United States
Environmental Protection
Agency
Filter Backwash Recycling Rule
Technical Guidance Manual
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Office of Ground Water and Drinking Water (4606M)
EPA816-R-02-014
www.epa.gov/safewater
December 2002
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 Filter Backwash
Recycling Rule (FBRR). 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 decisionmakers 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. Jerry Biberstine, National Rural Water Association
Dr. David Cornwell, Environmental Engineering & Technology, Inc.
Mr. Rich Haberman, Department of Health Services, Southern California Branch
Mr. David Hartman, Department of Water Works, City of Cincinnati
Mr. Peter Keenan, American Water Works Service Company, Inc.
Dr. Sun Liang, Metropolitan Water District of Southern California
Mr. Allen Roberson, American Water Works Association
*Mr. Jack Schulze, Texas Natural Resource Conservation Commission
Dr. John Tobiason, University of Massachusetts, Department of Civil and Environmental
Engineering
Mr. Steve Via, American Water Works Association
Mr. John Wroblewski, Pennsylvania Department of Environmental Protection
* Participation supported by Association of State Drinking Water Administrators.
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CONTENTS
1. Introduction 1
1.1 Overview 1
1.2 FBRR Components 1
1.3 FBRR Objective 4
1.4 Outline of the Document 5
1.5 Additional Information 6
Parti
2. Regulated Recycle Streams 9
2.1 Introduction 9
2.2 Treatment Processes and Origins of Recycle Streams 9
2.2.1 Conventional Treatment Plants 10
2.2.2 Direct Filtration Plants 11
2.3 Recycle Flows Regulated by the FBRR 12
2.3.1 Spent Filter Backwash 12
2.3.2 Thickener Supernatant 13
2.3.3 Liquids from Dewatering Processes 13
2.4 Reference 14
3. Reporting Requirements 15
3.1 Introduction 15
3.2 Recycle Notification 15
3.2.1 Plant Schematic 17
3.2.2 Flow Information 19
3.2.3 Recycle Notification Form 20
4. Recycle Return Location 23
4.1 Introduction 23
4.2 Timeline for Compliance 24
5. Recordkeeping Requirements 29
5.1 Introduction 29
5.2 Required Recordkeeping Information 31
5.2.1 Recycle Notification 31
5.2.2 Recycle Flows 31
5.2.3 Backwash Information 32
5.2.4 Filter Run Length and Termination of Filter Run 33
5.2.5 Recycle Stream Treatment 33
5.2.6 Equalization and Treatment Information 33
Part II
6. Part II Overview 39
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Contents
1. Recycle Streams 41
7.1 Introduction 41
7.2 Spent Filter Backwash Water 42
7.2.1 Frequency and Quantity 42
7.2.2 Quality 43
7.3 Thickener Supernatant 44
7.3.1 Frequency and Quantity 45
7.3.2 Quality 45
7.4 Liquids From Dewatering Processes 46
7.4.1 Quantity and Quality 46
7.5 Non-Regulated Recycle Streams 49
7.6 References 50
8. Operational Considerations and Modifications 51
8.1 Introduction 51
8.2 Adjust Chemical Feed Practices During Recycle Events 51
8.3 Return Recycle Stream(s) to Presedimentation Basin 53
8.4 Control Raw Water Flow or Recycle Return Flow 53
8.5 Reduce the Amount of Generated Spent Filter Backwash 53
8.5.1 Air Scour with Backwash 54
8.5.2 Surface Wash with Backwash 54
8.5.3 Reduce the Length of Backwash 55
8.5.4 Increase Filter Run Times 55
8.6 Reduce the Amount of Filter-to-Waste 56
8.7 References 58
9. Equalization 59
9.1 Introduction 59
9.2 Advantages 61
9.3 Disadvantages 63
9.4 Costs 64
9.5 Evaluating Equalization 64
9.6 References 68
10. Treatment of Recycle Streams 69
10.1 Introduction 69
10.2 Advantages 70
10.3 Disadvantages 71
10.4 Costs 71
10.5 Recommended Design Goals 71
10.5.1 Ten State Standards 71
10.5.2 California 71
10.5.3 Maryland 72
10.5.4 Ohio 72
10.5.5 Cornwell and Lee (1993) 72
10.5.6 United Kingdom Water Industry Research (UKWIR) (1998) 72
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10.6 Evaluating Treatment 73
10.7 Treatment Options 77
10.7.1 Sedimentation 77
10.7.2 Microsand-Assisted Sedimentation 85
10.7.3 Dissolved-Air Flotation 85
10.7.4 Granular Bed Filtration 87
10.7.5 Membrane Filtration 89
10.7.6 Disinfection 92
10.8 Comparison of Treatment Options 93
10.9 References 95
Appendices
Appendix A.
Appendix B.
Appendix C.
Appendix D.
Appendix E.
Appendix F.
Appendix G.
Appendix H.
Glossary
Worksheets
Reporting Example for 3.0 MGD Plant
Reporting Example for 20 MGD Plant
Reporting Example for 48 MGD Plant
Characteristics of Spent Filter Backwash Water
Characteristics of Thickener Supernatant
Characteristics of Liquids from Dewatering Processes
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Contents
Figures
Figure 1-1. Filter Backwash Recycling Rule Provisions 2
Figure 1-2. FBRR- Rule Requirements and Implementation Timeline 3
Figure 2-1. Example Conventional Filtration System With Recycle 10
Figure 2-2. Example Direct Filtration System With Recycle 11
Figure 3-1. FBRR Provisions- Reporting Requirements 16
Figure 3-2. Example Plant Schematic for Recycle Notification 17
Figure 3-3. Example Hand-drawn Plant Schematic for Recycle Notification 18
Figure 4-1. Examples of Recycle Return Locations 24
Figure 4-2. FBRR Provisions- Recycle Return Location 26
Figure 5-1. FBRR Provisions-Recordkeeping Requirements 30
Figure 5-2. Example of Recycle Flow Frequency Recordkeeping Information
(No Equalization or Treatment of Recycle Streams Provided) 31
Figure 5-3. Example of Recycle Flow Frequency Information (Equalization
and/or Treatment Provided) 32
Figure 7-1. Lagoons Used to Settle Solids 45
Figure 7-2. Sludge Drying Bed 47
Figure 7-3. Monofill Used for Dewatering Residuals 47
Figure 9-1. Example of Equalizing Recycle Streams 60
Figure 9-2. Existing Layout of James E. Quarles Water Treatment Plant 66
Figure 9-3. Proposed Improvements for Recycle Streams at the James E.
Quarles Water Treatment Plant 67
Figure 10-1. Crown Water Treatment Plant - Existing 76
Figure 10-2. Crown Water Treatment Plant - Proposed 76
Figure 10-3. General Sedimentation Process for Treatment of Recycle Stream 77
Figure 10-4. Circular Radial-flow Clarifier 79
Figure 10-5. Lagoon Process for Recycle Streams 80
Figure 10-6. Typical Plate Settler Design 81
Figure 10-7. Microsand-Assisted Sedimentation Process for Recycle Streams 85
Figure 10-8. Dissolved-Air Flotation Process for Recycle Streams 86
Figure 10-9. Granular Bed Filtration Process for Recycle Streams 88
Figure 10-10. Membrane Treatment Process for Recycle Streams 90
Figure C-l. Schematic for a 3.0 MGD Plant 117
Figure D-l. Schematic for a 20 MGD Plant 126
Figure E-l. Schematic for a 48 MGD Plant 136
Figure F-l. Mianus Water Treatment Plant 147
Figure F-2. Kanawha Valley Water Treatment Plant 149
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Contents
Figure F-3. Swimming River Water Treatment Plant 149
Figure F-4. New Castle Water Treatment Plant 150
Figure G-l. Mianus Water Treatment Plant 157
Figure G-2. Swimming River Water Treatment Plant 157
Figure G-3. New Castle Water Treatment Plant 158
Figure H-l. Mianus Water Treatment Plant 165
Figure H-2. New Castle Water Treatment Plant 165
Tables
Table 4-1. Recycle Return Location Compliance Schedule 25
Table 7-1. Commonly Produced Non-Regulated Residual Streams 49
Table 10-1. Results of AWWA FAX Survey on Systems that Recycle 69
Table 10-2. Spent Filter Backwash Turbidity and Particle Log Reductions by
Treatment Type 94
Table F-l. Comparison of Plant Influent to Spent Filter Backwash 145
Table F-2. Comparison of Raw Water to Spent Filter Backwash 146
Table F-3. Comparison of Plant Influent to Spent Filter Backwash Exiting the
Backwash Holding Tank 148
Table G-l. Comparison of Plant Influent to Sludge and Thickener
Supernatant 156
Table G-2. Lagoon Decant Data 158
Table H-l. Characteristics of Dewatered Plant Residuals 163
Table H-2. Pressate Quality in Comparison to Influent Water 164
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Contents
ABBREVIATIONS
List of abbreviations and acronyms used in this document:
ASCE
AWWA
AWWARF
CADD
CFR
CT
DAF
DBF
DE
DOC
EPA
FBRR
FR
gal
gpd
gpm
gpm/ft2
GWUDI
HAAS
hrs
IESWTR
Kgal
LT1ESWTR
MCL
MF
MG
American Society of Civil Engineers
American Water Works Association
American Water Works Association Research Foundation
Computer Aided Drafting and Design
Code of Federal Regulations
The Residual Concentration of Disinfectant (mg/1) Multiplied by the
Contact Time (minutes)
Dissolved-Air Floatation
Disinfection By-Products
Diatomaceous Earth
Dissolved Organic Carbon
Environmental Protection Agency
Filter Backwash Recycling Rule
Federal Register
gallons
gallons per day
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
Thousand Gallons
Long-Term 1 Enhanced Surface Water Treatment Rule
Maximum Contaminant Level
Microfiltration
Million Gallons
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Contents
mg/L
MOD
m/h
M/R
NOM
NTU
O&M
PN
PWS
PWSID
SOP
TOC
TSS
TT
TTHM
TTHMFP
UF
UV254
WTP
X log removal
|lor |
Hg/L
milligrams per liter
Million Gallons per Day
meters per hour
Monitoring/Reporting
Natural Organic Matter
Nephelometric Turbidity Unit
Operation and Maintenance
Public Notification
Public Water System
Public Water System Identification
Standard Operating Procedure
Total Organic Carbon
Total Suspended Solids
Treatment Technique
Total Trihalomethanes
Total Trihalomethanes Formation Potential
Ultrafiltration
Ultraviolet absorbance at 254 nanometers
Water Treatment Plant
Reduction to 1/1 Ox of original concentration
Micron (10A-6 meter)
Micrograms per liter
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Preceeding Page Blank
1. INTRODUCTION
1.1 OVERVIEW
The Filter Backwash Recycling Rule (FBRR) establishes regulatory provisions governing
the way that certain recycle streams are handled within the treatment processes of
conventional and direct filtration water treatment systems. The FBRR also establishes
reporting and recordkeeping requirements for recycle practices that will allow States and
EPA to better evaluate the impact of recycle practices on overall treatment plant
performance. The FBRR published in the Federal Register (66 FR 31086, June 8, 2001)
presents the specific regulatory requirements that must be met by affected systems. Figure
1-1 contains a flowchart that presents the FBRR requirements. Figure 1-2 contains a
timeline with the key dates for both States and systems. This document has been developed
to provide operators with the practical guidance and relevant information to assist them in
complying with the FBRR provisions. It outlines detailed methods for complying with each
portion of the FBRR, and provides other useful information regarding recycle practices and
filter backwashing not specifically required by the FBRR.
1.2 FBRR COMPONENTS
The FBRR applies to public water systems (PWSs) that meet all of the following three
criteria (40 CFR 141.76(a)):
System is a Subpart H system (i.e., uses surface water or ground water under the
direct influence of surface water);
System treats water by conventional or direct filtration processes; and,
System recycles one or more of the following: spent filter backwash water,
thickener supernatant or liquids from dewatering processes. Chapter 2 provides
more information on regulated recycle streams.
Conventional filtration, as defined in 40 CFR 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 141.2, is a series of processes including
coagulation and filtration, but excluding sedimentation, and resulting in substantial
particulate removal.
The FBRR consists of three distinct components:
Reporting (40 CFR 141.76(b)): The FBRR requires a system to notify the State
about its recycle practices if the system is a Subpart H system, a conventional or
direct filtration plant, and recycles one or more of the regulated recycle streams.
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1. Introduction
Figure 1-1. Filter Backwash Recycling Rule Provisions
Yes
Does
the system recycle
spent filter backwash,
thickener supernatant
or liquids from
vateringj
Does
the system use
surface water or ground water
under the direct
influence of surface
water?
Does the system
employ
conventional or
direct filtration?
FBRR does not apply
id the system
Yes / collect and retain
recycle flow information
for review beginning
6/08/04?
Yes / Did the system
otify the State in writing
byl^OS/OS1?
the system
ecycle through the processes
of a system's existing filtration
system as defined in
40 CFR 141.2?/ No
f No further requirements \
V. under FBRR )
Has the State
approved an
alternate recycle
return location
by 6/08/04':
Does the system
recycle to State approved
alternate location
by 6/08/04?
Are capital
improvements
necessary?
/\
Yes
Have capital
improvements been ^
completed by
6/08/06?
\ S
i
r
The system should
submit a schedule
for capital
improvements.
\
No
Yes
No further requirements \
under FBRR /
1. Notification includes information specified in 40 CFR 141.76 (b) (1) and (2)
2. Recycle flow information is specified in 40 CFR 141.76 (d) (1) through (6)
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1. Introduction
State Requirements
Final Rule
Promulgated
State Adopts Rule
Deadline for State
(without extension) to
submit Primacy
Revision Application
. to EPA
Figure 1-2. Filter Backwash Recycling Rule
Rule Requirements and Implementation Timeline
Treatment Technique and
Record keeping
Requirements Effective
State reviews
request for
alternative location
(recommended)
Reporting
Requirements
Effective
Begin review and
evaluation of system
recycle flow information
Deadline for State with
extension to submit
Primacy Revision
Application to EPA
6/8/01
6/8/03
12/8/03
6/8/04
-6/8/05-
-6/8/06-
Systems submit
justification to State
for alternative
location
(recommended)
Reporting Deadline:
Notify the State in writing
and provide information on
current practices.
System Requirements
Subpart H public water
system;
Conventional or direct
filtration system; and,
Returning spent filter
backwash water, thickener
supernatant, or liquids
from dewatering processes.
Treatment Technique and
Recordkeeping Deadline:
Retain data on recycle for
review and evaluation by
the State
Return recycle flows to an
appropriate location
Obtain State approval for
use of an alternative
location
Capital improvements
must be complete
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1. Introduction
Systems must notify the State by December 8, 2003. Reporting requirements are
contained in Chapter 3.
Recycle Return Location (40 CFR 141.76(c)): The FBRR requires spent filter
backwash, thickener supernatant, or liquids from dewatering processes to be
returned through all the processes of a system's existing conventional or direct
filtration system (if the system practices recycle), as defined in 40 CFR 141.2.
Systems can receive State approval to recycle at an alternate location. Details of
the recycle return location requirements are discussed in Chapter 4.
Recordkeeping (40 CFR 141.76(d)): The FBRR also includes recordkeeping
requirements related to recycling procedures. Systems must collect and retain
certain recycle information beginning June 8, 2004. Recordkeeping
requirements are presented in Chapter 5.
If systems are unsure if the rule applies to them, they should contact their State office or
Primacy Agency.
1.3 FBRR OBJECTIVE
What is Cryptosporidium?
Cryptosporidium is an intestinal parasite
that can be passed through a water
treatment plant and into the drinking water
supply. Infection can cause
gastrointestinal illness, lasting up to two
weeks, and may even be life threatening
for people with weakened immune
systems. Several outbreaks of
cryptosporidiosis have been traced to
Cryptosporidium in drinking water. The
worst outbreaks occurred in Milwaukee in
1993 when more than 400,000 people fell
ill with flu-like symptoms.
Cryptosporidium is difficult to treat
(inactivate) because it is resistant to most
disinfectants used by water treatment
systems. Consequently, other treatment
processes, such as sedimentation and
filtration, must be effective in removing
Cryptosporidium oocysts from raw water
and recycle streams.
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 ability of
treatment plants to produce safe drinking
water. Recycle streams have the potential to
contain higher concentrations of
Cryptosporidium oocysts than source water
streams and could therefore introduce
additional Cryptosporidium oocysts into the
treatment process. An increase in the
concentration of Cryptosporidium oocysts in
the treatment process may increase the risk
of Cryptosporidium oocysts in finished water
and threaten public health. Cryptosporidium
oocysts are of concern because they are not
easily inactivated by commonly used
disinfectants, such as chlorine (sedimentation
and filtration are the main barriers for
removal of Cryptosporidium).
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1. Introduction
1.4 OUTLINE OF THE DOCUMENT
This guidance manual is divided into two parts. Part I addresses issues specifically related
to the FBRR regulatory requirements. It is designed to guide systems through the
requirements for regulatory compliance with the FBRR. To make this process as
straightforward as possible, EPA has developed flowcharts and worksheets that can be used
as a reference during assessment of relevant filter backwash issues.
Part II provides guidance on recycle management options and operational considerations
that may assist systems in understanding recycle processes. It addresses issues that are
important to the effective management of potential recycle streams, but are not specifically
required by the FBRR regulations. While compliance with the regulatory requirements is
important for all affected systems, there are additional non-regulatory issues comprising the
full scope of management of potential recycle streams. By addressing this broader range of
recycling issues, systems will be able to develop strategies to achieve and maintain optimal
overall treatment plant performance. This guidance manual should be a useful tool for any
public water supply operator interested in improving plant performance, and not just those
affected by the FBRR provisions.
Part I of the guidance is organized into four chapters and presents rule requirements:
Chapter 2. Regulated Recycle Streams: This chapter identifies the three regulated
recycle streams and discusses the sources of recycle streams with respect to
conventional and direct filtration processes.
Chapter 3. Reporting Requirements: This chapter contains information on the
reporting requirements for systems.
Chapter 4. Recycle Return Location: This chapter presents the requirements for
recycle return location to ensure compliance with the FBRR. This chapter also
presents issues associated with recycling to a location that does not take advantage of
the entire treatment train.
Chapter 5. Recordkeeping Requirements: This chapter presents recordkeeping
requirements for systems and provides a detailed description of the data collection
components of the FBRR.
Part II of the document is organized as follows and is strictly guidance for systems:
Chapter 6. Part II Overview: This chapter discusses the purpose of Part II and how
to evaluate collected data on recycle practices.
Chapter 7. Recycle Streams: This chapter describes different recycle streams
(regulated and non-regulated) and characteristics of recycle streams.
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1. Introduction
Chapter 8. Operational Considerations and Modifications: This chapter presents
information on how to modify the main treatment train process or better manage
recycle streams to minimize the impacts of recycle streams on finished water.
Chapter 9. Equalization: This chapter describes equalization of recycle streams
and discusses the advantages and disadvantages of equalization. Case studies are
presented.
Chapter 10. Treatment of Recycle Streams: This chapter describes the concept of
treatment and discusses the advantages and disadvantages of treating recycle
streams. This chapter also describes specific treatment options and issues associated
with each treatment option. Case studies are presented.
Appendix A - Glossary
Appendix B - Worksheets
Appendix C - Reporting Example for 3.0 MGD Plant
Appendix D - Reporting Example for 20 MGD Plant
Appendix E - Reporting Example for 48 MGD Plant
Appendix F - Characteristics of Spent Filter Backwash
Appendix G - Characteristics of Thickener Supernatant
Appendix H - Characteristics of Liquids from Dewatering Processes
1.5 ADDITIONAL INFORMATION
A rule summary (eight pages long) and quick-reference guide (two pages) are available on
the FBRR and provide a brief summary of the rule requirements. The implementation guide
developed for States is also available. These documents can be obtained from your State
office or on EPA's website (www.epa.gov/safewater/filterbackwash.html). You can also
contact the Safe Drinking Water Hotline at 1-800-426-4791 for general information or visit
the EPA Office of Ground Water and Drinking Water website (www.epa.gov/safewater).
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PARTI
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Preceeding Page Blank
2. REGULATED RECYCLE STREAMS
2.1 INTRODUCTION
The prime objective of the FBRR is to ensure
an adequate level of public health protection
by minimizing the risk associated with
Cryptosporidium in recycle flows. Under the
Interim Enhanced Surface Water Treatment
Rule (IESWTR) and Long Term 1 Enhanced
Surface Water Treatment Rule (LT1ESWTR)
provisions, all surface water and ground water
under the direct influence of surface water
systems are required to achieve at least 2-log
removal of Cryptosporidium. The recycling
of spent filter backwash water and other
recycle streams could impact treatment
processes and finished water quality. Recycle
streams may affect treatment processes due to hydraulic surges or high concentrations of
contaminants in the recycle stream. The FBRR regulates three recycle streams: spent filter
backwash water, thickener supernatant, and liquids from dewatering processes. These three
recycle streams have the potential to adversely impact finished water quality because they
may occur in sufficient volumes to create unmanageable hydraulic surges and may contain
elevated concentrations of Cryptosporidium oocysts and other microbial and chemical
contaminants.
Rule Reference:
40 CFR 141.76 (a)
(a) Applicability. All subpart H
systems that employ conventional
filtration or direct filtration
treatment and that recycle spent
filter backwash water, thickener
supernatant, or liquids from
dewatering processes must meet
the requirements in paragraphs (b)
through (d) of this section.
2.2 TREATMENT PROCESSES AND ORIGINS OF
RECYCLE STREAMS
The FBRR applies to conventional and direct
filtration systems that recycle spent filter
backwash water, thickener supernatant, or
liquids from dewatering processes. While
conventional and direct filtration systems have
the potential to create other unregulated
recycle streams, such as filter-to-waste flows,
only the three aforementioned recycle streams
are regulated by the FBRR. The following
sections provide a general background on
conventional and direct filtration treatment
processes and the origin of recycle streams.
Although there are several variations of
conventional and direct filtration processes,
only the basic configurations will be presented
here. More detailed information on recycle stream origins is contained in Chapter 7.
Regulated Recycle Streams
Spent filter backwash water
Thickener supernatant
Liquids from dewatering processes
Unregulated Residual Streams (not all-
inclusive)
Filter-to-waste
Membrane concentrate
Ion exchange regenerate
Sludge
Diatomaceous earth slurry
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2. Regulated Recycle Streams
2.2.1 Conventional Treatment Plants
Conventional treatment plants, by definition (40 CFR 141.2), employ the following four unit
processes: coagulation, flocculation, sedimentation, and filtration. The coagulation and
rapid mix process usually has a short reaction time and is followed by the flocculation
process. The flocculation process forms floe, which then settle in the sedimentation basin.
Periodically, accumulated solids from sedimentation basins are removed. Solids can either
be disposed to the sanitary sewer, discharged to a sewer or surface water (this option
requires a discharge permit), or thickened and possibly dewatered, with ultimate disposal to
a landfill or land-application. Particles not removed by coagulation, flocculation, and
sedimentation are typically removed by the filters. Figure 2-1 shows a typical conventional
treatment system.
In a conventional plant, flows that may be recycled include: spent filter backwash
(regulated), gravity thickener supernatant from sedimentation solids (regulated), dewatering
liquids (regulated), and filter-to-waste (not regulated). The potential recycle stream origin
locations are shown in Figure 2-1.
Figure 2-1. Example Conventional Filtration System with Recycle
Raw Water
Influent i
0)
0
* 1 * c
Thickener Supernatant
(regu ated)
1
/\
T Dewatering Device
Pressate, Cent rate,
Leachate, or other
Liquids from
Dewatering
* * *
Flocculation
Thickener
|aar,f,er^J
^^r^
Solids
Sedimentation
\.
Sludge
^
(Unregulated)
Treatment
Unit*
~X
Filtration
i
(unregulated)
Dis nfectant
0
ซ
S-
=i
Spent Filter
Backwash '
=3'
Q.
g
M
3-
1. \ (regulated)
*Flow equalization and
treatment units are often
utilized to remove solids
from spent filter backwash
prior to recycle
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2. Regulated Recycle Streams
2.2.2 Direct Filtration Plants
Direct filtration treatment omits the sedimentation process but is otherwise similar to
conventional filtration treatment. Water in the treatment train goes directly from
coagulation/flocculation to filtration, where solids are removed (see Figure 2-2). Hence,
direct filtration systems do not produce sedimentation solids or clarification residuals during
primary processes. Although the raw water turbidity of direct filtration plants is usually
lower than most conventional plants, the solids loading to the filters may be higher because
of the absence of the sedimentation process prior to filtration. If spent filter backwash is not
treated prior to recycle, solids loading onto the filters will increase over time because there
is no other way for solids to be removed from the treatment train. Therefore, solids are
typically removed from recycle streams prior to being returned to the primary treatment
train/plant headworks.
Figure 2-2. Example Direct Filtration System with Recycle
Raw Water
Influent
a:
Spent Filter
Backwash
(regulated)
Filter-to-Waste ,
Treatment
Unit*
*Spent filter backwash
should be treated to
remove solids prior to
recycle
(unregulated)
Disinfectant
Finished Water to
Distribution
System
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2. Regulated Recycle Streams
2.3 RECYCLE FLOWS REGULATED BY THE FBRR
Many different types of residual streams may be recycled at drinking water treatment plants.
EPA originally identified twelve recycle streams for study in the proposed rule. Based on
Cryptosporidium occurrence data and possible effects on finished water, three recycle
streams were selected for regulation by the FBRR. These recycle streams are:
Spent filter backwash water;
Thickener supernatant (sometimes referred to as sludge thickener supernatant);
and,
Liquids from dewatering processes.
These three recycle streams are described in more detail in the following sections. Process
solids recycled from clarification units are not regulated by the FBRR. However, if
softening systems or contact clarification systems recycle any of the regulated flows (spent
filter backwash, thickener supernatant, or liquids from dewatering processes), then these
systems must comply with the requirements of the FBRR.
2.3.1 Spent Filter Backwash
Spent filter backwash is generated when
water is forced through the filter, counter
to the flow direction used during
treatment operations. This action cleans
the media by dislodging accumulated
particles, including microorganisms,
captured by the filter media.
Consequently, the resulting spent filter
backwash contains particles trapped in the
filter during treatment operations,
including particles produced from
coagulation and pathogens such as
Cryptosporidium. The practice of
recycling may reintroduce these particles
into the treatment process. Spent filter
backwash water typically averages 3% to 6% of total plant production (McGuire, 1997).
However, on an instantaneous basis, the spent filter backwash flows could be as high as
60% (or higher in some instances) of the plant flow. More information on spent filter
backwash water characteristics is available in Chapter 7.
Spent filter backwash can be recycled with or without treatment or flow equalization.
A filter during backwash
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December 2002
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2. Regulated Recycle Streams
2.3.2 Thickener Supernatant
Thickener supernatant is the decanted clear water that exits a sludge thickening basin after
gravity settling. Some plants recycle the supernatant from the thickener. Depending on
whether the thickener is operated in a batch mode or a continuous mode, the supernatant can
be recycled to the plant intermittently or continuously.
Some plants combine the flows from several plant processes prior to thickening. The flow
entering gravity thickeners primarily consist of sedimentation basin sludge but can also
include spent filter backwash and flows from dewatering devices. Factors affecting the
quantity of thickener supernatant produced include:
The raw water quality;
The quantity of residuals produced (dependant upon the raw water quality,
coagulation scheme, and the sludge collection/removal efficiency);
The level of treatment provided to thickener influent flows; and,
The volume of the spent filter backwash (if spent filter backwash is discharged to
the thickener).
More information on thickener supernatant is contained in Chapter 7.
2.3.3 Liquids from Dewatering Processes
The liquids removed from sludge, by mechanical or other means, are referred to as liquids
from dewatering processes. In mechanical dewatering processes, drinking water plants
often use belt presses, centrifuges, filter presses, vacuum presses, and other similar sludge-
concentrating equipment. Sludge can also be dewatered in a sludge drying bed, lagoon, or
monofill (sludge-only landfill). Sludges are dewatered in order to reduce their volume,
which facilitates handling and disposal. The volume of the dewatering liquid depends on
the volume and solids content of the thickened sludge fed to the dewatering devices.
