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Microbial fuel cell
From Wikipedia, the free encyclopedia
A microbial fuel cell (MFC) or biological
fuel cell is a device in which micro-organisms oxidize
compounds such as glucose, acetate or wastewater. The electrons
gained from this oxidation are transferred towards an electrode,
called the anode. From the anode, the electrons depart through
an electrical circuit towards a second electrode, the cathode.
At the cathode, the electrons are transferred towards a high
potential electron acceptor, preferrably oxygen. As current now
flows over a potential difference, power is generated as a
result of bacterial activity.
The power outputs reported thus far are usually small, in the
order of magnitude of about a
milliwatt. While no commercially available applications
exist at the moment, this is expected to change in the coming
years. Mainly electricity generation out of wastewater is one of
the main focuses at the moment. Also glucose-powered
pacemakers that would need no other power supply than the
glucose present in the
bloodstream, bio-sensors, and nutrient removal systems are
Microbial fuel cell
A microbial fuel cell is a device that converts chemical
energy to electrical energy by the catalytic reaction of
microorganisms (Allen and Bennetto, 1993). A typical
microbial fuel cell consists of
cathode compartments separated by a cation specific
membrane. In the anode compartment, fuel is oxidized by
protons. Electrons are transferred to the cathode
compartment through an external electric circuit, and the
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. In general,
there are two types of microbial
fuel cell, mediator and mediator-less microbial fuel cell.
Biological fuel cells take glucose and
methanol from food scraps and convert it into hydrogen and
food for the bacteria.
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
potassium ferric cyanide,
methyl viologen (methyl
neutral red and so on (Delaney et al., 1984; Lithgow et al.,
1986). Most of the mediators available are expensive and toxic.
Mediator-less Microbial Fuel Cell
Mediator-less microbial fuel cells have been engineered at
the Korea Institute of Science and Technology
, by a team led by Kim, Byung Hong
A mediator-less microbial fuel cell does 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 (Kim et al., 1999a), Aeromonas
hydrophila (Cuong et al., 2003), and others.
Mediator-less MFCs are a much more recent development and due
to this the factors that affect optimum operation, such as the
bacteria used in the system, the type of ion membrane, and the
system conditions such as temperature, are not particularly well
understood. Bacteria in mediator-less MFCs typically have
electrochemically-active redox enzymes such as
cytochromes on their outer membrane that can transfer
electrons to external materials(15).
When micro-organisms consume a substrate such as sugar in
aerobic conditions they produce carbon dioxide and water,
however when oxygen is not present they produce carbon dioxide,
protons and electrons as described below:
C12H22O11 + 13H2O
---> 12CO2 + 48H+ + 48e- Eqt. 1
Microbial fuel cells use inorganic mediators to tap into the
electron transport chain of cells and steal these electrons that
are produced. The mediator crosses the outer cell lipid
membranes and plasma wall; it then begins to liberate electrons
from the electron transport chain that would normally 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 then it will collect all the
electrons as it has a greater electronegativity than the
A number of mediators have been suggested for use in
microbial fuel cells, these include natural red, methylene blue,
thionine or resorfuin(21).
This is the principle behind generating a flow of electrons
from most micro-organisms. In order to turn this into a usable
supply of electricity this process has to be accommodated into a
In order to generate a useful current it is necessary to
create a complete circuit, not just shuttle electrons to a
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 an oxidizing 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
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.
Microbial fuel cells have a number of potential uses. The
first and most obvious is harvesting the electricity produced
for a power source. Virtually any organic material could be used
to ‘feed’ the fuel cell. MFCs could be installed to waste water
treatment plants. The 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. A fuel cell’s
emissions are well below regulations (16). MFCs also use energy
much more efficiently than standard combustion engines which are
limited by the
Carnot Cycle. In theory a MFC is capable of energy
efficiency far beyond 50%(17).
However MFCs do not have to be used on a large scale, it has
even been suggested that MFCs could be implanted in the body to
be employed as a power source for a pacemaker, a microsensor or
a microactuator. The MFC would take glucose from the blood
stream or possibly other substrates contained in the body and
use this to generate electricity to power these devices(18). The
advantages to using a 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 also be built very small, and they
operate well in mild conditions, 20°C to 40°C and also at
The electricity from the fuel cells could be harnessed for
use by applications such as
Since the current generated from a microbial fuel cell is
directly proportional to the strength of wastewater used as the
fuel, an MFC can be used to measure the strength of wastewater
[Kim, B. H., Chang, I. S., Gil, G. C., Park, H. S. and Kim, H.
