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Reuse of treated wastewater for irrigation purposes is a measure to reduce water stress and overexploitation of freshwater resources. This study aims to investigate the environmental and economic impacts of a current conventional wastewater treatment plant (WWTP) in Peschiera Borromeo (Milan, Italy), and compare possible scenarios to enable reclaimed water reuse for agriculture. Accordingly, we propose alternative disinfection methods (i.e. enhanced UV, peracetic acid) and replace conventional activated sludge (CAS) with upflow anaerobic sludge blanket (UASB) for biological treatment and use anaerobic membrane bioreactor (AnMBR) as the tertiary treatment. Life cycle assessment (LCA) and life cycle costing (LCC) were implemented on the existing full-scale wastewater treatment line and the hypothetical scenarios. In most cases, the impact categories are primarily influenced by fertilizer application and direct emissions to water (i.e. nutrients and heavy metals). The baseline scenario appears to have the largest environmental impact, except for freshwater eutrophication, human ecotoxicity and terrestrial ecotoxicity. As expected, water depletion is the most apparent impact category between the baseline and proposed scenarios. The UASB+AnMBR scenario gives relatively higher environmental benefits than the other proposed scenarios in climate change (−28%), fossil fuel depletion (−31%), mineral resource depletion (−52%), and terrestrial ecotoxicity compared to the baseline. On the other hand, the highest impact on freshwater eutrophication is also obtained by this scenario since the effluent from the anaerobic processes is rich in nutrients. Moreover, investment and operational costs vary remarkably between the scenarios, and the highest overall costs are obtained for the UASB+AnMBR line mostly due to the replacement of membrane modules (24% of the total cost). The results highlighted the importance of the life cycle approach to support decision making when considering possible upgrading scenarios in WWTPs for water reuse.

The lack scale-up and long-term demonstration in real environment of eco-innovative resource recovery and reuse solutions is one of the main barriers for circular economy principles in wastewater systems management. Within this context, since 2016 the Horizon2020 SMART-Plant Innovation Action (www.smart-plant.eu) is delivering scaled-up solutions in n.6 existing wastewater treatment plants (WWTPs) with the aim to recover and recycle chemicals and nutrients in an energy- and carbon efficient way. In those Water Resource Recovery Facility (WRRFs), besides CaPO4 and struvite, more than 400 kg per week of clean cellulose fibres or cellulosic sludge (Crutchik et al., 2018), more than 1 kg polyhydroxyalkanoates (PHA) per day are to produce sludge-wood-plastic bio-composites, fertilizer and biofertilizers, biomass fuel, sludge-added mortars and cement.

Reuse of treated wastewater for irrigation purposes is a measure to reduce water stress and overexploitation of freshwater resources. This study aims to investigate the environmental and economic impacts of a current conventional wastewater treatment plant (WWTP) in Peschiera Borromeo (Milan, Italy), and compare possible scenarios to enable reclaimed water reuse for agriculture. Accordingly, we propose alternative disinfection methods (i.e. enhanced UV, peracetic acid) and replace conventional activated sludge (CAS) with upflow anaerobic sludge blanket (UASB) for biological treatment and use anaerobic membrane bioreactor (AnMBR) as the tertiary treatment. Life cycle assessment (LCA) and life cycle costing (LCC) were implemented on the existing full-scale wastewater treatment line and the hypothetical scenarios. In most cases, the impact categories are primarily influenced by fertilizer application and direct emissions to water (i.e. nutrients and heavy metals). The baseline scenario appears to have the largest environmental impact, except for freshwater eutrophication, human ecotoxicity and terrestrial ecotoxicity. As expected, water depletion is the most apparent impact category between the baseline and proposed scenarios. The UASB + AnMBR scenario gives relatively higher environmental benefits than the other proposed scenarios in climate change (−28%), fossil fuel depletion (−31%), mineral resource depletion (−52%), and terrestrial ecotoxicity compared to the baseline. On the other hand, the highest impact on freshwater eutrophication is also obtained by this scenario since the effluent from the anaerobic processes is rich in nutrients. Moreover, investment and operational costs vary remarkably between the scenarios, and the highest overall costs are obtained for the UASB + AnMBR line mostly due to the replacement of membrane modules (24% of the total cost). The results highlighted the importance of the life cycle approach to support decision making when considering possible upgrading scenarios in WWTPs for water reuse.

This prospective study was critically assessed the EU directives, regulations and standards to reveal the barriers, pros and cons for integration of nature-based solutions within the concept of closed water loops approach developed by HYDROUSA project. The project aim to solve issues related to the water supply, the wastewater problem, the biodiversity and nutrient loss, by means of the implementation of six innovative technology solutions. In this work, proposed technologies were assessed to evaluate how their implementation is supported by the European Legislative Framework and if constrains or obstacles are detected for the replicability of the technologies. Main results of the Legislative analysis highlighted that no relevant barriers prevent the implementation of the HYDROUSA technologies in the European context and thus the replicability can be studied at further national level.

Water supply and reuse through non-conventional water resources can significantly decrease the stress on natural water resources. Decentralized systems can help not only to alleviate issues of water security in arid areas, but also to create a sustainable framework within a circular economy. Although these small-scale innovative technologies are able to achieve ready-to-use, high quality of recovered/treated water on-site, the loop cannot be closed in most cases due to legislative barriers. Similarly, the end-use of sewage sludge after treatment in decentralized systems still lacks specific regulations that limit its valorization. This work analyzes the current policy and legislation related to water supply, wastewater treatment, water reuse, and resource valorization within the context of decentralized state-of-the-art technologies applied in rural areas. The drawbacks in the current EU legislation that set barriers to close water-related loops in European countries are highlighted. A regulatory fitness check is applied to each type of loop to identify the key factors to accomplish the legislative compliance, and financing pathways are further evaluated at the EU level. As a possible solution, further development of an innovation deal approach is recommended to address the environmental, regulatory, and financial gaps in water management through an integrated framework, providing ad-hoc policies and prescriptions for the sustainable reuse of all water resources., This work was supported by the Innovation Action project "Demonstration of water loops with innovative regenerative business models for the Mediterranean region - HYDROUSA" which has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 776643.