-6
2.0 DEFINITIONS OF ENHANCED COAGULATION AND ENHANCED
PRECIPITATIVE SOFTENING
2.1 Introduction 2-1
2.2 Applicability of Treatment Technique Requirements 2-2
2.3 TOC Removal Performance Requirements 2-2
2.3.1 Step 1 TOC Removal Requirements 2-3
2.3.2 Step 2 Alternative TOC Removal Requirements 2-6
2.3.3 Frequency of Step 2 Testing 2-8
2.4 Alternative Compliance Criteria 2-8
2.4.1 Finished Water SUVA Jar Testing 2-10
2.5 Treatment Technique Waiver 2-11
2.6 Sampling Frequency for Compliance Calculations 2-11
2.7 Compliance Considerations When Blending Source Waters 2-12
3.0 THE STEP 2 PROCEDURE AND JAR TESTING
3.1 Introduction 3-1
3.2 Enhanced Coagulation 3-2
3.2.1 Full-Scale Evaluation of TOC Removal Requirements 3-2
3.2.2 Bench-Scale and Pilot-Scale Testing 3-3
3.2.2.1 Apparatus and Reagents 3-4
3.2.2.2 Protocol for Bench-Scale (Jar) Testing 3-6
3.2.2.3 Protocol for Pilot-Scale Testing 3-11
3.2.3 Application of Step 2 Protocol 3-11
3.2.3.1 Example 1: Adjusting the Full-Scale Dose to Meet
the Step 1 Requirement 3-13
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3.2.3.2 Example 2: Determining the Step 2 TOC Removal
Requirement 3-18
3.2.3.3 Example 3: Determining the Step 2 Requirement when
the POOR is Met Twice 3-26
3.2.3.4 Example 4: Adding Base to Maintain Minimum pH
During Step 2 Jar Testing 3-29
3.2.3.5 Example 5: Determining that the POOR is Never Met 3-32
3.3 Enhanced Precipitative Softening 3-35
3.3.1 Full-Scale Evaluation of TOC Removal Requirements 3-35
3.3.2 Bench-Scale and Pilot-Scale Testing 3-36
3.3.2.1 Apparatus and Reagents 3-36
3.3.2.2 Protocol for Bench-Scale (Jar) Testing 3-37
3.3.2.3 Protocol for Pilot-Scale Testing 3-39
4.0 MONITORING AND REPORTING
4.1 Introduction 4-1
4.2 Monitoring Plans 4-1
4.3 Sampling Locations and Monitoring Frequency 4-2
4.3.1 TOC 4-2
4.3.2 Alkalinity 4-2
4.3.3 Reduced Monitoring for TOC and Alkalinity 4-2
4.3.4 Monitoring for Alternative Compliance Criteria 4-2
4.3.4.1 Additional Alternative Compliance Criteria for
Softening Plants 4-3
4.3.4.2 Monitoring for TTFEVIs and HAAS 4-4
4.4 Enhanced Coagulation and Softening 4-5
4.4.1 Reporting Requirements for TOC Compliance 4-5
4.4.2 Reporting for Alternative Compliance Criteria 4-6
4.4.3 Compliance Calculations for Enhanced Coagulation and
Softening 4-8
4.4.4 Running Annual Average Calculation Flowcharts 4-8
4.5 Example Calculations 4-13
5.0 LABORATORY PROCEDURES
5.1 Introduction 5-1
5.2 Analytical Methods 5-1
5.2.1 Total Organic Carbon 5-2
5.2.2 Dissolved Organic Carbon 5-4
5.2.3 Ultraviolet Light Absorbance at 254 nm 5-5
5.2.4 Specific Ultraviolet Absorption (SUVA) 5-6
5.2.5 Alkalinity 5-6
5.2.6 Trihalomethanes 5-7
5.2.7 Haloacetic Acids 5-8
5.2.8 pH 5-9
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5.2.9 Magnesium Hardness 5-10
5.3 Sample Collection and Handling 5-12
5.4 Quality Assurance/Quality Control 5-16
5.4.1 Total Organic Carbon 5-16
5.4.2 Dissolved Organic Carbon 5-17
5.4.3 Ultraviolet Absorbance at 254 nm 5-17
5.4.4 Specific Ultraviolet Absorption 5-17
5.4.5 Alkalinity 5-18
5.4.6 Trihalomethanes 5-18
5.4.7 Haloacetic Acids 5-19
5.4.8 pH 5-20
5.4.9 Magnesium Hardness 5-20
6.0 SECONDARY EFFECTS OF ENHANCED COAGULATION AND ENHANCED
PRECIPITATIVE SOFTENING
6.1 Introduction 6-1
6.2 Evaluation and Implementation 6-1
6.3 Inorganic Contaminants 6-2
6.3.1 Manganese 6-3
6.3.2 Aluminum 6-7
6.3.3 Sulfate/Chloride/Sodium/Iron 6-11
6.4 Corrosion Control 6-12
6.5 Primary Disinfection 6-17
6.5.1 Chlorine 6-17
6.5.2 Ozone 6-18
6.5.3 Chloramine 6-19
6.5.4 Chlorine Dioxide 6-20
6.6 Particle and Pathogen Removal 6-20
6.7 Residuals Handling, Treatment, and Disposal 6-23
6.7.1 Increased Quantity of Sludge 6-24
6.7.2 Altered Characteristics of Sludge 6-29
6.8 Operation and Maintenance 6-33
6.9 Recycle Streams 6-34
7.0 FULL-SCALE IMPLEMENTATION OF TREATABILITY STUDIES
7.1 Introduction 7-1
7.2 Scale-Up Issues for Treatability Test Results 7-2
7.2.1 Coagulation and Flocculation 7-2
7.2.2 Sedimentation 7-3
7.3 Unit Process Issues 7-4
7.3.1 Chemical Addition 7-4
7.3.2 Rapid Mixing and Flocculation 7-6
7.3.3 Sedimentation 7-7
7.3.4 Filtration 7-9
VI
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7.3.5 Sludge Handling 7-10
7.4 Other Full-Scale Implementation Issues 7-10
APPENDICES
Appendix A: DBF Precursor Removal Processes
Appendix B: TOC Removal by Softening
Appendix C: Other DBF Precursor Removal Technologies
Appendix D: Coagulant Dosages for Step 2 Testing
REFERENCES
List of Tables
1-1 Compliance Dates for the DBPR and ESWTR 1-3
1-2 MCLGs for the Stage 1 DBPR 1-4
1-3 MCLs for the Stage 1 DBPR 1-4
1-4 MRDLGs for the DBPR 1-5
1-5 MRDLs for the DBPR 1-5
2-1 Required Removal of TOC by Enhanced Coagulation for Plants Using
Conventional Treatment: Step 1 Removal Percentages 2-5
2-2 Target pH Under Step 2 Requirements 2-7
2-3 Treatment Technique Compliance Schedule 2-8
3-1 Coagulant Dosage Equivalents 3-5
3-2 Example Data Sheet for Jar Tests to Evaluate Enhanced Coagulation 3-9
3-3 Example 1 Results of pH Titration 3-15
3-4 Example 1 Jar Test Results 3-16
3-5 Example 2 Jar Test Results 3-19
3-6 Example 3 Jar Test Results 3-27
3-7 Base Addition During Jar Testing 3-30
3-8 Example 4 Jar Test Results 3-30
3-9 Example 5 Jar Test Results 3-33
4-1 Monitoring Locations and Sampling Frequency for TTHM and HAAS 4-4
4-2 Reporting Requirements 4-7
4-3 DBF Precursor Removal Compliance Calculations for Example
Water Utility: Enhanced Coagulation, Year 1 4-14
4-4 DBF Precursor Removal Compliance Calculations for Example
Water Utility: Enhanced Coagulation, Year 2 4-15
4-5 DBF Precursor Removal Compliance Calculations for Example
Water Utility: Enhanced Precipitative Softening, Year 1 4-17
vii
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4-6 DBF Precursor Removal Compliance Calculations for Example
Water Utility: Enhanced Precipitative Softening, Year 2 4-18
5-1 Analytical Methods for Demonstration of Compliance 5-2
5-2 Sample Collection Containers and Preservatives/Dechlorinating Agents 5-12
5-3 Sample Handling and Storage 5-14
6-1 Disinfectant Effectiveness under Typical Operating Conditions 6-17
7-1 National Sanitation Foundation Limits on Chemical Additives 7-6
List of Figures
2-1 Guidelines for Achieving Compliance with Enhanced Coagulation/
Enhanced Softening Criteria 2-4
3-1 Example 1: Adjusting the Full-Scale Dose to Meet Step 1 Requirement
Settled Water TOC vs. Coagulant Dose 3-17
3-2 Example 2: Determining the Step 2 Removal Requirement
Settled Water TOC vs. Coagulant Dose (Point-to-point) 3-20
3-3 Example 2: Determining the Step 2 Removal Requirement
Settled Water TOC vs. Coagulant Dose (Continuous Curve) 3-21
3-4 Example 2: Determining the Step 2 Requirement
Settled Water TOC vs. Coagulant Dose 3-25
3-5 Example 3: Determining the Step 2 Requirement when the POOR is met Twice
Settled Water TOC vs. Coagulant Dose 3-28
3-6 Example 4: Adding Base to Maintain Minimum pH During Jar Testing
Settled Water TOC vs. Coagulant Dose 3-31
3-7 Example 5: Determining that the POOR is Never Met
Settled Water TOC vs. Coagulant Dose 3-34
4-1 Running Annual average Compliance Calculation -
First Year of TOC Compliance Monitoring 4-10
4-2 Running Annual Average Compliance Calculation
After First Year of TOC Compliance Monitoring, EC and ES 4-11
4-3 Calculation of Running Annual Average Under Step 2 -
EC Plants Only 4-12
6-1 Flowchart for Development of Manganese Removal Strategy with Enhanced
Coagulation 6-8
6-2 Flowchart for Development of Mitigation Strategy for Aluminum Carryover 6-10
6-3 Effect of Change of Various Water Quality Parameters due to Enhanced
Vlll
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Coagulation on Corrosion of Various Piping Materials 6-13
6-4 Effect of Change of Various Water Quality Parameters due to Enhanced
Softening on Corrosion of Various Piping Materials 6-14
6-5 Flowchart for Developing a Mitigation Strategy for Corrosion Control 6-16
6-6 Flowchart for Developing a Mitigation Strategy for Particle Removal
Problems due to Enhanced Coagulation or Softening 6-22
6-7 Impact Determination of Increased Sludge Volume 6-27
6-8 Mitigation of Impacts from Changes in Sludge Characteristics 6-32
IX
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LIST OF ACRONYMS
AA
AOP
ASTM
AWWA
AWWARF
Atomic Absorption
Advance Oxidation Process
American Society for Testing and Materials
American Water Works Association
American Water Works Association Research Foundation
BAT
BDCAA
CDBAA
CFR
CT
CWS
DAF
DBF
DBPFP
DBPR
DCAA
DC AN
DI
DOC
EBCT
EC
BCD
EDTA
IESWTR
EPA
ES
FACA
GAC
GC
HAA
HAAS
HAAFP
HAN
HANFP
Best Available Technology
Bromodichloroacetic Acid
Chlorodibromoacetic Acid
Code of Federal Regulations
Contact Time
Community Water System
Dissolved Air Flotation
Disinfection Byproduct
Disinfection Byproduct Formation Potential
Disinfection Byproduct Rule
Dichloroacetic acid
Di chl oroacetonitril e
Deionized
Dissolved Organic Carbon
Empty Bed Contact Time
Enhanced Coagulation
Electron Capture Detector
Ethylenediamine tetraacetic acid
Interim Enhanced Surface Water Treatment Rule
Environmental Protection Agency
Enhanced Softening
Federal Advisory Committee Act
Granulated Activated Carbon
Gas Chromatograph
Haloacetic Acid
Haloacetic Acids, group of 5: mono-, di-, and trichloroacetic acids; and
mono- and dibromoacetic acids
Haloacetic Acid Formation Potential
Haloacetonitrile
Haloacetonitrile Formation Potential
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ICP
ICR
IESWTR
Inductively Coupled Plasma
Information Collection Rule
Interim Enhanced Surface Water Treatment Rule
LT2ESWTR
MCL
MCLG
MF
MRDL
MRDLG
MRL
MTBE
MW
MWCO
NF
NIST
NOM
NPDWR
NSF
NTNCWS
PAC
PAC1
PE
POOR
PQL
RAA
RO
Long Term 2 Enhanced Surface Water Treatment Rule
Maximum Contaminant Level
Maximum Contaminant Level Goal
Microfiltration
Maximum Residual Disinfectant Level
Maximum Residual Disinfectant Level Goal
Minimum Reporting Level
Methyl-t-butyl ether
Molecular Weight
Molecular Weight Cutoff
Nanofiltration
National Institute of Sciences and Technology
Natural Organic Matter
National Primary Drinking Water Regulation
National Sanitation Foundation
Non-transient, Non-community Water System
Powdered Activated Carbon
Polyaluminum Chloride
Performance Evaluation
Point of Diminishing Return
Practical Quantitation Limit
Running Annual Average
Reverse Osmosis
SDS
SDWA
SMCL
SOC
SUVA
TBAA
TCAA
THM
THMFP
TMSD
TNCWS
Simulated Distribution System
Safe Drinking Water Act
Secondary Maximum Contaminant Level
Synthetic Organic Chemical
Specific Ultraviolet Absorption
Tribromacetic Acid
Trichloroacetic acid
Trihalomethane
Trichloromethane Formation Potential
Trimethysilyl Diazomethane
Transient Non-community Water System
XI
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TOC Total Organic Carbon
TOX Total Organic Halides
TOXFP Total Organic Halides Formation Potential
TTHM Total Trihalomethanes
UF Ultrafiltration
UFC Uniform Formation Condition
UV Ultraviolet
UV-254 Ultraviolet absorbance at a wavelength of 254 nm
WIDE Water Industry Data Base
Xll
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EXECUTIVE SUMMARY
BACKGROUND
The 1986 Amendments to the Safe Drinking Water Act (SOW A) required the United
States Environmental Protection Agency (EPA) to set maximum contaminant level goals
(MCLGs) for many contaminants found in drinking water. These MCLGs must provide an
adequate margin of safety from contaminant concentrations that are known or anticipated to
induce adverse effects on human health. For each contaminant, EPA must establish either
a treatment technique or a maximum contaminant level (MCL) that is as close to the MCLG
as is feasible with the use of best available technology (BAT).
Acting on the 1986 Amendments, EPA developed a list of disinfectants and
disinfection byproducts (DBFs) for possible regulation after several rounds of stakeholder
comments. The course of the Disinfection Byproduct Rule (DBPR) was decided by a
regulatory negotiation which took place among stakeholders in 1992-93. Following the
negotiation, EPA proposed three regulations: the Stage 1 DBPR, the Interim Enhanced
Surface Water Treatment Rule (IESWTR), and the Information Collection Rule (ICR). The
1994 proposed DBPR includes MCLs for selected DBFs and maximum residual disinfectant
levels (MRDLs) for selected disinfectants. Stage 1 of the DBPR, promulgated December 16,
1998, includes MCLs for trihalomethanes, haloacetic acids, bromate, and chlorite. MRDLs
were also finalized for chlorine, chloramines, and chlorine dioxide. The ICR, finalized in
May 1996, will provide occurrence data for DBFs and precursors, microbials, water quality
parameters, and treatment plant parameters. These data, along with the ICR treatment
studies, health effects research, and other research proj ects, will be used to develop the Stage
2 DBPR and the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR). The
Stage 2 DBPR will be promulgated in 2002.
The MCLs and MRDLs will provide protection against the potential adverse health
effects associated with disinfectants and DBFs. During the regulatory negotiation process,
however, it was realized that these limits alone may not address the potential health risks
from all DBFs, including those which have yet to be identified. Consequently, a treatment
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technique requirement is included in the DBPR to remove natural organic matter (NOM),
which serves as a primary precursor for DBF formation.
The goal of the treatment technique is to provide additional removal of NOM, as
measured by total organic carbon (TOC). The treatment technique applies to Subpart H
systems (systems using surface water or groundwater under the direct influence of surface
water) that practice conventional coagulation or softening treatment. This Guidance Manual
defines the treatment technique for the DBPR and provides implementation assistance for
affected systems.
Subsequent to the completion of the reg-neg process, the 1996 Amendments to
SDWA were passed by Congress. Under these Amendments, EPA was required to expedite
the rule-making process for microbiological contaminants and DBFs. Consequently, EPA
promulgated the Stage 1 DBPR in December 1998. EPA negotiated an agreement in
principle under the auspices of the Federal Advisory Committee Act (FACA) to review the
1994 DBPR proposal and to modify its requirements based upon additional data and
information generated since the proposal. This information is discussed in the November 3,
1997 Federal Register (62 FR 59388). Some requirements were modified based upon
significant experience and study performed by utilities, universities, consultants and the
American Water Works Association (AWWA). This document reflects these modifications.
ENHANCED COAGULATION/ENHANCED SOFTENING DEFINITIONS
The purpose of the treatment technique for DBF precursor removal is to reduce the
formation of DBFs. NOM reacts with disinfectants to form DBFs; therefore, lowering the
concentration of NOM (as measured by TOC) can reduce DBF formation.
"Enhanced coagulation" is the term used to define the process of obtaining improved
removal of DBF precursors by conventional treatment. "Enhanced softening" refers to the
process of obtaining improved removal of DBF precursors by precipitative softening.
ES-2
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Because TOC is easily measured and monitored, the treatment technique uses a TOC
removal requirement. However, basing a performance standard on a uniform TOC removal
requirement is inappropriate because some waters are especially difficult to treat. If the
TOC removal requirements were based solely upon the treatability of "difficult-to-treat"
waters, many systems with "easier-to-treat" waters would not be required to achieve
significant TOC removal. Alternatively, a standard based upon what many systems could
not readily achieve would introduce large transactional costs to States and utilities.
To address these concerns, a two-step standard for enhanced coagulation and
enhanced precipitative softening was developed. Step 1 includes TOC removal performance
criteria which, if achieved, define compliance. The Step 1 TOC removal percentages are
dependent on alkalinity, as TOC removal is generally more difficult in higher alkalinity
waters, and source water with low TOC levels. Step 2 allows systems with difficult-to-treat
waters to demonstrate to the State, through a specific protocol, an alternative TOC removal
level for defining compliance. The final rule also contains certain alternative compliance
criteria that allow a system to demonstrate compliance.
TESTING PROTOCOLS AND LABORATORY PROCEDURES
Initially, a utility should determine if it is required to implement the treatment
technique. If it is, it should evaluate full-scale TOC removal. If this evaluation shows that
the plant is not meeting the required TOC removal, some adjustment to the full-scale
coagulation or softening process will be needed. Before enhanced coagulation or enhanced
softening is implemented at full-scale, careful development of an implementation strategy,
adequate planning, and bench-, pilot-, and/or demonstration-scale (i.e. partial system) testing
should be performed. A system may also wish to evaluate whether any alternative
compliance criteria can be met.
Bench- and pilot-scale testing allow a utility to determine the TOC removal capability
of the plant for different treatment situations, determine the necessary adjustments to full-
scale operation, and, in some cases, to set an alternative percent TOC removal to comply
with the regulation under the Step 2 procedure. These tests are important and call for a well-
ES-3
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defined testing protocol and strict laboratory procedures. The testing protocols for the Step
2 enhanced coagulation bench- and pilot-scale tests are presented in this document.
Laboratory testing methods are also given.
The evaluation of data collected as part of bench- and pilot-scale tests is an important
step in the process of full-scale implementation. To assist utilities in this analysis, data
analysis protocols are presented here. In addition, a number of example analyses are
provided to guide utilities through the evaluation process. Once these evaluations have been
performed, full-scale implementation can be conducted. Utilities should take precautions to
minimize any detrimental side effects of enhanced coagulation or enhanced softening. Items
such as secondary treatment impacts and customer water quality expectations need to be
considered. Suggestions to help minimize these effects are also presented in this document.
SECONDARY EFFECTS
The implementation of enhanced coagulation or enhanced softening can involve
process modifications and can be accompanied by secondary impacts or side effects. Some
side effects will be beneficial to the treatment process while others may be detrimental. This
guidance manual identifies and characterizes the major secondary impacts utilities may
encounter and provides possible mitigation strategies. These impacts include the effect of
enhanced coagulation/enhanced softening on the following:
• Inorganic constituents levels (manganese, aluminum, sulfate, chloride, and sodium)
• Corrosion control
• Disinfection
• Particle and pathogen removal
• Residuals (handling, treatment, disposal)
• Operation and maintenance
• Recycle streams
Not all utilities will experience secondary impacts. Some utilities may experience
very minor secondary effects while others may experience more substantial effects. All
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utilities required to practice enhanced coagulation and enhanced softening, however, should
be aware of the potential effects implementation of enhanced coagulation and softening may
have on plant operation.
OTHER EPA GUIDANCE MANUALS
This manual is one in a series of guidance manuals published by EPA to assist both
States and public water systems in complying with the IESWTR and Stage 1 DBPR drinking
water regulations. Other EPA guidance manuals scheduled to be released in the Spring of
1999 include:
• Disinfection Profiling and Benchmarking Guidance Manual
• Alternative Disinfectants and Oxidants Guidance Manual
• Microbial and Disinfection Byproduct Simultaneous Compliance Guidance Manual
• Uncovered Finished Water Reservoirs Guidance Manual
• Guidance Manual for Compliance with the Interim Enhanced Surface Water
Treatment Rule: Turbidity Provisions
• Sanitary Surveys Guidance Manual
• Unfiltered Systems Guidance Manual
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Chapter 1
DISINFECTION BYPRODUCT RULE
OVERVIEW
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Table of Contents
Page
1.0 DISINFECTION BYPRODUCT RULE OVERVIEW
1.1 Introduction 1-1
1.2 General Requirements 1-1
1.2.1 Treatment Technique 1-1
1.2.2 Compliance Schedule 1-2
1.2.3 Maximum Contaminant Levels 1-3
1.2.4 Maximum Residual Disinfectant Levels 1-5
1.3 Analytical Requirements 1-6
1.4 Reporting Requirements 1-6
1.5 Compliance 1-6
List of Tables
1-1 Compliance Dates for the DBPR and ESWTR 1-3
1-2 MCLGs for the Stage 1 DBPR 1-4
1-3 MCLs for the Stage 1 DBPR 1-4
1-4 MRDLGs for the DBPR 1-5
1-5 MRDLs for the DBPR 1-5
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1.0 DISINFECTION BYPRODUCT RULE OVERVIEW
1.1 INTRODUCTION
The purpose of the Stage 1 Disinfection Byproduct Rule (DBPR) is to reduce
exposure to disinfection byproducts (DBFs) by limiting allowable DBF concentrations in
drinking water, and by removing DBF precursor material to reduce the formation of
identified and unidentified DBFs. Stage 1 of the DBPR establishes maximum contaminant
levels (MCLs) for some of the known DBFs, maximum residual disinfection levels
(MRDLs) for commonly used disinfectants, and a treatment technique for removal of DBF
precursor material to reduce the formation of DBFs. Microbial and chemical contaminant
data collected under the Information Collection Rule (ICR), as well as health effects and
treatment research, will be used in the development of the Long Term 2 Enhanced Surface
Water Treatment Rule (LT2ESWTR) and the Stage 2 DBPR. Negotiations for the
development of these rules began in December 1998 and will incorporate the additional
understanding of DBFs and the disinfection process developed from the ICR database.
1.2 GENERAL REQUIREMENTS
1.2.1 Treatment Technique
In addition to the MCLs and MRDLs, the DBPR requires the use of a treatment
technique to reduce DBF precursors and to minimize the formation of unknown DBFs.
This treatment technique is termed Enhanced Coagulation or Enhanced Precipitative
Softening. It requires that a specific percentage of influent total organic carbon (TOC) be
removed during treatment. The treatment technique uses TOC as a surrogate for natural
organic matter (NOM), the precursor material for DBFs. The treatment technique applies
to subpart H systems (plants using surface water or groundwater under the direct influence
of surface water) that practice conventional filtration treatment (including coagulation and
sedimentation) or softening treatment.
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A TOC concentration of greater than 2.0 mg/L in a system's raw water is the trigger
for implementation of the treatment technique. Specific definitions and alternative
compliance criteria for the treatment technique requirement are presented in Chapter 2.
If a plant is required to practice enhanced coagulation, it must reduce the TOC in the
raw water by a specified percentage before the treated water TOC sampling point, which can
be no later than the combined filter effluent turbidity monitoring location. The required
percent TOC reduction is based on the raw water TOC and alkalinity, and is defined as Step
1 of the treatment technique, as described in Chapter 2. Note that paired samples, one from
the raw water and one from the finished water, are taken simultaneously to determine
compliance. The raw water sample must be taken from untreated water, because the
application of oxidants or other treatment chemicals can change the nature of the TOC,
resulting in unrepresentative analytical results.
Both enhanced coagulation and enhanced softening plants may also use alternative
compliance criteria to demonstrate compliance with the treatment technique. If an enhanced
coagulation plant does not achieve the specified TOC removal as a running annual average,
or any of the alternative compliance criteria, it must proceed to Step 2 of the treatment
technique. For plants practicing enhanced coagulation, the Step 2 procedure requires jar
testing to set an alternative TOC percent removal for determining compliance. Enhanced
softening plants are not required to conduct jar or bench-scale testing. These and other
regulatory requirements are discussed in Chapter 2 of this guidance manual.
1.2.2 Compliance Schedule
The Stage 1 DBPR MCLs and MRDLs apply to community water systems (CWSs)
and non-transient, non-community water systems (NTNCWSs) that add a disinfectant to any
part of the treatment process, including residual disinfection. Table 1-1 summarizes a time
frame for proposed, final, and effective regulations for the Stage 1 DBPR and the IESWTR.
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TABLE 1-1
Compliance Dates for the DBPR and ESWTR
Rule
(Promulgation Date)
DBPR Stage 1
(December 16, 1998)
IESWTR
(December 16, 1998)
SubpartH
Public Water Systems
> 10,000
12/0 11
12/0 11
<10,000
12/03
N/A
Ground Water
Public Water Systems
> 10,000
12/01
N/A
<10,000
12/01
N/A
1. States may grant systems two additional years for compliance if capital improvements are necessary.
Because of potential acute health effects, the MRDL for chlorine dioxide also applies
to transient, non-community water systems (TNCWSs). The effective dates for this
regulation will be staggered based on system size and raw water sources as follows:
• CWSs and NTNCWSs: Subpart H systems serving 10,000 or more persons must
comply with the rule's provisions beginning December 2001. Subpart H systems
serving fewer than 10,000 persons and systems using only ground water not under
the direct influence of surface water must comply with this subpart beginning
December 2003.
• TNCWSs: Subpart H systems serving 10,000 or more persons and using chlorine
dioxide as a disinfectant or oxidant must comply with the chlorine dioxide MRDL
beginning December 2001. SubpartH systems serving fewer than 10,000 persons and
using chlorine dioxide as a disinfectant or oxidant, and systems using only ground
water not under the direct influence of surface water and using chlorine dioxide as
a disinfectant or oxidant must comply with the chlorine dioxide MRDL beginning
December 2003.
1.2.3 Maximum Contaminant Levels
Congress has given EPA broad authority to establish National Primary Drinking
Water Regulations (NPDWRs) and Maximum Contaminant Level Goals (MCLGs). The
MCLGs are developed as non-enforceable health goals. As defined in 40 CFR 141.2, the
MCLG is set "at the level at which no known or anticipated adverse effect on the health of
the person would occur, and which allows an adequate margin of safely." EPA policy is to
1-3
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establish MCLGs for suspected human carcinogens at zero. MCLs are the legally
enforceable standard, and are set as close to the MCLGs as feasible, taking technology and
cost into account.
The DBPR establishes MCLs for the most common and well-studied halogenated
DBFs: total trihalom ethanes (TTHMs) and five of the nine haloacetic acid species (HAAS),
as well as bromate and chlorite. TTHM is defined as the sum of chloroform, bromoform,
bromodichloromethane, and dibromochloromethane. HAAS is defined as the sum of mono-
, di-, and trichloroacetic acids, and mono- and dibromoacetic acids. The MCLGs for the
DBPR are listed in Table 1-2. MCLs for the DBPR are shown in Table 1-3.
TABLE 1-2
MCLGs for the Stage 1 DBPR
Bromoform
Chloroform
Bromodichloromethane
Dibromochloromethane
Dichloroacetic acid
Trichloroacetic acid
Bromate
Chlorite
0 mg/L
0 mg/L
0 mg/L
0.06 mg/L
0 mg/L
0.3 mg/L
0 mg/L
0.8 mg/L
TABLE 1-3
MCLs for the Stage 1 DBPR
Total Trihalomethanes (TTHMs)*
Haloacetic Acids (HAAS)*
Bromate*
Chlorite
0.080 mg/L
0.060 mg/L
0.010 mg/L
1.0 mg/L
! Compliance is based on a running annual average, computed quarterly
1-4
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1.2.4 Maximum Residual Disinfectant Levels
Similar to MCLGs, maximum residual disinfectant level goals (MRDLGs) are health
goals and are not legally enforceable. The MRDLGs for the DBPR are shown in Table 1 -4.
The DBPR also establishes maximum residual disinfectant levels (MRDLs) for the
most commonly used disinfectants, which are enforceable limits similar to MCLs. MRDLs
for the DBPR are shown in Table 1-5. The MRDLs for chlorine and chloramines, but not
chlorine dioxide, may be exceeded to protect public health from specific microbiological
contamination events. These exceedances would be for specific problems caused by
unusual conditions such as line breaks, cross-contamination events, or raw water
contamination.
TABLE 1-4
MRDLGs for the DBPR
Chlorine (as C12)
Chloramine (as C12)
Chlorine dioxide (as C1O2)
4 mg/L
4 mg/L
0.8 mg/L
TABLE 1-5
MRDLs for the DBPR
Chlorine (as C12)*
Chloramine (as C12)*
Chlorine Dioxide (as C1O2)
4.0 mg/L
4.0 mg/L
0.8 mg/L
* Compliance is based on a running annual average, computed quarterly
1-5
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1.3 ANALYTICAL REQUIREMENTS
Plants must use only the analytical methods specified in the regulation for monitoring
purposes. Approved analytical methods are outlined in Chapter 5.
1.4 REPORTING REQUIREMENTS
Plants are required to report their monitoring results to the State primacy agency
within ten days after the end of each monitoring quarter in which the samples were
collected. Plants required to sample less frequently than quarterly must report to the State
within ten days after the end of the monitoring period in which the samples were collected.
Monitoring and reporting requirements for the treatment technique are explained in Chapter
4 of this guidance manual.
1.5 COMPLIANCE
TTHM, HAAS, and Bromate
Compliance with the MCLs for TTHM and HAAS and with the MRDLs for chlorine
and chloramine is based on a running annual average, computed using quarterly samples.
Compliance with the MCL for bromate is based on a running annual average of monthly
samples, computed quarterly, or monthly averages if the system takes more than one sample
in a month.
Chlorite
Compliance with the MRDL for chlorite and chlorine dioxide is more complex as a
result of potential acute health effects. Plants that use chlorine dioxide for disinfection or
oxidation must conduct monitoring for chlorite and chlorine dioxide. Routine chlorite
monitoring requires analyzing one sample per day at the entrance to the distribution system,
as well as taking a three-sample set once per month from within the distribution system.
The distribution system sampling must consist of one sample from each of the following
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locations: near the first customer, at a location representative of average residence time, and
at a location reflecting maximum residence time in the distribution system.
Additional chlorite sampling also must be conducted in this manner. For any day
when the daily chlorite sample exceeds 1.0 mg/L, the plant must take a three-sample set
from within the distribution system on the following day, at the locations prescribed for
monthly monitoring. Compliance with the chlorite MCL is based on the arithmetic average
of any three-sample set taken as required in the distribution system.
Chlorine Dioxide
Routine chlorine dioxide monitoring requires taking one sample per day at the
entrance to the distribution system. In addition, for any daily sample that exceeds 0.8 mg/L,
the plant must take three chlorine dioxide samples in the distribution system on the
following day, located as follows: (1) If there are no disinfection addition points after the
entrance to the distribution system (i.e., no booster chlorination), the plant must take three
samples as close to the first customer as possible, at intervals of at least six hours. (2) If
there are disinfection addition points after the entrance to the distribution system, the plant
must take one sample at each of the following locations: as close to the first customer as
possible, in a location representative of average residence time, and as close to the end of
the distribution system as possible (reflecting maximum residence time in the distribution
system).
Violations of the chlorine dioxide MRDL can be either acute or non-acute. If any
daily sample taken at the entrance to the distribution system exceeds the MRDL, and on the
following day one (or more) of the three samples taken in the distribution system exceeds
the MRDL, the plant is in violation of the MRDL and must notify the public pursuant to the
procedures for acute health risks. If any two consecutive daily samples taken at the entrance
to the distribution system exceed the MRDL and all distribution system samples taken are
below the MRDL, the plant is in violation of the MRDL and must notify the public pursuant
to the procedures for non-acute health risks.
Compliance with the treatment technique for TOC removal is based on a running
annual average, which in turn is based on the quarterly average of monthly samples.
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Compliance calculations, monitoring, and reporting for the treatment technique are
discussed in Chapter 4. The Implementation Guidance Manual for the IESWTR and Stage
1 DBPR (1999) contains a detailed discussion of monitoring and reporting requirements,
and requirements for data submittal to the States.
1-8
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Chapter 2
DEFINITIONS OF ENHANCED COAGULATION AND
ENHANCED PRECIPITATIVE SOFTENING
-------
Table of Contents
Page
2.0 DEFINITIONS OF ENHANCED COAGULATION AND ENHANCED
PRECIPITATIVE SOFTENING
2.1 Introduction 2-1
2.2 Applicability of Treatment Technique Requirements 2-2
2.3 TOC Removal Performance Requirements 2-2
2.3.1 Step 1 TOC Removal Requirements 2-3
2.3.2 Step 2 Alternative TOC Removal Requirements 2-6
2.3.3 Frequency of Step 2 Testing 2-8
2.4 Alternative Compliance Criteria 2-8
2.4.1 Finished Water SUVA Jar Testing 2-10
2.5 Treatment Technique Waiver 2-11
2.6 Sampling Frequency for Compliance Calculations 2-11
2.7 Compliance Considerations When Blending Source Waters 2-12
List of Tables
2-1 Required Removal of TOC by Enhanced Coagulation for Plants Using
Conventional Treatment: Step 1 Removal Percentages 2-5
2-2 Target pH Under Step 2 Requirements 2-7
2-3 Treatment Technique Compliance Schedule 2-8
List of Figures
2-1 Guidelines for Achieving Compliance with Enhanced Coagulation/
Enhanced Softening Criteria 2-4
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2.0 DEFINITIONS OF ENHANCED COAGULATION
AND ENHANCED PRECIPITATIVE SOFTENING
2.1 INTRODUCTION
The term "enhanced coagulation" refers to the process of improving the removal of
disinfection byproduct (DBF) precursors in a conventional water treatment plant. "Enhanced
softening" refers to the improved removal of DBF precursors by precipitative softening.
The removal of natural organic matter (NOM) in conventional water treatment processes
by the addition of coagulant has been demonstrated by laboratory research and by pilot-,
demonstration-, and full-scale studies. Several researchers have shown that total organic carbon
(TOC) in water, used as an indicator of NOM, exhibits a wide range of responses to treatment
with aluminum and iron salts (Chowdhury et al., 1997; Edwards et al., 1997; White et al., 1997;
Owen et al., 1996; Krasner and Amy, 1995; Owen et al., 1993; James M. Montgomery, 1992;
Hubel and Edzwald, 1987; Knocke et al., 1986; Chadik and Amy, 1983; Semmens and Field,
1980; Young and Singer, 1979; Kavanaugh, 1978). The majority of these studies have been
conducted using regular and reagent grade alum (A12[SO4]3-14H2O and A12[SO4]3-18H2O,
respectively) as the coagulant, but iron salts also have been shown to be effective for removing
TOC from water. Polyaluminum chloride (PAC1) and cationic polymers also can be effective for
removing TOC. Cationic polymers (as well as anionic and non-ionic polymers) have proven to
be valuable in creating settleable floe when high dosages of aluminum or iron salts are used.
Specific organic polymers have been shown to remove color in water treatment applications, but
significant TOC removal by organic polymers in conventional facilities has not been
demonstrated, and organic polymers may actually increase the TOC level of the water
(AWWARF, 1989).
The intent of the treatment technique discussed in this document is to establish TOC
removal requirements based on enhanced coagulation/precipitative softening so that:
• significant TOC reductions can be achieved without the addition of unreasonable
amounts of coagulant; and
• regulatory criteria can easily be enforced with minimal State transactional costs.
2-1
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To achieve these objectives, a TOC-based performance standard has been developed for
enhanced coagulation and enhanced precipitative softening using a 2-step system. Step 1 requires
removal of a specific percentage of influent TOC to demonstrate compliance, based on the TOC
and alkalinity of the source water. Step 2 requires enhanced coagulation systems that cannot meet
the Step 1 criteria or the alternative compliance criteria to establish an alternative TOC removal
percentage for defining compliance. These steps are described in detail in Section 2.3. Enhanced
softening systems are expected to meet either the Step 1 removal requirements or one of the
alternative compliance criteria. Therefore, EPA has not developed a Step 2 procedure for systems
using enhanced softening.
2.2 APPLICABILITY OF TREATMENT TECHNIQUE REQUIREMENTS
Public water utilities must implement enhanced coagulation or enhanced softening to
achieve percent TOC removal levels specified in Section 2.3.1 if:
• the source water is surface water or ground water under the direct influence of surface
water (Subpart H systems); and
• the utility uses conventional treatment (i.e., flocculation, coagulation or precipitative
softening, sedimentation, and filtration).
Some types of treatment trains (e.g., direct filtration systems, diatomaceous earth filtration
systems, slow sand filtration) and ground water systems are excluded from the enhanced
coagulation/enhanced softening requirements because: (1) their source waters are generally
expected to be of a higher quality (have lower TOC levels) than waters treated by conventional
water treatment plants; and (2) the treatment trains are not typically configured to allow
significant TOC removal (i.e., they lack sedimentation basins to settle out TOC).
2.3 TOC REMOVAL PERFORMANCE REQUIREMENTS
Individual treatment plants are required to achieve a specified percent removal (Step 1)
of influent TOC between the raw water sampling point and the treated water TOC monitoring
2-2
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location (no later than the combined filter effluent turbidity monitoring location). Compliance
with the TOC removal requirement is based on a running annual average, computed quarterly.
Plants, therefore, will make four compliance determinations each year, one per quarter, based on
the most recent four quarters of data. If a plant practicing enhanced coagulation achieves a
running annual average removal ratio of less than 1.0 (the ratio of actual percent TOC removal
to required percent TOC removal) after the first year of TOC compliance monitoring and it does
not meet any alternative compliance criteria, it is required to perform jar or pilot-scale testing
(Step 2 testing) to set an alternative TOC removal requirement, and report the results of testing
to the State within three months of failing to achieve a running annual average removal ratio of
greater than or equal to 1.0. The alternative removal percentage i s subj ect to State approval. The
compliance process is illustrated in Figure 2-1.
Enhanced softening plants unable to meet the Step 1 TOC removal percentage on a
running annual average basis can also establish compliance by achieving either of two softening-
specific alternative compliance criteria. These two criteria are summarized in Section 2.4.2.
Enhanced softening plants are not required to perform Step 2 testing to set an alternative TOC
removal percentage.
2.3.1 Step 1 TOC Removal Requirements
Table 2-1 summarizes the percent TOC removal requirements for enhanced coagulation.
Enhanced softening plants are required to comply with the TOC removal percentages in the far
right column of Table 2-1 (i.e., where alkalinity >120 mg/L as CaCO3). The percent TOC
removals identified in this table are based upon a large database of bench-, pilot-, and full-scale
studies at a large number of utilities across the nation (Chowdhury et al., 1997).
The TOC removal criteria presented in Table 2-1 were selected so that a large majority
(e.g., 90 percent) of plants required to operate with enhanced coagulation or enhanced softening
will be able to meet the TOC removal percentages. Setting the removal criteria this way is
expected to result in: (1) smaller transact!onal costs to the State because fewer evaluations of Step
2 experimental data will be required; and (2) reasonable increases in coagulant doses at affected
plants.
2-3
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Figure 2-1. Guidelines for Achieving Compliance with Enhanced Coagulation/enhanced
Softening Criteria
Gather data on raw and treated water to compare with the compliance criteria
Qualify
for any
alternative compliance
criteria (see
Sec 2.4)
scale TOC
removal > required
TOC removal? (see
Table 2-1 Sec.