Recycle flows from dewatering devices are produced at low rates and unlikely to cause a
plant to exceed operating capacity. However, the dewatering liquid may contain
Cryptosporidium oocysts because it is derived from solids that may hold high concentrations
of oocysts. More information on liquids from dewatering processes is contained in Chapter
7.
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2. Regulated Recycle Streams
2.4 REFERENCE
McGuire, M. J. 1997. (Draft) Issue Paper on Waste Stream Recycle and Filter-to-Waste in
Water Treatment Plants. Prepared for an American Water Works Association (AWWA)
Technical Work Group.
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3. REPORTING REQUIREMENTS
3.1 INTRODUCTION
The FBRR has specific reporting requirements. Systems must submit the required
information to the State by December 8, 2003 (see Figure 3-1). This information is known
as the Recycle Notification and can provide useful data for evaluating system recycle
practices. A worksheet has been developed to assist systems with reporting the required
information (Recycle Notification form in Appendix B). A completed example of this
worksheet is included at the end of this chapter. Systems will want to check with their State
to make sure the reporting format is acceptable. Examples that may be useful when
completing the forms are presented in Appendices C, D, and E.
3.2 RECYCLE NOTIFICATION
Rule Reference:
40 CFR 141.76 (b)
(b) Reporting. A system must notify the
State in writing by December 8, 2003, if
the system recycles spent filter backwash
water, thickener supernatant, or liquids
from dewatering processes. This
notification must include, at a minimum,
the information specified in paragraphs
(b)(l) and (2) of this section.
Each system that uses conventional or direct
filtration and recycles spent filter backwash
water, thickener supernatant, or liquids from
dewatering processes must provide the State
with the following written information by
Decembers, 2003:
A plant schematic showing the origin
of all recycle streams, the hydraulic
conveyance used to transport the
recycle streams, and the location
where the recycled streams enter the
treatment process.
Typical recycle flow, highest
observed plant flow experienced in the previous year, and design flow for the
treatment plant. All flows must be reported in gallons per minute (gpm).
The State-approved operating capacity for the plant, if the State has made such a
determination.
The submitted data will be evaluated by the State to determine whether the system's current
recycle return location is acceptable or if the system must make modifications. A system
that fails to submit this information to the State commits a monitoring/reporting violation,
which requires Tier 3 public notification. Failure to notify the public within one year of the
violation is a violation of the Public Notification Rule.
The Recycle Notification form (provided in Appendix B and included as an example at the
end of this chapter) can be used for the Recycle Notification, if the form is accepted by the
State. Systems are required to keep a copy of the Recycle Notification and all other
information submitted to the State. Systems that use, or plan to use, an alternate recycle
return location may want to request approval for the alternate recycle location when
submitting the Recycle Notification to the State. All alternate recycle return locations must
be approved by the State by June 8, 2004. Chapter 4 provides more information on the
required recycle return location.
December 2002
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3. Reporting Requirements
Figure 3-1. Filter Backwash Recycling Rule Provisions- Reporting Requirements
Does
the system recycle
spent filter backwash,
thickener supernatant
or liquids from
dewatering?
Does
the system use
surface water or ground water
under the direct
influence of surface
water
Does the system
employ
Did the system
collect and retain
recycle flow information
Does the syster
gh the pr
. existing filtr
s defined
40 CER 141.2-
/""No further requirementsN
\. under FBRR )
Does the system
recycle to State-approved
alternate location
by 6/08/04?
Are capital
improvements
No further requiremen
under FBRR
1 1. Notification includes information specified in 40 CFR 141.76 (b) (1) and (2). 40 CFR 141.76 (b)(l) requires a plant schematic showing
| the origin of all recycle flows, the hydraulic conveyance used to transport them, and the recycle return location.
40 CFR 141.76 (b)(2) requires typical recycle flow (in gpm), highest observed plant flow for previous year (in gpm), treatment plant design
flow (in gpm), and State-approved operating capacity (if a State determination has been made).
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December 2002
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3. Reporting Requirements
3.2.1 Plant Schematic
The plant schematic may take a variety of formats, such as Computer Aided Drafting and
Design (CADD), Power Point, neatly hand-drawn figures, copy of an existing plant
schematic, or other formats acceptable to the State. The contents of the schematic are more
important than its format. The schematic must clearly show the following:
Origin of all recycle streams;
Method of transporting recycle streams, including conduits, pipes, pumps,
valves, and flow controllers; and,
Location of re-entry for recycled stream to the treatment process.
If the recycle streams undergo equalization or treatment prior to re-entering the main
treatment train, this information should also be displayed in the schematic. Figures 3-2 and
3-3 are examples of acceptable schematics.
Figure 3-2. Example Plant Schematic for Recycle Notification
Coagulant/Polymer
Feed
Flow Meter i
i T i
Raw Water Influent (gj-j
Peak Daily = 19.8 MG
(S
ฃ
55
>,
o:
12
Coagulation Flocculation 1^^^^^
6-inch
* Recycle 1 ^ Pipe
Flnu/metor _ .. , Sludge
Giavily 'pumped
Thickener
Supernatant Recycle Flow 6" Gravity Pipe ^^^^
100 gpm tri,t
100,000-gal Backwash
Spent Filter "Oป HoWng"ank 7,000 gpm
nn nwrr^ii gravity 12-inch
-inch Pipe RecVcle Flow Ripe
3,500 gpm M
Pumped 1
Sludge Manually
Removed Every
2 Months
Filtration
Disinfection
Clearwell
Finished Water to
Distribution System
December 2002
17
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3. Reporting Requirements
Figure 3-3 Example Hand-drawn Plant Schematic
for Recycle Notification
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December 2002
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3. Reporting Requirements
3.2.2 Flow Information
Under the FBRR, four types of flow information are required to be reported to the State:
Typical recycle flow (in gpm);
Highest observed plant flow experienced in the previous year (in gpm);
Design flow for the treatment plant (in gpm); and,
State-approved operating capacity (if available).
The State can evaluate this information to determine if recycle practices create design flow
exceedances or exceedances of the State-approved operating capacity.
Typical Recycle Flow
The typical recycle flow must be reported to the State. This value must include all recycle
flows covered by this rule (spent filter backwash, thickener supernatant and liquids from
dewatering processes) that are returned to the treatment train. Some States may regulate
additional recycle streams and may require these to be reported as well. Methods for
determining recycle flows include:
Metering at one location or individually;
Estimating based on backwash rates or basin overflow rates;
Estimating from pump records, if pumps are used;
Estimating from hydraulic conveyance capacity of the conduit; or,
Estimating by drop in water surface elevation in a tank.
Appendices C, D, and E provide examples of how to determine the typical recycle flow.
The recycle flow must be reported to the State in gpm.
Highest Observed Plant Flow in the Previous Year
To determine the highest observed plant flow experienced in the previous year, a review of
plant monitoring records should be conducted. The flow should be measured at a point that
accurately captures the total amount of water passing through the treatment system at a
given time, including raw water and recycle flows. Locations for measuring this flow may
include:
Flowmeters at the plant inlet that record both raw water and recycle flow. In
some plants, these flows may be measured separately or the flowmeter may be
located such that both flows are recorded simultaneously.
Flow into the clearwell (if representative of plant influent flow, such as in a small
system). This flow may be obtained from pumping records, metered, or
estimated. Measuring the flow exiting the clearwell may not provide an accurate
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3. Reporting Requirements
plant flow if clearwell water is used for backwashing filters or other plant
processes or if the distribution pump rate varies from the raw water rate.
Raw water and recycle pump records (if pumps are used).
The important point to remember is that both raw water and recycle flows should be
included in determining the highest observed plant flow for the previous year. The Recycle
Notification form (in Appendix B) can be used to report flow information to the State. A
completed example of this form is included at the end of this chapter. Systems will want to
check with their State first to make sure this reporting form is acceptable.
Examples in Appendices C, D, and E provide guidelines for identifying the highest observed
plant flow. Some plants may operate in a manner such that the highest observed raw water
flow will not coincide with the highest observed recycle flow. Also, the highest observed
raw water flow may not represent the highest observed plant flow if recycle flows are
significant (see example in Appendix C for an illustration of a situation where the highest
observed plant flow occurred when recycle flows were being returned at a significant rate).
The highest observed plant flow must be reported in gpm.
Design Flow
The design flow for the treatment plant does not require measurement and should be
available from design documents, facility plans, or operation and maintenance manuals. The
design flow must be reported to the State in gpm.
State-Approved Operating Capacity
If the State has determined and approved an operating capacity for a system, the system
must provide this information as part of the Recycle Notification. Systems may want to
contact the State to verify if they have a State-approved operating capacity.
3.2.3 Recycle Notification Form
The Recycle Notification form in Appendix B can be used for the Recycle Notification to
the State, if the form is acceptable to the State. A completed example of this form is shown
on the next page (also found in Appendix C). Other examples illustrating how to complete
this form can be found in Appendices C, D, and E.
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3. Reporting Requirements
FILTER BACKWASH RECYCLING RULE
RECYCLE NOTIFICATION FORM
SYSTEM NAME Example 3.0 MOD Plant
PWSID DATE Dec 1,2003
Check with your State or Primacy Agency to make sure this form is acceptable.
Does your system use conventional or direct filtration? Yes_(conventional)
Does your system recycle spent filter backwash water, thickener supernatant, or liquids from
dewatering processes? Yes (spent filter backwash)
If you answered yes to both questions, please report the following:
1. What is the typical recycle flow (in gpm)? 1.500 gpm
2. What was the highest observed plant flow for the system in the previous year (in gpm)?
2.500 gpm
3. What is the design flow for the treatment plant (in gpm)? 2,080 gpm
4. Has the State determined a maximum operating capacity for the plant? If so, what is it? 2.080
5. Please include a plant schematic that shows:
the origin of all recycle flows (spent filter backwash, thickener supernatant, liquids from
dewatering processes, and any other);
the location where all recycle flows re-enter the treatment plant process; and
the hydraulic conveyance used to transport all recycle flows.
Comments: The highest observed plant flow of 2.500 gpm exceeds State-approved operating
capacity.
6. Are you requesting an alternate recycle location? Yes X No
An alternate recycle location is one that does not incorporate all treatment processes of a
conventional filtration plant (coagulation, flocculation, sedimentation, and filtration) or direct
filtration plant (coagulation, flocculation, and filtration). The State or Primacy Agency must approve
the recycle location by June 8, 2004. Please contact your State or Primacy Agency on what
additional information may be needed.
Comments:
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Preceeding Page Blank
4. RECYCLE RETURN LOCATION
4.1 INTRODUCTION
To ensure at least 2-log removal of
Cryptosporidium, regulated recycle streams
must be introduced at a location where the
flow passes through the treatment processes
of the system's existing conventional or
direct filtration system or at an alternate
location approved by the State (see Figure 4-
1). The preamble of the FBRR cites eight
studies on conventional and direct filtration
systems that demonstrate 2-log
Cryptosporidium removal. The 2-log
Cryptosporidium removal was achieved in
those studies when:
Coagulation, flocculation,
sedimentation (in conventional
filtration only), and filtration were
employed; and,
Rule Reference:
40 CFR 141.76 (c)
(c) Treatment technique requirement.
Any system that recycles spent filter
backwash water, thickener supernatant,
or liquids from dewatering processes
must return these flows through the
processes of a system's existing
conventional or direct filtration system
as defined in 40 CFR 141.2 or at an
alternate location approved by the State
by June 8, 2004. If capital
improvements are required to modify
the recycle location to meet this
requirement, all capital improvements
must be completed no later than June 8,
2006.
The turbidity limits in the finished
water as specified in the IESWTR and LT1ESWTR were met.
To obtain the 2-log Cryptosporidium removal, the FBRR requires recycle streams to pass
through all conventional (coagulation, flocculation, sedimentation, and filtration) or direct
(coagulation, flocculation, and filtration) filtration processes to receive optimum treatment.
An existing system may have a recycle location that does not incorporate all conventional or
direct filtration treatment processes. The concerns associated with these recycle locations
are:
The return of the recycle stream after the point of primary coagulant addition
may disrupt the chemistry of the treatment process and may impair treatment
performance.
If the recycle stream is not treated through coagulation and flocculation, oocysts
and other contaminants could pass through the filters. Sedimentation and
filtration are the main barriers to Cryptosporidium since it is resistant to certain
disinfectants (primarily chlorine and chloramines) and proper coagulation and
flocculation are necessary for optimum filter performance.
The 2-log Cryptosporidium removal may not be achieved if the recycle stream
does not pass through all treatment processes in a conventional or direct filtration
system.
December 2002
23
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4. Recycle Return Location
Figure 4-1. Examples of Recycle Return Locations
Coagulation
Sedimentation
(Conventional
Treatment
Only)
Recycle Locations that comply
with 40 CFR 141.76 (c): Recycle
streams must pass through the
processes of a system's
existing conventional or direct
filtration system. An alternate
location may be approved by
the State.
Regulated Recycle Streams: Spent filter backwash water, thickener supernatant
and liquids from dewatering processes.
Disinfection
Finished Water to
Distribution System
Treatment plants that return recycle streams to an alternate location (i.e., a location other
than shown in Figure 4-1) in order to maintain optimal treatment performance may apply to
the State to recycle at an alternate location. If the system has questions regarding the
required recycle return location, they should contact the State or Primacy Agency.
4.2 TIMELINE FOR COMPLIANCE
A timeline for recycle location compliance is presented in Table 4-1. It presents several
compliance scenarios and deadlines for submitting information or completing activities.
Figure 4-2 contains a flowchart for recycle return location compliance. For a timeline of all
rule requirements and deadlines, see Figure 1-2 in Chapter 1.
If a system currently recycles to a location that allows the recycle stream to be processed
through the treatment processes of the existing conventional or direct filtration system, the
system is not required to make any changes to the recycle return location. However, the
system must comply with all reporting and recordkeeping requirements of the FBRR, as
presented in Chapters 3 and 5.
If a system currently recycles to a location in the treatment process that does not allow the
recycle stream to pass through the treatment processes of the system's existing conventional
or direct filtration processes, the system may submit a request to the State for approval of
this alternate recycle location. The checklist on page 27 may be useful when evaluating an
alternate recycle return location. The State must approve or deny such a request by June 8,
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December 2002
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4. Recycle Return Location
2004. Systems may want to consider submitting an alternate return location request with the
Recycle Notification information due on December 8, 2003 (see Chapter 3 for details).
If the State does not approve the alternate location and capital improvements are needed to
relocate the recycle return point, or if the State approves an alternate recycle location that
requires capital improvements, the system must complete the necessary capital
improvements by June 8, 2006.
If the system decides to relocate the existing recycle return point so that recycle is returned
through all processes of the system's existing conventional or direct filtration treatment train
(as defined in 40 CFR 141.2), capital improvements must be completed no later than June 8,
2006.
Table 4-1 Recycle Return Location Compliance Schedule
If:
No capital improvements are
necessary and the system is not
seeking approval for an
alternate location . . .
The system is planning to request
state approval for use of an
alternate location . . .
The system is planning to request
State approval for use of an
alternate location AND capital
improvements are necessary . . .
Capital improvements are
necessary to relocate the point
of recycle return . . .
The System Must:
meet only the reporting and record-
keeping requirements of the FBRR . . .
receive approval from the State . . .
receive approval from the State for
alternate recycle return location . . .
complete all improvements . . .
complete all improvements . . .
By:
See Chapters 3 and 5.
June 8, 2004.
June 8, 2004; and,
June 8, 2006.
June 8, 2006.
December 2002
25
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4. Recycle Return Location
Figure 4-2. Filter Backwash Recycling Rule Provisions- Recycle Return Location
Does
the system use
iurface water or ground water
under the direct
luence of surface
water?
Does
the system recycle
spent filter backwash,
thickener supernatant
or liquids from
vateringj
Does the system
employ
conventional or
direct filtration1;
id the system
Yes / collect and retain
recycle flow information
for review beginning
6/08/04?
otify the State in writing
Does the system
recycle through the processes
of the system's existing filtration
system as defined in
40 CFR 141.2?
r^o further requirements
under FBRR
Has the State
approved an
alternate recycle
return location
by 6/08/04?
Does the system
recycle to State-approved
alternate location
by 6/08/04?
Are capital
improvements
necessary?
Have capital
improvements been
completed by
6/08/06?
The svstem should
f No further requirements A
V under FBRR
EPA Guidance Manual
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December 2002
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4. Recycle Return Location
Systems seeking approval of an alternate recycle return location should consider
submitting:
A written request explaining the reason and/or rationale for using the alternate
recycle location (such as if the plant requires recycle to an alternate location
to maintain optimal finished water quality, or other reason), including an
explanation of why the alternate recycle location would not or does not cause
a negative impact upon the finished water quality.
A plant schematic identifying the alternate recycle location (which may be the
schematic required in 40 CFR 141.76(b) if the alternate location is currently
used).
Demonstration of compliance with IESWTR/LT1ESWTR turbidity limits
through submission of combined filter effluent and/or individual filter effluent
data.
A description of the type of treatment(s) applied to the recycle stream (if any).
A comparison of plant influent water quality to the recycle stream water
quality. Data for comparison may include, but are not limited to:
Turbidity;
Cysts and oocysts;
Cyst and oocyst-sized particles;
Iron and/or manganese;
Disinfection Byproduct (DBF) levels;
Level of organic matter (TOC, DOC, UV254); and,
pH.
Information on sedimentation performance (as evidenced by settled water
turbidity as related to recycle practices).
Design and monitoring data for the alternate recycle location.
Information on the current loading rates of unit processes, and the impact to
the loading rates caused by the alternate location.
Information on flow control during recycle.
An analysis of other impacts that the alternate location may have on finished
water quality.
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Preceeding Page Blank
5. RECORDKEEPING REQUIREMENTS
5.1 INTRODUCTION
The FBRR has specific recordkeeping
requirements in addition to the reporting
requirements (see Chapter 3) and recycle return
location requirements (see Chapter 4).
For FBRR compliance, a system must collect and
retain the following information for review and
evaluation by the State beginning June 8, 2004
(see Figure 5-1):
Rule Reference:
40 CFR 141.76 (d)
(d) Recordkeeping. The system must
collect and retain on file recycle flow
information specified in paragraphs
(d)(l) through (6) of this section for
review and evaluation by the State
beginning June 8, 2004.
A copy of the Recycle Notification (see Chapter 3);
A list of all recycle flows and the frequency at which they are returned;
Average and maximum backwash flow rates through the filters and the average
and maximum duration of the filter backwash process, in minutes;
Typical filter run length and a written summary of how filter run length is
determined (e.g., headloss, turbidity, time, etc.);
If applicable, the type of treatment provided for the recycle stream before it re-
enters the conventional or direct filtration process; and,
If applicable, data about the physical dimensions of the equalization and/or
treatment units, typical and maximum hydraulic loading rates, types of treatment
chemicals used, average dose of chemicals, frequency of chemical addition, and
frequency of solids removal.
With the exception of the Recycle Notification, systems are not required to submit this
information unless requested to do so by the State. However, all of the information must be
made available by the system for State review during sanitary surveys, Comprehensive
Performance Evaluations, or other inspections or activities. After the State reviews this
information, a system may be required to modify its recycling practices or undertake other
activities. Failure to comply with the recordkeeping requirements is a recordkeeping
violation, which requires Tier 3 public notification. Failure to notify the public of the
violation within the appropriate time frame is a public notification violation. The worksheet
in Appendix B (Recordkeeping Form) can be used for collecting data (if this form is
acceptable to the State). A completed example of this form is included at the end of this
chapter. Appendices C, D, and E contain examples that may be helpful when completing
the forms.
December 2002
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5. Recordkeeping Requirements
Figure 5-1. Filter Backwash Recycling Rule Provisions- Recordkeeping Requirements
Does
the system use
surface water or ground water
under the direct
influence of surface
water^
Does
the system recycle
spent filter backwash,
thickener supernatant
or liquids from
dewatering?
conventional or
t filtration'
Did the system
collect and retain
recycle flow information
for review beginning
6/08/041?
notify State in writing
Does the system
recycle through the processes
of the system's existing filtration
system as defined in
40 CER 141.2? / No
c
No further requiremei
under FBKR
Does the system
recycle to State-approved
alternate location
by 6/08/04?
Have capital
improvements been
completed by
6/08/06?
No further requirements
under FBKR
L _
r
1
MR
(PN
Has the State
approved an
alternate recycle
return location
by 6/08/04?
1
r
The system should
submit a schedule
for capital
improvements.
1. System must collect and retain the following information: a copy of the Recycle Notification; a list of all recycle
I flows and the frequency with which they are returned; average and maximum backwash flow rates through the filters and
the average and maximum durations of the filter backwash process, in minutes; typical filter run length and a written
summary of how filter run length is determined (e.g. headloss, turbidity, time, etc.); if applicable, the type of treatment
provided for the recycle flow before it re-enters the conventional or direct filtration process; if applicable, data about the
physical dimensions of the equalization or treatment units, typical and maximum hydraulic loading rates, type of
treatment chemicals used, average dose of chemicals, frequency of chemical addition, and frequency of solids removal.
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December 2002
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5. Recordkeeping Requirements
5.2 REQUIRED RECORDKEEPING INFORMATION
The following sections provide information on the required recordkeeping information the
system must collect. Systems should consult the State on frequency of data collection. The
State could require a system to collect data as operating conditions change, such as on a
seasonal basis.
5.2.1 Recycle Notification
Systems must maintain a copy of all information that is submitted to the State, as described
in Chapter 3.
5.2.2 Recycle Flows
The system must retain a list of all recycle flows (regulated and non-regulated) and the
frequency of return of each flow. Recycle streams are often generated at varying
frequencies and flow rates. It is important to recognize that the rate at which each recycle
stream is generated may differ from the rate at which these flows are returned to the
treatment train if equalization and/or treatment of recycle streams is provided. The FBRR
requires systems to record the frequency at which recycle flows are returned. If allowed by
the State, the Recordkeeping Form can be used to record recycle flow information (see
Appendix B). A completed example of this form is included at the end of this chapter.
Examples in Appendices C, D, and E provide examples of ways to collect recycle flow
information.
Recycle without Treatment or Equalization
If recycle streams are returned to the main treatment train without equalization and/or
treatment, then the system must record the frequency at which the flows are returned to the
main treatment train (see Figure 5-2).
Figure 5-2. Example of Recycle Flow Frequency Recordkeeping Information (No
Equalization or Treatment of Recycle Streams Provided)
To Main
Treatment Train
A
Spent Filter Backwash
4 times per day
Thickener
Supernatant
Continuously
Returned
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5. Recordkeeping Requirements
Recycle with Treatment and/or Equalization
If recycle streams are discharged to an equalization basin or treatment unit, then the
frequency at which these flows are returned to the main treatment train must be recorded.
States may want systems to also record the frequency at which recycle flows are generated if
equalization and/or treatment is provided to the recycle flows. Knowing the frequency at
which recycle flows are generated and returned will assist systems and States in assessing
recycle practices. Figure 5-3 provides a schematic that illustrates the required information
that systems must record and some of the types of optional information States could request.
Figure 5-3. Example of Recycle Flow Frequency Information (Equalization and/or
Treatment Provided)
Required Recordkeeping
Information
Returned to
Main Treatment Train
Continuously
Equalization Basin or
Treatment Unit for
Recycle Streams
Optional Information
(Consult the State)
Spent Filter Backwash
Generated 4 times per day
Sludge from Sedimentation Basin
Generated 1 time per day
Liquids from Dewatering
Processes
Generated 2 times per month
5.2.3 Backwash Information
Systems must collect the following backwash information for the filter(s):
Average backwash flow rate through the filter;
Average duration of filter backwash;
Maximum backwash flow rate through the filter; and,
Maximum duration of filter backwash.
Filters tend to be backwashed in a highly regulated and well-monitored manner. The plant
records should be specific about the filter backwash process. Some systems may not vary
the backwash rate throughout the backwash process, so that the average and maximum
backwash rates are the same. Other systems may vary the backwash rate throughout the
backwash process. For instance, a system may use air scour or surface wash in addition to
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5. Recordkeeping Requirements
backwashing. The average and maximum backwash rates are different in this case because
of the varying backwash rate. Also, some systems may vary the backwash rates seasonally
based on changing water temperature or system loading rates. States may require systems to
collect backwash information for different operating conditions. Systems should check with
the State to determine the frequency of data collection. Backwash flow rates can be reported
based on metered values, rise-rate tests, pump records, or other means.
The Recordkeeping Form in Appendix B can be used to record backwash information. A
completed example of this form is included at the end of this chapter. Examples in
Appendices C, D, and E illustrate how backwash information can be collected and recorded.
5.2.4 Filter Run Length and Termination of Filter Run
Systems must provide to the State the typical filter run length (typical time that a filter is
operated before it is backwashed). The filter run length is the sum of the time that the filter
is operating between backwashes. As water passes through, a filter becomes clogged with
particles that eventually could begin to compromise the treatment ability of the filter.
Systems may have different methods for determining typical filter run length.
Systems must maintain a written summary of the methods used to determine the run time
along with the typical filter run time. If turbidity, head loss, or filter effluent turbidity
thresholds are used to determine the filter run time, these thresholds should be provided. If
the filter run is terminated based on a pre-determined time established by the system or other
means, this determination should also be noted.
The Recordkeeping Form in Appendix B can be used to record this information. A
completed example of this form is included at the end of this chapter. Examples in
Appendices C, D, and E provide an example of how to report the information.
5.2.5 Recycle Stream Treatment
If a system treats or equalizes its recycle streams, then information about these processes
must be included in records maintained for the FBRR. The system must record information
on the type of treatment that is provided.
5.2.6 Equalization and Treatment Information
If equalization or treatment of the recycle stream is provided, systems must collect the
following information on the units:
Physical dimensions of the equalization and/or treatment units. A sketch of the
unit with dimensions may be helpful. This information will be used to determine
the capacity of the unit;
Typical and maximum hydraulic loading rates. This could include generated
rates for each recycle stream (see Figure 5-3);
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5. Recordkeeping Requirements
Type of treatment chemical(s) used, if the recycle stream is chemically treated. It
may be useful to note whether the chemical is introduced to the recycle stream
prior to entering the unit or directly into the unit;
Average dose rate of the treatment chemical and frequency of chemical use must
be provided; and,
Frequency of solids removal. Solids removal is important because solids can
reduce the equalization/treatment capability of the unit by occupying a
significant volume in the unit. Systems will need to record the frequency of
solids removal (for example, once a month).
The Recordkeeping Form in Appendix B can be used to record this information. A
completed example of this form is included at the end of this chapter. Examples in
Appendices D and E illustrate how this information can be collected and recorded.
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5. Recordkeeping Requirements
FILTER BACKWASH RECYCLING RULE RECORDKEEPING FORM
SYSTEM NAME Example 3.0 MOD Plant
PWSID
Operating Period1 Jun 2003-Jun 2004
Check with your State or Primacy Agency to make sure this form is acceptable.
Type of Recycle Stream
Spent Filter Backwash
Thickener Supernatant
Liquids from Dewatering Process
Other
Other
Frequency at which flow is
4 times/day returned to main
returned2
treatment train
Filter
Information
Average Duration of
Backwash (in minutes)
Maximum Duration of
Backwash (in minutes)
Average Backwash
Flow4 (in gpm)
Maximum Backwash
Flow4 (in gpm)
Run Length Time of
Filter5 (include units)
Criteria for Terminating
Filter Run6
Filter Number3
1-8, all filters the
same
15 minutes
15 minutes
1,500 gpm
1,500 gpm
48hrs
Time, unless
individual filter
turbidity exceeds
0.2 NTU.
Is treatment or equalization provided for recycle flows?
If yes, complete the following table.
Yes
X
No
Type of Treatment Provided
Physical Dimensions of Unit
Typical Hydraulic Loading
Rate
Maximum Hydraulic
Loading Rate
Type of Chemical Used
Average Dose of Chemical
(mg/L)
Frequency of Chemical
Addition
Frequency of Solids
Removal
See instructions on back.
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5. Recordkeeping Requirements
Instructions
1. Note the operating period for the information provided. Check with your State or Primacy
Agency for required operating period.
2. The frequency at which the recycle stream is returned can be described as continuous, once a
day, or as another frequency.
