Study on Influence of Sludge Recycle Ratio on Removal of Nitrogen and Phosphorous in A_2N 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 A2N system was investigated using municipal domestic sewage. When the ratios of two kinds of sludge are 0.3, 0.4 and 0.6 respectively, the resulting average COD removal rates are 92.5%, 90.3% and 91.6%, total nitrogen removal rates are 87.1%, 90% and 84.9%, and phosphorus removal rates are 99.5%, 99.6% and 99.0%, respectively. The effluent COD concentrations are 20.3 mg/L, 28.4 mg/L and 25.3mg/L, total nitrogen concentrations are 6.75 mg/L, 5.43 mg/L and 6.95 mg/L, and phosphorus concentrations are 0.02 mg/L, 0.02 mg/L and 0.05 mg/L, respectively. When the ratios of two kinds of sludge are 0.4, A2N system has best pollutant removal efficiency. Moreover, the exceeding sludge flow rate determines the amount of ammonia nitrogen flowing into the anoxic reactor and the effluent ammonia nitrogen concentration. In order to decrease the effluent ammonia nitrogen concentration, the exceeding sludge flow rate should be minimized on the basis that there is adequate sludge in the anoxic reactor.