Global ChangeIntersection of Nature and Culture

The promise and perils of algae-based biofuels

Monday, December 28th, 2009

In a forthcoming article¹ in Trends in Ecology and Evolution, Val Smith and colleagues describe why biofuels produced from algae have many benefits:

• The current production of biodiesel (~2 billion gallons in 2006) is far lower than annual consumption of diesel fuel (44 billion gallons per year).  Simply put, biodiesel crops can’t keep pace with demand.  We would have to grow significantly more biofuel crops, which would affect land use by reducing the acreage of food crops or natural habitats.
• Algae fats (lipids) can serve as the feedstocks for many types of fuels, including aviation fuel, which would be a major benefit because airline travel is a huge part of most people’s carbon footprints. Algae fuels are potentially carbon neutral.  Making air travel carbon neutral would be a game changer.
• Algae grow extremely fast—much faster than terrestrial plants (which are made into biodiesel or ethanol).  They lack anatomical parts like roots, flowers, and woody stems that don’t help plants photosynthesize (making them more productive than plants).
• One of the most amazing statistics in this paper is how much less land it would take to make algae based fuels compared to terrestrial plants because of the increased productivity of algae.  To produce an amount of fuel equivalent to the global demand for oil, we would only need an area of land equivalent to 3-20% of current croplands.  If we were to use biofuel plant crops instead, we would need about 2-8 times the amount of current global cropland. That’s so amazing I did a double take when I read it.
  
• Algae can be grown in tanks on lands that are marginally useful for crops so that we don’t have to sacrifice croplands.
• They can serve double-duty by removing excess nutrients from wastewater, thereby linking energy production and wastewater treatment.
• Algal production virtually eliminates the use of herbicides and insecticides and uses much less water than growing crops for fuels.

They also point out an interesting pitfall:

• Bioreactors containing algae are often unintentionally invaded by zooplankton that eat the algae.  This can lead to predator-prey-type cycles in algae biomass, which is not good when you want to maximize algal biomass production.
• The solution?  Add fish that eat the zooplankton.  This would cause “top-down” pressure on the zooplankton, keeping their populations in check.

¹Smith, V. et al (in press) The ecology of algal biodiesel production. Trends in Ecology and Evolution.

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