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The Kitsap County Sewer District No. 5/City of Port Orchard Joint Wastewater Treatment Facility (JWWTF) must be upgraded and expanded to accommodate a growing population and meet stricter effluent limits attributed to an ongoing TMDL study. The JWWTF is subject to high wet weather flows and has limited space available for expansion. New technology offers solutions that could potentially increase the capacity and treatment efficiency of the JWWTF within the limited space available in a cost-effective manner.

Pilot studies of a membrane bioreactor (MBR) and ballasted floc reactor (BFR) were conducted to evaluate their potential for application at the JWWTF. MBRs combine activated sludge with membrane filtration. Consequently, biological treatment, secondary clarification, and filtration are accomplished in a single tank. When placed in aeration tanks, membranes provide near complete separation of suspended solids and facilitate mixed liquor concentrations of 10,000 to 15,000 mg/L. BFRs are a physical/chemical liquid-solids separation process using continuously recycled fine sand ballast to increase settling properties of suspended solids and associated contaminants. Compared to conventional clarification, BFRs offer higher removal efficiencies, higher surface loading rates, smaller footprints, and more consistent effluent quality.

Effluent from the MBR pilot plant generally contained ≤ 5 mg/L BOD5, ≤ 0.1 mg/L TSS, ≤ 0.5 mg/L NH3, ≤ 1 mg/L TKN, ≤ 10 mg/L TN, and ≤ 100 cfu/100 mL fecal coliform at a hydraulic retention time (HRT) of 3 hours. The maximum membrane flux was 19 gfd, significantly less than the 30 gfd expected. Operating the BFR pilot plant at overflow rates between 30 and 60 gpm/sf, effluent concentrations of BOD5 and TSS were less than 65 mg/L (> 60% removal) and 20 mg/L (> 90% removal), respectively. Designing a BFR to treat high wet weather peak flows in excess of the MBR capacity would limit the number of membranes required and reduce cost.
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Document Type: Research Article

Publication date: 2000-01-01

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