Catalytic and Photocatalytic Oxidation of Aqueous Bisphenol A Solutions

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Catalytic and Photocatalytic Oxidation of Aqueous Bisphenol A Solutions: Removal, Toxicity, and Estrogenicity Mirjana Bistan, Tatjana Tisler, and Albin Pintar* Laboratory for Environmental Sciences and Engineering, National Institute of Chemistry, Hajdrihova 19, SI-1001 Ljubljana, Slovenia ABSTRACT: Catalytic wet-air oxidation (CWAO) of aqueous solutions of bisphenol A (BPA) was investigated in a trickle-bed reactor at temperatures up to 230 °C and oxygen partial pressure of 10.0 bar over TiO2 and Ru/TiO2 solids. It was observed that in the given range of operating conditions BPA undergoes both noncatalyzed and catalyzed oxidation routes. The employed Ru/TiO2 catalyst containing 3.0 wt % of metallic phase enabled complete removal of BPA and more than 96% of TOC removal at temperatures of 200 °C and above. No catalyst deactivation occurred that could be attributed to the dissolution of active ingredient material. At these conditions, no carbonaceous deposits were accumulated on the catalyst surface. The acute toxicity of end-product solutions to organisms from different taxonomic groups and estrogenicity determined by the genetically modified yeast, compared with those of the feed solutions, was significantly reduced by CWAO treatment over the Ru/TiO2 catalyst. For comparison, oxidative destruction of BPA was also investigated in this study by means of either photolytic or heterogeneous photocatalytic oxidation. A commercial TiO2 photocatalyst illuminated by UV light enabled complete removal of BPA; however, lower decrease of toxicity and estrogenicity in the treated solution was observed.

1. INTRODUCTION In recent years concern regarding the ubiquitous presence of endocrine-disrupting compounds (EDCs) in environment has increased considerably due to evidence of adverse effects on organisms, especially those from the aquatic environment. EDCs present in drinking water supplies may also pose a threat to the human population as increases of hormone-related cancers have been often attributed to EDCs.1,2 Thus, efficient treatment and removal of EDCs from wastewaters is necessary before they are discharged into the environment. It has been reported in many studies that levels of EDCs in wastewaters decreased after conventional biological treatment in WWTP.3 5 However, a large part of EDCs are in fact removed by adsorption onto activated sludge,6,7 which can cause further problems in sludge management.8 Furthermore, the steroid compounds and bisphenol A (BPA) are considered to be incompletely removed from wastewaters by conventional wastewater treatment processes,9 since concentrations causing estrogenic effects have been detected in treated wastewaters10,11 and also in aquatic organisms living in rivers and streams after WWTPs discharges.12,13 Use of advanced oxidation processes (AOPs) such as catalytic wet air oxidation, heterogeneous photocatalysis, ozone-based technologies, and ultrasound oxidation have also been investigated with respect to their ability to increase the biodegradability as well as the detoxification of polar and hydrophilic chemicals.14 16 Recently, elimination of BPA in water by AOPs has shown good results by many authors (see, for example, Kaneco et al.,17 Katsumata et al.,18 Zhou et al.19). However, these processes sometimes result in secondary products that are not eliminated significantly by the same technique and may be more hazardous than the original compound.15,20,21 According to Staples et al.21 and Torres et al.,22 the BPA intermediates which enhanced the toxicity in treated effluents may be phenol, 4-isopropylphenol, and semiquinone derivatives of BPA. r 2011 American Chemical Society

BPA is an organic pollutant, commonly used in the production of polycarbonate plastics and epoxy resins. It is toxic to aquatic organisms and estrogenic-active. It thus belongs to the group of EDCs as the representative of xenoestrogens.12,23,24 BPA is frequently present in industrial wastewaters, where concentrations as high as 1000 μg/L can be expected.25 Significantly higher concentrations, up to 17 000 μg/L of BPA, can be found especially in landfill leachates (via hydrolysis of BPA from plastics).12 One of the promising options for removal of toxic and nonbiodegradable organic compounds from industrial wastewaters is destruction of these contaminants by catalytic wet-air oxidation (CWAO).26,27 In the CWAO process, the organic pollutants are oxidized by activated O2 species in the presence of a solid catalyst, usually at temperatures of 130 250 °C and pressures of 10 50 bar, into biodegradable intermediate products or mineralized into CO2, water, and associated inorganic salts. The CWAO of various organic compounds has been studied over metal oxides, mixed metal oxide systems, ceriumbased composite oxides, and supported noble metal catalysts.28 From the economic point of view, the CWAO process might be efficiently used for direct treatment of BPA at concentration levels found in landfill leachates; for nano to micro levels, a preconcentration step would be needed in the process scheme. However, there is still a need to improve catalytic activity and long-term stability of heterogeneous catalysts in order to achieve effective oxidative degradation of organic pollutants at Special Issue: CAMURE 8 and ISMR 7 Received: August 31, 2011 Accepted: October 26, 2011 Revised: October 21, 2011 Published: October 26, 2011 8826

dx.doi.org/10.1021/ie201957z | Ind. Eng. Chem. Res. 2012, 51, 8826–8834

Industrial & Engineering Chemistry Research temperatures and pressures as low as possible.29 31 Titania- and zirconia-supported ruthenium catalysts have received much attention because they exhibited high activity and chemical resistance in CWAO of different model pollutants32 34 and industrial wastewaters.35,36 Recently, the performance of various Ru/TiO2 catalysts to promote oxidation of aqueous solutions of formic acid, acetic acid, and phenol was investigated in a continuousflow trickle-bed reactor.37 Complete oxidation of formic acid was obtained at mild operating conditions (110 °C), and no catalyst deactivation occurred that could be attributed to the dissolution of active ingredient material. Liquid-phase oxidation of recalcitrant acetic acid was found to be structure sensitive; the highest catalyst activity was obtained when Ru phase on the catalyst surface prevailed in zerovalent state. The Ru/TiO2 catalysts enabled complete removal of phenol as well as more than 99% removal of TOC at temperatures above 200 °C. In the presence of a Ru/TiO2 catalyst in the trickle-bed reactor, the acute toxicity to various aquatic organisms of the oxidized materials was greatly decreased; for example, acute toxicity of aqueous phenol solutions treated by the CWAO process was reduced by more than 98%. In the present study, CWAO of BPA model aqueous solutions was carried out in a continuous-flow trickle-bed reactor in order to investigate potential of bare TiO2 support and Ru/TiO2 catalyst for effective (i.e., long-term) removal of the parent molecule and intermediates from the liquid phase, with a noticeable accumulation of carbonaceous species on the catalyst surface. The properties of catalysts before and after CWAO runs were comparatively investigated by means of XRD, CHNS, ICPAES, and textural measurements. Chemical analyses (HPLC, TOC), toxicity tests with organisms from different taxonomic groups (bacteria Vibrio fischeri, water fleas Daphnia magna, unicellular green algae Desmodesmus subspicatus, and zebrafish embryos Danio rerio) and genetically modified yeast strain Saccharomyces cerevisiae were used to get information about the toxicity and estrogenicity of the feed and treated solutions as well as to examine global efficiencies of investigated catalysts for degradation and detoxification of BPA dissolved in water. For comparison, oxidative destruction of BPA was also investigated in this study by means of either photolytic or heterogeneous photocatalytic oxidations, as the most common representatives of low-temperature AOP processes, carried out at mild conditions in a batch slurry reactor. In the latter case, TiO2, as the most widely used heterogeneous photocatalyst that exhibits high oxidative power under UV light and resistance to photocorrosion, was employed.38,39

