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 growing demand for food products, driven by a growing world population, has increased Europe's dependence on conventional fertilizers, which have a high impact on the environment. In the last decade, new circular fertilizer value chains have appeared as promising alternatives to conventional fertilizers. Methods Because of the huge number of alternatives, this study aimed to develop a practical methodology that facilitates the analysis of data related to each value chain to identify and select the most promising circular fertilizer value chains to promote their wide-scale production and use in agriculture, replacing the dependence on conventional fertilizers in Europe. This methodology is based on two stages (funnelling process and scoring system) and considers the 16 criteria defined in the study. The methodology was tested for 48 value chains identified during the mapping of secondary raw materials in Europe with the potential to be used as circular fertilizers when processed, classifying them into seven different raw materials: urban wastewater (UWW), industrial wastewater (IWW), sewage sludge (SS), biowaste (BW), biological by-products (BBP), treated manure (TM), and digestate (DIG). The funnelling process is based on a GO/NO-GO approach that meets six criteria and allows the discarding of 18 value chains, from 30 to the second stage. The scoring system was a more complete analysis, including ten new scoring criteria. Results This system allowed the identification of the potential of the value chains analyzed, concluding that struvite from UWW, struvite from IWW, stabilized sludge from SS, composted biowaste from BW, feather meal from BBP, solid fraction from DIG, and spent mushroom substrate from TM are the most promising options for agriculture. Conclusions The develop methodology was used to evaluate 48 different value chains with the potential to generate promising circular fertlizers. Seven value chains were finally selected.

Background The growing demand for food products, driven by a growing world population, has increased Europe's dependence on conventional fertilisers, which have a high impact on the environment. In the last decade, new circular fertiliser value chains have appeared as promising alternatives to conventional fertilisers. Methods Because of the huge number of alternatives, this study aimed to develop a practical methodology that facilitates the analysis of data related to each value chain to identify and select the most promising circular fertiliser value chains to promote their wide-scale production and use in agriculture, replacing the dependence on conventional fertilisers in Europe. This methodology is based on two stages (funnelling process and scoring system) and considers the 16 criteria (e.g. technical viability, nutrient content, among others) defined in the study. The methodology was tested for 48 value chains identified during the mapping of secondary raw materials in Europe with the potential to be used as circular fertilisers, classifying them into seven different raw materials: urban wastewater (UWW), industrial wastewater (IWW), sewage sludge (SS), biowaste (BW), biological by-products (BBP), treated manure (TM), and digestate (DIG). The funnelling process is based on a GO/NO-GO approach that meets six criteria and allows the discarding of 18 value chains, from 30 to the second stage. The scoring system was a more complete analysis, including ten new scoring criteria. Results This system allowed the identification of the potential of the value chains analysed, concluding that struvite from UWW, struvite from IWW, stabilized sludge from SS, composted biowaste from BW, feather meal from BBP, solid fraction from DIG, and spent mushroom substrate from TM are the most promising options for agriculture. Conclusions The develop methodology was used to evaluate 48 different value chains with the potential to generate promising circular fertlizers. Seven value chains were finally selected.