EFFECT OF INFLUENT MODES AND RECIRCULATION POINT POSITION ON NITROGEN AND PHOSPHORUS REMOVAL BY A MULTI-STAGE BIOLOGICAL CONTACT OXIDATION PROCESS

Taking actual domestic sewage with C/N of about 3 as the treatment object, the influence of influent mode and the position of the recirculation point on the function of denitrification and dephosphorization on multi-stage biological contact oxidation porcess was evaluated. The results showed that the removal rate of COD was 87.61% and 78.94% respectively, under the conditions of continuous water inlet and intermittent water inflow. But the average concentration of effluent COD met the Grade A in China’s national standard, GB 18918—2002. And the system had stronger ability for resisting shock load. When the mixed liquid was returned from the sixth grid to the first grid, the removal rate of COD and TN was 88.78% and 83.10% respectively, and it met the Grade A standard of GB 18918—2002 sewage discharge. The treatment effect of TN was related to the position of the recirculation point, and the sludge volume of the system was very low, with no excess sludge discharged. While it had little effect on total phosphorus removal in this condition. The chemical removal of total phosphorus was used. The removal effect of total phosphorus was independent on the position of the recirculation point. Through the analysis of the system biodiversity and biofilm quality, it was found that the system microbial population structure was changed by increasing the reflux. It improved the system nitrogen removal efficiency.