Microbial fuel cells (MFCs) present a novel method for simultaneous bioelectricity generation and wastewater treatment.
In this study, an air–cathode MFC with membrane-electrode assembly was operated over three batch cycles (total of 160 days) and results indicated that molasses mixed sewage wastewater (high strength wastewater) containing 9978 mg/L of chemical oxygen demand (COD) could be used as substrate to produce bioelectricity with this system. Three different compositions of wastewater were used as substrate.
The original wastewater, half-diluted wastewater and centrifuged wastewater were used as substrate in MFCs. Maximum voltage output of 762 mV and maximal power density of 382.5 mW/m2 (5.06 W/m3) were obtained with the original wastewater by the 14th day of operation. During this time the system evolved to 0.93 Ω cm−2 internal resistance and 59% removal of the total COD were achieved. Centrifuged wastewater showed poor performance in terms of power production (0.12 mW/m2 or 4.2 mW/m3), presumably due to organic substrate limitations. The MFC running on diluted wastewater showed a power density of 56.17 mW/m2 (2.25 mW/m3), with 70% COD removal.
Energy-Dispersive X-ray spectroscopy (EDX) analysis, together with other characterization methods, confirmed the breakdown of organic compounds in the wastewater, EDX and Scanning Electron Microscopy (SEM) revealed the surface morphology of the materials utilized and showed the evolution in electrode and membrane composition after the long term MFC processes. Denaturing Gradient Gel Electrophoresis (DGGE) profiles showed the presence of mixed populations enclosing the electrochemically-active bacteria that established a biofilm on the anode surface and as such differed from the suspended bacterial community in the anode medium.
These results demonstrate that complex wastewater can be used as a substrate for power generation in MFCs and also can be treated with high COD removal efficiencies.