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.

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.

Brominated trihalamines in chlorinated seawaters: Quantification of tribromamine and identification of bromochloramines by Membrane Introduction Mass Spectrometry.

During chlorination of seawater, the presence of bromide and ammonia alters the speciation of the oxidant and lead to the formation of chlorinated and brominated amines. This can affect the effectiveness of the disinfection treatment and the formation of disinfection by-products released to the environment. In this study, a Membrane Introduction Mass Spectrometry (MIMS) analytical method was developed to differentiate brominated trihalamines (i.e. tribromamine NBr3, dibromochloramine NBr2Cl and bromodichloramine NBrCl2) in synthetic and natural chlorinated seawater. A mass-to-charge ratio of m/z = 253 corresponding to the parent ion was used for the quantification of NBr3 in absence of organic matter and the signal of the fragment at m/z = 177 was chosen in presence of high concentration of organic matter. Limits of detection were 0.23 µM (49 µg Cl2/L) and 0.18 µM (38 µg Cl2/L) for m/z 253 and m/z 177, respectively. Both NBr2Cl and NBrCl2 were monitored in chlorinated seawaters with their respective parent ion at m/z = 207 and m/z = 163 but were not quantified. MIMS results also showed that reaction of brominated trihalamines with natural organic matter (NOM) was a minor pathway for 1-2 mg C/L compared to their auto-decomposition in natural or synthetic seawater. Overall, MIMS was able to unambiguously differentiate and monitor brominated trihalamines for the first time in chlorinated seawater, which was not possible by using UV measurement, titration and colorimetric methods.

Methylparaben chlorination in the presence of bromide ions and ammonia: kinetic study and modeling.

The impacts of chlorination on methylparaben (MP) removal, as well as of bromide and ammonia on the MP elimination kinetics, were studied. Bromide and ammonia react with chlorine and are promptly transformed into bromine and chloramines, respectively. Rate constants of chlorine, bromine, and monochloramine with MP were determined under different pH conditions. At pH 8.5, the apparent second-order rate constants of MP reactions with chlorine and bromine were found to be 3.37(±0.50) × 101 and 2.37 (±0.11) × 106 M-1.s-1 for kChlorine/MP and kBromine/MP, respectively, yet there was low reactivity with monochloramine ([Formula: see text] = 0.045 M-1.s-1). Regarding chlorination and bromination, in order to gain further insight into the observed pH-dependence of the reaction, the elementary reactions were considered and the corresponding second-order rate constants were calculated. The experimental and modeled values were quite consistent under these conditions. Then, chlorination experiments with different bromide and/or ammonia concentrations were performed to assess the impact of inorganic water content on MP elimination and a kinetic model was designed to assess MP degradation. Under these conditions, MP degradation was found to be enhanced in the presence of bromide whereas it was inhibited in the presence of ammonia, and the overall impact was pH dependent.

Oxidation of 2-aminophenol to 2-amino-3H-phenoxazin-3-one with monochloramine in aqueous environment: A new method for APO synthesis?

Reaction of 2-aminophenol (2AP) with monochloramine in aqueous solution was investigated at pH 8.5 and 25 °C, with an excess of monochloramine. 2-Amino-3H-phenoxazin-3-one (APO) was the major product formed in about 70% yield. Despite low formation yields, adsorbable organic halides (AOX) were also formed over reaction time.

Kinetics of Chlorination of Benzophenone-3 in the Presence of Bromide and Ammonia.

The aim of this study was to assess the impact of chlorination on the degradation of one of the most commonly used UV filters (benzophenone-3 (BP-3)) and the effects of bromide and ammonia on the kinetics of BP-3 elimination. Bromide and ammonia are rapidly converted to bromine and chloramines during chlorination. At first, the rate constants of chlorine, bromine and monochloramine with BP-3 were determined at various pH levels. BP-3 was found to react rapidly with chlorine and bromine, with values of apparent second order rate constants equal to 1.25(±0.14) × 10(3) M(-1)·s(-1) and 4.04(±0.54) × 10(6) M(-1)·s(-1) at pH 8.5 for kChlorine/BP-3 and kBromine/BP-3, respectively, whereas low monochloramine reactivity was observed (kNH2Cl/BP-3 = 0.112 M(-1)·s(-1)). To assess the impact of the inorganic content of water on BP-3 degradation, chlorination experiments with different added concentrations of bromide and/or ammonia were conducted. Under these conditions, BP-3 degradation was found to be enhanced in the presence of bromide due to the formation of bromine, whereas it was inhibited in the presence of ammonia. However, the results obtained were pH dependent. Finally, a kinetic model considering 18 reactions was developed using Copasi to estimate BP-3 degradation during chlorination in the presence of bromide and ammonia.

Sensitivity of free-living amoeba trophozoites and cysts to water disinfectants.

