Study on Influence of Sludge Recycle Ratio on Removal of Nitrogen and Phosphorous in Two-Sludge BCR Denitrifying Phosphorus Removal Process

The influence of different sludge ratios from middle sedimentation tank to anoxic reactor( exceeding sludge ratio) and from final sedimentation tank to anaerobic reactor ( recycled sludge ratio) on denitrifying phosphorus removal in two-sludge BCR denitrifying phosphorus removal process was investigated using simulated domestic wastewater. Results showed that when the ratios of two kinds of sludge are 0.6, 0.4 and 0.2 respectively, the resulting average COD removal rates are 89.98%, 89.48% and 82.38% , total nitrogen removal rates are 79.94%, 80.58% and 65.47%, and phosphorus removal rates are 88.81%, 91.64% and 77.06%, respectively. The effluent COD concentrations are 20.94 mg/L, 21.67 mg/L and 37.66 mg/L, total nitrogen concentrations are 5.72 mg/L, 5.75 mg/L and 10.85mg/L, and phosphorus concentrations are 0.76 mg/L, 0.59 mg/L and 1.62mg/L, respectively. Compared to two-sludge A2N process, the problem of high ammonia nitrogen has been improved. When the ratios of two kinds of sludge are 0.4, two-sludge BCR denitrifying phosphorus removal process has best pollutant removal efficiency. Since the aeration tank and sedimentation tank are integrated, denitrifying dephosphatation with nitrate as electron acceptor was occur under anoxic condition due to contribution of denitrifying phosphorus removal bacteria.