Effects of bromide on the formation of THMs and HAAs

Article abstract of DOI:10.1016/S0045-6535(00)00210-1

The role of bromide in the formation and speciation of disinfection by-products (DBPs) during chlorination was investigated. The molar ratio of applied chlorine to bromide is an important factor in the formation and speciation of trihalomethanes (THMs) and halogenacetic acids (HAAs). A good relationship exists between the molar fractions of THMs and the bromide incorporation factor. The halogen substitution ability of HOBr and HOCl during the formation of THMs and HAAs can be determined based on probability theory. The formation of HAAs, and their respective concentrations, can also be estimated through use of the developed model.

Full text of DOI:10.1016/S0045-6535(00)00210-1

Chemosphere 43 ꢀ2001) 1029±1034
E€ects of bromide on the formation of THMs and HAAs
a,
E.E. Chang , Y.P. Lin , P.C. Chiang
b
b
*
a
Department of Biochemistry, Taipei Medical College, 250 Wu-Hsing Street, Taipei, 105 Taiwan, ROC
Graduate Institute of Environmental Engineering, National Taiwan University, Taipei, Taiwan, ROC
b
Received 12 April 2000; accepted 19 June 2000
Abstract
The role of bromide in the formation and speciation of disinfection by-products ꢀDBPs) during chlorination was
investigated. The molar ratio of applied chlorine to bromide is an important factor in the formation and speciation of
trihalomethanes ꢀTHMs) and halogenacetic acids ꢀHAAs). A good relationship exists between the molar fractions of
THMs and the bromide incorporation factor. The halogen substitution ability of HOBr and HOCl during the
formation of THMs and HAAs can be determined based on probability theory. The formation of HAAs, and their
respective concentrations, can also be estimated through use of the developed model. Ó 2001 Elsevier Science Ltd.
All rights reserved.
Keywords: Bromide; Chlorination; Trihalomethanes; Haloacetic acids
À
1
. Introduction
is a€ected by the ratios of HOCl/Br ꢀRebhun et al.,
À À
1
990), Br /NOM and Br /free chlorine ꢀShukairy et al.,
In water treatment plants, hypobromous acid
1995). The formation of bromate in the presence of
ozone also presents a problem in the light of the recent
D/DBP rule on the maximum permissible contaminant
level of bromate ꢀ0.01 mg/l) ꢀFederal Register, 1998).
The purpose of this study was to systematically in-
vestigate the role of bromide on the formation and
species distribution of THMs and HAAs. Speci®cally, a
model based on probability theory, developed by others,
was used to determine the relative reaction rates of
HOBr and HOCl and to estimate the concentration of
HAA species that could not be quanti®ed.
ꢀ
HOBr) and hypobromite are generated due to the re-
action of chlorine and bromide ꢀWong and Davidson,
977). HOBr is more powerful than hydrochlorous acid
Morris, 1978) and its role in the formation of disin-
1
ꢀ
fection by-products ꢀDBPs) is analogous to that of
HOCl. Symons et al. ꢀ1993) have indicated that HOBr
reacts with natural organic matter ꢀNOM) faster than
HOCl, and the ratio of HOBr/HOCl plays an important
role in the formation of trihalomenthanes ꢀTHMs) and
halogenacetic acids ꢀHAAs) ꢀCowman and Singer,
1
996). The bromide ion shifts the distribution of HAAs
to more brominated species ꢀPourmoghaddas et al.,
993), including bromodichloromethane, dibromochlo-
1
2
. Materials and methods
romethane, bromoform and brominated acetic acids; the
distribution of chlorinated DBPs and brominated DBPs
2
.1. Experiment design
Water samples used in this study were directly col-
*
lected without extraction from the source water of a
local treatment plant in Taipei County. Water quality
characteristics of the raw water were: dissolved organic
Corresponding author. Tel.: +886-22736-9236; fax: +886-
2736-9236.
E-mail address: eechang@tmc.edu.tw ꢀE.E. Chang).
2
0
045-6535/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved.
PII: S 0 0 4 5 - 6 5 3 5 ꢀ 0 0 ) 0 0 2 1 0 - 1

