Am. J. Trop. Med. Hyg., 83(1), 2010, pp. 135–143
Copyright © 2010 by The American Society of Tropical Medicine and Hygiene
The health consequences of inadequate water supplies
include an estimated 4 billion cases of diarrhea and 1.87 mil-
lion deaths each year, mostly among young children in devel-
oping countries. 1, 2 In addition, waterborne diarrheal diseases
lead to decreased food intake and nutrient absorption, malnu-
trition, reduced resistance to infection, 3 and impaired physi-
cal growth and cognitive development. 4 Recently, household
drinking water treatment and safe storage options have been
recognized as approaches that can reduce disease risk until the
longer term goal of universal access to piped, treated water
can be attained. 5, 6 Household water treatment and storage
practices can prevent disease, and thereby support poverty
alleviation and development goals.
Chlorination was first used for disinfection of public water
supplies in the early 1900s, and is one factor that contributed
to dramatic reductions in waterborne disease in cities in the
United States. 7 Chlorine gas, calcium hypochlorite powder, and
concentrated or locally produced liquid sodium hypochlorite
have historically been the chlorine donors used for water treat-
ment. Sodium dichloroisocyanurate (NaDCC) is an organic
compound that disassociates in water to form sodium cyanurate
and hypochlorous acid. Use of NaDCC tablets in Bangladesh
households was associated with a significant reduction of fecal
coliform bacteria in stored drinking water than in controls
(2.8 colonies/100 mL versus 604.1 colonies/100 mL). 8 Meden-
tech (Wexford, Ireland) is the largest producer of NaDCC
tablets worldwide, distributing more than 900 million water
purification tablets in 2008 for emergency and development
purposes; in total potentially treating greater than 15 billion
liters of water.
Although NaDCC has been widely used for emergency
response and recreational water treatment, concerns about
potential health impacts from sodium cyanurate had pre-
cluded approval as a long-term drinking water disinfectant. 9
In 2004, NaDCC was approved by the U.S. Environmental
Protection Agency for long-term drinking water use. 10 In
addition, the Joint Food and Agriculture Organization of the
United Nations/World Health Organization (WHO) Expert
Committee on Food Additives recommended a tolerable
daily intake for NaDCC for long-term drinking-water disin-
fection of 0–2.0 mg/kg of body weight. 11, 12 This recommenda-
tion was formally adopted by the WHO into the Guidelines
for Drinking Water Quality in the second addendum to the
Third Edition. 13
Sodium dichloroisocyanurate offers some advantages over
other chlorine-based disinfectants for household water treat-
ment in developing countries, including a shelf life of five
years, resistance to degradation from sunlight, single-use
packaging, and low weight in distribution. These advantages,
in some cases, outweigh the disadvantage of higher cost per
liter treated than locally-made sodium hypochlorite solu-
tion ($0.033/liter for sodium hypochlorite and $0.08/liter for
NaDCC). As access to NaDCC has expanded in developing
countries, where many water sources contain suspended and
dissolved organic material, some health officials and imple-
menting organizations have expressed concern about the for-
mation of disinfection by-products in NaDCC-treated water
and the attendant risk to consumers.
In 1974, it was discovered that hypochlorous acid and hypo-
bromous acid react with naturally occurring organic mat-
ter to create four compounds with potential human health
effects: chloroform (CHCl 3 ), bromoform (CHBr 3 ), bromod-
ichloromethane (CHCl 2 Br), and dibromochloromethane
(CHClBr 2 ). 14 These four compounds are collectively termed
trihalomethanes (THMs). Initially, THM research focused
on the effects of chloroform. However, further research has
shown that chlorination of drinking water leads to the for-
mation of many compounds that may or may not have muta-
genic activity. More than 600 water disinfection byproducts
have been identified in chlorinated tap water, including halo-
acetic acids. 15 The THMs, and to a lesser extent the haloacetic
acids, are currently used as indicator chemicals for all poten-
tially harmful compounds formed by the addition of chlorine
The WHO has established guideline values for the four THMs
that are fully protective for cancer and non-cancer effects,
based on epidemiologic and laboratory studies establishing
Disinfection By-Product Formation and Mitigation Strategies in Point-of-Use
Chlorination with Sodium Dichloroisocyanurate in Tanzania
Daniele S. Lantagne ,* Fred Cardinali , and Ben C. Blount
Enteric Diseases Epidemiology Branch, and Division of Laboratory Sciences, National Center for Environmental Health,
Centers for Disease Control and Prevention, Atlanta, Georgia
Abstract. Almost a billion persons lack access to improved drinking water, and diarrheal diseases cause an estimated
1.87 million deaths per year. Sodium dichloroisocyanurate (NaDCC) tablets are widely recommended for household water
treatment to reduce diarrhea. Because NaDCC is directly added to untreated water sources, concerns have been raised about
the potential health impact of disinfection by-products. This study investigated trihalomethane (THM) production in water
from six sources used for drinking (0.6–888.5 nephelometric turbidity units) near Arusha, Tanzania. No sample collected
at 1, 8, and 24 hours after NaDCC addition exceeded the World Health Organization guideline values for either individual
or total THMs. Ceramic filtration, sand filtration, cloth filtration, and settling and decanting were not effective mitigation
strategies to reduce THM formation. Chlorine residual and THM formation were not significantly different in NaDCC
and sodium hypochlorite treatment. Household chlorination of turbid and non-turbid waters did not create THM concen-
trations that exceeded health risk guidelines.
