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Cost effective activated carbon treatment process for removing free chlorine from water.

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ASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING
Asia-Pac. J. Chem. Eng. 2010; 5: 714–720
Published online 11 September 2009 in Wiley Online Library
(wileyonlinelibrary.com) DOI:10.1002/apj.396
Research Article
Cost effective activated carbon treatment process
for removing free chlorine from water
Bingjing Li, Huaixu Zhang, Wei Zhang, Liuya Huang, Jun Duan, Juan Hu and Weichi Ying*
School of Resources and Environmental Engineering, East China University of Science and Technology, Shanghai 200237, China
Received 22 January 2009; Revised 22 July 2009; Accepted 4 August 2009
ABSTRACT: Experiments of batch treatment and column breakthrough were conducted to compare the dechlorination
effectiveness of five activated carbons: three made from coal (of different activation) and one each from coconut shell
and fruit nut/shell. The removal of free chlorine was accomplished by physical adsorption and chemical reaction;
adsorption was the main removal mechanism initially while chemical reaction by catalytic reduction was responsible
for continued removal of free chlorine. Removal of free chlorine was enhanced by a longer contact time, a lower pH,
and a higher initial/influent free chlorine concentration. Using <180 mesh particles of activated carbon in mixed batch
reactors, the carbon’s adsorptive capacity for free chlorine was established in 2 h; the carbons’ adsorptive capacities
for free chlorine were in the same order as their phenol numbers, the indicator of small micropores. The coconut
carbon had the highest adsorptive capacity but was much less reactive relative to the commercial coal and fruit shell
carbons. Much more free chlorine was removed in the lab carbon columns than the carbons’ adsorptive capacities due
to catalytic reduction of the adsorbed free chlorine on carbon surface. The free chlorine removal capacities of the two
spent carbons were similar to the respective new carbons.  2009 Curtin University of Technology and John Wiley &
Sons, Ltd.
KEYWORDS: activated carbon; free chlorine; dechlorination; adsorption; catalytic reduction
INTRODUCTION
Chlorine is commonly employed for water disinfection
around the world. In the US, a residual free chlorine of
>0.2 mg/l after 4 h of standing is required.[1] However,
high free chlorine concentrations in tap water often
adversely affect its many beneficial uses and may
even be a health concern. Although sulfur dioxide
and sodium sulfite can be employed to remove free
chlorine, it is impractical to use them for most water
dechlorination cases due to the high chemical cost and
the residual foreign matters left in the product water.
Furthermore, the chemical reduction reactions are slow
and may be incomplete.[2] Activated carbon is ideal for
removing free chlorine from water since it needs no
chemical addition and most persistent organic pollutants
(POPs) are also removed at the same time.[3] Activated
carbon may react with free chlorine in two types of
chemical reactions; the first type (Eqns (1) and (2))
produces oxygen-containing organic compounds on the
carbon surface,[4] resulting in a net weight gain, while
the second type (Eqns (3) and (4)) produces carbon
*Correspondence to: Weichi Ying, School of Resources and Environmental Engineering, East China University of Science and Technology, Shanghai 200237, China. E-mail: wcying@ecust.edu.cn
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
dioxide as the final product and thus results in a net
weight loss:
HClO + C∗ −−→ C∗ O + Cl− + H+
(1)
OCl− + C∗ −−→ C∗ O + Cl−
(2)
−
+
HClO −−→ Cl + H + [O]
2[O] + C −−→ CO2 ↑
(3)
(4)
where C∗ is active sites of the carbon and C∗ O is the
surface oxides.
The study was performed with the following
objectives: 1) rank the chlorine removal capacities of
five activated carbons of different raw materials and
different degree of activation, 2) demonstrate that free
chlorine removal was accomplished by adsorption and
chemical reduction, 3) determine the effects of contact
time, initial concentration of free chlorine, and pH on
the chlorine removal capacity, 4) obtain the free chlorine breakthrough curves of different carbons at neutral
and basic pHs to compare their relative effectiveness
in removing free chlorine, 5) characterize the activated
carbon after long term contact with free chlorine, and
6) verify the mechanism of chlorine removal based on
the lab and actual field dechlorination results.
