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The Orange County Water District (OCWD) recently commissioned theGroundwater Replenishment (GWR) System, an advanced wastewatertreatment facility consisting of microfiltration (MF), followed by reverse osmosisand advanced oxidation (ultraviolet treatment with hydrogen peroxide).Developed as an indirect potable reuse facility, the GWR system provides70mgd of purified wastewater for groundwater recharge and maintenance of anintrusion barrier to protect the local groundwater basin from seawater infiltration.Source water to the GWR system consists of secondary municipal effluentprovided by the Orange County Sanitation District (OCSD). Secondarywastewater is produced by operating two processes, activated sludge (AS)treatment and trickling filter (TF) treatment.The GWR System design specifies a blended feed of AS effluent and TF effluentfrom OCSD. During GWR System MF feasibility testing, however, only ASeffluent was evaluated. Infrastructure limitations at the time prohibited blendingat the OCWD test facility. While the AS and TF processes produce acceptablesecondary effluent, there are disparities in water quality between the two,differences that could impact MF performance. The concentration of dissolvedorganic constituents and particulate material are generally higher in TF effluent,when compared to AS effluent. Trickling filters also provide a favorableenvironment for snails, which graze on the zoogenic biological slime present onthe TF media. Snails are problematic since they add to the organic andsuspended solid load when sloughed off and carried to the secondary clarifiers.The snails (and snail shells) could also physically damage the MF membranefibers if conveyed to the GWR system. MF membrane integrity would becompromised, resulting in a host of deleterious affects that reduce effective plantoperations. Given these concerns, TF effluent was not treated during the first 8-months of operation until further studies were performed. This decision resultedin the treatment plant being unable to operate at the design capacity, thereforeexpediting the need to resolve this issue in a timely manner.This paper documents the streamlined and innovative pilot testing effortsundertaken to verify the impact TF effluent would have on the MF treatmentprocess (and operations of the GWR system). In addition, a variety of waterquality analyses were performed to examine the differences in effluent waterquality between the two secondary treatment processes. Includes figures.

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Edition: Vol. - No. Published: 11/01/2009 Number of Pages: 9File Size: 1 file , 1.1 MB