vvEPA
            United States
            Environmental
            Protection Agency
                 Office of Water
                   (4601)
EPA815-D-03-008
June 2003
Proposal Draft
MEMBRANE FILTRATION GUIDANCE MANUAL

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        Note on the Membrane Filtration Guidance Manual
                               June 2003 Draft
Purpose

The purpose of this guidance manual, when finalized, is solely to provide technical information
on the use of membrane filtration and application of the technology for compliance with the
Long Term 2 Enhanced Surface Water Treatment Rule, which would require certain systems to
provide additional treatment for Cryptosporidium.  This rule, along with the companion Stage 2
Disinfectants and Disinfection Byproducts Rule, are summarized in Chapter 1 of this manual.

This guidance is not a substitute for applicable legal requirements, nor is it a regulation itself.
Thus, it does not impose legally binding requirements on any party, including USEPA, States, or
the regulated community. Interested parties are free to raise questions and objections to the
guidance and the appropriateness of using it in a particular situation.  Although this manual
covers many aspects of implementing membrane filtration, it is not intended to be a
comprehensive resource on the subject. The mention of trade names or commercial products
does not constitute endorsement or recommendation for use.
Authorship

This manual was developed under the direction of USEPA's Office of Water, and was prepared
by Malcolm Pirnie, Inc., Separation Processes, Inc., and The Cadmus Group, Inc.  Questions
concerning this document should be addressed to:

       Steve Allgeier
       United States Environmental Protection Agency
       Office of Ground Water and Drinking Water
       Technical Support Center (MS 140)
       26 West Martin Luther King Dr.
       Cincinnati, OH 45268
       Voice: (513)569-7131
       Fax:   (513)569-7191
       Email: allgeier.steve@epa.gov
Request for Comments

USEPA is releasing this manual in draft form in order to solicit public review and comment. The
Agency would appreciate comments on the content and organization of technical information
presented in this manual.  Please submit any comments no later than 90 days after publication of
the Long Term 2 Enhanced Surface Water Treatment Rule proposal in the Federal Register.

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Comments on this draft guidance manual should be submitted to USEPA's Water Docket.
Comments may be submitted electronically, by mail, or through hand deli very/courier, as
follows:

Submitting comments via USEPA's electronic public docket
Go directly to USEPA Dockets at http://www.epa.gov/edocket and follow the online instructions
for submitting comments. Once in the system, select "search," and then key in Docket ID No.
OW-2002-0039.

Submitting comments via e-mail
Send comments to OW Docket@epa.gov. Attention Docket ID No. OW-2002-0039. EPA's e-
mail system automatically captures the sender's e-mail address, which is then included as part of
the comment that is placed in the official public docket.

Submitting comments on a disk or CD ROM
Mail any comments on disk or CD to address given below.  These electronic submissions will be
accepted in WordPerfect or ASCII file format.  Avoid the use of special characters and any form
of encryption.

       Water Docket
       United States Environmental Protection Agency
       Mail Code 4101T
       1200 Pennsylvania Ave., NW
       Washington, DC, 20460
       Attention Docket ID No. OW-2002-0039

Submitting comments by mail
Send three copies of comments and any associated enclosures to:

       Water Docket
       United States Environmental Protection Agency
       Mail Code 4101T
       1200 Pennsylvania Ave., NW
       Washington, DC 20460
       Attention Docket ID No. OW-2002-0039

Submitting comments by hand delivery or courier
Deliver comments to:

       Water Docket
       USEPA Docket Center
       United States Environmental Protection Agency
       Room B102
       1301 Constitution Ave., NW
       Washington, DC 20460
       Attention Docket ID No. OW-2002-0039

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Please identify the appropriate docket identification number in the subject line on the first page
of your comment. If you submit an electronic comment, please include a name, mailing address,
and an e-mail address or other contact information in the body of the comment.  This contact
information should also be included on the outside of any disk or CD ROM submitted, as well as
in any cover letter accompanying the  disk or CD ROM.

USEPA policy is that public comments, whether submitted electronically or in paper, will be
made available for public viewing in  USEPA's electronic public docket as USEPA receives them
and without change, unless the comment contains copyrighted material, CBI, or other
information whose disclosure is restricted by statute.

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                             Acknowledgements
       This document was prepared by the United States Environmental Protection Agency,
Office of Ground Water and Drinking Water, Standards and Risk Management Division,
Technical Support Center.  The Work Assignment Manager was Steven Allgeier, and the
Contract Project Officer was Jane Holtorf.

       Technical consultants played a significant role in the development of this document.  The
work was conducted jointly by Malcolm Pirnie, Inc and Separation Processes, Inc. under contract
with The Cadmus Group, as administered by Maureen Donnelly. The primary contributors to the
document included:

   •   Steven Allgeier (USEPA)
   •   Brent Alspach (Malcolm Pirnie)
   •   James Vickers (Separation Processes).

Other contributors included Steve Alt (Separation Processes), Maureen Donnelly (The Cadmus
Group), Christopher Hill (Malcolm Pirnie), and Sheryl Patrick (Separation Processes).

       Addition support for this work was provided by a panel of peer reviewers, including:
Pierre Cote (ZENON Environmental), Scott Freeman (Black & Veatch), Joseph Jacangelo
(MWH), Larry Landsness (Wisconsin Department of Natural Resources), James Lozier
(CH2M Hill), Charles Liu (Pall Corporation), David Paulson (GE Osmonics), Richard Sakaji
(California Department of Health Services),  and James Schaefer (Pall Corporation).

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                                     Contents
1.0    INTRODUCTION	l-l
       1.1    Regulating Membranes for the Drinking Water Industry	1-2
       1.2    Summary of Applicable Regulations	1-3
             1.2.1   Long Term 2 Enhanced Surface Water Treatment Rule	1-3
             1.2.2   Stage 2 Disinfectants and Disinfection Byproducts Rule	1-4
       1.3    Requirements for Membrane Filtration Under the LT2ESWTR	1-5
             1.3.1   Definition of a Membrane Filtration Process	1-6
             1.3.2   Challenge Testing	1-7
             1.3.3   Direct Integrity Testing	1-7
             1.3.4   Continuous Indirect Integrity Monitoring	1-8
       1.4    Considering Existing Membrane Filtration Facilities Under the LT2ESWTR... 1-8
       1.5    Membrane Terminology Used in the Guidance Manual	1-10
       1.6    Guidance Manual Objectives	1-12
       1.7    Guidance Manual Organization	1-13

2.0    OVERVIEW OF MEMBRANE FILTRATION	2-1
       2.1    Introduction	2-1
       2.2    Basic Principles of Membrane Filtration	2-2
             2.2.1   Microfiltration and Ultrafiltration	2-3
             2.2.2   Nanofiltration and Reverse Osmosis	2-4
             2.2.3   Membrane Cartridge Filtration	2-5
             2.2.4   Membrane Pore Size and Filtration Removal Efficiency	2-6
             2.2.5   Electrodialysis and Electrodialysis Reversal	2-6
       2.3    Membrane Materials, Modules, and Systems	2-7
             2.3.1   Membrane Materials	2-7
             2.3.2   Membrane Modules	2-9
                    2.3.2.7   Hollow-Fiber Modules	2-10
                    2.3.2.2   Spiral-Wound Modules	2-11
                    2.3.2.3   Membrane Cartridges	2-13
                    2.3.2.4   Other Module Configurations	2-14
             2.3.3   Types of Membrane Filtration  Systems	2-15
                    2.3.3.7   Hollow-Fiber (MF/UF) Systems	2-15
                    2.3.3.2   Spiral-Wound(NF/RO) Systems	2-17
       2.4    Basic Principles of Membrane Filtration System Design and Operation	2-20
             2.4.1   General Concepts	2-20
             2.4.2   MF, UF, and MCF Processes	2-22
             2.4.3   NF and RO Processes	2-26
       2.5    Hydraulic Configurations	2-27
             2.5.1   Deposition Mode	2-29
             2.5.2   Suspension Mode	2-31
                    2.5.2.7   Plug Flow Reactor Model	2-32
                    2.5.2.2   Cross/low Model	2-36
                    2.5.2.3   Continuous Stirred Tank Reactor Model	2-42
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             2.5.3  Summary	2-48

3.0    CHALLENGE TESTING	3-1
       3.1    Introduction	3-1
       3.2    Summary of Challenge Testing Requirements	3-3
       3.3    Test Organization Qualification	3-5
       3.4    General Procedure for Designing a Challenge Test Protocol	3-6
       3.5    Module Specifications	3-8
       3.6    Non-Destructive Performance Testing	3-9
       3.7    Selection of Modules for Challenge Testing	3-11
       3.8    Small-Scale Module Testing	3-12
       3.9    Target Organisms and Challenge Particulates	3-13
             3.9.1  Selecting a Target Organism	3-13
             3.9.2  Surrogate Characteristics	3-14
             3.9.3  Surrogates for Cryptosporidium	3-16
                    3.9.3.1  Alternate Microorganisms	3-17
                    3.9.3.2  Inert Particles	3-18
                    3.9.3.3  Molecular Markers	3-19
       3.10  Challenge Test Solutions	3-19
             3.10.1 Test Solution Water Quality	3-20
             3.10.2 Test Solution Volume	3-21
             3.10.3 Test Solution Concentration	3-23
             3.10.4 Challenge Paniculate Seeding Method	3-25
             3.10.5 Example: Challenge Test Solution Design	3-27
       3.11  Challenge Test Systems	3-31
             3.11.1 Test Apparatus	3-31
             3.11.2 Test Operating Conditions	3-36
       3.12  Sampling	3-37
             3.12.1 Sampling Methods	3-38
             3.12.2 Sample Port Design and Location	3-38
             3.12.3 Process Monitoring	3-39
             3.12.4 Sample Plan Development	3-40
       3.13  Analysis and Reporting of Challenge Test Results	3-41
             3.13.1 Calculation of Removal Efficiency	3-41
             3.13.2 Statistical Analysis	3-42
             3.13.3 Reporting	3-43
       3.14  Re-Testing of Modified Membrane Modules	3-44
       3.15  Grandfathering Challenge Test Data From Previous Studies	3-45

4.0    DIRECT INTEGRITY TESTING	4-1
       4.1    Introduction	4-1
       4.2    Test Resolution	4-3
             4.2.1  Pressure-Based Tests	4-3
             4.2.2  Marker-Based Tests	4-5
       4.3    Test Sensitivity	4-6
             4.3.1  Pressure-Based Tests	4-6
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                     4.3.1.1  Basic Concepts	4-6
                     4.3.1.2  Calculating Sensitivity	4-8
                     4.3.1.3  Diffusive Losses / Baseline Decay	4-13
              4.3.2   Marker-Based Tests	4-18
       4.4    Test Frequency	4-19
       4.5    Establishing Control Limits	4-19
       4.6    Example: Established Direct Integrity Test Parameters	4-22
       4.7    Test Methods	4-29
              4.7.1   Pressure Decay Test	4-29
              4.7.2   Vacuum Decay Test	4-32
              4.7.3   Diffusive Airflow Test	4-33
              4.7.4   Water Displacement Test	4-35
              4.7.5   Marker-Based Integrity Tests	4-38
       4.8    Diagnostic Testing	4-41
              4.8.1   Visual Inspection	4-42
              4.8.2   Bubble Testing	4-42
              4.8.3   Sonic Testing	4-43
              4.8.4   Conductivity Profiling	4-44
              4.8.5   Single Module Testing	4-45
       4.9    Data Collection and Reporting	4-46

5.0    CONTINUOUS INDIRECT INTEGRITY MONITORING	5-1
       5.1    Introduction	5-1
       5.2    Turbidity Monitoring	5-4
              5.2.1   Methods	5-5
              5.2.2   Control Limits	5-6
              5.2.3   Advantages and Limitations	5-7
       5.3    Particle Counting and Particle Monitoring	5-8
              5.3.1   Methods	5-9
              5.3.2   Control Limits	5-10
              5.3.3   Advantages and Limitations	5-12
       5.4    Other Indirect Monitoring Methods	5-13
       5.5    Data Collection and Reporting	5-15

6.0    PILOT TESTING	6-1
       6.1    Introduction	6-1
       6.2    Planning	6-2
              6.2.1   Process Considerations	6-3
              6.2.2   Screening and  System Selection	6-3
              6.2.3   Scheduling	6-5
       6.3    Testing Objectives	6-6
              6.3.1   Membrane Flux Optimization	6-7
              6.3.2   Backwash Optimization	6-8
              6.3.3   Chemical Cleaning Optimization	6-9
       6.4    Testing and Monitoring	6-13
              6.4.1   Operational Parameter Monitoring	6-13
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              6.4.2  Water Quality Monitoring	6-13
              6.4.3  Microbial Monitoring	6-15
              6.4.4  Integrity Testing	6-15
       6.5     Report Development	6-16

7.0    IMPLEMENTATION CONSIDERATIONS	7-1
       7.1     Introduction	7-1
       7.2     Operational Unit Processes	7-1
              7.2.1  Pretreatment	7-2
                    7.2.7.7  Prefiltration	7-2
                    7.2.1.2  Chemical Conditioning	7-3
              7.2.2  Backwashing	7-5
              7.2.3  Chemical Cleaning	7-6
              7.2.4  Integrity Testing	7-8
              7.2.5  Post-Treatment	7-10
       7.3     System Design Considerations	7-11
              7.3.1  Membrane Flux	7-11
              7.3.2  Water Quality	7-11
              7.3.3  Temperature Compensation	7-15
              7.3.4  Cross-Connection Control	7-19
              7.3.5  System Reliability 	7-21
       7.4     Residuals Treatment and Disposal	7-22
              7.4.1  Backwash Residuals	7-24
              7.4.2  Chemical Cleaning Residuals	7-25
              7.4.3  Concentrate	7-26

8.0    INITIAL START-UP	8-1
       8.1     Introduction	8-1
       8.2     Temporary  System Interconnections	8-2
       8.3     Flushing and Testing Without Membranes	8-2
       8.4     Membrane Installation	8-3
       8.5     System Disinfection	8-4
              8.5.1  Chlorine-Tolerant Membrane	8-4
              8.5.2  Chlorine-Intolerant Membranes	8-5
       8.6     Initial Direct Integrity Testing	8-5
       8.7     Acceptance Testing	8-5
       8.8     Operator Training	8-6
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                                Appendices
A     DEVELOPMENT OF A COMPREHENSIVE INTEGRITY VERIFICATION PROGRAM	A-l
      A.I   Introduction	A-l
      A.2   Direct Integrity Testing	A-3
      A.3   Continuous Indirect Integrity Monitoring	A-10
      A.4   Diagnostic Testing	A-15
      A.5   Membrane Repair and Replacement	A-17
      A.6   Data Collection and Analysis	A-20
      A.7   Reporting	A-23
      A.8   Summary	A-24

B     OVERVIEW OF BUBBLE POINT THEORY	B-l
      B.I   Introduction	B-l
      B.2   The Bubble Point Equation	B-2
      B.3   Bubble Point Equation Parameters	B-4

C     CALCULATING THE AIR-LIQUID CONVERSION RATIO	C-l
      C.I   Introduction	C-l
      C.2   Darcy Pipe Flow Model	C-3
      C.3   Orifice Model	C-6
      C.4   Hagen-Poiseuille Model	C-8

D     EMPIRICAL METHOD FOR DETERMINING THE AIR-LIQUID CONVERSION RATIO
            FOR A HOLLOW-FIBER MEMBRANE FILTRATION SYSTEM	D-l
      D.I   Introduction	D-l
      D.2   Methodology	D-4
      D.3   Example: Using the CAM Method to Determine the ALCR	D-5
E     APPLICATION OF MEMBRANE FILTRATION FOR VIRUS REMOVAL	E-l
      E.I   Introduction	E-l
      E.2   Overview of Current Regulatory Policy	E-2
      E.3   Direct Integrity Testing	E-5
      E.4   Challenge Testing	E-7
      E.5   Continuous Indirect Integrity Monitoring	E-8
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                                 List of Tables

No.    Title	Page

1.1     LT2ESWTR Additional Treatment Requirements for Unfiltered Systems	1-4
2.1     Summary of VCF Values fora NF/RO System Modeled as a PFR	2-36
2.2     Increase in VCF as a Function of the Number of Detention Times	2-45
2.3     Typical Range of VCF Values for Various Hydraulic Configurations	2-48
2.4     Summary of VCF Equations for Various Hydraulic Configurations	2-49

3.1     Potential Target Organisms for Challenge Testing	3-14
3.2     Comparative Summary of Cryptosporidium and Potential Surrogates	3-16
3.3     Potential Microbiological Surrogates for Cryptosporidium	3-17
3.4     Example Challenge Test Solution Volume for Various Types of Modules	3-23
3.5     Typical Parameters for Various Types of Modules	3-37
3.6     Typical Range of VCF Values for Various Hydraulic Configurations	3-45
4.1     Approaches for Calculating the ALCR	4-12

6.1     Water Quality Parameters to Measure Prior to Piloting	6-8
6.2     Suggested Water Quality Sampling Schedule for Membrane Piloting	6-14
7.1     Typical Membrane System Prefiltration Requirements	7-3
7.2     Chemical Cleaning Agents	7-7
7.3     Estimated NF/RO Membrane Fluxes as a Function of SDI	7-12

8.1     Schedule  of Training Events	8-7
B.I     Surface Tension of Water at Various Temperatures	B-5
C.I     Approaches for Calculating the ALCR	C-2
E.I     Virus Removal  Studies Using MF and UF	E-3
E.2     Summary of State Virus Removal Credit for MF and UF	E-3
E.3     Summary of State Giardia and Cryptosporidium Removal Credit for MF/UF	E-4
E.4     Required Direct Integrity Test Pressure as a Function of Target Pathogen Size
             (i.e., Resolution)	E-6
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                                 List of Figures

No.    Title	Page

2.1     Filtration Application Guide for Pathogen Removal	2-3
2.2     Conceptual Diagram of Osmotic Pressure	2-5
2.3     Membrane Construction and Symmetry	2-9
2.4     Hollow Fiber Cross-Section Photomicrograph	2-11
2.5     Inside-Out and Outside-In Modes of Operation	2-12
2.6     Spiral-Wound Membrane Module	2-12
2.7     Membrane Cartridge Filter	2-13
2.8     Schematic of a Typical Pressure-Driven Hollow-Fiber (MF/UF) System	2-16
2.9     Schematic of a Typical Vacuum-Driven Hollow-Fiber (MF/UF) System	2-17
2.10   Typical Spiral-Wound (NF/RO) Module Pressure Vessel	2-18
2.11   Typical 2:1 (Relative) Array of Pressure Vessels	2-19
2.12   Schematic of a Typical Spiral-Wound (NF/RO) System	2-20
2.13   Schematic of a System Operating in Deposition Mode	2-29
2.14   Conceptual Illustration of Deposition Mode Operation	2-30
2.15   Conceptual Illustration of Suspension Mode Operation	2-31
2.16   Flow Diagram for a Plug Flow Reactor 	2-32
2.17   Schematic of a Typical Small Volume Crossflow System	2-37
2.18   Concentration Profile in a Small Volume Crossflow System	2-39
2.19   Schematic of a Typical Large Volume Crossflow System	2-40
2.20   Concentration Profile in a Large Volume Crossflow System	2-41
2.21   Schematic of a Typical Pressure-Driven CSTR Without Backwashing	2-44
2.22   Schematic of a Typical Vacuum-Driven CSTR Without Backwashing	2-44
2.23   Concentration Profile in a CSTR Without Backwashing	2-45
2.24   Schematic of a Typical Pressure-Driven CSTR With Backwashing	2-46
2.25   Concentration Profile in a CSTR With Backwashing	2-47

3.1     Schematic of Acceptable and Unacceptable Sample Injection Ports	3-26
3.2     Schematic of a Typical Pressure-Driven System in Deposition Mode with Batch
             Seeding and Composite Sampling	3-32
3.3     Schematic of a Typical Pressure-Driven System in Deposition Mode with
             Continuous Seeding and Grab Sampling	3-33
3.4     Schematic of a Typical Pressure-Driven System in Suspension Mode with
             Continuous Seeding and Grab Sampling	3-34
3.5     Schematic of a Typical Vacuum-Driven System in Deposition Mode with
             Continuous Seeding and Grab Sampling	3-35
3.6     Schematic of a Typical Vacuum-Driven System in Suspension Mode with
             Continuous Seeding and Grab Sampling	3-35
3.7     Schematic of Acceptable and Unacceptable Sampling Ports	3-39
4.1     Schematic Illustrating a Pressure Decay Test	4-30
4.2     Schematic Illustrating a Vacuum Decay Test	4-32
4.3     Schematic Illustrating a Diffusive Airflow Test	4-34
4.4     Schematic Illustrating a Water Displacement Test	4-36


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4.5    Schematic Illustrating a Particulate Marker Test	4-38
4.6    Schematic Illustrating a Molecular Marker Test	4-39
4.7    Sample Summary Report Form for Pressure Decay Testing	4-47
6.1    Sample Chemical Cleaning Test Profile	6-11
6.2    Sample Pilot Study Sequence Overview	6-12
7.1    Double Block and Bleed Valving Arrangement	7-20
B.I    Diagram of a Membrane Pore Modeled as a Capillary Tube	B-l
D.I    CAM Technique Airflow Measurement Apparatus	D-3
D.2    Example Airflow and Water Flow Correlation Curves	D-3
D.3    Example ALCR Correlation	D-6
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                                    Acronyms
AFT           Alternate Filtration Technology

ALCR         Air-Liquid Conversion Ratio

ANSI          American National Standards Institute

APHA         American Public Health Administration

ASTM         American Society for Testing and Materials

AWWA        American Water Works Association

AWWARF     American Water Works Association Research Foundation

BOD           Biochemical Oxygen Demand

CA            Cellulose Acetate

CAM          Correlated Airflow Measurement

CIP           Clean-In-Place

CL            Control Limit

CSTR         Continuous Stirred Tank Reactor

CT            (Disinfectant Residual) Concentration (mg/L) x (Contact) Time (minutes)

CWS           Community Water System

DBP           Disinfection Byproduct

DBPR         Disinfectants and Disinfection Byproducts Rule

DOC           Dissolved Organic Carbon

ED            Electrodialysis

EDR           Electrodialysis Reversal

ETV           Environmental Technology Verification

FR            Federal Register

GWR          Ground Water Rule
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GWUDI       Ground Water Under the Direct Influence (Of Surface Water)

HAA          Haloacetic Acid

HAAS         (sum of five) Haloacetic Acids

HFF           Hollow Fine Fiber

HPC           Heterotrophic Plate Count

IDSE          Initial Distribution System Evaluation

IESWTR       Interim Enhanced Surface Water Treatment Rule

IMS           Integrated Membrane System

ISO           International  Organization for Standardization

IVP           Integrity Verification Program

LCL           Lower Control Limit

LED           Light Emitting Diode

LRAA         Locational Running Annual Average

LRC           Log Removal Credit

LRV           Log Removal Value

LT1ESWTR   Long Term 1 Enhanced Surface Water Treatment Rule

LT2ESWTR   Long Term 2 Enhanced Surface Water Treatment Rule

MCF          Membrane Cartridge Filtration

MCL          Maximum Contaminant Level

MF           Microfiltration

MWCO        Molecular Weight Cut-Off

NA            Not Applicable

NDP           Net Driving Pressure

NDPT         Non-Destructive Performance Test

NF            Nanofiltration
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NSF           National Sanitation Foundation

NTNCWS      Non-Transient Non-Community Water System

OEM          Original Equipment Manufacturer

PA            Poly amide

PAC           Powdered Activated Carbon

PAN           Polyacrylonitrile

PES           Polyethersulfone

PFR           Plug Flow Reactor

PP            Polypropylene

PS            Polysulfone

PVDF         Polyvinylidene Fluoride

QA            Quality Assurance

QC            Quality Control

QCRV         Quality Control Release Value

RAA           Running Annual Average

RO            Reverse Osmosis

SDI           Silt Density Index

SEM           Scanning Electron Microscopy

SMP           Standard Monitoring Program

SSDR         Stock Solution Delivery Rate

SSS           System-Specific Study

SUVA         Specific Ultraviolet Absorbance

SWTR         Surface Water Treatment Rule

TCEQ         Texas Commission on Environmental Quality

TCF           Temperature Correction Factor
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TCPP

TDS

TMP

TOC

TSS

TTHM

UCL

UF

USEPA

UV

VCF
Total Challenge Particulate Population

Total Dissolved Solids

Transmembrane Pressure

Total Organic Carbon

Total Suspended Solids

Total Trihalomethanes

Upper Control Limit

Ultrafiltration

United States Environmental Protection Agency

Ultraviolet (Light)

Volumetric Concentration Factor
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                                   Symbols
Symbol
A!
A2
A20
Ad
An
ALCR
BP
-t^-tmax
RP
-D-rmin
c
Cc
Cf
n
^t-max
r1
^t-min
cm
^m-max
Description
Membrane area based on the inside of a hollow
fiber
Membrane area based on the outside of a hollow
fiber
Membrane area (required for design at a reference
temperature of 20 ฐC)
Design membrane area (corrected for temperature)
Membrane area
Air- liquid conversion ratio
Backpressure
Maximum backpressure
Minimum backpressure
Coefficient of discharge
Concentrate concentration
Influent feed water concentration
Maximum feed concentration (in a challenge test)
Minimum feed concentration (in a challenge test)
Concentration maintained on the feed side of the
membrane
Maximum concentration maintained on the feed
side of the membrane
Units
English
ft2
ft2
ft2
ft2
ft2
-
psi
psi
psi
-
-
-
-
-
-
-
Metric
m2
9
m
m2
2
m
2
m
-
kPa
dynes/cm2
kPa
dynes/cm2
kPa
dynes/cm2
-
mg/L
number/L
mg/L
number/L
mg/L
number/L
mg/L
number/L
mg/L
number/L
mg/L
number/L
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Symbol
Cm(t-l)
QnC*)
CP
Ctest
^ss
D^
Daw
(leap
Qfect
dfiber
dres
DL
DOC
e
f
Description
Concentration on the feed side of the membrane
immediately after the previous backwash
operation
Concentration maintained on the feed side of the
membrane at a function of position with the
membrane unit
Filtrate concentration
Feed concentration of the challenge paniculate in a
challenge test
Concentration of challenge parti culate in stock
solution
Diffusion coefficient for air through a saturated
semi-permeable membrane
Diffusion coefficient for air in a water matrix
Capillary diameter
Defect diameter
Fiber diameter
Integrity test resolution requirement
Detection limit
Dissolved organic carbon
Specific roughness
Moody friction factor
Units
English
-
-
-
-
-
-
-
in
in
ft
in
ft
in
-
-
in
-
Metric
mg/L
number/L
mg/L
number/L
mg/L
number/L
mg/L
number/L
mg/L
number/L
cm2/s
cm2/s
cm
mm
|j,m
cm
mm
|j,m
cm
mm
|j,m
cm
mm
|j,m
-
mg/L
cm
mm
-
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Symbol
g
H
J
^20
J25
JT
K
Kair
V
-•^water
L
LRC
LRV
LRVt
LRVDIT
LRVc-Test
M
NDP
P
p
L atm
Pbp
PC
Description
Gravitational constant
Henry's constant for air- water system
Flux
Normalized flux at 20 C
(common for MF, UF, and MCF systems)
Normalized flux at 25 C
(common for NF and RO systems)
Flux at temperature T
Flow resistance coefficient
Resistance coefficient of air
Resistance coefficient of water
Defect length
Log removal credit
Log removal value
Target log removal value in a challenge test
Log removal value that can be verified by the direct
integrity test (i.e., method sensitivity)
Log removal value demonstrated during challenge
testing
Permeability or specific flux
Net driving pressure
Pressure
Atmospheric pressure
Bubble point pressure
Concentrate pressure
Units
English
Ibm-ft
lbf-s2
Metric
kg-m
0
s
mol
psi -m3
gfd
gfd
gfd
gfd
-
-
-
in
ft
-
-
-
-
-
gfd/psi
psi
psi
psi
psi
psi
Lmh
Lmh
Lmh
Lmh
-
-
-
cm
mm
-
-
-
-
-
Lmh/kPa
kPa
kPa
kPa
dynes/cm2
atm
kPa
kPa
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Symbol
Pf
PP
Ptest
?P
?Peff
? Ptest
Qair
Qb
^< breach
Qc
Qdiff
Qf
QP
QP(X)
R
Re
R(x)
Rf
Description
Feed pressure
Filtrate pressure
Pressure at which a pressure-based direct integrity
test is conducted
Differential pressure across the membrane during
the direct integrity test
Effective integrity test pressure
Rate of pressure decay / loss
Flow of air
Backwash flow
Flow from an integrity breach associated with the
smallest integrity test response that can be
reliably measured
Concentrate (i.e., bleed or reject) flow
Diffusion of air through the water matrix in the
pores of a fully- wetted membrane
Feed flow
Filtrate flow
Filtrate flow as a function of position within a
membrane unit
Recovery
Reynolds number
Recovery as a function of position within a
membrane unit
Foulant layer resistance
Units
English
psi
psi
psi
psi
psi
psi/min
ft3/s
ft3/min
gpm
ft3/s
ft3/min
gpm
ft3/min
gpm
gpm
gpd
MOD
gpm
gpd
MOD
%
-
%
psi
gfd-cp
Metric
kPa
kPa
kPa
dynes/cm2
kPa
dynes/cm2
kPa
dynes/cm2
kPa/min
cffiVs
cffiVmin
L/min
L/min
cffiVs
cffiVmin
L/min
L/min
L/min
cffiVmin
L/min
L/hr
L/min
L/hr
L/min
%
-
%
bar -hr-m2
L-cp
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Symbol
Rg
Rm
Rt
ri
r2
SF
SSDR
SUVA
T
t
tb
tf
T
*- nun
TCP
TCPP
TDSC
TDSf
TDSP
IMP
TMP25
TMPT
Description
Universal gas constant
Intrinsic membrane resistance
Total membrane resistance
Inner radius of a hollow fiber
Outer radius of a hollow fiber
Safety factor
Stock solution delivery rate
Specific ultraviolet absorbance
Temperature
Filtration cycle time
Backwash duration
Filtration cycle duration
Challenge test duration
Temperature correction factor
Total challenge particulate population
Total dissolved solids concentration in the
concentrate stream
Total dissolved solids concentration in the feed
stream
Total dissolved solids concentration in the filtrate
stream
Transmembrane pressure
Transmembrane pressure at 25 C
Transmembrane pressure at temperature T
Units
English
Metric
L - psia
mol-K
psi
gfd-cp
psi
gfd-cp
in
in
-
gpm
-
ฐF
min
min
min
min
-
number
Ibs
-
-
-
psi
psi
psi
bar -hr-m2
L-cp
bar -hr-m2
L-cp
cm
cm
-
L/min
L/mg-m
ฐC
min
min
min
min
-
number
g
mg/L
mg/L
mg/L
kPa
dynes/cm2
kPa
kPa
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Symbol
u
UCL
UV254
VCF
VCF(jc)
VCF(t)
VCF
v ^i avg
VCFmax
* eq
Vhold
vr
vss
* sys
Mest
X
•^max
Y
z
Description
Membrane- specific temperature correction factor
constant (manufacturer- supplied)
Upper control limit (top = airflow)
(bottom = pressure decay rate)
Ultraviolet absorbance at 254 nm
Volumetric concentration factor
Volumetric concentration factor as a function of
position within a membrane unit
Volumetric concentration factor as a function of
time
Average volumetric concentration factor in a
membrane unit
Maximum volumetric concentration factor in a
membrane unit
System volume required to attain equilibrium feed
concentration during a challenge test
Unfiltered test solution volume remaining in the
system at the end of a challenge test (i.e. the
hold-up volume)
Total recirculation loop volume
Challenge particulate stock solution volume
Volume of pressurized air in a memb rane system
during a pressure- or vacuum-decay test
Minimum challenge test solution volume
Position in a membrane unit in the direction of flow
End position in a membrane unit in the direction of
flow
Net expansion factor for compressible flow through
a pipe to a larger area
Membrane thickness
Units
English
-
psi/min
-
-
-
-
-
-
gal
gal
gal
gal
ft3
gal
ft
ft
-
in
Metric
1/K
L/min
kPa/min
1/m
I/cm
-
-
-
-
-
L
L
L
L
L
L
m
m
-
cm
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Symbol
/(Qair)
AQbreach)
S
?
K
a
Pair
Pw
1*20
M*air
|LlT
M-w
T
Description
airflow correlation function
water flow correlation function
Membrane porosity
Liquid-membrane contact (i.e., "wetting") angle
Pore shape correction factor
Surface tension
Density of air
Density of water
Viscosity of water at 20 ฐC
Viscosity of air
Viscosity of water at temperature T
Viscosity of water
Solids retention time
Units
English
psi-min/mL
psi-min/mL
-
degrees
-
-
lb/ft3
lb/ft3
Ibs/ft-s
Ibs/ft-s
Ibs/ft-s
Ibs/ft-s
min
Metric
psi-min/mL
psi-min/mL
-
degrees
-
dynes/cm
g/m3
g/cm3
cp
cp
cp
cp
min
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                                      Glossary
Anion- a negatively charged ion resulting from the disassociation of salts, acids, or bases in
aqueous solution

Anti-Sealant - a chemical agent added to water to inhibit the precipitation or crystallization of
salt compounds; also referred to as a "scale-inhibitor"

Anti-Telescoping Device - a rigid structure firmly attached to each end of a spiral-wound
nanofiltration (NF) or reserve osmosis (RO) membrane module that prevents telescoping,
unwinding, or other undesirable movement of the membrane module

Array - a description of a nanofiltration (NF) or reverse osmosis (RO) membrane system based
upon the ratio of the number of pressure vessels in each stage that operate in parallel (e.g., a
24:12 (absolute) two-stage array or a 2:1 (relative) two-stage array

Asymmetric - having a varying consistency throughout (e.g., a membrane that varies in density
or porosity across its structure)

Backwash- the intermittent waste stream from a microfiltration (MF) or ultrafiltration (UF)
membrane system;  also, a term for a cleaning operation that typically involves periodic reverse
flow to remove foulants accumulated at the membrane surface

Biofouling - membrane fouling (and associated decreases in flux) that is attributable to the
deposition and growth of microorganisms on the membrane surface and/or the adsorptive fouling
of secretions from microorganisms

Bleed-the continuous waste stream from a microfiltration  (MF) or ultrafiltration (UF) system
operated in a crossflow hydraulic configuration

Boundary Layer- thin layer of water at the surface of a semi-permeable membrane containing
the rejected contaminants from the filtrate (i.e., permeate) flow in higher concentrations than the
bulk feed/brine stream (called concentration polarization), affecting the osmotic pressure and salt
passage

Brackish  Water- saline water in which the dissolved solids content generally falls between that
of drinking water and seawater

Breach -  see Integrity Breach

Brine - a  saline solution with a concentration of dissolved solids exceeding that of seawater (i.e.,
approximately 35,000 mg/L)
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Brine Seal - a rubber seal around the circumference of a spiral-wound module between the
module and the interior pressure vessel wall that separates the feed water from the concentrate
stream, preventing the bypass of feed between the module and the inside of the pressure vessel
wall

Bubble Point - the amount of applied air pressure required to evacuate the largest pores of a
fully-wetted porous membrane

Cation- a positively charged ion resulting from the dissociation of salts, acids, or bases in
aqueous solution

Cartridge - a term commonly used to describe a disposable backwashable or non-backwashable
filter element; included under the term "module" for the purposes of the LT2ESWTR

Challenge Particulate  - the target organism or acceptable surrogate used to determine the log
removal value (LRV) during a challenge test

Challenge Test - (as defined under the LT2ESWTR) a study conducted to determine the
removal efficiency (i.e., log removal value (LRV)) of a membrane material for a particular
organism, particulate, or surrogate

Clean-In Place (CIP) - the periodic application of a chemical solution or (series of solutions) to
a membrane unit for the intended purpose of removing accumulated foulants and thus restoring
permeability and resistance to baseline levels; commonly used term for in-situ chemical cleaning

Colloid - type of particulate matter ranging in size from approximately 2 - 1,000 nm in diameter
that does not settle out rapidly

Compaction- the compression or densification of a membrane as a result of exposure to applied
pressure over a period of time, which typically results in decreased productivity

Composite - made from different materials (e.g., a membrane manufactured from two or more
different materials in distinct layers)

Concentrate - the continuous waste stream (typically consisting of concentrated dissolved
solids) from a membrane process, usually in association with nanofiltration (NF) and reverse
osmosis (RO) processes; in some cases also used to describe a continuous bleed stream of
concentrated suspended solids wasted from microfiltration (MF) and ultrafiltration (UF) systems
operated in a crossflow (or feed-and-bleed), hydraulic configuration

Concentrate Staging - a configuration of spiral-wound nanofiltration (NF) and reverse osmosis
(RO) membrane systems in which the concentrate from each stage of a multi-stage system
becomes the feed for the subsequent stage

Concentration Polarization- a phenomenon that occurs when dissolved and/or colloidal
materials concentrate on or near the membrane surface in the boundary layer
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Conductivity - a measure of the ability of an aqueous solution to conduct an electric charge;
related to the amount of total dissolved solids (TDS)

Continuous Indirect Integrity Monitoring - (as defined under the LT2ESWTR) monitoring
some aspect of filtrate water quality that is indicative of the removal of parti culate matter at a
frequency of at least once every 15 minutes

Control Limit (CL) - (as defined under the LT2ESWTR) a response from an integrity test,
which, if exceeded, indicates a potential problem with the [membrane filtration] system and
triggers a response; synonymous with "upper control limit" (UCL) as used in the Membrane
Filtration  Guidance Manual to distinguish from additional voluntary  or state-mandated "lower
control limits" (LCLs)

Crossflow- the application of water at high velocity tangential to the surface of a membrane to
maintain contaminants in suspension; suspension mode hydraulic configuration typically
associated with spiral-wound nanofiltration (NF) and reverse osmosis (RO) systems and a few
hollow-fiber microfiltration (MF) and ultrafiltration (UF) systems

Dalton - a unit of mass equal to l/12th  the mass of a carbon-12 atom  (i.e., one atomic mass unit
(amu)); typically used as a unit of measure for the molecular weight cutoff (MWCO) of a
ultrafiltration (UF), nanofiltration (NF), or reverse osmosis (RO) membrane

Dead End Filtration- term commonly used to describe the deposition mode hydraulic
configuration of membrane filtration systems; also synonymous with  "direct filtration"

Deposition Mode - a hydraulic configuration of membrane filtration  systems in which
contaminants removed from the feed water accumulate at the membrane surface (and in
microfiltration (MF)/ultrafiltration (UF) systems subsequently removed via backwashing)

Desalination- the process of removing dissolved salts from water

Differential Pressure - pressure drop across a membrane module or  unit from the feed inlet to
concentrate outlet (as distinguished from transmembrane  pressure (TMP), which represents the
pressure drop across the membrane barrier)

Direct Filtration - (as used with respect to membrane filtration) term commonly used describe
the deposition  mode hydraulic configuration of membrane filtration systems;  also synonymous
with "dead end filtration"

Direct Integrity Testing -  (as defined under the LT2ESWTR) a physical test applied to a
membrane unit in order to identify and/or isolate integrity breaches

Electrodialysis (ED) -  a process in which ions are transferred through ion-selective membranes
by means  of an electromotive force from a less concentrated solution  to a more concentrated
solution
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Electrodialysis Reversal (EDR) - a variation of the electrodialysis process in which the polarity
of the electrodes is periodically reversed on a prescribed time cycle, thus changing the direction
of ion movement,  in order to reduce scaling

Element - a term  commonly used to describe an encased spiral-wound membrane module;
included under the term "module" for the purposes of the LT2ESWTR

Feed-and-Bleed Mode - a term used to describe a variation of the suspension mode hydraulic
configuration of membrane filtration systems in which a portion of the crossflow stream is
wasted (i.e., bled)  rather than recirculated

Feed Channel Spacer- a plastic mesh spacer that separates the various leaves  in a spiral-wound
module, providing a uniform channel for feed water to reach the membrane surface and
promoting turbulence in order to minimize the formation of a boundary layer at the membrane
surface

Feed Water - the influent stream to a water treatment process

Filtrate - the water produced from a filtration process; typically used to describe the water
produced by porous membranes such those used in membrane cartridge filtration (MCF),
microfiltration (MF), and ultrafiltration (UF) process, although used in the context of the
LT2ESWTR to  describe the water produced from all membrane filtration processes, including
nanofiltration (NF) and reverse osmosis (RO)

Flux - (as defined under the LT2ESWTR) the throughput of a pressure-driven membrane
filtration system expressed as flow per unit of membrane area (e.g., gallons per  square foot per
day (gfd) or liters  per hour per square meter (Lmh))

Foulant - any substance that causes fouling

Fouling - the gradual accumulation of contaminants on a membrane surface or within a porous
membrane structure that inhibits the passage of water, thus decreasing productivity

Heterogeneous - composed of a combination of different materials (e.g., composite and some
asymmetric membranes)

Hollov^Fiber Module - a configuration in which hollow-fiber membranes are  bundled
longitudinally and either encased in a pressure vessel or submerged in a basin; typically
associated with  microfiltration (MF) and ultrafiltration (UF)  membrane processes

Hollov^Fine-Fiber (HFF) Module - a relatively uncommon configuration in which very small
diameter (i.e., approximately 50 |j,m (inside diameter)) semi-permeable hollow-fiber membranes
are bundled in "U" shape and potted into a pressure vessel; typically associated with reverse
osmosis (RO) membrane processes
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Homogenous - composed of the same material throughout (e.g., symmetric and some
asymmetric membranes)

Hydraulic Configuration- the pattern of flow through a membrane process by which the feed
contaminants are removed or concentrated (e.g., crossflow, dead-end, etc.)

Hydrophilic - the water attracting property of membrane material

Hydrophobic - the water repelling property of membrane material

Integrity Breach - (as defined under the LT2ESWTR) one or more leaks that could result in the
contamination of the filtrate

Irreversible Fouling - any membrane fouling that is permanent and cannot be removed by
either backwashing (if applicable) or chemical cleaning

Leaf- a sandwich arrangement of flat sheet, semi-permeable membranes placed back-to-back
and separated by a fabric spacer (i.e., permeate carrier) in a spiral-wound module

Log Removal Value (LRV) -  (as defined under the LT2ESWTR) filtration removal efficiency
for a target organism, particulate, or surrogate expressed as logo (i.e., Iog0(feed concentration) -
Iog0(filtrate concentration))

Lower Control Limit (LCL) - an additional control limit (CL) that is not mandated by the
LT2ESWTR but which is instead voluntarily implemented or which may be required by the state
at its discretion

Lumen-the center or bore of a hollow-fiber membrane

Membrane Filtration- (as  defined under the LT2ESWTR) a pressure or vacuum-driven
separation process in which particulate matter larger than 1 |j,m is rejected by an engineered
barrier, primarily through a size-exclusion mechanism  and which has a measurable removal
efficiency of a target organism that can be verified through the application of a direct integrity
test (includes common membrane classifications microfiltration (MF), ultrafiltration (UF),
nanofiltration (NF), and reverse osmosis (RO), as well as any "membrane cartridge filtration"
(MCF) device that satisfies this definition)

Membrane Cartridge Filtration (MCF) - (as defined under the LT2ESWTR) any cartridge
filtration devices that meet the  definition of membrane filtration as specified under the
LT2ESWTR

Membrane Softening - semi-permeable membrane treatment process designed to selectively
remove hardness (i.e., calcium, magnesium, and certain other multi-valent cations) but allow
significant passage of monovalent ions; typically used  to describe the application of
nanofiltration (NF) for hardness removal
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Membrane Unit - (as defined under the LT2ESWTR) a group of membrane modules that share
common valving which allows the unit to be isolated from the rest of the system for the purpose
of integrity testing or other maintenance

Molecular Weight Cutoff (MWCO) - a measure of the removal characteristic of a membrane in
terms of atomic weight (or mass), as opposed to pore size; typically measured in terms of
Daltons

Microfiltration (MF) - a pressure-driven membrane filtration process that typically employs
hollow-fiber membranes with a pore size range of approximately 0.1 - 0.2 |j,m (nominally
0.1 urn)

Module - (as defined under the LT2ESWTR) the smallest component of a membrane unit in
which a specific membrane surface area is housed in a device with a filtrate outlet structure; used
in the Membrane Filtration Guidance Manual to refer to all types of membrane configurations,
including terms such as "element" or "cartridge" that are commonly used in the membrane
treatment industry

Nanofiltration (NF) - a pressure-driven membrane separation process that employs the
principles of reverse osmosis to remove dissolved contaminants from water; typically applied for
membrane softening or the removal of dissolved organic contaminants

Net Driving Pressure (NDP) - the pressure available to force water through a semi-permeable
nanofiltration (NF) or reverse osmosis (RO) membrane, defined as the average feed side pressure
(i.e., the average of the feed and concentrate pressures) less the filtrate side backpressure and the
osmotic pressure of the system

Non-Destructive Performance Test (NDPT) - a physical quality control test typically
conducted by a manufacturer to characterize some aspect of process performance without
damaging or altering the membrane or membrane module

Normalization- the process of evaluating membrane system performance at a given set of
reference conditions (e.g., at standard temperature, per unit pressure, etc.), allowing the direct
comparison and trending of day-to-day performance independent of changes to the actual system
operating conditions

Osmosis - the passage of a solvent (e.g., water) through a semi-permeable membrane from a
solution of lower concentration to a solution of higher concentration  so as to equalize the
concentrations on either side of the membrane

Osmotic Pressure  - the amount of pressure that must be applied to stop the natural process of
osmosis

Permeability - the ability of a membrane barrier to allow the passage or diffusion of a substance
(i.e., a gas, a liquid, or solute)
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Permeate - the water that passes through a nanofiltration (NF) or reverse osmosis (RO)
membrane; synonymous with the term filtrate, which is used in the context of the LT2ESWTR

Permeate Staging - a configuration of spiral-wound nanofiltration (NF) and reverse osmosis
(RO) membrane systems in which the permeate (or filtrate) from each stage of a multi-stage
system becomes the feed for the subsequent stage

Permeate Tube - the perforated tube in the center of a spiral-wound module that collects
permeate (or filtrate) and transports it out of the membrane module

Permeate (Filtrate) Carrier- the fabric spacer in between two sheets of membrane material in
one leaf of a spiral-wound module, serving to transfer the water that permeates through the
membrane(s) (i.e., the filtrate) to a perforated central collector tube (i.e., the permeate tube)

Plate-and-Frame Module - a relatively uncommon configuration consisting of a series of flat
sheet membranes separated by alternating filtrate spacers and feed/concentrate spacers; used with
electrodialysis reversal (EDR) membrane systems

Plugging - the physical blockage of the feed side flow passages of a membrane or membrane
module (e.g., a blockage in the lumen of an hollow-fiber module operated in inside-out mode  or
in the spacer of a spiral-wound  module)

Pore Size - the size of the openings in a porous membrane expressed either as nominal (average)
or the absolute (maximum), typically in terms of microns

Porosity - for a membrane material, the ratio of the volume of voids to the total volume

Post-Treatment - any treatment applied to the filtrate of a membrane process in order to meet
given water quality objectives

Pretreatment - any treatment applied to the feed water to a membrane process to achieve
desired water quality  objectives and/or protect the membranes from damage or fouling

Productivity - the amount of filtered water that  can be produced from a membrane filtration unit
or system over a period  of time, accounting for the use of filtrate in backwash and chemical
cleaning operations, as well as otherwise productive time that a unit or system is off-line for
routine maintenance processes such as backwashing, chemical cleaning, integrity testing, or
repair

Quality Control Release Value - a minimum quality standard of a non-destructive  performance
test (NDPT) established by the  manufacturer for membrane module production that ensures that
the module will attain the targeted log removal value (LRV) demonstrated during challenge
testing in compliance with the LT2ESTWR
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Rack - in a nanofiltration (NF) or reverse osmosis (RO) spiral-wound membrane filtration
system, a group of pressure vessels that share common valving and which can be isolated as a
group for testing, cleaning, or repair; synonymous with the terms train and skid; included under
the term "unit" for the purposes of the LT2ESWTR

Recovery - (as defined under the LT2ESWTR) the volumetric percent of feed water that is
converted to filtrate in the treatment process over the course of an uninterrupted (i.e., by
chemical cleaning or a solids removal process such as backwashing) operating cycle (i.e.,
excluding losses that occur due to the use of filtrate in backwashing or cleaning operations)

Reject - a continuous waste stream from a membrane system; used synonymously with the term
concentrate for nanofiltration (NF) and reverse osmosis (RO) membrane systems

Rejection - the prevention of feed water constituents from passing through a semi-permeable
membrane; typically  used in association with dissolved solids rather than particulate matter

Resistance - the measurement of degree to which the flow of water is impeded by a membrane
material or fouling

Resolution- (as defined under the LT2ESWTR) the smallest leak that contributes to a response
from a direct integrity test; also applicable to  some continuous indirect integrity monitoring
methods

Reverse Osmosis (RO) - the reverse of the natural osmosis process - i.e., the passage  of a
solvent (e.g., water) through a semi-permeable membrane from a solution of higher
concentration to a solution of lower concentration against the concentration gradient, achieved
by applying pressure greater than the osmotic pressure to the more concentrated solution; also,
the pressure-driven membrane separation process that employs the principles of reverse osmosis
to remove dissolved contaminants from water

Salinity - amount of salt in a solution;  usually used in association with salt solutions in excess of
1,000 mg/L and synonymously with  the term total dissolved solids (TDS)

Salt Passage - the transport of a salt through a semi-permeable membrane; typically expressed
either as a percentage or as mass of salt per unit of membrane area per unit time

Salt Rejection (Solids Rejection) - the amount of salt in the feed water that is rejected by a
semi-permeable membrane, expressed as a percentage

Scale Inhibitor- a chemical agent added to water to inhibit the precipitation or crystallization of
salt compounds; also referred to as "anti-sealant"

Scaling - the precipitation or crystallization of salts on a surface (e.g., on the feed side of a
membrane)
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Semi-Permeable - the property of a membrane barrier that allows it to selectively pass certain
molecules in a solution while restricting the passage of others

Sensitivity - (as defined under the LT2ESWTR) the maximum log removal value (LRV) that
can be reliably verified by a direct integrity test; also applicable to some continuous indirect
integrity monitoring methods

Skid - in a nanofiltration (NF) or reverse osmosis (RO) spiral-wound membrane filtration
system, a group of pressure vessels that share common valving and which can be isolated as a
group for testing, cleaning, or repair; synonymous with the terms train and rack; included under
the term "unit" for the purposes  of the LT2ESWTR

Softening - the removal of hardness (i.e., divalent metal ions, primarily calcium and
magnesium) from water

Spacer (Feed Water Spacer or Brine Spacer) - the material that separates the semi-permeable
membrane layers and creates flow passages in a spiral-wound module; also called feed water
spacer or brine spacer

Spiral-Wound Module - a configuration in which sheets of a semi-permeable membrane, a
porous support matrix, and a spacer are wrapped around a central filtrate collector tube; typically
associated with nanofiltration (NF) and reverse osmosis (RO) membrane processes

Stage - a group  of membrane units operating in parallel

Suspension Mode - a hydraulic configuration  of membrane filtration systems in which
contaminants  are maintained in suspension through the application of an external force, typically
either air or water tangential to the membrane surface

Surrogate - a challenge particulate that is a substitute for the target microorganism of interest
and which is removed to an equivalent or lesser extent by a membrane filtration device

Symmetric - having the same consistency throughout

Telescoping - the physical deformation of a spiral-wound membrane module due to high
differential pressure in which the membrane, support, and spacer layers are displaced axially
(i.e., in the direction of the feed flow) from the center, causing membrane fracture and  element
failure

Train - in a nanofiltration (NF) or reverse osmosis (RO) spiral-wound membrane filtration
system, a group of pressure vessels that share common valving and which can be isolated as a
group for testing, cleaning, or repair; synonymous with the terms rack and skid; included under
the term "unit" for the purposes  of the LT2ESWTR

Transmembrane Pressure (TMP) - the difference in pressure from the feed (or feed-
concentrate average, if applicable) to the filtrate across a membrane barrier
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Tubular Module - a relatively uncommon configuration (in drinking water applications) similar
to that of a hollow-fiber module but utilizing membranes of much larger diameter; may be
associated with either microfiltration (MF)/ultrafiltration (UF) or nanofiltration (NF)/reverse
osmosis (RO) membrane processes

Turbidimeter- an instrument used to measure turbidity via the scattering of a light beam
through a solution that contains suspended particulate matter

Volumetric Concentration Factor (VCF) - the degree to which the feed water becomes
concentrated in a membrane filtration system operating in a suspension mode hydraulic
configuration;  defined as the suspended solids concentration on the high pressure side of the
membrane relative  to the that of the ambient feed water

Ultrafiltration (UF) - a pressure-driven membrane filtration process that typically employs
hollow-fiber membranes with a pore size range of approximately 0.01 - 0.05 |j,m  (nominally
0.01 urn)

Upper Control Limit (UCL) - a control limit (CL) for a membrane filtration system that is
required by the LT2ESWTR; used in the Membrane Filtration Guidance Manual to distinguish
CLs mandated by the rule from additional "lower control limits" (LCLs) that are either
voluntarily implemented or which may be required by the state at its discretion
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                                 1.0  Introduction
       Currently, the most common form of drinking water treatment for surface water sources
involves the chemical/physical removal of particulate matter by coagulation, flocculation,
sedimentation, and filtration processes, along with disinfection to inactivate any remaining
pathogenic microorganisms. Filtration remains the cornerstone of drinking water treatment,
conventionally in the form of granular media depths filters.  Although granular media filters can
produce high quality water, they represent a probabilistic rather than an absolute barrier;
consequently, pathogens can still pass through the filters and pose a health risk. The disinfection
process provides an additional measure of public health protection by inactivating these
microorganisms. However, some microorganisms, such as Cryptosporidium, are resistant to
common primary disinfection practices such as chlorination and chloramination. Furthermore,
drinking water regulations have established maximum contaminant levels (MCLs) for
disinfection byproducts (DBFs) that may create incentive for drinking water utilities to minimize
the application of some disinfectants.  As a result of the concern over chlorine-resistant
microorganisms and DBF formation, the drinking water industry is increasingly utilizing
alternative treatment technologies in effort to balance the often-competing objectives of
disinfection and DBF control. One such alternative technology that has gained broad acceptance
is membrane  filtration.

       Although the use of membrane processes has increased rapidly in recent years, the
application of membranes for water treatment extends back several decades. Reverse osmosis
(RO) membranes have been used for the desalination of water since the 1960's, with more
widespread use of nanofiltration (NF) for softening and the removal of total organic carbon
(TOC) dating to the late 1980s.  However, the commercialization of backwashable hollow-fiber
microfiltration (MF) and ultrafiltration (UF) membrane processes for the removal of parti culate
matter (i.e., turbidity and microorganisms) in the early 1990's has had the most profound impact
on the use, acceptance, and regulation of all types of membrane processes for drinking water
treatment.

       USEPA developed this guidance manual in support of the Long Term 2 Enhanced
Surface Water Treatment Rule (LT2ESTWR), which has identified membrane filtration (i.e.,
MF,  UF, NF, RO and certain types  of cartridge filters) as one treatment technology in a
"toolbox"  of options that may be used to achieve the required level of Cryptosporidium
treatment.  Although the LT2ESWTR only regulates membrane filtration in terms of its
application for compliance with the requirements of the rule, the concepts and guidance provided
in this manual may also be relevant to the Interim Enhanced Surface Water Treatment Rule
(IESWTR), the Long Term  1 Enhanced Surface Water Treatment Rule (LT1ESWTR), the
Stage 2 Disinfectants and Disinfection Byproducts Rule (DBPR), the Ground Water Rule
(GWR), and other regulations, at the discretion of the state1.
1 For the purposes of this manual, the term "state" refers to the state or primacy agency that is responsible for
  enforcement of drinking water standards.

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1.1    Regulating Membranes for the Drinking Water Industry

       Driven by the need to protect public health from waterborne pathogens, USEPA has
progressively developed regulations that require higher standards for filtered water quality to
prevent the passage of infectious pathogens through the treatment process and into the finished
drinking water supply.  In 1986, the Surface Water Treatment Rule (SWTR) required surface
water systems to provide treatment equivalent to 3 log Giardia and 4 log virus reduction via a
combination of removal and inactivation. USEPA estimated conventional filtration plants (i.e.,
including coagulation and sedimentation) meeting the filter effluent turbidity requirements
provided a minimum of 2.5 log Giardia and 2 log virus reduction, while direct filtration plants
(i.e., without sedimentation) provided 2 log Giardia and 1 log virus removal. The IESWTR (FR
63(241):69518) focused on filter effluent turbidity control, setting a combined filter effluent
turbidity limit of 0.3 NTU (40 CFR 41.173) and requiring individual filter turbidity monitoring
(40 CFR141.174) for systems serving at least  10,000 people.  The rule also introduced a
requirement for 2 log Cryptosporidium removal.  The IESWTR also required that turbidity
monitoring be conducted "continuously" (i.e., every 15 minutes) on individual filters.  Based on
available data, USEPA believed conventional and direct filtration plants meeting the IESWTR
filter effluent turbidity requirements provided  a minimum 2 log removal of Cryptosporidium.
The LT1ESWTR (FR 67(9): 1812) promulgated the requirements of the IESWTR, with some
modifications, for all water systems serving less than  10,000 people.

       Under the existing surface water treatment rules, log removal credits for alternative
filtration technologies (AFTs), such as membrane processes and bag and cartridge filters, were
not explicitly addressed, but instead covered under  a special state primacy requirement. For
compliance with the SWTR, IESWTR, and LT1ESWTR, many states grant removal credits to
membrane processes based on the guidelines for AFTs in the Guidance Manual for Compliance
With the Filtration and Disinfection Requirements for Public Water Systems Using Surface
Water Sources (commonly called the SWTR Guidance Manual) (USEPA 1991).   However, there
is significant variability in the manner in which states regulate membrane processes, as
summarized for MF/UF systems in the USEPA report Low-Pressure Membrane Filtration for
Pathogen Removal: Application, Implementation, and Regulatory Issues (2001).

       The LT2ESWTR builds on the previous surface water treatment rules by requiring
additional treatment for those systems with elevated influent Cryptosporidium levels.  The rule
identifies a number of "toolbox" technologies that may be employed to achieve additional
Cryptosporidium treatment requirements. The range of removal or inactivation credits allocated
to each of the various toolbox options under the rule varies based on the capabilities of the
particular treatment technology. Because the various  types of membrane filtration processes
represent one of these toolbox alternatives, utilities  have the option of using membrane filtration
for compliance with the rule requirements as a distinct technology rather than simply as a general
AFT. Consequently, USEPA has developed specific regulatory requirements and associated
guidance, as contained in this manual, for membrane filtration processes used for  compliance
with the LT2ESWTR.
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1.2    Summary of Applicable Regulations

       Although the regulatory framework presented in this guidance manual is directly
applicable only to the use of membrane filtration for compliance with the LT2ESWTR, the
concepts may be extended to other applications of the technology at the discretion of the state.
Some regulations for which this regulatory framework may be useful  for utilities and states
include the Stage 2 DBPR and the various existing surface water treatment regulations. Because
the Stage 2 DBPR will make DBF limits more stringent, some utilities may consider shifting
treatment strategies to obtain a greater portion of their respective total pathogen control
requirements using removal processes such as membrane filtration rather and less from
disinfection, if such flexibility is permitted by the state.  Since membrane filtration will not be
specifically addressed under the Stage 2 DBPR, the Membrane Filtration Guidance Manual may
serve as a useful resource for states and utilities under the regulatory scenario noted  above. In
addition, this regulatory framework and associated guidance manual may also be a useful
resource for states to develop distinct regulatory policies for membrane filtration relative to the
existing surface water treatment rules (i.e., those promulgated prior to the LT2ESWTR) to
separate the technology from the broader AFT classification.

       The basic requirements of both the LT2ESWTR and the  Stage 2 DBPR are described in
the following subsections.  The information provided is not specific to membrane treatment, but
simply represents a general overview of the rule requirements.
1.2.1   Long Term 2 Enhanced Surface Water Treatment Rule

       Under the LT2ESWTR, systems that use either a surface water or ground water under the
direct influence of surface water (GWUDI) source (collectively referred to as surface water
systems) are required to conduct source water monitoring to determine average Cryptosporidium
concentrations.  Based on the average Cryptosporidium concentration, a system is classified in
one of four possible bins, as shown in Table 1.1 (40 CFR 141.720). The bin assignment dictates
the supplemental level of Cryptosporidium treatment required in addition to the existing
requirements of the SWTR, IESWTR, and LT1ESWTR. Utilities may comply with additional
treatment requirements by implementing one or more management or treatment techniques from
a toolbox of options that includes membrane filtration.  Guidance for the use of membrane
filtration for compliance  with the LT2ESWTR is provided in this manual.  A separate guidance
manual has also been developed for the use of ultraviolet (UV) disinfection for LT2ESWTR
compliance (USEPA 2003).  Guidance for the use of all other toolbox options is given in the
Toolbox Guidance Manual for the Long Term 2 Enhanced Surface Water Treatment Rule
(USEPA 2003).
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  Table 1.1  LT2ESWTR Additional Treatment Requirements for Filtered Systems
LT2ESWTR Category
Bin
1
2
3
4
Cryptosporidium
Concentration
(oocysts/L)
< 0.075
> 0.075 and < 1.0
> 1.0 and < 3.0
> 3.0
Type of Existing Filtration
Conventional
Filtration
No additional
treatment
1 log1
2 log2
2.5 log2
Direct
Filtration
No additional
treatment
1 .5 log1
2.5 log2
3 log2
Slow Sand
or
Diatomaceous
Earth Filtration
No additional
treatment
1 log1
2 log2
2.5 log2
Alternative
Filtration
Technologies6
No additional
treatment
As determined
by the state1 3
As determined
by the state2 4
As determined
by the state2 5
 1  Systems may use any technology or combination of technologies from the toolbox
 2  Systems must achieve at least 1 log of the required treatment using ozone, chlorine dioxide, UV disinfection, membranes,
   bag/cartridge filters, or bank filtration
 3  Total Cryptosporidium treatment must be at least 4 log
 4  Total Cryptosporidium treatment must be at least 5 log
 5  Total Cryptosporidium treatment must be at least 5.5 log
 6  Includes membrane filtration
1.2.2  Stage 2 Disinfectants and Disinfection Byproducts Rule

       The Stage 2 DBPR is designed to reduce DBF occurrence peaks in the distribution
system by changing compliance monitoring requirements.  The requirements of the
Stage 2 DBPR apply to all community water systems (CWSs) and non-transient non-community
water systems (NTNCWSs) - both ground and surface water systems - that either add a
chemical disinfectant (i.e., a disinfectant other than UV light) or deliver water that has been
treated with a chemical disinfectant.  The primary components of the rule are summarized as
follows.
       Initial Distribution System Evaluations

       Under the Stage 2 DBPR, systems are required to conduct an initial distribution system
evaluation (IDSE) to identify compliance monitoring locations with high total trihalomethane
(TTHM) and haloacetic acid (HAAS) levels. The IDSE consists of either a standard monitoring
program (SMP) or a system-specific study (SSS). NTNCWSs serving fewer than 10,000 people
are not required to conduct an IDSE, and other systems may be eligible to receive waivers from
the IDSE requirement.
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       Compliance Determination and Schedule

       The Stage 2 DBPR changes the way DBF sampling results are averaged to determine
compliance, implementing a methodology based on a locational running annual average (LRAA)
rather than the system-wide running annual average (RAA) used under the Stage  1 DBPR. This
new methodology introduced under the Stage 2 DBPR is introduced in two phases: Stage 2A
and Stage 2B. Under Stage 2A, all systems must comply with TTHM and HAAS MCLs of
120 (ig/L and 100 ng/L, respectively, measured as LRAAs at each Stage 1 DBPR monitoring
site, while continuing to comply with the respective TTHM and HAAS Stage 1 DBPR MCLs of
80 |j,g/L and 60 |J,g/L, measured as RAAs. Subsequently, under Stage 2B, systems must comply
with respective TTHM and HAAS MCLs of 80 |j,g/L and 60 |j,g/L at the sampling locations
identified under the IDSE.
       Compliance Monitoring

       Stage 2B compliance monitoring requirements (in terms of number of sites and frequency
of sampling) are expected to be similar to the Stage 1 DBPR requirements for most, but not all,
systems.  Some small systems will have to add an additional monitoring location if the highest
TTHM and highest HAAS site do not occur at the same location.
       Significant Excursion Evaluations

       Because Stage 2 DBPR MCL compliance is based on an annual average of DBF
measurements, a system could from time to time have DBF levels significantly higher than the
MCL (referred to as a significant excursion) while still maintaining compliance.  If a significant
excursion occurs, a system must conduct a significant excursion evaluation and discuss the
evaluation with the state prior to the next sanitary survey.
1.3    Requirements for Membrane Filtration Under the LT2ESWTR

     In order to receive removal credit for Cryptosporidium removal under the LT2ESWTR, a
membrane filtration system must meet the following three criteria (40 CFR 141.728):

       1.  The process must comply with the definition of membrane filtration as stipulated by
          the rule.

       2.  The removal efficiency of a membrane filtration process must be established through
          a product-specific challenge test and direct integrity testing.

       3.  The membrane filtration system  must undergo periodic direct integrity testing and
          continuous indirect integrity monitoring during operation.
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       The rule does not prescribe a specific removal credit for membrane filtration processes.
Instead, removal credit is based on system performance as determined by challenge testing and
verified by the direct integrity testing. Thus, the maximum removal credit that a membrane
filtration process may receive is the lower value of either (40 CFR 141.728):

       •  The removal efficiency demonstrated during challenge testing; OR

       •  The maximum log removal value that can be verified by the direct integrity test used
          to monitor the membrane filtration process

       Based on this framework, a membrane filtration process could potentially meet the Bin 4
Cryptosporidium treatment requirements, as shown in Table 1.1. Additionally, if a membrane
filtration system has been previously approved for 5.5 log Cryptosporidium removal by the state,
the utility would not be required to conduct source monitoring under the LT2ESWTR
(40 CFR 141.728).

       These primary elements of the regulatory requirements for membrane filtration under the
LT2ESWTR, including the definition of membrane  filtration, as well as challenge testing, direct
integrity testing, and continuous indirect integrity monitoring,  are summarized in the following
sections.
1.3.1   Definition of a Membrane Filtration Process

       For the purposes of compliance with the LT2ESWTR, membrane filtration is defined as a
pressure- or vacuum-driven separation process in which particulate matter larger than 1 |im is
rejected by a non-fibrous engineered barrier primarily through a size exclusion mechanism and
which has a measurable removal efficiency of a target organism that can be verified through the
application of a direct integrity test (40 CFR 141.2).  This definition is intended to include the
common membrane technology classifications: MF, UF, NF, and RO.  In addition, any cartridge
filtration device that meets the definition of membrane filtration and which can be subject to
direct integrity testing in accordance with rule requirements would also be eligible for
Cryptosporidium removal credit as a membrane filtration process under the LT2ESWTR
(40 CFR 141.728). In this guidance manual, such processes are called membrane cartridge
filtration (MCF). Filtration processes that are reliant on mechanisms such as adhesion to filter
media or accumulation of a fouling  layer to remove particulate matter are excluded from the
definition of membrane filtration. Examples of processes that would not be considered
membrane filtration devices for the  purposes of LT2ESWTR compliance include bag filters and
cartridge filters using a fibrous filtration media.
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1.3.2  Challenge Testing

       Since there are no uniform design criteria that can be used to assure the removal
efficiency of a membrane process, challenge testing is required to demonstrate the ability of a
treatment process to remove a specific target organism.  The removal efficiency demonstrated
during challenge testing establishes the maximum removal credit that a membrane process would
be eligible to receive, provided that this value is less than or equal to the maximum log removal
value that can be verified by the direct integrity test (40 CFR 141.728), as described in the
following section.  The LT2ESWTR only requires product-specific challenge testing; once the
removal efficiency has been demonstrated,  additional testing is not required unless the product is
significantly modified, as described in Chapter 3. Data from challenge studies conducted prior to
promulgation of this regulation can be considered in lieu of additional testing at the discretion of
the state (40 CFR 141, Subpart W, Appendix C). However, the prior testing must have been
conducted in a manner that demonstrates removal efficiency for Cryptosporidium equivalent to
or greater than the treatment credit awarded to the process.
1.3.3  Direct Integrity Testing

       While challenge testing can demonstrate the ability of an integral membrane process to
remove the target organism, integrity breaches can develop in the membrane during routine
operation that could allow the passage of microorganisms. In order to verify the removal
efficiency of a membrane process during operation, direct integrity testing is required for all
membrane filtration processes used to comply with LT2ESWTR (40 CFR 141.728).  A direct
integrity test is defined as a physical test applied to a membrane unit in order to identify and
isolate integrity breaches. The rule does not mandate the use of a specific type of direct integrity
test, but rather performance criteria that any direct integrity test must meet.  These criteria
include requirements for resolution, sensitivity, and frequency (40 CFR 141, Subpart W,
Appendix C):

       •  Resolution:  The direct integrity test must be applied in a  manner such that a 3 |j,m
          hole contributes to the response from the test.

       •  Sensitivity: The direct integrity test must be capable of verifying the log removal
          value awarded to the membrane process.

       •  Frequency:  The direct integrity test must be applied at a  frequency of at least once
          per day.
       A control limit must also be established for a direct integrity test, representing a threshold
response which, if exceeded, indicates a potential integrity problem and triggers subsequent
corrective action.  For the purposes of LT2ESWTR compliance, this threshold response must be
indicative of an integral membrane unit capable of achieving the Cryptosporidium removal credit
awarded by the state.
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       The criteria for direct integrity testing are discussed in greater detail in Chapter 4, along
with guidance describing how these criteria apply to commonly used direct integrity tests.
1.3.4  Continuous Indirect Integrity Monitoring

       Because currently available direct integrity test methods require the membrane unit to be
temporarily taken out of service, or are either too costly or infeasible to apply continuously,
direct testing is only conducted periodically. Thus, in the absence of continuous direct integrity
test that meets the resolution and sensitivity requirements of the LT2ESWTR, continuous
indirect integrity monitoring is required (40 CFR 141.728). Although the indirect monitoring
methods are typically not as sensitive as direct tests for detecting losses of membrane integrity,
the indirect methods do provide some measure of performance assessment between applications
of direct testing.  For the purposes of the LT2ESWTR, continuous indirect integrity monitoring
is defined as monitoring some filtrate water parameter that is indicative of the removal of
particulate matter at a frequency of no less than once every 15 minutes (40 CFR 141.728).
Although turbidity monitoring is specified as the default method of continuous indirect integrity
monitoring under the rule, other methods, such as particle counting or particle monitoring, may
be used in lieu of turbidity monitoring at the discretion of the state (40 CFR 141.728). For any
indirect method used, a control limit must be established that is indicative of acceptable
performance. Monitoring results exceeding the control limit for a period of more than 15
minutes must trigger direct integrity testing (40 CFR 141.728). The requirements and associated
guidance for continuous indirect integrity monitoring are detailed in Chapter 5.
1.4    Considering Existing Membrane Facilities Under the LT2ESWTR

       As shown in Table 1.1, the LT2ESWTR only requires additional treatment measure for
those drinking water systems with source water Cryptosporidium levels greater than or equal to
0.075 oocysts/L - bins 2, 3, or 4.  Thus, existing systems utilizing membrane filtration that fall
into bin 1 may continue to operate under the previous surface water treatment rules (i.e., the
SWTR and either the IESWTR or the LT1ESWTR) as administered by the state.

       Utilities with existing membrane filtration facilities will be affected by the LT2ESWTR
in one of five ways. These cases  are summarized as follows:

       •  Case 1:  The utility has previously been awarded 5.5 log Cryptosporidium treatment
          credit via a combination of physical removal (which may include membrane
          filtration) and chemical inactivation. In this case the utility is not required to conduct
          source water monitoring (40 CFR 141.701(f)).

       •  Case 2:  The utility conducts source water monitoring for Cryptosporidium., and
          determines that it is in bin 1 (i.e., concentrations less than 0.075 oocysts/L). In this
          case, the system may continue to operate under the previous surface water treatment
          rules (i.e., the SWTR and either the IESWTR or the LT1ESWTR) as administered by
          the state. No additional action is required under the LT2ESWTR.
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           Case 3: The utility conducts source water monitoring for Cryptosporidium, and
           determines that it is in either bins 2, 3, or 4 (i.e., concentrations greater than or equal
           to 0.075 oocysts/L). The utility then successfully demonstrates to the state that its
           membrane filtration system can achieve the total required Cryptosporidium treatment
           credit, as listed in the right hand column of Table 1.1, up to a maximum  of 5.5 log
           credit.

           Case 4: The utility conducts source water monitoring for Cryptosporidium, and
           determines that it is in either bins 2, 3, or 4 (i.e., concentrations greater than or equal
           to 0.075 oocysts/L). The utility then successfully demonstrates to the state that its
           membrane filtration system can achieve/jar* of the required Cryptosporidium
           treatment credit, as listed in the right hand column (i.e., under "Type of Existing
           Filtration - Alternative Filtration Technologies") of Table 1.1. In this case the utility
           would be required to use other toolbox options to obtain the balance of
           Cryptosporidium treatment credit required under the rule.

           Case 5: The utility conducts source water monitoring for Cryptosporidium, and
           determines that it is in either bins 2, 3 or 4 (i.e., concentrations greater than or equal
           to 0.075 oocysts/L). The utility then successfully demonstrates to the state that its
           membrane filtration system can achieve part of the required Cryptosporidium
           treatment credit, as listed in the right hand column (i.e., under "Type of Existing
           Filtration - Alternative Filtration Technologies") of Table 1.1.  However, the utility
           opts not to use its membrane filtration system for the purposes of LT2ESWTR
           compliance.  In this case the utility would be required use other toolbox  options to
           obtain all of the Cryptosporidium treatment credit required under the rule.
       Under the LT2ESTWR, the regulatory basis for a membrane filtration process to receive
treatment credit for Cryptosporidium is the demonstration of removal efficiency through
challenge testing and the demonstration of membrane system integrity through routine direct
integrity testing and continuous indirect integrity monitoring.  These criteria form the basis for
the potential for membrane filtration systems to be award up to a maximum of 5.5 log
Cryptosporidium removal credit for complying with the requirements of the previously
promulgated surface water treatment rules in combination with any additional Cryptosporidium
treatment credit that may be required under the LT2ESWTR.

       With respect to the challenge testing requirements of the rule, the two most likely options
available to utilities with existing membrane filtration systems are to grandfather data generated
during the pilot testing conducted as part of the permitting process (if applicable) or to use data
from challenge testing conducted by the membrane manufacturer in its effort to qualify its
product(s) for Cryptosporidium removal credit under LT2ESWTR (since challenge testing is
required on a product-specific and  not a site-specific basis). Challenge testing, including
recommendations for grandfathering data, is described in detail in Chapter 3.
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       Existing membrane facilities will also have to meet the direct integrity testing and
continuous indirect integrity monitoring requirements of the LT2ESWTR to qualify for treatment
credit under the rule. This may necessitate that some facilities implement new integrity
verification practices, since state requirements vary widely, and some may not require direct
integrity testing at all (USEPA 2001). However, this is not anticipated to be problematic for
many existing facilities, since most membrane filtration systems applied to surface water are
equipped with the ability to conduct some form of direct integrity testing.  In addition, although
states may not have explicit indirect integrity monitoring requirements, turbidity monitoring (the
default method of continuous indirect integrity monitoring under the LT2ESWTR) is nonetheless
required for compliance with the various existing surface water treatment rules.  In some cases,
utilities may need to purchase additional equipment to comply with the integrity verification
requirements of the rule. Detailed guidance on the use of direct integrity testing and continuous
indirect integrity monitoring for LT2ESWTR compliance  is provided in Chapters 4 and 5,
respectively.

       Another consideration for existing membrane facilities required to meet the LT2ESWTR
criteria is replacement membrane modules. When replacement modules are installed, it is
necessary  to verify that the specific modules used meet the quality control release value of the
nondestructive performance test as a means of indirectly verifying removal efficiency.
Additional guidance regarding the nondestructive performance test is provided in section 3.6.

       The regulatory framework developed for membrane filtration under the LT2ESWTR
addresses  many of the specific capabilities and requirements of the technology, and thus may
introduce new concepts that might not be included in a given state's current regulatory  approach
for membrane processes, particularly if the state currently considers membrane filtration as an
AFT, as described the Guidance Manual for Compliance With the Filtration and Disinfection
Requirements for Public Water Systems Using Surface Water Sources (USEPA 1991).  Although
states may choose to adopt aspects of the LT2ESWTR framework for broader regulation of
membrane filtration systems, USEPA only requires that this regulatory framework be applied to
systems that utilize membrane filtration to meet the additional Cryptosporidium treatment
requirements of the LT2ESWTR.
1.5    Membrane Terminology Used in the Guidance Manual

       In the development of the regulatory language and associated guidance for LT2ESWTR,
it was necessary to select the most appropriate terminology for various aspects of membrane
treatment, with the understanding that use of such terminology can vary widely throughout the
industry. The purpose of this section is to clarify the use of membrane treatment terminology
associated with the LT2ESWTR and note generally synonymous terms that are also in common
use, where applicable. This section also presents some new terms defined under the rule that are
critical to the regulatory framework.

