Effect of mixed-liquid return ratio on A2/O process performance.

This paper intends to investigate how the ratios of return mixed liquor and return sludge affect the removals of nitrogen and phosphorus in a municipal wastewater treatment plant with A2/O process.Thus an experiment was conducted on a pilot-plant-scale installation of a series of tanks with biofilm carriers added in the aeration tank.Result indicates the mixed-liquor return ratio value has less effect on removal of COD and TP than on that of ammonia nitrogen.In general,with the sludge return ratio increasing,the A2/O performance is improved,and the ratio of 75% is considered to be appropriate when energy consumption being taken into account.