United States
Environmental Protection
Agency
Long Term 1 Enhanced Surface
Water Treatment Rule
Turbidity Provisions
Technical Guidance Manual
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Office of Water (4606M)
EPA816-R-04-007
www.epa.gov/safewater
August 2004
Printed on Recycled Paper
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This document provides public water systems and States with Environmental Protection Agency's
(EPA's) current technical and policy recommendations for complying with the turbidity monitoring,
reporting, and recordkeeping requirements of the Long Term 1 Enhanced Surface Water Treatment
Rule (LT1ESWTR). The statutory provisions and EPA regulations described in this document contain
legally binding requirements. This document is not a regulation itself, nor does it change or substitute
for those provisions and regulations. Thus, it does not impose legally binding requirements on EPA,
States, or public water systems. This guidance does not confer legal rights or impose legal obligations
upon any member of the public.
While EPA has made every effort to ensure the accuracy of the discussion in this guidance, the
obligations of the regulated community are determined by statutes, regulations, or other legally binding
requirements. In the event of a conflict between the discussion in this document and any statute or
regulation, this document would not be controlling.
The general description provided here may not apply to a particular situation based upon the
circumstances. Interested parties are free to raise questions and objections about the substance of this
guidance and the appropriateness of the application of this guidance to a particular situation. EPA and
other decision makers retain the discretion to adopt approaches on a case-by-case basis that differ from
those described in this guidance where appropriate.
Mention of trade names or commercial products does not constitute endorsement or recommendation
for their use.
This is a living document and may be revised periodically without public notice. EPA welcomes public
input on this document at any time.
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Acknowledgements
The Environmental Protection Agency gratefully acknowledges the individual
contribution of the following:
Mr. Kevin W. Anderson, Pennsylvania Department of Environmental Protection
Mr. John E. Brutz, Gallitzin Water Authority
Mr. Jerry Biberstine, National Rural Water Association
Ms. Alicia Diehl, Texas Commission on Environmental Quality
Mr. Bryce Feighner, Michigan Department of Environmental Quality
Mr. J.W. Heliums, Jr., Community Resource Group, Inc.
Mr. Allen J. Lamm, New Ulm Public Utilities
*Ms. Rebecca Poole, Oklahoma Department of Environmental Quality
Mr. Jack Schulze, Texas Commission on Environmental Quality
Mr. Brian Tarbuck, Tolt Treatment Facility, Azurix CDM
Mr. Ritchie Taylor, Center for Water Resource Studies, Western Kentucky University
Mr. Steve Via, American Water Works Association
*Participation supported by Association of State Drinking Water Administrators.
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CONTENTS
1. Introduction 1
1.1 Purpose of Document 1
1.2 Overview of LT1ESWTR 1
1.3 Overview of Turbidity Provisions 2
1.4 Other Applicable Rules 4
1.5 Summary of Chapters 5
2. Turbidity Requirements 7
2.1 What are the Turbidity Requirements for Conventional and Direct Filtration
Plants? 7
2.1.1 Combined Filter Effluent Turbidity 7
2.1.2 Individual Filter Effluent Turbidity 10
2.2 What are the Turbidity Requirements for Slow Sand and Diatomaceous
Earth Systems? 17
2.2.1 Combined Filter Effluent Turbidity 17
2.2.2 Individual Filter Effluent Turbidity 18
2.3 What are the Turbidity Requirements for Alternative Filtration Systems? 20
2.3.1 Combined Filter Effluent Turbidity 20
2.3.2 Individual Filter Effluent Turbidity 21
2.4 Are There Special Provisions for Systems that Practice Lime Softening? 24
3. Turbidity Sampling Methods and Turbidimeters 25
3.1 Introduction 25
3.2 Approved Turbidity Methods 25
3.3 Sample Collection 28
3.3.1 Timeliness of Sample Analysis 29
3.3.2 Sampling Strategy and Procedures 30
3.3.3 Handling of Benchtop Turbidimeter Sample Cells 30
3.3.4 Orientation and Matching of Benchtop Turbidimeter Sample Cells 32
3.3.5 Degassing the Sample 33
3.4 Installation 34
3.5 Benchtop Turbidimeters 35
3.5.1 Preventive Maintenance 36
3.5.2 Corrective Maintenance 37
3.6 On-Line Turbidimeters 38
3.6.1 Preventive Maintenance 39
3.6.2 Corrective Maintenance 40
3.7 Calibration- General Information 41
3.7.1 Calibration Standards 42
3.7.2 Conducting the Calibration 45
3.7.3 Calibration Frequency and Procedures 47
3.8 Quality Assurance / Quality Control 49
3.8.1 QA/QC Organization and Responsibilities 50
3.8.2 QA/QC Objectives 50
3.8.3 SOPs 51
3.8.4 Performance and System Audits 53
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3.9 References 53
4. Data Collection and Management 55
4.1 Introduction 55
4.2 Data Collection Methods 55
4.2.1 Strip Recorders and Circular Chart Recorders 56
4.2.2 Data Loggers 56
4.2.3 SCADA 57
4.3 Data Management 59
4.3.1 Format 60
4.3.2 Storage 60
4.3.3 Interpreting and Analyzing Data 60
4.4 Data Management Tools 61
4.4.1 Conventional and Direct Filtration Systems 61
4.4.2 Slow Sand and Diatomaceous Earth Filters 66
4.4.3 Alternative Filtration Technologies 66
4.5 What Upgrades Should I Consider for My System? 66
4.5.1 Suggested System Configuration 68
4.6 References 71
5. Filter Self-Assessment 73
5.1 Introduction 73
5.2 Assessment of Filter Performance 79
5.3 Development of a Filter Profile 80
5.4 Identification and Prioritization of Factors Limiting Filter Performance 84
5.4.1 Assessing Filter Hydraulic Loading Conditions 85
5.4.2 Assessing Condition & Placement of Filter Media 89
5.4.3 Assessing Condition of Support Media and Underdrains 93
5.4.4 Assessing Backwash Practices 96
5.4.5 Assessment of Placing a Filter Back Into Service 106
5.4.6 Assessing Rate-Of-Flow Controllers and Filter Valve Infrastructure 108
5.4.7 Other Considerations 109
5.5 Assessment of Applicability of Corrections 110
5.6 Preparation of the Report Ill
5.7 References Ill
6. Comprehensive Performance Evaluation 113
6.1 Introduction 113
6.2 References 116
7. Turbidity and the Treatment Process 117
7.1 Turbidity - Why is it Important? 117
7.2 The Treatment Process 119
7.2.1 Pre-Sedimentation 121
7.2.2 Coagulation 121
7.2.3 Flocculation 124
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7.2.4 Sedimentation and Clarification 126
7.2.5 Filtration 132
7.2.6 Disinfection 149
7.3 Recycle Streams 140
7.4 References 141
Treatment Optimization 143
8.1 Introduction 143
8.2 Tools Available for Optimization 144
8.2.1 Composite Correction Program (CCP) 144
8.2.2 Area-Wide Optimization Program (AWOP) 144
8.2.3 Partnership for Safe Water 147
8.3 Evaluating System Processes 147
8.3.1 Coagulation and Rapid Mixing 148
8.3.2 Flocculation 154
8.3.3 Sedimentation 157
8.3.4 Filtration 159
8.4 References 166
Appendices
Appendix A. Glossary 167
Appendix B. Blank Forms and Checklists 181
Appendix C. Equations and Sample Calculations 197
Appendix D. Suggested Backwash Rates 213
Appendix E. Filter Self-Assessment Example Report 219
Appendix F. Jar Tests 229
Appendix G. Example of an Operating Procedure for Chemical Feed
System 235
Appendix H. Example of an Operating Procedure for Filters 259
Figures
Figure 1-1. Example of a Poorly Performing Filter Being Masked by Properly
Performing Filters 3
Figure 2-1. Combined Filter Effluent Provisions of the LT1ESWTR for Systems
Using Conventional or Direct Filtration 9
Figure 2-2. Individual Filter Effluent Turbidity Provisions of the LT1ESWTR
for Systems Using Conventional or Direct Filtration 12
Figure 2-3. Turbidity Monitoring Requirements for Conventional and Direct
Filtration Plants 14
Figure 2-4. Slow Sand Filter in Idaho 18
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Figure 2-5. Combined Filter Effluent Provisions of the LT1ESWTR for
Systems Using Slow Sand or Diatomaceous Earth Filtration 19
Figure 2-6. Cartridges Installed at a Small System 22
Figure 2-7. Combined Filter Effluent Provisions of the LT1ESWTR for
Systems Using Alternative Filtration Technologies 23
Figure 3-1. Continuous Monitoring Turbidimeter for Individual Filter Effluent
Measurements 26
Figure 3-2. Sample Locations for Removing Grab Samples 29
Figure 3-3. ABenchtop Turbidimeter 35
Figure 3-4. The Hach 1720C On-Line Turbidimeter 39
Figure 4-1. Central SCADAUnit 58
Figure 4-2. SCADA Control Monitor 58
Figure 4-3. SCADA Control Room 59
Figure 5-1. Filter Self-Assessment Checklist 75
Figure 5-2. Example Filter Profile of Optimized Filter Performance 81
Figure 5-3. Example Filter Profile of Optimized Filter with Turbidity Spike
During Filter Run 81
Figure 5-4. Example Filter Profile with Long and High Initial Spike 82
Figure 5-5. Example Filter Profile of Optimized Filter with Breakthrough at
End of Filter Run 82
Figure 5-6. Example Filter Profile with Multiple Spikes 83
Figure 5-7. Example Filter Profile with High Initial Spike and Turbidity Levels
Above l.ONTU 83
Figure 5-8. Box Excavation Demonstration 90
Figure 5-9. Box Used for Excavation 91
Figure 5-10. Mudball From a Filter 92
Figure 5-11. Underdrain System 94
Figure 5-12. Example Grid of Filter Support Gravel 95
Figure 5-13. Secchi Disk 102
Figure 5-14. "Pipe Organ" Expansion 103
Figure 5-15. Example of Floe Retention Analysis Results for 4-foot Deep Mono
Media Filter Bed 105
Figure 5-16. Example of Floe Retention Analysis Results for 4-foot Deep Dual
Media Filter Bed 105
Figure 6-1. Typical Components of Activities During a CPE 115
Figure 7-1. Particle Size Spectrum 118
Figure 7-2. Conventional Treatment System 120
Figure 7-3. Direct Filtration System 120
Figure 7-4. Chemical Feed Pump (Alum) 124
Figure 7-5. Rectangular Sedimentation Basin 127
Figure 7-6. Circular Radial-Flow Clarifier 128
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Figure 7-7. Plate Settlers Used for High-Rate Sedimentation 129
Figure 7-8. Acceleratorฎ Solids Contact Unit 131
Figure 7-9. Typical Covered Slow Sand Filter Installation 134
Figure 7-10. Typical Rapid Sand Filter 135
Figure 7-11. Cross-Section of a Typical Pressure Filter 136
Figure 7-12. Pressure-Driven Membrane Process Application Guide 138
Figure 8-1. Polymer Feed Pump 153
Figure 8-2. Circular Clarifier 159
Figure 8-3. Inspecting Filter Media 160
Tables
Table 2-1. LT1ESWTR Combined and Individual Filter Effluent Turbidity
Monitoring Requirements for Conventional and Direct Filtration
Systems 11
Table 3-1. Sampling Methods and Monitoring Capabilities of Some Commonly
Used Turbidimeters 27
Table 3-2. Sample Maintenance Form 38
Table 3-3. Some Commonly used Primary Calibration Standards and
Turbidimeters 44
Table 3-4. Some Commonly used Secondary Calibration Standards and
Turbidimeters 44
Table 3-5. Example Calibration Checklist 47
Table 3-6. Suggested On-line Turbidimeter Calibration and Verification
Schedule 49
Table 5-1. Sample Individual Filter Self Assessment Form 77
Table 5-2. General Guide to Typical Filter Hydraulic Loading Rates 85
Table 7-1. Typical Feed Pressures for Pressure Driven Membrane Processes 139
Table 8-1. Chemical Selection Guidelines Based on Raw Water
Characteristics 149
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Contents
ASCE
ASTM
AWOP
AWWA
CCP
CFE
CFR
CPE
CTA
DBF
DBPR
DE
EPA
FBRR
fps
gal
GLI
gpm
gpm/ft2
GWUDI
HAAS
hrs
IESWTR
IFE
LT1ESWTR
MCL
MG
mg/1
ABBREVIATIONS AND ACRONYMS
American Society of Civil Engineers
American Society for Testing and Materials
Area Wide Optimization Program
American Water Works Association
Composite Correction Program
Combined Filter Effluent
Code of Federal Regulations
Comprehensive Performance Evaluation
Comprehensive Technical Assistance
Disinfection By-Products
Disinfection By-Products Rule
Diatomaceous Earth
Environmental Protection Agency
Filter Backwash Recycling Rule
feet per second
gallons
Great Lakes International
gallons per minute
gallons per minute per square foot
Groundwater Under Direct Influence of Surface Water
Haloacetic Acids (monochloroacetic, dichloroacetic, trichloroacetic,
monobromoacetic, and dibromoacetic acids)
Hours
Interim Enhanced Surface Water Treatment Rule
Individual Filter Effluent
Long-Term 1 Enhanced Surface Water Treatment Rule
Maximum Contaminant Level
Million Gallons
milligrams per liter
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MOD
m/h
M/R
MSDS
NTU
O&M
OSHA
PWS
PWSID
QA/QC
RO
SCADA
SCU
SDWA
SOP
TOC
TTHM
TVT
WTP
(^
um
ug/L
Million Gallons per Day
meters per hour
Monitoring/Reporting
Material Safety Data Sheet
Nephelometric Turbidity Unit
Operation and Maintenance
Occupational Safety and Health Association
Public Water System
Public Water System Identification
Quality Assurance/Quality Control
Reverse Osmosis
Supervisory Control and Data Acquisition System
Solids Contact Unit
Safe Drinking Water Act
Standard Operating Procedure
Total Organic Carbon
Total Trihalomethanes
Triple Validation Turbidimeter
Water Treatment Plant
Micro
Micron
Micrograms per liter
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Contents
MARGIN ICONS
Icons and text have been placed in the margins of this document to highlight information
and additional resources. These icons are shown below with brief descriptions of their uses
or the types of information they may be used to highlight.
Indicates a reference to the federal regulations.
Indicates the need to consult with the State.
Indicates additional references or highlights important
information.
Indicates worksheets.
Indicates sampling or data collection requirements.
Indicates applicability criteria.
Indicates a helpful hint or suggestion.
Highlights a key point or key information.
Indicates that the system should be careful.
EPA Guidance Manual
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1. INTRODUCTION
In this Chapter:
Purpose of Document
Overview of
LT1ESWTR
Overview of Turbidity
Requirements
Other Applicable
Rules
Summary of Chapters
40 CFR Section 141.501
1.1 PURPOSE OF DOCUMENT
This document provides information on the combined filter
effluent and individual filter effluent requirements in the Long
Term 1 Enhanced Surface Water Treatment Rule
(LT1ESWTR).
Copies of this document and other referenced documents can
be obtained by:
Contacting the appropriate State office.
Calling the Safe Drinking Water Hotline at
1-800-426-4791.
Downloading from EPA's Web site at
http ://www. epa. gov/safewater/mdbp/lt 1 eswtr. html.
Calling the National Service Center for Environmental
Publications at 1-800-490-9198 or visiting its Web site
at http://www.epa.gov/ncepihom/.
Systems serving 10,000 or more persons should refer to the Interim
Enhanced Surface Water Treatment Rule Documents. For more
information see http://www.epa.gov/safewater/mdbp/implement.html.
Key components of
LT1 ESWTR
1.2 OVERVIEW OF LT1 ESWTR
The LT1ESWTR is a Federal regulation that establishes a
treatment technique to control Cryptosporidium. The rule
applies to public water systems serving fewer than 10,000
persons and classified as either a surface water system or a
ground water system under the direct influence of surface water
(GWUDI). Key components of the LT1ESWTR are:
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1. Introduction
Key components of
LT1ESWTR (cont.)
The term "State" as used in
this document means both
State and Primacy Agency.
The Glossary in Appendix
A contains the definition
for "State."
40 CFR Section 141.502
Systems must begin
complying with
LT1ESWTR turbidity
provisions by January 1,
2005. The compliance
date was changed from
January 14, 2005, to
January 1, 2005 (69 FR
38850; June 29, 2004).
Systems that filter their water must provide a minimum
of 2-1 og removal of Cryptosporidium.
Systems using conventional or direct filtration plants
must meet more stringent combined filter effluent
turbidity limits and must meet new requirements for
individual filter effluent turbidity.
Systems using alternative filtration techniques (defined
as filtration other than conventional, direct, slow sand,
or diatomaceous earth) must demonstrate to the State
the ability to consistently achieve 2-log removal of
Cryptosporidium and comply with specific State-
established combined filter effluent turbidity
requirements.
Systems that meet the filtration avoidance criteria must
comply with watershed control requirements to address
Cryptosporidium.
Systems must develop a disinfection profile unless the
State determines that the disinfection profile is
unnecessary. The State can only make this
determination if the system can demonstrate that the
levels of Total Trihalomethanes (TTHM) and
Haloacetic Acids (HAAS) are below 0.064 mg/L and
0.048 mg/L, respectively. Systems must develop a
disinfection benchmark if the system plans to make a
significant change to disinfection practices. For more
information on the LT1ESWTR disinfection profiling
and benchmarking requirements, refer to LT1ESWTR
Disinfection Profilng and Benchmarking Technical
Guidance Manual (EPA 816-R-03-004, 2003).
New, finished water reservoirs must be covered.
Cryptosporidium is now included in the Federal
definition of GWUDI.
1.3 OVERVIEW OF TURBIDITY PROVISIONS
Systems must begin complying with the turbidity provisions in
the LT1ESWTR by January 1, 2005.
The LT1ESWTR establishes combined filter effluent turbidity
requirements for conventional and direct filtration plants to
accomplish a 2-log removal of Cryptosporidium. These limits
are more stringent than the combined filter effluent limits
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1. Introduction
Adequate filtration is the
main defense against
Cryptosporidium.
Figure 1-1 Illustrating the
need to monitor individual
filters.
established for Giardia in 40 CFR Section 141.73. More
stringent limits were not set for slow sand and diatomaceous
earth filtration systems because data indicate that these
technologies are able to achieve 2-log Cryptosporidium
removal with the turbidity limits set in the Surface Water
Treatment Rule. Alternative filtration systems (defined as
filtration systems other than conventional, direct, slow sand,
and diatomaceous earth filtration) must meet State-specified
combined filter effluent turbidity requirements and conduct a
demonstration study that demonstrates the system's filtration
and disinfection treatment removes specified levels of
Cryptosporidium, Giardia, and viruses.
The combined filter effluent may meet regulatory requirements
for the combined filter effluent turbidity even though one filter
is producing high-turbidity water (see Figure 1-1).
Consequently, one poorly performing filter can create a health
risk by passing pathogens, including Cryptosporidium.
Because properly functioning filters can mask the poor
performance of another filter, the LT1ESWTR also requires
continuous monitoring of turbidity for each individual filter
(recorded at least once every 15 minutes) for conventional
and direct filtration systems.
0.05 NTU 0.05 NTU 0.05 NTU 1.1
\ITU
Combined
,, Filter
To Clearwell Effluent =
0.30 NTU
Figure 1-1. Example of a poorly performing filter
(Filter #4) being masked by properly performing
filters (Filters #1, #2, and #3). Note that the combined
filter effluent turbidity does not exceed the regulatory
standard for combined filter effluent.
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1. Introduction
DBPR = Disinfection
Byproducts Rule
FBRR = Filter Backwash
Recycling Rule
More information on the
FBRR is available in the
FBRR Technical Guidance
Maraa/(EPA816-R-02-
014) or on EPA's Web site
(http ://www. epa. gov/safewater/
filterbackwash.html').
The pathogens can then travel through the remaining treatment
plant processes and eventually reach customers, creating a
health risk. Cryptosporidium is of particular concern because it
is resistant to commonly used disinfectants, such as chlorine,
and, therefore, should be removed by the treatment process.
As explained in the chapters that follow, monitoring and
reporting requirements vary according to the type of filtration
technology used. Worksheets provided in Appendix B can be
used to record and report data to the State. Systems will want
to check with their State office to make sure the worksheets are
acceptable for reporting data to the State.
1.4 OTHER APPLICABLE RULES
Two other rules may also affect the treatment practices of
systems regulated by LT1ESWTR:
1) Stage 1 Disinfectants and Disinfection Byproducts Rule
(Stage 1 DBPR).
Surface water systems serving fewer than 10,000 persons
and all ground water systems that use a chemical
disinfectant must begin complying with the Stage 1 DBPR
by January 1, 2004. This rule requires monitoring of
disinfection residuals and disinfection byproducts. More
information on this rule is available at
http://www.epa.gov/safewater/mdbp/implement.html.
2) Filter Backwash Recycling Rule (FBRR).
The FBRR was published by EPA on June 8, 2001, and
affects systems that meet all of the following criteria:
The system is a surface water system or GWUDI
system.
The system treats water using conventional or direct
filtration.
The system recycles one or more of the following: spent
filter backwash, thickener supernatant, or liquids from
dewatering devices.
Affected systems were required to report information about
their system to the State by December 8, 2003. The FBRR also
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1. Introduction
Contents of Document
requires regulated recycle streams to be returned through all
processes of a system's existing conventional or direct
filtration system or at an alternate location approved by the
State. In addition, the FBRR has recordkeeping requirements
for affected systems.
1.5 SUMMARY OF CHAPTERS
This document is organized in the following sections and
chapters:
Chapter 1 - Introduction
Chapter 2 - Turbidity Requirements
This chapter presents the turbidity monitoring,
reporting, and recordkeeping requirements for
conventional, direct, slow sand, diatomaceous earth, and
alternative filtration technologies.
Chapter 3 - Turbidity Sampling Methods and
Turbidimeters
This chapter presents information on approved turbidity
sampling methods, and on the operation, maintenance,
and calibration of turbidimeters.
Chapter 4 - Data Collection and Management
This chapter provides information and tools for
collecting and managing turbidity data. Worksheets are
presented that can be used for recording and reporting
data to the State.
Chapter 5 - Filter Self-Assessment
This chapter provides a thorough explanation of the
filter self-assessment process, including analyses of a
typical filter profile, hydraulic loading, backwash
practices, examining filter media, and other issues
related to the filter.
Chapter 6 - Comprehensive Performance
Evaluation (CPE)
This chapter briefly describes the CPE process and
when a CPE is required. Systems can obtain detailed
information on the CPE process in the EPA Handbook
Optimizing Water Treatment Plant Performance Using
the Composite Correction Program, 1998 Edition (EPA
625-6-91-027).
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1. Introduction
Contents of Document
Chapter 7 - Turbidity and the Treatment
Process
This chapter explains why turbidity is used as a
measurement for treated water quality and why
pathogens must be removed and/or inactivated. It also
discusses the treatment processes used to remove and/or
inactivate pathogens.
Chapter 8 - Treatment Optimization
This chapter describes how types of coagulation
chemicals and their feed rates, pH, source water
characteristics, and other factors influence the treatment
process. Guidelines are provided for the type and
typical doses of chemicals to be used to optimize the
treatment process.
Appendices
Appendix A - Glossary
Appendix B - Worksheets
Appendix C - Equations and Sample Calculations
Appendix D - Suggested Backwash Rates
Appendix E - Filter Self-Assessment Example
Report
Appendix F - Jar Tests
Appendix G - Example of an Operating Procedure
for Chemical Feed System
Appendix H - Example of an Operating Procedure
for Filters
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2. TURBIDITY REQUIREMENTS
In this Chapter:
Conventional and
Direct Filtration
Turbidity
Requirements
(Combined and
Individual Filter
Effluent)
Slow Sand and
Diatomaceous Earth
Filtration Turbidity
Requirements
Alternative Filtration
Turbidity
Requirements
Lime Softening Plants
40 CFR Sections
141.74(c)(l) and 141.551
2.1 WHAT ARE THE TURBIDITY
REQUIREMENTS FOR CONVENTIONAL
AND DIRECT FILTRATION SYSTEMS?
The LT1ESWTR requirements for combined filter effluent
monitoring are more stringent than those of the Surface Water
Treatment Rule, and the LT1ESWTR has new requirements for
individual filter effluent turbidity monitoring for conventional
and direct filtration plants. These new turbidity monitoring
requirements were established to control Cryptosporidium.
Systems must comply with the LT1ESWTR requirements by
January 1, 2005, except where otherwise noted.
2.1.1 Combined Filter Effluent Turbidity
Combined filter effluent is generated when the effluent water
from individual filters in operation is combined into one
stream. Figure 2-1 is a flowchart that summarizes the
requirements for combined filter effluent monitoring for
conventional and direct filtration plants.
Monitoring Requirements
Combined filter effluent turbidity must be measured every 4
hours during plant operation. The combined filter effluent
turbidity for conventional and direct filtration systems must be
less than or equal to 0.3 nephelometric turbidity unit (NTU) for
95 percent of the readings taken each month and may at no time
exceed 1 NTU (based on turbidity measurements recorded
every 4 hours). The frequency of monitoring may be reduced
for systems serving 500 or fewer persons to once per day if the
State determines that less frequent monitoring is sufficient to
indicate effective filtration performance.
Systems will want to check with their State on combined filter
effluent requirements because the State may require additional
monitoring.
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2. Turbidity Requirements
40 CFR Section 141.570
Conventional filtration,
as defined in 40 CFR
Section 141.2, is a series of
processes including
coagulation, flocculation,
sedimentation, and
filtration resulting in
substantial particulate
removal.
Direct filtration, as
defined in 40 CFR Section
141.2, is a series of
processes including
coagulation and filtration,
but excluding
sedimentation, that result
in substantial particulate
removal.
Reporting and Recordkeeping Requirements
Monthly reports on turbidity from conventional and direct
filtration systems due to the State by the 10th of the following
month must contain:
Total number of combined filter effluent turbidity
measurements taken during the month.
The number and percentage of combined filter
effluent turbidity measurements taken during the
month which were less than or equal to the system's
required 95th percentile limit of 0.3 NTU.
The date and value of any combined filter effluent
turbidity measurement taken during the month that
exceeded 1 NTU.
As required by the Public Notification Rule (40 CFR Section
141.203(b)(3)), if the combined filter effluent exceeds 1 NTU
at any time, the system must consult the Primacy Agency
within 24 hours. Systems also need to provide public
notification of violations of the 95th percentile limit as soon as
practical, but no later than 30 days after the system learns of the
violation (Tier 2 Public Notice).
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2. Turbidity Requirements
Figure 2-1. Combined Filter Effluent Provisions of the LT1ESWTR
for Systems Using Conventional or Direct Filtration
Does the system use either
surface water or GWUDI, filter, and serve fewer
than 10,000 persons?
Does the system
use conventional or direct
filtration?
No combined filter effluent
requirements under LT1ESWTR
System must comply with combined
filter effluent provisions for either
slow sand, diatomaceous earth or
alternative filtration.
Yes
All systems using conventional or direct
filtration must comply with combined filter
effluent requirements (ง 141.550).
Did the
system monitor combined
filter effluent turbidity at 4-hour
intervals?1
Was turbidity less than or equal
to 0.3 NTU in at least 95% of the measurements
taken for the month (ง 141.551(a))'
Did turbidity exceed 1 NTU at
any time (ง 141.551(b))?2
Did the system report
ed filter effluent measurem
the 10th of each month?
/Relevant monthly reporting^
\^ requirements satisfied J
1. As per the SWTR, 40 CFR Section 141.74 (c)(l), the State may reduce this monitoring frequency for systems serving
500 or fewer persons to one sample per day if the State determines that less frequent monitoring is sufficient to indicate
effective filtration performance.
2. System must consult with the Primacy Agency no later than 24 hours after learning of the violation in accordance with
the Public Notification Rule (40 CFR Section 141.203(b)(3)).
3. Systems must report to the State the total number of combined filter effluent turbidity measurements taken during the
previous month, the number and percentage of turbidity measurements that were less than or equal to 0.3 NTU, and date
and value of any turbidity measurements exceeding 1 NTU (40 CFR Section 141.570(a)).
4. Public notification is required per Appendix A to Subpart Q of 40 CFR Section 141.
August 2004
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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2. Turbidity Requirements
40 CFR Sections
141.560-563
For systems subject to
these requirements,
individual filter effluent
turbidity must be
continuously monitored
and results must be
recorded at least every 15
minutes.
2.1.2 Individual Filter Effluent Turbidity
Filtration is one of the most critical treatment processes for
particle and pathogen removal. The LT1ESWTR requires
Subpart H systems using conventional or direct filtration to
conduct continuous monitoring of the turbidity of individual
filters to provide information on each filter's performance.
Performance problems, indicated by an exceedance of certain
turbidity limits for specified time periods, trigger follow-up
actions. Follow-up actions vary from notification of the
Primacy Agency to having a Comprehensive Performance
Evaluation (CPE). Figure 2-2 summarizes the individual filter
monitoring and reporting requirements.
Monitoring Requirements
Under LT1ESWTR, if a system only consists of two or fewer
filters, it may conduct continuous monitoring of combined filter
effluent turbidity in lieu of individual filter effluent turbidity.
As a practical matter, this means if a system has only one filter,
filter effluent turbidity must be continuously monitored and
recorded at least every 15 minutes. Systems that have two
filters are not required to monitor individual filters if the
combined filter effluent turbidity from both filters is
continuously monitored and recorded at least every 15 minutes.
(Systems should check with their State to see if this is
acceptable.) Otherwise, the system is required to continuously
monitor and record individual filter effluent turbidity at least
every 15 minutes. If a system has three or more filters, each
individual filter effluent turbidity must be monitored and
recorded. Regardless of the number of filters, all systems must
record and report the combined filter effluent in accordance
with 40 CFR Sections 141.551 and 141.570 (see Section 2.1.1
of this document). Follow-up actions are triggered based on
exceedances of 15-minute interval values (even if readings are
taken more frequently for operational purposes). It is important
to note that State regulations for individual filter monitoring
and reporting may be more stringent. A brief summary of
LT1ESWTR monitoring requirements for the specified number
of filters is shown in Table 2-1. Figure 2-3 also provides an
illustration of individual and combined filter turbidity
monitoring requirements.
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
10
August 2004
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2. Turbidity Requirements
Individual filter effluent
turbidimeters must use
EPA Method 180.1,
Standard Method 2130B,
Great Lakes Instrument
Method 2, or Hach
FilterTrak Method 10133.
Table 2-1. LT1ESWTR Combined and Individual Filter
Effluent Turbidity Monitoring Requirements for
Conventional and Direct Filtration Systems
Number of
Filters
More Than 2
Monitoring Requirements
Individual filter effluent turbidity continuously
monitored and recorded at least every 15 minutes.
In addition, 4-hour turbidity readings must be
recorded. Monthly reports must be provided in
accordance with 40 CFR Sections 141.551 and
141.570.
Combined filter effluent turbidity continuously
monitored and recorded at least every 15 minutes
or individual filter effluent turbidity recorded at
least every 15 minutes. In addition, combined
filter effluent turbidity must be recorded every 4
hours and monthly reports provided in accordance
with 40 CFR Sections 141.551 and 141.570.
Individual filters are continuously monitored and
the results are recorded at least every 15 minutes.
In addition, combined filter effluent turbidity must
be recorded every 4 hours and monthly reports
provided in accordance with 40 CFR Sections
141.55 land 141.570.
The following also apply to continuous individual filter
turbidity monitoring (or for systems with two or fewer filters
that monitor combined filter effluent continuously):
In the event of the failure of continuous turbidity
monitoring equipment, the system must conduct grab
sampling every 4 hours until the equipment is replaced
or repaired. The system has 14 days to resume
continuous monitoring.
Monitoring must be conducted using an approved
method listed in 40 CFR Section 141.74(a). Approved
methods are EPA Method 180.1, Standard Method
21 SOB, Great Lakes Instrument Method 2, and Hach
FilterTrak Method 10133. Turbidimeters must conform
to one of these methods. More information on turbidity
sampling, including the approved methods mentioned
here, is provided in Chapter 3 of this manual.
Calibration of turbidimeters must be conducted using
procedures specified by the manufacturer.
Systems must keep records from individual filter
turbidity monitoring for at least 3 years.
August 2004
11
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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2. Turbidity Requirements
Figure 2-2. Individual Filter Effluent Turbidity Provisions of the LT1ESWTR
for Systems Using Conventional or Direct Filtration
Part 1. Individual Filter Effluent Monitoring Provisions
System is not required to do individual
filter monitoring under LT1ESWTR (IESWTR
applies if system serves > 10,000 persons)
Does the system use either
surface water or GWUDI, filter, and serve
fewer than 10,000 persons';
Does the system use
conventional filtration treatment
or direct filtration?
System is not required to do \
idual filter monitorinjj/
perform individual
conduct grab
sampling every
4 hours in lieu
of continuous
monitoring,
not to exceed
14 working
days following
failure of
equipment.
the system
reestablish
continuous
monitoring by
as there
a failure in continuous
turbidity monitoring
equipment?
Was
monitoring conducted
continuously at each filter and were the
results recorded at least everv
15 minutes?1-2
Did the
system report to State
within 10 days after end of month
that relevant monitoring was
conducted?
M/R VIOLATION
(Return to previous
diamond and complete
requirement)
Did any
individual filter turbidity
measurement from the same
filter exceed 1.0 NTU for
2 consecutive 15-minute
readings?4
System is in compliance with individual
filter provisions of the LT1ESWTR
See Part 2 on next page.
1. Systems with two or fewer filters may conduct continuous monitoring of combined filter effluent in lieu of individual filter effluent
turbidity monitoring.
2. Monitoring must be conducted using an approved method in 40 CFR Section 141.74(a). Calibration of turbidimeters must be conducted
using procedures specified by the manufacturer.
3. System has an M/R violation until the relevant requirement is completed (such as conducting a filter self-assessment). Public
notification is required per Appendix A to Subpart Q of 40 CFR Section 141.
4. For systems with two or fewer filters, combined filter effluent can be substituted for individual filter effluent (see footnote 1). If a filter
self-assessment is triggered, the self-assessment must be conducted on both filters.
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
12
August 2004
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2. Turbidity Requirements
Figure 2.2 (cont.) Individual Filter Effluent Turbidity Provisions of the LT1ESWTR
for Systems Using Conventional and Direct Filtration
Part 2. Individual Filter Effluent Turbidity Exceedance Follow-up Actions
From Part 1
(previous page)
M7R VIOLATION3
(Return to previous
diamond and complete
requirement)
t
1
System must conduct
a self-assessment of the
filter within 14 days of
the exceedance and report
that self-assessment
was conducted unless a
CPE is required4
System must arrange to have
State or State-approved third
party conduct a Comprehensive
Performance Evaluation
(CPE) no later than 60 days
after exceedance and have the
evaluation completed and
submitted to the State no later
than 120 days following exceedance.
Was any
individual filter
urbidity measurement > 2.
NTU for 2 or more consecutive
15-minute readings for
two consecutive
months?4
Did this
exceedance occur at
the same filter in three
consecutive
months?4 .
System is in compliance with individual
filter provisions of the LT1ESWTR
1. Systems with two or fewer filters may conduct continuous monitoring of combined filter effluent in lieu of individual filter effluent
turbidity monitoring.
2. Monitoring must be conducted using an approved method in 40 CFR Section 141.74(a). Calibration of turbidimeters must be conducted
using procedures specified by the manufacturer.
3. System has an M/R violation until the relevant requirement is completed (such as conducting a filter self-assessment). Public
notification is required per Appendix A to Subpart Q of 40 CFR Section 141.
4. For systems with two or fewer filters, combined filter effluent can be substituted for individual filter effluent (see footnote 1). If a filter
self-assessment is triggered, the self-assessment must be conducted on both filters.
August 2004
13
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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2. Turbidity Requirements
Figure 2-3. Turbidity Monitoring Requirements for Conventional and Direct
Filtration Plants
To Clearwell
Record Combined
Filter Effluent Turbidity
every 4 hours
a)
For conventional and direct filtration systems with three or more filters:
individual filter turbidity effluent must be recorded at least every 15 minutes and
combined filter effluent must be recorded at least every 4 hours.
Record
Individual
Filter
Turbidity
OR
To Clearwell
To Clearwell
Record Combined Filter
Effluent Turbidity
every 4 Hours
b)
Record Combined Filter
Effluent Turbidity at
least every 15 minutes
and every 4 hours
For systems with two filters: combined filter effluent turbidity or individual filter
effluent turbidity must be recorded at least every 15 minutes. In addition,
combined filter effluent turbidity must be recorded every 4 hours.
c)
Record Filter Effluent
> Turbidity every 15 minutes
and every 4 hours
For systems with one filter: filter effluent turbidity must be recorded at least
every 15 minutes and every 4 hours.
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
14
August 2004
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2. Turbidity Requirements
40 CFR Sections 141.570-
571
Reporting and Recordkeeping
Systems must report the following information to the State for
individual filter effluent monitoring:
Description of
Information to Report
(1) That the system
conducted individual filter
turbidity monitoring during
the month.
(2) The filter number(s),
corresponding date(s), and
the turbidity value(s) which
exceeded 1.0 NTU during
the month, but only if two
consecutive measurements
exceeded 1.0 NTU.
(3) If a filter self-
assessment is required, the
date that it was triggered
and the date that it was
completed.
(4) If a CPE is required, that
the CPE is required and the
date that it was triggered.
(5) Copy of the completed
CPE report
Frequency
By the 10
month.
of the following
By the 10th of the following
month.
By the 10th of the following
month (or 14 days after the
filter self-assessment was
triggered only if the filter
self-assessment was
triggered during the last
four days of the month). See
Chapter 5 for more
information on the filter
self-assessment process.
By the lO^of the following
month.
Within 120 days after the
CPE was triggered.
August 2004
15
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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2. Turbidity Requirements
40 CFR Section 141.5 63
Required follow-up actions
for individual filter
effluent turbidity.
An exceedance of the
individual filter effluent
turbidity values does not
constitute a treatment
technique violation.
However, failure to
conduct the appropriate
follow-up actions does
create a treatment
technique violation.
The following chart describes follow-up actions that may be
required based on the 15-minute readings:
If the turbidity of an
individual filter (or the
turbidity of combined
filter effluent (CFE) for
systems with 2 filters
that monitor CFE in lieu
of individual filters)
exceeds...
1.0 NTU for two or more
consecutive 15-minute
readings in 1 month...
1.0 NTU in two or more
consecutive 15-minute
readings for 3 consecutive
months...
2.0 NTU in two or more
consecutive 15-minute
readings for 2 months in a
row...
Then the system must.,
Report to the State by the 10th of the
following month and include the filter
number(s), corresponding date(s), the
turbidity value(s) that exceeded 1.0 NTU,
and the cause (if known) for the
exceedance(s).
Conduct a filter self-assessment of the
filter(s) within 14 days of the day the filter
exceeded the 1.0 NTU in two consecutive
measurements for the third straight month
unless a CPE is required. Systems with
two filters that monitor combined filter
effluent instead of individual filter effluent
must conduct a self-assessment of both
filters. The self-assessment must consist of
at least the following components:
assessment of filter performance;
development of a filter profile;
identification and prioritization of factors
limiting filter performance; assessment of
the applicability of corrections; and
preparation of a filter self-assessment
report.
Arrange for a CPE conducted by the State
or third party approved by the State not
later than 60 days following the day the
filter exceeded 2.0 NTU for two
consecutive measurements for the second
straight month. If a CPE has been
completed by the State or a third party
approved by the State within the 12 prior
months or the system and State are jointly
participating in an ongoing Comprehensive
Technical Assistance project at the system,
a new CPE is not required. If conducted,
the CPE must be completed and submitted
to the State no later than 120 days
following the CPE trigger date.
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
16
August 2004
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2. Turbidity Requirements
40 CFR Section 141.550
2.2 WHAT ARE THE TURBIDITY
REQUIREMENTS FOR SLOW SAND AND
DlATOMACEOUS EARTH FILTRATION
SYSTEMS?
The turbidity standards for slow sand and diatomaceous earth
filters did not change from the requirements in the Surface
Water Treatment Rule (40 CFR Sections 141.73(b) and (c)).
These technologies accomplish 2-log Cryptosporidium removal
with the turbidity limits set in the Surface Water Treatment
Rule.
2.2.1 Combined Filter Effluent Turbidity
Figure 2-5 summarizes the combined filter effluent monitoring
requirements for slow sand and diatomaceous earth filtration
systems.
Monitoring Requirements
Combined filter effluent turbidity must be measured every 4
hours that the system serves water to the public. The combined
filter effluent turbidity for slow sand and diatomaceous earth
filtration systems must be less than or equal to 1 NTU for 95
percent of the readings taken each month (unless the State has
approved a higher limit as described in 40 CFR Section
141.73(b)(l)) and may at no time exceed 5 NTU (based on
turbidity measurements recorded every 4 hours).