2. MATERIALS AND METHODS Catalyst Preparation. The catalyst sample containing 3.0 wt % of Ru was prepared by incipient-wetness impregnation of TiO2 extrudates (Degussa-H€uls AG, Aerolyst type, dp: 1.4 mm, SBET: 51 m2/g, Vpore: 0.36 cm3/g, dpore: 28 nm) with an aqueous solution of RuCl3 3 xH2O (Acros Organics), concentration of which was accurately determined by ICP-AES before impregnation. The TiO2 support was dried at 100 °C in an oven for 2 h and then impregnated at room temperature with an appropriate volume of solution containing the Ru salt to obtain 3.0 wt % nominal Ru content. After the impregnation step, the catalyst precursor was dried (overnight at room temperature, then at 40 °C for 5 h, and finally at 105 °C for 2 h) and reduced directly in H2 flow of 250 mL/min at 300 °C for 1 h without previous

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Table 1. Experimental Conditions of the Catalytic Wet-Air Oxidation of BPA Carried out in a Continuous-Flow TrickleBed Reactor mass of catalyst in bed, g

3.0

bed density, g/cm3 bed porosity, /

0.94 0.41

equivalent catalyst particle diameter, mm

1.42

catalyst particle density, g/cm3

1.59

reaction temperature, °C

200, 230

total operating pressure, bar

25.5, a38.0

oxygen partial pressure, bar

10.0

gas flow rate, mL/min superficial gas flow rate (G), kg m liquid flow rate, mL/min

60 2

superficial liquid flow rate (L), kg m tres,L, min a

s 2

0.357, a0.500 0.5

1

s

1

0.134, a0.132 0.24, a0.23

T = 230 °C.

calcination. The reduced sample was cooled to room temperature under N2 flow. Reduction conditions were determined in this work by TPR analysis of dried catalyst precursor. The actual Ru loading in the synthesized Ru/TiO2 catalyst, determined by using ICP-AES analysis, was found equal to 2.9 wt %. Catalyst Characterization. The specific surface area, total pore volume, and average pore width of the supports and catalyst samples were determined from the adsorption and desorption isotherms of N2 at 196 °C using a Micromeritics ASAP 2020 MP/C instrument. This characterization was carried out after degassing of samples to 4 μm Hg for 1 h at 90 °C and 2 h at 300 °C. The same apparatus was used to perform static H2 chemisorption analyses following the procedure described by Shen et al.40 XRD patterns of fresh and used catalyst samples were obtained on a PANalytical X’Pert PRO diffractometer using Cu Kα radiation (λ = 0.15406 nm). Data were collected from 20 to 80° 2θ, at 0.034° and 100 s per step. Crystalline phases were identified by comparison with PDF standards from the International Centre for Diffraction Data (ICDD). The high-resolution electron micrographs of Ru/TiO2 catalyst sample were recorded on a FE-SEM SUPRA 35VP (Carl Zeiss) microscope equipped with an EDAX energy dispersive X-ray spectrometer Inca 400 (Oxford Instruments). Purity of TiO2 supports used in the present study was determined by means of XRF analysis (Rigaku, model NEX CG). The carbon content of carbonaceous deposits accumulated on the titania and catalyst surface during the reaction course was determined, after washing and drying the spent support and catalyst samples, using a CHNS elemental analyzer (PerkinElmer, model 2400 Series II). Eventual leaching of Ru and Ti from the titania support and Ru/TiO2 catalyst during the CWAO reaction was verified by ICP-AES analysis of collected liquidphase samples. CWAO Experiments. CWAO experiments were carried out in a Microactivity-Reference unit (PID Eng&Tech, Spain), which is an automated and computer-controlled, continuous-flow tricklebed reactor for catalytic microactivity tests. The properties of the catalyst bed and operating conditions are listed in Table 1. Concentration of BPA (min. 99%, Aldrich) in the feed aqueous solution was 20.0 mg/L. A fixed-bed tubular reactor (Autoclave Engineers, USA) was made of a 305 mm o.d. 9 mm i.d. 8827

dx.doi.org/10.1021/ie201957z |Ind. Eng. Chem. Res. 2012, 51, 8826–8834

Industrial & Engineering Chemistry Research stainless-steel (316-L) or Hastelloy C-276 tube that was heated with a reactor furnace and integrated within the hot box. Liquid and gaseous flows were introduced into the hot box system that includes an electric forced convection heater which permits the process route to be preheated and kept at temperatures up to 190 °C. The liquid reactant was introduced into the unit using a HPLC positive alternative displacement pump (Gilson, model 307). The oxygen source in these experiments was pure O2 (purity 5.0, Messer), which was fed to the system through an electronic HI-TEC mass-flow controller (Bronkhorst, model ELFLOW). The preheated gas and liquid streams merged in a T-joint and were then introduced to the top of the reactor through a 10-μm sintered stainless-steel (316) filter (another is located at the outlet of the reactor, which protected the arrangement from possible finely separated catalyst fines). A porous (2 μm) plate made of Hastelloy C-276, supported on a 316 stainless-steel pipe, was placed inside near the middle of the reactor tube to support the fixed bed composed of 3.0 g of either TiO2 extrudates or Ru/TiO2 catalyst. The reaction temperature was measured by a K-type thermocouple, which was inserted through the upper end of reactor and was in contact with the catalyst bed, and regulated within (1.0 °C from the preset temperature by a PID temperature controller (TOHO, model TTM-005). The gas and liquid phase, which passed the catalytic bed in a cocurrent downflow mode and flowed out at the bottom of the reactor, were separated in a high-pressure liquid gas (L/G) separator cooled with a Peltier cell. The L/G separator equipped with a micrometric servo-controlled valve and capacitive level sensor provided an efficient liquid discharge from the unit. The gas stream from the L/G separator was discharged through a second micrometric servo-controlled regulating valve, which was employed to provide continuous and constant flow of gases at the outlet (i.e., pressure control). In the off-gas stream, production of CO2 and eventual formation of CO were monitored by a nondispersive IR detector (Rosemount, model BINOS 1001). Photolytic/Photocatalytic Oxidation Experiments. Photolytic/photocatalytic oxidation of BPA (c0 = 20 mg/L in ultrapure water (resistance 18.2 MΩ-cm)) was tested at atmospheric pressure in a batch slurry reactor (V = 250 mL) thermostatted at T = 20 °C (Julabo, model FP 25), magnetically stirred (360 rpm) and continuously sparged with purified air (45 L/h). The catalyst concentration (TiO2 P-25 from Degussa; SBET: 52 m2/g, Vpore: 0.17 cm3/g, dpore: 13 nm) was in the range of 0 0.5 g/L. After 30 min “dark” period (for the establishing of equilibrium of the sorption process), the reactor content was illuminated by either (i) a UV high-pressure mercury lamp (150 W, emission in the 300 400 nm region with a maximum at ∼360 nm) laid in a water-cooling jacket immersed vertically in the slurry, (ii) a UV low-pressure mercury lamp (17 W, with a maximum at λ = 254 nm), or (iii) a halogen lamp (150 W; the irradiation is labeled in the text as visible light). Representative 2-mL samples were withdrawn from the reaction suspension after 6 h of operation and filtered through the 0.22-μm membrane filter (Sartorius) in order to remove catalyst particles. Analysis of End-Product Solutions (HPLC, TOC). Representative liquid-phase samples, which were continuously collected from the L/G condenser/separator during the CWAO experiments or from the batch slurry reactor during photolytic/ photocatalytic oxidation runs, were analyzed for residual BPA content by using HPLC analysis. Determinations were performed in the isocratic analytical mode using a 250 mm 4.6 mm

