In the first step of the MFC, an anode respiring bacterium breaks down the organic waste to carbon dioxide and transfers the electrons released to the anode. Next, the electrons travel from the anode, through an external circuit to generate electrical energy. Finally, the electrons complete the circuit by traveling to the cathode, where they are taken up by oxygen and hydrogen ions to form water.
What is the matrix?
"We knew that the MFC process is relatively stable, but one of the biggest questions is: How do the bacteria get the electrons to the anode?" said Marcus. The bacteria depend on the anode for life. The bacteria at the anode breathe the anode, much like people breathe air, by transferring electrons to the anode. Because bacteria use the anode in their metabolism, they strategically position themselves on the anode surface to form a bacterial community called a biofilm.
Bacteria in the biofilm produce a matrix of material so that they stick to the anode. The biofilm matrix is rich with material that can potentially transport electrons. The sticky biofilm matrix is made up of a complex of extracellular proteins, sugars, and bacterial cells. The matrix also has been shown to contain tiny conductive nanowires that may help facilitate electron conduction.
"Our numerical model develops and supports the idea that the bacterial matrix is conductive," said Marcus. In electronics, conductors are most commonly made of materials like copper that make it easier for a current to flow through . "In a conductive matrix, the movement of electrons is driven by the change in the electrical potential." Like a waterfall, the resulting voltage drop in the electrical potential pushes the flow of electrons.
The treatment of the biofilm matrix as a conductor allowed the team to desc
|Contact: Joe Caspermeyer|
Arizona State University