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How do methodological choices affect the carbon footprint of microalgal biodiesel? A harmonised life cycle assessment

Valente, Antonio, Iribarren, Diego, Dufour, Javier
Journal of cleaner production 2019 v.207 pp. 560-568
biodiesel, carbon dioxide, carbon footprint, case studies, energy, fossil fuels, greenhouse gas emissions, life cycle assessment, microalgae, oils, risk, transesterification
The environmental feasibility of microalgal energy systems is often evaluated through the Life Cycle Assessment (LCA) methodology. In particular, biodiesel derived from the transesterification of microalgal oil has been extensively assessed following a life-cycle perspective. When making comparisons between these LCA studies, the consistency of the methodological choices should be a key requirement to guarantee the reliability of the comparative results and interpretations. However, a harmonised LCA framework is not typically found in the scientific literature when addressing comparative studies. In this work, the carbon footprint of microalgal biodiesel is revisited for a sample of 31 LCA case studies in order to allow a reliable comparative study. As a key outcome, a harmonised LCA framework is defined with focus on consistent methodological choices regarding functional unit, system boundaries, multifunctionality approach, and CO2 balance approach. Furthermore, the application of this novel framework leads to the provision of a library of 31 robust carbon footprints of microalgal biodiesel. This harmonisation initiative proves to mitigate potential misinterpretation concerns by avoiding methodological inconsistencies. In fact, all the LCA methodological aspects harmonised in this work are found to play a significant role in mitigating misinterpretation risk. For instance, when benchmarking greenhouse gas emission savings with respect to fossil diesel, a robust comparative study using harmonised carbon footprints results in a significant reduction in the percentage of case studies meeting a 60% target. This highlights the relevance of LCA harmonisation when it comes to facilitating decision-making processes under sustainability and cleaner productions aspects.