Iodinated disinfection byproduct formation in a MnO2/I−/EPS system

Abstract

Manganese dioxide (MnO2) is a Mn deposit widely accumulated in the corrosion layer of pipelines, and iodide (I−) is a halogen ion frequently detected in waters. The biofilm dwelling on the corrosion scales often secretes extracellular polymeric substances (EPS) into drinking water. The paper aimed to study the I− oxidation by MnO2 and iodinated disinfection byproducts (I-DBPs) formation with biofilm EPS as a precursor. More than 93% of formed free iodine was finally converted into organic iodine in the MnO2/I−/EPS system. Compared with humic acid, EPS had a lower carbonaceous I-DBPs (C-IDBPs) formation while a higher nitrogenous I-DBPs (N-IDBPs) formation. The formation of iodomethanes (I-THMs), iodoacetonitriles (I-HANs) and iodoacetic acids (I-HAAs) decreased with the increase of pH due to the weakening of polarization effect and redox potential, while the iodoacetamides (I-HAcAms) formation achieved the maximum at pH 6.0 due to the difference between the hydrolysis rate of I-HANs and decomposition rate of I-HAcAms. The I-DBPs formation was positively correlated with I− concentration, while negatively correlated with MnO2 dose. Protein components displayed a higher formation of N-IDBPs and C-IDBPs than polysaccharide components due to higher nitrogen proportion and more iodination sites. Among 20 protein monomers, aspartic acid was considered as the most important precursor of the four investigated I-DBPs species. The paper is helpful to understand the I-DBPs formation when I− in the bulk water come into contact with Mn deposits attached by biofilm.