A report out today from the National Research Council (NRC) of the U.S. National Academies says that large-scale production of biofuels from algae is untenable with existing technology, as it would require the use of too much water, energy, and fertilizer. To improve matters, the report's authors suggest that the U.S. Department of Energy (DOE), which supports much of the research in the field, should conduct assessments of proposed technologies that examine sustainability at all stages of fuel production, including growing or collecting algae and harvesting their oil and converting it into transportation fuels.
Efforts to make biofuel from algae have been under way for more than 3 decades, and have picked up considerable steam in recent years. Algae's big advantage is that unlike traditional biofuels, such as ethanol made from corn kernels or sugar, algae wouldn't compete for agricultural land with food crops. It also has the potential to produce as much as 10 times more fuel per hectare, according to the DOE's 2010 National Algal Biofuels Technology Roadmap.
But there are many different approaches to growing algae, such as growing the microscopic plants in shallow outdoor ponds, or in enclosed plastic tubes called bioreactors. And the industry is far from settled on a single approach. No matter what the strategy, however, the NRC committee concluded that current technology scaled up to produce 39 billion liters a year—approximately 5% of U.S. transportation fuel needs—would require an unsustainable level of inputs. Current technologies, for example, need between 3.15 liters and 3650 liters of water to produce the amount of algal biofuel equivalent to 1 liter of gasoline, the panel concluded. (That's potentially less than the estimated 5 liters to 2140 liters of water required to produce a liter of ethanol from corn, but more than the 1.9 liters to 6.6 liters of water needed to produce a liter of petroleum-based gasoline.) Growers would also have to add between 6 million and 15 million metric tons of nitrogen and between 1 million and 2 million metric tons of phosphorus to produce 39 billion liters of algal biofuels. That's between 44% and 107% of the total use of nitrogen in the United States, and between 20% and 51% of the nation's phosphorus use for agriculture.
The good news is that there's still plenty of potential for improvement. "The committee does not consider any one of these sustainability concerns a definitive barrier to sustainable development of algal biofuels because mitigation strategies for each of those concerns have been proposed and are being developed," the report concludes. The use of water and added nutrients, for example, could drop markedly if engineers come up with ways to efficiently recycle used water and nutrients, perhaps even using nutrient-rich wastewater from agricultural or municipal sources. But for algal biofuels to reach their full potential, researchers will need to integrate these and other advances and ensure that at each stage algae is converted to fuels in the most sustainable way possible.