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Phenomenex Luna C18 5-μm column thermostatted at 30 °C (UV detection at λ = 210 nm with a mobile phase of methanol (75%) and ultrapure water (25%) at a flow rate of 0.8 mL/min). The total amount of organic substances in withdrawn aqueous-phase samples was determined by measuring the total organic carbon (TOC). TOC content was determined applying a high-temperature catalytic oxidation (HTCO) method carried out at 750 °C by using an advanced TOC analyzer (Teledyne Tekmar, model Torch) equipped with a high-pressure NDIR detector, by subtracting measured inorganic carbon (IC) content from measured total carbon (TC) content. In all analyses, 3 4 repeated measurements were taken for each liquid-phase sample, and the average value of TOC concentration was reported. The error of analysis was never greater than (0.5%. Estrogenicity. Estrogenic activity of initial/feed solution of BPA and treated samples was determined by yeast estrogen screen (YES) assay, which was performed according to Routledge and Sumpter.41 In YES assay a recombinant yeast strain Saccharomyces cerevisiae BJ1991, developed in the Genetics Department at Glaxo Corporation under the guidance of Professor John P. Sumpter, was used. For the purpose of YES assay, samples treated by CWAO were extracted and concentrated using the Oasis HLB 6 cm3 (500 mg) SPE cartridges (Milford, MA) and methanol as an eluting solvent. SPE extracted samples were transferred to 96-well optically flat-bottom microtiter plates (TPP, MIDSCI, USA) in sterile conditions. After methanol evaporated, 200 μL of the assay medium containing yeast culture were added to each hole on the microtiter plate and incubated at 34 °C for 48 52 h. The absorbance at 575 and 620 nm was measured on the microtiter plate reader PowerWave XS (BioTek, USA). Validity of the YES assay was confirmed with a positive control (27.2 μg/L of 17β-estradiol), a negative control (31.4 μg/L of progesterone), and a blank control (yeast exposed to the growth medium and chromogenic substrate β-D-galactopyranoside). Estrogenic activity (EA) was expressed as the activity of enzyme β-galactosidase42 and relative estrogenic activity (REA), where the estrogenic activity of treated samples was compared to the estrogenic activity of initial solution of BPA. Toxicity. The acute toxicity test with the freeze-dried bacteria Vibrio fischeri NRRL-B-11177 obtained from the manufacturer (Dr. Lange GmbH, Germany) was performed according to the ISO standard.43 The luminescence was measured on a LUMIStox 300 luminometer. The luminescent bacteria were exposed to initial solution of BPA and treated samples for 30 min at (15 ( 0.2) °C and the percentage of inhibition was calculated for each tested sample relative to the control. The green, unicellular alga Desmodesmus subspicatus Chodat 1926 (SAG 86.81) was obtained from the Collection of Algal Cultures, University of G€ottingen, Germany. A stock culture of alga was maintained in a nutrient solution according to Jaworski44 at constant room temperature of (21 ( 1) °C under continuous fluorescent illumination (4000 lx) provided by four 20-W cool-white fluorescent lights (Osram). Flasks with alga were agitated at 150 rpm for 15 min, alternating with 15 min elezniki, type EV 403). resting, on an orbital shaker (Tehtnica Z In a toxicity test, test flasks containing initial solution of BPA, treated samples, and a control (only dilution water) were constantly shaken at the same frequency as stock flasks; they were illuminated with four 40-W cool-white fluorescent lights giving an illumination of 7000 lx. After 72 h of exposure, algal growth was determined by counting cells in a B€urker counting chamber. The percentage of inhibition of specific growth rates 8828


Industrial & Engineering Chemistry Research for each tested sample was calculated in comparison to the control.45 Daphnia magna Straus 1820 were obtained from the Institut f€ur Wasser, Boden and Lufthygiene des Umweltbundesamtes, Berlin, Germany. They were cultured at (21 ( 1) °C in 3-L aquariums covered with glass plates containing 2.5 L of modified M4 medium, illuminated with fluorescent bulbs (approximately 1800 lx) for 12 h per day. They were fed daily a diet of the alga Desmodesmus subspicatus Chodat 1926 corresponding to 0.13 mg C/daphnia. One day before the start of the experiments reproductive daphnids were isolated and young neonates (about 24 h old) were used. In the acute toxicity tests, daphnids were exposed to initial solution of BPA and treated samples. After 24 h of exposure the daphnids, which were not able to swim, were counted and the percentages of immobile daphnids were calculated.46 The acute toxicity test with zebrafish Danio rerio HamiltonBuchanan 1822 embryos was performed according to the ISO standard.47 Adult zebrafish were bred in a temperature-controlled room in an aquarium (60 30 30 cm) containing 45 L of tap water with constant temperature (26 °C) and photoperiod (12 h light:12 h dark). Fish were fed three times daily with commercially available dried fish food. A day before breeding a plastic spawning box covered with stainless steel mesh was placed in the breeding tank. On the following day the spawning plastic box was removed from the tank and eggs were collected and rinsed with dilution water prepared according to ISO standard.47 A detailed description of zebrafish breeding to obtain eggs was published by Kammann et al.48 Fertilized eggs in the four to eight cell stages were placed in 24-well plates; each well contained 1 mL of initial solution of BPA and treated samples as well as a control containing only dilution water. After 48 h of exposure at 26 °C, lethal malformations i.e., egg coagulation, missing heartbeat, and missing tail detachment from the yolk sac were observed. The percentages of lethal malformations were calculated for each tested sample.

