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A microbial electrolysis cell

A microbial fuel cell (MFC) or biological fuel cell is a bio-electrochemical system that drives acurrent by

mimicking bacterial interactions found in nature.

Mediator-less MFCs are a more recent development; due to this, factors that affect optimum efficiency, such as

the strain of bacteria used in the system, type of ion-exchange membrane, and system conditions (temperature, pH,

etc.) are not particularly well understood.

Bacteria in mediator-less MFCs typically have electrochemically active redox proteins such ascytochromes on their

outer membrane that can transfer electrons to external materials.[1]

Contents

  [hide] 

1 History

2 Types

o 2.1 Definition

o 2.2 Mediator microbial fuel cell

o 2.3 Mediator-free microbial fuel cell

o 2.4 Microbial Electrolysis Cell

o 2.5 Soil-based Microbial Fuel Cell

3 Electrical generation process

4 Applications

o 4.1 Power generation

o 4.2 Education

o 4.3 Biosensor

5 Current research practices

6 Commercial applications

7 See also

8 References

9 Further reading

10 External links

[edit]History

The idea of using microbial cells in an attempt to produce electricity was first conceived at the turn of the nineteenth

century. M.C. Potter was the first to perform work on the subject in 1911.[2]

A professor of botany at the University of Durham, Potter managed to generate electricity from E. coli, but the work

was not to receive any major coverage. In 1931, however, Barnet Cohen drew more attention to the area when he

created a number of microbial half fuel cells that, when connected in series, were capable of producing over 35 volts,

though only with a current of 2 milliamps.[3]

More work on the subject came with a study by DelDuca et al. who used hydrogen produced by the fermentation of

glucose by Clostridium butyricum as the reactant at the anode of a hydrogen and air fuel cell. Though the cell

functioned, it was found to be unreliable owing to the unstable nature of hydrogen production by the micro-organisms.

[4] Although this issue was later resolved in work by Suzuki et al. in 1976[5]the current design concept of an MFC came

into existence a year later with work once again by Suzuki.[6]

By the time of Suzuki’s work in the late 1970s, little was understood about how microbial fuel cells functioned;

however, the idea was picked up and studied later in more detail first by MJ Allen and then later by H. Peter Bennetto

both from King's College London. Bennetto saw the fuel cell as a possible method for the generation of electricity

for developing countries. His work, starting in the early 1980s, helped build an understanding of how fuel cells

operate, and until his retirement, he was seen by many[who?] as the foremost authority on the subject.

It is now known that electricity can be produced directly from the degradation of organic matter in a microbial fuel cell,

although the exact mechanisms of the process are yet to be fully understood. Like a normal fuel cell, an MFC has

both an anode and a cathode chamber. Theanoxic anode chamber is connected internally to the cathode chamber

via an ion exchange membrane with the circuit completed by an external wire.

In May 2007, the University of Queensland, Australia, completed its prototype MFC, as a cooperative effort

with Foster's Brewing. The prototype, (a 10L design), converts brewery wastewater into carbon dioxide, clean water,

and electricity. With the prototype proven successful[citation needed], plans are in effect to produce a 660 gallon version for

the brewery, which is estimated to produce 2 kilowatts of power. While it is a negligible amount of power, the

production of clean water is of utmost importance to Australia, for which drought is a constant threat.

[edit]Types

[edit]Definition

A microbial fuel cell is a device that converts chemical energy to electrical energy by the catalytic reaction

of microorganisms.[7]

A typical microbial fuel cell consists of anode and cathode compartments separated by a cation (positively charged

ion) specific membrane. In the anode compartment, fuel is oxidized by microorganisms,

generating electrons and protons. Electrons are transferred to the cathode compartment through an external electric

circuit, while protons are transferred to the cathode compartment through the membrane. Electrons and protons are

consumed in the cathode compartment, combining with oxygen to form water[citation needed].

More broadly, there are two types of microbial fuel cell: mediator and mediator-less microbial fuel cells.

