Direct photodegradation of 36 organic micropollutants under simulated solar radiation: Comparison with free-water surface constructed wetland and influence of chemical structure

Micropollutants such as pharmaceuticals and pesticides are still found in treated municipal effluent and are discharged into the natural environment. Natural direct photodegradation may be one pathway for removing these micropollutants in treatment processes such as free-water surface constructed wetlands (CW). This work was set out to evaluate the half-life (t(1/2)) of direct photodegradation of 36 micropollutants under controlled conditions of light exposure close to solar radiation. The results allowed to classify the micropollutants into three groups (fast, medium and slow). Seven micropollutants were classified in the fast group with t(1/2) between 0.05 h and 0.79 h, 24 in the medium group with t(1/2) between 5.3 h and 49.7 h, and five in the slow group with t(1/2) between 56 h and 118 h. The t(1/2) values obtained in laboratory were compared with those from a CW receiving treated wastewater. Correction factors were calculated to adjust the in situ data for the light intensity in laboratory and improved the correspondence especially for the micropollutants of the fast and medium groups. Finally, an innovative method based on statistical tests highlighted the chemical functions characteristic of micropollutants sensitive to photodegradation (OH-(CO)-O-=, (CN)-N-=-O-, =N-OH, -CH=N, -O-(PO)-O-=, -(CC)-C-=-) and with low sensitivity (-O-R, -Cl).