INVESTIGATION OF PRE - DISINFECTION
WITH CHLORINE DIOXIDE OF AQUEOUS
SOLUTIONS CONTAINING FULVIC OR
HUMIC ACIDS AND BROMIDES.
NAVA NARKIS AND ARINA SHULMAN
ANAT STOLLER AND SVETLANA BANDEL
ENVIRONMENTAL ENGINEERING
TECHNION - ISRAEL INSTITUE OF TECHNOLOGY,
HAIFA ISRAEL
Fourth IWA Specialty Conference Natural Organic Matter:
From Source to Tap and Beyond
July 27– 29, 2011. Costa Mesa, California USA
Introduction
In the past pre - chlorination was used at
the early stages of treatment of highly
contaminated natural waters in order to
decrease the microbial pollution load in
the following treatment facilities.
Rook's (1974) identification of the THMs
formation during the reaction of chlorine
and naturally occurring organic matter,
NOMs, has led to the understanding that
pre-chlorination can form a huge amount
of halogenated disinfection by-products,
DBPs, suspected to be hazardous to
public health.
As a result, in many regions world wide, the
chlorine pre – disinfection was avoided.
The shortage of water requires development
and exploitation of new water sources which,
so far, have been refrained from use.
Alternative Disinfectants
For several years my group studied the use
of chlorine dioxide in disinfection of
wastewaters and in fulvic and humic acids
aqueous solutions.
Chlorine dioxide was found suitable, as
a replacement for chlorine, for disinfection
of surface waters extremely polluted by
NOMs,
bromides,
effluents'
organic
matreials, ammonium ions, pathogenic
bacteria and viruses.
Chlorine Dioxide Advantages
It is an effective disinfectant for killing
pathogenic microorganisms, and
especially successful in deactivating
viruses.
Relatively small doses are required at
a short contact time for disinfection.
It has a stable residue that can be
measured for control purposes.
It does not react with ammonium ions
and organic amines.
Chlorine dioxide does not create
THMs.
It is a strong oxidizing agent, which
oxidizes the organic matter and
barely creates chlororganic
compounds.
Chlorine dioxide is cheaper than
ozone, but more expensive than
chlorine.
Chlorine Dioxide Disadvantages
During the treatment of water and
wastewater, a part of the chlorine dioxide
is reduced to undesired chlorite ClO2– and
chlorate ClO3– ions, which are suspected
of being toxic and creating health hazards.
Narkis et al. showed that the higher the
organic load in the contaminated waters,
the more ClO2– ions are formed as DBPs;
or vice versa, the better the treated water
quality, the less ClO2– ions are formed .
The US EPA (Fed. Reg., 1994) proposed
the limiting maximum concentration of
residual chlorine dioxide to 0.8 mg/L, on
the basis of daily sampling,
and a maximum concentration of
residual chlorite ions of 1.0 mg/L, on a
basis of monthly average.
REMOVAL OF CHLORITE IONS
The undesired chlorite ion can
be completely removed either by
adding
chlorine
or Fe+2 ferrous ion.
Oxidation by chlorine.
Chlorine oxidizes chlorite ion to form
chlorine dioxide.
2ClO2– + HOCl --
2ClO2 (g) + Cl– + OH–
The newly formed chlorine dioxide is a
very effective disinfectant.
In the combined disinfection, a greater
advantage is obtained by using chlorine
dioxide prior to chlorine.
When chlorine dioxide is added first and
chlorine is inserted as the second
disinfectant, chlorite ions are oxidized to
chlorine dioxide, and their concentration
decrease until they are entirely removed.
This newly created ClO2 will act as a
disinfectant, as though another ClO2
portion has been added.
The addition of chlorine can be done
at the pre - disinfection stage, or at the
post - disinfection stage, when added
after flocculation and filtration, or after
activated carbon adsorption, as the final
disinfection before supplying the drinking
water.
Chlorite Ion Removal By Fe+2
4Fe+2 + ClO2– + 20H2O -- [Fe4 (OH)20]+4 + Cl–
+ 20H+
In the redox reaction, Fe+2 reduces ClO2– to
harmless Cl– ion, and is oxidized to Fe+3,
which reacts with water to form ferric
polyhydroxo complexes, used as the
flocculant, in the next flocculation step,
in the sequence of the conventional water
treatment, for removal of colloidal and
suspended solids, organic materials and
color.
8
Residual (mg/L)
7
6
ClO3
5
-
4
3
ClO 2
2
Fe +2
-
1
0
0
5
10
+2
Fe (mg/L)
15
20
Fig. 4. Effect of various doses of ferrous ions on removal
of chlorite and chlorate ions from an aqueous solution,
containing a constant initial concentration of chlorite and
chlorate ions, in an atmospheric open system.
Chlorite ions concentration decreased as
ferrous ions dose increased until they
were entirely removed, while chlorate
ions were almost unaffected.
At the same time Fe+2 was consumed
and oxidized to Fe+3, to form the flocculant
ferric polyhydroxo complexes.
Stoichiometry and Kinetics
The theoretical ratio, calculated from the
redox equations, of
3.31 mg Fe++ required for complete
reduction of 1.0 mg ClO2–,
and 4.14 mg Fe++ required for reduction
of 1.0 mg ClO2, matched the
experimental results.
Kinetics of Reaction
The kinetics experiments showed that
the reaction rate was very fast.
All chlorite ions were removed within
30 seconds and the ferrous ions were
oxidized to ferric ions.
In all pH values, the rate of Fe+2
oxidation by chlorite ions was much
faster than the oxidation by atmospheric
oxygen, which required at least
15 minutes.
Flocculation
The best way for controlling DBPs is the
removal of precursor compounds, namely,
dissolved and colloidal natural organic
matter, by flocculation,
when working in the right pH.
The optimal dose is the minimum dose
required for complete removal of the
NOMs.
In this study 50 mg/L FeCl3 were the
flocculant optimal dose for removal of
both NOMs, at controlled pH 6.0.
Optical Density (O.D)
Apparent Turbidity
0.045
0.040
0.035
0.030
0.025
0.020
0.015
0.010
0.005
0.000
5.0 mg/L FA
pH 6.0
True Color
True Turbidity
0
10 20 30 40 50 60 70 80 90 100
FeCl3 Dose (mg/L)
Fig. 1. Flocculation of an aqueous solution
of 5.0 mg/L Fulvic Acids with Ferric Chloride.
Controlled pH 6.0.
O ptical D ensity (O .D )
0.060
Apparent Turbidity
0.050
5.0 mg/L HA
pH 6.0
True Color
0.040
0.030
True Turbidity
0.020
0.010
0.000
0
10 20 30 40 50 60 70 80 90 100
FeCl3 Dose (mg/L)
Fig. 2. Flocculation of an aqueous solution
of 5.0 mg/L Humic Acids with Ferric Chloride.
Controlled pH 6.0.
Aims of Research
The Main Purpose
was to study if the use of chlorine dioxide
allows to return to pre-disinfection of
highly contaminated surface waters and
wastewaters, with organic materials and
pathogenic microorganisms and viruses.
The effects of addition of chlorine dioxide alone,
or chlorine alone, were studied in each of the
following water treatment stages:
At the pre - disinfection of "raw waters",
After direct flocculation with FeCl3
clarification, without pre – disinfection.
and
At the post disinfection, of water treated as
follows: pre–disinfection with ClO2 addition of
Fe+2 for ClO2– removal, completion with FeCl3,
flocculation and clarification.
At the post disinfection, after adsorption on
granular activated carbon of the water treated
as before.
The Second Research Objective
was to examine whether pre-disinfection
with ClO2 creates, or does not create,
undesirable by-products, which can affect
the extent of formation of additional DBPs
at the final post disinfection.
RESULTS AND DISCUSSION
PRE – DISINFECTION
This study has focused on the extent of
formation of DBPs, during pre - disinfection
with chlorine dioxide doses of 1.5, 3.0, and
5.0 mg/L, or with 1.5 mg/L chlorine, of
synthetic aqueous solutions of 5.0 mg/L fulvic
or humic acids, in the presence of 2.0 mg/L
bromide ion, at pH 6.0.
After 30 minutes water samples were taken
for chemical analysis of the inorganic and
organic halogenated DBPs.
Pre-disinfection with Chlorine formed a
wide variety of haloorganic compounds,
with the following order:
TTHMs > THAAs > THACNs,
where
DBAA > TBAA
As a result of removing the NOMs by
flocculation, a significant decrease was
observed in the creation of organic
DBPs from disinfection with 1.5 mg/L
chlorine.
Fulvic acids
80
TTH M s ( µ g/L)
70
1.5 mg/L HOCl added
60
50
as pre-disinfection
40
30
after flocculation with FeCl3
20
10
0
0
20
40
60
80
100
120
140
160
Time (hr)
Figure 5b. Comparision between TTHMs formation in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids
and 2.0 mg/L bromide ions at pH 6. A single disinfectant
1.5 mg/L chlorine was added before flocculation, as
a pre-disinfection, or after flocculation with FeCl3, and
clarification .
Fulvic acids
1.5 mg/L HOCl added
3.0
THACNs (µ g/L)
2.5
2.0
as pre-disinfection
1.5
1.0
after flocculation with FeCl3
0.5
0.0
0
20
40
60
80
100
120
140
160
Time (hr)
Figure 7b. Comparision between THACNs formation in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids
and 2.0 mg/L bromide ions at pH 6. A single disinfectant
1.5 mg/L chlorine was added before flocculation, as
a pre-disinfection, or after flocculation with FeCl3, and
clarification.
Addition of 1.5 mg/L chlorine after
flocculation, and clarification, forms very
small amounts of DBPs 20 g/L TTHMs
compared to 60 g/L formed during predisinfection with chlorine,
8 g/L THAAs after flocculation compared to
52 g/L in pre – disinfection with chlorine,
0.8 g/L THACNs after flocculation compared
to 2.4 g/L in pre – disinfection
with
chlorine.
Pre – Disinfection Is Not Always Required.
It should be emphasized that when the
raw waters are not heavily contaminated
with pathogenic bacteria and viruses,
pre – disinfection is not required.
Therefore, flocculation is the best
treatment for removal of the NOMs,
followed by post disinfection even
with chlorine.
Pre - Disinfection with
Chlorine Dioxide
It is still important to reinstate the
pre - disinfection in order to reduce
the danger of bacterial pollution and
growth in the water treatment lines,
and in the supplied drinking water.
Table 2. Effect of pre-disinfection with chlorine dioxide on formation of
organic and inorganic by-products in aqueous solutions of 5.0 mg/L
humic or fulvic acids, 2.0 mg/L bromide ions at pH 6, after 30 minutes
contact time.
DISINFECTANTS ADDED,
mg/L
Dose
ClO2
mg/L
1.5
3.0
5.0
1.5
3.0
5.0
DBPs, g/L
Contact
ClO2 ClO2- THAAs TTHMs THACNs
time
mg/L mg/L
min.
0.0
30
0.0
30
0.0
30
1.54
0.12
2.96
0.80
5.03
2.44
0.0
30
0.0
30
0.0
30
1.54
0.14
2.96
1.10
5.03
2.54
Humic acids
0.13
0.00
1.45
4.39
0.25
0.00
1.77
5.90
0.43
0.00
2.02
7.52
Fulvic acids
0.13
0.00
1.19
2.72
0.43
0.00
1.58
5.07
0.25
0.00
1.84
6.82
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Table 2 shows that pre-disinfection with
ClO2 of aqueous solutions of humic
compounds and bromide ions does not
form haloorganic compounds, such as
THMs and HACNs.
ClO2 forms negligible total amount of
dihaloacetic acids, up to 7.5 g/L, much
lower than in the chlorinated samples.
(Dibromoacetic acid and
Bromochloroacetic acid, only )
After 30 minutes residual ClO2 is found,
which is stable even after 7 days.
Some of the ClO2 is reduced to chlorite
ions as undesired by – products,
which should be removed.
Increasing ClO2 dose increased the
concentration of residual ClO2 and
ClO2–.
Chlorite Ions Removal
The removal of ClO2–, formed in the
pre–disinfection stage, was studied using
two methods:
1.
Adding chlorine to oxidize the chlorite
ions back to ClO2, which again serves
as a disinfectant.
ClO2– ions remained stable during all
stages of treatment and appeared in
the final effluents.
It was examined whether it is preferable to
add chlorine at the post disinfection stage,
for removal and oxidation of the chlorite ions
to form residual chlorine dioxide; or is it
better to refrain from adding chlorine.
2. Adding ferrous ions, Fe+2.
In the redox reaction Fe+2 reduces ClO2– to
harmless Cl– ion, and is oxidized to Fe+3 ion,
which forms ferric polyhydroxo complexes,
used
as
the
flocculant
in the next
flocculation step, for removal of humic and
fulvic acids.
For example, in pre - disinfection with 5.0 mg/L
ClO2 the following residuals were found:
2.44 mg/L ClO2 and 2.02 mg/L ClO2–.
The calculated amount of Fe+2 required for their
reduction was 16.8 mg/L as Fe+2, or 48.8 mg/L
as FeCl3 .
In order to reach the flocculant optimal dose of
50 mg/L FeCl3, only 1.2 mg/L FeCl3 were
added.
A significant economy in the flocculant dose
required for removing the humic substances
by flocculation.
Post Disinfection
The effect of the second addition of these
agents, as final or post disinfection, was
studied after each of the following water
treatment stages:
After ClO2 pre - disinfection,
After ClO2 pre – disinfection, Fe+2 addition
for ClO2– removal, completion with FeCl3 up
to the flocculant optimal dose of 50 mg/L as
FeCl3, flocculation and clarification.
After the previous treatment followed by
adsorption on granular activated carbon.
Chlorine Dioxide as
a Strong Oxidizing Agent
During pre-disinfection chlorine dioxide, as a
strong oxidizing agent, may react with the
NOMs, by attacking the aromatic rings and the
unsaturated functional groups, to
produce
small new compounds.
Among them are aldehydes, ketones,
hydroxybenzoic acids, mono- and dicarboxylic
acids, 2, 6 - dimethoxybenzoquinone and
p - benzoquinone.
Part of the newly created small molecules are
not completely removed by flocculation, and can
serve as precursors to DBPs formation in
reaction with chlorine, added in the final post
disinfection.
50
Humic acids
45
TTHM s (µ g/L)
40
35
1.5 mg/L ClO2
30
A
25
5.0 mg/L ClO2
20
15
10
5
A
C
B
3.0 mg/L ClO2
B
0
0
20
40
60
80
100
120
5.0 mg/L ClO2
140
160
180
Time (hr)
Figure 8a. Formation of TTHMs at various contact times in disinfection of
aqueous solutions of 5.0 mg/L humic acids and 2.0 mg/L bromide ions at pH 6,
by adding 1.5 mg/L chlorine as the post disinfection after the following
treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L,
reduction of chlorite ions by Fe+2 and completion with FeCl3 up to 50 mg/L,
flocculation, clarification and filtration.
B - The above treatment A followed by adsorbtion on GAC.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
Chlorine As The Final Disinfectant
Some of the small molecules, formed in
Pre - disinfection with ClO2, were not
removed by flocculation with FeCl3, but
reacted with 1.5 mg/L chlorine, added as
the final disinfectant, caused an increase
in concentration of TTHMs, THAAs and
THACNs, compared to the amount of DBPs
formed when 1.5 mg/L chlorine alone was
added after direct flocculation, without
ClO2 pre – disinfection.
