Journal of Environmental Protection, 2010, 1, 456-465
doi:10.4236/jep.2010.14053 Published Online December 2010 (http://www.SciRP.org/journal/jep)
Formation of Trihalomethanes during Seawater
Chlorination
Ahmed Abdel-Wahab1, Ahmed Khodary1, Nasr Bensalah2
1Chemical Engineering Program, Texas A&M University at Qatar, Doha, Qatar; 2Faculty of Sciences of Gabes, University of Gabes,
Gabes, Tunisia.
Received July 23rd, 2010; revised June 22nd, 2010; accepted June 26th, 2010
ABSTRACT
The use of seawater for industrial cooling is a vital technology that poses some of the most profound environmental
impact on the water quality in the Arabian Gulf. Biocide (chlorine) is added to the seawater to control biofouling of the
cooling system. This added chlorine reacts with bromide and other chemicals naturally exist in the water to form a wide
range of oxidants. Regrettably, reactions between the residual oxidants and natural organic matter in the water lead to
formation of toxic halogenated organic compounds that have detrimental effects on the environment when they are dis-
charged into the Gulf. This paper describes the formation of trihalomethanes (THMs) in seawater cooling systems. Re-
sults of kinetic experiments have shown that concentrations of THMs increased rapidly with time during the first half
hour. Chlorination of seawater has shown significant increase in total THMs (TTHMs) and in bromoform concentra-
tions. Rapid decrease of UV absorbance at 254 nm was also observed during seawater chlorination which is indicative
of natural organic matter degradation into small organic molecules including THMs and other by-products. The in-
crease in chlorine dose was accompanied with an increase in TTHMs and bromoform concentrations. Linear relation-
ships between total chlorine concentration and both final TTHMs and bromoform concentrations were established.
First order exponential decay and exponential associate functions were developed to correlate chlorine dose with
formed THMs.
Keywords: Chlorination by-Products, Seawater Cooling, Biocides, Trihalomethane, Bromoform
1. Introduction
The use of seawater in industrial cooling is a common
practice in many parts of the world that have limited
fresh-water resources. One of the primary operational
problems of using seawater in cooling is biofouling. Bio-
fouling can result from growth of microorganisms on
surfaces where they form biofilms or from the growth of
macro-organisms such as clams. Biofilms tend to stick to
heat-exchange surfaces, thereby significantly reducing
heat-transfer coefficients. In some cases, excessive bio-
fouling can lead to plugging of heat exchangers. There
are several techniques for preventing biofouling of both
types, but application of chlorine-based biocide is most
common.
Chlorine is added directly to the seawater to control
biofouling of the cooling system. The added chlorine
reacts with bromide and other compounds in the water to
produce a wide range of chemical oxidants. These in-
clude conversion of bromide ion to hypobromous acid
and other reactive forms of bromine. These brominated
products are the active forms of biocide in seawater sys-
tems and their relative concentrations change on time
scales from fractions of seconds to days. Understanding
their behavior is critical to insuring effective control of
biofouling within the plant and minimizing environ-
mental impacts outside the plant. Additionally, the bro-
minated residual biocide can react with natural organic
matter in the seawater to form a number of halogenated
organic compounds that are toxic to aquatic life as well
as humans. Brominated forms of biocide are much more
effective in producing halogenated organics than chlorine
[1], but have not been studied as extensively.
Understanding the reaction scheme of chlorine, bro-
minated products and natural organic matter is critical to
optimizing performance of biofouling control systems
while minimizing impacts to the aquatic environment and
to human health. Studies by Shams et al. [2] on Umm Al
Nar seawater desalination plant in Abu Dhabi showed
that bromoform represented 95% of the trihalomethanes

