Ultrasonics Sonochemistry 22 (2015) 182–187
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Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultson
Sulfamethoxazole degradation by ultrasound/ozone oxidation process in water: Kinetics, mechanisms, and pathways Wan-Qian Guo ⇑, Ren-Li Yin, Xian-Jiao Zhou, Juan-Shan Du, Hai-Ou Cao, Shan-Shan Yang, Nan-Qi Ren State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, PR China
a r t i c l e
i n f o
Article history: Received 19 May 2014 Received in revised form 7 July 2014 Accepted 8 July 2014 Available online 24 July 2014 Keywords: Sulfamethoxazole Ultrasound Ozone Kinetics Mechanisms Pathways
a b s t r a c t In this research, sulfamethoxazole (SMX) degradation was investigated using ultrasound (US), ozone (O3) and ultrasound/ozone oxidation process (UOOP). It was proved that ultrasound significantly enhanced SMX ozonation by assisting ozone in producing more hydroxyl radicals in UOOP. Ultrasound also made the rate constants improve by kinetics analysis. When ultrasound was added to the ozonation process, the reaction rate increased by 6–26% under different pH conditions. Moreover, main intermediates oxidized by US, O3 and UOOP system were identified. Although the main intermediates in ozonation and UOOP were similar, the introduction of ultrasound in UOOP had well improved the cleavage of S–N bond. In this condition SMX become much easier to be attacked, which led to enhanced SMX removal rate in UOOP compared to the other two examined processes. Finally, the SMX degradation pathways were proposed. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Contamination of natural waters by pharmaceuticals and personal care products are regarded as a rising environmental issue of global concern. Among various pharmaceutical compounds, antibiotics have been found in effluents of some sewage treatment plants as well as in surface water and groundwater in USA, UK, Canada, Germany and China [1–3]. Sulfamethoxazole (SMX) was a commonly used sulfonamide antibiotic and shared a large global consumption in animal food industry. In the year 2007, SMX is the 6th most pervasively prescribed antibiotic in Canada [4]. It is one of the most commonly used antibiotics in China as well [5]. The SMX can treat the coccidiosis, diarrhea and gastroenteritis, which are the most frequently outbreaking illnesses [6]. Due to insufficient control for the past, a great deal of SMX enters into the environment per annual. Although in recent years, pollution control of discharged antibiotics and their by-products have been drawing increasing attention by the government and researchers, SMX removal rate presents low between 20% and 30% in wastewater treatment plants [7]. As a result, large amount of untreated SMX residues have caused great pollution in the surface water and underground aquifers over years. Moreover, the antibiotic residuals can lead animals and people to evolve resistant genes, which would cause antibiotics finally disabled to the diseases. Therefore, ⇑ Corresponding author. Tel./fax: +86 451 86283008. E-mail address: [email protected] (W.-Q. Guo). http://dx.doi.org/10.1016/j.ultsonch.2014.07.008 1350-4177/Ó 2014 Elsevier B.V. All rights reserved.
it is necessary to increase the SMX removal rate by modified and optimal treatment techniques in water treatment process. Ultrasound (US), a promising and environmental friendly treatment technology for water and wastewater treatment, has raised a wide attention in environmental applications such as organic pollutants control [8–10], biological hydrogen production [11,12], and excess sludge reduction [13–15]. Recently, US has been frequently employed to degrade aquatic emergency micropollutants including sulfonamides and other pharmaceuticals, because the strong oxidizing hydroxyl radicals (OH) were generated by the collapse of bubbles cavitation in water environment. Naddeo et al. [16] evaluated the US process on pharmaceuticals degradation (diclofenac, amoxicillin, carbamazepine). It was found that sonication showed potential in pharmaceuticals removal, biodegradability increment and toxicity reduction. However, the effect of US itself still needs to improve and it is uneconomical to use US alone to remove pollutants completely. In order to achieve high efficient and economical removal of organic matters, ultrasound is a promising tool to combine with other traditional treatment technologies. In environmental protection area, ultrasound has been most widely used to combine with ozone for the removal of non-biodegradable organic contaminants [17–20]. Wang et al. [21] applied ozone combined with ultrasound for tetracycline (TC) degradation in a rectangular air-lift reactor, with high TC removal rate and increased biodegradability. However, the study only investigated the impact factors, mineralization and toxicity during SMX degradation. The degradation mechanism
W.-Q. Guo et al. / Ultrasonics Sonochemistry 22 (2015) 182–187
of pollutant was unclear, and the effect of ultrasound was not mentioned. Those subjects should not be ignored. In previous study, the ultrasonic-assisted ozone oxidation process (UAOOP) had been successfully employed for the degradation of triphenylmethane dye and the decolorization of malachite green (MG) that proposed a promising energy-saving way for refractory pollutant degradation [22,23]. The results showed that the UAOOP not only enhanced the MG wastewater decolorization rate but also saved reaction time and ozone dosage. Above all, ultrasound-combinedO3 process is an efficient wastewater treatment technology, which improved the biodegradability of wastewater, enhanced the dye decolorization, increased COD removal rate and reduced biological toxicity. Consequently, the trials on other organic matters degradation, taking SMX for example, by ultrasound/ozone oxidation process will be feasible and promising. Therefore, in this study, sulfamethoxazole (SMX) degradation was investigated using US, O3 and ultrasound/ozone oxidation process (UOOP). To clarify the ultrasound enhancement mechanism on SMX degradation, experiments were designed: (1) to clarify the effect of ultrasound for SMX ozonation, by the role of ultrasound played in the UOOP system; (2) to investigate the enhancement of ultrasound for SMX removal, by the means of determining the kinetic constants under different pH through the competitive kinetics; (3) to deduce the influence of ultrasound Table 1 Chemical structure and relevant data for SMX. Compound
Sulfamethoxazole (SMX)
Molecular Formula Structure
C10H11N3O3S
Formula weight (g mol-1) pKa1 pKa2 Protonated form
253.3 1.6 5.7
Deprotonated form
183
for SMX degradation pathways, by comparing the intermediates between O3 and UOOP system. 2. Materials and methods 2.1. Materials Sulfamethoxazole (C10H11N3O3S, analytical reagent, 99.0%) was purchased from Sigma and used as received without further purification. The structure and the relevant data of SMX were shown in Table 1. Fig. 1 showed the schematic illustration of experimental setup. 2.2. Methods SMX solutions were buffered by the addition of adequate quantities of Na2HPO4, H3PO4 and KH2PO4. Oxidation experiments were carried out in a 1.5L reactor with a continuous supply of O3. Ozone was generated using an ozone generator with gaseous flow meter (DHX-SS-1G, Jiujiu ozone, Harbin, China). Ultrasound (Shanghai Sonxi Ultrasonic Instrument, 20 kHz, 1200 W) was generated by an ultrasonic generator equipped with a titanium probe transducer 8 mm in diameter. Each run in the research was performed three times to ensure reproducibility. The gaseous product from the reactor was led to a terminator, where the remaining ozone was absorbed by KI solution. The hydroxyl radicals were quantified by fluorescence measurement (FS-6500) [24,25]. The OH was trapped by the direct addition reaction with terephthalic acid (TA). The initial concentrations of TA and NaOH were set at 2 mM and 5 mM respectively. It is emphasized that the apparent concentration of OH only reflected the portion of OH that has been trapped by the TA, and was a relative measure of the real concentration of OH in the water. The method applied in kinetics was based on the comparison reaction between the degradation rate of SMX and that of the reference compound. In this research, the reference compound was the fumaric acid (FA). To calculate the kinetic constant of the SMX in O3 alone process and UOOP system, buffered solutions containing both FA and SMX with concentration of 0.5 mM L1, which were mixed and the concentrations were tested. The runs were carried out at pH 5, 7 and 9. SMX concentration was determined by HPLC (Waters, C18, k = 270 nm). The mobile phase was a mixture of acetonitrile and 0.2% acetic acid with the volume ratio 40:60. A 10 lL volume was injected using the auto sampler. FA concentration was also determined by HPLC (k = 210 nm). The mobile phase was a mixture of acetonitrile and 0.5% phosphoric acid with the volume ratio 5:95.
