Article Written and published at
www.worldofchemicals.com
Microbial fuel cell – for conversion of chemical
energy to elect...
Abstract
 A microbial fuel cell (MFC) is a bio-electrochemical system
that converts the chemical energy in the organic
co...
Introduction
 MFC is considered to be a promising sustainable
technology to meet increasing energy needs,
especially by u...
Benefits
 Clean; Safe and quiet performance
 High energy efficiency and
 It is easy to operate.
 MFC Configuration
 M...
Single - Chamber MFC
 A simpler and more efficient MFC can be made by
omitting the cathode chamber and placing the
cathode electrode directly ...
 Two-compartment MFCs are typically run in batch
mode often with a chemically defined medium
such as glucose or acetate s...
Procedure
 MFC catalyzes the conversion of organic matter into
electricity by transferring electrons to circuit with the
...
Procedure Cont …
 In the second chamber of the MFC is another solution and
electrode (cathode). Cathode is positively cha...
Anodic reaction
 C12H22O11 +13H2O → 12CO2 + 48H+ + 48e−
 Cathodic reaction
 O2 + 4e− + 4H+ → 2H2O
 Applications
 Elec...
Wastewater treatment
 Municipal wastewater contains a multitude of organic compounds that
can fuel MFCs. The amount of po...
Biohydrogen
 MFCs can be readily modified to produce hydrogen
instead of electricity. This modified system, which was
rec...
Current research work
 Dr Orianna Bretschger, from the J. Craig Venter
Institute, Maryland, USA, and her team has made
im...
Conclusion
 The achievable power output from MFCs has increased
remarkably over the last decade, which was obtained by al...
More References
 1] Liliana Alzate-Gaviria, Microbial Fuel Cells for Wastewater Treatment, Available from -
http://cdn.in...
Microbial fuel cell – for conversion of chemical energy to electrical energy
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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 .

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Microbial fuel cell – for conversion of chemical energy to electrical energy

  1. 1. Article Written and published at www.worldofchemicals.com Microbial fuel cell – for conversion of chemical energy to electrical energy
  2. 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. 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. 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. 5. Single - Chamber MFC
  6. 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.
  7. 7.  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.
  8. 8. 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.
  9. 9. 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- .
  10. 10. Anodic reaction  C12H22O11 +13H2O → 12CO2 + 48H+ + 48e−  Cathodic reaction  O2 + 4e− + 4H+ → 2H2O  Applications  Electricity generation  Biohydrogen production  Wastewater treatment  Bioremediation
  11. 11. 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.
  12. 12. 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.
  13. 13. 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.
  14. 14. 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
  15. 15. 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  [4] B.K. Pandey , V. Mishra , S. Agrawal, Production of bio-electricity during wastewater treatment using a single chamber 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  To contact the author mail: articles@worldofchemicals.com  © WOC Article

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