18-19: Biological conversion of E-AFEXTM pretreated corn stover to ethanol by SSCF and CBP processes

Extractive ammonia fiber expansion (E-AFEX^TM) pretreatment provides a feedstock with high digestibility mainly due to the conversion of cellulose I to cellulose III and the removal of part of lignin. During the removal of acid soluble lignin, nutrients in the biomass and degradation products generated by pretreatment reactions may have some positive or negative effect on the fermentability of the pretreated biomass. In the present study, we examined the fermentability of the E-AFEX^TM pretreated corn stover and converted the rapid conversion of pretreated corn stover to ethanol by applying two different biological processes: simultaneous saccharification and co-fermentation (SSCF) with low enzyme loading, and consolidated bioprocessing (CBP) without any external addition. For the SSCF processes, commercial enzymes and Saccharomyces cerevisiae 424A are used, respectively for hydrolyzing biomass to fermentable sugars and fermenting sugars to ethanol. For CBP, both Clostridium thermocellum and Clostridium phytofermentans were investigated. Mass balances for these processes were completed to facilitate techno-economic analyses. We also performed preliminary economic study for comparing these processes and discuss the current technological status based on E-AFEX^TM pretreatment.