Fermentation of Pretreated High-Biomass Sorghum Hydrolysates to Biohydrogen by Mixed Consortia

In the present study, hydrolysate generated during pretreatment of high-biomass sorghum as a carbon source for biohydrogen production was investigated. The high-biomass sorghum bagasse (HBS) was pretreated using acid (H 2 SO 4 ) and alkali (NaOH) at various concentrations (0.5–5 % w/v) for the residence time of 30 min at 121 °C, 15 lbs pressure at 10 % (w/v) solid loading. At the optimal acid load of 2 % (w/v) H 2 SO 4 yielded 78.0 g COD/L of hydrolysate. The hydrolysate generated during this pretreatment was analyzed and noticed to contain glucose 10 g L −1 , xylose 23 g L −1 , arabinose 2.0 g L −1 , HMF 1.9 g L −1 , furfural 3.5 g −1 , acetic acid 9.3 g L −1 , formic acid 5.0 g L −1 , and phenols 1.9 g L −1 . The fermentation studies were conducted in dark conditions using all the hydrolysates by heat-treated mixed microbial consortia. Maximum H 2 production rate (HPR), cumulative H 2 production (CHP), and specific H 2 yield (SHY) were measured. Maximum CHP (328 mL) and SHY (4.68 mol/kg CODr) were registered with acid treatment-resulted hydrolysate, and volatile fatty acid analysis indicated higher acetic acid concentration (1.6 g L −1 ) showing acidogenic microenvironment directing fermentation toward acetate pathway. The present study assumes importance in safe disposal and simultaneous production of value-added byproducts during lignocellulosic biorefinery.