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In recent years, an ever-increasing body of research has underscored the healthrisks associated with the various byproducts of chemical disinfection in thepotable water treatment process. The widespread use of chlorine-baseddisinfectants has drawn particular regulatory attention to total trihalomethanes(TTHMs) and the sum of five haloacetic acids (HAA5s), two of the most commonchlorine-based classes of disinfection byproducts (DBPs). Over the years, aseries of federal regulations, including the Trihalomethane Rule (1979), theStage 1 Disinfectant/Disinfection Byproducts (D/DBP) Rule (1998), and theStage 2 D/DBP Rule (2002--projected), have progressively made TTHM and HAA5controls more stringent. Consequently, the water treatment community has taken anincreasing interest in alternate methods of pathogen inactivation and/or removalthat involve little or no chemical use.In an effort to lower DBP levels and ensure compliance with both the Stage 1 and Stage 2D/DBP Rules, the City of San Diego, California, identified low-pressure membrane filtration as themost appropriate technology to effectively meet its treatment objectives for the 40 million gallons per dayOtay Water Treatment Plant (WTP). The use of microfiltration (MF) or ultrafiltration(UF) in conjunction with the existing conventional treatment processes in an integratedmembrane system (IMS) would enable the City to lower free chlorine primarydisinfectant levels by providing an additional physical barrier for pathogen removal.However, the City also desired the option of high-rating the existing treatment processes,which would jeopardize the pathogen removal credit granted to conventional plants underthe Surface Water Treatment Rule (SWTR). Another complicating factor was Californiaregulations requiring potable water utilities to employ a multiple barrier approach totreatment consisting of both pathogen inactivation and removal. As a result, the City andthe team of Malcolm Pirnie and John Powell

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Edition: Vol. - No. Published: 05/01/2001 Number of Pages: 10File Size: 1 file , 210 KB