Performance evaluation of waste iron shavings (Fe0) for catalytic ozonation in removal of sulfamethoxazole from municipal wastewater treatment plant effluent in a batch mode pilot plant

Journal Pre-proofs Performance evaluation of waste iron shavings (Fe0) for catalytic ozonation in removal of sulfamethoxazole from municipal wastewater treatment plant effluent in a batch mode pilot plant Najmeh Shahmahdi, Reza Dehghanzadeh, Hassan Aslani, Sepideh Bakht Shokouhi PII: DOI: Reference:

S1385-8947(19)32505-7 https://doi.org/10.1016/j.cej.2019.123093 CEJ 123093

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Chemical Engineering Journal

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22 July 2019 23 September 2019 6 October 2019

Please cite this article as: N. Shahmahdi, R. Dehghanzadeh, H. Aslani, S. Bakht Shokouhi, Performance evaluation of waste iron shavings (Fe0) for catalytic ozonation in removal of sulfamethoxazole from municipal wastewater treatment plant effluent in a batch mode pilot plant, Chemical Engineering Journal (2019), doi: https://doi.org/ 10.1016/j.cej.2019.123093

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Performance evaluation of waste iron shavings (Fe0) for catalytic ozonation in removal of sulfamethoxazole from municipal wastewater treatment plant effluent in a batch mode pilot plant Najmeh Shahmahdi 1, Reza Dehghanzadeh1, 2, Hassan Aslani 1, Sepideh Bakht Shokouhi 1, 3 1 Health

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and Environment Research Center, Tabriz University of Medical Sciences, Tabriz, Iran.

Department of Environmental Health Engineering, Tabriz University of Medical Sciences,

Tabriz, Iran 3

Student Research Committee, Tabriz University of Medical Sciences, Tabriz, Iran

Corresponding author: Reza Dehghanzadeh, Department of Environmental Health Engineering, Tabriz



University of Medical Sciences, Golgasht St., Azadi Ave., Tabriz, Iran; Tel: +98 9144184167; Fax: +98 41 33344731; E-mail: [email protected] 1

Abstract Feasibility of iron shavings (Fe0) as a low-cost catalyst was evaluated in catalytic ozonation for degradation of sulfamethoxazole (SMX). The characterization of the catalyst studied by a variety of techniques like scanning electron microscopy with energy dispersive spectroscopy (SEMEDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR). Experimental results indicated a first order kinetics for Fe-based catalytic ozonation (O3/Fe0) and soleozonation (O3) in the removal of SMX with slightly greater rate constant for O3. In the both processes, the removal efficiency of SMX was more than 99% at the first 5 min. Average COD removal efficiency in the O3/Fe0 process was about 1.36 times greater than O3. The main intermediates detected by LC-MS/MS were 3-Amino-5-methylisoxazole, benzoquinone, sulfanilic acid, hydroxyl-SMX and nitroso SMX. The mineralization of SMX significantly increased concentration of sulfate and nitrate. Fe0 enhanced ozone utilization and transfer rate. Fe0 is not requiring any preparation before use and could be a promising catalyst for practical advanced wastewater treatment. Keywords: catalytic ozonation; iron scraps; zero-valent iron (ZVI); sulfamethoxazole; antibiotic; wastewater 1. Introduction Pharmaceutically active chemicals (PhACs) such as antibiotics have extensively been detected in many surface and ground waters, which mostly originate from effluents discharged by municipal wastewater treatment plants [1, 2]. An extensive number of investigations have shown that conventional wastewater and drinking water treatment plants can not completely remove many

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PhACs [3]. PhACs are suspected endocrine disruptors and potentially pose hazards for human being and aquatic and soil organisms. Antibiotics are an important group of PhACs widely used in medicine which leads development of antibiotic resistant bacteria in human body and environment. Then, highly effective processes are demanded for removal of PhACs from wastewater. As a matter of fact, a variety of novel chemical, physical and biological processes have been assessed, but, among them advanced oxidation processes (AOPs) have demonstrated to be most effective in removal of PhACs and refractory organic contaminants from wastewater [4].Sulfamethoxazole (SMX), is one of the most widely used sulfonamide type antibiotic for bacterial infections such as urinary tract infections, bronchitis, and prostatitis and is effective against both gram negative and positive bacteria [5]. SMX known as a recalcitrant compound to biodegradation and hydrolysis and frequently detected in the environment [6-8]. Amino group (NH2-) existing in SMX exhibits a high nucleophilic nature and increasing the electronic density of the aromatic ring in SMX that reacts and promotes the reactivity of SMX with ozone. However, many studies reported only a slight mineralization efficiency of SMX by soleozonation [9-11]. Overall, direct reaction of contaminants with ozone mainly converts them to other organics whereas hydroxyl radicals (HO•) can achieve good mineralization efficiency. In industrial scale of wastewater treatment it is worthless to transform contaminants without mineralization. Recently, catalytic based ozonation processes have been proposed as an effective technology for degradation and mineralization of organic pollutants. Gao et al. reported that mineralization of SMX increased from 27% by sole-ozonation to 80% with catalytic ozonation

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using composite iron-manganese silicate oxide [9]. Beside of increasing in degradation and mineralization efficiencies of the organic compounds, catalytic ozonation reduces operational time and cost [12]. The presence of catalyst in the ozonation process efficiently improves the ozone utilization efficiency and accelerates the transformation of ozone into HO• [13]. Commonly, catalytic based ozonation processes are classified into homogeneous and heterogeneous kinds. In homogeneous mode, transition metal ions are used as the catalyst whereas in heterogeneous form solid catalysts are spent for ozone decomposition. However, dissolution and remaining of metal ions in the homogeneous catalytic ozonation limited its wide application [14]. Then, more researches have concentrated on the heterogeneous catalytic ozonation processes by numerous catalysts for removal of various target organic pollutants from water or wastewater at different experimental conditions. The main catalysts used in heterogeneous catalytic ozonation include, metal oxides (MnO2, TiO2, Al2O3, iron oxides and bimetallic oxides), metals (Cu, Fe, Mn, Co, Ru) or metal oxides on supports (activated carbon, alumina, titania, silica, ceria and etc.)

