•  Unicellular algae and cyanobacteria have the advantage of being able to complete a reproductive cycle in a matter of hours or a few days. Therefore, they can be harvested on a daily or weekly basis.

•  The oil productivity of many species of algae exceeds that of oil crops (Patil et al., 2008).

During its two decades of operation, the Aquatic Species Program built a collection of more than 3,000 species of oil-producing microalgae (Sheehan et al., 1998). Program research shed light on algal physiology and biochemistry and the relationship between oil content in cells and algal productivity. Efforts also were made to demonstrate the feasibility of large-scale cultivation of algae in open ponds (Sheehan et al., 1998). The Aquatic Species Program was terminated in 1996 when DOE was under budget pressure. At that time, the price of oil was less than $20 per barrel (EIA, 1999). In contrast, a technoeconomic analysis conducted in 1982 estimated algal biofuels would cost about $60 per barrel of oil equivalent under an optimistic scenario and about $120 per barrel of oil equivalent under a conservative scenario (Benemann et al., 1982).

Volatile oil prices observed from 2000 to the present renewed interests in alternative fuels. In addition, mounting evidence of global climate change raised concern over the carbon footprint of using fossil fuels. Greenhouse gases (GHG)—such as carbon dioxide (CO2), nitrous oxide, and methane—are heat-trapping gases that produce a warming effect on the Earth’s atmosphere. CO2 emissions from burning of fossil fuels account for a large portion of GHG emissions (NRC, 2011a). In the United States, the use of petroleum-based fuel in the transportation sector accounted for 30 percent of the nation’s CO2 emissions in 2009. Although using algal biofuels for transportation would produce tailpipe emissions comparable to those from using petroleum-based fuels, algae and cyanobacteria take up CO2 during growth and thereby offset some of the CO2 emissions (Brune et al., 2009). In addition, the net impact on CO2 emissions also depends on the quantity of fossil fuels used throughout the algal biofuel production pathway. Life-cycle assessment (LCA), discussed later in this chapter, attempts to account for and aggregate the energy requirements and CO2 impacts over the whole production pathway.

Domestic production of renewable fuels including algal biofuels has the potential to meet the dual goals of improving energy security and decreasing GHG emissions from the transportation sector. However, a dramatic decrease in foreign oil importation and reduction in GHG emissions in the United States will require the production and use of multiple alternative transportation fuels. Biofuels produced from algal feedstock could be one of the alternatives. The number of startup companies working on the development of algal biofuels has been increasing, and some oil companies are investing in algal biofuels (Mascarelli, 2009; Mouawad, 2009). The U.S. military is interested in substituting part of its fuel use with renewable energy sources including algal biofuel (Physorg.com, 2010), and the Defense Advanced Research Projects Agency funded projects for developing technologies to produce affordable algal biofuels (Lundquist et al., 2010). Given the interest in algal biofuels, the DOE Energy Efficiency and Renewable Energy’s (DOE-EERE) Office of Biomass Program (OBP) held a workshop in 2008 “to discuss and identify the critical barriers currently preventing the economical production of algal biofuels at a commercial scale” (DOE, 2010). DOE and private companies are actively investing in R&D for algal biofuels to resolve technical barriers, improve feasibility of large-scale production, and reduce costs. In addition to developing production technologies, any developing industry also needs to consider sustainability. Addressing sustainability concerns and challenges as the industry develops can help ensure its success well into the future. Ignoring sustainability at the

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