Short Communication Algae biodiesel has potential despite inconclusive results to date Xiaowei Liu, Andres F. Clarens ⇑ , Lisa M. Colosi Civil and Environmental Engineering, University of Virginia, 351 McCormick Road, Thornton Hall, Charlottesville, VA 22904, USA article info Article history: Received 13 September 2011 Received in revised form 21 October 2011 Accepted 23 October 2011 Available online 3 November 2011 Keywords: Algae Biofuels Life cycle assessment Meta-analysis abstract A meta-analysis of several published life cycle assessments of algae-to-energy systems was developed to better understand the environmental implications of deploying this technology at large scales. Taken together, results from these six studies seemed largely inconclusive because of differences in modeling assumptions and system boundaries. To overcome this, the models were normalized using a generic pathway for cultivating algae in open ponds, converting it into biodiesel, and processing the nonlipid fraction using anaerobic digestion. Meta-analysis results suggest that algae-based biodiesel would result in energy consumption and greenhouse gas emissions on par with terrestrial alternatives such as corn ethanol and soy biodiesel. Net energy ratio and normalized greenhouse gas emissions were 1.4 MJ pro- duced/MJ consumed and 0.19 kg CO 2 -equivalent/km traveled, respectively. A scenario analysis under- scores the extent to which breakthroughs in key technologies are needed before algae-derived fuels become an attractive alternative to conventional biofuels. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Published reports on the anticipated environmental implica- tions of large-scale algae-to-energy systems, including those by the authors, have been seemingly divergent, not directly compara- ble, and widely debated (Campbell et al., 2010; Clarens et al., 2010; Jorquera et al., 2010; Lardon et al., 2009; Sander and Murthy, 2010; Stephenson et al., 2010). This is despite the fact that most studies have modeled essentially the same system (Fig. 1), wherein algae is cultivated in open ponds, the lipid fraction is converted into bio- diesel via transesterification, and the residual biomass is trans- formed into some useful byproduct (Benemann and Oswald, 1996; Kadam, 2002; Sialve et al., 2009; Spilling et al., 2010). It is hypothesized that seeming disparities among published results could be attributed to methodological differences in system boundaries, scope, and modeling assumptions, rather than a funda- mental lack of understanding of how these systems will perform. Overcoming these methodological differences could enable better understanding of algae’s potential as a low carbon intensity bioen- ergy source and streamline comparison with well-studied conven- tional biofuels (Hill et al., 2006). The current lack of understanding about algae’s potential as a feedstock for low carbon biofuels has arisen in the wake of seem- ingly conflicting life cycle assessment (LCA) results. This resembles the circumstances which gave rise to the ERG Bioenergy Meta-Mod- el (EBAMM) in 2006 (Farrell et al., 2006). At that time, it was unclear how corn-derived ethanol compared to petroleum fuels on the basis of life cycle energy use and greenhouse gas (GHG) emissions, be- cause six independent LCA analyses had generated seemingly con- flicting results (Dominguez-Faus et al., 2009; Farrell et al., 2006; Landis et al., 2007). EBAMM incorporated raw data from each of these analyses into a standardized modeling approach to generate composite estimates for both energy use and GHG emissions, ulti- mately showing that corn ethanol provides modest environmental benefits compared to conventional petroleum: on the order of 33% reductions in net energy and smaller reductions in GHG emissions. This paper describes the development of an analogous model for al- gae-to-energy production, the Meta-Model of Algae Bio-Energy Life Cycles (MABEL). 2. Methods MABEL offers insight about the sustainability of algae-derived energy sources by synthesizing results from six of the most widely cited algae LCA papers to date. To build MABEL, results were ab- stracted from each study, and individual models were deconstruct- ed for normalization to a common functional unit (FU) of 1000 L algae biodiesel. System boundaries and modeling assumptions about upstream burdens and co-product allocation were also stan- dardized to reflect emerging trends in the algae biofuels industry (Clarens et al., 2011). Full model documentation is available in the Supporting Information, and the model itself is available via the Internet to facilitate its use as an open-source analysis/design tool. 0960-8524/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2011.10.077 ⇑ Corresponding author. Tel.: +1 434 924 7966; fax: +1 434 982 2951. E-mail address: aclarens@virginia.edu (A.F. Clarens). Bioresource Technology 104 (2012) 803–806 Contents lists available at SciVerse ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech