A microbial fuel cells (MFC) or biological fuel cell is a bio-electrochemical system that drives a current by using bacteria and mimicking bacterial interactions found in nature. MFCs can be grouped into two general categories: mediated and unmediated.
Renewable and clean forms of energy are one of society’s greatest needs. At the same time, 2 billion people in the world lack adequate sanitation and the economic means to afford it. In this research, we are working to address both of these human needs. Energy costs are an important factor in wastewater treatment. In the USA, for example, 5% of electricity we produce is used for the water and wastewater infrastructure (all aspects, including pumping, treatment, etc.), with 1.5% used for wastewater treatment alone.
Microbial fuel cells (MFCs) represent a completely new method of renewable energy recovery: the direct conversion of organic matter to electricity using bacteria. While this sounds more like science fiction than science, it has been known for many years that bacteria could be used to generate electricity. However, expensive and toxic chemicals were needed to shuttle electrons from the bacteria to the electrode and purified chemicals (such as glucose) were needed for the bacteria to grow on. We now know that we can make electricity using any biodegradable material– even wastewater– and that we don’t have to add any special chemicals if we use bacteria already present in the wastewater. While some iron-reducing bacteria, such as Shewanella putrefacians and Geobacter metallireducens [they reduce Fe(III) to Fe(II)], can be used to make electricity, there are many other bacteria already present in wastewater that can do this.
How does a microbial fuel cell work? When bacteria are placed in the anode chamber of a specially-designed fuel cell that is free of oxygen, they attach to an electrode. Because they do not have oxygen, they must transfer the electrons that they obtain from consumption (oxidation) of their food somewhere else than to oxygen– they transfer them to the electrode. In a MFC these electrons therefore go to the anode, while the counter electrode (the cathode) is exposed to oxygen. At the cathode the electrons, oxygen and protons combine to form only water. The two electrodes are at different potentials (about 0.5 V), creating a bio-batter (if the system is not refilled) or a fuel cell (if we constantly put in new food or “fuel” for the bacteria).
At Penn State, we are working on developing MFCs that can generated electricity while accomplishing wastewater treatment. In a project supported by the National Science Foundation (NSF), we are researching methods to increase power generation from MFCs while at the same time recovering more of the energy as electricity (See: Listing of research projects). We have already proven that we can produce electricity from ordinary domestic wastewater (NSF-SGR), as well as many other types of wastewaters including animal/farm, food processing, and industrial wastewaters. (See: USDA Project). Virtually any biodegradable material can be used to produce power. We support from the Paul L. Busch Award from the Water Environment Research Foundation, we hope to improve on the technology and demonstrate it at larger scales (See:Busch Award). To see a short slide show, click here. To find out more about this and other hydrogen and fuel cell research at Penn State, visit the H2E Center webpage. If you’d like to try building a MFC yourself, see the Make one! page. You may also wish to visit the international MFC website at: www.microbialfuelcell.org
Sugar powered autonomous robot
Ecobot I is a 960g robot, powered by microbial fuel cells (MFCs) and performs a photo-tactic (light seeking) behaviour. This robot does not use any other form of power source such as batteries or solar panels. It is 22cm in diameter and 7.5cm high.
The biocatalyst in the MFCs’ anode was a freshly grown culture of E. colifed with refined sugar whereas the catholyte was ferricyanide. Methylene blue (MB) was used as the redox mediator to extract a portion of the electrons produced from breaking down the sugar in the metabolic pathways of E. coli. Electrons are then transferred to the anode electrode and flow through the external electrical circuit to the cathode, thus producing electrical current.
Energy produced by the MFCs is stored by an onboard ‘accumulator’ consisting of a bank of capacitors. Two photo-diodes provide the input to the “tracking system” of the robot and are indirectly connected to two high efficiency, high torque motors.
Once the energy is accumulated up to a specific threshold, it is then released to either or both of the motors according to the indication from the photo-diodes. The system does not employ any other form of power supply such as batteries or solar panels.
