The transition towards a more circular economy is seen as a key element to achieve a high degree of resource efficiency (EC 2015a). It aims at material cycles, where waste is minimized and turned into resources, which can be used in production processes and thereby increase overall resource productivity. This entails measures to reduce, reuse, recycle, energetically valorize, and safely dispose of (unavoidable) wastes. Because wastes can serve as resources in different production systems and may contain hazardous materials, identifying optimal waste solutions is a complex task, which requires a systems perspective. Material flow analysis (MFA) is typically applied to analyse the flows and stocks of materials in society (Brunner and Rechberger 2016). In the context of waste systems, it is used to determine waste amounts and compositions as well as the fate of materials in waste management and secondary production processes. Therefore, MFA provides the basis for assessing different waste and resource management solutions by mapping flows of materials and energy.

Environmental impacts often decrease with increasing circularity, but there are also tipping points where more recycling does not lead to better environmental performance. With respect to higher material recycling rates, this is, for instance, the case when the additional impact of an increasing energy demand per unit of recovered material is higher than the gains. With respect to the quality of the recycled materials, it occurs when increasing levels of contamination limit their utilization for high-value products, or when secondary production leads to higher exposure to hazardous substances (see Pivnenko et al. 2016). These dimensions are interlinked, because recovering more of a specific secondary raw material does typically mean sourcing different wastes or larger fractions of a (heterogeneous) waste stream. Consequently, the sole increase of recycling levels does not suffice to achieve more sustainable systems, but systemic changes are needed in different areas from product design to waste management. MFA can provide information on potentials for material recovery, track materials and substances along different product life cycles, and allow for material efficiency assessments reflecting circularity and losses of the system.