[edit]Mediator microbial fuel cell

Most of the microbial cells are electrochemically inactive. The electron transfer from microbial cells to the electrode is

facilitated by mediators such as thionine, methyl viologen, methyl blue, humic acid , neutral red and so on.[8][9] Most of

the mediators available are expensive and toxic.

[edit]Mediator-free microbial fuel cell

A plant microbial fuel cell (PMFC)

Mediator-free microbial fuel cells do not require a mediator but uses electrochemically active bacteria to transfer

electrons to the electrode (electrons are carried directly from the bacterial respiratory enzyme to the electrode).

Among the electrochemically active bacteria are, Shewanella putrefaciens [10] , Aeromonas hydrophila [11] , and others.

Some bacteria, which have pili on their external membrane, are able to transfer their electron production via these

pili.

Mediator-less microbial fuel cells can, besides running on wastewater, also derive energy directly from certain aquatic

plants. These include reed sweetgrass, cordgrass, rice, tomatoes, lupines, and algae.[12] These microbial fuel cells

are called Plant Microbial Fuel Cells (Plant-MFC).[13] Given that the power is thus derived from a living plant (in situ-

energy production), this variant can provide extra ecological advantages.

[edit]Microbial Electrolysis Cell

Main article: Microbial electrolysis cell

A variation of the mediator-less MFC is the microbial electrolysis cells (MEC). Whilst MFC's produce electric current

by the bacterial decomposition of organic compounds in water, MEC's partially reverse the process to generate

hydrogen or methane by applying a voltage to bacteria to supplement the voltage generated by the microbial

decomposition of organics sufficiently lead to the electrolysis of water or the production of methane.[14][15] A complete

reversal of the MFC principle is found in microbial electrosynthesis, in which carbon dioxide is reduced by bacteria

using an external electric current to form multi-carbon organic compounds.[16]

[edit]Soil-based Microbial Fuel Cell

A soil-based MFC

Soil-based microbial fuel cells adhere to the same basic MFC principles as described above, whereby soil acts as the

nutrient-rich anodic media, the inoculum, and the proton-exchange membrane (PEM). The anode is placed at a

certain depth within the soil, while the cathode rests on top the soil and is exposed to the oxygen in the air above it.

Soils are naturally teeming with a diverse consortium of microbes, including the electrogenic microbes needed for

MFCs, and are full of complex sugars and other nutrients that have accumulated over millions of years of plant and

animal material decay. Moreover, the aerobic (oxygen consuming) microbes present in the soil act as an oxygen

filter, much like the expensive PEM materials used in laboratory MFC systems, which cause the redox potential of the

soil to decrease with greater depth. Soil-based MFCs are becoming popular educational tools for science classrooms.

[17]

[edit]Electrical generation process

When micro-organisms consume a substrate such as sugar in aerobic conditions they produce carbon

dioxideand water. However when oxygen is not present they produce carbon dioxide, protons and electrons as

described below[18]:

C12H22O11 + 13H2O ---> 12CO2 + 48H+ + 48e- (Eqt. 1)

Microbial fuel cells use inorganic mediators to tap into the electron transport chain of cells and channel electrons

produced. The mediator crosses the outer cell lipid membranes and bacterial outer membrane; then, it begins to

liberate electrons from the electron transport chain that normally would be taken up by oxygen or other intermediates.

The now-reduced mediator exits the cell laden with electrons that it shuttles to an electrode where it deposits them;

this electrode becomes the electro-generic anode (negatively charged electrode). The release of the electrons means

that the mediator returns to its original oxidised state ready to repeat the process. It is important to note that this can

only happen under anaerobic conditions; if oxygen is present, it will collect all the electrons as it has a

greater electronegativity than mediators.

