Membrane and Desalination Technologies - TCE Moodle Website

Membrane Filtration Regulations and Determination of Log Removal Value 141
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 medium.
3.3.2. 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 LRV that can
be verified by the direct integrity test, 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.
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. 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.
Challenge testing is discussed in detail in Sect. 4.
3.3.3. 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. A direct integrity test is
defined as a physical test applied to a membrane unit to identify and isolate integrity breaches
(8–11). 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 (3):
1. Resolution: The direct integrity test must be applied in a manner such that a 3-mm hole contributes
to the response from the test.
2. Sensitivity: The direct integrity test must be capable of verifying the LRV awarded to the
membrane process.
3. 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.
3.3.4. 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,