The properties of a blofllm developed on a Rotating Biological Contactor (RBC), such as the spaclal distribution of blofllm density, bacterial population and Intrinsic biochemical reaction rates, were measured. The blofllm density and the number of heterotrophs, nltrlflers and denltrlflers per unit volume of blofllm Increased with the blofllm depth. However, the intrinsic reaction rates per unit blomass did not significantly change with depth. Based on the above evidence, experiments on simultaneous nitrification and denitrificatlon 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 organlcs to ammonia nitrogen.

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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This paper presents some important aspects of the Rotating Biological Contactor. (1) Steady-state biofilm kinetics and its application to the design of an RBC aiming at nitrification : Using the proposed kinetics in which the flux of rate-limiting substrate is expressed as a function of the bulk substrate concentration, liquid boundary layer thickness, liquid film thickness, and molecular diffusion coefficient and intrinsic reaction rate of the substrate, the relationship between the bulk ammonia concentration and ammonia flux was predicted at various sizes and rotating speeds of disk. Experimental verification of the predicted results was also made. A new disk media, i.e., reticulated media with surface protrusions,was proposed to promote the external diffusion of soluble substrates to the biofilm, and to reduce the disk weight. (2) Simultaneous removal of the detached biomass and precipitated phosphorous in a two-storey RBC:A two-storey RBC, whose upper and lower parts function as the RBC trough and storage space of the detached biomass, was operated in a four-staged unit. Experimental investigation showed that the phosphorus precipitated by aluminium was adsorbed to the biofilm, and settled into the lower part as the detached biomass. The removal efficiency of the detached biomass was very high resulting in an effluent suspended solids concentration of about 10 ppm.

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