CORVALLIS, Ore. — Engineers
at Oregon State University say a breakthrough has been made in the performance
of microbial fuel cells that can produce electricity directly from wastewater,
opening the door to a future in which waste treatment plants not only will
power themselves, but will sell excess electricity.
The
new technology developed at OSU is said to produce 10 to 50 more times the
electricity, per volume, than most other approaches using microbial fuel cells,
and 100 times more electricity than some.
Researchers
say this could eventually change the way that wastewater is treated all over
the world, replacing the widely used “activated sludge” process that has been
in use for almost a century. The new approach would produce significant amounts
of electricity while effectively cleaning the wastewater.
The
findings have been published in Energy and Environmental Science, a professional
journal, in work funded by the National Science Foundation.
“If
this technology works on a commercial scale the way we believe it will, the
treatment of wastewater could be a huge energy producer, not a huge energy
cost,” Hong Liu, an associate professor in the OSU Department of Biological and
Ecological Engineering, says. “This could have an impact around the world, save
a great deal of money, provide better water treatment and promote energy
sustainability.”
Experts
estimate that about 3% of the electrical energy consumed in the United States
and other developed countries is used to treat wastewater, and a majority of
that electricity is produced by fossil fuels that contribute to global warming.
But
the biodegradable characteristics of wastewater, if tapped to their full
potential, could theoretically provide many times the energy that is now being
used to process them, with no additional greenhouse emissions.
OSU
researchers reported several years ago on the promise of this technology, but
at that time the systems in use produced far less electrical power. With new
concepts – reduced anode-cathode spacing, evolved microbes and new separator
materials – the technology can now produce more than two kilowatts per cubic
meter of liquid reactor volume. This amount of power density far exceeds
anything else done with microbial fuel cells, researchers say.
The
system also works better than an alternative approach to creating electricity
from wastewater, based on anaerobic digestion that produces methane. The
researchers claim it treats the wastewater more effectively, and doesn’t have
any of the environmental drawbacks of that technology, such as production of
unwanted hydrogen sulfide or possible release of methane, a potent greenhouse
gas.
The
OSU system has now been proven at a substantial scale in the laboratory, Liu
said, and the next step would be a pilot study. Funding is now being sought for
such a test. A good candidate, she said, might initially be a food processing
plant, which is a contained system that produces a steady supply of certain
types of wastewater that would provide significant amounts of electricity.
Continued
research should also find even more optimal use of necessary microbes, reduced
material costs and improved function of the technology at commercial scales,
OSU scientists say.
Once
advances are made to reduce high initial costs, researchers estimate that the
capital construction costs of this new technology should be comparable to that
of the activated sludge systems now in widespread use today – and even less
expensive when future sales of excess electricity are factored in.
This
technology cleans sewage by a very different approach than the aerobic bacteria
used in the past. Bacteria oxidize the organic matter and, in the process, produce
electrons that run from the anode to the cathode within the fuel cell, creating
an electrical current. Almost any type of organic waste material can be used to
produce electricity — not only wastewater, but also grass straw, animal waste
and byproducts from such operations as the wine, beer or dairy industries.