Removal of dissolved methane from digestate in microbial fuel cells

Methane is a renewable energy source obtained through the anaerobic treatment of organic wastes. However, it is also a potent greenhouse gas whose emission into the atmosphere from anthropogenic sources must be avoided. Digestate discharged from anaerobic treatment systems contain important concentrations of dissolved methane, which are released in the subsequent steps, thus effective measures are demanded to prevent these furtive emissions. Here, anaerobic methane oxidation (AMO) is presented as a route for removing dissolved methane from digestate in a microbial fuel cell, with the advantage of energy generation at the same time. With this purpose, the biofilm developed in the anode of a continuous microbial fuel cell was evaluated for its capacity to remove dissolved methane from a digestate originated from a methanogenic reactor treating synthetic wastewater, generating electric current at the same time. Removal of chemical oxygen demand (COD) and dissolved methane occurred through the continuous fed, obtaining a removal of COD of 30 percent, a removal rate of dissolved methane of 14.1 g/m3-day, a simultaneous voltage generation of 311 mV, and an average current density of 125 mA/m2. Coulombic efficiency obtained, 20 percent, demonstrates that oxidation of dissolved methane by the biofilm contributes to the voltage generation. This treatment concept could contribute to prevent the emission of dissolved methane from digested effluents.