Ozonation of ketoprofen with nitrate in aquatic environments: Kinetics, pathways, and toxicity

Article abstract of DOI:10.1039/c7ra12894k

In this study, nitrate ion (NO₃^-) was found to collaborate with ozone thereby accelerating the degradation of ketoprofen. NO₃^- was discovered to induce the generation of hydroxyl radicals (·OH), which was crucial to the decomposition of PPCPs in wastewater treatment plants. Kinetic studies on the decomposition of ketoprofen were investigated under different concentrations of NO₃^-. The impact mechanisms and degradation by-products were experimentally determined. The results revealed that all reactions fitted the pseudo-first-order kinetic model well. The presence of NO₃^- had the capacity to accelerate the ozonation of ketoprofen. The reaction by-products were evaluated by UPLC-Q-TOF-MS, and a total of five intermediates generated via the ozonation of ketoprofen were assessed. The transformation pathways were concluded to be hydroxylation, nitration, and debenzophenone and ketonized reactions. Additionally, the toxicity of the by-products was evaluated by employing Chlorella and Daphnia magna.

Full text of DOI:10.1039/c7ra12894k

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Ozonation of ketoprofen with nitrate in aquatic
environments: kinetics, pathways, and toxicity
Cite this: RSC Adv., 2018, 8, 10541
Yongqin Zeng,†a Xiaoxuan Lin,†a Fuhua Li,b Ping Chen,c Qingqing Kong,d
a
and Wenying Lva
*
Guoguang Liu
In this study, nitrate ion (NO3ꢀ) was found to collaborate with ozone thereby accelerating the degradation
of ketoprofen. NO3ꢀ was discovered to induce the generation of hydroxyl radicals ($OH), which was crucial
to the decomposition of PPCPs in wastewater treatment plants. Kinetic studies on the decomposition of
ketoprofen were investigated under different concentrations of NO3ꢀ. The impact mechanisms and
degradation by-products were experimentally determined. The results revealed that all reactions fitted
ꢀ
the pseudo-first-order kinetic model well. The presence of NO3 had the capacity to accelerate the
Received 29th November 2017
Accepted 13th February 2018
ozonation of ketoprofen. The reaction by-products were evaluated by UPLC-Q-TOF-MS, and a total of
five intermediates generated via the ozonation of ketoprofen were assessed. The transformation
pathways were concluded to be hydroxylation, nitration, and debenzophenone and ketonized reactions.
Additionally, the toxicity of the by-products was evaluated by employing Chlorella and Daphnia magna.
DOI: 10.1039/c7ra12894k
rsc.li/rsc-advances
Moreover, Cao found that the maximum concentration of
1 Introduction
ketoprofen in the Zhangweinanyun River system was
31.35 ng Lꢀ1
,
whereas concentrations in the Yuecheng
5,6
Recently, pharmaceuticals and personal-care products (PPCPs)
have provoked much public consideration as “emerging
contaminants”.1 Such ubiquitous pollutants may cause poten-
tial risks to human health due to their biologically active
natures, accumulation, and persistent physicochemical prop-
erties.2 Among the PPCPs, ketoprofen ([2-(3-benzoylphenyl)
propionic acid]; KET) is one of the most widely used non-
steroidal anti-inammatory drugs (NSAIDs), which is
commonly employed in clinics to treat rheumatoid arthritis,
non-rheumatic diseases, ankylosis spondylitis as well as osteo-
arthritis or postoperative pain.3 Due its relatively high produc-
tion, widespread usage, direct or indirect emissions, and low
removal efficiency, ketoprofen has been investigated to
a signicant degree in wastewater treatment plants, surface
waters, groundwaters, and even drinking water sources at home
and abroad. Santos4 pointed out that the mean concentration of
ketoprofen approached 2.50 mg Lꢀ1 in wastewater effluents in
Spain. Furthermore, PPCPs found in the River Taff and River Ely
in the UK were investigated, among which ketoprofen was
Reservoir ranged from 1.33 to 8.40 ng Lꢀ1. Additionally, the
expanding aging “Baby boomer” population and improving
quality of life worldwide means that overall consumption of
ketoprofen is likely to increase over the next few years.7 Never-
theless, such adducts are difficult to effectively remove via
conventional drinking water treatment processes including
ltration, sedimentation and occulation. Subsequently,
certain contaminants may still be present during the disinfec-
tion step of the drinking water treatment process.
