Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)
Article
Mechanistic Aspects of the Formation of Adsorbable Organic Bromine during Chlorination of Bromide-containing Synthetic Waters Markus Langsa, Anna Heitz, Cynthia A. Joll, Urs von Gunten, and Sebastien Allard Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b00691 • Publication Date (Web): 30 Mar 2017 Downloaded from http://pubs.acs.org on April 1, 2017
Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.
Page 1 of 25
Environmental Science & Technology
Chlorine Subs6tu6on
Br-DOM-subs
Cl-DOM
Cl-Br-DOM HOCl DOM
Electrophilic Subs6tu6ons
Br-DOM
HOBr Oxida6on DOM Br-
HOCl
DOMox
+
Br-
Br- Recycling
ACS Paragon Plus Environment
AOBr
Environmental Science & Technology
Page 2 of 25
1
Mechanistic Aspects of the Formation of
2
Adsorbable Organic Bromine during Chlorination
3
of Bromide-containing Synthetic Waters
4
Markus Langsa,1,2 Anna Heitz,3 Cynthia A. Joll,1 Urs von Gunten,4,5,* and Sebastien Allard1** 1
5
Curtin Water Quality Research Centre, Department of Chemistry, Curtin University, GPO Box U1987, Perth WA 6845, Australia
6
7
2
Jurusan Kimia, Fakultas Matematika dan Ilmu Pengetahuan Alam, Universitas Papua, Manokwari Papua Barat 98314, Indonesia
8 3
9 4
10
Department of Civil Engineering, Curtin University, Perth WA 6845, Australia
Eawag, Swiss Federal Institute of Aquatic Science and Technology, ETH Zürich, Zürich, Switzerland
11 12
5
School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale Lausanne (EPFL), Switzerland
13 14 15
Corresponding authors
16
*Urs von Gunten, phone: +41 58 765 5270; email:
[email protected] 17
**Sebastien Allard, phone: +61 8 9266 7949 ; email:
[email protected] 18 19 20 21
ACS Paragon Plus Environment
1
Page 3 of 25
Environmental Science & Technology
22
Abstract
23
During chlorination of bromide-containing waters, a significant formation of brominated
24
disinfection by-products is expected. This is of concern because Br-DBPs are generally more
25
toxic than their chlorinated analogues. In this study, synthetic water samples containing
26
dissolved organic matter (DOM) extracts and bromide were treated under various disinfection
27
scenarios to elucidate the mechanisms of Br-DBP formation. The total concentration of Br-
28
DBPs was measured as adsorbable organic bromine (AOBr). A portion of the bromine
29
(HOBr) was found to react with DOM via electrophilic substitution (≤ 40%), forming AOBr,
30
and the remaining HOBr reacted with DOM via electron transfer with a reduction of HOBr to
31
bromide (≥ 60%). During chlorination, the released bromide is re-oxidised (“recycled”) by
32
chlorine to HOBr, leading to further electrophilic substitution of unaltered DOM sites and
33
chlorinated DOM moieties. This leads to an almost complete bromine incorporation to DOM
34
(≥ 87%). The type of DOM (3.06 ≤ SUVA254 ≤ 4.85) is not affecting this process, as long as
35
the bromine-reactive DOM sites are in excess and a sufficient chlorine exposure is achieved.
36
When most reactive sites were consumed by chlorine, Cl-substituted functional groups (Cl-
37
DOM) are reacting with HOBr by direct bromination leading to Br-Cl-DOM and by bromine
38
substitution of chlorine leading to Br-DOM. The later finding was supported by
39
hexachlorobenzene as a model compound from which bromoform was formed during HOBr
40
treatment. To better understand the experimental findings, a conceptual kinetic model
41
allowing to assess the contribution of each AOBr pathway was developed. A simulation of
42
distribution system conditions with a disinfectant residual of 1 mgCl2 L-1 showed complete
43
conversion of Br- to AOBr, with about 10% of the AOBr formed through chlorine
44
substitution by bromine.
45 46
ACS Paragon Plus Environment
2
Environmental Science & Technology
Page 4 of 25
47
INTRODUCTION
48
Disinfection processes are applied to provide hygienically safe drinking water.1-3 Worldwide,
49
the main chemical disinfectant used for drinking water treatment is chlorine (HOCl + OCl-).3
50
Chlorine is typically applied at much higher concentrations than the ubiquitously occurring
51
bromide, for which the concentrations range from 10 to 2000 µg L-1 in source waters.4-10
52
During chlorination, bromide is oxidised to hypobromous acid/hypobromite (HOBr/OBr-)
53
with a second order rate constant for the reaction of HOCl with bromide of kHOCl,Br-= 1550 M-
54
1 -1 11
55
publication. Once formed, bromine reacts with organic moieties of dissolved organic matter
56
(DOM), analogous to the reactions of chlorine with DOM.12, 13 Bromine can react either by
57
electron transfer (ET) (redox reaction) with a release of bromide or by electrophilic
58
substitution (ES) leading to the formation of brominated organic compounds, some of which
59
can be measured as individual brominated disinfection by-products (DBPs).14, 15 The presence
60
of both chlorine and bromine in the water induces competition for reactions with DOM
61
moieties and subsequent formation of chlorinated-DBPs (Cl-DBPs), brominated-DBPs (Br-
62
DBPs) or mixed products.16, 17 In one study, it has been reported that bromine reacts 10 times
63
faster than chlorine with DOM extracts.13 Moreover, Heeb et al.18 compiled the species-
64
specific second order rate constants for the reactions of bromine with a series of phenolate
65
compounds, representative of DOM reactive moieties, and showed that they are on average
66
3000 times higher than the corresponding second order rate constants for the chlorine
67
reactions. Bromine can also affect the yield/magnitude and species distribution of
68
halogenated DBPs.16, 19-22 Furthermore, bromine has been reported to increase the formation
69
of N-nitrosodimethylamine (NDMA) during ozonation or chloramination of specific
70
precursors.23,
71
compounds are expected to be formed more readily and with a higher yield than chlorinated
72
compounds. Bromide can also enhance some processes during chlorination such as the
73
oxidation of Cr(III) to Cr(VI),25 abatement of phenol-containing micropollutants,26 oxidation
74
of HOI to iodate thereby mitigating the formation of iodinated-DBPs,16,
s .
For simplicity, the term bromine will be used for the sum of HOBr and OBr- in this
24
Overall, during chlorination of Br-containing waters, brominated organic
27
and Mn(II)
28
75
oxidation avoiding its carryover to distribution systems.
76
Even though inactivation of microorganims is the main objective during chemical drinking
77
water disinfection, exposure to DBPs, some of which are of potential health concern, also has
78
to be considered. Therefore, it is crucial to understand the extent and mechanisms of DBP
79
formation, with a special emphasis on brominated compounds since they are generally of
ACS Paragon Plus Environment
3
Page 5 of 25
Environmental Science & Technology
80
greater potential health concern compared to their chlorinated analogues and they are
81
preferentially formed during chlorination of bromide-containing waters.29-32
82 83
The application of advanced analytical methods for measurement and identification of DBPs
84
allows continuous and indefinite discoveries of new halogenated DBPs.33 To date, hundreds
85
of halogenated DBPs have been reported.34 Nevertheless, a large portion of DBPs remains
86
unidentified and uncharacterised.35-37 Therefore, quantifying regulated and non-regulated
87
known DBPs may underestimate the total formation of halogenated compounds. To
88
overcome this problem, the measurement of halogen-specific adsorbable organic halogen
89
(AOX, which is similar to total organic halogen (TOX)) can be used to quantify the total
90
halogen incorporation into DOM.20, 38 Halogen-specific AOX measurements are designed to
91
quantify adsorbable organic chlorine (AOCl), bromine (AOBr) and iodine (AOI). Substantial
92
efforts have been made to reveal the contribution of single Br-DBPs to the total AOBr
93
concentration. However, most of these studies have focussed only on a few specific DBPs,
94
such as the regulated brominated trihalomethanes and brominated haloacetic acids, and the
95
non-regulated brominated haloacetonitriles, the sum of which have been found to constitute
96
less than 50% of the total AOBr.17,
21, 39, 40
The unknown fraction of AOBr may contain
37, 41
Yang et al.42 reported a good correlation
97
compounds with potential health effects.
