Modelling of Biogas Production from Glycerol by Anaerobic Process in a Baffled Multi-Stage Digestor

Abstract

ABSTRACTThe anaerobic conversion of glycerol by the bacterium Klebsiella sp. is a well-known process. According to its metabolism glycerol is converted into different products, e.g. 2,3-butanediol, 1,3-propanediol, acetic acid, formic acid, lactic acid and biogas. The latter is produced by two competitive ways: decarboxylation of acetic acid or self-reduction of carbon dioxide by hydrogen, acetic acid, carbon dioxide and hydrogen being intermediate products of one of the competitive metabolic routes. Which of these compounds is a desired final product depends on the purpose of the fermentation.In the present work a non-structured mathematical model is developed to describe these competitive processes. The model consists of nine ordinary non-linear differential equations for the kinetics of some selected more important reactions from the metabolic pathway. The model takes into account the microbial growth, the pH drop caused by the organic acid formation and the resulting inhibition of the methanogenic microbial activity. The pH-optima of the enzymes are approximated by Gaussian distribution. The enzyme sensitivity toward pH-variations is presented by the half-width of the Gaussian curve.A large set of experimental data for glycerol anaerobic digestion by Klebsiella sp. in a baffled multistage reactor was used for verification of the model. The comparison of the experimental data with the model results revealed the number of reactor stages, sufficient for complete methanization and to determine the optimum conditions for 2,3-butanediol or methane production.