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

Abstract

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 (H2SO4) 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) H2SO4 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 H2 production rate (HPR), cumulative H2 production (CHP), and specific H2 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.