and carbon materials [15]. Nonetheless, although

continuous research to introduce new solid catalysts are being accomplished, the mechanism of the heterogeneous catalyst for the ozonation process is still indistinct. Understanding heterogeneous catalytic ozonation mechanism is imperative to its widespread application at industrial scales. Fe-based catalysts have been widely used in catalytic ozonation of water and wastewater [13, 16-18]. Recently, zero-valent iron (ZVI) has attracted significant attention as a promising catalyst in the ozonation process due to easy preparation, superior catalytic performance and the abundance of iron in nature [13]. Fe-based catalytic ozonation has lower operating cost as well as the market price of iron shavings (~200 USD/t) is much lower than that of other form of Fe 4

based catalysts such as Fe2O3 and Fe3O4 (~800 USD/t) and ZVI (~15000 USD/t). The prices were obtained from www.alibaba.com. Thiruvenkatachari et al. (2007) reported that Fe2(SO4)3based catalytic ozonation seems to show a satisfactory organic degradation performance and to be economically more viable choice for the degradation of terephthalic acid than other AOP systems [19]. In addition, iron has some advantages including, less toxic than the other metals. Iron shavings can be oxidized to various iron oxides, which efficiently decompose ozone. In previous studies, Fe0 was used in removal of metronidazole [20], p-nitrophenol [21], bentazon [22], oxalic acid [23], and vinyl chloride from aqueous solutions [24]. Generally, various forms of iron i.e. Fe2+, Fe3+, Fe0 in the form of iron shavings and powder, Fe2O3, Fe3O4, doped and supported Fe0 have afforded acceptable results in catalytic ozonation of dye [25], phenolic compound [26], carboxylic acid [27], treatment of oil refining wastewater [28] and antibiotic production wastewater [25]. However, some of these catalysts are artificially synthesized by complicated or expensive chemical or physical methods, or the iron is doped on a support at little quantities that quickly consumed. Then, at industrial scale of wastewater treatment it is very costly to synthesize and add the new catalyst continuously. Whereas, Fe0 in the form of waste iron shavings could be economically obtained from machinery industries. Martins et al. (2014) tested low cost catalyst of iron shavings with ozone for olive mill effluent treatment [29]. Wu et al. (2016) indicated that recycled waste iron shavings could promote removal of organic pollutants with ozone from effluent of a biologically treated dyeing wastewater [17]. Pan et al. (2012) reported promoted role of ZVI as a heterogeneous catalyst for ozonation of disperse blue E-4R [30]. Ji et al. (2018) demonstrated that catalytic ozonation by ZVI powder is an effective advanced treatment for removal of refractory toxic compounds from effluent of a bio-treated antibiotic production wastewater [18]. However, performance of iron shavings based catalytic

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ozonation (O3/Fe0) has rarely been studied in removal of antibiotics in the practical real wastewater environment with coexistence of complex and various organic compounds. Still, more studies should be made to elucidate the mechanisms involving ozone decomposition and HO• production, degradation kinetics and the intermediate by-products by waste iron shavings. Also, the stability and reusability of the iron shavings are required to be further investigated in long time operation. Based on the above considerations, the objectives of this study were (1) to investigate the suitability of using inexpensive waste iron shavings as a catalyst to enhance the performance of ozone in removal of SMX from real wastewater, (2) to test impact of various operating parameters including initial pH, reaction time and impact of wastewater matrix on the rate of SMX degradation, (3) to determine the degradation kinetics of SMX by O3/Fe0and soleozonation (O3), (4) to rate ozone utilization efficiency in both processes and (5) to illustrate degradation pathways of SMX and detection of intermediate by-products in both processes, (6) to characterize iron shavings by X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FTIR) and scanning electron microscope with an energy dispersive X-ray spectroscope (SEM-EDS). In this study the catalyst was used as a packed bed which needed no separation operation. The findings could help optimize O3/Fe0 units reasonably and develop and scale up the technology. 2. Material and Methods 2.1. Chemicals SMX (C10H11N3O3S, MW: 253.27 g mol-1) was purchased in solid state (CAS number: 723-46-6, purity>98%) from a local pharmaceutical production factory (Tehrandaru Co., Tehran, Iran). 6

Waste iron shavings (Fe0) was obtained from a metal machinery factory. HPLC-grade acetonitrile and water were provided by Merck. For measuring of ozone in gas phase and aqueous samples, potassium dihydrogen phosphate (KH2PO4), anhydrous disodium hydrogen phosphate (Na2HPO4) and potassium iodide (KI) were provided from Darmstadt, Germany. Sodium thiosulfate (Na2S2O3) and Starch indicator were provided from Sigma Aldrich Co., Germany and Fluka Co., Switzerland, respectively. 2.2. Characteristic of wastewater Wastewater samples were obtained from effluent of a conventional activated sludge process of municipal wastewater treatment plant (Tabriz, Iran). The main characterizations of the effluent was in the range of pH=7.4±0.3, total organic carbon (TOC) =46.5±0.50 mg L-1, total suspended solids=23±5 mg L-1 and chemical oxygen demand (COD) =122±10 mg L-1. Background SMX concentration in effluent samples were analyzed and the concentrations were found lower than the limit of detection (LOD) value (11.49 µg L-1). So, the effluent samples were spiked with 20 mg L-1 of SMX to evaluate the objective of the study. 2.3. Characterization of Fe0 catalyst The particle size and morphology of the resulting Fe0 scraps were determined using a field emission scanning electron microscope (FE-SEM SU8030, Hitachi Ltd., Japan) with an energy dispersive X-ray spectroscope (EDS EX-250, Horiba Ltd., Japan). XRD (D8 Advance X, Bruker) analyses were conducted with Cu Ka operated at 40 kV and 30 mA; continuous scanned from 30˚ to 70˚, 2h were collected with a step size of 0.01 and a count time of 0.5 s per step.