1030
E.E. Chang et al. / Chemosphere 43 ꢀ2001) 1029±1034
carbon ꢀDOC) ˆ 1.5 mg/l and UV254 ˆ 0.047. Chlorina-
tion was performed in water bu€ered with 0.05 M
phosphate at pH 7.0. Stock solutions of sodium hypo-
chlorite were standardized by the iodometric method
ꢀ
ꢀ
APHA, 1995). A vial containing 100 ml ®ltered water
0.45 lm) was used for each kinetic experiment. The vial
was placed in an incubator ꢀ25°C), and the reaction was
quenched after 24 h with an Na SO solution. Five
2
3
chlorine concentrations, 2±6 mg/l ꢀ0.028±0.085 mM),
were used. For each chlorine dosage, six bromide con-
centrations, 0.1±4 mg/l ꢀ0.001±0.050 mM), were added
to form a ®ve by six matrix.
2
.2. THMs and HAAs: analytical methods
For THM analysis, the sample was ®rst extracted
with n-pentane, and the extract was then analyzed using
a gas chromatograph ꢀHP 5180-II) with a fused silica
capillary column ꢀRestek Mtx-5, 30 m ´ 0.28 mm ID and
1
.0 lm ®lm thickness) and an electronic capture detec-
tor. A micro-extraction procedure ꢀextracting with
methyl-tert-butyl ether and ester®ed with diazomethane)
5
was used to analyze HAA . The ester®ed extract was
analyzed using the same gas chromatograph. Supelco
standard solutions were prepared for calibrating four
THM compounds and six HAA compounds. All the
detailed analyses followed the QA/QC programs set
forth in Standard Methods ꢀAPHA, 1995) including
detection limits, internal standard, surrogate standard
and preservative agents for DBPs.
Fig. 1. THM formation as a function of bromide concentration
under various Cl concentrations. ꢀa) Cl
ˆ 4.0 mg/l ꢀ0.056 mM), ꢀc) Cl
2
2
ˆ 2.0 mg/l ꢀ0.028
ˆ 6.0 mg/l ꢀ0.085
3
. Results and discussion
mM), ꢀb) Cl
mM).
2
2
3
.1. THM and HAA formation
speciation gradually shifts to brominated species with
increasing bromide concentration. The formation of
The formation of THM in the source water spiked
with bromide is shown in Fig. 1. In general, total THM
concentration increases slightly with increasing bromide
concentration; a slight decrease in total THM with
5
HAA at the three applied chlorine dosages is di€erent.
For instance, at the lowest chlorine dosage used ꢀ0.028
mM), no chlorinated species was observed. Instead,
dibromoacetic acid ꢀDBAA) increases with increased
bromide concentration, whereas bromochloroacetic acid
ꢀBCAA) ®rst increases and then decreases. As the
chlorine dosage increases to 0.056 mM, four HAA spe-
cies are found and the chlorinated species are gradually
replaced by mixed or brominated species with increasing
À
higher Br concentration is noted at lower chlorine
dosage. The patterns of the four THM species with in-
À
creased Br concentrations are as follows: CHCl
CHCl Br decrease continuously; CHBr Cl increases
3
and
2
2
initially and then decreases, with the peaks occurring at
bromide concentrations of 0.0038±0.0063 mM ꢀ0.3±0.5
mg/l); CHBr
3
increases continuously. The patterns are
5
bromide concentration. The variation of total HAA at
similar for the di€erent applied chlorine dosages studied
in this paper. THM speciation gradually shifts from
chlorinated species to mixed bromochloro species to
brominated species with increasing bromide concentra-
tion. Even at the lowest bromide concentration used
this chlorine dosage with various bromide concentra-
tions is not dramatic, due to the balance between the
decreased chlorinated species and the increased detect-
able brominated species, DBAA. It is noted that the
2
formation of both dibromochloroacetic acid ꢀBr ClAA)
ꢀ
THM species are produced.
0.0013 mM), mixed bromochloro and brominated
and tribromoacetic acid ꢀTBAA) is expected at higher
bromide/chlorine ratios. Unfortunately, the standards of
three HAA species, i.e., bromodichloroacetic acid
The formation of ®ve species of HAAs is shown in
Fig. 2. Analogous to the formation of THM, HAA
2 2
ꢀBrCl AA), Br ClAA and TBAA, are not commercially

