Effect of chlorine on adsorption ultrafiltration treatment for removing natural organic matter in drink2

Journal of Colloid and Interface Science 274 (2004) 587–593
www.elsevier.com/locate/jcis
Effect of chlorine on adsorption/ultrafiltration treatment for removing
natural organic matter in drinking water
Tae-Wook Ha,
a
Kwang-Ho Choo,
b,∗
and Sang-June Choi
b
a
Department of Environmental Engineering, Taegu Science College, Buk-Gu, Daegu 702-724, South Korea
b
Department of Environmental Engineering, Kyungpook National University, Buk-Gu, Daegu 702-701, South Korea
Received 29 July 2003; accepted 5 March 2004
Available online 16 April 2004
Abstract
In drinking water treatment, prechlorination is often applied in order to control microorganisms and taste-and-odor-causing materials,
which may influence organics removal by adsorption and membrane filtration. Thus, the addition of chlorine into an advanced water treat-
ment process using a hybrid of adsorption and ultrafiltration (UF) was investigated in terms of natural organic matter (NOM) removal and
membrane permeability. A comparison between two adsorbents, iron oxide particles (IOP) and powdered activated carbon (PAC), was made
to understand the sorption behavior for NOM with and without chlorination. Chlorine modified the properties of dissolved and colloidal
NOM in raw water, which brought about lower TOC removal, during IOP/UF. The location of IOPs, whether they were in suspension or in a
cake layer, affected NOM removal, depending on the presence of colloidal particles in feedwater. Chlorine also played a role in reducing the
size of particulate matter in raw water, which could be in close association with a decline in permeate flux after chlorination.
 2004 Elsevier Inc. All rights reserved.
Keywords: Chlorination; Iron oxide; Adsorption; Ultrafiltration; Water treatment
1. Introduction
Ultrafiltration (UF) processes are increasingly popular in
drinking water treatment to produce better quality water and
meet more stringent treatment regulations, particularly con-

cerning removal of pathogens and turbidity [1–10]. How-
ever, the widespread use of UF membranesin drinking water
treatment is still limited due to two major drawbacks, mem-
brane fouling and insufficient removal of disinfection by-
products (DBPs) precursors [11–16]. Furthermore, several
studies on the membrane treatment of surface, lake, and river
waters have demonstrated that the DBPs precursors of nat-
ural organic matter (NOM) were one of the major foulants
of the membranes [17–22].
To overcome such problems caused by NOM in UF ap-
plications, conjunctive use of adsorbents and membranes is
thus becoming more attractive for water treatment because
the adsorbents can capture and retain NOM before it reaches
the membrane surface [13–15,23–28]. The combination of
UF with powdered activated carbon (PAC) adsorption re-
*
Corresponding author. Fax: +82-53-950-6579.
E-mail address: (K H. Choo).
vealed that PAC could play a role in removing NOM from
water but is not always helpful in reducing membrane foul-
ing [14,29,30]. Additionally, a large amount of spent carbon
sludge that should be disposed of was generated in the com-
bined process. Thus, an alternative adsorbent that can be
readily regenerated as such iron oxide particles (IOP) has re-
cently been developed and applied to water treatment in con-
junction with UF membranes [26–28]. The addition of IOP
into UF systems contributed to both an increase in NOM re-
moval efficiency and a decrease in membrane fouling. How-
ever, the interaction of IOPs with NOM and membranes was
not fully understood, nor was the effect of water chemistries

on IOP adsorption well evaluated.
Oxidation of raw water would have been done using chlo-
rine or ozone to control metals and microbial growth in
potable water treatment, which exerted an additional effect
on the coagulation efficiency [31,32]. The oxidation step im-
proved or deteriorated the coagulation process while chang-
ing the nature of the water to be treated. No information is
available, however, on whether preoxidation could affect the
treatment efficiency by adsorption and membrane filtration
for water treatment.
0021-9797/$ – see front matter  2004 Elsevier Inc. All rights reserved.
doi:10.1016/j.jcis.2004.03.010
588 T W. Ha et al. / Journal of Colloid and Interface Science 274 (2004) 587–593
The comparison of sorption behavior between PAC and
IOP would help understand the characteristics of adsorbents
with different surface structures and functionalities. Analy-
ses of the effects of chlorination of raw water during adsorp-
tion and UF could also establish some correlation of NOM
removal and membrane permeability with alteration of the
physicochemical nature of NOM and colloids. It may thus
provideinsight into the phenomenaoccurringat the interface
among the membranes, the adsorbents, and the adsorbates
present in intact and chlorinated waters.
In this work, therefore, the characteristics of adsorptive
NOM removal by IOPs were investigated in a combined
IOP/UF system with and without chlorination. The adsorp-
tion behavior of IOP was also compared with that of PAC
at different adsorbent doses. In particular, the influence of
prechlorination on IOP/UF was evaluated in terms of NOM
removal and membrane permeability, since chlorine was of-

