chemical and microbial decontamination of pool water using
TRANSCRIPT
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WAT E R R E S E A R C H 4 2 ( 2 0 0 8 ) 2 8 9 9 – 2 9 1 0
0043-1354/$ - see frodoi:10.1016/j.watres
�Corresponding auE-mail addresses
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Chemical and microbial decontamination of pool waterusing activated potassium peroxymonosulfate
George P. Anipsitakisa,�, Thomas P. Tufanob, Dionysios D. Dionysiouc
aChastain-Skillman, Inc., 4705 Old Highway 37, P.O. Box 5710, Lakeland, FL 33807-5710, USAbDuPont Chemical Solutions Enterprise, Experimental Station Laboratory, Building 402/Room 5234D, Wilmington, DE 19880-0402, USAcDepartment of Civil and Environmental Engineering, University of Cincinnati, 765 Baldwin Hall, Cincinnati, OH 45221-0071, USA
a r t i c l e i n f o
Article history:
Received 10 December 2007
Received in revised form
27 February 2008
Accepted 4 March 2008
Available online 18 March 2008
Keywords:
Potassium peroxymonosulfate
Monopersulfate
Cobalt
Sulfate radical
Free available chlorine
Combined chlorine
Pool water
Creatinine
Chlorinated creatinine
Arginine
Ammonium ion
E. coli.
Advanced oxidation processes
Disinfection
nt matter & 2008 Elsevie.2008.03.002
thor. Tel.: +1 863 646 1402;: ganipsitakis@chastains
[email protected] (D.D. Dionysio
a b s t r a c t
Potassium peroxymonosulfate activation leads to the formation of highly reactive species,
mainly the sulfate radicals. Activated potassium peroxymonosulfate (from now on
peroxymonosulfate) was tested against specific pollutants such as ammonium ion,
creatinine, chlorinated creatinine products, arginine and Escherichia coli (E. coli), all
constituents or derivatives of human discharges. The objective was to assess whether
activated peroxymonosulfate can be a viable treatment reagent in recreational water
applications. It was found that organic molecules such as creatinine, chlorinated creatinine
products and arginine could be effectively treated with activated peroxymonosulfate.
Ammonium ion was oxidized only by chlorine species and only in de-ionized water.
Chlorine species were formed from the reaction of sulfate radicals with chloride ions. In
pool water, the reaction of sulfate radicals with chloride ions and the subsequent
ammonium ion oxidation were scavenged by the presence of bicarbonate ions. The Co/
Peroxymonosulfate system was also shown to be an effective disinfection reagent, since
99.99% (4-log) kill of E. coli was achieved in 60 min of treatment. At the concentrations
tested here, however, it is still not efficacious enough to qualify as an EPA-registered
sanitizer for swimming pools (requires 6-log kill of E. coli, ATCC 11229, and Enterococcus
faecium, ATCC 6569, in 30 s).
& 2008 Elsevier Ltd. All rights reserved.
1. Introduction
In recreational water, human activities demote water quality
due to natural discharges of the human body. Chemical
contaminants released in water include urine and perspira-
tion constituents, such as ammonia, urea, creatinine and
arginine. Several microorganisms are also rinsed from the skin
and released through the mouth, as well as the urinary and
r Ltd. All rights reserved.
fax: +1 863 644 3589.killman.com (G.P. Anipsitu).
the gastrointestinal tracts. Chlorination, especially for disin-
fection purposes, is still the treatment option widely applied.
In recent years, however, there has been an increasing trend
towards replacing active chlorine chemicals for water decon-
tamination and disinfection, due to the detection and adverse
health effects of several by-products formed, such as trihalo-
methanes (THMs) and haloacetic acids (HAAs). Potassium
peroxymonosulfate (2KHSO5 �KHSO4 �K2SO4, commercially
akis), [email protected] (T.P. Tufano),
ARTICLE IN PRESS
WAT E R R E S E A R C H 4 2 ( 2 0 0 8 ) 2 8 9 9 – 2 9 1 02900
available as Oxones from DuPont Co.) is a widely used
oxidizer in a variety of industrial and consumer applications;
specifically, it is sold as a non-chlorine shock-oxidizer for
swimming pools and spas. Peroxymonosulfate alone, similarly
to hydrogen peroxide (Borgmann-Strahsen, 2003), is not as an
efficacious disinfectant as active chlorine compounds. If
activated catalytically, thermally or photolytically, however,
the radicals formed are very energetic and effective oxidizing
agents and may possess a potent disinfecting action.
In previous studies, we demonstrated the great potential
activated peroxymonosulfate technologies could have in
water treatment (Anipsitakis and Dionysiou, 2003, 2004a, b).
More specifically, it was reported that peroxymonosulfate can
be activated by transition metals, especially cobalt, or can be
coupled with UV radiation. The resulting radical species were
proven very effective towards degrading organic contami-
nants in water (see reactions 1 and 2 in Table 1).
Here, the efficiency of activated peroxymonosulfate, by
using cobalt as the catalyst or UV radiation as the activator,
was further explored for a specific water treatment applica-
tion, the destruction of chemical and microbial contaminants
in pool water. In particular, ammonium ion, creatinine,
chlorinated creatinine compounds, L-arginine and Escherichia
coli (E. coli) were the targeted contaminants. The results
showed that, among the chemical contaminants tested here,
activated peroxymonosulfate is particularly effective in
degrading organic compounds, such as creatinine, chlori-
Table 1 – Chemical reactions
Reactions k (M�1 s
1 Co2++HSO5�-Co3++SO4
d�+OH�
2 HSO5�+hv-SO4
d�+dOH
3 SO4d�+NH4
+-HSO4�+dNH2+H+ 3� 10
4 SO4d�+Cl�-SO4
2�+Cld 4.7� 1
5 Cld+Cl�-Cl2d� 8� 10
6 Cl2d�+Cl2
d�-Cl2+2Cl� 9� 10
7 Cld+Cld-Cl2 8.8� 1
8 Cl2(aq)+H2O-HOCl+H++Cl�
9 HOCl-�OCl+H+ pKa ¼ 7
10 SO4d�+HCO3
�-SO42�+CO3
d�+H+ 9.1� 1
11 Cld+HCO3�-Cl�+CO3
d�+H+ 2.2� 1
12 HOCl+NH3-NH2Cl+H2O 4.2� 1
13 HOCl+NH2Cl-NHCl2+H2O 3.5� 1
14 HOCl+NHCl2-NCl3+H2O 2.1
15 NH4++O3-no reaction
16 C4H7N3O (creatinine)+O3-products �2
17 C6H14N4O2 (arginine)+O3-products 280
18 Cl2+2e�-2Cl�
19 HClO+H++2e�-Cl�+H2O
20 HSO5�+H++2e�-SO4
2�+H2O
21 HSO5�+Cl�-SO4
2�+HOCl 1.35� 1
22 HSO5�+2Cl�+H+-SO4
2�+Cl2+H2O
23 Rd+Cl2d�-R-Cl+Cl�
24 R-H+HOCl-R-Cl+H2O
25 HOCl+RNH2-RNHCl+H2O
26 NH2Cl+3I�+H2O+H+-Cl�+I3�+NH4OH
27 NHCl2+3I�+H2O+2H+-2Cl�+I3�+NH4OH
28 NCl3+3I�+H2O+3H+-3Cl�+I3�+NH4OH
nated creatinine derivatives and arginine. On the other hand,
ammonium ion was very resistant to sulfate radical oxida-
tion. Instead, it was oxidized by active chlorine species
formed from the reaction of sulfate radicals with chloride
ions present in water. This took place only in de-ionized (DI)
water, however, since the presence of bicarbonate ions in pool
water inhibited all radical mechanisms contributing to
ammonium ion oxidation. The mechanisms of chlorine
reactivation from chloride ions, as well as that of bicarbonate
ion inhibition, are further discussed in this study and
rationalized taking into account reaction rate constants
reported in the literature. Efficacy tests showed that the
Co/Peroxymonosulfate reagent could also be a very effective
sanitizer in pool water, since E. coli colonies were 99.99%
destroyed within 1 h of reaction, using a relatively low
peroxymonosulfate dose (25 ppm as Oxones) and traces of
cobalt (0.1 ppm).
