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Impact of Water Heaters on the Formation
of Disinfection By-products
BONING LIU1 AND DAVID A. RECKHOW1
1Department
of Civil and Environmental Engineering, University of Massachusetts, Amherst
This study examined the effect of water heaters and home-heating
scenarios on the formation and decomposition of disinfection
by-products (DBPs). Residential concentrations of DBPs were
investigated in cold and hot tap water samples from 18 houses
equipped with conventional water heaters or on-demand, tankless
heaters. The houses were served by a western Massachusetts
water system. On-demand heating without long-term storage of
hot water resulted in little or no change in DBP formation. In
contrast, the research indicated that long-term storage could lead
to an increase in trihalomethanes, haloacetic acid, and
chloropicrin, whereas the concentrations of dichloroacetonitrile
and trichloropropane resulted from competition and
decomposition. In the bench-scale study for this article, laboratory
incubation and different heating scenarios (short-term and longterm) were tested to confirm the effect of stagnation and high
temperature on DBP concentrations in different types of heaters.
Keywords: degradation, disinfection by-products, premise plumbing, water heater
Disinfection by-products (DBPs) are formed during disinfection
of potable water through the reaction between natural organic
matter (NOM) and chemical disinfectants. These compounds
include regulated DBPs, such as trihalomethanes (THMs) and
haloacetic acids (HAAs), and nonregulated DBPs, such as nitrosamines, haloacetonitriles, haloketones, and many more (Yang &
Zhang 2014, Pan & Zhang 2013, Zhao et al. 2012, Zhai &
Zhang 2011, Richardson et al. 2007, USEPA 2006, Singer 1994).
The presence of DBPs in drinking water poses a health concern
because many are potential carcinogens (Singer 1994). In the
United States, maximum contaminant levels (MCLs) have been
established for total trihalomethanes (TTHMs) and five HAAs
(HAA5) at 80 µg/L and 60 µg/L, respectively.
Some of the nonregulated DBPs have shown greater developmental toxicity and growth inhibition than the regulated ones
(Li et al. 2015, Liu & Zhang 2014, Yang & Zhang 2013, Plewa
et al. 2004). However, assessing human exposure to DBPs is a
challenging task because of the high degree of temporal and
spatial variability and the multiple routes of exposure. In addition to ingestion of cold tap water, inhalation and dermal absorption during hot water–use activities (e.g., showering, bathing,
washing dishes, cooking) are likely to be significant pathways of
exposure (Becalski et al. 2006, Nuckols et al. 2005, King et al. 2004,
Whitaker et al. 2003, Maxwell et al. 1991). Therefore, DBP occurrence in hot tap water needs to be considered in assessing exposure.
Bench-scale heating studies have demonstrated significant
changes in the concentrations of THMs, HAAs, and some more
recently identified DBPs at temperatures equal to or above 50°C
in closed systems (Pan et al. 2014, Zhang et al. 2013, Wu et al.
2001, Weisel & Chen 1994). However, many unanswered questions remain regarding the effects of home heating on the full
range of DBPs. The study by Weisel and Chen (1994) did not
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include HAAs, and these researchers used a higher temperature
(65°C) than the 55°C recommended by the World Health
Organization for pathogen control without excessive risk of
scalding (WHO 2007). Wu et al. (2001) used an open heating
design and boiling-point temperatures for tap water studies and
a closed heating system for chlorinated synthetic water but without a chlorine residual. Zhang et al. (2013) used uniform formation conditions for different temperatures but without combining
low- and high-temperature incubation as normally occurs in the
home. Pan et al. (2014) demonstrated the detoxification effect of
high-temperature heating or boiling (80–100°C) on brominated
DBPs; however, the higher temperature is out of the range of a
domestic water heater.
Recent research has shown an increase in the concentrations
of THMs and HAAs between the distribution system and the
consumer’s hot water tap, and this has been attributed to the long
residence times in traditional hot water systems (Liu & Reckhow
2015, Chowdhury et al. 2011, Dion-Fortier et al. 2009, Eyring et
al. 2008) and simulated distribution systems (Liu & Reckhow
2013). The extended incubation of water in many domestic hot
water systems may accelerate the reactions between chlorine and
NOM (Sadiq & Rodriguez 2004). Therefore, unheated water
samples collected from the distribution system or from premise
plumbing systems may not represent the water that is important
in assessing human exposure during showering and other hot
water use activities.
Relatively few studies have been published regarding the occurrence of DBPs in premise plumbing systems, and even fewer have
examined the effect of different types of home water heaters on
water quality. Tankless water heaters have been gaining popularity in the United States. Instead of incorporating a storage tank
like a conventional water heater, tankless water heaters operate
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by heating and delivering hot water only as needed. As soon as
the hot water tap is opened, the flow detector delivers a signal
that leads to ignition of the burner (many of which are powered
by natural gas). The water circulates through the heat-exchange
coil and reaches the set temperature in about 5 s.
Bagh et al. (2004) found substantial chlorine decay and bacterial growth in a recirculating hot water system that had a long
period of high-temperature incubation. Brazeau (2012) compared
three types of hot water heaters—standard tank heaters with and
without hot water recirculation and an on-demand, tankless
water heater without hot water recirculation. She found that
decay of the disinfectant (monochloramine) was negligible in the
on-demand, tankless water heater, a bit higher in the tank heater
without recirculation, and very high in the tank heater with
recirculation. Until the current study, however, no research had
been conducted on the effect of different types of heaters on
regulated and some of the nonregulated DBPs.
MATERIALS AND METHODS
In the current study, both cold and hot water samples were
collected from homes using the two major types of water heaters.
The homes were located in a recently constructed housing development in western Massachusetts. Bench-scale heating experiments were also conducted as a companion study.
Field sampling. The Rocky Hill Cohousing Community is
located in the city of Northampton, Mass. The community comprises 28 dwellings on 6.5 acres of a 27.5-acre site off Florence
Road. Most of the units are duplexes that were built around the
same time and have similar infrastructure. The community’s
drinking water is supplied by the Northampton filtration plant
located in the neighboring town of Williamsburg, Mass. The
Northampton plant has a design flow of 6.5 mgd and delivers
2.9 mgd to its 28,000 customers on an average day. Approximately 90% of Northampton’s drinking water comes from three
surface water reservoirs, and the remaining 10% comes from two
groundwater sources. Since 2008, the operation of its filtration
plant, which consists of an upflow roughing filter (adsorption
clarifier) and a granular activated carbon filter, has significantly
reduced the concentrations of total organic carbon (TOC) and
DBPs in the system. As a result, the city’s DBP concentrations are
well below the MCL set by the Stage 2 Disinfectants and Disinfection Byproducts Rule. Sodium hypochlorite is added to the filtered water before it enters a 4-mil gal storage tank. As the water
leaves the storage tank, sodium carbonate is added for pH adjustment and corrosion control. Zinc orthophosphate is also added
as a corrosion inhibitor. At the time of this study, the free chlorine
residual of the finished water was in the range of 1.1–1.3 mg/L.