ten dosed into raw water to control microbial growth and
taste-and-odor-causing materials. Also, the effect of parti-
cles in the system, such as IOPs and particulate colloids, on
NOM removal efficiency was explored during UF.
2. Materials and methods
2.1. Raw water
Water samples used for this study were obtained from the
Maegok Water Treatment Plant, which receives raw water
from the Nakdong River, the major water source of the city
of Daegu, Korea. The water samples collected were moved
to the laboratory and then stored at 4
◦
C before use. The key
water quality characteristics are given in Table 1. To remove
colloidal particles from raw water, it was pretreated, using a
0.45-µm filter, and so the filtrate was defined as prefiltered
water.
2.2. Adsorbents
Two adsorbents, powdered activated carbons (PAC) and
iron oxide particles (IOP), were employed in this work.
A commercially available PAC adsorbent was purchased
from Dae Jung Chemicals and Metals (Korea), while an
amorphous IOP slurry (10 g/L as Fe) was prepared in the
laboratory by neutralizing a ferric chloride solution using
5 N NaOH [33]. The PAC and IOP adsorbents used had av-
erage surface areas of 1400 and 240 m
2
/g, respectively.
Table 1
Quality of raw water from the Nakdong River

Parameter pH Alkalinity
(mg/L
as
CaCO
3
)
Hardness
(mg/L
as
CaCO
3
)
Turbidity
(NTU)
DOC
(mg/L)
UV
absorbance
at 254 nm
(cm
−1
)
Value 7.4–7.8 59–71 95–97 31–39 2.4–2.9 0.071–0.079
2.3. Chlorination
A sodium hypochlorite dosing solution with 1000 mg/L
free chlorine was prepared from a 12% sodium hypochlo-
rite solution. Chlorine dosages were changed over the range
from 0 to 11mg/LasCl
2
at nativepH. Normally, a high con-

centration of chlorine (11 mg/LasCl
2
) was applied in order
to expedite the chlorination reactions within a short period
of time. The chlorination steps lasted 30 min and then resid-
ual free chlorine was immediately quenched by the addition
of sodium sulfite.
2.4. Adsorption tests
To evaluate efficiencies of NOM removal by different ad-
sorbents, such as IOP and PAC, adsorption isotherm tests
were performed at various adsorbent doses. For IOP adsorp-
tion tests, a certain amount of the stock IOP slurry (cor-
responding to 0–100 mg/L as Fe) was placed into several
300-ml Erlenmeyer flasks and the solution was then mixed
at 200 rpm and 20
◦
C for 30 min. The solution was filtered
through a 0.45-µm filter (Millipore, USA) and the filtrate
samples collected were used for analyses. PAC adsorption
tests with a PAC dosing range of 0–100 mg/L were per-
formed in the same manner as described above.
2.5. UF membranes and stirred cell UF tests
The UF membranes used in this study was made of poly-
ethersulfone and had a molecular weight cutoff of 100,000
and an effectivesurface area of 28.7 cm
2
. All the membranes
used were initially rinsed, using pure water as mentioned in
the instructions provided by the manufacturer. As shown in
Fig. 1, batch UF experimentswere performedusing a 180-ml

