Subcritical water hydrolysis of grape pomace as a sustainable pretreatment for anaerobic digestion in a biorefinery concept

This study presented a sustainable bioprocess based on the integration between subcritical water hydrolysis (SWH) and anaerobic digestion (AD) for the valorization of grape pomace (Vitis vinifera L.) in a biorefinery concept. The hydrolysate obtained by SWH (150 C, 150 bar, 10 mL min- 1, and solvent-to-feed ratio of 30 g water g(-1) grape pomace) was composed by glucose (0.37 g kg(- 1)), arabinose (0.25 g kg(- 1)), fructose (1.87 g kg(- 1)), and cellobiose (0.62 g kg(- 1)) as major sugars, demonstrating the rupture of the carbohydrates in the biomass and release of monosaccharides from the structure. The application of grape pomace hydrolysate obtained by SWH in AD process increased the methane yield (256.88 L CH4 kg(- 1) TVS) when compared with the AD without pretreatment (35.74 L CH4 kg(-1) TVS) after 40 days of experiment. The biogas produced in the process integrating SWH and AD (42.76 L kg(- 1) grape pomace) can be converted into electricity (72.33 kWh t(-1)) and heat (390.17 MJ t(-1)), mitigating greenhouse gases emissions (27.27 kg CO2-eq t(- 1)) and contributing for the development of a sustainable industry. The pretreatment favored the development of a stable and diverse microbial community, highlighting the presence of Clostridia, Lachnospiraceae and Trichococcus. The digestate generated after fermentation presented an IC50 of 8.8 g/L under lettuce germination, demonstrating that could be applied as biofertilizer in agriculture. In conclusion, the novel bioprocess integrating SWH and AD can be a promising alternative for the valorization of grape pomace in a biorefinery concept, producing biomethane, bioenergy, and biofertilizer from a by-product generated worldwide.