       There are twelve terms formally defined under the language for the LT2ESWTR, as
follows:
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       •  Membrane filtration- a pressure- or vacuum-driven separation process in which
          particulate matter larger than 1 |j,m is rejected by a nonfibrous engineered barrier,
          primarily through a size exclusion mechanism and which has a measurable removal
          efficiency of a target organism that can be verified through the application of a direct
          integrity test (40 CFR 141.2).  The definition of a membrane filtration process and
          what it represents is further discussed in section 1.3.1.

       •  Module - the smallest component of a membrane unit in which a specific membrane
          surface area is housed in a device with a filtrate outlet structure (40 CFR  141,
          Subpart W, Appendix C). For the purposes of the LT2ESWTR, this term
          encompasses hollow-fiber modules and cassettes, spiral-wound elements, cartridge
          filter elements, plate-and-frame modules, and tubular modules, among other
          membrane devices of similar scope and purpose.

       •  Membrane unit - a group of membrane modules that share common valving which
          allows the unit to be isolated from the rest of the system for the purpose of integrity
          testing or other maintenance (40 CFR 141, Subpart W, Appendix C). For the
          purposes of the  LT2ESWTR, "membrane unit" is intended to include the commonly-
          used synonymous terms rack, train, and skid.

       •  Challenge test - a study conducted to determine the  removal efficiency (i.e., log
          removal value (LRV)) of the membrane filtration media (40 CFR 141, Subpart W,
          Appendix C). Challenge testing is discussed in detail in Chapter 3, and the
          requirements for challenge testing under the LT2ESWTR are summarized  briefly in
          section 1.3.2.

       •  Flux -flow per unit of membrane area (40 CFR 141, Subpart W, Appendix C).

       •  Recovery - the ratio of filtrate volume produced by a membrane to feed water
          volume applied to a membrane over the course of an uninterrupted operating cycle
          (40 CFR 141, Subpart W, Appendix C). In the context of the LT2ESWTR, the term
          recovery  does not consider losses that occur due to the use of filtrate in backwashing
          or cleaning operations.

       •  Direct integrity test - a physical test applied to a membrane unit in order to identify
          and isolate integrity breaches (40 CFR 141, Subpart  W, Appendix C).  Direct
          integrity testing is discussed in detail in Chapter 4, and the requirements for direct
          integrity testing under the LT2ESWTR are summarized briefly in section 1.3.3.

       •  Integrity breach- one or more leaks [in a membrane filtration system} that could
          result in the contamination of the filtrate (40 CFR 141, Subpart W, Appendix C).

       •  Resolution- the smallest leak that [i.e., integrity breach] that  contributes to a
          response from a direct integrity test (40 CFR 141, Subpart W, Appendix C).
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       •  Sensitivity - the maximum log removal value that can be reliably verified by the
          direct integrity test [associated with a membrane filtration system} (40 CFR 141,
          Subpart W, Appendix C).

       •  Control limit - an integrity test response that, if exceeded, indicates a potential
          problem with the system and triggers a response (40 CFR 141, Subpart W, Appendix
          C). In the context of this guidance manual the terms upper control limit (UCL) and
          lower control limit (LCL) are also used.  The term upper control limit is always used
          in reference to the control limit that is mandated under the LT2ESWTR, or the last
          control limit that could be exceeded before the unit must be taken off-line for
          diagnostic testing and repair.  The term lower control limit was established to
          distinguish any more conservative voluntary or additional  state-mandated control
          limits that may trigger increased monitoring or other action short of taking the unit
          off-line.

       •  Indirect integrity monitoring - monitoring some aspect of filtrate water quality that
          is indicative of the removal of paniculate matter (40 CFR 141.728). In the context of
          indirect integrity monitoring, continuous is defined as a frequency of no less than
          once  every 15 minutes (40 CFR 141.728). Continuous indirect integrity monitoring is
          discussed in detail in Chapter 5, and the requirements for continuous indirect integrity
          monitoring under the LT2ESWTR are summarized briefly in section 1.3.4.
       In addition to these terms, it is important to note that the term filtrate, as used in both the
rule language and this guidance manual, includes the synonymous term permeate, which is
commonly used in the industry in association with the treated water from NF and RO semi-
permeable membrane processes. All of the terms  clarified in this section, as well as numerous
others used in the context of this manual, are defined in the glossary.
1.6    Guidance Manual Objectives

       The purpose of this manual is to establish a clear and consistent framework for the
application and regulation of membrane filtration for compliance with the requirements of the
LT2ESWTR.  Specifically, the objective of the manual is to provide utilities, state regulators,
membrane module and system manufacturers, and consulting engineers with guidance in the
following respective areas:

       •  Utilities and consulting engineers: specific guidance on meeting the criteria
          specified in LT2ESWTR in order to receive removal credit for Cryptosporidium
          through the application of membrane filtration, as well as additional guidance
          regarding industry practices for pilot testing, implementing, and starting up a
          membrane  filtration facility.
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          State regulators: guidance on evaluating membrane filtration systems and
          determining appropriate Cryptosporidium removal credits for these processes under
          the LT2ESWTR

          Manufacturers : guidance on qualifying membrane filtration systems for
          Cryptosporidium removal credits under the LT2ESWTR
       Note that the guidance provided in this manual applies to systems that meet the definition
of membrane filtration under the LT2ESWTR, including MF, UF, NF, and RO processes, as well
as qualifying cartridge filtration systems.  Electrodialysis (ED) and electrodialysis reversal
(EDR) processes are not considered in this document, since they do not provide a physical
barrier to pathogens and consequently are not considered membrane filtration under the rule.
1.7    Guidance Manual Organization

       The Membrane Filtration Guidance Manual expands on the requirements for utilizing
membrane filtration for compliance with the LT2ESWTR and provides guidance to facilitate
compliance with these requirements.  In addition, this manual describes some recommended
industry practices for the application of membrane filtration systems for the removal of
pathogens in the drinking water treatment process. These recommended practices are not
required under LT2ESTWR and are provided as general guidance only.

       Chapters 1,  3, 4, and 5 elaborates on LT2ESTWR requirements and associated guidance,
while Chapters 6, 7, and 8 discuss recommended industry practices for membrane filtration that
are not specifically related to the rule.  Chapter 2 presents an overview of membrane filtration for
readers unfamiliar with the technology. It is recommended that even readers with significant
membrane process  experience review Chapter 2 to better understand how the concepts and
terminology are used in the context of the guidance manual.

The guidance manual is organized  as follows:

       Chapter 1:    Introduction
                    Chapter 1 presents the objectives of the guidance manual and provides an
                    overview of the regulatory requirements for membrane filtration under the
                    LT2ESWTR.

       Chapter 2:    Overview of Membrane Filtration
                    Chapter 2 provides an overview of the basic theory and concepts of
                    membrane filtration, including: types of membrane processes; types of
                    membrane materials, modules, and systems; fundamental principles; and
                    hydraulic models describing various configurations.
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       Chapter 3:     Challenge Testing
                     Chapter 3 provides guidance on designing a challenge study to
                     demonstrate the removal efficiency of a membrane module with respect to
                     Cryptosporidium, as required under the LT2ESWTR.

       Chapter 4:     Direct Integrity Testing
                     Chapter 4 provides guidance on meeting the LT2ESWTR performance-
                     based requirements for direct integrity testing of membrane filtration
                     systems and describes the commonly used direct integrity test methods in
                     the context of these requirements.

       Chapter 5:     Continuous Indirect Integrity Monitoring
                     Chapter 5 provides guidance on meeting the LT2ESWTR requirements for
                     continuous indirect integrity monitoring, including both the default
                     approach using turbidity as well as a discussion of potential alternative
                     methods.

       Chapter 6:     Pilot Testing
                     Chapter 6 discusses aspects of pilot testing membrane filtration systems,
                     including objectives, planning, operation, and data collection and analysis.

       Chapter 7:     Implementation Considerations
                     Chapter 7 discusses a variety of design and operational considerations for
                     implementing membrane filtration processes.

       ChapterS:     Initial Startup
                     Chapter 8 discusses issues associated with the start-up and shakedown of a
                     new membrane filtration system, as well as some recommended practices
                     to facilitate this process.

       Appendix A:  Development of a Comprehensive Integrity Verification Program
                     Appendix A presents a framework for developing an integrity testing and
                     monitoring program that utilizes a variety of tools to ensure system
                     performance.

       Appendix B:  Overview of Bubble Point Theory
                     Appendix B presents an overview of bubble point theory, which serves as
                     the basis for pressure-based direct integrity tests.

       Appendix C:  Calculating the Air-Liquid Conversion Ratio
                     Appendix C provides supplemental guidance for calculating the air-liquid
                     conversion ratio (ALCR) (as described in Chapter 4), a method for
                     converting the results of pressure-based direct integrity tests to the flow of
                     water through an integrity breach during normal system operation for the
                     purpose of determining both test sensitivity and appropriate control limits.
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       Appendix D:  Empirical Method for Determining the Air-Liquid Conversion Ratio for a
                    Hollow-Fiber Membrane Filtration System
                    Appendix D describes an empirical method called the correlated airflow
                    measurement (CAM) procedure for determining the ALCR, as described
                    in Chapter 4.

       Appendix E:  Application of Membrane Filtration for Virus Removal
                    Appendix E provides a general overview of the issue of applying
                    membrane filtration, and in particular UF, for virus removal, including the
                    applicability of the LT2ESWTR regulatory framework for this objective.
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                   2.0  Overview of Membrane Filtration
 2.1     Introduction

        There are several classes of treatment processes that constitute membrane filtration for
 the purposes of Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR)
 compliance.  These processes include: microfiltration (MF), ultrafiltration (UF), nanofiltration
 (NF), and reverse osmosis (RO). In addition, cartridge filtration devices that meet the criteria for
 a membrane filtration process as defined under the rule (see sections 1.3.1 and 2.2) would also be
 eligible for Cryptosporidium removal credit as membrane filtration (40 CFR 141.728). For the
 purposes of this guidance manual, these devices are termed membrane cartridge filtration (MCF).

        Each of these technologies utilizes a membrane barrier that allows the passage of water
 but removes contaminants.  The membrane media is generally manufactured as flat sheets or as
 hollow fibers and then configured into membrane modules. The most common membrane
 module configurations are hollow-fiber (consisting of hollow-fiber membrane material),  spiral-
 wound (consisting of flat sheet membrane material wrapped around a central collection tube),
 and cartridge (consisting of flat sheet membrane material that is often pleated to increase the
 surface area). Although the spiral-wound and cartridge configurations are also termed as
 "elements" and "cartridges," respectively, under the LT2ESWTR the term "module" - defined as
 the smallest component  of a membrane unit in which a specific membrane surface area is housed
 in a device with a filtrate outlet structure (see section 1.5) - is used to refer to all of the various
 membrane module configurations for simplicity of nomenclature (40 CFR 141.728).

        In addition to the various module configurations, there are a number of different types of
 membrane materials, hydraulic modes of operation, and  operational driving forces (i.e., pressure
 or vacuum) that can vary among the different classes of membrane filtration (i.e., MF, UF, NF,
 RO, and MCF). Each of these characteristics of membrane filtration systems may be considered
 tools that a manufacturer may utilize to meet the particular treatment objectives for a given
 application.

        The  purpose of Chapter 2 of the Membrane Filtration Guidance Manual is to provide an
 overview of the various  membrane filtration processes, including descriptions of the various
 classes, membrane material, geometry, module construction, driving forces, basic principles of
 design  and operation, and hydraulic configuration(s). Emphasis is given to the manner in which
 each of these characteristics relates to membrane filtration  applied for pathogen removal, as
 would be the case for compliance with the LT2ESWTR.

This  chapter is divided into the following sections:

        Section 2.2:   Basic Principles of Membrane Filtration
                     This section reviews the basic treatment mechanisms of the various classes
                     of membrane  treatment processes, as well as the common principle of
                     operation that distinguishes membrane filtration systems,  particularly in
                     the context of the LT2ESWTR.
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       Section 2.3:   Membrane Materials, Modules, and Systems
                    This section describes the types of membrane materials, modules, and
                    types of systems associated with the various classes of membrane
                    filtration.

       Section 2.4:   Basic Principles of Membrane Filtration System Design and Operation
                    The section presents some the basic concepts and equations governing
                    membrane filtration system design and operation in order to facilitate a
                    more complete general understanding of membrane processes.

       Section 2.5:   Hydraulic Configurations
                    This section describes the various hydraulic modes of operation for
                    membrane filtration systems and provides equations for calculating the
                    volumetric concentration factor.
2.2    Basic Principles of Membrane Filtration

       For the purposes of the LT2ESWTR, a membrane filtration process is defined by two
basic criteria (40 CFR 141.2):

       1.  The filtration system must be a pressure- or vacuum-driven process and remove
          particulate matter larger than 1  micron (|J,m) using a non-fibrous,  engineered barrier,
          primarily via a size exclusion mechanism.

       2.  The process must have a measurable removal efficiency of a target organism that can
          be verified through the application of a direct integrity test.

       The ability of each of type of membrane filtration system to remove various drinking
water pathogens of interest on the basis of size is illustrated in Figure 2.1.  The figure shows the
approximate size range of viruses, bacteria, and Cryptosporidium and Giardia cysts, as well as
the ability of MF, UF, NF, RO, and MCF, respectively, to remove each of these pathogens on the
basis of size exclusion.  Overlap between the range covered by a membrane filtration processes
in the figure with a given pathogen size range indicates the ability of that process to remove the
pathogen.  Note that the molecular weights listed do not correspond precisely to the indicated
pathogen size range, but are rough generalizations depicted as a result of the  fact that NF,  RO,
and some UF processes are rated  according to a "molecular weight cutoff on the basis of their
ability to remove dissolved solids and larger macromolecules.

       Although each of the classes of membrane filtration functions as a filter for various sizes
of particulate matter, the basic principles of operation vary between MF/UF,  NF/RO, and MCF
systems. Each of these types of systems is described in the following  sections.
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              Figure 2.1  Filtration Application Guide for Pathogen Removal
Size (urn) 0.0001 0.001 0.01 0.1 1.0 10 100
Molecular Weight '
(Daltons)
Drinking Water
Pathogens
Membrane Filtration
Process
2

10 20,

000 200
cm
Viruses


i
000
i

| Bacteria |
tosporidium —

| Giardia \
-a



MCF
i
MF



1 UF

i
i
NF
i i
RO

i
2.2.1   Microfiltration and Ultrafiltration

       MF and UF are the two processes that are most often associated with the term
"membrane filtration."  MF and UF are characterized by their ability to remove suspended or
colloidal particles via a sieving mechanism based on the size of the membrane pores relative to
that of the particulate matter. However, all membranes have a distribution of pore sizes, and this
distribution will vary according to the membrane material and manufacturing process. When a
pore size is stated, it can be presented as either nominal (i.e., the average pore size), or absolute
(i.e., the maximum pore size) in terms of microns (|J,m). MF membranes are generally
considered to have a pore  size range of 0.1 - 0.2 |j,m (nominally 0.1  |j,m), although there are
exceptions, as MF membranes with pores sizes of up to 10 |j,m are available. For UF, pore  sizes
generally range from 0.01 - 0.05 |j,m (nominally 0.01|j,m) or less, decreasing to an extent at
which the  concept of a discernable "pore" becomes inappropriate, a  point at which some discrete
macromolecules can be retained by the membrane material. In terms of a pore size, the lower
cutoff for a UF membrane is approximately 0.005 |j,m.

       Because some UF membranes have the ability to retain larger organic macromolecules,
they have been historically characterized by a molecular weight cutoff (MWCO) rather than by a
particular pore size. The concept of the MWCO (expressed in Daltons - a unit of mass) is a
measure of the removal characteristic of a membrane in terms  of atomic weight (or mass) rather
than size.  Thus, UF membranes with a specified MWCO  are presumed to act as a barrier to
compounds or molecules with a molecular weight exceeding the MWCO. Because such organic
macromolecules are morphologically difficult to define and are typically found in solution rather
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than as suspended solids, it may be convenient in conceptual terms to use a MWCO rather than a
particular pore size to define UF membranes when discussed in reference to these types of
compounds. Typical MWCO levels for UF membranes range from 10,000 to 500,000 Daltons,
with most membranes used for water treatment at approximately 100,000 MWCO. However, UF
membranes remove particulate contaminants via a size exclusion mechanism and not on the basis
of weight or mass; thus, UF membranes used for drinking water treatment are also characterized
according to pore size with respect to microbial and particulate removal capabilities.
2.2.2  Nanofiltration and Reverse Osmosis

       NF and RO constitute the class of membrane processes that is most often used in
applications that require the removal of dissolved contaminants, as in the case of softening or
desalination.  The typical range of MWCO levels is less than 100 Daltons for RO membranes,
and between 200 and 1,000 Daltons for NF membranes. While NF and RO are sometimes
referred to as "filters" of dissolved solids, NF and RO utilize semi-permeable membranes that do
not have definable pores.  NF and RO processes achieve removal of dissolved contaminants
through the process of reverse osmosis, as described below.  However, these membrane
processes also represent a barrier to particulate matter and thus are considered membrane
filtration under the LT2ESWTR (40 CFR 141.2).

       NF/RO membranes are designed to remove dissolved solids through the process of
reverse osmosis. Osmosis is the natural  flow of a solvent, such as water, through a semi-
permeable membrane (acting as a barrier to dissolved solids) from a less concentrated solution to
a more concentrated solution.  This flow will continue until the chemical potentials (or
concentrations, for practical purposes) on both sides of the membrane are equal. The amount of
pressure that must be applied to the more concentrated solution to stop this flow of water is
called the osmotic pressure. An approximate rule of thumb for the osmotic pressure of fresh or
brackish water is approximately  1 psi for every 100 mg/L difference in total dissolved solids
(TDS) concentration  on opposite sides of the membrane.

       Reverse osmosis, as illustrated in Figure 2.2, is the reversal of the natural osmotic
process, accomplished by applying pressure in excess of the osmotic pressure to the more
concentrated solution. This pressure forces the water through the membrane against the natural
osmotic gradient, thereby  increasingly concentrating the water on one side (i.e., the feed) of the
membrane and increasing the volume of water with a lower concentration of dissolved solids on
the opposite side (i.e., the filtrate or permeate).  The required operating pressure varies
depending on the TDS of the feed water (i.e., osmotic potential), as well as on membrane
properties and temperature, and can range from less than 100 psi for some NF applications to
more than 1,000 psi for RO seawater desalting.
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                Figure 2.2  Conceptual Diagram of Osmotic Pressure
                   Semi-permeable
                   . membrane
Dilu
Soluti

1=
'
a
=>



•
r
e Concentrated
on Solution
              Osmosis
Osmotic
Pressure
Reverse
Osmosis
       Both the NF and RO are pressure driven separation processes that utilize semi-permeable
membrane barriers.  NF differs from RO only in terms of its lower removal efficiencies for
dissolved substances, particularly for monovalent ions.  This results in unique applications of
NF, such as the removal of hardness ions at lower pressures than would be possible using RO.
Consequently, NF is often called "membrane softening." The differences between NF and RO
are irrelevant with respect to the removal of particulate matter, and as a result, these two
membrane processes are functionally equivalent for the purposes of the LT2ESWTR.

       Because semi-permeable NF and RO membranes are not porous, they have the ability to
screen microorganisms and particulate matter in the feed water; however, they are not
necessarily absolute barriers. NF and RO membranes are specifically designed for the removal
of TDS and not particulate matter, and thus the elimination of all small seal leaks that have only
a nominal impact on the salt rejection characteristics is not the primary focus of the
manufacturing process.  Consequently, spiral-wound  elements are not intended to be sterilizing
filters and some passage of particulate matter may occur despite the absence of pores in the
membrane, which can be attributed to slight manufacturing imperfections (Meltzer 1997).
Nonetheless, NF  and RO are eligible for Cryptosporidium removal credit under the LT2ESWTR
based on the demonstrated ability of these technologies to remove pathogens, as well  as on the
high probability that these processes can meet the requirements for membrane filtration specified
in the rule.
2.2.3  Membrane Cartridge Filtration

       The principles of MCF system operation are similar those for MF/UF systems in that
MCF filters particles via a sieving mechanism on the basis of size exclusion. While cartridge
filtration has not traditionally been considered a membrane treatment process, a cartridge
filtration device that utilizes a membrane filtration media capable of removing particles 1.0 |j,m
and larger and which can be subjected to direct integrity testing would satisfy the requirements
for membrane filtration (40 CFR  141.728). However, many cartridge filters have pore sizes that
are larger than 1.0 |j,m,  and the utilization of a direct integrity test with these filters is  relatively
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new in drinking water treatment applications.  Thus, it is important to note that only cartridge
filters that meet both criteria of the definition are considered membrane filtration under the
LT2ESWTR.
2.2.4  Membrane Pore Size and Filtration Removal Efficiency

       Although the concept of using the nominal or absolute pore size is sometimes used in
reference to the filtration capabilities of membrane material, this concept is overly simplistic and
does not fully characterize the removal efficiency of a membrane. For example, the mechanisms
of filtering particles close in size to the pore distribution of a membrane becomes more complex
than sieving, as particles smaller than most pores may be removed through probabilistic
interception through the depth of the filter media.  In addition, for some membrane materials,
particles may be rejected through electrostatic repulsion and adsorption to the membrane
material.  The filtration properties of the membrane may also depend on the formation of a cake
layer during operation, as the deposition of particles can obscure the pores over the course of a
filter run, thus increasing the removal efficiency.

       Because there are  currently no standard methods for characterizing and reporting the pore
sizes for the various membrane filtration processes, the meaning of this information can vary
between different membrane manufactures, thereby limiting its value.  In addition, the concept of
pore size has no significance for NF and RO, which utilize semi-permeable membranes that do
not have pores.  The concept of pore size also does not address the integrity of the manufactured
membrane module assembly, which could potentially pass particles larger than the indicated pore
size.

       Consequently, for the purpose of LT2ESWTR compliance, the rule requires that
membrane filtration performance be determined by challenge testing in which the ability of the
membrane module to reject Cryptosporidium (or an approved surrogate) is demonstrated.  These
studies provide a means to empirically determine the actual exclusion characteristic of the
membrane module for Cryptosporidium (or other contaminant of interest) and thus account for
all the factors that contribute to removal efficiency.  Thus, unlike a measure of pore size, the use
of an empirically determined exclusion characteristic facilitates  the direct comparison of
different membrane filtration systems for the removal of a target contaminant and provides a
direct measure of membrane performance. Challenge testing is  described in further detail in
Chapter 3.
2.2.5  Electrodialysis and Electrodialysis Reversal

       Although both electrodialysis (ED) and electrodialysis reversal (EDR) utilize membranes
and are classified as membrane processes, these treatment technologies do not constitute
membrane filtration as defined by the LT2ESWTR (40 CFR 141.2). Unlike NF and RO, which
use pressure to force water through the membranes while rejecting dissolved solids, the driving
force for separation in ED and EDR processes is electric potential, and an applied current is
utilized to transport ionic species across selectively permeable membranes. Because the water
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does not physically pass through the membrane in either the ED or EDR process, particulate
matter is not removed. Thus, ED and EDR membranes are specifically applied for the removal
of dissolved ionic constituents and are not considered filters.  Consequently, ED/EDR processes
are not addressed further in this guidance manual.
2.3    Membrane Materials, Modules, and Systems

       There are a number of different types of membrane materials, modules, and associated
systems that are utilized by the  various classes of membrane filtration. While several different
types of membrane modules may be employed for any single membrane filtration technology,
each class of membrane technology is typically associated with only one type of membrane
module in water treatment applications. In general, MF and UF use hollow-fiber membranes,
and NF and RO use spiral-wound membranes. MCF systems use flat sheet material configured
into a cartridge filtration device. The terms hollow-fiber, spiral-wound, and cartridge refer to the
module in which the membrane media is manufactured. Section 2.3 describes each of these
types of membrane modules, as well as the materials from which the membranes are made and
the systems into which they are configured.
2.3.1   Membrane Materials

       The membrane material refers to the substance from which the membrane itself is made.
Normally, the membrane material is manufactured from a synthetic polymer, although other
forms, including ceramic and metallic membranes, may be available.  Currently, almost all
membranes manufactured for drinking water production are made of polymeric material,  since
they are significantly less expensive than membranes constructed of other materials.

       The material properties of the membrane may significantly impact the design and
operation of the filtration system. For example, membranes constructed of polymers that react
with oxidants commonly used in drinking water treatment should not be used with chlorinated
feed water. Mechanical strength is another consideration, since a membrane with greater
strength can withstand larger transmembrane pressure (TMP) allowing for greater operational
flexibility and the use of higher pressures with pressure-based direct integrity testing (see
section 4.7). Similarly, a membrane with bi-directional strength may allow cleaning operations
or integrity testing to be performed from either the feed or the filtrate side of the membrane.
Material  properties influence the exclusion characteristic of a membrane as well. A membrane
with a particular surface charge may achieve enhanced removal of particulate or microbial
contaminant of the opposite surface charge due to electrostatic attraction.  In addition, a
membrane can be characterized as being hydrophilic (i.e., water attracting) or hydrophobic (i.e.,
water repelling). These terms describe the ease with which membranes can be wetted, as well as
the propensity of the material to resist fouling to some degree.

       MF and UF membranes may be constructed from a wide variety of materials, including
cellulose acetate (CA), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polypropylene
(PP), polysulfone  (PS), polyethersulfone (PES), or other polymers.  Each of these materials has
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different properties with respect to surface charge, degree of hydrophobicity, pH and oxidant
tolerance, strength, and flexibility. NF and RO membranes are generally manufactured from
cellulose acetate or polyamide materials (and their respective derivatives), and there are various
advantages and disadvantages associated with each.  While cellulose membranes are susceptible
to biodegradation and must be operated within a relatively narrow pH range of about 4 to 8, they
do have some resistance to continuous low-level oxidant exposure.  In general, for example,
chlorine doses of 0.5 mg/L or less may control biodegradation as well as biological fouling
without damaging the membrane. Polyamide (PA) membranes, by contrast, are able to be used
under a wide range of pH conditions and are not subject to biodegradation.  Although PA
membranes have very limited tolerance for the presence of strong oxidants, they are compatible
with weaker oxidants such as chloramines. PA membranes require significantly less pressure to
operate and have become the predominant material used for NF and RO applications.

       A characteristic that influences the performance of all membranes is the trans-wall
symmetry, a quality that describes the level of uniformity throughout the cross-section of the
membrane. There are three types of construction that are commonly used in the production of
membranes: symmetric, asymmetric (including both skinned and graded density variations), and
composite.  Cross-sectional diagrams of membranes with different trans-wall  symmetry are
shown in Figure 2.3. Symmetric membranes are constructed of a single (i.e., homogenous)
material, while composite membranes use different (i.e., heterogeneous) materials. Asymmetric
membranes may be  either homogeneous or heterogeneous.

       In a symmetric membrane, the membrane is uniform in density or pore structure
throughout the cross-section, while  in an asymmetric membrane there is a change in the density
of the membrane material across the cross sectional area.  Some asymmetric membranes have a
graded construction, in  which the porous structure gradually decreases in density from the feed
to the filtrate side of the membrane.  In other asymmetric membranes, there may be a distinct
transition between the dense filtration layer (i.e., the skin) and support structure. The denser
skinned layer is exposed to the feed water and acts as the primary filtration barrier, while the
thicker and more porous understructure serves primarily as mechanical support.  Some hollow-
fibers may be manufactured as single- or double- skinned membranes, with the double skin
providing filtration at both the outer and inner walls of the fibers. Like the asymmetric skinned
membranes, composite  membranes  also have a thin,  dense layer that serves as the filtration
barrier. However, in composite membranes  the skin is a different material than the porous
substructure onto which it is cast. This surface layer is designed to be thin so as to limit the
resistance of the membrane to the flow of water, which passes more freely through the porous
substructure. NF and RO membrane construction is typically either asymmetric or composite,
while most MF, UF, and MCF membranes are either symmetric or asymmetric.
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                  Figure 2.3  Membrane Construction and Symmetry
      HOMOGENOUS
    TORE STRUCTURE
    (ซ1SO MICRONS)
                        MF/UF
  MF/UF
            CUTOFF LAYER
              TO 20 MICRONS)

            GRADUATED
            MEMBRANE STRUCTURE
            ICO TO 150  MICRONS)
   MEMBRANE
    SURFACE
                TYPE
               NF/RO
                             PQLYAM1DE
                             (4GG-1GOD ANGSTROMS)
                             POLYSULFONE
                             (75-ICO MCRONS)

                             POLYESTER FABRIC
                             (100 MICRONS)
           TOP
      MEMBRANE
       SURFACE
       (5 TO 20
       MICRONS)
        etrrcy
      MtWBRANt
       SLRFACF
       (5 TO 20
       MICRONS)
                                                              MF/UF
• POROUS
 SUBSTRATE
 SUPPORT
 (100 TO  150
 MICRONS)
2.3.2  Membrane Modules

       Membrane filtration media is usually manufactured as flat sheet stock or as hollow fibers
and then configured into one of several different types of membrane modules. As defined for the
purposes of the LT2ESWTR, a membrane module represents the smallest discrete filtration unit
in a membrane system (40 CFR  141.728).   (Terminology associated with the LT2ESWTR and
used in the Membrane Filtration  Guidance Manual is described  in section 1.5.)  Module
construction typically involves potting or sealing the membrane material into a corresponding
assembly, which may incorporate an integral containment structure, such as with hollow-fiber
modules.  These types of modules are designed for long-term use over the course of a number of
years.  Spiral-wound modules are also manufactured for long-term use,  although the design  of
membrane filtration systems that utilize spiral-wound modules Equires that the modules  be
encased in a  separate pressure vessel that is independent of the module  itself.  Alternatively, a
module may be configured as a disposable cartridge with a useful life that is typically measured
in weeks or months rather than years. Membrane cartridges may either be inserted into pressure
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vessels  that are separate  from the module (as  with spiral-wound modules) or manufactured
within a casing that serves as an integral pressure vessel.  Each of these three types of modules,
along with some other less common module designs, is discussed in the following subsections.
(The membrane filtration systems that utilize these types of modules are subsequently described
under section 2.3.3.)
       2.3.2.1    Hollow-Fiber Modules

       Most hollow-fiber modules used in drinking water treatment applications are
manufactured to accommodate porous MF or UF membranes and designed to filter particulate
matter.  As the name suggests, these modules are comprised of hollow-fiber membranes, which
are long and very narrow tubes that may be constructed of any of the various membrane
materials described in section 2.3.1.  The fibers may be bundled in one of several different
arrangements.  In one common configuration used by many manufacturers, the fibers are
bundled together longitudinally, potted in  a resin on both ends, and encased in a pressure vessel
that is included as a part of the hollow-fiber module. These modules are typically mounted
vertically, although horizontal mounting may also be utilized. One alternate  configuration is
similar to spiral-wound modules in that both are inserted into pressure vessels that are
independent of the module itself. These modules (and the associated pressure vessels) are
mounted horizontally. Another configuration in which the bundled hollow fibers are mounted
vertically and submerged in a basin does not utilize a pressure vessel.  A typical commercially
available hollow-fiber module may consist of several hundred to over  10,000 fibers.  Although
specific dimensions vary by manufacturer, approximate ranges for hollow-fiber construction are
as follows:

       •  Outside diameter:        0.5-2.Omm

       •  Inside diameter:         0.3-1.0 mm

       •  Fiber wall  thickness:     0.1- 0.6 mm

       •  Fiber length:            1-2 meters


A cross section of a symmetric hollow-fiber is shown in Figure 2.4.

       Hollow-fiber membrane modules may operate in either an "inside-out" or "outside-in"
mode.  In inside-out mode, the feed water enters the fiber lumen (i.e., center or bore of the fiber)
and is filtered radially through the fiber wall. The filtrate is then collected from outside  of the
fiber. During outside-in operation, the feed water passes from outside the fiber through  the fiber
wall to the inside, where the filtrate is collected in the lumen. Although inside-out mode utilizes
a well-defined feed flow path that is advantageous when operating under a crossflow hydraulic
configuration (see section 2.5), the membrane is somewhat more subject to plugging as a result
of the potential for the lumen to become clogged. The outside-in mode, utilizes a less well-
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defined flow feed flow path, but increases the available membrane surface area for filtration per
fiber and avoids potential problems with clogging of the lumen bore.
              Figure 2.4  Hollow Fiber Cross-Section Photomicrograph
       Both the inside-out and outside-in operating modes for hollow-fiber modules are
illustrated in Figure 2.5.  When a hollow-fiber module is operated in an inside-out mode, the
pressurized feed water may enter the fiber lumen at one or both ends of the module, with the
filtrate exiting in the center or end(s). In outside-in mode, the feed water typically enters the
module in the center at the ends  and is filtered into the fiber lumen, where the filtrate collects
before exiting at the end(s). Most hollow-fiber systems operate in "dead-end" or direct filtration
mode (see section 2.5) and are periodically backwashed to remove the accumulated solids.
       2.3.2.2    Spiral-Wound Modules

       Spiral-wound modules were developed as an efficient configuration for the use of semi-
permeable membranes to remove dissolved solids, and thus are most often associated with
NF/RO processes.  The basic unit of a spiral-wound module is a sandwich arrangement of flat
membrane sheets called a leaf wound around a central, perforated tube. One leaf consists of two
membrane sheets placed back to back and separated by a fabric spacer called a permeate carrier.
The layers of the leaf are glued along three edges, while the unglued edge is sealed around the
perforated central tube. A single spiral-wound module 8 inches in diameter may contain up to
approximately 20 leaves, each separated by a layer of plastic mesh called  a spacer that serves as
the feed water channel.

       Feed water  enters the spacer channels at the end of the spiral-wound element in a path
parallel to the central tube. As the feed water flows across the membrane surface through the
spacers, a portion permeates through either of the two surrounding membrane layers and into the
permeate carrier, leaving behind any dissolved and particulate contaminants that are rejected by
the semi-permeable membrane.  The filtered water in the permeate carrier travels spirally inward
around the element toward the central collector tube, while the water in the feed spacer that does
not permeate through the membrane layer continues to flow across the membrane surface,
becoming increasingly concentrated in  rejected contaminants.  This  concentrate stream exits the
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element parallel to the central tube through the opposite end from which the feed water entered.
A diagram of a spiral-wound element is shown in Figure 2.6.
             Figure 2.5 Inside-Out and Outside-ln Modes of Operation
                             OLT>
     Inside-Out Hollow-Fiber Configuration
        Outside-ln Hollow-Fiber Configuration
                        Figure 2.6 Spiral-Wound Membrane Module
               Permeate
                          Feed
                                     Feed/Reject Spacer
                                                          Concentrate
                                       Sealed Around
                                        Outside Edge
                                                                    Glue Line(s)

                                                                 Permeate Carrier
                                                          Membrane(s)
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       Spiral-wound membranes for drinking water treatment are commercially available in a
variety of sizes.  Modules that are either 4 or 8 inches in diameter and either 40 or 60 inches long
are most common, although other sizes may be used.  Some bench- and pilot-scale applications
utilize modules that are 2.5 inches in diameter, while modules up to 16 inches in diameter or
more may be used in full-scale facilities.
       2.3.2.3   Membrane Cartridges

       Under the LT2ESWTR, cartridge filters that meet the criteria specified in section 2.2
would be eligible to receive Cryptosporidium removal credit as a membrane filtration process,
even though cartridge filtration has not traditionally been considered a membrane process.  In
this case, the cartridge filter element would constitute a membrane module for the purposes of
the rule.  The ability of these modules to be subjected to direct integrity testing in the field during
the course of normal operation, a feature that has not been widely utilized in association with
cartridge filters in municipal water treatment applications, is a critical aspect of these systems
that distinguishes what is considered to be MCF under the LT2ESWTR.

       Membrane cartridge filters are manufactured by placing flat  sheet membrane media
between a feed and filtrate support layer and pleating the assembly to increase the membrane
surface area within the cartridge.  The pleat pack assembly is then placed around a center core
with a corresponding outer cage and subsequently sealed, via adhesive or thermal means, into its
cartridge configuration.  End adapters, typically designed with a double o-ring sealing
mechanism, are attached to the filter to provide a positive seal with the filter housing. A diagram
of membrane cartridge filter is shown in Figure 2.7.
                         Figure 2.7  Membrane Cartridge Filter
                                                         FEE3
     JPPER
   SUPPORT
      LAYER

  MEMBRANE
   DOWNSTREAV
     SUPPORT
        LAYLR
                         TOP END
                         ADAPTER
OLfTER
 CAGE
FILTER   yr- END
UED1A  /  CAP
              QJIL*
              CAGE
                                                         FEED
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       Most membrane cartridge filters are manufactured as disposable components that are
inserted into a housing.  Once the filter fouls to the point at which the maximum transmembrane
pressure (TMP) is reached, the cartridge is replaced.  Because the cartridges are designed to be
disposable, and thus relatively inexpensive to replace, cartridge filtration systems have not
historically utilized backwashing or chemical cleaning. However, some systems that feature
these processes have recently been introduced.  Cartridge filters are available in various sizes and
pore sizes, although the device would have to be constructed using a non-fibrous membrane
barrier and be capable of filtering paniculate matter larger than 1  |j,m to be considered a
membrane filter under the LT2ESWTR.
       2.3.2.4    Other Module Configurations

       In addition to hollow-fiber and spiral-wound modules, there are several other types of
less common configurations that may be used in membrane filtration systems.  These
configurations include hollow-fine-fiber (HFF), tubular, and pi ate-and-frame type modules.
While these configurations are seldom employed in membrane filtration systems applied for
drinking water treatment, each of these modules could be applied for LT2ESWTR compliance,
and thus are briefly described in this section.

       Semi-permeable HFF membranes were the original hollow-fiber type membranes and
were developed for desalting (i.e., RO) applications. With the development of widely used
porous hollow-fiber MF and UF membranes for particulate filtration with much larger fiber
diameters, the semi-permeable variety gradually became known as hollow-^/we-fiber membranes.
HFF membranes are bundled length-wise and shaped into a "U" arrangement (called a "U-
tube"), which is potted in a cylindrical pressure vessel.  Feed water enters a HFF module via a
perforated tube in the middle of the vessel and flows radially outward through the membrane
bundle. The water that permeates the membrane is collected in the fiber lumen and exits the
element at the open end of the U-tube. The remaining water that does not permeate into the fiber
lumen carries the concentrated salts and suspended solids out of the pressure vessel through the
concentrate port. Typical hollow-fine fibers are only about 40 |j,m in diameter  (inside), allowing
a very large number of fibers to be contained in a single pressure vessel and maximizing the
available membrane surface area per unit volume in the pressure vessel.  However, the high
packing density  also significantly increases the potential for fouling and reduces the flux to
levels well below those possible using spiral-wound membranes, more than offsetting the
advantage in increased surface area. HFF membranes are most commonly used today in
seawater desalting applications, particularly in the Middle East.

       Tubular  membranes are essentially  a larger, more rigid version of hollow-fiber
membranes.  With diameters as large as 1-2 inches, the tubes are not prone to clogging and the
membrane material (i.e., the tube wall) is comparatively easy to clean. However, the large tubes
also result in a very inefficient amount of membrane surface area per unit volume in the pressure
vessel. Both porous (for MF/UF) and  semi-permeable (for NF/RO) membranes have been
manufactured in tubular configurations.  Ceramics have been considered as non-traditional
material for tubular MF/UF membranes, although there are currently no commercially promoted
ceramic MF/UF systems for drinking water applications.
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       A plate-and-frame configuration, one of the earliest membrane modules developed, is
simply a series of flat sheet membranes separated by alternating filtrate spacers and
feed/concentrate spacers.  Because of the very low surface area to volume ratio, the plate-and-
firame configuration is considered inefficient and is therefore seldom used in drinking water
applications.  One notable exception (although not a membrane filtration process under the
LT2ESWTR) is in the case of EDR systems, which utilize a design that lends itself well to the
use of plate-and-frame membranes.
2.3.3  Types of Membrane Filtration Systems

       In drinking water treatment applications, each of the four traditional types of pressure-
driven membrane processes (i.e., MF, UF, NF, and RO) is generally associated with a single type
of membrane filtration system that is designed around a specific type of module.  MF and UF
systems typically utilize hollow-fiber modules,  while NF  and RO system typically utilize spiral-
wound modules. An overview of each of the two types of systems that utilize these respective
modules is provided in the following subsections. Because the concept of a MCF system as
defined under the LT2ESWTR is a new concept introduced with the rule, a standard type of
MCF system has not yet been developed.
       2.3.3.1    Hollow-Fiber (MF/UF) Systems

       With few exceptions, most MF/UF processes utilize systems designed around hollow-
fiber modules. Hollow-fiber membrane filtration systems are designed and constructed in one or
more discrete water production units, also called racks, trains, or skids.  A unit consists of a
number of membrane modules that share feed and filtrate valving, and the individual units can
usually be isolated from the rest of the system for testing, cleaning, or repair. A typical hollow-
fiber system is composed of a number of identical units that combine to produce the total filtrate
flow.

       Most of the currently available hollow-fiber membrane systems are proprietary, such that
a single supplier will manufacture the entire filtration system, including the membranes, piping,
appurtenances, control system, and other features.  The manufacturer also determines the
hydraulic configuration and designs the associated operational sub-processes - such as
backwashing, chemical cleaning, and integrity testing - that are specific to its particular system.
As a result, there are significant differences in the proprietary hollow-fiber membrane systems
produced by the various manufacturers, and the membranes and other components are not
interchangeable.

       Although each manufacturer's system is distinct, all of the hollow-fiber membrane
systems fall into one of two categories - pressure-driven or vacuum-driven - according to the
driving force for operation.  In a pressure-driven system, pressurized feed water is piped directly
to the membrane unit, where it enters the module and is filtered through the membrane. Typical
operating pressures for range from 3 to 40 psi.  Most applications require designated feed pumps
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to generate the required operating pressure, although there are some water treatment plants that
take advantage of favorable hydraulic conditions to operate a MF or UF via gravity flow.

       A schematic of a typical pressure-driven hollow-fiber membrane filtration system is
shown in Figure 2.8.  In the example shown, the system is operated in a "dead-end" hydraulic
configuration (see section 2.5) and uses a liquid backwash.
 Figure 2.8 Schematic of a Typical Pressure-Driven Hollow-Fiber (MF/UF) System
                                           30LLTICN
                                           RE5EFVOR
    POSITWC
  WWLAKWDfT
     PUP
  iWi   nan

r^-S-
                                                       VKXUKSH
                                                       VH.VC
                                                       SAWFLE
                                                       POfiT
       While all hollow-fiber systems employ pressure as a fundamental driving force, a
vacuum-driven system is distinguished by its utilization of negative pressure and, consequently,
its significantly different design and configuration. Unlike the pressure-driven systems, in which
each membrane module  incorporates a pressure vessel, vacuum-driven systems utilize hollow-
fiber modules that are "submerged" or "immersed" in an open tank or basin. While the ends are
fixed, the lengths of the  hollow-fibers are exposed to the feed water in the basin.

       Because the feed water is contained in an open basin, the outside of the fibers cannot be
pressurized above the static head in the tank.  Therefore, a vacuum of approximately -3 to -12 psi
is induced at the inside of the fibers via pump suction. The water in the tank is drawn through
the fiber walls, where it is filtered into the lumen. By design, vacuum-driven membrane
filtration systems cannot be operated via gravity nor in an inside-out mode.  However, a
favorable hydraulic gradient might enable the use of a gravity-based siphon to generate the
suction required to drive the filtration process in a vacuum-driven  system. In some cases with a
substantial hydraulic  gradient, the large amount of available head could be used to generate the
power for suction pumps via on-site turbines.

       A representative  schematic of a vacuum-driven system is shown in Figure 2.9. In the
example shown, the membrane process may be designed with either continuous (Option A) or
intermittent discharge (Option B) of concentrated waste.
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 Figure 2.9 Schematic of a Typical Vacuum-Driven Hollow-Fiber (MF/UF) System
                                                              (GFTON i)
       2.3.3.2    Spiral-Wound (NF/RO) Systems

       Virtually all NF and RO membrane processes applied for potable water treatment in the
United States utilize systems designed for spiral-wound membrane modules. Although some MF
and UF membranes may also be manufactured as spiral-wound modules, these are seldom used
in municipal drinking water applications.  Consequently, the discussion in this section is focused
on NF/RO spiral-wound systems.

       In a spiral-wound membrane filtration system, the spiral-wound modules are contained in
a pressure vessel that is independent of the module itself.  Typically, a single pressure vessel
houses six or seven modules, although vessels that accommodate other numbers of modules can
be custom manufactured.  The  modules are arranged in series in the pressure vessel such that the
concentrate from each preceding element represents the feed water for the next. A brine seal
around the outside of the feed end of each element separates the feed water from the concentrate
and prevents the feed water from bypassing the element. Although the recovery for a single
NF/RO module is typically less than 15 percent, the cumulative recovery associated with a six-
module pressure vessel may be 50 percent or more. A diagram of a typical pressure vessel
containing spiral-wound modules is shown in Figure 2.10.
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        Figure 2.10  Typical Spiral-Wound (NF/RO) Module Pressure Vessel
               Feed
                                        Interconnector
              Brine Seal
    Head
                                                  SSASSSSSSSSSSSSSSS*
                                                                              Permeate
                           End Adapter
            Thrust Cone    I
Spiral-Wound Module   concentrate
   Retaining Ring
       A group of pressure vessels operating in parallel collectively represent a single stage of
treatment in a NF/RO spiral-wound system. The total system recovery is increased by
incorporating multiple stages of treatment in series, such that the combined concentrate (or
reject) from the first stage becomes the feed for the second stage.  In some cases in which higher
recovery is an objective, a third stage may also be used. This configuration is sometimes
referred to as "concentrate staging." Because some fraction of the feed to the first stage has been
collected as filtrate (or permeate), the feed flow to the second stage will be reduced by that
fraction.  As a result, the number of total pressure vessels (and hence the number of modules) in
the second stage is also typically reduced by approximately that same fraction.  Similar flow,
module, and pressure vessel reductions are propagated through all successive stages, as well.
Although the potential system recovery is a function of the feed water  quality, as a rough
approximation, a two-stage design may allow recoveries up to 75 percent, while the addition of a
third stage can potentially achieve recoveries up to 90 percent.

       Although concentrate staging is most often used in drinking water applications, another
arrangement called "permeate staging" may also be employed.  In this configuration the filtrate
(or permeate) from a stage (rather than the  concentrate) becomes the feed water for the
subsequent stage.  This arrangement is more commonly employed in ultra-pure water
applications (typically in industry), it may also be used for drinking water treatment when the
source water salinity is very high, such as with seawater desalination.  In these cases, the product
water must pass through multiple stages to remove a sufficient amount of salinity to  make the
water potable quality.

       The combination of two or more stages in series is called an array, which is identified by
the ratio of pressure vessels in the sequential stages. An array may be  defined by the ratio of
either the actual number or relative number of pressure vessels in each stage. For example, a
32:16:8 array expressed as the actual number of pressure vessels) may be alternatively called a
4:2:1 array in relative terms. Two-stage arrays, such as 2:1 and 3:2 (relative), are most common

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in drinking water treatment, although the specific array required for a particular application is
dictated in part by the feed water quality and targeted overall system recovery. Figure 2.11
illustrates the configuration of a typical 2:1 (relative) array, showing both plan and end-
perspective views.
            Figure 2.11 Typical 2:1 (Relative) Array of Pressure Vessels
Stage 2: Stage 1 :
12 Vessels 24 Vessels
72 Modules 1 44 Modules
f
Permeate
<4-
1
i ^\ \ 1
T


*
J.




1
—
                                                   Concentrate
                                   Feed
                                          Feed
      Concentrate
                    Plan View
               End-Perspective View
       As with hollow-fiber systems, spiral-wound membrane systems are designed and
constructed in discrete units that share common valving and which can be isolated as a group for
testing, cleaning, or repair.  For spiral-wound systems these uniform units are typically called
trains,  or alternatively racks or skids.  NF and RO treatment processes consist of one or more
trains that are typically sized to accommodate a feed flow of up to about 5 MOD per train. A
schematic of a typical NF/RO system is shown in Figure 2.12.

       Unlike hollow-fiber systems, spiral-wound membrane filtration systems are not
manufactured as proprietary equipment. With the exception of the membrane modules, spiral-
wound systems are generally custom-designed by an engineer or an original equipment
manufacturer (OEM) to suit a particular application.  Although the membrane modules are
proprietary, standard-sized spiral-wound NF/RO modules share the same basic construction, and
thus membranes from one manufacturer are typically interchangeable with those from others.
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         Figure 2.12  Schematic of a Typical Spiral-Wound (NF/RO) System
2.4    Basic Principles of Membrane Filtration System Design and Operation

       Familiarity with the basic principles underlying membrane filtration system design and
operation is important to the comprehension and interpretation of the material presented in this
guidance manual.  The material presented in this subsection is intended to provide an overview
of these basic principles. Although all of the types of membrane filtration addressed in this
manual (i.e., MF, UF, NF, RO, and MCF) utilize pressure (or vacuum) as a driving force, there
are fundamental differences in the models used to describe systems using porous membranes
(MF, UF, and MCF) and semi-permeable membranes (NF and RO). The basic principles of
these respective models, along with some general concepts that are applicable to all membrane
filtration systems, are discussed in the following subsections.  Note that these discussions are
intended to be informative for the purposes of fostering an understanding the technology and not
a specific guide for system design and operation.
2.4.1   General Concepts

       There are a number of general concepts that are applicable to all types of pressure-driven
membrane filtration systems and which serve as the underlying basic principles for system
design and operation. These concepts include flux, recovery, and flow balance, each of which is
discussed in general terms below. Additional concepts that are specific to either MF, UF, and
MCF  systems or NF and RO systems are discussed in sections 2.4.2 and 2.4.3, respectively.
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       Membrane filtration system throughput or productivity is typically characterized by the
system flux, which is defined as the filtrate flow per unit of membrane filtration area, as shown
in Equation2.1:
                     J = ——                                         Equation 2.1
       Where:        J      =     flux (gfd)
                     Qp     =     filtrate flow (gpd)
                     Am     =     membrane surface area  (ft2)
       The recovery of a membrane unit, is defined under the LT2ESWTR as the amount of feed
flow that is converted to filtrate flow, expressed as a decimal percent, as shown in Equation 2.2:
                     R = —-                                         Equation 2.2
                         Qf

       Where:        R      =     recovery of the membrane unit (decimal percent)
                     Qp     =     filtrate flow produced by the membrane unit (gpd)
                     Qf     =     feed flow to the membrane unit (gpd)
The recovery as defined under the rule does not account for the use of filtrate for routine
maintenance purposes (such as chemical cleaning or backwashing) or lost production during
these maintenance operations.  Because the definition of recovery is not necessarily consistent
throughout the water treatment industry, it is important to identify how recovery is defined in any
particular discussion. However, the use of the term recovery as defined in Equation 2.2 is
consistent throughout the LT2ESWTR rule language and the Membrane Filtration Guidance
Manual. Note that for some types of membrane systems, particularly those that operate in
suspension mode that can be modeled as plug flow reactors (see section 2.5), recovery can also
be defined as a function of position within a membrane unit. This is simply a variation of
Equation 2.2 for systems in which the filtrate flow increases in the direction of feed flow through
the membrane unit, thus increasing the recovery in direct proportion.  The limit of this recovery
in the direction of flow (i.e., the recovery at the furthest position in the unit) is equivalent to the
overall membrane unit recovery, as defined in Equation 2.2.
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       A general flow balance that can be applied to all membrane filtration systems is shown in
Equation 2.3:
                     Qf = Qc + QP                                    Equation 2.3
       Where:        Qf     =     feed flow to the membrane unit (gpd)
                     Qc     =     concentrate flow from the membrane unit  (gpd)
                     Qp     =     filtrate flow from the membrane unit (gpd)
Note that the concentrate (i.e., bleed or reject) flow, Qc, is zero for systems operating in
deposition (i.e., dead-end) mode, as discussed in section 2.5. For the purpose of sizing a
membrane filtration system, it may be desirable to account for the additional filtered water used
for both backwashing and chemical cleaning in the determination of the filtrate flow, Qp.
Similarly, an estimate of the total required feed flow Qf to the system should incorporate any raw
water that may be used in these routine maintenance processes.
2.4.2  MF, UF, and MCF Processes

       The driving force for the transport of water across a microporous membrane - that
utilized by MF, UF, and MCF processes - is a pressure gradient across the membrane, or the
TMP.  The TMP is defined by the pressure on the feed side of the membrane minus the filtrate
pressure, commonly called the backpressure, as shown in Equation 2.4:
                     TMP =Pf-Pp                                  Equation 2.4

       Where:       TMP   =      transmembrane pressure  (psi)
                     Pf     =      feed pressure  (psi)
                     Pp     =      filtrate pressure (i.e., backpressure)  (psi)
       For systems that operate in suspension mode and thus utilize a concentrate stream that is
wasted or recirculated (as described in section 2.5), the pressure on the feed side of the
membrane is not constant, but can instead be approximated by a linear pressure gradient from the
feed inlet to the concentrate outlet.  In this case, the pressure on the feed side of the membrane
may be represented by the average of the feed and concentrate pressures, as shown in
Equation 2.5:
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                              fc
                     TMP = -i	 - P                              Equation 2.5
                                       F
       Where:       TMP   =      transmembrane pressure (psi)
                     Pf     =      feed pressure (psi)
                     Pc     =      concentrate pressure (psi)
                     Pp     =      filtrate pressure (i.e., backpressure) (psi)


       The resistance to flow acting in opposition to the driving force and inhibiting the
transport of water across the membrane can also be quantified.  This resistance has two
components: the intrinsic resistance of the membrane and the resistance attributable to the
accumulated foulant layer at the membrane  surface at any point during operation. The total
resistance is represented by the sum of these two components, as shown in Equation 2.6:
                     Rt=Rm+ Rf                                    Equation 2.6

       Where:       Rt     =      total membrane resistance  (psi/gfd-cp)
                     Rm     =      intrinsic membrane resistance (psi/gfd-cp)
                     Rf     =      resistance of the foulant layer (psi/gfd-cp)
While the intrinsic resistance of the membrane should remain constant for all practical purposes
and can generally be obtain from the membrane manufacturer (if necessary), the increase in
fouling during normal operation and the decrease in fouling as a result of backwashing and
chemical cleaning causes the fouling resistance to fluctuate.

       If the total membrane resistance is known, the flux can be calculated as a function of the
TMP and water viscosity, as shown in Equation 2.7:
                           TMP
                     JT = -                                    Equation 2.7
       Where:        JT     =      flux at temperature T (gfd)
                     TMP   =      transmembrane pressure (psi)
                     Rt     =      total membrane resistance  (psi/gfd-cp)
                     HT     =      viscosity of water at temperature T  (cp)
       Because the viscosity of water increases with decreasing temperature, larger TMPs (by
application of increased pressure or vacuum) are required to maintain constant flux. Values for
water viscosity can be found in the literature or approximated using the empirical relationship
expressed in Equation 2.8:


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              y,T  = 1.784- (0.0575 • T)+ (o.OOl 1 • T2)- (l(T5 • T3)     Equation 2.8

       Where:       HT     =      viscosity of water at temperature T  (cp)
                      T     =      water temperature (ฐC)
       Since water temperature can have a significant impact on flux, it is common practice to
"normalize" the flux to a reference temperature during operation for the purposes of monitoring
system productivity independent of changes in water temperature.  For MF/UF and MCF
processes, a reference temperature of 20 ฐC is typically used for convenience, since the viscosity
of water is approximately 1 cp at 20 ฐC.  For constant IMP and total membrane resistance, a
form of Equation 2.7 can be used to illustrate the relationship between the normalized flux and
viscosity at 20 ฐC and the actual flux and viscosity at a given temperature of interest T,  as shown
in Equation 2.9:
                     J20 • [120 = JT • [1T                              Equation 2.9

       Where:       J20     =      normalized flux at 20 ฐC (gfd)
                     H20    =      viscosity of water at 20 ฐC (cp)
                     JT      =      actual flux at temperature T (gfd)
                     HT     =      viscosity of water at temperature T  (cp)
       Substituting the value of 1 cp for the viscosity at 20 ฐC (|J,2o) and Equation 2.5 for the
viscosity of water at temperature T (JJ.T) yields and expression for normalized flux at 20 ฐC as a
function of the actual flux and the temperature, as shown in Equation 2.10:
       J20 =JT • [l.784-(0.0575 • T)+(o.OOl 1 • T2) - (lO~5 ปr3)]      Equation 2.10

       Where:       J20     =      normalized flux at 20 ฐC (gfd)
                     JT      =      actual flux at temperature T (gfd)
                     T      =      water temperature (ฐC)
       It is important to note that the normalized flux (J2o) does not represent an actual operating
condition. This term simply represents what the flux would be at 20 ฐC for a constant IMP and
total membrane resistance.  Thus, changes in the value of J2o during the course of normal
operation are indicative of changes in pressure and/or membrane resistance due to fouling. If
values for viscosity are known, the polynomial expression for viscosity as a function of
temperature in Equation 2.10 may be simplified to a temperature correction factor (TCF). For a
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MF, UF, or MCF process, the TCP is defined as the ratio of the viscosity at temperature T to the
viscosity at 20 ฐC, as shown in Equation 2.11:
                                                                     Equation 2. 11
       Where:        TCP   =     temperature correction factor (dimensionless)
                     |J,T     =     viscosity of water at temperature T  (cp)
                     H20    =     viscosity of water at 20 ฐC  (cp)
Note that the term TCP is often used genetically to refer to any type correction factor used to
adjust a parameter for temperature. Thus, the specific equation for the TCP may vary depending
on the parameter to which it is applied. For example, in the context of membrane filtration, the
TCP applied to reference MF, UF, and MCF flux to a standard temperature, as defined in
Equation 2.11, is different than that applied to NF and RO flux to a standard temperature, as
shown in Equation 2.15. Thus, it is important to always consider the context in which the term
TCF is used.

       Because the TCF is  a dimensionless ratio, the values for viscosity can be expressed in any
convenient and consistent units. Thus, the temperature-normalized flux can be expressed in
simplified as terms, as shown in Equation 2.12:
                     J20 =JT ปTCF                                  Equation 2.12

       Where:       J20     =     normalized flux at 20 ฐC (gfd)
                     JT      =     actual flux at temperature T (gfd)
                     TCF   =     temperature correction factor (dimensionless)
       Generally, in order to identify changes in productivity (as measured by flux) that are
specifically attributable to membrane fouling, it is desirable to normalize the flux for pressure as
well as temperature, as shown in Equation 2.13. Note that the temperature- and pressure-
normalized flux is often referred to as either the specific flux or permeability.
                                                                     Equation 2. 13
                          TMP

       Where:        M     =     temperature- and pressure- normalized flux  (gfd/psi)
                     J20     =     normalized flux at 20 ฐC (gfd)
                     TMP   =     transmembrane pressure (psi)
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2.4.3  NF and RO Processes

       As with the microporous MF, UF, and MCF membranes, the driving force for the
transport of water across a semi-permeable membrane - such as that utilized by NF and RO
processes - is a pressure gradient across the membrane. However, because NF and RO
processes reject dissolved salts, the resulting osmotic pressure gradient, which acts against the
transport of water from the feed to the filtrate side of the membrane, must also be taken into
account.  Typically, the osmotic pressure gradient is  approximated from the concentration of
total dissolved solids (TDS) on the feed and filtrate sides of the membrane.  The corrected
driving force across semi-permeable membrane is termed the net driving pressure (NDP) and can
be calculated using Equation 2.14 (AWWA 1999):
       NDP =
                              (TDS f + TDS
                           -TDS
                        0.01
                                                                psi
                                                              mg IL
       Where:
NDP
Pf
PC
TDSf
TDSC
TDSp
Pn
                                                                       Equation 2.14
net driving pressure  (psi)
feed pressure (psi)
concentrate pressure (psi)
feed TDS concentration  (mg/L)
concentrate TDS concentration (mg/L)
filtrate TDS concentration  (mg/L)
filtrate pressure (i.e., backpressure)  (psi)
       Equation 2.14 can be considered as three distinct components, each shown above in
parentheses. The first term represents the average pressure on the feed side of the membrane; the
second term represents the average osmotic backpressure; and the third term represents the
filtrate backpressure.  The conversion factor of 0.01 in the osmotic pressure term  comes from a
widely used rule of thumb for fresh and brackish waters indicating that there is approximately
1 psi of osmotic pressure for every 100 mg/L of TDS, as discussed in section 2.2.2. In many
cases the filtrate TDS concentration (TDSP) is small and can be neglected.

       While the flux associated with MF, UF, and MCF systems is typically referenced to a
temperature of 20 ฐC for the purposes of assessing operational performance, it is common to
reference the flux associated with NF and RO systems to 25 ฐC  (298 K).  Accordingly, the
appropriate TCF for NF and RO systems is shown in Equation 2.15:
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       Where:
                    TCP = exp
TCP   =
T
U
           U>
                                       1
                           1
                                    T +273   298
                                  Equation 2.15
temperature correction factor (dimensionless)
water temperature (ฐC)
membrane-specific manufacturer-supplied constant (1/K)
       Once the TCP has been determined, the flux normalized to 25 ฐC can be calculated
according to Equation 2.16:
                    J25=JT*(TCF)
                                               Equation 2.16
       Where:       J2s    =      normalized flux at 25 ฐC (gfd)
                    JT     =      actual flux at temperature T (gfd)
                    TCP   =      temperature correction factor (dimensionless)
       As with MF, UF, and MCF systems, it is important to note that the normalized flux (125)
for NF and RO systems does not represent an actual operating condition.  This term simply
represents what the flux would be at 25 ฐC for the purposes of comparing membrane
performance independent of temperature-related affects.  Similarly, it is also common to
normalize the flux for pressure in order to identify changes in productivity that are attributable to
fouling, as shown in Equation 2.17:
                    M =
      J25
     NDP
       Where:
M
J25
NDP   =
                                  Equation 2.17
temperature- and pressure-normalized flux (gfd/psi)
normalized flux at 25 ฐC (gfd)
net driving pressure (psi)
2.5    Hydraulic Configurations

       The term hydraulic configuration is used to describe the manner in which the feed water
and associated suspended solids are is processed by a membrane filtration system  Although
there are a number of different hydraulic configurations in which the various membrane filtration
systems can operate, each of these configurations can be categorized into one of two basic modes
of operation: deposition mode and suspension mode.  The hydraulic configuration of a system is
determined from operational conditions such backwash, concentrate flow, and recycle flow,
where applicable.
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       For the purposes of the LT2ESWTR, one of the most important implications of a
system's hydraulic configuration is its impact on the degree to which suspended solids are
concentrated on the feed side of the membrane. This concentration effect is characterized by the
volumetric concentration factor (VCF), a dimensionless parameter representing the ratio of the
concentration of suspended solids on the feed side of the membrane relative to that of the
influent feed to the membrane filtration process, as shown in Equation 2.18:
                           ^L                                     Equation 2. 18
       Where:       VCF     =   volumetric concentration factor  (dimensionless)
                    Cm       =   concentration of suspended solids maintained on the feed
                                  side of the membrane  (number or mass / volume)
                    Cf       =   concentration of suspended solids in the influent feed water
                                  to the membrane system (number or mass / volume)
       By definition, the VCF is equal to 1 for a system that does not concentrate suspended
solids on the feed side of the membrane (i.e., Cm = Cf); these are defined as deposition mode
systems.  However, some hydraulic configurations concentrate suspended solids on the feed side
of the membrane to degrees much greater than the influent feed concentration, with a
corresponding VCF greater than 1; these are the suspension mode systems. Consequently, the
VCF can significantly affect the quantity of particulate matter that can flow through an integrity
breach, and thus must be considered in the determination of direct integrity test method
sensitivity, as discussed in section 4.3 (40 CFR 141, Subpart W, Appendix C). For example, if a
system concentrates particulate matter by a factor of 10 (i.e., VCF = 10), then the direct integrity
test used  to monitor the system must be ten times more sensitive than a test applied to a system
that does not concentrate particulate matter (i.e., VCF = 1), in order to demonstrate the same log
removal value (LRV).

       The primary purposes of this section are to describe the various hydraulic configurations
in which  membrane filtration systems can operate and present the associated equations used to
determine the respective VCFs.  The discussion of the various hydraulic configurations in this
section is predicated on three basic assumptions:

       1. In the absence of a hydraulic force tangential to the membrane surface, particulate
          matter in the feed stream is deposited on the membrane and held in place by the TMP.

       2   In the presence of a hydraulic force tangential to the membrane surface, all  of the
          particulate matter remains  in suspension, resulting in elevated concentrations of
          suspended particulate matter on the feed  side of the membrane.  This increase in
          concentration is characterized by the VCF, which can vary as a function of position
          and/or time for various hydraulic configurations.

       3. The membrane is a complete barrier to the passage of the particulate contaminants.

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       Deposition modes systems and the various types of suspension mode systems are
discussed in sections 2.5.1 and 2.5.2, respectively. Although the majority of systems utilize one
of the hydraulic configurations described in this section, there may be unusual cases in which a
system-specific analysis is necessary to characterize the VCF.  For example, some systems that
are designed to operate in deposition mode may still exhibit some degree of particle suspension,
and conversely, some degree of particle deposition may occur in a system operating primarily in
suspension mode. In such cases in which characteristics of both types of hydraulic
configurations may be observed, the VCF should be calculated using the most conservative
applicable assumptions that result in the highest anticipated VCF values. (Note that the most
conservative condition for a particular system is that which results in the highest estimated
concentration of suspended particulate matter.)  As an alternative to the theoretical calculations,
the VCF may be measured experimentally under realistic operating conditions.  This approach
may be advantageous for  systems that may not necessarily be well described by mathematical
modeling. In addition to both the modeling and experimental approaches, there may be some
cases in which a manufacturer of a proprietary membrane filtration system has developed a
system-specific method for determining the VCF.
2.5.1   Deposition Mode

       Membrane filtration systems operating in deposition mode utilize no concentrate stream
such that there is only one influent (i.e., the feed) and one effluent (i.e., the filtrate) stream, as
shown in the schematic in Figure 2.13. These systems are also commonly call "dead-end" or
"direct" filtration systems and are analogous to conventional granular media filters in terms of
hydraulic configuration. In the deposition mode of operation, contaminants suspended in the
feed stream accumulate on the membrane surface and are held in place by hydraulic forces acting
perpendicular to the membrane, forming a cake layer, as illustrated in Figure 2.14.
        Figure 2.13: Schematic of a System Operating in Deposition Mode
  FEED
                    FEED
                    TANK
                                           Cm
                                                   MEMBRANE
                                   FILTRATE
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         Figure 2.14 Conceptual Illustration of Deposition Mode Operation
                                             "FFD
                <
CAKE

        '^ji
    MEMBRANE

                 I                  I                  \
                                         FILTRATE
       In a deposition mode hydraulic configuration, the concentration of suspended material on
the feed side of the membrane (Cm) is assumed to be equivalent to the concentration of influent
feed stream (Cf), independent of time or position in the membrane system, as the suspended
contaminants are removed from the process stream and deposited in the accumulated cake layer.
Therefore, all systems operating in deposition mode have a VCF equal to one. MCF and most
hollow-fiber MF and UF systems operate in deposition mode. Typically, the accumulated solids
are removed from MF/UF  systems by backwashing, while most MCF systems simply operate
until the accumulated solids reduce the flow and/or TMP to an unacceptable level, at which point
the membrane cartridge  is  replaced.

       Some MF/UF systems utilize a periodic "backpulse" - a short interval of reverse flow
(which may include air and/or the addition of small doses of oxidants) designed  to dislodge
particles from the membrane surface without removing these solids from the system.  This
process re-suspends particles, effectively concentrating the suspended solids in the feed near the
membrane surface and increasing the potential for pathogens or other paniculate to pass through
an integrity breach and contaminate the filtrate.  Consequently, systems that do not utilize a
concentrate stream but still practice backpulsing may be more appropriately and conservatively
modeled as operating in suspension mode.
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2.5.2  Suspension Mode

       In membrane filtration systems that operate in suspension mode, a scouring force using
water and/or air is applied parallel (i.e., tangential) to the membrane surface during the
production of filtrate in a continuous or intermittent manner, as illustrated in Figure 2.15.  The
objective of operating in this mode is to minimize the accumulation of contaminants at the
membrane surface or boundary layer, thus reducing fouling.  As shown in Equation 2.18, the
VCF quantifies the increase in the feed side concentration of suspended solids relative to that of
the influent feed stream that occurs in a suspension mode of operation.
        Figure 2.15  Conceptual Illustration of Suspension Mode Operation
        FEED           ป       ^     ซ*               ป  CONCENTRATE
  BOUNDARY
      LAYER
    MEMBRANE
               J  aS^f  agtsags*"    tzf	ฃSS3S^l_cฃ3SE~l_J
                p* 	;	• .  	   p
                                 FILTRATE
       The three most common suspension mode hydraulic configurations are the plug flow
reactor (PFR) model, the crossflow model, and the continuous stirred tank reactor (CSTR)
model. Systems operating under a crossflow hydraulic configuration may be further categorized
as either small volume or large volume systems, since the volume affects the manner in which
suspended solids are concentrated in such a system.  Depending on the particular hydraulic
configuration, the VCF may vary temporally or spatially. In a PFR, the VCF increases in the
direction of feed flow as a function of position in the system; however, in a CSTR or crossflow
reactor, the VCF increases with time over the course of a filtration cycle. Methods for
calculating both the average and maximum VCF are presented for PFR, crossflow, and CSTR
systems are discussed in the following subsections.
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       2.5.2.1  Plug Flow Reactor Model

       Membrane filtration systems that operate as PFRs have a VCF that varies as a function of
position in the system.  Examples of such systems include spiral-wound NF/RO systems and
vacuum-driven MF/UF systems submerged in tanks with large length-to-width ratios.  The
concentration profile of these two types of PFR systems is illustrated in Figure 2.16.
                 Figure 2.16 Flow Diagram for a Plug Flow Reactor
                        FEED
                          Pf
                          Cf
                            MEMBRANE
                                                                          FILTRATE
                                                                          CONCENTRATE
                            WLET                             EHT
                                   MOOULE =OSITION IN SYSTEM
         FEED
           Q,
                                                                          CONCENTRATE
                                                                         -Qt
                                                                          C:
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       The concentration of suspended solids on the feed side of the membrane in a PFR can be
expressed as a function of the recovery at any position within the system, as shown in
Equation 2.19:
                        / ^    Cf
                     Cm(x) = - J-—                               Equation 2. 19
                        ^ '
       Where:       Cm(x)  =    concentration on the feed side of the membrane at position x
                                in the membrane unit (number or mass / volume)
                    x      =    position in the membrane unit in the direction of tangential
                                flow (i.e., x = 0 at the entrance to the first module)
                    Cf     =    feed concentration at the inlet to the membrane unit
                                (number or mass / volume)
                    R(x)   =    recovery as a function of position within the membrane unit
                                (decimal percent)
       Equations 2.18 and 2.19 can be combined to create an expression for the VCF as a
function of position in a PFR:
                     VCF(x) =	-—                              Equation 2.20


       Where:       VCF(x)  =  VCF as a function of position the membrane unit
                                (dimensionless)
                    x        =  position in the membrane unit in the direction of tangential
                                flow (i.e., x = 0 at the entrance to the first module)
                    R(x)     =  recovery as a function of position within the membrane unit
                                (dimensionless decimal)
       The recovery in a PFR varies from zero at the inlet to membrane unit to the value of the
overall unit recovery at the outlet of the tangential flow stream in the membrane unit.
Accordingly, between these inlet and outlet boundary conditions, the VCF increases from 1.0 at
the system inlet (where the recovery is equal to zero), to a maximum value (VCFmax) at the
concentrate outlet of the membrane unit, as shown in Equation 2.21:
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                              17")
                              1 — K
                                                                   Equation 2.21
       Where       VCFmax  =   maximum VCF  (dimensionless)
                    R       =   membrane unit recovery  (decimal percent)
       The value of the VCF yielded by Equation 2.21 represents the largest (and thus most
conservative) such value in a PFR. Suspended particulate matter is concentrated to this degree
only at the far end of the unit (in the direction of flow) at the point of the tangential flow stream
outlet; the rest of the membrane unit may be characterized by a lower VCF.  Thus,  it may be
appropriate to consider an average value of the VCF that is more representative of concentrations
over the membrane unit as a whole.

       A simplistic method for estimating the average VCF (VCFavg) is to simply divide the
maximum VCF by  two.  However, a more accurate method involves calculating a  position-
averaged VCF(x) from the system inlet to the concentrate stream outlet. If a mathematical
expression for R(x) is known, it can be inserted into Equation 2.20 to yield a known expression
for the VCF as a function of position (VCF(x)) in a PFR. Subsequently, if this resulting
expression can be integrated, then the average value function can be applied to determine an
accurate value for VCFavg, as shown in Equation 2.22:
                     VCFavg =   - .  ~ JTfc)                 Equation 2.22


       Where:       VCFavg =  average VCF (dimensionless)
                    *max    =  end position of the membrane unit in the direction of
                                tangential flow  (i.e., at the outlet of the tangential flow
                                stream)
                    R(x)    =  recovery  as a function of position within the membrane unit
                                (dimensionless decimal)
                    x       =  position in the membrane unit in the direction of tangential
                                flow (i.e., x = 0 at the entrance to the first module)
       The parameter R(x) in Equation 2.20 is typically a function of pressure, membrane area,
and flow, all of which may vary as a function  of position within the membrane unit. For
example, NF and RO systems experience a decrease in NDP due to pressure losses through the
system and increasing osmotic pressure gradients.  For MF  and UF membrane systems operating
as PFRs, there may also be a flow imbalance across the membrane surface in the direction of
flow resulting from the increasing concentration of suspended solids, which may increase
resistance to the flow of water through the membrane (i.e., the filtrate flow) toward the outlet the
tangential flow stream. In addition, the back-mixing of suspended solids can also create non-
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ideal flow and concentration conditions (Cote et al. 2003).  However, in general, the VCF
increases exponentially in the direction of the tangential flow stream in a PFR.

       If an expression for the VCF as a function of position (VCF(x)) cannot be developed or if
the resulting equation cannot be integrated, a flow-weighted average can be computed using
numerical techniques, as shown in Equation 2.23:
                     VCFavg =               '                        Equation 2.23
       Where:       VCFavg   =   (flow-weighted) average VCF (dimensionless)
                    VCF(x)   =   VCF at discrete position "x" within the membrane unit
                                  (dimensionless)
                    x         =   position in the membrane unit in the direction of tangential
                                  flow (i.e., x = 0 at the entrance to the first module)
                    Qp(x)     =   filtrate flow at position "x" within the membrane unit (gpd)
                    Qp       =   filtrate flow (gpd)
The use of Equation 2.23 first requires determination of the filtrate flow over a differential
membrane area in the unit at a specific location.  The resulting filtrate flow at position "x"
(QpOO) can be used to calculate the recovery at position "x" (R(*0) within the membrane unit
using Equation 2.2 (see section 2.4).  The VCF at position "x" can then be calculated using
Equation 2.20. These calculation steps are repeated for numerous positions throughout the
membrane unit, and a flow-weighted average is computed from this data using Equation 2.23.
Typically, values for the filtrate flow at discrete intervals within a membrane unit may be
obtained from modeling software available from  the membrane module manufacturer, and the
various calculations can be facilitated by the use  of a spreadsheet.

      Both the maximum and flow-weighted  average VCFs (as calculated using Equations 2.21
and 2.23, respectively) for a typical NF/RO system over a range of overall systems recoveries
from 70 to 99 percent are summarized in Table 2.1.

