Bioconversion of alkali delignified cotton stalk using two-stage dilute acid hydrolysis and fermentation of detoxified hydrolysate into ethanol

⿢Cotton stalk is a potential agricultural residue for bioprocess.⿢Dilute NaOH pretreatment showed 52.48% delignification with 3.50% sugar loss.⿢Two-stage dilute acid hydrolysis of cotton stalk led to 63.50% saccharification.⿢Detoxification of hydrolysate led to significant reduction in furfurals and phenolics.⿢Coculture of S. cerevisiae and P. stipitis showed 0.47 g/g ethanol yield.

Green biotechnology offers a promising approach to convert most of the solid agricultural wastes particularly lignocellulosic biomass into liquid biofuels. In this study, pretreatment of cotton stalk with sodium hydroxide (3% w/v; room temperature for 24 h) removed lignin (52.48 ± 1.17%) with minimum sugar loss (3.50 ± 0.09%). Subsequent two-stage dilute acid hydrolysis of alkali delignified cotton stalk released 29.40 ± 0.85 g/L sugars with 63.50 ± 1.06% holocellulose hydrolysis along with furfurals (1.32 ± 0.10 g/L) and phenolics (2.18 ± 0.15 g/L) in the hydrolysate. Detoxification of hydrolysate with overliming and adsorption with activated charcoal caused 59.12% and 78.44% reduction in total furfurals and phenolics, respectively. Batch fermentation of detoxified acid hydrolysate with monoculture and cocultures of Saccharomyces cerevisiae VS3 and Pichia stipitis NCIM3498 showed ethanol production of 6.28 ± 0.08 g/L, (yield, 0.39 g/g); 10.14 ± 0.19 g/L (yield, 0.45 g/g) and 11.64 ± 0.32 g/L (yield, 0.47 g/g), respectively.

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