Fig. 1. The schematic illustration of experimental setup, 1 oxygen cylinder; 2 ozonator; 3 aerator; 4 reactor; 5 Ultrasonic generator; 6 ultrasonic probe; 7 gas absorption equipments.
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The intermediates of SMX degradation were measured by HPLC–MS/MS (Finnigan, LCQ-DECA-XP-MAX), which was equipped with a Zorbax SB-C18 HPLC column (150 mm 2.1 mm 3.5 lm, Agilent). The mobile phase was a mixture of acetonitrile and acetic acid. A 10 lL volume was injected using the auto sampler. In MS analysis, the ionization for MS was operated at APCI mode with negative ion mode. Concentrations of intermediates were measured using the same HPLC coupled with a UV detector set at wavelength of 220 nm. Solvent A and B were acetonitrile and water with 0.01% formic acid, respectively, at a flow rate of 0.4 mL min-1. The gradient expressed as the concentration of solvent A was as follows: 0–50 min, a linear increase from 10% to 95%; 50–55 min, held at 95% A; 55–65 min, a linear decrease from 95% to 10%; 65–75 min, held at 10% A [26]. 3. Results and discussion 3.1. SMX degradation by US process To reveal the roles of ultrasound in SMX removal, experiments were carried out at ultrasound power density 600 W L1, while the initial SMX concentration 100 mg L1, pH 7 and ozone dose 3 g h1. Ultrasonic energy using the calorimetric method was described [27]. The temperature rise was 1 K min1 and the mass of water was 1200 g. So the ultrasonic power dissipated to the liquid was 83 W, about 15% of the input power, which represented about 85% of the input energy was absorbed properly for acoustic energy. It can be seen from Fig. 2 that the SMX was just about 3% removal in the presence of ultrasound alone. Then we applied the fluorescent to quantify the amount of OH. It was found that the OH in water was 0.07, 0.11 and 0.15 lmol/L, when the pH was 5, 7, and 9 respectively. It showed the production of OH was limited in the solution when US was used alone, resulting in low SMX
removal rate. Hence, it was necessary to combine ultrasound with other technologies to improve the removal rate. 3.2. Effect of ultrasound on OH enhancement The ultrasound combined with ozone was adopted for SMX degradation in this study. And the ultrasound did enhance the SMX ozonation process, seen Fig. 2. To illustrate the role of ultrasound played in SMX degradation, the amount of OH was also determined. The results were listed in Table 2. It can be seen that the concentration of OH increased with the access of ultrasound. Similar results were reported in the literature [19]. In another word, the ultrasound did enhance ozone to produce more radical that was the core for pollutant degradation, which resulted in higher oxidation rate, shorter reaction time, less ozone input and lower costs for SMX degradation. However, the sum of concentration of OH for ultrasound and ozone-alone system was less than the UOOP system. Therefore, these results indicated that a synergistic effect on producing OH existed in the combination of ultrasound and ozone bubbles. And the synergistic effect on reaction constant was observed by the combined use of ultrasound and ozone bubbles in the Zheng’s research [28]. With the access of ultrasound, the cavitation was imported. The formation, growth and subsequent collapse of micro-bubbles or cavities occurred in extremely small timeframes (milliseconds) while releasing large magnitudes of energy. The energy can be used to promote ozone to produce more radicals to improve ozone oxidation rate. Moreover, according to the acoustic streaming method [19,20], ultrasound built turbulent flow conditions and accelerated the mass transfer of ozone. In addition, it also indicated that the amount of OH increased with pH increment in the ozone alone system as well as the UOOP system, which indicated that the higher pH resulted in larger oxidation rate. On one hand, the effect of ultrasound enhanced the ozone to produce more radicals was unquestionable; on the other hand, the degree and mechanism of promotion process was unclear. Therefore, the further research was carried out from the kinetic analysis. 3.3. Effect of ultrasound on kinetic enhancement In order to confirm the increase of the reaction rate with the assistant of ultrasound, competitive kinetics experiments were designed and operated to determine the reaction constants of O3 alone process and UOOP. Considering that the kinetic of both SMX and FA follow the equations:
d½SMX ¼ kSMX ½O3 ½SMX dt
ð1Þ
d½FA ¼ kFA ½O3 ½FA dt
ð2Þ
Dividing Eq. (1) by Eq. (2) and solving the resulting integration, Eq. (3) is obtained: Fig. 2. The SMX degradation curve under US-alone, ozone-alone and UOOP system.
Table 2 The reaction constants and amount of OH under various conditions. pH
Ratio kFA/kSMX
kFA
kSMX
Ratio kSMX
5 7 9
0.6028 0.3234 0.3908
1 105 1.5 105 –
1.66 105 4.64 105 –
1.2636 1.0699 1.0589
(O3+US)/kSMX
kSMX
(O3+US)
2.1 105 4.96 105 –
[OH]USlmol L1
[OH]O3lmol L1
[OH](US+O3) lmol L1
0.07 0.11 0.15
13.5 17.0 20.2
15.2 18.1 21.1
kFA: ozonation rate for FA; kSMX: ozonation rate for SMX; kSMX(O3+US): oxidation rate for SMX in UOOP system; [OH]US: the concentration of OH in US-alone system; [OH]O3: the concentration of OH in ozone-alone system; [OH](US+O3): the concentration of OH in UOOP system.
