GROWTH AND DECAY IN AN AUTO- HETEROTROPHIC BIOFILM/

The growth and decay of microorganisms in an auto-/heterotrophic biofi lm were investigated experimentally and by modelling. The long-term st udy (220 days) of the biofilm was based on measurement with microelect rodes and enabled the formulation of decay processes for the bacteria considered. The oxygen demand and, with it, the activity of the bacter ia during a phase without substrate feeding were demonstrated by measu ring the oxygen concentration in the diffusion field of the boundary l ayer above the biofilm by means of an oxygen microelectrode. For autot rophic bacteria, the formulation of the processes of death and endogen ous respiration by a first-order reaction is sufficient to describe th e loss of active bacteria in a biofilm. When modelling a biofilm with heterotrophic bacteria, the processes of growth and decay have to be d escribed 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 conside red. The interaction among the bacteria involved and their competition for existence in the biofilm have been worked out during the transiti on from a heterotrophic to an auto-/heterotrophic biofilm. (C) 1997 El sevier Science Ltd.