For slow sand filtration system of any size, the State may
reduce the sampling frequency to once per day if the State
determines that less frequent monitoring is sufficient to indicate
effective filtration performance.
For diatomaceous earth systems serving 500 or fewer persons,
the State may reduce the sampling frequency to once per day if
the State determines that less frequent monitoring is sufficient
to indicate effective filtration performance.
Reporting and Recordkeepinq Requirements
Monthly reports on turbidity from slow sand and diatomaceous
earth filtration systems due to the State by the 10th of the
following month must contain:
August 2004
17
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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2. Turbidity Requirements
While not required of
systems using slow sand
and diatomaceous earth
filtration, it is a good idea
to monitor individual
filters to identify any
individual filter problems
that could be masked by
monitoring only combined
filter effluent.
Total number of combined filter effluent turbidity
measurements taken during the month.
The number and percentage of combined filter
effluent turbidity measurements taken during the
month which were less than or equal to the system's
required 95th percentile limit of 1 NTU.
The date and value of any combined filter effluent
turbidity measurement taken during the month that
exceeded 5 NTU.
As required by the Public Notification Rule (40 CFR Section
141.203(b)(3)), if the combined filter effluent exceeds 5 NTU
at any time, the system must consult the Primacy Agency
within 24 hours.
2.2.2 Individual Filter Effluent Turbidity
Although there are no individual filter effluent turbidity
monitoring requirements for slow sand and diatomaceous earth
filters in LT1ESWTR, individual filter effluent turbidity
monitoring may help identify problems with an individual filter
that could be masked when the filtered effluent is blended with
filtered effluent from other, properly performing, filters.
Figure 2-4. Slow Sand Filter in Idaho
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
18
August 2004
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2. Turbidity Requirements
Figure 2-5. Combined Filter Effluent Provisions for Systems
Using Slow Sand or Diatomaceous Earth Filtration
Does the system use either
surface water or GWUDI, filter, and serve
fewer than 10,000 persons?
Does the system use
slow sand or diatomaceous
earth filtration?
No combined filter effluent
requirements under LT1ESWTR
System must comply with
combined filter effluent provisions
for either conventional, direct
or alternative filtration.
All systems using slow sand or diatomaceous earth filtration must comply
with combined filter effluent requirements as specified in the SWTR
Did the
system monitor combined filter effluent turbidity
at 4-hour intervals?1
Was turbidity less than or
equal to 1 NTU in at least 95% of the measurements
taken for the month?
Did turbidity exceed 5 NTU at any time?2
Did the system report
to the State by the 10th of each
month?3
Relevant monthly reporting
requirements satisfied.
1. As per the SWTR, 40 CFR Section 141.74 (c)(l), the State may reduce this monitoring frequency to one sample per day
for any systems using slow sand filtration or for systems using diatomaceous earth filtration serving 500 or fewer persons
if the State determines that less frequent monitoring is sufficient to indicate effective filtration performance.
2. System must consult with the Primacy Agency no later than 24 hours after learning of the violation in accordance with
the Public Notification Rule (40 CFR Section 141.203(b)(3)).
3. The total number of turbidity measurements taken during the previous month, the number and percentage of turbidity
measurements that were less than or equal to 1 NTU, and date and value of any turbidity measurements exceeding 5 NTU.
4. Public notification is required per Appendix A to Subpart Q of 40 CFR Section 141.
August 2004
19
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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2 Turbidity Requirements
40 CFR Sections 141.551,
141.552, and 141.570
Alternative filtration
technologies must provide
2-log Cryptosporidium
removal, 3-log Giardia
removal/inactivation, and
4-log virus
removal/inactivation.
2.3 WHAT ARE THE TURBIDITY
REQUIREMENTS FOR ALTERNATIVE
FILTRATION SYSTEMS?
Alternative filtration technologies are defined as technologies
other than conventional, direct, slow sand, and diatomaceous
earth filtration. Systems using alternative filtration
technologies such as cartridges (see Figure 2-6), bags, or
membranes must demonstrate (using pilot plant studies or other
means) to the State that they meet the following requirements:
2-log removal of Cryptosporidium oocysts;
3-log removal/inactivation of Giardia lamblia cysts
(referred to as Giardia} (also required by 40 CFR
Section 141.73(d) in the Surface Water Treatment
Rule); and,
4-log removal/inactivation of viruses (also required
by 40 CFR Section 141.73(d) in the Surface Water
Treatment Rule).
A system qualifying as an alternative filtration technology must
meet the turbidity limits established by the State by January 1,
2005. Figure 2-7 summarizes the requirements for alternative
technologies.
2.3.1 Combined Filter Effluent Turbidity
The State should establish the turbidity limits for the system
based on a demonstration that the system is required to conduct
under 40 CFR Section 141.552 (see previous paragraph).
Monitoring Requirements
Combined filter effluent turbidity must be measured every
4hours that the system serves water to the public. The
combined filter effluent turbidity for alternative filtration
systems must be less than or equal to the State-established limit
(not to exceed 1 NTU) for 95 percent of the readings taken
each month and may at no time exceed the State-established
maximum (not to exceed 5 NTU) for any reading. For
alternative filtration systems of any size, the State may reduce
the sampling frequency to once per day if the State determines
that less frequent monitoring is sufficient to indicate effective
filtration performance. Systems will want to check with their
August 2004
20
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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2. Turbidity Requirements
State on combined filter effluent requirements since the State
may require additional monitoring.
Reporting and Recordkeeping Requirements
Monthly reports on turbidity from alternative filtration systems
due to the State by the 10th of the following month must
contain:
Total number of combined filter effluent turbidity
measurements taken during the month.
The number and percentage of combined filter
effluent turbidity measurements taken during the
month which were less than or equal to the system's
required 95th percentile State-established limit (not
to exceed 1 NTU).
The date and value of any combined filter effluent
turbidity measurement taken during the month that
exceeded the State-established maximum limit (not
to exceed 5 NTU).
As required by the Public Notification Rule (40 CFR Section
141.203(b)(3)), if the combined filter effluent exceeds the
State-established maximum limit (not to exceed 5 NTU) at any
time, the system must consult the Primacy Agency within 24
hours.
2.3.2 Individual Filter Effluent Turbidity
Although there are no individual filter effluent turbidity
monitoring requirements for alternative filtration technologies
in LT1ESWTR, individual filter effluent turbidity monitoring
may help identify problems with an individual filter that could
be masked when blended with filtered effluent from properly
performing filters.
August 2004
21
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
-------
2. Turbidity Requirements
Figure 2-6. Cartridges Installed at a Small System
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
22
August 2004
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2. Turbidity Requirements
Figure 2-7. Combined Filter Effluent Provisions of the LT1ESWTR
for Systems Using Alternative Filtration Technologies
Does the system use either
surface water or GWUDI, filter, and serve
fewer than 10,000 persons';
Does the system use an
alternative technology (technology other than
conventional, direct, slow sand or
diatomaceous earth)1;
No
No
No combined filter effluent \
requirements under LT1ESWTR J
System must comply with combined N.
filter effluent requirements for \
conventional, direct, slow sand or i
diatomaceous earth filtration ./
System must demonstrate to the State that the alternative filtration technology, in combination with disinfection,
consistently achieves 2-log Cryptosporidium removal, 3-log Giardia removal and/or inactivation and 4-log virus
removal and/or inactivation.
7 ^""---^ No
dies? ^^^^^^
TT Violation4
Did the system momtor
combined filter effluent turbidity at
4-hour intervals';
Was turbidity
less than or equal to State-set limit
(not to exceed 1 NTU) in at least 95% of
the measurements taken
for the month?
id turbidity excee
State-set maximum (not to exceed 5 NTU)
at anv time?
Relevant monthly reporting
requirements satisfied.
1. As per the SWTR, 40 CFR Section 141.74 (c)(l), the State may reduce this frequency to one sample per day if the State
determines that less frequent monitoring is sufficient to indicate effective filtration performance.
2. System must consult the Primacy Agency no later than 24 hours after learning of the violation in accordance with the
Public Notification Rule (40 CFR Section 141.203(b)(3)).
3. The total number of turbidity measurements taken during the previous month, the number and percentage of combined
filter effluent turbidity measurements that were less than or equal to the State-set limit (not to exceed 1 NTU), and date and
value of any combined filter effluent turbidity measurements exceeding the State-set maximum value (not to exceed 5
NTU).
4. Public notification is required per Appendix A to Subpart Q of 40 CFR Section 141.
August 2004
23
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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2. Turbidity Requirements
40 CFR Sections 141.553
and 141.564
Systems that need to
acidify combined filter
effluent turbidity samples
should consult the State on
the proper procedure.
2.4 ARE THERE SPECIAL PROVISIONS FOR
SYSTEMS THAT PRACTICE LIME
SOFTENING?
Sometimes systems that practice lime softening may
experience elevated turbidities due to carryover of lime from
the softening processes. If this significantly affects filtered
effluent turbidities, systems may acidify representative
combined filter effluent turbidity samples prior to analysis
using a protocol approved by the State. EPA recommends that
acidification protocols lower the pH of samples to less than
8.3. The acid used should be either hydrochloric acid or
sulfuric acid of Standard Lab Grade. Care should be taken
when handling the acid. EPA recommends that systems
maintain documentation regarding the turbidity with and
without acidification, pH values (before and after
acidification), and the quantity of acid added to a given sample
volume.
For individual filter effluent turbidity requirements, systems
that practice lime softening may apply to the State for
alternative turbidity exceedance values. Systems must be able
to demonstrate to the State that the higher turbidity levels are
due to lime carryover only, and are not due to degraded filter
performance.
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
24
August 2004
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3. TURBIDITY SAMPLING METHODS AND
TURBIDIMETERS
In this Chapter:
Approved Turbidity
Methods
Sample Collection
Installation
Benchtop
Turbidimeters
On-Line
Turbidimeters
Calibration
Quality
Assurance/Quality
Control
^
See Chapter 2 for
monitoring, reporting, and
recordkeeping
requirements.
Remember, only
conventional and direct
filtration systems are
required to continuously
monitor individual filter
effluent turbidity.
3.1 INTRODUCTION
All filtered systems must measure the turbidity of combined
filter effluent, and conventional and direct filtration systems
with more than two filters must also measure individual filter
effluent turbidity. Because these measurements are used for
reporting and compliance purposes, accurate measurements
and the use of approved methods are extremely important. The
following sections describe approved methods, analytical
issues associated with turbidimeters, and quality assurance and
quality control issues. Because turbidity monitoring and
reporting are critical to compliance with the LT1ESWTR,
spare parts, spare units, and arrangements for rapidly obtaining
replacement or on-loan instruments are critical. Turbidity
monitoring must be performed as required and only limited
allowances are made to accommodate turbidimeter failure.
3.2 APPROVED TURBIDITY METHODS
A system will typically use a continuous monitoring
turbidimeter to monitor individual filter effluent, and either a
benchtop or a continuous monitoring turbidimeter for
combined filter effluent. If a system chooses to use continuous
monitoring units for monitoring combined filter effluent, it
must validate the continuous measurements for accuracy on a
regular basis using a protocol approved by the State.
August 2004
25
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
-------
3. Turbidity Sampling Methods and Turbidimeters
40 CFR Section 141.74
Approved methods for
measuring turbidity:
EPA Method 180.1
Standard Method
2130B
Great Lakes
Instrument Method 2
Hach FilterTrak
Method 10133
Figure 3-1. Continuous Monitoring
Turbidimeter for Individual Filter
Effluent Measurements
Currently, EPA has approved four methods for measuring
turbidity: EPA Method 180.1, Standard Method 21 SOB, Great
Lakes Instrument Method 2, or Hach FilterTrak Method
10133. These methods must be used regardless of whether the
turbidimeter is a benchtop model or an on-line unit. Each
method is described in Standard Methods, 20th Edition (1998)
and the Interim Enhanced Surface Water Treatment Rule
Turbidity Provisions Technical Guidance Manual. Table 3-1
lists commonly used turbidimeters, the corresponding
approved EPA method, and turbidimeter capabilities.
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
26
August 2004
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3. Turbidity Sampling Methods and Turbidimeters
Table 3-1. Sampling Methods and Monitoring Capabilities of Some Commonly
Used Turbidimeters
Brand1
Hach
Hach
LaMotte
Hach
Hach
HF Scientific
HF Scientific
Great Lakes
Model-
Application
21 OOP -Portable
2100NIS-
Benchtop
2020 - Portable
1720C - On-line
1720D - On-line
Micro 200BW -
On-line
MicroTOL -
On-line
Accu4
T53/8320-Low
Range- On-line
Approved
Sampling
Method
180.1
180.1
180.1
180.1
180.1
180.1
180.1
GLI2
Monitoring
Capability
N/A
N/A
N/A
15 -minute and
4-hour
15 -minute and
4-hour
4-hour
15 -minute and
4-hour
15 -minute and
4-hour
Form of
Output
Digital Readout
Digital Readout
Digital Readout
Digital, Printer
Output, and
Downloads to a
Computer
Digital, Printer
Output, and
Downloads to a
Computer
Digital, Printer
Output, and
Downloads to a
Computer
Digital, Printer
Output, and
Downloads to a
Computer
Digital, Printer
Output, and
Downloads to a
Computer
1 The listed brands and models are just a few of the units available to measure turbidity that
EPA is aware of. Please let us know if there are other manufacturers which were not
represented. Systems may use any turbidimeter provided it can be used with an EPA-
approved method.
Note: EPA does not endorse any particular manufacturer or product model.
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3. Turbidity Sampling Methods and Turbidimeters
You should install sample
lines so they are easy to
disconnect and clean.
Continuous flow through
the sample line is preferred
to prevent sediment build-
up in the sample line.
3.3 SAMPLE COLLECTION
Proper sample collection is important to ensure the sample is
representative of the water being analyzed. For both on-line
and grab sampling, the length of the sample piping or tubing
from the sampling location to the point where the sample is
drawn should be minimized. Long sample lines can lead to
problems with biological fouling and scaling which can impact
turbidity values. It is best to limit the length of sample lines to
10 feet or less. Long sample lines can also cause confusion due
to the lag time as the sample travels through the piping. The
longer the lag time, the more difficult it is to correlate turbidity
fluctuations to actual process changes that might be occurring.
For on-line units, lengthy sample runs can delay instrument
response time and may cause changes in sample quality (i.e.,
settling of particulate matter, increased opportunity for
biological growth).
Sample lines should be installed in a way that makes them easy
to disconnect and clean, because they sometimes plug. Care
should be taken to keep these lines open and clean. Rotameters
can be installed on the influent piping or on tubing to the
sample site to ensure good flow. The tubing or piping used for
the sample line should be made of PVC, copper, PTFE (teflon),
or a material recommended by the turbidimeter manufacturer.
You should carefully consider the location of the sample tap.
The tap should provide a representative sample of the water
being monitored. If an individual filter is being monitored,
locate the sample tap as close to the filter as possible. The
individual filter effluent tap should also be installed before the
filter-to-waste line. This way, operators can monitor filter
effluent turbidity during the filter-to-waste process so that
filters are not placed into service before their turbidity goal is
achieved. Sample taps or tubing/piping taps should be located
close to the centerline of individual filter effluent or combined
filter effluent pipes, not on the top or bottom of the pipe where
the turbidity of the water will not be accurately represented.
Samples taken from the bottom will often contain sediment,
while samples from the top may contain a greater number of air
bubbles. Ideally, sample taps should extend into the center of
the flow channel and should be angled into the water flow
between 0 and 45 degrees. Sample taps should also be located
away from items that disturb flow such as fittings, bends,
meters, or pump discharges (Logsdon et al., 2000).
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3. Turbidity Sampling Methods and Turbidimeters
You should avoid using
clear tubing for the sample
line because clear pipe is
prone to algae growth.
You should analyze
turbidity samples as
quickly as possible to
avoid issues related to
temperature changes and
settling.
Figure 3-2 illustrates two sample tap locations that could be
used for grab samples. If the tap located on the sample line is
used, then the line should be flushed to remove sediment prior
to taking a sample. The tap located on the on-line turbidimeter
could also be used and would typically not require flushing
prior to taking a grab sample.
Sample Line from Filter ^/^
\
\
\
\
Sample Tap off of Sample Line
On- Line
Turbidimeter
1 J w
V
CZ5
Sample Tap off of
Turbidimeter
"""" Provide Air Gap
Figure 3-2. Sample Locations for Removing Grab
Samples
In selecting sample tubing or piping, the required sample flow
rate and pressure should be considered. Sample lines of
insufficient diameter may not provide adequate flow to the
instrument and may be prone to clogging. Excessively large
diameter sample lines will delay the instrument response and
may permit settling of particulate matter. Line flushing valves
and ports may be necessary depending on the water being
sampled.
Some States require that a certified operator take all turbidity
samples. Check with your State on this requirement.
3.3.1 Timeliness of Sample Analysis
Samples analyzed by a benchtop turbidimeter should be
analyzed as quickly as possible after being taken to prevent
changes in particle characteristics due to temperature changes
and settling. Temperature changes can affect particles by
changing their behavior, by causing reactions that result in the
creation of new particles, and by reducing the number of
particles through solubilization. Operators are encouraged to
draw samples only when turbidimeters are ready to be
operated. Operators should not draw a sample and allow it to
sit while the instrument warms up or is being readied.
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Sampling Standard
Operating Procedures
should include:
Sample location
and frequency
Collection
methods
Sample handling
Necessary
logistical
considerations
Safety precautions
You should handle sample
cells with care and check
for cleanliness and
scratches prior to use.
Samples entering the turbidimeters should be at the same
temperature as the process flow samples. Changes in
temperature can cause precipitation or cause compounds to
become soluble and affect readings.
3.3.2 Sampling Strategy and Procedures
The procedure for conducting sampling should be laid out
clearly and concisely in Standard Operating Procedures (SOPs)
(discussed in Section 3.8.3) and should be incorporated in the
plant's operation and maintenance plan. It should include
information such as sampling location and frequency,
collection methods, sample handling, and any necessary
logistical considerations or safety precautions. Adherence to
proper techniques is important to minimizing the effects of
instrument variables and other interferences (Sadar, 1996).
Measurements will likely be more accurate, precise, and
repeatable if operators follow and incorporate the techniques
listed in this section.
All turbidimeter manufacturers emphasize proper techniques
and include detailed instructions in their literature. Water
treatment plant operators responsible for conducting turbidity
measurements are urged to review these instructions and
incorporate them into their SOPs. Specific instructions for
securing samples and measuring turbidity will differ for the
various instrument manufacturers and models, but there are
certain universally accepted techniques that should be used
when conducting measurements. The following paragraphs
highlight some of these techniques.
3.3.3 Handling of Benchtop Turbidimeter
Sample Cells
Sample cells used in benchtop turbidimeters should be handled
with absolute care to avoid contamination or damage, such as
marks and scratches, which might change the optical
characteristics of the glass. Scratches, fingerprints, and water
droplets on the sample cell or inside the light chamber can
cause stray light interference leading to inaccurate results. For
this reason, it is important to visually inspect the sample cell
every time a measurement is made and verify the cell is clean
and free of scratches. If there is a question as to whether a
sample cell is too scratched or stained, it should be discarded.
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Personal protective
clothing should be worn
when handling acid.
You should not add water
to acid when preparing a
dilute acid solution. The
acid should be added to the
water.
Cells should be cleaned by washing with laboratory soap,
inside and out, followed by multiple rinses with distilled or
deionized water and air-drying. Cells can also be acid washed
periodically. To acid wash, first wash the cell as just described
and rinse with a 1:1 hydrochloric acid solution or 1:1 nitric acid
solution (i.e., one part acid to one part distilled or deionized
water). If required to prepare the acid rinse solution, you
should use extreme caution. For this procedure, the acid should
be added to the water. You should not add water to acid. Then
rinse the sample cell with distilled or deionized water and let
air dry. Chromic acid may also be used to remove organic
deposits, but you should make sure the cell is rinsed thoroughly
to remove traces of chromium (Sadar, 1996). The frequency of
cleaning depends on the frequency of use of the sample cell
and will vary from plant to plant.
You may want to consider coating the sample cell exterior with
a special silicone oil to fill small scratches and mask the
imperfections in the glass. Since the silicone oil required for
this application should have the same refractive characteristics
as glass, it is recommended that the oil be obtained from the
instrument manufacturer. Care should be taken not to apply
excessive oil that could attract dirt or contaminate the sample
chamber in the instrument. Once the oil has been applied to the
cell, the excess oil should be removed with a lint-free cloth.
The result should be a sample cell surface with a dry
appearance, but with all imperfections filled with oil. Sample
cells should be handled at the top of the cell or by the cap to
avoid fingerprints or smudges. After a cell has been filled with
a sample and capped, the outside surface should be wiped with
a clean, lint-free absorbent cloth until it is dry.
Before placing the clean sample cell in a turbidimeter, gently
swirl the sample cell to reduce particle settling. You should
verify that there are no visible bubbles in the sample before
measuring turbidity.
The cells should be stored in an inverted position on clean
surfaces to reduce contamination by dirt and dust or stored
capped and filled with low-turbidity water (e.g., tap, distilled,
or deionized water). The cells should be replaced after their
useful life as recommended by the manufacturer or if damaged.
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At the Philadelphia Water
Department, new cells are
indexed and are not
allowed to vary by more
than 0.01NTU.
Philadelphia reports that as
many as one quarter of the
sample cells are never
used due to imperfections
(Burlingame, 1998).
You should allow the
benchtop turbidimeter to
stabilize prior to recording
a reading.
3.3.4 Orientation and Matching of Benchtop
Turbidimeter Sample Cells
Because imperfections in the sample cell glass can influence
light scattering, the cell should be inserted in the benchtop
turbidimeter with the same orientation each time it is used.
Matched sample cells should be used to minimize the effects of
optical variation among cells. If possible, it is best to use a
single sample cell for all measurements to minimize the
variability due to cell-to-cell imperfections. Once the
orientation of a cell has been established, the operator should
always use the same orientation when placing the sample cell
into the instrument. Suggested techniques for indexing and
matching cells are described below.
To index cells, follow steps 1 and 2; to match cells, follow
steps 1-3:
Step 1. Pour ultra-pure dilution or deionized water
(may be available from the manufacturer or a
laboratory) into a sample cell (there will be several
cells if the operator is performing matching) that has
been cleaned according to the techniques described
previously in this section.
Step 2. Place the sample cell in the turbidimeter.
Rotate the cell within the instrument until the display
reads the lowest value. Record the reading. Using a
marker or pen, place a mark on the top of the neck of
the sample cell. Do not put the mark on the cap. Place
a corresponding mark on the turbidimeter (or select a
mark on the turbidimeter that is in a fixed position and
can be used to align the sample cell each time). Use
these marks to align sample cells each time a
measurement is made.
Step 3. Select another sample cell, place it in the
turbidimeter, and rotate the cell slightly until the
reading matches that of the first sample cell (within
0.01 NTU). Using a marker or pen, place a mark on
the top of the neck of the sample cell. If unable to
match the readings, select a different sample cell.
Repeat the process until the appropriate number of
cells have been matched.
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Bubbles can act much like
particles and scatter light
resulting in a falsely
higher turbidity reading.
Some degassing options
may include:
Creating a partial
vacuum in the
sample line
Adding a
surfactant
Using an
ultrasonic bath
If the evaluation for matching cells determines that a cell is
corrupted, the cell should be discarded. Systems should
consider conducting this evaluation weekly.
3.3.5 Degassing the Sample
Water samples almost always contain substantial amounts of
air bubbles that can be released during turbidity measurements.
Bubbles are generated during the filling of a sample container,
occur due to released dissolved oxygen at increased water
temperature, or are due to chemical or biological processes.
Samples collected from a pressurized line may also release
dissolved oxygen and generate bubbles. Bubbles within a
sample act much like particles and can scatter light and cause
an incorrect measurement. Some on-line turbidimeters have
internal bubble traps and degassing capabilities to reduce the
amount of bubbles.
There are several options for removing bubbles from a sample
(a process called degassing) to reduce the effect they have on
measurements made using a benchtop turbidimeter. These
include application of a partial vacuum, addition of a
surfactant, and use of an ultrasonic bath (Hach et al., 1990).
These degassing methods can be difficult to use, and turbidity
measurements may be affected if not done correctly.
One method for degassing samples is to apply a partial vacuum
to the sample. A partial vacuum can be created using a syringe
or a vacuum pump. A 50-cubic-centimeter plastic syringe
fitted with a small rubber stopper is the easiest, most cost-
effective method. After the sample cell is filled with the
appropriate volume of sample, the stopper is inserted into the
top of the cell. As the syringe plunger is withdrawn, pressure
within the cell drops and gas bubbles escape. Some instrument
manufacturers and suppliers provide pre-made vacuum kits that
include syringes for degassing samples.
Another method is the addition of a surfactant. The surfactant
lowers the surface tension of the water and causes the air
bubbles to be released. Surfactants are recommended for high
turbidity water, such as raw water, and the surfactant used
should be supplied by the instrument manufacturer because of
the high variability of surfactants.
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If pumping is necessary,
you should select a pump
that does not contact the
water or excessively
agitate it.
The third method is to use an ultrasonic bath. The ultrasonic
bath is recommended when numerous air bubbles are present or
if the sample is viscous. The ultrasonic bath uses high
frequency sound waves that cause the air bubbles to collapse.
Using a partial vacuum or ultrasonic bath should be approached
with caution. Both of these techniques can result in more air
bubbles if not used properly (Hach et al., 1990).
3.4 INSTALLATION
Although turbidimeters are built to be durable, they should be
stored and operated in a safe and protected environment.
Moisture and dust can accumulate inside turbidimeters that are
not adequately protected and may affect the functioning of the
turbidimeter. Humidity should also be controlled to prevent
condensation inside the instrument. Turbidimeters should not
be located where they will be exposed to corrosive chemicals
or fumes because chemicals such as chlorine and acids can ruin
instrumentation. They should be protected from direct
sunlight, extreme temperatures, and rapid temperature
fluctuations. Finally, turbidimeters should be located in a
temperature-controlled environment at a consistent temperature
between 0ฐ C (32ฐ F) and 40ฐ C (104ฐ F).
On-line turbidimeters should be installed in accordance with
manufacturer instructions. The goal of proper installation is to
ensure correct operation and easy access for routine
maintenance and calibration. These units should also be firmly
mounted to avoid vibrations that may interfere with the
accuracy of the turbidity measurements.
Sample pumps can affect the turbidity measurements of on-line
units. It is good practice to have on-line turbidimeters near
sample collection points to avoid having to pump the sample
across the plant. A good sample tap location and plumbing
arrangement will minimize potential bubble formation. Most
on-line turbidimeters have the capability to eliminate minor
bubble interference through baffles or degassing chambers, but
if the problem is severe, the turbidity measurements may be
affected.
For on-line turbidimeters, the drain should provide easy access
for flow verification and collection of calibration and
verification samples. Flow rate and calibration verification
samples are important in establishing data validity. Therefore,
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Turbidimeters should be
checked after lightning
storms or any time that the
power has gone out.
Preventive maintenance
can extend the life of any
type of turbidimeter.
hard piping the turbidimeter drain without an airgap is not
recommended.
3.5 BENCHTOP TURBIDIMETERS
Benchtop units are used exclusively for grab samples. They
have glass sample cells (or "cuvettes") for holding the sample.
Measurements with benchtop units require strict adherence to
the manufacturer's sampling procedure to reduce errors from
dirt, scratches, condensation on glassware, air bubbles in the
sample, and particle settling. Operators should read and be
fully familiar with the operation manuals for all benchtop
turbidimeters used in the plant. Many maintenance and
operational issues are specific to the turbidimeter make and
model, and instruments are usually shipped with a thorough
user's manual.
Figure 3-3. A Benchtop Turbidimeter.
Benchtop turbidimeters should be connected to an
uninterruptible power supply or a constant voltage. Loss of
power or voltage fluctations can damage the turbidimeter and
result in faulty readings. Generally, the instrument should be
left on at all times (unless otherwise specified in the user's
manual), otherwise the instrument may require a warm-up
period before sample analysis. The need for an uninterruptible
power supply and leaving the instrument on at all times will
depend on the site-specific application of the benchtop
turbidimeter (e.g., is the benchtop turbidimeter used for
measuring combined filter effluent on a regular basis, backup,
or to measure raw water turbidity?).
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You should not touch the
optical components with
bare hands. (Soft cotton
gloves are recommended.)
Good working
turbidimeter = accurate
and reliable turbidimeter
measurements.
3.5.1 Preventive Maintenance
Preventive maintenance should be conducted on all benchtop
turbidimeters. Preventive maintenance includes procedures
that are regularly scheduled, even when there are no apparent
problems with the instrument. Systems should follow the
preventive maintenance schedule recommended by the
instrument manufacturer. Manufacturers' procedures identify
the schedule for servicing critical items to minimize downtime
of the instrument.
The preventive maintenance program should include:
Regular battery checks.
Maintenance of a sufficient stock of spare instruments,
spare parts, and supplies.
Regular (such as monthly or quarterly) inspection of
the cleanliness of bulbs and lenses. Remember when
cleaning the lenses, light sources, and other instrument
components, you should use appropriate materials
recommended by the manufacturer to avoid scratches
and dust accumulation. You should recalibrate the
instrument after the cleaning procedure is complete.
Annual replacement of incandescent turbidimeter
lamps. You should replace lamps more frequently if
recommended by the manufacturer. You should
recalibrate the instrument whenever optical
components (e.g., lamp, lens, photodetector) of the
turbidimeter are replaced.
Recording of calibrations, bulb replacements, and any
other maintenance in a maintenance log to ensure
consistency in measurements and performance.
In addition, systems may consider annual servicing of
benchtop turbidimeters by a third party, preferably a
manufacturer's representative or technical assistance provider.
However, servicing by a third party may not always be
desirable or affordable.
Benchtop turbidimeters, like most instruments, have a limited
service life. Various elements in the instrument can deteriorate
over time and with repeated use. Daily usage can result in
wear on electronics due to movement and temperature.
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3. Turbidity Sampling Methods and Turbidimeters
Keeping a spare benchtop
turbidimeter on hand at all
times could save time and
money in the long run.
Microprocessor-based electronics are also prone to memory
loss during power supply fluctuations. Manufacturer's service
personnel can often provide insight on instrument life and can
make recommendations for specific maintenance items. Most
manufacturers have a technical support hotline and can provide
expert advice about turbidimeters. Since turbidimeters have
become an integral part of water treatment plant operation and
reporting, the system should maintain instruments and budget
for replacements.
3.5.2 Corrective Maintenance
Corrective maintenance should be carried out according to the
manufacturer's instructions. You should not make repairs to
the benchtop turbidimeter unless they are specified in the
instruction manual. Even if a repair can be made in-house,
consider sending the unit back to the manufacturer for repair.
The warranty may become void if repair is performed in-
house. You should keep track of maintenance and repair on a
log sheet for each unit. Even if a unit is sent away for repairs,
required turbidity monitoring must still be performed and
recorded. Therefore, systems should consider keeping a spare
turbidimeter on hand.
Always recalibrate the instrument after any significant
maintenance or cleaning procedure, but only as directed by the
manufacturer.
Any maintenance that is done should be documented and the
record kept in a designated place (such as next to the
instrument or in an operation and maintenance manual).
Maintenance procedures and schedules for equipment used
should always be available to the staff that conducts the
maintenance. A sample maintenance form for recording
maintenance milestones for bench-top turbidimeters is
provided in Table 3-2. Blank sample maintenance forms can
be found in Appendix B.
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Table 3-2. Sample Maintenance Form
Instrument: Benchtop in Lab
Date
1/8/05
1/16/05
1/23/05
Verification
^
^
^
Acceptable/
Unacceptable
Acceptable
Unacceptable
Acceptable
Maintenance
Performed
None
Changed Bulb
Replaced sample cell
Initials
S.S.
S.S.
T.T.
Comments
Bulb was
bad
For further information
regarding on-line
turbidimeter requirements
and recommendations,
refer to the American
Society for Testing and
Materials (ASTM)
Standard D6698-01.
3.6 ON-LINE TURBIDIMETERS
On-line turbidimeters are process instruments that continuously
sample a side stream split-off from the treatment process. The
sample flows through the on-line instrument for measurement
and then is wasted to a drain or recycled through the treatment
process.
The flow rate through on-line turbidimeters should be set in
accordance with manufacturer specifications. The sample flow
should be as constant as possible without variations due to
pressure changes or surges. Installation of a flow control
device such as a rotameter on the sample line can control
fluctuations.
To the extent possible, turbidimeter samples should be
obtained directly from the process flow and not pumped to a
remote instrument location. Pumped samples can be
non-representative of the process flow due to changes in the
character of particles caused by the pump or the addition of
bubbles due to rapid pressure changes. If pumping is required,
the use of peristaltic pumps is desirable, because they have the
least impact on particles in the sample.
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3. Turbidity Sampling Methods and Turbidimeters
Preventive maintenance
can save time and money
in the long run.
Figure 3-4. The Hach 1720C On-Line Turbidimeter
3.6.1 Preventive Maintenance
Preventive maintenance should be conducted on all
instruments. Preventive maintenance includes procedures that
are regularly scheduled, even when there are no apparent
problems with the instrument. Systems should follow the
preventive maintenance schedule recommended by the
instrument manufacturer. Manufacturers' procedures identify
the schedule for servicing critical items to minimize downtime
of the measurement system.
The preventive maintenance program should include:
Regular battery checks.
Maintenance of a sufficient stock of spare
turbidimeters, spare parts, and supplies.
Routine inspections of turbidimeters and sample lines
for scaling, algae, and cleanliness.
Recalibration of the instrument whenever maintenance
is performed.
Recording of any maintenance, calibration, or
verification on a form or in a log book to ensure
consistency in measurements and performance.
Systems may consider annual servicing of turbidimeters by a
third party, preferably a manufacturer's representative or
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Cracks or biological
growth in the sample line
can affect turbidity
readings.
When calling a technical
support hotline, it is
helpful to have available
the model number of the
turbidimeter and
information on process
conditions that may be
adversely affecting the
instrument.
technical assistance provider. However, servicing by a third
party may not always be desirable or affordable.
A regular cleaning schedule ensures proper operation of on-
line turbidimeters. On-line turbidimeters should be cleaned
according to the manufacturer's instructions. A weekly
inspection is recommended, but the frequency may vary
depending on instrument location and water quality. A
turbidimeter that measures warm or turbid raw water samples,
or that is mounted in a dusty area, may need more frequent
cleaning. Items to inspect and clean include, but are not
limited to, lenses, light sources, sample reservoirs, air bubble
traps, and sample lines. Clean lenses, light sources, and other
glassware with appropriate materials to avoid scratches and
dust accumulation. During maintenance, care needs to be
taken not to touch the surface of any bulbs or detectors without
proper covering on the fingers. Soft, clean cotton gloves
should be worn when changing bulbs or detectors. The
instrument should be recalibrated after any significant
maintenance or cleaning. Also, the condition of the sample
line should be checked for cracks or biological growth. When
cleaning the sample line, you should make sure the line is
flushed thoroughly before reconnecting it to the turbidimeter.
3.6.2 Corrective Maintenance
On-line turbidimeters, like most instruments, have a limited
useful service life. Various elements in the instrument can
deteriorate over time and with repeated use. Daily usage can
result in wear on electronics due to movement and temperature.
Microprocessor-based electronics are also prone to memory
loss during power supply fluctuations. Many on-line units with
unsealed sensor electronics are vulnerable to damage by
outside contamination and splashing. Service personnel can
often provide insight on instrument life and can make
recommendations for specific maintenance items. Most
manufacturers have a technical support hotline where expert
advice about on-line turbidimeters can be obtained. Since
turbidimeters have become an integral part of water treatment
plant operation and reporting, it is important to maintain
instruments and budget for replacements.
Any maintenance that is done should be documented.
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Calibration - A
procedure that adjusts or
checks the accuracy of an
instrument (turbidimeter)
by comparison with a
standard (primary
standard) or reference.
Verification - A
procedure using secondary
standards to verify the
calibration of an
instrument (turbidimeter).
Consult the turbidimeter
owner's manual to
determine proper
calibration procedures
associated with the
instrument.
3.7 CALIBRATION AND VERIFICATION OF
TURBIDIMETERS
Calibration is an essential part of accurate turbidity
measurement. Calibration refers to the process of
programming a turbidimeter to read the turbidity of one or
more solutions of known turbidity value (called primary
standards). Once calibrated, the unit should provide accurate
measurement of the turbidity of a water sample.
Secondary standards are used for verification. If verification
indicates significant deviation from the secondary standard
stock solution (for example, greater than ฑ10 percent for 1
NTU standard solutions), you should thoroughly clean the
instrument and recalibrate it using a primary standard. If
problems persist, the manufacturer should be contacted.
Turbidimeters, like all instrumentation, need to be calibrated
periodically to ensure that they are working properly and
providing true and accurate readings.
Calibration procedures for one turbidimeter may not be the
same for another turbidimeter. Therefore, you should make
sure the procedures you are using are for the turbidimeter's
particular:
Manufacturer;
Model name and/or number;
Parameters to be calibrated;
Range to be calibrated; and,
Acceptance criteria.
After calibration, you should verify instrument performance
with a secondary standard or by comparison with another
properly calibrated instrument. If the instrument has internal
electronic diagnostics designed to assist in determining proper
calibration, the operator should use these tools to verify proper
calibration and operation.
If verification indicates significant deviation from the
secondary standard (ฑ10 percent for 1 NTU standard
solutions), the instrument should be thoroughly cleaned and
recalibrated using a primary standard. If problems persist, the
manufacturer should be contacted. Regardless of verification
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You should realize that
some instruments have
been designed and
calibrated on specific
primary standard(s). For
optimal results, users
should contact the
manufacturer of the
instrument to determine
the recommended primary
standard to be used for
calibration.
results, turbidimeters should be calibrated with primary
standards at least quarterly or more frequently if specified by
the manufacturer.
You should not calibrate on-line instruments by comparison
with a bench-top turbidimeter. It has been determined that
this procedure is likely to introduce unacceptable levels of
error into the calibration. However, verification by comparison
is acceptable.
3.7.1 Calibration and Verification Standards
A known standard must be used to conduct a primary
calibration. Standards are materials with a known value which,
when placed in the instrument, should be used to adjust the
instrument to read the known value.
There are a variety of standards on the market today, which are
used to calibrate turbidimeters. They are most often
characterized as primary, secondary, or alternative standards.
Standard Methods, 20th Edition (1998), describes a primary
standard as one that is prepared by the user from traceable raw
materials, using precise methodologies and under controlled
environmental conditions. Secondary standards are defined as
standards a manufacturer (or an independent testing
organization) has certified to give instrument results equivalent
(within certain limits) to results obtained when an instrument is
calibrated with a primary standard.
EPA recognizes the following three standards for approved use
in the primary calibration of turbidimeters:
Formazin (user prepared and commercially produced);
AMCO-AEPA-1ฎ Microspheres; and,
STABLCALฎ (Stabilized Formazin).
In addition, EPA recognizes secondary standards for use in
monitoring the day-to-day accuracy of turbidimeters by
checking the calibration. This check is used to determine if
calibration with a primary standard is necessary. Secondary
standards are used to check or verify whether an instrument
produces measurements within acceptable limits around a
nominal value (typically +10 percent). Examples of secondary
standards are:
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Ensure the standards used
for calibration and
verification are in the
appropriate ranges.
GELEXฎ;
Glass/ceramic cubes; and,
Manufacturer-provided instrument-specific secondary
standards.
Standard Methods, 20th Edition (1998), and EPA differ in their
definitions of each of these standards. The need to reconcile
the definitions and differences between primary and secondary
standards will be a continuing issue. It has been recognized
that the standards need to be unbiased, easy to use, safe,
reproducible, and available for a range of turbidities. Future
efforts of the Agency, in concert with other organizations and
manufacturers, will focus on ensuring the most appropriate,
variation-free, and technologically feasible standards are
available and used for calibration of turbidimeters. Tables 3-3
and 3-4 contain a list of commonly used turbidimeters and the
calibration standard.
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Table 3-3. Some Commonly Used Primary Calibration Standards and
Turbidimeters
Brand1
Hach
Hach
LaMotte
Hach
Hach
HF Scientific
HF Scientific
Great Lakes Instruments
International
Model - Type
21 OOP -Portable
2100NIS-Benchtop
2020 - Portable
1720C- On-line
1720D- On-line
Micro 200 - On-line
Micro TOL - On-line
Accu4 T53/8320 -
Low Range - On-line
Primary Calibration
Standard Formula2
Formazin or StableCal
Formazin or StableCal
AMCO 2020 Turbidity
Standards or Formazin
Formazin or StableCalฎ
Formazin or StableCalฎ
Formazin
Formazin
Formazin - Primary Calibration
not Required3
1 The listed turbidimeters are just a few of the units available to measure turbidity that EPA is aware of. Please
let us know if there are other manufacturers which were not represented. Other turbidimeters can be used
provided they can be used with an EPA approved method.
