Fig. 1

Basic setup for the microbial fuel cell operation. Electrogens that inhabit the anode compartment (shown in violet) catalyze the oxidation of organic substrates, which generate electrons and protons. The anode (black) absorbs and transports the electrons to the cathode (red) via an external circuit. After crossing a PEM or a salt bridge (dotted square), the protons enter the cathodic chamber where they combine with oxygen to form water. The combination of redox couple represented by the green arrow in cathode and anode chambers, respectively, gives a positive electromotive force (emf) (E _emf = E _cat - E _ano), which means the generation of electricity. In order for catalysis to happen for the redox couple represented by the red arrow, an input of energy is needed.