The properties of a biofilm developed on a Rotating Biological Contactor (RBC), such as the spacial distribution of biofilm density, bacterial population and intrinsic biochemical reaction rates, were measured. The biofilm density and the number of heterotrophs, nitrifiers and denitrifiers per unit volume of biofilm increased with the biofilm depth. However, the intrinsic reaction rates per unit biomass did not significantly change with depth. Based on the above evidence, experiments on simultaneous nitrification and denitrification were carried out using a covered RBC in which the oxygen pressure was controlled. The experimental results demonstrated that nitrogen removal efficiency in an aerobic RBC depends on the oxygen partial-pressure in the air phase, water temperature, hydraulic detention time and ratio of the influent concentration of organics to ammonia nitrogen.
