Pond Scum Prized Again
as Potential Biofuel

Algae is a broad term that refers to most of the organisms that live in water and capture energy from the sun. One kind, called cyanobacteria, is also known as blue-green algae for its color. Like other bacteria, cyanobacteria are very small, have few genes and normally make a small supply of lipids. Other kinds of algae, often called microalgae, have cells much more like ours. (That’s because they’re more closely related to us than to bacteria.) The cells of these microalgae are big and complex. In many cases, they also have many times more genes than cyanobacteria. And—most importantly for the search for new kinds of fuel—they produce a remarkable quantity of lipids. In some species of microalgae, lipids can take up over half the mass of a cell.

Thirty years ago, the U.S. Department of Energy launched the Aquatic Species Program to investigate the possibility of getting fuel from microalgae. It might be possible, scientists reasoned, to grow algae, extract lipids from them and  transform those lipids into diesel or other kinds of fuel. Fanning out across North America, they gathered 3,000 promising, lipid-rich strains. They tested the algae in massive racetrack-shaped tanks. They engineered algae with genes to make them churn out extra lipids. And they explored different kinds of chemical reactions that could pull those lipids out of the algae.

Over its 17-year lifetime, the Aquatic Species Program made a lot of important discoveries about the basic biology of algae. But despite these achievements, the program’s scientists never got the cost of algae-derived fuel down low enough to make it a practical alternative to fossil fuels. In 1996, the Department of Energy closed the program down in a wave of budget cuts.

Thirteen years later, however, the algae are back. “The landscape has changed,” says Zimmerman, assistant professor of green engineering at F&ES.

Many experts are now warning that  the world’s oil supply cannot expand fast enough to satisfy the growing demand for energy. As a result, they warn, we can expect more price spikes like the ones that have shocked the economy in recent years. At the same time, petroleum’s toll on the environment is becoming clearer, especially its huge role in warming the Earth’s climate.

Concerns like these have led the U.S. government and the energy industry to get serious about all kinds of alternative fuels. And that includes biofuels—the fuels derived from living things. Today ethanol from corn and diesel from other crops, such as soybeans, make up the majority of biofuels on the market. These biofuels emit carbon dioxide just like petroleum when they power a car, but they have, at least in theory, a big advantage over fossil fuels. In order for biofuels to be made in the first place, plants have to suck carbon dioxide out of the air. The gas they draw down could potentially balance the climate books.

Unfortunately, many experts now argue, biofuels from crops have hidden costs. “When you count all the pesticides and fertilizer and farming and the water that goes into it, it isn’t really a good environmental strategy,” says Zimmerman.

It’s also a strategy that can force us to choose between food and fuel. That’s because it takes a lot of land to grow corn and soybeans for biofuel, land that could otherwise be dedicated to feeding people. In 2006, University of Minnesota biologist David Tilman and his colleagues reported that dedicating all of the current U.S. corn crop to ethanol would satisfy just 12 percent of the country’s demand for gasoline. If all the soybean farms shipped their beans to refineries, they would satisfy only 6 percent of the country’s demand for diesel fuel.

Outside the United States, biofuels are having even more devastating impacts. The demand for palm oil for biofuel has spurred corporations to clear millions of acres of tropical forests for plantations. Conservation biologists have warned that the rapid destruction of these forests will threaten many species of plants and animals. Oil palm plantations may drive many populations of orangutans extinct within 10 years, for example.

These drawbacks to crop biofuels have led a number of researchers to take another look at algae. On paper, at least, algae don’t carry the risks of crop biofuels. They may be a much more efficient source of lipids, for example. “In soybeans, it’s just in the beans,” says Peccia. “In algae, it’s the whole thing.”

Unlike soybeans, Peccia points out, algae don’t need soil. “They can just live on wastewater.” Engineers would have a lot of options about where to put their algae tanks. Some species would thrive in the sunny deserts of the Southwest, while others would do well in the cloudy Northeast. It might even be possible to grow marine algae in the ocean, in much the same way that fish are farmed. “You can grow algae everywhere, so you can make them where people are using them,” says Zimmerman.

One of the reasons that crop biofuels aren’t as green as they may seem is that they require lots of fertilizers, which then get carried into rivers and oceans, where they foster the growth of oxygen-devouring bacteria, creating so-called dead zones where few animals can survive. Algae, on the other hand, can be fertilized with materials that can then be captured as they leave a tank. And algae can also be fertilized in ways that crops cannot. The carbon dioxide belched out of a coal-fired power plant, for example, can get piped into an algae tank, stimulating growth.

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Top of Page | Fall 2009 | environment:YALE