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Fourier transform infrared (FTIR) spectrum of the catalyst was recorded using FTIR (Bruker, Vertex 70) before and after ozonation. 2.4. Experimental setup All experiments were performed in a pilot plant with batch mode at ambient temperature (25 ± 2°C). Fig. 1 displays schematic diagram of the ozonation setup. The pilot system was consisted two glass columns each with an inner diameter of 4.6 and a total height of 250 cm. One column was filled with 750 g waste iron shavings (Fe0) for O3/Fe0. Fe0 was pretreated in order to remove possible impurities and oils. First, it was immersed in 1 mol L-1 NaOH for 24 h and, afterwards rinsed by 0.1 mol L-1 HCL for 1 h and finally, washed several times with distilled water and dried in an oven at 120°C. Ozone was produced using a laboratory ozone generator (Jahad Research Center, Iran) fed by an oxygen generator (Type CFS-1, New Life Elite oxygen concentrator, AirSep corporation company, USA). Ozone gas was bubbled at constant flow rate of 1.5 L min-1 into the wastewater through a diffuser located at the bottom of the columns and the concentration of ozone was about 178.8 mg L-1 throughout all the ozonation experiments. The off-gas was absorbed by a 2% KI solution. At predetermined time intervals, wastewater samples were withdrawn from the sampling port. After settling of samples for 60 min, the supernatants were filtered with a 0.45 µm membrane filter to remove any particles and analyzed for COD, nitrate, nitrite, sulfate and pH. After each run, iron shavings rinsed with water to remove the remaining wastewater and dried by passing air to prepare for the next run. Effect of pH (3, 7 and 10 for wastewater effluent and 7 for distilled water) on reactions was studied by adjusting the initial pH of wastewater with NaOH (0.1 mol L-1) or HCL (0.1 mol L-1). In order to discriminate the role of HO• radicals in processes, tert-butanol alcohol (TBA) was used as a

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radical scavenger. All experiments were conducted in triplicates and the averaged data were presented. The amount of ozone required for micropollutants degradation during the ozonation processes was calculated by transferred ozone dose (TOD). TOD is defined as the absorbed mass of ozone transferred into the unit volume of liquid and reacts with the oxidizable compounds. . TOD was calculated by Eq. (1): t

TOD (mg L-1 )   0

Q gas Vliquid

 (C Oin3  C Oout3 ) dt

(1)

where, Qgas represents the gas flow rate (1.5 L min-1), Vliquid is the volume of liquid in the out reactor and Cin O3and CO3 are the ozone concentration in the inlet and outlet gas, respectively. The

amount of accumulated TOD in O3 and O3/Fe0 plotted as a function of applied ozone dose (AOD) according to Eq. (2).

AOD (mg L-1 ) 

T  Q gas  C ino3

(2)

Vliquid

In this equation, T is the time of sampling expressed in minutes. Also, ozone utilization efficiency (OUE) was determined in both O3 and O3/Fe0 to assess the effect of Fe0 on adsorption and decomposition of ozone vs. SMX. OUE was calculated by Eq. (3) [31]:

OUE (%) 

O 3 In  O 3 Out  O 3 D O 3 In

(3)

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where [𝑂3]𝐼𝑛 is the total dosage of the inlet ozone, [𝑂3]𝑂𝑢𝑡 represents the total amount of outlet ozone, and [𝑂3]𝐷 is the total dissolved ozone mass in the aqueous solution. 2.5. Preparation of standards and extraction of SMX Spiked samples of distilled water and the wastewater effluent with known amount of SMX were extracted and analyzed to prepare calibration curves. The limit of detection (LOD) and quantification (LOQ) of SMX were found 11.49 and 34.82 µg L-1, respectively. To extract SMX from wastewater matrix and distilled water, a seven mL aliquot of samples transferred to a 12 mL screw cap glass tube with a conical bottom. Then, it was acidified to pH 4 with 1 M acetic acid. Next, a mixture of 300 μL dichloromethane as extracting solvent and 600 μL acetonitrile as a disperser solvent were rapidly injected into the sample using a one mL syringe. The cloudy formed solution was immediately centrifuged at 5400 rpm for seven min. Then, the bottom phase was transferred to a vial using a micro-syringe. Last extraction steps were repeated twice to complete recovery of SMX. After that, the solution was evaporated with a gentle nitrogen gas stream at 35°C. Then, the residue was dissolved in 100 µL acetonitrile and water solution at volume ratio of 40:60 and was mixed by vortex for 60 s. Finally, an aliquot of 10 μL was injected into the HPLC. 2.6. Analytical methods The concentration of SMX was determined using an HPLC equipped with a UV detector (Agilent Co., USA) at wavelength of 270 nm using a C18 column (Restek Co.: 250 mm × 4.6 mm ID ×5 μm particles). The mobile phase was a mixture of acetonitrile and water at a volume ratio of 40:60 and at a flow rate of one ml min-1. Intermediates of SMX degradation were 10

identified using an HPLC (Waters, Milford, MA, USA) coupled with a Quattro Micro API Triple Quadrupole LC–MS/MS (Waters Corporation, USA) equipped with an electrospray source (Zspray) and operated in positive and ionization mode. The ESI positive source values were: capillary voltage 4.0 kV, extractor 1.0 V, RF lens 0.0 V, source temperature 110 C, desolvation temperature 350 C. Dissolvation and cone gas flow were set at 600 and 50 L h−1, respectively. Separation of analytes was achieved on a Penomenex Gemini C18 column (100 mm × 2 mm ID × 5 μm particles). The mobile phase consisted of: phase A (90% H2O, 10% acetonitrile, and 0.1% formic acid) and phase B (90% acetonitrile, 10% H2O, and 0.1% formic acid). The mobile phase A was maintained at 100% for the first 3 min, then the percentage of the phase B was linearly increased to 60% during the next 30 min, then to 90% in the following 10 min. Flow rate was set to 0.2 mL min-1. The detection limit for the method was 0.15 μg L-1. The concentration of ozone in the inlet and outlet gases was measured by iodometric method [32]. For this purpose, the gas was bubbled through two impingers in series, each filled with 200 ml of 2% KI solution. The solution was acidified with 10 ml of 2 N H2SO4 and titrated with standard 0.005 N Na2S2O3 until disappearance of yellow iodine color. One mL starch indicator was added to the solution and continued titration until disappearance of the blue color. Concentration of ozone in aqueous solution was determined using spectrophotometric method [33]. In this method, 5 ml of the sample were transferred in a test tube containing 5 ml of 2% KI solution. After about 30 min the intensity of the absorption was read using cells with 20 mm light path. The COD, nitrate, nitrite, and sulfate were determined by standard methods [16]. The pH value was examined with a pH meter (Sartorius PB-10, German). 2.7. Statistical analysis