Adsorption on GAC
Adsorption on granular activated carbon
removed a significant part of the small organic
substances and haloacetic acids, formed in the
pre - disinfection with ClO2, and were not
removed by flocculation.
The very high quality of water, obtained from the
advanced treatment, including adsorption on
GAC, enabled to use chlorine for the final
disinfection, which formed negligible amounts of
haloorganic DBPs.
Only 4.85 g/L TTHMs, 0.10 g/L THACNs and
0.53 g/L THAAs were formed by chlorine after
7 days.
Table 6. Effect of post disinfection with chlorine on formation of organic
by-products after the following treatments: pre-disinfection with chlorine dioxide in aqueous
solutions of humic and fulvic acids, in the presence of 2 mg/L bromide ions, at pH 6,
reduction of ClO2 and chlorite ions residuals by Fe+2, addition of FeCl3 up to the optimal
dose of 50 mg/L as FeCl3, flocculation, settling, filtration and adsorption on granular
activated carbon after various contact times.
DBPs, g/L
DISINFECTANTS ADDED
Pre-disinfection
Postdisinfection
Time, hr.
Residual
HOCl mg/L
TTHMs
THAAs
THACNs
Humic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
1.5 mg/L
HOCl
1.5 mg/L
HOCl
0.0
1.55
0.00
000
0.00
24
0.83
1.99
0.20
0.06
72
0.58
4.09
0.62
0.17
168
0.40
6.80
0.76
0.20
0.0
1.55
0.00
0.00
0.00
24
1.10
0.09
0.00
0.00
72
0.71
2.62
0.40
0.08
168
0.56
4.85
0.53
0.10
Fulvic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
1.5 mg/L
HOCl
1.5 mg/L
HOCl
0.0
1.55
0.00
0.00
0.00
24
0.99
5.69
0.51
0.22
72
0.75
9.90
0.87
0.39
168
0.51
12.92
0.93
0.44
0.0
1.55
0.00
0.00
0.00
24
1.16
3.13
0.00
0.08
72
0.99
5.43
0.29
0.17
168
0.65
8.80
0.44
0.25
Chlorine Dioxide As
The Final Disinfectant
Tables 4 and 5 summarize the effect of post
disinfection with ClO2 on formation of organic
and inorganic by - products after the following
treatments:
pre-disinfection with chlorine dioxide in aqueous
solutions of fulvic and humic acids, in the
presence of bromide ions, at pH 6, reduction of
chlorite ions and ClO2 residuals by Fe+2, addition
of FeCl3 up to the flocculant optimal dose,
flocculation, settling and filtration, and final
disinfection with ClO2 , did not form THMs and
HACNs but formed up to 13.8 g/L HAAs.
Table 4. Effect of post disinfection with ClO2 on formation of organic and inorganic
by-products after the following treatments: pre-disinfection with chlorine dioxide in aqueous
solution of humic acids, in the presence of 2 mg/L bromide ions, at pH 6, reduction of ClO2 and
chlorite ions residuals by Fe+2, addition of FeCl3 up to the optimal dose of 50 mg/L as FeCl3,
flocculation, settling and filtration after various contact times.
DISINFECTANTS ADDED, mg/L
Predisinfection
1.5 mg/L
ClO2
3.0 mg/L
ClO2
5.0 mg/L
ClO2
1.5 mg/L
ClO2
5.0 mg/L
ClO2
Post disinfection
1.5 mg/L
ClO2
1.5 mg/L
ClO2
1.5 mg/L
ClO2
0.8 mg/L
ClO2
0.8 mg/L
ClO2
DBPs, g/L
Time,
hr.
ClO2
mg/L
ClO2mg/L
TTHMs
THAAs
THACNs
0.0
1.54
0.13
0.00
4.39
0.00
0.5
24
72
168
1.43
1.12
0.15
0.18
0.47
1.24
0.00
0.00
0.00
0.00
9.11
9.35
9.78
10.10
0.00
0.00
0.00
0.00
0.0
1.54
0.13
0.00
5.90
0.5
24
72
168
1.45
0.25
0.18
1.08
0.00
0.00
0.00
0.00
11.79
12.21
13.08
13.80
0.00
0.00
0.00
0.00
0.0
1.54
0.13
0.00
7.52
0.00
0.5
24
72
168
1.45
1.22
0.46
0.17
0.35
0.83
0.00
0.00
0.00
0.00
8.52
10.45
12.55
15.69
0.00
0.00
0.00
0.00
0.0
0.78
0.07
0.00
4.39
0.00
0.5
24
168
0.71
0.08
0.10
0.59
0.00
0.00
0.00
4.92
5.28
7.00
0.00
0.00
0.00
0.0
0.78
0.07
0.00
7.52
0.00
0.5
24
168
0.73
0.21
0.08
0.38
0.00
0.00
0.00
8.79
8.36
9.31
0.00
0.00
0.00
Table 5. Effect of post disinfection with ClO2 on formation of organic and inorganic
by-products after the following treatments: pre-disinfection with chlorine dioxide in aqueous
solution of fulvic acids, in the presence of 2 mg/L bromide ions, at pH 6, reduction of
chlorite ions and ClO2 residuals by Fe+2, addition of FeCl3 up to the optimal dose of 50 mg/L
as FeCl3, flocculation, settling and filtration after various contact times.
DISINFECTANTS ADDED, mg/L
PrePostdisinfection disinfection
1.5 mg/L
ClO2
5.0 mg/L
ClO2
1.5 mg/L
ClO2
5.0 mg/L
ClO2
1.5 mg/L
ClO2
1.5 mg/L
ClO2
0.8 mg/L
ClO2
0.8 mg/L
ClO2
Time,
hr.
DBPs, g/L
TTHMs THAAs THACNs
ClO2
mg/L
ClO2mg/L
0.0
1.54
0.13
0.00
2.72
0.00
0.5
24
72
168
1.48
1.15
0.19
0.17
0.44
1.18
0.00
0.00
0.00
0.00
5.35
5.70
6.00
6.34
0.00
0.00
0.00
0.00
0.0
1.54
0.13
0.00
6.82
0.00
0.5
24
72
168
1.50
1.26
0.54
0.15
0.33
0.76
0.00
0.00
0.00
0.00
7.34
8.49
10.60
11.78
0.00
0.00
0.00
0.00
0.0
0.78
0.07
0.00
2.72
0.00
0.5
24
168
0.74
0.11
0.09
0.49
0.00
0.00
0.00
3.28
3.69
4.01
0.00
0.00
0.00
0.0
0.78
0.07
0.00
6.82
0.00
0.5
24
168
0.76
0.62
0.25
0.07
0.15
0.34
0.00
0.00
0.00
6.87
7.30
8.29
0.00
0.00
0.00
Table 7 summarizes the effect of post
disinfection with ClO2 on formation of
DBPS after the same treatment followed
by adsorption on granular
activated
carbon.
No THMs, HAAs and HACNs were formed
in the post disinfection with ClO2 of water
after the advanced treatment, including
adsorption.
Table 7. Effect of post disinfection with chlorine dioxide on formation of organic
and inorganic by-products after the following treatments: pre-disinfection with chlorine
dioxide in aqueous solution of humic and fulvic acids, in the presence of 2 mg/L bromide
ions, at pH 6, reduction of chlorite ions and ClO2 residuals by Fe+2, addition of FeCl3 up to
the optimal dose of 50 mg/L as FeCl3, flocculation, settling, filtration and adsorption on
granular activated carbon after various contact times.
DISINFECTANTS ADDED
Pre-disinfection Post-disinfection
RESIDUALS, mg/L
Time,
hr.
ClO2
mg/L
DBPs, g/L
ClO2mg/L
TTHMs
THAAs
THACNs
Humic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
0.8 mg/L ClO2
0.8 mg/L ClO2
0.0
0.78
0.07
0.00
0.00
0.00
24
0.65
0.17
0.00
0.40
0.00
72
0.30
0.24
0.00
0.40
0.00
168
0.23
0.29
0.00
0.40
0.00
0.0
0.78
0.07
0.00
0.00
0.00
24
0.68
0.10
0.00
0.00
0.00
72
0.34
0.18
0.00
0.00
0.00
168
0.23
0.27
0.00
0.00
0.00
Fulvic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
0.8 mg/L ClO2
0.8 mg/L ClO2
0.0
0.78
0.07
0.00
0.00
0.00
24
0.72
0.08
0.00
0.00
0.00
72
0.36
0.20
0.00
0.00
0.00
168
0.27
0.26
0.00
0.00
0.00
0.0
0.78
0.07
0.00
0.00
0.00
24
0.76
0.07
0.00
0.00
0.00
72
0.42
0.19
0.00
0.00
0.00
168
0.30
0.24
0.00
0.00
0.00
SUMMARY
The results of this research have proven
that it is possible to recommend a
reliable and effective disinfection
method of treating problematic waters
polluted by natural organic matter,
NOMs, microorganisms and viruses.
This method includes both disinfection
and physico-chemical treatment stages.
SUMMARY (cont. 1)
It
is
recommended
to
reinstate
pre-disinfection with chlorine dioxide at
a large dose, above 3.0 mg/L ClO2, which
does not form DBPs, particularly THMs
and haloacetonitriles, but can form
chlorite ions.
ClO2– can be removed by adding Fe+2
ions, which are oxidized to Fe+3 and act
as a flocculant, economizing the FeCl3
dose used for effective removal of humic
compounds by flocculation.
SUMMARY (cont. 2)
Subsequently, the adsorption on granular
activated carbon removes a part of the
residual small soluble organic substances
and haloacetic acids, formed in very low
concentrations during pre-disinfection
with chlorine dioxide, and are not removed
by flocculation with FeCl3, clarification
and filtration.
At the end of the water treatment
process, a post disinfection step
is required.
SUMMARY (cont. 3)
Both chlorine dioxide or chlorine can be
used for the final disinfection stage, to
prevent the re-growth of microorganisms
in the water supply systems, and produce
an environmentally healthy and safe
drinking water.
Reduction by Fe+2 ferrous ion.
Chlorite ions can be removed completely
by adding ferrous ions Fe+2, as shown
in following equations :
4Fe+2 + ClO2– + 20H2O -+ 20H+
5Fe+2 + ClO2 ----4Fe+3 + 20H2O ----
[Fe4 (OH)20]+4 + Cl–
5Fe+3 + Cl–
[Fe4 (OH)20]+4 + 20H+
Fulvic acids
60
THAAs (µ g/L)
50
1.5 mg/L HOCl added
40
as pre-disinfection
30
20
after flocculation with FeCl3
10
0
0
20
40
60
80
100
120
140
160
Time (hr)
Figure 6b. Comparision between THAAs formation in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids
and 2.0 mg/L bromide ions at pH 6. A single disinfectant
1.5 mg/L chlorine was added before flocculation, as
a pre-disinfection, or after flocculation with FeCl3, and
clarification .
50
45
TTHMs (µ g/L)
40
1.5 mg/L ClO2
Fulvic acids
A
35
3.0 mg/L ClO2
A
30
25
20
C
15
10
5
3.0 mg/L ClO2
B
B
5.0 mg/L ClO2
0
Figure 8b. Formation
of TTHMs by 1.5 mg/L chlorine at
0
20
40
60
80
100
120
140
160
180
various contact times in disinfection of aqueous solutions of
Time (hr)
5.0 mg/L fulvic acids and 2.0 mg/L bromide ions at pH 6. The
chlorine was added as the post disinfection after the
following treatments:
A - Pre-disinfection with various doses of chlorine dioxide
1.5, 3.0 and 5.0 mg/L, reduction of chlorine dioxide and
chlorite ions residuals by Fe+2 and completion with FeCl3 up
to 50 mg/L, flocculation, clarification and filtration.
B - - The above treatment A followed by adsorbtion on GAC..
40
T TH M s (µ g/L)
1.5 mg/L ClO2
Fulvic acids
45
A
3.0 mg/L ClO2
35
A
30
25
20
C
15
3.0 mg/L ClO2
10
B
B
5
0
0
20
40
60
80
100
5.0 mg/L ClO2
120
140
160
180
Figure 8b. Formation of TTHMs by 1.5Time
mg/L(hr)
chlorine at various contact times in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids and 2.0 mg/L bromide
ions at pH 6. The chlorine was added as the post disinfection after the following
treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L,
reduction of chlorine dioxide and chlorite ions residuals by Fe+2 and completion
with FeCl3 up to 50 mg/L, flocculation, clarification and filtration.
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration..
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
Table 2 - Effect of pre-disinfection with chlorine dioxide on
formation of organic and inorganic by-products in aqueous
solutions of 5.0 mg/L humic or fulvic acids, 2.0 mg/L bromide
ions at pH 6, after 30 minutes contact time.
DISINFECTANTS ADDED, mg/L
Dose ClO2
mg/L
Contact
time
min.
DBPs, g/L
-
ClO2
ClO2
mg/L
mg/L
MBAA
DCAA
TCAA
BCAA
DBAA BDCAA CDBAA
TBAA
THAAs TTHMs THACNs
Humic acids
1.5
3.0
5.0
0.0
1.54
0.13
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
0.12
1.45
0.00
0.00
0.00
0.89
3.50
0.00
0.00
0.00
4.39
0.00
0.00
0.0
2.96
0.25
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
0.80
1.77
0.00
0.00
0.00
1.15
4.75
0.00
0.00
0.00
5.90
0.00
0.00
0.0
5.03
0.43
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
2.44
2.02
0.00
0.00
0.00
1.32
6.20
0.00
0.00
0.00
7.52
0.00
0.00
Fulvic acids
1.5
3.0
5.0
0.0
1.54
0.13
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
0.14
1.19
0.00
0.00
0.00
0.51
2.21
0.00
0.00
0.00
2.72
0.00
0.00
0.0
2.96
0.43
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
1.10
1.58
0.00
0.00
0.00
0.85
4.22
0.00
0.00
0.00
5.07
0.00
0.00
0.0
5.03
0.25
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
2.54
1.84
0.00
0.00
0.00
1.06
5.76
0.00
0.00
0.00
6.82
0.00
0.00
Table 6 - Effect of post disinfection with chlorine on formation of DBPs
after the following treatments: pre-disinfection with chlorine dioxide in
aqueous solutions of humic and fulvic acids, in the presence of 2 mg/L
bromide ions, at pH 6, reduction of ClO2 and chlorite ions residuals by Fe+2,
addition of FeCl3 up to the optimal dose of 50 mg/L as FeCl3, flocculation,
settling, filtration and adsorption on granular activated carbon after various
contact times.
DISINFECTANTS ADDED
Predisinfec
tion
Postdisinfec
tion
Time,
hr.
