【作者】 殷瑶；

【导师】 刘勇弟； 黄光团；

【作者基本信息】 华东理工大学 ， 环境科学与工程， 2013， 博士

【摘要】 微生物燃料电池(Microbial fuel cell, MFC)作为一种通过胞外产电菌的生物催化作用降解有机化合物产生电能的装置受到了全世界的广泛关注。MFC按照电子由细菌阳极的传递过程分为两类：有介体MFC和无介体MFC。然而,由于外源介体的成本高、寿命短和对微生物的毒性,无介体MFC成为近年研究的重点。本论文以无介体MFC为研究对象,构建了以污水中混合菌接种的两类双室无介体MFC,系统地研究了无介体MFC的启动过程、产电性能及产电机理。同时以提高MFC系统的产电性能为目标,采用纳米二氧化铈(CeO2)修饰阳极及阳极加载磁场的方法强化MFC产电。以H型MFC为研究对象考察电池启动过程发现,MFC开路电压的变化要先于闭路电压。阳极电位在启动期间降低的幅度远大于阴极电位,电池启动过程电压的变化由阳极主导。启动过程中闭路电压的变化对应了电池内阻的变化。阳极电荷转移内阻随着启动过程的进行呈现不断下降的趋势。在MFC稳定产电阶段,H型MFC的最大功率密度达到0.70W/m2,低于圆柱型MFC的最大功率密度1.61W/m2。电化学阻抗谱(Electrochemical impedance spectroscopy, EIS)测试结果表明,圆柱型MFC的欧姆内阻和扩散内阻均小于H型MFC,而阳极电荷转移内阻则大于H型MFC。考察外电阻及进水基质浓度对库仑效率的影响发现,降低电池外阻,减小进水基质浓度可以提高电池的库仑效率。在H型MFC中利用实际废水成功实现产电及同步污水处理,MFC最大功率密度达到0.041W/m2。经过H型MFC处理后,污水COD明显下降,去除率为45.9%,pH和电导率也有一定程度的下降。利用扫描电镜观察MFC阳极发现,经过长时间的运行,MFC阳极表面覆盖有一定厚度的生物膜。通过循环伏安法(Cyclic Voltammetry, CV)对阳极出水混合液和阳极生物膜进行测试,确认所构建的无介体MFC的电子传递类型为直接电子传递,而不是依靠介体传递。对产电菌群落结构的分析可知,采用相同初沉池水样接种,均以乙酸钠为基质的H型MFC和圆柱型MFC其阳极生物膜富集的主要菌群是相同的。MFC阳极生物膜菌以变形菌Proteobacteriaa为主,存在典型的属于α-Proteobacteria纲的红假单胞菌(Rhodopseudomonas)属产电菌及ε-Proteobacteria纲的弓形菌(Arcobacter)属产电菌。此外,阳极上的优势菌群还包括厚壁菌门(Firmicutes)和拟杆菌门(Bacteroidetes)的菌种。在圆柱形MFC中,采用纳米CeO2修饰碳毡阳极强化MFC产电。利用溶胶凝胶法制备纳米CeO2颗粒并采用X-射线衍射(X-ray diffraction, XRD)和透射电子显微镜(Transmission electron microscopy, TEM)进行材料表征。结果显示合成产物为萤石结构的CeO2晶体,颗粒的平均粒径分布在30nm左右。通过溶胶浸渍法制备纳米CeO2修饰的碳毡电极。CV测试发现修饰阳极具有更大的比表面积,并且能够提高产电菌的生物电化学活性。相比对照MFC,应用纳米Ce02修饰阳极的MFC获得了更低的阳极电位,从而提高了电池的闭路电压。修饰阳极的MFC最大功率密度为2.94W/m2,内阻为77.1Ω。纳米Ce02修饰阳极促进了电池的产电性能。EIS结果表明碳毡阳极的电荷转移内阻显著下降。纳米Ce02作为催化剂可以有效改善无介体MFC的阳极性能。采用阳极加载磁场强化MFC产电。将MFC置于不同方向(与阳极垂直、平行)、不同强度(0mT,100mT,200mT,300mT)的稳恒磁场下,采用多种电化学手段考察稳恒磁场对MFC产电特性的影响。结果发现,一定强度的磁场能够强化MFC的产电,但不同磁场方向对MFC的影响有差异。当磁场方向与阳极垂直时,强化效果较好；垂直磁场-MFC的最大输出功率达到1.93W/m2。阳极加载磁场加速了MFC的启动,加载100mT磁场的MFC启动最快,闭路电压于第7天达到稳定,相比不加载磁场的MFC提前了4d。MFC在加载200mT磁场强度时,性能达到最佳,其最大功率密度为1.56W/m2。采用EIS分析磁场对全电池、阴极、阳极的电荷转移内阻的影响。拟合结果显示,阳极电荷转移内阻远高于阴极。在200mT磁场强度下,全电池和阳极的电荷转移内阻分别下降了56.6%和57.2%。结果也发现磁场强化MFC产电存在合适的强度范围。更多还原

【Abstract】 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.更多还原