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

Abstract

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 I-DBPs 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•- 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 μM 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.