      Table 2.1 shows that maximum VCF is substantially higher than the average VCF,
particularly for higher recoveries.  For example, a NF/RO system operating at an overall
recovery of 85 percent has a maximum VCF approximately three times larger than its average
VCF. Thus, the concentration of suspended particulate matter at the outlet of the tangential flow
stream in the membrane unit is similarly three times higher than the average concentration. As a
result, a membrane breach located close to the  outlet of the tangential flow stream in membrane
unit operating as a PFR has the potential to allow a significantly larger concentration of
contaminants to pass into the filtrate than a breach occurring at a location further upstream.
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     Table 2.1 Summary of VCF Values for a NF/RO System Modeled as a PFR
Recovery
(percent)
70
71
72
73
74
75
76
77
78
79
VCF
Avg.1
1.73
1.75
1.78
1.80
1.83
1.86
1.89
1.92
1.95
1.99
Max.
3.33
3.45
3.57
3.70
3.84
4.0
4.17
4.35
4.55
4.76
Recovery
(percent)
80
81
82
83
84
85
86
87
88
89
VCF
Avg.1
2.02
2.06
2.11
2.15
2.20
2.25
2.31
2.37
2.43
2.49
Max.
5.0
5.26
5.56
5.88
6.25
6.67
7.14
7.69
8.33
9.09
Recovery
(percent)
90
91
92
93
94
95
96
97
98
99
VCF
Avg.1
2.56
2.65
2.75
2.87
3.00
3.16
3.37
3.63
4.01
4.68
Max.
10.0
11.1
12.5
14.3
16.7
20.0
25.0
33.3
50
100
 1  Ideal, theoretical average
       If information regarding the filtrate flow as a function of membrane position cannot be
obtained or approximated, the VCF data presented in Table 2.1  may be used as an estimate for
NF/RO systems. However, it is strongly recommended that Equation 2.20, 2.22, or 2.23 be used
to obtain a more accurate,  system-specific estimate for the average VCF.   Alternatively, the
maximum VCF (i.e., the most  conservative value) can be  calculated from the overall recovery
using Equation2.21.
       2.5.2.2  Crossflow Model

       The objective of crossflow filtration is to maintain a high scour velocity across the
membrane surface to minimize particle deposition and membrane fouling. Crossflow membrane
processes operate in an unsteady-state manner in which suspended solids accumulate on the feed
side of the membrane over the course of a filtration cycle.  Thus, in crossflow systems, the VCF
varies as a function of time.  At the end of each filtration cycle the membrane unit is backwashed
to remove the accumulated solids. Crossflow filtration has traditionally been used in conjunction
with inside-out hollow-fiber membrane processes to increase the scouring velocity in the fiber
lumen in order to minimize fouling.

       For crossflow systems, a portion of the concentrate stream (i.e., the tangential flow) is
recirculated or recycled to the system inlet and mixed with the incoming feed stream.  Because
the  concentrate stream has a higher concentration of suspended solids than the influent feed
stream to the membrane process, the VCF for crossflow systems is greater than one.  Although
the  recycled concentrate stream in a crossflow system may be as small as 10 percent of the
combined feed flow or less, it is typically 5 to 20 times higher than the influent feed flow. The
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manner in which crossflow systems concentrate suspended paniculate matter depends on the
volume of the feed in the membrane process.  For simplicity, two variations of the crossflow
configuration are considered in this discussion: small volume and large volume systems.
       Small Volume Crossflow Systems

       In a small volume crossflow system, the unfiltered concentrate stream is returned to the
inlet of the membrane system and blended with the incoming feed after any prefiltration that may
be incorporated into the treatment process. The line that connects the concentrate outlet to the
feed inlet is termed the recirculation loop. A schematic of a typical small volume crossflow
system configuration is shown in Figure 2.17. The small volume crossflow configuration, in
which the contaminants accumulated during a filtration cycle are removed via backwashing, is
relatively common among hollow-fiber MF/UF membrane systems.
        Figure 2.17  Schematic of a Typical Small Volume Crossflow System
                                                                         FILTRATE
       In crossflow systems, the concentration of suspended solids on the feed side of the
membrane (Cm in Figure 2.17) increases linearly over the filtration cycle.  The rate at which the
concentration increases is a function of the feed flow (Qf in Figure 2.17) and volume of the
recirculation loop (Vr).  As shown in Figure 2.17 this volume would include the volume on the
feed side of the membrane modules back to the recirculation blending point, as well as the
recirculation loop piping.

       In analyzing such systems, it is useful to define the solids retention time (T), which
represents the time  required for a one-fold increase in the concentration of suspended paniculate
matter on the feed side of the membrane. The solids retention time is calculated as the ratio of
the total volume of the recirculation loop to the feed flow, as shown in Equation 2.24:
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                        Qf
                                                                    Equation 2.24
       Where:       u      =      solids retention time  (min)
                    Vr     =      total volume of the recirculation loop (gallons)
                    Qf    =      feed flow  (gpm)
       The VCF is a function of the solids retention time and the operational time within a
filtration cycle, as shown in Equation 2.25:
                     VCF(t)=-                                     Equation 2.25
                              1

       Where:        VCF(t)  =    VCF as a function of filtration cycle time  (dimensionless)
                     t        =    filtration cycle time (min)
                     T        =    solids retention time  (min)
       At the end of the filtration cycle, backwashing is used to flush the accumulated solids
from the membrane system. Since most crossflow systems are backwashed with filtrate water,
and the concentration of solids in the filtrate is negligible relative to that of the feed and
recirculation streams, it can be assumed that the backwash removes all of the solids from the
entire volume of the recirculation loop. Consequently, the concentration of suspended solids at
the membrane surface is equal to zero immediately after backwash (i.e., at t = 0, both Cm = 0 and
VCF = 0). Figure 2.18 illustrates the periodic variation in the concentration of suspended solids
on the feed side of the membrane for a typical  small volume crossflow system with a 20 minute
filtration cycle.

       As shown in Figure 2.18, for a small volume crossflow system, the maximum VCF
occurs at the end of the filtration cycle (i.e., t = tf) and is calculated according to Equation2.35.
                     FCFmax = -^                                    Equation 2.26


       Where:        VCFmax  =   maximum VCF (dimensionless)
                     tf        =   filtration cycle duration (min)
                     T         =   hydraulic detention time (min)
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                          Chapter 2 - Overview of Membrane Filtration
      Figure 2.18  Concentration Profile in a Small Volume Crossflow System
           100
                           20
 40           60
Filtration Time
    (minutes)
80
100
       Since the VCF increases linearly from zero to VCFmax over the course of a filtration cycle
in a crossflow system, the average VCF is simply one half of the maximum value, as shown in
Equation 2.27:
                    VCF.,  =0.5. M-
                           Equation 2.27
       Where:       VCFavg =    average VCF (dimensionless)
                    tf        =   filtration cycle duration (min)
                    T       =    hydraulic detention time (min)
       Note that some small volume crossflow systems may be operated at lower crossflow
velocities, resulting in incomplete particle suspension. In these cases the mathematical model
may overestimate the VCF. While this calculated VCF would represent conservative estimate,
the VCF could also be measured experimentally under realistic operating conditions in order to
determine a more accurate value.
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       Large Volume Crossflow Systems

       In a large volume crossflow system the concentrate recycle stream is returned to a large
feed tank, as shown in Figure 2.19, which greatly increases the total volume of the recirculation
loop (Vr) and changes the manner in which solids accumulate in the membrane system.
       Figure 2.19 Schematic of a Typical Large Volume Crossflow System
                                                                         FILTRATE
       Like small volume systems, large volume crossflow systems experience a linear increase
in the solids concentration on the feed side of the membrane over the course of a filtration cycle.
However, in a large volume system, backwashing does not remove all of the contaminants that
have accumulated in the recirculation loop and on the feed side of the membrane; thus
concentration on the feed side of the membrane (Cm) and the VCF do not return to zero after a
backwash operation.  As a result, the solids concentration gradually increases over multiple
filtration cycles, a phenomenon which must be considered when calculating the VCF.  The
periodic decrease in concentration occurs during a backwash operation when a portion of the
suspended solids is removed. The suspended particulate matter continues to accumulate over
successive filtration cycles until a stable process condition is reached, in which the amount of
solids delivered to the membrane system during a filtration cycle is equal to the amount of solids
that are discharged during the backwash process.  The "saw-tooth  pattern" concentration profile
and the gradual establishment of a stable process condition for a large volume crossflow system
are illustrated in Figure 2.20.
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                          Chapter 2 - Overview of Membrane Filtration
      Figure 2.20 Concentration Profile in a Large Volume Crossflow System
                                 Hydraulic Detention Time
                                          (minutes)
       Equation 2.28 describes VCF as a function of time for a large volume crossflow system,
taking into account both the buildup of solids over a filtration cycle and the partial removal of
solids during backwash:
                                   C,
                                                                  Equation 2.28
       Where:       VCF(t)  =    VCF as a function of filtration cycle time (dimensionless)
                    t        =    filtration cycle time (min)
                    T        =    solids retention time (min)
                    Cm(t-l)  =    concentration on the feed side of the membrane
                                 immediately after the previous backwash operation
                                 (number or mass / volume)
                    Cf      =    feed concentration at the inlet to the membrane unit
                                 (number or mass / volume)
                    Qb      =    backwash flow (gpm)
                    tb       =    backwash duration  (min)
                    Vr      =    total volume of the recirculation loop  (gallons)
       The maximum VCF for a large volume crossflow system can be calculated as the ratio of
feed volume processed over a filtration cycle to backwash water volume, as shown in
Equation2.29:
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                                                                   Equation 2.29
       Where:
VCF
tf
Qf
tb
Qb
                                 maximum volumetric concentration factor (dimensionless)
                                 filtration cycle duration  (min)
                                 feed flow (gpm)
                                 backwash duration (min)
                                 backwash flow (gpm)
       The average VCF for a large volume crossflow system can be calculated using
Equation 2.30:
                        avg
       Where:
VCFavg
tf
Qf
tb
Qb

                                                                   Equation 2.30
                                  average VCF (dimensionless)
                                  filtration cycle duration  (min)
                                  feed flow rate (gpm)
                                  backwash duration (min)
                                  backwash flow (gpm)
                                  solids retention time  (min)
       2.5.2.3  Continuous Stirred Tank Reactor Model

       The CSTR (also known as feed-and-bleed in some applications) hydraulic configuration
is similar to that of a crossflow system in that the particulate matter is held in suspension and
increases in concentration on the feed side of the membrane as a function of time. However, the
CSTR incorporates a continuous concentrate waste stream (also referred to as the reject or bleed
stream) that removes suspended solids from the system.  Since the solids are continuously
removed from the system, steady-state operation is achieved when the rate at which solids are
removed with the concentrate stream is equal to the rate at which solids enter the system with the
feed water. Although a PFR also utilizes a continuous concentrate stream and operates at stead-
state, the CSTR model assumes complete mixing and thus a uniform concentration of suspended
solids on the feed side of the membrane. A PFR, by contrast, has a feed side concentration
profile that increases in the direction of feed flow through the membrane unit. Thus, the CSTR
model is more appropriate than the PFR model for systems that are expected to have a relatively
uniform suspended solids concentration on the feed side of the membrane.
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       CSTR theory generally describes systems that operate continuously without
backwashing. For example, some MF and UF systems utilize a periodic short duration reverse
flow operation (i.e., a back-pulse) to remove solids from the membrane surface but collect the
dislodged solids in the feed tank.  Since this operation does not constitute backwashing (i.e.,
removal of solids from the system), these MF and UF systems can be modeled as CSTRs without
backwashing. In addition, a small-scale NF or RO membrane unit that is too small to be
considered a PFR (e.g., a single stage system using a high recirculation flow or a single module
system) can also be modeled as CSTR that  does not utilize backwashing. However, there may be
types of membrane filtration systems that can be effectively modeled as a CSTR with
backwashing, such as a small, immersed vacuum-driven membrane system in which the
backwash water is removed from the tank after the backwash operation. Thus, CSTR models
both with and without backwashing, respectively,  are described as follows.
       CSTR Without Backwashing

       Figures 2.21 and 2.22 provide representative schematics illustrating the types of pressure-
and vacuum-driven membrane filtration systems, respectively, that can be modeled as CSTRs
without backwashing. Note that a submerged, vacuum-driven system with mechanical agitation
(e.g., due to aeration) can be modeled as either a CSTR without backwashing or a PFR,
depending on the number of modules.  Systems with a very small number of modules may be
modeled as a CSTR without backwashing, as shown in Figure 2.22.  However, vacuum-driven
systems with a larger number of modules may be more accurately modeled as a PFR, as shown
in Figure 2.16. Alternatively, the VCF may be measured experimentally if neither model is
sufficient to describe the system within an acceptable degree of accuracy.

       The VCF for a CSTR without backwashing increases as a function of filtration cycle time
and can be defined in terms of the hydraulic detention time and the recovery, as shown in
Equation 2.31:
              VCF(t) =
       Where:
                        l-R
VCF(t)  =
R
t
                                              Equation 2.31
VCF as a function of filtration cycle time  (dimensionless)
recovery  (dimensionless decimal)
filtration cycle time  (min)
solids retention time (min)
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                         Chapter 2 - Overview of Membrane Filtration
 Figure 2.21 Schematic of a Typical Pressure-Driven CSTR Without Backwashing
    FEED
                   FEED
                   TANK
                                       MEMBRANE
                                       FEED
                                             MEMBRANE
                                             MODULES
                                RECIRCULATION
                                                                    FILTRATE
                            CONCENTRATE
                           •0*
                            Cc
Figure 2.22  Schematic of a Typical Vacuum-Driven CSTR Without Backwashing
      FEED
         Qt
         C,
                                                                     FILTRATE
           MEMBRANE
             MODUt.il •
  PROCESS
       AIR
                                 Cm
                                                                     CONCENTRATE
                                                                     •Ob
                                                                     Cc
       The concentration profile for a CSTR without backwash exhibits an exponential rise in
the VCF over time to an equilibrium value of VCFmax, as illustrated in Figure 2.23.  Additional
detail is provided in Table 2.2, which shows the percent of equilibrium value (i.e., VCFmax)that
is achieved in a CSTR without backwashing as a function of the number of hydraulic detention
times.  In general, a CSTR without backwashing approaches equilibrium rapidly - Table 2.2
shows that the concentration of suspended solids within a CSTR without backwashing reaches
95 percent of the equilibrium value after only three hydraulic detention times have elapsed.
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                         Chapter 2 - Overview of Membrane Filtration
        Figure 2.23 Concentration Profile in a CSTR Without Backwashing
             100
       E
      o
                                Hydraulic Detention Time
                                         (minutes)
      Table 2.2 Increase in VCF as a Function of Number of Detention Times
No. of Detention
Times
(t/T)
0
1
2
3
4
5
Fraction of
VCFmax
0
.632
.865
.950
.982
.993
       Since most systems are operated significantly longer than three hydraulic detention times
before being purged and cleaned, a CSTR without backwashing generally operates under steady-
state conditions at the maximum VCF. Consequently, the average and maximum VCF are
equivalent, and both can be calculated as shown in Equation 2.41.
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                          Chapter 2 - Overview of Membrane Filtration
                    VCF   = VCF  =
                    y L-1 max   Y ^-L avg
                                     l-R
                         Equation 2.32
       Where:       VCFmax  =   maximum VCF  (dimensionless)
                    VCFavg   =   average VCF  (dimensionless)
                    R        =   recovery  (dimensionless decimal)
       CSTR With Backwashing

       Figure 2.24 shows a schematic of a representative pressure-driven membrane system that
can be modeled as a CSTR with periodic backwashing. Note that the concentration profile for a
CSTR with backwashing is similar to that for a small volume crossflow system, although the
latter the maximum VCF is approached linearly rather than exponentially.  Another important
difference between these two types of hydraulic configurations is that the CSTR with
backwashing utilizes a concentrate waste (i.e., bleed) stream, whereas a crossflow system does
not use a concentrate bleed.
  Figure 2.24 Schematic of a Typical Pressure-Driven CSTR With Backwashing
     -LED
       Of
       c,
                     FEED
                     TANK
                                         MEMBRANE
                                         FEED
                                         Om
                                         Gn
                             FILTRATE
                                  RECIRCULATION
                             Bl KKD
                            •a
                                                                      BACKWASH
                                                                      q,
       As with a CSTR without backwashing, the VCF for a CSTR with backwashing increases
over time according to the first order exponential function given in Equation 2.31.  However, in a
CSTR with backwashing, the concentration of suspended solids on the feed side of the
membrane is periodically reduced. Because filtrate is typically used in the backwash process, the
backwash water introduces a negligible amount of particulate matter into the system; thus, it
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                          Chapter 2 - Overview of Membrane Filtration
reasonable to assume that the backwash process removes all suspended solids from the feed side
of the membrane.  As a result, the VCF is reduced to zero at beginning of each successive
filtration cycle (i.e., at t = 0).  Figure 2.25 illustrates the concentration profile of a CSTR with
backwashing over time for a system that is backwash once every four hydraulic detention times.
          Figure 2.25  Concentration Profile in a CSTR With Backwashing
-i nn —
IUU
an -
X
5 C" Kl~\ -
EC bU
E ฎ
o a
"p 8 40-
c Q. t\J
o —
on -
zu
/^~~
/
/ Ra r kwa ^ h 	 ^

/
/
x/^-"~"
/
/
/
/

0.
i i i i iii
012345678
Hydraulic Detention Time
(minutes)
       The maximum VCF for a CSTR with backwashing is determined by evaluating
Equation 2.31 at the end of the filtration cycle (i.e., t = tf), just prior to backwashing, as shown in
Equation 2.33:
                    VCF   =
                    '  ^-^-L max
                              l-R
1-exp
                                              -t.
Equation 2.33
       Where:       VCFmax  =   maximum VCF (dimensionless)
                    R        =   recovery (dimensionless decimal)
                    tf        =   filtration cycle duration (min)
                    T        =   solids retention time (min)
       The average VCF for a CSTR with backwashing is determined by applying the average
value function to Equation 2.33 over a filtration cycle.  The resulting expression for VCFavg is
shown in Equation 2.34:
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                          Chapter 2 - Overview of Membrane Filtration
                             l-R
       Where:
VCFa
R
tf
T
                                              1 - exp
                                                      -t.
                                      Equation 2.43
=   average VCF (dimensionless)
=   water recovery  (dimensionless decimal)
=   duration of the filtration cycle (min)
=   solids detention time (min)
2.5.3  Summary

       The hydraulic configuration of a membrane filtration system governs the concentration of
suspended solids on the feed side of membrane and whether it increases as a function of time or
position in a membrane unit. Accordingly, the VCF has a significant impact on the amount of
paniculate matter that could pass through an integrity breach and thus on the sensitivity of a
direct integrity test (as discussed in section 4.3).  Systems that operate in deposition mode have a
VCF equal to one, while the various suspension mode hydraulic configurations have VCFs
greater than one, as summarized in Table 2.3.
   Table 2.3  Typical Range of VCF Values for Various Hydraulic Configurations
Hydraulic Configuration
Deposition
mode
Suspension
mode
Dead-end
PFR
Crossflow
CSTR
VCF
1
3-20
4-20
4-20
       A summary of the equations used to calculate the average and maximum VCFs for each
of the various hydraulic configurations is presented in Table 2.4. The table also indicates the
types of membrane filtration systems that are generally associated with the respective hydraulic
configurations.  Note that it is also possible to determine the VCF experimentally for a particular
system (either full-scale or representative pilot-scale) by measuring the influent feed
concentration (Cm) and the concentration on the feed side of the membrane (Cf).
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                            Chapter 2 - Overview of Membrane Filtration
     Table 2.4 Summary of VCF Equations for Various Hydraulic Configurations
Hydraulic
Configuration
Deposition
Mode
Small Volume
Crossflow
[(tb ?Qb) < Vf]
Large Volume
Crossflow
[(tb ?Qb) > Vf]
CSTR
w/o
backwashing
CSTR
w/ backwashing
PFR
Typical
Membrane
Process(es)
• MCF
• MF/UF
• MF/UF
(w/o feed tank)
• MF/UF
(w/feed tank)
• NF/RO
(small-scale)
• MF/UF
(w/ bleed)
• MF/UF
(w/ bleed)
• NF/RO
VCF Equation
Average1
1
2r
'f-Qf
*>•&



1
/•
A
]
'/
> r/ * 2/
4ซa_
L



l-R
I
\-R

\ \
_ {
IT
s
T
Jf
CFO
[ f-rV
exp
L I T J.
oปe,w
)]



Q,
Maximum
1
T
','Q,
ซ,.&
1
I-/?
r ! -i T f^Yl
1 — /v V ^ y
1
I-/?
1  Ideal, theoretical average
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                            3.0  Challenge Testing
3.1    Introduction
       The Long-Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) requires that
any membrane filtration system used to comply with the Cryptosporidium treatment
requirements of the rule undergo challenge testing (40 CFR 141.728).  The primary purpose of
this challenge testing is to establish the log removal value (LRV) that an integral membrane can
achieve.  Under the LT2ESWTR, the maximum removal credit that a membrane filtration system
is eligible to receive is the lower of the two values established as follows (40 CFR 141.728):

       •  The removal efficiency demonstrated during challenge testing; or

       •  The maximum LRV that can be verified by the particular direct integrity test used
          during the course of normal operation

       The requirement for challenge testing under the LT2ESWTR is intended to be product-
specific such that site-specific demonstration of Cryptosporidium removal efficiency  is not
necessary. Once the LRV of a membrane has been established through a challenge test that
meets the requirements of LT2ESWTR, additional challenge testing is not required unless
significant modifications are made to the membrane process (as discussed in section 3.14). The
rule specifies criteria for the following aspects of challenge testing:

       •  Full-scale vs. small-scale module testing

       •  Appropriate challenge particulates

       •  Challenge particulate concentrations

       •  Test operating conditions

       •  Calculation of removal efficiency

       •  Verifying characteristic removal efficiency for untested modules

       •  Module modifications

Specific requirements of the rule are summarized in section 3.2 and further discussed in the
appropriate context in subsequent sections of Chapter 3. The discussion of challenge testing in
this chapter applies similarly to microfiltration (MF), ultrafiltration (UF), nanofiltration (NF),
reverse osmosis (RO), and membrane cartridge filtration (MCF), except as otherwise noted.
Although the primary focus of challenge testing as required under the LT2ESTWR is
demonstration  of Cryptosporidium removal, the general framework for challenge testing
developed in this guidance manual may be adapted for use in establishing removal efficiencies
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                                 Chapter 3 - Challenge Testing
for other microbial pathogens of concern, including bacteria, viruses, and other protozoa such as
Giardia.

       Chapter 3 is organized into sections that describe the various issues to be considered in
the design and implementation of a challenge test. Furthermore, it presents the various aspects
of challenge testing in order from the planning and design phase, through test implementation,
and finally to the analysis and interpretation of results.

This chapter is divided into the following sections:

       Section 3.2:   Summary of Challenge Testing Requirements
                     This section summarizes the requirements for challenge testing under the
                     LT2ESWTR.

       Section 3.3:   Test Organization Qualification
                     This section provides an overview of factors to consider when selecting an
                     organization for conducting a challenge test.

       Section 3.4:   General Procedure for Developing a Challenge Test Protocol
                     This section describes the general procedures for developing a challenge
                     testing protocol that meets the requirements of the LT2ESWTR.

       Section 3.5:   Module Specifications
                     This section outlines the particular module specifications that are
                     important considerations in the development of a challenge test.

       Section 3.6:   Non-Destructive Performance Testing
                     This section describes the important role of non-destructive performance
                     testing - a common quality control procedure used in the production of
                     membrane modules - in the challenge testing process.

       Section3.7:   Selection of Modules for Challenge Testing
                     This section discusses some considerations and two potential approaches
                     for both selecting particular modules for challenge testing and identifying
                     an appropriate number of modules to test

       Section 3.8:   Small-Scale Module Testing
                     This section describes some the issues associated with testing small-scale
                     rather than full- scale modules.

       Section 3.9:   Target Organisms and Challenge Particulates
                     This section discusses factors to consider in selecting a challenge
                     particulate for evaluating the removal efficiency of a membrane filtration
                     process, including attributes of potential surrogates for Cryptosporidium.
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                                Chapter 3 - Challenge Testing
       Section 3.10: Challenge Test Solutions
                    This section describes methods and procedures for preparing a challenge
                    test solution and for seeding challenge particulates into the solution.

       Section 3.11: Challenge Test Systems
                    This section provides some examples of typical challenge test apparatuses
                    used under different conditions, as well as the appropriate operational
                    parameters to use during the testing.

       Section 3.12: Sampling
                    This section describes aspects of challenge testing associated with
                    sampling, including sampling methods, sample port design and location,
                    process monitoring, and the development of a thorough sampling plan.

       Section 3.13: Analysis and Reporting of Challenge Test Results
                    This section discusses the calculation of removal  efficiency based on the
                    results of challenge testing, as well as suggestions for statistical analyses
                    and the preparation of a summary report for state  review.

       Section 3.14: Re-Testing of Modified Membrane Modules
                    This section provides guidance with respect to product modifications that
                    would warrant re-testing of a membrane filtration device.

       Section 3.15: Grandfathering Challenge Test Data From Previous Studies
                    This section discusses factors that should be considered when evaluating
                    data from previously conducted removal studies, that may not meet all of
                    the specific requirements for challenge testing under the LT2ESWTR, for
                    potential acceptance for satisfying the rule requirements.
3.2    Summary of Challenge Testing Requirements

       The LT2ESWTR specifies the core requirements that a challenge test must meet in order
to demonstrate the removal efficiency of a membrane filtration system with respect to
Cryptosporidium. These requirements are summarized as follows:

       •  Full-Scale vs. Small-Scale Module Testing:
          Challenge testing must be conducted on a full- scale membrane module identical in
          material and construction to the membrane modules proposed for use in full-scale
          treatment facilities.  Alternatively, challenge testing may be conducted on a smaller
          scale module that is identical in material and similar in construction to the full-scale
          modules. (40 CFR 141, Subpart W, Appendix C).
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       •  Appropriate Challenge Particulates:
          Challenge testing must be conducted using Cryptosporidium oocysts or a surrogate
          that has been determined to be removed no more efficiently than Cryptosporidium
          oocysts.  The organism or surrogate used during challenge testing is referred to as the
          challenge particulate.  The concentration of the challenge particulate must be
          determined using a method capable of discretely quantifying the specific challenge
          particulate used in the test; indirect water quality measurements such as turbidity,
          particle counting, or conductivity cannot be used for this purpose (40 CFR 141,
          Subpart W, Appendix C).

       •  Challenge Particulate Concentrations:
          The maximum allowable feed water concentration used during a challenge test is
          based on the detection limit of the challenge particulate in the  filtrate and is
          determined according to the following equation:

                 Maximum Feed Concentration = (3.16 x 106) x (Filtrate Detection Limit)

          This expression allows for the demonstration of up to 6.5 log removal during
          challenge testing if the challenge particulate is removed to the detection limit
          (40 CFR 141, Subpart W, Appendix C).

       •  Test Operating Conditions :
          Challenge testing must be conducted under representative hydraulic conditions at the
          maximum design flux and maximum design system recovery specified  by the
          manufacturer (40 CFR 141, Subpart W, Appendix C).

       •  Calculation of Removal Efficiency:
          The removal efficiency of a membrane filtration process as determined from the
          results of the  challenge test is expressed in terms of a LRV according to the following
          equation:

                 LRV = \0g(Cf)-\og(Cp)

          Where:   LRV   =    log removal value demonstrated during challenge testing
                    Cf    =    feed concentration used during challenge testing
                                (number or mass / volume)
                    Cp    =    filtrate concentration observed during challenge testing
                                (number or mass / volume)

          In order for this equation to be valid, equivalent units must be  used for  both the feed
          and filtrate concentrations. If the challenge particulate is not detected in the filtrate,
          then the term Cp  is set equal to the detection limit. A single LRV is calculated for
          each module tested.  The overall removal efficiency  demonstrated during challenge
          testing is referred to as LRVc-iest • If fewer than 20 modules are tested,  then LRVc-iest
          is assigned a value equal to the lowest of the representative LRVs among the various
          modules tested. If 20 or more modules are tested, then LRVc-iest is assigned a value

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                                Chapter 3 - Challenge Testing
          equal to the 10th percentile of the representative LRVs among the various modules, as
          defined by [i/(n+l)], where "i" is the rank of "n" individual data points ordered from
          lowest to highest.  It may be necessary to calculate the 10th percentile using linear
          interpolation (40 CFR 141, Subpart W, Appendix C).

       •  Verifying Characteristic Removal Efficiency for Untested Modules:
          Because the LT2ESWTR does not require that every membrane module be subject to
          challenge testing,  a non-destructive performance test (NDPT) (e.g., bubble point test,
          diffusive airflow test, pressure or vacuum decay test, etc.) must be applied to each
          production membrane module that did not undergo challenge testing  in order to verify
          removal efficiency.  A quality control release value (QCRV) must be established for
          the NDPT that is directly related to the removal efficiency of the membrane filtration
          process as demonstrated during challenge testing. Membrane modules that do not
          meet the established QCRV are not eligible for the removal credit demonstrated
          during challenge testing (40 CFR 141, Subpart W, Appendix C).

       •  Module Modifications:
          Any significant modification to the membrane media (e.g., a change in the polymer
          chemistry), hydraulic configuration (e.g., changing from suspension to deposition
          mode), or any other modification that could potentially affect removal efficiency or
          NDPT parameters would require additional challenge testing to both  demonstrate the
          removal efficiency of the modified module and define  a new QCRV for the NDPT
          (40 CFR 141, Subpart W, Appendix C).
       Beyond these core requirements, the rule provides substantial flexibility in the design of a
challenge test. Guidance for planning, designing, and implementing a challenge test, including
elaboration on the core requirements in the appropriate context, is provided in the subsequent
sections of this chapter.
3.3    Test Organization Qualification

       The LT2ESWTR does not specify any requirements with respect to the qualifications of
an organization conducting a challenge test, as long as the test is performed according to the
criteria mandated under the rule (40 CFR 141,  Subpart W, Appendix C). Each state has
discretion in approving the results from a challenge test conducted by any organization.
However, since challenge testing is intended to be product-specific,  it is important that there be
some consensus regarding what constitutes an acceptable test. Thus guidance provided in this
section is intended to outline the skills and capabilities that a test organization should posses in
order to produce quality data.
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       In general, conducting a successful challenge test necessitates that the testing
organization demonstrate effective knowledge of the following:

       •  The various membrane processes commonly used in drinking water treatment

       •  Operation of membrane filtration equipment and related system processes, including
          pretreatment, post-treatment, backwashing,  chemical cleaning, and integrity testing

       •  Proper challenge paniculate seeding and sampling techniques

       •  Analytical techniques for the enumeration of the challenge particulate used in the
          challenge test, including analyses of microorganisms, inert parti culate markers, or
          molecular markers (as applicable)

       •  Adequate quality assurance (QA)/quality control (QC) procedures to ensure that data
          quality objectives are achieved

       •  Basic statistical procedures that may be used in data analysis

       •  Preparation  of reports for regulatory agencies

Historically, many utilities and states have used independent, third party organizations to conduct
verification testing (i.e., challenge testing) in order to ensure an unbiased evaluation of the
process.  While there are advantages to this approach, a membrane manufacturer may have the
ability to conduct an acceptable challenge test if it can  demonstrate that appropriate QA/QC
procedures are used.
3.4    General Procedure for Designing a Challenge Test Protocol

       The core challenge test requirements of the LT2ESWTR should be incorporated into a
detailed protocol for implementing the test that documents the necessary equipment, procedures,
and analyses. Due to the variety of membrane systems available from numerous suppliers, it is
not possible to develop a single comprehensive protocol.  However, the following general list of
procedures describes the basic steps in the development of such a protocol.

       1.  Document basic membrane module specifications (as indicated in section 3.5),
          including:

          •   Maximum design flux

          •   Mode of operation
              (i.e., inside-out or outside-in)

          •   Hydraulic configuration
              (i.e., deposition or suspension)

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           •   Module dimensions and filtration area

           •   Operating constraints
              (e.g., maximum feed pressure, temperature, pH range, oxidant tolerance, etc.)

           •   Backwash and chemical cleaning procedures

       2.  Document the manufacturer's procedure for conducting non-destructive performance
           testing and ensure that the associated quality control release value (i.e., the minimal
           result from the NDPT that constitutes an acceptable product) is indicative of a NDPT
           resolution of 3  |j,m in order to demonstrate Cryptosporidium removal capability, as
           discussed in section 3.6. If available, the statistical distribution of the NDPT results
           for the product line may also be useful.

       3.  Determine the number of modules that will be evaluated during the challenge test and
           the method or criteria that will be used to select specific modules for testing (see
           section3.7).

       4.  Determine whether or not small-scale module testing is an option (see section 3.8).

       5.  Identify the target organism or contaminant for the test. For the purposes of
           compliance with the LT2ESWTR, the target organism is Cryptosporidium (see
           section 3.9).

       6.  Establish the target LRV for the challenge test. Because challenge testing is intended
           to be product-specific under the LT2ESWTR, it is generally advantageous for a
           manufacturer to set this target at the maximum  LRV for which it is  anticipated that
           the system will qualify.

       7.  Select the challenge particulate to be used for testing. If it is not feasible or desirable
           to use the target organism as the challenge particulate, it is necessary to identify an
           acceptable surrogate that is removed on an equivalent or more conservative basis (see
           section 3.9).

       8.  Select an analytical method that will be used to discretely quantify (i.e., enumerate)
           the challenge particulate and collect information relevant to the methodology for use
           in developing a sampling plan (see section 3.9). Determine the detection limit for the
           challenge particulate in the filtrate based on the method capabilities and filtrate
           sample volume.

       9.  Design the challenge test solution and establish the method for seeding the challenge
           particulates into the solution (e.g., continuous or batch seeding) (see section 3.10).

       10. Design and construct the testing apparatus, and select appropriate operational
           parameters (see section 3.11).


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       11. Develop a sampling and monitoring plan that specifies (as described in section 3.12):

          •   The number of feed and filtrate samples to be collected and analyzed

          •   The frequency of feed and filtrate sample collection

          •   The feed and filtrate sample volumes

          •   Procedures for sample collection

          •   Additional operating and water quality parameters to be monitored and associated
              monitoring frequency
       After completing the steps outlined above, the specific protocol for conducting challenge
testing should be documented and submitted for state approval, if required. Note that the
LT2ESWTR does not require that the challenge test protocol be reviewed or approved by the
USEPA; however, each state may exercise its discretion regarding whether approval of the
protocol is required before results of the challenge testing are accepted in that state.
3.5    Module Specifications

       Because there are significant differences in the numerous types of membrane modules
that are commercially available from various suppliers, it is important to document the particular
specifications of the module of interest prior to developing a product-specific challenge test.
Membrane equipment suppliers typically provide product specification sheets that contain
general information about a particular product line.  These sheets are generally applicable to all
the modules in a particular product line and typically contain the following information:

       •   Membrane module (i.e., product) designation

       •   Type of membrane material

       •   Membrane pore size or molecular weight cut-off (MWCO) - both mean and
          maximum values

       •   Feed side membrane filtration area within a module

       •   Module configuration
          (e.g., hollow-fiber, spiral-wound, etc.)

       •   Module dimensions
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          Membrane media dimensions

              ?  Hollow-fiber modules: inside and outside fiber diameters, membrane
                 thickness, fiber length, etc.

              ?  Spiral-wound modules: sheet dimensions, sheet thickness, etc.

          Membrane media symmetry
          (e.g., symmetric, asymmetric, composite, etc.)

          Maximum design flux

          Maximum feed and transmembrane pressure (TMP)

          Mode of operation
          (i.e., inside-out or outside-in)

          Hydraulic configuration
          (i.e., deposition or suspension)

          Operating constraints
          (e.g., temperature limit, pH range, oxidant tolerance, etc.)
       Although not all of the information listed above or provided with any particular product
specification sheet may be necessary for developing a challenge test, it is nevertheless prudent to
compile as much available information about the product as possible not only for its potential use
in challenge testing, but for long-term use during operation of the full-scale facility.

       It is also common for manufacturers to supply data for each specific module produced.
Membrane module data sheets are applicable only to the particular module with the listed serial
number and typically contain the results from a manufacturer's QC process.  If available, it is
important that these data sheets be obtained for each module that is to undergo  challenge testing,
since it is critical to document as much information about these particular modules, as possible.
For reference, it may also be useful to document the QC procedures associated  with the
production of modules to be used for challenge testing.
3.6    Non-Destructive Performance Testing

       While challenge testing is used to establish the LRV of an integral module of a particular
product type, it does not necessarily guarantee that all such modules produced will achieve the
same level of performance due to variability in the manufacturing process. In order to address
this issue, aNDPT is applied to all  subsequently manufactured modules that are not subject to
challenge testing to ensure that these modules comply with the minimum standards for
Cryptosporidium removal under the LT2ESWTR.  A NDPT is a physical test applied to the

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membrane module with the objective of characterizing some aspect of process performance and
which does not alter or damage the membrane.

       In order to be utilized in a membrane filtration system that is applied for the purpose of
receiving Cryptosporidium removal credit under the LT2ESWTR, each module must pass a
NDPT that is consistent with the 3-|j,m resolution requirement of the rule. For example, one
commonly used type of NDPT is the bubble point test, which characterizes the largest pore (or
defect) in a membrane module.  (Note that the "bubble point test" - in this context a type of
NDPT - is not the same as the "bubble test" - a diagnostic direct integrity test - described in
Chapter 4, although these two procedures are both based on the same principles of bubble point
theory, as described in Appendix B.) In a bubble point test, a pressure is applied to a fully-
wetted membrane module and gradually increased.  The pressure at which water is first
evacuated from the pores represents the bubble point of the membrane associated with a
particular module.  If the established bubble point of the membrane is sufficient to demonstrate
that there are no pores  (or defects) larger than 3 |j,m (as described in section 4.2.1.), then the
NDPT is  consistent with resolution specified in the rule for the removal of Cryptosporidium.

       The minimum passing test result for a NDPT is known as the quality control release
value (QCRV). In the  context of the LT2ESWTR, a test result that surpasses the QCRV
indicates  both that a module can adequately remove Cryptosporidium and is sufficiently similar
in quality to the modules subjected to challenge testing to demonstrate the ability of the module
of interest (which would not have been subject to challenge testing) to achieve the same LRV.
After a group of modules has been subject to challenge testing, the NDPT is applied to those
modules to determine an appropriate QCRV associated with  the removal efficiency observed
during the test.  Subsequently, all modules that are not subjected to challenge testing must pass
the same  NDPT by exceeding the established QCRV applicable to Cryptosporidium removal
under the LT2ESWTR. Modules that do not pass the NDPT at the QCRV would not be eligible
for Cryptosporidium removal credit under the rule and could not be used in any membrane
filtration  systems applied for this purpose.

       The LT2ESWTR does not specify a particular procedure for determining the QCRV from
the various modules that are subjected to challenge testing.  Thus, the manufacturer or
independent testing organization may exercise its discretion in  selecting an appropriate
methodology.  The QCRV may be selected as the average result among the various modules
tested, the most conservative result (to establish the most stringent QA/QC standards), or the
least conservative result (to maximize the number of modules eligible for removal credit under
the LT2ESWTR). Alternatively, a methodology similar to that required by the LT2ESWTR for
determining the overall removal efficiency based on the number of LRV observations could be
applied to the various NDPT results to yield an appropriate QCRV, as described in section 3.13.1
(40 CFR  141, Subpart  W, Appendix C). The method of module selection for challenge testing,
as discussed in section3.7, should also be considered when determining the QCRV from the test
data.

       Note that the rule does not specify the manner in which the QCRV is determined from the
challenge test data; however, the methodology must be acceptable to each state in which the
product line is applied  for the purpose of receiving Cryptosporidium removal credit under the
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LT2ESWTR. It is recommended that each module subjected to challenge testing also undergo
subsequent non-destructive performance testing for the purpose of establishing a QCRV. The
manner in which the NDPT results are used to determine the QCRV should reflect the manner in
which modules are selected, as well as the range of LRVs observed during the test.  If modules
are selected in a conservative manner (see section 3.7), and if the range of LRVs observed during
challenge testing is small, the average of the respective NDPT results from the modules
subjected to challenge testing might be selected to represent the QCRV. However, if a statistical
distribution of modules is selected for challenge testing, or if the range of LRVs observed during
challenge testing is significant, a more conservative value is recommended for the QCRV, such
as the minimum of the NDPT results observed among the tested modules.

       Because it is common for manufacturers to conduct some type of NDPT on every module
as a routine component of its QA/QC program, the NDPT requirements of the LT2ESWTR
simply ensure that the QCRV used by the manufacturer is sufficient to justify the LRV for
Cryptosporidium demonstrated via challenge testing. Note that because different NDPTs may be
used by the various membrane module manufacturers, the rule does not specify a particular type
of NDPT.  However, the NDPT used must be consistent with the resolution requirements of the
LT2ESWTR in order for a module to be eligible for Cryptosporidium removal credit.
3.7    Selection of Modules for Challenge Testing

       The intent of challenge testing under the LT2ESWTR is to characterize the removal
efficiency of a specific membrane product without requiring challenge testing for all production
modules. In addition, the rule does not specify a particular number of modules that are required
to undergo challenge testing in order to demonstrate Cryptosporidium removal efficiency.
However, because it is important that manufacturing variability in the product line be considered
in the development of an appropriate challenge test, the number of modules subject to challenge
testing, as well as the particular modules chosen, should be carefully selected on a rational and
scientific basis. Although manufacturers or independent testing organizations may develop any
number of different procedures for module selection, two common approaches are discussed in
this guidance as illustrative examples:

       1.  Selection of modules based on previously collected QC data for the product line

       2.  Random sampling of membrane modules from several manufactured lots according to
          a statistical sample design
       Use of the first approach listed above is predicated on the existence of significant QC
data for the product line accumulated over time by the manufacturer.  Since manufacturers
typically conduct some kind of NDPT on all modules produced to ensure quality and
characterize the variability of a product line independent of the link established between non-
destructive performance testing and challenge testing under the LT2ESWTR, such data should
generally be available. Because the modules subject to challenge testing will be subsequently re-
characterized with the NDPT to establish an acceptable QCRV required for all modules to be
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eligible for Cryptosporidium removal credit under the LT2ESWTR, it may be most
advantageous for a manufacturer to select modules for challenge testing that are near the lower
end of the statistical distribution of acceptable (i.e., under the manufacturer's in-house QC
procedures) NDPT results based on historical data. If these tested modules yield a QCRV that is
consistent with the resolution requirement of the rule, then it is likely that the majority of
production modules will also meet the established QCRV and thus be eligible for
Cryptosporidium removal credit. Using this approach, the number of modules selected for
challenge testing is generally at the discretion of the manufacturer or independent testing
organization.

       If historical QC data for the product line is not available from the manufacturer, the
second approach listed above may represent an appropriate option. This method involves the
evaluation of a statistically significant random sample of modules from a number of production
lots.  Because the modules at the lower end of the QC data are not artificially selected (as with
the first approach described above), it is likely that this method will result in a higher  QCRV,
resulting in a somewhat higher rejection rate of modules  eligible for Cryptosporidium removal
credit under LT2ESWTR. This number of modules selected for challenge testing using this
approach will likely be dictated by the particular statistical sampling technique used.

       Either of these two approaches or other rationale approach developed by the
manufacturer or independent testing organization could be utilized to select modules for
challenge testing. Regardless of the method used, it is suggested that at least five (5) membrane
modules from different manufactured lots be evaluated during a challenge test.
3.8    Small-Scale Module Testing

       The evaluation of small-scale (as opposed to full-scale) modules during a challenge test is
permitted under the LT2ESWTR to allow for cases in which it may not be feasible or practical to
test a full-scale module (40 CFR 141, Subpart W, Appendix C).  For example, if it is desirable to
conduct challenge testing using the target organism (i.e., Cryptosporidium for the purposes of the
LT2ESWTR) rather than a surrogate, the use of a small-scale module may be the only
economically viable alternative.

       All challenge testing requirements under the LT2ESWTR (as well as the associated
guidance) are equally applicable to both full-scale and small-scale modules. However, any
small-scale module tested must be similar in design to the full-scale modules of the product of
interest such that it can be operated (and thus tested) under a hydraulic configuration and at a
maximum design flux and recovery that are representative of the full-scale modules.  Simulating
the full-scale recovery and hydraulic configuration are important considerations for small-scale
challenge testing, since both of these parameters affect the concentration of suspended solids on
the feed side of the membrane.

       Although the decision to allow the use of small-scale module testing is left to the
discretion of the state, the option is permitted under the LT2ESWTR since it is considered a
valid approach for  characterizing removal efficiencies. For the purposes of consistency, it is
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recommended that manufacturers or independent testing agencies that opt to subject a product
line to challenge testing using small-scale modules utilize a protocol that has been accepted by a
wide range of stakeholders. Such a protocol has been proposed for use under the National
Sanitation Foundation (NSF) Environmental Technology Verification (ETV) program and is
available online at http://www.nsf.org/etv/dws/pdf/Bench  Memo  Protocol Stakeholders.pdf If
the link is inactive, contact the NSF at (800) 673-6275 for  further information.
3.9    Target Organisms and Challenge Particulates

       The purpose of a challenge test is to determine the removal efficiency of a membrane
module for one or more target organisms or pathogens. Challenge testing can be conducted
using either the target organism itself or an appropriate surrogate; the organism or surrogate used
in the test is referred to as the challenge particulate. The selection of a suitable challenge
particulate is critical to the design of a challenge test.

       This section provides guidance for selecting an appropriate challenge particulate,
including the selection of a target organism for the test and characteristics of suitable surrogates
for the target organism. A more detailed discussion of particular surrogates for Cryptosporidium
is also provided.
3.9.1   Selecting a Target Organism

       The target organism or pathogen of interest for the purposes of challenge testing is
selected based on the treatment objectives for the membrane filtration system.  For example,
Cryptosporidium would be the target organism in a challenge test conducted to demonstrate the
ability of a membrane filtration system to  comply with the treatment requirements of the
LT2ESWTR. However, in some cases it may be desirable to determine the removal efficiency of
a system for multiple target organisms. In such cases, the most conservative target organism
should be  selected for  the purpose of designing a challenge test.  For example, if the challenge
test is designed to evaluate the removal efficiency of a system for both Cryptosporidium and
Giardia, then the smaller of these two pathogens should be used as the target organism.
Although the approximate size ranges for  these two organisms overlap to some degree, as shown
in Table 3.1, Cryptosporidium has the smaller lower bound. Since membrane filtration is a
barrier technology based primarily on the  principle of size exclusion, the removal efficiency for
the smallest organism  of interest  should be conservative for larger pathogens.
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            Table 3.1 Potential Target Organisms for Challenge Testing
Target Organism
Enteric viruses
Fecal coliform
Cryptosporidium
Giardia
Size Range
(\im)
0.03-0.1
1 -4
3-7
7-15
3.9.2  Surrogate Characteristics

       Although use of the target organism as the challenge paniculate offers the advantages of
directly measuring removal efficiency for the pathogen of interest and eliminates issues
regarding the appropriateness of a surrogate, it may not be practical or feasible as a result of
economic considerations or concerns about working directly with the pathogen. Thus, the use of
surrogates may be the most viable option for challenge testing.  An ideal surrogate should have
characteristics that are likely to affect removal efficiency which are similar to those of the target
organism, while a conservative surrogate would have  characteristics that may result in a lower
removal efficiency relative to the target organism.  In general, it is necessary to use a
conservative surrogate unless there are data to support  the use of an ideal surrogate.

       As a result of the cost and potential health concerns associated with conducting a
challenge test using Cryptosporidium oocysts, the LT2ESWTR allows challenge testing to be
administered with a surrogate that has been verified to  be removed no more efficiently than
Cryptosporidium oocysts (i.e., an ideal or conservative surrogate) (40 CFR 141, Subpart W,
Appendix C).  The most direct means of demonstrating that a surrogate is ideal or conservative is
through a comparative test in which removal of the surrogate and the target organisms are
evaluated side-by-side. However, if the characteristics of a surrogate are sufficiently
conservative,  direct verification may not be necessary.  Key physical characteristics to consider
when evaluating the suitability of a surrogate for Cryptosporidium removal using membrane
filtration include size, shape, and surface charge. Other important considerations include ease of
use and measurement, as well as cost. Each of these factors is discussed as follows.
       Particle size and shape

       The effective size of an appropriate surrogate should be equivalent to or smaller than the
lower bound of the size range of the target organism.  Furthermore, the effective size of the
surrogate should be characterized using an upper bound of its size distribution such the 99th or
99.9th percentile  rather than the median.  Ideally, a surrogate would have a relatively narrow size
distribution and a high uniformity coefficient. For example, the lower size range of
Cryptosporidium is approximately 3 |j,m, and thus a conservative surrogate might be one in
which 99 percent of particles have a diameter of 1 |j,m or less.
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       Generally, it is desirable to use a surrogate that is the same shape as the target organism.
In the case of Cryptosporidium, an appropriate surrogate would have a spherical shape, although
in some cases a non-spherical surrogate might be considered. If a non-spherical surrogate is
used, it is recommended that the smallest dimension be considered as the effective size since
particles can interact with a membrane barrier at any orientation.

       Another consideration is the surface structure of the proposed surrogate.  A particle that
has a highly irregular surface structure may be removed more efficiently than a similarly sized
particle that has a smooth surface.  While it may be difficult to completely characterize the
surface of a potential surrogate, those with rough surfaces that are known to exhibit a high
degree of adherence may be removed through mechanisms other than size exclusion, and thus
may not provide a conservative estimate of removal efficiency.

       The manner in which the surrogate disperses in the challenge test solution has a
significant impact on the effective size and shape of the challenge particulate.  Some may
agglomerate or become attached to other particles while in solution, which would yield larger
effective particle sizes. For example, organisms such as Staphylococci exist as clumps and
Streptococci exist as chains. In its aggregate form each of these organisms is too large to be
considered conservative surrogates for Cryptosporidium.  Surface structure also impacts the
tendency of particles to agglomerate, and in general particles with a smooth  surface are more
likely to be mono-dispersed in solution.
       Particle surface charge

       A conservative challenge particulate should have a neutral surface charge, since charged
particles may interact with other particles and surfaces, thus enhancing removal. The solution
pH can also affect the charge of some surrogates and thus should be considered in the
preparation of a test solution. If there is a concern regarding the charge of the surrogate such that
mechanisms of particle retention other than size exclusion may be responsible for surrogate
removal in a MF or UF system, a nonionic surfactant could be used in the challenge test solution
to significantly reduce the impact of charge-related removal mechanisms.
       Ease of Use and Measurement

       Although factors such as ease of handling and measurement are not critical to
determining the appropriateness of a surrogate, these nevertheless may be important factors to
consider.  Handling the surrogate could expose personnel to the challenge particulate, and thus
should the surrogate should be selected to minimize unacceptable risk to the technicians
conducting the test. The material should also be easy to work with and dose accurately since
repeated tests may be  conducted in which reproducibility is desirable.  Surrogates that could
degrade during the test, resulting in an inconsistent challenge concentration, should be avoided.
It is also desirable to use a surrogate that is easy to enumerate through established analytical
techniques. Furthermore, the LT2ESWTR requires that the concentration of challenge particles
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determined using a discrete measuring technique such that gross measurements such as turbidity
are not acceptable.
       Cost

       The cost of seeding and analysis may preclude the use of some surrogates. Both the cost
of the surrogate itself and cost of the required analytical techniques should be considered, as well
as any other miscellaneous costs associated with the surrogate.
3.9.3  Surrogates for Cryptosporidium

       In the absence of an acceptable surrogate, formalin- or heat-fixed Cryptosporidium
parvum could be used as the challenge particulate for compliance with the requirements of the
LT2ESWTR. However, the rule does permit surrogates for the purpose of challenge testing, and
several different surrogates have been successfully used in studies evaluating physical removal
of Cryptosporidium.  There are three general classifications of surrogates: alternate
microorganisms, inert particles,  and molecular markers.  It important to note that not all of these
classes of surrogates  are appropriate for each type of membrane filtration system, and it is critical
that these be compatible for the  purposes of challenge testing. Generally, paniculate surrogates
such as alternate microorganisms and inert particles are appropriate for MF, UF, and MCF
systems,  while molecular markers would not be removed by these types of membranes. It may
be necessary to use molecular makers with NF and RO membrane systems that can remove
dissolved substances and which  are not designed to accommodate large particulate
concentrations.  Each of these surrogate classes is discussed in further detail in the following
subsections. Some of the potential advantages and disadvantages associated with each class are
summarized in Table 3.2.
  Table 3.2 Comparative Summary of Cryptosporidium and Potential Surrogates
Challenge
Particulate
Cryptosporidium
parvum
Alternate
microorganisms
Inert particles
Molecular markers
Size Range
3 -5 |im
0.01 - 1 |_im
< 1 |im
< 100,000 Daltons
Advantages
• No verification of
surrogate required
• Low cost
• Easy to measure
• Accepted use
• Moderate cost
• High uniformity
• Easy to use
• Low cost
• Easy to measure
Disadvantages
• High cost
• Difficult to measure
• Difficult to handle
• Potential clumping
• Difficult to measure
accurately
• Inappropriate for
some applications
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       3.9.3.1   Alternate Microorganisms

       Microorganisms other than the target can be used as surrogates for the purposes of
challenge testing for MF, UF, and MCF systems. Numerous organisms that have a history of use
in filter evaluation studies are smaller than 1 |j,m (when mono-dispersed in solution), and these
could be considered conservative surrogates for Cryptosporidium.  A number of these organisms
and an appropriate enumeration method are listed in Table 3.3, including both bacterial and
viruses.  Table 3.3 also includes common surrogates for Giardia and enteric viruses. S.
marcesscms and P. dimunita have been widely used as surrogates within the membrane filtration
industry, and the use of MS2 bacteriophage has generally been accepted as  a surrogate for enteric
viruses, since it is similar in size and shape to the poliovirus and hepatitis virus.
        Table 3.3 Potential Microbiological Surrogates for Cryptosporidium
Microorganism
Micrococcus 1.
Bacillus subtilis
E. coli
P. dimunita
S. marcessans
MS2 bacteriophage
Size Range
(y,m)
7-12
~ 1
1 -4
0.3
0.5
0.01
Target Organism
Giardia
Cryptosporidium
Cryptosporidium
Cryptosporidium
Cryptosporidium
Enteric virus
Enumeration
Method
Standard Methods
9222
Barbeau et al.
(1997)
Standard Methods
9222
Standard Methods
9222
Standard Methods
9222
Adams (1959)
       Although Bacillus subtilis has been used as a surrogate for Cryptosporidium for testing
the removal efficiencies of conventional treatment processes, it is not necessarily a suitable
Cryptosporidium surrogate for challenge testing membrane filtration devices. Because there is
limited data currently available regarding the use of Bacillus subtilis in membrane challenge
studies, a rigorous characterization of this organism would be necessary in order to determine
whether it could be used as a Cryptosporidium surrogate for the purposes of challenge testing
under the LT2ESWTR.  Based on the size range cited in Table 3.3, Bacillus subtilis could
potentially be considered an ideal surrogate (see section 3.9.2) for Cryptosporidium, pending a
rigorous comparison of other characteristics (e.g., shape, surface charge, etc.) between these two
organisms. However, because of this same size range overlap, Bacillus subtilis could not be
considered a conservative surrogate for Cryptosporidium.

       The primary advantage of many microbial surrogates is that enumeration is fairly simple
and inexpensive, typically involving culturing the test organisms present in the feed and filtrate
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samples. The ease with which these organisms can be cultured allows many to be grown in a
laboratory to produce a stock for use in challenge testing.  Bacteria can be cultured to yield stock
concentrations in the range of 105 to 109 organisms per 100 mL, while MS2 bacteriophage can be
grown at concentrations in the  range of 107 to 1012  organisms per 100 mL.  Any microbial  stock
used for the purpose of seeding during a challenge test should be enumerated prior to conducting
the challenge test in order to facilitate seeding at the target level.
       3.9.3.2   Inert Particles

       Inert particles may also be used as a surrogate for Cryptosporidium under the
LT2ESWTR.  For example, polystyrene latex microspheres (i.e., latex beads) have been used as
a surrogate for Cryptosporidium in a number of studies. Historically, microspheres have been
used in the calibration of particle counters and similar optical equipment in which a challenge
particle of a known size and geometry is required by the investigator. Microspheres can be
manufactured  with very high particle uniformity and a smooth surface, both of which are
important considerations when selecting a conservative surrogate.  Microspheres are chemically
inert, easy to handle, and relatively inexpensive. Furthermore, microspheres without a
significant surface charge can be produced to minimize the potential for adsorption and
interaction with either other particles or the membrane surface.  Microspheres are also readily
available with particle concentrations ranging from 107 to 109 particles per mL.

       The primary difficulty associated with the use of microspheres is particulate
enumeration.  Although particle counting is a simple means of enumeration, this technique may
not meet the rule requirement that the challenge particulate be discretely quantified as a result of
the potential for background particles other than the microspheres to affect the results.
Furthermore, other problems such as coincidence error and the dynamic range of most particle
counting instruments may  also skew the results. Any clumping of microspheres may also
complicate particulate enumeration. A more reliable, albeit more expensive, means of
enumerating microspheres is through capture (normally on a laboratory grade membrane filter)
and direct examination.  The use of fluorescent microspheres is recommended to facilitate
particulate identification. Methods for microscopic analysis of fluorescent microspheres are
reported in the literature (Abbaszadegan et al. 1997; Li et al. 1997).

       The appropriateness of microspheres as a surrogate for Cryptosporidium could be directly
verified through a comparative study; however,  microspheres that meet certain criteria might be
deemed conservative surrogates that would not require direct verification. For example, neutral,
spherical shaped microspheres with a maximum diameter of 1 |j,m and which are completely
mono-dispersed in solution might constitute a conservative surrogate for Cryptosporidium that
would  not require direct verification.
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       3.9.3.3   Molecular Markers

       The suitability of molecular markers as surrogates for Cryptosporidium should be
considered on a case-by-case basis. While the justification for using microorganisms and inert
particles as surrogates for Cryptosporidium is more straightforward given that all are
particulates, molecular markers are dissolved substances that are fundamentally different from
particulate contaminants. As such, the removal mechanisms for molecular markers may be
different than for those associated with discrete particles in many cases.  However, semi-
permeable membranes that are capable of achieving very high removal efficiencies for dissolved
substances may be capable of achieving similar removal of particulates such as Cryptosporidium.
In addition, porous membranes with very fine pore sizes may be able to remove large
macromolecules via mechanisms similar to those that filter discrete particles.  Thus, the use of
molecular challenge particulates is permitted for the purposes of challenge testing under the
LT2ESWTR if the molecular marker used is determined to be conservative for Cryptosporidium
and is discretely quantifiable.

       A variety of molecular markers have been historically used to characterize the pore size
or removal capabilities of membrane processes.  For example, macromolecular protein
compounds are used to determine the MWCO for many UF membranes. In addition, fluorescent
dyes such as Rhodamine WT and FDC Red #40 are used to characterize NF and RO  membranes.
These substances have high spectrophotometric absorbance characteristics that allow
measurement and detection at the ng/L level (Lozier et al. 2003). However, these low molecular
weight (-500 Daltons) solutions could only be used with RO and less permeable NF  membranes.
If molecular markers are considered for challenge testing, it is desirable to use compounds that
are more similar to discrete particles such as macromolecular proteins. It is also  recommended
that a mass balance be conducted on the feed, filtrate, and  concentrate streams prior to challenge
testing to assess the efficacy of using a particular molecular marker.

       With some molecular markers, it may difficult to demonstrate removal in excess of 3 log
unless sufficiently sensitive instrumentation is used.  For challenge tests conducted with
molecular markers, the feed and filtrate concentrations are typically quantified in terms of mass
per unit volume. If the analytical method is specific for the molecular marker used in the test,
use of a mass based concentration is acceptable since the mass of a known substance can be
related to moles, which is a discrete quantification.  As is the case with any challenge particulate,
gross measurements cannot be used for the purpose of quantification.   This requirement would
preclude the use  of analytical techniques such as total organic carbon (TOC) monitoring and
conductivity monitoring  in most  cases.
3.10   Challenge Test Solutions

       Generation of an appropriate challenge test solution is an essential component of an
effective test program.  The purpose of the challenge test solution is to deliver the challenge
particulate to the module of interest under the established test conditions.  The design of the
challenge test solution includes establishing acceptable water quality of the solution, determining
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volume requirements and the challenge paniculate concentration, and selecting a seeding
method.  These considerations are discussed in the following subsections.
3.10.1   Test Solution Water Quality

       While the LT2ESWTR does not stipulate any constraints on the design of the challenge
test solution, it is desirable to conduct the test in a manner that would be considered valid under
any anticipated conditions to which the product undergoing testing might be applied in the field.
Thus, the water quality of the test solution should be taken into consideration. In designing the
test solution, it is important to consider that the primary objective of challenge testing is to
evaluate the removal efficiency of the challenge particulate during filtration.  While water quality
may not have a significant impact on the removal efficiency, paniculate matter in the feed water
can enhance removal of smaller contaminants.  Thus, it is generally accepted that a test solution
matrix comprised of high-quality water provides the most conservative estimate of removal
efficiency.  Note that challenge testing is  not intended to yield meaningful information regarding
membrane productivity and fouling potential, and thus the use of a high quality water matrix
should not be considered inhibitory to testing these measures of membrane performance that are
unrelated to the primary objective of challenge testing - to evaluate the removal efficiency of the
challenge parti culate.  Productivity and fouling are addressed using site-specific pilot testing (see
Chapter 6) and not on a product-specific basis.

       Some particular considerations regarding water quality characteristics and their
implications for challenge testing are as follows:

       •  High quality water or "particle-free water" with a low  concentration of suspended
          solids (e.g., membrane filtrate) should be used as the matrix for the challenge
          solution, minimizing the potential for formation of a fouling layer during the
          challenge test that would enhance removal of the challenge paniculate.

       •  No oxidants, disinfectants, or other pretreatment chemicals should be added to the test
          solution unless necessitated by process requirements (e.g., acid addition and/or scale
          inhibitor which may be necessary with NF/RO processes).

       •  If the challenge paniculate is a molecular marker, the water quality of the matrix for
          the test solution should not interfere with the introduction, dispersion, or
          measurement of the marker. Thus,  the impact of water quality parameters, such as
          pH and ionic strength, on the chemical characteristics and speciation of molecular
          markers should be considered  in the design of the test solution.  This is particularly
          critical for NF or RO membrane modules, which can concentrate organic and
          inorganic solutes, potentially interfering with some molecular markers.

       •  If a microbial challenge particulate  is used, it may be necessary to add buffers or
          other materials to maintain the viability  of the organisms.  Any additives used must
          not interfere with any aspect of the  test or result in a change in the concentration  of
          the challenge particulate over the duration of the test. In addition, because water


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           quality parameters such as pH and ionic strength can affect microbial aggregation,
           these solution characteristics should also be considered.

           It is recommended that the challenge test solution be characterized with respect to
           basic water quality parameters, such as pH, turbidity, temperature, total dissolved
           solids (IDS), TOC, and any other water quality parameters that are critical to the test
           or interpretation of the results.
3.10.2   Test Solution Volume

       The solution volume necessary to conduct a challenge test depends on several factors
determined during the test design, including:

       •  Filtrate flow

       •  Recovery

       •  Test duration

       •  Hold-up volume of the test system

       •  Equilibration time for the test solution
       Taking these factors into account, the volume of solution required for challenge testing
may be calculated using Equations. 1:
                     T7-     *^ P    min   rr     ~t7  \  cii~>               T--   j_*    o  i
                     ^terf =  	o	+ ^ow + Veq\ • 5F               Equation 3.1
       Where:       Vtest   =      minimum challenge test solution volume  (gallons)
                     Qp     =      filtrate flow (gpm)
                     Tm;n   =      challenge test duration (min)
                     R      =      system recovery during test  (decimal percent)
                     Vhoid   =      hold-up volume of the test system  (gallons)
                     Veq    =      system volume required to attain equilibrium feed
                                   concentration (gallons)
                     SF     =      safety factor (dimensionless)
       The  safety factor in Equation  3.1  accounts  for unanticipated  circumstances that might
require additional solution volume. The value of the safety factor should be at least 1.0 and may
be as high as 2.0 under conservative conditions.
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       The parameters Qp and R are dictated by the system operating conditions (see
section 3.11.2). The LT2ESWTR requires that the flux and recovery used during the challenge
test be set at the maximum design values for each parameter, as per manufacturer specifications.

       The hold-up volume of the test system, Vhoid, is the unfiltered test solution volume that
would remain in the system on the feed side of the membrane barrier at the end of the test (i.e.,
after the system is shut down). At a minimum, this volume would include the feed side volume
of the membrane module and  associated piping.  In general, it is desirable to design the system
with a small hold-up volume,  which could potentially allow Vhoid to be ignored in Equation 3.1.
However, the hold-up volume can be significant in some systems, and in such cases Vhoid should
be measured and taken into account.  Another approach for dealing with the system hold-up
volume is to finish the test with a "chaser" of clean water (i.e., without the challenge paniculate)
through the system allowing the entire test solution to be filtered.  However, because this
approach can dilute  the feed concentration of the challenge particulate, the use of a clean water
chaser is  only recommended when the entire filtrate stream is sampled as a single composite (see
Figure 3.1).

       The equilibrium volume (Veq) is the  quantity of the test solution that must pass through
the membrane module(s) at the beginning of the test before the system stabilizes (i.e., the feed
side concentration reaches an  equilibrium value). In general, filtrate sampling cannot begin until
at least this equilibrium volume has passed through the system.  For most test apparatuses, a
reasonable assumption is that  a system achieves  90 percent of its equilibrium condition after
three hold-up volumes (i.e., 3? Vhoid) have passed through the system.

       The duration of the challenge test, Tmin, as given in Equation 3.1, does not include the
time required for the test solution to come to equilibrium, as this is taken into account by the
parameter Veq.  Thus,  Tm;n represents the time necessary to implement the sampling program
associated with the challenge  test (see section 3.12), which typically requires less than one hour.

       Table 3.4 provides examples of the challenge test solution volumes (i.e., Vest) required as
calculated using Equation 3.1  for various membrane configurations under the listed conditions,
in these cases assuming the system hold-up volume (Vhoid) and volume required to achieve
equilibrium (Veq) are negligible and a safety factor of 1.1. The filtrate flow (Qp) is not shown
specifically in the table, but is calculated simply by multiplying the membrane area and
maximum flux. Table 3.4 is intended to be illustrative only. Thus, it is recommended that the
solution volume requirements for a specific  challenge test be determined according to the
procedure described above. Also, note that the values listed in Table 3.4 are examples only, and
that particular product specifications will vary by module manufacturer.
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Table 3.4 Example Challenge Test Solution Volume for Various Types of Modules
Module
Cartridge filter1
Spiral-wound
Hollow-fiber
4" diameter
8" diameter
Outside-in
Inside-out
Example
Membrane
Area
(ff(m2)}
5 (0.46)
75 (7.0)
350 (32.5)
350 (32.5)
1,400 (130)
Example
Maximum
Flux
(gfd(Lmh)}
1,364 (2,316)
17.8 (30.2)
17.8 (30.2)
53.5 (90.8)
107 (182)
Test
Duration
(min)
30
30
30
30
30
Recovery
(percent)
100
85
85
100
100
Volume (V,est)
(gal(L)}
155(586)
36.1 (137)
168 (635)
429 (1623)
3,438 (13,013)
1  Note that because MCF is a new concept introduced with the LT2ESWTR, the example specifications cited are for cartridge
  filters, in general, not necessarily for MCF devices
3.10.3   Test Solution Concentration

       The concentration of the test solution is based on the target LRV to be demonstrated
during the challenge test (LRVt) and the detection limit for the challenge particulate in the filtrate
samples. Since challenge testing is intended to be a one-time, product-specific requirement, it is
generally advantageous to select a LRVt at or near the maximum of 6.5 log removal that can be
demonstrated under the LT2ESWTR. The detection limit is a function of the analytical technique
used to enumerate the challenge particulate and the filtrate sample volume. For example, if the
method can detect 1 particle in a sample,  and the filtrate sample volume is one liter, the detection
limit is 1 particle/L. The detection limit and maximum  6.5 LRV are used to calculate the
maximum feed concentration that can be  used during a  challenge test, as shown in Equation 3.2
(40 CFR 141, Subpart W, Appendix C):
                                                                    Equation 3.2
       Where:
                    DL
maximum feed concentration (number or mass / volume)
detection limit in the filtrate (number or mass / volume)
The coefficient in Equation 3.2 represents the antilog 6.5, thus capping the maximum feed
concentration in the test solution to allow a maximum of 6.5 log removal to be demonstrated if
the challenge particulate is removed to the detection limit in the filtrate.  The 6.5 log limit under
the rule is intended to prevent excessive over-seeding that can result in artificially high LRVs.

       The minimum required feed concentration can be calculated from the LRV and the
detection limit using Equation 3.3:
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                     Cf_^n = WLRn • DL                             Equation 3.3

       Where:        Cf.min    =    minimum feed concentration (number or mass / volume)
                     LRVt    =    the target log removal value for the challenge test
                                  (dimensionless)
                     DL      =    detection limit in the filtrate (number or mass / volume)

Equation 3.3 implicitly assumes complete removal of the challenge parti culate by an integral
membrane as a conservative means of estimating the minimum feed concentration. Note that
Equations 3.2 and 3.3  are identical for a LRVt of 6.5. Equations 3.2 and 3.3 also demonstrate
that the requisite feed concentration is a function of the detection limit associated with the
analytical technique used to enumerate the challenge particulate in the filtrate.  The detection
limit is typically  expressed in terms of the number of challenge particulates per unit volume, or
in the case of a molecular marker, mass per unit volume. For a given analytical method with a
known sensitivity, the detection limit can be reduced by increasing the sample volume analyzed.
For example, if a microbiological method is capable of detecting one organism in a sample, the
detection limit can be improved by an order of magnitude by increasing the volume analyzed
from 100 mL to  1,000 mL; however, many methods have limitations with respect to the
maximum sample volume that can be analyzed. Also note that the feed and filtrate
concentrations must be expressed in terms of equivalent volumes for the purposes of calculating
log removal, even if different sample volumes are collected and analyzed during the test.

       If the LRVt selected is less than the maximum of 6.5 permitted under the LT2ESWTR,
the maximum and minimum feed concentrations will be different. Note that it is desirable to use
a concentration greater than the minimum since use of the minimum feed concentration would
only demonstrate the LRVt if the challenge particulate were removed to the detection limit in the
filtrate.  After the maximum and minimum concentrations are established using Equations 3.2
and 3.3, respectively, a convenient value between these boundaries can be  selected for the
challenge particulate concentration (Ctest)-

       Once the  required test solution volume and concentration have been determined, the total
number of challenge particulates required for the test can be calculated using Equation 3.4. If a
molecular marker is used, Equation 3.4 would be used to determine the total mass  of the marker
required.
                     TCPP = Ctest • Vtest                               Equation 3.4

       Where:        TCPP  =   total challenge particulate population
                                (number or mass of particles)
                     Ctest    =   feed concentration of challenge particulate
                                (number or mass / volume)
                     Vtest    =   challenge test solution volume (gallons)
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3.10.4   Challenge Participate Seeding Method

       There are two approaches commonly used to introduce the challenge particulate into the
test solution: batch seeding and in-line injection.  Batch seeding involves the introduction of the
total challenge particle population (TCPP) into the entire volume of test solution followed by
complete mixing to a uniform concentration.  In-line injection allows for continuous or
intermittent introduction of challenge particulates into the feed stream entering the membrane
filtration system. The specific method used may depend on the circumstances of the particular
challenge test, although either is permitted under the LT2ESWTR.

       Batch seeding is simpler and requires less equipment than in-line injection, but it is only
feasible when the entire test solution volume is contained in a reservoir.  Furthermore, mixing
the challenge particulates into large volumes of water to create a uniform concentration can be
logistically problematic. For these reasons, batch seeding is typically only used in challenge
studies for  small-scale modules with a relatively  small membrane area, for which test  solution
volumes are easier to handle and mix.

       In-line injection is the most common seeding approach used in challenge studies,
particularly for those involving full-scale modules with greater membrane area.  In-line injection
allows the challenge particulate to be introduced  into the feed on either a continuous or
intermittent basis.  In general, continuous seeding is advantageous for challenge testing, although
intermittent seeding may be appropriate  for long-term studies in which it is only necessary to
seed organisms at key times during an operational cycle.  If intermittent seeding is used, it is
necessary to ensure that equilibrium is achieved during each seeding event prior to collection of
any feed or filtrate samples.

       In-line injection requires additional equipment, such as chemical feed pumps, injection
ports, and in-line mixers. These components must be properly  designed and integrated into the
test apparatus to ensure a consistent challenge particulate concentration in the feed. A chemical
metering pump that delivers an accurate  and steady flow of challenge material is recommended,
while pumps that create a pulsing action should be avoided. The injection port should introduce
the challenge material directly  into the bulk feed stream to aid in dispersion. Examples of
acceptable  and unacceptable injection ports  are shown in Figure 3.1. An in-line static mixer
should be placed downstream of the injection port, and a feed sample tap should be located
approximately ten pipe diameters downstream of the mixer.
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  Figure 3.1  Schematic of Acceptable and Unacceptable Sample Injection Ports
            INJECTICH QUILL
             VMIIH INItGFWL
              CHECK VALVE
                        INJFCTKN
                        CHEMICAL
                        PLOW
                        ACCEPTABLE
                                        CHECK VALVE
                                           REDJCING
                                            BUSHING

                                          BALL VALVE
                                         PIP-
                                               17-
                                                                  INACTION
                                                                  CHEW CA.
                                                                  Fl
                                                          UNACCEPTABLE


       The in-line injection method of seeding delivers challenge particulates from a stock
solution with a known concentration as calculated using Equation 3.5:
Where:
                           TCPP
^ ss ~

css

TCPP

Vss
                                                                     Equation 3.5
                              ss
                                 challenge parti culate concentration in the stock solution
                                 (number or mass / volume)
                                 total challenge paniculate population
                                 (number or mass of particles)
                                 challenge parti culate stock solution volume (gallons)
The TCPP is calculated according to Equation 3.4, while the stock solution volume, Vss, can be
selected for convenience.  However, the Vss should be between 0.5 and 2 percent of the total test
solution volume, as determined using Equation 3.1.

       Once the concentration of the stock solution has been determined, the stock solution
delivery rate (SSDR) for the in-line injection method of seeding can be calculated using
Equation 3.6:
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                     SSDR =  test *  p                               Equation 3.6
       Where:        SSDR   =    stock solution delivery rate (gpm)
                     Ctest     =    feed concentration of challenge parti culate
                                  (number or mass / volume)
                     Qp      =    filtrate flow (gpm)
                     Css      =    challenge particulate concentration in the  stock  solution
                                  (number or mass / volume)
                     R       =    system recovery during test (decimal percent)
The SSDR represents the setting for the chemical feed pump used to inject the challenge
particulate into the feed stream.
3.10.5   Example: Challenge Test Solution Design

Scenario:

       Using the methodology described in sections 3.10.1 through 3.10.4, design a challenge
test solution using the following assumptions and parameters:

   •   The target LRV for the challenge test is 4 log.
   •   The membrane module has an area of 100 m2.
   •   The maximum flux for the module 85 Lmh.
   •   The module operates in deposition mode.
   •   A test duration of 30 minutes is required to conduct the required sampling
   •   A system hold-up volume of 200 L.
   •   The filtrate sample volume used during the challenge test is 500 milliliters.
   •   The detection limit for the filtrate sampling technique is 1 particle per 500 mL.
   •   Challenge particulate seeding is  conducted via continuous in-line injection.


Solution:

Step 1:  Determine the required test solution volume.

         TT      *--p    rnin   Tr     T7-      or^            T^   j.'   01
         Vtest =	+ Vhold +Veq  • SF            Equation 3.1
               I    R                )

               Tmin  =30 minutes                    from given information

               R    =100 percent                    standard for deposition mode
                                                      hydraulic configuration

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                 hold
                     = 200 L
               V
                 eq
                SF   = ?
                            from given information

                            to be determined

                            to be determined
                     = ?
                            to be determined
              Assume that assume that the equilibrium volume is equal to three times the hold-
              up volume, as discussed in section 3.10.2:
                     Veq  =  3.Vh
      old
                     Veq =  3ซ(200L)

                     Veq =  600 L

              Also, as discussed in  section 3.10.2, a suitable safety factor is approximately in
              the range of 1.1 to 1.5.  Since no other information is givenin this example, a
              value for the safety factor is arbitrarily assumed.

                     SF  =  1.2

              The filtrate flow, Qp,  can be calculated simply by multiplying the given maximum
              flux and the membrane area (and converting to convenient units), as shown
              below:
                     Q,=
                              60-2EJ
                                \hour )
                     Qp  =  142L/min
         Therefore, the required test solution volume can be calculated as follows:
          test
                142
                     L
                    mm
30(min)
                                  • + 200Z + 600Z
                         1.2
              =  6072 L
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Step 2:   Determine feed challenge particulate concentration within the bounds established by
         Equations 3.2 and 3.3.
         Minimum feed concentration:
       LRVt =  4 log

       DL   =  1 particles per 500 mL

             =  2 particles per L

C/_min = 104 • 2particles IL

C/_min = 2 • 104 particles IL


Maximum feed concentration:

C/__=(3.16.106).DZ

       DL   =  1 particles per 500 mL

             =  2 particles per L

Cf^ = (3.16 • 106) • 2particles IL


c f-max = 6-32 *! ฐ6 particles IL
                                                       Equation 3.3

                                                       from given information

                                                       from given information
                                                       from given information
         Select a feed challenge particle concentration between the minimum
         (2 • 104 particles/L) and maximum (6.32 • 106 particles/L).  Arbitrarily:

         Ctest  =  5 • 104 particles/L
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Step 3:   Determine the total challenge paniculate population required for the test solution.