2. Methods and materials
2.1. Chemicals
Ammonium ion was derived from NH4Cl and (NH4)2SO4
(Fisher), Co(II) from CoCl2 � 6H2O (98%, Aldrich), CoSO4 � xH2O
(Aldrich) and Co(NO3)2 � 6H2O (99.3%, Sigma), Cu(II) from
CuSO4 � 5H2O (98+%, Aldrich) and Zn(II) from ZnCl2 (98%,
�1) Eo (V) References
5 Neta et al. (1978)
08 Huie et al. (1991)9 Nagarajan and Fessenden (1985)8 Yu and Barker (2003)
07 Wu et al. (1980)
.5
06 Dogliotti and Hayon (1967)
08 Mertens and von Sonntag (1995)
06 AWWA (1990)
02 AWWA (1990)
AWWA (1990)
Haag and Hoigne (1983)
Haag and Hoigne (1983)
Ignatenko and Cherenkevich (1985)
1.36 CRC, 2003–2004
1.48 CRC, 2003–2004
1.85 O’Hare et al. (1985)
0�3 0.37 Fortnum et al. (1960)
0.49
Harp (2002)
Harp (2002)
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WA T E R R E S E A R C H 4 2 ( 2 0 0 8 ) 2 8 9 9 – 2 9 1 0 2901
Aldrich). Creatinine (C4H7N3O, 98%), L-arginine (C6H14N4O2,
98+%) as well as Oxones (manufactured by DuPont, not 100%
triple salt, 681 g/mole, containing 43% KHSO5) were all
purchased from Aldrich. Stock solutions of all chemicals
were prepared in advance and, prior to an experiment,
specific aliquots were transferred to the reactor vessel to
obtain the concentrations reported in the figures. Pool water
was synthesized by dissolving 8.08 g of CaSO4 � 2H2O (98%,
Sigma-Aldrich) and 3.15 g of NaHCO3 (Fisher) in 21 L of DI
water. The pH was adjusted to the reported value with KHSO4
(Fisher). The resulting total alkalinity, calcium hardness and
pH as well as the methods used for these measurements are
summarized in Table 2.
Commercial bleach (6% as NaClO) was the chlorine source
used. The actual chlorine content was measured with the
DPD Ferrous (DPD–FAS) Titrimetric standard method equal to
5.8% (APHA et al., 1995). Based on this value, appropriate
aliquots were transferred in pool water to obtain the initial
chlorine (Cl2) concentration required in each case.
A solution of stable chlorinated creatinine derivatives,
measured as combined chlorine (CC), was prepared in pool
water by mixing 4 ppm of creatinine with 5 ppm of Cl2. This
led to the formation of stable chlorinated creatinine species at
a concentration of approximately 2.5 ppm as CC.
2.2. Analysis
The concentration of the ammonium ion was monitored
directly using a Dionex DX 500 Ion Chromatography system
with a conductivity detector. An IonPac CS 14 analytical
column was used, coupled with an IonPac CG 14–4 mm guard
column. Methanesulfonic acid (10 mM) was used as the mobile
phase (eluent) and the flow rate was set at 1.0 mL/min.
The suppressor CSRS-I 4-mm was set to operate at 100 mA
and the background conductivity was less than 3mS.
Transformation of creatinine was monitored with an 1100
Agilent HPLC System using a Discovery RP Amide C16 column
(SUPELCO) and a Luna 5 m NH2 100A column (Phenomenex).
The flowrate was set at 0.5 and 1.0 mL/min and the UV
detector at 212 and 200 nm, respectively. The mobile phase in
both cases was 70:30 0.01 N H2SO4:acetonitrile. The concen-
tration of arginine was also monitored with HPLC. The
column used was the Discovery RP Amide C16 (SUPELCO).
The flowrate was set at 0.5 mL/min, the temperature at 40 1C
and the UV detector at 205 nm. The mobile phase in both
cases was 70:30 0.01 N H2SO4:acetonitrile.
Table 2 – Quality of synthetic pool water
Parameter Value Method
Total
alkalinity
85 ppm
CaCO3
Titration with 0.02 N H2SO4 to a pH
end point of 4.6 (Hach methods, 2003:
8221 adapted from standard method
2320B, USEPA accepted; 8203)
Ca
hardness
240 ppm
CaCO3
Taylor total hardness kit K-1503
pH 7.6 pH meter
The concentrations of free chlorine (FC) and CC were
monitored with the DPD–FAS standard method (APHA et al.,
1995). To overcome the interference of peroxymonosulfate
some modifications were incorporated in the analysis and are
reported below:
�
Free chlorine: (i) 5 mL buffer, (ii) 5 mL DPD, (iii) 10 mL 5%EDTA (when peroxymonosulfate was used), (iv) 50–100 mL
sample, (v) titration with FAS (1 mL FAS ¼ 0.1 mg Cl2).
�
Combined chlorine, continuing from FC: (vi) 10 mL 25% KI, (vii)titration again with FAS.
Control experiments monitoring the evolution of FC with
the Co/Peroxymonosulfate reagent were also performed with
the HACH DPD-FEAS modified method (HACH, 2003).
2.3. UV reactor
The rectangular reactor vessel (base: 10 cm�10 cm, height:
25 cm), used here, was made of quartz and was placed on a
magnetic stirrer allowing sufficient and constant mixing of
the solution (total volume of 1 L). A schematic of the reactor is
provided in Balasubramanian et al. (2004). No flow recircula-
tion or external air blowing was used here. Four germicidal
lamps (15 W, Sankyo Denki G15T8), two at each side of the
reactor, were emitting almost monochromatic UV-C radiation
at 253.7 nm. Using potassium ferrioxalate actinometry (Murov
et al., 1993), the photon flux entering the reactor was
measured equal to 8.5�10�6 E/s, corresponding to 4.01 W of
photon flux power at 253.7 nm (1 Einstein at 253.7 nm equals
471,528 J). Total photon energy in Einsteins may then be
calculated for the UV experiments reported here by multi-
plying the reaction time with the photon flux. The lamps were
positioned parallel to the longest dimension of the reactor at
a distance of 6 cm from each side. From a port close to the
bottom of the vessel, a syringe was adjusted and samples
were withdrawn at specific time intervals for 4 h.
