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Going Green With Algae

by Bill Chameides | August 16th, 2011
posted by Wendy Graber (Researcher)

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Can algae make the grade as a bioenergy feedstock? (Alt.Energy)

Do little one-celled plants hold the key to our energy future?

How to wean ourselves off fossil fuels? A tough question with a seemingly simple answer: use renewables. But alas, not that simple. As we all know, there are significant technological and economic hurdles. But hurdles are opportunities for the enterprising and the race is on to win the renewable energy sweepstakes. Already wind and to a lesser extent solar energy are making inroads. Bioenergy is also very much in the running.

Bioenergy Then

The use of bioenergy has a long and storied history. Have you ever been around a campfire? Those marshmallows were cooked with bioenergy. In fact, our use of bioenergy for cooking, heating, and keeping the lions and tigers away goes way back. How far back? Well according to some, we can thank Prometheus for giving us the secret of fire.  Archeologists will tell you that that is just a myth and that humankind’s use of fire began some 400,000800,000 years ago without intervention from the gods.

Fire’s cool, but not the only way to use bioenergy. A more complicated way is to convert biomass to liquid fuel – a form that is more easily stored and transported than wood. In fact we’ve been converting grains to ethanol for quite some time. Of course, while ethanol makes a very nice liquid fuel, most of the ethanol we’ve made down through the ages was used for a different, shall we say recreational purpose.

Nevertheless, bioenergy in the form of biomass and biofuels like ethanol have been used to make and power engines throughout the Industrial Revolution. (Ford even included ethanol as a fuel for its first Model T in 1908.) But with the discovery of cheap and readily available oil, bioenergy fell out of favor.

Bioenergy Now

But times have changed and with the drive to find renewable energy sources, bioenergy is back on the table both as a source of heat and electricity and a transportation fuel. Most ideas for harnessing bioenergy focus on using terrestrial plants:

  • Typical sources for heat and electricity include wood, biomass (wood, agricultural, animal) waste, and garbage.
  • Typical sources for transportation fuels include sugarcane, grains like corn, plant oils like soybean and canola, and (one day) cellulosic material like switchgrass and stover.

Algae Joins the Ranks of Bioenergy Alternatives

But while work proceeds to bring these terrestrial sources to market, others have taken the plunge and are pursuing algae. No, they’re not planning to tool around lakes with skimmers collecting green stuff. It’s more of a farming/industrial process. The idea is pretty simple. The algae are either grown in tanks or shallow ponds in either an open or closed loop system. The best part is that algae appear to have several inherent advantages over terrestrial feedstocks that include fast growth rates and high biomass yields per unit area. Moreover, unlike land plants, algae can be grown on marginal land with degraded or saltwater.

Sounds good, but is it any good? How does it stack up against the terrestrial candidates? Andres Clarens of the University of Virginia and colleagues have attempted to answer those questions by doing what is knows as a “well-to-wheel” life cycle analysis of algae-derived and terrestrial-plant-derived bioenergy. Their results published last month in Environmental Science & Technology appear to put algae in a favorable light.

The authors considered a variety of pathways for growing algae (e.g., using manufactured CO2, using flue gas for CO2 and wastewater for nutrients) and for converting algae to energy (e.g., direct combustion to produce bioelectricity and production of biodiesel). Their analysis indicated that the most energy efficient process would use flue gas (instead of manufactured CO2) and wastewater. This is not surprising. They also found that using the algae to produce bioelectricity through direct combustion was more energy efficient than making liquid fuels. This later result simply reflects that fact that conversion of any biomass to a liquid fuel requires additional energy and thus is less efficient than simply burning the stuff. Of course the disadvantage of bioelectricity is that we also require liquid fuels that can be pumped to your local gas station and then into your gas tank. Presumable that won’t be a problem if and when the electric-vehicle technology is fully developed.

A Side-by-Side Comparison

The authors then compared the energy and environmental impacts of algae-derived fuel with bioenergy derived from canola and switchgrass. The results were mixed. The bioelectricity algal system was less energy efficient than one based on switchgrass-derived bioelectricity But the algae system scored better in terms of water use and greenhouse gas emissions.

A Glimpse of the Future?

The neat thing about algae production is you don’t need a farm or even acres of land. They can be located anywhere as long as you have light. And because they can be mounted in vertical tanks you don’t even need that much space. Can’t you just imagine a future in which everyone has several vertical tanks of algae growing in their living rooms? What about the light the little guys need to grow? No prob –the TV’s glow has been tuned to the necessary spectrum. And what about the nutrients? Again, no prob – just hook up a pipe that runs from the tank to your … well never mind.

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