Subcritical water pretreatment enhanced methane-rich biogas production from the anaerobic digestion of brewer's spent grains.

ABSTRACT This study evaluated the effectiveness of a semi-continuous flow-through subcritical water hydrolysis (SWH) pretreatment of brewer's spent grains (BSG) for subsequent application in the anaerobic digestion (AD) process. BSG pretreatment was conducted at 160 °C and 15 MPa with a flow rate of 10 mL water min -1 and 15 g water g -1 BSG. The results revealed that SWH attacked the hemicellulose structure, releasing arabinose (46.54 mg g -1 ) and xylose (39.90 mg g -1 ) sugars, and proteins (34.89 mg g -1 ). The start-up of anaerobic reactors using pretreated BSG (747.71 L CH 4 kg -1 TVS) increased the methane yield compared with the reactor without pretreatment (53.21 L CH 4 kg -1 TVS). For the process with pretreatment, the generation of electricity (134 kWh t -1 BSG) and heat (604 MJ t -1 ) are responsible for the mitigation of 43.90 kg CO 2 eq t -1 BSG. The adoption of SWH as an eco-friendly pretreatment of biomass for AD could be a technological route to increase methane-rich biogas and bioenergy production, supporting the circular economy transition by reducing the carbon footprint of the beer industry.