Harvesting energy from the marine sediment-water interface II. Kinetic activity of anode materials

Here, we report a comparative study on the kinetic activity of various anodes of a recently described microbial fuel cell consisting of an anode imbedded in marine sediment and a cathode in overlying seawater. Using plain graphite anodes, it was demonstrated that a significant portion of the anodic current results from oxidation of sediment organic matter catalyzed by microorganisms colonizing the anode and capable of directly reducing the anode without added exogenous electron-transfer mediators. Here, graphite anodes incorporating microbial oxidants are evaluated in the laboratory relative to plain graphite with the goal of increasing power density by increasing current density. Anodes evaluated include graphite modified by adsorption of anthraquinone-1,6-disulfonic acid (AQDS) or 1,4-naphthoquinone (NQ), a graphite-ceramic composite containing Mn2+ and Ni2+, and graphite modified with a graphite paste containing Fe3O4 or Fe3O4 and Ni2+. It was found that these anodes possess between 1.5- and 2.2-fold greater kinetic activity than plain graphite. Fuel cells were deployed in a coastal site near Tuckerton, NJ (USA) that utilized two of these anodes. These fuel cells generated ca. 5-fold greater current density than a previously characterized fuel cell equipped with a plain graphite anode, and operated at the same site.     

Microbial fuel cell energy from an ocean cold seep

Benthic microbial fuel cells are devices that generate modest levels of electrical power in seafloor environments by a mechanism analogous to the coupled biogeochemical reactions that transfer electrons from organic carbon through redox intermediates to oxygen. Two benthic microbial fuel cells were deployed at a deep-ocean cold seep within Monterey Canyon, California, and were monitored for 125 days. Their anodes consisted of single graphite rods that were placed within microbial mat patches of the seep, while the cathodes consisted of carbon-fibre/titanium wire brushes attached to graphite plates suspended ∼0.5 m above the sediment. Power records demonstrated a maximal sustained power density of 34 mW·m⁻² of anode surface area, equating to 1100 mW m⁻² of seafloor. Molecular phylogenetic analyses of microbial biofilms that formed on the electrode surfaces revealed changes in microbial community composition along the anode as a function of sediment depth and surrounding geochemistry. Near the sediment surface (20–29 cm depth), the anodic biofilm was dominated by micro-organisms closely related to Desulfuromonas acetoxidans. At horizons 46–55 and 70–76 cm below the sediment–water interface, clone libraries showed more diverse populations, with increasing representation of δ-proteobacteria such as Desulfocapsa and Syntrophus, as well as ɛ-proteobacteria. Genes from phylotypes related to Pseudomonas dominated the cathode clone library. These results confound ascribing a single electron transport role performed by only a few members of the microbial community to explain energy harvesting from marine sediments. In addition, the microbial fuel cells exhibited slowly decreasing current attributable to a combination of anode passivation and sulfide mass transport limitation. Electron micrographs of fuel cell anodes and laboratory experiments confirmed that sulfide oxidation products can build up on anode surfaces and impede electron transfer. Thus, while cold seeps have the potential to provide more power than neighbouring ocean sediments, the limits of mass transport as well as the proclivity for passivation must be considered when developing new benthic microbial fuel cell designs to meet specific power requirements.     

Electricity generation from wastewaters with starch as carbon source using a mediatorless microbial fuel cell

Microbial fuel cells represent a new method for producing electricity from the oxidation of organic matter. A mediatorless microbial fuel cell was developed using Escherichia coli as the active bacterial component with synthetic wastewater of potato extract as the energy source. The two-chamber fuel cell, with a relation of volume between anode and cathode chamber of 8:1, was operated in batch mode. The response was similar to that obtained when glucose was used as the carbon source. The performance characteristics of the fuel cell were evaluated with two different anode and cathode shapes, platinised titanium strip or mesh; the highest maximum power density (502mWm(-2)) was achieved in the microbial fuel cell with mesh electrodes. In addition to electricity generation, the MFC exhibited efficient treatment of wastewater so that significant reduction of initial oxygen demand of wastewater by 61% was observed. These results demonstrate that potato starch can be used for power generation in a mediatorless microbial fuel cell with high removal efficiency of chemical oxygen demand.     

