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The U.S. Environmental Protection Agency (USEPA) published the final rule of the Long-Term 2 Enhanced Surface WaterTreatment Rule (LT2ESWTR) in January 2006. In this rule, the USEPA specifies theperformance criteria of direct membrane integrity testing: resolution; sensitivity; and, testingfrequency. In respect to testing frequency, the rule states that in general it should not be lessthan once per day. However, the rule also gives states latitude to determine if less testing isacceptable, but it provides no guidance on how the testing frequency should be determined.The testing frequency is the result of balancing the safeguard of the integrity of a membranesystem and the need to maintain productivity as direct integrity testing may require the plantoff-line. This paper proposes a risk-based approach for determining testing frequency of directintegrity testing for which the testing frequency of a membrane system directly relates to therisks of membrane integrity breaches.The approach is developed based on the risk assessment of membrane system integrity,taking considerations of the occurrence and consequence of a membrane-integrity breach. Therisks of membrane integrity breach can be affected by several factors: probability of integritybreach occurrences, the magnitude of the breach (relative to the size of the plant), probability ofbreach detection by integrity testing, and the presence/absence of other barriers for thebreakthrough of pathogens. Among those factors, the probability of membrane breachoccurrences is very important and may be difficult to establish. It suggests that historicaloperating data and fatigue testing can be a used as two practical approaches for establishing theprobability of membrane breach occurrences. The consequences of membrane integrity can bequantified by the dilution of bypass flow through a breach. Hydraulic modeling based onconservative assumptions can be used for the purpose. The microbial challenge data used tovalidate the results indicate that this approach generates a sufficient safety margin.Risk assessment indicates that the membrane systems with inferior quality (highprobability of occurrence) and low dilution (small system flow) incur the highest risks. As aresult, they may need to be integrity-tested with higher frequency than those of low-risksystems. Includes 8 references, table, figures, appendix.

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Edition: Vol. - No. Published: 11/01/2006 Number of Pages: 16File Size: 1 file , 380 KB