ARTICLE pubs.acs.org/IECR
Photocatalysis of Clofibric Acid under Solar Light in Summer and Winter Seasons Wenzhen Li, Shuguang Lu,* Zhaofu Qiu, and Kuangfei Lin State Environmental Protection Key Laboratory of Environmental Risk Assessment and Control on Chemical Process, College of Resource and Environmental Engineering, East China University of Science and Technology, Shanghai 200237, China ABSTRACT: The performance of clofibric acid (CA) degradation in Milli-Q water and wastewater treatment plant (WWTP) effluent by solar/TiO2 and solar/ZnO was investigated in summer and winter seasons. The effects of NO3 and HCO3 anions, humic acid (HA), and H2O2 on CA photocatalysis were evaluated. Significant difference in CA degradation in two seasons was observed. Both NO3 and HCO3 anions adversely affected CA degradation, particularly at high HCO3 concentration. CA degradation slightly increased with 0.5 mg L1 HA in solar/TiO2 in summer, but was significantly inhibited in winter at 20 mg L1 HA. However, the inhibitive effect of 20 mg L1 HA on CA removal in solar/ZnO had no remarkable difference in two seasons. The degradation in solar/TiO2/H2O2 was similar to that in solar/TiO2, but was inhibited obviously in solar/ZnO/H2O2. When applying photocatalytic process into WWTP effluent, degradation rates were apparently lower compared to Milli-Q water and temperature caused a great adverse effect on CA elimination.
1. INTRODUCTION Pharmaceuticals and personal care products (PPCPs) have appeared as a new class of pollutants and much research has been conducted to investigate the sources and occurrence of these compounds in the environment. They have been detected often in WWTP effluents, rivers, lakes, seawater, groundwater, and even drinking water at trace levels and may accumulate in soils and sediments due to their physicalchemical properties.14 Among these compounds blood lipid regulators are paid much more attention by researchers due to their large consumption in terms of thousands of tons annually. They are used for therapeutic purposes for those suffering from angiocardiopathy problems such as coronary heart disease, high blood pressure, arrhythmia, and cardiac function failure, etc. This usage leads to clofibric acid (CA), the active metabolite of clofibrate and other lipid regulators, being frequently detected in the aquatic environment such as groundwater and drinking water, as well as the North Sea with concentrations ranging from 0.5 to 7.8 ng L1.5 For instance, CA was also detected in Berlin tap water samples at concentrations between 10 and 165 ng L1.6,7 Municipal wastewater is the main means of disposal of pharmaceuticals into environment. In many cases, the concentration levels of pharmaceuticals are reduced during the treatment process through microbial degradation or adsorption onto activated sludge, but they are hardly completely eliminated.810 Several studies have demonstrated that biodegradation of CA in wastewater treatment plant (WWTP) was limited. For example, Zorita et al. reported 55% CA removal in a conventional WWTP in Sweden and it could be improved to 61% in tertiary treatment process by additional chemical treatment following a sand filter.11 However, Zwiener and Frimmel investigated the biodegradation of CA in short-term tests with a pilot WWTP and biofilm reactor for municipal wastewater treatment, and found only 5% of CA could be eliminated.12 Once the pharmaceuticals are released into the environment, their fate, degradation pathways, r 2011 American Chemical Society
persistence, and impact on the aquatic environment have to be considered.13 It is likely that photochemical degradation is the most important mechanism for loss of many pharmaceuticals in the aquatic environment. For instance, several authors have shown a rapid decomposition of diclofenac in surface waters when exposed to natural sunlight.14,15 However, it is worthy to note that CA tends to be hardly biodegraded in natural environment, and abiotic losses and adsorption play only a minimal role in the fate of CA in aquatic system.16 Andreozzi et al. reported that half-life times for the direct CA photolysis were around 40 days in spring and up to 250 days in winter, indicating its high stability toward conventional biodegradation and persistency in aquatic environment.9 Therefore, significantly irreversible adversity might be induced due to its accumulation in the natural environment, such as the resistance of bacteria and adverse change of current ecological system, and hence further threatening the human health.1719 In addition, reactions occurring with these contaminants in the environment can yield transformation products with significantly different properties regarding their environmental behavior such as greater toxicity or environmental persistence.2023 Therefore, improving removal efficiency of the pharmaceuticals and their metabolites in WWTPs must be emphasized and new techniques are needed to completely mineralize drugs disposed in water at large scale. Some research has shown promising results in the removal of pharmaceutical pollutants through advanced oxidation processes (AOPs).24,25 Most of the AOPs apply a combination of either oxidants and irradiation (O3/H2O2/UV), or a catalyst and irradiation (Fe2þ/H2O2; UV/ TiO2), which are mainly characterized by the production of Received: August 13, 2010 Accepted: March 15, 2011 Revised: March 10, 2011 Published: March 22, 2011 5384
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Table 1. Characteristics of Longhua WWTP Effluent parameter pH
value 7.0
turbidity (NTU)
8.0
dissolved organic carbon (DOC, mg L1)
16.4
chemical oxygen demand (COD, mg L1)
39.0
Cl (mg L1)
177.5
NO3 (mg L1)
41.6
SO42- (mg L1)
155.2
CA
not detectable
hydroxyl radicals with consecutively unselective attack on the organics. Their application for the degradation of some pharmaceuticals has been reported.2428 Among the AOPs, heterogeneous photocatalysis in the presence of oxides semiconductor is a fast growing field of fundamental and applied research, especially for oxidation of organic pollutants in water or in air.29,30 Metal oxide semiconductors such as TiO2, ZnO, SnO2, WO3, ZrO2, SrO2, and CdS, etc. have been attempted for the photocatalytic degradation of a wide variety of environmental contaminants. TiO2 is widely used due to its nontoxic and inexpensive as well as biologically and chemically inert properties.31 They can employ solar renewable energy, and so far photocatalytic degradation by both TiO2 and ZnO catalysis has been established as effective treatments for trace organic contaminants.3236 Several trials have been tested on CA removal using various processes, including anodic oxidation with Pt and boron-doped diamond, electronFenton, and photoelectronFenton processes, UV and UV/H2O2, Xe lamp radiation, etc.33,3739 However, there have been no tests performed on CA photocatalytic degradation under solar light. Moreover, the effectiveness of photodecomposition depends on light intensity and also varies with season and local latitude.40 In addition, the combination of oxidants (i.e., H2O2, O3, persulphate (PDS), and peroxymonosulphate (PMS)) with the photocatalyst could elevate the oxidization of several highly refractory compounds.4143 When applying solar/ TiO2 and/or solar/ZnO processes for CA removal in real WWTP effluent, CA degradation is also influenced significantly by water matrixes, such as nitrate and bicarbonate anions, and dissolved organic matters (DOMs) such as humic acid (HA), because they all can work as photosensitizer and/or 3 OH scanvenger.44,45 Therefore, the objective of this study is to investigate CA degradation by solar/TiO2 and solar/ZnO in Milli-Q waters and WWTP effluent in both summer and winter seasons. The influences of H2O2 addition, solution constituents including nitrate and bicarbonate anions, and HA on CA photocatalysis were evaluated. CA degradation patterns were simulated using the pseudo-first-order kinetic model, and the apparent rate constants and half-life times were calculated under various operational conditions.