Formation of Trihalomethanes during Seawater Chlorination 457
(THMs) that were formed. Ali and Riley [3] reported that
THMs concentrations as high as 90 µg/L were observed
in the vicinity of discharges from combined power/de-
salination plants in Kuwait. Many other reports are
available on the production of halogenated organics in
freshwater systems such as water treatment plants and
water distribution systems [4-11]. However, limited data
are available on biocides chemistry and their reaction
by-products in seawater.
The purpose of this paper is to study the formation of
trihalomethanes in seawater and to quantitatively predict
changes in concentrations of biocides and reaction prod-
ucts in cooling water. This will provide the basis for de-
veloping a full kinetic model to describe the biocide
chemistry in seawater and for developing a simulation
tool to determine the fate and transport of biocides and
their reaction products in the environment.
2. Materials and Methods
2.1. Chemicals
Seawater samples were collected in October 2008 from
side tap of Doha costal sea at Qatar. Samples were placed
in amber glass bottles and chlorinated immediately after
collection whenever possible; otherwise, they were kept
in the refrigerator at 4℃. Analytical standard mix solu-
tions of halogenated volatiles (2000 ppb each in acetone)
were of analytical grade (purity 99%). The THMs con-
tained in the standard solution were chloroform, bromo-
form, bromodichloromethane (BDCM), and dibromo-
chloromethane (DBCM). Standard solutions (1, 5, 10, 20,
50 and 100 ppb) were prepared from analytical standard
mix solutions by dilution in acetone for calibration me-
thod. Organic solvents used in dilution and extraction
were high purity grade. All chemicals used in the ex-
periments were prepared from analytical grade chemical
reagents without any further purification.
2.2. Kinetic Experiments
Seawater chlorination was performed using sodium hy-
pochlorite (NaOCl) solution (12%) as the chlorine source.
Four different doses of chlorine were studied (1, 2, 3 and
4 ppm as Cl2). The reactors were 60 ml borosilicate glass
bottles with TFE-faced septa and polypropylene screw
caps. The vials were carefully filled so that trapping of
air bubbles inside was prevented (headspace free) and
possible volatilization of THMs was evaded. Then they
were allowed to react at room temperature (25℃) and
were analyzed after reaction times of 0.0, 0.5, 1, 6, 18, 24,
48, 72, 96, 120 and 168 hours. Sodium thiosulfate was
instantaneously added to each sample taken at a desired
time during experiment to quench chlorine and stop any
further formation of halogenated organic components.
These samples were then analyzed for free chlorine, total
chlorine, total organic carbon (TOC), dissolved organic
carbon (DOC), pH and THMs concentrations.
2.3. Analytical Procedures
TOC and DOC concentrations were analyzed using a
Skalar TOC/TN analyzer. pH measurement was per-
formed using a VWR SympHony pH-meter. UV absorb-
ance measurements were carried out for raw seawater as
well as for chlorinated seawater samples at 254 nm by
use of a Perkin-Elmer (Lambda 25) UV-visible spectro-
photometer with 1 cm quartz cells. Bromide ions con-
centration was determined according to standard method
phenol red colorimetric method [12]. Free and total chlo-
rine were measured according to DPD colorimetric me-
thod [12]. THMs were analyzed using gas chromatogra-
phy (GC) equipped with micro-electron capture detector
(µ-ECD). The gas chromatograph Agilent technologies
7890A GC system equipped with a capillary fused silica
DB-1 column (30 m length × 0.32 mm id × 0.25 mm film
thickness) was used. Injections were made in splitless
mode, with helium as carrier gas (flow rate 1.6 mL min-1)
and auto-sampler. For THMs analysis, 35 mL were taken
from each vial and extracted with 2 mL methyl-tert-butyl
ether (MTBE). 1 µL of the extract was then injected into
the GC system. Temperature was programmed from
35℃ to 120℃ as follows: an initial hold of nine minutes
at 35℃, increase from 35℃ to 40℃ at 1℃ mn-1, a hold
of 3 minutes at 40℃, temperature increase from 40℃ to
120℃ at 6℃ mn-1 with a final hold time of 3 minutes.
Total THMs concentrations (TTHMs) were calculated (in
ppb as CHCl3) from THMs concentrations (in pbb) using
the following Equation (1):




3
3
TTHMsCHCl0.728* BDCM
0.574* DBCM0.472* CHBr

 (1)
3. Results and Discussion
Table 1 illustrates concentrations TOC, DOC, UV-absor-
bance and THMs in seawater collected from Arabian
Gulf in Qatar before any treatment. As it can be seen,
raw seawater contains residual amounts of free chlorine
(0.14 ppm), 0.35 ppm total oxidants and 7 ppm TOC.
This could be due to the discharge of large quantities of
chlorinated treated domestic wastewaters into the Ara-
bian Gulf near Doha. Organic carbon content was mostly
dissolved organic matter as revealed by the little differ-
ence between TOC and DOC concentrations. As it can be
also observed, 1 ppb TTHMs is monitored in raw sea-
water with bromoform as the main halogenated product
present. Little amounts of bromodichloromethane (DBCM)
and dibromochloromethane (DBCM) were also detected,