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All experimental data were analyzed with SPSS software (IBM SPSS Statistics 19, SPSS Inc., USA). Normality of the numeric variables was checked by Kolmogorov-Smirnov test and Skewness (within the range ±1.5) and Kurtosis (within the range ±2). In every stage of the experiments, each wastewater sample was ozonized with three discrete runs both in O3 and O3/Fe0 processes. Then the average and standard deviation of the data of examined parameters were calculated. Paired sample t-Test was accomplished to determine if there was a statistically significant difference in the measured concentrations of parameters in the inlet and outlet of one process. Statistically significant difference between mean removal efficiency of the parameters in the two processes was performed using One-way analysis of variance (ANOVA). In all analyses, P-values less than 0.05 were considered as significant. 3. Results and discussion 3.1. Characterization of the Fe0 catalyst SEM-EDS was used to detect the surface morphology and chemical compositions of raw and reacted Fe0 after 60 min treatment by O3/Fe0 process. Fig. 2a shows that the surface morphology of raw Fe0 was flaky and smooth which chemical composition was about 97.75% Fe0. After ozonation, it could be observed that the corrosion of Fe0 produced a larger specific surface area where formed numerous concave porous and shapeless holes (Fig. 2b). The detection of 17.05% O indicates generation of iron corrosion products at the surface of iron particles. To further confirm the ingredient of these corrosion products, the raw and reacted Fe0 particles were also analyzed by XRD. As shown in Fig. 3a before use of iron scraps in catalytic ozonation, the diffraction peaks at 2ϴ = 44.6° and 65° indicate elemental iron. After treatment process, FeOOH and Fe2O3 were found, which may be the catalytic constituents of the process (Fig. 3b).

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The FTIR spectra of newly and used catalyst is shown in Fig. 3c. The peaks locating at 568 cm-1 can be ascribed to stretching vibrations of the FeO bonds in Fe0 [34], which confirms the formation of spinel Fe3O4 [35-37]. The bands in the region of 1000–1200 cm−1 is difficult to assign because of superposition of a number of broad overlapping bands. Then, they cannot be explained in terms of simple motion of specific functional groups or chemical bonds [33]. Band locating at 1636 cm-1 arise from COC and C=O stretching band [38]. This peak at used catalyst, indicates the adsorption of SMX and ozone on the surface of catalyst. The adsorption band at 1636 cm-1 was also related to the residual H2O [39]. The peaks at 2841 cm-1 and 2933 cm-1 were assigned to CH stretching. For the used catalyst, a wide and strong peak occurred at 3423 cm-1 belonging to OH bond was observed, which suggested the generation of OH• during the ozonation reaction. Therefore, the results indicated the interaction among catalyst, ozone and organic molecules could effectively occur in aqueous solution [40]. 3.2. Impact of Fe0 on TOD and OUE The amount of accumulated TOD in ozonation of distilled water and wastewater effluent spiked with 20 mg L-1 SMX was calculated at different time intervals and plotted as a function of AOD. Fig. 4a indicates that presence of Fe0 catalyst improves TOD from gas to the liquid phase with increasing interaction between liquid and gas bubbles. In O3/Fe0, the value of TOD for distilled water and effluent was 1.28 and 1.16 times higher than in O3, respectively. Moreover, regardless of the process, effluent constituents promoted TOD in the effluent in comparison with the distilled water. Dissolved ozone concentration profile in the solutions with or without the catalyst was also determined and shown in Fig. 4b. In O3 system, the dissolved ozone concentration increased 13

rapidly at the first 20 min and then reached a steady state. But in O3/Fe0, residual dissolved ozone concentration increased gradually and reached maximum value of 1.48 and 2.33 in effluent and distilled water, respectively. Lower values of dissolved ozone were observed in O3/Fe0. At ozonation of wastewater effluent, dissolved ozone was gradually appeared after 5 min where in distilled water it was near to 3 mg L-1 (about 1.5 and 2 times more than in effluent at O3 and O3/Fe0, respectively). The amount of ozone demand for distilled water spiked with SMX was slightly less than the effluent with the same amount of antibiotic. This indicates that higher ozone demand is required by the effluent constituents. At sole-ozonation of distilled water spiked with SMX, dissolved ozone concentration was not observed at the first few minutes. This result may have been caused by the fast reaction of SMX with ozone. The instant ozone demand (applied ozone dosage-ozone residual concentration) which represents the amount of ozone consumed at the initial stage of the oxidation process was obtained 479 and 1031 mg L-1 for O3 and O3/Fe0, respectively. As shown at Fig. 4b, the first residual of ozone was determined at five and 10 min for O3 (0.06 mg L-1) and O3/Fe0 (0.14 mg L-1), respectively. Accordingly, instant absorbed ozone for 20 mg L-1 SMX at effluent was 50.48 and 25.29 mg ozone/mg SMX for O3 and O3/Fe0 processes, respectively. The detail of specific absorbed ozone calculations have been presented later at part 3.6. The OUE of the processes at different time intervals were listed in Table 1. The OUE was significantly improved at the presence of Fe0 catalyst. Improvement of OUE is very important for application of ozonation technology in full scale. According to the results, at O3 process, the average OUE for treating wastewater effluent was around 90%, being higher than that for distilled water with around 80%. Also, Table 1 clearly indicates the outlet ozone mass in the ozonation processes is nearly two times higher than that of catalytic ozonation, indicating that 14

