A novel system integrating anaerobic/anoxic/oxic (A(2)/O) and biological aerated filter (BAF), which could solve the sludge retention time (SRT) conflicting problem between nitrifiers and polyphosphate accumulating organisms (PAOs) by shortening SRT for PAOs in A(2)/O and lengthening SRT for nitrifiers in BAF, was investigated in this study. Various nitrate recycling ratios (100%, 200%, 300% and 400%) were applied to a lab-scaled A(2)/O-BAF system to detect the simultaneous biological nitrogen and phosphorus removal performance while treating real domestic wastewater with low carbon to nitrogen (C/N) ratio. The concentrations of chemical oxygen demand (COD), NH(4)(+)-N and total phosphorus (TP) in the effluent were less than 50.0, 0.5 and 0.5mg/L, respectively, throughout the experiments. The removal efficiencies of total nitrogen (TN) were 64.9%, 77.0%, 82.0% and 87.0%, under respective nitrate recycling ratios (increasing from 100% to 400%). By contrast, nitrate recycling ratios had neglectable effect on the removal efficiencies of COD and NH(4)(+)-N.
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