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Upgrading treated wastewater systems can provide reclaimed water for different uses. In this paper, the potential for wetland creation and maintenance is evaluated. The upgrading treatment consists of intensified vertical flow constructed wetlands (VFCWs), where the physicochemical and microbiological water quality is improved, followed by free-water surface constructed wetlands (FWSCWs), where biodiversity is enhanced. This renaturalization system has been implemented in two wastewater treatment plants (WWTPs): Monasterios, where one VFCW 60 m2 and two FWSCWs (50 m2 each) have been built, and Carricola, where two VFCWs in series (20 m2 each) have been constructed. The VFCWs were filled with drinking water treatment sludge (DWTS), a waste produced in drinking water treatment plants, hence the circularity of the project. Data obtained during the first year of operation is presented. The mean hydraulic loading rates in the VFCWs were 0.79 and 0.62 m/d in Monasterios and Carricola, respectively. In FWSCWs, the HLRs were 0.35 and 0.32 m/d in FWSCW1, which receives the effluent of the VFCW, and FWSCW2, which receives the secondary treatment effluent, respectively. In the VFCWs, an important reduction of total phosphorus was achieved, 77% in Monasterios and 70% in Carricola, and other pollutants were fairly reduced as well. In FWSCWs, some pollutants, such as total nitrogen or phosphorus, were reduced, but other, such as total suspended solids or organic matter, increased due to algae growth and external inputs. The critical point is that biodiversity is increased thanks to these systems, aquatic invertebrate presented better diversity indexes in the FWSCW receiving the upgraded water from the intensified VFCW. Birds, amphibians, and reptiles have also colonised the created habitats. • Treated wastewater can be upgraded by intensified vertical flow constructed wetlands. • Drinking water treatment sludge is an appropriate adsorbent material. • Valorisation of drinking water treatment sludge integrates circularity in urban water cycle. • Upgraded water benefits the receiving water bodies, enhancing biodiversity. • Birds use the created wetlands to feed, rest and nest. [ABSTRACT FROM AUTHOR]

Managed treatment wetlands technology is now used around the world to treat wastewater and stormwater by removing nutrients and other contaminants to obtain a desired water quality. In this paper we present a brief review of a large-scale application of the nature-based technology known as stormwater treatment areas (STAs). These STAs were constructed to treat agricultural and urban runoff to reduce outflow total phosphorus (TP) concentrations to <20 μg P L−1, which is required to protect downstream water quality and preserve the remaining Everglades ecosystem. Five STAs with a total area of approximately 25,000 ha were built at strategic locations to reduce TP loads to the Everglades Protection Area. For the past three decades, these Everglades STAs have done remarkable job by 70 to 85% TP load reduction, with an average outflow TP concentrations of 15-40 μg P L−1. In this Everglades STAs special issue, we present research findings on the influence of both external and internal drivers influencing STA performance and potential adaptive management strategies to enhance treatment efficiency to further reduce outflow TP concentrations. • Introduction of the Everglades STAs – largest constructed treatment wetland network in the world. • Everglades STAs serve as 'kidneys' of the Everglades ecosystem by reducing phosphorus loads to downstream waterbodies. • Phosphorus loading is one of the key drivers regulating treatment efficiency STAs. [ABSTRACT FROM AUTHOR]