Growing algae for jet fuel

Try floating it in giant plastic bags and feeding it sewage.

NASA has been experimenting with growing fresh-water algae in large plastic bags that float in the ocean. The plants feed on municipal wastewater and draw energy for photosynthesis from the sun.

The ocean helps regulate the temperature of the algae, and the movement of the waves keeps it mixed. As the algae absorbs the nutrients in the wastewater and converts CO2 into oxygen, a forward-osmosis membrane in the bag releases the wastewater, now cleaned, into the ocean.

Deputy project manager Ed Austin of NASA Ames says the scheme – which is called OMEGA (Off-shore Membrane Enclosure for Growing Algae) – has several advantages over the way algae is grown now. Open ponds tend to evaporate and can be contaminated with weeds, while closed containers need energy to pump water in and out, regulate the temperature, and keep the algae mixed.

Austin also points out that the bags could be used to clean dead zones in the ocean, and they wouldn’t interfere with fishermen or boats if they were placed far enough offshore -- he’s thinking five miles, so the bags could take advantage of wastewater outfalls there.

With help from several universities and companies, NASA is now working on scaling the $10 million, two-year project – prototype bags have been four liters, and there’s a 200-liter bag off the coast of Santa Cruz. The goal is to get to 400 liters, and to hand off OMEGA to the Navy, the DOE and private companies after a feasibility study in 2012.

There are other problems to be solved too – how the bags should be made, how they should be filled and maintained, how much greenhouse gas the process might emit, and several more.

But NASA needs a system that can grow enough algae to produce jet fuel, not the smaller scale cosmetics and pharmaceuticals that have been made from algae so far.

“If you’re trying to supply a jet fleet with 21 billion gallons of fuel per year with a soy crop, you need 120 million acres – the size of the state of Alaska,” Austin said today at NASA’s Green Aviation Summit, where I talked to him. “If you go to micro algae producing 2,000 gallons per acre per year, you could scale down the algae farms to 10.5 million acres. You still need a lot of area to grow that.”

And that’s another advantage of OMEGA, Austin says – it would use less water, less energy and less land.

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