Asia-Pacific Journal of Chemical Engineering
REMOVAL OF FREE CHLORINE FROM WATER
EXPERIMENTAL
Materials and instruments
Five domestic activated carbons: three coal carbons
(Coal I-III), a fruit nut (Fruit, apricot nut and walnut
shell) carbon and a coconut shell carbon (Coconut);
Table 1 summarizes the adsorptive capacities and properties of the carbon samples as represented by their
phenol and iodine numbers. The phenol number indicates the abundance of small micro pores (<1.0 nm in
diameter) and the capacities for adsorbing very small,
highly mobile, polar and/or aromatic organic molecules;
the iodine number indicates the specific surface area,
the abundance of micro pores (1.0–1.5 nm in diameter), and the capacities for small and/or non-polar
molecules.[5,6]
Sodium hypochlorite solution (chemical grade, free
chlorine ≥5.2%, NaOH = 7.8–8.0%); N ,N -diethyl-pphenylenediamine sulfate (DPD); silver nitrate (analytical grade).
De-ionized tap water was used to prepare the stock
sodium hypochlorite solution which was diluted to the
desired free chlorine concentration (2–15 mg/l) for the
experiments. Dilute NaOH and H2 SO4 were used to
adjust the pH. The test solutions were prepared for
each new series of experiments. The free chlorine
was measured by the DPD photometric method, while
the chloride concentration was measured by the silver
nitrate titration method of the US Standard Methods.[7]
Batch experiments of free chlorine removal
capacity
The batch experiments of free chlorine removal capacity
were conducted by contacting the carbon samples
(180–325 mesh) with free chlorine in the test solutions
for a fixed period of time (2, 5 and 8 h) in 40-ml glass
bottles packed in a rotating drum. The amount of free
chlorine removed was calculated for each test sample
as: X/M (mg/g) = (C0 − Cf )×V/m, where C0 : the initial
free chlorine concentration (mg/l), Cf : the residual free
Table 1. Adsorptive properties of the activated carbon
samples.
Activated carbon
Coal I
Fruit
Coconut
Coal II
Coal III
Phenol numbera
Iodine numberb
81.0
111
131
74.6
61.9
1114
1033
999
902
543
a
The amount (mg) of phenol adsorbed by 1 g of carbon at an
equilibrium phenol concentration of 20 mg/l.
b
The amount (mg) of iodine adsorbed by 1 g of carbon at an
equilibrium iodine concentration of 0.02 N.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
chlorine concentration (mg/l), V: sample volume (0.04
l), and m: carbon weight (g). The pairs of X/M and Cf
were correlated by the Freundlich Adsorption Isotherm
1/n
Model: X/M = k Cf . The experimental data and
the model best-fit lines (the isotherms) were plotted in
log–log scale.[5]
Removal of free chlorine due to chemical reduction is
affected by temperature, contact time, initial free chlorine concentration and pH.[8] Given that temperature
is generally not a control parameter in dechlorination,
the effects of the other three factors on free chlorine
removal are investigated. In another series of batch contact experiments (mass balance test runs), about 10 g of
Coal I was added to each of five 4-l beakers filled with
2 l of dilute NaClO solution of 5, 25 and 50 mg/l of free
chlorine and subsequently 5 ml of dilute NaClO solution (2–5%) was added to each beaker every 2–4 h for
up to 4 days to make up for the free chlorine removed
by the carbon; the final carbon weight and the amount
chloride released were measured.
Continuous flow experiments of
dechlorination in carbon columns
Due to the high adsorptive capacity of activated carbon for free chlorine, the column breakthrough experiments employed the efficient micro column rapid breakthrough (MCRB) method to obtain free chlorine breakthrough curves in a small fraction of the time that would
have been necessary employing the conventional test
method.[5] Six MCRB test runs (Table 2) were conducted using micro columns charged with 0.7–1.0 g of
120–180 mesh of carbon samples; operating at a very
short empty bed contact time (EBCT) of 5s; the effluent samples were taken periodically and analyzed for
free chlorine and chloride. One week of MCRB data
can predict more than 1 year of treatment performance
of a carbon adsorber employed for dechlorination at an
EBCT of 4.5 min.
