Degradation of diatrizoate in water by Fe(II)-activated persulfate oxidation

As a type of iodinated contrast medium (ICM), the diatrizoate (DTZ) found in aquatic systems has posed a serious threat to the ecosystem and to human health. In this study, Fe(II)-activated persulfate (Fe2+/PS) oxidation was employed to degrade DTZ, and the optimal operating conditions were determined. Electron paramagnetic resonance (EPR) spectra and density functional theory (DFT) calculations were adopted to determine the dominant radicals and analyze the degradation paths, respectively. It was found that a PS concentration of 10 mmol/L, an n (Fe2+)/n(PS) ratio of 1: 10, an initial pH of 3.0, and a high temperature increased the degradation efficiency of DTZ. After suppression of the oxidation process by tertiary butyl alcohol (TBA) and methanol (MtOH), the EPR spectra demonstrated that DTZ degradation was attributed to the combined effects of SO4-center dot and (OH)-O-center dot and that (OH)-O-center dot played a more important role. Based on the theoretical calculation and comparison of the reduction energies of possible degradation products, the path from DTZ to TP630 and then to TP628 and finally to TP602 was recognized as the main DTZ degradation pathway during the Fe2+/PS oxidation process. These findings validated and demonstrated that DTZ could be effectively degraded by Fe2+/PS oxidation, which is a promising approach to remove DTZ from water.