98
between the formation of AOBr and AOI and an increase in cytotoxicity and genotoxicity for
99
chlorinated and chloraminated waters. Therefore, AOBr measurements may be appropriate as
100
a proxy for the formation of brominated DBPs of potential health concern.
101 102
A recent study by Zhu and Zhang (2016)43 reported the application of a kinetic model to
103
predict the formation of halogen-specific AOX compounds (AOCl, AOBr, and AOI) during
104
chlorination and chloramination of raw waters. This model involved a total of 47 reactions
105
with 25 rate constants which were determined using methods based on “best fit” with AOX
106
measurements. The outcomes of their model calculations for AOCl, AOBr, and AOI
107
formation, as well as predictions of total oxidant residual concentrations, fitted well with their
108
experimental data, indicating the usefulness of kinetic modelling for simulation of
109
halogenated DBP formation during oxidative treatment processes.43 However, it is
110
questionable whether such a modelling effort will be transferrable to other systems, because
111
of the large number of variables.
112
This paper focuses on the formation of brominated organic compounds under simulated
113
drinking water chlorination conditions. The influence of water quality parameters (i.e.,
ACS Paragon Plus Environment
4
Environmental Science & Technology
Page 6 of 25
114
bromide/bromine concentration, DOM type and concentration, chlorine dose) on AOBr
115
formation was investigated for synthetic waters. Furthermore, the impact of bromide
116
recycling during chlorination of Br-containing waters on AOBr formation was assessed. To
117
evaluate the competition between chlorine and bromine for reactive sites in DOM,
118
chlorination of DOM (i.e., formation of chlorine-substituted functional groups) followed by
119
bromine addition was investigated. Finally, an empirical kinetic model was proposed to
120
explore pathways for AOBr formation during drinking water chlorination of bromide-
121
containing waters.
122 123
MATERIALS AND METHODS
124
Chemicals
125
Inorganic and organic chemicals used in this study were all of analytical grade quality.
126
Ultrapurified water (resistivity of 18.2 mΩ) produced with a Purelab Ultra Analytic
127
purification system (Elga, UK) was used for all experiments. Three commercial DOM
128
extracts from the International Humic Substances Society (IHSS) were used in this study:
129
Suwannee River DOM (SR-DOM; catalogue number: 2R101N), Nordic Reservoir DOM
130
(NR-DOM; 1R108N), and Pony Lake Fulvic Acid (PL-DOM; 1R109F). The SUVA254 values
131
of the SR-, NR- and PL-DOM samples determined in this study were 4.45, 4.85, and 3.06 L
132
mgC-1 m-1, respectively.
133 134
Preparation of Oxidant Solutions
135
Aqueous stock solutions of sodium hypochlorite (approximately 1300 mM, 90 g L-1 as Cl2)
136
were standardized (in the concentration range 5 to 30 µM, pH 11) by direct UV measurement
137
at 292 nm using a CARY 60 UV-VIS Agilent Technologies spectrophotometer
138
(ε292nm (ClO-) = 350 M-1 cm-1 44). A bromine stock solution of 500 µM was produced by
139
mixing HOCl with a slight stoichiometric excess of bromide (5%).28 The solution was
140
vigorously stirred for at least 15 min to allow complete oxidation of bromide to bromine. The
141
concentration of the bromine stock solution was standardized as OBr- at pH 11 by
142
measurement of the UV absorbance at 329 nm (ε329 nm = 332 M-1 cm-1
143
residual, measured as the sum of bromine and chlorine, was analysed by the N,N-
144
diethylphenylene-1,4-diamine (DPD) colorimetric method.45
145
Analytical Methods for Halogen-Specific AOX, Bromide, Trihalomethanes and
146
Dissolved Organic Carbon
ACS Paragon Plus Environment
27
). The oxidant
5
Page 7 of 25
Environmental Science & Technology
147
Halogen-specific AOX (AOCl and AOBr) was measured using a method developed by Hua
148
and Reckhow20 and modified by Kristiana, et al.39 (see Text S1). The quantification limit was
149
5 (±0.2) µg L-1 as Cl- for AOCl and 2 (±0.1) µg L-1 as Br- for AOBr. Bromide was measured
150
by ion chromatography using an AG9H/AS9H column and a 9 mM Na2CO3 eluent with a
151
flow rate of 1 mL min-1. The injection volume was 100 µL. The quantification limit was 2.8
152
(±0.9) µg L-1. The 4 regulated THMs, i.e., CHCl3, CHBrCl2, CHBr2Cl, and CHBr3, were
153
analysed by headspace solid-phase microextraction followed by gas chromatography-mass
154
spectrometry according to a published method.46 The quantification limits for CHCl3,
155
CHBrCl2, CHBr2Cl, and CHBr3 were 0.3 (±0.06) µg L-1 (2.6 nM), 0.2 (±0.07) µg L-1 (1.2
156
nM), 0.4 (±0.08) µg L-1 (1.9 nM), and 0.5 (±0.05) µg L-1 (2.1 nM), respectively. DOC
157
concentrations were determined by the UV/persulfate oxidation method using a Shimadzu
158
TOC Analyser. The quantification limit was 0.1 (±0.06) mgC L-1.
159 160
Experimental Procedures
161
Kinetic Study of AOBr Formation
162
Synthetic waters were prepared with purified water containing bromide (500 µg L-1 (6.26
163
µM)) and SR-DOM or PL-DOM (4 mgC L-1). These solutions were chlorinated (75 µM, ~5
164
mg Cl2 L-1) and samples were withdrawn at 5, 15, 30, and 60 min.
165
Bromination (HOBr) versus Chlorination (Br-+HOCl) Experiments
166
For bromination experiments (HOBr), synthetic waters containing various concentrations of
167
DOM (1.0–8.0 mgC L-1) were prepared in purified water and HOBr added to achieve initial
168
concentrations of 1.0, 3.13, and 6.26 µM (80–500 µg L-1). For chlorination experiments (Br-
169
+HOCl), similar synthetic waters containing various concentrations of SR-DOM (1.0–8.0
170
mgC L-1) and differing concentrations of Br- ranging from 1.0 to 6.26 µM were prepared in
171
purified water. A chlorine solution was added to achieve initial concentrations of 30, 50, 75,
172
and 140 µM Cl2 for 1, 2, 4 and 8 mgC L-1 of SR-DOM, respectively. Analyses of AOBr and
173
bromide for bromination and chlorination experiments were performed after 1 h reaction
174
time.
175
Pre-Chlorination Experiments
176
Synthetic waters containing SR-DOM (4 mgC L-1) were pre-chlorinated at differing initial
177
concentrations (15, 30, 45, 60, 75, and 90 µM) for 1 h before addition of bromine or bromide
178
(6.26 µM) followed by a holding time of 1 h. Differing pre-chlorination scenarios were also
179
investigated including pre-chlorination with fixed initial concentrations (30 and 75 µM) at
180
differing chlorine contact times of 5, 15, 30, and 60 min before bromine addition for 1 h.
ACS Paragon Plus Environment
6
Environmental Science & Technology
Page 8 of 25
181
Another experiment was conducted in which SR-DOM (4 mgC L-1) was pre-chlorinated until
182
the oxidant was completely consumed (24 h). Thereafter, bromine was added to the reaction
183
mixture in the concentration range of 5–50 µM for 1 h.
