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The Olivenhain Municipal Water District (the District) has been a pioneer in the use ofultrafiltration (UF) membranes for the treatment of drinking water. The Olivenhain WaterTreatment Plant (OWTP), which began operation in 2002, utilizes immersed UF to produceup to 34 mgd of finished water from the treatment of State Project and Colorado Riverwater, both characterized by low and consistent levels of total organic carbon (TOC) andturbidity.In response to projected population growth and increasing water demand, the Districtbegan evaluating an expansion of the OWTP in early 2006. The District also facedintroduction of new source water, Lake Hodges, into Olivenhain Reservoir, which currentlystores State Project and Colorado River water blends for use at OWTP. Lake Hodges waterpresents a significant change in water quality and new challenges for treatment, includinghigher levels of TOC, taste and odor, iron and manganese, and disinfection byproductformation. The existing OWTP utilizes UF and chlorine disinfection and is not equipped toadequately address these water quality challenges.The District's objective was to identify the optimum approach for expanding the OWTP,including addressing water quality changes from Lake Hodges, while continuing to use theexisting UF system. The evaluation considered 26 water treatment alternatives includingmembrane pretreatment, UF, membrane post-treatment, and residuals handling anddisposal, with an emphasis on effective control of organics and taste and odors and onachieving a sustainable membrane flux and cleaning frequency interval, despite variationsin anticipated source water quality. Laboratory-scale treatability testing was conducted tosupplement the evaluation by filling identified data gaps as part of the decision process. Akey challenge was to make optimum use of older generation UF modules having lowerpacking density that are not compliant with LT2ESWTR requirements for direct integritytesting, which will take effect in 2012. This paper provides an overview of the decision evaluation, including a brief summary ofthe alternatives considered, implications for the existing UF system, distinguishingcharacteristics of each alternative, key lab-scale test results, and the option identified asoffering the optimum solution from a benefit-cost perspective. The results will be valuableto utilities that are interested in implementing membrane treatment and will have toconsider the need to address new challenges in their source water, while meeting morestringent drinking water regulations. The results will be important to improve the watertreatment community's understanding of how integrated treatment strategies coupled withUF (or microfiltration) can be used to provide effective pre- or post treatment approachesfor addressing these additional challenges for existing UF facilities that may not be able toaddress changes in raw water quality or regulatory requirements. Includes table, figures.

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Edition: Vol. - No. Published: 03/01/2007 Number of Pages: 10File Size: 1 file , 360 KB