Growing algae for use in biofuels has a greater environmental impact than sources such as corn, switch grass and canola, researchers found in the first life-cycle assessment of algae growth.
Interest in algae-based biofuels has blossomed in the past year, sparking major investments from Exxon Mobil Corp. and Dow Chemical Co., and it has gained steam on Capitol Hill, as well. But the nascent industry has major environmental hurdles to overcome before ramping up production, according to research published this week in Environmental Science and Technology.
"What we found was sort of surprising," said Andres Clarens, a civil and environmental engineering professor at the University of Virginia and lead author of the paper. "We started doing this with as much optimism as everybody else."
Algae production consumes more energy, has higher greenhouse gas emissions and uses more water than other biofuel sources, like corn, switch grass and canola, Clarens and his colleagues found by using a statistical model to compare growth data of algae with conventional crops.
"From a life-cycle standpoint, algae are not nearly as desirable as you would think they are," Clarens said. "And that was surprising to us."
The culprit, the researchers say, is fertilizer. Growing algae in open ponds is akin to producing them in a shallow swimming pool, Clarens said, so all of the nutrients -- nitrogen and phosphorus -- needed to keep them alive and boost their production come from outside sources.
And that fertilizer has an environmental impact because it's often made from petroleum feedstocks, Clarens said.
"If you grow corn, you rotate the field with soybeans so you get nitrogen fixation," Clarens said. "You still have to fertilize a lot, but if you're growing algae ... all that fertilizer has to come from you, and the fertilizing demands are much higher."
Carbon dioxide also contributes to algae's environmental footprint. Algae use sunlight and water to convert carbon dioxide into materials that can be easily converted into fuel. But that CO2 has to come from somewhere, Clarens said. And until it's economical to pull it out of coal-fired power plant smokestacks or other industrial sources, it comes from petroleum-based sources, as well.
Algae production has some other negative environmental impacts, Clarens said. For one, to convert algae into fuel, producers centrifuge the algae-laden water to separate the two, and that takes "a fair amount of energy," Clarens said.
But Clarens and his colleagues aren't writing off algae as a potential future energy source.
"We wanted to point to areas where algae performs poorly so we'll have a bit of a road map if we do decide to go down the algae road," Clarens said.
The algae industry has called for life-cycle assessments and is working on its own complete analysis, Mary Rosenthal, executive director of the Algal Biomass Organization, said in an e-mailed statement. She said her organization had not had time to fully review the paper and could not comment on it specifically.
"However, in general, the Algal Biomass Organization firmly believes life cycle assessments are critical to the development of the industry, given the need to accurately assess and quantify the environmental impact of algae-derived energy," she said. "Our membership supports the development of robust [life-cycle assessments], but believes that the process should include input from a multitude of stakeholders, including algae technology companies, [nongovernmental organizations] and other scientists."