2.3.1)
Yes
In compliance with requirements
STEP 1
Yes
Evaluate full-scale capability to comply with required TOC removal
STEP 2
For Enhanced Coagulation
Plants Only
Can
system achieve
required TOC removal
at full scale?
(see Sec.
2.3.2)
(All Softening Plants
Follow Right Side
of Diagram)
I
Perform jar tests to
establish alternative
TOC removal percentage
(Not applicable to
softening plants)
State Denies
Apply to State for
approval of alternative
TOC removal criteria
(see Sec.2.5 re. waiver)
No
Figure 2-1. Guidelines for Achieving
Compliance with Enhanced Coagulation/
Enhanced Softening Criteria
OC removal
required TOC
removal?
Develop strategy to
implement enhanced
coagulation/enhanced
softening at full scale
Conduct pilot-scale or demonstration-scale tests
to consider secondary effects (see Chapter 6)
Implement enhanced coagulation/
enhanced softening at full scale
Yes
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TABLE 2-1
Required Removal of TOC by Enhanced Coagulation
For Plants Using Conventional Treatment:
Step 1 Removal Percentages'1'b
SOURCE
WATER
TOC (mg/L)
>2.0-4.0
>4.0 - 8.0
>8.0
SOURCE WATER ALKALINITY (mg/L as CaCO3)
Oto60
35.0%
45.0%
50.0%
>60 to 120
25.0%
35.0%
40.0%
>120C
15.0%
25.0%
30.0%
Notes:
a. Enhanced coagulation and enhanced softening plants meeting at least one of the six alternative compliance criteria in
Section 2.4 are not required to meet the removal percentages in this table.
b. Softening plants meeting one of the two alternative compliance criteria for softening in Section 2.4 are not required to
meet the removal percentages in this table.
c. Plants practicing precipitative softening must meet the TOC removal requirements in this column.
The percent removal requirements specified in Table 2-1 were developed with recognition
of the tendency for TOC removal to become more difficult as alkalinity increases and TOC
decreases. In higher alkalinity waters, pH depression to a level at which TOC removal is optimal
(e.g., pH between 5.5 and 6.5) is more difficult and cannot be achieved easily through the addition
of coagulant alone. Compliance with the TOC removal requirements is calculated with a running
annual average, computed quarterly. Month to month changes in source water TOC and/or
alkalinity levels will cause some plants to move from one box of Table 2-1 to another. The
required TOC removal, therefore, may change month to month based on the TOC and alkalinity
level of the monthly source water compliance sample. See Chapter 4 for example compliance
calculations that address this possibility.
Plants not currently in compliance with the values in Table 2-1 may wish to perform jar
testing to evaluate modifications to coagulant dose and/or pH conditions to determine whether
the required TOC removals can be achieved. If the TOC removal performance criteria identified
in Table 2-1 cannot be met, enhanced coagulation systems must implement the Step 2
requirements discussed below.
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2.3.2 Step 2 Alternative TOC Removal Requirements
Some plants required to implement enhanced coagulation will not achieve the removals
in Table 2-1 because of unique water quality characteristics. These plants are required to conduct
jar or bench scale testing under the Step 2 procedure to establish an alternative TOC removal
requirement.
The purpose of the jar tests is to establish an alternative TOC removal requirement,
not to determine full-scale operating conditions Once an alternative removal requirement is
defined by bench- or pilot-scale testing and approved by the State, the utility is free to achieve that
removal in the full-scale plant with any combination of coagulant, coagulant aid, filter aid, and
acid addition. Plants may wish to perform further jar and pilot testing before implementing full-
scale changes. The National Sanitation Foundation has established maximum limits for the
addition of some treatment chemicals; these limits are summarized in Section 7.3.1. Utilities
required to implement the Step 2 requirements should follow the procedures described in Chapter
3.
Under the Step 2 procedure, 10 mg/L increments of alum (or an equivalent amount of
ferric salt) are added, without acid addition for pH adjustment, to determine the incremental
removal of TOC. The Step 2 procedure can be performed through either batch (bench-scale) or
continuous flow (pilot- or full-scale) testing. TOC removal is calculated for each 10 mg/L
increment of regular-grade alum or equivalent amount of iron salt added during jar testing.
Coagulant must be added in the required increments until the target pH shown in Table 2-2 is
achieved. The point of diminishing return (PODR) for coagulant addition is defined as the point
on the TOC removal vs. coagulant addition plot where the slope changes from greater than 0.3/10
to less than 0.3/10, and remains less than 0.3/10 until the target pH is reached. The percent TOC
removal achieved at the PODR is defined, per approval by the State, as the alternative
percent TOC removal requirement.
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TABLE 2-2
Target pH Under Step 2 Requirements
ALKALINITY
(mg/L as CaCO3)
0-60
> 60 - 120
> 120 - 240
>240
TARGET
pH
5.5
6.3
7.0
7.5
The Step 2 procedure requires that incremental coagulant addition be continued until the
pH of the tested sample is at or below the "target pH" (Table 2-2) to ensure that the treatability
of the sample is examined over a range of pH values (see Chapter 3 for details). The target pH
values are dependent upon the alkalinity of the raw water to account for the fact that higher
coagulant dosages are needed to reduce pH in higher alkalinity waters. The regulation requires
that waters with alkalinities of less than 60 mg/L (as CaCO3), for which addition of small amounts
of coagulant drives the pH below the target pH before significant TOC removal is achieved, add
necessary chemicals to maintain the pH between 5.3 and 5.7 until the PODR criterion is met. The
chemical used to adjust the pH should be the same chemical used in the full-scale plant, unless
that chemical does not perform adequately in j ar tests. Substitute chemicals should be used in this
case. A bench-scale method for determining the PODR and alternative TOC removal requirement
under the Step 2 procedure is described in Section 3.2.2.
Compliance with the TOC removal requirements is based on a running annual average;
therefore, systems need 12 months of TOC monitoring data to make a compliance determination.
Since Step 2 bench- or pilot-scale testing is only required when a system fails to achieve a
running annual average removal ratio greater than or equal to 1.0 (i.e., the system is out of
compliance), Step 2 testing will not be performed until the second year of TOC compliance
sampling. If the State approves the Step 2 TOC removal percentage, the State may make that
percentage retroactive for determining compliance. The schedule for compliance with the
treatment technique is shown in Table 2-3.
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TABLE 2-3
Treatment Technique Compliance Schedule
COMPLIANCE ACTION
1 . Begin TOC compliance monitoring
2. Calculate first Running Annual Average (RAA)
for TOC removal compliance
3. Plants with RAA < 1.0 submit results of Step 2
testing to State
POPULATION SERVED
£10,000
January 20021
January 2003
February through
April 2003
<10,000
January 20041
January 2005
February through
April 2005
Note: 1 EPA recommends that systems begin at least one year earlier to determine whether compliance can be achieved.
2.3.3 Frequency of Step 2 Testing
States may wish to have plants perform Step 2 jar testing at least once per quarter for the
first year after treatment technique implementation to examine seasonal changes in treatability.
The State can consider the variability and characteristics of source waters to detemine site-specific
Step 2 testing frequency. An alternative TOC removal percentage set with the Step 2 procedure
remains in effect until the State approves a new value based on the results of new Step 2 testing.
2.4 ALTERNATIVE COMPLIANCE CRITERIA
Certain waters are less amenable to effective removal of TOC by coagulation or
precipitative softening. For this reason, alternative compliance criteria have been developed to
allow plants flexibility for establishing compliance with the treatment technique requirements.
These criteria recognize the low potential of certain waters to produce DBFs, and also account
for those waters not amenable to good TOC removal that may not meet the Step 1 TOC removal
requirement.
A plant can establish compliance with the enhanced coagulation or enhanced softening
TOC removal requirement if any one of the following six alternative compliance criteria is met:
1. Source water TOC <2.0 mg/L: If the source water contains less than 2.0 mg/L of TOC,
calculated quarterly as a running annual average, the utility is in compliance with the
2-S
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treatment technique. This criterion also can be used on a monthly basis, i.e., for
individual months in which raw water TOC is less than 2.0 mg/L, the plant can establish
compliance for that month by meeting this criterion.
2. Treated water TOC <2.0 mg/L: If a treated water contains less than 2.0 mg/L TOC,
calculated quarterly as a running annual average, the utility is in compliance with the
treatment technique. This criterion also can be used on a monthly basis, i.e., for
individual months in which treated water TOC is less than 2.0 mg/L, the plant can
establish compliance for that month by meeting this criterion. Treated water TOC
sampling is conducted no later than combined filter effluent turbidity monitoring.
3. Raw water SUVA <2.0 L/mg-m: If the raw water specific ultraviolet absorption (SUVA)
is less than or equal to 2.0 L/mg-m, calculated quarterly as a running annual average, the
utility is in compliance with the treatment technique requirements. This criterion is also
available on a monthly basis, i.e., for individual months in which raw water SUVA is less
than or equal to 2.0 L/mg-m, the plant can establish compliance for that month by meeting
this criterion. See section 5.2.4 for a discussion of SUVA.
4. Treated Water SUVA <2.0 L/mg-m: If the treated water SUVA is less than or equal to
2.0 L/mg-m, calculated quarterly as a running annual average, the utility is in compliance
with the treatment technique requirements. This criterion is also available on a monthly
basis, i.e., for individual months in which treated water SUVA is less than or equal to 2.0
L/mg-m, the plant can establish compliance for that month by meeting this criterion. See
Section 5.2.4 for a discussion of SUVA. Treated water SUVA sampling is to be
conducted no later than combined filter effluent turbidity monitoring.
5. Raw Water TOC <4.0 mg/L: Raw Water Alkalinity >60 mg/L (as CaCO^: TTHM <40
|ig/L: HAAS <30 |ig/L: It is more difficult to remove appreciable amounts of TOC from
waters with higher alkalinity and lower TOC levels. Therefore, utilities that meet the
above criteria can establish compliance with the treatment technique requirements. All
of the parameters (e.g., TOC, alkalinity, TTHM, HAAS) are based on running annual
averages, computed quarterly. TTHM and HAAS compliance samples are used to qualify
for this alternative performance criterion.
Additionally, utilities that have made a clear and irrevocable financial commitment (prior
to the utility's effective compliance date for the DBPR) to technologies that will limit
TTHM and HAAS to 40 jig/L and 30 jig/L respectively, do not have to practice enhanced
coagulation if the TOC and alkalinity levels of this criterion also are met.
6. TTHM <40 |ig/L and HAAS <30 |ig/L with only chlorine for disinfection: Plants that use
only free chlorine as their primary disinfectant and for maintenance of a residual in the
distribution system, and achieve the stated TTHM and HAAS levels, are in compliance
with the treatment technique. The TTHM and HAAS levels are based on running annual
2-9
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averages, computed quarterly. TTHM and HAAS compliance samples are used to qualify
for this alternative performance criterion.
Example compliance calculations using these alternative compliance criteria are included
in Chapter 4.
Softening plants may demonstrate compliance if they meet any of the six alternative
compliance criteria listed above or one of the two alternative compliance criteria listed below:
1. Softening that results in lowering the treated water alkalinity to less than 60 mg/L (as
CaCO3), measured monthly and calculated quarterly as a running annual average.
2. Softening that results in removing at least 10 mg/L of magnesium hardness (as CaCO3),
measured monthly and calculated quarterly as a running annual average.
Softening plants that currently practice lime softening are not required to change to lime-
soda ash softening by the enhanced softening treatment technique.
If a utility takes more than one compliance sample any month to demonstrate compliance
with an alternative compliance criterion, the results of those samples should be averaged to
determine whether the alternative compliance criterion has been met.
2.4.1 Finished Water SUVA Jar Testing
Specific ultraviolet absorption (SUVA) is an indicator of the humic content of water. It
is a calculated parameter equal to the ultraviolet (UV) absorption at a wavelength of 254 nm
divided by the dissolved organic carbon (DOC) content of the water (in mg/L). The principle
behind this measurement is that UV-absorbing constituents will absorb UV light in proportion
to their concentration. Waters with low SUVA values contain primarily non-humic organic
matter and are not amenable to enhanced coagulation. On the other hand, waters with high SUVA
values generally are amenable to enhanced coagulation.
A treated water SUVA criterion may allow some utilities to determine compliance with
the treatment technique if the SUVA value is less than 2.0 L/mg-m. The determination of SUVA
should be made on finished water that has not been exposed to any oxidant during treatment. If
there is no oxidant (such as chlorine) added prior to the finished water TOC and UV-254
monitoring, full-scale samples can be used to calculate SUVA to allow comparison with this
criterion. However, if oxidants are added prior to the finished water TOC and UV-254
2-10
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monitoring, the utilities are required to establish treated water SUVA by conducting ajar test in
which no disinfectants are added. The jar test can be performed by adding an equivalent amount
of coagulant (metal coagulant plus any polymer that is used in full-scale) in a jar test apparatus
and performing bench-scale coagulation tests. Details on jar testing are presented in Section 3.2.
After completion of the jar test, the settled water should be characterized for its DOC
and UV-254 parameters to calculate SUVA. (Filtration with a pre-washed 0.45 //m membrane
is required for DOC and UV-254 determination). Due to interference from iron in the UV-254
measurement, utilities using ferric salts for coagulation are required to conduct the jar test
described above using equivalent amounts of alum.
2.5 TREATMENT TECHNIQUE WAIVER
Plants that consistently fail to achieve the POOR (i.e., the slope of the TOC vs. coagulant
dose curve is never greater than 0.3 mg/L TOC removed per 10 mg/L alum or equivalent dose of
ferric salt added) at all coagulant dosages during the Step 2 jar test procedure, are considered to
have a water unamenable to enhanced coagulation, and may apply to the State for a waiver from
the enhanced coagulation requirements. The plant should provide supporting documentation to
the State to demonstrate that it was unable to achieve the POOR. States may require plants to
continue quarterly Step 2 testing to demonstrate that the water is unamenable to enhanced
coagulation.
2.6 SAMPLING FREQUENCY FOR COMPLIANCE CALCULATIONS
Utilities must collect at least one paired TOC sample per month to demonstrate
compliance with the TOC removal requirements or to qualify for an alternative compliance
criterion. However, there is no limit to the number of paired TOC samples a utility can collect
and use for compliance calculations, provided the sampling is performed at a regular interval
within the month and during normal operating and water quality conditions.
Utilities must identify in their monitoring plan the number, frequency, and day(s) of the
month TOC compliance samples will be taken. A utility could, for example, take one paired TOC
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sample every Friday of the month, every other day, every fifth day, every day, or at any other
regular sampling interval. Samples taken on designated days should be used in compliance
calculations; samples collected on other days should not be used for compliance. The sampling
interval can be changed month to month, but it should not be changed during the month.
Sampling within a particular month should be representative of the water quality and
treatment operations for that month. If the sample fails laboratory quality assurance/quality
control standards, or some other unforeseen event occurs to render the analysis invalid, a
replacement sample should be taken as soon as possible.
Plants wishing to change their TOC sampling scheme should amend their monitoring plan
before doing so. Plants serving more than 3,300 people are required to submit a copy of their
monitoring plan to the State no later than the first time data are submitted to the State to
demonstrate compliance with any portion of the DBPR. Systems serving fewer than 3,300 people
must keep a copy of their monitoring plan on file.
If a utility takes more than one compliance sample in a month to demonstrate compliance
with an alternative compliance criterion, the results of those samples should be averaged to
determine whether the alternative compliance criterion has been met.
2.7 COMPLIANCE CONSIDERATIONS WHEN BLENDING SOURCE WATERS
Many utilities use more than one raw water source on a continuous or seasonal basis.
These sources, which may be various surface waters or a combination of surface and ground
water, are blended together to create the plant influent. Utilities also may introduce ground water
directly into a treatment train unit process. There are numerous ways for utilities to blend
different source waters and introduce them to the treatment train. Therefore, only general
guidelines are provided here that States and utilities can use to develop and evaluate monitoring
plans submitted to the State.
TOC samples must be taken from untreated source water (i.e., before any disinfectant,
oxidant, or other treatment is applied). Compliance sampling is complicated by this requirement
because utilities frequently apply disinfectant in the source-to-plant transmission lines. This may
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preclude sampling the plant influent immediately after the sources are blended because
disinfectant is present. Sampling schemes that address this difficulty are discussed below.
One or More Surface Water Sources Disinfected or Oxidized Prior to Blending
Sampling of the blended water is not allowed in this case because disinfectant or oxidant
is present. Sample each of the sources prior to disinfectant application by using one of the
schemes below.
Weighted Calculation: Sample each source and perform a TOC analysis. Calculate the
blended water's TOC based on the flow from each source. For example, if three sources
are used and they contribute 50%, 20%, and 30% of the plant influent flow and the
sources' TOC values are 6.0, 4.0, and 3.0 mg/L respectively, and the alkalinity values are
70, 90, and 85 mg/L, respectively, the calculated concentrations will be:
Blended TOC = (.5 x 6.0 + .2 x 4.0 + .3 x 3.0) = 4.7 mg/L
Blended alkalinity = (.5 x 70 + .2 x 90 + .3 x 85) = 78.5 mg/L
Composite Sample: Sample each source and create a composite sample by mixing the
samples in proportion to the percent of the influent each comprises. For example, if a
source is 30% of the plant influent flow, it should comprise 30% of the composite
sample's volume. Once the composite sample is created, a single TOC or alkalinity
analysis can be performed.
Blending of Surface and Ground Waters
Ground and surface waters blended before the application of disinfectant can simply be
sampled after blending. If disinfectant or oxidant is applied to either the surface or ground water
source prior to blending, the TOC should be calculated with the methods discussed above
(disinfectant/oxidant in the ground water will react with TOC in the surface water during
blending). Ground water introduced to the treatment train after rapid mix should not be included
in the raw water TOC sampling. However, the TOC in the ground water will contribute to the
effluent TOC levels, and States and utilities should take this into account when evaluating TOC
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levels in the treated water. States and utilities should work together to develop a monitoring plan
that accurately characterizes the plant's influent TOC level (note that development of a
monitoring plan is required by the rule, as discussed in Chapter 4). The plan should ensure that
required TOC removal is achieved, but it should not place an undue burden on the plant's capacity
to remove TOC.
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Chapter 3
THE STEP 2 PROCEDURE AND JAR TESTING
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Table of Contents
Page
3.0 THE STEP 2 PROCEDURE AND JAR TESTING
3.1 Introduction 3-1
3.2 Enhanced Coagulation 3-2
3.2.1 Full-Scale Evaluation of TOC Removal Requirements 3-2
3.2.2 Bench-Scale and Pilot-Scale Testing 3-3
3.2.2.1 Apparatus and Reagents 3-4
3.2.2.2 Protocol for Bench-Scale (Jar) Testing 3-6
3.2.2.3 Protocol for Pilot-Scale Testing 3-11
3.2.3 Application of Step 2 Protocol 3-11
3.2.3.1 Example 1: Adjusting the Full-Scale Dose to Meet
the Step 1 Requirement 3-13
3.2.3.2 Example 2: Determining the Step 2 TOC Removal
Requirement 3-18
3.2.3.3 Example 3: Determining the Step 2 Requirement when
the POOR is Met Twice 3-26
3.2.3.4 Example 4: Adding Base to Maintain Minimum pH
During Step 2 Jar Testing 3-29
3.2.3.5 Example 5: Determining that the POOR is Never Met 3-32
3.3 Enhanced Precipitative Softening 3-35
3.3.1 Full-Scale Evaluation of TOC Removal Requirements 3-35
3.3.2 Bench-Scale and Pilot-Scale Testing 3-36
3.3.2.1 Apparatus and Reagents 3-36
3.3.2.2 Protocol for Bench-Scale (Jar) Testing 3-37
3.3.2.3 Protocol for Pilot-Scale Testing 3-39
List of Tables
3-1 Coagulant Dosage Equivalents 3-5
3-2 Example Data Sheet for Jar Tests to Evaluate Enhanced Coagulation 3-9
3-3 Example 1 Results of pH Titration 3-15
3-4 Example 1 Jar Test Results 3-16
3-5 Example 2 Jar Test Results 3-19
3-6 Example 3 Jar Test Results 3-27
3-7 Base Addition During Jar Testing 3-30
3-8 Example 4 Jar Test Results 3-30
3-9 Example 5 Jar Test Results 3-33
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List of Figures
3-1 Example 1: Adjusting the Full-Scale Dose to Meet Step 1 Requirement
Settled Water TOC vs. Coagulant Dose 3-17
3-2 Example 2: Determining the Step 2 Removal Requirement
Settled Water TOC vs. Coagulant Dose (Point-to-point) 3-20
3-3 Example 2: Determining the Step 2 Removal Requirement
Settled Water TOC vs. Coagulant Dose (Continuous Curve) 3-21
3-4 Example 2: Determining the Step 2 Requirement
Settled Water TOC vs. Coagulant Dose 3-25
3-5 Example 3: Determining the Step 2 Requirement when the POOR is met Twice
Settled Water TOC vs. Coagulant Dose 3-28
3-6 Example 4: Adding Base to Maintain Minimum pH During Jar Testing
Settled Water TOC vs. Coagulant Dose 3-31
3-7 Example 5: Determining that the POOR is Never Met
Settled Water TOC vs. Coagulant Dose 3-34
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3.0 THE STEP 2 PROCEDURE AND JAR TESTING
3.1 INTRODUCTION
Water treatment plants required to implement enhanced coagulation or enhanced precipitative
softening must demonstrate TOC removals that comply with either the Step 1 TOC removal
requirements, an alternative Step 2 TOC removal requirement approved by the State, or meet the
requirements of alternative compliance criteria presented in Section 2.4. Plants that are unable to
achieve the required Step 1 TOC removal are required to apply to the State, within three months of
their failure to achieve the Step 1 TOC removal, for an alternative TOC removal percentage as
defined by the Step 2 procedure. It is in every plant's best interest to examine TOC removal via
full-scale monitoring and bench- or pilot-scale studies prior to the beginning of compliance
sampling. Compliance with the TOC removal requirement is based on a running annual average;
therefore, the first twelve months of compliance sampling will determine compliance status.
Utilities should make necessary adjustments to their full-scale operations to achieve required TOC
removals before compliance sampling is required.
The implementation of enhanced coagulation and enhanced precipitative softening should
be approached in a planned step-by-step process that includes a desktop evaluation and bench- or
pilot-scale evaluations prior to full-scale evaluation and implementation. In some instances,
however, a desktop evaluation may lead directly to full-scale testing and implementation. For
example, if the desktop evaluation convinces the utility that the existing operation needs no
modification or only slight modification (e.g., slightly adjusting coagulant dose to increase TOC
removal) to achieve required TOC removals, it may be beneficial for the utility to go directly to full-
scale testing and implementation. On the other hand, if a utility determines from the desktop
analysis that they will have to make significant process changes or that the TOC in their water is not
readily removable, the utility should proceed with bench-scale or pilot-scale testing. In such cases,
the utility needs to develop a detailed plan and schedule for an enhanced coagulation or enhanced
precipitative softening testing program prior to proceeding with the testing. The testing program
should clearly identify the testing protocol, sampling needs, and data analysis protocol. Bench- or
pilot-scale evaluations for enhanced coagulation/enhanced precipitative softening may be necessary
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for either: (1) the determination of coagulation conditions for meeting Step 1 performance criteria
(not required by regulation); or (2) the establishment of alternative Step 2 performance criteria
(required by regulation for some systems).
This chapter describes the general treatability procedures and discusses the analysis and
interpretation of data from these tests.
3.2 ENHANCED COAGULATION
3.2.1 Full-Scale Evaluation of TOC Removal Requirements
Initially, plants should determine the current status of the full-scale coagulation process by
collecting TOC samples from the raw water source and the finished water. Raw water TOC must
be sampled prior to the addition of any oxidant or any other treatment. The presence of oxidant in
the treated water TOC sample, however, is acceptable. After collecting source and treated water
samples under existing operations and analyzing for TOC, the percent removal of TOC may be
calculated. Since compliance is based on a running annual average, plants may wish to begin
monitoring TOC removal at least 12 months prior to the rule's effective date to determine whether
they can achieve compliance. If the Step 1 TOC removal requirements (Table 2-1), based on a
running annual average, or any of the alternative compliance criteria (Section 2.4) are met, then the
plant will probably be able to establish compliance once the rule becomes effective. Plants also may
use alternative compliance criteria on a monthly basis to demonstrate compliance. The running
annual average used to calculate compliance may be comprised of months in which the Step 1 TOC
removals are achieved and used in compliance calculations, and other months where an alternative
compliance criterion is met and used in compliance calculations. See Section 4.4.4 to review
compliance calculation procedures, and Section 4.5 for example compliance calculations.
If the plant is not achieving the required TOC removal or satisfying one of the alternative
compliance criteria, it may investigate whether minor changes to its full-scale coagulation scheme
can bring it into compliance. If more than 'minor' adjustments are necessary to achieve compliance,
then bench- or pilot-scale evaluations should be conducted to determine if modifications to full-scale
treatment will allow the utility to achieve required TOC removal. It may be necessary to perform
these evaluations more than once to account for seasonal variations in water quality. It is always
O O
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desirable, however, to estimate the performance of the full-scale system through the use of bench-
scale or pilot-scale testing even when only minor adjustments are necessary. Enhanced coagulation
plants that cannot achieve the required TOC removal on a running annual average basis (i.e., at the
end of the first 12 months of compliance sampling) are required to perform Step 2 testing and apply
to the State for an alternative TOC removal requirement.
3.2.2 Bench-Scale and Pilot-Scale Testing
If a full-scale plant is unable to meet the TOC removal requirements specified in Table 2-1
under current operation, treatability testing should be performed. Treatability testing will assist the
utility in determining chemical dosages or other modifications to full-scale operation to achieve the
requisite TOC removals specified in Table 2-1 (Step 1). Treatability testing can be performed on
a batch basis or on a continuous flow basis.
The protocol described in this chapter has been developed for bench-scale testing to evaluate
TOC removal for enhanced coagulation. Pilot-scale evaluations use the same approach, but should
be conducted on a continuous flow basis using chemical feed adjustments one pilot run at a time.
Sampling and analyses should be conducted to collect the same data as for the bench-scale testing
program described below.
The Step 2 procedure described here is based on the incremental addition of coagulant to
define an alternative TOC removal percentage. Only aluminum- or iron-based coagulants may be
used for the Step 2 procedure. Addition of acid, polymers, or other treatment chemicals is not
permitted. Once the alternative TOC removal percentage is determined via Step 2 testing, a plant
may achieve this removal at full-scale using any combination of coagulant, coagulant aid, filter aid,
or pH adjustment by acid addition. The goal of the Step 2 procedure is to determine the amount of
TOC that can be removed with reasonable amounts of coagulant, and to define an alternative TOC
removal percentage. The procedure is not designed nor intended to be used to establish a full-scale
coagulant dose requirement.
The maj ority of the data for removal of TOC in drinking water treatment has been developed
with the use of regular-grade alum (A12[SO4]3 -14H2O). Iron salts are also effective for removing
TOC, and equivalent dosages for iron salts have been developed to compare all coagulants on a
"metal-equivalent" basis, as shown in Table 3-1. An example calculation for the conversion of a 10
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mg/L dose of alum to a metal equivalent dosage of another coagulant is included in Appendix D.
A list of common coagulants along with typical characteristics can be found in "Water Treatment
Principles and Design," by James M. Montgomery Consulting Engineers (1985).
The concentrations and characteristics of TOC in source waters may change over time. In
some source waters, the change can be rapid, such as during storm events. Other source waters have
a consistent TOC concentration and characteristic as a result of source water storage in reservoirs.
Still other waters exhibit seasonal changes in TOC characteristics as a result of algal activity or snow
melt. Therefore, States may wish to have Step 2 testing performed on at least a quarterly basis to
reflect seasonal changes in source water quality for the first year after treatment technique
implementation. After the first year, the State may wish to modify the Step 2 testing frequency to
a level that adequately characterizes treatability.
3.2.2.1 Apparatus and Reagents
The following equipment and chemical reagents are needed to perform the testing. All
glassware should be Class A.
Jar test apparatus with 1 or 2 liter (L) beakers or square mixing jars. Square jars are
preferred because they more efficiently distribute the mixing energy into the water.
The use of covers is recommended during jar testing to limit the transfer of CO2 and other
gases. Covers should be constructed of an inert material.
pH meter. The pH meter should be calibrated daily with fresh buffers. A two-point
calibration using buffer solutions with pH of 4.0 and 7.0 is necessary, at a minimum; a three-
point calibration using buffer solutions with pH of 4.0, 7.0, and 10.0 is recommended.
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TABLE 3-1
Coagulant Dosage Equivalents 1
Regular Grade Alum
(Aluminum Sulfate)
A12(S04)3*14 H20
(mg/L)
10
20
30
40
50
60
70
80
90
100
Reagent Grade
Alum (Aluminum
Sulfate)
A12(SO4)3*18 H2O
(mg/L)
11.2
22
34
45
56
67
78
90
101
112
Ferric
Chloride
FeCl3*
6H2O
(mg/L)
9.1
18
27
36
46
55
64
73
82
91
Ferric
Chloride
FeCl3
(mg/L)
5.5
11
16
22
27
33
38
44
49
55
Ferric
Sulfate
Fe2(S04)3*
9H2O
(mg/L)
9.5
19
28
38
47
57
66
76
85
95
Ferrous
Sulfate
FeSO4*
7H2O
(mg/L)
9.4
19
28
37
47
56
66
75
84
94
Notes:
1. All dosages reported as '
"active" chemicals, prior to dilution
Freshly prepared (no more than seven days old) stock solution of alum or other coagulant.
(See step 2 of Section 3.2.2.2 for an example of preparation of a stock solution.)
Sample bottles compatible with analysis of coagulated water for alkalinity and pH
measurement.
Sample bottles suitable for TOC analysis.
25 and 50 mL pipettes, with 10 mL graduated pipette bulbs. Pipettes are used to accurately
measure volumes during preparation of stock solutions. Pipette bulbs are available with
start/stop buttons for very accurate measurement. Volumetric pipettes may be used for more
precise dosages. Plastic disposable syringes (without needles) may be used to measure
coagulant doses to be applied during the jar tests.
1 L graduated cylinders.
Miscellaneous beakers and other glassware.
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20 L carboys with siphons or taps for dispensing water (for bench-scale tests only). A
suitable laboratory tap also may be used.
Magnetic stirrer with stirring bars.
3.2.2.2 Protocol for Bench-Scale (Jar) Testing
The following jar test method should be used to conduct the Step 2 procedure. This method
relies on the addition of coagulant only; acid and polymers cannot be used.
Step 1. Gather testing supplies.
Step 2. Prepare coagulant stock solution by diluting the coagulant available at the plant to result in
a desired concentration. The concentration of the stock solution should be selected so that
when an easily measurable volume of the stock solution (e.g., 1 mL) is added to a 2-liter jar
of raw water the resulting dose becomes 10 mg/L of alum or an equivalent concentration
of other coagulant (see Table 3-1). For example, if alum (A12(SO4)3- 14H2O) is the
coagulant to be evaluated, the strength of the stock solution should be 20 mg/mL (or 20
g/L). On the other hand, if ferric sulfate (Fe2(SO4)3- 9H2O) is the coagulant to be evaluated,
the strength of the stock solution should be 19 mg/mL (or 19 g/L).
Alum is typically available as an aqueous solution containing approximately 49 percent
A12(SO4)3-14H2O and a specific gravity of 1.2. The concentration can be converted to g/L
as follows:
Alum concentration = 49 % as A12(SO4)3- 14H2O
= 49 x (g-alum/100 g-solution)
x (1.2 g-solution/1 mL-solution)
x (1000 mL/L)
= 588 g-alum/L (or 0.588 g/mL)
To prepare a 20 g/L stock solution, add 34 mL (= 20/0.588) of the "neat" (original shelf
stock) A12(SO4)3-14H2O solution to 1 liter of deionized water using a volumetric flask. Each
mL of this stock solution will contain 20 mg of A12(SO4)3- 14H2O. Adding 1 mL (or 20 mg)
to a 2-liter jar will result in a A12(SO4)3-14H2O concentration of 10 mg/L.
Ferric sulfate is also typically available as an aqueous solution. The concentration of the
solution is typically reported as percent iron in the coagulant (e.g., 14.6 percent). Knowing
the specific gravity of the chemical (e.g., 1.5) the concentration can be converted to g/L as
follows:
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Iron concentration = 14.6 % as Fe
= 14.6 x (g-Fe/100 g-solution)
x (1.5 g-solution/1 mL-solution)
x (1000 mL/L) x (562 g-Fe2(SO4)3-9H2O/(56x2) g-Fe)
= 1098 g-Fe2(SO4)3- 9H2O/L (or 1.098 g/mL)
where:
562 = molecular weight of Fe2(SO4)3- 9H2O
56 = atomic weight of Fe.
To prepare a 19 g/L stock solution, add 17.3 mL (= 19/1.098) of the "neat" Fe2(SO4)3- 9H2O
solution tol liter of DI water using a volumetric flask. Each mL of the stock solution will
contain 19 mg of Fe2(SO4)3- 9H2O. Adding 1 mL (or 19 mg) to a 2-liter jar will result in a
Fe2(SO4)3- 9H2O concentration of 9.5 mg/L (equivalent to 10 mg/L of alum).
The pH of the coagulant stock solution prepared according to the above procedure should
generally be below 3.0. If the pH of the coagulant stock solution is allowed to increase
significantly above 3.0, some precipitation of metal hydroxide may occur resulting in the
loss of active coagulant.
Step3. Collect20 to 30 liters of raw water forthejar testing. The temperature of the sample should
be maintained at ambient conditions prior to and during testing. If the collected water must
be stored for subsequent testing, the sample should be refrigerated (approximately 4°C).
The temperature of the sample should be adjusted to the ambient water temperature during
collection before starting any testing with the sample. Every effort should be made to
conduct tests with freshly collected water. It may be difficult, however, to maintain ambient
water temperatures during j ar testing, especially in colder climates. Jar testing may take up
to two hours (including the mixing and settling times), during which time the water
temperature will gradually change to equilibrate with the air temperature of the room in
which testing is being performed. Temperature change during j ar testing may interfere with
the settling of floe due to convection currents or release of dissolved air. Efforts should be
taken to minimize temperature change during jar testing. This can be accomplished by
conducting jar tests in a room which is not climate controlled (e.g., filter gallery), or by
immersing the jars in a water bath through which plant water is circulated.
Step 4. Measure pH and alkalinity of the raw water sample.
Step 5. Determine the maximum alum or ferric dose to be evaluated during enhanced coagulation
jar testing using the following procedure:
Place a 1 L or a 2 L sample on a magnetic stirrer. Add alum to the sample in 10 mg/L
increments (or equivalent ferric dosages shown in Table 3-1). Measure and record the pH
after each incremental coagulant dose. Determine the alum or ferric dose required to reach
the target pH (listed in Table 2-2 for various raw water qualities).
5-7
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In low alkalinity waters (e.g., less than 60 mg/L as CaCO3), small dosages of metal
coagulant can depress the pH below 5.5 (the target pH for source waters with alkalinity <
60 mg/L as CaCO3). Accordingly, when the pH drops below 5.5 for a given incremental
addition of coagulant in low alkalinity waters, add base (lime or caustic soda) at dosages
necessary to maintain the pH between 5.3 and 5.7. If lime or caustic soda addition is
necessary to maintain a pH between 5.3 and 5.7, note the amount of lime or caustic needed
to maintain the coagulation pH. A pre-evaluation using small volumes of sample (e.g., 100
mL) may be useful to determine the pH depression caused by coagulant addition, and the
amount of base needed to adjust the pH to between 5.3 and 5.7. The facility should use the
same caustic in the jar test as that used at full-scale.
Step 6. Measure 1 to 2 L of sample into the required number of beakers or mixing j ars (determined
from step 5) and place the jars on the jar test apparatus. The volume of sample needed
depends on the jar size. Begin filling out a data sheet similar to the one shown in Table 3-2.
Enter the type of coagulant, the concentration of the stock solution, and the desired mixing
conditions. These conditions should reflect mixing conditions and detention times at the
plant's maximum daily flow for the quarter being tested. For rapid mixing, a detention time
of at least one minute should be used. If the plant mixing intensities and durations are not
known, use a rapid mix at 100 rpm for one minute, and flocculate at 30 rpm for 30 minutes.
Also enter the desired coagulant doses for each of the j ars and calculate the volume of stock
solution needed to achieve the desired dose. Coagulant doses should be selected at an
increment of 10 mg/L (or equivalent dose of iron coagulant). For example, a series of doses
for alum coagulation jar tests could be 10,20, 30, 40, 50 and 60 mg/L. An equivalent series
of doses for ferric chloride (FeCl3-6H2O) would be 9.1, 18, 27, 36, 46 and 55 mg/L.
Additional jars would be needed if the maximum coagulant dose to be evaluated is greater
than 60 mg/L of alum.
Add coagulant dosages while mixing at high speeds. Concurrently, add lime or caustic soda
to low alkalinity waters (at previously determined doses) if necessary to maintain a pH
between 5.3 and 5.7 (see step 5 above). (If it is difficult to add the two chemicals
simultaneously, add the base first, followed by the coagulant.)
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TABLE 3-2
EXAMPLE DATA SHEET FOR JAR TESTS TO EVALUATE ENHANCED
COAGULATION
COAGULANT
Coagulant tested
Stock solution concentration
MIXING CONDITIONS
Rapid mix rpm
Rapid mix duration (min.)
Flocculation rpm
Flocculation duration (min.)_
Settling duration (min.)
Coagulant
Dose
Volume of
Coag. Stock
Solution
Units
mg/L
mL
RAW
JAR#1
JAR #2
JAR #3
JAR #4
JAR #5
JAR #6
TOC
DOCa
Wa
254
SUVA3
pH
Alkalinity
ID#
mg/L
ID#
mg/L
ID#
I/cm
L/mg-m
mg/L as
CaCO,
Note: a - Optional parameters. These parameters are not necessary to establish the PODR, however,
utilities may use them, for example, to determine treated water SUVA in a plant using ferric coagulation
or prechlorination.
3-9
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Rapid mix, flocculate, and settle using times listed on the data sheet. The coagulant should
be added during rapid mixing, with the timer on the process being started after the chemical
is added. All jars, regardless of mixing conditions, should be allowed to settle for 60
minutes, without stirring, prior to sampling.
Step 7. After settling, sample the supernatant for TOC analysis using 25 or 50 mL wide-bore
pipettes, a siphon apparatus, or sampling ports located on the side of the mixing jars.
During sampling, the tip of the pipette should be approximately 10 cm (4 inches) below the
water surface. In a typical 2-liter square jar, the sampling port is also located approximately
10 cm below the 2-liter mark on the side of the jar. Be careful not to disturb the settled floe,
and to avoid suspended floe, while sampling. Preserve and/or refrigerate the samples for
subsequent TOC analysis as described in Chapter 5. Provide unique sample ID for each
sample and note the ID numbers on the data sheet.
Step 8. Withdraw additional supernatant samples for pH and alkalinity, and analyze within
appropriate holding times. Note the values on the data sheet.
In the jar testing program, TOC removal is based upon removal by coagulation and settling
only, which has been shown to remove the bulk of the TOC. Filtration may provide some additional
removal of TOC beyond that achieved in the jar tests, and plants are allowed to include TOC
removal by filtration as part of their full-scale compliance with the enhanced coagulation
requirements.
Once the required percent TOC removal is determined for the Step 2 procedure using the
incremental addition of metal coagulant at bench- or pilot-scale, it may be desirable for a system to
achieve this removal at full-scale using a combination of coagulant and acid addition to depress pH
(thereby improving TOC removal for a given coagulant dosage by depressing pH beyond that
achieved with coagulant addition alone). Refer to the example in Section 6.7.1 to review the
comparative costs of using coagulant alone or coagulant with acid addition. The implementation of
any full-scale operational changes should always be preceded by extensive bench- and pilot-scale
testing.
Higher doses of coagulant may result in a poorly settling floe. Therefore, it may be useful
to perform additional jar tests to evaluate polymer aids to assist in settling for full-scale
implementation. The use of polymers, however, is not allowed in the Step 2 jar testing protocol to
establish alternative TOC removal requirements. Many polymers are available for use as coagulant
aids. A cationic or non-ionic polymer with high molecular weight may work well as a coagulant aid.
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The polymer in use at the full-scale facility or an alternative polymer could be evaluated. Using
polymer coagulant aids, if necessary, will improve floe settleability and thereby reduce particulate
organic carbon during sampling of the supernatant.
3.2.2.3 Protocol for Pilot-Scale Testing
Pilot-scale testing can be used to establish an alternative TOC removal percentage if a utility
has access to a pilot plant that simulates the full-scale water treatment plant with respect to rapid
mix, flocculation, and sedimentation. Coagulant doses at an increment of 10 rng/L of alum (or
equivalent ferric salt) need to be applied at the rapid mix process. Appropriate base (for waters that
may require base addition to maintain pH between 5.3 and 5.7) may also be applied at the rapid mix.
