Harnessing the power of bacteria
 ooking for alternatives to world reliance on fossil
fuels for energy, an interdisciplinary team of UW-Madison researchers
is studying ways to generate electricity by feeding a species of photosynthetic
bacteria a steady diet of sunshine and wastewater.
The concept of such so-called microbial fuel cells
emerged nearly three decades ago when an English researcher fed carbohydrates
to a bacteria culture, connected electrodes and produced tiny amounts
of electricity. Although a few research groups are studying them, microbial
fuel cells largely live in the realm of laboratory entertainment and
high-school science experiments, says Professor Daniel
Noguera. “Now, the idea is taking shape that this could become
a real alternative source for energy,” he says.
PICTURED (Standing, from left):
Noguera, Bacteriology Professor Timothy Donohue,
Senior Scientist Isabel Tejedor-Anderson,
Assistant Professor Trina McMahon, Professor
Marc Anderson and (kneeling)
graduate students Yun Kyung Cho and Rodolfo
Perez, hope to develop a large-scale microbial fuel cell system
for use in wastewater treatment plants. “It’s inexpensive,”
says Noguera, of the nutrient-rich wastewater food source. “We
treat the wastewater anyway, so you are using a lot of energy to do
that.”
In nature, says McMahon, photosynthetic bacteria
effectively extract energy from their food—and microbial fuel
cells capitalize on that efficiency. “By having the microbes strip
the electrons out of the organic waste, and turning that into electricity,
then we can make a process of conversion more efficient,” she
says. “And they’re very good at doing that—much better
than we are with our high-tech extraction methods.”
Through machinery like plants, photosynthetic bacteria
harvest solar energy. They also make products to power microbial fuel
cells. “In many ways, this is the best of both worlds—generating
electricity from a ‘free’ energy source like sunlight and
removing wastes at the same time,” says Donohue. “The trick
is to bring ideas from different disciplines to develop biorefineries
and fuel cells that take advantage of the capabilities of photosynthetic
bacteria.” The benefit of using photosynthetic bacteria, he says,
is that solar-powered microbial fuel cells can generate additional electricity
when sunlight is available.
Currently, the microbes live in sealed, oxygen-free
test tubes configured to resemble an electrical circuit. Known as a
microbial fuel cell, this environment tricks the organisms into delivering
byproducts of their wastewater dinner—in this case, extra electrons—to
an anode, where they travel through a circuit toward a cathode. Protons,
another byproduct, pass through an ion-exchange membrane en route to
the cathode. There, the electrons and protons react with oxygen to form
water.
One microbial fuel cell produces a theoretical maximum
of 1.2 volts; however, like a battery, several connected fuel cells
could generate enough voltage to be useful power sources. “The
challenge is thinking about how to scale this up from the little toys
we have in the lab to something that works in the home, on farms, or
is as large as a wastewater treatment plant,” says Noguera. For
now, the researchers are combining their expertise in materials science,
bacteriology and engineering
to optimize fuel cell configuration.
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