Influence of anode pretreatment on its microbial colonization

AIMS: To assess the influence of chemical treatment of the anode of a marine sediment biofuel cell (MSBFC) on the microbial diversity of the anode biofilm. METHODS AND RESULTS: A MSBFC was equipped with two graphite plate anodes, one pretreated by electrochemical oxidation in sulfuric acid and the other untreated. After 6 weeks of operation, 16S rRNA clone libraries were constructed from each anode biofilm. The pretreated anode exhibited a fourfold depletion in gamma-proteobacteria, a fourfold enrichment in delta-proteobacteria, a sixfold increase in sulfate reducers, a fivefold enrichment in unclassified micro-organisms, and 6% of the colonies were sulfur oxidizers while none were detected on the untreated anode. CONCLUSION: Anode pretreatment significantly affects the anode-colonized microbial communities of MSBFCs. SIGNIFICANCE AND IMPACT OF THE STUDY: The MSBFC is one of a new class of microbial fuel cells in which the anode is spontaneously colonized by a subset of micro-organisms indigenous to a complex anaerobic mixture (such as sewage and food processing effluents). These micro-organisms utilize the anode as an oxidant, catalysing power generation by oxidizing fuel in the mixture and reducing the anode. This study reveals that pretreatment of the anode can greatly affect the composition of the microbial colony of such fuel cells.     

沉积型海底微生物燃料电池构建及其影响因素研究

海底微生物燃料电池具有底物丰富、可长期运行、维护成本低和环境友好等特点,具有很好的研究价值和广阔的发展前景。但由于其低的功率密度输出和长期运行的不稳定性,使海底微生物燃料电池尚未得到广泛地实际应用。选取海底沉积泥用于实验室构建的海底微生物燃料电池装置中,比较了在不同阳极材料、阴阳极面积比、阳极修饰、阳极泥下深度条件下海底微生物燃料电池的功率密度输出及其电化学性能,得出最佳的海底微生物燃料电池阳极材料为碳毡;阴极及电极最佳面积比为1∶1;最佳阳极修饰为氨水浸渍;最佳阳极泥下深度为2 cm。     

海洋沉积物微生物介导有机碳转化研究进展

海洋沉积物是地球上最大的有机碳库,其中生存的微生物总量大、分布范围广、类群多样、代谢方式复杂,并共同构成海洋沉积物微生物组。海洋沉积物微生物组介导的有机碳降解与矿化过程不但能为沉积物中的生命活动提供物质和能量,也能参与调控碳循环过程,并在长时间尺度上对地球气候系统产生重大影响。沉积物中的有机碳在复杂多样的微生物代谢活动下被逐步降解,其最终的矿化过程与不同的电子受体消耗相偶合,并形成对应的地球化学分区。研究海洋沉积物微生物及其介导的有机碳转化过程对我们深入认识沉积物中的元素循环过程,并进一步评估其对整个地球系统的影响具有重要科学意义。本文对海洋沉积物微生物组的体量、包含的微生物多样性、代谢活性以及在不同地球化学分区中主要的微生物类群和代谢机制进行综述,最后基于研究现状展望了海洋沉积物微生物组的未来研究方向。     

Power output and columbic efficiencies from biofilms of Geobacter sulfurreducens comparable to mixed community microbial fuel cells

