A microbial fuel cell (MFC) is a bio-electrochemical system that converts the chemical energy in the organic compounds/renewable energy sources to electrical energy/bio-electrical energy through microbial catalysis at the anode under anaerobic conditions. This process is becoming attractive and alternative methodology for generation of electricity. MFC can convert chemical energy directly into electricity without an intermediate conversion into mechanical power. MFC as various benefits Clean; Safe and quiet performance High energy efficiency and It is easy to operate, Electricity generation, Biohydrogen production, Wastewater treatment, Bioremediation .

1. Article Written and published at
www.worldofchemicals.com
Microbial fuel cell – for conversion of chemical
energy to electrical energy

2. Abstract
 A microbial fuel cell (MFC) is a bio-electrochemical system
that converts the chemical energy in the organic
compounds/renewable energy sources to electrical
energy/bio-electrical energy through microbial catalysis at
the anode under anaerobic conditions. This process is
becoming attractive and alternative methodology for
generation of electricity.
 MFC is even considering as the completely new approach
to wastewater treatment and electricity generation. MFC
performed well for chemical oxygen demand (COD) and
biological oxygen demand (BOD) removal from the
wastewater. MFC has the capability of production of
maximum power of 6.73mW/m2 and it is a cost effective
process.
 Newly emerging concepts with alternative materials for
electrodes and catalysts as well as innovative designs
have made MFCs a promising technology. In this context,

3. Introduction
 MFC is considered to be a promising sustainable
technology to meet increasing energy needs,
especially by using wastewaters as substrates,
resulting in electricity and clean water as final
products.
 MFC can convert biomass spontaneously into
electricity through the metabolic activity of the
microorganisms. In a MFC, microorganisms
interact with electrodes using electrons, which are
either removed or supplied through an electrical
circuit.

4. Benefits
 Clean; Safe and quiet performance
 High energy efficiency and
 It is easy to operate.
 MFC Configuration
 MFC are being constructed using a variety of
materials. These systems are operated under a
range of conditions that include differences in
temperature, pH, electron acceptor, electrode
surface areas, and reactor size and operation
time.
 Types of MFCs
 Single - Chamber MFC
 Two - Chambered MFC

5. Single - Chamber MFC

6.  A simpler and more efficient MFC can be made by
omitting the cathode chamber and placing the
cathode electrode directly onto the proton exchange
membrane (PEM). Single chamber MFC avoids the
need to aerate water because the oxygen in air can
be directly transferred to the cathode. It offer simpler
designs and cost savings.
 Single-chambered MFCs are quite attractive for
increasing the power output because they can be run
without artificial aeration in an open air cathode
systems and can reduce the internal ohmic resistance
by avoiding the use of a catholyte as a result of
combining two chambers.
 Graphite rods were placed inside the anode chamber
and these rods extended outside of the anode
chamber and were connected to the cathode via an
external circuit.

8.  Two-compartment MFCs are typically run in batch
mode often with a chemically defined medium
such as glucose or acetate solution to generate
energy. They are currently used only in
laboratories.
 A typical two-compartment MFC has an anodic
chamber and a cathodic chamber connected by a
PEM, or sometimes a salt bridge, to allow protons
to move across to the cathode while blocking the
diffusion of oxygen into the anode.

9. Procedure
 MFC catalyzes the conversion of organic matter into
electricity by transferring electrons to circuit with the
aid of bacteria. Further the microorganisms can
transfer electrons to the anode electro in three ways,
firstly by using exogenous mediators such as
potassium ferricyanide, thonine or natural red;
secondly by using mediators produced by the bacteria
and lastly by direct transfer of electrons from the
respiratory enzymes to the electrodes.
 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.

10. Procedure Cont …
 In the second chamber of the MFC is another solution and
electrode (cathode). Cathode is positively charged and is the
equivalent of the oxygen sink at the end of the electron transport
chain. The solution is an oxidizing agent that picks up the
electrons at the cathode.
 Two electrodes are connected by salt bridge or PEM or ion-
exchange membrane to allow protons to move across to the
cathode while blocking the diffusion of oxygen into the anode.
 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. A critical anodic potential exist at
which a maximum power output of a microbial fuel cell is
achieved.
 The basic reactions are presented below; when microorganisms
consume a substrate such as sugar in aerobic condition they
produce CO2 and H2 O. However when oxygen is not present
i.e. under anaerobic condition they produce CO2, H+ and e- .

11. Anodic reaction
 C12H22O11 +13H2O → 12CO2 + 48H+ + 48e−
 Cathodic reaction
 O2 + 4e− + 4H+ → 2H2O
 Applications
 Electricity generation
 Biohydrogen production
 Wastewater treatment
 Bioremediation

12. Wastewater treatment
 Municipal wastewater contains a multitude of organic compounds that
can fuel MFCs. The amount of power generated by MFCs in the
wastewater treatment process can potentially reduce the electricity
needed in a conventional treatment.
 MFCs using certain microbes have a special ability to remove sulfides
as required in wastewater treatment. MFCs can enhance the growth of
bioelectrochemically active microbes during wastewater treatment thus
they have good operational stabilities.
 Continuous flow and single-compartment MFCs and membrane-less
MFCs are favoured for wastewater treatment due to concerns in scale-
up. Sanitary wastes, food processing wastewater, swine wastewater
and corn stover are all great biomass sources for MFCs because they
are rich in organic matters. It can even break the organic molecules
such as acetate, propionate, and butyrate to CO2 and H2O.
 MFC can remove the COD and BOD of wastewater of about 90 per
cent. MFCs yield 50-90 per cent less excess sludge, which eventually
reduces the sludge disposal cost. This showseffectiveness of MFC
performance in wastewater treatment.