After setting the chemical feed for one set of coagulation conditions, operate the pilot plant long
enough to achieve a steady-state. This may require a minimum of three to four times the theoretical
detention time in the flocculation and sedimentation basins. After achieving steady-state, collect
samples of raw and treated waters as described in Section 3.2.2.2.
3.2.3 Application of the Step 2 Protocol
This section provides examples of how to analyze the results of Step 2 jar testing to set an
alternative TOC removal requirement. Results of the Step 2 procedure should be analyzed as
described in this section. Although jar testing is not required for utilities that achieve the Step 1
TOC removal requirement, some utilities may opt to perform jar or bench-scale tests to develop a
better understanding of TOC removal for different coagulant doses and raw water conditions. Due
to inherent differences between full-scale and jar testing mixing conditions (which result in
differences in carbon dioxide dissolution), jar testing may not always accurately predict full-scale
behavior. Consequently, an adequate margin of safety should be incorporated into translating jar
testing results to the full-scale application. Also, systems may find that additional TOC removal may
provide greater flexibility in achieving compliance with DBF MCLs.
Bench-scale or pilot-scale testing may assist utilities that are close (e.g., within 5%) to
achieving the required Step 1 TOC removal to develop a treatment strategy that will enable them to
improve TOC removal and meet the Step 1 requirement. In such tests, utilities should examine and
note the effectiveness of different combinations of coagulant, polymers, and acid addition (the NSF
3-11
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International limit on sulfuric acid addition is 50 mg/L). However, jar tests performed to set an
alternative TOC removal requirement under the Step 2 procedure must be conducted with addition
of only alum or ferric coagulant. Other treatment chemicals cannot be used.
The following examples are presented in this section:
• Example 1: Adjusting the full-scale dose to meet or exceed the Step 1 requirement
A utility that is close to meeting the Step 1 TOC removal requirement examines a range of
coagulant doses to adjust full-scale coagulation practice to improve TOC removal.
• Example 2: Determining the Step 2 TOC removal requirement
A utility conducts jar testing to define an alternative Step 2 TOC removal requirement. Two
methods of data analysis are presented to determine the point of diminishing returns (PODR)
discussed in Section 2.3.2. First, data points are connected with straight line segments (a
"point-to-point" approach), and second, regression analysis is used to fit a curve to the data
points. Systems should receive approval from the State before they use regression techniques
to perform analysis of Step 2 data.
• Example 3: Determining the Step 2 requirement when the PODR is met twice
A utility conducts jar testing to define an alternative Step 2 requirement and finds they satisfy
the PODR, first at a lower dose and then at a higher dose.
• Example 4: Adding base to maintain minimum pH during Step 2 jar testing
A utility with a low alkalinity water conducts jar testing to define an alternative Step 2
requirement and finds they are required to add base to maintain the coagulation pH between
5.3 and 5.7 during Step 2 jar testing.
• Example 5: Determining that the PODR is never met
A utility conducts jar testing to define an alternative Step 2 requirement and obtains a very
flat TOC removal curve that does not satisfy the PODR, causing them to apply to the State
for a waiver from enhanced coagulation requirements.
In all of the examples it is assumed that the utility in question monitored TOC removal
during the 12 months prior to the beginning of the required TOC compliance sampling. As a result
of this monitoring (see sections 4.4.4 and 4.5), the utilities determined that their current TOC
removal, on a running annual average basis, was inadequate to establish compliance with the Step
1 removal requirements. This prompted them to conduct bench-scale testing in order to evaluate
alternative compliance requirements. The jar tests described in the following examples followed the
step-by-step protocol described in Section 3.2.2.2.
3-12
-------
Monitoring full-scale TOC removal is not required prior to the effective date of the rule.
However, early monitoring will allow utilities to make minor modifications in their operation and
better position themselves for achieving compliance with the treatment technique. Utilities which
cannot meet the Step 1 compliance criteria during the first!2 months of monitoring (after the rule
is effective) must conduct testing using the Step 2 procedure and must submit an application to the
State for an alternative compliance requirement. The application must be submitted within three
months of the utility's failure to achieve compliance and must provide the results of bench-scale or
pilot-scale testing. Quarterly Step 2 testing is recommended in the first year the utility uses Step 2
testing to demonstrate compliance.
Once the alternative performance criteria have been approved, the utility will develop
strategies to implement any full-scale changes to meet the Step 2 TOC removal. Proper
consideration should be given to additional bench- and pilot-scale testing and to the mitigation of
any potential secondary effects that may arise as a result of full-scale implementation of enhanced
coagulation. The utility may achieve the Step 2 TOC removal percentage through any combination
of coagulant, polymer, and acid addition at full-scale.
3.2.3.1 Example 1 - Adjusting the Full-Scale Dose to Meet the Step 1 Requirement
After the first 12 months of monitoring, this utility's calculated running annual average
compliance ratio was 0.95. Since this utility was close to meeting the Step 1 requirement, it had two
choices: (1) adjust the full-scale alum dose in small increments, without disrupting other processes
in the treatment train, so TOC removal is increased to the Step 1 requirement; or (2) conduct bench-
scale tests to examine the coagulant doses that will allow it to meet the Step 1 requirement.
By examining the monthly variation in raw water TOC and alkalinity levels, the utility
determined that if it consistently achieves a monthly TOC removal of 25 percent, it should be able
to maintain a running annual average compliance ratio greater than 1.0. The utility decided to
proceed with bench-scale tests to examine the alum dose needed to achieve a 25 percent TOC
removal. To examine appropriate coagulant doses, jar tests were performed. First, the utility
determined the range of alum dose to be tested. This was accomplished by conducting a pH titration
with alum to the target pH of 7.0 (see Table 2-2). Therefore, alum was added to the raw water in 10
mg/L increments until a pH of 7.0 was reached. The results of this titration are shown in Table 3-3.
3-13
-------
The utility was not required to reach the target pH during this test because the test was not being
conducted to set an alternative TOC removal requirement. However, the target pH can serve as a
good endpoint for maximum coagulant doses during treatability testing. As a result of the pH
titration results (shown in Table 3-3), alum doses between 0 and 100 mg/L were evaluated during
jar testing. TOC levels were evaluated for each alum dose. The TOC results are given in Table 3-4
and shown graphically in Figure 3-1. Figure 3-1 presents the point-to-point TOC removal curve.
The next step this utility took was to estimate the dose needed to achieve 25 percent TOC
removal. In Table 3-4, TOC removal is given for each alum dose. As shown, an alum dose of 50
mg/L produced 22 percent TOC removal while an alum dose of 60 mg/L produced 34 percent TOC
removal. Therefore, the estimated alum dose range required to meet the Step 1 requirement of 25
percent TOC removal is between 50 and 60 mg/L (Figure 3-1 indicates a dose of 55 mg/L). The
utility may conduct additional jar tests to capture the effect of seasonal water quality changes and
determine a range of coagulant doses for different water quality conditions. The system may also
decide to remove the additional TOC in order to more easily meet TTHM and HAAS MCLs and the
TOC removal requirements, to qualify for reduced monitoring, or to limit the potential disinfection
modifications that may be needed. By evaluating SUVA results, the system may be able to identify
periods during the year when TOC is more easily removed.
3-14
-------
TABLE 3-3
Example 1 Results of pH Titration
Alum Dose
(mg/L)
0
10
20
30
40
50
60
70
80
90
100
Resulting pH
7.95
7.8
7.7
7.5
7.4
7.35
7.25
7.2
7.15
7.05
6.9
3-15
-------
TABLE 3-4
Example 1 Jar Test Results
Alum Dose
(mg/L)
0
10
20
30
40
50
60
70
80
90
100
Settled Water
TOC (mg/L)
5.45
5.50
5.50
5.00
4.78
4.52
3.60
3.24
3.00
2.78
2.53
TOC Removal
(%)
0
0
8
12
17*
34*
41
45
49
54
*This utility's standard is 25 percent TOC removal.
3-16
-------
Figure 3-1
Example 1: Adjusting the full-scale dose to meet Step 1 requirement
Settled Water TOC vs. Coagulant Dose
10 20
30
40 50
Alum Dose
60
70 80 90 100
3-17
-------
3.2.3.2 Example 2 - Determining the Step 2 TOC Removal Requirement
The first 12 months of monitoring for TOC removal resulted in the calculation of a running
annual average removal ratio of 0.75 for this utility, which prompted it to conduct jar testing under
the Step 2 procedure. A pH titration was first performed to the required target pH of 6.3 (see Table
2-2). A ferric sulfate addition of 95 mg/L was needed to reach the target pH of 6.3, therefore, ferric
sulfate doses up to 95 mg/L were evaluated during jar testing. Jar tests were run according to the
protocol set forth in Section 3.2.2.2 using ferric sulfate solution doses of 0 through 95 mg/L in 9.5
mg/L (equivalent to 10 mg/L alum as shown in Table 3 -1) increments. After performing the j ar tests,
TOC levels were evaluated for each dose. The TOC results are given in Table 3-5 and shown
graphically in Figures 3-2 and 3-3. Figure 3-2 presents the point-to-point TOC removal curve.
Figure 3-3 presents the TOC removal curve drawn using a regression technique.
The Step 2 TOC removal percentage is set at the last point (i.e. highest coagulant dose) on
the TOC removal vs. coagulant dose plot where the magnitude of the slope is greater than or equal
to 0.3 mg/L TOC removal per 10 mg/L of alum or equivalent alum dose. The data analysis used to
determine the Step 2 TOC removal requirement is presented in two ways for this example: Part A
uses the point-to-point curve shown in Figure 3-2, and Part B uses the continuous curve shown in
Figure 3-3 developed using regression techniques to determine the PODR.
Part A - Point-to-point curve
Table 3-5 documents TOC removal as a function of ferric sulfate dose. In addition, the
equivalent alum dose and incremental TOC removal is given at each point for calculation of the
incremental slope in units of mg-TOC/mg-alum. Calculation of the slope in terms of mg-alum
allows direct comparison of the incremental slope with the PODR requirement of 0.3 mg-TOC/10
mg-alum. The slope between each point is calculated according to equation 3-1:
3-18
-------
Slope = (TOC2-TOC1)/(DOSE2-DOSE1)
(3-1)
where: TOCj = TOC level of first data point in mg/L
TOC2 = TOC level of second data point in mg/L
DOSEj = Coagulant dose of first data point in mg/L
DOSE2 = Coagulant dose of second data point in mg/L
TABLE 3-5
Example 2 Jar Test Results
Ferric
Sulfate
Dose
(mg/L)
0
9.5
19
28.5
38
47.5
57
66.5
76
85.5
95
Equivalent
Alum Dose
(mg/L)
0
10
20
30
40
50
60
70
80
90
100
Settled
Water
TOC
(mg/L)
4.2
3.8
3.3
2.9
2.8
2.55
2.3
2.3
2.1
2.0
2.0
Incremental
TOC
Removal
(mg/L)
-
0.4
0.5
0.4
0.1
0.25
0.25
0
0.2
0.1
0
Incremental
Slope (mg-
TOC/mg-alum)
-
-0.04
-0.05
-0.04
-0.01
-0.025
-0.025
0
-0.02
-0.01
0
TOC
Removal
(%)
-
9
21
31
33
40
45
45
50
52
52
3-19
-------
Figure 3-2
Example 2: Determining the Step 2 removal requirement
Settled Water TOC vs. Coagulant Dose
5.0
4.5 -
2.0 -
1.5 -
1.0 Jr
PODRat2.8mg/LTOC
or 33% removal
0 10 20 30 40 50 60 70
Equivalent Alum Dose [mg/L]
90 100
Note: The dashed line corresponds to a slope of 0.3 mg-TOC/10 mg-alum.
3-20
-------
-J
Ta
u
o
H
Figure 3-3
Example 2: Determining the Step 2 requirement
Settled Water TOC vs. Coagulant Dose
Regression Line
y = 2.53 exp (-0.0224 * x) + 1.70
R2=0.99
3.04 mg/L TOC or 28% removal
1.0
0 10 20 30 40 50 60 70
Equivalent Alum Dose [mg/L]
90 100
3-21
-------
As shown in Table 3-5, the slope of the point-to-point curve reaches -0.03 between ferric
sulfate doses of 28.5 and 38 mg/L and does not fall below-0.03 (i.e. more than 0.3 mg/L TOC is not
removed in a 10 mg/L alum addition) at any point on the curve to the right of 38 mg/L. Therefore
the PODR occurs at the second (i.e. higher) dose of 38 mg/L. The calculated TOC removal at this
point where the slope criteria is satisfied is shown in Table 3-5 as 33 percent. The alternative Step
2 TOC removal should therefore be set at 33 percent. This is shown graphically on Figure 3-2 (note
that Figure 3-2 is drawn using equivalent alum dose). Based upon the results of this jar test, the
utility will apply to the State for an alternative TOC removal of 33 percent.
If in this example the slope had fallen below -0.03 at a point further to the right on the curve,
that point further to the right would have set the alternative TOC removal percentage (see Example
3). If the slope had been exactly -0.03 between these two points, the PODR would be set at the
second (i.e. higher) dose of 38 mg/L, since the slope of that entire line segment meets the requisite
slope (see Example 4).
Part B - Continuous curve
In this alternative data analysis approach, the utility received permission from the State to
use regression techniques to draw a best-fit continuous curve through the data points (data shown
in Table 3-5). To obtain a continuous curve, this utility fitted the experimentally observed residual
TOC levels versus the ferric sulfate solution dose data with an exponential decay model of the form
given in Equation 3-2 below. Commercially available curve-fitting programs can be used for this
type of regression analysis.
y = a*e-b(x) + C0 (3-2)
where:
x = coagulant dose in mg/L
y = residual TOC in mg/L
a, 6, and C0 are fitting parameters, found using regression techniques.
C0 is significant since it represents the asymptote of the equation and therefore provides an estimate
of the refractory TOC (i.e. the amount that could not be easily removed by coagulation). The
3-22
-------
summation of a and C0 were set equal to raw water TOC (y = a + C0 at x = 0) as a constraint in the
curve-fitting algorithm.
Using a curve-fitting program and fitting the data to an equation of the above form, the utility
derived Equation 3-3 to represent the jar test data. Equation 3-3 was determined using equivalent
alum dose; therefore, x in the equation represents equivalent alum dose in mg/L.
y = 2.53 e(-ao24x)+1.70 (3-3)
A plot of this equation is given in Figure 3-3, which is drawn using equivalent alum dose.
The slope of this equation at any point can be found by taking the first derivative of the equation as
shown below:
y' = a*(-b)*e-b(x) (3-4)
where:
y' = slope of the line at any point (first derivative)
a and b are fitting parameters from Equation 3-1
The slope of the curve at any equivalent alum dose (i.e. x value) can be found by plugging
in the coagulant dose. To determine the PODR, the point on the curve in Figure 3-3 at which the
slope is 0.3 mg/L TOC removal per 10 mg/L of alum must be found, as given in Table 3-1. The
slope of the regression line is given by Equation 3-4. By equating y' to -0.03, the value of x may be
determined as shown below:
-0.03 = (2.53)*(-0.0224)*e-ao224x (3-5)
By solving Equation 3-4 for x, the coagulant dose (i.e. x from Equation 3-5) was determined
to be 28.4 mg/L. This coagulant dose was then used to identify the TOC level at which the PODR
occurred by using Equation 3-2 as demonstrated below in Equation 3-6.
y = 2.53 *e-ao224x+1.70 (3-6)
3-23
-------
Solving for y (i.e. TOC level) at x = 28.4 in this equation gives y = 3.04 mg/L. Since the raw
water TOC is 4.2 mg/L, this corresponds to a TOC removal of 28 percent. The utility has now
determined that the Step 2 PODR TOC removal is 28 percent, and will apply to the State for an
alternative performance criteria of 28 percent TOC removal.
In some instances, jar test results may not indicate significant TOC removal until a certain
coagulant dose is reached. In other words, the TOC vs coagulant dose curve may be flat for the first
one or two applied doses. This phenomenon is sometimes referred to as the "threshold effect."
Figure 3-4 shows an example of such ajar test result. If a utility is permitted by the State to use
regression analysis using this type of jar test result, they may need to use an alternative model such
as that described in Equation 3-7.
y = a*e-b(x-d) + C0 (3-7)
The first derivative of this equation is given by Equation 3-8:
y' = a*(-b)*e-b(x-d) (3-8)
where:
x = coagulant dose in mg/L
y = residual TOC in mg/L
a, 6, d, and C0 are fitting parameters, found using regression techniques.
As with Equation 3-2, the summation of a and C0 were set equal to the raw water TOC at all
doses prior to the 'threshold' dose (y = a + C0 when x
-------
5.0
2.5 -
2.0 -
1.5 -
1.0
Figure 3-4
Example 2: Determining the Step 2 requirement
Settled Water TOC vs. Coagulant Dose
regression curve after threshold
coagulation dose is achieved
y = 1.802 exp (-0.027*(x-10)) + 2.212
R2=0.99
point at which slope is 0.3 mg-TOC/10 mg-alum
PODRat3.1mg/LTOC
or 23% removal
0 10 20 30 40 50 60 70
Alum Dose [mg/L]
90 100
3-25
-------
workers (1995) addressed other methods of curve fitting for jar test results. These methods include
polynomial expressions and isopleths in addition to the exponential decay models described above.
It should be noted that due to the peculiarity of a given data set, a single prescription for a curve-
fitting model may not be appropriate, and the user may need to search for the appropriate models
from those described here and in the literature.
3.2.3.3 Example 3 - Determining the Step 2 Requirement when the PODR is Met Twice
This utility determined that its running annual average compliance ratio was 0.85 at the end
of the first 12 months of monitoring and decided to conduct jar testing using the Step 2 procedure.
Jar tests were conducted following the protocol described in Section 3.2.2.2. A pH titration was
performed as described in Example 1 to the required "target pH" of 5.5 (see Table 2-2). Alum
addition of 90 mg/L was needed to reach a pH of 5.5, therefore, alum doses up to 90 mg/L (at 10
mg/L increments) were evaluated during j ar testing. After performing the j ar tests, TOC levels were
evaluated for each dose. The TOC results are given in Table 3-6 and shown graphically in Figure
3-5. Figure 3-5 presents the point-to-point TOC removal curve which will be used to determine the
PODR.
Table 3-6 shows the residual TOC level for each alum dose along with the slope between
each data point. The slope between each point is calculated according to Equation 3-1 as given in
Example 2. The slope of the point-to-point curve is calculated in this way to compare it to the Step
2 PODR criterion of 0.3 mg/L TOC removal per 10 mg/L alum (i.e., a slope of-0.03). As shown
in Table 3-6, the slope of the point-to-point curve reaches -0.03 between alum doses of 20 and 30
mg/L. However, the slope falls below or equals -0.03 further to the right on the curve at a higher
alum dose between 50 and 60 mg/L. This is shown graphically on Figure 3-5. The slope falls to -
0.03 again between alum doses of 50 and 60 mg/L. Since the slope does not equal or fall below -
0.03 beyond this point, this point is the PODR and will set the alternative TOC removal percentage.
Since the slope is exactly -0.03 between the two points at 50 and 60 mg/L, the alternative TOC
removal percentage is set at the second (i.e. higher) dose of 60 mg/L.
As shown in Table 3-6, at a dose of 60 mg/L the TOC removal is 27 percent. Therefore the
utility will apply to the State for an alternative performance criteria of 27 percent TOC removal.
3-26
-------
TABLE 3-6
Example 3 Jar Test Results
Alum Dose
(mg/L)
0
10
20
30
40
50
60
70
80
90
Settled
Water TOC
(mg/L)
4.15
4.20
3.85
3.55
3.46
3.35
3.05
2.79
2.58
2.55
Incremental
TOC
Removal
(mg/L)
-
-
0.35
0.3
0.09
0.11
0.3
0.26
0.21
0.03
Incremental Slope
(mg-TOC/mg-Alum)
-
0.005
-0.035
-0.03
-0.009
-0.011
-0.03
-0.026
-0.021
-0.003
TOC Removal
(%)
-
-
7
14
17
19
27
33
38
39
POOR for alum is a slope of-0.03.
3-27
-------
Figure 3-5
Example 3: Determining the Step 2 requirement when the PODR is met twice
Settled Water TOC vs. Coagulant Dose
5.0
4.5 -
4.0 -
3.5 -
I
"8 3.0 -
2.5 -
2.0
PODR at 3.05 mg/L TOC
or 27% removal
\
0 10 20 30 40 50 60
Alum Dose [mg/L]
70 80 90
Note: The dashed line corresponds to a slope of 0.3 mg-TOC/10 mg-alum.
3-28
-------
3.2.3.4 Example 4 -Adding Base to Maintain Minimum pH During Step 2 Jar Testing
This utility has a source water with low alkalinity. The alkalinity never rises above 60 mg/L
as CaCO3, and the utility is unable to achieve good TOC removal. After the first year of TOC
compliance sampling, the utility's running annual average compliance ratio was 0.50. Therefore it
conducted the requisite Step 2 testing to set an alternative TOC removal percentage. A pH titration
was first performed to determine the ferric chloride dose range to be evaluated, as described in
Example 1. Based on titration results, it was apparent that the pH of the test sample would fall
below the target pH of 5.5 before additional TOC removal occurred. The treatment technique
requires that systems performing Step 2 testing on a sample with an alkalinity of less than 60 mg/L
as CaCO3 add a necessary amount of base to maintain the pH between 5.3 and 5.7. Incremental
coagulant addition should continue until the PODR is met, while the addition of base maintains the
pH between 5.3 and 5.7. The same type of base should be used during the Step 2 procedure as is
used at full-scale. The base doses required to maintain the "target pH" for the jar tests and resulting
pH levels are shown in Table 3-7. These doses were used during subsequent jar testing.
The utility conducted jar tests (while maintaining the sample pH in the required range
through base addition) to evaluate the Step 2 TOC removal requirement. After performing the jar
tests, TOC levels were evaluated for each dose. The TOC results are given in Table 3-8 and shown
graphically in Figure 3-6. Figure 3-6 presents the point-to-point TOC removal curve. Table 3-8
shows the residual TOC level for each ferric chloride dose. In addition, the equivalent alum dose
and incremental TOC removal is given at each point for calculation of the incremental slope in units
of mg-TOC/mg-alum. Calculation of the slope in terms of mg-alum allows direct comparison of
the incremental slope with the PODR requirement of 0.3 mg-TOC/10 mg-alum. The slope between
each point is calculated according to Equation 3-1 as given in Example 2.
3-29
-------
TABLE 3-7
Base Addition During Jar Testing
Jar#
Blank
1
2
3
4
5
6
7
Ferric Dose
(mg/L)
0
9
18
27
36
46
55
64
Base (NaOH)
Dose (mg/L)
0
0
0
0
1.2
2.8
3.5
5.2
pH
Rapid Mix
7.2
6.5
6.2
5.9
5.5
5.5
5.5
5.5
Settled Water
7.2
6.6
6.6
6.1
5.7
5.7
5.6
5.6
TABLE 3-8
Example 4 Jar Test Results
Ferric Chloride
Hexahydrate
Dose (mg/L)
0
9
18
27
36
45
55
64
Equivalent
Alum Dose
(mg/L)
0
10
20
30
40
50
60
70
Settled
Water
TOC
(mg/L)
3.2
2.92
2.60
2.43
2.38
2.35
2.35
2.33
Incremental
TOC
Removal
(mg/L)
-
0.28
0.32
0.17
0.05
0.03
0
0.02
Incremental Slope
(mg-TOC/mg-alum)
-
-0.028
-0.032
-0.017
-0.005
-0.003
0
-0.002
TOC
Removal
(%)
-
9
19
24
26
27
27
27
3-30
-------
Figure 3-6
Example 4: Adding base to maintain minimum pH during jar testing
Settled Water TOC vs. Coagulant Dose
4.0
3.5 -
3.0-
H 2.5 H
I
"g 2.0
1
1.5 -
1.0
0
POOR at 2.43 mg/L TOC
or 24% removal
10
50
20 30 40
Equivalent Alum Dose [mg/L]
Note: The dashed line corresponds to a slope of 0.3 mg-TOC/10 mg-alum.
60
3-31
-------
As shown in Table 3-8, the slope of the point-to-point curve reaches -0.03 farthest to the
right on the curve between ferric chloride doses of 18 and 27 mg/L. Therefore the PODR is set at
the second (i.e. higher) dose of 27 mg/L since the slope does not equal or fall below -0.03 further to
the right of this point. This is shown graphically on Figure 3-6. As shown in Table 3-8, at the Step
2 PODR the TOC removal is 24 percent. Therefore the utility will apply to the State for an
alternative performance criteria of 24 percent TOC removal.
3.2.3.5 Example 5 - Determining that the PODR is Never Met
The running annual average compliance ratio was 0.88 at the end of first year of monitoring,
which prompted this utility to conduct jar tests using the Step 2 procedure. The utility first
performed a pH titration as described in Example 1 to the "target pH" of 7.0 (see Table 2-2). Alum
addition of 100 mg/L was needed to reach a pH of 7.0, therefore, alum doses up to 100 mg/L (at 10
mg/L increments) were evaluated during] ar testing. After performing the j ar tests, TOC levels were
evaluated for each dose. The TOC results are given in Table 3-9 and shown graphically in Figure
3-7. Figure 3-7 presents the point-to-point TOC removal curve.
The utility's TOC data are shown in Table 3-9. Table 3-9 shows the residual TOC level for
each alum dose along with the slope between each data point. The slope is calculated according to
Equation 3-1 in Example 2. The PODR is defined as the point at which the slope of the curve
reaches 0.3 mg/L TOC removal per 10 mg/L alum addition, corresponding to a slope of-0.03. As
shown in Table 3-9 and Figure 3-7, the slope of the point-to-point curve never falls below -0.03.
Consequently, this utility may apply to the State for a waiver from enhanced coagulation. The
treatment technique allows systems to apply for a waiver from the enhanced coagulation
requirements if the TOC removal achieved during Step 2 testing is consistently less than 0.3 mg/L
of TOC removal per 10 mg/L of alum or equivalent metal weight of ferric salt. States may require
that systems operating under a waiver perform Step 2 testing quarterly.
3-32
-------
TABLE 3-9
Example 5 Jar Test Results
Alum Dose
(mg/L)
0
10
20
30
40
50
60
70
80
90
100
Settled
Water TOC
(mg/L)
4.05
4
3.85
3.7
3.8
3.6
3.4
3.3
3.2
O O
3.2
O O
3.2
Incremental
TOC Removal
(mg/L)
-
0.05
0.15
0.15
-
0.2
0.2
0.1
0.1
0
0
Incremental Slope
(mg-TOC/mg-alum)
-
-0.005
-0.015
-0.015
0.01
-0.02
-0.02
-0.01
-0.01
0
0
TOC Removal
(%)
-
1
5
9
6
11
16
19
21
21
21
3-33
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Figure 3-7
Example 5: Determining that the PODR is never met
Settled Water TOC vs. Coagulant Dose
curve never reaches 0.3 mg-TOC/10 mg-arum
i.o
0 10 20 30 40 50 60 70
Alum Dose [mg/L]
90 100
Note: The dashed line corresponds to a slope of 0.3 mg-TOC/10 mg-alum.
3-34
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3.3 ENHANCED PRECIPITATIVE SOFTENING
Enhanced precipitative softening requires that softening systems achieve TOC removals
ranging from 15 to 30 percent based upon their raw water TOC level (see Table 2-1). Systems that
cannot achieve these removal levels may demonstrate compliance by meeting the alternative
compliance criteria listed in Section 2.4.
Utilities using enhanced softening are not allowed to perform the bench- or pilot-scale
testing outlined in Section 3.2 for regulatory compliance. It is strongly recommended, however, that
these utilities perform bench- or pilot-scale studies to characterize the performance of the plant under
enhanced precipitative softening conditions, and to ascertain its ability to achieve the TOC removals
or meet one of the alternative compliance criteria. The treatment technique does not require systems
to modify their existing treatment processes to include a chemical or a process (e.g., soda ash) that
is not currently in use. For example, if a treatment plant is a lime-softening facility that does not use
soda ash, processes would not have to be modified to include lime-soda ash softening just to meet
the TOC removal requirements.
3.3.1 Full-Scale Evaluation of TOC Removal Requirements
Initially, utilities should evaluate TOC removal between the raw water source and the final
TOC monitoring location in the full-scale treatment plant. After collecting raw and treated water
samples and analyzing for TOC, the percent removal of TOC may be calculated. If the Step 1
removal requirements (Table 2-1) are met, then the utility is in compliance. If the utility is very close
to meeting the percent removal of TOC requirements, full-scale increases of lime and/or coagulant
may be made to increase the amount of TOC removal. If the full-scale coagulant and lime
adjustments achieve the required TOC removal, then the utility is in compliance and no further
evaluation will be necessary. However, if the lime-coagulant doses do not achieve the TOC removal
required and more than "minor" adjustments are necessary to achieve the required removal of TOC,
then bench- or pilot-scale evaluation is advisable.
3-35
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3.3.2 Bench-Scale and Pilot-Scale Testing
If a precipitative softening system is unable to meet the TOC requirements specified in
Table 2-1 under current operation or with increased lime and coagulant doses, and does not meet any
of the alternative compliance criteria, treatability testing should be performed. Treatability testing
can be performed on a batch basis or on a continuous flow, pilot-scale basis. Treatability testing will
assist the utility in determining lime, soda ash, and/or coagulant dosages that will achieve the TOC
removals specified in Table 2-1.
Bench-scale procedures described below are based on the ASTM D 2035-80 method,
"Standard Practice for Coagulation-Flocculation Jar Test of Water." These procedures have been
modified for evaluations of treatment plants using lime softening.
3.3.2.1 Apparatus and Reagents
The following equipment and chemicals are required, at a minimum, to perform the testing:
• Jar test apparatus with 1 liter (L) beakers or 2 L square mixing jars.
• pH meter. The pH meter should be calibrated daily with fresh buffers. A two-point
calibration using buffer solutions with pH = 4.0 and pH = 7.0 is necessary at a minimum; a
three-point calibration using pH = 4.0, pH = 7.0, and pH = 10.0 is preferred.
• Lime stock solution made so that, for example, 1.0 mL into 2 L = 20 mg/L of lime (i.e., stock
concentration is 40 mg/mL). The type (hydrated or slaked) and the grade (90 to 100 percent
active) of lime will affect the preparation of the stock solution.
• Ferric chloride or ferric sulfate stock solution made so that, for example, 1.0 mL into 2 L =
10 mg/L of ferric coagulant (i.e., stock concentration is 20 mg/mL).
• Sample bottles suitable for analysis of coagulated water for alkalinity, hardness (calcium and
magnesium), and pH measurement.
• Sample bottles suitable for TOC, DOC, and UV-254 analysis.
• 25 and 50 mL pipettes, with 10 mL graduated pipette bulbs.
• 1L graduated cylinders.
• Miscellaneous beakers and other glassware.
• 20 L carboys with siphons for dispensing water. A suitable laboratory tap also may be used.
3-36
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• Magnetic stirrer with stirring bars.
3.3.2.2 Protocol for Bench-Scale (Jar) Testing
The following method can be used to evaluate incremental TOC removal by lime softening
using the bench-scale apparatus described above. Most available data on TOC removal in lime-
softening plants indicate that varying the lime dose has a greater effect on TOC removal than does
varying the coagulant dose.
Step 1. Gather testing supplies.
Step 2. Prepare lime stock solution.
Example - Developing a Lime Stock Solution.
Given: A recent quality assurance analysis from the lab indicates that the unslaked
lime delivered to a water plant is 90% active chemical. The density of the
lime is approximately 60 Ib/ft3.
Assume: A stock concentration is desired such that 1.0 mL into 2 L equals 20 mg/L
of lime.
Calculate the amount of lime needed to make 1L of a stock solution.
CstockVst0ck = CjarVjar C = Concentration; V = Volume)
Cstock ~~ ^jar ' jar ' 'stock
Cstock = (20 mg/L lime x 2 L) + 1 mL lime stock solution
Cstock = 40 mg/niL lime
Therefore, add 40 g of active lime to 1 L of water.
Massunslakedlime = 40 g active lime - 0.90 = 44 g
Therefore, add 44 g of the unslaked lime into a 1 L volumetric flask, then fill the
flask to the 1 L mark. Mix well. The resulting solution is a 40 g/L stock solution of
active lime; adding 1 mL of stock into a 2 L jar will result in a 20 mg/L dose of lime.
Step3. Collect20to301itersofrawwaterforthejartesting. The temperature of the sample should
be maintained at ambient conditions prior to and during testing. If the collected water must
be stored for subsequent testing, the sample should be refrigerated (approximately 4°C).
The temperature of the sample should be adjusted to the ambient temperature during
3-37
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collection before starting any testing with the sample. Every effort should be made to
conduct tests with freshly collected water.
Step 4. Measure pH and alkalinity of the raw water sample.
Step 5. Determine the lime dosages to evaluate for enhanced softening by titrating lime into 1000
or 2000 mL of raw water (depending on the available jar test apparatus) on a magnetic stir
plate in 10 mg/L increments. If coagulant is added concurrently with lime or preceding lime
addition in the full-scale plant, the plant dose of coagulant should be added to the beakers
prior to lime titration. On the other hand, if coagulant is added in a subsequent stage
following lime (or lime-soda ash) softening, no coagulant addition is needed for this lime
titration.
Measure and record the pH after each incremental lime dose. The highest pH to be
investigated should not exceed approximately 11.2, which is the optimum pH for
magnesium hydroxide removal.
Step 6. Pour the raw water sample into a series of six beakers or mixing jars and place the jars on
the jar test apparatus. Add the lime dosages needed to achieve pH increments of 0.2
(including coagulant addition) in individual beakers. For example, the softening pH in each
of the six jars could be 10.2, 10.4, 10.6, 10.8, 11.0, and 11.2.
Rapid mix, flocculate, and settle using times corresponding to the detention time at the plant
maximum daily flow rate. Rapid mix and flocculation mixing intensities and durations
should be matched to those in the plant, if known. If coagulant is added concurrently with
lime or preceding lime addition in the full-scale plant, the plant dose of coagulant should
be added to each beaker or mixing j ar prior to lime addition. On the other hand, if coagulant
is added in a subsequent stage following lime (or lime-soda ash) softening, coagulant
addition should be done after flocculation is complete with lime addition. A subsequent
flocculation stage (corresponding to full-scale) will be necessary to complete the
coagulation process. Alternatively, coagulant can be added during bench-scale
recarbonation (step 7). The timer on the process should be started after the chemicals are
added.
If the plant intensities and durations are not known, the following j ar-test mixing conditions
can be used for the softening and/or coagulation steps:
• Rapid mix at 120 rpm for 30 seconds
• Flocculate at 80 rpm for 2 minutes
3-38
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• Flocculate at 60 rpm for 20 minutes
• Flocculate at 40 rpm for 20 minutes
All jars, regardless of mixing conditions, should settle for 60 minutes, without stirring,
prior to sampling.
Step 7. After settling, carefully remove as large a batch of supernatant as possible and adjust pH by
recarbonation. Be careful not to disturb the settled floe, and to avoid suspended floe, while
sampling. Each sample should be titrated on a magnetic stir plate while bubbling CO2
through a diffuser, stirring and measuring pH until the pH of the plant recarbonated water
is achieved. Alternatively, if CO2 addition could not be performed at bench-scale, pH
adjustment should be done by adding dilute hydrochloric or sulfuric acid until the pH of the
water matches full-scale recarbonated pH values.
Step 8. Sample the supernatant for TOC, total hardness, and magnesium hardness analysis using
25 or 50 mL pipettes, a siphon apparatus, or sampling ports located on the side of the
mixing j ars. Preserve and refrigerate the samples for subsequent TOC analysis as described
in Chapter 5.
Step 9. Withdraw additional supernatant samples for pH, hardness (calcium and magnesium),
alkalinity, and UV-254 and DOC (for SUVA calculations), and analyze within appropriate
holding times.
TOC removals achieved in the jar tests may provide a reasonable representation of TOC
removals achievable on a plant-scale. Filtration may provide some additional removal of TOC
beyond that achieved in the jar tests, and a system may wish to include TOC removal by filtration
as part of their full-scale compliance with the enhanced softening requirements.
3.3.2.3 Protocol for Pilot-Scale Testing
It is important to simulate physical conditions such as mixing, detention times, and solids
recycle in the pilot plant corresponding to those conditions in the full-scale water treatment plant.
Alternative softening and coagulation conditions can be evaluated using the pilot plant by varying
lime (or lime, soda ash combination) and/or coagulant dosages. Increments of lime (or lime, soda
ash combination) dosages should be selected to result in increments of softening pH that are at least
0.2 units apart. For example, softening pHs of 10.2, 10.4, 10.6, 10.8, 11.0 and 11.2 could be
evaluated. The coagulant dose range should be selected based upon the range of operation of the
full-scale water treatment plant. Appropriate coagulant aid polymers may also be added during pilot
3-39
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tests. The pilot plant should be operated long enough for each of the alternative conditions to
achieve steady-state. This may require a minimum of three to four times the theoretical detention
time of the pilot plant. After achieving steady-state, samples should be collected as discussed in
Section 3.3.2.2.
3-40
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Chapter 4
MONITORING AND REPORTING
-------
Table of Contents
Page
4.0 MONITORING AND REPORTING
4.1 Introduction 4-1
4.2 Monitoring Plans 4-1
4.3 Sampling Locations and Monitoring Frequency 4-2
4.3.1 TOC 4-2
4.3.2 Alkalinity 4-2
4.3.3 Reduced Monitoring for TOC and Alkalinity 4-2
4.3.4 Monitoring for Alternative Compliance Criteria 4-2
4.3.4.1 Additional Alternative Compliance Criteria for
Softening Plants 4-3
4.3.4.2 Monitoring for TTHM and HAAS 4-4
4.4 Enhanced Coagulation and Softening 4-5
4.4.1 Reporting Requirements for TOC Compliance 4-5
4.4.2 Reporting for Alternative Compliance Criteria 4-6
4.4.3 Compliance Calculations for Enhanced Coagulation and
Softening 4-8
4.4.4 Running Annual Average Calculation Flowcharts 4-8
4.5 Example Calculations 4-13
List of Tables
4-1 Monitoring Locations and Sampling Frequency for TTFDVI and HAAS 4-4
4-2 Reporting Requirements 4-7
4-3 DBF Precursor Removal Compliance Calculations for Example
Water Utility: Enhanced Coagulation, Year 1 4-14
4-4 DBF Precursor Removal Compliance Calculations for Example
Water Utility: Enhanced Coagulation, Year 2 4-15
4-5 DBF Precursor Removal Compliance Calculations for Example
Water Utility: Enhanced Precipitative Softening, Year 1 4-17
4-6 DBF Precursor Removal Compliance Calculations for Example
Water Utility: Enhanced Precipitative Softening, Year 2 4-18
List of Figures
4-1 Running Annual average Compliance Calculation -
First Year of TOC Compliance Monitoring 4-10
4-2 Running Annual Average Compliance Calculation
After First Year of TOC Compliance Monitoring, EC and ES 4-11
4-3 Calculation of Running Annual Average Under Step 2 -
EC Plants Only 4-12
-------
4.0 MONITORING AND REPORTING
4.1 INTRODUCTION
Compliance with the enhanced coagulation/enhanced softening treatment technique is based
on a running annual average of quarterly averages; one full year of monitoring data is
necessary to demonstrate compliance. Water treatment plants must sample source and
finished water for TOC and source water alkalinity. Alkalinity samples must be collected
at the same time and location as the source water TOC samples. If a plant intends to
establish compliance with an alternative compliance criterion, it also may need to sample for
TTHMs, HAAS, magnesium hardness removal, DOC, and UV-254.
4.2 MONITORING PLANS
Plants required to monitor for TOC removal compliance must develop and
implement a monitoring plan. The plant must maintain the plan and make it available for
inspection by the State and the general public. Subpart H systems serving more than 3,300
people must submit a copy of the monitoring plan to the State no later than the first time data
are submitted to demonstrate compliance with any portion of the DBPR. Following its
review, the State may require changes to the monitoring plan. The State also may require
monitoring plans to be submitted by other systems. The monitoring plan must include at
least the following elements:
• Locations for collecting samples used to demonstrate compliance (frequency and
day(s) of sampling also should be included for source and finished water TOC
sampling).
• An explanation of the enhanced coagulation/enhanced softening treatment technique
to be used, and how the system will calculate compliance with MCLs and MRDLs.
The monitoring plan sampling locations for TTHM and HAAS must be
representative of the entire distribution system if water is provided to consecutive systems,
or if the system is approved for monitoring as a consecutive system.