2 Always consult the manufacturer for proper calibration formulas. Manufacturers typically supply these
formulas.
3 Practical lifetime calibration is provided by GLFs patented 4-beam ratiometric measurement method: US EPA
approved GLI Method 2. After performing initial calibration, only periodic verification of calibration is
required.
Note: EPA does not endorse any particular manufacturer or product model.
Table 3-4. Some Commonly Used Secondary Calibration Standards and
Turbidimeters
Brand1
Hach
Hach
LaMotte
Hach
Hach
HF Scientific
HF Scientific
Great Lakes Instruments
International
Model - Type
21 OOP -Portable
2100NIS-Benchtop
2020 - Portable
1720C- On-line
1720D- On-line
Micro 200 - On-line
Micro TOL - On-line
Accu4 T53/8320 -
Low Range - On-line
Secondary Calibration
Standard Formula2
Gelexฎ
Gelexฎ
No secondary standards
ICE-PIC Calibration Module
ICE-PIC Calibration Module
HF Scientific Calibration Set
HF Scientific Calibration Set
Cal-Cube
1 The listed turbidimeters are just a few of the units available to measure turbidity that EPA is aware of. Please
let us know if there are other manufacturers which were not represented. Other turbidimeters can be used
provided they can be used with an EPA approved method.
2 Always consult the manufacturer for proper calibration formulas. Manufacturers typically supply these
formulas.
Note: EPA does not endorse any particular manufacturer or product model.
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Suggested tips for
calibration:
>^ Use current and correct
standards
>^ Use clean cells
>^ Record all calibrations
S Perform calibration
consistently
S Check with the
turbidimeter
manufacturer or State
with questions
3.7.2 Conducting the Calibration
Most turbidimeters are calibrated before leaving the factory.
As described previously, turbidimeters, like most
instrumentation, tend to lose accuracy over time due to a
variety of factors, making periodic calibration very important to
maintain accurate measurements. The most important point to
remember is:
Calibration must be conducted using procedures specified by
the manufacturer.
Manufacturers differ in the steps to conduct a calibration, but
the following points should be considered when calibrating a
turbidimeter:
Standards should be checked to ensure they have not
expired. You should not pour a standard back into its
original container.
Secondary standards may be different from the system's
primary standard.
Care should be taken when preparing Formazin or
another standard. If a spill occurs, you should clean it
up immediately according to the Material Safety Data
Sheets (MSDSs) provided with the chemicals.
You should inspect the cell for scratches and chips prior
to pouring the solution into the cell (specific to
benchtop and portable units).
You should make sure the cell is lined up properly
according to the indexing (specific to benchtop and
portable units). You should be sure not to scratch the
tube when inserting it, and you should ensure that the
cell is free of dust, smudges, and scratches.
When obtaining the reading, you should write the value
legibly onto a form similar to the one found in Table 3-
5. (Blank forms are available in Appendix B.) A
separate calibration checklist should be used for each
instrument. You should make sure to record the date of
the calibration, the individual conducting the
calibration, the value, and any peculiar situations or
deviations from normal calibration procedures (e.g.,
switch to a new lot of Formazin, switch in standards,
use of a new cell). These measurements will indicate
whether the performance of a turbidimeter is in
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Due to the importance of
accurate and reliable
turbidity measurements,
adequately training new
operators on calibration
and verification procedures
is very important.
question. For example, if for 6 months a turbidimeter
reads approximately 20.152 when calibrated using
polystyrene beads and one morning it reads 25.768, this
change could be an indication that the bulb in the
turbidimeter has a problem. Conversely, if the standard
in use was switched that morning, the resulting change
might be due to the change in standards.
You should conduct the calibration the same way each
time. Variations in how the calibration is conducted
could yield inaccurate measurements.
Individuals should be trained on the calibration
procedures. Systems should create SOPs to be read,
learned, and followed by operators at the plant.
The turbidimeter manufacturer is the best resource for
specific calibration techniques applicable to the
turbidimeter.
The State may have more information about proper
calibration standards and requirements.
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Table 3-5. Example Calibration Checklist
CALIBRATION CHECKLIST
Instrument: Turbidimeter #3
Date
3/28/05
6/29/05
9/30/05
12/27/05
3/27/06
6/23/06
Initials
AZ
AZ
AZ
AZ
AZ
AZ
Recorded
Value
(NTU)
20.127
20.183
20.156
19.980
20.062
20.168
Value of Standard
(NTU)
20.000
20.000
20.000
20.000
20.000
20.000
Comments
new lot of formazin used
You should calibrate
turbidimeters at least
quarterly, or more
frequently if specified by
the manufacturer.
3.7.3 Calibration and Verification Frequency
and Procedures
Calibration Frequency and Procedures
Both benchtop and on-line turbidimeters should be thoroughly
cleaned with the appropriate cleaning solution and calibrated
with primary standards at least quarterly (or more frequently if
specified by the manufacturer), even if there do not appear to
be any problems with the instrument. Calibration schedules
should be kept in the plant's operation and maintenance
manual or other designated place. The State or primacy
agency may have more information about the appropriate
protocol. Specific calibration procedures should be developed
for each individual instrument location. Suggested guidelines
include:
Selecting a frequency for full re-calibration of
instruments with primary standards.
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You should use fresh
standards when
performing calibrations.
Performing primary calibration on all turbidimeters at
least quarterly.
Performing primary calibration on any turbidimeter
that has drifted 10 percent from the value assigned to
the standard used for secondary calibration.
Identifying and scheduling in advance the dates for
full turbidimeter calibration and marking them on the
plant calendar or work scheduling chart.
Making preparations and maintaining adequate
supplies to prevent delays in the calibration schedule.
It is important to keep an appropriate stock of
standards. Due to the limited shelf life of various
standards, the age of the stored standards should be
monitored so they can be replaced or reformulated as
needed.
If you have several operators, assigning calibration
duties to a select group of individuals, and making it
one of their standard activities. All appropriate
individuals/operators should be trained in conducting a
calibration in the event that one of the regular
individuals is not available.
Creating an SOP for conducting a calibration and
posting it near the turbidimeter.
Table 3-6 can be used as a guide for scheduling calibration of
on-line turbidimeters.
Verification Frequency and Procedures
EPA recommends that systems using on-line turbidimeters for
combined filter effluent monitoring verify the calibration on a
weekly basis. Less frequent verification may be appropriate
for turbidimeters monitoring individual filter effluent turbidity
because on-line combined filter effluent turbidimeters that
monitor the collective individual filter effluent turbidities are
verified more frequently. Still, EPA recommends verification
be conducted for individual filters at least once per month.
Suggested guidelines include:
Selecting a frequency for checking (verifying)
instrument calibration with secondary standards.
Making preparations and maintaining adequate
supplies to prevent delays in the verification schedule.
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QA/QC = Quality
Assurance/Quality Control
It is important to keep an appropriate stock of
standards. Due to the limited shelf life of various
standards, the age of the stored standards should be
monitored so they can be replaced or reformulated as
needed.
If you have several operators, assigning verification
duties to a select group of individuals, and making it
one of their standard activities. All appropriate
individuals/operators should be trained in conducting a
verification in the event that one of the regular
individuals is not available.
Creating an SOP for conducting a verification and
posting it near the turbidimeter.
Table 3-6 can be used as a guide for scheduling verification of
on-line turbidimeters.
Table 3-6. Suggested On-line Turbidimeter
Calibration and Verification Schedule
Monitoring Location
All Locations
Individual Filter
Effluent
Combined Filter
Effluent
Procedure
Calibration
Verification
Verification
Recommended
Frequency
Quarterly*
Monthly or
Weekly
Weekly
* If the manufacturer specifies more frequent calibration, 40 CFR
Section 141.560(b) requires you to do so.
3.8 QUALITY ASSURANCE / QUALITY
CONTROL
Systems may want to establish plans to ensure that
measurements are being made accurately and consistently.
Using proper techniques and equipment is an important part of
conducting proper turbidity measurements, but operators
should be aware of other factors in the process that may lead to
poor-quality data. Such factors include poor lab techniques,
calculation mistakes, malfunctioning or poorly functioning
instrumentation, and out-of-date or deteriorated chemicals.
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Development of a quality assurance and quality control
(QA/QC) program can help ensure that lapses leading to
inaccurate measurements or erroneous reporting do not occur.
Systems should maintain records and logs of all turbidimeter
maintenance activities. Systems may also want to consider
separate log books for each turbidimeter. Separate log books
may allow the operators to better track the performance of
each turbidimeter and could help them recognize instruments
that drift out of calibration and may need to be replaced.
Separate log books may also assist future operators by tracking
maintenance procedures, such as the frequency of cleaning. In
some situations, however, separate log books for each
turbidimeter may not be the best option. Ultimately, systems
should determine what turbidimeter tracking method works
best for them.
3.8.1 QA/QC Organization and
Responsibilities
A QA/QC plan should be clearly organized. For larger
systems with more personnel, this plan should include an
organizational chart with a section that assigns responsibilities
to specific personnel for each part of the plan. This section
should include a list of personnel positions (by title) and the
responsibilities associated with each position. The appropriate
training or skills necessary for each of the positions listed
should also be included.
3.8.2 QA/QC Objectives
The objectives of the QA/QC program should be laid out and
understood by management and staff members. Systems may
wish to include one primary objective, followed by a number
of goals that relate to the objective. Objectives should be
specific and clear. An example might look like the following:
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SOP = Standard Operating
Procedure
Example QA/QC Plan
The primary objective of the QA/QC program is to ensure
that turbidity measurements are accurate and consistent.
Based on this objective, the goals of the QA/QC program
should include the following:
To adhere to proper sampling techniques as set forth
in the SOPs.
To maintain and operate all turbidimeters at the plant
properly in accordance with manufacturer instructions
and SOPs.
To calibrate instruments on a routine and as-necessary
basis.
To provide the necessary training to allow proper
operation and maintenance of turbidimeters
To communicate and report all turbidimeter
malfunctions, abnormalities, or problems that may
compromise the accuracy and consistency of turbidity
measurements.
3.8.3 SOPs
SOPs are a way to ensure that activities are accomplished in an
accurate, consistent manner and that each activity is
understood by all involved. SOPs should be kept as simple as
possible in order to ensure that each operator is consistent in
carrying out the task at hand. The title of the procedure should
be clear, concise, and descriptive of the equipment, process, or
activity. SOPs should be developed with input from staff
members, enabling them to effectively conduct work activities
in compliance with applicable requirements. Systems should
consider adopting SOPs for activities such as:
Cleaning turbidimeters;
Creating Formazin standards;
Calibrating turbidimeters;
Referencing index samples; or,
Verifying turbidimeters.
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Operators should be
involved in writing SOPs
to ensure the procedures
are accurate, feasible, and
make sense.
When instrument or
process changes occur that
affect procedures, you
should remember to update
the appropriate SOP to
reflect the change and
inform all affected
personnel.
Instructional steps should be concise, precise, and use the
following guidelines:
Each step should contain only one action.
Limits and/or tolerances for operating parameters
should be specific values that are consistent with the
accuracy of the instrumentation. Procedures should not
include mental arithmetic.
"Cautions" should be used to attract attention to
information that is essential to safe performance.
"Notes" should be used to call attention to important or
supplemental information. Notes present information
that assists the user in making decisions or improving
task performance.
Documentation methods should be incorporated as part
of the procedure including what data needs to be
recorded, whether the individual needs to sign or date
data, etc.
Identification and location of equipment necessary to
perform procedures outlined in SOPs should be
specified.
After developing an SOP, the author(s) should consider the
following questions:
Can the procedure be performed in the sequence as
written?
Can the user locate and identify all equipment referred
to in the SOP?
Can the user perform the procedure without needing to
obtain direct assistance or additional information from
persons not specified by the SOP?
Are words, phrases, abbreviations, or acronyms that
have special or unique meaning to the procedure
adequately defined?
Is there a need for special controls on data collection
and recordkeeping?
After completing the SOP it should be tested to the extent
possible. It is also a good idea to ask a technical reviewer to
verify the accuracy of the SOP. SOPs should be reviewed
routinely to determine if the procedures and requirements are
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Feedback from an audit in
the form of a report, staff
meeting, or other means
may aid operators.
still accurate. As equipment is replaced or other operational
changes are made, the SOPs should be reviewed and updated
accordingly.
The following is a simplified example of an SOP written for
the development of Formazin (4,000 NTU standard):
Example SOP for Preparing
4,000 NTU Formazin Standard
1. Dissolve 1.000 g of ACD grade hydrazine sulfate,
N2H4 H2SO4, in ultra filtered deionized water and
dilute to 100 mL in a Class A 100 mL volumetric
flask.
2. Dissolve 10.00 g of analytical grade
hexamethylenetetramine, (CH^eN^ in ultra filtered
deionized water and dilute to 100 mL in a Class A 100
mL volumetric flask.
3. Combine the 100 mL of hydrazine sulfate solution and
the 100 mL of hexamethylenetetramine solution in a
clean, dry flask that is large enough to allow mixing (a
500 mL flask is best) and mix thoroughly.
4. Let the mixture stand for 48 hours at approximately
75ฐ F (24ฐ C) in a covered container.
5. Store in a properly labeled bottle that displays the
standard (4,000 NTU Formazin), the date prepared,
the expiration date, and the preparer's name.
6. Store the suspension in a bottle that filters ultraviolet
light at a temperature between 40ฐ F (5ฐ C) and 75ฐ F
(24ฐ C). Before using the suspension, allow it to come
to room temperature.
3.8.4 Performance and System Audits
Performance and system audits should be conducted
periodically to determine the overall accuracy of the sampling
and measurement systems, as well as to test the accuracy of
each instrument. Performance audits may include reviews of
documentation and log books to make sure that they are legible
and complete. During the audit, all components of the
sampling and measurement procedures should be evaluated to
determine the best methods to be used for sampling,
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calibration, and other operational-related procedures. This
audit should include a careful evaluation of both field and
laboratory quality control procedures. It can verify that SOPs
work correctly, that the personnel understand the procedures,
and that procedures are carried out and recorded properly.
3.9 REFERENCES
1. APHA, AWWA, and WEF (American Public Health Association, American Water
Works Association, and Water Environment Federation). 1998. Standard Methods for
the Examination of Water and Wastewater, 20th edition. American Public Health
Association. Washington, D.C.
2. Burlingame, G.A., MJ. Picket, and J.T. Roman. 1998. Practical Applications of
Turbidity Monitoring. Journal AWWA, 90(8):57-69.
3. Hach, Clifford C., R.D. Vanous, and J.M. Heer. 1990. Understanding Turbidity
Measurement. Technical Information Series-Booklet No. 11, First Edition. Hach
Company. Loveland, CO.
4. Logsdon, G., A. Hess, P. Moorman, and M. Chipps. 2000. Turbidity Monitoring and
Compliance for the Interim Enhanced Surface Water Treatment Rule. AWWA Annual
Conference, Denver, CO.
5. Sadar, M. 1996. Understanding Turbidity Science, Technical Information Series-
Booklet No. 11, Hach Company. Loveland, CO.
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4. DATA COLLECTION AND MANAGEMENT
In this Chapter:
Data Collection
Methods
Data Management
Data Management
Tools
System Upgrades to
Consider
4.1 INTRODUCTION
Water systems subject to individual filter effluent turbidity
monitoring will be faced with the task of collecting and
managing much more data than they have in the past. The
requirements in the LT1ESWTR will result in more time
associated with collecting, analyzing, reporting, and managing
data. Upgrades to the treatment plant may also be needed to
install new or additional turbidimeters. Systems should
consider how best to collect and manage the data, what
additional equipment will be needed, and whether to use a
computer to assist with data collection and management.
Remember, only conventional and direct filtration systems are
required to continuously monitor individual filter effluent
turbidity. This chapter contains information on how conventional
and direct filtration systems may want to modify data collection
and management processes. Systems using filtration technologies
other than conventional and direct may find some useful
information (refer to Sections 4.4.2 and 4.4.3), but this chapter
primarily focuses on conventional and direct filtration systems.
4.2 DATA COLLECTION METHODS
Many methods of data collection exist. Systems may be using
grab samples and benchtop units to comply with the 4-hour
combined filter effluent readings. Readings from benchtop
units are typically recorded by hand or entered into a computer
without the use of data collection equipment. Grab samples are
generally not feasible for individual filter readings because
these samples must be taken every 15 minutes (for
conventional and direct filtration systems). Therefore, systems
will likely use on-line, continuous recording turbidimeters.
Continuous turbidity readings can be recorded by strip
recorders, data loggers, or supervisory control and data
acquisition (SCADA) systems.
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See Chapter 3 for more
information on calibrating
turbidimeters.
If using strip charts or
circular charts, you should
make sure the scale is set
such that values can be
read accurately.
For more information on
instrumentation and
control, refer to the
American Water Works
Association's (AWWA's)
manual Instrumentation
and Control, 3rd edition.
Data obtained from strip charts, data recorders, and SCADA
systems should be verified at least annually by comparing the
turbidimeter reading with the data recording device reading. If
verification indicates greater than iO percent deviation, the
electronic signal should be recalibrated according to the
manufacturer's instructions.
4.2.1 Strip Recorders and Circular Chart
Recorders
Strip chart and circular chart recorders are relatively well-
established equipment for recording data. The recording units
are set to obtain a reading at a timed interval. A pen records
the reading on paper. As additional readings are taken, the pen
moves back and forth (or up and down, in the case of a circular
recorder), recording the values that are being monitored.
Newer models include digital readouts and the capability to
transfer data to data loggers or other data acquisition systems.
The greatest disadvantage to using chart recorders is the
difficulty in incorporating data into electronic format and
archiving the data. Recorders also require the purchase of
replacement pens and charts.
Some paper chart recorders have the option of using either a
24-hour or 7-day chart. For individual filter monitoring,
systems should consider using a 24-hour chart that can record
measurements at 15-minute increments.
When using a chart recorder, the range should be set to allow
turbidities of 2.0 NTU to be accurately recorded for individual
filter effluent turbidity monitoring (see Section 2.1.2).
4.2.2 Data Loggers
Data loggers are "black boxes" that store data received from
input channels. The box records the data in memory that can
then be downloaded at a future time. Data loggers consist of
two distinct components: hardware and software.
Hardware
The units typically consist of a device containing solid state
memory encased in a plastic weatherproof enclosure. Units can
record either analog (actual numbers) or digital (a series of Os
and Is) inputs and also have an output port for downloading
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The combined filter
effluent must be recorded
every 4 hours and the
individual filter effluent
must be recorded at least
every 15 minutes for
conventional and direct
filtration systems.
However, better process
control may be achieved
by collecting
measurements more often
than 15 minutes.
data. Systems can be battery powered or connected to a power
supply. Nearly all systems contain lithium or other types of
batteries to keep memory active in the event of a power failure.
Software
Data loggers and acquisition devices have two software
components. First, specialized software is necessary to
configure the logging unit to take turbidity readings at the
desired frequency. The second part of the software retrieves
the data from the logger and exports it into a usable format on a
personal computer. Most companies offer packages that enable
users to export data to a computer and immediately plot and
graph the data to depict trends or produce reports. Data should
be downloaded to a computer at regular intervals, because data
loggers cannot store data indefinitely.
Several methods exist to transfer data from the logger to the
computer. Data acquisition systems are often equipped to be
compatible with telemetry to upload data to personal computers
via telephone, cellular telephone, or radio. Alternatively, either
a laptop or palmtop can be connected to the unit to download
information, or the data logger can be brought into the office
where the computer is located and plugged into one of the
input/output ports on the computer. Systems may want to have
a second data logger to take the place of the first logger when it
is being downloaded to avoid missing readings. Systems may
wish to schedule downloads to occur at times when a filter is
not in operation (e.g., when off-line or during backwash).
4.2.3 SCADA
SCADA systems are devices used for measurement, data
acquisition, and control. They consist of a central host (base
unit), one or more field gathering and control units (remotes),
and software that monitors and controls remotely located field
data elements. The base unit and the remote units are linked
via telemetry, and the base unit controls the remote units and
receives data. Control may be automatic or initiated by
operator commands.
SCADA systems can collect and display inputs from a variety
of sources and instruments, so the plant operator can monitor
the entire treatment process from one (or many) location(s).
SCADA systems are typically used for flow control, pH,
turbidity, and temperature monitoring, automated disinfection
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SCADA allows real-time
monitoring from a remote
location.
dosing, and a host of other functions. A SCADA system can be
configured to record individual filter effluent turbidity
measurements every 15 minutes, as required by the
LT1ESWTR for conventional and direct filtration systems.
LL - '.'.'''^f
'^yf'",.., ^i. ',";;,,*
Figure 4-1. Central SCADA Unit
SCADA systems can also be used to log and store data for
recording purposes. Signals are sent from remote instruments
located on the plant site to the base unit. This unit interprets all
of the different signals and displays real-time measurements. It
can be programmed to automatically transfer data to other
storage media such a tape drive or a Zipฎ disk.
Figure 4-2. SCADA Control Monitor
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As part of data
management, it is strongly
recommended that systems
frequently back up
electronic data, for
example, every 24 hours
and keep all hard copy
records.
Figure 4-3. SCADA Control Room
It is important for the operator to check the readings on the
SCADA against readings from the field. For instance, if a 4-20
milliamp (mA) signal comes out of a turbidimeter and into a
computer, two separate calibrations should be done. If a 20
mA raw signal (high end) correlates with 100 NTUs on the
turbidimeter but only 98 NTUs on the SCADA, this means
there is an accuracy and reporting problem. The reported
SCADA values are too low and the electronic signal will
probably need to be recalibrated.
4.3 DATA MANAGEMENT
There are two objectives for turbidity data management: (1)
regulatory compliance, and (2) process control and treatment
plant optimization. The turbidity reporting and monitoring
requirements are described in Chapter 2. In order to meet these
requirements, operators should understand three areas of data
management:
Data format;
Data storage; and,
Data analysis.
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Spreadsheets for turbidity
data management are
available from the
Partnership for Safe Water
(http://www.awwa.org/
science/partnership or 303-
347-6169) or in EPA's
Optimizing Water
Treatment Plant
Performance Using
Composite Correction
Program, 1998 Edition.
When a water system
understands the dynamics
of its filtration system by
analyzing turbidity data,
turbidity values that
deviate from the norm will
be easier to troubleshoot.
4.3.1 Format
Formatting the data into a usable form should be the first step
in effective data management. Operators should have the
ability to download data from their acquisition equipment in a
usable and manageable format. Data should be placed in one
of many different spreadsheet formats and databases. Certain
software packages allow users to create reports, tables, or
graphs based on the data. The key to selecting a format is the
ease with which the data can be viewed, manipulated, and
converted.
4.3.2 Storage
Storage of the data should be the next step in effective data
management. Maintaining data points for future analysis may
pose a problem due to the amount of disk space required.
Systems should consider the use of Zipฎ disks, data CDs, or
tapes to store data. Computer hard drives can be used to
temporarily store data while it is being analyzed, but the system
should have CD, tape, or Zipฎ disk backups in case the
computer crashes. You should contact the State or primacy
agency to coordinate data storage protocol.
4.3.3 Interpreting and Analyzing Data
Data analysis should be the last step in effective data
management. One good approach is to use a spreadsheet or
database that can generate reports, tables, graphs, and filter
profiles, as suggested in Section 4.3.1. The worksheets in
Appendix B can also be used. You should check with the State
before using the worksheets to make sure all the information
required by the State is included in the forms. Some States
have already created spreadsheet-based forms and could show
systems how to use them.
Analyzing turbidity data is useful because it allows systems to
determine how well a process is being controlled over time and
to identify and understand turbidity trends, which will assist in
plant optimization. With adequate data collection, systems
could evaluate post-backwash turbidity spikes for individual
filters, the effect of storm events on the filtration capabilities,
or the impact of various chemical dosages on filtered effluent.
Analyses could be undertaken to compare different filters
within a system or the effect of different flow rates. Chapter 5
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4. Data Collection and Management
Check with the State
before adopting the
worksheets in this
document. States may
have their own worksheets
or may require some
additional or different
information.
Suggested guidelines for
systems that do not operate
24 hours per day.
provides information on how to conduct a filter self-assessment
and other filter analyses.
4.4 DATA MANAGEMENT TOOLS
This section presents worksheets and spreadsheets that can be
used to record and report data. Check with the State to
determine the proper format for reporting turbidity readings.
4.4.1 Conventional and Direct Filtration
Systems
Combined Filter Effluent
One way to report combined filter effluent readings is to use
Worksheet 1 (located in Appendix B). A completed example
of Worksheet 1 is included later in this section. You should
check with the State before using this worksheet to ensure that
all of the required information is reported.
Combined filter effluent values must be recorded every 4 hours
during plant operation. For plants that operate 24 hours a day
and discharge combined filter effluent continuously to the
clearwell, the 4-hour intervals are easily determined. For
instance, combined filter effluent readings can be taken at
12:00 a.m., 4:00 a.m., 8:00 a.m., 12:00 p.m., 4:00 p.m., 8:00
p.m., and so on. Plants that operate intermittently will have a
more difficult time determining the 4-hour intervals.
The following are some suggested guidelines for determining
the recording intervals for plants that do not operate 24 hours a
day:
Time begins (t=0) when the system starts discharging
filter effluent to the clearwell.
If the plant operates for more than 4 hours per day, you
may record the combined filter effluent any time during
the first 4 hours of operation and then every 4 hours
from the time of the initial turbidity sample. For
instance, say the plant starts discharging to the clearwell
at 6:00 a.m. and the first combined filter effluent
turbidity reading is taken at 10:00 a.m. The operator
would need to take the next turbidity readings at 2:00
p.m., 6:00 p.m., and 10:00 p.m. The plant stops
discharging to the clearwell at 11:30 p.m., so the
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If spreadsheet software is
available, consider
generating a worksheet on
the computer. If formulas
are already programmed in
the spreadsheet, entering
data to calculate
compliance for combined
filter effluent turbidities
will require less time and
ensure greater accuracy.
operator would not need to take any additional readings
until the plants starts discharging to the clearwell again.
If the plant operates for less than 4 hours at a time, you
should record the turbidity values at the end of each
operating period.
Once the combined filter effluent values have been recorded,
the operator should calculate the percentage of readings less
than or equal to 0.3 NTU. LT1ESWTR requires 95 percent of
the monthly readings to be less than or equal to 0.3 NTU for
conventional and direct filtration systems. The following page
provides an example of a completed worksheet and how to
calculate the 95th percentile reading.
You should check with the State for any recording or reporting
policies or requirements for plants that do not operate 24 hours
a day.
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SAMPLE WORKSHEET 1
CONVENTIONAL AND DIRECT FILTRATION PLANTS
MONTHLY REPORT FOR COMBINED FILTER EFFLUENT
Due by the 10th of the Following Month
Check with your State or Primacy Agency to make sure this form is acceptable.
Month: May
Year: 2005
System/Treatment Plant: Townville
PWSID:AB 1234567
A
Day
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
B
Number of
Samples
Required
Per Day
Samples/Day
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
c1
Maximum
Combined
Filter
Effluent
NTU
0.2
0.1
0.4
0.4
0.2
0.1
0.5
0.2
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
0.
Totals:
D2
No. of
Turbidity
Measurements
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
186
E
No. of
Turbidity
Measurements
<= 0.3 NTU
6
6
5
5
6
6
4
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
182
F
No. of
Turbidity
Measurements
>1 NTU
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Number of monthly readings (Total of Column D) = 186
Number of monthly readings <= 0.3 NTU (Total of Column E) = 182
The percentage of turbidity measurements meeting the specified limits.
= (Total of Column E / Total of Column D) x 100 = 98 %
Record the date and turbidity value for any measurements exceeding 1 NTU (Contact State within 24 hours):
If none, enter "None."
Prepared by: J. Operator
Date: June 3, 2005
Date
Turbidity Readings >
1NTU
None
Was individual filter effluent monitored continuously (at least every 15 minutes) during the month?
Yes X No
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You should check with the
State for acceptable forms
for reporting and recording
individual filter effluent
turbidity data. Chapter 2
presents the monitoring,
reporting, and
recordkeeping
requirements for individual
filters.
Individual Filter Effluent
The LT1ESWTR will require conventional and direct filtration
systems with more than two filters to take individual filter
turbidity effluent readings every 15 minutes. Sample
Worksheet 2 (located in Appendix B) can be used for recording
turbidity data from a filter. Remember, if any individual filter
reading exceeds 1.0 NTU in two consecutive 15-minute
readings, then the system must report the filter number(s),
corresponding date(s), turbidity value(s) that exceeded 1.0
NTU, and the cause (if known) for the exceedances (see
Section 2.1.2). This information is due to the State by the 10th
of the following month.
The 15-minute readings should begin when the system starts
discharging individual filter effluent to the clearwell and should
continue until the filter is taken off-line.
Following is a completed excerpt from sample Worksheet 2.
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4. Data Collection and Management
SAMPLE WORKSHEET 2
CONVENTIONAL AND DIRECT FILTRATION PLANTS
MONTHLY SUMMARY REPORT OF DATA FOR INDIVIDUAL FILTER EFFLUENT
Check with your State or Primacy Agency to make sure this form is acceptable.
2005
Year:
PWSID: NY1234567
System Name: AnytownPWS
Filter Number: 3
A
Date
2/5
2/8
B
Were 15-min
Turbidity
Values
Recorded?
Yes
Yes
C
Values of Turbidity
Measurements > 1.0 NTU for
two or more consecutive
15-min readings
1.1, 1.2
1.1, 1.15, 1.1
D
Value of Turbidity
Measurements
> 2.0 NTU
for two or more
consecutive
15-min readings
Did the filter exceed 1.0 NTU in two or more consecutive 15-minute readings this month?
No
X Yes - Report to the State by the 10th of the following month the filter number(s),
corresponding date(s), and turbidity value(s) which exceeded 1.0 NTU and
the cause, if known.
Did this occur in the two previous months? X No
Yes - Must conduct a filter self-assessment within 14 days of the
exceedance unless a CPE was required.
Did the filter exceed 2.0 NTU in two or more consecutive 15-minute readings this month? X
Yes - Did this occur in the previous month? No
Yes - Must arrange for a CPE unless a CPE has been completed by
the State or third party approved by the State within the 12
prior months or the system and State are jointly participating
in an ongoing Comprehensive Technical Assistance project
at the system.
No
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The monitoring, reporting,
and recordkeeping
requirements for slow
sand, diatomaceous earth,
and alternative filtration
systems are presented in
Chapter 2.
The system should
properly plan for
anticipated staff and
revenue needs to achieve
compliance with the
LT1ESWTR.
4.4.2 Slow Sand and Diatomaceous Earth
Filters
The requirements for slow sand and diatomaceous earth filters
have not changed from the requirements in the Surface Water
Treatment Rule. Systems must still take combined filter
effluent readings every 4 hours, with a maximum allowed
turbidity of 1 NTU in at least 95 percent of the measurements
taken each month and 5 NTU in any single measurement (see
Section 2.2). The State may allow less frequent measurements
for slow sand systems. Sample Worksheet 3 (located in
Appendix B) can be used to record and report turbidity
readings. Monitoring individual filters in slow sand and
diatomaceous earth filtration systems is not required by the
LT1ESWTR. However, the operator may choose to monitor
individual filters for optimum plant performance.
4.4.3 Alternative Filtration Technologies
The State is expected to establish the turbidity limits and
frequency of measurements for alternative filtration
technologies, such as membranes or cartridges. Sample
Worksheet 3 (located in Appendix B) can be used to record and
report data. The monitoring, reporting, and recordkeeping
requirements for alternative filtration technologies are
presented in Section 2.3.
4.5 WHAT UPGRADES SHOULD I CONSIDER
FOR MY SYSTEM?
The LT1ESWTR requires the collection, analysis, reporting,
and storage of a larger volume of data than previously
collected. As a result, more personnel time may be required to
maintain instruments and to collect and report data. Systems
may also need to develop financing (and may need to generate
additional revenue) to purchase additional equipment.
Conventional and direct filtration systems that do not currently
have the capability to monitor individual filter effluent turbidity
will need to install turbidimeters and the necessary equipment
to record individual filter effluent turbidities every 15 minutes.
The turbidimeter and associated equipment used to monitor and
record individual filter effluent turbidity should be capable of
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4. Data Collection and Management
System upgrades and
modifications require a lot
of considerations.
the following:
Recording individual filter effluent turbidity readings at
least every 15 minutes per LT1ESWTR;
Compiling turbidity readings on a monthly basis; and,
Tracking instances when the turbidity values exceed 1.0
NTU for two consecutive measurements because
follow-up actions are required.
Systems that cannot record, track, or store turbidity
measurements with their existing turbidimeter and associated
equipment to comply with LT1ESWTR requirements may
consider incorporating one of the following configurations
(assuming the analyzer/controller portion of their turbidimeter
unit has 0-20 mA or 4-20 mA capabilities) into their
turbidimeter units:
Connecting the turbidimeter unit to a data or strip chart
recorder to record, track, and store data;
Hardwiring the turbidimeter unit to a Programmable
Logic Controller (PLC) or SCADA system; or,
Providing necessary connection to allow data to be
downloaded from the turbidimeter unit to a lap-top
computer.
In order to implement some of these and other changes,
systems may evaluate new equipment or upgrades for their
turbidimeters, data recorders, controllers, and other system
components. The following list contains issues the operator
and system owner may want to consider during this evaluation:
Is the turbidimeter intended for measurements over the
expected operational range (such as 0.01 - 5 NTUs)?
Systems may not want a device that cannot handle low-
range turbidities.
Will the system need to upgrade the electrical service to
its building in order to accommodate more and different
equipment?
Can the analyzer portion of the turbidimeter unit display
turbidity level alarms in situations where SCADA or
data chart recorders are not used? Alarms should be
displayed in some fashion so that operators can address
filter issues in a timely manner. For instance, alarms
could be initiated if the individual filter effluent
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Many turbidimeters and
data logging equipment
exist. You should make
sure all equipment is
compatible and can be
used to meet all applicable
monitoring, reporting, and
recordkeeping
requirements.
turbidity approaches 1.0 NTU.
Can the turbidimeter data be downloaded and a filter
profile be generated?
What type of alarm system does the turbidimeter have?
The system may want to have multiple alarm
capabilities (an alarm if individual filter effluent
turbidity approaches 1.0 NTU, a separate alarm for
individual filter effluent turbidity that approaches 2.0
NTU, and an alarm for combined filter effluent that
approaches 0.3 NTU).
Can the operator be notified when the alarms are
activated? Operators may want a mechanism that
notifies them by pager or other means when trigger
turbidity values occur.
Is there local support for repair and maintenance of
turbidimeters? Systems should make sure a
manufacturer's representative can be at the plant on
short notice.
What experiences have other systems had? Operators
may want to consult nearby utilities to see which
turbidimeters they are using and to discuss what has and
has not worked for them.
4.5.1 Suggested System Configuration
The following descriptions of three turbidimeters may help the
operator get started with where to look and what to look for
when selecting a turbidimeter.
The following does not constitute an EPA endorsement or
recommendation for use. The listed turbidimeters are just a few
of the units available to measure turbidity that EPA is aware of.
Please let us know if there are other manufacturers which were
not represented. Systems may use any turbidimeter provided it
can be used with an EPA-approved method.
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4. Data Collection and Management
HACK 1720D:
The Hach 1720D is a low-range process turbidimeter
with power supply and one AquaTrendฎ Interface with
Signal Output Module.
Power requirements: 95-240 Vac, 50/60 Hz, auto-
select, 40 VA.
Recorder outputs: selectable for 0-20 or 4-20 mA.
Measures turbidity from 0.001-100.0 NTU.
A single AquaTrendฎ Interface can network up to eight
1720D Turbidimeters from eight individual filters; it
provides a significant hardware cost savings in
installations where multiple sensors are required.
No sample cell to clean, reducing maintenance and
downtime.
Response time: 1 minute and 15 seconds; allows
consecutive 15-minute readings.
Calibration time: about 1 minute and 45 seconds.
Stores up to 30 days worth of readings, allowing
monthly generation of a filter profile. Data can be
downloaded to a computer.
Two alarms: low range and high range. Also has
system alarms.
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When selecting monitoring
and data analyzing
equipment, you should
verify that a supplier
representative is available
to respond to problems in a
timely manner.
HF Scientific MicroTOL:
Power requirements: 100-250Vac, 50/60 Hz, wall
adapter.
Analog Output: 4-20 mA.
Digital Output.
Designed for smaller systems.
Sensor and analyzer are one unit.
Measures turbidities from 0-1,000 NTU.
Measures individual filter effluent turbidity every 15
minutes and combined filter effluent turbidity every 4
hours.
Calibration time: 5 minutes or less.
Response time: 1 to 20 seconds.
Two alarms: low and high turbidities.
Software available that allows logging, comparisons,
graphs, and data acquisition from up to 256 on-line
turbidimeters to a computer (RS-485).
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4. Data Collection and Management
Operators should be
involved with equipment
selection to avoid the
purchase of improper or
complicated equipment.
GLI International Accu4 Low-Range Turbidimeter
System:
System consists of:
1. Analyzer: T53A4AIN;
2. Sensor: 8320TIAOC3N; and,
3. Calibration Cube Assembly: 8220-1300.
Operates in accordance with EPA-approved GLI
Method 2 and ISO 7027 - 1984 (E).
Power requirements: 90-130 or 180-260 VAC, 50-60
Hz.
Analog outputs: Two isolated 0-20 mA, or 4-20 mA.
Digital display.
Measures turbidities from 0.000-100.0 NTU.
Analyzer Performance:
1. Accuracy: ฑ 2% of reading, all ranges;
2. Stability: 0.1% of span; and,
3. Repeatability: 0.1% of span or better.
Optional Cal-Cube assembly to conveniently verify
calibration.
Alarms.
Software available to allow download of data to IBM-
compatible computers (RS-232).
4.6 REFERENCES
USEPA. 1998. Handbook: Optimizing Water Treatment Plant Performance Using the
Composite Correction Program (EPA 625-6-91-027). Washington, D.C.
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5. FILTER SELF-ASSESSMENT
Filter self-assessments are required only under certain
circumstances for conventional and direct filtration systems (see
Section 2.1.2). However, systems using filtration technologies other
than conventional and direct may find some useful information in
this chapter.
In this Chapter:
Assessment of
Filter Performance
Development of a
Filter Profile
Identification and
Prioritization of
Factors Limiting
Filter Performance
Assessment of
Applicability of
Corrections
Preparation of the
Report
See Section 2.1.2 for more
information on individual
filter effluent turbidity
monitoring requirements
when a filter self-
assessment is required and
when a CPE is required.
5.1 INTRODUCTION
Conventional and direct filtration systems must conduct a filter
self-assessment for any filter that has a turbidity level greater
than 1.0 NTU in two consecutive measurements taken 15 minutes
apart for three consecutive months unless a CPE as specified in
40 CFR Section 141.563(c) was required. Conventional and
direct filtration systems that have no more than two filters and
monitor combined filter effluent turbidity only, instead of
individual filter effluent turbidity, must conduct a self-assessment
on all of its filters if the combined filter effluent exceeds 1.0 NTU
in two consecutive measurements taken 15 minutes apart for
three consecutive months. The date the filter exceeded 1.0 NTU
in two consecutive 15-minute readings for the third consecutive
month is called the trigger date. The filter self-assessment must
be conducted within 14 days of the trigger date. Systems must
report to the State that the filter self-assessment was required, the
trigger date, and the date the filter self-assessment was
completed. This information is due to the State by the 10th of the
following month (or 14 days after the self-assessment was
triggered if the self-assessment was triggered during the last 4
days of the month). In addition, systems must report the filter
number, the turbidity measurement, date on which the
exceedances occurred, and reason for the exceedance (if known)
in the monthly report due the 10th of the following month.
Systems may also want to conduct a filter self-assessment
whenever a filter's effluent quality indicates a potential problem,
even if it is not required by the regulation.
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40 CFR Section
141.563(b)
The filter self-assessment
must consist of at least the
following components:
Assessment of the
filter performance;
Development of a
filter profile;
Identification and
prioritization of
factors limiting
filter performance;
Assessment of the
applicability of
corrections; and,
Preparation of a
filter self-
assessment report.
The filter self-assessment must consist of at least the following
components (40 CFR Section 141.563(b)):
Assessment of the filter performance;
Development of a filter profile;
Identification and prioritization of factors limiting filter
performance;
Assessment of the applicability of corrections; and,
Preparation of a filter self-assessment report.