E.E. Chang et al. / Chemosphere 43 ꢀ2001) 1029±1034
1031
À
HAAs as a function of the Cl
2
/Br ratio is shown in
/Br molar ratio increases, the con-
centrations of CHClBr , CHCl Br and CHCl increase.
À
Fig. 3. As the Cl
2
2
2
3
CHBr
Cl /Br . At Cl
3
À
is the only species that decreases with increasing
À
2
2
/Br ˆ 7, CHBr
3
is about 50% of total
and CHClBr
is 79% of total THMs. Similar results are also reported
À
THMs. At Cl
2
/Br ˆ 9, the sum of CHBr
3
2
À
by Rebhun et al. ꢀ1990), or 40% and 90% for Cl
and 10, respectively. As for HAAs, the formation of
2
/Br ˆ 7
BCAA and, to a lesser extent, DCAA and TCAA
À
increases with increasing Cl
tration decreases.
2
/Br while DBAA concen-
3
.2. Bromine incorporation
Gould et al. ꢀ1983) introduce bromine incorporation
factor n, a dimensionless factor, to evaluate THM spe-
ciation, in which n is the molar amount of bromine in
2 2 3
the THMs ꢀCHBrCl + 2CHClBr + 3CHBr ) divided by
the molar TTHM concentration:
CHBrCl
2
‡ 2CHClBr
2
‡ 3CHBr
3
n ˆ
ꢀ0 6 n 6 3†
TTHM
ꢀ
1†
The value of n varies between 0 and 3, with 0 corre-
sponding to the formation of only CHCl and 3 to that
of CHBr . In order to investigate the relationship
3
3
Fig. 2. HAA formation as a function of bromide concentration
under various Cl concentrations. ꢀa) Cl
ˆ 4.0 mg/l ꢀ0.056 mM), ꢀc) Cl
2
2
ˆ 2.0 mg/l ꢀ0.028
ˆ 6.0 mg/l ꢀ0.085
mM), ꢀb) Cl
mM).
2
2
available resulting in inability to detect these com-
pounds.
At the highest chlorine dosage used ꢀ0.085 mM), the
concentration of HAA
with the increasing bromide concentration. The initial
decrease in HAA concentration may result from the
non-detection of BrCl AA, Br ClAA and TBAA. The
5
decreases and then increases
5
2
2
concentrations of the three species should be greater
than those in lower chlorine dosage conditions because
of higher concentrations of HOBr generated from the
reaction of chlorine and bromide. As bromide concen-
tration further increases, DBAA, as well as two unde-
2
tected Br ClAAs and TBAAs, increases gradually with
the corresponding decrease of other chlorinated species,
resulting in an overall increase in observed HAA
other undetectable bromo-dominant species.
5
and
The molar ratio of applied chlorine to bromide is an
important factor to be considered while examining DBP
formation and speciation. The formation of THMs and
À
Fig. 3. DBP formation as a function of Cl /Br molar ratio. ꢀa)
2
THMs, ꢀb) HAAs.

