How do microbial fuel cells work?

Answer 1

When an organism respires it produces electrons which are normally passed to a terminal electron acceptor. For many organisms this is oxygen. In environments where there is no oxygen, such as in sediments and in soils, organisms use different terminal electron acceptors. Common alternatives are Nitrate and Sulphate but some bacteria are known to use solid compounds as a terminal electron acceptor. There are some species of bacteria that can use iron as a terminal electron acceptor.

The ability of some bacteria to reduce (that means give electrons to) iron in sediments is exploited in Microbial Fuel Cells. The microbes (bacteria) reduce an electrode (called the anode) by using it as a terminal electron acceptor as they metabolise (eat) high energy compounds such as sugars. By linking the anode to another electrode (called the cathode) you can make a circuit that electrons can flow through. Just imagine it like a battery, the anode is the negative terminal and the cathode is the positive terminal and the electrons come from the sugar, pass through the bacteria (giving it energy on the way) and are then passed to the anode.