Residual
HOCl
mg/L
DBPs, g/L
CHCl3
CHBrCl2
CHBr2Cl
BCAN
CHBr3
DBAN
MBAA
DCAA
TCAA
BCAA
DBAA
BDCAA
CDBAA
TBAA
TTHMs
THAAs
THACNs
Humic Acids
3.0
mg/L
ClO2
5.0
mg/L
ClO2
1.5
mg/L
HOCl
1.5
mg/L
HOCl
0.0
1.55
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
000
0.00
24
0.83
0.00
0.03
0.14
0.00
1.82
0.06
0.00
0.00
0.00
0.00
0.20
0.00
0.00
0.00
1.99
0.20
0.06
72
0.58
0.00
0.03
0.16
0.00
3.90
0.17
0.00
0.00
0.00
0.00
0.62
0.00
0.00
0.00
4.09
0.62
0.17
168
0.40
0.00
0.03
0.22
0.00
6.55
0.17
0.00
0.00
0.00
0.00
0.76
0.00
0.00
0.00
6.80
0.76
0.20
0.0
1.55
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
24
1.10
0.00
0.00
0.00
0.00
0.09
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.09
0.00
0.00
72
0.71
0.00
0.00
0.06
0.00
2.56
0.08
0.00
0.00
0.00
0.00
0.40
0.00
0.00
0.00
2.62
0.40
0.08
168
0.56
0.00
0.00
0.11
0.00
4.74
0.10
0.00
0.00
0.00
0.00
0.53
0.00
0.00
0.00
4.85
0.53
0.10
Fulvic Acids
3.0
mg/L
ClO2
5.0
mg/L
ClO2
1.5
mg/L
HOCl
1.5
mg/L
HOCl
0.0
1.55
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
24
0.99
0.00
0.12
0.47
0.00
5.10
0.22
0.00
0.00
0.00
0.00
0.51
0.00
0.00
0.00
5.69
0.51
0.22
72
0.75
0.00
0.12
0.56
0.02
9.22
0.37
0.00
0.00
0.00
0.00
0.87
0.00
0.00
0.00
9.90
0.87
0.39
168
0.51
0.00
0.12
0.65
0.03
12.15
0.41
0.00
0.00
0.00
0.00
0.93
0.00
0.00
0.00
12.92
0.93
0.44
0.0
1.55
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
24
1.16
0.00
0.00
0.15
0.00
2.98
0.08
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
3.13
0.00
0.08
72
0.99
0.00
0.00
0.24
0.00
5.19
0.17
0.00
0.00
0.00
0.00
0.29
0.00
0.00
0.00
5.43
0.29
0.17
168
0.65
0.00
0.05
0.33
0.00
8.42
0.25
0.00
0.00
0.00
0.00
0.44
0.00
0.00
0.00
8.80
0.44
0.25
Table 4 - Effect of post disinfection with ClO2 on formation of organic and
inorganic by-products after the following treatments: pre-disinfection with
chlorine dioxide in aqueous solution of humic acids, in the presence of
2 mg/L bromide ions, at pH 6, reduction of chlorite ions by Fe+2, addition
of FeCl3 up to the optimal dose of 50 mg/L as FeCl3, flocculation, settling
and filtration after various contact times.
DISINFECTANTS ADDED, mg/L
Predisinfection
1.5 mg/L
ClO2
3.0 mg/L
ClO2
5.0 mg/L
ClO2
1.5 mg/L
ClO2
5.0 mg/L
ClO2
Post disinfection
1.5 mg/L
ClO2
1.5 mg/L
ClO2
1.5 mg/L
ClO2
0.8 mg/L
ClO2
0.8 mg/L
ClO2
DBPs, g/L
-
Time,
hr.
ClO2
0.0
1.54
0.5
1.43
24
1.12
0.47
0.00
0.00
0.00
1.81
7.54
0.00
72
-
-
0.00
0.00
0.00
1.85
7.93
0.00
168
0.15
1.24
0.00
0.00
0.00
1.94
8.16
0.00
0.0
1.54
0.13
0.00
0.00
0.00
1.15
4.75
0.00
0.5
1.45
0.18
0.00
0.00
0.00
2.01
9.78
0.00
0.00
0.00
0.00
11.79
0.00
24
-
-
0.00
0.00
0.00
2.10
10.11
0.00
0.00
0.00
0.00
12.21
0.00
72
-
-
0.00
0.00
0.00
2.23
10.85
0.00
0.00
0.00
0.00
13.08
0.00
168
0.25
1.08
0.00
0.00
0.00
2.44
11.36
0.00
0.00
0.00
0.00
13.80
0.00
0.0
1.54
0.13
0.00
0.00
0.00
1.32
6.20
0.00
0.00
0.00
0.00
7.52
0.00
0.5
1.45
0.17
0.00
0.00
0.00
2.08
6.44
0.00
0.00
0.00
0.00
8.52
0.00
24
1.22
0.35
0.00
0.00
0.00
2.09
8.36
0.00
0.00
0.00
0.00
10.45
0.00
72
-
-
0.00
0.00
0.00
2.43
10.12
0.00
0.00
0.00
0.00
12.55
0.00
168
0.46
0.83
0.00
0.00
0.00
2.67
13.02
0.00
0.00
0.00
0.00
15.69
0.00
0.0
0.78
0.07
0.00
0.00
0.00
0.89
3.50
0.00
0.00
0.00
0.00
4.39
0.00
0.5
0.71
0.10
0.00
0.00
0.00
0.96
3.96
0.00
0.00
0.00
0.00
4.92
0.00
24
-
-
0.00
0.00
0.00
1.08
4.20
0.00
0.00
0.00
0.00
5.28
0.00
168
0.08
0.59
0.00
0.00
0.00
1.56
5.44
0.00
0.00
0.00
0.00
7.00
0.00
0.0
0.78
0.07
0.00
0.00
0.00
1.32
6.20
0.00
0.00
0.00
0.00
7.52
0.00
0.5
0.73
0.08
0.00
0.00
0.00
2.08
6.28
0.00
0.00
0.00
0.00
8.79
0.00
24
-
-
0.00
0.00
0.00
2.08
6.71
0.00
0.00
0.00
0.00
8.36
0.00
168
0.21
0.38
0.00
0.00
0.00
2.17
7.14
0.00
0.00
0.00
0.00
9.31
0.00
mg/L
MBAA
DCAA
TCAA
BCAA
DBAA
BDCAA
CDBAA
TBAA
TTHMs
THAAs
THACNs
0.13
0.00
0.00
0.00
0.89
3.50
0.00
0.00
0.00
0.00
4.39
0.00
0.18
0.00
0.00
0.00
1.79
7.32
0.00
0.00
0.00
0.00
9.11
0.00
0.00
0.00
0.00
9.35
0.00
0.00
0.00
0.00
9.78
0.00
0.00
0.00
0.00
10.10
0.00
0.00
0.00
0.00
5.90
ClO2
mg/L
Table 5 - Effect of post disinfection with ClO2 on formation of organic and
inorganic by-products after the following treatments: pre-disinfection with
chlorine dioxide in aqueous solution of fulvic acids, in the presence of
2 mg/L bromide ions, at pH 6, reduction of chlorite ions by Fe+2, addition
of FeCl3 up to the optimal dose of 50 mg/L as FeCl3, flocculation, settling
and filtration after various contact times.
DISINFECTANTS ADDED, mg/L
Predisinfection
1.5 mg/L
ClO2
5.0 mg/L
ClO2
1.5 mg/L
ClO2
5.0 mg/L
ClO2
Postdisinfection
1.5 mg/L
ClO2
1.5 mg/L
ClO2
0.8 mg/L
ClO2
0.8 mg/L
ClO2
Time,
hr.
ClO2
0.0
1.54
0.5
DBPs, g/L
-
MBAA
DCAA
TCAA
BCAA
DBAA
BDCAA
CDBAA
TBAA
TTHMs
THAAs
THACNs
0.13
0.00
0.00
0.00
0.51
2.21
0.00
0.00
0.00
0.00
2.72
0.00
1.48
0.17
0.00
0.00
0.00
0.79
4.56
0.00
0.00
0.00
0.00
5.35
0.00
24
1.15
0.44
0.00
0.00
0.00
0.82
4.88
0.00
0.00
0.00
0.00
5.70
0.00
72
-
-
0.00
0.00
0.00
0.94
5.06
0.00
0.00
0.00
0.00
6.00
0.00
168
0.19
1.18
0.00
0.00
0.00
1.06
5.28
0.00
0.00
0.00
0.00
6.34
0.00
0.0
1.54
0.13
0.00
0.00
0.00
1.06
5.76
0.00
0.00
0.00
0.00
6.82
0.00
0.5
1.50
0.15
0.00
0.00
0.00
1.16
6.18
0.00
0.00
0.00
0.00
7.34
0.00
24
1.26
0.33
0.00
0.00
0.00
1.25
7.24
0.00
0.00
0.00
0.00
8.49
0.00
72
-
-
0.00
0.00
0.00
1.47
9.13
0.00
0.00
0.00
0.00
10.60
0.00
168
0.54
0.76
0.00
0.00
0.00
1.73
10.05
0.00
0.00
0.00
0.00
11.78
0.00
0.0
0.78
0.07
0.00
0.00
0.00
0.51
2.21
0.00
0.00
0.00
0.00
2.72
0.00
0.5
0.74
0.09
0.00
0.00
0.00
0.64
2.64
0.00
0.00
0.00
0.00
3.28
0.00
24
-
-
0.00
0.00
0.00
0.76
2.93
0.00
0.00
0.00
0.00
3.69
0.00
168
0.11
0.49
0.00
0.00
0.00
0.82
3.19
0.00
0.00
0.00
0.00
4.01
0.00
0.0
0.78
0.07
0.00
0.00
0.00
1.06
5.76
0.00
0.00
0.00
0.00
6.82
0.00
0.5
0.76
0.07
0.00
0.00
0.00
0.99
5.88
0.00
0.00
0.00
0.00
6.87
0.00
24
0.62
0.15
0.00
0.00
0.00
1.06
6.24
0.00
0.00
0.00
0.00
7.30
0.00
168
0.25
0.34
0.00
0.00
0.00
1.18
7.11
0.00
0.00
0.00
0.00
8.29
0.00
mg/L
ClO2
mg/L
Table 7 - Effect of post disinfection with chlorine dioxide on formation of
organic and inorganic by-products after the following treatments: predisinfection with chlorine dioxide in aqueous solution of humic and fulvic
acids, in the presence of 2 mg/L bromide ions, at pH 6, reduction of
chlorite ions and ClO2 residuals by Fe+2, addition of FeCl3 up to the
optimal dose of 50 mg/L as FeCl3, flocculation, settling, filtration and
adsorption on granular activated carbon after various contact times.
DISINFECTANTS ADDED
Pre-disinfection
Post-disinfection
RESIDUALS, mg/L
Time,
hr.
DBPs, g/L
-
ClO2
mg/L
ClO2
mg/L
BCAA
DBAA
TTHMs
THAAs
THACNs
Humic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
0.8 mg/L ClO2
0.8 mg/L ClO2
0.0
0.78
0.07
0.00
0.00
0.00
0.00
0.00
24
0.65
0.17
0.40
0.00
0.00
0.40
0.00
72
0.30
0.24
0.40
0.00
0.00
0.40
0.00
168
0.23
0.29
0.40
0.00
0.00
0.40
0.00
0.0
0.78
0.07
0.00
0.00
0.00
0.00
0.00
24
0.68
0.10
0.00
0.00
0.00
0.00
0.00
72
0.34
0.18
0.00
0.00
0.00
0.00
0.00
168
0.23
0.27
0.00
0.00
0.00
0.00
0.00
Fulvic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
0.8 mg/L ClO2
0.8 mg/L ClO2
0.0
0.78
0.07
0.00
0.00
0.00
0.00
0.00
24
0.72
0.08
0.00
0.00
0.00
0.00
0.00
72
0.36
0.20
0.00
0.00
0.00
0.00
0.00
168
0.27
0.26
0.00
0.00
0.00
0.00
0.00
0.0
0.78
0.07
0.00
0.00
0.00
0.00
0.00
24
0.76
0.07
0.00
0.00
0.00
0.00
0.00
72
0.42
0.19
0.00
0.00
0.00
0.00
0.00
168
0.30
0.24
0.00
0.00
0.00
0.00
0.00
Humic acids
80
TTHMs (µ g/L)
70
1.5 mg/L HOCl added
60
50
40
as pre-disinfection
30
20
after flocculation with FeCl3
10
0
0
20
40
60
80
100
120
140
160
Time (hr)
Figure 5a. Comparision between TTHMs formation in
disinfection of aqueous solutions of 5.0 mg/L humic acids
and 2.0 mg/L bromide ions at pH 6. A single disinfectant
1.5 mg/L chlorine was added before flocculation, as
a pre-disinfection, or after flocculation with FeCl3, and
clarification .
CHLORITE ION TOXICITY
In spite of the advantages, there is a serious
problem when using chlorine dioxide.
During the treatment of water and wastewater,
part of the chlorine dioxide is reduced
to undesired chlorite and chlorate ions,
suspected of being toxic and creating health
hazards (Werdehoff and Singer, 1987; Gordon
et al., 1990).
Chlorite ion caused hemolytic anemia when
fed in a very high concentration, 500 mg/L, to
rats and mice via drinking water (Gates, 1994;
Gates and Harrington, 1992, 1995).
Similar to other oxidants, it can damage the
membranes during dialysis and as a result,
chlorite ions will reach the blood cells and
cause hemolysis.
When there is deficiency, due to an
hereditary disturbance of the G-6PD enzyme
(Glucose-6-phosphate dehydrogenaze), the
body's defensive mechanism malfunctions
and does not prevent interaction between
oxidant agents and sensitive biological
macromolecules.
Therefore, a state of G-6PD deficienccy
causes hemolysis and destruction of the red
blood cells.
DBPs criteria
In 1998 the US Environmental Protection
Agency established a Stage 1 maximum
contaminant level (MCL) for THMs, as THM4 :
the
sum
of
bromodichloromethane,
and
dibromochloromethane,
bromoform,
chloroform concentrations, from 100 to 80
g/L due to their greater perceived health risk.
DBPs criteria (cont 1)
Under Stage 2, MCL THM4 is expected to
be reduced to 40 g/L. Recently, the
European Union issued a proposed
directive on the quality of water for
human consumption which, would set
maximum
concentrations
for
bromodichloromethane at 15 g/L and
chloroform at 40 g/L.
Cyanogen halides, CNX, are part of the
volatile DBPs.
WHO DBPs criteria
Cyanogen halides, CNX, are part of
the volatile DBPs.
The World Health Organization
(WHO) proposed a guideline value of
70 g/L as the sum of all cyanide
species, which includes cyanogens.
For bromate, the WHO set a guide
value of 25 g/L, while the US EPA
and the proposed EU Directive set a
value of 10 g/L.
EXPERIMENTAL
Materials
Chlorine dioxide. Chlorine dioxide was
produced from sodium chlorite activated by
HCl 10% solution. The ClO2 gas formed was
driven off by air bubbling and then absorbed
into distilled water, cooled in an ice bath.
Stock ClO2– and ClO3– solutions. The working
solutions were prepared from NaClO2 80% pure,
or NaClO3 99.99% pure, in deionized water to
which 1.0 meq/L sodium bicarbonate was added
as a buffer.
EXPERIMENTAL (cont. 1)
Stock Fe+2 solution. Analytical grade
FeSO4.7H2O crystals were used for
preparation of Fe+2 stock solutions, at
pH = 2.0. The Fe+2 stock solutions were
kept
under
nitrogen
atmospheric
conditions, in order to prevent oxygen
penetration and subsequent Fe+2 oxidation.
