Research On Formation Rules Of Iodinated Products For Three Emerging Aromatic Contaminats In Monochloramine Conditions

As a alternative disinfectants of chlorine, monochloramine has gained increasing attentions due to its less formation of trihalomethane(THMs) and haloacetic acid(HAAs). When water containing iodide was treated with monochloramine, reactive iodide species(RIS), like hypoiodous acid(HOI), is quickly formed via the fast reaction between monochloramine with iodide. Aromatic iodinated disinfect byproducts(I-DBPs) will then subsequently be formed when phenolic pollutants is coexisted in the monochloramine/iodide conditions.Those products were reported to be more toxic than reported iodoacetic acid, whose toxicity is already very high.Unfortunately, however, there is fewer studies about the formation patterns of those products during monochloramine disinfection process.This paper investigated the impacts of iodide on the transformation of three emerging organic pollutants, i.e.bisphenol A(BPA), triclosan(TCS) and methyl paraben(4-Me P) in monochloramine conditions, including the transformation kinetics aspect and the products aspect. In kinectics part, impacts of iodide concentrations and p H on transformation kinetics during monochloramine were investigated and the kinetics between HOI and those compounds were also conducted. In products part, reaction products between HOI and those compounds were detected and the possible reaction pathways were also tentatively presented.Experimental results indicated that iodide addition greately enhanced the transformation rate of compounds during monochloramine and the degree of this enhancement increases with the increasing of iodide concentration.Take BPA for example, at p H=7, BPA transformed less than 10% after 30 min reaction during monochloramine; while transformation reached 40% after 1min when 5μm iodide was added to the solutions, the transformation even reached to 60% after 1min when 10μm iodide was added. Meanwhile, p H showed influence on the initial transformtion rate of those compound during monochloramine/iodide conditions, which probably related to the reaction rates between monochloramine with iodide to form HOI and the reaction rates bewteen HOI with those compounds.Kineitcs experiments suggested that hypoiodous acid(HOI) showed high reactivity towards those three compounds and the apparent reaction rates(kapp) showed great dependence toward p H.For BPA, the kapp increase with the increasing of p H and reached the highest at p H=10 to 5.15×107 M-1s-1. Classic acid-base model perfectly fitted the relationships between kapp of HOI with BPA and p H. For TCS and 4-Me P, kapp reached the highest value at p H=7and p H=8, respectively. However, classic acid-base model failed to fit the relationships between kapp of HOI with them and p H, which was speculated to be caused by the existence of other RIS, like I2、H2OI+, whose contribution to the transformation of this two compounds cannot be ignored.Products between HOI and those compounds revealed that HOI tends to react with the ortho- and para- positions of hydroxyl on the benzene ring and forms correponding monoiodinated or multiiodinated products. For BPA, totally seven kinds of products were detected, including monoiodinated-, diiodinated, triiodinated and tetraiodinated-BPA; two iodinated products formed by the iodination of secondary products, which formed by the break down of C-C bond and diiondinated pbenzoquione. While for TCS and 4-Me P, substitution reactions with HOI dorminated and corresponding iodinated products were detected, including monoiodinated and biiodinated products.