Received: 14 November 2009 Revised: 10 January 2010 Accepted: 26 January 2010 Published online in Wiley Interscience: 23 March 2010

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1 Research Article Received: 14 November 29 Revised: 1 January 21 Accepted: 26 January 21 Published online in Wiley Interscience: 23 March 21 ( DOI 1.12/jctb.2374 Effect of sonication assisted by titanium dioxide and ferrous ions on polyaromatic hydrocarbons (PAHs) and toxicity removals from a petrochemical industry wastewater in Turkey Delia Teresa Sponza and Rukiye Oztekin Abstract BACKGROUND: In Izmir (Turkey) polyaromatic hydracarbon (PAH) removal efficiencies are low in petrochemical industry aerobic biological wastewater treatment plants because bacteria are not able to overcome the inhibition of these toxic and refractory organics. In order to increase PAHs removal, sonication process was chosen among other advanced treatment processes include sonication processes. The effects of ambient conditions, increasing sonication time, sonication temperature, TiO 2 and Fe +2 concentrations on sonication at a petrochemical industry wastewater treatment plant in Izmir (Turkey) was investigated in a 65 W sonicator, at a frequency of 35 khz and a 5 ml glass reactor. RESULTS: Increasing the temperature improved PAH removal after 15 min sonication at 3 Cand6 C. The maximum total PAH removal efficiencies were the same in a reactor containing 2 mg L 1 TiO 2 and in a TiO 2 -free reactor at 3 Cand6 Cafter 15 min sonication. Maximum 91% and 97% total PAH removals were obtained in a control reactor and a reactor containing 2 mg L 1 Fe +2 at 3 Cand6 C, respectively, after 15 min sonication. The PAH concentration was toxic to Daphnia magna, so that the EC 5 value decreased significantly from ng ml 1 to EC 5 = 9.88 ng ml 1 and to EC 5 = 3.35 ng ml 1,atthe lowest TiO 2 (.1 mg L 1 )andfe +2 (2 mg L 1 ) concentrations, respectively, after 15 min sonication at 3 C. CONCLUSION: PAHs and the acute toxicity in a petrochemical industry wastewater were removed efficiently through sonication. c 21 Society of Chemical Industry Keywords: Daphnia magna; pyrolysis; pseudo-first-order kinetic; polyaromatic hydrocarbons (PAHs); removal INTRODUCTION Polyaromatic hydrocarbons (PAHs), a class of environmental pollutants mainly derived from the incomplete combustion of fossil fuels, enter groundwaters and surface waters through leaching processes. While their solubility is generally quite low and usually decreases with increasing molecular weight, their hazard potential can be relatively high, thus making their presence in the water cycle both an acute and a chronic risk to human health and environmental quality. Wastewater treatment plants, especially those serving industrial areas, consistently receive complex mixtures containing a wide variety of organic pollutants. Groups of compounds present in the petrochemical industries include polycyclic aromatic hydrocarbons (PAHs), which are listed as US-EPA and EU priority pollutants, and concentrations of these pollutants therefore need to be controlled in treated wastewater effluents. 1,2 Owing to the associated health concerns, some PAHs are possible or probable human carcinogens, such as benzo(a)pyrene, and all PAHs which have four condensed rings pose these risks. 3 PAHs are ubiquitous environmental pollutants with mutagenic properties, which have not been included in the Turkish guidelines for treated waste monitoring programs. 4 As a consequence of their strongly hydrophobic properties and their resistance to biodegradation, PAHs are not always removed from wastewaters by activated sludge treatments, which very efficiently relocate them into treated effluents. Studies reported in recent literature show that sonication may be a useful tool in removing aqueous pollutants. 5 8 The sonication process is capable of effectively degrading target compounds including chlorophenols, chloroaromatics and PAHs present in dilute solutions, typically in the micro and nano ranges. Sonochemical destruction of pollutants in the aqueous phase generally occurs as the result of imploding cavitation bubbles and involves several reaction pathways and zones such as pyrolysis inside the bubble and/or at the bubble liquid interface and hydroxyl radical-induced reactions at Correspondence to: Delia Teresa Sponza, Dokuz Eylül University, Engineering Faculty, Department of Environmental Engineering, Tınaztepe Campus, 3516 Buca/Izmir, Turkey. delya.sponza@deu.edu.tr Dokuz Eylül University, Engineering Faculty, Department of Environmental Engineering, Tınaztepe Campus, 3516 Buca/Izmir, Turkey 913 J Chem Technol Biotechnol 21; 85: c 21 Society of Chemical Industry

