The basket-of-functions approach applied to compare the climate aspects of high-quality mechanical recycling and downcycling of plastics

The Swedish Extended Producer Responsibility stipulates recycling rates but does not address the quality of the recycling. This gives an incentive for downcycling, which affects what primary material can be substituted by recycled plastics. To shed light on the climate aspects of high-quality plastics recycling, we compare the climate impacts of (1) no recycling, (2) downcycling and (3) advanced sorting that allows for substantial high-quality mechanical recycling. We discuss the limitations of common approaches to modelling recycling; we then select a basket-of-functions approach with a broad systems perspective. In our model, each tonne of high-quality recyclate replaces 900 kg primary plastics in a closed loop. Downcycled plastics instead compete with wood in railway sleepers that are incinerated with energy recovery at the end of their service life. The model accounts for impacts of recycling and downcycling on both near-term and future Swedish waste incineration, the waste imports, and the waste management and energy systems in the rest of Europe. The basket of functions generated by the system model includes packaging, supply of railway sleepers, treatment of near-term and future European waste, near-term and future European gas supply, and future electricity supply. Our results include no avoided burdens but only the emissions associated with generating the many functions of the system. They indicate that downcycling is better for the climate than no recycling, mainly because the incineration of downcycled material is postponed until after the end of the second use. This allows for a greater near-term import of waste that, in turn, reduces landfill disposal of mixed waste in other countries. The case with advanced sorting has the lowest climate impact because it involves the least primary production of polymers and the least total incineration of waste plastics. Common approaches to model recycling fail to account for key aspects in the assessment. The basket-of-functions approach allows for assessing complex impacts of recycling in a broad systems perspective, although it requires multiple assumptions to be made in the model. High-quality recycling increases the chance that the recycled plastics replace primary plastics. This leads to a greater climate benefit. The basket-of-functions approach should be considered when a decision on a material flow has complex foreseeable system impacts. A plastics-recycling policy generates greater climate benefits if it gives incentives for high-quality recycling.