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DOWNFLOW GRANULAR FILTRATION OF ACTIVATED SLUDGE EFFLUENTS
Citation:
Bowker, R. DOWNFLOW GRANULAR FILTRATION OF ACTIVATED SLUDGE EFFLUENTS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/2-77/144.
Description:
The performance of downflow granular filters subjected to effluents from activated sludge processes was investigated at the EPA-DC Pilot Plant in Washington, D.C. Several media combinations were investigated, including both single anthracite and dual anthracite-sand configurations. Effluents from step aeration, plug flow, and completely mixed activated sludge systems were used as feeds. Breakthrough of the suspended solids into the effluent occurred with both the 1.65 mm and 2.0 mm effective size (E.S.) single anthracite configurations, becoming more evident at the higher flow rates. A dual media filter, consisting of 2.0 mm E.S. coal over 0.9 mm E.S. sand, exhibited the most desirable characteristics for filtration of the secondary effluents investigated. The advantages were longer run times and higher suspended solids loadings with virtually no deterioration of effluent quality. A backwash study conducted at a variety of backwash flowrates showed that a 13 percent bed fluidization was achieved with the coarse media (2.0 mm E.S. coal/0.9 mm E.S. sand) at a flow rate of 1.43 cu m/min/sq m (35 gpm/sq ft). This was sufficient to effectively cleanse the media.