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ln
½FA kFA ½SMX ¼ ln ½FA0 kSMX ½SMX0
ð3Þ
To calculate the ratio kFA/kSMX, the Nigerian logarithm of the normalized concentration of both compounds was plotted thus obtaining a straight line (Fig. 3). As the kFA for the studied pH values are collected from the literature [6,29,30], the kSMX can be calculated. In Table 2, calculated values of kSMX are presented along with the values of the ratio kFA/kSMX recorded from the experimental data and the kFA found in literature. It can be seen from Table 2 that the ultrasound improved ozone oxidation rate. On one hand, the ultrasound increased ozone oxidation rate by 26% when pH was 5. For the ozone direct-oxidation was predominant under acidic conditions, the access of ultrasound can result in turbulent flow and cut the ozone bubble into smaller bubbles, which promoted the ozone molecular diffusion in water and increased the contact area between O3 and SMX, so that the oxidation rate raised. On the other hand, under neutral and alkali conditions, the assistant effect of ultrasound increased the oxidation rate by 6–7%. The ozone indirect-oxidation (OH oxidation) was predominant under this condition, and the ultrasound enhanced the ozone to produce more OH to improve the oxidation rate, see Table 2. In addition, when pH > 5.7(pKa2), the protonated form of SMX was the predominant form, which structure was higher reactivity to the oxidant [6,31]. Above all, the ultrasound did enhance the SMX ozonation process but in different ozone oxidation ways including direct and indirect oxidation mechanism. Furthermore, the oxidation rate was adversely proportion to t1/2, which meant the increase of kinetic rate led to shorter reaction time. Therefore, it reduced the ozone input and saved operation costs. The SMX degradation curve indicated that SMX degradation reaction followed a pseudo-first-order kinetic model under the experimental operating conditions (both O3 and UOOP). The fitting curve was shown in Fig. 4. It can be seen that the ozone oxidation for SMX degradation reaction fit the kinetic model well. However, in the UOOP system, it showed a clear deviation from the fitting curve. As the intermediates accumulation with the access of ultrasound affected the degradation of parent SMX molecular to make the rate lower than theoretical values. And the rate became higher than the theoretical values prolonging with the time due to SMX and its intermediates degrading gradually. Thus, it was assumed that the ultrasound influenced the SMX degradation on the intermediates (species or quantity) and pathways.
Fig. 3. Nigerian logarithm of the concentration of FA and SMX.
185
Fig. 4. The fitting curve of SMX degradation under ozone-alone and UOOP system.
3.4. Influence of ultrasound on SMX degradation pathways To investigate the influence of ultrasound made in SMX degradation mechanism, the intermediates were identified precisely by HPLC–ESI-MS–MS. The intermediates ions of SMX, which were produced by US, O3 and UOOP oxidations, were showed in Fig. 5. The peak of m/z 252 was the deprotonated ion of SMX. Following the precursor ion, only two products of m/z 156 and 97 were observed in US oxidation system. While, in the O3 and UOOP oxidation system, other five products of m/z 298, 282, 268, 226, and 196 were detected. It can be seen from the ion m/z figure that there was little difference in the kind of the main intermediates. However, due to the US process degraded the SMX just in one way, the amount of the by-products 3-Amino-5-methylisoxazole (AMI) was tested at the same reaction time between O3 and UOOP system. The amount of AMI in UOOP system was about three times to the O3 system. Therefore, although the main intermediates in ozone-alone process and UOOP were similar, it was found the ultrasound introduction in UOOP has well improved the cleavage of S–N bond, so that SMX become easier to be attacked and its removal rate was improved, compared to ozone-alone process. Based on the results obtained in this work and literature [32,33], major fragments corresponded to the fragmentation of byproducts through the loss of H and the addition of O. So the structures of the possible intermediates and their major fragments could be determined. The identified intermediates in this study have provided firm evidences for the occurrence of various degradation reactions. As be seen from Fig. 5, the only pathway by US process occurred at the S–N bond of SMX, and the products were AMI (P-97) and p-amino benzene sulfonic acid (P-156). Moreover, comparison of the ion fragments between O3-alone process and UOOP showed little difference for SMX degradation pathways with the same ion m/z ratio. As was shown in Fig. 6, the similar degradation reactions included: (i) hydroxylation of the benzene ring (P-268); (ii) oxidation of the amine group at the benzene ring (P-282a); (iii) oxidation of the methyl group at the isoxazole ring (P-284b); (iv) oxidation of the amine group at the benzene ring and addition of the double bond at the isoxazole ring (P-298); (v) S–N bond cleavage (P-98, P-156); and (vi) oxidation of the amino group at the benzene ring and bond cleavage of the isoxazole ring (P-226). Based on the above pathways analysis, the oxidation position mainly occurred at the S–N bond, benzene ring and amino group. This is because ozone selectively attacked activated aromatic rings or double bonds, which are both present in SMX.
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Fig. 5. The SMX intermediates ions under US-alone, ozone-alone and UOOP system.
Fig. 6. Probable degradation pathway of SMX in UOOP system.
In fact, the amino group (NH2) is an electron-donating group, activating the aromatic ring by increasing its electronic density. Furthermore, aromatic compounds, such as SMX, have a high delocalization of electrons and exhibit more reactivity towards ozone. In Alexandra’s study [33], it demonstrated one pathway of SMX to turn to small organic acid. However, in this study, other main pathways were listed to give a more clear understanding for
SMX degradation. The ultrasound enhancement mechanism was also identified. That is, although there was little difference in the main intermediates between ozone-alone process and UOOP, it was found the ultrasound introduction in UOOP has well improved the cleavage of S–N bond, so that SMX become easier to be attacked, which resulted in a higher SMX removal rate, shorter reaction time, less ozone input and lower operation costs in UOOP.
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4. Conclusions Ultrasound was proved to be an effective method to facilitate and enhance SMX ozonation in water, with the evidence of assisting ozone to produce more hydroxyl radicals. The kinetic constants also demonstrated that SMX degradation rate was improved with the access of ultrasound. Although the main intermediates in O3 and UOOP were similar, ultrasound introduction in UOOP showed superior for effective S–N bond cleavage in SMX, which was vital for the overall SMX degradation rate. Thus, higher SMX removal rate in UOOP was achieved compared to the other two tested processes in this research. Main intermediates were examined and the degradation pathways were deduced.
Acknowledgements This work was financially supported by National Nature Science Foundation of China (51121062 and 51008105). The authors also gratefully acknowledge the financial support by State Key Laboratory of Urban Water Resource and Environment (2014TS06), the Department of Education Fund for Doctoral Tutor (20122302110054), the Harbin Institute of Technology Fund for young top-notch talent teachers (AUGA5710052514) and the Academician Workstation Construction in Guangdong Province (2012B090500018).
