Environmental life cycle assessment (LCA) of aviation biofuel from microalgae, Pongamia pinnata, and sugarcane molasses

The environmental benefits and trade-offs of automotive biofuels are well known, but less is known about aviation biofuels. We modeled the environmental impacts of three pathways for aviation biofuel in Australia (from microalgae, pongamia, and sugarcane molasses) using attributional life cycle assessments (LCAs), applying both economic allocation and system expansion. Based on economic allocation, sugarcane molasses has the better fossil energy ratio FER (1.7 MJ out/MJ in) and GHG abatement (73% less than aviation kerosene) of the three, but with trade-offs of higher water use and eutrophication potential. Microalgae and pongamia have lower FER and GHG abatement (1.0 and 1.1; 53% and 43%), but mostly avoid eutrophication and reduce water use trade-offs. All have similar and relatively low land use intensities. If produced on land where existing carbon stocks are not compromised, the sugarcane and microalgae pathways would currently meet a 50% GHG abatement requirement. Based on system expansion, microalgae and pongamia had lower impacts than sugarcane for all categories except energy input, highlighting the positive aspects of these next-generation feedstocks. The low fossil energy conservation potential of these pathways was found to be a drawback, and significant energy efficiencies will be needed before they can affect fossil energy conservation. Energy recovery from processing residues (base case) was preferable over use as animal feed (variant case), and crucial for favorable energy and GHG conservation. However this finding is at odds with the economic preferences identified in a companion technoeconomic study.