Photo-oxidation of three major pharmaceuticals in urban wastewater under artificial and solar irradiations
Résumé
The conditions of wastewater treatment by photo-oxidation are addressed in this work with the aim of highlighting the importance of the matrix, concentration and cocktail effects of pharmaceutical pollutants very present in wastewater treatment plant. The idea is to operate under real conditions, i.e. effluent from the WWTP, representative concentrations and natural irradiation. Photospheres are micrometric glass spheres coated with TiO2 which have the particularity to float and therefore be much easier to separate from treated water during photocatalysis. Three pharmaceutical target molecules were chosen: carbamazepine (CBZ), diclofenac (DCF) and ibuprofen (IBU) to evaluate, in a controlled 2 L artificial UV photoreactor, the individual and coupled effects of three strategic points: i) the matrix effect (tap water vs filtered treated wastewater), ii) the cocktail effect (one molecule vs the three mixed together) and iii) the initial concentration level effect (µg/L vs mg/L). A 300 L solar photoreactor was also designed for this study to evaluate the transferability of performances. Experiments conducted under controlled conditions highlighted that i) the molecule removal was most negatively impacted by the matrix effect, ii) the cocktail effect, even if still negative, appeared to decrease the difference between the degradation rates and iii) initial low concentrations were easier to degrade than higher laboratory concentrations. Transposition to the larger scale solar photoreactor confirmed the order of molecule degradation: DCF > IBU > DCF when alone and DCF > CBZ > IBU when mixed together but also showed that this set up was actually more efficient in the degradation of these molecules than the artificial photoreactor.
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