Eighteen houses from the Rocky Hill community were selected
for this study. Eight of the houses were equipped with wholehouse, tankless, gas water heaters, and the remaining 10 houses
used conventional tank heaters. Hot and cold tap water samples
were collected from each house over a two-day period during
the summer. Each house was sampled once during that period
(on the assumption that the water in each hot water tank was
evenly mixed so the sample from the tap represented the water
quality in that tank). Sampling was conducted early in the day
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before any heavy use of hot water. Before sampling, the faucet
aerator was removed and replaced with a custom-made,
threaded connector with attached tubing. These steps were
taken to minimize volatilization of the THMs and other DBPs.
In each case, the cold tap water was sampled after being flushed
for a period of 10 min and after the water temperature had
stabilized (this protocol was followed in order to ensure that
samples consisted of fresh water from the main).
Cold water samples were collected in 300-mL, chlorine
demand–free, glass-stoppered bottles containing ascorbic acid
and sodium azide (Liu & Reckhow 2015). Just before the bottles
were capped, two drops of 6-mol sulfuric acid were added at the
top of the liquid phase of the sample, and then the sample was
capped and mixed thoroughly. Hot water samples were collected
as soon as the temperature stabilized to avoid substantially
depleting the hot water from the water tank. Eyring et al. (2008)
reported the problem of bubble formation in the containers of
their hot tap water samples during cooling; therefore, in the current study, hot tap water samples were collected in serum piston
bottles (described in Liu & Reckhow 2013). All quenched water
samples were placed in a cooler and transported to the University
of Massachusetts Amherst laboratory for DBP analysis. Temperature, chlorine residual, and pH were measured in the field in
all of the hot and cold tap water samples at the time of collection.
Bench-scale testing. Complementary bench-scale testing was
conducted to evaluate the effect of heating on DBP concentrations in the Northampton water supply. Drinking water was
first chlorinated and incubated for different contact times at
20°C to produce samples that could mimic cold tap water
samples at different locations along the distribution system.
Then those incubated samples were heated to 55°C for shortterm (10 min) or long-term (24 h) heating, representing tankless
and tank water heating systems, respectively.
A large sample of filter effluent from the Northampton water
treatment plant was collected and transported on ice to the university laboratory. Tests were performed on a 4-L sample of the
water that was transferred to a 20°C incubator and equilibrated
for 8 h. The sample was then buffered at pH 8.0 ± 0.2 with
monopotassium phosphate and sodium hydroxide. A stock solution of sodium hypochlorite1 was used for chlorination, and it was
standardized by the N, N-diethyl-p-phenylenediamine (DPD)
ferrous titrimetric method (method 4500-Cl F, Standard Methods
1998). The chlorine dosage was set at 5 mg/L to reach a target
chlorine residual of 0.5 mg/L after 24 h of heating.
The 4-L borosilicate bottles containing chlorinated samples
were incubated at 20°C for various contact times (6, 24, 48, 72,
and 96 h). At the end of each contact time, a subsample that
would not be subjected to further heating was collected by transferring 300 mL to a chlorine demand–free, glass-stoppered bottle.
A portion of this subsample was used to measure chlorine residual. The remaining portion was partitioned into glass vials containing ascorbic acid; a drop of concentrated sulfuric acid was
added to each vial; and the glass vials were sealed headspace-free
for subsequent DBP analysis.
After these first subsamples were collected, the remaining volume of each chlorinated sample was carefully partitioned into
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TABLE 1
Quality of finished water and tap water in the
Northampton (Mass.) water supply system
Finished
Water
Cold Tap Watera
Hot Tap Watera
TOC—mg/L
0.96
0.89 (0.12)
1.01 (0.11)
DOC— mg/L
0.78
—
—
UV254—cm–1
—
Parameter
0.006
—
SUVA—L/mg/m
0.8
—
—
pH
7.52
7.56 (0.017)
7.55 (0.027)
17
20.3 (0.97)
53.3 (2.97)
Temperature—°C
Significant Delta Values (∆) for the
Difference Between Two Types of
Water Heaters
p
Significant or Not
Chlorine residual—mg/L
1.02
0.00002
Yes
DCAA—µg/L
7.23
0.0018
Yes
TCAA—µg/L
6.76
0.398
No
BCAA—µg/L
1.52
0.0639
No
BDCAA—µg/L
0.55
0.22742
No
TTHMs—µg/L
20.57
0.04
Yes
CP—µg/L
BDL
0.00775
Yes
TCP—µg/L
0.36
0.003449
Yes
DCAN—µg/L
2.36
0.0000002135
Yes
BDL—below detection limit, CP—chloropicrin, BCAA—bromochloroacetic acid, BDCAA—
bromodichloroacetic acid, DCAA—dichloroacetic acid, DCAN—dichloroacetonitrile, DOC—
dissolved organic carbon, SUVA—specific ultraviolet absorbance, TCAA—trichloroacetic
acid, TCP—trichloropropanone, TOC—total organic carbon, TTHMs—total trihalomethanes,
UV254—ultraviolet absorbance at 254 nm
∆ = difference in the chlorine or DBP concentration between the cold and hot tap water in
the field
aValues
in parentheses are standard deviations.
FIGURE 1
Chlorine residual in the cold (C) and hot (H) tap
water from homes with tank and tankless
water-heating systems
Chlorine residual
Median
0.6
Chlorine Residual—mg/L
0.5
0.4
0.3
0.2
0.1
BDL
BDL
0.0
Tank:
C
Tank:
H
Tankless:
C
Tankless:
H
Type of Water-Heating System
BDL—below detection limit
Detection limit for chlorine residual is 0.02mg/L.
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piston bottles, headspace-free, with the piston in place at the fully
depressed level so that it could rise as the water sample expanded
during incubation in the warm water bath. Each bottle was sealed
tightly and placed in a water bath pre-equilibrated to 55°C. It
took about 30 min for each bottle to reach 55°C. At each of the
two defined contact times (10 min and 24 h), one of the piston
bottles was withdrawn from the 55°C water bath and immediately placed in the cold water bath (4°C) to cool down. The
chlorine residuals were measured as soon as the samples were
collected, and the remaining samples were quenched and preserved in preparation for subsequent DBP analysis.
