| Microbial fuel cell (MFC) as a device of degrading organic compounds to generate electricity by the biocatalysis of exoelectrogens attracts extensive attention of researchers worldwide. MFCs are classified into mediator-based and mediator-less MFC according to the electron transfer mode from the bacteria to the anode.However, the exogenous mediators are of high cost, short lifetime and toxicity to the microorganisms. Therefore, mediator-less MFCs have been extensively investigated in recent years. In this study, two types of mixed bacteria inoculated two-chamber MFCs were constructed. The start-up period, the performance and mechanism of electricity production were investigated systematically. In addition, nano-CeO2modified anode and static magnetic field were applied to improve the electricity generation of MFC.The study on the start-up period was conducted in H type MFC. The results showed that the open circuit voltage started to change before the closed circuit voltage. Anodic and cathodic potential reduced during the start-up, and the changes of MFC voltage dominated by the anode. The changes of output voltage revealed the decrease of the internal resistance. Anode charge transfer resistance (Rct) reduced during the start-up period. After the reactor start-up, the electricity production of two types of MFCs was examined. The maximum power density of H-type MFC was0.70W/m2, lower than1.61W/m2of cylindrical MFC. The results of electrochemical impedance spectroscopy (EIS) implied that the ohmic and diffusion resistances of cylindrical MFC were lower than that of H-type MFC, while the anode charge transfer resistance was higher. The external resistance and substrate concentration of influent would influence the coulombic efficiency. Reducing the external resistance and substrate concentration can improve the coulombic efficiency of MFC. The H-type MFC successfully recovered elelctricity from actual wastewater while treating the wastewater at the same time. The maximum power density achieved0.041W/m2. The COD of effluent declined considerably, with COD removal efficiency of45.9%. The pH and conductivity of anodic effluent also declined.The anode surface was observed by scanning electron microscope (SEM). It was found that the anode surface was covered by a certain thickness of the biofilm after long-time operation of MFC. And based on the results of cyclic voltammetry (CV) for anodic mixed effluent and anodic bioflm, it was confirmed that the main mechanism of power production for the exoelectrogens was through direct transfer of electrons to the electrode by bacteria and not by bacteria-produced mediators. The analysis of microbial diversity showed that the main bacteria were the same on the anodes of two-types of MFCs. And the MFCs anode biofilm were dominated by bacteria which were phylogenetically very closely related to Proteobacteriua. Rhodopseudomonus-like and Arcobucler-like species as the representative electrochemically active bacteria were found to be integral members of bacterial community in the two-types of MFCs. Additionally, bacterial community also contained Firmicutes-Uke and Bacteroidetes-like species.Nano ceria was used to modify the carbon felt anode in cylindrical mediator-less MFC. Ceria nanoparticles were prepared by sol-gel method and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Morphology characterization showed that the synthesized product is fluorite structure CeO2crystal and the average particle size is around30nm. The modified carbon felt electrode was prepared by sol-dipping method. CV results implied that the modified anode had the larger specific surface area and the bioelectrochemical activity of direct electron transfer based exoelectrogens were promoted by nano-CeO2. The MFC with the modified anode obtained the higher closed circuit voltage resulting from the lower anode potential, the higher maximum power density (2.94W/m), and the lower internal resistance (77.1Ω). EIS results revealed that the anodic charge transfer resistance of the MFC was lower with the modified anode. All the results demonstrate that the nano-CeO2can be an effective anodic catalyst for enhancing the power generation of mediator-less MFC.MFCs were exposed to static magnetic field (MF) of different directions (vertical and parallel to the anode) and field strengths (0mT,100mT,200mT, and300mT), and the electricity production of the MFCs under the influence of the magnetic field was investigated using electrochemical methods.The results showed that a certain intensity of magnetic field improved the MFC electricity production, but there was a difference for MFCs when different MF directions were applied. When the magnetic field direction was vertical to the anode, the MFC obtained the higher maximum power density of1.93W/m2. In the study on the influence of different magnetic field intensity, the results showed that the start-up periods of MFCs in MF were shorter than that without MF. The MFC with a100-mT MF needed the shortest time (7days) to obtain a stable voltage output,4days earlier than the MFC without magnetic field. The maximum power density of1.56W/m2was for the field strength of200mT, which was the best among the MFCs with different field strengths. The impact of the MF on the charge transfer resistances of the anode, cathode, and whole MFC were analyzed by EIS. The simulated results showed that anode Rct values were much higher compared with that at the cathode. The whole cell and anode Rc, values were reduced by56.6%and57.2%, respectively, for the200-mT MF. It was also found that there was an optimal intensity MF range for enhancing the electricity production of MFC. |
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