3. Fill out all information for each of your filters. If some or all filters are operated the same, note
the appropriate filter numbers.
4. The backwash flow is obtained by multiplying filter surface area (in ft2) by backwash rate
(gpm/ft2). Use the average backwash rate to get the average flow and the maximum backwash
rate to get the maximum flow. If the flow is varied throughout the backwash process, then the
average can be computed on a time-weighted basis as follows:
(Backwash Rate 1 X Duration 1) + (Backwash Rate 2 X Duration 2) + ...
Duration 1 + Duration 2+ ...
5. The filter run length time is the sum of the time that the filter is producing water between
backwashes.
6. Describe how run length time is determined. For example, is the run length based on head loss
across the filter, turbidity levels of filter effluent, a predetermined amount of time, or another
method?
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PART II
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6. PART II OVERVIEW
Water treatment systems typically recycle residual streams for one or both of the following
reasons:
Water resources are limited, such as in the arid southwest, and the system may
not be able to access additional water. Therefore, certain residual streams (such
as spent filter backwash) are recycled to maximize production.
Recycling of residual streams may be more cost-effective than disposal, such as
discharge to a storm sewer or sanitary sewer. Therefore, the system recycles the
residual stream.
For those systems regulated by the FBRR, specific reporting, recycle return location, and
recordkeeping requirements apply (as described in Chapters 3, 4, and 5). States will most
likely evaluate the information collected and submitted by systems and decide if recycle
practices are impacting finished water quality. If the State identifies problems with recycle
practices or the recycle return location, then States and systems should revise or alter main
treatment plant processes and/or recycle practices to minimize impacts on finished water.
For instance, an exceedance of turbidity limits may be linked to recycle practices. Part II of
this document provides information on how States and systems can evaluate recycle
practices, recycle stream characteristics, and alternatives to consider to minimize the
impacts of recycle practices on treatment plant performance and in particular, finished water
quality States and systems should note that the information presented in Part II is
provided as an additional resource and is not required by the FBRR. In some
instances the information is very site specific. Therefore, if systems are considering
modifying their treatment process or recycle practices, the State should be consulted
prior to any modification.
Part II contains the following chapters:
Chapter 7. Recycle Streams: This chapter describes different recycle streams
(regulated and non-regulated) and characteristics of recycle streams.
Chapter 8. Operational Considerations and Modifications: This chapter
presents information on how to modify the main treatment train process or better
manage recycle streams to minimize the impacts of recycle streams on finished
water.
Chapter 9. Equalization: This chapter describes equalization of recycle streams
and discusses the advantages and disadvantages of equalization. Case studies are
presented.
Chapter 10. Treatment of Recycle Streams: This chapter describes the concept
of treatment and discusses the advantages and disadvantages of treating recycle
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6. Part II Overview
streams. This chapter also describes specific treatment options and the issues
associated with each treatment option. Case studies are presented.
States and systems can also refer to the references listed at the end of each chapter and
AWWA's Self Assessment of Recycle Practices (2002) for more detailed information on a
specific case study or evaluation of recycle practices.
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7. RECYCLE STREAMS
7.1 INTRODUCTION
Water treatment plants throughout the United States recycle or reintroduce a variety of
residual streams back into their treatment plants. Some of these flows may contain
Cryptosporidium oocysts and other contaminants, while others may be quite harmless. As
indicated elsewhere in this document, only three recycle streams (spent filter backwash
water, thickener supernatant, and liquids from dewatering processes) are regulated by the
FBRR. (Note: The FBRR only applies to conventional and direct filtration systems that
recycle one or more of the regulated recycle streams.) These streams are regulated because
they are the recycle streams most likely to contain Cryptosporidium oocysts (and other
contaminants) and may represent a large percentage of overall plant production. Spent filter
backwash water data indicates that both Cryptosporidium and Giardia cysts can occur in
greater concentrations than raw water
concentrations. Thickener supernatant and
Regulated Recycle Streams
Spent filter backwash water
Thickener supernatant
Liquids from dewatering processes
Unregulated Residual Streams (not
all-inclusive)
Filter-to-waste
Membrane concentrate
Ion exchange regenerate
Sludge
Diatomaceous earth slurry
liquids from dewatering processes both result
from sludge that may contain elevated
Cryptosporidium and Giardia cyst
concentrations in comparison to raw water
concentrations. Data show that microbial
contaminants, in addition to other contaminants,
can be released from the sludge into the recycle
stream if the sludge is not properly settled,
treated, and/or removed. In addition to
contaminants, the volume and/or flow rates of
the recycle stream are also of concern. Two of
the regulated streams- spent filter backwash
water and thickener supernatant- can be
produced at sufficient rates to create hydraulic
surges or cause a water treatment plant to exceed operating capacity.
In addition to the regulated recycle streams, water treatment plants produce other streams
that, as of yet, are not regulated. Examples of typical unregulated streams are filter-to-waste,
membrane concentrate, ion exchange regenerate, and sludge. These streams were not
regulated in the FBRR because of one or more of the following:
The quality of the stream was of high quality and probably would not adversely
impact overall treatment plant efficiency (such as filter-to-waste);
The stream was of such small volume that the chance of hydraulic surge was
minimal (such as waste flows from turbidimeters); or,
The stream was not typically recycled due to the quality of the stream (such as ion
exchange regenerate).
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7. Recycle Streams
This chapter provides a discussion of each of the regulated recycle streams and a brief
discussion of some recycle streams not regulated by the FBRR.
7.2 SPENT FILTER BACKWASH WATER
Filter backwashing is an integral part of treatment plant operation. Filters are typically
cleaned by flushing them with water in the reverse direction to normal flow. The water flow
must have sufficient force to separate particles from the filter media, so a greater than normal
flow is used. The resulting water, which carries particles flushed from the filters including
microbes (such as Cryptosporidium), raw water particles, and particles from the coagulation
process, is called waste or spent filter backwash water. The backwash period generally lasts
for 10-25 minutes at a rate of approximately 15 to 20 gpm/ft2, and produces a significant
volume of spent filter backwash. Of all the processes that produce residual streams, filter
backwash typically produces the largest volume of water and at the highest rate.
7.2.1 Frequency and Quantity
Filter runs generally last between 24 and
72 hours in length, but vary from plant to
plant. Filters are taken off-line for
backwashing based on time (hours of
filter run time), turbidity and/or particle
counts in filter effluent, head loss across
the filter, or other system-specific
methods. A typical backwashing
operation lasts for 10-25 minutes with
maximum rates of 15 to 20 gpm/ft2, but
the backwash rate varies for each plant
and filter type. Since a high water flow is
used, a large volume of spent filter
backwash water is produced in a
relatively short amount of time. Some
plants only produce spent filter backwash
sporadically (small plants), but larger
plants with numerous filters may produce
it continuously as filters are rotated for
backwashing. Medium and small plants
typically produce spent filter backwash as an intermittent stream in large volumes over a
short time span. The return of the spent filter backwash to the main treatment train without
treatment or equalization is known as direct recycle. Direct recycle could result in the plant
exceeding its operating capacity or experiencing hydraulic disruptions if the raw water flow
is not properly managed during recycle.
Spent filter backwash can comprise 2% to 10% of the total plant production, but on the
average accounts for 2.5% of average plant production (Environmental Engineering and
This backwash holding basin is used to
allow settling of spent filter backwash.
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7. Recycle Streams
Technology, 1999). Recycled spent filter backwash can represent a significant percentage of
plant instantaneous flow during recycle events, particularly if no equalization is provided.
High recycle flows can result in hydraulic surges and possibly upset treatment plant
performance. For instance, the spent filter backwash scenario presented in the example in
Appendix C illustrates that the spent filter backwash recycle volume constitutes 4% of the
total plant production, but during periods of recycle it constitutes 60% of the plant
instantaneous flow.
7.2.2 Quality
The quality of spent filter backwash varies from plant to plant. Spent filter backwash quality
has been analyzed in several studies. One research project funded by the American Water
Works Association Research Foundation (AWWARF) surveyed 25 representative water
treatment plants to compare the differences in microbial, physical, and chemical water
quality of raw waters to untreated spent filter backwash (Cornwell et al., 2001). Of the 146
raw water samples collected, Giordia and Cryptosporidium were detected in 30% and 11% of
samples, respectively. The observed geometric mean levels of Giardia and Cryptosporidium
in the raw water samples for the detections were 89 and 108/100 L, respectively. For the 148
spent filter backwash samples, 8% and 5% were positive for Giardia and Cryptosporidium,
respectively. The geometric mean levels of Giardia and Cryptosporidium in the spent filter
backwash samples with detections were 203 and 175/100 L, respectively. All of the data
were collected by means of the immunofluorescence assay method. Concentrations of
Giardia and Cryptosporidium in spent filter backwash were observed to be approximately 16
and 21 times higher than corresponding raw water samples, respectively, after adjusting for
recovery efficiency. Infectious Cryptosporidium was observed in six raw water samples
(4.9%) and nine spent filter backwash samples (7.4%). Other water quality parameters were
also sampled, including dissolved organic carbon (DOC), TTHMs, HAASs, and metals.
DOC and zinc concentrations showed a three-
fold increase and TTHMs had a 92-fold
increase in concentration in spent filter
backwash when compared to raw water
samples after chemical addition. Appendix F
has additional information on contaminants in
spent filter backwash.
Kawamura (2000) indicates that spent filter
backwash water from a conventional
treatment plant generally has a turbidity of
150 to 250 NTU. Other data shows a range
from 7 to 148 NTU for spent filter backwash
turbidity from conventional treatment plants
(HDR, 1997). Data from another study
(Cornwell and Lee, 1993) showed that
turbidity during backwash at one plant varied
between 0.57 and 97 NTU (See Table F-l,
Appendix F). A study by Tobiason et al.,
This newly constructed lagoon will
be used to equalize and settle spent
filter backwash prior to recycling.
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7. Recycle Streams
(1999) found high peak turbidity levels of 150 to 400 NTU that fell to 1 to 7 NTU at later
stages of recycle. The peak turbidity levels were associated with the settling of solids in the
backwash storage tank after the flow of spent filter backwash water into the tank ended. The
variability of the spent filter backwash turbidity is due to the variability of raw water,
upstream treatment processes, filter design and operation, and backwashing practices. For
example, the amount of solids trapped in a filter will be highly dependent upon the amount of
solids in the raw water, the amount and type of coagulant used, whether lime softening is
used (as it can add greatly to the solids load), and the efficiency of the sedimentation unit
process (in conventional treatment systems). The quality of the spent filter backwash water
also depends on the volume of backwash water used. The more water used, the more diluted
the spent backwash water will become (HDR, 1997).
Other contaminants contained in the spent filter backwash can impact plant performance and
finished water. TOC, aluminum, manganese, and iron concentrations in the spent filter
backwash can be higher than those found in both the raw water and raw water after chemical
addition. In a study by Levesque, et al., (1999) a facility with flow equalization but no solids
removal had peak grab sample concentrations of 143 mg/L TOC, 158 mg/L total aluminum,
and 1.23 mg/L total manganese. These contaminants are typically more of a concern when
thickener supernatant is recycled in combination with the spent filter backwash (HDR, 1997).
Total suspended solids (TSS) may also be a concern. TSS in the spent filter backwash varies
between plants and during the backwash cycle. A study by Bashaw et al., (2000) indicated
that TSS was very high, with a peak of approximately 300 mg/L and an average TSS of 71
mg/L, during the first three minutes of backwash. Another study by Myers et al., (2000)
showed an average TSS of backwash water of 300 mg/L. A study by Tobiason et al., (1999)
found high peak levels of 600 to 7,000 mg/L TSS in recycled spent filter backwash water.
These peak levels were associated with the settling of solids in the backwash storage tank
after the flow of spent filter backwash water into the tank ended. The recycled spent filter
backwash from a backwash holding tank may have lower TSS values since solids are settled
in the holding tank. However, if the backwash holding tank is mixed, no solids removal will
occur and TSS could be high in the recycle stream.
7.3 THICKENER SUPERNATANT
Thickener supernatant results from gravity thickening of solids. In the gravity thickener unit,
solids in the water stream settle out as a result of gravity. Gravity-thickeners can consist of
clarifiers, sedimentation basins, backwash holding tanks, lagoons, and other similar units.
After settling, the clarified water or decant that exits the unit is called thickener supernatant
(see Figure 7-1). The sludge at the bottom of the sedimentation basin and other sludge-
holding units could contain elevated levels of microbial (such as Cryptosporidium and
Giardia cysts), organic, and inorganic contaminants as compared to the raw water. These
contaminants can remain in the supernatant if the sludge is not properly settled, treated,
and/or removed. The supernatant should be removed from the thickener unit in a manner
such that the settled solids are not disturbed to minimize contamination issues.
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7. Recycle Streams
Figure 7-1. Lagoon Used to Settle Solids
Lagoon
Decant
Sludge
Removal
7.3.1 Frequency and Quantity
Thickener supernatant can be recycled continuously or intermittently. The frequency of
thickener supernatant recycling depends on the quantity of sludge that is produced and
thickener supernatant recycle practices. Thickener supernatant is often combined with other
plant flows (such as spent filter backwash, filter-to-waste, or liquids from dewatering
processes).
Approximately 65% to 75% or more of the sludge generated at a treatment facility settles out
in sedimentation basins at a conventional alum coagulant plant. Generally, the sludge is
0.05% to 3% solids and the remainder is water. Sludge volumes are typically 0.1% to 3% of
the plant flow (Environmental Engineering and Technology, 1999). The volume of
sedimentation basin sludge supernatant is dependent on sludge production, sludge solids
content, and method of thickener operation. Sludge production is a function of plant
production, raw water suspended solids, plant process (such as lime softening), coagulant
type and coagulant dose. The quantity of sedimentation basin thickener supernatant is
approximately 75% to 90% of the original volume of sedimentation basin sludge produced
(Environmental Engineering and Technology, 1999). The volume of lagoon decant depends
on the volume of influent waste streams, concentration of solids in the waste stream, loading
duration and frequency, drainage rates, overflow rates, and evaporation rates (Environmental
Engineering and Technology, 1999).
7.3.2 Quality
Contaminant concentrations in thickener supernatant depend on the raw water characteristics,
thickener design, thickener loading rate, and the type and amount of coagulant added.
Data for Giordia and Cryptosporidium in untreated sedimentation basin sludge showed
concentrations of 3,000 to 5,000 cysts/100 L in a plant with two sampling points
(Environmental Engineering and Technology, 1999). In another study, the Giardia
concentration was 40 cysts/L and the Cryptosporidium concentration was 80 cysts/L in the
sludge (Cornwell and Lee, 1993). The same study indicated that recycling the supernatant
did not impact finished water quality. More detailed influent water, sludge, and supernatant
data can be found in Table G-l, Appendix G, Characteristics of Thickener Supernatant.
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7. Recycle Streams
Residual characteristics in lagoon decant are altered due to treatment in the lagoon and
storage. Anaerobic conditions may occur, promoting the release of some metals from solid
state to dissolved form. This may also occur for organics, and could result in taste and odor
problems. However, anaerobic biological decomposition may reduce virus, parasite, or
pathogenic microbial concentrations. Data on lagoon decant characteristics are presented in
Table G-2, Appendix G.
A study by Hoehn, et al., (1987) reported significant release of manganese, iron, and TOC
from sludges held in manually cleaned, anaerobic sedimentation basins (sedimentation basins
that receive sludge and act as gravity thickeners). The study also concluded that sludge
stored in lagoons can also be expected to degrade the overlying water, a consideration when
recycling thickener supernatant.
Another study confirmed Hoehn's observations that manually-cleaned sedimentation basins
caused more manganese to be released than mechanically cleaned basins (Cornwell and Lee,
1993). As the sludge accumulated in a manually cleaned basin, manganese levels in the
clarified water gradually increased. Generally, if solids were removed from the waste stream
prior to recycle, TTHM formation potential and TOC in the recycle stream was no higher
than in the raw water.
7.4 LIQUIDS FROM DEWATERING PROCESSES
Some filtration plants prepare waste solids (sludge) for disposal by concentrating solids and
removing excess water, which reduces the volume of waste that must be disposed. The
sludge typically comes from sedimentation basins, clarifiers, backwash holding tanks, or
other units, and contains only 1% to 2% solids. Removing liquids from these waste solids
can concentrate the sludge up to 50% solids (Kawamura, 2000). The liquids that are
removed are referred to as liquids from dewatering processes.
Liquids from dewatering can be produced from a lagoon or sludge drying bed as decant and
underflow, from monofill as leachate, or from mechanical dewatering devices as pressate,
filtrate, or centrate. If recycled, these liquids are subject to the FBRR.
7.4.1 Quantity and Quality
Liquids from dewatering processes can be of reduced quality since they consist of water
extracted from thickened sludge. Most of the Cryptosporidium oocysts that are removed
from raw water by treatment are concentrated, first as sludge in the sedimentation basin,
clarifier, or other treatment processes. They can be settled a second time in a gravity
thickener and then dewatered. The recycle stream created by the dewatering process
typically has a smaller volume than spent filter backwash, but its size depends on the volume
of sludge produced in the plant, and on the solids content of the sludge. Most plants will
produce a small, intermittent stream as a result of the dewatering process.
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7. Recycle Streams
Non-mechanically Dewatered Sludge Recycle Streams
Sludge drying beds, lagoons, and
monofills can be used as non-mechanical
processes to dewater sludge. Each of
these dewatering processes creates a waste
stream. Sludge drying beds are used for
dewatering sludge through draining,
percolation, decanting, and evaporation
(see Figure 7-2). The quantity of decant
and underflow depends on the volume of
sludge applied to a bed, the sludge solids
content, loading duration and frequency,
and drainage and evaporation rates. The
Thickened_
Residuals
Drying Bed
Figure 7-2. Sludge Drying Bed
underflow and decant account for 50% to 75% of applied volume. If a thickener is not used,
the underflow and decant volume would be in the range of 0.3% to 0.4% of plant production
based on average sludge volumes reported elsewhere (Environmental Engineering and
Technology, 1999). No published data exists that demonstrates the potential impact of
recycling sludge drying bed decant and underflow. See Appendix H, Table H-l, for data on
sludge drying bed underflow. Lagoons can be designed and operated in a manner similar to a
sludge drying bed for dewatering.
Monofill (sludge-only landfill) is available in some States as a means of disposal of
dewatered plant residuals from a water treatment plant. Water percolates through the
monofill and is a potential recycle stream if it is collected by an underdrain (see Figure 7-3).
The quantity of monofill leachate is dependent on the quantity and quality of dewatered
residuals and the quantity of rainfall entering
the monofill. The rate of seepage through the
monofill is a function of sludge permeability
and hydraulic gradient (Environmental
Engineering and Technology, 1999). Three sets
of pilot data from a study are presented in Table
H-l, Appendix H. The leachate was generated
by constructing pilot-scale monofills using two
alum sludges and one ferric sludge. Although
none of the metals concentrations shown in
Table H-l exceed primary MCLs, dissolved
iron and manganese concentrations for a few of
the data sets exceeded secondary MCLs.
Metals and pH are typically the constituents of
concern in leachate.
Dewatered Residuals
Leachate Co ection Zone
Monofill
Leachate
Figure 7-3. Monofill used for
Dewatering Residuals
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7. Recycle Streams
Zfj!
I1IBP
Mechanically Dewatered Sludge Recycle Streams
Water treatment plant residuals can also be
dewatered by mechanical means, such as a
centrifuge or belt filter press. The quantity
depends on the volume and solids content
of the thi ckened re si dual s feed. If the
sedimentation basin average sludge flow is
0.6% of plant production, the dewatering
device concentrate flow may be
approximately 0.1% to 0.2% of plant flow.
Belt filter presses and centrifuges,
particularly at smaller facilities, are
typically operated for only 8 to 12 hour
shifts per day, often only five days per
week. Operating routines would also affect
potential recycle rates (Environmental
Engineering and Technology, 1999). Data
presented in Table H-2, Appendix H, shows
that turbidity, TOC, and TTHMs can be
high in liquids from mechanically
dewatered sludge. Both total and dissolved
aluminum and manganese concentrations
may also be high. Elevated aluminum is expected to be present in waste streams of water
plants practicing alum coagulation, and release of significant levels of manganese from
residuals has been demonstrated. No published data exists on the potential impacts of
recycling mechanical dewatering device concentrates. Plants generally dilute the dewatered
residuals stream with other recycle streams prior to return to the main treatment train. The
concentrates may often undergo further settling when put into thickeners prior to recycle.
The conveyer is used to transport sludge
from the centrifuge (background) after
dewatering.
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7. Recycle Streams
7.5 NON-REGULATED RECYCLE STREAMS
The FBRR only regulates spent filter backwash water, thickener supernatant, and liquids
from dewatering processes at conventional and direct filtration systems. However, other
residual streams are produced at treatment plants. Table 7-1 provides a summary of some
common residual streams produced by water treatment plants.
Table 7-1. Commonly Produced Non-Regulated Residual Streams
Residual Stream
Filter-to-Waste
Membrane
Concentrate Reject
Stream
Ion Exchange
Residual Streams
Sludge from
Softening Plants
and Contact
Clarifiers
Slow Sand Filter-
to-waste
Diatomaceous
Earth (DE) slurry
Minor Streams
Description
Generated by filters when the filter is placed back on-line after
backwashing and prior to discharging to the clearwell. Typically of
high quality since the stream has been treated by all treatment
processes. Typically 0.5% of total amount of filtered water and second
largest potential waste stream (after spent filter backwash) generated at
a plant (FtDR, 1997). Can be recycled or disposed.
Generated when the source water is passed through the membrane for
treatment. Either returned back through the membrane for treatment or
disposed (discharged to surface water, sanitary sewer, or land-applied).
Generated when the resins are regenerated, rinsed, or backwashed.
Quality may be of concern if recycled.
Solids generated in the sedimentation basin or contact clarifiers.
Recycled as an intrinsic part of the treatment process.
Generated over 1 to 2 days during the slow sand filter ripening period.
Quality and volume may be of concern if recycled.
Generated when the DE filter is cleaned. Consists of filter medium and
particles removed from the source water. Quality and volume may be
of concern if recycled.
Streams that result due to spills, laboratory analyses, washdown of
plant facilities, and leaks. Typically of small volume, but quality may
be a concern if recycled. AWWA' s Self-Assessment of Recycle
Practices (2002) provides more information on minor streams.
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7. Recycle Streams
7.6 REFERENCES
AWWA. 2002. Self Assessment of Recycle Practices. Denver, CO.
AWWA/ASCE. 1998. Water Treatment Plant Design. Third Edition. McGrawHill. New
York, NY.
Bashaw, W., T. Ginn, and R. Thomson. 2000. Design for Reclaiming Filter Backwash
Water at the James E. Quarles Water Treatment Plant. Proceedings from AWWA 2000
Annual Conference. Denver, CO.
Cornwell, D., C. Vandermeyden, and G. Dillow. 1992. Landfilling of Water Treatment
Plant Coagulant Sludges. AWWARF. Denver, CO.
Cornwell, D., M. MacPhee, N. McTigue, H. Arora, G. DiGiovanni, M. LeChevallier, and J.
Taylor. 2001. Treatment Options for Giardia, Cryptosporidium, and Other Contaminants in
Recycled Backwash Water. AWWARF. Denver, CO.
Cornwell, D., and R. Lee. 1993. Recycle Stream Effects on Water Treatment. AWWARF
Report #90624. Denver, CO.
Environmental Engineering and Technology. 1999. Background Papers on Potential
Recycle Streams in Drinking Water Treatment Plants. AWWA.
HDR. 1997. Draft EPA Guidance Manual - Recycle of Spent Filter Backwash Water and
Other Waste Streams, Filter-to-Waste, and Uncovered Finished Reservoirs.
Hoehn, R.C., J.T. Novak, and W.T. Cumbie. 1987. Effects of Storage and Preoxidation on
Sludge and Water Quality. AWWA Journal, Vol. 9, No. 6.
Kawamura, S. 2000. Integrated Design and Operation of Water Treatment Facilities.
Second Edition. John Wiley & Sons, Inc. New York, NY.
Levesque, B.R., J.E. Tobiason, W. Parmenter, and J.K. Edswald. 1999. Filter Backwash
Recycle: Quality Characteristics and Impacts on Treatment. Proceedings from AWWA 1999
Annual Conference. Denver, CO.
Myers, T., J. Skadsen, and L. Sanford. 2000. Coping with Filter Backwash Recycle in Water
Treatment. Proceedings from AWWA 2000 Annual Conference. Denver, CO.
Tobiason, J.E., B.R. Levesque, J.K. Edzwald, G.S. Kaminski, H.J. Dunn, and P.B. Galant.
1999. Water Quality Impacts of Filter Backwash Recycle. Proceedings from AWWA 1999
Water Quality Technology Conference. Tampa, FL.
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8. OPERATIONAL CONSIDERATIONS AND
MODIFICATIONS
8.1 INTRODUCTION
As States and systems evaluate recycle practices, there are operational considerations and
modifications that can be employed by water systems to minimize the impacts that the
recycle of process flows and backwashing practices have on treatment. They all may not be
appropriate for any given system; however, they have been proven appropriate in site
specific situations. Operational considerations that systems may investigate include the
following:
Adjust chemical feed practices in the main treatment train during recycle events;
Return recycle stream(s) to presedimentation basin;
Control raw water or recycle stream flow to avoid unmanageable hydraulic
surges;
Reduce the amount of spent filter backwash generated through backwash
modifications or increased filter run times;
Reduce the filter-to-waste volume if filter-to-waste flows are recycled; and,
Equalize (see Chapter 9) and/or treat (see Chapter 10) recycle stream(s) prior to
returning stream(s) to the main treatment train.
While these operational considerations and modifications are not required by the FBRR,
they are practices that can help systems optimize treatment and minimize the impact of
recycle on treatment plant performance. Modifications can be implemented with or without
pretreatment and/or equalization of the recycle stream. In addition, system modifications
may or may not involve capital improvements at the plant. Each operational consideration
and modification is site-specific and pilot- or full-scale testing is recommended prior to
modifying plant operations. Also, the State should be consulted prior to modifying any
processes. The operational considerations and modifications presented in this section are
not all-inclusive.
8.2 ADJUST CHEMICAL FEED PRACTICES DURING
RECYCLE EVENTS
Some plants have successfully tracked influent
changes by streaming current readings, zeta
potential readings, or other means and adjusted
the chemical feed rate and type accordingly
during recycle events. Jar testing prior to any
modifications will be important to identify the
Jar Testing References
Q Draft LT IBS WTR Tuibidity Provisions
Technical Guidance Manual
(under development by EPA)
a Operational Control of Coagulation and
Filtration Processes, AWWA M37, 1992
[Denver, CO] (available from AWWA)
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8. Operational Considerations and Modifications
type and amount of chemicals that perform best when recycle streams are introduced to the
plant. Most systems will want to develop a Standard Operating Procedure (SOP) to assist
operators with proper chemical feed operations during recycle events. Also, maintaining the
recycle stream flow at a certain percentage of the total plant flow may be essential to
properly implement this operational modification without major plant upsets. Equalization
of the recycle stream may be necessary to maintain the target recycle percentage (see
Chapter 9). The case studies presented in this section illustrate successes and concerns with
modifying chemical feed practices during recycle events.
Case Study- Success with chemical
feed modifications (Moss, 2000)
The Salt Lake City Public Utilities
Department (SLCPUD) noticed an
increase in particle counts and
decrease in streaming current values
during spent filter backwash recycle
events. Operators were able to adjust
coagulant feed rates to compensate for
influent water quality variations such
that finished water was not effected
during recycle. In addition, SLCPUD
fed polymer (high charge anionic
polymer) to the spent filter backwash
clarifier to increase sedimentation of
the spent filter backwash prior to
recycling.
Case Study- Issues with chemical feed
modifications (Goldgrabe-Brewen, 1994)
A study of three plants in northern
California reported coagulant underdosing
when a streaming current detector was used
in coagulant dosage control mode.
Positively charged particles contained in
the spent filter backwash caused the
streaming current monitor reading to
increase, resulting in chemical
underdosing. This same study also
demonstrated that using polymer
exclusively for coagulation had negative
impacts on clarification when the recycle
percentage exceeded five percent of the
total raw water treated.
