Wastewater transfer during dry and wet weather in Parisian combined sewer

The study of wastewater transfer in dry and wet weather was made following various approaches: in dry weather (relationship between pollutant loads and flows, evolution of the nature of particulate and dissolved pollutants, variations of VSS/SS and of SS/TKN_d ratios); in wet weather (evaluation of the proportion of wastewater effluent during the rain event from conductivity and water volumes). Results obtained from dry weather show that the dilution by parasitic waters allows to explain a great part of the concentration variations observed at OPUR outlets. Moreover, the difference in the nature of wastewater produced during the day and the variation in the solid transport capacity, leading to erosion and/or sedimentation can also explain the daily cycles of wastewater concentrations. Indeed, results obtained from wet weather, show, whatever the size of the catchment, that there is direct correspondence between the volumetric and the conductivity methods. This indicates that wastewater volumes, at outlets during rain events, do not appear to be affected by the hydrodynamics of wet weather, whatever the size of the catchment.