Allocation strategies in comparative life cycle assessment for recycling: Considerations from case studies

- Two allocation strategies for recycling are analyzed and compared.
- Two real comparative LCAs are performed with primary data.
- Allocation is implemented in the modeling of input waste, mass and energy recovery.
- A simulation is developed to combine the two real case studies.
- The results of the comparisons are partially affected by the allocation formulas.

The objective of this research is to verify whether an end-of-life allocation strategy can affect the choice between two products or two processes. This study evaluates whether a comparison between two products/processes that is obtained by applying the cut-off (CO) approach and substitution method (Sub) can cause a sign reversal for products/processes with different recyclability features. The main intent is to provide a clear picture for Life Cycle Assessment practitioners, who analyze recycling systems and would benefit by knowing whether an end-of-life allocation strategy can affect the preference ranking between products or processes. Two comparative case studies were developed using primary data. The case studies were very different because they referred to different sectors. In the first case study, the analyzed subjects were two plastic products; in the second case study, the analyzed subjects were an incineration line under design and an incineration line under operative conditions. For the first case study, the allocation strategies were implemented in the modeling of the burdens of input waste and end-of-life disposal. For the second case study, the allocation strategies were implemented in the modeling of input waste; in the burdens of end-of-life disposal of slag, ashes and dust; in the recovery of construction materials; and in energy recovery. To confirm the main findings of the first and second cases, an additional case was simulated by combining the first and second cases. The results obtained in the two case studies and in the combined case indicate that comparisons between the analyzed products/processes are only marginally affected by the applied end-of-life allocation strategies and are consistent with both the allocation strategies for almost all of the analyzed impact categories.