Deciphering iopamidol transformation during the joint disinfection of monochloramine and peroxymonosulfate: A base-catalyzed mutual activation

The joint disinfection of monochloramine (MCA) and peroxymonosulfate (PMS) can combine the advantages of both sides; and the iodine-containing micropollutants are widely present in drinking water. For the first time, the conversion of iopamidol (IPM) was investigated in the MCA/PMS system. For IPM degradation, the observed pseudo-first-order rate constant ( k obs ) was 0.0076 min −1 , and the apparent rate constant ( k app ) was 6.14 × 10 −7  μM −2.16  min −1 . The reaction orders for MCA ( m ) and PMS ( n ) were fitted to be 1.14 and 1.02, respectively. The mutual activation of MCA and PMS was a base-catalyzed reaction, which was highly exothermic and thermodynamically favored with a free energy of − 78.74 kcal/mol. It is believed that Cl • and 1 O 2 contributed to IPM degradation. The k obs value was increased by an alkaline pH and the presence of Cl − , while reduced by the existence of NOM, HCO 3 − and NH 4 + . The N in MCA was converted to NH 4 + -N, NO 2 − -N and NO 3 − -N, and 47.0 % of I in IPM was converted to IO 3 − . In the MCA/PMS system, IPM transformation was mainly via amide hydrolysis, deiodination and substitution reaction by reactive species. The study provides an insight into the fate of iodine-containing micropollutants during the joint disinfection of MCA and PMS.