1032
E.E. Chang et al. / Chemosphere 43 ꢀ2001) 1029±1034
and HOBr in the halogen substitution reactions with
NOM. Analogous to the development of Cowman and
Singer ꢀ1996) for HAA speciation with the assumption
that the reactivity of HOBr is set c times stronger than
that of HOCl, the same approach is used for THM
speciation as follows:
,
ꢀ
ꢁ
ꢂ
2
‰
HOBrŠ
‰HOBrŠ
‰HOClŠ
2
X
CHCl3 ˆ 1
1 ‡ 3c
‡ 3c
‰
HOClŠ
)
ꢁ ‰
ꢂ
3
HOBrŠ
HOClŠ
3
‡
c
ꢀ7†
ꢀ8†
ꢀ9†
‰
,
ꢀ
ꢃ
ꢄ
Fig. 4. Molar fraction of each THM species vs. bromine in-
corporation factor.
‰HOBrŠ
‰HOClŠ
ꢁ
‰HOBrŠ
‰HOClŠ
X
CHCl Br
2
ˆ
3c
1 ‡ 3c
)
ꢂ
ꢁ
ꢂ
2
3
‰
HOBrŠ
‰HOBrŠ
‰HOClŠ
2
3
‡
3c
‡ c
‰
HOClŠ
between the formation of each THM species and bro-
mine incorporation factor, the molar fraction of each
THM species is plotted vs. bromine incorporation factor
as shown in Fig. 4.
ꢀ
),ꢀ
ꢁ
ꢁ ‰
ꢂ
2
HOBrŠ
HOClŠ
‰HOBrŠ
‰HOClŠ
2
XCHClBr2
ˆ
3c
1 ‡ 3c
‰
Each molar fraction can be expressed by a third-
order polynomial via regression.
)
ꢁ
ꢂ
ꢂ
2
3
‰
HOBrŠ
‰HOBrŠ
‰HOClŠ
2
3
‡
3c
‡ c
3
2
‰HOClŠ
X
X
X
X
CHCl3 ˆ À0:018n ‡ 0:216n À 0:82n ‡ 1;
R ˆ 0:994
ꢀ
ꢀ
ꢀ
2†
3†
4†
2
3
2
CHCl Br ˆ 0:055n À 0:355n ‡ 0:538n ‡ 0:096;
2
2
R ˆ 0:998
3
2
CHClBr2 ˆ À0:054n ‡ 0:062n ‡ 0:332n À 0:061;
2
R ˆ 0:986
3
2
2
CHBr3 ˆ 0:018n ‡ 0:077n À 0:06n; R ˆ 0:987
ꢀ5†
The peak value locations of XCHCl Br and XCHClBr2 can be
determined as:
2
dX
dn
ˆ
0
ꢀ6†
The peak value of each molar fraction occurs at n ˆ 0 for
X
CHCl , n ˆ 1.0 for XCHCl Br, n ˆ 1.85 for XCHClBr and
3
2
2
n ˆ 3.0 for XCHBr . The results indicate that the peak
3
molar fraction of each THM species can be determined
by the incorporated bromine concentration.
3.3. THM and HAA speciation and concentration based
on probability theory
From the results presented above, the speciation of
THM and HAA is related to the reactivities of HOCl
Fig. 5. Modeling the molar fraction by probability theory. ꢀa)
THMs, ꢀb) dihalogenated HAAs.

