Activation of ferrate(VI) by sulfite for effectively degrading iodinated contrast media and synchronously controlling I-DBPs formation

Iodinated X-ray contrast media (ICM) are widely detected in the aqueous environment, which pose risks of iodinated disinfection by-products (I-DBPs) in the subsequent disinfection treatment. Herein, a novel advanced oxidation process of ferrate(VI) and sulfite (Fe(VI)/sulfite) was employed in removing ICM and controlling IDBPs formation. The results showed that the Fe(VI)/sulfite process effectively degraded ICM and the removal efficiency of iopamidol (IPM) ranged from 55.4% to 87.7% at pH 6-10 within 120 s. Based on the results of quenching and probing experiments, SO4 center dot- was identified as the predominant oxidant for IPM decomposition at pH 6-10. IPM transformation pathway mainly involved deiodination, hydrogen abstraction, hydroxyl addition, amide hydrolysis, and amino oxidation. The iodine on the benzene ring was released into the solution as I- and then I- was partly oxidized to IO3- during the oxidation of IPM, the concentration of I- and IO3- was 0.34 and 0.13 mu M at pH 6, respectively. Then, the formation of I-DBPs in the subsequent disinfection was investigated. It was found that I-DBPs concentration increased with increasing pH and enlarging Fe(VI) dosage as well as slightly increased in the presence of humic acid. Additionally, when solutions were filtered at pH 6 after oxidation, the removal ratios of I- and IO3- were 41.2% and 53.8%, respectively. Because the generated I- and IO3- were adsorbed by in-situ formed ferric (oxyhydr)oxides from Fe(VI) reduction, the yield of I-DBPs was thereby reduced in the subsequent disinfection. Therefore, the Fe(VI)/sulfite process can effectively remove ICM and synchronously control I-DBPs formation in the subsequent disinfection.

Automated summary

In this study, the Fe(VI)/sulfite process was used to effectively remove ICM and control the formation of I-DBPs in the subsequent disinfection.