         TCPP = Ctest • Vtest                             Equation 3.4



                Qest  =  5? 104 particles/L              as calculated in step 2 above



                Vtest  =  6,072 L                        as calculated in step 1 above



         TCPP = (5 • 104 particles I L) • (6,072Z)



         TCPP = 3.036 • 108 particles





Step 4:   Determine the challenge particulate stock solution concentration using Equation 3.5.



               TCPP
         Css =	                                   Equation 3.5

                 *ss



                TCPP   =  3.036? 108 particles           as calculated in step 3 above



                Vss      =  ?                             to be determined



                As discussed in section 3.10.4, select a stock solution volume that is between

                0.5 and 2 percent of the total test solution volume of 6,072 L (as determined in

                step 1 above).  Thus:



                       (0.005  ? 6,072 L) < Vss < (0.02 ? 6,072 L)



                       (30.4 L) < Vss < (121.4 L)



                       Vss  =  100L                   arbitrary selection



         Substituting values:



             _ 3.036 ปWSparticles
         V^< (->(->
                       1001



         C55 = 3.03 6 • 106 particles IL
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Step 5 :   Determine the challenge parti culate stock solution delivery rate for continuous, in-line
         injection.


         SSDR =  test *  p                              Equation 3.6
               Qest  =5?  104 parti cles/L              as calculated in step 2 above

               Qp   =142 L/min                      as calculated in step 2 above

               Css   = 3.036?  106 parti cles/L          as calculated in step 4 above

               R    =100 percent                     standard for deposition mode
                                                       hydraulic configuration

         Substituting values:

                 (5 • 1 04 particles / Z) • (1 42L I min)
                    (3.036 • \Qb particles I L) • 1

          SSDR =  2.53 L/min


3.11   Challenge  Test Systems

       A system used for challenge testing must be carefully designed to both meet the
objectives of the test and simulate full-scale operation to the greatest practical extent.  Guidance
for both designing an appropriate test apparatus and determining operational parameters for
challenge testing is provided in the following subsections.


3.11.1  Test Apparatus

       The equipment used to conduct challenge testing is product-specific to some extent,
although there are some basic components that are common to all systems. In many cases, a
manufacturer may maintain a special test apparatus to check individual modules as a component
of its QA/QC program. Such an apparatus may be suitable for conducting challenge testing and
typically includes equipment such as pumps, valves, instrumentation, and controls necessary to
evaluate full-scale modules. This same type of equipment would be used in the design of
systems for testing small-scale modules.

       Both the seeding and sampling methods selected for challenge testing, as well as the
hydraulic configuration of the system, affect the design of the test apparatus.  Batch seeding
requires a feed tank  and mixing equipment, while continuous seeding requires a stock solution
reservoir, chemical metering pump, and in-line mixers. Sampling requirements may dictate the
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                                 Chapter 3 - Challenge Testing
location and design of sample taps in the system. In addition, the test apparatus should be
designed to mimic the hydraulic configuration of the full-scale system as much as practical;
however, the test apparatus may alternatively utilize a more conservative recovery than the full-
scale system. If 100 percent recovery (i.e., the most conservative scenario) is used, a crossflow
system must operate without a bleed stream such that all of the concentrate is recirculated (see
section 2.5.2.2), and a deposition mode system (see section 2.5.1) must filter the entire test
solution volume. Note that a full-scale crossflow system could not operate at 100 percent
recovery on a sustained basis, since the feed would become increasingly concentrated.  However,
operation at 100 percent recovery is feasible for  a short-term challenge test in the interest of
generating conservative results. The test apparatus should allow the membrane module to
undergo direct integrity testing both before and after the challenge test. Figures 3.2 through
Figure 3.6 are schematic representations of typical apparatuses for challenge testing under
various conditions.  Note that ancillary equipment and operational processes (e.g., backwash,
chemical cleaning, and integrity testing) are not  shown.

       Figure 3.2 illustrates a pressure-driven apparatus operating in deposition mode with batch
seeding and composite sampling.  This type of system may be well suited for a MCF or other
membrane module with limited surface area. With this apparatus the test solution is prepared as
a batch and a composite filtrate sample would be generated, yielding a single data pair (i.e., a
feed sample and a composite filtrate sample) for the purposes of calculating the log removal
efficiency for the challenge paniculate.
  Figure 3.2 Schematic of a Typical Pressure-Driven System in Deposition Mode
                    with Batch Seeding and Composite Sampling
    rrn
             TANK
CONTAINS
STOCK
SO-U'OS
                                    T
                  FEED
                  PLMP
      FIEB
      VALVE

                                                                   I LOW
                                                                   METER
                                                    RL.TRATF
                                                     VALVE
                                                   	X3	1
                                         MEW3RANE MODULf
                                                                      HLTHVi
                                                                       AWfl_E
                                                                       POM
                                                                              (OPTIONAL)
       Figure 3.3 illustrates an apparatus similar to that shown in Figure 3.2, but designed for
continuous in-line seeding and grab sampling rather than batch seeding and composite sampling.
With this apparatus the challenge particulate is introduced from a stock solution reservoir and
mixed prior to the feed sampling point. The use of grab sampling allows the collection of
multiple feed and filtrate samples from a single test run.
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                                Chapter 3 - Challenge Testing
  Figure 3.3 Schematic of a Typical Pressure-Driven System in Deposition Mode
                    with Continuous Seeding and Grab Sampling
            BOOLJUrtlNC
           LEVEL COMT=K>-
              VALVC
             	IX-
        PWTLTES
       Figure 3.4 shows a schematic of a pressure-driven apparatus operated in suspension mode
with continuous seeding and grab sampling. In systems that operate in suspension mode, the
concentration of suspended solids increases on the feed side of the membrane, as discussed in
section 2.5.  While it may not be practical to accurately replicate the solids concentration profile
for a membrane system in which the feed side concentration of suspended solids varies as a
function of filtration time, concentrate recirculation can produce conservative feed side
conditions for the purpose of challenge testing, assuming appropriate operating conditions  for
recovery and recycle ratio are selected.  Selection of an appropriate recovery for challenge
testing can be complicated by the fact that system recoveries can vary significantly in some cases
(particularly for NF/RO systems).  Guidance regarding the selection of an appropriate recovery
for a challenge test of a membrane system operated in suspension mode is provided in section
3.11.2. The recycle ratio should be selected such that velocities  across the membrane surface are
high enough to keep particles in suspension. The manufacturer can typically recommend a
minimum scour velocity for a crossflow system.

       For systems that utilize concentrate recycle there are some additional considerations that
are important to take  into account regarding the feed side system volume and the location of the
feed sample point. In general, larger feed side system volumes require longer system
equilibration times.  For example, Figure 3.4 shows the concentrate return location at the feed
tank rather than directly into  the module feed line, thus increasing the effective feed side system
volume significantly. If such an arrangement is necessary (e.g., to provide an air break in the
recirculation system), then the feed tank volume should be minimized.  In an apparatus utilizing
concentrate recycling, the feed sample point must be located upstream of the return point, as
shown in Figure 3.4.
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                               Chapter 3 - Challenge Testing
        Figure 3.4 Schematic of a Typical Pressure-Driven System in Suspension
                Mode with Continuous Seeding and Grab Sampling
       Figure 3.5 shows a typical vacuum-driven test apparatus operated in deposition mode
with continuous seeding and grab sampling.  Although the module is immersed in a tank, the
feed water is not agitated, thus allowing particles to deposit on the membrane surface. With this
apparatus, the filtrate sampling point must be located downstream of the vacuum pump.

       Figure 3.6 illustrates an apparatus for a vacuum-driven system operated in suspension
mode with continuous seeding and grab sampling. With this apparatus the feed tank is
mechanically agitated to keep particles in suspension and can be modeled as a continuous stirred
tank reactor (CSTR) (see section 2.5). As with the vacuum-driven apparatus shown in
Figure 3.5, the filtrate sampling point must be located downstream of the vacuum pump.
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                              Chapter 3 - Challenge Testing
  Figure 3.5 Schematic of a Typical Vacuum-Driven System in Deposition Mode
                   with Continuous Seeding and Grab Sampling
                                                                           TANK
                                                                         (OPTIONAL)
  Figure 3.6 Schematic of a Typical Vacuum-Driven System in Suspension Mode
                   with Continuous Seeding and Grab Sampling
    CALlBfUtiON
     COLUMN
                STOCK
               SO LJLF1OS
               RCSEHVOIH
             WJSITWE
            C1SPLACE14ENT
              HUUH




PROCESS
AW


*
•
*



>>J
MEMBRANE^
UQQU'J
t 1 t

1
. .1 .

x,:
t * t

XJ FLXW
FlLTftfcTE COW1RQL
PtJMP v^vc


__

                                                              FLOW
                                                              MfEfi
                                                              FM
                              HM-O.U
                               VALVE
                                                                  FILTRATE
                                                                  5AMPLE
                                                                   POM
                                                                    DKMH1
                                                                         RLTRATE
                                                        FLOW
                                                        METER
                                                               "FLOW
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                                 Chapter 3 - Challenge Testing
3.11.2   Test Operating Conditions

       The design of a challenge test includes specifications for the following operating
conditions: flux, recovery, and hydraulic configuration.  The LT2ESWTR requires the challenge
test to be conducted at the maximum design flux and recovery (40 CFR 141, Subpart W,
Appendix C), and that the test apparatus be operated under representative or conservative
hydraulic conditions (40 CFR 141, Subpart W, Appendix C).  These requirements dictate the
operating conditions for the test apparatus during challenge testing. Note that under the
LT2ESWTR, recovery is defined as the volumetric percent of feed water that is converted to
filtrate in the treatment process over the course of an uninterrupted operating cycle (i.e.,
excluding losses that occur due to the use of filtrate in backwashing or cleaning operations).

       Testing at the maximum recovery is important to ensure that the volumetric concentration
factor (VCF) simulated during challenge testing is representative of (or conservative for) full-
scale system operation. For systems that operate in deposition (i.e., direct flow or "dead-end")
mode, such as most MF/UF and MCF systems, the value of the VCF is one, and thus the
recovery does not have a significant impact on the suspended solids concentration. However, it
is still recommended that systems operating in deposition mode process at least 90 percent of the
challenge test solution, thus resulting in an effective recovery of at least 90 percent. Similarly,
for MF/UF systems that operate in suspension mode but without a concentrate waste stream (i.e.,
a bleed stream), it is also recommended that at least 90 percent of the challenge test solution be
processed in order to generate an effective recovery of at least 90 percent. For MF/UF  systems
that operate with a concentrate waste stream, it is recommended that a recovery of at least
75 percent be utilized for challenge testing unless a more representative system recovery can be
demonstrated by the manufacturer; a recovery of 100 percent would represent the most
conservative case.  NF/RO systems, for which the utilization of a concentrate waste stream is
standard, should be operated at a recovery of at least 45 percent for the purposes of challenge
testing, which is representative of a flow-weighted average recovery for a module in such a
system operating at an overall recovery of greater than 90 percent for a  single stage. If challenge
testing is conducted on a small-scale NF/RO system (such as one using  a single module), then
concentrate recycle should be used to increase the recovery to at least 45 percent.

       The membrane area is also typically  given in the specifications,  and the maximum filtrate
flow can be calculated by multiplying the membrane area and the maximum flux. Although the
LT2ESWTR stipulates specific requirements for challenge testing flux,  the filtrate flow is also
necessary for designing the challenge test solution, as described in section 3.10.  Table  3.5
summarizes some typical specifications for membrane area and maximum flux associated with
various types of membrane modules, as well as the corresponding filtrate flow.  For the purposes
of challenge testing, the membrane area exposed to the feed (i.e., as opposed to that to the
filtrate) should be used in all calculations. Note that the values listed in Table 3.5 are examples
only, and that particular product specifications will vary by module manufacturer.
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            Table 3.5 Typical Parameters for Various Types of Modules
Module
Cartridge filter
Spiral-wound
Hollow-fiber
4" diameter
8" diameter
Outside-in
Inside-out
Example
Membrane Area
(ff(m2)}
5 (0.46)
75 (7.0)
350 (32.5)
350 (32.5)
1,400 (130)
Example
Maximum Flux
(gfd(Lmh)}
1,364 (2,316)
17.8 (30.2)
17.8 (30.2)
53.5 (90.8)
107 (182)
Filtrate Flow
{gpm (L/min)}
4.8 (18.2)
0.9 (3.4)
4.3 (16.3)
13.1 (49.6)
103 (390)
      1  Note that because MCF is a new concept introduced with the LT2ESWTR, the example specifications cited
        are for cartridge filters, in general, not necessarily for MCF devices
       A challenge test should be designed to simulate the hydraulic configuration of full-scale
system operation, since it affects the concentration of suspended solids on the feed side of the
membrane and thus the removal efficiency of the process. A membrane filtration  system can be
operated in either suspension of deposition mode.  (The various hydraulic configurations for
membrane filtration systems are discussed in further detail in section 2.5.) While it is relatively
straightforward to simulate a system operating in deposition mode during a challenge test, it may
not be possible to simulate all variations of suspension mode operation using a single module
challenge test apparatus. For example, it is not practical to simulate a plug flow reactor (PFR)
configuration typical of full-scale RO systems. In such cases, the challenge test apparatus should
be designed and operated as a CSTR, since a CSTR configuration generally results in the highest
concentration of suspended solids  on the feed side of the membrane.  If the challenge test can
successfully demonstrate the target LRV with a higher concentration of suspended solids on the
feed side of the membrane than expected with the full-scale  system, then the use of a CSTR in
place of a PFR configuration would represent more conservative, and thus acceptable, challenge
test conditions. A single RO module can be operated as a CSTR by including a concentrate
recycle loop, as shown in Figure 3.4.
3.12   Sampling

       Although the LT2ESWTR does not stipulate any particular requirements for sampling, it
is an important component of a challenge test. An effective sampling program is dependent on
the development of detailed and thoroughly documented sampling plan, as well as the selection
of appropriate sampling methods and locations.  These critical aspects of sampling, along with
the monitoring of operational parameters during the execution of the challenge test, are discussed
in  the following subsections.
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3.12.1   Sampling Methods

       The two most common approaches for sampling are the grab and composite methods.
Grab sampling involves the collection of one or more aliquots from the feed or filtrate stream,
while composite sampling involves collection of the entire process stream for processing and
subsequent analysis.  The concentration of challenge particulates in the feed solution is typically
characterized through grab sampling, while the filtrate stream may be sampled using either grab
or composite sampling. If grab sampling is used for both the feed and filtrate streams, the
number of feed and filtrate samples does not need to be equivalent, and samples can be collected
on different schedules during the challenge test. In many cases, it may be advantageous to
collect more filtrate samples than feed samples, since filtrate concentrations are expected to be
very low, and an error of just a few particles in a filtrate sample can have a significant impact on
the demonstrated removal efficiency.  Moreover, if batch seeding is used, the feed concentration
should not vary significantly over the course of challenge testing, assuming appropriate feed
stock mixing. However, if continuous seeding is used, paired sampling may be preferred for
simplicity of data reduction.

       Grab sampling typically involves the collection of a predetermined volume of water in an
appropriate collection vessel at predetermined times, as documented in the sampling plan. In
some cases, a composite sample is collected directly into a sampling vessel; however, it is more
common to capture the challenge paniculate during composite sampling. A composite sample is
usually compiled by passing the entire filtrate stream through an absolute filter capable of 100
percent capture of the challenge particulate.  The challenge particulate would then be enumerated
either directly from the filter media or removed from the filter for subsequent analysis. Grab
samples typically do not require this type of processing in the field, and  any extraction or
concentration steps for grab samples are typically  conduct in the lab.

       It is important that good sampling practices be employed during  challenge testing, such
as flushing  taps prior to sample collection (if applicable) and isolating filtrate sampling locations
from feed sampling locations to prevent cross-contamination.  Furthermore, appropriate QA/QC
measures should be implemented during sampling, such as collection  of duplicate samples and
blanks.
3.12.2   Sample Port Design and Location

       As with the challenge paniculate injection port, the design of the feed and filtrate sample
withdraw ports should yield a uniform sample. Figure 3.7 illustrates examples of both
acceptable and unacceptable sampling ports. The unacceptable apparatus requires the sample to
be pulled from a large section of pipe and has an area where stagnation of sample flow may
occur.  By contrast, the acceptable apparatus has a quill that extends into the center of the pipe to
obtain a more representative sample.
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                                 Chapter 3 - Challenge Testing
      Figure 3.7 Schematic of Acceptable and Unacceptable Sampling Ports
                                              BALL VALVE
   REDUCING
   BUSHING

 BULL VALVE
                           F.OW
                                    FLOW
            ACCEPTABLE
           UNACCEPTABLE
       The feed sample tap should be located at least ten pipe diameters downstream of
challenge particulate injection points and in-line mixers to ensure uniform concentration. For
apparatuses that utilize concentrate recycle, as illustrated in Figure 3.4, the feed sample tap
should be located upstream of the T-connection where the concentrate is blended with the
incoming feed water.  A check valve may be used to prevent backflow of concentrate into the
feed line. As a  guideline, the feed sample rate should be no more than 1 percent of the flow to
the membrane.  Filtrate samples should be collected at a point after the filtrate passes through
any filtrate side instrumentation such that any important measurements are not affected by the
sampling event.  In vacuum-driven apparatuses, the filtrate sample tap must be located
downstream of the filtrate pump, as shown in Figures 3.5  and 3.6.  Note that the filtrate
sampling valve  should be positioned as close as possible to the filtrate port in order to minimize
error due to any potential for adhesion of the challenge particulate to the piping prior to the
sampling point.  In addition, if a microorganism is used as the challenge particulate, it is prudent
to use a metal or heat-resistant  sampling valve to allow the tips of the valve to be flame-
sterilized.
3.12.3   Process Monitoring

       During the challenge test it is important that the operational parameters be monitored to
ensure that the test conditions remain constant.  Continuous monitoring for flow (or flux) and
pressure is should be conducted if the apparatus is equipped with the appropriate
instrumentation.  If periodic monitoring must be utilized, it is important that operational
parameters be checked at least both before beginning and after completing sampling for the
challenge particulate.  Operational data collected prior to initiating sampling should be used
verify that the flux and recovery are at the required levels.  It is also important that the membrane
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                                 Chapter 3 - Challenge Testing
module(s) undergo direct integrity testing both before and after challenge testing to verify that
the modules were integral during the test.

       If the water quality of the test solution matrix is a particular concern, other water quality
parameters should be sampled accordingly.  Some examples of other parameters that may be
important in some cases include pH, temperature, turbidity,  TDS, TOC, and ionic strength.  The
measurement of such water quality parameters may be most relevant if a molecule  marker is
used as the challenge particulate, as discussed in section 3.10.1.

       All aspects of process monitoring, including what parameters to monitor, how often to
monitor, and the range of acceptable results should be included the sampling plan for the
challenge test (see section3.12.4). If any results are outside acceptable tolerances, the challenge
test should be restarted.
3.12.4   Sample Plan Development

       The primary purpose of a sampling plan is to define the samples to be collected and
provide an accompanying sampling schedule for the challenge test. A sampling plan should
include:

       •  Type of sample(s) (i.e., composite vs. grab)

       •  Number of feed and filtrate samples to be collected

       •  Sample locations

       •  Sampling interval

       •  Estimate of time required to collect each sample

       •  Sampling equipment required

       •  Sample volume(s)

       •  Process monitoring  requirements (see section 3.12.3)

The sampling plan should also  specify any particular requirements associated with the analytical
technique to be employed,  and  well as procedures for shipping the sample(s) if they are to be
analyzed at an off-site laboratory. Samples should be  collected, preserved, stored, prepared, and
analyzed using methods and techniques appropriate for the challenge particulate.

       Sampling should not begin until the system has stabilized (i.e., reached equilibrium
concentration). Most test apparatuses achieve greater than 90 percent of equilibrium
concentrations after three hold-up volumes have passed through the system. Thus, the system
hold-up volume and feed flow  can be used to estimate the point at which the system is near

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equilibrium and thus the time at which sampling can begin. Both the hold-up volume and time
required for system stabilization (as discussed in section 3.10.2) should be included in the
sampling plan.
3.13   Analysis and Reporting of Challenge Test Results

       After challenge testing is completed for a particular product, the results must be analyzed
to determine the established removal efficiency of the module (i.e., LRV c-Test) for the purposes of
LT2ESWTR compliance. The following subsections provide guidance regarding the calculation
of removal efficiency under the rule, the statistical analysis of the challenge test results, and
summarizing challenge testing in a report for state review.
3.13.1   Calculation of Removal Efficiency

       The removal efficiency established during challenge testing - LRVc-iest - is determined
from the various LRVs generated during the testing process. The LT2ESWTR requires that a
single LRV be generated for each module tested for the product line under evaluation. The
LRVs for each respective module tested are then combined to yield a single value of LRVc-iest
that is representative of the product line.

       Under the LT2ESWTR, the LRV is calculated according to Equation 3.7 (40 CFR 141,
SubpartW, Appendix C):
                     LRV = \og(Cf)- log( Cp)                       Equation 3.7

       Where:       LRV  =   log removal value demonstrated during a challenge test
                    Cf     =   feed concentration of the challenge particulate
                               (number or mass / volume)
                    Cp     =   filtrate concentration of the challenge particulate
                               (number or mass / volume)
Note that the feed and filtrate concentrations must be expressed in identical units (i.e., based on
equivalent volumes) in order for Equation 3.7 to yield a valid LRV.  If the challenge particulate
is not detected in the filtrate, then the term Cp is set equal to the detection limit.

       The overall value of LRVc-iest (i.e., the removal efficiency of the product) is based on the
entire set of LRVs obtained during challenge testing, with one representative LRV established
per module tested.  The manner in which LRVc-iest is determined from these individual LRVs
depends on the number of modules tested. Under the LT2ESWTR, if fewer than 20 modules are
tested, then the lowest representative LRV among the various modules tested is the LRVc-iest
If 20 or more modules are tested, then the 10th percentile of the representative LRVs is the
LRVc-iest-  The percentile is defined by [i/(n+l)J where "i" is the rank of "n" individual data


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points ordered from lowest to highest.  It may be necessary to calculate the 10th percentile using
linear interpolation (40 CFR 141, Subpart W, Appendix C).

       Although the LT2ESWTR requires that one representative LRV be established per
module tested, the rule does not restrict the manner in which the representative LRV for each
module is calculated.  Consequently, there are numerous methods that could be used to calculate
the representative LRV for a module. If multiple feed/filtrate sample pairs are collected, a LRV
can be calculated for each set of paired data, and the LRV for the tested module could be
selected as the lowest LRV (more conservative) or the average of the LRVs (less conservative).
Another approach is to average all the respective feed and filtrate concentrations from among the
various samples collected and calculate a single LRV for a tested module using Equation 3.7. A
more conservative approach would be to use the average feed concentration but the maximum
filtrate concentration sampled, which would result  in a lower representative LRV for a tested
module.  Likewise, a still more conservative approach would be to use the minimum feed and
maximum filtrate concentrations.  Note that these methods simply represent potential options;
other approaches may  be used for calculating a representative LRV for each module tested.
Regardless of the particular method used, the range of data collected for a single module can
provide some indication about the experimental error associated with the study (i.e., errors due to
seeding, sampling, analysis, etc.).  If a statistically  valid sampling method was used to select the
modules for challenge testing (as described in section 3.7), a comparison of the LRVs across the
different modules tested would provide an indication of variability within the product line.
3.13.2   Statistical Analysis

       If a sufficient number of modules are evaluated in the course of a challenge test to be
considered a statistically significant sample of the product line, it may be useful to conduct a
formal statistical analysis of the data in order to make inferences about the entire population
from the sample set.  Note that such a statistical analysis is not considered a substitute for the
methodology for determining LRVc-iest required under the rule, but could provide the
manufacturer with useful information.  For example, if challenge testing were conducted using a
random sampling of membranes from a production lot, a statistical analysis of the challenge test
data (i.e., the LRV observed for each of the modules tested) would provide an estimate of the
range of removal efficiency for the entire product line.  This information could  be used to infer
the number of membrane modules in the product line that would be expected to achieve the
LRVc-iest.  If it is desirable to apply a statistical analysis to the LRV data generated during
challenge testing, the particular method of analysis should be considered in the  design of the
challenge test protocol, since the method to be employed may dictated the number of modules
selected for testing.
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3.13.3   Reporting

       The LT2ESWTR does not mandate any reporting requirements for challenge testing.
However, the results of the challenge test must be acceptable to any state that permits a particular
membrane module product line to be used for obtaining Cryptosporidium removal credit under
the rule.  In order to facilitate this acceptance by the various states, a sample outline of a
challenge test report is provided as follows.  Note that this outline should be customized to meet
any particular state requirements.
       1) Introduction
          a)  Description of testing organization
          b)  Test site
          c)  Description of membrane filtration product
          d)  Testing objectives (including target LRV)

       2) Membrane Modules and Test Apparatus
          a)  Membrane module specifications for each module evaluated
          b)  Considerations for small-scale module testing (if applicable)
          c)  Non-destructive performance testing
          d)  Description of test apparatus

       3) Challenge Test Protocol
          a)  Challenge paniculate (including rationale for selection)
          b)  System operating conditions
          c)  Challenge test solution design
          d)  Seeding method
          e)  Process monitoring
          f)  Detailed sampling plan
          g)  QA/QC procedures
          h)  Data management

       4) Results and Discussion
          a)  Summary of measured system operating conditions
          b)  Summary of LRV results for each module tested
          c)  Summary of system integrity evaluation
          d)  Determination of removal efficiency
          e)  Summary of NDPT results  for each module tested
          f)  QCRV determination based on the results of non-destructive performance testing
          g)  Statistical evaluation of results  (if applicable)

       5) Summary and Conclusions
          a)  Summary description of membrane filtration product
          b)  Summary of challenge test protocol
          c)  LRV demonstrated during challenge testing
          d)  Quality control release value for non-destructive performance testing
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3.14   Re-Testing of Modified Membrane Modules

       As a component of ongoing innovation and product development, manufacturers may
make changes to a particular product line or its associated manufacturing process. If such a
change affects the fundamental characteristics of the module, the removal efficiency, and/or the
NDPT results and associated QCRV, the LT2ESWTR requires the modified product to be re-
subjected to challenge testing (40 CFR 141, Subpart W, Appendix C).

       Because it is not possible to develop a comprehensive listing of the potential
modifications that would require re-testing, the need to re-test a modified product must be
evaluated on a case-by-case basis and at the discretion of the state.  Some examples of membrane
properties, which if modified, might alter the fundamental removal characteristics of a module,
include:

       •  Membrane material
          (e.g., a change in the polymer or backing material)

       •  Pore size (nominal and absolute)

       •  Porosity

       •  Permeability

       •  Membrane symmetry
          (i.e., symmetric,  asymmetric, or composite)
       As shown in the examples given above, most of the changes that may necessitate re-
testing are modifications to the membrane material itself, such as changes to the polymer
chemistry and/or pore size distribution. Even if the change to the membrane media is not
intended to affect removal efficiency or NDPT parameters, it may be necessary to re-test the
module, since a modification to an intrinsic property of the membrane media could have an
impact on one or both of these criteria.

       Minor changes or changes that are not related to the fundamental removal characteristics
of the membrane media or NDPT parameters, would not require re-testing. For example, a
change in the membrane area within a module would not be expected to affect either the removal
efficiency or non-destructive performance testing.

       Although not directly related to the product itself, any modifications to the
manufacturer's NDPT may also require that the product line be re-subjected to challenge testing,
since the results of the specific NDPT used ensure that the modules produced meet the minimum
requirements for achieving the demonstrate LRV. However, if the modified NDPT can be
correlated to the specific test associated with product line's challenge test, additional challenge
testing may not need to be conducted, at the discretion of the state.
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       Modifications to the hydraulic configuration of a membrane filtration system might
warrant re-testing, since the concentration of suspended solids on the feed side of the membrane
may be affected, in turn potentially affecting removal efficiency. In determining whether or not
a modification to the hydraulic configuration would require re-testing, one significant factor is
whether the hydraulic conditions of the original challenge test are conservative for the new
hydraulic configuration of the system.  In general, testing performed under a hydraulic
configuration with a higher VCF than that associated with the modification would be considered
conservative. A summary of the various hydraulic configurations and associated VCFs is
provided in Table 2.3, and duplicated for reference as Table 3.6, below.
   Table 3.6 Typical Range of VCF Values for Various Hydraulic Configurations
Hydraulic Configuration
Deposition
mode
Suspension
mode
Dead-end
PFR
Crossflow
CSTR
VCF
1
3-20
4-20
4-20
       In general, most modifications to the module itself (as opposed to the membrane media)
are unlikely to affect either removal efficiency or non-destructive performance testing, although
re-testing might be warranted in some cases.

       The product modifications addressed in this section are provided as guidance to help
assess whether or not a particular change might require a product line to undergo a new
challenge test under the LT2ESWTR. This discussion is not intended to be comprehensive.  In
addition, the inclusion of a particular modification in this section does not necessarily imply that
re-testing is required for all such modifications. Although the manufacturer can exercise its
discretion in deciding the circumstances under which additional testing  is necessary, the state has
authority regarding whether or not to accept a particular change such that the product line would
still be eligible to receive Cryptosporidium removal credit under the rule without re-testing.
3.15   Grandfathering Challenge Test Data From Previous Studies

       As a result of the commercialization of membrane treatment processes for drinking water
production, a number of states, consulting engineers, and independent testing organizations have
developed programs to demonstrate the removal efficiency  of membrane systems.  Under these
existing programs, numerous challenge studies have been conducted in which complete removal
of Cryptosporidium was demonstrated, independent of the challenge level (USEPA2001).  The
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state has the discretion to accept data from a previous study provided that the testing was
conducted in a manner that demonstrates removal efficiency for Cryptosporidium commensurate
with the treatment credit awarded to the process (40 CFR 141, Subpart W, Appendix C).

       While a previously conducted challenge test may adequately demonstrate the required
Cryptosporidium removal efficiency, it may be more difficult to correlate the results of a prior
test to the NDPT currently used by the manufacturer. If the state determines that the
grandfathered test does not meet the intent of the LT2ESWTR, a new challenge test that is
consistent with the rule requirements must be conducted.

       As a general guide, the following challenge test conditions have been identified as
potentially yielding results that do not satisfy the intent of the rule:

       •  Challenge testing conducted on obsolete products: Refer to section 3.14 for guidance
          on the re-testing of modified membrane modules.

       •  Challenge testing conducted on small-scale modules:  Small-scale module testing is
          permitted under the LT2ESWTR if certain criteria are met.  Refer to section 3.8 for
          guidance regarding the testing of small-scale modules.

       •  Challenge testing using unacceptable surrogates for Cryptosporidium: The challenge
          paniculate  used in a grandfathered test must provide equivalent or sufficiently
          conservative removal efficiency relative to Cryptosporidium oocysts. Refer to
          section 3.9 regarding the selection of surrogates for use in challenge testing.

       •  Challenge particulate enumeration using unacceptable methodology: The challenge
          particulate  must have been quantified using an acceptable method. Specifically, gross
          measurements are generally considered unacceptable.  Refer to section 3.9 regarding
          methods for enumerating various challenge particulates.

       •  Unavailable QCRV: If non-destructive performance testing was not used to establish
          a suitable QCRV  in a previous study, it may be difficult or impossible to relate the
          demonstrated removal efficiency to the NDPT results for untested modules that are
          produced.
       There may also be cases in which deviations from challenge testing requirements under
the LT2ESWTR may not be significant, such that additional testing would not be required.
Some potential cases in which challenge test data that do not specifically comply with the rule
might receive favorable consideration for grandfathering, at the discretion of the state, are listed
below.

       •  Removal efficiency determine using different method: It may be necessary to
          recalculate the removal efficiency (i.e., LRVc-iest) from a previous challenge test
          according to the requirements of the LT2ESWTR. If some moderate deficiencies
          exist in the data such that the LRVc-iest cannot be calculated according to the


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          procedure described in this guidance manual, the state may exercise discretion as to
          whether or not to approve the prior test.  The state may also evaluate the impact of
          such deficiencies and consequently consider reducing the LRVc-iest on the basis of
          this evaluation.

       •  Elevated feed challenge particulate concentration: The LT2ESTR places a limit on
          the feed concentration of the challenge particulate that essentially establishes a
          maximum LRV of 6.5 in order to prevent excessive over-seeding during challenge
          studies. However, exceeding this maximum feed concentration does not necessarily
          invalidate a prior test. In reviewing grandfathered data, it is most important to
          consider whether or not high LRVs were achieved through excessive over-seeding.
          For example, if a removal study was conducted at a challenge level of 108 particles/L
          and all filtrate concentrations were less than 10 parti cles/L, the process could
          potentially qualify for the maximum removal credit of 6.5 log. By contrast, if the
          same challenge level was applied to a membrane that allowed 103 parti cles/L to pass
          into the filtrate, states may opt not to qualify the test for a LRV of 5,  since the high
          LRV is likely a result of over-seeding  an otherwise inadequate or non-integral
          membrane.

       •  Challenge testing at a flux or recovery other than the maximum design value(s):
          Deviations from testing at the maximum flux and/or recovery might not exclude a
          prior test from consideration for grandfathering. Most available data suggests  that
          flux and recovery will not significantly impact the removal efficiency of a membrane
          filtration process  for Cryptosporidium-sized particles. If complete removal of the
          challenge particulate was achieved during the challenge test, then deviations from
          testing at maximum design flux and recovery values can probably be ignored.

       •  Challenge testing using a poor quality feed water matrix: Although it is
          recommended that challenge testing be conducted using clean make-up water for the
          test solution and unfouled membranes to provide a conservative estimate of removal
          efficiency, prior studies conducted with waters with a greater fouling potential  (e.g.,
          untreated surface waters) can potentially be considered to meet the LT2ESWTR
          challenge test requirement, since the removal of Cryptosporidium-sized particles is
          generally unaffected by the presence of foulants for membrane filtration processes as
          defined under the LT2ESWTR. However, recent research suggests that integrity
          defects  on the order of 200 |j,m can be obscured by foulants in some cases, improving
          pathogen rejection (Lozier et al. 2003). Thus, prior studies conducted with poorer
          quality water should be considered for grandfathering on a case-by-case basis.
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                         4.0   Direct Integrity Testing
4.1    Introduction
       In order for a membrane process to be an effective barrier against pathogens and other
particulate matter, the filtration system must be integral, or free of any leaks or defects resulting
in an integrity breach. Thus, it is critical that operators are able to demonstrate the integrity of
this barrier on an ongoing basis during system operation. Direct integrity testing represents the
most accurate means of assessing the integrity of a membrane filtration system that is currently
available.

       Under the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), a direct
integrity test is defined as a physical test applied to a membrane unit in order to identify and
isolate integrity breaches (40 CFR 141, Subpart W, Appendix C). In order to receive
Cryptosporidium removal credit for compliance with the rule, the removal efficiency of a
membrane filtration process must be routinely verified during operation using direct integrity
testing. The direct integrity test must be applied to the physical elements of the entire membrane
unit, including membranes, seals, potting material, associated valves and piping, and all other
components which could result in contamination of the filtrate under compromised conditions
(40 CFR 141, Subpart W, Appendix C).

       There are two general classes of direct integrity tests that are commonly used in
membrane filtration facilities: pressure-based tests and marker-based tests. The pressure-based
tests are based on bubble point theory (as described in Appendix B) and involve applying a
pressure or vacuum (i.e.,  negative pressure) to one side of a membrane barrier and monitoring for
parameters such as pressure loss or the displacement of air or water in order to establish whether
an integrity breach is present. The various pressure-based tests include the pressure- and vacuum
decay tests, the diffusive airflow test, and the water displacement test.  Marker-based tests utilize
either a spiked particulate or molecular marker to verify membrane integrity by directly
assessing removal of the marker, similar to a challenge test.

       The LT2ESWTR does not require the use of a particular direct integrity test for rule
compliance, but rather that any test used meet the specified performance criteria for resolution,
sensitivity, and frequency.  Thus, a particular system may utilize an appropriate pressure- or
marker-based test or any  other method that both meets the performance criteria and is approved
by the state.  The performance criteria for direct integrity tests are summarized as follows:

       •  Resolution:  The direct integrity test must be responsive to an integrity breach on the
          order of 3 urn or less (40 CFR 141, Subpart W, Appendix C).

       •  Sensitivity: The direct integrity test must be  able to verify a log removal value
          (LRV) equal to or greater than the removal credit awarded to the membrane filtration
          process (40 CFR 141, Subpart W, Appendix C).
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       •   Frequency: A direct integrity test must be conducted on each membrane unit at a
           frequency of no less than once every 24 hours of operation (40 CFR 141.728). (The
           definition of a membrane unit under the LT2ESWTR is provided in section 1.5.)

In addition to the performance criteria, the rule also requires the establishment of a control limit
for the direct integrity test that is indicative of an integral membrane unit capable of achieving
the Cryptosporidium removal credit awarded by the state.  If the results of the direct integrity test
exceed this limit, the rule requires that the affected membrane unit be taken off-line for
diagnostic testing and repair (40 CFR 141.728). The performance criteria for direct integrity
tests, as well as the establishment of control limits, are described in further detail in section 4.2.

       The objective of Chapter 4 is to describe the various pressure- and marker-based direct
integrity tests currently in use and how these tests can be applied to meet the performance criteria
specified under the LT2ESWTR. Diagnostic tests, data collection, and reporting are also
addressed.

This chapter is divided into the following sections:

       Section 4.2:   Test Resolution
                     This section discusses the determination of pressure- and marker-based
                     direct integrity test resolution for meeting the performance criteria
                     required by the rule.

       Section 4.3:   Test Sensitivity
                     This section discusses the determination of pressure- and marker-based
                     direct integrity test sensitivity for meeting the performance criteria
                     required by the rule, including general concepts and methods.

       Section 4.4:   Test Frequency
                     This section reviews the direct integrity testing frequency requirement of
                     the rule.

       Section 4.5:   Establishing Control Limits
                     This section describes the mathematical and experimental determination of
                     control limits for direct integrity testing.

       Section 4.6:   Example: Establishing Direct Integrity Test Parameters
                     This section illustrates the  calculation of some of the critical direct
                     integrity test performance criteria, including test resolution, sensitivity,
                     and control limits for an example membrane filtration system.

       Section 4.7:   Test Methods
                     This section provides an overview of the various types of pressure- and
                     marker-based tests, including generic test protocols as well as some
                     advantages and disadvantages of each.
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       Section 4.8:   Diagnostic Testing
                     This section describes some of the diagnostic tests that are used to identify
                     and isolate integrity breaches following a failed direct integrity test.

       Section 4.9:   Data Collection and Reporting
                     This section provides guidance on direct integrity test data collection and
                     reviews the associated reporting requirements of the rule.
4.2    Test Resolution

       Resolution is defined as the smallest leak that contributes to the response from a direct
integrity test. Any direct integrity test applied to meet the requirements of the LT2ESTWR is
required to have a resolution of 3 jim or less (40 CFR 141, Subpart W, Appendix C). This
resolution criterion is based on the lower size range of Cryptosporidium oocysts and is intended
to ensure that any integrity breach large enough to pass oocysts contributes to a response from
the direct integrity test used. The manner in which the resolution criterion is met depends on
whether the direct integrity test is pressure-based or marker-based, as described in the following
subsections.
4.2.1  Pressure-Based Tests

       In order to achieve a resolution of 3 |j,m with pressure-based direct integrity tests, the net
pressure applied during the test must be great enough to overcome the capillary forces in a 3 |j,m
hole, thus ensuring that any breach large enough to pass Cryptosporidium oocysts would also
pass air during the test.  The minimum applied test pressure necessary to achieve a resolution of
3 |j,m is calculated using Equation 4.1:
                     Ptest = (0.193 • K: • (7 • cos 0 ) + BPmax               Equation 4.1

       Where:       Ptest     =     minimum test pressure  (psi)
                     K       =     pore shape correction factor (dimensionless)
                     s       =     surface tension at the air-liquid interface (dynes/cm)
                     9       =     liquid-membrane contact angle  (degrees)
                     BPmax   =     maximum backpressure on the system during the test  (psi)
                     0.193   =     constant that includes the defect diameter (i.e., 3 |j,m
                                   resolution requirement) and unit conversion factors
       Equation 4.1 is based on bubble point theory and is derived from the balancing of
capillary static forces. Note that the constant of 0.193 accounts for the LT2ESWTR resolution
requirement of responding to a defect of 3 |j,m in diameter, as well as the appropriate unit
conversion factors, in order to simplify the equation for the purposes of rule compliance.  The
general form of Equation 4.1 includes the capillary diameter as a variable and represents an

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expression relating this diameter to the bubble point pressure. A discussion of bubble point
theory and a derivation of Equation 4.1 is provided in Appendix B.

       Values for several parameters in Equation 4.1 must be determined in order to calculate
the minimum test pressure necessary to achieve a resolution of 3 |j,m when using a pressure-
based integrity test. The parameters  K and 9 are intrinsic properties of the membrane. In the
absence of data supplied by the membrane manufacturer, conservative values of K = 1 and 9 = 0
should be used.  Appendix B provides an additional discussion of these parameters.  The surface
tension, s, is  inversely related to temperature; consequently, the surface tension at the coldest
anticipated water temperature should be used to calculate a conservative value for the minimum
required test pressure. As a point of reference, the surface tension of water at 5 ฐC is
74.9 dynes/cm.  Substituting these three values (i.e., K = 1, 9 = 0, and s = 74.9 dynes/cm) into
Equation 4.1 yields the following simplified equation:
                     Ptest=l4.5+BPm!K                                Equation 4.2

        Where:      Ptest    =    minimum test pressure  (psi)
                         ax =    maximum backpressure on the system during the test  (psi)
       Equation 4.2 indicates that the minimum test pressure necessary to achieve a 3-|j,m
resolution is 14.5 psi plus the maximum backpressure on the system during application of a
pressure-based direct integrity test.  Ideally, there should be no hydrostatic backpressure on the
system during the test.  However, it is not always  practical to perform the test without any
hydrostatic backpressure, and in these cases the additional backpressure must be considered in
establishing the minimum test pressure necessary  to meet the resolution criterion.  For example,
there might be hydrostatic pressure on the undrained side of the membrane if a pressure- driven
membrane module remains filled with water or if a vacuum-driven (i.e., immersed) membrane
remains under water in a basin. Thus, if the bottom of the membrane is under 7 feet of water,
BPmax would be approximately 3 psi, yielding a Ptest value of 17.5 psi to achieve a resolution of
3
       Both Equations 4.1 and 4.2 assume that the applied pressure remains constant during the
direct integrity test. However, in many cases there may be some baseline decay (e.g., that
attributable to diffusion) that is measurable over the duration of the test. In this case, it is
important to account for this baseline decay in the resolution calculation.  Thus, in order to
ensure that the resolution requirement is satisfied throughout the duration of the test, the
anticipated pressure at the end of the direct integrity test should be used to calculate the
resolution. This value can be estimated using the initial applied pressure, the typical rate of
baseline pressure decay for a fully integral system, and the duration  of the test. If the baseline
decay is small enough such that the final test pressure is within approximately 5 percent of the
initial applied pressure, the baseline decay can be assumed to be negligible, and the initial
applied pressure may  be used to  calculate the test resolution.
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       The LT2ESTWR does not establish the minimum test pressure to be used during a
pressure-based direct integrity test, but rather only requires that the test achieve a 3-|j,m
resolution. If a membrane manufacturer has information to support the use of values other than
K = 1 and 9 = 0,  and these less conservative values are approved by the state,  then Equation 4.1
can be used to calculate the minimum required test pressure.  It is essential that the use of values
other than K = 1  and 9 = 0 be scientifically defensible, since the use of inappropriate values could
result in the use  of a test pressure that does not meet the resolution criterion established by the
rule.  One approach for determining membrane specific values for K and 9 is through direct
experimental evaluation. It is also possible that data from the non-destructive performance test
(NDPT) (as described in section 3.6) may be used to support the use of a (K ?  cos9) product less
than 1.0 (i.e. K < 1 and/or 9 > 0). The latter approach would require an empirical correlation to
be developed between test pressure and minimum pore size.

       Although the rule does not include a frequency requirement for the recalculation of
resolution, the resolution should be recalculated if the system backpressure during direct
integrity testing  is adjusted.  Alternatively, if desired, direct integrity test instrumentation and
data recording system could be configured to calculate the resolution after each application of the
direct integrity test using the applied test pressure, system backpressure, and surface tension
corresponding to the temperature at which the  test is conducted.  Note that the liquid-membrane
contact angle can also change over the life of a membrane module (e.g., as a result of the
adsorption of organic matter by the membrane material), and these changes may not necessarily
be uniform among the various modules in a unit (Childress et al. 1996; Tucker et al. 1994).  Thus,
if a value other 9 = 0 (i.e., the most conservative value) is used, then it may be appropriate to
periodically recalculate the resolution based on a  revised estimate of the actual value of 9, an
exercise that may necessitate destructive testing of a representative sample of membrane
modules in the system.
4.2.2  Marker-Based Tests

       A marker-based direct integrity test can be viewed as a "mini-challenge study," in which
a surrogate is periodically applied to the feed water in order to verify the integrity of a membrane
filtration system.  In order to meet the resolution criterion of the rule, the surrogate used in a
marker-based test must have an effective size of 3 |j,m or smaller, as described in section 3.9.2.
A marker-based direct integrity test can use either particulate or molecular surrogates, but in
either case, it must be established that the surrogate meets the resolution criterion.  Section 3.9
presents guidelines for the selection of a conservative surrogate for Cryptosporidium during
challenge testing, and these  same guidelines are applicable to selection of an appropriate
surrogate for a marker-based direct integrity test.  The effective size of the marker can be
established through any accepted methodology such as size distribution analysis of particulate
markers or estimation techniques based on the molecular weight and geometry of molecular
markers.
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4.3    Test Sensitivity

       Sensitivity is defined as the maximum log removal value that can be verified by the direct
integrity test (i.e., LRVoii) (40 CFR 141, Subpart W, Appendix C). The sensitivity of the direct
integrity test establishes the maximum log removal credit that a membrane filtration process is
eligible to receive if it is less than or equal to that demonstrated during challenge testing (i.e.,
LRVc-iest)-  For example, if the challenge test demonstrated a LRVc-iest of 5.5 log, and the direct
integrity test is capable of verifying a LRVoii of 4.5 log, the membrane filtration process would
be eligible for removal credit up to 4.5 log. Although the sensitivity of the direct integrity test
should not be expected to vary significantly over time, the determination of sensitivity as
described in this section is design to produce  a conservative result that would remain applicable
over the life of the membrane  filtration system.  However, if significant changes occur in terms
of operational parameters, direct integrity test conditions, or any basic assumptions that might
affect the value of the direct integrity test sensitivity, it is suggested that the sensitivity be
reestablished to verify that it is at least equal to the removal credit awarded to the process.

       The sensitivity of a direct integrity test is logarithmic in nature. For example, a test with
a LRVoii of 5 log is 100 times more sensitive than a test with a LRVoii of 3 log.  Thus, when a
higher sensitivity is required, the test must be capable of measuring very small changes in the
direct integrity test response and distinguishing these results from background or baseline data.
Data suggest that many direct  integrity tests, as currently applied, have sensitivities in excess  of
4 log; however, sensitivity must be determined on a case-by-case basis using the information
provided by the membrane manufacturer and  the guidance in this document. While
determination of integrity test  sensitivity is complex, it provides a rational basis for awarding
high removal credits to membrane processes that are commensurate with their abilities. As was
the case with resolution, the manner in which sensitivity is determined depends on whether the
type of direct integrity test used is pressure- or marker-based.
4.3.1  Pressure-Based Tests

       The discussion in this section regarding the calculation of sensitivity for pressure-based
direct integrity tests is divided into three parts, as follow. First, the basic concepts that are
applicable to all pressure-based tests are introduced.  The subsequent section describes
calculation of the sensitivity for pressure-based direct integrity tests based on this general
conceptual framework.  A third section discusses the determination of diffusive (or baseline)
losses in a fully integral system during the application of a pressure-based direct integrity test.
       4.3.1.1  Basic Concepts

       The determination of sensitivity for pressure- based direct integrity tests is more complex
than for marker-based tests. The equation used to determine the sensitivity of a pressure-based
integrity test is specified in the LT2ESWTR (40 CFR 141, Subpart W, Appendix C) and given
below as Equation 4.3:
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                     LRVnrr = log - — -                      Equation 4.3
                         L)l 1     O T T- /" T 7—7  X-V                            1
       Where:       LRVoii  =   direct integrity test sensitivity in terms of LRV
                                  (dimensionless)
                    Qp       =   membrane unit design capacity filtrate flow (L/min)
                    Qbreach    =   flow from the breach associated with the smallest integrity
                                  test response that can be reliably measured, referred to as
                                  the critical breach size (L/min)
                    VCF     =   volumetric concentration factor (dimensionless)
       Equation 4.3 represents a dilution model that assumes water passing through the intact
membrane barrier is free of the particulate contaminant of interest and that water flowing through
an integrity breach has a particulate contaminant concentration equal to that on the high pressure
side of the membrane. Under these assumptions, LRVoii is a function of the ratio of total filtrate
flow to flow through the critical breach (i.e., Qp/Qbreach), which quantifies the dilution of the
contaminated stream passing through the breach as it mixes with treated filtrate. For a
membrane unit of a given capacity (i.e., constant Qp), LRVon will increase as Qbreach decreases.
This implies that a more sensitive direct integrity test capable of detecting a smaller breach can
verify a higher log removal value and thus potentially increase the removal credit that a
membrane filtration system is eligible to receive.

       The term VCF is a dimensionless term that accounts for the increase in the suspended
solids concentration that occurs on the feed side of the membrane for some hydraulic
configurations. In the denominator of Equation 4.3, the term Qbreach is multiplied by the VCF to
incorporate the impact of this concentration effect on the sensitivity of the direct integrity test.
The VCF is calculated as the ratio of the concentration  of suspended solids maintained  on the
feed side of the membrane to that in the influent feed water, as shown in Equation 4.4:
                            C
                     VCF = —=-                                     Equation 4.4  (2.18)
                             /

       Where:        VCF     =   volumetric concentration factor (dimensionless)
                     Cm       =   concentration of suspended solids maintained on the feed
                                  side of the membrane (number or mass / volume)
                     Cf       =   concentration of suspended solids in the influent feed water
                                  to the membrane system  (number or mass / volume)
       The VCF generally ranges between 1 and 20, and the value depends on the hydraulic
configuration of the system.  Membrane systems that operate in deposition mode do not increase


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the concentration of suspended solids on the feed side of the membrane and thus have a VCF
equal to 1.  In contrast, membrane systems that operate in suspension mode, such as a crossflow
hydraulic configuration, typically have a VCF in the range of 4 to 20, representing a 4 to 20-fold
increase in the suspended particle concentration on the feed side of the membrane.  The methods
and equations used to calculate the VCF for various hydraulic configurations are provided in
section 2.5, and Table 2.4 presents equations for calculating both the average and maximum
VCF for various hydraulic configurations.  Alternatively, the VCF could be determined
experimentally.

       Note that the LT2ESWTR does not specify use of the maximum or average VCF value in
calculating sensitivity, but the rule does require that the increase in suspended solids
concentration on the high-pressure side of the membrane, as occurs with some hydraulic
configurations, be considered in the calculation. The maximum VCF typically ranges from 1 to
20 and provides the most conservative value for LRVoii, while the average VCF typically ranges
from 1 to 7.  In selecting between the maximum, average, or any other value for the VCF,
consideration should be given to the concentration profile along the membrane surface in the
direction of water flow and the implication of integrity breaches at various locations within in the
membrane unit.  For example, although the maximum VCF does provide the most conservative
value for LRVoii, this value represents  only a very small portion of the concentration profile and
thus is only representative of breaches that occur at the extreme end of the membrane unit.
Similarly, some systems exhibit a concentration profile as a function of time within a filtration
cycle, and the maximum VCF only occurs  at the end of the filtration cycle immediately before a
backwash event; prior to this time, the VCF is significantly lower.
       4.3.1.2  Calculating Sensitivity

       The sensitivity of a pressure-based direct integrity test can be calculated by converting
the response from a pressure-based test that measures the flow of air (e.g., the diffusive airflow
test) or rate of pressure loss (e.g., the pressure decay test) to an equivalent flow of water through
an integrity breach during normal operation, as described in the following subsection.  The
second subsection outlines a general procedure for determining the threshold response  of a
pressure-based direct integrity test experimentally, if this information is not available from the
membrane filtration system manufacturer.
       Calculating Sensitivity Using the Air-Liquid Conversion Ratio

       In order to calculate the LRVoii, the flow through the critical breach for a direct integrity
test (i.e., Qbreach) must be determined (as shown in Equation 4.3).  Since most direct integrity
tests do not directly measure Qbreach, it is necessary to establish a correlation between the direct
integrity test response and the flow of water through the critical breach during system operation.
In some of the most commonly used pressure-based direct integrity tests, including the pressure-
or vacuum-decay test and the diffusive airflow test, air is applied to the drained  side of a
membrane and subsequently flows through any integrity breach that exceeds the test resolution.
The response from such a test is typically measured as pressure decay or airflow. In order to
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relate the response from a pressure-based integrity test to Qbreach, it is necessary to establish a
correlation between airflow and liquid flow through the critical integrity breach.

       This correlation can be characterized through the air-liquid conversion ratio (ALCR),
which is defined as the ratio of air that would flow through a breach  during a direct integrity test
to the amount of water that would flow through the breach during filtration, as defined in
Equation 4.5:
                      ALCR =  -^—                                 Equation 4.5
                              V ^breach )

       Where:       ALCR   =    air-liquid conversion ratio (dimensionless)
                     Qair     =    flow of air through the critical breach during a pressure-
                                   based direct integrity test (L/min)
                     Qbreach   =    flow of water through the critical breach during filtration
                                   (L/min)
       The ALCR can be used to express the liquid flow through a breach in terms of an
equivalent flow of air, as shown in Equation 4.6:
                     Qbreach =  ~f^                                 Equation 4.6
                              V f\-J-^\_si\ J

       Where:       Qbreach   =    flow of water through the critical breach during filtration
                                   (L/min)
                     Qair     =    flow of air through the critical breach during a pressure-
                                   based direct integrity test (L/min)
                     ALCR   =    air-liquid conversion ratio (dimensionless)
       Substituting Equation 4.6 into the general expression for sensitivity (Equation 4.3) yields
the following expression:
                                  (Q*ALCR]
                     LRVDIT = log -^	—-                        Equation 4.7
       Where:       LRVoii   =   direct integrity test sensitivity in terms of LRV
                                   (dimensionless)
                     Qp       =   membrane unit design capacity filtrate flow (L/min)
                     ALCR    =   air-liquid conversion ratio (dimensionless)
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                     Qair      =   flow of air through the critical breach during a pressure-
                                   based direct integrity test  (L/min)
                     VCF      =   volumetric concentration factor  (dimensionless)
Equation 4.7 can be used to directly calculate the sensitivity for any pressure-based direct
integrity test that is based on bubble point theory and measures the flow of air (Qair) through an
integrity breach. The four parameters that need to be determined to calculate sensitivity are:  Qp,
VCF, ALCR, and Qa;r. The VCF can be established as previously described in section 4.3.1.1.
Qp is the design capacity filtrate flow approved by the state, expressed in liters per minute, from
the membrane unit to which the direct integrity test is applied. For a constant Qbreach, higher
filtrate flows yield greater direct integrity test sensitivity. Thus, if different sizes of membrane
units with varying capacity are used in the same treatment system, the sensitivity of the direct
integrity test should be independently determined for each unit size.  The flow of air, Qa;r, is
related to the response from the direct integrity test. For tests that measure the airflow through
an integrity breach directly, such as the diffusive airflow test, Qa;r is simply the results of the test.
On the other hand, methods such as the pressure- and vacuum-decay tests yield results in terms
of pressure loss per unit time, which must be converted to an equivalent flow of air using
Equation 4.8:
                                   '                                   „     .    . 0
                                                                      Equation 4.8
                            fiP+14.7
       Where:       Qa;r     =    flow of air (L/min)
                     APtest    =    rate of pressure decay during the integrity test (psi/min)
                     Vsys     =    volume of pressurized air in the system during the test (L)
                     BP      =    backpressure on the system during the test (psi)
       Note that Equation 4.8 assumes that the temperature of the water and air are the same
since the air temperature should rapidly equilibrate with the water temperature. In addition, Vsys
and the ALCR should be measured at the same reference temperature and pressure. Vsys
encompasses the entire pressurized volume, including all fibers (typically the inside of the fibers
is pressurized), piping, and other void space on the pressurized  side.

       Substituting Equation 4.8 into Equation 4.7 yields Equation 4.9, which can be used to
calculate the sensitivity of a direct integrity test that measures the rate of pressure or vacuum
decay.
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                                   Q  •ALCR* CSP+ 14.7)
                     LRVDIT = log ^— - -  V                     Equation 4.9
       Where:       LRVoii  =    direct integrity test sensitivity in terms of LRV
                                   (dimensionless)
                     Qp       =    membrane unit design capacity filtrate flow (L/min)
                     ALCR   =    air- liquid conversion ratio (dimensionless)
                     BP       =    backpressure on the  system during the test  (psi)
                     APtest    =    rate of pressure decay during the integrity test (psi/min)
                     Vsys      =    volume of pressurized air in the system during the test (L)
                     VCF     =    volumetric concentration factor (dimensionless)
       Regardless of whether the flow of air (Qa;r) or pressure decay rate (APtest) is measured
during the direct integrity test, the smallest response from the test that can be reliably measured
and associated with an integrity breach should be used in the sensitivity calculation. This should
not be confused with the baseline integrity test response from an integral membrane unit, since
there may be a small flow of air or pressure decay due to diffusion of air through water in the
wetted pores, even if there are no breaches in the system.  In many cases, this smallest
measurable response associated with an integrity breach may be provided by the membrane
filtration system manufacturer.  If this information is not available from the system
manufacturer, it may be determined experimentally by progressively creating small integrity
breaches of a known size in an otherwise integral membrane unit in order to determine the
smallest measurable response from the direct integrity test that is distinguishable from the
baseline response for an integral membrane unit. A general procedure for this experimental
method is described in the following subsection ("Measuring The Threshold Direct Integrity Test
Response Experimentally").

       The basic procedure for calculating the ALCR involves first making a reasonable
assumption regarding whether the flow through  the critical breach is laminar or turbulent for the
particular membrane filtration system of interest. Then the ALCR can be calculated using the
appropriate equation, as summarized in Table 4.1. Note that the equations in Table 4.1 assume
that the flow regimes for the passage of air and water through an integrity breach are the same
(i.e., both either laminar or turbulent).  If this assumption is not considered appropriate for a
specific system and/or application such that inaccurate estimates for direct integrity test
sensitivity may result, a hybrid approach may be considered, as described in Appendix C.
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                    Table 4.1  Approaches for Calculating the ALCR
Module Type
Hollow-fiber1
Flat sheet4
Defect Flow
Regime
Turbulent2
Laminar
Turbulent
Laminar
Model
Darcy pipe
flow
Hagen-
Poiseuille3
Orifice
Hagen-
Poiseuille3
ALCR Equation

173.7. \(PM-RP)*(PM+W)
V (460 + T)*TMP
527ป&Peff • (1 75 -2.71.7 + 0.0137. J2)
IMP • (460 + T)

1-3,7, l(^-ฃP)ซtf-,+14.7)
V (460 + T)*mP
527ป&Peff • (1 75 -2.71.7 + 0.0137. J2)
IMP • (460 + T)
Appendix C
Equation
C.4
C.15
C.9
C.15
 1  Or hollow -fine-fiber
 2 Typically characteristic of larger diameter fibers and higher differential pressures
 3 The binomial in the Hagen_Poiseuille equation (C.15) approximates the ratio of water viscosity to air viscosity and is valid for
   temperatures ranging from approximately 32 to 86 ฐF. Additional details are provided in Appendix C.
 4 Includes spiral-wound and cartridge configurations
       The various parameters given in the ALCR equations listed in Table 4.1 include the
following:
              Y       =   net expansion factor for compressible flow through a pipe to a larger
                           flow area (dimensionless)
              Ptest     =   direct integrity test pressure  (psi)
              BP      =   backpressure on the system during the direct integrity test (psi)
              pw      =   density of water (lbs/ft3)
              T       =   water temperature  (ฐF)
              TMP    =   transmembrane pressure  (psi)
              APeff    =   effective integrity test pressure  (psi)
Additional guidance for both calculating the ALCR and determining appropriate values for the
component parameters of the respective ALCR equations (as listed above) is provided in
Appendix C, along with derivations of the ALCR equations. Further information regarding the
net expansion factor (Y) may be found in various hydraulics references, including Crane (1988).
Note that although the Darcy and orifice equations for the ALCR are identical, the method for
determining the net expansion  factor (Y) is different for these two models, as described in
Appendix C.
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       The ALCR can also be determined via empirical means, which would be applicable to
any flow regime or configuration of membrane material and are independent of a particular
hydraulic model.  Some manufacturers may have developed empirical models that could be used
to determine the ALCR. If an empirical approach is preferred for determining the ALCR, and a
valid empirical model is not available for the system, it may be necessary to develop one. One
conceptual procedure for empirically deriving the ALCR for hollow-fiber membrane filtration
systems is the correlated airflow measurement (CAM) technique; the details of this procedure are
presented in Appendix D.
       Measuring the Threshold Direct Integrity Test Response Experimentally

       The smallest measurable response of a pressure-based direct integrity test that is
associated with a known breach can be evaluated experimentally if this information is not
available from the membrane filtration system manufacturer.  For pressure-based tests, this
response corresponds to the value of APtest that should be used in the calculation of sensitivity.
This experimental evaluation involves intentionally compromising system integrity in small,
discrete, and quantifiable steps and monitoring the corresponding integrity test responses.  In the
case of MF/UF systems, several fiber-cutting studies conducted to evaluate the threshold
response of various direct integrity tests have been documented in the literature (Adham et al.
1995; Landsness 2001). In general, the procedure for measuring the threshold response
experimentally involves the following steps:
       1.  The membrane system is determined to be integral through the application of a direct
          integrity test.

       2.  The investigator intentionally compromises a membrane to generate a known defect.
          Examples of such compromises include generating a hole in the membrane using a
          pin of a known diameter or cutting a hollow fiber at a predetermined location. In
          order to identify the threshold response,  it is desirable to utilize a small integrity
          breach, such as a single  cut fiber in a membrane unit.

       3.  After compromising the membrane,  the integrity of the membrane unit is measured
          using the designated direct integrity  test.

       4.  The process is repeated with additional defects of progressively increasing size or
          quantity until a measurable response from the direct integrity test is detected.  This
          minimum measurable response represents APtest for the purposes of calculating the
          sensitivity of a direct integrity test.
       4.3.1.3 Diffusive Losses / Baseline Decay

       If it is determined to be appropriate for the membrane under consideration, the diffusive
losses that constitute the baseline integrity test response may be subtracted from the smallest
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measurable response associated with an integrity breach for the purpose of determining
sensitivity. For example, if a pressure decay rate of 0.05 psi/min is typical for an integral
membrane unit and the limitations of the test are such that the smallest pressure decay rate that
can be reliably associated with an integrity breach is 0.12 psi/min, the incremental response
associated with an integrity breach is 0.07 psi/min, and this value may be used in the sensitivity
calculation.  In general, diffusive losses are most likely to be observed over the duration of the
direct integrity test for thin-skinned, asymmetric membranes.  The manufacturer should be able
to provide information regarding whether or not diffusive losses are expected to be significant.
If a high level of sensitivity is required for a membrane filtration system, baseline diffusive
losses may be an important consideration.

       For porous MF, UF, and MCF membranes, diffusive losses occur during direct integrity
testing because a certain amount of compressed air used during the test dissolves into the water
in the fully-wetted pores and is transported across the membrane surface.  In order to calculate
the diffusive losses, it can be assumed that the water fills the pores of the membrane and forms a
film of thickness z, and that diffusion directly through the membrane material itself is
insignificant in comparison to the diffusion across the film of water.  Using these assumptions,
Equation 4.10 illustrates the relationship between diffusive losses and the various parameters that
influence these losses.
                              •A  •(?  -BP)ปHป<=\  ( R   *T \
                                m   V  test     '        1J   gas      '      Equation 4.10
              ^!//      ^             z              )  {BP + 14.7)

       Where:       Qdiff     =    diffusion of air through the water held in the membrane
                                   pores  (L/min)
                     Daw      =    diffusion coefficient for air in water (cm2/s)
                     Am      =    total membrane surface area to which the direct integrity
                                   test is applied (m2)
                     Ptest      =    membrane test pressure (psi)
                     BP      =    backpressure on the system during the test (psi)
                     H        =    Henry's constant for air-water system  (mol/psi-m3)
                     s        =    membrane porosity (dimensionless decimal)
                     z        =    membrane thickness  (mm)
                     Rgas      =    universal gas constant (L-psia/mol-K)
                     T        =    water temperature during direct integrity test (K)
                     6        =    unit conversion  factor
       Note that the dimensionless porosity (s) is defined as the ratio of area of pores to the total
membrane area in the unit.  This term should not be confused with the pore size of porous MF,
UF, and MCF membranes, which is given in terms of the limiting dimension of the openings in
the membrane. The porosity of the membrane material can typically be provided by the
manufacturer, if necessary.  In addition, the diffusion flow path, which is affected by porosity,
tortuosity, and the differential pressure  across the membrane, is approximated by the membrane
thickness (z) in Equation 4.10.  Because membrane porosity and tortuosity may be difficult to

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measure, thus making it problematic to accurately quantify the actual length of the diffusion flow
path, a more precise empirical method accounting for these two factors as a combined term has
been developed by Farahbakhsh (2003). Both the diffusion coefficient (Daw) and Henry's
constant (H) vary with temperature, and Henry's constant also varies somewhat with the
concentration of dissolved solids in the water. However, these affects may partially offset and
may not be significant.  Values  for Daw and H as a function of these variables (as applicable) may
be found in standard tables in the literature.

       The parameters given above for Equation 4.10 are applicable to flat sheet porous
membranes, such as those used  in membrane cartridge configurations.  For porous membranes in
a hollow-fiber configuration, such as most MF and UF systems, the following modifications are
required:
                                   log mean total membrane area to which the direct integrity
                                   test is applied  (m2)

                                   (A2-Ai)/ln(A2/Ai)

                                   AI =   total membrane surface area to which the direct
                                          integrity test is applied based on the inside fiber
                                          diameter
                                   A2 =   total membrane surface area to which the direct
                                          integrity test is applied based on the outside fiber
                                          diameter

                                   differential fiber radius (mm)

                                   r2- n

                                   ri  =   inside radius of the hollow fiber
                                   r2  =   outside radius of the hollow fiber
       It is generally accepted that diffusion of air across the membrane can reduce the
measured LRVoii.  Under most circumstances, the amount of diffusion is small in comparison to
the flow of air through a breach.  However, if the membrane has a propensity to diffuse a
significant amount of air (e.g., if the porosity is unusually high) or if a high level of sensitivity is
required, it may be necessary to account for diffusive losses. Typically, there is only limited
information available regarding the amount of diffusion that occurs for membrane processes used
in water treatment under production conditions;  however, MF/UF membrane manufacturers can
typically provide a value for the baseline decay during a pressure-based direct integrity test for
their specific proprietary systems, so it is generally not necessary to explicitly calculate diffusive
losses using Equation 4.10.
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       In the absence of information provided by the manufacturer, it may be advantageous to
directly measure the baseline pressure decay on an integral membrane unit, a process that should
be conducted using clean memb ranes to avoid the potential for fouling to artificially hinder
diffusion. Because the diffusive loss is directly proportional to temperature (as shown in
Equation 4.10), and the diffusion coefficient (which is also directly proportional to diffusive
loss) also increases with temperature, it is also important to characterize the baseline decay for
membrane filtration system at the highest anticipated water temperature in order to generate a
conservative value for diffusive loss.

       With semi-permeable NF and RO membranes, diffusive losses occur via the diffusion of
air through the saturated membrane material itself. However, because NF and RO modules are
manufactured separately from the accompanying filtration systems and inserted manually into
pressure vessels, small seal leaks may occur that can be difficult to distinguish from baseline
decay. Thus, it is recommended that baseline response for a pressure-based direct integrity test
be evaluated for each unit in a NF/RO system on a site-specific basis.

       If the membrane module manufacturer has information for typical diffusion airflow rates
per unit of membrane area, the expected diffusive airflow for the entire membrane unit should be
calculated and compared against the baseline observed during the unit-specific evaluation. If the
observed baseline is significantly higher than the predicted diffusive losses, the result could be
indicative of an integrity problem, and diagnostic testing (see section 4.8) may be necessary to
identify the source of additional airflow or pressure loss. If the membrane module manufacturer
is only able to provide a diffusion coefficient for air through the membrane material,
Equation 4.11 may be used to estimate the diffusive airflow for a membrane unit with a known
membrane area, if necessary:
                          )  •A  •(Ptt-BP)*H}  (RgasปT}
                                                   '-'           '     Equation 4.11
              ^am      ^            z            )  [BP + 14.7)

       Where:       Qdiff   =    diffusion of air through a semi-permeable membrane
                                   (L/min)
                     Dam    =    diffusion coefficient for air through a saturated semi-
                                  permeable membrane material  (cm2/s)
                     Am    =    total membrane surface area to which the direct integrity
                                  test is applied (m2)
                     Ptest    =    membrane test pressure (psi)
                     BP    =    backpressure on the system during the test (psi)
                     z      =    membrane thickness (mm)
                     Rgas    =    universal gas constant  (L-psia/mol-K)
                     T      =    water temperature during direct integrity test  (K)
                     6      =    unit conversion factor
       Note that the equations for the diffusion of air through porous and semi-permeable
membranes - Equation 4.10 and 4.11, respectively - are very similar.  These equations differ

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only in that Equation 4.11 for semi-permeable membranes does not require the membrane
porosity and utilizes a diffusion coefficient for a composite membrane layer consisting of both
the membrane and the water of saturation bound in the microscopic interstices of the membrane
material.

       Because spiral-wound NF/RO membranes are typically composite structures consisting
of two or more layers (as described in section 2.3.1), it is important that the membrane thickness
(z) used corresponds to the layer to which the diffusion coefficient (Dam) provided by the
membrane manufacturer applies. For example, the diffusion coefficient may apply to the thin,
active, semi-permeable layer, in which case the membrane thickness would correspond to this
layer only. Alternatively, if the diffusion coefficient is a composite representing the diffusion of
air through all the layers of the membrane taken as whole, then the thickness used should be that
of the entire membrane, including all layers.

       Both Equations 4.10 and 4.11 show that diffusive airflow is directly proportional to
membrane area, the applied direct integrity test pressure, and the system backpressure. As a
result, the decay should be quantified for each membrane unit of different size in the system and
also  recalculated if either the applied test pressure or system backpressure are modified.

       If the sensitivity is calculated using the ALCR approach described in section 4.3.1.2 and
if diffusion is significant, Equation 4.6 can be modified to compensate for diffusive airflow as
shown in Equation 4.12:
                                                                     „     .    . -. _
                                                                     Equation 4.12
                                .,
                               ALL.K
       Where:       Qbreach  =    flow of water through the critical breach during filtration
                                   (L/min)
                     Qair     =    flow of air through the critical breach during a pressure-
                                   based direct integrity test (L/min)
                     Qdiff    =    diffusive air flow (L/min)
                     ALCR  =    air- liquid conversion ratio (dimensionless)
       Combining Equation 4.12 with Equation 4.7 yields Equation 4.13, which enables the
calculation of sensitivity using the ALCR approach, taking into account diffusive losses.
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                                      Q^ALCR
                     LRVDIT = log 	^7	r                 Equation 4.13
                                 \VCF.(Qmr-Qdiff)]

       Where:       LRVoii  =   direct integrity test sensitivity in terms of LRV
                                  (dimensionless)
                     Qp       =   filtrate flow (L/min)
                     ALCR   =   air-liquid conversion ratio  (dimensionless)
                     VCF     =   volumetric concentration factor (dimensionless)
                     Qair      =   flow of air (L/min)
                     Qdiff     =   diffusive air flow  (L/min)
       Note that Equations 4.12 and 4.13 are applicable to MCF, MF/UF, and NF/RO membrane
filtration systems.
4.3.2  Marker-Based Tests

       Sensitivity for marker-based direct integrity tests is determined via a straightforward
calculation of the log removal value, similar to the determination of log removal values during a
challenge study, as shown in Equation 4.14 (reference to similar equation in Chapter 3 is given in
parentheses):
                     LRVDIT = log( Cf) - log( Cp)                      Equation 4.14  (3.7)

       Where:        LRVoii  =    direct integrity test sensitivity in terms of LRV
                                  (dimensionless)
                     Cf       =    feed concentration (number or mass / volume)
                     Cp       =    filtrate concentration  (number or mass / volume)
       In the use Equation 4.14 to calculate sensitivity of a marker-based test, the LT2ESWTR
specifies that the feed concentration, Cf, is the typical feed concentration of the marker used in
the test, and that the filtrate concentration, Cp, is the baseline filtrate concentration of the marker
from an integral membrane unit.  Due to variability in dosing the marker, the day-to-day LRV is
likely to vary during system operation.  Thus, in order to establish the sensitivity of a marker-
based direct integrity test using Equation 4.14, it is necessary to assume an appropriately
conservative feed concentration such that the LRVs determined on a day-to-day basis meet or
exceed the LRVon unless there is an integrity breach.  An example of such a conservative
approach would be the use of the lower bound of the anticipated concentration range of seeded
marker as the feed concentration for the purposes of calculating the sensitivity of the test.

       In order to optimize sensitivity and reliability of a marker-based direct integrity test, it is
important to use an accurate method for quantifying the feed and filtrate concentrations.  Since


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the feed and filtrate concentrations will differ by orders of magnitude, an analytical method with
a wide dynamic range is desired.  If such a range is not available using a single device, two
different instruments may need to be used to measure these respective concentrations.
Regardless of the dynamic range of the instrument(s), it is likely that different analytical volumes
will need to be used to deal with the different concentration ranges, but the concentrations will
have to be expressed in terms of equivalent volumes for the purpose of calculating an LRV.
Some specific considerations regarding the use of particulate and molecular marker-based direct
integrity tests are discussed in  section 4.7.5.
4.4    Test Frequency

       Most currently available direct integrity tests require the membrane unit to be taken off-
line for testing and thus are conducted in a periodic manner, requiring a balance between the
need to verify system integrity with desire to minimize system downtime and lost productivity.
In addition, although some marker-based tests may be conducted while the membrane unit is on-
line and in production, it is general neither practical nor cost effective to implement these tests
on a continual basis. Thus, the frequency at which direct integrity testing is conducted for
membrane filtration systems represents a compromise between these competing objectives.

       The LT2ESWTR requires that direct integrity testing be conducted on each membrane
unit at least once every 24 hours of unit operation for rule compliance. This minimum test
frequency is intended to balance the need to verify system integrity as often as possible with cost
and production considerations and is based in part on a USEPA report that indicated daily direct
integrity testing was relatively common practice at membrane filtration facilities (USEPA 2001).

       The state may require more frequent integrity testing for compliance with the rule at its
discretion. An alternate test frequency may be based on  a variety of considerations, such as the
frequency at which integrity breaches occur and the integration of process safety practices, such
as maintaining filtrate storage with a detention time equivalent to or longer than the time
between direct integrity test events.  Although unrelated  to rule compliance, more frequent
testing may also be  appropriate under certain specific circumstances, such during initial facility
start-up, as described in Chapter 8.

       If the state utilizes the LT2ESWTR regulatory framework for membrane filtration for
applications other than rule compliance, it may also permit less frequent direct integrity testing.
However,  an underlying factor that should be considered before implementing less frequent
testing is the implication of letting an integrity breach remain undetected for an extended period
of time while water is being supplied to the public.
4.5    Establishing Control Limits

       A control limit (CL) is defined as a response that, if exceeded, indicates a potential
problem with the system and triggers a response. Multiple CLs can be set at different levels to
indicate the severity of the potential problem. In the context of direct integrity testing, CLs are
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set at levels associated with various degrees of integrity loss. Under the provisions of the
LT2ESWTR, a control limit (CL) for direct integrity testing must be established at the threshold
test response that is indicative of an integral membrane unit capable of achieving the
Cryptosporidium removal credit awarded by the state for rule compliance (40 CFR 141.728).
Because utilities or states would have the option to implement a series of tiered CLs that may
represent progressively greater levels of integrity loss leading up to the specific CL required
under the rule, in this guidance manual the LT2ESWTR-mandated CL is referred to as an upper
control limit (UCL). If the integrity test response is below the UCL, the membrane unit should
be achieving a LRV equal to or greater than the removal credit awarded to the process.
Alternatively, if the UCL is exceeded, the membrane unit is required to be taken off-line for
diagnostic testing (as describe in section 4.8) and repair.

