Oxidation of diatrizoate in aqueous phase by advanced oxidation processes based on solar radiation

• Direct photolysis by solar irradiation shows a low effectiveness in DTZ degradation.
• The solar radiation/K2S2O8 system yields low percentage degradation.
• Processes with iron salts permit total DTZ degradation.
• DTZ degradation products were detected for each process.
• Degradation byproducts are more toxic than the baseline product.

The aim of this study was to investigate the use of solar radiation to treat recalcitrant pollutants, using sodium diatrizoate (DTZ), an ionic X-ray contrast media, as reference compound. The effectiveness in DTZ removal was compared among solar radiation, H2O2, solar radiation/H2O2, K2S2O8, solar radiation/K2S2O8, Fenton, solar radiation/Fenton, Fenton-Like, and solar radiation/Fenton-Like systems. Using direct DTZ photolysis, the percentage DTZ degradation is low and independent of the medium pH, but not of the irradiance level. However, in the presence of radical-promoting species, 100% DTZ degradation is achieved. Results obtained with solar radiation/Fenton and solar radiation/Fenton-like systems suggest that the formation of peroxo and iron hydroperoxy complexes susceptible of absorbing radiation in the solar radiation area represents a new source of OH and/or OH2 radicals in the medium, favoring DTZ degradation. The byproducts formed in each process and the post-treatment medium toxicity were studied, observing an increased toxicity after all oxidation treatments, indicating that the degradation products generated are more toxic than DTZ. Moreover, a direct relationship was found between percentage DTZ degradation and aqueous medium toxicity.

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