siting and permitting processes, making it more difficult for developers to secure land and obtain permits. If the public is not made aware of these potential effects prior to the siting and permitting of a facility, there is a risk that the production of undesirable compounds will be viewed as unacceptable after the construction of the facility has been completed. If this is the case, litigation or protests may slow or shut down operations, resulting in financial losses for the developer and negative attention for the industry at large.

5.5.4 Opportunities for Mitigation

The more contained a process is, whether it is the biomass cultivation process, drying, solvent extraction, pyrolysis, or digestion, the lower the emissions to air will be. Therefore, photobioreactors could have reduced air-quality impacts compared to open-pond systems. However, full LCA of the air pollutant emissions associated with the production of the bioreactor materials and system operation also would be needed to assess whether photobioreactors represent a small or negligible impact on air quality. Although passive processes (for example, solar drying) reduce air quality impacts compared to active processes that generate dust or increase volatilization rates, they are not practical solutions at large scale. Siting facilities at a distance from human population centers and ecological species of concern would mitigate potential adverse effects of air pollution on humans.

5.5.5 Sustainability Indicators

Appropriate sustainability metrics for air quality would depend on the processes used in algal biofuel production. Concentrations would have to be measured or modeled at scales appropriate to bound regulatory levels or potential human health or annoyance effects. These may include:

•  For open pond systems, concentrations of VOCs and odorous secondary metabolites.

•  For active drying processes, concentrations of particulates in air.

•  For extraction processes, air concentrations of the solvent used.

•  For pyrolysis, particulates, hydrocarbons, and acid gases.

5.5.6 Information and Data Gaps

Measuring air emissions from large open ponds can provide information for occupational and other environmental exposure estimates that can be compared to thresholds for human health or environmental effects. Information and data gaps include the relationship between particular drying technologies and the types and concentrations of particulates released, releases of solvents during extraction, likely concentrations of NH3 in air during anaerobic digestion, and chemicals potentially released during pyrolysis. That information would be submitted when the biorefineries seek air-quality permits.

5.6 SPECIES INVASIVENESS AND AQUATIC BIODIVERSITY

Species invasiveness is a concern unique to biofuels produced from algae and vascular plants. In addition, changing land use or altering landscapes to produce algal biofuel feedstocks can affect biodiversity. Effects of many biofuel feedstocks on biodiversity and mechanisms leading to those effects are beginning to be understood. However, existing studies (Fargione et al., 2009; Fletcher et al., 2011; Wiens et al., 2011) focus primarily on



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