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144 N.K. Shammas and L.K. Wang
broader regulation of membrane filtration systems, US EPA only requires that this regulatory
framework be applied to systems that utilize membrane filtration to meet the additional
Cryptosporidium treatment requirements of the LT2ESWTR.
3.5. 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 to 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 12 terms formally defined under the language for the LT2ESWTR, as follows:
l Membrane filtration – a pressure- or vacuum-driven separation process in which particulate matter
larger than 1 mm 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.
l 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. 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.
l 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.
For the purposes of the LT2ESWTR, “membrane unit” is intended to include the commonly used
synonymous terms rack, train, and skid.
l Challenge test – a study conducted to determine the removal efficiency (i.e., LRV) of the
membrane filtration media.
l Flux – flow per unit of membrane area.
l 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. 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.
l Direct integrity test – a physical test applied to a membrane unit to identify and isolate integrity
breaches.
l Integrity breach – one or more leaks (in a membrane filtration system) that could result in the
contamination of the filtrate.
l Resolution – the smallest leak that (i.e., integrity breach) contributes to a response from a direct
integrity test.
l Sensitivity – the maximum LRV that can be reliably verified by the direct integrity test associated
with a membrane filtration system.
l Control limit – an integrity test response that, if exceeded, indicates a potential problem with the
system and triggers a response. In this context, the terms upper control limit (UCL) and lower
control limit (LCL) are also used. The term UCL is always used in reference to the control limit that
is mandated under the LT2ESWTR, or to the last control limit that could be exceeded before the