Modelling the Effect of Biofilm Morphology on Detachment

Abstract

A biofilm is an assembly of organisms attached to a surface and this feature is utilized in biofilm reactors to retain a high biomass concentration. Biofilm detachment, which is the release of biomass to the surrounding liquid, may significantly alter the performance. It is a local phenomenon which depends on the local shear stress and biofilm morphology. An empirical expression for the effect of morphology on fluid shear stress was constructed based on: (i) deviation of local biofilm thickness from its mean, (ii) from its maximum and (iii) a reference shear stress defined from flow conditions around the biofilm. The expression was calibrated with numerical results in literature obtained from computational fluid dynamics. The expression was integrated with an individual-based model platform where the biofilm morphology was determined by simulation of particles resembling individual bacteria that grow and divide. Biofilm detachment occurred locally where the shear stress exceeded biofilm cohesiveness, after which a new morphology was generated. The model developed was especially useful for predicting the detachment of biofilm when the shear stress suddenly changes. Biofilm detachment and sloughing were more pronounced in pulse shear conditions than biofilms under a constant shear stress.