This option may be complicated due to residual chemicals contained in the recycle stream
and the intermittent nature of some recycle streams. These residuals can cause a fluctuation
of chemical demands at the head of the plant when mixed with raw water. Also,
determining the appropriate chemical dose may be difficult, as presented in the case studies.
A polymer feed system may need to be installed for successful treatment if one does not
already exist. EPA estimates the cost of installing a polymer feed system on a 1.8 MGD
plant was $8,900 in capital costs and $4,000 in operation and maintenance costs (EPA,
2000).
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8. Operational Considerations and Modifications
8.3 RETURN RECYCLE STREAM(S) TO
PRESEDIMENTATION BASIN
If presedimentation basins are available, the recycle stream can be returned to the
presedimentation basin prior to coagulation. Additional settling prior to the main treatment
train may reduce particle loading onto the filters. Another added benefit of discharging
recycle streams to a presedimentation basin, if configured to avoid short-circuiting, is the
mixing that will occur with the raw water. A more consistent influent water quality to the
plant allows for more uniform chemical feed operations and overall improved treatment
plant efficiency. A disadvantage with this operational consideration is that more frequent
sediment/solids removal will be required.
8.4 CONTROL RAW WATER FLOW OR RECYCLE
RETURN FLOW
Systems should be careful to avoid unmanageable hydraulic surges or plant capacity
exceedances during recycle events. Two options systems may want to consider to avoid
unmanageable hydraulic surges or plant capacity exceedances are:
Control raw water flow during recycle events such that the raw water flow plus
recycle flow will not create a hydraulic surge or plant capacity exceedance.
Control the rate of return of recycle flows by providing equalization of recycle
streams (see Chapter 9).
Maintaining the recycle flow at or below 10 percent of the plant influent (raw water flow
plus recycle flow) should be sufficient (SPHEM, 1992; Kawamura, 2000; Cornwell and
Lee, 1994). The appropriate recycle flow percentage will vary from system to system
depending on site specific water quality and treatment conditions.
8.5 REDUCE THE AMOUNT OF GENERATED SPENT
FILTER BACKWASH
Several options are available for reducing the amount of generated spent filter backwash,
including:
Using air scour or surface wash to supplement the backwash process;
Determining the minimum backwash duration necessary to produce optimum
filtered water; and,
Increasing filter run times and decreasing the frequency of backwashes.
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8. Operational Considerations and Modifications
Systems should be careful, when modifying backwash practices, to monitor the
resulting impact on filtered water quality. Modifying backwash practices can affect
filtered water turbidity (causing either increases or decreases in turbidity) and systems
must maintain compliance with all filter effluent turbidity standards. The LT1ESWTR
Turbidity Provisions Technical Guidance Manual has additional information on filter
assessments and backwash practices (under development by EPA).
8.5.1 Air Scour with Backwash
Air scour can be used in conjunction with backwash and in some instances has been shown
to provide better cleaning than water-only backwash, and saves on backwash water. A
water works in southern Nevada that upgraded to an air/water backwash system was able to
reduce its backwash water volume by 500 million gallons per year (Logsdon et al., 2000).
The process can consist of three scenarios (AWWA, 1999):
Air scour alone before backwash. This process is recommended for fine sand,
dual media, and triple media filters.
Simultaneous air scour and backwash during rising water level but before
overflow. Air scour and backwash can be done simultaneously, with air scour
terminating before overflow. This process is recommended for fine sand, dual
media, triple media, and coarse monomedium anthracite.
Simultaneous air scour and water backwash during overflow. This process
consists of air scour with water backwash throughout the overflow period. This
process is recommended for coarse monomedium sand or anthracite filters.
Special baffled overflow troughs are essential for anthracite filters to prevent loss
of anthracite.
The use of air scour in the backwash process may allow a reduction in the backwash rate and
duration, producing less spent filter backwash.
8.5.2 Surface Wash with Backwash
Surface wash systems inject jets of water from orifices
located about 1 to 2 inches above the surface of the
fixed bed. Surface wash jets are operated for 1 to 2
minutes before the upflow wash and usually are
continued during most of the upflow wash. Surface
wash is terminated 2 or 3 minutes before overflow to
prevent media loss. Surface wash may allow the time
of backwash to be decreased and result in less generated
spent filter backwash. EPA estimates that the cost of
installing a surface wash system at a 1.8 MOD plant was
$159,400 in capital costs and $5,700 in operation and maintenance costs (EPA, 2000).
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Case Study (Myers, et al, 2000)
The Ann Arbor Water Treatment Plant
(WTP) (50 MOD lime softening plant)
evaluated four backwash durations: 5, 8,
10, and 15 minutes. Particle counts were
measured in the subsequent filter run for
each backwash duration. The results
indicated the 8- or 10-minute backwash
duration produced the best particle removal
for their system configuration in the
subsequent filter run. Eight minutes
produced the lowest particles in the first
hour and 10 minutes produced the lowest
particles over the filter run. A backwash
duration of 8 minutes was selected,
resulting in approximately 20% reduction
in backwash volume as opposed to a 10-
minute backwash duration.
8.5.3 Reduce the Length of
Backwash
Under some conditions, it may be possible to
reduce the time of backwash and still comply
with turbidity standards. In fact, backwashing
for too long can be detrimental to the media and
filter performance. Backwashing should
typically be terminated when the filter
backwash turbidity is between 10 and 15 NTU
(Kawamura, 2000); however, the optimum filter
backwash turbidity value will vary from system
to system. Full-scale tests are necessary to
determine the backwash duration that
minimizes the filter ripening time when the
filter is placed back on-line and results in the
optimum filtered water quality.
8.5.4 Increase Filter Run Times
Evaluating an increase in the filter run time may be worthwhile and can result in a
significant reduction in generated spent filter backwash volume over time. Caution should
be exercised so as not to compromise finished water by operating a filter to or past the
point of breakthrough. Chemical feed practices can also be modified to optimize
coagulation, flocculation, and sedimentation, resulting in increased filter run times.
Case Study (Myers, et al., 2000)
Pilot and full-scale tests were conducted on extending filter run times at the Ann Arbor
WTP (50 MGD lime softening plant). The addition of a fine garnet layer to the filters
allowed the filter run times to be increased from 75 hours to 96 hours. Headloss in all
the extended filter runs did not exceed three feet. Extending the filter runs resulted in a
30% decrease in backwash volume and also eliminated about 700 filter backwashes per
year, simplifying operations and reducing costs.
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8.6 REDUCE THE AMOUNT OF FILTER-TO-WASTE
If filter-to-waste flows are recycled, several options exist to reduce this particular stream.
Although this stream is not regulated by the FBRR, systems may be concerned about its
potential for causing hydraulic surge. Such systems may consider terminating the filter-to-
waste process when the filtered water turbidity level reaches a predetermined level, as
opposed to terminating the filter-to-waste process after a preset time. For example, some
systems may filter-to-waste for a preset time limit of 15 minutes on all filters during initial
filter start-up. Systems may want to re-evaluate the filter-to-waste procedure. Evaluation of
filter-to-waste practices may reveal that desired turbidity or particle count levels in the
filtered water may be achieved prior to the preset time limit.
Another option is to reduce the filter ripening period, which will in turn reduce the filter-to-
waste volume. The following practices have been demonstrated in certain systems to
decrease the initial turbidity spike that occurs when a filter is placed back on-line:
Delayed start. The delayed start consists of letting the filter rest for a period of
time between backwashing and placing the filter back into service. This option
may not be possible during peak flow periods, but is a good option to consider
for reducing initial turbidity spikes.
Slow start. The slow start is a technique that involves a gradual increase of flow
to the filter until the desired hydraulic loading rate is achieved. Again, this
option can potentially reduce initial turbidity spikes but may require modification
of the system to properly control the flow to the filter.
Add a coagulant or polymer during the backwash process. Some studies
have shown that coagulants added to the backwash water during the later stages
of the backwash process could accelerate the filter ripening process (Hess et al.,
2000).
Add polymer during initial start-up of filter. A polymer can be fed to the
filter influent during the initial start-up period to enhance initial filtration
performance. Polymer feed is then terminated once the filter has reached optimal
performance. Systems should be careful when adding polymer during initial
filter start-up. Polymer addition can create mud balls and other problems in the
filter.
Systems should exercise caution when modifying filter-to-waste practices. Systems will
need to verify that their filter-to-waste practices maintain compliance with finished
water turbidity standards.
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Case Study (Carmichael, Lewis, and Aquino, 1998)
The Milwaukee Water Works compared filter performance for three different
scenarios:
Backwash with no polymer addition;
Backwash with cationic polymer (Cat-Floe T) added to the backwash
water; and,
Adding cationic polymer to the filter influent water for the last hour of a
filter run and then adding it again during the first hour of the following
run.
The strategy of adding polymer to the filter influent water both before and after
backwash at a dosage of 0.4 mg/L 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 the 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 in the last hour of a filter run before backwash, as
this did not improve filter performance.
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8. Operational Considerations and Modifications
8.7 REFERENCES
AWWA. 1999. Water Quality and Treatment. Fifth Edition. McGraw Hill, Inc. New
York, NY.
Carmichael, G., C.M. Lewis, and M. A. Aquino. 1998. Enhanced Treatment Plant
Optimization and Microbiological Source Water Study. Draft final report to EPA.
Cornwell, D.A., and R.G. Lee. 1994. Waste Stream Recycling: Its Effect on Water Quality.
Journal AWWA. 86(11) p 50-63.
Goldgrabe-Brewen, J. 1994. Impact of Recycle Streams on Water Quality. AWWA
Proceedings.
Hess, A., et al. 2000. An International Survey of Filter O&M Practices. Proceedings from
the AWWA Annual Conference. Denver, CO.
Kawamura, S. 2000. Integrated Design and Operations of Water Treatment Facilities.
Second Edition. John Wiley & Sons, Inc. New York, NY.
Logsdon, G. S., A. F. Hess, M. J. Chipps, and A. J. Rachwal. 2000. Filter Backwash Water
Processing Practices. Proceedings from the AWWA Annual Conference. Denver, CO.
Moss, Linda. 2000. Backwash Water Return Effects: Evaluation and Mitigation.
Proceedings from the AWWA Water Quality Technology Conference. Salt Lake City, UT.
Myers, T., J. Skadsen, and L. Sanford. 2000. Coping with Filter Backwash Recycle in
Water Treatment. Proceedings from the AWWA 2000 Annual Conference. Denver, CO.
SPHEM (Great Lakes- Upper Mississippi River Board State Public Health and Environment
Managers). 1997. Recommended Standards for Water Works ("Ten State Standards").
Health Education Services. Albany, NY.
U.S. EPA. February 2000. Cost and Technology Document for the Proposed Long Term 1
Enhanced Surface Water Treatment Rule and Filter Backwash Rule. Office of Ground
Water and DrinkingWater.
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9. EQUALIZATION
9.1 INTRODUCTION
Water treatment plants are designed to treat up to a specific flow rate and water is typically
introduced to the plant via pumps at a controlled rate. When additional flows during recycle
events are introduced, the recycle stream may cause one or more of the following:
The plant exceeds the design capacity. Recycle streams (spent filter backwash
water in particular) can be generated rapidly and in large volumes, and have the
potential to cause a plant to exceed its design capacity.
Hydraulic surge. The introduction of recycle streams can cause the flow to the
plant to increase suddenly, which can disrupt treatment processes.
The influent water quality is significantly altered by the recycle stream. The
potential exists for recycle streams to contain higher concentrations of
contaminants, particularly pathogens, than the raw water. Also, the chemistry of
the recycle stream may influence water quality such that the overall treatment
efficiency of the plant may be affected.
Equalization of recycle streams can be provided to help reduce the impacts of recycle
streams on plant processes. Equalization consists of providing storage or detention of the
recycle stream and returning the recycle stream at a rate different than the generated rate.
For instance, spent filter backwash is generated at a particular plant at a rate of 2,000 gpm.
Equalization is provided in a spent filter backwash holding tank, and the holding is operated
such that the spent filter backwash is returned at a rate of 500 gpm. Figure 9-1 provides a
schematic for equalization of spent filter backwash. With equalization, flows can be
returned at a rate less than the generated flow rate. Equalization of recycle streams can be
provided by basins similar to sedimentation basins, lagoons, or other similar units. The case
studies presented in this chapter provide information on equalization tank design
considerations.
When determining the rate of return from the equalization basin, the rule of thumb has been
to maintain the recycle flow at or below 10% of the plant flow (SPHEM 1997; Kawamura,
2000; Cornwell and Lee, 1994). However, the actual percentage varies from plant to plant
and systems need to evaluate the percentage of recycle stream that creates the minimal
impacts on finished water. In addition, a continuous recycle return flow (as opposed to
intermittent recycle return flow) has been recommended for optimum plant performance
(McGuire, 1997; Petersen and Calhoun, 1995).
This chapter discusses the advantages and disadvantages of equalization and methods for
assessing the impacts of equalization or lack of equalization at a system. Two case studies
are presented later in this chapter to provide real-life scenarios and concerns.
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9. Equalization
Figure 9-1. Example of Equalizing Recycle Streams
Raw Water
Influent
Disinfection
Solids
*Solids removal/disposal
may need to be addressed
Note: Equalization is typically used for
spent filter backwash, but may be
used for other unregulated
recycle streams such as filter-to-
waste. Pumps may be required to
convey the recycle streams from
the equalization tank.
Finished Water to
Distribution System
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9. Equalization
Benefits of Equalization
Minimize hydraulic surge
Better flow pacing of
chemicals
Subsequent recycle stream
treatment processes may be
downsized
9.2 ADVANTAGES
Flow equalization provides hydraulic stabilization that
can help to maintain optimal finished water quality.
Equalization of recycle streams can provide the
following benefits:
Minimize hydraulic surges and the
possibility of hydraulic overload of
sedimentation basins, filters, and other
treatment units. Settled water quality has been shown to deteriorate as surface-
loading rates of the sedimentation basin increase (AWWA, 1999). Hydraulic
overload can compromise overall treatment plant efficiency and removal of
pathogens and other contaminants. Hydraulic surges can also result in a plant
exceeding its design or State-approved capacity. Equalization can help
eliminate the situation where clarification and filtration operating rates may be
exceeded at precisely the time recycle streams may be returning large numbers of
oocysts to the treatment process. Example 9-1 illustrates a situation where direct
recycle practices resulted in a plant exceedance and other plant process impacts.
Allow better flow pacing of chemicals at the head of the treatment plant when the
flow is more consistent. Recycle streams vary with quality as the stream is
produced. For instance, spent filter backwash typically contains more particles
during the beginning of filter backwash than at the end of the backwash process.
Equalization can allow the spent filter backwash to be mixed (if mixing is
provided in the equalization basin) and of a more consistent quality, in addition
to controlling the flow. A more consistent recycle stream, both in quantity and
quality, will allow for consistent chemical feed operation.
Equalization can allow a reduction in the size of a recycle stream treatment unit
(if provided) by reducing the peak recycle stream flow.
Equalization basins can be operated such that settling of particles can occur. Chapter 10 has
more information on treatment through sedimentation.
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9. Equalization
Example 9-1. Evaluating Recycle Practices
Note: The following example is intended to illustrate how a system or State could
evaluate recycle practices and resulting modifications. This example is not intended
to establish plant operation or modification criteria.
Using the example and information for the 3.0 MGD plant presented in Appendix C,
recycle practices were evaluated. Following is a quick summary of the plant
information:
Plant design flow: 3.0 MGD (2,080 gpm);
Observed Peak Plant Influent: 2,500 gpm, consisting of 1,000 gpm raw water
flow and 1,500 gpm spent filter backwash recycle flow; and,
Typical Recycle Flow: 1,500 gpm- This flow represents spent filter
backwash. Backwash is conducted at a rate of 15 gpm/ft2 and each filter has a
surface are of 100 ft2. Filters are backwashed individually, four filters per
night. Filters were backwashed for a duration of 15 minutes.
To evaluate their recycle practices, the system determined the percent of peak plant
influent flow that was recycle flow on an instantaneous basis:
% Recycle flow = Recycle Flow = 1,500 gpm = 60%
Total Plant Flow 2,500 gpm
The percent recycle flow on an instantaneous basis of 60% was rather high. Also, the
peak plant influent flow of 2,500 gpm exceeds the plant design flow of 2,080 gpm.
Further evaluation of plant flows during recycle indicated the design flow was typically
exceeded during recycle events. The sedimentation basin and filters were both subjected
to hydraulic surges during recycle. Turbidity and particle counts in the finished water
were recorded at 30-second intervals as another means of evaluating impact of recycle
practices. The results indicated substantial increases in both turbidity and particle counts
during recycle events as opposed to periods where recycle was not occurring.
The system decided to install a lagoon to provide equalization. The lagoon was sized for
two backwash volumes plus adequate freeboard. The lagoon was operated such that
recycle flows were reduced from 1,500 gpm under direct recycle practices to 500 gpm.
The lagoon was allowed to fill completely during backwash (15 minutes) to allow mixing
and then pumped back to the plant before the next backwash commenced.
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9.3 DISADVANTAGES
Few disadvantages are associated with flow equalization, however, as with any water
treatment plant improvement, costs are a consideration. Multiple or redundant facilities may
be required for adequate operation. Should the equalization basin not be operated on a
continuous basis or operation suspended for an extended time (2 to 3 days), sludge may
form in the bottom and be subsequently discharged to the plant influent. Sludge can taint
the equalized flow, create objectionable tastes and odors, and carry other undesirable
substances in the recycle stream. Another disadvantage is the required amount of space
needed to accommodate the equalization basin.
Case Study (Myers, et al, 2000)
Four alternatives for handling spent filter backwash at the Ann Arbor WTP (50 MGD
lime softening plant) were evaluated:
Discharge to a storm sewer (equalization required to meet discharge permit
flow requirements);
Discharge to a sanitary sewer (equalization required by receiving
wastewater plant);
Discharge to a lime sludge lagoon; and,
Equalization with recycle.
The system evaluated all four alternatives for feasibility, flexibility, and cost-
effectiveness. For this particular plant, equalization with recycle in conjunction with
discharge to the lime sludge lagoon was the most feasible and cost-effective option.
Discharge to the lime sludge lagoon was recommended to be included as a back-up and
added operational flexibility.
The conceptual equalization basin design included an equalization basin with a capacity
of at least two backwash volumes and variable speed pumps to maintain the recycle
flow between 5% and 10% of the raw water flow. Equalization of recycle provided the
following benefits for the Ann Arbor WTP:
Reduced the possibility of plant capacity exceedance during recycle;
Reduced hydraulic surge through the plant, resulting in better settling and
particle removal through the filters; and,
Allowed for more consistent chemical feed, which resulted in more
consistent water quality.
The conceptual design also included a recommendation that the equalization basin
allow for future chemical addition if treatment becomes necessary in the future.
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9.4 COSTS
Costs are associated with both the construction and operation and maintenance (O&M) of
equalization basins. EPA developed a range of costs as part of the FBRR making process.
Capital costs associated with equalization basins for design recycle flows into the
equalization basins of 0.59 MOD and 83.59 MOD were $317,000 per MOD and $14,360 per
MOD, respectively. O&M costs associated with equalization basins for design flows of 0.59
MOD and 83.59 MOD were $11,000 per MOD and $130 per MOD, respectively (EPA,
2000).
9.5 EVALUATING EQUALIZATION
Evaluating existing equalization or evaluating the need for equalization is an important step
in examining the effects of recycle practices on a system, particularly when a plant is out of
compliance (for example, unable to meet current turbidity standards). In order to evaluate if
equalization improvements would be beneficial, the following information and plant
performance data should be assessed:
Evaluate the data collected on recycle practices, as discussed in Chapters 3, 4,
and 5. Systems may want to examine frequency of recycle streams, recycle
stream flow rates, backwash practices, and other information. Systems may be
able to determine that plant capacity and individual treatment unit process
loading rates are exceeded during recycle events. The system should then
evaluate the impact to finished water quality as a result of recycle practices.
Evaluate loading rates to treatment units (specifically clarifiers, sedimentation
basins, and filters) during recycle events. Compare the loading rates during
recycle events to the design loading rates. In order to ensure finished water
quality meets all standards, the design loading rates should rarely be exceeded.
Examine turbidity and/or particle count levels in finished water during recycle
events. If turbidity and particle counts increase during recycle events,
equalization may be one option to reduce these impacts (see Example 9-1).
Examine daily operation information and assess the chemical feed practices
during recycle events. If the system must modify chemical feed practices during
recycle events, equalization may allow a more consistent chemical feed practice.
Again, equalization can allow the recycle stream to be returned at a more controlled rate and
at a more consistent quality. As the system evaluates equalization, treatment options may
also be considered. Chapters 10 provides more information on treatment for recycle
streams. If treatment is not installed at the time the equalization units are installed, the
system may want to allow room in the design for future treatment.
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Case Study (Bashaw, et al, 2000)
The James E. Quarles WTP is a 64 MOD conventional filtration treatment plant located in Marietta,
Georgia. The recycle practices were evaluated as part of the expansion process (upgrade to a capacity
of 96 MGD) and recycle stream equalization and treatment alternatives were investigated. As seen in
Figure 9-2, the existing system recycles spent filter backwash, thickener supernatant, filtrate, and
filter-to-waste. All recycle streams are treated in a clarifier, equalized in a recycle tank, and then
recycled to the raw water reservoir.
Four alternatives were evaluated for the recycle streams:
1. Adding polymer to flocculate the solids in the spent filter backwash water before settling.
Jar tests were conducted to determine the type and dose of polymer needed.
2. Equalizing backwash flows and thickener overflows prior to settling. Flows to the
clarifier during backwash were 2.7 times the average flow to the clarifier. Equalization
would provide a consistent flow to the backwash clarifier for better detention and
treatment. Also, the suspended solids in the spent filter backwash varied greatly over the
backwash cycle. With mixing the full backwash flow volume in the equalization tank, a
more uniform concentration of solids is obtained. The added benefit of mixing is that the
polymer feed rate could be maintained at a more uniform rate.
3. Discharge filter-to-waste flows downstream of the clarifier. Since filter-to-waste contains
almost no solids, little treatment is accomplished in the clarifier. By-passing the clarifier
reduces the loading to the clarifier and provides better detention and treatment (removal
of solids) of spent filter backwash flow.
4. Provide additional treatment after the clarifier.
The following options were selected for final design and are presented in Figure 9-3:
Two new equalization tanks will be installed to receive spent filter backwash and
thickener supernatant. The equalization tanks were designed to accommodate two
backwash volumes plus thickener overflows. Each tank will be equipped with
submersible mixers for blending contents and with vertical, mixed flow transfer pumps
that will discharge to a flocculation tank.
The discharge piping from the equalization tanks will be equipped with polymer feed
injection capabilities.
A two-stage flocculation tank will be installed downstream of the equalization tanks and
will provide 10 minutes of detention time at peak flow rate.
Filter-to-waste flows will be discharged downstream of the clarifier.
The existing clarifier capacity will not be modified due to the elimination of filter-to-
waste flows and longer filter runs (to be achieved with deep-bed filters that will be
installed as part of the plant upgrades). The clarifier will be able to provide 4.2 hours of
detention time.
Treatment of the flow exiting the clarifier was not included as part of the final design, but
the final design allows for installation of treatment if needed in the future.
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9. Equalization
Figure 9-2. Existing Layout of James E. Quarles Water Treatment Plant
Disinfectant
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9. Equalization
Figure 9-3. Proposed Improvements for Recycle Streams at the James E. Quarles
Water Treatment Plant
Disinfectant
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9. Equalization
9.6 REFERENCES
AWWA. 1999. Water Quality and Treatment-Fifth Edition. McGraw Hill, Inc. New
York, NY.
Bashaw, W., T. Ginn, and R. Thomson. 2000. Design for Reclaiming Filter Backwash
Water at the James E. Quarles Water Treatment Plant. Proceedings from the AWWA
Annual Conference. Denver, CO.
Cornwell, D.A., and R.G. Lee. 1994. Waste Stream Recycling: Its Effect on Water Quality.
Journal AWWA. 86(11) p50-63.
Kawamura, S. 2000. Integrated Design of Water Treatment Facilities-Second Edition. John
Wiley & Sons, Inc. New York.
McGuire, M.J. 1997. (Draft) Issue Paper on Waste Stream Recycle and Filter-to-waste in
Water Treatment Plants. Prepared for AWWA Technical Work Group.
Myers, T., J. Skadsen, and L. Sanford. 2000. Coping with Filter Backwash Recycle in
Water Treatment. Proceedings from AWWA Annual Conference. Denver, CO.
Petersen, D. W., and B. Calhoun. 1995. Do You Recycle? Results of AWWA's Recycle
Practices Survey. AWWA Annual Conference.
SPEHM (Great Lakes- Upper Mississippi River Board State Public Health and
Environmental Managers). 1997. Recommended Standards for Water Works ("Ten State
Standards"). Health Education Services. Albany, NY.
U.S. EPA. February, 2000. Cost and Technology Document for the Proposed Long Term 1
Enhanced Surface Water Treatment Rule and Filter Backwash Recycling Rule. Office of
Ground Water and Drinking Water.
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10. TREATMENT OF RECYCLE STREAMS
10.1 INTRODUCTION
Residual streams are often high in particulates, solids, and other contaminants. It may be
necessary to treat residual streams prior to recycling so finished water quality is not
compromised. An AWWA FAX survey taken in 1998 found that the majority of systems
that recycle (approximately 70%) treat and/or equalize the stream prior to its return to the
main treatment train (AWWA, 1998). The most common type of treatment is
sedimentation. See Table 10-1 for the results of the AWWA FAX survey.
The FBRR does not require treatment of recycle streams beyond returning flows through the
processes of a system's existing conventional or direction filtration system. However, EPA
recognizes that additional treatment of recycle streams may be appropriate to reduce risks of
microbial contamination and optimize the operational performance of the system. As
systems and States begin to evaluate recycle practices, they may decide that treatment of
recycle streams or modifications to existing recycle stream treatment processes is warranted.
Table 10-1. Results of AWWA FAX Survey on Systems that Recycle
TREATMENT TYPE
No Treatment
Sedimentation
Equalization
Sedimentation and
Equalization
Lagoon
Other
PERCENTAGE
OF SYSTEMS
30
38
14
10
3
5
Some systems may decide that recycle of residual streams is not cost-effective and may elect
to dispose of residual streams. Disposal of residual streams may need to meet requirements
under other Federal and State statutes and regulations. Some options that may be available
include:
Discharge to the sanitary sewer;
Discharge to a surface or ground water body; or,
Irrigation/land application.
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Systems should check with their State and EPA regional offices to determine what
restrictions or permit requirements apply to any of these disposal options. This document
will not cover disposal options.
This chapter presents a description of recycle stream treatment concepts, the advantages and
disadvantages associated with treatment, guidelines for treatment, methods for assessing
existing recycle stream treatment or the need for treatment, and a brief description of
different treatment options. Case studies are also provided that give examples of different
recycle stream treatment options.
10.2 ADVANTAGES
Treatment processes for recycle streams that are properly designed and operated can reduce
levels of Cryptosporidium and Giardia, contaminants of concern in recycle streams.
Treatment processes can also be designed and operated to remove other contaminants, such
as solids, particulates, DBF precursors, TOC, aluminum, iron, and manganese. These
contaminants can create aesthetic and health issues in the finished water if not removed from
recycle streams. Other benefits of treatment are as follows:
Treatment of recycle streams may be
cheaper and less time- intensive for the
operator than modifying main
treatment train processes during
recycle events. Because both quantity
and quality of plant influent change
during recycle events, operators may
need to modify chemical feed
processes and other main treatment
plant processes to ensure that finished
water quality is not compromised.
Treatment of recycle streams can allow
more consistent operation of the main
treatment train processes.
Treatment of recycle streams can
reduce particle loading on
sedimentation basins (in conventional
filtration plants) and filters in the main treatment train, thus possibly extending
the useful life of these units.
Benefits of Treating Recycle
Streams
S Removal of contaminants,
particularly Cryptosporidium
and Giardia.
/ Allows more consistent
operation of main treatment
train, resulting in saved
money and operator time.
s May extend useful life of
sedimentation basins and
filters in main treatment train.
It may be necessary to equalize flow in addition to providing treatment to control the recycle
stream flow. The use of equalization may also reduce the size of the treatment unit required
to handle the recycle flow.
