Intensified degradation and mineralization of antibiotic metronidazole in photo-assisted microbial fuel cells with Mo-W catalytic cathodes under anaerobic or aerobic conditions in the presence of Fe(III)

A novel strategy to intensify the degradation and mineralization of the antibiotic drug metronidazole (MNZ) in water with simultaneous production of renewable electrical energy was achieved in photo-assisted microbial fuel cells (MFCs). In this system Mo and W catalytic species immobilized onto a graphite felt cathode intensified the cathodic reduction of MNZ under anaerobic conditions and the oxidation of MNZ under aerobic conditions. The aerobic oxidation process was further accelerated in the presence of Fe(III), realizing a combined photo-assisted MFCs and Fenton-MFCs process. The highest rates of MNZ degradation (94.5 +/- 1.4%; 75.6 +/- 1.1 mg/L/h) and mineralization (89.5 +/- 1.1%; 71.6 +/- 0.9 mg/L/h), and power production (251 mW/m(2); 0.015 kWh/m(3); 0.22 kWh/kg COD) were achieved at a Mo/W loading of 0.18 mg/cm(2) with a Mo/W ratio of 0.17:1.0, in the presence of 10 mg/L of Fe(III) and at an incident photon flux of 23.3 mW/cm(2). Photo-generated holes were directly involved into the oxidation of MNZ under anaerobic conditions. Conversely, under aerobic conditions, the photo-generated electrons favored the production of O-2 center dot(-) over center dot OH, while in the presence of Fe(III), center dot OH was predominant over O-2 center dot(-), explaining the intensification of the MNZ mineralization observed. This study demonstrates an alternative and environmentally benign approach for the intensification of the removal of the antibiotic MNZ in water and possibly other contaminants of emerging concern by combining photo-assisted MFCs and Fenton-MFCs in a single process with simultaneous production of renewable electrical energy.