Pond Scum Prized Again
as Potential Biofuel
By Carl Zimmer
The four flasks look like they’re filled with bubbling lime juice. “If you look closely,” says Hamid Rismani-Yazdi, a Yale postdoctoral researcher, “you can see the algae.” It’s true: put your nose to the Pyrex, and you can make out tiny flecks of Dunaliella tertiolecta, an ocean-dwelling species, riding the turbulence.
Rismani-Yazdi’s flasks may look like nothing more than improvised aquariums. But Rismani-Yazdi and his colleagues have great hopes for the algae they’re rearing. It’s possible that these organisms may help start an industrial revolution.
Like a growing number of other scientists, they think algae may someday be able to churn out huge amounts of environmentally friendly fuel. It’s an idea on which investors are also betting, and in a big way. Some $800 million in venture capital has flowed into companies working on algae fuels, most of it arriving over just the past few months. From green flasks like these may come a postpetroleum economy.
At least that’s the idea. Despite all the cash and all the headlines, the quest for algae biofuel has a long way to go. There are many open questions about whether it can really work on an industrial scale. Last year three professors at Yale—Jordan Peccia, Julie Zimmerman and Paul Anastas—decided to combine the brainpower in their labs to solve many of the mysteries about algae fuel. They are deciphering the complex network of genes inside of algae to learn how to manipulate them to be better fuel factories. And they are also deciphering the complex economic network that will emerge to support the industrial-scale production of fuel from algae. After all is said and done, they want to know if we would actually be better off environmentally if algae, like the ones in Rismani-Yazdi’s flasks, fueled our cars and airplanes.
“You can grow algae everywhere, so you can make them where people are using them.”
Today the algae have decided to be particularly mysterious. Rismani-Yazdi, who works in Peccia’s lab, has been adjusting his recipe of artificial seawater to coax his Dunaliella tertiolecta into growing quickly. The algae have become dense enough to give his flasks a lime-green hue. But Rismani-Yazdi would like them to grow a thousand times denser. To show what he’s shooting for, he picks up another flask, which looks as if it’s full of spinach soup. It’s crammed with a freshwater species called Scenedesmus dimorphus.
“Something is limiting their growth,” he says, looking back to the lime-green flasks of Dunaliella teriolecta. Maybe his fluorescent lamps are too bright. Maybe he’s giving them too much carbon dioxide. Or maybe it’s something he hasn’t thought of yet.
Peccia listens to Rismani-Yazdi describe his frustration. He shrugs his shoulders with a faint smile. It’s a puzzle that he’s very familiar with. “One alga looks just like another, but they respond so differently,” says Peccia, associate professor of chemical engineering. “Sometimes they don’t want so much light; sometimes they don’t like the nitrogen. After a while, we talk about them like people.”
The current excitement over algae may be new, but the basic concept underlying it is old. Today we produce fossil fuels, like gasoline and diesel, from crude oil buried deep in the ground. That crude oil got its start as carbon compounds in organisms that lived millions of years ago. Scientists have long wondered whether it would be possible to skip those millions of years of waiting—not to mention the drilling and the other demands of petroleum production—and gather energy-rich compounds from living things.
Some of the most promising compounds are oily molecules called lipids. All living things make them. Our bodies make lipids to build the membranes of our cells and to store extra energy for lean times. In the past, people have extracted lipids from animals for fuel. Lipid-rich whale oil fueled lamps and lighthouses across the United States during the 19th century, for example.
You can’t fuel a modern economy on whale oil, though. Whales are just too scarce and reproduce themselves too slowly. As a result, whalers nearly drove many species of whales extinct by the early 20th century. But there are other organisms that make lipids in far greater quantities and at a far-faster rate. They are algae.
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.
Few people outside of the alternative-energy world knew about algae’s renaissance until last July. Exxon announced that it was plowing $600 million into algae research. The oil giant entered into a partnership with Synthetic Genomics, headed by Craig Venter, who pioneered sequencing the human genome in the 1990s. Over the past few years, Venter and his colleagues have been inserting genes into cyanobacteria to increase their production of lipids. Exxon expects to have small-scale plants in operation in five to 10 years.
The Wall Street Journal reacted to the news by declaring that the world had entered “the summer of algae.” Other companies were getting into the algae game as well. Solazyme, a corporation based in San Francisco, announced in June that its funding had reached $76 million. In September it announced that the Department of Defense had picked Solazyme to supply 20,000 gallons of fuel for Navy jets. Another company, Sapphire Energy, has $100 million in funding and promises that by 2011 it will be producing 1 million gallons of diesel and jet fuel from algae.
Yet these promises do not, in themselves, guarantee that algae fuel will actu-ally make financial sense. According to one estimate, it’s still 20 times more expensive to make than crude oil. And some skeptics don’t believe that the recent flurry of investment reflects any profound advances in dealing with the great problems associated with fuel derived from algae.
The best way to get a lot of lipids out of algae, for example, is to put them under stress. If Scenedesmus dimorphus is fertilized with a lot of nitrogen, for example, its cells will end up 20 percent lipids. On a low-nitrogen diet, that figure rises to 35 percent. Algae probably evolved this strategy as a way to survive temporary famines. In other words, it’s not something they can do indefinitely. If you stress algae for too long, says Peccia, “they’ll just give out.”
In 2008, Peccia, Zimmerman and Anastas decided to get into the algae fuel game. While corporations were just tweaking the algae and observing how many lipids they could get out, the Yale researchers chose a different strategy. “It’s a different way of going about things,” says Anastas, Teresa and H. John Heinz III Professor in the Practice of Chemistry for the Environment.
Peccia has been leading the team’s effort to get to know algae in their most intimate details. “We just want to understand how they operate, really in the most fundamental way,” says Peccia. For all the research that has gone into algae, for example, scientists still know nearly nothing about the genes they use to make lipids. No one has even sequenced the genomes of any of the lipid-rich microalgae. “We don’t really know how it all works,” says Peccia.
Because the genomes of microalgae are so big, Peccia and his colleagues have decided not to sequence all of their DNA. Instead, they’re just searching for the genes they use to make extra lipids. To find them, the scientists raise algae in different conditions. For instance, they rear some of their algae with a lot of nitrogen and some of them with barely any. The algae respond to these different conditions by switching on different genes. Peccia and his colleagues then rip open the algae. They fish out copies of the active genes, called messenger RNAs. From those molecules, the scientists can determine the sequence of the genes and start to gather clues about their function.
Peccia and his colleagues are now mapping out the gene networks that algae use to ramp up their lipid production. They hope that this knowledge will allow them to precisely manipulate algae into making more lipids with few side effects. It will then be possible to abandon the current brute-force methods of starvation.
Even if Peccia and his colleagues can manipulate algae to become champion lipid makers, however, they will still face some serious challenges in getting the organisms to thrive outside of a laboratory flask. The Earth’s waters are loaded with algae, and their diversity is so vast that scientists are only just starting to catalog it. Some of those species will inevitably slip into the tanks where engineers rear their designer algae. “They’re going to have to learn how to compete with these constant insults of micro-algae coming in,” says Peccia. If they don’t, they’ll get outcompeted and the tank will become overwhelmed by the wrong kinds of algae.
Peccia has been probing the biology of algae to look for ways that he can help them win in the real world. He and his colleagues have found that Scenedesmus dimorphus grows nicely when levels of carbon dioxide are high. In fact, they keep growing when other species of algae die from carbon dioxide poisoning. By pumping extra carbon dioxide into algae tanks, engineers may be able to keep the right species thriving. “If we don’t bubble high CO2 in, the natural algae outcompete it,” says Peccia.
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.