Ecobot I diagram
What is the BEAMR/MEC process? By adding a small amount of voltage (0.25 V) to that produced by bacteria at the anode in an MFC, and by not using oxygen at the cathode, you can produce pure hydrogen gas at the cathode! This is a modified MFC process has many different names, including: a “bioelectrochemically assisted microbial reactor” or BEAMR process; biocatalyzed electrolysis cells (BECs); and microbial electrolysis cells (MECs). These names are based on the idea is that fuel cells produce electricity, and electrolysis cells produce hydrogen. This MEC/BEAMR system is operated in a completely anaerobic manner, with the potential produced by bacteria increased by a small amount (using power from an MFC or hydrogen produced by the MEC in a fuel cell). The protons and electrons produced by the bacteria then form hydrogen gas at the cathode– a process called the hydrogen evolution reaction (HER). Theoretically we need 0.41 V to make H2 from acetate, and the bacteria produce ~0.2 to 0.3 V. Thus, we only need to add about 0.2 V or more to make hydrogen gas in the MEC/BEAMR. You can read more about this process see the BEAMR page.
Renewable and clean forms of energy are one of society’s greatest needs. At the same time, 2 billion people in the world lack adequate sanitation and the economic means to afford it. In this research, we are working to address both of these human needs. Energy costs are an important factor in wastewater treatment. In the USA, for example, 5% of electricity we produce is used for the water and wastewater infrastructure (all aspects, including pumping, treatment, etc.), with 1.5% used for wastewater treatment alone.
Microbial fuel cells (MFCs) represent a completely new method of renewable energy recovery: the direct conversion of organic matter to electricity using bacteria. While this sounds more like science fiction than science, it has been known for many years that bacteria could be used to generate electricity. However, expensive and toxic chemicals were needed to shuttle electrons from the bacteria to the electrode and purified chemicals (such as glucose) were needed for the bacteria to grow on. We now know that we can make electricity using any biodegradable material– even wastewater– and that we don’t have to add any special chemicals if we use bacteria already present in the wastewater. While some iron-reducing bacteria, such as Shewanella putrefacians and Geobacter metallireducens [they reduce Fe(III) to Fe(II)], can be used to make electricity, there are many other bacteria already present in wastewater that can do this.
How does a microbial fuel cell work? When bacteria are placed in the anode chamber of a specially-designed fuel cell that is free of oxygen, they attach to an electrode. Because they do not have oxygen, they must transfer the electrons that they obtain from consumption (oxidation) of their food somewhere else than to oxygen– they transfer them to the electrode. In a MFC these electrons therefore go to the anode, while the counter electrode (the cathode) is exposed to oxygen. At the cathode the electrons, oxygen and protons combine to form only water. The two electrodes are at different potentials (about 0.5 V), creating a bio-batter (if the system is not refilled) or a fuel cell (if we constantly put in new food or “fuel” for the bacteria).
At Penn State, we are working on developing MFCs that can generated electricity while accomplishing wastewater treatment. In a project supported by the National Science Foundation (NSF), we are researching methods to increase power generation from MFCs while at the same time recovering more of the energy as electricity (See: Listing of research projects). We have already proven that we can produce electricity from ordinary domestic wastewater (NSF-SGR), as well as many other types of wastewaters including animal/farm, food processing, and industrial wastewaters. (See: USDA Project). Virtually any biodegradable material can be used to produce power. We support from the Paul L. Busch Award from the Water Environment Research Foundation, we hope to improve on the technology and demonstrate it at larger scales (See: Busch Award). To see a short slide show, click here. To find out more about this and other hydrogen and fuel cell research at Penn State, visit the H2E Center webpage. If you’d like to try building a MFC yourself, see the Make one! page. You may also wish to visit the international MFC website at: www.microbialfuelcell.org
What is the BEAMR/MEC process? By adding a small amount of voltage (0.25 V) to that produced by bacteria at the anode in an MFC, and by not using oxygen at the cathode, you can produce pure hydrogen gas at the cathode! This is a modified MFC process has many different names, including: a “bioelectrochemically assisted microbial reactor” or BEAMR process; biocatalyzed electrolysis cells (BECs); and microbial electrolysis cells (MECs). These names are based on the idea is that fuel cells produce electricity, and electrolysis cells produce hydrogen. This MEC/BEAMR system is operated in a completely anaerobic manner, with the potential produced by bacteria increased by a small amount (using power from an MFC or hydrogen produced by the MEC in a fuel cell). The protons and electrons produced by the bacteria then form hydrogen gas at the cathode– a process called the hydrogen evolution reaction (HER). Theoretically we need 0.41 V to make H2 from acetate, and the bacteria produce ~0.2 to 0.3 V. Thus, we only need to add about 0.2 V or more to make hydrogen gas in the MEC/BEAMR. You can read more about this process see the BEAMR page.