184
Simulation of Realistic Drinking Water Treatment Conditions
185
A solution containing SR-DOM (4 mgC L-1) and bromide (6.26 µM) was chlorinated at
186
differing initial concentrations (15, 30, 45, 60, 75, and 90 µM) for 1 h and 24 h.
187 188
For all experiments, the pH of the solution was kept constant at pH 8.0 using phosphate
189
buffer (1 mM). Chlorine equivalent residual was measured for all experiments. All samples
190
from all experiments were quenched using aqueous Na2SO3 solution (10% molar excess
191
calculated based on the chlorine equivalent residual) and stored at 4oC prior to analysis. The
192
samples were analysed for halogen-specific AOX, Br-, and THMs within 24 h. All
193
experiments were conducted in duplicate.
194 195
RESULTS AND DISCUSSION
196
Kinetics of AOBr Formation
197
In a solution containing bromide (6.26 µM), chlorine (75 µM) and SR-DOM (4 mgC L-1),
198
HOBr was formed rapidly and reacted with the SR-DOM to form AOBr.12, 13 This is shown in
199
Figure 1 by the evolution of AOBr and inorganic bromine species (HOBr+Br- measured as
200
Br- after quenching). Most of the HOBr (83%) was incorporated into DOM as AOBr in the
201
first 5 min, reaching a maximum of 88% after 15 min. The decrease in inorganic bromine
202
species was inversely correlated with the formation of AOBr, with 23% of the initial Br-
203
remaining after 5 min and 13% after 1 h. The bromine mass balance (recovery) ranged from
204
97% to 103%, indicating that AOBr and Br-/HOBr were the main forms of bromine in this
205
system and that bromine loss by volatilisation was minimal. The evolution of inorganic
206
bromine species and AOBr for the corresponding experiment with PL-DOM is presented in
207
the supporting information (SI) Figure S1. A slightly lower Br-incorporation (71% after 5
208
min) was observed for PL-DOM compared to SR-DOM, in agreement with previously
209
published data.15 However, after 1 h, the AOBr concentration was similar to the SR-DOM
210
experiment with 85% Br-incorporation.
ACS Paragon Plus Environment
7
Page 9 of 25
Environmental Science & Technology
Bromine Species (%)
100
80
60 AOBr Bromide Total bromine
40
20
0 0
5
15
30
60
211
Reaction time (min)
212
Figure 1. AOBr concentrations as a measure for Br-incorporation (%) and the inorganic
213
bromine species measured as bromide after quenching during chlorination of SR-DOM.
214
Experimental conditions: SR-DOM (4 mgC L-1), bromide (6.26 µM, 500 µg L-1), phosphate
215
buffer (1 mM), pH = 8, chlorine (75 µM, ~5 mg L-1), Na2SO3 solution (10% excess based on
216
chlorine equivalent residual) for quenching. Lines are shown to guide the eye.
217 218
During drinking water treatment, HOCl reacts with DOM but also oxidises Br- to HOBr (k=
219
1550 M-1 s-1)11 (reaction (1) Scheme 1).13, 18 HOBr can then react with DOM moieties via ES
220
to form AOBr (reactions (3), (4) and (5) in Scheme 1).47-49 Alternatively, HOBr can oxidise
221
the electron-rich moieties of DOM resulting in a release of Br- (reaction (6), Scheme 1).48, 49
222
The released Br- can then be re-oxidised to HOBr (reaction (1), Scheme 1) by the excess
223
HOCl. This re-formed HOBr can again react with DOM moieties with the formation of
224
AOBr.
225
ACS Paragon Plus Environment
8
Environmental Science & Technology
Page 10 of 25
226 227
Scheme 1. Main reactions involved in a DOM-containing system during chlorination in the
228
presence of bromide (Br-+HOCl) or during bromination (HOBr). The numbers in brackets
229
refer to reactions in the kinetic model in the SI, Table S1.
230 231
The extent to which HOBr reacts with DOM moieties to AOBr via ES or ET whereby Br- is
232
released, depends on the composition and the concentration of the organic functional groups
233
in the DOM.12, 15
234 235
Effect of Water Matrix Constituents and Impact of Bromide Recycling on AOBr
236
Formation: Chlorination of Bromide-Containing Water (Br-+HOCl) or Bromination
237
(HOBr)
238
General Observations
239
To better understand the differing mechanisms involved during chlorination of bromide-
240
containing waters, synthetic waters containing DOM (1.0–8.0 mgC L-1) and Br- (1.0–6.26
241
µM) were treated with HOCl (30–140 µM) and compared to similar bromination experiments
242
for which synthetic waters were treated directly with the same HOBr doses (1.0–6.26 µM).
243
The formation of AOBr (presented as % Br-incorporation) for chlorination (Br-+HOCl) and
244
bromination (HOBr) of various types of DOM, differing concentrations of SR-DOM and
245
differing concentrations of HOBr/Br- is shown in Figure 2. Generally, AOBr formation was
ACS Paragon Plus Environment
9
Page 11 of 25
Environmental Science & Technology
246
much higher for chlorination (Br-+HOCl, grey bars) compared to bromination only (HOBr,
247
black bars). The maximum % Br-incorporation obtained in chlorination experiments was
248
98%, while in bromination experiments, it only accounted for up to 42% of the initial
249
bromine concentration. As illustrated in Figures S2a-c, the bromide concentration after
250
quenching the oxidant residual reached a maximum of 72% in bromination experiments
251
compared to only 18% after chlorination for 1 h. The bromine mass balance was ranging
252
from 97% to 103% indicating that most of the initial bromide was accounted for by AOBr
253
and inorganic bromine. This indicates that the dominant reaction pathway during the
254
bromination experiments (HOBr alone) is an electron transfer (ET) between HOBr and
255
DOM, with bromide and oxidised DOM being formed (reaction (6), Scheme 1). Therefore,
256
the formation of AOBr is only a minor reaction pathway in the bromination experiments. For
257
chlorination experiments (Br-+HOCl), high residual concentrations of the oxidants (15–32
258
µM), mostly chlorine, were available during the 1 h contact time (Figures S2d-f). This
259
enabled re-oxidation of bromide to HOBr (bromide recycling; reaction (1), Scheme 1), which
260
could further react with DOM forming more AOBr and resulting in a much lower sum of
261
HOBr and bromide at the end of the experiment. For experiments with bromine only, no
262
oxidant was left in solution after 1 h (Figures S2d-f), indicating all HOBr had been
263
consumed. These results emphasize the fact that Br- re-oxidation (bromide recycling) is a key
264
factor that impacts the extent of AOBr formation.
265 266
Influence of DOM Type
267
In a previous study it has been shown that DOM type (i.e., structure and functionality) can
268
play a role in the extent of Br-incorporation.15 Bromination (HOBr only, black bars) of
269
various types of DOM showed that SR-DOM and NR-DOM had a higher yield of AOBr
270
compared to PL-DOM (Figure 2a). For SR-DOM and NR-DOM, the % Br-incorporation was
271
38% and 42%, respectively, while it was only 27% for PL-DOM. This observation coincides
272
with the SUVA254 values, which indicate that SR-DOM and NR-DOM contain more reactive
273
aromatic sites for AOBr formation (SUVA254 of 4.45 and 4.85 L mgC-1 m-1, respectively)
274
than PL-DOM (SUVA254 of 3.06 L mgC-1 m-1). This result is consistent with various studies
275
showing that DOM sources with high SUVA254 are more reactive with oxidants than DOM
276
sources with low SUVA254.50, 51 Furthermore, the electron donating capacity (EDC) of DOM,
277
a measure of electron rich and potentially bromine-reactive moieties, also reflects the same
278
trend.52
For chlorination experiments (Br-+HOCl, grey bars, Figure 2a), no significant
ACS Paragon Plus Environment
10
Environmental Science & Technology
Page 12 of 25
279
differences in AOBr formation between the different DOM samples could be observed, with
280
an average % Br-incorporation for SR-DOM, NR-DOM and PL-DOM of 93%, 90%, and
281
87%, respectively.
