Optimization of bioethanol production from a brewers' spent grain and sugarcane molasses mixture utilizing Saccharomyces cerevisiae

This study investigates the production and optimization of bioethanol from a blend of brewer's spent grain (BSG) and sugarcane molasses to enhance process efficiency and reduce manufacturing costs. BSG, a lignocellulosic biomass, underwent microwave-assisted alkaline hydrogen peroxide pretreatment to improve its fermentability. The pretreatment employed a 4% v/v hydrogen peroxide solution at a pH of 11.5 and a solid-to-liquid ratio of 10% w/v, with optimal conditions determined through central composite design experiments. The optimal microwave power and irradiation time were found to be 282.25 W and 7.27 min, respectively. Additionally, dilute phosphoric acid hydrolysis was optimized using response surface methodology, considering acid concentration (2-4% v/v), hydrolysis time (20-60 min), and molasses mixing proportion (0-50% w/w) to maximize reducing sugar concentration. The optimal conditions were identified as an acid concentration of 3.16% v/v, hydrolysis time of 42.5 min, and molasses proportion of 38.1% w/w. Bioethanol was then produced by fermenting the hydrolysate with Saccharomyces cerevisiae for 72 h, followed by simple distillation. The bioethanol was characterized using FTIR spectroscopy, density, viscosity, and flash point tests, with a final concentration of 39.34% v/v. The yield of bioethanol was 0.28 g per gram of dry BSG. This research demonstrates an effective approach for converting waste materials into bioethanol, contributing to sustainable waste-to-energy solutions.