Supplementation of Carbon-Based Conductive Materials and Trace Metals to Improve Biogas Production from Apple Pomace

Due to its high water and organic content, management of apple pomace (AP) imposes several waste management challenges on the apple juice and cider producing industries. On the other hand, bioconversion of AP into biogas provides an excellent possibility to reduce the environmental challenge posed the management of AP waste along with producing renewable energy in the form of methane. This study investigated the effect of carbon-based conductive materials (biochar and graphene) and trace metals supplementation to improve biogas production from AP. The results indicated that supplementation of biochar, trace metals and graphene improve the biogas production from AP significantly. Trace metal and biochar supplementation at a COD concentration of 6,000 mg/L resulted in 7.2 and 13.3% increase in the biogas production, respectively. When trace metals and biochar were supplemented together, the biogas production increased by 22.7%. This synergistic effect was also observed at the COD concentration of 12,000 mg/L. The improvement in the biogas formation was significantly higher for graphene supplemented reactors (27.8%). Moreover, biochar and trace metals supplementation also led to 19.6 and 23.0% increase in the methane yield relative to the reactor fed only with AP, respectively. These results suggest that anaerobic digestion supplemented with carbon-based conductive materials and trace metals is viable option of valorizing apple pomace.