4-1
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4.3 SAMPLING LOCATIONS AND MONITORING FREQUENCY
4.3.1 TOC
Plants required to implement enhanced coagulation or enhanced softening must
monitor for TOC in the source water prior to any treatment, including oxidant addition.
Treated water TOC also must be monitored no later than the combined filter effluent
turbidity monitoring location. These samples (source water and treated water) are referred
to as paired samples. Plants must take a minimum of one paired sample per month per plant
at a time representative of normal operating conditions and influent water quality.
4.3.2 Alkalinity
At the time of paired sampling for TOC, the plant also must sample for source water
alkalinity at the same location.
4.3.3 Reduced Monitoring for TOC and Alkalinity
Plants may reduce TOC monitoring under the following conditions:
1. Plants with a treated water TOC running annual average of less than 2.0 mg/L
for two consecutive years may reduce monitoring for both TOC and alkalinity
to one paired sample per plant per quarter, or
2. Plants with a treated water TOC running annual average of less than 1.0 mg/L
for one year may reduce monitoring for both TOC and alkalinity to one paired
sample per plant per quarter.
Plants under reduced monitoring must revert to routine monitoring in the month
following the quarter when the average treated water TOC is greater than or equal to 2.0
mg/L.
4.3.4 Monitoring for Alternative Compliance Criteria
Running annual averages are used to demonstrate compliance with alternative
compliance criteria. Four quarters of data are needed to demonstrate that the alternative
compliance criteria are being met on a running annual average basis. However, alternative
4-2
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compliance criteria also may be used to demonstrate compliance for a single month. For
example, a plant might not achieve the required Step 1 TOC removal in a given month, but
may determine that the finished water SUVA for that monthly sample is less than or equal
to 2.0 L/mg-m. The plant is therefore able to assign a value of 1.0 (a value of 1.0 or greater
indicates compliance with the TOC removal requirements) for the monthly removal ratio to
use in the running annual average compliance calculation. For months in which alternative
compliance criteria are used, a monthly removal ratio of 1.0 must be used for compliance
calculations (see Section 4.4.3, step 3). A plant can demonstrate compliance with enhanced
coagulation and enhanced precipitative softening if any one of the alternative compliance
criteria listed in Section 2.4 is met. These criteria are listed below. See Section 2.4 for a
complete description of the requirements.
1. Source water TOC < 2.0 mg/L.
2. Treated water TOC < 2.0 mg/L.
3. Source water SUVA < 2.0 L/mg-m.
4. Treated water SUVA < 2.0 L/mg-m.
5. Source water TOC < 4.0 mg/L, source water alkalinity > 60 mg/L (as CaCOs),
TTHM < 40 ug/L, HAAS < 30 ug/L.
6. TTFDVI < 40 ug/L and HAAS < 30ug/L with only chlorine for primary disinfection
and maintenance of a residual.
4.3.4.1 Additional Alternative Compliance Criteria for Softening Plants
Utilities that use softening may demonstrate compliance if they meet any of the six
alternative compliance criteria listed above or one of the two alternative compliance criteria
listed below (see also Section 2.4):
1. Softening that results in lowering the treated water alkalinity to less than 60 mg/L (as CaCO3),
measured monthly and calculated quarterly as a running annual average.
2. Softening that results in removing at least 10 mg/L of magnesium hardness (as CaCO3),
measured monthly and calculated quarterly as a running annual average.
4-3
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4.3.4.2 Monitoring for TTHM and HAAS
Utilities monitoring to meet alternative compliance requirements 5 or 6 in Section 4.3.4
must use the TTHM and HAAS samples used to calculate compliance with the MCLs to determine
compliance with alternative compliance criteria 5 and 6. Monitoring locations and sampling
frequency for TTHM and HAAS depend on the source water type and the population served, as shown
in Table 4-1.
TABLE 4-1
Monitoring Locations and Sampling Frequency for TTHM and HAAS
Type of System
Minimum Monitoring
Frequency
Sample Location in the
Distribution System
Subpart H system serving
at least 10,000 persons
Four water samples per
quarter per treatment plant
At least 25 percent of all samples collected each quarter at
locations representing maximum residence time. Remaining
samples taken at locations representative of at least average
residence time in the distribution system and representing
the entire distribution system, taking into account number
of persons served, different sources of water, and different
treatment methods.'
Subpart H system serving
from 500 to 9,999 persons
One sample per quarter
per treatment plant1
Locations representing maximum residence time.'
Subpart H system serving
fewer than 500 persons
One sample per year per
treatment plant during
month of warmest water
temperature
Locations representing maximum residence time.1 If the
sample (or average of annual samples, if more than one
sample is taken) exceeds MCL, system must increase
monitoring to one sample per treatment plant per quarter,
taken at a point reflecting the maximum residence time in
the distribution system, until system meets reduced
monitoring criteria specified in the regulation.
System using only ground
water not under direct
influence of surface water,
using chemical disinfectant
and serving at least 10,000
people
One sample per quarter
per treatment plant2
Locations representing maximum residence time.'
System using only ground
water not under direct
influence of surface water,
using chemical disinfectant
and serving fewer than
10,000 people
One sample per year per
treatment plant2 during
month of warmest water
temperature
Locations representing maximum residence time.1 If the
sample (or average of annual samples, if more than one
sample is taken)exceeds MCL, system must increase
monitoring to one sample per treatment plant per quarter,
taken at a point reflecting the maximum residence time in
the distribution system, until system meets reduced
monitoring criteria specified in the regulation.
1 If a system elects to sample more frequently than the minimum required, at least 25 percent of all samples collected each quarter
(including those taken in excess of the required frequency) must be taken at locations that represent the maximum residence time of the water
in the distribution system. The remaining samples must be taken at locations representative of at least average residence time in the
distribution system.
2 Multiple wells drawing water from a single aquifer may be considered one treatment plant for determining the minimum number of
samples required, with State approval in accordance with criteria developed under Part 142.16(h)(5), title 40 Code of Regulations.
4-4
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4.4 ENHANCED COAGULATION AND SOFTENING
4.4.1 Reporting Requirements for TOC Compliance
Reports from plants monitoring monthly or quarterly to demonstrate compliance
with Step 1 or Step 2 TOC removal requirements must provide the following information to
the State. Monitoring results must be reported to the State within ten days after the end of
the quarter in which samples were collected. Plants sampling less frequently than quarterly
must report monitoring results to the State within ten days of the end of the monitoring
period in which the samples were collected. Reporting information includes:
1. The number of paired (source water and treated water) samples taken during the last
quarter.
2. The location, date, and result of each paired sample taken during the last quarter and
the associated source water alkalinity.
3. For each month in the reporting period that paired samples were taken, the arithmetic
average of the actual TOC percent removal for each paired sample and the required
TOC percent removal.
4. Calculations for determining compliance with the TOC percent removal requirements
(see discussion below).
5. Whether the system is in compliance with the enhanced coagulation/enhanced
softening TOC removal requirements for the last four quarters for which TOC
percent removal calculations were required.
6. TOC percent removal calculations are not required for quarters in which all three
months use an alternative compliance criterion to demonstrate compliance. Systems
that use an alternative criterion to demonstrate compliance for a particular month
should specify which criterion was used (see step 3 in Section 4.4.3).
The system must ensure that all results are compiled and presented to the State. The
State, however, may choose to perform items 3, 4, and 5 above in lieu of having the system
report that information.
4-5
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4.4.2 Reporting for Alternative Compliance Criteria
Plants wishing to demonstrate compliance with one of the alternative compliance
criteria, on a running annual average basis, must report the following information to the
State. Monitoring results must be reported to the State within ten days after the end of the
quarter in which samples were collected. Plants sampling less frequently than quarterly must
report monitoring results to the State within ten days of the end of the monitoring period in
which the samples were collected. Reporting information includes:
1. The alternative compliance criterion that the system is using to demonstrate
compliance.
2. The number of paired samples taken during the last quarter.
3. The location, date, and result of each paired sample and associated alkalinity taken
during the last quarter.
4. The running annual arithmetic average based on monthly averages (or quarterly
samples) of source water TOC for systems using alternative compliance criteria 1 or
5, or of treated water TOC for systems using alternative compliance criterion 2 (see
Section 4.3.4).
5. The running annual arithmetic average based on monthly averages (or quarterly
samples) of source water SUVA for systems using alternative compliance criterion
3, or of treated water SUVA for systems using alternative compliance criterion 4 (see
Section 4.3.4).
6. The running annual average of source water alkalinity for systems using alternative
compliance criterion 5 (see Section 4.3.4), and of treated water alkalinity for systems
using alternative compliance criterion 1 for softening systems (see Section 4.3.4.1).
7. The running annual average for both TTHMs and HAAS for systems using alternative
compliance criteria 5 or 6 (see Section 4.3.4).
8. The running annual average of the amount of magnesium hardness removal (as
CaCO3, in mg/L) for systems using alternative compliance criterion 2 for softening
systems (see Section 4.3.4.1).
9. Whether the system is in compliance with the particular alternative compliance
criterion in Section 4.3.4 or 4.3.4.1.
4-6
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The system must ensure that all results are compiled and presented to the State. The
State may, however, choose to perform the above calculations in lieu of having the system
report that information. Table 4-2 summarizes reporting requirements by referencing
specific provisions of the final regulatory language.
TABLE 4-2
Reporting Requirements
If you are a...
You must Report.. -1
System monitoring monthly or
quarterly for TOC and required
to meet the enhanced
coagulation or softening
requirements.
(1) The number of paired (source water and treated water, prior to continuous
disinfection) samples taken during the last quarter.
(2) The location, date, and result of each paired sample and associated alkalinity
taken during the last quarter.
(3) For each month in the reporting period that paired samples were taken, the
arithmetic average of the percent reduction of TOC for each paired sample
and the required TOC percent removal.
(4) Calculations for determining compliance with the TOC percent removal
requirements.
(5) Whether the system is in compliance with the enhanced coagulation or
enhanced softening percent removal requirements for the last four quarters.
System monitoring monthly or
quarterly for TOC and meeting
one or more of the alternative
compliance criteria.
(1) The alternative compliance criterion that the system is using.
(2) The number of paired samples taken during the last quarter.
(3) The location, date, and result of each paired sample and associated alkalinity
taken during the last quarter.
(4) One (or more) of the following, depending on the alternative compliance
criterion used:
a. The running annual arithmetic average based on monthly averages (or
quarterly samples) of source water TOC or treated water TOC.
b. The running annual arithmetic average based on monthly averages (or
quarterly samples) of source water SUVA or treated water SUVA.
c. The running annual average of source water alkalinity or treated water
alkalinity (depending on the alternative compliance criterion used).
d. The running annual average for both TTHM and HAAS.
e. The running annual average of the amount of magnesium hardness
removal (as CaCO3 in mg/L).
(5) Whether the system is in compliance with the particular alternative
compliance criterion.
The State may choose to perform calculations and determine whether the treatment technique was met, in lieu of having
the system report that information.
4-7
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4.4.3 Compliance Calculations for Enhanced Coagulation and Softening
Compliance with the DBF precursor removal requirements is based on achieving the
required TOC removal. Compliance is calculated quarterly by the following method:
1. Determine actual monthly TOC percent removal for each compliance sample, using
the equation:
percent removal = (1 - (treated water TOC/source water TOC)) x 100.
2. Determine the required monthly TOC percent removal based on either Step 1 or Step
2 requirements (see Section 2.3).
3. To determine the monthly removal ratio, divide the answer from step 1 by the answer
from step 2 for each compliance sample taken. For those months that an alternative
compliance criterion is used, a value of 1.0 shall be assigned. If more than one
compliance sample is taken during the month, calculate the arithmetic average of
removal ratios and use that average for the monthly value.
4. Sum the answers from step 3 for the last three months, and divide by three. The
result is the quarterly removal ratio.
5. Sum the results of step 4 for the last four quarters, and divide by four.
6. If the result from step 5 is greater than or equal to 1.0, the system is in compliance
with the TOC percent removal requirements.
4.4.4 Running Annual Average Calculation Flowcharts
Utilities can use the flowcharts shown in Figures 4-1, 4-2, and 4-3 to calculate their
running annual average for TOC removal compliance. Example compliance calculations are
provided in Section 4.5.
The flowchart in Figure 4-1 shows how utilities can calculate their annual running
average for the first year of compliance monitoring. Note that alternative compliance criteria
can be used on a monthly basis during the first year (and subsequent years) of compliance
monitoring. A monthly removal ratio of 1.0 must be used for those months in which
alternative compliance criteria are used. Compliance with the TOC removal requirements
is based on a running annual average, therefore utilities need 12 months of TOC monitoring
4-8
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data to make a compliance determination. Since Step 2 bench- or pilot-scale testing is only
required when an enhanced coagulation system fails to achieve a running annual average
greater than or equal to 1.0 (i.e., the system is out of compliance), Step 2 testing generally
will not be performed until the second year of TOC compliance sampling. If the State
approves the Step 2 TOC removal percentage, the State may make that percentage retroactive
for determining compliance.
The flowchart in Figure 4-2 illustrates how utilities can compute their running annual
average after the first year of TOC compliance sampling. Enhanced coagulation plants are
required to perform Step 2 testing if their running annual average falls below 1.0. Figure 4-3
shows the calculation of a running annual average when compliance is determined by the
Step 2 TOC removal percentage. Plants operating under a Step 2 alternative TOC removal
percentage should consult with the State when their running annual average achieves a value
equal to or greater than 1.0 to determine whether they should return to the Step 1
requirements for compliance calculations. Quarterly Step 2 testing is recommended the
firstyear a plant determines compliance with the Step 2 TOC procedure. EPA recommends
that this frequency not be reduced to less than annually.
4-9
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Perform monthly raw and
treated water TOC sampling
Is the
Step 1
removal percentage
achieved?
Are
any of the
alternative
compliance
criteria
satisfied?
Record actual TOC removal
divided by required TOC
removal for monthly removal ratio
Record 1.0 as the
monthly removal ratio
Record actual TOC removal
divided by required TOC
removal for monthly removal ratio
Has
utility
completed 12
months of TOC
sampling?
Yes
Compute running annual average (RAA)
Go to Figure 4-2
Figure 4-1. Running Annual Average
Compliance Calculation - First Year
of TOC Compliance Monitoring
Go to Figure 4-3
(EC systems only)
4-10
-------
Perform monthly raw and
treated water TOC sampling
Is the
Step 1
removal percentage
achieved?
Are
any of the
alternative
compliance
criteria
satisfied?
Is
quarterly
average and new
RAA computed
this month?
Is
RAA > 1.0?
Does the
utility perform
enhanced
softening?
Utility is out
of compliance
Figure 4-2. Running Annual Average
Compliance Calculation After First Year
of TOC Compliance Monitoring, EC and ES
Record actual TOC removal
divided by required TOC
removal for monthly removal ratio
Record 1.0 as the
monthly removal ratio
Go to Figure 4-3
(EC systems only)
4-11
-------
Submit results of Step 2 testing
to State within 3 months of
achieving RAA < 1.0
Perform monthly
TOC sampling
Is State
approved Step 2
removal percentage
achieved?
Are
any of the
alternative
compliance
criteria
satisfied?
Record actual TOC removal
divided by required TOC
removal for monthly removal ratio
Record 1.0 as the
monthly removal ratio
Record actual TOC removal
divided by required TOC
removal for monthly removal ratio
System is out
of compliance
Is a
quarterly
average and new
RAA calculated
this month?
Yes
Consult with State to
determine if system returns
to Step 1 TOC requirements
Figure 4-3. Calculation of
Running Annual Average
Under Step 2 - EC Plants Only
4-12
-------
4.5 EXAMPLE CALCULATIONS
Example 1 - Enhanced Coagulation
Tables 4-3 and 4-4 show sample running annual average calculations for a plant
experiencing frequent changes in source water TOC and alkalinity. In year one (Table 4-3),
compliance is based upon achieving a running annual average of 1.0 or greater after TOC
sampling in month 12 is complete (at the end of the fourth quarter). The monthly removal
ratios shown in column C are calculated from the required Step 1 TOC removal matrix
(Table 2-1) and by meeting alternative performance criteria. Months in which an alternative
compliance criterion is used are assigned a monthly removal ratio of 1.0.
The running annual average calculation in the second year (Table 4-3) uses monthly
removal ratios calculated from the Step 1 removal percentages and alternative compliance
criteria 2 and 4 (discussed in Section 2.4). The quarterly average in the third quarter of year
one (Table 4-3) is less than 1.0, however, the running annual average is greater than 1.0 and
the system is in compliance at the end of the first year. The second running annual average
(calculated after the first quarter of the second year) is below 1.0, and the plant uses the Step
2 procedure to establish alternative TOC removal requirements, with State approval. Note
that the plant is in violation the first quarter of the second year if the State does not allow the
Step 2 TOC removal percentage to be applied retroactively.
Alternative compliance criteria 5 and 6 (discussed in Section 2.4) may not be used
on a monthly basis.
4-13
-------
TABLE 4-3
DBF Precursor Removal Compliance Calculations for Example Water Utility:
Enhanced Coagulation Year 1
Month
January
February
March
April
May
June
July
August
September
October
November
December
Source Water
Alk
(mg/L)
50
40
58
65
63
67
46
33
70
34
55
66
TOC
(mg/L)
3.9
3.3
4.2
4.1
4.3
4.0
3.5
4.8
4.9
3.5
4.2
3.5
Treated
Water TOC
(mg/L)
2.1
2.1
2.0
2.2
2.2
2.3
2.2
2.6
3.4
2.2
2.3
2.2
(A)
Actual
% TOC
Removal
46.2%
36.4%
52.4%
46.3%
48.8%
42.5%
37.1%
45.8%
30.6%
37.1%
45.2%
37.1%
(B)
Required
% TOC
Removal
35.0%
35.0%
45.0%
45.0%
45.0%
NA
35.0%
45.0%
35.0%
35.0%
45.0%
35.0%
Basis for
Required %
Removal
Step 1
Step 1
Step 1
Step 1
Step 1
Altern. 4C
Step 1
Step 1
Step 1
Step 1
Step 1
Step 1
(C)
Removal
Ratio
(A)/(B)
1.32
1.04
1.16
1.03
1.09
1.0
1.06
1.02
0.87
1.06
1.01
1.06
(D)a
Quarterly
Average
Ratio
-
-
1.17
-
-
1.04
-
-
0.98
-
-
1.04
(E)b
RAA Ratio
(Last 4
Quarters)
-
-
-
-
-
-
-
-
-
-
-
1.06
a Quarterly ratio calculated as an average of the actual / required removal ratio for the three months in that quarter.
b Running Annual Average (RAA) of quarterly TOC % removal ratios for the last four quarters; if the result in column (E) is greater than or equal to 1.0, then the
system is in compliance with the TOC removal requirements.
c Alternative Compliance Criterion 4: Treated water SUVA < 2.0 mg/L (not shown on Table) (see Section 2.4).
NOTE: Figures in bold show monthly TOC % removal less than required TOC % removal.
NA: Not Applicable.
-------
TABLE 4-4
DBF Precursor Removal Compliance Calculations For Example Water Utility:
Enhanced Coagulation Year 2
Month
January
February
March
April
May
June
July
August
September
October
November
December
Source Water
Alk
(mg/L)
50
52
58
65
70
80
47
58
68
65
50
62
TOC
(mg/L)
2.5
2.3
2.8
3.0
3.5
3.9
3.1
4.6
4.3
3.8
4.4
4.9
Treated
Water TOC
(mg/L)
1.9
1.9
2.1
2.4
2.9
3.6
2.3
2.6
o o
J.J
2.8
3.1
3.4
(A)
Actual
% TOC
Removal
24.0%
17.4%
25.0%
20.0%
17.1%
7.7%
25.8%
43.5%
23.3%
26.3%
29.5%
30.6%
(B)
Required
% TOC
Removal
NA
NA
35.0%
15.0%
15.0%
15.0%
NA
NA
20.0%
25.0%
25.0%
25.0%
Basis for
Required %
Removal
Altern. 2 c
Altern. 2
Step 1
Step 2
Step 2
Step 2
Altern. 4d
Altern. 4
Step 2
Step T
Step T
Step T
(Q
Removal
Ratio
(A)/(B)
1.0
1.0
0.71
1.33
1.14
0.51
1.0
1.0
1.16
1.05
1.18
1.22
(D)a
Quarterly
Average
Ratio
-
-
0.90
-
-
1.00
-
-
1.05
-
-
1.15
(E)b
RAA Ratio
(Last 4
Quarters)
-
-
0.99
-
-
0.98
-
-
1.00
-
-
1.03
a Quarterly ratio calculated as an average of the actual / required % removal ratio for the three months in that quarter.
b Running Annual Average (RAA) of quarterly TOC % removal ratios for the last four quarters; if the result in column (E) is greater than or equal to 1.0, then the
system is in compliance with the TOC removal requirements.
c Alternative Compliance Criterion 2: Treated water TOC < 2.0 mg/L (see Section 2.4).
d Alternative Compliance Criterion 4: Treated water SUVA < 2.0 mg/L (not shown on Table) (see Section 2.4).
e Plant may consult with the State to return to Step 1.
NOTE: Figures in bold show monthly TOC % removal less than required TOC % removal.
NA: Not Applicable.
-------
Example 2 - Enhanced Precipitative Softening
Tables 4-5 and 4-6 show sample running annual average calculations for a softening
plant. In year one (Table 4-5), compliance is based upon achieving a running annual average
of 1.0 or greater after TOC sampling in month 12 is complete (at the end of the fourth
quarter). The monthly removal ratios shown in column C are calculated from the required
Step 1 TOC removal matrix (Table 2-1) and by meeting alternative performance criteria.
Months in which an alternative compliance criterion is used are assigned a monthly removal
ratio of 1.0.
The plant in the example maintains a running annual average greater than 1.0 in year
two and is therefore in compliance. If the plant's running annual average had fallen below
1.0, it would have been out of compliance. It is important that softening plants utilize the
softening-specific alternative compliance criteria discussed in Section 2.4 to maximize their
ability to establish compliance.
4-16
-------
TABLE 4-5
DBF Precursor Removal Compliance Calculations for Example Water Utility:
Enhanced Precipitative Softening Year 1
Month
January
February
March
April
May
June
July
August
September
October
November
December
Source Water
Alk
(mg/L)
187
180
195
200
208
212
220
218
206
196
190
182
TOC
(mg/L)
3.0
3.3
9.3
10.4
8.7
6.0
4.8
3.5
4.9
9.2
6.4
4.4
Treated
Water TOC
(mg/L)
2.1
2.1
5.8
6.4
5.5
4.6
3.1
2.6
3.4
6.6
5.1
3.2
(A)
Actual
% TOC
Removal
30.0%
36.4%
37.6%
38.5%
36.8%
23.3%
35.4%
25.7%
30.6%
28.3%
20.3%
27.3%
(B)
Required
% TOC
Removal
15.0%
15.0%
30.0%
30.0%
30.0%
NA
25.0%
15.0%
25.0%
30.0%
25.0%
25.0%
Basis for
Required %
Removal
Step 1 c
Step 1
Step 1
Step 1
Step 1
Altern. 2d
Step 1
Step 1
Step 1
Step 1
Step 1
Step 1
(C)
Removal
Ratio
(A)/(B)
2.00
2.43
1.25
1.28
1.23
1.0
1.42
1.71
1.22
0.94
0.81
1.09
(D)a
Quarterly
Average
Ratio
-
-
1.89
-
-
1.17
-
-
1.45
-
-
0.95
(E)b
RAA Ratio
(Last 4
Quarters)
-
-
-
-
-
-
-
-
-
-
-
1.37
a Quarterly ratio calculated as an average of the actual / required removal ratio for the three months in that quarter.
b Running Annual Average (RAA) of quarterly TOC % removal ratios for the last four quarters; if the result in column (E) is greater than or equal to 1.0, then the
system is in compliance with the TOC removal requirements.
c Step 1 Required TOC% Removal from Table 2-1 (see Section 2.3.1).
d Alternative Compliance Criterion 2 for softening plants: Magnesium hardness removal greater than or equal to 10 mg/L between source water and treated
water (not shown on Table) (see Section 2.4.2).
NOTE: Figures in bold show monthly TOC % removal less than required TOC % removal.
NA: Not Applicable.
-------
TABLE 4-6
DBF Precursor Removal Compliance Calculations for Example Water Utility:
Enhanced Precipitative Softening Year 2
Month
January
February
March
April
May
June
July
August
September
October
November
December
Source Water
Alk
(mg/L)
185
193
197
190
200
209
213
222
204
198
180
184
TOC
(mg/L)
2.2
3.3
3.2
9.6
8.4
5.7
4.1
4.4
4.3
8.2
7.0
4.9
Treated
Water TOC
(mg/L)
1.9
2.2
2.5
6.5
5.7
3.8
3.1
2.9
3.0
5.6
4.9
O O
3.3
(A)
Actual
% TOC
Removal
13.6%
33.3%
21.9%
32.3%
32.1%
33.3%
24.4%
34.1%
30.2%
31.7%
30.0%
32.7%
(B)
Required
% TOC
Removal
NA
15.0%
15.0%
30.0%
30.0%
25.0%
NA
25.0%
25.0%
30.0%
25.0%
25.0%
Basis for
Required %
Removal
Altern. 1 c
Step 1 d
Step 1
Step 1
Step 1
Step 1
Altern. 2 e
Step 1
Step 1
Step 1
Step 1
Step 1
(C)
Removal
Ratio
(A)/(B)
1.0
2.22
1.46
1.08
1.07
1.33
1.0
1.36
1.21
1.06
1.20
1.31
(D)a
Quarterly
Average
Ratio
-
-
1.56
-
-
1.16
-
-
1.19
-
-
1.19
(E)b
RAA Ratio
(Last 4
Quarters)
-
-
1.28
-
-
1.28
-
-
1.22
-
-
1.27
a Quarterly ratio calculated as an average of the actual / required removal ratio for the three months in that quarter.
b Running Annual Average (RAA) of quarterly TOC % removal ratios for the last four quarters; if the result in column (E) is greater than or equal to 1.0, then the
system is in compliance with the TOC removal requirements.
c Alternative Compliance Criterion 1: Treated water TOC < 2.0 mg/L (see Section 2.4).
d Step 1 Required TOC% Removal from Table 2-1 (see Section 2.3.1).
e Alternative Compliance Criterion 2 for softening plants: Magnesium hardness removal greater than or equal to 10 mg/L between source water and treated
water (not shown on Table) (see Section 2.4.2).
NA Not Applicable.
-------
Chapter 5
LABORATORY PROCEDURES
-------
Table of Contents
Page
5.0 LABORATORY PROCEDURES
5.1 Introduction 5-1
5.2 Analytical Methods 5-1
5.2.1 Total Organic Carbon 5-2
5.2.2 Dissolved Organic Carbon 5-4
5.2.3 Ultraviolet Light Absorbance at 254 nm 5-5
5.2.4 Specific Ultraviolet Absorption (SUVA) 5-6
5.2.5 Alkalinity 5-6
5.2.6 Trihalomethanes 5-7
5.2.7 Haloacetic Acids 5-8
5.2.8 pH 5-9
5.2.9 Magnesium Hardness 5-10
5.3 Sample Collection and Handling 5-11
5.4 Quality Assurance/Quality Control 5-16
5.4.1 Total Organic Carbon 5-16
5.4.2 Dissolved Organic Carbon 5-17
5.4.3 Ultraviolet Absorbance at 254 nm 5-17
5.4.4 Specific Ultraviolet Absorption 5-17
5.4.5 Alkalinity 5-18
5.4.6 Trihalomethanes 5-18
5.4.7 Haloacetic Acids 5-19
5.4.8 pH 5-20
5.4.9 Magnesium Hardness 5-20
List of Tables
5-1 Analytical Methods for Demonstration of Compliance 5-2
5-2 Sample Collection Containers and Preservatives/Dechlorinating Agents .... 5-12
5-3 Sample Handling and Storage 5-14
-------
5.0 LABORATORY PROCEDURES
5.1 INTRODUCTION
The water quality parameters that are important for compliance with the treatment
requirement of the DBPR include TOC, alkalinity, pH, TTHM, HAAS, UV-254, DOC,
SUVA, and magnesium hardness. TOC and alkalinity data are needed to demonstrate
compliance with the Step 1 TOC removal requirements (Section 2.3.1). Analysis for pH is
important to ensure that the treatability of samples is examined over an acceptable range of
pH values. TTHM and HAAS analyses are necessary to qualify for an alternative
compliance criterion (Section 2.4). DOC and UV-254 analyses are used to calculate a
SUVA value which may be needed if alternative compliance criteria are used (Section 2.4).
Magnesium hardness and alkalinity are needed for the alternative compliance criteria for
softening systems (Section 2.4.2). This chapter provides an overview of acceptable
analytical methodologies for each of these water quality parameters. Required procedures
for sample collection, sample handling, and analysis are summarized, along with
recommended quality assurance and quality control practices. The purpose of this chapter
is to provide a general review of laboratory procedures necessary to implement the DBPR,
not to supplant the direction contained in analytical methods required by the DBPR. For
purposes of compliance, the final regulatory language and documents referenced therein
should be used.
5.2 ANALYTICAL METHODS
Only the analytical method(s) specified in the rule, or otherwise approved by the EPA
for monitoring under subpart L section 141.131, may be used to demonstrate compliance
with the enhanced coagulation or enhanced softening requirements of the DBPR. This
chapter is not comprehensive for all water quality parameters and methods required for
compliance with the DBPR. Only those methods necessary for the treatment requirement
of the DBPR are included. Table 5.1 summarizes the analytical methods for the parameters
5-1
-------
related to this portion of the regulation.
TABLE 5-1
Analytical Methods for Demonstration of Compliance with
Enhanced Coagulation/Enhanced Precipitative Softening Requirements
Parameter
Total Organic Carbon
(TOC)
Dissolved Organic Carbon (DOC)
Ultraviolet Absorbance at 254 nm
(UV-254)
Specific Ultraviolet Absorption
(SUVA)
Alkalinity
pH
Haloacetic Acids (HAAS)
Total Trihalomethanes (TTHMs)
Magnesium Hardness*
Method
SM53 10 B Combustion-Infrared
SM5310 C Persulfate-Ultraviolet Oxidation
SM5310D Wet Oxidation
Same as TOC except for filtration step. See discussion on
SUVA in this chapter.
SM5910B Ultraviolet Absorption Method
Calculated - requires methods for DOC and UV-254.
SM2320 B (Titration), ASTM D-1067-92B, USGS 1-1030-85
SM4500-H+B, EPA 150.1, EPA 150.2, ASTM 1293-84
EPA 552.1, EPA 552.2, SM6251B
EPA 502.2, EPA 524.2, EPA 551.1
SM3500-MgB -Atomic Absorption
SM3500-MgC - Inductively Coupled Plasma
SM3500-MgE - Titrametric
ASTMD 5 11-93 A -Titrametric
ASTMD 511-93 B - Atomic Absorption
EPA 200. 7 - Inductively Coupled Plasma
* proposed in the Federal Register (64 FR 2537, January 14, 1999)
5.2.1 Total Organic Carbon
Total organic carbon (TOC) is measured using heat, oxygen, ultraviolet irradiation,
chemical oxidants, or combinations of oxidants that convert organic carbon to carbon
dioxide. Results are reported in mg/L and are typically rounded to two significant figures.
A minimum reporting level (MRL) of 0.7 mg/L was established by a panel of experts for
the Information Collection Rule (ICR). The practical quantitation limit (PQL) reported by
5-2
-------
laboratories performing TOC analysis should be consistent with this MRL. Values reported
by the laboratory at less than the PQL should be reported by the plant as half of the PQL.
Three Standard Methods: 5310B, 5310C, and 5310D are included in the DBPR (Table 5-1).
These methods should be followed in accordance with the Supplement to the 19th Edition
of Standard Methods for the Examination of Water and Wastewater, American Public
Health Association, 1998. Method 5310B is a combustion-infrared method; Method 53 IOC
is a persulfate-ultraviolet oxidation method; and Method 531OD is a wet-oxidation method.
A summary of these methods for the determination of TOC is provided below.
Combustion-Infrared Method (Standard Method 5310B) measures organic carbon
via infrared absorption of the carbon dioxide gas that is produced when the organic carbon
in the sample is heated and reacted with an oxidative catalyst. Inorganic carbon is
converted to CO2 by acidification to pH <2 and is purged from the sample prior to analysis.
This process also removes volatile organic carbon from the sample, which contributes to
carbon loss. However, this loss is generally insignificant. The CO2 from oxidation of
organic and inorganic carbon is measured using a nondispersive infrared analyzer or titrated
colometrically. Any combustion instrument used for compliance purposes under the DBPR
should be capable of providing quantitative data at concentrations <0.5 mg/L.
Persulfate-Ultraviolet Oxidation Method (StandardMethod 53 IOC) measures organic
carbon via infrared absorption of the carbon dioxide gas that is produced when the organic
carbon in the sample is simultaneously oxidized by a persulfate solution and irradiated with
ultraviolet light. Inorganic carbon is converted to CO2 by acidification to pH <2, and is
purged from the sample prior to analysis. Significant concentrations of chloride (>0.1
percent) and a low sample pH (< 1) can impede the analysis; precautions are specified in
the method.
Wet-Oxidation Method(StandardMethod5310D) has a detection limit of 0.10 mg/L,
and is subject to the same interferences as the persulfate-ultraviolet method. Persulfate and
phosphoric acid are added to the sample, and the sample is purged with pure oxygen to
remove inorganic carbon in the form of CO2. The purged sample is sealed in an ampule and
5-3
-------
combusted for four hours at 116-130°C in an oven. This causes the persulfate to oxidize
the organic carbon to CO2. TOC is measured via nondispersive infrared absorption of CO2.
5.2.2 Dissolved Organic Carbon
DOC measurements are performed using the same analytical techniques used to
measure TOC (Combustion-Infrared Method 531 OB, Persulfate-Ultraviolet Oxidation
Method 53IOC, and Wet Oxidation Method 5310D). However, samples for DOC
measurement must be vacuum-filtered or pressure filtered through a 0.45 jim pore size filter
prior to analysis. Filtering should occur before preservation, storing or shippingthe sample.
To ensure sample integrity, no contamination or dilution of the sample during filtration
should occur. To prevent contamination from organic binding material on membrane filters,
the membrane filter must be washed with reagent-grade water. Typically, washing with
several 100 ml volumes of water is required for a 47-mm diameter filter. Vacuum or
pressure filtration can be used to facilitate the process. The laboratory should demonstrate
adequate washing procedures for each batch of filter membranes. EPA suggests that
adequate washing is demonstrated when the DOC of the filtered water is no higher than the
TOC of the water prior to filtration.
Water passed through the filter prior to sample filtration must be saved and used as
a filtered blank. This filtered blank must be analyzed using procedures identical to those
used for analysis of the samples, and must have a DOC content of less than 0.5 mg/L. The
filtration apparatus should be adequately washed to remove organic matter. Highly turbid
samples may require using more than one membrane filter if a filter becomes clogged.
When multiple filter membranes are required for a sample, each filter membrane must be
taken through the same washing procedure as described above, and a filter blank should be
analyzed.
DOC samples must be acidified to a pH of less than 2.0 by adding phosphoric or
sulfuric acid as soon as possible, but not to exceed 48 hours, after sampling and filtration.
Acidified samples must be analyzed within 28 days of sample collection. The DOC of the
5-4
-------
analyzed sample should be less than or equal to the TOC concentration; if not, sample
contamination may have occurred.
5.2.3 Ultraviolet Light Absorbance at 254 nm
Method 591 OB should be performed according to Standard Methods for the
Examination of Water and Wastewater, 19th Edition, American Public Health Association,
1998. The principle behind this method is that UV-absorbing constituents will absorb UV
light in proportion to their concentration. UV samples must be measured in waters prior to
the addition of an oxidant or disinfectant. This is necessary because oxidants react with
organic compounds and cleave the double bonds that absorb UV. Samples must be filtered
through a 0.45 //m pore-sized membrane filter. To prevent contamination from organic
material binding on membrane filters, the filters must be washed with reagent-grade water.
Typically, several 100 ml volumes of water are required for a 47-mm diameter filter. UV
absorbance is measured at a wavelength of 253.7 nm (rounded to 254 nm) at ambient pH
using a spectrophotometer. Select sample volume on the basis of the cell path length or
dilution required to produce a UV absorbance between 0.005 and 0.900 cm"1. The
spectrophotometer must be zeroed using an organic-free water blank. UV-254 should be
measured for at least two filtered portions of the sample at room temperature. The average
value is then reported in cm"1 (i.e., the result must be divided by the cell length). UV
measurements are typically made with a 1-cm cell.
A MRL of 0.009 cm"1 was established by a panel of experts for the ICR. It is
recommended that laboratories performing UV254 analysis obtain a PQL of at least 0.009
cm"1. Plants should use half of the PQL for compliance calculations when results are
reported to them by the laboratory as less than the PQL. Samples must be analyzed as soon
as practical, but not to exceed 48 hours, after sampling. The pH of a UV sample may not
be adjusted.
5-5
-------
5.2.4 Specific Ultraviolet Absorption (SUVA)
SUVA at 254 nm is an indicator of the humic content of water (Edzwald and Van
Benschoten, 1990). It is a calculated parameter equal to UV absorption at 254 nm (measured
in m"1) divided by DOC (measured as mg/L). The equation is:
SUVA (L/mg-m) = 100 (cm/m) [UV254 (m'^/DOC mg/L]
Waters with low SUVA values contain primarily non-humic matter and are not
amenable to enhanced coagulation. SUVA is an alternative compliance criterion for
demonstrating compliance with TOC removal requirements. Systems are not required to
perform enhanced coagulation or enhanced softening if the raw water SUVA is < 2.0 L/mg-
m. Two separate analytical methods are necessary to make this measurement: UV-254 and
DOC. These methods are described in Sections 5.2.2 and 5.2.3. DOC and UV-254 samples
used to determine a SUVA value must be taken at the same time and the same location.
Both samples are filtered according to the procedures outlined in Sections 5.2.2 and 5.2.3.
EPA recommends, but does not require, that both DOC and UV samples be filtered as one
large aliquot.
5.2.5 Alkalinity
Titration methods (StandardMethod2320B, ASTMD1067-92B, or USGSI-1030-85)
are approved for alkalinity measurements at 40 CFR 141.89. Standard Method 2320B can
be found in Standard Methods for the Examination of Water and Wastewater, 19th Edition,
American Public Health Association, 1998. Method ASTM D1067-92B is in the Annual
Book of ASTMMethods, 1998, Vol. 11.01. USGS 1-1030-85 can be found in Methods for
Determination of Inorganic Substances in Water and Fluvial Sediments: U.S. Geological
Survey Techniques of Water-Resources Investigations.
Total alkalinity in these methods is measured by titration of the sample to an
electrochemically determined endpoint (e.g., pH 4.5). Alkalinity is reported in milligrams
per liter as calcium carbonate (CaCO3). The methods ascribe the entire alkalinity
concentration to the sum of carbonate, bicarbonate, and hydroxide concentrations, and
5-6
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assume an absence of other alkalinity contributing compounds. The measured values may
include contributions from borates, phosphate, silicates, or other bases if these are present
(Standard Methods, 1989, p 2-35).
All procedures and precautions described here and in the methods must be followed
carefully to ensure an accurate measurement of alkalinity. The sample pH of the source
water where the sample was collected must be recorded. Care must be used in sampling and
storage, and in preparation of the primary standards for sodium carbonate, sulfuric acid, and
hydrochloric acid.
5.2.6 Trihalomethanes
EPAMethods 502.2,524.2, and 551.1 are acceptable for analysis of trihalomethanes.
These methods can be found in Methods for the Determination of Organic Compounds in
Drinking Water - Supplement III, USEPA, August 1995, EPA/600/R-95/131 (available
through NTIS, PB95-262616). The references for methods 502.2 and 524.2 are also
provided in the Federal Register (63 FR 69390, December 16,1998). The specific reference
for method 551.1 in Supplement HI is: Munch, D.J., Hautman, D.P. Method 551.1:
Determination of Chlorination Disinfection Byproducts, Chlorinated Solvents, and
Halogenated Pesticides/Herbicides in Drinking Water by Liquid-Liquid Extraction and Gas
Chromatography with Electron-Capture Detection; Revision 1.0, USEPA, National
Exposure Research Laboratory, Cincinnati, Ohio (1995).