Analytical methods. In the field, chlorine residuals were measured
by the DPD colorimetric method using a field kit.2 Temperature
and pH were measured with a portable meter.3 In the lab, four
chlorine- and bromine-containing THMs, dihaloacetonitriles,
chloropicrin (CP), and 1,1,1-trichloropropanone (TCP) were
quantified by liquid–liquid extraction with pentane and by gas
chromatography with electron capture detection (GC–ECD),
according to US Environmental Protection Agency (USEPA)
method 551.1. Nine haloacetic acids (HAA9) were analyzed by
liquid–liquid extraction with methyl tertiary butyl ether, followed
by derivatization with acidic methanol and by GC–ECD on the basis
of USEPA method 552.2. TOC was analyzed by the high-temperature
combustion method using a commercial TOC analyzer.4
RESULTS AND DISCUSSION
Field sampling. Temperatures of the cold tap water samples
ranged from 18 to 22°C, which is typical of Northampton water
during the sampling period (July 2010). The temperature of the
water exiting the tankless water heaters was set by the factory at
55°C in order to prevent scalding, and on-site measurements
showed it to be in the range of 50–60°C. Temperatures of the
pipes exiting the tankless water heaters were cool to ambient,
whereas the pipes exiting the standard tank heater were warm
because of heat conduction from the tank. Nevertheless, there
was no significant temperature difference in the samples collected
from the two types of heaters. Small variations in TOC, pH, and
ultraviolet light absorbance at 254 nm (UV254) were found in cold
and hot tap water. The quality of the finished water and the tap
water is summarized in Table 1.
Chlorine residual. In tap water, chlorine decay is attributed
mainly to reactions with NOM. The water age, the presence of
dissolved reactive substances (e.g., NOM, sulfide, ferrous iron),
and reactive pipe materials could also affect chlorine decay in a
distribution system (Mutoti et al. 2007, Rossman et al. 1994).
The age of the water between the plant and the sampled homes
at the Rocky Hill community was essentially identical and in the
range of 24–96 h. Chlorine residuals in the cold tap water samples
ranged from 0.23 to 0.52 mg/L. Analytical results for the hot tap
water samples indicated a significant decrease in the chlorine
residual in homes equipped with a tank water heater but only a
marginal decrease in homes with a tankless heater (Figure 1).
The loss of chlorine residual when the water was heated is
unlikely to have been caused by thermal decomposition (i.e.,
disproportionation) because sodium hypochlorite was found to
be stable around 50°C (Gambarini et al. 1998). Rather, it seems
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FIGURE 3
0.8
CP, DCAN, and TCP in the cold (C) and hot (H)
tap water from homes with tank and tankless
water-heating systems
CP
DCAN
TCP
Median
CP—µg/L
0.6
0.4
0.2
BDL
BDL
BDL
Tankless:
C
Tankless:
H
0.0
Tank:
C
Tank:
H
Type of Water-Heating System
2.5
2.0
DCAN—µg/L
most likely to have been caused by a higher rate of reaction with
NOM and other reduced solutes in the water. The longer exposure
to high temperatures makes the standard tank heating system
more vulnerable to the loss of chlorine residual. The hot water
from one home with a tank heater had a relatively high chlorine
residual, and this seems to have resulted from heavy use of the
hot water just before sample collection.
Trihalomethanes. Because the organic content of the finished
water was low, the yield of TTHMs in the consumer’s cold tap
water was well below the MCL established by the Stage 2 Disinfectant and Disinfection Byproducts Rule (Figure 2). The concentration of TTHMs in the cold tap water samples ranged from 17.6
to 27.5 µg/L, whereas the concentration of TTHMs in the hot tap
water samples ranged from 21.9 to 42.5 µg/L, exceeding those in
the cold water samples by as much as 120%. All of the significant
differences in TTHM concentrations between hot and cold water
samples were observed in homes with traditional tank water
heating systems. Small TTHM variations between cold and hot
tap water samples were observed in homes with tankless water
heaters. Individual THMs exhibited trends similar to the TTHMs;
therefore, the individual THM species are not discussed.
Other neutral DBPs. The occurrence of three other neutral
DBPs—dichloroacetonitrile (DCAN), CP, and TCP—in the cold and
hot tap water samples is shown in Figure 3. The concentrations of
DCAN, the only chlorinated haloacetonitrile detected, were comparable in all cold water samples as well as in hot water samples
from tankless systems. A large decrease in the DCAN concentration
was observed in hot tap water from traditional, tank water-heating
systems. A very slight increase in DCAN concentration was observed
in hot tap water from tankless water heaters. DCAN is known to
undergo base-catalyzed decomposition (Reckhow et al. 2001;
1.5
1.0
0.5
0.0
FIGURE 2
THMs in the cold (C) and hot (H) tap water from homes
with tank and tankless water-heating systems
Tank:
C
Tank:
H
Tankless:
C
Tankless:
H
Type of Water-Heating System
Chlorine residual
Median
3.0
50
2.5
2.0
TCP—µg/L
THMs—µg/L
40
30
1.5
1.0
20
0.5
10
0
0.0
Tank:
C
Tank:
H
Tankless:
C
Tankless:
H
Type of Water-Heating System
THMs—trihalomethanes
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Tank:
C
Tank:
H
Tankless:
C
Tankless:
H
Type of Water-Heating System
BDL—below detection limit, CP—chloropicrin, DCAN—dichloroacetonitrile,
TCP—1,1,1-trichloropropanone
Detection limit for DCAN = 0.06 µg/L, CP = 0.02 µg/L, and TCP = 0.10 µg/L
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Trehy & Bieber 1981). In the presence of a chlorine residual, the
concentration of DCAN increased initially and then decreased
because of autodecomposition (Zhang et al. 2013). Exner et al.
(1973) suggested that DCAN would transform to dichloroacetamide, which in the absence of free chlorine would undergo rapid
hydrolysis to form dichloroacetic acid (DCAA). Therefore, the
decomposition of DCAN could also contribute to the increase in
DCAA observed in the hot tap water, albeit by a rather small amount.
CP was not detected in either the cold tap water or the hot
water from tankless heaters. The presence of CP in the hot tap
FIGURE 4
water samples from conventional water heating systems suggests
that high temperatures enhance the formation of CP more than
its degradation. The analytical results for TCP were much like
those for DCAN. A slight decrease in TCP was observed in hot
water samples from the tankless water heaters. In contrast, a
significant loss of TCP was observed in hot water samples from
the conventional water-heating systems.