Filters represent a key unit process for the removal of particles in
surface water treatment. Although filters represent only one of
the barriers in a treatment process, their role is the most critical as
the final physical barrier to prevent pathogenic microorganisms
that are resistant to disinfection from entering distribution
systems. Properly designed filters, when in proper physical and
operational condition and used in conjunction with coagulation,
flocculation and/or sedimentation are capable of treating raw
water to an acceptable level.
Filter performance problems may only be obvious during
excessive hydraulic loading or chemical failure, but you should
not assume all turbidity spikes are due to hydraulic overloading.
In some circumstances performance problems from other causes
may be evident only during these hydraulic episodes. This
chapter describes the process of an individual filter self-
assessment and is intended to provide information to help you
assess which of these areas are limiting the performance of a
filter.
This chapter describes some of the possible components of an
individual filter assessment:
An assessment of filter performance (Section 5.2).
A general description of the filter.
The development of a filter profile (Section 5.3).
Identification and prioritization of factors limiting filter
performance (Section 5.4).
An assessment of the hydraulic loading conditions of
the filter.
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5. Filter Self-Assessment
You should consult the
State regarding the
requirements and format of
the filter self-assessment.
You may want to perform
filter self-assessments
routinely as preventive
maintenance.
An assessment of the actual condition and placement
of the media.
An assessment of the condition of the support media
and underdrains.
An assessment of backwash practices.
An assessment of how the filter is placed back into
service.
An assessment of the filter rate-of-flow controllers
and filter valving infrastructure adequacy.
An assessment of other plant processes, such as
chemical feed rates, raw water quality changes, and
turbidimeters.
An assessment of the applicability of corrections (Section
5.5).
Preparation of the filter self-assessment report (Section
5.6).
The checklist in Figure 5-1 can be used to assist with the filter
self-assessment. A blank copy of this checklist can be found in
Appendix B.
XYZ Water System
3
System Name
Filter # _ _
Date Self- Assessment was Triggered 6/3/05
Date of Self-Assessment 6/8/05
Assessment of Filter Performance
Development of a Filter Profile
Identification and Prioritization of Factors
Limiting Filter Performance
Assessment of the Applicability of
Corrections
Preparation of a Filter Self- Assessment
Report
Figure 5-1. Filter Self-Assessment Checklist
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The information in Table
5-1 may be useful in
assembling information
required by the Filter
Backwash Recycling Rule.
Table 5-1 can also be used to assist with the filter self-assessment
process. The Filter Self-Assessment video (under development)
provides guidance on collecting the information to complete
Table 5-1. Equations in Appendix C may also be helpful in
completing the table. You may already have the information
needed to complete Table 5-1, while others may have to collect or
verify the needed information. The following sections will
explain how to collect and verify information.
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5. Filter Self-Assessment
Table 5-1. Sample Individual Filter Self-Assessment Form*
Topic
General Filter
Information
Hydraulic
Loading
Conditions
Media
Conditions
Description
Type (mono, dual, mixed, pressure,
gravity)
Number of filters
Filter/rate control (constant,
declining)
Type of flow control (influent weir,
valves)
Surface wash type (rotary, fixed,
none)/air scour
Configuration (rectangular, circular,
square, horizontal, vertical)
Dimensions (length, width,
diameter, height of side walls)
Max depth of water above media
Surface area per filter (ft2)
Average operating flow (mgd or
gpm)
Peak instantaneous operating flow
(mgd or gpm)
Average hydraulic surface loading
rate (gpm/ft2)
Peak hydraulic surface loading rate
(gpm/ft2)
Changes in hydraulic loading rate
(gpm/ft2)
Depth, type, uniformity coefficient*,
and effective size*
Media 1
Media 2 (if applicable)
Media 3 (if applicable)
Presence of mudballs, debris, excess
chemical, cracking, worn media,
media coating
Information
Actual
Design
is worksheet is designed to elicit additional information and is not required under 40 CFR Section
141.563(b).
*You may want to have a sieve analysis done on the media. Note that a sieve analysis may not be able to be
completed within the 14-day time frame required for a filter self-assessment.
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Table 5-1. Individual Filter Self-Assessment Form (continued)
Topic
Support
Media/Under-
drain
Conditions
Backwash
Practices
Placing a Filter
Back into
Service
Rate-of-Flow
Controllers
and Filter
Valves
Other
Considerations
Description
Is the support media evenly placed
(deviation <2 inches measured
vertically) in the filter bed?
Type of underdrains
Evidence of media in the clearwell
or plenum
Evidence of boils during backwash
Backwash initiation (headless,
turbidity /particle counts, time)
Sequence (surface wash,
air scour, flow ramping,
filter-to-waste)
Duration (minutes) of each step
Introduction of wash water (via
pump, head tank, distribution
system pressure)
Backwash rate (gpm/ft2)
at each step
Bed expansion (percent)
Dose of coagulants or polymers
added to wash water
Backwash termination (time,
backwash turbidity, visual
inspection, or other)
Backwash SOP (exists and current)
Delayed start, slow start, polymer
addition, or filter to waste
Leaking valves
Malfunction rate of flow control
valves
Equal flow distribution to each filter
Chemical feed problems
Rapid changes in raw water quality
Turbidimeters (calibrated)
Other
Information
Actual
Design
Note: Excerpts from this table including sample data can be found throughout this chapter. An additional
blank copy of this form is found in Appendix B.
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5. Filter Self-Assessment
5.2 ASSESSMENT OF FILTER
PERFORMANCE
Topic
General
Filter
Information
Description
Type (mono, dual,
mixed, pressure,
gravity)
Number of filters
Filter/rate control
(constant, declining)
Type of flow control
(influent weir,
valves)
Surface wash type
(rotary, fixed,
none)/air scour
Configuration
(rectangular,
circular, square,
horizontal, vertical)
Dimensions (length,
width, diameter,
height of side walls)
Max depth of water
above media
Surface area per
filter (ft2)
Information
Actual
dual
4
constant
valves
fixed
rectangular
length = 10 ft
width = 8 ft
height = 12 ft
6ft
80ft2
Design
dual
4
constant
valves
fixed
rectangular
length = 10 ft
width = 8 ft
height = 12 ft
6ft
80ft2
Excerpt from Table 5-1 containing sample data.
Blank copies of the full version of this table can be
found in Table 5-1 and in Appendix B.
You should evaluate overall performance of the filter(s) being
assessed. For instance, you may want to further investigate any
of the following observations:
Filter has required more frequent backwashing than
usual;
Filter has experienced shorter run times; or,
Unusual events (such as boiling) have been noticed
during backwashing.
You may wish to also examine the historical performance of
other filters at the plant to determine if the problem is filter
specific.
These items are just some of the filter performance issues that
should be investigated further during a filter self-assessment.
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Remember, you are
required to continuously
monitor and record the
individual filter effluent
turbidity at least every 15
minutes. If readings are
taken more frequently than
15 minutes, you should
check with the State on
how to report this
information.
The use of particle
counting in conjunction
with turbidity monitoring
of filter effluent may offer
additional insights to filter
performance; however,
care should be taken in the
interpretation of particle
count results. The
interpretation should focus
on the change in count
levels as opposed to the
discrete particle count
numbers.
5.3 DEVELOPMENT OF A FILTER PROFILE
A filter profile must be developed as part of the filter self-
assessment process. The purpose of this requirement is to help
you identify turbidity spikes (sudden increases in turbidity) or
high turbidity levels during the filter run and to determine the
probable causes of those spikes. The profile for the filter being
evaluated should include a graphical summary of filter
performance for an entire filter run from start-up (when filtered
water goes to the clearwell) to the time the filter is taken off-
line. Performance should be shown by turbidity or particle
count measurements. Plotting the performance data versus
time on a continuous basis is one good approach for
development of the filter profile (see Figures 5-2 through 5-7).
While the LT1ESWTR requires recording turbidity
measurements at least every 15 minutes for purposes of
developing a filter profile, you may want to consider taking
turbidity readings once every 5 minutes, every minute, or more
frequently. This increased frequency will allow you to more
accurately capture spikes. The filter profile should represent a
typical run and should include (if representative of normal filter
operations) the time period when another filter is being
backwashed or is out of service (in order to determine if such
practices have an impact on finished water quality). The filter
profile should include an explanation of the cause (if known) of
performance spikes during the run. You should identify flow
and changes in flow to the filter on the filter profile. When
possible, plot the profile using data collected during the
turbidity event that prompted the filter self-assessment. If
assistance is needed with this portion of the filter assessment,
you may contact your State. Figures 5-2 through 5-7 are
examples of filter profiles with explanations of each profile.
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5. Filter Self-Assessment
0.3 -,
= 0.2-
>
ฃ
3 0.1 -
n
s Filter Ripening Spike
< Initial spike after placing filter back on-line after
backwashing. This spike is typical of a properly
functioning filter. Note that the spike is short in duration
(typically less than 15 minutes).
0 4 8 12 16 20 24
t Time (hrs) A
k
Start Off-Line for Backwash
Figure 5-2. Example Filter Profile of Optimized Filter Performance
1.8 -,
1.6 -
1.4 -
|1.2
"> 1 "
ii 0.8
= 0.6 -
0.4 -
0.2 -
n -
Filter Ripening i
Period /
A/ /
0 4
Start
/ \ failure or a hydraulic surge due to
/ I varying raw water pumping rates or
/ \ other filters being off-line.
8 12 16 20 24
Time (hrs) T
Off-Line for Backwash
Figure 5-3. Example Filter Profile of Optimized Filter
with Turbidity Spike During Filter Run
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--ป
1-
z^
&
15
S
3
1-
1.4 -
1.2 -
1 -
0.8 -
0.6 -
0.4 -
0.2 -
n
/ \ -* This type of spike can be caused by:
/ \
/ \ 1 ) Placing the filter on-line too soon after backwashing;
/ \ 2) Not filtering to waste long enough; or,
/ \ 3) Excessive backwashing and over cleaning the filter.
/ \
/ \ See Chapter 8 for more details on how to address this type of spike.
/ \
f Filter Ripening \
Period \
U n i i i i i i
0 4 8 12 16 20 24
T Time (hrs) T
Start Off-line for Backwash
Figure 5-4. Example Filter Profile with Long and High Initial Spike
Filter Ripening Spike
Filter run length exceeded.
Filter should have been taken
out of service before 30 hours.
12
18
24
Time (hrs)
30
36
42
48
Start
Off-line for Backwash
Figure 5-5. Example Filter Profile of Optimized Filter
with Breakthrough at End of Filter Run
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5. Filter Self-Assessment
1.4 -,
1.2 -
S 1
SO.B-
>
+j
ii 0.6 -
s
K 0.4 -
0.2 -
0 -
Multiple spikes due to hydrauic surge as a result of variable raw water rates or
one or more filters taken out of service. Systems should check loading rates on
all filters (flow through the filter in gpm/square ft).
Filter
Ripening
Spike
12
Time (hrs)
16
20
24
Start
Off-Line for Backwash
Figure 5-6. Example Filter Profile with Multiple Spikes
2.0 n
High turbidity levels due to:
1) Incorrect chemical feed;
2) Improper backwash; or,
3) Problems with the filter media or underdrain.
12
Time (hrs)
16
20
24
Start
Off-Line for Backwash
Figure 5-7. Example Filter Profile with High Initial
Spike and Turbidity Levels Above 1.0 NTU
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You should try to tie
factors identified as
limiting filter performance
to the events on the filter
profile.
5.4 IDENTIFICATION AND PRIORITIZATION OF
FACTORS LIMITING FILTER
PERFORMANCE
The following activities discussed in this section are means of
identifying and prioritizing the potential problems with filter
performance:
Assessing filter hydraulic loading conditions;
Assessing condition and placement of filter media;
Assessing condition of support media and underdrains;
Assessing backwash practices;
Assessment of placing a filter back into service;
Assessing rate-of-flow controllers and filter valve
infrastructure; and,
Assessing other plant processes, such as chemical feed
rates, raw water quality changes, and turbidimeters.
You may not need to complete all of the activities listed in this
section in order to identify the factors limiting filter
performance. After the factors limiting filter performance have
been identified, it may be possible to tie them to events in the
filter profile. You should contact the State if you need
assistance.
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You should check with the
State on acceptable filter
hydraulic loading rates.
5.4.1 Assessing Filter Hydraulic Loading
Conditions
Topic
Hydraulic
Loading
Conditions
Description
Average operating
flow (mgd or gpm)
Peak instantaneous
operating flow
(mgd or gpm)
Average hydraulic
surface loading
rate (gpm/ft2)
Peak hydraulic
surface loading
rate (gpm/ft2)
Changes in
hydraulic loading
rate (gpm/ft2)
Information
Actual
960 gpm
1,440 gpm
3.0 gpm/ft2
4.5 gpm/ft2
range from 2.0
to 4.5 gpm/ft2
Design
896 gpm
1,248 gpm
2.8 gpm/ft2
3. 9 gpm/ft2
range from 2.0
to 3.9 gpm/ft2
Excerpt from Table 5-
Blank copies of the full
found in Table 5-1 and
1 containing sample data
version of this table can be
in Appendix B.
Filters may operate poorly when peak loading rates exceed
filter design or when hydraulic loading rates change suddenly.
Table 5-2 presents a summary of industry standard loading
rates for various filters Filters may perform satisfactorily at
loading rates other than those in Table 5-2; these values are
general and provide a basis for evaluating excessive filter
hydraulic loading. State requirements may differ from
acceptable industry loading rates and should be considered
during the assessment.
Table 5-2. General Guide to Typical Filter Hydraulic
Loading Rates
Filtration Type
Sand Media
Dual/Mixed Media
Deep bed
(anthracite > 60 in.)
Loading Rate
-2.0 gpm/ft2
-4.0 gpm/ft2
-6.0 gpm/ft2
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For additional equations
and mathematical
reference see Appendix C.
You should check to see if
the chemical pumps can
operate at lower flow rates
before decreasing flow
rates through the plant.
Peak hydraulic loading rate should be calculated by dividing
the peak flow to the filter (gpm) by the surface area of the filter
(ft2). Equation 5-1 demonstrates this method of calculating the
peak hydraulic loading rate.
Equation 5-1 - Peak Hydraulic Loading Rate
Peak hydraulic loading rate = Peak filter flow (gpm)
Filter area (ft2)
Since the filters can be most vulnerable during excessive
loading rates, it is critical to determine the peak instantaneous
flow that filters are experiencing and to minimize the occasions
when filters are overloaded. You can identify the peak
instantaneous operating flow rate by looking at operating
records, operational practices, and flow control capability.
A review of plant flow records can be misleading in
determining the peak instantaneous operating flow. You can
easily calculate average daily flow rate if the plant keeps track
of total daily flow (total daily flow/minutes of plant operation).
However, it is difficult to calculate instantaneous flow with
total daily flow information. You should correctly identify the
peak instantaneous operating conditions when reviewing flow
data. If pumps are used in multiple combinations throughout
the operational day, care should be taken to determine the
actual peak loading on the filters during the day. As seen in
Example 5-1, the peak hydraulic loading rate to the filters did
not occur during peak plant flows. You may need to examine
more than one operating scenario to correctly identify peak
filter hydraulic loading rate.
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Example 5-1 - Calculating Peak Hydraulic Loading Rate
A plant that operates 24 hours per day uses three 300-gpm pumps in various
combinations throughout the year to meet system demand. The peak flow occurs for a
2-hour period each evening when all three pumps are used to fill on-site storage. Two
pumps are used for the first hour and a half, while the third pump is used with the other
two pumps only for the last 30 minutes of the 2-hour period. During that 30-minute
period plant flow increases to 800 gpm. The peak instantaneous operating flow that
goes onto the filters is 800 gpm. The plant has two dual media filters (each 100 ft2)
and would have a peak hydraulic loading rate of 4.0 gpm/ft2 at the 800 gpm peak flow.
Using Equation 5-1:
Peak hydraulic loading rate = Peak flow (gpm)/Filter Surface Area (ft2)
= 800 gpm / ((2 filters) X (100 ft2/filter))
= 800 gpm / 200 ft2
= 4.0 gpm/ft2
This loading rate is within suggested rates. However, the system would want to avoid
loading rates much higher than 4 gpm/ft2 unless higher rates are allowed by design or
recommended by the manufacturer and as long as the filtered water quality is
acceptable.
For the same plant, the peak filter hydraulic loading rate could occur under a different
set of circumstances. During the first hour and a half when the two pumps are on, one
of the filters is taken off-line for backwashing. The peak flow is 540 gpm.
Peak hydraulic loading rate = 540 gpm / ((1 filter) X (100 ft2/filter))
= 540 gpm/100 ft2
= 5.4 gpm/ft2
This loading rate to the filter is higher than the loading rate realized during the peak
flow and exceeds the suggested range.
You may decide to calculate the loading rate to the filters if the system does not have
flowmeters or if you want to check the flowmeters in the plant. Example 5-2 provides an
example of how to perform this calculation.
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Example 5-2 - Calculating Individual Filter Loading
A system has three filters, each with a surface area of 40 ft2. A rise rate of 5 feet has been
observed over a 1-hour period in the clearwell. The clearwell has a surface area of 200 ft2.
The system should calculate the flow to the clearwell and the hydraulic loading rate on each
filter.
To calculate the flow, determine the volume of effluent discharging to the clearwell over a
certain time period.
Flow to clearwell (gpm)= Volume to clearwell (gal)
Time (minutes)
= Rise in clearwell (ft) X Clearwell Surface Area (ft2) X 7.48 gal/ft3
Time (minutes)
= 5ft X 200 ft2 X 7.48 gal/ft3 = 125 gpm
1 hour X (60 min/hr)
To calculate the hydraulic loading rate to each filter, divide the flow to the clearwell by the
total filter surface area.
Hydraulic Loading to Each Filter (gpm/ft2) = Flow to clearwell (gpm)
# of Filters X Surface Area of Each Filter (ft2)
125 gpm
3 filters X 40 ft
Hydraulic Loading to Each Filter = 1 gpm/ft2
.2
If only two filters are on-line, the hydraulic loading rate to each filter would be 1.6 gpm/ft .
This example assumes equal loading to each filter, and it provides an estimate of hydraulic
loading to each filter. This example also assumes no flow is leaving the clearwell. If flow is
leaving the clearwell, this flow should be added back in to estimate the filter hydraulic loading
rate.
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The activities associated
with the assessment of
filter media will probably
require that the filter be
off-line for a period of
time. The system should
plan accordingly to avoid
plant upsets while the filter
is off-line.
You should physically
inspect the filter media and
then compare the findings
to the original media
specifications.
5.4.2 Assessing Condition & Placement of
Filter Media
Topic
Media
Condition
s
Description
Depth, type, uniformity
coefficient, and
effective size
Media 1
Media 2 (if applicable)
Media 3 (if applicable)
Presence of mudballs,
debris, excess
chemical, cracking,
worn media, media
coating
Information
Actual
44 in., dual,
gravity
anthracite,
21 in.
sand, 23 in.
mudballs,
media coating
Design
48 in., dual,
gravity
anthracite,
24 in.
sand, 24 in.
Excerpt from Table 5-1 containing sample data.
Blank copies of the full version of this table can be
found in Table 5-1 and in Appendix B.
Assessment of the condition and placement of the filter media
is one of the steps you should take in identifying factors
limiting performance of the filtration process. The presence of
mudballs, surface cracking, or displaced media may often be
attributed to excessive use of coagulant chemicals, inadequate
backwashing, or a more serious problem related to the
underdrain system. The assessment of the condition and
placement of the filter media should include a physical
inspection of the filter bed and a comparison of the actual
media findings to the original specifications. The filter bed
should be investigated for the following:
Irregularities in the surface;
Surface cracking;
Proper media depth;
Presence of mudballs; and,
Segregation of media.
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You should avoid
disrupting the support
gravel or media when
coring or probing in the
filter bed.
Figure 5-8. Box Excavation
Demonstration
Inspection
The inspection of the filter should consist of the following
steps:
1) The filter inspection should begin by draining the filter.
2) As the filter is drained, you should observe the filter
surface carefully. You should note areas where
vortexing or ponding occurs. Areas of vortexing should
be inspected for proper media and underdrain
placement. Areas of ponding are a good indicator that
the filter surface is not level.
3) The filter should be drained enough to allow for
excavation of the media to assess the depths of each
media type as well as each media interface (i.e., just
below the anthracite/sand interface in a dual media
filter).
4) Deeper excavation of the filter may be warranted if
evidence suggests disrupted support gravels or an
inadequate underdrain system (see Section 5.4.3).
5) Care should be taken not to disrupt the support
gravel or media while coring or probing.
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\
You should place pieces of
plywood on the media
before getting on the filters
to support you and to
avoid sinking into the
media.
Additional Safety
References include:
AWWA Video Safety
First: Confined Spaces
AWWA Video Series
Safety Basics for
Water Utilities
AWWA Manual
Safety Practices for
Water Utilities (M3)
For more information on
media inspection, refer to
Filter Maintenance and
Operations Guidance
Manual (American Water
Works Association
Research Foundation,
2002).
Media Inspection
If the filter is a pressure filter, coring the filter may be difficult
or impossible. You should take any necessary safety
precautions when entering a pressure filter since it may be
considered a confined space. If the pressure filter has a
viewing port the length of the filter media, you should
periodically view the media for any signs of cracking,
mudballs, media segregation, or any other changes in the
media.
Filter media assessments may be conducted using a variety of
coring devices (typically a !1/2- to 2-inch thin-walled,
galvanized pipe), a hand dig, a shovel, or if needed, a gross
excavation technique. The gross excavation technique may be
conducted using a plexiglass box like the ones shown in
Figures 5-8 and 5-9. The box excavation consists of sinking a
plexiglass box into the media and excavating inside the box
down to the support media. The box excavation technique
allows for visual observation of the media depths and interfaces
after the excavation is completed.
Anyone who enters a filter box needs to be aware of
confined space entry and lockout/tagout issues. Confined
spaces may present safety hazards. Check with the local
Occupational Safety and Health Association (OSHA) office
for confined space entry requirements.
Figure 5-9. Box Used for Excavation
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You may want to have a
sieve analysis done on the
media. Note that it may
not be possible to
complete a sieve analysis
within the 14-day time
frame required for a filter
self-assessment.
Media Placement
Whatever media excavation technique is used, you should note
the depth of each media type, compare these depths to the
original specifications, note the general condition of the media
interface, and the presence of any mudballs (see Figure 5-10)
or excess chemical. After the excavation is completed, the
excavation team should make certain that the media is placed
back in the excavation hole in the same sequence that it was
removed.
Figure 5-10. Mudball from a Filter
Media Analyses
Coring methods offer the advantage of being able to apply the
Floe Retention Analysis procedure (presented in Section 5.4.4),
if conditions warrant. If media samples have been collected
from the filter, you may want to consider having a sieve
analysis conducted. A sieve analysis is recommended if it is
suspected that the filter media size is wrong. The sieve
analysis should be performed by a soils laboratory. The soils
laboratory should determine the effective size and coefficient
of uniformity for the different media; this will allow you to
compare the laboratory results with filter media design
specifications.
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You should make a list of
your tools before entering
the filter so that you can
check them off as you
leave.
Completing the Inspection
Before placing the filter back on-line after an inspection,
consider these steps:
You should make sure all the tools used to inspect
the filter have been collected and removed from the
filter. You should make a list of your tools before
entering the filter so you can check them off as you
leave.
You should backwash the filter thoroughly before
placing it back on-line. You should start the backwash
very slowly to remove air, and you may want to add a
disinfectant to the filter prior to backwash. You may
also want to filter-to-waste after an inspection and
before discharging to the clearwell.
5.4.3 Assessing Condition Of Support Media
and Underdrains
Topic
Support
Media/Under
-drain
Conditions
Description
Is the support
media evenly
placed (deviation
<2 inches
measured
vertically) in the
filter bed?
Type of
underdrains
Evidence of media
in the clearwell or
plenum
Evidence of boils
during backwash
Information
Actual
no
lateral
no
no
Design
yes
lateral
Excerpt from Table 5-1 containing sample data.
Blank copies of the full version of this table can be
found in Table 5-1 and in Appendix B.
Maintaining the integrity of the support gravels and
underdrains (see Figure 5-11) is extremely important to the
performance of a rapid rate granular filter. Disrupted or
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Underdrains have a limited
useful life and require
periodic maintenance and
inspection.
Uncontrolled air can
disrupt support gravel.
Some underdrain systems
do not require support
gravel. Design documents
should be reviewed to
verify the presence or
absence of support gravel.
unevenly placed support media can lead to rapid deterioration
of the filtered water quality identified by quick turbidity
breakthroughs and excessively short filter runs. Should
disruption of the support media be significant, the impacted
area of the filter may act as a "short-circuit" and may allow
particulates and microbial pathogens to pass directly into the
clearwell. Filter support gravels can become disrupted by
various means including sudden violent backwash, excessive
backwashing flow rates, entrained air in the filter, or uneven
flow distribution during backwash. The number one cause of
support gravel disruption is uncontrolled air. Also, air that
accumulates during the filter run can disrupt gravel as it is
released at the start of a backwash. This is why it is so
important to start backwashes slowly at a low rate.
Figure 5-11. Underdrain System.
The condition of the support gravel can be assessed in three
steps:
Step One - As part of the normal backwash procedure,
you should visually inspect the filter during a backwash
to see if there is excessive air boiling or noticeable
vortexing as the filter is drained. You should also look
for any signs of pooling in low areas, which may
indicate that the support gravel is not level.
Step Two - You should "map" the filter using a steel or
solid probe. This is the most common method of
assessing the placement of filter support media. The
mapping procedure involves a systematic probing
through the filter media down to the support gravels of
a drained filter at various locations in a grid-like
manner. At each probe location, the depth of
penetration into the filter should be measured against a
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When probing a filter, be
careful not to disrupt the
support gravel or damage
the filter media.
If the depth to the filter
support gravel varies by
more than 2 inches across
the filter, further
evaluation may be needed.
Some systems have used
professional divers to
inspect the clearwell for
filter media. The
advantage to using divers
is that the clearwell will
not need to be taken off-
line and plant operations
are only minimally
disturbed.
fixed reference point such as the top of the wash water
troughs. The distance from the fixed reference point to
the top of the support gravel should not deviate
vertically more than 2 inches. A grid map of the filter
will help with tracking and recording measurements.
Figure 5-12 shows an example of a grid. Care should
be taken during the filter probing not to disrupt the
support gravel and to avoid damaging the filter
media.
A
2'
c
n
F
F
n.
o
1
1
2'
;
i :
3 i
\ J
5 e
o
z
\
0'
7 ฃ
5 ฃ
5 1
0 1
1
o
z
O1
Figure 5-12. Example Grid of Filter Support Gravel.
In the example, shown in Figure 5-12, measurements of
the support gravel are taken every 2 feet. A unique
number is assigned to each sampling location and depth
measurements are recorded at each location. If depths
vary by more than two inches, the filter media, support
gravel, and underdrain should be further evaluated.
Step Three - You should determine whether filter
media has ever been found in the clearwell. You should
look for media in the clearwell and review recent
clearwell maintenance records. Clearwell inspections
should be conducted only following appropriate safety
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procedures while minimizing negative impacts on
necessary plant operations. A record of media in the
clearwell may indicate a greater problem than just
disrupted support gravels. The problem may be
attributed to a severe disruption of the filter underdrain
system. An in-depth assessment of the underdrains
typically involves excavation of the entire filter bed.
You should use best professional judgment and seek additional
guidance if undertaking an underdrain assessment, because it is
outside the scope of a typical filter self-assessment.
5.4.4 Assessing Backwash Practices
Topic
Backwash
Conditions
Description
Backwash initiation
(headless, turbidity/
particle counts, time)
Sequence (surface
wash, air scour, flow
ramping, filter-to-
waste)
Duration (minutes) of
each step
Introduction of wash
water (via pump, head
tank, distribution
system pressure)
Backwash rate
(gpm/ft2) at each step
Bed expansion (%)
Dose of coagulants or
polymers added to
wash water
Backwash termination
(time, backwash
turbidity, visual
inspection, or other)
Backwash SOP (exists
and current)
Information
Actual
turbidity
1) surface wash
2) flow ramping
3) delayed start
1) 3 min
2) 12 min
3) 30 min
pump
15 gpm/ft2
14%
none
time
available,
current
Design
turbidity
1) surface wash
2) flow ramping
3) delayed start
1) 3 min
2) 12 min
3) 30 min
pump
15 gpm/ft2
30%
none
time
available
Excerpt from Table 5-1 containing sample data.
Blank copies of the full version of this table can be
found in Table 5-1 and in Appendix B.
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Proper maintenance is essential to preserve the integrity of the
filter as constructed. Filters that perform poorly as a result of
filter media degradation or disruption of support gravel
placement are often linked to problems with backwash. Both
the flow rate and the duration of the backwash should be
examined and adjusted if necessary. The optimal post-
backwash condition for the filter varies for each treatment
plant. Site-specific circumstances should be considered when
making recommendations regarding filter backwash
procedures. The focus should be on filter effluent water
quality. Information to be collected, examined, and compared
to filter specifications is contained in Table 5-1.
An assessment of the filter backwash procedure should include
the following:
Collection of general information related to the
backwash (such as when to initiate backwash and
length of backwash);
Reviewing the backwash SOP;
Visual inspection of a filter during backwash; and,
Determination of the backwash rate and expansion of
the filter media during the wash.
One indicator of filter performance is the ratio of water used
for backwashing to the amount of water that was filtered during
a typical filter run:
Filter to backwash ratio = Backwash Water Volume x 100
Filtered Water Volume
The filter to backwash ratio should typically be between 3 and
6 percent for conventional filtration plants and 6 to 10 percent
for direct filtration plants. This ratio may also vary with
seasons, being lower in the summer and higher in the winter. If
the ratio exceeds these ranges, filter performance is considered
poor because frequent backwashing is being conducted. It may
also indicate an inadequate level of pretreatment.
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Backwash initiation can be
based on:
1. Time
2. Headless
3. Turbidity
4. Particle Counts
Surface washing is
recommended during
backwash whenever
coagulants or polymer are
used in pretreatment.
Initiation of Backwash
The backwash process is usually initiated when the head loss
across the filter reaches a certain limit (established by the
supplier or designer), when the filter effluent increases in
turbidity or particle counts to an unacceptable level, or at a
preset time limit determined by the system. You should verify
that backwash is initiated in accordance with design
specifications and established SOPs.
Backwash Sequence
The backwash process can consist of just backwashing with
water, a combination of surface wash and backwash, ordinary
air-scour, or simultaneous air and water wash. The backwash
rate could also vary throughout the process. For example, the
backwash rate could start at 10 gpm/ft2 in combination with air
scour or surface wash and then increase to 20 gpm/ft2 after air
scour or surface wash.
With the air-scouring wash, the violent boiling action typically
occurs in the top 6 to 8 inches of the filter. In this case,
mudballs that are present below this depth are not broken and
will remain in the filter. Surface washing is recommended
during backwash whenever coagulants or polymer are used in
the pretreatment process. Surface washing should be done
first, with backwash starting 2 to 3 minutes after surface
washing begins (Kawamura, 2000). Operation of the surface
wash during the backwash should be closely monitored
because this can cause media loss in some filters, especially
when the backwash rate is increased.
Identifying the Backwash Rate
Backwash rates should be adjusted to provide adequate
cleaning of the filter media without washing media into the
collection troughs or disrupting the support gravels.
Backwash rates in gpm/ft2 are calculated using backwash pump
rates or backwash flows (see Equation 5-2).
If pump rates or flows are unavailable or suspect, backwash
rates can be determined by performing a rise rate test of the
filter. Periodic rise rate tests can also be used to verify the
backwash flow measurement instruments. In the rise rate test,
you can determine the amount of time it takes backwash water
to rise a known distance in the filter bed. For this test, a metal
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See Appendix C for more
information and examples
on calculating filter
loading rates.
rod marked at 1-inch intervals (or similar device) is fixed in the
filter to enable measurement of the distance that water rises
during the wash. The rise rate test should be conducted so that
measurements are taken without the interference of the wash
water troughs in the rise volume calculation. Extreme care and
great attention to safety should be followed while conducting
the rise rate test. See Equations 5-2 and 5-3 and Example 5-3
for details on how to calculate the rise rate and backwash rate.
Equation 5-2 - Backwash Rate
Backwash Rate (gpm/ft2) = Backwash Flow (gpm)
Filter Surface Area (ft2)
Equation 5-3 - Backwash Flow Using Rise Rate Test
Backwash Flow (gpm) = Filter Surface Area (ft2) X Rise Distance (ft) X 7.48 gal/ft3
Rise Time (minutes)
Example 5-3 - Determining the Backwash Rate from the Rise Rate
A filter having a 150 ft2 surface area has a wash water rise of 10.7 inches in 20 seconds
during the rise rate test. You should calculate the backwash rate.
First, you should determine the backwash flow in the filter using Equation 5-3.
Backwash Flow (gpm) = 150 ft2 X 10.7 inches (1 ft/12 inches) X 7.48 gal/ft3
20 seconds (1 minute/60 seconds)
= 3,000 gpm
Second, you should determine the backwash rate using Equation 5-2.
Backwash Rate (gpm/ft2) = 3.000 gpm = 20 gpm/ft2
150ft2
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You should contact the
manufacturer to determine
the proper bed expansion
for the media in the filters.
Bed Expansion
It is also extremely important to expand the filter media during
the wash to maximize the removal of particles held in the filter
or by the media. However, care should be taken to ensure that
none of the media is lost through over-expansion, air scour, or
surface wash. Bed expansion may be determined by measuring
the distance from the top of the unexpanded media to a
reference point (e.g., top of the filter wall) and from the top of
the expanded media to the same reference point. Percent bed
expansion may be determined by dividing the bed expansion by
the total depth of expandable media (i.e., media depth less
support gravels) and multiplied by 100 (see Equation 5-4 and
Example 5-4). A proper backwash rate should expand the filter
20 to 25 percent, but expansion can be as high as 50 percent.
Attention should be given to the influence of seasonal
temperature changes on bed expansion during application of
this procedure (see Appendix D). You should contact the
manufacturer to determine the proper bed expansion for the
media in the filters.
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Equation 5-4 - Percent Bed Expansion
B
Top of Media
Support Gravel
A
A
w
Top of Media
During Backwash
Support Gravel
Before Backwash During Backwash
A = Depth to media as measured from top of sidewall before backwash.*
B = Media depth (less support gravel).*
C = Depth to expanded media as measured from top of sidewall during backwash.*
Percent Bed Expansion = A- C x 100
B
*Make sure all measurements have the same units.
Example 5-4 - Evaluating Filter Backwash Bed Expansion Using a Secchi
Disk
The backwashing practices for a filter with 30 inches of anthracite and sand is being
evaluated. While at rest, the distance from the top of the filter sidewall to the top of the
media is measured to be 41 inches. After the backwash has been started and the
maximum backwash rate is achieved, a probe containing a white disk (referred to as a
Secchi disk) is slowly lowered into the filter bed until anthracite is observed on the disk.
The distance from the expanded media to the top of the filter sidewall is measured to be
34 inches. The resultant percent bed expansion would be 23 percent.
Depth to media as measured from top of sidewall before backwash = A = 41 inches
Depth to expanded media as measured from top of sidewall during backwash = C = 34
inches
Depth of filter media = B = 30 inches
Percent Bed Expansion = (41 inches - 34 inches) * 100 =23%
30 inches
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Bed expansion should not
be measured during high
surface wash agitation.
A flashlight or high-power
cordless spotlight may be
useful when using a Secchi
disk to better identify
when media is on the disk.
When using a pipe organ
apparatus to measure bed
expansion, you should
make sure that the
apparatus is positioned
where not all of the pipe
segments will be filled.
A variety of devices can be used to measure bed expansion.
One common apparatus is a metal shaft with a white disk
(called a "Secchi" disk) attached on one end (Figure 5-13).
The disk unit is used by placing the disk on the unexpanded
media prior to backwash and recording the length of the metal
rod to the reference point. The disk unit is then removed and
backwashing is initiated. After the backwash is allowed to
reach its peak rate, the disk is lowered slowly into the
backwashing filter until media is observed on the disk. The
measurement of the expanded media is then recorded and the
percent bed expansion may then be determined. The media
expansion should be measured at several locations to see if
expansion occurs over the full surface area of the filter.
Uneven bed expansion throughout the filter could indicate
uneven distribution of backwash water or an underdrain or
support gravel problem. The key attribute of any method is
that determination of the top of the expanded media be
accurately characterized.
Figure 5-13. Secchi Disk
Another device used to measure bed expansion is a steel
measuring tape fitted along the shaft to a metal pole with an
attached collection of plugged pipe segments of varying
lengths. The pipes are arranged like a set of church organ pipes
with each pipe one inch longer than the next (see Figure 5-14).
The unit is solidly affixed, resting on the top of the media.
During backwashing the expanded media fills each successive
piece of pipe until the rise stops. Care should be taken to affix
the pipe organ apparatus so it can easily be determined where
bed expansion ended because if it is placed too low, all of the
pipe segments will be filled with expanded media, making it
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If a filter is meeting
backwash guidelines but is
not achieving turbidity
performance criteria, a
Floe Retention Analysis
may need to be conducted.
impossible to accurately determine media expansion. If this
occurs, the apparatus should be emptied, affixed higher in the
filter above the media and the bed expansion test repeated.
Figure 5-14. "Pipe Organ" Expansion
Backwash Effectiveness
A Floe Retention Analysis may be warranted if the filter is
meeting backwash expansion and backwash rate guidelines, but
still not achieving turbidity performance criteria (Kawamura,
2000). The Floe Retention Analysis procedure allows for an
in-depth analysis of the effectiveness of backwash practices.
The Floe Retention Analysis procedure, sometimes referred to
as the Sludge Retention Analysis procedure, can be used to
determine the amount of particle retention occurring at each
depth and area of the filter bed and the effectiveness of
backwash procedures.
The Floe Retention Analysis can be performed using the
following steps:
1. Completely drain the filter at the end of a filter run and
let stand for 2-1/2 hours.
2. Mark a one-gallon plastic bag (best to use a waterproof
marker) for each depth interval and collect four to eight
samples at representative sites in the filter bed at the
following depths: 0-2, 2-6, 6-12, 12-18, 18-24, 24-30,
and 30-36 inches. If the filter is more than 36 inches
deep, collect additional core samples in increments of 6
inches. Place the composite media samples from each
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When backwashing a
drained filter, be sure to
start the backwash very
slowly to remove air from
the filter.
depth in the appropriate one-gallon plastic bag. The
core samples can be obtained using a thin-walled 1-1/2-
inch galvanized pipe.
3. Prepare a 50 milliliter (mL) test sample from each of
the sample bags by lightly tamping the core samples
into a graduated cylinder. Transfer the 50 mL media
sample to a large (500 mL) flask or beaker and add 100
mL of water. Swirl for 1 minute. Decant the turbid
water from the sample into another beaker. Repeat this
washing procedure with each sample four more times so
that a total of 500 mL of water is used to wash out the
sludge adhered to the media from each sample depth.
Measure the turbidity of the 500 mL of wash water.
Multiply the recorded turbidity by two so that the final
tabulations for each depth will list the turbidity for 100
mL of sample instead of the 50 mL sample used.
Record the turbidity results for each depth of the media.
4. Be sure to start the backwash cycle very slowly to
remove air.
5. After the backwash is done, drain the filter completely.
6. Repeat Steps 2 and 3 in the same locations.
7. Backwash the filter and place it back in service. Be
sure to start the backwash very slowly to remove air.
8. The results should then be plotted to determine the floe
retention before and after backwash.
An ideal floe retention profile should show linear results with
more particle retention at the top of the filter than at the bottom
of the filter. Figures 5-15 and 5-16 show examples of Floe
Retention Analysis plots. Figure 5-15 indicates that most
particles are captured in the upper media of the filter and the
backwash effectively cleaned the media at all depths. Figure 5-
16 indicates that most particles are retained in the upper media
and at the sand/anthracite interface. In addition, the backwash
was not effective in cleaning the sand/anthracite interface.
Additional data on the filter media can be gathered, including
effective size and uniformity coefficient of the media.
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5. Filter Self-Assessment
Q.
O
I-
o
0.0
il -g 1.0
? I" 2.0
ฑ; il
E "S 3.0
5. 4.0
a>
Q
After
Backwash
Before
Backwash
0 100 200 300 400 500 600
Turbidity, NTU
Figure 5-15. Example of Floe Retention Analysis Results
for 4-foot Deep Mono Media Filter Bed
o
a
0.0
1.0
Sand / Anthracite
Interface
Si? 2.0
o
+j
a.
a>
Q
a 3.0
4.0
After
Backwash
Before
Backwash
0 100 200 300 400
Turbidity, NTU
500 600
Figure 5-16. Example of Floe Retention Analysis Results for
4-foot Deep Dual Media Filter Bed
(Note increased particle retention at media interface)
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You may need to vary the
backwash rate with
temperature changes
because water properties
vary with temperature.