*Address correspondence to Daniele S. Lantagne, Enteric Diseases
Epidemiology Branch, Centers for Disease Control and Prevention,
1600 Clifton Road, Mailstop A38, Atlanta, GA 30333. E-mail: dlan
LANTAGNE AND OTHERS
a non-linear dose-response relationship between THM ana-
lyte and health impact. The guideline values are set below the
expected threshold for these effects. Chloroform has been
classified as possibly carcinogenic to humans, based on suf-
ficient evidence for carcinogenicity in experimental animals
but inadequate evidence in humans. 16 The WHO guideline
value for chloroform is 300 µg/L (or 300 parts per billion). 17
Bromodichloromethane has been classified as probably car-
cinogenic to humans, with sufficient evidence in animals and
inadequate evidence in humans. 18 The WHO guideline value is
60 µg/L. 19 The International Agency for Research on Cancer
of the WHO has classified dibromochloromethane and bro-
moform as not classifiable in humans for carcinogenicity, 18 and
the WHO guideline values for both are 100 µg/L. 19
The WHO also proposes the use of an additive toxicity
guideline value, using a fractionation approach. The sum of the
four actual values of the THMs divided by their guideline value
should not be greater than one. 19 Lastly, the WHO Guidelines
specifically state that “Where local circumstances require that
a choice must be made between meeting either microbiolog-
ical guidelines or guidelines for disinfectants or disinfectant
by-products, the microbiological quality must always take pre-
cedence, and where necessary, a chemical guideline value can
be adopted corresponding to a higher level of risk. Efficient
disinfection must never be compromised.” 20
Most research on THMs has been conducted in water
treatment plants in developed countries, analyzing THM for-
mation potential of source waters and mitigation strategies
such as the use of alternate disinfectants. The one exception
is a 2008 study of household (point-of-use) drinking water
treatment with sodium hypochlorite that documented THM
concentrations did not exceed WHO individual analyte or
additive guideline values 24 hours after sodium hypochlo-
rite addition in waters with 4.23–305 nephelometric turbidity
units (NTU) in Kenya. 21 However, NaDCC was not tested.
Previous research on THM formation with NaDCC has been
limited. In Seine River water of 3–4 NTU, added NaDCC
concentrations leading to chlorine residuals of 3.8–10 mg/L
had chloroform concentrations of 2–21.7 µg/L 24 hours after
treatment. 22 Other THM analytes were not tested. In a study
from the food industry, as added NaDCC concentration
increased, leading to chlorine residuals of 6.98–210.11 mg/L,
corresponding increases in THM concentrations did not occur,
regardless of how the water was chlorinated before NaDCC
addition. 23 However, the THM concentrations increased with
similarly increased sodium hypochlorite residuals. The utility
of this data for household drinking water treatment is lim-
ited because the maximum household added hypochlorite
concentration used would be 5 mg/L and water is unlikely
to be chlorinated before NaDCC addition in developing
In this report, we compare WHO THM Guidelines with THM
levels formed by sodium dichloroisocyanurate and sodium
hypochlorite disinfection of water from a variety of sources
with varying turbidity levels in rural western Tanzania.
Setting. This study was conducted in May 2008 in areas
surrounding Arusha, Tanzania that are targeted by Filter Pure
(Arusha, Tanzania) for ceramic filter promotion because of
high source water turbidity.
Water collection and treatment procedures. Source water
was collected in eight cleaned 20-liter plastic jerry cans from
each source the day before analysis occurred. A total of six
representative water sources, including a river, lake, public tap,
private lake, open well, and borehole connected to a tap, were
analyzed over a four-day period ( Figure 1 ). All study water
sources were used for drinking by local communities.
