ANALYTICAL EFFECTIVENESS CALCULATIONS CONCERNING THE DEGRADATION OF AN INHIBITIVE SUBSTRATE BY A STEADY-STATE BIOFILM

A reaction engineering model for the degradation of an inhibitory subs trate by a steady-state biofilm is presented. The model describes both the metabolic rate controlling behavior of this substrate in the biof ilm and the effect of diffusion limitation caused by an arbitrary subs trate on the active biofilm thickness. An analytical expression for th e biocatalyst effectiveness factor is presented on the basis of Pirt k inetics for cell maintenance, first order substrate inhibition kinetic s, and zero order substrate consumption kinetics. The proposed express ion for the biocatalyst effectiveness factor is much more convenient t o incorporate into a macroreactor model than the numerical alternative s. Simple criteria are presented to check the applicability of the mod el in case of true Monod kinetics. The analytical solution is expected to be particularly applicable to processes where a low soluble organi c substrate controls the biomass growth, a situation which is often me t in wastewater purification processes of industrial importance. The d egradation of phenol by Pseudomonas sp. is treated as an example.