Ozonation is a promising and environmentally compatible
oxidation process. It is favorable for use in drinking water
disinfection for its ability to degrade various recalcitrant
organic pollutants through the direct use of ozone (O3, E ¼
2.07 V) and indirect use of hydroxyl radicals ($OH, E ¼ 2.8 V).8–10
Several studies have revealed that ozone shows great capacity in
decomposing PPCPs.11–13 To the best of our knowledge, infor-
mation regarding ketoprofen being efficiently eliminated by the
ozonation process in pure water has been long known for a long
time.14,15 However, until now, detailed research pertaining to
the degradation of target pollutants under the repercussions of
coexisting ions has been negligible.
found at concentrations that ranged between 0.5 and 14 ng Lꢀ1
.
aSchool of Environmental Science and Engineering, Guangdong University of
Technology, No. 100 Waihuan Xi Road, Guangzhou Higher Education Mega Center,
Panyu District, Guangzhou 510006, China. E-mail: liugg615@163.com
Inorganic nitrogen (including primarily nitrate, nitrite, and
ammonium ions) has been frequently detected in both surface
and groundwaters at concentrations of 10ꢀ6 to 10ꢀ3 M.16,17 Over
the last few years, inorganic nitrogen has been extensively
studied, and it has been proven that these nitrogen-containing
ions may produce hydroxyl radicals and other reactive groups,
thereby promoting or restraining the oxidation of dissolved
bSchool of Environment and Chemical Engineering, Foshan University, Guangdong
528000, China
cSchool of Environment, Tsinghua University, Beijing 100084, China
dSchool of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou
510275, China
† The rst two authors contributed equally to this work.
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ꢀ
organic pollutants.18,19 As a matter of fact, NO3 has been 16 mmol Lꢀ1. Degradation experiments were conducted with
considered as an environmental impact factor instead of laboratory-fabricated glass equipment (Fig. 1) using a gas
a major research object in most studies.20,21 Thus, it is critically dispersing device with a tap at the bottom. Ultimately, the
ꢀ
important to investigate the impact of NO3 on ketoprofen unused portion of the gas mixture was absorbed by the potas-
degradation by ozone during the drinking water disinfection sium iodide solution.
process.
Given the lack of data and knowledge in this eld, the goals
2.3 Analytical methods
of this study were to (1) technically evaluate the inuence of
ꢀ
During the course of the experiments, 1.5 mL volumes of reac-
tion liquid were incrementally extracted from the tap at 2, 4, 8,
12, 16, and 24 min. The samples were immediately analyzed via
the reversed-phase high-performance liquid chromatography
system (Waters, USA), which was equipped with a Zorbax
Eclipse XDB-C18 column (4.6 ꢁ 150 mm, 5 mm, Agilent, USA).
The analytical column temperature was 40 ꢂC, and 45% HPLC-
grade acetonitrile and 55% Milli-Q-Water (containing 0.5%
glacial acetic acid) were used as the mobile phase at a constant
ow rate of 1.0 mL minꢀ1. The injection volume was 10 mL, and
the UV wavelength for detection was 260 nm. The elution time
of KET was approximately 9.0 min.
NO3 toward the removal of ketoprofen by ozone under simu-
lated water disinfection conditions including an elucidation of
both the reaction kinetics and overall mechanism; (2) identify
ꢀ
the disinfection by-products of KET with NO3 present in the
system, presuming a tentative degradation pathway for KET
during the process; (3) simply evaluate the toxicity of the by-
products with the employment of Chlorella and D. magna.
2 Materials and methods
2.1 Reagents
Ketoprofen, (KET, 2-(3-benzoylphenyl) propionic acid (purity $
98%)) and ibuprofen were both purchased from TCI Reagent
Co. Ltd. (Shanghai, China). Acetonitrile of HPLC-grade was
purchased from U. S. ACS Enke Chemistry Co. Ltd. (Guangzhou,
China). Benzoic acid was obtained from Aladdin Industrial Co.
