Microbial Fuel Cells
Power from Waste
H
By Kevin Lewis
Kevin Lewis is an R&D
Microbiologist and Technical
Support Specialist at Hardy
Diagnostics.
He earned his dual degree in
microbiology and biochemistry
from California State
Polytechnic University, San
Luis Obispo.
www.HardyDiagnostics.com
umans utilize bacteria
every day to produce
some of our favorite
foods; we take probiotics to
help our digestion, bacteria
help us remove organic
wastes from our water
supplies, and bacteria produce
chemicals used in a wide
range of industries.
Did you ever stop to think
that one day we might also
use bacteria to produce
electricity?
The idea of producing
electricity from
microorganisms is not new.
M. C. Potter, a professor of
Botany at the University of
Durham, experimented with
the production of electricity
from microorganisms in the
early 1900s. Potter was able
to detect electricity production
from yeast and E. coli when
they were placed in a
rudimentary microbial fuel
cell (MFC).
Research continued in the
field, but it was not until the
1970s and 1980s when major
breakthroughs in technology
began. M. J. Allen and H.
Peter Benneto redesigned the
model of the microbial fuel
cell to the basic design that is
still used today. Furthermore,
pioneering work by B. H. Kim
in the 1990s found that
several organisms are capable
of donating electrons directly
to the anode and do not
require a mediator molecule
to transport electrons from the
cell membrane to the anode.
Current research in this field
is ongoing and is focused on
optimizing electrical
production by using special
materials for the electrodes
and experimenting with
various combinations of
organisms.
At first glance, microbial fuel
cells look a lot like the
pictures of galvanic cells
previously used in chemistry
and physics classes. They
consist of a cathode, an anode,
and a semi-permeable
membrane between two halfcells.
The anode is submerged in a
nutrient rich medium along
with bacteria, and the device
is sealed to create an
anaerobic environment. The
medium can be anything from
lab prepared nutrients in water
to waste water and urine.
Bacteria metabolize organic
compounds in the medium
into CO2, protons, and
electrons. With no oxygen
present, the bacteria can no
longer perform normal
cellular respiration, using
oxygen as the terminal
electron acceptor and,
therefore, use the anode as the
terminal electron acceptor.
They do this by donating
electrons directly to the anode
or by going through a
chemical mediator that
shuffles the electrons from the
bacteria’s membrane to the
anode. During this process,
hydrogen ions travel across
the semi-permeable
membrane where they
combine with electrons and
oxygen at the cathode to
produce water.
One of the most fascinating
aspects about MFCs is what
materials can be put in them
to produce electricity. Using
various designs, electricity
has been produced from sugar
solutions, soil, ocean
sediment, urine, and waste
water. These different
substrates create limitless
possibilities for what MFCs
could be used for in the
future. Some of the current
research is focused on
adapting MFCs for waste
water treatment, desalination,
hydrogen production, and
remote device powering.
An experimental Microbial
Desalination Cell (MDC) being
tested at Penn State.
Waste water treatment
requires a large amount of
water. It is estimated that
municipal and industrial waste
water plants consume two
percent of the electrical power
in the U.S. The introduction
of MFCs into waste water
treatment could cut back on
the solid waste produced and
the electricity consumed to
treat the water. Microbial fuel
cells have been shown to
reduce the organic waste in
sewage water by up to 80%.
An MFC that uses wastewater
being tested at Foster’s brewery in
Australia
Foster’s Brewery in Australia
has been experimenting with
microbial fuel cells to clean
up the brewery’s waste water.
Foster’s plans on building a
660 gallon microbial fuel cell
that would clean the nutrient
rich waste water from the
brewery.
Another potential use for
MFCs is desalination. By
modifying the normal design
to add an additional chamber
filled with salt water, the
MFC can remove the salt with
no electrical input. Salt water
is placed in a chamber
between the anode and
cathode and is separated from
the other chambers with a
semi-permeable membrane.
The charges on the electrodes
cause the positive and
negative ions in the salt to
travel out of the chamber
towards the oppositely
charged electrode.
Desalinating MFCs with high
efficiencies have been made,
but none of them have been
efficient enough to produce
drinking quality water from
salt water. However,
combined with other
desalination technologies, this
could provide a cheaper way
to produce drinking water
from salt water or could
provide acceptable quality
water for irrigation or
industrial use.
With a diminishing supply of
fossil fuels and the pressing
need to reduce greenhouse
gases, one alternative fuel
source that has been getting a
lot of attention lately is
hydrogen. Hydrogen is a
popular alternative fuel
because the only byproduct of
its use is water.
One of the major problems
with hydrogen is that it must
be industrially produced,
which may require large
amounts of electricity or
generate greenhouse gases by
conventional methods. By
adding a small amount of
electricity to the MFC,
hydrogen gas rather than
oxygen can be created at the
cathode. Although an input of
electricity is still required to
produce hydrogen, it takes 10
times less electricity than
conventional methods.
Microbial fuel cells could
provide a clean, reliable, and
cost-effective source of
hydrogen.
Microbial fuel cells also have
the potential to provide an
inexpensive source of power
to remote locations.
Some remote sensors and
monitoring devices are
already using MFCs as their
power source. The anode can
be placed in nutrient rich mud
or sediment with the cathode
positioned in the water just
above. A sensor or monitoring
device can be hooked up to
the MFC to provide a source
of electricity that has a
significantly longer life than
conventional power sources.
This MFC was invented by students
at MIT. It uses plant waste and
microorganisms to generate
electricity – enough to charge a cell
phone in six months. However, it
becomes more practical when these
cells are connected in series.
Similar designs can provide
low cost energy to people in
remote locations. The Lebone
group has been working on
developing MFCs that cost no
more than $15. Their designs
have been able to provide
enough electricity to charge a
cell phone, power a radio, or
turn on a light bulb. They plan
to refine the technology to
provide a cheap, reliable
source of power for people
with limited energy resources.
Steven Lwendo, one of the
founders of Lebone, holds an
empty prototype of the dirt-powered
battery that he and his team are
developing for use in African
homes. They can produce
electricity for 8 to 12 months before
they need to be refilled.
Microbial fuel cells may be
the next addition to the
growing list of uses we have
for bacteria. As our
understanding of bacterial
genetics and metabolism
advances, the possibilities of
what we may accomplish is
vast from something
microscopic.
Kevin Lewis
Santa Maria, California