Description of two-step kinetics in methane formation during psychrophilicH-2/CO2 and mesophilic glucose conversions

The model of anaerobic digestion presented before (Vasiliev et al., 1993. W at. Resources 20, 633-643; Vavilin et al., 1994. Biores. Techn. 48, 1-8; Va vilin et al., 1997. Wat. Sci. Techn. 36, 531-538) was used to describe biph asic kinetics of methane formation during batch tests of psychrophilic H-2/ CO2 consumption by microbiota of tundra soil, and mesophilic glucose degrad ation by glucose-pregrown inocula. Two possible routes of biphasic methane formation were tested: one with hydrogenotrophic and acetoclastic methanoge nesis in the first and second step, respectively. The other route followed acetoclastic methanogenesis in both the first and the second step, taking t he potential inhibition of acetoclastic methanogenesis into account. Simula tions showed that the hydrogenotrophic and acetoclastic methanogenesis in t he first and second steps, respectively, described the system dynamics of m esophilic glucose degradation comparatively well. For psychrophilic H-2/CO2 consumption by tundra soil microflora it was shown that the second option with temporary inhibition of acetoclastic methanogenesis in acidic conditio ns was more probable. Considered in the model were a direct pH inhibition, with Monod kinetics, for total acetate concentration, or a non-ionized acet ate inhibition with Haldane kinetics for non-ionized acetate concentration. Both approaches were able to fit the experimental data rather closely. The kinetic coefficients of hydrogenotrophic methanogens, acetoclastic methano gens and acetogens are presented. (C) 1999 Elsevier Science Ltd. All rights reserved.