Ltd. (Shanghai, China). Other reagents employed in this study
(e.g., sodium nitrate, sodium nitrite, ammonium sulfate,
sulfuric acid, sodium hydroxide, and acetic acid) were all of
analytical grade and were used without further purication.
These reagents were obtained from the Guangzhou Chemical
Reagent Factory. Ultrapure water (18.25 MU cmꢀ1), obtained
from a Milli-Q apparatus (Smart2 Pure ultrapure water/water
system integration, TKA, Germany), was used in the prepara-
tion of all aqueous solutions during the experiment.
The KET degradation by-products were determined with the
UPLC-Q-TOF-MS microsystem (Waters, USA) under chromato-
graphic conditions (Table 1). The chromatographic column was
introduced into a UV-vis detector equipped with an electrospray
ionization (ESI) interface and mass analyzer, and the experi-
ment was performed using a Waters TQ detector. The electro-
spray source voltages were as follows: capillary (3.0 kV), sample
cone (30 V), and extraction cone (4.0 V) under negative mode.
The source block and desolvation gas were heated at 100 and
ꢀ
300 ꢂC, respectively. The concentrations of NO3 were deter-
mined by ion chromatography (882, Metrohm AG, Switzerland).
3 Results and discussion
3.1 Ozonation performance: ketoprofen inuenced by NO3
ꢀ
2.2 Experimental apparatus and procedures
500 mL of 20 mmol Lꢀ1 KET solution was prepared, and the
initial pH values were adjusted by NaOH or H2SO4 solution to
keep the initial pH of each sample consistent and to reduce the
experimental error. As shown in Fig. 1, the reactions were
initiated by the introduction of ozone gas from an ozone
generator (Quanju Technology, China), aer which the gas was
passed into an ozone concentration detector (UT-500, Adel
Measurement and Control Technology Co., LTD, USA)
where the ozone content in mixed gas was determined to be
As displayed in Fig. 2, the degradation of ketoprofen tted pseudo
rst-order kinetics well. The degradation rate constants were
3.0 ꢁ 10ꢀ2, 3.6 ꢁ 10ꢀ2, 4.2 ꢁ 10ꢀ2 and 4.6 ꢁ 10ꢀ2 minꢀ1 when
the concentrations of NO3 were 0, 0.01, 0.1, and 1 mmol Lꢀ1
,
ꢀ
respectively; the corresponding percentages (h) were calculated to
be 53%, 58%, 64%, and 70%. The results indicated that keto-
profen reacted effectively with O3, and more than half of the
ketoprofen used for this study was degraded within 24 min. It
could be inferred that further degradation might be achieved with
ꢀ
the prolongation of the reaction time. It was observed that NO3
could accelerate the ozonation of ketoprofen, and as the
ꢀ
concentration of NO3 was increased, a stronger effect was
Table 1 Chromatographic conditions
Time (min)
Flow (mL minꢀ1
)
A%
B%
0
6
13
14
16
0.3
0.3
0.3
0.3
0.3
95
80
0
95
95
5
20
100
5
5
Fig. 1 Reaction equipment.
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respꢀectively. Thus, it could preliminarily be determined that
NO3 might induce the generation of $OH.
According to eqn (5), if the reaction rate constant between
ketoprofen and $OH was known, the steady-state concentration
of $OH in the system could be calculated. Therefore, a compet-
itive experiment was conducted to obtain this constant. In this
section, benzoic acid (BA) was selected as a probe in this
competitive experiment to evaluate the reaction rate constant
between ketoprofen and $OH. The initial concentration of both
ketoprofen and benzoic acid was 20 mmol Lꢀ1, and the pH value
was adjusted to 10 to ensure a sufficient quantity of $OH as well
as to neglect the degradation caused by O3. The degradation
rate constants of ketoprofen and benzoic acid were 2.9 ꢁ 10ꢀ2
and 1.9 ꢁ 10ꢀ2 minꢀ1, respectively.
