A microbial fuel cell (MFC) converts
chemical energy, available in
a bio-convertible substrate, directly into electricity.
To achieve this, bacteria are used as a catalyst to convert
substrate into electrons.
Bacteria are very small (size
appr. 1 µm) organisms which can convert a huge variety of
organic compounds into CO2, water and energy. The
micro-organsisms use the produced energy to grow and to maintain
there metabolism. However, by using a MFC we can harvest a part
of this microbial energy in the form of electricity.
A MFC consists of an anode,
a cathode, a proton or cation exchange membrane
and an electrical circuit.
If bacteria want to survive, grow or become dominant
within a microbial community, they do not only require
substrate and nutrients but they also need the presence of an appropriate
electron acceptor. Based on the usage of a final electron acceptor, there are two main modes of microbial
energy conservation: respiration and fermentation. These processes are
ubiquitous in various natural environments.
Recently, they have been accompanied
by a new exciting respiration process occurring in bioelectrochemical systems
The working principles of these three processes are covered in this item.
The microbial conversion of substrates is a key process to generate
electricity in BESs. Despite, the microbial nature of the process, it is
affected by electrochemical laws and principles which generally results in a
lowering of the attainable voltage. The main electrical principles and the
processes governing these losses are briefly described. Subsequently, the various
conversions efficiencies are discussed.