It has been previously noted that mixed communities typically produce more power in microbial fuel cells than pure cultures. If true, this has important implications for the design of microbial fuel cells and for studying the process of electron transfer on anode biofilms. To further evaluate this, Geobacter sulfurreducens was grown with acetate as fuel in a continuous flow 'ministack' system in which the carbon cloth anode and cathode were positioned in close proximity, and the cation-selective membrane surface area was maximized in order to overcome some of the electrochemical limitations that were inherent in fuel cells previously employed for the study of pure cultures. Reducing the size of the anode in order to eliminate cathode limitation resulted in maximum current and power densities per m(2) of anode surface of 4.56 A m(-2) and 1.88 W m(-2) respectively. Electron recovery as current from acetate oxidation was c. 100% when oxygen diffusion into the system was minimized. This performance is comparable to the highest levels previously reported for mixed communities in similar microbial fuel cells and slightly higher than the power output of an anaerobic sludge inoculum in the same ministack system. Minimizing the volume of the anode chamber yielded a volumetric power density of 2.15 kW m(-3), which is the highest power density per volume yet reported for a microbial fuel cell. Geobacter sulfurreducens formed relatively uniform biofilms 3-18 mum thick on the carbon cloth anodes. When graphite sticks served as the anode, the current density (3.10 A m(-2)) was somewhat less than with the carbon cloth anodes, but the biofilms were thicker (c. 50 mum) with a more complex pillar and channel structure. These results suggest that the previously observed disparity in power production in pure and mixed culture microbial fuel cell systems can be attributed more to differences in the fuel cell designs than to any inherent superior capability of mixed cultures to produce more power than pure cultures.     

Microbial fuel cells: novel microbial physiologies and engineering approaches

The possibility of generating electricity with microbial fuel cells has been recognized for some time, but practical applications have been slow to develop. The recent development of a microbial fuel cell that can harvest electricity from the organic matter stored in marine sediments has demonstrated the feasibility of producing useful amounts of electricity in remote environments. Further study of these systems has led to the discovery of microorganisms that conserve energy to support their growth by completely oxidizing organic compounds to carbon dioxide with direct electron transfer to electrodes. This suggests that self-sustaining microbial fuel cells that can effectively convert a diverse range of waste organic matter or renewable biomass to electricity are feasible. Significant progress has recently been made to increase the power output of systems designed to convert organic wastes to electricity, but substantial additional optimization will be required for large-scale electricity production.     

Long-term performance of a plant microbial fuel cell with Spartina anglica

The plant microbial fuel cell is a sustainable and renewable way of electricity production. The plant is integrated in the anode of the microbial fuel cell which consists of a bed of graphite granules. In the anode, organic compounds deposited by plant roots are oxidized by electrochemically active bacteria. In this research, salt marsh species Spartina anglica generated current for up to 119 days in a plant microbial fuel cell. Maximum power production was 100 mW m⁻² geometric anode area, highest reported power output for a plant microbial fuel cell. Cathode overpotential was the main potential loss in the period of oxygen reduction due to slow oxygen reduction kinetics at the cathode. Ferricyanide reduction improved the kinetics at the cathode and increased current generation with a maximum of 254%. In the period of ferricyanide reduction, the main potential loss was transport loss. This research shows potential application of microbial fuel cell technology in salt marshes for bio-energy production with the plant microbial fuel cell.     

Outlook for benefits of sediment microbial fuel cells with two bio‐electrodes

The benefits of sediment microbial fuel cells (SMFCs) go beyond energy generation for low‐power applications. Aside from producing electrical energy, SMFCs can enhance the oxidation of reduced compounds at the anode, thus bringing about the removal of excessive or unwanted reducing equivalents from submerged soils. Moreover, an SMFC could be applied to control redox‐dependent processes in sediment layers. Several cathodic reactions that may drive these sediment oxidation reactions are examined. Special attention is given to two biologically mediated cathodic reactions, respectively employing an oxygen reduction and a manganese cycle. Both reactions imply a low cost and a high electrode potential and are of interest for reactor‐type MFCs as well as for SMFCs.     