       The same principles used to establish direct integrity test sensitivity are also used to
establish the UCL.  For pressure-based tests, the UCL may be calculated using the ALCR
methodology.  A modified version of Equation 4.7 yields an expression for the UCL for, as
shown in Equation 4.15:
                            Q  •ALCR
                     UCL=   p
Where:
       10

UCL
QP
ALCR   =
LRC
VCF
                             LRC
                                  VCF
                                                             Equation 4.15
                                  upper control limit in terms of airflow  (L/min)
                                  membrane unit design capacity filtrate flow  (L/min)
                                  air- liquid conversion ratio (dimensionless)
                                  log removal credit awarded (dimensionless)
                                  volumetric  concentration factor (dimensionless)
       Similarly, Equation 4.9 can be rearranged to establish an expression for calculating the
UCL in terms of a pressure decay rate, as shown in Equation 4.16:
                     UCL =
                     Qp • ALCR*(BP +14.7)
                        10MC.F  *VCF
                                                Equation 4.16
       Where:       UCL   =   upper control limit in terms of pressure decay rate  (psi/min)
                    Qp     =   membrane unit design capacity filtrate flow (L/min)
                    ALCR  =   air-liquid conversion ratio (dimensionless)
                    BP     =   backpressure on the system during the test (psi)
                    LRC   =   log removal credit (dimensionless)
                    Vsys    =   volume of pressurized air in the system during the test  (L)
                    VCF   =   volumetric concentration factor (dimensionless)
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Values for the other parameters in Equations 4.15 and 4.16 should be the same as those used to
calculate sensitivity using Equations 4.7 and 4.9, respectively. Note that to the extent possible,
these values should be selected to yield a conservative result for the UCL.

       Equations 4.15 and 4.16 establish the maximum direct integrity test response that can be
used as a UCL for the log removal credit (LRC) awarded by the state.  The LRC, in turn, must be
less than or equal to the lower value of either the log removal value determined during challenge
testing (LRVc-iest) or the sensitivity of the direct integrity test used (LRVoii).

       In the context of Equations 4.15 and 4.16, CLs are expressed in terms of the actual
response from the direct integrity test (i.e., flow or air or pressure decay rate, respectively).  In
this form the CLs may be most useful for operators, since these could be directly compared to
integrity test results.  However, it may also be useful to calculate the corresponding LRVs for
both the CL(s) and the individual direct integrity test responses using the generic forms of
Equations 4.7  (for tests yielding results in terms of the flow of air) or 4.9 (for tests yielding
results in terms of pressure decay).  In this case these equations will simply yield a LRV
corresponding to a particular direct integrity test result (i.e., a general LRV) rather than the
sensitivity of the test (i.e., LRVoii). Many membrane systems have automated data acquisition
equipment that could be programmed to calculate the LRV based upon the results of the most
recent integrity test results and current operating conditions. These parameters may be displayed
and trended  to track system performance.  Additional guidance on data analysis is provided in
section 4.9.

       For marker-based tests., which yield results in terms of log removal, the UCL is simply
equal to the  log removal credit awarded by the state.

       Any  CLs other than that mandated by the LT2ESWTR that are either voluntarily
implemented by the utility or required by the state are referred to as lower control limits (LCLs).
For example, a LCL may be established to provide operators with an indication that there may be
an integrity breach before the breach becomes a compliance concern. In this scenario the LCL
could be used  in the context of preventative maintenance,  and excursions above the LCL could
prompt investigation and repair during scheduled downtime for the unit rather than require an
immediate shutdown. The use of CLs and integrity testing in the context of a comprehensive
integrity verification program is discussed further in Appendix A.

       Unlike the UCL that is established by the log removal credit awarded to the process, a
LCL can be  established based on the needs and objectives of the utility. However, any LCLs
should be above the baseline for an integral membrane and below the UCL in order to be useful.
The baseline integrity test value for a membrane unit can be established during the
commissioning of the facility, after the membrane system has been fully wetted and determined
to be integral.  The baseline level is described as the normal range of direct integrity test results
that would occur for an integral membrane unit. A practical lower bound for any LCLs is the
sensitivity of the direct integrity test (i.e., the lowest response that can be reliably measured that
is indicative of an integrity breach).
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4.6    Example: Establishing Direct Integrity Test Parameters

Scenario:

A submerged, vacuum-driven hollow-fiber membrane system that operates in a deposition (i.e.,
dead-end) mode hydraulic configuration is required to provide a total of at least 3 log removal
for Cryptosporidium by the state under the LT2ESWTR.  A pressure decay test is applied to one
of the membrane units in the system. Applicable parameters are as follows:

       Operational parameters
       •  The permitted design capacity of the membrane unit is 1,200 gpm.
       •  The maximum anticipated water temperature is 75 ฐF (24 ฐC).
       •  The maximum anticipated backpressure that might be exerted on the units during
          direct integrity testing is 75 inches of water column.
       •  The minimum anticipated backpressure that might be exerted on the units during
          direct integrity testing is 60 inches of water column.
       •  The backpressure measured prior to the most recent pressure decay test was 65 inches
          of water column.
       •  The filtrate flow measured prior to the most recent pressure decay test was
          1,000 gpm.
       •  The TMP measured prior to the most recent pressure decay test was 10 psi.

       Direct integrity test parameters
       •  The volume of pressurized piping during the test is 285 L.
       •  The initial applied test pressure is 15 psi.
       •  The duration of the pressure decay test is 10 minutes.
       •  Baseline (i.e., diffusive) decay is negligible over the duration of the test.
       •  The smallest verifiable rate of pressure decay under known compromised conditions
          is 0.10 psi/min.
       •  The most recent pressure decay test yielded a result of 0.13 psi/min.
       •  The temperature of both the water and the applied air were 68 ฐF (20 ฐC) during the
          most recent pressure decay test.

       Unit and membrane characteristics
       •  The maximum rated  TMP is 30 psi.
       •  The pore shape correction factor (?) for the membrane material was not determined
          experimentally, and thus a conservative value of 1 is assumed.
       •  The membrane material is relatively hydrophilic and has a liquid-membrane contact
          angle (i.e., "wetting angle") of 30ฐ.
       •  The membrane surface variation (i.e., roughness) is 0.3 |j,m, as provided by the
          manufacturer.
       •  The hollow-fiber lumen diameter is 500 (j,m.
       •  The depth of the membrane into the potting material is 50 mm.
       •  All flow through any integrity breach that may be present is assumed to be turbulent.
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Calculate:

1 .  The minimum direct integrity test pressure commensurate with the required resolution of
   3 |j,m for the removal of Cryptosporidium

2.  The sensitivity of the direct integrity test

3.  The UCL for this system

4.  The LRV verified by the most recent direct integrity test


Solution:

1.  Calculate the minimum direct integrity test pressure commensurate with the required
   resolution of 3 urn for the removal of Cryptosporidium.
Ptest = (0 . 1 93 • K: • (7 • cos 0 ) + BPmK

       ? =  1

       s =  72 dynes/cm

       9 =  30ฐ

            x  = 75 inches (of water column)
                                                        Equation 4 . 1

                                                        from given information

                                                        the surface tension of water at 20 ฐC

                                                        from given information

                                                        from given information
              dyne
       Ptest = 12.0 psi + 2.7 psi
                                     cm

                                                                psi
   Because the problem scenario states that baseline diffusive losses are negligible, the pressure
   calculated above represents the lowest permissible initial applied test pressure. If diffusive
   losses could not be neglected, Ptest would represent the lower bound above which the pressure
   must be maintained to ensure that the resolution is maintained throughout the duration of the
   test.  If this were the case, the applied test would have to be increased over Ptest by total
   anticipated pressure decay over the duration of the test.  In this particular example above,
   since the applied test pressure is given as 15 psi, the resolution requirement of the
   LT2ESWTR is satisfied.
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2.  Calculate the sensitivity of the direct integrity test.
                      v • ALCR*(BP+14.7)I
       LRVDIT = log — - - - -           Equation 4.9
                   '                         '
              Qp =  1,200 gpm                         design capacity filtrate flow
                                                      (from given information)

              BP =  60 inches (of water column)         minimum backpressure
                                                      (from given information)

              Note that the minimum backpressure that might be exerted during direct integrity
              testing is used to establish a conservative value for sensitivity.

              ?Ptest  = O.lOpsi/min                     smallest verifiable decay rate
                                                      (from given information)

              Vsys =  285 L                            from given information

              VCF =  1                                standard for deposition mode
                                                      hydraulic configuration

              ALCR = ?                              to be determined

              Consult Table 4. 1 and Appendix C - use Darcy pipe flow model for a hollow-
              fiber membrane filtration system under conditions of turbulent flow (as specified):
              ALCR=m.Y                                Equationc.4
                    Ptest  = 1 5 psi                             initial applied test pressure
                                                             (from given information)

                    Note that if diffusion through an integral membrane unit (i.e., baseline
                    pressure decay was significant, the cumulative decay over the duration of
                    the test would be subtracted from the initial test pressure before applying
                    this parameter to Equation C.4 to yield a conservative result for the
                    ALCR.

                    BP =  60 inches (of water column)          minimum backpressure
                                                             (from given information)

                    T  = 75 ฐF                               maximum anticipated
                                                             temperature
                                                             (from given information)

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                     IMP = 30psi
                   maximum allowable TMP
                   (from given information)
                     Note that the values for system backpressure, temperature, and TMP were
                     selected establish a conservative (i.e., lower) value for the ALCR, which
                     in turn yields a conservative value for sensitivity.

                     Y = ?                                    net expansion factor
                                                               (to be determined)

                            As indicated in Equation C.5 in Appendix C, the gas
                            compressibility factor (Y) is a function of the applied test pressure
                            (Ptest), the system backpressure during the test (BP), and a flow
                            resistance coefficient (K), as follows:
                            7oc
                                   Ptest~BP
   ,K
Equation C.5
                            Note that smaller values for Y are generated with larger values of
                            the first parameter in Equation C.5 and smaller values for K.  Thus,
                            values for these variables should be selected to produce smaller
                            values of Y, which in turn yield smaller values for the ALCR and a
                            more conservative value for the test sensitivity.

                            Quantifying the first parameter in Equation C.5:

                                   Ptest  = 15psi

                                   BP = 75 inches (of water column)
                                                  f         75 inches • H,
                                                   15psi - -
                                                           27.7
                                                               inches •
                                                                    psi
                                                        \5psi +14.7 psi
                                                                             = 0.41
                            The flow resistance coefficient is defined by Equation C.6, as
                            described in Appendix C:
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                                   K = f •	               Equation C.6
                                             fiber

                                   L  = 50 mm                 potting depth
                                                               (from given information)

                                   daer =  0.5mm              fiber diameter
                                                               (from given information)

                                  / = ?                       Darcy friction factor
                                                               (to be determined)

                                   The Darcy friction factor can be obtained the iterative
                                   method described in Appendix C.

                                  / = 0.037                   Darcy friction factor
                                                               (from iterative method)
                                                 = (0.037)*
                                                  \     /  \
                                            /
                                           dfiber
                            Using the appropriate chart on page A-22 from Crane (1988) with
                            the values calculated above:
                                     Ptest   BP   =(X41      ฃ = 3/7
                            .. .yields a value for Y as shown below.

                            Y = 0.79


              Having determined a value for Y, the ALCR can be calculated follows:
              ALCR-m.Y.
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                             15 psi - -
                                            75 inches-
                                                inches -H2O
                                           27.7
                                                              (15 psi+14.7 psi)
                                                    psi     )
              ALCR = 7.0
       Substituting values into Equation 4.9 for sensitivity:
       LRVDIT = log
1 ฐOOcrr>/77ซ ^ 79S • 7 0 •
I gal)
Q]QpSt
min
60inches • H2O
0^ n inches • H2O ' *""
1 psi )
• 285Zซ1
               =  4.1
   Therefore, the  maximum  removal value that this membrane  filtration system is capable of

   verifying is 4. 1 log.
3.  Calculate the UCL for this system
       Qn • ALCR*(BP+14.7)
T T/~lT    P
UCL =	—	
                                                      Equation 4.16
              Qp =  1,200 gpm
              ALCR = 7.0
              BP =  60 inches (of water column)
                                               design capacity filtrate flow

                                               (from given information)




                                               as determined in Part 2 of this

                                               example, above




                                               minimum backpressure
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                                                       (from given information)

              Note that the minimum backpressure that might be exerted during direct integrity
              testing is used to establish a conservative value for the UCL.
              LRC = 3

              Vsys  = 285 L

              VCF = 1
                                                from given information

                                                from given information

                                                standard for deposition mode
                                                hydraulic configuration
l,200gpyปซ3.7
3c -^ LT n •
ซo/J
{\CM~nc~hpv • f-f O
\J\J it l-\^f i-'C-tJ J. J. n \_S
^nn inches • H2O

\-\4.7psi
)
       UCL =
       UCL  = 1.9psi/min
4. Calculate the LRV verified by the most recent integrity test.

   In addition to calculating the sensitivity, Equation 4.9 can also be used to determine the LRV
   verified by the most recent direct integrity test via applying values for the variables specific to
   this test event.
LRV = log
                                                       Equation 4.9
              Qp = 1,000 gpm
              BP  = 65 inches (of water column)
              ?Ptest =  0.13psi/min
              Vsys  = 285 L
              VCF  = 1
                                                flow measured prior to testing
                                                (from given information)

                                                backpressure measured prior to
                                                testing
                                                (from given information)

                                                measure test decay rate
                                                (from given information)

                                                from given information

                                                standard for deposition mode
                                                hydraulic configuration
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              ALCR =  7.0
             as determined in part 2, above
              Note that because the ALCR is designed to be a conservative value, it is not
              necessary to recalculate the ALCR for a specific pressure decay test in order to
              use Equation 4.9 for the purpose of determining the LRV verified by that test.

       Substituting values into Equation 4.9 for sensitivity:
       LRV = log
                               i.785-
                                    gal
7.0<
65inches • H^O
           2   -+14.7/MZ
          inches • H2O
                                                  1.1
                                          mn
                                                285Zซ1
       LRV  = 4.1
4.7    Test Methods

       The LT2ESWTR does not specify a particular type of direct integrity test for rule
compliance, but instead allows the use any test that meets the requirements of the rule
(40 CFR 141.728). The two general classes of tests currently employed in municipal water
treatment applications are pressure- and marker-based tests.  Within these two categories, the
particular types of tests most commonly used are described in the following subsections,
including the pressure- and vacuum-decay tests, the diffusive airflow test, the water displacement
test, and particulate- and molecular-marker tests. General procedures for conducting each of
these tests are provided, along with a listing of some of the advantages and disadvantages of each
method.  The particular manner in which each of these tests is applied may vary according to
manufacturer or site- or system-specific conditions.

       The specific tests addressed in this guidance manual are not intended to represent a
comprehensive list of all types of direct integrity tests that could be used to comply with the
requirements of the LT2ESWTR. Any method that is both consistent with the definition of a
direct integrity test under the rule and capable of meeting the specified resolution, sensitivity,
and frequency requirements could be used for rule compliance at the discretion of the state.
4.7.1  Pressure Decay Test

       The pressure-based pressure decay test is the most common direct integrity test currently
in use and is generally associated with microfiltration (MF), ultrafiltration (UF), membrane
cartridge filtration (MCF) systems, which utilize porous membranes. In a pressure decay test, a
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pressure below the bubble point value of the membrane is applied, and the subsequent loss in
pressure is monitored over several minutes.  An integral membrane unit will maintain the initial
test pressure or exhibit a very slow rate of decay. Note that the pressure decay test is applicable
to currently available pressure-driven and vacuum-driven systems, since this test is conducted
under positive pressure for both types of systems.  A schematic illustrating a pressure decay test
is shown in Figure 4.1.
              Figure 4.1 Schematic Illustrating a Pressure Decay Test
                         VENT
                                                                         COMPRESSED AIH
                                                                         SUPPLY
                                                                         FILTRATE
                                 MEMBRANE MODULE
An outline of a generic protocol for a pressure decay test as is as follows:

       1.  Drain the water from one side of the membrane.
          For hollow-fiber systems, typically the inside of the fiber lumen is drained, which
          may represent the feed or the filtrate, depending on whether the system is operated in
          an "inside-out" or "outside-in" mode, respectively.

       2.  Pressurize the drained side of the fully wetted membrane.
          The applied pressure must be lower than the bubble point pressure of the membrane
          (i.e., the pressure required to overcome the capillary forces that hold water in the
          membrane pores).  Pressures ranging from 4 to 30 psi are typically applied during the
          pressure decay test, depending on the particular system.  Membrane construction may
          limit the pressure at which a membrane can be tested. For compliance with
          LT2ESWTR requirements, the applied pressure must be sufficient to meet the
          resolution criterion of 3 |j,m  based on Equation 4.1. For systems that utilize
          membranes submerged in an open basin, the test is typically applied to the filtrate
          side of the membranes without draining of the basins. As a result, the hydrostatic
          pressure at the deepest part of the membrane unit at which feed water passes through
          the membrane must be considered in determining the resolution actually achieved by
          the test, as discussed in section 4.2.
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       3.  Isolate the pressure source and monitor the decay for a designated period of time.
          If there are no leaks in the membrane, process plumbing, or other pressurized system
          components, then air can only escape by diffusing through the water contained in the
          pores of the fully wetted membrane.  Typically, this test is monitored over a period of
          5 to 10 minutes such that a stable rate of decay can be determined.  The rate of
          pressure decay should be compared to the UCL (or any LCLs that may also be
          established) for the test to determine what, if any, subsequent action is triggered.
Advantages of the pressure decay test include:

       •  Ability to meet the resolution criterion of 3 |j,m under most conditions

       •  Able to detect integrity breaches on the order of single fiber breaks and small holes in
          the lumen wall of a hollow fiber, depending on test parameters and system-specific
          conditions

       •  Standard feature of most MF and UF systems

       •  High degree of automation

       •  Widespread use by utilities and acceptance by states

       •  Simultaneous use as a diagnostic test to isolate a compromised module in a
          membrane unit in  some cases (e.g., see section 4.8.1)


Limitations of the pressure decay test include:

       •  Inability to continuously monitor integrity

       •  Calculation of test method sensitivity requires measurement of the volume of
          pressurized air in the system (see Equation 4.8)

       •  Potential to yield false positive results if the membrane is not fully wetted (which
          may occur with newly installed and hydrophobic membranes that are difficult to wet,
          or when the test is applied immediately after a backwash process that includes air)

       •  More difficult to apply to  membranes that are oriented horizontally as a result of
          potential draining and air venting problems
       In addition to the disadvantages cited above, another important concern associated with
the pressure decay test is the potential for larger decay rates even within the UCL to affect the
accuracy of the test. For example, if the total pressure decay over the duration of the test reduces
the applied pressure on the membrane to a level below that sufficient to meet the resolution

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criterion, the test would not comply with the requirements of the rule. Consequently, parameters
should be established so as to ensure that the pressure decay test meets the 3-|j,m resolution
criterion throughout the duration of the test, as discussed in section 4.2.
4.7.2  Vacuum Decay Test

       The vacuum decay test is analogous to the pressure decay test with the exception that the
test pressure is applied by drawing a vacuum on the membrane and monitoring the rate of
vacuum (as opposed to pressure) decay over a period of time.  An integral membrane unit will
maintain the initial test vacuum or exhibit a very slow rate of decay.  This test is generally
associated with spiral-wound nanofiltration (NF) and reverse osmosis (RO) membranes. A
schematic illustrating  a vacuum decay test is shown in Figure 4.2.
              Figure 4.2 Schematic Illustrating a Vacuum Decay Test
                          VENT

                           I:
  FEED
                                                   VACUUM
                                                   ^
                                                    Cv
                                    MEMBRANE UNIT
                                                                         -*-
                                                                  VACUUM  A
                                                                   PUMP   T
An outline of a generic protocol for a vacuum decay test as is as follows:

       1.  Drain the water from one side of the membrane.
          Typically, the filtrate side of a spiral-wound NF or RO membrane is drained.

       2.  Apply a vacuum to the drained side of the fully wetted membrane.
          A vacuum of 20 to 26 inches Hg is typically applied during the test. Membrane
          construction may limit the vacuum at which a membrane can be tested. For
          compliance with LT2ESWTR requirements, the applied vacuum must be sufficient to
          meet the resolution criterion of 3 |j,m.
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       3.  Isolate the vacuum source and monitor the decay for a designated period of time.
          If there are no leaks in the membrane, process plumbing, or other system components
          under vacuum, then the vacuum should not decay over the duration of the test.
          Typically, this test is monitored over a period of 5 to 10 minutes to allow a stable rate
          of decay to be determined.  The rate of pressure decay should be compared to the
          UCL (or any LCLs that may also be established) for the test to determine what, if any,
          subsequent action is triggered.
Advantages of the vacuum decay test include:

       •  Ability to test spiral-wound membranes or other systems that cannot be pressurized
          on the filtrate side of the membrane

       •  Ability to meet the resolution criterion of 3  |j,m under most conditions
Limitations of the vacuum decay test include:

       •  Inability to continuously monitor integrity

       •  Not widely used for full-scale systems in current practice

       •  Difficulty in removing entrained air after the test has been completed

       •  Calculation of test method sensitivity requires measurement of the volume of air
          under vacuum in the system (see Equation 4.8)
       As with the pressure decay test, another important concern associated with the vacuum
decay test is the potential for larger decay rates even within the UCL to affect the accuracy of the
test.  Thus, if the total vacuum decay over the duration of the test reduces the applied vacuum on
the membrane to a level below that sufficient to meet the resolution criterion, then the test would
not comply with the requirements of the rule. Consequently, test parameters should be
established so  as to ensure that the vacuum decay test meets the 3-|j,m resolution criterion
throughout the duration of the test.
4.7.3  Diffusive Airflow Test

       The diffusive airflow test provides a direct measurement of the airflow through an
integrity breach (i.e., Qair).  Like the pressure decay test, the diffusive airflow test is also based
bubble point theory and generally associated withMF, UF, and MCF membranes. However,
instead of measuring the rate of pressure decay, the test pressure is kept constant and the airflow
through a breach is measured.  If there are no breaches in the system, there will typically be a
small flow of air resulting from the diffusion of air through water held in the fully wetted

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membrane pores. This diffusive airflow represents the baseline test response that is indicative of
an integral membrane.

       The diffusive airflow test has not been commonly used in municipal water treatment
plants, at least partially as a result of the incorporation of pressure decay test as a standard
feature with most MF and UF systems. However, the diffusive airflow test has long been used
for measuring the integrity of cartridge filters used in sterilization applications and has been
described in the literature by a number of authors, including Meltzer (1987), Vickers (1993), and
Johnson (1997), among others.  Note that this test is not applicable to submerged membrane
filtration systems.  A schematic illustrating a diffusive airflow test is shown in Figure 4.3.
              Figure 4.3 Schematic Illustrating a Diffusive Airflow Test
                    AIR FLOW
                     MOEf?
                                                                          COMPRESSED
                                                                          SlfPPLY
                                                                       — FILTRATE
                                  MEMBRANE UNiT
The outline of a generic protocol for a diffusive airflow test is similar to that for the pressure
decay test, and is as follows:

    1.  Drain the water from one side of the membrane.
       For hollow-fiber systems, typically the inside of the fiber lumen is drained, which may
       represent the feed or the filtrate, depending on whether the system is operated in an
       "inside-out" or "outside-in" mode, respectively.

    2.  Pressurize the  drained side of the fully wetted membrane.
       The applied pressure must be lower than the bubble point pressure of the membrane (i.e.,
       the pressure required to overcome the capillary forces that hold water in the membrane
       pores).  As with the pressure decay test, pressures ranging from 4 to 30 psi are typically
       applied during the diffusive airflow test, depending on the particular system. Membrane
       construction may limit the pressure at which a membrane can be tested. For compliance
       with LT2ESWTR requirements, the applied pressure must be sufficient to meet the
       resolution criterion of 3 |j,m.
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    3.  Maintain constant pressure and monitor the airflow for a designated period of time.
       If there are no leaks in the membrane, process plumbing, or other pressurized system
       components, then air can only escape is by diffusing through the water contained in the
       pores of the fully wetted membrane.  Typically, this test is monitored over a period of 5
       to 10 minutes to allow a stable airflow to be established.  The flow of air should be
       compared to the UCL (or any LCLs that may also be established) for the test to determine
       what, if any, subsequent action is triggered.
Advantages of the diffusive airflow test include:

       •  Ability to directly measure the flow of air through an integrity breach

       •  Ability to meet the resolution criterion of 3 |j,m under most conditions


Limitations of the diffusive airflow test include:

       •  Inability to continuously monitor integrity

       •  Requires measurement equipment to measure flow of air that is generally not a
          standard inclusion with a membrane filtration system

       •  Not widely used for full-scale systems in current practice

       •  Potential to yield false positive results if the membrane is not fully wetted (which
          may occur with newly installed and hydrophobic membranes that are difficult to wet,
          or when the test is applied immediately after a backwash process that includes air)


4.7.4  Water Displacement Test

       The water displacement test is similar to the diffusive airflow test with the exception that
the volume of displaced water as a result of an integrity breach is measured rather than the flow
of air through a breach.  Specifically, the air that  passes across the membrane displaces an
equivalent volume of water on the opposite side.  This test can only be applied to membrane
systems operated under positive pressure (i.e., as  opposed to immersed systems that operate
under vacuum).  The volume of displaced water collected over a known period of time is
measured and converted to equivalent volume of air to determine the airflow (Qair). If there are
no breaches in the system, there will typically be  a small flow of displaced water resulting from
the diffusion of air.  This flow represents the baseline test response that is indicative of an
integral membrane.  A larger volume (or flow) of displaced water would indicate an integrity
breach. It is important to note that although this test measures the flow of water through an
integrity breach, it does not constitute the flow of water through the critical breach (Qbreach) that
is necessary for determining the direct integrity test sensitivity.
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       The water displacement test is described in an American Water Works Association
Research Foundation (AWWARF) report prepared by Jacangelo et al. (1997). While this test is
not commonly used in municipal drinking water treatment plants, it is relatively easy to use,
requires minimal equipment, and can detect very small integrity breaches on the order of a single
broken fiber.  Since publication of this AWWARF report, a membrane filtration facility in
Tauranga, New Zealand has adopted the use of this integrity test. A schematic illustrating a
water displacement test is shown in Figure 4.4.
            Figure 4.4 Schematic Illustrating a Water Displacement Test
            BOTTOM OF
          PIFINS SfSTfM
  FEED
                                                                                   MR
                                                                         SUPPLY
                              f'iLffWTt
       The outline of a generic protocol for a water displacement test is similar to that for the
diffusive airflow test, and is as follows:

       1.  Drain the water from one side of the membrane.
          For hollow-fiber systems, typically the inside of the fiber lumen is drained, which
          may represent the feed or the filtrate, depending on whether the system is operated in
          an "inside-out" or "outside-in" mode, respectively.

       2.  Pressurize the drained side of the fully wetted membrane.
          The applied pressure must be lower than the bubble point pressure of the membrane
          (i.e., the pressure required to overcome the capillary forces that hold water in the
          membrane pores).  Pressures ranging from 4 to 30 psi are typically applied during the
          pressure decay test, depending on the particular system. Membrane construction may
          limit the pressure at which a membrane can be tested. For compliance with
          LT2ESWTR requirements, the applied pressure must be sufficient to meet the
          resolution criterion of 3 |j,m. Since one side of the membrane must remain flooded
          with water during the test, there is a potential for some hydrostatic backpressure. If
          this pressure  is determined to be significant, it must be considered in the resolution
          calculations as discussed in section 4.2.
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       3.  Maintain constant pressure and monitor the flow for a designated period of time.
          If there are no leaks in the membrane, process plumbing, or other pressurized system
          components, then air can only escape is by diffusing through the water contained in
          the pores of the fully wetted membrane.  Typically, this test is monitored over a
          period of 5 to 10 minutes to allow a stable flow to be established. The air displaces
          water that in turn is measured via either a flow meter or a graduated cylinder and
          timing device.  Since the flow of water is equivalent to the flow of air, the resulting
          flow should be compared to the UCL (or any LCLs that may also be established) for
          the test to determine what, if any, subsequent action is triggered. Note that the flow
          meter and associated sample line used in this test must be configured to prevent the
          gravity flow of water.
Advantages of the water displacement test include:

       •  Ability to directly measure the flow of air via an equivalent flow of water provided
          the backpressure on the system does not result in the compression of diffused air

       •  Ability to meet the resolution criterion of 3 |j,m under most conditions

       •  Able to detect integrity breaches on the order of single fiber breaks and small holes in
          the fiber lumen wall of a hollow

       •  Ease of measuring flow of water relative to that of air
Limitations of the water displacement test include:

       •  Inability to continuously monitor integrity

       •  Not widely used for full-scale systems

       •  Potential to yield false positive results if the membrane is not fully wetted (which
          may occur with newly installed and hydrophobic membranes that are difficult to wet,
          or when the test is applied immediately after a backwash process that includes air)
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4.7.5  Marker-Based Integrity Tests

       Marker-based tests are advantageous in that they provide a direct assessment of the LRV
achieved by the process.  Both paniculate- and molecular marker-based direct integrity tests may
be used to meet the direct integrity test requirements of the LT2ESWTR provided the specified
performance criteria for resolution, sensitivity, and frequency are satisfied (40 CFR 141, Subpart
W, Appendix C).  Since a marker-based direct integrity test is essentially a form of challenge
testing, much of the guidance provided in Chapter 3 may be useful in designing a marker-based
test.  Because these tests are applied to water treatment equipment in active use, the particulate or
molecular marker used must be inert and suitable for use in a water treatment facility  (e.g.,
approved by Food and Drug Administration (FDA) or certified by the National Sanitation
Foundation (NSF) as an NSF-60 approved material). Because MF, UF, and MCF systems utilize
porous membranes that would not remove a molecular marker, only particulate marker tests
should be used with these systems. (Note that one possible exception is  a system utilizing UF
membranes with a low MWCO, which could potentially remove larger molecular markers.)
Conversely, because the semi-permeable NF and RO membranes are not specifically designed to
accommodate large particle loads and typically cannot be backwashed to removed particulate
matter from the membrane surface, only molecular markers should be used with NF and RO
systems.  Schematics illustrating the particulate and molecular marker tests are shown in
Figures 4.5 and 4.6, respectively.
             Figure 4.5  Schematic Illustrating a Particulate Marker Test
   fEED
                                                                            • flLTfWd
                                                           nan
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                                Chapter 4 - Direct Integrity Testing
              Figure 4.6  Schematic Illustrating a Molecular Marker Test
    fEQJ
                                            MEMBRANE UNIT
                                                                             — RUfWt
                                                                    flLTHAHl
                                                                    SOLU1ION
                                                                    ASW.YZER
The generic protocols for both particulate and molecular marker tests are similar, and are as
follows:

       1.   Select an appropriate marker and verify that it meets the resolution criterion.
           (Additional guidance is given in section 3.9.)

       2.   Ensure that the expected feed and filtrate sampling concentrations fall within the
           limits for the measuring instrumentation used.

       3.   Calculate the feed dosage rate and filtrate sample volume(s).
           (Additional guidance is given in section 3.10.)

       4.   Make sure that any operational processes such as chemical cleaning orbackwashing
           are not initiated during the marker-based test.

       5.   Determine the amount of time the marker has to be applied to attain a steady  state or
           equilibrium condition.
           (Additional guidance is given in section 3.10.)

       6.   Feed the marker into the system.

       7.   Commence filtrate sampling when the equilibrium is reached.

       8.   Continue simultaneous feed and filtrate sampling until results are attained.

       9.   Discontinue dosing.
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Advantages of marker-based integrity tests include:

       •  Provides direct evaluation of the LRV of a membrane unit

       •  Potential for application while unit is on-line and producing water (i.e., normal
          operation)

       •  Instruments used for filtrate monitoring may also potentially be used for continuous
          indirect integrity monitoring between application for the direct integrity test at the
          discretion of the state


Limitations  of marker-based integrity tests include:

       •  Potential for an improperly selected marker to cause fouling and interfere with normal
          system operation

       •  Cost and calibration of instrumentation

       •  Cost of marker

       •  May require disposal of filtered water produced during the test

       •  May require special considerations for disposal of the filtered marker waste

       •  Measurement of marker concentrations is typically  not continuous


       Additional Considerations for Particulate Marker Tests

       Typically  particulate marker tests require the use of particle counters to measure the feed
and filtrate particle concentrations during the test, thus enabling the LRV to be directly
calculated.  Consequently, there are some important considerations regarding particle counters to
consider in implementing a particulate marker test.  First, it is important that the feed and filtrate
particle counters continually monitor baseline concentrations between test events so that
background particle levels can be taken into  account in the determination of the LRV of
measured by the test during routine operation. The background levels recorded in both the feed
and the filtrate should be subtracted from the respective particle count measurements  during the
test event in order to yield an accurate LRV.  In addition, particle counters are subject to
coincidence error (i.e., two or more particles passing through the sensor simultaneously that are
consequently measured as a single larger particle), particularly at high particle concentrations.
This potential error may limit the maximum  particle concentration that can be counted, which
may in some cases be problematic for measuring the feed concentration during a particulate
marker test.  In order to compensate for possible coincidence error, some particle counters can
allow for the sample to be diluted. However, because any particles in the dilution water would

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introduce error into the measurement, the quality of any dilution water used should be also be
taken into account in measuring the particle concentration of interest during a particulate marker
test. It is also important that the particulate marker selected does not clump, which could
exacerbate coincidence error or clog the instrument sensor.

       All particle counters (or other instruments used to measure particulate concentrations
during a particulate marker-based test)  should be routinely calibrated at a frequency
recommended by the manufacturer or required by the state.  The calibration should be targeted
toward counting particles at the specified size and concentration used in the particulate marker
test. The particles used for the particulate marker test  should be inert and compatible with the
membrane in order to avoid irreversible fouling.
       Additional Considerations for Molecular Marker Tests

       Although the ambient levels of a molecular marker in the feed and filtrate may be
negligible in many cases, these background concentrations should nevertheless still be measured
and accounted for in the LRV calculation. The background concentrations of the molecular
marker in the feed and filtrate should be subtracted from the respective measurements collected
during the molecular marker-based direct integrity test in order to accurately quantify the LRV of
the membrane unit.  In addition, as with particle counters, all instruments that may be used to
measure molecular marker concentrations should be calibrated regularly at a frequency
recommended by the manufacturer or required by the state.
4.8    Diagnostic Testing

       Diagnostic tests are types of direct integrity tests that are specifically used to identify and
isolate any integrity breaches that are detected, thus supplementing primary methods such as the
pressure- or marker-based test described in section 4.7, which simply determine whether or a not
a leak is present in a membrane unit. Note that there are no sensitivity or resolution requirements
for diagnostic tests under the LT2ESWTR, since the objective of these test is simply to isolate
particular compromised module and/or broken fiber.  However, it is important that a diagnostic
test have sufficient resolution to enable the detection of the integrity breach that caused the UCL
to be exceeded.

       Many diagnostic tests are most useful for identifying a particular compromised module
within a unit; however, for hollow-fiber MF/UF systems some diagnostic tests may be used
locate a specific broken fiber in a module. The LT2ESWTR requires that if the results of a direct
integrity test exceed the UCL,  the affected unit be immediately taken off-line for diagnostic
testing and subsequent repair (40 CFR 141.728). Although many different types of diagnostic
tests may be available, four of the tests most commonly used are described in the following
subsections, including visual inspection, bubble testing, sonic testing, conductivity profiling, and
single module testing. Note that not all of these tests are applicable to every type of membrane
filtration.  Visual  inspection, bubble testing, and sonic testing are generally applicable to MF,
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UF, and MCF systems, while conductivity probing is used with NF and RO systems.  Single
module testing may be applicable to all types of membrane filtration systems.
4.8.1   Visual Inspection

       Visually inspecting a membrane unit for leaks is the simplest form of diagnostic testing
and is generally applicable to MF, UF, and MCF systems.  Since many pressure-based direct
integrity tests apply air to one side of the membrane while maintaining water on the other side, it
may be possible to see air bubbles form in a compromised module.  If a pressure-based direct
integrity is used, visual inspection may be able to be conducted simultaneously with the direct
integrity test to identify a compromised module.  In order to perform a visual inspection, some
component of the  module housing must be transparent; accordingly, some pressure-driven
membrane systems have inspection ports or clear tubing at the top of the membrane module to
allow an operator  to identify the particular compromised module. For vacuum-driven membrane
systems submerged in basins, this test simply involves observing the water surface to identify the
module that is the source of the bubbles rising to the surface.
Advantages of visual inspection include:

       •  Ability to identify specific compromised fibers and leaking seals

       •  Easy to use and interpret results

       •  No additional equipment required

       •  Equally applicable to systems using enclosed pressure vessels or immersed modules

       •  Does not require membrane modules to be removed from the unit


Limitations of visual inspection include:

       •  Manual application

       •  Requires system design considerations for implementation (e.g., sight tubes,
          removable plates or carriages, etc.)


4.8.2  Bubble Testing

       The bubble test is based on bubble point theory (as described in Appendix B) and is
applicable to MF, UF, and MCF membranes.  In conducting a bubble test, the module of interest
is first removed from the membrane unit.  The external shell of the module is then drained and
pressurized to a level below the bubble point of the membrane but higher than the pressure

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required to achieve the required 3-|j,m resolution for compliance with the LT2ESWTR. The
pressures applied in a bubble test are generally similar to those applied for the pressure-based
direct integrity tests.  The end cap is removed and a dilute surfactant solution is applied to the
open ends of the membrane fibers at the end of the module.  The formation of bubbles in the
surfactant solution can be used pinpoint specific leaking fibers.  The defective fiber may be
repaired by plugging the lumen with a stainless steel pin or epoxy adhesive dispensed from a
syringe. The membrane module manufacturer should be consulted for specific recommendations
regarding module repair.  Note that the bubble test is distinct from the bubble point test described
in section 3.7.3.  The bubble test described in this  section is applied to identify leaks, and thus
the pressure must be kept below the bubble point of the porous membrane.  By contrast, the
bubble point test is applied for the specific purpose of determining the bubble point of the
membrane, and thus the pressure must be gradually increased until the bubble point is achieved.
Advantages of the bubble test include:

       •  Ability to identify specific compromised fibers and leaking seals

       •  Easy to use and interpret results

       •  Equally applicable to systems using enclosed pressure vessels or immersed modules


Limitations of the bubble test include:

       •  Manual application

       •  May require removal of a membrane module from the rack


4.8.3  Sonic Testing

       The principle of sonic testing is that water passing through broken fibers or other
damaged system components will make a unique sound that can be detected using specialized
equipment. The analysis is typically conducted by manually applying an accelerometer (an
instrument used to detect vibrations) to one or more locations on each membrane module.  Using
headphones, the operator listens for  vibrations generated by leaking air.  Since the test is applied
to modules on an  individual basis, it is useful for identifying the module that has a potential
integrity breach when the direct integrity test indicates that there may be a problem in a
membrane unit. Sonic testing is generally applicable to MF, UF, and MCF systems.

       A  sonic test is most effectively administered by a skilled and  experienced operator,
particularly since  the results are more subjective than the other forms of integrity testing, either
direct or indirect.  Nonetheless, it is a useful diagnostic tool that can help isolate a compromised
membrane module.  Adham et al. (1995) reported that  sonic testing was able to detect a breach as
small as a 0.6 mm needle puncture in the wall of one out of over 22,000 hollow fibers.

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       An automated sonic testing system could have the potential to eliminate the subjectivity
of this test and serve as an on-line, continuous, and direct means of integrity testing.  The early-
stages of development and testing of such an automated system was described in a paper by
Glucina et al. (1999). This new acoustic monitoring system utilizes a sensor on each membrane
module to detect changes in noise caused by pressure fluctuations in any compromised fibers.
Test results indicated that the system was capable of detecting a single compromised fiber,
although performance was affected by the level of background mechanical noise associated with
the membrane filtration system. The system described by Glucina et al. is currently still under
development.
Advantages of sonic testing include:

       •  Ability to identify a specific compromised module within a membrane unit

       •  Ease of use (assuming the test is conducted by a trained operator)


Limitations of sonic testing include:

       •  Manual application

       •  Potential for subjective interpretations of results

       •  Requires the purchase of additional equipment

       •  Not feasible for immersed membrane systems


4.8.4  Conductivity Profiling

       Conductivity profiling is a common practice associated with NF and RO systems to
identify leaks in modules, o-rings, and seals.  A long sample tube is inserted into the permeate
port and used to withdraw a sample. The conductivity of the sample is monitored at various
points within the module and then indexed  along the length of the permeate tube.  Any integrity
breaches are identified by significant changes in conductivity.  The most common location of
leaks in a NF or RO system is at the module filtrate tube collector and end adaptor o-ring seals.
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Advantages of conductivity profiling include:

       •  Ability to identify a specific compromised module within pressure vessel


Limitations of conductivity profiling include:

       •  Manual application

       •  Requires operator skill for indexing probe

       •  Potential for subjective interpretations of results

       •  Requires the purchase of additional equip ment


4.8.5  Single Module Testing

       Single module testing may be applicable to all types of membrane filtration systems and
involves removing potentially compromised modules from a membrane unit that is known to
contain an integrity breach and testing  each module on an individual basis. Although a number
of different methods of integrity testing could potentially be utilized screen individual modules
with this diagnostic technique, single module testing generally refers to the use of a small
apparatus to conduct a pressure or vacuum decay test on one module at a time. One advantage of
this diagnostic test is that the pressure or vacuum decay associated with an integrity breach may
be much more pronounced in a single compromised module at a given test pressure than in one
compromised module in an entire membrane unit that is otherwise integral, enabling  a breach to
be more readily detected. Thus, while the process of single module testing is labor-intensive, it
may be especially useful for isolating a compromised module in cases in which other methods of
diagnostic testing have not been successful.


Advantages of the single module testing include:

       •  Increased ability to detect compromised modules compared to in-situ testing applied
          to an entire membrane unit

       •  May be able to isolate compromised modules in cases in which other diagnostic tests
          have been unsuccessful

       •  Generally applicable to MF, UF, NF, RO, and MCF systems
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Limitations of single module testing include:

       •  Manual application

       •  Labor-intensive testing process

       •  May require modules to be removed from the membrane unit

       •  May require separate testing apparatus


4.9    Data Collection and Reporting

       The LT2ESWTR requires that direct integrity testing be conducted on each membrane
unit at a frequency of at least once each 24 hours of operation (40 CFR 141.728).  At a
minimum, the direct integrity test results that exceed the UCL and result in a membrane unit
being taken offline must be reported (40 CFR 141.728).  The corrective action taken as a result
of the UCL exceedance should also be reported.  Routine direct integrity test results that do not
exceed the UCL are not required to be reported under the LT2ESWTR; however, the state may
require that additional results be reported at its discretion.  The state may require that direct
integrity test results be reported as measured (e.g., the rate of pressure decay rate for the pressure
decay test or the flow of air for a diffusive airflow test) and/or as converted to equivalent LRVs,
as calculating using the methodology described under section 4.5. Note that it is often most
advantageous for a utility to record the actual process value(s) measured (e.g., the rate of
pressure decay) to track the results of the direct integrity test over time.  Additional guidance
regarding data collection and the use of this data for system optimization is provided in
Appendix A in the context of developing a comprehensive integrity verification program.

       A sample summary report form for a hollow-fiber system using the pressure decay test
(the most common type of direct integrity test) is provided in Figure 4.8.  The form includes the
following components:

          •   Facility information, membrane unit no., and date (i.e., month and year)

          •   System parameters and test constants

          •   Test conditions and results

          •   UCL violations

The sample summary report form also contains a column for recording the LRV that is verified
for  each particular daily application of the direct integrity test, as well as for the flow, TMP, and
ALCR parameters that are required to calculate the LRV. Note that these data are not required
for  reporting purposes under the LT2ESWTR, but are included to underscore the utility of these
values for tracking overall unit performance over time.
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         Figure 4.7 Sample Summary Report Form for Pressure Decay Testing
   Month
   Year
   Membrane Unit No.
   Volume of System (Vsys)
   UCL
   Signed
  Utility
  Facility Name
  Test Duration
                                                                              mm
  VCF
  Total No. of UCL Violations
  Dated
Day
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Min
Max
Ave
Pressure
(psi)
Initial


































Final


































AP
(psi/min)


































Within
UCL?


































Corrective Action Taken
(if required)


































Filtrate
Flow
(9pn>)


































TMP
(psi)


































ALCR


































LRV
Verified


































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            5.0  Continuous Indirect  Integrity Monitoring
5.1    Introduction

     As the name suggests, the various indirect integrity monitoring methods are not physical
tests applied specifically to a membrane module or membrane unit, but instead involve
monitoring some aspect of filtrate water quality as a surrogate measure of membrane integrity.
Because the quality of membrane filtrate is very consistent and independent of fluctuations in
feed water turbidity or particle levels, a marked decline in filtrate quality may indicate an
integrity problem. Although indirect integrity monitoring is not as sensitive as direct testing for
detecting integrity breaches, the indirect methods offer some significant benefits that make them
an important and useful tool in  an overall integrity verification strategy.  These benefits include
both the ability to be  operated in a continuous, on-line mode and the non-proprietary nature of
the indirect techniques, such that the same indirect method is similarly applicable to any
membrane filtration system independent of manufacturer, configuration, or other system
parameters.

       Chapter 4 discussed the use of direct integrity testing as a means of verifying the removal
efficiency of a membrane filtration process at a level commensurate with the removal  credit
awarded by the state.  However, while direct integrity tests can be extremely sensitive and thus
can potentially verify high log removal values, most direct test methods require that the
membranes be taken off-line (i.e., out of production mode) to undergo testing. Thus, these direct
tests are limited to periodic application  in order to minimize system down time.  A failed
periodic direct integrity test indicates that an integrity breach occurred at some time between the
most recent direct test in which integrity has been verified and the failed test, but indicates
nothing about integrity over the period between direct test applications. Continuous monitoring
using indirect methods does provide a real-time indication of membrane integrity, albeit with less
sensitivity in most cases.  Consequently, the advantages of the direct and indirect integrity
monitoring approaches are complementary, and both are critical elements of a comprehensive
integrity verification program (IVP). (The development of a comprehensive IVP, including the
complementary value of direct and indirect methods of assessing system integrity, is discussed in
Appendix A.)

       The Long Term 2 Enhanced Surface Water  Treatment Rule (LT2ESWTR) requires
continuous indirect integrity monitoring in the absence of a continuous direct integrity test
method (40 CFR 141.728). Currently, continuous direct integrity monitoring techniques that
meet the performance criteria of the rule are not available, and thus it is anticipated that utilities
employing membrane filtration to comply with the LT2ESWTR requirements will have to
implement both periodic direct integrity testing and continuous indirect integrity monitoring at
the time of rule promulgation. However, the development of a sufficiently sensitive and reliable
continuous direct integrity test is potentially feasible, and implementation of such a test would
preclude the requirement to conduct indirect integrity monitoring, additional state integrity
monitoring requirements notwithstanding.
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       "Continuous" indirect integrity monitoring is defined as monitoring some aspect or
component of filtrate water quality that is indicative of the removal of particulate matter at a
frequency of no less than once every fifteen minutes (40 CFR 141.728).  The LT2ESWTR
specifies turbidity monitoring on the filtrate of each membrane unit as the default methodology
for continuous indirect integrity monitoring, and that two consecutive filtrate turbidity readings
above 0.15 NTU triggers direct integrity testing (40 CFR 141.728).  Turbidity was selected as the
default indirect integrity monitoring technique because it is an accepted monitoring technology
within the water treatment industry, it is used as both a relative and an absolute indicator of water
quality, and it is required for plants employing both conventional and alternative technologies
under both the Surface Water Treatment Rule  (SWTR) and the Interim Enhanced Surface Water
Treatment Rule (IESWTR) (54 FR 27486, 63 FR 69477, and 65 FR 19046).  However, because
several other techniques are generally accepted for indirect integrity monitoring in the water
treatment industry, a number of which are more sensitive than turbidity monitoring, the
LT2ESWTR contains a provision to allow states to approve alternative methods for continuous
indirect integrity monitoring.

       Independent of the method used (i.e., turbidity monitoring or an alternative method
approved by the state), the LT2ESWTR specifies the following requirements for indirect
integrity monitoring:

       1.  The filtrate from each membrane unit of the filtration system must  be monitored
           independently. (The definition of a membrane unit under the LT2ESWTR is
           provided in section 1.5.)

       2.  The filtrate must be monitored continuously from each membrane unit.  For the
           purposes of indirect integrity  monitoring under the LT2ESWTR, continuous
           monitoring is defined as taking measurements at least once every 15 minutes.

       3.  A performance-based control limit must be  established such that readings exceeding
           the control limit for a period of greater than 15 minutes (or two consecutive 15-
           minute readings exceeding the upper control  limit) would trigger direct integrity
           testing.  (The establishment of control limits  is further discussed in the context of
           each indirect integrity monitoring method addressed in Chapter 5. Additional
           information regarding control limits and their role in a comprehensive IVP is
           provided in Appendix A.)

       4.  Utilities must report a summary of all excursions above the established control limit
           that trigger direct integrity testing to the state on a monthly basis.

       Aside from turbidity monitoring,  particle counting may be the most commonly employed
means of indirect integrity monitoring for compliance with the LT2ESWTR. Both of these
techniques are widely used throughout the water treatment industry.  Particle monitoring is
similar to particle counting, although the collected data are presented in a relative manner rather
than as absolute values.  The tracking of particles and turbidity in the filtrate is  based on the
passage of particulate matter through a membrane and is thus appropriate for all types of
membrane filtration systems.  However, other  surrogate  measures of integrity that monitor
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dissolved solids or other miscible water quality parameters such as conductivity may also satisfy
the indirect integrity monitoring requirements of the LT2ESWTR for nanofiltration (NF) and
reverse osmosis (RO) membranes capable of removing these water quality constituents.  Still, it
is important to note that any indirect integrity monitoring method used for the purposes of
LT2ESWTR compliance other than turbidity monitoring must be approved by the state.

       Under the LT2ESWTR, resolution and sensitivity are both defined with respect to their
applicability to direct integrity testing, as described in Chapter 4.  However, unlike the direct
methods, there are no requirements relating to test sensitivity  or resolution with respect to the
indirect integrity monitoring methods under the LT2ESWTR. Nevertheless, these two concepts,
where applicable, may be useful tools for optimizing the ability of an indirect test to yield
meaningful information about potential  integrity breaches. Within the context of continuous
indirect integrity monitoring, resolution and sensitivity may be described as specified in
Chapter 4, although without the references to direct integrity testing, as specified in the rule
language. Thus, resolution may be described as the smallest leak that contributes to a response
to an indirect integrity monitoring method, and sensitivity may be expressed as the maximum log
removal value that can be reliably verified by an indirect integrity monitoring method.
Resolution and sensitivity are discussed in association with each respective indirect integrity
monitoring method addressed in Chapter 5, noting the extent to which each concept  applies to
each method.

       The purpose of Chapter 5 is to describe the most commonly used techniques for indirect
integrity monitoring and discuss their use for compliance with the requirements of the
LT2ESWTR.  Considerations for selecting other indirect integrity monitoring methods are also
addressed.

This chapter is divided into the following  sections:

       Section 5.2:   Turbidity  Monitoring
                     This section discusses the use of turbidity monitoring as the default
                     indirect integrity monitoring technique under the LT2ESWR,  including
                     methods of application, control limits, and advantages and limitations.

       Section 5.3:   Particle Counting and Particle Monitoring
                     This section describes the use of particle counting or particle monitoring
                     as a potential alternative to turbidity monitoring for indirect integrity
                     monitoring, including methods of application, control limits, and
                     advantages and limitations.

       Section 5.4:   Other Indirect Monitoring Surrogates
                     This section discusses some general considerations for selecting an
                     alternative indirect integrity monitoring method not specifically addressed
                     in this guidance.
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       Section 5.5:    Data Analysis and Reporting
                     This section summarizes the reporting requirements for continuous
                     indirect integrity monitoring results and provides guidance on the analysis
                     and interpretation of the results.
       Note that a non-continuous indirect method (e.g., a silt density index (SDI) test) has
limited value for integrity monitoring, offering neither the ability to directly test the membranes
nor the advantage of continuous, on-line monitoring.  As a result, non-continuous indirect
methods do not satisfy the indirect integrity monitoring requirements of the LT2ESWTR and are
not addressed in this chapter
5.2    Turbidity Monitoring

       Conventional turbidimeters (also referred to as "turbidity meters") detect the intensity of
light scattered at one or more angles to an incident beam of light.  The angular distribution of
scattered light depends on a number of conditions, including the wavelength of the incident light,
as well as particle size, shape, and composition. Consequently, it is difficult to correlate the
turbidity with the number or mass concentration of particles in suspension.  However,
turbidimeters are in widespread use throughout the water industry, and the turbidity data
generated by these instruments is broadly recognized as a meaningful gauge of water quality.  As
such, turbidity measurements have been used as an indicator of finished water quality for
previous surface water regulations.

       Under the LT2ESWTR, turbidity monitoring is specified as the default method for
continuous indirect integrity monitoring unless the state approves an alternate approach. Using
the default approach specified in the rule, filtrate turbidity must be monitored on each discrete
membrane unit at a minimum frequency  of once every 15 minutes.  Two consecutive readings
that exceed a control limit of 0.15 NTU for any one unit would require that unit to undergo direct
integrity testing and subsequent diagnostic testing, as necessary. Any such events that trigger
direct integrity testing must be reported to the state on a monthly basis.  Further information
regarding data collection, analysis,  and reporting is provided in section 5.5.

       Because turbidimeters do not yield any information about particulate size,  these
instruments cannot provide any specific indication about the size of an integrity breach through
which turbidity may have passed.  Similar turbidity readings may result  from either significant
particulate material passing through a small breach, or a smaller amount of larger  particulate
matter passing through a larger breach.  As a result, the concept of test method resolution as
defined under the LT2ESWTR is not applicable to turbidity monitoring.  However, the concept
of method sensitivity can apply to turbidity monitoring,  even though there is no formal
sensitivity requirement for continuous indirect integrity  monitoring methods, as fiber cutting
studies may be conducted to correlate a particular reduction in log removal  capability of the
membrane system to approximate increases in filtrate turbidity. The sensitivity of turbidity
monitoring and the use of this technique to detect integrity breaches are  further discussed in the
context of establishing control limits in section 5.2.2.
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       The following sections describe turbidity monitoring methods, approaches for
establishing control limits, and advantages and limitations, respectively.
5.2.1   Methods

       There are two basic types of on-line turbidimeters that may have the capability to provide
continuous indirect integrity monitoring as required under the LT2ESWTR: conventional
turbidimeters and laser turbidimeters. The primary difference between these two types of
instruments lies in the type of light source used.  Conventional turbidimeters typically utilize a
tungsten lamp or other light-emitting diode (LED) as a light source, whereas laser turbidimeters
employ a laser light source.

       Because laser turbidimetry is a relatively new technique, its effectiveness as a monitoring
tool is still being evaluated within the water industry.  However, recent research generally
indicates that laser turbidimeters are more sensitive than conventional turbidimeters and may
perform comparably to particle counters for detecting membrane integrity breaches (Banerjee et
al. 2000; Colvin et al.  2001). Available manufacturer specifications indicate that laser
turbidimeters may have increased sensitivity in excess of two orders of magnitude over
conventional turbidimeters (in terms of measuring turbidity, not necessarily with respect to the
ability of the technique to measure reductions in log removal efficiency resulting from
membrane integrity breaches).  Additional research indicates laser turbidimeters can be
optimized to measure very low turbidities, in the range of 0 to 1  NTU (Banerjee et al.  1999a;
1999b; and 2000).  Since most microfiltration (MF) and ultrafiltration (UF) systems produce
filtrate water consistently in the range of 0.03 to 0.07 NTU as measured by conventional
turbidimeters, laser turbidimeters may be better suited to monitor membrane filtrate.

       Currently, there are four USEPA-approved analytical methods for the measurement of
turbidity (USEPA 1999). These are as follows:

       •   USEPA Method 180.1, Determination of Turbidity by Nephelometry (USEPA 1993)

       •   Standard Method 2130B, Turbidity - Nephelometric Method  (American Public
           Health Association (APHA) 1998)

       •   Great Lakes Instrument Method 2 (GLI 2) (USEPA 1999)

       •   Hach FilterTrak Method 10133
       Systems must utilize turbidimeters that conform to one of these four methods for
compliance monitoring purposes. Additional guidance on the installation, calibration, operation,
and maintenance of on-line turbidimeters is provided in Guidance Manual for Compliance with
the Interim Enhanced Surface Water Treatment Rule: Turbidity Provisions (USEPA-815-R-99-
010, April 1999).
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5.2.2  Control Limits

       A control limit (CL) is defined as a threshold response from an integrity test that triggers
a specific action.  The LT2ESWTR requires CLs to be established for both direct and indirect
integrity testing. In the context of this guidance manual the CLs required under the rule are
referenced as upper control limits (UCLs), signifying that these limits serve as indicators of
minimally acceptable system performance. For direct integrity tests, the UCL corresponds to the
smallest integrity breach that would compromise the log removal credit awarded by the state.
However, for indirect integrity monitoring methods the UCL is simply designed to serve as a
general indication that a system integrity breach may have occurred.

       Unless the state approves an alternate approach (e.g., particle counting, particle
monitoring, or other method), the LT2ESWTR requires continuous  filtrate turbidity monitoring
on each membrane unit with a control limit of 0.15 NTU. Because most membrane filtration
systems consistently produce filtrate well-below 0.15 NTU, a sustained high-turbidity event with
filtrate readings above 0.15 NTU may suggest a potentially serious integrity problem.
Consequently, the LT2ESWTR requires that two consecutive filtrate turbidity readings above
0.15 NTU on any membrane unit trigger direct integrity testing on that unit, as described in
Chapter 4.  (Note that the state may require a more stringent UCL at its discretion.)  If the unit in
question passes the triggered direct integrity test, the unit may continue in production. However,
if the unit fails the direct integrity test, further diagnostic testing and repair of any integrity
breach(es) would be required.  The unit may only be returned to service upon passing a direct
integrity test.

       The LT2ESWTR defines  continuous monitoring as one reading at least every 15 minutes.
The rule is designed to allow  states latitude for interpreting how the continuous indirect
monitoring data collected by a utility would translate into a measurement for the purposes of
reporting and rule compliance. Some potential strategies that states may adopt for data
collection and reporting in interpretation of this requirement are further discussed in both
section 5.5 and  Appendix A. In the absence of any particular state requirements, a utility may
adopt a data interpretation strategy  that is most appropriate for its system.

       While only the UCL is required under the LT2ESWTR, some utilities may choose to
establish a tiered approach to  control limits with one or more lower control limits (LCLs), in
which the level of corrective action increases with each successive CL that is further removed
from normal system performance.  For example, a utility may opt to implement a LCL in which
a filtrate turbidity reading exceeding 0.10 NTU triggers increased monitoring frequency.
Alternatively, with hollow-fiber membrane filtration systems, a utility may choose to conduct
fiber-cutting studies to correlate a quantifiable loss of log removal capability with a certain level
of increased filtrate turbidity.  Research has indicated that turbidity monitoring may be sensitive
to some smaller integrity breaches, although this sensitivity is dependent on the type membrane
system, the number of modules linked to a single instrument, the  number of fibers per module,
the  hydraulic configuration, and other system-specific parameters (Adham et al.  1995). One
study conducted by the Wisconsin Department of Natural Resources demonstrated that for one
system in Kenosha, WI turbidity  monitoring was unable to detect any loss of system integrity
even with a substantial number of cut fibers (Landsness 2001).  Consequently, as this study
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indicates, for some systems turbidity monitoring may not be sufficiently sensitive to allow a
meaningful correlation with integrity loss for the purposes of establishing LCLs.  In general, it is
suggested that a utility work with the state and its membrane manufacturer to establish any
additional CLs and associated corrective actions that may be appropriate for a particular
membrane filtration system.
5.2.3  Advantages and Limitations

       One of the most significant advantages of tracking turbidity as a means of indirect
integrity testing is that system operators throughout the water treatment industry are familiar
with the use of conventional turbidimeters. Because filtrate turbidity monitoring has been
required for media filtration under previous federal regulations for surface water treatment,
conventional turbidimeters are widely used in water treatment plants across the country.

       Many of the other advantages of both conventional and laser turbidimeters are relative to
other continuous indirect integrity monitoring methods.  For example, neither conventional nor
laser turbidimeters are subject to the same accuracy and precision inconsistencies that can be
problematic for particle counters.  While two well-calibrated turbidimeters are likely to yield
similar data for the same water, achieving such consistency from two separate particle counters
may be more difficult. In addition, turbidimeters have the advantages of measuring a parameter
that is absolute (as opposed to a relative measure, as with particle monitors), broad acceptance as
a meaningful gauge of water quality, and application as a water quality benchmark in federal
surface water treatment regulations.

       Conventional turbidimeters are also significantly less expensive than particle counters.
Although laser turbidimeters are typically more expensive than conventional turbidimeters, the
ability to multiplex these instruments may help to minimize the associated cost of utilizing laser
turbidimetry (Banerjee et al. 2001).  In multiplexing, multiple sensors are connected to a single
laser light source,  detector, and control system via fiber optics.  Sensors can be attached to
monitor the filtrate from each membrane unit or individual membrane module, if desired.  At the
time of publication, however, multiplexing laser turbidimetry systems are still under
development and not yet commercially available.

       The most significant limitation of on-line turbidimeters is insensitivity to small  changes
in water quality.  Since membrane systems produce a high quality filtrate, a turbidimeter may be
unable to detect minor changes in filtrate water quality as a result of a small integrity breach.
Laser turbidimeters are more sensitive than conventional turbidimeters, but this sensitivity is still
subject to variation based on the number of modules per sensor, the  system hydraulic
configuration, and other system-specific parameters.

       Turbidimeters are also subject to air entrainment error. Any air bubbles introduced into
the system  either during production, backwashing, chemical cleaning, or integrity testing may be
falsely detected as particulate matter, artificially increasing the turbidity reading. Consequently,
after a backwash cycle or chemical cleaning (particularly if air is utilized in the process),
turbidity measurements may not be representative of filtrate quality until any entrained air is
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purged from the system.  This purge time will vary between different membrane filtration
systems and their respective backwash or chemical cleaning practices. Typically, bubble traps
are employed with turbidimeters (both conventional and laser) to minimize or eliminate this
error.
Advantages of turbidity monitoring include:

       •  Widely used in surface water treatment plants throughout the country

       •  Less expensive instrumentation (conventional turbidimeters)

       •  Consistent, precise measurements

       •  Absolute (as opposed to relative) measure of water quality


Limitations of turbidity monitoring include:

       •  Less sensitive to smaller integrity breaches than particle counters or particle monitors
          (conventional turbidimeters)

       •  Susceptible to air entrainment error


5.3    Particle Counting and Particle Monitoring

       Particle counters use a laser-based light scattering technique to count particles and group
them according to size.  Particle monitors  also operate on the principle of light obstruction;
however, rather than counting particles and grouping them by size, particle monitors measure
particulate water quality on a dimensionless scale relative to an established baseline.

       Although neither particle counting nor particle monitoring are specified under the
LT2ESWTR, either may potentially be approved by a state as an alternative technique for
satisfying the continuous indirect integrity monitoring requirement of the rule. However, any
approved technique must still be utilized in such a way as to satisfy the four basic criteria for
indirect integrity monitoring, as specified  in section5.1. In summary, these criteria are that the
filtrate of each membrane unit must be monitored independently; indirect integrity monitoring on
the filtrate of each membrane unit must be continuous (i.e., at a frequency no less than once
every 15 minutes); two consecutive excursions above a pre-established, performance-based
upper control limit must trigger direct integrity testing; and all excursions above the control limit
that trigger direct integrity testing must be reported to the state on a monthly basis.

       The ability of particle counters to convey information about particle size renders the
concept of resolution (as defined under the LT2ESWTR) applicable to this method of integrity
monitoring.  Although there are no requirements for continuous indirect integrity monitoring

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method resolution (or sensitivity) under the LT2ESWTR, the ability of particle counters to yield
resolution information may help to optimize the usefulness of this technique for detecting
potential integrity breaches. Any significant increase in the number of particles exceeding 3 |j,m
in size may indicate that a breach allowing the passage of Cryptosporidium oocysts may have
occurred.  Any particle counters that are used for the purpose of membrane filtrate monitoring to
satisfy the continuous indirect integrity monitoring requirement of the LT2ESWTR should be
well calibrated to detect particles in the size range of Cryptosporidium oocysts (i.e., 3 to 8 |j,m).
Conversely, because particle monitoring instruments do not measure particulate size, there is no
specific resolution associated with the particle monitoring technique.

       As with turbidity monitoring, the concept of test method sensitivity (as defined under the
LT2ESWTR) applies to both particle counting and particle monitoring in that fiber cutting
studies may be conducted to correlate  a particular reduction in log removal capability to
increases in the quantity of particles in the filtrate.  Although Adham et al. (1995) determined
that particle counting was the most sensitive of the three common methods of continuous indirect
integrity monitoring  (i.e., conventional turbidity monitoring, particle counting, and particle
monitoring), particle counting instruments have a number of well-established operational
problems that  can potentially distort both the accuracy and precision of their measurements.
Particle monitoring devices, which are more sensitive then conventional turbidimeters but less
sensitive than particle counters, share many of the same limitations of particle counters (Adham
et al. 1995). The advantages and limitations of both particle counters and particle monitors are
discussed in sections.3.3. The sensitivity of particle counting and particle monitoring methods
for the detection of integrity breaches is further discussed in section 5.3.2 in the context of
establishing control  limits for these indirect integrity monitoring techniques.
5.3.1  Methods

       USEPA does not currently approve particle counting and particle monitoring as
compliance monitoring methods. However, either of these methods may be used for compliance
with the continuous indirect integrity monitoring requirements of the LT2ESWTR if approval is
granted by the state.  Both the International Organization for Standardization (ISO) and the
American Society for Testing and Materials (ASTM) have published standards relating to
particle counting techniques,  as follows:

       •  ISO 11943 - Hydraulic fluid power - On-line automatic particle counting systems for
          liquids - Methods of calibration and validation (1999)

       •  ASTM F658-OOa - Standard Practice for Calibration of a Liquid-Borne Particle
          Counter Using an  Optical System Based Upon Light Extinction (2000)
       In addition, there are some relevant references on the use of particle counters in water
treatment applications that may serve as a useful source  of additional information:
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          Particle Count Method Development for Concentration Standards and Sample
          Stabilization.  American Water Works Association Research Foundation
          (AWWARF) 2000.

          Fundamentals of Drinking Water Particle Counting. AWWARF 2000.
       Currently there are no standards for particle monitoring, and little information has been
published regarding the use of particle monitors in potable water treatment applications.
5.3.2  Control Limits

       As discussed in section 5.2.2 (and throughout Chapter 4), a CL is a response to an
integrity test that results in some measure of corrective action. UCLs refer to the required limits
mandated under the LT2ESWTR, while LCLs are voluntary or additional state-mandated limits.
In the context of continuous indirect integrity monitoring, the UCL is a response to the results of
an indirect integrity method that triggers  direct integrity testing. The UCL for the default method
of turbidity monitoring is defined in the LT2ESWTR; however, the rule does not establish
control limits for other continuous indirect integrity monitoring methods (e.g., particle counting
or particle monitoring).

       Because particle count and particle monitoring data can vary significantly between two
different instruments, even between adjacent membrane units applied to the same source water
and within the same filtration system, site-specific CLs must be established when particle
counting or particle monitoring is used as an alternative method of continuous indirect integrity
monitoring.  Moreover, it is recommended for these two techniques that CLs be developed on a
membrane-unit-specific basis.  One such approach that has been used by the Texas Commission
on Environmental Quality (TCEQ) is establishing a CL for particle counting at the 95-percent
confidence interval for all the data collected by a particular instrument monitoring the filtrate of
a particular membrane unit over the previous month. However, because the particle counts could
slowly increase over time without exceeding the 95-percent confidence interval (either as a result
of slow membrane degradation or the instrument slipping out of calibration), this approach also
incorporates an additional, higher control limit that is absolute (i.e., at a fixed number of particles
per unit volume) (Schulze 2001). The magnitude of this UCL would be sufficient to indicate a
probable membrane integrity breach independent of variations in particle count readings between
different instruments.  Note that if the 95-percent  confidence interval of the data collected over
the previous month is used to establish a new CL  on an ongoing basis, it is important to exclude
any data corresponding to a known integrity breach. Otherwise, a small amount of abnormally
elevated data that are not indicative of typical membrane unit performance could  skew the CL
for the following month to an unacceptably high level, thereby diminishing the ability to detect
small integrity breaches.

       Absolute CLs may also be used without a  lower, relative CL (e.g., the 95-percent
confidence interval of the previous month's data)  provided the absolute CLs  are  sufficiently
conservative and established using  a scientific methodology that is approved by the state. For
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example, studies may be conducted prior to placing the membrane filtration system into service
in order to establish baseline particle count or particle monitoring data levels for each membrane
unit. Building on the example of the framework developed by the TCEQ, the 95-percent
confidence interval of this fixed data set could then represent an absolute CL. Although this
method (and other membrane-unit-specific methods) may result in different CLs for each
membrane unit, if studies indicate that baseline filtrate particle  count or particle monitoring data
are  similar among all the units (such that the control limits would also be similar), the most
conservative (i.e., lowest) CL may be applied to all the units. One advantage of using a
statistical method such as the 95-percent confidence interval for setting CLs is that it minimizes
the  possibility that normal fluctuations and noise in the data that are unrelated to an integrity
problem will exceed the control limit, triggering additional testing and resulting in lost unit
productivity.

       For hollow-fiber membrane filtration systems, fiber cutting studies may also be used to
establish control limits for particle counting or particle monitoring by correlating quantifiable
losses of log removal capability to specific increases in the number of particles in the 3 to 8 |j,m
size range. However, while Adham et al. (1995) demonstrated that particle counting and particle
monitoring were both more sensitive than turbidity monitoring  (and that particle counting was
more sensitive than particle monitoring) for detecting integrity breaches, a study conducted by
Landsness (2001) indicated that both particle counting and turbidity monitoring may be unable to
reliably detect an integrity breach of fewer than the equivalent of several hundred fibers in a
membrane unit.  As with turbidity monitoring, however, the sensitivity of both particle counters
and particle monitors is dependent on the type of membrane system, the number of modules
linked to a single instrument, the number of fibers per module,  the hydraulic configuration, and
other system-specific parameters.

       For particle counting, particle monitoring, or any approved method of continuous indirect
integrity monitoring, one reading must be taken  on the filtrate of each membrane unit at least
every 15  minutes. If the readings exceed the UCL for a period  of fifteen minutes (or, in the case
that readings are taken only at 15 minute intervals, if two consecutive 15 minute readings exceed
the  UCL), then direct integrity testing is required (40 CFR 141.728). Any membrane unit taken
off-line for further integrity testing (i.e., direct and potentially diagnostic testing) may be
returned to service upon passing a direct integrity test.  All excursions beyond the UCL that
trigger direct integrity testing must be reported to the state on a monthly basis (40 CFR 141.728).
Also, although not required under the LT2ESWTR, utilities may also voluntarily choose to
establish one or more LCLs that would trigger increased data collection frequency or require an
operator to monitor the membrane performance for a specified period of time.  Data analysis and
reporting for continuous indirect integrity monitoring are further discussed in section 5.5, and
guidance for the development of a comprehensive integrity verification program is provided in
Appendix A.
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5.3.3  Advantages and Limitations

       The primary advantage associated with particle counters and particle monitors is the
sensitivity of the instruments relative to conventional turbidimeters.  Both have been shown to be
more sensitive to breaches in membrane integrity than conventional turbidimeters, with particle
counters being the most sensitive of the three instruments (Adham et al. 1995; Jacangelo et al.
1997).

       However, particle counters and particle monitors have a number of well-known potential
operational problems that may distort the accuracy and precision of their measurements. First,
two separate but otherwise identical particle counters or particle monitors applied to the filtrate
of the same membrane unit may yield different responses, the magnitude of which may be
particularly significant at the very low particle concentrations that are typical of membrane
filtrate quality.  This inconsistency could potentially make it necessary to establish CLs on  a
membrane-unit-specific basis, since the magnitude of a particle count or particle monitor reading
that may begin to suggest a small integrity breach may not be the same for two different
instruments applied to the  filtrate of different membrane units. In addition, once baseline filtrate
data are established for each membrane unit, this inconsistency could complicate changing
instruments, if necessary, since new baseline data may need to be generated.  The impact of this
potential problem may not be significant, however, if the relative differences between
instruments are negligible  in comparison to the differences between the baseline filtrate quality
and that associated with an integrity breach of sufficient magnitude to exceed the CL.

       The variation between the readings of different instruments at low particle concentrations
may be particularly problematic for using particle counters to verify log removal capabilities in
association with challenge testing or a particulate-based direct integrity test.  For example, the
difference between 1.0 particles/mL and 0.1  particles/mL, which is within the range of observed
variance for different particle counters at very low particulate concentrations, translates into a
1 log discrepancy in terms of removal capability.  This variation must be considered when using
particle counters to verify log removals.  Considerations and guidance for challenge testing are
addressed in Chapter 3, and particulate-based direct integrity tests are discussed in section4.7.5.

       Another disadvantage associated with particle counters and particle monitors is the
potential for air entrainment to cause the instruments to overestimate filtrate particle
concentrations. For example, in hollow-fiber membrane filtration systems, a significant amount
of air may be introduced into the piping during the backwash process, particularly if the process
utilizes air for scouring or pulsing the membranes.  Any air bubbles remaining in the system after
the backwash cycle is complete and the unit is returned to production may be falsely detected as
particles.  Thus, anomalous particle concentration spikes that may indicate an integrity problem
could be masked until the air is purged from the system. As a result, the effective use of particle
counters and particle monitors as an integrity monitoring tool  is somewhat diminished after
backwashing until  the air is expelled and the particle concentrations return to baseline levels.
The time required for this air purge varies with the particular membrane system and the
backwash operating parameters.  As with turbidimeters, bubble traps can be used in some cases
to minimize or eliminate this potential source of error.
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       Particle counters and particle monitors are also susceptible to coincidence error and
sensor clogging, both of which can cause particle concentrations to be underestimated.
However, this may not represent a significant problem for these instruments when applied to
monitor membrane filtrate. Because membrane filtrate consistently has a very low concentration
of particulate matter, even under compromised conditions, coincidence or clogging errors are
much less likely with membrane filtration systems than for most other potable water treatment
applications.
Advantages of particle counting and particle monitoring are generally similar, and include the
following:

       •  More sensitive to smaller integrity breaches than conventional turbidimeters

       •  Widely used in surface water treatment plants (particle counters)

       •  Absolute (as opposed to relative) measure of water quality (particle counters)

       •  Ability to yield information regarding test resolution (particle counters)


Limitations of particle counting and particle monitoring include:

       •  Imprecision between instruments at low particulate concentrations

       •  Susceptible to air entrainment error

       •  Susceptible to coincidence and clogging error at higher particle concentrations

       •  More expensive instrumentation (particle counters)

       •  Relative measure of water  quality (particle monitors)

       •  More operation and maintenance support


5.4    Other Indirect Monitoring  Methods

       In addition to the three methods of continuous indirect integrity monitoring described in
this chapter - turbidity monitoring, particle counting, and particle monitoring - other methods
may also be used.  Note that turbidity  monitoring is the only method specified under the
LT2ESWTR for compliance with the rule, although other methods (including both particle
counting and particle monitoring) may be used with state approval. All three of the methods
described in this chapter relate to monitoring particulate matter in the filtrate, as these methods
are applicable  to all types  of membrane filtration systems - MF/UF, NF/RO,  and membrane
cartridge filtration (MCF). However, because NF/RO processes also remove dissolved

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constituents, methods that monitor these constituents in the filtrate have the potential to be used
for continuous indirect integrity monitoring with NF/RO systems.

       An example of one potential method that could be used for continuous indirect integrity
monitoring with NF/RO systems is conductivity monitoring.  Because monitoring filtrate (i.e.,
permeate) conductivity is routinely used as a means of assessing semi-permeable membrane
performance, it may be advantageous for utilities using NF/RO systems for compliance with the
LT2ESWTRto employ this technique for continuous indirect integrity monitoring, if approved
by the state. However, there are some limitations with conductivity monitoring that are also
applicable to other indirect methods that monitor dissolved constituents. First, increased salt
passage over time may be a function of either an uncontrolled increase in membrane
permeability or a planned increase in system recovery or flow, parameters  unrelated to the
physical integrity of the membranes and their ability to serve as a barrier to particulate matter
such as Cryptosporidium. Although increases in membrane permeability that do not represent
integrity breaches can manifest over longer periods of time and may not occur over the 15-
minute intervals at which continuous indirect integrity  monitoring must be conducted, this is a
consideration that should be taken into account by utilities. In addition, filtrate conductivity (and
other dissolved constituents) may vary with water quality parameters such  as pH and
temperature, factors that are likewise unrelated to membrane integrity.  While fluctuations in
conductivity with these factors may potentially be minimal relative to those that might occur as a
result of an integrity breach, it is nevertheless important that a NF/RO system be operated under
consistent water quality and operational conditions for conductivity to yield reliable and
meaningful results relative to membrane integrity.