Br-Incorporation (%)
120
(b)
(a)
HOBr Br-+HOCl
(c)
100 80 60 40 20
2
4
8
-D
O
O M
1
1
3.13
6.26
PL
-D
O M NR
-D SR
M
0
Types of DOM
[SR-DOM] (mgC L-1)
[HOBr/Br-] (µ µM)
282 283
Figure 2. AOBr formation presented as % Br-incorporation resulting from bromination only
284
(HOBr, black bars) or chlorination of DOM in the presence of bromide (Br-+HOCl, grey
285
bars). (a) DOM types (SR-, NR-, PL-DOM) (4 mgC L-1); for bromination: [HOBr] = 6.26
286
µM; for chlorination: [Br-] = 6.26 µM, [HOCl] = 75 µM. (b) SR-DOM (1, 2, 4 and 8 mgC L-
287
1
288
75 and 140 µM for 1, 2, 4 and 8 mgC L-1 of SR-DOM, respectively. (c) SR-DOM (4 mgC L-
289
1
290
µM, [HOCl] = 75 µM. Phosphate buffer (1 mM), pH = 8 for all experiments. Na2SO3
291
solution (10% excess based on chlorine equivalent residual) was used to quench the reactions.
292
Reaction time: 1 h for both chlorination and bromination.
): for bromination: [HOBr] = 6.26 µM; for chlorination: [Br-] = 6.26 µM, [HOCl] = 30, 50, ): for bromination: [HOBr] = 1.0, 3.13, 6.26 µM; for chlorination: [Br-] = 1.0, 3.13, 6.26
293 294
Influence of DOM Concentration
295
Chlorination/bromination experiments were conducted to study the effect of differing SR-
296
DOM concentrations on AOBr formation (Figure 2b). The % Br-incorporation for the
297
bromination experiments slightly and continuously increased from 28% to 39% with
ACS Paragon Plus Environment
11
Page 13 of 25
Environmental Science & Technology
298
increasing DOM concentrations from 1 and 8 mgC L-1, respectively. In parallel, the bromide
299
fraction of the initial bromine concentration decreased from 72% to 63% for 1 mgC L-1 and 8
300
mgC L-1, respectively (Figure S2b). Therefore, even for 8 mgC L-1, oxidation of DOM was
301
still the dominant pathway during bromination and, since bromide recycling was not possible,
302
only about 40% of bromine was incorporated into DOM as AOBr. Overall, the ratios between
303
ET and ES reactions are quite similar for all DOM concentrations. Even though, increasing
304
the SR-DOM concentration increases the number of reactive sites, a constant ratio of DOM
305
moieties reacting with ET or ES is available for reaction with bromine. For the chlorination
306
experiments, the chlorine dose was increased with increasing NOM concentrations to ensure
307
a chlorine residual for bromide recycling. An increasing chlorine dose may impact the rate of
308
bromide oxidation/recycling by increasing the HOCl/Br- ratios. However, based on kinetic
309
experiments, after 1 h contact time, only a small influence of the chlorine dose on AOBr
310
formation is expected. Increasing the concentration of SR-DOM from 1 to 2 mgC L-1
311
increased AOBr formation by around 20 % from 71 % to 90 %. Further increases in DOC
312
concentration to 4 mgC L-1 and 8 mgC L-1 resulted in only slight increases in % Br-
313
incorporation to 93% and 95%, respectively. When the SR-DOM concentration was 1 mgC
314
L-1, bromine appears to have been in excess compared to the concentration of reactive sites,
315
resulting in only 71% Br-incorporation. However, increasing the SR-DOM concentration to 2
316
mgC L-1 appeared to allow most of the bromine to be incorporated into the DOM. Therefore,
317
increasing the DOM concentration further to 4 and 8 mgC L-1 did not significantly influence
318
AOBr formation since almost all the HOBr could be incorporated into DOM for a DOM
319
concentration of 2 mgC L-1.
320 321
Influence of Bromide Concentration
322
Experiments to test the effect of the initial inorganic bromine concentrations (HOBr or Br-)
323
on AOBr formation showed that increasing the HOBr concentrations in bromination
324
experiments increased the absolute concentration of AOBr (results not shown) but did not
325
affect the fraction of bromine which formed AOBr as the % Br-incorporation remained
326
unchanged (37% to 39%) (Figure 2c, black bars). Oxidation of DOM (ET) was still the
327
dominant reaction in bromination with more than 60% of the initial HOBr being reduced to
328
bromide (Figure S2c, black bars). This indicates that even for the highest HOBr dose and 4
329
mgC/L of SR-DOM, the reactive sites were not limiting for the AOBr formation. This is
330
illustrated by the same partitioning between ET and ES (reactions (3), (4), (5), Scheme 1).
ACS Paragon Plus Environment
12
Environmental Science & Technology
Page 14 of 25
331
Analogous results were obtained for the chlorination experiments, where bromine was
332
incorporated with a higher but similar yield (93 to 98%) for all bromide concentrations.
333 334
Overall, in bromination experiments, around 35 - 40% of HOBr reacted through ES, while 60
335
- 65% reacted through electron transfer reactions (ET). In chlorination experiments, the %
336
Br-incorporation reached almost 100%. This is the result of a re-oxidation of bromide formed
337
from the ET reactions by HOCl to HOBr (bromide recycling, reaction (1), Scheme 1), until
338
an almost complete bromine incorporation into DOM is achieved.
339 340
To better understand whether competition between chlorine (HOCl) and bromine (HOBr) for
341
DOM reactive sites affects the extent of AOBr formation, pre-chlorination experiments
342
followed by HOBr/Br- addition were conducted and are described in the next section.
343 344
Competition between Chlorine and Bromine for Reactive DOM Moieties
345
Influence of Bromine
346
The effect of the pre-chlorination conditions on the formation of AOCl and AOBr from SR-
347
DOM was investigated by pre-chlorination at varying doses for 1 h, before addition of the
348
same HOBr dose followed by a reaction time of 1 h. Figure 3a shows that increasing the
349
chlorine dose during pre-chlorination resulted in an expected increase in the AOCl
350
concentration but also led to an increase in AOBr concentrations. A pre-chlorination dose of
351
zero reflects the reactivity of the unaltered SR-DOM with HOBr (bromination of 4 mgC L-1
352
SR-DOM, Figure 2a). With increasing pre-chlorination doses (Figure 3a), the % Br-
353
incorporation increased from 40% (2.2 µM AOBr) for a HOCl dose of 15 µM to nearly 100%
354
(5.7 µM AOBr) with 90 µM of HOCl. In accordance with the % Br-incorporation, the
355
inorganic bromine species (measured as bromide after quenching) decreased with increasing
356
pre-chlorination dose, from 54% (3.0 µM) to 7% (0.4 µM) for 15 and 90 µM of HOCl,
357
respectively (Figure 3a). For low chlorine doses (15 - 45 µM), even though there was some
358
chlorine residual before HOBr addition (0.3 – 15.6 µM HOCl (Figure S3)), AOCl
359
concentrations after 1 h contact time (HOCl only) and after 2 h contact time (1 h HOCl and
360
1 h HOCl + HOBr) were similar (Figure 3a, right axis). This shows that HOBr-DOM
361
reactions are favoured over HOCl-DOM reactions since both HOCl and HOBr were present
362
in solution in the second hour, but minimal additional AOCl was formed during that time.
363
However, HOCl is partly consumed by oxidation of the released bromide (from HOBr
ACS Paragon Plus Environment
13
Page 15 of 25
Environmental Science & Technology
364
oxidation of DOM) to form additional HOBr. Nevertheless, for the highest chlorine doses (60
365
- 90 µM), small increases in AOCl concentrations were observed after bromine addition
366
(Figure 3a, right axis), since significant concentrations of chlorine were still present after 1 h
367
reaction time (Figure S3). In these cases, both HOCl and HOBr were in competition for
368
DOM reactive sites, i.e., both AOBr and AOCl concentrations increased.