Haloacetic acids. Small amounts of precursor material in this
water supply kept the HAA5 concentrations well below the MCL
of 60 µg/L set by USEPA (Figure 4). Among the HAA9 species,
Haloacetic acids in the cold (C) and hot (H) tap water from homes with tank and tankless water-heating systems
DCAA
TCAA
BCAA
BDCAA
Median
12
20
18
10
16
8
12
TCAA—µg/L
DCAA—µg/L
14
10
8
6
4
6
4
2
2
0
Tank:
C
Tank:
H
Tankless:
C
0
Tankless:
H
Tank:
C
Tank:
H
Tankless:
C
Tankless:
H
Type of Water-Heating System
Type of Water-Heating System
0.7
1.2
0.6
1.0
0.5
BDCAA—µg/L
BCAA—µg/L
0.8
0.6
0.4
0.3
0.2
0.2
0.0
0.4
0.1
Tank:
C
Tank:
H
Tankless:
C
Tankless:
H
0.0
Tank:
C
Type of Water-Heating System
Tank:
H
Tankless:
C
Tankless:
H
Type of Water-Heating System
BCAA—bromochloroacetic acid, BDCAA—bromodichloroacetic acid, DCAA—dichloroacetic acid, TCAA—trichloroacetic acid
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only DCAA and trichloroacetic acid (TCAA) were detected in
samples collected at the Rocky Hill community. The concentration of DCAA was higher in the hot tap water from conventional
water heating systems compared with the cold tap water at the
same sampling locations. In contrast, the difference was minor in
most of the homes equipped with tankless heating systems. Conversely, regardless of the type of water heater, TCAA concentrations in cold and hot tap water were comparable in most of the
sampling locations.
Although bromochloroacetic acid (BCAA) and bromodichloroacetic acid (BDCAA) are not currently regulated by USEPA,
these compounds were detected and are discussed because they
are believed to be more genotoxic than their chlorinated analogs
(Plewa et al. 2004). Very minor differences in BDCAA concentrations were observed between the cold and hot tap water samples
from homes equipped with tankless heaters (Figure 4). However,
FIGURE 5
Time-dependent formation of TTHMs during the heating
process (pH = 8 ± 0.2)
No heating
Heating for 10 min (55ºC)
Heating for 24 h (55ºC)
120
THM s —µg/L
100
80
60
40
20
0
0
20
40
60
80
Low-Temperature (20ºC) Incubation Time—h
100
20
100
Chlorine Residual—mg/L as Cl2
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
40
60
80
Low-Temperature (20ºC) Incubation Time—h
TTHMs—total trihalomethanes
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significant reductions in BDCAA concentrations were observed
in the hot tap water samples from homes equipped with traditional water heaters. Thermal decarboxylation was found to
occur faster with BDCAA than with TCAA, forming bromodichloromethane with a first-order rate constant of 0.234/d at 50°C
(Zhang & Minear 2002). Therefore, the net decrease in BDCAA
concentrations in tank water systems may be attributed to accelerated decomposition superimposed over little change in the
TCAAs as a group. As shown in Figure 4, the concentration of
BCAA in the cold tap water from all the sampled homes was
comparable. The tiny increase in BCAA concentration noted in
the hot water from homes with tank systems may mirror a similar relative increase observed for the more abundant DCAA.
Of the four HAAs analyzed in this study, only the dihaloacetic
acids (DCAA and possibly BCAA) exhibited behavior similar to
that of the THMs (i.e., higher concentrations in the hot water
from tank systems), whereas the trihaloacetic acids (TCAA and
BDCAA) showed the opposite behavior. Differences between
these two groups stem from differences in precursor origins to
differences in formation and degradation kinetics (e.g., Reckhow
& Singer 2011). Other researchers have found the concentration
of HAA5 to be significantly higher in hot tap water than in cold
tap water (Chowdhury et al. 2011). Eyring et al. (2008) found
that HAA5 tended to increase only a minor amount in a distribution system containing chloramine as the final disinfectant
(winter–spring seasons). However, these authors reported only
the sum of HAAs, whereas this study compared individual
haloacetic acids.
Previous studies found the precursors of DCAA to be overall
less hydrophobic than TCAA precursors, and their formation
kinetics were quite different (Liang & Singer 2003). Therefore,
TCAA and DCAA may exhibit significant differences in occurrence. Also, chlorine decay in hot water tanks could lead to the
growth of thermophilic bacteria in these tanks and the associated
plumbing (Bagh et al. 2004). Bacteria collected from water distribution systems were capable of degrading haloacetic acids
(Williams et al. 1996). A thermophilic dehalogenase enzyme was
found to be active and capable of degrading haloacetic acids at
temperatures above 50°C (Bachas-Daunert et al. 2009). Nevertheless, no reports of organisms identified in home hot water systems
have been shown to be responsible for biodegradation of DBPs
in these systems. Additionally, TCAA was not readily biodegradable by different enrichment cultures (Zhang et al. 2009, McRae
et al. 2004). Therefore, it is unlikely that a large amount of TCAA
could have been biologically degraded in the hot water tank. The
existence of competitive formation pathways between TCAA and
THM may be a more reasonable explanation for the small difference TCAA concentrations between samples of cold and hot
tap water. The work of Reckhow and Singer (1985) suggests that
the formation of THMs and trihaloacetic acids occurs through
competitive pathways including hydrolysis and oxidation. The
low level of chlorine residual may restrict the formation of TCAA.
Significant testing of field data. In order to assess the statistical significance of the effect of water heaters on water quality
parameters, paired t-tests were conducted on the chlorine residual
and DBP concentrations in hot and cold tap water from the two
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types of water heating systems. The results are shown in Table 1.
A value of p > 0.05 is considered an indication of no significant
difference. The paired t-tests confirmed that changes in the
concentrations of chlorine residual, DCAA, TTHMs, CP, TCP,
and DCAN between cold tap water and hot water from conventional water heaters differed significantly from those changes
between cold tap water and hot water from tankless heaters.
The changes in TCAA, BCAA, and BDCAA concentrations were
not considered significant.
Bench-scale testing. Samples collected for bench-scale testing
were finished water without the addition of chlorine at the plant.
As shown in Table 1, Northampton’s finished water contained
very low concentrations of organic carbon and had a low specific
UV254 value, which is indicative of NOM with a hydrophilic
character, not heavily affected by condensed tannins or lignin.
