Corncob Mild Alkaline Pretreatment for High 2,3-Butanediol Production by Spent Liquor Recycle Process

The aim of the present work was to enable valorization of glucan and xylan in corncob using a mild alkaline pretreatment route and lower the alkaline and water consumptions by spent liquor recycle process. Alkaline pretreatment at 80 °C, 2 h, 2% NaOH was proposed to recover glucan and xylan of corncob. For decreasing the alkaline and water consumptions in pretreatment process, spent liquor recycle process was carried out. Six batch spent liquor recycle pretreatment did not decrease the pretreatment and enzymatic hydrolysis efficiencies, and the consumptions of alkaline and wastewater would be saved by 22.5 and 63.1%, respectively. The pulp could be well converted to glucose and xylose with a low loading of enzymes. With 2% substrate loading, 15 FPU g−1 solid enzyme loading and 72-h incubation, the enzymatic glycan and xylan conversion ratios could reach about 95 and 98%, respectively. A maximal sugar concentration of 170.2 g l−1 was obtained with a yield of 0.54 g g−1 corncob. The sugar from enzymatic hydrolysis was used as substrate for 2,3-butanediol production. Under an optimized condition, a maximal 2,3-butanediol concentration of 52.5 g l−1 was obtained with a yield of 0.42 g g−1 sugar (84.8% of the theoretical yield) and a productivity of 0.88 g l−1 h−1 after 60-h fed-batch fermentation. This study opened up a promising route for high value application for glucan and xylan at the same time.