Influence of detachment mechanisms on competition in biofilms

Organism distribution in and morphology of biofilms are determined by suppl y of substrate and oxygen and by detachment mechanisms. Based on mathematic al simulations, competition of autotrophic and heterotrophic biomass in a b iofilm is discussed for three cases: (1) constant biofilm thickness, (2) da ily backwashing of the biofilm support media and (3) sloughing events in we ekly intervals. It is shown that the different detachment patterns have a s ignificant 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 wi th resulting high variations of the biofilm thickness. It is concluded that the application of results from mathematical models assuming a constant bi ofilm thickness may be misleading when predicting the performance of system s with large fluctuations of the biofilm thickness over time (e.g. biofilte rs 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 biof ilms in full-scale biofilm reactors with large lime dependent fluctuations of the biofilm thickness. (C) 1999 Elsevier Science Ltd. All rights reserve d.