Incubation of the samples for different periods of time and at
different temperatures was intended to represent different water
ages in the distribution system. Short-term (10 min) and longterm (24 h) heating were used to represent the heating processes
of the two types of hot water systems—tankless, on-demand
systems and conventional, tank systems, respectively. Figure 5
FIGURE 6
shows the TTHM formation and chlorine residual profiles during sample incubation and during the heating process. Substantial chlorine residuals were observed throughout the four days
of incubation at an ambient temperature of 20°C. Short-term
heating caused a small increase in the consumption of chlorine
at each time interval of incubation at ambient temperature. After
the samples had been heated for 24 h, the chlorine residuals
dropped to 0.6 mg/L or less. TTHM formation increased with
increasing reaction time during incubation at ambient temperature. After 10 min of heating, the TTHMs increased by a very
small amount, but after 24 h of heating, TTHM concentrations
increased by a factor of 2.5–4.9 compared with the samples that
had not been heated.
The rapid formation of TTHMs at the early stage of chlorination is often attributed to fast-reactive NOM sites (Amy et al.
1998). Zhang et al. (2013) demonstrated that the formation of
chloroform increased rapidly during chlorination’s early stages,
regardless of temperature. It is generally accepted that reaction
rates increase with increasing temperature. However, because
heating was initiated midway through the chlorine contact time
in the current study, short-term (10-min) heating did not
Time-dependent formation of haloacetic acids during the heating process (pH = 8 ± 0.2)
25
0.5
20
0.4
BCAA—µg/L
DCAA—µg/L
No heating
Heating for 10 min (55ºC)
Heating for 24 hr (55ºC)
15
10
0
20
40
60
80
Low-Temperature (20ºC) Incubation Time—h
0.0
100
12
0.7
10
0.6
8
BDCAA—µg/L
TCAA—µg/L
0.2
0.1
5
0
0.3
6
4
2
0
20
40
60
80
Low-Temperature (20ºC) Incubation Time—h
100
0
20
40
60
80
Low-Temperature (20ºC) Incubation Time—h
100
0.5
0.4
0.3
0.2
0.1
0.0
0
0
20
40
60
80
Low-Temperature (20ºC) Incubation Time—h
100
BCAA—bromochloroacetic acid, BDCAA—bromodichloroacetic acid, DCAA—dichloroacetic acid, TCAA—trichloroacetic acid
JOURNAL AWWA
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Liu & Reckhow | http://dx.doi.org/10.5942/jawwa.2015.107.0080
Peer-Reviewed
significantly change the formation of THMs in the samples
because the fast-reactive NOM had already been consumed.
After 24 h of heating, further formation of TTHMs (through
reaction with slower NOM sites) increased with increasing
incubation time, despite the fact that less additional TTHM
formation had been expected as the chlorine residual decreased
with increasing incubation time. It is possible that some
unknown halogenated by-products might accumulate during
ambient-temperature incubation and react with the chlorine
residual to form additional THMs at a higher temperature.
Simultaneous thermal decarboxylation of TCAAs could also
contribute to the increase in THMs (Zhang & Minear 2002,
Verhoek 1934), but this contribution might be minor.
DCAA and TCAA concentrations increased with increasing
incubation time, whereas BCAA and BDCAA reached maximum
concentrations at about 48 h (Figure 6). Because the water contained only a small amount of bromide, the concentrations of
BCAA and BDCAA were quite low. There was little change in
DCAA and TCAA concentrations after short-term heating. After
24 h of heating, the DCAA concentration tripled in samples
incubated for 24 and 48 h at the ambient temperature of 20°C,
FIGURE 6
whereas it doubled for samples incubated for 72 and 96 h at the
ambient temperature. The increase in TCAA concentration after
24 h of heating was in the range of 31–66%, significantly lower
than the increase in TTHMs and DCAA. This result was a bit
different from the field results, in which no significant difference
in TCAA concentration was noted between cold and hot tap
water. This may be attributable to the low chlorine residual in the
field, and the alkaline condition favors the chloroform formation
pathway (Liu & Reckhow 2013, Reckhow & Singer 1985).
Noticeable reductions in BDCAA and BCAA were observed after
24 h of heating. The first-order decomposition rate constants for
BDCAA and BCAA at 50°C were 2.7 × 10–6/s and 1.6 × 10–6/s,
respectively (Lifongo et al. 2010, Zhang & Minear 2002). The
reductions appeared to be smaller at the shorter incubation times,
though formation was probably continuing to occur at these
shorter incubation periods.
The effect of incubation time on the formation of CP, DCAN,
and TCP is shown in Figure 7. The concentration of CP in the
samples incubated at ambient temperature was quite low, starting
at 0.04 µg/L and slowly increasing to 0.12 µg/L. The 10-min
heating time caused a modest increase in the CP concentration.
Time-dependent formation of haloacetic acids during the heating process (pH = 8 ± 0.2)
25
0.5
20
0.4
BCAA—µg/L
DCAA—µg/L
No heating
Heating for 10 min (55ºC)
Heating for 24 hr (55ºC)
15
10
0
20
40
60
80
Low-Temperature (20ºC) Incubation Time—h
0.0
100
12
0.7
10
0.6
8
BDCAA—µg/L
TCAA—µg/L
0.2
0.1
5
0
0.3
6
4
2
0
20
40
60
80
Low-Temperature (20ºC) Incubation Time—h
100
0
20
40
60
80
Low-Temperature (20ºC) Incubation Time—h
100
0.5
0.4
0.3
0.2
0.1
0.0
0
0
20
40
60
80
Low-Temperature (20ºC) Incubation Time—h
100
BCAA—bromochloroacetic acid, BDCAA—bromodichloroacetic acid, DCAA—dichloroacetic acid, TCAA—trichloroacetic acid
JOURNAL AWWA
2015 © American Water Works Association
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Liu & Reckhow | http://dx.doi.org/10.5942/jawwa.2015.107.0080
Peer-Reviewed
However, the 24-h heating time resulted in substantial increases
in the concentration of CP, elevating the final concentration by a
factor of 3.7–7.8. This result is not consistent with previous
research conducted by Weisel and Chen (1994), who found that
the CP concentration in the heated solution was unchanged during 8 h of heating. In the current study, however, the bench-scale
results were consistent with the results of the field study, which
showed a significant amount of CP in the hot tap water, although
it was below the detection limit in the cold water samples. In
many drinking water supplies, the CP concentrations are low—at
or near the detection limit (typically ~0.16 µg/L), as reported by
Yang et al. (2007) and Krasner et al. (1989). The observation that
long-term heating could significantly increase CP concentrations
is troubling because this family of compounds is considered
among the more toxic of the DBPs (e.g., Plewa et al. 2004).
