Growth and decay in an auto-/heterotrophic biofilm

The growth and decay of microoganisms in an auto-/heterotrophic biofilm were investigated experimentally and by modelling. The long-term study (220 days) of the biofilm was based on measurement with microelectrodes and enabled the formulation of decay processes for the bacteria considered. The oxygen demand and, with it, the activity of the bacteria during a phase without substrate feeding were demonstrated by measuring the oxygen concentration in the diffusion field of the boundary layer above the biofilm by means of an oxygen microelectrode. For autotrophic bacteria, the formulation of the processes of death and endogenous respiration by a first-order reaction is sufficient to describe the loss of active bacteria in a biofilm. When modelling a biofilm with heterotrophic bacteria, the processes of growth and decay have to be described in more detail. In order to achieve an agreement between the model and the experimental results, the process of maintenance as well as the process of lysis of the heterotrophic bacteria must be considered. The interaction among the bacteria involved and their competition for existence in the biofilm have been worked out during the transition from a heterotrophic to an auto-/heterotrophic biofilm.