3. RESULTS AND DISCUSSION Catalyst Characterization. Specific surface area, total pore volume, and average pore width of TiO2 in the form of extrudates and fresh Ru(3.0 wt %)/TiO2 catalyst (SBET: 50 m2/g, Vpore: 0.34 cm3/g, dpore: 27 nm) show that the deposition of Ru did not significantly modify the textural properties and the corresponding XRD powder patterns (not shown). The XRD pattern of titania supports, which contain more than 99.5% TiO2 as determined by XRF analysis, revealed the presence of anatase (titanium oxide, PDF 03-065-5714) and rutile (titanium oxide, PDF 00-004-0551) phases, and that anatase is the prevailing crystallographic form. The XRD pattern is not affected by the deposition of ruthenium, as the diffraction peaks of metallic Ru (ruthenium, syn, PDF 06-0663: 2θ = 38.39°, 42.15°, and 44.01°) were not observed. It was further found that the accessibility of ruthenium is poor on Ru(3.0 wt %)/TiO2 catalyst. Low dispersion (5.4%) determined on the catalyst after reduction at 300 °C can be, at least partially, explained by an inhibiting effect of residual chloride on the fraction of Ru surface available for H2 chemisorption49 51 and the use of large-sized TiO2 extrudates.35 The presence of rather large and discrete Ru particles on the surface of synthesized catalyst, as determined by H2 chemisorption measurements (25 nm) is supported by SEM examination (Figure 1), which reveals the presence of Ru clusters in the range of 14 34 nm.

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Figure 1. SEM micrograph of fresh Ru(3.0 wt %)/TiO2 catalyst sample.

To elucidate an influence of reaction medium and reaction conditions on eventual structural and textural modifications of catalysts (i.e., poisoning, sintering), XRD, N2 adsorption desorption isotherms (at 196 °C), and ICP-AES analyses were performed on catalysts (i.e., bare TiO2 extrudates and Rucontaining solid) before and after the CWAO runs (used catalyst samples were thoroughly washed with distilled water and dried prior to analysis). A comparison of X-ray powder diffraction pattern of spent Ru(3.0 wt %)/TiO2 catalyst to that of the fresh one reveals that no peak characteristic of metallic Ru, ruthenium oxide phases, or other phases (i.e., Fe, Fe-oxides, carbon) was identified; the reflections correspond to those of the TiO2 support (not shown). Furthermore, the measurements of textural properties of used catalysts revealed no differences in total pore volume and average pore width, while a small drop of specific surface area at an extent of about 5% was observed in comparison to fresh solids. In light of these findings, Ru dispersion in spent Ru(3.0 wt %)/TiO2 catalyst was found to be equal to 5.3%. This is very similar to the value reported above, which confirms that in the applied range of CWAO operating conditions sintering of Ru particles does not occur to a measurable extent. Hydrodynamic Considerations of CWAO Runs. Liquid hold-up, residence time of the liquid phase in the catalytic bed, and catalyst external wetting efficiency during CWAO runs were determined using a procedure described in detail in our previous study.35,36 Given the experimental conditions listed in Table 1, all CWAO runs performed in this study were conducted in a lowinteraction (LIR) trickle-flow regime (L was in the range of 0.132 0.134 kg m 2 s 1), which means that the liquid trickles down the packing in the form of droplets, films, and rivulets, while the continuous gas phase occupies the remaining porous space and flows separately.52,53 At the employed operating conditions about 10% of voids were occupied with the liquid phase, which is also in very good agreement with the liquid hold-up measurements of Goto and Smith.54 It can be further seen in Table 1 that the residence time of the liquid phase in the catalytic bed was in the range from 0.23 to 0.24 min. Analysis of the wetting efficiency has shown that at the used operating conditions this parameter was equal to 0.75, which implies that the external surface of catalyst particles was only partially wetted and thus directly exposed to the gas phase stream. The calculated values of wetting efficiency are in good agreement with the results of other investigations.52,55 BPA Oxidation. Figures 2 and 3 show BPA conversion as a function of time on stream in consecutive CWAO runs performed 8829


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Figure 4. TOC conversion as a function of temperature obtained over various catalysts during CWAO of BPA. For operating conditions see Figure 2. Figure 2. BPA conversion as a function of time on stream obtained over various catalysts at 200 °C. Operating conditions: p(O2): 10.0 bar, Φvol,L: 0.5 mL/min, c(BPA)feed: 20.0 mg/L.

Figure 3. BPA conversion as a function of time on stream obtained over various catalysts at 230 °C. For operating conditions see Figure 2.

at different reaction temperatures (200 and 230 °C, respectively) in the presence of inert SiC, bare TiO2 support, or Ru(3.0 wt %)/ TiO2 catalyst. The effect of temperature was investigated in this range because it was observed in our previous studies37,56 that CWAO of phenol carried out over titania- or CNF-supported catalysts at temperatures below 200 °C resulted in catalyst deactivation due to strong adsorption of partially oxidized C-6 intermediates (such as benzoquinones and hydroquinones) on the catalyst surface. Under He, there was no removal of organic carbon from the liquid phase; thus, the BPA conversion is only a result of oxidation pathways. In any of the runs, no carbon monoxide was detected in the off-gas stream. Moderate BPA conversions were obtained when the reactor was filled with SiC, even at short residence time of the liquid phase calculated to be about 0.23 0.24 min (Table 1). These observations confirm that in the given range of operating conditions BPA oxidation undergoes both noncatalytic and catalytic oxidative routes. The BPA removal over the bare TiO2 support was significantly improved as compared to runs conducted in the presence of SiC (Figures 2 and 3). As titania extrudates are more than 99% pure (XRF analysis), it is obvious that the observed activity for BPA oxidation is solely caused by TiO2 itself. These measurements further demonstrate good reproducibility of data and confirm that the material of construction

(either stainless steel or Hastelloy C-276) exhibits no measurable effect on BPA conversion. It can be seen in Figure 2 that at T = 200 °C slight increase of BPA conversion as a function of time on stream was observed in the presence of TiO2 support. This is attributed to the nonstoichiometric nature of TiO2 and consequently establishment of gas liquid solid equilibrium during the initial stage of reaction course.57 Furthermore, complete conversion of BPA was attained in the presence of Ru(3.0 wt %)/TiO2 catalyst, and no drop of activity was observed in the investigated time period. This is in agreement with the finding that the TiO2 support and Ru(3.0 wt %)/TiO2 catalyst were found to be very stable in the CWAO conditions used. Indeed, no leaching of either titanium or ruthenium was detected in the experiments performed in the presence of these solids. γ-Al2O3 and CeO2 exhibited an accelerating effect in the WAO of a model domestic wastewater,58 while in the oxidation of acetic acid CeO2, CeO2 ZrO2, ZrO2, and TiO2 were identified to possess detectable catalytic properties.59,60 The oxidation promoted by these solids can be interpreted by their redox properties via a free-radical mechanism. The TiO2 surface may first interact with oxygen to produce O2•‑ and HO2• radicals. These species are able to initiate a radical mechanism by abstracting H• radicals from the adsorbed organic components. The ability of oxides to activate oxygen derives from the ease with which they deviate from the stoichiometric composition resulting in an oxygen-deficient surface. The activity enhancement with ruthenium is likely due to the possibility of this metal to undergo a redox cycle between two oxidation states and thus to activate oxygen. TOC conversions in end-product solutions derived from corresponding BPA oxidation runs are depicted in Figure 4. Rather moderate TOC conversions were obtained in the presence of SiC or TiO2 support. Comparing further TOC conversions obtained on the TiO2 oxide and on the corresponding supported ruthenium catalyst (41 vs 96% at T = 200 °C), one may note that addition of ruthenium drastically increased the overall oxidative transformation of BPA to carbon dioxide. This is attributed to the fact that ruthenium exhibits an ability to oxidize small organic compounds, such as acetic acid, that are resistant and not easily degraded by oxides. In the end-product solution obtained after the CWAO of BPA carried out in the presence of Ru(3.0 wt %)/TiO2 catalyst, only acetic acid was identified, as determined by ion chromatography. Furthermore, examination of SiC, TiO2 support, and Ru(3.0 wt %)/TiO2 catalyst after reaction under oxidative conditions by means of CHNS analysis 8830



