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Microbial Fuel Cells Methodology and Technology
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and equipment indicating there is a need in the literature. for a paper that provides a more comprehensive source of. this information In this paper we therefore review existing. types of MFCs provide information on construction materials. and give examples of manufacturers although this should. not be considered an endorsement of a particular company. and describe methods of data analysis and reporting in order. to provide information to researchers interested in dupli. cating or advancing MFCs technologies Additional infor. mation is available on the microbial fuel cell website. www microbialfuelcell org,MFC Designs, Many different configurations are possible for MFCs Figures. 2 and 3 A widely used and inexpensive design is a two. chamber MFC built in a traditional H shape consisting. usually of two bottles connected by a tube containing a. separator which is usually a cation exchange membrane. CEM such as Nafion 12 13 23 27 or Ultrex 18 or a plain. salt bridge 27 Figure 2a f The key to this design is to. choose a membrane that allows protons to pass between the. FIGURE 1 Operating principles of a MFC not to scale A bacterium chambers the CEM is also called a proton exchange. in the anode compartment transfers electrons obtained from an membrane PEM but optimally not the substrate or electron. electron donor glucose to the anode electrode This occurs either acceptor in the cathode chamber typically oxygen In the. through direct contact nanowires or mobile electron shuttles small. H configuration the membrane is clamped in the middle of. spheres represent the final membrane associated shuttle During. the tubes connecting the bottle Figure 2f However the. electron production protons are also produced in excess These. protons migrate through the cation exchange membrane CEM into tube itself is not needed As long as the two chambers are. the cathode chamber The electrons flow from the anode through kept separated they can be pressed up onto either side of. an external resistance or load to the cathode where they react the membrane and clamped together to form a large surface. with the final electron acceptor oxygen and protons 26 Figure 2b An inexpensive way to join the bottles is to use. a glass tube that is heated and bent into a U shape filled. are reported with different reference states and sometimes with agar and salt to serve the same function as a cation. only under a single load resistor The range of conditions exchange membrane and inserted through the lid of each. and in some cases a lack of important data like the internal bottle Figure 2a The salt bridge MFC however produces. resistance or power densities derived from polarization curves little power due the high internal resistance observed. taken using different methods has made it difficult to H shape systems are acceptable for basic parameter. interpret and compare results among these systems 26 research such as examining power production using new. The variation in reported data has created a need to clarify materials or types of microbial communities that arise during. methods of data collection and reporting We have individu the degradation of specific compounds but they typically. ally received many requests from researchers for details on produce low power densities The amount of power that is. construction of MFCs and for names of providers of materials generated in these systems is affected by the surface area of. FIGURE 2 Types of MFCs used in studies A easily constructed system containing a salt bridge shown by arrow 27 B four batch type. MFCs where the chambers are separated by the membrane without a tube and held together by bolts 7 C same as B but with a. continuous flow through anode granular graphite matrix and close anode cathode placement 75 D photoheterotrophic type MFC 76. E single chamber air cathode system in a simple tube arrangement 30 F two chamber H type system showing anode and cathode. chambers equipped for gas sparging 23, 5182 9 ENVIRONMENTAL SCIENCE TECHNOLOGY VOL 40 NO 17 2006. FIGURE 3 MFCs used for continuous operation A upflow tubular type MFC with inner graphite bed anode and outer cathode 35 B. upflow tubular type MFC with anode below and cathode above the membrane is inclinated 36 C flat plate design where a channel. is cut in the blocks so that liquid can flow in a serpentine pattern across the electrode 17 D single chamber system with an inner. concentric air cathode surrounded by a chamber containing graphite rods as anode 34 E stacked MFC in which 6 separate MFCs are. joined in one reactor block 25, the cathode relative to that of the anode 28 and the surface coatings such as polytetrafloroethylene PTFE to the outside. of the membrane 29 The power density P produced by of the cathode that permit oxygen diffusion but limit bulk. these systems is typically limited by high internal resistance water loss 32. and electrode based losses see below When comparing Several variations on these basic designs have emerged. power produced by these systems it makes the most sense in an effort to increase power density or provide for. to compare them on the basis of equally sized anodes continuous flow through the anode chamber in contrast to. cathodes and membranes 29 the above systems which were all operated in batch mode. Using ferricyanide as the electron acceptor in the cathode Systems have been designed with an outer cylindrical reactor. chamber increases the power density due to the availability with a concentric inner tube that is the cathode 33 34 Figure. of a good electron acceptor at high concentrations Ferri 3d and with an inner cylindrical reactor anode consisting. cyanide increased power by 1 5 to 1 8 times compared to a of granular media with the cathode on the outside 35. Pt catalyst cathode and dissolved oxygen H design reactor Figure 3a Another variation is to design the system like an. with a Nafion CEM 29 The highest power densities so far upflow fixed bed biofilm reactor with the fluid flowing. reported for MFC systems have been low internal resistance continuously through porous anodes toward a membrane. systems with ferricyanide at the cathode 6 18 While separating the anode from the cathode chamber 36 Figure. ferricyanide is an excellent catholyte in terms of system 3b Systems have been designed to resemble hydrogen fuel. performance it must be chemically regenerated and its use cells where a CEM is sandwiched between the anode and. is not sustainable in practice Thus the use of ferricyanide cathode Figure 3c To increase the overall system voltage. is restricted to fundamental laboratory studies MFCs can be stacked with the systems shaped as a series of. It is not essential to place the cathode in water or in a flat plates or linked together in series 25 Figure 3e. separate chamber when using oxygen at the cathode The Sediment MFCs By placing one electrode into a marine. cathode can be placed in direct contact with air Figures 2e sediment rich in organic matter and sulfides and the other. 3c 3d either in the presence or absence of a membrane in the overlying oxic water electricity can be generated at. 30 In one system a kaolin clay based separator and graphite sufficient levels to power some marine devices 37 38. cathode were joined to form a combined separator cathode Protons conducted by the seawater can produce a power. structure 31 Much larger power densities have been density of up to 28 mW m2 Graphite disks can be used for. achieved using oxygen as the electron acceptor when the electrodes 12 37 although platinum mesh electrodes. aqueous cathodes are replaced with air cathodes In the have also been used 38 Bottle brush cathodes used for. simplest configuration the anode and cathode are placed seawater batteries may hold the most promise for long term. on either side of a tube with the anode sealed against a flat operation of unattended systems as these electrodes provide. plate and the cathode exposed to air on one side and water a high surface area and are made of noncorrosive materials. on the other Figure 2e When a membrane is used in this 39 Sediments have also been placed into H tube configured. air cathode system it serves primarily to keep water from two chamber systems to allow investigation of the bacterial. leaking through the cathode although it also reduces oxygen community 12. diffusion into the anode chamber The utilization of oxygen Modifications for Hydrogen Production By assisting. by bacteria in the anode chamber can result in a lower the potential generated by the bacteria at the anode with a. Coulombic efficiency defined as the fraction of electrons small potential by an external power source 0 25 V it is. recovered as current versus the maximum possible recovery possible to generate hydrogen at the cathode 40 43 These. see below 30 Hydrostatic pressure on the cathode will reactors called bioelectrochemically assisted microbial reac. make it leak water but that can be minimized by applying tors BEAMRs or biocatalyzed electrolysis systems are not. VOL 40 NO 17 2006 ENVIRONMENTAL SCIENCE TECHNOLOGY 9 5183. true fuel cells however as they are operated to produce Oxygen is the most suitable electron acceptor for an MFC. hydrogen not electricity Through modifications of the MFC due to its high oxidation potential availability low cost it. designs described above to contain a second chamber for is free sustainability and the lack of a chemical waste. capturing the hydrogen gas it should be possible to develop product water is formed as the only endproduct The choice. many new systems for hydrogen production of the cathode material greatly affects performance and is. varied based on application For sediment fuel cells plain. Materials of Construction graphite disk electrodes immersed in the seawater above the. sediment have been used 38 Due to the very slow kinetics. Anode Anodic materials must be conductive biocompatible. of the oxygen reduction at plain carbon and the resulting. and chemically stable in the reactor solution Metal anodes. large overpotential the use of such cathodes restricts the. consisting of noncorrosive stainless steel mesh can be utilized. use of this noncatalyzed material to systems that can tolerate. 44 but copper is not useful due to the toxicity of even trace. low performance In seawater oxygen reduction on carbon. copper ions to bacteria The most versatile electrode material. cathodes has been shown to be microbially supported 19. is carbon available as compact graphite plates rods or. 20 Such microbially assisted reduction has also been. granules as fibrous material felt cloth paper fibers foam. observed for stainless steel cathodes which rapidly reduces. and as glassy carbon There are numerous carbon suppliers. oxygen when aided by a bacterial biofilm 53, worldwide for example E TEK and Electrosynthesis Co Inc. To increase the rate of oxygen reduction Pt catalysts are. USA GEE Graphite Limited Dewsbury UK Morgan, usually used for dissolved oxygen 37 or open air gas.