stirred cell plus an 800-ml reservoir (Amicon 8200, USA).
So the overall working volume of the batch unit was 980 ml.
The applied pressure was kept at 0.49 bar using a nitrogen
cylinder, while the stirring speed was adjusted to 160 rpm
using a magnetic stirrer. During UF, the mass of permeate
was measured using an electronic balance and recorded si-
multaneously on an on-line personal computer to calculate
permeation flux.
Fig. 1. Schematic of a stirred-cell UF system unit with a reservoir.
T W. Ha et al. / Journal of Colloid and Interface Science 274 (2004) 587–593 589
2.6. Analytical methods
Feedwater and permeate samples were analyzed for UV
absorbance at 254 nm and total organic carbon (TOC) con-
centrations. Light absorbance at 254 nm, which is associated
with the aromatic groups in NOM, is used as a surrogate
parameter for monitoring the concentration of dissolved or-
ganic matter in a fast and easy manner during water treat-
ment [34]. The UV absorbance was determined using a
UV/vis spectrophotometer (Hewlett Packard 8452A, USA)
and the TOC concentration was measured using a TOC ana-
lyzer (Sievers 8200, USA). In particular, the UV absorbance
and the dissolved organic carbon (DOC) concentration of
raw water were measured after removal of particulate matter
using a 0.45-µm membrane (Millipore, USA). Free chlo-
rine concentrations were determined by a DPD colorimetric
method using a Hach spectrophotometer (DR2500, USA)
and reagent pillows.
When the prechlorination of raw water was applied in the
experiments, the initial UV absorbance was defined as the
UV absorbance of raw water after chlorination and used for

the evaluation of UV absorbance removal efficiency.
3. Results and discussion
3.1. Comparison of sorption behavior of NOM onto IOP
and PAC
Fig. 2 shows UV removal efficiencies for treatment of
prefiltered Nakdong River water at various dosages of IOP
and PAC. The UV removal efficiency increased sharply, to
approximately 40%, with increasing IOP dosages and nearly
leveled off at such a small dosage as 10 mg Fe/L, whereas
a gradual increase in UV removal was achieved with higher
PAC dosages. The distinctively different trends in adsorp-
tive NOM removal for IOP and PAC could be attributed
primarily to the discrepancy in structures and sorption mech-
Fig. 2. Comparison of UV removal efficiency between IOP and PAC adsor-
bents: adsorption time, 30 min.
anisms of the adsorbents. The majority of active sorption
sites of nonporous IOP are located on the outer surface lay-
ers, with an amorphous structure which is wide open to the
bulk solution phase. So NOM removal by IOP sorption can
occur rapidly through surface coordinative reactions with-
out any limitation on mass transfer of NOM molecules. In
case of PAC, however, most of the active surface sites are
present inside the pores in which NOM sorption normally
occurs through van der Waals attraction. The rate of sur-
face diffusion of NOM molecules inside PAC pores should
be very low because of high molecular weights, so the ad-
sorption equilibrium would take more than a few days. In
fact, the initial external mass transfer coefficient of IOP
(1.17 × 10
−7

m/s), which was determined in a complete
mixed reactor, was nearly one order of magnitude higher
than that of PAC (1.26 × 10
−8
m/s). In this regard, IOP
could be a better adsorbent for removing NOM within lim-
ited hydraulic residence times. If the combination of adsorp-
tion and membrane separation (e.g., UF or MF) is applied
to drinking water treatment, residence times in the systems
must be less than a few hours and thereby IOP would be
more desirable due to faster adsorption.
Fig. 3 compares the effect of prechlorination on UV re-
moval efficiency by IOP and PAC during the treatment of
prefiltered water. The UV removal efficiency for river wa-
ter by IOP decreased with higher dosages of chlorine, while
no reduction in UV removal efficiency occurred for PAC ad-
sorption. A possible explanation of the difference between
IOP and PAC adsorption abilities after chlorination is that
chlorine reacts with NOM to form DBPs such as THMs,
which are not adsorbable onto IOP but still adsorbable onto
PAC. As a result, it was found that the prechlorination of
raw water could have an effect on NOM removal efficiency
by IOP. However, furtherstudies on the influence of chlorine
during treatment of raw water by IOP adsorption and UF are
needed (which will be discussed in the next sections).
Fig. 3. UV removal efficiencies using IOP and PAC adsorbents at different
chlorine dosages: chlorination time, 30 min; IOP dose, 100 mg/LasFe;
PAC dose, 80 mg/L.
590 T W. Ha et al. / Journal of Colloid and Interface Science 274 (2004) 587–593
(a)

