Deep eutectic solvent pretreatment of Bambara groundnut haulm for enhanced saccharification and bioethanol production

Five deep eutectic solvents (DES) were screened for their effectiveness in improving biosugar yield in Bambara groundnut haulm (BGH) for bioethanol production. Choline chloride-lactic acid (ChCl-LA) treatment provided the most promising result and was further optimised by investigating the effect of temperature and time on cellulose loss and enzymatic sugar yield. ChCl-LA pretreatment at 100 °C for 1 h was observed to be the best condition for hemicellulose (54.5%) and lignin (60.7%) removal along with optimum sugar recovery of 94.8%. The resulting hydrolysate was concentrated and fermented for 72 h with Saccharomyces cerevisiae BY4743, and a maximum ethanol concentration of 11.57 g/L was achieved with an ethanol yield of 0.38 g/g sugar and productivity of 0.19 g/L/h. From the results obtained, it is evident that deep eutectic solvents are effective for breaking the recalcitrance in BGH due to their high delignification capacity. Furthermore, a recovery of the amorphous glucose and xylose in the BGH prior to DES pretreatment is vital to prevent sugar loss, thereby improving the biosugar yield for bioethanol production.