Grimbergen Belgium and Alfa Aesar Germany, diffusion cathodes 34 48 To decrease the costs for the. The simplest materials for anode electrodes are graphite MFC the Pt load can be kept as low as 0 1 mg cm 2 54 The. plates or rods as they are relatively inexpensive easy to long term stability of Pt needs to be more fully investigated. handle and have a defined surface area Much larger surface and there remains a need for new types of inexpensive. areas are achieved with graphite felt electrodes 13 45 which catalysts Recently noble metal free catalysts that use. can have high surface areas 0 47 m2g 1 GF series GEE pyrolyzed iron II phthalocyanine or CoTMPP have been. Graphite limited Dewsbury UK However not all the proposed as MFC cathodes 54 55. indicated surface area will necessarily be available to bacteria Membrane The majority of MFC designs require the. Carbon fiber paper foam and cloth Toray have been separation of the anode and the cathode compartments by. extensively used as electrodes It has been shown that current a CEM Exceptions are naturally separated systems such as. increases with overall internal surface area in the order carbon sediment MFCs 37 or specially designed single compart. felt carbon foam graphite 46 Substantially higher ment MFCs 30 32 The most commonly used CEM is Nafion. surface areas are achieved either by using a compact material Dupont Co USA which is available from numerous. like reticulated vitreous carbon RVC ERG Materials and suppliers e g Aldrich and Ion Power Inc Alternatives to. Aerospace Corp Oakland CA 36 47 which is available Nafion such as Ultrex CMI 7000 Membranes International. with different pore sizes or by using layers of packed carbon Incorp Glen Rock NJ also are well suited for MFC. granules Le Carbone Grimbergen Belgium or beads 35 applications 6 and are considerably more cost effective than. 48 In both cases maintaining high porosity is important to Nafion When a CEM is used in an MFC it is important to. prevent clogging The long term effect of biofilm growth or recognize that it may be permeable to chemicals such as. particles in the flow on any of the above surfaces has not oxygen ferricyanide other ions or organic matter used as. been adequately examined the substrate The market for ion exchange membranes is. To increase the anode performance different chemical constantly growing and more systematic studies are neces. and physical strategies have been followed Park et al 31 sary to evaluate the effect of the membrane on performance. incorporated Mn IV and Fe III and used covalently linked and long term stability 56. neutral red to mediate the electron transfer to the anode. Electrocatalytic materials such as polyanilins Pt composites Fundamentals of Voltage Generation in MFCs. have also been shown to improve the current generation Thermodynamics and the Electromotive Force Electricity. through assisting the direct oxidation of microbial metabolites is generated in an MFC only if the overall reaction is. 49 51 thermodynamically favorable The reaction can be evaluated. Directing the water flow through the anode material can in terms of Gibbs free energy expressed in units of Joules J. be used to increase power Cheng et al 52 found that flow which is a measure of the maximal work that can be derived. directed through carbon cloth toward the anode and from the reaction 57 58 calculated as. decreasing electrode spacing from 2 to 1 cm increased power. densities normalized to the cathode projected surface area Gr G0r RTln 1. from 811 to 1540 mW m2 in an air cathode MFC The increase. was thought to be due to restricted oxygen diffusion into the where Gr J is the Gibbs free energy for the specific. anode chamber although the advective flow could have conditions Gr0 J is the Gibbs free energy under standard. helped with proton transport toward the cathode as well conditions usually defined as 298 15 K 1 bar pressure and. Increased power densities have been achieved using RVC in 1 M concentration for all species R 8 31447 J mol 1 K 1 is. an upflow UASB type MFC 36 or in a granular anode reactor the universal gas constant T K is the absolute temperature. 35 with ferricyanide cathodes Flow through an anode has and unitless is the reaction quotient calculated as the. also been used in reactors using exogenous mediators 48 activities of the products divided by those of the reactants. Cathode Due to its good performance ferricyanide The standard reaction Gibbs free energy is calculated from. K3 Fe CN 6 is very popular as an experimental electron tabulated energies of formation for organic compounds in. acceptor in microbial fuel cells 31 The greatest advantage water available from many sources 59 61. of ferricyanide is the low overpotential using a plain carbon For MFC calculations it is more convenient to evaluate. cathode resulting in a cathode working potential close to its the reaction in terms of the overall cell electromotive force. open circuit potential The greatest disadvantage however emf Eemf V defined as the potential difference between. is the insufficient reoxidation by oxygen which requires the the cathode and anode This is related to the work W J. catholyte to be regularly replaced 35 In addition the long produced by the cell or. term performance of the system can be affected by diffusion. of ferricyanide across the CEM and into the anode chamber W Eemf Q Gr 2. 5184 9 ENVIRONMENTAL SCIENCE TECHNOLOGY VOL 40 NO 17 2006. TABLE 1 Standard Potentials E0 and Theoretical Potentials for Typical Conditions in MFCs EMFC EMFC Was Calculated Using Eq 5. and Half Cell Values from Ref 57 All Potentials Are Shown against NHE. electrode reaction E0 V conditions EMFC V,2 HCO3 9 H. 8 f e CH3COO,4 H2O 0 187a HCO3 5 mM CH3COO 5 mM pH 7 0 296b. cathode O2 4 H 4 e f 2 H2O 1 229 pO2 0 2 pH 7 0 805b. O2 4 H 4 e f 2 H2O 1 229 pO2 0 2 pH 10 0 627, MnO2 s 4 H 2 e f Mn2 2 H2O 1 23 Mn2 5 mM pH 7 0 470. O2 2 H 2 e f H2O2 0 695 pO2 0 2 H2O2 5 mM pH 7 0 328. Fe CN 63 e f Fe CN 64 0 361 Fe CN 63 Fe CN 64 0 361. a Calculated from Gibbs free energy data tabulated in ref 61 b Note that an MFC with an acetate oxidizing anode HCO 5 mM. CH3COO 5 mM pH 7 and an oxygen reducing cathode pO2 0 2 pH 7 has a cell emf of 0 805 0 296 1 101 V. where Q nF is the charge transferred in the reaction the reaction we can write. expressed in Coulomb C which is determined by the, number of electrons exchanged in the reaction n is the O2 4 H 4 e f 2 H2O 8.
