MFCs

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 make electricity, but generally bacteria belonging to the genus Geobacter are the ones that can produce the highest power densities.

How does a microbial fuel cell work? When a solution containing exoelectrogenic bacteria (such as Geobacter) and a fuel (organic matter, such as acetic acid or other volatile fatty acids) are placed in the anode chamber of a microbial fuel cell, and the solution does not contain dissolved oxygen, bacteria can attach to the anode. In the absence of oxygen, the bacteria need to release the electrodes from oxidation of the fuel (their food) somewhere else than to oxygen– so they transfer them to the anode. In a MFC these electrons are then transferred through the circuit to the counter electrode (the cathode), which is exposed to oxygen. At the cathode the electrons, oxygen, and protons combine to form water.  The two electrodes are at different potentials (about 0.5 V), which creates the cell voltage (U). The system can be considered a bio-battery (if the system is not refilled) or a fuel cell (if we constantly put in new food or “fuel” for the bacteria). The amount of current (I) generated is dependent on the total resistance (R), which is sum of the external resistance (the circuit load, for example a light bulb) and the internal resistance (due to limited ion mobility, the distance between the electrodes, and other factors). The current that can be obtained can be calculated from from Ohm’s Law I=U/R. The power produced (P) is calculated as P=IU.
 
 Cube MFC (28 mL) Modular MFC Schematic
At Penn State, we are working on developing MFCs that can generate electricity while accomplishing wastewater treatment. We have developed materials that can be used to make inexpensive electrodes, designed configurations that are modular and thus can enable mass manufacturing of the electrodes and reactors, and conducted tests on performance. MFCs can be used to generate electricity from just about anything in water that is biodegradable. We have shown that electricity can be produced from ordinary domestic wastewater as well as many other types of wastewaters including animal/farm, food processing, and industrial wastewaters. Our research has been supported by: a number of federal agencies, including the US National Science Foundation, the Department of Energy and the Department of Defense; international sponsors such as King Abdullah University of Science and Technology (KAUST); and industries. We are currently working on a project to demonstrate simultaneous wastewater treatment and electricity generation in collaboration with others.

This website contains a number of sections to introduce MFCs and other microbial electrochemical technologies (METs). For example, to see slide shows and videos, go to our Presentations page; to learn how to make anodes, cathodes or prepare media for laboratory experiments, go to our Make One page. There area also other types of METs described on the Logan Lab MFC website, for example: there is a page on microbial electrolysis cells (MECs) that can be used to electrochemically produce hydrogen gas at the cathode from current generated by bacteria on the anode; and a page on other types of METs the that can be used to desalinate water, capture nutrients, or capture CO2

There are also links to other websites that may be of interest, for example, the International Society of Microbial Electrochemistry and Technologies (ISMET) site. ISMET is an organization created to link together researchers from around the world that are working on MFCs and other types of METs. 

Links to Public Reports 

This research has been covered by Penn State Press releases, and published in various media (see below). Click on those links for more general descriptions of our findings.

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