MICROBIAL FUEL CELLS

MICROBIAL FUEL CELLS

Presented bySHABEEBA.V4PA11BT023

CONTENTSIntroductionWhat are fuel cells?What are microbial fuel cellsprincipleConstruction of MFCComponents of MFCWorking of MFCThermodynamics of MFCMFC DesignTypes of MFCApplications of MFCAdvantages of MFCLimitations of MFCConclusionReferences

INTRODUCTIONUse of the fossil fuels can trigger global energy crisis and increased global warming hence there is considerable interest in research fraternity on green productionIn an era of climate change, alternate energy sources are desired to replace oil and carbon resources. Subsequently, climate change effects in some areas and the increasing production of biofuels are also putting pressure on available water resources. Microbial Fuel Cells have the potential to simultaneously treat wastewater for reuse and to generate electricity; thereby producing two increasingly scarce resourcesMicrobial fuel cell technology represents a new form of renewable energy by generating electricity from what would otherwise be considered waste, such as industrial wastes or waste water etc

Continuation.M.C Potter was the first to perform work on the subject in 1911 in E.coli,A professor of botany at theUniversity of DurhamIn 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 milliampsIn 1911 B.H. Kim devoloped mediatorless MFC was a milestone in MFC, Enhanced the commercial viablity,by eleiminating costly mediator chemicals.Microbial fuel cells have come a long way since the early 20th century.

Cellular respiration s a collection of metabolic reactions that cells use to convert nutrients into ATP which fuels cellular activity.overalll reaction is an exothermic redox reaction.4

What are fuel cells? Device that converts chemical energy from fuel into electricity through chemical reaction with oxygen or another oxidizing agent.

What are Microbial fuel cells?

Chemical energy to electrical energyCatalytic reaction of microorganismsBio-electrochemical systemMimics bacterial interaction

primary flow diagram

Meaning;mfc is a bec system that drives a current by mimicking bacterial interactions found in nature6

Based on redox reactionsHarness the natural metabolism of microbes to produce electricityBacteria converts substrate into electronsElectrons run through the circuit to generate powerPrinciple

CONSTRUCTION OF MFC:

Components of MFCAnodeCathodeExchange membraneSubstrateElectrical circuitMicrobes

Anode;Conductive,bio compatible & chemicaly stable with substrateStainless steel mesh,graphite plates or rodsBacteria live in the anode compartment and convert substrate to CO2,H2O and energyBacteria are kept in an oxygen less environment

Anode compartment

Oxygen free enviornment:to promote the flow of electrons through anode10

Cathode;Electrons and protons recombine at the cathodeO2 reduced to waterPt catalyst is used

Cathode compartment

Pt catalyst:to reduce O2 sufficiently11

Exchange membrane;NAFION or ULTREXProtons flows through the EMProton and electrons recombine on the other side.Can b a proton or cation exchange membrane

Exchange membrane

Electrical circuitAfter leaving anode, electrons travel through the circuitThese electrons power the load

Electrical circuit

Substrates;Substrates provide energy for the bacterial cellInfluences the economic viability and overall performance such as power density and coloumbic efficiency of MFCConcentration,composition and type Organic substrates-carbohydrates, protein,volatile acids,cellulose and waste waterAcetate is commonly used as substrate

Y acetate:due to its inertness towards alternative microbial conversions(fermentations and methenogenisis) that lead to high colombic efficiency and power output.14

Substrates used in MFCSubstrate typeConcentrationsCurrent density (m A/cm2)Acetate1g/L0.8Lactate18mM0.005Glucose6.7Mm0.7Sucrose2674mg/L0.19Glucaronic acid6.7mM0.18Phenol400mg/L0.1Sodium fumerate25mM2.05Starch10g/L1.3Cellulosic particles4g/L0.02Xylose6.7mM0.74Domestic wastewater600mg/L0.06Brewery wastewater2240mg/L0.2

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Microbes used in MFCAxenic bacterial cultureMetal reducing bacteriaShewanella putrefaciensGeobacter sulfurreducens Rhodoferax ferrireducensClostridium beijerinckiiMixed bacterial fuel cultureDesulfuromonas, Alcaligenes faecalis, Enterococcus faecium, Pseudomonas aeruginosa, Proteobacteria,

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Continuation..Clostridium butricumBacteroides and Aeromonas species nitrogen fixing bacteria (e.g. Azoarcus and Azospirillum)

Working of MFC

Continuation.Anode and cathode separated by cathode specific membraneMicrobes at anode oxidize organic fuel generates electrons and protonsProtons move to the cathode compartment through the membraneElectrons transferred to the cathode compartment through external circuit to generate currentElectrons and protons are consumed in cathode chamber, combining with O2 to form water Anodic reaction: CH3COO- + H2O 2CO2 + 2H+ +8e- acetate Cathodic reaction: O2 + 4e- + 4 H+ 2 H2O

Mfc work by allowing bactera to do what dey do best,oxidize and reduce organic moleculesBacterial respiration is basically one big redox reaction in which electrons being move around19

Thermodynamics of MFCUsing Gibbs free energy G r = Gr0 + RT ( ln)Cell electromotive force W = EemfQ = Gr , Q = nF Eemf = Gr nFOverall reaction in terms of the potential as Eemf = E0emf RTnF ln() positive for a favourabl reaction directly produces a value of emf for the reaction

Emf is potential difference bw cathode and anode.this is related to work W(J)20

MFC DesignDifferent configurations are possibleWidely used is a two chamber MFC built in traditional H shapeTwo chamber connected by a tube containing a seperator usually CEM or plain salt bridge

Types of MFCsMediator MFCMediator free MFC

Microbial electrolysis fuel cell

ContinuationSoil based MFC

Phototrophic biofilm MFCNanoporous MFCSediment MFCMembrane less MFC

Applications of MFCWaste water treatmentPower generationSecondary fuel productionBio-SensorsDesalinationEducational tool

Advantages of MFCGeneration of energy out of biowaste / organic matterDirect conversion of substrate energy to electricityOmission of gas treatmentAeration Bioremediation of toxic compounds

Limitations of MFCLow power densityHigh initial costActivation lossesOhmic lossesBacterial metabolic losses

ConclusionMFCs have been explored as a new source of electricity generation during operational waste water treatment. Phototropic MFCs and solar powered MFC also represent an exceptional attempt in the progress of MFCs technology for electricity production.It can be used for production of secondary fuel as well as in bioremediation of toxic compounds. However, this technology is only in research stage and more research is required before domestic MFCs can be made available for commercializationProvided the biological understanding increases, the electrochemical technology advances and the overall electrode prices decrease, this technology might qualify as a new core technology for conversion of carbohydrates to electricity in years to come.

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