Water supplies for algal fuels studied

Water supplies for algal fuels studied

- Gulf Coast, Southeastern Seaboard promising for algae growth.

- Water availability a concern with broad-scale algae production.

- Water for algae farms could come from several sources.

A NEW analysis shows that U.S. land and water resources could likely support the growth of enough algae to produce up to 25 billion gal. of algae-based fuel per year, one-twelfth of the country's yearly needs.

The findings come from an in-depth look at the water resources needed to grow significant amounts of algae in large, specially built, shallow ponds. The results were published in the May 7 issue of Environmental Science & Technology, a publication of the American Chemical Society.

"While there are many details still to be worked out, we don't see water issues as a deal breaker for the development of an algae biofuels industry in many areas of the country," said first author Erik Venteris of the U.S. Department of Energy's Pacific Northwest National Laboratory (PNNL).

The best places to produce algae for fuel are hot, humid and wet. Especially promising are the Gulf Coast and the Southeastern Seaboard, according to the news release.

"The Gulf Coast offers a good combination of warm temperatures, low evaporation, access to an abundance of water and plenty of fuel processing facilities," said hydrologist Mark Wigmosta, leader of the team that did the analysis.

 

Algae as fuel

Algae are plump with oil, and several research teams and companies are pursuing ways to improve the creation of algae-based biofuels: growing algae composed of more oil, creating algae that live longer and thrive in cooler temperatures or devising new ways to separate the useful oil from the rest of the algae.

First, though, the algae simply must grow, with the chief requirements being sunlight and water. Antagonists include clouds, a shortage of water and evaporation.

A previous study by the same team looked mainly at how much demand algae farms would create for fresh water. It demonstrated that oil based on algae has the potential to replace a significant portion of the nation's oil imports.

The new report focuses on actual water supplies and looks at a range of possible sources of water, including fresh, salty or saline groundwater and seawater. The team estimated that up to 25 billion gal. of algal oil could be produced annually, an increase of 4 billion gal. over the previous study's estimate.

The new amount is enough to fulfill the nation's current oil needs for one month — about 600 million barrels — of every year. The authors noted that the new estimate is exactly that — an estimate — based, to some degree, on assumptions about land and water availability and use.

"I'm confident that algal biofuels can be part of the solution to our energy needs, but algal biofuels certainly aren't the whole solution," Wigmosta said.

Most important, he noted that the cost of making the fuel right now far exceeds the cost of traditional gasoline-based products.

 

Water availability

An algae farm would likely consist of many ponds, with water maybe 6-15 in. deep.

A few companies have built smaller algae farms and are just beginning to churn out large amounts of algae to convert to fuel.

The availability of water has been one of the biggest concerns regarding the adoption of broad-scale production of algal biofuels. Scientists estimate that fuel created with algae would use much more water than industrial processes used to harness energy from oil, wind, sunlight or most other forms of raw energy.

To produce 25 billion gal. of algal oil, the team estimates that the process annually would require the equivalent of about one-quarter of the amount of water the entire U.S. agriculture industry currently uses each year. While that is a huge amount, the team noted that the water would come from a multitude of sources: fresh and salty groundwater and seawater.

For its analysis, the team limited the amount of fresh water that could be drawn in any one area, assuming that no more than 5% of a given watershed's mean annual water flow could be used in algae production. That number is a starting point, Venteris said, noting that it's the same percentage the Environmental Protection Agency allows power plants to use for cooling.

"In arid areas such as the desert Southwest, 5% is probably an overstatement of the amount of water available, but in many other areas that are a lot wetter, such as much of the East, it's likely that much more water would be available," Venteris said.

"While the nation's desert Southwest has been considered a possible site for vast algae growth using saline water, rapid evaporation in this region makes success there more challenging for low-cost production," Venteris added.

Venteris and his colleagues weighed the pluses and minuses of the various water sources. They noted that freshwater is cheap but in very limited supply in many areas. Saline groundwater is attractive because it's widely available, but usually at a much greater depth, requiring more equipment and technology to pump it to the surface and make it suitable for algae production. Seawater is plentiful but would require much more infrastructure, most notably the creation of pipelines to move the water from the coast to processing plants.

The team noted that special circumstances, such as particularly tight water restrictions in some areas or severe drought or above-average rainfall in others, could affect its estimates of water availability.

The work was funded by DOE's Office of Energy Efficiency & Renewable Energy. In addition to Venteris and Wigmosta, PNNL scientists Richard Skaggs and Andre Coleman contributed to the project and authored the study.

Interdisciplinary teams at PNNL address many of America's most pressing issues in energy, the environment and national security through advances in basic and applied science. PNNL employs 4,500 staff, has an annual budget of nearly $1 billion and has been managed for DOE by Ohio-based Battelle since the lab's inception in 1965.

Volume:85 Issue:21

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