Efficient L-lactic acid production from corncob by deep eutectic solvent pretreatment with reduced washing demand

Deep eutectic solvent (DES), characterized by low toxicity and selective lignin removal capacity, serves as highly effective pretreatment agents for lignocellulose. However, DES pretreatment requires multiple washing cycles for residue removal, consequently elevating operational costs and wastewater generation. In this study, a sustainable lignocellulosic biorefinery approach with low washing demand was proposed for L-lactic acid production from corncob. Firstly, the choline chloride/lactic acid ([ChCl][LA]) DES pretreatment condition was optimized to be water content of 30 %, L/S ratio of 20:1, 110 °C for 60 min. This optimization enhanced the cellulose retention (from 73.2 % to 83.2 %) and xylan retention (from 19.3 % to 40.7 %) in residue solid, while achieving relatively high delignification (87.6 %) and enzymatic hydrolysis yield (89.4 %). Importantly, the solvents usage (water and ethanol) during washing process was reduced by 57.1 %. Then, the recycled [ChCl][LA] DES was evaluated for its performance in corncob pretreatment, and it displayed high pretreatment efficiency even after 5 rounds of reuse. Finally, the cellulose and xylan in the pretreated residue were utilized through simultaneous saccharification and co-fermentation (SSCF) by Bacillus coagulans, achieving 77.0 g/L L-lactic acid with a yield of 0.38 g/g corncob. This study provides a promising low-washing-demand biorefinery process for L-lactic acid production from lignocellulose biomass.