ADVANCED PERFORMANCE OF SMALL-SCALE DOMESTIC SEWAGE-TREATMENT PLANTS USING ANAEROBIC-AEROBIC FILTER SYSTEMS WITH FLOW-EQUALIZATION AND RECIRCULATION

The treatment characteristics of small-scale domestic sewage treatment plants (SDSTP) using anaerobic-aerobic filler systems with flow-equal ization and recirculation were investigated. Plant experiments were co nducted under three different operating conditions (Runs 1, 2, and 3), and were carried out in sequence using the same SDSTP. Run 1 was the control series with continuous fixed feeding and recirculation In Runs 2 and 3, the influent had two maximum flow rates (peak coefficient 6) and a feeding time of 14 hours. This inflow pattern simulates the typ ical inflow pattern of domestic sewage. Run 2 was an operating series with no flow-equalization and no recirculation, and was the convention al treatment mode for SDSTPs installed in Japan. On the other hand, th e SDSTP in Run 3 had a novel operational mode with flow-equalization a nd recirculation for denitrification. The SDSTP in Run 3 demonstrated a high performance for flow-equalization and stable effluent quality i n comparison with that in Run 2. In Run 3, the removal percentages of BOD and SS were more than 90%, the effluent BOD was less than 10 mg l( -1), and the effluent SS was less than 5 mg l(-1). The nitrogen remova l and effluent nitrogen in Run 3 were about 60% and less than 10 mg l( -1), respectively. The treatment efficiency in Run 3 was almost the sa me as that in Run 1. Furthermore, it is suggested that flow-equalizati on and denitrification could reduce sludge production.