AWWA ACE60014

This paper presents the results of a challenge study conducted on two immersed low-pressure membrane pilot plants using Bacillus megaterium spores. The reliability of available theoretical models for relating direct integrity monitoring results to microbial LRV is also evaluated. The challenge study was conducted in the light of the proposed Long Term 2 Enhanced Surface Water Treatment Rules (LT2ESWTR). Two important requirements of the proposed rule, namely resolution and sensitivity of the direct integrity tests, were evaluated. Spores of Bacillus megaterium (0.7 µm x 1.4µm) were used as surrogates for Cryptosporidium spp. Duplicate challenge studies were conducted for each pilot plant. One of the main differences in the two pilot plants was the fiber inside diameter with ZW1000a having an inside fiber diameter of 0.35 mm vs. 0.75 mm for the ZW500d©. Membranes were compromised with one and two pinholes, followed by one, two, or three cut fibers. Multiple pressure decay tests were conducted for each condition. Includes 9 references, table, figures.