THF co-solvent pretreatment enhances total sugar recovery and ethanol yields from corn stover at low enzyme loadings

In the biological conversion of lignocellulosic biomass to ethanol, an effective pretreatment strategy is important to obtain high product yields that are critical to economic competitiveness. In this study, a novel tetrahydrofuran (THF) co-solvent strategy enhanced total glucose and xylose recovery from pretreatment and enzymatic hydrolysis over conventional dilute acid (DA) pretreatment. Most notably, unprecedented sugar recovery yields were achieved by THF co-solvent pretreatment at very low enzyme loadings (2 mg enzyme/g glucan). At 2, 5 and 15 mg enzyme/g glucan, co-solvent pretreated solids achieved day 7 total sugar yields of 87.2%, 96.6% and 97.1%, respectively, whereas DA pretreated solids yields were 60.3%, 71.1%, and 82.6% in the same sequence. The highly digestible nature of co-solvent pretreated solids is believed to result from biomass fractionation, in which the majority of the hemicellulose and lignin were removed. Co-solvent pretreatment produced solids with glucan, xylan, and lignin contents of 72%, 4%, and 6%, respectively, while the dilute acid solids contained 52%, 5% and 25% in the same order. Additionally, ethanol yields from simultaneous saccharification and fermentation (SSF) of THF co-solvent pretreated corn stover solids gave much higher ethanol yields at low enzyme loadings (5 mg/g glucan) than solids from DA pretreatment (90% vs. 54%). Because enzymes generally contribute to the largest portion of operating costs aside from feedstock, THF co-solvent pretreatment could prove valuable in lowering biological conversion costs, although further study is needed to understand trade-offs in pretreatment costs and enzyme savings.