References [1] K. Kummerer, Antibiotics in the aquatic environment–a review–part I, Chemosphere 75 (2009) 417–434. [2] K. Kummerer, Antibiotics in the aquatic environment–a review–part II, Chemosphere 75 (2009) 435–441. [3] P. Verlicchi, M. Al Aukidy, E. Zambello, Occurrence of pharmaceutical compounds in urban wastewater: removal, mass load and environmental risk after a secondary treatment–a review, Sci. Total Environ. 429 (2012) 123–155. [4] D. Nasuhoglu, V. Yargeau, D. Berk, Photo-removal of sulfamethoxazole (SMX) by photolytic and photocatalytic processes in a batch reactor under UV-C radiation (lambdamax=254 nm), J. Hazard. Mater. 186 (2011) 67–75. [5] H.W. Leung, T.B. Minh, M.B. Murphy, J.C. Lam, M.K. So, M. Martin, P.K. Lam, B.J. Richardson, Distribution, fate and risk assessment of antibiotics in sewage treatment plants in Hong Kong, South China, Environ. Int. 42 (2012) 1–9. [6] R.F. Dantas, S. Contreras, C. Sans, S. Esplugas, Sulfamethoxazole abatement by means of ozonation, J. Hazard. Mater. 150 (2008) 790–794. [7] X. Liu, T. Garoma, Z. Chen, L. Wang, Y. Wu, SMX degradation by ozonation and UV radiation: a kinetic study, Chemosphere 87 (2012) 1134–1140. [8] Y.S. Ladola, S. Chowdhury, S.B. Roy, A.B. Pandit, Application of cavitation in uranium leaching, Desalin. Water Treat. 52 (2014) 407–414. [9] S. Mallakpour, M. Madani, S. Roshandel, Applications of ultrasound for modification of zinc oxide and fabrication of optically active poly(amideimide)/zinc oxide bionanocomposites, Des. Monomers Polym. 17 (2014) 364– 371. [10] G. Saccani, M. Bernasconi, M. Antonelli, Optimization of low energy sonication treatment for granular activated carbon colonizing biomass assessment, Environ. Technol. 35 (2014) 851–858. [11] W.-Q. Guo, J. Ding, G.-L. Cao, N.-Q. Ren, F.-Y. Cui, Treatability study of using low frequency ultrasonic pretreatment to augment continuous biohydrogen production, Int. J. Hydrogen Energy 36 (2011) 14180–14185.
187
[12] S.S. Yang, W.Q. Guo, G.L. Cao, H.S. Zheng, N.Q. Ren, Simultaneous waste activated sludge disintegration and biological hydrogen production using an ozone/ultrasound pretreatment, Bioresour. Technol. 124 (2012) 347–354. [13] J. He, T. Wan, G. Zhang, J. Yang, Ultrasonic reduction of excess sludge from activated sludge system: energy efficiency improvement via operation optimization, Ultrason. Sonochem. 18 (2011) 99–103. [14] S.S. Yang, W.Q. Guo, Z.H. Meng, X.J. Zhou, X.C. Feng, H.S. Zheng, B. Liu, N.Q. Ren, Y.S. Cui, Characterizing the fluorescent products of waste activated sludge in dissolved organic matter following ultrasound assisted ozone pretreatments, Bioresour. Technol. 131 (2013) 560–563. [15] W.Q. Guo, S.S. Yang, W.S. Xiang, X.J. Wang, N.Q. Ren, Minimization of excess sludge production by in-situ activated sludge treatment processes – a comprehensive review, Biotechnol. Adv. 31 (2013) 1386–1396. [16] V. Naddeo, S. Meric, D. Kassinos, V. Belgiorno, M. Guida, Fate of pharmaceuticals in contaminated urban wastewater effluent under ultrasonic irradiation, Water Res. 43 (2009) 4019–4027. [17] G. Ji, B. Zhang, Y. Wu, Combined ultrasound/ozone degradation of carbazole in APG1214 surfactant solution, J. Hazard. Mater. 225–226 (2012) 1–7. [18] P.C. Sangave, P.R. Gogate, A.B. Pandit, Ultrasound and ozone assisted biological degradation of thermally pretreated and anaerobically pretreated distillery wastewater, Chemosphere 68 (2007) 42–50. [19] P.R. Gogate, S. Mededovic-Thagard, D. McGuire, G. Chapas, J. Blackmon, R. Cathey, Hybrid reactor based on combined cavitation and ozonation: from concept to practical reality, Ultrason. Sonochem. 21 (2014) 590–598. [20] L. Zhao, W. Ma, J. Ma, J. Yang, G. Wen, Z. Sun, Characteristic mechanism of ceramic honeycomb catalytic ozonation enhanced by ultrasound with triple frequencies for the degradation of nitrobenzene in aqueous solution, Ultrason. Sonochem. 21 (2014) 104–112. [21] Y. Wang, H. Zhang, L. Chen, S. Wang, D. Zhang, Ozonation combined with ultrasound for the degradation of tetracycline in a rectangular air-lift reactor, Sep. Purif. Technol. 84 (2012) 138–146. [22] X.J. Zhou, W.Q. Guo, S.S. Yang, N.Q. Ren, A rapid and low energy consumption method to decolorize the high concentration triphenylmethane dye wastewater: operational parameters optimization for the ultrasonic-assisted ozone oxidation process, Bioresour. Technol. 105 (2012) 40–47. [23] X.J. Zhou, W.Q. Guo, S.S. Yang, H.S. Zheng, N.Q. Ren, Ultrasonic-assisted ozone oxidation process of triphenylmethane dye degradation: evidence for the promotion effects of ultrasonic on malachite green decolorization and degradation mechanism, Bioresour. Technol. 128 (2013) 827–830. [24] N. Milan-Segovia, Y. Wang, F.S. Cannon, R.C. Voigt, J.C. Furness, Comparison of hydroxyl radical generation for various advanced oxidation combinations as applied to foundries, Ozone Sci. Eng. 29 (2007) 461–471. [25] I. Hua, M.R. Hoffmann, Optimization of ultrasonic irradiation as an advanced oxidation technology, Environ. Sci. Technol. 31 (1997) 2237–2243. [26] S. Ding, J. Niu, Y. Bao, L. Hu, Evidence of superoxide radical contribution to demineralization of sulfamethoxazole by visible-light-driven Bi2O3/ Bi2O2CO3/Sr6Bi2O9 photocatalyst, J. Hazard. Mater. 262 (2013) 812–818. [27] S. Koda, T. Kimura, T. Kondo, H. Mitome, A standard method to calibrate sonochemical efficiency of an individual reaction system, Ultrason. Sonochem. 10 (2003) 149–156. [28] Z. Xu, K. Mochida, T. Naito, K. Yasuda, Effects of operational conditions on 1,4dioxane degradation by combined use of ultrasound and ozone microbubbles, Jpn. J. Appl. Phys. 51 (2012) 07GD08. [29] H. Benbelkacem, S. Mathe, H. Debellefontaine, Taking mass transfer limitation into account during ozonation of pollutants reacting fairly quickly, Water Sci. Technol. 49 (2004) 25–30. [30] H.B.J. Hoigné, Rate constants of reactions of ozone with organic and inorganic compounds in water II, Water Res. 17 (1983) 185–194. [31] L. Hou, H. Zhang, L. Wang, L. Chen, Y. Xiong, X. Xue, Removal of sulfamethoxazole from aqueous solution by sono-ozonation in the presence of a magnetic catalyst, Sep. Purif. Technol. 117 (2013) 46–52. [32] M. Gomez-Ramos Mdel, M. Mezcua, A. Aguera, A.R. Fernandez-Alba, S. Gonzalo, A. Rodriguez, R. Rosal, Chemical and toxicological evolution of the antibiotic sulfamethoxazole under ozone treatment in water solution, J. Hazard. Mater. 192 (2011) 18–25. [33] A.G. Goncalves, J.J. Orfao, M.F. Pereira, Catalytic ozonation of sulphamethoxazole in the presence of carbon materials: catalytic performance and reaction pathways, J. Hazard. Mater. 239–240 (2012) 167– 174.