369 370
Influence of Bromide
371
An additional set of pre-chlorination experiments was carried out for which bromide was
372
added instead of bromine (Figure S4). For a HOCl pre-chlorination dose of 15 µM, where no
373
oxidant residual was measured after 1 h (Figure S4), no AOBr was detected, because bromide
374
could not be oxidised to HOBr. However, as soon as a chlorine residual was measured after
375
1 h reaction time (for HOCl doses ≥ 30 µM), a formation of HOBr upon addition of bromide
376
occurs. This can react with DOM leading to AOBr concentrations after the second hour
377
similar to the corresponding pre-chlorination of DOM experiments with subsequent HOBr
378
addition (Figures S4, 3a left axis).
379
Under these experimental conditions, increasing the pre-chlorination dose increased the
381
formation of AOBr. It was expected that a pre-chlorination step would consume part of the
382
DOM sites, which can react with HOX, thereby decreasing the number of reactive sites
383
available for ES with bromine, resulting in a reduction in AOBr formation. However, since
384
such an effect could not be observed, it was hypothesised that HOCl activated DOM moieties
385
for reaction with HOBr, which then favoured AOBr formation. (a)
(b) b
14 12
80 10 60
8 AOBr Bromide AOCl after 1 hour pre-chlorination AOCl after 1 hour HOBr addition
40
6 4
AOCl concentration (µ µM) AOBr concentration (µ µ M)
100
AOBr Experimental data AOCl after pre-chlorination AOCl after 1 hour HOBr addition
Br-DOM1 Br-DOM1-subs Cl-Br-DOM1
14 12
6 10 8
4
6 4
2
20 2 0
0 0
15
30
45
60
75
Pre-chlorination dose (µ µM)
90
AOCl concentration (µ µ M)
8
-
Br-Incorporation and reduced bromine (as Br ) (%)
380
2 0
0 5
15
30
60
Pre-chlorination time (min)
386 387
Figure 3. Effect of pre-chlorination dose on AOBr and AOCl formation. (a) SR-DOM pre-
388
chlorinated with differing doses before bromine addition. (b) SR-DOM pre-chlorinated for
ACS Paragon Plus Environment
14
Environmental Science & Technology
Page 16 of 25
389
differing durations with a fixed initial HOCl dose before bromine addition: experimental data
390
and kinetic model calculations are shown. Experimental conditions: (a) pre-chlorination
391
(doses: 15, 30, 45, 60, 75, 90 µM) for 1 h, (b) pre-chlorination (dose: 75 µM) for 5, 15, 30
392
and 60 min; SR-DOM (4 mgC L-1), phosphate buffer (1 mM), pH = 8, HOBr (6.26 µM) for
393
1 h, Na2SO3 solution (10% excess based on chlorine equivalent residual) for quenching. The
394
stacked bars (left side of each pre-chlorination time) represent the modeled data, the striped
395
bars (right side of each pre-chlorination time) represent the experimental data.
396 397
To investigate the role of the pre-chlorination contact time on AOBr formation during post-
398
bromination, SR-DOM was pre-chlorinated with a fixed chlorine dose of 75 µM for various
399
contact times (Figure 3b). This leads to differing (pre-)chlorine exposures, before bromine
400
addition (6.26 µM for 1 h). The (pre-)chlorination exposure (pre-chlorination times: 5-60
401
min) did not affect the AOBr formation, which was relatively high (approx. 6.0 µM) (Figure
402
3b, left axis). A slight decrease of AOBr formation from 3.70 µM to 3.35 µM for pre-
403
chlorination times of 5 min and 60 min was observed for a similar experiment with a lower
404
HOCl dose of 30 µM (Figure S5). Conversely, the concentration of AOCl increased
405
continuously with increasing pre-chlorination exposure (time), from 6.7 µM to 10.5 µM for
406
pre-chlorination times of 5 min or 60 min, respectively. A further slight increase of AOCl
407
was observed 1 h after HOBr addition (from 9.9 to 11.9 µM for pre-chlorination times of 5
408
min or 60 min, respectively) (Figure 3b, right axis), because of the high chlorine equivalent
409
residual in all experiments (Figure S6). However, even though the concentration of AOCl
410
increased 1 h after HOBr addition for low pre-chlorination contact times (0 to 30 min) for a
411
chlorine dose of 30 µM, for the highest contact time of 60 min, the AOCl concentration
412
decreased (Figure S7). The AOCl concentrations were 9.1 µM after 60 min contact time with
413
HOCl only and 6.4 µM after HOBr addition (overall 2 h contact time with oxidants) (Figure
414
S7). In this case, the total oxidant concentration (HOCl + HOBr) was consumed within 120
415
min (60 min pre-chlorination + 60 min after HOBr addition) (Figure S8). This suggests that,
416
as expected, HOBr reacted with reactive DOM sites to form AOBr. However, because AOCl
417
decreased for the highest contact time (Figure S7), HOBr may have led to a substitution of
418
chlorine by bromine.
419 420
Chlorine Substitution by Bromine in DOM
421
Bromination of Chlorinated Water
ACS Paragon Plus Environment
15
Page 17 of 25
Environmental Science & Technology
422
To further test the hypothesis of chlorine substitution by bromine in DOM, a subsequent
423
experiment was conducted in which the oxidant residual from pre-chlorination was
424
completely consumed before bromine addition to avoid competition between HOCl and
425
HOBr for DOM reactive sites. SR-DOM samples (4 mgC L-1) were pre-chlorinated (45 µM)
426
until full consumption of the oxidant. Thereafter, HOBr was added to the samples to achieve
427
differing doses (5–50 µM).
428 429
In these experiments, AOBr increased from 1 to 7 µM, for bromine doses ranging from 5 to
430
50 µM (Figure 4), while AOCl gradually decreased from 12 µM (without addition of HOBr)
431
to 8 µM for a HOBr dose of 50 µM. Furthermore, an increase of total AOX (sum of AOCl
432
and AOBr) with increasing doses of bromine was observed (∆Total AOX in Figure 4). This
433
was assigned to DOM reactive sites which were already chlorinated with only a low
434
reactivity with chlorine for a further chlorination. Therefore, these sites react preferentially
435
with bromine to form Cl-Br-DOM moieties (reaction (4) in Scheme 1). For example, second
436
order rate constants for the reaction of 4-chlorophenolate, 2,4-dichlorophenolate and 2,4,6-
437
trichlorophenolate with HOBr are around three orders of magnitude higher than for HOCl.53,
438
54
439
reaction (5) in Scheme 1), while the AOBr concentration increased.
Overall, AOCl decreased (~ 33% reduction of the AOCl concentration, ∆AOCl in Figure 4,
16 AOCl AOBr Total AOX
AOX Concentration (µM)
14
∆ Total AOX = Cl-Br-DOM1
12
∆ AOCl = Br-DOM1-subs
10 8 6 4 2 0 0
440
5
10
20
50
HOBr dose (µ µM)
ACS Paragon Plus Environment
16
Environmental Science & Technology
Page 18 of 25
441
Figure 4. Pre-chlorination (complete depletion of chlorine) followed by HOBr addition:
442
Effect of HOBr doses on AOX formation. Experimental conditions: SR-DOM (4 mgC L-1),
443
phosphate buffer (1 mM), pH = 8, pre-chlorination (dose: 45 µM) for 24 h then HOBr (5 – 50
444
µM) for 1 h, Na2SO3 solution (10% excess based on chlorine equivalent residual) for
445
quenching.
