Effect of nitrate recycling ratio on simultaneous biological nutrient removal in a novel anaerobic/anoxic/oxic (A2/O)-biological aerated filter (BAF) system

A novel system integrating anaerobic/anoxic/oxic (A2/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 A2/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 A2/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), NH4+–N and total phosphorus (TP) in the effluent were less than 50.0, 0.5 and 0.5 mg/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 NH4+–N.

► The A2/O-BAF system solved the SRT conflicting problem between nitrifiers and PAOs.
► Short SRT was applied in A2/O and relatively longer SRT was applied in BAF.
► The A2/O was mainly used for phosphorus removal and denitrification.
► The BAF was used for nitrification.
► Effect of nitrate recycling ratio on biological nutrient removal was investigated.