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Membrane Filtration Regulations and Determination of Log Removal Value 153
4.6. 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. 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 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 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
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 (20).
4.7. 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.
4.7.1. 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