number of electrons per reaction mol and F is Faraday s. constant 9 64853 104 C mol Combining these two RT 1. equations we have Ecat E0cat ln 9, Eemf 3 A variety of catholytes has been used and for each of these. nF the cell voltage varies For example manganese oxide and. ferricyanide have been used as alternatives to oxygen The. If all reactions are evaluated at standard conditions pH of the cathode solution can also vary affecting the overall. 1 then cathode potential Using eq 9 and tabulated standard. potentials available for inorganic compounds 57 for several. G0r different conditions it can be seen that the theoretical. E0emf 4 cathode potential for these different catholytes range from. nF 0 361 to 0 805 V,The cell emf is calculated as, where E0emf V is the standard cell electromotive force We. can therefore use the above equations to express the overall Eemf Ecat Ean 10. reaction in terms of the potentials as, where the minus sign is a result of the definition of the anode. RT potential as reduction reaction although an oxidation. Eemf E0emf ln 5, nF reaction is occurring Note that the result using eq 10 equals. that of eq 3 and eq 5 only if the pH at the anode and the. The advantage of eq 5 is that it is positive for a favorable cathode are equal Equation 10 demonstrates that using the. reaction and directly produces a value of the emf for the same anode in a system with different cathode conditions. reaction This calculated emf provides an upper limit for the as listed in Table 1 would produce significantly different cell. cell voltage the actual potential derived from the MFC will voltages and thus different levels of power output The power. be lower due to various potential losses see below produced by an MFC therefore depends on the choice of the. Standard Electrode Potentials The reactions occurring cathode and this should be taken into account when. in the MFC can be analyzed in terms of the half cell reactions comparing power densities achieved by different MFCs. or the separate reactions occurring at the anode and the Open Circuit Voltage OCV The cell emf is a thermo. cathode According to the IUPAC convention standard dynamic value that does not take into account internal losses. potentials at 298 K 1 bar 1 M are reported as a reduction The open circuit voltage OCV is the cell voltage that can be. potential i e the reaction is written as consuming electrons measured after some time in the absence of current. 57 For example if acetate is oxidized by bacteria at the Theoretically the OCV should approach the cell emf In. anode we write the reaction as practice however the OCV is substantially lower than the. cell emf due to various potential losses For example a typical. measured potential of a cathode using oxygen at pH 7 is. 2HCO3 9H 8e f CH3COO 4H2O 6, about 0 2 V This is clearly lower than the expected value of.
0 805 V indicating the large energy loss occurring at the. The standard potentials are reported relative to the normal cathode This energy loss is often referred to as overpotential. hydrogen electrode NHE which has a potential of zero at or the difference between the potential under equilibrium. standard conditions 298 K pH2 1 bar H 1 M To conditions and the actual potential which for this case is. obtain the theoretical anode potential EAn under specific 0 605 V 0 805 V 0 2 V This illustrates that the main. conditions we use eq 5 with the activities of the different application of thermodynamic calculations is to identify the. species assumed to be equal to their concentrations For size and nature of energy losses. acetate oxidation Table 1 we therefore have,Identifying Factors that Decrease Cell Voltage. RT CH3COO The maximum attainable MFC voltage emf is theoretically. EAn E0An ln 7 on the order of 1 1 V see above However the measured. 8F HCO 2 H 9, 3 MFC voltage is considerably lower due to a number of losses. In an open circuit when no current is flowing the maximum. For the theoretical cathode potential Ecat if we consider MFC voltage achieved thus far is 0 80 V 62 During current. the case where oxygen is used as the electron acceptor for generation voltages achieved up to now remain below 0 62. VOL 40 NO 17 2006 ENVIRONMENTAL SCIENCE TECHNOLOGY 9 5185. V 35 In general the difference between the measured cell. voltage and the cell emf is referred to as overvoltage and is. the sum of the overpotentials of the anode and the cathode. and the ohmic loss of the system,Ecell Eemf a c IR 11. where a and c are the overpotentials of the anode and. the cathode respectively and IR is the sum of all ohmic. losses which are proportional to the generated current I. and ohmic resistance of the system R The overpotentials. of the electrodes are generally current dependent and in an. MFC they can roughly be categorized as follows i activation. losses ii bacterial metabolic losses and iii mass transport. or concentration losses see below, In MFCs the measured cell voltage is usually a linear. function of the current see discussion of the polarization. curve below and can be described simply as,Ecell OCV IRint 12.
where IRint is the sum of all internal losses of the MFC which. are proportional to the generated current I and internal. resistance of the system Rint A comparison of eqs 11 and. 12 shows that the overpotentials of the anode and the cathode. that occur under open circuit conditions are included in the FIGURE 4 Electrochemical analysis of microbial fuel cells A. value of OCV in eq 12 while the current dependent Anodic blue solid line and cathodic red dashed line voltage. profiles over time when applying the current interrupt method for. overpotentials of the electrodes and ohmic losses of the. determination of the ohmic resistance of an MFC Sections 2 and. system are captured in IRint MFC systems that are well. 3 indicate the voltage differences related to the ohmic resistance. described by eq 12 show a maximum power output when sections 1 and 4 indicate voltage losses caused by the activation. the internal resistance Rint is equal to external resistance overpotentials B Cyclic voltammogram solid line of an elec. Rext 52 Although Rint includes more than just ohmic trochemically active mixed microbial community The dashed lines. resistance R both terms are often used interchangeably connect the oxidation and reduction peaks of redox active. but MFC researchers should be aware of the differences in compounds 6. these two terms MFC performance can be assessed in terms. of both overpotentials and ohmic losses or in terms of OCV maximize the MFC voltage therefore the potential of the. and internal losses based on various techniques discussed anode should be kept as low negative as possible However. below if the anode potential becomes too low electron transport. Ohmic Losses The ohmic losses or ohmic polarization will be inhibited and fermentation of the substrate if possible. in an MFC include both the resistance to the flow of electrons may provide greater energy for the microorganisms The. through the electrodes and interconnections and the impact of a low anode potential and its possible impact on. resistance to the flow of ions through the CEM if present the stability of power generation should be addressed in. and the anodic and cathodic electrolytes 63 64 Ohmic future studies. losses can be reduced by minimizing the electrode spacing. Concentration Losses Concentration losses or concen. using a membrane with a low resistivity checking thoroughly. tration polarization occur when the rate of mass transport. all contacts and if practical increasing solution conductivity. of a species to or from the electrode limits current production. to the maximum tolerated by the bacteria, 63 64 Concentration losses occur mainly at high current. Activation Losses Due to the activation energy needed. densities due to limited mass transfer of chemical species by. for an oxidation reduction reaction activation losses or. diffusion to the electrode surface At the anode