O CDA Membrane Filtration Guidance Manual:
Overview and Summary
United Slates
Environmental Protection
Agency
About This Document
The purpose of this document is to provide a concise summary of the regulatory framework for
membrane filtration under the Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) as
presented in the Membrane Filtration Guidance Manual (MFGM).
Important Note: This document is not intended to be comprehensive or to serve as a surrogate for a
careful and thorough reading of the MFGM, but rather to be used as a convenient reference guide for the
core components of the regulatory framework. Furthermore, although this document summarizes the
regulatory requirements for the application of membrane filtration under the LT2ESWTR, it is not a
substitute for the rule language as published in the Federal Register notice.
Scope and Purpose of the Membrane Filtration Guidance Manual
The EPA has developed the LT2ESWTR to reduce the incidence of disease associated with
Cryptosporidium and other pathogenic microorganisms that may occur in drinking water. The
LT2ESWTR supplements existing regulations by mandating additional Cryptosporidium treatment
requirements for higher risk systems, as determined by source water quality. Systems may satisfy these
additional requirements (if applicable) by utilizing one or more of the specified treatment and/or
management strategies collectively termed the "microbial toolbox," a range of options that includes
membrane filtration. For each of the options comprising the microbial toolbox, the rule mandates a
series of requirements specifying the manner in which each option must be implemented for compliance
(i.e., in order to receive the potential Cryptosporidium removal / inactivation credit associated with each
option). The MFGM was developed in conjunction with the LT2ESWTR to elaborate on the rule
requirements associated with membrane filtration and to assist utilities with the application of this
particular toolbox option for compliance with the rule.
It is important to note that the regulatory framework for membrane filtration developed under the
LT2ESWTR and the associated MFGM are only applicable by federal mandate to those systems that
employ membrane filtration for the explicit purpose of achieving compliance with the LT2ESWTR.
Accordingly, the MFGM is not intended to broadly govern membrane treatment technology or to serve
as a general "how-to" guide for membrane filtration systems. However, States may apply the
LT2ESWTR framework in a more comprehensive regulatory context, at their discretion, as permitted
under their respective primacy agreements with the EPA.
Guidance Manual Organization
The MFGM includes an initial introductory chapter with an overview of the document and summary of
the rule requirements (Chapter 1) and three chapters with detailed guidance for complying with each of
three primary aspects of the rule: challenge testing, direct integrity testing, and continuous indirect
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integrity monitoring (Chapters 3, 4, and 5, respectively). The document also contains a chapter with
background information regarding membrane processes for readers less familiar with the technology,
particularly as it relates to concepts and terminology essential to a thorough understanding of the rule
requirements and associated guidance (Chapter 2). In addition, the MFGM includes three chapters
describing recommended and industry-accepted practice in several important facets of developing a
membrane filtration facility that are not related to rule compliance (Chapters 6, 7, and 8). Because
these latter three chapters do not contain LT2ESWTR regulatory requirements, the associated guidance
is not addressed in this summary. An outline of the MFGM is provided in the following table:
MFGM Outline
Chapter
Chapter 1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8
Title
Introduction
Overview of Membrane Filtration
Challenge Testing
Direct Integrity Testing
Continuous Indirect Integrity Monitoring
Pilot Testing
Implementation Considerations
Initial Start-Up
Applicability
Overview / Summary
Background
Information
Regulatory
Requirements
Recommended
Practice
The MFGM also includes several appendices with supplemental information that is applicable to the
membrane regulatory framework under the LT2ESWTR:
• Appendix A: Development of a Comprehensive Integrity Verification Program
• Appendix B: Overview of Bubble Point Theory
• Appendix C: Calculating the Air-Liquid Conversion Ratio
• Appendix D: Empirical Method for Determining the Air-Liquid Conversion Ratio for a
Hollow-Fiber Membrane Filtration System
• Appendix E: Application of Membrane Filtration for Virus Removal
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Overview of Regulatory Framework
Under the LT2ESWTR, systems may be required to achieve as much as 3 log additional
Cryptosporidium removal and/or inactivation credit depending on the results of source water quality
monitoring and the subsequent Bin assignment. Thus, when combined with the prescribed
Cryptosporidium treatment credit awarded to a system in compliance with the Interim Enhanced Surface
Water Treatment Rule (ffiSWTR) or the Long Term 1 Enhanced Surface Water Treatment Rule
(LT1ESWTR), as applicable, the total Cryptosporidium treatment credit required for a system in Bins 2,
3, and 4 is 4 log, 5 log, and 5.5 log, respectively. Membrane filtration is one of several toolbox options
that has been determined to be capable of achieving the maximum required credit as a stand-alone
process. In order to receive Cryptosporidium removal credit under the rule, a membrane filtration
system must meet the following three criteria.
