Comparison of Different Advanced Oxidation Processes (AOPs) and Photocatalysts for the Degradation of Diclofenac

Diclofenac sodium salt was photodegraded by means of advanced oxidation processes (AOPs), such as Fenton, photo-Fenton and heterogeneous photocatalysis. For the latter different photocatalysts were compared, namely commercial titania P25 and titania metallized with gold (0.1 % Au/P25), silver (1 % Ag/P25) and palladium (0.1 % Pd/P25). Homogeneous treatments demonstrated effective in the degradation of the selected pollutant (>80 % conversion @2 h) when the irradiation occurred within the solution. Also, photo-Fenton process assisted by visible light rather than UV was effective but slower and characterized by a toxicity of the residual solution due to unreacted H2O2. The photocatalyzed treatment performed at its best when P25 was used (70 % conversion @2 h), while modified photocatalysts reached the same conversion when H2O2 was added to the solution. Overall, in vitro toxicity tests using Daphnia Magna unveiled that the wastewater treated via M/TiO2 treatment and photo-Fenton under UV in combination with H2O2 showed an acute toxicity comparable with the control group (almost 100 % viability @48 h). Conversely, the other processes failed to degrade completely either the pollutant or the hydrogen peroxide, leading to the mortality of 30–80 % of the individuals. An important outcome of the work is the direct comparison of different treatments to optimise the outcome, i. e. rapidity of degradation and non toxicity of the treated solution for living bodies.