Chlorine dioxide decay and ClO 2

Hrvoje JURETIĆ, Ph.D.
University of Zagreb, Faculty of Mechanical
Engineering and Naval Architecture
hrvoje.juretic@fsb.hr
Comparison of Disinfection Byproducts
from Using Chlorine and Chlorine Dioxide
in Drinking Water Distribution Systems
Fourth IWA Specialty Conference on Natural Organic Matter: From Source to Tap and Beyond
July 27, 2011, Costa Mesa, California
1

Background, aim and scope
Microbiological safety of drinking water is generally achieved
by treating the water with a chemical disinfectant such as
chlorine, chlorine dioxide and ozone.
Despite the well-known problems of undesired DBPs formation,
chlorination is still the most widely used method of disinfection.
n.
Trihalomethanes (THMs)) have been found to be the most
prevalent organic contaminants after drinking water chlorination
and typically occur at higher concentrations than other
disinfection by-products.
THMs and chlorites are the only regulated DBPs in Croatia. . The
sum of four THMs is limited to a maximum value of 100 µg g L -1 ,
while the MCL for chlorite is set at 400 µg g L -1 .
2

There is a pressing need to examine alternative
disinfectants to chlorine in order to reduce potential
health risks.
Chlorine dioxide (ClO 2 ) is widely used as an
alternative disinfectant because it does not produce
appreciable levels of THMs (some possible
hazardous by-products, including chlorite and
chlorate are produced).
Information such as reaction rate constants and by-
products formation can be used as important factors
in determining whether disinfection with ClO 2 are
suitable for the decreasing unwanted by-products.
3

The aim of the study was to evaluate what impact the
switch from chlorine to chlorine dioxide would have on
the concentration of the major DBPs in groundwater
samples from the Eastern Slavonia region, Croatia and
to compare these two disinfectants by performing
mutagenicity testing.
This is the first study of this kind in Croatia and is
associated with the development of the Eastern Slavonia
Regional Water Supply System with a design flow rate of
2000 L s -1 .
4

For this purpose we examined:
THMFP
Chlorine decay and THMs formation during
chlorination
Chlorine dioxide decay and formation of
chlorite during the treatment of groundwater
samples with ClO 2
Short-term
term mutagenicity test (Comet assay
on isolated human lymphocytes)
5

Materials and Methods
Water Samples
Groundwater samples were collected from three locations throughout ut the
Eastern Slavonia region.
Parameter SIK RET OSI
pH 8.28 7.85 7.94
Conductivity (μS cm -1 ) 414 659 751
Alkalinity (mg L -1 as CaCO 3 ) 182 258 330
Hardness (mg L -1 as CaCO 3 ) 196 161 207
UV 254 , cm -1 0.017 0.073 0.104
NPOC (mg L -1 ) 0.27 2.03 3.06
TN (mg L -1 ) 0.12 0.67 1.76
THMFP (µg L -1 as CHCl 3 ) 12.9 78.1 80.4
Bromide (μg L -1 ) 5 36 7.5
Chloride (mg L -1 ) 4.4 21.6 15.5
Sulfate (mg L -1 ) 11.4 10.4 3.94
Phosphate (mg L -1 P) 0.025 0.097
As (μg L -1 ) 2.33 35.7 26.9
Fe (μg L -1 ) 15 4.14 4.2
Mn (μg L -1 ) 37 136 20.9
6

Analytical Methods
A chlorine stock solution was prepared by dissolving chlorine gas into Milli-
Q water and standardized spectrophotometrically by using a molar absorption
coefficient of the triiodide ion, calculated to be 25,024 M -1 cm -1 at 351 nm.
A chlorine dioxide stock solution was prepared by adding dilute H 2 SO 4 to a
sodium chlorite solution according to Standard Method 4500-ClO
2 B (APHA
et al., 1995) and standardized by the direct spectrophotometrical
determination of ClO 2 at 360 nm using a calculated absorption coefficient of
1182 M -1 cm -1 .
The bulk chlorine decay rates were measured by absorbance measurement
at 351 nm using a Hewlett Packard 8453 UV-visible spectrophotometer.
The bulk chlorine dioxide decay rates were determined according to US
EPA Method 327.0 Rev. 1.1 by measurement the absorbance difference
between the reagent water blank and the samples at 633 nm, which is the
absorbance maximum for Lissamine Green B (LGB) in the citric acid/glycine
buffer.
7