1. The process must comply with the definition of membrane filtration as stipulated by the rule.
Membrane filtration is defined under the rule as a pressure- or vacuum-driven separation process in
which particulate matter larger than 1 (im 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. This definition includes the following
membrane processes commonly used in drinking water treatment:
• Microfiltration (ME)
• Ultrafiltration (UF)
• Nanofiltration (NF)
• Reverse Osmosis (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. The MFGM
refers to these processes as membrane cartridge filtration (MCF).
2. The removal efficiency of a membrane filtration process must be established through a
product-specific challenge test and direct integrity testing.
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
direct integrity testing. Thus, the maximum removal credit that a membrane filtration process may
receive is the lower value of either:
• The removal efficiency demonstrated during challenge testing; OR
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The maximum log removal value that can be verified by the direct integrity test used to monitor
the membrane filtration process
3. The membrane filtration system must undergo periodic direct integrity testing and
continuous indirect integrity monitoring during operation.
The LT2ESWTR requires that the Cryptosporidium log removal credit awarded to the membrane
filtration process be verified on an ongoing basis during operation. This verification is accomplished by
the use of direct integrity testing. Currently available direct integrity test methods represent the most
sensitive means of detecting integrity breaches, but these tests cannot be conducted on a continuous
basis while the membrane filtration system is in operation. Thus, direct integrity testing is implemented
at regular intervals and complemented by indirect integrity monitoring, which is generally less sensitive
but can be conducted continuously during filtration. This continuous indirect integrity monitoring
allows for a coarser assessment of membrane integrity in between periodic applications of a more
sensitive direct integrity test.
Summary of Rule Requirements
The LT2ESWTR specifies requirements for three critical aspects of implementing membrane filtration
for the removal of Cryptosporidium in compliance with the rule:
1. Challenge Testing
2. Direct Integrity Testing
3. Continuous Indirect Integrity Monitoring
As a whole, these rule requirements are designed to first establish what Cryptosporidium removal
credit a membrane product is able to achieve and subsequently how the allocated removal credit for a
site-specific system (as determined by the State) is verified on an ongoing basis during operation. The
requirements for challenge testing, direct integrity testing, and continuous indirect integrity monitoring
are addressed in Chapters 3, 4, and 5 of the MFGM, respectively, and summarized in this document.
Challenge Testing
The Cryptosporidium log removal that a membrane product is capable of achieving is determined via
challenge testing. Thus, the objective of challenge testing is to demonstrate Cryptosporidium removal
efficiency. Challenge testing is intended to be a one-time, product-specific test to establish the
maximum Cryptosporidium log removal credit that the product is eligible to receive as applied for
LT2ESWTR compliance (subject to State approval); however, the demonstrated sensitivity of the site-
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and system-specific direct integrity test utilized may limit the maximum log removal credit that can be
awarded. Retesting for a specific membrane product may be required if the manufacturer makes
significant changes to the product. Guidance to assist membrane manufacturers and State regulators
with assessing what types of changes may require retesting is provided in the MFGM. A general
overview of challenge testing under the LT2ESWTR is provided in the following table.
Challenge Testing: General Overview
Description
Purpose
Applicability
Frequency
MFGM
Reference
One-time, product-specific test event designed to demonstrate Cryptosporidium
removal ability
Demonstrate Cryptosporidium removal efficiency of an integral membrane product and
establish the maximum removal credit that product is eligible to receive
Membrane product
Once
Chapter 3
Challenge testing involves seeding the feed water with Cryptosporidium or an acceptable surrogate
(i.e., a "challenge particulate") and measuring the log reduction in the concentration of the challenge
paniculate between the feed and filtrate, as shown in Equation 1.
Challenge Test Removal Efficiency
L/?V=log(Cf)-log(CJ
[Equation 1]
Where: LRV =
Cf
CD
log removal value demonstrated during challenge testing
feed concentration measured during challenge testing
filtrate concentration measured during challenge testing
The rule requirements associated with challenge testing are summarized in the following table. A
detailed explanation of these requirements, along with guidance for compliance, is provided in
Chapter 3 of the MFGM.