446
Based on these results, a new pathway for the formation of AOBr is proposed which involves
447
the substitution of chlorine in AOCl by bromine. An experiment with a model compound
448
(hexachlorobenzene) was conducted to further investigate this hypothesis.
449 450
Bromination of hexachlorobenzene
451
Hexachlorobenzene (HCB) was chosen for the bromination experiments because its aromatic
452
ring is fully substituted by chlorine. HCB solutions (50 µM) were treated with differing
453
doses of HOBr (250 to 1000 µM) for 120 h (for experimental details see Text S2).
454
Bromoform was the only THM detected after this reaction time (Figure S9). Although these
455
experiments were carried out with high concentrations of reactants (due to the low reactivity
456
of HCB) and the yield of CHBr3 was low, they provide evidence that chlorine can be
457
substituted by bromine in organic compounds.
458 459
Modelling of AOBr Formation
460
For a better mechanistic understanding of AOBr formation, a conceptual kinetic model is
461
proposed to simulate the experimental data (see Table S1, Text S3 for the model assumptions,
462
Text S4 for a step-by-step description of the modelling process and Text S5 for a sensitivity
463
analysis of the rate constants). The kinetic model calculations were performed with the
464
software Kintecus.55 According to our experimental results, there are 5 main reactions
465
involved in the formation of AOBr (Scheme 1):
466
(i) Reaction of HOBr with DOM by electrophilic substitution (ES). DOM1 was
467
assigned to the fraction of sites reacting with both HOBr and HOCl (reactions (2, 3), Scheme
468
1 and Table S1), leading to the formation of Br-DOM1 and Cl-DOM1. Cl-DOM1 represented
469
intermediate products (chlorine-substituted functional groups) that may react further with
470
HOBr.
471 472
(ii) Reaction of HOBr with DOM by electron transfer (ET, redox reaction). DOM2 was allocated to ET reactions with HOBr (reaction (6), Scheme 1 and Table S1).
ACS Paragon Plus Environment
17
Page 19 of 25
Environmental Science & Technology
473
(iii) Reaction of HOBr with chlorinated DOM moieties by electrophilic substitution
474
(ES). Reaction of Cl-DOM1 with HOBr leading to Cl-Br-DOM1 (reaction (4), Scheme 1 and
475
Table S1). Cl-Br-DOM1 accounted for both AOCl and AOBr.
476
(iv) Chlorine substitution by bromine in DOM (reaction of AOCl to AOBr). Based on
477
the experimental evidence, this reaction was used generically to encompass the decrease of
478
AOCl along with an increase of AOBr. Reaction of Cl-DOM1 with HOBr leading to Br-
479
DOM1-subs (reaction (5), Scheme 1 and Table S1).
480
(v) HOBr formation by reaction of bromide, formed from electron transfer reactions
481
(ET), with chlorine (reaction (1), Scheme 1 and Table S1).
482
The total AOBr concentration in the model calculations is the sum of Br-DOM1, Br-DOM1-
483
subs and Cl-Br-DOM1.
484
Reactions related to the reactivity of HOCl and the formation of AOCl are described in the SI
485
(see Table S1, Text S3 for the model assumptions, Text S4 for a step-by-step description of
486
the modelling process and Text S5 for a sensitivity analysis of the rate constants).
487 488
Simulation of AOBr formation
489
In bromination experiments in the absence of chlorine, AOBr was solely formed from
490
reaction of HOBr with DOM1 (Br-DOM1) (Figure S10). For the chlorination experiments
491
(Figures S12 and Figure 5), the ES was still the major contributor to AOBr formation.
492
However, because chlorine was in excess, the competition between chlorine and bromine for
493
reactive sites reduced the portion of Br-DOM1, while the proportion of Cl-Br-DOM1 to the
494
total AOBr became significant. Chlorine substitution by bromine (Br-DOM1-subs) increased
495
with bromide/bromine (Figure S12) and chlorine concentrations (Figure 5), even though it
496
represents only a small portion of the total AOBr.
497
For the pre-chlorination experiments, the unexpected trend obtained for differing pre-
498
chlorination times for which similar AOBr concentrations were measured (Figure 3b) could
499
be explained by the model. DOM1 was used up by competing reactions with HOCl (reaction
500
(2), Scheme 1), while the Cl-DOM1 concentration increased with increasing (pre-
501
)chlorination exposure. Therefore, in terms of the total AOBr, the increasing contribution of
502
both Cl-Br-DOM1 and the chlorine substitution by bromine pathway (Br-DOM1-subs)
503
(reaction (4-5), Scheme 1) with increasing (pre-)chlorination exposure was compensated by
504
the decreasing contribution of ES to form Br-DOM1 (reaction (3), Scheme 1). Overall, a
505
similar total AOBr was measured.
ACS Paragon Plus Environment
18
Environmental Science & Technology
Page 20 of 25
506
For the experiments with complete chlorine consumption after pre-chlorination (Figures 4
507
and S11), DOM1 was totally consumed by HOCl. Therefore, after HOBr addition, AOBr was
508
formed by direct ES with chlorinated DOM moities (Cl-Br-DOM1) and through chlorine
509
substitution by bromine (Br-DOM1-subs).
510 511 512
Implications for Drinking Water Distribution Systems
513
To simulate real drinking water treatment conditions, synthetic waters containing bromide
514
were chlorinated with doses ranging from 15 to 90 µM (1 to 6.4 mgCl2 L-1) and sampled at
515
two contact times (1 h and 24 h) to mimic residence times in distribution systems. Kinetic
516
model calculations were performed to better understand the experimental results.
517 518
Figure 5 shows that the model is able to predict AOBr formation for these conditions AOBr
519
formation was similar for the two sampling times (1 h and 24 h). The formation of AOBr
520
increased from 1.75 µM (30% Br-incorporation) to 5.61 µM (94% Br-incorporation) for
521
HOCl doses of 15 µM or 90 µM, respectively. AOCl formation showed a different behaviour.
522
For low chlorine doses (15 - 45 µM) with low residual chlorine concentrations after 1 h
523
(Figure S17), the AOCl concentration was similar for 1 h and 24 h. For the highest chlorine
524
dose with a substantial residual chlorine concentration after 1 h, an increase in AOCl was
525
observed up to 24 h. For example, for a chlorine dose of 90 µM, AOCl increased from 11.5
526
µM to 14.5 µM, while the oxidant residual decreased from 33 µM (2.3 mgCl2 L-1) to 13 µM
527
(0.9 mgCl2 L-1), for contact times of 1 h or 24 h, respectively.
ACS Paragon Plus Environment
19
Page 21 of 25
Environmental Science & Technology
25
20
80 15 60 10 40
AOCl concentration (µ (µM)
100
Br-Incorporation (%)
Br-DOM1 Br-DOM1-subs Cl-Br-DOM1
AOBr after 1h AOBr after 24h AOCl after 1h AOCl after 24h
5
20
0
0 0
15
30
45
60
75
90
528
HOCl dose (µ µM)
529
Figure 5. Experimental and modelled AOX formation during chlorination of a water
530
containing SR-DOM and bromide for 1 h and 24 h. Experimental conditions: SR-DOM (4
531
mgC L-1), Br- (6.26 µM, 500 µg L-1), phosphate buffer (1 mM), pH = 8, HOCl doses: 15, 30,
532
45, 60, 75, 90 µM, Na2SO3 (10% molar excess calculated based on chlorine equivalent
533
residual) for quenching. The symbols represent experimental results: AOBr, circles, left axis,
534
AOCl triangles, right axis. Stacked bars represent the modeled contribution of various
535
reactive DOM sites to AOBr formation after 24 h.
