Sewer networks are nowadays considered as biochemical reactor and their overflows contribute to the alteration of the receiving waters. So a research project aims at improving the knowledge of solids dynamics as contributors to pollutant fluxes. Therefore, a preliminary experimental study was conducted in a combined sewer of Nantes (France), from March to August 2010, by dry weather conditions. It consisted of measurements of global parameters and concentrations of major ions, trace metals and sulphur species in wastewater but also at the interface with the sediment. The main finding was the evolution of global parameters (pH, conductivity, Eh) at the water-sediment interface in relationship with the profile of sulphur species, indicating the synthesis of hydrogen sulphide by sulfate-reducing bacteria at the interface and in relationship with the history of the deposit. Moreover the vertical gradient of trace metals is strongly related to those of total suspended solids.