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10.3 DISADVANTAGES
There are some disadvantages associated with treatment of recycle streams. As with any
other treatment plant improvement, more equipment requires more maintenance. Again,
when compared to other residual management options (such as disposal), the O & M of
treatment units may be a more cost-effective option.
10.4 COSTS
The costs will vary depending on the type of treatment, flows, level of treatment, and other
site-specific issues. However, treatment may be cheaper than other alternatives (such as
discharge to a surface water body or wastewater treatment plant). EPA estimated a
sedimentation basin with polymer feed and tube settlers to have a capital cost of $228,000
and $1,560,000 for design loading rates to the sedimentation basin of 0.022 MGD and 19.87
MGD, respectively (EPA, 2000). Annual operation and maintenance costs were estimated
to be $4,600 and $34,700 for design loading rates to the sedimentation basin of 0.022 MGD
and 19.87 MGD, respectively (EPA, 2000).
10.5 RECOMMENDED DESIGN GOALS
The FBRR does not provide specific requirements for treatment. Some States and
professionals have developed treatment guidelines that are presented for consideration in the
following sections. Systems should check with their State on specific treatment
requirements or guidelines when considering treatment for recycle streams.
10.5.1 Ten States Standards
The Great Lakes Upper Mississippi River Board of State Public Health and Environmental
Managers, (or Ten States Standards) (SPHEM, 1997), recommend that spent filter backwash
be returned at a rate less than 10% of the raw water flow entering the plant. Spent filter
backwash should not be recycled when raw water contains excessive algae, when finished
water taste and odor problems occur, or when trihalomethane levels in the distribution
system exceed allowable levels.
10.5.2 California
California recommends that treatment plants establish an operational goal for turbidity of
less than 2.0 NTU for recycled spent filter backwash and other recycle streams. If this
turbidity limit cannot be achieved, the system should treat the recycle stream to a quality
equal to the average raw water quality. In addition, new facilities should remove 80% of
solids before recycle and the recycle flow should be less than 10% of the plant flow.
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10.5.3 Maryland
Maryland has a policy for both new and existing surface water treatment plants. New
surface water plants should provide treatment for recycle streams. Existing systems can
continue to recycle under the following controlled circumstances:
The recycle ratio should be less than 5%;
A minimum of two hours of polymer-enhanced sedimentation should be
provided; and,
Sedimentation should be provided with very low, continuous overflow rates (0.3
gpm/ft2).
10.5.4 Ohio
Ohio recommends recycle streams be treated prior to their return to the main treatment train.
In addition, the recycle flow should be less than 10% of the plant flow.
10.5.5 Cornwell and Lee (1993)
Based on an evaluation of eight systems, Cornwell and Lee (1993) made the following
observations which may minimize impacts on finished water quality:
Equalization should be provided so that recycle is continuous rather than
intermittent.
The recycle stream should be properly treated for cyst removal with an 80
percent treatment efficiency.
Overflow rates from the backwash water clarifier should be less than 0.07
gpm/ft2 to achieve the 80% treatment efficiency (when chemical addition is not
used).
10.5.6 United Kingdom Water Industry Research (UKWIR) (1998)
The UKWIR developed a water treatment guidance manual that addresses recycling of spent
filter backwash water (Logsdon, et al., 2000). The UKWIR recognized the risk posed by
concentrated suspensions of Cryptosporidium oocysts in spent filter backwash. UKWIR
developed the following guidelines to prevent passing oocysts into finished water:
Backwash water should be settled to achieve a treatment objective of greater than
90% solids removal before recycling.
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10. Treatment of Recycle Streams
Recycle flows should be at less than 10% of raw water flow and continuous
rather than intermittent.
Continuous monitoring of the recycle stream with on-line turbidimeters should
be conducted.
Jar tests should be conducted on plant influent containing both recycle streams
and raw water to properly determine coagulant demand.
Polymers should be considered if high floe shear or poor settling occurs.
The recycle of liquids from dewatering processes should be minimized,
particularly when quality is unsuitable for recycling.
10.6 EVALUATING TREATMENT
The evaluation of existing treatment processes used for recycle streams or evaluating the
need for treatment is an important process. The following checklist can be used to conduct
the evaluation:
S Compare finished water quality during periods of recycle to periods when
recycling is not occurring. Contaminants of concern are Cryptosporidium,
Giardici, DBFs, DBF precursors, TOC, iron, aluminum, and manganese. Other
water quality parameters that could be examined are pH, turbidity, particle
counts, and taste and odor. If contaminant concentrations increase during recycle
events as compared to periods when recycling is not occurring, then treatment (or
improvements to existing recycle stream treatment processes) may be warranted.
Also, if treatment technique violations or MCL violations occur during recycle
events, then treatment (or improvements to existing recycle stream treatment
processes) should seriously be considered.
^ Perform a similar process as previously described on individual treatment unit
processes in the main treatment train for more information on how individual
units are being impacted during recycle events.
^ Examine flows and hydraulic loading rates during periods of recycle events.
Make sure that hydraulic surge, plant capacity exceedance, and/or hydraulic
loading rates of individual treatment units in excess of design rates are not
occurring.
As a system considers treatment options for recycle streams, the following items should be
considered:
^ Estimate or measure the amount of residuals produced by the plant. Mass
balance calculations can be used to determine residual stream loading rates. The
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10. Treatment of Recycle Streams
liquid and solid residual stream quantities (peak and overall volume) should be
obtained to properly size treatment units.
-S Consider the benefits of adding equalization. Equalizing the recycle stream may
allow a reduction in the required treatment unit loading rates.
^ When designing any treatment process, allow for future modifications- flexibility
is key.
The AWWA Self-Assessment of Recycle Practices provides additional information on how
to evaluate existing recycle stream treatment facilities or the need for treatment (AWWA,
2002).
The case study (Bashaw, et al., 2000) presented in Chapter 9 (page 65) provides information
on how treatment and equalization options for recycle streams can be evaluated. The
following case study presents additional information on evaluating treatment.
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Case Study (Niehon, et al, 1995)
The Cleveland Division of Water (CDW) is upgrading one of its four water treatment plants
(Crown WTP) from 50 MGD to 125 MGD capacity. The upgrade will involve modifying
existing conventional unit treatment processes (coagulation, flocculation, sedimentation and
filtration) to high-rate processes. As part of the upgrades, the system evaluated recycle
practices. Figure 10-1 contains a schematic of the existing system and residual streams. The
Crown WTP handles residual streams as follows:
Spent filter backwash is either equalized and recycled to the head of the plant or sent to the
gravity thickeners for ultimate discharge to Lake Erie.
Solids are thickened, dewatered, and the filter cake disposed in sanitary landfills. The
pressate is sent to the sanitary sewer after pH adjustments. Thickener supernatant is
discharged to Lake Erie.
In evaluating recycle practices, CDW developed a residual solids management plan. CDW
considered the following to develop this plan:
Existing data on both the quantity and quality of residual streams. An important part of this
process was identifying additional data collection needs.
Solids production throughout the treatment process. A mass balance was conducted to
identify the point in the treatment train where solids were generated. The mass balance
showed how residual solids were processed, and checking the results against existing data
enabled the identification of erroneous data. Average quantity and average quality of
residual streams in addition to maximum day, maximum week, and maximum monthly
values were calculated.
Cost and non-cost issues associated with each residual solids management alternative.
The impacts on individual treatment processes or operational practice in the main treatment
train during recycle events. For instance, the TOC concentrations in water leaving
clarifiers and filters during recycle events was compared to periods of no recycling. In
addition, DBF levels in the distribution system were monitored.
Future needs and flexibility for future upgrades and expansions.
CDW selected the following options for residual solids management as part of the overall plant
upgrade (see Figure 10-2):
Filter-to-waste capabilities would be installed and filter-to-waste streams would be recycled
directly to the head of the plant. This alternative was selected based on costs, the fact that
the stream would be treated again by plant processes, and that the stream's quantity and
quality would have little impact on operation of the expanded WTP.
Spent filter backwash would be discharged to Lake Erie after being equalized and clarified.
Spent filter backwash would not be recycled (and would not undergo chemical treatment).
This alternative was selected to reduce solids loading on treatment units and eliminate
water quality issues in the finished water (taste and odor, iron, manganese, TOC, DBF and
DBF precursor concentrations, Giardia, and Cryptosporidium).
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10. Treatment of Recycle Streams
Figure 10-1. Crown Water Treatment Plant - Existing
To Truck For Solids
Disposal
I Liquids From
/ Dewatering
To Sanitary
Sewer
Figure 10-2. Crown Water Treatment Plant - Proposed
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10. Treatment of Recycle Streams
10.7 TREATMENT OPTIONS
Treatment options for recycle streams are similar to the treatment options used for raw water
at a water treatment plant. Treatment can consist of solids removal and/or disinfection.
There are several options for solids separation from spent filter backwash water and other
recycle streams: sedimentation, granular-bed filtration, and membrane filtration.
Disinfection can also be employed for treatment of recycle streams to provide inactivation of
pathogens. This chapter presents general treatment capabilities, advantages, disadvantages,
operational considerations, and case studies (where available) for each treatment type. Not
all aspects of recycle stream treatment are discussed.
10.7.1 Sedimentation
General
Sedimentation is a process for removal of solids from liquids either by gravity or physical
separation. The use of sedimentation on recycle streams has been shown to be effective in
removing particles and pathogens. An example of atypical sedimentation process for
recycle streams (in addition to the main treatment train) is shown in Figure 10-3.
Sedimentation can either be batch-flow or continuous-flow. Batch-flow sedimentation
processes combine equalization and treatment in a single unit, and for this reason, are
commonly used to treat recycle streams. Generally, batch flow systems consist of one or
more basins sized to receive a large volume of flow, such as spent filter backwash water, in
a short period of time.
Figure 10-3. General Sedimentation Process for Treatment of Recycle Streams (In
Addition to the Main Treatment Train)
Spent Filter
Backwash or Other
Recycle Stream
Equalization(l)
Residuals/Sludge to
Solids Handling or
Disposal
(1) Equalization is optional except for continuous-flow sedimentation.
(2) Chemical addition can consist of a coagulant or polymer. Chemical addition is optional but
has been shown to improve treatment of the recycle stream.
(3) Flocculation is optional but may enhance treatment.
(4) Sedimentation unit can consist of a circular clarifier, a unit equipped with tube or plate
settlers, or a solids contact clarifier.
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Continuous flow sedimentation basins (both circular and rectangular), similar to those used
to treat the main process flow, may also be considered for recycle stream treatment. It is
best to avoid operating continuous-flow systems intermittently. If generation of the recycle
stream is too variable, then accommodation in the design for operational flexibility (e.g.,
variable flow rate from pumps) may be needed to maintain continuous flow.
A sedimentation basin typically consists of an inlet, an outlet for clarified water, and a solids
collector and removal mechanism (see Figure 10-4). Clarified water may be removed by a
floating decanter or from one or more fixed outlets above which all water is collected. The
recycle stream can either be pumped or conveyed by gravity to the main treatment train. A
pretreatment chemical may or may not be added to the flow before it enters the basin. The
chemical mixing process could use a static in-line mixer or rapid-mix basin depending on
the plant layout, hydraulic grade line, and capacity.
If recontamination of the recycle flow by the settled sludge is a concern, the system should
employ a method to remove the solids frequently. This contamination could lead to
objectionable taste, odors, and other undesirable qualities in finished water. Sludge removal
should also be conducted at an appropriate frequency to avoid compromising the active
storage and treatment capability in the sedimentation basin. Systems should use
sedimentation basins with automatic sludge removal since manual cleaning has been shown
to release significant amounts of manganese, iron, and TOC into the supernatant (Cornwell
and Lee, 1993). For continuous-flow units, sludge removal should be automatic and
continuous so as not to disrupt the continuous-flow process.
The remainder of this section provides information on three types of sedimentation
processes: lagoons, chemical additions, and tube and plate settlers. Advantages and
disadvantages of sedimentation are also provided and case studies of each type of
sedimentation are included to further describe each.
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Figure 10-4. Circular Radial-flow Clarifier
FEEDWELL
EFFLUENT DROP-OUT
LAUNDER
WALKWAY
WEIR
INFLUENT PIPE
Source: AVWVA and ASCE, 1990.
SLUDGE DRAW-OFF PIPE
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Lagoons
Where adequate land is available, lagooning may be an economical alternative for treating
spent filter backwash water and other recycle streams. Lagoons are relatively simple
earthen structures for sedimentation. They have an inlet for the recycle stream, an outlet for
the settled water, access to remove the settled solids, and (typically) drain and overflow
provisions. A generic schematic diagram for treating recycle streams in lagoons is presented
in Figure 10-5.
Lagoons do not require a separate tank to equalize the incoming flow. However, the
potential mixing effect created by a high rate of incoming flow does require special
consideration. To minimize resuspension of settled solids by the influent, Kawamura (2000)
recommends that the lagoon be sized to contain at least 10 backwashes. A series of three or
more smaller lagoons, each holding three or four filter backwash volumes, may also be used.
All lagoons should be elongated in shape to maximize the distance between the inlet and
outlet, and the inlet should be provided with an energy dissipator. The outlet should be
designed to decant as well as drain the lagoon, and should act as an overflow facility.
Depending on the design conditions, either a mixing device or a static in-line mixer that uses
the turbulence of the influent flow may provide chemical mixing when chemical addition is
used.
Additional considerations when using lagoons are the release of contaminants by the settled
sludge, contamination by outside sources, or contamination to the local environment from
the lagoon. Lagoons are often designed for infrequent sludge removal by equipment such as
a front loader. If recontamination of the recycle flow from constituents of the stored sludge
(e.g., manganese) is a concern, then the design should incorporate a method of frequent
sludge removal. Also, contamination of the recycle flow by sources outside the lagoon, such
as chemical delivery trucks, should be considered. The lagoon should be lined with an
impervious liner to prevent contamination to the ground water. Another option is to install
underdrains to collect leachate. Underdrains may be included in the lagoon design to collect
and recycle the leachate, although quality of this water may be of concern. All of these
considerations add costs to the installation of a lagoon.
Figure 10-5. Lagoon Process for Recycle Streams
pen!FNter Chemical
Backwash or Other
Recycle Stream
Addition(1)
Lagoon
To Main
Treatment
Train
Rapid Mix(1)
Residuals/Sludge to
Solids Handling or
Disposal
(1) Chemical addition and rapid mix are optional but may enhance treatment of recycle stream.
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Chemical Addition
The sedimentation process can be enhanced by the addition of chemicals. The use of
flocculation prior to sedimentation is recommended when the settling characteristics of the
spent filter backwash water are less than desired unless conventional flocculation and
sedimentation are implemented (Kawamura, 2000). A schematic diagram of this treatment
train is shown in Figure 10-3. The optimal chemical type and dose should be determined
based on jar tests and the particular application. The overflow rate should also be based on
the desired amount of sedimentation. The case studies presented in this section demonstrate
the benefits that can be realized with chemical addition.
Tube and Plate Settlers
Inclined tubes and plates can be used in sedimentation basins to allow greater loading rates
than conventional sedimentation. Figure 10-6 shows a typical plate settler design. This
technology relies on the theory of reduced-depth sedimentation: particles need only settle to
the surface of the tube or plate 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
Figure 10-6. Typical Plate Settler Design
ADJUSTABLE WEIR
OUTLET TROUG
INLET BOTTOM
INLET FLUME
INLET ORIFACE
Source: AWWA and ASCE, 1998.
OUTLET
BOTTOM
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angle of inclination is about 60 degrees, so that settled solids slide down to the bottom of the
basin. The disadvantages of these processes are that the tubes and plates can become easily
clogged in some applications, can serve as a surface for biological growth (often algae when
uncovered), and can be difficult to clean. Uneven flow distribution at the inlet and
inadequate spacing of the discharge flumes can create inefficiencies.
A generic process schematic diagram for tube and plate settling is shown in Figure 10-3.
Flocculation may be beneficial for recycle streams, depending on the settling characteristics
of the recycle stream. The type of chemical mixing used, if necessary, depends on factors
such as the plant layout, hydraulic grade line, and design flow rate.
Tube and Plate Settler Case Study (Ashcroft,
et al, 1997)
A full-scale plant was using both tube and
plate settlers. The tube settlers were installed
in an existing circular clarifier and the plate
settlers were installed in a new circular basin.
The spent filter backwash water was pumped
to the clarifiers from an equalization basin.
No separate flocculation facilities were
provided.
Both clarifiers consistently achieved greater
than 90% reductions in turbidity and 2- to 5-
|im particles with the addition of 0.7 mg/L
anionic polymer. Treated turbidities were in
the range of 2.0-3.6 NTU. Loading rates of
0.20-0.38 gpm/ft2 were tested with little
variation in performance. These loading rates
are very low when compared to the typical
rates of 2-3 gpm/ft2 used in treating main
process flows.
TTHMs and TTHM formation potential were
also measured in the untreated and treated
backwash waters. TTHMs were about 40
|ig/L in the untreated water, and were not
significantly affected by treatment. Total
TTHM formation potential, however, was
reduced by 45% to 55%, to approximately 100
|ig/L. Little difference between the
performance of the tube and plate settlers was
shown.
Plate Settler Case Study (Narasimhan, 1997)
Two full-scale WTPs in metropolitan Phoenix,
AZ- the Verde and Mesa plants- have plate-
settling facilities that include polymer feed,
rapid mix, flocculation, and plate settlers to
treat recycle streams. At the Verde plant, a
combination of spent filter backwash water,
centrate, and gravity thickener overflow is
treated; the Mesa plant treats only spent-filter
backwash water. Facilities at both plants are
operated continuously for six to eight hours
per day.
Results from the Verde plant showed
consistent treated turbidities of less than 25
NTU with the addition of 0.4 mg/L polymer
and loading rates of up to 0.39 gpm/ft2 (0.95
m/h). At the Mesa plant, treated turbidities
were consistently below 20 NTU at loading
rates of up to 0.6 gpm/ft2. Polymer addition
did not have much impact on turbidity removal
at Mesa. Turbidities of the influents to the
recycle treatment facilities at both plants
ranged from below 20 NTU to about 100
NTU.
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10. Treatment of Recycle Streams
Tube Settler Case Study (Cornwell, et al, 2001)
A full-scale study on a Central Utah Water Conservancy District direct filtration plant was
conducted. The plant was equipped with a sidestream plant to treat spent filter backwash prior to
recycle. The sidestream was equipped with rapid mix, flocculation, and sedimentation with tube
settlers. The tube settler overflow rate range investigated in the plant was 0.19 to 0.37 gpm/ft2
and treatment was compared with and without polymer. Average settled turbidities without and
with polymer were 2.4 NTU and 1.2 NTU, respectively. The addition of 0.1 mg/L of the
appropriate polymer resulted in 50% reduction in average settled turbidities. This study also
demonstrated that the turbidity levels from the sedimentation basin increased steadily as the
overflow rate was increased from 0.19 to 0.37 gpm/ft2 when no polymer was added. In contrast,
the turbidity levels from the sedimentation basin only increased marginally as overflow rates
were increased when polymer was added.
Plate Settler Case Study (Hess, et al., 1993)
Plate settlers were used to treat spent filter backwash water from a direct filtration plant. The
backwash solids were of low density, were highly organic, and had poor settling characteristics.
The plate settlers were operated at a maximum of 0.25 gpm/ft2 with polymer addition. The
treated water averaged less than 1.5 NTU and was returned to the headworks, where the raw
water is typically less than 1.0 NTU.
Advantages
When properly designed and operated, the sedimentation unit can remove significant
amounts of turbidity and particles, including Cryptosporidium and Giardia. If overflow
rates are low enough, additional contaminants, such as disinfection byproduct precursors,
may also be removed.
Disadvantages
If not properly designed and operated, solids removal capabilities will be compromised.
Adequate equalization and storage should be provided to avoid this situation. Sludge
removal should be conducted frequently enough to avoid compromising the active storage
and treatment capability of the sedimentation basin.
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10. Treatment of Recycle Streams
Sedimentation with Polymer Addition Case Study (Moss, 2000)
The Salt Lake City Public Utilities Department (SLCPUD) examined optimization of its recycle
practices. SLCPUD recycles spent filter backwash at all three of its plants. The spent filter
backwash passes through clarifiers prior to its return to the plant headworks. Turbidity levels in
filtered water did not exhibit significant changes during recycle; however, increased particle
counts in filtered water were very noticeable during recycle events. At one plant, particle counts
in the filtered water (measured as particles greater than 2 (im) went from approximately 1,800
prior to recycle to greater than 8,000 during recycle. Recycle of spent filter backwash also
resulted in an increase of Cryptosporidium and Giardia in plant influent as compared to raw
water. SLCPUD examined a combination of treatment strategies to reduce the impacts of recycle
on its plants. Optimization consisted of increasing settling time, polymer addition, adjusting rate
of return at one of the plants, and adjusting coagulant dose at one of the plants in response to
streaming current monitoring data. SLCPUD conducted jar testing to determine which polymer
to feed to the spent filter backwash. A high charge anionic polymer was selected for two plants
and a medium charge anionic polymer was selected for the other plant. The polymer dose at all
plants was 0.1 mg/L. All plants exhibited a decrease in particle counts in filtered water due to
optimization of recycle practices. Also, turbidity and TOC concentrations in the recycled spent
filter backwash decreased as a result of optimization.
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10. Treatment of Recycle Streams
10.7.2 Microsand-Assisted Sedimentation
Microsand-assisted settling is not a new principle. The process has been used in the water
treatment industry since the 1970's and has been identified by numerous names such as
ballasted floe, ballasted sand, and Actifloฎ. Microsand-assisted sedimentation relies on
improved settling through the addition of microsand and a coagulant chemical to improve
flocculation and clarification. The microsand is separated and recycled through the system
numerous times. Figure 10-7 shows the typical process of microsand-assisted
sedimentation. This process may have application in facilities that need clarification and do
not have the space for conventional sedimentation or that need rapid startup clarification
ability for variable source water qualities.
Advantages
According to Kawamura (2000) the advantages of this process are: requires a small
footprint, has good performance, has a very quick process start up time, and may have
reduced capital costs. As a result, systems may want to consider microsand-assissted
sedimentation versus other sedimentation processes if space or money is limited.
Disadvantages
The disadvantages include heavy dependence on mechanical equipment and short
processing time, dependence upon power, and may require higher dosage of coagulant.
Figure 10-7. Microsand-Assisted Sedimentation Process for Recycle Streams (In
Addition to the Main Treatment Train)
Spent Filter
Backwash or Other ^
Recycle Stream
Eqi
(1) Equalization is
alizatior
Dptiona
Polymer
, I
cJo
Coagulatio
(1) T
Microsand
I.
n
r^Jt-^-i r^le^ r^Jfcr^l
W^f0
Flocculation
Supernatant
k ^oHimontitinn k To Main
Treatment
k^ ^^ Train
1 ^\ ^^
1
Residuals/Sludge to
Solids Handling for
Microsand Recovery
10.7.3 Dissolved-Air Flotation
Dissolved-air flotation (DAF) is most commonly used in two applications: potable water
treatment as a clarification step prior to filtration, and wastewater treatment for sludge
thickening. The DAF process is another form of solids separation and may be an
appropriate technology for treating recycle streams.
In a typical water treatment system installation, DAF replaces sedimentation in a
conventional treatment train. The upstream and downstream processes are similar; the raw
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10. Treatment of Recycle Streams
water is coagulated and flocculated, and the DAF effluent is sent to the filters. A similar
process train is likely to be used for treating recycle streams, as shown in Figure 10-8, where
the treated stream is recycled to the head of the plant.
Figure 10-8. Dissolved-Air Flotation Process for Recycle Streams (In Addition to the
Main Treatment Train)
Air Saturation
Tank
Chemical
Addition(2)
Compressor
Spent Filter
Backwash or Other -
Recycle Stream
Coagulation
Flocculation (3)
Dissolved-Air
Flotation Unit
To Main
Treatment
Train
Equal ization(1)
(1) Equalization is optional but will allow reduction of dissolved-air flotation treatment unit size.
(2) Chemical addition is optional but has been shown to enhance treatment of the recycle stream.
(3) Flocculation is optional.
In the DAF process itself, a side-stream is saturated with air at high pressure and then
injected into the flotation tank to mix with the incoming recycle stream. 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 (also called float) at the surface
of the tank. The float is removed either by a mechanical scraper or by flooding the tank over
a weir. The clarified water is collected near the bottom of the tank.
DAF can be highly effective at removing low-density particles such as algae, protozoan
cysts, coagulated natural organic material, and alum floe from low-turbidity, soft waters. In
a bench-scale study on Cryptosporidium removal, DAF was shown to achieve at least 2-log
removal of oocysts under most process conditions (Plummer, et al., 1995). In a pilot-scale
study of DAF and lamella sedimentation, the average log removals by DAF for Giardia and
Cryptosporidium were 2.4 and 2.1 respectively, compared to 1 to 1.2 and 0.91 to 1.1,
respectively, for lamella sedimentation (Edzwald, et al., 2000). However, this study was
conducted on a main treatment process rather than a recycle stream. These results were
included in another study by Edzwald, et al., (2001). The same considerations for sludge
removal, storage, and equalization apply to DAF, as discussed in Section 10.7.1.
Advantages
DAF has several advantages over sedimentation:
More compact: DAF loading rates are high, so that much smaller tanks can be used
than in sedimentation.
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10. Treatment of Recycle Streams
Shorter startup time: The smaller tanks result in good effluent quality in less time.
Lower chemical dose: In many cases DAF requires less coagulant than
sedimentation.
Shorter flocculation time: Flocculation times for DAF are normally one-half to one-
fifth of those for sedimentation.
Thicker sludge: The floated sludge from a DAF unit typically has a much higher
solids concentration than does sludge from a sedimentation basin.
Disadvantages
The main disadvantage of DAF compared to sedimentation is that it requires more complex
equipment, particularly the air saturation and recycle control equipment. A higher level of
skill is needed to operate and maintain this equipment than is needed for equipment
associated with sedimentation facilities.
As with sedimentation, the need for chemical pretreatment and flocculation prior to DAF
treatment of the recycle stream is uncertain. DAF normally requires less coagulant and
shorter flocculation times than does sedimentation, and particles in spent filter backwash
water have already been coagulated and flocculated to some degree in the main treatment
train. If DAF can provide adequate treatment without pretreatment, then DAF becomes a
cost-effective option to treat recycle streams.
DAF Case Study (Cornwell, et al, 2001)
A bench-scale study was conducted using
DAF with polymer addition to treat spent
filter backwash. The pilot DAF plant could
treat spent filter backwash at a rate between
36 and 54 gpm and had varying surface
overflow rates and recycle ratio range
capabilities. The spent filter backwash fed to
the pilot plant had turbidity levels ranging
from 30 to 300 NTU. The DAF was able to
produce clarified effluent with turbidities of
1 to 2 NTU (99% or 2-log turbidity
reduction) with 0.3 mg/L of polymer at
surface overflow rates of 4 to 5 gpm/ft2. A
DAF recycle ratio of 10% was found to be
adequate for effective treatment.
DAF Case Study (Lew andPatawaran 2000)
The Betasso Water Treatment Plant (Boulder,
CO) selected DAF as the best treatment
technology for spent filter backwash after
assessing six alternative treatment types. The
DAF process was able to achieve turbidity
levels of 1 NTU on a consistent basis without
extensive chemical manipulation. With
consistent dosage of polymer, DAF was able to
adsorb significant turbidity spikes and varying
loading rates without compromising effluent
water quality.
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10. Treatment of Recycle Streams
10.7.4 Granular Bed Filtration
Granular bed filtration may be an effective treatment method for spent filter backwash water
and other recycle streams. Pretreatment by chemical addition with or without flocculation
prior to the filter should be practiced. The high solids content of some backwash waters
may result in unacceptable short filter runs, suggesting that clarification is needed prior to
filtration, but higher-quality spent filter backwash waters may be quite amenable to filtration
without sedimentation. A process schematic diagram for granular bed filtration, with
pretreatment by chemical mixing, flocculation, and sedimentation, is shown in Figure 10-9.
Pumping facilities may be required to convey the treated recycle stream depending on site-
specific conditions.
