Cycles and sinks: two key elements of a circular economy

Modern products contain a wide range of substances. Some of them are hazardous, cause risks for human and environmental health, and impair the quality of future secondary resources produced by recycling. Ways must be explored to extract detrimental substances during recycling and direct them to safe final sinks. Final sinks can be end-of-pipe technologies (man-made sinks) or environmental media (natural sinks). The latter are limited in capacity and need to be protected against overloading. The paper presents a rationale for sinks in a circular economy, and supports decision-making regarding recycling materials with detrimental constituents. It is based on two case studies of regional flows of polycyclic aromatic hydrocarbons in spent asphalt pavements, and copper in waste flows. Applying a scenario approach, effective measures are discussed for circulating safe and high-quality materials while observing sink limitations. The results demonstrate the link between mass flows, quality of recycled material, and the need for final sinks. The optimization challenge of keeping cycles clean by costly measures for safe disposal of hazardous materials in sinks is discussed. Man-made sinks such as waste to energy plants and sanitary landfills are key for designing a circular economy that meets environmental and resource-oriented goals.