13. Biohydrogen
 MFCs can be readily modified to produce hydrogen
instead of electricity. This modified system, which was
recently suggested and referred to as biocatalyzed
electrolysis or a bio-electrochemically assisted microbial
reactor (BEAMR) process or electrohydrogenesis, has
been considered an interesting new technology for the
production of biohydrogen from organics.
 However, hydrogen generation from the protons and
electrons produced by the anaerobic degradation of a
substrate by electrochemically active bacteria in a modified
MFC is thermodynamically unfavourable. this
thermodynamic barrier can be overcome by applying an
external potential. In this system, the protons and electrons
produced by the anodic reaction migrate and combine at
the cathode to form hydrogen under anaerobic conditions.
 The potential for the oxidation of acetate (1M) at the anode
and the reduction of protons to hydrogen at the cathode
are -0.28 and -0.42 V (NHE), respectively.

14. Current research work
 Dr Orianna Bretschger, from the J. Craig Venter
Institute, Maryland, USA, and her team has made
improvements to one version of the MFC.
 "We've improved its energy recovery capacity from
about two per cent to as much as thirteen per cent,
which is a great step in the right direction. That
actually puts us in a realm where we could produce a
meaningful amount of electricity if this technology is
implemented commercially. Eventually, we could have
wastewater treatment for free."
 - Dr Orianna Bretschger
 MFC also removes organic material from sewage and
prevents bad microbes that can spread diseases. Dr
Orianna Bretschger team’s MFC can remove around
97 per cent of organic materials and it is converting
around 13 per cent of slurry's energy into electricity.

15. Conclusion
 The achievable power output from MFCs has increased
remarkably over the last decade, which was obtained by altering
their designs, such as optimization of the MFC configurations,
their physical and chemical operating conditions, and their
choice of biocatalyst.
 MFCs are capable of converting biomass at temperatures below
20 °C and with low substrate concentrations, both of which are
problematic for methanogenic digesters.
 A major disadvantage of MFCs is their reliance on biofilms for
mediator-less electron transport, while anaerobic digesters such
as up-flow anaerobic sludge blanket reactors eliminate this need
by efficiently reusing the microbial consortium without cell
immobilization. Another limitation is the inherent naturally low
catalytic rate of the microbes.
 Although some basic knowledge has been gained in MFC
research, there is still a lot to be learned in the scaleup of MFC
for large-scale applications. However, the recent advances might
shorten the time required for their large-scale applications for
both energy harves

16. More References
 1] Liliana Alzate-Gaviria, Microbial Fuel Cells for Wastewater Treatment, Available from -
http://cdn.intechopen.com/pdfs/14554/InTech-Microbial_fuel_cells_for_wastewater_treatment.pdf
 [2] Microbial fuel cell, Eco-friendly sewage treatment, Orianna Bretschger - correction Available from -
http://www.earthtimes.org/energy/microbiol-fuel-cell-eco-friendly-sewage-treatment/1900/
 [3] Zhuwei Du, Haoran Li, Tingyue Gu, A state of the art review on microbial fuel cells: A promising technology for wastewater
treatment and bioenergy, 10 May 2007, Biotechnology Advances 25 (2007) 464–482, Available from - http://132.235.17.4/Paper-
gu/MFCreview.pdf
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microbial fuel cell, Vol. 3, No. 4, 2011, pp. 42-47, Available from - http://www.ajol.info/index.php/ijest/article/viewFile/68540/56618
 [5] Deepak Pant, Gilbert Van Bogaert, Ludo Diels, Karolien Vanbroekhoven, A review of the substrates used in microbial fuel cells
(MFCs) for sustainable energy production, 7 October 2009, Available from - http://www.microbialfuelcell.org/Publications/2010-
Pant-Areviewofthesubstratesusedinmicrobialfuelcellsforsustainableenergyproduction.pdf
 [6] In S. Kim, Kyu-Jung Chae, Mi-Jin Choi, and Willy Verstraete, Microbial Fuel Cells: Recent Advances, Bacterial Communities
and Application Beyond Electricity Generation, Vol. 13, No. 2, pp. 51-65, 2008, Available from -
http://www.eer.or.kr/home/pdf/In%20S.%20Kim.pdf
 Image Reference
 Fig 1) Schematic diagram of single chamber MFC - Deepak Pant , Gilbert Van Bogaert, Ludo Diels, Karolien Vanbroekhoven, A
review of the substrates used in microbial fuel cells (MFCs) for sustainable energy production, 4 October 2009, Available from -
http://www.microbialfuelcell.org/Publications/2010-Pant-
Areviewofthesubstratesusedinmicrobialfuelcellsforsustainableenergyproduction.pdf
 Fig 2) Schematic diagram of two-chambered MFC - Deepak Pant, Gilbert Van Bogaert, Ludo Diels, Karolien Vanbroekhoven, A
review of the substrates used in microbial fuel cells (MFCs) for sustainable energy production, 4 October 2009, Available from -
http://www.microbialfuelcell.org/Publications/2010-Pant-
Areviewofthesubstratesusedinmicrobialfuelcellsforsustainableenergyproduction.pdf
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