How should recycling be modelled in LCA?
Recycling creates a link between the system that supplies a used material and the system that uses it again. How this link is represented in a Life Cycle Assessment (LCA) can significantly influence results, particularly for products with high recycled content or high recovery rates.
There is no single approach suitable for every study. Methods distribute burdens and benefits between the life cycle supplying material for recycling and the life cycle receiving it.
Why are there different methods?
A central question is how to allocate the impacts of producing the original material, collecting and recycling it, and the benefits associated with replacing virgin material. Different methods answer this question in different ways. Approaches discussed in the literature include methods based on recycled content, end of life, and formulas for sharing burdens and benefits.
The choice can affect comparisons between alternatives. A product with high recycled content may be favoured by one approach and produce different results when its contribution to end-of-life recycling is considered.
How should a method be selected?
The approach should be consistent with the study's goal and scope, applicable product category rules and the requirements of the selected programme or method. Assumptions such as collection rates, process losses, secondary-material quality and the substitution rate for virgin material need to be documented.
When the methodological choice could influence conclusions, sensitivity analyses using plausible alternative approaches are recommended. This helps assess the robustness of results and avoids conclusions that depend excessively on a single modelling convention.
Recycling modelling is not merely a secondary technical decision. It is an allocation choice that should be transparent, consistent and appropriate to the question the study is intended to answer.