2. EXPERIMENTAL SECTION 2.1. Chemicals. CA (99% purity) was purchased from J & K Chemical Ltd. (Beijing, China). High-performance liquid chromatography (HPLC) grade methanol and acetonitrile, and all other reagents (analytical reagent) including H2O2 (30% (w/w) solution), NaNO3, NaHCO3, KH2PO4, HA (fulvic acid >90%), and acetic acid were purchased from Shanghai Jingchun Reagent Co. Ltd. (Shanghai, China). TiO2 Degussa P25 and ZnO (provided by Aladdin Reagent Database Inc.) were used for
heterogeneous photocatalysis. A Milli-Q ultrapure water system (Classic DI, ELGA, UK) was used for solution preparations. NaOH (0.1 M) was used for solution pH adjustment. The secondary effluent (see Table 1) of a WWTP employing conventional activated sludge process was collected from Longhua WWTP, Shanghai, China, and filtered using fiber filters (0.45-μm, Waters Corporation, Shanghai, China) before being spiked with CA compound. For all the tests, CA was spiked in the solution and controlled at initial concentration of 10 mg L1. 2.2. Photodegradation Experiments. The test site was located at 31.145° N and 121.418° E. All solar photochemical experiments were performed in a 500-mL beaker with magnetic stirring, which was kept dark to avoid any photoreaction during preparation. CA solution (10 mg L1) was added into the beaker and pH was adjusted to 7.0. Then TiO2 and ZnO were added and well homogenized for 15 min before starting reaction. A series of tests were conducted under various conditions as summarized in Table 2. The total solar light intensity during the experiments was measured by a digital light meter (TES-1332A, TES Electrical Electronic Corp.) (Figure 1). According to the meteorology in Shanghai, the amounts of UV radiation as well as the ratio of UV radiation to total solar radiation in summer are more intensive than those in winter.46 The most important solar radiation variation is the UV solar radiation incident on the reactor window for photocatalytic processes. Therefore, in order to evaluate the photodegradation with seasonal variation, the experiments were carried out during the coldest period in winter and the hottest period in summer when the average temperatures of the solution under the sunshine were around 10 and 35 °C, respectively. 2.3. Analytical Methods. All samples for CA concentration measurement were prefiltered through a 0.22-μm glass fiber filter before injection into HPLC. Modified CA analysis protocol based on Doll and Frimmel was conducted by HPLC (LC-VP, Shimadzu, Japan) equipped with a diode array detector at λ = 230 nm using Kromasil 100-5C18 column (4.6 250 mm, 5 μm) with a constant temperature of 35 °C.7 The mobile phase consisted of a 75:25 methanol/acetonitrile mixed solution (1:1, 0.1% acetic acid) and buffered aqueous solution KH2PO4 (5 mM, 0.1% acetic acid). The flow rate was 1.0 mL min1, and the injection volume of samples was 20 μL. The limit of detection (LODs; S/N g 3) and the limit of quantification (LOQs; S/N g 10) were 5 μg L1 and 18 μg L1, respectively. The reproducibility of standard solution was within 2% (injection number of sample n = 7) as indicated by the relative standard deviation (RSD). The dissolved organic carbon (DOC) of samples was measured by an Elementar liquid TOC analyzer (Germany) after filtration through 0.45-μm membrane. Ultraviolet absorbance at 254 nm (UV254) was recorded by ultraviolet spectrophotometer (UV 2100, UNICO (Shanghai) Instruments Co., Ltd., China). The chloride ion was detected by ion chromatograph (ICSI000, Dionex Corporation, USA). The intermediate products were identified by gas chromatographymass spectrometry (GCMS, QP2010, Shimadzu, Japan) using a DB-5MS 0.25 μm, 30 m 0.25 mm (i.d.) column. The temperature ramp for this column was 40 °C for 1 min, 10 °C/min up to 200 °C and hold time 3 min, and the temperatures of the inlet, transfer line, and detector were 280, 280, and 250 °C, respectively.
3. RESULTS AND DISCUSSION 3.1. CA Degradation in Solar/TiO2 and Solar/ZnO Processes. To clarify the individual effect on CA degradation by
either solar light photolysis or CA adsorption onto TiO2 catalyst, 5385
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Table 2. Summary of CA Degradation Performance under Various Conditions test
rate constant kap (min1)
operational conditions
half-life time t1/2 (min)
correlation coefficient R2
CA removal (%)
solar/TiO2, CA = 10 mg L1, TiO2 = 1 g L1, T = 35 °C (summer) 1
pH = 7.0
0.1041
6.66
0.8885
99.7 (50 min)
2
NO3 = 1.0 103 mol L1, pH = 7.0
0.0846
8.19
0.9594
99.5 (60 min)
3
NO3 = 0.1 mol L1, pH = 7.0
0.0593
11.7
0.9828
97.3 (60 min)
4
HCO3 = 1.0 103 mol L1, pH = 7.0
0.0618
11.2
0.9821
97.8 (60 min)
5
HCO3 = 0.1 mol L1, pH = 7.0
0.0033
210.0
0.9971
32.6 (120 min)
6
HA = 0.5 mg L1, pH = 7.0
0.1098
0.9893
99.8 (60 min)
7
HA = 5 mg L1, pH = 7.0
0.0659
10.5
0.9696
99.4 (80 min)
8 9
HA = 20 mg L1, pH = 7.0 H2O2 = 50 mg L1, pH = 7.0
0.0285 0.1058
24.3 6.55
0.8333 0.9580
96.5 (100 min) 99.6 (50 min)
10
H2O2 = 100 mg L1, pH = 7.0
0.0952
7.28
0.9901
99.0 (50 min)
11
H2O2 = 150 mg L1, pH = 7.0
0.0872
7.95
0.9777
98.0 (50 min)
12
WWTP effluent, pH = 7.0
0.0119
0.9958
75.3 (120 min)
98.8 (100 min)
6.31
58.2 1
1
solar/TiO2, CA = 10 mg L , TiO2 = 1 g L , T = 10 °C (winter) 13
pH = 7.0
0.0437
15.9
0.9821
14
NO3 = 1.0 103 mol L1, pH = 7.0
0.0430
16.1
0.9849
98.8 (100 min)
15 16
NO3 = 0.1 mol L1, pH = 7.0 HCO3 = 1.0 103 mol L1, pH = 7.0
0.0233 0.0221
29.7 31.4
0.9870 0.9849
94.6 (120 min) 93.7 (120 min)
17
HCO3 = 0.1 mol L1, pH = 7.0
0.0023
301.3
0.9935
23.0 (120 min)
18
HA = 20 mg L1, pH = 7.0
