Bioelectromethanogenesis reaction in a tubular microbial electrolysis cell (MEC) for biogas upgrading

The utilization of a pilot scale tubular Microbial Electrolysis Cell (MEC), has been tested as an innovative biogas upgrading technology. The bioelectromethanogenesis reaction permits the reduction of the CO2 into CH4 by using a biocathode as electrons donor, while the electroactive oxidation of organic matter in the bioanode partially sustains the energy demand of the process. The MEC has been tested with a synthetic wastewater and biogas by using two different polarization strategies, i.e. the three-electrode configuration, in which a reference electrode is utilized to set the potential at a chosen value, and a two-electrode configuration in which a fixed potential difference is applied between the anode and the cathode. The tubular MEC showed that the utilization of a simple two electrode configuration does not allow to control the electrodic reaction in the anodic chamber, which causes the increase of the energy consumption of the process. Indeed, the most promising performances regarding the COD and CO2 removal have been obtained by controlling the anode potential at +0.2 V vs SHE with a three electrode configuration, with an energy consumption of 0.47 kWh/kgCOD and 0.33 kWh/Nm3 of CO2 removed, which is a comparable energy consumption with respect the available technologies on the market.