Ultrasound-assisted pretreatment of brewer's spent grains to improve enzymatic hydrolysis yield of fermentable sugars

The brewing industry generates a considerable quantity of co-products, with brewer's spent grain (BSG) representing the most abundant. In this study, BSG pretreatment using ultrasound was investigated to enhance the enzymatic hydrolysis yield of fermentable sugars (FS). Several ultrasound systems were evaluated, and the optimal pretreatment conditions were obtained using the ultrasound bath (130 kHz/200 W/27.7 W dm −3 ) and the ultrasound probe (20 kHz/130 W/70.6 W dm −3 ) at room temperature after 30 min, in a 5:100 w v −1 (biomass:water) ratio. Under these conditions, the solid was enriched in cellulose, and the content of hemicellulose and soluble lignin were reduced, without inhibitors formation. Additionally, experiments without ultrasound (silent conditions) were carried out, and no differences were observed in the pretreated BSG in comparison with the untreated BSG. During the enzymatic hydrolysis , the pretreated BSG achieved a FS yield (Y FS ) of 27.5 ± 3.5 g/100 g BSG after pretreatment with ultrasound bath (130 kHz/200 W/27.2 W dm −3 ) and 33.2 ± 3.1 g/100 g BSG using the ultrasound probe (20 kHz/130 W/70.6 W dm −3 ). Additionally, the total FS yield was 2.27 times higher for the ultrasound probe and 2.13 times higher for the ultrasound bath compared to untreated BSG. These results demonstrate that ultrasound-assisted pretreatment can be effectively integrated into industrial processes to valorize BSG, offering a sustainable pathway for biofuel production and reducing waste generation in the brewing industry. This approach aligns with circular economy principles, providing a practical solution for the utilization of brewery by-products. • High efficiency of ultrasound-assisted pretreatment of brewer's spent grains (BSG). • Environmentally friendly technology for BSG pretreatment using water and avoiding hard conditions. • Enrichment of cellulose content in BSG after ultrasound-assisted pretreatment. • High yield of fermentable sugars after enzymatic hydrolysis for pretreated BSG. • Feasible application of circular economy to reduce the waste generation.