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showed that carbonaceous deposits, which could be produced by oxidative coupling reactions, were not accumulated on the surface of these solids during the CWAO of BPA (Table 2). Conversions of BPA obtained during the photolytic/photocatalytic of the pollutant in a batch reactor after 6 h of operation under various light sources are listed in Table 4. It is seen that BPA is prone to oxidation under UVC illumination, while UVA and visible lights exhibit much less potential for photolytic removal of BPA. Complete oxidative removal of BPA was in the given range of experimental conditions obtained only in the presence of TiO2 P-25 photocatalyst in the reaction suspension. Observed activity of the latter under illumination with visible light is attributed to the fact that no UV cutoff filter was used in this work; the employed halogen lamp emitted about 3% of light in the UV range (300 400 nm). In heterogeneously photocatalyzed runs performed in this study, no dissolution of titania in the liquid phase was observed. Toxicity and Estrogenicity. Results of toxicity and estrogenicity tests of the initial BPA sample (feed solutions) and samples treated by means of CWAO process in the continuous-flow trickle-bed reactor are presented in Table 3 as well as in Figures 5 and 6. It is clearly seen that BPA conversions (%) increased by the operating temperature and the use of catalysts. The same trend is also seen from the results of luminescence inhibition of marine bacteria V. fischeri and from the results of growth rate inhibition of green algae D. subspicatus, where at higher temperature used in the CWAO process (i.e., 230 °C) the luminescence inhibition and the algal growth rate inhibition was for up to 30% lower. However, the results of mortality of zebrafish embryos D. rerio did not follow the same trend; the mortality of zebrafish embryos increased by higher operating temperature. Since TOC conversion increased with an increase of reaction temperature (Figure 3), this cannot be attributed to higher accumulation of

intermediates in the liquid phase. Higher mortality of zebrafish embryos observed when conducting CWAO of BPA at 230 °C (sample 4b) is probably due to enhanced leaching of metallic parts of the reactor setup;61 however, this remains to be investigated. A significant drop of toxicity for zebrafish embryos was

Figure 5. Intact zebrafish embryo D. rerio at the beginning of the test 128 cell stadium (upper left), after 24 h (upper in the middle) and after 48 h (upper right). Observed lethal effects of zebrafish embryo D. rerio after 48 h: coagulated zebrafish embryo (bottom left) run 1; missing tail detachment from the yolk sac (bottom middle) runs 4b and 9; deformation of the zebrafish embryo (bottom right) runs 3b and 4b.

Table 2. Carbon Content (Measured by Means of CHNS Elemental Analysis) on the Surface of Fresh and Spent Catalyst Samples Used in the CWAO Process of BPA (c(BPA)feed: 20.0 mg/L) catalyst sample SiC TiO2

3% Ru/TiO2 a

carbon content, wt % fresh

0.03

spenta

0.02

fresh

0.11

spent

0.13

spent, HC reactor

0.09

fresh

0.07

spent

0.04

Figure 6. YES assay results after (a) CWAO runs (samples 2 4) and after (b) photolytic/photocatalytic oxidation experiments (samples 5 9). “1” indicates the response of yeast to feed/initial BPA solution and “blank” indicates the response of yeast when no estrogenic active substance is present (yeast growth in assay medium). See Tables 3 and 4 for sample notification.

After CWAO of BPA carried out at both 200 and 230 °C.

Table 3. Toxicity and Estrogenicity of BPA Samples Treated by Means of CWAO Process (c(BPA)feed: 20.0 mg/L) sample 1: BPA, feed solution

conversion (%)

V. fischeri luminiscence

D. subsp. growth

D. rerio

inh. (%)

inh. (%)

mortality (%)

REA (%)

20

72

51

100

100

2a: BPA, SiC, T = 200 °C

38.5

12.3

42

31

100

100

2b: BPA, SiC, T = 230 °C 3a: BPA, TiO2, T = 200 °C

58.5 87.5

8.3 2.5

11 34

0 28

90 80

100 0

96.2

0.76

0

3b: BPA, TiO2, T = 230 °C

/

remained BPA (mg/L)

0

0

90

4a: BPA, 3% Ru/TiO2, T = 200 °C

100

0

27

22

10

0

4b: BPA, 3% Ru/TiO2, T = 230 °C

100

0

0

0

60

0

8831



ARTICLE

Table 4. Toxicity and Estrogenicity of Photolytically/Photocatalytically Treated BPA Samples (c(BPA)0: 20.0 mg/L) conversion

remained BPA

V. fischeri luminiscence inh.

D. magna immobility

(%)

(mg/L)

(%)

(%)

a

sample 1: BPA, initial solution

/

20

72

100

90

100

5: BPA, visible light (150 W)

3

19.4

75

45

20

87

6: BPA, UV 150 W (365 nm)

15.9

16.8

71

30

10

52

7: BPA, UV 17 W (254 nm)

83.9

3.2

79

20

10

22

8: BPA, TiO2 P-25, visible light (150 W) 9: BPA, TiO2 P-25, UV 150 W (365 nm) a

REA D. rerio mortality (%) (%)

82.2 100

3.6

62

100

10

100

0

80

100

40

77

Reaction time: 6 h.

