Efficient Bioethanol Production from Spent Coffee Grounds Using Liquid Hot Water Pretreatment without Detoxification

Coffee beans, a popular commodity in the world, are processed into coffee, which generates a considerable quantity of spent coffee grounds (SCGs). However, SCGs, a byproduct rich in hemicellulose, poses a challenge due to fermentable sugar loss during conventional pretreatment. This study investigates the efficient production of bioethanol from SCG using an optimized liquid hot water (LHW) pretreatment combined with separate hydrolysis and fermentation (SHF) process. LHW pretreatment at 180 °C for 20 min with a high solid-to-liquid ratio (SLR) of 1:6 (w/v) was optimized to disrupt the lignocellulosic structure and retain high levels of fermentable sugars, which included mannose and glucose. This approach achieved a bioethanol concentration of 15.02 ± 0.05 g/L and a productivity rate of 1.252 g/(L·h), demonstrating the efficiency of this integrated process. Interestingly, the high SLR LHW pretreatment significantly reduces water usage and enhances product concentration, offering a promising, environmentally friendly, and economically viable method for industrial bioethanol production from SCGs without the necessity of detoxification.