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The Marin Municipal Water District (MMWD) Seawater Desalination PilotProgram was a successful year-long desalination pilot study of advancedpretreatment and seawater reverse osmosis (SWRO) technologies for desalting water from San FranciscoBay (Bay) from June 2005 to May 2006. Based on the favorable outcome of the pilot program, seawater desalination can be a local, reliable drought-proofsource of drinking water supply for Marin, California. The MMWD SeawaterDesalination Pilot Program included:determining that microfiltration (MF)/ultrafiltration (UF) is the recommended pretreatment forNorth San Francisco Bay water;developing preliminary design criteria and conceptual costs for a fullscale desalination facility;demonstrating that the desalinated water is safe and meets all state andfederal requirements; and, demonstrating that the brine discharge blended with CMSA effluent willnot adversely impact the San Francisco Bay environment. Theprimary objective of the pilot testing program was to compare theperformance of high rejection SWRO membranes with two different pretreatment alternatives, MF/UF and conventional pretreatment. Thisobjective was accomplished through the concurrent operation of two parallelSWRO pilot units of identical design, with Unit 1 treating MF/UF filtrate andUnit 2 treating conventional filtrate.The source water for the MMWD SWRO pilot plant, the North San FranciscoBay, is a complex estuarine water body with influences from the ocean, rivers,and bay discharges that affect water quality on a daily as well as seasonalbasis. Total dissolved solids (TDS) varied from approximately 25,000 mg/l in the summer to less than5,000 mg/l in the winter. While both the conventional and MF/UFpretreatment produced suitable quality RO feedwater, MF/UF filtrate waslower in SDI and less impacted by source water variations. Four differenthigh rejection SWRO membranes were tested. All membranes providedsatisfactory performance, although differences were observed betweenelement types in both trains. No significant differences were observed in ROperformance between the two trains based on changes in normalizedpermeate flow or salt passage. However, based on normalized differentialpressure and autopsy results, elements operated with conventionalpretreatment exhibited greater overall particulate, organic, protein andcarbohydrate fouling than those with MF/UF filtrate.The pilot program also included analytical testing of over 100 regulated and500 non-regulated constituents in the Bay water and RO permeate, as well asan evaluation of second pass RO to meet MMWD's stringent finished waterboron and sodium requirements. Environmental studies conducted inconjunction with the pilot testing included fish entrainment studies, bioassaystudies and California Toxics Rule analysis of the brine discharge and toxicityanalysis of the residuals from the pretreatment systems. Includes tables, figures.

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Edition: Vol. - No. Published: 03/01/2007 Number of Pages: 25File Size: 1 file , 590 KB