Circular economy is increasingly promoted as a solution to decouple economic growth and environmental impacts. To design a circular and sustainable system, a structured approach is needed. In this study, we suggest to follow a 3-step approach. First, the status quo is evaluated using environmental assessment methods. We determine current circularity (share of assessed product and materials retained and further used in the system), environmental impacts, the most impactful products and processes, and assess contaminants and impurities. Second, scenarios favoring circularity strategies are developed and their environmental impacts evaluated. Third, the scenarios are compared and measures for environmental impact mitigation derived.The suggested approach was applied to the case study of thermal insulation in residential buildings in Switzerland. Coupling dynamic, prospective material flow analysis with life cycle impact assessment enabled to determine current and future environmental impacts. Current material circularity is low due to lacking incentives for recycling and legally required incineration of flame retardant containing oil-based materials. The most impact-intensive processes were the production of insulation materials and the incineration of oil-based materials including their adhering residues. The investigated scenarios include (i) increased recycling, (ii) augmented use of biogenic materials, and (iii) a combination thereof. All scenarios lead to reduced climate change and human toxicity impacts. The second and third scenarios showed increased impacts for land use, ozone depletion, and ecotoxicity. Taking into consideration end-of-life already in the design process, phasing out toxic materials and increasing usage of renewable materials are crucial for sustainable, circular system design.

Ion exchange is a promising option for recovering nutrients (nitrogen, phosphorus, and potassium) from source-separated urine.

According to the waste hierarchy, waste prevention is environmentally superior to recycling or recovery, hence its inclusion in government policy. The assessment and prioritization of waste prevention strategies are impeded, inter alia, by ambiguous definitions and the lack of a sound environmental assessment method. In this study, a systematic approach to the environmental assessment of waste prevention activities (WPAs), covering the whole life cycle of products, was developed. The approach combines material flow analysis and life cycle assessment with a sustainable circular system design framework whilst giving special consideration to pivotal factors such as diffusion factor (share of population engaging in WPA), substitutability (degree to which a new product is replaced), effects on use‐phase impacts, and rebound effects. The application of the approach to the case studies of clothing and household furniture in Switzerland revealed lower impact saving potential than assumed initially, due to lack of participation, low substitutability, or high rebounds. For example, reusing clothing locally, instead of exporting it to low‐income countries, as currently done, displayed no or even negative impact savings since secondhand clothing in high‐income countries is often consumed in addition to new clothing. Drastic scenarios for clothes led to only moderate impact reductions of less than 15%, whereas a take‐back scheme for furniture reduced impacts by 70%. Concluding, the four factors (diffusion rate, substitutability, effects on use‐phase impacts, and rebounds) proved crucial in the assessment of waste prevention strategies and the approach presented was able to pinpoint improvement potentials of the waste prevention scenarios investigated.

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Industrial ecology (IE) methodologies, such as input/output or material flow analysis and life cycle assessment (LCA), are often used for the environmental evaluation of circular economy strategies. Up to now, an approach that utilizes these methods in a systematic, integrated framework for a holistic assessment of a geographic region's sustainable circular economy potential has been lacking. The approach developed in this study (IE4CE approach) combines IE methodologies to determine the environmental impact mitigation potential of circular economy strategies for a defined geographic region. The approach foresees five steps. First, input/output analysis helps identify sectors with high environmental impacts. Second, a refined analysis is conducted using material flow and LCA. In step 3, circular strategies are used for scenario design and evaluated in step 4. In step 5, the assessment results are compiled and compared across sectors. The approach was applied to a case study of Switzerland, analyzing 8 sectors and more than 30 scenarios in depth. Carbon capture and storage (CCS) from waste incineration, biogas and cement production, food waste prevention in households, hospitality and production, and the increased recycling of plastics had the highest mitigation potential. Most of the scenarios do not influence each other. One exception is the CCS scenarios: waste avoidance scenarios decrease the reduction potential of CCS. A combination of scenarios from different sectors, including their impact on the CCS scenario potential, led to an environmental impact mitigation potential of 11.9