RESULTS AND DISCUSSION
Effect of contact time on free chlorine removal
capacity
Figure 1 presents the batch 2-h, 5-h and 8-h chlorine
removal data of Coal I at the initial free chlorine concentration of 5 mg/l and pH of 6.8 and the corresponding
Freundlich isotherms. The removal capacity increased
with contact time; the Coal I’s 5-h removal capacity
was much greater than the 2-h removal capacity while
the 8-h removal capacity was only slightly higher due
to depletion of free chlorine. With the reactivity order
ranked in decreasing order, Coal II, Fruit shell and
Coconut carbons were also reactive since their removal
Asia-Pac. J. Chem. Eng. 2010; 5: 714–720
DOI: 10.1002/apj
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B. LI et al.
Asia-Pacific Journal of Chemical Engineering
Table 2. Summary of the free chlorine breakthrough runs.
Carbon
pH
Carbon
weight (g)
Coal I
Fruit
Coconut
Coal II
Coal I
Fruit
6.9
6.9
6.9
6.9
10.6
10.6
0.732
0.736
0.734
0.733
1.001
1.002
a
Free Cl
feed
(mg/l)
Flow
rate
(ml/min)
Run
time
(h)
Free
Cl fed
(mg)
Free Cl
removed
(mg/g)
2-h
capacity
(mg/g)
Removed/
capacity (%)
14.27
14.27
15.90
15.90
15.12
14.65
12.0
14.0
11.4
13.5
17.0
21.0
149
149
118
118
48
27
1531
1782
1297
1517
609
490
1858
1708
1214
1457
360
268
453
304
401
316
165a
184a
410
562
303
461
218
146
Based on the 5-h removal data as shown in Fig. 4.
Figure 1. Effect of contact time on free
chlorine removal capacity of Coal I carbon.
Figure 2. Effect of initial concentration on
5-h free chlorine removal: Coal I carbon.
capacities all increased with the contact times. Activated
carbon removed free chlorine by both adsorption and
chemical reduction; adsorption was nearly completed
in the first 2 h while catalytic reduction went on during
the entire test periods. Adsorption accounted for most of
the initial removal while catalytic reduction was responsible for removing adsorbed free chlorine to provide a
long service life of the carbon dechlorination system.
Effect of initial concentration of free chlorine
on its removal capacity
To demonstrate that chemical reduction was a component of the observed total free chlorine removal,
additional 5-h removal runs were performed employing initial free chlorine concentration of 2 and 15 mg/l.
Figure 2 shows that, as expected, for the chemically
active Coal I carbon, the higher initial free chlorine concentration resulted in the higher 5-h removals
due to faster reaction. Figure 3 shows that for the
less chemically active Coconut carbon, the higher initial free chlorine concentration produced even more
enhancement in its 5-h removals as the chemical
reduction became a more important component of
the total removal at the higher initial concentration.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Figure 3. Effect of initial concentration on
5-h free chlorine removal: Coconut carbon.
Since the adsorptive capacity of activated carbon is
not strongly affected by the adsorbate’s initial concentration, the strong positive effect of initial concentration on the removal capacity has demonstrated that a
major part of the observed total free chlorine removal
was due to chemical reduction of the adsorbed free
chlorine.
Asia-Pac. J. Chem. Eng. 2010; 5: 714–720
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
REMOVAL OF FREE CHLORINE FROM WATER
Effect of pH on the free chlorine removal
capacity
pH governs the distribution of free chlorine species:
HClO ←−−−−→ OCl− + H+ pKa = 7.5 (20 ◦ C)
(5)
At pH = 7.0, there are much more HClO molecules
than OCl− ions (75% vs 25%), while at pH = 10.6,
OCl− ions predominate. There are many slightly negatively charged sites on activated carbon surface due
to the presence of oxygen containing organic functional groups resulting in a lower capacity for OCl−
compared to the non-charge HClO. Therefore, activated
carbon’ adsorptive capacity for free chlorine increases
as the liquid phase pH goes down from 10.6. Furthermore, HClO is a much more powerful oxidant
than OCl− , hence more free chlorine is removed at
a lower pH of 7 by chemical reduction.[8] Both factors contributed to the higher 5-h free chlorine removal
capacities of Coal I and Fruit shell carbon observed
as the pH went down from 10.6 to 7.0 as illustrated in Fig. 4 (initial free chlorine concentration =
15 mg/l).