Formation of Trihalomethanes during Seawater Chlorination 458
Table 1. Physic-chemical analyses of unchlorinated sea-
water collected from Arabian Gulf in Doha-Qatar.
Parameters Values
pH 8.2
TOC (mg L-1) 6.6
DOC (mg L-1) 5.8
UV absorbance at 254 nm 2.0
Br- (mg L-1) 64.0
Bromoform (ppb) 1.71
TTHMs (ppb) 1.03
but no chloroform was detected in the collected fresh
seawater.
The formation of brominated THMS is due to the high
concentration of bromide present in the Arabian Gulf
seawater (~64 ppm) [2]. This results in the conversion of
hypochlorous acid to hypobromous acid as shown in Eq-
uation 2 below.
HOCl BrHOBrCl

 (2)
The formed HBrO and other forms of brominated oxi-
dants generated from bromide oxidation react with or-
ganic precursors present in the water and form the bro-
minated methanes.
In addition, high UV absorbance at 254 nm was meas-
ured (about 2.00) indicating that Doha seawater contains
significant amount of aromatic compounds mainly re-
sulting from natural distribution of humic acids. The
presence of humic substances favors THMs formation
from their reactions with halogenated oxidants.
The preservation of seawater at room temperature
leads to important changes in organic and inorganic con-
tent in Doha seawater. Rapid decrease of free and total
chlorine is observed, ending to their total disappearance
after half hour from collecting seawater samples. The
disappearance of chlorine was accompanied with a rapid
decrease in UV absorbance at 254 nm, a slight decrease
in organic carbon concentration and a large increase in
TTTMs content. The decrease of TOC from 6.64 ppm to
5.02 ppm indicates that only 25% of organic carbon is
transformed into CO2, H2O and other inorganic ions. UV
absorbance at 254 nm decreased from 1.99 to 0.265 up to
120 hours which is indicative of natural organic matter
degradation to small organic molecules without TOC
removal, but only small fraction of organic carbon is
transformed into trihalogenated methanes.
TTHMs concentration increased with time up to 120
hours to reach 23 ppb, before it became invariant for 168
hours. Particularly, chloroform (CHCl3) and bromodi-
chloromethane (CHCl2Br) became the major halogenated
components in seawater, while, in fresh seawater, CHCl3
was not detected and only traces of BDCM were moni-
tored. Chloroform was detected, for the first time, after
18 hours seawater preservation at room temperature.
Chloroform concentration was found to increase with
time up to 120 hours before it leveled off and remained
constant for 168 hours. Furthermore, a significant in-
crease with time of bromodichloromethane concentration
was observed to reach 4.25 ppb after 168 hours. Results
indicate also that bromoform concentration increased
with time to reach a maximum after 6 hours before it
slightly decreased with time up to 18 hours and ended to
be constant. The evolution of dibromochloromethane
concentration was markedly different from other THMs
since it was quickly disappeared during seawater preser-
vation. The evolution of THMs with time can be ex-
plained by the nature of residual chlorine present in sea-
water. Less than 40% of total chlorine contained in sea-
water was free chlorine. As it is largely reported, free
chlorine mainly reacts with bromide to form bromine that
oxidizes natural organic matter leading to an increase in
bromoform concentration. In contrast, other forms of
chlorine such as chloroamines react directly with natural
organic matter to form chlorinated methanes which is in
agreement with the increase of chloroform and BDCM
content and the disappearance of DBCM.
3.2. THMs Formation during Chlorination of
Doha Seawater
Figure 1 shows the evolution of free and total chlorine
concentrations as function of time during chlorination of
seawater with 1ppm chlorine dose.
As it can be seen, the two concentrations decreased
continuously with time. Free chlorine disappeared from
solution after less than 48 hours, while at this time 80%
total chlorine is consumed. The disappearance of chlo-
rine from seawater is indicative of consumption of high
oxidation state chlorine element during redox reactions
including oxidation of bromide to bromine and formation
of chlorination by-products from natural organic matter
degradation. It is generally reported that seawater con-
tains high amounts of bromide which is rapidly trans-
formed by chlorine to hypobromous acid and other forms
of bromine. These compounds are well known to be
more powerful oxidant than chlorine species transform-
ing organic matter mainly to brominated by-products.
The evolution with time of TOC and DOC concentra-
tions and UV absorbance during chlorination of seawater
samples is shown in Figure 2.
During the first half hour of the treatment, a rapid de-
crease in the UV absorbance at 254 nm was observed and