0.0042
165.0
0.9718
40.4 (120 min)
19
WWTP effluent, pH = 7.0
0.0061
113.6
0.9943
76.7 (240 min)
1
1
solar/ZnO, CA = 10 mg L , ZnO = 1 g L , T = 35 °C (summer) 20
pH = 7.0
0.0411
16.8
0.9946
99.4 (120 min)
21
NO3 = 0.1 mol L1, pH = 7.0
0.0429
16.2
0.9920
99.8 (140 min)
22
HCO3 = 0.1 mol L1, pH = 7.0
0.0010
693.1
0.9270
13.5 (140 min)
23 24
HA = 20 mg L1, pH = 7.0 H2O2 = 100 mg L1, pH = 7.0
0.0049 0.0228
141.4 30.4
0.9923 0.9970
50.5 (140 min) 95.3 (140 min)
25
WWTP effluent, pH = 7.0
0.0099
70.0
0.9814
69.1 (120 min)
1
1
solar/ZnO, CA = 10 mg L , ZnO = 1 g L , T = 10 °C (winter) 26
pH = 7.0
0.0122
56.8
0.9967
98.7 (360 min)
27
NO3 = 0.1 mol L1, pH = 7.0
0.0085
81.5
0.9880
94.9 (360 min)
28
HCO3 = 0.1 mol L1, pH = 7.0
0.0006
1155.2
0.8970
20.7 (360 min)
29
HA = 20 mg L1, pH = 7.0
0.0032
216.6
0.9907
65.6 (360 min)
30
WWTP effluent, pH = 7.0
0.0071
97.6
0.9952
92.0 (360 min)
preliminary experiments were conducted and found that there were no significant changes in dissolved CA concentration either by exposure to solar light directly or by mixture with TiO2 in dark for 4 h, suggesting that CA was not degraded by only solar light directly and no adsorption of CA onto TiO2 occurred (data not shown). However, CA was almost completely degraded in 60 min after exposure to solar light in summer when mixed with 0.25 g L1 of TiO2 (Figure 2). CA degradation during photocatalysis with TiO2 followed pseudo-first-order kinetic model, as suggested by Augugliaro et al.47 The reaction rates were accelerated when increasing TiO2 dosage from 0.25 to 2.0 g L1 and there was no significant improvement for rate constants when increasing TiO2 from 2.0 to 3.0 g L1. Apparently, with more TiO2 addition, scattering phenomena may happen and active sites on the surface of the catalyst do not bring more e/hþ generation and therefore result in no promotion for degradation rate. Thus, TiO2 concentration was kept at 1.0 g L1 in our further experiments. The same phenomenon appeared in solar/ZnO process. The photodegradation of CA could be promoted by
increasing ZnO dosage from 0.5 to 1.0 g L1 and had no significant change when increasing from 1.0 to 2.0 g L1. Therefore, ZnO dosage was also set at 1.0 g L1 in order to compare with solar/TiO2 system. Figure 3 shows the CA degradation in solar/TiO2 and solar/ ZnO processes in summer and winter seasons. The experimental conditions are shown in Table 2. All initial solution pH in the test was adjusted to 7.0 for consistence with the real WWTP effluent, and the solution pH hardly changed during the test period, suggesting no significant effect on CA degradation rate. It was obvious that the degradation rates were significantly different in summer and winter both using TiO2 and ZnO as catalyst. The catalytical efficiency of TiO2 was better than that of ZnO in both seasons. The intensity level of solar radiation for each season, especially for UV solar radiation part, might have a very important effect on the degradation of CA because the photocatalysis is driven by solar energy. To distinguish the effect of the radiation from the reaction temperature, several experiments have been carried out under different radiations with various 5386
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Figure 1. Solar light intensity measured in summer (T = 35 °C) and winter (T = 10 °C) seasons during the experiments.
Figure 2. Effect of TiO2 dosage on CA degradation in solar/TiO2 process in summer (CA = 10 mg L1, T = 35 °C, average light intensity = 79 000 lx).
solar light intensity but all at the same controlled temperature condition, and the results are shown in Figure 4. The total solar light intensity on October 4, 2010 was relatively stable. On the contrary, solar radiation on November 23, 2010 and September 6, 2009 fluctuated due to the weather conditions and the average solar light intensities were lower than that on October 4, 2010. It was found that various radiations had less effect on CA degradation in solar/TiO2 process when the temperature was set at 28.5 °C by heating when needed. However, the lower solar light intensity could significantly hinder CA degradation in solar/ZnO process and the rate constant decreased to 0.0411 from 0.0677 min1, suggesting that the solar light intensity has great impact on CA degradation. Some research suggested that ZnO could absorb
Figure 3. CA degradation in solar/TiO2 and solar/ZnO processes in summer and winter seasons (CA = 10 mg L1, TiO2 = 1.0 g L1, ZnO = 1.0 g L1, T = 35 °C, average light intensity = 79000 lx (summer), T = 10 °C, average light intensity = 39300 lx (winter)).
more solar energy than TiO2. For instance, Palominos et al. investigated the photocatalytic oxidation of the antibiotic tetracycline (TC) in aqueous suspension containing TiO2 or ZnO under simulated solar light and found that ZnO presented a slightly higher oxidative rate than TiO2.34 However, their conclusions were obtained under optimized conditions, i.e., 1.5 g L1 TiO2 and pH 8.7, and 1.0 g L1 ZnO and pH 11. Shukla et al. also found that ZnO exhibited higher activity than TiO2 in photocatalytic degradation of phenol under simulated solar light when they performed photocatalytic degradation of phenolic compounds in TiO2/persulphate/UVvis and ZnO/persulphate/ UVvis light.36 The lower CA removal by solar/ZnO in our 5387
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Figure 5. Cl release, DOC mineralization, and specific ultraviolet absorption at 254 nm (SUVA254) for CA oxidation in solar/TiO2 processes (C0 = 100 mg L1, TiO2 = 1.0 g L1, T = 25 °C).