noticeable only when using Ru(3.0 wt %)/TiO2 at the operating temperature of 200 °C (sample 4a), where only 10% of embryos revealed lethal effects. As for the estrogenicity, the REA remarkably drops to 0% in all treated samples with either bare TiO2 (runs 3a and 3b) or Ru-containing catalyst (runs 4a and 4b), independent of the reaction temperature. Overall, the CWAO process seems to be most effective for BPA treatment when Ru(3.0 wt %)/TiO2 catalyst was used at the operating temperature equal to 230 °C. Under those conditions, the conversion of BPA was 100%, accompanied with TOC conversion higher than 97%, and there was no toxicity measured for V. fischeri and D. subspicatus as well as no estrogenicity (REA) detected. On the other hand, zebrafish embryos D. rerio were more sensitive, since in 60% of embryos the lethal effects were detected. Nevertheless, these observations are in very good agreement with the results of our previous investigation,37 in which great potential of Ru/TiO2 catalysts for the detoxification of aqueous solutions of formic acid, acetic acid, and phenol by means of CWAO was reported. As noticed from Table 4, luminescence inhibition of V. fischeri in all tested samples treated either photolytically or photocatalytically remained similar to that of the initial sample of BPA. However, in some cases even higher toxicity was detected that might be attributed to the occurrence of partially oxidized intermediates in the liquid phase. Only slight decrease of inhibition was observed in sample 8 (treated in the presence of TiO2 photocatalyst illuminated by visible light). On the contrary, Chiang et al.15 observed decreased toxicity toward V. fischeri after photocatalytic oxidation of BPA, which depended on the pH of the initial solution. At higher pH values (pH = 10) during photocatalytic experiment, toxicity decreased significantly, but at pH = 3 only slight toxicity decrease was observed, which was the result of different intermediates formed during the oxidation reaction. But, the toxicity after photolytic oxidation of BPA remained more or less the same, which is in agreement with our observations. Frontistis et al.62 studied BPA degradation by solar electrocatalysis over immobilized Ti/TiO2 films and possible effects of photocatalysis on toxicity to luminescence of bacteria V. fischeri and estrogenicity of treated samples. They found that the photoelectrocatalytic degradation byproducts are less toxic (about 33%) and estrogenic (about 25%) than initial BPA solution. A strong relationship between high mineralization ratio and decreased toxicity was observed also by Rodríguez et al.,20 whose results also indicate that some phenolic intermediates formed could be more toxic than BPA. The same was also observed during the CWAO of aqueous phenol solutions over TiO2 and Ru/TiO2 solids.37 The lowest toxicity toward water fleas D. magna and the lowest estrogenicity (REA) were detected when organisms were exposed to sample 7, which was

treated photolytically by the UV 17 W (254 nm) light (Table 4 and Figure 6). In the case of zebrafish embryos examined as shown in Figure 5, significantly lower toxicity of all treated samples was observed in comparison to the initial BPA solution. This finding confirms the above assumption that enhanced leaching of metals from the high-temperature and high-pressure reactor unit might be responsible for higher toxicity toward D. rerio when conducting CWAO of BPA at elevated temperature. Furthermore, it was found that the use of TiO2 photocatalyst in oxidation experiments did not play any important role regarding the removal toxicity and estrogenicity from end-product solutions. One can see in Table 4 that the lowest toxicity and estrogenicity results were not detected when samples were treated by the UV 150 W light in the presence of TiO2 photocatalyst, even though the 100% conversion of BPA was achieved. However, toxic effects to daphnids D. magna significantly increased in BPA samples treated with TiO2 (samples 8 and 9) in comparison to the samples without using it (samples 5 and 6). A comparison of TOC values depicted in Figure 4 with toxicity and estrogenicity data for experiments in which complete removal of BPA was achieved (runs 4a and 4b in Table 3 and run 9 in Table 4) shows that the CWAO process enables deeper oxidation than heterogeneous photocatalytic oxidation. The above toxicity and estrogenicity results of photolytic and/ or photocatalytic oxidation of aqueous solution of BPA depend on the reaction conditions, which favored different BPA conversions as well as reactions pathways. Therefore, different byproducts at various concentration levels were formed, which were more or less toxic and/or estrogenic active to tested organisms. This is, for instance, in agreement with the results reported by Mutou et al.63 who found that cytotoxicity of BPA on Jurkat cells increased after being illuminated by UVB and UVC radiation, but remained rather the same when illuminated by UVA light. Comparing the results of CWAO experiments (Table 3) with the results of photolytic/photocatalytic oxidation runs (Table 4), we can conclude that the CWAO process, because of more severe operating and reaction conditions, seems to be much more effective in obtaining deep oxidative destruction of BPA, especially in the presence of Ru/TiO2 catalyst, as well as in decreasing the toxicity and estrogenicity of the initial/feed BPA solution.

4. CONCLUSIONS In the present work, TiO2 in the form of extrudates and Ru/ TiO2 catalyst (metal loading of 3.0 wt %) were examined in the process of catalytic wet-air oxidation (CWAO) of aqueous solutions of bisphenol A (BPA) in a continuous-flow tricklebed reactor at temperatures up to 230 °C and oxygen partial pressure of 10.0 bar. BPA undergoes both noncatalyzed and 8832


Industrial & Engineering Chemistry Research catalyzed oxidation routes in the presence of inert SiC particles. Moderate conversions of BPA and TOC were obtained when carrying out the reaction over bare TiO2 support; the observed activity of this solid is attributed to the nonstoichiometric nature of TiO2 oxide. On the other hand, the employed Ru/TiO2 catalyst enabled complete removal of BPA and more than 96% of TOC removal at temperatures of 200 °C and above. The rest of carbon was found in the form of acetic acid. In the period of 50 h, no catalyst deactivation occurred that could be attributed either to the dissolution of active ingredient material in the liquid phase, or coke formation on the catalyst surface. Furthermore, it was found that BPA is prone to photolytic degradation under UVC illumination. A commercial TiO2 P-25 photocatalyst illuminated by UV light enabled complete removal of BPA. It is common to both oxidation techniques examined in this study that in principle the acute toxicity of end-product solutions to organisms from different taxonomic groups and estrogenicity determined by the genetically modified yeast, compared with those of the feed solutions, were reduced. Remarkable extent of detoxification of BPA feed solution as well as complete removal of estrogenicity exerted by this emerging pollutant was achieved when BPA was treated by means of CWAO process in the tricklebed reactor filled with the Ru/TiO2 catalyst. Due to more severe reaction conditions, CWAO process is more effective in decreasing the toxicity and estrogenicity of aqueous BPA solution in comparison to photolytic/photocatalytic oxidation.

’ AUTHOR INFORMATION Corresponding Author

*Tel.: +386 1 47 60 237. Fax: +386 1 47 60 300. E-mail: albin. [email protected].

’ ACKNOWLEDGMENT We gratefully acknowledge the financial support of the Ministry of Higher Education, Science and Technology of the Republic of Slovenia through Research program P2-0150. ’ REFERENCES (1) Nicolopoulou-Stamati, P.; Hens, L.; Howard, C. V. Endocrine Disrupters, Environmental Health and Policies; Kluwer Academic Publishers: Dordrecht, 2001. (2) Preziosi, P. Endocrine Disrupters as Environmental Signallers: An introduction. Pure Appl. Chem. 1998, 70 (9), 1617. (3) Behnisch, P. A.; Fujii, K.; Shiozaki, K.; Kawakami, I.; Sakai, S. Estrogenic and Dioxin-like Potency in Each Step of a Controlled Landfill Leachate Treatment Plant in Japan. Chemosphere 2001, 43, 977. (4) Jiang, J. Q.; Yin, Q.; Zhou, J. L.; Pearce, P. Occurrence and Treatment Trials of Endocrine Disrupting Chemicals (EDCs) in Wastewaters. Chemosphere 2005, 61, 544. (5) Ying, G.-G.; Kookana, R. S.; Kumar, A. Fate of Estrogens and Xenoestrogens in Four Sewage Treatment Plants with Different Technologies. Environ. Toxicol. Chem. 2008, 27 (1), 87. (6) Marttinen, S. K.; Kettunen, R. H.; Rintala, J. A. Occurrence and Removal of Organic Pollutants in Sewages and Landfill Leachates. Sci. Total Environ. 2003, 301, 1. (7) Clara, M.; Strenn, B.; Saracevic, E.; Kreuzinger, N. Adsorption of Bisphenol-A, 17β-estradiole and 17α-ethinylestradiole to Sewage Sludge. Chemosphere 2004, 56, 843. (8) Mohapatra, D. P.; Brar, S. K.; Tyagi, R. D.; Surampalli, R. Y. Physico-chemical Pretreatment and Biotransformation of Wastewater and Wastewater Sludge- Fate of Bisphenol A. Chemosphere 2010, 78, 923.

