Modeling of volatile fatty acids degradation kinetics and evaluation of microorganism activity

Particular cases of Monod kinetics (zero order and exponential growth) were used for the description of VFA degradation by acetate and glucose pregrown inocula measured by Aguilar et al. (1995), and kinetic constants were evaluated. The equations with inhibition were used for description of the degradation kinetics of VFA mixtures measured by Mawson et al. (1991) and by Ozturk (1991). A good agreement between the model and the batch data with synthetic media and molasses pregrown inoculum was obtained and microorganism activity was evaluated. Using the generalized METHANE model of anaerobic digestion described earlier, the Monod and Haldane kinetics were tested for the experimental data of Noike et al. (1985), where mesophilic conversion of acetate was studied in a continuous-flow reactor under a wide range of acetate-loading values. The system failed at high influent acetate concentration because of pH inhibition for Monod kinetics and of unionized-acetate inhibition for Haldane kinetics. However, the model could not describe the change of effluent acetate concentration. To describe that, the corrected Monod and Haldane function with changeable half-saturation coefficients was introduced.