 
UC
Berkeley and Colorado scientists find valuable new source of
hydrogen fuel, produced by common algae
20
Feb 2000
By
Kathleen Scalise, Public Affairs
WASHINGTON,
D.C.-- A metabolic switch that triggers algae to turn sunlight
into large quantities of hydrogen gas, a valuable fuel, is the
subject of a new discovery to be presented by University of
California, Berkeley, scientists and their Colorado colleagues
during a Feb. 21 press briefing at the annual meeting of the
American Association for the Advancement of Science in Washington,
D.C.
"I
guess it's the equivalent of striking oil," said UC Berkeley
plant and microbial biology professor Tasios Melis. "It
was enormously exciting, it was unbelievable." He first
described the discovery in the January 2000 issue of the journal
Plant Physiology.
Melis
and postdoctoral associate Liping Zhang of UC Berkeley made
the discovery - funded by the U.S. Department of Energy (DOE)
Hydrogen Program - with Dr. Michael Seibert, Dr. Maria Ghirardi
and postdoctoral associate Marc Forestier of the National Renewable
Energy Laboratory (NREL) in Golden, Colorado.
Currently,
hydrogen fuel is extracted from natural gas, a non-renewable
energy source. The new discovery makes it possible to harness
nature's own tool, photosynthesis, to produce the promising
alternative fuel from sunlight and water. A joint patent on
this new technique for capturing solar energy has been taken
out by the two institutions.
So
far, only small-scale cultures of the microscopic green alga
Chlamydomonas reinhardtii have been examined in the laboratory
for their hydrogen production capabilities, Melis said.
"In
the future, both small-scale industrial and commercial operations
and larger utility photobioreactor complexes can be envisioned
using this process," he said.
While
current production rates are not high enough to make the process
immediately viable commercially, the researchers believe that
yields could rise by at least 10 fold with further research,
someday making the technique an attractive fuel-producing option.
Preliminary
rough estimates, for instance, suggest it is conceivable that
a single, small commercial pond could produce enough hydrogen
gas to meet the weekly fuel needs of a dozen or so automobiles,
Melis said.
The
scientific team is just beginning to test ways to maximize hydrogen
production, including varying the particular type of microalga
used and its growth conditions.
Many
energy experts believe hydrogen gas one day could become the
world's best renewable source of energy and an environmentally
friendly replacement for fossil fuels.
"Hydrogen
is so clean burning that what comes out of the exhaust pipe
is pure water," Melis said. "You can drink it."
Engineering
advances for hydrogen storage, transportation and utilization,
many sponsored by the U.S. DOE Hydrogen Program, are beginning
to make the fuel feasible to power automobiles and buses and
to generate electricity in this country, Seibert said.
"What
has been lacking is a renewable source of hydrogen," he
said.
For
nearly 60 years, scientists have known that certain types of
algae can produce the gas in this way, but only in trace amounts.
Despite tinkering with the process, no one has been able to
make the yield rise significantly without elaborate and costly
procedures until the UC Berkeley and NREL teams made this discovery.
The
breakthrough, Melis said, was discovering what he calls a "molecular
switch." This is a process by which the cell's usual photosynthetic
apparatus can be turned off at will, and the cell can be directed
to use stored energy with hydrogen as the byproduct.
"The
switch is actually very simple to activate," Melis said.
"It depends on the absence of an essential element, sulfur,
from the microalga growth medium."
The
absence of sulfur stops photosynthesis and thus halts the cell's
internal production of oxygen. Without oxygen from any source,
the anaerobic cells are not able to burn stored fuel in the
usual way, through metabolic respiration. In order to survive,
they are forced to activate the alternative metabolic pathway,
which generates the hydrogen and may be universal in many types
of algae.
"They're
utilizing stored compounds and bleeding hydrogen just to survive,"
Melis said. "It's probably an ancient strategy that the
organism developed to live in sulfur-poor anaerobic conditions."
He
said the alga culture cannot live forever when it is switched
over to hydrogen production, but that it can manage for a considerable
period of time without negative effects.
The
researchers first grow the alga "photosynthetically, like
every other plant on Earth," Melis said. This allows the
green-colored microorganisms to collect sunlight and accumulate
a generous supply of carbohydrates and other fuels.
When
enough energy has been banked in this manner, the researchers
tap it and turn it into hydrogen. To do this, they transfer
the liquid alga culture, which resembles a lime-green soft drink,
to stoppered one-liter glass bottles with no sulfur present.
Then, the culture is allowed to consume away all oxygen.
After
about 24 hours, photosynthesis and normal metabolic respiration
stop, and hydrogen begins to bubble to the top of the bottles
and bleed off into tall, hydrogen-collection glass tubes.
"It
was actually a surprise when we detected significant amounts
of hydrogen coming out of the culture," Melis said. "We
thought we would get trace amounts, but we got bulk amounts."
After
up to four days of generating an hourly average of about three
milliliters of hydrogen per liter of culture, the culture is
depleted of stored fuel and must be allowed to return to photosynthesis.
Then, two or three days later, it again can be tapped for hydrogen,
Melis said.
"The
cell culture can go back and forth like this many times,"
said Dr. Maria Ghirardi of NREL in Colorado.
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