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Ultrasonics Sonochemistry journal homepage: www.elsevier.com/locate/ultson
Sulfamethoxazole degradation by ultrasound/ozone oxidation process in water: Kinetics, mechanisms, and pathways Wan-Qian Guo ⇑, Ren-Li Yin, Xian-Jiao Zhou, Juan-Shan Du, Hai-Ou Cao, Shan-Shan Yang, Nan-Qi Ren State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, PR China
a r t i c l e
i n f o
Article history: Received 19 May 2014 Received in revised form 7 July 2014 Accepted 8 July 2014 Available online 24 July 2014 Keywords: Sulfamethoxazole Ultrasound Ozone Kinetics Mechanisms Pathways
a b s t r a c t In this research, sulfamethoxazole (SMX) degradation was investigated using ultrasound (US), ozone (O3) and ultrasound/ozone oxidation process (UOOP). It was proved that ultrasound significantly enhanced SMX ozonation by assisting ozone in producing more hydroxyl radicals in UOOP. Ultrasound also made the rate constants improve by kinetics analysis. When ultrasound was added to the ozonation process, the reaction rate increased by 6–26% under different pH conditions. Moreover, main intermediates oxidized by US, O3 and UOOP system were identified. Although the main intermediates in ozonation and UOOP were similar, the introduction of ultrasound in UOOP had well improved the cleavage of S–N bond. In this condition SMX become much easier to be attacked, which led to enhanced SMX removal rate in UOOP compared to the other two examined processes. Finally, the SMX degradation pathways were proposed. Ó 2014 Elsevier B.V. All rights reserved.
1. Introduction Contamination of natural waters by pharmaceuticals and personal care products are regarded as a rising environmental issue of global concern. Among various pharmaceutical compounds, antibiotics have been found in effluents of some sewage treatment plants as well as in surface water and groundwater in USA, UK, Canada, Germany and China [1–3]. Sulfamethoxazole (SMX) was a commonly used sulfonamide antibiotic and shared a large global consumption in animal food industry. In the year 2007, SMX is the 6th most pervasively prescribed antibiotic in Canada [4]. It is one of the most commonly used antibiotics in China as well [5]. The SMX can treat the coccidiosis, diarrhea and gastroenteritis, which are the most frequently outbreaking illnesses [6]. Due to insufficient control for the past, a great deal of SMX enters into the environment per annual. Although in recent years, pollution control of discharged antibiotics and their by-products have been drawing increasing attention by the government and researchers, SMX removal rate presents low between 20% and 30% in wastewater treatment plants [7]. As a result, large amount of untreated SMX residues have caused great pollution in the surface water and underground aquifers over years. Moreover, the antibiotic residuals can lead animals and people to evolve resistant genes, which would cause antibiotics finally disabled to the diseases. Therefore, ⇑ Corresponding author. Tel./fax: +86 451 86283008. E-mail address: [email protected] (W.-Q. Guo). http://dx.doi.org/10.1016/j.ultsonch.2014.07.008 1350-4177/Ó 2014 Elsevier B.V. All rights reserved.
it is necessary to increase the SMX removal rate by modified and optimal treatment techniques in water treatment process. Ultrasound (US), a promising and environmental friendly treatment technology for water and wastewater treatment, has raised a wide attention in environmental applications such as organic pollutants control [8–10], biological hydrogen production [11,12], and excess sludge reduction [13–15]. Recently, US has been frequently employed to degrade aquatic emergency micropollutants including sulfonamides and other pharmaceuticals, because the strong oxidizing hydroxyl radicals (OH) were generated by the collapse of bubbles cavitation in water environment. Naddeo et al. [16] evaluated the US process on pharmaceuticals degradation (diclofenac, amoxicillin, carbamazepine). It was found that sonication showed potential in pharmaceuticals removal, biodegradability increment and toxicity reduction. However, the effect of US itself still needs to improve and it is uneconomical to use US alone to remove pollutants completely. In order to achieve high efficient and economical removal of organic matters, ultrasound is a promising tool to combine with other traditional treatment technologies. In environmental protection area, ultrasound has been most widely used to combine with ozone for the removal of non-biodegradable organic contaminants [17–20]. Wang et al. [21] applied ozone combined with ultrasound for tetracycline (TC) degradation in a rectangular air-lift reactor, with high TC removal rate and increased biodegradability. However, the study only investigated the impact factors, mineralization and toxicity during SMX degradation. The degradation mechanism
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of pollutant was unclear, and the effect of ultrasound was not mentioned. Those subjects should not be ignored. In previous study, the ultrasonic-assisted ozone oxidation process (UAOOP) had been successfully employed for the degradation of triphenylmethane dye and the decolorization of malachite green (MG) that proposed a promising energy-saving way for refractory pollutant degradation [22,23]. The results showed that the UAOOP not only enhanced the MG wastewater decolorization rate but also saved reaction time and ozone dosage. Above all, ultrasound-combinedO3 process is an efficient wastewater treatment technology, which improved the biodegradability of wastewater, enhanced the dye decolorization, increased COD removal rate and reduced biological toxicity. Consequently, the trials on other organic matters degradation, taking SMX for example, by ultrasound/ozone oxidation process will be feasible and promising. Therefore, in this study, sulfamethoxazole (SMX) degradation was investigated using US, O3 and ultrasound/ozone oxidation process (UOOP). To clarify the ultrasound enhancement mechanism on SMX degradation, experiments were designed: (1) to clarify the effect of ultrasound for SMX ozonation, by the role of ultrasound played in the UOOP system; (2) to investigate the enhancement of ultrasound for SMX removal, by the means of determining the kinetic constants under different pH through the competitive kinetics; (3) to deduce the influence of ultrasound Table 1 Chemical structure and relevant data for SMX. Compound
Sulfamethoxazole (SMX)
Molecular Formula Structure
C10H11N3O3S
Formula weight (g mol-1) pKa1 pKa2 Protonated form
253.3 1.6 5.7
Deprotonated form
183
for SMX degradation pathways, by comparing the intermediates between O3 and UOOP system. 2. Materials and methods 2.1. Materials Sulfamethoxazole (C10H11N3O3S, analytical reagent, 99.0%) was purchased from Sigma and used as received without further purification. The structure and the relevant data of SMX were shown in Table 1. Fig. 1 showed the schematic illustration of experimental setup. 2.2. Methods SMX solutions were buffered by the addition of adequate quantities of Na2HPO4, H3PO4 and KH2PO4. Oxidation experiments were carried out in a 1.5L reactor with a continuous supply of O3. Ozone was generated using an ozone generator with gaseous flow meter (DHX-SS-1G, Jiujiu ozone, Harbin, China). Ultrasound (Shanghai Sonxi Ultrasonic Instrument, 20 kHz, 1200 W) was generated by an ultrasonic generator equipped with a titanium probe transducer 8 mm in diameter. Each run in the research was performed three times to ensure reproducibility. The gaseous product from the reactor was led to a terminator, where the remaining ozone was absorbed by KI solution. The hydroxyl radicals were quantified by fluorescence measurement (FS-6500) [24,25]. The OH was trapped by the direct addition reaction with terephthalic acid (TA). The initial concentrations of TA and NaOH were set at 2 mM and 5 mM respectively. It is emphasized that the apparent concentration of OH only reflected the portion of OH that has been trapped by the TA, and was a relative measure of the real concentration of OH in the water. The method applied in kinetics was based on the comparison reaction between the degradation rate of SMX and that of the reference compound. In this research, the reference compound was the fumaric acid (FA). To calculate the kinetic constant of the SMX in O3 alone process and UOOP system, buffered solutions containing both FA and SMX with concentration of 0.5 mM L1, which were mixed and the concentrations were tested. The runs were carried out at pH 5, 7 and 9. SMX concentration was determined by HPLC (Waters, C18, k = 270 nm). The mobile phase was a mixture of acetonitrile and 0.2% acetic acid with the volume ratio 40:60. A 10 lL volume was injected using the auto sampler. FA concentration was also determined by HPLC (k = 210 nm). The mobile phase was a mixture of acetonitrile and 0.5% phosphoric acid with the volume ratio 5:95.
