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The Marin Municipal Water District (MMWD) conducted an 11-month Seawater Desalination Pilot Program(Program) of advanced pretreatment and SWRO technologies for desalting estuarial water from San FranciscoBay during the period from June 2005 to May 2006 with the objective of developing preliminary design criteria andcosting for a full-scale desalination facility and to demonstrate that seawater desalination could produce a finishedwater quality comparable to or better than Marin's current, conventionally treated surface water supply. Theprogram comprised two independently operated treatment trains to enable concurrent testing of the alternativepretreatment technologies and associated SWRO units. Each SWRO unit consisted of three subtrains, eachcontaining six elements utilizing different high rejection RO membrane types. One SWRO unit was fed withcombined filtrate from submerged MF and submerged UF units. The second SWRO unit was fed with effluentfrom a two-stage granular media filter system preceded by ferric coagulation, flocculation and sedimentation. Inaddition to normal monitoring of SWRO performance during operation, a post-operation autopsy of selected ROelements can be a useful tool in investigating the cause(s) of performance declines. The information from theautopsy analysis can assist in determining mass of foulant deposited, and to identify the nature of the foulantwith respect to how much is inorganic versus organic, and to what extent the organic fouling is microbiallyderived.Following completion of pilot plant testing, selected elements from one manufacturer's array were autopsied by:the element manufacturer using industry-typical methods including element wet test for water flow and saltrejection determination, internal visual inspection, dye/Fujiwara test for oxidant uptake, inductively coupledplasma emission spectroscopy (ICP) for metals, and loss on ignition (LOI) for inorganic versus organic content;and, by more specialized analysis by the Orange County Water District (OCWD) focusing on microbial foulingincluding high resolution visual microscopy, visual color enhancement of foulant distribution, ATR/FTIRspectroscopy, protein and carbohydrate content analysis, and total bacterial count. These analyses indicate thatthe SWRO elements operated on conventional treatment effluent exhibited greater particulate, inorganic andorganic fouling than those receiving MF/UF filtrate despite generally comparable levels of filtrate turbidity andSDI. However, the latter elements had greater microbial levels with a more monoculture-like appearance,suggesting differences in the pretreated feed chemistry due to the use or non-use of coagulation affectedmicrobial community structure. This paper describes the autopsy results and how the results help to explaindifferences in SWRO performance and fouling based on different pretreatment as well as provide insight intooperational strategies for minimizing fouling in a full-scale facility. Includes reference, tables, figures.

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Edition: Vol. - No. Published: 03/01/2007 Number of Pages: 19File Size: 1 file , 670 KB