Formation of Trihalomethanes during Seawater Chlorination 459
Figure 1. Evolution with time of free and total chlorine
concentrations during Doha seawater chlorination with 1
ppm chlorine at room temperature (25℃) and natural pH
(pH = 8.3).
Figure 2. Evolution with time of TOC, DOC and UV ab-
sorbance at 254 nm during Doha seawater chlorination with
1 ppm chlorine at room temperature (25℃) and natural pH
(pH = 8.3).
then it hung about 0.4-0.5 after 6 hours. TOC and DOC
undergone a little decrease at the beginning of seawater
chlorination up to 72 hours and they became invariant for
the rest of experiment. These results are indicative of the
degradation of the natural organic matter during Doha
seawater chlorination to form several chlorination by-
products including THMs, haloacetic acids and other
volatile halogenated compounds (haloacetonitriles and
haloketones).
Chlorination of fresh seawater with 1 ppm chlorine
dose has shown a significant increase in TTHMs concen-
tration. Figure 3 presents the evolution with time of
THMs concentrations during chlorination of Doha sea-
water with 1ppm chlorine dose. As it can be seen, TTHMs
Figure 3. Evolution with time of THMs concentrations
during Doha seawater chlorination with 1 ppm chlorine at
room temperature (25℃) and natural pH (pH = 8.3).
concentration increased rapidly with time and reached a
plateau at 0.5 µmol L-1 (50 ppb) after 72 hours chlorina-
tion with only 1ppm chlorine dose which indicates that a
part of the natural organic matter contained in seawater
was transformed into halogenated by-products. Bromo-
form, chloroform, DBCM and BDCM were identified as
chlorination by-products in Doha seawater with molecu-
lar fractions of 40.3, 31.4, 22.8 and 5.4 %, respectively.
THMs concentrations increased with time during chlo-
rination, but in different manner. Bromoform concentra-
tion has shown the most rapid increase to remaining con-
stant at 0.2 µmol L-1 after half hour. The increase with
time in BDCM and DBCM concentrations is similar, but
less rapid than that of bromoform concentration since
they reached highest concentrations after 18 and 72 hours
from the beginning of experiments. Chloroform concen-
tration evolution presented different pattern than other
THMs; chloroform is not detectable at the beginning, but
after 18 hours chlorination its concentration increased
with time up to 120 hours and then leveled off and re-
mained constant for the rest of experiment. It is remark-
able that at the end of experiments CHBr3 and CHCl3
have comparable molar concentrations which are indica-
tive of a competitive formation of chlorinated and bro-
minated chlorination by-products from natural organic
matter oxidation contained in Doha seawater by 1ppm
chlorine dose.
Regarding these results, it can be perceived that both
THMs concentrations and their speciation were noticea-
bly different from those recently reported in literature
concerning seawater chlorination by-products. Fabbricino
and Korshin [13], reported that THMs concentration de-
pends largely on seawater quality and TOC content, but
in all cases they found that bromoform was the predomi-

Formation of Trihalomethanes during Seawater Chlorination 460
nant trihalomethane detected during chlorination with
1ppm chlorine dose of Pacific Ocean and Seattle (Wash-
ington State, USA) coastal seawaters. Fayad and Iqbal
[14] have shown that the nature of chlorination by-pro-
ducts resulting from seawater treatment depend on the
chemical structure of humic materials present in seawater.
They also identified bromoform and DBCM as main
chlorination by-products during treatment with chlorine
doses 0.8-1.6 ppm of Halfmoon Bay beach seawater in
Saudi Arabia. According to the results obtained here and
those reported in literature [4-14], it can be concluded
that THMs levels formed during seawater chlorination
(with low chlorine dose) depend on different parameters
including seawater location (costal, Ocean and depth),
TOC concentration, organic matter chemical structure,
and bromide concentration.
The influence of chlorine dose on the evolution of
THMs concentrations during chlorination of Doha sea-
water is illustrated in Figure 4. As it can be observed,
only bromoform concentration and predominance were
largely affected by chlorine dose change. Increasing
chlorine dose from 1 ppm to 4 ppm, bromoform concen-
tration increased also from 50 ppb to 260 ppb and its
molar fraction in TTHMs passed from 4.6% with residual
chlorine to 75.4% with 4 ppm chlorine (see Table 2).
As it can be also seen, seawater chlorination had no
significant influence on concentrations of chloroform,
BDCM and DBCM, but their molar fractions were largely
decreased. These observations show that the contribution
of bromine in the formation of THMs in chlorinated
(a) (b)
(c) (d)
Figure 4. Influence of chlorine dose on the evolution with time of THMs concentrations during Doha seawater chlorination at
room temperature (25℃) and natural pH (pH = 8.3); (a) bromoform; (b) chloroform; (c) DBCM and (d) BDCM.

