A microbial fuel cell, or biological fuel cell, is a bio-electrochemical system that drives an electric current by using bacteria and mimicking bacterial interactions found in nature. MFCs can be grouped into two general categories: mediated and unmediated.

1. MICROBIAL FUEL CELL
DESIGNING
• A bacterium in the anode compartment transfers
electrons obtained from an electron donor
(glucose) to the anode electrode.
• This occurs either through direct contact,
nanowires, or mobile electron shuttles (small
spheres represent the final membrane
associated shuttle).
• During electron production protons are also
produced in excess.
• These protons migrate through the cation
exchange membrane (CEM) into the cathode
chamber.
• The electrons flow from the anode through an
external resistance (or load) to the cathode
where they react with the final electron acceptor
(oxygen) and protons (26).
Operating principles of a MFC (not to scale).

2. MICROBIAL FUEL CELL COSTING
(A) Upflow, tubular type MFC with inner
graphite bed anode and outer cathode.
(B) Upflow, tubular type MFC with anode
below and cathode above, the membrane is
inclinated.
(C) Flat plate design where a channel is cut in
the blocks so that liquid can flow in a
serpentine pattern across the electrode.
(D) Single-chamber system with an inner
concentric air cathode surrounded by a
chamber containing graphite rods as anode.
(E) Stacked MFC, in which 6 separate MFCs are
joined in one reactor block.
MFCs used for continuous operation