concentration. activation polarization occur during the transfer of electrons. losses are caused by either a limited discharge of oxidized. from or to a compound reacting at the electrode surface. species from the electrode surface or a limited supply of. This compound can be present at the bacterial surface as. reduced species toward the electrode This increases the ratio. a mediator in the solution Figure 4 or as the final electron. between the oxidized and the reduced species at the electrode. acceptor reacting at the cathode Activation losses often show. surface which can produce an increase in the electrode. a strong increase at low currents and steadily increase when. potential At the cathode side the reverse may occur causing. current density increases Low activation losses can be. a drop in cathode potential In poorly mixed systems. achieved by increasing the electrode surface area improving. diffusional gradients may also arise in the bulk liquid Mass. electrode catalysis increasing the operating temperature. transport limitations in the bulk fluid can limit the substrate. and through the establishment of an enriched biofilm on the. flux to the biofilm which is a separate type of concentration. electrode s, loss By recording polarization curves the onset of concen. Bacterial Metabolic Losses To generate metabolic energy. tration losses can be determined as described below. bacteria transport electrons from a substrate at a low potential. e g Table 1 acetate 0 296 V through the electron, transport chain to the final electron acceptor such as oxygen Instruments for Measurement. or nitrate at a higher potential In an MFC the anode is the In addition to conventional instruments used for chemical. final electron acceptor and its potential determines the energy measurements in microbial systems e g for determining. gain for the bacteria The higher the difference between the substrate concentrations and degradation products MFC. redox potential of the substrate and the anode potential the experiments can require specialized electrochemical instru. higher the possible metabolic energy gain for the bacteria mentation 6 30 In most cases cell voltages and electrode. but the lower the maximum attainable MFC voltage To potentials are adequately measured with commonly available. 5186 9 ENVIRONMENTAL SCIENCE TECHNOLOGY VOL 40 NO 17 2006. voltage meters multimeters and data acquisition systems the NHE Electrode potentials are often strongly dependent. connected in parallel with the circuit Cell voltages can be on the pH in the system and it is therefore important to. determined directly from the voltage difference between the report the solution pH Preferably electrode potentials are. anode and cathode electrode potentials can only be deter reported in the literature back calculated against the NHE. mined against a reference electrode that needs to be included expressed in V or V vs NHE but are also often reported as. in the electrode compartment 65 Current is calculated using a voltage difference against the reference electrode that was. Ohm s law I Ecell R using the measured voltage used in the study e g V vs Ag AgCl. A more detailed understanding of the bio electrochem As a consequence of these different methods the potential. ical system can be obtained using a potentiostat e g of the electrodes appears to vary dependent on the electrode. Ecochemie The Netherlands Princeton Applied Research used the pH and for the cathode the concentration of the. USA Gamry Scientific USA With a potentiostat either the electron acceptor For example at pH 7 a typical anode. potential or the current of an electrode can be controlled in potential is 0 20 to 0 28 V NHE equivalent to 0 40 to. order to study the electrochemical response of the electrode 0 48 V vs Ag AgCl At the same pH a typical cathode potential. at that specific condition The potentiostat is typically is 0 30 to 0 10 V NHE equivalent to 0 10 to 0 10 V vs Ag. operated in a three electrode setup consisting of a working AgCl. electrode anode or cathode a reference electrode and a Power The overall performance of an MFC is evaluated. counter electrode 65 In MFC experiments the potentio in many ways but principally through power output and. static mode of this instrument is often used for voltammetry Coulombic efficiency Power is calculated as. tests in which the potential of the working electrode anode. or cathode is varied at a certain scan rate expressed in V P IEcell 13. s 1 In the case where a scan only goes in one direction the. method is referred to as linear sweep voltammetry LSV if Normally the voltage is measured across a fixed external. the scan is also continued in the reverse direction and comes resistor Rext while the current is calculated from Ohm s law. back to the start potential the method is cyclic voltammetry I Ecell Rext Thus power is usually calculated as. CV Figure 4B Voltammetry can be used for assessing the. electrochemical activity of microbial strains or consortia 6 Ecell. 16 50 51 determining the standard redox potentials of redox P 14. active components 7 and testing the performance of novel. cathode materials 55 A potentiostat can also be operated This is the direct measure of the electric power The maximum. in a two electrode setup to obtain polarization curves or to power is calculated from the polarization curve see below. determine the ohmic resistance using the current interrupt Power Density Power is often normalized to some. technique Figure 4A as described below In the two characteristic of the reactor in order to make it possible to. electrode setup the working electrode connector is connected compare power output of different systems The choice of. to the cathode positive terminal and both the counter the parameter that is used for normalization depends on. electrode and reference electrode connectors are connected application as many systems are not optimized for power. to the anode production The power output is usually normalized to the. More advanced measurements can be done when the projected anode surface area because the anode is where. potentiostat is equipped with a frequency response analyzer the biological reaction occurs 6 31 34 67 The power density. FRA allowing electrochemical impedance spectroscopy PAn W m2 is therefore calculated on the basis of the area. measurements EIS 65 In EIS a sinusoidal signal with small of the anode AAn as. amplitude is superimposed on the applied potential of the. working electrode By varying the frequency of the sinusoidal 2. signal over a wide range typically 10 4 to 106 Hz and plotting PAn 15. the measured electrode impedance detailed information can AAnRext. be obtained about the electrochemical system EIS can be. used to measure the ohmic and internal resistance of an In many instances however the cathode reaction is. MFC 27 66 as well as to provide additional insight into the thought to limit overall power generation 30 32 or the anode. operation of an MFC The interpretation of EIS data can be consists of a material which can be difficult to express in. rather complex however and therefore EIS techniques will terms of surface area i e granular material 35 In such. not be discussed further here cases the area of the cathode ACat can alternatively be used. to obtain a power density PCat The projected surface areas. Calculations and Procedures for Reporting Data of all components should always be clearly stated as well as. the specific surface area if known and the method of its. Electrode Potential The potential of an electrode anode or. determination, cathode can only be determined by measuring the voltage. To perform engineering calculations for size and costing. against an electrode with a known potential i e a reference. of reactors and as a useful comparison to chemical fuel cells. electrode A reference electrode consists of several phases of. the power is normalized to the reactor volume or, constant composition 65 and therefore has a constant.