Analyses for TTHMs measure the concentrations of chloroform,
bromodichloromethane, dibromochloromethane, and bromoform. The individual
concentrations of these species are summed together on a mass basis to obtain TTHM. EPA
method 502.2 is a purge and trap gas chromatography (GC) method utilizing an electrolytic
conductivity detector. EPA method 524.2 is a purge and trap gas chromatography/mass
spectrometry method. EPA method 5 51.1, a GC/electron capture detection method, utilizes
a microextraction technique which allows for the use of pentane or MTBE as the extraction
solvent. This method was developed for the simultaneous analysis of THMs,
haloacetonitriles, haloketones, and chloropicrin. As part of this method, samples are
5-7
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preserved with a phosphate buffer that reduces the pH to 5.2, in order to eliminate
degradation of DBFs that can undergo a base-catalyzed hydrolysis. Sodium sulfate is added
to the sample to increase the partitioning of the DBFs from the aqueous phase to the solvent
during the extraction step. The extracts are analyzed by GC with an electron capture detector
(BCD).
Aqueous samples should be extracted for Method 551.1 within two weeks of sample
collection. Extracts can be held for up to two weeks prior to analysis. If transfer of the
samples to other bottles is necessary, pouring should be done slowly to minimize agitation
and contact with the air. However, transfer of the sample to another container is not
recommended. The extraction should be performed in the sample bottle to prevent loss of
chloroform.
5.2.7 Haloacetic Acids
EPA Methods 552.1 and 552.2 are approved methods for the analysis of haloacetic
acids. EPA Method 552.1 can be found in Methods for the Determination of Organic
Compounds in Drinking Water - Supplement //, USEPA, August 1992, EPA/600/R-92/129
(available through NTIS, PB92-207703). EPA Method 552.2 can be found in Methods for
the Determination Organic Compounds inDrinking Water-Supplement III, USEPA, August
1995, EPA/600/R-95/131. The specific reference in Supplement HI is: Munch, D.J., J. W.
Munch, and A. W. Pawlecki. Method 552.2: Determination of Haloacetic Acids andDalapon
inDrinking Water by Liquid-Liquid Extraction, Derivitization and Gas Chromatography
with Electron Capture Detection; revision 1.0, USEPA, National Exposure Research
Laboratory, Cincinnati, Ohio (1995). The micro liquid-liquid extraction gas
chromatographic method (Standard Method 6251B) is also an acceptable method for HAAS
and can be found in Standard Methods for the Examination of Water and Wastewater, 19th
Edition, American Public Health Association, 1998. Standard Method 625IB was
developed to analyze simultaneously for each of the HAAS compounds plus 2,3,5-
trichlorophenol. Distribution system samples collected as part of monitoring for an
exemption from the treatment technique for control of disinfection by-product precursors
5-S
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should be analyzed for HAAS. The HAAS list consists of the following five haloacetic
acids: monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic
acid, and dibromoacetic acid. The ICR required reporting of HAA6, which consists of
HAAS plus bromochloroacetic acid. Three additional trihalogenated HAAs can now be
detected using Method 552.2, Gas Chromatography'/Electron Capture Detection method,
utilizing a microextraction patterned after SM 625 IB. This is an improvement over the
solid phase extraction utilized in EPA Method 552.1 which is subject to considerable
variability in sample matrices containing competing ionic species. A Fisher esterification
(an acid-catalyzed reaction of carboxylic acids with alcohols to form esters) is utilized in
method 552.2. A back extraction with saturated sodium bicarbonate is incorporated to
neutralize the acidic extracts and prevent any damage to the GC column. Finally, acidic
methanol derivitization utilized in Method 552.2 provides an alternative to trimethysilyl
diazomethane (TMSD) used in Standard Method 625 IB which has carcinogenic and
explosive characteristics. The three additional HAAs are: bromodichloroacetic acid
(BDCAA), chlorodibromoacetic acid (CDBAA) andtribromoacetic acid (TBAA). Analyses
for HAA6 and HAA9 are optional.
5.2.8 pH
Standard Method 4500-H+B, EPA Method 150.1 and 150.2, and ASTM 1293-84 are
acceptable methods for the analysis of pH. Standard Method 4500-H+B can be found in
Standard Methods for the Examination of Water and Wastewater, 19th Edition, American
Public Health Association, 1998. ASTM 1293-84 should be performed according to the
Annual Book of ASTM Methods, 1998, Vol. 11.01. The typical electrometric apparatus (pH
meter) consists of a potentiometer, a glass electrode, a reference electrode, and a
temperature-compensating device. When the electrodes are immersed in the sample
solution, a circuit is completed through the potentiometer; the potentiometer measurement
is used to determine the activity of the hydrogen ions.
5-9
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5.2.9 Magnesium Hardness
Precipitative softening systems monitoring to meet alternative performance criteria
(magnesium hardness removal greater than or equal to 10 mg/L as CaCO3) will need to
perform analyses for magnesium. Six magnesium methods have been proposed to
demonstrate compliance with the treatment requirement of the DBPR (64 FR 2537, January
14, 1999). These methods can be grouped into three analytical techniques: (1) atomic
absorption (AA) methods; (2) inductively coupled plasma (ICP) methods; and (3)
complexation titrametric methods.
Atomic Absorption Methods
Method 3500-MgB should be followed as described in Standard Methods for the
Examination of Water and Wastewater, 19th Edition, American Public Health Association,
1995. ASTM D511-93B should be performed according to the Annual Book of ASTM
Methods, 1998, Vol. 11.01.
In the measurement of magnesium by atomic absorption, a sample is aspirated into
a flame and atomized. The addition of interference-suppressing agents may be necessary.
A light beam is directed through the flame, into a filter or monochromator set at 285.2 nm,
and onto a detector which determines the light absorbed by the magnesium. The
concentration of magnesium is proportional to absorbance within the linear range of the
instrument. These methods are generally applicable to magnesium concentrations in the
range 0.02-3.0 mg/L, depending on the instrument and method employed. Higher
concentrations may be analyzed by dilution of the sample prior to analysis.
Inductively Coupled Plasma Methods
Standard Method 3500-Mg C can be found in Standard Methods for the
Examination of Water and Wastewater, 19th Edition, American Public Health Association,
1995. EPA Method 200.7 should be performed according to Methodsfor the Determination
of Metals in Environmental Samples-Supplement /, EPA 600/R-94-111.
5-10
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An ICP source consists of a stream of argon gas ionized by an applied radio
frequency field. The field is inductively coupled to the ionized gas by a coil surrounding a
quartz torch that supports and confines the plasma. Analysis of magnesium by ICP involves
generation of a sample aerosol in a nebulizer and subsequent injection into the ICP. This
subjects the constituent atoms to temperatures of 6000 to 8000 °K resulting in almost
complete dissociation of molecules and excitation of atomic emission. A portion of the
emission spectrum (usually 279.08 or 279.55 nm for magnesium) from the ICP is isolated
for intensity measurement. The efficient excitation provided by the ICP results in low
detection limits, and the linear range of the instrument may span four orders of magnitude.
Complexation Titrametric Methods
Standard Method 3500-Mg E can be found in Standard Methods for the
Examination of Water and Wastewater, 19th Edition, American Public Health Association,
1995. ASTM D 511-93 A can be found in the Annual Book of AS IM Methods, 1998, Vol.
11.01.
The complexation titrametric methods measure magnesium as the difference between
hardness (equal to calcium plus magnesium) and calcium. Hardness is measured by titration
of a sample with EDTA (ethylenediamine tetraacetic acid) at pH 10. Calcium is determined
by titration of a separate aliquot of sample with EDTA at a pH of 12-13, where the
magnesium is precipitated. A chemical indicator is added to the sample to allow
observation of the endpoint. These methods are generally applicable in a range from 1 to
1000mg/l of calcium plus magnesium expressed as calcium, but may fail in the analysis of
highly colored waters that contain high concentrations of metals.
5.3 SAMPLE COLLECTION AND HANDLING
All samples should be collected in accordance with the approved methods. A
summary of various aspects of sample collection and preservation is provided in Tables 5-2
and 5-3.
5-11
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TABLE 5-2
Sample Collection Containers and Preservatives/Dechlorinating Agents
PARAMETER
Alkalinity
Magnesium
Hardness
(Calculation)
THM
TOC
METHOD
SM2320B'
ASTMD1067-
92B5
USGS I- 1030-85*
SM3500-MgB'
SM3500-MgC2
SM3500-MgE2
ASTMD 511-
93A5
ASTMD 511-
93B5
EPA200.77
EPA 502. 23
EPA 524. f
EPA 551. 13
SM5310B'
SM5310C'
SM5310D'
BOTTLE
MATERIAL
Polyethylene or
borosilicate glass
(not acid washed)
Polypropylene or
liner polyethylene
or borosilicate
glass
Glass
Amber Glass
CAP/SEPTA
MATERIAL
No
specifications
Polyethylene
Cap
Teflon Lined
Septa
Teflon Lined
Septa
PRESERVATIVES/
DECHLORINATING AGENTS
NONE
Acidify with nitric acid (1 : 1) to pH <2
For 502.2 & 524.2: add 3 mg
Na2S2O3/40 ml sample or 3 mg
Na2S2O3/40 ml sample and
acidification using HC1 to pH < 2.0 or
25 mg ascorbic acid/40 ml sample and
immediate acidification using HC1 to
pH<2. Note: Samples must be
dechlorinated prior to acidification).
For method 551.1 preserve and
dechlorinate using Ig phosphate
buffer* and NH4C1 or Na2SO3
mixture/60 ml sample (mixture consist
of 1 part Na2HPO4, 99 parts KH2PO4
and 0.6 parts NH4C1 or Na2SO3. 1 g per
60 ml results in a pH of 4.5 - 5.5 and
0. 1 mg NH4C1 or Na2SO3 per ml of
sample.
* 2 g phosphate buffer may be needed
Adjust to pH <2 using phosphoric or
sulfuric acid (or alternate acid if
recommended by the instrument
manufacturer)
5-12
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SUVA
•DOC
•UV-254
pH
HAA
SM5310B'
SM5310C'
SM5310D'
SM5910'
SM4500-H+B'
EPA 150.1
EPA 150.2
ASTMD1293-845
EPA 5 52. 14
EPA 5S2.23
SM6251B
Amber Glass
Amber Glass
Field Analysis
only - rule
requires
immediate
analysis
Glass
Teflon lined
Septa
Teflon lined
Septa
NA
Teflon Lined
Septa
Acidify to pH <2 with phosphoric or
sulfiiric acid after filtration
Refrigerate sample to 4 ° C
NONE
Dechlorination:
0. 1 mg NH4C1 /ml of sample for
methods 552.1 & 552.2; 55 mg NH4C1
/40-50 ml sample for Method 625 IB
Referenced analytical methods are found in:
1 Standard Methods for the Examination of Water and Wastewater, 20th Edition, American Public Health Association, 1998.
2 Standard Methods for the Examination of Water and Wastewater, 19th Edition, American Public Health Association, 1995.
3 Methods for the Determination of Organic Compounds in Drinking Water-Supplement III, USEPA, August 1995, EPA/600/R-
95/131
4 Methods for the Determination of Organic Compounds in Drinking Water - Supplement II, USEPA, August 1992, EPA/600/R-
92/129
5 Annual Book of 'ASTMMethods, 1998, Vol. 11.01.
6 Methods for determination of inorganic substances in water and fluvial sediments: U.S. Geological Survey Techniques of Water-
Resources Investigations
1 Methods for the determination of metals in environmental samples-Supplement I, EPA 600/R-94-111
5-13
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TABLE 5-3
Sample Handling and Storage
PARAMETER
Alkalinity
Magnesium
Hardness
PH
TOC
SUVA
•DOC
•UV-254
METHOD
SM2320B'
ASTMD 1067-92B5
USGS I - 1030-
856
SM3500-MgB'
SM3500-MgC2
SM3500-MgE2
ASTMD 51 1-93 A5
ASTMD 51 1-93 B5
EPA200.77
SM4500-H+B'
EPA 150.1
EPA 150.2
ASTMD1293-84S
SM5310B'
SM5310C'
SM5310D'
SM5310B'
SM5310C'
SM5310D'
SM5910'
STORAGE
TEMP
(preferred)
Keep at 4°C
Keep at 4°C
NA
Keep at 4°C
Keep at 4°C
Keep at 4°C
MAX HOLD
TIME
ASAP not to
exceed 14
days
6 months
Field
Analysis
28 Days
28 Days
ASAP; not to
exceed 48
hours
SPECIAL SAMPLE COLLECTION
GUIDELINES
Fill bottle completely and cap tightly.
Avoid sample agitation and prolonged
exposure to air. A minimum sample
size of 200 mL is recommended for a
single alkalinity analysis. The sample
pH at the source where the sample is
collected must be recorded.
A volume of at least 500 ml is
recommended.
None Specified
Fill bottle but do not overflow and
flush out preservatives. No air bubbles.
Sample must be headspace free. A
minimum of 100 mL should be taken.
1. Fill bottles
2. Filter ASAP (not to exceed 48 hrs)
3. Acidify DOC to pH < 2.0
Note: Add preservative to DOC sample
after filtration.
Refrigerate the UV 254 sample for
preservation.
5-14
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TABLE 5-3 (cont.)
Sample Handling and Storage
PARAMETER
THM
HAA
METHOD
EPA 502.23
EPA S24.23
EPA 5 51. 13
EPA 5 52. 14
EPA S52.23
SM6251B
STORAGE
TEMP
Keep at 4°C
Keep at 4°C
MAX HOLD
TIME
14 days
14 days
SPECIAL SAMPLE COLLECTION
GUIDELINES
Fill bottle but do not overflow, do not
flush out preservatives and place on a
level surface; the TFE side of the
septum seal should then be slid across
the convex meniscus of the sample, and
the lid screwed on tightly. No air
bubbles. Sample must be headspace
free. Bottles must have a capacity of at
least 50 mL.
Fill bottle but do not overflow, do not
flush out preservatives. No air bubbles.
Samples should be headspace free.
Bottles must have a capacity of at least
50 mL.
Referenced analytical methods are found in:
1 Standard Methods for the Examination of Water and Wastewater, 20th Edition, American Public Health Association, 1998.
2 Standard Methods for the Examination of Water and Wastewater, 19th Edition, American Public Health Association, 1995.
3 Methods for the Determination of Organic Compounds in Drinking Water-Supplement III, USEPA, August 1995, EPA/600/R-
95/131
4 Methods for the Determination of Organic Compounds in Drinking Water - Supplement II, USEPA, August 1992, EPA/600/R-
92/129
5 Annual Book of ASTMMethods, 1998, Vol. 11.01.
6 Methods for determination of inorganic substances in water and fluvial sediments: U.S. Geological Survey Techniques of Water-
Resources Investigations
1 Methods for the determination of metals in environmental samples-Supplement I, EPA 600/R-94-111
5-15
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5.4 QUALITY ASSURANCE/QUALITY CONTROL
Quality Assurance/Quality Control (QA/QC) should follow the practices in the
approved methods described in the previous sections, or other practices approved by the
EPA for each of the methods found in Table 5-1. Other suggested QA/QC practices and
highlights from the methods are summarized in the following subsections.
5.4.1 Total Organic Carbon
Analyses under this section must be conducted by a laboratory approved by the State
or EPA. The QA program should include analysis of replicate samples for precision and
of spiked samples for accuracy. Spiked samples are those to which a known amount of
organic carbon has been added and are used to indicate the degree to which the sample
matrix impacts analytical accuracy. The laboratory should analyze blanks to demonstrate
that interferences from background contamination do not occur. Measurements of spikes,
blanks, and replicate samples should be recorded and reported by the laboratory performing
the analyses. The calibration curves should be linear and should bracket both the low and
high end of the concentration levels to be reported. If the TOC level exceeds the highest
calibration standard, the sample can be diluted into the calibration range with organic-free
water. If the TOC level is below the lowest standard, then TOC should not be quantified.
The lowest standard should representthe lowest TOC concentration that is quantitated (i.e.,
the minimum reporting level).
PE samples may be obtained from a commercial PE provider approved by the
National Institute of Sciences and Technology (NIST). TOC samples are provided in the
wastewater PE studies and may eventually be provided in the drinking water PE studies.
Samples should be precise to at least a two percent relative standard deviation (up to a
maximum of 0.2 mg/L TOC), or to 0.05 mg/L, whichever is larger.
5-16
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5.4.2 Dissolved Organic Carbon
The QA program for DOC measurements should include those QA/QC guidelines
described for TOC analysis. The analyst should take great care to ensure that the filtration
step does not result in a loss or gain of DOC. As stated above, DOC can be altered during
the filtration process both by desorption of organic material from the filter into the sample
and by adsorption of DOC from the sample onto the filter. The contribution of filters to
DOC must be checked by analyzing a filtered blank, and the contact of the sample with
organic material, such as contaminated glassware, plastic ontainers, and rubber tubing,
should be avoided as this may contaminate the sample.
5.4.3 Ultraviolet Absorbance at 254 nm
The QA program should include replicate sample analyses. At least two portions of
each sample should be tested. After every tenth sample a duplicate analysis should be
performed to assess analytical precision by repeating the entire sample preparation and
testing process. The baseline absorbance for the spectrophotometer should be checked after
every ten samples by testing the absorbance of organic-free water. A non-zero reading may
indicate the need for cell cleaning, a problem with the reference cell, or a fluctuating
spectrophotometer response caused by heating or power fluctuations. Spectrophotometer
performance can be verified as described in Standard Method 5910B. The same filtration
requirements as for DOC should be repeated and the filter blanks should be < 0.0045 cm-1.
5.4.4 Specific Ultraviolet Absorption
If the DOC measured for a sample is greater than the TOC, sample contamination has
occurred due either to the filter or to an alternate carbon source like contaminated glassware,
rubber tubing, or plastic containers. Filters should be evaluated by analyzing filtrate (in a
fresh flask) from an aliquot of organic-free water. If the filter washing step was adequate,
a post-wash filtrate with organic-free water should be free of DOC. Some brands of 0.45
|im filter paper have surfactant in them which facilitates filtration of microbial samples but
are difficult to wash. Filters with surfactants or those made of cellulose acetate should be
avoided.
5-17
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Because disinfectants/oxidants (chlorine, ozone, chlorine dioxide, potassium
permanganate) can degrade UV absorbing compounds without affecting the DOC
concentration, SUVA should be determined on water prior to the application of
disinfectants/oxidants. If disinfectants/oxidants are applied in raw water transmission lines
upstream of the plant, the raw water SUVA determination should be based on a sample
collected upstream of the point of disinfectant/oxidant addition. If the plant applies
disinfectants/oxidants prior to the settled water sample tap, settled water SUVA
measurements should be obtained from jar tests. Finally, the use of iron-based coagulants
can interfere with UV measurements, since dissolved iron can penetrate the filter paper. To
determine settled water SUVA, jar tests with aluminum-based coagulants, and not iron-
based coagulants, should be performed.
5.4.5 Alkalinity
The QA program should include replicate sample analysis for precision. Two
important items affecting the accuracy of the alkalinity method are reagent preparation and
meter calibration. Procedures for standardization of the reagents are specified in the
titration method and should be followed. Both the pH meter and the potentiometer should
be calibrated just prior to the analysis.
5.4.6 Trihalomethanes
The QA program should include replicate sample analysis for precision, and spiked
samples for accuracy. The laboratory should analyze blanks to demonstrate that
interferences from background contamination do not occur. If THMs are not routinely
found in samples, replicate spiked samples should be run periodically to develop precision
THM data. Measurements of spikes, blanks, and replicate samples should be recorded and
reported by the laboratory performing the analyses. The calibration curve should have
sufficient points to describe the shape of the curve, and the curve should bracket both the
low and high ends of the concentration levels to be reported. If the THM level exceeds the
highest calibration standard, the extract can be diluted into the calibration range and re-
injected into the GC. If the THM level is below the lowest standard, then THM levels
5-18
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should not be quantified. A PE standard is available for THMs, and procedural standards
should be run.
Each sample should be quenched according to the instructions in Table 5-2 at the
time of sample collection to halt additional production of THMs during the sample holding
time. The quenching converts free chlorine residual to chloramines. Chloramines will not
react with natural organic matter (NOM) to form THMs if the sample is kept at 4°C and the
two-week holding time is not violated. Finally, the solvent used for the extraction should
be free of THMs.
5.4.7 Haloacetic Acids
The QA program should include replicate sample analysis for precision, and spiked
samples for accuracy. The laboratory should analyze blanks to demonstrate that
interferences from background contamination do not occur. If HAAs are not routinely
found in samples, replicate spiked samples should be run periodically to develop precision
HAA data. Measurements of spikes, blanks, and replicate samples should be recorded and
reported by the laboratory performing the analyses. The calibration curve should have
sufficient points to describe the shape of the curve, and the curve should bracket both the
low and high ends of the concentration levels to be reported. If the HAA level exceeds the
highest calibration standard, the extract can be diluted into the calibration range and re-
injected into the GC. If the HAA level is below the lowest standard, then HAA levels
should not be quantified, since the shape of the curve is not always linear to "zero."
Commercially available PE standards are available for HAAs. The PE standards may
include some chlorinated phenols. Chlorinated phenols are not subject to this requirement,
so acceptable performance for the PE standards will only be based on the HAAs.
5-19
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5.4.8 pH
The QA program should include replicate sample analysis for precision. Storage and
preparation of the electrodes should be in accordance with the manufacturer's instructions.
The electrode system should be calibrated against standard buffer solutions of known pH.
When taking a measurement, gently stir the sample to insure homogeneity and to establish
equilibrium between electrodes.
5.4.9 Magnesium Hardness
When performing the magnesium methods, the QA program should include replicate
sample analysis for precision. Select a sample volume that requires less than 15 ml EDTA
titrate. Typical sample volumes are 25 to 50 ml. For low-hardness waters (<5 mg/L), take
a larger sample volume (Standard Methods, 1989, pp. 2-54).
Additional QA items when performing the atomic absorption methods include the
analysis of a blank between samples, and standard readings to verify baseline stability. A
known amount of metal should be added to one out of every ten samples, then analyzed to
confirm recovery. A standard solution also should be measured for every ten samples in
order to assure that the test is in control.
5-20
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Chapter 6
SECONDARY EFFECTS OF ENHANCED COAGULATION
AND ENHANCED PRECIPITATIVE SOFTENING
-------
Table of Contents
Page
6.0 SECONDARY EFFECTS OF ENHANCED COAGULATION AND ENHANCED
PRECIPITATIVE SOFTENING
6.1 Introduction 6-1
6.2 Evaluation and Implementation 6-1
6.3 Inorganic Contaminants 6-2
6.3.1 Manganese 6-3
6.3.2 Aluminum 6-7
6.3.3 Sulfate/Chloride/Sodium/Iron 6-11
6.4 Corrosion Control 6-12
6.5 Primary Disinfection 6-17
6.5.1 Chlorine 6-17
6.5.2 Ozone 6-18
6.5.3 Chloramine 6-19
6.5.4 Chlorine Dioxide 6-20
6.6 Particle and Pathogen Removal 6-20
6.7 Residuals Handling, Treatment, and Disposal 6-23
6.7.1 Increased Quantity of Sludge 6-24
6.7.2 Altered Characteristics of Sludge 6-29
6.8 Operation and Maintenance 6-33
6.9 Recycle Streams 6-34
List of Tables
6-1 Disinfectant Effectiveness under Typical Operating Conditions 6-17
List of Figures
6-1 Flowchart for Development of Manganese Removal Strategy with Enhanced
Coagulation 6-8
6-2 Flowchart for Development of Mitigation Strategy for Aluminum Carryover 6-10
6-3 Effect of Change of Various Water Quality Parameters due to Enhanced
Coagulation on Corrosion of Various Piping Materials 6-13
6-4 Effect of Change of Various Water Quality Parameters due to Enhanced
Softening on Corrosion of Various Piping Materials 6-14
6-5 Flowchart for Developing a Mitigation Strategy for Corrosion Control 6-16
6-6 Flowchart for Developing a Mitigation Strategy for Particle Removal
Problems due to Enhanced Coagulation or Softening 6-22
6-7 Impact Determination of Increased Sludge Volume 6-27
6-8 Mitigation of Impacts from Changes in Sludge Characteristics 6-32
-------
6.0 SECONDARY EFFECTS OF ENHANCED COAGULATION
AND ENHANCED PRECIPITATIVE SOFTENING
6.1 INTRODUCTION
The implementation of enhanced coagulation or enhanced softening may require
process modifications for some utilities. The process modification could have secondary
effects, some of which are expected to be beneficial (e.g., improved disinfection at lower
pH), while others could be detrimental (e.g., production of larger sludge quantities). Most
systems should be able to implement enhanced coagulation or enhanced softening with
minimal secondary effects. This chapter provides guidance to systems that experience
secondary effects to help them mitigate their occurrence and severity. A clear understanding
of potential secondary effects and adequate planning to develop mitigation strategies is
important to minimize the impact of secondary effects the plants may experience while
implementing the treatment technique.
6.2 EVALUATION AND IMPLEMENTATION
Problems related to the implementation of enhanced coagulation or enhanced
softening can be reduced if the affected process has been evaluated with potential secondary
effects in mind. In many cases, bench- or pilot-scale testing can be conducted before
enhanced coagulation or enhanced softening is implemented to completely characterize the
secondary effect and to develop a mitigation strategy. The bench- or pilot-scale study should
be well planned prior to beginning any tests. A comprehensive test plan should be prepared.
The test plan should consider all aspects of the process in question including corrosion,
particle removal, metals removal, disinfection and disinfection byproducts, and other site-
specific concerns.
6-1
-------
Testing should follow a sequence of increasing complexity to screen out variables
that may not be the source of the problem. A test plan may have the following sequential
components:
• Desktop study (review of existing data and literature)
• Jar testing
• Pilot testing
• Partial or full-scale demonstration
Utilities should consider site-specific needs when developing a test plan. Changes in
water quality characteristics that result from a process change can be determined by
comparing the test results for the new conditions with test results simulating existing
conditions. Testing should be calibrated to simulate existing full-scale conditions. These
comparisons will help estimate the type and magnitude of any expected changes due to
enhanced coagulation and softening.
Implementation of the process change may proceed if the test plan results indicate the
change will be successful. The highest risk to operational success and water quality will
occur during initial full-scale operational changeover. Careful planning and extended
monitoring should be practiced to minimize risk and detect any short- or long-term impacts.
An operations plan and a thorough monitoring plan should be developed for the change.
Operational changes should be made during a non-critical treatment period (e.g., warm water
or low demand). Experience should be gained operating under the new conditions when
operations are stable and the water quality is relatively constant. Implementing operational
changes during low flow periods will allow operators to reduce loading rates and compensate
for possible problems in process control.
6.3 INORGANIC CONTAMINANTS
Enhanced coagulation or softening can affect the control of inorganic contaminants,
including iron, manganese, aluminum, sulfate, chloride, and sodium. Maximum contaminant
levels (MCLs) do not currently exist for these contaminants. A secondary maximum
6-2
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contaminant level (SMCL) is currently in effect for manganese, aluminum, iron, and
chloride. In addition, some states regulate sodium as a contaminant. The following
subsections provide guidance on techniques applicable to maintaining existing levels of these
contaminants in finished water under enhanced coagulation or enhanced softening
operations.
6.3.1 Manganese
Manganese, even at levels well below the SMCL of 0.05 mg/L, causes discolored
water and can prompt customer complaints. Also, once manganese settles out in the
distribution system, it is difficult to remove and can lead to severe discoloration problems
during significant increases in flow (e.g., fire fighting efforts and main breaks). Manganese
is typically removed from raw water using direct oxidation/coagulation/filtration or filter
adsorption/oxidation (i.e., green sand).
The direct oxidation process uses an oxidant to transform manganese from a
-1-9
dissolved state (Mn ) to a solid (MnO2) that can be removed during sedimentation and
filtration (Knocke et al., 1990a). The filter adsorption process occurs when the filter medium
is coated with manganese oxide (i.e., green sand). The Mn+2 adsorbs to the oxide surface and
regenerates the sorption site upon oxidation. Chlorine is usually used for oxidation. Both of
these manganese removal processes can be impacted by enhanced coagulation.
Characteristics of the potential impacts to manganese removal processes are described below.
Slower oxidation at lower coagulation pH
A low pH hinders the direct oxidation process because the oxidation rate of
manganese increases as pH increases. Enhanced coagulation will increase metal salt
coagulant dose and suppress the pH; therefore, slower rates of oxidation can be expected. If
the manganese is being completely oxidized before the coagulation process, however,
enhanced coagulation should not have an impact on the oxidation process. If manganese is
oxidized after the coagulation process (e.g., intermediate ozonation), pH depression can
affect the efficiency of the removal process.
6-3
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When manganese is removed with chlorine (Cb), the oxidation can be relatively slow
(15 minutes to greater than 4 hours), and there may be insufficient contact time before
coagulation for complete oxidation. If potassium permanganate (KMnO/O, chlorine dioxide
(C1O2), or ozone (63) is applied before coagulation, the oxidation rate is fast enough that
complete reaction can occur in the contact time available before coagulation (typically less
than 5 minutes), even at pH values as low as 4.5 (Knocke and Van Benschoten, 1989). The
impact of enhanced coagulation on manganese removal efficiency will be greatest when Cb
is used with a high rate process (e.g., plate settling) that provides less than two hours of
contact time between the coagulation and filtration processes.
The manganese removal efficiency of the filter adsorption/oxidation process is
reduced when the filter influent pH is below approximately 6.2. The reduction in efficiency
is probably due to the lower oxidation rate of the sorbed Mn+2 ions, i.e., the lower pH reduces
the oxidation rate, and the regeneration of surface adsorption sites (MnO2 surfaces) is not
occurring fast enough to prevent dissolved manganese from passing through the filters into
the finished water. The pH at which the filter adsorption/oxidation process becomes less
effective will vary depending on the pre-filter chlorine dose, the filter loading rate, the filter
media configuration, and the overall water quality.
Manganese contamination of ferric salts
Another impact of enhanced coagulation on the manganese removal process is the
relatively high concentration of this element typically found in ferric chloride and ferric
sulfate. If a utility switches from low doses of ferric or alum to high doses of ferric, the
coagulant itself may significantly increase the amount of dissolved manganese added to the
water stream.
Mitigation Strategies
The flowchart shown in Figure 6-1 describes the potential mitigation strategy for
manganese removal problems due to the implementation of enhanced coagulation. As with
all secondary effects, characterization studies should be conducted before proceeding with
the development of mitigation strategies.
6-4
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There are three fractions of manganese that are important for drinking water
treatment; dissolved, colloidal, and particulate. Dissolved manganese can be either Mn+2 or
MnO/f. Colloidal manganese is MnO2 that has not coagulated to a particulate size.
Procedures for determining the fractionation of manganese have been described by Carlson et
al. (1997). Manganese fractionation should be determined in the raw water, after pre-
oxidation, after rapid mix, before the filters, and after the filters. The fractionation data allow
the utility to determine whether a manganese removal problem is due to the direct oxidation
process, the filter adsorption/oxidation process or ferric coagulant addition.
Based on the results of the characterization, one of the three flowchart branches in
Figure 6-1 should be used to develop a mitigation strategy. If the problem appears to be the
direct oxidation process, four modifications should be evaluated:
1) increasing the contact time for oxidation before coagulant addition
2) increasing the oxidant dose
3) increasing the pH during oxidation and then decreasing the pH for coagulation
4) changing the oxidant type to complete the reaction before coagulation
The oxidant contact time may be increased by moving the oxidant addition point as
far upstream as possible. A detention basin could be built to provide contact time prior to
coagulation, but this may be costly. When the oxidant dose is increased, the oxidation rate
increases, and less contact time will be needed before coagulation. There may be limits on
how much the dose can be increased due to disinfection byproduct formation, or concern
regarding residual oxidant reaching the filters. Increasing the pH for oxidation, followed by
acid addition for coagulation, may increase the oxidation rate to an acceptable level.
However, it may require an extensive chemical feed system. In some cases, it may make
sense to switch to a stronger oxidant that can oxidize the manganese within the available
contact time. For example, chlorine dioxide could be used instead of KMnO4 and the capital
investment required may be small. However, C1O2 byproducts and an increase in operating
costs can be expected.
6-5
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The feasibility and cost of each of these process modifications will be site-specific;
therefore, a general cost quantification cannot be provided. If these modifications do not
provide acceptable manganese removal, the filter adsorption/oxidation process should be
used in addition to the direct oxidation process. The filters may need to be seeded with
manganese oxide to initiate this process as described by Knocke et al. (1990b) and Merkle et
al. (1997).
If the characterization indicates the utility has a problem with the filter
adsorption/oxidation process, the chlorine dose applied to the filter influent should be
increased. An increased dose will increase the oxidation rate and may offset the decrease in
pH caused by enhanced coagulation. If an increased chlorine dose does not provide
acceptable manganese removal it may be necessary to increase the pH before filtration. The
pH should be increased to the minimum value that will yield acceptable manganese removal
without producing excessive soluble aluminum (see Section 6.3.2). Also, particle removal
may decrease and cause this alternative to be an unacceptable mitigation measure.
When the manganese removal problem is due to contaminated ferric salt, the first
remediation step should be to optimize the procurement purity specification. The maximum
acceptable contribution of manganese from the ferric coagulant should be calculated based
on the anticipated maximum coagulant dose, raw water manganese concentrations, and the
utility's finished water manganese goals. If the required purity cannot be achieved, the utility
should consider switching to an alternative coagulant (e.g., alum) that is not contaminated
with manganese. If an alternative coagulant is not feasible, the utility should pursue
optimization of the filter adsorption/oxidation process to remove the manganese added with
the ferric coagulant.
The flowchart in Figure 6-1 should help utilities develop an acceptable mitigation
strategy. If the manganese concentration in the finished water is still not acceptable after
implementation of the process modifications, additional characterization studies should be
conducted. This should rarely occur, and when it does occur, it will most likely be due to
inadequate initial characterization studies.
Pre-ozonation can complicate the removal of manganese with or without enhanced
coagulation. Removal of manganese before ozonation prevents the formation of the soluble
6-6
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MnO/f ion. Mixed results have been reported on the effectiveness of pre-ozonation for
manganese removal, and pilot testing is recommended before this strategy is chosen.
Cost Implications
The cost impact associated with mitigating these secondary impacts can vary widely.
Minor cost increases can result from a change in the chemical quantities added to the process.
Moderate costs can be incurred if new chemical facilities are required. Higher costs may be
incurred if there is a requirement for new detention facilities or major changes in oxidants or
other chemical systems.
6.3.2 Aluminum
Aluminum can pass through the filters and cause several problems in the distribution
system. For example, when soluble aluminum precipitates after filtration, the turbidity of the
water can increase and "dirty water" complaints from customers may result. Also, aluminum
deposition in the distribution system can lead to reduced hydraulic capacity due to friction
and the thickness of the aluminum films (Kriewall, 1996). Aluminum is also frequently
found in deposits in transmission mains and service lines and has shown some tendency to
function as a film that reduces the leaching of metals into the water (Fuge et al., 1992; Lauer
and Lohman, 1994). The secondary maximum contaminant level (SMCL) for aluminum was
promulgated on January 30, 1991 at 0.05 to 0.2 mg/L to prevent postprecipitation of
aluminum and discoloration of drinking water in distribution systems (Federal Register, 56
FR 3526, January 30, 1991). Aluminum is typically controlled in drinking water by 1)
lowering solubility by controlling pH prior to filters, 2) optimizing the filtration process,
and 3) minimizing aluminum contamination from downstream lime sources. Potential
impacts to these process operations are presented below.
Aluminum solubility at low pH
The minimum solubility of aluminum occurs at a pH of 6.2 to 6.5. Utilities operating
at a pH of less than 6.0 that do not increase the pH before filtration may be impacted the most
due to the solubility of aluminum at this pH. Aluminum solubility also increases significantly
above a pH of 8.0. If a utility practices enhanced softening and does not adjust pH before
filtration, aluminum carryover problems may result.
6-7
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Direct oxidation
problem
Optimize direct
oxidation process
-pH
- oxidant dose
- contact time
- oxidant type
Characterize Problem
- Mn Fractionation
- Establish goals
Mn concentrations
acceptable?
Filter adsorption/
oxidation problem
Ferric contamination
problem
Optimize filter adsorption/
oxidation process
- C12 dose
-pH
Mn concentrations
acceptable?
Mn concentrations
acceptable?
Optimize ferric coagulant
purity specification
Figure 6-1. Flowchart for development
of manganese removal strategy
with enhanced coagulation.
Mn concentrations
acceptable?
Perform further
characterization studies
-------
Presence of colloidal aluminum hydroxide at high alum doses
Colloidal aluminum can pass through filter processes that have not been optimized.
This fraction of aluminum may not show up as turbidity and can cause distribution system
problems. If a utility currently allows colloidal aluminum to pass through its filters, the
implementation of enhanced coagulation can make the problem worse.
Aluminum contamination of lime
Lime can be contaminated with soluble aluminum. Significant amounts of aluminum
can be added to the water at high lime doses. If lime is added before filtration and the pH is
uncontrolled, soluble aluminum can pass through the filters. If lime is added after the filters,
the aluminum contaminant will pass directly into the distribution system.
Mitigation Strategies
The flowchart shown in Figure 6-2 assists in the selection of a mitigation strategy for
aluminum carryover. If a problem with aluminum carryover is suspected, characterization
studies similar to those described for manganese removal should be conducted. Since
aluminum is not currently regulated for health effects (i.e., a MCL), the utility should
establish a finished water goal based on customer expectations before beginning remediation
actions. Also, a baseline of aluminum concentration should be established to assist in
assessing the impact of any future regulation.
In the case of aluminum, particulate and soluble fractions can be determined as
described by Teefy et al. (1992). The soluble and particulate (including colloidal) fractions
should be determined at the raw water, post-filtration, post-lime addition, and pre-filtration
stages. The characterization results will indicate which of three potential aluminum
carryover mechanisms are contributing to the problem. If soluble aluminum is passing
through the filters, the pH of the filter influent should be optimized. This can be
accomplished by adding base to bring the pH up to the minimum solubility level of
aluminum (6.2 - 6.8), but not significantly higher. Any adverse impact to particle removal
should be monitored.
6-9
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Soluble aluminum
problem
Lime contamination
problem
Characterize Problem
- Al Fractionation
- Establish goals
Al concentrations
acceptable?
Colloidal Al
Problem
Optimize
Coagulant pH
Optimize Lime
purity specification
Optimize coagulation/filtration
process for particle removal
- filter aid
- coagulant aid
- coagulant dose
- coagulation pH
Al concentrations
acceptable?
Al concentrations
acceptable?
Switch to ferric
salt coagulant
Al concentrations
acceptable?
Switch to caustic
soda (NaOH)
Perform further
characterization studies
Figure 6-2. Flowchart for
development of mitigation
strategy for aluminum carryover
-------
If the prefiltration pH is increased to 8.0 or greater, particles can be restabilized and
thereby compromise filter effectiveness. Additionally, at this pH, higher concentrations of
aluminum will carry over. Excessive lime application before filtration can also lead to media
clogging problems. If the prefiltration pH cannot be optimized to provide the targeted soluble
aluminum concentration, an alternative coagulant (e.g., ferric salt) should be considered.
If the problem characterization indicates that colloidal aluminum is the problem, the
filters need to be optimized for particle removal. This can be done by adding/optimizing filter
aid and coagulant aid polymers. This can also be done by adjusting the coagulant dose and/or
pH.
If contaminated lime is contributing significant amounts of aluminum to the finished
water, the same approach used for manganese contamination by ferric salts should be
followed. Calculate the maximum contamination that can be tolerated based on utility goals,
and work with lime vendors to determine the feasibility of this specification. If the
specification is not feasible, the utility should consider switching to caustic soda (NaOH).
Cost Implications
Capital cost impacts may be relatively minor for these mitigation measures. Costs can
be incurred for the following changes: additional chemical use, more costly chemicals, or
new chemical facilities. Switching to caustic soda from lime may increase operating costs.
6.3.3 Sulfate/Chloride/Sodium/Iron
The SMCL for both sulfate and chloride is 250 mg/L. Currently sodium is not
regulated by EPA. A MCL for sulfate has been proposed (59 FR 65578, December 20,
1994), and some states do set limits on sodium. In addition, the concentrations of chloride
and sulfate will impact pitting corrosion, which is discussed in a later section.
Removal of sulfate, chloride or sodium from drinking water is not usually
economically feasible. A utility can mitigate this problem by switching to alternative acids,
bases, or coagulants that do not contain the particular anion or cation.
Increase in iron-based coagulant dose or conversion from alum to ferric coagulation
in treatment plants may result in increased dissolved iron concentration in the finished water.
6-11
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If proper coagulation pH is maintained, however, problems with dissolved iron are expected
to be minimal. If utilities consider substantial increases in iron-based coagulant or a change
over from alum to iron-based coagulant, particular attention should be paid to the dissolved
iron concentration in the finished water. Bench- or pilot-scale testing should precede such
changes. During the bench- or pilot-scale tests, the problem of higher dissolved iron
concentration needs to be addressed by evaluating alternative pH levels during coagulation,
before filtration and after filtration.