A backwash SOP may
help train new operators
and improve operational
consistency.
Backwash Rate
You may want to consider varying the backwash rate as the
water temperature varies, because water properties vary with
temperature. Cold water is more viscous than warm water.
Therefore, you should decrease the backwash rate for colder
water and increase the backwash rate for warmer water. A
guide for adjusting the backwash rates is available in Appendix
D.
Terminating the Backwash
You should also evaluate criteria for terminating the backwash
process. Termination of the backwash should be based on
measured turbidity in the backwash water. Backwash samples
can be obtained every 30 seconds or every minute and analyzed
using a benchtop turbidimeter. A suggested guideline is that
the backwash process should be terminated if the backwash
turbidity is 10 to 15 NTU (Kawamura, 2000). Utilities should
watch the backwash and observe water quality routinely.
Backwash SOP
An adequate backwash SOP should describe specific steps
regarding when to initiate backwash, how flows are increased
or decreased during the wash, when to start and stop surface
wash or air scour, and the duration of the wash. The SOP may
help in training new operators and should improve operational
consistency.
5.4.5 Assessment of Placing a Filter Back Into
Service
Topic
Placing a Filter
Back into
Service
Description
Delayed start, slow
start, polymer
addition, or filter to
waste
Information
Actual
delayed start
Design
delayed start
Excerpt from Table 5-1 containing sample data.
Blank copies of the full version of this table can be
found in Table 5-1 and in Appendix B.
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Avoid starting dirty filters!
The methods used for placing a filter back into service after
backwashing varies. The following methods are used in some
water treatment plants:
Delayed start - The delayed start consists of letting the
filter rest for a period of time after backwashing and
before placing the filter back into service. This practice
has been found to reduce filter ripening times. The
length of this delay varies, so the rest period should be
determined by doing a study.
Slow start - The slow start technique involves a gradual
increase of flow through the filter until the desired
hydraulic loading rate is achieved. This practice can
reduce initial turbidity spikes but may require
modification of the system or manual operation of the
valve to control the feed rate to the filter.
Filter-to-waste - Filter-to-waste is a common practice
that allows filtered effluent to be sent to a part of the
plant other than the clearwell after the filter goes back
on-line. Once turbidity reaches an acceptable level, the
filtered effluent is discharged to the clearwell. You
should make sure that no cross connection exists
between the filter effluent and the waste location.
Addition of a coagulant or filter aid during initial
start-up of the filter or backwash - You may also
want to consider feeding a coagulant or filter aid during
the initial start-up of the filter or during the last part of
the backwash process. This option has been shown to
reduce initial turbidity spikes.
Some plants use a combination of the techniques above to
minimize filter turbidity spikes. Chapter 8 contains additional
information on these techniques.
You should avoid placing a dirty filter (one that has not been
backwashed) into service. This practice can result in very high
turbidities and has the potential to pass pathogens into the
finished water.
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5.4.6 Assessing Rate-Of-Flow Controllers and
Filter Valve Infrastructure
Topic
Rate-of-Flow
Controllers
and Filter
Valves
Description
Leaking valves
Malfunction rate
of flow control
valves
Equal flow
distribution to
each filter
Information
Actual
none
yes
no
Design
Yes
Excerpt from Table 5-1 containing sample data.
Blank copies of the full version of this table can be
found in Table 5-1 and in Appendix B.
The rate-of-flow controllers and ancillary valving related to the
filter can have a significant impact on filter performance.
Rapid hydraulic changes may cause filters to shed particles.
Maintaining and calibrating or verifying the accuracy of rate-
of-flow controllers is an important part of minimizing
hydraulic changes through the filter.
Improperly seated valves can leak and affect filter
performance. All filter assessments should include an
evaluation of all rate-of-flow controllers and filter valving.
Leaking Valves
One way to check for leaking effluent valves is to close the
filter influent and effluent valves and observe the water level
change in the filter. If the water level continues to drop with
the valves closed, there may be a leaking effluent valve. If the
water continues to rise, then there may be a leaking influent
valve. The filter profile may be useful in determining if a
leaking valve exists. Also, listening to the valves can help
detect problems.
Flowmeters
If individual filter effluent totalizers are available, you should
compare total daily effluent volumes for each filter. This
process may help identify which filter is operating too high or
too low compared to other filters. The problem may be a
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5. Filter Self-Assessment
See Section 7.2.2 for
information on
coagulation.
poorly operating valve, a controller malfunction, or problems
in the filter media.
Level Indicators and Speed Control Valves
If your plant is automated, it is critical to ensure that the
instruments that govern filtration work properly.
5.4.7 Other Considerations
Topic
Other
Considerations
Description
Chemical feed
problems
Rapid changes in
raw water quality
Turbidimeters
(calibrated)
Other
Information
Actual
no
no
properly
calibrated
Design
yes
Excerpt from Table 5-1 containing sample data.
Blank copies of the full version of this table can be
found in Table 5-1 and in Appendix B.
You may want to investigate other plant processes and data if
any of the previously discussed areas do not seem to be causing
the problem that triggered the filter self-assessment. You may
want to examine chemical feed processes, raw water quality,
and turbidimeters.
Chemical Feed Rates
Chemical feed processes and coagulation are important for
proper floe formation. Poor floe formation can result in
particles being passed through the filter. You may want to
investigate chemical pumps and make sure the proper
chemicals and feed rates are being used.
Raw Water Quality
A sudden change in raw water quality can cause particles to be
passed through the filter, particularly if chemical feed rates
cannot be adjusted in a timely manner. You may want to check
raw water turbidity values and see if the turbidity spike was
caused by a sudden increase in raw water turbidities.
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See Chapter 3 for more
information on calibrating
turbidimeters.
You should consult with
the State to ensure
agreement with your
interpretation of the data.
Turbidimeters
You may want to calibrate and verify that turbidimeters are
properly recording filtered water turbidimeter values.
Turbidimeters can lose their accuracy over time and require
calibration.
5.5 ASSESSMENT OF APPLICABILITY OF
CORRECTIONS
After all the information on the filter has been collected on
Table 5-1, you can start assessing factors that caused the
turbidity levels that triggered the filter self-assessment. You
may need to modify one or more of the filter features or
operating conditions to address the event that triggered the
filter self-assessment. In more severe instances, system-wide
modifications may be needed. (These modifications would be
identified through a CPE effort.) Table 5-1 may help identify
areas of modification for the filter. Following are some
examples of how corrections could be applied:
Modifying filter run times.
Creating or modifying a backwash SOP.
Extending the filter backwash period to a time that
results in acceptable filter turbidity levels.
Replacing filter media if the filter media was
determined to have reached its useful life.
Adding more filters if filter loading rates were
determined to be too high and additional filters are
needed.
Many combinations of filter modifications exist, and you may
have to try more than one modification to solve the problem.
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You should consult the
State regarding the proper
format and reporting
requirements for the filter
self-assessment report.
5.6 PREPARATION OF THE REPORT
A system must prepare a report of the filter self-assessment.
You should consult with the State on the proper format and
State-specific reporting requirements. The report should
include all the areas of the filter and filter operations examined
and modifications that resulted in acceptable turbidity levels.
If the problem cannot be identified within the timeframe
allowed for completion of the self-assessment, the report
should specify the anomalies that were observed and explain
whether any corrective actions have yielded improvements. An
example of a completed filter self-assessment report is included
in Appendix E.
5.7 REFERENCES
1. AWWA. 1999. Water Quality and Treatment. Fifth Edition. McGraw-Hill, Inc. New
York, New York.
2. Kawamura, S. 2000. Integrated Design of Water Treatment Facilities. John Wiley &
Sons, Incorporated. New York, NY.
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6. COMPREHENSIVE PERFORMANCE
EVALUATION
Detailed CPE procedures
are not included in this
guidance manual, but can
be found in Optimizing
Water Treatment Plant
Performance Using the
Composite Correction
Program Handbook (EPA,
1998). This document can
be obtained by calling the
EPA Safe Drinking Water
Hotline at 1-800-426-4791.
40 CFR Section
141.563(c)
If individual filter effluent
turbidity exceeds 2.0 NTU
in two consecutive
recordings taken 15
minutes apart for two
consecutive months, then a
CPE must be conducted.
6.1 INTRODUCTION
The Comprehensive Performance Evaluation (CPE) is the
evaluation phase of the Composite Correction Program (CCP).
The goal of this chapter is to present a fundamental discussion
of CPE concepts and provide an overview of what a system
should expect when a CPE is completed.
Based on results of individual filter monitoring requirements
in the LT1ESWTR, some systems may be required to arrange
for a CPE. Specifically, systems must arrange for a CPE if any
individual filter has a measured turbidity level greater than 2.0
NTU in two consecutive recordings taken 15 minutes apart for
2 months in a row (or if the combined filter effluent has a
measured turbidity greater than 2.0 NTU in two consecutive
recordings taken 15 minutes apart for 2 months in a row for
systems with two filters that monitor combined filter effluent
in lieu of individual filters). In addition, systems must report
the filter number, the turbidity value, the date(s) on which the
exceedance occurred, and the reason for the exceedance (if
known) as part of the monthly report. The system must
arrange for a CPE no later than 60 days following the day the
filter exceeded 2.0 NTU in two consecutive 15-minute
measurements for the second straight month. The CPE must
be completed and submitted to the State no later than 120 days
following the day the filter exceeded 2.0 NTU in two
consecutive measurements for the second straight month. A
separate CPE is not required if the State or State-approved
third party has completed a CPE of the system within 12
months prior to the exceedance or the system and State are
jointly participating in an ongoing Comprehensive Technical
Assistance (CTA) project. The CPE must be conducted by the
State or a third party approved by the State.
The CPE is a thorough review and analysis of a treatment
plant's performance-based capabilities and associated
administrative, operation, and maintenance practices. It is
conducted to identify factors that may be adversely impacting
a plant's capability to achieve compliance and emphasizes
approaches that can be implemented without significant capital
improvements. The CPE typically takes 3 to 5 days and is
conducted by a team of two or more personnel. The major
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Major Components of a
CPE
components of the CPE process must include:
1. Assessment of plant performance;
2. Evaluation of major unit processes;
3. Identification and prioritization of factors limiting
performance;
4. Assessment of applicability of the follow-up phase (i.e.
comprehensive technical assistance); and,
5. Preparation of a CPE report..
At the core of the CPE is the assumption that if a filtration
plant cannot achieve specific performance, there is a unique
combination of interrelated factors with respect to the design,
maintenance, administration, or operations of the filtration
plant that are limiting its performance. The purpose of the
CPE is to identify these factors and prioritize them according
to their relative importance in preventing compliance or
optimized performance. Once the factors are identified and
prioritized, they can be corrected so that performance can be
improved and compliance can be achieved.
During a CPE, the historic performance of the plant should be
assessed with respect to pathogen removal and inactivation.
The design, administration, and maintenance of the plant
should be completely reviewed to determine if they properly
support a plant capable of meeting specified filtration goals. If
they are not supporting a capable plant, the root causes are
identified as to how they are contributing to the performance
problem. Operational practices should also be reviewed to
determine whether operators have the necessary skills to
achieve required performance and compliance when provided
with a capable plant.
Figure 6-1 provides an overview of the CPE process.
For more information on the CPE process, refer to Optimizing
Water Treatment Plant Performance Using the Composite
Correction Program Handbook (EPA, 1998).
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6. Comprehensive Performance Evaluation
Initial Activities
| Kick-Off Meeting
Plant Tour
Location
Off -Site
t
Data Collection Activities
Administrative Design Data Operations Data
Data
Conduct
Performance
Assessment
Perform
Field Evaluations
Conduct Interviews
Identify and Prioritize
Factors
Assess Applicability of
Comprehensive
Technical Assistance
Exit Meeting
CPE Report
Maintenance Performance
Data Data
k
Evaluate
Major Unit On-Site
Processes
1
r
Off -Site
Figure 6-1. Typical Components of Activities During a CPE
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6. Comprehensive Performance Evaluation
6.2 REFERENCES
USEPA. 1998. Handbook: Optimizing Water Treatment Plant Performance Using the
Composite Correction Program (EPA 625-6-91-027). Washington, D.C.
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7. TURBIDITY AND THE TREATMENT
PROCESS
In this Chapter:
The Treatment Process
Recycle Streams
This chapter does not
cover all aspects of water
treatment. For more
information, review the
cited references.
7.1 TURBIDITY- WHY is IT IMPORTANT?
Turbidity is the measure of how clear a liquid is and how much
light is scattered by the sample (AWWA, 1990). It is measured
in nephelometric turbidity units (NTU). Turbidity should not
be confused with suspended solids, which expresses the weight
of suspended material in the sample. There is no direct
relationship between suspended solids and turbidity and exact
comparisons between the two are difficult to make. Factors that
contribute to turbidity in surface water are soil particles,
organic matter, and pathogens (bacteria, viruses, and protozoa).
Figure 7-1 provides a detailed overview of particle types and
sizes found in surface water.
Turbidity in the water creates both aesthetic and health issues.
Surface water treatment plants remove particles because they
can cause objectionable appearances, tastes, and odors and can
interfere with disinfection. Also, some pathogens, such as
Cryptosporidium., which have been linked to waterborne
diseases, are resistant to certain disinfectants. The most
effective treatment for Cryptosporidium is filtration to ensure
its removal. The LT1ESWTR requires filtered systems to
achieve a 2-log removal of Cryptosporidium to reduce the
possibility of waterborne diseases. Chapter 2 contains
information on the turbidity monitoring requirements.
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7. Turbidity and the Treatment Process
MACRO
MICRO
MACRO
MOLECULAR
MOLECULAR
IONIC
SUSPENDED PARTICLES
DISSOLVED PARTICLES
Micron
Scale
1,000
Source: Osmonics, Inc., 1996; AWWA, 1990.
Note: 1 micron = 1 x 10~6 meters = 4 x 10~5 inches
Figure 7-1. Particle Size Spectrum
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7. Turbidity and the Treatment Process
Producing consistently low
effluent turbidity values
ensures the public safety
regarding drinking water.
7.2 THE TREATMENT PROCESS
Turbidity measurements are used to assess filter performance at
a treatment plant. However, many other processes are involved
in treating surface water. The surface water treatment process
includes some or all of the following processes:
Pre-sedimentation;
Coagulation;
Flocculation;
Sedimentation and/or Clarification;
Filtration; and,
Disinfection.
Turbidity readings are usually taken of raw water, settled water,
and filtered water to provide information for process control
and to measure plant performance. Operators track raw water
quality and adjust the treatment processes as necessary (such as
coagulant and polymer feed rates). The two most common
types of processes used to treat surface water are conventional
treatment and direct filtration. Conventional treatment is
typically used for source water that is high in turbidity, and
direct filtration is more suitable for low-turbidity water.
Figures 7-2 and 7-3 provide schematics for these two treatment
processes.
In combination, all of the treatment processes of a surface water
treatment plant provide a multiple barrier strategy. Microbial
pathogens can be physically removed as particles through
coagulation, flocculation, sedimentation, and filtration and are
inactivated by disinfection. The level of protection achieved in
a water system can be increased by optimizing the particle
removal processes and by properly operating the disinfection
processes (see Chapter 8). A brief discussion of each treatment
process follows.
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7. Turbidity and the Treatment Process
Spent Filter
Backwash
Figure 7-2. Conventional Treatment System
Raw Water
Influent
Finished Water to
Distribution
System
Figure 7-3. Direct Filtration System
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7. Turbidity and the Treatment Process
40 CFR Section 141.2
defines coagulation as a
process using coagulant
chemicals and mixing by
which colloidal and
suspended materials are
destabilized and
agglomerated into floes.
You should perform jar
tests or pilot tests prior to
modifying chemical feed
practices. You should
check with the State if
considering modifications
to chemical feed practices.
7.2.1 Pre-Sedimentation
Not all systems use pre-sedimentation, but pre-sedimentation is
often used when raw water turbidity is high or highly variable.
Pre-sedimentation basins range in size, depending on the flow,
and the water is sometimes pre-treated with a coagulant and/or
a polymer prior to entering the pre-sedimentation basin
(AWWA, 1999). The addition of coagulants and/or polymers
at this point in the treatment process could be helpful if a
system needs to reduce the natural organic matter entering the
plant. Natural organic matter is a disinfection byproduct
precursor, and if a system has high organic matter (measured as
total organic carbon, or TOC), then pre-sedimentation could be
beneficial for system compliance.
7.2.2 Coagulation
Coagulation is a process used for increasing the tendency of
small particles in suspension to attach to one another and to
attach to surfaces, such as the grains in the filter bed (AWWA,
1999). Typical coagulants used are discussed below:
Primary coagulants: Primary coagulants are used to
cause particles to become destabilized and begin to
clump together (California State University, 1994).
Examples of primary coagulants are metallic salts, such
as aluminum sulfate (referred to as alum), ferric sulfate,
and ferric chloride. Cationic polymers may also be
used as primary coagulants.
Coagulant Aids and Enhanced Coagulants:
Coagulant aids and enhanced coagulants add density to
slow-settling floe and help maintain floe formation
(California State University, 1994). Organic polymers,
such as polyaluminum hydroxychloride (PAC1), are
typically used to enhance coagulation in combination
with a primary coagulant. The advantage of these
organic polymers is that they have a high positive
charge and are much more effective at small dosages.
Even though they may be more expensive, a smaller
amount may be needed, thereby saving money. Organic
polymers also typically produce less sludge.
Mixing distributes the coagulant, which may actually
temporarily increase the turbidity. Additional treatment
processes (flocculation, sedimentation, and filtration) remove
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The pH range will vary
from plant to plant. For
instance, softening plants
typically operate at higher
pHs for effective softening.
You should be careful if
alum is used at a low pH
and then pH is suddenly
increased later in the
treatment process. This
sudden increase in pH can
result in floe settling out in
subsequent treatment units,
such as the clearwell.
particles. Temperature, nature of turbidity, coagulant dose,
mixing intensity, and pH affect the coagulation process.
Coagulants and Polymers
Chemicals commonly used in the coagulation process include
aluminum or iron salts and organic polymers. The most
common aluminum salt used for coagulation is aluminum
sulfate, or alum. Alum may react in different ways to achieve
coagulation. When used at relatively low doses (<5 mg/L),
charge neutralization (destabilization) is believed to be the
primary mechanism involved. At higher dosages, the primary
coagulation mechanism tends to be entrapment. In this case,
aluminum hydroxide (A1(OH)2) precipitates forming a "sweep-
floe" that tends to capture suspended solids as it settles out of
suspension.
The pH of the water plays an important role when alum is used
for coagulation because the solubility of the aluminum species
in water is pH dependent. If the pH of the water is between 4
and 5, alum is generally present in the form of positive ions
(i.e., A1(OH)2+, A18(OH)4+, and A13+). However, optimum
coagulation occurs when negatively charged forms of alum
predominate, which occurs when the pH is between 6 and 8.
When alum is used and charge neutralization is the primary
coagulation mechanism, effective flash mixing is critical to the
success of the process. When the primary mechanism is
entrapment, effective flash mixing is less critical than
flocculation.
Ferric chloride (FeCls) is the most common iron salt used to
achieve coagulation. Its reactions in the coagulation process
are similar to those of alum, but its relative solubility and pH
range differ significantly from those of alum.
Both alum and ferric chloride can be used to generate inorganic
polymeric coagulants. These coagulants are typically
generated by partially neutralizing concentrated solutions of
alum or ferric chloride with a base such as sodium hydroxide
prior to their use in the coagulation process (AWWA and
ASCE, 1990). The resulting inorganic polymers may have
some advantages over alum or ferric chloride for turbidity
removal in cold waters or in low-alkalinity waters.
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7. Turbidity and the Treatment Process
Mixing intensity is
typically quantified with a
number known as the
"velocity gradient" or "G"
value. The G value is a
function of the power input
into the mixing process
and the volume of the
reaction basin. Typical G
values for coagulation
mixing range from 300 to
8,000 sec"1 (Hudson,
1981).
Organic polymers tend to be large molecules composed of
chains of smaller "monomer" groups (AWWA and ASCE,
1990). Because of their large size and charge characteristics,
polymers can promote destabilization through bridging, charge
neutralization, or both. Polymers are often used in conjunction
with other coagulants such as alum or ferric chloride to
optimize solids removal.
Rapid Mixing
Mixing distributes the coagulant chemicals throughout the
water stream. When alum or ferric chloride is used to achieve
destabilization through charge neutralization, it is extremely
important that the coagulant chemical be distributed quickly
and efficiently because the intermediate products of the
coagulant reaction are the destabilizing agents. These
intermediate species are short-lived and they must contact the
solids particles in the water if destabilization is to be achieved.
When other mechanisms are predominant in the coagulation
process, or when organic polymers are being used as the
coagulant chemical, immediate distribution of the coagulant
chemical is not as critical and less-intense mixing may be
acceptable, or even desirable. In some cases, excessive mixing
may serve to break up coagulant molecules or floe particles,
thereby reducing the effectiveness of subsequent solids removal
processes.
The time needed to achieve efficient coagulation varies
depending on the coagulation mechanism involved. When the
mechanism is charge neutralization, the detention time needed
may be one second or less. When the mechanism is sweep floe
or entrapment, longer detention times on the order of 1 to 30
seconds may be appropriate (Kawumara, 2000; AWWA and
ASCE, 1998; Hudson, 1981).
In general, the lower the coagulant dosage, the faster the
mixing should occur because chemical reactions happen very
quickly at low dosages. Rapid mixing disperses a coagulant
through the raw water faster than the reaction takes place.
When alum or ferric chloride are used in lower dosages (for
charge destabilization; not sweep floe development), it is
important to ensure that they mix very quickly with the raw
water to be effective.
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7. Turbidity and the Treatment Process
40 CFR Section 141.2
defines flocculation as a
process to enhance
agglomeration or
collection of smaller floe
particles into larger, more
easily settleable particles
through gentle stirring by
hydraulic or mechanical
means.
Figure 7-4. Chemical Feed Pump (Alum)
Effect on Turbidity
Coagulation by itself does not reduce turbidity. In fact,
turbidity may increase during the coagulation process due to
additional insoluble compounds that are generated by chemical
addition. The processes of flocculation, sedimentation, and
filtration should be used with coagulation to reduce suspended
solids and turbidity.
7.2.3 Flocculation
Flocculation is the "snowballing" of small particles into larger
particles (called "floe") that can be more easily removed from
water. Particles grow by colliding with other particles, and
sticking together. Detention time is necessary for the formation
of floe. The longer the detention time, the larger the floe.
Temperature and pH also affect the flocculation process.
Flocculation is almost always used in the water treatment
process after coagulation. Large particles are then more readily
removed from the water in subsequent sedimentation and
filtration processes.
Slow Mixing
Slow mixing is a key aspect of the flocculation process. In
slow mixing, the water is stirred to encourage floe particles to
clump together. Stirring too fast can break large particles apart,
while stirring too slowly can prevent particles from clumping
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7. Turbidity and the Treatment Process
When floe is stirred
rapidly, "shearing" can
occur. Shearing is when
the floe itself breaks down
into smaller polymer
chains. It is extremely
difficult to remove both
the sheared flocculant and
the particles.
enough. A wide variety of flocculation-mixing mechanisms
have been used in water treatment. They include vertical shaft
mechanical mixers, horizontal shaft mechanical mixers, and
hydraulic mixing systems. Often, optimum performance is
achieved by reducing the intensity of mixing as the water
proceeds through flocculation (known as tapered or staged
flocculati on). Engineers have developed methods of
determining appropriate stir rates, called "mixing intensity
values," abbreviated as the letter "G." Generally, slow mixing
should start out relatively fast (G values of 60 to 70 sec"1) to
promote clumping, and end up slower to prevent the larger
clumps from breaking apart (G values of 10 to 30 sec"1)
(Kawamura, 2000). Many plants have found that changing
mixers or mixing speed can improve floe characteristics,
leading to lower clarified or settled turbidity before filtration.
Detention Time
The amount of time the water spends in the flocculation
process is a key performance parameter. Adequate time should
be provided to allow the generation of particles that are large
enough to be removed efficiently in subsequent treatment
processes. There is a wide range of optimum particle sizes,
depending on what treatment processes are used downstream.
For example, when sedimentation is used (conventional
treatment), large floe particles are typically desirable because
they readily settle out of suspension. If filtration directly
follows the flocculation process (direct filtration), smaller floe
particles may be the most desirable since they tend to be
stronger and less susceptible to breaking up from the shear
forces within the filters. Overall detention time in the
flocculation process typically ranges from 10 to 30 minutes and
is generally provided in several different basins or basin
segments so the mixing intensity can be varied through the
process.
Effect on Turbidity
As with coagulation, the purpose of flocculation is not to
directly reduce turbidity or suspended solids, but to prepare the
solids for subsequent removal. Flocculation reduces the
number of suspended solids particles as smaller particles
combine to form larger ones. This process may, or may not,
result in reduced turbidity in the flocculation chamber.
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7. Turbidity and the Treatment Process
40 CFR Section 141.2
defines sedimentation as a
process for removal of
solids before filtration by
gravity or separation.
The efficiency of
sedimentation directly
affects sedimentation basin
effluent turbidity.
7.2.4 Sedimentation and Clarification
Sedimentation is the process by which suspended particles are
removed from the water by means of gravity or separation. In
the sedimentation process, the water passes through a relatively
quiet and still basin. In these conditions, the floe particles
settle to the bottom of the basin, while "clear" water passes out
of the basin over an effluent baffle or weir. Figure 7-5
illustrates a typical rectangular sedimentation basin. The solids
collect on the basin bottom and are removed by a mechanical
"sludge collection" device. As shown in Figure 7-6, the sludge
collection device scrapes the solids (sludge) to a collection
point within the basin from which it is pumped to disposal or to
a sludge treatment process.
Sedimentation involves one or more basins, called "clarifiers."
Clarifiers are relatively large open tanks that are either circular
or rectangular in shape. In properly designed clarifiers, the
velocity of the water is reduced so that gravity is the
predominant force acting on the water/solids suspension. The
key factor in this process is speed. The rate at which a floe
particle drops out of the water has to be faster than the rate at
which the water flows from the tank's inlet or slow mix end to
its outlet or filtration end. The difference in specific gravity
between the water and the particles causes the particles to settle
to the bottom of the basin. Some plants have added baffles or
weirs in their sedimentation basins to limit short-circuiting
through the basins, promoting better settling.
Other forms of sedimentation used in the water industry are:
Tube and plate settlers;
Solids contact clarifiers, sludge blanket clarifiers, and
contact clarifiers; and,
Dissolved air flotation.
These forms of sedimentation typically allow for higher
loading rates and/or improved particle removal than the basins
illustrated in Figures 7-5 and 7-6. More information on these
sedimentation processes is presented in the following sections.
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7. Turbidity and the Treatment Process
Inlet
Inlet
Weirs
Plan View
Side View
Outlet
Outlet
Figure 7-5. Rectangular Sedimentation Basin
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7. Turbidity and the Treatment Process
FEEDWELL
EFFLUENT DROP-OUT
LAUNDER
WALKWAY
WEIR
INFLUENT PIPE -
Source: AVWVA and ASCE, 1990.
SLUDGE DRAW-OFF PIPE
Figure 7-6. Circular Radial-Flow Clarifier
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7. Turbidity and the Treatment Process
Tube and Plate Settlers
Inclined tubes and plates can be used in sedimentation basins to
allow greater loading rates. This technology relies on the theory
of reduced-depth sedimentation: particles need only settle to the
surface of the tube or plate below for removal from the process
flow. Generally, a space of two inches is provided between tube
walls or plates to maximize settling efficiency. The typical angle
of inclination is about 60 degrees, so that settled solids slide down
to the bottom of the basin. Figure 7-7 illustrates a plate settler
used for high-rate sedimentation.
ADJUSTABLE WEIR
OUTLET TROUG
INLET BOTTOM
INLET FLUME
INLET ORIFICE
OUTLET
BOTTOM
Source: AVWVA and ASCE, 1998.
Figure 7-7. Plate Settlers Used for High-Rate Sedimentation
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7. Turbidity and the Treatment Process
Accelatorฎ solids
contact clarifier
Sludge blanket
clarifier ^^ป
Contact clarifiers
Solids Contact Clarifiers. Sludge Blanket Clarifiers.
and Contact Clarifiers
Solids contact clarifiers represent an entirely different approach
to high-rate clarification. They consist of a basin similar to that
used for a conventional clarifier, but with a sludge recycle
system to promote development of a dense sludge blanket that
captures floe. There are numerous types of solids contact units
on the market in the United States. These units are all similar in
design in that they combine solids contact mixing, flocculation,
solids-water-separation, and continuous removal of sludge in a
single package-type basin. The recirculation rate of water and
solids in solids contact units is critical to the units' effective
operation. Too high a recirculation rate will cause the sludge
blanket to lift and create increased loading to the filters.
An Accelatorฎ solids contact clarifier is shown in Figure 7-8.
Raw water enters the primary mixing and reaction zone, where
it receives the coagulant chemical. Coagulation and
flocculation begin in this chamber in the presence of previously
formed floe particles. These particles provide the nucleus of
new floe particles. The resulting solids precipitant is pumped
up into a secondary mixing and reaction zone. More gentle
mix energy in this chamber allows completion of the
flocculation process and separation of the solids. The mixture
of solids and water flows down a draft tube. The downward
flow starts the solids particles on a path down the hood to the
sludge blanket at the bottom of the basin. Clear water flows up
at a constantly reducing velocity that allows small particles to
settle out. Other manufacturers of solids contact units may
have flow patterns different than the Accelatorฎ flow pattern.
Sludge blanket clarifiers are a variation of solids contact units
in which coagulated water flows up through a blanket of
previously formed solids. As the small, coagulated particles
enter the sludge blanket, contact with other particles in the
blanket causes flocculation to occur. The floe grows in size
and becomes part of the blanket. A blanket depth of several
feet is required for efficient clarification (AWWA and ASCE,
1998).
Contact clarifiers (sometimes referred to as contact adsorption
clarifiers) are designed to provide flocculation and clarification
in a single process. These clarifiers consist of a basin filled
with adsorption media, generally plastic or rock about the size
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7. Turbidity and the Treatment Process
of pea gravel. As water passes through the media, hydraulic
mixing promotes flocculation and the flocculated particles
adhere to the surface of the media particles. The media is
cleaned periodically using an air, or air and water, backwash
process to remove the solids.
Orifice
Effluent
Impeller
Drive
r~H"h
Secondary mixing
and Reaction
>Draft Tubes
Rotor Impeller / III \ _ -ซ-^
Clarified
Water
/ Return /
Primary nbibcmg anql I I \
\ tฃeacti^ Zone/ / / /
X ^. s ^ -' -' '
Influent
M H
Hood
Source: AVWVA and ASCE, 1998.
Sludge Discharge
Blow-off
and Drain
Figure 7-8. Accelatorฎ Solids Contact Unit
Dissolved Air Flotation
Dissolved air flotation clarifiers bubble air into the flocculated
water and cause the floe particles to float to the surface.
Dissolved air flotation clarification allows for loading rates up
to 10 times that of conventional clarifiers (AWWA and ASCE,
1998). Dissolved air flotation consists of saturating a side-
stream with air at high pressure and then injecting it into a
flotation tank to mix with incoming water. As the side-stream
enters the flotation tank, the pressure drop releases the
dissolved air. The air bubbles then rise, attaching to floe
particles and creating a layer of sludge at the surface of the
tank. The clarified water is collected near the bottom of the
tank.
Effect on Turbidity
Reducing filter loads may
extend filter run times and
decrease the frequency of
backwashes.
Sedimentation may remove suspended solids and reduce
turbidity by about 50 to 90 percent, depending on the nature of
the solids, the level of pretreatment provided, and the design of
the clarifiers. Common values are in the 60 to 80 percent range
(Hudson, 1981). A primary function of the sedimentation/
clarification process is to reduce the load of solids going to the
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40 CFR Section 141.2
defines filtration as a
process for removing
participate matter from
water by passage through
porous media.
Filter-to-waste is also
referred to as rinse cycle or
re wash cycle.
filters. Optimization of the clarification process will minimize
solids loading on the filters and will contribute to enhanced
filter performance and better overall treated water quality.
7.2.5 Filtration
Filtration removes particles and decreases turbidity. Operators
should be familiar with the following terms that relate to filters:
Backwashing: A process used to clean the filter. In
backwashing, an upward flow of water or a combination
of upflowing water and air is pushed backwards through
the filter. The flow washes out the load of particles in
the filter. Backwashing is typically triggered at systems
based on any one or a combination of three criteria:
when the head loss across the filter reaches a certain
limit (established by the supplier, design engineer, or
operator), the filter effluent increases in turbidity (or
particle counts) to an unacceptable level, or at a regular
interval of time established by experience or by the
supplier. Typical time limits for a filter run can range
from 24 hours to 96 hours.
Breakthrough: Towards the end of a filter run, the
filter contains a large number of particles. When the
filter carries too large a load, its removal ability
decreases and increased numbers of particles pass
through the filter. This is referred to as breakthrough.
The result is decreasing filter effluent quality.
Breakthrough can result due to excessive filter run time,
poor chemical treatment, or other reasons.
Backwashing is necessary to clean the filter.
Filter-to-waste: The process of discharging filtered
water back to the plant headworks, raw water reservoir,
sanitary sewer, or surface water. This occurs during the
filter ripening period, the initial filter operating period
after backwashing.
Several technologies exist to accomplish particle removal:
Granular Bed Filters (i.e., slow sand, rapid granular bed,
and pressure filters);
Diatomaceous Earth (Precoat) Filters; and,
Membranes.
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Granular bed filters can be
gravity or pressure driven
and can consist of one or
several types of media.
Slow sand filter
Schmutzdecke is the
biologically active layer in
a slow sand filter.
Granular Bed Filters
Granular bed filters pass pre-treated water through a granular
bed at varying rates. Flow is typically downward and can
either be by gravity or pressure. As pre-treated water passes
through the filter, solids are removed and accumulate within
the filter. This clogging results in a gradual increase in head
loss, which is one method used to determine when the filter
needs backwashing. The materials commonly used in the filter
(the filter media) are sand, crushed anthracite coal, granular
activated carbon, or garnet. The filter can use just one of these
materials or a combination of materials. When two materials
are used, the filter is called a dual-media filter. If more than
two materials are used, then the filter is classified as a multi-
media filter. When more than one medium is used, the coarser
material is placed at the top and the finer material is placed on
the bottom. There are various types of granular bed filters,
such as slow sand filters, rapid granular bed filters, and
pressure filters.
Chemical pretreatment is important for proper particle removal
in rapid granular bed filters and pressure filters. Chemical
pretreatment is necessary to cause small particles to become
larger particles. Larger particles are easier to remove in the
processes preceding filtration and improve the transport
mechanisms in filtration. In addition, chemical pretreatment
enhances the attachment forces that help retain the particles in
the filter (AWWA, 1999). On occasion, chemical pretreatment
is used for slow sand filtration and is being studied further to
allow slow sand filtration to be used for a wider range of source
water characteristics.
Slow sand filters use a low application rate of water over a bed
of fine sand. Application rates are typically between 0.016
gpm/ft2 and 0.16 gpm/ft2 (AWWA, 1999). Figure 7-9 depicts
the general configuration of a slow sand filter. The filtered
water is collected at the bottom of the filter in a gravel bed
containing perforated pipe. A slow sand filter develops a
biologically active layer called a schmutzdecke on the top that
provides biological treatment of the water. Within the
schmutzdecke, biological action breaks down some of the
organic matter. Inert suspended particles may be physically
strained out of the water. As the water moves through the
filter, additional biological treatment and physical straining
occurs. Slow sand filters are cleaned by removing the
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7. Turbidity and the Treatment Process
Rapid granular bed
filter
schmutzdecke along with a small amount of sand. This process
is called scraping. The scraping process can by repeated
several times until the depth of the filter bed has decreased to
about 16 to 20 inches. The filter material that is removed needs
to be replaced.
Rapid granular bed filters consist of one or more media. Water
is applied at higher flow rates between 2 gpm/ft2 and 10
gpm/ft2. Rapid granular bed filters are equipped with an
underdrain system that supports the filter media, collects
filtered water, and evenly distributes backwash water and air
scour (if air is used). The underdrain system sometimes
consists of slotted pipe in a gravel bed. Figure 7-10 depicts a
rapid granular bed filter.
SLOW SAND FILTER
FINISHED WATER
STORAGE
SOURCE WATER
SUPERNATANT
WATER DRAIN
FILTER TO WASTE
AND BACKFILLING
^ ^ ft
^7 HEAD SPACE
SUPERNATANT WATER
SCHMUTZDECKE
' SAND MEDIA
SUPPORT GRAVEL
rcPfK-ffcPj^^cP^tflJcQ?^^
II Illlllll II II II II Illllllllll [-
FLOW METER
VENT
n
V
UNDERDRAIN
EFFLUENT
Cl,
TO
DISTRIBUTION
Source: AVWVA and ASCE, 1998.
Figure 7-9. Typical Covered Slow Sand Filter Installation
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7. Turbidity and the Treatment Process
FILTER MEDIA
GRAVEL
UNDERDRAIN BLOCKS
Source: AVWVA and ASCE, 1998.
Figure 7-10. Typical Rapid Granular Bed
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7. Turbidity and the Treatment Process
Pressure filter
Pressure filters are similar in design to rapid granular bed
filters, except that the water enters the filter under pressure and
leaves the filter at a slightly reduced pressure (AWWA, 1999).
Pressure filters are typically designed to operate in a downward
flow manner. Figure 7-11 depicts a pressure filter that is
designed to operate in a downward flow.
INFLUENT
EFFLUENT
BAFFLE PLATE
^ FILTERING SURFACE
o o
SAND
GRAVEL
o o o o o o
o o
-------
7. Turbidity and the Treatment Process
Membranes can adequately
remove several
contaminants of concern
from water. The
contaminants removed
depend on the pore size of
the membrane used.
Membranes
Four basic classes of membrane technology are currently used
in the water treatment industry: reverse osmosis, nanofiltration,
ultrafiltration, and microfiltration. Figure 7-12 presents the
typical pore size range and removal capabilities of these
membrane process classes. Membranes have a distribution of
pore sizes, which varies according to the membrane material
and manufacturing process. When a pore size is stated, it can
be presented as either nominal (i.e., the average pore size) or
absolute (i.e., the maximum pore size) in terms of microns
(|im). The removal capabilities of reverse osmosis and
nanofiltration membranes are typically not stated in terms of
pore size, but instead as a molecular weight cutoff representing
the approximate size of the smallest molecule that can be
removed by the membrane.
All of these membrane processes are effective at removing
Giardia, Cryptosporidium, and most bacteria (provided the
membrane has no leaks). The amount of removal depends on
the type of membrane used. Reverse osmosis, nanofiltration,
and ultrafiltration should also remove viruses, assuming there
are no leaks in the membranes. Reverse osmosis and
nanofiltration are capable of removing inorganic and organic
contaminants, including DBF precursors (AWWA, 1999).
Membranes can be effective in decreasing the amount of DBFs
formed:
The removal of pathogens by membranes should reduce
the amount of disinfectant required for inactivation and
should result in lower finished water DBF
concentrations; and,
The removal of DBF precursors should result in lower
finished water DBF concentrations (when reverse
osmosis or nanofiltration is used).
It is important to remember that these membrane processes are
physical barriers only, and they should be followed by
disinfection to ensure inactivation of pathogens not removed by
the membrane barrier, control of bacterial regrowth in
downstream system plumbing, and an adequate distribution
system residual. Membranes can also be used to achieve other
treatment objectives. More information on membranes can be
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7. Turbidity and the Treatment Process
obtained from the Membrane Filtration Guidance Manual
(EPA, 2003).
Micron Scale
Approximate
Molecular
Weight
Typical Size
Range of
Selected
Water
Constituents
Membrane
Process*
* Particle Fill
, r, . , , , 1 Macro Molecular
Ionic Range Molecular Range 1 R
O.C
100
Sa
ration is shown 1
01 0.
1000 10,000
Dissolved
Its
^^| Nanof
| Reverse Osr
or reference only
31 0
100,000
Jrganics
Viruses
Co
^^m
Itration
nosis
. It is not a men
1 1
500,000
bids
Particle Filtra
^f Ultrafiltra
ibrane separatic
Micro Particle Range Macro Particle Range
0 1
Bacteria
Cryptospork
tion ^^^^^|
^H Microfiltra
tion
n process.
0 1
ium
r
tion
30 10
Sand
^M
00
Source: Kawamura, 2000.
Figure 7-12. Pressure-Driven Membrane Process Application Guide
Table 7-1 provides information on the typical pressure
operating ranges for different types of pressure-driven
membrane processes. Most pressure-driven membrane
processes use either cellulose acetate or synthetic organic
polymer membranes (AWWA and ASCE, 1998). Standard
pressure membrane configurations include spiral wound
membrane units and hollow fiber membrane units.