E.E. Chang et al. / Chemosphere 43 ꢀ2001) 1029±1034
1033
Table 1
Comparison of experimental conditions
À
Source
pH
Temperature
°C)
NOM ꢀmg/l)
Cl
2
ꢀmM)
Br ꢀlM)
ꢀ
Subject study
Cowman and
Singer ꢀ1996)
Nokes et al.
7
6 and 8
25
20
1.5 ꢀDOC)
4.0 ꢀTOC)
0.028±0.085
0.113
1.3±50.0
0±25.0
6.9±8.4
13±23
0.6±4.2
0.014±0.070
0.6±10.0
ꢀ1999)
Table 2
Simulation of the formation of trihalogenated HAA species
Ã
Cl
2
/Br ꢀmolar ratio)
TCAA
ꢀ
BrCl
ꢀlM)
2
AA
Br ClAA
ꢀlM)
2
TBAA
ꢀlM)
Total trihalogenated HAA ꢀlM)
lM)
6
.8
6.3
82358
519
966
356
113
88
2
9.0
11.4
7.7
107
56
339
138
130
814
314
293
1
1
1
1
2
3
4
5
6
1.3
3.5
5.0
8.8
2.5
3.8
5.1
6.4
7.6
10.6
13.3
17.5
26.9
27.4
26.1
47.1
58.6
64
72130
7 98 3
75
95
66
47
67
70
107
111
53
51
44
14
6
250
277
160
107
28
325
28
151
4
161
*
Experimental values.
ꢀ
),ꢀ
ꢁ ‰
‰
HOBrŠ
HOClŠ
ꢂ
‰HOBrŠ
‰HOClŠ
3
the total molar concentration of trihalogenated HAAs
from the given TCAA molar concentration. The results
are shown in Table 2. Unfortunately, the formation of
monohalogenated HAA cannot be simulated because of
undetectable levels of bromoacetic acid ꢀMBAA).
3
X
CHBr3
ˆ
c
1 ‡ 3c
)
ꢁ
ꢂ
ꢁ
ꢂ
2
3
‰
HOBrŠ
HOClŠ
‰HOBrŠ
‰HOClŠ
2
3
‡
3c
‡ c
ꢀ10†
‰
The experimental data of THM and dihalogenated
HAAs are used for the best-®tting values of c, as shown
in Fig. 5. For THM, the best-®tting value of c is 25,
which means that HOBr is 25 times stronger than HOCl
in halogen substitution for THM formation. For di-
halogenated HAA, the best ®tting value of c is again 25.
The c values for THM formation and HAA formation,
reported by Bird ꢀ1979) and Cowman and Singer ꢀ1996),
are 20 and 10, respectively. Nokes et al. ꢀ1999) also re-
ported that the relative rate constant ratio of bromina-
tion to chlorination has an approximate value of 9,
determined by a three-step formation model of THM.
The deviation among the c values reported by these in-
vestigators may be caused by the di€erent experimental
parameters, i.e., pH, chlorine dosages, temperature and
the nature and concentration of NOM. Table 1 presents
the comparison of experimental conditions.
4. Conclusions
The molar ratio of applied chlorine to bromide dos-
age is an important factor in examining DBP formation
À
and speciation. For instance, as Cl
increases, the concentrations of CHClBr
2
/Br molar ratio
2
, CHCl
is the only species that decreases
2
Br and
CHCl
with increasing Cl
3
increase. CHBr
3
À
2
/Br ratios. As for HAAs, the for-
mation of BCAA and, to a lesser extent, DCAA and
À
TCAA, increases with increasing Cl
2
/Br while DBAA
formation decreases. Each molar fraction of THM and
its peak value can be expressed by a third-order poly-
nomial in terms of the bromide incorporation factor.
The halogen substitution ability of HOBr and HOCl
during the formation of THMs and HAAs can be de-
termined based on probability theory. In both halogen
substitution for THM and dihalogenated HAA forma-
tion, HOBr is 25 times stronger than HOCl. Undetect-
able HAA species can be determined through use of the
developed model based on the halogen substitution
ability of HOBr and HOCl.
The undetectable HAA species can be determined by
the assumption that the halogen substitution abilities of
HOBr and HOCl are the same among monohalogenat-
ed, dihalogenated and trihalogenated groups. In the case
of this study, the c value of 25 can be used to determine

1
034
E.E. Chang et al. / Chemosphere 43 ꢀ2001) 1029±1034
Chlorination: Environmental Impact and Health E€ects,
vol. 3. Ann Arbor Science, Ann Arbor, MI.
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