12 May 2011
Biofuels' "green" credentials questioned
by Kate Melville
Biofuels might not be so "green" after all, say researchers at MIT, who have been doing some calculations based on the complete carbon footprint of fossil fuels and their biofuel equivalents. They contend that when a biofuel's origins are factored in - for example, taking into account whether the fuel is grown in a clear-cut rainforest - conventional fossil fuels may sometimes be "greener."
"[Biofuel] technologies that look very promising could also result in high emissions, if done improperly," says MIT's James Hileman, who has published his findings in the journal Environmental Science and Technology.
Hileman and his team performed a life-cycle analysis of 14 fuel sources "from well to wake" - that is, from acquiring the biomass to transporting it, to converting it to fuel, as well as its combustion. "All those processes require energy," he adds, "and that ends up in the release of carbon dioxide."
The team found that emissions varied widely depending on the type of land used to grow biofuel components such as soy, palm and rapeseed. For example, Hileman and his team calculated that biofuels derived from palm oil emitted 55 times more carbon dioxide if the palm oil came from a plantation located in a converted rainforest rather than a previously cleared area. Depending on the type of land used, biofuels could ultimately emit 10 times more carbon dioxide than conventional fuel.
"Severe cases of land-use change could make coal-to-liquid fuels look green," says Hileman (coal-to-liquid is considered to be extremely un-green). The challenge, he contends, is not how to scale up biofuel production, but how to do it in a sustainable fashion. One solution he suggests is to work with crops like algae and salicornia, that don't require fertile soil or freshwater to grow.
He notes that total emissions from biofuel production may also be mitigated by a biofuel's byproducts. For example, the process of converting jatropha to biofuel also yields solid biomass: For every kilogram of jatropha oil produced, 0.8 kilograms of meal, 1.1 kilograms of shells and 1.7 kilograms of husks are created. These co-products could be used to produce electricity, for animal feed or as fertilizer. Hileman says that this is a great example of how co-products can have a large impact on the carbon dioxide emissions of a fuel.
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Source: Massachusetts Institute of Technology