ARTICLE

(9) Ternes, T. A.; Stumpf, M.; Mueller, J.; Haberer, K.; Wilken, R.D.; Servos, M. Behavior and Occurrence of Estrogens in Municipal Sewage Treatment Plants- I. Investigations in Germany, Canada and Brazil. Sci. Total Environ. 1999, 225, 81. (10) Gomez, M.; Garralon, G.; Plaza, F.; Vílchez, R.; Hontoria, E.; Gomez, M. A. Rejection of Endocrine Disrupting Compounds (Bisphenol A, Bisphenol F and Triethyleneglycol Dimethacrylate) by Membrane Technologies. Desalination 2007, 212, 79. (11) Sumpter, J. P. Endocrine disrupters in the aquatic environment: An overview. Acta Hydrochim. Hydrobiol. 2005, 33 (1), 9. (12) Kang, J.-H.; Kondo, F.; Katayama, Y. Human Exposure to Bisphenol A. Toxicology 2006, 226, 79. (13) Larsson, D. G. J.; Adolfsson-Erici, M.; Parkkonen, J.; Pettersson, M.; Berg, A. H.; Olsson, P.-E.; F€ orlin, L. Ethinyloestradiol- An Undesired Fish Contraceptive?. Aquat. Toxicol. 1999, 45, 91. (14) Ara~ na, J.; Herrera Melian, J. A.; Do~ na Rodríguez, J. M.; Gonzalez Díaz, O.; Viera, A.; Perez Pe~ na, J.; Marrero Sosa, P. M.; Espino Jimenez, V. TiO2-photocatalysis as a Tertiary Treatment of Naturally Treated Wastewater. Catal. Today 2002, 76, 279. (15) Chiang, K.; Lim, T. M.; Tsen, L.; Lee, C. C. Photocatalytic Degradation and Mineralization of Bisphenol A by TiO2 and Platinized TiO2. Appl. Catal., A 2004, 261, 225. (16) Jiang, Y.; Petrier, C.; Waite, D. T. Sonolysis of 4-chlorophenol in aqueous solution: Effects of substrate concentration, aqueous temperature and ultrasonic frequency. Ultrason. Sonochem. 2006, 13, 415. (17) Kaneco, S.; Rahmana, M. A.; Suzuki, T.; Katsumata, H.; Ohta, K. Optimization of Solar Photocatalytic Degradation Conditions of Bisphenol A in Water Using Titanium Dioxide. J. Photochem. Photobiol., A 2004, 163, 419. (18) Katsumata, H.; Kawabe, S.; Kaneco, S.; Suzuki, T.; Ohta, K. Degradation of Bisphenol A in Water by the Photo-Fenton Reaction. J. Photochem. Photobiol., A 2004, 162, 297. (19) Zhou, D.; Wu, F.; Deng, N.; Xiang, W. Photooxidation of Bisphenol A (BPA) in Water in the Presence of Ferric and Carboxylate Salts. Water Res. 2004, 38, 4107. (20) Rodríguez, E. M.; Fernandez, G.; Klamerth, N.; Maldonado, M. I.; Alvarez, P. M.; Malato, S. Efficiency of Different Solar Advanced Oxidation Processes on the Oxidation of Bisphenol A in Water. Appl. Catal., B 2010, 95, 228. (21) Staples, C. A.; Dorn, P. B.; Klecka, G. M.; O’Blook, S. T.; Harris, L. R. A Review of the Environmental Fate, Effects and Exposures of Bisphenol A. Chemosphere 1998, 36 (10), 2149. (22) Torres, R. A.; Sarantakos, G.; Combet, E.; Petrier, C.; Pulgarin, C. Sequential Helio-photo-Fenton and Sonication Processes for the Treatment of Bisphenol A. J. Photochem. Photobiol., A 2008, 199, 197. (23) Brennan, S. J.; Brougham, C. A.; Roche, J. J.; Fogarty, A. M. Multi-generational Effects of Four Selected Environmental Oestrogens on Daphnia magna. Chemosphere 2006, 64, 49. (24) Dorn, P. B.; Chou, C.-S.; Gentempo, J. J. Degradation of Bisphenol A in Natural Waters. Chemosphere 1987, 16 (7), 1501. (25) Suzuki, T.; Nakagawa, Y.; Takano, I.; Yaguchi, K.; Yasuda, K. Environmental Fate of Bisphenol A and Its Biological Metabolites in River Water and Their Xenoestrogenic Activity. Environ. Sci. Technol. 2004, 38, 2389. (26) Levec, J.; Pintar, A. Catalytic wet-air oxidation processes: A review. Catal. Today 2007, 124, 172. (27) Luck, F. Wet air oxidation: Past, present and future. Catal. Today 1999, 53, 81. (28) Cybulski, A. Catalytic Wet Air Oxidation: Are Monolithic Catalysts and Reactors Feasible?. Ind. Eng. Chem. Res. 2007, 46, 4007. (29) Abecassis-Wolfovich, M.; Landau, M. V.; Brenner, A.; Herskowitz, M. Low-temperature combustion of 2,4,6-trichlorophenol in catalytic wet oxidation with nanocasted Mn Ce-oxide catalyst. J. Catal. 2007, 247, 201. (30) Cybulski, A.; Trawczy nski, J. Catalytic wet air oxidation of phenol over platinum and ruthenium catalysts. Appl. Catal., B 2004, 47, 1. 8833


