Photodegradation Kinetics of Organic Micropollutants in Water
Résumé
The widespread use of organic compounds in daily products such as cosmetics, shampoos, pharmaceuticals or laundry detergents contributes to the continuous contamination of urban effluents. Many of these pollutants pass through classic wastewater treatment plants without substantial removal. Understanding the fate of pollutants during tertiary treatment processes initially dedicated to disinfection purpose and their transport in receiving water is essential to maintain water quality in downstream ecosystems. This work aims at studying the photodegradation rate constants and the degradation byproducts of musks (AHTN, HHCB), sunscreens (EHMC, OC), hormones (E1, E2, EE2) and pharmaceuticals (Carbamazepine, Ketoprofen, Ofloxacin, Oxazepam) when exposed to solar irradiation in simulated summertime (24 h;44 mW/cm²) and wintertime (21 mW/cm²), UVc irradiation (2h;0.75 mW/cm²) and UVc irradiation in the presence of H2O2 (45 mg/L). Irradiation experiments were carried out in ultrapure water, acidified water (3 mg/L performic acid), filtered (< 0.45 μm) and unfiltered wastewater. Aliquots of the irradiated samples were collected at specific times and internal standards were added. Half the aliquots were extracted in Ethyl Acetate and analysed by Gas Chromatography Mass Spectrometry (GC-MS) for musks and sunscreens. The other half was directly analysed by Liquid Chromatography tandem Mass Spectrometry (LC-MS-MS) for pharmaceuticals and hormones. First results in ultrapure water showed solar irradiations were efficient to remove Ofloxacin and Ketoprofen (>95% in 24 hours) while UVc irradiations highly degraded AHTN, E1 and Ketoprofen (>90% in 2 hours). In the presence of H2O2, UVc irradiations allowed the degradation (>90%) of all studied compounds. Obtained results gave important information on the efficiency of tertiary treatments in reducing domestic pollution. Calculated half-lives of studied micropollutants allowed to estimate the capacity of an aquatic system in recovering from disturbance and helped in understanding their potential dispersion pattern from a point source