Free chlorine removal capacity of different
activated carbons
Using <180 mesh carbon, initial free chlorine concentration of 5 mg/l, pH of 6.5–7.0, several series of
batch experiments were conducted to determine the 2-h
and 5-h free chlorine removal capacities for five carbons. Free chlorine has a small molecular size and
also a high diffusivity;[8] its adsorption on activated
carbon was complete in less than 2 h; therefore, the
2-h free chlorine removal capacity was taken as its
adsorptive capacity for free chlorine for the ranking
purpose.
Figure 5 shows the order of the adsorptive capacities
for chlorine (Coconut > Fruit shell > Coal I > Coal
Figure 5.
capacity.
Figure 6.
capacity.
2-h free chlorine removal
5-h free chlorine removal
II > Coal III) is the same as that of their phenol
numbers (Table 1). At a pH of 7, the free chlorine
species are mostly HClO molecules which are small,
polar and fast diffusing like phenol molecules. The
results have demonstrated that the phenol number is
a better indicator than the iodine number of carbon’s
adsorptive capacity for free chlorine.
Figure 6 shows the 5-h chlorine removal capacities
were all higher than the respective 2-h removal capacities; however the order was changed due to the relatively high reactivities of Coal I, and, to a less degree,
Coal II associated with their well developed microporous structure (high phenol and iodine numbers) and
unique surface chemistry developed under the specific
activation conditions. The poorly activated Coal III carbon performed the worst in both 2-h and 5-h test runs
due both to its low adsorptive capacity and its low
reactivity. Both the raw material and the activation conditions of the activated carbon affect its reactivity with
free chlorine.
Dechlorination in carbon columns
Figure 4. Effect of 5-h free chlorine
removal capacity.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Figure 7 presents results of two sets of free chlorine breakthrough experiments employing micro carbon
Asia-Pac. J. Chem. Eng. 2010; 5: 714–720
DOI: 10.1002/apj
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B. LI et al.
Asia-Pacific Journal of Chemical Engineering
adsorption accounted for most of the initial removal
while catalytic reduction was responsible for removing
adsorbed free chlorine to provide a long service life of
the carbon dechlorination system.
Effect of free chlorine removal on weight
change and chloride release
Figure 7. Removing free chlorine from water: MCRB curves
for three carbons at two pHs.
breakthrough columns (EBCT = 5s); the operating conditions and the performance data are summarized in
Table 2. For the 4 test runs with a feed pH of 6.9, the
order of chlorine removal was Coal I > Fruit shell >
Coal II > Coconut. The much smaller removal capacities of the carbon at a higher pH of 10.6 (Fig. 4) was
responsible for the observed early breakthroughs of the
two high pH MCRB runs.
Due to the continuous catalytic reduction of the
adsorbed free chlorine in the carbon particles, the
amount removed was much more than the respective adsorptive capacities, even for the least reactive Coconut carbon. Catalytic reduction was also
notable in a shorter time at a higher pH of 10.6,
as the amounts removed were higher, although to
lesser degrees, than the respective adsorptive capacities. Such observed higher degrees of free chlorine
removal than the equivalent adsorptive capacities of
the activated carbons are consistent with the performance of the three full size dechlorination systems described in the section on Effect of Free
Chlorine Removal on Weight Change and Chloride
Release.
The batch and continuous flow dechlorination results
have demonstrated that activated carbon removes free
chlorine by both adsorption and chemical reduction;
The mass balance test runs were performed to determine
which of the two free chlorine removal mechanisms
[Eqns (1) and (2) and Eqns (3) and (4)] was more
important in the overall removal process. The results
of five runs are summarized in Table 3. Giving the
high potential of weight loss in the multiple steps of
handling the samples and the short testing period (up
to 4 days), the small weight gains found in the final
carbon samples of No. 2 and 5 runs suggest that the
oxide formation was the predominant mechanism. At a
total removal rate below the corresponding adsorptive
capacity of Coal I for free chlorine, the positive
correlation of amount of chloride released with total free
chlorine removed is a further evidence that chemical
reduction was the major cause of observed free chlorine
removal.
