Improved enzymatic saccharification of steam exploded cotton stalk using alkaline extraction and fermentation of cellulosic sugars into ethanol

•Steam exploded cotton stalk can be promising substrate for ethanol production.•Steam explosion at 200 °C and 5 min led to 71.90% hemicellulose solubilization.•SECOH showed 85.07% lignin reduction with complete hemicellulose solubilization.•Steam explosion coupled with NaOH extraction showed promising sugar yield.•Fermentation with S. cerevisiae strain produced 0.44 g/g ethanol yield.

Cotton stalk, a widely available and cheap agricultural residue lacking economic alternatives, was subjected to steam explosion in the range 170–200 °C for 5 min. Steam explosion at 200 °C and 5 min led to significant hemicellulose solubilization (71.90 ± 0.10%). Alkaline extraction of steam exploded cotton stalk (SECOH) using 3% NaOH at room temperature for 6 h led to 85.07 ± 1.43% lignin removal with complete hemicellulose solubilization. Besides, this combined pretreatment allowed a high recovery of the cellulosic fraction from the biomass. Enzymatic saccharification was studied between steam exploded cotton stalk (SECS) and SECOH using different cellulase loadings. SECOH gave a maximum of 785.30 ± 8.28 mg/g reducing sugars with saccharification efficiency of 82.13 ± 0.72%. Subsequently, fermentation of SECOH hydrolysate containing sugars (68.20 ± 1.16 g/L) with Saccharomyces cerevisiae produced 23.17 ± 0.84 g/L ethanol with 0.44 g/g yield.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slide