(b)
Fig. 4. Effect of prechlorination on UV and TOC removal efficiencies in
IOP/UF and UF only, treating (a) prefiltered and (b) raw waters: IOP dose,
100 mg/L as Fe; chlorine dose, 11 mg/LasCl
2
; chlorination time, 30 min.
3.2. Interaction of chlorine with dissolved and colloidal
NOM in IOP/UF
To examine the interaction of chlorine with dissolved
NOM and colloidal particles during IOP/UF and UF alone,
UV and TOC removal efficiencies using prefiltered and
raw water were compared and are shown in Fig. 4. During
IOP/UF treatment of prefiltered water samples, there was a
negligible decrease in TOC removal efficiency with chlori-
nation, though the UV removal efficiency decreased by ap-
proximately 10%. For raw water, however, the TOC removal
efficiency also decreased comparatively significantly with
prechlorination in IOP/UF. On the other hand, in UF treat-
ment alone, the UV removalefficiency declined slightly with
prechlorination, but negligible TOC removal occurred for
both waters. Thus, the lower UV and TOC removal efficien-
cies with prechlorination in IOP/UF might be attributed to a
decrease in the reactivity (adsorption ability) of NOM after
chlorination. The specific UV absorbance (SUVA) related
Fig. 5. Variation of UV of different water samples with time during chlo-
rination: chlorine dose, 11 mg/LasCl
2
. Particles collected from raw water
were obtained using a 0.45-µm filter and then resuspended in pure water.
to the dissolved portion of organic matter in river water de-

creased with higher chlorine doses (e.g., from 1.95 L/mg m
with no chlorine addition to 1.57 L/mg m with a chlorine
dose of 11 mg/LasCl
2
), suggesting that the reactivity of
TOC in river water was lowered by chlorination.
However, it was not enough to explain why the TOC re-
moval efficiency for raw water decreased more significantly
than that for prefiltered water. Thus, the variation of UV ab-
sorbance differentials (UV) for three feedwater samples
of raw and prefiltered waters and a particle suspension was
examined in the course of chlorination time (Fig. 5). The
UV value for the prefiltered and raw water samples de-
creased from 0 to −2.1m
−1
and 0 to −1.2m
−1
, whereas
UV increased from 0 to 0.65 m
−1
with the suspension
containing 30 NTU of colloidal particles from river water.
These results implied that during chlorination the structure
of dissolved NOM was modified, leading to a decrease of
UV absorbance, but some organic matter could be released
from colloidal particles to supply more carbon into the bulk
liquid phase. When a feedwater sample containing 100 NTU
of particles was chlorinated, UV increased up to 1.0 m
−1
within 30 min of reaction time (data not shown). Conse-

quently, during prechlorination the breakage of aromatic
moieties in NOM molecules occurred without mineraliza-
tion of NOM, which reduced the sorption capacity of NOM.
The conversion of particulate matter to dissolved matter by
chlorination should contribute to an increase of carbon con-
tent in the dissolved NOM pool, resulting in lower DOC
removal during IOP/UF.
3.3. Effect of IOP deposition and colloidal particles on
NOM rejection
Since IOPs injected into the IOP/UF system exist either
in the bulk liquid phase or at the membrane surface, the ef-
fect of IOP locations on NOM removal during IOP/UF was
examined. As shown in Fig. 6, the UV and DOC removal
T W. Ha et al. / Journal of Colloid and Interface Science 274 (2004) 587–593 591
Fig. 6. UV and DOC removal efficiencies using raw water during UF with
IOPs in suspension and in deposited layers: IOP dose, 100 mg/LasFe.
efficiencies with deposited IOPs were always at higher lev-
els than those with suspended IOPs. It could be hypothesized
that the formationof IOP cake layers at the membrane would
contribute to further NOM rejection due to a sieving effect
during IOP/UF. However, it was not clear that IOPs in the
deposited layer had such similar sorption capacity for NOM
as those in suspension.
Any changes of the sorption capacity of IOPs located
at different places were examined for raw water and are
compared in Fig. 7. Different trends in NOM removal us-
ing IOP-deposited and suspended systems were observed
when prechlorination and/or prefiltration runs were per-
formed. The DOC removal efficiency for the IOP-deposited
system declined substantially when the colloidal particles