2.4. Biocidal tests
E. coli colonies (ATCC 11229), as specified by method 965.13
(AOAC, 1990), were initially grown in 100 mL tryptic soy broth
(TSB) in a shaking incubator at 37 1C for 24 h and then
transferred to tryptic soy agar plates (TSA, 20 mL). The plates
were incubated at 37 1C for 24 h and then stored in the
refrigerator. One day prior to an experiment, colonies from a
plate were transferred to 100 mL of fresh TSB solution. The
inoculated TSB was placed in a shaking incubator at 37 1C for
24 h and from there, after consecutive centrifugations and
suspensions, the E. coli stock solution used for the inoculation
of the test water was derived (Donnermair and Blatchley,
2003; Thompson and Blatchley, 2000).
More specifically, 10 mL of the E. coli/TSB were transferred in
a centrifuge tube and were centrifuged for 15 min at 3300 rpm
(force 1380�G). The supernatant was discarded, the pellet
was re-suspended in 10 mL of phosphate buffer dilution water
and centrifuged again for 15 min. The suspension/centrifuga-
tion procedure was repeated twice more to separate E. coli
from the culture medium. The final pellet was suspended in
ARTICLE IN PRESS
nium
ion 1.0
WAT E R R E S E A R C H 4 2 ( 2 0 0 8 ) 2 8 9 9 – 2 9 1 02902
10 mL phosphate buffer dilution water (APHA et al., 1995) and
this served as the stock solution for each experiment. The E. coli
stock solution was measured to contain initially 109–1010
cfu/mL. The procedure from inoculating the broth to the
preparation of the stock E. coli solution was performed daily.
From the E. coli stock solution 0.5 mL was transferred in pool
water. The final volume of the pool water after the addition of
the E. coli and the reagents was 500 mL. After this dilution,
E. coli was initially present at 106–107 cfu/mL in the test water.
After the addition of cobalt followed by that of peroxymono-
sulfate and the initiation of the reaction, 1 mL of sample was
withdrawn at 2, 5, 10, 30 and 60 min. The samples were again
diluted and quenched with excess sodium thiosulfate (Joret
et al., 1997). Several consecutive dilutions were then per-
formed to bracket the optimum E. coli concentration for
colony enumeration.
The membrane filtration technique was selected for
the analysis (APHA et al., 1995; HACH, 2003). Using a
vacuum pump, a sample was filtered through a squared
47-mm-membrane filter. The filter was then placed in a Petri
dish on top of an absorbent pad that was soaked in
m-ColiBlue24 broth (enrichment medium, HACH). The dish
was placed upside down in an incubator for 24 h at 35 1C. After
that, the E. coli colonies were colored blue and were readily
visible on the filter. As mentioned, several consecutive
sample dilutions were performed in order to obtain 20–80
coliform-forming units per membrane filter.
Time (min)0 30 60 90 120 150 180 210 240
Nor
mal
ized
con
cent
ratio
n of
am
mo
0.0
0.2
0.4
0.6
0.8NH4Cl; CoCl2; NaHCO3(NH4)2SO4; CoSO4NH4Cl; CoCl2; NaHCO3; CaSO4.2H2O (Pool)(NH4)2SO4; CoSO4; NaClNH4Cl; CoCl2
Fig. 1 – Effect of water characteristics (Cl�, NaHCO3; CaSO4) on
the transformation of 5ppm (0.2772mM) NH4+ with the
Co/Peroxymonosulfate reagent in DI water. Conditions:
[Co(II)] ¼ 10ppm (0.1697mM); [peroxymonosulfate] ¼
0.5874mM or 200ppm as Oxones, [NaHCO3] ¼ 1.787mM,
3. Results and discussion
3.1. Treatment of the ammonium ion
First, the control of peroxymonosulfate alone (no catalyst or
UV), at 200 ppm as Oxones, either in DI or in DI/NaHCO3 did
not induce any significant transformation of the ammonium
ion within 4 h of reaction time, as shown in Table 3. When
CoCl2 � 6H2O at 0.1 ppm-Co(II) was used for the catalytic
activation of 50 and 200 ppm of Oxones, approximately 18%
and 25% of the ammonium ion was transformed within 4 h of
treatment, respectively. The 200 ppm Oxones dose led to
slightly higher transformation as expected, but both percent
transformation values were close, although the difference in
the Oxones dose employed was significant. This indicates
that the catalyst might limit the process. Ammonium ion
Table 3 – Treatment of 5 ppm of ammonium ion (0.2772 mM) freagent
CoCl2 in ppm of Co(mM)
Peroxymonosulfate in ppmas Oxones
Oxones imM
– 200 0.2937
– 200 0.2937
0.1 (0.0017) 50 0.0734
0.1 (0.0017) 100 0.1468
0.1 (0.0017) 200 0.2937
Results reported after 4 h of reaction.
transformation was also tested in DI water buffered with
bicarbonate ions at the same concentration (109 ppm, no
adjustment was made for hardness) found in the synthesized
pool water used here. Table 3 shows that the presence of
bicarbonate ions inhibited the transformation of ammonium
ion and bicarbonate ions appear to demonstrate a quenching
effect in the process, since the transformation of ammonium
ion was only 7% under such conditions. This was even below
the value obtained using a lower peroxymonosulfate dose
(50 ppm as Oxones) in just DI water.
The quenching effect of bicarbonate ions at 109 ppm was
confirmed in Fig. 1 (see full symbols), since even at higher
concentrations of Co(II) (10 ppm or 0.1697 mM from CoCl2),
the ammonium ion transformation was again minimal in
DI/NaHCO3, but significant in DI water (70% in 30 min). When
the ammonium ion was treated in pool water (109 ppm
bicarbonate ions and 96.6 ppm Ca2+ from CaSO4 � 2H2O) the
quenching effect of bicarbonate ions was slightly suppressed
and the transformation of ammonium ion was greater (15%)
than in the case of DI/NaHCO3 with no hardness adjustment
(7%). However, the efficiency achieved in just DI water was
still far greater than that in both former cases.
rom NH4Cl in DI water with the Co/Peroxymonosulfate
n Peroxymonosulfatein mM
HCO3� in ppm(mM)
% NH4+
transformed
0.5874 – 1
0.5874 109 (1.787) 3
0.1468 – 18
0.2937 109 (1.787) 7
0.5874 – 25
[CaSO4 .2H2O] ¼ 2.410mM.
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Time (min)0 30 60 90 120 150 180 210 240 270 300
Nor
mal
ized
con
cent
ratio
nof
am
mon
ium
ion
0.0
0.2
0.4
0.6
0.8
1.0
Co(II) 0.1 ppmCo(II) 1 ppmCo(II) 10 ppm
Fig. 2 – Effect of cobalt concentration on the transformation
of 5 ppm (0.2772 mM) NH4+ (from NH4Cl) with the
CoCl2/Peroxymonosulfate reagent in DI water. Conditions:
[Peroxymonosulfate] ¼ 0.5874 mM or 200 ppm as Oxones.
