Pacific Northwest National Laboratory

A new PNNL study shows that 17 percent of the United States' imported oil for transportation could be replaced by biofuel made from algae grown in outdoor raceway ponds located in the Gulf Coast, the Southeastern Seaboard, and the Great Lakes. This June 2010 satellite photo shows raceway ponds in southern California.

Biofuel produced from algae, essentially pond scum, has long titillated green energy boosters as a potential big time player in the U.S. renewable fuels portfolio. Now, a-first-of-its-kind look at industrial-scale freshwater farming of algae suggests it could indeed make a sizeable dent in U.S. oil imports, but drain water resources.

Specifically, the U.S. could produce enough of the algae-derived fuel to eliminate 48 percent of the fuel it currently imports for transportation needs, according to researchers at the Department of Energy's Pacific Northwest National Laboratory. But doing so would require 5.5 percent of the land area in the lower 48 states and consume about three times the water currently used to irrigate crops.

"The water use is significant," Mark Wigmosta, a hydrologist at the lab who led the study, told me today.

Flat lands
To arrive at the figure, he and colleagues used a geographic information system database to identify land areas that don't compete with agriculture or parks, wetlands, and wildlife habitat. The land had to be relatively flat over about 1,200 acres to support freshwater ponds to grow the algae, a well-tested method to grow algae that the team selected for this baseline study.

The team also factored in 30 years of local climate data to determine how that would impact growth, including factors such as pond temperature and water loss to evaporation. Think of an algae pond like a backyard swimming pool. Water is constantly lost to evaporation — more in a hot, sunny and windy climate; less when it is humid and calm.

A calculation based on all this data led to the 48 percent of transportation imports figure. But the water cost seems like a non-starter for serious consideration of the biofuel. So, the team went looking for ways to reduce water use and found that if the ponds are placed in sunny and humid climates such as the Gulf Coast, the southeastern seaboard, and the Great Lakes, enough fuel can be grown to replace 17 percent of imports and use 25 percent of the water currently used for irrigation.

"So, you've got a significant drop in water use and still have production that is consistent with the renewable fuel targets for 2022," Wigmosta said. The fuel target is set forth in the Energy Independence and Security Act.

"It is still a lot of water," Wigmosta noted, adding the study just takes into account the water lost through evaporation. Additional water is likely to be lost such as during the algae harvest.

While the water loss is significant, the researchers found that algae's water use is comparable to most other biofuel sources.

Considering the gas efficiency of a standard light-utility vehicle, for example, they estimated growing algae uses anywhere between 8.6 and 50.2 gallons of water per mile driven on algal biofuel. In comparison, data from previously published research indicated that corn ethanol can be made with less water, but showed a larger usage range: between 0.6 and 61.9 gallons of water per mile driven.

Several factors — including the differing water needs of specific growing regions and the different assumptions and methods used by various researchers — cause the estimates to range greatly, they found, notes a DOE press release on the study.

Another limiting factor not included in this study is the availability of nutrients for the algae to grow — they eat phosphates and nitrogen-containing compounds, producing the lipids that are converted to biofuel. Future studies will factor this in, Wigmosta told me.

"As we continue to refine this analysis, the number is going to change, but we did want to get a good look at how much land is available and how much water is it going to take," he said.

Non-freshwater algae
Other areas the team will examine include growing algae in non-freshwater, such as saline water that is produced during oil and gas extraction or co-locating a pond next to a water treatment plant. One such pilot project is underway at a waste treatment plant in Rochester, N.Y., led by Eric Lannan, who is getting his masters degree in mechanical engineering at Rochester Institute of Technology.

The project is billed as "doubly green" because the algae clean up the wastewater as they produce biofuel.

"Algae — as a renewable feedstock — grow a lot quicker than crops of corn or soybeans," Lannan said in a news release about the project. "We can start a new batch of algae about every seven days. It’s a more continuous source that could offset 50 percent of our total gas use for equipment that uses diesel."

According to Wigmosta, algae biofuel is still a long ways off from meeting its potential promise as a green fuel of the future, "but it is these kinds of studies that we need to do to really properly evaluate to what extent it can be a player in the renewable fuels portfolio."

A paper describing the research was published online April 13 in the journal Water Resources Research.

More stories on algae biofuel:

• It's pond scum, but algae could be green fuel
• Algae attracts investors, but obstacles remain
• NASA grows algae for biofuel, treats waste
• Green power from algae?
• Plastic made from algae is crazy green 

John Roach is a contributing writer for msnbc.com. Connect with the Cosmic Log community by hitting the "like" button on the Cosmic Log Facebook page or following msnbc.com's science editor, Alan Boyle, on Twitter (@b0yle).