Dynamics of pollutant discharge in combined sewer systems during rain events: chance or determinism?

International audienceA large database of continuous flow and turbidity measurements cumulating data on hundreds of rain events and dry weather days from two sites in Paris (called Quais and Clichy) and one in Lyon (called Ecully) is presented. This database is used to characterize and compare the behaviour of the three sites at the inter-events scale. The analysis is probed through three various variables: total volumes and total suspended solids (TSS) masses and concentrations during both wet and dry weather periods in addition to the contributions of diverse-origin sources to event flow volume and TSS load values. The results obtained confirm the previous findings regarding the spatial consistency of TSS fluxes and concentrations between both sites in Paris having similar land uses. Moreover, masses and concentrations are proven to be correlated between Parisian sites in a way that implies the possibility of some deterministic processes being reproducible from one catchment to another for a particular rain event. The results also demonstrate the importance of the contribution of wastewater and sewer deposits to the total events' loads and show that such contributions are not specific to Paris sewer networks

Biofiltration vs conventional activated sludge plants: what about priority and emerging pollutants removal?

International audience: This paper compares the removal performances of two complete wastewater treatment plants (WWTPs) for all priority substances listed in the Water Framework Directive and additional compounds of interest including flame retardants, surfactants, pesticides, and personal care products (PCPs) (n = 104). First, primary treatments such as physicochemical lamellar settling (PCLS) and primary settling (PS) are compared. Similarly, biofiltration (BF) and conventional activated sludge (CAS) are then examined. Finally, the removal efficiency per unit of nitrogen removed of both WWTPs for micropollutants is discussed, as nitrogenous pollution treatment results in a special design of processes and operational conditions. For primary treatments, hydrophobic pollutants (log K ow > 4) are well removed (>70 %) for both systems despite high variations of removal. PCLS allows an obvious gain of about 20 % regarding pollutant removals, as a result of better suspended solids elimination and possible coagulant impact on soluble compounds. For biological treatments, variations of removal are much weaker, and the majority of pollutants are comparably removed within both systems. Hydrophobic and volatile compounds are well (>60 %) or very well removed (>80 %) by sorption and volatilization. Some readily biodegradable molecules are better removed by CAS, indicating a better biodegradation. A better sorption of pollutants on activated sludge could be also expected considering the differences of characteristics between a biofilm and flocs. Finally, comparison of global processes efficiency using removals of micropollutants load normalized to nitrogen shows that PCLS + BF is as efficient as PS + CAS despite a higher compactness and a shorter hydraulic retention time (HRT). Only some groups of pollutants seem better removed by PS + CAS like alkylphenols, flame retardants, or di-2-ethylhexyl phthalate (DEHP), thanks to better biodegradation and sorption resulting from HRT and biomass characteristics. For both processes, and out of the 68 molecules found in raw water, only half of them are still detected in the water discharged, most of the time close to their detection limit. However, some of them are detected at higher concentrations (>1 μg/L and/or lower than environmental quality standards), which is problematic as they represent a threat for aquatic environment

Typology of roofing materials and evaluation of their pollutant potential

A Paris, les eaux de ruissellement de toitures ont été identifiées comme contribuant largement aux fortes concentrations en éléments traces métalliques (ETM) dans les rejets urbains de temps de pluie. Lévaluation des flux dETM issus des toitures est donc nécessaire, tant à léchelle du toit lui-même quà léchelle, plus large, de la zone daménagement ou du bassin versant. Nos travaux ont débuté par une typologie des toits de la région Île de France, tant concernant les matériaux que leur mise en uvre. Il apparaît alors que tous les types de toits sont susceptibles de relarguer des ETM. Une première modélisation des flux métalliques à léchelle du toit a été testée. Les résultats, bien quencourageants, mettent en évidence un manque de données concernant les mécanismes et taux de relargage pour de nombreux matériaux. A léchelle du bassin versant, un travail sappuyant sur des banques de données urbaines existantes et des photographies aériennes BD Ortho de lIGN et utilisant un logiciel de classification dimage nous a donné des résultats prometteurs quant à la classification automatique des types de toits