This solution was prepared and calibrated
daily.
Analytical procedures of ClO2, ClO2– and HOCl
Initial and final concentration of chlorine
dioxide, chlorite ion, and chlorine were
determined by the amperometric dead stop end
titration
method,
utilizing
PAO
for
determinations at pH 7.0 and above, and
sodium thiosulfate for determinations at
pH 2.5, as described by Aieta and Roberts
(1981).
The concentrations of ClO2– and ClO3– ions in
the working solutions, and in the solutions
after the reaction with the ferrous ions, were
analyzed by using an ion chromatograph.
Analytical Procedures ClO2– , ClO3– , Fe+2 and
Fe+3 The concentration of chlorite ions in
the solutions after the reaction with the
ferrous ions, were analyzed using ion
chromotograph. The ion chromotograph
DIONEX AL 450 is equipped with AS9 for
anions. The elluent solution is a mixture
of Na2CO3 1.8 mmole/L and NaHCO3 1.7
mmole/L.
Initial and final concentrations of ferrous
ions were determined colorimetrically by
the phenantroline method.
Methods
Two sets of experiments were carried out
to study the redox reactions of ferrous
ions with ClO2– and ClO3– and the
flocculation process in the presence and
in the absence of atmospheric oxygen.
The experiments were carried out in
especially developed reactors, in order to
drive off the oxygen and keep it as a
closed system.
The flocculation tests were carried out in a
jar test system, manufactured by Phipps
and Bird, USA.
The flocculation tests in the absence of
oxygen were carried out in specially
designed clogged beakers. The cover had
three openings. The central opening was
used for the stirrer, the second opening for
purging nitrogen, and the third opening
was used for introducing the chemicals
such as the flocculants, ClO2 and acid or
base for pH corrections.
Fflocculation of humic or fulvic acids
The flocculation of 5.0 mg/L humic or
fulvic acids solutions in the presence of
0.5 meq/L NaHCO3, and 2.0 mg/L bromide
ions was carried out at a constant pH 6.0,
in the following conditions:
5 minutes of rapid mixing at 100 rpms,
followed by 25 minutes of slow mixing at
25 rpms, and 30 minutes of settling.
Fflocculation O.D.(cont. 1)
The samples were taken from 4 cm below
the water surface to determine the
residual apparent and true turbidities,
true color, ClO2, ClO2– , ClO3– , Fe+2 and
Fe+3 concentrations.
Spectrophotometer
Spectronic
601,
manufactured by Milton Roy, was used
for optical densities determination; for
the apparent and true turbidities and
true color at = 405 nm, and again for
true color at = 254 nm, in a quartz cell.
DBPs standards
High purity commercial standards
BCAA, BCAN, BDCAA, CDBAA, DBAA,
DBAN, DCAA, DCAN, TBAA, TCAN, and
1,2,3-Trichloropropane were obtained
from Supelco, USA.
CHBrCl2, CHBr2Cl, MCAA, MBAA and
1,2-Dibromopropane were obtained from
Fluka, Germany.
was
obtained
from
BDH
CHBr3
Chemicals, England.
DBPs standards (cont.1)
CHCl3 and MtBE (methyl tertiary buthyl ether)
were obtained from Merck, Germany.
TCAA was obtained from Riedel and Haen,
Germany.
TAME (tertiary amyl methyl ether), was
obtained from Sigma (Aldrich), USA.
Acetone Spectrofluopure (BioLab, Israel) was
used as solvent for the preparation of stock
solutions for THMs and HACNs.
MtBE was used as solvent for the preparation
of stock solutions for HAAs.
Analytical Procedures DPBPs
At the end of the specified contact time of the
disinfection aliquot of the sample is transferred
to a 60 ml vial. Water was added to fill the
bottle. To the samples 0.3 ml of 2 X 104 mg/L
ascorbic acid C6H8O6 (to give a final
concentration of 100 mg/L) was added to
quench disinfectant residues. In addition, in
the
samples
for
THMs
and
HACNs
determination, phosphate buffer was added, to
lower the pH between 4.8 and 5.5, in order to
inhibit base catalyzed degradation of the
haloacetonitriles.
Analytical Procedures DBPs (cont 1)
Those aliquots were stored in a
refrigerator at 4 C for less than 2 days
prior to analysis. Two aliquots were
analyzed, one for THMs and HACNs and
one for HAAs.
The THMs and the
HACNs, as well as the HAAs, were
measured immediately after extraction
and quantified with a calibration curve,
using a slightly modified EPA Methods
551.1 (41), 552.2 (42) and 552.3 (43).
Analytical Procedures DBPs (cont 2)
HAAs analysis: A 42 ml of the second
sample, containing 18 grams of Na2SO4,
was acidified using 2 ml concentrated
sulfuric acid H2SO4. Thereafter 4 ml of
TAME, (tertiary amyl methyl ether), was
added, which contained the internal
standard
1,2,3-trichloropropane. A 3 ml
aliquot of the TAME extract was transferred
to a conical tube, and 3 ml of 10% sulfuric
acid in methanol was added.
Analytical Procedures DBPs (cont 3)
The reaction was heated at 60 C for 2 hours
and then allowed to return to room
temperature. A 7 ml aliquot of reagent
water containing 150 g/L of sodium sulfate
was added to effect phase separation.
Residual sulfuric acid in the extract was
neutralized by adding 1 ml of reagent water
saturated with sodium bicarbonate. Two l
of the extract were then injected into a GC.
THMs and HACNs analysis: A 45 ml
treated water sample aliquot, containing
18 grams of Na2SO4 was extracted with
3 ml of MtBE (methyl tertiary buthyl ether),
which contains the internal standard
1,2-dibromopropane. Two l of the extract
were then injected into a GC.
Gas chromatography with an electron
capture detector (Varian) was used for
determination of THMs, HACNs and HAAs
using slightly modified EPA Methods
551.1 (107), 552.2 (108) and 552.3 (109).
Analytical Procedures DBPs (cont 5)
The DBPs were well separated with the
same CP 5850 WCOT, fused silica capillary
column (30m 0.39mm i.d., 0.25 m film
thickness) under two different procedures.
The temperature program for the analysis
of THMs and HACNs was: 35 C for 4.2 min,
ramp to 68 C at 10 C/min and hold for
3.0 min. Injector temperature: 200 C.
Detector temperature: 290 C. Helium gas
flow rate: 2.0 ml/min. Injection volume: 2.0
l
Analytical Procedures DBPs HAAs (cont
6)
Temperature program for the analysis of
HAAs was: 35 C for 10.0 min, ramp to 40 C
at 5 C/min, ramp to 50 C at 10 C/min and
hold for 15.0 min, ramp to 80 C at 30 C/min,
ramp to 120 C at 10 C/min and hold for
1.5 min. Injector temperature: 200 C.
Detector temperature: 260 C.
Helium gas flow rate: 2.0 ml/min.
Injection volume: 2.0 l.
Organic Halogenated DBPs THMs and HACNs
At the end of the specified contact time
of the disinfection water samples were
transferred to a bottle, into which
ascorbic acid was added to quench
disinfectant residuals. In addition, when
the THMs and HACNs were measured,
phosphate buffer was added, to lower the
pH between 4.8 to 5.5, in order to inhibit
base catalyzed degradation of the
haloacetonitriles.
Organic Halogenated THMs and HACNs (cont.1)
Those aliquots were stored in a
refrigerator at 4 C, for no more than
2 days prior to analysis. Two aliquots
were analyzed, one for THMs and HACNs
and one for HAAs.
The THMs and HACNs were measured
immediately after being extracted with
MtBE, (methyl tertiary buthyl ether)
which contained the internal standard
1,2-dibromopropane, and then injected
into a GC.
HAAs analysis
The aliquot for the HAAs analysis , was
acidified, extracted with TAME, (tertiary
amyl methyl ether), which contained the
internal standard 1,2,3-trichloropropane.
The TAME extract was transferred to a
conical tube, and sulfuric acid in
methanol was added for esterification at
60 C for 2 hours, followed by cooling ,
phase separation after saturation with
sodium sulfate, neutralization by sodium
bicarbonate and finally injection into a
GC.
Gas chromatograph with an electron
capture detector (Varian) was used for
determination of THMs, HACNs and HAAs
by using slightly modified EPA Methods .
The DBPs were well separated with the
same CP 5850 WCOT, fused silica capillary
column under two different procedures for
temperature programming for the analysis
of THMs and HACNs and for the analysis of
HAAs. Helium flow rate 2ml/min.
OXIDATION POTENTIAL
OZONE IS THE STRONGEST OXIDANT USED IN WATER
AND WASTEWATER TREATMENT.
NO OTHER DISINFECTANT WILL BE ABLE
TO ACHIEVE OXIDATION PERFORMANCE SUPERIOR
THAN OZONE.
CHLORINATED SPECIES
AMONG THE CHLORINATED SPECIES CHLORINE
DIOXIDE HAS THE HIGHEST OXIDATION POTENTIAL.
THE OXIDATIVE CAPACITY OF CHLORINE DIOXIDE IS pH
DEPENDENT.
AT NEUTRAL AND BASIC pH CIO2 ACCEPTS ONLY
1 ELECTRON.
AT ACIDIC pH, 2 to 3 , ClO2 ACCEPTS 5 ELECTRONS.
50
40
TTHMs (µ g/L)
1.5 mg/L ClO2
Fulvic acids
45
A
35
3.0 mg/L ClO2
A
30
25
20
C
15
3.0 mg/L ClO2
10
B
B
5
0
0
20
40
60
80
100
5.0 mg/L ClO2
120
140
160
180
Figure 8b. Formation of TTHMs byTime
1.5 mg/L
(hr) chlorine at various contact
times in disinfection of aqueous solutions of 5.0 mg/L fulvic acids and 2.0
mg/L bromide ions at pH 6. The chlorine was added as the post
disinfection after the following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0
mg/L, reduction of chlorine dioxide and chlorite ions residuals by Fe+2
and completion with FeCl3 up to 50 mg/L, flocculation, clarification and
filtration.
B - - The above treatment A followed by adsorbtion on GAC..
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-
50
Humic acids
45
TTHMs (µ g/L)
40
35
1.5 mg/L ClO2
30
A
25
A
20
15
5.0 mg/L ClO2
B
B
1.5 mg/L ClO2
10
3.0 mg/L ClO2
C
5
0
0
20
40
60
80
100
120
140
160
180
Time (hr)
Figure 9a. Formation of TTHMs by 1.5 mg/L chlorine at various contact times in disinfection
of aqueous solutions of 5.0 mg/L humic acids and 2.0 mg/L bromide ions at pH 6. The
chlorine was added as the post disinfection after the following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L, reduction of
chlorine dioxide and chlorite ions residuals by Fe+2 and completion with FeCl3 up to50 mg/L,
flocculation, clarification and filtration.
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
50
Fulvic acids
45
3.0 mg/L ClO2
TTHMs (µg/L)
40
A
A
A
5.0 mg/L ClO
1.5 mg/L ClO2
35
30
2
25
B
20
1.5 mg/L ClO2
15
C
10
5
0
0
20
40
60
80
100
120
140
160
180
Time (hr)
Figure 9b. Formation of TTHMs by 1.5 mg/L chlorine at various contact times in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids and 2.0 mg/L bromide ions at pH
6. The chlorine was added as the post disinfection after the following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L, reduction of
chlorine dioxide and chlorite ions residuals by Fe+2 and completion with FeCl3 up to 50 mg/L
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
1.6
Humic acids
THACNs (µg/L)
1.4
1.2
1.0
A
1.5 mg/L ClO 2
A
0.8
0.6
5.0 mg/L ClO 2
1.5 mg/L ClO2
B
C
0.4
B
3.0 mg/L ClO 2
0.2
0.0
0
20
40
60
80
100
120
140
160
180
Figure 10a. Formation of THACNsTime
by 1.5
(hr)mg/L chlorine at various contact times
in disinfection of aqueous solutions of 5.0 mg/L humic acids and 2.0 mg/L
bromide ions at pH 6. The chlorine was added as the post disinfection after the
following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L,
reduction of chlorine dioxide and chlorite ions residuals by Fe+2 and completion
with FeCl3 up to
50 mg/L, flocculation, clarification and filtration.
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L,
flocculation with 50 mg/L FeCl3 , clarification, filtration, followed by adsorbtion
on GAC.
1.6
1.5 mg/L ClO2
Fulvic acids
1.4
THACNs (µg/L)
A
1.2
3.0 mg/L ClO2
A
1.0
0.8
B 1.5 mg/L ClO2
0.6
A 5.0 mg/L ClO2
0.4
C
0.2
0.0
0
20
40
60
80
100
120
140
160
180
Time (hr)
Figure 10a. Formation of THACNs by 1.5 mg/L chlorine at various contact times in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids and 2.0 mg/L bromide ions at
pH 6. The chlorine was added as the post disinfection after the following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L, reduction of
chlorine dioxide and chlorite ions residuals by Fe+2 and completion with FeCl3 up to
50 mg/L, flocculation, clarification and filtration.
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
50
40
TTHMs (µ g/L)
1.5 mg/L ClO2
Fulvic acids
45
A
35
3.0 mg/L ClO2
A
30
25
20
C
15
3.0 mg/L ClO2
10
B
B
5
0
0
20
40
60
80
100
5.0 mg/L ClO2
120
140
160
180
Time (hr)
Figure 8b. Formation of TTHMs by 1.5 mg/L chlorine at various contact times in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids and 2.0 mg/L bromide
ions at pH 6. The chlorine was added as the post disinfection after the following
treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L,
reduction of chlorine dioxide and chlorite ions residuals by Fe+2 and completion
with FeCl3 up to 50 mg/L, flocculation, clarification and filtration.
B - - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
To minimize DBPs formation, many water
treatment plants turned to chloramine,
chlorine dioxide, ozone, or U.V. irradiation
as a total or partial replacement to
chlorine.
In considering the advantages of using chlorine
dioxide as a disinfectant it is desirable to find
ways of reducing the unwanted by-products of
chlorine dioxide.
Elimination of these reaction by-products could
greatly enhance the potential for chlorine dioxide
usage in drinking water and effluents treatment,
and lower the limitations imposed by the
regulations.
50
Humic acids
45
TTHMs (µ g/L)
40
35
1.5 mg/L ClO2
30
A
25
A
20
15
5.0 mg/L ClO2
B
B
1.5 mg/L ClO2
10
3.0 mg/L ClO2
C
5
0
0
20
40
60
80
100
120
140
160
180
Time (hr)
Figure 9a. Formation of TTHMs by 1.5 mg/L chlorine at various contact times in disinfection
of aqueous solutions of 5.0 mg/L humic acids and 2.0 mg/L bromide ions at pH 6. The
chlorine was added as the post disinfection after the following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L, reduction of
chlorine dioxide and chlorite ions residuals by Fe+2 and completion with FeCl3 up to50 mg/L,
flocculation, clarification and filtration.
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
INVESTIGATION OF PRE - DISINFECTION
WITH CHLORINE DIOXIDE OF AQUEOUS
SOLUTIONS CONTAINING FULVIC OR
HUMIC ACIDS AND BROMIDES.
