Biokinetic modeling and scale‐up considerations for rotating biological contactors

Abstract

ABSTRACT: Available growth kinetic models and a combined growth kinetic and mass transport model were applied to describe the performance of bench‐scale rotating biological contactors (RBCs) in treating low‐BOD, high‐ammonia landfill leachate. The growth kinetic models could describe the observed organic carbon and ammonia removals individually, but as currently formulated they are not capable of describing the simultaneous removal of multiple substrates. Moreover, these models assume that substrate removal is not oxygen limited, an assumption that renders them of little use for prediction of substrate removal under high loading conditions where oxygen deficiency may occur. Such conditions occurred in the first stages of the bench‐scale RBC units as has been observed at full‐scale in various wastewater treatment applications. To examine the effect of oxygen transfer on the simultaneous removal of organic carbon and ammonia, a combined growth kinetic and mass transport model, RBC Sector, was developed. RBC Sector described successfully the observed substrate removal rates and was useful in identifying the tank dissolved oxygen concentration (1.8 mg/L) at which RBC performance started to decline as a result of oxygen limitation. Because RBC Sector can predict the simultaneous removal of multiple substrates under oxygen‐limiting conditions, it is potentially useful as a scale‐up tool. Investigation of a key scale‐up issue, namely the radial variation of biomass thickness and density, would improve the utility of the model for scale‐up.