Municipal wastewater treatment through an aerobic biofilm SBR integrated with a submerged filtration bed

A biofilm reactor and a gravitational filtration bed were integrated as a sequencing batch reactor (SBR) to aerobically treat a municipal wastewater. Polyacrylonitrile balls (50 mm diameter, 90% porosity) were filled into the upper part of the SBR as biofilm attaching materials and anthracite coal (particle size similar to 1.17 mm) was placed into the lower part as filter media. The SBR was aerated during filling and reaction phases, followed by a 10 min discharge phase during which the wastewater went through the filtration bed without aeration. The SBR was tested with raw wastewater from a municipal WWTP in Wuhan, China from July 2006 to January 2007, during both a warm season and a cold season. The SBR showed a capability to accept COD and turbidity fluctuations in the receiving wastewater. Seasonal influence on COD and nitrogen removal by the biofilm reactor was significant. Nitrogen and phosphorus removals were limited by COD levels in the wastewater. The filtration process removed considerable COD, nitrogen, phosphorus, and turbidity. The overall SBR effluent quality consistently satisfied the national secondary effluent discharge standard of China, except for total phosphorus. An anaerobic phase before the aerobic reaction is proposed to improve phosphorus and nitrogen removal. The filter normally required a backwash every seven days and the water needed for backwash was less than 4% of the wastewater treated by the SBR. This experiment provides information needed for further investigation to improve performance of the SBR.