Accelerated Degradation of Aqueous Recalcitrant Iodinated Contrasting Media Using a UV/SO32- Advanced Reduction Process

Abstract

Based on the formation of free radical-hydrated electrons by the activation of sulfite (SO32-), the UV/SO32- process is an advanced reduction process that can reduce pollutants. This study investigated the degradation kinetics, mechanism, influencing factors, and degradation pathways of sodium diatrizoate (DTZ), an iodinated contrasting media, during the UV/SO32- process. The degradation kinetics of DTZ were well fitted by the pseudo-first-order model, the degradation rate of which was higher than that of UV only and UV/H2 O2. The degradation rate of DTZ during the UV/SO32- process was positively correlated with the initial SO32- concentration. Weakly alkaline and alkaline conditions promoted the degradation of DTZ, while organic matter inhibited degradation during the UV/SO32- process. The degradation mechanism included direct photolysis and free radical attack, whereby free radical attack played a more important role than direct photolysis. Sulfite radicals dominated DTZ degradation efficiency, and hydrated electrons controlled the deiodination efficiency. The degradation pathways of DTZ during the UV/SO32- process included substitution, decarboxylation-hydroxylation, and amide bond cleavage.