FIGURE 7
CONCLUSIONS
Time-dependent formation of CP, DCAN, and TCP
during the heating process (pH = 8 ± 0.2)
No heating
Heating for 10 min (55ºC)
Heating for 24 h (55ºC)
0.6
CP—µg/L
0.5
0.4
0.3
0.2
0.1
0.0
0
20
40
60
80
100
80
100
Incubation Time Under 20ºC—h
DCAN—µg/L
0.6
0.4
0.2
0.0
0
20
40
60
Incubation Time Under 20ºC—h
1.0
0.8
TCP—µg/L
The concentration of DCAN increased with increasing incubation time and leveled off at 48 h. Short-term heating led to
an increase in DCAN concentration in samples with shorter
incubation times at the ambient temperature, but it decreased
the DCAN concentration in samples with longer incubation
times at the ambient temperature. Because DCAN is not stable
in aqueous solution, it can decompose, especially under alkaline conditions (Reckhow et al. 2001, Stevens et al. 1989).
Increasing the temperature also enhanced the decomposition
rate of DCAN (Nikolaou et al. 2000). Therefore, the occurrence of DCAN depends on the relative rates of formation and
decomposition. After 24 h of heating, a substantial amount of
DCAN was lost.
TCP decomposed quickly with time after its fast initial formation in samples at pH 8. Short-term heating accelerated the
decomposition of TCP, reducing it by 40–67%. After 24 h of
heating, only very low concentrations of TCP were detected.
The results of this study showed that DBPs could change
significantly during in-home heating of drinking water. On-demand
heating without long-term storage of hot water resulted in little or
no change in the DBP formation profile. In contrast, longer-term
storage of hot water (which typically occurs with conventional,
tank water-heating systems) yielded more THMs and HAAs when
the influent water contained a chlorine residual.
In addition to high-temperature incubation, chlorine residual
also affected the increase in TCAA in the water heater. Analytical results indicated that a significant increase in TCAA may
not occur after incubation in a water heater if the cold tap water
contains a low chlorine residual. The results also showed that
incubation of tap water in a tank water heater could lead to a
significant increase in CP. The concentration of DCAN resulted
from competition between formation and decomposition. An
increase in DCAN concentration was observed after short-term
heating, whereas a substantial decrease in DCAN was the outcome after long-term heating. The TCP concentration decreased
with both incubation time and higher temperature. Overall
results indicated that different types of water heaters and heating scenarios could lead to different DBP formation profiles.
Therefore, because tankless water heaters are becoming popular,
their specific effects should be considered when human exposure
to DBPs is assessed. Additionally, investigation of the effect of
water heaters on chloraminated water is recommended for a
better understanding of the effect of water heaters on DBPs in
drinking water.
0.6
ENDNOTES
0.4
1Fisher
Scientific, Pittsburgh, Pa.
CN-70, Hach Company, Loveland, Colo.
3Model AP85, Fisher Scientific, Pittsburgh, Pa.
4TOC-VCPH, Shimadzu, Santa Clara, Calif.
2Model
0.2
0.0
0
20
40
60
80
Incubation Time Under 20ºC—h
CP—chloropicrin, DCAN—dichloroacetonitrile,
TCP—1,1,1-trichloropropanone
JOURNAL AWWA
100
ACKNOWLEDGMENT
The authors thank the residents of Rocky Hill Housing Community for their help in carrying out this study.
2015 © American Water Works Association
JUNE 2015 | 107:6
E337
Liu & Reckhow | http://dx.doi.org/10.5942/jawwa.2015.107.0080
Peer-Reviewed
ABOUT THE AUTHORS
Boning Liu (to whom correspondence may be
addressed) is an engineer at the New York
City Department of Health and Mental
Hygiene. She may be contacted at boning.
liu@gmail.com. This study was part of Liu’s
doctoral research at the University of
Massachusetts Amherst, where she earned MS
and PhD degrees in civil engineering. She also
holds a BE degree in environmental engineering from Harbin
Institute of Technology in Harbin, China. David A. Reckhow is
a professor in the Department of Civil and Environmental
Engineering, University of Massachusetts Amherst, 130 Natural
Resource Rd., Amherst, MA 01003.
Krasner, S.W.; McGuire, M.J.; Jacangelo, J.G.; Patania, N.L.; Reagan, K.M.; &
Aieta, E.M., 1989. The Occurrence of Disinfection By-products in US Drinking
Water. Journal AWWA, 81:8:41.
Li, J.; Wang, W.; Moe, B.; Wang, H.; & Li, X.F., 2015. Chemical and
Toxicological Characterization of Halobenzoquinones, an Emerging
Class of Disinfection Byproducts. Chemical Research in Toxicology,
28:3:306. http://dx.doi.org/10.1021/tx500494r.
Liang, L. & Singer, P.C., 2003. Factors Influencing the Formation and Relative
Distribution of Haloacetic Acids and Trihalomethanes in Drinking
Water. Environmental Science & Technology, 37:13:2920.
http://dx.doi.org/10.1021/es026230q.
Lifongo, L.L.; Bowden, D.J.; & Brimblecombe, P., 2010. Thermal Degradation of
Haloacetic Acids in Water. International Journal of the Physical Sciences,
5:6:738.
Liu, B. & Reckhow, D.A., 2015. Disparity in Disinfection Byproducts Concen­
tration Between Hot and Cold Tap Water. Water Research, 170:196.
http://dx.doi.org/10.1016/j.watres.2014.11.045.
PEER REVIEW
Date of submission: 01/09/2015
Date of acceptance: 02/24/2015
REFERENCES
Amy, G.; Siddiqui, M.; Ozekin, K.; Zhu, H.W.; & Wang, C., 1998. Empirically Based
Models for Predicting Chlorination and Ozonation By-products:
Trihalomethanes, Haloacetic Acids, Chloral Hydrate, and Bromate. EPA 815R-98-005. USEPA Office of Water, Washington.
Bachas-Daunert, P.G.; Sellers, Z.P.; & Wei, Y., 2009. Detection of Halogenated
Organic Compounds Using Immobilized Thermophilic Dehalogenase.
Analytical and Bioanalytical Chemistry, 395:4:1173. http://dx.doi.org/10.1007/
s00216-009-3057-5.
Bagh, L.K.; Albrechtsen, H.J.; Arvin, E.; & Ovesen, K., 2004. Distribution of Bacteria
in a Domestic Hot Water System in a Danish Apartment Building. Water
Research, 38:1:225. http://dx.doi.org/10.1016/j.watres.2003.08.026.
