Microbial Fuel Cell (MFC) - Green Technology PDF

# Microbial Fuel Cell ## Diagram A diagram of a microbial fuel cell is shown. - The diagram depicts a cube containing a fuel cell with a membrane separating the anode and cathode sides. - The anode side shows a plant that is degrading and releasing decomposed organic matter (DOM), biodegradable...

# Microbial Fuel Cell ## Diagram A diagram of a microbial fuel cell is shown. - The diagram depicts a cube containing a fuel cell with a membrane separating the anode and cathode sides. - The anode side shows a plant that is degrading and releasing decomposed organic matter (DOM), biodegradable matter (BDM), and electroactive microorganisms (EAM). These are all being catalyzed by the electron flow (e-) to create carbon dioxide, hydrogen, and energy, which are then used to power a light bulb at the top of the diagram. - The cathode side shows the process of reduction, where oxygen is recombining with hydrogen to create water. ## Introduction - The use of fossil fuels can result in global energy crisis and increased global warming, sparking interest in green production. - In an era of climate change, alternative energy sources are desired to replace oil and carbon resources. - Climate change effects in some areas and increasing biofuel production is putting pressure on available water resources. - Microbial Fuel Cells (MFCs) hold the potential to treat wastewater simultaneously and generate electricity, producing two increasingly scarce resources. - Microbial fuel cell technology is a new form of renewable energy, generating electricity from industrial or wastewater. ## Continuation - M.C Potter was the first to perform work on the subject in 1911 in E.coli at the University of Durham. - In 1931, Barnett Cohen drew more attention to the area by creating microbial half fuel cells that could produce 35 volts when connected in series, producing only 2 milliamps of current. - In 1911, B.H. Kim’s development of mediatorless MFC was a major milestone in MFC, enhancing commercial viability by eliminating expensive mediator chemicals. - Microbial fuel cells have come a long way since the early 20th century. ## What are fuel cells? A fuel cell is a device that converts chemical energy from fuel into electricity through a chemical reaction with oxygen or another oxidizing agent. ## What are Microbial fuel cells? - Convert chemical energy into electrical energy. - Use a catalytic reaction of microorganisms. - Involves a bio-electrochemical system. - Mimic bacterial interactions. ## Applications of MFC - Wastewater treatment - Power generation - Secondary fuel production - Bio-sensors - Desalination - Educational tool ## Advantages - Wider variety of applications than conventional fuel cells. - Solution for environmental problems. - Wastewater treatment and power generation at the same time. - Good alternative to conventional power generation systems. ## Limitations - The surface area of the anode is limited, as bacteria can clog the small pores and limit current. - Still not economically competitive. - Power production is lower than conventional cells. - Very slow performance in wastewater treatment. ## Principle - Based on redox reactions. - Harness the natural metabolism of microbes to produce electricity. - Bacteria converts substrate into electrons. - Electron flow through the circuit to generate power. ## Construction of MFC A diagram of a microbe fuel cell is shown. - The diagram shows a fuel cell with an anode and cathode side being separated by a membrane. - The anode side shows bacteria consuming glucose, releasing electrons, and hydrogen ions. - The cathode side shows oxygen and hydrogen ions recombining to form water. ## Electrochemical Cell A diagram of a simple voltaic cell is shown. - The cell consists of an anode and cathode in separate compartments. - The anode is made of copper, and the cathode is made of silver. - The compartments are connected by a salt bridge made of potassium nitrate (KNO3). - The anode is connected to the cathode by a wire. - The electrons flow from the copper electrode to the silver electrode. - The salt bridge allows the flow of ions, which keeps the solution electrically neutral. ## Components of MFC - Anode - Cathode - Exchange membrane - Substrate - Electrical circuit - Microbes ## Basic Design A diagram of a basic MFC design is shown. - Oxygen-poor fuel is being catalyzed by an anode biofilm to create carbon dioxide, hydrogen ions, and electrons. - The electrons flow through a circuit and power a load. - Hydrogen ions flow through the proton exchange membrane to recombine with oxygen in the cathode chamber to form water. ## Redox Reactions Involved - **Anodic Reaction (Oxidation)** - **CH3COO-** + 2H2O → 2CO2 + 7H+ + 8e- (Acetic Acid Ion) - **C6H12O6** + 6H2O → 6CO2 + 24H+ + 24e- (Glucose) - **Cathodic Reaction (Reduction)** - **O2** + 4H+ + 4e- → 2H2O - **6O2** + 24H+ + 24e- → 12H2O ## Organic Material as Fuel - Several organic materials, such as glucose and acetate, can be used as fuel. - They can be obtained from wastewater and solid waste, especially domestic waste. ## Anode - Conductive, bio-compatible and chemically stable to substrate. - Made of stainless steel mesh, graphite plates or rods. - Bacteria live in the anode compartment and convert substrate to CO2, H2O, and energy. - Bacteria are kept in an oxygen-less environment. ## Cathode - Electrons and protons recombine at the cathode. - Oxygen is reduced to water. - A platinum catalyst is used. ## Exchange