Two chief areas of environmental biotechnology are bioremediation, or the clean up of environmental contaminants, and the production of clean energy. As the authors note, an MFC can perform double duty, targeting electrons from waste streams and converting them into useful energy.
An MFC is a unique kind of batterypart electrochemical cell, part biological reactor. Typically, it contains two electrodes, separated by an ion exchange membrane. On the anode side, bacteria grow and proliferate, forming a dense cell aggregate known as a biofilm that adheres to the MFC's anode. In the course of their microbial metabolism, the bacteria act as catalysts for converting the organic substrate into CO2, protons, and electrons.
Under natural conditions, many bacteria use oxygen as a final electron acceptor to produce water, but in the oxygen-free environment of the MFC, specialized bacteria that send the electrons to an insoluble electron acceptor, namely the MFC's anode, dominate.
The anode-respiring bacteria are able to oxidize organic pollutants, such as those found in waste streams, and transfer the electrons to the anode. The scavenged electrons then flow through an electrical circuit, terminating at the MFC's cathode, thus generating electricity. Ions are transported through the fuel cell's ion membrane, to maintain electroneutrality, although the membrane is often excluded. The basic setup is pictured in Figure 1.
In an effort to refine the technology and address losses in MFC efficiency, the group looked at the oxygen reduction reaction at the MFC cathode. While it had earlier been speculated that efficiency loss at the cathode was due to a low availability of protons, the new research showed instead that the transport of hydroxide ions (OH-) away from the catalyst layer of the cathode and into the surrounding liquid largely governed cathode potential
|Contact: Joseph Caspermeyer|
Arizona State University