National Academies: Algae Biofuels aren't sustainable...yet

This week, the National Academy of Sciences released a report on the Sustainability of Algae Biofuels, the drafting of which I had the privilege to be a part of as a member of the Study Committee.  Coverage can be found here, here, here and here.  The report’s conclusions are not the most optimistic on algae biofuels, but we believe they are fair, based on a detailed reading of all available scientific literature on the subject and testimony from dozens of experts in a range of disciplines.  The report also highlights the future potential of algae biofuels and the steps needed to ensure its sustainable development.

Among the report's many conclusions:

First, the existing approaches for producing algae biofuels are not currently capable of creating fuels in a sustainable fashion

The scale-up of algal biofuel production sufficient to meet at least 5 percent of U.S. demand for transportation fuels would place unsustainable demands on energy, water, and nutrients with current technologies and knowledge. However, the potential to shift this dynamic through improvements in biological and engineering variables exists.

Essentially, while projected freshwater usage rates range widely, getting 5 percent of our fuel from algae could consume up to 123 billion liters of freshwater (and using other studies, many multiples of that).  For comparative purposes, that would represent nearly 10% of current total U.S. freshwater consumption. More challenging is the nitrogen and phosphorous requirements for this level of production – “44 to 107 percent of the total nitrogen use and 20 to 51 percent of total phosphorus use in the United States”

Second, to create algae biofuels sustainably will require enhanced algae strains, a reduction in the energy usage in the fuel production process, a system that uses wastewater or recycles harvest water, and extensive nutrient recycling. 

Third, land area (specifically the availability of suitable land) for algae cultivation could actually be quite limited given the number of factors required for production, and therefore:

A national assessment of land requirements for algae cultivation that takes into account climatic conditions; freshwater, inland and coastal saline water, and wastewater resources; sources of CO2; and land prices is needed to inform the potential amount of algal biofuels that could be produced economically in the United States.

Fourth, large-scale production of algae biofuels are expected to have a wide range of environmental impacts, some of which are possible to analyze now, but many other impacts that we simply don’t have any information on.  Even more complicated, there will be a number of effects that are going to be unique to the specific algae production pathway.

However, this report also highlights the tremendous potential for innovation in algae biofuels, with a strong call for further research and development.  Examples of R&D and engineering innovation proposed in the report include:

Algal strain development is needed to enhance traits that contribute to increasing fuel production per unit resource use, reducing the environmental effects per unit fuel produced, and enhancing economic viability. Improvements in biomass or product (lipid, alcohol, or hydrocarbons) yield, culture density, nutrient uptake, ease of harvest, and photosynthetic efficiency are some of the improvements that would improve sustainability of algal biofuels.

Engineering solutions to enhance algae cultivation, to facilitate biomass or product collection, and to improve processing of algae-derived fuels can increase the EROI and reduce the GHG emissions of algal biofuel production.

Further, the report provides a framework to help in assessing future sustainable development in algae, proposing use of a number of different tools, including lifecycle analyses, cumulative impact analyses and cost benefit analyses.

At the same time, the report takes pains to point out that a comparative analysis to other fuel options is also vital in getting the full picture of sustainable development on a system-wide basis:

The environmental, economic, and social effects of algal biofuel production and use have to be compared with those of petroleum-based fuels and other fuel alternatives to determine whether algal biofuels contribute to improving sustainability. Such comparison will be possible only if thorough assessments of each step in the various pathways for algal biofuel production are conducted.

This kind of report is critical in moving the new algae biofuels industry forward.  With a nascent, breakthrough technology like algae biofuels, projecting future environmental impacts is extremely difficult.  That lack of clarity brings it with considerable environmental risk, given the scope and scale of transformation involved.  As algae biofuels move from the lab to the field (as they are already), this kind of analysis can be helpful in ensuring these smaller demonstration projects are developed sustainably, so that when we reach the billions of gallons scale, we do not face game changing, show stopping environmental impacts. 

Ultimately, the conclusions of this report mirror many of NRDC’s original conclusions in its report on algae biofuels sustainability in 2009 (although in much greater and deeper detail).  Algae biofuels have tremendous potential due to their innate productivity (and accompanying reduced land use impacts), ability to use non-potable water, and potential for siting on previously unproductive lands.  However, there remain a number of issues that must be resolved, if we are to move forward and cultivate the immense quantities of fuel to make a dent in our current fossil intensive infrastructure

UPDATE: slight edit to water consumption rates

About the Authors

Cai Steger

Director, Energy Efficiency for All, and Senior Adviser, Urban Solutions

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