Examining a Pretty Simple and Low Cost Method for Modeling of Biogas Production from Biodegradable Solids

Abstract

This paper evaluates the application of consecutive multistage first order kinetics for mathematical modeling of biogas generation trend during anaerobic digestion (AD) of typical farm-based biodegradable solids within batch reactors. The input parameters of the model are mass of biodegradables (as VM), initial content of total volatile fatty acids (TVFA) and recorded values of biogas or methane production. Multistage consecutive equations of first order reaction in combination with numerical solution procedure for multi-parameter differential equations can provide a pretty high precision modeling of biogas production and consequently estimation of achievable energy from biodegradable solids even though it is less sophisticated than frequently used AD models. Four types of biodegradable solids including pig feces, hot water-treated cotton stalks, rice straw and dairy manure were examined through bench-scale experiments at mesophilic conditions in order to determine the biogas production potential as well as the first order kinetic constants for consecutive stages of the process. All modeling trials produced reasonable output regarding the fitting between model predicted values and experimental results. The best fitted first order rate constants of hydrolysis, acidogenesis and methanogensis obtained from the observed data were in the range of 0.022 to 0.105 d-1, 0.106 to 0.970d-1, and 0.140 to 2.300d-1 respectively. Determination of initial content of volatile fatty acids could increase the goodness of fit between the model and experimental data. The proposed modeling procedure can predict the biogas generation trend within ±10% accuracy.