The eight household water treatments completed with the
collected water are detailed in Table 1 and included 1) addi-
tion of WaterGuard brand sodium hypochlorite for com-
parison to previous study; 21 2) addition of Aquatabs brand
NaDCC; 3) addition of an experimental flavored Aquatabs
NaDCC; 4) addition of trial flocculant/disinfectant Aquatabs
aluminum sulfate and NaDCC tablet in 1.5-liter polyethyl-
ene terephthalate (PET) bottles; 5) filtration through a simple
sand filter before NaDCC addition; 6) filtration through a
ceramic filter before NaDCC addition; 7) filtration through
a cloth filter before NaDCC addition; and, 8) settling for
12 hours and decanting supernatant water before NaDCC
addition. All hypochlorite addition occurred in 20-liter jerry
cans except where noted.
The hypochlorite concentration used in the above treat-
ments was 2 mg/L for clear water (turbidity < 10 NTU or from
a protected source) and 4 mg/L for turbid waters (turbid-
ity > 10 NTU from an unprotected source) for the NaDCC,
and 1.875 mg/L for clear water (as defined above, 1 cap) and
3.75 mg/L (2 caps) for turbid water for sodium hypochlorite. 24
Single doses were added to the tap, open well, and borehole
samples. Double doses were added to the river, lake, and
pond sources. The double dose was used in the 5.1 NTU river
source despite the < 10 NTU turbidity to represent worst-case
THM formation potential because users might double-dose an
Plastic jerry cans used for water storage were purchased
locally. WaterGuard sodium hypochlorite solution distributed
by Population Services International was obtained locally, and
tested to ensure correct concentration with a portable iodo-
metric digital titration kit (Hach, Loveland, CO) for high-range
total chlorine using Method 8209. The three types of Aquatabs
tablets were provided by Medentech to the researchers and
transported to Tanzania, including 1) standard 67-mg Aquatab
NaDCC tablet; 2) an experimental Aquatab 67-mg NaDCC
flavored tablet; and 3) an experimental Aquatab flocculant
tablet containing aluminum sulfate and NaDCC. The first two
types of tablets were added to 20 liters of water and allowed to
dissolve. The flocculant tablet was added to 1.5 liters of water
in a clean PET water bottle, capped, and shaken for 1 minute.
The mixture was uncapped and allowed to settle for 4 minutes,
shaken for 10 seconds, and let sit uncapped for 15 minutes. The
top layer was decanted into a clean 1.5-liter PET water bottle.
The simple sand filter was constructed in a 15-liter bucket
( Figure 2 ) and was composed of a three-inch layer of gravel
beneath a nine-inch layer of sand. Sand and gravel were cho-
sen based on local availability at the ceramics facility and
were rinsed with tap water before use until the water ran
clear. Approximately three inches of head space was available
above the sand layer, and a spigot was installed approximately
two inches from the bottom of the bucket. Note that sand fil-
ters used in this study were simply sand filters. They were not
biosand filters, a specific household water treatment filter that
includes a biologically active schmutzdecke layer to assist in
removal of microbiologic contaminants.
DISINFECTION BY-PRODUCT FORMATION IN POINT-OF-USE CHLORINATION
The ceramic filters used in the study were manufactured by
Filter Pure, using a mixture of clay soil, sawdust, water, and
colloidal silver. The mixture was pressed into a round-bottom
filter, air-dried, and fired in a kiln at a gradually increasing
temperature eventually reaching 900–950°C. Fired filters were
placed in buckets fitted with a plastic spigot ( Figure 2 ). Water
filtered through the filter was poured into a clean jerry can
before chlorine addition.
A commonly available cloth was used for filtration ( Figure 2 ).
For the settling/decanting testing, the 20 liters of water were
allowed to stand for 12 hours. Eighteen liters of the superna-
tant water were then decanted into a clean jerry can, taking
care not to resuspend any settled solids.
Water testing procedures. Before any potential mitigation
strategy or treatment, the sample water was first analyzed
for turbidity, pH, conductivity, and free and total chlorine.
A total organic carbon (TOC) sample was collected in a glass
container, acidified, and stored on ice for later analysis.
At 1 hour, 8 hours, and 24 hours after chlorine addition,
free and total chlorine was measured in each sample, and a
THM sample was collected and stored on ice for later analysis.
