Full scale application of combined SBF- AS process for municipal wastewater treatment in small towns

The combined submerged biofilm (SBF)-activated sludge (AS) process for treatment of municipal wastewater in a small city in China is described in this paper. The process exhibited high removal efficiencies for carbonaceous substances, nitrogen and phosphorus which mainly took place in the combined SBF-AS bioreactor. The SBF-AS bioreactor was divided into pre-anoxic, anaerobic, anoxic and aerobic zones from inlet to outlet, in which fixed biofilm carriers were packed. Excellent performance had been obtained under normal operating conditions in more than one year of operation in Dong' e municipal WWTP, Shandong province, with mean removal efficiencies of BOD5 93.4% , COD 88% , SS 92% , NH4+ - N 82.1% , TP 75% and TN 66. 7%, and quite high effluent quality such as BOD5 6 to 10 mg/L, COD 20 to 40 mg/L, SS 5 to 10 mg/L,TN 10 to 20 mg/L, NH4+ - N 4 to 8 mg/L and TP 0.6 to 1.0 mg/L. The effluent was reused multi-purposely,such as toilet flushing, green belt watering and artificial lake pounding. Simultaneous nitrification and denitrification took place due to the DO gradient in biofilm in aerobic zone of the SBF-AS bioreactor, which made TN removal efficiency improved remarkably in system. Some activated sludge was returned from final clarifiers to the bioreactor for phosphorus removal. The process had the advantages of low investment and low operational/maintenance (O/M) costs, low sludge yield and was preferably employed in small towns and cities.