Fermentation or photosynthesis: The debate in algae fuel

Sugar or sunlight?

That's one of the fundamental questions for companies trying to transform algae into transportation fuel or dietary supplements. Solazyme says it will grow algae through fermentation--for instance, feeding the algae sugars in a heated, sealed environment.

Algae in the lab at Solazyme. Later, the vat.

(Credit: Solazyme)

"We're not growing it photosynthetically. We put it in stainless steel tanks similar to what you see in a brew pub," said Solazyme President Harrison Dillon.

By contrast, GreenFuel Technologies and LiveFuels will exploit the sun to grow the single-celled creatures. And here there is a divide, too. GreenFuel grows its algae in sealed, transparent tubes it calls bioreactors. LiveFuels, by contrast, is setting up an open pond near the Salton Sea in Southern California.

Which solution will win? Who knows? "There is a spectrum of options from high control and high cost to low control and low cost," said B. Greg Mitchell, a research scientist who specializes in plant biology at the University of California at San Diego. Although national labs began researching the concept of converting algae to fuel in the late '80s, this is the first time people are seriously considering going forward.

Fermentation offers the most control. Each fermentation vat contains a single species. Temperature, pressure, and other environmental conditions can be minutely controlled. Additionally, fermentation offers flexibility: A row of vats can be used to make auto fuel, and then scrubbed and prepped for cooking up algae for cooking fuel.

The added sugar also doesn't necessarily need to be expensive.

"There's a lot of organic matter in the world," Mitchell said. "We make a lot of beer at low cost with fermentation systems."

Still, fermentation overall does cost more. As a result, it might make the most sense for higher-value oils. Martek Biosciences, in fact, ferments algae and sells it as a baby food additive. It remains to be seen if the model will work for fuel that gets burned in cars. (Although crude costs $100 a barrel, it's a more low value oil than others, Mitchell said.)

The big advantage of photosynthesis is that the sun is free. But temperatures vary daily. "Temperature regulation adds cost, and the amount of sunlight is variable and seasonal," he added. Controlling the rate of growth was a problem Greenfuel had last year at its Arizona facility.

Open ponds are less expensive than closed systems. In open ponds, however, it can be difficult to control invasive species. Then again, having multiple species can be an advantage, Dave Jones, one of LiveFuel's founders has said. Different species can absorb different wavelengths of light.