Figure 4. Effect of temperature and total solar intensity on CA degradation in solar/TiO2 and solar/ZnO processes (TiO2 = 1.0 g L1, ZnO = 1.0 g L1, pH = 7.0, the average light intensity was 102 800 lx on October 4, 2010, 66 000 lx on November 23, 2010, 74 100 lx on September 6, 2009).
experiments might be caused by the experimental conditions in which the pH of CA solution was 7.0. As Table 2 showed, the rate constants for solar/TiO2 and solar/ZnO were 0.0437, 0.0122 min1 in winter, and 0.1041, 0.0411 min1 in summer. The reaction times taken for achieving 99% CA removal were 50, 100, 120, and 360 min in solar/TiO2 (summer and winter) and solar/ZnO (summer and winter), respectively. Figure 4 also illustrates that besides the solar light intensity, the temperature played an important role on CA photocatalysis. There was a significant promotion in CA degradation in solar/ TiO2 process by increasing 10 °C in temperature (from 28.5 to 38.5 °C on October 4, 2010) under the same solar radiation and the rate constant increased from 0.1052 to 0.3251 min1. It is consistent with our previous studies on the degradation of CA with a real WWTP effluent in UV254/H2O2 process under three temperature, i.e., 10, 20, 30 °C, in which over 99% of CA removal (initial concentration of CA = 10 mg L1) could be achieved under 30 °C within only 15 min compared with 40 and 80 min under 20 and 10 °C, respectively, suggesting a great promotion in CA removal under higher temperature.48 Several authors obtained the similar results when investigating the effect of temperature on contaminants degradation.27,32,49,50 Neamt-u et al. studied the influence of temperature on photolysis of octylphenol (OP) and nonylphenol (NP) using a solar simulator.49,50 After the same exposure time at 25 °C, 29.55% of octylphenol and 41% of nonylphenol removal was obtained, while the removal efficiency for octylphenol and nonylphenol was 14% and 11% at low temperature (10 and 15 °C). However, MendezArriaga et al. compared the degradation for three drugs by heterogeneous TiO2 photocatalytic in aqueous solution and found that temperature had a significant effect only for naproxen degradation, and no evident differences for diclofenac and ibuprofen at 20, 30, and 40 °C.27 Hilal et al. studied the
temperature effect on phenazopyridine degradation rate under solar simulator radiation over the temperature range of 1040 °C.32 The results showed there was no obvious effect on catalyst efficiency with only a slight increase in degradation rate at 40 °C. These widely discrepant results may be due to the different degradation pathways. Some researchers pointed out that the reactions associated with temperature, including adsorption, desorption, surface migration, and rearrangement, are not the key factors influencing the degradation rate and the apparent activation energy of photocatalytic reaction is very low. Therefore, the degradation of pollutants is not closely relative to temperature. However, a series of oxidationreduction reactions that followed the photoreactions, usually called “dark reactions”, are endothermic or exothermic processes and hence the effect of temperature can not be neglected, and our results might be belong to this situation. It is worthy to note that during CA degradation in solar/TiO2 process (initial CA concentration was 100 mg L1), the dissolved organic carbon (DOC) decreased from 56.25 to 21.17 mg L1, and at the same time, Cl increased from 2.16 to 14.24 mg L1. Several intermediate products during CA degradation were detected by GC-MS, such as phenol, hydroquinone, p-benzoquinone, and 4-chlorophenol, which was consistent with other research.7,33 Whereas the SUVA254 results, shown in Figure 5, indicated that intermediate aromatic compounds only slightly accumulated during the first 2 h, then further broke into hydrocarbon compounds which was in agreement with DOC decrease pattern. 3.2. Effects of Anions on CA Degradation in Solar/TiO2 and Solar/ZnO Processes. WWTP effluent always consists of a wide variety of inorganic anions such as Cl, SO42-, NO3, CO32-, and HCO3, etc., some of which have significant influence on organic compounds photodegradation. Neamt-u et al. reported that the degradation rates of nonylphenol and octylphenol were accelerated by the addition of 61 mg NO3 L1.49,50 The increase in photolytic degradation rate could be explained via reaction of the compounds with 3 OH radicals generated during the photolysis of nitrate. Trovo et al. investigated the photochemical transformation of sulfamethoxazole in different water matrices and pointed out that the presence of nitrate and humic acids in the solution could increase the efficiency of degradation, since these naturally occurring constituents could generate strong oxidant species such as 3 OH radicals and singlet oxygen under solar irradiation.51 In contrast, nitrate can also absorb light in the UV range and acts as an inner filter for the UV light.52 On the other hand, the presence of carbonate and bicarbonate can also strongly decrease the degradation efficiency by scavenging 3 OH radicals. 5388
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Figure 7. Effect of HA on CA degradation in solar/TiO2 and solar/ ZnO processes in summer and winter seasons (CA = 10 mg L1, TiO2 = 1.0 g L1, ZnO = 1.0 g L1, T = 35 °C (summer), T = 10 °C (winter)).
Figure 6. Effect of anions (NO3 and HCO3) on CA degradation in solar/TiO2 and solar/ZnO processes in summer and winter seasons (CA = 10 mg L1, TiO2 = 1.0 g L1, ZnO = 1.0 g L1, T = 35 °C (summer), T = 10 °C (winter)).
