Microbial fuel cells (MFCs) are bioelectrochemical systems that use bacteria to generate electricity. MFCs can be categorized as mediated or unmediated. Mediated MFCs use chemical mediators to transfer electrons from bacteria to an anode, while unmediated MFCs directly transfer electrons via bacterial membrane proteins. MFCs have the potential to generate electricity from wastewater treatment and can be used as biosensors to measure pollutant levels. However, challenges remain in improving catalytic rates, energy production levels, and reducing costs before widespread applications can be realized.

2. Microbial fuel cells
Topic:

3. Introduction
A microbial fuel cell (MFC) or biological fuel cell is a bio-
electrochemical system that drives a current by using bacteria and
mimicking bacterial interactions found in nature. MFCs can be
grouped into two general categories:
 Mediated
 Unmediated

4. Definition
A microbial fuel cell (MFC) is a device that converts chemical energy to electrical
energy by the action of microorganisms. These electrochemical cells are constructed
using either a bioanode and/or a biocathode.

5. History
The first MFCs, demonstrated in the early 20th century, used a mediator: a
chemical that transfers electrons from the bacteria in the cell to the
anode. Unmediated MFCs emerged in the 1970s; in this type of MFC the
bacteria typically have electrochemically active redoxproteins such
as cytochromeson their outer membrane that can transfer electrons
directly to the anode. In the 21st century MFCs started to find a
commercial use in wastewater treatment.

6. Types of MFCs
Single - Chamber MFC:
A simpler and more efficient MFC can be made by omitting the cathode
chamber and placing the cathode electrode directly onto the proton exchange
membrane (PEM)
Two - Chambered MFC
A typical two-compartment MFC has an anodic chamber and a cathodic
chamber connected by a PEM, or sometimes a salt bridge, to allow protons to move
across to the cathode while blocking the diffusion of oxygen into the anode.

7. Single - Chamber MFC

8. Two - Chambered MFC

9. Procedure
MFC catalyzes the conversion of organic matter into electricity by transferring
electrons to circuit with the aid of bacteria. Further the microorganisms can
transfer electrons to the anode electrode in three ways:
 By using exogenous mediators such as potassium ferricyanide, thionine or
natural red
 By using mediators produced by the bacteria
 By direct transfer of electrons from the respiratory enzymes to the electrodes.

10. Reaction
The basic reactions are presented below; when microorganisms consume a substrate
such as sugar in aerobic condition they produce CO2 and H2 O. However when oxygen
is not present i.e. under anaerobic condition they produce CO2, H+ and e- .
 Anodic reaction
C12H22O11 +13H2O → 12CO2 + 48H+ + 48e−
 Cathodic reaction
O2 + 4e− + 4H+ → 2H2O

11. Applications
Electricity generation:

12. Wastewater treatment:

13. Biosensors:
The current generated from a microbial fuel cell is directly
proportional to the energy content of wastewater used as the fuel. MFCs
can measure the solute concentration of wastewater (i.e., as a biosensor)

14. Biohydrogen production:

15. Disadvantages
Low catalytic rate
Low energy production
Expensive
Reliance on biofilm

16. Conclusion
 Although some basic knowledge has been gained in MFC research, there is
still a lot to be learned in the scaleup of MFC for large-scale applications.
However, the recent advances might shorten the time required for their
large-scale applications for both energy harvesting and wastewater
treatment systems and for the scaleup process.