Figure 10-9. Granular Bed Filtration Process for Recycle Streams (In Addition to the
Main Treatment Train)
Chemical
Addition
sPentFilter 1 1 999 Sedimentation
Coagulation Flocculation (2) ^^ ^^
' ' [sludge
Equalization(l) y
Residuals/Sludge to
Solids Handling or '
Disposal T^ Filter Granu
Backwash Fil
arBed
er
(2) Flocculation is optional but may enhance treatment. ^
Filtered Water
(3) Sedimentation unit is optional but may enhance treatment. To Main
Treatment
Train
Advantages
The expected advantage of granular bed filtration over sedimentation and DAF is that it has
a much higher rate of particle removal. Depending on water quality, pretreatment, filter
media, and loading rates (among other factors), filtration of recycle streams may remove
particles at or above the level achieved by the main treatment train.
Disadvantages
The disadvantages of filtration, compared to either sedimentation or DAF alone, are its high
cost, process complexity, and greater volume of waste. Waste would be generated through
the backwash of the recycle stream filter.
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10. Treatment of Recycle Streams
Granular Filtration Case Study (MacPhee, et al, 2000)
Several treatment scenarios were examined for spent filter backwash. The treatment scenarios
consisted of sedimentation with polymer and DAF with polymer followed by granular media
filtration. This treatment scenario provided 2.2 to 3.0 log reduction of turbidity and 2.4 to 4.4
particle log reduction of the spent filter backwash.
10.7.5 Membrane Filtration
A membrane treatment process, such as microfiltration (MF) or ultrafiltration (UF), is
capable of very high levels of particle removal. MF has been used for a variety of industrial
applications and, in recent years, has been used for particle removal in potable water
treatment. Limited information is available on MF treatment of spent filter backwash water
and other recycle streams, but research continues on this technology.
Microfilters provide an absolute barrier to particulates by straining them from the flow
stream at the membrane surface. Nominal pore sizes for microfilters fall in the range of 0.05
to 5.0 |im. Microfilters with smaller pore sizes (<0.2 |im) can remove virtually all bacteria
and protozoa, including Cryptosporidium and Giardia (Jacangelo and Buckley, 1996). The
removal of viruses is more highly dependent upon the specific virus, membrane, and water
quality (Jacangelo and Buckley, 1996), though the removal of viruses may be less of a
concern because of their high susceptibility to inactivation by most disinfectants.
Depending on the membrane and water quality, MF membranes can remove some natural
organic matter (NOM), DBF, and TOC. The removal of NOM by MF membranes can also
be improved by coagulation. NOM found in spent filter backwash water, having previously
been coagulated to an extent, may be removed to a good degree by MF. Some membranes
are susceptible to fouling by chemicals and chemical use should be carefully evaluated for
each membrane type. A simple process schematic diagram for membrane filtration of
recycle streams is shown in Figure 10-10. As noted above, microfiltration may require
chemical pretreatment, depending on the recycle stream characteristics and treatment goals.
Also, facilities for membrane cleaning would be required.
Advantages
One advantage of MF for recycle stream treatment is that it can normally treat wide
variations in influent water quality with little or no adjustment to the process. Another
advantage is that MF systems are compact and available as prefabricated, modular units that
can easily be expanded. Also, hydraulic head is not typically "broken" in membrane
systems, so a unit may be located at any elevation and require only one pumping facility.
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Disadvantages
The primary disadvantage of a MF system, when compared to sedimentation or DAF, is the
greater complexity of its equipment. Another disadvantage is that membranes are subject to
fouling from bacteria, chlorine residual, coagulants, and polymers. The contaminants
contained in the recycle stream may be substantial enough to foul the membranes.
Therefore, extensive pilot testing should be conducted on the membrane for each type of
recycle stream to evaluate potential fouling.
Figure 10-10. Membrane Treatment Process for Recycle Streams (In Addition to the
Main Treatment Train)
Spent Filter
Backwash or Other
Recycle Stream
Equalization(l)
Residuals/Sludge to
Solids Handling or
Disposal
(1) Equalization is recommended to provide some treatment (sedimentation) and reduce
the size of membrane footprint.
(2) Depending on the type of membrane, pumps may be needed.
Chemical pretreatment may be necessary to remove organics but chemicals may cause
membrane fouling.
Microfiltmtion (MF) Case Study (Thompson, et al, 1995)
Thompson, et al. (1995) reported on pilot-scale testing of MF for recycle stream treatment. A
membrane with a nominal pore size of 0.2 |im was used in all tests. In these tests, spent filter
backwash water with turbidities around 500 NTU were reduced to less than 5 NTU. At another
plant, MF was used to treat a combination of spent filter backwash water and clarifier sludge
blowdown from a conventional treatment train. The recycle stream was spiked with Giardia
cysts and Cryptosporidium oocysts before MF treatment. No cysts, oocysts, or coliforms were
detected in the MF-treated water, and turbidities were consistently 0.1 NTU. High levels of
particle removal were also shown using particle counters.
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10. Treatment of Recycle Streams
Ultmfiltmtion (UF) Case Study (Shealy, et al, 2000)
Several recycle water treatment alternatives were evaluated at the Orangeburg, SC plant. After
narrowing the alternatives, the system chose to pilot test micro/ultrafiltration membrane
treatment. The main objectives of the study were: contaminant removal and membrane flux
rate, feasibility of full-scale application, and potential capital and operating costs. After months
of research and evaluation, membrane treatment with immersed UF technology was selected for
full- scale implementation. The conclusion was that, coupled with equalization basins, UF
membranes produced excellent treated water quality. The permeate from the membrane unit is
proposed to discharge to the head of the plant.
Microfiltration Case Study (Taylor, et al., 2000)
Bench-scale testing of MF to treat spent filter backwash water was conducted at the University
of Central Florida. Backwash waters from nine water treatment plants across the United States
were used in the testing. The treatment unit used in the study was an MF unit fitted with a
single microfilter membrane (surface area of 1 m2). One liter of filtrate water was collected
approximately five minutes into filtration for chemical water quality analysis. True color, UV-
254, total suspended solids (TSS), turbidity, and particle counts were the parameters measured.
The changes in UV-254 and true color were not significant and therefore not considered a
consequence of treatment. However, turbidity and TSS were significantly reduced by MF.
Water turbidity was reduced from 31-168 NTU to 0.02-0.16 NTU. TSS was reduced from 66-
206 mg/L to 1-3 mg/L (the limit of accurate TSS measurements).
A cost estimate for applying membrane filtration (MF and UF) to the treatment and recovery of
spent filter backwash water was included in the study. Estimates for flows of 0.01, 0.1, 1.0, and
10.0 MGD were developed. The membrane system cost included feed water pumps, backwash
and recycle pumps, air compressor, membrane modules and racks, piping and valves,
instrumentation and controls, and the membrane cleaning system. The researchers found that
unit capital and O & M costs decreased significantly by capacity and varied significantly by
source. Unit capital costs varied from $10.35/gpd at 0.01 MGD to $0.38/gpd at 10 MGD. Unit
O & M costs varied from $2.68/Kgal at 0.01 MGD to $0.16/Kgal at 10 MGD.
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10. Treatment of Recycle Streams
10.7.6 Disinfection
Disinfection can be a barrier to the recycling of pathogens from recycle streams. Results
from the AWWA utility survey show that a small percentage of plants that do recycle
practice disinfection of those streams (Pedersen and Calhoun, 1995). The most common
disinfectant used by far was chlorine. The California Department of Health Services
recommends that disinfection be considered for recycle streams (CDHS, 1995).
The main issues to be addressed when considering disinfection of recycle streams are:
The level of inactivation to be provided for specific organisms;
Whether disinfection is to be used alone or with a solids removal process; and,
The potential impacts of recycle stream disinfection on finished water quality,
particularly the formation of DBFs.
If disinfection is to be applied to
recycle streams, the required level
of disinfection and inactivation
must be known in order to size the
facility. No guidelines have yet
been issued in regard to pathogen
inactivation or removal from
recycle streams. Under the current
SWTR, IESWTR, and
LT1ESWTR, the amount of
disinfection provided to water
supplies is determined by the
inactivation and removal of
Giardia and viruses. Credit is
given for the removal of pathogens
by properly operated treatment
processes, such as filtration, and
credit for inactivation is given
based on the disinfectant
concentration and contact time
provided.
Disinfection Case Study (Cornwell, et al, 2001)
The oxidant demand of both potassium permanganate
and chlorine dioxide was examined for spent filter
backwash samples from five participating water
utilities. Overall, the potassium permanganate
demands were approximately 5.5 times higher for
spent filter backwash with particles than in samples
without particles. Potassium permanganate
disinfection at 2,400 mg-min/L (CT value) with and
without particles resulted in Cryptosporidium
inactivations of 0.21 and 0.27-log, respectively. The
presence of particles in spent filter backwash increased
the chlorine dioxide demand by a factor of four when
compared to samples without particles. Chlorine
dioxide dosed at 115 mg-min/L (CT value) produced
2.7 and 2.1-log inactivation of Cryptosporidium for
spent filter backwash with and without particles,
respectively. Ultraviolet (UV) treatment was also
examined for its effectiveness on Cryptosporidium in
clarified spent filter backwash with turbidities between
10 and 14 NTU. UV doses as low as 3 milliJoules per
square centimeter used in collimated beam
experiments resulted in Cryptosporidium inactivations
greater than 4 logs.
For the treatment of recycle
streams, the removal and/or
inactivation of Cryptosporidium,
Giardia, and viruses is a concern.
Disinfection options and inactivation levels are well known for Giardia and viruses. Ozone
and UV both appear to provide inactivation of Cryptosporidium.
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10. Treatment of Recycle Streams
Advantages
Pathogens are contaminants of concern in recycle streams. Depending on the type and
amount of disinfectant used, Cryptosporidium, Giardia, and/or viruses can be inactivated.
More advantages may be realized through disinfection of recycle streams as more studies are
conducted on this practice.
Disadvantages
Recycle stream disinfection should be examined for its potential effects on the main
treatment train and finished water quality. Untreated recycle streams can have significant
concentrations of TTHM precursors and TOC (Cornwell and Lee, 1993). If the recycle
stream is treated with chlorine, then recycling may cause problems for the treatment plant in
meeting DBF limits. The potential formation of DBFs through disinfection should be
considered. Chapter 7 provides more information on DBF and DBF precursor levels in
recycle streams.
10.8 COMPARISON OF TREATMENT OPTIONS
Seven different treatment scenarios for spent filter backwash at seven different treatment
plants were examined (Cornwell, et al., 2001). Table 10-2 presents the turbidity and particle
log reductions obtained from each treatment type. The results in Table 10-2 are based on
both pilot-scale and full-scale plants. Sedimentation with polymer, DAF with polymer,
granular media filtration with pretreatment, and membrane microfiltration appear to provide
the best turbidity and particle reduction. Table 10-2 also presents relative costs of each
treatment type. Membrane microfiltration was the most expensive treatment option based
on this study. However, costs will vary from plant to plant depending on site-specific
conditions, recycle stream characteristics, and desired level of treatment.
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10. Treatment of Recycle Streams
Table 10-2. Spent Filter Backwash Turbidity and Particle Log Reductions by
Treatment Type
Treatment Process
Sedimentation
without polymer3
Dissolved Air
Flotation (DAF)
without polymer
Sedimentation with
polymer3
DAF with polymer
Coagulation/
followed by
Sedimentation3
Granular Media
Filtration with
pretreatment4
Membrane
Microfiltration
Turbidity Log
Reduction
0.1 to 0.8
0.7 to 1.4
1.4 to 2.3
1.7 to 2.7
0 S tn 1 7
2.2 to 3.0
2.6 to 3.9
Particle Log
Reduction
0.2 to 0.9
0.8 to 1.7
1.9 to 3.3
1.9 to 3. 5
0 4 tn 7 1
2.4 to 4.4
1.6 to 3. 5
Relative Cost
Ranking2
1
2
3
4
5
1 Treatment processes were conducted at seven different sites and consisted of both pilot-scale and
full-scale studies.
2Relative costs are presented with 1 being the lowest-cost treatment process and 5 being the highest-
cost treatment process. Costs were not available for DAF without polymer and
coagulation/flocculation followed by sedimentation.
3Sedimentation consisted of either tube settlers or plate settlers.
4Pretreatment consisted of either sedimentation with polymer or DAF with polymer.
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10. Treatment of Recycle Streams
10.9 REFERENCES
Ashcroft, C.T., et al. 1997. Modifications to Existing Water Recovery Facilities for
Enhanced Removal of Giardia and Cryptosporidium. Proceedings of Conference on Water
Residuals and Biosolids Management: Approaching the Year 2000. WEF/AWWA.
AWWA. 1998. Spent Filter Backwash Water Survey. Denver, CO.
AWWA. 2002. Self Assessment of Recycle Practices. Denver, CO.
AWWA/ASCE. 1990. Water Treatment Plant Design. Second Edition. McGrawHill.
New York, NY.
AWWA/ASCE. 1998. Water Treatment Plant Design. Third Edition. McGrawHill. New
York, NY.
CDHS. 1995. California Safe Drinking Water Act, California Health and Safety Code,
Articles 4 and 5.
Cornwell, D., M. MacPhee, N. McTigue, H. Arora, G. DiGiovanni, M. LeChevallier, and J.
Taylor. 2001. Treatment Options for Giardia, Cryptosporidium, and Other Contaminants in
Recycled Backwash Water. AWWARF. Denver, CO.
Cornwell, D., and R. Lee. 1993. Recycle Stream Effects on Water Treatment. AWWARF
Report #90629. Denver, CO.
Edzwald, J.K., I.E. Tobiason, L.M. Parento, M.B. Kelley, G.S. Kaminski, HJ. Dunn, and
P.B. Galant. 2000. Giardia and Cryptosporidium Removals by Clarification and Filtration
Under Challenge Conditions. Journal AWWA 92(12):70-84.
Edzwald, J.K., I.E. Tobiason, M.B. Kelley, HJ. Dunn, P.B. Galant, and G.S. Kaminski.
2001. Impacts of Filter Backwash Recycle on Clarification and Filtration. AWWARF and
AWWA. Denver, CO.
Hess, A., A. Affmito, H. Dunn, P Gaewski, and E. Norris. 1993. Relationship of WTP
Residual Characteristics, Facility Design and Operational Practices on the Performance of
Residual Treatment Facilities at a Direct Filtration Plant. Proceedings of the Joint Residuals
Conference. AWWA/WEF. Phoenix, Arizona.
Jacangelo, J. G., and C. A. Buckley. 1996. Microfiltration. Water Treatment Membrane
Processes, Ch. 11, AWWARF, Lyonnaise des Eaux, and Water Research Commission of
South Africa. McGraw-Hill, Inc., New York, NY.
Kawamura, S. 2000. Integrated Design and Operations of Water Treatment Facilities.
Second Edition. John Wiley & Sons, Inc., New York, NY.
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10. Treatment of Recycle Streams
Lew, J., and R. Patawaran. 2000. Pilot Identifies Best Backwash Pretreatment. AWWA.
Opflow. Denver, CO.
Logsdon, G.S., A.F. Hess, MJ. Chipps, and AJ. Rachwal. 2000. Filter Backwash Water
Processing Practices. Proceedings from the AWWA Annual Conference. Denver, CO.
MacPhee, M., et al. 2000. Critical Assessment of Alternatives for Treatment of Spent Filter
Backwash Water. Proceedings AWWA Water Quality Technology Conference. Salt Lake
City, UT.
Moss, Linda. 2000. Backwash Water Return Effects: Evaluation and Mitigation.
Proceedings from the AWWA Water Quality Technology Conference. Salt Lake City, UT.
Narasimhan, R., et al. 1997. Design Criteria Evaluation for Washwater Treatment and
Water Residuals Thickening Processes. Proceedings of Conference on Water Residuals and
Biosolids Management: Approaching the Year 2000. WEF/AWWA.
Nielson, J.C., R. O. Schwarzwalder, and T. Wolfe. 1995. Evaluation of Waste Stream
Recycling Alternatives. 1994 AWWA Annual Conference Proceedings. Denver, CO.
Pedersen, D. W., and B. Calhoun. 1995. Do You Recycle? Results of AWWA's Recycle
Practices Survey. AWWA Annual Conference.
Plummer, Jeannie D., J. K. Edzwald, and M. B. Bailey. 1995. Removing Cryptosporidium
by Dissolved-Air Flotation. Journal AWWA. (87)(9).
Shealy, C. E., F. L. Yandle, and H. G. Rutland. 2000. Membrane Treatment for Water
Plant Residuals Handling and Water Reclamation. Proceedings from the AWWA Annual
Conference. Denver, CO.
SPEHM. (Great Lakes- Upper Mississippi River Board of State Public Health and
Environmental Managers). 1997. Recommended Standards for Water Works ("Ten State
Standardss"). Health Education Services. Albany, NY.
Taylor, J., C.D. Norris, and L.A. Mufford. 2000. Recovery of Backwash Water by Size
Exclusion Membrane Filtration. Proceedings from the AWWA Water Quality Technology
Conference.
Thompson, M. A., J. C. Vickers, Dr. M. R. Wiesner, and Dr. J. L. Clancy. 1995. Membrane
Filtration for Backwash Water Recycle. AWWA Annual Conference on Water Quality
Proceedings, pp. 1051-1064.
U.S. EPA. February 2000. Cost and Technology Document for the Proposed Long-Term 1
Enhanced Surface Water Treatment Rule and Filter Backwash Recycling Rule. Office of
Ground Water and Drinking Water.
United Kingdom Water Industry Research. 1998. Guidance Manual Supporting the Water
Treatment Recommendations from the Badenoch Group of Experts on Cryptosporidium.
First Edition. UK Water Industry Research Limited, London.
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APPENDIX A.
GLOSSARY
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Preceeding Page Blank
Appendix A. Glossary
Glossary of Terms Used in this Manual:
air scour- Introduction of air to the full filter area from orifices located under the filter
medium, in order to improve the effectiveness of the backwashing operation and to improve
cleaning of media during filter backwash.
backwash- The process of reversing the flow of water back through the filter media to
remove the entrapped solids.
batch-flow sedimentation- One or more basins sized to receive a volume of flow, such as
spent filter backwash water, in a specific period of time. The flow is detained for a specific
period of time to allow sedimentation, and then the tank is emptied.
best available technology (BAT)- As defined in 40 CFR 141.2, the best technology,
treatment techniques, or other means which the [U.S. EPA] Administrator finds, after
examination for efficacy under field conditions and not solely under laboratory conditions,
are available (taking cost into consideration).
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.
centrate- Water separated from the solids by a centrifuge.
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.
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.
contact clarification- A water treatment process in which flocculation and clarification
(and often the rapid mix) are combined in one unit, such as an upflow solids contactor or
contact clarifier.
continuous flow sedimentation- A process by which flow is received on a continuous
basis at its normal flow rate and solids are allowed to settle.
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.
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Appendix A. Glossary
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 chlorine and chloramine disinfectants. When water containing these
cysts is ingested, the protozoan causes a severe gastrointestinal disease called
cryptosporidiosis.
decant- To draw off the liquid from a basin or tank without stirring up the sediment in the
bottom.
dewatering processes- Mechanical and non-mechanical methods used to remove excess
liquids from residual solids in order to concentrate the solids. These methods include belt
presses, centrifuges, filter presses, vacuum presses, lagoons, and monofill.
diatomaceous earth filtration- As defined in 40 CFR 141.2, a process resulting in
substantial paniculate removal 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.
direct recycle- The return of recycle flow within the treatment process without first passing
the recycle flow through treatment or equalization.
disinfectant- As defined in 40 CFR 141.2, any oxidant, including but not limited to
chlorine, chlorine dioxide, chloramines, and ozone added to water in any part of the
treatment or distribution process, that is intended to kill or inactivate pathogenic
microorganisms.
disinfection- As defined in 40 CFR 141.2, a process which inactivates pathogenic
organisms in water by chemical oxidants or equivalent agents.
disinfection by-products (DBFs)- Organic compounds formed by the reaction of the
disinfectant, natural organic matter, and the bromide ion during water disinfection process.
Regulated DBFs include TTHMs, HAASs, bromate, and chlorite.
dissolved-air flotation- A method of solids separation, whereby a side stream is saturated
with air at high pressure and then injected into the flotation tank to mix with the incoming
water stream. As the air bubbles rise to the surface they attach to floe particles and create a
sludge layer at the surface of the tank, which is then removed for disposal.
equalization- A method used to control the flow of water or residual stream by providing
storage and detention time between the point of origin and the return location of the water or
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Appendix A. Glossary
residual stream. The water or residual stream is then removed from the storage unit at a
controlled, uniform rate.
filter-to-waste- The practice of discarding filter effluent that is produced during the "filter
ripening" period immediately after backwash due to its impaired quality.
filtrate- The water separated from the solids by a belt filter press or the liquid that has
passed through a filter.
filtration- As defined in 40 CFR 141.2, a process for removing particulate matter from
water by passage through porous media.
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.
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.
ground water under the direct influence of surface water (GWUDI)- 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.
haloacetic acids (HAA5)- As defined in 40 CFR 141.2, the sum of the concentrations in
milligrams per liter of the haloacetic acid compounds (monochloroacetic acid, dichloroacetic
acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid), rounded to two
significant figures after addition.
hydraulic surge- A sudden increase in flow to the plant or treatment process.
influent water- Raw water plus recycle streams.
ion-exchange regenerant- A chemical solution used to restore an exhausted bed of ion
exchange resins to the fully ionic (regenerated) form necessary for the desired ion exchange
to again take place effectively.
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Appendix A. Glossary
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.
lagooning- The placement of solid or liquid material in a basin, reservoir, or artificial
impoundment for purposes of storage, treatment, or disposal.
leachate- The underflow from a dewatering unit such as a sludge-drying bed or monofill.
liquids from dewatering processes- A stream containing liquids generated from a unit
used to concentrate solids for disposal.
membrane concentrate- The reject stream generated when the source water is passed
through a membrane for treatment.
membrane filtration- A filtration process (e.g., reverse osmosis, nanofiltration,
ultrafiltration, and microfiltration) using tubular or spiral-wound elements that exhibits the
ability to mechanically separate water from other ions and solids by creating a pressure
differential and flow across a membrane with an absolute pore size <1 micron.
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.
microsand- A small-grain sand used to improve settling.
minor streams- Waste streams that result due to spills, laboratory analyses, washdown of
plant facilities, leaks, and other similar streams that are small in volume.
monofill- An ultimate disposal technique for water treatment plant sludge in which the
sludge is applied to a landfill for sludge only.
operating capacity- The maximum finished water production rate approved by the State
drinking water program.
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.
pilot plant- A small-scale water treatment plant set up on a raw water source to determine
the feasibility and impacts of a treatment scheme for a given water supply. Pilot plants are
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Appendix A. Glossary
used to test alternative technologies and experiment with chemical dosages for new water
treatment plants or upgrades to existing plants.
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).
pressate- The water separated from the solids by a filter press.
presedimentation- A water treatment process in which solid particles are settled out of the
water in a clarifier or sedimentation basin prior to entering the treatment plant.
raw water- Source water prior to any treatment or addition of chemicals.
recycle- The act of returning a residual stream to a plant's primary treatment process.
recycle stream- Any water, solid, or semi-solid generated by a plant's treatment processes,
operational processes, and residual treatment processes that is returned to the plant's primary
treatment process.
recycle notification- Information on recycling practices that must be provided to the State
by conventional and direct filtration water treatment plants that recycle spent filter
backwash, thickener supernatant, or liquids from dewatering processes, as required in 40
CFR141.76(b).
schmutzdecke- The surface dirt cake of accumulated particulates, including a variety of
living and non-living micro- and macroorganisms, on top of a slow sand filter, that assists in
turbidity removal.
sedimentation- As defined in 40 CFR 141.2, a process for removal of solids before
filtration by gravity or separation. (Note: The Federal definition refers to the sedimentation
process used in the main treatment train, but sedimentation can also be used for recycle
streams.)
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 m/h) resulting in
substantial particulate removal by physical and biological mechanisms.
sludge thickener- A tank or other piece of equipment designed to concentrate water
treatment sludges.
spent filter backwash water- A stream containing particles that are dislodged from filter
media when water is forced back through a filter (backwashed) to clean the filter.
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Appendix A. Glossary
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.
streaming current- A current gradient generated when a solution or suspension containing
electrolytes, polyelectrolytes, or charged particles passes through a capillary space, as
influenced by adsorption and electrical double layers. This phenomenon is used in
monitoring and controlling coagulation and flocculation processes.
subpart H systems- As defined in 40 CFR 141.2, public water systems using surface water
or ground water under the direct influence of surface water as a source that are subject to the
requirements of subpart H of the Code of Federal Regulations.
suspended solids- Solid organic and inorganic particles that are held in suspension by the
action of flowing water and are not dissolved.
thickener supernatant- A stream containing the decant from a sedimentation basin,
clarifier, or other unit that is used to treat water, solids, or semi-solids from the primary
treatment processes. The clarified water that exits the units after particles have been allowed
to settle out is thickener supernatant.
total organic carbon (TOC)- As defined in 40 CFR 141.2, total organic carbon in mg/L
measured using heat, oxygen, ultraviolet irradiation, chemical oxidants, or combinations of
these oxidants that convert organic carbon to carbon dioxide, rounded to two significant
figures.
total trihalomethane precursors- Organic materials in the raw water that promote the
formation of trihalomethanes.
total trihalomethanes (TTHM)- As defined in 40 CFR 141.2, the sum of the concentration
in milligrams per liter of the trihalomethane compounds (trichloromethane [chloroform],
dibromochloromethane, bromodichloromethane and tribromomethane [bromoform]),
rounded to two significant figures.
total trihalomethanes formation potential (TTHMFP)- A measure of the ability of a
water to create trihalomethanes.
trihalomethane (THM)- As defined in 40 CFR 141.2, one of the family of organic
compounds, named as derivatives of methane, wherein three of the four hydrogen atoms in
methane are each substituted by a halogen atom in the molecular structure.
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
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Appendix A. Glossary
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.
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 which cause the scattering and adsorption of light. In the waterworks field,
a turbidity measurement is used to indicate the clarity of water. Technically, turbidity is an
optical property of the water based on the amount of light reflected by suspended particles.
Turbidity cannot be directly equated to suspended solids because white particles will reflect
more light than dark-colored particles and many small particles will reflect more light than
an equivalent large particle.
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
References
Symons, J., L. Bradley, Jr., and T. Cleveland, Editors. 2000. The Drinking Water
Dictionary. AWWA. Denver, CO.
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APPENDIX B.
WORKSHEETS
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Appendix B. Worksheets
The following pages contain worksheets with guidelines that can be used to collect recycle
information and, if necessary, report it to the State/Primacy Agency. The worksheets
provided are:
Recycle Notification Form
Recordkeeping Form
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Appendix B. Worksheets
FILTER BACKWASH RECYCLING RULE
RECYCLE NOTIFICATION FORM
SYSTEM NAME
PWSID DATE
Check with your State or Primacy Agency to make sure this form is acceptable.
Does your system use conventional or direct filtration?
Does your system recycle spent filter backwash water, thickener supernatant, or liquids from
dewatering processes?
If you answered yes to both questions, please report the following:
1. What is the typical recycle flow (in gpm)?
2. What was the highest observed plant flow for the system in the previous year (in gpm)?
3. What is the design flow for the treatment plant (in gpm)?
4. Has the State determined a maximum operating capacity for the plant? If so, what is it?
5. Please include a plant schematic that shows:
the origin of all recycle flows (spent filter backwash, thickener supernatant, liquids from
dewatering processes, and any other);
the location where all recycle flows re-enter the treatment plant process; and,
the hydraulic conveyance used to transport all recycle flows.
Comments:
6. Are you requesting an alternate recycle location? Yes No
An alternate recycle location is one that does not incorporate all treatment processes of a
conventional filtration plant (coagulation, flocculation, sedimentation, and filtration) or direct
filtration plant (coagulation, flocculation, and filtration). The State or Primacy Agency must approve
the recycle location by June 8, 2004. Please contact your State or Primacy Agency on what
additional information may be needed.
Comments:
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Appendix B. Worksheets
FILTER BACKWASH RECYCLING RULE RECORDKEEPING FORM
SYSTEM NAME
PWSID
Operating Period1
Check with your State or Primacy Agency to make sure this form is acceptable.
