Liquid transportation biofuels are viewed as a promising alternative to fossil fuels to address energy security and climate change mitigation. Algae biomass and rapeseed were considering among the promising sources for renewable diesel (RD) and hydrotreated renewable jet (HRJ) fuel production. However, there are many challenges and technical barriers to implementation of a viable commercial process to produce biofuels. The impacts of production pathway in terms of greenhouse gas (GHG) emission, land use impact, fossil energy demand have not been comprehensively studied and concerns have been raised about that large-scale biofuel production may place pressure on fresh water, biodiversity, soil quality, and other sustainability impacts.

Chapter 2 investigated the GHG emission of algae biofuel when evaluating several potential usages for lipid-extracted algae (LEA) to displace animal feed. Results indicated that the benefit from displacing animal feed does not outweigh the incremental burdens associated with replacing the requirements that LEA currently satisfies, resulting in higher GHG emissions for the algae biofuels life cycle. Chapter 3 assessed the LUC impacts from the conversion of proposed algae facility sites in the U.S. Gulf Coast. Direct LUC impacts appear to be roughly 6.3%~12.5% of the total GHG emission over the entire algae RD life cycle. Chapter 4 investigated the environmental impacts associated with novel algae harvesting and oil extraction technologies. Results show that all novel technologies appear to have the potential to provide at least modest GHG reductions compared to current default technologies. Chapter 5 developed a life cycle water footprint (WF) analysis for rapeseed HRJ fuel production in North Dakota and evaluated the environmental impacts on water utilization and water quality due to large-scale jet production. Discussions also carried out the importance of incorporating allocation within a life cycle approach when conducting biofuel WF analysis. Chapter 6 employed a model-based approach to conduct LCA of HRJ fuel produced from rotation of rapeseed with grain crops (mostly wheat) to replace the fallow period. Results show that introducing fuel oilseeds to existing crop rotations have significant advantages compared to the current cropping practices. These results provide insights on the potential impacts of expanded biofuel production systems in regional and national contexts compared to the current cropping systems and answered the questions of what is the best practice to enhance the sustainability of biofuel production.