       Whether using a technique that measures particulate matter or dissolved constituents,
there are several general criteria that should be considered when selecting an alternative method
for continuous indirect integrity monitoring:

       •  The monitoring technique should be approved for use by the state.

       •  For systems that apply membrane filtration specifically for compliance with the
          LT2ESWTR, the technique must be approved by the  state specifically for  compliance
          with the rule.

       •  The monitored parameter must be able  to be measure on-line.
          (i.e., while the membrane unit is in production)

       •  The parameter must be able to be monitored continuously.
          (i.e., at  a frequency of at least one measurement every 15 minutes for the purposes of
          compliance with the  LT2ESWTR)

       •  The parameter must be monitored on the filtrate of each  membrane unit.

       •  A significant change in the levels of the parameter should generally be indicative of
          an integrity breach.
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          The instrumentation used to measure the parameter should be sufficiently sensitive
          such that relatively small integrity breaches can be detected, thus enabling the
          establishment of a meaningful UCL. (Note that there are no specific sensitivity
          requirements for continuous indirect integrity monitoring under the LT2ESWTR.)
5.5    Data Collection And Reporting

       The LT2ESWTR requires utilities both to record a continuous indirect integrity
monitoring reading for each membrane unit at least once every 15 minutes and to report any
sequence of two consecutive excursions above the upper control limit (which would trigger
direct integrity testing) to the state on a monthly basis (40 CFR 141.728). Within this regulatory
framework, utilities and/or states have some latitude with respect to the specifics of how
continuous indirect integrity monitoring data are collected and reported. For example, provided
the basic requirements specified in the rule are satisfied, compliance strategies may vary in
regard to the following:

       •  Frequency of data collection

       •  Method of data reduction

       •  Monitoring location
       Some utilities may desire to collect data more frequently than once every 15 minutes,
particularly since most of the instruments associated with the various methods of continuous
indirect integrity monitoring are capable of recording data at much shorter intervals.  Even if a
utility is not required by the state to report data any more frequently than at 15-minute intervals,
the additional data may be useful for monitoring system performance with greater precision,
identifying trends and patterns, and ultimately optimizing system operation.  If a utility chooses
to measure and record indirect integrity monitoring data at a frequency greater than every
15 minutes (or is required to do so by the state), the state may require that data collected at
intervals shorter than 15 minutes be compared to the UCL for purposes of potentially triggering
direct integrity testing and compliance reporting.

       If a utility does opt to collect continuous indirect integrity monitoring data more
frequently than every 15 minutes, the LT2ESWTR allows some flexibility regarding how the
collected data are utilized for compliance purposes. For example, if a utility records one
turbidity reading each minute, there are several methods in which the data collected over a 15-
minute period may be reduced.  One option would be to average the data to yield a single
statistic that is representative  of the performance of each membrane unit for a given 15-minute
interval. Two consecutive 15-minute averages exceeding the UCL would trigger direct integrity
testing and subsequent notification of the state in the next monthly report. Another option for
this example would be to make the maximum value of the 15  measurements the representative
statistic. Likewise, any two consecutive 15-minute intervals with maximum values exceeding
the UCL would trigger direct integrity testing and require the  excursion to be reported.


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Alternatively, independent of how often data are collected, a utility may opt to use only the
reading recorded at the 15-minute mark for comparison with the UCL. Note that while the rule
allows for some flexibility for data collection and reduction, the state may require a specific
methodology at its discretion.

       The critical interval of 15 minutes cited in the LT2ESWTR may also be shortened at the
discretion of the utility if a more conservative approach to monitoring membrane integrity is
desired. For example, a utility that records a particle count measurement once every five
minutes may configure its system to trigger direct integrity testing if any two consecutive 5
minute readings exceed the UCL. A more conservative approach to the location of indirect
integrity monitoring may be adopted, as well, if desired. Although monitoring is required for the
filtrate of every membrane unit, additional monitoring may be conducted on one or more
individual membrane modules, pressure vessels, or stages within a membrane unit.  Monitoring
smaller incremental membrane process units, where applicable and cost-effective, may help to
isolate any integrity breaches that are detected and provide additional data for process
optimization and control.

       The LT2ESWTR does not require utilities to report all excursions above the UCL, but
rather only those sequences of two consecutive UCL excursions that would  trigger direct
integrity testing. While single excursions may be anomalous measurements and not be indicative
of an integrity breach, two consecutive measurements exceeding the UCL represent more
sustained evidence of an integrity problem that warrants further testing and  subsequent reporting.
In conjunction with these exceedances, the rule also requires a corresponding summary of any
corrective action taken in each case, including direct integrity testing  and subsequent measures
(40 CFR 141.728). The ongoing record of these responses over time  should also help the utility
identify and streamline any appropriate future corrective action that may be  necessary. Note that
the state may require more detailed reporting at its discretion.

       In general, the LT2ESWTR allows for some flexibility in compliance strategy with
respect to continuous indirect integrity monitoring data collection and reporting to accommodate
site-specific considerations, provided the basic requirements of both the rule and those of the
state are satisfied.  Additional guidance for data collection and analysis strategies, as well as for
using this data for system optimization, is provided in Appendix A in the context of developing a
comprehensive integrity verification program.
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                                 6.0  Pilot Testing
6.1    Introduction
       Pilot testing a membrane filtration process is often conducted as part of the design effort
for a membrane treatment facility.  The purpose of this chapter is to describe the considerations
that are associated with pilot testing.  It should be noted that the Long Term 2 Enhanced Surface
Water Treatment Rule (LT2ESWTR) does not contain any requirements for pilot testing
membrane filtration systems; thus, this chapter is simply intended to provide general guidance in
terms of widely recognized industry practices. However, any particular state requirements would
supersede the guidance provided in this chapter.   This chapter is not intended to serve as a
comprehensive guide, but rather to highlight some of the important benefits and considerations
associated with pilot testing.

       Pilot testing should not be confused with challenge testing. Challenge testing, as
described in Chapter 3, is typically conducted on a product-specific basis and characterizes a
membrane filtration module in terms of removal efficiency. Pilot testing, by contrast, is
conducted on a site- and system-specific basis and is used to collect information for full-scale
facility design.  Pilot testing need not include challenge testing unless specifically required by
the state.  In cases in which a particular membrane product that has not undergone challenge
testing is proposed for compliance with LT2ESWTR requirements, it may be convenient to
include a challenge test in the scope of pilot testing.

       The primary goal of a membrane pilot study  is to obtain information such as treated water
quality (e.g., turbidity) and operating parameters (e.g., flux) that are necessary for the design of a
membrane filtration facility. The treated water quality data provides assurance that the treatment
objectives can be achieved, while the pre-determination of operating parameters allows for
proper sizing of the membrane facility and minimizes the uncertainties regarding footprint and
utility requirements.  In general, the use of pilot data helps account for unforeseen conditions that
may otherwise have gone undetected. Pilot testing also helps to familiarize operators with the
membrane treatment equipment.

This chapter is divided into the following sections:

       Section 6.2:   Planning
                    This  section discusses important considerations that should be taken into
                    account before conducting a pilot test.

       Section 6.3:  Testing Objectives
                    This  section provides an overview of testing objectives such as the
                    optimization of membrane flux, backwashing, and chemical cleaning, as
                    well as balancing the flux with backwashing and chemical cleaning
                    frequencies to maximize operational efficiency.
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                                    Chapter 6 - Pilot Testing
       Section 6.4:   Testing and Monitoring
                     This section discusses important data that are typically collected during
                     pilot testing, including operational, water quality, microbial, and integrity
                     testing parameters.

       Section 6.5:   Report Development
                     This section outlines considerations for preparing a summary report after
                     the pilot testing is completed.
       Most of the information contained in this chapter is generally applicable to both
microfiltration (MF)/ultrafiltration (UF) and nanofiltration (NF)/reverse osmosis (RO) systems.
Distinctions between the two systems are noted where differences occur.  Pilot testing for
membrane cartridge filtration (MCF) systems is typically simpler relative to testing other types
of membrane filtration and is often performed simply to verify the replacement frequency and
productivity for the filters.  Consequently, pilot testing MCF systems is not specifically
addressed in this chapter.  However, MCF piloting guidelines are generally similar to those for
MF/UF with the exception of references to cleaning intervals, since membrane cartridges are not
typically cleaned and instead disposed of when fouled.
6.2    Planning

       The planning phase prior to implementing pilot testing is an important component of an
overall pilot test program. Careful planning helps ensure that all the pilot test objectives are
achieved both efficiently and economically without unexpected  delays. The most important
element of the planning process is the development of a comprehensive pilot test protocol
specifying how the testing should be conducted.  This protocol should include not only
instructions for carrying out the testing, but also specific testing objectives and strategies for
optimizing performance in terms of flux, backwashing, and chemical cleaning (see  section 6.3).
A plan for collecting water quality, integrity test, and microbial  (where applicable)  data should
also be incorporated in the test protocol (see section 6.4). In addition, it is recommended that the
pilot protocol be developed in conjunction with the state to ensure that any particular state
requirements are satisfied.

       In addition to the test protocol, a number of other planning considerations should be
taken into account.  For example, it should be determined whether the pilot test units can be
provided by the membrane manufacturers at no cost, rented or custom-fabricated, as budget
constraints allow.  Also, once the particular membrane  filtration systems to be tested are
selected, the utility requirements (i.e., water, electricity, and/or air) for the pilot units must be
accommodated at the test site. Appropriately sized plumbing connections should be provided for
the feed, filtrate, and concentrate streams, and provisions must be made for the disposal of
backwash (for MF/UF)  and chemical cleaning residuals.  Labor requirements for operating the
pilot units should be estimated, and it is also important to ensure that the designated testing site
has sufficient area to accommodate all the units to be tested.  One consideration that is
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                                   Chapter 6 - Pilot Testing
sometimes overlooked is shipping the pilot units; the proper equipment for loading and
unloading the pilot units must be available at the testing site or be provided with the unit(s).

       Special attention in the planning phase should be given to process considerations such as
scalability, screening appropriate membrane filtration systems to test, and test scheduling. These
three aspects of pilot test planning are discussed in sections 6.2.1, 6.2.2, and 6.2.3, respectively.
6.2.1  Process Considerations

       It is important that the pilot process be representative of the full-scale system. For
example, if pretreatment is part of the planned full-scale process, then the pilot process should
incorporate similar pretreatment. Likewise, piloting should also accommodate production (e.g.,
filtration) and intermittent (e.g., backwashing) design considerations to the extent that these
parameters have been defined prior to the pilot testing phase. Thus, if it has been determined
that the membrane filtration system(s) that will be used at full-scale (e.g., if an MF/UF system
has been pre-selected) requires air at a specified flow rate and duration during a backwash
process, then the pilot system should be designed and operated in a similar manner.  The design
of the membrane system should also mimic the hydraulic configuration of the full-scale system,
as described in section 2.4.  However, it should be recognized that it might not be possible to
design a pilot system using the same hydraulic configuration used at full scale for all membrane
processes. For example, it may not be economically feasible to design a NF/RO pilot unit with
hydraulic characteristics identical to the full-scale system.  In this case, the methodology of
conversion from pilot-scale data to full-scale design should be included in the development of
the pilot test protocol.

       Membrane modules should also be scaleable with respect to appropriate operational
characteristics.  Section 3.8 includes a discussion pertaining to the use of a small-scale
membrane module, which may be appropriate under some circumstances. Although the
discussion in section 3.8 is presented in the context of challenge testing, the concepts are also
applicable to piloting, and small-scale module testing may be viable for pilot testing depending
on the objectives of the study
6.2.2  Screening and System Selection

       Spiral-wound NF and RO membrane modules are standardized such that the membranes
from different manufacturers are interchangeable and system design is somewhat uniform. Thus,
in terms of screening for appropriates membranes, the primary consideration involves the
selection of a membrane material that provides desirable productivity, resistance to fouling, and
removal characteristics.

       Screening is somewhat more complex for MF/UF systems, which are largely proprietary
in design. The various commercially available systems may use either pressure or vacuum as the
driving force and can be designed to filter from the inside-out or outside-in direction relative to
the fiber lumen.  In addition, the various membrane materials have differences that may be
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                                   Chapter 6 - Pilot Testing
important, including removal efficiency and pH and oxidant tolerance. Membranes of different
materials also have varying degrees of compatibility with water treatment chemicals such as
coagulants and powdered activated carbon (PAC) that may affect performance and cost.  It is
important to consider such differences in MF/UF membranes and membrane systems and how
these may impact system selection.  For example, if the source water were periodically
prechlorinated, a membrane that is not compatible with chlorine would be undesirable.

       A list of some questions to consider when screening membranes for a pilot study  is
provided below:

       •  What are the treatment objectives of the application?

       •  What operational constraints/goals are to be considered in membrane selection?

       •  Has the membrane been used on similar waters at other sites?

       •  What are the pH and oxidant tolerances of the membrane? Are these compatible with
          the application?

       •  Is the membrane compatible with any pretreatment chemicals aside from oxidants
          that may be in use, such as alum, ferric chloride, PAC, and polymers?

       •  Is this membrane compatible with solids and total organic carbon (TOC) levels in the
          raw water?

       •  Does  the membrane have prior applicable state regulatory approval and any required
          certifications (e.g., NSF 61)?

       •  Does  the supplier have experience with full-scale operation for a facility of this size
          and for treating similar water with the same configuration to be used in the pilot?

       •  Does  the system require proprietary items such as spare parts or cleaning chemicals?

       •  Are there any unusual operational considerations associated with the membrane
          filtration system, such as  significant power requirements, frequent membrane
          replacement, or substantial or undesirable chemical use?

These types of questions should be considered as a part of the screening process before selecting
any membrane filtration systems to pilot. An additional consideration for MF/UF systems is that
because these systems are proprietary, the membrane modules vary in design and are not
presently interchangeable.  Thus, a utility is limited to obtaining replacement membranes from
only one supplier after a system has been installed.

       In some cases,  screening tools for MF/UF membranes may be limited to experience at
other sites or chemical incompatibility.  Therefore, pilot testing is an important consideration.
For NF/RO, proprietary software programs that are available from the various membrane

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                                   Chapter 6 - Pilot Testing
manufacturers can predict membrane system removal performance with a fairly good degree of
accuracy for a particular membrane product.  Small-scale module testing (see section 3.8) may
be an option for screening some MF/UF membranes. Similarly, NF/RO membranes could be
screened for some parameters using flat-sheet studies or single element tests.
6.2.3  Scheduling

       Scheduling is another important aspect of pilot test planning.  One factor to consider
when scheduling a pilot test for surface waters is seasonal variations in water quality, since
turbidity, temperature, algae content, taste and odor, and other parameters can potentially vary
significantly throughout the year.  A description of typical seasonal variation in surface water
quality is summarized below. Note that not all of the seasonal variations described will be
applicable for every site, or necessarily pertinent for all types of membrane filtration systems.

       Summer- Because user demand is typically highest in the summer, the filtration system
       may also have to produce more water during this season. However, greater production is
       facilitated by warmer water temperature.  The  degree to which a membrane process is
       affected by a change in water temperature is related to the viscosity of the water.  Since
       the viscosity of the water is lower at higher temperatures, the membrane flux will likely
       be at its peak in this season. (The relationship between water temperature and viscosity
       as it relates to flux is discussed in further detail in Chapter 7.) Warmer water also
       facilitates enhanced algae growth that may be  problematic for membrane system
       operation.  Taste and odor events may also manifest during the summer months.

       Autumn -  In areas with hardwood cover in the watershed, autumn months typically
       bring  an increase in the organic content of surface water resulting from the decay of
       fallen leaves. Turbidity may sharply increase, as well.  Furthermore, cooler air
       temperatures and wind cause surface waters in reservoirs to "turnover," bringing deeper,
       more  anaerobic water to the surface  and thus creating the potential for both taste and odor
       and iron and manganese problems.

       Winter- Although winter months yield the coldest water temperatures and thus typically
       the lowest membrane fluxes, the demand for water is typically at its lowest, as well.  Both
       the cold temperature and decrease in demand are likely to minimize required membrane
       flux in this  season.   (As previously noted, the relationship between water temperature and
       viscosity as it relates to flux is  discussed  in Chapter 7.) Most membrane manufacturers
       have membrane-specific temperature compensation  factors for cold-water operations.

       Spring - Spring months usually yield increases in water temperature, as well as in the
       potential for turbidity spikes related  to run-off caused from snow melt. There is also
       potential for springtime turnover of a reservoir, resulting in subsequent degradation in
       feed water quality.
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                                   Chapter 6 - Pilot Testing
       Ideally, the pilot study should be conducted during the time of year yielding the most
difficult water quality to treat, so that design parameters resulting from the study, such as flux
and chemical cleaning frequency, would be conservative for year round operation. Some water
quality effects can be accurately modeled, such as that of temperature on productivity. Multi-
season piloting is advantageous if scheduling and cost constraints will allow. In fact,  some states
require multi-season  piloting for membrane treatment facilities.

       The duration  of the pilot study is also an important scheduling consideration. In general,
piloting through at least three cleaning cycles is recommended  practice. The target cleaning
frequency for hollow-fiber MF/UF systems is typically at least 30 days of continuous  operation.
Through the first cleaning cycle the membrane flux and backwash frequency are usually targeted
to provide for 30 days of operation before cleaning is required. The second cycle provides an
opportunity for optimization and  operational improvement. The third cycle establishes
repeatability if the operating conditions remain the same. Note that because new membranes
typically perform better than membranes that have been previously fouled and subsequently
cleaned, it may be beneficial to add an extra cycle; to study the effects of repeated fouling and
cleaning on membrane performance.  Because this strategy represents three operational cycles of
at least 30 days, a pilot test duration of 90 days  (or 3 months) is recommended, if possible.  For
spiral-wound NF/RO membrane systems, longer cleaning intervals are desirable, which  results in
fewer operational cycles than for a MF/UF pilot of similar duration.

       For more thorough MF/UF pilot studies, approximately 4 to 7 months (3,000 to 5,000
hours) of cumulative operational  time is usually recommended. A longer pilot study may be
appropriate for newer, less proven membrane filtration systems or for applications in which the
water quality is extremely variable.  NF/RO pilot  studies generally  range from about 2 to 7
months (1,500 to 5,000 hours)  of cumulative operational time,  with longer studies used for
waters of variable quality. The state may also have minimum requirements for the duration of
pilot studies.
6.3    Testing Objectives

       Membrane flux and system productivity are typically the most important design
parameters to optimize, as these dictate the number of membranes (and hence a large portion of
the capital cost) required for the full- scale plant. Because these two parameters are inversely
related to a certain extent, the pilot testing process may help to establish the optimum balance.
For example, typically operating at higher fluxes increases the rate of fouling, in turn requiring
more frequent backwashing and chemical cleaning. However, the system productivity is limited
by the backwashing (where applicable) and chemical cleaning frequency. Backwashing and
chemical cleaning not only use filtrate as process water (thus affecting the productivity), but also
represents time during which filtrate cannot be produced (thus affecting overall system
productivity). The effect of more frequent backwashes and chemical cleanings on the system
productivity may be an important consideration if the source water is limited, or alternatively if
waste disposal is problematic.  In addition, chemical cleaning may be a labor-intensive operation
that requires the handling of harsh chemicals and produces a waste stream that may be difficult
to dispose. However, chemical cleaning is a necessary process associated with membrane
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                                   Chapter 6 - Pilot Testing
filtration, and establishing operating practices that extend the time between cleanings is one
objective of a membrane pilot study.

       This section provides guidelines for balancing flux, productivity, backwash frequency
(where applicable), and chemical cleaning intervals during pilot testing.  It is important to note
that in order for cause and effect to be analyzed properly, only one process variable should be
changed at a time during the pilot study.  Economic and time constraints often dictate the
duration of the pilot study and may not allow complete optimization of each of these parameters.
Therefore, it is important to understand which of these parameters is most important for a
particular application of membrane filtration and to structure the pilot test protocol accordingly.
Thus, the result of a pilot study is not necessarily the "optimum" design, but rather a set of
operational conditions that will result in feasible and economic water treatment over the
anticipated range of operating and source water conditions.
6.3.1  Membrane Flux Optimization

       Membrane manufacturers can recommend fluxes for particular applications and a given
water quality.  Table 6.1 lists some of the important water quality data that should be provided to
membrane suppliers to facilitate a fairly accurate initial estimation of anticipated membrane
productivity.

       If scheduling permits, it is typically advantageous to begin piloting MF/UF systems at a
conservative flux and then increase it based upon the rate of fouling observed.  The flux may be
increased either after a chemical cleaning or during a filter run if the pilot unit has undergone
sustained operation with only a nominal increase in fouling. In subsequent filter runs (i.e.,
between  chemical cleanings) the pilot unit flux may be either increased if the fouling rate of the
previous run was still within acceptable tolerances or decreased if the fouling occurred at an
unacceptably high rate. Note that the backwash frequency may also be adjusted either during a
filter run or between filter runs to minimize fouling at a particular flux (see section 6.3.2). This
fine-tuning process of adjusting the flux and/or backwashing interval (if possible, only one
parameter should be adjusted at a time) between filter runs may be repeated to the extent that
budget and scheduling constraints allow, or to the point at which such adjustments reach the
point of diminishing returns. NF/RO performance can typically be accurately gauged by the
manufacturers based on water quality models, although it is often beneficial to adjust the flux
over a series of filter runs to optimize productivity based on pilot test results. (Note, however,
that manufacturers' models do  not predict fouling.) The pilot test protocol should include the
expected range of membrane fluxes and guidelines on how these fluxes should be adjusted based
upon the results of early testing.  Models may also indicate chemical pretreatment requirements
necessary to control scaling on NF/RO  membranes and thus to help maintain acceptable fluxes.
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                                  Chapter 6 - Pilot Testing
          Table 6.1 Water Quality Parameters to Measure Prior to Piloting
Parameter
MF/UF
NF/RO
Cations
Aluminum
Ammonia
Barium
Calcium
Iron
Magnesium
Manganese
Potassium
Sodium
Strontium



X
X
X
X



X
X
X
X
X
X
X
X
X
X
Anions
Chloride
Fluoride
Nitrate
Silica
Sulfate



X

X
X
X
X
X
Other Chemical / Physical Parameters
Algae
Alkalinity
pH
SDI
IDS
TOC
TSS
Turbidity
UV-254
X

X


X
X
X
X

X
X
X
X
X

X
X
6.3.2  Backwash Optimization

       Backwashing is a periodic reverse flow process used with many hollow-fiber MF/UF
systems to remove accumulated contaminants from the membrane surface, thus maintaining
sufficient flux and minimizing the rate of long-term, irreversible fouling.  A MF/UF membrane
manufacturer can provide information on the backwash protocol required for its system, as well
as a recommended backwash frequency.  It is important to understand the following issues
regarding the backwash process, which are applicable to both piloting and full-scale operation:

       •  Large water and/or air flows over short periods of time may be included as a part of
          the backwash  process.  The flows of air and water vary depending on the system
          manufacturer.
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                                   Chapter 6 - Pilot Testing
       •  Backwash effluent water contains approximately 10 to 20 times the concentration of
          the feed contaminants.

       •  Many manufacturers add free chlorine to the backwash process water to reduce
          membrane fouling via disinfection (a process often referred to as a "chemically
          enhanced backwash").  Other manufacturers may include acid or caustic solution to
          remove inorganic or organic foulants. As a result, the backwash effluent may contain
          both solids and/or chemical residuals.

       •  In locations where the disposal of backwash water may be problematic, consideration
          should be given to the volume of backwash water generated.  Backwash water
          treatment should also be considered in order to maximize system productivity and
          minimize residuals.

       •  Increased backwash efficiency can significantly enhance system performance,
          allowing higher fluxes and recoveries.
       Variations in the backwash frequency will influence the waste flow, as well as the
productivity of the system. If higher residual flows can be easily accommodated and
productivity is not a critical design consideration, increasing the backwashing frequency may be
a viable strategy for achieving longer filter run times or higher membrane fluxes.

       Based upon the water quality data provided, MF/UF manufacturers can estimate the
initial membrane flux and backwash frequency for the pilot test. The backwash frequency can be
optimized during pilot testing to provide the most economical process.  The potential for
increased flux and useful membrane life that may be commensurate with increased backwash
frequency should be balanced against decreased productivity, increased waste volume, and
higher chemical usage (if applicable).
6.3.3  Chemical Cleaning Optimization

       The chemical cleaning of a membrane filtration system is a necessary process that results
in lost production time, produces chemical waste, and requires operator attention.  Consequently,
pilot testing should be used to minimize chemical cleaning frequency for both MF/UF and
NF/RO systems, while maintaining acceptable productivity and controlling long-term fouling.
The typical membrane cleaning cycle consists of recirculating a heated cleaning solution for a
period of several hours.  Some manufacturers require that the cleaning solution be prepared with
softened or demineralized water, which should be accounted for during the pilot test.  The
specific cleaning regime will depend upon the feed water quality and the particular membrane
system. Some membranes may be degraded by excessive cleaning frequencies, shortening
membrane life.  For MF/UF systems the typical chemical cleaning frequency assumed for design
purposes is approximately once every 30 to 60 days. NF/RO systems are generally designed
with significantly longer cleaning intervals, typically in the range of 3 months to 1 year.  It is
important for a utility to understand the impacts of chemical cleaning on the system and to


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                                    Chapter 6 - Pilot Testing
determine whether to increase the flux at the expense of the consequent increase in chemical
cleaning frequency.  One of the objectives of a pilot test should be to determine a chemical
cleaning strategy that restores membrane permeability without damaging the membrane
integrity.  Thus, the pilot test should be designed to include at least one chemical cleaning, even
if the pilot schedule is very restrictive.  If necessary, the flux can be significantly increased to
induce membrane fouling for the purposes of conducting chemical cleaning.

       It is important to demonstrate the effectiveness of the chemical cleaning during the pilot
study. Because membrane cleaning is a time-, labor-, and chemical-intensive process, it is
important to avoid experimentation on the full- scale plant.  The best way to evaluate the success
of a particular chemical cleaning scheme is to conduct the cleaning in a methodical manner and
evaluate the performance of each step in the process. Before and after each step, a plot of the
transmembrane pressure (TMP) as a function of flux (or filtrate flow) should be  developed.  This
method of evaluation is normally described as a "clean water flux test." This test requires that
the membrane unit be placed into filtration mode in between each of the various steps in the
chemical cleaning process in  order to observe the effect on the flux (or filtrate flow). (Note that
filtrate produced during this process should be considered chemical waste.) For example, if a
chemical cleaning process consists of recirculating citric acid  and caustic in succession, three
plots  of TMP versus flux (or  filtrate flow)  should be generated. Figure 6.1 illustrates the clean
water flux test technique  for this example. The three applicable plots shown in Figure 6.1 are as
follows:

       1.  TMP vs. flux  (or filtrate flow) for the fouled membrane prior to cleaning

       2.  TMP vs. flux  (or filtrate flow) after citric acid recirculation / cleaning

       3.  TMP vs. flux  (or filtrate flow) after caustic recirculation / cleaning
          (i.e., after all cleaning steps are completed)
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                                    Chapter 6 - Pilot Testing
                  Figure 6.1  Sample Chemical Cleaning Test Profile
          TM-




i
4f^ _ — -—



/
/>
C ^.x'
,**
.-^


,
x
X
^ r-
^ /^
v— ^
X
/
H.^"
y
,--^
y '
fr


V" ~^"
                                                          3EFCRE C.EANNG
                                                              AFTER CITRIC ACID
                                                        - — .  AFTER CAUSTIC
                               FLUX  OR  FLOW
       In an ideal cleaning, the final plot (i.e., after caustic) of IMP versus flux (or filtrate flow)
would be  similar to that after the previous  clean  such that the plots generated after each
successive chemical cleaning (i.e., the final plot of each cleaning) would overlap.  Thus, the plots
established during a clean water flux test facilitate this comparison and provide an indication as
to the effectiveness of the cleaning regimen.  This is illustrated in Figure 6.1 with plots showing
the  increase in TMP per  incremental change in flux  (or filtrate flow).   Smaller slopes indicate
lower pressure requirements for  operation at a given  flux (or filtrate  flow),  and thus a more
effective step in the chemical cleaning process.

       After cleaning, a direct integrity test should be conducted before the pilot unit is returned
to service.  If the membrane is integral and an acceptable flux has been restored, then the
cleaning is deemed successful. If not, alternate  cleaning strategies should be considered. A flow
chart outlining a general pilot study sequence of events is shown in Figure 6.2, illustrating  a
typical series of test runs and subsequent chemical cleaning events.
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                 Figure 6.2 Sample Pilot Study Sequence Overview
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6.4    Testing and Monitoring

       A thorough and carefully developed testing and monitoring plan is a critical component
of a pilot test program, as this is the means by which system performance is assessed.  There are
several categories of testing and monitoring that should be addressed in a pilot test protocol,
including operational parameters, water quality, and microbial monitoring (where applicable),
and integrity testing.  Each of these four categories is discussed in further detail in the following
subsections.
6.4.1  Operational Parameter Monitoring

       Monitoring pilot unit operational parameters is an important means of assessing system
performance and tracking the rate of membrane fouling.  The following operational parameters
should be monitored continuously, if possible:

       1.  Elapsed run time

       2.  Pressure (feed, filtrate, concentrate)

       3.  Flow (feed, filtrate, concentrate)

       4.  Temperature (feed or filtrate)
       Another important consideration in the evaluation of a membrane process is operational
data collection for the intermittent process sequences, such as backwashing.  For these
intermittent processes, the design parameters (e.g., flows, times, volumes)  associated with air,
water, or chemical usage during the sequence should be established and verified during pilot
testing.  It is not uncommon for the pilot unit to operate under different parameters than those
that would be considered appropriate for a full-scale unit.  For example, a pilot system generally
has faster pneumatic valve actuation times and  a shorter overall backwash  sequence than a full-
scale unit.  Some of these discrepancies are unavoidable; however, these scale-up  issues should
be noted for consideration prior to initiating pilot testing.
6.4.2  Water Quality Monitoring

       The particular water quality data collected during a pilot study will depend upon the type
of membrane filtration system, site-specific treatment objectives,  and foulants of concern. In
general, the following table can be used as a guideline:
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                                    Chapter 6 - Pilot Testing
  Table 6.2  Suggested Water Quality Sampling Schedule for Membrane Piloting1
Parameter
MF/UF
Feed
Concentrate"1
Filtrate
NF/RO
Feed
Concentrate
Filtrate
General Water Quality Parameters
Algae
Color
HPC
Particle counts
PH
SDI
Taste & odor
Temperature
TOC
Total coliform
TSS
Turbidity
UV-254
W
W
M
C
D

M
C
W
W
M
C
W

M


W

M

M

M
M
M
W
W
M
C
W

M

W
W
M
C
W
W
W
M

C
W
M
C
W
W

C
W

M


W

M

M





W
M

W

M

W


W
W
Dissolved Solids
Alkalinity
Barium
Hardness
Iron
Manganese
Silica
Sulfate
TDS
W


W
W

W

M







W

M




M
W
W
W
W
W
W
W
C
W
W
W
W
W
W
W
W
W
W
W
W
W
W
W
C
Simulated Distribution Svstem Disinfection Byproducts
HAAs
TTHMs




M
M




M
M
       1 Generic recommendations only; the specific applicable parameters will vary with each application
       2 Where applicable, based on particular hydraulic configuration used

       Key:
       C  = Continuous
       D  = Daily
       W  = Weekly
       M  = Monthly
In addition to those flows listed in Table 6.2, it is recommended that the MF/UF backwash flow
be checked weekly for total suspended solids (TSS) and turbidity. Note that the recommended
parameters and sampling frequencies should be modified to meet the requirements and objectives
of each particular site-specific pilot study. The sampling frequencies may also be modified
during the  course of a pilot study if conditions warrant.
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6.4.3  Microbial Monitoring

       One advantage of membrane filtration is that it provides a physical barrier through which
water must pass, virtually eliminating pathogens larger than the membrane exclusion
characteristic.  As with the full-scale facility, it is important that the pilot test demonstrate that
this barrier is intact and is rejecting pathogens.  A site-specific microbial challenge test may not
be required by the state during the pilot study for a membrane filtration system that has received
prior regulatory approval.  For the purposes of LT2ESWTR compliance, product-specific
demonstration of Cryptosporidium removal efficiency is accomplished during challenge testing,
although microbial monitoring may be conducted during a pilot study for additional verification
of membrane performance at the discretion of the utility or if required by the state.  Although
additional microbial testing can be conduct for any pathogen of concern during piloting,
typically, coliform bacteria, and sometimes Heterotrophic plate count (HPC) are used as an
indicator for microbial removal efficiency.
6.4.4  Integrity Testing

       The importance of integrity testing under the LT2ESWTR necessitates that greater
emphasis be placed upon integrity testing during piloting for applications of membrane filtration
intended for LT2ESWTR compliance.  For direct integrity testing, the membrane manufacturer
should use a method approved or mandated by the state. The standard direct integrity test
sequences intended for the full-scale system should be incorporated into the pilot unit.  Direct
integrity testing should be conducted at least as frequently as required by the state for the full-
scale facility.  In the absence of a particular state requirement, it is generally recommended that
direct integrity testing be conducted on a daily basis, a frequency consistent with the
LT2ESWTR requirements. If an integrity breach occurs during the piloting testing, then
diagnostic testing and membrane repair techniques may also be practiced.  Continuous indirect
integrity monitoring can usually  be accomplished using data that are collected during a typical
pilot test program (e.g., turbidity or particle count data).  However, any state requirements
regarding data that must be collected for the purposes of continuous indirect integrity monitoring
for the full-scale facility should also be implemented during the pilot test, and may be required
by the state in any case.

       Note that because the number of membrane modules to which an integrity test is applied
affects the sensitivity of the test (for both direct integrity testing and continuous indirect integrity
monitoring), any control limits established for a full-scale system will generally not be applicable
to a pilot unit, which typically utilizes only  a small fraction of the  number of modules in a full-
scale membrane unit.  Guidance  on establishing full-scale system control limits for both direct
integrity testing and continuous indirect integrity monitoring for the purposes of compliance with
the LT2ESWTR are provided in  Chapters 4 and 5, respectively, and also in Appendix A -
Development of a Comprehensive Integrity Monitoring Program.
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6.5    Report Development

       After the pilot test is complete, a report should be prepared to summarize the procedures
and the test results. The pilot study report should contain sufficient detail to establish design
parameters for the full-scale plant to the extent for which the testing was intended.  Flux,
chemical cleaning, backwashing, and integrity testing, should be addressed, where applicable.
Collected water quality data should also be included with emphasis given to unanticipated test
results. Details on the operational parameters for each filter run (i.e., between chemical
cleanings) should be summarized.  The state may also have specific requirements for the report if
the piloting is required.
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                   7.0  Implementation Considerations
7.1    Introduction

       The successful implementation of a membrane filtration system requires a general
understanding of the major considerations that influence system design and operation.  Although
there are many such considerations, this chapter focuses on the most significant of these issues,
categorized as operational unit processes, system design considerations, and residuals treatment
and disposal.  The purpose of this chapter is to present a general overview of some of these
critical considerations, highlighting their respective roles in the implementation of the
technology. Note that this chapter is intended to provide information and recommendations
regarding industry practices, and is not directly related to compliance with the Long Term 2
Enhanced Surface Water Treatment Rule (LT2ESWTR).

This chapter is divided into the following sections:

       Section 7.2:    Operational Unit Processes
                     This section reviews the purpose(s) and practices associated with the
                     major operational unit processes of membrane filtration  systems, including
                     pretreatment, backwashing, chemical cleaning, integrity  testing, and post-
                     treatment.

       Section 7.3:    System Design Considerations
                     This section discusses some of the most significant conceptual design
                     issues associated with membrane filtration systems, including flux, water
                     quality, temperature compensation, cross-connection control, and system
                     reliability.

       Section 7.4:    Residuals Treatment and Disposal
                     This section outlines management practices for the various waste streams
                     produced by membrane filtration systems, such as backwash and chemical
                     cleaning residuals, as well as concentrate.
7.2    Operational Unit Processes

       All membrane filtration systems have associated operational unit processes that are
essential for maintaining and optimizing system performance and therefore critical to the
successful implementation of the technology. These operational processes include backwashing,
chemical cleaning, and integrity testing. For the purposes of this discussion, pretreatment and
post-treatment are also considered operational unit processes associated with membrane
filtration.  Each of these processes and its role in the operation of a membrane filtration system is
described in the following sections. Although not every membrane filtration system utilizes all
of these processes, many utilize each process to some degree.  The optimization of these
operational unit processes can be address during pilot testing, as discussed in Chapter 6.


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7.2.1   Pretreatment

       Pretreatment is typically applied to the feed water prior to entering the membrane system
in order to minimize membrane fouling, but in some cases may be used to address other water
quality concerns or treatment objectives.  Pretreatment is most often utilized to remove foulants,
optimize  recovery and system productivity, and extend membrane life. Pretreatment may also be
used to prevent physical  damage to the membranes. Different types of pretreatment can be used
in conjunction with  any given membrane filtration  system, as determined by site-specific
conditions and treatment objectives.  Pilot testing can be used to compare various pretreatment
options, optimize pretreatment, and/or demonstrate pretreatment performance. Several different
types of commonly used pretreatment for membrane filtration systems are discussed in the
following subsections.
       7.2.1.1    Prefiltration

       Prefiltration, including screening or coarse filtration, is a common means of pretreatment
for membrane filtration systems that is designed to remove large particles and debris.
Prefiltration can either be applied to the membrane filtration system as a whole or to each
membrane unit separately. The particular pore size associated with the prefiltration process
varies depending on the type of membrane filtration system and the feed water quality. For
example, although hollow-fiber microfiltration (MF) and ultrafiltration (UF) systems are
designed specifically to remove suspended solids, large particulate matter can damage or plug
the membranes fibers. For these types of systems the pore size of the selected prefiltration
process may range from as small 100 |j,m to as large as 3,000 |j,m or higher, depending on the
influent water quality and manufacturer specifications.  Generally, hollow-fiber MF/UF systems
that are operated in an inside-out mode are more  susceptible to fiber plugging and thus may
require finer prefiltration.

       Because nanofiltration (NF) and reverse osmosis (RO) utilize non-porous semi-
permeable membranes that cannot be backwashed and are almost exclusively designed in a
spiral-wound configuration for municipal water treatment, these systems must utilize much finer
prefiltration in order to minimize exposure of the membranes to particulate matter of any size.
Spiral-wound modules are highly susceptible to particulate fouling, which can reduce system
productivity, create operational problems, reduce membrane life, or in some cases damage or
destroy the membranes.  If the feed water has a turbidity less than approximately 1 NTU or a silt
density index (SDI) less than approximately 5, cartridge filters with a pore size range from about
5 to 20 |j,m are commonly used NF/RO prefiltration. However, if the feed water turbidity or SDI
exceeds these values, a more rigorous method of particulate removal, such as conventional
treatment (including media filtration) or MF/UF membranes, is recommended as pretreatment for
NF/RO.

       In conventional applications of cartridge filtration technology, high quality source waters
are treated, and thus additional prefiltration is typically not required. However, membrane
cartridge filtration (MCF) systems may warrant some level of prefiltration, possibly using more
conventional cartridge or bag filters, to protect and extend the life of the more effective and more
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expensive MCF, particularly if the MCF system is applied to surface waters specifically for the
purposes ofLT2ESWTR compliance. Since MCF is a new class of technology defined under the
LT2ESTWR, pretreatment practices for MCF will likely evolve as this technology is applied.
Prefiltration requirements will likely be similar to those for MF/UF.

       A summary of the typical prefiltration requirements associated with the various types of
membrane filtration is presented in Table 7.1.
          Table 7.1  Typical Membrane System Prefiltration Requirements
Membrane System
Classification
Membrane Cartridge
Filtration (MCF)1
Microfiltration (MF) /
Ultrafiltration (UF)
Nanofiltration (NF) /
Reverse Osmosis (RO)
Configuration
Cartridge
Hollow-Fiber,
Inside-Out
Hollow-Fiber,
Outside-ln
Spiral-Wound
Prefiltration Requirements
Size
fijm)
300 - 3,000
100-300
300 - 3,000
5-20
Type(s)
Strainers;
Bag Filters
Strainers;
Bag Filters
Strainers;
Bag Filters
Cartridge Filters
            1  Prefiltration is not necessarily required for MCF systems
       In some cases, one type of membrane filtration may be used as prefiltration for another.
This type of treatment scheme is commonly known as an integrated membrane system (IMS).
Typically, this involves the use of MF/UF as pretreatment for NF/RO in applications that require
the removal of particulate matter and microorganisms as well as some dissolved contaminants
such as hardness, iron and manganese, or disinfection byproduct (DBF) precursors.  One of the
most significant advantages of an IMS treatment scheme is that the MF/UF filtrate is of
consistently high quality and allows the NF/RO system to maintain stable operation by reducing
the rate of membrane fouling.
       7.2.1.2    Chemical Conditioning

       Chemical conditioning may be used for a number of pretreatment purposes, including pH
adjustment, disinfection, biofouling control, scale inhibition, or coagulation.  Some type of
chemical conditioning is almost always used with NF/RO systems, most often the addition of an
acid (to reduce the pH) or a proprietary scale inhibitor recommended by the membrane
manufacturer to prevent the precipitation of sparingly soluble salts such as calcium carbonate
(CaCOs), barium sulfate (BaSO/O, strontium sulfate (SrSO4), or silica species (e.g., SiO2).
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Software programs that simulate NF/RO scaling potential based on feed water quality are
available from the various membrane manufactures.  In some cases, such as for those NF and RO
membranes manufactured from cellulose acetate, the feed water pH must also be adjusted to
maintain the pH within an acceptable operating range to minimize the hydrolysis (i.e., chemical
deterioration) of the membrane.  The addition of chlorine or other disinfectants may also be used
as pretreatment for primary disinfection or to control biofouling. However, because some
NF/RO membrane materials are readily damaged by oxidants, it is important that any
disinfectants added upstream be quenched prior to contact with such membranes.

       A number of different chemicals may be  added as pretreatment for MF or UF, depending
on the treatment objectives for the system. For example, lime may be added for softening
applications; coagulants may be added to enhance removal of total organic carbon (TOC) with
the intent of minimizing the formation of DBFs or increasing particulate removal; disinfectants
may be applied for either primary disinfection or biofouling control; and various  oxidants can be
used to precipitate metals such iron and manganese for subsequent filtration. However, as with
NF and RO membranes, it is important to ensure that the applied pretreatment chemicals are
compatible with the particular membrane material used.  As with conventional media filters, pre-
settling may be used in conjunction with pretreatment processes such as coagulation and lime
softening. While a MF/UF system may be able to operate efficiently with the in-line addition of
lime or coagulants, pre-settling in association with these pretreatment processes can enhance
membrane flux and increase system productivity by minimizing backwashing and chemical
cleaning frequency.

       Although chemical pretreatment is generally  not associated with cartridge filters, if the
filters are compatible, disinfectants may be added upstream of MCF systems to maximize the
time for primary disinfection (i.e., CT). Because cartridge filters are designed to be disposable
and are generally not backwashed, pretreatment chemicals such as lime or coagulants could
rapidly foul the cartridges and thus are  not applied upstream these systems.

       With any form of chemical pretreatment, it is very important to understand whether any
chemical under consideration for use is compatible with the membrane material.  In addition to
irreversible fouling and/or physical damage to the membranes, the use of an incompatible
chemical may void the manufacturer's warranty.  Some chemicals such as oxidants can be
quenched upstream, while others such as coagulants  and lime cannot be counteracted prior to
membrane exposure. In general, most NF/RO membranes and some MF/UF membranes are not
compatible with disinfectants and other oxidants. However, some MF/UF membranes that are
incompatible with stronger oxidants such as chlorine may have a greater tolerance for weaker
disinfectants such as chloramine, which may allow for a measure of biofouling control without
damaging the membranes.  Certain types of both MF/UF and NF/RO membranes require
operation within a certain pH range.  Coagulants and lime are incompatible with many NF/RO
membranes but are typically compatible with most types of MF/UF membranes.  Polymers are
incompatible with NF/RO membranes,  and generally not compatible with MF/UF membranes, as
well, although this depends to some degree on the charge of the polymer relative to the  charge
associated with the membrane.  A polymer with  a charge opposite to that of the membrane  is
likely to cause rapid and potentially irreversible  fouling. Chemical compatibility with various
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types of membrane materials is briefly discussed in section 2.3.1; however, it is critical to consult
with the membrane manufacturer prior to implementing any form of chemical pretreatment.
7.2.2  Backwashing

       The backwash process for membrane filtration systems is similar in principle to that for
conventional media filters and is designed to remove contaminants accumulated on the
membrane surface. Each membrane unit is backwashed separately and in a staggered pattern so
as to minimize the number of units in simultaneous backwash at any given time. During a
backwash cycle, the direction of flow is reversed for a period ranging from about 30 seconds to 3
minutes.  The force and direction of the flow dislodge the contaminants at the membrane surface
and wash accumulated solids out through the discharge line. Membrane filtration systems are
generally backwashed more frequently than conventional media filters, with intervals of
approximately 15  to 60 minutes between backwash events.  Typically the membrane backwash
process reduces system productivity in the range of 5 to 10  percent due to the volume of filtrate
used during the backwash operation.

       Of the various types of membrane filtration systems, backwashing is almost exclusively
associated with hollow-fiber MF and UF processes. Some MCF systems may also be
backwashed, depending on how the system is designed and configured; however it is more
common to replace the cartridge filters, which are manufactured to be  disposable, when they
become fouled.

       Backwashing  is conducted periodically according to manufacturer specifications and site-
specific considerations. Although more frequent backwashing maintains higher fluxes, this
benefit is counterbalanced by the decrease in system productivity.  In general, a backwash cycle
is triggered when  a performance-based benchmark is exceeded, such as a threshold for operating
time, volumetric throughput, increase in transmembrane pressure (TMP), and/or flux decline.
Ideally, the backwash process restores the TMP to its baseline  (i.e., clean) level; however,  most
membranes exhibit a  gradual increase in the TMP that is observed after each backwash,
indicating that the accumulation of foulants that cannot be removed by the backwash process
alone.  These foulants are addressed through chemical cleaning (see section 7.2.3).

       Some systems also utilize pressurized air and/or chlorine (if a compatible membrane
material is used) in combination with filtered water to remove solids, provide a measure of
pathogen inactivation and biofouling control, and improve overall backwash effectiveness.  A
disinfectant such as chlorine may be added at a frequency ranging from every backwash to about
once per day. If chloramines are added upstream of the membrane process, the benefits of
adding chlorine during the backwash process should weighed against the cost of breakpoint
chlorination to achieve a free chlorine residual and possible subsequent ammonia addition to
regenerate a chloramine residual for secondary disinfection in the distribution system.

       Some manufacturers have implemented backwash strategies for their proprietary MF/UF
systems that involve the use of chemicals other than chlorine (such as acids, bases, surfactants, or
other proprietary chemicals). These strategies are used as a method to enhance membrane flux
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and extend intervals between chemical cleanings, thus lowering the cost of operation. In these
cases state regulators may require enhanced cross-connection control measures for the backwash
piping similar to those used for chemical cleaning systems (see section 7.3.4), depending on the
backwash frequency and the type(s) and concentration(s) of chemical(s) used.  Special
provisions for rinsing the membranes at the end of the backwash process may also be required.

       Because the design of spiral-wound membranes generally does not permit reverse flow,
NF and RO membrane systems are not backwashed.  For these systems, membrane fouling is
controlled primarily with chemical cleaning, as well as through flux control and crossflow
velocity.  The inability of spiral-wound membranes to be backwashed is one reason that NF and
RO membranes are seldom applied to directly treat water with high turbidity and/or suspended
solids.
7.2.3  Chemical Cleaning

       Chemical cleaning is another means of controlling membrane fouling, particularly those
foulants such as inorganic scaling and some forms of organic and biofouling that are not
removed via the backwash process. As with backwashing, chemical cleaning is conducted for
each membrane unit separately and is typically staggered to minimize the number of units
undergoing cleaning at any time.  While chemical cleaning is conducted on both MF/UF and
NF/RO systems, because non-porous, semi-permeable membranes cannot be backwashed,
chemical cleaning represents the primary means of removing foulants in NF/RO systems.
Although cleaning intervals may vary widely on a system-by-system basis, the gradual
accumulation of foulants makes eventual chemical cleaning virtually inevitable. Membrane
cartridge filters are an exception, however, in that cartridge filters are usually designed to be
disposable and thus are typically not subject to chemical cleaning.

       As with backwashing, the goal of chemical cleaning is to restore the TMP of the system
to its baseline (i.e., clean) level. Any foulant that is removed by either the backwash or chemical
cleaning process is known as reversible fouling.  Over time, membrane processes will also
typically experience some degree of irreversible fouling which cannot be removed through either
chemical cleaning or backwashing. Irreversible fouling occurs in all membrane systems, albeit
over a wide range of rates, and eventually necessitates membrane replacement.

       There are a variety of different chemicals that may be used for membrane cleaning, and
each is generally targeted to remove a specific form of fouling. For example, citric acid is
commonly used to dissolve inorganic scaling, and other acids may be used for this purpose as
well.  Strong bases such as caustic are typically employed to dissolve organic material.
Detergents and surfactants may also be used to remove organic and particulate foulants,
particularly those that are difficult to dissolve. Chemical cleaning may also utilize concentrated
disinfectants such as a strong chlorine solution to control biofouling. Due to the variety of
foulants that are present in many source waters, it is often necessary to use a combination of
different chemicals in series to address multiple types of fouling.  The various types of chemical
cleaning agents used are summarized in Table 7.2.
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                         Table 7.2  Chemical Cleaning Agents
Category
Acid
Base
Oxidants /
Disinfectants
Surfactants
Chemicals Commonly Used
• Citric Acid
• Hydrochloric Acid (HCI)
• Caustic (NaOH)
• Sodium Hypochlorite (NaOCI)
• Chlorine (CI2) Gas
• Hydrogen Peroxide
• Various
Typical Target
Contaminant(s)
Inorganic scale
Organics
Organics;
Biofilms
Organics;
Inert particles
       Numerous proprietary cleaning chemicals are also available, and these specialty cleaning
agents may be useful in cases in which more conventional chemicals are ineffective. For
example, under some circumstances enzymatic cleaners have been found to be effective at
dissolving organic contaminants. Chemical cleaning options are more limited for membranes
that cannot tolerate oxidants and/or extreme pH levels. A chemical cleaning regimen may be
specified by the manufacturer or identified based on site-specific pilot testing and source water
quality analyses to determine the prevalent form(s) of fouling experienced at a particular facility.

       The term clean-in-place (CIP) is often used to describe the chemical cleaning process,
since it is typically conducted while the membrane modules remain in the membrane unit (i.e.,
in-situ). The cleaning process generally involves recirculating a cleaning  solution through the
membrane system at high velocities (to generate scouring action)  and elevated temperature (to
enhance the solubility of the foulants). A soak cycle follows the recirculation phase. After the
soak cycle is completed, the membrane system is flushed to remove residual traces of the
cleaning solution(s).  The process may be repeated using  a different cleaning solution to target
different types of foulants until the membranes have been successfully cleaned.  Under some
circumstances the use of softened or demineralized water may be required for the cleaning
solution or as rinse water.

       While backwashing may be conducted at more regular intervals or on a routine basis,
chemical cleaning is typically conducted only when necessary.  A chemical cleaning is generally
necessary for MF and UF systems when the ability of periodic backwashing to restore system
productivity (i.e., increase flux and reduce TMP) reaches  a point of diminishing returns.  For NF
and RO systems, a 10 to 15 percent decline in temperature- and pressure-normalized flux or
about a 50 percent increase in differential pressure may indicate the need for chemical cleaning.
Delaying necessary chemical cleaning can accelerate irreversible fouling,  reduce production
capacity, and shorten membrane life.
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       Isolating the cleaning chemicals from the treated (i.e., filtered) water is an important
consideration for membrane filtration systems.  Guidelines for cross-connection control are
discussed in section 7.3.4. In addition, it is important to properly flush the membrane unit after
the cleaning process and before restarting the filtration cycle. The flushed water should be
diverted to waste until filtrate water quality parameters (such as turbidity for MF/UF systems and
pH for NF/RO systems) return to normal production mode levels.  Note that the volume of
flushed water can be significant in cases in which surfactants are used.

       For MF/UF systems, it is common to recycle as much as 90 percent of the cleaning
chemicals for reuse, thus  reducing the volume of chemical waste as well as the cost associated
with cleaning. Recycling cleaning solutions is less common with NF/RO systems, since the used
cleaning solutions accumulate  dissolved constituents with repeated use, diminishing the
effectiveness of the cleaning agents.  The treatment and disposal of spent chemical cleaning
waste is discussed in section 7.4.2.
7.2.4  Integrity Testing

       Integrity testing is a means of determining whether or not a membrane system is
"integral," or free of any breaches, leaks, or defects that might allow unfiltered water to bypass
the membrane barrier, passing contaminants that are normally removed.  As with both
backwashing and chemical cleaning, integrity testing is conducted on each membrane unit (or
smaller division in some cases) separately and is typically staggered to minimize the number of
units simultaneously undergoing testing. The use of periodic or continuous integrity testing and
monitoring methods allows ongoing operational verification that the membranes are performing
as expected based on their established exclusion characteristics. This verification is an essential
component of any membrane filtration system, particularly when the constituents of concern are
pathogenic microorganisms.  Integrity testing and is described  in detail in Chapters 4 and 5 in the
context of applying membrane filtration for compliance with the LT2ESWTR.  The discussion in
this section is intended to be a general overview of integrity testing as an important operational
unit process for membrane filtration systems.

       There are a number of potential modes of failure associated with membrane filtration
systems that would result in an integrity breach. For example, membranes may become damaged
via exposure to oxidants,  pH levels outside the recommended range, or other chemicals or
operating conditions to which the membranes are sensitive. In addition, membranes may break
or puncture as a result of extreme pressure, scratches or abrasions, or operational fatigue over
time.  Spiral-wound membranes can be damaged at glue lines if the pressure on the filtrate side
of the membrane exceeds that on the feed side. Factory imperfections such as glue line gaps or
potting defects may cause integrity breaches, as well.  Improper installation of membrane
modules can also create integrity problems at o-rings or interconnections.

       The various types of integrity tests are generally divided into two categories: direct and
indirect test methods.  Direct methods are physical tests that are applied specifically to the
membrane unit to detect integrity breaches and/or determine their sources.  Indirect methods are
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surrogate measures of integrity that involve filtrate water quality monitoring such that a
significant decline in filtrate quality may indicate an integrity problem. Both direct integrity
testing and continuous indirect integrity monitoring are required for compliance with
LT2ESWTR.

       Direct test methods are non-destructive techniques that can be used to identify and/or
isolate leaks. While these methods yield direct information about membrane integrity, they
cannot be conducted  continuously while the membrane filtration system is in operation.  Thus,
the longer and more often that a direct test is conducted, the greater the impact on the overall
system productivity.  The minimum frequency requirements for direct testing vary among
different states, although daily testing is commonly recommended as good practice and is
required for those utilities using membrane filtration for LT2ESWTR compliance.

       Although there are a number of types of direct integrity tests, the most common method
is the pressure decay test, which measures the rate of pressure loss across the membrane relative
to a maximum acceptable threshold.  Almost all currently available proprietary MF and UF
systems are designed with the capability to conduct this test automatically at regular intervals.
MCF systems may also be equipped to conduct automatic pressure decay tests.  A similar test
using a vacuum can also be conducted on NF and RO membranes, although currently spiral-
wound systems are generally not designed to conduct this testing automatically during the course
of normal operation.  Other on-line direct test methods measure the flow of air or water from
integrity breaches, or the concentration of either spiked inert particles or a molecular marker.
Additional information regarding direct integrity  testing, including  common methods and their
application for facilitating compliance with the LT2ESWTR, is provided in Chapter 4.

       The various indirect methods  consist primarily  of water quality monitoring practices that
are common throughout the water treatment industry, such as turbidity monitoring and particle
counting.  Particulate-based indirect monitoring techniques are applicable to all membrane
classes used for filtration. For NF/RO membranes capable of removing dissolved contaminants,
other parameters such as conductivity or sulfide may also potentially be used as surrogate
measures of membrane integrity. The effectiveness of indirect methods is a function of the
ability of membrane filtration to produce very consistent, high quality filtrate, such that a marked
decline in filtrate quality is likely to indicate an integrity problem.  Although indirect methods
are not as sensitive as the direct methods for detecting  integrity breaches, the primary advantage
of indirect methods is that they allow continuous  monitoring, a capability not possible with
currently available direct testing methods.  Typically, if an indirect method indicates a potential
integrity problem, a direct test will be conducted to determine more conclusively whether or not
a breach has occurred.  Indirect monitoring methods are further addressed in Chapter 5, including
advantages and disadvantages of the various techniques, as well as requirements for utilizing
these tests in the course of applying membrane filtration for LT2ESWTR compliance.

       Guidance for the development of comprehensive integrity verification program, including
the use of both direct and indirect methods, is included in Appendix A.
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7.2.5  Post-Treatment

       Post-treatment for membrane filtration systems typically consists of chemical
conditioning and/or disinfection and is typically applied to combined filtrate.  Most chemical
conditioning is associated with NF and RO systems, because the removal of dissolved
constituents that is achieved by these processes has a more significant impact on water chemistry
than the filtering of suspended solids alone. For example, because NF and RO pretreatment
often includes acid addition to lower the pH and, consequently, increase the solubility of
potential inorganic foulants, a portion of the carbonate and bicarbonate alkalinity in the water is
converted to aqueous carbon dioxide, which is not rejected by the membranes. The resulting
filtrate can thus be corrosive given the combination of a low pH, elevated carbon dioxide levels,
and minimal buffering capacity of the filtrate. Other dissolved gases such as hydrogen sulfide,
will also readily pass through the semi-permeable membranes, further augmenting  the corrosivity
of the filtrate and potentially causing turbidity and taste and odor problems.  As a result, the
primary goal of chemical conditioning is the stabilization of NF/RO filtrate with respect to pH,
buffering capacity, and dissolved gases.

       Degasification is commonly achieved via packed tower aeration (i.e., air stripping).  Air
stripping also increases dissolved oxygen levels, which may be very low in the case of an
anaerobic groundwater source. The pH of the water may subsequently be readjusted to typical
finished water levels (i.e., approximately 6.5 - 8.5) by adding a base such as lime or caustic.
Alkalinity (e.g., in the form of sodium bicarbonate) may also be added, if necessary, to increase
the buffering capacity of the water.  Alternatively, if the pH is raised prior to degasification (thus
converting the dissolved carbon dioxide to bicarbonate),  much of the alkalinity may be
recovered. However, this post-treatment strategy also converts any dissolved hydrogen sulfide
gas into dissociated sulfide, which may readily react with other dissolved species to produce
sparingly soluble sulfide compounds that may precipitate. Because MF, UF, and MCF systems
do not directly affect the pH or remove alkalinity, these processes do not generally require
chemical conditioning to stabilize the filtrate.

       While the use of membrane filtration does not specifically necessitate disinfection post-
treatment as a result of process considerations, the need for post-disinfection is generally
required by regulation for primary and/or secondary disinfection. However, in some states the
use of membrane filtration may reduce primary disinfection (i.e., CT) requirements, thus helping
to control DBF formation. Because membrane filtration is often the last major process in the
treatment scheme, it is common to apply a disinfectant to the filtrate prior to entry into a
clearwell and/or the distribution system.  This application is particularly important  if
disinfectants were either neutralized or not added at all prior to the membrane filtration process
to avoid damaging oxidant-intolerant membranes.

       For NF and RO membrane processes, if the disinfectant is applied prior to filtrate pH
adjustment, post-disinfection may have the additional benefit of oxidizing sulfide to sulfate, thus
reducing the potential for both sulfide precipitation and taste and odor concerns.  Corrosion
inhibitors may also be added prior to distribution, particularly for NF and RO systems that
produce more corrosive water.
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7.3    System Design Considerations

       In the process of planning and implementing a membrane filtration system, there are
several important issues that can have a particularly significant impact on system design and
operation, thus warranting special consideration.  These issues include membrane flux, water
quality, temperature compensation, cross-connection control, and system reliability. Each of
these subjects is discussed briefly in the following subsections.
7.3.1   Membrane Flux

       The flux - the flow per unit of membrane area, as defined in section 2.4 - is one of the
most fundamental considerations in the design of a membrane filtration system, since this
parameter dictates the amount of membrane area necessary to achieve the desired system
capacity and thus the number of membrane modules required.  Because the membrane modules
represent a substantial component of the capital cost of a membrane filtration system,
considerable attention is given to maximizing the membrane flux without inducing excessive
reversible fouling, thereby minimizing the number of modules required.

       Typically, the maximum flux associated with a particular membrane filtration system is
determined during pilot testing, mandated by the state, or established via a combination of these
two in cases in which the state specifies a maximum operating flux based on the pilot results.
Independent of maximum flux,  pilot testing is also commonly used to determine a reasonable
operating range that balances flux with backwash and chemical cleaning frequencies. Because
higher fluxes accelerate fouling, backwashing and chemical cleaning must usually be conducted
more frequently at higher fluxes. The process of using pilot testing to optimize the flux relative
to the backwash and chemical cleaning frequencies is described in section 6.3.  The upper bound
of the range of acceptable operating fluxes (provided this bound does not exceed the state-
mandate maximum) is sometimes called the "critical" flux, or the point at which a small increase
in flux results in  a significant decrease in the run time between chemical cleanings.  A membrane
filtration system  should operate below this critical flux to avoid excessive downtime for cleaning
and the consequent wear on the membranes over time due to increased chemical exposure.

       The flux through a membrane is influenced by a number of factors, including pore size
(for MF, UF, and MCF  membranes), module type (i.e., cartridge, hollow-fiber, spiral-wound,
etc.), membrane material, and water quality.  However, it is important to note that higher fluxes
do not necessarily indicate that  one membrane is better than another for a particular application.
Factors such as estimated membrane life, fouling potential, frequency and effectiveness of
chemical cleaning, chemical use, and energy  requirements to maintain a given flux should also
be considered.
7.3.2  Water Quality

       Because water quality can have a significant impact on membrane flux, feed water
quality is also a primary design consideration for membrane filtration systems.  Poorer water
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quality will require lower fluxes, which in turn increase the necessary membrane area and
required number of modules, augmenting both the cost and the size of the system.  However,
pretreatment (as described in section 7.2.1) can often improve feed water quality at a lower cost
than additional membrane area.  Conversely, better water quality will allow higher fluxes,
reducing the required membrane area, the size of the system, and the capital cost.  Typically,
membrane flux  is determined through pilot testing, as described in Chapter 6. In the absence of
pilot test data, it is  important to have some understanding of how critical water quality
parameters such as SDI, turbidity, organic carbon, and dissolved solids affect the flux. The
influence of each of these parameters on flux is briefly described in this section. Temperature
also has a significant impact on membrane flux, and this relationship is discussed separately in
section 7.3.3.
       Silt Density Index

       The silt density index, or SDI, is an empirical dimensionless measure of particulate
matter in water and is generally useful as a rough gauge of the suitability of a source water for
efficient treatment using NF/RO processes. The American Society for Testing and Materials
(ASTM)  Standard D 4189-95: Standard Test Method for Silt Density Index (SDI) of Water
details the procedure for determining SDI.  In general, SDI measurements are taken by filtering a
water sample through a 0.45-|j,m flat sheet filter with a 47-mm diameter at a pressure of 30 psi.
The time required to collect two separate 500 mL volumes of filtrate is measured, and the
resulting  data become the inputs to a formula used to calculate SDI.  Water samples that contain
greater quantities of particulate matter require longer to filter and thus have higher SDI values.

       As a general rule of thumb, spiral-wound NF and RO modules are not effective for
treating water with a SDI of 5 or greater, as this quality of water contains too much particulate
matter for the non-porous, semi-permeable  membranes, which would foul at an unacceptably
high rate.  Thus, some form of pretreatment to remove particulate matter is  generally required for
SDI values exceeding five in NF/RO applications. NF/RO membrane module manufacturers can
usually provide a rough estimate of the range of anticipated operating fluxes based on the type of
source water, which is roughly associated with a corresponding range of SDI values. A
summary of these estimates is included in Table 7.3.
        Table 7.3 Estimated NF/RO Membrane Fluxes as a Function of SDI
Source
Surface Water
Ground Water
SDI
(dimensionless)
2-4
< 2
Estimated NF/RO Flux
(9fd)
8-14
14-18
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       However, SDI is only one measure of water quality, and there are a number of site- and
system-specific water quality and operational factors that combine to dictate the flux for a given
system. Thus, the ranges cited in Table 7.3 should only be used as a rough guideline. Caution
should also be exercised when  interpreting SDI results, as measurements can vary from test to
test and with the analyst, as well as with both temperature and the specific type of membrane
used.  Consequently, it is important that the results are given for comparable conditions when
evaluating SDI data. Note that because SDI is a batch process, it is not conducted continuously
on-line and thus is not typically utilized as gauge of water quality or system performance during
daily operation in the way turbidity or conductivity monitoring are often employed.

       SDI is typically not used as a tool for estimating flux for MF, UF, and MCF systems.
Since these systems are designed to filter particulate matter, parameters such turbidity that more
commonly associated with conventional drinking water filtration are used to assess system
performance.
       Turbidity

       Turbidity is a measure of the scatter of incident light caused by particulate matter in
water.  Because turbidity is widely used as a performance gauge for conventional media filters,
among the various types of membrane filtration systems turbidity is most often used as an
assessment tool for MF, UF, and MCF, since these systems are specifically designed to remove
particulate matter.  Higher turbidity measurements are indicative of greater quantities of
suspended solids, and thus the potential to cause more rapid membrane fouling. Therefore, water
with higher turbidity is usually filtered at lower fluxes to minimize fouling and the consequent
backwash and chemical cleaning frequency. In some cases when turbidity levels are extremely
elevated, it may be more economical to provide pretreatment for a MF/UF system to reduce the
solids loading to the membranes.  In general, if the turbidity of the water normally exceeds
10 NTU on a sustained basis, some type of pretreatment (e.g., prefiltration or pre-settling) should
be considered. MCF systems may be applied to untreated source waters; however, as turbidity
levels increase, disposable MCF cartridges will foul more rapidly, requiring more frequent
replacement.  In some applications with higher turbidity source water, coarse bag or cartridge
filters may be used as pretreatment for MCF systems.

       Because spiral-wound NF  and RO membrane modules are not designed to handle
significant solids loading, these systems are typically not applied to treat water with turbidity
levels exceeding approximately 1 NTU. For water turbidity levels greater than 1 NTU,
pretreatment would be necessary to reduce solids loading upstream of NF or RO.
       Organic Carbon

       Another water quality constituent that influences membrane flux is the organic carbon
content, which is typically expressed in terms of either total or dissolved organic carbon (DOC).
Organic carbon in the feed water can contribute to membrane fouling, either by adsorption of the
dissolved fraction onto the membrane material  or obstruction by the particulate fraction. Thus,
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lower fluxes may be necessary if membrane filtration is applied to treat a water with significant
organic carbon content.  The tendency for a membrane to be affected by TOC is partially
influenced by the nature of the organic matter in the water.  TOC can be characterized as either
hydrophilic or hydrophobic in composition, and studies suggest that the hydrophobic fraction
contributes more significantly to membrane fouling.  The character of the organic carbon content
can be roughly quantified by measuring the specific ultraviolet absorbance (SUVA) of the water,
as calculated using the following equation:
                             IJV
                     SUVA =	251                                   Equation 7.1
                             DOC

       Where:        SUVA  =   Specific UV absorbance (L/mg-m)
                     UV254   =   UV absorbance at 254 nm  (1/m)
                     DOC    =   Dissolved organic carbon (mg/L)
Because TOC is more commonly measured than DOC in drinking water treatment, SUVA is
sometimes estimating using values for TOC in place of those for DOC.

       Higher SUVA values tend to indicate a greater fraction of hydrophobic organic material,
thus suggesting a greater potential for membrane fouling.  Generally SUVA values exceeding
4 L/mg-m are considered somewhat more difficult to treat.  However, organic carbon (as well as
turbidity) can often be removed effectively via coagulation and pre-settling, particularly if more
hydrophobic in character, thus minimizing the potential for membrane fouling and facilitating
operation at higher fluxes. Coagulation can also be conducted in-line (i.e., without pre-settling)
with MF/UF systems. Pretreatment using the injection of powdered activated carbon (PAC) may
also reduce DOC in the membrane feed; however, because spiral-wound membrane modules
cannot be backwashed, PAC should not be used in conjunction with NF/RO systems unless
provisions are made to remove the particles upstream.
       Dissolved Solids

       The total dissolved solids (TDS) and the particular species of dissolved solids present in
the membrane feed are both critical considerations for NF/RO systems. Species such as silica,
calcium, barium, and strontium, which can precipitate as sparingly soluble salts, can cause
scaling and a consequent rapid decline in flux under certain conditions. Scaling is typically
controlled using pretreatment chemicals such as an acid to lower the pH and/or a proprietary
scale inhibitor, as discussed in section 7.2.1.2.  However, the total quantity of dissolved solids of
any species also influences system operation, as the net driving pressure required to achieve a
target flux is related to the osmotic pressure of the system, which is directly proportional to the
TDS (as discussed in section 2.2.2).  Thus, as the TDS increases, so does the required feed
pressure.
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       IDS is generally not a significant consideration for MF, UF, and MCF systems, since
these processes do not remove dissolved solids. In some cases, however, the use of upstream
oxidants may cause the precipitation of iron or manganese salts (either unintentionally or by
design as a pretreatment process), which could accelerate membrane fouling.
7.3.3  Temperature Compensation

       Like other water quality parameters such as turbidity and TDS (for NF/RO systems), the
temperature of the feed water also affects the flux of a membrane filtration system.  At lower
temperatures water becomes increasingly viscous; thus, lower temperatures reduce the flux
across the membrane at constant TMP or require an increase in pressure to maintain constant
flux. The means of compensating for this phenomenon varies with the type of membrane
filtration system used. General viscosity-based means of compensating for temperature
fluctuations for both MF/UF and NF/RO systems are described below, although membrane
manufacturers may have a preferred product-specific approach.

       MF/UF membrane systems usually operate within a relatively narrow range of TMPs,
which may limit increasing the TMP in order to maintain constant flux as the water temperature
decreases.  Because the membrane modules can be  damaged if the TMP exceeds an upper limit,
as specified by the manufacturer, it may not be possible to operate the system at a TMP that is
sufficient to meet the required treated water production during colder months if demand remains
high.  As a result, additional treatment capacity (i.e., membrane area or number of membrane
modules) is incorporated into the design of the system such that the water treatment production
requirements can be satisfied throughout the year.

       For the microporous MF/UF membranes, the relationship between flux, TMP, and water
viscosity is given by the following equation, with a cross-reference to the same equation as listed
in Chapter 2 given in parentheses:
                          TMP
                     J = -                                    Equation 7.2  (2.7)
       Where:       J      =      flux  (gfd)
                    TMP  =      transmembrane pressure (psi)
                    Rt     =      total  membrane resistance (psi/gfd-cp)
                    (j,w    =      viscosity of water (cp)
       If the system is operated at constant flux, then increases in viscosity require proportional
increases in operating TMP (assuming constant membrane resistance).  However, once the TMP
approaches the rated maximum for the membranes, further increases in viscosity necessitate a
reduction in flux.  Thus, in order to maintain the required filtered water production flow (so as to
satisfy customer demand), the membrane area must increase in proportion to the flux decrease, as
shown in Equation 7.3:

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                        —                                         Equation 7.3  (2.1)
       Where:        J      =     flux (gfd)
                     Qp    =     filtrate flow (gpd)
                     Am    =     membrane surface area  (ft2)
       Combining Equations 7.2 and 7.3 demonstrates that the additional membrane area
required is directly proportional to the increase in water viscosity (for constant flow, TMP, and
membrane resistance), as shown in Equation 7.4:
                     QP     ™P                                     V   +•   -7A
                     	=	                                   Equation 7.4
       Where:        Qp    =     filtrate flow (gpd)
                     A-n    =     membrane surface area  (ft2)
                     TMP  =     transmembrane pressure  (psi)
                     Rt     =     total membrane resistance (psi/gfd-cp)
                     (iw    =     viscosity of water (cp)
       Membrane filtration systems are commonly designed to operate at a particular flux (e.g.,
as determined via pilot testing or mandated by the state) to produce a specific flow (i.e., rated
system capacity) at a reference temperature of 20 ฐC.  Thus, the required membrane area at 20 ฐC
can be calculated using Equation 7.3. The increased membrane area required to compensate for
cold weather flow can be determined by multiplying this area by the ratio of the viscosity at the
coldest anticipated temperature (e.g., the coldest average monthly temperature) to that at the
reference temperature of 20 ฐC.  Values for water viscosity can be found in the literature or
approximated using Equation 7.5:
              y,T =1.784 -(0.0575 •r)+o.0011ซ r2-lO~5 ซr3       Equation7.5  (2.8)

       Where:        HT    =     viscosity of water at temperature T (cp)
                      T    =     water temperature  (ฐC)
       After the appropriate values for water viscosity have been determined for both the
reference temperature (commonly 20 ฐC for MF/UF systems) and the coldest anticipated
temperature, then the design membrane area, as compensated for seasonal temperature variation,
can be calculated as shown in Equation 7.6:
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                                 LLT
                     Ad = A20 • -                                 Equation 7.6
       Where:       Ad     =     design membrane area (as adjusted for temperature)  (ft2)
                     A2o    =     membrane area required at 20 ฐC reference temperature (ft2)
                     HT     =     viscosity of water at temperature T (cp)
                     H20    =     viscosity of water at temperature T (cp)
       Equation 7.4 can also be utilized to calculate the required membrane area using a less
conservative approach that accounts for seasonal fluctuations in demand. First, if the
information is available, the average daily flow over and temperature over each calendar month
can be tabulated, and the temperature data converted into associated values for water viscosity
using Equation 7.5. Then, the  12 sets of paired flow (Qp) and viscosity (n) data can be applied to
Equation 7.4 to generate 12 values of membrane area.  The largest of these values for the
required membrane area over each of the 12 calendar months, along with its corresponding flow,
is applied to Equation 7.3 to generate an associated flux.  If this flux is less than the maximum
permitted value, then this largest of the 12 calculated values for membrane area represents the
design value for the system. However, the resulting flux exceeds this threshold, the design area
must be increased to lower the flux to the maximum permitted value.

       Note that that use of Equation 7.4 in this approach requires values for both the TMP and
the total membrane resistance,  Rt, both of which should be considered constants for the purposes
of calculate the various values  for membrane area.  While a reasonable TMP can be easily
identified, appropriate values of Rt are more difficult to determine.  The total membrane
resistance represents the sum of the intrinsic resistance of the membrane (which may be
considered a constant and can generally be obtained from the manufacturer) and the resistance
attributable to fouling at any given point during operation, as shown in Equation 7.7:
                     Rt=Rm+Rf                                    Equation 7.7  (2.6)

       Where:       Rt     =      total membrane resistance  (psi/gfd-cp)
                     Rm     =      intrinsic membrane resistance (psi/gfd-cp)
                     Rf     =      resistance of the foulant layer (psi/gfd-cp)
        Because it difficult to both identify and justify a single, specific value for the fouling
resistance for use with this approach, the contribution attributable to fouling may be ignored for
practical purposes. Thus, for the purposes of calculating membrane area, the total resistance
used in Equation 7.4 may be approximated by the membrane's intrinsic resistance. This
approximation may be reasonable for the membrane system at the start of a filtration cycle when
the fouling resistance is minimal.  Since the minimum value for membrane resistance expected
over a filtration cycle is used, the minimum TMP anticipated over a filtration cycle should also
be used.  This minimum TMP  occurs at the beginning of a filtration cycle before gradually

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increasing until the system must be backwashed. Use of the intrinsic membrane resistance and
minimum IMP should result in a reasonable and not excessively conservative estimate of the
membrane area requirements. In rare cases in which the membrane is experiencing significant
fouling under conditions of peak demand such that the flux and/or IMP are approaching their
maximum values, the backwash and/or chemical cleaning frequencies can be increased
temporarily to compensate and keep fouling to a minimum.  Alternatively, standby membrane
units may be used when necessary, as described in section?.3.5.