536 537
Model calculations (bars in Figure 5) show that for low HOCl doses (15 – 30 µM), Br-DOM1
538
(reaction (3), Scheme 1) and Cl-Br-DOM1 (reaction (4), Scheme1) are the two main
539
processes for AOBr formation. For increasing HOCl doses, AOBr increased with an
540
increasing contribution of the chlorine substitution by bromine pathway (Br-DOM1-subs,
541
reaction (5), Scheme 1). At high HOCl doses (> 60 µM), the contribution of Br-DOM1 to the
542
total AOBr concentration slightly decreased with increasing chlorine doses and Br-DOM1-
543
subs contributed increasingly to AOBr formation. This shows that in distribution systems for
544
which a residual disinfectant of ~ 1 mgCl2 L-1 (chlorine dose 90 µM in Figure S17) or higher
545
is needed due to long residence times, Br-DOM1-subs may contribute >10% to the overall
546
AOBr formation. Furthermore, almost 100% of the bromide is expected to be converted to
ACS Paragon Plus Environment
20
Environmental Science & Technology
Page 22 of 25
547
AOBr, while the AOCl will continually increase with increasing residence time. This is in
548
agreement with a recent study where more than 90% of the bromide was present as AOBr in
549
a distribution system.40 However, the current study was carried out with synthetic waters and
550
additional experiments need to be performed with real waters or in real distribution system
551
samples to validate these findings. Furthermore, the model was validated only with the SR-
552
DOM extract, different rate constants and DOM fractions might be needed for other DOM
553
types.
554 555
Supporting information
556
5 texts, 1 table and 17 figures with further information addressing model calculations and
557
additional data are available in the supporting information.
558 559
Acknowledgements
560
The authors would like to acknowledge the Australian Research Council (ARC
561
LP100100285), Water Corporation of Western Australia, Curtin University, the Swiss
562
Federal Institute for Aquatic Science and Technology (Eawag) and Water Research Australia
563
for support for this project. The authors also acknowledge the Australian Government
564
through The Department of Foreign Affairs and Trade for providing a PhD scholarship
565
under the Australian Award Scholarship (AAS) scheme for M. Langsa.
566 567 568
References
569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584
(1) Gordon, M. F.; Morris, J. C.; Chang, S. L.; Weil, I.; Burden, R. P. The Behavior of Chlorine as a Water Disinfectant. J. Am. Water Works Ass. 1948, 40, (10), 1051-1061. (2) Rosario-Ortiz, F.; Rose, J.; Speight, V.; von Gunten, U.; Schnoor, J. How do you like your tap water? Science 2016, 351, (6276), 912-914. (3) Sedlak, D. L.; von Gunten, U. The Chlorine Dilemma. Science 2011, 331, (6013), 4243. (4) Agus, E.; Voutchkov, N.; Sedlak, D. L. Disinfection by-products and their potential impact on the quality of water produced by desalination systems: A literature review. Desalination 2009, 237, (1–3), 214-237. (5) D'alessandro, W.; Bellomo, S.; Parello, F.; Brusca, L.; Longo, M. Survey on fluoride, bromide and chloride contents in public drinking water supplies in sicily (italy). Environ. Monit. Assess. 2008, 145, (1-3), 303-313. (6) Flury, M.; Papritz, A. Bromide in the Natural Environment: Occurrence and Toxicity. J. Environ. Qual. 1993, 22, (4), 747-758. (7) Gruchlik, Y.; Tan, J.; Allard, S.; Heitz, A.; Bowman, M.; Halliwell, D.; Von Gunten, U.; Criquet, J.; Joll, C. Impact of bromide and iodide during drinking water disinfection and
ACS Paragon Plus Environment
21
Page 23 of 25
585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634
Environmental Science & Technology
potential treatment processes for their removal or mitigation. Water J. Aust. Water Ass. 2014, 41, (8), 38-43. (8) Heller-Grossman, L.; Idin, A.; Limoni-Relis, B.; Rebhun, M. Formation of Cyanogen Bromide and Other Volatile DBPs in the Disinfection of Bromide-Rich Lake Water. Environ. Sci. Technol. 1999, 33, (6), 932-937. (9) Magazinovic, R. S.; Nicholson, B. C.; Mulcahy, D. E.; Davey, D. E. Bromide levels in natural waters: its relationship to levels of both chloride and total dissolved solids and the implications for water treatment. Chemosphere 2004, 57, (4), 329-335. (10) Soltermann, F.; Abegglen, C.; Götz, C.; von Gunten, U. Bromide Sources and Loads in Swiss Surface Waters and Their Relevance for Bromate Formation during Wastewater Ozonation. Environ. Sci. Technol. 2016, 50, (18), 9825-9834. (11) Kumar, K.; Margerum, D. W. Kinetics and mechanism of general-acid-assisted oxidation of bromide by hypochlorite and hypochlorous acid. Inorg. Chem. 1987, 26, (16), 2706-2711. (12) Nokes, C. J.; Fenton, E.; Randall, C. J. Modelling the formation of brominated trihalomethanes in chlorinated drinking waters. Water Res. 1999, 33, (17), 3557-3568. (13) Westerhoff, P.; Chao, P.; Mash, H. Reactivity of natural organic matter with aqueous chlorine and bromine. Water Res. 2004, 38, (6), 1502-1513. (14) Acero, J. L.; Piriou, P.; von Gunten, U. Kinetics and mechanisms of formation of bromophenols during drinking water chlorination: assessment of taste and odor development. Water Res. 2005, 39, 2979 - 2993. (15) Criquet, J.; Rodriguez, E. M.; Allard, S.; Wellauer, S.; Salhi, E.; Joll, C. A.; von Gunten, U. Reaction of bromine and chlorine with phenolic compounds and natural organic matter extracts – Electrophilic aromatic substitution and oxidation. Water Res. 2015, 85, 476486. (16) Allard, S.; Tan, J.; Joll, C. A.; von Gunten, U. Mechanistic Study on the Formation of Cl-/Br-/I-Trihalomethanes during Chlorination/Chloramination Combined with a Theoretical Cytotoxicity Evaluation. Environ. Sci. Technol. 2015, 49, (18), 11105-11114. (17) Hua, G.; Reckhow, D. A.; Kim, J. Effect of bromide ion and iodide ions on the formation and speciation of disinfection byproducts during chlorination. Environ. Sci. Technol. 2006, 40, 3050-3056. (18) Heeb, M. B.; Criquet, J.; Zimmermann-Steffens, S. G.; von Gunten, U. Oxidative treatment of bromide-containing waters: Formation of bromine and its reactions with inorganic and organic compounds — A critical review. Water Res. 2014, 48, (0), 15-42. (19) Cowman, G. A.; Singer, P. C. Effect of Bromide Ion on Haloacetic Acid Speciation Resulting from Chlorination and Chloramination of Aquatic Humic Substances. Environ. Sci. Technol. 1995, 30, (1), 16-24. (20) Hua, G.; Reckhow, D. A. Determination of TOCl, TOBr and TOI in drinking water by pyrolysis and off-line ion chromatography. Anal. Bioanal. Chem. 2006, 384, 495-504. (21) Richardson, S. D. Disinfection by-products and other emerging contaminants in drinking water. TrAC-Trend Anal Chem 2003, 22, (10), 666-684. (22) Symons, J. M.; Krasner, S. W.; Simms, L. A.; Sclimenti, M. Measurement of THM and Precursor Concentrations Revisited: The Effect of Bromide Ion. J. Am. Water Works Ass. 1993, 85, (1), 51-62. (23) Le Roux, J.; Gallard, H.; Croué, J.-P. Formation of NDMA and Halogenated DBPs by Chloramination of Tertiary Amines: The Influence of Bromide Ion. Environ. Sci. Technol. 2012, 46, (3), 1581-1589. (24) von Gunten, U.; Salhi, E.; Schmidt, C. K.; Arnold, W. A. Kinetics and Mechanisms of N-Nitrosodimethylamine Formation upon Ozonation of N,N-Dimethylsulfamide-Containing Waters: Bromide Catalysis. Environ. Sci. Technol. 2010, 44, (15), 5762-5768.