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Challenge Testing: Summary of Requirements
Topic
Scale of Testing
Challenge
Particulates
Maximum Feed
Concentration
Test Operating
Conditions
Removal Efficiency
Equation
Calculating
Removal Efficiency
Verifying Removal
Efficiency for
Untested Modules
Module
Modifications
Reporting
Grandfathered Data
Requirement Synopsis
• Testing must be conducted on a full-scale membrane module or small-scale
module that is identical in material and similar in construction
• Testing must be conducted using Cryptosporidium oocysts or a suitable
surrogate that is removed no more efficiently than Cryptosporidium
• Challenge particulate concentration must be measured using a method
capable of discrete quantification; gross measurements may not be used
• Maximum Feed Concentration = (3.16-106) x Filtrate Detection Limit
• Testing must be conducted under representative hydraulic conditions at the
maximum design flux and maximum design system recovery specified by
the membrane module manufacturer
• LRV = log(C,) - log(Cp)
• Calculate a single LRV value for each module tested
• Overall membrane product removal efficiency:
- For sample size < 20 modules: product LRV = lowest value in sample set
- For sample size > 20 modules: product LRV = 10th percentile value
• Apply a non-destructive performance test (NDPT) to all modules subjected to
challenge testing process
• Establish a quality control release value (QCRV) from NDPT results that is
directly related to the LRV demonstrated during challenge testing
• Apply identical NDPT to all modules of that product
• Modules not meeting the QCRV are not eligible for the Cryptosporidium
removal credit demonstrated during challenge testing
• Additional challenge testing must be conducted for a membrane product that
is modified in manner that could affect the established removal efficiency or
the applicability of the NDPT, and a new QCRV must be determined
• Systems must report the results of challenge testing associated with the
membrane filtration system to be used for rule compliance to the State
• All data submitted to the State for grandfathering consideration must originate
from studies that can be demonstrated to have been conducted in a
manner consistent with the challenge testing requirements of the rule
• The maximum credit for which the process is eligible cannot exceed the
removal efficiency demonstrated by the grandfathered data
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Direct Integrity Testing
After the Cryptosporidium removal capability of an integral membrane product is demonstrated via
challenge testing, the LT2ESWTR requires that the removal efficiency of a membrane filtration system
be verified on an ongoing basis during operation. This verification is accomplished by the use of direct
integrity testing. Thus, the objective of direct integrity testing is to verify that the membrane has no
integrity breaches (i.e., leaks) of a magnitude that would compromise the ability of the membrane to
achieve the Cryptosporidium removal credit awarded by the State. It is important to note that direct
integrity testing is not necessarily intended to validate the Cryptosporidium log removal demonstrated
by challenge testing, but rather the log removal credit that has been awarded to the membrane filtration
system by the State, even if the sensitivity of the direct integrity test allows for the validation of a greater
log removal value (LRV). A general overview of direct integrity testing under the LT2ESWTR is
provided in the following table.
Direct Integrity Testinq: General Overview
Description
Purpose
Applicability
Frequency
MFGM
Reference
Physical testing applied directly to the pathogen barrier associated with a membrane
unit (i.e., a rack, a skid, etc.) in order to identify and isolate integrity breaches
Verify that the membrane pathogen barrier has no integrity breaches that would
compromise the ability to achieve the Cryptosporidium removal credit awarded
the State on an ongoing basis during operation
Membrane units
in a site-specific membrane filtration system
by
Once per day
Chapter 4
The LT2ESWTR does not specify the use of a particular type of direct integrity test, but rather allows
for the utilization of any type of test meeting the requirements for test resolution, sensitivity, and
frequency. The MFGM provides specific guidance for the use of both pressure-based tests (e.g.,
pressure or vacuum decay test) and marker-based tests (both paniculate markers for MF/UF systems
and molecular markers for NF/RO systems), the two types of direct integrity tests that are currently in
most common use. However, the rule does not preclude the use of other types of direct integrity tests
that may be developed in the future, provided the basic requirements for test resolution, sensitivity, and
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frequency can be satisfied. It should also be noted that by definition a direct integrity test must directly
test the membrane barrier by some physical means. For example, pressure-based tests apply
pressurized air directly to the membrane detect integrity breaches, and marker-based tests involve
spiking the feed water to the membrane with a known concentration of a marker to directly challenge
the membrane and demonstrate the log removal ability of the process.