Becalski, A.; Lau, B.P.; Schrader, T.J.; Seaman, S.W.; & Sun, W.F., 2006. Formation
of Iodoacetic Acids During Cooking: Interaction of Iodized Table Salt With
Chlorinated Drinking Water. Food Additives and Contaminants, 23:10:957.
http://dx.doi.org/10.1080/02652030600838407.
Brazeau, R.H., 2012. Sustainability of Residential Hot Water Infrastructure: Public
Health, Environmental Impacts, and Consumer Drivers. Doctoral dissertation,
Department of Civil and Environmental Engineering, Virginia Polytechnic
Institute and State University, Blacksburg, Va.
Chowdhury, S.; Rodriguez, M.J.; Sadiq, R.; & Sérodes, J., 2011. Modeling DBPs
Formation in Drinking Water in Residential Plumbing Pipes and Hot Water
Tanks. Water Research, 45:1:337. http://dx.doi.org/10.1016/j.watres.
2010.08.002.
Dion-Fortier, A.; Rodriguez, M.J.; Sérodes, J.; & Proulx, F., 2009. Impact of Water
Stagnation in Residential Cold and Hot Water Plumbing on Concentrations
of Trihalomethanes and Haloacetic Acids. Water Research, 43:12:3057.
http://dx.doi.org/10.1016/j.watres.2009.04.019.
Exner, J.H.; Burk, G.A.; & Kyriacou, D., 1973. Rates and Products of Decomposition
of 2,2-dibromo-3-nitrilopropionamide. Journal of Agricultural and Food
Chemistry, 21:5:838. http://dx.doi.org/10.1021/jf60189a012.
Eyring, A.; St. Denis, F.; & Burlingame, G., 2008. Changes in Water Quality in
Premise Plumbing: Cold Water vs. Hot Water. Proc. AWWA 2008 Water
Quality Technology Conference, Cincinnati.
Gambarini, G.; De Luca, M.; & Gerosa, R., 1998. Chemical Stability of Heated
Sodium Hypochlorite Endodontic Irrigants. Journal of Endodontics, 24:6:432.
http://dx.doi.org/10.1016/S0099-2399(98)80027-7.
King, W.D.; Dodds, L.; Armson, B.A.; Allen, A.C.; Fell, D.B.; & Nimrod, C., 2004.
Exposure Assessment in Epidemiologic Studies of Adverse Pregnancy
JOURNAL AWWA
Outcomes and Disinfection Byproducts. Journal of Exposure Analysis and
Environmental Epidemiology, 14:6:466. http://dx.doi.org/10.1038/sj.jea.7500345.
Liu, B. & Reckhow, D.A., 2013. DBP Formation in Hot and Cold Water Across a
Simulated Distribution System: Effect of Incubation Time, Heating Time, pH,
Chlorine Dose, and Incubation Temperature. Environmental Science &
Technology, 47:20:11584. http://dx.doi.org/10.1021/es402840g.
Liu, J. & Zhang, X., 2014. Comparative Toxicity of New Halophenolic DBPs in
Chlorinated Saline Wastewater Effluents Against a Marine Alga:
Halophenolic DBPs Are Generally More Toxic Than Haloaliphatic Ones.
Water Research, 65:64. http://dx.doi.org/10.1016/j.watres.2014.07.024.
Maxwell, N.I.; Burmaster, D.E.; & Ozonoff, D., 1991. Trihalomethanes and
Maximum Contaminant Levels: The Significance of Inhalation and Dermal
Exposures to Chloroform in Household Water. Regulatory Toxicology and
Pharmacology, 14:3:297. http://dx.doi.org/10.1016/0273-2300(91)90032-Q.
McRae, B.M.; LaPara, T.M.; & Hozalski, R.M., 2004. Biodegradation of Haloacetic
Acids by Bacterial Enrichment Cultures. Chemosphere, 55:6:915.
http://dx.doi.org/10.1016/j.chemosphere.2003.11.048.
Mutoti, G.I.; Dietz, J.D.; Arevalo, J.; & Taylor, J.S., 2007. Combined Chlorine
Dissipation: Pipe Material, Water Quality, and Hydraulic Effects. Journal
AWWA, 99:10:96.
Nikolaou, A.D.; Golfinopoulos, S.K.; Kostopoulou, M.N.; & Lekkas, T.D., 2000.
Decomposition of Dihaloacetonitriles in Water Solutions and Fortified
Drinking Water Samples. Chemosphere, 41:8:1149. http://dx.doi.
org/10.1016/S0045-6535(00)00025-4.
Nuckols, J.R.; Ashley, D.L.; Lyu, C.; Gordon, S.M.; Hinckley, A.F.; & Singer, P., 2005.
Influence of Tap Water Quality and Household Water Use Activities on
Indoor Air and Internal Dose Levels of Trihalomethanes. Environmental
Health Perspectives, 113:7:863. http://dx.doi.org/10.1289/ehp.7141.
Pan, Y.; Zhang, X.; Wagner, E.D.; Osiol, J.; & Plewa, M.J., 2014. Boiling of
Simulated Tap Water: Effect on Polar Brominated Disinfection Byproducts,
Halogen Speciation, and Cytotoxicity. Environmental Science & Technology,
48:1:149. http://dx.doi.org/10.1021/es403775v.
Pan, Y. & Zhang, X., 2013. Four Groups of New Aromatic Halogenated Disinfection
Byproducts: Effect of Bromide Concentration on Their Formation and
Speciation in Chlorinated Drinking Water. Environmental Science &
Technology, 47:3:1265. http://dx.doi.org/10.1021/es303729n.
Plewa, M.J.; Wagner, E.D.; Jazwierska, P.; Richardson, S.D.; Chen, P.H.; &
McKague, A.B., 2004. Halonitromethane Drinking Water Disinfection
Byproducts: Chemical Characterization and Mammalian Cell Cytotoxicity and
Genotoxicity. Environmental Science & Technology, 38:1:62. http://dx.doi.
org/10.1021/es030477l.
Reckhow, D.A. & Singer, P.C., 2011 (6th ed.). Formation and Control of Disinfection
By-products. Water Quality and Treatment (J.K. Edzwald, editor). McGrawHill, New York.
2015 © American Water Works Association
JUNE 2015 | 107:6
E338
Liu & Reckhow | http://dx.doi.org/10.5942/jawwa.2015.107.0080
Peer-Reviewed
Reckhow, D.A. & Singer, P.C., 1985. Mechanisms of Organic Halide Formation
During Fulvic Acid Chlorination and Implications With Respect to Preozonation. Water Chlorination: Chemistry, Environmental Impact and Health
Effects, Vol. 5 (R.L. Jolley; R.J. Bull; W.P. Davis; & S. Katz, editors). Lewis
Publishers, Chelsea, Mich.
