Microbial fuel cells

Microbial fuel cells

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  Microbial fuel cells Topic:
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  Introduction A microbial fuelcell (MFC) or biological fuel cell is a bio- electrochemical system that drives a current by using bacteria and mimicking bacterial interactions found in nature. MFCs can be grouped into two general categories:  Mediated  Unmediated
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  Definition A microbial fuelcell (MFC) is a device that converts chemical energy to electrical energy by the action of microorganisms. These electrochemical cells are constructed using either a bioanode and/or a biocathode.
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  History The first MFCs,demonstrated in the early 20th century, used a mediator: a chemical that transfers electrons from the bacteria in the cell to the anode. Unmediated MFCs emerged in the 1970s; in this type of MFC the bacteria typically have electrochemically active redoxproteins such as cytochromeson their outer membrane that can transfer electrons directly to the anode. In the 21st century MFCs started to find a commercial use in wastewater treatment.
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  Types of MFCs Single- Chamber MFC: 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) Two - Chambered MFC 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.
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  Single - ChamberMFC
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  Two - ChamberedMFC
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  Procedure MFC catalyzes theconversion of organic matter into electricity by transferring electrons to circuit with the aid of bacteria. Further the microorganisms can transfer electrons to the anode electrode in three ways:  By using exogenous mediators such as potassium ferricyanide, thionine or natural red  By using mediators produced by the bacteria  By direct transfer of electrons from the respiratory enzymes to the electrodes.
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  Reaction The basic reactionsare 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- .  Anodic reaction C12H22O11 +13H2O → 12CO2 + 48H+ + 48e−  Cathodic reaction O2 + 4e− + 4H+ → 2H2O
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  Applications Electricity generation:
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  Wastewater treatment:
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  Biosensors: The current generatedfrom a microbial fuel cell is directly proportional to the energy content of wastewater used as the fuel. MFCs can measure the solute concentration of wastewater (i.e., as a biosensor)
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  Biohydrogen production:
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  Disadvantages Low catalytic rate Lowenergy production Expensive Reliance on biofilm
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  Conclusion  Although somebasic 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 harvesting and wastewater treatment systems and for the scaleup process.