UPGRADING LONGITUDINAL FLOW RECTANGULAR SECONDARY CLARIFIER TO TRANSVERSE, FOLDED FLOW CLARIFIER WITH FIXED HYDRAULIC HEADERS

摘要

A new concept in rectangular activated sludge secondary clarifier design isrnpresented. The East half of the Gwinnett Co., GA,Yellow River/Sweetwater Creekrn(GCYRSC) WWTP was plagued with high maintenance and frequent high effluentrnsolids losses from four (4) rectangular clarifiers equipped with floating siphon sludgernremoval devices. The County chose to upgrade existing mechanisms and tankage withrntransverse, folded flow influent/effluent channels placed along one sidewall, in effect,rnduplicating the flow pattern established in the more consistently performing circularrnperipheral-feed, peripheral-overflow basins of the plant抯 West half. Four (4)rntransverse hydraulic removal headers, evenly spaced along the length of each basin,rnwere embedded in the floors and piped to transport settled solids to the existing returnrnsludge channels. Four-shaft chain and flight collectors were installed to both scrapernsolids to the headers and skim the surface. Plant performance data, blanket profilernand dispersed suspended solids (DSS) tests, under average and stress conditions,rnare presented. Performance of the new design is compared to the identicallyrnoperated circular clarifiers.rnConsistency of clarifier effluent suspended solids levels from the East Plant improvedrndramatically with this upgrade. A solids profile demonstrated a fairly uniform blanketrndepth across the tank (See Figure 2). Dispersed suspended solids (DSS) testsrnat Stress flow demonstrate a reduction in DSS through the tank with only modestrnincrease in effluent total suspended solids (ETSS). Return solids concentrations fromrnembedded tapered headers paralleled concentrations from rotating hydraulic removalrnheaders.