Background:
Caldicellulosiruptor saccharolyticus has attracted increased interest as an industrial hydrogen producer. The aim of the present study was to develop a kinetic growth model for this extreme thermophile. The model is based on Monod kinetics supplemented with the inhibitory effects of hydrogen and osmotic pressure, and the liquid-to-gas mass transfer of H2.
Results:
Mathematical expressions were developed to enable the simulation of microbial growth, substrate consumption and product formation. The model parameters were determined by fitting to experimental data. The derived model corresponded well with experimental data from batch fermentations in which the stripping rates and substrate concentrations were varied. The model was used to simulate the inhibition of growth by hydrogen and solute concentrations, giving a critical dissolved hydrogen concentration 2.2 mmol/L and an osmolarity of 0.27-0.29 osm/L of 2.2 mmol/L. The inhibition by hydrogen, being a function of the dissolved hydrogen concentration, was demonstrated to be mainly dependent on the hydrogen productivity and mass-transfer rate. The latter can be improved by increasing the stripping rate, thereby allowing higher hydrogen productivity. The experimentally determined degree of oversaturation of dissolved hydrogen was 12 to 34 times the equilibrium concentration, and was comparable to the values given by the model.
Conclusions:
The derived model is the first mechanistically based model for fermentative hydrogen production, and provides useful information to improve our understanding of the growth behavior of C. saccharolyticus. The model can be used to determine optimal operating conditions for hydrogen production regarding the substrate concentration and the stripping rate.Source:
http://www.biotechnologyforbiofuels.com/rss/