Industrial & Engineering Chemistry Research (31) Li, N.; Descorme, C.; Besson, M. Catalytic wet air oxidation of 2-chlorophenol over Ru loaded CexZr1 xO2 solid solutions. Appl. Catal., B 2007, 76, 92. (32) Duprez, D.; Delano€e, F.; Barbier, J., Jr.; Isnard, P.; Blanchard, G. Catalytic oxidation of organic compounds in aqueous media. Catal. Today 1996, 29, 317. (33) Kojima, Y.; Fukuta, T.; Yamada, T.; Onyango, M. S.; Bernardo, E. C.; Matsuda, H.; Yagishita, K. Catalytic wet oxidation of o-chlorophenol at mild temperatures under alkaline conditions. Water Res. 2005, 39, 29. (34) Perkas, N.; Pham Minh, D.; Gallezot, P.; Gedanken, A.; Besson, M. Platinum and ruthenium catalysts on mesoporous titanium and zirconium oxides for the catalytic wet air oxidation of model compounds. Appl. Catal., B 2005, 59, 121. (35) Pintar, A.; Besson, M.; Gallezot, P. Catalytic wet air oxidation of Kraft bleaching plant effluents in the presence of titania and zirconia supported ruthenium. Appl. Catal., B 2001, 30, 123. (36) Pintar, A.; Besson, M.; Gallezot, P. Catalytic wet air oxidation of Kraft bleach plant effluents in a trickle-bed reactor over a Ru/TiO2 catalyst. Appl. Catal., B 2001, 31, 275. (37) Pintar, A.; Batista, J.; Tisler, T. Catalytic wet-air oxidation of aqueous solutions of formic acid, acetic acid and phenol in a continuousflow trickle-bed reactor over Ru/TiO2 catalysts. Appl. Catal., B 2008, 84, 30. (38) Hoffmann, M. R.; Martin, S. T.; Choi, W.; Bahnemann, D. W. Environmental Applications of Semiconductor Photocatalysis. Chem. Rev. 1995, 95, 69. (39) Chong, M. N.; Jin, B.; Chow, C. W. K.; Saint, C. Recent developments in photocatalytic water treatment technology: A review. Water Res. 2010, 44, 2997. (40) Shen, X.; Garces, L.-J.; Ding, Y.; Laubernds, K.; Zerger, R. P.; Aindow, M.; Neth, E. J.; Suib, S. L. Behavior of H2 chemisorption on Ru/ TiO2 surface and its application in evaluation of Ru particle sizes compared with TEM and XRD analyses. Appl. Catal., A 2008, 335, 187. (41) Routledge, E. J.; Sumpter, J. P. Estrogenic Activity of Surfactants and Some of Their Degradation Products Assessed Using a Recombinant Yeast Screen. Environ. Toxicol. Chem. 1996, 15, 241. (42) Fent, K.; Escher, C.; Caminada, D. Estrogenic Activity of Pharmaceuticals and Pharmaceutical Mixtures in a Yeast Reporter Gene System. Reprod. Toxicol. 2006, 22, 175. (43) Water quality - Determination of the inhibitory effect of water samples on the light emission of Vibrio fischeri (Luminescent bacteria test)Part 2: Method using liquid-dried bacteria; ISO 11348-2; International Organization for Standardization: Geneva, Switzerland, 2007. (44) Thompson, A. S.; Rhodes, J. C.; Pettman, I. Culture Collection of Algae and Protozoa, Catalogue of Strains; Culture Collection of Algae and Protozoa Freshwater Biological Association: Cumbria, UK, 1988. (45) Water quality - Freshwater algal growth inhibition test with unicellular green algae; ISO 8692; International Organization for Standardization: Geneva, Switzerland, 2004. (46) Water quality - Determination of the inhibition of the mobility of Daphnia magna Straus (Cladocera, Crustacea)- Acute toxicity test; ISO 6341; International Organization for Standardization: Geneva, Switzerland, 1996. (47) Water quality - Determination of the acute toxicity of waste water to zebrafish eggs (Danio rerio); ISO 15088; International Organization for Standardization: Geneva, Switzerland, 2007. (48) Kammann, U.; Biselli, S.; H€uhnerfuss, H.; Reineke, N.; Theobald, N.; Vobach, M.; Wosniok, W. Genotoxic and Teratogenic Potential of Marine Sediment Extracts Investigated with Comet Assay and Zebrafish Test. Environ. Pollut. 2004, 132, 279. (49) Bond, G. C.; Rajaram, R. R.; Burch, R. Thermal analysis of catalyst precursors. Part 1. Temperature-programmed evolution of hydrogen chloride during the reduction of supported ruthenium trichloride. Appl. Catal. 1986, 27, 379. (50) Bond, G. C.; Rajaram, R. R.; Burch, R. Hydrogenolysis of propane, n-butane, and isobutane over variously pretreated ruthenium/ titanium dioxide catalysts. J. Phys. Chem. 1986, 90, 4877.

ARTICLE

(51) Bradford, M. C. J.; Vannice, M. A. CO2 Reforming of CH4 over Supported Ru Catalysts. J. Catal. 1999, 183, 69. (52) Lakota, A.; Levec, J. Solid-liquid mass transfer in packed beds with cocurrent downward two-phase flow. AIChE J. 1990, 36, 1444. (53) Wammes, W. J. A.; Westerterp, K. R. The influence of the reactor pressure on the hydrodynamics in a cocurrent gas-liquid tricklebed reactor. Chem. Eng. Sci. 1990, 45, 2247. (54) Goto, S.; Smith, J. M. Trickle-bed reactor performance. Part I. Holdup and mass transfer effects. AIChE J. 1975, 21, 706. (55) Satterfield, C. N. Trickle-bed reactors. AIChE J. 1975, 21, 209. (56) Taboada, C. D.; Batista, J.; Pintar, A.; Levec, J. Preparation, characterization and catalytic properties of carbon nanofiber-supported Pt, Pd, Ru monometallic particles in aqueous-phase reactions. Appl. Catal., B 2009, 89, 375. (57) Bielanski, A.; Haber, J. Oxygen in Catalysis; M. Dekker: New York, 1991. (58) Imamura, S.; Okumura, Y.; Nishio, T.; Utani, K.; Matsumara, Y. Wet-Oxidation of a Model Domestic Wastewater on a Ru/Mn/Ce Composite Catalyst. Ind. Eng. Chem. Res. 1998, 37, 1136. (59) de Leitenburg, C.; Goi, D.; Primavera, A.; Trovarelli, A.; Dolcetti, G. Wet oxidation of acetic acid catalyzed by doped ceria. Appl. Catal., B 1996, 11, L29. (60) Barbier, J., Jr.; Delano€e, F.; Jabouille, F.; Blanchard, G.; Isnard, P. Total Oxidation of Acetic Acid in Aqueous Solutions over Noble Metal Catalysts. J. Catal. 1998, 177, 378. (61) Dave, G.; Xiu, R. Toxicity of Mercury, Copper, Nickel, Lead, and Cobalt to Embryos and Larvae of Zebrafish Brachydanio rerio. Arch. Environ. Contam. Toxicol. 1991, 21, 126. (62) Frontistis, Z.; Daskalaki, V. M.; Katsaounis, A.; Poulios, I.; Mantzavinos, D. Electrochemical enhancement of solar photocatalysis: Degradation of endocrine disruptor bisphenol-A on Ti/TiO2 films. Water Res. 2011, 45, 2996. (63) Mutou, Y.; Ibuki, Y.; Terao, Y.; Kojima, S.; Goto, R. Chemical Change of Chlorinated Bisphenol A by Ultraviolet Irradiation and Cytotoxicity of Their Products on Jurkat Cells. Environ. Toxicol. Pharmacol. 2006, 21, 283.

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Catalytic and Photocatalytic Oxidation of Aqueous Bisphenol A Solutions

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