Electrochemical characteriztion of the bioanode during simultaneous azo dye decolorization and bioelectricity generation in an air-cathode single chambered microbial fuel cell

To achieve high power output based on simultaneously azo dye decolorization using microbial fuel cell (MFC), the bioanode responses during decolorization of a representative azo dye, Congo red, were investigated in an air-cathode single chambered MFC using representative electrochemical techniques. It has been found that the maximum stable voltage output was delayed due to slowly developed anode potential during Congo red decolorization, indicating that the electrons recovered from co-substrate are preferentially transferred to Congo red rather than the bioanode of the MFC and Congo red decolorization is prior to electricity generation. Addition of Congo red had a negligible effect on the Ohmic resistance (R_ohm) of the bioanode, but the charge-transfer resistance (R_c) and the diffusion resistance (R_d) were significantly influenced. The R_c and R_d firstly decreased then increased with increase of Congo red concentration, probably due to the fact that the Congo red and its decolorization products can act as electron shuttle for conveniently electrons transfer from bacteria to the anode at low concentration, but result in accelerated consumption of electrons at high concentration. Cyclic voltammetry results suggested that Congo red was a more favorable electron acceptor than the bioanode of the MFC. Congo red decolorization did not result in a noticeable decrease in peak catalytic current until Congo red concentration up to 900 mg l⁻¹. Long-term decolorization of Congo red resulted in change in catalytic active site of anode biofilm.     

微生物燃料电池最新研究进展

介绍了微生物燃料电池(MFC)的原理、组成和特点,并针对MFC功率密度过低、构造成本高等问题,从筛选优势产电微生物、改善MFC的构造、优化电极材料以及提高电子传递效率等方面进行了介绍,同时还提到了提高产电性能的各种途径,最后对MFC的发展前景进行了展望.     

Effect of temperature on the performance of microbial fuel cells

Single and double chamber microbial fuel cells (MFCs) were tested in batch mode at different temperatures ranging from 4 to 35 °C; results were analysed in terms of efficiency in soluble organic matter removal and capability of energy generation. Brewery wastewater diluted in domestic wastewater (initial soluble chemical oxygen demand of 1200 and 492 mg L⁻¹ of volatile suspended solids) was the source of carbon and inoculum for the experiments. Control reactors (sealed container with support for biofilm formation) as well as baseline reactors (sealed container with no support) were run in parallel to the MFCs at each temperature to assess the differences between water treatment including electrochemical processes and conventional anaerobic digestion (in the presence of a biofilm, or by planktonic cells). MFCs showed improvements regarding rate and extent of COD removal in comparison to control and baseline reactors at low temperatures (4, 8 and 15 °C), whilst differences became negligible at higher temperatures (20, 25, 30 and 35 °C). Temperature was a crucial factor in the yield of MFCs both, for COD removal and electricity production, with results that ranged from 58% final COD removal and maximum power of 15.1 mW m⁻³ reactor (8.1 mW m⁻² cathode) during polarization at 4 °C, to 94% final COD removal and maximum power of 174.0 mW m⁻³ reactor (92.8 mW m⁻² cathode) at 35 °C for single chamber MFCs with carbon cloth-based cathodes. Bioelectrochemical processes in these MFCs were found to have a temperature coefficient, Q10 of 1.6.A membrane-based cathode configuration was tested and gave promising results at 4 °C, where a maximum power output of 294.6 mW m⁻³ reactor (98.1 mW m⁻² cathode) was obtained during polarization and a maximum Coulombic efficiency (Y_Q) of 25% was achieved. This exceeded the performance at 35 °C with cloth-based cathodes (174.0 mW m⁻³; Y_Q 1.76%).     

A dual-chamber microbial fuel cell with conductive film-modified anode and cathode and its application for the neutral electro-Fenton process

This study reports on the modification of the anode and the cathode in a dual-chamber microbial fuel cell (MFC) with a polypyrrole (PPy)/anthraquinone-2,6-disulfonate (AQDS) conductive film to boost its performance and the application of the MFC to drive neutral electron-Fenton reactions occurring in the cathode chamber. The MFC equipped with the conductive film-coated anode and cathode delivered the maximum power density of 823 mW cm⁻² that was one order of magnitude larger than that obtained in the MFC with the unmodified electrodes. This was resulted from the enhanced activities of microbial metabolism in the anode and oxygen reduction in the cathode owing to the decoration of both electrodes with the PPy/AQDS composite. The MFC with the modified electrodes resulted in the largest rate of H₂O₂ generation in the cathode chamber by the two-electron reduction of O₂. The increase in the concentration of H₂O₂ was beneficial for the enhancement in the amount of hydroxyl radicals produced by the reaction of H₂O₂ with Fe²⁺, thus allowing an increased oxidative ability of the electro-Fenton process towards the decolorization and mineralization of an azo dye (i.e., Orange II) at pH 7.0.     

