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

Abstract

The environmental benefi ts 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 effi ciencies 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 fi nding is at odds with the economic 580

Microalgal culture strategies for biofuel production: a review

“…Microalgal biofuels, known as third‐generation biofuels, are treated as a technically viable alternative energy solution that overcomes the major drawbacks related to the first and second generations. Compared to the first‐ and second‐generation biofuels, microalgal biofuels offer many more advantages, such as a high growth rate, high‐efficiency CO 2 mitigation, non‐competition for farmland, less water demand than land crops, toleration of wastewaters during cultivation, and more cost‐effective farming …”

Evaluating microalgae‐to‐energy ‐systems: different approaches to life cycle assessment (LCA) studies

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Well-to-wake analysis of ethanol-to-jet and sugar-to-jet pathways

“…Cox et al [25] evaluated the STJ from sugarcane molasses, and estimated its GHG emissions at 80 g CO 2 e/MJ, using a system expansion method. On the other hand, Moreira et al [26] estimated the GHG emissions of STJ from sugarcane at 8.5 g CO 2 e/MJ, using a system expansion method.…”

“…The large difference in the GHG emissions between these two studies stemmed from differing approaches to estimating indirect effects. Cox et al [25] assumed that sorghum production will increase as sugarcane is used as a jet fuel feedstock, resulting in LUC GHG emissions of over 100 g CO 2 e/MJ from the increased sorghum production. Moreira et al [26], on the other hand, used the Global Trade Analysis Project model to estimate the LUC, and reported subsequent LUC GHG emissions of 12 g CO 2 e/MJ.…”

“…Cox et al [25] and Moreira et al [26], however, examined only STJ produced via biological conversion from sugarcane, which is not widely available for fuel production outside Brazil. Staples et al [27] included corn and corn stover, which are more relevant to the US biofuel industry.…”