Mineralization and photodegradation of oxytetracycline by UV/H2O2/Fe2+ and UV/PS/Fe2+ process: quantification of radicals

In this study, different oxidation processes UVA-365 nm (photolysis), UV-A/H2O2, UV-A/H2O2/Fe2+, UV-A/S2O8, and UV-A/S2O8/Fe2+ were investigated to compare removal rates efficiencies of Oxytetracycline (OTC). The role of the initial concentration of oxidants, as well as their inhibitory threshold regarding degradation and mineralization of OTC, was investigated at different pH. It was found that the initial pH solution had an important role in the photolysis of OTC, since in alkaline solutions, the degradation rate was faster than in acidic solutions, but in terms of mineralization yield, it did not exceed 3%. The addition of oxidants (H2O2, S2O8) had an impact on the mineralization, which reached 50% for the UV/S2O8 system. To improve mineralization, ferrous ions were added to UVA/oxidants, leading to 85% mineralization. Quantification of the main radicals involved in the oxidation process can help in the understanding of the free radical mechanism and their respective contributions to the degradation of OTC. The ability of Dimethylsulfoxide (DMSO) to act as a free radical scavenger was considered in UV/H2O2 and UV/H2O2/Fe2+ systems. The hydroxyl radicals can react directly with DMSO to produce a stable intermediate, methanesulfonate. Otherwise, isopropanol, tert-butanol and 1,4, benzoquinone were used as indirect methods to catch and to quantify the main radicals generated during UV/S2O8 and UV/S2O8/Fe(2+)processes. Finally, the results allowed to quantify the contributions of each radical involved in photo-oxidation for both systems, UV/H2O2 and UV/ S2O8.

Automated summary

Different oxidation processes were studied to compare the removal efficiency of Oxytetracycline (OTC). The initial pH solution was found to have an important role in the photolysis of OTC. The addition of oxidants had an impact on mineralization. Quantification of the main radicals involved in the oxidation process was performed.