The management of the organic fraction of municipal solid waste (OFMSW), also called urban biowaste, and urban wastewater sludge (UWWS) represents a challenge for cities and regions, which want to adopt innovative urban bioeconomy approaches for their treatment and production of high-added-value products beyond the traditional anaerobic digestion (AD) and compost. This adoption is often restricted by the availability and maturity of technologies. The research object of this manuscript, based on the findings of EU Horizon 2020 project HOOP, is the identification of state-of-the-art circular technologies for material valorisation of OFMSW and UWWS, following a novel screening methodology based on the scale of implementation (tested at least at pilot scale). The screening resulted in 25 technologies, which have been compared and discussed under a multidisciplinary assessment approach, showing their enabling factors and challenges, their current or potential commercial status and their compatibility with the traditional technologies for urban biowaste treatment (composting and AD). The bioproducts cover market sectors such as agriculture, chemistry, nutrition, bioplastics, materials or cosmetics. Therefore, the results of this review help project promoters at city/region level to select innovative technologies for the conversion of OFMWS and UWWS into high value products.

The circular economy has a huge potential to make our societies more sustainable and decarbonised, with a reduced impact on the planet’s resources. The deployment of innovative solutions in the field of urban biowaste valorisation and reuse is still hindered by numerous bottlenecks, such as technological readiness, funding and financing tools availability, quality and quantity of biowaste and regulatory barriers. The European Green Deal and associated legislative initiatives provide the opportunity to overcome the last ones. To promote innovative solutions for the European circular bioeconomy and help to overcome the barriers for the deployment of a circular bioeconomy, five Horizon 2020 projects working on biowaste valorisation have teamed up. This joint initiative is named ROOTS - circulaR pOlicies for changing the biOwasTe System. The projects HOOP, VALUEWASTE, SCALIBUR, WaysTUP! and CITYLOOPS are piloting new solutions to transform urban biowaste (food waste and green waste) and wastewater into valuable products like feed, fertilisers, bioplastics, biopesticides, proteins and bioethanol. They use different processes and technologies, but they all rely on high levels of recycling/upcycling and propose valorisation solutions relevant to the uptake of a truly circular bioeconomy. As a result of the work performed and experience acquired, a number of bottlenecks have been identified, on the following topics: biowaste prevention, recycling targets and treatment plants, waste and by-products, biopesticides, insects for animal feed, single cell protein, citizen behaviour, investment needs. For each identified bottleneck, this open letter proposes specifically 1) policy recommendations for each level of governance, and 2) information about solutions, good practices and concrete experiences from the participating projects.

Background The European Commission is promoting the Circular Economy (CE) to replace the linear model with one based on recycling and reuse. A genuine commitment to the CE requires that organizations and cities first identify and quantify the value leakages within their resource flows before designing and implementing any CE-related initiatives. Methods This study presents an innovative set of Urban Bioeconomy Indicators (UBI) designed to assess and enhance CE initiatives in cities and regions, with a particular focus on biowaste management and valorization. Addressing the need for standardized yet locally adaptable metrics, this research proposes a comprehensive methodology for evaluating urban bioeconomy performance. The study’s methodology involved an extensive review of existing CE indicators, followed by a structured selection and adaptation process. This led to the development of 20 indicators across six key dimensions: Waste, Water, Energy, Economy, Society, and Policy. The UBI set uniquely integrates both quantitative and qualitative indicators, including 'enabling factors' that capture crucial but hard-to-quantify aspects of CE implementation. Results Key innovations of this research include: (1) a specific focus on urban bioeconomy, (2) emphasis on material valorization over energy recovery, (3) introduction of self-sufficiency indicators, and (4) incorporation of qualitative enabling factors. Nevertheless, the indicators are designed to measure both citizen behavior and waste management system performance, providing a holistic assessment of urban CE progress. Conclusions By providing a standardized yet flexible methodology, this work contributes to the advancement of urban bioeconomy assessment. It serves as a valuable tool for local authorities to measure, compare, and enhance their bioeconomy performance, potentially laying the groundwork for future urban CE evaluations and policy development.

Background The European Commission is promoting the Circular Economy (CE) to replace the linear model with one based on recycling and reuse. A genuine commitment to the CE requires that organizations and cities first identify and quantify the value leakages within their resource flows before designing and implementing any CE-related initiatives. Methods This study presents an innovative set of Urban Bioeconomy Indicators (UBI) designed to assess and enhance CE initiatives in cities and regions, with a particular focus on biowaste management and valorization. Addressing the need for standardized yet locally adaptable metrics, this research proposes a comprehensive methodology for evaluating urban bioeconomy performance. The study’s methodology involved an extensive review of existing CE indicators, followed by a structured selection and adaptation process. This led to the development of 20 indicators across six key dimensions: Waste, Water, Energy, Economy, Society, and Policy. The UBI set uniquely integrates both quantitative and qualitative indicators, including ‘enabling factors’ that capture crucial but hard-to-quantify aspects of CE implementation. Results Key innovations of this research include: (1) a specific focus on urban bioeconomy, (2) emphasis on material valorization over energy recovery, (3) introduction of self-sufficiency indicators, and (4) incorporation of qualitative enabling factors. Nevertheless, the indicators are designed to measure both citizen behavior and waste management system performance, providing a holistic assessment of urban CE progress. Conclusions By providing a standardized yet flexible methodology, this work contributes to the advancement of urban bioeconomy assessment. It serves as a valuable tool for local authorities to measure, compare, and enhance their bioeconomy performance, potentially laying the groundwork for future urban CE evaluations and policy development.