Design of multistage rotating biological contactors

Analysis of performance data from rotating biological contactor (RBC) plants showed that a simple apparent growth model, based on Michaelis-Menten kinetics, can satisfactorily simulate the performance of an RBC with respect to organic carbon removal. The model was applied for the design of multistage RBC systems under two different conditions: (1) so that the minimum total biodisc area is obtained; and (2) so that the biodisc areas for each stage are equal. It was shown that in the latter case the total required area is only marginally (\N 1%) larger than the minimum total area (case 1). Therefore the adoption of uniform stages seem to be justified in view of the resulting construction simplicity. Although under these conditions (uniform stages) the design, based on the proposed model, would entail the simultaneous solution of a system of nonlinear equations, the simpler analytical expression derived under optimum conditions (case 1) can be used, due to the proximity of the results for the total biodisc area. The model was verified with the aid of data from a variety of treatment plants and was found to provide a satisfactory preliminary approximation for design purposes.