Kinetic considerations on the performance of activated sludge reactors and rotating biological contactors

This study compares the performance characteristics of laboratory-scale activated sludge and rotating biological contactor (RBC) units treating an industrial effluent. It is found that, within the range of hydraulic detention time examined (0.3–1.7 days), the two plants show very similar BOD₅ removal kinetics. These results indicate that an RBC unit with a geometrical area of the discs of 1340 cm²1⁻¹ of aeration reactor is equivalent to an activated sludge plant with an MLVSS concentration of about 2000 mg 1⁻¹. Experimental data from the two units are also analyzed by two steady-state kinetic models. It is proved that the kinetic constants of suspended microbial growths may be used successfully for fixed biological films. At the same time, a simplified design equation for RBC systems is verified and an estimation procedure for the effective surface area of the biofilm developed.