Studies on the effect of concentration of a self-inhibitory substrate on biofilm reaction rate under co-diffusion and counter-diffusion configurations

A simple mathematical model was developed to investigate the utilzation rate of a self-inhibitory substrate in idealised biofilm reactors operating with either counter-diffusion or co-diffusion of oxygen and phenol. This study has implications for the development of membrane-supported biofilm technologies, such as the membrane-aerated biofilm reactor. An unsteady-state formulation of the model was used to investigate the effect of shock loads of phenol on biofilm performance. It was found that the counter-diffusion configuration may be advantageous under high phenol concentrations provided the biofilm thickness is above a critical value. The performance advantage of the counter-diffusion configuration is gained by the presence of an oxygen depleted layer, adjacent to the liquid–biofilm interface which acts as a diffusive barrier to phenol transport to the region of respiratory activity.