more ozone is consumed in O3/Fe0 process. The lower ozone in the off-gas is very desirable to reduce the treatment costs and diminish off-gas treatment requirements. Overall, it could be concluded that the addition of catalyst enhances ozone decay, produces more free radical and improves the OUE and TOD of ozonation process. The result could be related to the high adsorption affinity of the Fe0 catalyst towards ozone molecules and simultaneous transforming them into more reactive radicals [16, 41]. 3.3. Variations at pH during the processes The pH value of the solution is important since it influences the generation rate of HO•, OUE, surface properties of catalyst, and charge of ionic or ionisable organic molecules [42]. During sole-ozonation of SMX, several acid compounds are produced and accumulated in solution especially at the first minutes of reaction which leads to decrease pH values (Fig. 5). The value of pH in O3/Fe0 process will also be reduced due to the formation of acid intermediates. But on the contrary, the final pH of the reaction increased unavoidably in O3/Fe0, being more obvious in the acidic pH. For example, the pH value increased from 3 to 8 in O3/Fe0. According to previous studies [43, 44], in iron catalyzed ozonation, generation of HO• simultaneously consumes H+ and OH- in a series of reactions. Then, presence of sufficient Fe0 may react with H+ and prevents the decrease in pH value. Accordingly, the reactions between ozone and Fe0 was proposed in Fig. 6 [45, 46]. In O3/Fe0 process, the pH of reaction solution was increased nearby to 8.5 at any initial pH which could provide OH- for the catalytic ozonation (see Fig. 5a-c). At acidic condition, oxidation of iron into Fe++ and Fe+++ could be accelerated that generates more HO•. In contrast, at alkaline pH the precipitation of iron as hydroxides and/or oxides will tend to reduce the catalytic 15

activity [47]. However, the effect of pH when the internal electrolysis and ozonation were carried out simultaneously is different. This is due to the fact that at a high pH the formation of ferrous hydroxide (FeOH2) and ferric hydroxide (FeOH3), which are a kind of coagulant with strong adsorption capability, could adsorb big molecules and improve process efficiency [48]. Additionally, Xiong et al. [49] reported that in Fe-based catalytic ozonation, Fe and other corrosion products (Fe2O3, Fe3O4 and FeOOH) could simultaneously improve catalytic effectiveness. During the single ozonation process, rapid decrease of pH at first 10 min could be assigned to the generation of small molecular carboxylic acids and alcohols, but, the later increase in pH may be due to the further decomposition of acids into CO2 and H2O (Fig. 5b). While the corrosion of Fe0 can completely consume the acid in reaction solution and generate some alkaline substances (iron hydroxides) which cause increase of pH. In addition, the low pH of 3.26 in single ozonation suggests that the generated organic acids were hard to be further mineralized. In O3/Fe0, however, generated organic acids could enhance corrosion of Fe0 and, corrosion products could catalyze decomposition of ozone which shows a synergetic effect between ozone and Fe0. So this synergetic effect could play a vital role in the further mineralization of intermediates and could cause high SMX removal. 3.4. Kinetic of SMX degradation Kinetic of SMX degradation was undertaken at both processes (Fig. 7). First of all, both processes were found to follow the first order kinetic. At the all examined initial pH values, SMX is completely removed at 10 min. However, at first three min of the reaction, SMX removal rate was almost higher in the single ozonation than the catalytic ozonation. On the contrary, in O3/Fe0, no significant differences between the first-order rate constants (k) were

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obtained for SMX removal at different pH values. The results show that the combination of Fe0 and ozone probably does not have a significant effect on the rate of SMX removal. Table 2 shows the degradation of different pollutants by catalytic ozonation with iron shavings. At both processes, highest SMX removal was obtained at initial pH of 3 and the performance of ozone was better than O3/Fe0. As shown at Fig. 7a, at the initial pH of 3, SMX degradation by ozone (8.21×10-1 min-1) was about 1.27 times greater than O3/Fe0 (6.42×10-1 min-1). This could be concluded that SMX is mainly eliminated through the direct electrophilic oxidation by ozone. The amino group (-NH2-) of SMX molecule exhibits a high nucleophilic nature and intensifies the electronic density of the aromatic ring and then promotes reactivity of SMX with ozone [50]. Fig.7 shows that removal of SMX was not significantly affected by the presence of TBA radical scavenger. TBA can be adsorbed on the surface of the catalyst and constrain the reaction process by occupying the reactive sites [51]. In the other words, SMX showed high k values and good percentage removals even with low ozone doses, because this pharmaceutical has electron-rich functional groups that are highly reactive with molecular ozone [52, 53]. Also, at present of TBA, the removal efficiency was decreased at alkaline pH. Hydroxide ions accelerate the decay of ozone to HO• at higher pH, leading to the decrease of ozone concentration [54]. In contrast, the addition of TBA will terminate the radical chain reaction, thus inhibit the decay of ozone reduce the local concentration of hydroxyl radical in the solution [55]. In short, both low pH and presence of TBA led to less formation of hydroxyl radical, and therefore reduced ozone decay. At such conditions, a good removal of SMX was observed, mainly due to the presence of high concentration of ozone. 3.5. Removal of COD

17

Due to the importance of whole removal of organic pollutants, the rate of COD reductions were analyzed at pH values of 3, 7 and 10 with O3 and O3/Fe0 (Fig. 8). The highest removal rate was obtained at first 10 min of the process. As indicated in Fig. 8a, almost no differences were found between two processes in COD removal at acidic pH and the concentration was decreased from 120 to 24 mg L-1 corresponding to a removal efficiency of 80%. As shown in Fig. 8b and c there was an obvious difference in COD removal between ozonation and catalytic ozonation and was much higher at pH 7 and 10 than pH 3. However, the Fe based ozonation could be effective at alkaline pH. Also, Pan et al. (2012) reported that highest removal of COD is obtained at alkaline pH by Fe-based catalytic ozonation from biologically treated dye wastewater effluent [30]. At alkaline pH the formation of ferrous and ferric hydroxides could adsorb large and colloidal organic molecules and increase the process efficiency [30]. 3.6. Specific ozone consumption by SMX Besides applied ozone dose and contact time, specific ozone consumption (mg O3/mg compound) by the target pollutant has an important role in ozone treatment applications. Therefore, amount of ozone that was solely consumed by SMX was calculated in the processes (Fig. 9a). The mg of ozone gas absorbed by the solution per mg of SMX removed during O3 and O3/Fe0 was estimated using the following expression [56]:

