Microalgal biodiesel and the Renewable Fuel Standard’s greenhouse gas requirement Kullapa Soratana n , Willie F. Harper Jr., Amy E. Landis Department of Civil and Environmental Engineering, University of Pittsburgh, 949 Benedum Hall, Pittsburgh, PA 15261, USA article info Article history: Received 31 August 2011 Accepted 9 April 2012 Available online 23 April 2012 Keywords: Microalgal biodiesel Life cycle assessment Renewable Fuel Standard abstract The Renewable Fuel Standard (RFS2) under the Energy Independence and Security Act of 2007 requires 15.2 billion gallons of domestic alternative fuels per year by 2012, of which 2 billion gallons must be from advanced biofuel and emit 50% less life-cycle greenhouse gas (GHG) emissions than petroleum- based transportation fuels. Microalgal biodiesel, one type of advanced biofuel, has the qualities and potential to meet the RFS’s requirement. A comparative life cycle assessment (LCA) of four microalgal biodiesel production conditions was investigated using a process LCA model with Monte Carlo simulation to assess global warming potential (GWP), eutrophication, ozone depletion and ecotoxicity potentials. The four conditions represent minimum and maximum production efficiencies and different sources of carbon dioxide and nutrient resources, i.e. synthetic and waste resources. The GWP results of the four CO 2 microalgal biodiesel production conditions showed that none of the assumed production conditions meet the RFS’s GHG requirement. The GWP results are sensitive to energy consumption in harvesting process. Other impacts such as eutrophication, ozone depletion and ecotoxicity potentials, are sensitive to percent lipid content of microalgae, service lifetime of PBRs and quantity of hexane in extraction process, respectively. Net energy ratio and other emissions should be included in future RFS for a more sustainable fuel. & 2012 Elsevier Ltd. All rights reserved. 1. Introduction The Renewable Fuel Standard (RFS) under the Energy Inde- pendence and Security Act (EISA) of 2007 requires domestic alternative fuels to meet 15.2 billion gallons by 2012, of which 2 billion gallons must be from advanced biofuels. Advanced biofuels, which include cellulosic biofuel, biomass-based diesel and other advanced biofuel, are the renewable fuels other than corn ethanol (U.S. Environmental Protection Agency, 2010). In addition, life-cycle greenhouse gas (GHG) emissions from advanced biofuels must be at least 50% less than GHG emissions from petroleum-based transportation fuels distributed in 2005 (Office of Transportation and Air Quality, 2010a, b). Microalgal biodiesel, an advanced biofuel, has the potential to support the U.S. transportation fuel and meet the RFS’s advanced biofuels requirement (U.S. Department of Energy, 2010). Microalgae have been investigated for the production of a number of different products including methane, ethanol, electricity and biodiesel (Batan et al., 2010; Li Q., et al., 2008; Sander and Murthy, 2010; Stephenson et al., 2010). Microalgae as biodiesel feedstock have a high growth rate, high productivity, and high photosynthetic efficiency (Avagyan, 2008; Bruce, 2008; Lehr and Posten, 2009; Li Y., et al., 2008; U.S. Department of Energy, 2010). These characteristics comply with the needs established by the Roadmap for Bioenergy and Biobased Products in the U.S. which are that it is easy to grow, exhibits high yields, and provides good quality fuel (Avagyan, 2008; Biomass Research and Development Technical Advisory Committee and Biomass Research and Development Initiative, 2007). The quality of microalgal biodiesel meets American Society for Testing and Materials (ASTM) Biodiesel Standard D6751, thus can substitute for petroleum diesel (Bruce, 2008; Chisti, 2007). Microalgal cultivation has been shown to consume limited land and less water resources than terrestrial biofuel crops. The study by Chisti in 2007 suggested that the land for microalgal cultivation requires only 1–3% of the total agricultural area in the U.S. for the same oil- crop diesel yield (Chisti, 2007). Microalgal cultivation considered in this study was assumed to occur in a closed photobioreactor (PBR). Compared to open ponds, the PBR has a better control of cultivation conditions such as mass transfer, water loss by evaporation, and contamination (Li Y., et al., 2008; Posten, 2009). The PBR system is suitable for sensitive strains since contamination can be controlled more easily than in an open pond. The cell mass productivity of PBRs is about three times higher than the productivity of open ponds; hence Contents lists available at SciVerse ScienceDirect journal homepage: www.elsevier.com/locate/enpol Energy Policy 0301-4215/$ - see front matter & 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.enpol.2012.04.016 n Corresponding author. Tel.: þ1 412 805 5055; fax: þ1 412 624 1168. E-mail address: kus8@pitt.edu (K. Soratana). Energy Policy 46 (2012) 498–510