Alkaline Peroxide Pretreatment of Corn Stover for Enzymatic Saccharification and Ethanol Production

Abstract

Alkaline hydrogen peroxide (AHP) pretreatment and enzymatic saccharification were evaluated for conversion of corn stover cellulose and hemicellulose to fermentable sugars. Corn stover used in this study contained 37.0±0.2% cellulose, 26.8±0.2% hemicellulose, and 18.0±0.1% lignin on dry basis. Under the optimum conditions of AHP pretreatment [2% H₂O₂ (v/v), pH 11.5, 35°C, 24 h] of corn stover (10%, w/v) and enzymatic saccharification (45°C, pH 5.0, 72 h) with 0.1% (w/v) Tween 20, a total of 558±12 mg of fermentable sugars was obtained per g stover, which is equivalent to 79.5% of theoretical sugar yield. Most of the lignin (82%) was removed from corn stover. The AHP pretreated and enzymatically saccharified corn stover hydrolyzate was fermented by recombinant Escherichia coli strain FBR 5 at pH 6.5 and 37°C for 96 h to produce 23.9±0.9 g ethanol from 56.6±1.6 g total sugars per L with an ethanol yield of 0.42 g/g available sugars and 0.24 g/g corn stover, which is equivalent to 67% of theoretical ethanol yield from corn stover. The strain produced 25.0±0.3 g ethanol per L in 120 h from AHP pretreated corn stover (10%, w/v) by simultaneous saccharification and fermentation at pH 6.0 and 37^oC with a yield of 0.25 g/g stover. This is the first report on the production of ethanol from AHP pretreated corn stover by a recombinant bacterium.