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Comment on “Environmental Life Cycle Comparison of Algae to Other Bioenergy Feedstocks” Introduction The recent publication of “Environmental Life Cycle Comparison of Algae to Other Bioenergy Feedstocks” in Environmental Science & Technology by Clarens et al. (1), has generated significant attention within the bioenergy field. The authors of the study report that algae has greater greenhouse gas emissions, higher nutrient requirements, and greater water use relative to corn, switchgrass, and canola bioenergy feedstocks. The analysis presented by Clarens et al. (1) contains numerous assumptions that significantly affect the published result that algae is inferior to current terrestrial bioenergy feedstocks from a life cycle analysis (LCA) perspective. The most serious critique of the Clarens et al. (1) analysis is that the negative lifecycle analysis for algal fuel is directly determined by the choice of input values and assumptions. Source of CO2. Clarens et al. (1) assume that algal production must use CO2 and that the source of this CO2 will be derived from fossil-fuel sources. The choice of CO2 and production technology significantly affects the results and will determine the ultimate environmental and economic sustainability of an algal fuel industry. The result that using steam reformed CO2 for algae production is not environmentally or economically viable has been well-known for numerous years and as such, it is generally accepted that the CO2 will be derived from waste streams in any commercial system (2-4). By choosing steamreformed CO2, the authors are forcing a negative LCA calculation and then reporting this as a new result. Geographic Areas Chosen. An interesting feature of the Clarens et al. (1) study is the use of Virginia, California, and Iowa as the geographic areas upon which production values and resource uses were calculated. The production yields in Virginia and Iowa on currently cultivated land for corn and other terrestrial crops is not well suited to algal production. Numerous researchers at Sandia National Laboratories, Los Alamos National Laboratories, Pacific Northwest National Laboratories, National Renewable Energy Laboratory, and others have determined that the southwestern states of: New Mexico, Arizona, Texas, and Nevada, as well as portions of California and Utah are ideal for growing algae due to solar insolation rates and average temperatures (4). These same areas also have abundant brackish water resources for capture as inputs to production. Agricultural Fossil Fuel Based Fertilizers. It is important to note that Clarens et al. (1) conclude that the energy and GHG profile of algae changes substantially when municipal waste sources are utilized. This conclusion has been reached by many researchers in algae, and was a prominent feature of the Algal Biomass Organization (ABO) summit in October 2009, with multiple publications on the topic. There is significant progress around the world on utilizing municipal, dairy, and industrial effluent streams for algal fuel production. Clarens et al. (1) LCA calculation was based on the use of agricultural, fossil-fuel based nutrients. Flocculation and Centrifugation Harvesting. It is wellknown that using centrifugation will result in an algal system that is uneconomic and unsustainable, and this is a key area where research funds are being expended by institutions like Los Alamos National Laboratories (5, 4).
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2011 American Chemical Society
Published on Web 11/30/2010
Energy Content of Algae. The choice of the energy content estimate is a key component in an LCA of any biomass crop. Publically available and standardized measures of the energy content of algae are less available than for those of switchgrass, canola, and corn. For corn and canola the authors compute a mass-weighted average HHV, but do not do this for algae. Fuel Conversion Energy Use. A final assumption used in the Clarens et al. (1) analysis that can lead to misinterpretation of their findings is the end-point of the LCA. For first generation systems that use steam reformed CO2, agricultural land in rainy areas, and fossil-fuel derived nutrients, the cultivation impacts will swamp any conversion and transportation benefits from algal fuels. However, once a second-generation system is analyzed using waste CO2, waste nutrients, and nonfresh water the conversion and energy density of algal fuels become significant (4).
Summary The Clarens et al. (1) analysis is conducted for a first generation algal production system, and does provide a comprehensive analysis of the potential environmental impacts that could be generated from an unoptimized algal production system. The results presented by Clarens et al. (2010) restate conclusions from the U.S. Department of Energy’s Aquatic Species Program and the Department of Energy’s Algal Roadmap Project (3, 4). It is clear that if algae production does not utilize waste streams and under-utilized resources (noncultivated land and brackish water) that the environmental profile of algae is far inferior to fossil fuels and traditional biomass feedstocks. Algal researchers are addressing the key barriers highlighted by Clarens et al. (1) and this research path is clearly documented in the U.S. DOE Algal Roadmap (2010).
Acknowledgments The author would like to thank Dr. Richard Sayre for his helpful comments on the original manuscript. This work was supported by the U.S. Department of Energy under funding number: DEEE0003046.
Literature Cited (1) Clarens, A. F.; Resurrenccion, E. P.; White, M. A.; Colosi, L. M. Environmental life cycle comparison of algae to other bioenergy feedstocks. Environ. Sci. Technol. 2010441813-1819. (2) Brown, L. M.; Prague, S.; Jarvis, E. E.; Dunahay, T. G.; Roessler, P. G.; Zeiler, K. G. Biodiesel from Aquatic Species Project Report: FY 1993, NREL/TP-422-5726; National Renewable Energy Laboratory: Golden, CO, 1994. (3) Sheehan, J.; Dunahay, T.; Benemann, J.; Roessler, P. A Look Back at the U.S. Department of Energy’s Aquatic Species Program - Biodiesel from Algae, U.S. Department of EnergysOffice of Fuels Development NREL/TP-580-24190. National Renewable Energy Laboratory: Golden, CO, 1998, p 328. (4) U.S. Department of Energy, Biomass Program. May 2010 National Algal Biofuels Technology Roadmap. http://www1. eere.energy.gov/biomass/pdfs/algal_biofuels_roadmap.pdf. (Accessed January 27, 2010.) (5) Goddard, G.; Sanders, C.; Martin, J.; Kaduchak, G.; Graves, S. Analytical performance of an ultrasonic particle focusing flow cytometer. Anal. Chem. 2007, 79, 8740–6.
C. Meghan Starbuck Economics and International Business, New Mexico State University, National Alliance for Advanced Biofuels and Bioproducts (NAABB) ES103102S
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