PhD defense : Devenir des résidus médicamenteux et de leurs métabolites au sein des Zones de Rejet Végétalisées

PhD defense : Maximilien NUEL

Team : MecaFlu

Title : Devenir des résidus médicamenteux et de leurs métabolites au sein des Zones de Rejet Végétalisées

Abstract : Wastewater Treatment Plants (WWTP) are considered as one of the most important pharmaceutical compound discharges into the environment, due to incomplete degradation processes. Since 2009, French Water Agencies, promote Surface Flow Treatment Wetlands (SFTWs) at the outlet of WWTPs, between the WWTP and the receiving aquatic environment. In this configuration, they are not considered as a regulatory treatment step. Thus, their removal efficiencies are not well investigated and their design and sizing are empirical. To overcome these lacks of knowledge, the aim of this study was to bring new elements about their global operations and their pollutant removal efficiencies. During two years, the removal efficiencies of two full-scale WWTPs, composed by two stages vertical flow constructed wetland (VFCW) and their SFTW, were monitored thanks to liquid and solid sampling sessions. At the same time, many tracer studies were carry out on three SFWTS, including the two last, to qualify and to quantify seasonal and ageing effects the hydraulic behavior throughout the seasons. The results showed that suspended solid (especially in rainy days), nitrate and total phosphorus are retained in a SFTW (a pond). In contrary, water quality is degraded in a SFTW (a pond fallowing by a vegetated ditch). Actually, this last one study site is almost filled, thus the mean residence time is reduced and should limit degradation processes. In regard to pharmaceutical compounds, SFTW removal efficiency rates ranged from 30 to 70 % with maximum values in summer and minimum values in winter. It can be noted an important number of null values and few releases. The SFTW removal efficiency contributions to VFCW were inferior to 30 %. SFTW (pond fallowing by a vegetated ditch) inflow reductions were correlated with an increase of drug compound concentrations in the outflow. Furthermore, there was a specific absorption of these micro pollutants by plants whereas there were dynamic interactions between sampled mud and drugs residues with an adsorption during summer and a release during winter. Lastly, aging effects by mud accumulation in SFTW, as a pond, was highlighted thanks to seasonal tracer measurement. However the mean residence time of a pond fallowing by the vegetated ditch was more influenced by seasonal weather conditions. We also observed that SFTW (pond) allow a better mitigation of pic tracer (which can be considered to a conservative pollutants) than a SFTW (pond fallowing by a vegetated ditch).

This thesis was supervised by Adrien Wanko, associate professor at the ENGEES.

The PhD defense will be held on Tuesday 19th september 2017 at 2.00pm in the Brunotte amphitheater of the ENGEES (1 quai Koch in Strasbourg).