for two reasons. First, there is not one alternative fuel that can replace all the petroleumbased fuels used in U.S. transportation. Few options are available to reduce petroleum use (NAS-NAE-NRC, 2009), and algal biofuels could become a future option for reducing petroleum use and GHG emissions from the transportation sector. Second, every fuel source has its positive and negative effects on the resource base or other aspects of the environment. Therefore, the overall sustainabilities of different fuels have to be compared to assess whether replacing one fuel with another would contribute to improving sustainability. Therefore, the committee cautions that the report is not to be read as a mere list of sustainability concerns, but as a discussion of resource use and environmental effects that need to be compared with those of other fuels to see which fuel option is more sustainable or better balances the various sustainability objectives.

1.3 TOOLS AND METHODOLOGIES FOR ASSESSING SUSTAINABLE DEVELOPMENT OF ALGAL BIOFUELS

This section presents a brief overview of the tools and methodologies used for assessing the sustainability of algal biofuels in this report. The objective here is not to provide results from the application of these methodologies to algal biofuels, but to provide a brief description of the approaches used in this report and how they help meet the overall objectives of providing indicators and approaches to measuring the sustainability of algal biofuels. It focuses on several basic concepts: the systems analysis framework, indicators of sustainability, LCA, and futures or scenario analysis. Indicators are repeated measurements, observations, or model results that “are used to represent or serve as proxies for impacts of outcomes of concerns” (NRC 2010b, p.32). LCA and futures analysis are methodologies for estimating resource use and environmental effects. Systems analysis is an integrating conceptual approach for evaluating impacts of algal biofuels.

1.3.1 Systems Analysis Framework

As Holmes and Wolman (2001) have pointed out, the systems analysis approach emphasizes the development of comprehensive strategies and impact assessments by integrating all “critical physical, biological, socioeconomic, and engineering processes and constraints into a unified framework” (Figure 1-1). Typically quantitative models are used to define the most effective outcome or tradeoffs among multiple outcomes for a given set of system inputs. Historically, the application of this methodology involved “elucidating the objective(s) in the solution, developing a comprehensive description [of the system], formulating alternative solutions, and [quantitatively] analyzing the alternatives with respect to the magnitude and distribution of their consequences” (Holmes and Wolman, 2001, p. 177). The systems analysis framework is particularly applicable to algal biofuels. Of all of the current renewable energy alternatives, biofuels derived from algae and plant-based resources represent one of the most complex systems integration challenges. Part of the complexity is due to the diverse set of feedstocks, and logistical and conversion technologies that designers of bioenergy systems can select from as major components of a biofuel industrial ecology. In addition, many of these technologies are at different evolutionary stages of development ranging from an intriguing possibility to large-scale pilot demonstrations. Further adding to this complexity is the diverse way that these technologies can be integrated to design and implement advanced biofuel systems. This diversity in the mixing of technologies and the possible integration schemes is a driver for innovation as currently seen in the diverse commercial approaches to algal biofuel development. At the



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