University Park, Pa. -- Using a new
electrically-assisted microbial fuel cell (MFC) that does not require oxygen,
Penn State environmental engineers and a scientist at Ion Power Inc. have
developed the first process that enables bacteria to coax four times as much
hydrogen directly out of biomass than can be generated typically by
fermentation alone.
Bruce Logan, the Kappe professor of environmental engineering and an inventor
of the MFC, says, "This MFC process is not limited to using only
carbohydrate-based biomass for hydrogen production like conventional
fermentation processes. We can theoretically use our MFC to obtain high yields
of hydrogen from any biodegradable, dissolved, organic matter -- human,
agricultural or industrial wastewater, for example -- and simultaneously clean
the wastewater.
"While there is likely insufficient waste biomass to sustain a global
hydrogen economy, this form of renewable energy production may help offset the
substantial costs of wastewater treatment as well as provide a contribution to
nations able to harness hydrogen as an energy source," Logan notes,.
The new approach is described in a paper, “Electrochemically Assisted
Microbial Production of Hydrogen from Acetate,” released online currently
and scheduled for a future issue of Environmental Science and Technology. The
authors are Hong Liu, postdoctoral researcher in environmental engineering;
Stephen Grot, president and founder of Ion Power, Inc.; and Logan. Grot, a
former Penn State student, suggested the idea of modifying an MFC to generate
hydrogen.
In their paper, the researchers explain that hydrogen production by bacterial
fermentation is currently limited by the "fermentation barrier" --
the fact that bacteria, without a power boost, can only convert carbohydrates
to a limited amount of hydrogen and a mixture of "dead end"
fermentation end products such as acetic and butyric acids.
However, giving the bacteria a small assist with a tiny amount of electricity
-- about 0.25 volts or a small fraction of the voltage needed to run a typical
6 volt cell phone -- they can leap over the fermentation barrier and convert a
"dead end" fermentation product, acetic acid, into carbon dioxide
and hydrogen.
Logan notes, "Basically, we use the same microbial fuel cell we developed
to clean wastewater and produce electricity. However, to produce hydrogen, we
keep oxygen out of the MFC and add a small amount of power into the
system."
In the new MFC, when the bacteria eat biomass, they transfer electrons to an
anode. The bacteria also release protons, hydrogen atoms stripped of their
electrons, which go into solution. The electrons on the anode migrate via a
wire to the cathode, the other electrode in the fuel cell, where they are
electrochemically assisted to combine with the protons and produce hydrogen
gas.
A voltage in the range of 0.25 volts or more is applied to the circuit by
connecting the positive pole of a programmable power supply to the anode and
the negative pole to the cathode.
The researchers call their hydrogen-producing MFC a BioElectrochemically-Assisted
Microbial Reactor or BEAMR. The BEAMR not only produces hydrogen but
simultaneously cleans the wastewater used as its feedstock. It uses about
one-tenth of the voltage needed for electrolysis, the process that uses
electricity to break water down into hydrogen and oxygen.
Logan adds, "This new process demonstrates, for the first time, that
there is real potential to capture hydrogen for fuel from renewable sources
for clean transportation."
The Penn State researchers were supported by grants from the National Science
Foundation, the U.S. Department of Agriculture, the Penn State Huck Life
Sciences Institute and the Stan and Flora Kappe Endowment.
Photos available at http://www.psu.edu/ur/2005/hydrogensourcephotos.htm
Contact Barbara Hale bah@psu.edu http://live.psu.edu 814-865-9481 |
Contact Vicki Fong vfong@psu.edu http://live.psu.edu 814-865-9481 |