WA T E R R E S E A R C H 4 2 ( 2 0 0 8 ) 2 8 9 9 – 2 9 1 0 2903
Varying the ammonium and cobalt salts as the sources of
ammonium and cobalt ions led to the conclusion that
presence/absence of chloride ions in DI water is critical for
the oxidation process. In particular the systems (i) CoSO4/
(NH4)2SO4; (ii) CoCl2/NH4Cl and (iii) CoSO4/(NH4)2SO4/NaCl
were tested in combination with 200 ppm Oxones in DI water.
These correspond to (i) chloride ion free solution; (ii) 21.9 ppm
(0.6177 mM) chloride ion coming from the cobalt and ammo-
nium salts; (iii) 21.9 ppm (0.6177 mM) chloride ion coming
from sodium chloride, respectively. It was found that only
when chloride ions are present in DI water, regardless
whether they are released from CoCl2/NH4Cl or NaCl, the
degradation of the ammonium ion is significant. This
suggests that sulfate radicals failed to oxidize ammonium
ions directly, according to reaction 3 (Table 1). Instead, sulfate
radicals oxidize chloride ions to chlorine radicals (reaction 4,
Table 1), which either directly react with ammonium ions or
most probably recombine forming free available chlorine
(aqueous chlorine, hypochlorous acid and hypochlorite,
reactions 5–9, Table 1). Hypochlorous acid, in particular, is
then involved in ammonium ion oxidation in DI water since
the pH drops from 6.4 to 2.9 following addition of peroxy-
monosulfate.
The role of bicarbonate ions was still the critical parameter
here, since, in buffered water, either pool or DI water, and
despite the presence of chloride ions, the transformation of
ammonium ion was very limited. Judging from the concen-
tration of the species present: HCO3� 1.787 mM (109 ppm), Cl�
0.6177 mM (21.9 ppm) and NH4+ 0.2772 mM (5 ppm) as well as
their reaction rates with sulfate radicals (reactions 10, 4 and 3,
Table 1), it is evident that sulfate radicals react preferentially
with bicarbonate ions, then with chloride ions and lastly with
ammonium ions. Although the highest reaction rate constant
is reported with chloride ions, the higher concentration of
bicarbonate ions, as well as the very high rate of reaction of
the chlorine atom radical with bicarbonate ions (reaction 11,
Table 1), make the chloride ion the most probable sink of the
radicals formed in the process.
Fig. 2 shows the effect of Co concentration on the efficiency
of the Co/Peroxymonosulfate reagent for the treatment of
ammonium ion in DI water. It can be seen that as the Co
concentration increases, the ammonium ion oxidation be-
comes faster. The use of 1 ppm (0.0170 mM) of Co leads to the
same transformation efficiency of ammonium ion as in the
case of using 10 ppm (0.1697 mM). With the latter conditions,
this was achieved in 30 min whereas when 1 ppm (0.0170 mM)
of Co was used, the required reaction time was 5 h. It was
reported earlier that free available chlorine oxidizes the
ammonium ion, but still the generation of FC is controlled
by the generation of sulfate radicals and this is dependent on
the concentration of the catalyst as shown in Fig. 2. At the last
point of the 10-ppm line, ammonium and nitrate ions were
measured equal to 1.58 ppm (0.0876 mM) and 0.47 ppm
(0.076 mM), respectively. No nitrite was detected. Although
no free or CC titration data are reported here for the
ammonium ion tests, it is believed that the oxidation of
ammonium ion by the Co/Peroxymonosulfate system in the
presence of chloride ions and in DI water leads primarily to
the formation of the typical inorganic chloramine species
shown in reactions 12–14 (Table 1).
3.2. Treatment of creatinine
Co/Peroxymonosulfate was also tested against creatinine
(2 ppm or 0.1428 mM as nitrogen), but the results were
different than those with the ammonium ion, as shown in
Fig. 3. Partial inhibition of creatinine destruction due to the
presence of bicarbonate ions was also detected, but the
scavenging effect of bicarbonate ions was less pronounced,
since, as discussed in Section 3.3, creatinine appears to be
more amenable to oxidation than the ammonium ion
(reaction rate constants have not been reported in the
literature). Using 10 ppm (0.1697 mM) of Co from CoCl2 and
200 ppm of Oxones, creatinine was completely oxidized in DI
water while 75% of creatinine was transformed in pool water.
It was also found that sulfate radicals, and not chlorine
species, are responsible for the transformation of creatinine,
since similar results were obtained both in the presence and
absence of chloride ions in solution, or else by using either
CoCl2 or CoSO4 (1 ppm or 0.017 mM of Co) as the source of the
peroxymonosulfate catalyst. Fig. 3 also shows that as the
catalyst concentration increases, the creatinine transforma-
tion becomes faster.
The use of UV radiation as a means of activating perox-
ymonosulfate was also tested against creatinine. Fig. 4
summarizes the comparative experiments from the treat-
ment of creatinine (2 ppm or 0.1428 mM as nitrogen) with
the use of peroxymonosulfate, Co/Peroxymonosulfate, UV
alone, UV/Peroxymonosulfate and UV/Co/Peroxymonosul-
fate. UV/Peroxymonosulfate and UV/Co/Peroxymonosulfate
demonstrated almost identical efficiencies in degrading
creatinine and were the most efficient techniques from those
tested here, achieving greater than 95% conversion of
creatinine in 3 h of treatment time. The use of UV alone
(direct photolysis) led to 65% destruction of creatinine in 4 h
and the ‘‘dark’’ Co/Peroxymonosulfate reagent to 30% within
the same reaction time. Finally, the use of peroxymonosulfate
alone led to 9% destruction of creatinine for an extended
reaction time of 24 h (note the break in the x-axis of Fig. 4). It
ARTICLE IN PRESS
Time (min)0 15 30 45 60
Nor
mal
ized
Con
cent
ratio
nof
Cre
atin
ine
as N
0.0
0.2
0.4
0.6
0.8
1.0 0.1 ppm-Co; CoCl2; Pool1 ppm-Co; CoCl2; Pool1 ppm-Co; CoSO4; Pool10 ppm-Co; CoCl2; Pool10 ppm-Co; CoCl2; DI
Fig. 3 – Treatment of creatinine (2 ppm or 0.1428 mM as
nitrogen) with the Co/Peroxymonosulfate reagent. Effect of
water quality and cobalt concentration. Conditions:
[Peroxymonosulfate] ¼ 0.5874 mM or 200 ppm as Oxones.
Time (min)0 30 60 90 120 150 180 210 240 270 1440
Nor
mal
ized
con
cent
ratio
nof
cre
atin
ine
as N
0.0
0.2
0.4
0.6
0.8
1.0
PeroxymonosulfateCo/PeroxymonosulfateUV aloneUV/PeroxymonosulfateUV/Co/Peroxymonosulfate
Fig. 4 – Treatment of creatinine (2 ppm or 0.1428 mM as
nitrogen) in pool water with activated peroxymonosulfate.
