Combined sewer overflows (CSOs) are of major environmental concern for impacted surface waterbodies. In the last decades, major storm events have become increasingly regular in some areas, and meteorological scenarios predict a further rise in their frequency. Consequently, control and treatment of CSOs with respect to best practice examples, innovative treatment solutions and management of sewer systems is an inevitable necessity. As a result, the number of publications concerning quality, quantity and type of treatments has recently increased. This review therefore aims to provide a critical overview on the effects, control and treatment of CSOs in terms of impact on the environment and public health, strict measures addressed by regulations, and the various treatment alternatives including natural and compact treatments. Drawing together the previous studies, an innovative treatment and control guideline is also proposed for the better management practices.

The authors acknowledge the European Union's Horizon2020 research and innovation programme for co-funding INTCATCH innovation action under grant agreement No.689341.