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Membrane Filtration Regulations and Determination of Log Removal Value 147
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. The rule specifies criteria for the
following aspects of challenge testing:
1. Full-scale versus small-scale module testing.
2. Appropriate challenge particulates.
3. Challenge particulate concentrations.
4. Test operating conditions.
5. Calculation of removal efficiency.
6. Verifying characteristic removal efficiency for untested modules.
7. Module modifications.
The discussion of challenge testing in this chapter applies similarly to MF, UF, NF, RO,
and 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 may be adapted for use in establishing removal efficiencies
for other microbial pathogens of concern, including bacteria, viruses, and other protozoa such
as Giardia.
4.1. Core Requirements for Challenge Testing
The LT2ESWTR specifies the core requirements that a challenge test must meet to
demonstrate the removal efficiency of a membrane filtration system with respect to Cryptosporidium.
These requirements are summarized as follows:
1. 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.
2. 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.
3. 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 as follows:
Maximum feed concentration ¼ 3:16 10 6
ðFiltrate detection limitÞ:
(1Þ
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.