Microbial Community Analysis of Anodes from Sediment Microbial Fuel Cells Powered by Rhizodeposits of Living Rice Plants

By placing the anode of a sediment microbial fuel cell (SMFC) in the rhizosphere of a rice plant, root-excreted rhizodeposits can be microbially oxidized with concomitant current generation. Here, various molecular techniques were used to characterize the composition of bacterial and archaeal communities on such anodes, as influenced by electrical circuitry, sediment matrix, and the presence of plants. Closed-circuit anodes in potting soil were enriched with Desulfobulbus-like species, members of the family Geobacteraceae, and as yet uncultured representatives of the domain Archaea.Living plants release substantial amounts of carbon in the soil as rhizodeposits, which are to a large extent transformed into the greenhouse gas methane in wetlands (21). It was recently demonstrated (8, 33) that the rhizodeposits can be harvested by plant microbial fuel cells (plant MFCs) and transformed into electricity. In its most straightforward form, a plant MFC is an adaptation of a sediment MFC (SMFC), which has an anode buried in (planted) sediment, allowing (microbial) oxidation of reduced compounds, and a cathode in the overlying water.The roots and surrounding rhizosphere in a plant SMFC add an extra parameter to the as yet multifaceted SMFC system. In the present study, two molecular profiling techniques (denaturing gradient gel electrophoresis [DGGE] and terminal restriction fragment length polymorphism [T-RFLP]) will be applied to evaluate the effect of plant presence, support material, operation of the electrical circuit, and anode depth on the bacterial and archaeal communities associated with rice SMFC anodes. Phylogenetic analysis will give further insight in their composition.     

A mediated glucose/oxygen enzymatic fuel cell based on printed carbon inks containing aldose dehydrogenase and laccase as anode and cathode

Enzyme electrodes show great potential for many applications, as biosensors and more recently as anodes and cathodes in biocatalytic fuel cells for power generation. Enzymes have advantages over metal catalysts, as they provide high specificity and reaction rates, while operating under mild conditions. Here we report on studies related to development of mass-producible, completely enzymatic printed glucose/oxygen biofuel cells. The cells are based on filter paper coated with conducting carbon inks containing mediators and laccase, for reduction of oxygen, or aldose dehydrogenase, for oxidation of glucose. Mediator performance in these printed formats is compared to relative rate constants for the enzyme-mediator reaction in solution, for a range of anode and cathode mediators. The power output and stability of fuels cells using an acidophilic laccase isolated from Trametes hirsuta is greater, at pH 5, than that for cells based on Melanocarpus albomyces laccase, that shows optimal activity closer to neutral pH, at pH 6. Highest power output, although of limited stability, was observed for ThL/ABTS cathodes, providing a maximum power density of 3.5 μWcm(-2) at 0.34 V, when coupled to an ALDH glucose anode mediated by an osmium complex. The stability of cell voltage above a threshold of 200 mV under a moderate 75 kΩ load is used to benchmark printed fuel cell performance. Highest stability was obtained for a printed fuel cell using osmium complexes as mediators of glucose oxidation by aldose dehydrogenase, and oxygen reduction by T. hirsuta laccase, maintaining cell voltage above 200 mV for 137 h at pH 5. These results provide promising directions for further development of mass-producible, completely enzymatic, printed biofuel cells.     

Electrochemical surface modification of carbon mesh anode to improve the performance of air-cathode microbial fuel cells

A convenient and promising alternative to surface modification of carbon mesh anode was fulfilled by electrochemical oxidation in the electrolyte of nitric acid or ammonium nitrate at ambient temperature. It was confirmed that such an anode modification method was low cost and effective not only in improving the efficiency of power generation in microbial fuel cells (MFCs) for synthetic wastewater treatment, but also helping to reduce the period for MFCs start-up. The MFCs with anode modification in electrolyte of nitric acid performed the best, achieving a Coulombic efficiency enhancement of 71 %. As characterized, the electrochemical modification resulted in the decrease of the anode potential and internal resistance but the increase of current response and nitrogen-containing and oxygen-containing functional groups on the carbon surface, which might contribute to the enhancement on the performances of MFCs.     