Membrane - NAFION or ULTREX - Protons flow through the Exchange Membrane (EM). - Protons and electrons recombine on the other side. - Can be a proton or cation exchange membrane. ## Electrical Circuit - After leaving the anode, electrons travel through the electrical circuit. - These electrons power the load. ## Substrates - Substrates provide energy for the bacterial cell. - Influence economic viability and overall performance, such as power density and coulombic efficiency in MFC. - Several factors influence substrate efficacy: concentration, composition, and type. - Organic substrates include: carbohydrates, proteins, volatile acids, cellulose, and wastewater. - Acetate is commonly used as substrate. ## Substrates Used in MFC | Substrate Type | Concentrations | Current Density (mA/cm2) | | ------------- | ------------- | ------------- | | Acetate | 1g/L | 0.8 | | Lactate | 18mM | 0.005 | | Glucose | 6.7Mm | 0.7 | | Sucrose | 2674mg/L | 0.19 | | Glucaronic Acid | 6.7mM | 0.18 | | Phenol | 400mg/L | 0.1 | | Sodium Fumerate | 25mM | 2.05 | | Starch | 10g/L | 1.3 | | Cellulosic Particles | 4g/L | 0.02 | | Xylose | 6.7mM | 0.74 | | Domestic Wastewater | 600mg/L | 0.06 | | Brewery Wastewater | 2240mg/L | 0.2 | ## Microbes Used in MFC **Axenic Bacterial Culture** - Metal-reducing bacteria - *Shewanella putrefaciens* - *Geobacter sulfurreducens* - *Rhodoferax ferrireducens* - *Clostridium beijerinckii* **Mixed Bacterial Fuel Cultures** - *Desulfuromonas* - *Alcaligenes faecalis* - *Enterococcus faecium* - *Pseudomonas aeruginosa* - *Proteobacteria* ## Continuation - *Clostridium butrycum* - *Bacteroides and Aeromonas* species - Nitrogen-fixing bacteria: *Azoarcus and Azospirillum* ## Working of MFC - Anode and cathode separated by a cathode-specific membrane. - Microbes in the anode oxidize organic fuel and create electrons and protons. - Protons move to the cathode compartment through the membrane. - Electrons are transferred to the cathode compartment through an external circuit to generate current. - Electrons and protons are consumed in the cathode chamber, combining with O2 to form water. ### Anodic reaction: CH3COO- + H2O → 2CO2 + 2H+ + 8e- (acetate) ### Cathodic reaction: O2 + 4e- + 4 H+ → 2H2O ## Thermodynamics of MFC - Using Gibbs free energy: - ∆G' = G'r + RT (lnπ ) - Cell electromotive force: - W = EemfQ = ∆Gr, Q = nF - Eemf = ∆G/nF - Overall reaction in terms of potential: - Eemf = E°emf-RT/nF ln(π) - A positive result is favorable. - Directly produces a value of emf for the reaction. ## MFC Design - Different configurations are possible. - A two-chamber MFC built in the shape of a traditional "H" is commonly used. - The chambers are connected by a tube containing a separator, usually a CEM or plain salt bridge. ## Microbial Electrolysis Cell A diagram of a microbial electrolisis cell is shown. - The diagram depicts a plant waste fermentation taking place. - Acetic acid is produced. - Bacteria consume acetic acid, releasing electrons, proteins, and carbon dioxide. - The electrons flow through a circuit and power a load. - The load sends 0.2 Volts, which is used to combine electrons and protons to create hydrogen gas. - The hydrogen gas can be used in vehicles that run on natural gas. ## Types of MFCs - Mediator MFC - Mediator free MFC - Microbial electrolysis fuel cell ## Continuation - Soil-based MFC - Phototrophic biofilm MFC - Nanoporous MFC - Sediment MFC - Membrane-less MFC ## Conclusion - MFCs are explored for electricity generation during wastewater treatment. - Phototropic MFCs and solar-powered MFCs are an exceptional attempt for MFC technology development in the future. - Can be used to produce secondary fuels and for bioremediation. - More research is needed before domestic MFCs can be commercially available. - As biological understanding increases, electrochemical technology advances, and electrode prices decrease, this technology will likely become a core technology for converting carbohydrates into electricity in years to come. ## Diagram A diagram of a MFC design is shown here: - Sampling ports are at the top. - The anode is on the left. - The proton exchange layer is to the right of the anode. - The porous cathode is on the right side of the fuel cell. - Air environment is at the top of the cathode. - Water drainage at the bottom of the fuel cell. ## Diagram A diagram of a five-cell MFC stack is shown. - Each MFC cell (MFC1 - MFC5) is labeled. - The anode side is denoted with "A" - The cathode side is denoted with "C" - The cells are separated by a proton exchange membrane (PEM). - The stack is held together with a rubber gasket at the bottom. ## Diagram A Diagram of a MFC designed to produce algal biomass is shown. - The diagram shows a microbial fuel cell with an anode and cathode side being separated by a proton exchange membrane. - The anode side shows bacteria consuming organic matter, releasing electrons, and hydrogen ions. - The cathode side shows algae absorbing hydrogen ions and carbon dioxide, producing biomass that is then used to extract lipids. ## Diagram A diagram of phototropic MFC is shown. - The cathode is above the anode. - The anode side shows bacteria consuming sugars, releasing electrons, and hydrogen ions. - The cathode side shows oxygen reacting with hydrogen ions to produce water. - Plants grow above the cathode, absorbing the carbon dioxide released at the anode and releasing oxygen to the cathode. ## Reference - Microbial fuel cells. 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