It is known that the reaction rate constant between benzoic
acid and $OH is 5.9 ꢁ 109 Mꢀ1 Sꢀ1
, according to eqn (5)–(7),
26
Fig. 2 Influence of NO3ꢀ on ozonation of KET.
and the reaction rate constant between ketoprofen and $OH is
calculated to be 8.82 ꢁ 109 Mꢀ1 Sꢀ1, which coincided with
results of previous research (8.4 ꢁ 109 Mꢀ1 Sꢀ1).15 Therefore, the
steady state concentration of $OH could be calculated from eqn
(8). As evidenced in Table 2, the concentration of NO3ꢀ increased
from 0 to 1 mmol Lꢀ1, and the steady state concentration of $OH
increased from 5.10 ꢁ 10ꢀ11 to 6.42 ꢁ 10ꢀ11 mmol Lꢀ1. These
elicited. The same phenomenon occurred when Miao investi-
ꢀ
gated the effect of NO3 on the ozonation of phenazone.22
Typically, the degradation of organics by ozone is initiated
through the combined activities of ozone molecules and
hydroxyl radicals that are decomposed from O3;23 the mecha-
nism is illustratꢀed in eqn (1) and (2). As previous studies have
indicated, NO3 might induce the generation of $OH to
promote the degradation of organic matter in an oxidation
system;18 the mechanism is articulated in eqn (3).
ꢀ
results affirmed that NO3 could induce the generation of $OH
ꢀ
and that the concentration of $OH increased with higher NO3
concentrations within a certain range (0–1 mmol Lꢀ1).
k$OH
kobs
kobs ꢀ kTBA
R$OH
¼
z
(4)
(5)
kobs
O3 + OHꢀ / HO2 + O2
(1)
(2)
(3)
ꢀ
½KETꢃ
½KETꢃ
ln
¼ kobst ¼ k$OH;KET½$OHꢃ t
ꢀ
O3 + HO2 / $OH + O2cꢀ + O2
0
ꢀ
NO3 + O2cꢀ + 2H2O /$NO3 + 2$OH + 2OHꢀ
½BAꢃ
½BAꢃ
ln
¼ kBAt ¼ k$OH;BA½$OHꢃ t
(6)
(7)
(8)
0
ꢀ
To further explore the mechanism of inuence of NO3 on
the ozonation of ketoprofen, quenching experiments were
conducted to identify the generation of $OH. tert-Butyl alcohol
(TBA), a widely used $OH scavenger in many quenching exper-
iments,10,24,25 was selected to conrm the existence of $OH in the
system and to evaluate the contribution of $OH to the degra-
dation of ketoprofen in accordance with eqn (4). As exhibited in
Table 2, TBA dramatically reduced the degradation of ketopro-
fen, which indicated that $OH existed in the system and
contributed to the degradation of ketoprofen, with the contri-
bution rates of 90%, 8ꢀ0.56%, 76.19%, and 73.91% when the
kobs
k$OH;KET
¼
k$OH;BA
kBA
k$OH
k$OH;KET
½$OHꢃ ¼
here, R$OH is the contribution of $OH, k$OH is the degradation
rate constant of ketoprofen with $OH, kTBA is the degradation
rate of ketoprofen with the existence of TBA in the system, kBA
represents the overall degradation rate of benzoic acid in the
system, [BA] is the molar concentration of benzoic acid at
a specied time, kcOH,KET and k$OH,BA are the reaction rate
concentrations of NO3 were 0, 0.01, 0.1, and 1 mmol Lꢀ1
,
Table 2 Ketoprofen degradation kinetics, kobs, kOH, R$OH and [$OH]
Kobs ꢁ 10ꢀ2 minꢀ1
[$OH]
Items
[NO3ꢀ] (mM)
Without TBA
With TBA
k
$OH (minꢀ1
)
R
$OH (%)
(10ꢀ11mmol Lꢀ1
)
1
2
3
4
0
3.0 ꢄ 0.126
3.6 ꢄ 0.136
4.2 ꢄ 0.105
4.6 ꢄ 0.102
0.3 ꢄ 0.0111
0.7 ꢄ 0.0245
1.0 ꢄ 0.0435
1.2 ꢄ 0.0504
2.7 ꢄ 0.1149
2.9 ꢄ 0.1115
3.2 ꢄ 0.0615
3.4 ꢄ 0.0516
90.00
80.56
76.19
73.91
5.10
5.48
6.05
6.42
0.01
0.1
1
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constants of $OH with ketoprofen and benzoic acid, respec- contribution rate on the degradation of ketoprofen than O3 did.