present in raw water were removed, whereas that for the
IOP-suspended system was not so much dependent on the
absence of colloidal particles. This indicated that a signifi-
cant loss of adsorption sites took place when IOPs formed a
cake layer at the membrane surface. Thus it supported the
above reasoning that higher DOC removal with the IOP-
deposited system was mainly caused by the formation of
a denser cake layer associated with colloids in raw water.
In addition, it could be thought that crossflow UF that can
keep IOPs in suspension would be better in regard to NOM
removal compared to dead-end membrane filtration if raw
water had a very low turbidity.
3.4. Effect of chlorination on membrane permeability
Relative flux decline profiles for different treatment sys-
tems using raw and filtered waters are shown in Fig. 8. The
IOP/UF system had a flux more than two times that of UF
alone. It was thus clear that IOP addition helped to enhance
the membrane flux substantially, since IOP removed NOM
that can otherwise cause membrane fouling [26–28]. On the
other hand, the fluxes with the prechlorination of raw water
were always kept at a relatively low level in both IOP/UF and
(a)
(b)
Fig. 7. Effect of chlorine and colloidal particles on DOC removal during
IOP/UF when (a) IOPs are in deposited cake layers and (b) in suspension:
chlorine dose, 11 mg/LasCl
2
; chlorination time, 30 min.
UF-only systems, whereas the permeate flux was indepen-
dent of chlorination when colloidal particles were removed

prior to UF. Although a change of the nature of dissolved
organic matter was obvious during chlorination, it did not
affect membrane flux so much (Fig. 8). Considering the
lower DOC removal efficiency with prechlorination shown
in Fig. 4, a possible explanation for the above result was that
the interaction of chlorine with colloidal particles in raw wa-
ter may bring about a change of their characteristics (e.g.,
particle size reduction) leading to flux decline. As shown
in Fig. 9, the size distribution of particles in raw water was
shifted to lower ranges with chlorination, which can make
the cake layer of particles at the membrane surface denser.
This supports the above explanation about flux decline with
chlorination. Accordingly, it was found that membrane flux
was not sensitive to the change of physicochemical proper-
ties of the DOC by chlorination, but it was affected by that
of particulate matter characteristics.
592 T W. Ha et al. / Journal of Colloid and Interface Science 274 (2004) 587–593
(a)
(b)
Fig. 8. Effect of prechlorination on flux in IOP/UF and UF alone treating
(a) raw and (b) filtered waters: chlorine dose, 11 mg/LasCl
2
; chlorination
time, 30 min.
Fig. 9. Particle size distributions of raw water before and after chlorination:
chlorine dose, 11 mg/LasCl
2
; chlorination time, 30 min.
4. Summary and conclusions
Prechlorination of river water during UF in combination

with adsorption was conducted and evaluated with respect to
NOM removal and membrane permeability.IOP had a larger
sorption capacity for NOM at lower dosages than PAC,
though the sorption capacity of IOP declined slightly after
chlorination of raw water. The interaction of chlorine with
dissolved NOM in raw water caused a decrease in UV ab-
sorbance, while that with particulate matter did an increase
in it. During the chlorination reactions, part of the particu-
late matter was converted to dissolved matter, leading to an
increase of dissolved carboncontentin the NOM total.These
results contributed to the lower TOC removal efficiency by
IOP/UF after chlorination. When the IOPs injected into an
UF system formed a cake layer at the membrane surface,
further NOM removal was achieved due to a sieving effect
by the physical barrier. As colloidal particles were removed
from raw water, however, a significant decrease in NOM re-
moval efficiency occurred in the IOP-deposited system. It
was revealed that IOPs in the cake layer were not so effective
for adsorption as those in suspension because of their ag-
gregation. During prechlorination, colloidal particles in raw
water became smaller in size, so flux decline was relatively
large due to the formation of a denser cake layer on top of
the membrane.
Acknowledgments
This work was supported by the Korea Research Foun-
dation (Grant 2002-003-D00171). The authors thank public
servants of the Maegok Water Utility for their help in ob-
taining water samples. The laboratory assistance provided
by Suck-Ki Kang and Jang-Hyun Kim at Daegu University
is appreciated.

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