Photocatalytic ozonation to remove the pharmaceutical diclofenac from water: Influence of variables

Photocatalytic ozonation (O3/UVA/TiO2) of diclofenac (DCF), a non-steroidal anti-inflammatory drug (NSAID) and emerging water pollutant, was studied through the influence of some operational variables (gas flow rate, initial concentrations of ozone, DCF and TiO2), ozone consumption and ecotoxicity. Further, the stability and activity of the catalyst was investigated. Both ozone gas and initial diclofenac concentrations highly affected DCF and total organic carbon (TOC) removals while the gas flow rate exerted a negligible influence under the experimental conditions here applied. Complete elimination of DCF was achieved within 6 min and from 60 to 75% of TOC removals were observed after 60 min of reaction regardless of the water matrix used, ultrapure water or urban waste wastewater. Optimum concentration of TiO2 was found between 0.5 and 2.5 g L−1 and ozone consumption around 6 mg per mg TOC consumed was obtained after 30 min of reaction. Daphnia magna exposition to untreated DCF aqueous solution led to 65% of death of these organisms, though after treatment, ecotoxicity levels of 20% were achieved. Photocatalytic ozonation showed the lowest ozone consumption and ecotoxicity compared to the other ozonation systems tested. Moreover, loss in the catalyst activity was not observed after 8 h of use as well as no leaching of Ti was detected.

► Slight positive effect of ozone gas concentration on the DCF and TOC removal rates.
► The higher initial DCF concentration the faster DCF and TOC ozonation rates.
► Photocatalytic ozonation leads to the lowest ozone consumption per mg TOC consumed.
► Photocatalytic oxidation processes studied lead to the lowest ecotoxicity values.