NAVA NARKIS AND ARINA SHULMAN
ANAT STOLLER AND SVETLANA BANDEL
ENVIRONMENTAL ENGINEERING
TECHNION - ISRAEL INSTITUE OF TECHNOLOGY,
HAIFA ISRAEL
Fourth IWA Specialty Conference Natural Organic Matter:
From Source to Tap and Beyond
July 27– 29, 2011. Costa Mesa, California USA
Introduction
In the past pre - chlorination was used at
the early stages of treatment of highly
contaminated natural waters in order to
decrease the microbial pollution load in
the following treatment facilities.
Rook'
s (1974) identification of the THMs
formation during the reaction of chlorine
and naturally occurring organic matter,
NOMs, has led to the understanding that
pre-chlorination can form a huge amount
of halogenated disinfection by-products,
DBPs, suspected to be hazardous to
public health.
As a result, in many regions world wide, the
chlorine pre – disinfection was avoided.
The shortage of water requires development
and exploitation of new water sources which,
so far, have been refrained from use.
Alternative Disinfectants
For several years my group studied the use
of chlorine dioxide in disinfection of
wastewaters and in fulvic and humic acids
aqueous solutions.
Chlorine dioxide was found suitable, as
a replacement for chlorine, for disinfection
of surface waters extremely polluted by
NOMs,
bromides,
effluents' organic
matreials, ammonium ions, pathogenic
bacteria and viruses.
Chlorine Dioxide Advantages
It is an effective disinfectant for killing
pathogenic microorganisms, and
especially successful in deactivating
viruses.
Relatively small doses are required at
a short contact time for disinfection.
It has a stable residue that can be
measured for control purposes.
It does not react with ammonium ions
and organic amines.
Chlorine dioxide does not create
THMs.
It is a strong oxidizing agent, which
oxidizes the organic matter and
barely creates chlororganic
compounds.
Chlorine dioxide is cheaper than
ozone, but more expensive than
chlorine.
Chlorine Dioxide Disadvantages
During the treatment of water and
wastewater, a part of the chlorine dioxide
is reduced to undesired chlorite ClO2– and
chlorate ClO3– ions, which are suspected
of being toxic and creating health hazards.
Narkis et al. showed that the higher the
organic load in the contaminated waters,
the more ClO2– ions are formed as DBPs;
or vice versa, the better the treated water
quality, the less ClO2– ions are formed .
The US EPA (Fed. Reg., 1994) proposed
the limiting maximum concentration of
residual chlorine dioxide to 0.8 mg/L, on
the basis of daily sampling,
and a maximum concentration of
residual chlorite ions of 1.0 mg/L, on a
basis of monthly average.
REMOVAL OF CHLORITE IONS
The undesired chlorite ion can
be completely removed either by
adding
chlorine
or Fe+2 ferrous ion.
Oxidation by chlorine.
Chlorine oxidizes chlorite ion to form
chlorine dioxide.
2ClO2– + HOCl --
2ClO2 (g) + Cl– + OH–
The newly formed chlorine dioxide is a
very effective disinfectant.
In the combined disinfection, a greater
advantage is obtained by using chlorine
dioxide prior to chlorine.
When chlorine dioxide is added first and
chlorine is inserted as the second
disinfectant, chlorite ions are oxidized to
chlorine dioxide, and their concentration
decrease until they are entirely removed.
This newly created ClO2 will act as a
disinfectant, as though another ClO2
portion has been added.
The addition of chlorine can be done
at the pre - disinfection stage, or at the
post - disinfection stage, when added
after flocculation and filtration, or after
activated carbon adsorption, as the final
disinfection before supplying the drinking
water.
Chlorite Ion Removal By Fe+2
4Fe+2 + ClO2– + 20H2O -- [Fe4 (OH)20]+4 + Cl–
+ 20H+
In the redox reaction, Fe+2 reduces ClO2– to
harmless Cl– ion, and is oxidized to Fe+3,
which reacts with water to form ferric
polyhydroxo complexes, used as the
flocculant, in the next flocculation step,
in the sequence of the conventional water
treatment, for removal of colloidal and
suspended solids, organic materials and
color.
8
Residual (mg/L)
7
6
ClO3
5
-
4
3
ClO 2
2
Fe +2
-
1
0
0
5
10
+2
Fe (mg/L)
15
20
Fig. 4. Effect of various doses of ferrous ions on removal
of chlorite and chlorate ions from an aqueous solution,
containing a constant initial concentration of chlorite and
chlorate ions, in an atmospheric open system.
Chlorite ions concentration decreased as
ferrous ions dose increased until they
were entirely removed, while chlorate
ions were almost unaffected.
At the same time Fe+2 was consumed
and oxidized to Fe+3, to form the flocculant
ferric polyhydroxo complexes.
Stoichiometry and Kinetics
The theoretical ratio, calculated from the
redox equations, of
3.31 mg Fe++ required for complete
reduction of 1.0 mg ClO2–,
and 4.14 mg Fe++ required for reduction
of 1.0 mg ClO2, matched the
experimental results.
Kinetics of Reaction
The kinetics experiments showed that
the reaction rate was very fast.
All chlorite ions were removed within
30 seconds and the ferrous ions were
oxidized to ferric ions.
In all pH values, the rate of Fe+2
oxidation by chlorite ions was much
faster than the oxidation by atmospheric
oxygen, which required at least
15 minutes.
Flocculation
The best way for controlling DBPs is the
removal of precursor compounds, namely,
dissolved and colloidal natural organic
matter, by flocculation,
when working in the right pH.
The optimal dose is the minimum dose
required for complete removal of the
NOMs.
In this study 50 mg/L FeCl3 were the
flocculant optimal dose for removal of
both NOMs, at controlled pH 6.0.
Optical Density (O.D)
Apparent Turbidity
0.045
0.040
0.035
0.030
0.025
0.020
0.015
0.010
0.005
0.000
5.0 mg/L FA
pH 6.0
True Color
True Turbidity
0
10 20 30 40 50 60 70 80 90 100
FeCl3 Dose (mg/L)
Fig. 1. Flocculation of an aqueous solution
of 5.0 mg/L Fulvic Acids with Ferric Chloride.
Controlled pH 6.0.
O ptical D ensity (O .D )
0.060
Apparent Turbidity
0.050
5.0 mg/L HA
pH 6.0
True Color
0.040
0.030
True Turbidity
0.020
0.010
0.000
0
10 20 30 40 50 60 70 80 90 100
FeCl3 Dose (mg/L)
Fig. 2. Flocculation of an aqueous solution
of 5.0 mg/L Humic Acids with Ferric Chloride.
Controlled pH 6.0.
Aims of Research
The Main Purpose
was to study if the use of chlorine dioxide
allows to return to pre-disinfection of
highly contaminated surface waters and
wastewaters, with organic materials and
pathogenic microorganisms and viruses.
The effects of addition of chlorine dioxide alone,
or chlorine alone, were studied in each of the
following water treatment stages:
At the pre - disinfection of "raw waters",
After direct flocculation with FeCl3
clarification, without pre – disinfection.
and
At the post disinfection, of water treated as
follows: pre–disinfection with ClO2 addition of
Fe+2 for ClO2– removal, completion with FeCl3,
flocculation and clarification.
At the post disinfection, after adsorption on
granular activated carbon of the water treated
as before.
The Second Research Objective
was to examine whether pre-disinfection
with ClO2 creates, or does not create,
undesirable by-products, which can affect
the extent of formation of additional DBPs
at the final post disinfection.
RESULTS AND DISCUSSION
PRE – DISINFECTION
This study has focused on the extent of
formation of DBPs, during pre - disinfection
with chlorine dioxide doses of 1.5, 3.0, and
5.0 mg/L, or with 1.5 mg/L chlorine, of
synthetic aqueous solutions of 5.0 mg/L fulvic
or humic acids, in the presence of 2.0 mg/L
bromide ion, at pH 6.0.
After 30 minutes water samples were taken
for chemical analysis of the inorganic and
organic halogenated DBPs.
Pre-disinfection with Chlorine formed a
wide variety of haloorganic compounds,
with the following order:
TTHMs > THAAs > THACNs,
where
DBAA > TBAA
As a result of removing the NOMs by
flocculation, a significant decrease was
observed in the creation of organic
DBPs from disinfection with 1.5 mg/L
chlorine.
Fulvic acids
80
TTH M s ( µ g/L)
70
1.5 mg/L HOCl added
60
50
as pre-disinfection
40
30
after flocculation with FeCl3
20
10
0
0
20
40
60
80
100
120
140
160
Time (hr)
Figure 5b. Comparision between TTHMs formation in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids
and 2.0 mg/L bromide ions at pH 6. A single disinfectant
1.5 mg/L chlorine was added before flocculation, as
a pre-disinfection, or after flocculation with FeCl3, and
clarification .
Fulvic acids
1.5 mg/L HOCl added
3.0
THACNs (µ g/L)
2.5
2.0
as pre-disinfection
1.5
1.0
after flocculation with FeCl3
0.5
0.0
0
20
40
60
80
100
120
140
160
Time (hr)
Figure 7b. Comparision between THACNs formation in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids
and 2.0 mg/L bromide ions at pH 6. A single disinfectant
1.5 mg/L chlorine was added before flocculation, as
a pre-disinfection, or after flocculation with FeCl3, and
clarification.
Addition of 1.5 mg/L chlorine after
flocculation, and clarification, forms very
small amounts of DBPs 20 g/L TTHMs
compared to 60 g/L formed during predisinfection with chlorine,
8 g/L THAAs after flocculation compared to
52 g/L in pre – disinfection with chlorine,
0.8 g/L THACNs after flocculation compared
to 2.4 g/L in pre – disinfection
with
chlorine.
Pre – Disinfection Is Not Always Required.
It should be emphasized that when the
raw waters are not heavily contaminated
with pathogenic bacteria and viruses,
pre – disinfection is not required.
Therefore, flocculation is the best
treatment for removal of the NOMs,
followed by post disinfection even
with chlorine.
Pre - Disinfection with
Chlorine Dioxide
It is still important to reinstate the
pre - disinfection in order to reduce
the danger of bacterial pollution and
growth in the water treatment lines,
and in the supplied drinking water.
Table 2. Effect of pre-disinfection with chlorine dioxide on formation of
organic and inorganic by-products in aqueous solutions of 5.0 mg/L
humic or fulvic acids, 2.0 mg/L bromide ions at pH 6, after 30 minutes
contact time.
DISINFECTANTS ADDED,
mg/L
Dose
ClO2
mg/L
1.5
3.0
5.0
1.5
3.0
5.0
DBPs, g/L
Contact
ClO2 ClO2- THAAs TTHMs THACNs
time
mg/L mg/L
min.
0.0
30
0.0
30
0.0
30
1.54
0.12
2.96
0.80
5.03
2.44
0.0
30
0.0
30
0.0
30
1.54
0.14
2.96
1.10
5.03
2.54
Humic acids
0.13
0.00
1.45
4.39
0.25
0.00
1.77
5.90
0.43
0.00
2.02
7.52
Fulvic acids
0.13
0.00
1.19
2.72
0.43
0.00
1.58
5.07
0.25
0.00
1.84
6.82
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
Table 2 shows that pre-disinfection with
ClO2 of aqueous solutions of humic
compounds and bromide ions does not
form haloorganic compounds, such as
THMs and HACNs.
ClO2 forms negligible total amount of
dihaloacetic acids, up to 7.5 g/L, much
lower than in the chlorinated samples.
(Dibromoacetic acid and
Bromochloroacetic acid, only )
After 30 minutes residual ClO2 is found,
which is stable even after 7 days.
Some of the ClO2 is reduced to chlorite
ions as undesired by – products,
which should be removed.
Increasing ClO2 dose increased the
concentration of residual ClO2 and
ClO2–.
Chlorite Ions Removal
The removal of ClO2–, formed in the
pre–disinfection stage, was studied using
two methods:
1.
Adding chlorine to oxidize the chlorite
ions back to ClO2, which again serves
as a disinfectant.
ClO2– ions remained stable during all
stages of treatment and appeared in
the final effluents.
It was examined whether it is preferable to
add chlorine at the post disinfection stage,
for removal and oxidation of the chlorite ions
to form residual chlorine dioxide; or is it
better to refrain from adding chlorine.
2. Adding ferrous ions, Fe+2.
In the redox reaction Fe+2 reduces ClO2– to
harmless Cl– ion, and is oxidized to Fe+3 ion,
which forms ferric polyhydroxo complexes,
used
as
the
flocculant
in the next
flocculation step, for removal of humic and
fulvic acids.
For example, in pre - disinfection with 5.0 mg/L
ClO2 the following residuals were found:
2.44 mg/L ClO2 and 2.02 mg/L ClO2–.
The calculated amount of Fe+2 required for their
reduction was 16.8 mg/L as Fe+2, or 48.8 mg/L
as FeCl3 .
In order to reach the flocculant optimal dose of
50 mg/L FeCl3, only 1.2 mg/L FeCl3 were
added.
A significant economy in the flocculant dose
required for removing the humic substances
by flocculation.
Post Disinfection
The effect of the second addition of these
agents, as final or post disinfection, was
studied after each of the following water
treatment stages:
After ClO2 pre - disinfection,
After ClO2 pre – disinfection, Fe+2 addition
for ClO2– removal, completion with FeCl3 up
to the flocculant optimal dose of 50 mg/L as
FeCl3, flocculation and clarification.
After the previous treatment followed by
adsorption on granular activated carbon.
Chlorine Dioxide as
a Strong Oxidizing Agent
During pre-disinfection chlorine dioxide, as a
strong oxidizing agent, may react with the
NOMs, by attacking the aromatic rings and the
unsaturated functional groups, to
produce
small new compounds.
Among them are aldehydes, ketones,
hydroxybenzoic acids, mono- and dicarboxylic
acids, 2, 6 - dimethoxybenzoquinone and
p - benzoquinone.
Part of the newly created small molecules are
not completely removed by flocculation, and can
serve as precursors to DBPs formation in
reaction with chlorine, added in the final post
disinfection.
50
Humic acids
TTHM s (µ g/L)
45
40
35
1.5 mg/L ClO2
30
A
25
20
5.0 mg/L ClO2
A
15
10
C
3.0 mg/L ClO2
B
5
B
0
0
20
40
60
80
100
120
5.0 mg/L ClO2
140
160
180
Time (hr)
Figure 8a. Formation of TTHMs at various contact times in disinfection of
aqueous solutions of 5.0 mg/L humic acids and 2.0 mg/L bromide ions at pH 6,
by adding 1.5 mg/L chlorine as the post disinfection after the following
treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L,
reduction of chlorite ions by Fe+2 and completion with FeCl3 up to 50 mg/L,
flocculation, clarification and filtration.
B - The above treatment A followed by adsorbtion on GAC.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
Chlorine As The Final Disinfectant
Some of the small molecules, formed in
Pre - disinfection with ClO2, were not
removed by flocculation with FeCl3, but
reacted with 1.5 mg/L chlorine, added as
the final disinfectant, caused an increase
in concentration of TTHMs, THAAs and
THACNs, compared to the amount of DBPs
formed when 1.5 mg/L chlorine alone was
added after direct flocculation, without
ClO2 pre – disinfection.
Adsorption on GAC
Adsorption on granular activated carbon
removed a significant part of the small organic
substances and haloacetic acids, formed in the
pre - disinfection with ClO2, and were not
removed by flocculation.