2 DT Sponza, R Oztekin 914 thebubble liquidinterfaceand/orintheliquid This process is capable of effectively degrading several target compounds including phenol, chlorophenols, nitrophenols, polychlorinated biphenyls, chloroaromatics, pesticides, dyes, polycyclic aromatic hydrocarbons and surfactants. 13 The operating costs appear to be less than those for conventional thermochemical methods (e.g. wet air oxidation), which require high temperatures and pressures. 6 Furthermore, the process does not require the use of extra chemicals (e.g. oxidants and catalysts) commonly employed in several advanced oxidation processes (e.g. ozonation, Fenton s reagent), thus avoiding the respective costs as well as the need to remove the excess of toxic compounds prior to discharge. 4 In recent years, the technology of ultrasonic degradation has been studied and used extensively to treat some organic pollutants. 2 Irradiation with high power ultrasound can result in acoustic cavitation, namely, the process of the formation, growth and implosive collapse of gas bubbles in liquids, releasing energy. 14 The cleavage of chemical bonds, the oxidation and the pyrolysis and/or combustion of organic compounds are observed when chemistry is involved. 15,16 The literature data concerning sonodegradation of PAHs is scarce, and results are contradictory. Some work states that PAHs are (i) oxidized by means of H o,oh o and OOH o (hydrogen, hydroxyl and hydroperoxyl radicals), 6,17 whereas other studies argue that (ii) a pyrolytic process can occur 18,19 and finally that (iii) both processes are possible. 2,21 The first process is evidenced by the identification of hydroxylated byproducts. These radicals can result in the destruction of solutes containing organic pollutants. 22 In the second pathway the formation of hydroxylated byproducts is not observed under ultrasonic irradiation; it is suggested that hydroxyl radicals are not important species and PAH radicals were formed via hightemperature pyrolysis. 2 Few studies have been performed with PAHs, to investigate the effects of TiO 2 and Fe +2 on their sonodegradation efficiencies. Wheat and Tumeo 17 studied the sonochemical removal of phenanthrene and biphenyl in aerated aqueous solutions in the presence of Fe 3+ ions at a frequency of 32 khz and a power of 56 W after 9 min. In further studies, Taylor et al. 18 and Laughrey et al. 2 studied the sonochemical removal of anthracene, phenanthrene and pyrene at 2 khz, with emphasis on the effect of purging gases (i.e. nitrogen and oxygen) on the kinetics of PAHs degradation at frequencies and powers varying between 25 and 32 khz and W, respectively, after 3 18 min sonication. Park et al. 23 studied the effect of various operating conditions (i.e. ph value, ultrasound intensity), and the presence of matrix components (i.e. hydrogen peroxide) and purging gases (i.e. argon) on the sonochemical degradation of phenanthrene (PHE), anthracene (ANT), pyrene (PY), at 2 khz and a power of 42 W at sonication times varying between 3 and 18 min in water : ethanol mixtures. Little et al. 21 studied the sonochemical degradation of phenanthrene at 3 khz, monitoring the influence of parameters such as applied power, liquid phase temperature and light at different sonication times. Whang et al. 2 showed that the parathion in aqueous solution can be decomposed by the method of sonocatalytic degradation in the presence of 1 mg L 1 TiO 2 powder as sonocatalyst. In Izmir, Turkey, petrochemical plant wastewaters are treated with conventional activated sludge systems. Since such systems are unable to completely remove the main PAHs present (ca.17) these are released into receiving bodies. Although some studies have appeared with research aimed at increasing the biodegradation of some PAHs with low benzene rings [NAP, PHE, ANT, PY and acenaphthalene (ACT)] with sonication have appeared, these have been limited to only a few of those generally present(3 5)insyntheticwastewaters. 