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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]

This special issue of Ecological Engineering provides an overview of research within the Everglades Stormwater Treatment Areas (STAs) over the past decade to understand the ecology and the biogeochemical processes that affect phosphorus (P) retention in these constructed wetlands. This research was established within the South Florida Water Management District's Restoration Strategies Science Plan (RSSP). The RSSP was developed in 2012, updated in 2018, and produced a total of 21 studies. The goal of RSSP research is improve understanding of the factors contributing to P retention, to support management of the STAs to attain and sustain a stringent outflow total P concentration goal (i.e., the Water Quality Based Effluent Limit or WQBEL) and to maintain the wetland plant communities used to achieve this goal. Compliance with the WQBEL will reduce P loads to the Everglades to support restore and maintain this special ecosystem. This synthesis paper presents an overview of the STAs and their purpose and then summarizes the findings from the publications included in this special issue as well as previous STA related research. From this synthesis, a list of potential management options to enhance P retention in the STAs is presented. • Stormwater Treatment Areas (STAs) built to reduce P in runoff entering the Everglades. • STA discharge must meet strict low P concentration limits. • P biogeochemistry research conducted to support management of the STAs. • P removed by particle settling, biogeochemical processes and plant uptake. • Fauna excretion, bioturbation, and internal loads substantially affect P retention. [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]