Clarifying configurations of reaction rate constant for first-order and Monod-type kinetics: A comparative manner and a pursuit of parametric definition

The mechanisms of first-order and Monod-type kinetics describes degradation in distinct manner and yet too little attention is paid on the fact that first-order kinetic was derived from pure elementary reaction while Monod-type degradation was based on microbial uptake. Both mechanisms are basic theories in developing sophisticated degradation models and there are needs to give more guidance on selection of kinetics. The objective of this study was to compare the two kinetics when used for modeling degradation and biodegradability during composting. With both experimental data, from reactor composting of swine manure/wheat straw, and simulated results, it was found that Monod-type kinetic was more capable of modeling the lag phase, while first-order kinetic could explain the fast oxygen uptake rate for the oxidation of soluble substrate. Comparison of growth rate constants, based on Monod-type equation, with maximum degradation rate constants, based on first-order kinetic, showed that the former was generally one magnitude greater, which could be explained with the fact that part of growth of cell weight was from water consumption.