Photocatalytic degradation of non-steroidal anti-inflammatory drugs with TiO2 and simulated solar irradiation

The aim of this work is to evaluate and compare the degradation achieved for three non-steroidal anti-inflammatory drugs (NSAIDs) by heterogeneous TiO2 photocatalytic means in aqueous solution at laboratory scale. The selected pharmaceutical compounds were diclofenac (DCF), naproxen (NPX) and ibuprofen (IBP). These compounds were used in their sodium salt chemical form. Previous experiments (adsorption, photolysis and thermodegradation) were developed to evaluate non-catalytic degradation for each NSAID. Photocatalytic experiments were carried out in a Xe-lamp reactor in order to study the influences of different operational conditions (catalyst load, temperature and dissolved oxygen concentration). These results showed that the optimum amount of TiO2, to achieve maximum degradation, of IBP was 1 g/L. In contrast, the maximum degradation for DCF or NPX was observed at a TiO2 loading of 0.1 g/L. Temperature had a significant effect only for NPX degradation, achieving almost 99% phototransformation. No significant differences were observed for DCF and IBP at 20, 30 and 40 °C. Dissolved oxygen concentration was an important parameter to increase the degradation for NPX and IBP. However, it was observed that its rate of mineralization did not increase. Intermediate metabolites were detected in all cases. Hydroxyl metabolites were the most important residual compounds after the photocatalytic treatment of IBP. The inhibition percentage of bioluminescence from Vibro fischeri—as a toxicity parameter—increased during the irradiation time due to the residual concentration of the hydroxyl metabolites generated. However, after 120 min, in experiments with 40 mg/L of dissolved oxygen, a decrease of the % inhibition was observed. Only photocatalytic treatment of IBP drives to a satisfactory biodegradability index BOD5/COD (between 0.16 and 0.42) and, only in this case, a post-biological treatment could be suggested.