不同温度下微生物燃料电池的运行特性

实验采用双室型微生物燃料电池（MFC）,以生活废水中厌氧菌作为生物催化剂,葡萄糖为燃料,通过5个不同温度条件下的间歇运行,应用循环伏安、交流阻抗、极化测试等电化学方法考察温度对电池产电性能的影响。结果表明,一定温度范围内,提高温度有助于增强微生物的电化学活性,降低传荷阻抗,提高电池输出功率密度和交换电流密度。32 ℃时,电池产电效能最佳,电池功率密度和交换电流密度分别达到156.2 mW/m2和8.02×10?5 mA/m2,温度太低或太高均不利于细菌的电化学活性。体系温度为18 ℃、25 ℃、32 ℃、39 ℃、46 ℃时,传荷阻抗Rct在阳极内阻中占的比例分别为97.99%、84.02%、47.36%、91.30%、99.61%,说明传荷阻抗在阳极内阻中占绝对份额,MFC是传荷过程控制下的电化学反应体系。     

带有蛇形流场的微生物燃料电池串联堆性能特性

以四个成功启动的带有蛇形流场的单电池构造了微生物燃料电池串联堆(MFCS-S),测试了MFCS-S性能,探讨了其性能提升的限制因素,研究了增加反极电池阴、阳极电解液流量,采取混联的方式运行,移除反极电池和反接反极电池对电堆性能的影响。实验结果表明:MFCS-S在输出电压为2.11 V时获得最大功率密度(2226 mW·m^-2);在一定电流条件下,性能较差的单电池发生电压反极,这是限制MFCS-S性能提高的主要原因;增加反极电池阴、阳极流量虽然不能较大幅度地改善单电池反极,但是却能大幅度提高电堆功率密度;采用混联方式运行不但可以有效避免电池反极,而且可以大幅度提高电堆功率密度;移除反极电池并不能有效地避免电池的反极,反接反极电池反而进一步加剧反极。     

Influence of NO3 and SO4 on power generation from microbial fuel cells

Potential competition in terms of electron transfer from bacteria to electron acceptors such as nitrate (NO₃) and sulfate (SO₄) or the anode of a microbial fuel cell (MFC) was investigated to determine how alternative electron acceptors would influence power generation in an MFC. The cell voltage was not initially affected when these electron acceptors were introduced into the MFCs. However, the presence of NO₃ decreased the CE of the MFC compared to the injections of SO₄ or control salt (sodium chloride). This suggests that the growth of nitrate-reducing bacteria independent of the microbial populations on the MFC anode were not utilizing the anode as an electron acceptor, rather, they were consuming organic carbon in the anodic chamber of the MFC, resulting in a decrease of the CE of this MFC with no immediate impact on power output. This suggests that the bacterial consortium in the nitrate-MFC still preferred the anode over nitrate as the electron acceptor, although the theoretical reduction voltage of nitrate (+0.74 V) is higher than the reduction voltage in an MFC air cathode (as high as +0.425). These results are useful when considering whether MFC technology can be applied in situ to enhance biodegradation of organic contaminants in the presence of alternative electron acceptors.     

微生物燃料电池处理偶氮含盐废水的产电性能和降解过程

偶氮含盐废水生化处理流程复杂、电耗高,且降解机理尚不明确。本研究基于酸性重铬酸钾法水热处理获取改性阳极,进而构建微生物燃料电池（microbial fuel cell,MFC）对偶氮含盐废水进行处理。考察了不同二价阴离子对MFC产电性能和降解有机物效果的影响,并探究了MFC对直接红13的降解机理。结果表明,偶氮含盐废水中含有硫酸钠时的产电性能高于含有碳酸钠的情况,MFC最大功率密度为265.38mW/m²、最大电流密度为1.10A/m²;MFC处理偶氮含盐废水时,对直接红13的去除率低于无额外添加盐时的效果（71.13%）,对葡萄糖共基质的降解影响程度为：添加硫酸钠>添加碳酸钠>无额外添加盐。微生物群落和降解产物分析表明,MFC阳极生物膜通过变形菌门、拟杆菌门等微生物的协同作用实现了对直接红13的生物电化学降解,产电下降解产物以还原产物芳香胺为主。     

