ADVANCED CHEMICAL PHOSPHORUS REMOVAL BY DIRECT FILTRATION WITHOUT TERTIARY CLARIFIERS

摘要

Direct granular media filtration of alum-dosed secondary effluent for advancedrnphosphorus removal represents further innovation in chemical phosphorus removalrntechnology beyond traditional high lime treatment and the more recent process of flocrnentrapment in tertiary clarifiers followed by filtration. The Unified Sewerage Agency ofrnWashington County, Oregon conducted full-scale testing of the direct filtration processrnin 1998 to determine feasibility of meeting a summer season plant effluent TP limit ofrn0.07 mg/L. The process setup involved isolation of a full-scale (900 square-foot area)rngranular media filter to directly receive secondary effluent dosed with alum usingrntemporary pumping, dosing, and piping equipment. Results indicate that directrnfiltration can produce an effluent TP of about 0.15 mg/L, which may be blended withrnfiltered tertiary clarifier effluent to produce a plant effluent TP of 0.07 mg/L. Arn"feasibility boundary" was developed based on a filtration rate of 3 gpm/sf with a 900rnsf filter, target direct filtered TP of 0.15 mg/L, filter run length of about 22 hours, 10rnfeet of available filtration head, and an alum dose to phosphorus removal relationshiprnderived from current study data. The process was found to be feasible with secondaryrneffluent quality (TP and TSS) similar to that achieved in summer 1998. Neither the alumrndose nor filter solids capture were optimized for this study and are suggested as topicsrnfor further investigations.