With an oxygen microelectrode developed by the authors for the measurement of dissolved oxygen (DO) concentration profiles of biofilms in a rotating biological contactor (RBC), DO concentration profiles in the inside and outside of rotating biofilms were measured continuously in the air and water phases. Thicknesses of attached-water film (Lw) and the diffusion layer (Ld) formed on the biofilms were estimated from DO concentration profiles. The oxygen transfer rate to the biofilm was determined with measured DO concentration profiles and a steady state biofilm kinetic model by use of the thicknesses of attached-water film and the diffusion layer. The oxygen transfer rates obtained by two independent methods agreed well, so that the method of the measurement of DO concentration profilesis considered highly reliable. The conclusions in this study are summarized as follows: (1) Lw and Ld on a biofilm attached on a partially submerged rotating biological contactor were 50 and 70 μm thick, respectively; (2) The measured oxygen fluxes were about 10 g-O2/m2/day, and reasonably agreed with those calculated from removing rates of ammonia nitrogen.

Nitrification in a partially submerged rotating biological contactor was analyzed by computer simulation. Results of the simulation showed that the ammonia flux to the biofilm is a function of its spatial position as it rotates alternately in air and liquid phases. However, the simulation and the steady-state model proposed by the authors gave almost similar results in terms of the average ammonia flux to the biofilm. The latter provides the basis behind the application of the steady-state biofilm kinetics to the nitrification process in a partially submerged rotating biological contactor. Then steady-state kinetics was applied to the analysis of the nitrification process in the dynamic state. A pseudo-steady-state approach was verified using the pulse and step forcing functions.

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