Will Thurmond, chairman of research and development at the National Algae Association in America (where all but one of the major algae biodiesel firms are based), believes that pure economics will eventually choose between them: "For research purposes, growing algae in photo-bioreactors is better, because you can control all the variables. But once the research has been completed by all the companies involved and moves into large-scale production, the debate will be resolved."
But once you've got the vast amounts of green sludge, how do you go about extracting oil from pond scum? "The old method is to take algae out of a pond with a fishing net, dry it out and literally squeeze the oil out," says Thurmond. "More modern methods have required chemical solvents, but recently the University of Texas has developed a way of using ultrasonic waves to rupture the cell walls: the oil rises to the top of the container and you can skim it off the top of the cells. This is the preferred method, as it's non-polluting, but it's not yet advanced enough to be commercially viable."
Whatever the method employed, the extraction procedure can be costly and complicated, and further processing is still required before the algae can be turned into vehicle fuel. The cost of this has dropped dramatically: to make algae biodiesel in the lab 25 years ago cost $3,000 per gallon; today it is less than $20. However, in the US, petrol costs $2 per gallon and diesel $2.70 – to be competitive, algae biodiesel would need to be around the $2 mark, too. As Thurmond admits, "It's the last yard that's hard."
Yet a solution to that cost problem could be available from a familiar figure in the world of genetic engineering. The renowned American scientist Craig Venter has – with his team at Synthetic Genomics in California – developed bacteria that require only sunlight and water to grow, and secrete the required oil as a by-product of the metabolic process. Professor Venter, who was the first person to have his entire genome sequenced and hopes to become the first to create an entirely synthetic life form, says that if he can raise the funding to build a pilot plant, his bacterial oil could be pumped straight into an existing refinery.
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Jessica Brock
Valcent