Fig. 1. The schematic illustration of experimental setup, 1 oxygen cylinder; 2 ozonator; 3 aerator; 4 reactor; 5 Ultrasonic generator; 6 ultrasonic probe; 7 gas absorption equipments.
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The intermediates of SMX degradation were measured by HPLC–MS/MS (Finnigan, LCQ-DECA-XP-MAX), which was equipped with a Zorbax SB-C18 HPLC column (150 mm 2.1 mm 3.5 lm, Agilent). The mobile phase was a mixture of acetonitrile and acetic acid. A 10 lL volume was injected using the auto sampler. In MS analysis, the ionization for MS was operated at APCI mode with negative ion mode. Concentrations of intermediates were measured using the same HPLC coupled with a UV detector set at wavelength of 220 nm. Solvent A and B were acetonitrile and water with 0.01% formic acid, respectively, at a flow rate of 0.4 mL min-1. The gradient expressed as the concentration of solvent A was as follows: 0–50 min, a linear increase from 10% to 95%; 50–55 min, held at 95% A; 55–65 min, a linear decrease from 95% to 10%; 65–75 min, held at 10% A [26]. 3. Results and discussion 3.1. SMX degradation by US process To reveal the roles of ultrasound in SMX removal, experiments were carried out at ultrasound power density 600 W L1, while the initial SMX concentration 100 mg L1, pH 7 and ozone dose 3 g h1. Ultrasonic energy using the calorimetric method was described [27]. The temperature rise was 1 K min1 and the mass of water was 1200 g. So the ultrasonic power dissipated to the liquid was 83 W, about 15% of the input power, which represented about 85% of the input energy was absorbed properly for acoustic energy. It can be seen from Fig. 2 that the SMX was just about 3% removal in the presence of ultrasound alone. Then we applied the fluorescent to quantify the amount of OH. It was found that the OH in water was 0.07, 0.11 and 0.15 lmol/L, when the pH was 5, 7, and 9 respectively. It showed the production of OH was limited in the solution when US was used alone, resulting in low SMX
removal rate. Hence, it was necessary to combine ultrasound with other technologies to improve the removal rate. 3.2. Effect of ultrasound on OH enhancement The ultrasound combined with ozone was adopted for SMX degradation in this study. And the ultrasound did enhance the SMX ozonation process, seen Fig. 2. To illustrate the role of ultrasound played in SMX degradation, the amount of OH was also determined. The results were listed in Table 2. It can be seen that the concentration of OH increased with the access of ultrasound. Similar results were reported in the literature [19]. In another word, the ultrasound did enhance ozone to produce more radical that was the core for pollutant degradation, which resulted in higher oxidation rate, shorter reaction time, less ozone input and lower costs for SMX degradation. However, the sum of concentration of OH for ultrasound and ozone-alone system was less than the UOOP system. Therefore, these results indicated that a synergistic effect on producing OH existed in the combination of ultrasound and ozone bubbles. And the synergistic effect on reaction constant was observed by the combined use of ultrasound and ozone bubbles in the Zheng’s research [28]. With the access of ultrasound, the cavitation was imported. The formation, growth and subsequent collapse of micro-bubbles or cavities occurred in extremely small timeframes (milliseconds) while releasing large magnitudes of energy. The energy can be used to promote ozone to produce more radicals to improve ozone oxidation rate. Moreover, according to the acoustic streaming method [19,20], ultrasound built turbulent flow conditions and accelerated the mass transfer of ozone. In addition, it also indicated that the amount of OH increased with pH increment in the ozone alone system as well as the UOOP system, which indicated that the higher pH resulted in larger oxidation rate. On one hand, the effect of ultrasound enhanced the ozone to produce more radicals was unquestionable; on the other hand, the degree and mechanism of promotion process was unclear. Therefore, the further research was carried out from the kinetic analysis. 3.3. Effect of ultrasound on kinetic enhancement In order to confirm the increase of the reaction rate with the assistant of ultrasound, competitive kinetics experiments were designed and operated to determine the reaction constants of O3 alone process and UOOP. Considering that the kinetic of both SMX and FA follow the equations:
d½SMX ¼ kSMX ½O3 ½SMX dt
ð1Þ
d½FA ¼ kFA ½O3 ½FA dt
ð2Þ
Dividing Eq. (1) by Eq. (2) and solving the resulting integration, Eq. (3) is obtained: Fig. 2. The SMX degradation curve under US-alone, ozone-alone and UOOP system.
Table 2 The reaction constants and amount of OH under various conditions. pH
Ratio kFA/kSMX
kFA
kSMX
Ratio kSMX
5 7 9
0.6028 0.3234 0.3908
1 105 1.5 105 –
1.66 105 4.64 105 –
1.2636 1.0699 1.0589
(O3+US)/kSMX
kSMX
(O3+US)
2.1 105 4.96 105 –
[OH]USlmol L1
[OH]O3lmol L1
[OH](US+O3) lmol L1
0.07 0.11 0.15
13.5 17.0 20.2
15.2 18.1 21.1
kFA: ozonation rate for FA; kSMX: ozonation rate for SMX; kSMX(O3+US): oxidation rate for SMX in UOOP system; [OH]US: the concentration of OH in US-alone system; [OH]O3: the concentration of OH in ozone-alone system; [OH](US+O3): the concentration of OH in UOOP system.
