Most people consider algae a nuisance. But it turns out that one man's pond scum is another man's gold, to draw on an old expression. An algal species with the right properties could be immensely valuable. That's why we and others at the National Renewable Energy Laboratory, in Golden, Colo., have been busy "bioprospecting" for promising scoops of slime.
Recently, we dispatched a graduate student to pan for algae in a nearby creek, in Utah's Great Salt Lake, and in other spots where we hoped to find organisms thriving in extremes of temperature, pH, and sun exposure. We're hunting for novel strains that can grow quickly and efficiently enough to provide a renewable source for diesel, gasoline, and jet fuel, which would help reduce the world's dependence on fossil fuels while slowing the buildup of carbon dioxide in the atmosphere.
What kind of algae could do all that? Right now, that's an unanswered question. Algae are microscopic organisms, which, like plants, use photosynthesis to convert light into chemical energy while at the same time absorbing carbon dioxide from the atmosphere. Algae turn the carbon they take in first into sugars and then into oil, which can be made into fuel. But some strains produce much more oil than others.
Our recent bioprospecting ventures have unearthed hundreds of different algae types. There are also about 30 000 known species to consider. We want to figure out which of them could thrive on polluted or salty water, reproduce rapidly, and of course, make copious amounts of oil. Luckily, we can go through them pretty quickly, using a microscope, a few other specialized instruments, and a dye that fluoresces when it contacts oil. Several strains we examined recently exploded in glowing green halos when we tested them in this way.
The simple elegance of these microscopic oil factories has motivated a hundred or so start-ups to try to tackle algal biofuel production. Major oil companies, including Chevron, ConocoPhillips, ExxonMobil, and Royal Dutch Shell, are studying this idea. Several airlines have even performed test flights using fuel blends consisting of a petroleum-based fuel, algal oil, and oils from more traditional biofuel crops, such as Jatropha, a genus of succulent plant that produces oil-rich seeds.
If you can make biofuel with jatropha or other vegetable crops, why consider algae? In short, because they grow much faster and produce more oil than terrestrial plants. A glance at the mossy film on the surface of virtually any pond will confirm that the needs of these organisms are truly humble. Like houseplants, algae require water, sunlight, a few nutrients, and carbon dioxide from the air. They grow prolifically and accumulate large amounts of oil when they experience environmental stress.
That algae produce oil isn't a great surprise. The fossil fuels that run our cars likely came from ancient algal cells that dropped to the bottom of former oceans and were covered by sediment. Algae use their oil the same way animals use body fat, as a source of energy when times are lean. For animals, lean times come between feedings; for algae, this happens every night, when there isn't any light to power photosynthesis.
Oil production also helps algae overcome the stress of growing in full sunlight, which can be hard on these cells, particularly when they are starved of one or more nutrients. Such deprived algae tend to generate highly reactive chemicals called free radicals, which can cause molecular havoc within. The conversion of CO2 to oil prevents the buildup of free radicals, helping the cells avoid internal damage. This oil is very similar to the vegetable oil you might buy at the grocery store.
But unlike corn or olives or soybeans, which can be harvested only once a season, algae grow rapidly enough to be reaped continuously. They also have a higher oil content—some as high as 50 percent. A hectare of soybeans, for example, typically produces only about 500 liters of oil each year, whereas a hectare of algae growing in a shallow pond can easily generate 9000 L of oil—and perhaps as much as 47 000 L—annually. That makes algae many times as productive as oil palms, the most oil-rich source of biodiesel now in use. (The expanding cultivation of oil palms is problematic, however, as they are responsible for much of the deforestation across Southeast Asia.)
For making the most oil in the least amount of space, algae win hands down. But there are other reasons to believe they provide the most promising source for biofuel. To understand why, you need to take a closer look at the competition.