MODELING THE GROWTH OF METHANE-OXIDIZING BACTERIA IN A FIXED BIOFILM

Methane-oxidizing bacteria were grown in a fixed biofilm reactor in order to study their ability to degrade chlorinated aliphatic hydrocarbons. Focus is on the growth behaviour of the mixed culture. The growth is described by a model that includes methanotrophic bacteria in the active biomass fraction. The inactive biomass fraction consists of exocellular polymers and biodegradable and inert particulate biomass. The model describes the oxygen respiration in detail. Yield coefficients, decay constants and hydrolysis constants are estimated based on the oxygen respiration. An analysis of the observability of the system reveals that several of the coefficients cannot be determined explicitly due to the complexity of the model and the limited amount of variables measured. Estimation procedures based on least squares methods are employed and parameter estimates and confidence intervals are computed. The study forms the basis for setting up a future measuring programme. This work indicates a yield coefficient for methanotrophs of 0.36 mg biomass COD per mg CH4. In weight units this corresponds to approx. 1.44 mg biomass per mg CH4. This is close to the theoretical maximum growth yield for methanotrophs.