Removal of sanitarian microbial indicators after the combined process of a primary sedimentation and a down-flow hanging sponge (PS+DHS system)

Abstract

 A Down-flow Hanging Sponge (DHS) reactor combined with a primary sedimentation tank (PS+DHS system) was operated over 1,000 days to investigate the effect of HRT on treatment efficiencies. Insufficient effluent water quality was obtained when an HRT was set at 0.8 hours for DHS. After elongating HRT to 3.2 hours, high effluent water quality in terms of organic matter removals (>90% for BOD and SS) and microbial indicators (2.73 log for F.coli and 3.15 log for T.coli) was achieved. A removal efficiencies of sanitarian microbial indicators of an activated sludge process treating the same sewage were 2.55 log for F.coli and 2.19 log for T.coli, indicating that the PS+DHS system has comparable removal efficiencies to the activated sludge process. From the result obtained, the PS+DHS system with longer HRT (3.2 hours) can be an alternative process of an activated sludge process for sewage treatment.