Gautam et al. reported that the presence of carbonates and bicarbonates significantly affected the degradation rate of 4-nitroaniline, while the presence of sulfates and chlorides had negligible effect on photocatalytic degradation rate of 4-nitroaniline.30 The same results were also reported by other authors in degradation of herbicide ametryn and endocrine disrupting chemical octylphenol.49,53 In this study, NO3 and HCO3 anions were selected due to their significant influence on organic compound degradation, and their effects on CA degradation in photocatalytic process in Milli-Q waters with two concentrations of 1.0 103 mol L1 (typical concentration in WWTP effluent) and 0.1 mol L1 (100 fold of the former value) in summer and winter seasons were investigated. The results are shown in Figure 6 and the experimental conditions are listed in Table 2. NO3 anion had a slightly inhibitive effect on CA degradation in solar/TiO2 process for these two concentrations in summer, while 0.1 mol L1 HCO3 significantly decreased the CA photodegradation rate (Figure 6a). Figure 6b shows the influence of anions in solar/TiO2 process in
winter. In comparison to the results in summer, the NO3 anion had no evident effect on CA degradation at low concentration, while 0.1 mol L1 NO3 and 1.0 103 mol L1 HCO3 had an obvious inhibitive effect on photocatalytic process, indicating that the high concentration of HCO3 still had serious negative influence on CA removal. In solar/ZnO process, only the high concentration of anions was investigated and their effects in both seasons were almost the same, namely, NO3 had no obvious influence while HCO3 had significant depression on CA photodegradation (Figure 6c). Furthermore, under anion existence, the degradation rate constants were decreased much more in winter than in summer in both solar/TiO2 and solar/ZnO systems (Table 2). 3.3. Effects of HA on CA Degradation in Solar/TiO2 and Solar/ZnO Processes. Some DOMs are usually contained in WWTPs effluent which exhibit marked recalcitrance to biological degradation and are chromophoric, particularly to UV radiation. It is reported that DOMs are very photoactive and contribute to the degradation of contaminants through the generation of a suite of reactive oxygen species (ROS), including the superoxide anion, hydroxyl radical, singlet oxygen, solvated electrons, reactive triplet states of natural organic matter, and organic alkoxy and peroxy radicals.6,54,55 For example, Neamt-u et al. found the degradation of octylphenol was faster in the two natural waters than in the lab tests using Milli-Q water due to oxidation reactions triggered by the reactive species such as singlet oxygen and hydroxyl radicals generated through photoprocesses involving excited state of DOM.49 In the present work, three concentrations (0.5, 5, 20 mg L1) of HA, corresponding to total organic carbon of 0.20, 1.80, and 8.63 mg L1 respectively, were added in Milli-Q water to study 5389
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Industrial & Engineering Chemistry Research their effect on CA removal in the photocatalytic process. The results are shown in Figure 7 and Table 2. The CA degradation was slightly increased by 0.5 mg L1 HA which was assumed to be triggered with the generation of ROS, and decreased with increasing HA addition to 5 and 20 mg L1 in solar/TiO2 process in summer (Figure 7a). The rate constants were 0.1098, 0.0659, and 0.0285 min1 in comparison to 0.1041 min1 in Milli-Q water, while it was decreased from 0.0437 (Milli-Q water) to 0.0042 min1 with 20 mg L1 HA addition in winter due to the weak light intensity and low temperature (Table 2). In addition, the inhibitive effect of 20 mg L1 HA on CA removal efficiency in solar/ZnO process was also different in two seasons, showing much less of CA degradation rate in winter than in summer. One possible explanation for these results was that light attenuation with increasing HA concentration reduced the number of photons available to interact with CA and the scavenging of ROS by reaction with HA, which may effectively lower the steady state concentration of ROS and compete with CA for ROS. Therefore, in this study increasing HA concentration acted mainly as inner filter and its addition resulted in a decrease of CA photodegradation rate compared to that measured in Milli-Q water.56 In fact, our results are consistent with other researchers.50,57 For example, Neamt-u et al. obtained the lower degradation rate of nonylphenol in the Lake Hohloh sample (high DOC content) than that in Milli-Q water.50 Leech et al. found the photodegradation rate of 17β-estradiol reached a threshold value at approximate 5.0 mg L1 DOC.57 3.4. Effects of H2O2 on CA Degradation in Solar/TiO2 and Solar/ZnO Processes. The undesired electronhole recombination is one practical problem in photocatalyst process which represents the major energy-wasting step thereby limiting the achievable quantum yield. Addition of H2O2 as irreversible electron acceptor is one strategy to inhibit electronhole recombination for enhancing formation of hydroxyl radicals.58 This has been demonstrated by Mendez-Arriaga et al. in evaluating the degradation of the emerging pharmaceutical contaminant ibuprofen in water by heterogeneous photocatalysis of TiO2 in three different solar pilot plants which found ibuprofen and TOC removal could be increased by addition of H2O2.35 However, the negative influence of H2O2 on compound oxidation was also reported. Wang and Hong compared the effect of three different types of oxidants (peroxide, persulphate, and periodate) and found that addition of oxidants along with UV and TiO2 had a negative effect on the oxidation efficiency, except for persulphate.59 The major reason was assumed to be the scavenging effect of H2O2 on the hydroxyl radicals. It is believed that there is an optimal dosage for H2O2 addition. Below the optimal dosage, the enhancement of degradation rate could be obtained which attributes to the production of reactive hydroxyl radical. When H2O2 presents at higher dosage, the degradation efficiency decreases. As the reactive 3 OH radicals and valence band holes may be consumed by H2O2 itself and, at the same time, radicalradical may recombine as a competitive reaction. In this work, we evaluated the effect of H2O2 addition on the photocatalytic degradation of CA under solar light in summer (T = 35 °C). The initial CA and catalysts concentration were 10 mg L1 and 1.0 g L1, respectively. The concentration of H2O2 was set from 50 to 150 mg L1 for solar/TiO2 process, while it was 100 mg L1 in solar/ZnO process for comparison. The results are shown in Figure 8 and Table 2. The degradation efficiency in solar/TiO2/H2O2 was similar to that in solar/TiO2 and was slightly enhanced with H2O2 addition, suggesting that H2O2 had
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Figure 8. CA degradation in solar/TiO2 and solar/ZnO processes with H2O2 addition in summer (CA = 10 mg L1, TiO2 = 1.0 g L1, ZnO = 1.0 g L1, T = 35 °C).
Figure 9. CA degradation in real WWTP effluent in solar/TiO2 and solar/ZnO processes (CA = 10 mg L1, TiO2 = 1.0 g L1, ZnO = 1.0 g L1, T = 35 °C (summer) or 10 °C (winter)).
no significant improvement on CA degradation in solar/TiO2 process. In solar/ZnO/H2O2 process, however, the H2O2 addition obviously inhibited the photocatalytic degradation and the rate constant decreased from 0.0411 to 0.0228 min1, indicating that H2O2 had a negative effect on CA degradation in solar/ZnO process under the conditions applied in this study. According to our previous work, the initial concentration of H2O2 100 mg L1 was the optimal dosage during CA degradation under UV/H2O2.50 Unfortunately, this result could not be applied to photocatalytic degradation under solar light which may result from the difference in wavelength and intensity of two light sources used. 3.5. CA Degradation in a Real WWTP Effluent in Solar/TiO2 and Solar/ZnO Processes. To confirm the behavior of CA degradation in treated wastewater, CA was spiked in a real WWTP effluent after filtration and the experimental results are shown in Figure 9 and Table 2. It was apparent that the season had a great effect on CA elimination which contributed from both solar light radiation intensity and exposed temperature, as explained in Section 3.1. On the other hand, degradation rates were observed to be distinctly lower in contrast to the CA photodegradation in Milli-Q water. The rate constants calculated from the pseudo-first-order kinetic model were 0.0061 (solar/ TiO2, 10 °C), 0.0119 (solar/TiO2, 35 °C), 0.0071 (solar/ZnO, 10 °C) and 0.0099 min1 (solar/ZnO, 35 °C) for WWTP effluent compared with 0.0437 (solar/TiO2, 10 °C), 0.1041 (solar/TiO2, 35 °C), 0.0122 (solar/ZnO, 10 °C), and 0.0411 min1 (solar/ZnO, 35 °C) for Milli-Q water, respectively. This may be explained by the presence of DOM and inorganic species acting 5390
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Industrial & Engineering Chemistry Research as hydroxyl radical scavengers, and directly affecting the efficiency of the photocatalysis process. The high content of Cl species in the effluent (177.5 mg L1) could generate less reactive species as 3 OH radicals can form chlorine radicals, such as chlorine radical (Cl 3 ) and dichloride anion radical (Cl2 3 ) which are less reactive than 3 OH radical.60 In addition, carbonate species (CO32- and HCO3), especially CO32-, compete with organic contaminants for hydroxyl radical reactions, and significantly decrease the degradation efficiencies of CA, in which carbonate ion is over 40 times as kinetically effective as bicarbonate ion in scavenging hydroxyl radicals.61 Furthermore, the different results between solar/TiO2 and solar/ZnO processes were minimized in WWTP effluent, which might be due to the above integrated influence. On the other hand, based on this lab-scale test, it is difficult so far to conduct cost analysis of this process for PPCPs removal. However, it might have great potential when applying solar/TiO2 and/or solar/ZnO process for several goals which include not only PPCPs removal, but also for other organic or persistent organic pollutants removal altogether.
