Description of two-step kinetics in methane formation during psychrophilic H2/CO2 and mesophilic glucose conversions

The model of anaerobic digestion presented before (Vasiliev et al., 1993. Wat. Resources 20, 633±643; Vavilin et al., 1994. Biores. Techn. 48, 1±8; Vavilin et al., 1997. Wat. Sci. Techn. 36, 531±538) was used to describe biphasic kinetics of methane formation during batch tests of psychrophilic H2/CO2 consumption by microbiota of tundra soil, and mesophilic glucose degradation by glucose-pregrown inocula. Two possible routes of biphasic methane formation were tested: one with hydrogenotrophic and acetoclastic methanogenesis in the ®rst and second step, respectively. The other route followed acetoclastic methanogenesis in both the ®rst and the second step, taking the potential inhibition of acetoclastic methanogenesis into account. Simulations showed that the hydrogenotrophic and acetoclastic methanogenesis in the ®rst and second steps, respectively, described the system dynamics of mesophilic glucose degradation comparatively well. For psychrophilic H2/CO2 consumption by tundra soil micro¯ora it was shown that the second option with temporary inhibition of acetoclastic methanogenesis in acidic conditions was more probable. Considered in the model were a direct pH inhibition, with Monod kinetics, for total acetate concentration, or a non-ionized acetate inhibition with Haldane kinetics for non-ionized acetate concentration. Both approaches were able to ®t the experimental data rather closely. The kinetic coecients of hydrogenotrophic methanogens, acetoclastic methanogens and acetogens are presented