In a microbial fuel cell operation, the anode is the terminal electron acceptor recognized by bacteria in the anodic

chamber. Therefore, the microbial activity is strongly dependent on the redox potential of the anode. In fact, it was

recently published that a Michaelis-Menten curve was obtained between the anodic potential and the power output of

an acetate driven microbial fuel cell. A critical anodic potential seems to exist at which a maximum power output of a

microbial fuel cell is achieved.[19]

A number of mediators have been suggested for use in microbial fuel cells. These include natural red, methylene

blue, thionine or resorufin.[20]

This is the principle behind generating a flow of electrons from most micro-organisms (the organisms capable of

producing an electric current are termed Exoelectrogens. In order to turn this into a usable supply of electricity this

process has to be accommodated in a fuel cell. In order to generate a useful current it is necessary to create a

complete circuit, and not just shuttle electrons to a single point.

The mediator and micro-organism, in this case yeast, are mixed together in a solution to which is added a suitable

substrate such as glucose. This mixture is placed in a sealed chamber to stop oxygen entering, thus forcing the

micro-organism to use anaerobic respiration. An electrode is placed in the solution that will act as the anode as

described previously.

In the second chamber of the MFC is another solution and electrode. This electrode, called the cathode is positively

charged and is the equivalent of the oxygen sink at the end of the electron transport chain, only now it is external to

the biological cell. The solution is anoxidizing agent that picks up the electrons at the cathode. As with the electron

chain in the yeast cell, this could be a number of molecules such as oxygen. However, this is not particularly practical

as it would require large volumes of circulating gas. A more convenient option is to use a solution of a solid oxidizing

agent.

Connecting the two electrodes is a wire (or other electrically conductive path which may include some electrically

powered device such as a light bulb) and completing the circuit and connecting the two chambers is a salt bridge or

ion-exchange membrane. This last feature allows the protons produced, as described in Eqt. 1 to pass from the

anode chamber to the cathode chamber.

The reduced mediator carries electrons from the cell to the electrode. Here the mediator is oxidized as it deposits the

electrons. These then flow across the wire to the second electrode, which acts as an electron sink. From here they

pass to an oxidising material.

[edit]Applications

[edit]Power generation

Microbial fuel cells have a number of potential uses. The most readily apparent is harvesting electricity produced for

use as a power source. Virtually any organic material could be used to feed the fuel cell, including coupling cells

to wastewater treatment plants.

Bacteria would consume waste material from the water and produce supplementary power for the plant. The gains to

be made from doing this are that MFCs are a very clean and efficient method of energy production. Chemical

processing wastewater[21][22] and designed synthetic wastewater[23][24] have been used to produce bioelectricity in dual

and single chambered mediatorless MFCs (non-coated graphite electrodes) apart from wastewater treatment.

Higher power production was observed with biofilm covered anode (graphite).[25][26] A fuel cell’s emissions are well

below regulations.[27]MFCs also use energy much more efficiently than standard combustion engines which are

limited by the Carnot Cycle. In theory an MFC is capable of energy efficiency far beyond 50% (Yue & Lowther, 1986).

According to new research conducted by René Rozendal, using the new microbial fuel cells, conversion of the energy

to hydrogen is 8x as high as conventional hydrogen production technologies.

However MFCs do not have to be used on a large scale, as the electrodes in some cases need only be 7 μm thick by

2 cm long.[28] The advantages to using an MFC in this situation as opposed to a normal battery is that it uses a

renewable form of energy and would not need to be recharged like a standard battery would. In addition to this they

could operate well in mild conditions, 20°C to 40°C and also at pH of around 7.[29] Although more powerful than metal

catalysts, they are currently too unstable for long term medical applications such as inpacemakers (Biotech/Life

Sciences Portal).

Besides wastewater power plants, as mentioned before, energy can also be derived directly from crops. This allows

the set-up of power stations based on algae platforms or other plants incorporating a large field of aquatic plants.