tively, and [$OH] represents the steady state concentration of Thus, the nucleophilic substitution of $OH in the benzene ring
$OH in the system.
was inferred to be the dominant mechanism of benzene
29
´
hydroxylation. As Illes mentioned in his study of the photo-
induced degradation of ketoprofen in pure water, the hydroxyl-
ation by-products formed during the degradation of ketoprofen
were preferentially due to the attack of $OH on the benzene ring.
Furthermore, P5 (C16H13NO5, m/z 299) in the MS2 fragmen-
tation spectrum of m/z 298 and the major fragments at m/z 252
(ꢀ46) and 254(ꢀ44) might correspond to the loss of –NO2 and
–COOH. However, $NO2 was generated according to eqn (2). The
delocalization of a positive charge from $NO2 to the aromatic
ring brought about a strong electron-deciency in the meta-
positions on the aromatic ring,30 with a nitration-derivative of
ketoprofen.
Apart from the two above-mentioned pathways, P4 (phenyl-
propionic acid, C9H10O2, m/z 149) was analyzed by UPLC-Q-TOF-
MS at a retention time of 5.92 min, and it was dened as a by-
product of ketoprofen debenzophenone pathway. Previous
investigations were supportive of this pathway during the
advanced oxidation of benzophenone-3.31,32 Subsequently, P3
compounds (ortho-hydroxybenzene propanoic acid, C9H10O3, m/z
166) were determined to be hydroxylated intermediates of P4
formed by undergoing further attacks on the meta-position of the
benzene ring. Moreover, the –COOH group on the side-chain of P3
was observed to be further oxidized to form P1 (C8H8O2, m/z 136).
3.2 By-products and degradation pathway speculation
This section summarizes the content mentioned above with the
aim of further investigating the ketoprofen degradation mech-
anism under the presence of 1 mM nitrate ions as well as the
identication of all degradation by-products.
The ketoprofen degradation products were analyzed by
UPLC-Q-TOF-MS using the ESI negative ion mode, which
allowed for the identication of a total of six compounds
including the unaltered parent ketoprofen and ve intermedi-
ates. The complete ion chromatograms are depicted in Fig. 3,
with ve major degradation by-product peaks at 1.68, 2.67, 5.00,
5.92, and 8.29 min assigned to P1, P2, P3, P4, and P5, respec-
tively. Mass spectra and mass characteristics (e.g., retention
time, m/z, fragments, and prediction formula) of the above-
mentioned substances are summarized in Table 3, whereas
fragment chart analyses of the secondary ion mass spectrometry
of the P1–P5 photolysis products are displayed in Fig. 4. Overall,
the degradation of ketoprofen appeared to have at least four
pathways: (1) hydroxylation on benzene ring pathway, (2)
nitration on benzene ring pathway, (3) debenzophenone
pathway, (4) ketonized pathway.
Due to the cogent electron-withdrawing effect of the
carboxylic acid group and benzophenone group in the keto-
profen structure, the oxidation reaction preferentially occurred
3.3 Toxicity measurement
at the phenyl ring I rather than II. In addition, the meta- Toxicity measurement of organic pollutants is an essential
positions were easily activated and were vulnerable to attack, indicator for practical wastewater treatment. As shown in Fig. 6,
and this resulted in the formation of meta-by-products.27
the initial immobilization rates of D. magna were 26.72% and
On one hand, the formula of P2 is C16H14O4, and the m/z was 61.44% at 24 h and 48 h exposure, respectively. During the
270 with an additional O compared to those of the parents; ozonation process, the immobilization rate was reduced slightly
major fragments at m/z 253(ꢀ16), 225(ꢀ44), and 209(ꢀ60) might during treatment for 4 min. However, an evident increment
correspond to the observed –OH loss, –COOH loss and the loss occurred as the treatment proceeded and reached up to 50%
of both, respectively. These results resulted in the assumption and ultimately 80.56%. A similar trend was observed in the
that P6 was a monohydric derivative compound of ketoprofen assay of algae, suggesting that the decomposition of initial KET
degradation, which was formed from an electrophilic substitu- led to the decrease of immobilization rate at the beginning. The
tion (H by $OH) on the aromatic ring. The mechanism of accumulation of by-products resulted in the constant increase
hydroxylation in ozonation is illustrated in Fig. 5 including the in the immobilization rate, indicating that the ecological risks
electrophilic substitution by O3 or nucleophilic attack by $OH.28 of ozonation process are worthy of attention in practical
Thus, Section 3.1 indicated that $OH had a much higher treatment.