Based on extensive prior literature documenting absence of
F igure 1. Water sources in study in Tanzania (clockwise from top left: river, pond, private pond, open well, borehole with tap). Public tap not
T able 1
Water storage, clarification, and treatment procedures completed for each of six water sources, Tanzania
Treatment * Container size (liters)Water clarification procedure Disinfection procedure
Aluminum sulfate/sodium dichloroisocyanurate tablet
Filtered through simple sand filter
Filtered through ceramic filter
Filtered through locally-available cloth
Settled for 12 hours and decanted
* 1 = addition of WaterGuard brand sodium hypochlorite; 2 = addition of Aquatabs brand NaDCC; 3 = addition of an experimental flavored Aquatabs sodium dichloroisocyanurate (NaDCC);
4 = addition of trial flocculant/disinfectant Aquatabs aluminum sulfate and NaDCC tablet in 1.5-liter polyethylene terephthalate bottles; 5 = filtration through a simple sand filter before NaDCC
addition; 6 = filtration through a ceramic filter before NaDCC addition; 7 = filtration through a cloth filter before NaDCC addition; 8 = settling for 24 hours and decanting supernatant water before
LANTAGNE AND OTHERS
microbiologic indicators in water with chlorine residual,
total coliform and Escherichia coli were not analyzed in this
study. 25– 28
Turbidity was measured with a 2020 turbidimeter (LaMotte
Company, Chestertown, MD) calibrated weekly with non-
expired stock calibration solutions. The pH and conductiv-
ity were measured with a multimeter (Hanna Instruments
Ltd., Bedfordshire, United Kingdom) calibrated weekly with
non-expired stock calibration solutions. Free and total chlo-
rine was measured immediately after collecting samples using
a 1200 single wavelength chlorine colorimeter (LaMotte
Company) and DPD-1 and DPD-3 tablets. The meter was
calibrated daily using non-expired stock calibration solutions
from 0 to 2.65 mg/L.
Water samples for total organic carbon analysis were col-
lected in glass containers, acidified to a pH of < 2.0, stored
below 6°C, and delivered to Analytical Services, Incorporated
(Norcross, GA) within two weeks of collection. Method 9060
(using a carbonaceous analyzer to convert the carbon to gas)
of the Environmental Protection Agency (Washington, DC)
was used to analyze the samples, and all laboratory quality
control guidelines were met.
Trihalomethane sampling. Water samples for THM analysis
were collected into a pre-cleaned 40-mL glass vial and
immediately transferred into a pre-cleaned 12-mL glass vial
containing 125 µL of a buffer-quench solution. 29 The 12-mL
vial was slightly overfilled to create an inverted meniscus and
avoid air bubbles. The sample vials were then sealed with
Teflon-lined silicone septa and stored in a chilled (4–8°C) and
dark location before shipping. Samples were stored no longer
than two weeks before shipment to the Division of Laboratory
Sciences of the Centers for Disease Control and Prevention
(Atlanta, GA) for THM analysis.
Water samples were analyzed for THMs (chloroform, bro-
modichloromethane, dibromochloromethane, and bromo-
form) using stable isotope dilution headspace SPME GC-MS. 29
Briefly, water vials were removed from refrigerated storage and
allowed to equilibrate to room temperature before analysis.
Immediately after removal of the vial cap, water (5.0 mL) was
removed using a pre-cleaned gas-tight syringe and transferred
into a SPME headspace vial. Stable isotope labeled analog
solution was added to the sample and the SPME vial immedi-
ately crimp-sealed using Teflon-lined septum.
We then analyzed samples using solid phase microextrac-
tion/gas chromatography–mass spectrometry (SPME/GC-MS)
on a TraceMS (ThermoFisher, Austin, TX) attached to a Trace
2000 gas chromatograph equipped with a split/splitless injec-
tor and operated in the splitless mode. Because of the volatil-
ity of the THMs, a cryo-trap (model 961; Scientific Instrument
Services, Ringoes, NJ) was used to cryofocus the analytes
at the head of the GC column. Volatile organic compounds
were chromatographically separated on a VRX capillary col-
umn (30 m × 0.25 mm internal diameter × 1.4 µm film; Restek,
Bellefonte, PA) during a thermal gradient from 20°C to 200°C.
Automated sampling was done using a CombiPAL autosam-
pler (CTC Analytics AG, Zwingen, Switzerland) equipped
with a 75-µm carboxen/polydimethylsiloxane/divinylbenzene
SPME fiber assembly and heated/agitated headspace extrac-
tion (8 minutes for 500 rpm at 50°C). The fiber was promptly
desorbed by insertion into the hot GC inlet (200°C). The mass
spectrometer was equipped with an electron impact source
and run in the selected ion monitoring mode at unit mass res-
olution. Xcalibur Quan software (ThermoFisher) was used
for peak integration, calibration, and quantification. We inte-
grated peaks with the integrated collaborative information
systems integrator and confirmed by visual inspection. We
calculated relative response factors on the basis of the rela-
tive peak areas of analyte quantitation ion and labeled analog
ion. Quality control consisted of daily analysis of blind quality
control material and pure water blanks. Trihalomethanes were
quantified by comparing the ratios of analyte peak areas with
labeled analog areas for both unknowns and freshly prepared
Source water quality. All six source water samples were tested
for chemical water quality parameters on the day of testing
before any treatment was initiated ( Table 2 ). The pH averaged
7.6, with no sample exceeding the WHO recommended value
for chlorination alone treatment (maximum pH = 8.0). 19 Con-
ductivities ranged from 86 to 525 µS/cm. The TOC also had a
large range, from 0 to 9.8 mg/L (SD = 3.7). Turbidity had a large
range (0.6–888.5 NTU, SD = 360.6). However, only one sample
was in the 10–100 NTU range normally used for a double chlorine
dose. Turbidity and TOC were not correlated (R 2 = 0.10).
