Wastewater treatment plants (WWTPs) require an urgent transition from a linear to a circular economy operation/design concept with a consequent resource recovery and more sustainable waste management. Natural resources have to be preserved, and wastes have to become an opportunity for recovering resources and materials (water reuse, energy, sludge reuse). However, the transition toward a circular economy is a complex and long process due to the existence of technical, economic, social and regulatory barriers. These existing barriers are critical challenges for a modern and sustainable WWTP concept. The recovery of resources must be considered a strategic target from the earliest process-design phase. In this context, the European Union’s Horizon 2020 project “Achieving wider uptake of water-smart solutions—WIDER UPTAKE” aims to overcome the existing barriers (technological, regulatory, organizational, social and economic) toward the transition from a linear to a circular economy model for WWTPs. This study is aimed at increasing the awareness of the existing barriers to a circular economy and summarizes the key contributions of the WIDER UPTAKE project in terms of water reuse, sludge reuse and nutrient recovery.

The wastewater sector paradigm is shifting from wastewater treatment to resource recovery. In addition, concerns regarding sustainability during the operation have increased. In this sense, there is a need to break barriers (i.e., social, economic, technological, legal, etc.) for moving forward towards water resource recovery facilities and demonstration case studies can be very effective and insightful. This paper presents a new water resource recovery case study which is part of the Horizon 2020 EU Project “Achieving wider uptake of water-smart solutions—Wider Uptake”. The final aim is to demonstrate the importance of a resource recovery system based on the circular economy concept. The recovery facilities at Palermo University (Italy) are first presented. Afterwards, the resource recovery pilot plants are described. Preliminary results have underlined the great potential of the wastewater treatment plant in terms of resources recovery and the central role of the University in fostering the transition towards circular economy. The fermentation batch test highlighted a volatile fatty acids (VFAs) accumulation suitable for polyhydroxyalkanoates (PHAs) production. The results of static adsorption and desorption tests showed that the highest amount of adsorbed NH₄⁺ was recorded for untreated and HCl-Na treated clinoptilolite.

The current exploitation of freshwater, as well as the significant increase in sewage sludge production from wastewater treatment plants (WWTPs), represent nowadays a critical issue for the implementation of sustainable development consistent with the circular economy concept. There is an urgent need to rethink the concept of WWTPs from the conventional approach consisting in pollutant removal plants to water resource recovery facilities (WRRFs). The aim of this paper is to provide an overview of the demonstration case studies at the Marineo and Corleone WRRFs in Sicily (IT), with the final aim showing the effectiveness of the resources recovery systems, as well as the importance of plant optimization to reduce greenhouse gas (GHG) emissions from WRRFs. This study is part of the H2020 European Project “Achieving wider uptake of water-smart solutions—Wider-Uptake”, which final aim is to demonstrate the water-smart solution feasibility in the wastewater sector. The main project goal is to overcome the existing barriers that hamper the transition to circularity through the implementation of a governance analysis tool. The preliminary actions in the two demonstration cases are first presented, while, subsequently, the water-smart solutions to be implemented are thoroughly described, highlighting their roles in the transition process. The achieved preliminary results underlined the significant potential of WRRF application, a great chance to demonstrate the feasibility of innovative solutions in the wastewater sector to overcome the existing social, administrative and technical barriers.

Resource recovery from wastewater treatment is the key for sustainable environment management. Treated wastewater (TWW) represents a promising opportunity not only as irrigation water but also as a source of nutrients that can be recovered with adsorbent materials, such as biochar and zeolite. These materials efficiently adsorb phosphate and ammonium, respectively, from wastewater, and once enriched can act as soil fertilizer. This study investigated, the impact of PO₄^3--enriched biochar and NH₄⁺-enriched zeolite, combined or not with treated wastewater (TWW) irrigation, on soil fertility and growth of tomato plants, through a pot experiment. Five treatments were tested: control soil irrigated with tap water, soil amended with enriched biochar and zeolite with tap water or TWW, and soil amended with natural biochar and zeolite with TWW. After 80 days, shoot dry weights of tomato plants showed no significant differences across treatments. However, root dry weights decreased in plants irrigated with TWW, whether unamended or amended with natural biochar and zeolite. The TWW irrigation, both with and without enriched amendments improved soil total N and available P by 22 and 15 %, respectively, but increased soil salinity, as evidenced by 27 % rise in electrical conductivity. However, enriched and natural biochar and zeolite effectively mitigated salinity effect, promoting a more salinity-tolerant microbial community, and increasing microbial biomass carbon. These results support the integrated use of TWW with nutrient-enriched amendments to support the transition to a circular economy in the water sector.