Modeling of fermentative hydrogen production from the bacterium Ruminococcus albus: Definition of metabolism and kinetics during growth on glucose

The aim of the present study was to describe the fermentative pathway of Ruminococcus albus during hydrogen production from glucose by a quantitative kinetic model, taking into account the interactions among the metabolic products during their generation. Proper mathematical expressions were developed in order to adequately describe the microbial growth and metabolism of R. albus. For the estimation of kinetics constants of the process, the experimental data from batch experiments were simulated using a simplified and modified version of Anaerobic Digestion Model 1 on Aquasim as a modeling platform. Subsequently the accuracy of the model was verified by simulating the performance of a CSTR in four different hydraulic retention times. Batch experiments with different initial substrate concentrations and different initial hydrogen partial pressures were carried out in order to calculate the growth kinetics of the microorganism and investigate the effect of hydrogen partial pressure to the production of metabolites. Microbial growth was described using Monod kinetics, taking into account the inhibition at lower pH values as well as the substrate inhibition, and the metabolites' profile was described using suitable kinetic expressions. Acetate and ethanol production were assumed to occur simultaneously, by direct sugar consumption and the H2 final yield was reversely connected to the accumulation of ethanol. Formate was considered to be produced by direct sugar consumption, and subsequently to break down to H2 and CO2. The degradation rate of formate, and consequently hydrogen production were shown to be influenced by hydrogen partial pressure.