Conditions: [Peroxymonosulfate] ¼ 0.1468 mM or 50 ppm as
Oxones; when used, [Co2+] ¼ 0.1 ppm or 0.0017 mM from
CoCl2.
Time (min)0 30 60 90 120
Nor
mal
ized
con
cent
ratio
nof
arg
inin
e as
N
0.0
0.2
0.4
0.6
0.8
1.00.1 ppm-Co; CoCl21 ppm-Co; CoSO4
10 ppm-Co; CoCl2
Fig. 5 – Treatment of arginine (2 ppm or 0.1428 mM as
nitrogen) in pool water with the Co/Peroxymonosulfate
reagent. Conditions: [Peroxymonosulfate] ¼ 0.5874 mM or
200 ppm Oxones.
WAT E R R E S E A R C H 4 2 ( 2 0 0 8 ) 2 8 9 9 – 2 9 1 02904
must be noted here that the concentration of cobalt was only
100 ppb (mg/L, 0.0017 mM), which corresponds to a 1:86 molar
ratio versus peroxymonosulfate (KHSO5), the active ingredi-
ent of Oxones, when the Oxones dose was 50 ppm
(0.1468 mM as peroxymonosulfate). With higher cobalt con-
centrations, higher degradation rates are expected.
In our previous studies, several other transition metals such
as Ag(I), Ce(III), Fe(II), Fe(III), Mn(II), Ni(II), Ru(III), V(III) were
also tested for peroxymonosulfate activation and the oxida-
tion of another target contaminant, 2,4-dichlorophenol
(Anipsitakis and Dionysiou, 2004a, b). Co(II) and Ru(III) were
proven the most effective. In this study, Zn(II) and Cu(II) at
1 ppm were also tested as potential catalysts/activators of
peroxymonosulfate (200 ppm as Oxones) with creatinine
(2 ppm as N) being the targeted compound in pool water. It
must be noted here that the metals were added last in
solution (after creatinine and peroxymonosulfate) to mini-
mize initial metal complexation that might reduce potential
catalytic activity. At the pool water pH (7.6), copper and zinc
are expected to form hydroxo and oxyhydroxo complexes,
which will minimize their activity. Under these conditions,
both Zn(II)/Peroxymonosulfate and Cu(II)/Peroxymonosulfate
couples induced minimal degradation of creatinine (data not
shown).
3.3. Treatment of arginine
The same set of experiments with the Co/Peroxymonosulfate
reagent was also performed against L-arginine in pool water.
Fig. 5 shows the degradation of arginine in pool water using
different cobalt sources at different concentrations. It is
shown that sulfate radicals, not chlorine species, are the
species responsible for the transformation of the contami-
nant since the use of CoSO4 in a chlorine free solution led to
the same transformation (490%) of arginine as in the case of
using CoCl2. Fig. 5 also shows that as the initial cobalt
concentration increases, the rate of arginine oxidation also
increases.
Among the three contaminants tested so far it seems that
arginine is more amenable to oxidation by the Co/Peroxy-
monosulfate reagent than creatinine, whereas the ammonium
ion is oxidized only by chlorine species, not by sulfate
radicals, and only in DI water. Ozone is the only oxidizing
reagent for which reaction rates have been reported in
the literature with all three contaminants tested here. The
reaction rate constants involving ozone and reported in the
literature follow the same order proposed in this study (see
reactions 15–17 in Table 1). Although ozonation is not
completely relevant to the Co/Peroxymonosulfate reagent,
since it does not exclusively proceed through radical species,
nor the same radicals are formed, one can have an indication
of the relative order in terms of the oxidation rate for these
compounds.
ARTICLE IN PRESS
WA T E R R E S E A R C H 4 2 ( 2 0 0 8 ) 2 8 9 9 – 2 9 1 0 2905
3.4. Treatment of chlorinated creatinine derivatives
Chlorine addition to a creatinine solution leads to the
formation of chlorinated creatinine species, several of which
register as CC in the DPD–FAS method. Using a specific mass
ratio of creatinine:chlorine equal to 4:5 or a molar ratio equal
to 1:2 in pool water, approximately 2.0–2.5 ppm of organic and
inorganic chloramines as CC are formed. At that particular
ratio of reactants and a pH between 7.0 and 9.5, Alouini and
Seux (1988) have reported the formation of dichloramine,
trichloramine, chloride, carbon dioxide, creatine, chlorocrea-
tinines (including creatinine chloramine), chlorocreatine and
1-methylhydantoin. Tachikawa et al. (2005) using EI-MS and
NMR verified the formation of creatinine chloramine in
addition to detecting hydroxyl-creatinine chloramine, methyl-
amine and urea as stable products of the chlorination of
creatinine. More recently, Li and Blatchley (2007) reported the
formation of trichloramine and dichloromethylamine follow-
ing chlorination of creatinine. All these derivatives are fairly
stable since they were detected more than 24 h post-
chlorination. From these, the ones that contain chloride and
nitrogen in their molecule most probably register as CC in the
DPD–FAS method (Fig. 6).
CC, or the stable product of the chlorination of creatinine,
was tested against several peroxymonosulfate-containing
reagents. Potassium peroxymonosulfate is expected to inter-
fere in the DPD–FAS method and for this several control
experiments were performed to identify the conditions that
N
NO
2-chloroamino-1-methylimi(creatinine chloramine, Tac
2005, Alouini and Seu
NNH
NO
ClChlorocreatinine (Alouini and Seux, 1988)
NHN
NH
ClN-chlorocreatine (Alouini an
NCl
Trichloramine (Alouini andLi and Blatchley III,
HN
ClClDichloramine (Alouini and Seux, 1988)
NN
NO
Cl
Cl
Dichlorocreatinine (Alouini and Seux, 1988)
Fig. 6 – Stable compounds possibly formed from the chlorina
expected to register as combined chlorine in the DPD–FAS meth
minimize such interference of peroxymonosulfate. In parti-
cular, excess EDTA (see Materials and methods) was used in
all the cases that potassium peroxymonosulfate was present
in solution to suppress its interference in the chlorine
measurements.
3.4.1. Co/Peroxymonosulfate against chlorinated creatininederivativesPeroxymonosulfate at a 12 ppm dose as Oxones (with the
EDTA modification) does not interfere with FC in DI water, but
it reads as 0.15 ppm of CC. Also, 50 ppm of Oxones in pool
water read as 2.13 ppm of CC (Table 4). This suggests that the
presence of EDTA inhibits peroxymonosulfate from interfer-
ing with FC measurements, but not with those of CC. When
cobalt and/or UV are used, peroxymonosulfate is consumed
fairly rapidly and the above CC values are expected to be
much lower.
To check whether peroxymonosulfate, after being activated
by Co, would still interfere with the CC measurements, FC and
CC measurements of a mixture of 0.1 ppm-Co from CoSO4 and
50 ppm of Oxones in MilliQ water were taken. The measure-
ments, shown in Fig. 7, did not register any FC whereas CC
was always below 0.16 ppm (Table 4). The same was
performed in pool water, free of chloride, with or without
creatinine and the CC readings in both cases were very
similar, giving approximately 1 ppm of CC as Cl2 (Table 4).