Removal of organic matter in freshwater sediment by microbial fuel cells at various external resistances

BACKGROUND: Besides acting as power sources, sediment microbial fuel cells (SMFC) could be explored to remove organic matter in sediments and then maintain the water quality in aquatic environments. Until now, the role of the external resistance in the removal of organic matter by SMFC has received only limited attention. In this work, the removal of organic matters in sediments by lab‐scale SMFCs at five different external resistances from 10 to 1000 Ω was investigated. RESLUTS: The external resistance in SMFCs had a strong influence on the working potentials of anodes. Application of a 100 Ω external resistance corresponded to the lowest internal resistance and highest removal efficiency of organic matter in sediment. The removal efficiency of readily oxidizable organic matter in a layer of sediment with a distance of 0–1 cm to the anode reached 28.3 ± 1.9% at 100 Ω external resistance after 2 months of operation. In addition, there existed a linear relationship between current production from the SMFCs and removal efficiency of organic matter from sediments. CONCLUSIONS: The performance of SMFCs for the removal of organic matter in sediments could be enhanced through the selection of optimal external resistance. The SMFC real‐time removal process could be monitored remotely using current generated. Thus, SMFCs offer an attractive alternative for the environmentally‐friendly removal of organic matter in sediments. Copyright © 2010 Society of Chemical Industry     

On the repeatability and reproducibility of experimental two-chambered microbial fuel cells

The capability of the experimental systems used in two-chambered microbial fuel cell experimentation was tested in terms of repeatability and reproducibility. The optimal number of replicates needed to discriminate between responses of technical interest, both in open-circuit and closed-circuit experiments was studied. For N = 4 replicates, these differences were set to 9.0% COD_R units, 261 mV and 63 mg/L in VFAs for open-circuit experiments and 3.6%, 30.2 mV and 45 mg/L in closed circuit experiments. Cycling operation with several reactor refills using fresh wastewater and keeping the same biofilm between cycles almost has no influence in COD_R and VFAs but voltage standard deviation reduces by one half between the first and fourth cycle. This study takes part by the option of increasing the number of replicates because although it may have lower repeatability, the amount of data generated per unit time is larger than running the experiments in cycles.     

Multi-objective steady-state optimization of two-chamber microbial fuel cells

A microbial fuel cell (MFC) is a novel promising technology for simultaneous renewable electricity generation and wastewater treatment. Three non-comparable objectives, i.e. power density, attainable current density and waste removal ratio, are often conflicting. A thorough understanding of the relationship among these three con-flicting objectives can be greatly helpful to assist in optimal operation of MFC system. In this study, a multi-objective genetic algorithm is used to simultaneously maximizing power density, attainable current density and waste removal ratio based on a mathematical model for an acetate two-chamber MFC. Moreover, the level diagrams method is utilized to aid in graphical visualization of Pareto front and decision making. Three bi-objective optimization problems and one three-objective optimization problem are thoroughly investigated. The obtained Pareto fronts illustrate the complex relationships among these three objectives, which is helpful for final decision support. Therefore, the integrated methodology of a multi-objective genetic algorithm and a graphical visualization technique provides a promising tool for the optimal operation of MFCs by simultaneously considering multiple conflicting objectives.     

Investigation of ionic polymer cathode binders for microbial fuel cells

Microbial fuel cell (MFC) air cathodes examined here were made using poly(phenylsulfone) (Radel^®) binders sulfonated to various ion exchange capacities (IECs). We examined the effect of increasing the IEC of poly(phenylsulfone) Radel binders from 0 to 2.54 meq/g on cathode performance using linear sweep voltammetry (LSV), impedance, and single chamber air-cathode MFC tests. Unsulfonated Radel, which is a non-ionic, hydrophobic polymer, showed the highest current in LSV tests and the lowest charge transfer resistance. Increasing the binder IEC resulted in a decreased current response in LSV tests and an increased charge transfer resistance from 8 to 23 Ω. It is proposed that the presence of sulfonate groups in the cathode binder impeded the oxygen reduction activity of the cathodes by adsorption of the sulfonate to catalytic sites and by impeding proton diffusion to the catalyst surface. The unsulfonated Radel binder produced the most stable performance, and eventually the highest power density, in MFCs operated over 20 cycles (55 days). These results suggest that the use of a non-ionic binder is advantageous in an MFC cathode to facilitate charge transfer and stable performance in the neutral pH conditions found in MFCs.     