According to Bert Hamelers, the fields are best set-up in synergy with existing renewable plants (e.g. offshore

windturbines). This reduces costs as the microbial fuel cell plant can then make use of the same electricity lines as

the wind turbines.[30]

[edit]Education

Soil-based microbial fuel cells are popular educational tools, as they employ a range of scientific disciplines

(microbiology, geochemistry, electrical engineering, etc.), and can be made using commonly available materials, such

as soils and items from the refrigerator. There are also kits available for classrooms and hobbyists,[31] and research-

grade kits for scientific laboratories and corporations.[32]

[edit]Biosensor

Since the current generated from a microbial fuel cell is directly proportional to the energy content of wastewater used

as the fuel, an MFC can be used to measure the solute concentration of wastewater (i.e. as a biosensor system).[33]

The strength of wastewater is commonly evaluated as biochemical oxygen demand (BOD) values.[clarification needed] BOD

values are determined incubating samples for 5 days with proper source of microbes, usually activate sludge

collected from sewage works. When BOD values are used as a real time control parameter, 5 days' incubation is too

long.

An MFC-type BOD sensor can be used to measure real time BOD values. Oxygen and nitrate are preferred electron

acceptors over the electrode reducing current generation from an MFC. MFC-type BOD sensors underestimate BOD

values in the presence of these electron acceptors. This can be avoided by inhibiting aerobic and nitrate respirations

in the MFC using terminal oxidase inhibitors such as cyanide and azide.[34] This type of BOD sensor is commercially

available.

[edit]Current research practices

Some researchers[35] point out some undesirable practices, such as recording the maximum current obtained by the

cell when connecting it to a resistance as an indication of its performance, instead of the steady-state current that is

often a degree of magnitude lower. Sometimes[weasel words], data about the value of the used resistance is scanty,

leading to non-comparable data between publications.

[edit]Commercial applications

A number of companies have emerged to commercialize Microbial Fuel Cells. These companies have attempted to

tap into both the remediation and electricity generating aspects of the technologies. Some of these are companies

are mentioned here.[36]

[edit]See also

Sustainable development portal

Fermentative hydrogen production

Dark fermentation

Glossary of fuel cell terms

Photofermentation

Electrohydrogenesis

Electromethanogenesis

Hydrogen technologies

Hydrogen hypothesis

[edit]References

1. ̂  Min, B., Cheng, S. and Logan B. E. (2005). Electricity generation using membrane and salt bridge microbial fuel cells,

Water Research, 39 (9), pp1675–86

2. ̂  Potter, M. C. (1911). Electrical effects accompanying the decomposition of organic compounds. Royal Society

(Formerly Proceedings of the Royal Society) B, 84, p260-276

3. ̂  Cohen, B. (1931). The Bacterial Culture as an Electrical Half-Cell, Journal of Bacteriology, 21, pp18–19

4. ̂  DelDuca, M. G., Friscoe, J. M. and Zurilla, R. W. (1963). Developments in Industrial Microbiology. American Institute of

Biological Sciences, 4, pp81–84.

5. ̂  Karube, I., T. Matasunga, S. Suzuki & S. Tsuru 1976 Continuous hydrogen production by immobilized whole cells

of Clostridium butyricumBiocheimica et Biophysica Acta 24:2 338–343

6. ̂  Karube, Isao; Matsunaga, Tadashi; Tsuru, Shinya; Suzuki, Shuichi (November 1977). "Biochemical cells utilizing

immobilized cells ofClostridium butyricum". Biotechnology and Bioengineering 19 (11): 1727–

1733. doi:10.1002/bit.260191112.

7. ̂  Allen, R.M. and Bennetto, H.P. 1993. Microbial fuel cells—Electricity production from carbohydrates. Appl. Biochem.

Biotechnol., 39/40, pp. 27–40

8. ̂  Delaney, G.M., Bennetto, H.P., Mason, J.R., Roller, H.D.,Stirling, J.L., and Thurston, C.F. 1984. Electron-transfer

coupling in microbial fuel cells: 2. Performance of fuel cells containing selected micoorganism-mediator-substrate

combinations. J Chem. Tech. Biotechnol., 34B: 13–27.

9. ̂  Lithgow, A.M., Romero, L., Sanchez, I.C., Souto, F.A.,and Vega, C.A. 1986. Interception of electron-transport chain in

bacteria with hydrophilic redox mediators. J. Chem. Research, (S):178–179.

