Simultaneous nitrification and denitrification (SND) occurs in a micro-aerobic biofilm. Using a partially submerged rotating biological contactor(RBC) whose air phase oxygen partial-pressure is controllable, an experimental investigation was made into the effects of the oxygen flux to the biofilm on the SND. The lower the oxygen flux the lower the nitrification efficiency and the higher the denitrification efficiency until the maximum nitrogen removal efficiency was obtained. The state was reached at an oxygen partial-pressure of about 0.1 atm. (oxygen flux= 0.35 g/m2/hour) in this study. Computer simulation of the SND was carried out based on the biofilm kinetic model proposed by the authors. There was adequate agreement between the experimental and simulation results. The simulation study demonstrated that the nitrification and denitrification occur mainly in the biofilm rotating through the air and water phase, respectively, and that the optimum disk rotating speed is around 3 rpm.

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