potential The standard hydrogen electrode SHE or normal 2. hydrogen electrode NHE consisting of a platinum electrode Ecell. in a hydrogen saturated acidic solution all components at vRext. unit activity has a potential of 0 V Because the NHE is not. a very practical reference electrode to work with in an where Pv is the volumetric power W m3 68 and v is the. experimental setup other reference electrodes are often used total reactor volume i e the empty bed volume The use. The most popular reference electrode in MFC experiments of the total bed reactor volume is consistent with a tradition. is the silver silver chloride Ag AgCl reference electrode in environmental engineering to use the total reactor size as. because of its simplicity stability and nontoxicity In a a basis for the calculation A comparison on the basis of total. saturated potassium chloride solution at 25 C the Ag AgCl reactor volume however is not always level when comparing. reference electrode develops a potential of 0 197 V against two and single chambered reactors because there is no. the NHE Also practical but less common in MFC experi second chamber for an open air cathode In such cases it. ments is the saturated calomel electrode SCE 0 242 V against is useful to compare reactors on the basis of the total anode. VOL 40 NO 17 2006 ENVIRONMENTAL SCIENCE TECHNOLOGY 9 5187. compartment volume If multiple reactors are operated in. concert for example as a series of stacked reactors the volume. used for the air space for the cathode or volume for the. catholyte is then included for the overall reactor volume. Thus the volume used in the calculation should be clearly. stated and volumes of the individual chambers must always. be clearly noted,Ohmic Resistance Using the Current Interrupt Tech. nique The ohmic resistance R of an MFC can be, determined using the current interrupt technique 63 64 by. operating the MFC at a current at which no concentration. losses occur Next the electrical circuit is opened which. results in zero current i e an infinite resistance and a steep. initial potential rise ER Figure 4A voltage differences 2 3. is observed followed by a slower further increase of the. potential EA Figure 4A voltage differences 1 4 to the OCV. The determination of the steep potential rise after current. interrupting requires the fastest possible recording of the. potential up to s scale 64 Ohmic losses IR are FIGURE 5 Polarization a and power b curves of a microbial fuel. proportional to the produced current and the ohmic resis cell operating on starch The solid curves are the original data 70. tance When the current is interrupted the ohmic losses the dashed curves represent a mathematically manipulated dataset. instantaneously disappear This results in a steep potential in which the effect of an increase of the ohmic resistance with 20. rise ER in potential that is proportional to the ohmic is illustrated The increase of the ohmic resistance resulted in. resistance R and the current I produced before the a linear polarization curve dashed line From the slope of this. interruption Figure 4A see sections 2 and 3 Using Ohms curve an internal resistance of 30 ohm can be determined. law R is estimated using this approach as R ER I The. slower further increase of the potential EA to the OCV after losses mass transport effects are dominant solid line Figure. the initial steep potential rise gives the electrode overpo 5A In MFCs linear polarization curves are most often. tentials that occurred during current generation encountered dashed line Figure 5A For a linear polarization. Polarization Curves Polarization curves represent a curve the value of the internal resistance Rint of the MFC. powerful tool for the analysis and characterization of fuel is easily obtained from the polarization curve as it is equal. cells 63 A polarization curve represents the voltage as a to the slope e g Rint E I 26 Figure 5A dashed. function of the current density Polarization curves can be line. recorded for the anode the cathode or for the whole MFC Power Curves A power curve that describes the power. using a potentiostat If a potentiostat is not available a or power density as the function of the current or current. variable resistor box can be used to set variable external loads density is calculated from the polarization curve Figure 5B. Using a periodical decrease or increase when starting at solid line shows a typical power curve based on a previously. short circuit of the load the voltage is measured and the reported polarization curve Figure 5A 70 As no current. current is calculated using Ohms law To separately study flows for open circuit conditions no power is produced From. the performance of the system in terms of anode or cathode this point onward the power increases with current to a. potentials a reference electrode is used as described above maximum power point MPP 14 6 mW Figure 5B Beyond. When a potentiostat is used to record a polarization curve this point the power drops due to the increasing ohmic losses. an appropriate scan rate should be chosen such as 1 mV s 1 and electrode overpotentials to the point where no more. 25 The polarization curve should be recorded both up and power is produced short circuit conditions. down i e from high to low external resistance and vice In many MFCs the ohmic resistance plays a dominant. versa When a variable external resistance is used to obtain role in defining the point of the maximum attainable power. a polarization curve the current and potential values need MPP partially due to the low ionic conductivity of the. to be taken only when pseudo steady state conditions have substrate solutions 71 but usually to a low degree of. been established The establishment of this pseudo steady optimization in the fuel cell design The effect of increased. state may take several minutes or more depending on the ohmic resistance on the shape of a polarization curve is shown. system and the external resistance This condition is only a in Figure 5A The solid curve is the original data set while. temporary steady state because over longer times the the dashed curve was calculated by including an additional. substrate concentration in the reactor will change due to ohmic resistance of R 20 by subtracting a potential. substrate demand at the anode unless continuously re drop of EIR I R Increasing the ohmic resistance by this. plenished This will in turn affect the incidence of substrate amount produces a polarization curve that is linear Figure. products mass transfer over voltage and current Care should 5A dashed line which is typically observed for MFCs When. therefore be taken not to wait too long for the establishment a polarization curve is linear the slope is equal to the internal. of the pseudo steady state Polarization curves can also be resistance eq 12 which for this example is calculated as. obtained over multiple batch cycles i e with one resistor Rint 30 dashed line If the polarization curve is not. used for the whole cycle allowing measurement of Coulombic linear solid line a current independent Rint cannot be. efficiency see below for each resistor see ref 69 for a defined and the system is better expressed in term of ohmic. comparison of these two methods Long term recording may resistance R and the electrode overpotentials a and c. risk shifts in the microbial community eq 11 which can be determined using the current interrupt. Polarization curves can generally be divided in three method or EIS Increasing the ohmic resistance decreases. zones i starting from the OCV at zero current there is an the MPP from 14 6 to 4 8 mW A symmetrical semi cycle. initial steep decrease of the voltage in this zone the activation power density curve is typical for a high internal resistance. losses are dominant ii the voltage then falls more slowly MFC limited by ohmic resistance dashed line Figure 5B. and the voltage drop is fairly linear with current in this zone rather than a fuel cell limited by mass transfer solid line. the ohmic losses are dominant iii there is a rapid fall of Figure 5B In the case of a symmetrical semi cycle the MPP. the voltage at higher currents in this zone the concentration will occur at a point where the Rint Rext. 5188 9 ENVIRONMENTAL SCIENCE TECHNOLOGY VOL 40 NO 17 2006. Treatment Efficiency MFCs have been proposed as a an MFC is the lower cell yield compared to aerobic processes. method to treat wastewater and thus it is important to This is caused by the reduced energy available for biomass. evaluate the overall performance in terms of biochemical growth as a significant part of the substrate energy is. oxygen demand BOD chemical oxygen demand COD or converted to electrical power Reported MFC net yields range. total organic carbon TOC removal Other factors may also from 0 07 and 0 22 g biomass COD g substrate COD 1 while. be important such as soluble versus particulate removal typical aerobic yields for wastewater treatment are generally. and nutrient removal We focus here on performance in terms around 0 4 g biomass COD g substrate COD 1 26 The. of COD removal as it is a common measure for wastewater growth rate can be measured directly by determining the. treatment efficiency and the COD removal is needed for biomass g COD built up on the electrode surface and. Coulombic and energy calculations The COD removal discharged in the effluent for continuous operation The. efficiency COD can be calculated as the ratio between the low biomass production in MFCs is an especially attractive. removed and influent COD This parameter measures how benefit since sludge disposal by combustion becoming the. much of the available fuel has been converted in the MFC standard technology in Europe costs approximately 600. either into electrical current via the Coulombic efficiency Euros per tonne. or biomass via the growth yield or through competitive COD Balance Once the efficiencies for electricity and. reactions with alternative electron acceptors e g oxygen biomass production are completed the fraction of COD that. nitrate and sulfate As the MFC influent can contain both was removed by unknown processes can be calculated. dissolved and particulate COD it can be difficult to specify as. what fraction of the effluent particulate COD was due to. biomass produced in the reactor or untreated COD that was 1 C Y 20. originally in the reactor influent, Coulombic Efficiency The Coulombic efficiency C is. defined as the ratio of total Coulombs actually transferred Loading Rate When examining the use of MFCs for. to the anode from the substrate to maximum possible wastewater treatment it is useful to examine performance. Coulombs if all substrate removal produced current The achieved with this new technology in terms of loading rates. total Coulombs obtained is determined by integrating the with those typically obtained in conventional treatment. current over time so that the Coulombic efficiency for an systems To do this we calculate the loading based on. MFC run in fed batch mode Cb evaluated over a period of volumetric loading rates as Bv kg COD m 3 d 1 Typical. time tb is calculated as 35 52 values for Bv achieved to date are up to 3 kg COD m 3 d 1. 18 compared to values for high rate anaerobic digestion. M of 8 20 kg COD m 3 d 1 or activated sludge processes of. 17 0 5 2 kg COD m 3 d 1 These loading rates can be normalized. FbvAn COD to the total anode volume for comparison with suspended. biomass processes e g activated sludge anaerobic diges. where M 32 the molecular weight of oxygen F is Faraday s tion and to total anode surface area for comparison with. constant b 4 is the number of electrons exchanged per biofilm processes Based on the reported areal short term. mole of oxygen vAn is the volume of liquid in the anode peak power productions 3 46 the anode surface specific. compartment and COD is the change in COD over time tb conversion rates for MFCs are up to 25 35 g COD m 2 d 1. For continuous flow through the system we calculate the which is higher than typical loading rates for rotating. Coulombic efficiency Cb on the basis of current generated biological contactors RBCs 10 20 g COD m 2 d 1 72 and. under steady conditions as comparable to those of high rate aerobic biofilm processes. such as the moving bed bio reactors MBBRs, Cb 18 Energy Efficiency The most important factor for evalu. Fbq COD ating the performance of an MFC for making electricity. compared to more traditional techniques is to evaluate the. where q is the volumetric influent flow rate and COD is the. system in terms of the energy recovery The overall energetic. difference in the influent and effluent COD, efficiency E is calculated as the ratio of power produced by.
