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 illions of years ago ocean beds
became the repositories of the hydrocarbons oil and gas we use as fuel.
Now scientists are looking at ways to put the carbon dioxide released by
burning those fuels back into the ocean deeps.
 A proposal by LSU scientists to do just that
has won a grant from the U.S. Department of Energy. The scientists,
chemical engineering chair Carl Knopf, chemical engineering professor
Kerry Dooley and professor of oceanography Robert Gambrell, received the
go-ahead recently to develop a means of increasing the quantity of
attached as distinguished from free-floating microalgae in shallow
estuarial waters.
"Attached microalgae are 20 times more
efficient in the fixation of carbon dioxide than their unattached
counterparts," Dooley said.
The researchers propose to do this with
"reef-balls": large, hollow half-spheres of specially made concrete. The
idea is to use the attached microalgae to remove carbon dioxide from the
water, which will in turn absorb it from the atmosphere. When the algae
die or are consumed, they will eventually become part of the sediment of
the seafloor, replicating the process by which carbon dioxide was stored
in fossil fuels more than 60 million years ago.
The trick to getting microalgae to establish
themselves on the reef-balls is making the concrete pH neutral, Knopf
said. Normal concrete is too alkaline for microalgae, and in the year or
so it takes for seawater to neutralize it, other organisms not as
sensitive to alkalinity have already attached, preventing the microalgae
from doing so.
The reef-balls will be made pH neutral by the
application of high-pressure carbon dioxide while the concrete is still
wet, Knopf said. In addition, the wet concrete will be treated with
foaming agents to give the hemispheres a sponge-like texture with a
greater surface area. Nutrients that microalgae feed on can be added to
the mix.
"A one-meter hemisphere can remove one ton of
carbon dioxide a year," Knopf said. U.S. power plants generate
approximately 1.7 billion tons of carbon dioxide a year, about 20 percent
of the world's carbon dioxide emissions, according to Dooley.
Another advantage of the concrete hemispheres
is that they will act as an artificial reef, providing habitat for fish
and other marine creatures, Dooley said.
Increased efficiency might be obtained by
injecting carbon dioxide into the water near the fixed microalgae, or
putting the reef-balls in the vicinity of such injection wells to give
them a rich carbon dioxide environment in which to grow.
The development of artificial reefs with the
reef-balls is part of the Department of Energy's "Global Climate Change
Novel Concepts for Management of Greenhouse Gases" program. The LSU
researchers could receive more than $700,000 over the next five years to
develop their ideas.  | 
