may be intensified if food security concerns escalate. This pressure would be magnified significantly should breakthroughs in desalination technology make farming viable in areas where it was previously uneconomical to move fresh ground or surface water. In such a scenario, the acceptability of an algae development that has been permitted successfully and previously in good standing with local communities and the public at large could be called into question.

Land may have more value for development or recreational purposes than for massive open-pond systems. Local municipalities and communities may not be open to production facilities being located close to areas that might be developed to attract retirees, tourists, or other economic development projects. Wind turbines are perceived by some to be aesthetically unpleasing, and so could these large open or closed algal production systems. The advantages and disadvantages of using prime recreational or production lands for algal biofuel production will have to be discussed, debated, and decided upon by the stakeholder community. If oil prices continue to rise, or if foreign oil supplies suddenly were no longer available, then the argument to use land for algae production for biofuels over any economic development or aesthetic might be more pro than con.

4.4 ENERGY

To exploit the high photosynthetic efficiency of algae, energy must be invested in cultivation systems and biorefineries to grow the algae, to manage water utilizations, and to process algae into the desired fuel. Given the considerable energy use in the supply chains of other biofuels, (for example, Farrell et al., 2006), analysis of the full fuel cycle of algal supply chains is critical to understanding energy implications. This section reviews the state of knowledge of the energy properties of algal biofuel production systems.

4.4.1 Life Cycle Energy Studies of Algal Biofuels

The method to assess energy and material flows of supply chains is LCA (see also Chapter 1). The primary challenge in applying LCAs to algal biofuel production is the early stage of development of the technology. It is not yet clear what technologies along the processing chain will emerge as the most commercially feasible. Also, many technologies are in the laboratory or pilot-scale stage. Their technical (and energy) characteristics when scaled up to the industrial level are not yet clear. Nonetheless, there is a great deal of recent research activity to assess life-cycle energy use of algal biofuel production. Table 4-6 shows the energy return on investment (EROI) from a selection of recent publicly available studies of raceway systems. EROI is defined as the ratio of total energy outputs (biofuel + coproducts) to energy inputs, where energy inputs are summed over the life cycle: cultivation, nutrient procurement, harvesting, extraction, processing, and associated supply chains (Eq. 4-3).

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Unless the EROI for an energy production system is greater than 1.0, energy needed to make a fuel is greater than energy contained in the fuel and coproducts. Thus, production pathways for algal biofuels that have EROI less than 1 clearly are unsustainable. Ideally, the EROI of an algal biofuel is at least comparable to the EROI of other alternative fuels.



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