The Coulombic efficiency is diminished by utilization of. the cell over a time interval t to the heat of combustion of. alternate electron acceptors by the bacteria either those. the organic substrate added in that time frame or, present in the medium or wastewater or those diffusing. through the CEM such as oxygen Other factors that reduce. Coulombic efficiency are competitive processes and bacterial. growth Bacteria unable to utilize the electrode as electron E 21. acceptor are likely to use substrate for fermentation and or Hmadded. methanogenesis It has been observed that fermentative. patterns diminish through time during enrichment of the where H is the heat of combustion J mol 1 and madded is. microbial consortium in the MFC 6 As long as the anode the amount mol of substrate added This is usually. remains attractive enough for the bacteria due to its potential calculated only for influents with known composition i e. alternative electron acceptors will not be used However for synthetic wastewaters as H is not known for actual. high potential compounds such as nitrate 0 55 V will wastewaters In MFCs energy efficiencies range from 2 to. almost certainly be used 50 or more when easily biodegradable substrates are used. Growth Yield Cell growth will reduce C due to diversion 18 30 As a basis for comparison the electric energy. of electrons into biomass The substrate utilization for growth efficiency for thermal conversion of methane does not exceed. is measured by the net or observed cell yield Y calculated 40. Distinguishing Methods of Electron Transfer, Y 19 Presence of Mediators Bacteria can reduce activation losses. by increasing their extracellularly oriented mediation capac. where X is the biomass g COD produced over time either ity Three pathways are discerned at this point direct. tb or hydraulic retention time An important advantage of membrane complex mediated electron transfer 8 mobile. VOL 40 NO 17 2006 ENVIRONMENTAL SCIENCE TECHNOLOGY 9 5189. redox shuttle mediated electron transfer 7 and electron anodic materials commonly used in MFC reactors such as. transfer through conductive pili also referred to as nanowires graphite foams reticulated vitreous carbon graphite and. 9 11 others are quite expensive Simplified electrodes such as. Cyclic voltammetry CV offers a rapid and proven method carbon fibers may alleviate these electrode costs The use. to discern whether bacteria use mobile redox shuttles to of expensive catalysts for the cathode must also be avoided. transfer their electrons or pass the electrons directly Another crucial aspect is the removal of non carbon based. through membrane associated compounds 6 For CV a substrates from the waste streams nitrogen sulfur and. reference electrode is placed in the anode chamber of the phosphorus containing compounds often cannot be dis. MFC close to the anode working electrode the counter charged into the environment at influent concentrations. electrode e g platinum wire is preferably placed in the Similarly even particulate organic compounds will need to. cathode chamber but can also be placed in the anode be removed and converted to easily biodegradable com. chamber A potentiostat is used to obtain a scan of potential pounds as part of an effective wastewater treatment opera. For bacterial suspensions a scan rate of 25 mV s 1 appears tion. to be reasonable based on the work of several researchers Applications One of the first applications could be the. 6 73 For the analysis of mediators in biofilms however development of pilot scale reactors at industrial locations. this scan rate needs to be decreased possibly to 10 mV s 1 where a high quality and reliable influent is available Food. and lower This decrease can affect the accuracy of peak processing wastewaters and digester effluents are good. discrimination as the peaks tend to broaden candidates To examine the potential for electricity generation. The extent of the redox mediation and the midpoint at such a site consider a food processing plant producing. potentials can be determined through analysis of i the MFC 7500 kg d of waste organics in an effluent 14 This represents. derived culture within its medium ii the MFC culture after a potential for 950 kW of power or 330 kW assuming 30. centrifugation and resuspension in physiological solution efficiency At an attained power of 1 kW m3 a reactor of 350. and iii the supernatant of the centrifuged MFC culture If m3 is needed which would roughly cost 2 6 M Euros 26 at. a peak is found both in case i and ii it indicates a shuttle current prices The produced energy calculated on the basis. which is membrane associated If a peak is found in case i of 0 1 Euros per kWh is worth about 0 3 M Euros per year. and iii it indicates that a mobile suspended shuttle is providing a ten year payback without other considerations. present The size of the peaks as integrated upon the of energy losses or gains compared to other aerobic. voltammogram either arbitrarily as I E 1 or through technologies Moreover decreased sludge production could. convolution analysis does not correlate unequivocally to substantially decrease the payback time. the extent of the membrane associated electron transfer and In the long term more dilute substrates such as domestic. the mobile shuttle mediated electron transfer This is caused sewage could be treated with MFCs decreasing society s. by the restricted accessibility of the membrane associated need to invest substantial amounts of energy in their. shuttles for oxidation reduction by the working electrode treatment A varied array of alternative applications could. Presence of Nanowires Electrically conductive bacterial also emerge ranging from biosensor development and. appendages known as nanowires have only recently been sustained energy generation from the seafloor to biobatteries. discovered so their structure s are therefore not well studied operating on various biodegradable fuels. or understood Pili produced by some bacteria have so far. While full scale highly effective MFCs are not yet within. been shown to be electrically conductive using scanning. our grasp the technology holds considerable promise and. tunneling electron microscopy 11 There is no data at the. major hurdles will undoubtedly be overcome by engineers. present time whether nanowires can be detected or can be. and scientists The growing pressure on our environment. distinguished from adsorbed chemical shuttles via standard. and the call for renewable energy sources will further. electrochemical methods such as CV If electron shuttles. stimulate development of this technology leading soon we. associate with a nonconductive pili or if the pili are covered. hope to its successful implementation, with metal precipitates they will be included in the CV. measurements as membrane associated shuttles or may. appear to be nanowires using STM If redox shuttles are Acknowledgments. enclosed within the pilus tubular structure they are unlikely This research was supported by National Science Foundation. to be detected using CV Additional research will be needed Grant BES 0401885 to B L the Belgian Science Foundation. to determine the best methods for detecting nanowires and FWO grant G 0172 05 to W V a Ph D grant IWT grant 41294. determining their importance relative to other methods of to P A of the Institute for the Promotion of Innovation. electron transfer from cells to electrodes through Science and Technology in Flanders IWT Vlaan. deren Australian Research Council DP 0666927 to J K. Outlook the Office of Naval Research N00014 03 1 0431 to U S and. MFC designs need improvements before a marketable the German Research Foundation Wetsus is funded by the. product will be possible 26 74 Both the issues identified city of Leeuwarden the Province of Frysla n the European. above and the scale up of the process remain critical issues Union European Regional Development Fund and the EZ. Most of the designs reviewed here cannot be scaled to the KOMPAS program of the Samenwerkingsverband Noord. level needed for a large wastewater treatment plant which Nederland. requires hundreds of cubic meters of reactor volume Either. the intrinsic conversion rate of MFCs will need to be Literature Cited. increased or the design will need to be simplified so that a. cost effective large scale system can be developed Designs 1 Berk R S Canfield J H Bioelectrochemical energy conversion. Appl Microbiol 1964 12 10 12, that can most easily be manufactured in stacks to produce. increased voltages will be useful as the voltage for a single 2 Rao J R Richter G J Von Sturm F Weidlich E The. performance of glucose electrodes and the characteristics of. cell is low different biofuel cell constructions Bioelectrochem Bioenerg. The success of specific MFC applications in wastewater 1976 3 139 150. treatment will depend on the concentration and biodegrad 3 Davis J B Yarbrough H F Preliminary experiments on a. ability of the organic matter in the influent the wastewater microbial fuel cell Science 1962 137 615 616. temperature and the absence of toxic chemicals Materials 4 Cohen B The bacterial culture as an electrical half cell J. costs will be a large factor in the total reactor costs Mainly Bacteriol 1931 21 18 19. 5190 9 ENVIRONMENTAL SCIENCE TECHNOLOGY VOL 40 NO 17 2006. 5 Potter M C Electrical effects accompanying the decomposition 28 Oh S Min B Logan B E Cathode performance as a factor. of organic compounds Proc R Soc London Ser B 1911 84 in electricity generation in microbial fuel cells Environ Sci. 260 276 Technol 2004 38 4900 4904, 6 Rabaey K Boon N Siciliano S D Verhaege M Verstraete 29 Oh S Logan B E Proton exchange membrane and electrode.
