Influence of detachment mechanisms on competition in biofilms

Organism distribution in and morphology of biofilms are determined by supply of substrate and oxygen and by detachment mechanisms. Based on mathematical simulations, competition of autotrophic and heterotrophic biomass in a biofilm is discussed for three cases: (1) constant biofilm thickness, (2) daily backwashing of the biofilm support media and (3) sloughing events in weekly intervals. It is shown that the different detachment patterns have a significant influence on the organism distribution within the biofilm and on overall process performance. Faster growing heterotrophs are favored over autotrophic biomass in situations with long intervals between detachment with resulting high variations of the biofilm thickness. It is concluded that the application of results from mathematical models assuming a constant biofilm thickness may be misleading when predicting the performance of systems with large fluctuations of the biofilm thickness over time (e.g. biofilters with backwashing or trickling filters). Thus, it must also be questioned whether results from laboratory experiments in laminar flow channels (with a constant erosion) can be used to describe structure and function of biofilms in full-scale biofilm reactors with large time dependent fluctuations of the biofilm thickness.