technologies to modify them increase. Some clearly desirable modifications would provide increases in tolerance to temperature, salinity, pH ranges, and metal concentrations. Tolerances to a range of conditions contribute to crop robustness. Prior demonstrations of such modifications include the conversion of freshwater cyanobacteria to use saline water sources (Waditee et al., 2002; Laloknam et al., 2006). Other aspects of the supply chain can be targeted through genetic modifications, including genetic engineering. For example, groups at Los Alamos National Laboratory have transplanted genes from magnetotactic bacteria. These genes direct the production of magnetic nanoparticles in green algae, which allows simple harvesting by magnetic collection of cells and reduces energy input for centrifugation and dewatering steps (Los Alamos National Laboratory, 2011).
Evaluating the sustainability of algal cultivation systems for biofuel production requires examining the various material and energy inputs needed for the cultivation systems to maintain scalable productivity, maximize system robustness, and minimize costs (Figure 2-3). Scalable productivity refers to a cultivation system’s ability to maintain productivities with respect to algal biomass and algal product (mass/area-time or mass/volume-time) from the laboratory scale to the commercial scale. System robustness refers to a cultivation system’s ability to reliably and dependably deliver consistent productivity and avoid system crashes or failures as a result of either biological or physicochemical causes. Costs pertain to capital and operating costs for a cultivation system.
FIGURE 2-3 Material and energy inputs required by a cultivation scheme. Together with the biological scheme, these inputs determine the cultivation system’s productivity, robustness, and cost.