Improving volumetric hydrogen production by using immobilization methods in a modified continuous stirred tank reactor

Hydrogen is a very alluring source of energy and new sources of hydrogen production via sustainable and clean sources is of high priority. Dark fermentation has the potential to be this new sustainable clean source of hydrogen but requires profound optimization. Caldicellulosiruptor is a genus of thermophilic bacteria that is capable of producing hydrogen near the stoichiometric limits of 4 mol / mol hexose while using waste from paper industries, palm oil refining effluents etc. The drawbacks of this organism are the low volumetric H2 production due to growing only in low cell densities and low tolerance to high sugar concentrations. In this study, an attempt to decouple cell growth rate from dilution rate in chemostat cultures by immobilization of co-cultures of C. kronotskyensis and C. owensensis was made. This was coupled with the estimation of the population dynamics in the co-culture in both the planktonic and biofilm phases, by designing probes for quantitative PCR to reliably differentiate four species of this genus. Thus, when a substrate for attachment was provided, C. owensensis is the dominant population accounting for more than 99 % of the biomass in the co-culture. However, pure cultures of C. kronotskyensis in the presence of a substrate for attachment could also improve the volumetric H2 production (QH2), which suggests that co-cultures may not be required as previously thought. An elucidation of sugar uptake characteristics of C. kronotskyensis was also undertaken. An initial analysis revealed that C. kronotskyensis most likely has a competitive uptake system for at least xylose and glucose where a single transporter is responsible for uptake of both sugars. (Less)