Location: Bioenergy Research Unit
Title: Dilute sulfuric acid pretreatment of corn stover for enzymatic hydrolysis and efficient ethanol production by recombinant Escherichia coli FBR5 without detoxification Authors
Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 2, 2013
Publication Date: May 10, 2013
Citation: Avci, A., Saha, B.C., Kennedy, G.J., Cotta, M.A. 2013. Dilute sulfuric acid pretreatment of corn stover for enzymatic hydrolysis and efficient ethanol production by recombinant Escherichia coli FBR5 without detoxification. Bioresource Technology. 142:312-319. Interpretive Summary: Corn stover contains 68% carbohydrates that could potentially be used for production of fuel ethanol. Generally, three steps are involved for its conversion to ethanol: pretreatment, enzymatic hydrolysis and fermentation. Pretreatment is crucial because corn stover in its native state is resistant to enzymatic hydrolysis. However, some compounds are produced during dilute acid pretreatment that are inhibitory to fermentation. The removal of these inhibitory compounds (detoxification) involves additional process step which adds cost and process complexity. In this research, we have developed a pretreatment strategy for dilute sulfuric acid pretreatment of corn stover for the purpose of reducing the formation of inhibitory compounds during pretreatment so that a detoxification step is not required prior to fermentation while maximizing the sugar yield. These findings are important for development of a commercially viable biomass to ethanol conversion process technology without removing the fermentation inhibitors.
Technical Abstract: A pretreatment strategy for dilute H2SO4 pretreatment of corn stover was developed for the purpose of reducing the generation of inhibitory substances during pretreatment so that a detoxification step is not required prior to fermentation while maximizing the sugar yield. We have optimized dilute sulfuric acid (0.0-1.0%, v/v; 140-200 oC; 0-15 min) pretreatment and enzymatic saccharification (pH 5.0, 45oC, 72 h) of corn stover (10%, w/v) using commercial cellulase, hemicellulase and ß-glucosidase preparations. The optimal conditions for dilute acid pretreatment were: 0.75% H2SO4, 160 oC, and 0 to 5 min holding time. The conditions were chosen based on maximum glucose release, minimum loss of pentose sugars and minimum formation of sugar degradation products such as furfural and hydroxymethyl furfural (HMF). The pretreated corn stover after enzymatic saccharification using cellulase and ß-glucosidase generated 63.2±2.2 and 63.4±3.4 g total sugars per L which is equivalent to 89.5 and 90.2% of the theoretical sugar yields at 0 min and 5 min holding times, respectively. Furfural production under these conditions was 0.45±0.1 and 0.87±0.4 g/L, respectively. The fermentative performance of the mixed sugar utilizing ethanologenic recombinant Escherichia coli strain FBR5 on the non-detoxified corn stover hydrolyzate by both separate hydrolysis and fermentation (0.31 g ethanol per g corn stover) and simultaneous saccharification and fermentation (0.30 g ethanol per g stover) demonstrated that the strain can efficiently ferment corn stover (100 g/L) hydrolyzate if the furfural content is < 0.5 g/L.