Article révisé par les pairs
Résumé : To understand the effect of combined sewer overflows on the river Seine (France), a characterization of effluent in terms of organic matter and bacterial biomass was carried out during several sampling campaigns performed in a combined sewer located in Parisian suburbs under wet and dry weather conditions. Measurements classically used to study wastewater (suspended matter, chemical oxygen demand [COD] and biochemical oxygen demand [BOD]) were compared with the estimate of biodegradable and refractory fractions of particulate and dissolved organic carbon. Relationships among different parameters used to describe organic material in effluent were established. Even for large fluctuations in organic matter concentrations, highly homogeneous ratios between the different descriptors during wet and dry weather were observed, and no significant differences could be observed in two catchments strongly differing by their sizes. The only two small differences in relative composition that could be observed between dry and wet weather were slightly lower content of organic carbon in suspended solids and a lower biodegradability of this material during rain events. Accordingly, with the help of obtained relationships and values of classical variables like turbidity, BOD, and COD for a given effluent, it is possible to make reasonably accurate estimates of its composition in terms of biodegradable and refractory fractions of dissolved and particulate organic matter and bacterial biomass.