Continuous SSCF of AFEX™ pretreated corn stover for enhanced ethanol productivity using commercial enzymes andSaccharomyces cerevisiae424A (LNH-ST)

High productivity processes are critical forcommercial production of cellulosic ethanol. One highproductivity process—continuous hydrolysis and fermen-tation—has been applied in corn ethanol industry. Howev-er, little research related to this process has been conductedon cellulosic ethanol production. Here, we report andcomparethe kinetics of both batchSHF (separate hydrolysisand co-fermentation) and SSCF (simultaneous saccharifica-tion and co-fermentation) of AFEX TM (Ammonia FiberExpansion) pretreated corn stover (AFEX TM -CS). Subse-quently, we designed a SSCF process to evaluate continuoushydrolysisandfermentationperformanceonAFEX TM -CSina series of continuous stirred tank reactors (CSTRs). Basedon similar sugar to ethanol conversions (around 80% glu-cose-to-ethanol conversion and 47% xylose-to-ethanol con-version), the overall process ethanol productivity forcontinuous SSCF was 2.3- and 1.8-fold higher than batchSHF and SSCF, respectively. Slow xylose fermentation andhigh concentrations of xylose oligomers were the majorfactors limiting further enhancement of productivity.Biotechnol. Bioeng. 2013;110: 1302–1311. 2012 Wiley Periodicals, Inc.KEYWORDS: continuous fermentation; SSCF; SHF; cellu-losic ethanol; AFEX; enzymatic hydrolysis