Paper

Microbial Fuel Cell

Global Warming is an issue that will face our country for centuries to come. Rising sea levels and global temperatures have already and will continue to cause biological disasters. Species that have spent years adapting to their environment will have to migrate in response to the changing temperatures, cities on the coasts will be destroyed, and unpredictable weather will threaten many parts of the world. In order to reduce the amount of CO₂ released into the atmosphere, researchers are looking towards natural processes, such as respiration and fermentation. One major breakthrough has come in the form of the microbial fuel cell. This cell is powered by the natural processes of bacteria, which turns energy stored biologically into chemical energy. These cells rely on the electron transport chain, a molecular machine which creates both electrons and energy. Those electrons are the basis of the electrical energy created by the microbial fuel cells. Research in this area has flourished in the last few decades and several research groups have made very promising discoveries. Hopefully, these discoveries will lead to a cleaner and more efficient energy source that ultimately will help control the ever-growing problem of global warming.

The microbial fuel cell is a fairly simple machine which harnesses natural energy to make fuel. It converts chemical energy, available in a biological substrate, into electrical energy. In this process, bacteria is used to convert substrate into electrons. The bacteria used can convert organic compounds into CO2, water, and energy. The produced energy is used by the bacteria to grow and maintain their metabolism. The microbial fuel cell is able to harness the energy and turn it into electricity. A general MFC consists of an anode, cathode, proton exchange membrane and electrical circuit. The bacteria live in the anode and convert a substrate into CO₂, protons, and electrons. The MFC captures those electrons originating from the microbial metabolism. The electrons then flow through an electrical circuit to the cathode. The potential difference between the anode and cathode along with the flow of electrons creates electric power. The protons flow through the proton exchange membrane (Logan 2008). The processes involved within the microbial fuel cell get more complex. A diagram of the cell follows.

One complex aspect of the microbial fuel cell is generating electrons to capture and create a concentration gradient. This is carried out by two natural processes: respiration and fermentation. During respiration, a substrate is oxidized and electrons and protons are liberated. The electrons are added to a NAD+ molecule to form NADH. The NADH is later oxidized and the electrons flow through the electron transport chain. The energy released during the electron transport chain allows the bacteria to pump protons outwardly into the periplasm, the space between the plasma and outer membrane. A proton motive force is generated by this movement, allowing the formation of ATP by the activity of ATP synthase. All electrons not captured for growth can be transported to the electron acceptor.

Fermentation is used when no readily available electron acceptors are present in the environment. During fermentation, the bacteria will place the liberated electrons into the oxidized substrate. These electrons, along with other metabolites produced by the bacteria, are used in the microbial fuel cell. These natural processes allow for the minimizing of waste that would be produced by man-made machines.

Research concerning the microbial fuel cell is being conducted around the world, from Gwangju Institute of Science and Technology in Korea to Washington University in St. Louis. These labs are working on harnessing the energy of microbial fuel cells and working with several species of bacteria. One specific project, the Geobacter Project conducted in U Mass Amherst, is working with metal-reducing bacteria. They have found that species such as Geobacter and Rhodoferax have the ability to directly transfer electrons to the surface of electrodes. Using this information, the lab has built MFCs that are more efficient. They also do not require the addition of toxic electron mediators which had been previously required by fuel cells. Lastly, the MFC’s have long-term stability and can harness energy from many types of organic waste. The research group plans on using these cells to power electronic monitoring devices in remote locations. There are many more applications possible, but little kinks need to be worked out for mass production. Currently, researchers are working on genetically engineering better microbes to increase electricity production.

A main goal of microbial fuel cells is to harness energy to produce hydrogen, thus making hydrogen a reliable resource for the future. Researchers at Penn State have recently developed the first process that allows bacteria to produce four times as much hydrogen directly from biomass than can be generated by fermentation (State 2005). They can theoretically use the MFC to obtain large amounts of hydrogen from dissolved organic matter, such as industrial wastewater, and simultaneously clean that wastewater. Previously, researchers had had problems because bacteria, without a power boost, can only convert carbohydrates into a small amount of hydrogen and other useless products. But, as the researchers at Penn have discovered, with the addition of a small amount of power they can convert these useless products into carbon dioxide and hydrogen (State 2005). This discovery marks tremendous progress in making hydrogen one of the world’s main resources.

A research team at Oregon State University had similar success in developing a faster microbial fuel cell. Within the past year, they have created a fuel cell that is able to generate about ten times as much electricity as the previous model (Kleiner 2003). Ultimately, the new design could lead to portable designs for power generation. These models would also provide reusable water for developing nations and remote areas of the world. The new design places a cloth layer between the anode and cathode to reduce the internal resistance. In the lab, the team generated enough power to light 16 60-watt light bulbs, more power than has ever been generated by a microbial fuel cell (Kleiner 2003). This microbial fuel cell could substantially reduce the amount of energy wastewater plants use, and the cost to operate them. Before these large scale microbial fuel cells can be built, small household models will be created. These small MFC could be used in many households to clean wastewater and would prove very helpful in places such as India and China. Their research is funded by the U.S Department of Transportation, the OSU General Research Fund, and the OSU Agricultural Research Foundation.

Companies in the United States have been slow to pick up and take interest in this new research, but around the world big companies are beginning to take interest. In Japan, the Sony Company has helped make a microbial fuel cell to generate hydrogen power. In Spain, the power company Elecnor announced that it has built Spain’s largest microbial fuel cell. It is obvious to this nation and the world that global warming is one of the most threatening environmental problems and quick solutions are necessary. The microbial fuel cell harnesses the natural power of bacteria to generate power with little waste or outside power. It is only a matter of time before companies take serious interest in this research and the world gets a start on combating this serious problem.