Development and verification of a general approach to describe the efficiency of vortex separators in combined sewer systems

The water framework directive (CEC, 2000) asks for cost-effective measures for achieving good ecological conditions in receiving waters. Because of low operation costs and good pollutant removal efficiency, vortex separators (VS) are an attractive alternative to traditional stormwater tanks. The German design standard for CSO structures, ATV-A 128 (1992), demands long-term pollution load simulations. Today's simulation software, however, considers the removal processes in CSO structures either very rudimentarily or not at all. The higher pollutant removal efficiency of a structure like a VS cannot be taken into account. This might be one reason why VS are used still comparatively scarcely. A mathematical model describing the removal efficiency could increase the acceptance of VS. Several functions describing the removal efficiency have been derived from model tests or large-scale studies within the last few years. Within this paper, the data from three large-scale studies are used to verify the general applicability of one steady-state and one dynamic approach. The results show that the complex processes involved with CSO facilities and the large error related to monitoring make the validation of models a difficult task. Anyhow, especially the dynamic approach was applicable at all considered facilities.