Fig. 3 The total ion current of oxidation by-products.
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Table 3 Mass data obtained from the UPLC/MS/MS of ketoprofen oxidation by-products
Retention time
(min)
Peak
ESI(ꢀ)MW
mDa
Fragments of MS2
Prediction formula
P1
P2
P3
P4
P5
1.68
8.29
5.00
5.92
7.41
136.1464 [M ꢀ H]ꢀ
269.2845 [M ꢀ H]ꢀ
165.1732 [M ꢀ H]ꢀ
149.1746 [M ꢀ H]ꢀ
298.2833 [M ꢀ H]ꢀ
ꢀ3.5
0.4
2.8
2.4
ꢀ0.3
135, 119, 94
269, 254, 226, 210
165, 149, 121,
149, 105
C8H8O2
C16H14O4
C9H10O3
C9H10O2
C16H13NO5
298, 252, 254
Fig. 4 Fragment chart analyses of the secondary ion mass spectrometry of P1–P5.
ꢀ
+
that directly converted N(ꢀ3) into N(+5) as revealed in
3.4 Ozonation of ketoprofen inuenced by NO2 and NH4
eqn (9),33–35 thereby facilitating the degradation of organic
It was revealed in Fig. 7 and Table 4 that NH4+ also had the capacity
to accelerate the degradation of ketoprofen, which was similar to
that of NO3ꢀ, but this capacity was less aggressive. On the contrary,
NO2ꢀ showed inhibitory effect in the degradation of ketoprofen, in
ꢀ
matter in the same manner as that with NO3
.
+
ꢀ
NH4 + 4O3 / NO3 + 2H+ + H2O + 4O2
(9)
ꢀ
ꢀ
that, as the NO2 concentration increased, a stronger inhibition
NO2 comprises a type of reductive substance that has the
capacity to perform redox reactions with substances in oxida-
tion systems. This mechanism is elucidated in eqnꢀ(10) and (11),
would occur. It was reported that the existence of NO2ꢀ negatively
affected the degradation of organic matter by AOPs.18
As for NH4+, previous studies have suggested that ozone
might transform NH4+ to NO3ꢀ via the strong oxidizing capacity
where the reaction rate constant between NO2 and ozone
molecules is 2.27 ꢁ 107 Mꢀ1 Sꢀ1
. According to eqn (12)–(14),
36
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Fig. 5 Possible oxidation pathways of KET in nitrate aqueous solution.
ꢀ
+
Fig. 6 Variation of immobilization rates of D. magna in 24 h and 48 h
(rectangle) and inhibition rate of algae in 96 h (line).
Fig. 7 Effect of different concentrations of NO2 and NH4 on
ozonation of KET.
whereas it is 3.3 ꢁ 10ꢀ2 minꢀ1 for ibuprofen. It is known that
the reaction rate constant between ketoprofen and O3 can be
elucidated through competitive experiments using ibuprofen
(IBP) as a probe. During the experiments, the initial concen-
trations of both ketoprofen and ibuprofen are 20 mmol Lꢀ1, and
the degradation initiated by $OH can be ignored via the addi-
tion of excess TBA and the adjustment of the pH value to 2. The
the reaction rate constant between IBP and O3 is 7.2 Mꢀ1 Sꢀ1
,
37
and the reaction rate constant between ketoprofen and O3 is
1.09 Mꢀ1 Sꢀ1
.
