Photocatalytic removal of the antidepressant fluoxetine from aqueous media using TiO2 P25 and g-C3N4 catalysts

Abstract

In the present work, photocatalysis using TiO2 P25 and g-C3N4 was utilized to remove the commonly detected antidepressant fluoxetine (FLX) from aquatic media. Experiments were conducted both on lab-scale using ultrapure water and on pilot-scale using real secondary treated hospital wastewater (HWW). The results revealed that TiO2 P25 is more efficient in removing FLX in both lab and pilot-scale experiments (klab = 3.9 × 10−2 min−1 & kpilot = 2 × 10−2 min−1) compared to g-C3N4 (klab = 10−4 min−1 & kpilot = 10−2 min−1). Through the application of liquid chromatography-high-resolution mass spectrometry (LC-HR-MS-Orbitrap), a total of thirteen different transformation products (TPs) of FLX were tentatively identified, and transformation pathways were proposed per photocatalyst case. Ιn-vitro assessment results revealed that the ecotoxicity levels initially began to increase in both of the applied photocatalytic processes, while significant detoxification was achieved only when TiO2 P25 was used. Interestingly, the in-silico toxicity assessment tools predicted that none of the TPs were more toxic than FLX, and thus the initial increase in toxicity was attributed to possible synergistic effects between them or the formation of toxic non-identified TPs. Furthermore, the bioconcentration factor for each TP was estimated to be significantly lower than that of the parent compound, indicating that photocatalytic oxidation can indirectly limit the accumulation of FLX in aquatic organisms. Finally, the pilot-scale results were rather promising, as the applied processes seems to have the potential to efficiently remove FLX from the complex HWW matrix under reasonable irradiation periods, thus paving the way for future larger scale applications.