4. CONCLUSIONS The degradation of CA by solar/TiO2 and solar/ZnO in MilliQ water and WWTP effluent was studied in summer and winter seasons. CA degradation could be simulated using the pseudofirst-order kinetic model. The reaction rates were accelerated by increasing TiO2 amount and the degradation rates were significantly different in summer and winter for both catalysts TiO2 and ZnO. The catalytical efficiency of TiO2 was better than that of ZnO and less affected by season variation (light intensity and temperature). NO3 anion had slightly inhibitive effect on CA degradation in solar/TiO2 process at two concentrations in summer. In comparison, the NO3 anion had no evident effect on CA degradation at low concentration, while 0.1 mol L1 NO3 and 1.0 103 mol L1 HCO3 had obvious inhibitive effect on photocatalytic process. In solar/ZnO process, NO3 had no obvious influence while HCO3 had significant depression on CA photodegradation at a high concentration in summer and winter seasons. The inhibition effect on CA removal was most significant when HA concentration increased to 20 mg L1. The degradation efficiency in solar/TiO2/H2O2 process was similar to that in solar/TiO2 and even decreased slightly with increasing H2O2 dosage. In solar/ZnO/H2O2 process, the H2O2 addition obviously inhibited the photocatalytic degradation. When applying photocatalytic process to WWTP effluent, degradation rates were observed to be distinctly lower in contrast to the CA photodegradation in Milli-Q water and temperature caused a great adverse effect on CA elimination. Although solar/TiO2 is efficient to remove CA, some problems still need to be clarified. For instance, the identification of CA degradation intermediates and determination of their degradation kinetics are crucial due to their potential presence in the treated effluent, and comprehensive understanding of their degradation pathways is necessary in order to determine the key steps in CA photodecomposition. In some cases, incomplete phototransformation and photodegradation might lead to more or less stable or toxic compounds. Therefore more research needs to be studied in our future work. ’ AUTHOR INFORMATION Corresponding Author
*Tel: þ86 21 64250709; fax: þ86 21 64252737; e-mail:
[email protected].
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’ ACKNOWLEDGMENT This study was supported by the Ministry of Environmental Protection Public Project (201109013), the National High Technology Research and Development Program (863 program) of China (2007AA06Z331), and Chinese Shanghai Leading Academic Discipline Project (B506). ’ REFERENCES (1) Jones, O. A. H.; Voulvoulis, N.; Lester, J. N. Aquatic Environmental Assessment of the Top 25 English Prescription Pharmaceuticals. Water Res. 2002, 36, 5013. (2) Lindqvist, N.; Tuhkanen, T.; Kronberg, L. Occurrence of Acidic Pharmaceuticals in Raw and Treated Sewages and in Receiving Waters. Water Res. 2005, 39, 2219. (3) Bound, J. P.; Voulvoulis, N. Predicted and Measured Concentration for Selected Pharmaceuticals in UK Rivers: Implications for Risk Assessment. Water Res. 2006, 40, 2885. (4) Bueno, M. J. M.; Ag€uera, A.; Gomez, M. J.; Hernando, M. D.; Garcia-Reyes, J. F.; Fernandez-Alba, A. R. Applications of Liquid Chromatography/Quadrupole-Linear Ion Trap Mass Spectrometry and Time-of-Flight Mass Spectrometry to Determination of Pharmaceuticals and Related Contaminants in Wastewater. Anal. Chem. 2007, 79, 9372. (5) Buser, H. R.; M€uller, M. D.; Teobald, N. Occurrence of Pharmaceutical Drug Clofibric Acid and the Herbicide Mecoprop in Various Swiss Lakes and in North Sea. Environ. Sci. Technol. 1998, 32, 188. (6) Heberer, T.; Schmidt-B€aumler, K.; Stan, H. J. Occurrence and Distribution of Organic Contaminants in Aquatic Systems in Berlin. Part I. Drug Residues and Other Polar Contaminants in Berlin Surface and Groundwater. Acta Hydrochim. Hydrobiol. 1998, 26, 272. (7) Doll, T. E.; Frimmel, F. H. Fate of Pharmaceuticals-Photodegradation by Simulated Solar UV-light. Chemosphere 2003, 52, 1757. (8) Ternes, T. A.; Meisenheimer, M.; Mcdowell, D.; Sacher, F.; Brauch, H. J.; Haist-Gulde, B.; Preuss, G.; Wilme, U.; Zulei-Seibert, N. Removal of Pharmaceuticals During Drinking Water Treatment. Environ. Sci. Technol. 2002, 36, 3855. (9) Andreozzi, R.; Raffaele, M.; Nichlas, P. Pharmaceuticals in STP Effluents and Their Solar Photodegradation in Aquatic Environment. Chemosphere 2003, 50, 1319. (10) Wiegel, S.; Aulinger, A.; Brockmeyer, R.; Harms, H.; L€offler, J.; Reincke, H.; Schmidt, R.; Stachel, B.; von T€umpling, W.; Wanke, A. Pharmaceuticals in the River Elbe and Its Tributaries. Chemosphere 2004, 57, 107. (11) Zorita, S.; Martensson, L.; Mathiasson, L. Occurrence and Removal of Pharmaceuticals in a Municipal Sewage Treatment System in the South of Sweden. Sci. Total Environ. 2009, 407, 2760. (12) Zwiener, C.; Frimmel, F. H. Short-Term Tests with a Pilot Sewage Plant and Biofilm Reactors for the Biological Degradation of the Pharmaceutical Compounds Clofibric Acid, Ibuprofen, and Diclofenac. Sci. Total Environ. 