This paper describes a laboratory scale experiment using a combined biofilm and activated sludge process to enhance biological nitrogen and phosphorus removal. In the system, fibrous carriers were packed in an anoxic tank for the attached growth of denitrifying bacteria and the sludge of the clarifier was returned to the anaerobic tank to release phosphate. In this configuration, nitrification, denitrification and phosphorus removal could be performed at their respective optimum conditions. The influent was domestic wastewater; the mean concentrations of COD, NH4-N and total phosphorus in the influent were about 319 mg/l, 60 mg/l and 10 mg/l respectively. At a total HRT of the system of 20-30 hours, based on the influent flow of the system, and a temperature of 10-15°C, the mean concentrations of COD, NH4-N, NO3-N, NO2-N and total phosphorus in the effluent were about 39.4 mg/l, 1.3 mg/l, 13.4 mg/l, 0.6 mg/l, and 0.8 mg/l respectively.

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