technological developments. Although this report does not address costs of algal biofuels, it makes occasional reference to economics if there are known critical synergies or tradeoffs between economics, productivity, resource use, and environmental effects. Resource Use and Environmental Effects

Land, water, and nutrients are required for cultivating plants and algae. Cropland acreage in the United States has been decreasing in the past few decades (Nickerson et al., 2011), and the water levels of some aquifers used for irrigated agriculture have been declining (NRC, 2001). Nutrient runoff from row-crop agriculture into surface water and its environmental effects has raised concerns (NRC, 2009). Some of these concerns for resource use and availability and for the environment might be alleviated by developing algal biofuels because the production of algae and cyanobacteria biomass does not require high-quality land resources, as in the case of the production of sugar cane or corn for ethanol, and soybean or other oilseeds for biodiesel (Schenk et al., 2008). Algae and cyanobacteria can be grown in saline waters or nutrient-rich wastewater that is not suitable for agriculture or human consumption (Woertz et al., 2009; Bhatnagar et al., 2010; Chinnasamy et al., 2010; Craggs et al., 2011). In addition, enriching algae and cyanobacteria cultures with CO2 and other nutrients helps maximize photosynthetic algal biomass production on a large scale. One suggestion is to co-locate algal biomass production sites with stationary industrial CO2 emission sources like fossil fuel-fired power plants to integrate the plant CO2 emissions with the algal cultivation system. Another suggestion is to locate algal biomass production facilities near wastewater sources, such as municipal wastewater treatment plants. Algae cultivation systems can use the nutrients present in wastewater that has undergone primary or secondary treatment thereby serving as a nutrient removal component of wastewater treatment. An important issue then to assess is the number of potential sites for algae cultivation that are near both a source of CO2, such as fossil-fired power plants, and a source of nonpotable water, such as wastewater or saline water. Resource use and maintaining the quality of the natural resource base necessary for developing algal biofuels will play a role in the sustainable development of algal biofuel. This report focuses on the sustainable development of algal biofuels with respect to resource use and effects on the environment. Social Well Being

Although biomass production of algae and cyanobacteria is not likely to compete for high-quality arable land with crops, there could be social concerns about land use that need to be considered in the development of algal biofuels. For example, situating algae and cyanobacteria biomass production in the U.S. desert Southwest could be perceived as a good use of low-value land by some, but as an intrusion into pristine land by others. Similarly, the use of genetically engineered organisms in production systems could affect social acceptability. This report discusses how the resource use and environmental effects of large-scale algal biofuel production could affect the social acceptability of algal biofuels.

1.2.3 Sustainability of Transportation Fuel

The preceding section mentioned some potential sustainability concerns for large-scale development of algal biofuels (which will be discussed in detail in later chapters along with opportunities to mitigate them), but the sustainability of algal biofuels cannot be viewed in isolation and needs to be put into the broader context of the transportation-fuel sector

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