Formation of Trihalomethanes during Seawater Chlorination 461
Table 2. Evolution of THMs molar fraction in TTHMs as
function of chlorine dose after 168 hours chlorination of
Doha coastal seawater at room temperature (25℃) and
natural pH (initial pH = 8.3).
Chlorine dose Chloroform BDCM DBCM Bromoform
Residual chlorine 82.8% 12.6% 0 4.6%
1 ppm chlorine 30.2 5.25 22.0% 42.6%
2 ppm chlorine 22.2% 3.6% 12.4% 61.8 %
3 ppm chlorine 18.6% 2.5% 5.7% 73.2%
4 ppm chlorine 15.7% 2.0% 6.9% 75.4%
Doha seawater is more important at high chlorine doses.
In fact, chlorine reacts immediately with bromide ions to
form hypobromous acid and other bromine forms; more
the chlorine dose is high, more reaction 2 is shifted to
right.
The levels of brominated oxidants increase with chlo-
rine dose and then large amounts of brominated THMs,
mainly bromoform, can be measured. Furthermore, Fig-
ure 5 shows the evolution of TTHMs concentration as
function of both time and chlorine dose. It appears that
chlorine level had an important influence on kinetics and
yields of THMs formation. The increase of chlorine dose
from 1 ppm to 4 ppm has led to an increase of TTHMs
concentration from about 60 ppb to 165 ppb. As it can be
seen also from Figure 5, THMs formation rate was ini-
tially rapid matching with the rapid consumption of chlo-
rine, followed by a declining rate. Maximum TTHMs
concentration was reached as faster as chlorine concen-
tration is high. These results show that the increase of
chlorine dose leads to a significant increase in TTHMs
concentration.
At high chlorine doses, bromoform becomes the main
trihalomethane component formed in chlorinated Doha
seawater. Similar results were stated by several studies
regarding THMs formation during seawater chlorination,
and it was commonly reported that bromoform was the
predominant THM identified during seawater chlorina-
tion with 1 ppm chlorine dose. In contrast, with 1 ppm
chlorine dose, no such predominance was seen for Doha
seawater, although the bromide concentration was likely
to be somewhat higher than in other costal seawaters.
Figure 6 shows that final TTHMs and bromoform
concentrations (monitored after 168 hours chlorination)
increased linearly with initial total chlorine concentration
measured at the beginning of seawater chlorination. It
can be deduced from this figure that the evolution of fi-
nal TTHMs and bromoform concentrations could be es-
timated using linear functions of initial total chlorine
concentration (0
tot
C), as given by Equations (3) and (4):
Figure 5. Evolution of TTHMs concentration as function of
time and chlorine dose during Doha seawater chlorination
at room temperature (25℃) and natural pH (pH = 8.3).



02
tot
TTHMsppb10.331.8C R0.99038
 (3)



