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

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 (R-ext.) from 1.0 to 0.5 k Omega. Electrochemical impedance spectroscopy analysis indicated the formation of more complex biointerface associated with change of R-ext. 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.