A biorefinery based on brewer`s spent grains: Arabinoxylans recovery by microwave assisted pretreatment integrated with butanol production

Abstract

This study proposes an integrated biorefinery of brewer’s spent grain (BSG) based on the application of a microwave pretreatment to obtain bioproducts, such as arabinoxylans (AX) and an advanced biofuel, such as biobutanol. A prehydrolysate with 17 g/L AX was obtained at 172 °C and 0.38 M NaOH, which were subsequently precipitated using an organosolvent process, recovering 133 kg AX/t BSG. The subsequent enzymatic hydrolysis with endo-xylanases significantly increased the concentration of oligomers with 2–6 units of xylose. The presence of oligosaccharides with a degree of polymerization (DP) from 3 to 27 was confirmed by MALDI-TOF MS. On the other hand, the pretreated solid residue obtained in the microwave assisted alkaline pretreatment was enzymatically hydrolyzed with cellulases and fermented by Clostridium beijerinckii, producing 9.9 g/L butanol (28 kg butanol/t BSG and 37 kg ABE/t BSG). Thus, the potential for the efficient use of BSG in an integrated biorefinery was demonstrated.