Increased Power in Sediment Microbial Fuel Cell: Facilitated Mass Transfer via a Water-Layer Anode Embedded in Sediment

We report a methodology for enhancing the mass transfer at the anode electrode of sediment microbial fuel cells (SMFCs), by employing a fabric baffle to create a separate water-layer for installing the anode electrode in sediment. The maximum power in an SMFC with the anode installed in the separate water-layer (SMFC-wFB) was improved by factor of 6.6 compared to an SMFC having the anode embedded in the sediment (SMFC-woFB). The maximum current density in the SMFC-wFB was also 3.9 times higher (220.46 mA/m²) than for the SMFC-woFB. We found that the increased performance in the SMFC-wFB was due to the improved mass transfer rate of organic matter obtained by employing the water-layer during anode installation in the sediment layer. Acetate injection tests revealed that the SMFC-wFB could be applied to natural water bodies in which there is frequent organic contamination, based on the acetate flux from the cathode to the anode.     

微生物燃料电池利用乳酸产电性能与微生物群落分布特征

【目的】为探讨以乳酸为基质的微生物燃料电池(Microbial fuel cell,MFC)产电性能以及微生物群落在阳极膜、悬浮液、阳极沉淀污泥中的分布特征,【方法】试验建立了双室MFC,以乳酸为阳极主要碳源,研究了反应器的启动过程及产电效能,同时以电镜和PCR-变性梯度凝胶电泳(Denaturing gradient gelelectrophoresis,DGGE)技术解析了微生物群落的空间分布特征。【结果】结果表明,反应器启动第7天时外电压达到0.56 V,当外阻为80Ω时,电流密度为415 mA/m2,MFC的功率密度达到最大值82 mW/m2。电镜观察发现大量杆菌附着在阳极表面,结合较为紧密;DGGE图谱显示阳极膜表面微生物与种泥最为相似,与阳极悬浮液、底部沉淀污泥中的主要菌群一致,条带序列与睾丸酮丛毛单胞菌(Comamonas testosteroni)和布氏弓形菌(Arcobacter butzleri)等最为相似。【结论】本研究表明以乳酸为基质MFC可产生较高的功率密度,阳极附着的优势菌与接种污泥来源密切相关。     

Granular activated carbon based microbial fuel cell for simultaneous decolorization of real dye wastewater and electricity generation

Decolorization of dye wastewater before discharge is pivotal because of its immense color and toxicities. In this study, a granular activated carbon based microbial fuel cell (GACB-MFC) was used without using any expensive materials like Nafion membrane and platinum catalyst for simultaneous decolorization of real dye wastewater and bioelectricity generation. After 48 hours of GACB-MFC operation, 73% color was removed at anode and 77% color was removed at cathode. COD removal was 71% at the anode and 76% at the cathode after 48 hours. Toxicity measurements showed that cathode effluent was almost nontoxic after 24 hours. The anode effluent was threefold less toxic compared to original dye wastewater after 48 hours. The GACB-MFC produced a power density of 1.7 W/m(3) with an open circuit voltage 0.45 V. One of the advantages of the GACB-MFC system is that pH was automatically adjusted from 12.4 to 7.2 and 8.0 at the anode and cathode during 48 hours operation.     

