Reactions of Monobromamine and Dibromamine with Phenolic Compounds and Organic Matter: Kinetics and Formation of Bromophenols and Bromoform.

Monobromamine (NH2Br) and dibromamine (NHBr2) produced from reactions of hypobromous acid (HOBr) with ammonia can react with phenolic structures of natural organic matter (NOM) to produce disinfection byproducts such as bromoform (CHBr3). The reactivity of NH2Br was controlled by the reaction of the bromoammonium ion (NH3Br+) with phenolate species, with specific rate constants ranging from 6.32 × 102 for 2,4,6-tribromophenol to 1.22 × 108 M-1 s-1 for phenol. Reactions of NHBr2 with phenol and bromophenols were negligible compared to its self-decomposition; rate constants could be determined only with resorcinol for pH > 7. At pH 8.1-8.2, no formation of CHBr3 was observed from the reaction of NH2Br with phenol while the reaction of NH2Br with resorcinol produced a significant concentration of CHBr3. In contrast to NH2Br, a significant amount of CHBr3 produced with an excess of NHBr2 over phenol was explained by the reactions of HOBr produced from NHBr2 decomposition. A comprehensive kinetic model including the formation and decomposition of bromamines and the reactivity of HOBr and NH2Br with phenolic compounds was developed at pH 8.0-8.3. Furthermore, the kinetic model was used to evaluate the significance of the NH2Br and NHBr2 reactions with the phenolic structures of two NOM isolates.

Organic chloramines in chlorine-based disinfected water systems: A critical review.

This paper is a critical review of current knowledge of organic chloramines in water systems, including their formation, stability, toxicity, analytical methods for detection, and their impact on drinking water treatment and quality. The term organic chloramines may refer to any halogenated organic compounds measured as part of combined chlorine (the difference between the measured free and total chlorine concentrations), and may include N-chloramines, N-chloramino acids, N-chloraldimines and N-chloramides. Organic chloramines can form when dissolved organic nitrogen or dissolved organic carbon react with either free chlorine or inorganic chloramines. They are potentially harmful to humans and may exist as an intermediate for other disinfection by-products. However, little information is available on the formation or occurrence of organic chloramines in water due to a number of challenges. One of the biggest challenges for the identification and quantification of organic chloramines in water systems is the lack of appropriate analytical methods. In addition, many of the organic chloramines that form during disinfection are unstable, which results in difficulties in sampling and detection. To date research has focussed on the study of organic monochloramines. However, given that breakpoint chlorination is commonly undertaken in water treatment systems, the formation of organic dichloramines should also be considered. Organic chloramines can be formed from many different precursors and pathways. Therefore, studying the occurrence of their precursors in water systems would enable better prediction and management of their formation.

Enhanced formation of haloacetonitriles during chlorination with bromide: Unveiling the important roles of organic bromamines.

The formation of brominated disinfection byproducts (Br-DBPs) is an emerging issue in drinking water disinfection because its toxicity is tens to hundreds of times higher than that of chlorinated analogues and because of the widespread presence of bromide in source water. However, the mechanism and pathways of Br-DBPs formation remain unclear. In this study, we used glycine, alanine, and serine as model precursors and observed that brominated haloacetonitriles (Br-HANs) were more likely to be formed than brominated trihalomethanes. The results showed that there is not only one important way to HAN formation in the presence of bromide. We propose that organic bromamines, similar to organic chloramines, play a significant role in the formation of Br-HANs. Both the experimental and theoretical results confirmed that the decay of organic bromamines was faster than that of organic chloramines, which verified our assumption. The effect of the pH was investigated to further confirm the role of organic bromamines. In addition, we found that the formation of Br-HANs was significantly inhibited when monochloramine was used as a disinfectant, because the formation of organic bromamines was blocked. However, the formation of Br-HANs was promoted during the UV/chlorine process because of the faster decay of organic bromamines under UV photolysis. Overall, our study reveals the formation mechanism of Br-HANs and provides an alternative method to prevent Br-HAN formation.

Kinetic modelling of the bromine-ammonia system: Formation and decomposition of bromamines.

Bromamines i.e. monobromamine (NH2Br), dibromamine (NHBr2), and tribromamine (NBr3) can be formed during oxidative treatment of waters containing bromide and ammonia. The formation and decomposition of bromamines in aqueous solution was investigated and a comprehensive kinetic model of the bromine-ammonia system was developed at 23 ± 1 °C. Determination of rate constants and model validation were primarily performed at pH 8.0 - 8.3 for subsequent application to seawater disinfection. The rate constant of NHBr2 self-decomposition was determined by second-order rate law linearization with k9 = 5.5 (± 0.8) M-1s-1 at pH 8.10. The rate constant of NBr3 self-decomposition increased proportionately to the concentration of hydroxide ions (OH-) according to the equation k10 = 4.4 (± 0.1) × 107. [OH-] over the pH range 6.0 - 8.5, which gave k10 = 56 (± 1) M-1s-1 at pH 8.10. The rate constants of NHBr2 and NBr3 formation were obtained by fitting model-predicted data to the experimental results and were found to be k3 = 2.3 (± 0.2) × 104M-1s-1 and k5 = 4.0 (± 0.6) × 103M-1s-1, respectively at pH 8.10. NBr3 was also found to react with NHBr2 with k11 = 3.4 (± 0.2) × 103M-1s-1 at pH 8.10. A kinetic model was proposed based on these experimental rate constants and literature values, which provided a good prediction of bromamines formation and decomposition for various initial bromine and ammonia concentrations. The kinetic model was also used to accurately predict the total oxidant concentration and the speciation of bromamines during breakpoint bromination. This study provides kinetic data to model more complex oxidative systems such as seawater chlorination in the presence of ammonia.

Formation and reactivity of inorganic and organic chloramines and bromamines during oxidative water treatment.

The formation and further reactions of halamines during oxidative water treatment can be relevant for water quality. In this study, we investigated the formation and reactivity of several inorganic and organic halamines (monochloramine, N-chloromethylamine, N-chlorodimethylamine, monobromamine, dibromamine, N-bromomethylamine, N,N-dibromomethylamine, and N-bromodimethylamine) by kinetic experiments, transformation product analysis, and quantum chemical computations. Kinetic model simulations were conducted to evaluate the relevance of halamines for various water treatment scenarios. Halamines were quickly formed from the reaction of chlorine and bromine with ammonia or organic amines. Species-specific second-order rate constants for the reaction of chlorine and bromine with ammonia, methyl- and dimethylamine were in the order of 106-108 M-1s-1. The formed halamines were found to be reactive towards phenolic compounds, forming halogenated phenols via electrophilic aromatic substitution (phenol and resorcinol) or quinones via electron transfer (catechol and hydroquinone). At near neutral pH, apparent second-order rate constants for these reactions were in the order of 10-4-10-1 M-1s-1 for chloramines and 101-102 M-1s-1 for bromamines. Quantum chemical computations were used to determine previously unknown aqueous pKa values, gas phase bond dissociation energies (BDE) and partial atomic charges of the halamines, allowing a better understanding of their reactivities. Kinetic model simulations, based on the results of this study, showed that during chlorination inorganic and organic chloramines are the main halamines formed. However, their further reactions with organic matter are outcompeted kinetically by chlorine. During ozonation, mainly inorganic bromamines are formed, since ozone quickly oxidizes organic amines. The further reactions of bromamine are typically outcompeted by ozone and thus generally of minor importance. The use of peracetic acid for saline ballast water treatment can result in the formation of substantial amounts of bromamines, which can react with dissolved organic matter and contribute to the formation of brominated products.