6.4 CORROSION CONTROL
The water quality parameters that can impact the corrosion of distribution system and
domestic piping systems include pH, alkalinity, TOC, aluminum, sulfate, chloride, hardness,
oxygen levels, and disinfectant residual. Corrosion of lead and copper pipes has been
described by various researchers (AWWARF, 1985; AWWARF, 1990; AWWARF, 1996;
Snoeyink et. al., 1989; Schock, 1990; Schock et al., 1994; Korshin et al., 1996; Edwards et
al., 1994; and Edwards et al., 1996). The "Lead and Copper Rule" (National Primary
Drinking Water Regulations for Lead and Copper, 56 FR 26460), promulgated by EPA on
June 7, 1991, sets limits on lead and copper in drinking water, and requires systems that are
not in compliance to implement corrosion control measures.
Controlling corrosion in the distribution and domestic piping systems is dependent on
multiple water quality parameters (listed above), all of which can change when enhanced
coagulation or enhanced softening is implemented. This section provides guidance on how to
mitigate distribution system corrosion problems while implementing enhanced coagulation or
enhanced softening.
The effect of enhanced coagulation on the corrosion of various distribution system
materials is presented in Figure 6-3. The first two columns list the finished water quality
parameters of concern and the effect that enhanced coagulation is expected to have on each.
An up arrow indicates that this parameter will increase with enhanced coagulation, a down
arrow indicates it will decrease, and a sideways arrow means it will not change. For example,
the sulfate concentration of the finished water is expected to either stay the same or go up
6-12
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due to the additional use of alum or sulfuric acid. The last five columns predict how the
change in a particular water quality parameter will impact corrosion of that material. For
example, the increasing sulfate concentration is expected to decrease lead (Pb) corrosion but
increase copper (Cu) and iron (Fe) corrosion.
Figure 6-3 can be used in the following manner. If a utility identifies or suspects a
problem with corrosion of distribution system materials, the column corresponding to the
material of interest can be used to determine water quality parameters that increase the
corrosion rate. If a significant change in the parameter is caused by enhanced coagulation,
strategies to mitigate the change can be explored.
Parameter
TOC
Alkalinity
Aluminum
pH
Sulfate
Chloride
Enhanced
Effect
*
*
| f
Jl
^ ^
t -*-
Impact
Pb
E=>
ft
ft
ft
*
ft
Cu
ft,*2
f
ft, ^2
*
ft
f
Fe
0
ft
?
t
t
t
Pb from
Brass
^ ESO
ft
?
t
|
t
Concrete
t =>
ft
ft 4
ft
E=>
dj>
1 Applies to copper Increase Decrease Same Impact
2 Applies to copper by-products ^ (g°n°d) ?
Figure 6-3 Effect of the change of various water quality parameters due to enhanced coagulation on
the corrosion of various piping system materials.
The information in Figure 6-3 is intended only to characterize existing and future
corrosion control strategies. The figure can be used proactively to anticipate problems that
may develop if specific enhanced coagulation process strategies are pursued. If the raw water
for a utility has a relatively high concentration of chloride and a history of lead corrosion
problems, coagulants that add to chloride concentration should be avoided. Also, since a
lower pH will increase corrosion in almost all cases, a utility should consider the finished
water pH goal before implementing enhanced coagulation.
6-13
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Figure 6-4 applies to systems implementing enhanced softening. Enhanced softening
does not impact corrosion as much as enhanced coagulation because additional sulfate or
chloride is not usually added. The biggest issue for softening systems is allowing the pH of
the finished water to be higher in the distribution system concurrent with reduced carbonate
buffering capacity. This may lead to widely varying pH values in the distribution system.
Parameter
TOC
Alkalinity
Ca Hardness
pH
Sulfate
Chloride
Enhanced
Effect
|
1
|[
cz>
E=>
Impact
Pb
E£>
E=£>
0
$=>
E=£>
=s>
Cu
Jj,
1 V 2
E=£>
o
0 =>
E=£>
=>
Fe
f
f ^>
ft-=>
$=>
cs^»
•^p^
Pb from
Brass
^ =£>
| ^>
E=>
|}^>
C=>
Concrete
!
{f •=>
ft
E=>
E>
E=>
1 Applies to copper Increase Decrease Same
A i • i i (bad) (good) (no change)
2 Applies to copper by-products A n
ft f •*•
Figure 6-4 Effect of the change of various water quality parameters due to enhanced softening on the
corrosion of various piping system materials.
Mitigation Strategies
Enhanced coagulation and enhanced softening may change the chemistry of the water
entering the distribution system. Before enhanced coagulation or enhanced softening is
implemented, the current corrosion control strategy should be reviewed. This is the first step
in the corrosion control mitigation flowchart shown in Figure 6-5.
The finished water quality parameters discussed in Figures 6-3 and 6-4 can be
examined during a desktop analysis. Based on existing data and literature, a mitigation
strategy can be developed. For example, the finished water pH may be reduced from 7.8 to
7.0 when enhanced coagulation is implemented. The mitigation action may be to provide
6-14
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chemical feed facilities to supply base to increase the pH back to 7.8. The characterization
matrices presented earlier can be used to select a mitigation strategy.
After the corrosion control mitigation strategy has been developed, the utility can
ascertain whether the strategy represents a significant change from the current strategy. For
example, if corrosion was minimized by maintaining pH at 7.8 and alkalinity at 60-80 mg/L,
increasing the pH to approximately 7.8 or alkalinity to 60-80 mg/L after enhanced
coagulation would not represent a major change in corrosion control strategy. In this case,
the utility can implement the mitigation actions and continue to monitor the distribution
system for Pb, Cu, and Fe. If the recommended mitigation actions represent a major change
in corrosion control, the utility can conduct pilot-scale (pipe loop) studies to confirm that the
mitigation actions will meet the existing corrosion control goals.
If the utility conducts pilot testing and the results are acceptable, the mitigation
actions can be implemented and the distribution system monitored. If the pilot testing
indicates that the recommended mitigation actions will not provide adequate corrosion
control or the distribution system monitoring identifies a problem, the utility can once again
conduct a corrosion control desktop analysis taking into account the pilot testing data or the
additional distribution monitoring results. This review may lead to another set of
recommended mitigation actions that can be tested.
Cost Implications
Cost impacts may be relatively minor. However, corrosion potential is highly dependent on
site-specific conditions, and some utilities may incur significant costs. Corrosion impacts
may be controlled by changing the pH or by the use of other chemicals. The cost may include
additional chemical facilities or an increase in chemical use. An additional cost also may be
incurred for pilot testing to demonstrate that the corrosion control program is optimized.
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Review/complete desktop analysis of corrosion
control strategy with EC/ES conditions
- Collect finished water quality data
- Collect distribution system water quality data
Corrosion
control
acceptable?
Re-evaluate potential impact of
enhanced coagulation/softening
Recommend mitigation actions
Mitigation
actions change corrosion
control strategy?
Conduct pilot-scale corrosion
control confirmation testing
Implement mitigation actions
Monitor Pb, Cu, Fe in distribution system
Confirmation
test results
acceptable?
Is the
distribution
system adversely
impacted?
Figure 6-5. Flowchart for developing a mitigation strategy for corrosion
control problems due to enhanced coagulation and enhanced softening
-------
6.5 PRIMARY DISINFECTION
Enhanced coagulation and softening will have an effect on disinfection by changing
the pH and disinfectant demand. Over the typical plant pH operating range (5.5 - 9.5),
decreasing pH values improves the disinfection characteristics of chlorine and ozone;
decreases the effectiveness of chlorine dioxide; and below a pH of 7.5, tends to lower
chloramine concentrations. The reverse is true for increasing pH values. Disinfection
characteristics outside these pH values are not well understood. The potential effect of
enhanced coagulation and softening on disinfectant effectiveness is summarized in Table 6-1,
and explained in greater detail in this section. Secondary effects and associated mitigation
strategies are discussed in the following sections for chlorine, chloramine, chlorine dioxide,
TABLE 6-1 Disinfectant effectiveness under typical operating conditions.
Enhanced
Coagulation
Enhanced
Softening
Chlorine
ft
v
Chlorine
Dioxide
^
ft
Ozone
ft
V
Chlor-
amines
^
ft
and ozone.
6.5.1 Chlorine
Lowering pH during enhanced coagulation improves the disinfection characteristic of
chlorine. Increasing pH during enhanced softening decreases the effectiveness of chlorine.
Enhanced coagulation and enhanced softening will reduce the demand for chlorine by
reducing NOM which in turn will improve disinfection efficiency. For enhanced
coagulation, the overall effect of pH reduction and reduced oxidant demand should improve
disinfection efficiency. For enhanced softening, the combined effects of increased pH and
reduced oxidant demand may result in a decrease in disinfection effectiveness. Enhanced
coagulation and softening impacts on chlorine disinfection can be estimated through pilot or
6-17
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jar testing. These tests allow a determination of the pH, chlorine demand, and resultant
chlorine residual before and after enhanced coagulation is implemented. The contact time
(CT) tables in the SWTR Guidance Manual and Part 141, 40 Code of Federal Regulation can
be used to determine if there is a reduction or increase in the level of disinfection.
Mitigation Strategies
Mitigation measures will be minor, if at all necessary, for chlorination secondary
impacts because enhanced coagulation usually provides a positive impact. Mitigation
measures for enhanced softening systems should not be significant if the new disinfection
requirements exceed the available chlorination capabilities or available detention time for
chlorine disinfection. The pH can be lowered by recarbonation or acid addition; however,
this should be balanced with the softening and final pH requirements of the process.
Additional chemical facilities to increase the chlorine dose, additional basins to increase the
detention time, process changes, or a change in primary disinfectant can all be used as
mitigation measures, if necessary.
Cost Implications
Cost impacts can be calculated based on a change in the chlorine dose, a change in
detention time, or a change in primary disinfectant. The change in chlorine dose will result in
a change in operating costs. If a change is required in the chlorine feed equipment, there may
be a capital cost increase. If the detention time needs to be increased with new facilities, there
will be a capital cost increase for these facilities. Cost estimates can only be made after the
magnitude of the changes is defined.
6.5.2 Ozone
Reducing the pH and TOC level during enhanced coagulation reduces the ozone
demand and the ozone decay rate. Due to these reductions, a lower ozone dose is required to
achieve an equivalent amount of disinfection. When enhanced softening is practiced prior to
ozonation, the pH of the water should be lowered prior to the ozonation; this may increase
the CO2 dose required during recarbonation. For enhanced coagulation, it is important to
determine the new ozone demand and decay rates. Lower demand and slower decay is
expected. For enhanced softening, it is important to determine the relationship between the
6-18
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chemical quantities associated with lowering pH after softening and the additional ozone
dose necessary to achieve the ozonation objectives. Jar and pilot-scale testing procedures
and analysis are presented in Ozone in Water Treatment (AWWARF, 1991).
Mitigation Strategies
Enhanced coagulation should reduce ozone demand and decay, resulting in little or no
need for mitigation. There may be a need to more closely monitor the ozone residual leaving
the ozone contactor, because the residual will be longer lived and could carry over to the
filters or other processes. Enhanced softening can cause an increase in CO2 dosage during
the recarbonation step.
Cost Implications
There should be a cost reduction due to reduced ozone application after enhanced
coagulation. Capital cost for new facilities and operating cost for new and existing facilities
may also be reduced. The reduction in dose will result in less generation equipment and a
reduced use of power and gas feed to the ozone generation equipment (e.g., air preparation or
oxygen feed). Changes in cost can be estimated based on the cost estimating procedures
presented in Ozone in Water Treatment (AWWARF, 1991).
6.5.3 Chloramine
Chloramine use and disinfection capabilities will be adversely impacted by enhanced
coagulation. At lower pH, monochloramine is less prevalent, and more di- and tri-
chloramines form which can cause taste and odor problems. At lower pH, there are also
volatility and corrosion problems associated with chloramines.
Mitigation Strategies
The pH should be raised prior to chloramination and kept above 7.5 - 8.0 for optimum
chloramine formation. Increasing the pH in the distribution system would have to be
compatible with the corrosion control strategy. An alternate disinfectant also can be
considered. After enhanced coagulation and a corresponding reduction in pH and disinfection
byproduct precursors, it may be possible to use free chlorine for primary disinfection
followed by chloramines for distribution system residual disinfectant. It also may be useful to
6-19
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consider changing to an alternative disinfection strategy when considering possible
operational changes.
Cost Implications
Cost impacts may include the need to change pH or change the primary disinfectant.
Capital costs may be incurred if alternative disinfection schemes are used, and operating
costs may be impacted if either an alternative disinfectant is used or the pH is adjusted.
6.5.4 Chlorine Dioxide
Lowering pH may reduce the effectiveness of chlorine dioxide for disinfection,
although the inactivation table in the SWTR Guidance Manual does not reflect this. There
has been some work that suggests that disinfection effectiveness may change with changes in
pH (Finch et al., 1995). There is insufficient data to recommend mitigation of any effects
that enhanced coagulation or softening may have on disinfection effectiveness.
6.6 PARTICLE AND PATHOGEN REMOVAL
Floe Settleability
In some cases, enhanced coagulation may produce a floe that is lighter and more
fragile. This can result in floe carryover from the clarifier to the filters, which could result in
shorter filter runs or premature filter breakthrough and an increase in backwash requirements.
Different Optimal Condition for TOC and particle removal
The lower pH, higher coagulant dose conditions for enhanced coagulation may result
in the restabilization of particles and an increase in the settled water turbidity. Raw waters
that are coagulated under charge neutralization conditions are particularly susceptible to this
problem, because optimal coagulation for TOC and particle removal are different (Carlson et
al., 1996). In one study, Vrijenhoek et al. (1998) observed that under optimized pH
conditions, particle removal may not be adversely affected. Problems also can occur in
solids blanket-type clarifiers. Blanket upset in solids blanket clarifiers may occur with lighter
floe, and control of the system may be harder if the floe is lighter.
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Pre-FilterpH adjustment
Changing the pH prior to filtration may be desirable for additional process objectives
(e.g., Mn removal); however, a change in pH may increase particle breakthrough as well as
increase alum or iron carryover. Adding lime prior to filtration to raise the pH may create
additional problems. It can lead to particle breakthrough, increased solids loading onto the
filters, and reduced filter productivity. For GAC media, it can cause regeneration problems
by increasing the required temperature of regeneration and leaving behind calcium oxide,
which will impact treatment effectiveness when the GAC is reinstalled.
Improved performance is also possible. Less floe carryover and improved filterability
of floe may occur, which improves G. lamblia and C. parvum removal. This can result when
the enhanced coagulation assists in optimizing the coagulation process. Enhanced softening
to a level for magnesium removal may improve particle removal if the plant is designed to
settle magnesium floe. Magnesium floe is lighter and fluffier than calcium carbonate floe and
may carryover in significant amounts if this is not incorporated into the plant design.
Mitigation Strategies
The development of a mitigation strategy for particle removal problems due to
enhanced coagulation or softening is presented in Figure 6-6. The first step in the flowchart is
to conduct pilot testing to determine what effect the enhanced coagulation conditions will
have on filter particle removal. Settling performance can be judged with jar testing if the
existing process is used as the control, but filtration must be studied at either pilot- or full-
scale. Ultimately, the full-scale implementation of enhanced coagulation will have to be
monitored and changes to the mitigation strategy may be required due to scale-up issues.
After enhanced coagulation or softening has been tested at pilot-scale, the settled and
filtered water turbidity and particle counts should be compared with the results from the
existing full-scale process. If the enhanced process yields unacceptable settled water results,
the coagulation process should be adjusted to improve particle removal. Polymer addition
(coagulant or floe aid) should be studied to determine if it can improve particle removal.
6-21
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Adjust coagulation process
- dose
-pH
- coagulant type
- polymer addition
Test enhanced coagulation particle removal
with settling and filtration processes
- Pilot scale
Adjust filtration process
- filter aid
- filter operation
- coagulant aid
- coagulant chemistry
Settled water
turbidity
acceptable?
Settled water
turbidity
acceptable?
Filtered water
particle counts
acceptable?
Filtered water
particle counts
acceptable?
Consider derating
clarification
process and buildin
additional capacity
Optimize filter media
configuration
Filtered water
particle counts
acceptable?
Figure 6-6. Flowchart for development
of mitigation strategy for particle removal
problems due to enhanced coagulation or softening
Consider derating filter loading
and building additional capacity
-------
If these actions do not produce settled water that can meet both TOC and particle
removal goals, utilities may wish to consider derating the clarification process or installing
additional capacity.
Once acceptable settled water turbidity and TOC results are achieved, the filtration
process should be studied. If the filtration process allows unacceptable particle counts in the
filtered water, the filtration process should be adjusted and optimized through the addition of
filter aids. If these remedial actions are not successful, the media configuration should be
studied within the structural constraints of the existing filter boxes.
If the optimized media configuration does not provide acceptable filtered water
particle results, the filters will most likely need to be down-rated. Replacement capacity may
need to be developed. In this case, the cost should be judged relative to the water quality
improvement that will result from enhanced coagulation or softening. If the water quality
improvement is justified, the utility may need to build new filters.
Cost Implications
The cost to mitigate particle removal problems associated with enhanced coagulation
or softening may not be insignificant. As shown in Figure 6-6, the ultimate mitigation
strategy may be the down-rating of existing clarification or filtration facilities. The cost for
mitigation will be considerably less if the coagulation or filtration processes can be improved
by optimizing chemistry, including polymer addition.
Operating costs may rise with an increase in chemical use, increased monitoring due
to less stable operations, and increased operations attention to the processes (e.g., jar testing,
solids monitoring, and increased filter backwashing).
6.7 RESIDUALS HANDLING, TREATMENT, AND DISPOSAL
Implementation of enhanced coagulation or enhanced softening may result in an
increase in the amount of residuals produced during coagulation/softening and filtration. The
increased quantity of solids will result from both the increased coagulant dose and the
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increase in the amount of TOC in the sludge (Hecht et al., 1993). In some cases, the nature
of the residuals will change. Both of these secondary impacts are described in this section.
6.7.1 Increased Quantity of Sludge
Utilities that make significant increases to their coagulant dose or utilities that have
limited facilities to process sludge will be most affected by implementation of enhanced
coagulation. To determine whether the impact will be significant, the increase in sludge
quantity should be estimated and compared to the excess capacity of the current system. The
following steps are recommended to help determine how significant the impact may be.
1. Determine coagulant dose to be used at full-scale for enhanced coagulation. Jar
test procedures are detailed elsewhere in this guidance manual.
2. For enhanced coagulation, calculate the amount (dry weight and volume) of
sludge generated.
• If a site-specific relationship between coagulant dose and amount of sludge
generated exists, use this relationship.
• If a site-specific relationship
does not exist use a general
equation.
• Calculations should be
performed for maximum
daily flows to determine if
existing sludge handling
and treatment systems are
adequate. Calculations
should be performed with
average daily flows and the
average increase in alum
dose.
For Alum
S = Q*8.34*((AD * 0.36) +X + TOC)
where,
S = sludge generated in pounds per day
Q = flow in MGD
AD = alum dose in mg/L
X = other chemical doses used for
coagulation such as polymers or PAC
in mg/L
TOC = TOC removed in mg/L
6-24
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• The volume of residuals can be calculated by assuming a percent solids (based
on the dry-weight calculated
For Ferric-based coagulants
above). It is best to use a site-
S = Q*8.34*((FD * 0.5) + X + TOC)
specific value for percent
where,
solids, but if one is not
available, 0.5 percent is
typical of sludge from a
clarifier.
FD = dose of ferric based coagulant
other variables as defined for alum
3. Compare the calculated volume to each step of the current residuals management
plan or capacity of the existing residuals operation. Look at the following issues:
• basis of system design
• equipment capacity from manufacturers
• permit limits
• sewer capacity
• ultimate disposal capacity
• frequency of cleaning required
Mitigation Strategies
Mitigation may involve adjusting the coagulation process to minimize sludge
production. Minimization of sludge production should be balanced with other costs by
optimizing the total cost of treatment, including chemical costs, operating costs, and the cost
of sludge handling. Jar tests can be performed to determine the optimum coagulant type,
coagulation pH, acid dose, and coagulant dose. To mitigate increased residuals produced
during enhanced coagulation, the following variables should be considered when performing
jar tests:
• acid
• acidified coagulant
• polymers
• flocculation pH
• mixing intensity
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Employing acid, acidified coagulant, or polymers may reduce the coagulant dose
necessary to achieve TOC and particle removal. A flowchart for the suggested mitigation
strategy is shown in Figure 6-7. An example is provided below:
Example: Solids Handling Costs
In this example, the EPA water treatment model and plant-scale data were used to
determine the most cost-effective conditions for meeting the requirements for enhanced
coagulation. This example does not include considerations for sludge treatment, but does
demonstrate an approach for comparing coagulation alternatives. In this case, it was
determined that the utility's two feasible options for enhanced coagulation were alum alone
or a combination of alum and sulfuric acid. Since a new plant was being considered, the
comparison considered capital costs and operating costs for the new plant.
EPA's water treatment plant model was used to determine the alum dose or the alum
plus acid doses required to reach an optimum coagulation pH of 6.0. The model used the raw
water characteristics for the period September 1996 to August 1997. (Utilities should use
site-specific data to determine coagulant and acid doses.)
The capital cost for a sulfuric acid feed system was estimated to be $282,000, which
does not include any cost savings for a smaller alum system, which would be required if acid
were used.
Operating Costs
There are two areas of significant cost savings associated with the use of sulfuric acid
for coagulation: (1) sulfuric acid is less expensive than alum for pH reduction; and (2) the
amount of sludge produced by using sulfuric acid is considerably less than alum alone.
Chemical Cost Savings
The period of September 1996 to August 1997 was analyzed to determine the
chemical requirements of both options. The following table summarizes the chemical
requirements.
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Enhanced coagulation or softening
implemented or planned for implementation
Impact likely negligible.
Implement and monitor
discharge against permit.
Consider use of acid to minimize
sludge and cost of treatment.
Figure 6-7. Impact determination
of increased sludge volume
Evaluate impact of enhanced
coagulation treatment on
sludge handling.
-------
Comparison of Average Doses for Enhanced Coagulation
Coagulation Conditions Alum dose (mg/L) Sulfuric Acid dose (mg/L)
Alum alone 90 0
Alum and Sulfuric Acid 45 22
The following costs were based on the annual chemical usage for the period. The unit
price for sulfuric acid used was $125 per ton for 93 percent acid and alum's unit cost was
$109 per dry ton. The following costs are based on an average daily raw water flow of 30
mgd.
Comparison of Annual Chemical Costs
Coagulation Conditions
Annual costs for alum
Annual costs for acid
Total Annual Costs
Cost for Alum
$448,000
$0
$448,000
Cost for Alum and Acid
$224,000
$137,000
$361,000
Sludge Costs
The amount of sludge generated by the alum-only scenario is 53.3 mg/L at a dose of
90 mg/L alum (based on EPA's water treatment plant model). The alum plus acid option,
with alum dosed at 45 mg/L and acid dosed at 22 mg/L, produces 22.8 mg/L of sludge. From
historical data, Waterworks variable costs of residuals handling is $176 per dry ton. Thus, the
alum-only option will produce 6.7 dry tons per day (dpd) versus 2.85 dpd for alum plus acid
under worst case conditions.
On an annual basis, the alum-only solution produces 1,776 dry tons per year (dpy),
versus 1,039 dpy for alum plus acid. The annual cost increase for the alum-only solution is
$130,000. The actual handling costs are $312,576 and $182,864 respectively.
6-28
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Total Annual Cost
The total annual costs of concern for this analysis are:
1. Alum only - $761,000
2. Alum + Acid - $544,000
The present value of these differences for an interest rate of 6 percent over twenty
years is:
1. Alum only-$8,729,000
2. Alum + Acid - $6,522,000
Thus, the present value of the cost savings associated with using sulfuric acid is
$2,200,000. The calculations demonstrate that the combination of alum and sulfuric acid is a
more cost-effective solution to reaching optimal coagulation conditions than alum alone, and
that optimal coagulation will produce significant water quality benefits. It is recommended
that a sulfuric acid feed system be designed into the new plant.
To mitigate increased residuals production at enhanced softening facilities consider:
• increasing lime dose, but not exceeding the pH of magnesium hydroxide
precipitation (typically between pH 10.5 to 10.7);
• augmenting with a ferric coagulant;
• avoiding alum because the high pH required for lime softening is outside the
workable pH for alum.
6.7.2 Altered Characteristics of Sludge
When enhanced coagulation is implemented, sludge characteristics may change and
impact its dewaterability (Knocke et al., 1987; Kelkar and Schafran, 1994; McTigue, 1995).
The following are potential changes to sludge characteristics:
• Increased coagulant doses may result in increased percentages of hydroxide
precipitate in the sludge (ferric or alum).
• If acid is used to depress the pH, and the coagulant dose is not decreased, there
may be an increase in the relative TOC content of the sludge.
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• Increased metal concentrations may be experienced. The increased concentrations
may be from natural sources, contaminants in the coagulant, and the coagulant
itself.
• Arsenate not removed by previous coagulation practice may be removed by ferric
coagulants at low pH resulting in arsenate in the sludge.
• When the coagulant dose is increased, there may be a decrease in natural solids to
total solids ratio.
• The time that the sludge is in the clarification basins will decrease if the basins are
cleaned more frequently; therefore, the sludge age will be less.
Typically, these changes are expected to decrease dewaterability; however, in some
cases dewaterability may be improved. If significant changes in coagulant dose or pH are
required, pilot testing of residuals dewatering is recommended. If no residuals treatment is
provided, then the impact is limited to changes related to the permit for ultimate disposal.
Monitoring may be appropriate to determine the nature of the discharge after enhanced
coagulation is implemented; monitoring issues are discussed in greater detail later in this
section.
One issue that is specific to enhanced softening is the potential formation of
magnesium hydroxide [Mg(OH)2 ] precipitate. Softening plants that are designed for CaCCb
removal may form Mg(OH)2 at the increased pH levels that result from increased lime doses
required to meet enhanced softening requirements. Mg(OH)2 production can increase
quickly as pH levels of 10.5 to 10.7 are approached. The exact pH varies with each water
type, and the amount of Mg(OH)2 produced depends on how much Mg is present in the water
before treatment. Since Mg(OH)2 is more difficult to dewater than CaCCb, enhanced
softening may significantly increase solids handling requirements. In addition, the amount of
additional lime required to change the pH can result in a significant increase in sludge
volume regardless of whether magnesium is precipitated.
6-30
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Mitigation Strategies
The mitigation steps for enhanced coagulation are summarized in the flowchart
presented in Figure 6-8. The mitigation steps are divided into two categories, based on
whether the residuals are treated by thickening or dewatering. If no residuals treatment is
provided, then the impacts may be negligible. The nature of the sludge should be monitored
for items covered by the discharge permit to determine whether enhanced coagulation
conditions will jeopardize permit conditions. If testing indicates that permit conditions cannot
be met when enhanced coagulation is implemented, utilities should consider altering
coagulation conditions as previously discussed (e.g., using acid to depress pH), or consider
providing some treatment for the residuals. Treatment could be as simple as providing
additional settling time.
If residuals treatment is provided, then pilot-scale testing of residuals treatment under
the enhanced coagulation conditions can be considered. Pilot-scale testing would focus on
determining whether the existing residuals treatment facilities need to be adjusted to provide
desired treatment. During pilot testing, the water quality of any permitted disposal streams
should be monitored to verify that permit conditions can be met. If existing facilities are
found to be inadequate, consider the following options:
• Change the chemical conditioning of the sludge; for example, try a different
polymer or bentonite addition.
• Use alternative technologies to treat the sludge; for example, dewatering with a
centrifuge rather than a belt press.
• Alter the water treatment mechanisms that may affect sludge treatment; for
example, implement air scour during backwash to minimize the production of
waste washwater.
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Enhanced coagulation or softening
implemented or planned for implementation
Negligible impact.
Monitor metals in sludge
relative to permit(s).
Can permit limits
be met?
Complete pilot test
of dewaterability.
No
No
Figure 6-8. Mitigation of impacts
from changes in sludge characteristics.
Optimize solids generation/treatment
- coagulation conditions
- sludge treatment
Implement modifications
to solids generation/
treatment processes.
-------
6.8 OPERATION AND MAINTENANCE
Changing from an operational strategy designed to remove turbidity to one that
includes TOC removal will require some changes in the operation and maintenance of the
coagulation system. The following are some changes that may result due to the
implementation of enhanced coagulation and enhanced softening:
• A change in type or dose of coagulant and/or polymer aid may be required. Also,
the optimal range of coagulant aid can be reduced. Increasing the lime dose in
softening plants can result in the production of more Mg(OH)2, which does not
settle as readily as CaCCb.
• A change in coagulation conditions may require greater vigilance by operators to
control the carryover of floe from the settling basins to the filters. If floe
carryover to the filters occurs, more frequent backwashing of the filters will be
necessary requiring more water, electricity and labor. Also, increased floe
carryover may cause "mudballs" to form in the filter media if the backwash is not
sufficient.
• Increased coagulant and lime doses may increase the sludge removal frequency.
• Corrosion in metals or concrete may occur at low pH values. The potential for and
extent of this impact is uncertain.
Mitigation Strategies
The following points could be considered in developing mitigation strategies for
resolving operation and maintenance problems:
• Education of the operations staff to communicate the regulatory needs, operating
philosophy, and the benefit of the enhanced coagulation/enhanced softening may
be helpful.
6-33
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A streaming current monitoring system can be augmented with a pH control
monitoring system. TOC or UV-254 (in oxidant-free situations) can be monitored
more frequently or in-line to provide a better handle on the operation of the
coagulation process.
Frequent jar testing should be carried out to determine appropriate coagulation
conditions (simultaneous removal of TOC and particles).
Operators should be more vigilant about removal of precipitated solids from
sedimentation basins and sludge-blanket clarifier and backwashing of filters.
Proper use of polymers is expected to improve settleability and filterability of
floes, however, the operators should be cautious about overdosing of polymers
which can adversely effect the filter media.
Installation of plate or tube settlers may improve removal of solids in clarifiers.
Periodic application of paints or acid resistant coating on the submerged
mechanical parts and concrete surfaces is expected to reduce in-plant corrosion.
6.9 RECYCLE STREAMS
The effect of enhanced coagulation or enhanced softening on the quality of recycle
streams can be substantial if the coagulant dose is increased significantly. Conversely, if the
coagulation conditions are not significantly changed, the recycle stream may not be
impacted. The nature of the effect will depend on whether or not the recycle stream is treated.
If recycle treatment is provided, an increase in the volume of the recycle may overwhelm the
existing recycle treatment system, especially if this system is near capacity.
In the context of this document, untreated recycle refers to recycle streams that are
not treated and are added directly into the process flow stream. In some cases, increased
recycle flow may upset the treatment process. Typically, process flow may not be impacted
when the recycle comprises less than five percent of the process flow.
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With softening plants, the potential to form a Mg(OH)2 precipitate presents a special
issue related to recycling during enhanced softening. In plants treating water with more than
approximately 40 mg/L of Mg, there is potential to form a Mg(OH)2 precipitate. Once this
precipitate is in the recycle system, it would be difficult to remove from the plant because it
settles poorly compared to calcium carbonate.
Mitigation Strategies
The mitigation efforts are different for plants that treat recycle and those that do not
provide treatment. For plants that do not provide treatment (i.e., those that recycle directly)
the operational impacts can be mitigated by:
• adding a new equalization basin or increasing the capacity of the existing
equalization basin;
• treating the recycle, for example, installing solids separation;
• eliminating all recycling; and
• send flow to a sanitary sewer.
For those plants that do provide treatment of the recycle system, the mitigation efforts
are somewhat site-specific, depending on the nature of the treatment provided. Some of the
more common mitigation steps include the following:
• Optimize existing equalization provided by existing recycle treatment facilities
(e.g., thickener).
• Expand the recycle treatment system.
• Consider alternate disposal options; for example, send the waste or a portion of
the waste to the sewer.
• Consider chemical treatment, such as polymer, to increase the capacity of the
treatment system.
• Consider upgrades to thickener, such as plates or tubes, to augment settling.
• Avoid increasing pH beyond the threshold where significant formation of
Mg(OH)2 occurs (approximately 10.5).
6-35
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Chapter 7
FULL-SCALE IMPLEMENTATION
OF TREATABILITY STUDIES
-------
Table of Contents
Page
7.0 FULL-SCALE IMPLEMENTATION OF TREATABILITY STUDIES
7.1 Introduction 7-1
7.2 Scale-Up Issues for Treatability Test Results 7-2
7.2.1 Coagulation and Flocculation 7-2
7.2.2 Sedimentation 7-3
7.3 Unit Process Issues 7-4
7.3.1 Chemical Addition 7-4
7.3.2 Rapid Mixing and Flocculation 7-6
7.3.3 Sedimentation 7-7
7.3.4 Filtration 7-9
7.3.5 Sludge Handling 7-10
7.4 Other Full-Scale Implementation Issues 7-10
List of Tables
7-1 National Sanitation Foundation Product Limits on Chemical Additives 7-6
-------
7.0 FULL-SCALE IMPLEMENTATION
OF TREATABILITY STUDIES
7.1 INTRODUCTION
Previous chapters have described the contents of the DBPR, methods for removal of
NOM, the definitions of enhanced coagulation and enhanced precipitative softening, and
testing and laboratory protocols. This chapter provides guidance on how to use these
methods and protocols to enhance full-scale performance. This chapter provides guidance
on the incorporation of treatability studies (i.e., jar or pilot-scale testing) into full-scale
processes, and offers suggestions for unit process changes which may help meet the TOC
removal requirements. The success and ease of full-scale implementation of enhanced
coagulation and enhanced precipitative softening will depend on a utility's planning and
development of implementation strategies, as well as the incorporation of these strategies.
Results of treatability testing should be evaluated in the light of the secondary effects
of enhanced coagulation (discussed in Chapter 6) in order to adequately plan for process
modifications in the full-scale facilities. Based upon the extent of process modifications
required, some utilities may need to begin the planning process significantly ahead of the
effective date of the rule so that adequate capital improvement budgets are available to make
the necessary process changes. Planning for full-scale process modifications for compliance
with enhanced coagulation requirements may include modifications to: (1) chemical feed
systems (e.g., metal coagulant, polymeric coagulant, pH depressing chemicals, and pH
raising chemicals); (2) operation of unit processes (e.g., flocculation, sedimentation, and
filtration); and (3) operation of sludge handling systems. In the planning efforts, the issues
related to scaling up of bench- or pilot-scale process studies also need to be considered. This
chapter presents a discussion of potential modifications to various plant operations resulting
from enhanced coagulation, and offers suggestions for the development of full-scale
implementation strategies.
7-1
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7.2 SCALE-UP ISSUES FOR TREATABILITY TEST RESULTS
7.2.1 Coagulation and Flocculation
Coagulation/flocculation is a physical/chemical process that can usually be adequately
simulated through jar testing, and the effectiveness of a coagulant can often be determined
using jar tests (Amirtharajah and O'Melia, 1990). Coagulation/flocculation involves
chemical reactions and interparticle contacts that occur very rapidly, which allows rapid
mixing to be reasonably simulated at the bench (batch) scale. Short-circuiting does not occur
during jar testing. Thus, results from jar-test trials of flocculation may be superior to those
in plants where short-circuiting in the mixing and flocculating processes occurs. However,
flocculation at full-scale facilities typically uses external energy input through a variety of
mixing mechanisms (e.g., turbine, horizontal paddle) as well as a designated detention time.
Therefore, as long as the energy input and detention times are simulated accurately during
jar testing, full-scale performance of flocculation can be relatively well-simulated.
The carbon dioxide exchange between the water in the jars during bench-scale testing
and the ambient atmosphere could potentially be different compared to full-scale basins and
pipe lines (for static mixers). In a full-scale facility the amount of surface area exposed to
the atmosphere for a given volume of water may be significantly smaller than the exposed
area in a 1- or 2-liter jar. As a result, carbon dioxide can more readily transfer between the
water and the air during jar tests, resulting in more dramatic pH changes compared to the
full-scale process. Since the pH of coagulation is closely associated with the NOM removal
ability of metal coagulants, jar testing results may not always be reproducible at full-scale.
The jar test results may overestimate particle removal and underestimate TOC removal. If
the jar test pH values are also used to determine the amount of base necessary to raise the pH
before distribution, this amount may also be underestimated compared to the amount
necessary at full-scale. Covers on the jars will help reduce the exchange of carbon dioxide
during jar tests (see Section 3.2.2.1).
7-2
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7.2.2 Sedimentation
For many waters, there is a wide range of conditions in which floe adequately entraps
organic matter and turbidity, but finding the optimum condition for rapid settling of the floe
can be a difficult task (Hudson, 1981). Efficient settling is extremely important because it
minimizes the floe loading onto the filters. Shorter filter runs and a reduction in treatment
capacity can result from poor sedimentation. Settling velocity distribution curves are used
to analyze floe settling characteristics during jar testing by collecting samples at a given
depth over discrete time intervals. The settling velocities can be compared to full-scale
surface loading (overflow) rates on sedimentation basins. Therefore, when floe settling
characteristics are compared for different jar test conditions, the settling velocity distribution
curves should be translated to the surface loading rate of the sedimentation basin.
Care should be taken in proj ecting j ar test settling data to full-scale plant operation due
to the longer detention time at full-scale compared to jar tests. For a given settling velocity,
the detention time in the jar test procedure is about 1/60 of that in a conventional plant.
Residence time in full-scale plants is commonly on the order of several hours, although
shorter detention times may be found in plants using tube or tray settlers with short settling
times. Experience has shown that the settling obtained in plants with well-designed mixing
and flocculation facilities is usually superior to jar test results. This is likely caused by
continued flocculation in the settling basin due to differential settling velocities for different
size particles. Another factor is the continued rotation of the water in the jar testing
equipment after the flocculating paddles are stopped. The use of stators or square jars helps
reduce this rotation (see Section 3.2.2.1). Apparently, the effect of continued rotation after
the paddles have stopped approximates the typical effect of turbulence at the settling basin
inlet. For these reasons, j ar test results may underestimate the settling performance that may
be achieved at full-scale.
Given these considerations, the recommended period for settling during jar testing is
between 30 and 60 minutes. This duration has been shown to produce a clear supernatant
for floe that will settle adequately at full-scale.
7-3
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7.3 UNIT PROCESS ISSUES
7.3.1 Chemical Addition
Implementation of enhanced coagulation may require substantial alteration of
coagulant doses at some treatment plants. Some plants may also need to add new chemicals,
such as acid or caustic, to improve coagulation. Other plants may require only minor
adjustments to their chemical additives to comply with enhanced coagulation requirements.
For plants that may require significant changes, adequate planning should be done to assure
compliance with treatment requirements.
Based on the results of treatability testing, utilities should estimate changes in current
chemical doses as well as the potential need for additional chemicals such as: (1) acid to
depress pH for enhanced coagulation (in such instances, increased dosages of lime and
caustic also will be required to increase pH prior to distribution); or (2) increased dosages
of CO2 if lime dosages are increased in lime softening systems. The utility should develop
a plan for compliance based upon the treatability testing, the operator's experience, and the
condition and capacity of the existing facilities (chemical feed, chemical storage, and sludge
handling). Some important factors to consider in assessing the potential need for facility
modifications include:
• Adequacy of the storage (bulk-storage and day tanks) and feed facility (metering
pumps, electronic controls for metering pumps, etc.) for metal coagulants, polymeric
coagulants and filtration aids. Many States require utilities to have at least a 30-day,
on-site, bulk-storage capacity under average demand conditions. An increase in
chemical dosages, therefore, may require the utility to design and construct additional
storage and feed facilities.
• The need for an additional chemical to depress pH in enhanced coagulation to
achieve more effective TOC removal at lower pH values. Sulfuric acid is the most
commonly used chemical for lowering pH during coagulation. Softening plants use
carbon dioxide for pH depression during recarbonation, however, carbon dioxide is
also used in some plants for lowering coagulation pH. In selecting an appropriate
chemical to modify pH, relative costs, handling considerations, and operator safety
need to be considered. It should be noted that the addition of carbon dioxide is often
more expensive than sulfuric acid, but does not require handling of a listed hazardous
chemical.
7-4
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• If the pH of coagulation is too low (or in the case of lime softening, too high) for
distribution, the pH needs to be increased (or decreased for lime softening). In plants
practicing coagulation, lime is often added in the coagulation process to control
finished water pH. Unfortunately, this practice does not allow the utility to achieve
the full benefit of a lower coagulation pH. Consequently, increasing pH after
filtration could be a better alternative with respect to TOC removal and chlorine
disinfection. Sodium hydroxide is often recommended for raising pH after filtration.
