As mentioned earlier, LCA studies of biofuels (including project report, research papers, pol­icy documents, etc.) are numerous and have become even more popular with the recent imple­mentation of sustainability criteria in biofuels policy worldwide (especially in the European Union and the United States) and the increased research activities in advanced biofuel pathways (e. g., biofuels from microalgae). The results of biofuels LCA studies may vary significantly from one author to another for a variety of reasons: these include methodological choices as described in Table 1, but also the type of biofuel (including bioethanol, biodiesel, e. g., methyl esters of veg­etable oils, so-called renewable diesel, e. g., from Fischer-Tropsch synthesis, biobutanol, etc.), the type of technology (including first-, second-, and third-generation technologies, biochemical or biothermal, dedicated biofuel production, or multioutput biorefinery concept, etc.) and their corresponding level of maturity, the type of feedstock considered for a given biofuel, and the conditions under which a given feedstock is produced (dedicated production, agricultural, for­estry or industrial residues, wastes, etc.). In relation to the various aspects listed, the inventory data to characterize the production of biofuel may differ significantly depending on the level of detail (e. g., proven and long-lived technology, technology based on pilot/demonstration plant, laboratory-level experiments, physicochemical computer-based modeling, etc.). In addition, biofuels LCA studies will also vary with respect to the inventory database.

Many recent LCA studies have evaluated the environmental impact of biofuel production from microalgae (Batan et al., 2010; Campbell et al., 2011; Clarens et al., 2010; Collet et al., 2011; to cite only a few of the latest research papers). The large variety of research and develop­ment areas in this field (including biomass production, harvesting, separation, processing, transformation, and the possible products and applications) is detailed in Brennan and Owende (2010), Wijffels and Barbosa (2010), and Singh and Gu (2010). Wijffels and Barbosa (2010) con­clude by emphasizing the need for life-cycle assessment of algal biofuel production processes, while Singh and Gu (2010) report: "An adequate LCA study is still not available which may help to present a clear picture of the situation. The reason is nonavailability of commercial plant data." A similar situation can be found concerning the production of cellulosic bioethanol (Singh et al., 2010; Spatari et al., 2010) and more generally with the concept of biorefinery and the coproduction of biofuels, biochemicals and/or biomaterials (thereby stressing even more the significance of the allocation method).

All the aspects listed make it very complicated to compare the results of various biofuels LCA studies, even for a given feedstock-technology-biofuel system, according to the hypotheses and methodological choices. This is illustrated in a detailed case study in the following sections of this chapter.