02
3tot
CHBrppb32.460.4C R0.98823
 (4)
These observations are interesting and practical to con-
trol TTHMs and bromoform concentrations (under regu-
lation limits) during Doha seawater chlorination and then
avoid their hazardous effects on marine environment.
These results imply also that Doha seawater chlorination
with low chlorine doses is preferable to preventing bio-
fouling, controlling THMs formation and maintaining
TTHMs and bromoform levels lower than maximum
contaminant limits (MCL) [10].
3.3. Chlorine Decay and TTHMs Formation
Kinetics, Curve-Fitting and Parameters
Numerous researches proposed mathematical models to
predict chlorine decay and THMs formation in chlorin-
ated natural and drinking waters [13-18]. Especially,
chlorine decay was evaluated with first-order decay
model [19], the EPA model [19], Hass and Karra model
[20] and Clark’s model [21]. However, only limited re-
searches have been focused on modeling chlorine decay
and THMs formation in chlorinated seawaters. In our
work, OriginLab (Origin version 6.1) software was used
to predict the evolution with time of total chlorine, free
chlorine, TTHMs and bromoform concentrations.
For each chlorine level, a parallel exponential first or-
der decay curve was fitted to experimental data corre-
sponding to total chlorine (Ctot) and free chlorine (CFree)
concentrations evolution with time, according to the fol-

Formation of Trihalomethanes during Seawater Chlorination 462
(a) (b)
Figure 6. Evolution of final concentrations of (a) TTHMs and (b) bromoform as function total chlorine concentration during
Doha seawater chlorination at room temperature (25℃) and natural pH (pH = 8.3). () fitting curve with OriginLab soft-
ware.
lowing Equations (5)-(6):


 
tot1 2
Ctexpkt expkt     (5)


 
Free34
Ctexpktexpkt    (6)
The parameters α, β, , ,  k1, k2, k3 and k4 were de-
termined using curve-fitting software. Values of these
parameters and regression coefficient (R2), for each ini-
tial chlorine dose, are listed in Tables 3 and 4.
As it can be seen from Figure 7, parallel exponential
first order decay functions exploited by the Origin soft-
ware provided good fit with chlorine experimental data.
The R2 values were close to 1 for both free and total
chlorine concentrations. This model divided chlorine
decay into two parts, fast reaction and slow reaction.
Thus, it appears that parallel exponential first order decay
is suitable for prediction of chlorine evolution with time
during Doha seawater chlorination (up to 168 hours).
This model is comparable to that proposed by Hass and
Karra [20] for simulation of chlorine decay for filtered
natural water.
Similar fitting method was used to predict the evolu-
tion with time TTHMs and bromoform concentrations.
TTHMs and bromoform profiles can be also approxi-
mated using OriginLab curve-fitting software by Equa-
tions (7) and (8):


01
1
2
2
t
TTHMs ppbtxA1expt
t
A1exp
t



 

 











(7)


03
3
3
4
4
t
CHBrppbtyA1exp t
t
A1exp
t



 













(8)
Values of fitting parameters (x0, y0, A1, A2, A3, A4, t1
and t2) and regression coefficients for TTHMs and bro-
moform profiles are given in Tables 5 and 6, respec-
tively. In addition, Figure 8 presents the evolution with
time of both experimental and predicted (using Equations
(7) and (8) and parameters from Tables 5 and 6) data for
TTHMs and bromoform concentrations. As it can be ob-
served predictive curves fit well experimental data for
both TTHMs and CHBr3 concentrations; which is con-
firmed by regression coefficients (R2) > 0.98.
Although OriginLab software gives excellent curve-
fitting results for chlorine decay and THMs formation
during Doha seawater chlorination, the influence of
many other parameters in seawater, including DOC con-
tent, natural organic matter, bromide concentration, pH
and temperature, should be detailed. Therefore, further
research is needed for modeling chlorine decay and
THMs formation in seawater.
4. Conclusions
The main conclusions of this work can be summarized in
the following points:
 Collected seawater was characterized by the pres-
ence of 0.35 ppm total chlorine, 6.64 ppm TOC, 64
ppm bromide and 1 ppb TTHMs. A rapid disap-
pearance of chlorine, a decrease in UV absorbance