Analytical Methods
The THMs analysis was carried out on HS/GC/MS according to the EPA
Method 8260b .
Chlorite concentrations were calculated after the samples are sparged to
remove chlorine dioxide according to US EPA Method 327.0 Rev. 1.1.
THMFP was determined according to Standard Method 5710 B (APHA et
al., 1995).
Alkaline comet assay was carried out according to Singh et al. (1988).
Blood sample was used for the isolation of lymphocytes. Total of 300
comets per sample were measured (100 comets per each of three replicate
slides). As a measure of DNA damage we evaluated the tail intensity
ity
(DNA% in the comet tail).
8

SIK_15
5
Chlorine_HD
Chlorine_LD
4
3
2
1
0
0 20 40 60 80 100 120
9
Residual chlorine concentration (mg L -1 )
Time (h)
25
20
TTHM (µg L -1 as CHCl3 )
Results Chlorine decay and THMs formation
TTHM_HD
TTHM_LD
15
10
5
0

Results Chlorine decay and THMs formation
5
Chlorine_HD
Chlorine_LD
4
3
2
1
15
10
5
0
0 20 40 60 80 100 120
10
Residual chlorine concentration (mg L -1 )
TTHM (µg L -1 as CHCl3 )
SIK_25
20
TTHM_HD
TTHM_LD
0
Time (h)

Results Chlorine decay and THMs formation
5
4
3
2
1
Chlorine_HD
Chlorine_LD
0
0 5 10 15 20 25
11
Residual chlorine concentration (mg L -1 )
Time (h)
50
40
TTHM (µg L -1 as CHCl3 )
RET_15
TTHM_HD
TTHM_LD
30
20
10
0

Results
Chlorine decay and THMs formation
RET_25
2.5
60
Chlorine_HD
Chlorine_LD
Residual chlorine concentration (mg L -1 )
2.0
1.5
1.0
0.5
0.0
TTHM_HD
TTHM_LD
50
40
30
20
10
TTHM (µg L -1 as CHCl 3
)
0
0 5 10 15 20 25
Time (h)
12

Results Chlorine decay and THMs formation
OSI_15
4
3
2
1
Chlorine_HD
Chlorine_LD
0
0 20 40 60 80 100 120
13
Residual chlorine concentration (mg L -1 )
TTHM (µg L -1 as CHCl3 )
50
40
TTHM_HD
TTHM_LD
30
20
10
0
Time (h)

Results Chlorine decay and THMs formation
OSI_25
4
3
2
1
Chlorine_HD
Chlorine_LD
0
0 20 40 60 80 100 120
14
Residual chlorine concentration (mg L -1 )
TTHM (µg L -1 as CHCl3 )
50
TTHM_HD
40
30
20
10
0
Time (h)

Results
Chlorine dioxide decay and ClO 2- formation
SIK_15
3.0
1.0
Residual chlorine dioxide concentration (mg L -1 )
2.5
2.0
1.5
1.0
0.5
Chlorine dioxide_HD
Chlorine dioxide_LD
Chlorite_HD
Chlorite_LD
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Chlorite concentration (mg L -1 )
0.0
0 20 40 60 80 100 120
0.0
Time (h)
15

Results
Chlorine dioxide decay and ClO 2- formation
SIK_25
Residual chlorine dioxide concentration (mg L -1 )
2.5
2.0
1.5
1.0
0.5
Chlorine dioxide_HD
Chlorine dioxide_LD
Chlorite_HD
Chlorite_LD
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Chlorite concentration (mg L -1 )
0.0
0 20 40 60 80 100 120
0.0
Time (h)
16

Results
Chlorine dioxide decay and ClO 2- formation
RET_15
Residual chlorine dioxide concentration (mg L -1 )
2.0
1.6
1.2
0.8
0.4
0.0
Chlorine dioxide_HD
Chlorine dioxide_LD
Chlorite_HD
Chlorite_LD
2.0
1.6
1.2
0.8
0.4
Chlorite concentration (mg L -1 )
0 20 40 60 80 100 120
Time (h)
0.0
17