ꢀ
ꢀ
NO2 + O3 / NO3 + O2 2.27 ꢁ 107 Mꢀ1 Sꢀ1
(10)
degradation rate constant of ketoprofen is 0.5 ꢁ 10ꢀ2 minꢀ1
,
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+
Table 4 Reaction rate of different concentration of NO2ꢀ and NH4
ꢀ
+
Species
NO2
NH4
Concentration (mM)
0.00
3.0
0.01
2.2
0.10
1.1
1.00
0.3
0.00
3.0
0.01
3.3
0.10
3.7
1.00
4.0
Reaction rate (ꢁ10ꢀ2
)
ꢀ
NO2 + $OH / NO2$ + OHꢀ (1–10) ꢁ 109 Mꢀ1 Sꢀ1 (11)
and Technology Planning Project of Guangdong Province (No.
2017A050506052). The authors would like to thank all the
editors and reviewers for their aid in the improvement of this
paper.
½KETꢃ
ln
¼ kobst ¼ kO ;KET½O3ꢃ t
(12)
(13)
(14)
3
½KETꢃ
0
½IBPꢃ
½IBPꢃ
ln
¼ kIBPt ¼ kO ;IBP½O3ꢃ t
3
0
Notes and references
kobs
1 L. P. Padhye, H. Yao, F. T. Kung'U and C. H. Huang, Water
Res., 2014, 51, 266–276.
kO ;KET
¼
k
O3;IBP
3
kIBP
2 P. Verlicchi, A. M. Al and E. Zambello, Sci. Total Environ.,
2012, 429, 123.
here, k$O ,KET and k$O ,BA are the reaction rate constants of O3
with ketoprofen and benzoic acid, respectively.
3
3
3 K. A. K. Musa, J. M. Matxain and L. A. Eriksson, J. Med.
Chem., 2007, 50, 1735–1743.
4 J. L. Santos, I. Aparicio and E. Alonso, Environ. Int., 2007, 33,
596–601.
5 J. L. Cao, J. H. Shi, R. Han, Y. X. Li and Z. F. Yang, Chin. Sci.
Bull., 2010, 55, 3138–3144.
6 B. Kasprzyk-Hordern, R. M. Dinsdale and A. J. Guwy, Water
Res., 2008, 42, 3498–3518.
In comparison, the reaction rate of ozone molecules with
NO2ꢀ (2.27 ꢁ 107 Mꢀ1 Sꢀ1) was much more rapꢀid than that with
ketoprofen (1.09 Mꢀ1 Sꢀ1). In this way, NO2 restrained the
ozonation of ketoprofeꢀn as the ozone molecule scavenger. On the
other hand, both NO2 and ketoprofen exhibited high reactive
activities with $OH, with reaction rate constants between (1–10)
ꢀ
ꢁ 109.17,19,38 The competition for $OH between NO2 and KET
directly led to the decrease of the degradation rate of ketoprofen.
As mentioned in Section 3.1, the contribution of $OH to keto-
profen was approximately 90%, whereas the contribution of $OH
to ozone it was 10%. In this way, the competition for $OH
between NO2ꢀ and KET was considered as the dominant factor in
the reduction of the ketoprofen degradation rate.
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¨
11 I. Zucker, Y. Lester, D. Avisar, U. Hubner, M. Jekel,
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demonstrated that the ketoprofen ozonation reactions aligned
ꢀ
well with the pseudo rst-order kinetics in the presence of NO3
.
Five intermediates were simultaneously identied during the
ozonation of ketoprofen, and four types of reaction pathways were
speculated: hydroxylation and nitration on benzene ring, keto
break, and ketonized reactions on the side chains. Furthermore,
toxicity evaluation revealed that more harmful by-products were
generated, which suggested that more attention should be paid to
the wastewater disinfection process. Additionally, the experiment
´
¨
13 M. M. Gomez-Ramos, M. Mezcua, A. Aguera,
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+
of NO2 and NH4 simply implied that the presence of nitroge-
´
16 M. V. Shankar, S. Nelieu, L. Kerhoas and J. Einhorn,
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´
17 M. V. Shankar, S. Nelieu, L. Kerhoas and J. Einhorn,
Conflicts of interest
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There are no conicts to declare.
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Acknowledgements
This study is supported by the National Natural Science Foun- 20 Y. Feng, Q. Song, W. Lv and G. Liu, Chemosphere, 2017, 189,
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