O3 absorbed  O3 In dt   O3 Out dt Qg  M0   M V Mremoved

(4)

In this Equation [𝑂3]𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑑 is the mg of ozone gas absorbed by the solution, [𝑀]𝑟𝑒𝑚𝑜𝑣𝑒𝑑 represents mg of the target compound removed, ∫(𝑂3)𝐼𝑛𝑑𝑡 and∫(𝑂3)𝑂𝑢𝑡𝑑𝑡 are the area under the 18

influent and effluent ozone gas curve plotted as function of time, respectively, 𝑄𝑔 is ozone gas flow rate in Ls-1, [𝑀]0 is initial concentration of compound in mg L-1, and V is volume of reactor in L. To verify the mineralization of intermediates in the course of ozonation, the ratio of mg O3/mg COD at different ozonation times was followed (Fig. 9b). Ozonation presents a high efficiency to remove SMX but not to mineralize the by-products of the reaction. The antibiotic was almost completely removed (up to 99%) at reaction time of 5 min by 18 mg O3/mg SMX at the both processes, while 28 and 56% of COD had been depleted by ozone and O3/Fe0, respectively. At this condition, the amount of ozone absorbed per mg of COD removed was 10 and 7 mg O3/mg COD for single and catalytic ozonation respectively. 3.7. Inorganic ions and organic intermediates evolution during the processes The whole mineralization of SMX could be accompanied by the release of sulfate, inorganic nitrogen and carbonate species. Upon bond cleavage of the SMX molecules, the sulphur atom is recovered as sulphate (SO42−) and the N atom will be transformed to NH4+, NO3−, and/or NO2−. The ions of NO3−, NO2− and SO42− were surveyed in the both processes (Fig. 10). Nitrite ion concentration increased at first followed by a decrease in the solution due to the rapid conversion to nitrate. More nitrate was produced by O3 process. Goncalves et al. (2012) showed that degradation of SMX with activated carbon catalyzed ozonation can convert 100% of sulfur to sulfate and 30% of nitrogen to nitrate and ammonium [57]. As shown at Fig. 10, the nitrate concentration increased over time of reaction in both processes. But after 3 minutes of reaction, the sulfate concentration decreased. Some inorganic anions such as sulphate can be adsorbed on metal oxide surface hydroxyl groups via ligand exchange [58]. 19

3.8. Organic intermediates production during the processes In order to identify the organic intermediates products during O3 and O3/Fe0 and to determine a probable reaction pathway map, LC-MS/MS was employed on some samples (the detail of the intermediates are presented in supplementary). All identified SMX degradation products by LC– MS-MS in both catalytic and non-catalytic ozonation were presented in Table S1. Considering the previous studies on identification of oxidation intermediates of SMX [59-66], several degradation pathways were proposed (Fig. 11). The major reaction mechanisms involve isomerization, electron transfer, hydroxylation of benzene and isoxazole rings, cleavage of the sulfonamide bond, and oxidation/release of the amino group in the benzene ring to yield nitrotransformation by products (nitro-TBPs). The accurate mass spectrum of SMX presented a molecular ion [M+H] + at 254 m/z in positive ionization (Fig. S1). In pathway A (Fig.S2), TP254 was identified and illustrated that is as a result of an isomerization of O-N bond at the isoxazole ring. In pathway B, TP201 was likely formed by the cleavage bond between sulfur and benzene. In pathway C, TP157 presented an ion fragment at m/z 157 (C6H6NO2S) which corresponds to the loss of the C4H6N2O+ moiety due to the attack of OH• radicals on the isoxazole ring. In pathway D, the presence of fragment at m/z 284 indicates the oxidation of amino group (-NH2) on the aromatic ring and the formation of the nitro-derivative of SMX (NO2-SMX). NO2-SMX can also be released as a secondary product of NO-SMX. NO-SMX has been previously reported in other advanced oxidation processes [63, 67] but was not observed in this study, likely due to low yields and instability. In pathway E, there are two products with the same m/z = 173 for [M+H] +. Sulphanilic acid (pathway E1) forms via cleavage of the S-N bond, and are widely reported in the previous studies as SMX TPs [61, 63, 68]. Sulphanilamide (pathway E2) is another compound that was identified as a results of cleavage bond, which is an important 20

oxidation product of SMX in the photocatalysis [69], solar photo-Fenton [62], photolysis [68] and ozonation [70, 71] processes. In addition, the bond cleavage between sulfur and nitrogen resulted in the formation of TP129 with m/z of 129 (pathway F). This compound was also observed in degradation of SMX during Fenton process. In pathway G, TP99 at [M+H] + 99 mass units was identified as 3-amino-5-methylisoxazole (AMI) originated by the cleavage of S-N bond of the original and hydroxylated SMX molecules. AMI which is a common reaction in sulfonamide antibiotics degradation has frequently observed in both OH• [72, 73] and SO4•−mediated oxidation of SMX [18, 74]. In pathway H, the [M+H] + peak at m/z 288 (TP288), i.e., 2OH-SMX, the intermediate generated from hydroxylation of double bond (C=C) on the isoxazole ring in SMX, formation through electron-transfer process by Hydroxyl radicals. And in the last pathway (I), TP207, with an [M+H] + of 207, not only verified the reaction of hydroxyl radicals at the benzene ring, but also demonstrated isoxazole ring opening. Another products including TP93, TP108, TP114, and TP132 were also identified. The TP108 (benzoquinone) and TP93 (aniline) were present in most of the transformation products of SMX. Cleavage of S-C bond leads to the formation of TP93. Aniline is also produced through release of SO42- due to the reaction of sulfonated moiety with OH• [57]. TP108 was also formed due to the attack of OH• on the isoxazole ring. Finally, opening of the aniline and isoxazole rings through a series of oxidation steps could result lower molecular weight organic compounds (e.g., carboxylic acids). 3.9. Operating cost of O3/Fe0 As shown at Fig. 7 and 8 the highest removal rate of SMX (98.43) and COD (92.6%) by O3/Fe0 was almost obtained at pH 10 and up to 5 min reaction time. Then, the operating cost of O3/Fe0 for treating 20 mg L-1 SMX regarding the removal of COD was calculated by the loss of Fe0. The

