Slimy Green Power
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SLIMY GREEN POWER
Monday, January 31, 2000
Getting unlimited, clean energy from green slime is the lead-into-gold
discovery reported this month by American biologists. They have found a
metabolic switch that triggers algae to turn sunlight into large quantities
of hydrogen gas; an alternative fuel that many hope will power the
automobiles of the future, leaving only water vapour as exhaust fumes.
"I guess it's the equivalent of striking oil," said UC Berkeley plant and
microbial biology professor Tasios Melis. "It was enormously exciting, it
Currently, hydrogen has to be extracted from natural gas, a non-renewable
energy source. The new discovery harnesses nature's own method of energy
production, 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 behind the research, UC
Berkeley and the National Renewable Energy Laboratory (NREL) in Golden,
The group used cultures the microscopic green alga Chlamydomonas reinhardtii
in their bid to find an abundant hydrogen source. For nearly 60 years,
scientists have known that this and certain other types of algae can produce
the gas, but only in trace amounts. Despite tinkering with the process, no
one had been able to make the yield rise significantly without elaborate and
costly procedures. Until now.
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
energy already stored within itself. The by-product of this process is
"The switch is actually very simple to activate," Melis said. "It depends on
the absence of an essential element, sulfur, from the micro-alga growth
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 their usual way. In order to
survive, they are forced to activate an alternative metabolic pathway, which
generates the hydrogen. This may be universal in many types of algae. The
alga culture cannot live forever with this arrangement but it can manage for
a considerable period of time without any apparent negative effects.
"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."
The researchers first cultivate the alga under normal photosynthetic
methods, just like every other plant on Earth. This allows the green-colored
micro-organisms to collect sunlight and accumulate a generous supply of
carbohydrates and other fuels. When enough energy has been banked in this
manner, the scientists transfer the liquid alga culture, which resembles a
lime-green soft drink, to sealed bottles with no sulfur present. Then the
culture is allowed to consume all remaining oxygen.
After about 24 hours, photosynthesis and normal metabolic respiration stop.
Hydrogen then begins to bubble to the top of the bottles and bleed off into
tall collecting 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 traces, but
we got bulk amounts."
After up to four days of generating the gas, the culture is depleted of
stored fuel and must be allowed to return to photosynthesis. Two or three
days later it can again be tapped for hydrogen. The process can be repeated
While current production rates are not high enough to make the process
commercially viable, the researchers believe that yields could rise by at
least 10 fold with further research, someday making the technique an
attractive fuel-producing option. "In the future, both small-scale
industrial and commercial operations and larger utility photo-bioreactor
complexes can be envisioned using this process," Melis said.
Preliminary 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.
The team is just beginning to test ways to maximize hydrogen production,
including varying the particular type of micro-alga used and its growth
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."
Up till now, all that has been lacking is a cheap, renewable source of the
gas. Now, thanks to pond slime, we might just have it.
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