Quality control. Duplicate sampling was conducted for each
water quality parameter tested. Analysis of duplicate samples
indicated a high degree of precision for all tests performed,
with data easily meeting high quality control standards of
below a 10% allowable relative percent different (RPD)
( Table 3 ). The RPD of duplicate free (n = 16) and total (n = 14)
chlorine samples were 4.7% and 2.9%, respectively. Duplicate
F igure 2. Treatment methods used in Tanzania (clockwise
from left: simple sand filtration, ceramic filtration, cloth filtration,
Medentech flocculation/disinfection tablet)
DISINFECTION BY-PRODUCT FORMATION IN POINT-OF-USE CHLORINATION
turbidity measurements had an RPD (n = 11) of 5.9%. The pH
(n = 8) and conductivity (n = 7) duplicate RPD were 0.39% and
0.73%, respectively. The RPDs of duplicate individual analyte
THM samples (n = 19–35) ranged from 1.45% to 2.5%.
Overall data. Post-treatment water sample THM con-
centrations from all treatment methods are shown in Table 4 .
The average chloroform concentration was 18.9 µg/L (range
= < 4.0–97.6 µg/L, SD = 20.9 µg/L) across all samples. The
average bromodichloromethane concentration was 3.8 µg/L
(range = < 0.6–17.8 µg/L, SD = 3.5 µg/L). The average
chlorodi bromomethane concentration was 1.6 µg/L (range =
< 0.1–7.3 µg/L, SD = 1.3 µg/L). The average concentration for
the four THMs was 0.3 µg/L (range = < 0.1–1.2 µg/L, SD =
0.3 µg/L). No sample exceeded the WHO guideline values for
any of the four THMs. Samples below the detection limits of 4.0,
0.6, 0.1, and 0.1 µg/L for chloroform, bromodichloromethane,
chlorodibromomethane, and bromoform, respectively, were
imputed as the detection limit divided by radical 2 for analysis
and averaging purposes. The WHO additive ratio guideline
was also not exceeded: ratios ranged from 0.018 to 0.666, with
an average of 0.144 and an SD of 0.114.
The relative percentage of each individual THM analyte by
source is shown in Table 5 . Most (95.0%) river water THMs
was chloroform. Lake and pond water also had mostly chlo-
roform (78.7% and 73.9%, respectively), but had a non-
negligible percentage of bromodichloromethane (18.2% and
20.1%, respectively). In the groundwater sources (tap, open
well, and borehole), we did not calculate analyte percentages
because many chloroform results were below the detection
limit, although the other three analytes were present above
their detection limits.
For simplicity in the following analysis by treatment method,
all results will be total THMs (TTHMs). Results from all treat-
ments in each source are shown in Figure 3 . A general trend of
increasing TTHM concentration from 1 to 24 hours was seen
in almost all samples. The maximum TTHM concentration
24 hours after treatment in the three groundwater sources
(tap, open well, and borehole) was 28.5 µg/L in the sand-
filtered borehole water. The maximum TTHM concentration
across all samples was 119.8 µg/L in the flocculant/disinfec-
tant tablet in pond water. To reduce turbidity in this sample,
two tablets were used. Thus, this sample had a correspondingly
higher added dichloroisocyanurate concentration.
Chlorination results. The free chlorine residual concentra-
tion was maintained in all but the pond source for 24 hours
in all samples ( Figure 4 ). River, lake, open well, and borehole
water residual levels were within the appropriate range (< 2.0 to
> 0.2 mg/L) with all three treatments (sodium hypochlorite,
NaDCC, and experimental NaDCC). Values were slightly
higher in tap water when two NaDCC tablets were used,
likely because of presence of pre-treatment chlorine residual.
Chlorine residual was slightly less in sodium hypochlorite–
treated samples than in NaDCC-treated samples, even
after accounting for the slightly lower sodium hypochlorite
concentration. This difference was not significant by Wilcoxon
rank sum text ( P = 0.69).
No chlorination only sample exceeded any of the WHO
guideline values for the four THMs up to 24 hours after chlo-
rine addition. The average TTHM concentration in sodium
hypochlorite–treated samples 24 hours after treatment was
31.8 µg/L (range = 7.7–93.6 µg/L, SD = 33.7 µg/L), and the
average TTHM concentration in NaDCC-treated samples was
27.0 µg/L (range = 6.8–73.3 µg/L, SD = 26.4 µg/L). This differ-
ence was not statistically significant ( P = 0.52). The average
TTHM concentration in the experimental flavored NaDCC
was 24.0 µg/L (range = 6.9–69.2 µg/L, SD = 24.3 µg/L).