If a plant is not already equipped with a caustic feed system, proper planning and
design need to be considered for this chemical if enhanced coagulation pH is lower
than the acceptable distribution system pH.
In addition to the above considerations, the following general factors need to be
considered for any new design or modification of chemical feed systems:
Chemicals should be added to ensure proper dispersion across the entire flow. In
most cases coagulant should be applied through perforated troughs or perforated pipe
diffuser systems in order to distribute it across the stream of water. A confined,
narrow path at the chemical injection point is recommended to improve chemical
distribution. The diffuser should be located at a point immediately upstream of the
zone of highest available turbulence. If a mixing device such as a turbine or pump
is used, the coagulant should be applied as close to the impeller as possible. This
method has been found to be more effective than a channel diffuser, which lacks
supplemental mechanical agitation.
• For effective flash mixing, dilution of the coagulant solution to a concentration of 2.5
to 5 percent is recommended (James M. Montgomery, 1985). Larger volumes are
more easily and quickly dispersed into a large body of raw water than smaller
volumes. At concentrations of less than 1 percent, however, alum may dissociate and
alum floe or scale [A1(OH)3] may form, clogging feed lines or orifices. For this
reason, alum or ferric salts generally should not be diluted below 2.5 percent prior
to addition to raw water.
• The proper sequence of chemical inj ection is important when more than one chemical
is added to the raw water. As discussed previously, it may be necessary to add a
coagulant aid to assist in forming a well-settling floe. The proper chemical sequence
is best determined by testing the raw water and chemical combination during jar
testing. For example, anionic polymers are usually most efficient when they are fed
to raw water after alum addition, once pin-point floes have been formed. If a cationic
polymer is used as a coagulant aid, the time of mixing becomes less important
because polymers react directly with NOM and particulate matter.
• Some lime softening plants add ferric sulfate or ferric chloride to the lime floe to
improve settling and TOC removal, in lieu of a polymer. The extent to which this is
successful depends on the nature of the source water and the lime softening dosage.
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Table 7-1 lists some product limits for the addition of chemicals commonly used in
coagulation and flocculation systems. These limits are based on National Sanitation
Foundation (NSF) standards (ANSI/NSF Standard 60), and are product-specific, depending,
in part, on the impurities present in the chemical products.
TABLE 7-1
National Science Foundation
Product Limits on Chemical Additives
Chemical Additive
Alum
Ferric Sulfate
Ferric Chloride
Sulfuric Acid
Polyaluminum chloride (PAC1)
Maximum Use a
150mg/L
200 - 600 mg/L
141 -250 mg/L
50 mg/L
100 -454 mg/L
Note: a- The limits shown here are for general guidance only. Each product (i.e., brand or trademark)
has limits specific to that product, depending on the chemical nature of the additive and
impurities present. The numbers in this column represent a range of the limits recommended
for several brands of additives.
7.3.2 Rapid Mixing and Flocculation
Changes in chemical feed systems as a result of the implementation of enhanced
coagulation are not expected to alter the rapid mixing and flocculation processes in a water
treatment plant. Potentially greater quantities of floe could form if significantly larger doses
of coagulant chemicals are used for compliance with the enhanced coagulation requirements.
For this reason, care should be taken to ensure adequate agitation during the flocculation
stage so that floe does not settle out in this process. Settling of floe in the flocculation stage
may result in loss of effective volumes since flocculation basins are often not equipped with
any sludge removal mechanisms.
Significantly altering chemical addition schemes for compliance with enhanced
coagulation may require some changes in the mixing conditions to properly develop
settleable and filterable floe. Utilities are encouraged to conduct bench- or pilot-scale
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evaluations to determine the optimum mixing conditions under the altered chemical addition
schemes for enhanced coagulation. The following general design issues need to be
considered during the development of enhanced coagulation implementation strategies:
• The purpose of rapid mixing is to obtain instantaneous, uniform dispersion of the
coagulant through the raw water, since the most efficient use of the coagulant is
achieved with instantaneous dispersion. Rapid chemical dispersion is generally
obtained by some type of diffuser in combination with hydraulic turbulence.
Conventional rapid-mixing chambers, which have a 10 to 30 second retention time
and use 0.25 to 1.0 hp/mgd of mechanical mixing, have velocity gradients in the range
of 3 00 to 1000 sec'1.
• The aggregation of optimum-size floes (0.1 to 2.0 mm effective size) requires gentle
mixing in the energy gradient range of 20 to 70 s"1 for a period of approximately 20
minutes (Hudson, 1981). For settling, a larger visible floe is normally required, and
lower energy levels are applied. Smaller, more dense floe is formed at the high end
of the energy range.
• The gentle mixing process of flocculation is designed to maximize contact of
destabilized particles and build settleable or filterable floe particles. Shear forces
should be maintained constant within the mixing process. Flocculator mechanisms
tend to be slow and tend to cover the maximum possible cross-sectional area of the
flocculation basins.
• Dividing the process into two or more defined stages or compartments will help
prevent short-circuiting and permit defined zones of reduced energy input. To ensure
that short-circuiting does not occur, baffles are typically placed between each stage of
flocculation. For mechanical (non-hydraulic) flocculation basins, the baffles are
designed to provide an orifice ratio of approximately 3 to 6 percent or a velocity of 0.3
m/s (0.9 fps) under maximum flow conditions.
7.3.3 Sedimentation
Higher coagulant and lime dosages result in greater quantities of settleable particles
that will be separated during the sedimentation process. For this reason, the sludge removal
mechanisms may need to be operated on a more frequent basis. This may, in turn, increase
the short-circuiting induced by the movement of the sludge removal device. As discussed
in Section 7.3.2, utilities need to consider bench- and pilot-scale testing to ensure that the
particles produced during enhanced coagulation can settle properly in the sedimentation
process. In developing strategies for implementing enhanced coagulation or enhanced
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precipitative softening, utilities need to consider the settling characteristics of the floe.
Although it is unlikely that the utilities will need to substantially modify the design or
operation of their sedimentation basins, some utilities may need to consider minor
modifications to improve solids removal by settling. The following factors should be
considered in deciding on sedimentation process improvement:
• Control measures to aid sedimentation and to minimize or eliminate short-circuiting
caused by density currents include: (1) use of a surface weir or launder takeoff over
a large part of the settling basin, (2) improved inlet arrangements, and (3) schemes to
provide increased basin drag and friction (Hudson, 1981).
• Various baffling methods could be considered for improving the turbulence at the
entrance to the sedimentation basins. One of the most successful methods is the
perforated baffle (Hudson, 1981). Proper design of perforated baffles requires four
conditions to be met:
1. The head loss through the ports should be about four times higher than the kinetic
energy of approaching velocities to equalize both horizontal and vertical flow
distribution.
2. To avoid break-up of floe, the velocity gradient through inlet conduits and ports
should be kept close to that in the last compartment of the flocculators.
3. The maximum feasible number of ports should be provided to minimize the length
of the turbulent entry zone produced by the diffusion of the submerged jets from
the ports in the perforated-baffle inlet.
4. The port configuration should assure that the discharge jets will direct the flow
toward the basin outlet.
• Discharge weirs can be extended into the basin up to half of the basin length. This
reduces the localized upflow velocity and discourages re-entrainment of settled floe.
Perforated launders can also be used to minimize passage of floatable material (that
sometimes can accumulate as the result of polymer addition or with metal coagulants)
and further reduce local, upflow velocities.
• The performance of existing basins may be substantially improved by adding tube or
plate settlers. These units use inclined tubes or plates to increase the overall removal
surface area and decrease the distance a particle must settle before it is captured. For
efficient self-cleaning, tube or plate settlers are typically installed at a 45° to 60° angle
above horizontal. The open distance between the plates (or the diameter of the tube)
is typically about 2 inches (5 cm), although there are a variety of configurations
marketed by several manufacturers (Hudson, 1981).
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7.3.4 Filtration
If the implementation of a modified chemical treatment strategy affects the settled water
quality in a treatment plant, the performance of the filters can also be affected. This may
manifest itself by early particle or turbidity breakthrough in the filters, which may ultimately
result in shorter filter runs. Utilities may need to evaluate alternatives to improve filter
performance or to plan for shorter filter runs. One impact of shorter filter runs is an increase
in the amount of filter backwash water. If a utility recycles filter backwash water, an increase
in the volume of filter backwash water may stress the unit processes (such as equalization
basin, backwash water treatment processes, etc.) that treat the recycle stream. Adequate
planning for implementation of enhanced coagulation and enhanced precipitative softening
should include an assessment of the volume of filter backwash and its subsequent
downstream impacts. Utilities which expect to have large increases in chemical doses should
consider pilot-scale evaluations to estimate the quality of settled water and the performance
of filters. The following chemical improvements to the operation of filters may be
considered as a part of the planning for enhanced coagulation and enhanced precipitative
softening:
• Careful selection of a coagulant aid and filter aid is critical to improve settling in the
sedimentation basin and minimize particle breakthrough in the filters. The use of a
filter-aid polymer can result in improved particle capture, better filtrate quality, longer
filter runs, and higher headloss prior to turbidity breakthrough. Filter aids are often
fed in dilute liquid form to allow dispersion without mechanical agitation just prior
to filtration. Filter-aid polymer dosages to gravity filters are usually low (0.03 to 0.05
mg/L). Doses required for pressure filters may be higher if a higher operating
headloss is employed. Because the viscosity of water increases with decreasing
temperature, breakthrough as a result of floe shearing is more likely at lower water
temperatures. Consequently, increased polymer doses may be required in cold
weather. A longer contact time prior to filtration may also be necessary in cold
weather.
• The type of polymer to be added also needs careful consideration. Polymers used as
filter aids are generally categorized into cationic, anionic, and nonionic groups. The
most appropriate choice will be site-specific, and typically will be verified through
trial and error. Many plants, however, have had greater success with nonionic and
anionic polymer filter aids. Cationic polymers have shown superior performance as
coagulant aids rather than as filter aids. The molecular weight of the polymer must
also be considered. Many plants have had greater success with higher molecular
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weight compounds, but individual applications will be very dependent on site-specific
conditions.
• Two methods are typically used to determine the optimum dose for filter aids. To
determine the optimum dose for particle destabilization, jar tests with extended
flocculation periods may be used, especially for the destabilization of low-turbidity
waters. Another obvious method to determine optimum dose consists simply of
systematically varying the dosage over a filter run and monitoring the effluent water
quality and filter performance. Both these techniques have been found to produce
similar results (AWWARF, 1989).
7.3.5 Sludge Handling
Increasing coagulant and lime dosages for enhanced coagulation and enhanced
precipitative softening, respectively, will have an impact on sludge production. Depending
upon the extent of the dosage increases and the nature of the sludge handling system, the
impacts of increased sludge production can be significant. If dosages are modified
significantly, it is critical that systems evaluate the capacity of their sludge handling systems
and consider whether upgrades and expansions are required. In some instances, the method
of sludge handling may change. For example, if a system has been discharging to the sewer,
but the capacity of the piping and/or the allowable discharge to the wastewater system is
limited, it may be necessary to provide some sludge handling on-site. These types of changes
are particularly significant and represent costs which are not directly related to the chemical
feed facilities. These impacts are discussed in detail in Section 6.7.
7.4 OTHER FULL-SCALE IMPLEMENTATION ISSUES
Some secondary effects can be anticipated with the implementation of enhanced
coagulation, such as increased corrosion (due to pH reductions), increased sludge production,
decreased sludge dewaterability and settleability, and increases in inorganic contaminants
(i.e., Al, Mn, Fe). Other concerns also arise upon implementation of enhanced coagulation,
such as the potential degradation of a plant's ability to produce a safe and aesthetically
acceptable water; customer perception of the new water quality; and the long-term
distribution system integrity. Treatment techniques and changes in operation may be
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required to resolve these problems. The underlying issue revolving around these concerns
is ultimately an increase in operational costs. Utilities need to address these concerns before
implementing enhanced coagulation to avoid future problems. Chapter 6 provides an outline
of the important secondary effects of enhanced coagulation, and includes some guidance to
resolve these foreseeable problems.
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Appendix A
DBF PRECURSOR REMOVAL PROCESSES
-------
Table of Contents
Page
A.O DBF PRECURSOR REMOVAL PROCESSES
A.I Introduction A-l
A.2 Surrogate Parameters for NOM (DBF Precursor) Removal A-2
A.2.1 Introduction A-2
A.2.2 Total and Dissolved Organic Carbon A-3
A.2.3 Ultraviolet Light Absorbance at 254 nm A-4
A.2.4 Specific Ultraviolet Absorption (SUVA) A-4
A.2.5 Trihalomethane Formation Potential A-5
A.2.5.1 THMFP Test A-5
A.2.5.2 Simulated Distribution System Test A-6
A.2.5.3 Uniform Formation Conditions Test A-6
A.2.6 Summary A-7
A.3 Characteristics of Natural Organic Matter A-7
A.3.1 Humic/Non-Humic Fractionation A-7
A.3.2 Molecular Weight Fractionation A-8
A.4 Treatment Technologies for DBF Precursor Removal A-9
A.4.1 Chemical Coagulation A-9
A.4.2 Precipitative Softening A-12
A.4.3 Preoxidation A-14
A.4.3.1 Chlorine A-14
A.4.3.2 Chloramines A-17
A.4.3.3 Ozone A-18
A.4.3.4 Chlorine Dioxide A-19
A.4.3.5 Potassium Permanganate A-20
A.4.3.6 Advanced Oxidation Processes A-21
A.4.4 Separation Processes A-21
A.4.4.1 Sedimentation A-21
A.4.4.2 Dissolved Air Flotation A-22
A.4.4.3 Filtration A-22
A.5 Other Precursor Removal Technologies A-23
A.6 Summary A-23
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List of Tables
A-l Impact of Moving Point of Chlorination on DBF Formation A-17
A-2 Use of Chlorine Dioxide for THMFP and TOXFP Removal A-19
List of Figures
A-l Process Flow Schematic for a Conventional Water Treatment Plant A-10
A-2 Process Flow Schematic for a Lime Softening Water Treatment Plant A-13
A-3 Typical Ozone Oxidation Process A-l5
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APPENDIX A
DBP PRECURSOR REMOVAL PROCESSES
A.1 INTRODUCTION
Natural organic matter (NOM) is ubiquitous in surface and ground water sources.
NOM consists of humic substances, amino acids, sugars, aliphatic acids, aromatic acids and
a large number of other organic molecules. Although interest in NOM research and removal
has primarily revolved around the reactions between NOM and chemical disinfectants, a water
system should consider enhancing existing treatment practices for removal of NOM for
several other reasons. NOM has been shown to bind with harmful metals and synthetic
organic chemicals (SOCs), thereby allowing these contaminants to proceed through treatment
processes not designed to remove NOM. In addition, NOM creates a disinfectant demand
and forces utilities to use higher disinfectant dosages to maintain an adequate residual in water
distribution systems. Some NOM components may also provide food for microorganisms in
these distribution systems. NOM also competes with other organic compounds which are
amenable to adsorption by powdered activated carbon (PAC) or granulated activated carbon
(GAC).
This appendix focuses on treatment technologies that have been evaluated for their
ability to remove NOM, and how coagulation and precipitative softening compare to other
NOM (DBP precursor) removal processes. However, the characteristics and measures of
NOM have important implications with regards to the performance and evaluation of these
processes. Sections A.2 and A.3 summarize these characteristics and measures; Section A.4
describes treatment technologies for DBP precursor removal.
A-l
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A.2 SURROGATE PARAMETERS FOR NOM (DBF PRECURSOR) REMOVAL
A.2.1 Introduction
Because NOM characteristics are widely varied chemically and physically, no single
analytical technique is available to characterize NOM. As a result, surrogate parameters such
as organic carbon content must be used to describe generalized NOM characteristics. The
use of surrogate parameters for monitoring plant performance and measuring water quality
is not new to the water industry. Turbidity, for example, is widely used for controlling and
monitoring the operation of treatment plants for the removal of particulate matter. Other
surrogates currently used are color (as a measure of NOM) and coliform bacteria (as a
measure of pathogen presence).
An ideal surrogate parameter should possess the following qualities:
• Can be measured rapidly
• Does not require sophisticated equipment or special training
• Permits accurate estimation of target parameter
Commonly used surrogate measures of DBF precursor concentration include:
• Total and dissolved organic carbon (TOC and DOC)
• Ultraviolet (UV) absorbance at a wavelength of 254 nm (UV-254)
• Specific ultraviolet absorption (SUVA)
• Trihalomethane formation potential (THMFP)
These surrogates may be used to screen raw water sources for DBF precursor content
and to determine the performance of unit treatment processes for removal of DBF precursors.
The following sections briefly summarize these NOM characteristics that the above surrogates
measure, and some of the limitations associated with each. An excellent review of the status
of many surrogate parameters was published in 1988 by a joint effort of AWWARF and the
Keuringsinstituut voor Waterleidingartikelen (AWWARF and KIWA, 1988). In addition,
AWWARF-sponsored projects studied the characteristics of NOM and its relationship to
treatability (Owen et al., 1993; Krasner et al., 1996). The reader is referred to these reports
for an in-depth discussion of the analytical methods and application of surrogate measures for
NOM.
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A.2.2 Total and Dissolved Organic Carbon
Several methods are available for measuring the TOC of a water sample; proper use
of these methods can be assumed to produce directly comparable results. Most of the TOC
results reported in the drinking water literature may be assumed as representative of the
dissolved organic carbon in the water being tested. Typically, particulate organic carbon is
only a minor fraction of TOC, however, some river systems, especially during runoff events,
have a significant amount of particulate organic carbon.
Although TOC is a direct measure of a water's organic carbon content, it is not
necessarily a consistent measure of DBF precursor concentrations. One explanation for this
observation is that TOC does not provide an indication of the aromaticity, aliphatic nature,
functional group chemistry, or chemical bonding associated with natural organic molecules.
The reactivity of chemical bonds and functional groups is likely to be a significant factor in
explaining why different waters with the same TOC concentration will form different DBF
concentrations under identical disinfection conditions and bromide levels.
DOC is also a commonly used surrogate measure of DBF precursor concentrations.
DOC is operationally defined as that portion of TOC which passes through a 0.45 jim
membrane filter. Therefore, DOC measures the amount of organic carbon dissolved in a
given water. Dissolved phase organics may be more reactive than particulate phase organics.
Thus, the ratio of DOC to TOC may also be considered an important factor in explaining why
different waters having the same TOC concentration will form different DBF concentrations
under identical disinfection conditions and bromide levels.
If the DOC/TOC ratio is relatively low (i.e., a large amount of organic material is in
particulate form), physical processes such as sedimentation and filtration can be expected to
remove a significant fraction of the NOM. On the other hand, relatively high DOC/TOC
ratios indicate that much of the NOM is in soluble form. Therefore, other processes such as
coagulation, GAC adsorption, and membrane filtration are required to achieve significant
removal.
A-3
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A.2.3 Ultraviolet Light Absorbance at 254 nm
One of the most commonly used surrogates in drinking water research has been the
measurement of a water's ability to absorb ultraviolet light at a wavelength of 254 nm (UV-
254) (Edzwald et al., 1985). UV-254 absorbance indicates the concentration of organic
molecules with aromatic groupings or extended conjugation. Interstudy comparisons of unit
process performance for UV-254 reduction may be limited to some extent because UV-254
results are dependent on the pH and turbidity of the water being tested. Recent reports
suggest that a standard pH should be used for UV-254 measurements and that prewashed
0.45 jim membrane filters be used to remove paniculate matter prior to UV-254 analysis
(Owenetal., 1993).
Other limitations may also affect the use of UV-254 as an indicator of unit process
performance for DBF precursor removal. These limitations primarily result from interference
by inorganic species that also absorb ultraviolet light at wavelengths near 254 nm. For
instance, monochloramine and dissolved ozone absorb ultraviolet light at wavelengths of 243
nm and 260 nm, respectively. Evaluations of unit process performance for reduction of UV-
254 should recognize these potential interferences.
A.2.4 Specific Ultraviolet Absorption (SUVA)
SUVA has proven to be a good indicator of the humic content of a water (Edzwald
and Van Benschoten, 1990). SUVA is defined as UV-254 (measured in m"1) divided by the
DOC concentration (in mg/L), resulting in SUVA units of L/mg-m. SUVA values of less than
about 3 L/mg-m signify a water containing mostly nonhumic material. SUVA values of 4 to
5 L/mg-m are typical of waters containing primarily humic material (Edzwald and Van
Benschoten, 1990).
SUVA can also be predictive of the removal capability of water treatment practices
(Edzwald et al., 1985). Several studies (Krasner et al., 1994; Cheng et al., 1995; White et al.,
1997; Chowdhury et al., 1997) reported that waters with a high SUVA value exhibited large
reductions in SUVA and TOC as a result of enhanced coagulation, indicating an overall
substantial removal of NOM. Waters with low SUVA values, however, exhibited relatively
low reductions in SUVA and TOC, indicating an overall insignificant removal of NOM.
A-4
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A.2.5 Trihalomethane Formation Potential
DBF formation can be evaluated at the bench scale using either trihalomethane
formation potential (THMFP) methods (Stevens and Symons, 1977; Symons et al., 1993),
simulated distribution system (SDS) testing (Koch et al., 1991), and/or uniform formation
condition (UFC) tests (Summers et al., 1996). Each test method has been optimized to yield
specific information because the water quality parameters used in each procedure highly
influence the yield and speciation of DBF formation. Brief descriptions of each of these
testing protocols are included here.
The value of these tests is that they can provide an indirect measure of THM
precursor removal across a unit treatment process. The removal of TOC may be quite
different from the removal of THMFP, which may indicate that THM precursor molecules are
preferentially removed over other natural organic molecules, or vice versa. This type of
information can be critical when evaluating unit process performance, and, despite their
limitations, the THM precursor tests should be included as an integral part of evaluating
treatment processes.
The formation potential concept is not limited to the study of THM precursors. The
concept has been extended by several researchers to other DBFs including the HAAs and the
haloacetonitriles (HANs) (McGuire et al., 1989; Stevens et al., 1989; Reckhow and Singer,
1984). Total organic halide formation potential (TOXFP) has also been evaluated (Singer and
Chang, 1988), however, the majority of the research to date has evaluated THMFP.
A.2.5.1 THMFP Test
The THMFP test determines the potential of NOM to form THMs under relatively
extreme chlorination conditions. The test is done by measuring the concentration of THMs
at the time of sampling (Inst-THM) and the concentration of THMs after the collected sample
has been subjected to chlorination (Term-THM). THMFP is defined as the difference
between Term-THM and Inst-THM. If the sample has not been chlorinated, Inst-THM
should be zero or close to zero. If chlorine is present at the time of sampling, the difference
between Term-THM and Inst-THM becomes THMFP.
A-5
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The recommended (Standard Methods, 1995) chlorination conditions for THMFP
tests include an incubation time of seven days with a free chlorine residual of 3 to 5 mg/L at
the end of the incubation period. The recommended incubation temperature is 25 ± 2°C and
the recommended pH is 7.0 ± 0.2 (with phosphate buffer).
Researchers have measured THMFP by using a wide range of pH conditions, chlorine
dosages, and contact times. Therefore, when summarizing research work, it is necessary to
report the conditions under which THMFP was measured. Unfortunately, direct quantitative
interstudy comparisons of THMFP removal across unit processes cannot be performed if
different test conditions were used to determine THMFP.
A.2.5.2 Simulated Distribution System Test
The SDS test is an alternative THM formation test using test conditions (e.g., chlorine
dosages, pH, incubation time, temperature) selected to be representative of actual conditions
in the distribution system (Koch et al., 1991; De Marco et al., 1983; Standard Methods,
1995). While SDS tests may provide more accurate indications of actual distribution system
THM levels, SDS test results must also be reported with their accompanying test conditions.
A.2.5.3 Uniform Formation Conditions Test
The THMFP test described in A.2.5.1 portrays THM formation under extreme
conditions. As a result of these extreme chlorination conditions, the distribution of THMs
between the chlorinated and brominated species becomes skewed and often does not
represent actual conditions in operating systems (Symons et al., 1993). The SDS test does
not have the limitation of the THMFP test, since more realistic chlorination conditions are
used. SDS tests from one utility, however, cannot be compared with SDS tests from another
utility because of differing chlorination conditions. A set of uniform formation conditions was
proposed to overcome these limitations.
Because SDS conditions are site-specific, Summers and colleagues (1996) developed
the UFC test to enable direct comparisons of DBF formation in different waters using
conditions representative of many U.S. distribution systems. UFC tests are conducted at a
pH of 8.0 ±0.2, a temperature of 20.0 ±1.0°C, and an incubation time of 24 ±1 hr, with a
A-6
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chlorine residual after 24 hr of 1.0 ±0.4 mg/L (Summers et al., 1996). The storage time was
selected, in part, because the average mean detention time in the distribution systems
surveyed in the AWWA Water Industry Database (WIDE) was 1.3 days. The pH value was
chosen to reflect the influence of the Lead and Copper Rule on distribution-system pH. The
temperature chosen reflected the average temperature used in SDS testing according to a
survey conducted by Summers and colleagues (1996). The chlorine residual goal was based,
in part, on the average mean chlorine residual (i.e., 0.9 mg/L) in the distribution systems in
the WIDE.
These conditions were developed by conducting a survey of 318 utilities across the
nation. This protocol allows DBF formation to be analyzed under representative formation
conditions, and to directly compare DBF formation between waters under similar conditions.
This test can also be used to analyze how treatment conditions affect DBF formation. The
test can be used to assess how seasonal variability in water quality can affect DBF formation.
A.2.6 Summary
Surrogate parameters must be used to describe NOM because no single analytical
technique is capable of measuring the widely varied characteristics of NOM. Commonly used
NOM surrogates include TOC and DOC, UV-254, SUVA, and THMFP. Each parameter
has advantages and disadvantages as discussed above. TOC is used here to quantitatively
compare the results of different studies to determine relationships between operational
practice and process performance. However, THMFP removals are also presented to
highlight any differences between TOC removal and THMFP removal.
A.3 CHARACTERISTICS OF NATURAL ORGANIC MATTER
A.3.1 Humic/Non-humic Fractionation
NOM characteristics vary considerably and have important implications for drinking
water treatment processes. Of those constituents which comprise NOM, humic substances
have arguably received the largest amount of research. Humic substances comprise about 50
percent of the DOC in surface waters, but this percentage can vary considerably and may be
A-7
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as high as 80 percent in some colored surface waters (MacCarthy and Suffet, 1989). These
substances are formed by the biodegradation of plant and animal tissue in both soil and
aquatic environments, and may be fractionated into humic acids and fulvic acids. Humic
substances vary widely in chemical and physical characteristics but can generally be classified
as large polyelectrolytic macromolecules. The chemical composition of humic substances
ranges, by weight, from 40 to 60 percent carbon, 30 to 50 percent oxygen, 3 to 6 percent
hydrogen, and 1 to 4 percent nitrogen (MacCarthy and Suffet, 1989; Steinberg and Muenster,
1985). In addition, the major functional groups on these polyelectrolytes are carboxyl,
phenolic hydroxyl, and alcoholic hydroxyl compounds. Typical average molecular weights
for aquatic humic substances vary between 800 and 3,000 daltons, while average molecular
weights can be greater than 100,000 daltons for soil humic acids (MacCarthy and Suffet,
1989).
A.3.2 Molecular Weight Fractionation
NOM can be further classified into molecular weight (MW) fractions or size ranges.
Although the molecular weight of NOM is a specifically defined value, in practice, the term
carries the connotation simply of relative size. Although it is important to categorize NOM
into certain size ranges, the usefulness of the measurement is found in the relative comparison
of higher versus lower MW material.
NOM removal during coagulation is not consistent for all molecular weight ranges.
Owen et al. (1993) found that coagulation has a preferential removal of higher MW
compounds over lower MW compounds. Hence enhanced coagulation preferentially removes
humic substances. They found that the majority of DOC removal was a result of reductions
in larger and medium size range NOM (>1K). Furthermore, they documented NOM increases
in the smallest MW range (<0.5 K) upon ozonation. This indicates a breakdown of some
higher MW NOM compounds during ozonation.
An experimental protocol was developed to provide a simple characterization of the
NOM of raw and corresponding coagulated waters (Krasner et al., 1994). As part of this
protocol, a 1000-dalton (IK) ultrafilter was used to determine what fraction of the bulk or
coagulated water was of a lower versus higher molecular weight. Typically, as the dosage
A-8
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of coagulant (alum or ferric chloride) was increased, the removal of bulk TOC concentration
generally paralleled the reduction in the humic and >1K fractions of the TOC concentration,
indicating preferential removal of these fractions. In most waters, the residual TOC
remaining after enhanced coagulation was primarily made up of low-MW and non-humic
material. The latter NOM fractions represent the part of the bulk TOC that is resistant to
removal by coagulation. When selected waters were ozonated (at ozone-to-TOC ratios
of 1:1 and 2:1 mg/mg), the bulk TOC was only slightly reduced (oxidatively mineralized);
however, high-MW and humic NOM were transformed to low-MW and non-humic NOM,
respectively (Krasner et al., 1994). As a result of preozonation, the coagulation efficiency
was reduced because a higher percentage of the NOM was less amenable to coagulation.
A.4 TREATMENT TECHNOLOGIES FOR DBF PRECURSOR REMOVAL
A.4.1 Chemical Coagulation
Coagulation/filtration is a treatment process by which the physical or chemical
properties of colloidal or suspended particles are altered such that agglomeration is enhanced
to an extent that these solids will settle out of solution by gravity or will be removed by
filtration. Coagulants change surface charge properties of solids to promote agglomeration
and/or enmeshment of smaller particles into larger floes (Amirtharajah and O'Melia, 1990).
These larger agglomerates are removed by sedimentation and/or filtration.
The coagulation/filtration process has traditionally been used to remove turbidity from
drinking water supplies. However, the process is not restricted to the removal of particles
(Amirtharajah and O'Melia, 1990). Coagulants render some dissolved species (e.g., NOM,
inorganics, and hydrophobic SOCs) insoluble, and the metal hydroxide particles produced by
the addition of metal salt coagulants can adsorb other dissolved species. Humic substances
react with most coagulants (Amirtharajah and O'Melia, 1990). Major components of a basic
coagulation/ filtration facility, as shown in Figure A-l, include chemical feed systems; mixing
equipment; basins for rapid mix, flocculation, settling, and filtration; filter media; sludge
handling equipment; and filter backwash facilities. The process schematic shown in Figure
A-l is typical of conventional coagulation/filtration facilities.
A-9
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Figure A-l
PROCESS FLOW SCHEMATIC FOR A
CONVENTIONAL WATER TREATMENT PLANT
RAW
WATER
FLOC
BASIN
PRESED
BASIN
Cl,
SED
BASIN
Cl,
Alum
,f / /////// \
RAPID
MIX
Caustic (or Lime)
Cl,
Ammonium
FILTERS
t I
TO
DISTRIBUTION
STORAGE
O
c
A-10
-------
Systems with low-turbidity waters pass flocculated water directly on to the filters.
These type of facilities are commonly called direct filtration facilities. Direct and in-line
filtration plants are not required to practice enhanced coagulation because they do not have
a sedimentation basin to facilitate NOM removal, and the higher coagulant doses associated
with enhanced coagulation may significantly shorten filter run times.
Coagulants are selected based upon their ability to destabilize particles and create a
floe that can be removed by subsequent physical processes. Aluminum and iron salts are
typically used as primary coagulants because they are trivalent and form insoluble hydrolyzed
species that destabilize negatively-charged material in natural waters that keep particles in
suspension. Both charged and uncharged polymers are also used as coagulant aids for
destabilization and particle bridging to improve the development and subsequent removal of
floe. Polymerized forms of aluminum, such as polyaluminum chloride (PAC1), also can be
used as a primary coagulant in low turbidity waters, and can be as effective as alum or iron
salts for NOM removal in some instances.
In granular media filtration, solids removal occurs primarily as a two-step process.
During the initial step, particles are transported to the surfaces of media grains or previously
captured floe. Transport is believed to be largely a result of hydrodynamic forces, with
contact occurring as streamlines converge in pore restrictions. The second step is attachment
of the particles to either grain or floe surfaces. Electrokinetic and molecular forces are
responsible for the adherence of the particles on the surfaces within the bed. Physical
straining is generally a minor means of solids removal in granular media filters.
In traditional water treatment practice, biological activity within a filter is discouraged
through the addition of a disinfectant (e.g., chlorine) prior to filtration. However, in many
systems in Europe, particularly those using ozone as a preoxidant, biological activity is
encouraged in filtration to remove biodegradable organic matter and make the plant effluent
water biologically stable. In systems which want to reduce DBF formation by moving the
point of chlorination further into the treatment train, biological activity in filtration can
provide some steady-state removal of NOM. The extent of removal is dependent upon the
concentration of biodegradable organic material in the filter influent.
A-ll
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A.4.2 Precipitative Softening
Precipitative softening processes are employed to remove hardness from raw drinking
water sources. In most waters, hardness is primarily due to the presence of calcium and
magnesium. The American Water Works Association (AWWA) recommends that finished
water hardness levels not exceed 80 mg/L as calcium carbonate (CaCO3). The precipitative
softening process removes hardness by producing a shift in carbonate equilibrium conditions.
This shift is attained by raising pH to convert bicarbonate ions to carbonate ions and to
minimize the solubility of calcium carbonate. Lime (calcium hydroxide) or caustic (sodium
hydroxide) is commonly added to achieve the pH increase. Soda ash (sodium carbonate) is
added if insufficient carbonate is present to precipitate calcium to the desired level. Softening
for calcium removal is usually operated in a pH range between 9.5 and 10.5.
For magnesium removal, excess lime is added beyond the point of calcium carbonate
precipitation in order to precipitate magnesium hydroxide. Magnesium removal is usually
achieved in sufficient quantities if the pH is greater than 10.5.
pH adjustment is required if the softened water pH is too high for potable use or if the
finished water remains supersaturated with respect to calcium. The most common form of
pH adjustment in softening plants is recarbonation with carbon dioxide.
Lime, caustic and/or soda ash dosages are dependent on several raw water quality
parameters including hardness, alkalinity, pH, temperature, and total dissolved solids. A
typical softening plant is illustrated schematically in Figure A-2. Major components of this
process include:
• Lime or caustic feed system
Coagulant and/or polymer feed system
• Soda ash feed system (optional)
• Upflow solids clarification or conventional sedimentation
• Carbon dioxide feed system (optional)
• Recarbonation basin (optional)
• Filtration.
A more detailed discussion of TOC removal by precipitative softening is found in
Appendix B.
A-12
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Figure A-2
PROCESS FLOW SCHEMATIC FOR A
LIME SOFTENING WATER TREATMENT PLANT
Caustic (or Lime)
CI2
Ammonium
RECARBONATION
BASIN
(Optional)
FILTERS
TO
DISTRIBUTION
STORAGE
O
A-13
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A.4.3 Preoxidation
NOM molecules that are precursors to a given DBF can be partially oxidized to
molecules that are not precursors to that DBF, or NOM molecules that are not precursors
to a given DBF can be oxidized to molecules that are precursor to that DBF. Therefore,
some DBF precursors are partially destroyed by oxidation while others are created. If the
destruction of organic precursors for a given DBF exceeds the creation of new organic
precursors for that DBF, then oxidation may be considered a precursor removal process for
that DBF. However, oxidation cannot be considered a precursor removal process in those
cases when the opposite is true. A typical oxidation process utilizing ozone is illustrated in
Figure A-3. A significant amount of research has been done on the impact of oxidation on
the precursors of non-THM DBFs. The direct action of the ozone molecule and the addition
and substitution reactions of chlorine both proceed, in part, through electrophilic attack by
these oxidizing agents on precursor sites having strong densities of electronic charge (e.g.,
on aromatic rings) (Dore et al., 1988). Thus, preozonation can degrade some of the
molecular sites reactive to chlorine. Reckhow and Singer (1984) found that preozonation
destroyed a certain percentage of the precursors for THMs, total organic halides (TOX),
trichloroacetic acid (TCAA), and dichloroacetonitrile (DCAN). However, ozonation
resulted in no net effect on the precursors of dichloroacetic acid (DCAA), and an increase
in the precursors for 1,1,1 -trichloroacetone. Increases in precursor levels may be caused by
the transitory formation of polyhydroxylated aromatic compounds or by the accumulation
of methylketone functions that are only slightly reactive with ozone (Dore et al., 1988).
A.4.3.1 Chlorine
Chlorine is widely used throughout the United States for oxidation/disinfection
purposes. Chlorine may be derived from a number of sources, including dry chemical feed,
liquified gas, or gaseous systems. A utility may also generate chlorine on-site.
Prechlorination is often used to minimize operational problems associated with biological
growth on filters, pipes or tanks. Although there are concerns over DBF formation,
prechlorination is still practiced by many utilities. A survey of 329 large surface-water
A-14
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Figure A-3
TYPICAL OZON
i
OZONE OFF-GAS
E OXIDATION PROCESS
1 ( 'VV S S -| VENT^
Xs.>< ( Y
' /\ 'xx
n7"NF FXHAH^T
\v_^^^/ DESTRUCT BLOWER
DEMISTER
t t t t
WATER
•'•.'. •'•.'. OZONATED
WATER
"J* *t~ f* "T
T T T _*
I I 1 I
t
OZONE | f^ ^
AIR / r1 v V v'V "1 1 ;
• — i ^ j y x y^ ^>t v y
V J WATER/ ^ /
> ^
k — . —
AIR AFTERCOOLER REFRIGERANT DEsTcCANT AIR FILTER u c IM c nn I u n
COMPRESSOR (OPTIONAL) DRYER DRYER
A-15
-------
treatment plants indicated that 80 percent of these plants use predisinfection for one or more
reasons (Fed. Reg., Nov. 3, 1997, p. 59450). Prechlorination may also impact NOM
removal. Bench-scale studies conducted by Johnson and Randtke (1983) indicate that
prechlorination will reduce the amount of NOM removal achieved with coagulation.
However, Summers and colleagues (1996) found similar removals of TOC during enhanced
coagulation with or without prechlorination.
Recently, prechlorination has come under scrutiny due to its potential to increase DBF
levels during enhanced coagulation. However, many plants rely on prechlorination to help
solve operational problems, including taste and odor control, turbidity control, algae growth
control, inorganic oxidation, and microbial inactivation (see the Alternative Disinfectants and
Oxidants Guidance Manual, released in the Spring of 1999, for further information). The
1994 DBPR proposal did not plan to allow disinfection credit prior to enhanced coagulation.
Recent research (Summers et al., 1997) and the analyses performed by the Technologies
Working Group, however, demonstrated that disinfection prior to enhanced coagulation is
a viable practice. Therefore, the final DBPR allows disinfection credit prior to enhanced
coagulation.
A study performed by Summers et al. (1997) examined the effects of enhanced
coagulation and the predisinfection application point on DBF levels. They found that
enhanced coagulation, even with predisinfection, reduces DBF levels by up to 20 percent as
long as the point of predisinfection is no more than three minutes ahead of the rapid mix. For
this reason, enhanced coagulation is believed to provide substantial benefit, even with
prechlorination. These results led the EPA to revisit the proposed predisinfection credit
limitations. In the absence of ICR data and in an effort to not increase microbial risk, the
EPA has decided to allow disinfection credit prior to enhanced coagulation.
Table A-l shows the effect of moving the point of chlorination on DBFs during
conventional and enhanced coagulation. In this table, percent benefit is based on the decrease
in DBF concentration compared to baseline coagulation when pre-rapid mix is the point of
chlorination. As shown in this table, the benefit increases significantly as the point of
chlorination is moved farther from the pre-rapid mix, or the coagulation process is enhanced.
Also, a minimum benefit of 5 to 17 percent was seen in going to enhanced coagulation even
if the point of chlorination was maintained prior to the rapid mix.
A-16
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TABLE A-l
Impact of Moving Point of Chlorination on DBF Formation
Point-of-
Application
Pre-RM
Post-RM
Mid-Floe
Post-Sed
Median Reduction in DBF Formation (%)
TOX (n=7)
Baseline Enhanced
Coagulation Coagulation
11%
0.3% 10%
3.9% 23%
11% 40%
TTHM (n=9)
Baseline Enhanced
Coagulation Coagulation
17%
1.6% 21%
8.7% 36%
21% 48%
HAAS (n=6)
Baseline Enhanced
Coagulation Coagulation
4.7%
5.3% 21%
14% 36%
35% 61%
(Table from Summers et al., 1997)
A.4.3.2 Chloramines
Chloramination is typically practiced because significantly fewer DBFs are formed as
compared to chlorination. Chloramines are primarily used for secondary disinfection. For
disinfection using chloramines, the addition of ammonia is required to form monochloramine
from free residual chlorine. Chloramines can be formed during water treatment by several
methods: (1) simultaneous addition of chlorine and ammonia; (2) addition of ammonia after
chlorine addition; (3) addition of ammonia prior to chlorine addition; and (4) preformed
chloramines. The method used depends to a large degree on the need to provide adequate
primary disinfection and the need to limit DBF formation. The most common methods are
simultaneous addition of chlorine and ammonia (after primary disinfection using chlorine or
ozone) and the addition of ammonia after chlorine addition. The addition of ammonia prior
to chlorine and the use of preformed chloramines are strategies of systems that need to limit
DBF formation, because free chlorine contact time is significantly reduced or eliminated
(depending on mixing conditions and pH levels). However, systems may wish to evaluate loss
of virus kill by assuming no free chlorine contact.
