Nature-based solutions coupled with advanced technologies: An opportunity for decentralized water reuse in cities

Decentralized water reuse in cities is a prominent alternative to mainstream top-down models for urban treatment, which are based on centralized, linear dynamics of resource management. In this sense, Nature-based Solutions (“green” technologies) coupled with advanced technologies (“grey” constitute promising approach fomenting onsite treatment and cities, while also providing multiple co-benefits. This article puts forward conceptual advancement by better understanding “green-grey”/“grey-green” (CGGT). To do this, we critically discuss the main reasons pairing these instead using them separately, as well their performance constraints regarding data reporting issues. Moreover, discloses most common configurations, quality parameters being evaluated, potential schemes, costs, energy requirements. A systematic selection analysis scientific articles was carried out end. Of 395 pre-selected articles, only 17 addressed (green-grey/grey-green) wastewaters further or safe discharge onsite. Despite relatively low number 80% were published past five years, showing increased interest novel topic. The selected analysed here present resulting comprehensive Excel database (343 datasets) containing detailed information about design, operation, such systems. Green-grey found be predominant, configuration constructed wetlands followed oxidation process electrochemical studied. Grey normally applied at second stage remove pathogens compliance standards (normally when green alone cannot deliver standards). Meanwhile, commonly used break down slowly biodegradable substances that have not been completely removed grey polishing step following technology). design combining yet fully optimized, since they mainly designed sole forcibly put together treatment. Hence, studies should focus variables influencing functioning whole. Finally, due novelty relevance topic, transparency consistency essential support optimization competitiveness green-grey/grey-green against existing decentralized/centralized approaches.