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7. Turbidity and the Treatment Process
Table 7-1. Typical Feed Pressures for Pressure Driven Membrane Processes
Membrane Process
Typical Feed Pressure (psi)
Reverse Osmosis - Brackish Water Application
Low Pressure
Standard Pressure
Seawater Application
Nanofiltration
Ultrafiltration
Microfiltration
125 to 300
350 to 600
800 to 1,200
50 to 150
20 to 75
15 to 30
Source: AVWVA and ASCE, 1998.
More information on
disinfection can be found
in the LT1ESWTR
Disinfection Profiling and
Benchmarking Technical
Guidance Manual (EPA,
2003).
Effects on Turbidity
When designed and operated properly, filters should be capable
of complying with the LT1ESWTR turbidity requirements.
Modifications to filter operation, such as decreasing the filter
run time or modifying filter start-up procedures, may be
necessary to achieve optimum filter performance. Chapter 5
provides information on the filter self-assessment process and
includes suggestions for improving filter performance. Chapter
8 also contains case studies that address filter performance
optimization.
7.2.6 Disinfection
Disinfection is required under the SWTR to ensure inactivation
of pathogens. Disinfection is accomplished in several ways; the
most common is a chlorine-based disinfectant. Chlorine is
available in the gas, liquid, and solid form. Ozone and
ultraviolet radiation (UV) are also used for disinfection.
Sufficient contact time of the disinfectant with the treated water
is important to obtain the proper inactivation of pathogens.
Turbidity removal is important to improve inactivation of
pathogens. Removal of particles prior to disinfection offers the
following advantages:
Larger particles can shield pathogens. Pathogens are
difficult to inactivate if the disinfectant cannot come
into contact with the pathogen. Therefore, removing
larger particles reduces shielding and may allow the
disinfectant to come into contact with pathogens.
The disinfectant demand is less when fewer particles are
present.
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7. Turbidity and the Treatment Process
40 CFR Section 141.76
FBRR applies only to
conventional and direct
filtration systems that
recycle spent filter
backwash. The FBRR
regulates three recycle
streams: spent filter
backwash water, thickener
supernatant, and liquids
from dewatering processes.
For more information on
this rule, refer to the FBRR
Technical Guidance
Manual (EPA, 2003).
Generally, particle removal results in fewer DBFs by
removing DBF precursors.
7.3 Recycle Streams
The Filter Backwash Recycling Rule (FBRR) regulates three
recycle streams: spent filter backwash water, thickener
supernatant, and liquids from dewatering processes. The
objective of the FBRR is to improve the control of microbial
pathogens, particularly Cryptosporidium, in public drinking
water systems by helping to ensure that recycle practices do not
compromise the treatment plants' capabilities to produce safe
drinking water. The FBRR applies only to systems using
conventional or direct filtration. It requires conventional and
direct filtration plants to submit information to the State on their
recycling practices. The system must also return recycle flows
through the processes of its existing conventional or direct
filtration system or at an alternate location approved by the
State. The State will evaluate the system's recycling practice
and may also require the system to modify its recycle practices.
For more information on this rule, refer to the FBRR Technical
Guidance Manual or the EPA Web site at
http ://www. epa. gov/safewater/filterbackwash.html.
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7. Turbidity and the Treatment Process
7.4 REFERENCES
1. AWWA. 1999. Water Quality and Treatment. Fifth Edition. McGraw-Hill, Inc.
New York, NY.
2. AWWA. 1990. Water Quality and Treatment. Fourth Edition. McGraw-Hill, Inc.
New York, NY.
3. AWWA and ASCE. 1998. Water Treatment Plant Design. Third Edition. McGraw-
Hill, Inc. New York, NY.
4. AWWA and ASCE. 1990. Water Treatment Plant Design. Second Edition.
McGraw-Hill, Inc. New York, NY.
5. California State University. 1994. Water Treatment Plant Operation, Volume 1,
Third Edition. Sacramento, California.
6. EPA. 2003. FBRR Technical Guidance Manual (EPA 816-R-02-014). Washington,
D.C.
7. EPA. 2003. Membrane Filtration Guidance Manual (EPA 815-D-03-008).
Washington, D.C.
8. Hudson, H.E. Jr. 1981. Water Clarification Processes, Practical Design and
Evaluation. Van Nostrand Reinhold Environmental Engineering Series. Litton
Educational Publishing, Inc. New York, NY.
9. Kawumara, S. 2000. Integrated Design of Water Treatment Facilities. Second
Edition. John Wiley & Sons, Inc. New York, NY.
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8. TREATMENT OPTIMIZATION
In this Chapter:
Tools Available
for Optimization
Evaluating System
Processes
Case Studies
Systems should consider
treatment optimization
prior to investigating major
capital improvements to
meet new turbidity
requirements.
8.1 INTRODUCTION
While many systems already meet or will meet turbidity
requirements prior to LT1ESWTR compliance deadlines,
systems may choose to evaluate their treatment plants to
determine what changes, if any, are needed to comply with the
LT1ESWTR requirements. Optimizing treatment plants to
improve effluent turbidity may be necessary for systems that
are currently not performing as desired or are not in
compliance. To optimize a facility, utilities should first
evaluate the system and identify which processes could be
modified. Although it is anticipated that compliance with the
LT1ESWTR will generally be possible through adjustments to
existing treatment processes, additional treatment processes or
other treatment technologies or enhancements may be required
in some cases. It is not anticipated that systems will need to
make major capital improvements, but systems considering
capital improvements in order to meet requirements of the
LT1ESWTR should conduct an optimization evaluation similar
to the Composite Correction Program (CCP) to assess the real
need for construction.
The goals of treatment optimization are to:
-S Provide safe drinking water and achieve compliance
with required standards.
S Save money for the system without compromising safe
drinking water.
These goals should be kept in mind when considering process
modifications.
It is important to remember that the items listed in this chapter
may not apply to all systems. Optimizing water treatment
plants is a site-specific job. As such, this chapter does not try
to provide one plan for optimizing a water treatment plant. It
does highlight the areas which, in the experience of EPA and
other water treatment professionals, most often can be
improved to optimize water treatment and reduce water
turbidity at water treatment plants.
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8. Treatment Optimization
Three existing programs
can be used to assist with
optimization:
Composite
Correction
Program
Area-Wide
Optimization
Program
Partnership for
Safe Water
8.2 TOOLS AVAILABLE FOR OPTIMIZATION
A thorough treatment plant evaluation and improvement
program is the best way to ensure pathogen-free drinking
water. With an emphasis on improved performance at minimal
cost, optimization is an economical alternative for compliance
with the turbidity requirements. Currently, three programs
serve as excellent resources for systems wishing to follow a
systematic and proven approach to optimizing water treatment
plant performance. These are:
CCP;
Area-wide Optimization Program (AWOP); and,
Partnership for Safe Water.
8.2.1 Composite Correction Program (CCP)
The CCP is a systematic, action-oriented approach that Federal
or State regulators, consultants, or utility personnel can
implement to improve performance of existing water treatment
plants. The Comprehensive Performance Evaluation (CPE)
phase of the CCP is described in greater detail in Chapter 6.
EPA has developed a guidance manual, Optimizing Water
Treatment Plant Performance Using the Composite Correction
Program Handbook (EPA, 1998) that may be obtained by
calling the EPA Safe Drinking Water Hotline at (800) 426-
4791.
8.2.2 Area-Wide Optimization Program
(AWOP)
EPA and State drinking water programs are responsible for
oversight of surface water systems that represent a variety of
source water characteristics, plant capabilities, and finished
water quality supplied. An AWOP may be used to prioritize
water systems for targeted regulatory oversight and possible
technical assistance. An AWOP may be used to provide a
process to identify systems with the highest public health risk
and to implement proactive measures to improve performance
of lower performing systems before they fall out of compliance
with the LT1ESWTR. Participation in an AWOP is voluntary,
however, States and systems that use AWOPs are realizing
tangible benefits.
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8. Treatment Optimization
AWOP enables States to
target systems that may
need additional assistance.
Overview of an AWOP
Implementation of an AWOP uses processes designed to
optimize performance of existing particle removal and
disinfection facilities of surface water treatment plants. The
program facilitates water system regulatory compliance while
building an awareness of the benefit of moving beyond
regulatory requirements by optimizing treatment processes and
thus increasing public health protection. AWOP activities
focus on optimization of existing treatment processes using
more effective process control, which will often limit the need
for major capital expenditures.
Under an AWOP, a State develops its own criteria to prioritize
surface water systems relative to indicators of public health risk
(e.g., turbidity removal performance, population served,
violations). The State then uses the criteria to rank its surface
water systems. This ranking provides a framework for
effectively applying available resources and appropriate tools
to the surface water treatment systems within a defined area.
As an example, a State may choose its ranking criteria to assure
it will focus on plants that have the greatest problems
complying with the regulation. The process also includes tools
that would assist the State to implement and document plant
specific performance improvements, which allows for an
assessment of the results of LT1ESWTR oversight activities.
Components of an AWOP
To establish an AWOP in a State, the drinking water program
activities should be organized to support three interrelated
functional areas of activities. These areas are:
Status;
Targeted Performance Improvement; and,
Maintenance.
The intent of these activities is to create an ongoing, dynamic
State implementation program that can respond to variations in
surface water treatment plant performance requirements in a
proactive and effective manner.
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8. Treatment Optimization
Status Activities
Targeted
Performance
Improvement
Activities
Status activities currently center around establishing turbidity
performance goals that the State will pursue with its filtration
plants. States work on developing their prioritization criteria
they will use to rank and prioritize their systems. Once
established, the State then uses turbidity data and other
information obtained about the participating utilities to
prioritize the plants based on their relative public health risk.
This framework allows a State to monitor and assess these
plants on a regular basis. Another benefit of the status
activities is that it allows State staff to develop or strengthen
relationships with the water utilities while encouraging them to
pursue continuous performance improvement.
The focus of the targeted performance improvement activities
is to assess which of the various assistance tools is most
appropriate to enhance the performance of each treatment plant
based on their relative ranking (as determined by the status
activities). In development of an AWOP, the States develop
new tools as well as assess how their existing activities can be
used to assist plants with achieving the AWOP performance
goals for the long-term.
A variety of tools are developed or used to improve
performance at surface water plants. These can range from
inspections to direct technical assistance. Options for an
AWOP include, but are not limited to, enhanced inspections
and surveys, CPEs, performance based training (PBT), and
enforcement. States have the flexibility to incorporate the tools
they find most appropriate given their skill level and resource
constraints. Implementing an AWOP can help States utilize
already existing information and organize it in a way to target
oversight activities to achieve long-lasting improved
performance on a system-by-system basis.
Other sources of assistance that do not use State personnel can
also be used. Systems may be encouraged to join national
programs such as the Partnership for Safe Water. States may
also choose to work with third-party technical assistance
providers to make sure that their assistance complements the
AWOP performance goals.
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8. Treatment Optimization
Maintenance
Activities
Information presented in
this section is site specific.
Systems should perform
jar tests or pilot tests and
consult the State prior to
implementing any changes.
Maintenance activities center around taking lessons learned
from implementation of the status and targeted performance
improvement activities to integrate with or enhance other
related State programs (e.g., design reviews, permitting,
training activities, inspections, sanitary surveys). Any training
of staff on new technical tools could also be included in this
activity, as well as efforts to sustain capability and quality
control of all AWOP activities.
8.2.3 Partnership for Safe Water
The Partnership for Safe Water is a voluntary cooperative effort
of EPA, the American Water Works Association, other
drinking water organizations, and over 186 surface water
utilities representing 245 water treatment plants throughout the
United States. Its goal is to provide a new measure of safety to
millions of Americans by implementing common-sense
prevention programs where legislation or regulation does not
exist. The preventative measures are based on optimizing
treatment plant performance and thus increasing protection
against microbial contamination in America's drinking water
supply. Information about the Partnership can be found at the
AWWA Web site at http://www.awwa.org/partnerl .htm or may
be obtained by calling (303) 347-6169.
8.3 EVALUATING SYSTEM PROCESSES
This section provides suggestions for evaluating the system to
identify which processes to modify. The objective is to
optimize plant performance to more easily meet all required
drinking water standards. Optimizing the plant to meet the
requirements for one rule (such as the LT1ESWTR) will not
necessarily optimize water treatment for compliance with all
standards. Certain technologies, especially those involving
large financial expenditures, should be implemented only with
appropriate engineering guidance. The following should be
considered during the evaluation:
S Quality and type of source water;
S Turbidity of source water;
S Economies of scale and potential economic impact on
the community being served;
S Treatment and waste disposal requirements; and,
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8. Treatment Optimization
When optimizing a facility
for compliance with one
rule, take care not to
adversely affect
compliance with another
rule.
See Section 7.2.2 for more
information on
coagulation.
Poor coagulation
techniques can result in
high effluent turbidities.
Jar tests should be
conducted to identify the
optimal type and dosage of
chemicals. Operational
Control of Coagulation
and Filtration Processes,
AWWAM37, 1992
(available from AWWA,
Denver, CO) is a good
reference for jar testing.
S Future rules and requirements.
An engineering study should be conducted, if needed, to select
a technically feasible and cost-effective method to meet the
system's unique needs for improved filter effluent quality.
Some situations may require more extensive water quality
analyses or bench or pilot-scale testing. The engineering study
may include preliminary designs and estimated capital,
operating, and maintenance costs for full-scale treatment.
Many States require a water system to seek approval for any
major change to its treatment process. Consequently, a public
water system should contact its regulatory agency before
making major changes to the treatment plant.
8.3.1 Coagulation and Rapid Mixing
Coagulation is the process by which particles become
destabilized and begin to clump together. Coagulation is an
essential component in water treatment operations. Evaluation
and optimization of the coagulation/rapid mixing step of the
water treatment process includes a variety of aspects. Optimal
coagulant dosages are critical to proper floe formation and filter
performance. Maintaining the proper control of these chemicals
can mean the difference between an optimized surface plant
and a poorly run surface plant. Inadequate mixing of chemicals
or their addition at inappropriate points in the treatment plant
can also limit performance.
The raw water characteristics will affect the type and amount of
chemicals used. Changes in raw water pH, temperature,
alkalinity, total organic carbon, and turbidity will affect
coagulation and, subsequently, filtration and finished water
quality. Jar tests are an excellent way to determine the best
type and amount of chemical (or combination of chemicals) to
use for varying raw water characteristics. Appendix F provides
information on jar testing. Also, documenting actual plant
operations on a daily basis will give operators a resource for
information about past treatment for various raw water
conditions.
Table 8-1 provides some guidelines for selecting the proper
chemical based on some raw water characteristics.
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8. Treatment Optimization
Table 8-1. Chemical Selection Guidelines Based on Raw Water
Characteristics
Raw Water
Parameter
Alkalinity
Alkalinity is a measure
of the ability to
neutralize acid.
Alkalinity levels are
typically expressed as
calcium carbonate
(CaCOs) in mg/L.
Alkalinity < 50 mg/L
Increase in total organic
carbon
pH between 5.5 and 7.5
pH between 5.0 and 8.5
pH>8.5
Temperature < 5ปC
Chemical Consideration
Alkalinity influences how chemicals react with raw water. Too
little alkalinity will result in poor floe formation, so the system
may want to consider adding a supplemental source of alkalinity
(such as lime, soda ash, or caustic soda). Beware that these
supplemental sources of alkalinity may raise the pH of the
water, and further pH adjustment may be needed to obtain
proper floe formation. Systems should discuss this issue with a
technical assistance provider or a chemical supplier. One rule of
thumb is that alum consumes half as much alkalinity as ferric
chloride.1
This concentration of alkalinity is considered low, and acidic
metallic salts, such as ferric chloride or alum, may not provide
proper floe formation. Systems may want to consider a high
basicity polymer, such as polyaluminum hydroxychloride (PAC1),
or an alum/polymer blend.1
More coagulant is typically needed. Remember, organics
influence the formation of disinfection byproducts and systems
will need to comply with the Stage 1 Disinfection Byproduct
Rule. A good resource is the EPA guidance manual Enhanced
Coagulation and Enhanced Precipitative Softening Guidance
Manual (May 1999).
Optimum pH range for alum.2
Optimum pH range for ferric salts.
Ferric salts might work or other high acidic coagulants .
Alum and ferric salts may not provide proper floe formation.
May want to consider using PAC11 or non-sulphated polyhydroxy
aluminum chloride.3
1 Lind and Ruehl, 1998.
2 AWWA and ASCE, 1998.
3Greville, 1997.
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8. Treatment Optimization
If a process change is
made to the plant based on
the results of jar testing,
systems should remember
to update the pertinent
SOPs.
Cost may be a consideration when selecting chemicals. The
system should perform an economic analysis when comparing
chemicals and not just compare unit cost. For instance, a
polymer may cost more per unit than alum, but less polymer
may be needed than alum. Therefore, the total cost for polymer
may not be much different than the total cost for alum. The
following issues may be evaluated as options to consider for
treatment process enhancement.
Chemicals
An evaluation of the chemicals used in the treatment process
can identify the appropriateness of the coagulation chemicals
being used. A thorough understanding of coagulation
chemistry is important, and changes to coagulation chemicals
should not be made without careful consideration. The
following items should be considered when evaluating
chemicals and coagulation:
What is the protocol for low-turbidity water? The
primary coagulant should never be shut off, regardless
of raw water turbidity.
Are chemicals being dosed properly with regard to pH,
alkalinity, and turbidity? Is dose selection based on
frequent jar testing or other testing methods such as
streaming current monitoring, zeta potential, or pilot
filters? Relying exclusively on past practice may not be
enough. The system may want to consider doing ajar
test while the plant is running well to see how floe in
the jar should look (see Appendix F for jar test
information).
Do standard operating procedures (SOPs) exist for
coagulation controls? Systems should develop SOPs
and establish a testing method that is suited to the plant
and personnel. SOPs should be based on the consensus
of all operators to ensure shared knowledge and
experience. Also, all processes should be documented
as they are performed so they may be reproduced in the
future. An example SOP is provided in Appendix G.
Are the correct chemicals being used? Is the best
coagulant being used for the situation? Changing
coagulant chemicals or adding coagulant aids may
improve the settleability of the flocculated water and in
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8. Treatment Optimization
This practice is not
recommended for lime
softening plants.
Overdosing chemicals can
be just as detrimental as
under dosing. More is not
always better.
turn optimize performance. Coagulants may also be
changed seasonally. The system should be carefully
evaluated before full-scale plant changes of chemicals
are made. If the system does change chemicals and
needs an immediate response, the operator may need to
purge the chemical feed line, particularly if the
chemicals are far (several hundred feet or more) from
the point of application.
Does the pH need to be increased through supplemental
alkalinity? Adding a supplemental source of alkalinity,
such as lime or soda ash, may be necessary for proper
floe formation. However, adding lime (or other alkali
supplements) and iron- or aluminum-based coagulants
at the same point can degrade turbidity removal
performance. The coagulant works on the high pH
lime, the same as it does with naturally occuring
turbidity or alkalinity. Therefore, the addition of lime
typically creates the demand for more ferric- or alum-
based coagulant and the operator will probably add
more coagulant in response to this demand. More
coagulant can cause the pH to decrease, and more lime
is typically added to compensate. Although finished
water quality may be adequate when the raw water is
stable, the plant pays a high cost in chemicals and
sludge removal. This particular procedure is not
foolproof and may not be effective at all when raw
water characteristics change rapidly. One solution to
this issue is to shift the feed line locations. Moving the
coagulant line as far downstream as practicable from
the lime addition point may allow the turbidity from the
lime to fully dissolve. Placing the lime line well
downstream of the coagulant addition point may allow
for the coagulation of DBF precursors at a lower, more
efficient pH before the lime addition elevates pH (Lind
andRuehl, 1998). Note that this mode of operation will
not work for lime softening plants.
Do operators have the ability to respond to varying
water quality conditions by adjusting coagulation
controls? Systems should provide operators with
learning opportunities so that they are able to react to
unusual situations quickly and appropriately. Heavy
rains or lake turnover may happen rarely, but noting
indicators of these events will help with planning. For
example, a sudden drop in pH may occur prior to the
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You should check with the
State prior to modifying
chemical feed processes.
first heavy rain reaching the intake. Systems should use
this as a trigger to change the coagulant dosage.
Are chemicals used before manufacturer recommended
expiration or use-by dates? Does the chemical supplier
operate an ISO 9000 production facility and provide
quality certification? Chemical purity is important in
all treatment systems.
Are chemicals being added in the correct order? The
order of chemical addition is very important, because
certain chemicals interfere with others. Jar tests should
be used to develop optimal sequences. The system may
also want to consider changing the location of chemical
feed points. For instance, some utilities have found that
optimum water quality was achieved when a coagulant
was fed in raw water and a polymer was fed prior to
filtration.
Is the chemical feed system operating properly?
Operators should consider checking the accuracy of
chemical feed systems at least once daily or once per
shift. The system may want to install calibration
columns on chemical feed lines to verify proper dosage
or provide some other form of calibration. Systems
should not set the chemical feed pumps to operate at
maximum stroke and feed rates, which can damage the
pumps.
Are chemicals properly mixed, particularly chemicals
that are diluted? The system may want to consider an
automatic mixer in the chemical tank to provide
thorough mixing.
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Due to the consistency of
chemicals, systems with
polymer pumps should
perform preventive
maintenance such as
periodically moving hoses
located in peristaltic pump
heads or lubricating pump
motors.
Systems should check feed
rates and calibrate pumps
as necessary.
Figure 8-1. Polymer Feed Pump
Feed Systems
Feed systems are another important aspect of the coagulation
step in typical treatment processes. Figure 8-1 shows an
example of a polymer feed pump. Feed systems deliver
coagulants into the treatment system at rates necessary for
optimal performance. The following aspects of feed systems
should be evaluated:
Is redundancy a consideration? Redundancy should be
built into the feed systems so that proper feeding of
chemicals can be maintained if primary systems fail or
malfunction.
Do chemical feed pumps have sufficient dosage range?
Feed systems should be sized so that chemical dosages
can be changed to meet varying conditions.
Are chemical feed systems and solution piping checked
regularly? Preventive maintenance is critical for
avoiding process upsets due to equipment breakdown.
Coagulant lines should be flushed out frequently to
prevent buildup. Where possible, chemical feed lines
should be easy to take apart for quick replacement or
simpler maintenance.
Is a diaphragm pump used? A continuous pump allows
coagulants to be added in a way that avoids pulsed flow
patterns.
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Stocking spare parts for
pumps, tubing, etc. can
save time and money.
See Section 7.2.3 for more
information on
flocculation.
Does the plant stock repair parts for all critical
equipment? Repair parts with a long lead-time for
delivery should be reordered as soon as possible after
removal from inventory.
Satisfactory Dispersal/Application Points
Ccoagulation and mixing also depends on satisfactory dispersal
of coagulation chemicals and appropriate application points.
Coagulants should be well-dispersed so that optimal
coagulation may occur. Enough feed points should be used so
chemicals are able to mix completely. The system should
evaluate the following items:
Is dispersion taking place? Coagulation reactions occur
rapidly, probably in less than 1 second. When injecting
at hydraulic jumps, weirs, or flumes, the coagulant
should be distributed uniformly across the width of the
flow.
Where are coagulants being added? Generally, metal
salts should be introduced at the point of maximum
energy input. Low-molecular weight cationic polymers
can be fed with metal salts at the rapid mix or at second
stage mixing following the metal salt. High-molecular
weight nonionic/anionic floe/filter aids should be
introduced to the process stream at a point of gentle
mixing. Most polymer feed solutions should be
provided with a "cure time" or "aged" before use. Use
of an inline blender with carrier water aids in further
dispersal at application. Most polymers have specific
preparation instructions and should not be added
directly in the raw, concentrated form in which they are
received.
Is rapid mixing equipment checked frequently? Systems
should check the condition of equipment and ensure
that baffling provides for adequate, even flow.
8.3.2 Flocculation
Flocculation is the next step in most treatment plants (in-line
filtration plants being the exception). It is a time-dependent
process that directly affects clarification efficiency by
providing multiple opportunities for particles suspended in
water to collide through gentle and prolonged agitation. The
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For more information on
"G" values, see Section
7.2.3.
process generally takes place in a basin equipped with a mixer
that provides agitation. This agitation should be thorough
enough to encourage inter-particle contact, but gentle enough
to prevent disintegration of existing flocculated particles.
Several issues regarding flocculation should be evaluated by
utilities to ensure optimal operation of flocculation basins.
Flocculation Mixing and Time
Proper flocculation typically requires long, gentle mixing.
Mixing energy should be high enough to bring coagulated
particles constantly into contact with each other, but not so
high it breaks up those particles already flocculated. The
system should consider evaluating:
How many stages are present in the flocculation
system? Three or four are ideal to create plug flow
conditions and allow desired floe formation.
Is the mixing adequate to form desired floe particles?
The system should consider decreasing the mixing rate
for each subsequent stage. "G" values should be
variable through the various stages from 70 sec"1 to 10
sec"1.
Are mechanical mixers functioning properly? Are
flocculator paddles rotating at the correct speed or
rates?
If flow is split between two flocculators, are they
mixing at the same speed and "G" value?
Flocculator Inlets and Outlets
Short-circuiting occurs when water bypasses the normal flow
path through the basin and reaches the outlet in less than the
normal detention time. Inlet and outlet turbulence is sometimes
the source of floe-destructive energy and short-circuiting in
flocculation basins. The system should evaluate the following:
Do basin outlet conditions prevent the break-up of
formed floe particles? Basin outlets should avoid floe
breakup. Port velocities should be less than 0.5 feet per
second (fps).
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Systems should check that
the proper detention time is
achieved in all flocculation
basins under all flow
conditions.
Do inlet conditions prevent the breakup of formed floe
particles? Inlet diffusers may improve the uniformity of
the distribution of incoming water. Secondary entry
baffles across inlets to basins may impart headloss for
uniform water entry.
What size are the conduits between the rapid mix basin
and the flocculation basin? Larger connecting conduits
help reduce turbulence which may otherwise upset floe.
Flocculator Basin Circulation
Baffles are used in flocculation basins to direct the movement
of water through the basin. Baffling near the basin inlet and
outlet improves basin hydraulics and achieves more uniform
flow patterns. Systems should consider the following items
when evaluating flocculation:
Is current baffling adequate? Can baffling be added to
improve performance, or does existing baffling require
repair? Serpentine baffling is more effective than
over/under because it provides for slower flow
conditions and more time for floe formation. Baffling
should prevent short-circuiting and promote plug flow
conditions.
If the system uses solids contact units (SCUs), it may
want to evaluate the recirculation rate of water through
primary and secondary reaction zones, sludge blanket
depth and percent solids, and raw water flow rate.
Sudden changes in raw water flow rate may upset the
sludge blanket and cause sludge carry-over to the
effluent collectors. There are several types of SCUs,
and each has unique flow patterns and sludge blanket
requirements. Therefore, the system should consult the
SCU operations manual for proper operation and
troubleshooting of performance problems.
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See Section 7.2.4 for more
information on
sedimentation.
8.3.3 Sedimentation
Sedimentation is the next step in conventional filtration plants.
(Direct filtration plants omit this step.) The purpose of
sedimentation is to enhance the filtration process by removing
participates. In sedimentation, water flows through the basin
slowly enough to permit particles to settle to the bottom before
the water exits the basin. The system should consider the
following items when evaluating sedimentation basins:
Conducting a tracer study in the sedimentation basin.
Often, very simple design changes can be made to
improve sedimentation basin performance. For
information on tracer studies, see the LT1ESWTR
Disinfection Profiling and Benchmarking Technical
Guidance Manual (EPA, 2003).
Is sludge collection and removal adequate? Inadequate
sludge collection and removal can cause particles to
become re-suspended in water or upset circulation.
Systems should disrupt the sludge blanket as little as
possible. Sludge draw-off rates can affect the sludge
blanket. Sludge draw-off procedures should be checked
periodically, making sure sludge levels are low and
sludge should be wasted if necessary. Sludge pumping
lines should be inspected routinely to ensure that they
are not becoming plugged. These lines should also be
flushed occasionally to prevent the buildup of solids.
Do basin inlet and outlet conditions prevent the break-
up of formed floe particles? Settling basin inlets are
often responsible for creating turbulence that can break
up floe. Improperly designed outlets are also often
responsible for the breakup of floe. Finger launders
(small troughs with V-notch weir openings that collect
water uniformly over a large area of a basin) can be
used to decrease the chance of floe breakup.
Is the floe the correct size and density? Poorly formed
floe is characterized by small or loosely held particles
that do not settle properly and are carried out of the
settling basin. Such floe may be the result of
inadequate rapid mixing, improper coagulant dosages,
or improper flocculation. Systems should look to
previous steps in the treatment train to solve this
problem.
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Systems should verify that
the proper detention time is
achieved in all
sedimentation basins under
all flow conditions.
Maintaining an adequate
sludge layer will give
settling particles something
to attach to and reduce the
tendency for "floaters."
Is the basin subject to short-circuiting? If the basin is
not properly designed, water bypasses the normal flow
path through the basin and reaches the outlet in less
than the normal detention time. Causes of short-
circuiting may include poor influent baffling or
improperly placed collection troughs. If the influent
enters the basin and hits a solid baffle, strong currents
may result. A perforated baffle may distribute inlet
water without causing strong currents. Tube or plate
settlers may also improve efficiency, especially if flows
have increased beyond original design conditions. The
installation of tube settlers can sometimes double a
basin's original settling capacity.
Are basins located outside and subject to windy
conditions? Wind can create currents in open basins that
can cause short-circuiting or disturb the floe. If wind
poses a problem, installing barriers may reduce the
effect and keep debris out of the unit.
Are basins subject to algal growth? Although primarily
a problem in open, outdoor basins, algae can also grow
as a result of window placement around indoor basins.
Algae should be removed regularly to avoid buildup.
Is the sludge blanket in SCUs maintained properly?
Operators should be able to measure the sludge depth
and percent solids to ensure the sludge blanket is within
the manufacturer's recommendations. A timing device
to ensure consistent blanket quality characteristics
should control sludge removal rates and schedule.
Is the recirculation rate for SCUs within the
manufacturer's recommendations? Various designs
have different recirculation rates and flow patterns.
Systems should refer to the manufacturer's operation
manual.
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See Chapter 5 for more
information on filters and
filter self-assessments.
If additional media is
needed due to loss of
media, systems should
order media that has the
same characteristics (based
on effective size and
uniformity coefficient) as
the existing media.
Figure 8-2. Circular Clarifier
8.3.4 Filtration
Filtration is the last step in the particle removal process.
Improperly designed, operated, or maintained filters can
contribute to poor water quality and sub-optimal performance.
A host of factors may be contributing to poor performance, and
systems should make a comprehensive evaluation of the filter
to identify which factors are responsible. Many of the items
listed below are detailed in Chapter 5, Filter Self-Assessment.
Appendix H contains an example operating procedure for filter
operations.
Design of Filter Beds
Systems should verify that the filters are constructed and
maintained according to design specifications. Figure 8-3
shows an inspection of filter media. The system should
consider the following items when evaluating the design of
filter beds:
Is the correct media being used? Issues such as size and
uniformity coefficient should be evaluated. Is the
media at the proper depth? Media can be lost during
backwash operations or when air trapped in the media is
suddenly released. Only a small amount of media may
be lost at a time, but it will add up to a substantial
reduction in media depth over time. Media depth
should be verified and recorded at least annually.
Consistent losses may be indicative of other problems
such as inadequate freeboard to the wash water
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Systems should verify that
filters are not loaded at
rates in excess of the
design rate under all
operational scenarios, such
as when other filters are
off-line for backwashing.
collectors. Media should be added any time the depth
changes by more than 2 inches across the filter.
Are underdrains adequate, or have they been damaged
or disturbed?
Figure 8-3. Inspecting Filter Media
Filter Rate and Rate Control
The rate of filtration and rate control are other important
aspects of filters that should be evaluated. Without proper
control, surges may occur which force suspended particles
through the filter media. Items to consider are:
Do the filters experience sudden flow surges? Systems
should avoid sudden changes to filter rates.
Is the plant operating at the appropriate flow rate? At
some plants, the flow is sometimes operated at a level
that hydraulically overloads unit processes. Operating
at lower flow rates over longer periods of time may
prevent overloading and increase plant performance.
Underloading filters can also be a problem. If a plant is
treating an extremely low flow rate (less than 50
percent of design flow), it may choose to take some
filters off-line for a period of time. When filters are
taken off-line, they still have standing water in them. A
system should not drain the filters since it may take a
considerable period of time to regain the proper filter
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See Chapter 5 for more
information on filter
backwash practices.
Criteria that may initiate a
backwash could be:
time;
headless; or,
turbidity/particle
counts.
bed conditions if the filter is drained and allowed to dry.
It is usually better to use all filters and allow water to
move through the filters instead of taking filters off-line
during low plant flow periods. Keeping all filters active
typically prevents the growth of microorganisms and
anaerobic conditions (Kawamura, 2000). If this mode
of operation is not possible, the system may want to
consider disinfection of the filter prior to placing it back
on-line.
At what flows are the filters rated? Systems should
make sure not to exceed flow rates on remaining in-
service filters when taking other filters off-line or out of
service for backwash. If possible, systems should take
one filter off-line at a time or reduce plant flow to avoid
over-loading the filters remaining online. Another issue
to consider is not underloading filters. Some filters
perform best at the design loading rate. Therefore, the
system may need to take filters off-line to achieve the
design loading rate during low-flow periods.
Filter Backwashing
Filter backwashing has been identified as a critical step in the
filtration process. Many of the operating problems associated
with filters may be a result of inadequate or improper
backwashing. The system should consider the following items
when evaluating filter backwash practices:
Is the rate of filter backwash appropriate for the filter?
Filters can be either underwashed or overwashed.
Utilities should determine the appropriate flow that will
clean the filter, but will not upset the filter media to the
extent that the underdrain is damaged or filter media are
lost.
Are criteria set for initiating backwash? Systems should
establish criteria such as time, headloss, turbidity, or
particle counts for initiating backwash procedures. If
more than one criterion is used, the criteria should be
prioritized to identify which one is most critical for
establishing when to backwash the filter.
How are filters brought back on-line? Media should be
allowed to settle after backwashing and before bringing
filters back on-line. Filters should be brought back on-
line slowly. They should not be brought back on-line
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See Chapter 5 for more
information on filter
spikes.
without backwashing first.
When a filter is backwashed, is more water diverted to
the remaining filters, causing them to be overloaded
during backwash? During the backwash, flow going to
the remaining filters may need to be cut back to ensure
the filters are not overloaded or "bumped" with a
hydraulic surge causing particle pass-through.
Is flow divided equally among the filters that are on-
line?
Is the filter started slowly (i.e., is the loading rate
gradually increased until the design hydraulic loading
rate is achieved)? This will purge air trapped in the
media. The use of a backwash pump to purge air to
"bump" the filter is generally not considered a safe or
acceptable practice. It can disrupt the filter media or
underdrain system, resulting in filter breakthrough.
Air Binding
Air binding happens when large amounts of air bubbles
accumulate in the filter bed. This may result in large
headlosses through the filter bed. If a high water level is
maintained in the filter, air binding may be minimized due to
the increased head applied to the bed. This practice may not be
possible with some package plants because package plants are
limited in the depth of water over the filter. Air binding may
be more common with cold water or during the spring, when
there is a high concentration of dissolved air in the water. The
degree of air binding may be reduced or even eliminated if
filter backwashing is frequently initiated whenever the headloss
reaches 4 to 5 feet (Kawamura, 2000).
Control of Initial Turbidity Breakthrough
Systems may sometimes have a high initial turbidity
breakthrough after placing a filter back on-line after
backwashing. This breakthrough can be controlled by
(Logsdon, et al., 2000):
Filter to waste;
Delayed start of the filter;
Slowly starting the filter;
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Filter-to-waste
Delayed start of
the filter
Slow-starting the
filter'
Adding polymer or coagulant to backwash water;
and/or,
Adding coagulant chemical or cationic polymer to
settled water as it fills the filter box after backwash is
terminated.
Filter-to-waste consists of wasting water to a site other than the
clearwell until the filter effluent meets an acceptable turbidity
(0.3 NTU for direct and conventional treatment plants) or
particle count value. Some utilities may filter-to-waste for a
preset time, but filter-to-waste may be more effective if
terminated based on a specific turbidity or particle count value.
Some filtration plants may not have adequate piping to carry
the wasted filtrate when the filter is operated at its full filtration
rate. In this circumstance, filter-to-waste should be conducted
with the filter operating at a reduced rate, and after filter-to-
waste has ended, the filtration rate should be increased to the
appropriate level (Logsdon, et al, 2000). Systems should
carefully manage the filter rate change, because sudden
increases in the hydraulic loading rate could also result in
unwanted turbidity spikes. If a plant does have filter-to-waste
capabilities, it should make sure that the waste line does not
create a cross connection for the plant. One method to consider
is to provide an air gap between the filter waste line and the
receiving device (whether it is a recycle line, sanitary sewer
pipe, or trough).
Delayed start of the filter has also been shown to reduce initial
turbidity spikes. One study of three plants showed up to 50
percent reduction in peak particle counts between delayed start
filters and filters that were placed on-line immediately after
backwash (Hess, et al., 2000). Systems should be aware that
resting a filter before starting a new run is not a cure-all; some
plants have reported that the delayed start did not consistently
control initial turbidity.
Slow-starting a filter consists of starting the filter at a low
filtration rate and gradually increasing the rate over a period of
time, such as 15 minutes. To slow-start a filter, the filter
should be equipped with rate control valves that can be
gradually increased. Again, this approach is not a cure-all. It
has been found to be effective at some plants while failing to
eliminate the initial turbidity spike at other plants (Hess, et al.,
2000).
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Systems should
consider adding
polymer and/or
coagulant
Systems should be careful
not to overfeed chemicals
since this practice can
result in mudballs and
plugging of the filter.
Systems could also consider adding a coagulant during the
backwash process. Some studies have shown that coagulants
added during backwash can accelerate the filter ripening
process and reduce initial turbidity spikes (Hess, et al., 2000).
The coagulant is typically added during the last couple of
minutes of backwash.
The Milwaukee Water Works compared filter performance for
three different scenarios (Carmichael, Lewis, and Aquino,
1998):
Backwash with no polymer addition;
Backwash with cationic polymer (Cat-Floe T) added to
the backwash water; and,
Cationic polymer added to the influent settled water for
the last hour of a filter run and again during the first
hour of the following run.
Adding 0.4 mg/L of polymer to the influent settled water
before and after backwash controlled the initial spike better
than adding polymer to the backwash water. Filter
performance was measured based on particle counting. Full-
scale practice has been modified to include addition of a slug
dose (0.4 mg/L) of undiluted cationic polymer in the filter box
in front of the influent valve as the settled water flows into the
filter box after the influent valve is opened. Then, during the
first hour of the filter run, polymer is fed at a dose of 0.4 mg/L.
Polymer is no longer fed during the last hour of a filter run
before backwash, because it did not improve filter performance
(Hess, et al., 2000).
If a system chooses to add a coagulant or polymer, keep in
mind that more is not always better. Overdosing either an
inorganic coagulant or a polymer could have a negative
effect on the filter. Applying chemical overdose for too long
at the beginning of a run may cause filtered water turbidity
to rise at the end of the dosing. In addition, if excessive
alum is added to the influent settled water, mudballs might
develop in the filter. Excess polymer dosages can also
result in short filter runs and mudball formation (Hess, et
al., 2000). Systems should start at very low coagulant or
polymer dosages and gradually increase the dose until
positive effects are seen in the filtered effluent quality.
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When adding polymers as
a filtration aide, systems
should be careful not to
add a polymer that will
counteract another
chemical. Counteraction
will not improve filtration
and may cause additional
problems.
Systems should also perform filter runs with and without
the coagulant or polymer for comparison purposes.
Some utilities have found that using a combination of the
above procedures provides the best control of initial turbidity
spikes.
Turbidity Breakthrough in Late Stages of the Filter
Cycle
Filters may sometimes experience high turbidity or sudden
spikes prior to the end of the filter cycle, as shown in Figure 5-
5. This type of breakthrough can be controlled by
strengthening the floe and increasing the adsorption capability
of the filter bed. Two options a system should consider are to
feed cationic polymer as a coagulant, with or without alum, or
to feed minute amounts of nonionic polymer to the filter
influent as a filtration aid. Systems should be careful to limit
the dosage of the nonionic polymer (0.015 to 0.025 mg/L) to
prevent short filter runs or mudballs (Kawamura, 2000).
Beware that polymers can sometimes counteract each other,
and the addition of one polymer may require a system to
increase the feed amount of another polymer. Again, keep in
mind that more is not always better.