W Biofuel cells select for microbial consortia that self mediate surface areas as factors that affect power generation in microbial. electron transfer Appl Environ Microbiol 2004 70 5373 fuel cells Appl Microbiol Biotechnol 2006 70 162 169. 5382 30 Liu H Logan B E Electricity generation using an air cathode. 7 Rabaey K Boon N Hofte M Verstraete W Microbial single chamber microbial fuel cell in the presence and absence. phenazine production enhances electron transfer in biofuel cells of a proton exchange membrane Environ Sci Technol 2004. Environ Sci Technol 2005 39 3401 3408 38 4040 4046. 8 Bond D R Lovley D R Electricity production by Geobacter 31 Park D H Zeikus J G Improved fuel cell and electrode designs. sulfurreducens attached to electrodes Appl Environ Microbiol for producing electricity from microbial degradation Biotechnol. 2003 69 1548 1555 Bioeng 2003 81 348 355, 9 Gorby Y A Beveridge T J Composition reactivity and 32 Cheng S Liu H Logan B E Increased performance of single. regulation of extracellular metal reducing structures nanowires chamber microbial fuel cells using an improved cathode. produced by dissimilatory metal reducing bacteria Presented structure Electrochem Commun 2006 8 489 494. at DOE NABIR meeting April 20 2005 Warrenton VA 33 Habermann W Pommer E H Biological fuel cells with sulphide. 10 Gorby Y A Yanina S McLean J S Rosso K M Moyles D storage capacity Appl Microbiol Biotechnol 1991 35 128. Dohnalkova A Beveridge T J Chang I S Kim B H Kim 133. K S Culley D E Reed S B Romine M F Saffarini D A 34 Liu H Ramnarayanan R Logan B E Production of electricity. Hill E A Shi L Elias D A Kennedy D W Pinchuk G during wastewater treatment using a single chamber microbial. Watanabe K Ishii S Logan B E Nealson K H Fredrickson fuel cell Environ Sci Technol 2004 38 2281 2285. J K Electrically conductive bacterial nanowires produced by 35 Rabaey K Clauwaert P Aelterman P Verstraete W Tubular. Shewanella oneidensis strain MR 1 and other microorganisms microbial fuel cells for efficient electricity generation Environ. PNAS 2006 in press Sci Technol 2005 39 8077 8082, 11 Reguera G McCarthy K D Mehta T Nicoll J S Tuominen 36 He Z Minteer S D Angenent L T Electricity generation. M T Lovley D R Extracellular electron transfer via microbial from artificial wastewater using an upflow microbial fuel cell. nanowires Nature 2005 435 1098 1101 Environ Sci Technol 2005 39 5262 5267. 12 Bond D R Holmes D E Tender L M Lovley D R Electrode 37 Reimers C E Tender L M Fertig S Wang W Harvesting. reducing microorganisms that harvest energy from marine energy from the marine sediment water interface Environ. sediments Science 2002 295 483 485 Sci Technol 2001 35 192 195. 13 Park D H Zeikus J G Utilization of electrically reduced neutral 38 Tender L M Reimers C E Stecher H A Holmes D E. red by Actinobacillus succinogenes physiological function of Bond D R Lowy D A Pilobello K Fertig S J Lovley D. neutral red in membrane driven fumarate reduction and energy R Harnessing microbially generated power on the seafloor Nat. conservation J Bacteriol 1999 181 2403 2410 Biotechnol 2002 20 821 825. 14 Logan B E Extracting hydrogen and electricity from renewable 39 Hasvold Henriksen H Melvaer E Citi G Johansen B. resources Environ Sci Technol 2004 38 160a 167a Kj nigsen T Galetti R Sea water battery for subsea control. 15 Kim B H Park D H Shin P K Chang I S Kim H J systems J Power Sources 1997 65 253 261. Mediator less biofuel cell U S Patent 5976719 1999 40 Heilmann J Microbial fuel cells proteinaceous substrates and. 16 Kim H J Park H S Hyun M S Chang I S Kim M Kim hydrogen production using domestic wastewater Department. B H A mediator less microbial fuel cell using a metal reducing Civil and Environmental Engineering Penn State University. bacterium Shewanella putrefaciens Enzyme Microb Technol University Park PA. 2002 30 145 152 41 a Liu H Grot S Logan B E Electrochemically assisted. 17 Min B Logan B E Continuous electricity generation from microbial production of hydrogen from acetate Environ Sci. domestic wastewater and organic substrates in a flat plate Technol 2005 39 4317 4320 b Logan B E Grof S A. microbial fuel cell Environ Sci Technol 2004 38 5809 5814 bioelectrochemically assisted microbial reactor BEAMR that. 18 Rabaey K Lissens G Siciliano S D Verstraete W A microbial generates hydrogen gas Patent application 60 588 022. fuel cell capable of converting glucose to electricity at high rate 42 Rozendal R A Buisman C J N Process for producing. and efficiency Biotechnol Lett 2003 25 1531 1535 hydrogen Patent WO2005005981 2005. 19 Rhoads A Beyenal H Lewandowski Z Microbial fuel cell 43 Rozendal R A Hamelers H V M Euverink G J W Metz. using anaerobic respiration as an anodic reaction and bio S J Buisman C J N Principle and perspectives of hydrogen. mineralized manganese as a cathodic reactant Environ Sci production through biocatalyzed electrolysis Int J Hydrogen. Technol 2005 39 4666 4671 Energy 2006 in press DOI 10 1016 j ijhydene 2005 12 006. 20 Shantaram A Beyenal H Raajan R Veluchamy A Lewan 44 Tanisho S Kamiya N Wakao N Microbial fuel cell using. dowski Z Wireless sensors powered by microbial fuel cells Enterobacter aerogenes Bioelectrochem Bioenerg 1989 21 25. Environ Sci Technol 2005 39 5037 5042 32, 21 Barton S C Gallaway J Atanassov P Enzymatic biofuel cells 45 Gil G C Chang I S Kim B H Kim M Jang J K Park H. for implantable and microscale devices Chem Rev 2004 104 S Kim H J Operational parameters affecting the performance. 4867 4886 of a mediator less microbial fuel cell Biosens Bioelectron 2003. 22 Ringeisen B R Henderson E Wu P K Pietron J Ray R 18 327 334. Little B Biffinger J C Jones Meehan J M High power density 46 Chaudhuri S K Lovley D R Electricity generation by direct. from a miniature microbial fuel cell using Shewanella oneidensis oxidation of glucose in mediatorless microbial fuel cells Nat. DSP10 Environ Sci Technol 2006 40 2629 2634 Biotechnol 2003 21 1229 1232. 23 Logan B E Murano C Scott K Gray N D Head I M 47 Kim N Choi Y Jung S Kim S Development of microbial. Electricity generation from cysteine in a microbial fuel cell Water fuel cell using Proteus vulgaris Bull Korean Chem Soc 2000. Res 2005 39 942 952 21 44 49, 24 Phung N T Lee J Kang K H Chang I S Gadd G M Kim 48 Sell D Kra mer P Kreysa G Use of an oxygen gas diffusion. B H Analysis of microbial diversity in oligotrophic microbial cathode and a three dimensional packed bed anode in a. fuel cells using 16S rDNA sequences FEMS Microbiol Lett 2004 bioelectrochemical fuel cell Appl Microbiol Biotechnol 1989. 233 77 82 31 211 213, 25 Aelterman P Rabaey K Pham T H Boon N Verstraete W 49 Lowy D A Tender L M Zeikus J G Park D H Lovley D.
