MICROBIAL FUEL CELL DMCE, MUMBAI.

BYPUSHPAK ELLEEDU

Use of the fossil fuels can trigger global energy crisis & increased global warming hence there is considerable interest in research fraternity on green energy production.

MFC converts chemical energy to electrical energy by catalytic reaction of microorganisms.

Electrons produced by metabolism of microorganisms are utilized for generation of electricity.

MFC operates at near about ambient temperature & nearly neutral solutions.

They operate on complex substrate present in waste water.

MICROBIAL FUEL CELL

Principle is based on redox reaction between replenishable agents.

Consists of anode, cathode, PEM or Salt bridge.

Anode at anaerobic conditions & cathode at aerobic.

PEM joining two chambers allows only protons to diffuse.

Principle

At anode microbes oxidize substrate to CO2.

Released electrons absorbed by anode & transported to cathode by electric circuit.

The released protons diffuse through PEM & form water by combining with Oxygen.

Anodic Reaction

CH3COO + 2H2O -------- ► 2CO2 + 7H+ + 8e – orC6H12O6 + 6H2O 6CO2 -------- ► 24H+ + 24e‐

Cathodic ReactionO2 + 4H+ + 4e- -------- ► 2H2O or24H+ + 24e‐ -------- ► 6O2 12H2O

Working

Designs of MFC

Two compartments MFC power output

Designs of MFC

Single compartment MFC power output

Types of MFC

Limit on surface area of anode as bacteria can clog small pores and hence limit on current.

Still not economically competitive.

Power produced way below when compared with conventional cells.

The practical value of maximum voltage achieved is very low when compared to the theoretical value

This can be attributed to• Activation losses.• Bacterial metabolic losses.• Concentration losses.

Limitations of MFCs

Non conductive lipid membrane, lipopoly saccharides & peptididoglycans in microbes hinder electron transfer to anode.

Hence they require mediator for transport of electrons.

Mediator in oxidizing state reduces by capturing electrons & transports it to anode & reoxidises.

Synthetic mediators : Thionine, Methylene Blue, Neutral Red.

Natural mediators : Anthraquione, Humic acid, Sulphate & Thiosulphate.

Performance Enhancement of MFC

Uses bioelectrochemically active bacteria to transfer electrons to electrode.

They have electrochemically active redox enzymes like cytochromes on outer membrane that helps in electron transfer.

Form a biofilm on the anode surface & transfer electrons directly by conductance to anode.

Shewanella Putrefaciens & Aeromonas Hydrophila are some examples of bioelectrochemically active bacteria used.

Performance Enhancement of MFC

Microbes Substrate Applications

Actinobacillus succinogenes Glucose Neutral red or thionin as electron mediator

Aeromonas hydrophila Acetate Mediator-less MFC

Alcaligenes faecalis, Enterococcus gallinarum, Pseudomonas aeruginosa

Glucose Self-mediate consortia isolated from MFC with a maximal level of 4.31 W m− 2.

Clostridium beijerinckii Starch, glucose, lactate, molasses

Fermentative bacterium

Clostridium butyricum Starch, glucose, lactate, molasses

Fermentative bacterium

Various Microbes used in MFCs

Modifying the anodes of a MFC using nanofabrication techniques can result in increase of the current density output of the MFC.

Characterizing the Nanomodified anodes using microscopy can result in increase in efficiency of MFCs.

Growing gold, iron, and nickel Nanoparticles (NPs) and Multi Walled Carbon Nanotubes(MWCNTs) on anode plate will increase the attracting power of anode towards electrons and hence will result in increase in efficiency of MFC.

Carbon nanotubes

Performance Enhancement of MFC

Nanoscale: 1x 10-9m = 1nm.

A hair is ≈ 10 μm (10,000 larger) Nanostructures are thought to improve e- transfer from bacteria to Anode.

Performance comparison of MFC

Applications of MFC

Municipal wastewater, Sanitary waste, Organic waste from farms or industry has multitude of organic compounds that fuel MFCs.

About 50-90% of organic solids like aceate, propionate and butyrate are degraded.

COD upto 80% can be removed and has a high coulombic efficiency of 80%.

Since the current generated from a microbial fuel cell is directly proportional to the strength of wastewater used as the fuel, an MFC can be used to measure the strength of wastewater.

Continuous flow and single compartment MFCs preferred because of scale up concerns.

Applications of MFC

Efficient and direct conversion of organic substrate to electricity.

Unlike conventional cells MFC could operate well in mild conditions, 20°C to 40°C and also at pH of around 7.

Can be installed in locations lacking electrical infrastructures.

Alternative to present source of fuel to meet energy needs.

The gains to be made are that MFCs are a very clean and efficient method of energy production and they also treat waste generated in daily life so use of MFCs are like “Hitting two birds with one stone”.

Advantages of MFC

MFCs in Future