Impact of recycling effect in comparative life cycle assessment for materials selection - A case study of light-weighting vehicles

Abstract

Selection of recycling approaches is one of the remaining issues in the life cycle assessment (LCA) and a critical factor for materials selection based on the LCA. While several recycling approaches and allocation methods have been proposed, the impact of the recycling effect determined by different allocation methods on materials selection has yet to be addressed. In this study, we demonstrate the impact of the recycling effect on materials selection in the LCA. First, the appropriateness of the avoided burden approach for the purpose of materials selection is addressed and practical equations for the three typical allocation methods in the avoided burden approach are proposed, for waste mining, end-of-life recycling, and 50-50 methods. Next, a material flow analysis is used to justify the recycling parameters associated with each allocation method. Finally, an LCA case study on different materials used for the light-weighting vehicle is conducted to show the impact of recycling effect on materials selection. According to the results of the life cycle greenhouse gas emissions, for the battery electric vehicles manufactured with intensive use of different materials, the preferred material is different depending on the waste mining and end-of-life recycling methods selected. Due to the different greenhouse gas emissions during the use phase, the recycling effect in the life cycle of battery electric vehicles is more substantial than that of internal combustion engine vehicles. The results of this study clearly indicate that attention should be given to the recycling effect when an LCA study is conducted for materials selection, especially when considering the products associated with a heavy environmental burden in the production phase. Future work on the development of a concrete selection methodology for different allocation methods is necessary. In addition, a high-resolution material flow analysis would be useful to obtain values of the part-specific recycled content of the designated product to ensure transparency and fairness when quantifying the recycling effect.