J. (2003) Novel BOD (biological oxygen demand) sensor using
mediator-less microbial fuel cell. Biotechnology Letters, 25,
541-545.] The strength of wastewater is commonly evaluated as
biochemical oxygen demand (BOD) values. BOD values are
determiined 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. An MFC-type BOD sensors underestimate
BOD values in the presence of these electron acceptors. This can
be avoided inhibiting aerobic and nitrate respirations in the
MFC using terminal oxydase inhibitors such as cyanide and azide
[Chang, I. S., Moon, H., Jang, J. K. and Kim, B. H. (2005)
Improvement of a microbial fuel cell performance as a BOD sensor
using respiratory inhibitors. Biosensors and Bioelectronics 20,
1856-1859.] This type of BOD sensor is commercially available.
Current research practices
Currently, most researchers in this field are
biologists rather than
engineers. This has prompted some researchers (Menicucci,
2005) to 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, data about the value of the used resistance is
scanty, leading to non-comparable data.
At the turn of the last century, the idea of using microbial
cells in an attempt to produce
electricity was first conceived. M. C. Potter was the first
to perform work on the subject in 1912(10). A professor of
botany at the
University of Durham Potter managed to generate electricity
E. Coli, however 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(11). 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. Unfortunately, though the cell
functioned it was found to be unreliable due to the unstable
nature of the hydrogen production from the micro-organisms(12).
Although this issue was later resolved in work by Suzuki et al.
in 1976(13) the current design concept of a MFC came into
existence a year later with work once again by Suzuki(14).
Even by the time of Suzuki’s work in the late seventies
little was understood about how these 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
Kings College In London. Bennetto saw the fuel cell as a
possible method for the generation of electricity for third
world countries. His work, starting in the early 1980s helped
build an understanding of how fuel cells operate and until his
retirement was seen by many as the foremost authority on the
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 still to be
fully understood. Like a normal fuel cell an MFC has both an
anode and a cathode chamber. The
anaerobic anode chamber is connected internally to the
cathode chamber by an ion exchange membrane, the circuit is
completed by an external wire.
- - Allen, R.M. and Bennetto, H.P. 1993. Microbial fuel
cells—Electricity production from carbohydrates. Appl.
Biochem. Biotechnol., 39/40, pp. 27–40.
- - 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.
- - 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.
- - Gil, G.C., Chang, I.S., Kim, B.H., Kim, M., Jang,
J.K., Park, H.S., Kim, H.J., 2003. Operational parameters
affecting the performance of a mediator-less microbial fuel.
Biosen. Bioelectron. 18, 327–334.
- - 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.
- - Kim, H.J., Hyun, M.S., Chang, I.S., Kim, B.H. 1999b. A
microbial fuel cell type lactate biosensor using a
metal-reducing bacterium, Shewanella putrefaciens.
J Microbiol. Biotechnol. 9:365–367.
- - Kim HJ, Park HS, Hyun MS, Chang IS, Kim M, Kim BH. A
mediator-less microbial fuel cell using a metal reducing
bacterium, Shewanella putrefaciens. Enzyme Microb.
Technol. 2002;30: 145–152.
- - 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.
- -Joseph Anthony Menicucci 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,
- - Potter, M. C. (1912). Electrical effects accompanying
the decomposition of organic compounds. Royal Society
(Formerly Proceedings of the Royal Society) B, 84, p290-276.
- - Cohen, B. (1931). The Bacterial Culture as an
Electrical Half-Cell, Journal of Bacteriology, 21, pp18-19
- - DelDuca, M. G., Friscoe, J. M. and Zurilla, R. W.
(1963). Developments in Industrial Microbiology. American
Institute of Biological Sciences, 4, pp81-84.
- - Karube, I., Matasunga, T., Suzuki, S. and Tsuru, S.
(1976) Continuous Hydrogen Production by Immobilized Whole
Cells of Clostridium Butyricum. Biocheimica et Biophysica
Acta, 24 (2), pp338-343
- - Karube, I., Matasunga, T., Suzuki, S. and Tsuru, S.
(1977). Biochemical Cells Utilizing Immobilized Cells of
Clostridium butyricum. Biotechnology and Bioengineering, 19,
- - 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
- - 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
- - Yue P.L. and Lowther K. (1986). Enzymatic Oxidation of
C1 compounds in a Biochemical Fuel Cell The Chemical
Engineering Journal 33
- - Chen, T., Barton, S. C., Binyamin, G., Gao, Z., Zhang,
Y., Kim, H-H. and Heller, A. (2001). A miniature Biofuel
Cell, Journal of the American Chemical Society, 123,
- - Bullen, R. A., Arnot, T. C., Lakeman, J. B. and Walsh,
F.C. (2005). Biofuel cells and their development Biosensors
& Bioelectronics, 21 (11), pp2015-2045
- - Bennetto, H. P. (1990). Electricity Generation by
Micro-organisms Biotechnology Education, 1 (4), pp163-168
- - 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.
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