The performance of biochar waste-derived electrodes in different bio-electrochemical applications

This work studied the performances of two ad hoc biochar-based cathode materials: one obtained from pyrolysis of the organic fraction of municipal solid waste (OW) and the other of wood chips (WC), in the context of three different bio-electrochemical reactors’ scope: MFC, MEC and MES. Cathodes were characterized through composition, pH, specific surface area and infrared spectroscopy; then production of electricity, methane (CH4), and volatile fatty acids (VFAs) from carbon dioxide (CO2) was described, and finally the microbial community was explored through 16S rRNA gene sequencing. WC-based electrodes performed better than OW-based ones. WC (200 ± 25 mV) generated twice the amount of electricity compared to OW (100 ± 10 mV) in MFC modality. In MEC modality, WC achieved both higher CH4 production and concentration (3.6 ± 0.7 mL per day, 73.2 ± 3.9 % v/v, respectively) than OW (3.0 ± 0.3 mL per day, 70 ± 8 % v/v, respectively). In MES modality, WC produced ten times more acetic acid (0.3 ± 0.13 g L−1 per day) than OW (0.03 ± 0.04 g L−1 per day). The better performance of the WC-biochar cathode was attributed to its higher Brunauer–Emmett–Teller (BET) value and its carbonaceous graphite-like structure. NGS analysis highlighted the presence of specific genera of microorganisms leading to the differential functioning of the systems.