In the context of membrane treatment technology, resolution and sensitivity are new terms introduced
with the LT2ESWTR and defined as follows:
Resolution: the size of the smallest integrity breach that contributes to a response from a direct
integrity test
Note that resolution is expressed as a size of integrity breach. Because the LT2ESWTR is specifically
concerned with Cryptosporidium, the rule requires that a direct integrity test must have a resolution of
3 (im, the lower bound of the Cryptosporidium size range. For marker-based tests, the resolution
requirement dictates that the surrogate (i.e., the "marker") used must have an effective size of 3 (im or
smaller in order to demonstrate Cryptosporidium removal ability. In order to meet the resolution
requirement with a pressure-based test, the net pressure applied must be sufficient to overcome the
capillary forces in a 3 (im breach, thus ensuring that any breach large enough to pass Cryptosporidium
oocysts would also pass air during the direct integrity test. Guidance for determining the resolution of
both pressure- and marker-based tests is provided in Chapter 4 of the MFGM.
Sensitivity: the maximum log removal value that can be reliably verified by the direct integrity
test associated with a given membrane filtration system
The sensitivity of a direct integrity test is expressed in terms of a LRV, which must be equal to or
greater than the Cryptosporidium removal credit awarded to the system in order to achieve compliance
with the LT2ESWTR. If the direct integrity test used is not sensitive enough to verify Cryptosporidium
removal on the order of that demonstrated in challenge testing, the sensitivity dictates the maximum
removal credit for which the process is eligible. Accordingly, the results of a direct integrity test must
be correlated to a corresponding LRV. This correlation is straightforward for marker-based tests,
which can use water quality monitoring instrumentation to quantify the concentration of the marker in
both the spiked feed and the filtrate under fully-integral conditions. The rule-specified expression for
calculating the sensitivity of marker-based direct integrity tests is shown as Equation 2.
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Sensitivity of Marker-Based Tests
LRVDIT = log(C/) - log(Cp) [Equation 2]
Where: LRVorr = direct integrity test sensitivity in terms of LRV
Cf = feed concentration
Cp = filtrate concentration
The correlation between the results of pressure-based tests and sensitivity (expressed as a LRV) is more
complex, given that these types of tests typically yield results in terms of airflow (e.g., mL/min) or rate
of pressure change per unit time (e.g., psi/min). The rule-specified expression for calculating the
sensitivity of pressure-based direct integrity tests is shown as Equation 3.
Sensitivity of Pressure-Based Tests
( Q
= log
LRVDIT = log — — -^ - [Equation 3]
\_ V C-T \2breach )
Where: LRVorr = direct integrity test sensitivity in terms of LRV
Qp = membrane unit design capacity filtrate flow
Qbreach = flow from the breach associated with the smallest integrity test
response that can be reliably measured
VCF = volumetric concentration factor
If the pressure-based test used does not yield results in terms of the flow of water through an integrity
breach, these results must be converted in order for Equation 3 to be utilized. Guidance for converting
the rate of pressure change or the flow of air through an integrity breach to an equivalent flow of water
is provided in Chapter 4 of the MFGM. Additional guidance for determining the volumetric
concentration factor (VCF) for a site-specific membrane filtration system is provided in Chapter 2.
This parameter accounts for the degree to which some systems concentrate particulate matter in the
feed water just above the membrane surface.
A summary of the rule requirements associated with direct integrity testing is provided in the following
table.
