Comparative study of oxidative degradation of sodium diatrizoate in aqueous solution by H2O2/Fe2+, H2O2/Fe3+, Fe (VI) and UV, H2O2/UV, K2S2O8/UV

• Systems based on ferrate salts are strongly dependent on the solution pH.
• Fenton-like system is more efficient than Fenton system in removal of diatrizoate.
• UV/K2S2O8 system is a promising process to remove pharmaceuticals in natural water.
• Natural organic matter improves the efficiency in systems using UV radiation.

This study centers on Advanced Oxidation Processes (AOPs) based on the use of iron salts and ultraviolet (UV) radiation for the removal of diatrizoate (DTZ) contrast medium, selected as a model compound resistant to all conventional natural and waste water treatment methods. We studied the effectiveness of Fenton’s reagent, Iron (III) and Iron (VI) salts, and oxidation processes based on the use of UV radiation, UV/H2O2 and UV/K2S2O8, for the degradation of DTZ in aqueous medium. With Fenton’s reagent, the percentage DTZ removal was independent of the initial Fe2+ concentration and was most influenced by the initial hydrogen peroxide concentration. In contrast, the Fenton-like system was affected by both initial Fe3+ and H2O2 concentration. The effects of ferrate salt-bases methods were highly dependent on the solution pH, and a higher rate constant (1.74 × 102 M−1 s−1) was obtained when dihydrogen ferrate species predominated in the medium. The UV/H2O2 system was strongly dependent on the pH and initial H2O2 concentration, showing a favorable synergic effect at H2O2 concentrations <10.0 mM. The UV/K2S2O8 system proved to be more effective than the UV/H2O2 system, with higher rate constants, which were 24.0% higher for pH = 6.5 and [DTZ]0 = 25 mg L−1. Study of the influence of the matrix on these AOPs revealed a markedly higher percentage DTZ removal and reaction rate in surface water with the UV radiation-based systems than with the iron salt-based systems. According to the total organic carbon values obtained, a high degree of mineralization was only attained with the UV/K2S2O8 system.