Bacteria in the anode of a microbial fuel cell convert organic substrates like glucose into electrons, protons, and carbon dioxide. The electrons flow through an electrical circuit to power a load while the protons flow through an exchange membrane to the cathode. At the cathode, the protons and electrons recombine and oxygen is reduced to water. Key components include the anode where bacteria live, a cathode, an exchange membrane, and an electrical circuit connecting the anode and cathode. Microbial fuel cells operate at mild temperatures and can be used to generate electricity from wastewater while also producing clean water or fertilizer.
2. Concept
Bacteria convert substrate into electrons.
The electrons run through the circuit and to power the
load.
The byproducts include carbon dioxide, water, and
energy.
4. Anode
The bacteria live in the anode and
convert substrate to carbon dioxide,
water, and energy.
Various things like glucose and
acetate can be used.
The bacteria are kept in an oxygen-
less environment to promote the
flow of electrons through the
anode.
5. Electrical Circuit
After leaving the anode, the electrons travel through
the circuit.
These electrons power the load.
The voltage multiplied by the current shows the power.
6. Exchange Membrane
The protons that the bacteria separated
from the electrons flows through the
exchange membrane.
They recombine on the other side.
Can be a proton or cation exchange
membrane.
7. Cathode
The electrons and protons recombine
at the cathode.
Oxygen is reduced to water.
A platinum catalyst is used so the
oxygen is sufficiently reduced.
11. BEAMR
Utilizes electrohydrogenesis, which uses an anaerobic
environment to produce pure hydrogen.
It uses about one ninth of the energy required by
normal electrolysis.
It has many different names:
Bioelectrochemically assisted microbial reactor
Biocatalyzed electrolysis cells
Microbial electrolysis cells
12. Hydrogen Evolution Reaction
The bacteria in the anode separate the protons and
electrons.
This reaction occurs at the cathode, where they
recombine to form hydrogen gas.
13. History
M.C. Potter first performed work on the concept in 1911
with E. coli at the University of Durham
In 1976 the current design was came into existence by
the work of Suzuki
15. Uses
Beer breweries produce biodegradable
wastewater, which MFCs clean.
Desalinating water
Creating fertilizer
16. Environmental Impact
If the variety of substrates is increased, waste can be
used to create more energy.
Instead of big factory manufacturing, fertilizer for
farmers can be created with MFCs and common
materials.
MFCs can be used to desalinate seawater without
burning fossil fuels, although not very efficiently yet.
17. Efficiency
The efficiency varies based on the substrate used, but
it can reach very high efficiencies.
91% efficiency has been reached.
18. Cost
Power density = 150 mW/m2
Volume (MFC): 28 x 10^-6 m3
A/V-ratio: 25 m2/m3
Anode surface area (single chamber) = 7 x 10^-4 m2
Power = 0.165 mW
Cost of single-chamber fuel cell: (lab-scale)
Toray paper (10x10 cm): $ 11
XC-72 (10x10 cm): $65
Others (perspex, glue, wire): $ 25
Total = $ 100
Cost per Watt = $ 600/mW
20. Substrate
Currently there is a limit to what can be used as a
substrate for the bacteria.
Scientists hope to increase these fuel types to include
things like sewage and manure.
21. Ammonia-Treated Anodes
Anodes of MFCs are naturally
negative in charge.
The anodes can be changed to a
positive charge by being treated
with ammonia.
This will make the anode more
receptive to the electron
transfer from the bacteria.
The energy trade-off to produce
this might not be worth the
increase in production.