The values for the additive guideline at 24 hours ranged
from 0.074 to 0.365 µg/L, 0.061 to 0.301 µg/L, and 0.063 to
0.275 µg/L in the sodium hypochlorite-, NaDCC-, and experi-
mental NaDCC-treated waters, respectively. River water sam-
ples had the highest additive values for sodium hypochlorite
and experimental NaDCC treatments, and pond water had the
highest value for NaDCC treatment. Tap water had the lowest
value in all three treatments.
Potential mitigation strategies results. As described in
the Methods, five pre-treatment strategies to potentially
mitigate THM production were tested in each of the six water
sources: 1) the Medentech flocculant/disinfection tablet,
2) sand filtration, 3) ceramic filtration, 4) cloth filtration, and,
5) settling and decanting.
The Medentech flocculant/disinfectant tablet increased
turbidity (from 0.4–17.3 NTU to 17.5–30 NTU) in five of
the six sources ( Table 6 ). In the highly turbid pond source,
the use of two tablets reduced turbidity 60.7% from 861 to
338 NTU. Sand filtration increased turbidity (from 0–4.6 NTU
T able 2
Source water physical and chemical characteristics, Tanzania *
Characteristic Source 1: RiverSource 2: Lake Source 3: TapSource 4: Pond Source 5: Open Well Source 6: Borehole
Free chlorine (mg/L)
Total chlorine (mg/L)
* NTU = nephelometric turbidity units; TOC = total organic carbon; BDL = below detection limit.
T able 3
Quality control for water quality parameters, Tanzania
No. (%) of
23 (15.1) †
* Not all 48 possible tested because of laboratory timing.
† Number of duplicates varies between trihalomethane analytes because of dropping
duplicate samples collected when one or both samples were below the detection limit.
LANTAGNE AND OTHERS
to 7.0–15.4 NTU) in the four lowest turbidity sources, and
reduced turbidity by 25.6% and 27.0%, in the lake and pond
sources. Ceramic filtration reduced turbidity in all sam-
ples except in tap water with an NTU of 0.53. The efficacy
of ceramic filtration increased as initial turbidity increased.
Cloth filtration or settling and decanting did not significantly
reduced turbidity in any of the water samples.
The use of ceramic filtration before NaDCC was associated
with a marginally significant reduction of chlorine residual
24 hours after chlorine addition compared with NaDCC only
controls ( P = 0.075). No other associations between treatment
method and chlorine residual were noted.
We tested several locally available strategies for mitigat-
ing THM formation (settling and decanting and cloth, sand,
and ceramic filtration). None of these treatments consistently
reduced THM concentrations in all types of water tested.
However, in the river source, ceramic filtration was effective
in removing THM precursors, and the NaDCC flocculant/
disinfectant tablet increased THM concentrations in the pond
source ( Figure 3 ).
None of the disinfection methods evaluated in this study
resulted in THM concentrations that exceeded individual or
additive WHO guideline values. All disinfected water from
surface water sources contained more chloroform than other
THMs, indicating low bromine in the water supplies, which is
consistent with a non-coastal study location. All ground water
sources (tap, open well, borehole) had low TTHM concentra-
tions, with a maximum of 28.5 µg/L 24 hours after chlorine
addition. By inference, it appears that chloroform did not
form the large majority of these samples TTHM concentra-
tion, although the relatively higher minimum detection limit
of chlorform (4.0 µg/L compared with 0.1–0.6 µg/L) prevented
calculation of the individual analyte contribution to TTHM in
The maximum chloroform value observed (97.6 µg/L)
was only approximately 30% of the WHO guideline value
(300 µg/L). These results are consistent with previous research
on THM formation after sodium hypochlorite addition to tur-
bid waters in developing countries, 21 and confirm that appro-
priate chlorination of household water does not form THM at
concentrations in excess of WHO guidelines. This result is not
surprising. In contrast to public utilities in the United States
and Europe, which devote considerable expense to reducing
THM concentrations in their treated water through technol-
ogy improvements as part of balancing the risk of waterborne
disease and reducing disinfection by-products to mitigate
potential risks, 30 WHO simply considers health effects and
health risk to potential users from exposure to a certain com-
pound when developing guideline values. 13 The WHO has
defined the acceptable risk from the individual THMs as one
extra cancer in every 100,000 persons who drink two liters of
chlorinated water for 70 years. The WHO guidelines, which
are considered separately from the goal of providing highly
treated water through infrastructure, are applicable to health-
based household chlorination water treatment interventions.