Free-living amoebae are naturally present in water. These protozoa could be pathogenic and could also shelter pathogenic bacteria. Thus, they are described as a potential hazard for health. Also, free-living amoebae have been described to be resistant to biocides, especially under their cyst resistant form. There are several studies on amoeba treatments but none of them compare sensitivity of trophozoites and cysts from different genus to various water disinfectants. In our study, we tested chlorine, monochloramine and chlorine dioxide on both cysts and trophozoites from three strains, belonging to the three main genera of free-living amoebae. The results show that, comparing cysts to trophozoites inactivation, only the Acanthamoeba cysts were highly more resistant to treatment than trophozoites. Comparison of the disinfectant efficiency led to conclude that chlorine dioxide was the most efficient treatment in our conditions and was particularly efficient against cysts. In conclusion, our results would help to adapt water treatments in order to target free-living amoebae in water networks.

Concentration levels of urea in swimming pool water and reactivity of chlorine with urea.

This study investigated the reactivity of chlorine with urea which is the main nitrogen contaminant introduced into swimming pool water by bathers. In the first part of this study, analyses showed that the mean concentrations of urea and TOC determined from 50 samples of municipal swimming pool were equal to 18.0 µM (s.d. 11.7) and 3.5 mg C L(-1) (s.d. 1.6), respectively. The mean value for the urea contribution to the TOC content was 6.3% (s.d. 3.3). The rate of decomposition of urea in swimming pool water measured during the closure time of the facility was very slow (decay at the rate of ≈ 1% per hour in the presence of 1.6-1.8 mg L(-1) of free chlorine). In the second part of this work, experiments carried out with phosphate buffered solutions of urea ([Urea](0) = 1 mM; [Cl(2)](0)/[Urea](0): 0.5-15 mol/mol; pH 7.4 ± 0.2; reaction time: 0-200 h) showed that long term chlorine demand of urea was about 5 mol Cl(2)/mol of urea. Chlorination led to a complete mineralization of organic carbon into CO(2) for a chlorine dose of 3.5 mol/mol and to the formation of 0.7-0.8 mol NO(3)(-)/mol of urea for chlorine dose of 8-10 mol/mol. Experiments conducted with dilute solutions of urea ([Urea](0) = 50 µM; pH ≈ 7.3) confirmed that the degradation rate of urea by chlorine is very slow under conditions simulating real swimming pool water.

Efficiency of water disinfectants against Legionella pneumophila and Acanthamoeba.

Free-living amoebae might be pathogenic by themselves and be a reservoir for bacterial pathogens, such as Legionella pneumophila. Not only could amoebae protect intra-cellular Legionella but Legionella grown within amoebae could undergo physiological modifications and become more resistant and more virulent. Therefore, it is important to study the efficiency of treatments on amoebae and Legionella grown within these amoebae to improve their application and to limit their impact on the environment. With this aim, we compared various water disinfectants against trophozoites of three Acanthamoeba strains and L. pneumophila alone or in co-culture. Three oxidizing disinfectants (chlorine, monochloramine, and chlorine dioxide) were assessed. All the samples were treated with disinfectants for 1 h and the disinfectant concentration was followed to calculate disinfectant exposure (Ct). We noticed that there were significant differences of susceptibility among the Acanthamoeba strains. However no difference was observed between infected and non-infected amoebae. Also, the comparison between the three disinfectants indicates that monochloramine was efficient at the same level towards free or co-cultured L. pneumophila while chlorine and chlorine dioxide were less efficient on co-cultured L. pneumophila. It suggests that these disinfectants should have different modes of action. Finally, our results provide for the first time disinfectant exposure values for Acanthamoeba treatments that might be used as references for disinfection of water systems.

Effect of some parameters on the formation of chloroform during chloramination of aqueous solutions of resorcinol.

The effects of various factors (N/Cl ratio used to prepare monochloramine, monochloramine doses, pH and contact time) on the monochloramine demand and on the chloroform yield during chloramination of resorcinol have been investigated. Chloramination experiments were carried out at 24+/-1 degrees C, at pH values ranging from 6.5 to 12 using a bicarbonate/carbonate buffer and preformed monochloramine solutions prepared at pH 8.5 with N/Cl ratios ([NH(4)Cl](0)/[Total free Cl(2)](0) ranging from 1.0 to 150 mol/mol). Kinetic experiments ([Resorcinol](0)=5 or 100 microM, [NH(2)Cl](0)/[Resorcinol](0)=20 mol/mol, pH=8.5+/-0.1) showed a slow increase of the monochloramine consumption with reaction time. The monochloramine demands after reaction times of 7 days ([Resorcinol](0)=100 microM) and 14 days ([Resorcinol](0)=5 microM) were equal to 8.5 mol of NH(2)Cl/mole of resorcinol and were higher than the chlorine demands (approximately 7.3 mol/mol). Chloroform yields from monochloramination of resorcinol were lower than 8% (<80 mmol of CHCl(3)/mole of resorcinol) and were less than the yields obtained by chlorination (0.9-0.95 mol/mol). Chloroform productions increased with increasing monochloramine dose and reaction time and decreased with increasing pH values within the pH range 6.5-10. Chloroform formation markedly decreased when the N/Cl ratio increased from 1 to 1.5 mol/mol and was suppressed at N/Cl>100 mol/mol. The data obtained in the present work suggest that free chlorine released from monochloramine hydrolysis plays a significant role on the formation of chloroform during chloramination of resorcinol at N/Cl ratios close to unity (1.0

Effect of dissolved oxygen on the photodecomposition of monochloramine and dichloramine in aqueous solution by UV irradiation at 253.7 nm.

