In a month-long pilot project, PropelFuels and Solazyme are selling Solazyme's Soladiesel®BD, a form of biodiesel derived from algae rather than from oil crops or agricultural waste, as is the case with most currently available biodiesel. The new fuel is being sold through Propel's network of renewable fuel services stations, with the test limited to four locations in Berkeley, Oakland, Redwood City, and San Jose.

Solazyme's fuel is derived from algae grown in tanks, fed on sugars that prompt the algae to synthesize oils which are then turned into biodiesel. According to the Redwood-City-based Solazyme, the resulting fuel outperforms ultra-low sulfur diesel in tailpipe emissions of total hydrocarbons (THC), carbon monoxide (CO) and particulate matter.

But according to a National Academy of Sciences report released in October, "Sustainable Development of Algal Biofuels in the United States", algal fuels don't necessarily come without a significant cost. The report's authors say that it can take up to 3,600 gallons of water to create each gallon of algal biodiesel, depending on the procedure used. Providing a source of nutrients for the algae that doen't decrease the net energy output can also be a problem, say the report's authors.

However, as the authors of the report point out,

[N]one of the sustainability concerns is a definitive barrier to the development of algal biofuel as a fuel alternative. Biological and engineering innovations have the potential to mitigate the resource demands associated with algal biofuel.

Chief among these possible innovations are developing algal strains that can tolerate saltwater or brackish water, and developing ways of using urban wastewater to both irrigate and fertilize the algae. Your toilet and your car may yet be joined in a great Fuel Cycle of Life.

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