Quality Degradation from Recycling Quality Degradation and Substitutability Between Glass Cullet and Virgin Raw Material in LCA

Abstract

The focus in society to become more circular has increased lately and therefore also the focus on recycling. Recycling is a key factor to keep the material inside the loop, but an important aspect of the applicability of the secondary material is its quality and its possibility to replace virgin raw material. The benefit of recycling is there- fore depending on the quality of the output product. Life cycle assessment (LCA) is often used as a tool to evaluate the benefits of recycling, however, the quality of the output product is seldom considered and there is no common and clear way how to evaluate the quality loss from recycling. A major problem lies in how to quantify to what degree the materials are functionally equal and by that substitutable, and in the quantification, it must be kept in mind that the secondary material might have gone through a quality degradation that would impact the substitutability. Most LCA studies do not consider this aspect and instead assume that the functionality of the secondary material is fully equal to the replaced material and can fully replace the material with a one-to-one (1:1) substitution rate. A material that is commonly recycled and used as a secondary material is glass. Glass is often considered a fully circular material and few studies have focused on the quality degradation of glass, even though several aspects affect the quality of glass cullet as a secondary material. This thesis has therefore resulted in a proposal for evaluating quality degradation and for quantifying the substitutability of glass when recycled. The model takes its base in existing models for other materials and information regarding important factors and quality aspects of glass cullet. The model was then implemented in two case studies, one about the life cycle of a bottle and one regarding the treatment of waste glass. For each of the case studies, sub- stitutability coefficients for the secondary material were calculated and the effect of using these instead of a 1:1 substitutability was compared. The results from the case studies were then used to evaluate the model and its functionality. The results showed that accounting for the quality degradation could have an important effect on the results of the study and the total impact of the system, especially when eval- uating waste treatment systems. A proper way of quantifying the substitutability between the glass cullet and the replaced material is therefore important to evaluate the environmental impact of the studied system. Quantifying substitutability prop- erly is difficult since the quality depends on many different aspects. The introduced model is therefore a simplification that is adapted for some quality aspects. It could be improved by evaluating the quality requirements for glass cullet further and by including more quality aspects and considering their relative importance.