A glucose fuel cell for implantable brain-machine interfaces

We have developed an implantable fuel cell that generates power through glucose oxidation, producing 3.4 μW cm(-2) steady-state power and up to 180 μW cm(-2) peak power. The fuel cell is manufactured using a novel approach, employing semiconductor fabrication techniques, and is therefore well suited for manufacture together with integrated circuits on a single silicon wafer. Thus, it can help enable implantable microelectronic systems with long-lifetime power sources that harvest energy from their surrounds. The fuel reactions are mediated by robust, solid state catalysts. Glucose is oxidized at the nanostructured surface of an activated platinum anode. Oxygen is reduced to water at the surface of a self-assembled network of single-walled carbon nanotubes, embedded in a Nafion film that forms the cathode and is exposed to the biological environment. The catalytic electrodes are separated by a Nafion membrane. The availability of fuel cell reactants, oxygen and glucose, only as a mixture in the physiologic environment, has traditionally posed a design challenge: Net current production requires oxidation and reduction to occur separately and selectively at the anode and cathode, respectively, to prevent electrochemical short circuits. Our fuel cell is configured in a half-open geometry that shields the anode while exposing the cathode, resulting in an oxygen gradient that strongly favors oxygen reduction at the cathode. Glucose reaches the shielded anode by diffusing through the nanotube mesh, which does not catalyze glucose oxidation, and the Nafion layers, which are permeable to small neutral and cationic species. We demonstrate computationally that the natural recirculation of cerebrospinal fluid around the human brain theoretically permits glucose energy harvesting at a rate on the order of at least 1 mW with no adverse physiologic effects. Low-power brain-machine interfaces can thus potentially benefit from having their implanted units powered or recharged by glucose fuel cells.     

Electricity generation in a microbial fuel cell with a microbially catalyzed cathode

A microbial fuel cell using aerobic microorganisms as the cathodic catalysts is described. By using anaerobic sludge in the anode and aerobic sludge in the cathode as inocula, the microbial fuel cell could be started up after a short lag time of 9 days, generating a stable voltage of 0.324 V (R (ex) = 500 Omega). At an aeration rate of 300 ml min(-1) in the cathode, a maximum volumetric power density of up to 24.7 W m(-3) (117.2 A m(-3)) was reached. This research demonstrates an economic system for recovering electrical energy from organic compounds.     

铁还原菌在水资源再生与能源转化领域的研究进展

铁还原菌是一种典型的异化金属还原菌,广泛分布于海洋沉积物、陆地深地层等自然环境,该类细菌可以将铁氧化物中的Fe(Ⅲ)还原为Fe(Ⅱ),在铁、碳的生物地球化学铁循环中发挥重要作用。铁还原菌的末端电子不局限于Fe(Ⅲ),还可以是其他高价金属、有机污染物,可用于土壤、地下水的污染修复和毒性削减。在微生物电化学系统中,铁还原菌氧化有机物产生的电子直接传递给电极,可以产生电能。基于这种独特的胞外电子传递方式,衍生出了微生物燃料电池、微生物电解池、微生物脱盐电池、微生物燃料电池耦合芬顿反应以及光催化微生物燃料电池,常用于微生物发电、生物传感器、生物制氢、定向发酵、海水淡化、生物脱盐和污染物分解矿化。本文从异化铁还原菌的代谢机制、微生态作用、环境修复、水资源再生与能源转化四个方面,综述了铁还原菌的作用原理及国内外研究现状,分析论述了目前亟需解决的关键问题和未来的研究方向,以期为铁还原菌的基础理论研究和应用技术研发提供参考。     

Microbial electricity generation via microfluidic flow control

Next generation battery technology is rapidly evolving to meet the demand for higher power densities and smaller footprints through novel catalysts and battery architecture. We present a μ-scale, biological fuel cell which utilizes microbial electricity generation enabled by microfluidic flow control to produce power. The new fuel cell, the smallest of its kind, with a total volume of 0.3 μL, produces scalable and controllable electrical energy from organic matter which is sustained through microbial respiration and laminar flow separation of the electrolytes. Electrical currents are dependent on specific biofilm formation on the anode, the concentration of electron donor, and a diffusion-limited flow regime. A maximum current density of 18.40 ± 3.48 mA m(-2) (92 ± 17 A m(-3)) was produced by Geobacter sulfurreducens, and 25.42 mA m(-2) (127 A m(-3)) by Shewanella oneidensis. The μ-scale biological fuel cell introduces the necessary small size and fuel flexibility for applications in vivo and in situ sensors which may be remotely deployed and self-powered.