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

Different advanced oxidation processes (AOPs), such as Fenton, photo-Fenton and heterogeneous photocatalysis have been tested towards the degradation of Diclofenac sodium salt. Toxicity tests performed using Daphnia magna as model species unveiled the type of treatment which allows detoxification of the solution.

Abstract

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.

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