The WHO currently does not regulate other disinfection by-
products besides THMs, considering THMs to be surrogate
compounds for all disinfection by-products in drinking water.
Although average chlorine residual concentration was
slightly higher in NaDCC-treated water than in sodium
hypochlorite–treated water 24 hours after chlorine addition,
the difference was not statistically significant. In addition, this
difference was not programmatically significant. The recom-
mended minimum free chlorine residual concentration for
household water treatment is 0.2 mg/L 24 hours after chlo-
rine addition. Sodium hypochlorite and NaDCC treatment
maintained concentrations above the minimum residual level
in all sources except the pond source. There was no incidence
where that minimum residual was maintained with one treat-
ment and not with the other treatment. At 888.5 NTUs, the
pond source was well above the recommend maximum tur-
bidity (100 NTU) for chlorination-alone treatment and pre-
treatment to reduce the turbidity < 100 NTU is recommended
before chlorination. Residual chlorine concentration greater
than 0.2 mg/L was seen 24 hours after chlorination in pond
water samples treated with ceramic filtration and a double
dose of flocculant/disinfection tablets.
The experimental flavored Aquatab and the floccu-
lant/disinfectant Aquatab were not effective in increasing
T able 5
Average trihalomethane analyte percentage and concentration by source, Tanzania
Source ChloroformBromodichloromethane DibromochloromethaneBromoform
Open well *
95.0%, 47.1 µg/L
78.7%, 24.4 µg/L
–, 4.1 µg/L
73.9%, 33.4 µg/L
–, 4.5 µg/L
–, 4.8 µg/L
4.6%, 2.3 µg/L
18.2%, 5.6 µg/L
–, 1.7 µg/L
20.1%, 9.1 µg/L
–, 2.6 µg/L
–, 2.2 µg/L
0.2%, 0.1 µg/L
2.8%, 0.9 µg/L
–, 1.2 µg/L
5.7%, 2.6 µg/L
–, 2.8 µg/L
–, 1.8 µg/L
0.1%, 0.1 µg/L
0.2%, 0.1 µg/L
–, 0.3 µg/L
0.2%, 0.1 µg/L
–, 0.7 µg/L
–, 0.4 µg/L
* Percentages not included for these sources because all average analyte concentrations were below the 4.0 µg/L minimum detection limit for chloroform.
T able 4
Individual analyte trihalomethane results, all samples, Tanzania *
Characteristic Average (ppb, µg/L) Minimum (ppb, µg/L)Maximum (ppb, µg/L) Standard deviation (ppb, µg/L)
World Health Organization
guideline value (ppb, µg/L)
* ppb = parts per billion.
DISINFECTION BY-PRODUCT FORMATION IN POINT-OF-USE CHLORINATION
chlorine residual concentration 24 hours after chlorine addition
or reducing THM formation. The flavoring was not expected
to affect chlorine residual concentration or THM formation
potential, and these results confirm this finding. The flocculant/
disinfectant tablet did not reliably reduce turbidity in these
samples, which was an unexpected result because the addition
of a flocculant should have reduced turbidity. Medentech is
conducting ongoing research to redesign this product using a
higher quality flocculant than aluminum sulfate.
Filtration through a cloth, settling for 12 hours and decant-
ing supernatant water, ceramic filtration, and sand filtration
did not reduce TTHM concentrations 24 hours after chlori-
nation compared with chlorination alone. Thus, these mecha-
nisms are not effective THM mitigation strategies. These are
not unexpected results because THM precursor compounds
have been identified as primarily organic carbon particles
smaller than 0.45 µm. 31 It is unlikely that these gross filtration
mechanisms tested in this study would remove such small par-
ticles, although ceramic filtration of river water yielded prom-
ising results. However, it was important to test these potential
mitigation strategies because they 1) are practical and inex-
pensive strategies available to and used by the populations
who are targeted by point-of-use water treatment interven-
tion programs using sodium hypochlorite and sodium dichlor-
oisocyanurate; 2) potentially reduce turbidity and increase
user acceptability of chlorination as a treatment option; and
3) potentially decrease chlorine demand and maintain chlo-
rine residual and safe storage for a longer period.
These source waters tested were appropriate for the THM
study because they encompassed a wide range of representa-
tive developing world water sources. Although the turbidity
range of source waters (0.6–888.5 NTU) was appropriate for
the THM portion of the study, the distribution (0.6, 0.9, 1.9, 5.1,
18.7, and 888.5 NTU) was not ideal to assess the effectiveness
F igure 3. Total trihalomethane concentration over 24 hours in six sources with eight treatments, Tanzania.
