Fe3+-enhanced zero valent iron/peroxymonosulfate (ZVI/PMS) process for the transformation of iopamidol during coagulation and reduction of iodinated disinfection by-products

Abstract

The traditional coagulation process in drinking water treatment cannot effectively remove the organic precursors of highly toxic iodinated disinfection by-products (I-DBPs). This study proposes a combination of zero-valent iron (ZVI) and peroxymonosulfate (PMS) to remove the organic precursor of I-DBPs during the coagulation stage. This study investigated the degradation of iopamidol (IPM), a typical organic precursor of I-DBPs, by the combination of ZVI/peroxymonosulfate (PMS) and the influence on the generation of I-DBPs during disinfection. IPM was effectively decomposed by ZVI/PMS, because of the formation of hydroxyl (HO•) and sulfate (SO4•−) radicals. SO4•− was a major contributor (>64.7 %) to the degradation. The anions (Cl− and SO42−) in the conventional coagulants have a weak effect on the removal of IPM by the ZVI/PMS process, while the common cations (Fe3+) further enhance the removal of IPM by the ZVI/PMS process. The formation of I-THMs was obviously decreased during the chlorination of IPM in the presence of the ZVI/PMS process (14.4 μg/L) compared to that in the presence of the ZVI process (258.1 μg/L) and the chlorination alone process (29.7 μg/L). The formation of I-THMs was increased by more than 1.7-fold in the presence of natural organic matter (NOM). The presence of Fe3+ further reduced the formation of I-DBPs to below the limit of quantitation (LOQ). Therefore, it is feasible to use the ZVI/PMS process to degrade IPM in the coagulation stage of drinking water treatment, and it can also reduce the I-DBPs formed by subsequent disinfection.