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ln
½FA kFA ½SMX ¼ ln ½FA0 kSMX ½SMX0
ð3Þ
To calculate the ratio kFA/kSMX, the Nigerian logarithm of the normalized concentration of both compounds was plotted thus obtaining a straight line (Fig. 3). As the kFA for the studied pH values are collected from the literature [6,29,30], the kSMX can be calculated. In Table 2, calculated values of kSMX are presented along with the values of the ratio kFA/kSMX recorded from the experimental data and the kFA found in literature. It can be seen from Table 2 that the ultrasound improved ozone oxidation rate. On one hand, the ultrasound increased ozone oxidation rate by 26% when pH was 5. For the ozone direct-oxidation was predominant under acidic conditions, the access of ultrasound can result in turbulent flow and cut the ozone bubble into smaller bubbles, which promoted the ozone molecular diffusion in water and increased the contact area between O3 and SMX, so that the oxidation rate raised. On the other hand, under neutral and alkali conditions, the assistant effect of ultrasound increased the oxidation rate by 6–7%. The ozone indirect-oxidation (OH oxidation) was predominant under this condition, and the ultrasound enhanced the ozone to produce more OH to improve the oxidation rate, see Table 2. In addition, when pH > 5.7(pKa2), the protonated form of SMX was the predominant form, which structure was higher reactivity to the oxidant [6,31]. Above all, the ultrasound did enhance the SMX ozonation process but in different ozone oxidation ways including direct and indirect oxidation mechanism. Furthermore, the oxidation rate was adversely proportion to t1/2, which meant the increase of kinetic rate led to shorter reaction time. Therefore, it reduced the ozone input and saved operation costs. The SMX degradation curve indicated that SMX degradation reaction followed a pseudo-first-order kinetic model under the experimental operating conditions (both O3 and UOOP). The fitting curve was shown in Fig. 4. It can be seen that the ozone oxidation for SMX degradation reaction fit the kinetic model well. However, in the UOOP system, it showed a clear deviation from the fitting curve. As the intermediates accumulation with the access of ultrasound affected the degradation of parent SMX molecular to make the rate lower than theoretical values. And the rate became higher than the theoretical values prolonging with the time due to SMX and its intermediates degrading gradually. Thus, it was assumed that the ultrasound influenced the SMX degradation on the intermediates (species or quantity) and pathways.
Fig. 3. Nigerian logarithm of the concentration of FA and SMX.
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Fig. 4. The fitting curve of SMX degradation under ozone-alone and UOOP system.
3.4. Influence of ultrasound on SMX degradation pathways To investigate the influence of ultrasound made in SMX degradation mechanism, the intermediates were identified precisely by HPLC–ESI-MS–MS. The intermediates ions of SMX, which were produced by US, O3 and UOOP oxidations, were showed in Fig. 5. The peak of m/z 252 was the deprotonated ion of SMX. Following the precursor ion, only two products of m/z 156 and 97 were observed in US oxidation system. While, in the O3 and UOOP oxidation system, other five products of m/z 298, 282, 268, 226, and 196 were detected. It can be seen from the ion m/z figure that there was little difference in the kind of the main intermediates. However, due to the US process degraded the SMX just in one way, the amount of the by-products 3-Amino-5-methylisoxazole (AMI) was tested at the same reaction time between O3 and UOOP system. The amount of AMI in UOOP system was about three times to the O3 system. Therefore, although the main intermediates in ozone-alone process and UOOP were similar, it was found the ultrasound introduction in UOOP has well improved the cleavage of S–N bond, so that SMX become easier to be attacked and its removal rate was improved, compared to ozone-alone process. Based on the results obtained in this work and literature [32,33], major fragments corresponded to the fragmentation of byproducts through the loss of H and the addition of O. So the structures of the possible intermediates and their major fragments could be determined. The identified intermediates in this study have provided firm evidences for the occurrence of various degradation reactions. As be seen from Fig. 5, the only pathway by US process occurred at the S–N bond of SMX, and the products were AMI (P-97) and p-amino benzene sulfonic acid (P-156). Moreover, comparison of the ion fragments between O3-alone process and UOOP showed little difference for SMX degradation pathways with the same ion m/z ratio. As was shown in Fig. 6, the similar degradation reactions included: (i) hydroxylation of the benzene ring (P-268); (ii) oxidation of the amine group at the benzene ring (P-282a); (iii) oxidation of the methyl group at the isoxazole ring (P-284b); (iv) oxidation of the amine group at the benzene ring and addition of the double bond at the isoxazole ring (P-298); (v) S–N bond cleavage (P-98, P-156); and (vi) oxidation of the amino group at the benzene ring and bond cleavage of the isoxazole ring (P-226). Based on the above pathways analysis, the oxidation position mainly occurred at the S–N bond, benzene ring and amino group. This is because ozone selectively attacked activated aromatic rings or double bonds, which are both present in SMX.
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Fig. 5. The SMX intermediates ions under US-alone, ozone-alone and UOOP system.
Fig. 6. Probable degradation pathway of SMX in UOOP system.
In fact, the amino group (NH2) is an electron-donating group, activating the aromatic ring by increasing its electronic density. Furthermore, aromatic compounds, such as SMX, have a high delocalization of electrons and exhibit more reactivity towards ozone. In Alexandra’s study [33], it demonstrated one pathway of SMX to turn to small organic acid. However, in this study, other main pathways were listed to give a more clear understanding for
SMX degradation. The ultrasound enhancement mechanism was also identified. That is, although there was little difference in the main intermediates between ozone-alone process and UOOP, it was found the ultrasound introduction in UOOP has well improved the cleavage of S–N bond, so that SMX become easier to be attacked, which resulted in a higher SMX removal rate, shorter reaction time, less ozone input and lower operation costs in UOOP.
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4. Conclusions Ultrasound was proved to be an effective method to facilitate and enhance SMX ozonation in water, with the evidence of assisting ozone to produce more hydroxyl radicals. The kinetic constants also demonstrated that SMX degradation rate was improved with the access of ultrasound. Although the main intermediates in O3 and UOOP were similar, ultrasound introduction in UOOP showed superior for effective S–N bond cleavage in SMX, which was vital for the overall SMX degradation rate. Thus, higher SMX removal rate in UOOP was achieved compared to the other two tested processes in this research. Main intermediates were examined and the degradation pathways were deduced.
Acknowledgements This work was financially supported by National Nature Science Foundation of China (51121062 and 51008105). The authors also gratefully acknowledge the financial support by State Key Laboratory of Urban Water Resource and Environment (2014TS06), the Department of Education Fund for Doctoral Tutor (20122302110054), the Harbin Institute of Technology Fund for young top-notch talent teachers (AUGA5710052514) and the Academician Workstation Construction in Guangdong Province (2012B090500018).