       The MF/UF membrane manufacturer may have an alternate preferred method of
determining the design membrane area for a particular application based on temperature,
membrane material, or other site- or system-specific factors. It is recommended that the utility
collaborate with the state,  the membrane manufacturer, and its engineer (if applicable) to  select
the most appropriate method for determining the required area.  Note that the addition of
membrane area to compensate for low-temperature flow will also help the system to meet higher
flow demands during warm weather without operating at an exceedingly high membrane  flux.
Temperature compensation for MCF systems, if necessary, can be determined using the
methodology  for MF/UF systems.

       Because spiral-wound NF/RO membrane modules are designed to operate over a larger
range of TMPs than MF/UF modules, in NF/RO systems the TMP is simply increased to
maintain constant flux as the temperature of the feed water decreases. The required increase in
TMP at the temperature of interest relative to that at a given reference temperature (typically
25 ฐC for NF/RO systems) is dependent on the specific proprietary membrane used and can be
calculated by  means of a temperature correction factor (TCF), as shown in Equation 7.8:
                    TCP = exp
U>
                                       1       1
                                    T +273  298
Equation 7.8  (2.15)
       Where:       TCF   =     temperature correction factor (dimensionless)
                    T      =     water temperature (ฐC)
                    U      =     membrane-specific manufacturer-supplied constant
       Alternatively, many NF/RO membrane manufacturers may supply tables specifying TCF
values over a range of temperatures for a given membrane. Once the appropriate TCF is known,
the required TMP at temperature T of interest can be calculated by dividing the TMP at the
reference (i.e., design) temperature (commonly 25 ฐC for NF/RO systems) by the TCF value, as
shown in Equation 7.9:
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                     IMPT =	—                                 Equation 7.9
                             TCP

       Where:        TMPT =    transmembrane pressure (temperature-corrected)  (psi)
                     TMP25 =    transmembrane pressure at 25 ฐC reference temperature (psi)
                     TCP   =    temperature correction factor (dimensionless)
       Note that Equations 7.7 and 7.8 also allow the calculation of the IMP reduction resulting
from decreased water viscosity at higher feed water temperatures during warmer months of the
year.
7.3.4  Cross-Connection Control

       In the context of membrane filtration systems, cross-connection control measures are
implemented to prevent chemicals from the cleaning process from contaminating the feed or
filtrate streams. States may have particular requirements for cross-connection control, although
in general there are two strategies that are commonly used: a double block and bleed valving
arrangement or a removable spool.  These strategies are applicable to both MF/UF and NF/RO
systems; however, because MCF systems typically utilize modules that are disposable cartridges,
these systems are  not usually subject to chemical cleaning and thus cross-connection control
measure are generally unnecessary for these systems.

       The double block and bleed valve arrangement is the most common method of cross-
connection control for large membrane filtration systems. A schematic illustrating this method is
shown in Figure 7.1. In summary, two isolation valves (V-1A and V-2A in Figure 7.1) are
placed in the feed line to isolate it from the cleaning chemicals.  These are the block and bleed
valves, respectively.  During the cleaning process, valve V-4A and V-6A are opened to bring
cleaning solution(s)  into Membrane Rack (i.e., unit) A.  Although valve V-3A is kept closed
during this operation, if it were to leak it would allow chemicals to pass into the common feed
manifold, causing contamination. In order to prevent this potential contamination, valve V-1A is
also closed and valve V-2A is opened. With this configuration, if valve V-3A leaks, the cleaning
solution(s) simply flows through valve V-2A to waste. A similar block and bleed valve
arrangement is utilized to prevent the cleaning chemicals from contaminating the filtrate
manifold as they are recirculated, which gives rise to the term "double" block and bleed.  If the
cleaning process starts automatically, valves V-1A and V-2A (i.e., the block and bleed valves)
must be actuated automatically.

       As an alternative to the double block and bleed valving arrangement,  a removable spool
(i.e., a short section  of pipe) can be placed between valves V-l A and V-3A in lieu of utilizing
valve V-2A. The  spool is then removed during the chemical cleaning.  A  removal spool should
not be used for cross-connection control if chemical cleaning is automated, since the process
could potentially be initiated with the spool still in place.
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             Figure 7.1  Double Block and Bleed Valving Arrangement
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7.3.5  System Reliability

       System reliability is an important consideration in the design of a membrane filtration
system. Design capacities are typically maximum values and may not necessarily account for
the possibility of one or more units being taken out of service for repair or routine maintenance.
Even standard operational unit processes such as backwashing, chemical cleaning, and integrity
testing that are normally accounted for in accurately sizing the facility and determining system
capacity may be problematic if it becomes necessary to conduct these processes more frequently
than was planned.  For example, most membrane filtration systems are designed with sufficient
storage and equalization capacity to meet average demand even when a unit is taken out of
service for chemical cleaning. However, this storage would generally not allow the system to
operate at capacity for extended periods (e.g., longer than about 24 hours) with a unit of out
service for repair. Reliability issues such as this may be particularly pronounced for smaller
systems with fewer membrane units, since one out-of-service unit may significantly impact
overall system capacity. Note that any state sizing and redundancy requirements should be
considered in the design of the facility.

       In order to ensure system reliability, it is common for filtration systems to incorporate
some measure of redundancy. One method of providing this redundancy is by  oversizing the
membrane units at the design flux.  Oversizing the membrane units generally allows for
operation at average flow as a minimum with one unit out of service and may allow for operation
at or near system capacity in some cases. For example, a water treatment plant with rated
capacity of 7 MGD may be designed with four membrane units rated at 2 MGD each rather than
1.75 MGD.  Thus, with one unit out of service and the  remaining three operating at capacity, the
system can produce as much as  6 MGD (at the design flux) consistently. Although the design in
this example would not allow the system to operate at maximum capacity, it is  likely that the
average flow could be met or  exceeded.

       A system could also be designed to operate at the maximum rated capacity with one unit
out of service (in this example, using four units at 2.33  MGD each), although this ability  may be
cost prohibitive,  particularly for smaller systems, since the percentage that each unit must be
oversized increases as the total number of units is reduced. Note that because this method of
providing system redundancy is based on the assumption that the rated capacities are all
specified with respect to the same design flux, the rate of fouling would not be  increased  by
operating three of the four oversized units at capacity.  In addition, continuing this example of a
treatment plant with 7 MGD of permitted capacity consisting of four 2.33-MGD membrane
filtration units, with all four units in operation the system could operate at reduced flux and still
produce 7 MGD in accordance with its permit.  This operation at reduced flux would  decrease
the rate of fouling and lower operating costs to partially offset the increase in capital cost
associated with the extra unit capacity.

       Another method of adding system redundancy is by providing an additional membrane
unit. Thus, using the same example of a water treatment plant permitted for a maximum rated
capacity of 7 MGD, the membrane filtration system would consist of five 1.75-MGD units,
rather than four.  This design would always allow for operation at capacity with one unit either
out of service or in standby mode. In this case the standby unit can be rotated such that any time
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a unit is taken offline for chemical cleaning the standby unit is activated.  The newly cleaned unit
then reverts to standby mode until the next unit is due for chemical cleaning. This method of
adding redundancy is more cost effective for larger facilities with a greater number of membrane
units, such that the addition of an extra unit does not represent a large percent increase in capital
cost.  This approach is recommended when the treatment facility utilizing membrane filtration is
the primary source of drinking water for the public water system, such that operating the
membrane system at capacity may be critical to the ability of the utility to satisfy customer
demand.  Alternatively, under this scenario all  the units may be operated at lower flux to extend
the interval between chemical cleanings.

       Independent of the particular strategy for providing some redundant capacity for the
membrane filtration system, utilities should also provide some redundancy for any major
ancillary mechanical equipment that may be utilized, such as pumps, compressors, and blowers.
Utilities must comply with any state-mandated redundancy requirements  for either membrane
capacity or ancillary equipment.

       Membrane filtration systems may also have some inherent redundancy if the system is
normally operated significantly below the maximum flux permitted by the state. In this case, if
one membrane unit is taken out of the service,  the utility can increase the temperature- and
pressure-normalized flux through the remaining units to partially or fully compensate for the loss
of production attributable to the out-of-service unit.  However, if a unit is out of service for a
prolonged period, the increase in flux may accelerate fouling in the remaining in-service units to
an unacceptable rate.

       Timely membrane replacement is another consideration for maintaining system
performance and reliability.  Membrane replacement is usually conducted on an as-needed basis,
typically either in cases in which the membranes have been damaged or the flux has declined to
an unacceptable level as a result of  irreversible fouling. Although the useful life of membranes
is commonly cited in the range of 5 to 10 years (a period generally consistent with manufacturer
warranties), the use of membrane technology - particularly MF and UF - has increased almost
exponentially in the decade preceding this guidance manual, and thus most membrane filtration
systems have not been in continuous operation for more than 5 to 10 years. Consequently, there
is limited field data available to document the typical useful life of membrane filtration modules.
Nevertheless, it is recommended that utilities keep a small number of surplus membrane modules
on site in the event that emergency  replacement becomes necessary.
7.4    Residuals Treatment and Disposal

       As with many water treatment processes, membrane filtration systems may generate
several different types of residuals that must be treated and/or disposed of, including backwash
and chemical cleaning residuals and concentrate. The types of residuals that are generated vary
with both the type of membrane filtration system and the hydraulic configuration in which
system in operated. For example, NF/RO systems produce a continuous concentrate stream and
periodic chemical cleaning waste, but because these systems are not backwashed, no backwash
residuals are generated.  MF/UF systems are regularly backwashed and undergo periodic
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chemical cleanings and thus produce residuals from both these operational unit processes.
However, only MF/UF systems that are operated in a crossflow hydraulic configuration and
waste (rather than recirculate or recycle to the plant influent) the unfiltered flow - the so-called
"feed and bleed" mode - will generate a concentrate stream. Because cartridge filters operate in
a deposition mode hydraulic configuration (see section 2.5) and are designed to be disposable,
there are typically no residuals streams associated with MCF systems. Nevertheless, the spent
filter cartridges (as well as all membrane filtration residuals) must be properly disposed of in
accordance with  any applicable state and local regulations, particularly if the cartridges have
been used to filter any potentially hazardous materials.

       The various potential residuals streams from membrane filtration systems - backwash
residuals, chemical cleaning residuals, and concentrate - are discussed in the following
subsections. Note that these discussions are not meant to represent a comprehensive review of
residuals treatment and disposal, but rather a general overview of some of the primary
considerations that should be taken into account when planning and designing a membrane
filtration system. For additional information, the reader is referred to the following references:

       •  Water Treatment Plant Waste  Management (1987)
          (Prepared by Cornwell et al. of Environmental Engineering & Technology for the
          American Water Works Association Research Foundation)

       •  Treatment ofMF Residuals for Contaminant Removal Prior to Recycle (2002)
          (Prepared by MacPhee et al. of Environmental Engineering & Technology for the
          American Water Works Association Research Foundation)

       •  Current Management of Membrane Plant Concentrate (2000)
          (Prepared by Kenna et al. of Clarkson University for the American Water Works
          Association Research Foundation)

       •  Major Ion Toxicity in Membrane Concentrate (2000)
          (Prepared by Mickley of Mickley & Associates for the American Water Works
          Association Research Foundation)

       •  Membrane Concentrate Disposal: Practices and Regulation (2001)
          (Prepared by Mickley of Mickley & Associates for the United States Bureau of
          Reclemation)

       •  Membrane Concentrate Disposal (1993)
          (Prepared by Mickley et al. for the American Water Works Association Research
          Foundation)

       •  The Desalting and Water Treatment Membrane Manual: A Guide to Membranes
         for Municipal Water Treatment (2nd Ed.) (1998)
          (Prepared by the United States  Bureau of Reclamation)
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          Reverse Osmosis and Nanofiltration (M46) (1999)
          (Prepared the American Water Works Association)
7.4.1   Backwash Residuals

       Among the various types of membrane filtration, only MF/UF systems employ
backwashing, thus generating backwash residuals. Although the frequency varies on a site- and
system-specific basis, backwashing is typically conducted every 15 to 60 minutes. Under normal
operating conditions the backwash frequency should remain relatively consistent, allowing for
the quantity of residuals generated to be estimated fairly accurately.

       As a general rule of thumb, the residual stream produced from backwashing MF/UF
membranes has a concentration of suspended solids that is approximately 10 to 20 times greater
than that of the feed water. Although MF/UF systems remove approximately the same types of
feed water constituents as conventional media filters, the volume and characteristics of the
residuals may be significantly different. In many current applications of MF/UF for municipal
water treatment, filter aids such as coagulants and polymers are not necessary.  In these cases,
the amount of solids removed in the backwash process may be significantly less than that for a
comparable conventional filtration plant. In addition, disposal of these coagulant- and polymer-
free MF/UF backwash residuals may be less problematic.  However, in some applications of
MF/UF, coagulants may be added in-line (i.e., without pre-settling) to help facilitate the removal
of TOC, which is  not normally removed to a significant degree by MF or UF. In such
applications the MF/UF backwash residuals characteristics will generally be similar to those for
conventional media filtration.

       Disposal options for MF/UF backwash residuals are similar to those for conventional
water treatment plants,  and typically include the following:

       •  Discharge to a suitable surface water body

       •  Discharge to the sanitary sewer

       •  Treatment with supernatant recycle and solids disposal
       The discharge of backwash residuals to surface water bodies or the sanitary sewer is
likely to be subject to state and/or local regulations and, in the case of surface water discharge, to
require a permit. Moreover, the potential to utilize one of these options may be complicated if
the residuals include chemical wastes. In addition to the use of coagulants added to the feed,
some backwash procedures utilize chlorine or other chemicals, as described in section 7.2.2.
Small amounts of chlorine may be quenched and acids or bases can be neutralized prior to
discharge, although larger amounts or other types of chemicals added to the backwashing
processes may require additional treatment or preclude discharge to a surface water body or
sanitary sewer.
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                            Chapter 7 - Implementation Considerations
       On-site treatment options for MF/UF backwash residuals are also similar to those that
might be used with conventional media filtration, and include clarification, sedimentation
lagoons, gravity thickening, centrifuging, belt filter presses, or a combination of these processes.
A second stage of MF or UF may also be utilized to further concentrate residuals and increase
process recovery. If a sedimentation process is used to treat MF/UF backwash residuals, the
addition of a coagulant may be necessary to improve the settling characteristics of the solids if
coagulant is not already applied in the MF/UF pretreatment process.  With on-site treatment, the
supernatant is generally recycled to the treatment plant influent while the concentrated solids are
transported off site for landfilling or other means of disposal.  As with discharging, the addition
of chlorine or other chemicals to the backwash process may complicate residuals treatment.

       It is important to note that backwash residuals concentrate any pathogenic organisms that
are present in the feed water, as well as other suspended solids.  Although the control of such
concentrated pathogens in filter backwash residuals is largely unregulated, the potential
treatment of this stream should be taken into consideration if these residuals are to be discharged
into a surface water receiving body.
7.4.2  Chemical Cleaning Residuals

       Both MF/UF and NF/RO membranes undergo periodic chemical cleaning, and thus both
types of systems generate spent chemical waste as a byproduct of these processes. As with the
backwashing process for MF/UF, the frequency of chemical cleaning varies on both a site- and
system-specific basis.  Although chemical cleaning is conducted much less frequently than
backwashing, the frequency is also more difficult to predict. Generally, MF/UF systems are
cleaned no more frequently than once every month for efficient operation and the minimization
of system downtime, although it is not uncommon for these systems to  operate for much longer
without requiring chemical cleaning.  The cleaning frequency for NF/RO  may vary anywhere
from 3 months to 1 year, depending on the feed water quality and the effectiveness of feed water
pretreatment for minimizing fouling.  However, because chemical cleaning is a relatively
infrequent batch process, estimating the quantity of residuals generated is not as critical for day-
to-day operation, as is the case with backwashing.

       Chemical cleaning residuals are generally treated on-site and discharged to either a
suitable surface water body or sanitary sewer, subject to state and/or local regulations.  Oxidants
such as chlorine used in the chemical cleaning process can be quenched prior to discharge, and
acids and bases can be neutralized. The use of other chemicals, such as surfactants or proprietary
cleaning  agents, may complicate the process of obtaining regulatory approval for discharge and
could require additional treatment.

       Note that the rinse water applied to the membranes after the cleaning process also
represents a chemical waste and must be treated prior to discharge. Although the rinse water
increases the volume the chemical cleaning residuals, this increase  can be balanced somewhat by
the recovery and reuse of a significant portion of the  cleaning solutions. In some cases, as much
as 90 percent of the applied cleaning solutions can be reused, reducing residuals treatment and
disposal costs, as well as chemical usage.
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7.4.3  Concentrate

       The term "concentrate" is usually associated with the continuous waste stream of
concentrated dissolved solids produced by NF and RO processes.  This waste stream is typically
4 to 10 times more concentrated than the feed with respect to suspended and dissolved
constituents and represents about 15 to 25 percent of the total feed flow, although it can exceed
50 percent or more in some cases.  As a result, concentrate disposal is a significant logistical and
regulatory concern for utilities and is often a critical factor in the planning and design of an NF
or RO facility.

       There are a number of methods for concentrate treatment and disposal, including the
following options:

       •   Surface water discharge

       •   Sanitary sewer discharge

       •   Land application / irrigation

       •   Deep well injection

       •   Evaporation

Because there are complicating factors associated with each of these options, no single option is
ideal or most appropriate for every application. In many  cases surface water discharge is the
least expensive option, although the permitting process may be difficult, since there are potential
environmental impacts if the salinity of the concentrate is significantly higher than that of the
receiving body. Discharge to the sanitary sewer may have similar issues, since the wastewater
treatment process does not typically affect dissolved solids concentrations, and the  treatment
plant effluent may ultimately be discharged to surface water receiving body.   High salinity or
major ion toxicity may also preclude land application of the concentrate if levels exceed
threshold levels tolerated by the irrigated crops. Bioaccumulation of metals has also been cited
as a potential concern for land application of NF/RO concentrate.  Deep well injection is an
effective and commonly used technique for concentrate disposal, although this method risks the
escape of brackish water into less saline or freshwater aquifers and may have unknown long-term
environmental affects.  The use of evaporation ponds is generally  limited to areas with low
precipitation and high evaporation rates, as well as an abundance of inexpensive and available
land.

       Another option for dealing with NF/RO concentrate is the concept of "zero  liquid
discharge," which involves sufficiently concentrating the residual stream through the use of such
technologies as crystalizers and evaporators to allow remaining solids to be landfilled. While
zero liquid discharge is typically an expensive option, is does offer a  number of advantages,
including avoiding the discharge permitting process and the ability to be utilized at any location
independent of factors such as the proximity to a suitable surface water body or available land
for  evaporation ponds. In addition, zero liquid discharge maximizes facility recovery and has


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                            Chapter 7 - Implementation Considerations
minimal environmental impact. Although still fairly uncommon, this option has become
increasingly feasible relative to other methods as environmental and discharge regulations have
become more stringent.

       The considerations noted above represent only a cursory discussion of the issues
associated with the various options for concentrate treatment and disposal. More detailed
information is available in several of the references cited in section 7.4.  Note that all of these
options are subject to applicable federal, state, and local regulations.

       Some MF/UF systems that are operated in a suspension mode and waste the unfiltered
flow generate a continuous concentrate  stream. This stream differs from that associated with
NF/RO systems in two significant ways:  MF/UF systems concentrate suspended rather than
dissolved solids; and the concentrate stream represents only a small fraction of total feed flow.
(Note that NF/RO membranes  represent a barrier to particulate matter, and thus these systems
will also concentrate suspended solids;  however,  because suspended solids rapidly foul the semi-
permeable membranes (which  cannot be backwashed), most particulate matter is typically
removed with pre-filters.) An  MF/UF concentrate stream has characteristics similar to those of
backwash residuals, and therefore can be considered comparable for the purposes of treatment
and disposal. Alternatively, these two residuals streams may be blended together.
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                                8.0  Initial Start-Up
8.1    Introduction
       The initial start-up phase is a critical step in the successful installation of a full-scale
membrane filtration system and thus is an essential consideration in the facility planning and
design process. This period includes such tasks as initial system flushing and disinfection,
system diagnostic checks, membrane module installation, integrity testing new equipment, and
operator training, all of which must be completed prior to placing the system into service. Note
that the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) does not contain
any requirements for the initial start-up of a membrane filtration system. Consequently, this
chapter is  included in the Membrane Filtration Guidance Manual as a useful reference for
utilities that summarizes widely recognized industry best practices and important considerations
for the start-up process.  However, state requirements that overlap with any of the subjects
covered under this reference on initial start-up would supersede the guidance provided in this
chapter.

       In  general, the primary objectives of the initial phase are to ensure that the installation is
successfully completed and that the equipment  is in proper working order and  ready to produce
potable water that achieves all target quality standards. A well-planned initial  start-up phase can
thus help facilitate the proper execution of the membrane filtration system start-up and create a
smooth transition from testing to drinking water production.  This chapter discusses important
general start-up considerations, pointing out any significant differences between nanofiltration
(NF)/reverse osmosis (RO) and microfiltration  (MF)/ultrafiltration (UF) systems.  For the
purposes of this discussion, membrane cartridge filtration (MCF) systems are considered to be
similar to  MF/UF systems, except as otherwise noted.

This chapter is divided into the following sections.

       Section 8.2:    Temporary System Interconnections
                     This section describes the provisional requirements that may be necessary
                     during start-up of a membrane filtration system.

       Section 8.3:    Flushing and Testing Without Membranes
                     This section describes the general procedures that are associated with
                     flushing a membrane filtration system and confirming that each unit is
                     operating properly without the membrane modules installed.

       Section 8.4:    Membrane Installation
                     This section reviews considerations associated with the installation of
                     membrane modules.

       Section 8.5:    System Disinfection
                     This section discusses the initial disinfection process for systems using
                     both chlorine-tolerant and chlorine-intolerant membranes.
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                                  Chapter 8 - Initial Start-Up
       Section 8.6:    Initial Direct Integrity Testing
                     This section outlines some considerations for conducting initial direct
                     integrity testing on the newly installed membrane modules.

       Section 8.7:    Acceptance Testing
                     This section describes some of the typical practices associated with
                     acceptance testing.

       Section 8.8:    Operator Training
                     This section describes the operator training that the equipment supplier
                     should provide during the start-up phase.
8.2    Temporary System Interconnections

       During the start-up process, the filtered water produced from the membrane units may not
be acceptable for distribution. Therefore, facility design should include provisions for the
recycle and/or temporary disposal of feed and filtrate water. Provisions for disposal usually
consist of a removable pipe spool or a tee with a "dump" valve placed in the common feed or
filtrate line.  This water can usually be diverted to the sanitary sewer.  If the feed and filtrate
piping are interconnected, the connection is removed and replaced with blind flanges after start-
up has been completed.  Some facilities simply divert and recycle the treated water to the inlet
structure until the system is fully commissioned.  Any state requirements governing the disposal
and potential recycle of the water produced during the start-up phase should be incorporated  into
the planning process.
8.3    Flushing and Testing Without Membranes

       Prior to installing the membrane modules, any debris introduced during construction
should be flushed from the system. This flushing is usually conducted by running the
appropriate pump (s) at high velocity and low pressure through the piping and discharging the
water to a suitable drain.  Typically, the flush water can be discharged to the sanitary sewer,
although the utility should comply with any state requirements for disposal.  Because the intent
of the flushing process is to remove debris from the system, this water should not be recycled
unless pretreatment processes would be expected to remove contaminants flushed from the
system.

       After the piping system has been flushed, the operational sequences and chemical
addition systems should be tested to ensure that they are operating properly before installing the
membrane modules.  Because of the complexity of the equipment involved, it is suggested that a
plan for conducting these diagnostic checks be developed in advance.  In general, the
recommended testing can be divided into the following categories:
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       •  Mechanical Equipment - Inspect automated mechanical equipment to ensure that it
          is properly installed and that there are no leaks in the piping system. Operate
          mechanical equipment in manual mode and then in automatic mode to verify that it is
          working as designed.

       •  Instrumentation - Verify that the instrumentation is properly installed and
          calibrated. Confirm that the instruments are operating correctly and are responsive to
          the control system.

       •  Control System- Verify control inputs and outputs (both digital and analog),
          instrumentation alarm limits, programming logic, instrumentation loops, and
          operational sequences.

       •  Membrane Units  and Related Systems - Verify that the membrane filtration system
          and each respective membrane unit can be both started and shutdown smoothly.
          Operate the chemical feed systems (if any) to verify that they are each in proper
          working condition  and that all chemicals are delivered at the proper dosages.
       For NF/RO systems, the procedure for testing the operating sequences is commonly
known as the "48-hour test," as it may take two or more days to complete.  Unlike the initial
flushing, the 48-hour test should be conducted at actual operating parameters, including both
typical pressures and flows.  Therefore, it is common to insert flow restriction devices in the
system in place of the membrane modules during this operation to simulate the  anticipated
system backpressure.  These devices typically consist of orifice plugs placed in the permeate
(i.e., filtrate) port inside the pressure vessel. The orifice plugs are sized to  simulate the flow and
pressure parameters of the operating membrane filtration system.  Alternatively, an isolation
valve on the permeate piping could be throttled to the appropriate backpressure. Although the
term "48-hour test" is less  commonly used  in association with MF and UF, these systems are
also generally tested either with "dummy" modules that have similarly designed orifices or by
throttling filtrate effluent valves to create sufficient backpressure during the testing sequences.
8.4    Membrane Installation

       Membrane module installation should be conducted according to the instructions
obtained from the manufacturer.  Care should be taken not to damage the membranes during the
installation process. It is recommended that the location of each individual membrane in the
system be recorded according to its serial number.  Factory test data are often shipped with the
membranes, and this information should be collected and filed.

       Membrane modules are typically shipped "wet" with a liquid preservative solution.  The
particular preservative depends upon the type of membrane. Most membranes are preserved
with a 1 percent solution of sodium bisulfite, a reducing agent that acts as a biocide to control
microbial growth. Prior to installation, the membrane modules should be stored in an
appropriate manner such that they are not subjected to freezing conditions that could damage the


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                                  Chapter 8 - Initial Start-Up
membranes. Regardless of the membrane type, the preservative should be flushed to waste after
the membranes are installed. Note that the disposal of any preservative solutions should be
conducted in accordance with any applicable regulations.

       Some membrane modules are shipped with more problematic storage solutions.  For
example, glycerin solutions may pose a waste treatment issue because of the biochemical oxygen
demand (BOD) that may result from the solution being flushed down the drain.  The use of
formaldehyde, once a common membrane preservative is generally no longer acceptable, and it
may pose a significant disposal problem. Both state and local regulations regarding chemical
disposal may apply to membrane preservative solutions, and these may dictate whether it is
permissible to discharge these preservatives to the sanitary sewer or if collection and alternate
disposal and/or treatment is required.
8.5    System Disinfection

       Initial system disinfection typically involves the application of a disinfectant, such as a
chlorine solution, throughout the entire system, including both the feed and filtrate piping.
Although both soaking and recirculating procedures are used, recirculating the solution through
the system will generally provide more effective disinfection. This disinfection step may be
required by the state, and in any case is recommended to inactivate bacteria or other pathogenic
organisms that may contaminate the membrane filtration system and associated piping.  Because
some membranes have limited compatibility with disinfecting chemicals, the manufacturer may
have specific requirements for the disinfection process, and approval will be necessary if
manufacturer recommendations differ from state requirements.  General procedures for the
disinfection of both chlorine-tolerant and chlorine-intolerant membranes are described in the
following sections.  In either case, once the system disinfection  is complete, the entire system
(including the membranes) should be flushed prior placing the membrane unit(s) into continuous
service. This final flush can be  conducted according same guidelines outlined in section 8.3 and
should continue until the desired filtered  water quality is attained as measured by site- or
membrane system-specific water quality  parameters.
8.5.1  Chlorine-Tolerant Membranes

       The American Water Works Association (AWWA) and the American National Standards
Institute (ANSI) have developed standards pertaining to the disinfection of water treatment
facilities.  Specifically, ANSI/AWWA Standards C651 and C653 provide guidance for the
disinfection of water treatment plants and associated piping systems.  The procedure involves
surface contact with a high strength chlorine solution for a specific time period.  The disinfection
is complete when bacteriological sampling and testing indicate the absence of coliform
organisms. For systems that use chlorine-tolerant membranes, the membrane modules should be
installed prior to initiating the disinfection procedure. If the disinfection process is conducted
while the membranes are in place, sufficient pressure should be applied to ensure adequate flow
across the membranes such the filtrate side piping is thoroughly disinfected. Some MF/UF
membranes and most MCF membrane are chlorine-tolerant.
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8.5.2  Chlorine-Intolerant Membranes

       Most NF and RO membranes, as well as some MF and UF membranes, are not chlorine-
tolerant.  For systems that use these types of membranes, there are two options that are generally
available for system disinfection.  One option consists of conducting the system disinfection with
chlorine as described in section 8.5.1 but prior to membrane installation. Subsequently, the
membranes are installed and flushed, and then another disinfection specific to the chlorine-
intolerant membrane is conducted. This second disinfection typically utilizes a high pH (i.e.,
-10 or greater) solution of caustic or other alkaline chemical that is very effective for
bacteriological inactivation.  The membrane manufacturer should be consulted to ensure that this
second disinfection is conducted within the pH tolerance limits of the membrane. A second
option, if permissible under state regulatory requirements, involves the  elimination of chlorine or
other oxidants and using caustic (or other alkaline chemical) to disinfect the entire system,
including the membranes. The  state should be consulted prior to performing this type of
alternative  disinfection procedure. If an alternate disinfection procedure is used, additional
microbiological monitoring may be warranted to ensure the efficacy of the disinfection process.
8.6    Initial Direct Integrity Testing

       Once the system is thoroughly flushed and disinfected, a direct integrity test should be
conducted on each membrane unit.  (Both general guidance for direct integrity testing and
specific requirements for compliance with the LT2ESWTR are provided in Chapter 4.)  If the
direct integrity test utilized requires that the membrane be fully wetted, the system may need to
be operated for a period of time prior to conducting the test.  After the direct integrity test has
been completed, any defective membrane modules or leaks in o-rings, pipe connections, or valve
seals should be repaired or replaced, as necessary. Until the direct integrity test has been
successfully completed, the filtrate should be discharged to waste or recycled, as appropriate.

       For most membrane systems it is advisable to conduct relatively frequent direct integrity
testing during the initial start-up phase, as there may be a higher incidence of integrity failure
observed during the initial stages of facility operation. As a general rule, most membrane
manufacturing related defects will manifest within 72 hours of continuous operation.  However,
the propensity to exhibit such defects varies significantly among different membranes. In order
to ensure that  all initial manufacturing defects are detected,  it is recommended that direct
integrity testing be conducted 2 to 6 times per day during start-up until the test results are stable.
8.7    Acceptance Testing

       The purpose of acceptance testing is to demonstrate equipment performance as a
condition for transferring responsibility over the membrane filtration equipment from the
manufacturer or contractor to the utility. Acceptance testing is conducted after other phases of
the start-up and commissioning process (i.e., flushing disinfection, and integrity testing) have
been completed. Typically, acceptance testing is the final phase of the commissioning process
and consists of the following two criteria:
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                                   Chapter 8 - Initial Start-Up
           Operation- The entire system, including all membrane units, is continuously
           operated for a pre-determined period of time, usually from 3 to 30 days. Any
           interruptions in continuous operation as a result of faulty equipment or controls
           during this period of time may result in restarting or temporarily suspending the test.
           Design parameters (e.g., flux and backwash frequency (if applicable)) are also
           typically verified as a component of the operational criterion.

           Water  Quality Testing - Periodic sampling and analysis is conducted to ensure that
           the treated water quality objectives are continuously satisfied.  The required sampling
           can vary widely in terms of the number of constituents of interest and is very  site-
           specific. The sampling frequency for each parameter is typically once per day.  If the
           system  is unable to produce the required water quality, the manufacturer or contractor
           should be obligated to correct the problem before the acceptance testing is determined
           to be successfully completed.
       Utilities that apply membrane filtration for compliance with the LT2ESWTR may use the
acceptance testing period to establish the required control limits for direct integrity testing and
continuous indirect integrity monitoring, as discussed in Chapters 4 and 5, respectively, subject
to any particular state requirements.
8.8    Operator Training

       Because operators may not be familiar with the various types of membrane filtration
systems, operator training is an important program element to include in the initial start-up
phase. Even if some experience was gained during pilot testing, this experience should serve as
a supplement to training on the completed full-scale facility, rather than a substitute. This
training can also help facilitate a smooth transition of responsibility from the equipment supplier
to the utility. A sample operator training schedule is shown in Table 8.1.
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                                      Chapter 8 - Initial Start-Up
                           Table 8.1  Schedule of Training Events
Time Period
During Construction
and Commissioning
After Commissioning
After Three Months
Topic
System Overview / Review of Unit Operations
Facility Walk Through
Principles of Membrane Operation
Control System
Pretreatment Unit Operations
Operation / Pumps / Instrumentation
Post-Treatment
Chemical Cleaning (Including Demonstration)
Integrity Testing / Module Isolation and Repair
Monitoring / Troubleshooting / Data Normalization
Details of Control System / Remote Monitoring
Total
Open Discussion with Membrane Manufacturer
Open Discussion with Membrane Manufacturer
Duration1
(hours)
1 -4
1 -2
1 -4
4-24
1 -4
4-16
1 -2
4-16
4-8
2-4
1 -2
24-86
1 - 3 days
1 - 3 days
        1  Higher ends of the ranges cited are associated with more complex systems and less operator familiarity
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                                    References
Abbaszadegan, M., M.N. Hansan, C.P. Gerba, P.P. Roessler, B.R. Wilson, R. Kuennen, and E.
       Van Dellen.  1997.  The disinfection efficacy of a point-of-use water treatment system
       against bacterial, viral, and protozoan waterborne pathogens. Water Research.
       31(3):574-582.

Adams, B.H.  1959. Methods of study of bacterial viruses.  In Bacteriophages.  pp. 443-522.
       New York: Interscience Publishers.

Adham, S.S., J.G. Jacangelo, and J-M. Laine.  1995. Low-pressure membranes: assessing
       integrity.  J. AWWA, 87:3:62.

American Public Health Association, American Water Works Association,  and Water
       Environment Federation. 1998. Standard Methods for the Examination of Water and
       Wastewater. 20th Edition. Baltimore, MD.

American Society for Testing and Materials.  2000. F 658-OOa - Standard practice for
       calibration of a liquid-borne particle counter using an optical system based upon light
       extinction. West Conshohocken, PA

American Society for Testing and Materials.  1995. D 4189-95 - Standard testing method for silt
       density index (SDI) of water. West Conshohocken, PA

American Society for Testing and Materials.  1998. D 3923-94 - Standard practices for
       detecting leaks in reverse osmosis devices. West Conshohocken, PA

American Society for Testing and Materials.  1993. F 838-83 -  Standard test method for
       determining bacterial retention of membrane filters utilized for liquid filtration.  West
       Conshohocken, PA

American Water Works Association. 1999. Reverse Osmosis and Nemo filtration (M46).
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American Water Works Association Research Foundation.  2000. Fundamentals of drinking
       water particle counting. New York: McGraw-FIill.

American Water Works Association Research Foundation.  2000. Particle count method
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American Water Works Association Research Foundation, Lyonnaise des Eaux, and Water
       Research Commission of South Africa.  1996. Water treatment membrane processes.
       New York: McGraw-Hill.
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                                       References
Banerjee, A., F. Hanson, E. Paoli, C. Korbe, R. Kolman, D. Nelson, K. Smith, and M.
       Lambertson. 1999a. Ultra low range instrument increases turbidimetric sensitivity by
       two orders of magnitude. AWWA Water Quality  Technology Conference Proceedings,
       October 31-November 4, 1999. Tampa, FL.

Banerjee, A., J. Lozier, and K. Carlson. 2001. An on-line, multi-sensor, membrane filtration
       permeate water quality monitoring system. AWWA Membrane Technology Conference
       Proceedings, March 4-7, 2001.  San Antonio, TX.

Banerjee, A., K. Carlson, and J. Lozier. 2000. Monitoring membrane integrity using ultra high
       sensitive laser light. AWWA Water Quality Technology Conference Proceedings,
       November 5-9, 2000.  Salt Lake City, UT.

Banerjee, A., M. Lambertson, and K. Carlson. 1999b. Sub-micron particles in drinking water
       and their role in monitoring the performance of filtration processes.  AWWA Water
       Quality Technology Conference Proceedings, October 31 - November 4, 1999. Tampa,
       FL.

Barbeau, B., L. Boulos, R. Desjardins, J. Coallier, M. Prevost, and D. Duchesne.  1997. A
       modified method for the enumeration of aerobic spore-forming bacteria. Canadian
       Journal of Microbiology. 43:976-980.

Childress, A. and M. Elimelech  1996.  Effect of solution chemistry on the surface charge of
       polymeric reverse osmosis and nanofiltration membranes.  J. Membrane Science
       119:253-268.

Colvin, C., R. Brauer, N. DiNatale, and T. Scribner. 2001. Comparing laser turbidimetry with
       conventional methods for monitoring MF and UF membrane integrity.  AWWA
       Membrane Technology Conference Proceedings, March 4-7, 2001.  San Antonio, TX.

Cote, P., I. Sutherland, N. Adams, and J. Cadera. 2003.  Validation of membrane integrity
       methods in a challenge test with Bacillus subtillis. AWWA Membrane Technology
       Conference Proceedings, March 2-5, 2003. Atlanta, GA.

Cornwell,  D., M. Bishop, R. Gould, and C. Vandermeyden.  1987. Water treatment plant waste
       management. Denver, CO: American Water Works Association Research Foundation.

Crane Co.  1988. Flow of Fluids Through  Valves, Fittings, and Pipe. Technical Paper No. 410.
       Stamford, CT.

Farahbakhsh, K., and D. Smith. 2003. Estimating air diffusion contribution to pressure decay
       during membrane integrity tests. AWWA Membrane Technology Conference
       Proceedings, March 2-5, 2003.  Atlanta, GA.
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                                       References
Glucina, K., J-M Laine, C. Anselme, M. Chamant, and P. Simonie.  1999.  Acoustic sensor: a
       novel technique for low pressure membrane integrity monitoring. A WWA Membrane
       Technology Conference Proceedings, February 28 -March 3, 1999. Long Beach, CA.

International Organization for Standardization (1999) 11943 - Hydraulic fluid power - on-line
       automatic particle counting systems for liquids - methods of calibration and validation.
       Geneva, Switzerland.

Jacangelo, J., S. Adham, and J-M Laine.  1997.  Membrane filtration for microbial removal.
       Report No. 90715. Denver, CO: American Water Works Association Research
       Foundation.

Johnson, W.T.   1997. Predicting log removal performance of membrane systems using in-situ
       integrity testing. A WWA Annual Conference Proceedings, June 15 - 19, 1997.
       Atlanta,  GA.

Jucker, C.  and M. Clark. 1994. Adsorption of aquatic humic  substances on hydrophobic
       ultrafiltration membranes. J. Membrane Science.  97:253-268.

Kenna, Eric N., and Amy K. Zander.  2000.  Current management of membrane plant
       concentrate. Denver, CO: American Water Works Association Research Foundation.

Landsness, L.B. 2001. Accepting MF/UF technology - making the final cut.  AWWA Membrane
       Technology Conference Proceedings, March 4-7, 2001.  San Antonio, TX.

Li, S.Y., J.A. Goodrich, J.H. Owens, G.E. Willeke, F.W. Schaefer III, and R.M. Clark. 1997.
       Reliability of non-hazardous surrogates for determining Cryptosporidium removal in bag
       filters. Journal AWWA. 89(5):90-99.

Lozier, Jim, Christian Colvin, Jae-Hong Kim, Mehmet Kitis,  Benito Marinas, and Baoxia Mi.
       2003. Microbial removal and integrity monitoring of high-pressure membranes. Denver,
       CO: American Water Works Association Research Foundation.

MacPhee, Michael J., Yann LeGouellec, and David Cornwell. 2002. Treatment of MF residuals
      for contaminant removal prior to recycle.  Denver, CO: American Water Works
       Association Research Foundation.

Meltzer, Theodore H.  1997. High-purity water preparation for the semiconductor,
      pharmaceutical, and power industries. Littleton, CO: Tall Oaks Publishing, Inc.

Meltzer, Theodore H.  1987. Filtration in the pharmaceutical industry. New York, NY: Marcel
       Dekker,  Inc.

Mickley, Michael M. 2001. Membrane concentrate disposal: practices and regulation. Denver,
       CO: United States Bureau of Reclamation Technical Service Center, Water Treatment
       Engineering and Research.
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                                       References
Mickley, Michael M. 2000. Major ion toxicity in membrane concentrate.  Denver, CO:
       American Water Works Association Research Foundation.

Mickley, Michael M., Robert Hamilton, Lana Gallegos, and Jeffrey Truesdall.  1993. Membrane
       concentrate disposal. Denver, CO: American Water Works Association Research
       Foundation.

National Sanitation Foundation International.  2002. ETV protocol for equipment verification
       testing for physical removal of microbiological and particulate contaminants. Ann Arbor,
       MI.

Schulze, Jack C. 2001.  The Texas approach to regulating MF/UF drinking water applications.
       A WWA Membrane Technology Conference Proceedings, March 4-7, 2001. San Antonio,
       TX.

United States Bureau of Reclamation. 1998.  The desalting and water treatment membrane
       manual: a guide to membranes for municipal water treatment (2nd Ed). Technical
       Service Center, Water Treatment Engineering and Research, Denver, CO.

United States Department of Health and Human Services, Food and Drug Administration.  2002.
       Code of Federal Regulations Title 21 (Food and Drugs), Part 820 - Quality System
       Regulation (21 CFR 820).

USEPA. 2003. Toolbox guidance manual for the Long Term 2 Enhanced Surface Water
       Treatment Rule, Proposal Draft.

USEPA. 2003. UV disinfection guidance manual, Proposal Draft.

USEPA. 2001. Low-pressure membrane filtration for pathogen removal: application,
       implementation, and regulatory issues. EPA 815-C-01-001, April 2001.

USEPA. 1999. Guidance manual for compliance with the Interim Enhanced Surface Water
       Treatment Rule: turbidity provisions.  EPA 815-R-99-010, April 1999.

USEPA. 1993. Methods for the determination of inorganic substances in environmental
       samples. EPA 600-R-93-100, August 1993.

USEPA. 1990. Guidance manual for compliance with the filtration and disinfection
       requirements for public water systems using surface water sources.  EPA 68-01-6989,
       March 1991.

Vickers, J.  1993.  Aspects of integrity testing and module construction for microporous
       membrane filters. Technical Paper - Memtec America Corporation.
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                         Appendix A

    Development of a Comprehensive Integrity Verification
                           Program
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                                    Appendix A:

    Development of a Comprehensive Integrity Verification Program


A.1    Introduction

       The ability to maintain system integrity is one of the most important operational concerns
associated with any membrane filtration facility, whether applied for compliance with the Long
Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) or for any other treatment
objective.  Because a membrane represents a physical barrier to pathogens and other drinking
water contaminants, the means to ensure that this barrier remains uncompromised is critical for
the ongoing protection of public health.  Moreover, the number and variety of integrity-related
compliance requirements for membrane filtration under the LT2ESWTR, ranging from various
forms of testing to repair to data collection and reporting, as specified in Chapters 4 and 5,
illustrate the potential complexity of the process of maintaining system integrity. As a result,
this appendix has been prepared to serve as a tool to guide utilities in the development of a
comprehensive, effective, and efficient integrity verification program (IVP). The various
sections of this appendix are organized into a series of introductory questions that would be
posed in the preparation of an IVP and corresponding discussions to elaborate on how these
questions would be addressed in the context of an IVP.


What is a comprehensive IVP?

       A comprehensive IVP is a customized site- and system-specific program that details all
operating procedures associated with maintaining membrane filtration system integrity, including
both federal and state requirements and any additional practices that are voluntarily implemented
at the discretion of the utility. In the broadest terms, an IVP should serve as a master plan for
preserving system integrity.


What is the purpose of an IVP?

       The primary purpose of an IVP is to provide a utility with rational  and systematic
blueprint for applying appropriate tools and techniques to efficiently conduct the following
procedures:

       1.  Verifying integrity on  an ongoing basis

       2.  Identifying and correcting any integrity problems

       3.  Recording and analyzing integrity test data

       4.  Preparing any required compliance reporting
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              Appendix A - Development of a Comprehensive Integrity Verification Program


The successful execution of these procedures, in turn, allows a utility to track system
performance and determine whether or not it is consistent with either that established by
challenge testing or other requirements that may be applicable.


Why is an IVP important?

       Because the process of maintaining system integrity has many aspects, an IVP is critical
for organizing all of the various operating procedures relating to system integrity into a
comprehensive plan.  As an organizational tool,  an IVP is also important for its ability to provide
a framework to assist operators with conducting  the proper procedures in the correct sequence
under both normal  operating conditions and when an integrity breach is either suspected or
confirmed.  As a whole, these IVP functions help to both ensure the production of safe drinking
water and facilitate regulatory compliance.


What are the regulatory requirements associated with an IVP?

       Although an IVP is not required for membrane filtration systems under the LT2ESWTR,
the development of IVP can facilitate regulatory compliance by organizing the rule requirements
into a comprehensive operational program.  However, whether membrane filtration is applied for
LT2ESWTR compliance or to meet any other treatment objectives, any IVP should be consistent
with all USEPA and state requirements governing the operation of membrane treatment
facilities. In addition, any requirements relating to maintaining system integrity should be
incorporated into an IVP. Thus, while the development of an  IVP is not required under the
LT2ESWTR, it is strongly recommended for all  utilities that utilize membrane filtration,
particularly for disinfection applications.


What are the components of an IVP?

       An IVP should incorporate all of the operational procedures associated with maintaining
system integrity, including as a minimum the following major program elements:

       •   Direct integrity testing

       •   Continuous indirect integrity monitoring

       •   Diagnostic testing

       •   Membrane repair and replacement

       •   Data collection and analysis

       •   Reporting
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              Appendix A - Development of a Comprehensive Integrity Verification Program


Other site-specific procedures or compliance requirements applicable to system integrity, but not
specifically addressed under any of the above program elements, should also be included as
components of an IVP.


How is IVP guidance presented in this appendix?

       This appendix is organized into sections according to the major program elements
described above.  Each of these sections provides an overview of what the IVP should address
with respect to that particular element and the various associated considerations that should be
taken into account in the process of developing and implementing an IVP. Because compliance
with the LT2ESWTR is critically related to maintaining system integrity, requirements from the
rule are used as examples to illustrate program development, as well as how the various IVP
components fit together into an integrated program.

       The order of the sections in this appendix also illustrates the tiered approached to an IVP,
ranging from the fundamental direct integrity test to successive levels  of monitoring, testing, and
repair that may be necessary. Note that this appendix is applicable to all types of membrane
filtration addressed under the LT2ESWTR and consequently covered in this Membrane
Filtration Guidance Manual, including microfiltration (MF), ultrafiltration (UF), nanofiltration
(NF), reverse osmosis (RO), and membrane cartridge filtration (MCF).  Significant technology-
specific nuances associated with one or more particular types of membrane filtration are
addressed in context whenever practical.


A.2   Direct Integrity Testing

       Direct  integrity testing  is the primary means of verifying  system integrity and thus
represents a fundamental component of an IVP. The series of questions into which this section is
organized represents important aspects direct integrity testing that should be  addressed in an IVP.
In addition, the questions are presented in a logical progression designed to parallel the step-by-
step process of formulating a direct integrity testing strategy.
What is the purpose of direct integrity testing?

       Under the LT2ESWTR, direct integrity testing is defined as a physical test applied to a
membrane unit in order to identify and isolate integrity breaches.  Because direct integrity testing
is the most accurate and precise means of determining whether or not a breach has occurred, it
has historically been the primary means used to assess membrane integrity in potable water
treatment  applications in which pathogen removal is a principal concern.  In addition, the test
parameters and results can be correlated to the desired treatment objectives (e.g., log removal
values) to yield a quantifiable assessment of system performance. In terms of LT2ESWTR
compliance, as discussed in Chapter 4, requirements for direct integrity test resolution and
sensitivity are specified for ensuring the necessary level of Cryptosporidium removal at a
particular  facility.
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              Appendix A - Development of a Comprehensive Integrity Verification Program
       For example, the LT2ESWTR resolution requirement specifies that the direct integrity
test parameters must be fixed such that a breach on the order of the smallest Cryptosporidium
oocyst (i.e., 3 |j,m) is physically capable of contributing to a test response. Thus, for pressure-
based direct integrity tests, the applied pressure (or vacuum) must be great enough to overcome
the capillary static forces that hold water in a breach (i.e., the bubble point) of 3 |j,m in diameter
in a fully-wetted membrane, thereby allowing air to escape through a Cryptosporidium-sized
hole and consequently enabling this loss of air to be potentially detected. If the applied pressure
(or vacuum) were insufficient to overcome the bubble point, then the direct integrity test would
be physically incapable of detecting any number of Cryptosporidium-sized breaches that would
allow the passage of pathogens to the filtrate.  Similarly, with marker-based tests, the marker
used must be smaller than 3 |j,m to ensure that it would pass through a Cryptosporidium-sized
hole, thus enabling a breach of this size to be potentially detected by the instrumentation that
measures the concentration of the marker in the filtrate. Note that the 3  |j,m (or less) resolution
requirement applies to all facilities utilizing membrane filtration for compliance with the
LT2ESWTR.

       However, unlike the resolution, the required sensitivity - the maximum log removal value
(LRV) that can be reliably verified by the direct integrity test - may vary among different
facilities under the LT2ESWTR, as the rule stipulates only that the test used have a sensitivity
that exceeds the Cryptosporidium log removal credit awarded by the state.  In some cases, the
sensitivity of the test may be determined from the threshold test result that signifies  the smallest
detectable integrity breach, information that can be provided by the membrane filtration system
supplier. This result, which represents the test sensitivity, may then be converted into a LRV
using the methodology described in Chapter 4 or an alternative methodology  approved by the
state.

       Although the compliance framework developed for direct integrity testing under the
LT2ESWTR applies only to those utilities that are subject to the Cryptosporidium removal
requirements of the rule,  the methodology could be applied for other pathogen either by mandate
of the state or at the discretion of the utility. If this methodology is applied to more  than one
different pathogen simultaneously at the same treatment facility, then the direct integrity test
used would be required to have a resolution corresponding to the smallest of the pathogens; in
addition, the test would have to have  a sensitivity greater than the removal credit awarded by the
state for each pathogen to which the methodology was applied.  Even if a compliance framework
similar to that for the LT2ESWTR is  not applicable to a particular utility's membrane filtration
system, a direct integrity  test is still the most reliable means of determining whether or not a
breach has occurred.

       For any system to which a compliance framework similar to that for the LT2ESWTR is
applied,  the resolution and sensitivity requirements for direct integrity testing should be
established prior to placing the facility into service  and specified in the IVP.  If a different
method is used to determine threshold integrity test results for applications other than for
LT2ESWTR compliance (e.g., fiber-cutting studies), these critical values should also be
incorporated into the IVP. As a minimum, the IVP should include the direct integrity test result
threshold specified by the manufacturer as indicative  of a potential integrity breach.


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              Appendix A - Development of a Comprehensive Integrity Verification Program
What type of direct integrity test should be used?

       Currently, there are two general types of direct integrity tests that are commercially
available for use with membrane filtration facilities: 1) pressure-based tests; and 2) marker-based
tests.  The various specific tests that fall under each of these two general categories are described
in Chapter 4. The particular test utilized in conjunction with a given system may depend on
regulatory requirements, the type of membrane filtration system, target organism (i.e., in terms of
the required test resolution), test sensitivity, or utility preference.

       The LT2ESWTR does not mandate the use of a particular direct integrity test for
regulatory compliance; any test utilized must simply meet the criteria specified under the rule for
resolution, sensitivity, and frequency (40 CFR 141, subpart W, Appendix C).  However, some
states do stipulate the use  of a specific test. In some cases, even if no particular test is specified,
the required sensitivity relative to that of each potential direct integrity test method may govern
which test(s) may be used. If no specific test is required by regulatory mandate, then any type of
direct integrity test approved for use by the state may be used at the utility's discretion.

       The direct integrity test used also depends to some extent on the type of membrane
filtration system utilized, as some tests are not compatible with certain types of systems. For
example, while a particulate marker test may be used with a MCF, MF, or UF system, a
molecular marker test would not be a feasible means of assessing MCF, MF, or UF integrity,
since the molecular marker may not be sufficiently removed by these membrane systems to
demonstrate a reasonable LRV (e.g., 3 log).  Conversely, a particulate marker test would not be
used with NF or RO systems, since the particles could not easily be flushed from a spiral-wound
membrane module and would be likely to irreversibly foul or otherwise damage the membranes.
Thus, for NF/RO systems, a molecular marker would be a more appropriate marker-based direct
integrity test.

       Pressure (or vacuum) decay tests are  compatible with all the various types of membrane
filtration as defined under  the LT2ESWTR (i.e., MF, UF, NF, RO, and MCF), and the equipment
necessary to conduct this type of test is typically included with most of the currently available
proprietary MF/UF systems.  Similarly, some types of direct integrity tests may not be available
from a proprietary membrane filtration system supplier.  If several types of tests are available
and the utility is not otherwise constrained by regulatory requirements, the selection of a direct
integrity test should take into account any  site- or system-specific considerations that would
either favor or preclude certain tests.

       The type of direct  integrity  test used for a particular system and the justifying rationale
should both be included in the facility IVP, as well as specific procedures for conducting the test.
If the  test is automated (as is common), the procedures specified in the IVP should include how
the test works in terms of  the automatic sequencing that the system undergoes. In addition, the
procedure for manually conducting the test whenever necessary should also be specified, as  well
as any other responsibilities that system  operators may have with respect to direct integrity
testing. One particular consideration for systems with automated direct integrity testing is
whether or not an operator must be present during the test.  Although the presence of an operator
may be beneficial, particularly if an integrity breach is detected, the ability of an operator to
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              Appendix A - Development of a Comprehensive Integrity Verification Program


respond quickly to an automated alarm and notification system may render this unnecessary.  If
the state does not require direct operator supervision during direct integrity testing, the utility
should exercise its own discretion in determining whether the presence of an operator is critical
based on site- and system-specific considerations and degree of comfort with unsupervised
testing.


How frequently should  direct integrity testing be conducted?

       Because none of the various types  of direct integrity tests currently available can feasibly
assess  integrity on a continuous basis while the system is on-line and producing filtered water,  a
membrane unit to be tested must be taken  off-line and out of production during the testing
process.  Thus, more frequent direct integrity testing results in increased downtime for each
membrane unit and consequently decreased system productivity. As a result, the frequency of
direct integrity testing is  an important parameter that hinges on striking an acceptable balance
between the competing desires to maximize both confirmation of system integrity and treated
water production.

       A number of states have established minimum test frequency requirements for membrane
filtration systems; currently, these requirements range from as often as every four hours to as
relatively infrequently as once per week, depending on the state.  If a utility applies membrane
filtration for compliance  with the LT2ESWTR, the rule requires that direct integrity testing be
conducted on each membrane unit once per day at a minimum (40 CFR  141.728). However, the
state may require testing  on a more  frequent basis at its discretion.

       Even if subject to minimum test frequency requirements by federal or state regulations,  a
utility could opt to conduct direct integrity testing more frequently. In addition, a utility that is
not otherwise constrained by  any regulatory requirements should use its  discretion to determine
an appropriate direct integrity test frequency.  In establishing a test frequency, careful
consideration should be given to the factors that may influence this decision. For example,
testing less frequently may increase overall facility production and minimize the mechanical
stress on the membrane module(s) that repeating testing might induce. However, increased
testing provides more frequent assurance of system integrity,  or in the case of an integrity
breach, less operating time under compromised conditions that may allow the passage of
pathogens or other undesirable pre-filtered water constituents.  The most important concern
should be the maximum length of time that a utility feels comfortable potentially operating with
an integrity breach of any magnitude, which would dictate the minimum acceptable integrity test
frequency. Although the use  of continuous indirect integrity monitoring (see Chapter 5 and
section A.3) provides some measure of integrity confirmation between direct test applications,
currently available indirect integrity monitoring techniques may not be able to detect a breach of
potentially significant magnitude. It is  important to note that the frequency of direct integrity
testing should be based on public health considerations rather than the observed or anticipated
frequency of the occurrence of integrity breaches.
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              Appendix A - Development of a Comprehensive Integrity Verification Program
When should direct integrity testing be conducted?

       In the process of developing an IVP, some consideration should be given to the timing of
conducting direct integrity testing relative to the normal operating cycle(s) of the system. For
example, with systems that utilize some type of regular reverse flow process to remove foulants
from the membrane surface (e.g., backwashing), the membrane will be the least obstructed
immediately after this reverse flow process is complete.  Implementing a direct integrity test at
this point in the operational cycle would provide the most conservative estimate of system
integrity, since the accumulated foulants that could plug any breaches, and thus effectively mask
potential integrity problems, would be minimized.  However, using this same example, for
systems that employ a pressure-based direct integrity test, it is important that the  test not be
conducted too soon after the reverse flow processes (particularly if air is used), since the
membrane must be fully-wetted for the integrity test to be effective.

       It is also recommended that a direct integrity test be conducted after chemical cleaning or
any other routine or emergency maintenance in order to ensure that the system integrity has not
been compromised by the procedure(s). The affected membrane module(s) or unit(s) should be
returned to service only after system integrity has been confirmed by a direct integrity test.  In
cases in which a membrane unit has been taken out of service for diagnostic testing  and/or repair,
systems applying  membrane filtration for LT2ESWTR compliance are required to conduct direct
integrity testing on the affected unit to demonstrate system integrity prior to returning the unit to
service.

       Any special circumstances that might call for direct integrity testing (i.e.,  in addition to
the regularly scheduled periodic testing), such as subsequent to chemical  cleaning or membrane
repair, whether in accordance with federal or state requirements or at the  discretion of the utility,
should be specified in the IVP.
How should the direct integrity test results be interpreted?

       For a given resolution, a marker- or pressure-based direct integrity test indicates whether
or not an integrity breach has occurred by comparing the results of the test to the threshold result
known to represent a breach. This threshold represents the test sensitivity and can be determined
either by information provided by the manufacturer or through an on-site, system-specific
assessment such as a fiber-cutting study.

       Under the compliance framework of the LT2ESWTR, the ongoing test results obtained
during facility  operation for each membrane  unit (as well as the threshold result representing the
test sensitivity) can be converted into LRVs using the methodology described in Chapter 4 or
other method approved by the state.  Each  successive test result (or LRV, as converted) is then
compared to the log removal credit allocated to the system by the state (either as per the
requirements of the LT2ESWTR or for other treatment objectives) to determine compliance on
an ongoing basis.  If the LRV yielded by the direct integrity test is greater than the regulatory
allocation, the  system remains in compliance. However, if the LRV is below the required log
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              Appendix A - Development of a Comprehensive Integrity Verification Program


removal, the membrane unit must be taken off-line for diagnostic testing and repair (see sections
A.4 and A. 5, respectively).

       Thus, under the LT2ESWTR compliance framework, the direct integrity test results yield
two important pieces of information: 1) whether or not an integrity breach has occurred; and 2)
the maximum LRV that can be verified at the time of the test (when converted using the
technique(s) described in Chapter 4 or alternate methodology approved by the state).  Because
the test sensitivity may  often be greater (i.e., higher LRV) than the required log removal for any
particular pathogen, it is possible for the  direct integrity test to indicate that an integrity breach of
some magnitude has occurred without the system being out of compliance.  Thus, under the
LT2ESWTR framework, a system could  knowingly continue to operate with some level of
integrity breach and still meet regulatory  requirements. However, USEPA recommends (and the
state may require) that a membrane unit with a detectable integrity breach of any magnitude be
immediately taken out of service for diagnostic testing and repair.  At a minimum, should
conduct diagnostic testing and potential repair when the unit is taken off-line for chemical
cleaning, previously scheduled maintenance, or other routine purpose.

       The LT2ESWTR defines a control limit as an integrity test response, which, if exceeded,
indicates a potential integrity problem and triggers subsequent action. For the purposes of
LT2ESWTR compliance, a direct integrity test control limit would be established as the test
result that translates into an LRV equal to the Cryptosporidium removal credit awarded by the
state. As noted previously, any membrane unit for which the test results exceed the control limit
(i.e., the LRV drops below the awarded removal credit) must be immediately taken off-line for
diagnostic testing and repair.  Other control limits could also be established if the LT2ESWTR
compliance framework is simultaneously applied for the removal of other pathogens with
membrane filtration.  However, because the  system would be out of compliance if either of the
two (or more) control limits were exceeded,  the most stringent control limit (i.e., the highest log
required log removal value) would always represent the governing limit.

       In  addition to the critical or "upper" control limit (UCL) that governs regulatory
compliance for a membrane filtration facility under the LT2ESWTR framework, "lower" control
limits (LCLs) may be established as performance benchmarks either at the discretion of the
utility or by mandate of the state. One or more LCLs may be identified between the integrity test
result that indicates the smallest detectable breach and a breach that reduces the performance of
the system such that it is just capable of meeting the require log removal (i.e., the UCL). LCLs
may be useful for alerting system operators to the presence of an integrity breach, even if the
detected breach is not sufficient to bring  the  system out of compliance.  Rather than triggering
unit shutdown and subsequent diagnostic testing, as with an UCL, exceeding a LCL might
trigger increased operator attention or an investigation that can be conducted by operators while
the system is still on-line in an attempt to determine the cause of the integrity problem and
prevent the breach from expanding, if possible.  Alternatively, in cases in which there is a
particularly large gap between the test sensitivity and the UCL a utility may  choose to
voluntarily take a membrane unit off-line for diagnostic testing if a preferred LCL is exceeded in
order to minimize the risk to public health via the potential for pathogens to pass through a
barrier known to be compromised, even if only to a small degree that is within regulatory
tolerances.
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               Appendix A - Development of a Comprehensive Integrity Verification Program
       As an example, even with the smallest detectable breach the direct integrity test might
still be able to verify 6 log removal (i.e., the test sensitivity), although the state only awards
2.5 log Cryptosporidium removal credit (i.e., the UCL) for the membrane filtration process.
Under this scenario, a  direct integrity test result yielding a LRV of 4 would indicate the presence
of a significant integrity breach, even though the membrane filtration system would still be
capable of achieving the required log removal.   Thus, a utility might opt to establish a LCL at a
LRV  of 4 if an integrity breach of this magnitude  represents an unacceptable public health risk
independent of the ability of the system to maintain regulatory compliance.

       Fiber-cutting studies that allow integrity test results to be quantified and correlated to
certain number of fiber breaks or particular reductions in log removal capacity may be used to
determine a single appropriate LCL or a series  of tiered LCLs. Setting a LCL equal to the test
sensitivity (i.e., the maximum log removal value that can be reliably verified by the direct
integrity test) would represent the most conservative  scenario, as in this case any detectable
integrity breach would, at a minimum, alert an operator and potentially trigger some responsive
action.  All control limits and the action triggered  by  exceeding each limit should be clearly
specified in the IVP.

       Another issue that should be addressed in the  IVP is the possibility of false positive and
false negative direct integrity test results.  For example, if a periodic direct integrity test indicates
the presence of a significant integrity breach, but the  instrumentation used for continuous indirect
integrity monitoring (e.g., turbidimeters - see section A.3) has consistently yielded baseline
results that are well  within normal operating tolerances, the direct integrity test may have
generated a false positive result (i.e., a result incorrectly indicating a breach in a fully integral
system). Alternatively, if the continuous  indirect integrity monitoring data are also unusually
high after the direct integrity test, an integrity breach  may have occurred during the direct test.
Nevertheless, because the direct integrity tests  are more  sensitive to integrity breaches,
LT2ESWTR compliance requires that any membrane unit for which a direct integrity test result
exceeds an UCL be  taken off-line for diagnostic testing  and repair, independent of indirect
monitoring data.  However, evidence such as indirect monitoring results that may suggest a false
positive result may used to help guide an operator investigation and identify the source of the
problem, which may be a function of the  direct integrity test rather than an integrity breach. If a
false positive result is  suspected, the operator should  check isolation valves and fittings on the
system that are associated with the direct integrity test. In addition, a follow-up direct integrity
test should be conducted both to confirm  the results of the first test and to closely monitor the
test for  any system malfunctions.

       False negative  results (i.e., results that indicate either a fully integral system in the
presence of an integrity breach or which significantly underestimate a substantial integrity
breach) of direct integrity tests may be more difficult to identify; since the methods of
continuous indirect integrity monitoring are less sensitive to integrity breaches, indirect
monitoring data may not be capable of detecting a breach that is masked by a false negative
direct test result.  However, if the continuous indirect integrity monitoring data does suggest an
integrity breach in contradiction of the direct test results, the membrane unit should be taken out
of service to investigate the source of the discrepancy. One potential scenario that might result
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in a false negative result is an integrity breach that occurs in a membrane that is partially fouled.
The accumulated foulants may obscure the breach, thus masking the integrity problem until after
the next backwash or chemical cleaning.  Nevertheless, in this case the false negative result may
not represent a significant concern; if the direct integrity test is functioning properly, the false
negative result would suggest that the system is functionally integral even with an integrity
problem as a result of the breach being plugged. In this case, the breach would likely be detected
after the next backwash or chemical cleaning that successfully removes the foulants from
blocking the breach.  A more problematic scenario involving false negative results might occur if
the integrity test equipment is malfunctioning.  Thus, is it important to incorporate a routine
maintenance  program for the integrity test system as part of the IVP.

       Any particular strategies for minimizing the potential for false positive and false negative
results should be specified in IVP documentation. A maintenance schedule for direct integrity
monitoring equipment should also be specified. It is recommended that the direct integrity
monitoring system receive a thorough check-up on at least an annual  basis.
A.3    Continuous Indirect Integrity Monitoring

       Continuous indirect integrity monitoring is a secondary means of verifying membrane
filtration system integrity intended to detect significant breaches between direct test applications.
Thus, in the absence of a continuously applied direct test, continuous indirect integrity
monitoring is critical to an IVP. As with section A.2, this section is organized into a series of
questions that parallel the  step-by-step process of formulating strategy for continuous indirect
integrity  monitoring.  Each of these questions represents an important aspect of that strategy that
should be included to some extent in an IVP.
What is the purpose of indirect integrity monitoring?

       For the purposes of LT2ESWTR compliance, indirect integrity monitoring is defined as
monitoring some aspect of filtrate water quality that is indicative of the removal of particulate
matter.  Although the various indirect monitoring methods are less sensitive techniques for
assessing membrane integrity than the direct integrity tests, the value of utilizing the indirect
methods is that they can be applied to assess integrity continuously while the system is on-line
and producing water. In fact, since by definition indirect monitoring is applied to the filtrate,
these techniques require that the membrane unit be in continuous production to assess membrane
integrity.

       Because currently available methods of direct integrity testing cannot be applied
continuously, a successful direct test only indicates that no breach has occurred since the
previous application of the test.  Consequently, if the system were to become compromised
immediately after a successful direct integrity test had been conducted, the breach might not be
detected until the next regularly scheduled direct test, which may be as long as 24 hours for the
purposes of LT2ESWTR compliance. During this interval, a potentially significant breach could
have occurred, allowing pathogens or other particulate matter to contaminate the filtrate for a
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period as long as an entire day.  For applications other than LT2ESWTR compliance, this
interval may be as short as four hours or as long as one week or more, depending on the state of
jurisdiction. Thus, although continuous indirect integrity monitoring may not be able to detect
small compromises in integrity,  these techniques do provide the ability to identify larger
breaches on an ongoing basis during production. As a result, periodic direct integrity testing and
continuous indirect integrity monitoring are complementary tools for assessing system integrity,
and both are critical for a comprehensive IVP.

       Under the LT2ESWTR,  continuous indirect integrity monitoring is required in the
absence of a direct integrity test that can be applied continuously and which meets the resolution
and sensitivity requirements of the rule. States may also have regulations requiring some form of
continuous indirect integrity monitoring. In the absence of any applicable requirements, a utility
may opt to employ some form of continuous indirect integrity monitoring at its discretion;
however, note that turbidity monitoring, which is required under  the various federal surface
water treatment regulations as a measure of overall system performance, may also serve the dual
purpose of a means of continuous indirect integrity monitoring.

       Unlike direct testing, there are no specific resolution or sensitivity requirements for
continuous indirect integrity monitoring under the LT2ESWTR.  However, these concepts,
where applicable, may be useful tools for optimizing the ability of the various continuous
indirect integrity monitoring methods to yield meaningful information about potential integrity
breaches, as described in Chapter 5.
What type of indirect integrity monitoring method should be used?

       There are a number of different methods and associated devices that may be used for
continuous indirect integrity monitoring, including particle counting, particle monitoring,
turbidimetry, laser turbidimetry, and conductivity monitoring. In general, any method that
measures paniculate matter in the filtrate as an indirect means of assessing integrity (such as
particle counting, turbidimetry, etc.) is applicable to any of the various types of membrane
filtration systems.  Other methods that may measure dissolved constituents in the filtrate, such as
conductivity monitoring, would only be applicable to NF or RO systems.  The particular method
of continuous indirect integrity monitoring employed by a utility for its system may be a function
of regulatory requirements, test resolution or sensitivity, cost, confidence in the technology, or
simply preference based on prior experience or other subjective criteria.

       The LT2ESWTR requires the use of turbidity monitoring on each membrane unit as the
default method of continuous indirect integrity monitoring for compliance, unless an alternate
method is approved by the state.  Because the  various federal surface water treatment regulations
(i.e., the Surface Water Treatment Rule (SWTR), the Long-Term 1 Enhanced  Surface Water
Treatment Rule (LT1ESWTR), and the Interim Enhanced Surface Water Treatment Rule
(IESWTR)) require turbidity monitoring as a means of assessing filtration performance, surface
water facilities implementing membrane filtration for LT2ESWTR compliance may use turbidity
monitoring to satisfy both requirements.  States may have  other specific requirements for
continuous indirect integrity monitoring independent of the LT2ESWTR or may approve other
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methods for LT2ESWTR compliance. All federal and state requirements must be satisfied in a
utility'sIVP.

       If not otherwise constrained by regulatory requirements, a utility's decision to use a
specific type of indirect integrity monitoring technique may be influenced by the ability of a
particular method to provide sufficient resolution or sensitivity. For example, because particle
counters have been demonstrated to be more sensitive to breaches than particle monitors or
conventional turbidimeters, a utility may choose to use particle counting to maximize the ability
to detect compromises in system integrity between periodic direct integrity test events
(Jacangelo, et al., 1997).  Other utilities may select laser turbidimetry, which has been shown in
some studies to perform comparably to particle counting in terms of sensitivity to integrity
breaches (Banerjee, et al., 2000; Colvin, et al., 2001). In this case, if laser turbidimetry is
approved by the state  for both purposes, a utility may use laser turbidimeters for compliance with
the applicable surface water treatment rules with the additional benefit of improved sensitivity
for detecting integrity breaches  over conventional turbidimeters.

       Sensitivity  may also be improved for any given continuous indirect integrity monitoring
method by applying instrumentation to smaller groupings of membrane modules, such that any
integrity breach would have a greater impact on filtrate quality.  In this case, the benefits of the
increased sensitivity should be weighed against the cost of additional instruments.  This approach
may be advantageous  if the gain in sensitivity by using a greater number of less expensive
instruments is justified by the comparable cost of fewer more expensive instruments. Note that
for LT2ESWTR compliance, an instrument for continuous indirect integrity  monitoring must be
applied to each membrane unit.  A utility may apply instruments to smaller groupings of
membrane modules at its discretion. For other applications, state requirements for monitoring
various groupings  of membrane modules in an overall system must be satisfied in a utility's IVP.

       If test resolution is an important criterion, than a utility might strongly consider particle
counting. Because particle counting is the only method that assesses the size of particulate
matter, it is the only method of  indirect integrity monitoring to which the concept of resolution
applies. For example, if membranes are applied specifically to remove Cryptosporidium, the
particle counters should be well-calibrated to accurately detect particles approximately  3 |j,m in
size or larger.  The target resolution may vary depending on the particular contaminant of
concern.
What constitutes "continuous" indirect integrity monitoring?

       Under the LT2ESWTR, "continuous" monitoring is defined as monitoring conducted at a
frequency of no less than once every 15 minutes. However, because the instrumentation used for
the various methods of indirect integrity monitoring may allow data collection at much more
frequent intervals, the state may have more stringent data collection requirements.  In the
absence of specific regulatory requirements,  a utility may collect data at a frequency it
determines to be appropriate. Nevertheless, since data acquisition can be automated, it is
recommended that data be collected at interval no less than every 15 minutes, even if no other
regulatory requirements apply.
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       While more frequent data collection both provides increased integrity monitoring and
additional data to track system performance, there may be some potential complications from
collecting data too frequently.  For example, data could be collected frequently enough such that
a backwash (for applicable systems) cannot be completed between readings. In this case, a
utility must program the system to cease data collection during the backwash cycle and for any
length of time afterwards that the data remain artificially high, such that a direct integrity test is
not triggered. Data collection and analysis are further discussed in section A.6. The implications
of collecting indirect integrity monitoring data at different intervals should be considered in
developing an IVP, and the frequency and any other associated qualifying guidelines or
restrictions should be specified in the facility IVP documentation.
How should indirect integrity monitoring results be interpreted?

       Continuous indirect integrity monitoring is primarily intended to provide some indication
of system integrity between direct integrity test applications.  The indirect monitoring results are
continuously compared to an established performance threshold that is known to represent a
potential integrity breach.  If this threshold level is exceeded, some type of response is triggered
to further investigate the problem.

       Under the LT2ESWTR, this performance threshold represents the UCL for continuous
indirect integrity monitoring.  If the UCL is exceeded,  direct integrity testing is automatically
triggered as a means to assess system integrity using a more sensitive technique. Unlike that for
direct testing, the UCL for continuous indirect integrity monitoring does not necessarily
correspond to a specific and quantifiable integrity loss. For example,  the UCL established by the
LT2ESWTR for turbidity monitoring (i.e., the default method in the absence of another
technique specified by the state) is 0.15 NTU independent of site- or system-specific
considerations; filtrate turbidity readings exceeding 0.15 NTU for a period of 15 minutes (or two
consecutive 15-minute readings exceeding 0.15 NTU)  would trigger direct testing. The 0.15
NTU threshold was selected because it is significantly  below the 0.3 NTU threshold for filter
performance required by the IESWTR for 95 percent of all turbidity samples, yet because
membrane filtrations systems are well-documented to consistently produce filtered water below
0.05 NTU, a sustained filtrate turbidity exceeding 0.15 NTU strongly  suggests a potential
integrity problem.  Note that if turbidity monitoring with the default UCL of 0.15 NTU is used as
a means of continuous indirect integrity monitoring, a utility could simultaneously be in
compliance with the IESWTR but not with the LT2ESWTR.

       Although the LT2ESWTR specifies a UCL of 0.15 NTU with  the default method of
turbidity monitoring, the state may establish a more stringent standard at its discretion.  In
addition, for any approved method of continuous indirect integrity monitoring, the state may
require a site- or system-specific performance-based UCL that is linked to a certain level of
integrity loss (in terms of a specific number of broken fibers or LRV) as determined by a fiber
cutting study. These studies may also serve as the basis for establishing LCLs that trigger  a
particular response at a threshold prior to the point at which direct integrity testing would be
required, either mandated by the state or voluntarily implemented by the utility.  Voluntary LCLs
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could also be implemented after the membrane filtration system has been in operation for a
certain period of time; this staggered implementation would allow sufficient baseline data to be
collected such that operators could identify threshold levels that represent elevated or otherwise
unusual results that are still below the UCL and which do not necessarily indicate an integrity
breach, but nevertheless warrant observation.  Some examples of actions associated with LCLs
might be increased operator attention or diagnostic checks of the continuous indirect integrity
monitoring instrumentation. All CLs both mandated by the state and voluntarily implemented by
the utility should be documented in an IVP, along with the rationale supporting the establishment
of the CLs as well as the respective subsequent action associated with the exceedance of each.

       As with direct integrity tests, false negative and false positive results are also possible
with indirect integrity monitoring. For example, some indirect integrity monitoring instruments
may indicate elevated levels of a parameter (e.g., turbidity, particle counts, etc.) after a routine
maintenance event such as a backwash, particularly if air is employed in the process to scour or
pulse the membrane surface.  If significant, this air entrainment error could cause a CL to be
exceeded, generating a false positive result (i.e., a result incorrectly suggesting a breach  in a fully
integral system); in the case of the UCL, this exceedance would inappropriately trigger direct
integrity testing  (and,  under the LT2ESWTR, consequent reporting). This type of false positive
result can be minimized by first characterizing typical system performance under a variety of
operating conditions (such as after a backwash) and subsequently programming the data
acquisition system to account for regularly occurring data aberrations of previously quantified
magnitude and duration which are known  not to represent an integrity problem, even if CLs are
exceeded. (The  importance collecting and analyzing baseline data for IVP optimization  is
further discussed in section A.6.)  In some cases, devices such as bubble traps (e.g., in the case of
air entrainment)  may be utilized to minimize modes of error that might generate false positive
results.