The very high quality of water, obtained from the
advanced treatment, including adsorption on
GAC, enabled to use chlorine for the final
disinfection, which formed negligible amounts of
haloorganic DBPs.
Only 4.85 g/L TTHMs, 0.10 g/L THACNs and
0.53 g/L THAAs were formed by chlorine after
7 days.
Table 6. Effect of post disinfection with chlorine on formation of organic
by-products after the following treatments: pre-disinfection with chlorine dioxide in aqueous
solutions of humic and fulvic acids, in the presence of 2 mg/L bromide ions, at pH 6,
reduction of ClO2 and chlorite ions residuals by Fe+2, addition of FeCl3 up to the optimal
dose of 50 mg/L as FeCl3, flocculation, settling, filtration and adsorption on granular
activated carbon after various contact times.
DBPs, g/L
DISINFECTANTS ADDED
Pre-disinfection
Postdisinfection
Time, hr.
Residual
HOCl mg/L
TTHMs
THAAs
THACNs
Humic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
1.5 mg/L
HOCl
1.5 mg/L
HOCl
0.0
1.55
0.00
000
0.00
24
0.83
1.99
0.20
0.06
72
0.58
4.09
0.62
0.17
168
0.40
6.80
0.76
0.20
0.0
1.55
0.00
0.00
0.00
24
1.10
0.09
0.00
0.00
72
0.71
2.62
0.40
0.08
168
0.56
4.85
0.53
0.10
Fulvic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
1.5 mg/L
HOCl
1.5 mg/L
HOCl
0.0
1.55
0.00
0.00
0.00
24
0.99
5.69
0.51
0.22
72
0.75
9.90
0.87
0.39
168
0.51
12.92
0.93
0.44
0.0
1.55
0.00
0.00
0.00
24
1.16
3.13
0.00
0.08
72
0.99
5.43
0.29
0.17
168
0.65
8.80
0.44
0.25
Chlorine Dioxide As
The Final Disinfectant
Tables 4 and 5 summarize the effect of post
disinfection with ClO2 on formation of organic
and inorganic by - products after the following
treatments:
pre-disinfection with chlorine dioxide in aqueous
solutions of fulvic and humic acids, in the
presence of bromide ions, at pH 6, reduction of
chlorite ions and ClO2 residuals by Fe+2, addition
of FeCl3 up to the flocculant optimal dose,
flocculation, settling and filtration, and final
disinfection with ClO2 , did not form THMs and
HACNs but formed up to 13.8 g/L HAAs.
Table 4. Effect of post disinfection with ClO2 on formation of organic and inorganic
by-products after the following treatments: pre-disinfection with chlorine dioxide in aqueous
solution of humic acids, in the presence of 2 mg/L bromide ions, at pH 6, reduction of ClO2 and
chlorite ions residuals by Fe+2, addition of FeCl3 up to the optimal dose of 50 mg/L as FeCl3,
flocculation, settling and filtration after various contact times.
DISINFECTANTS ADDED, mg/L
Predisinfection
1.5 mg/L
ClO2
3.0 mg/L
ClO2
5.0 mg/L
ClO2
1.5 mg/L
ClO2
5.0 mg/L
ClO2
Post disinfection
1.5 mg/L
ClO2
1.5 mg/L
ClO2
1.5 mg/L
ClO2
0.8 mg/L
ClO2
0.8 mg/L
ClO2
DBPs, g/L
Time,
hr.
ClO2
mg/L
ClO2mg/L
TTHMs
THAAs
THACNs
0.0
1.54
0.13
0.00
4.39
0.00
0.5
24
72
168
1.43
1.12
0.15
0.18
0.47
1.24
0.00
0.00
0.00
0.00
9.11
9.35
9.78
10.10
0.00
0.00
0.00
0.00
0.0
1.54
0.13
0.00
5.90
0.5
24
72
168
1.45
0.25
0.18
1.08
0.00
0.00
0.00
0.00
11.79
12.21
13.08
13.80
0.00
0.00
0.00
0.00
0.0
1.54
0.13
0.00
7.52
0.00
0.5
24
72
168
1.45
1.22
0.46
0.17
0.35
0.83
0.00
0.00
0.00
0.00
8.52
10.45
12.55
15.69
0.00
0.00
0.00
0.00
0.0
0.78
0.07
0.00
4.39
0.00
0.5
24
168
0.71
0.08
0.10
0.59
0.00
0.00
0.00
4.92
5.28
7.00
0.00
0.00
0.00
0.0
0.78
0.07
0.00
7.52
0.00
0.5
24
168
0.73
0.21
0.08
0.38
0.00
0.00
0.00
8.79
8.36
9.31
0.00
0.00
0.00
Table 5. Effect of post disinfection with ClO2 on formation of organic and inorganic
by-products after the following treatments: pre-disinfection with chlorine dioxide in aqueous
solution of fulvic acids, in the presence of 2 mg/L bromide ions, at pH 6, reduction of
chlorite ions and ClO2 residuals by Fe+2, addition of FeCl3 up to the optimal dose of 50 mg/L
as FeCl3, flocculation, settling and filtration after various contact times.
DISINFECTANTS ADDED, mg/L
PrePostdisinfection disinfection
1.5 mg/L
ClO2
5.0 mg/L
ClO2
1.5 mg/L
ClO2
5.0 mg/L
ClO2
1.5 mg/L
ClO2
1.5 mg/L
ClO2
0.8 mg/L
ClO2
0.8 mg/L
ClO2
Time,
hr.
DBPs, g/L
TTHMs THAAs THACNs
ClO2
mg/L
ClO2mg/L
0.0
1.54
0.13
0.00
2.72
0.00
0.5
24
72
168
1.48
1.15
0.19
0.17
0.44
1.18
0.00
0.00
0.00
0.00
5.35
5.70
6.00
6.34
0.00
0.00
0.00
0.00
0.0
1.54
0.13
0.00
6.82
0.00
0.5
24
72
168
1.50
1.26
0.54
0.15
0.33
0.76
0.00
0.00
0.00
0.00
7.34
8.49
10.60
11.78
0.00
0.00
0.00
0.00
0.0
0.78
0.07
0.00
2.72
0.00
0.5
24
168
0.74
0.11
0.09
0.49
0.00
0.00
0.00
3.28
3.69
4.01
0.00
0.00
0.00
0.0
0.78
0.07
0.00
6.82
0.00
0.5
24
168
0.76
0.62
0.25
0.07
0.15
0.34
0.00
0.00
0.00
6.87
7.30
8.29
0.00
0.00
0.00
Table 7 summarizes the effect of post
disinfection with ClO2 on formation of
DBPS after the same treatment followed
by adsorption on granular
activated
carbon.
No THMs, HAAs and HACNs were formed
in the post disinfection with ClO2 of water
after the advanced treatment, including
adsorption.
Table 7. Effect of post disinfection with chlorine dioxide on formation of organic
and inorganic by-products after the following treatments: pre-disinfection with chlorine
dioxide in aqueous solution of humic and fulvic acids, in the presence of 2 mg/L bromide
ions, at pH 6, reduction of chlorite ions and ClO2 residuals by Fe+2, addition of FeCl3 up to
the optimal dose of 50 mg/L as FeCl3, flocculation, settling, filtration and adsorption on
granular activated carbon after various contact times.
DISINFECTANTS ADDED
Pre-disinfection Post-disinfection
RESIDUALS, mg/L
Time,
hr.
ClO2
mg/L
DBPs, g/L
ClO2mg/L
TTHMs
THAAs
THACNs
Humic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
0.8 mg/L ClO2
0.8 mg/L ClO2
0.0
0.78
0.07
0.00
0.00
0.00
24
0.65
0.17
0.00
0.40
0.00
72
0.30
0.24
0.00
0.40
0.00
168
0.23
0.29
0.00
0.40
0.00
0.0
0.78
0.07
0.00
0.00
0.00
24
0.68
0.10
0.00
0.00
0.00
72
0.34
0.18
0.00
0.00
0.00
168
0.23
0.27
0.00
0.00
0.00
Fulvic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
0.8 mg/L ClO2
0.8 mg/L ClO2
0.0
0.78
0.07
0.00
0.00
0.00
24
0.72
0.08
0.00
0.00
0.00
72
0.36
0.20
0.00
0.00
0.00
168
0.27
0.26
0.00
0.00
0.00
0.0
0.78
0.07
0.00
0.00
0.00
24
0.76
0.07
0.00
0.00
0.00
72
0.42
0.19
0.00
0.00
0.00
168
0.30
0.24
0.00
0.00
0.00
SUMMARY
The results of this research have proven
that it is possible to recommend a
reliable and effective disinfection
method of treating problematic waters
polluted by natural organic matter,
NOMs, microorganisms and viruses.
This method includes both disinfection
and physico-chemical treatment stages.
SUMMARY (cont. 1)
It
is
recommended
to
reinstate
pre-disinfection with chlorine dioxide at
a large dose, above 3.0 mg/L ClO2, which
does not form DBPs, particularly THMs
and haloacetonitriles, but can form
chlorite ions.
ClO2– can be removed by adding Fe+2
ions, which are oxidized to Fe+3 and act
as a flocculant, economizing the FeCl3
dose used for effective removal of humic
compounds by flocculation.
SUMMARY (cont. 2)
Subsequently, the adsorption on granular
activated carbon removes a part of the
residual small soluble organic substances
and haloacetic acids, formed in very low
concentrations during pre-disinfection
with chlorine dioxide, and are not removed
by flocculation with FeCl3, clarification
and filtration.
At the end of the water treatment
process, a post disinfection step
is required.
SUMMARY (cont. 3)
Both chlorine dioxide or chlorine can be
used for the final disinfection stage, to
prevent the re-growth of microorganisms
in the water supply systems, and produce
an environmentally healthy and safe
drinking water.
Reduction by Fe+2 ferrous ion.
Chlorite ions can be removed completely
by adding ferrous ions Fe+2, as shown
in following equations :
4Fe+2 + ClO2– + 20H2O -+ 20H+
5Fe+2 + ClO2 ----4Fe+3 + 20H2O ----
[Fe4 (OH)20]+4 + Cl–
5Fe+3 + Cl–
[Fe4 (OH)20]+4 + 20H+
Fulvic acids
60
1.5 mg/L HOCl added
THAAs (µ g/L)
50
40
as pre-disinfection
30
20
after flocculation with FeCl3
10
0
0
20
40
60
80
100
120
140
160
Time (hr)
Figure 6b. Comparision between THAAs formation in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids
and 2.0 mg/L bromide ions at pH 6. A single disinfectant
1.5 mg/L chlorine was added before flocculation, as
a pre-disinfection, or after flocculation with FeCl3, and
clarification .
50
45
TTHMs (µ g/L)
40
35
1.5 mg/L ClO2
Fulvic acids
A
3.0 mg/L ClO2
A
30
25
20
C
15
10
5
B
B
3.0 mg/L ClO2
5.0 mg/L ClO2
0
Figure 8b. Formation
of TTHMs by 1.5 mg/L chlorine at
0
20
40
60
80
100
120
140
160
180
various contact times in disinfection of aqueous solutions of
Time (hr)
5.0 mg/L fulvic acids and 2.0 mg/L bromide ions at pH 6. The
chlorine was added as the post disinfection after the
following treatments:
A - Pre-disinfection with various doses of chlorine dioxide
1.5, 3.0 and 5.0 mg/L, reduction of chlorine dioxide and
chlorite ions residuals by Fe+2 and completion with FeCl3 up
to 50 mg/L, flocculation, clarification and filtration.
B - - The above treatment A followed by adsorbtion on GAC..
40
T TH M s (µ g/L)
1.5 mg/L ClO2
Fulvic acids
45
A
35
3.0 mg/L ClO2
A
30
25
20
C
15
10
3.0 mg/L ClO2
B
B
5
0
0
20
40
60
80
100
5.0 mg/L ClO2
120
140
160
180
Figure 8b. Formation of TTHMs by 1.5Time
mg/L(hr)
chlorine at various contact times in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids and 2.0 mg/L bromide
ions at pH 6. The chlorine was added as the post disinfection after the following
treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L,
reduction of chlorine dioxide and chlorite ions residuals by Fe+2 and completion
with FeCl3 up to 50 mg/L, flocculation, clarification and filtration.
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration..
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
Table 2 - Effect of pre-disinfection with chlorine dioxide on
formation of organic and inorganic by-products in aqueous
solutions of 5.0 mg/L humic or fulvic acids, 2.0 mg/L bromide
ions at pH 6, after 30 minutes contact time.
DISINFECTANTS ADDED, mg/L
Dose ClO2
mg/L
Contact
time
min.
ClO2
mg/L
ClO2
-
mg/L
DBPs, g/L
MBAA
DCAA
TCAA
BCAA
DBAA BDCAA CDBAA
TBAA
THAAs TTHMs THACNs
Humic acids
1.5
3.0
5.0
0.0
1.54
0.13
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
0.12
1.45
0.00
0.00
0.00
0.89
3.50
0.00
0.00
0.00
4.39
0.00
0.00
0.0
2.96
0.25
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
0.80
1.77
0.00
0.00
0.00
1.15
4.75
0.00
0.00
0.00
5.90
0.00
0.00
0.0
5.03
0.43
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
2.44
2.02
0.00
0.00
0.00
1.32
6.20
0.00
0.00
0.00
7.52
0.00
0.00
Fulvic acids
1.5
3.0
5.0
0.0
1.54
0.13
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
0.14
1.19
0.00
0.00
0.00
0.51
2.21
0.00
0.00
0.00
2.72
0.00
0.00
0.0
2.96
0.43
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
1.10
1.58
0.00
0.00
0.00
0.85
4.22
0.00
0.00
0.00
5.07
0.00
0.00
0.0
5.03
0.25
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
30
2.54
1.84
0.00
0.00
0.00
1.06
5.76
0.00
0.00
0.00
6.82
0.00
0.00
Table 6 - Effect of post disinfection with chlorine on formation of DBPs
after the following treatments: pre-disinfection with chlorine dioxide in
aqueous solutions of humic and fulvic acids, in the presence of 2 mg/L
bromide ions, at pH 6, reduction of ClO2 and chlorite ions residuals by Fe+2,
addition of FeCl3 up to the optimal dose of 50 mg/L as FeCl3, flocculation,
settling, filtration and adsorption on granular activated carbon after various
contact times.
DISINFECTANTS ADDED
Predisinfec
tion
Postdisinfec
tion
Time,
hr.
