Fermentation of pentose and hexose sugars from corncob, a low cost feedstock into ethanol

Corncob containing ∼70% mass fraction of holocellulose has been used as a low-cost feedstock for ethanol production. Among various inorganic and organic acids tested, the acid hydrolysis of corncob using HCl (1.5% mass divided by volume) at 120 °C for 30 min resulted in optimal recovery of 360.0 g kg−1 sugars along with fermentation inhibitors like phenolics and furans. In order to make the acid hydrolysate fermentable, various detoxification strategies were applied, of these activated charcoal method was found comparatively more effective in removing 95% mass fraction of phenolics and 80% mass fraction of furans. The acid hydrolysed biomass was treated with sodium chlorite (4.0%) to remove ∼80% mass fraction of lignin. The delignified substrate containing mostly cellulose was enzymatically hydrolysed to ∼78% saccharification. The acid and enzymatic hydrolysates containing 38.43 g L−1 and 36.47 g L−1 sugars, when fermented with Pichia stipitis NCIM 3499 and Saccharomyces cerevisiae HAU produced 11.84 and 16.08 g L−1 of ethanol with corresponding yield of 0.31 g g−1 and 0.43 g g−1, respectively. Moreover, the mass balance of the complete process showed 62% mass fraction of ethanol conversion from the carbohydrate fraction of corncob.