Constructed wetlands for combined sewer over flow treatment: A state-of-the-art review

Combined sewer overflows (CSOs) are a major source of surface water pollution and degradation. This is particularly visible where sewage collectionwith combined sewer and centralized treatment arewell established, such as in Europe and North America: an over whelming number of surface water bodies are in insufficient status of ecology, hydrology and physico-chemical parameters. Therefore, several countries have started implementing constructed wetlands (CWs) as mainstream on-spot treatment. This paper summarizes the main design approaches that can be adopted. We identified eight different schemes for the implementation of CSO-CWs, based on our international experience and documented by a literature analysis. The performance review includes conventional water quality parameters, as well as pathogen and emergent contaminant removal. Furthermore, modelling tools for advanced design and for understanding a wide applicability of these green infrastructures are presented. This paper also provides a review on other side benefits offered by the adoption of Nature-Based Solutions for CSO treatment, such as ecosystem services, and the most common issues related to their operation and maintenance. Our analysis has produced a list of key factors for design and operation, all derived from full-scale installations in operation up to more than ten years. (C) 2020 Elsevier B.V. All rights reserved.