Sustainable bioprocess combining subcritical water pretreatment followed by anaerobic digestion for the valorization of jabuticaba (Myrciaria cauliflora) agro-industrial by-product in bioenergy and biofertilizer

Abstract

The management of agri-food by-products has received worldwide attention due to concerns about the environmental impacts caused by incorrect deposition. This study presented a sustainable bioprocess combining subcritical water pretreatment (SWP) followed by semi-continuous anaerobic digestion (AD) for the valorization of jabuticaba (Myrciaria cauliflora) agro-industrial by-product in bioenergy and agricultural fertilizer. The SWP was conducted at 180 °C, 15 MPa, water flow rate of 10 mL min−1, solvent to feed of 22.5 g g−1, and a kinetic time of 45 min. The AD process was operated in semi-continuous mode under mesophilic and methanogenic conditions. The results demonstrated that the hydrolysate presented glucose (5.78 g L−1), fructose (3.63 g L−1), arabinose (1.82 g L−1), and cellobiose (1.28 g L−1) as major compounds. The use of pretreated jabuticaca by-product increased the methane yield (239.04 L CH4 kg−1 TVS) in the designed bioprocess combining SWP and AD when compared to the AD without pretreatment (42.31 L CH4 kg−1 TVS). The methane produced in the bioprocess with SWP followed by AD can generate 543 kWh t−1 of electricity and 2,243.17 MJ t−1 of heat, avoiding a total of 177.54 kg CO2-eq t−1. The digestate generated after AD can be used as a biofertilizer up to a concentration of 0.3 g L−1, without toxic effects on the germination of Lactuca sativa. Finally, the sustainable bioprocess designed could be an alternative to the management of jabuticaba by-product within a circular economy framework, producing bioenergy and agricultural fertilizer that can reduce greenhouse gas emissions and environmental pollution in the food industry.