Abstract
The treatment characteristics of small-scale domestic sewage treatment plants (SDSTPs), i.e., Kogata Gappei-shori Johkaso systems, using anaerobic-aerobic filter systems with flow-equalization, recirculation, and aluminum biofilter media were investigated for the purpose of simultaneous removal of BOD, Nitrogen, and Phosphorus, i.e., further improvement of effluent qualityin SDSTPs. Plant experiments were conducted under four different operating conditions. Run 1 was the control series with continuous fixed feeding and recirculation, but without aluminum biofilter media. In Runs 2, 3, and 4, the influent had two maximum flow rates (peak coefficient 6) and a feeding time of 14 hours. Run 2 was an operating series with no flow-equalization, no recirculation, and no aluminum biofilter media, and was the conventional treatment mode for SDSTPs installed in Japan. On the other hand, the SDSTP in Run 3 was a novel operational mode with flow-equalization and recirculation for denitrification. In addition, the SDSTP in Run 4 had a newer operational mode with flow-equalization, recirculation, and aluminum biofilter media for both denitrification and phosphorus removal. Run 3 showed a good performance for BOD and SS removals and denitrification, and the treatment efficiency in Run 3 was almost the same asthat in Run 1. The SDSTP in Run 4 demonstrated the simultaneous removal of BOD, Nitrogen, and Phosphorus because of flow-equalization, recirculation, and aluminum biofilter media. In Run 4, the effluent BOD was less than 10mg⋅l-1, and the effluent SS was less than 5mg⋅l-1. Furthermore, the effluent nitrogen and the effluent phosphorus in Run 4 were less than 10mg⋅l-1 and less than 1 mg⋅l-1, respectively.
