Modelling the growth of a methanotrophic biofilm: Estimation of parametersand variability

This article discusses the growth of methanotrophic biofilms. Several indep endent biofilm growths scenarios involving different inocula were examined. Biofilm growth, substrate removal and product formation were monitored thr oughout the experiments. Based on the oxygen consumption it was concluded t hat heterotrophs and nitrifiers co-existed with methanotrophs in the biofil m. Heterotrophic biomass grew on soluble polymers formed by the hydrolysis of dead biomass entrapped in the biofilm. Nitrifier populations developed b ecause of the presence of ammonia in the mineral medium. Based on these exp erimental results, the computer program AQUASIM was used to develop a biolo gical model involving methanotrophs, heterotrophs and nitrifiers. The model ling of six independent growth experiments showed that stoichiometric and k inetic parameters were within the same order of magnitude. Parameter estima tion yielded an average maximum growth rate for methanotrophs, mu(m), of 1. 5 +/- 0.5 d(-1), at 20 degrees C, a decay rate, b(m), of 0.24 +/- 0.1 d(-1) , a half saturation constant, K-S(CH4), of 0.06 +/- 0.05 mg CH4/L, and a yi eld coefficient, Y-CH4, of 0.57 +/- 0.04 g X/g CH4. In addition, a sensitiv ity analysis was performed on this model. It indicated that the most influe ntial parameters were those related to the biofilm (i.e. density; solid-vol ume fraction; thickness). This suggests that in order to improve the model, further research regarding the biofilm structure and composition is needed .