Continuous electricity generation at high voltages and currents R Harvesting energy from the marine sediment water interface. using stacked microbial fuel cells Environ Sci Technol 2006 II Kinetic activity of anode materials Biosens Bioelectron. 40 3388 3394 2006 21 2058 2063, 26 Rabaey K Verstraete W Microbial fuel cells novel biotech 50 Niessen J Schro der U Rosenbaum M Scholz F Fluorinated. nology for energy generation Trends Biotechnol 2005 23 polyanilines as superior materials for electrocatalytic anodes in. 291 298 bacterial fuel cells Electrochem Commun 2004 6 571 575. 27 Min B Cheng S Logan B E Electricity generation using 51 Schro der U Niessen J Scholz F A generation of microbial. membrane and salt bridge microbial fuel cells Water Res 2005 fuel cells with current outputs boosted by more than one order. 39 1675 1686 of magnitude Angew Chem Int Ed 2003 42 2880 2883. VOL 40 NO 17 2006 ENVIRONMENTAL SCIENCE TECHNOLOGY 9 5191. 52 Cheng S Liu H Logan B E Increased power generation in 66 He Z Wagner N Minteer S D Angenent L T The upflow. a continuous flow MFC with advective flow through the porous microbial fuel cell with an interior cathode assessment of the. anode and reduced electrode spacing Environ Sci Technol internal resistance by impedance spectroscopy Environ Sci. 2006 40 2426 2432 Technol 2006 40 5212 5217, 53 Bergel A Feron D Mollica A Catalysis of oxygen reduction 67 Park D H Laivenieks M Guettler M V Jain M K Zeikus. in PEM fuel cell by seawater biofilm Electrochem Commun J G Microbial utilization of electrically reduced neutral red as. 2005 7 900 904 the sole electron donor for growth and metabolite production. 54 Cheng S Liu H Logan B E Power densities using different Appl Environ Microbiol 1999 65 2912 2917. cathode catalysts Pt and CoTMPP and polymer binders Nafion 68 Bullen R A Arnot T C Lakeman J B Walsh F C Biofuel. and PTFE in single chamber microbial fuel cells Environ Sci cells and their development Biosens Bioelectron 2006 21. Technol 2006 40 364 369 2015 2045, 69 Heilmann J Logan B E Production of electricity from proteins. 55 Zhao F Harnisch F Schro der U Scholz F Bogdanoff P. using a single chamber microbial fuel cell Water Environ Res. Herrmann I Application of pyrolysed iron II phthalocyanine. 2006 78 531 537, and CoTMPP based oxygen reduction catalysts as cathode. 70 Niessen J Schro der U Scholz F Exploiting complex carbo. materials in microbial fuel cells Electrochem Commun 2005. hydrates for microbial electricity generation a bacterial fuel. 7 1405 1410, cell operating on starch Electrochem Commun 2004 6 955.
56 Rozendal R A Hamelers H V M Buisman C J N Effects 958. of membrane cation transport on pH and microbial fuel cell 71 Liu H Cheng S A Logan B E Power generation in fed batch. performance Environ Sci Technol published online June 9 microbial fuel cells as a function of ionic strength temperature. http dx doi org 10 1021 es060387r and reactor configuration Environ Sci Technol 2005 39 5488. 57 Bard A J Parsons R Jordan J Eds Standard Potentials in 5493. Aqueous Solution Marcel Dekker New York 1985 72 Tchobanoglous G Burton F L Wastewater Engineering. 58 Newman J S Electrochemical Systems Prentice Hall Englewood Treatment Disposal and Reuse 3rd ed Metcalf Eddy. Cliffs NJ 1973 McGraw Hill New York 1991, 59 Alberty R A Thermodynamics of Biochemical Reactions John 73 Park H S Kim B H Kim H S Kim H J Kim G T Kim. Wiley Sons New York 2003 M Chang I S Park Y K Chang H I A novel electrochemically. active and Fe III reducing bacterium phylogenetically related. 60 Amend J P Shock E L Energetics of overall metabolic reactions. to Clostridium butyricum isolated from a microbial fuel cell. of thermophilic and hyperthermophilic Archaea and Bacteria. Anaerobe 2001 7 297 306,FEMS Microbiol Rev 2001 25 175 243. 74 Logan B E Regan J M Microbial fuel cells challenges and. 61 Thauer R K Jungermann K Decker K Energy conservation applications Environ Sci Technol 2006 40 5172 5180. in chemotrophic anaerobic bacteria Bacteriol Rev 1977 41 75 Rabaey K Ossieur W Verhaege M Verstraete W Continuous. 100 180 microbial fuel cells convert carbohydrates to electricity Water. 62 Liu H Cheng S A Logan B E Production of electricity from Sci Technol 2005 52 515 523. acetate or butyrate using a single chamber microbial fuel cell 76 Rosenbaum M Schro der U Scholz F In situ electrooxidation. Environ Sci Technol 2005 39 658 662 of photobiological hydrogen in a photobioelectrochemical fuel. 63 Hoogers G Ed Fuel Cell Technology Handbook CRC Press cell based on Rhodobacter sphaeroides Environ Sci Technol. Boca Raton FL 2003 2005 39 6328 6333, 64 Larminie J Dicks A Fuel Cell Systems Explained John Wiley. Sons Chichester 2000 Received for review March 2 2006 Revised manuscript re. 65 Bard A J Faulkner L R Electrochemical Methods Funda ceived May 22 2006 Accepted June 7 2006. mentals and Applications 2nd ed John Wiley Sons New. York 2001 ES0605016, 5192 9 ENVIRONMENTAL SCIENCE TECHNOLOGY VOL 40 NO 17 2006.


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