10. ̂  Kim, B.H., Kim, H.J., Hyun, M.S., Park, D.H. 1999a. Direct electrode reaction of Fe (III) reducing bacterium, Shewanella

putrefacience. J Microbiol. Biotechnol. 9:127–131.

11. ̂  Cuong, A.P. , Jung, S.J., Phung, N.T., Lee, J., Chang, I.S., Kim, B.H., Yi, H. and Chun, J. 2003. A novel

electrochemically active and Fe(III)-reducing bacterium phylogenetically related to Aeromonas hydrophila, isolated from a

microbial fuel cell. FEMS Microbiol. Lett., Volume 223(1) : 129-134.

12. ̂  Mediator-less microbial fuel cell schematic + explanation

13. ̂  Plant MFC term

14. ̂  Microbial Electrolysis Cell

15. ̂  Bruce Logan developing MEC's

16. ̂  http://mbio.asm.org/content/1/2/e00103-10.full

17. ̂  Soil-based MFCs

18. ̂  Bennetto, H. P. (1990). Electricity Generation by Micro-organisms Biotechnology Education, 1 (4), pp. 163–168

19. ̂  Cheng, Ky; Ho, G; Cord-Ruwisch, R. "Affinity of microbial fuel cell biofilm for the anodic potential.". Environmental

Science & Technology 42(10): 3828–34. doi:10.1021/es8003969. ISSN 0013-936X.

20. ̂  Bennetto, H. P., Stirling, J. L., Tanaka, K. and Vega C. A. (1983). Anodic Reaction in Microbial Fuel Cells

Biotechnology and Bioengineering, 25, pp 559–568

21. ̂  Venkata Mohan, S., Mohanakrishna, G., Srikanth, S., Sarma, P.N., 2008. Harnessing of bioelectricity in microbial fuel

cell (MFC) employing aerated cathode through anaerobic treatment of chemical wastewater using selectively enriched

hydrogen producing mixed consortia. “Fuel”. 87, 2667–2676.

22. ̂  Venkata Mohan, S., Mohanakrishna, G., Purushotam Reddy, B., Sarvanan, R., Sarma. P.N., 2008. Bioelectricity

generation from chemical wastewater treatment in mediatorless (anode) microbial fuel cell (MFC) using selectively

enriched hydrogen producing mixed culture under acidophilic microenvironment. “Biochem. Engng. J.” 39, 121-130

23. ̂  Venkata Mohan, S., Veer Raghuvulu, S., Srikanth, S., Sarma, P.N., 2007. Bioelectricity production by meditorless

microbial fuel cell (MFC) under acidophilic condition using wastewater as substrate: influence of substrate loading rate.

“Current Sci.” 92(12), 1720-1726.

24. ̂  Venkata Mohan, S., Sarvanan, R., Veer Raghuvulu, S., Mohankrishna, G., Sarma. P.N., 2008. Bioelectricity production

from wastewater treatment in dual chambered microbial fuel cell (MFC) using selectively enriched mixed microflora:

Effect of catholyte. “Biores. Technol.” 99(3), 596-603.

25. ̂  Venkata Mohan, S., Veer Raghuvulu, S., Sarma, P.N., 2008d. Biochemical evaluation of bioelectricity production

process from anaerobic wastewater treatment in a single chambered microbial fuel cell (MFC) employing glass wool

membrane. “Biosen. Bioelectron.” 23, 1326–1332.

26. ̂  Venkata Mohan, S., Veer Raghuvulu, S., Sarma, P.N., 2008e. Influence of anodic biofilm growth on bioelectricity

production in single chambered mediatorless microbial fuel cell using mixed anaerobic consortia. “Biosen. Bioelectron.”

24(1), 41-47.

