Pond Scum Prized Again
as Potential Biofuel

The challenges don’t stop there, however. Once scientists can successfully rear their algae outside of the lab, they’ll then have to extract lipids from them. Right now, the only practical method involves pumping chlorinated compounds similar to PCBs and dioxin into the algae. “It’s not very efficient, and it’s not very green,” says Zimmerman. In fact, it’s poisonous. Chlorinated compounds can pollute soil and groundwater for decades.

Zimmerman is now trying to borrow a trick from dry cleaners. A lot of the dirt that dry cleaners get out of clothes is made up of lipids. In the past, they’ve used chlorinated compounds, but recently they’ve switched over to high-pressure, superheated carbon dioxide. If you squeeze and heat carbon dioxide enough, it starts to act like chlorin-ated compounds and can grab certain kinds of lipids. “It’s really nice: you can recapture the CO2 and reuse it. It’s a much greener way to go,” says Zimmerman.

Anastas is investigating what to do with another major source of waste: the algae. Once lipids for fuel are extracted from algae, there’s still a lot of biomass left over. Anastas is approaching the problem of this waste the way oil companies do when they refine petroleum. They don’t simply throw out what’s left over when they’ve produced gasoline. “Every little bit of that black stuff coming out of the ground is finding some kind of purpose,” says Anastas.

Just as petroleum can be turned into everything from plastic to asphalt, Anastas wants to develop new products using what’s left over from the production of fuel from algae. It’s a fertile field for invention, he says, because the molecules in algae are more intricate than the simple straight chains of hydrogen and carbon that come out of petroleum. “You can take advantage of their complexity to make new molecules,” he says.

By developing new products (such as fire-retardant building materials, for example), Anastas hopes to both reduce the environmental impact of algae and boost their value. “Green is the color of the environment, and it’s also the color of money,” he says. “Taking things out of the waste stream changes the economic equation.”

The Yale researchers are spending a lot of their time investigating particular steps in the process of turning algae into fuel. But they also want to see how the whole system will work in advance. This may sound like clairvoyance, but engineers have a fairly well-developed method for modeling complicated industrial processes. Zimmerman herself has made these models for Ford to help them plan out new systems for manufacturing lubricants for their cars. Now she’s building a model of the entire process of getting fuel from algae. “We’re looking at it from the cradle to the end of life,” she says.

The model is still in its early stages, but Zimmerman can already see that algae do indeed promise to have much less impact on the environment than crop biofuels. She is also using the models to evaluate which methods for growing algae are the greenest. It appears, for example, that conventional racetrack-shaped tanks are not the best design. Her model points instead to designs in which water flows through spiraling tubes, allowing more sunlight to penetrate the water and spur the algae to grow.

Zimmerman’s model may also help engineers cope with the complexities of the energy economy. As the market changes, the profits from algae fuel may change in mysterious ways. Zimmerman wants to use her model to determine how much fuel or how many other products should be generated from algae to make the entire process as valuable as possible.

That’s a lot of complexity to add to a project that’s already enormously ambitious. But if Zimmerman and her colleagues can figure out how to make millions of gallons of green fuel from the algae living in their lab, it will be well worth the extra effort.

“You feel like, if you could figure it out, it would make a huge difference,” she says.

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Top of Page | Fall 2009 | environment:YALE