Evaluation of kinetic coefficients using integrated monod and haldane models for low-temperature acetoclastic methanogenesis

The integrated Monod and Haldane models were used to evaluate the kinetic coefficients and their standard deviations using the methane accumulation curves of low-temperature acetoclastic methanogenesis. The linear and exponential approximations and the limitations of their applicability were deduced from the integrated models. The samples of lake sediments and biomass taken from a low-temperature upflow anaerobic sludge blanket (UASB) reactor were used as inoculum in batch assays for acetate methanation. In comparison, the Monod and Haldane models were applied to evaluate the kinetic coefficients for mesophilic acetoclastic methanogenesis accomplished by the pure culture of Methanosarcina barkeri strain MS. The Monod and Haldane models and their approximations were fitted by using non-linear regression. For the wide range of initial acetateconcentrations (4.2-84 mM: 5-100 mM) applied to the UASB biomass at 11 and 22 degrees C and for the lake sediment samples at 6 and 15 degrees C, a better fit was obtained with the Haldane models and their exponential approximations, respectively. For the lake sediments the values of inhibition coefficients decreased at decreasing temperatures. At the highest temperature of 30 degrees C no difference was found between the Haldane and Monod models and the simpler Monod model should be preferred. The values of the maximum growth rate of biomass were highest at 30 degrees C (lake sediment) and 22 degrees C (the UASB biomass) being in a range presented in the literature for mesophilic acetoclastic methanogenesis.