27. ̂  Choi Y., Jung S. and Kim S. (2000) Development of Microbial Fuel Cells Using Proteus Vulgaris Bulletin of the Korean

Chemical Society, 21 (1), pp44–48

28. ̂  Chen, T.; Barton, S.C.; Binyamin, G.; Gao, Z.; Zhang, Y.; Kim, H.-H.; Heller, A. (Sep 2001). "A miniature biofuel cell.". J

Am Chem Soc 123 (35): 8630-1. doi:10.1021/ja0163164. PMID 11525685.

29. ̂  Bullen RA, Arnot TC, Lakeman JB, Walsh FC (2006). "Biofuel cells and their development.". Biosensors &

Bioelectronics 21 (11): 2015-45.doi:10.1016/j.bios.2006.01.030. PMID 16569499.

30. ̂  Eos magazine, Waterstof uit het riool, June 2008

31. ̂  Keego Technologies - MudWatt MFC

32. ̂  Research-Grade BES Test Kits

33. ̂  Kim, BH.; Chang, IS.; Gil, GC.; Park, HS.; Kim, HJ. (April 2003). "Novel BOD (biological oxygen demand) sensor using

mediator-less microbial fuel cell.". Biotechnology Letters 25 (7): 541-

545. doi:10.1023/A:1022891231369. PMID 12882142.

34. ̂  Chang, I. S.; Moon, H.; Jang, J. K.; Kim, B. H. (2005). "Improvement of a microbial fuel cell performance as a BOD

sensor using respiratory inhibitors". Biosensors and Bioelectronics 20 (9): 1856–

1859. doi:10.1016/j.bios.2004.06.003. PMID 15681205.

35. ̂  Menicucci, Joseph Anthony Jr., Haluk Beyenal, Enrico Marsili, Raaja Raajan Angathevar Veluchamy, Goksel Demir,

and Zbigniew Lewandowski, Sustainable Power Measurement for a Microbial Fuel Cell, AIChE Annual Meeting

2005, Cincinnati, USA

36. ̂  [Pant et al., 2011. An introduction to the life cycle assessment (LCA) of bioelectrochemical systems (BES) for

sustainable energy and product generation: Relevance and key aspects. Renewable and Sustainable Energy Reviews.

15 (2),1305-1313 ]

The Biotech/Life Sciences Portal (20 Jan 2006). "Impressive idea – self-sufficient fuel cells". Baden-Württemberg GmbH.

Retrieved 2011-02-07.

Liu H, Cheng S and Logan BE (2005). "Production of electricity from acetate or butyrate using a single-chamber microbial fuel

cell". Environ Sci Technol 32 (2): 658–62. doi:10.1021/es048927c.

Rabaey, K. & W. Verstraete (2005). "Microbial fuel cells: novel biotechnology for energy generations". Trends

Biotechnol 23 (6): 291–298.doi:10.1016/j.tibtech.2005.04.008. PMID 15922081.

Yue P.L. and Lowther K. (1986). Enzymatic Oxidation of C1 compounds in a Biochemical Fuel Cell. The Chemical Engineering

Journal, 33B, p 69-77

[edit]Further reading

Rabaey, K. et al. (May, 2007). "Microbial ecology meets electrochemistry: electricity-driven and driving

communities". Isme J. 1 (1): 9–18.doi:10.1038/ismej.2007.4. PMID 18043609.

Pant, D. et al. (March, 2010). "A review of the substrates used in microbial fuel cells (MFCs) for sustainable

energy production".Bioresource Technology 101 (6): 1533–

1543. doi:10.1016/j.biortech.2009.10.017. PMID 19892549.

[edit]External links

Sustainable and efficient biohydrogen production via electrohydrogenesis -Nov 2007

Microbial Fuel Cell blog  A research-type blog on common techniques used in MFC research.

Microbial Fuel Cells  This website is originating from a few of the research groups currently active in the MFC

research domain.

Microbial Fuel Cells from Rhodopherax Ferrireducens  An overview from the Science Creative Quarterly.

Building a Two-Chamber Microbial Fuel Cell

Discussion group on Microbial Fuel Cells

Innovation company developing MFC technology