A-17
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A.4.3.3 Ozone
The use of ozonation has been growing rapidly in the U.S. as utilities have been
meeting the requirements of the Surface Water Treatment Rule, anticipating the DBPR,
meeting regulations for volatile and synthetic organic chemicals, and for controlling taste
and odor (Ferguson et al., 1991; Tate, 1991). The first U.S. ozone plant was put in service
in 1978, and the number increased to 18 by June 1990 (Tate, 1991). A survey in 1992 (Rice,
1992) identified an additional 11 facilities under construction, as well as at least 37 U.S.
ozone pilot-plant studies underway.
Ozone is one of the most powerful oxidants available for water treatment (second only
to the hydroxyl free radical). Because ozone reacts with hydroxide ions to form hydroxyl
radicals, the pH and alkalinity of the water during ozonation are very important parameters
in determining the degree and rate of oxidation. Oxidation with ozone is also influenced by
other water quality characteristics, such as temperature and the concentration of reduced
chemical species. Other important considerations include ozone dose and contact time.
Studies on ozone for removal of DBF formation potential (DBPFP) (Chang and
Singer, 1991; Singer and Chang, 1988; Reckhow and Singer, 1984) concluded the following:
• Although preozonation alone has an almost negligible impact on the overall TOC
concentration of raw water, the organic material is altered such that the color and UV
absorbance of the water are reduced.
• Preozonation alone can lower TFUVIFP by about 10 percent at the ozone dosages
commonly used in water treatment practice. With regard to THM control, the
principal benefit derived from employing preozonation in place of prechlorination is
that chlorine or chloramines can be added later in the treatment train since ozone
provides the required inactivation.
• Hardness and TOC have a major impact on the stability of particulate material. The
aggregation rate of suspended parti culate matter is very sensitive to the hardness-to-
TOC ratio of the non-ozonated raw water.
• When used as a preoxidant in water treatment, ozone can destabilize particulate
material. The optimal dosage of ozone for this benefit depends on the hardness and
TOC concentration of the water. Optimal ozone-induced coagulation occurs in
waters with hardness-to-TOC ratios greater than 25 (mg CaCO3/mg C), and ozone
doses of about 0.4-0.8 (mg O3/mg C).
A-18
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A.4.3.4 Chlorine Dioxide
Chlorine dioxide cannot be transported because of its instability and explosiveness;
therefore, it is generated at the site of application. The most common method for producing
chlorine dioxide is by mixing a high strength chlorine solution with a high strength sodium
chlorite solution. The reaction between chlorine and chlorite is typically allowed to proceed
in a PVC chamber, filled with porcelain rings, designed for a detention time on the order of
0.2 minutes. Generally, 1.7 pounds of sodium chlorite are required for each pound of chlorine
dioxide to be generated. Chlorine is normally used at a 1:1 molar ratio with sodium chlorite
to ensure completion of the reaction and to lower the pH to between 3.5 and 4. Lowering
the pH helps drive the reaction and increases the C1O2 yield. It is important to optimize the
yield of the C1O2 generator because unconverted free chlorine can form DBFs if it enters the
influent water. For additional information on chlorine dioxide, see the Alternative
Disinfectants and Oxidants Guidance Manual.
Typical equipment requirements for chlorine dioxide generation include sodium
chlorite mixing and metering systems; chlorine dioxide generators; and other miscellaneous
storage, mixing, and metering systems. Chlorine dioxide may also be generated by acidifying
solutions of sodium chlorite and sodium hypochlorite. This method is only applicable for
small systems where little operator time is available.
Limited research has been performed on the effectiveness of chlorine dioxide for the
reduction of THMFP and TOXFP. Chlorine dioxide is most often used as an alternative
disinfectant to chlorine for reducing DBFs. One study (Werdehoff and Singer, 1987), yielded
the results shown in Table A-2.
TABLE A-2
Use of Chlorine Dioxide for THMFP and TOXFP Removal
Chlorine Dioxide Dose
(mg ClO2/mg TOC)
0.44
0.55
1.11
Initial TOC
(mg/L)
4.5
1.8
1.8
Removal (%)1
THMFP
13
19
33
TOXFP
14
17
30
Note: 1. Removal based on THMFP/TOXFP of water before C1O2 application.
A-19
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These removals were similar to those observed from ozone oxidation when compared
on a mass ratio of oxidant applied to initial TOC. However, none of the chlorine dioxide
dosages noted above were capable of producing any removal of TOC.
A.4.3.5 Potassium Permanganate
The most common use of potassium permanganate is oxidation of reduced metals
(particularly iron and manganese) and trace organic compounds associated with taste and
odor problems, and control of algae and other biological growth. Potassium permanganate
may be added at several different points in drinking water treatment facilities. However, this
chemical must be used prior to a particulate removal step, such as settling or filtration,
because the permanganate ion forms insoluble manganese dioxide when it oxidizes chemical
species in the water source. Additional sludge handling is necessary as a result of manganese
dioxide formation. Caution must also be exercised with potassium permanganate dosages
since overdosing produces an easily detected pink color in finished waters, a condition that
must be avoided from a customer relations standpoint. Potassium permanganate is usually
delivered to treatment plants in dry form and mixed on-site. Equipment needs include
miscellaneous storage, mixing, and metering systems.
Several studies evaluating the removal of THMFP by potassium permanganate
indicated marginal results (Colthurst and Singer, 1982; Singer et al., 1980). None of the
permanganate dosages were capable of producing a detectable change in TOC.
Full-scale evaluations of potassium permanganate were conducted by the Fairfax
County Water Authority in Northern Virginia (Bonacquisti and Petrovitch, 1988). The
authors found no relationship between permanganate dose and TOC removal. However, it
is unclear how much of the permanganate had reacted between the point of permanganate
application and the point of TOC sampling, and the presence of inorganic species which
create permanganate demand was also unknown. Despite these unknowns, a 25 percent
removal achieved in June 1987 was significantly higher than removals observed in the bench-
scale studies described above.
A-20
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A.4.3.6 Advanced Oxidation Processes
Advanced oxidation processes (AOPs) are defined as those oxidation processes which
involve the generation of hydroxyl free radicals in sufficient quantity to impact water
purification. Examples of AOPs include ozone at high pH levels; ozone/hydrogen peroxide;
and either ozone or hydrogen peroxide with other free radical initiators such as ultraviolet
light, metals, and metal oxides. The hydroxyl free radical has a higher oxidation potential, and
frequently reacts at faster rates than more conventional oxidants such as chlorine,
permanganate, chlorine dioxide, and ozone. In some situations, AOPs may be reasonably cost
effective. As a result, AOPs show promise for removal of a variety of contaminants which
were previously not treatable with more conventional oxidation processes. The
ozone/hydrogen peroxide AOP process essentially requires the same equipment as the ozone
process, except that hydrogen peroxide feed equipment is also necessary.
Research has demonstrated that advanced oxidation processes may increase DBPFP
at lower ozone dosages typical of water treatment, but can reduce DBPFP at higher dosages
(Wallace etal., 1988;Duguetetal., 1985). Although AOPs in combination with chloramines
can successfully reduce the formation of DBFs, under typical AOP operating conditions there
is little or no ozone residual, which results in little or no CT credit for this oxidation scenario.
Therefore, utilities that use AOPs and chloramines will typically first use ozone for
disinfection, then the AOP for micropollutant destruction, and finally chloramines for residual
disinfection (Gramith et al., 1991).
A.4.4 Separation Processes
A.4.4.1 Sedimentation
Sedimentation is a process used to remove easily settleable, heavier solids. In water
treatment this pertains primarily to the settling of floes to reduce the solids load sent to the
filter media (Westerhoff and Chowdhury, 1996). Sedimentation will remove some NOM by
settling floe particles to which NOM is bound. The amount of NOM removed is dependent
on the amount of NOM which can be incorporated into the floe particles and also on the
settling environment. The amount of NOM bound in floe is dependent on the coagulant type,
NOM concentration and type, alkalinity, pH, and various other water quality parameters.
A-21
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With increased coagulation doses, appreciable amounts of NOM can be removed. NOM
removal with coagulation is covered in greater detail in Section A.4.1.
A.4.4.2 Dissolved Air Flotation
Dissolved air flotation (DAF) is another clarification process often used to remove
lighter weight solids (Westerhoff and Chowdhury, 1996). DAF processes can remove a range
of particles. However, unlike sedimentation processes which remove heavier solids, they tend
to achieve better removal of low-density solids. DAF has the ability to remove small
microorganisms, floes, some NOM, and turbidity. Typically, a stream ofwater supersaturated
with air is fed near the bottom of the DAF chamber. As the pressure is reduced, the dissolved
air is released and rises to the top along with the low-density floes present in the already
coagulated water. The lifted solids may then be removed from the top of the tank by a
mechanical scraper or other process.
The amount of NOM removed through DAF is dependent on both the amount of
NOM bound in the floe particles and the efficiency with which the air can attach to suspended
particles. The amount of NOM bound in the floe will depend on conditions such as coagulant
type, NOM concentration and type, alkalinity, pH, and various other water quality
parameters. The successful attachment of air bubbles to floe will be a function of the
destabilization of floe particles during coagulation/flocculation, which is in turn highly
dependent on coagulant type and water quality conditions (Westerhoff and Chowdhury,
1996). TOC removal with coagulation is discussed in more detail in Section A.4.1.
A.4.4.3 Filtration
Filtration is a process used to clarify water by removing suspended particulate
material, typically by removing flocculated particles from a coagulated water by passing the
water through a granular media filter. Particle removal takes place either on the surface of
the media (cake filtration) or throughout the depth of the media (depth filtration). Filtration
will remove only a very small portion of unbound NOM. Some NOM removal may be
achieved from organic compounds adsorbing to the filter media (Westerhoff and Chowdhury,
1996). However, filtration removes NOM primarily by removing flocculated particles which
contain NOM-bound material. The removal of floe, and therefore removal of NOM, depends
A-22
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on a number of factors, including surface chemistry of the floe, media type, headloss through
the filter, filtration rate, and backwashing regime. The amount of NOM removed, however,
will be a function of the amount of NOM bound in the floe, which in turn is dependent on
coagulant type and various water quality characteristics (Westerhoff and Chowdhury,
AWWARF, 1996). TOC removal by coagulation/filtration is discussed in more detail in
Section A.4.1.
A.5 OTHER PRECURSOR REMOVAL TECHNOLOGIES
Other processes, such as adsorption and membrane filtration, are effective methods
for removing DBF precursors. These processes and the related technologies are discussed
in more detail in Appendix C.
A.6 SUMMARY
The removal of NOM from drinking water sources is important for a number of
reasons. In the context of this document, NOM removal is important because of its ability
to react with oxidizing agents to form by-products that may be harmful to humans.
Carlson (1991) reviewed several technologies for DBF precursor removal based on
process experience, important considerations, expected performance, and limitations. A
comparison of the technologies in order of general feasibility is presented in Appendix C.
Carlson indicated that the order of technologies is somewhat arbitrary, that the order may
change depending on site specific conditions, and that major technologies may become more
feasible as improvements are made.
A-23
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Based on the information presented here, the following processes are considered most
effective for NOM removal:
Coagulation/filtration, particularly at low pH
• Precipitative softening, particularly at high pH
GAC adsorption (see Appendix C)
• Membrane processes (see Appendix C)
These processes were included here because of their ability to remove a wide range of DBF
precursors to extents greater than 40 percent. These conclusions were based on technological
feasibility only, and a cost feasibility analysis may alter them.
A-24
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Appendix B
TOC REMOVAL BY SOFTENING
-------
Table of Contents
Page
B.O TOC REMOVAL BY SOFTENING
B. 1 Introduction B-l
B.2 Fundamentals of Precipitative Softening B-2
B.3 Relationships Between Physicochemical Characteristics of Natural
Organic Matter and Coagulation/Filtration Performance B-3
B.4 Lime Dose and pH Impact B-5
B.5 Summary B-8
List of Tables
B-l Effect of Sludge Recycle Ratio on TOC Removal B-6
B-2 TOC Prediction Equations for Lime Softening B-7
-------
APPENDIX B
TOC REMOVAL BY SOFTENING
B.I INTRODUCTION
Lime softening is typically not thought of as an organics removal process. However, lime
softening removes NOM by the same mechanism as coagulants, and can remove NOM to a
significant degree in some cases. The primary differences between softening and metal-salt
coagulation are that CaCO3 solids, unlike iron or alum hydroxides, have a small surface area and a
negative charge. Coagulants typically have a larger surface area and a neutral or positive charge and
therefore have a higher affinity for the negatively charge NOM. However, because calcium has an
affinity for certain functional groups (mainly carboxylic acids), some NOM removal will be possible.
Also, when MgOH is precipitated at high pH, significant NOM removal can occur. This is because
MgOH acts very much like a coagulant and is an effective absorbent for NOM (Randtke, 1988).
The degree of removal of NOM by precipitative softening depends on a number of factors
including the following:
• Nature and concentration of NOM entering the process.
• Other water quality characteristics including calcium hardness and magnesium hardness.
• Treatment processes, such as oxidation, used prior to the precipitative softening process.
• Type and dose of the chemical being used for hardness removal.
The following section provides some basic information on precipitative softening processes.
Subsequent sections briefly describe some key results observed in several precipitative softening
studies with respect to NOM removal.
B-l
-------
B.2 FUNDAMENTALS OF PRECIPITATIVE SOFTENING
The following description of precipitative softening is taken in large part from the Water
Resources Handbook (Mays, 1996). Hardness in water is caused by the presence of polyvalent metal
ions (cations) which generally interfere with the cleaning action of soap by preventing foam
formation. Hardness also may cause scaling problems. Most abundant of the polyvalent metal ions
found in source waters are those of calcium and magnesium. Corresponding maj or anions associated
with the calcium and magnesium ions are carbonates (CO3"2) and sulfates (SO4"2).
While hard water is not known to cause any adverse health effects, relatively softer water
enhances consumer acceptability. There is no well-defined distinction between hard water and soft
water. In general, however, hardness values of less than 75 mg/L as CaCO3 represent soft water, and
values above 150 mg/L as CaCO3 represent hard water. Perception of hard water varies significantly
among people and between geographical regions.
The removal of hardness from water, termed softening, can be achieved through chemical
addition. The chemical reactions involved cause calcium and magnesium ions to precipitate out of
solution. Chemical precipitation for water softening involves shifting the equilibrium of calcium
and magnesium solubility by increasing the pH (lime softening), and possibly adding a source of
carbonate (lime-soda ash softening). During precipitative softening, the calcium ion is normally
removed as calcium hydroxide precipitate. Alkalinity and pH of the source water play important
roles in precipitative softening.
During precipitative softening, hydroxide ions (as Ca(OH)2) are added to shift the carbonate
speciation to CO3"2 which facilitates the precipitation of CaCO3. This process generally takes place
at a pH of 10. Ca(OH)2 is often produced on-site by slaking lime (CaO). Removal of magnesium
hardness is caused by the precipitation of Mg(OH)2 which generally takes place at a pH of 10.5 or
higher. Depending on the characteristics of the source water and the relative concentrations of
calcium and magnesium ions and carbonate and noncarbonate ions, the amount of lime and soda ash
required for precipitative softening may vary. Quantities can be calculated based on the
stoichiometry of the chemical reactions involved in the process.
B-2
-------
B.3 RELATIONSHIPS BETWEEN PHYSICOCHEMICAL CHARACTERISTICS OF
NATURAL ORGANIC MATTER AND COAGULATION/FILTRATION
PERFORMANCE
NOM removal during precipitative softening depends on many factors, both process and non-
process related. Physicochemical characteristics of the NOM will greatly affect the ability of a
softening process to remove adsorbable organics. These characteristics include: molecular weight,
charge, solubility, functionality, and molecular geometry. These are discussed below.
Molecular Weight
Semmens and Staples (1986) reported that larger molecules, particularly those with molecular
weights greater than 10,000, were readily removed by precipitative softening. However, an increased
level of TOC was observed for the fraction containing molecules with molecular weights less than
1,000. According to the authors, this may have resulted from hydrolytic decomposition of large
molecules at the high pH levels used in the process. Changes in water chemistry also may have
affected the rejection efficiency of the membranes used for fractionation. El-Rehaili and Weber
(1987) also reported that larger organic molecules were preferentially removed by precipitative
softening. Liao and Randtke (1985) also found during bench-scale tests that most of the removable
NOM was the high molecular weight fraction.
Charge
CaCO3 precipitates are negatively charged. Therefore, electrostatic adsorption of only
positively charged contaminants is expected. Since most NOM is negatively charged, adsorption
will not occur unless sufficient chemical interaction is available to overcome the charge repulsion.
Although electrostatic forces are weak compared to chemical interactions, if a positively charged
contaminant is sufficiently polymerized, electrostatic adsorption could be substantial. The influence
of molecular charge distributions on NOM removal by precipitative softening was evaluated by
Semmens and Staples (1986). They found that acidic molecules were poorly removed, while neutral
and basic molecules were effectively removed.
B-3
-------
Solubility
In general, for a compound to adsorb to CaCO3 precipitate, it must be slightly hydrophilic.
However, if a compound is too hydrophilic, it will remain in the aqueous phase. If it is too
hydrophobic, it will not have the charge or the functional groups necessary to adsorb. Therefore
compounds with solubility distribution extremes probably will not be readily removed.
The influence of organic matter solubility on NOM removal by precipitative softening was
evaluated by Semmens and Staples (1986). They found that hydrophobic molecules were more
readily removed by precipitative softening than were hydrophilic molecules.
Functionality and Molecular Geometry
The type of functional group on a compound will affect its complexation with CaCO3
precipitate. Calcium will preferentially bond with oxygen-containing species, therefore, NOM with
oxygenated functional groups may be more easily removed. Additionally, alteration of the functional
groups upon disinfection also may aid in NOM removal. Jekel and Ernst (1981) found that
ozonation increased the adsorption of NOM during lime softening.
Molecular geometry also is an important factor in the ability of a compound to bind to a solid.
Geometry affects whether a NOM substance will be adsorbed and if so, to what extent the NOM will
be adsorbed. Molecular deformability and degree of hydration also affect the adsorption of organic
compounds (Liao and Randtke, 1985).
B-4
-------
B.4 LIME DOSE AND pH IMPACTS
Several reports in the literature have described the performance of precipitative softening for
NOM removal at a bench-scale level (Johnson and Randtke, 1983; Liao and Randtke, 1985;
Semmens and Staples, 1986; Jodellah and Weber, 1985; Weber and Jodellah, 1985; Collins et al.,
1985; El-Rehaili and Weber, 1987; Randtke et al., 1982). The most extensive evaluations of NOM
removal by precipitative softening were performed by Randtke and co-workers. Using fulvic acid
isolated from an Illinois groundwater, Liao and Randtke (1985) reported that NOM removal in the
precipitative softening process was primarily achieved by adsorption onto calcium carbonate and
magnesium hydroxide. Therefore, NOM removal depends on the amount of calcium carbonate and
magnesium hydroxide produced in the softening process. The amount of calcium carbonate
produced depends on raw water calcium and carbonate concentrations, the amounts of calcium and
carbonate added to the process, and the pH of the softening process. The amount of magnesium
hydroxide produced depends on raw water magnesium concentration and the pH of the softening
process.
In addition, when the ratio of raw water magnesium to total calcium is increased, the removal
of NOM also increases (Randtke et al., 1982, and Liao and Randtke, 1985). Total calcium refers to
the sum of raw water calcium and the calcium added by lime addition. Results reported by Randtke
et al. (1982) for a fulvic acid isolated from an Illinois groundwater suggest that magnesium
hydroxide adsorbs NOM to a stronger degree than does calcium carbonate.
Liao and Randtke (1985) also demonstrated that NOM removal is influenced by the manner
in which calcium carbonate is precipitated. NOM removal was enhanced by the formation of finely
divided, poorly crystallized, calcium carbonate. Because of this, NOM removal is inhibited by
processes that favor the rapid formation of large calcium carbonate particles. Such conditions are
present when softening plants recycle sludge to increase the rate and extent of hardness removal.
Using a fulvic acid isolated from groundwater, and a softening pH of 11, Liao and Randtke (1985)
reported the results shown in Table B-l.
B-5
-------
TABLE B-l
Effect of Sludge Recycle Ratio on TOC Removal
Ratio of Recycled Solids
to Solids Precipitated
0
1
2
TOC Removed
(percent)
35
31
23
In addition, NOM removal was enhanced when calcium was in excess with respect to
carbonate. In contrast, hardness removal is enhanced when an excess supply of carbonate is
available. Therefore, NOM removal appears to be favored by conditions that inhibit satisfactory
removal of hardness (e.g., no sludge recycle and excess calcium). The authors suggest a two-stage
process be used to effectively remove both NOM and hardness:
• Stage 1: Optimize NOM removal by adding excess lime to elevate pH and calcium levels.
• Stage 2: Optimize hardness removal by adding carbonate alkalinity and by recycling sludge.
For plants using both lime and soda ash in a single stage process, the authors suggest delaying the
addition of soda ash for several minutes after lime addition.
During earlier work, Randtke et al. (1982) found that the removal of humic substances during
lime-soda ash softening was increased with increased pH, increased precipitate formation, and
decreased TOC concentrations. Also, they found that organics removal was enhanced by the
presence of magnesium or phosphate.
Using the softening data contained in an AWWA database, empirical models were
formulated which predict precursor removal as a function of lime/soda ash dose. Table B-2 gives
the equations for each TOC range. In developing these equations, cases with high ferric dose (>10
mg/L) were excluded.
B-6
-------
TABLE B-2
TOC Prediction Equations for Lime Softening
TOC
2
4
8
<
<
<
TOC
TOC
TOC
Range
<
<
4
8
Equation
TOC
TOC
TOC
= 1
30
= 2.84
= 7
35
+ 2.30*e
+ 2.89*e
+ 5
68*e
-0.12*Dose(meq/L)
-0.21*Dose(meq/L)
-0.24*Dose(meq/L)
(n=84)
(n=119)
(n=51)
Field-scale data from eight softening plants (James M. Montgomery, 1989; Singer, 1988)
showed that precipitative softening plants can achieve the same level of NOM removal as alum
coagulation/filtration plants. TOC removal in these plants ranged from 12 to 88 percent while UV-
254 removal ranged from 44 to 96 percent. Median removals of TOC and UV-254 were 37 and 76
percent, respectively. It should be noted that in full-scale softening plants, alum or ferric chloride
addition is often practiced. Lime addition may create small particles that are difficult to filter; plants
often add coagulants to remove these particles. Coagulants also are combined with lime softening
to remove precursor material not removed by softening. The benefit of adding a coagulant during
lime softening with respect to precursor removal is a function of raw water quality (Shorney and
Randtke, 1994).
Pilot-scale softening tests were performed to evaluate the removal of different DBF
precursors from Ohio River water at Cincinnati, Ohio (USEPA, 1988; Stevens, et al., 1989).
Chlorine dosages were applied in accordance with the standard method for THMFP (Clesceri et al.,
1989). The temperature of the chlorination period was maintained at 25 °C. In general, DBPFP
removals ranged from 30 to 60 percent under the conditions used in this evaluation. The data do not
clearly show which precursor fractions are least readily removed. HAAFP appeared to be removed
to a greater extent than THMFP; however, the authors concluded that DBPFP and THMFP removal s
were essentially the same.
The pilot plant also achieved 39 percent removal of TOC. In most cases, this level of
removal was lower than the removals of THMFP, HAAFP and HANFP. Thus, TOC removal may
be a conservative indicator of the removal of THM, HAA, and HAN precursors.
Johnson and Randtke (1983) examined the removal of TOC during bench-scale lime
softening for several different source waters. Softening with postchlorination resulted in TOC
B-7
-------
reductions of 14 and 32 percent for a river water and groundwater, respectively. Softening with
postchlorination of a fulvic acid solution resulted in TOC reductions of 46, 85, and 92 percent for
lime doses of 100, 200, and 300 mg/L, respectively.
B.5 SUMMARY
Precipitative softening can achieve the same range of TOC removal as achieved by alum
coagulation/filtration processes. Field-scale data from eight softening plants showed that these
plants were achieving TOC removals of 12 to 88 percent and UV-254 removals of 44 to 96 percent.
Pilot-scale studies with Ohio River water showed that TOC removal may be a generally conservative
indicator of THMFP, HAAFP, and HANFP removal.
Like coagulation/filtration processes, the precipitative softening process can be modified to
increase NOM removal. In general, NOM removal is enhanced by conditions that favor the
formation of magnesium hydroxide and small calcium carbonate particles. These conditions are
achieved by:
• Elevating pH to approximately 10.8 or higher.
• Delaying carbonate addition for several minutes.
• Delaying sludge recycling.
The last two modifications inhibit the removal of hardness. Thus, process modifications
should be implemented cautiously. For systems employing a multi-staged process, satisfactory NOM
and hardness removal might be achieved by the two-stage process noted above. In many full-scale
cases, alum or ferric coagulants also are used.
-------
Appendix C
OTHER DBF PRECURSOR REMOVAL TECHNOLOGIES
-------
Table of Contents
Page
C.O OTHER DBF PRECURSOR REMOVAL TECHNOLOGIES
C.I Adsorption Processes C-l
C.I.I Granular Activated Carbon C-l
C.I.2 Powdered Activated Carbon C-5
C.2 Membranes C-7
-------
APPENDIX C
OTHER DBP PRECURSOR REMOVAL TECHNOLOGIES
C.I ADSORPTION PROCESSES
C.I.I Granular Activated Carbon
The application of granular activated carbon (GAC) adsorption for drinking water
treatment involves the following major process design considerations:
• Empty bed contact time (EBCT, volume of empty contactor divided by flow rate).
• Reactivation interval or frequency.
• GAC usage rate (pounds of GAC used per gallon of water treated).
• Pretreatment.
• Contactor configuration (e.g., downflow versus upflow, pressure versus gravity,
single-stage versus multi-stage or parallel, filter adsorber versus post-filter GAC
contactor).
• Method of GAC reactivation (e.g., on-site versus off-site).
The EBCT provides an indication of the quantity of GAC on-line at any one time, and
thus reflects the capital cost for the system. The EBCT is an important design parameter and
may have some impact on the GAC usage rate for removal of NOM.
GAC adsorption, as practiced in water treatment, is not a steady-state process, with
the effluent concentration increasing with time. Once the effluent concentration meets the
maximum allowable concentration for a contaminant, the GAC column must be taken off-
line and the GAC replaced with reactivated or fresh GAC. The operation time to this
maximum effluent concentration is termed the reactivation interval.
The GAC usage rate provides an indication of the rate at which the GAC is exhausted
or replaced and, therefore, primarily affects the operating cost of the GAC treatment system.
C-l
-------
For a full-scale GAC installation, the GAC usage rate often dictates the choice between
providing an on-site reactivation system or replacing the spent GAC with virgin GAC. It
also affects the costs of GAC handling (i.e., storage, dewatering, attrition losses, and
transportation).
GAC systems may require some kind of pretreatment to prevent clogging of the GAC
bed, to minimize the organic loading on the GAC, and to improve cost effectiveness.
Clogging of the GAC bed could be caused by suspended solids in the raw water or by
precipitation of calcium carbonate, iron, and manganese on the GAC. Suspended solids
typically cause problems in surface water systems, while carbonate scaling and iron and
manganese precipitation may occur in both surface and ground waters. When the GAC bed
life is long, clogging may also be caused by biological growths. Pretreatment methods
include coagulation, filtration, or softening ahead of the GAC system. Conventional
coagulation, clarification, and filtration processes may be optimized for organics removal to
reduce natural organic loading to the GAC bed.
Based on the estimates of GAC usage rate and contact time, a conceptual process
design can be developed by evaluating various contactor configurations. The two basic
modes of contactor operation are downflow and upflow. Upflow beds typically have been
applied to situations where very long contact times (greater than 120 minutes) are required
and/or where the level of suspended solids is high. Downflow fixed bed contactors offer the
simplest and most common contactor configuration for drinking water treatment. The
contactors can be operated either under pressure or by gravity.
The choice of pressure or gravity is generally dependent upon the hydraulic
constraints of a given system. Pressure contactors may be more applicable to ground water
systems because pumping of the ground water is required. Gravity contactors are generally
more suitable for surface water systems if sufficient head is available. Gravity contactors,
when used, are typically placed downstream of surface water filtration systems.
GAC contactors may be operated in a series or parallel configuration. In a series
configuration, GAC in the first contactor is reactivated when the effluent of the second
contactor no longer meets the treatment objective. Once the GAC in the first contactor is
replaced, the roles of the two contactors may be reversed, where the second contactor
C-2
-------
becomes the first contactor and vice versa. NOM is a mixture of unknown compounds which
separate along the bed in a manner proportional to their adsorption potential. Weakly
adsorbing components of NOM may irreversibly preload the GAC at the downstream end
of the bed and may, therefore, reduce the capacity of the bed for stronger adsorbing
components at the end of the bed.
In parallel operation, multiple GAC beds can be operated in a staggered pattern such
that effluents from beds with breakthrough concentrations higher than the treatment obj ective
are blended with effluents from beds with little or no breakthrough. In this manner, the
combined effluent concentration from the GAC beds can be kept less than the specified
treatment objective, and exhausted beds would be reactivated in a staggered manner.
The choice between a single contactor and contactors in series or parallel is site
specific and depends on the type and concentration of the contaminant to be removed and its
rate of adsorption. This choice also depends on the types, concentrations, and adsorption
rates of competing contaminants. Furthermore, an economic analysis should be performed
based on site specific data to decide on an optimal contactor configuration.
GAC contactors should be used when longer EBCTs are required, while filter-
adsorbers, where the top portion of the sand is replaced by GAC, can be used when shorter
EBCTs are feasible. Because of their short EBCTs, filter-adsorbers meet desired water
quality goals for a much shorter period of time than GAC contactors. For treating seasonal
changes in water quality or contaminant shock loads, filter-adsorbers may have an economic
advantage over post-filter GAC contactors. One disadvantage of filter-adsorbers is that GAC
losses are high during backwashing and reactivation, and equipment separating GAC from
sand may be required before reactivation. An economic analysis considering GAC usage rate
and treatment goals should be performed to decide between GAC contactor and filter-
adsorber modes of operation.
Another consideration in the design of a GAC system is the method of GAC
reactivation. The two basic approaches to regenerating GAC are:
• Off-site disposal or reactivation
• On-site reactivation.
C-3
-------
Based on information from GAC manufacturers, on-site reactivation is not generally
economical for systems where the GAC usage rate is less than 2,000 Ib/day.
Under the throwaway concept of off-site disposal, virgin GAC is generally purchased
in bags or drums. Once the GAC becomes exhausted, it is generally slurried by gravity to
a draining bin where the free water is removed and returned for treatment. The drained GAC
is then manually drummed and shipped for landfilling or incineration.
The advantage of this approach lies mainly in its technical simplicity. It is a sound
approach for applications requiring a relatively small GAC usage rate, generally less than 500
Ib/day. The need to dispose of the spent GAC, however, is a definite drawback, especially
if testing demonstrates that the spent GAC is considered a hazardous waste. If this occurs,
it may become necessary to consider incineration of the spent GAC prior to disposal in a
landfill. Alternatively, a hazardous waste landfill could be used at increased cost.
The off-site reactivation approach is somewhat similar to the throwaway concept
from a GAC handling standpoint; however, it assumes some of the economies associated
with GAC reuse. When compared to other alternatives, however, the number of handling
steps and resulting GAC losses are a major disadvantage. The off-site reactivation approach
has generally proven most cost effective in applications where the GAC usage rate falls in
the 500 to 2,000 Ib/day range (Kornegay, 1979).
The major equipment typically found in a GAC installation includes:
• GAC Contactors - either common wall concrete or lined steel vessels. In either case,
provisions for underdrainage, backwashing, and removing the spent GAC must be
made.
• GAC Storage - additional storage facilities may be required for handling of virgin,
reactivated, and spent GAC, depending on the type and size of the facility.
GAC Transport Facilities - includes piping, valves, and pumps.
GAC Fill - the actual initial GAC charge depends on the type and volume of GAC
required for treatment.
C-4
-------
C.1.2 Powdered Activated Carbon
PAC has been successfully used for taste and odor control in many water treatment
facilities. PAC can also be used to remove NOM. The application of PAC for removal of
NOM from drinking water supplies involves the following major process design
consideration:
• PAC usage rate
• Contact time
• PAC disposal.
In typical water treatment situations, PAC is added at the rapid mix stage, along with
coagulants, and settles out in the sedimentation stage. The growth of floe around PAC
particles, however, may block adsorption onto PAC to some degree. Many studies have
indicated that PAC capacity for NOM increases with contact time up to seven days or longer.
Therefore, the contact time in conventional settling basins (typically several hours) may not
be long enough to produce effective removal of NOM by PAC.
Two different PACs, Westvaco AquaNuchar and Westvaco Nuchar S A, were studied
for precursor removal in conjunction with alum coagulation (Malcolm Pirnie 1988
unpublished data). Results indicate that alum coagulation alone achieved an average 55
percent reduction of THMFP. Alum coagulation combined with Aqua Nuchar dosed at 25
mg/L (0.21 lb/1,000 gal) reduced THMFP by 70 percent with preozonation (0.05 to 0.2 mg
03/mgTOC) and 60 percent without preozonation. Alum coagulation combined with Nuchar
SA dosed at 16 to 21 mg/L (0.13 to 0.18 lb/1,000 gal) reduced THMFP by 75 percent with
preozonation and 70 percent without preozonation. These dosages are significantly higher
than those typically used in drinking water treatment and represent a significant increase in
sludge production. With these relatively high dosages, PAC enhanced TOC removal by 10
to 20 percent and THMFP removal by 0 to 20 percent.
Two additional applications of PAC in water treatment include: (1) prior to an
upflow solids contact clarifier, and (2) in conjunction with low pressure membranes. An
upflow solids contact clarifier may retain PAC in the sludge blanket, significantly increasing
C-5
-------
PAC contact time and capacity for NOM removal beyond that seen when PAC is simply
added to a point in the treatment train. Kassam et al. (1991) reported mean carbon residence
times in contact recirculating clarifiers from nine hours to 8.5 days. Hoehn et al. (1987) and
Najm et al. (1989) documented the addition of PAC to pilot-scale floe blanket reactors and
found PAC retention times of between nine hours and two days. Increasing PAC retention
time can significantly decrease the required dose. PAC dose was reduced by 25-40 percent
for the adsorption of a detergent (Najm et al., 1991).
PAC is often used with membrane processes. Combining PAC with membrane
filtration improves process performance in two ways: (1) organics removal is increased, and
(2) membrane fouling by organic absorption is decreased. Typically, low-pressure membrane
processes, such as microfiltration (MF) and ultrafiltration (UF), cannot remove a substantial
amount of organic material due to their relatively large pore size. PAC addition improves
NOM removal by associating NOM, which alone would pass through the pores, with the
filterable particulate phase. PAC combined with crossflow membrane processes can also
greatly increase the PAC detention time by recycling PAC through the membrane fibers.
Many PAC/UF studies have evaluated organic carbon removal (Anselme and Charles, 1990;
Laine et al., 1990; Heneghan and Clark, 1991; Adham et al., 1991; Adham et al., 1993;
Jacangelo, 1995; Marriott et al., 1997; Jack, 1997). TOC removals between 13 and 85
percent and DOC removals between 13 and 76 percent have been documented.
PAC can also reduce membrane fouling by preventing organics from adsorbing to the
membrane surface. This enhances membrane flux, reduces the frequency of chemical
cleanings, and prolongs the life of the membrane (Laine et al., 1990; Marriott et al., 1997;
Henegan and Clark, 1991; Jacangelo, 1995).
C-6
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C.2 MEMBRANES
Membrane processes can remove DBF precursors through filtration and adsorption
of organics. If NOM molecules are larger than the membrane pores, NOM will be rejected
and DBPFP will be reduced. Size, however, is only one factor which influences NOM
rejection. Shape and chemical characteristics of organic compounds also play important
roles in the permeation of NOM through a membrane (AWWARF, 1996). Membranes may
also remove NOM through adsorption of organics on the membrane surface. Adsorption
depends on the chemical characteristics, particularly charge and hydrophobicity, of both the
membrane material and organic compounds. Unfortunately, organic adsorption is
undesirable since it has proven to be a primary cause of irreversible fouling.
Pressure-driven membrane processes are typically categorized into MF, UF,
nanofiltration (NF), and reverse osmosis (RO). High-pressure processes (i.e., NF and RO)
have a relatively smaller pore size allowing significant DBF precursor removal. Low-
pressure processes (i.e., MF and UF), however, have a relatively larger pore size and cannot
remove NOM substantially without pretreatment.
DBF precursor removal will be a function of the type of membrane process,
membrane material characteristics, and water quality characteristics (e.g., NOM
characterization and concentration, pH). Some major design considerations for the use of
membranes for the removal of DBF precursors include the following (Carlson, 1991):
• Removal efficiency of NOM.
• Preliminary treatment required to provide a satisfactory membrane feed water quality
and to limit membrane fouling.
• Frequency of fouling and recovery and NOM removal efficiency after repeated
fouling/cleaning cycles.
Without pretreatment, membrane processes remove NOM to varying degrees. MF
and UF removals typically range between about 5 and 30 percent. Typically NF and RO
removals are on the order of 50 to 99 percent. Membranes, particularly those with molecular
weight cutoffs (MWCOs) in the 100 to 500 range, appear to be very effective as a means of
C-7
-------
DBF precursor removal. TOC, THMFP, and TOXFP removals of 70 to 95 percent are
commonly achieved in systems using such membranes. Larger MWCO membranes,
however, will not be as effective for these removals.
While MWCO is an important indicator of process performance, it is also an
important indicator of process costs. Systems using membranes with higher MWCOs are
likely to achieve higher product water flux and operate at lower pressures (and lower costs)
than those using membranes with lower MWCOs. In effect, improved effluent water quality
is traded for higher costs. Higher MWCO membranes can be combined with PAC or
coagulations to allow substantial DBF precursor removal. This increases costs as well.
However, with recent advances in membrane technology, increasing popularity, and the
threat of stricter regulations, membranes are becoming cost competitive with traditional
processes.
C-8
-------
Appendix D
COAGULANT DOSAGES FOR STEP 2 TESTING
-------
APPENDIX D
COAGULANT DOSAGES FOR STEP 2 TESTING
D.I EQUIVALENT DOSAGES FOR COAGULANTS OTHER THAN
ALUMINUM SULFATE
For systems using chemicals other than alum (A12[SO4]3»14H2O) as a primary
coagulant, equivalent dosages (based on molar equivalents of metals) may be used for bench
or pilot-scale testing. Equivalent dosages for two types of ferric chloride (FeQ3»6H2O and
FeCl3), ferric sulfate (Fe2[SO4]3»9H2O) and ferrous sulfate (FeSO4»7H2O) are summarized
in Table 3-1 in Chapter 3. A sample calculation for the conversion of a dosage of alum to
an equivalent dosage of another coagulant is included here for reference.
For example, a lOmg/L dose of alum [A12(SO4)3»14H2O] is equivalent to a 9.1 mg/L
dose of ferric chloride [FeCl3»6H2O] as follows.
Converting 10 mg/L of aluminum sulfate to a molar-equivalent metal dose:
mM A12(SO4)^H2O 2 mM Alr .Q
'
L 594 mg A12(SO4)^\4H2O mM A12(SO4}^\4H2O L
On a metal-equivalent basis, 1 mM A13+ = 1 mM Fe3+, so the metal-equivalent dose may be
converted to an equivalent ferric chloride dose as follows.
mM Fer mM FeCL*6H7O 270 mg Fed *6H7O
0.03367 x —x —=9.\mg/L FeCL-6H7O
L I mM Fer mM FeCl3"6H2O
All dosages in Table 3-1 are reported as active chemical. Therefore, for a 42 percent
ferric chloride solution, the 9.1 mg/L dosage of active chemical would become 21.7 mg/L
of a 42 percent ferric chloride solution.
D-l
-------
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Ref-2
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