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Direct Integrity Testing: Summary of Requirements
Requirement Synopsis
Scale of Testing
• Testing must be conducted on each membrane unit (i.e., rack, skid, etc.) in
service
Resolution
The test method used must have a resolution of 3 jam or less
Sensitivity
The test method used must have sensitivity sufficient to verify the ability of the
membrane filtration system to remove Cryptosporidium at a level
commensurate with the credit awarded by the State
Formulae for sensitivity calculation:
- For pressure-based tests: LRVD,T = log[Qp/(VCF'Qbreach)]
- For marker-based tests: LRVD|T = log(Cf) - log(Cp)
Control Limit
A control limit must be established within the sensitivity limits of the direct
integrity test that is indicative of an integral membrane unit capable of
achieving the log removal credit awarded by the State
If the direct integrity test results exceed the control limit for any membrane
unit, that unit must be removed from service
Any unit taken out of service for exceeding a direct integrity test control limit
cannot be returned to service until repairs are confirmed by subsequent
direct integrity test results that are within the control limit
Frequency
Direct integrity testing must be conducted on each membrane unit at a
frequency of at least once per day that the unit is in operation
States may approve less frequent testing based on demonstrated process
reliability, the use of multiple barriers effective for Cryptosporidium, or
reliable process safeties
Reporting
The sensitivity, resolution, and frequency of the direct integrity test proposed
for use with the full-scale facility must be reported to the State
Any direct integrity test results exceeding the control limit, as well as the
corrective action taken in response, must be reported to the State within
10 days of the end of the monthly monitoring cycle
All direct integrity test results must be retained for a minimum of three years
Continuous Indirect Integrity Monitoring
Indirect methods do not assess the integrity of the membrane barrier directly, but instead utilize water
quality parameters as a surrogate to infer information about membrane integrity based on the levels of
the monitored parameters relative to the known baseline in a fully integral system. Although indirect
integrity monitoring is generally not as sensitive for detecting integrity breaches as the various direct
methods, the indirect methods do have the advantage of being able to be applied to continuously monitor
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membrane filtrate quality during production, thus providing some means of assessing integrity between
direct integrity test applications. Consequently, the objective of continuous indirect integrity monitoring
is to monitor a membrane filtrate system for significant integrity problems between direct integrity test
applications. Note that the LT2ESWTR does allow the requirement for continuous indirect integrity
monitoring to be waived if a continuous method of direct testing that meets the resolution and sensitivity
requirements of the rule is used. A general overview of continuous indirect integrity monitoring under
the LT2ESWTR is provided in the following table.
Continuous Indirect Intearitv Monitorinq: General Overview
Description
Purpose
Applicability
Frequency
MFGM
Reference
Monitoring some aspect of filtrate water quality that is indicative of the
particulate matter
Monitor a membrane filtration system for significant integrity problems
integrity test applications
removal of
between direct
Membrane units in a site-specific membrane filtration system
Continuous
Chapter 5
The LT2ESWTR requires filtrate turbidity monitoring (for each membrane unit) as the default method
for continuous indirect integrity monitoring. However, alternative methods such as particle counting,
particle monitoring, conductivity monitoring (for NF/RO systems), or others may also be approved at
the discretion of the State. Independent of the method used, "continuous" monitoring is defined as one
reading at least every 15 minutes. The rule specifies a control limit of 0.15 NTU for turbidity
monitoring, such that if the filtrate turbidity associated with any membrane unit exceeds 0.15 NTU for
a period greater than 15 minutes (i.e., two consecutive 15-minute readings higher than 0.15 NTU), that
unit must immediately undergo direct integrity testing. Although control limits for alternative methods
are determined at the discretion of the State, two consecutive 15-minute readings exceeding the State-
approved control limit for any alternate method would likewise trigger immediate direct integrity
testing for the associated membrane unit. A summary of the rule requirements associated with direct
integrity testing is provided in the following table.
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Continuous Indirect Integrity Monitoring: Summary of Requirements
Requirement Synopsis
Scale of Testing
Monitoring must be conducted separately on each membrane unit (i.e., rack,
skid, etc.) in service
Monitoring
Method
Continuous indirect integrity monitoring must be conducted using turbidity
monitoring unless the State approves an alternative method
Frequency
Continuous indirect integrity monitoring must be conducted at a frequency of
at least one reading every 15 minutes
Control Limit
If the continuous indirect integrity monitoring results exceed the specified
control limit for any membrane unit for a period greater than 15 minutes
(i.e., two consecutive readings at 15-minute intervals), direct integrity
testing must be immediately conducted on that unit
The control limit for turbidity monitoring is 0.15 NTU
Control limits for State-approved alternative methods must be established by
the State
Reporting
Any continuous indirect integrity monitoring results triggering direct integrity
testing, as well as any corrective action taken in response, must be
reported to the State within 10 days of the end of the monthly monitoring
cycle
All continuous indirect integrity monitoring results must be retained for a
minimum of three years
Additional Information
The full text of the Membrane Filtration Guidance Manual is available on the EPA website at
http://www.epa.gov/safewater/lt2/guides.html. A copy of the Federal Register notice of the final
regulation is available from the Safe Drinking Water Act Hotline at (800) 426-4791 - open Monday
through Friday, excluding Federal holidays, from 9:00 am to 5:30 pm Eastern Time.
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