Formation of Trihalomethanes during Seawater Chlorination 463
Table 3. Parameters calculated by curve-fitting using OriginLab Origin 6.1 software of total chlorine concentration evolution
with time during chlorination of Doha seawater with different chlorine dose at room temperature and natural pH.
Chlorine dose α β  k1 k
2 R
2
1 ppm 0 1.29340 0.46870 1.055186 0.025026 0.988
2 ppm 0 0.61820 2.07768 2.080689 0.020918 0.982
3 ppm 0.331 1.92588 1.81310 0.269293 0.018558 0.985
4 ppm 0.646 0.99147 2.75343 0.057341 0.026583 0.991
Table 4. Parameters calculated by curve-fitting using OriginLab Origin 6.1 software of free chlorine concentration evolution
with time during chlorination of Doha seawater with different chlorine dose at room temperature and natural pH.
Chlorine dose   k3 k
4 R
2
1 ppm 0.74435 0.29346 1.301744 0.036162 0.945
2 ppm 1.29342 0.46867 1.055045 0.025573 0.988
3 ppm 1.28489 1.29226 0.955393 0.023503 0.98156
4 ppm 1.40883 1.56595 1.008441 0.018031 0.97162
Table 5. Parameters calculated by curve-fitting using OriginLab Origin 6.1 software of TTHMs concentration evolution with
time during chlorination of Doha seawater with different chlorine dose at room temperature and natural pH.
Chlorine dose x0 A
1 A 2 t 1 t 2 R
2
1 ppm 1.02466 42.60321 19.77469 56.67088 0.32594 0.98132
2 ppm 0.98117 51.15133 52.80093 38.60196 0.2887 0.99698
3 ppm 1.38706 43.76408 89.17082 44.15398 0.38491 0.99262
4 ppm 0.93447 34.92287 34.67155 128.04165 0.32724 0.99744
Table 6. Parameters calculated by curve-fitting using OriginLab Origin 6.1 software of CHBr3 concentration evolution with
time during chlorination of Doha seawater with different chlorine dose at room temperature and natural pH.
Chlorine dose y0 A
3 A 4 t 3 t 4 R
2
1 ppm 1.41806 11.26989 39.28299 41.11591 0.35191 0.98132
2 ppm 1.787 20.29675 111.64617 37.08255 0.34555 0.99504
3 ppm 1.61331 33.15593 172.39088 29.90523 0.35355 0.99611
4 ppm 1.44775 42.15865 229.60479 21.72216 0.35191 0.98281
and an increase of TTHMs concentration were ob-
served during Doha seawater preservation at room
temperature. THMs concentrations and speciation
changed with time. Chloroform which is not de-
tectable in raw seawater became the main THM
component after 168 hours.
 Chlorination of Doha seawater with 1 ppm chlorine
dose led to increase in TTHMs concentration.
Bromoform, chloroform, DBCM and BDCM were
identified as chlorination by-products in Doha
seawater with molecular fractions of 40.3, 31.4,
22.8 and 5.4%, respectively. CHBr3 and CHCl3
have comparable molar concentrations which is in-
dicative of competitive reaction of chlorine and
bromine with natural organic matter in Doha sea-
water to form a mixture of chlorinated and bromi-
nated by-products.
 The results obtained have shown that chlorine dose
has a significant influence on THMs concentrations
and speciation. The increase of chlorine dose in-
creased TTHMs and bromoform concentration,
while bromoform, BDCM and DBCM concentra-

Formation of Trihalomethanes during Seawater Chlorination 464
(a) (b)
Figure 7. Fitting curves exploited from OriginLab software (lines) and experimental data (symbols) of (a) total chlorine and
(b) free chlorine concentrations during Doha seawater chlorination with different chlorine doses at room temperature (25℃)
and natural pH (pH = 8.3).
(a) (b)
Figure 8. Fitting curves exploited from OriginLab software (lines) and experimental data (symbols) of (a) TTHMs and (b)
bromoform concentrations during Doha seawater chlorination with different chlorine doses.
tions were almost invariant. Bromoform molar
fraction was then increased to becoming the domi-
nant THM component formed during seawater
chlorination with chlorine dose increase. Linear
behaviors were observed for TTHMs and bromo-
form concentrations with initial total chlorine con-
centration indicating good opportunity to control
THMs formation to minimizing their environ-
mental impacts.
 Curve-fitting method using OriginLab (Origin ver-
sion 6.1) software was used to predict the evolution
with time of total chlorine, free chlorine, TTHMs
and bromoform concentrations during Doha sea-
water chlorination with different chlorine doses.
Parallel exponential first order decay functions ex-
ploited by the Origin software provided good fit
with free and total chlorine experimental data, but
exponential associate profiles was established for
TTHMs and CHBr3 concentrations.
5. Acknowledgement
This research was supported by a research grant from the
Qatar National Research Fund under its National Priority
Research Program (NPRP). Its contents are solely the
responsibility of the authors and do not necessarily rep-
resent the official views of the Qatar National Research

Formation of Trihalomethanes during Seawater Chlorination 465
Fund.
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