Conversion of biomass to biofuels: Integration of a ternary deep eutectic solvent pretreatment and microbial fermentation for C2-C4 bioalcohols production from lignocellulose

Efficient production of second-generation biofuels (bioethanol and biobutanol) from renewable lignocellulosic biomass holds strategic importance and aligns with sustainability objectives. However, it poses a persistent long-term challenge because of the biomass recalcitrance. Therefore, development of mild, environmentally friendly biomass pretreatment methods is a critical concern. To this end, in this study, a ternary deep eutectic solvent (DES) was synthesized with choline chloride , succinic acid , and glycerol at a molar ratio of 1:0.5:0.5. The ternary DES pretreatment largely enhanced glucan digestibility of corn stover (CS) to 94.7 % which was 4.60-fold to untreated CS. Mechanism of improved enzymatic efficiency of DES-pretreated CS was revealed by characterization methods such as SEM, XRD, and FTIR technologies. In addition, adding 1.0 % H 2 SO 4 to the ternary DES further increased enzymatic hydrolysis yield to nearly 100 %. Subsequently, the H 2 SO 4 -assisted DES-pretreated CS was used as substrate to produce C2-C4 bioalcohols (ethanol and butanol) by microbial fermentations. The results indicate that 46.6–49.2 g/L ethanol could be obtained by S. cerevisiae under separate hydrolysis and fermentation (SHF), and simultaneous saccharification and fermentation (SSF) strategies. Meanwhile, up to 11.9 g/L butanol was achieved from CS hydrolysate by Clostridium acetobutylicum with fed-batch mode. Finally, an artificial microbial consortium by co-culturing C. acetobutylicum and S. cerevisiae was developed which efficiently co-produced 12.4 g/L biobutanol and 5.7 g/L bioethanol from CS hydrolysate. Overall, this study provides a sustainable and green pretreatment technology that deconstruct lignocellulose and possess universality to produce various low-carbon bioalcohols by microbial fermentations.