Combination of hydrothermal pretreatment and sodium hydroxide post-treatment applied on wheat straw for enhancing its enzymatic hydrolysis

Wheat straw was respectively pretreated by water, dilute sulfuric acid, and sodium hydroxide solution at elevated temperature. Among the pretreatments, hydrothermal process was carried out with different severities. Hydrothermal pretreated sample and dilute acid pretreated sample were subsequently extracted by sodium hydroxide solution at room temperature which was applied as post-treatment. The pretreated samples were then enzymatically hydrolyzed to evaluate reducing sugar recovery. The result indicated that alkaline pretreatment removed a significant amount of lignin. While hydrothermal pretreatment and dilute acid pretreatment solubilized a significant amount of hemicellulose. And the hydrothermal pretreatment severity affected the solubilization of hemicellulose. The alkaline pretreated sample achieved the highest reducing sugar recovery e.g. 38.5 g sugar/100 g wheat straw. The alkaline post-treatment enhanced the enzymatic hydrolysis of acidic pretreated samples by removing additional hemicellulose and lignin. The best reducing sugar recovery was obtained at 43.6 g sugar/100 g wheat straw which indicated that the combination of hydrothermal pretreatment and alkaline extraction is a promising method in terms of reducing sugar production.