Manganese dioxide (MnO 2 ) 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 MnO 2 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 MnO 2 /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 MnO 2 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.
Iodinated disinfection by-products (I-DBPs) have raised concerns due to their potential cytotoxicity and genotoxicity compared to chlorine and bromine-based by-products. In aquaculture, high-dose iodine-based disinfectants can react with natural organic matter (NOM) in water, generating significant amounts of I-DBPs that might pose environmental risks. This research explored the reaction characteristics of I-DBPs by using two commonly used iodine-based disinfectants (iodine tincture and Polyvinylpyrrolidone-iodine (PVP–I)) in aquaculture. The results indicated that controlling pH at around 8.0 effectively reduced I-DBP formation. A higher concentration of PVP-I (10 μM) was required to produce triiodomethane (TIM) compared to iodine tincture (2.5 μM), likely due to the slower release of iodine from PVP-I. The concentrations of I-DBPs showed a multiplicative growth trend as the concentrations of the iodine-based disinfectants increased. Humic acid (HA) demonstrated a stronger potential for I-DBP formation than algal-derived organic matter (AOM), including extracellular organic matter (EOM) and intracellular organic matter (IOM), due to its strong electron-withdrawing aromatic structure. While EOM led to a greater variety of I-DBPs, IOM contributed more significantly to TIM formation at higher disinfectant concentrations, probably due to its large molecular size and abundance of reactive carbon atoms. The I-DBP formation patterns in the aquaculture water are similar to those of HA, possibly due to the presence of similar compositional components, such as lignin and proteins. The study provides important insights for optimizing iodine disinfectant use in aquaculture and managing I-DBP risks.
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