LANTAGNE AND OTHERS
of mitigation strategies at improving water quality. A 2.0 mg/L
hypochlorite concentration is recommended for waters < 10
NTU, a 4.0 mg/L concentration for samples 10–100 NTU, and
chlorination alone is not recommended in waters with turbid-
ity > 100 NTU. 24 Thus, locally available mitigation strategies
are most appropriate in the 10–100 NTU range, when chlo-
rination is recommended, but user acceptability is enhanced
with a esthetic improvement to the water. Because of the
unexpectedly low turbidity in unimproved sources (such as
the open well and river) used for drinking water at the time
of the study, only one sample was in the 10–100 NTU range.
Previous laboratory research investigating the turbidity and
chlorine demand reduction of cloth filtration, sand filtration,
and settling and decanting in 10–300 NTU waters found all
three locally available physical filtration mechanisms were
effective in reducing turbidity. 32 However, cloth filtration did
not reduce turbidity at 10 NTU, but reduced turbidity more
effectively as initial turbidity increased to 300 NTU. The cloth
filtration turbidity reduction results are consistent with results
presented herein, with no turbidity reduction seen in low-
turbidity (< 20 NTU) sources.
The use of ceramic filters before chlorination appeared
to reduce chlorine residual 24 hours after chlorine addition,
although more research is needed to fully characterize this
result. Ceramic filters used in this study were recently manu-
factured, and small particles not removed in firing may have
leached into finished water and reacted with the disinfectant,
exerting chlorine demand and reducing the free chlorine resid-
ual concentration available. Further testing on ceramic filtra-
tion before chlorination should use aged filters (as opposed to
new filters) to fully characterize the effects of ceramic filtra-
tion on free chlorine residual concentration over time.
Further research is needed to 1) develop chemical models
to describe THM formation after sodium dichloroisocyanu-
rate addition in the laboratory setting by varying key con-
trolling water quality parameters such as pH, bromide, TOC,
and conductivity; and 2) characterize THM formation differ-
ences between various chlorine donors. Programmatically,
such research might be of limited value because health gains
associated with diarrheal disease reduction far outweigh any
small potential risk from drinking water with THM concen-
trations significantly lower than WHO guidelines values.
Further research on locally available mechanisms to reduce
chlorine demand and turbidity is not indicated in the lab-
oratory setting because this research has already been well
established in the literature. 32, 33 Targeted research in specific
locations where household chlorination is promoted with
known high concentrations of THM precursors, such as bro-
mine, is indicated. Bromine presence increases the health
risks associated with THMs, as brominated THMs, with
higher risk and therefore lower guideline values than chlo-
roform, are formed.
Diarrheal diseases kill an estimated 1.8 million persons
each year, and point-of-use chlorination options are proven
interventions that can reduce diarrheal disease incidence and
protect health in developing countries. Concerns have been
raised about potential human health effects from disinfec-
tion byproducts that form during chlorination of raw water.
The data presented herein clearly show that chlorination
using sodium dichloroisocyanurate or sodium hypochlorite
of turbid and non-turbid waters does not lead to THM con-
centrations that exceed WHO guideline values. No mitigation
strategy tested in this study reduced THM formation potential
consistently across source water types. Proper chlorination of
household water does not form disinfection byproducts in
excess of WHO guideline values and offers a valuable method
for reducing diarrheal disease and saving lives in developing
F igure 4. Chlorine residual concentration after 24 hours in waters treated with chlorination-only options, Tanzania.
T able 6
Turbidity change after treatment with potential mitigation strategy, Tanzania *
Source Flocculant/ disinfectantSimple sand filtration Ceramic filtrationCloth filtration Settling and decanting
River (5.1 NTU)
Lake (18.7 NTU)
Pond (888.5 NTU)
* NTU = nephelometric turbidity units. Negative percentages indicate a reduction in turbidity and positive percentages indicate an increase. Tap, open well, and borehole sources not included
because of low initial turbidity.
143 Download full-text
DISINFECTION BY-PRODUCT FORMATION IN POINT-OF-USE CHLORINATION
Received July 28, 2009. Accepted for publication February 11, 2010.
Acknowledgments: We thank Mesiaki Kimirei, Elias Nnko, Omary
Bura, Petro William, Ndeshi Sauli, and Baba Juma (Filter Pure,
Arusha, Tanzania) for assistance with sample collection and logisti-
Financial support: This study was supported by Medentech, Ltd. and
the United States Agency for International Development. A written
agreement was signed specifying that the Centers for Disease Control
and Prevention could interpret and publish data without influence
Authors’ addresses: Daniele S. Lantagne, Enteric Diseases
Epidemiology Branch, Centers for Disease Control and Prevention,
Atlanta, GA, E-mail: email@example.com . Fred Cardinali and Ben
C. Blount, Division of Laboratory Sciences, National Center for
Environmental Health, Centers for Disease Control and Prevention,
Chamblee, GA, E-mails: firstname.lastname@example.org and email@example.com .
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