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8.4 REFERENCES
1. AWWA and ASCE. 1998. Water Treatment Plant Design, Third Edition. McGraw
Hill. New York, NY.
2. Carmichael, G., Lewis, C. M, and Aquino, M. A. 1998. Enhanced Treatment Plant
Optimization and Microbiological Source Water Study, Enhanced Treatment Plant
Optimization. Draft final report to EPA.
3. EPA. 1998. Optimizing Water Treatment Plant Performance Using the Composite
Correction Program (EPA 625-6-91-027). Washington, D.C.
4. EPA. 1999. Enhanced Coagulation and Enhanced Precipitative Softening Guidance
Manual (EPA 815-R-99-012). Washington, D.C.
5. EPA. 2003. LT1ESWTR Disinfection Profiling and Benchmarking Technical
Guidance Manual (EPA 816-R-03-004). Washington, D.C.
6. Greville, Anthony S. 1997. How to Select a Chemical Coagulant and Flocculant.
Alberta Water & Wastewater Operators Association, 22nd Annual Seminar.
7. Hess, Alan, Sr., et al. 2000. An International Survey of Filter O&M Practices.
National American Water Works Association Conference, Denver, CO.
8. Kawamura, Susumu. 2000. Integrated Design and Operation of Water Treatment
Facilities, Second Edition. John Wiley & Sons, Inc., New York.
9. Lind, Christopher, and Ruehl, Karen. 1998. A Practical Summary of Water
Treatment Practices, Parts 1 and 2. Public Works, General Chemical Corporation.
10. Logsdon, Gary, et al. 2000. Turbidity Monitoring and Compliance for the Interim
Enhanced Surface Water Treatment Rule. National American Water Works
Association Conference, Denver, CO.
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Appendix A
Glossary
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Appendix A. Glossary
A.1 GLOSSARY
accuracy. How closely an instrument measures the true or actual value of the process
variable being measured or sensed. Also see precision.
acidic. The condition of water or soil that contains a sufficient amount of acid substances to
lower the pH below 7.0.
activated carbon. Adsorptive particles or granules of carbon usually obtained by heating
carbon (such as wood). These particles or granules have a high capacity to selectively
remove certain trace and soluble organic materials from water.
air binding. A situation where air collects within the filter media.
algae. Microscopic plants which contain chlorophyll and live floating or suspended in
water. They also may be attached to structures, rocks or other submerged surfaces. They are
food for fish and small aquatic animals.
alkaline. The condition of water or soil that contains a sufficient amount of alkali
substances to raise the pH above 7.0.
alkalinity. The capacity of water to neutralize strong acids. This capacity is caused by the
water's content of carbonate, bicarbonate, hydroxide and occasionally borate, silicate, and
phosphate. Alkalinity is expressed in milligrams per liter of equivalent calcium carbonate.
Alkalinity is not the same as pH because water does not have to be strongly basic (high pH)
to have a high alkalinity. Alkalinity is a measure of how much acid can be added to a liquid
without causing a great change in pH.
available expansion. The vertical distance from the filter surface to the overflow level of a
trough in a filter. This distance is also called freeboard.
backwash. The process of reversing the flow of water back through the filter media to
remove the entrapped solids.
bacteria. Singular: bacterium. Microscopic living organisms usually consisting of a single
cell. Some bacteria in soil, water or air may also cause human, animal and plant health
problems.
baffle. A flat board or plate, deflector, guide or similar device constructed or placed in
flowing water or slurry systems to cause more uniform flow velocities, to absorb energy,
and to divert, guide, or agitate liquids (water, chemical solutions, slurry).
breakthrough. A condition whereby filter effluent water quality deteriorates (as measured
by an increase in turbidity, particle count, or other contaminant). This may occur due to
excessive filter run time or hydraulic surge.
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Appendix A. Glossary
calcium carbonate (CaCOs) equivalent. An expression of the concentration of specified
constituents in water in terms of their equivalent value to calcium carbonate. For example,
the hardness in water that is caused by calcium, magnesium and other ions is usually
described as calcium carbonate equivalent.
calibration. A procedure that checks or adjusts an instrument's accuracy by comparison
with a standard or reference sample that has a known value.
capital costs. Costs of construction and equipment. Capital costs are usually fixed,
one-time expenses, although they may be paid-off over longer periods of time.
carcinogen. Any substance which tends to cause cancer in an organism.
clarifier. A large circular or rectangular tank or basin in which water is held for a period of
time, during which the heavier suspended solids settle to the bottom by gravity. Clarifiers
are also called settling basins and sedimentation basins.
clearwell. A reservoir for the storage of filtered water with sufficient capacity to prevent
the need to vary the filtration rate in response to short-term changes in customer demand.
Also used to provide chlorine contact time for disinfection.
coagulant aid. A chemical added during coagulation to improve the process by stimulating
floe formation or by strengthening the floe so it holds together better.
coagulant. A chemical added to water that has suspended and colloidal solids to destabilize
particles, allowing subsequent floe formation and removal by sedimentation, filtration, or
both.
coagulation. As defined in 40 CFR 141.2, a process using coagulant chemicals and mixing
by which colloidal and suspended materials are destabilized and agglomerated into floes.
cohesion. Molecular attraction that holds two particles together.
colloid. A small, discrete solid particle in water that is suspended (not dissolved) and will
not settle by gravity because of molecular bombardment.
combined filter effluent. Generated when the effluent water from individual filters in
operation is combined into one stream.
combined sewer. A sewer that transports surface runoff and human domestic wastes
(sewage), and sometimes industrial wastes.
community water system (CWS). As defined in 40 CFR 141.2, a public water system
which serves at least 15 service connections used by year round residents or regularly serves
at least 25 year-round residents.
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Appendix A. Glossary
continuous sample. A constant flow of water from a particular place in a plant to the
location where samples are collected for testing.
conventional filtration treatment. As defined in 40 CFR 141.2, a series of processes
including coagulation, flocculation, sedimentation, and filtration resulting in substantial
particulate removal.
cross connection. Any actual or potential connection between a drinking (potable) water
system and an unapproved water supply or other source of contamination. For example, if a
pump moving nonpotable water is hooked into the water system to supply water for the
pump seal, a cross-connection or mixing between the two water systems can occur. This
mixing may lead to contamination of the drinking water.
Cryptosporidium. A disease-causing protozoan widely found in surface water sources.
Cryptosporidium is spread as a dormant oocyst from human and animal feces to surface
water. In its dormant stage, Cryptosporidium is housed in a very small, hard-shelled oocyst
form that is resistant to chorine and chloramine disinfectants. When water containing these
oocysts is ingested, the protozoan causes a severe gastrointestinal disease called
cryptosporidiosis.
CT or CTcaic- As defined in 40 CFR 141.2, the product of "residual disinfectant
concentration" (C) in mg/L determined before or at the first customer, and the corresponding
"disinfectant contact time" (T) in minutes, i.e., "C" x "T". If a public water system applies
disinfectants at more than one point prior to the first customer, it must determine the CT of
each disinfectant sequence before or at the first customer to determine the total percent
inactivation or "total inactivation ratio". In determining the total inactivation ratio, the
public water system must determine the residual disinfectant concentration of each
disinfection sequence and corresponding contact time before any subsequent disinfection
application point(s). "CT99.9" is the CT value required for 99.9 percent (3-log) inactivation
of Giardia lamblia cysts. CT99.9 for a variety of disinfectants and conditions appear in 40
CFR 141.74(b)(3) Tables 1.1- 1.6, 2.1, and 3.1. CTcaic/CT99.9 is the inactivation ratio. The
sum of the inactivation ratios, or total inactivation ratio shown as ฃ [(CTcaic) / (CT99.9)] is
calculated by adding together the inactivation ratio for each disinfection sequence. A total
inactivation ratio equal to or greater than 1.0 is assumed to provide a 3-log inactivation of
Giardia lamblia cysts.
d6o%. The diameter of the particles in a granular sample (filter media) for which 60 percent
of the total grains are smaller and 40 percent are larger on a weight basis. The deo% is
obtained by passing granular material through sieves with varying dimensions of mesh and
weighing the material retained by each sieve.
degasification. A process that removes dissolved gases from the water. The gases may be
removed by either mechanical or chemical treatment methods or a combination of both.
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Appendix A. Glossary
degradation. Chemical or biological breakdown of a complex compound into simpler
compounds.
diatomaceous earth filtration. As defined in 40 CFR 141.2, a process resulting in
substantial particulate removal, that uses a process in which: (1) a "precoat" cake of
diatomaceous earth filter media is deposited on a support membrane (septum), and (2) while
the water is filtered by passing through the cake on the septum, additional filter media,
known as "body feed," is continuously added to the feed water to maintain the permeability
of the filter cake.
direct filtration. As defined in 40 CFR 141.2, a series of processes including coagulation
and filtration but excluding sedimentation resulting in substantial particulate removal.
effective range. That portion of the design range (usually upper 90 percent) in which an
instrument has acceptable accuracy.
effective size (E.S.). The diameter of the particles in a granular sample (filter media) for
which 10 percent of the total grains are smaller and 90 percent larger on a weight basis.
Effective size is obtained by passing granular material through sieves with varying
dimensions of mesh and weighing the material retained by each sieve. The effective size is
also approximately the average size of the grains.
effluent. Water or some other liquid that is raw, partially treated or completely treated that
is flowing from a reservoir, basin, treatment process or treatment plant.
enteric. Of intestinal origin, especially applied to wastes or bacteria.
entrain. To trap bubbles in water either mechanically through turbulence or chemically
through a reaction.
EPA. United States Environmental Protection Agency.
epidemic. An occurrence of cases of disease in a community or geographic area clearly in
excess of the number of cases normally found (or expected) in that population for a
particular season or other specific time period. Disease may spread from person to person,
and/or by the exposure of many persons to a single source, such as a water supply.
filtration. As defined in 40 CFR 141.2, a process for removing particulate matter from
water by passage through porous media.
finished water. Water that has passed through a water treatment plant such that all the
treatment processes are completed or "finished." This water is ready to be delivered to
consumers. Also called product water.
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Appendix A. Glossary
floe. Collections of smaller particles that have come together (agglomerated) into larger,
more settleable particles as a result of the coagulation-flocculation process.
flocculation. As defined in 40 CFR 141.2, a process to enhance agglomeration or collection
of smaller floe particles into larger, more easily settleable particles through gentle stirring by
hydraulic or mechanical means.
fluidization. The upward flow of a fluid through a granular bed at sufficient velocity to
suspend the grains in the fluid and depends on filter media properties, backwash
temperature, and backwash water flow rates.
garnet. A group of hard, reddish, glassy, mineral sands made up of silicates of base metals
(calcium, magnesium, iron and manganese). Garnet has a higher density than sand.
gastroenteritis. An inflammation of the stomach and intestine resulting in diarrhea, with
vomiting and cramps when irritation is excessive. When caused by an infectious agent, it is
often associated with fever.
Giardia lamblia. Flagellated protozoan which is shed during its cyst-stage with the feces of
man and animals. When water containing these cysts is ingested, the protozoan causes a
severe gastrointestinal disease called giardiasis.
giardiasis. Intestinal disease caused by an infestation of Giardia flagellates.
grab sample. A single sample collected at a particular time and place that represents the
composition of the water only at that time and place.
ground water under the direct influence (GWUDI) of surface water. As defined in 40
CFR 141.2, any water beneath the surface of the ground with significant occurrence of
insects or other macroorganisms, algae, or large-diameter pathogens such as Giardia
lamblia or Cryptosporidium, or significant and relatively rapid shifts in water characteristics
such as turbidity, temperature, conductivity, or pH which closely correlate to climatological
or surface water conditions. Direct influence must be determined for individual sources in
accordance with criteria established by the State. The State determination of direct influence
must be based on site-specific measurements of water quality and/or documentation of well
construction characteristics and geology with field evaluation.
hardness, water. A characteristic of water caused mainly by the salts of calcium and
magnesium, such as bicarbonate, carbonate, sulfate, chloride and nitrate. Excessive hardness
in water is undesirable because it causes the formation of soap curds, increased use of soap,
deposition of scale in boilers, damage in some industrial processes, and sometimes causes
objectionable tastes in drinking water.
head. The vertical distance (in feet) equal to the pressure (in psi) at a specific point. The
pressure head is equal to the pressure in psi times 2.31 ft/psi.
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Appendix A. Glossary
head loss. A reduction of water pressure in a hydraulic or plumbing system.
humus. Organic portion of the soil remaining after prolonged microbial decomposition.
influent water. Raw water plus recycle streams.
in-line filtration. The addition of chemical coagulants directly to the filter inlet pipe. The
chemicals are mixed by the flowing water. Flocculation and sedimentation facilities are
eliminated. This pretreatment method is commonly used in pressure filter installations.
jar test. A laboratory procedure that simulates a water treatment plant's coagulation, rapid
mix, flocculation, and sedimentation processes. Differing chemical doses, energy of rapid
mix, energy of slow mix, and settling time can be examined. The purpose of this procedure
is to estimate the minimum or optimal coagulant dose required to achieve certain water
quality goals. Samples of water to be treated are commonly placed in six jars. Various
amounts of a single chemical are added to each jar while holding all other chemicals at a
consistent dose, and observing the formation of floe, settling of solids, and resulting water
quality.
microbial growth. The activity and growth of microorganisms such as bacteria, algae,
diatoms, plankton and fungi.
micrograms per liter (|J,g/L). One microgram of a substance dissolved in each liter of
water. This unit is equal to parts per billion (ppb) since one liter of water is equal in weight
to one billion micrograms.
micron. A unit of length equal to one micrometer (|im), one millionth of a meter or one
thousandth of a millimeter. One micron equals 0.00004 of an inch.
microorganisms. Living organisms that can be seen individually only with the aid of a
microscope.
milligrams per liter (mg/L). A measure of concentration of a dissolved substance. A
concentration of one mg/L means that one milligram of a substance is dissolved in each liter
of water. For practical purposes, this unit is equal to parts per million (ppm) since one liter
of water is equal in weight to one million milligrams.
mudball. Material that is approximately round in shape and varies from pea-sized up to two
or more inches in diameter. This material forms in filters and gradually increases in size
when not removed by the backwashing process.
nephelometric. A means of measuring turbidity in a sample by using an instrument called a
nephelometer. A nephelometer passes light through a sample and the amount of light
deflected (usually at a 90-degree angle) is then measured.
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Appendix A. Glossary
nephelometric turbidity unit (NTU). The unit of measure for turbidity
non-community water system (NCWS). As defined in 40 CFR 141.2, a public water
system that is not a community water system. A non-community water system is either a
"transient non-community water system (TWS)" or a "non-transient non-community water
system (NTNCWS)."
non-transient non-community water system (NTNCWS). As defined in 40 CFR 141.2, a
public water system that is not a community water system and that regularly serves at least
25 of the same persons over six months per year.
operation and maintenance costs. The ongoing, repetitive costs of operating and
maintaining a water system; for example, employee wages and costs for treatment chemicals
and periodic equipment repairs.
organics. Carbon-containing compounds that are derived from living organisms.
overflow rate. A measurement used in the design of settling tanks and clarifiers in
treatment plants which relates the flow to the surface area. It is used by operators to
determine if tanks and clarifiers are hydraulically (flow) over- or underloaded. Overflow
rate may be expressed as either gallons per day per square foot (gpd/sq ft) or gallons per
minute per square foot (gpm/ sq ft). Overflow Rate (GDP/sq ft) = Flow (GPD)/Surface Area
(sq ft).
particle count. The results of a microscopic-scale examination of treated water with a
special "particle counter" that classifies suspended particles by number and size.
particulate. A very small solid suspended in water which can vary widely in shape,
density, and electrical charge. Colloidal and dispersed particulates are artificially gathered
together by the processes of coagulation and flocculation.
pathogens, or pathogenic organisms. Microorganisms that can cause disease (such as
typhoid, cholera, dysentery) in other organisms or in humans, animals and plants. They may
be bacteria, viruses, or protozoans and are found in sewage, in runoff from animal farms or
rural areas populated with domestic and/or wild animals, and in water used for swimming.
There are many types of organisms which do not cause disease. These organisms are called
non-pathogens.
pH. pH is an expression of the intensity of the basic or acid condition of a solution.
Mathematically, pH is the negative logarithm (base 10) of the hydrogen ion concentration,
[H+]. [pH = log (1/H+)]. The pH may range from 0 to 14, where 0 is most acidic, 14 most
basic, and 7 neutral. Natural waters usually have a pH between 6.5 and 8.5.
plug flow. The water travels through a basin, pipe, or unit process in such a fashion that the
entire mass or volume is discharged at exactly the theoretical detention time of the unit.
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Appendix A. Glossary
polymer. A synthetic organic compound with high molecular weight and composed of
repeating chemical units (monomers). Polymers may be polyelectrolytes (such as water-
soluble flocculants), water-insoluble ion exchange resins, or insoluble uncharged materials
(such as those used for plastic or plastic-lined pipe).
pore. A very small open space.
precision. The ability of an instrument to measure a process variable and to repeatedly
obtain the same result.
primary standard. A solution used to calibrate an instrument.
public water system. As defined in 40 CFR 141.2, a system for the provision to the public
of water for human consumption through pipes or, after August 5, 1998, other constructed
conveyances, if such system has at least fifteen service connections or regularly serves an
average of at least twenty-five individuals daily, at least 60 days out of the year. Such term
includes: any collection, treatment, storage, and distribution facilities under control of the
operator of such system and used primarily in connection with such system; and any
collection or pretreatment storage facilities not under such control which are used primarily
in connection with such system. Such term does not include any "special irrigation district."
A public water system is either a "community water system" or a "non-community water
system".
reservoir. Any natural or artificial holding area used to store, regulate, or control water.
reverse osmosis. The application of pressure to a concentrated solution which causes the
passage of a liquid from the concentrated solution to a weaker solution across a
semipermeable membrane. The membrane allows the passage of the solvent (water) but not
the dissolved solids (solutes). The liquid produced is a demineralized water.
Safe Drinking Water Act (SDWA). Commonly referred to as SDWA. A law passed by the
U.S. Congress in 1974.
sand. Soil particles between 0.05 and 2.0 mm in diameter.
sand filter. The oldest and most basic filtration process, which generally uses two grades of
sand (coarse and fine) for turbidity and particle removal. A sand filter can serve as a first-
stage roughing filter or prefilter in more complex processing systems.
secondary standard (for turbidity). Commercially prepared, stabilized, sealed liquid or gel
turbidity standards that are used to verify the continued accuracy of a calibrated instrument.
The actual value of the secondary standard must be determined by comparing it against
properly prepared and diluted primary standard such as formazin or styrene divinylbenzene
polymers. Secondary standards should not be used to calibrate an instrument.
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Appendix A. Glossary
sedimentation. As defined in 40 CFR 141.2, a process for removal of solids before
filtration by gravity or separation.
slow sand filtration. As defined in 40 CFR 141.2, a process involving passage of raw
water through a bed of sand at low velocity (generally less than 0.4 meters per hour)
resulting in substantial particulate removal by physical and biological mechanisms.
standard. A physical or chemical quantity whose value is known exactly, and is used to
calibrate or standardize instruments. See also primary standards and secondary standards.
standardize. To compare with a standard. 1) In wet chemistry, to find out the exact
strength of a solution by comparing it with a standard of known strength. 2) To set up an
instrument or device to read a standard. This allows you to adjust the instrument so that it
reads accurately, or enables you to apply a correction factor to the readings.
State. As defined in 40 CFR 141.2, the agency of the State or Tribal government which has
jurisdiction over public water systems. During any period when a State or Tribal
government does not have primary enforcement responsibility pursuant to Section 1413 of
the Safe Drinking Water Act, the term "State" means the Regional Administrator, U.S.
Environmental Protection Agency.
surface water. As defined in 40 CFR 141.2, all water which is open to the atmosphere and
subject to surface runoff.
surfactant. Abbreviation for surface-active agent. A chemical that, when added to water,
lowers surface tension and increases the "wetting" capabilities of the water. Reduced surface
tension allows water to spread and to penetrate fabrics or other substances, enabling them to
be washed or cleaned. Soaps and wetting agents are typical surfactants.
suspended solids. Solid organic and inorganic particles that are held in suspension by the
action of flowing water and are not dissolved.
transient non-community water system. As defined in 40 CFR 141.2, a non-community
water system that does not regularly serve at least 25 of the same persons over six months
per year.
tube settlers. Bundles of small-bore (2 to 3 inches or 50 to 75 mm) tubes installed on an
incline as an aid to sedimentation. As water rises in the tubes, settling solids fall to the tube
surface. As the sludge (from the settled solids) in the tube gains weight, it moves down the
tubes and settles to the bottom of the basin for removal by conventional sludge collection
means. Tube settlers are sometimes installed in sedimentation basins and clarifiers to
improve settling of particles.
turbid. Having a cloudy or muddy appearance.
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Appendix A. Glossary
turbidimeter. A device that measures the amount of light scattered by suspended particles
in a liquid under specified conditions.
turbidity. The cloudy appearance of water caused by the presence of suspended and
colloidal matter.
uniformity coefficient. A measure of how well a sediment is graded.
verification. A procedure to verify the calibration of an instrument such as a turbidimeter.
virus. As defined in 40 CFR 141.2, a virus of fecal origin which is infectious to humans by
waterborne transmission.
water supplier. A person who owns or operates a public water system.
water supply system. The collection, treatment, storage, and distribution of potable water
from source to consumer.
zeta potential. The electric potential arising due to the difference in the electrical charge
between the dense layer of ions surrounding a particle and the net charge of the bulk of the
suspended fluid surrounding the particle. The zeta potential, also known as the electrokinetic
potential, is usually measured in millivolts and provides a means of assessing particle
destabilization or charge neutralization in coagulation and flocculation procedures.
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Appendix A. Glossary
A.2 REFERENCES
APHA, AWWA, WEF. 1998. Standard Methods for the Examination of Water and
Wastewater, 20th Edition. APHA, Washington, D.C.
Calabrese, E.J., C.E. Gilbert, and H. Pastides, editors. 1988. Safe Drinking Water Act
Amendments, Regulations and Standards. Lewis Publishers. Chelsea, MI.
California State University. 1988. Water Treatment Plant Operation. School of
Engineering, Applied Research and Design Center. Sacramento, CA.
Dzurik, A.A., Rowman, and Littlefield. 1990. Water Resources Planning. Savage, MD.
Symons, J., L. Bradley, Jr., and T. Cleveland, Editors. 2000. The Drinking Water
Dictionary. AWWA. Denver, CO.
USEPA. 1991. Code of Federal Regulations, Title 40, Chapter I, Section 141.2. July 1.
von Huben, H. 1991. Surface Water Treatment: The New Rules. AWWA. Denver, CO.
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Appendix A. Glossary
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Appendix B
Blank Forms and Checklists
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Appendix B. Worksheets
This appendix contains blank versions of the forms, checklists, and worksheets found in
Chapters 1 through 8 of this Guidance Manual.
A completed example of the Turbidimeter Maintenance Form can be found in
Chapter 3 of this Guidance Manual.
A completed example of the Calibration Checklist Form can be found in Chapter
3 of this Guidance Manual.
A completed example of the Filter Self-Assessment Checklist can be found in
Chapter 5 of this Guidance Manual.
A completed example of the Individual Filter Self-Assessment Form can be
found in Chapter 5 of this Guidance Manual.
Completed Worksheets 1 and 2 can be found in Chapter 4.
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Appendix B. Worksheets
Turbidimeter Maintenance Form
Instrument:
Date
Verification
Acceptable/
Unacceptable
Maintenance
Performed
Initials
Comments
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Appendix B. Worksheets
CALIBRATION CHECKLIST
Instrument
Date
Initials
Recorded
Value
(NTU)
Value of Standard
(NTU)
Comments
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Appendix B. Worksheets
Filter Self-Assessment Checklist
System Name
Filter #
Date Self-Assessment was Triggered
Date of Self-Assessment
Assessment of Filter Performance
Development of a Filter Profile
Identification and Prioritization of Factors Limiting Filter Performance
Assessment of the Applicability of Corrections
Preparation of a Filter Self-Assessment Report
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Appendix B. Worksheets
Individual Filter Self-Assessment Form*
Topic
General Filter
Information
Hydraulic
Loading
Conditions
Media
Conditions
Description
Type (mono, dual, mixed, pressure,
gravity)
Number of filters
Filter/rate control (constant,
declining)
Type of flow control (influent weir,
valves)
Surface wash type (rotary, fixed,
none)/air scour
Configuration (rectangular, circular,
square, horizontal, vertical)
Dimensions (length, width,
diameter, height of side walls)
Max depth of water above media
Surface area per filter (ft2)
Average operating flow (mgd or
gpm)
Peak instantaneous operating flow
(mgd or gpm)
Average hydraulic surface loading
rate (gpm/ft2)
Peak hydraulic surface loading rate
(gpm/ft2)
Changes in hydraulic loading rate
(gpm/ft2)
Depth, type, uniformity coefficient*,
and effective size*
Media 1*
Media 2* (if applicable)
Media 3* (if applicable)
Presence of mudballs, debris, excess
chemical, cracking, worn media,
media coating
Information
Actual
Design
worksheet is designed to elicit additional information and is not required under 40 CFR Section
141.563(b).
*You may want to have a sieve analysis done on the media. Note that a sieve analysis may not be completed
within the 14-day time frame required for a filter self-assessment.
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Appendix B. Worksheets
Individual Filter Self-Assessment Form (continued)
Topic
Support
Media/Under-
drain
Conditions
Backwash
Practices
Placing a Filter
Back into
Service
Rate-of-Flow
Controllers and
Filter Valves
Other
Considerations
Description
Is the support media evenly placed
(deviation <2 inches measured
vertically) in the filter bed?
Type of underdrains
Evidence of media in the clearwell
or plenum
Evidence of boils during backwash
Backwash initiation (headless,
turbidity/particle counts, time)
Sequence (surface wash,
air scour, flow ramping,
filter-to-waste)
Duration (minutes) of each step
Introduction of wash water (via
pump, head tank, distribution
system pressure)
Backwash rate (gpm/ft2)
at each step
Bed expansion (percent)
Dose of coagulants or polymers
added to wash water
Backwash termination (time,
backwash turbidity, visual
inspection, or other)
Backwash SOP (exists and current)
Delayed start, slow start, polymer
addition, or filter to waste
Leaking valves
Malfunction rate of flow control
valves
Equal flow distribution to each filter
Chemical feed problems
Rapid changes in raw water quality
Turbidimeters (calibrated)
Other
Information
Actual
Design
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Appendix B. Worksheets
The following worksheets can be used to collect data to be submitted to the State. Systems
should check with the State before using these worksheets to make sure they are acceptable.
Worksheet lisa monthly report for combined filter effluent in conventional and direct
filtration plants. The worksheet tracks the number of samples per day, maximum daily
combined filter effluent, number of turbidity measurements, number of turbidity
measurements <= 0.3 NTU, and number of turbidity measurements > 1 NTU. The
worksheet will then total the number of turbidity measurements, the number of turbidity
measurements <= 0.3 NTU, and the number of turbidity measurements > 1 NTU. The
worksheet then finds the percentage of turbidity measurements that meet the specified
limits.
Worksheet 2 is a monthly summary report of data for individual filter effluent in
conventional and direct filtration plants. This worksheet tracks the filter #, whether or not
15-minute turbidity values were recorded, and the values of turbidity measurements where
two or more consecutive 15-minute turbidity readings were greater than 1.0 NTU. It also
tracks the values of turbidity measurements > 2.0 NTU for two or more consecutive 15-
minute readings.
Worksheet 3 is a monthly report for combined filter effluent in slow sand, diatomaceous
earth, or other alternative filtration technology plants. This worksheet is the same as
worksheet 1, but formatted for slow sand, diatomaceous earth, or other alternative filtration
technologies.
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Appendix B. Worksheets
Month: _
Year:
PWSID:
WORKSHEET 1
CONVENTIONAL AND DIRECT FILTRATION PLANTS
MONTHLY REPORT FOR COMBINED FILTER EFFLUENT
Due by the 10th of the Following Month
Check with your State or Primacy Agency to make sure this form is acceptable.
System/Treatment Plant:
A
Day
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
B
Number of
Samples
Required
Per Day
Samples/Day
c1
Maximum
Combined
Filter
Effluent
NTU
Totals:
D2
No. of
Turbidity
Measurements
E
No. of
Turbidity
Measurements
<= 0.3 NTU
F
No. of
Turbidity
Measurements
>1NTU
Number of monthly readings (Total of Column D) =
Number of monthly readings <= 0.3 NTU (Total of Column E) =
The percentage of turbidity measurements meeting the specified limits.
= (Total of Column E / Total of Column D) x 100 =
Record the date and turbidity value for any measurements exceeding 1 NTU (Contact State within 24 hours):
If none, enter "None."
Prepared by:
Date:
Date
Turbidity Readings >
1NTU
Was individual filter effluent monitored continuously (at least every 15 minutes) during the month?
Yes No
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Appendix B. Worksheets
Notes:
1. To complete Column B, enter the number of required samples for the day based on hours of plant
operation or as allowed by the State. Systems that do not operate 24 hours per day will need to
check with their State on required sampling frequency.
2. To complete Column C, report the highest combined filter effluent turbidity value of those
recorded at the 4-hour intervals.
3. To complete Column D, enter the number of turbidity measurements taken each day, not the
actual turbidity values obtained.
Records of the combined filter effluent turbidity monitoring results must be retained by the public
water system supplier. The system must report to the State or Primacy Agency by the 10th of the
following month:
The total number of filtered water turbidity measurements taken during the month.
The number and percentage of filtered water turbidity measurements taken during the month
which are less than or equal to 0.3 NTU.
The date and value of any turbidity measurements taken during the month which exceed 1
NTU.
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Appendix B. Worksheets
WORKSHEET 2
CONVENTIONAL AND DIRECT FILTRATION PLANTS
MONTHLY SUMMARY REPORT OF DATA FOR INDIVIDUAL FILTER EFFLUENT
Check with your State or Primacy Agency to make sure this form is acceptable.
Year:
PWSID:
System Name:
Filter Number:
A
Date
B
Were 15-min
Turbidity
Values
Recorded?
C
Values of Turbidity
Measurements > 1.0 NTU for
two or more consecutive
15-min readings
D
Value of Turbidity
Measurements
> 2.0 NTU
for two or more
consecutive
15-min readings
Did the filter exceed 1.0 NTU in two or more consecutive 15-minute readings this month? No
Yes - Report to the State by the 10th of the following month the filter number(s),
corresponding date(s), and turbidity value(s) which exceeded 1.0 NTU and
the cause, if known.
Did this occur in the two previous months? No
Yes - Must conduct a filter self-assessment within 14 days of the
exceedance unless a CPE was required.
Did the filter exceed 2.0 NTU in two or more consecutive 15-minute readings this month? No
Yes - Did this occur in the previous month? No
Yes - Must arrange for a CPE unless a CPE has been completed by
the State or third party approved by the State within the 12
prior months or the system and State are jointly participating
in an ongoing Comprehensive Technical Assistance project
at the system.
August 2004
193
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Appendix B. Worksheets
Notes:
This worksheet can be used for multiple months as a recordkeeping tool for the system. The system
may want to modify this sheet to allow daily recording of individual filter effluent turbidity monitoring
and the system could use a new worksheet for each month.
A. Enter the date in this column.
B. System must report by 10th of the following month that the individual filter effluent turbidity was
continuously monitored.
C. Enter number of incidents where two or more consecutive 15-minute turbidity readings for an
individual filter exceeded 1.0 NTU. The system must report to the State the filter number,
corresponding date(s), and turbidity value(s) which exceeded 1.0 NTU for two consecutive 15-
minute measurements each month by the 10th of the following month.
D. Enter the number of incidents where two or more consecutive 15-minute turbidity readings for an
individual filter exceeded 2.0 NTU.
EPA Guidance Manual 194 August 2004
LT1ESWTR Turbidity Provisions
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Appendix B. Worksheets
WORKSHEET 3
SLOW SAND, DIATOMACEOUS EARTH, OR ALTERNATIVE FILTRATION TECHNOLOGY
MONTHLY REPORT FOR COMBINED FILTER EFFLUENT
Due by the 10th of the Following Month
Month:
Year:_
PWSID:
Check with your State or Primacy Agency to make sure this form is acceptable.
System/Treatment Plant:
Treatment Type :
A
Day
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
B
Number of
Samples
Required
Per Day
Samples/Day
c2
Maximum
Combined
Filter
Effluent
NTU
Totals:
D3
No. of
Turbidity
Measurements
E
No. of
Turbidity
Measurements
<=1NTU
F
No. of
Turbidity
Measurements
>5NTU
Number of monthly readings (Total of Column D) =
Number of monthly readings <= 1 NTU (Total of Column E) =
The percentage of turbidity measurements meeting the specified limits.
= (Total of Column E / Total of Column D) x 100 =
Record the date and turbidity value for any measurements exceeding 5 NTU (Contact State within 24 hours):
If none, enter "None."
Prepared by:
Date:
Date
Turbidity Readings > 5 NTU
August 2004
195
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Appendix B. Worksheets
Notes:
1. Treatment type refers to Slow Sand, Diatomaceous Earth, or alternative filtration technology.
Treatment type should be your current operational practice.
2. To complete Column B, enter the number of required samples for the day based on hours of plant
operation or as allowed by the State. Systems that do not operate 24 hours per day will need to
check with their State on required sampling frequency.
3. To complete Column C, report the highest combined filter effluent turbidity value of those
recorded at the 4-hour intervals.
4. To complete Column D, enter the number of turbidity measurements taken each day, not the
actual turbidity values obtained.
EPA Guidance Manual 196 August 2004
LT1ESWTR Turbidity Provisions
-------
Appendix C
Equations and Sample
Calculations
-------
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-------
Appendix C. Equations and Sample Calculations
ABBREVIATIONS
ac = acre ha
cfs = cubic feet per second hr
cm = centimeter in
d = diameter in3
ft = feet kg
ft3 = cubic feet L
gal = gallons Ibs
gpd = gallons per day mg
gpm = gallons per minute MG
งPg = grains per gallon MGD
g = grams m3
hectare mi
hour min
inches mL
cubic inches ppm
kilogram r
liter sec
pounds Sp Gr
milligrams sq ft
million gallons sq in
million gallons sq m
per day
cubic meters yd
mile
minute
milliliter
parts per
million (mg/L)
inner radius
second
specific gravity
square feet
square inches
square meters
= yard
CONVERSION FACTORS
AREA:
1 sq ft = 144 sq in or 144 sq in/sq ft
1 ac = 43,560 sq ft or 43,560 sq ft/ac
DOSAGE:
1 grain/gal =17.1 mg/L or 17.1 mg/L/gpg
1 mg = 64.7 grains or 64.7 grains/mg
DENSITY:
1 gal = 8.34 Ibs or 8.34 Ibs/gal
1 ft3 = 62.4 Ibs or 62.4 Ibs/ ft3
FLOW:
1 MGD = 694 gpm or 694 gpm/MGD
1 MGD = 1.55 cfs or 1.55 cfs/MGD
LENGTH:
1 ft = 12 in or 12 in/ft
1 yd = 3 ft or 3 ft/yd
1 mi = 5,280 ft or 5,280 ft/mi
UNITS:
1 million = 1,000,000 = IxlO6
VOLUME:
1 ft3 = 7.48 gal or 7.48 gal/ft3
1 liter =1,000 mL or 1,000 mL/L
lgal = 3.785Lor3.785L/gal
1 gal = 231 in3 or 231 in3/gal
TIME:
1 min = 60 sec or 60 sec/min
1 hr =60 min or 60 min/hr
1 day = 24 hr or 24 hr/day
WEIGHT:
1 g = 1,000 mg or 1,000 mg/g
1 kg= l,000gor l,000g/kg
1 Ib = 454 g or 454 g/lb
1 kg = 2.2 Ibs or 2.2 Ibs/kg
August 2004
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Appendix C. Equations and Sample Calculations
CONVERSION FACTORS (Metric System)
AREA:
1 ha = 2.47 ac or 2.47 ac/ha
1 ha = 10,000 sq m or 1,000 sq m/ha
DENSITY:
1 liter = 1 kg or 1 kg/L
VOLUME:
1 m3 = 1,000 L or 1,000 L/ m3
1 gal = 3.785Lor3.785L/gal
LENGTH:
1 m = 100 cm or 100 cm/m
Im = 3.28ftor3.28ft/m
FLOW:
1 MOD = 3,785 m3 or 3,785 m3/MGD
WEIGHT:
1 gm = 1,000 mg or 1,000 mg/gm
1 kg = 1,000 gm or 1,000 gm/kg
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
200
August 2004
-------
Appendix C. Equations and Sample Calculations
FORMULAS
/. FLOWS:
(Flow, MGD)( 1,000,000 gal / MG)
1) Flow, gpm
or
2) Flow, MOD
(60min/hr)(24hr/day)
or
(Flow, GPM)(60 min / hr)(24 hr / day)
1,000,000 gal/MG
//. CHEMICAL FEEDS:
A. Dry Chemicals (Weight-based)
_ (FeedRate,g/min)(1440min/day)
1) Feed Rate, Ib/day
2) Dosage, ppm
454g/lb
Feed Rate, Ib / day
(Flow, MGD)(8.341b/gal)
B. Liquid Chemicals (Volume-based)
(Feed Rate, mL / min)(1440 min / day)
1) Feed Rate, gal/day
2) Dosage, ppm
3,785 mL/gal
_ Feed Rate, gal / day
Flow, MOD
C. Liquid Chemicals (Liquid Weight-based)
_ (Feed Rate, mL/ min)(1440min / day)(SpGr)(8.34Ib /gal)
1) Feed Rate, Ib/day
2) Dosage, ppm
3,785 mL/gal
Feed Rate, Ib / day
(Flow, MGD)(8.341b/gal)
D. Liquid Chemicals (Dry Weight-based)
1) Feed Rate, dry Ib/day
= (Feed Rate, mL / min)(1440 min / day)(Sp Gr)(%concentration)^.34 Ib / gal)
(3,785 mL/gal)( 100%)
August 2004 201 EPA Guidance Manual
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-------
Appendix C. Equations and Sample Calculations
_x Feed Rate, dry Ib / day
2) Dosage, ppm
(Flow, MGD)(8.341b/gal)
///. CHEMICAL DOSES:
A. Calibration of a Dry Chemical Feeder:
Chemical Applied, Ibs
Chemical Feed Rate, Ib/day =
Length of Application, day
B. Calibration of a Solution Chemical Feeder:
1) Chemical Feed, Ibs/day
_ (Chem Cone, mg / L)(Vol Pumped, mL)(60 min / hr)(24 hr / day)
(Time Pumped, min)(1000 mL / L)(1000 mg /gm)(454 gm / Ib)
_ Chemical Used, gal
2) Chemical Feed, gpm
Length of Application, min
_x , . ,_ , . ,, , , (Chemical Solution, %)(SpGr)(8.34 Ibs/gal)
3) Chemical Solution, Ibs/gal = F &
4) Feed Pump, gpd
100%
Chemical Feed, Ibs / day
Chemical Solution, Ibs / gal
C. Chemical Feeder Setting :
1) Chemical Feed, Ibs/day = (Flow, MGD)(Dose, mg/L)(8.34 Ibs/gal)
2) Chemical Feeder Setting, mL/min
_ (Flow, MGD)(Chemical Dose, mg / L)(3.785 L / gal)(l,000,000 gal / MG)
(Liquid Chemical, mg / mL)(24 hr / day)(60 min / hr)
3) Chemical Feeder Setting, gal/day
= (Flow, MGD)(Chemical Dose, mg / L)(8.34 Ibs / gal)
Liquid Chemical, Ibs / gal
4) Chemical Feeder Setting, %
= (Desired Feed Pump Rate, gpd)(100%)
Maximum Feed Pump Rate, gpd
EPA Guidance Manual 202 August 2004
LT1ESWTR Turbidity Provisions
-------
Appendix C. Equations and Sample Calculations
IV. COAGULATION AND FLOCCULATION:
_ (PolymerSolution,gal)(Polymer, %)(Sp Gr)(8.34Ibs / gal)
1) Polymer, Ibs
2) Dose, mg/L
3) Polymer, %
4) Liquid Polymer, gal
100%
_ Chemical Feed, Ibs / day
(Flow, MGD)(8.34 Ibs / gal)
_ (Dry Polymer, lbs)(100%)
(Dry Polymer, Ibs + Water, Ibs)
(Polymer Solution, %)(Vol of Solution, gal)
Liquid Polymer, %
V. FILTRATION:
_ (Water Drop, ft)(Surface Area, sq ft)(7.48 gal / ft3)
1) Filtration Flow, gpm
2) Hydraulic Surface Loading Rate, gpm/sq ft =
Time, min
Flow, gpm
Surface Area of Filter, sq ft
Note: Flow = flow onto the filter
ox A TT j i- c f T j- n 4. Total Volume Filtered,gal
3) Average Hydraulic Surface Loading Rate, gpm =
(Filter Run, hr)(60 min / hr)
A\ 1 TT j i- o c T j- n + / r*. Peak Filter Flow,gpm
4) Peak Hydraulic Surface Loading Rate, gpm/sq ft =
Filter Area, sq ft
5) Backwash Flow (Using Rise Rate Test), gpm
= (Filter Surface Area, sq ft)(Rise Distance, ft)(7.48 gal / ft3)
Rise Time, min
s\ r> i i TI 4. / A Backwash Flow, gpm
6) Backwash Rate, gpm/sq ft = -^-
Filter Surface Area, sq ft
August 2004 203 EPA Guidance Manual
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-------
Appendix C. Equations and Sample Calculations
~x , . . . Total Backwash Volume, gal
7) Backwash Time, mm ~
(Backwash Rate, gpm)(Filter Surface Area, sq ft)
8) Total Backwash, gal = (Backwash Flowrate, gpm)(Backwash Time, min)
(Total Backwash, gal)( 100%)
= '
,_, , , 0/
9) Backwash, %
Total Volume Filtered, gal
mM> + o AV o/ (A-C)(100%)
10) Percent Bed Expansion, % = - - - - -
A = Depth to media as measured from top of sidewall before backwash, inches.*
B = Media depth (less support gravel), inches.*
C = Depth to expanded media as measured from top of sidewall during backwash,
inches.*
* Systems should make sure all measurements have the same units.