Type of Recycle Stream
Spent Filter Backwash
Thickener Supernatant
Liquids from Dewatering Process
Other
Other
Frequency at which flow is returned2
Filter
Information
Average Duration of
Backwash (in minutes)
Maximum Duration of
Backwash (in minutes)
Average Backwash
Flow4 (in gpm)
Maximum Backwash
Flow4 (in gpm)
Run Length Time of
Filter5 (include units)
Criteria for Terminating
Filter Run6
Filter Number3
Example
Filters 1-6
20
22
2,000 gpm
2,000 gpm
36hrs
Taken off-line
when filter ef-
fluent turbidity
=0.2 NTU
Is treatment or equalization provided for recycle flows?
If yes, complete the following table.
Yes
No
Type of Treatment Provided
Physical Dimensions of Unit
Typical Hydraulic Loading
Rate
Maximum Hydraulic
Loading Rate
Type of Chemical Used
Average Dose of Chemical
(mg/L)
Frequency of Chemical
Addition
Frequency of Solids
Removal
Example
Spent filter backwash holding tank
100'xlOO'xlO'deep
20gpm/ft2
20gpm/ft2
Polymer
0.2 mg/L
During backwash events-
4 times per day
Once per month
See instructions on back.
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Appendix B. Worksheets
Instructions
1. Note the operating period for the information provided. Check with your State or Primacy
Agency for required operating period.
2. The frequency at which the recycle stream is returned can be described as continuous, once a
day, or as another frequency.
3. Fill out all information for each of your filters. If some or all filters are operated the same, note
the appropriate filter numbers.
4. The backwash flow is obtained by multiplying filter surface area (in ft2) by backwash rate
(gpm/ft2). Use the average backwash rate to get the average flow and the maximum backwash
rate to get the maximum flow. If the flow is varied throughout the backwash process, then the
average can be computed on a time-weighted basis as follows:
(Backwash Rate 1 X Duration 1) + (Backwash Rate 2 X Duration 2) + ...
Duration 1 + Duration 2+ ...
5. The filter run length time is the sum of the time that the filter is producing water between
backwashes.
6. Describe how run length time is determined. For example, is the run length based on head loss
across the filter, turbidity levels of filter effluent, a predetermined amount of time, or another
method?
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Appendix C.
Reporting Example for 3.0
MGD Plant
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Appendix C. Reporting Example for 3.0 MGD Plant
A 3.0 MGD plant consists of eight filters and the raw water flow is metered at the plant inlet
(see plant schematic in Figure C-l). The flowmeter records total daily flow in million
gallons and instantaneous flows in gallons per minute. The system recycles spent filter
backwash. The recycled flow is not equalized or treated and is piped directly to the plant
headworks. In order to meet daily demands, all eight filters are typically on-line between
7:00 a.m. and 6:00 p.m. The filters are loaded at 2.6 gpm/ft2. The design flow for the plant
is 2,080 gpm and the State-approved operating capacity is 3.0 MGD (or 2,080 gpm).
The plant is typically operated with one set of four filters being backwashed during late
night and early morning hours (between 11:00 p.m. and 5:00 a.m.) of one day and the other
set of four filters being backwashed the next day between 11:00 p.m. and 5:00 a.m. Each
filter is typically backwashed separately. Recycle flows are not metered but the operator
knows the backwash rate (15 gpm/ft2), filter surface area (100 ft2 each), and length of
backwash (15 minutes).
1. Determine Highest Observed Plant Flow
In order to obtain the highest observed plant flow, the system examined when the highest
observed raw water flow occurred and added in any recycle flow and examined when the
highest observed recycle flow occurred and added in raw water flow. Then, the two values
were compared and the overall highest plant flow was reported to the State.
A. Highest Plant Flow Based on Peak Raw Water Flow
The operator reviewed raw water flow meter records and determined that the peak raw water
flow occurred at 5:30 p.m. with a flow of 2,080 gpm. The highest observed raw water flow
occured at a time of day when recycle flows are not produced. Spent filter backwash is only
generated during the late night and early morning hours (11:00 p.m. and 5:00 a.m.) when the
filters are scheduled for backwashing.
B. Highest Plant Flow Based on Peak Recycle Flow
To account for recycle flows, the backwash information can be used as follows:
Backwash rate =15 gpm/ft2
Filter surface area =100 ft2
Backwash flow = (15 gpm/ft2) X (100 ft2) = 1,500 gpm
Since each filter is backwashed separately, the typical recycle flow is 1,500 gpm.
To properly identify the highest observed plant flow, the operator had to identify the raw
water flow that occurred during the return of spent filter backwash. The operator reviewed
the raw water flow meter records and determined that the raw water flow rate that occurred
between 11:00 p.m. and 5:00 a.m. was 1,000 gpm.
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Appendix C. Reporting Example for 3.0 MGD Plant
C. Compare Plant Flows Calculated Based on Raw Water and Recycle Flows
to Obtain Overall Highest Observed Plant Flow
The highest observed raw water flow was 2,080 gpm. This flow occurred between 7:00 a.m.
and 6:00 p.m. and does not include any recycle flows since recycling was not conducted
during this time period. The highest observed recycle flow was 1,500 gpm. This flow
occurred between 11:00 p.m. and 5:00 a.m. when filter backwashing was conducted and the
raw water flow during this time period was 1,000 gpm, resulting in a total plant flow of
2,500 gpm. Therefore, the highest observed plant flow occurred between 11:00 p.m. and
5:00 a.m. during backwashing and the flow was estimated to be 2,500 gpm. Note that this
flow exceeds the State-approved operating capacity of the plant of 2,080 gpm.
2. Determine Typical Recycle Flow
For this plant, the filters are consistently backwashed in the same manner. Each of 8 filters
is backwashed at a rate of 15 gpm/ft2 and each filter has a surface area of 100 ft2. No
equalization or treatment is provided and the flow is recycled directly to the head of the
plant. The typical recycle flow is:
(15 gpm/ft2) X (100 ft2) = 1,500 gpm
3. Complete Recycle Notification Form
The system completed the Recycle Notification Form and it appears on Page 118.
4. Complete Recordkeepinq Form
The system completed the Recordkeeping Form and it appears on Page 119.
5. Evaluation of Data
The State may want to request additional information on this system since its highest
observed plant flow exceeds the design flow and State-approved operating capacity. The
system may want to examine turbidity and/or particle count data (as a starting point) during
recycle events and assess if finished water quality is impacted. The system may also want to
consider equalization of recycle flows such that the peak spent filter backwash return rate to
the main treatment train does not create a plant capacity exceedance.
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Appendix C. Reporting Example for 3.0 MGD Plant
Figure C-l. Schematic for a 3.0 MGD Plant
Coagulant/Polymer
Feed
Flow
Meter
Raw Water Influent gง _
Peak Daily = 2.2 MG *
Peak Instantaneous = 2,080 gpm
Coagulation
Flocculation
Recycled Spent
Filter Backwash
1,500 gpm
8-inch Pipe
Spent filter backwash is
conveyed in an 8-inch
pipe
Sedimentation
Pump
Filtration
Disinfection"
Finished Water to
Distribution System
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Appendix C. Reporting Example for 3.0 MGD Plant
FILTER BACKWASH RECYCLING RULE
RECYCLE NOTIFICATION FORM
SYSTEM NAME Example 3.0 MGD Plant
PWSID DATE Dec 1,2003
Check with your State or Primacy Agency to make sure this form is acceptable.
Does your system use conventional or direct filtration? Yes_(conventional)
Does your system recycle spent filter backwash water, thickener supernatant, or liquids from
dewatering processes? Yes (spent filter backwash)
If you answered yes to both questions, please report the following:
1. What is the typical recycle flow (in gpm)? 1.500 gpm
2. What was the highest observed plant flow for the system in the previous year (in gpm)?
2.500 gpm
3. What is the design flow for the treatment plant (in gpm)? 2,080 gpm
4. Has the State determined a maximum operating capacity for the plant? If so, what is it? 2.080
5. Please include a plant schematic that shows:
the origin of all recycle flows (spent filter backwash, thickener supernatant, liquids from
dewatering processes, and any other);
the location where all recycle flows re-enter the treatment plant process; and
the hydraulic conveyance used to transport all recycle flows.
Comments: The highest observed plant flow of 2.500 gpm exceeds State-approved operating
capacity.
6. Are you requesting an alternate recycle location? Yes X No
An alternate recycle location is one that does not incorporate all treatment processes of a
conventional filtration plant (coagulation, flocculation, sedimentation, and filtration) or direct
filtration plant (coagulation, flocculation, and filtration). The State or Primacy Agency must approve
the recycle location by June 8, 2004. Please contact your State or Primacy Agency on what
additional information may be needed.
Comments:
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Appendix C. Reporting Example for 3.0 MGD Plant
FILTER BACKWASH RECYCLING RULE RECORDKEEPING FORM
SYSTEM NAME Example 3.0 MGD Plant
PWSID
Operating Period1 Jun 2003-Jun 2004
Check with your State or Primacy Agency to make sure this form is acceptable.
Type of Recycle Stream
Spent Filter Backwash
Thickener Supernatant
Liquids from Dewatering Process
Other
Other
Frequency at which flow is
4 times/day returned to main
returned2
treatment train
Filter
Information
Average Duration of
Backwash (in minutes)
Maximum Duration of
Backwash (in minutes)
Average Backwash
Flow4 (in gpm)
Maximum Backwash
Flow4 (in gpm)
Run Length Time of
Filter5 (include units)
Criteria for Terminating
Filter Run6
Filter Number3
1-8, all filters the
same
15 minutes
15 minutes
1,500 gpm
1,500 gpm
48hrs
Time, unless
individual filter
turbidity exceeds
0.2 NTU.
Is treatment or equalization provided for recycle flows?
If yes, complete the following table.
Yes
X
No
Type of Treatment Provided
Physical Dimensions of Unit
Typical Hydraulic Loading
Rate
Maximum Hydraulic
Loading Rate
Type of Chemical Used
Average Dose of Chemical
(mg/L)
Frequency of Chemical
Addition
Frequency of Solids
Removal
See instructions on back.
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Appendix C. Reporting Example for 3.0 MGD Plant
Instructions
1. Note the operating period for the information provided. Check with your State or Primacy
Agency for required operating period.
2. The frequency at which the recycle stream is returned can be described as continuous, once a
day, or as another frequency.
3. Fill out all information for each of your filters. If some or all filters are operated the same, note
the appropriate filter numbers.
4. The backwash flow is obtained by multiplying filter surface area (in ft2) by backwash rate
(gpm/ft2). Use the average backwash rate to get the average flow and the maximum backwash
rate to get the maximum flow. If the flow is varied throughout the backwash process, then the
average can be computed on a time-weighted basis as follows:
(Backwash Rate 1 X Duration 1) + (Backwash Rate 2 X Duration 2) + ...
Duration 1 + Duration 2+ ...
5. The filter run length time is the sum of the time that the filter is producing water between
backwashes.
6. Describe how run length time is determined. For example, is the run length based on head loss
across the filter, turbidity levels of filter effluent, a predetermined amount of time, or another
method?
EPA Guidance Manual 120 December 2002
FBRR Technical Guidance Manual
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Appendix D.
Reporting Example for 20
MGD Plant
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Appendix D. Reporting Example for 20 MGD Plant
A 20 MGD plant records total raw water flow at the plant inlet. The flowmeter can record
total daily flow and peak instantaneous flow. The recycle flow is measured separately prior
to the point where the recycle flow enters the raw water line (see plant schematic in Figure
D-l). The plant was designed for a flow of 14,000 gpm and has a State-approved operating
capacity of 20 MGD (or 14,000 gpm based on the design criteria for the plant). The plant
recycles spent filter backwash, that is equalized and partially treated, and sludge thickener
supernatant.
The system consists of 10 filters and each filter has a surface area of 350 ft2. The filters
have a maximum loading rate of 4 gpm/ft2 and filter run time is typically 48 hours. All
filters are on-line during peak demand, which typically occurs between 3:00 p.m. and 6:30
p.m. Filters are backwashed on a rotating schedule, with filter backwash occurring between
9:00 p.m. and 5:00 a.m. Five filters are individually backwashed every night at 2-hour
intervals. Filters are backwashed for 10 minutes at 20 gpm/ft2 in combination with surface
wash. Spent filter backwash recycle flows are equalized and partially treated in a 100,000-
gallon backwash holding tank. The outlet rate of the backwash holding tank is controlled
with an outlet rate of 1,500 gpm. Thickener supernatant is recycled intermittently during the
day (8:00 a.m. to 6:00 p.m.).
1. Determine Highest Observed Plant Flow
In order to obtain the highest observed plant flow, the system examined when the highest
observed raw water flow occurred and added in any recycle flow and examined when the
highest observed recycle flow occurred and added in raw water. Then, the two values were
compared and the overall highest plant flow was reported to the State.
A. Highest Plant Flow Based on Peak Raw Water Flow
A review of the previous year's records indicates the peak plant flow occurred on July 20.
The following values were recorded on July 20:
Highest observed raw water flow = 14,100 gpm (metered)
Time of day highest observed raw water flow occurred: 5:30 p.m.
Recycle flow that occurred at 5:30 p.m. = 100 gpm (all sludge thickener supernatant
and metered)
Sum raw water flow plus sludge thickener supernatant:
14,100 gpm + 100 gpm = 14,200 gpm
December 2002 123 EPA Guidance Manual
FBRR Technical Guidance Manual
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Appendix D. Reporting Example for 20 MGD Plant
B. Highest Plant Flow Based on Peak Recycle Flow
Total daily recycle flow = 0.36 MGD (includes both spent filter backwash and
sludge thickener supernatant.)
Highest observed recycle flow = 1,500 gpm (constant outflow rate from backwash
holding tank. Sludge thickener supernatant flow is not occurring at this time of day.)
Time of day highest observed recycle flow occurred: 9:00 p.m. to 6:00 a.m.
Raw water flow that occurred between 9:00 p.m. and 6:00 a.m. = 10,000 gpm
Sum recycle flow plus raw water flow:
1,500 gpm + 10,000 gpm = 11,500 gpm
C. Compare Plant Flows Calculated Based on Raw Water and Recycle Flows
to Obtain Overall Highest Observed Plant Flow
The highest observed plant flow occurred at 5:30 p.m. when the raw water flow reached a
peak of 14,100 gpm plus the recycle of sludge thickener supernatant at 100 gpm, for a total
highest observed plant flow of 14,200 gpm.
2. Determine Typical Recycle Flows
The recycle flow for this system varies significantly throughout the day, with 100 gpm being
the typical flow during the day (flow generated from the gravity thickener basin) and 1,500
gpm being the typical recycle flow returned to the main treatment train as spent filter
backwash (backwash is generated at 7,000 gpm and equalized to 1,500 gpm between 9:00
p.m. and 6:00 a.m.). The State may want to know the time of day these recycle flows occur
(not required by the FBRR, but may be useful to the State).
3. Complete Recycle Notification Form
The system filled out the Recycle Notification Form and it appears on Page 127.
4. Recycle Flow Information
A. Sludge Thickener Supernatant
Sludge thickener supernatant is recycled during the day between 8:00 a.m. and 6:00 p.m.
The overflow rate is controlled at 100 gpm and the flow is intermittent.
EPA Guidance Manual 124 December 2002
FBRR Technical Guidance Manual
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Appendix D. Reporting Example for 20 MGD Plant
B. Spent Filter Backwash
Spent filter backwash is partially treated and equalized prior to being recycled to the head of
the plant. Filters are backwashed individually at a rate of 20 gpm/ft2. The spent filter
backwash is generated at the following rate:
Spent filter backwash flow = (20 gpm/ft2) X (1 filter) X (350 ft2/filter) = 7,000 gpm
This flow is generated when the filters are backwashed between 9:00 p.m. and 5:00 a.m.
The spent filter backwash flow is equalized and partially treated and the return recycle flow
is maintained at 1,500 gpm.
5. Complete Recordkeepinq Form
The system completed the Recordkeeping Form and the information appears on Page 129.
Equalization information is also included in the Recordkeeping Form.
6. Data Evaluation
The system's highest observed plant flow was slightly greater than the design and State-
approved operating capacity. The system has had no treatment technique violations. The
equalization basin is working properly. The system will want to monitor peak flows and
avoid operating at a rate greater than the design operating capacity.
December 2002 125 EPA Guidance Manual
FBRR Technical Guidance Manual
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Appendix D. Reporting Example for 20 MGD Plant
Figure D-l. Schematic for a 20 MGD Plant
Flow
Meter
Raw Water Influent ^ฎ-,
Peak Daily - 19 8 MG '
i!
ฃ
(0
s
CO
QJ
I
8
Coagulant/Polymer
Feed
Coagulation Flocculation 1^^^^^
6-inch
'Recycle 1 ~~~$ " Pipe
Fhwmpt^r ^" Gravity Sludge
Pipe GidViLy pumped
Thickener
Supernatant Recycle Flow (
100gpm ",--ntnit-r
100,000-gal Backwash
Spent Filter V>< Holding Tank 7,000 gpm
Gravity 12-inch
inch Pipe RecVcle Flow Pipe
M 1,500 gpm P
Pumped X
Sludge Manually
Removed Every
2 Months
Filtration
Disinfection
Clearwell
Finished Water to
Distribution System
EPA Guidance Manual
FBRR Technical Guidance Manual
126
December 2002
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Appendix D. Reporting Example for 20 MGD Plant
FILTER BACKWASH RECYCLING RULE
RECYCLE NOTIFICATION FORM
SYSTEM NAME Example 20 MGD Plant
PWSID DATE Dec 1. 2003
Check with your State or Primacy Agency to make sure this form is acceptable.
Does your system use conventional or direct filtration? Yes (conventional)
Does your system recycle spent filter backwash water, thickener supernatant, or liquids from
dewatering processes? Yes (spent Filter backwash and thickener supernatant)
If you answered yes to both questions, please report the following:
1. What is the typical recycle flow (in gpm)? 100 gpm for sludge thickener supernatant and 1.500
gpm for spent filter backwash (rate at which spent filter backwash is returned)
2. What was the highest observed plant flow for the system in the previous year (in gpm)?
14.200 gpm
3. What is the design flow for the treatment plant (in gpm)? 14.000 gpm
4. Has the State determined a maximum operating capacity for the plant? If so, what is it?
14.000 gpm or 20 MGD
5. Please include a plant schematic that shows:
the origin of all recycle flows (spent filter backwash, thickener supernatant, liquids from
dewatering processes, and any other);
the location where all recycle flows re-enter the treatment plant process; and
the hydraulic conveyance used to transport all recycle flows.
Comments: _Sludge thickener supernatant and spent filter backwash are metered at the same
location. Spent filter backwash recycle flow is generated at 7.000 gpm. equalized, and returned
to the main treatment train at 1.500 gpm.
6. Are you requesting an alternate recycle location? Yes X No
An alternate recycle location is one that does not incorporate all treatment processes of a
conventional filtration plant (coagulation, flocculation, sedimentation, and filtration) or direct
filtration plant (coagulation, flocculation, and filtration). The State or Primacy Agency must approve
the recycle location by June 8, 2004. Please contact your State or Primacy Agency on what
additional information may be needed.
Comments:
December 2002 127 EPA Guidance Manual
FBRR Technical Guidance Manual
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Appendix D. Reporting Example for 20 MGD Plant
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Appendix D. Reporting Example for 20 MGD Plant
FILTER BACKWASH RECYCLING RULE RECORDKEEPING FORM
SYSTEM NAME
PWSID
Example 20 MGD Plant
Operating Period1 Jun 2003 to Jun 2004
Check with your State or Primacy Agency to make sure this form is acceptable.
Type of Recycle Stream
Spent Filter Backwash
Thickener Supernatant
Liquids from Dewatering Process
Other
Other
Frequency at which flow is returned2
Continuously between 9 pm and 6 am
Intermittently between 8 am and 6 pm
Filter
Information
Average Duration of
Backwash (in minutes)
Maximum Duration of
Backwash (in minutes)
Average Backwash
Flow4 (in gpm)
Maximum Backwash
Flow4 (in gpm)
Run Length Time of
Filter5 (include units)
Criteria for Terminating
Filter Run6
Filter Number3
Filters 1-10
10 minutes
10 minutes
7,000 gpm
7,000 gpm
48hrs
Time, unless
individual filter
turbidity exceeds
0.2 NTU.
Is treatment or equalization provided for recycle flows? X
If yes, complete the following table.
Yes
No
Type of Treatment Provided
Physical Dimensions of Unit
Typical Hydraulic Loading
Rate
Maximum Hydraulic
Loading Rate
Type of Chemical Used
Average Dose of Chemical
(mg/L)
Frequency of Chemical
Addition
Frequency of Solids
Removal
Equalization with partial treatment
(sedimentation occurs in the
backwash holding tank)
100,000 gal tank with baffles
70' X 35' X 5.5' active depth
2.9 gpm/ft2 from filter backwash
2.9 gpm/ft2 from filter backwash
None
None
None
Solids are manually removed every
2 months
See instructions on back.
December 2002
129
EPA Guidance Manual
FBRR Technical Guidance Manual
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Appendix D. Reporting Example for 20 MGD Plant
Instructions
1. Note the operating period for the information provided. Check with your State or Primacy
Agency for required operating period.
2. The frequency at which the recycle stream is returned can be described as continuous, once a
day, or as another frequency.
3. Fill out all information for each of your filters. If some or all filters are operated the same, note
the appropriate filter numbers.
4. The backwash flow is obtained by multiplying filter surface area (in ft2) by backwash rate
(gpm/ft2). Use the average backwash rate to get the average flow and the maximum backwash
rate to get the maximum flow. If the flow is varied throughout the backwash process, then the
average can be computed on a time-weighted basis as follows:
(Backwash Rate 1 X Duration 1) + (Backwash Rate 2 X Duration 2) + ...
Duration 1 + Duration 2+ ...
5. The filter run length time is the sum of the time that the filter is producing water between
backwashes.
6. Describe how run length time is determined. For example, is the run length based on head loss
across the filter, turbidity levels of filter effluent, a predetermined amount of time, or another
method?
EPA Guidance Manual 130 December 2002
FBRR Technical Guidance Manual
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Appendix E.
Reporting Example for 48
MGD Plant
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Appendix E. Reporting Example for 48 MGD Plant
A 48 MGD surface water treatment plant records total daily and peak instantaneous flows at
the plant inlet. In addition, the water treatment plant operators analyze raw and filtered
water quality daily and record detailed meter readings for flow at many plant locations. The
treatment scheme consists of a pre-sedimentation basin and fourteen upflow contact
absorption clarifiers, followed by fourteen rapid sand multimedia filters. Chemical addition
with coagulant, chlorine, potassium permanganate, and powdered activated carbon is
possible before the upflow clarifiers. The tri-media clarifiers are run approximately 24 hours
before air scour and backflushing with raw water. Backwashing of clarifiers occurs for 15
minutes at a backwash rate of 15 gpm/ ft2. Clarifiers are backwashed individually every 30
minutes between 9:00 p.m. and 4:00 a.m. The clarifiers each have 500 ft2 of surface area.
The rapid sand multimedia filters are comprised of anthracite, silica, and garnet sands and
each have a surface area of 590 ft2. They are air-scoured and backwashed with finished
water every 80 to 100 hours. A backwash rate of 20 gpm/ ft2 is utilized for 15 minutes. Prior
to backwashing, the filter is drained down six inches. After backwashing is complete, the
first 30 minutes of water produced is wasted. Four filters are typically backwashed each day
and individually backwashed every hour between 1:00 a.m. and 5:00 a.m. The filter feed
rate is 4 gpm/ ft2.
The water treatment plant reuses all of its residual streams (i.e., filter-to-waste water, pre-
backwash drain-down, spent filter backwash water, clarifier backwash water, and drying bed
leachate). All of the recycle streams are first directed to an equalization basin and the outlet
flow rate is regulated at 2,000 gpm. This flow is then treated by four flocculators and four
dissolved air flotation units on a continuous basis. Chemical addition with coagulant,
chlorine, potassium permanganate, and powdered activated carbon is possible prior to the
flocculation basins. Residuals are dewatered using sixteen sludge-drying beds, with the
leachate being directed back to the equalization basin. The amount of leachate from the
drying beds has been determined to be about 192,000 gpd, which is 0.4% of the finished
water production. The treated recycle stream is returned to the presedimentation basin.
1. Determine Highest Observed Plant Flow
A. Highest Plant Flow Based on Peak Raw Water Flow
A review of the water treatment plant's annual records indicates that the peak plant flow
occurred on August 15th. The following values were recorded on that day:
Total plant flow = 48 MGD (metered)
Highest observed raw water flow = 35,000 gallons per minute (metered)
Time of day highest observed raw water flow occurred: 5:30 p.m.
Recycle flow that occurred at 5:30 p.m. = 2,000 gpm (regulated by an outlet control
valve on the equalization basin)
Sum raw water flow plus recycle flow:
35,000 gpm + 2,000 gpm = 37,000 gpm
December 2002 133 EPA Guidance Manual
FBRR Technical Guidance Manual
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Appendix E. Reporting Example for 48 MGD Plant
B. Highest Plant Flow Based on Peak Recycle Flow
The quantity of water treatment plant recycle streams was calculated using plant operating
parameters and flow estimates.
Filter backwash: 708,000 gpd (based on 4 filters backwashed each day for 15
minutes at a rate of 20 gpm/ft2). Filters are backwashed
individually at one-hour intervals between 1:00 a.m. and 5:00
a.m. This flow is generated at a rate of 11,800 gpm.
Clarifier backwash: 1,575,000 gpd (based on each clarifier backwashed once per
day for 15 minutes at a rate of 15 gpm/ft2). Clarifiers are
individually backwashed every 30 minutes between 9:00 p.m.
and 4:00 a.m. This flow is generated at a rate of 7,500 gpm.
Filter-to-Waste: 283,200 gpd (based on disposal of filtered water produced in
the first 30 minutes after a filter is backwashed, four filters per
day). This flow is generated between 1:00 a.m. and 5:00 a.m.
at a rate of 2,360 gpm.
Pre-backwash draindown: 8,830 gpd (based on 0.5-foot drawdown of filters prior to
backwash, 4 filter backwashed each day). This flow is
generated between 1:00 a.m. and 5:00 a.m. at a rate of 200
gpm.
Sludge drying beds: 192,000 gpd (based on flow measurement). The leachate is
generated at a continuous rate of 140 gpm throughout the day.
Total daily recycle flow = 2.77 MGD (includes all plant waste streams)
Highest observed recycle flow = 2,000 gpm (constant outflow rate from equalization
basin)
Highest observed raw water flow = 35,000 gpm
Sum recycle flow plus raw water flow:
2,000 gpm + 35,000 gpm = 37,000 gpm
C. Compare Plant Flows Calculated Based on Raw Water and Recycle Flows
to Obtain Overall Highest Observed Plant Flow
The highest observed plant flow occurred at 5:30 p.m. and is the sum of the highest
observed raw water flow (35,000 gpm) and the controlled recycle return flow (2,000 gpm)
for a total of 37,000 gpm.
EPA Guidance Manual 134 December2002
FBRR Technical Guidance Manual
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Appendix E. Reporting Example for 48 MGD Plant
2. Determine Typical Recycle Flows
Recycle flows are generated at different frequencies and at different times during the day.
The recycle flow information is contained on the previous page. All generated recycle flows
for this system go to the equalization basin and are discharged from the equalization basin at
a constant rate of 2,000 gpm continuously throughout the day.
3. Complete Recycle Notification Form
The Recycle Notification Form was completed for this system and is contained on Page 137.
4. Complete Recordkeepinq Form
The Recordkeeping Form was completed for this system and is contained on Page 139.
Recycle flows were included for each of the recycle streams.
5. Data Evaluation
Based on the information provided, the system exceeds its design and State-approved
operating capacity by 3,700 gpm. The system may want to examine finished water quality
(such as turbidity and/or particle count data) to assess if recycle practices are impacting
finished water quality. If so, the State may request that the system modify its recycle
practices.
