The Effect of pH Control on Acetone–Butanol–Ethanol Fermentation by Clostridium acetobutylicum ATCC 824 with Xylose and d-Glucose and d-Xylose Mixture ☆

Abstract d -Glucose, l -arabinose, d -mannose, d -xylose, and cellobiose are saccharification products of lignocellulose and important carbon sources for industrial fermentation. The fermentation efficiency with each of the five sugars and the mixture of the two most dominant sugars, d -glucose and d -xylose, was evaluated for acetone–butanol–ethanol (ABE) fermentation by Clostridium acetobutylicum ATCC 824. The utilization efficacy of the five reducing sugars was in the order of d -glucose, l -arabinose, d -mannose, d -xylose and cellobiose. d -Xylose, the second most abundant component in lignocellulosic hydrolysate, was used in the fermentation either as sole carbon source or mixed with glucose. The results indicated that maintaining pH at 4.8, the optimal pH value for solventogenesis, could increase d -xylose consumption when it was the sole carbon source. Different media containing d -glucose and d -xylose at different ratios (1:2, 1:5, 1.5:1, 2:1) were then attempted for the ABE fermentation. When pH was at 4.8 and xylose concentration was five times that of glucose, a 256.9% increase in xylose utilization and 263.7% increase in solvent production were obtained compared to those without pH control. These results demonstrate a possible approach combining optimized pH control and d -glucose and d -xylose ratio to increase the fermentation efficiency of lignocellulosic hydrolysate.