1 1) Uniform Filter Run Volume (UFRV)
Volume Filtered, gal
UFRV, gal/sq ft = - -
Filter Surface Area, sq ft
gal/sq ft = (Filter Rate, gpm/sq ft)(Filter Run, hr)(60 min/hr)
EPA Guidance Manual 204 August 2004
LT1ESWTR Turbidity Provisions
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Appendix C. Equations and Sample Calculations
SAMPLE CALCULATIONS FOR DETERMINING FLOWS AND
CHEMICAL DOSES
The following examples demonstrate how the previously presented equations can be used if
a system is conducting jar tests or modifying chemical feed practices to improve filter
effluent turbidity. Systems may find these examples useful for calculating flow values or
determining chemical feed settings.
EXAMPLE 1: Flow Conversion
To convert a flow from gpm to MGD:
Scenario: If a system's flow is 900 gpm and the flow needs to be converted to MGD, the
following equation can be used:
Flow MGD = (Flow' งPm)(60 min / hr)(24 hr / day)
1,000,000 gal/MG
= (900 gpm)(60 min / hr)(24 hr / day)
1,000,000 gal/MG
Flow =1.3 MGD
EXAMPLE 2: Chemical Doses
To calculate the liquid alum chemical feeder setting in milliliters per minute:
Scenario: The optimum liquid alum dose based on the jar tests at a particular plant is 12
mg/L. The system wants to determine the setting on the liquid alum chemical feeder in
milliliters per minute when the plant flow is 5.3 MGD. The liquid alum delivered to the
plant contains 439.8 milligrams of alum per milliliter of liquid solution.
Chemical Feeder Setting, mL/min
= (Flow, MGD)(Alum Dose, mg / L)(3.785 L / gal)( 1,000,000 gal / MG)
(Liquid Alum, mg / mL)(24 hr / day)(60 min / hr)
(5.3 MGD)(12 mg / L)(3.785 L /gal)(l,000,000 gal / MG)
(439.8 mg / mL)(24 hr / day)(60 min / hr)
Chemical Feeder Setting = 380 mL/min
August 2004 205 EPA Guidance Manual
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Appendix C. Equations and Sample Calculations
EXAMPLES: Chemical Dose
To calculate the liquid alum chemical feeder setting in gallons per day:
Scenario: The optimum liquid alum dose based on the jar tests at a particular plant is 12
mg/L. The system wants to determine the setting on the liquid alum chemical feeder in
gallons per day when the flow is 5.3 MOD. The liquid alum delivered to the plant contains
4.42 pounds of alum per gallon of liquid solution.
(Flow, MGD)(Alum Dose, mg / L)(8.34 Ibs / gal)
Chemical Feeder Setting, gpd =
LiquidAlum, Ibs/gal
_ (5.3 MGD)(12mg/L)(8.341bs/gal)
4.42 Ibs/gal
Chemical Feeder Setting = 120 gpd
EXAMPLE 4: Chemical Dose
To calculate the polymer fed by the chemical feed pump in pounds of polymer per day:
Scenario: A system wants to determine the chemical feed in pounds of polymer per day
from a chemical feed pump. The polymer solution contains 18,000 mg polymer per liter.
Assume the specific gravity of the polymer solution is 1.0. During a test run, the chemical
feed pump delivered 700 mL of polymer solution during 7 minutes.
(Chemical Cone, mg / L)(Vol Pumped, mL)(60 min / hr)(24 hr / day)
Polymer Feed, Ibs/day =
(Time Pumped, min)(1000 mL / L)(1000 mg / gm)(454 gm / Ib)
_ (18,000 mg / L)(700 mL)(60 min / hr)(24 hr / day)
(7 min)(1000 mL / L)(1000 mg / gm)(454 gm / Ib)
Polymer Feed = 5.7 Ibs polymer/day
EPA Guidance Manual 206 August 2004
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Appendix C. Equations and Sample Calculations
EXAMPLES: Chemical Dose
To calculate the flow delivered by the pump in gallons per minute and gallons per day:
Scenario: A small chemical feed pump lowered the chemical solution in a 4-foot diameter
tank 1 foot and 3 inches during a 6-hour period.
3 in
1. Tank Drop, in feet = 1 ft H
12 in/ft
= 1ft+ 0.25 ft
Tank Drop = 1.25 ft
2. Determine the gallons of solution pumped.
Volume Pumped = (Area, sq ft)(Drop, ft)(7.48 gal/cu ft)
Area = nr2
K = 3.1416 (constant)
r = radius, ft = (diameter / 2) = 4 ft/2 = 2 ft
Area = (3.1416)(2ft)2= 12.5664ft2
Volume Pumped = (12.5664 ft2)(1.25 ft)(7.48 gal/cu ft)
Volume Pumped =117.5 gal
3. Estimate the flow delivered by the pump in gallons per minute and gallons per day.
Volume Pumped, gal
Flow, gpm= :
(Time, hr)(60 min / hr)
117.5 gal
(6 hr)(60 min/hr)
Flow = 0.33 gpm
OR
(Volume Pumped, gal)(24 hr / day)
Flow, gpd =
Time, hr
(117.5 gal)(24hr/day)
6hr
Flow = 470 gpd
August 2004 207 EPA Guidance Manual
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Appendix C. Equations and Sample Calculations
EXAMPLE 6: Chemical Dose
To determine the settings in percent stroke on a chemical feed pump (the chemical could be
chlorine, polymer, potassium permanganate or any other chemical solution fed by a pump)
for various doses of a chemical in milligrams per liter:
Scenario: The raw water flow rate to which the chemicals are delivered is 315 gpm. The
solution strength of the chemical being pumped is 3.8 percent. Assume the specific gravity
of the chemical solution is 1.0. The chemical feed pump has a maximum capacity of 97
gallons per day at a setting of 100 percent capacity.
1. Convert the raw water flow from gallons per minute to million gallons per day.
Raw Water Flow, gpd = (Raw Water Flow, gpm)(60 min/hr)(24 hr/day)
= (315 gal/min)(60 min/hr)(24 hr/day)
= 454,000 gal/day
Raw Water Flow = 454,000 gpd = 0.454 MGD
2. Change the chemical solution strength from a percentage to pounds of chemical per
gallon of solution. A 3.8-percent solution means we have 3.8 pounds of chemical in a
solution of water and chemical weighing 100 pounds.
, . , , . 11/1 (ChemicalSolution, %)(8.34Ibs / gal)(Sp Gr)
Chemical Solution, Ibs/gal = - & F-
100%
= (3.8%)(8.341bs/gal)(1.0)
100%
Chemical Solution = 0.32 Ibs chemical/gallon solution
3. Calculate the chemical feed in pounds per day for a chemical dose of 0.5 milligrams per
liter. Assume various chemical doses of 0.5, 1.0, 1.5, 2.0, 2.5 mg/L and upward so that
if we know the desired chemical dose, we can easily determine the setting (percent
stroke) on the chemical feed pump.
Chemical Feed, Ibs/day = (Raw Water Flow, MGD)(Dose, mg/L)(8.34 Ibs/gal)
= (0.454 MGD)(0.5 mg/L)(8.34 Ibs/gal)
Chemical Feed = 1.9 Ibs/day
EPA Guidance Manual 208 August 2004
LT1ESWTR Turbidity Provisions
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Appendix C. Equations and Sample Calculations
4. Determine the desired flow from the chemical feed pump in gallons per day.
Chemical Feed, Ibs / day
Feed Pump, gpd =
Chemical Solution, Ibs / gal
_ 1.9 Ibs/day
0.32 Ibs/gal
Feed Pump = 5.9 gpd
5. Determine the setting on the chemical feed pump as a percent. In this case we want to
know the setting as a percent of the pump stroke.
. = (Desired Feed Pump, gpd)(100%)
O t lllll^i., /O
Maximum Feed Pump, gpd
= (5.9gpd)(100%)
97 gpd
Setting = 6%
6. Now change the chemical dose in Step 3 from 0.5 mg/L to 1.0 mg/L and other higher
doses and repeat the remainder of the steps, to calculate the data in Table 1.
7. Plot the data in Table 1 (Chemical Dose, mg/L vs. Pump Setting, % stroke) to obtain
Figure 1. For any desired chemical dose in milligrams per liter, use Figure 1 to
determine the necessary chemical feed pump setting.
August 2004 209 EPA Guidance Manual
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Appendix C. Equations and Sample Calculations
TABLE 1 - SETTING FOR CHEMICAL FEED PUMP
Pump Flow, GPM =315 gpm
Solution Strength, % =3.8%
Chemical
Dose, mg/L
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
6.5
7.0
7.5
Chemical
Feed, Ibs/day
1.9
3.8
5.7
7.6
9.5
11.4
13.2
15.1
17.0
18.9
20.8
22.7
24.6
26.5
28.4
Feed
Pump, gpd
5.9
11.8
17.8
23.7
29.7
35.6
41.2
47.2
53.1
59.1
65.0
70.9
76.9
82.8
88.7
Pump Setting,
% stroke
6.0
12.2
18.4
24.4
30.6
36.7
42.5
48.7
54.7
60.9
67.0
73.1
79.3
85.4
91.4
o
LU
(/)
Q_
I
0_
LU
*
O
FIGURE 1 - CHEMICAL FEED PUMP SETTINGS FOR
VARIOUS CHEMICAL DOSES FROM TABLE 1,
ABOVE
100.0
80.0
60.0
40.0
20.0
0.0
0123456
CHEMICAL DOSE, mg/L
7
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
210
August 2004
-------
Appendix C. Equations and Sample Calculations
VOLUME EQUATIONS
Water Pipe (raw or treated):
Fluid Volume = Length x Cross-Sectional Area
Side View
Cross-Section View
Length
Cross-Sectional Area = 3.1416 * r2
r = inner radius = d / 2
d = inner diameter
Rectangular Basins:
Fluid Volume = Length x Width x Depth of Water
Length
Width
\
\
\
Water Level
~7
\
)l
Depth of Water
Cylindrical Basins:
Fluid Volume = Water Depth x Cross-Sectional Area
Side
A
Water Depth
Top View
Cross-Sectional Area = 3.1416 * r2
r = inner radius = d / 2
d = inner diameter
August 2004
211
EPA Guidance Manual
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Appendix C. Equations and Sample Calculations
Filters
Fluid Volume = Volume of Water Above Filter Surface
Fluid Volume = Length x Width x Depth of Water Above Filter Surface
Length
"Width
Depth of
Water Above
Filter Surface
Note: Some States may have other equations to account for the volume in the media.
Check with the State for additional information.
ADDITIONAL RESOURCES
Additional equations, conversions, and examples can be found in the following resources:
Small Water System Operation and Maintenance: A Field Study Training Program.
California Department of Health Services and USEP A. 1995.
Applied Math for Water Plant Operators. Available at http://www.awwa. org/ and at
http://www.usabluebook.com.
Basic Math Concepts for Water and Wastewater Plant Operators. Available at
http://www.awwa.org/ and at http://www.usabluebook.com.
Operator Math Made Easy (Video). Available at http ://www. awwa. org/.
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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August 2004
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Appendix D
Suggested Backwash Rates
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Appendix D. Suggested Backwash Rates
The following tables provide information about backwash rates for different water
temperatures and filter media sizes. The properties of water change with temperature. For
instance, water becomes more viscous when it is cold. Particles tend to take longer to sink
when the water is cold.
The information in Tables D-l and D-2 are guidelines for how to adjust the backwash rate
based on temperature. These tables should be used with caution because the backwash
adjustment rates are general and not site specific. Systems should develop their own site-
specific backwash rates based on temperature that provide proper fluidization and bed
expansion.
Table D-l provides guidelines for adjusting the backwash rate to address the change in
water properties and to provide a better backwash of the filter. For example, assume the
backwash rate is typically 15 gpm/ft2 (at 71.6ฐC) during the summer. It is now winter and
the wash water temperature is 41ปF. Based on the following table, the backwash rate could
be adjusted to 12.8 gpm/ft2. It may not be possible to adjust the backwash rate due to the
system configuration. However, if the backwash rate can be adjusted, the suggested
backwash rates in the table may enhance the backwashing process.
Table D-2 provides guidelines for determining an appropriate backwash rate for a given
temperature and media size. The media size in the table is described by deo%, which is the
diameter of the particles the filter media for which 60 percent of the total grains are smaller
and 40 percent are larger on a weight basis. Effective size is also commonly used to
describe the size of the particles in filter media. The effective size is the particle diameter in
a granular sample (filter media) for which 10 percent of the total grains are smaller and 90
percent are larger on a weight basis. If d6o% is not known it can be calculated by multiplying
the effective size by the uniformity coefficient of the media. The uniformity coefficient is a
media-specific ratio that relates deo%to the effective size.
August 2004 215 EPA Guidance Manual
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Appendix D. Suggested Backwash Rates
Table D-1. Backwash Rate Adjustment for Various Water Temperatures
Wash-Water
Temperature
(ฐC)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Wash-Water
Temperature
(ฐF)
33.8
35.6
37.4
39.2
41.0
42.8
44.6
46.4
48.2
50.0
51.8
53.6
55.4
57.2
59.0
60.8
62.6
64.4
66.2
68.0
69.8
71.6
73.4
75.2
77.0
78.8
80.6
82.4
84.2
86.0
Water
Viscosity
(cP)a
1.728
1.671
1.618
1.567
1.519
1.472
1.428
1.386
1.346
1.307
1.271
1.235
1.202
1.169
1.139
1.109
1.081
1.053
1.027
1.002
0.9779
0.9548
0.9325
0.9111
0.8904
0.8705
0.8513
0.8327
0.8148
0.7975
12 gpm/ft2
(30 m/h)
at71.6ฐF
(22ฐC)
9.8
9.9
10.0
10.1
10.2
10.3
10.5
10.6
10.7
10.8
10.9
11.0
11.1
11.2
11.3
11.4
11.5
11.6
11.7
11.8
11.9
12.0
12.0
12.1
12.2
12.3
12.4
12.5
12.6
12.7
15 gpm/ft2
(37.5 m/h)
at71.6ฐF
(22ฐC)
12.3
12.4
12.6
12.7
12.8
13.0
13.1
13.2
13.4
13.5
13.6
13.8
13.9
14.0
14.1
14.3
14.4
14.5
14.6
14.8
14.9
15.0
15.1
15.2
15.4
15.5
15.6
15.7
15.8
15.9
18 gpm/ft2
(45 m/h)
at71.6ฐF
(22ฐC)
14.8
14.9
15.1
15.2
15.4
15.6
15.7
15.9
16.0
16.2
16.3
16.5
16.6
16.8
16.9
17.1
17.2
17.4
17.5
17.7
17.8
18.0
18.1
18.3
18.4
18.5
18.7
18.8
19.0
19.1
21 gpm/ft2
(52.5 m/h)
at71.6ฐF
(22ฐC)
17.3
17.5
17.7
17.9
18.1
18.3
18.4
18.6
18.8
19.0
19.2
19.4
19.5
19.7
19.9
20.1
20.2
20.4
20.6
20.8
20.9
21.1
21.3
21.4
21.6
21.8
21.9
22.1
22.2
22.4
acP, centipoise.
Reference: Kawamura, Susumu. 2000. Integrated Design and Operation of Water
Treatment Facilities, Second Edition. John Wiley & Sons, Inc. New York,
NY.
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
216
August 2004
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Appendix D. Suggested Backwash Rates
Table D-2. Appropriate Fluidization Backwash Rates
Fluidization Backwash Rate, gpm/ft2
Water Temperature
Sand Anthracite Coal
(d6o% size of 0.7 mm) (deo% size of 1.5 mm)
5
10
15
20
25
30
41
50
59
68
77
86
12
13.5
15
16.5
18
20
15
16.5
18
20
22
24
Note: These fluidization backwash rates are guidelines for media with a grain size of d60% (effective size x
uniformity coefficient). The specific gravities are: sand = 2.65 and anthracite coal = 1.65. The rates should be
adjusted as necessary for other filter materials. An appropriate fluidization backwash rate is one that fluidizes
the bed with adequate expansion and attains sufficient velocities to bring fines to the surface. Fluidization is
the upward flow of a fluid through a granular bed at sufficient velocity to suspend the grains in the fluid and
depends on filter media properties, backwash temperature, and backwash water flow rates.
Reference: AWWAB100-01.
August 2004 217 EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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Appendix D. Suggested Backwash Rates
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Appendix E
Filter Self-Assessment
Example Report
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Appendix E. Filter Self-Assessment Example Report
This example of a filter self-assessment report was modified from an example filter self-
assessment report created by the Pennsylvania Department of Environmental Protection.
The format used in this report is only an example. Before using this format, check with the
State to ensure that this format is acceptable.
Filter Self-Assessment
Example Report
Introduction
XYZ Water Treatment Plant was required to perform a filter self-assessment on filter #1 as a
result of elevated turbidities over the past 3 months. The Long Term 1 Enhanced Surface
Water Treatment Rule (LT1ESWTR) requires that a filter self-assessment be conducted for
any individual filter that has a measured turbidity level greater than 1.0 nephelometric
turbidity units (NTU) in two consecutive measurements taken 15 minutes apart in each of
three consecutive months. This report summarizes the findings of our self-assessment on
filter #1 and shows our plans to correct the problems that we found.
Filter Self-Assessment Components
The self-assessment of filter # 1 must include the following components:
An assessment of filter performance;
The development of a filter run profile;
Identification and prioritization of factors limiting filter performance; and,
An assessment of the applicability of corrections.
The factors we investigated are:
Hydraulic loading conditions of the filter;
Condition and placement of the media;
Backwash practices;
Support media and underdrains; and,
Rate-of-flow controllers and filter valving.
August 2004 221 EPA Guidance Manual
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Appendix E. Filter Self-Assessment Example Report
Assessment of Filter Performance
Filter # 1 is one of four dual media filters at the XYZ Water Treatment Plant. Each filter is
10' x 10' with 100 ft2 of filter surface area. Each filter is designed to have 20 inches of
anthracite and 9 inches of sand. None of the filters are equipped with filter-to-waste
capabilities.
Filter Profile
Figure 1 shows a turbidity profile for filter #1. The filter run ended at 80 hours of run time.
The filter was then backwashed and placed into service with a turbidity of about 0.56 NTU.
Filter #1 then recovered to a turbidity of approximately 0.5 NTU within 3.5 hours. This is
not typical of the other three filters at the XYZ Water Treatment Plant. The other filters
typically recover to <0.1 NTU within 15 minutes. This is an indication that the problem is
within filter #1 and not a result of poor pre-treatment.
EPA Guidance Manual 222 August 2004
LT1ESWTR Turbidity Provisions
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Appendix E. Filter Self-Assessment Example Report
Filter #1 Profile 3/11/02
Q_ Q_ Q_
Q_ Q_
Q_ Q_ Q_
000
000
0000000000000000000
0000000000000000000
00
00
00 CM
00 CM
00 CM
00 CM
00 CM
TIME
Figure 1. Effluent turbidity profile of filter #1
A. 10:30 AM Day 1 filter #1 backwashed @ 0.65 NTU
B. 12:29 PM Day 1 filter # 1 placed into service @ 0.65 NTU
C. 2:59 PM Day 1 filter #1 recovers @ 0.5 NTU
D. 8:45 AM Day 2 filter #3 backwashes
E. 9:30 AM Day 2 performance of filter #1 improves because filter # 3 has been
washed which reduces the loading on filter #1
F. 8:29 PM Day 3 performance of filter #1 begins to degrade
G. 6:59 PM Day 4 filter #1 backwashed @ 0.51 NTU
H. 8:44 PM Day 4 filter #1 placed into service @ 0.56 NTU
I. 12:14 AM Day 5 filter #1 recovers @ 0.5 NTU
August 2004
223
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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Appendix E. Filter Self-Assessment Example Report
Hydraulic Loading Conditions of the Filter
The permitted capacity of XYZ Water Treatment Plant is 1,728,000 gallons/day or 1,200
gpm maximum instantaneous flow rate. This is based on the designed filtration rate of 4
gpm/ft2 with one filter out-of-service. The plant is always operated at or under 1,200 gpm
with the average being 1,100 gpm. In addition, the flow is divided evenly among all filters.
When a filter is being backwashed, the flow is divided among the remaining filters, still not
exceeding 400 gpm/filter.
Condition and Placement of the Media
The design specifications for the media in all filters are as follows:
Design Media Conditions
Anthracite
effective size 1.0 mm
uniformity coefficient 1.3
Sand
effective size 0.45 mm
uniformity coefficient 1.3
We collected core samples of filter # 1 and had our lab conduct a media analysis according
to AWWA Standard B100-01. We found that the current condition of the media is as
follows:
Current Media Conditions
Anthracite
effective size 1.3mm
uniformity coefficient 1.5
Sand
effective size 0.55 mm
uniformity coefficient 1.4
These results show that a coating has developed on our media. The coating is black in color.
According to our lab and our media supplier, it is probably a manganese dioxide coating.
Our media are 10 years old and we were advised to consider cleaning or replacing the media
in the near future.
EPA Guidance Manual 224 August 2004
LT1ESWTR Turbidity Provisions
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Appendix E. Filter Self-Assessment Example Report
During the filter inspection there were no signs of surface cracking, mounding of media or
separation from the walls. We saw no boiling of media or vortexing. As a result we felt no
need to do an extensive inspection of the underdrains. However, mudballs were present on
the surface of the filter bed. Inspection of the core samples showed an interface of about 2
to 3 inches between the sand and anthracite.
Our operators also conducted a floe retention analysis as described in Integrated Design and
Operation of Water Treatment Facilities, 2nd edition, by Susumu Kawamura. The results of
the floe retention analysis were 740 NTU/100 grams of media. These results indicate that
filter # 1 has mudball problems within the filter media.
While mapping the support gravel, operators found that filter # 1 had only 25 inches of filter
media. This is of some concern to us, because we thought that we had 29 inches of media.
Backwash Practices
Filters are backwashed when they reach:
a terminal head loss >=6 ft
individual filter effluent turbidity >= 0.3 NTU
filter run time >=80 hours
The backwash procedures are as follows:
5 minutes-filter draw down
3 minutes-low wash at 8 gpm/ft2
5 minutes-high wash at 14 gpm/ft2
3 minutes-low wash at 8 gpm/ft2
The filter is placed into service after a rest period.
The backwash procedure is programmed into the computer and is not routinely changed.
The backwash duration is not extended if the filter is still dirty at the end of the wash.
Backwash rates are limited by the amount of head pressure in the backwash storage tank.
All waste backwash water is sent to the lagoon and then the supernatant is slowly pumped to
the sanitary sewer at a rate of 10 gpm. The sludge from the lagoon is cleaned two times per
year and the sludge is sent to a landfill.
Our operators built a media expansion tool using a telescopic paint roller pole. A white disk
is attached at the end of the pole. The expansion tool is similar to the one used by DEP
during filter plant performance evaluations (FPPE) to measure the percent bed expansion.
We determined that filter # 1 is getting about 23 percent bed expansion.
August 2004 225 EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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Appendix E. Filter Self-Assessment Example Report
Support Media and Underdrains
Our operators mapped the gravel layer using a 1A inch diameter steel rod as described in an
AWWA Filter Surveillance video that we purchased for operator training. They found that
the gravel layer was within 2 inches of variance. According to Chapter 5 of EPA's
Guidance Manual for Compliance with the Long Term 1 Enhanced Surface Water
Treatment Rule: Turbidity Provisions, the gravel layer should not deviate more than 2
inches. The operators also discovered that we only have a total of 25 inches of filter media.
This was verified by digging a test hole and measuring the depth to the gravel layer. Please
see figure 2 below for a map of filter #1 support gravel.
Filter #1 Support Gravel Map
-Rear
Inches Below
Backwash Trough
Middle
44.5-45
D 44-44.5
D 43.5-44
D 43-43.5
Front
Figure 2. Map of filter #1 support gravel in inches below the backwash
trough.
In addition, no media was found in the clearwell, no air boiling was observed during the
backwash, and no vortexing was seen while the filter was draining.
Rate-of-Flow Controllers and Filter Valving
No major problems were found with the rate-of-flow control valves or any other valves.
EPA Guidance Manual
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226
August 2004
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Appendix E. Filter Self-Assessment Example Report
Limiting Factors
Below are the performance-limiting factors identified during the self-assessment of filter #1.
These factors are listed in priority order with number one having the highest priority. In
addition, each limiting factor has an assessment of the applicability of corrections beneath it.
In other words, this is how we determined how effective it would be to correct each limiting
factor. We feel that making the corrections listed below will improve the performance of
filter #1 and ensure that turbidity excursions over 1 NTU will not occur in the future.
1. Significant turbidity spike when placing filter #1 into service following
backwash. No special procedures for placing a filter into service after
backwashing. No filter-to-waste capabilities.
Applicability of Corrections: Our plant was designed without filter-to-waste
capabilities, otherwise we would be able to send this spike to waste. While reading
some filter optimization literature we found a couple of procedures for placing a
filter into service after backwashing. The first two that we plan to try immediately
are:
Allow the filter to rest for one hour before placing it into service; and,
Ramp valves open slowly when placing the filter online.
If these two procedures do not reduce our turbidity spike when placing a filter in
service, we will try using a filter aid polymer.
The addition of filter-to-waste piping has been budgeted into our 3-year plan.
2. Backwash duration is not extended if the filter is still dirty.
Applicability of Corrections: This has already been resolved. Operators have been
instructed to observe each backwash. If the water over the filter is still dirty at the
end of the high wash, then the high wash is extended until the filter is clean. The
time is then programmed into the computer so that the next backwash will
automatically be adjusted.
3. Mudballs on the surface of filter #1. Floe retention analysis results indicate that
the filter is still dirty.
Applicability of Corrections: Scraping and removing the surface of the filter bed
have removed most mudballs. The formation of these mudballs is probably a
combination of:
Excessive floe carry-over to the filter
No surface wash
Low filter bed expansion
Low backwash rate
August 2004 227 EPA Guidance Manual
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Appendix E. Filter Self-Assessment Example Report
Inadequate backwash duration.
These are all limiting factors that will be addressed independently.
4. Only 25 inches of media in filter #1.
Applicability of Corrections: Filter media is expensive; we feel that topping off
the filters with new media now would be a waste of new media, since we plan to
rebuild this filter. All media will be replaced within the next 6 months. The filter
will then be brought up to the design standard of 20 inches of anthracite and 9 inches
of sand.
5. Manganese dioxide coating on the filter media.
Applicability of Corrections: As stated earlier, the filter media will be replaced
with all new media within the next 6 months. In addition, we are looking into
optimizing our manganese removal in the sedimentation basin. We are planning to
move the potassium permanganate feed point upstream to the raw water intake to
give more contact time prior to adding our coagulant. We are also planning to add
intra-basin baffling to our sedimentation basin and pilot the use of a polymer as a
floe aid to help settle our floe in the basin. We plan to have these changes
implemented by this winter so that this problem can be resolved before filter #1 has
new media. Hopefully these changes will reduce the formation of mudballs and
manganese dioxide on the new filter media.
6. Filter #1 recovers to 0.5 NTU after backwash while other filters recover to 0.1
NTU. Filter #1 turbidity increases significantly when filter # 3 is backwashed.
Applicability of Corrections: Although these are two of our greatest concerns, they
have received a lower priority because we are uncertain of the cause. Hopefully, this
problem will be remedied once the filter is rebuilt. We plan to do a thorough
inspection of the underdrains in filter #1 when it gets rebuilt within the next 6
months. This will continue to be a limiting factor that we will stay aware of until the
cause is identified and resolved.
EPA Guidance Manual 228 August 2004
LT1ESWTR Turbidity Provisions
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Appendix F
Jar Tests
-------
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Appendix F. Jar Tests
Jar tests are a valuable tool to determine types and amounts of chemicals to use for optimum
floe formation. Jar tests allow a system to experiment with different coagulants, polymers,
pH controllers, and oxidants. The jar test should simulate actual plant operating conditions,
such as mixing rates and detention times. The information obtained from the jar test can
prove invaluable as a system considers different treatment techniques. The most important
part of the jar test is to document the procedures used to enable replication in the future.
The following worksheets can be used for the jar test. These worksheets are from EPA's
Handbook Optimizing Water Treatment Plant Performance Using the Composite Correction
Program, 1998 Edition (EPA 625-6-91-027). An operator who has never performed ajar
test may want to seek technical assistance.
Procedures for the actual jar test are not presented due to the volume of information
required. The following references are recommended for detailed instructions for
performing ajar test:
AWWA. 1992. Operational Control of Coagulation and Filtration Processes. M37.
American Water Works Association. Denver, Colorado.
California State University. 1994. Water Treatment Plant Operation, Volume 1.
Third Edition. California State University. Sacramento, California.
August 2004 231 EPA Guidance Manual
LT1ESWTR Turbidity Provisions
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Appendix F. Jar Tests
JAR TEST PROCEDURE (page 1)
TEST CONDITIONS
Facility Date
Water Source
Time Turbidity Temperature pH
Coagulant Coagulant Aid
Alkalinity
PREPARING STOCK SOLUTIONS
. , Select desired stock concentration (see Table 1).
P Choose a stock solution concentration that will be practical for transferring chemicals to jars.
Table 1
Stock
Solution Concentration
(%) (mg/L)
0.01 100
0.05 500
0.1
1,000
0.2 2,000
0.5 5,000
1.0 10,000
1.5 15,000
2.0 20,000
mg/L dosage per mL
of stock solution
added to 2 liter jar
0.05
0.25
0.5
1.0
2.5
5.0
7.5
10.0
Desired Stock Solution
(%)
Coagulant Coag. Aid
,.,. Determine chemical amount to add to 1 -liter flask.
P If using dry products, see Table 2. If using liquid products, go to step 3.
Table 2
Stock Solution Cone.
(%) (mg/L)
0.01 100
0.05 500
0
0
1 1,000
2 2,000
0.5 5,000
1
0 10,000
1.5 15,000
2
0 20,000
mg of alum added
to 1 -liter flask
100
500
1,000
2,000
5,000
10,000
15,000
20,000
Desired Amount
In
1 -liter flask (mL)
Coagulant Coag. Aid
,.,. _ Determine liquid chemical amount to add to volumetric flask.
P For liquid chemicals, use the equation
mL coagulant =
1 Note: Chemical Strength =
(stock sol ution %)x (fl ask vol ume, ml_)x (8.34 b/gal )
100x(chemical strength, Ib/gal)
Chemical Strength (Ib/gal)1
Stock Solution Volume (mL)
Desired Volume of Chemical
to add to Flask (mL)
Coagulant Polymer
chemical density x % strength
EPA Guidance Manual
LT1ESWTR Turbidity Provisions
232
August 2004
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Appendix F. Jar Tests
JAR TEST PROCEDURE (page 2)
JAR SETUP
Set up individual jar doses based on desired range of test.
Determine amount of stock solution by dividing doses by mg/L per ml_ (see Table 1).
Coagulant- Jar #
Dose (mg/L)
Stock Solution (ml_)
Coagulant Aid - Jar #
Dose (mg/L)
Stock Solution (mL)
Dose (mg/L)
Stock Solution (mL)
1
1
1
TEST PROCEDURE
Step 1
Rapid mix time (min
Step 2
Floe time (min
Step3
Step 4
Sample time (mir
2
2
2
3
3
3
4
4
4
5 6
5 6
5 6
Set rapid mix time equal to rapid mix detention time.
To determine rapid mix time, use the following equation -
(r apid mix vol ume, gal )x (1,440 min/day)x (60 sec / min )
) -
Mix Volume
(plant flowrate, gal/d)
(gai)
Plant Flow Rate (gal/d)
Mix Time (sec)
Set total flocculation time equal to total flocculation time in plant.
To determine total flocculation time, use the following equation -
(f I occu
) -
at or vol u me, gal )x (1,440 mi n/day)
(plant flowrate, gal/d)
Floe Volume (gal)
Floe Time (min)
Use Figure 1* to determine the jar mixing energy values (rpm) that correspond to the
approximate flocculator mixing energy values (G). Flocculator mixing energy can be
estimated from the plant design information (O&M manual) or can be calculated from the
equation described in Appendix F - B.1 .Flocculation*.
Flocculator Stage
Flocculator Mixing (G)
Jar Mixing (rpm)
1st
2nd
3rd
Set sample time based on particle settling velocity. Use the equation below to determine
sample time when using 2-liter gator jars as described in Figure 1*.
(10cm)
) -
x (surface area, ft2)x (1,440 min/day)x (7.48 gal/ft3)
(plant f owrate, gal / d) x (3 0.48 cm/ft)
Sedimentation Surface Area (ft2)
Plant Flow Rate (gal/day)
Sample Time (min)
* Figure 1 and Appendix F can be found in Optimizing Water Treatment Plant Performance Using the
Composite Correction Program, 1998 Edition (EPA 625-6-91-027).
August 2004
233
EPA Guidance Manual
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Appendix F. Jar Tests
JAR TEST PROCEDURE (page 3)
TEST RESULTS
Record test results in the table below.
Settled Turbidity (NTU)
Settled pH
Filtered Turbidity (NTU)
Comments:
EPA Guidance Manual
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234
August 2004
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Appendix G
Example of an Operating
Procedure for Chemical
Feed System
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Appendix G. Example of an Operating Procedure for Chemical Feed System
Following is an example of an operating procedure for the chemical feed practices when raw
water turbidity is between 10 and 20 NTU. It may be used as a standard operating
procedure (SOP). It is an example and may provide valuable guidelines for systems.
However, be careful when conducting any of the procedures contained in the following
example operating procedure. Each system is unique and what works well for one system
may not work for another. Chemical feed SOPs should be developed based on specific
filtered water turbidity goals, jar testing, experience, and other site-specific conditions.
August2004 237 EPA Guidance Manual
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Appendix G. Example of an Operating Procedure for Chemical Feed System
EXAMPLE OPERATING PROCEDURE
Chemical Feed Practices for Raw Water Turbidity Between 10 and 20 NTU1
1. Set the alum feed rate at 15 mg/L (metering pump speed at 50 percent speed; do not
change the stroke setting).
2. Set the polymer feed rate at 3 mg/L (metering pump speed at 50 percent speed; do
not change the stroke setting).
3. Start the plant with clean filters. If filters are not clean, backwash them using SOPs
for backwashing.
4. After 20 minutes, note the effluent turbidity readings from the sedimentation basins
and from individual filters.
5. The settled water turbidity should be less than 2 NTU. If turbidity exceeds 2 NTU
off of a sedimentation basin, check the individual filter effluent (IFE) turbidities:
a. If IFE turbidities are less than 0.1 NTU, do not adjust the chemical feed rates.
b. If IFE turbidities are greater than 0.1 NTU but less than 0.25 NTU, increase
the alum feed rate by 5 percent. Wait another 20 minutes to observe.
6. Repeat procedures in Step 5 as necessary.
7. If any of the IFE turbidity readings exceed 0.25 NTU, take the appropriate filter(s)
off-line and reduce the flow through the plant by 200 gpm for each filter that is off-
line.
8. If IFE turbidity remains between 0.10 NTU and 0.25 NTU after 4 hours of operation,
or if a filter(s) is still off-line after 4 hours of operation, call the plant supervisor at
555-5050.
a. Begin jar testing using alum doses of 10 mg/L, 20 mg/L, 30 mg/L and 40
mg/L.
b. After results are obtained, run another jar test using alum doses that are
slightly above and below the best result from the first test. For example, if the
best results were obtained at 30 mg/L, run another set of tests at 26 mg/L, 28
mg/L, 30 mg/L and 32 mg/L.
c. After the best alum dose is determined from the second jar test, reduce that
alum dose by 5 mg/L, and run another set of tests using that alum dose and
polymer doses of 2 mg/L, 3 mg/L, 4 mg/L and 5 mg/L. Select the best results
from this jar test as the full-scale plant doses for alum and polymer.
IFE Turbidity Goals (for aH raw water quality conditions): < 0.10 NTU within 15 minutes
of start-up, < 0.10 NTU 95 percent of the time, and always < 0.3 NTU. Raw water turbidity
changes should not affect finished water quality.
1 These procedures assume that:
Process control decisions are based upon jar testing results and on past records and experience with similar water
conditions.
Chemical feed pumps have been calibrated recently.
Chemicals have been mixed in accordance with standard practices and manufacturers recommendations.
EPA Guidance Manual 238 August 2004
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Appendix H
Example of an Operating
Procedure for Filters
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Appendix H. Example of an Operating Procedure for Filters
Following is an example operating procedure for backwashing a filter. It may be used as a
standard operating procedure (SOP). The following example may provide valuable
guidelines for your system. However, be careful when conducting any of the procedures
contained in the following example operating procedure to a system. Each system is unique
and what works well for one system may not work for another.
August 2004 241 EPA Guidance Manual
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Appendix H. Example of an Operating Procedure for Filters
EXAMPLE OPERATING PROCEDURE
Filter Backwash1
(If the plant is off-line, Step 1 is not necessary. If the plant is on-line, Steps 1 and 2
should be done simultaneously to minimize the effects of flow changes to the filters.
Similarly, Steps 18 and 19 should be done simultaneously.)
1. Reduce the flow rate into the plant to prevent increased flow to the other filters.
2. Close the filter influent valve.
3. Close the filter effluent valve when the water level is 6 inches above the media.
4. Disable filter alarms (for example, turbidity and headloss) and shut off flow to the
individual filter effluent (IFE) turbidimeter.
5. Allow entrained air to escape from the filter before backwashing (if air is present).
6. Record the filtered water volume from the flow meter (if available).
7. Open the backwash drain valve.
8. Record the backwash water meter reading.
9. Open the surface water supply valve.
10. After the surface washer has run alone for 2 minutes, slowly open the backwash
water supply valve to the filter. Backwash at 1,000 gpm (10 gpm/ft2). Hold for 2
minutes. 2
11. Close the surface water wash supply after it has run for a total of 3 minutes (which
includes 1 minute into the backwash cycle).
12. After the filter has backwashed for 3 minutes at 1,000 gpm, slowly increase the flow
rate to 1,500 gpm (15 gpm/ft2). Hold for 8 minutes (see 13 below).
13. After backwashing at 1,500 gpm for 8 minutes, or after the effluent turbidity reaches
15 NTU, slowly reduce the backwash rate to 1,000 gpm. Hold for 2 minutes.
14. Slowly close the backwash valve (over a period of 1 minute).
15. Record the backwash water meter reading.
16. Open the influent valve and slowly fill the filter.
17. Whenever possible, allow the filter to rest for 30 minutes after backwashing.
18. Open the filter-to-waste valve.
19. Increase the flow through the plant to the previous setting.
20. Return flow to the IFE turbidimeter.
21. Filter to waste for 15 minutes or until the IFE is less than 0.1 NTU.
22. Close the filter to waste valve and open the filter effluent valve.
23. Enable filter alarms.
24. Double-check all valve, alarm, and instrumentation settings to make sure that they
have been set correctly.
1 This example procedure does not include air scour. If air scour is available, the facility should ensure that
appropriate steps are added to the SOP.
2 This example assumes that appropriate backwash rates have been established through experience. In colder
climates, backwash rates are typically decreased during cold water conditions because cold water is more
viscous. Excessive amounts of anthracite media will be lost into the backwash troughs if the backwash rates
are too high for the specific conditions at a facility.
EPA Guidance Manual 242 August 2004
LT1ESWTR Turbidity Provisions
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