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FEATURE ARTICLE

Making Biofuel from Microalgae

So much potential coexists with so many scientific, environmental and economic challenges

Philip T. Pienkos, Lieve Laurens, Andy Aden

Sorting Out Sustainability

2011-11PienkosF8.jpgClick to Enlarge ImageIn order for a biofuel process to be successful, it must be sustainable as well as profitable. One measure of sustainability is the amount of CO2 released per unit of energy in the fuel. For biofuels this is reported as the fraction of CO2 released relative to gasoline or another appropriate fuel. But other factors must be considered. These include land usage—especially if land will be taken away from food production or will lead to deforestation—and nutrient usage, including nitrogen and other nutrients. This is especially true for phosphorus, which is believed to be in short supply and whose use could place algal cultivation in competition with food production. Water usage is also an issue, especially if freshwater is used in open ponds and allowed to evaporate. Finally it is important to be able to show that it takes less energy to produce a biofuel than a biofuel can generate.

Although these concepts of sustainability may seem obvious, they are notoriously difficult to calculate, as the continuing debate over corn ethanol demonstrates. They are especially difficult for algal biofuels because so many of the values needed for the calculations are available only as estimates or assumptions. Only a few life-cycle assessments have been performed thus far, but the results have shown unpromising energy returns and weak greenhouse-gas benefits. It is vital to get the sustainability calculations right. Huge investments in research, development and deployment are only justifiable with evidence that algal biofuels will be superior to the petroleum-based fuels they may one day replace.

The field of algal biofuels has been criticized because the technical challenges are great and because commercialization is five to ten years away. Nonetheless, significant improvements are being made in all of the technical areas outlined above: algal biology, cultivation, harvest, extraction and analysis. Technoeconomic models have increased in sophistication, and new data are now available to populate models. The best available cost estimates, while high, are becoming more accurate and more useful. These models are reducing uncertainty and quantifying risk, which can give investors more confidence in the likelihood of success in commercialization. With that confidence, more resources from both public and private sectors have been brought to bear on the technical barriers. Although the path to commercialization may be long and may require many millions of dollars, the potential for algal biofuels to contribute to national goals of reduced dependence on fossil fuels, reduced CO2 emissions and greater energy security are worth the investment. We are confident that the barriers will fall.

Bibliography

  • Clarens, A. F., E. P. Resurreccion, M. A. White and L. M. Colosi. 2010. Environmental life cycle comparison of algae to other bioenergy feedstocks. Environmental Science & Technology 44:1813–1819.
  • Davis, R., A. Aden and P. T. Pienkos. 2011. Techno-economic analysis of autotrophic microalgae for fuel production. Applied Energy 88:3524–3531.
  • Greenwell, H. C., L. M. L. Laurens, R. J. Shields, R. W. Lovitt and K. J. Flynn. 2009. Placing microalgae on the biofuels priority list: A review of the technological challenges. Journal of the Royal Society Interface 7:46.
  • Laurens, L., and E. Wolfrum. 2010. Feasibility of spectroscopic characterization of algal lipids: Chemometric correlation of NIR and FTIR spectra with exogenous lipids in algal biomass. BioEnergy Research 4:22–35.
  • Pate, R., G. Klise and B. Wu. 2011. Resource demand implications for U.S. algae biofuels production scale-up. Applied Energy 88:3377–3388.
  • Sun, A. C., R. Davis, M. Starbuck, A. Ben-Amotz, R. C. Pate and P. T. Pienkos. 2011. Comparative Cost Analysis of Algal Oil Production for Biofuels. Energy 36:5169–5179.
  • U.S. Department of Energy. 2011. U.S. Billion-Ton Update: Biomass Supply for a Bioenergy and Bioproducts Industry. Oak Ridge, Tenn.: Oak Ridge National Laboratory.




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