Where possible, this chapter discusses the potential for algal biofuels to improve aspects of sustainability compared to petroleum-based fuels and other biofuels and the potential for mitigating negative effects along the life cycle of algal biofuel. Environmental indicators of sustainability and data to be collected to assess sustainability are suggested. In some environments and biofuel management systems, metrics for assessing environmental performance are easy to measure and adequate baseline data are available, but that is not the case in all systems.
A number of potential environmental concerns are evident, and if the concerns are not addressed they could become significant risks under large-scale deployment. As in any other industrial or agricultural enterprise, once they are recognized, such risks can be managed by standards or regulations so that industry is required to reduce effects to acceptable levels. For the sake of comprehensiveness, a number of potential environmental risks are mentioned in this chapter, but some are less likely to occur than others. Some of the environmental risks might require exploratory assessment and subsequent monitoring to ensure that they do not become sustainability concerns if algal biofuel production is scaled up.
Producing algal biofuels could improve or harm water quality depending on the resource input and management used in algae cultivation, weather events, integrity of infrastructure, and processing of spent water. Water-quality concerns associated with commercial-scale production of algal biofuels, if sufficient culture waters are released to natural environments, include eutrophication of waters, contamination of groundwater, and salinization of water sources. Potential water-quality benefits are reduced runoff of herbicides and insecticides compared to corn-grain ethanol or soybean-based biodiesel because of their reduced use, and reduced eutrophication if there are no releases of culture water or if algae are used as a means to remove nutrients from municipal waste, confined animal feeding operations, and other liquid wastes. Water-quality effects will depend on the nutrient content of the algal culture medium; whether feedstock production systems are sealed, artificially lined, or clay lined; and the likelihood of extreme precipitation events. Leakage of culture fluid to groundwater or surface water could occur if the integrity of the pond or trough system is compromised, if flooding occurs, or if spills occur during transfers of fluid during process stages or waste removal, but most of these events could be avoided with proper management.
5.1.1 Releases of Culture and Process Water
As discussed in Chapter 4, the water for algae cultivation is likely to be reclaimed and reused to reduce the water requirement and consumptive water use. The liquid effluent also can be recycled from anaerobic digestion of lipid-extracted algae to produce biogas (Davis et al., 2011). If harvest water is to be released instead of recycled, it or effluent from anaerobic digestion would contain nitrogen (N) and phosphorus (P), the concentrations of which depend on the nitrogen and phosphorus taken up by the harvested algal biomass (Sturm and Lamer, 2011). Released waters could be more saline than receiving waters, particularly if water from saline aquifers is used for algae cultivation. Such point-source discharge will be regulated by the Clean Water Act, and a National Pollutant Discharge Elimination System permit would have to be obtained to operate the algae cultivation facilities (EPA, 2011a). However, permit violation has been observed in some biofuel refineries