Biodiesel from algae may not be as green as it seems

NewScientist.com
21 July 2010 by Helen Knight
Magazine issue 2770.

BUBBLING green tubes filled with algae gobbling up carbon dioxide and producing biodiesel may sound like the perfect way to make clean fuel, but it could generate nearly four times the greenhouse emissions from regular diesel.

How we farm algae is crucial to making algal biodiesel environmentally viable, says Anna Stephenson at the University of Cambridge. She has developed a computer model that calculates the carbon footprint of producing, refining and burning algal biodiesel.

"Making algal biodiesel in clear tubes has a carbon footprint nearly four times that of producing diesel."

When algae are farmed in perspex tubes, she says, the energy needed to pump the algae around to ensure adequate exposure to sunlight results in a carbon footprint of 320 grams per megajoule equivalent of fuel. This compares with 86 g/MJ to extract, refine and burn regular diesel (Energy and Fuels, DOI: 10.1021/ef1003123).

"If you use tubular bioreactors, frictional losses mean the energy required to pump the culture around is so high that the biodiesel would have a much greater greenhouse gas emission than fossil diesel," she says.

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