Residual
HOCl
mg/L
DBPs, g/L
CHCl3
CHBrCl2
CHBr2Cl
BCAN
CHBr3
DBAN
MBAA
DCAA
TCAA
BCAA
DBAA
BDCAA
CDBAA
TBAA
TTHMs
THAAs
THACNs
Humic Acids
3.0
mg/L
ClO2
5.0
mg/L
ClO2
1.5
mg/L
HOCl
1.5
mg/L
HOCl
0.0
1.55
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
000
0.00
24
0.83
0.00
0.03
0.14
0.00
1.82
0.06
0.00
0.00
0.00
0.00
0.20
0.00
0.00
0.00
1.99
0.20
0.06
72
0.58
0.00
0.03
0.16
0.00
3.90
0.17
0.00
0.00
0.00
0.00
0.62
0.00
0.00
0.00
4.09
0.62
0.17
168
0.40
0.00
0.03
0.22
0.00
6.55
0.17
0.00
0.00
0.00
0.00
0.76
0.00
0.00
0.00
6.80
0.76
0.20
0.0
1.55
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
24
1.10
0.00
0.00
0.00
0.00
0.09
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.09
0.00
0.00
72
0.71
0.00
0.00
0.06
0.00
2.56
0.08
0.00
0.00
0.00
0.00
0.40
0.00
0.00
0.00
2.62
0.40
0.08
168
0.56
0.00
0.00
0.11
0.00
4.74
0.10
0.00
0.00
0.00
0.00
0.53
0.00
0.00
0.00
4.85
0.53
0.10
Fulvic Acids
3.0
mg/L
ClO2
5.0
mg/L
ClO2
1.5
mg/L
HOCl
1.5
mg/L
HOCl
0.0
1.55
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
24
0.99
0.00
0.12
0.47
0.00
5.10
0.22
0.00
0.00
0.00
0.00
0.51
0.00
0.00
0.00
5.69
0.51
0.22
72
0.75
0.00
0.12
0.56
0.02
9.22
0.37
0.00
0.00
0.00
0.00
0.87
0.00
0.00
0.00
9.90
0.87
0.39
168
0.51
0.00
0.12
0.65
0.03
12.15
0.41
0.00
0.00
0.00
0.00
0.93
0.00
0.00
0.00
12.92
0.93
0.44
0.0
1.55
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
24
1.16
0.00
0.00
0.15
0.00
2.98
0.08
0.00
0.00
0.00
0.00
0.00
0.00
0.00
0.00
3.13
0.00
0.08
72
0.99
0.00
0.00
0.24
0.00
5.19
0.17
0.00
0.00
0.00
0.00
0.29
0.00
0.00
0.00
5.43
0.29
0.17
168
0.65
0.00
0.05
0.33
0.00
8.42
0.25
0.00
0.00
0.00
0.00
0.44
0.00
0.00
0.00
8.80
0.44
0.25
Table 4 - Effect of post disinfection with ClO2 on formation of organic and
inorganic by-products after the following treatments: pre-disinfection with
chlorine dioxide in aqueous solution of humic acids, in the presence of
2 mg/L bromide ions, at pH 6, reduction of chlorite ions by Fe+2, addition
of FeCl3 up to the optimal dose of 50 mg/L as FeCl3, flocculation, settling
and filtration after various contact times.
DISINFECTANTS ADDED, mg/L
Predisinfection
1.5 mg/L
ClO2
3.0 mg/L
ClO2
5.0 mg/L
ClO2
1.5 mg/L
ClO2
5.0 mg/L
ClO2
Post disinfection
1.5 mg/L
ClO2
1.5 mg/L
ClO2
1.5 mg/L
ClO2
0.8 mg/L
ClO2
0.8 mg/L
ClO2
-
DBPs, g/L
Time,
hr.
ClO2
0.0
1.54
0.5
1.43
24
1.12
0.47
0.00
0.00
0.00
1.81
7.54
0.00
72
-
-
0.00
0.00
0.00
1.85
7.93
0.00
168
0.15
1.24
0.00
0.00
0.00
1.94
8.16
0.00
0.0
1.54
0.13
0.00
0.00
0.00
1.15
4.75
0.00
0.5
1.45
0.18
0.00
0.00
0.00
2.01
9.78
0.00
0.00
0.00
0.00
11.79
0.00
24
-
-
0.00
0.00
0.00
2.10
10.11
0.00
0.00
0.00
0.00
12.21
0.00
72
-
-
0.00
0.00
0.00
2.23
10.85
0.00
0.00
0.00
0.00
13.08
0.00
168
0.25
1.08
0.00
0.00
0.00
2.44
11.36
0.00
0.00
0.00
0.00
13.80
0.00
0.0
1.54
0.13
0.00
0.00
0.00
1.32
6.20
0.00
0.00
0.00
0.00
7.52
0.00
0.5
1.45
0.17
0.00
0.00
0.00
2.08
6.44
0.00
0.00
0.00
0.00
8.52
0.00
24
1.22
0.35
0.00
0.00
0.00
2.09
8.36
0.00
0.00
0.00
0.00
10.45
0.00
72
-
-
0.00
0.00
0.00
2.43
10.12
0.00
0.00
0.00
0.00
12.55
0.00
168
0.46
0.83
0.00
0.00
0.00
2.67
13.02
0.00
0.00
0.00
0.00
15.69
0.00
0.0
0.78
0.07
0.00
0.00
0.00
0.89
3.50
0.00
0.00
0.00
0.00
4.39
0.00
0.5
0.71
0.10
0.00
0.00
0.00
0.96
3.96
0.00
0.00
0.00
0.00
4.92
0.00
24
-
-
0.00
0.00
0.00
1.08
4.20
0.00
0.00
0.00
0.00
5.28
0.00
168
0.08
0.59
0.00
0.00
0.00
1.56
5.44
0.00
0.00
0.00
0.00
7.00
0.00
0.0
0.78
0.07
0.00
0.00
0.00
1.32
6.20
0.00
0.00
0.00
0.00
7.52
0.00
0.5
0.73
0.08
0.00
0.00
0.00
2.08
6.28
0.00
0.00
0.00
0.00
8.79
0.00
24
-
-
0.00
0.00
0.00
2.08
6.71
0.00
0.00
0.00
0.00
8.36
0.00
168
0.21
0.38
0.00
0.00
0.00
2.17
7.14
0.00
0.00
0.00
0.00
9.31
0.00
mg/L
MBAA
DCAA
TCAA
BCAA
DBAA
BDCAA
CDBAA
TBAA
TTHMs
THAAs
THACNs
0.13
0.00
0.00
0.00
0.89
3.50
0.00
0.00
0.00
0.00
4.39
0.00
0.18
0.00
0.00
0.00
1.79
7.32
0.00
0.00
0.00
0.00
9.11
0.00
0.00
0.00
0.00
9.35
0.00
0.00
0.00
0.00
9.78
0.00
0.00
0.00
0.00
10.10
0.00
0.00
0.00
0.00
5.90
ClO2
mg/L
Table 5 - Effect of post disinfection with ClO2 on formation of organic and
inorganic by-products after the following treatments: pre-disinfection with
chlorine dioxide in aqueous solution of fulvic acids, in the presence of
2 mg/L bromide ions, at pH 6, reduction of chlorite ions by Fe+2, addition
of FeCl3 up to the optimal dose of 50 mg/L as FeCl3, flocculation, settling
and filtration after various contact times.
DISINFECTANTS ADDED, mg/L
Predisinfection
1.5 mg/L
ClO2
5.0 mg/L
ClO2
1.5 mg/L
ClO2
5.0 mg/L
ClO2
Postdisinfection
1.5 mg/L
ClO2
1.5 mg/L
ClO2
0.8 mg/L
ClO2
0.8 mg/L
ClO2
Time,
hr.
ClO2
0.0
1.54
0.5
-
DBPs, g/L
MBAA
DCAA
TCAA
BCAA
DBAA
BDCAA
CDBAA
TBAA
TTHMs
THAAs
THACNs
0.13
0.00
0.00
0.00
0.51
2.21
0.00
0.00
0.00
0.00
2.72
0.00
1.48
0.17
0.00
0.00
0.00
0.79
4.56
0.00
0.00
0.00
0.00
5.35
0.00
24
1.15
0.44
0.00
0.00
0.00
0.82
4.88
0.00
0.00
0.00
0.00
5.70
0.00
72
-
-
0.00
0.00
0.00
0.94
5.06
0.00
0.00
0.00
0.00
6.00
0.00
168
0.19
1.18
0.00
0.00
0.00
1.06
5.28
0.00
0.00
0.00
0.00
6.34
0.00
0.0
1.54
0.13
0.00
0.00
0.00
1.06
5.76
0.00
0.00
0.00
0.00
6.82
0.00
0.5
1.50
0.15
0.00
0.00
0.00
1.16
6.18
0.00
0.00
0.00
0.00
7.34
0.00
24
1.26
0.33
0.00
0.00
0.00
1.25
7.24
0.00
0.00
0.00
0.00
8.49
0.00
72
-
-
0.00
0.00
0.00
1.47
9.13
0.00
0.00
0.00
0.00
10.60
0.00
168
0.54
0.76
0.00
0.00
0.00
1.73
10.05
0.00
0.00
0.00
0.00
11.78
0.00
0.0
0.78
0.07
0.00
0.00
0.00
0.51
2.21
0.00
0.00
0.00
0.00
2.72
0.00
0.5
0.74
0.09
0.00
0.00
0.00
0.64
2.64
0.00
0.00
0.00
0.00
3.28
0.00
24
-
-
0.00
0.00
0.00
0.76
2.93
0.00
0.00
0.00
0.00
3.69
0.00
168
0.11
0.49
0.00
0.00
0.00
0.82
3.19
0.00
0.00
0.00
0.00
4.01
0.00
0.0
0.78
0.07
0.00
0.00
0.00
1.06
5.76
0.00
0.00
0.00
0.00
6.82
0.00
0.5
0.76
0.07
0.00
0.00
0.00
0.99
5.88
0.00
0.00
0.00
0.00
6.87
0.00
24
0.62
0.15
0.00
0.00
0.00
1.06
6.24
0.00
0.00
0.00
0.00
7.30
0.00
168
0.25
0.34
0.00
0.00
0.00
1.18
7.11
0.00
0.00
0.00
0.00
8.29
0.00
mg/L
ClO2
mg/L
Table 7 - Effect of post disinfection with chlorine dioxide on formation of
organic and inorganic by-products after the following treatments: predisinfection with chlorine dioxide in aqueous solution of humic and fulvic
acids, in the presence of 2 mg/L bromide ions, at pH 6, reduction of
chlorite ions and ClO2 residuals by Fe+2, addition of FeCl3 up to the
optimal dose of 50 mg/L as FeCl3, flocculation, settling, filtration and
adsorption on granular activated carbon after various contact times.
DISINFECTANTS ADDED
Pre-disinfection
Post-disinfection
RESIDUALS, mg/L
Time,
hr.
DBPs, g/L
-
ClO2
mg/L
ClO2
mg/L
BCAA
DBAA
TTHMs
THAAs
THACNs
Humic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
0.8 mg/L ClO2
0.8 mg/L ClO2
0.0
0.78
0.07
0.00
0.00
0.00
0.00
0.00
24
0.65
0.17
0.40
0.00
0.00
0.40
0.00
72
0.30
0.24
0.40
0.00
0.00
0.40
0.00
168
0.23
0.29
0.40
0.00
0.00
0.40
0.00
0.0
0.78
0.07
0.00
0.00
0.00
0.00
0.00
24
0.68
0.10
0.00
0.00
0.00
0.00
0.00
72
0.34
0.18
0.00
0.00
0.00
0.00
0.00
168
0.23
0.27
0.00
0.00
0.00
0.00
0.00
Fulvic Acids
3.0 mg/L ClO2
5.0 mg/L ClO2
0.8 mg/L ClO2
0.8 mg/L ClO2
0.0
0.78
0.07
0.00
0.00
0.00
0.00
0.00
24
0.72
0.08
0.00
0.00
0.00
0.00
0.00
72
0.36
0.20
0.00
0.00
0.00
0.00
0.00
168
0.27
0.26
0.00
0.00
0.00
0.00
0.00
0.0
0.78
0.07
0.00
0.00
0.00
0.00
0.00
24
0.76
0.07
0.00
0.00
0.00
0.00
0.00
72
0.42
0.19
0.00
0.00
0.00
0.00
0.00
168
0.30
0.24
0.00
0.00
0.00
0.00
0.00
Humic acids
80
TTHMs (µ g/L)
70
1.5 mg/L HOCl added
60
50
40
as pre-disinfection
30
20
after flocculation with FeCl3
10
0
0
20
40
60
80
100
120
140
160
Time (hr)
Figure 5a. Comparision between TTHMs formation in
disinfection of aqueous solutions of 5.0 mg/L humic acids
and 2.0 mg/L bromide ions at pH 6. A single disinfectant
1.5 mg/L chlorine was added before flocculation, as
a pre-disinfection, or after flocculation with FeCl3, and
clarification .
CHLORITE ION TOXICITY
In spite of the advantages, there is a serious
problem when using chlorine dioxide.
During the treatment of water and wastewater,
part of the chlorine dioxide is reduced
to undesired chlorite and chlorate ions,
suspected of being toxic and creating health
hazards (Werdehoff and Singer, 1987; Gordon
et al., 1990).
Chlorite ion caused hemolytic anemia when
fed in a very high concentration, 500 mg/L, to
rats and mice via drinking water (Gates, 1994;
Gates and Harrington, 1992, 1995).
Similar to other oxidants, it can damage the
membranes during dialysis and as a result,
chlorite ions will reach the blood cells and
cause hemolysis.
When there is deficiency, due to an
hereditary disturbance of the G-6PD enzyme
(Glucose-6-phosphate dehydrogenaze), the
body's defensive mechanism malfunctions
and does not prevent interaction between
oxidant agents and sensitive biological
macromolecules.
Therefore, a state of G-6PD deficienccy
causes hemolysis and destruction of the red
blood cells.
DBPs criteria
In 1998 the US Environmental Protection
Agency established a Stage 1 maximum
contaminant level (MCL) for THMs, as THM4 :
the
sum
of
bromodichloromethane,
and
dibromochloromethane,
bromoform,
chloroform concentrations, from 100 to 80
g/L due to their greater perceived health risk.
DBPs criteria (cont 1)
Under Stage 2, MCL THM4 is expected to
be reduced to 40 g/L. Recently, the
European Union issued a proposed
directive on the quality of water for
human consumption which, would set
maximum
concentrations
for
bromodichloromethane at 15 g/L and
chloroform at 40 g/L.
Cyanogen halides, CNX, are part of the
volatile DBPs.
WHO DBPs criteria
Cyanogen halides, CNX, are part of
the volatile DBPs.
The World Health Organization
(WHO) proposed a guideline value of
70 g/L as the sum of all cyanide
species, which includes cyanogens.
For bromate, the WHO set a guide
value of 25 g/L, while the US EPA
and the proposed EU Directive set a
value of 10 g/L.
EXPERIMENTAL
Materials
Chlorine dioxide. Chlorine dioxide was
produced from sodium chlorite activated by
HCl 10% solution. The ClO2 gas formed was
driven off by air bubbling and then absorbed
into distilled water, cooled in an ice bath.
Stock ClO2– and ClO3– solutions. The working
solutions were prepared from NaClO2 80% pure,
or NaClO3 99.99% pure, in deionized water to
which 1.0 meq/L sodium bicarbonate was added
as a buffer.
EXPERIMENTAL (cont. 1)
Stock Fe+2 solution. Analytical grade
FeSO4.7H2O crystals were used for
preparation of Fe+2 stock solutions, at
pH = 2.0. The Fe+2 stock solutions were
kept
under
nitrogen
atmospheric
conditions, in order to prevent oxygen
penetration and subsequent Fe+2 oxidation.
This solution was prepared and calibrated
daily.
