AWWA WQTC58927

The traditional method for determining whether a membrane is considered an ultrafiltration (UF) or microfiltration (MF) membrane is based upon the molecular weight cutoff of the membrane or the nominal pore size. Microbial removal performance does not currently play a quantitative role in determining whether a membrane is classified as MF or UF. A pilot- /full-scale comparison study was conducted at the Saratoga Filtration Plant, California with a continuous microfiltration (CMF) unit to evaluate their capability to remove microorganisms under selected water quality and operational conditions. In order to monitor and compare the fouling rates and the associated microbial rejection performances of membrane modules of different ages, three modules were challenged with microbes: one mature module that had been in use on the full-scale plant for 5 years, and two brand new modules (one operated on the pilot unit, the other operated on the full-scale system). The microorganisms tested were MS2 phage, PRD1 phage and Pseudomonas diminuta. The results showed that the pilot unit mirrored the hydraulic behavior of the full-scale system and also documented satisfactorily the performance of the membrane system from a microbial removal standpoint. Indeed, higher phage removals were recorded with the mature module exhibiting a greater fouling as compared to the two new modules. Also, it was found that the extent of the impact of fouling on microbial removal greatly depends on the size of the target microorganism. Includes 14 references, tables, figures.