微生物燃料电池在污水生物脱氮中的研究进展

微生物燃料电池(MFC)是一种新型污水处理技术,其在处理污水的同时能产生电能,引起众多研究者的关注.将MFC应用于含氮污水的处理中便形成了反硝化或同步硝化反硝化MFC系统.本文回顾了MFC生物脱氮的发展历程,并从MFC实验装置的设计构造(空间构型、电极材料、分隔材料)、影响因素(含氮污染物浓度、水力停留时间、溶解氧、碳源与碳氮比、温度、pH值、外电阻)和反硝化细菌的基因表达与多样性等3个方面进行了综述与分析,提出需要从以下方面进行MFC生物脱氮效能的强化:开发具有强电子传输能力和氨氧化催化功能的廉价高效电极材料,优化MFC脱氮的运行条件和探索不同环境下的脱氮机理,通过研究MFC阴极微生物种群构成筛选培育优势反硝化功能菌.     

Performance of non-porous graphite and titanium-based anodes in microbial fuel cells

Four non-porous materials were compared for their suitability as bio-anode in microbial fuel cells (MFCs). These materials were flat graphite, roughened graphite, Pt-coated titanium, and uncoated titanium. The materials were placed in four identical MFCs, of which the anode compartments were hydraulically connected in series, as well as the cathode compartments. The MFCs were operated with four resistors. The anode kinetics at these electrode materials were studied by means of dc-voltammetry and electrochemical impedance spectroscopy (EIS). Both techniques were compared and showed that the bio-anode performance decreased in the order roughened graphite > Pt-coated titanium > flat graphite > uncoated titanium. Uncoated titanium was unsuitable as anode material. For the other three materials, specific surface area was not the single variable explaining the differences in current density for the different materials. All polarization curves showed a clear limiting current. This limit could not be attributed to mass transfer of the substrate and reflected the maximum biomass activity. The current density of the non-porous bio-anodes, except for the uncoated titanium anode, was comparable to the reported current densities of porous materials when normalized to the projected surface area. The high current densities that were recorded by dc-voltammetry, however, could not be maintained in a stable way for a longer period. This shows that polarization curves of MFCs should be evaluated critically.     

Electron-transfer coupling in microbial fuel cells. 2. performance of fuel cells containing selected microorganism—mediator—substrate combinations

Various phenoxazine, phenothiazine, phenazine, indophenol and bipyridilium derivatives were tested for their effectiveness as redox mediators in microbial fuel cells containing Alcaligenes eutrophus, Bacillus subtilis, Escherichia coli, or Proteus vulgaris as the active biological agent, and glucose or succinate as the oxidisable substrate. A ferricyanide-Pt cathode was used. The open-circuit cell e.m.f.′s increased in the order of increasing negative formal redox potentials at pH 7(E⁷_m) of the redox compounds. Several of the redox agents worked well as mediators, maintaining steady currents over several hours, and thionine was found to be particularly effective in maintaining relatively high cell voltages when current was drawn from the cell. A number of the compounds tested did not function well, either because they were incompletely or slowly reduced by the microorganisms or because of their instability. P. vulgaris, with thionine as mediator and glucose as substrate, showed the best performance in a fuel cell. This system was examined in some detail under various conditions of external load to establish the effects of organism concentration, mediator concentration, and substrate addition. Coulombic outputs from these cells were calculated by integration of the current-time plots. Coulombic yields of 30–60% were obtained, on the basis of (theoretical) complete oxidation of added substrate to CO₂ and water.     

Evaluation of catalytic properties of tungsten carbide for the anode of microbial fuel cells

In this communication we discuss the properties of tungsten carbide, WC, as anodic electrocatalyst for microbial fuel cell application. The electrocatalytic activity of tungsten carbide is evaluated in the light of its preparation procedure, its structural properties as well as the pH and the composition of the anolyte solution and the catalyst load. The activity of the noble-metal-free electrocatalyst towards the oxidation of several common microbial fermentation products (hydrogen, formate, lactate, ethanol) is studied for microbial fuel cell conditions (e.g., pH 5, room temperature and ambient pressure). Current densities of up to 8.8 mA cm⁻² are achieved for hydrogen (hydrogen saturated electrolyte solution), and up to 2 mA cm⁻² for formate and lactate, respectively. No activity was observed for ethanol electrooxidation.

The electrocatalytic activity and chemical stability of tungsten carbide is excellent in acidic to pH neutral potassium chloride electrolyte solutions, whereas higher phosphate concentrations at neutral pH support an oxidative degradation.