Analytical procedures of ClO2, ClO2– and HOCl
Initial and final concentration of chlorine
dioxide, chlorite ion, and chlorine were
determined by the amperometric dead stop end
titration
method,
utilizing
PAO
for
determinations at pH 7.0 and above, and
sodium thiosulfate for determinations at
pH 2.5, as described by Aieta and Roberts
(1981).
The concentrations of ClO2– and ClO3– ions in
the working solutions, and in the solutions
after the reaction with the ferrous ions, were
analyzed by using an ion chromatograph.
Analytical Procedures ClO2– , ClO3– , Fe+2 and
Fe+3 The concentration of chlorite ions in
the solutions after the reaction with the
ferrous ions, were analyzed using ion
chromotograph. The ion chromotograph
DIONEX AL 450 is equipped with AS9 for
anions. The elluent solution is a mixture
of Na2CO3 1.8 mmole/L and NaHCO3 1.7
mmole/L.
Initial and final concentrations of ferrous
ions were determined colorimetrically by
the phenantroline method.
Methods
Two sets of experiments were carried out
to study the redox reactions of ferrous
ions with ClO2– and ClO3– and the
flocculation process in the presence and
in the absence of atmospheric oxygen.
The experiments were carried out in
especially developed reactors, in order to
drive off the oxygen and keep it as a
closed system.
The flocculation tests were carried out in a
jar test system, manufactured by Phipps
and Bird, USA.
The flocculation tests in the absence of
oxygen were carried out in specially
designed clogged beakers. The cover had
three openings. The central opening was
used for the stirrer, the second opening for
purging nitrogen, and the third opening
was used for introducing the chemicals
such as the flocculants, ClO2 and acid or
base for pH corrections.
Fflocculation of humic or fulvic acids
The flocculation of 5.0 mg/L humic or
fulvic acids solutions in the presence of
0.5 meq/L NaHCO3, and 2.0 mg/L bromide
ions was carried out at a constant pH 6.0,
in the following conditions:
5 minutes of rapid mixing at 100 rpms,
followed by 25 minutes of slow mixing at
25 rpms, and 30 minutes of settling.
Fflocculation O.D.(cont. 1)
The samples were taken from 4 cm below
the water surface to determine the
residual apparent and true turbidities,
true color, ClO2, ClO2– , ClO3– , Fe+2 and
Fe+3 concentrations.
Spectrophotometer
Spectronic
601,
manufactured by Milton Roy, was used
for optical densities determination; for
the apparent and true turbidities and
true color at = 405 nm, and again for
true color at = 254 nm, in a quartz cell.
DBPs standards
High purity commercial standards
BCAA, BCAN, BDCAA, CDBAA, DBAA,
DBAN, DCAA, DCAN, TBAA, TCAN, and
1,2,3-Trichloropropane were obtained
from Supelco, USA.
CHBrCl2, CHBr2Cl, MCAA, MBAA and
1,2-Dibromopropane were obtained from
Fluka, Germany.
was
obtained
from
BDH
CHBr3
Chemicals, England.
DBPs standards (cont.1)
CHCl3 and MtBE (methyl tertiary buthyl ether)
were obtained from Merck, Germany.
TCAA was obtained from Riedel and Haen,
Germany.
TAME (tertiary amyl methyl ether), was
obtained from Sigma (Aldrich), USA.
Acetone Spectrofluopure (BioLab, Israel) was
used as solvent for the preparation of stock
solutions for THMs and HACNs.
MtBE was used as solvent for the preparation
of stock solutions for HAAs.
Analytical Procedures DPBPs
At the end of the specified contact time of the
disinfection aliquot of the sample is transferred
to a 60 ml vial. Water was added to fill the
bottle. To the samples 0.3 ml of 2 X 104 mg/L
ascorbic acid C6H8O6 (to give a final
concentration of 100 mg/L) was added to
quench disinfectant residues. In addition, in
the
samples
for
THMs
and
HACNs
determination, phosphate buffer was added, to
lower the pH between 4.8 and 5.5, in order to
inhibit base catalyzed degradation of the
haloacetonitriles.
Analytical Procedures DBPs (cont 1)
Those aliquots were stored in a
refrigerator at 4 C for less than 2 days
prior to analysis. Two aliquots were
analyzed, one for THMs and HACNs and
one for HAAs.
The THMs and the
HACNs, as well as the HAAs, were
measured immediately after extraction
and quantified with a calibration curve,
using a slightly modified EPA Methods
551.1 (41), 552.2 (42) and 552.3 (43).
Analytical Procedures DBPs (cont 2)
HAAs analysis: A 42 ml of the second
sample, containing 18 grams of Na2SO4,
was acidified using 2 ml concentrated
sulfuric acid H2SO4. Thereafter 4 ml of
TAME, (tertiary amyl methyl ether), was
added, which contained the internal
standard
1,2,3-trichloropropane. A 3 ml
aliquot of the TAME extract was transferred
to a conical tube, and 3 ml of 10% sulfuric
acid in methanol was added.
Analytical Procedures DBPs (cont 3)
The reaction was heated at 60 C for 2 hours
and then allowed to return to room
temperature. A 7 ml aliquot of reagent
water containing 150 g/L of sodium sulfate
was added to effect phase separation.
Residual sulfuric acid in the extract was
neutralized by adding 1 ml of reagent water
saturated with sodium bicarbonate. Two l
of the extract were then injected into a GC.
THMs and HACNs analysis: A 45 ml
treated water sample aliquot, containing
18 grams of Na2SO4 was extracted with
3 ml of MtBE (methyl tertiary buthyl ether),
which contains the internal standard
1,2-dibromopropane. Two l of the extract
were then injected into a GC.
Gas chromatography with an electron
capture detector (Varian) was used for
determination of THMs, HACNs and HAAs
using slightly modified EPA Methods
551.1 (107), 552.2 (108) and 552.3 (109).
Analytical Procedures DBPs (cont 5)
The DBPs were well separated with the
same CP 5850 WCOT, fused silica capillary
column (30m 0.39mm i.d., 0.25 m film
thickness) under two different procedures.
The temperature program for the analysis
of THMs and HACNs was: 35 C for 4.2 min,
ramp to 68 C at 10 C/min and hold for
3.0 min. Injector temperature: 200 C.
Detector temperature: 290 C. Helium gas
flow rate: 2.0 ml/min. Injection volume: 2.0
l
Analytical Procedures DBPs HAAs (cont
6)
Temperature program for the analysis of
HAAs was: 35 C for 10.0 min, ramp to 40 C
at 5 C/min, ramp to 50 C at 10 C/min and
hold for 15.0 min, ramp to 80 C at 30 C/min,
ramp to 120 C at 10 C/min and hold for
1.5 min. Injector temperature: 200 C.
Detector temperature: 260 C.
Helium gas flow rate: 2.0 ml/min.
Injection volume: 2.0 l.
Organic Halogenated DBPs THMs and HACNs
At the end of the specified contact time
of the disinfection water samples were
transferred to a bottle, into which
ascorbic acid was added to quench
disinfectant residuals. In addition, when
the THMs and HACNs were measured,
phosphate buffer was added, to lower the
pH between 4.8 to 5.5, in order to inhibit
base catalyzed degradation of the
haloacetonitriles.
Organic Halogenated THMs and HACNs (cont.1)
Those aliquots were stored in a
refrigerator at 4 C, for no more than
2 days prior to analysis. Two aliquots
were analyzed, one for THMs and HACNs
and one for HAAs.
The THMs and HACNs were measured
immediately after being extracted with
MtBE, (methyl tertiary buthyl ether)
which contained the internal standard
1,2-dibromopropane, and then injected
into a GC.
HAAs analysis
The aliquot for the HAAs analysis , was
acidified, extracted with TAME, (tertiary
amyl methyl ether), which contained the
internal standard 1,2,3-trichloropropane.
The TAME extract was transferred to a
conical tube, and sulfuric acid in
methanol was added for esterification at
60 C for 2 hours, followed by cooling ,
phase separation after saturation with
sodium sulfate, neutralization by sodium
bicarbonate and finally injection into a
GC.
Gas chromatograph with an electron
capture detector (Varian) was used for
determination of THMs, HACNs and HAAs
by using slightly modified EPA Methods .
The DBPs were well separated with the
same CP 5850 WCOT, fused silica capillary
column under two different procedures for
temperature programming for the analysis
of THMs and HACNs and for the analysis of
HAAs. Helium flow rate 2ml/min.
OXIDATION POTENTIAL
OZONE IS THE STRONGEST OXIDANT USED IN WATER
AND WASTEWATER TREATMENT.
NO OTHER DISINFECTANT WILL BE ABLE
TO ACHIEVE OXIDATION PERFORMANCE SUPERIOR
THAN OZONE.
CHLORINATED SPECIES
AMONG THE CHLORINATED SPECIES CHLORINE
DIOXIDE HAS THE HIGHEST OXIDATION POTENTIAL.
THE OXIDATIVE CAPACITY OF CHLORINE DIOXIDE IS pH
DEPENDENT.
AT NEUTRAL AND BASIC pH CIO2 ACCEPTS ONLY
1 ELECTRON.
AT ACIDIC pH, 2 to 3 , ClO2 ACCEPTS 5 ELECTRONS.
50
40
TTHMs (µ g/L)
1.5 mg/L ClO2
Fulvic acids
45
A
35
3.0 mg/L ClO2
A
30
25
20
C
15
10
3.0 mg/L ClO2
B
B
5
0
0
20
40
60
80
100
5.0 mg/L ClO2
120
140
160
180
Figure 8b. Formation of TTHMs byTime
1.5 mg/L
(hr) chlorine at various contact
times in disinfection of aqueous solutions of 5.0 mg/L fulvic acids and 2.0
mg/L bromide ions at pH 6. The chlorine was added as the post
disinfection after the following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0
mg/L, reduction of chlorine dioxide and chlorite ions residuals by Fe+2
and completion with FeCl3 up to 50 mg/L, flocculation, clarification and
filtration.
B - - The above treatment A followed by adsorbtion on GAC..
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-
50
Humic acids
45
TTHMs (µ g/L)
40
35
30
A
25
20
15
B
B
1.5 mg/L ClO2
10
1.5 mg/L ClO2
A
3.0 mg/L ClO2
C
5
5.0 mg/L ClO2
0
0
20
40
60
80
100
120
140
160
180
Time (hr)
Figure 9a. Formation of TTHMs by 1.5 mg/L chlorine at various contact times in disinfection
of aqueous solutions of 5.0 mg/L humic acids and 2.0 mg/L bromide ions at pH 6. The
chlorine was added as the post disinfection after the following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L, reduction of
chlorine dioxide and chlorite ions residuals by Fe+2 and completion with FeCl3 up to50 mg/L,
flocculation, clarification and filtration.
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
50
Fulvic acids
45
3.0 mg/L ClO2
TTHMs (µg/L)
40
A
A
A
5.0 mg/L ClO
1.5 mg/L ClO2
35
30
2
25
B
20
1.5 mg/L ClO2
15
C
10
5
0
0
20
40
60
80
100
120
140
160
180
Time (hr)
Figure 9b. Formation of TTHMs by 1.5 mg/L chlorine at various contact times in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids and 2.0 mg/L bromide ions at pH
6. The chlorine was added as the post disinfection after the following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L, reduction of
chlorine dioxide and chlorite ions residuals by Fe+2 and completion with FeCl3 up to 50 mg/L
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
1.6
Humic acids
THACNs (µg/L)
1.4
1.2
1.0
A
1.5 mg/L ClO 2
A
0.8
0.6
B
C
0.4
5.0 mg/L ClO 2
B
0.2
1.5 mg/L ClO2
3.0 mg/L ClO 2
0.0
0
20
40
60
80
100
120
140
160
180
Figure 10a. Formation of THACNsTime
by 1.5
(hr)mg/L chlorine at various contact times
in disinfection of aqueous solutions of 5.0 mg/L humic acids and 2.0 mg/L
bromide ions at pH 6. The chlorine was added as the post disinfection after the
following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L,
reduction of chlorine dioxide and chlorite ions residuals by Fe+2 and completion
with FeCl3 up to
50 mg/L, flocculation, clarification and filtration.
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L,
flocculation with 50 mg/L FeCl3 , clarification, filtration, followed by adsorbtion
on GAC.
1.6
1.4
THACNs (µg/L)
1.5 mg/L ClO2
Fulvic acids
A
1.2
A
1.0
0.8
3.0 mg/L ClO2
B 1.5 mg/L ClO2
0.6
A 5.0 mg/L ClO2
0.4
C
0.2
0.0
0
20
40
60
80
100
120
140
160
180
Time (hr)
Figure 10a. Formation of THACNs by 1.5 mg/L chlorine at various contact times in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids and 2.0 mg/L bromide ions at
pH 6. The chlorine was added as the post disinfection after the following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L, reduction of
chlorine dioxide and chlorite ions residuals by Fe+2 and completion with FeCl3 up to
50 mg/L, flocculation, clarification and filtration.
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
50
40
TTHMs (µ g/L)
1.5 mg/L ClO2
Fulvic acids
45
A
35
3.0 mg/L ClO2
A
30
25
20
C
15
10
3.0 mg/L ClO2
B
B
5
0
0
20
40
60
80
100
5.0 mg/L ClO2
120
140
160
180
Time (hr)
Figure 8b. Formation of TTHMs by 1.5 mg/L chlorine at various contact times in
disinfection of aqueous solutions of 5.0 mg/L fulvic acids and 2.0 mg/L bromide
ions at pH 6. The chlorine was added as the post disinfection after the following
treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L,
reduction of chlorine dioxide and chlorite ions residuals by Fe+2 and completion
with FeCl3 up to 50 mg/L, flocculation, clarification and filtration.
B - - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.
To minimize DBPs formation, many water
treatment plants turned to chloramine,
chlorine dioxide, ozone, or U.V. irradiation
as a total or partial replacement to
chlorine.
In considering the advantages of using chlorine
dioxide as a disinfectant it is desirable to find
ways of reducing the unwanted by-products of
chlorine dioxide.
Elimination of these reaction by-products could
greatly enhance the potential for chlorine dioxide
usage in drinking water and effluents treatment,
and lower the limitations imposed by the
regulations.
50
Humic acids
45
TTHMs (µ g/L)
40
35
30
A
25
20
15
B
B
1.5 mg/L ClO2
10
1.5 mg/L ClO2
A
3.0 mg/L ClO2
C
5
5.0 mg/L ClO2
0
0
20
40
60
80
100
120
140
160
180
Time (hr)
Figure 9a. Formation of TTHMs by 1.5 mg/L chlorine at various contact times in disinfection
of aqueous solutions of 5.0 mg/L humic acids and 2.0 mg/L bromide ions at pH 6. The
chlorine was added as the post disinfection after the following treatments:
A - Pre-disinfection with various doses of chlorine dioxide 1.5, 3.0 and 5.0 mg/L, reduction of
chlorine dioxide and chlorite ions residuals by Fe+2 and completion with FeCl3 up to50 mg/L,
flocculation, clarification and filtration.
B - Pre-disinfection with various doses of chlorine dioxide 1.5 and 3.0 mg/L, flocculation
with 50 mg/L FeCl3 , clarification and filtration.
C- Direct flocculation of the NOMs solutions with FeCl3 without pre-disinfection.