2003, 309, 201. (13) Borren, A. L.; Arnold, W. A.; Mcneill, K. Photodegradation of Pharmaceuticals in the Aquatic Environment: a Review. Aquat. Sci. 2003, 65, 320. (14) Packer, J. L.; Werner, J. J.; Latch, D. E.; McNeill, K.; Arnold, W. A. Photochemical Fate of Pharmaceuticals in the Environment: Naproxen, Diclofenac, Clofibric Acid, and Ibuprofen. Aquat. Sci. 2003, 65, 342. (15) Bartels, P.; von T€umpling, W., Jr. Solar Radiation Influence on the Decomposition Process of Diclofenac in Surface Waters. Sci. Total Environ. 2007, 371, 143. (16) Wingkler, M.; Lawrence, J. R.; Neu, T. R. Selective Degradation of Ibuprofen and Clofribric Acid in Two Model River Biofilm Systems. Water Res. 2001, 35, 3197. (17) Ferrari, B.; Paxeus, N.; Giudice, R. L.; Pollio, A.; Garric, J. Ecotoxicological Impact of Pharmaceuticals Found in Treated 5391
dx.doi.org/10.1021/ie1017145 |Ind. Eng. Chem. Res. 2011, 50, 5384–5393
Industrial & Engineering Chemistry Research Wastewaters: Study of Carbamazepine, Clofibric Acid and Diclofenac. Ecotoxicol. Environ. Saf. 2003, 55, 359. (18) Canesi, L.; Lorusso, L. C.; Ciacci, C.; Betti, M.; Regoli, F.; Poiana, G.; Gallo, G.; Marcomini, A. Effects of Blood Lipid Lowering Pharmaceuticals (Bezafibrate and Gemfibrozil) on Immune and Digestive Gland Functions of the Bivalve Molluse, Mytilus galloprovincialis. Chemosphere 2007, 69, 994. (19) Dordio, A. V.; Duarte, C.; Barreiros, M.; Palace Carvalho, A. J.; Pinto, A. P.; Costa, C. T. D. Toxicity and Removal Effciency of Pharmaceutical Metabolite Clofibric Acid by Typha spp.- Potential Use for Phytoremediation. Bioresour. Technol. 2009, 100, 1156. (20) Quintana, J. B.; Weiss, S.; Reemtsma, T. Pathways and Metabolites of Microbial Degradation of Selected Acidic Pharmaceutical and Their Occurrence in Municipal Wastewater Treated by a Membrane Bioreactor. Water Res. 2005, 39, 2654. (21) Abellan, M. N.; Bayarri, B.; Gimenez, J.; Costa, J. Photodegradation of Sulfamethoxazole in Aqueous Suspension of TiO2. Appl. Catal. B: Environ. 2007, 74, 233. (22) Perea-Estrada, L. A.; Malato, S.; Ag€uera, A.; Fernandez-Alba, A. R. Degradation of Dipyrone and its Main Intermediates by Solar AOPs - Identification of Intermediate Products and Toxicity Assessment. Catal. Today 2007, 129, 207. (23) Gomez, M. J.; Sirtori, C.; Mezcua, M.; Fernandez-Alba, A. R.; Ag€uera, A. Photodegradation Study of Three Dypirone Metabiolites in Various Water Systems: Identification and Toxicity of their Photodegradation Products. Water Res. 2008, 42, 2698. (24) Esplugas, S.; Bila, D. M.; Krause, L. G. T.; Dezotti, M. Ozonation and Advance Oxidation Technologies to Remove Endocrine Disrupting Chemicals (ECDs) and Pharmaceuticals and Personal Care Products (PPCPs) in Water Effluents. J. Hazard. Mater. 2007, 149, 631. (25) Klavarioti, M.; Mantsavinos, D.; Kassinos, D. Removal of Residual Pharmaceuticals from Aqueous Systems by Advanced Oxidation Processes. Environ. Int. 2009, 35, 402. (26) Malato, S.; Blanco, J.; Vidal, A.; Richter, C. Photocatalysis with Solar Energy at a Pilot-Plant Scale: an Overview. Appl. Catal. B: Environ. 2001, 37, 1. (27) Mendez-Arriaga, F.; Esplugas, S.; Gimenez, J. Photocatalytic Degradation of Non-steroidal Anti-inflammatory Drugs with TiO2 and Simulated Solar Irradiation. Water Res. 2008, 42, 585. (28) Torres, R.; Sarria, V.; Torres, W.; Peringer, P.; Pulgarin, C. Electrochemical Treatment of Industrial Wastewater Containing 5-amino-6-methyl-2-benzimidazolone: Toward an Electrochemical-Biological Coupling. Water Res. 2003, 37, 7. (29) Bhatkhnade, D. S.; Pangarkar, V. G.; Beenackers, A. A. C. M. Photocatalytic Degradation for Environmental Applications - a Review. J. Chem. Technol. Biotechnol. 2001, 77, 102. (30) Gautam, S.; Kamble, S. P.; Sawant, S. B.; Pangarkar, V. G. Photocatalytic Degradation of 4-nitroaniline using Solar and Artificial UV Radiation. Chem. Eng. J. 2005, 110, 129. (31) Oppenlander, T. Photochemical Purification of Water and Air; Wiley-VCH: Weinheim, 2003. (32) Hilal, H. S.; Al-Nour, G. Y. M.; Zyoud, A.; Helal, M. H.; Saadeddin, I. Pristine and Supported ZnO-based Catalysts for Phenazopyridine Degradation with Direct and Solar Light. Solid State Sci. 2010, 12, 578. (33) Doll, T. E.; Frimmel, F. H. Kinetic Study of Photocatalytic Degradation of Carbamazepine, Clofibric Acid, Iomeprol and Iopromide Assisted by Different TiO2 Materials - Determination of Intermediates and Reaction Pathways. Water Res. 2004, 38, 955. (34) Palominos, R. A.; Mondaca, M. A.; Giraldo, A.; Pe~ nuela, G.; Perez-Moya, M.; Mansilla, H. D. Photocatalytic Oxidation of the Antibiotic Tetracycline on TiO2 and ZnO Suspensions. Catal. Today 2009, 144, 100. (35) Mendez-Arriaga, F.; Ignacio Maldonado, M.; Gimenez, J.; Esplugas, S.; Malato, S. Abatement of Ibuprofen by Solar Photocatalysis Process: Enhancement and Scale up. Catal. Today 2009, 144, 112. (36) Shukla, P. R.; Wang, S. B.; Ming Ang, H.; Tade, M. O. Photocatalytic Oxidation of Phenolic Compounds using Zinc Oxide