The difference between the two waters tested is the
presence of sodium bicarbonate and calcium sulfate that
NH
Cl
dazolin-4-onehikawa et al.,x, 1988)
N
NO
HO
NH
Cl2-chloroamino-5-hydroxy-1-methylimidazolin-4-one
(hydroxycreatinine chloramine,Tachikawa et al., 2005)
OH
Od Seux, 1988)
Cl
Cl Seux, 1988;2007)
N
Cl
Cl
Dichloromethylamine (Li and Blatchley III, 2007)
tion of creatinine under the conditions of this study and
od.
ARTICLE IN PRESS
Table 4 – Free and combined chlorine measurements under different peroxymonosulfate dosages and experimentalconditions
Water ppm
Oxones
CoSO4
in ppm
as Co
ppm
of Cl�FC in
mg/L in
1 h of
reaction
FCmax in
mg/L
(min)
CC in
mg/L in
1 h of
reaction
CCmax in
mg/L
(min)
Notes
De-ionized 12 0 0 0 – – 0.15 (n/a) Std. methods
Pool 50 0 0 0 – – 2.13 (n/a) Std. methods
MilliQ 50 0.1 0 0 – 0.00 0.16 (15) Std. methods, Fig. 7
Pool 50 0.1 0 0 – 1.82 2.93 (20) Std. methods, Fig. 7
Pool+creatinine 50 0.1 0 0 – 1.44 1.44 (60) Std. methods, Fig. 7
MilliQ+UV 50 0 0 0 – – 0.30 (2) Std. methods
De-ionized 12 0.1 50 1.91 1.91 (60) – – Std. methods
De-ionized 12 0.1 100 2.00 2.51 (240) – – Std. methods
De-ionized 12 0.1 200 2.38 2.38 (60) – – Std. methods
Pool 50 0.1 200 0.18 0.30 (15) – – Std. methods
De-ionized 12 1.0 100 2.21 2.21 (60) – – HACH
Tapa 12 1.0 100 1.01 1.75 (3) – – HACH
Pool 12 1.0 100 0.56 1.11 (3) – – HACH
n/a: not applicable, time was not monitored as there is no redox reaction occurring.a Background free chlorine in tap water ¼ 0.76 mg/L.
Time (min)0 30 60 90 120 150 180 210 240
Com
bine
d C
hlor
ine
(mg/
L C
l 2)
0
2
4
6
8
10 Pool; Cl2 + CreatinineControl-3: PoolControl-2: Pool + CreatinineControl-1: MilliQ
Fig. 7 – Combined chlorine (CC) evolution with the
Co/Peroxymonosulfate reagent. Conditions: [Co2+] ¼ 0.1 ppm
or 0.0017 mM (CoSO4 was used in the three controls, CoCl2was used in the other case), [Peroxymonosulfate]
¼ 0.1468 mM or 50 ppm as Oxones.
WAT E R R E S E A R C H 4 2 ( 2 0 0 8 ) 2 8 9 9 – 2 9 1 02906
make up the alkalinity and hardness of the pool water. EDTA
is added during chlorine analysis to inhibit the oxidizing
action of peroxymonosulfate and any other resulting oxidiz-
ing species or radicals that may register as free or CC. Such
inhibition, however, seems not to be working completely as
expected due to the presence of the additional species in pool
water. It seems that a portion of oxidizing species, such as
peroxymonosulfate, sulfate radicals or even carbonate radi-
cals (reaction 10, Table 1) may react with the excess iodide
added in the CC analysis to give iodine.
Fig. 7 shows the evolution of CC, when chlorinated pool
water (5 ppm of Cl2) with creatinine (4 ppm as free base) was
treated with the use of 0.1 ppm of Co from CoCl2 and 50 ppm
of Oxones. It is shown that for up to 30 min of reaction, CC
increases to concentrations far greater than the initial
concentration. These concentrations are also greater than
the control tests reported previously and are attributed to the
formation of additional species that react with iodide in the
DPD–FAS method. CC then gradually decreases to values
below 2 ppm after 4 h of reaction time. Fig. 7 shows, in
essence, a breakpoint chlorination curve. Chlorine (hypo-
chlorous acid and hypochlorite ion) is generated by the
reaction of sulfate radicals with chloride ions. It then further
reacts with compounds, such as the remaining creatinine,
creatine, 1-methylhydantoin (Alouini and Seux, 1988), urea
and methylamine (Tachikawa et al., 2005) to give rise to other
compounds of the chloramine type that register as CC in the
DPD–FAS test. After all, more than half (0.9 ppm) of the
organic nitrogen that had been available within the creatinine
molecule (4 ppm as free base or 1.5 ppm as nitrogen initially)
was still not reacted as discussed further below (Fig. 9).
Possible mechanisms of the reaction of creatinine with
chlorine have been reported in the literature by several
researchers (Alouini and Seux, 1988; Tachikawa et al., 2005;
Li and Blatchley, 2007). The general mechanism involves
electrophilic substitution and hydrolysis (Alouini and Seux,
1988; Tachikawa et al., 2005; Anipsitakis et al., 2006; Fiss et al.,
2007; Li and Blatchley, 2007). The typical breakpoint chlorina-
tion curves reported in the literature often do not capture the
very early stages (first few minutes) of the chlorination
process. In this work, it is shown that the CC concentration
increases dramatically beyond its original value, once the
sulfate radicals attack the chloride ions and once these
further react with the remaining organic material in solution.
Under such conditions, the chlorine-to-organic material
ratio increases significantly. That ratio then pushes the
reaction equilibrium previously attained towards the forma-
tion of more chlorinated organic amines. The bell-shaped
curve, shown in Fig. 7, is typical of a by-product (possibly
highly chlorinated) as it is being formed and decayed (Rule
ARTICLE IN PRESS
Time (min)0 15 30 45 60 120
Com
bine
d C
hlor
ine
(mg/
L C
l 2)
0
2
4
6
8
10
12 UV/PeroxymonosulfateUV/Co/PeroxymonosulfateUV alone
Fig. 8 – Evolution of combined chlorine with the UV-utilizing
technologies in pool water containing chlorinated creatinine
derivatives. Conditions: [Co2+] ¼ 0.1 ppm or 0.0017 mM (from
CoCl2), [peroxymonosulfate] ¼ 0.1468 mM or 50 ppm as
Oxones.
Time (min)0 15 30 45 60
Cre
atin
ine
in m
g/L
as N
0.0
0.2
0.4
0.6
0.8
1.0
Co/PeroxymonosulfateUV aloneUV/PeroxymonosulfateUV/Co/Peroxymonosulfate
Fig. 9 – Evolution of creatinine with the peroxymonosulfate-
utilizing technologies in pool water also containing
chlorinated creatinine derivatives (combined chlorine).
Fig. 9 complements Figs. 7 and 8. Conditions: Initial
[Co2+] ¼ 0.1 ppm or 0.0017 mM (from CoCl2),
[peroxymonosulfate] ¼ 0.1468 mM or 50 ppm as Oxones.