Reckhow, D.A.; Platt, T.L.; MacNeill, A.; & McClellan, J.N., 2001. Formation and
Degradation of Dichloroacetonitrile in Drinking Waters. Journal of Water
Supply Research and Technology—Aqua, 50:1:1.
Richardson, S.D.; Plewa, M.J.; Wagner, E.D.; Schoeny, R.; & Demarini, D.M., 2007.
Occurrence, Genotoxicity and Carcinogenicity of Regulated and Emerging
Disinfection By-Products in Drinking Water: A Review and Roadmap for
Research. Mutation Research/Reviews in Mutation Research, 636:1–3:178.
http://dx.doi.org/10.1016/j.mrrev.2007.09.001.
Rossman, L.A.; Clark, R.M.; & Grayman, W.M., 1994. Modeling Chlorine Residuals in
Drinking-Water Distribution Systems. Journal of Environmental Engineering,
120:4:803. http://dx.doi.org/10.1061/(ASCE)0733-9372(1994)120:4(803).
Sadiq, R. & Rodriguez, M.J., 2004. Disinfection By-Products (DBPs) in Drinking Water
and Predictive Models for Their Occurrence: A Review. Science of the Total
Environment, 321:1–3:21. http://dx.doi.org/10.1016/j.scitotenv.2003.05.001.
Singer, P.C., 1994. Control of Disinfection By-products in Drinking Water. Journal
of Environmental Engineering, 120:4:727. http://dx.doi.org/10.1061/
(ASCE)0733-9372(1994)120:4(727).
Standard Methods for the Examination of Water and Wastewater, 1998 (20th ed.).
APHA, AWWA, and WEF, Washington.
Stevens, A.A.; Moore, L.A.; & Miltner, R.J., 1989. Formation and Control of NonTrihalomethane Disinfection By-Products. Journal AWWA, 81:8:54.
Trehy, M.L. & Bieber, T.I., 1981. Detection, Identification and Quantitative Analysis
of Dihaloacetonitriles in Chlorinated Natural Waters. Advances in the
Identification and Analysis of Organic Pollutants in Water, Vol. 2 (L.H. Keith,
editor). Ann Arbor Science Publishers, Ann Arbor, Mich.
USEPA (US Environmental Protection Agency), 2006. National Primary Drinking
Water Regulations: Stage 2 Disinfectants and Disinfection Byproducts Rule.
Final Rule. Federal Register, 71:2:387.
Verhoek, F.H., 1934. The Kinetics of the Decomposition of the Trichloroacetates in
Various Solvents. Journal of the American Chemical Society, 56:3:571.
http://dx.doi.org/10.1021/ja01318a014.
Weisel, C.P. & Chen, W.J., 1994. Exposure to Chlorination Byproducts From Hot-Water
Uses. Risk Analysis, 14:1:101. http://dx.doi.org/10.1111/j.1539-6924.1994.tb00032.x.
Whitaker, H.J.; Nieuwenhuijsen, M.J.; & Best, N.G., 2003. The Relationship Between
Water Concentrations and Individual Uptake of Chloroform: A Simulation Study.
Environmental Health Perspectives, 111:5:688. http://dx.doi.org/10.1289/ehp.5963.
JOURNAL AWWA
WHO (World Health Organization), 2007. Legionella and the Prevention of
Legionellosis. World Health Organization, Geneva. http://whqlibdoc.who.
int/publications/2007/9241562978_eng.pdf (accessed April 2013).
Williams, S.L.; Williams, R.L.; & Gordon, A.S., 1996. The Impact of Bacterial
Degradation of Haloacetic Acids (HAAs) in the Distribution System. Proc.
AWWA 1996 Water Quality Technology Conference, Boston.
Wu, W.W.; Benjamin, M.M.; & Korshin, G.V., 2001. Effects of Thermal Treatment on
Halogenated Disinfection By-Products in Drinking Water. Water Research,
35:15:3545. http://dx.doi.org/10.1016/S0043-1354(01)00080-X.
Yang, M. & Zhang, X., 2014. Halopyrroles: A New Group of Highly Toxic
Disinfection Byproducts Formed in Chlorinated Saline Wastewater.
Environmental Science & Technology, 48:20:11846. http://dx.doi.
org/10.1021/es503312k.
Yang, M. & Zhang, X., 2013. Comparative Developmental Toxicity of New Aromatic
Halogenated DBPs in a Chlorinated Saline Sewage Effluent to the Marine
Polychaete Platynereis dumerilii. Environmental Science & Technology,
47:19:10868. http://dx.doi.org/10.1021/es401841t.
Yang, X.; Shang, C.; & Westerhoff, P., 2007. Factors Affecting Formation of
Haloacetonitriles, Haloketones, Chloropicrin and Cyanogen Halides
During Chloramination. Water Research, 41:6:1193. http://dx.doi.
org/10.1016/j.watres.2006.12.004.
Zhai, H. & Zhang, X., 2011. Formation and Decomposition of New and Unknown Polar
Brominated Disinfection Byproducts During Chlorination. Environmental Science
& Technology, 45:6:2194. http://dx.doi.org/10.1021/es1034427.
Zhang, P.; LaPara, T.M.; Goslan, E.H.; Xie, Y.; Parsons, S.A.; & Hozalski, R.M., 2009.
Biodegradation of Haloacetic Acids by Bacterial Isolates and Enrichment
Cultures From Drinking Water Systems. Environmental Science &
Technology, 43:9:3169. http://dx.doi.org/10.1021/es802990e.
Zhang, X. & Minear, R.A., 2002. Decomposition of Trihaloacetic Acids and
Formation of the Corresponding Trihalomethanes in Drinking Water. Water
Research, 36:14:3665. http://dx.doi.org/10.1016/S0043-1354(02)00072-6.
Zhang, X.L.; Yang, H.W.; Wang, X.M.; Fu, J.; & Xie, Y.F., 2013. Formation of
Disinfection By-Products: Effect of Temperature and Kinetic Modeling.
Chemosphere, 9:2:634. http://dx.doi.org/10.1016/j.chemosphere.2012.08.060.
Zhao, Y.; Anichina, J.; Lu, X.; Bull, R.J.; Krasner, S.W.; Hrudey, S.E.; & Li, X.F.,
2012. Occurrence and Formation of Chloro- and Bromo-Benzoquinones
During Drinking Water Disinfection. Water Research, 46:14:4351.
http://dx.doi.org/10.1016/j.watres.2012.05.032.
2015 © American Water Works Association
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