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and Sulphate Radicals under Artificial Solar Light. Sep. Purif. Technol. 2010, 70, 338. (37) Sires, I.; Cabot, P. L.; Centellas, F.; Garrido, J. A.; Rodríguez, R. M.; Arias, C.; Brillas, E. Electrochemical Degradation of Clofibric Acid in Water by Anodic Oxidation Comparative Study with Platinum and Boron-doped Diamond Electrodes. Electrochim. Acta 2006, 52, 75. (38) Sires, I.; Arias, C.; Cabot, P. L.; Centellas, F.; Garrido, J. A.; Rodríguez, R. M.; Brillas, E. Degradation of Clofibric Acid in Acidic Aqueous Medium by Electro-Fenton and Photoelectron-Fenton. Chemosphere 2007, 66, 1660. (39) Andreozzi, R.; Caprio, V.; Marotta, R.; Radovnikovic, A. Ozonation and H2O2/UV Treatment of Clofibric Acid in Water: a Kinetic Investigation. J. Hazard. Mater. 2003, 103, 233. (40) Sirtori, C.; Ag€uera, A.; Gerniak, W.; Malato, S. Effect of Watermatrix Composition on Trimethoprim Solar Photodegradation Kinetics and Pathways. Water Res. 2010, 44, 2735. (41) Malato, S.; Blanco, J.; Richter, C.; Braun, B.; Maldonado, M. I. Enhancement of the Rate of Solar Photocatalytic Mineralization of Organic Pollutants by Inorganic Oxidizing Species. Appl. Catal. B: Environ. 1998, 17, 347. (42) Doong, R.; Chang, W. Photoassisted Titanium Dioxide Mediated Degradation of Organophosphorus Pesticides by Hydrogen Peroxide. J. Photochem. Photobiol. A: Chem 1997, 107, 239. (43) Agustina, T. E.; Ang, H. M.; Vareek, V. K. A Review of Synergistic Effect of Photocatalysis and Ozonation on Wastewater Treatment. J. Photochem. Photobiol. C: Photochem. Rev. 2005, 6, 264. (44) Miller, P. L.; Chin, Y. P. Indirect Photolysis Promoted by Natural and Engineered Wetland Water Constituents: Processes Leading to Alachlor Degradation. Environ. Sci. Technol. 2005, 39, 4454. (45) Halladja, S.; Amine-Khodja, A.; Halle, A. T.; Boulkamh, A.; Richard, C. Photolysis of Fluometuron in the Presence of Natural Water Constituents. Chemosphere 2007, 69, 1647. (46) Yin, J.; Tan, J. The observation and analysis of the surface solar ultraviolet vadiation in Shanghai. J. Trop. Meteorol. 2006, 22, 86 (in Chinese). (47) Augugliaro, V.; García-Lopez, E.; Loddo, V.; Malato-Rodríguez, S.; Maldonado, I.; Marc, G.; Molinari, R.; Palmisano, L. Degradation of Lincomycin in Aqueous Medium: Coupling of Solar Photocatalysis and Membrane Separation. Sol. Energy 2005, 79, 402. (48) Li, W. Z.; Lu, S. G.; Qiu, Z. F.; Lin, K. F. Clofibric Acid Degradation in UV254/H2O2 Process: Effect of Temperature. J. Hazard. Mater. 2010, 176, 1051. (49) Neamt-u, M.; Popa, D. M.; Frimmel, F. H. Simulated Solar UVirradiation of Endocrine Disrupting Chemical Octylphenol. J. Hazard. Mater. 2009, 164, 1561. (50) Neamt-u, M.; Frimmel, F. H. Photodegradation of Endocrine Disrupting Chemical Nonylphenol by Simulated Solar UV-irradiation. Sci. Total Environ. 2006, 369, 295. (51) Trovo, A. G.; Nogueira, R. F. P.; Ag€uera, A.; Sirtori, C.; Fernandez-Alba, A. R. Photodegradation of Sulfamethoxazole in Various Aqueous Media: Persistence, Toxicity and Photoproducts Assessment. Chemosphere 2009, 77, 1292. (52) Zepp, R. G.; Hoigne, J.; Bader, H. Nitrate-induced Photooxidation of Trace Organic Chemicals in Water. Environ. Sci. Technol. 1987, 21, 443. (53) Gao, N. Y.; Deng, Y.; Zhao, D. D. Ametryn Degradation in the Ultraviolet (UV) Irradiation/ Hydrogen Peroxide (H2O2) Treatment J. Hazard. Mater. 2009, 164, 640. (54) Canonica, S.; Freiburghaus, M. Electron-rich Phenols for Probing the Photochemical Reactivity of Freshwaters. Environ. Sci. Technol. 2001, 35, 690. (55) Chin, Y. P.; Miller, P. L.; Zeng, L.; Cawley, K.; Weavers, L. K. Photosensitized Degradation of Bisphenol A by Dissolved Organic Matter. Environ. Sci. Technol. 2004, 38, 5888. (56) Gao, H.; Zepp, R. G. Factors Influencing Photoreaction of Dissolved Organic Matter in a Coastal River of the Southeastern United States. Environ. Sci. Technol. 1998, 32, 2940. (57) Leech, D. M.; Snyder, M. T.; Wetzel, R. G. Natural Organic Matter and Sunlight Accelerate the Degradation of 17β-estradiol in Water. Sci. Total Environ. 2009, 407, 2087. 5392
dx.doi.org/10.1021/ie1017145 |Ind. Eng. Chem. Res. 2011, 50, 5384–5393
Industrial & Engineering Chemistry Research
ARTICLE
(58) Daneshvar, N.; Salari, D.; Khataee, A. R. Photocatalytic Degradation of Azo Dye Acid Red 14 in Water: Investigation of the Effect of Operational Parameters. J. Photochem. Photobiol. A: Chem 2003, 157, 111. (59) Wang, Y. H.; Hong, C. S. Effect of Hydrogen Peroxide, Periodate and Persulfate on Photocatalysis of 2-chlorobiphenyl in Aqueous TiO2 Suspensions. Water Res. 1999, 33, 2031. (60) De Laat, J.; Truong, L. G. Effects of Chloride Ions on the Iron (III) - Catalyzed Decomposition of Hydrogen Peroxide and on the Efficiency of the Fenton-like Oxidation Process. Appl. Catal., B 2006, 66, 137. (61) Klamerth, N.; Miranada, N.; Malato, S.; Ag€uera, A.; FernandezAlba, A. R.; Maldonado, M. I.; Coronado, J. M. Degradation of Emerging Contaminants at Low Concentrations in MWTPs Effluents with Mild Solar Photo-Fenton and TiO2. Catal. Today 2009, 144, 124.
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