In the midst of the worldwide
energy crisis, researchers at Washington University
in St. Louis have been continuing their work on
a microbial fuel cell that generates electricity
from wastewater. Advances in the design of this
fuel cell in the last year have increased the
power output by a factor of 10 and future designs,
already in the minds of the researchers, hope
to multiple that power output by 10 times again.
If that goal can be achieved, the fuel cell could
be scaled up for use in food and agricultural
industries to generate electrical power - all
with the wastewater that today goes right down
the drain.
Lars Angenent, Ph.D., Assistant
professor of Chemical Engineering, and a member
of the University's Environmental Engineering
Science Program has devised a continually fed
upflow microbial fuel cell (UMFC). In a paper
published online in the Environmental Science
Technology, Angenent describes how wastewater
enters from the bottom of a system and is continuously
pumped up through a cylinder filled with granules
of activated carbon. Many previous microbial experiments
used closed systems with a single batch of nutrient
solution, but because this system is continuously
fed from a fresh supply of wastewater, Angenent's
UMFC has more applications for industry since
wastewater is continually outputted during industrial
production.
The organic matter in the wastewater
provides food for a diverse community of bacteria
that have developed a biofilm (a thick-layered
colony of bacteria) on a simple electrode in the
anode chamber. An inexpensive U-shaped proton
exchange membrane inside the anode chamber separates
the anode from the cathode.
As the bacteria feed on the organic
material in the wastewater they release electrons
to the anodic electrode. These electrons then
move to the cathodic electrode via a copper wire.
The formed protons are transferred through the
membrane towards the cathode where they react
with electrons and oxygen to form water. This
is the second design of the UMFC. Last year, Angenent's
design used a cathode on top of the anode. This
time, using the U-shaped design the surface area
was increased and he reduced the distance between
the anode and cathode, which helped reduce power
loss due to resistance. These two changes are
largely responsible for the boost in power by
a magnitude of 10 times from a maximum of 3 watts
per cubic meter of solution last year to a maximum
of 29 w/m3 today. Sustained power in the system
can average 20 watts per cubic meter - enough
to run a small light bulb.
Angenent and his doctoral student Jason He are
exploring other anode-cathode shapes, surface
areas, and distances to both increase power and
reduce the resistance in the system so that less
power is lost as it runs.
Angenent says that for the UMFC
to be economical he "needs two more breakthroughs,
but [he doesn't] know what they are yet.”
The economic viability level
for this microbial fuel cell is around 160 watts
per cubic meter of solution and the goal of increasing
the power output by 10 times would double that
level to around 300. If that can happen, this
microbial fuel cell system would be a proof of
concept with far-reaching applications in the
food and agricultural industries. Since this experiment
uses common and inexpensive materials and wastewater
is plentiful in industry, a scaleable version
of this system at one food industry could one
day generate enough power for 900 American single-family
households. A clean and renewable energy source,
all with what's already just going down the drain.
Source:
http://www.azom.com