Evolution of butyric acid and the methanogenic microbial population in a thermophilic dry anaerobic reactor

Knowledge of the relationship between the evolution of butyric acid, the main precursor of methane, and the methanogenic microbial population, quantified by fluorescent in situ hybridization (FISH), is important for understating and controlling the anaerobic digestion of solid waste. In this study, a statistical analysis has been made of this relationship in a laboratory-scale continuously stirred tank reactor (CSTR) without recycling of biomass. The CSTR has been operated at four organic loading rates (OLR) between 4.42 and 7.50 kg VS m^?3 day^?1, using the Organic Fraction of Municipal Solid Waste (OFMSW) as the substrate. During the start-up stage, the consumption of butyric acid is related to the population of H₂-utilising methanogens (R² = 0.774), whereas in the stabilization stage, it is related to that of acetoclastic methanogens (R² = 0.716). Therefore, it can be concluded that the methanogenic population dynamics are closely correlated with the concentration of volatile fatty acids, and in particular, with that of butyric acid.