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NASA Uses Algae to Turn Sewage into Fuel

Harvesting algae

An illustration of an OMEGA ship harvesting algae to turn into fuel.NASA

NASA may concern itself largely with space exploration, but it also wants to keep Earth on a steady course in the face of rising energy costs and climate change. Now the U.S. space agency has thrown its weight behind a clever method of growing algae in wastewater for the purpose of making biofuel.

The OMEGA system consists of algae grown in flexible plastic bags floating offshore, where cities typically dump their wastewater. Oil-producing freshwater algae would naturally clean the wastewater by feeding on nutrients in the sewage. The cleansed freshwater could then release into the ocean through forward-osmosis membranes in the sides of the plastic bags.

"You're concentrating nutrients and releasing extremely clean water into the ocean," said Jonathan Trent, a bioengineer at NASA Ames Research Center in Moffett Field, Calif. The forward-osmosis membranes only release fresh water into the ocean, and don't permit salty water to contaminate the bags.

Trent envisions harvesting the algae with barges every ten days, and then flushing the plastic bags with salt water to clean out any freshwater algae that might foul the sides of the bags or the forward-osmosis membranes. The algae would be turned into fuel in a manner similar to using corn to make ethanol.

Municipal wastewater pumped into the bags would then start the cycle all over again.

Such a process would mainly rely on the energy of the ocean waves to mix the algae, as well as sunlight and carbon dioxide. The offshore locations and the wide oceans would also have more than enough room to grow massive amounts of algae needed to produce biofuels for an energy-hungry world.

Algae for a greener economy

Many experts see algae as the biofuel source of the future for several reasons. Algae's biofuel yield could range from 1,000-4,000 gallons per acre each year, compared to just hundreds of gallons per acre annually from oil palm, sunflower and soybeans, according to a U.S. Department of Energy (DOE) report. The DOE added that algae alone could theoretically take care of transportation fuel demands for the entire United States.

That early promise has led the DOE to invest in algae-focused ventures through its new ARPA-E agency, and to put together a report titled the "National Algal Biofuels Technology Roadmap."

Some private companies have tried growing algae in vats or through other methods on land. But Trent decided to take advantage of the ocean's natural waves and open spaces. His initial investigation drew support through a grant from the philanthropic arm of Google, the U.S. Internet search giant.

"This would ultimately cover acres and acres of ocean," Trent told SPACE.com. He noted that each plastic bag might take up as much as a quarter of an acre. The millions of acres required to meet U.S. transportation fuel needs would not take the form of one huge ocean patch, but would instead spread across many locations off the U.S. coasts.

The basic technologies behind the plastic bags and forward-osmosis membranes are well tested, but Trent expects to spend more time ensuring that the system can work efficiently and without problems. For instance, plastics have a known weakness to ultraviolet rays from the sun, and so long exposure might represent an issue.

Still, Trent wants to eventually make the plastic bags biodegradable. A future source of such biodegradable plastics might even come from algae-derived oil.

Fuel for the world

Both NASA and the California Energy Commission have helped fund the latest round of Trent's work, in which he aims to get a pilot demonstration up and running. The first experiments might start in closed ponds, and then spread to California offshore locations near San Francisco and Santa Cruz.

Trent acknowledges that challenges remain in figuring out the right algae strains, and in engineering the system to make algae biofuels a cost-effective alternative to existing fossil fuels. In fact, biofuels currently represent one of the least lucrative possibilities from growing algae — converting algae into animal food, fertilizer and cosmetics represents just a few of the more profitable ventures.

Still, the NASA bioengineer hopes that algae biofuels can eventually help satiate rising energy demands, and cut back on greenhouse gas emissions from burning fossil fuels that contribute to climate change. The fact that the OMEGA process would clean up wastewater and help sequester carbon dioxide doesn't hurt, either.

A U.S. company, Algae Systems of Carson City, Nev., has already licensed the NASA tech, and plans to deploy its own algae bioreactors somewhere off the coast of Tampa Bay, Florida. Trent would like to see the technology spread among companies as an open-source solution.

"I don't want to see any one company that owns the technology," Trent said. He has already begun discussing his work with international delegates at the United Nations Climate Change Conference hosted in Copenhagen, Denmark.

One possible future plan would combine the algae-growth system with a gigantic offshore wind farm being built by Germany, Sweden and Denmark. Wind power could then provide lights to keep algae growing underwater and during the nighttime hours — a fitting vision for the sustainable future of spaceship Earth.

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