Using a statistical approach to model hydrogen production from a steam exploded corn stalk hydrolysate fed to mixed anaerobic cultures in an ASBR

In this study, hydrogen (H2) production from the fermentation of steam exploded corn stalk (CS) liquor was statistically optimized using a fractional factorial design approach. The factors under consideration included temperature, pH and hydraulic retention time (HRT). Under optimal conditions at 53 °C, a pH at 4.5 and a 9.5 h HRT, the observed maximum H2 yield of 98 ± 2 mL g−1 TVS together with negligible CH4 were similar to the model predicted responses. A flux analysis revealed negligible homoacetogenic activity in cultures at 53 °C and low pH (≤5.5). Both homoacetogenic (R17) and methanogenic (R28 and R29) fluxes accounted for more than 68–90% of H2 consumption in cultures at low temperatures. The low H2 yields observed in cultures maintained at 21 °C and 37 °C was associated with high lactate and solvent levels. High H2 yields in cultures at 53 °C were associated with a higher abundance of Clostrdium sp. and CH4 production at low temperatures was due to the presence of hydrogenotrophic methanogens (Methanothermobacter marburgensis and Methanobrevibacter ruminatum) and aceticlastic methanogens (Methanosaeta sp. and Methanosarcina sp.). The results obtained from this study (within the factor ranges investigated) indicated that steam exploded CS liquor could be a potential substrate for H2 production using mixed microbial cultures.