Efficient dairy wastewater treatment and power production using graphite cylinders electrodes as a biofilter in microbial fuel cell

Abstract The goal of this work was to evaluate the efficiency of an air-cathode microbial fuel cell (MFC), operating in semi-continuous downflow mode. The MFC was inoculated with a consortium of Shewanella oneidensis and Clostridium butyricum. It was fed using a synthetic medium with progressively increasing dairy wastewater (DWW) concentrations in the startup (15 days), acclimatization (30 days), and treatment (75 days) phases. This approach enabled removal of 89% of the total COD and 91% of the total BOD, after 90 days of operation. These efficiencies were improved with step change of external resistance (Rext.) from 1.0 to 0.5 kΩ. Electrochemical impedance spectroscopy analysis indicated the formation of more complex biointerface associated with change of Rext. The maximum power density was 3.5 W∙m-3 at 1.0 A∙m-3, during the startup, while the Coulombic efficiency (CE) was 4.5 at the end of the operation. The MFC process showed high efficiency for the removal of organic nitrogen (85%), phosphorus (92%), nitrate (100%), and sulfate (88%). Additionally, the treated DWW effluent presented no acute toxic effect towards Daphnia similis. Overall, it could be concluded that applying gradual increments of the DWW concentration resulted in highly efficient treatment.