Influence of Returned Sludge and T_HR in the Pre-zone on Nitrogen and Phosphorus Removal in Oxidation Ditch

To optimize the function effect of the micropore aeration oxidation ditch with selector and anaerobic zone (pre-zone), the influence of returned sludge ratio, its distribution proportion and T_HR in the pre-zone on nitrogen and phosphorus removal were studied by conducting the three-level orthogonal experiments. Through the analysis of range and variance of TN and TP removal efficiency, the results showed that returned sludge ratio had a deep effect on nitrogen and phosphorus removal, and the distribution proportion of retuned sludge and T_HR in the pre-zone had a certain influence on phosphorus removal but had a little influence on nitrogen removal. And the optimal performance was when the returned sludge ratio was 100% to 125%, the distribution propotion was 3 to 7, and T_HR in pre-zone was 1.9 h. When ρ_TN and ρ_TP in the effluent were lower than 15 mg/L and 2.5 mg/L, respectively, TN can be discharged within the standard, but the effect of TP removal in effluent was not good.