The role of constructed wetlands in a new circular economy, resource oriented, and ecosystem services paradigm.

Wastewater management is included in one of the 17 Sustainable Development Goals (SDGs): SDG 6 is dedicated to water and sanitation and sets out to "ensure availability and sustainable management of water and sanitation for all". SDG 6 expands the Millennium Development Goals (MDGs) focus on drinking water and basic sanitation to now cover the entire water cycle, including the management of water, wastewater and ecosystem resources. A UN report in 2017 states that likely over 80% of the wastewater worldwide is still discharged without adequate treatment. In several countries the wastewater management is nowadays a norm, but still there are open discussions about the kind of approach to be adopted, i.e. centralisation vs. decentralisation. The choice of the adopted technologies is strictly linked to environmental performances and economical aspects; one of the possible causes for the still enormous amount of untreated wastewater discharged into the environment can be the low "willingness to pay" for this kind of service and therefore a great focus should be given to all the technologies that are able to lower the treatment costs still maintaining reliable and robust performances in the long term. When considering wastewater as a carrier of valuable primary chemicals that can be easily converted to marketable products (fertilisers, bio-plastics, soil conditioners, biofuels, etc.), and as well as a relevant source of "new water" to be used for specific purposes, wastewater and runoff management can be highlighted as one of the most exciting challenges and occasions for a sustainable development in the near future. The paper aims to clarify the future role of CWs in circular economy, resource-oriented, and ecosystem services approaches, which want to respond to sanitation worldwide and the future research needs. We give an overview on how the conventional wastewater treatment scheme (what we call "waste paradigm") should move towards more sustainable water and biogeochemical cycles following the new resource-oriented, circular economy and ecosystem service views. On this basis, we review the potential application of CWs within this new, and needed, paradigm. Finally, a meta-analysis shows that the scientific community involved in CWs should put more effort in making CWs more suitable for these new tasks.