       False negative results (i.e., results that indicate either a fully integral system in the
presence of an integrity breach or which significantly underestimate a substantial integrity
breach) may be more  common with indirect integrity monitoring methods. Because currently
available indirect integrity monitoring techniques are less sensitive to breaches than direct
integrity tests, it is possible that small breaches may occur that could be detectable via direct but
not indirect methods.  This potential may be minimized by utilizing a more sensitive method of
continuous indirect integrity monitoring (such as the use of laser vs. conventional turbidimeters),
if a utility is permitted such flexibility under state regulations.  Alternatively, a utility could
increase indirect method sensitivity by utilizing a greater number of instruments  (i.e., decreasing
the number of membrane modules monitored per instrument).  However, a utility considering
these options should evaluate whether the  cost of increasing indirect method sensitivity (i.e., via
purchasing a greater number of instruments or more sensitive instruments or both) is justified by
the consequent level of heightened integrity monitoring ability between direct test events.

       Any particular strategies for minimizing the potential for false positive and false  negative
results should be specified in IVP documentation.  A calibration schedule for continuous indirect
integrity monitoring instrumentation should also be specified.  It is recommended that this
instrumentation  be calibrated on at least an annual basis.
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A.4    Diagnostic Testing

       Diagnostic testing is a process of identifying and isolating integrity breaches that have
already been detected and confirmed using other methods, and thus is a critical component of an
IVP.  As with previous sections in this appendix, this section is organized into a series of
questions that parallel the step-by-step process of formulating a diagnostic testing strategy for an
IVP.  Each of the questions presented in this section represents some aspect of diagnostic testing
that should be clearly addressed and documented in an IVP.
What is the purpose of diagnostic testing?

       The purpose of diagnostic testing is to identify and isolate integrity breaches in a
membrane module that are detected via other methods. Because direct integrity testing and
continuous indirect integrity monitoring techniques can only detect the existence of a breach,
diagnostic testing complements these methods, serving as a tool to pinpoint the exact location of
a breach.  In this way, diagnostic testing also serves as a critical link between identifying an
integrity problem during the course of operation and repairing the breach.  (Membrane repair and
replacement is further discussed in section A.5).  Thus, if an integrity breach is known or
suspected in a membrane unit, that unit should be taken out of service for diagnostic testing in
order to facilitate repairs.  IVP documentation should clearly note the purpose of diagnostic
testing so as to distinguish it from other forms of testing.
Under what circumstances should diagnostic testing be applied?

       The LT2ESWTR requires that a membrane unit be taken out of service for diagnostic
testing and repair if the established upper control limit (i.e., that associated with the log removal
credit awarded to the membrane process) is exceeded during a direct integrity test. The use of
diagnostic testing under these circumstances is also suggested for those utilities that do not use
their respective membrane filtration systems for LT2ESWTR compliance.  Thus, in essence
diagnostic testing is recommended any time an integrity breach is detected from the results of a
direct integrity test.

       Note that the LT2ESWTR does not link diagnostic testing directly to continuous indirect
integrity monitoring. Even if indirect monitoring results clearly indicate an integrity problem, it
is advisable to confirm the existence of a breach using more sensitive direct integrity testing
methods. In any case, under the compliance framework for the LT2ESWTR, any continuous
indirect integrity monitoring results that would clearly indicate an integrity breach would almost
certainly exceed the upper control limit and thus  trigger direct integrity testing, as required.
However, a utility that is not otherwise constrained by regulatory requirements could voluntarily
take a membrane unit out of service for diagnostic  testing based on indirect monitoring results
alone.

       An IVP should clearly identify the specific circumstances under which diagnostic testing
should be applied, including both those conditions  that require diagnostic testing under a
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regulatory framework and those that might trigger the use of diagnostic testing on a voluntary
basis by the utility.


What type(s) of diagnostic testing should be used?

       By definition, most diagnostic tests are categorized as types of direct integrity tests;
however,  diagnostic tests are distinguished from other types of direct tests by their ability to not
just detect an integrity breach, but to help locate the specific module or fiber containing the
breach, as well.  In addition, most methods considered to be diagnostic tests are designed to be
applied to specific membrane units on an as-needed basis, and thus are impractical for
implementation  on a scale that would satisfy the direct integrity testing requirements of the
LT2ESWTR.  For example, sonic testing - one type of diagnostic test - requires an operator to
manually  apply  an accelerometer to various locations on the membrane module to listen for
vibrations caused by leaking air.  While this technique fits the definition of direct integrity test, it
would be  infeasible to use such a test to check every module in a membrane filtration system for
integrity breaches  every 24 hours.

       In addition to the sonic test described above, other methods of diagnostic testing include
bubble testing, conductivity probing, and simple visual inspection (where applicable). Each of
these methods is described in further detail in section 4.8. A pressure (or vacuum) decay test
applied to a smaller number of modules (i.e., a subset of a full membrane unit) in order to
identify a particular breached module may also be used as a form of diagnostic test.  Single
module testing represents the smallest form of incremental membrane unit testing.  This type of
diagnostic test generally involves removing the individual modules from the membrane unit and
testing each on a specially designed single module apparatus.  Other types of direct integrity tests
may also  have the potential to serve as diagnostic tests in a  scaled-down form.

       In some  cases, a battery of diagnostic tests may be used to identify an integrity breach.
For example, if  a MF membrane unit fails a direct integrity test (i.e.,  the results exceed the upper
control limit), after the unit is taken out of service a sonic test might be applied to each module in
the unit in turn to identify the  affected module(s).  (Note that although the membrane unit is
taken out  of service, it must still remain in operation in order to facilitate some types of
diagnostic tests,  such as the sonic test referenced in this example and described in section 4.8.3.
Therefore, in such cases, the unit must be operating in filter-to-waste mode.)  The module(s) may
then be removed from the unit to conduct a bubble test (see section 4.8.2) in order to isolate
particular fibers  that may be subsequently removed from service permanently by pinning or
sealing (as described in section A.5).  Thus, just as diagnostic testing complements direct
integrity testing  or continuous indirect integrity monitoring,  different diagnostic tests can also
complement each other.

       A  utility  should develop its own system-specific protocol for diagnostic testing and
document the procedures in its IVP.  The IVP  should specify which diagnostic tests are
prescribed, the particular purpose of each test (e.g., to isolate a module or identify a particular
fiber), the circumstances under which each test should be conducted,  a list of necessary testing
equipment, and  detailed instructions for conducting the test.  Some membrane filtration system
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manufacturers may provide guidance in developing an appropriate diagnostic testing plan.
Although diagnostic testing may not be commonly employed, a utility should still keep all the
equipment necessary to conduct each diagnostic test specified in its system IVP both on site and
in good working order. Note that some diagnostic tests (such as sonic testing) require more
some level of skill in both conducting the test and interpreting the results; operators that will
have responsibility for conducting these tests should be designated and trained in advance in
order to minimize membrane unit downtime.
A.5    Membrane Repair and Replacement

       In the context of this guidance, "membrane repair and replacement" does not necessarily
apply to just the membranes themselves, but to any component of a membrane filtration system
that might allow an integrity breach if it were to fail.  This section is organized into a series of
questions presented in a logical order intended to parallel the step-by-step process of considering
membrane repair and replacement in the context of an IVP. Each of the questions presented in
this section should be addressed in a utility's IVP to an appropriate degree.
What is the purpose of membrane repair / replacement?

       The purpose of conducting repairs on a membrane filtration system or replacing
irreparably damaged components is to correct any integrity breaches that have been detected,
thus restoring and maintaining a fully-integral system.  In cases in which membrane filtration is
applied for the removal of one or more specific pathogens of interest (e.g., for compliance with
the LT2ESWTR), a more specific objective is to enable the system to maintain the full removal
credit allocated by the state.  As previously noted, although other system components may be
essential for overall system operation, in this context repair and replacement are discussed in
regard to only those system components that are critical to system integrity.
When should membrane repair / replacement be conducted?

       In the simplest terms, repair or replacement should be conducted whenever an integrity
breach is detected (e.g., using direct integrity testing or continuous indirect integrity monitoring).
After the source of the breach has been isolated (e.g., via diagnostic testing), the problem should
be corrected via component repair or replacement, as appropriate.

       Under the LT2ESWTR, if the results of a direct integrity test exceed the upper (i.e.,
mandated) control limit, the affected membrane unit(s) must be taken out of service for
diagnostic testing and repair.  Because the membrane unit(s) cannot be returned to service until a
direct integrity test confirms that the UCL is no longer exceeded, some type of repair must be
conducted to correct the integrity problem.  If a utility has  voluntarily implemented one or more
tiered LCLs, it may in some cases be able to detect an integrity problem without exceeding the
UCL. In this case the utility could opt to take corrective action, conducting diagnostic testing
and subsequent repair immediately, or instead keep the affected membrane unit(s) in continued
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operation under increased  observation until the next scheduled maintenance event. Although
repair of any breach is recommended as soon as possible, a utility may exercise discretion in
determining whether or not to implement any repairs based on severity of the breach (assuming
the UCL has not been exceeded).  For example, if a utility is required to achieve only 2 log
Cryptosporidium removal  credit for LT2ESWTR compliance, it is possible that a significant
integrity breach could occur without jeopardizing the ability of the membrane filtration system to
obtain this credit. However, continued operation with a known integrity breach of any
magnitude may not be permitted by a state. Even if operation under some compromised
conditions is not explicitly prohibited, a utility should carefully consider the risk associated with
the potential for pathogen  passage before engaging in continued operation.

       If a utility does not apply its membrane filtration system for compliance with the
LT2ESWTR, it may have  more flexibility with respect to the timing and necessity of conducting
immediate repairs if an integrity breach is detected, unless otherwise constrained by state
requirements.  In the absence of any regulations prescribing system repair requirements, it is
recommended that utilities adopt a conservative approach in order to help ensure the integrity of
the membrane barrier against pathogens. The system IVP should clearly specify any regulatory
requirements relating to membrane system repair, as well as other circumstances under which the
utility would conduct repairs.

       Membrane module repair - as opposed to replacement - is often advisable, if possible,
since new membranes are  typically expensive.  However, if a membrane module is subject to
repeated integrity breaches, a utility should consider replacing the module.  Chronic repairs
adversely affect treated water production and prevent operators from carrying out regular plant
responsibilities.  Also, if it is critical that an integrity breach be repaired as quickly as possible,
for some types of membrane filtration systems it may be more efficient to replace the module
with a new one from the utility's supply of spare components maintained on-site.  Thus, in some
cases the most expedient and cost-effective system "repair" could actually be membrane
replacement.

       Although the LT2ESWTR requires the use of direct integrity testing to confirm the
success of any system repairs concerning integrity problems before returning the affect
membrane unit(s) to service, this practice is recommended for all utilities, even if membrane
filtration is not conducted  for LT2ESWTR compliance. It is also recommended that this testing
be conducted after the module has been inserted into the system, as in this case the direct
integrity test would not only be able to confirm the success of the module repair, but also
whether it was properly re-installed. After any repair or replacement measures have been
completed, both direct integrity test and continuous indirect integrity monitoring results for the
repair unit(s) should be closely tracked for an extended period to gauge the long-term success of
the repair and  perhaps whether the problem would be likely to recur.
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What are some common modes of integrity breaches?

       The types of integrity breaches to which a particular membrane filtration system is most
susceptible can depend on both the type of system (i.e., MCF, MF/UF, or NF/RO) and the
manufacturer.  For example, while many NF/RO membranes are subject to chemical degradation
by oxidants such as chlorine, only some MF/UF membranes are vulnerable to oxidation,
depending on the membrane material used.  This same example of chemical oxidation illustrates
potential causes of integrity breaches that are specific to a particular treatment application of
membrane filtration, as well. A treatment process that utilizes chlorine as a disinfectant
upstream of RO membranes has an inherent potential source of chemical degradation, even
though dechlorination may be implemented prior to the membranes. If the dechlorination system
fails or is miscalibrated, the membranes could be  subject to chlorine exposure. By contrast, an
identical RO system used for a different application in which upstream disinfection is not
required to meet treatment objectives would not have this additional element of risk.  It is
important to note that this example should not be  interpreted as a recommendation against
utilizing oxidants upstream  of oxidant intolerant membranes.  It is not uncommon to use
upstream oxidants effectively, particularly for disinfection and biofouling control. However, a
utility should be aware of the potential for chemical degradation of membrane material and take
appropriate measures to prevent potential integrity breaches and protect treatment equipment.

       In addition to chemical degradation, the most common causes of integrity breaches with
NF and RO membranes are associated with o-rings and seals,  which can be cracked, rolled,
and/or improperly sized. Each of these defects can result in an integrity breach, as can  foreign
matter such as hairs or other fibrous  material underneath o-rings. Other mechanisms for integrity
breaches may be related to membrane defects, such as failures that may occur along glue lines or
at weak spots in the membrane (i.e.,  creases or thin areas). Fiber breaks and potting problems
are the most common types of integrity breaches associated with MF/UF membranes, although
chemical degradation may also result in membrane failure. MCF systems are most likely to be
compromised by improperly seated/sealed membrane cartridges or tears or punctures in the
membrane material. MCF membranes may also exhibit integrity breaches along folds and
creases, depending on the construction of the filter.

       Although it is possible for breaches to occur at any time during operation, it is most
common for integrity problems to occur during system start-up. These breaches typically result
from either manufacturing defects or improper installation.  As a result, it is important that an
initial shakedown period be included as a part of the start-up process to enable these initial
problems to be identified and corrected prior to putting the system into service.

       An IVP should identify and document the  most probable types of integrity breaches for a
utility's specific membrane filtration system. These modes may be identified initially by
consultation with the membrane manufacturer and consideration of site-specific circumstances
(e.g., the use of upstream  oxidants).  Subsequently, the shakedown period and ongoing
operational experience may yield important information about the most frequently occurring
types of integrity problems. Also, the experience  of other utilities using the same or similar
filtration equipment may yield valuable information about the types of integrity failures common
to a particular system.
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How should membrane repair / replacement be conducted?

       The types of repairs that may be conducted to correct integrity breaches vary significantly
with the type of membrane filtration system. For example, for MF/UF systems, fiber breaks (the
most common mode of failure) are not technically repaired, but rather isolated by inserting small
pins or epoxy in the end(s) of the broken fiber, effectively removing them from service
permanently and thus eliminating the system integrity breach. By contrast,  it is generally not
possible to repair comprised NF/RO membranes, although problems with o-rings and other seals
may often be corrected by replacing the seals and making sure the membrane is properly seated
in its housing.  Likewise, because MCF systems utilize cartridges that are designed to be
disposable, unless an integrity breach is the result of a seal problem, a damaged membrane
cartridge would generally not be repaired.  Thus, any integrity problems associated directly with
either NF/RO or MCF membranes themselves generally necessitate membrane replacement.

       Prior to placing the system into operation, it is important to consult with the membrane
manufacturer to determine what types of repairs can be made and which types of integrity
breaches require membrane replacement. The  manufacturer should also be  able to provide both
instructions and training for all applicable repair procedures.  Because it is somewhat common
for  some types of integrity problems to occur during the  system shakedown phase, it is
recommended that this period be use for practicing repair procedures under the directions of a
qualified manufacturer's representative.

       When integrity problems occur during operation, it is  important to identify the cause of
the  integrity problem, as well as its  source.  While some fiber breaks in MF/UF systems may be
expected due to wear or mechanical stress over time, other breaches may have a specific cause
that can be isolated and corrected to avoid further integrity problems.  If an  integrity breach
occurs, it is important to check both the membrane filtration system as well  as any upstream
treatment process to ensure that these are operating properly.  For example,  if a chemical
incompatible with the membrane material is added upstream but is not being properly removed
or quenched, some membrane damage and loss of integrity may  occur.

       Any necessary repair  equipment or spare parts, including replacement modules that may
be required in the event of an integrity breach should be  kept on site. The system IVP should
specify a list of these components, along with any applicable  instructions. The IVP should also
include suggestions for troubleshooting integrity problems.
A.6    Data Collection and Analysis

       Diligent and rigorous collection and analysis of integrity testing and monitoring data are
an important component of any IVP. Careful data collection and analysis can serve as useful
tools for preventing integrity problems, as well as for optimizing system performance and
troubleshooting problems.  Like other sections in this appendix, the following discussion is
organized by addressing a series of frequently asked questions in regard to data collection and
analysis, each of which should be encompassed in a comprehensive IVP.
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What is the purpose of data collection and analysis?

       Although the primary purpose of data collection and analysis may be to demonstrate
regulatory compliance, a thorough and well-planned program can result in a number of other
important benefits for preventing integrity problems and optimizing system performance. For
example, a consistently maintained record of membrane unit performance during both direct
integrity testing and continuous indirect integrity monitoring may help determine when some
membranes are approaching the end of their useful lives. In addition, because the resistance or
permeability of some membranes changes after an initial "setting" period, a careful record of
integrity test results may indicate that either the UCL (subject to regulatory approval) or any
voluntarily implemented LCLs should be adjusted.

       Continuous indirect integrity monitoring data also have a number of advantages in
addition to helping gauge membrane integrity.  This data may be used to identify performance
trends, such as those that may occur between backwashing or chemical cleaning events, or over
the entire life of the membranes. A well-documented data record  can also identify any
systematic  or periodic trends and potentially  help isolate the cause(s).  In addition, data records
facilitate the comparison of performance trends among different membrane units. (Note  that a
normal amount of instrument variation should be taken into  account when conducting a
statistical analysis comparing data among different membrane units.) A substantial amount of
data collected over time may also enable operators to identify aberrations that do not necessarily
indicate integrity problems. For example, if the turbidity is consistently higher than normal after
a backwash, operators may be able to attribute this consistent aberration to air-entrainment error
associated with the instrumentation. It is important that these types of aberrations are identified
such that the system  can be programmed not to trigger direct integrity testing during these
events. Direct integrity testing data can also be a valuable tool for identifying trends; however,
because continuous indirect integrity monitoring data are typically collected much more
frequently and while the unit is on-line, it may often be the most practical means of tracking
performance trends.
What data should be collected?

       In addition to any regulatory requirements regarding data collection during operation, a
utility should collect baseline data for each membrane unit (both with respect to direct integrity
testing and continuous indirect integrity monitoring) before putting the plant into service.  This
data will serve as a reference baseline against which to evaluate membrane unit performance and
also help refine a utility's strategy for collecting continuous indirect integrity monitoring data
during regular operation. For example, for MF/UF systems the baseline data should demonstrate
how long after a backwash event turbidity or particle count data might remain elevated. Based
on this information, a utility  can account for such data spikes that are known to not represent
integrity problems, such that direct integrity testing and consequent loss of production are not
unnecessarily triggered.  Throughout operation, as well as during  integrity testing conducted
during routine maintenance or repair, it is recommended that data be  collected in a spreadsheet or
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with software that establishes a database and allows data to be readily plotted in order to identify
trends occurring over time.


What are some methods for reducing continuous indirect integrity monitoring data?

       As noted in section A.3, the LT2ESWTR defines "continuous" monitoring as a frequency
of no less than once every 15 minutes. However, instruments used to collect integrity
monitoring data - particle counters, particle monitors, turbidimeters, etc. - may allow data
collection at much more frequency intervals. Thus, in the absence of more specific requirements
from the state, a utility may collect data as often as possible, if desired, provided the minimum
frequency is met or exceeded.  Furthermore, in the absence of specific guidelines for how a large
amount of data should be reduced for compliance and reporting purposes,  a utility has the
latitude to select a statistical  method that it determines to be appropriate for its system.  Some
potential methods include:

       •  Maximum value

       •  95th percentile

       •  Average value

       •  Singular timed measurement

Using the example of "continuous" monitoring as  defined under the LT2ESWTR (i.e., minimum
frequency of once every 15 minutes), each of the above methods are described in context as
follows.

Maximum Value
Using this method, the maximum value that occurs over every 15-minute period represents the
entire data set.  Thus, direct integrity testing is triggered if even one measurement exceeds the
UCL. This method is very conservative and could potentially result in excessive direct integrity
testing and subsequent loss of filtered water production  from any  anomalous data spikes, which
may be attributable to any number of factors aside from an integrity problem.

95th Percentile
With this method, 95th percentile datum represents the entire  15-minute data set, effectively
screening out the largest five percent of data spikes.  Direct integrity testing would be triggered if
this datum exceeded the UCL. This method is less conservative than the maximum value
approach and is more likely to screen anomalous data spikes that are not indicative of an
integrity problem.  The rationale behind this method is that if an integrity breach occurs, it may
be likely that more than five percent of the data collected exceed the UCL. The premise for this
method may be used  with any percentile, and it may be  advantageous for a utility using this
technique to conduct a statistical analysis to determine an  appropriate percentile to eliminate
anomalous spikes without  screening data that might indicate an integrity breach.
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Average Value
Using this method, the average value represents the entire 15-minute data set. This technique is
roughly equivalent to a 50th percentile approach, and thus is less conservative than the 95th
percentile method. However, average value method lessens the need to artificially exclude
anticipated integrity spikes that are known not to indicate an integrity problem (e.g., data
collected immediate after a backwash with MF/UF systems), as the effect of these spikes may be
sufficiently dampened such that the average value is below the UCL.

Singular Timed Measurement
The singular timed measurement approach uses one reading collected exactly every  15 minutes
for comparison to the UCL (i.e., for regulatory compliance), independent of how frequently data
are collected between these compliance readings. Because many other non-compliance
measurements collected during these  15-minute intervals could exceed the UCL without
triggering direct integrity testing, this method is one of the least conservative approaches.  This
technique represents the minimum requirement for compliance with the LT2ESWTR.

       Note that because the LT2ESWTR does not specify a statistical reduction technique for
data collected more frequently that at 15-minute intervals, the methods described in this section
are not specific compliance options under the rule. These methods are not meant to represent an
exclusive or exhaustive list and are simply examples of approaches that utilities could employ if
not otherwise constrained by state requirements. A utility's IVP should clearly specify its data
collection and analysis practices for both continuous indirect integrity monitoring and direct
integrity testing.
A.7    Reporting

       Utilities that use membrane filtration for compliance with the LT2ESWTR are required to
submit a monthly operating report to the state.  Because these monthly reports are directly linked
to integrity testing results, it is important that reporting be incorporated into a comprehensive
IVP. As with other sections in this appendix, the following discussion on reporting is organized
into a series of critical questions that should be addressed in an IVP.
What is the purpose of reporting?

       As it relates to integrity verification, the primary purpose of reporting is to document the
ability of a membrane filtration system to meet its required log removal or other performance-
based objectives on an ongoing basis.  Under the minimum requirements of the LT2ESWTR, this
documentation generally consists of all direct integrity test and continuous indirect integrity
monitoring results that exceed the respective UCL and the subsequent corrective action that was
taken in each case. Note that collecting,  recording, and storing an abundance of integrity test
data may be very beneficial for optimizing membrane filtration system performance, as
discussed in section A.6, even if the majority of the accumulated data are not necessary for
complying with reporting requirements.
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       If membrane filtration is not applied specifically for LT2ESWTR compliance, reporting
may not necessarily be directly related to integrity verification, depending on state requirements.
For example, membrane filtration might be considered an alternative filtration technology (as
provided for under the federal SWTR), in which case reporting requirements might simply
include turbidity, similar to those for conventional media filters. In this case, including reporting
requirements in an IVP may  not be critical for a utility.  Nevertheless, because verifying and
preserving membrane integrity are critical to successful membrane filtration system operation, it
is recommended that even turbidity, particle counts, or other required filtrate quality data always
be considered continuous indirect integrity monitoring results, thus linking reporting
requirements to membrane integrity and, subsequently, an IVP.
What should an IVP include with respect to reporting?

       An IVP should specify any state requirements for reporting, including both the content
and the reporting frequency.  (Reporting requirements for utilities that employ membrane
filtration for compliance with the LT2ESWTR are addressed in Chapters 4 and 5 for direct
integrity  testing and continuous indirect integrity monitoring, respectively.)  Any utility-specific
procedures for preparing the compliance report should also be included in an IVP, along with a
sample report form.
A.8    Summary

       Although not required under the LT2ESWTR, the development of a comprehensive IVP
can be a valuable organizational tool to help a utility verify and maintain membrane system
integrity.  An IVP should essentially serve as a utility's system-specific "how-to" guide for all
aspects operation and maintenance that are related to system integrity, including (but not
necessarily limited to) the following:

       •  Regulatory requirements

       •  Voluntarily implemented system-specific practices

       •  Clear objectives for all IVP procedures

       •  Instructions for all IVP procedures

       •  Equipment listing, description, and purpose

       •  System troubleshooting tips

       •  Guidelines for interpreting test results

       •  Sample calculations (where applicable)
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       •   Membrane manufacturer contact information

A well-developed IVP containing these elements can make the process of integrity verification
more effective and efficient, thus helping a utility maximize the benefit of its membrane
filtration system for serving as a barrier to pathogens and other particulate matter.
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                           Appendix B

                Overview of Bubble Point Theory
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                                   Appendix B:
                      Overview of Bubble Point Theory
B.1    Introduction
       The various methods of pressure-based direct integrity testing are all predicated on
capillary theory as described by the bubble point equation, which is derived from a balance of
static forces on the meniscus in a capillary tube.  The bubble point itself is defined as the
threshold gas pressure required to displace liquid from the pores or capillary-like breaches of a
fully-wetted membrane.  In the context of porous membranes, bubble point theory was originally
used as the basis for developing a test to characterize the pore sizes.  Because the bubble point
equation describes an inverse relationship between the applied pressure and capillary (or pore)
diameter, the pressure at which bubbles are first detected in a fully-wetted membrane can be used
to calculate the diameter of the largest pore (see Equation B. 1).  Accordingly, larger threshold
pressures are indicative of membranes with smaller pores. A diagram illustrating a membrane
pore as a capillary tube is shown in Figure B.I.
       Figure B.1 Diagram of a Membrane Pore Modeled as a Capillary Tube
                                      AIR
                 1EV1BRANE
                                  UR
                 DIAMFTFR  OF
                   MEMBRANE
                          PORE.
d
            WA~ER -FILLED
            MEMBRANE  PORE
      Bubble point theory has also been applied to the detection of integrity breaches in the
form of the various pressure-based direct integrity tests, such as the pressure or vacuum decay
tests (sections 4.7.1  and 4.7.2, respectively), the diffusive airflow test (section 4.7.3), and the
water displacement test (section 4.7.4).  Integrity breaches such as broken hollow fibers or holes
in the surface of the membrane are analogous to pores, and larger test pressures enable the
detection of smaller breaches. If the applied pressure is below the bubble point of the rated
membrane pore size and does not decay (pressure and vacuum decay tests), generate airflow
(diffusive airflow test), or displace water (water displacement test) to a degree that exceeds

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                          Appendix B - Overview of Bubble Point Theory
normal tolerances over the duration of the direct integrity test, the membrane is determined to be
integral at the level of the threshold pore or breach size corresponding to that applied pressure.
In the context of the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR), this
threshold pore or breach size is called the test resolution, as described in section 4.2.

       The purpose of this appendix is to provide a general overview of bubble point theory as it
relates to direct integrity testing under the LT2ESWTR. In addition to the background provided
in this introduction, subsequent sections of this appendix describe the bubble point equation and
its parameters.
B.2   The Bubble Point Equation

       The bubble point equation is derived from a balance of static forces on the meniscus in a
capillary tube and is given as Equation B.I (without specific units).  A derivation of this equation
is given in the literature by Meltzer (1987).
                           4 • <7 • cos 9
                     Php =	                                Equation B. 1
                                cap

       Where:        Pbp     =     bubble point pressure
                     s       =     surface tension at the air-liquid interface
                     9       =     liquid-membrane contact angle
                     dcap      =    capillary diameter
       Converting Equation B.I to a form that utilizes convenient units for the various
parameters yields Equation B.2:
                           0.58*<7*cos0
                               ~d
Php = —	;	                             Equation B.2
                                  cap
       Where:        Pbp     =     bubble point pressure (psi)
                     s       =     surface tension at the air-liquid interface  (dynes/cm)
                     9       =     liquid-membrane contact angle (degrees)
                     dcap     =     capillary diameter (|j,m)
       Because the structure of most membranes cannot be accurately represented by a perfectly
cylindrical capillary, a shape correction factor, K, is typically applied to account for non-ideal
conditions, as shown in Equation B.3:
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                           Appendix B - Overview of Bubble Point Theory
                           0.58* K*
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                          Appendix B - Overview of Bubble Point Theory
                     Ptest = (0.193 • K • cr • cos#)+ BPmax               Equation B.6 (4.1)

       Where:       Ptest    =    minimum test pressure (psi)
                     K      =    pore shape correction factor (dimensionless)
                     s      =    surface tension at the air-liquid interface  (dynes/cm)
                     9      =    liquid-membrane contact angle (degrees)
                            =    maximum backpressure on the system during the test (psi)
       For the purposes of pressure-based direct integrity testing, Equation B.3 can be
rearranged to yield an expression for the diameter of smallest integrity breach that can be
detected for a given applied pressure, as shown in Equation B.7:
                           0.58 • K*a                               ^    .   „ „
                     dfect=	                        Equation B.7
                                    test

       Where:        dfect    =    defect diameter  (|j,m)
                     K      =    pore shape correction factor (dimensionless)
                     s      =    surface tension at the air-liquid interface  (dynes/cm)
                     9      =    liquid-membrane contact angle (degrees)
                     Ptest    =    integrity test pressure (psi)
B.3    Bubble Point Equation Parameters

       As shown in Equations B.4-B.6, the pore shape correction factor (K), liquid-membrane
contact angle (9), and the surface tension (s) all affect the minimum direct integrity test pressure
necessary to meet a given resolution requirement.  Each of these parameters is discussed in the
following subsections, including considerations for selecting appropriate values.
       Liquid-Membrane Contact Angle (9)

       The liquid-membrane contact angle ranges from 0-90ฐ and is primarily a function of the
membrane hydrophilicity, which can be characterized in general terms as the affinity of the
membrane material for water or ability of the membrane to become wetted with water. For an
ideally hydrophilic membrane, the liquid-membrane contact angle is 0 degrees.  Although many
membranes used for drinking water applications are manufactured using hydrophilic materials,
an ideally hydrophilic membrane is purely  theoretical.  However,  a value of 0 degrees yields the
largest minimum integrity test pressure (as shown in Equations B.4-B.6), and thus represents the
most conservative contact angle. In the absence of specific information from the membrane
manufacturer regarding a more accurate value of 9 for a particular material, a  contact angle of
0 degrees should be assumed. The determination of values for 9 is discussed in  the literature

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                          Appendix B - Overview of Bubble Point Theory
(Meltzer 1987). Because a less conservative contact angle can significantly reduce the minimum
required integrity test pressure, any value for 9 other than 0 degrees should be well-documented
and approved by the state if used for the purposes of regulatory compliance, such as under the
LT2ESWTR.
       Pore Shape Correction Factor (K)

       The dimensionless pore shape correction factor ranges from 0-1 and is a function of the
pore structure, accounting for deviations from perfectly cylindrical pores, as well as for the
torturous flow path across the membrane.  A correction factor of 1 represents a perfectly
cylindrical pore, and as shown in Equations  B.4-B.6, maximizes the value of the minimum
required test pressure. However, it is generally recognized that almost all microporous
membranes used for drinking water treatment do not have perfectly or approximately cylindrical
pores, thus have associated correction factors less than 1. Nevertheless, because pore shape
correction factor can significantly reduce the minimum required test pressure, it is important that
any value less than 1 be well-documented and approved by the state if used for the purposes of
regulatory compliance, such  as under the LT2ESWTR. In the absence of such data supporting
the use of a non-ideal pore shape correction  factor, a conservative value of 1 should be used.
       Surface Tension

       Although the surface tension of water does not vary significantly over the typical range of
ambient water temperatures, it still can affect the minimum direct integrity test pressure
necessary to meet a given resolution requirement, as shown in Equations B.4-B.6.  Thus, because
the surface tension varies inversely with temperature, the surface tension at the lowest
anticipated water temperature should be used to calculate a conservative value for the minimum
required test pressure.  For reference, Table B. 1 includes values of surface tension over a range
of water temperatures.
           Table B.1 Surface Tension of Water at Various Temperatures1
Temperature
fC)
5
10
15
20
25
30
40
Surface Tension
(dynes/cm)
74.9
74.2
73.5
72.8
72.0
71.2
69.6
                          1  CRC Handbook, 66th ed., 1985-1986
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                            Appendix C

          Calculating the Air-Liquid Conversion Ratio
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                                    Appendix C:
                 Calculating the Air-Liquid Conversion Ratio
C.1    Introduction

       As described in Chapter 4, the regulatory framework for the Long-Term 2 Enhanced
Surface Water Treatment Rule (LT2ESWTR) requires that the flow through the smallest
integrity breach that generates a measurable response from the direct integrity test (i.e., the
critical breach size - Qbreach) be determined in order to establish the sensitivity of the test method
(40 CFR 141, Subpart W, Appendix C).  (Under the LT2ESWTR, sensitivity is defined as the
maximum log removal value (LRV) that can be reliably verified by the direct integrity test (i.e.,
LR.VDIT) (40 CFR 141, Subpart W, Appendix C).)  However, because most pressure-based direct
integrity tests yield results in terms of airflow or pressure decay, it may be necessary to convert
these results to an equivalent value for the flow of water through the critical breach under typical
filtration conditions.  This conversion is necessary for calculating both the sensitivity and the
upper control  limit (UCL) for a direct integrity  test.

       Although there are a number of methods for converting a direct integrity test response to
a corresponding flow of water, each can be generally categorized as one of two types of
approaches: mathematical modeling or experimental determination. This appendix describes a
mathematical approach based on a parameter called the air-liquid conversion ratio (ALCR),
which is defined as the ratio of air that would flow through a breach during a direct integrity test
to the amount of water that would flow through the breach during filtration, as shown in
Equation C.I  (also Equation 4.5):
                     ALCR = \-^—\                               Equation C.I  (4.5)
                            V ^breach j

       Where:       ALCR  =    air-liquid conversion ratio (dimensionless)
                    Qair     =    flow of air through the critical breach during a pressure-
                                  based direct integrity test (volume / time)
                    Qbreach  =    flow of water through the critical breach during filtration
                                  (volume / time)
       Because of the many variations in membrane configurations, breaches in the membrane
may exhibit either turbulent or laminar flow characteristics depending upon the location and size
of the defect, as well as the applied pressure differential.  In addition, there are fundamental
differences between hollow-fiber and flat sheet membrane breaches, since the most common
breaches associated with hollow-fiber modules exhibit pipe flow characteristics, while flat sheet
breaches are best represented by an orifice model.  Consequently, three different hydraulic
models have been developed  for determining the ALCR for a particular membrane system,
depending on the configuration of the membrane material (i.e., hollow-fiber vs. flat sheet) and

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                      Appendix C - Calculating the Air-Liquid Conversion Ratio
the type of flow (i.e., laminar vs. turbulent) that is expected through the critical breach.  These
three models include the Darcy pipe flow model (for breaches in a hollow-fiber (or hollow-fine-
fiber) module under conditions of turbulent flow), the orifice model (for modules utilizing flat
sheet membranes such as spiral-wound and membrane cartridge configurations under conditions
of turbulent flow), and the Hagen-Poiseuille model (for any configuration under conditions of
laminar flow).  Table C.I summarizes the various approaches for calculating the ALCR based on
these three models and the conditions under which the use of each model is  appropriate.
                   Table C.1  Approaches for Calculating the ALCR
Module Type
Hollow-fiber1
Flat sheet3
Defect Flow
Regime
Turbulent2
Laminar
Turbulent
Laminar
Model
Darcy Pipe Flow
Hagen-
Poiseuille
Orifice
Hagen-
Poiseuille
                       1 Or hollow -fine-fiber
                       2 Typically characteristic of larger diameter fibers and higher
                        differential pressures
                       3 Includes spiral-wound and cartridge configurations
       Note that the various methods presented in this appendix for determining the ALCR
implicitly assume that the flow regime for airflow through a breach during direct integrity testing
is the same as that for liquid flow though a breach during filtration (i.e., either both laminar or
both turbulent). If this assumption is determined to be inappropriate for a given membrane
filtration system such that inaccurate and non-conservative estimates for sensitivity may result,
then a hybrid approach may be considered.  An example of such a hybrid approach is to assume
laminar water flow and turbulent airflow, which could be modeled through the application of the
Hagen-Poiseuille  equation for water and the Darcy equation for air.

       Procedures for calculating the ALCR and subsequently the sensitivity and upper control
limit (UCL) for applicable pressure-based direct integrity tests are given  in Chapter 4, but the
derivations of the various hydraulic models that form the basis for the respective ALCR
equations are provided in the following sections of this appendix as additional information. Note
that while the derivation of the ALCR equations relies on various hydraulic models that could be
used to directly calculate the flow of air (Qair) and water (Qbreach) through an integrity breach,
direct application of these equations requires knowledge of the critical breach size, which is
difficult and impractical to accurately quantify.  The advantage of the ALCR is that the terms
relating to the size of the breach cancel out, yielding equations for the ALCR that are a function
of either known and/or more easily determined parameters and independent of the critical breach
size or geometry.
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                      Appendix C - Calculating the Air-Liquid Conversion Ratio
       For the derivation of the various models described in this appendix, airflow equations
have been developed using a standard temperature and pressure of 68 ฐF (528 R, 293 K, or
20 ฐC) and 0 psi (14.7 psia) as.  These standard conditions were selected to be consistent with the
convention for airflow measurement devices. The equations can be modified to different set of
reference conditions through application of the ideal gas law expressed in terms of absolute
temperature and pressure, if necessary.  In addition, the temperature of the air used in a pressure-
based direct integrity test is assumed to be the same as that for the water in the membrane
filtration system, since these temperatures are expected to rapidly equilibrate.

       Additional background on the hydraulic modeling developed in this appendix may be
found in Crane's Flow of Fluids Through Valves, Fittings, and Pipes (1988). All of the basic
hydraulic equations used in the derivation of the ALCR equations are included in this text.
C.2   Darcy Pipe Flow Model

       The Darcy pipe flow model is used to describe turbulent flow through an integrity breach
with characteristics similar to broken hollow-fiber. Generally, turbulent flow may be expected
through larger diameter broken fibers and at higher differential pressures.  The Darcy equations
for the flow of air and water through a pipe are given in Equations C.2 and C.3, respectively:
Where:
                     Qair
                     Y

                     dfiber
                     Ptest
                     BP
                     T
                                                                     Equation C.2
                            flow of air at standard conditions (ft3/sec)
                            net expansion factor for compressible flow through a pipe
                            to a larger flow area (dimensionless)
                            fiber diameter  (in)
                            integrity test pressure  (psi)
                            backpressure on the system during the integrity test  (psi)
                            water temperature  (ฐF)
                            resistance coefficient of air (dimensionless)
                     2^=0.525.^
                                                 IMP
                                             ' Kwater *
                                                              Equation C.3
Where:
              Qbreach  =
              TMP
                                   flow of water through the critical breach during filtration
                                   (ft3/s)
                                   fiber diameter  (in)
                                   transmembrane pressure (psi)
                                   resistance coefficient of water  (dimensionless)
                                   density of water  (lbs/ft3
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                      Appendix C - Calculating the Air-Liquid Conversion Ratio
       Assuming that the resistance coefficients for air and water are similar (i.e., Ka;r ~ Kwater)
and applying a value of 62.4 Ibs/ft3 for the density of water, the ratio of Equation C.2 to
Equation C.3 yields an expression for the ALCR, as given by Equation C.4:
              ALCR =
                                \(PM-EP).(PM+\4.T)
                                                 Equation C.4
      Where:        ALCR   =    air-liquid conversion ratio (dimensionless)
                     Y        =    net expansion factor for compressible flow through a pipe
                                   to a larger flow area  (dimensionless)
                     Ptest      =    direct integrity test pressure  (psi)
                     BP       =    backpressure on the system during the integrity test (psi)
                     T        =    water temperature  (ฐF)
                     TMP     =    transmembrane pressure (psi)
       The ALCR is used in the equations for determining both the sensitivity and the upper
control limit (UCL) for direct integrity testing, as described in Chapter 4.  Consequently, the
values of the parameters in Equation C.4 should be selected to yield a conservative value for the
ALCR.

       The net expansion factor for compressible flow (Y) may be obtained from charts in
various hydraulics references, such as Crane (1988) (page A-22). Using the appropriate chart for
airflow, values for Y are given as a function of pressure and the flow resistance coefficient, as
shown in Equation C.5 (a non-specific expression illustrating the relationship between Y and its
variables):
                     7oc
                  ,K
                                   Equation C.5
       Where:
Y

Ptest
BP
K
net expansion factor for compressible flow through a pipe
to a larger area (dimensionless)
direct integrity test pressure (psi)
backpressure on the system during the integrity test  (psi)
flow resistance coefficient  (dimensionless)
       The flow resistance coefficient (K) is a common fluid flow parameter described by most
hydraulics texts and is defined as shown in Equation C.6:
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                      Appendix C - Calculating the Air-Liquid Conversion Ratio
                     K = f •	                                    Equation C.6
                             "• fiber

       Where:       K     =      flow resistance coefficient  (dimensionless)
                     /      =      Darcy friction factor (dimensionless)
                     L      =      length of the defect (in)
                            =      fiber diameter (in)
Using the conservative scenario of a fiber break at the point where the fiber enters the pot, the
length of the defect (L) is represented by the length  of the lumen encasement into the membrane
pot.  The friction factor (f) may be estimated from a Moody diagram or the corresponding
tabulated values, both of which are readily in available in most hydraulics references.  The
relative roughness (e/dfiber) that is required to estimate the value for the Darcy fiction faction may
be calculated by either obtaining a product-specific value for the specific roughness (e) from the
manufacturer or by using the membrane pore size as an estimate of the specific roughness.

       Note that the net  expansion factor (Y) should remain constant over time for practical
purposes if appropriately conservative values are used. Thus, the determination of Y should
represent a one-time, site-specific calculation. Also, because the ALCR is directly proportional
to Y (as shown in Equation C.4), lower values for Y result in lower, more conservative values for
the ALCR.

       An iterative solution may be required to determine a value for the net expansion
factor (Y). A general outline for one such iterative process is given as follows.  The use of a
spreadsheet  may help facilitate the various calculations required.

        1. Select a reasonable value for the friction factor (f).

       2. Calculate the flow resistance coefficient (K) using Equation C.6.

       3. Obtain a value for the Reynolds number (Re) from tabulated values for the friction
          factor (f) as a function of the Reynolds number (Re) and the relative roughness
          (e/dfiber).

       4. Calculate airflow (Qair) from the equation for the Reynolds number (Re) as a function
          of equivalent diameter, air velocity, and dynamic viscosity (as referenced in fluid
          mechanics and dynamics texts). For the purposes of determining the equivalent
          diameter and velocity (i.e., the flow (Qair) divided by the cross-sectional area), assume
          that the applicable integrity breach may be represented by a pipe (e.g., a hollow fiber)
          flowing  full with air. Use the maximum anticipated temperature and the minimum
          pressure applied  over the duration of the direct integrity test (i.e., accounting for
          baseline decay) to generate a conservative (i.e., low) value for the dynamic viscosity
          and, thus, in turn conservative (i.e., low) values for airflow (Qair) and the ALCR.
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                      Appendix C - Calculating the Air-Liquid Conversion Ratio
       5. Using tables available in hydraulics texts (e.g., page A-22 of Crane (1988)), apply the
          flow resistance coefficient (K) and the pressure ratio to determine a value for the net
          expansion factor (Y), as shown in Equation C.5.

       6. Calculate airflow (Qair) using Equation C.2. Assume that K ซ Ka;r.

       7. If the airflow (Qair) calculated in steps 4 and 6 (above) is approximately the same, then
          the net expansion factor (Y) determined in step 5 is correct.  Otherwise, select a revise
          value for the friction factor (f) and repeat steps 1-7 in an iterative process until the two
          calculated values for airflow (Qair) converge.
C.3   Orifice Model

       The orifice flow model may be used to approximate turbulent flow through an integrity
breach with characteristics similar to a hole in a flat sheet membrane that may be configured as a
disposable cartridge or a spiral-wound module.  The representative equations for airflow and
water flow through an orifice are given as Equations C.7 and C.8, respectively:
       Where:
Qair
Y

dfiber
C
Ptest
BP
T
                                          l(Ptest-BP).(Ptest+\4.7)
                                                   460 + T
                                                                          Equation C.7
flow of air at standard conditions (ft3/s)
net expansion factor for compressible flow through a pipe
to a larger area (dimensionless)
fiber diameter (in)
coefficient of discharge (dimensionless)
direct integrity test pressure (psi)
backpressure on the system during the integrity test (psi)
water temperature (ฐF)
                     Qbreach= 0.525
                                                 Equation C.8
       Where:
Q
                       breach
                     dfiber
                     C
                     TMP
                     Pw
flow of water through the critical breach during filtration
(ft3/s)
fiber diameter (in)
coefficient of discharge (dimensionless)
transmembrane pressure (psi)
density of water (lbs/ft3)
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                      Appendix C - Calculating the Air-Liquid Conversion Ratio
       The ratio of Equation C.7 to Equation C.8 yields an expression for the ALCR, as given in
Equation C.9. Note that this equation incorporates a value of 62.4 Ibs/ft3 for density of water.
                                                                     Equation C.9
      Where:        ALCR   =    air-liquid conversion ratio (dimensionless)
                     Y        =    net expansion factor for compressib le flow through a pipe
                                   to a larger area  (dimensionless)
                     Ptest      =    direct integrity test pressure  (psi)
                     BP       =    backpressure on the system during the integrity test (psi)
                     pw       =    density of water (Ibs/ft3)
                     T        =    water temperature  (ฐF)
                     TMP     =    transmembrane pressure (psi)
Note that although derivations are slightly different, the resulting ALCR equations for the Darcy
and orifice models (Equations C.4 and C.9, respectively) are identical. However, the two models
utilize different methodologies for determining the net expansion factor for compressible flow
(Y).  As described in section C.2 for the Darcy model, the values of the parameters in
Equation C. 10 should be selected to yield a conservative value for the ALCR.

       Also, as with the Darcy model, the net expansion factor for compressible flow (Y) may
be obtained from charts in various hydraulics references, such as Crane (1988) (page A-21).
However, for the orifice model, EquationC.10 may also be used to calculate the net expansion
factor, as follows:
                     7 = 1-
0.293*  1--
BP +14.7
P^t +14.7
                                         test
Equation C.10
       Where:       Y       =     net expansion factor for compressible flow through a pipe
                                   to a larger area  (dimensionless)
                     BP      =     backpressure on the system during the integrity test (psi)
                     Ptest     =     direct integrity test pressure (psi)
       As with the Darcy model, because the ALCR is directly proportional to Y (as shown in
Equation C.9), lower values for Y result in lower, more conservative values for the ALCR.  Also
like Darcy model, note that the net expansion factor (Y) should remain constant over time for
practical purposes if appropriately conservative values are used. Thus, the determination of Y
should represent a  one-time, site-specific calculation.
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                      Appendix C - Calculating the Air-Liquid Conversion Ratio
C.4   Hagen-Poiseuille Model

       The Hagen-Poiseuille model is appropriate for small integrity breaches (such as a pin
hole or flow through a broken, small-diameter hollow-fiber under low differential pressure) that
would result in laminar flow. Using this model, the equation for airflow through a small defect
under laminar flow conditions is given by Equation C.I 1:
                                                                      Equation C. 1 1
       Where:
Qair
dfect
APeff
g
L
Hair
T
                                   flow of air at standard conditions  (ft3/s)
                                   defect diameter (in)
                                   effective integrity test pressure  (psi)
                                   gravitational constant (32.2 lbm-ft/lbf-s2)
                                   length of the defect (in)
                                   viscosity of air  (Ibs/ft-s)
                                   water temperature  (ฐF)
       Because air is a compressible fluid, the airflow is determined using the effective integrity
test pressure, APeff, calculated according to Equation C.12.
                                \Ptest + 14.7) + (BP+U.7)
                                         2*14.7
                                        (BP +14.7)
                                            14.7
                                                        Equation C.12
       Where:
APeff
Ptest
BP
                                   effective air integrity test pressure  (psi)
                                   direct integrity test pressure  (psi)
                                   backpressure on the system during the integrity test (psi)
       The elements of the effective integrity test pressure include three primary terms, as
individually bracketed in Equation C.12.  These three terms are, respectively:

       •  the differential pressure across the membrane during the integrity test

       •  a term that accounts for the average velocity gradient of the compressed air as it
          passes across the membrane

       •  a multiplier that is necessary to convert the backpressure as it leaves the membrane to
          standard atmospheric conditions
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                       Appendix C - Calculating the Air-Liquid Conversion Ratio
       The Hagan-Poiseuille equation for liquid flow through a breach under conditions of
laminar flow is shown as Equation C.13:
                               .
                      Qbreach = - T   -               Equation C.13
       Where:       Qbreach   =    flow of water through the critical breach during filtration
                                   (ft3/s)
                     dfect     =    defect diameter (in)
                     g        =    gravitational constant (32.2 lbm-ft/lbf-s2)
                     TMP    =    transmembrane pressure (psi)
                     L        =    length of the defect (in)
                     |j,w      =    viscosity of water  (Ibs/ft-s)
       The ratio of Equation C. 11 to Equation C.13 yields an expression for the ALCR, as given
by Equation C.14:
                                         e
                      ALCR = -       -                    Equation C.14
       Where:       ALCR  =    air- liquid conversion ratio (dimensionless)
                     APeff    =    effective integrity test pressure  (psi)
                     (j,w      =    viscosity of water (Ibs/ft-s)
                     TMP    =    transmembrane pressure (psi)
                     Hair      =    viscosity of air (Ibs/ft-sec)
                     T       =    water temperature (ฐF)
       The ratio of the viscosity of water to the viscosity of air (|j,w /(j,air) may be combined and
expressed as a single function of the water temperature that is derived by fitting a curve to
discrete data points for the viscosity ratio.  Equation C. 15 simplifies the calculation of the ALCR
to an expression that is function of only measured pressures and the water temperature. Note
that this form of the equation is only valid in the temperature range from 32 to 86 ฐF, in
accordance with the limitations of the binomial fit for the viscosity ratio.  If the temperature is
outside of this range, the more general expression in Equation C.14 should be used.
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                      Appendix C - Calculating the Air-Liquid Conversion Ratio
           ALCR =
Where:
            527 • AP -.• (175- 2.71ซ T + 0.0137 • T2)
            - ^— - - -
                        IMP* (460 + T)
                                                                        Equation C. 1 5
                     ALCR  =    air- liquid conversion ratio (dimensionless)
                     APeff    =    effective integrity test pressure (psi)
                     T       =    water temperature (ฐF)
                     TMP    =    transmembrane pressure (psi)
       As with the Darcy and orifice models, the values for the parameters APefr and TMP used
in Equation C.14 or C.15 should be selected to yield a conservative value for the ALCR.
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                         Appendix D

 Empirical Method for Determining the Air-Liquid Conversion
     Ratio for a Hollow-Fiber Membrane Filtration System
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                                   Appendix D:
 Empirical Method for Determining the Air-Liquid Conversion Ratio for
                a Hollow-Fiber Membrane Filtration System
D.1    Introduction

       As described in Chapter 4, the regulatory framework for the Long-Term 2 Enhanced
Surface Water Treatment Rule (LT2ESWTR) requires that the flow through the smallest
integrity breach that generates a measurable response from the direct integrity test (i.e., the
critical breach size) be determined in order to establish the sensitivity of the test method.  (Under
the LT2ESWTR, sensitivity is defined as the maximum log removal value (LRV) that can be
reliably verified by the direct integrity test (i.e., LRVoii).)  However, because most pressure-
based direct integrity tests yield results in terms of airflow or pressure decay, it may be necessary
to convert these results to an equivalent value for the flow of water through the critical breach
under typical filtration conditions. Although there are a number of methods for converting a
direct integrity test response to a corresponding flow of water, each can be generally categorized
as one of two  types of approaches: mathematical modeling or experimental determination. This
appendix describes an empirical approach based on a parameter called the air-liquid conversion
ratio (ALCR), which is defined as the ratio of air that would flow through a breach during a
direct integrity test to the amount of water that would flow through the breach during filtration,
as shown in Equation D.I (also Equation 4.5):
                    ALCR=  -_                               Equation D.I  (4.5)
                            V ^breach )

       Where:       ALCR   =    air-liquid conversion ratio (dimensionless)
                    Qair     =    flow of air through the critical breach during a pressure-
                                 based direct integrity test (L/min)
                    Qbreach   =    flow of water through the critical breach during filtration
                                 (L/min)
       While Appendix C describes the hydraulic models that could be used to calculate the
ALCR for various types of membrane filtration systems and under different flow regimes, this
appendix provides an example of an empirical method that can be used to determine the ALCR
for system using microporous hollow-fiber membranes based on bubble point theory - the
correlated airflow measurement (CAM) technique. The CAM technique measures the flow of air
and water through a worst-case fiber break scenario to empirically determine the ALCR of a
membrane filtration unit. This method is specific to hollow-fiber membrane processes in which
the geometry of the fiber and associated module is known.

       The test involves applying air pressure that is below the bubble point of the membrane to
determine the airflow that corresponds to the worst-case broken fiber scenario.  For most hollow-

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 Appendix D - Empirical Method for Determining the Air-Liquid Conversion Ratio for a Hollow-Fiber Membrane
                                      Filtration System

fiber systems, this condition occurs when the fiber is broken at the membrane pot, since it
represents the shortest flow path for feed water to pass unfiltered to the filtrate side of the
membrane.  Thus, for any fiber of a given length and diameter, the flow of water through a
breach during normal operation can be correlated to the flow of air via the integrity test pressure,
as shown in Equation D.2:
                     f(Qbreach) = f(Qa,r) = P                          Equation D.2

       Where:      /(Qbreach)  =  water flow correlation function (psi-min/mL)
                     Qbreach     =  flow of water through a broken fiber (mL/min)
                    /(Qair)     =  airflow correlation function (psi-min/mL)
                     Qair       =  flow of air through a broken fiber (mL/min)
                     P         =  pressure  (psi)
       The relationship between the air and water flow is determined through empirical
determination of the water flow and airflow correlation functions -/(Qbreach) and/(Qair) -
respectively - which require the water flow and airflow through a broken fiber to be measured at
various differential pressures. (A schematic illustrating an apparatus for measuring airflow using
the CAM technique is shown in Figure D. 1.) These relationships  are mathematical functions that
may be linear or non-linear in nature and are dependent upon the type of defect. The data
obtained  from these measurements  may be fitted with respective equations to establish empirical
relationships, as illustrated in Figure D.2.  Since both functions are measurements of flow (either
air or water) and pressure, this commonality can be used to establish a direct relationship
between the flow of air to water, which can in turn be used to determine the ALCR.  As
illustrated in Figure D.2, one such relationship exists at the direct  integrity test pressure (Ptest).
However, it is also possible to determine the relationship between air and water flow at other
conditions, as well, such as the integrity test pressure and the transmembrane pressure (TMP).
The ALCR varies as a function of the TMP during operation, since a higher TMP results in a
greater flow of water through  the defect and thus a lower ALCR.  Note that the relationship
between the airflow and water flow correlation functions assumes constant temperature, since
changes in air or water temperature may change the functional relationships.
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 Appendix D - Empirical Method for Determining the Air-Liquid Conversion Ratio for a Hollow-Fiber Membrane
                                     Filtration System


            Figure D.1  CAM Technique Airflow Measurement Apparatus
 COMPRESSED
  AIR SUPPLY
                           o
                 UPSTREAM
                 PRESSURE
                 REGULATION
                   VALVE
                                     MEMBRANE
                                     UNIT
 AI8 MASS
FLOW METER
            PRESSURE
           8EGUIATIQN
             VALVE
          Figure D.2 Example Airflow and Water Flow Correlation Curves
               PRESSURE
                   OR
                  Ty;i
                                      AIR OR  WA~CR FLOW
       Although the CAM technique for determining the ALCR empirically is more labor-
intensive than calculating the ALCR using a hydraulic model, the procedure does have several
advantages.  First, because the measurement is empirical, it is more accurate than calculations
based on general hydraulic models.  In addition, the CAM procedure does not rely on
assumptions that are necessary to estimate the ALCR from hydraulic models, but instead
facilitates direct determination of the ALCR based on measured air and water flows through a
known defect.
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 Appendix D - Empirical Method for Determining the Air-Liquid Conversion Ratio for a Hollow-Fiber Membrane
                                       Filtration System

D.2   Methodology

       The following general procedure is provided as a guide for conducting the CAM
technique for experimentally determining the ALCR:

      1.  Determine the worst-case integrity breach scenario.  For example, for a single-exit
         hollow-fiber module, the worst-case integrity breach is at the interface of the membrane
         fiber and the potting at the filtrate outlet end of the module.  Modify a bench or full-
         scale module to artificially create this worst-case integrity breach.

      2.  Measure and characterize the water flow through the integrity breach  (i.e., Qbreach) over
         the range of operating TMPs.

      3.  Develop an equation for a fitted curve that represents the water flow through the worst-
         case integrity breach as a function of TMP.  This relationship is characterized by the
         parameter/(Qbreach) in Equation D.2.

      4.  Determine the minimum bubble point of the porous membrane material. (This
         information should generally be available from the manufacturer.)

      5.  Establish the direct integrity test pressure.  As a general rule, the test pressure should be
         less than 80 percent of the bubble point pressure for  the membrane and below the
         maximum TMP. However, the test pressure must be sufficient to meet the resolution
         requirement of the LT2ESWTR for the removal of Cryptosporidium.

      6.  Determine the baseline integrity response for an integral membrane (see section 4.3.1.3
         for a discussion of diffusive flow through the wetted pores of an integral membrane).

      7.  If the diffusive flow is significant (i.e., approximately  10 percent of the total airflow),
         then lower test pressures should be evaluated (or the diffusive flow will have to be
         accounted for in determining the ALCR, as described in section 4.3.1.3).

      8.  Measure the airflow from the worst-case integrity breach at the intended test pressure
         (Ptest) during the pressure-based direct integrity test.

      9.  If Ptest is not known or is potentially variable, it may be necessary to measure airflow
         over  a range of integrity test pressures and develop an empirical relationship to
         characterize the/(Qair) function. For example, if the hydrostatic backpressure is may
         vary between different direct integrity test applications, it may be advantageous to
         measure airflow at a variety of potential integrity test pressures.
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 Appendix D - Empirical Method for Determining the Air-Liquid Conversion Ratio for a Hollow-Fiber Membrane
                                      Filtration System

     10. Determine the ALCR using Equation D.I.


                            ALCR =  ^air
                                    z-'breach

              Where:        ALCR  =     air-liquid conversion ratio  (dimensionless)
                            Qair     =     flow of air through a broken fiber at the direct
                                          integrity test pressure  (mL/min)
                            Qbreach   =     flow of water through a broken fiber at the
                                          reference TMP (mL/min)

        Note that the reference TMP described in association with the variable Qbreach above
        refers to the TMP that is used in the determination of the ALCR for the purpose of
        establishing the direct integrity test sensitivity for regulatory compliance, as described
        in section 4.3.1.2 and Appendix  C.

     11. Calculate the direct integrity test method sensitivity (i.e., LRVoii) using the test result
        (Qair) (either as directly measured with the diffusive airflow test or as converted from
        the pressure decay rate (APtest) using Equation4.8 as measured with the pressure decay
        test) and the ALCR determined in the previous step, as described in Chapter 4.


D.3    Example: Using the CAM Method to Determine the ALCR

Scenario:

       Airflow and water flow correlation curves have been established for a hollow fiber, as
shown in Figure D.3. Determine the ALCR for a direct integrity test pressure of 15 psi and a
reference TMP of 10 psi.


Solution:

Step 1:  Determine the airflow (Qair) at the direct integrity test pressure from the/(Qair) curve in
        Figure D.3 (denoted as Point A).

        Qair  =   180 mL/min
         Determine the water flow (Qbreach) at the reference TMP from the/(Qbreach) curve in
         Figure D.3 (denoted as Point C).

         Qbreach  = 15 mL/min
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 Appendix D - Empirical Method for Determining the Air-Liquid Conversion Ratio for a Hollow-Fiber Membrane
                                    Filtration System


Step 3:  Calculate the ALCR.
               Qb,a,.^   l5mL/mn
                                   =12
                       Figure D.3  Example ALCR Correlation
            PRESSURE
                OR
               TMP
                          15

                          10
             A =  180mL/min
             B =   20mL/min
             C =   15mL/min
                                    AIR OR WATER  FLOW
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                          Appendix E

    Application of Membrane Filtration for Virus Removal
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                                    Appendix E:
          Application of Membrane Filtration for Virus Removal
E.1    Introduction

       Although the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) only
regulates the use of membrane filtration for the removal of Cryptosporidium for the purposes of
compliance with the rule requirements, states could opt to apply the regulatory framework in a
broader context to other applications of membrane filtration, at their discretion.  For the removal
ofGiardia or other relatively large pathogens that are approximately the same size as
Cryptosporidium in order-of-magnitude terms, the LT2ESWTR regulatory framework can be
applied almost directly with only minor modifications, such as adjusting the direct integrity test
resolution to coincide with the lower bound of the  size range characterizing the pathogen of
interest. However, for pathogens that are significantly smaller than Cryptosporidium, there are a
number of important considerations that must be taken into account and which may limit the
applicability of the LT2ESWTR regulatory framework in some cases.  The purpose of this
appendix is to summarize some of the critical issues associated with the application of membrane
filtration for the removal of very small pathogens using the LT2ESWTR regulatory framework.
Because viruses represent the smallest class of pathogen and are directly regulated under the
Surface Water Treatment Rule (SWTR), this appendix is primarily focused  on the application of
membrane filtration for virus removal; however, it is important to note that these same issues
may generally apply to other small pathogens of comparable size, as well.

       Among the five classes of membrane filtration discussed in the Membrane Filtration
Guidance Manual - MF, UF, nanofiltration (NF), reverse osmosis (RO), and membrane cartridge
filtration (MCF) - only MF, UF and MCF are typically applied specifically  for the purpose of
pathogen (or other particulate) removal.  However, because the nominal pore sizes of the types
of membranes associated with these processes vary widely (UF = 0.01 |j,m;  MF = 0.1 |j,m;
MCF = 1 |j,m or smaller), their removal characteristics are different. While all three processes
can remove Cryptosporidium, with a size range lower bound of about  3 |j,m, only UF membranes
have pores small enough to filter viruses, which generally range in size from about 0.01  to
0.1  |j,m. Thus, UF is the primary membrane filtration technology utilized for the objective of
virus reduction. Accordingly, the discussion in this appendix is primarily presented in the
context of virus removal  using UF. Nevertheless, note that while MF  cannot generally be used
as an effective means of virus treatment, it may be applied to remove  organisms such as some
species of bacteria that are larger than 0.1 |j,m but still as much as an order of magnitude smaller
than Giardia or Cryptosporidium. In these cases, some of the issues addressed in the appendix
may be applicable to MF. It is important to note that although some virus removal by MF has
been reported in the literature,  it is generally attributed to formation of a cake layer on the
membrane surface. Since this cake layer is dynamic and removed by the backwash process, the
removal of parti culate matter via this mechanism varies during the course of an operational cycle
and thus is not consistent with the LT2ESWTR framework, which considers only the removal
efficiency of the membrane barrier itself.
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                  Appendix E - Application of Membrane Filtration for Virus Removal
       While NF and RO utilize non-porous semi-permeable membranes that represent a barrier
to viruses, the associated modules are generally not manufactured to be aseptic.  In addition,
because these membranes are not able to be backwashed, particulate matter can cause rapid
irreversible fouling. As a result, NF and RO are not typically applied to directly treat raw water
supplies with significant concentrations of suspended solids. However, NF or RO may be
directly applied (i.e., without significant pretreatment for particulate removal) to remove
dissolved solids from a groundwater source that is subject to virus contamination but very low in
suspended solids. In such cases,  NF and RO may be used to obtain virus reduction credits under
the Ground Water Rule (GWR).  Under these circumstances, the issues addressed in this
appendix may also be applicable  to NF or RO.

       In general, application of the LT2ESWTR regulatory framework for the removal of
viruses necessitates that the membrane filtration process comply with appropriate pathogen-
specific criteria for the three primary regulatory elements: challenge testing, direct integrity
testing, and continuous indirect integrity monitoring. The subsequent sections of this appendix
address some of the practical and regulatory issues with respect to virus removal for each of
these three program elements.  An additional preceding section summarizes current state
regulatory policy for the use of UF for virus removal and highlights  some associated
considerations for the application of the LT2ESWTR regulatory framework.
E.2    Overview of Current Regulatory Policy

       Because there is no general federal framework for the broad regulation of membrane
filtration as a water treatment technology, states have developed policies that are widely varying
in some cases. However, most states are consistent in allowing very little virus removal credit
for membrane filtration. While numerous challenge studies have demonstrated a clear difference
in the ability of MF and UF to remove viruses (as shown in Table E.I), a 2001 survey of state
primacy agencies conducted by USEPA indicated that only 6 of 29 states with regulatory policies
specific to membrane filtration technology differentiated between these two processes in terms of
the virus removal credit awarded, as summarized in Table E.2 (USEPA 2001).

       The most significant factor limiting the virus removal credit awarded to UF is the
infeasibility of using current direct integrity test methods to detect a virus-sized breach (as
discussed in sectionE.3). Thus, it is possible that a number of very small integrity breaches
could allow the passage of viruses through the membrane barrier undetected, contaminating the
filtrate.  While this mode of failure may not be as common as a broken fiber, such a very small
integrity breach may occur as the membranes age or as a result of exposure to incompatible
treatment chemicals.
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                  Appendix E - Application of Membrane Filtration for Virus Removal
                 Table E.1  Virus Removal Studies Using MF and UF
Researcher(s)
Jacangelo et al.
Wilinghan et al.
Schneider et al.
Trussel et al.
Jacangelo et al.
Dwyer et al.
Trussel et al.
Kruithof et al.
Year
1997
1992
1999
1998
1997
1994
1998
1999
Process
MF
MF
MF
MF
UF
UF
UF
UF
Log Removal
0-2.4
0.3-4
1.1
0.4-3.2
6.0-7.9
6.2-6.81
> 6.91
> 5.4
                1 Removal to levels below detection limit
         Table E.2  Summary of State Virus Removal Credit for MF and UF
Virus Log
Removal Credit
No standard credit1
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Number of States
MF
8
18
3
-
-
-
-
-
-
-
UF
8
14
1
1
-
-
-
1
-
4
                        1 Credit typically awarded on a case-by-case basis
       Although this rigorous degree of testing and performance verification is generally not
required of conventional treatment (e.g, daily testing to ensure the absence of short-circuiting in
media filters), the combined processes of flocculation/sedimentation and media filtration
represent a multiple contaminant barrier that provides some degree of insurance against difficult-
to-detect treatment deficiencies (such as small integrity breaches or short-circuiting).  The
removal credits awarded to conventional treatment under the SWTR account for this multiple
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                  Appendix E - Application of Membrane Filtration for Virus Removal
barrier treatment concept, while the log removal credits referenced for UF in Tables E. 1 and E.2
represent membrane filtration as a stand-alone process. Consequently, is possible that a multi-
barrier treatment process scheme including flocculation, sedimentation, and UF (or other
membrane filtration process) could be awarded equivalent or greater virus removal credit than
conventional treatment by some states, at their discretion.

       In addition, because viruses are easily inactivated by low chlorine doses and contact
times that are unlikely to yield  significant disinfection byproducts (DBFs), there is less of a
necessity for states to award high virus removal credits to any alternative treatment process if
some level of primary disinfection is required. By contrast, states generally award removal
credit on par with that for conventional treatment for both MF and UF for larger pathogens such
as Giardia and Cryptosporidium, which have more robust chlorine inactivation requirements
relative to viruses and which are large enough such that similarly sized integrity breaches can be
detected using common direct integrity test techniques (as discussed in section E.3).  State-
awarded log removal credits for both Giardia and Cryptosporidium using MF/UF (which are
considered comparable technologies for Giardia and Cryptosporidium removal) are summarized
in Table E.3 for the same 29 states with specific membrane filtration policies (USEPA 2001).
   Table E.3 Summary of State Giardia and Cryptosporidium Removal Credit for
                                         MF/UF
Virus Log
Removal Credit
No standard credit1
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Number of States
Giardia
8
-
-
1
1
2
7
9
-
1
Cryptosporidium
22
-
-
-
-
4
-
2
-
1
                   1  Credit typically awarded on a case-by-case basis
       In awarding virus removal credit to UF, states must balance the studies that consistently
demonstrate the ability of UF to achieve 5 to 7 log virus removal with the practical problem of
verifying virus-sized integrity breaches during operation (as discussed in section E.3) and the
potential impact that such small integrity breaches might have on the ability of UF to achieve the
awarded credit. Another consideration is the emphasis that many states place on multiple barrier
protection.  In cases in which chemical disinfection is utilized as a component of multiple barrier
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                  Appendix E - Application of Membrane Filtration for Virus Removal
treatment, the level of virus inactivation generally negates the need to award virus removal
credits to UF. As shown in Table E.2, most states currently consider the issues of integrity
verification and/or multiple barrier protection more significant factors, since few states award UF
any virus removal credit as a stand-alone process. However, even without significant state-
awarded removal credit, utilities may  still specifically opt to install UF as a barrier against
viruses on the basis of the many studies indicating near complete virus removal and that even
with some very small and undetectable integrity breaches UF  may remove viruses more
efficiently than either MF or conventional treatment.
E.3    Direct Integrity Testing

       In terms of direct integrity testing, a membrane process applied to obtain virus removal
under the LT2ESWTR regulatory framework would need to meet applicable criteria for
sensitivity, resolution, and frequency. While applying the LT2ESWTR framework for virus
removal is similar to that for Cryptosporidium for sensitivity and frequency of direct integrity
testing (since both of these concepts are independent of the target pathogen), the resolution that
would be necessary for very small pathogens such as viruses is more problematic. Because
viruses range in size from approximately 0.01 - 0.10 |j,m, the resolution must be a very small
0.01 |j,m- two orders of magnitude smaller than that for Cryptosporidium - in order to provide
an appropriate level of conservatism.  A resolution requirement this small may be very difficult
to achieve with currently available direct integrity tests.

       A virus-sized resolution requirement is particularly problematic for pressure-based direct
integrity tests, which are based on bubble point theory (as described in Appendix B). A form of
the bubble point equation is shown as Equation E.I, which relates the required direct integrity
test pressure to the size of an integrity breach.
                           0.58 •ฃ *<7 *cos0
                     ptest =	-,	                         Equation E. 1
                                   feet

       Where:       Ptest   =      required test pressure (psi)
                     0.58   =      constant including applicable unit conversion factors
                     K      =      pore shape correction factor (dimensionless)
                     s      =      surface tension at the air-liquid interface  (dynes/cm)
                     9      =      liquid-membrane contact angle (degrees)
                     dfect   =      defect diameter (|J,m)
       In the context of determining a minimum necessary test pressure, the defect diameter is
equal to the required resolution (i.e., the lower bound on the size range of the pathogen of
interest).  Table E.4 summarizes the required direct integrity test pressure as a function of the
target pathogen size (i.e., the test resolution) for two sets of conditions. In the most conservative
case, the pore shape correction factor (K) is equal to 1, and the liquid-membrane contact angle (9)
is equal to zero (indicating a perfectly hydrophilic membrane).  These respective values should

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                  Appendix E - Application of Membrane Filtration for Virus Removal
be used as a default in the absence of more specific information about the true values of these
two parameters.  The second case utilizes less conservative values of K = 0.25 and 9 = 45ฐ to
illustrate the affect that these two parameters can have on the required test pressure. Both cases
assume a conservative surface tension (s ) of 74.9 dynes/cm (i.e., at a temperature of 5 ฐC). Note
that Table E.4 is logarithmic, citing pathogen sizes from 0.01 to 0.1  |j,m in 0.01 |j,m increments,
and then continuing to 1.0 |j,m in 0.1 |j,m increments.
     Table E.4 Required Direct Integrity Test Pressure as a Function of Target
                            Pathogen Size (i.e., Resolution)
Target
Pathogen
Size
(tun)
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Required Test Pressure
(psi)
Most Conservative
K = 1
9 = 0ฐ
4,344
2,172
1,448
1,086
869
724
621
543
483
434
217
145
109
87
72
62
54
48
43
Less Conservative
K = 0.25
9 = 45ฐ
768
384
256
192
154
128
110
96
85
77
38
26
19
15
13
11
10
9
8
       As shown in Table E.4, for the most conservative case, the required test pressure for a
virus-sized resolution 0.01 |j,m is over 4,000 psi, a value far in excessive of what any current,
commercially available water treatment membrane could withstand without rupturing.  Even the
strongest hollow-fiber membrane can withstand a transmembrane pressure (TMP) of no more
than 100 psi at most, limiting the smallest target pathogen (and thus the resolution) to about
0.4 |j,m in the most conservative case and perhaps just below 0.1  |j,m if more  specific, less
conservative values of K and 9  are known.  Other small pathogens that are larger than viruses
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                  Appendix E - Application of Membrane Filtration for Virus Removal
(e.g., bacteria in the 0.5 - 1.0 |j,m range) require lower test pressures and may allow more
feasible application of LT2ESWTR regulatory framework.  In addition, some manufacturers
have experimented with stronger ceramic "membrane" processes with pore sizes similar to MF
or UF, which may allow the application of direct integrity tests at higher pressures, thus
facilitating the use of the LT2ESTWR regulatory framework for smaller pathogens than are
possible with current polymeric membrane materials.  Note that Table E.4 does not account for
the system backpressure during the application of a pressure-based direct integrity test, which
can increase the required test pressure to achieve a target resolution, as described in Equation 4.1
in Chapter 4.

       Resolution requirements on the order of virus also present some problems for the use of
marker-based direct integrity tests.  Suitable virus-sized challenge parti culates may be
prohibitively expensive, making daily testing infeasible.  In addition, it may be difficult to
manufacture these particulates to meet acceptable tolerances for size range variation. Thus, even
if the practical problems associated with virus-sized direct integrity test resolution could be
overcome and significant virus removal credit would be awarded by the state under the
LT2ESWTR regulatory framework, it may be substantially less expensive for a utility using UF
to apply a small amount of chlorine to inactivate viruses. In this case, because the achievement
of virus removal credit using UF is an issue of operational verification and not removal
efficiency as demonstrated in challenge studies, the utility would have the benefit of a multiple
barrier treatment process even if no removal credit is awarded to UF by the state.
E.4    Challenge Testing

       As shown in Table E.I, a number of studies conducted in recent years have demonstrated
the ability of UF to achieve high log removals of viruses.  While it is not necessary to use the
pathogen of interest itself for the purposes of conducting a challenge test in accordance with the
LT2ESWTR regulatory framework, it is important to ensure that any challenge particulate
selected is conservatively (i.e., equivalently or less efficiently) removed (as discussed in
section 3.9).

       One significant consideration  in regard to challenge testing under the LT2ESWTR
regulatory framework as applied to virus removal is the issue of representative performance
testing to verify the removal efficiency of all membrane modules in a product line that are not
subject to challenge testing.  In order to demonstrate Cryptosporidium removal efficiency, all
modules must be subjected to non-destructive performance testing that is consistent with the
appropriate resolution requirement, as discussed in section 3.6.  The results of this testing are
compared to the  results of similar testing conducted on the representative modules in the same
product line that were subject to challenge modules as an indicator of performance.  Common
non-destructive performance tests (NDPTs) are types of direct integrity tests, such as the bubble
test (see section4.8.2). However, as  discussed in section E.3, because pressure-based direct
integrity tests may not be able to achieve the required 0.01 |j,m resolution requirement for
viruses, non-destructive performance  testing may not be possible.  Thus, it may be necessary to
develop different criteria and methods for validating the virus removal  capability of modules in a
product line that are not subjected to  challenge testing, such as representative destructive
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                  Appendix E - Application of Membrane Filtration for Virus Removal
performance testing on a statistically significant number of modules in each production lot. One
example of such a destructive performance test might be a scanning electron microscopy (SEM)
analysis of the membrane media to confirm the pore size distribution.
E.5    Continuous Indirect Integrity Monitoring

       Although the LT2ESWTR regulatory framework does not specify any particular
resolution or sensitivity criteria for continuous indirect integrity monitoring, related issues may
impact the effectiveness of indirect integrity monitoring if the framework is applied to virus
removal.  For example, very small integrity breaches that permit the passage of viruses may not
allow enough particulate matter across the membrane to be detected by indirect methods such as
turbidity monitoring or particle counting. Thus, it may be difficult to establish a meaningful
control limit for continuous indirect integrity monitoring that is specific to the application of
membrane filtration for virus removal.  As a result, continuous indirect integrity  monitoring
should be used as a general gauge of gross membrane integrity that is independent of the
particular pathogen of concern.
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