The effect of dissolved oxygen on the photodecomposition of monochloramine (7.5 < pH < 10) and dichloramine (pH = 3.7 +/- 0.2) at 253.7 nm has been investigated. The kinetic study shows that the rate of photodecomposition of monochloramine is about two times faster in the absence of oxygen than in the presence of oxygen, is not significantly affected by pH and by the presence of hydroxyl radical scavengers (hydrogenocarbonate ion and tert-butanol). The apparent quantum yields of photodecomposition of monochloramine at 253.7 nm ([NH(2)Cl](0) approximately 1.5-2 mM, epsilon(253.7 nm) = 371 M(-1) cm(-1)) were equal to 0.28 +/- 0.03 and 0.54 +/- 0.03 mol E(-1) in oxygenated-saturated and in oxygen-free solutions, respectively. The photodecomposition rates or the apparent quantum yields of photodecomposition of dichloramine ([NHCl(2)](0) approximately 1.5-2 mM, pH = 3.7 +/- 0.2) in oxygen-free and in oxygen-saturated solutions were quite identical (Phi = 0.82 +/- 0.08 mol E(-1); epsilon(253.7 nm) = 126 M(-1) cm(-1)). Under O(2) saturation, UV irradiation of NH(2)Cl leads to the formation of nitrite ( approximately 0.37 mol/mol of NH(2)Cl decomposed), nitrate ( approximately 0.073 mol/mol) and does not form ammonia (<0.01 mol/mol). In oxygen-free solutions, monochloramine decomposes to form ammonia ( approximately 0.37 mol/mol). Photodecomposition of dichloramine did not lead to significant amounts of nitrite and nitrate in the presence and in the absence of oxygen. The nitrogen mass balances also indicate the formation of other nitrogen species (probably N(2) and/or N(2)O) during the photodecomposition of monochloramine and dichloramine by UV irradiation at 253.7 nm.

Monochloramination of resorcinol: mechanism and kinetic modeling.

The kinetics of monochloramination of resorcinol, 4-chlororesorcinol, and 4,6-dichlororesorcinol have been investigated over the pH range of 5-12, at 23 +/- 2 degrees C. Monochloramine solutions were prepared with ammonia-to-chlorine ratios (N/Cl) ranging from 1.08 to 31 mol/mol. Under conditions that minimize free chlorine reactions (N/Cl > 2 mol/mol), the apparent second-order rate constants of monochloramination of resorcinol compounds show a maximum at pH values between 8.6 and 10.2. The intrinsic second-order rate constants for the reaction of monochloramine with the acid-base forms of the dihydroxybenzenes (Ar(OH)(2), Ar(OH)O(-), and Ar(O(-))(2)) were calculated from the apparent second-order rate constants. The stoichiometric coefficients for the formation of 4-chlororesorcinol by monochloramination of resorcinol and 4,6-dichlororesorcinol by monochloramination of 4-chlororesorcinol were found to be equal to 0.66 +/- 0.05 and 0.25 +/- 0.02 mol/mol, respectively at pH 8.6. A kinetic model that incorporates reactions of free chlorine and monochloramine with the different acid-base forms of resorcinol compounds simulated well the initial rates of degradation of resorcinol compounds and was useful to evaluate the contribution of free chlorine reactions to the overall rates of degradation of resorcinol at low N/Cl ratios.

Modeling of bromate formation by ozonation of surface waters in drinking water treatment.

The main objective of this paper is to try to develop statistically and chemically rational models for bromate formation by ozonation of clarified surface waters. The results presented here show that bromate formation by ozonation of natural waters in drinking water treatment is directly proportional to the "Ct" value ("Ctau" in this study). Moreover, this proportionality strongly depends on many parameters: increasing of pH, temperature and bromide level leading to an increase of bromate formation; ammonia and dissolved organic carbon concentrations causing a reverse effect. Taking into account limitation of theoretical modeling, we proposed to predict bromate formation by stochastic simulations (multi-linear regression and artificial neural networks methods) from 40 experiments (BrO(3)(-) vs. "Ctau") carried out with three sand filtered waters sampled on three different waterworks. With seven selected variables we used a simple architecture of neural networks, optimized by "neural connection" of SPSS Inc./Recognition Inc. The bromate modeling by artificial neural networks gives better result than multi-linear regression. The artificial neural networks model allowed us classifying variables by decreasing order of influence (for the studied cases in our variables scale): "Ctau", [N-NH(4)(+)], [Br(-)], pH, temperature, DOC, alkalinity.