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CaseStudy7.1 AlgalBiofuelProduction(USA)
Algae have an obvious attraction when it comes to biofuel production. While
terrestrial plants such as soy, canola and palm yield around 470, 1500 and 5700 l of
oil per hectare respectively, some kinds of algae can provide approaching 20 000.
The problem in realising this potential tends to come down to the demands for
resources and land necessary to make it possible - and in the case of enclosed
bioreactors, the cost of construction and operation too.
As part of its 'Spaceship Earth' project, NASA has come up with the idea
of huge plastic osmotic containers, filled with sewage and floating at sea, in
which to grow algae. The concept is a simple but effective one. NASA has been
developing semi-permeable 'forward-osmosis membranes' for some time to recycle
water on future long-haul space missions. By using them to create their offshore
membrane enclosures for growing algae (OMEGA), additional internal fresh water
can safely escape, without the danger of ingress into the system of the external
salt water. In addition, the nature of the material also allows for the necessary
gaseous exchange, while temperature control - a major cost element in land-based
enclosed bioreactors - is provided by the natural buffer effect of the sea's specific
heat capacity. Wave action will help keep the system mixed, avoiding the need for
paddles, motors and an external power supply.
In addition to the eventual potential fuel production from the harvested algae,
the OMEGA system also promises sustainable wastewater treatment, fertiliser pro-
duction and carbon sequestration. Significantly, given the environmental question
mark hanging over some forms of terrestrial bio-energy, it entirely circumvents
any necessity to compete with food production for increasingly scarce land and
water resources.