Results
Chlorine dioxide decay and ClO 2- formation
RET_25
Residual chlorine dioxide concentration (mg L -1 )
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Chlorine dioxide_HD
Chlorine dioxide_LD
Chlorite_HD
Chlorite_LD
2.0
1.6
1.2
0.8
0.4
Chlorite concentration (mg L -1 )
-0.2
0 10 20 30 40 50
Time (h)
0.0
18

Results
Chlorine dioxide decay and ClO 2- formation
OSI_15
1.2
2.0
Residual chlorine dioxide concentration (mg L -1 )
1.0
0.8
0.6
0.4
0.2
0.0
Chlorine dioxide_HD
Chlorine dioxide_LD
Chlorite_HD
Chlorite_LD
1.6
1.2
0.8
0.4
Chlorite concentration (mg L -1 )
-0.2
0 10 20 30 40 50
0.0
Time (h)
19

Results
Chlorine dioxide decay and ClO 2- formation
OSI_25
2.0
Residual chlorine dioxide concentration (mg L -1 )
0.8 Chlorine dioxide_HD
Chlorine dioxide_LD
Chlorite_HD
Chlorite_LD
0.6
0.4
0.2
0.0
1.6
1.2
0.8
0.4
Chlorite concentration (mg L -1 )
0 5 10 15 20 25
0.0
Time (h)
20

Chlorine decay parameters
Water
samples
SIK_15
SIK_25
RET_15
RET_25
OSI_15
OSI_25
Chlorine
dose
a (mgL -1 ) b (mgL -1 ) k (h -1 ) r 2
HD 3.874 0.4745 0.0375 0.96
LD 1.681 0.3695 0.0740 0.88
HD 3.436 0.4641 0.0371 0.97
LD 1.447 0.3835 0.0391 0.96
HD 2.499 1.2176 0.2145 0.96
LD 0.725 0.8683 0.3681 0.95
HD 0.178 1.1294 0.2762 0.89
LD 0.440 0.3535 0.2650 0.99
HD 0.414 2.0086 0.0475 0.96
LD 0.177 1.2077 0.5256 0.98
HD 0 1.8581 0.0491 0.99
LD 0 0.7345 0.1405 0.80
C t = a + b × exp(-kt)
21

Water
samples
SIK_15
SIK_25
RET_15
RET_25
OSI_15
OSI_25
Chlorine dioxide decay parameters
Chlorine
dioxide a (mgL -1 ) b (mgL -1 ) k (h -1 ) r 2
dose
HD 2.031 0.4336 0.0250 0.97
LD 1.041 0.1448 0.0187 0.91
HD 1.683 0.6260 0.0178 0.96
LD 0.885 0.2424 0.0262 0.90
HD 0 1.6549 0.0583 0.98
LD 0 0.4858 0.4999 0.99
HD 0 1.5335 0.1444 0.99
LD 0 0.7006 3.9047 0.99
HD 0 1.0084 0.3398 0.99
LD 0 0.0872 3.7007 0.99
HD 0 0.7644 0.6229 0.98
LD 0.019 0.0123 0.1076 0.99
C t = a + b × exp(-kt)
22

THMFP
Trihalomethane Formation Potential
100
THM (µg L -1 as CHCl3)
80
60
40
20
Tribromomethane
Dibromochloromethane
Bromodichloromethane
Trichloromethane
0
SIK OSI RET
Test water
23

Results
8
7
6
5
4
3
2
1
0
Genotoxicity
Control Raw water ClO2 Cl2
Sik
Ret
Osi
24

Conclusions
In all of the treated water samples the TTHM concentration never
exceed the maximum permissible value of 100 µg L -1 , while for some
waters the observed chlorite concentrations exceeded the MCL.
Different chlorine demand may be attributed to different content
and nature of dissolved organic matter in water samples used in this
study. The experimental kinetic data could be used to predict the
chlorine/chlorine dioxide demand and TTHM formation at any time in a
distribution system.
It should be noted that the chlorine/chlorine dioxide demand of
water samples measured in the laboratory differ from the actual
disinfectant demand in a distribution system. Factors such as
reactions of chlorine/chlorine dioxide with biofilms and with pipe walls
have not been investigated in our laboratory experiments.
25

Conclusions
Relatively low bromide level in all water samples is the reason for
typically very low concentration of brominated THMs .
Other classes of DBPs have not been investigated – further
research is needed!
Low genotoxic potency of all water samples was observed (no prior
extraction)
26