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Algae for Biodiesel? What does it take?
by Sarah Curry With diesel fuel retailing around $4.00 a gallon, algae-based oil sources are beginning to look better. More than 50 companies in the U.S. are working to commercialize algae-generated biodiesel.
Most start-ups begin with the findings of the Aquatic Species Program, which ran at the National Renewable Energy Lab (NREL) from 1978-1996. The Lab collected and screened more than 3000 algal strains, looking for species that naturally produce a useful quantity of oil. After narrowing the collection down to 300 strains, mainly green algae and diatoms, NREL grew the algae in test ponds in Roswell, New Mexico for a year. They also studied the process for lipid extraction and conversion to biodiesel. In the last few years of the program, they worked to genetically modify the algae to produce more oil.
Microalgae are fast-growing beasts with a voracious appetite for carbon dioxide. They have the potential to produce more oil per acre than any other feedstock being used to make biodiesel, and they can be grown on land that's unsuitable for food crops.
In theory, producing algadiesel should be easy: Just separate CO2 from a coal plant's exhaust, bubble it through an algae tank, squeee out the oil and pipe it into a refinery. As part of their photosynthesis process, the algae also "exhale" oxygen. According to Al Darzins, group manager of NREL's National Bioenergy Center, some algal strains can produce upwards of 50-60% of their total body weight in oil. But to do that, they must be stressed. Researchers usually remove a nutrient such as nitrogen to induce this stress. "It's the same reason we store excess food as fat on various areas of our body," said Doug Henston, CEO of Solix Biofuels in Fort Collins, Colorado. "When the algae feel like they're going into an environment where they're not going to have readily available nutrients, they start to produce oil to store energy."
Stress reduces growth rate, so the trick is to find a balance between growth and oiliness that optimizes oil output. At that optimum stress, Darzins says, algae can produce over 5000 gallons of oil per acre per year (soybeans produce about 50 gallons per acre). If diesel sells for $5 a gallon, the annual retail value of the algae crop is $16 million per square mile. That's rich enough for oil companies to pay attention. The Energy Security Act of 2007 calls for 36 billion gallons of domestic biofuels to produced each year by 2022. The Act mandates that 20 billion gallons must come from "advanced" biofuels, meaning non-corn-based biofuels. Companies are working hard to make algae-based biodiesel available as an "advanced" biofuel. 20 billion gallons might be grown on about 1.5% of America real estate.
Doing it in the lab and doing it on an industrial scale are two very different things. It's a matter of maintaining just the right environmental conditions on a large scale, while facilitating rapid harvesting. "There's lots of challenges and technical barriers that need to be overcome," Darzins said. "The new system biology tools will really help delineate where the bottlenecks are in the biochemistry of this organism." Each of the new companies approaches the growth and harvesting of the algae in a different way. Henston's company, Solix Biofuels, is progressing toward the fourth-generation technology of its photobioreactor, which is used to grow the algae. "This technology works, that's been proven," he said. "Bringing cost down is the biggest hurdle."
There are three types of algae-fuel companies according to Bryan Willson, professor of mechanical engineering at Colorado State University. There are closed bioreactors like Solix, open ponds and genetic modification specialists. According to Willson, credible companies in the bioreactor category include Solix and GreenFuels Technology Corp. of Cambridge, MA. Leading-edge firms in the open-pond category include LiveFuels Inc. (Menlo Park, CA); Aurora BioFuels (Alameda, CA) and Seambiotic Ltd. (Tel Aviv, Israel), which demonstrated a system to create clean CO2 from coal-plant emissions.
Genetic modification specialists include Solazyme Inc. (San Francisco), which in June received ASTM D-975 certification of its SolaDieselRD motor fuel; and Sapphire Energy (San Diego), which demonstrated in May a 91-octane gasoline. Defense contractors are working on algal sources for jet fuel.
"The higher oil prices go, the more attractive algae starts looking," said Darzins, but realistically, fuel products at marketable volume are still years away.
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