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Microfiltration (MF) membranes were used in a nonbiological application during a demonstrationscale study performed at Orange County Sanitation District's (OCSD) Plant 2 to treat effluentfrom an advanced primary treatment process. The MF unit was operated for two years fromJanuary 2002 through January 2004 using 0.2 m polypropylene hollow fiber membranes. Theprimary objective of this work was to test the technical and economic feasibility of treatingprimary effluent (average TSS = 58 mg/L) directly using membranes, to produce an effluentsuitable for direct discharge to the ocean. Such a nonbiological option for treatment of primaryeffluent is particularly important to OCSD since the high quality effluent produced bymicrofiltration could allow the District to use the shorter of their two ocean outfalls. Currently, theshorter outfall is permitted only for emergency discharges because it discharges closer to theshoreline and would require a significantly higher quality effluent. Regular use of the "short"ocean outfall could save the District millions of dollars by delaying the need to build anotherdeep-water outfall.During the two years of operation, excellent quality effluent was consistently produced by theMF with average TSS and turbidity values of 2.7 mg/L and less than 3 NTU, respectively. Fecaland total coliform concentrations were reduced by between 3 to 4 logs. For the first nine monthsof testing, average chemical cleaning intervals of about 3 to 4 days were observed. An apparentdecline in the normalized chemical cleaning interval was observed during some intermediateperiods of testing. This is possibly attributed to changes in the operation of the full-scale primarytreatment at OCSD, and isolated instances of functional problems with the Clean-In-Place (CIP)heating system of the demonstration unit. The cleaning interval was restored later in theinvestigation.This paper presents the results of the testing performed from October 2002 through January2004. During this period, several changes were made in the operating conditions to optimizeoperation based on the changing influent quality. Lower fluxes and backwash cleaning intervals,and alternative feed types were tested. Several autopsies were also performed on the fibers atregular intervals to determine the condition of the fibers with respect to membrane fouling tohelp assess a reasonable membrane life for such an application. No signs of irreversibledegradation were observed. The results show that nonbiological treatment of primary effluentwith MF membranes is technically achievable and produces effluent that could be discharged tothe ocean or used as feed water for a final stage of treatment before reuse. Includes 3 references, table, figures.

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Edition: Vol. - No. Published: 03/01/2005 Number of Pages: 13 File Size: 1 file , 400 KB