WA T E R R E S E A R C H 4 2 ( 2 0 0 8 ) 2 8 9 9 – 2 9 1 0 2907
et al., 2005; Anipsitakis et al., 2006; Li and Blatchley,
2007). Unstable, short-lived, or volatile compounds of
the chloramine type are formed within the early stages
and, as the oxidation proceeds, they are stripped out of
solution or converted to other products some of which do not
contribute anymore to CC readings. Li and Blatchley (2007), in
their work, specifically underlined the formation of volatile
by-products that are not limited to inorganic chloramines and
haloforms.
3.4.2. UV/Peroxymonosulfate and UV/Co/Peroxymonosulfateagainst chlorinated creatinine derivativesControl CC measurements of UV irradiated MilliQ water
containing peroxymonosulfate at 50 ppm as Oxones, but free
of chloride and any target molecules were also performed.
The maximum CC obtained was 0.3 ppm at the first sample
(2 min), indicating that peroxymonosulfate interference is
minimal under UV activation (Table 4). Fig. 8 shows the
evolution of CC when chlorinated pool water containing
creatinine was treated with: (i) UV radiation, (ii) UV/Peroxy-
monosulfate and (iii) UV/Co/Peroxymonosulfate. At the very
early stages of the UV/Peroxymonosulfate and UV/Co/Peroxy-
monosulfate systems, a spike in the concentration of CC was
detected. After further treatment and more specifically within
60 min with UV/Co/Peroxymonosulfate and 120 min with
UV/Peroxymonosulfate, CC was eliminated. With the UV/Co/
Peroxymonosulfate the spike in CC concentration appeared
earlier than the case of UV/Peroxymonosulfate, due to the
synergistic effect of UV and Co. Fig. 8 also shows that with just
UV and no peroxymonosulfate, thus no sulfate radicals
present, no chloramines-type species are formed and the
amount initially present as CC is destroyed very fast. This also
supports our hypothesis of the reactivation of chlorine and
the subsequent formation of species that register as CC from
the reaction of chlorine with the remaining creatinine or
other organic matter.
3.4.3. Simultaneous evolution of creatinine and free chlorinein pool water containing chlorinated creatinine derivativestreated with peroxymonosulfate reagentsFig. 9 shows the evolution of the remaining creatinine
(1.5 ppm as N or 4 ppm as free base were originally present)
in pool water, after the chlorination of creatinine has
occurred (the stable chlorinated species are already formed)
and the system is treated with cobalt, UV and/or peroxy-
monosulfate reagents.
Fig. 10 shows the evolution of FC during the experiments
shown in Figs. 7–9. Fig. 10 confirms that what is depicted in
Figs. 7 and 8 is a breakpoint chlorination experiment. Very
high concentrations of FC are formed initially following the
generation of the sulfate radicals. That FC further reacts with
the remaining creatinine and the other organic compounds
present in water to form more chlorine-nitrogen containing
compounds that register as CC along with the initial, stable
chlorinated creatinine derivatives present. A maximum CC
concentration is attained in all cases, which then gradually
disappears as the oxidation proceeds. In this case, FC does
not build up as in a typical breakpoint chlorination of an
amine. Instead, FC is consumed by the sulfate radicals
formed.
3.5. Free chlorine formation with theCo/Peroxymonosulfate reagent
So far there has been strong evidence of the formation of FC
from the reaction of chloride ions with sulfate radicals. To
validate this, control experiments in different waters were
performed by using NaCl as the source of the chloride ion and
peroxymonosulfate at 12 ppm as Oxones (a typical dose in
pool water) activated by Co from CoSO4.
First, the evolution of FC was monitored in DI and pool
water at three chloride ion concentrations (50, 100 and
200 ppm), using 0.1 ppm-Co. FC was monitored with the
DPD–FAS standard method. The values of FC obtained were
between 1.5 and 2.5 ppm in DI water, with the FC slightly
ARTICLE IN PRESS
Time (min)0 30 60 90 120 150 180 210 240
Free
Chl
orin
e in
mg/
L as
Cl 2
0.0
2.5
5.0
7.5
10.0Co/PeroxymonosulfateUV/PeroxymonosulfateUV/Co/PeroxymonosulfateUV alone
Fig. 10 – Evolution of free chlorine with the
peroxymonosulfate-utilizing technologies in pool water
also containing creatinine and chlorinated creatinine
derivatives (combined chlorine). Fig. 10 complements
Figs. 7–9. Conditions: Initial [Co2+] ¼ 0.1 ppm or 0.0017 mM
(from CoCl2), [peroxymonosulfate] ¼ 0.1468 mM or 50 ppm
as Oxones.
Time (min)0 10 20 30 40 50 60
E.coli c
once
ntra
tion
as lo
g of
cfu
/ml
1
2
3
4
5
6
7
CoPeroxymonosulfateCo/PeroxymonosulfateCl2
Fig. 11 – E. coli disinfection. Conditions: [Co2+] ¼ 0.1 ppm or
0.0017 mM from Co(NO3)2, [peroxymonosulfate] ¼
0.0734 mM or 25 ppm as Oxones, [Cl2] ¼ 1 ppm or
0.0141 mM from commercial bleach.
WAT E R R E S E A R C H 4 2 ( 2 0 0 8 ) 2 8 9 9 – 2 9 1 02908
increasing following the increase in chloride ion concentra-
tion (Table 4). The same was performed in pool water, but the
FC formed was below 0.2 ppm when peroxymonosulfate was
used at 12 and 24 ppm as Oxones. At a peroxymonosulfate
concentration of 50 ppm as Oxones the maximum FC
attained was 0.3 mg/L (Table 4). It is suggested again that
other species such as bicarbonate ions compete with chloride
ions in their reactions with sulfate radicals and to this is
attributed the very limited generation of FC in pool water.
Second, the evolution of FC in DI, tap and pool water was
monitored at a chloride ion concentration of 100 ppm using
1 ppm-Co (0.017) mM. In that case, FC was monitored with the
HACH DPD-FEAS modified method. Using this higher cobalt
dose it appears that more FC is formed in pool water than in
the previous case. It is also noted that, in DI water, the results
obtained in both cases were similar, with FC values in the
area of 2.0 ppm. In tap water, 0.76 ppm of FC were initially
present, but some additional FC was also formed from the
reaction of sulfate radicals with chloride ions. It must be
mentioned here that, in both cases, control experiments,
without cobalt present, were initially performed. These
experiments did not demonstrate any interference of peroxy-
monosulfate in the FC measurements. To further validate our
findings and taking into account the redox equivalence of
chlorine with peroxymonosulfate (1 ppm Cl2 ¼ 4.8 ppm Ox-
ones, calculated by equivalent weights of redox reactions),
one can see that 2.51 ppm of Cl2, which was the maximum FC
recorded in DI water (Table 4), are equal to 12.0 ppm of
Oxones, the typical dosage of Oxones used in pool water.
This means that, in DI water and having excess chloride ions,
almost all peroxymonosulfate, via the radical mechanism
previously discussed, reacts to give free available chlorine.
Taking into account the redox potential of peroxymonosul-
fate and chlorine species and as shown in reactions 18–22
(Table 1), it is thermodynamically feasible for peroxymono-
sulfate to oxidize chloride ions into free available chlorine
species.
