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A case study of Membrane Testing, Integrity and Estimations of Log Removal Value per the Long Term 2 Enhanced Surface Water Treatment Rule.
Citation:
BARTLEY, B., M. BLUMSTEIN, AND J. ADAMS. A case study of Membrane Testing, Integrity and Estimations of Log Removal Value per the Long Term 2 Enhanced Surface Water Treatment Rule. Presented at 2008 BORCHARDT CONFERENCE: A SEMINAR ON ADVANCEMENTS IN WATER AND WASTEWATER, ANN ARBOR, MI, February 27 - 28, 2008.
Impact/Purpose:
to share information
Description:
The SWTR-LT2 Rule addresses the use of membranes that may be used to achieve credits for the reduction of Cryptosporidium. The LT2 Rule requires product-specific testing of membranes, considered an alternative filtration technology by the rule. LT2 Rule allows the product specific test results to be used in assigning log10 removal credits for Giardia, Cryptosporidium, viruses and bacteria if the membrane module can be scaled to full size (as installed) and if the membrane integrity can be confirmed in the field. A critical requirement for the product specific microbiological challenge testing is to assess the membrane integrity of the test module that is consistent with the integrity test method used in the field. Direct Integrity Tests (DIT) may also be used in the calculation of an estimate of log10 removal credits. Several assumptions are needed to estimate the log removal from DIT. The EPA and NSF applied the LT2 rule during the ETV testing of the US Army’s Expeditionary Unit Water Purifier (EUWP). The EUWP uses a bank of ultrafiltration (UF) membranes, followed by a bank of reverse osmosis (RO) membranes, to treat raw water. Laboratory microbiological challenges of small scale UF membranes that are used in the EUWP showed significant log reduction capabilities for viruses, bacteria and oocysts. Field testing of the EUWP did not show similar log reduction of indigenous bacteria and particles of the size range of Cryptosporidium. The UF cartridges in the EUWP were modified to enhance seals and membrane integrity. Testing was then performed at the Selfridge Air National Guard base. Membrane integrity was measured using a pressure decay procedure. Also measured were the reductions in particles of the size range as Cryptosporidium and actual reduction of indigenous Bacillus endospores. Although the membranes appeared to maintain integrity, samples indicated results were less than that observed in laboratory challenges. Two full scale UF modules were removed from the bank and challenged in the laboratory with formalin fixed Cryptosporidium parvum and Bacillus endospores. Results will be presented on the various ways to assess and determine log removal from laboratory challenge tests, DIT, and field sampling and monitoring.