Improving xylose utilization and ethanol production from dry dilute acid pretreated corn stover by two-step and fed-batch fermentation

It is a great challenge to efficiently utilize xylose in fermentation with high solid loadings for the economically feasible production of lignocellulosic ethanol. However, 20% solid loading of dry dilute acid pretreated corn stover (DDAPCS) decreased 66.3% of the xylose consumption compared to yeast extract peptone dextrose and xylose (YPDX) medium, which was significantly larger than 16% solid loading (9.4%). To overcome those problems, several two-step processes for simultaneous saccharification and co-fermentation (SSCF) were developed by inoculating a water extract of 16% solid loading DDAPCS with microorganisms in the first fermentation step. During the first step, the relatively lower inhibitor concentrations (compared to 20% solid loading), decreased glucose concentration, and the absence of enzymatic hydrolysis residues (EHR) were beneficial for the use of xylose and enabled up to 75.6% of the xylose to be converted to ethanol. With an optimized fed-batch strategy of two-step process, the residual xylose concentration reduced by 55.6% with 20% solid loading, and the maximum ethanol concentration and yield increased by 30% and 16.6%, respectively.