Literature review willprovide handy information about MFCs. It will reveal the relevant informationabout the technology used in Microbial Fuel Cell. It will let the reader tounderstand its design and function. MICROBES:In order to understand thefundamental principle of Microbial fuel cell it is important to haveinformation about the microorganisms.
Bacteria are the major microbes which areinvolved in this process. Bacteria breakdown organic matter and release energyin the process. Some bacteria have the ability to generate electricity and totransfer electrons effectively to anode. The bacteria which have this abilityare known as “Exoelectrogens”. Exoelectrogens have the ability to generateelectricity in microbial fuel cells by extracellular electron transfer toanode. It directly transfers electrons to a chemical or material that is notimmediate electron acceptor.
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These electrogens can besourced in sand, water and many other sources. But here we are using soil as asource.TYPES OF MFCs:There are two types of MFCs:1. Mediated2. Mediator-free3. Soil basedMediated: In this type of microbialcells a mediator is used o transfer electrons to electrode. Examples ofcommonly used mediators are thionine, methyl blue and neutral red etc. Mediator-free: Mediator free MFCs used electrochemically activemicrobes (mostly bacteria) to transfer electrons directly to electrode.
Mediator-free cells can directly obtain energy from certain plants. This isknown as plant microbial fuel cell. Possible plants include sweet grass,tomatoes and algae etc.
It can provide ecological advantages.Figure 2: A plant microbial fuel cell Soil Based: In soil based MFC, soilacts as a nutrient rich anodic media, the inoculum and proton exchangemembrane. The anode is placed at the bottom whereas cathode is placed at thetop and is exposed to the air. Soil is filled with diverse microbes, includingelectrogenic bacteria, is full of complex sugars and other nutrients obtained fromplants and animal material decay. Figure 3: Soil based MFC MFC DESIGN:Double-ChamberMFC Design:This type of MFC is usedwidely.
It contains two chambers. Anode is placed in one chamber whereascathode in another and is separated by a proton exchange membrane. The anodechamber is kept oxygen free for anaerobic breakdown process to occur. Though itis widely used by it is still challenging because of its impracticalconfiguration.
Thisset up can accommodate various electrode shapes, i.e. plane, granular and brushas it has a dedicated chambers for the anode and cathode.
It can also use othercatholyte besides air, which is any source of oxygen. According to a recentresearch document, use of algae (seaweed) enhances the oxygen production due tophotosynthetic process in the plant which can be facilitated by this type ofMFC configuration. A. González del Campo, P. Cañizares , M.
A. Rodrigo, “Microbialfuel cell with an algae-assisted cathode: A preliminary assessment,” Nov. 2013Figure 4: A Double-Chamber MFCSingle-chamber MFC Design:A one-compartmentMFC eliminates the need for the cathodic chamber by exposing the cathodedirectly to the air. We are dealing with sand based MFC which has one Chamber. Anodeis dug inside the soil and cathode is at the top in exposed air as shown inFigure 3. COMPONENTS:A microbial fuel cell consists of single but effectivecomponents to effectively harness the energy.
Components are as follows:· Electrodes: Both in cathode and anode.· Substrate: Any organic matter used as source formicroorganisms such as “Sand”.· Bacteria: Exoelectrogens are most suited for Microbial fuelcells.Table 1: Basic components of Microbial Fuel cell Serial no. Item Material 1.
Anode Graphite, graphite felt, carbon paper, carbon-cloth, Pt, Pt black, reticulated vitreous carbon (RVC). 2. Cathode Graphite, graphite felt, carbon paper, carbon-cloth, Pt, Pt black, RVC. 3. Electrode Catalyst Pt, Pt black, MnO2, Fe3+, polyaniline, electron mediator immobilized on anode. PRINCIPLE OF MICROBIALFUEL CELL:”Microbial fuelcells (MFCs) are electrochemical devices that use the metabolic activity of microorganismsto oxidize fuels, generating current by direct or mediated electron transfer toelectrodes.” K. Rabaey and W.
Verstraete, “Microbial fuel cells: novelbiotechnology for energy generation” , page 291–298, Jun. 2005. The deviceconsists of anode, cathode, proton exchange membrane and an external circuit.The MFC convert biodegradable substrate directly into electricity.
Anode holdsthe bacteria and the organic matter in an anaerobic environment. Cathode isexposed to air. Bacteria generate protons and electrons as organic substanceconverts to energy. Microbes use this energy for growth. The electrons aretransferred directly to the anode (if mediator-free MFC) and then to copperelectrode via conduction.Some bacteriaare unable to transfer electrons on their own, so a mediator is used forelectron transfer such as methyl blue, thionine.
These are called Redoxmediators. H. J. Mansoorian, A. H. Mahvi, “Bioelectricity generation usingtwo chamber microbial fuel cell treating wastewater from food processing”, May2013Chemical energyis converted into electricity by microbial activity. Microbes releaseelectrons.
Oxygen is supplied to the cathode by air source. Materials use inthe electrodes influence the energy produced.Figure 5: Schematic of the basic components of a MFC APPLICATIONS OF MFCs:The main applications of MFCs are:Generation ofBioelectricity:MFC is mostrecent and fantastic technology that uses wide variety of substrates, materialswith bacteria to achieve to produce bio energy despite the fact that powerlevel in these systems is relatively low. Themain objective of MFCs is to achieve a suitable current and power for theapplication in small electrical devices. It is specially used for sustainable long-term powerapplications.
Rahimnejad and et al. turn on ten LED lamps and onedigital clock with fabricated stacked MFC as power source and both devices weresuccessfully operated for the duration of 2 days. M. Rahimnejad, A. Ghoreyshi, G.
Najafpour”A novel microbial fuel cell stack for continuous production of clean energy”(Article),2012Waste Water Treatment:Different typeof waste water like sanitary waste, food processing waste water etc. cancontain energy in the form of biodegradable organic matter. MFC can captureenergy as electricity or hydrogen gas. MFCs using specific microbes areexcellent techniques to remove sulfides from wastewater. Up to 90% of the CODcan be removed in some cases.MICROBIOLOGICAL ASPECT:As fossil fuels aredepleting soon we are looking for more sustainable methods and one of them ismicrobial fuel cell technology for long term energy generation. Microbial fuelcell concept is possible due to exocellular electron transfer. Microbes areinvolved in this activity.
Main step i.e. electron transfer, is done bymicrobes. All the study of these microbes is done in a microbiology lab.
Without microbes this process is incomplete. It does not produce harmful byproducts so it is more sustainable.