In fact, several previous studies have showed that the
mechanism of choice to generate chlorine radicals is via the
reaction of sulfate radicals with chloride ions (Alegre et al.,
2000; Beitz et al., 1998; Huie et al., 1991; McElroy, 1990;
Nagarajan and Fessenden, 1985) and the potential of generat-
ing active chlorine species from monosubstituted peroxides
such as peroxymonosulfate is known for quite some time
(reaction 21, Table 1) (Fortnum et al., 1960; Francis et al., 1994).
When peroxymonosulfate is used without activation, no
radical mechanism is taking place and the rates of active
chlorine formation are extremely low (Fortnum et al., 1960;
Narender et al., 2002) compared to the rates observed via
radical processes. For reaction 21 (Table 1), for instance, the
rate has been reported equal to 1.35�10�3 M�1 s�1 (25 1C and
ionic strength m ¼ 0.2, Fortnum et al., 1960).
3.6. Disinfection: Co/Peroxymonosulfate against E. coli
In recreational waters, effective disinfection is perhaps more
important than chemical decontamination. To this, viability
of E. coli colonies after treatment with peroxymonosulfate
and Co/Peroxymonosulfate was tested in pool water and is
shown in Fig. 11. Control experiments with the use of cobalt
nitrate (0.1 ppm as Co) only, as well as 1 ppm of FC from
commercial bleach are also depicted. Fig. 11 shows that
peroxymonosulfate alone, at a dose of 25 ppm as Oxones,
induced a 2-log destruction of E. coli within 60 min of
treatment time whereas peroxymonosulfate activated by
traces of Co led to a 4-log kill of E. coli within the same
treatment time. In the latter case, no chloride ion was present
in solution to eliminate the potential formation of chlorine
from the interaction of chloride ions with sulfate radicals.
Compared to chlorine, Co/Peroxymonosulfate was proven
slower and less efficient sanitizer. It is believed though that it
is much faster than TiO2-photocatalysis, another advanced
ARTICLE IN PRESS
WA T E R R E S E A R C H 4 2 ( 2 0 0 8 ) 2 8 9 9 – 2 9 1 0 2909
oxidation technology previously tested against E. coli (Cho
et al., 2004). In addition, when chloride ions are present,
the coupling of Co with peroxymonosulfate and the reaction
of sulfate radicals with chloride ions lead to the generation
of FC, hence indirectly and even at these doses the
Co/Peroxymonosulfate system can be a much more effective
disinfection alternative. Also, at higher peroxymonosulfate
doses the disinfection efficacy increases. In another study,
when Oxones was used at a concentration 4000 times greater
than the one reported here, an 8-log kill of E. coli was achieved
(Delcomyn et al., 2006). Co/Peroxymonosulfate can be a viable
stand-alone disinfection system and the presence of cobalt as
an activator certainly helps decreasing the peroxymonosul-
fate demand. Another alternative sanitizer with tremendous
potential would be the coupling of UV radiation with
peroxymonosulfate (UV/Peroxymonosulfate, Anipsitakis
and Dionysiou, 2004a, b; Wang and Hong, 1999). After all,
UV/oxidant technologies have demonstrated exceptional
efficiencies in chemical decontamination and UV alone is a
very powerful physical disinfectant.
4. Conclusions
The coupling of cobalt with peroxymonosulfate in water leads
to the generation of the highly reactive sulfate radicals, which
readily attack and degrade organic contaminants in water.
Sulfate radicals participate in several propagation reactions and
it was shown that they react with chloride ions present in water
to generate chlorine radicals and consequently free available
chlorine species. Chlorine radicals or free available chlorine
species may then react with other species present in solution to
give rise to chlorinated compounds as shown in reactions 23–25
(Table 1). In fact, in control experiments, chlorine was generated
in almost thermodynamically equivalent amounts to the
peroxymonosulfate dose used. Chlorine speciation depends
upon the pH. In pool water where the pH is almost equal to the
pKa value of hypochlorous acid, active chlorine species include
hypochlorous acid and hypochlorite ion.
Ammonium ion was proven highly resistant to oxidation by
the sulfate radicals generated by the Co/Peroxymonosulfate
reagent. Only chlorine species generated by propagation
reactions of sulfate radicals with chloride ions were capable
of oxidizing ammonium ions in DI water. In pool water, the
presence of bicarbonate buffering species inhibited the
ammonium ion oxidation. Sulfate radicals reacted preferen-
tially with bicarbonate ions rather than chloride ions. The
carbonate radicals formed are far less reactive compared to
sulfate radicals and failed to induce any ammonium ion
oxidation.
Creatinine and arginine, being organic molecules, were
proven more amenable to radical oxidation than the ammo-
nium ion and were extensively transformed by sulfate
radicals, even in pool water. Bicarbonate ions slightly
inhibited creatinine transformation. At elevated peroxymo-
nosulfate concentrations, however, the bicarbonate scaven-
ging effect was overcome. As expected, the use of UV
radiation and in particular the UV/Peroxymonosulfate and
UV/Co/Peroxymonosulfate reagents led to very high rates of
creatinine destruction in pool water.
Chlorination of creatinine generates stable chlorinated
creatinine derivatives. The Co/Peroxymonosulfate, UV/Peroxy-
monosulfate and UV/Co/Peroxymonosulfate reagents suc-
cessfully destroyed these derivatives in pool water. In all three
cases, the use of the reagent against CC in chlorinated
pool water, still containing creatinine and other organic
compounds as reported in the literature (i.e., creatine, urea,
1-methylhydantoin and methylamine) led initially to the
formation of more chloramine-type compounds that regis-
tered, along with the original species, as CC in the DPD–FAS
method. Additional active chlorine species were initially
formed from the reaction of sulfate radicals with chloride
ions, which then further reacted with creatinine and the
other organic compounds to form these chloramines-type
compounds. As the reaction proceeded, these CC species
either, being unstable, decomposed; being volatile, were
stripped out of the solution; or underwent further transfor-
mation to compounds that did not register anymore in the
DPD–FAS method as they did not induce any iodide oxidation
of the type shown in reactions 26–28 (Table 1).
Finally, the Co/Peroxymonosulfate reagent at a relative low
peroxymonosulfate dose (25 ppm as Oxones) and a low cobalt
dose (0.1 ppm) was proven an efficient, but rather slow
sanitizer. Under these conditions in pool water, a 4-log kill
of E. coli colonies was achieved in 60 min of treatment.
Acknowledgments
This work was performed from September 2003 to August
2005 under an industry sponsored research agreement
between DuPont Co. and the University of Cincinnati.
Dr. Anipsitakis was then working towards his doctorate
degree at the University of Cincinnati. DuPont’s financial
support is greatly appreciated.
R E F E R E N C E S
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Alouini, Z., Seux, R., 1988. Kinetics and mechanisms of hypo-chlorite oxidation of creatinine. Water Res. 22, 1519–1526.
Anipsitakis, G.P., Dionysiou, D.D., 2003. Degradation of organiccontaminants in water with sulfate radicals generated by theconjunction of peroxymonosulfate with cobalt. Environ. Sci.Technol. 37, 4790–4797.
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