Integral valorization of cellulosic and hemicellulosic sugars for biobutanol production: ABE fermentation of the whole slurry from microwave pretreated brewer's spent grain

Abstract In this study, an innovative approach is proposed for the integral valorization of all sugars (cellulosic and hemicellulosic) contained in a lignocellulosic residue, as is brewer's spent grain (BSG), through the production of an advanced biofuel such as biobutanol. For this purpose, the whole slurry obtained in the microwave assisted dilute sulfuric acid pretreatment under optimized conditions (147 °C, 2 min and 1.26% H2SO4) at a biomass loading as high as 15% (w/v) was enzymatically hydrolyzed without previous solid-liquid separation and the highly concentrated solution of sugars recovered was fermented to butanol by Clostridium beijerinckii after detoxification with activated charcoal. In this way, all sugars (pentoses and hexoses) contained in BSG could be fermented using a single bioreactor, leading to 11 g/L of butanol and 16 g/L of ABE, which correspond with butanol and ABE yields of 0.21 and 0.32 g/g, respectively. The mass balance revealed then an overall yield of 91 kg butanol/t BSG and 138 kg ABE/t BSG.