Algae could replace 17% of U.S. oil imports
throughout the United States, which is a much more detailed view than previous research.
This data allowed them to identify available areas that are better suited for algae growth, such as those with flat land that is not used for farming and isn’t near cities or environmentally sensitive areas like wetlands or national parks.
Next, the researchers gathered thirty years of meteorological information. That helped them determine the amount of sunlight that algae could realistically photosynthesize and how warm the ponds would become. Combined with a mathematical model on how much typical algae could grow under those specific conditions, the weather data allowed Wigmosta and team to calculate the amount of algae that could realistically be produced hourly at each specific site.
Water for oil
The PNNL release notes that the researchers found that twenty-one billion gallons of algal oil, equal to the 2022 advanced biofuels goal set out by the Energy Independence and Security Act, can be produced with American-grown algae. This is 17 percent of the petroleum that the United States imported in 2008 for transportation fuels, and it could be grown on land roughly the size of South Carolina. The authors also found, however, that 350 gallons of water per gallon of oil — or a quarter of what the United States currently uses for irrigated agriculture — would be needed to produce that much algal biofuel.
The study also showed that up to 48 percent of the current transportation oil imports could be replaced with algae, though that higher production level would require significantly more water and land. So the authors focused their research on the U.S. regions that would use less water to grow algae, those with the U.S. sunniest and most humid climates.
The authors also found that algae’s water use is not that different from most other biofuel sources. While considering the gas efficiency of a standard light-utility vehicle, 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.
Because conventional petroleum gas does not need to be grown like algae or corn, it does not need as much water.
Previously published data indicated conventional gas uses between about 0.09 and 0.3 gallons of water per mile.
More to consider
Looking beyond freshwater, the authors noted algae has several advantages over other biofuel sources. For example, algae can produce more than eighty times more oil than corn per hectare a year. Unlike corn and soybeans, algae are not a widespread food source that many people depend on for nutrition. As carbon dioxide-consuming organisms, algae are considered a carbon-neutral energy source. Algae can feed off carbon emissions from power plants, delaying the emissions’ entry into the atmosphere. Algae also digest nitrogen and phosphorous, which are common water pollutants. That means algae can also grow in — and clean — municipal waste water.
“Water is an important consideration when choosing a biofuel source,” Wigmosta said. “And so are many other factors. Algae could be part of the solution to the nation’s energy puzzle — if we’re smart about where we place growth ponds and the technical challenges to achieving commercial-scale algal biofuel production are met.”
Next up for Wigmosta and his colleagues is to examine non-freshwater sources like salt water and waste water. They are also researching greenhouse ponds for use in colder climates, as well as economic considerations for algal biofuel production.
— Read more in Mark S. Wigmosta et al., “National microalgae biofuel production potential and resource demand,” Water Resources Research 47, W00H04 (13 April 2011) (doi:10.1029/2010WR009966)
