Extracts From Other Sources
Could algal colonies be the answer to global warming?
Great balls of concrete could take some of the heat out of
global warming, claim chemical engineers from Lousiana State University. They
say the balls will be colonised by algae which "fix" carbon from the atmosphere
and trap it in sediment.
Their plan is to dump concrete hemispheres dubbed "reef balls"
into estuaries and coastal waters, providing large surface areas for marine
algae to colonise. The researchers believe that each hemisphere could remove
hundreds of kilograms of carbon from the atmosphere every year.
The Louisiana team aims to attract algae that grow 20 times
faster than free-floating forms. As they grow and photosynthesis they extract
carbon dioxide from the surrounding waters, which is replenished by co2 from the
atmosphere. When the algae die, they fall to the seabed and become part of the
sediment. The net result is the removal of CO2 from the
Carl Knof, chair of chemical engineering at the university,
said: "We are trying the idea out in the lab now using balls 15 centimeters
across. But in the next stage, in the ocean we will be sinking balls three
meters across or more."
One challenge has been to make the concrete chemically neutral.
Normal concrete is too alkaline for microalgae to colonies. Sea water will
eventually neutralize it, but not before organisms with less power to "fix"
CO2 have invaded the concrete surface.
Ironically, neutralizing the concrete means applying
CO2 to it under high pressure, while the concrete is still wet.
Treating the concrete with a foaming agent creates a sponge-like surface which
has a bigger surface area for the algae to grow on. "A hollow hemisphere or reef
ball about 100 square metres of active surface area for microalgae growth. Each
reef hemisphere could remove 200 kilograms of carbon from the atmosphere each
year, and this process would continue indefinitely," says Knopf. The team has
calculated that to soak up all the CO2 the US produces in a year
would require almost a billion-and-a-half balls. Still, the team reckons, itís a
start. The balls could eventually be used to dispose of carbon dioxide from
fossil-fuel power plants. Emissions could be pumped into the ocean close to a
concrete reef system, say the researchers.
The first test balls could be lowered into the ocean as early
as next year. Knopf plans to make the hollow balls buoyant enough to float into
place by putting an inflated rubber ball inside them, and to sink them by
gradually deflating the ball. Once in place, says the teamís marine biologist
Bob Gambella, the balls will both consume carbon dioxide from the ocean and
provide conditions on the sea bed similar to those of a natural reef.
New scientist, June 1998