A pseudo-stoichiometric dynamic model of anaerobic hydrogen production from molasses

Despite many mathematical models available in the literature for simulation and optimization of anaerobic digestion processes, only few can accurately account for hydrogen production. In the present study, experiments were performed in a continuous stirred tank reactor with a hydraulic retention time close to 6 h. pH was regulated to 5.5 and agitation was maintained at 300 rpm. Molasses were used as substrate with feeding concentrations varying between 5 and 20 g L-1. Experimental data were used to estimate the pseudo-stoichiometric coefficients with a constrained nonlinear optimization. The obtained pseudo-stoichiometric matrix is made of two reactions, one being associated with hydrogen production and the other one with acetate production. Finally, a dynamic model is derived and is demonstrated to simulate very accurately the dynamic evolution of hydrogen production, but also biomass and intermediate compounds (i.e., individual volatile fatty acids) concentrations while being very close to the stoichiometric balance. Finally, the best hydrogen production was 15.3 L-H2 d(-1) L-1 for a concentration of substrate of 20.09 g L-1 and a liquid feed flow of 5 L d(-1) (i.e., 1.47 mol-H-2 mol-glucose(-1)). (c) 2008 Elsevier Ltd. All rights reserved.