Maleic acid treatment of bioabated corn stover liquors imporves cellulose conversion to ethanol

Elimination of inhibitory compounds released during pretreatment of lignocellulose is critical for efficient cellulose conversion and ethanol fermentation. This study examined the effect of bioabated liquor from pretreated corn stover on enzyme hydrolysis of Solka Floc or pretreated corn stover solids. Xylo-oligosaccharides in the liquor were hydrolyzed by hemicellulase or maleic acid. Pretreatment was at 20% solids, 190 °C, 45min, and subsequent hydrolysis, after bioabatement was done with 5% corn stover, and ethanol fermentation by Saccharomyces cerevisiae. The fungus Coniochaeta ligniariaNRRL30616 removed inhibitory compounds in the liquor from LHW-pretreated corn stover. The conversion of cellulose to glucose in bioabated liquor was higher when the liquor was treated with maleic acid than with hemicellulase. For corn stover slurried in hemicellulase treated liquor, cellulose conversion was 39%, while corn stover in maleic acid treated liquor was gave 68% yield. The observed lower glucose yield may be related to inhibition of beta-xylosidase caused by accumulation of xylo-oligomers, which in turn inhibited beta-glucosidase, leading to accumulation of cellobiose. The use of maleic acid alleviated the inhibitory effect on beta-glucosidase by hydrolyzing the xylo-oligomers to xylose. Ethanol production from Solka Floc hydrolysate or sugars from corn stover solids was 20 to 30% higher for bioabated liquor compared to non-bioabated liquor. Furthermore, the fermentation lag phase was decreased by 3 hours. Our results confirm bioabatement removes compounds that inhibit enzyme hydrolysis and fermentation.  The treatment of bioabated samples with maleic acid improved overall cellulose conversion due to hydrolysis of xylo-oligomers to xylose, where xylose is much less inhibitory towards beta-glucosidase.