December 2002 135 EPA Guidance Manual
FBRR Technical Guidance Manual
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Appendix E. Reporting Example for 48 MGD Plant
Figure E-l. Schematic for a 48 MGD Plant
Peak Daily Flow =48 MGD
Peak Instantaneous Flow = 35,000 GP
(^"Taw \ Flet
\ Water \ (M)-
\ Reservoir )
(t
Recycled
Waste Stream
(2,000 gpm)
* Number in parenthesis indica
VI Coagu ant/Polymer Multimedia Filters
Feed (14)*
I
llpflnw Contact ป
ป Ple" ป Cbrificr-
J Sedimentation Clarities
Basin ( ' ^R,,it,,
L ^^ ^^ 12-inch Pipe
A ^^^^ Backwash
"J | < ป Backwash, Filter-to
Pre-Backwash Dra
Pumped J
8 inch Pipe t
Sludge Gravity Equalization
6-inch Pipe Basin
Flocculators (4)* _. . ...... JL Outlet Flow
Chemica Addition r"h Contro|
I I t \ 1 V (2000 gpm)
!
<^0 ^^ 8-^^
4
Dissolved Air Sludge-Drying
Flotat on (4)* t Beds (1 6)*
Pumped
Pumped
8-inch Pipe
tes number of treatment units.
* Clean/veil
Waste,
ndown I
Finished Water
To Distribution
System
Gravity
10-inch Pipe
EPA Guidance Manual
FBRR Technical Guidance Manual
136
December 2002
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Appendix E. Reporting Example for 48 MGD Plant
FILTER BACKWASH RECYCLING RULE
RECYCLE NOTIFICATION FORM
SYSTEM NAME Example 48 MGD Plant
PWSID DATE _Dec 1.2003
Check with your State or Primacy Agency to make sure this form is acceptable.
Does your system use conventional or direct filtration? Yes_(conventional)
Does your system recycle spent filter backwash water, thickener supernatant, or liquids from
dewatering processes? Yes (all)
If you answered yes to both questions, please report the following:
1. What is the typical recycle flow (in gpm)? 2.000 gpm (Equalized flow for spent filter
backwash.clarifier backwash, filter-to-waste. pre-backwash draindowru and leachate
2. What was the highest observed plant flow for the system in the previous year (in gpm)?
37.000 gpm
3. What is the design flow for the treatment plant (in gpm)? 33.333 gpm
4. Has the State determined a maximum operating capacity for the plant? If so, what is it? _33.333
gpm or 48 MGD
5. Please include a plant schematic that shows:
the origin of all recycle flows (spent filter backwash, thickener supernatant, liquids from
dewatering processes, and any other);
the location where all recycle flows re-enter the treatment plant process; and
the hydraulic conveyance used to transport all recycle flows.
Comments: All residual flows (filter-to-wate water, pre-backwash drain-down, filter backwash.
clarifier backwash water, and drying bed leachate) are directed to an equalization basin before
treatment. Recycle streams are returned to the main treatment train at a rate of 2,000 gpm.
6. Are you requesting an alternate recycle location? Yes X No
An alternate recycle location is one that does not incorporate all treatment processes of a
conventional filtration plant (coagulation, flocculation, sedimentation, and filtration) or direct
filtration plant (coagulation, flocculation, and filtration). The State or Primacy Agency must approve
the recycle location by June 8, 2004. Please contact your State or Primacy Agency on what
additional information may be needed.
Comments:
December 2002 137 EPA Guidance Manual
FBRR Technical Guidance Manual
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Appendix E. Reporting Example for 48 MGD Plant
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Appendix E. Reporting Example for 48 MGD Plant
FILTER BACKWASH RECYCLING RULE RECORDKEEPING FORM
SYSTEM NAME
PWSID
Example 48 MGD Plant
Operating Period1 Jun 2003 to Jun 2004
Check with your State or Primacy Agency to make sure this form is acceptable.
Type of Recycle Stream
Spent Filter Backwash
Thickener Supernatant
Liquids from Dewatering Process
Other See attached sheet
Other
Frequency at which flow is returned2
Continuously (equalized with all recycle streams)
Continuously (equalized with all recycle streams)
Filter
Information
Average Duration of
Backwash (in minutes)
Maximum Duration of
Backwash (in minutes)
Average Backwash
Flow4 (in gpm)
Maximum Backwash
Flow4 (in gpm)
Run Length Time of
Filter5 (include units)
Criteria for Terminating
Filter Run6
Filter Number3
Filters 1-14
15 minutes
15 minutes
11,800 gpm
11,800 gpm
80 to 100 hours
Time, unless individual filter
turbidity exceeds 0.2 NTU
Is treatment or equalization provided for recycle flows? X_
If yes, complete the following table.
Yes
No
Type of Treatment
Provided
Physical Dimensions of
Unit
Typical Hydraulic
Loading Rate (gpm/ft2)
Maximum Hydraulic
Loading Rate (gpm/ft2)
Type of Chemical Used
Average Dose of Chemical
(mg/L)
Frequency of Chemical
Addition
Frequency of Solids
Removal
Equalization with full treatment (flocculation and dissolved air flotation
(DAF)
3.0 MG equalization tank with baffles (200' x 200' X 10'), four
flocculation basins (each 13,800 gal), and two DAF basins (each 500 ft2)
0.004 to 0.49 gpm/ft2 to equalization basin and 0.53 gpm/ft2 to DAF basins
0.49 gpm/ft2 (1 1,800 gpm spent filter backwash plus 7,500 gpm clarifier
backwash plus 140 gpm leachate) to equalization basin and 0.53 gpm/ft2 to
DAF basins (flow controlled from equalization basin to treatment)
The DAF chemical feed systems are capable of providing potassium
permanganate, caustic soda, polymer, and coagulant
None. Operators found that treatment goals could be achieved without
chemical addition and so it was dropped.
None.
Solids are manually removed every 2 months from the equalization basin.
Float solids from the DAF units are pumped on a batch basis once a day to
the sludge drying beds.
See instructions on back.
December 2002
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Appendix E. Reporting Example for 48 MGD Plant
Instructions
1. Note the operating period for the information provided. Check with your State or Primacy
Agency for required operating period.
2. The frequency at which the recycle stream is returned can be described as continuous, once a
day, or as another frequency.
3. Fill out all information for each of your filters. If some or all filters are operated the same, note
the appropriate filter numbers.
4. The backwash flow is obtained by multiplying filter surface area (in ft2) by backwash rate
(gpm/ft2). Use the average backwash rate to get the average flow and the maximum backwash
rate to get the maximum flow. If the flow is varied throughout the backwash process, then the
average can be computed on a time-weighted basis as follows:
(Backwash Rate 1 X Duration 1) + (Backwash Rate 2 X Duration 2) + ...
Duration 1 + Duration 2+ ...
5. The run length time of the filter starts when filter effluent goes to the clearwell and ends when
the filter is taken off-line.
6. Describe how run length time is determined. For example, is the run length based on head loss
across the filter, turbidity levels of filter effluent, a predetermined amount of time, or another
method?
EPA Guidance Manual 140 December 2002
FBRR Technical Guidance Manual
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Appendix E. Reporting Example for 48 MGD Plant
FILTER BACKWASH RECYCLING RULE RECORDKEEPING FORM
Recycle Stream Attachement
Type of Recycle Stream (Additional Flows)
Other Clarifier Backwash
Other Pre-backwash draindown
Other Filter-to-waste
Frequency at which flow is returned
Continuously (equalized with all recycle streams)
Continuously (equalized with all recycle streams)
Continuously (equalized with all recycle streams)
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Appendix E. Reporting Example for 48 MGD Plant
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Appendix F.
Characteristics of Spent
Filter Backwash Water
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Appendix F. Characteristics of Spent Filter Backwash Water
The American Water Works Association Research Foundation (AWWARF) funded a
study (Cornwell and Lee, 1993) that examined recycle stream effects at eight different
utilities throughout the country.
Table F-l compares data on spent filter backwash (prior to treatment) and plant influent
(Cornwell and Lee, 1993). The spent filter backwash had higher TTHM, TTHM
formation potential and TOC concentrations than the plant influent. Turbidity and
inorganics in the spent filter backwash were also higher than the plant influent. Figure F-
1 provides a schematic of one of the studied plants (Mianus Water Treatment Plant) and
monitoring locations.
Table F-l. Comparison of Plant Influent to Spent Filter Backwash
Contaminant
TTHM, |ig/L
TTHM Formation Potential, |ig/L
Turbidity, NTU
TOC, mg/L
PH
Aluminum- Dissolved, mg/L
Aluminum- Total, mg/L
Manganese- Dissolved, mg/L
Manganese- Total, mg/L
Iron- Dissolved, mg/L
Iron- Total, mg/L
Mianus Water Treatment Plant
Plant Influent1
8-19
169-200
4.5-10.0
2.37-4.4
5.5-6.5
0.026-3.3
2.2-3.6
0.04-0.16
0.04-0.24
0.18
0.23
Spent Filter Backwash
46-97
302-465
0.57-97
5.54-7.1
6.2-6.8
0.03-49.6
55.00-76
0.15-0.75
1.4-12
2.60
3.19
1 Plant influent represents the raw water plus chemicals (chlorine, alum, and lime for this
plant) that enters the clarifier filter when recycle was not occurring. This sampling point
is just after the recycle return location.
2 Spent filter backwash is the backwash directly from the filter that has not been treated or
equalized.
Source: Cornwell and Lee, 1993.
December 2002
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Appendix F. Characteristics of Spent Filter Backwash Water
Table F-2 presents additional information on contaminants in spent filter backwash
(Cornwell et al., 2001). These data are based on samples from 25 systems.
Table F-2. Comparison of Raw Water to Spent Filter Backwash1
Parameter
DOC (mg/L)
TTHM
(H8/L)
HAA6
(Hg/L)
Br (mg/L)
Al (mg/L)
Fe (mg/L)
Mn (mg/L)
Zn (mg/L)
Raw Water
Range
0.7-5.4
ND-21.8
ND-21.5
ND-0.68
ND-30
ND-56.6
0.01 -5.5
ND-0.5
Average
2.4
0.6
1.9
0.038
0.72
1.2
0.11
0.03
Spent Filter Backwash
Water
Range
0.8-191
ND-198
ND-211
ND-0.46
ND-145.8
ND-132
0.01-17.9
ND-1.0
Average
8.0
55.0
46.1
0.033
14.7
8.7
1.4
0.1
Multiple
increase
3.3
91.7
24.3
-0.1
20.4
7.3
12.7
3.3
Source: Cornwell et al., 2001.
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146
December 2002
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Appendix F. Characteristics of Spent Filter Backwash Water
Figure F-l. Mianus Water Treatment Plant
Chlorine
1 Alum
Raw j
Water ^ i i
Intake,^
Bac
Supernatant
Recycle
ฉ
> =-
| Filtered Water w >. jo
* Cleaiwell _. . .. ..
Clarififir Filter
(wash
ฉ Sludge
Supernatant
* * ' 1 ฉ Supernatant Pressate
Thickener]
Y Sludge Think
-------
Appendix F. Characteristics of Spent Filter Backwash Water
Table F-3. Comparison of Plant Influent to Spent Filter Backwash Exiting the
Backwash Holding Tank
Contaminant
TTHM, |ig/L
TTHM
Formation
Potential,
Hg/L
Turbidity,
NTU
TOC, mg/L
PH
Aluminum-
Dissolved,
mg/L
Aluminum-
Total, mg/L
Manganese-
Dissolved,
mg/L
Manganese-
Total, mg/L
Kanawha Treatment
Plant
Plant
Influent1
4-14
82-145
6.2-27
1.85-3.2
6.6-7.0
SFBW
Super-
natant 2
28-98
160-265
78-400
2.96-4.1
8.5-9.6
Swimming River
Treatment Plant
Plant
Influent3
4
153
12
2.4
6.4
0.039
2.904
0.04
0.16
SFBW
Super-
natant 2
40
126
1.2
2.1
6.8
0.051
0.252
<0.02
<0.02
New Castle Treatment
Plant
Plant
Influent4
14-25
214-400
10-23
4.51-5.64
6.5-6.8
0.09-3.77
0.7-4.7
<0.02-0.04
<0.02-2.51
SFBW
Super-
natant 2
60-118
259-658
50-75
5.11-7.4
7.2-7.5
0.23-18.78
18.98-29.4
0.15-0.92
0.89-21.7
1 Plant influent represents the raw water plus chemicals (chlorine, lime, and polymer) that
enters the mixing chamber when recycle is not occurring. This sampling point is just
after the recycle return location.
2 Spent filter backwash supernatant is the recycle stream exiting the backwash holding
tank that has been partially equalized and settled. This flow consists solely of spent filter
backwash.
3 Plant influent represents the raw water plus powdered activated carbon prior to
additional chemical feed points that enters the clarifier/filters (Aldrich Units) when
recycle is not occurring. This sampling point is just after the recycle return location.
4 Plant influent represents the raw water plus chemicals (potassium permanganate, alum,
polymer, carbon, and chlorine or chlorine dioxide) that enters the rapid mix basin when
recycle is not occurring. This sampling point is just after the recycle return location.
Source: Cornwell and Lee, 1993.
EPA Guidance Manual
FBRR Technical Guidance Manual
148
December 2002
-------
Appendix F. Characteristics of Spent Filter Backwash Water
Figure F-2. Kanawha Valley Water Treatment Plant
Chlorine
Lime Polymer
ฉ
(1) Raw Water monitoring location
(2) Influent Water monitoring location
(3) Backwash Recycle monitoring location
Filters
Filter
Clean/veil
To
Sewer Sludge
Backwash Recycle
* Tu
Distribution
Figure F-3. Swimming River Water Treatment Plant
PAC
Raw
Water ฉ
i
,
'
CI2
1 Alum
1 Polymer
S^ T T T T ป ~ Filtered Water
Clarifier Filter
Backwash
(A) ฉ
Mr, , Sludge
Backwash
Tank 0 sludge
Supernatant
-> Clean/veil
Pressat
^
> To
Distribution
Lagoon
Sludge
(1) Raw Water monitoring location
(2) Influent Water monitoring location
(3) Backwash Holding Tank Supernatant monitoring location
(4) Backwash Holding Tank Sludge monitoring location
(5) Clarifier Filter Sludge monitoring location
(6) Lagoon Supernatant monitoring location
Cake to
Landfill
December 2002
149
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Appendix F. Characteristics of Spent Filter Backwash Water
Figure F-4. New Castle Water Treatment Plant
Raw
Water (T) -j
KMn04 Polymer c|20rC|Q2
Alum Carbon 1
II A'"m 1 >
^^^^x^ Pj|ter Distribution
Sludge | T
ฉBackwash
Holding
^ Tank
^ Backwash Recycle ^
1 ฎ
ฉ TSer ' ^dge , Be,t Press ^n^
Polymer
(1) Raw Water monitoring location
(2) Influent Water monitoring location
(3) Backwash Recycle monitoring location
(4) Sedimentation Basin Sludge monitor ng locaton
(5) Gravity Thickener Supernatant monitoring location
(6) Pressate monitoring location
EPA Guidance Manual
FBRR Technical Guidance Manual
150
December 2002
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Appendix F. Characteristics of Spent Filter Backwash Water
References
Cornwell, D., M. MacPhee, N. McTigue, H. Arora, G. DiGiovanni, M. LeChevallier, and
J. Taylor. 2001. Treatment Options for Giardia, Cryptosporidium, and Other
Contaminants in Recycled Backwash Water. AWWARF. Denver, CO.
Cornwell, D., and R. Lee. 1993. Recycle Stream Effects on Water Treatment.
AWWARF. Denver, CO.
December 2002 151 EPA Guidance Manual
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Appendix F. Characteristics of Spent Filter Backwash Water
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Appendix G.
Characteristics of
Thickener Supernatant
-------
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Appendix G. Characteristics of Thickener Supernatant
Table G-l summarizes data from three different plants in the AWWARF study (Cornwell
and Lee, 1993) for influent water, sludge, and supernatant. Figures G-l, G-2, and G-3
present plant schematics and monitoring locations for the plants presented in Table G-l.
The sludge had significantly higher TTHM, TTHM formation potential, and TOC than raw
water and plant influent (raw water data not presented in Table G-l). The supernatant also
exhibited higher concentrations for these same three contaminants than the plant influent
and raw water (raw water data not presented). Recycle of the supernatant, however, did not
impact filtered water quality at any of these three systems.
With regard to inorganics, the results were more varied. Aluminum and manganese levels in
the sludge were very high in comparison to plant influent. The aluminum concentrations in
the supernatant were less than aluminum concentrations in the plant influent. Conversely,
manganese levels in the supernatant were greater than levels in the influent water. Again,
recycle of the supernatant did not affect filtered water quality.
Table G-2 presents data on decant from lagoons.
December 2002 155 EPA Guidance Manual
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Appendix G. Characteristics of Thickener Supernatant
Table G-l. Comparison of Plant Influent to Sludge and Thickener Supernatant
Contami-
nant
TTHM,
ug/L
TTHM
Formation
Potential,
ug/L
Turbidity,
NTU
TOC, mg/L
pH
Aluminum-
Dissolved,
mg/L
Aluminum-
Total, mg/L
Manganese-
Dissolved,
mg/L
Manganese-
Total, mg/L
Iron-
Dissolved,
mg/L
Iron- Total,
mg/L
Mianus Water
Treatment Plant
Plant
Influent1
8-19
169-200
4.5-10.0
2.37-4.4
5.5-6.5
0.026-3.3
2.2-3.6
0.04-0.16
0.04-0.24
0.18
0.23
Super-
Natant2
156-525
349-444
0.7-5.0
3.75-5.0
6.0-6.7
O.001-
0.27
0.18-
0.62
1.14-4.1
1.25-4.5
O.05
0.08
Swimming River Water Treatment Plant
Plant
Influent3
4
153
12
2.4
6.4
0.039
2.904
0.04
0.16
Backwash
Holding
Tank
Sludge
36
190
75
6.3
0.013
110.2
0.47
6.22
Clarifier
Filter
Sludge
25
209
245
6.3
0.024
808.3
1.66
48.61
Super-
natant4
19
192
4.5
3.6
6.8
0.003
0.976
0.62
0.70
New Castle Water Treatment
Plant
Plant
Influent5
14-25
214-400
10-23
4.51-5.64
6.5-6.8
0.09-3.77
0.7-4.7
<0.02-
0.04
O.02-
2.51
Sludge
from
Sedimen-
tation
Basin
321-674
468-
2,032
14-59.4
0.45-300
300-
1,021
2.4-5.22
5.24-73.9
Super-
natant6
113-197
270-686
1-10
5.06-
15.1
7.0-7.5
0.04-
0.66
0.215-
0.92
0.26-
3.08
0.26-
3.69
1 Plant influent represents the raw water plus chemicals (chlorine, alum, and lime for this
plant) that enters the clarifier filter when recycle was not occurring. This sampling point is
just after the recycle return location.
2 Thickener treats sludge from supernatant tanks that receive sludge and spent filter
backwash from clarifier filter, supernatant from the thickener, and pressate.
3 Plant influent represents the raw water plus powdered activated carbon prior to additional
chemical feed points that enter the clarifier/filters (Aldrich Units) when recycle is not
occurring. This sampling point is just after the recycle return location.
4 Includes sludge from clarifier filter and backwash holding tank, plus pressate.
5 Plant influent represents the raw water plus chemicals (potassium permanganate, alum,
polymer, carbon, and chlorine or chlorine dioxide) that enters the rapid mix basin when
recycle is not occurring. This sampling point is just after the recycle return location.
6 Gravity thickener receives sludge from sedimentation basin and pressate from belt press.
Source: Cornwell and Lee, 1993.
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FBRR Technical Guidance Manual
156
December 2002
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Appendix G. Characteristics of Thickener Supernatant
Figure G-l. Mianus Water Treatment Plant
Chlorine
Alum
Lime
Filtered Water
> To
Distribution
Supernatant
Sludge
Thickener
(1) Raw Water monitoring location
(2) Influent Water monitoring location
(3) Spent Filter Backwash monitoring location
(4) Supernatant monitoring location
(5) Sludge Thickener Supernatant monitoring location
(6) Pressate monitoring location
Sludge
I
Supernatant
Sludge
Thickener
\ ^
Press
r-> Belt Press
Sludge
Cake to
^Landfill
Figure G-2. Swimming River Water Treatment Plant
PAC
CI2
| Alum
Raw (2) \ \
Water 0 " V T Y '
Intake
Backv
^Supernatant
ne
Polymer
' * > Filtered Water ^ >. TO
* Clean/veil * .
Clarifier Filter
vash
0
T nil. Sludge
V Backwash a
Holding
Tank 0 sludge Pressate
Supernatant
/^\ Laaoon
Belt Press ^Landfill
Cl::,l,,n
(1) Raw Water monitoring location
(2) Influent Water monitoring location
(3) Backwash Holding Tank Supernatant monitoring location
(4) Backwash Holding Tank Sludge monitoring location
(5) Clarifier Filter Sludge monitoring location
(6) Lagoon Supernatant monitoring location
December 2002
157
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Appendix G. Characteristics of Thickener Supernatant
Figure G-3. New Castle Water Treatment Plant
Sedimentation
Filters
Filter
Clearwell
> To
Distribution
Polymer
(1) Raw Water monitoring location
(2) Influent Water monitoring location
(3) Backwash Recycle monitoring location
(4) Sedimentation Basin Sludge monitoring location
(5)
Gravity Thickener Supernatant monitoring ocation
(6) Pressate monitoring location
Table G-2. Lagoon Decant Data
Contaminant
TTHM, |ig/L
TTHM Formation Potential,
Hg/L
Turbidity, NTU
TOC, mg/L
PH
Aluminum- Dissolved, mg/L
Aluminum- Total, mg/L
Manganese- Dissolved, mg/L
Manganese- Total, mg/L
Iron- Dissolved, mg/L
Iron- Total, mg/L
Giardia, cysts/ L
^Vun/^cn^W/yy-i/w? rป\7ctc/T
Lagoon Decant
15.8-85.2
192
1.94-4.5
3.6
6.8-8.1
0.003
O.01-1.24
0.62
O.01-0.7
Source: Environmental Engineering and Technology, 1999.
EPA Guidance Manual
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158
December 2002
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Appendix G. Characteristics of Thickener Supernatant
References
Cornwell, D. and R. Lee. 1993. Recycle Stream Effects on Water Treatment. AWWARF.
Denver, CO.
Environmental Engineering and Technology. 1999. Background Papers on Potential
Recycle Streams in Drinking Water Treatment Plants. AWWA.
December 2002 159 EPA Guidance Manual
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Appendix G. Characteristics of Thickener Supernatant
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Appendix H.
Characteristics of
Liquids from Dewatering
Processes
-------
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Appendix H. Characteristics of Liquids from Dewatering Processes
Dewatering can be accomplished through non-mechanical and mechanical means. Table
H-l presents information on dewatered residuals.
Table H-l. Characteristics of Dewatered Plant Residuals
Contaminant
TTHM, |ig/L
TTHM
Formation
Potential, |ig/L
Turbidity, NTU
TOC, mg/L
PH
Aluminum-
Dissolved, mg/L
Aluminum-
Total, mg/L
Manganese-
Dissolved, mg/L
Manganese-
Total, mg/L
Iron- Dissolved,
mg/L
Iron- Total, mg/L
Giardia, cysts/ L
Cryptosporidium
cysts/L
Sludge Drying
Bed Underflow1
1.6-32
6.9-7.8
O.05-177
0.05-12.34
0.06-8.45
0.210
<0.210
Monofill
Leachate2
5.5-7.5
<0.6
0.03-22.8
O.01-1.42
Mechanical
Dewatered3
128-276
397-499
30-200
5.8-14.3
6.6-9.1
0.12-0.81
0.15-129.0
5.21-12.2
3.47.31.45
<0.05
0.4-165
1 Source: Environmental Engineering and Technology, 1999. Data is based on one to 17
samples.
2 Source: Cornwell et al., 1992. Data is from three pilot-scale monofills.
3 Source: Environmental Engineering and Technology, 1999. Data represents samples
from two water treatment plants with belt filter presses, one plant with a plate and frame
press, and one plant with a centrifuge.
December 2002
163
EPA Guidance Manual
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Appendix H. Characteristics of Liquids from Dewatering Processes
Another AWWARF study (Cornwell and Lee, 1993) examined pressate from two
different plants. The data is presented in Table H-2. Figures H-l and H-2 present plant
schematics and pressate monitoring locations. The pressate exceeded influent water
concentrations for most contaminants listed in Table H-2. The pressate in both plants
was mixed with other waste streams prior to being recycled. The water quality of the
recycled supernatant is shown in Table H-3. The impacts of the recycled pressate are
unknown since the pressate is mixed with other waste streams prior to being recycled.
Table H-2. Pressate Quality in Comparison to Influent Water
Contaminant
TTHM, |ig/L
TTHM
Formation
Potential, |ig/L
Turbidity, NTU
TOC, mg/L
PH
Aluminum-
Dissolved, mg/L
Aluminum-
Total, mg/L
Manganese-
Dissolved, mg/L
Manganese-
Total, mg/L
Iron- Dissolved,
mg/L
Trrm- Total mo/T
Mianus Water Treatment Plant
Influent Water1
8-19
169-200
4.5-10.0
2.37-4.4
5.5-6.5
0.026-3.3
2.2-3.6
0.04-0.16
0.04-0.24
0.18
n 9^
Pressate
128-276
397-448
30-40
5.82-9.2
6.8-7.2
0.021-0.81
6.4-31.8
7.43-12.2
8-16
<0.05
n 66
New Castle Water Treatment
Plant
Influent Water3
14-25
214-400
10-23
4.51-5.64
6.5-6.8
0.09-3.77
0.7-4.7
<0.02-0.04
<0.02-2.51
Pressate
114-151
366-616
50-75
14.34-18.2
7.3
0.12-3.94
7.6-186
1.5-5.21
1.49-20.3
1 Plant influent represents the raw water plus chemicals (chlorine, alum, and lime for this
plant) that enters the clarifier filter when recycle was not occurring. This sampling point
is just after the recycle return location.
2 Pressate is from a belt press that dewaters sludge from a thickener. Polymer is added
prior to the belt press.
3 Plant influent represents the raw water plus chemicals (potassium permanganate, alum,
polymer, carbon, and chlorine or chlorine dioxide) that enters the rapid mix basin when
recycle is not occurring. This sampling point is just after the recycle return location.
Source: Cornwell and Lee, 1993.
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FBRR Technical Guidance Manual
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December 2002
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Appendix H. Characteristics of Liquids from Dewatering Processes
Figure H-l. Mianus Water Treatment Plant
Chlorine
1 Alum
Raw
Water
Intake --.
Ill CD.
Supernatant
Recycle
Backwash
1
ป
Filtered Wat
Clarifier Filter
er
* Clear well
Sludge
Supernatant
Sludge
"hickener I
ฉ Supernatant
T_ Sludge
(1) Raw Water monitoring location
(2) Influent Water monitoring location
(3) Spent Filter Backwash monitoring location
(4) Supernatant monitoring location
(5) Sludge Thickener Supernatant monitoring location
(6) Pressate monitoring location
Sludge Polymer
ThinkPPr
IP
> To
Distribution
ฉ
Pressate
Belt Press
Cake to
Landfill
Sludge
Figure H-2. New Castle Water Treatment Plant
KMn04 Poymer
Cl 2 or CIO 2
Alum Carbon |
I I Alum ,
l^lr ,n;
Filters
Filter
Clearwell
Polymer
(1) Raw Water monitoring location
(2) Influent Water monitoring location
(3) Backwash Recycle monitoring location
(4) Sedimentation Basin Sludge monitoring location
(5) Gravity Thickener Supernatant monitoring location
(6) Pressate monitoring location
> To
Distribution
December 2002
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Appendix H. Characteristics of Liquids from Dewatering Processes
References
Cornwell, D. and R. Lee. 1993. Recycle Stream Effects on Water Treatment.
AWWARF. Denver, CO.
Cornwell D.A., C. Vandermeyden, G. Dillow. 1992. Landfilling of Water Treatment
Plant Coagulant Sludges. AWWARF. Denver, CO.
Environmental and Engineering Technology. 1999. Background Papers on Potential
Recycle Streams in Drinking Water Treatment Plants. AWWA.
EPA Guidance Manual 166 December 2002
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