References [1] K. Kummerer, Antibiotics in the aquatic environment–a review–part I, Chemosphere 75 (2009) 417–434. [2] K. Kummerer, Antibiotics in the aquatic environment–a review–part II, Chemosphere 75 (2009) 435–441. [3] P. Verlicchi, M. Al Aukidy, E. Zambello, Occurrence of pharmaceutical compounds in urban wastewater: removal, mass load and environmental risk after a secondary treatment–a review, Sci. Total Environ. 429 (2012) 123–155. [4] D. Nasuhoglu, V. Yargeau, D. Berk, Photo-removal of sulfamethoxazole (SMX) by photolytic and photocatalytic processes in a batch reactor under UV-C radiation (lambdamax=254 nm), J. Hazard. Mater. 186 (2011) 67–75. [5] H.W. Leung, T.B. Minh, M.B. Murphy, J.C. Lam, M.K. So, M. Martin, P.K. Lam, B.J. Richardson, Distribution, fate and risk assessment of antibiotics in sewage treatment plants in Hong Kong, South China, Environ. Int. 42 (2012) 1–9. [6] R.F. Dantas, S. Contreras, C. Sans, S. Esplugas, Sulfamethoxazole abatement by means of ozonation, J. Hazard. Mater. 150 (2008) 790–794. [7] X. Liu, T. Garoma, Z. Chen, L. Wang, Y. Wu, SMX degradation by ozonation and UV radiation: a kinetic study, Chemosphere 87 (2012) 1134–1140. [8] Y.S. Ladola, S. Chowdhury, S.B. Roy, A.B. Pandit, Application of cavitation in uranium leaching, Desalin. Water Treat. 52 (2014) 407–414. [9] S. Mallakpour, M. Madani, S. Roshandel, Applications of ultrasound for modification of zinc oxide and fabrication of optically active poly(amideimide)/zinc oxide bionanocomposites, Des. Monomers Polym. 17 (2014) 364– 371. [10] G. Saccani, M. Bernasconi, M. Antonelli, Optimization of low energy sonication treatment for granular activated carbon colonizing biomass assessment, Environ. Technol. 35 (2014) 851–858. [11] W.-Q. Guo, J. Ding, G.-L. Cao, N.-Q. Ren, F.-Y. Cui, Treatability study of using low frequency ultrasonic pretreatment to augment continuous biohydrogen production, Int. J. Hydrogen Energy 36 (2011) 14180–14185.
187
[12] S.S. Yang, W.Q. Guo, G.L. Cao, H.S. Zheng, N.Q. Ren, Simultaneous waste activated sludge disintegration and biological hydrogen production using an ozone/ultrasound pretreatment, Bioresour. Technol. 124 (2012) 347–354. [13] J. He, T. Wan, G. Zhang, J. Yang, Ultrasonic reduction of excess sludge from activated sludge system: energy efficiency improvement via operation optimization, Ultrason. Sonochem. 18 (2011) 99–103. [14] S.S. Yang, W.Q. Guo, Z.H. Meng, X.J. Zhou, X.C. Feng, H.S. Zheng, B. Liu, N.Q. Ren, Y.S. Cui, Characterizing the fluorescent products of waste activated sludge in dissolved organic matter following ultrasound assisted ozone pretreatments, Bioresour. Technol. 131 (2013) 560–563. [15] W.Q. Guo, S.S. Yang, W.S. Xiang, X.J. Wang, N.Q. Ren, Minimization of excess sludge production by in-situ activated sludge treatment processes – a comprehensive review, Biotechnol. Adv. 31 (2013) 1386–1396. [16] V. Naddeo, S. Meric, D. Kassinos, V. Belgiorno, M. Guida, Fate of pharmaceuticals in contaminated urban wastewater effluent under ultrasonic irradiation, Water Res. 43 (2009) 4019–4027. [17] G. Ji, B. Zhang, Y. Wu, Combined ultrasound/ozone degradation of carbazole in APG1214 surfactant solution, J. Hazard. Mater. 225–226 (2012) 1–7. [18] P.C. Sangave, P.R. Gogate, A.B. Pandit, Ultrasound and ozone assisted biological degradation of thermally pretreated and anaerobically pretreated distillery wastewater, Chemosphere 68 (2007) 42–50. [19] P.R. Gogate, S. Mededovic-Thagard, D. McGuire, G. Chapas, J. Blackmon, R. Cathey, Hybrid reactor based on combined cavitation and ozonation: from concept to practical reality, Ultrason. Sonochem. 21 (2014) 590–598. [20] L. Zhao, W. Ma, J. Ma, J. Yang, G. Wen, Z. Sun, Characteristic mechanism of ceramic honeycomb catalytic ozonation enhanced by ultrasound with triple frequencies for the degradation of nitrobenzene in aqueous solution, Ultrason. Sonochem. 21 (2014) 104–112. [21] Y. Wang, H. Zhang, L. Chen, S. Wang, D. Zhang, Ozonation combined with ultrasound for the degradation of tetracycline in a rectangular air-lift reactor, Sep. Purif. Technol. 84 (2012) 138–146. [22] X.J. Zhou, W.Q. Guo, S.S. Yang, N.Q. Ren, A rapid and low energy consumption method to decolorize the high concentration triphenylmethane dye wastewater: operational parameters optimization for the ultrasonic-assisted ozone oxidation process, Bioresour. Technol. 105 (2012) 40–47. [23] X.J. Zhou, W.Q. Guo, S.S. Yang, H.S. Zheng, N.Q. Ren, Ultrasonic-assisted ozone oxidation process of triphenylmethane dye degradation: evidence for the promotion effects of ultrasonic on malachite green decolorization and degradation mechanism, Bioresour. Technol. 128 (2013) 827–830. [24] N. Milan-Segovia, Y. Wang, F.S. Cannon, R.C. Voigt, J.C. Furness, Comparison of hydroxyl radical generation for various advanced oxidation combinations as applied to foundries, Ozone Sci. Eng. 29 (2007) 461–471. [25] I. Hua, M.R. Hoffmann, Optimization of ultrasonic irradiation as an advanced oxidation technology, Environ. Sci. Technol. 31 (1997) 2237–2243. [26] S. Ding, J. Niu, Y. Bao, L. Hu, Evidence of superoxide radical contribution to demineralization of sulfamethoxazole by visible-light-driven Bi2O3/ Bi2O2CO3/Sr6Bi2O9 photocatalyst, J. Hazard. Mater. 262 (2013) 812–818. [27] S. Koda, T. Kimura, T. Kondo, H. Mitome, A standard method to calibrate sonochemical efficiency of an individual reaction system, Ultrason. Sonochem. 10 (2003) 149–156. [28] Z. Xu, K. Mochida, T. Naito, K. Yasuda, Effects of operational conditions on 1,4dioxane degradation by combined use of ultrasound and ozone microbubbles, Jpn. J. Appl. Phys. 51 (2012) 07GD08. [29] H. Benbelkacem, S. Mathe, H. Debellefontaine, Taking mass transfer limitation into account during ozonation of pollutants reacting fairly quickly, Water Sci. Technol. 49 (2004) 25–30. [30] H.B.J. Hoigné, Rate constants of reactions of ozone with organic and inorganic compounds in water II, Water Res. 17 (1983) 185–194. [31] L. Hou, H. Zhang, L. Wang, L. Chen, Y. Xiong, X. Xue, Removal of sulfamethoxazole from aqueous solution by sono-ozonation in the presence of a magnetic catalyst, Sep. Purif. Technol. 117 (2013) 46–52. [32] M. Gomez-Ramos Mdel, M. Mezcua, A. Aguera, A.R. Fernandez-Alba, S. Gonzalo, A. Rodriguez, R. Rosal, Chemical and toxicological evolution of the antibiotic sulfamethoxazole under ozone treatment in water solution, J. Hazard. Mater. 192 (2011) 18–25. [33] A.G. Goncalves, J.J. Orfao, M.F. Pereira, Catalytic ozonation of sulphamethoxazole in the presence of carbon materials: catalytic performance and reaction pathways, J. Hazard. Mater. 239–240 (2012) 167– 174.
