CONSTRUCTION AND OPERATION OF A SUBMERGED AERATED FILTER SEWAGE-TREATMENT WORKS

The capacity of the sewage-treatment works at Silchester in Hampshire has been enhanced and the effluent quality improved to a high standard by the installation of a new submerged biological aerated filter plan t. Ten prefabricated steel submerged aerated filters reduce BOD and fu lly nitrify settled domestic sewage from a population equivalent of 20 000. Comprehensive operating data are presented to demonstrate the abi lity of single-stage submerged downflow aerated biological filters to produce a nitrified effluent. The final effluent quality remains consi stently within consent limits at 4.8 mg/l BOD, 7.0 mg/l SS and 0.5 mg/ l NH3-N, all 95 percentiles. (Consent 7 mg/l BOD, 25 mg/l SS, and 5 mg /l NH3-N, 95 percentiles.) Data are presented on total coliform and E. Coli concentrations through the filter plant, showing better than 3 l og reductions in the effluent.