Degradation of pharmaceuticals in UV/H₂O₂ process: EEM-based kinetic model, transformation products and corresponding toxicity evaluation

Advanced oxidation process (AOP) by UV/H2O2 presented excellent performance on removing trace pharmaceuticals in wastewater. Monitoring the removal efficiency of pharmaceuticals rapidly can evaluate the effectiveness of UV/H2O2 process. And evaluating the potential risks of this technology is essential to facilitate its engineering application. In this study, diclofenac, ibuprofen, naproxen, carbamazepine and citalopram, which have potential biological effect to ecological environment, were degraded by UV/H2O2 in wastewater. Results suggested that UV/H2O2 could degrade 5 pharmaceuticals effectively. An EEM-based degradation kinetic model was constructed by combining pseudo first-order kinetic patterns of pharmaceuticals degradation and multiple exponential decay pattern of fluorescence degradation. This model could estimate the removal of pharmaceuticals rapidly and exhibited excellent predictive capability (R-2 values > 0.90). Based on suspect and untargeted screening, 40 transformation products (TPs) were identified, with hydroxylation, (de)methylation and decarboxylation being the dominant pathways. Among them, 20 TPs were newly discovered. Furthermore, the predicted toxicity results from Ecological Structure-Activity Relationship (ECOSAR) model suggested that 37.5%- 42.5% of TPs exhibited higher toxicity than parent compounds. The increased toxicity of TPs of DCF and IBP could be attributed to decarboxylation. This study provides a promising and rapid method for monitoring the degradation of pharmaceuticals and estimating the toxicity of TPs. These findings facilitate further evaluation of the practicality and risks associated with the UV/H2O2 process for pharmaceutical removal in wastewater.