21

market prices of Fe0 is approximately 200 USD t-1. Thereafter, Fe0 consumption within 5 min by O3/Fe0 system for treatment of 20 mg L-1 SMX spiked in wastewater effluent with overall COD of 122 mg L-1 was approximately 0.45 mg. Then, approximately 0.0225 ton Fe0 would be consumed per treatment of 1 ton of SMX corresponding to 6.1 ton COD. Thus, the cost of consumed Fe0 in O3/Fe0 process would be 4.4 USD t-1 of SMX which is reasonable for treating the antibiotic. 4. Conclusions

1) A higher ozone utilization efficiency in O3/Fe0 was observed relative to O3 process. Furthermore, The O3/Fe0 significantly enhanced decomposition of ozone to OH•. 2) Sole-ozonation presents a high efficiency to remove SMX but not to mineralize the byproducts of the reaction. 3) Greater COD removal rates were observed when the catalytic ozonation was applied. Also, in O3/Fe0 process, the COD removal efficiency was higher in alkaline pH. 4) The main degradation routes identified in this work were isomerization, electron transfer, hydroxylation of benzene and isoxazole rings, cleavage of the sulfonamide bond, and oxidation/release of the amino group in the benzene ring to yield nitro-TBPs. 5) The purpose of this study was the utilization of iron shavings as an inexpensive catalyst to enhance ozone activity in the degradation of SMX. One of the advantages of using iron shavings as catalyst, is that not needing any modification before being applied to catalytic ozonation process. Acknowledgments

22

The authors acknowledge the financial and technical support provided by Health and Environment Research Center, Tabriz University of Medical Sciences, Tabriz, Iran. References [1] U. Szymańska, M. Wiergowski, I. Sołtyszewski, J. Kuzemko, G. Wiergowska, M.K. Woźniak, Presence of antibiotics in the aquatic environment in Europe and their analytical monitoring: recent trends and perspectives, Microchem. J. (2019) 729-740. [2] M.-C. Danner, A. Robertson, V. Behrends, J. Reiss, Antibiotic pollution in surface fresh waters: Occurrence and effects, Sci. Total Environ. (2019) 793-804. [3] J. Du, W. Guo, H. Wang, R. Yin, H. Zheng, X. Feng, D. Che, N. Ren, Hydroxyl radical dominated degradation of aquatic sulfamethoxazole by Fe0/bisulfite/O2: Kinetics, mechanisms, and pathways, Water Res. 138 (2018) 323-332. [4] G. Liu, X. Li, B. Han, L. Chen, L. Zhu, L.C. Campos, Efficient degradation of sulfamethoxazole by the Fe (II)/HSO5− process enhanced by hydroxylamine: efficiency and mechanism, J. Hazard. Mater. 322 (2017) 461-468. [5] C.R. Craig, R.E. Stitzel, Modern pharmacology with clinical applications, Lippincott Williams & Wilkins2004. [6] V. Osorio, J. Sanchís, J.L. Abad, A. Ginebreda, M. Farré, S. Pérez, D. Barceló, Investigating the formation and toxicity of nitrogen transformation products of diclofenac and sulfamethoxazole in wastewater treatment plants, J. Hazard. Mater. 309 (2016) 157-164.

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Figure captions Figure 1. Schematic diagram of the O3 and O3/Fe0 processes. Figure 2. SEM and EDS spectra of Fe0 before and after O3/Fe0 system treatment. Figure 3. XRD pattern and FTIR spectra of Fe0 before and after O3/Fe0 system treatment. Figure 4. (a) Transferred ozone dose (TOD) as a function of applied ozone dose (AOD), (b) the change of dissolved ozone concentration versus time during different ozonation processes of SMX. Experimental conditions: initial SMX concentration = 20 mg L-1, initial pH value = 7, amount of Fe0 = 288.46 g L-1, ozone gas concentration = 178.8 mg L-1, ozone gas flow rate = 1.5 L min-1,

34

Figure 5. The variation of pH value during SMX ozonation with or without catalyst at initial pH of 3, 7 and 10. Experimental conditions: initial SMX concentration = 20 mg L-1, ozone gas flow rate = 1.5 L min−1, ozone gas concentration =178.8 mg L-1, amount of Fe0 = 288.46 g L−1. Figure 6. Reactions between ozone and Fe0. Figure 7. Comparison of performance on a) b) c) degradation efficiencies and degradation kinetics for SMX treatment by O3 and O3/Fe0 at various pH. Experimental conditions: initial SMX concentration = 20 mg L-1, amount of Fe0 = 288.46 g L-1, ozone gas flow rate = 1.5 L min−1, ozone gas concentration = 178.8 mg L-1, TBA = 2.69 ml. Figure. 8. Effect of reaction time and initial pH on COD removal from wastewater effluent by O3 and Fe0/O3. Experimental conditions: initial SMX concentration = 20 mg L-1, applied Fe0 = 288.46 g L-1, ozone gas flow rate = 1.5 L min-1. Figure. 9. Absorbed ozone dose during single and catalytic ozonation over Fe0 for distilled water and effluent: a) mg of ozone absorbed per mg of SMX removed in O3 and Fe0/O3 processes and b) mg of ozone per mg of COD removed by O3 and Fe0/O3 on the degradation of SMX in effluent. Experimental conditions: initial SMX concentration = 20 mg L-1, gas flow rate = 1.5 L min-1 and inlet ozone concentration = 178.8 mg L-1 Figure. 10. Evolution of inorganic ions concentrations of sulfate, nitrate and nitrite as a function of time during the SMX degradation by O3 and Fe0/O3. Experimental conditions: initial SMX concentration = 20 mg L-1, gas flow rate = 1.5 L min-1 and inlet ozone concentration = 178.8 mg L-1

