Keywords: 
• integrated A/O process /
• biofilm reactor /
• domestic sewage /
• nitrification and denitrification /
• nitrogen removal

Abstract: A novel integrated biofilm A/O reactor was used to treat domestic sewage. The effect of dissolved oxygen (DO) mass concentration on nitrification and denitrification was investigated, and the nitrogen removal performance and mechanism of the reactor were discussed. The experimental results show that the DO is a major factor affecting nitrogen removal from the sewage in the integrated biofilm A/O reactor, and the reactor can simultaneously carry out nitrification and denitrification in one unit. The removal efficiency of NH3-N and TN increases with the increasing of DO mass concentration in oxic zone of the reactor. When DO mass concentration of oxic zone is about 2～4 mg/L, the reactor can perform simultaneous nitrification and denitrification, so the removal efficiency of NH3-N and TN is equal almostly. When DO mass concentration is about 5～6 mg/L, the average removal efficiency of NH3-N and TN reaches 97.0% and 68.6%, respectively, the effluent mass concentration of NH3-N is less than 2 mg/L, and TN is less than 15 mg/L. But the mass concentration of NO-3-N and NO-2-N in the reactor would be accumulated at high DO mass concentration. The integrated biofilm A/O reactor is nearly mixed completely by aeration, the nitrification is carried out in oxic zone, and the denitrification is carried out in anoxic zone, the pH value would be kept stable in the reactor. The biofilm media of suspended ball can form oxic/anoxic microenvironment, so denitrification can perform under aerobic condition.