Applying material flow assessment-based system expansion with multiple functions to solve for multifunctionality of recycling in life cycle assessment

Abstract

Purpose: There are several LCA methods in existence today that solve for the multifunctionality of recycling at the product level for determining the burden profiles of individual products. These product-level methods, however, often give varying environmental burden profiles and occasionally different conclusions for determining whether recycling causes greater or lesser burdens than linear product strategies. Such ambiguous results and findings across LCA methods confuse the public and decision-makers regarding the environmental implication of recycling compared to other material strategies. In this paper system expansion with multiple functions (SEMF) is investigated as a possible solution to the multifunctionality issue of recycling within life cycle assessment (LCA) whilst also providing a product-level perspective. Methods: The background life cycle inventory (LCI) is based on ecoinvent 3.9 and the life cycle impact assessment (LCIA) method is based on ReCiPe 2016 (H). The study investigates the use of product-level methods and SEMF, both as separate approaches and as a proposal to combine them for addressing recycling in LCA. Simplified material flow assessment (MFA) is employed for calculating the foreground life cycle inventories (LCIs). Results/discussion: Product-level LCA methods of recycling strategies lead to a wide range of global warming potential (GWP) results for the same case scenario. This ambiguity prevents a uniform conclusion as to whether recycling causes lesser or greater burdens than linear material strategies. By contrast, it is demonstrated that SEMF finds one GWP for each recycling scenario, allowing for a less methodologically uncertain comparison with linear material strategies. It is also shown that attributional LCA (ALCA) in combination with MFA, can be used to build the SEMF study, bridging the informational gap between the product level and SEMF scopes of recycling in LCA. Conclusion: The sum of each product level ALCA can be used to assemble an LCA with the SEMF perspective. In this way, one can easily transition between the product level whilst comparing material strategies within a SEMF scope. To perform a SEMF-based LCA, it is necessary to include the number of times a recycled material is utilised and to employ MFA to track resource use, mass flows, and check balances. From this research further investigation is recommended into existing methods for establishing how many times a recycled material is or can be used. The authors also recommend further testing and use of the SEMF LCA method through its application in real-life scenarios.