Effect of free chlorine removal on surface
chemistry of activated carbons
Surface acidity was measured[9] for Coal I, Coconut
and Fruit shell activated carbons and two activated
carbons which were spent after 1 year of dechlorination
services (Case 1 and Case 3 of Table 3); the pHzpc
values for them were 9.2, 9.3, 9.1, 7.1 and 7.0,
respectively. The finding of more acidic surface of
activated carbons spent on dechlorination service is
consistent with the finding of increased amount of
oxygen containing organic functional groups (carboxyl,
lactone, phenolic hydroxyl and carbonyl) found on the
surface of activated carbons after removing a large
amount of free chlorine.[10]
Table 3. Summary of the mass balance test runs (Coal I carbon, <180 mesh).
Carbon samples
Weight before testing (g)
Weight after testing (g)
Initial free Cl concentration (mg/l)
Total free Cl removed (mg)
Free Cl removal (mg/g)
Chloride before testing (mg/l)
Chloride after testing (mg/l)
Chloride increase (mg/l)
1
2
3
4
5
9.9594
9.7446
25
455
46
1557
1932
375
9.9392
9.9887
25
1077
108
5721
6398
677
9.8660
9.8322
25
1942
197
8679
9744
1065
10.2141
9.8684
5
940
92
3696
4430
734
9.9726
10.0147
50
1062
106
6178
7078
900
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pac. J. Chem. Eng. 2010; 5: 714–720
DOI: 10.1002/apj
Asia-Pacific Journal of Chemical Engineering
REMOVAL OF FREE CHLORINE FROM WATER
Table 4. Three cases of full scale activated carbon adsorbers employed for water dechlorination.
Characteristics of the feed
Free chlorination of the feed (mg/l)
Effluent limit on free chlorine (mg/l)
pH
Flow rate (m3 /h)
Activated carbon and adsorber
Raw material of activated carbon
Particle size (mesh)
Bed height of the adsorber (m)
Diameter of the adsorber (m)
Amount of carbon per adsorber (t)
Adsorber packing density (kg/m3 )
Backwash frequency (times/day)
Service time (d)
Amount of carbon changed (t)
Calculated results
Volume of the carbon section (m3 )
Empty bed contact timea (min)
Total free chlorine removedb (mg/g)
Adsorptive capacityc (mg/g)
Capacity utilization rate (%)
Case 1
Case 2
Case 3
≈2
≤0.1
≈7
3
≈2
≤0.05
≈7
10
5–8
0.02
7.5
100
Fruit shell
8–20
1.35
0.8
0.3
≈460
2
365
0.3
Coconut
8–20
1.25
0.7
0.2
≈500
1
165
0.2
Coconut
8–20
1.1
2.65
2.43
500
3
365
2.43
0.652
13.0
166
206
80.6
0.400
2.4
386
227
170
4.86
2.9
2340
314
745
a
Volume of the carbon section/flow rate.
b
(Concentration reduced × flow rate × service
c
time)/amount carbon changed.
Capacity at the feed concentration, based on the 2-h removal capacities of Fig. 5.
Three cases of full size activated carbon
adsorbers employed for water
dechlorination
Three full size carbon dechlorination systems were
operated in the past 1 year. One fruit shell carbon and
two kinds of coconut shell activated carbon were used.
The important system parameters and performance data
were shown in Table 4. The EBCT of three activated
carbon columns were 13, 2.4, 2.9 min, separately. It’s
much longer than the EBCT of coconut carbon MCRB
column which is 5 s. The highest utilization rate of
coconut carbon had increased into 745%, eight times
larger than full-scale fruit shell carbon column (80.6%)
and one time larger than small-scale coconut carbon
MCRB column (303%), even though the fruit shell
carbon utilization rate is higher than that of coconut
carbon in the small-scale experiment. The results have
demonstrated that catalytic reduction is the predominant
cause of free chlorine removal in an actual carbon
dechlorinator even if it is charged with a less reactive
carbon. The data also suggest that less frequent carbon
replacement practices may be adapted for the Systems
1 and 2 to reduce carbon consumption without the
fear of increased free chlorine in the effluent. The
use of less costly and more reactive high quality coal
based activated carbon may reduce the carbon cost even
more.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Figure 8. Free chlorine removal capacities
of activated carbons after 1 year of
dechlorination.
