Mathematical modeling of competition and coexistence of sulfate-reducing bacteria, acetogens, and methanogens in multispecies biofilms

This work presents an integrated mathematical model able to simulate the physical, chemical, and biological processes prevailing in a sulfate-reducing biofilm under dynamic conditions. The model includes sulfate reduction by complete and incomplete sulfate-reducing bacteria (SRB); lactate removal by sulfate reduction and by acetogenic bacteria and acetate consumption via methanogenesis. Numerical integration based on the method of characteristics has been developed. The major problem of sulfate-reducing fixed-growth reactors is the formation of undesired bacterial species, which compete for space and substrate within the biofilm with SRB. The effect of COD/SO42- ratio on the reactor performances in terms of bacterial species distribution and substrate diffusion trends in the biofilm has been assessed. The simulation results reveal a stratification of microbial activities in biofilm reflecting the different ecological niches created by substrate gradients.