35

Figure 11. Proposed possible degradation pathways of SMX by O3 and Fe0/O3

Fig. 1

36

Fig. 2

37

a) Fe0 before used

b) Fe0 after used

Fig. 3

38

Fig. 4 39

Fig. 5 40

Fig. 6 41

Chain reaction between ozone and iron

O3

O3/Fe0 Alkaline pH

O3 + H2O → 2HO° + O2

Fe2+ + 2OH- → Fe (OH) 2

O3 + OH- → HO2° + O°-2

Fe2+ + 8OH- + O2 + 2H2O → 4Fe (OH) 3

O3 + OH° → HO2° + O2 ↔ 2O2° + H+ O3 + HO2° → 2O2 + OH° HO2° → O2 + H2O2

When the iron is used:

Fe0 + 2H+ + O3 → Fe2+ + O2 + H2O

Fe2+ + O3 → FeO2+ + O2

Acidic pH

FeO2+ + H+ → Fe3+ + OH° Fe2+ + H2O2 + H+ → Fe3+ + OH° + H2O Fe2+ + H2O2 → Fe3+ + OH° + OH-

Fig. 7

42

Fig. 8

43

Fig. 9

44

Fig. 10 45

Fig. 11 46

Sulfamethoxazole O S O

H2N

CH3

H N

O

N

m/z=254

A

B

C

D

E1

E2

F

NH2

OH

NH2

NO2

NH2

NH2

NH2

O S O

O S O

NH HN

NH N

OH

O

TP201

OH

N

TP157

O S O

O S O

NH

H

OH

HO

OH

HO O

O

O

OH CH3

CH3

NH2

HO

OH N

N

N

CH3

TP254

H2N

HN

NH

TP129

NH2

TP173

TP284

I

NH2

O S O

O S O

OH

O

CH3

H

OH

O S O O S O

G

NH CH3

TP207

TP288

NH2 O

O

H3C

OH

TP108

TP93

TP93

O S O

HO

NH2

H3C

OH NH2 O N

TP132

O N

TP99 OH H3C

NH2 O N

TP114

Organic compound O H2N

OH

O Oxamic acid

O

O

HO

OH O Oxalic acid

O Glyoxal

OH

O

O

OHO O

OH Acetic acid

Maleic acid

OH O Pyruvic acid

OH•

Final products -

O

C O

O

H

O

H O

S

O O-

-

O

O N+

O-

-

O

N O

Table 1. Ozone utilization efficiency (OUE) in both ozonation and Fe-based catalytic ozonation 47

ozonation

Time Matrix

[O3]I

[O3]O

[O3]D

OUE

[O3]I

[O3]o

[O3]D

OUE

(mg)

(mg)

(mg)

(%)

(mg)

(mg)

(mg)

(%)

1

268

1

0.20

99.70

268

43

0.18

91.91

5

1341

300

7.59

77.06

1341

339

0.09

74.71

10

2682

612

14.26

76.65

2682

666

5.48

74.96

20

5364

1440

18.62

72.81

5364

924

11.40

82.56

40

10728

2856

22.62

73.17

10728

1752

12.69

83.55

60

16092

4464

21.82

72.12

16092

2484

12.96

84.43

1

268

10

0.26

96.28

268

0.36

0.37

99.73

5

1341

252

2.26

81.04

1341

93

0.17

93.01

10

2682

396

3.05

85.12

2682

151

0.14

94.36

20

5364

806

4.53

84.88

5364

439

0.67

91.80

40

10728

1552

4.76

85.46

10728

993

3.03

90.71

60

16092

2268

6.07

85.87

16092

1360

3.85

91.52

(min) distilled water

wastewater

6)

Fe-based catalytic ozonation

O3 I (mg)  T(min)Qin (l / min)Cin (mg / l)

O3out(mg)  T(min)Qout(l / min)Cout(mg/ l)

Table. 2 Application of catalytic ozonation with iron shavings in different aqueous matrix. Matrix

Pollutants

Operational parameters

Treatment efficiency

Bio-treated dyeing and finishing wastewater

Organic compounds

pH: 7-7.5, [Fe0]: 20 g l-1 [O3]: 10.8 mg l-

Proteins removal: 100% Polysaccharides removal: 42% COD removal: 50 %

1

Flow rate: 500 ml mim-1 48

Reference [17]

Textile mill wastewater

Disperse blue E-4R

Olive mill wastewaters

Industrial wastewater

Bio-treated dyeing and finishing wastewater

Organic compounds

Reaction time: 120 min Reaction time: 180 min

pH: 3, [Fe0]: 20 g l-1 [O3]: 20 g m-3 Reaction time: 120 min pH: 7 Flow rate: 0.23 dm3 mim-1 Reaction time: 60 min pH: 7 Flow rate: 5.8 m3 h-1 Reaction time: 60 min

Color removal: 63%, COD removal: 32%, TOC removal: 28%, Absorbable organic halogen: 31% Total phenolic content removal: 93% , COD removal: 46%, TOC: removal: 71%

[30]

Color removal: 90%, COD removal: 80%, Turbidity removal: 99%

[43]

Proteins removal: 80% Polysaccharides removal: 85% COD removal: 67 % DOC removal: 79 %

[76]

Highlights 

Higher ozone utilization efficiency was observed in O3/Fe0 than O3.



In O3 and O3/Fe0, sulfamethoxazole removed more than 99% at the first 5 min.



COD removed in O3/Fe0 1.4 times greater than O3.



The cost of consumed Fe0 in O3/Fe0 process would be 4.4 USD t-1 of SMX.

49

[29]

50