Free chlorine removal capacities of the spent
activated carbons
The 2- and 5-h free chlorine removal experiments were
performed on two activated carbons (one fruit and one
coconut based) taken from the adsorbers after 1 year of
dechlorination services. Figure 8 has demonstrated that
they were still effective for removing free chlorine as
evidenced by their large adsorptive capacities (2-h free
chlorine removal capacities) and continuing chemical
Asia-Pac. J. Chem. Eng. 2010; 5: 714–720
DOI: 10.1002/apj
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B. LI et al.
activity (differences in 5-h and 2-h removal capacities).
The adsorptive capacity and chemical activity of the
spent activated carbons were not significantly different
from the respective new carbons, which suggests that
they could have been used for a much longer period
of time. The results of this study have demonstrated
that activated carbon in a well designed and operated
dechlorinator may be employed for long term service
without the need of periodic replacement.
CONCLUSIONS
1. Activated carbon removes free chlorine by both
adsorption and chemical reduction; adsorption
accounted for most of the initial removal while
catalytic reduction was responsible for removing
adsorbed free chlorine to provide a long service life
of the carbon dechlorination system.
2. A higher chlorine removal capacity was obtained in
the batch experiments with a higher initial chlorine
concentration, a lower pH, and a longer contact
time. Release of chloride confirmed that the chemical
reduction was a factor of the overall removal.
3. The adsorptive capacity of carbon (<180 mesh)
for free chlorine was indicated by its 2-h chlorine removal capacity since adsorption is a much
faster process than chemical reduction. Relative to
the iodine number, the carbon’s phenol number is
a better indicator of its adsorptive capacity for free
chlorine; the coconut carbon had the highest adsorptive capacity for free chlorine consistent with its
highest phenol numbers of the three types of carbons.
4. Coal I was the most reactive carbon to reduce free
chlorine followed by the fruit carbon; the coconut
carbon was the least reactive. The raw material and
the activation conditions of the activated carbon
affect its reactivity with free chlorine. The use
of a commercial coal based activated carbon for
dechlorination is especially cost effective since it is
less costly than a coconut or fruit shell based carbon.
5. Dechlorination breakthrough data have demonstrated
a much higher total removal of free chlorine than
the respective adsorptive capacity as a result of
catalytic reduction of adsorbed free chlorine. The
enhancement was most notable in the case of Coal I
consistent with its highly reactive nature.
6. The MCRB method (EBCT = 5s) was effective
to simulate long term dechlorination operation in a
conventional carbon system in few days.
 2009 Curtin University of Technology and John Wiley & Sons, Ltd.
Asia-Pacific Journal of Chemical Engineering
7. Weight gain in activated carbon samples after long
time of contact with free chlorine was consistent with the surface oxide formation mechanism
[Eqns (1) and (2)]. This mechanism was further supported by the much more acidic surfaces of the activated carbons after 1 year of dechlorination services.
8. The adsorptive capacity and chemical activity of the
activated carbons (one fruit and one coconut based)
spent after 1 year of dechlorination services were
not significantly different from the respective new
carbons due to the continuing catalytic reduction of
the adsorbed free chlorine.
9. Employing a well designed activated carbon adsorber and practicing clean and safe operating procedure
are the most cost effective and environment friendly
method of dechlorination.
Acknowledgements
This research was supported by Shanghai Leading
Academic Discipline Project, Project Number: B506.
You-liang Liu of Shanghai Activated Carbon provided
most of the fresh activated and the two spent activated
carbon samples; he also provided the operating data of
the three cases of full size activated carbon adsorbers
employed for water dechlorination.
REFERENCES
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[2] G.R. Helz, A.C. Nweke. Environ. Sci. Technol., 1995; 29,
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[3] M.T. Suisan, W.H. Cross. J. Water Pollution Control Fed.,
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[4] M.T. Suisan, V.L. Snoeyink. Environ. Sci. Technol., 1977; 11,
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[5] W.C. Ying, W. Zhang. Environ. Prog., 2006; 25, 110–120.
[6] W. Zhang, Q.G. Chang. Environ. Prog., 2007; 26, 289–299.
[7] L.S. Clesceri, A.E. Greenberg, A.D. Eaton. Standard Methods
for the Examination of Water and Wastewater, 20th edn,
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[8] V.L. Snoeyink. In Water Chemistry (Chlorine Chemistry)
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Asia-Pac. J. Chem. Eng. 2010; 5: 714–720
DOI: 10.1002/apj
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