ACS Paragon Plus Environment
22
Environmental Science & Technology
635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684
Page 24 of 25
(25) Chebeir, M.; Liu, H. Kinetics and Mechanisms of Cr(VI) Formation via the Oxidation of Cr(III) Solid Phases by Chlorine in Drinking Water. Environ. Sci. Technol. 2016, 50, (2), 701-710. (26) Lee, Y.; von Gunten, U. Transformation of 17α-Ethinylestradiol during Water Chlorination: Effects of Bromide on Kinetics, Products, and Transformation Pathways. Environ. Sci. Technol. 2009, 43, (2), 480-487. (27) Criquet, J.; Allard, S.; Sallhi, E.; Joll, C. A.; Heitz, A.; von Gunten, U. Iodate and Iodo-Trihalomethane Formation during Chlorination of Iodide-Containing Waters: Role of Bromide. Environ. Sci. Technol. 2012, 46, (13), 7350-7357. (28) Allard, S.; Fouche, L.; Dick, J.; Heitz, A.; von Gunten, U. Oxidation of manganese (II) during chlorination: role of bromide. Environ. Sci. Technol. 2013, 47, 8716 - 8723. (29) Plewa, M. J.; Kargalioglu, Y.; Vankerk, D.; Minear, R. A.; Wagner, E. D. Mammalian cell cytotoxicity and genotoxicity analysis of drinking water disinfection by-products. Environ. Mol. Mutagen. 2002, 40, (2), 134-142. (30) Richardson, S. D.; Plewa, M. J.; Wagner, E. D.; Schoeny, R.; DeMarini, D. M. Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection byproducts in drinking water: A review and roadmap for research. Mutat. Res-Rev. Mutat. 2007, 636, (1–3), 178-242. (31) Sharma, V. K.; Zboril, R.; McDonald, T. J. Formation and toxicity of brominated disinfection byproducts during chlorination and chloramination of water: A review. J. Environ. Sci. Heal B. 2013, 49, (3), 212-228. (32) Stalter, D.; O'Malley, E.; von Gunten, U.; Escher, B. I. Fingerprinting the reactive toxicity pathways of 50 drinking water disinfection by-products. Water Res. 2016, 91, 19-30. (33) Pan, Y.; Zhang, X. Four Groups of New Aromatic Halogenated Disinfection Byproducts: Effect of Bromide Concentration on Their Formation and Speciation in Chlorinated Drinking Water. Environ. Sci. Technol. 2013, 47, (3), 1265-1273. (34) Richardson, S. D.; Postigo, C., Formation of DBPs: state of the science. American Chemical Society: Washington DC., 2015; Vol. 1190, p 189-214. (35) Hua, G.; Reckhow, D. A. Comparison of disinfection byproduct formation from chlorine and alternative disinfectants. Water Res. 2007, 41, (8), 1667-1678. (36) Krasner, S. W.; Weinberg, H. S.; Richardson, S. D.; Pastor, S. J.; Chinn, R.; Sclimenti, M. J.; Onstad, G. D.; Thruston, A. D. Occurrence of a New Generation of Disinfection Byproducts†. Environ. Sci. Technol. 2006, 40, (23), 7175-7185. (37) Stalter, D.; Peters, L. I.; O’Malley, E.; Tang, J. Y.-M.; Revalor, M.; Farré, M. J.; Watson, K.; von Gunten, U.; Escher, B. I. Sample Enrichment for Bioanalytical Assessment of Disinfected Drinking Water: Concentrating the Polar, the Volatiles, and the Unknowns. Environ. Sci. Technol. 2016, 50, (12), 6495-6505. (38) Kristiana, I.; McDonald, S.; Tan, J.; Joll, C.; Heitz, A. Analysis of halogen-specific TOX revisited: Method improvement and application. Talanta 2015, 139, (0), 104-110. (39) Kristiana, I.; Gallard, H.; Joll, C.; Croué, J.-P. The formation of halogen-specific TOX from chlorination and chloramination of natural organic matter isolates. Water Res. 2009, 43, (17), 4177-4186. (40) Tan, J.; Allard, S.; Gruchlik, Y.; McDonald, S.; Joll, C. A.; Heitz, A. Impact of bromide on halogen incorporation into organic moieties in chlorinated drinking water treatment and distribution systems. Sci. Total Environ. 2016, 541, 1572-1580. (41) Hua, G.; Reckhow, D. DBP formation during chlorination and chloramination: Effect of reaction time, pH, dosage, and temperature. J. Am. Water Works Ass. 2008, 100, (8), 82. (42) Yang, Y.; Komaki, Y.; Kimura, S. Y.; Hu, H.-Y.; Wagner, E. D.; Mariñas, B. J.; Plewa, M. J. Toxic Impact of Bromide and Iodide on Drinking Water Disinfected with Chlorine or Chloramines. Environ. Sci. Technol. 2014, 48, (20), 12362-12369.
ACS Paragon Plus Environment
23
Page 25 of 25
685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715
Environmental Science & Technology
(43) Zhu, X.; Zhang, X. Modeling the formation of TOCl, TOBr and TOI during chlor(am)ination of drinking water. Water Res. 2016, 96, 166-176. (44) Morris, J. C. The Acid Ionization Constant of HOCl from 5 to 35°. J. Phys. Chem. 1966, 70, (12), 3798-3805. (45) Eaton, A. D.; Clesceri, L. S.; Rice, E. W.; Greenberg, A. E., Standard Methods for the Examination of Water and Wastewater, 21st Edition. APHA: Washington DC, USA, 2005. (46) Allard, S.; Charrois, J. W. A.; Joll, C. A.; Heitz, A. Simultaneous analysis of 10 trihalomethanes at nanogram per liter levels in water using solid-phase microextraction and gas chromatography mass-spectrometry. J. Chromatogr A. 2012, 1238, (0), 15-21. (47) Bousher, A.; Brimblecombe, P.; Midgley, D. Rate of hypobromite formation in chlorinated seawater. Water Res. 1986, 20, (7), 865-870. (48) Echigo, S.; Minear, R. A. Kinetics of the reaction of hypobromous acid and organic matters in water treatment processes. Water Sci. Technol. 2006, 53, (11), 235-243. (49) Song, R.; Westerhoff, P.; Minear Roger, A.; Amy Gary, L., Interactions Between Bromine and Natural Organic Matter. In Water Disinfection and Natural Organic Matter, Minear Roger, A.; Amy Gary, L., Eds. American Chemical Society: Washington, DC., USA, 1996; Vol. 649, pp 298-321. (50) Peters, C. J.; Young, R. J.; Perry, R. Factors influencing the formation of haloforms in the chlorination of humic materials. Environ. Sci. Technol. 1980, 14, (11), 1391-1395. (51) Reckhow, D. A.; Singer, P. C.; Malcolm, R. L. Chlorination of humic materials: byproduct formation and chemical interpretations. Environ. Sci. Technol. 1990, 24, (11), 1655-1664. (52) Wenk, J.; Aeschbacher, M.; Salhi, E.; Canonica, S.; von Gunten, U.; Sander, M. Chemical Oxidation of Dissolved Organic Matter by Chlorine Dioxide, Chlorine, and Ozone: Effect on Its Optical and Antioxidant Properties. Environ. Sci. Technol. 2013, 47, 1114711156. (53) Gallard, H.; von Gunten, U. Chlorination of Phenols: Kinetics and Formation of Chloroform. Environ. Sci. Technol. 2002, 36, (5), 884-890. (54) Gallard, H.; Pellizzari, F.; Croué, J. P.; Legube, B. Rate constants of reactions of bromine with phenols in aqueous solution. Water Res. 2003, 37, (12), 2883-2892. (55) Ianni, J. C. Kintecus Version 5.5. www.kintecus.com. 2015.
716
ACS Paragon Plus Environment
24