6,13,17,24 Nostudywasfound investigating the effects of operational conditions (sonication time, temperature, TiO 2,Fe +2 ) on the sonication of PAHs with high benzene rings present in a real petrochemical industry wastewater (PCI ww) treatment plant. Furthermore, the effects of the aforementioned operational conditions on acute toxicity removal have not been determined for PCI ww. The sonication kinetics, the sonication mechanism and the acute toxicity of the sonicated PAHs with high benzene rings in petrochemical wastewater enhanced with TiO 2,Fe +2 have not been investigated. The innovative aspects of this study are: (i) to determine the effects of ambient conditions, increasing sonication time (6 min, 12 and 15 min), sonication temperatures(25 C,3 Cand6 C),TiO 2 (.1 mg L 1,.5mgL 1, 1 and 2 mg L 1 ) and Fe +2 (2 mg L 1, 8 and 2mgL 1 ) concentrations on the sonodegradation of 17 PAHs with both low and high benzene rings; (ii) to monitor the responses of sonicated petrochemical wastewaters on the acute toxicity of Daphnia magna for the aforementioned operational conditions; and (iii) to determine the reaction kinetic of seven PAHs (FLN, FL, CHR, BbF, IcdP, DahA and BghıP) and the mechanism of PAH sono-removal. MATERIALS AND METHODS Sonicator A Bandelın Electronic RK51 H (Bandelin, Berlin- Germany) sonicator was used for sonication of the PCI ww samples. The sonication frequency and power were 35 khz and 65 W, respectively. Glass serum bottles in a glass reactor were filled to 5 ml with raw PCI ww and closed with teflon-coated stoppers for the measurement of volatile compounds (evaporation) of the raw PCI ww. The evaporation losses of PAHs were estimated to be.1% in the reactor and, therefore, assumed to be negligible. The serum bottles were filled with.1 ml of methanol in order to prevent adsorption on the walls of the bottles and to minimize evaporation. Temperatures of 25 C, 3 Cand6 C were adjusted electronically in the sonicator with two thermostatic heaters. The stainless steel sonicator was equipped with a teflon holder to prevent temperature losses. The shematic configuration of the sonicator used in this study is shown in Fig. 1. Operational conditions The effects of ambient conditions (25 C), increasing sonication time (6, 12 and 15 min), sonication temperature (3 and 6 C), different TiO 2 (.1 mg L 1,.5mgL 1,1and2mgL 1 )and Fe +2 (2 mg L 1,8and2mgL 1 ) concentrations on sonication of PCI ww taken from the influent of the aeration tank of a petrochemical industry wastewater treatment plant in Izmir (Turkey) were investigated. Fresh solutions of FeSO 4 and TiO 2 were added to the petrochemical wastewater before sonication was begun. Sonicated samples were taken at 6, 12 and 15 min sonication times and they were kept in a refrigerator at +4 Cuntil experimental analysis begun. Deionized pure water (conductivity of the system is 18 M cm 1 while the resistivity is.2 µsiemens) was obtained through a SESA, (İzmir-Turkey) Ultrapure water system. Reagent grade ferrous sulfate and titanium dioxide (were 99% purity and they were obtained from Sigma Chemicals Co (St. Louis, MO, USA) as analytical grades) were used during PAH analysis. Characterization of raw PCI ww taken from the influent c 21 Society of Chemical Industry J Chem Technol Biotechnol 21; 85:

3 Sonication enhanced toxicity removals from a petrochemical industry wastewater PAHs were identified on the basis of their retention times, target and qualifier ions and were quantified using the internal standard calibration procedure. The physical and chemical properties of the PAHs studied in this work are summarized in Table 2. Temperature, ph, ORP, COD and TOC concentrations were monitored following Standard Methods 255, 258, 522 D and Figure 1. Structural diagram of the sonicator used in this study: (1) glass reactor,(2) stirrer,(3) energyconversitiondevice,(4) thermometer,(5) heater, (6) stainless stell bath, (7) water exit valve, (8) thermostate, (9) teflon cover. of the aeration unit of a PCI ww treatment plant was given as the mean values of triplicate samplings (Table 1). Analytical methods Sample preparation and PAHs analysis For PAH analyses the water samples were filtered through a glass fiber filter (47 mm-diameter) to collect particle phase in series with a resin column ( 1 g XAD-2) and to collect dissolvedphase polybrominated diphenyl ethers. Resin and water filters were ultrasonically extracted for 6 min with a mixture of 1 : 1 acetone: hexane. All extracts were analyzed for 17 PAHs with a gas chromatograph (GC) (Agilent Technology model 689N) equipped with a mass selective detector (Agilent 5973 inert MSD). A capillary column (HP5-MS, 3 m,.25 mm,.25 µm) was used. The initial oven temperature was kept at 5 C for 1 min, then raised to 2 C at 25 Cmin 1 and from 2 to 3 Cat8 Cmin 1, and was then maintained for 5.5 min. High purity He (g) was used as the carrier gasatconstantflowmode(1.5 ml min 1,45cms 1 linearvelocity). Oxidation products and gas analysis The phenanthrenediol analysis was performed using highpressure liquid chromatography (HPLC) (Agilent-11) with a method developed by Lindsey and Tarr. 18 The chromatographic conditions to determine phenanthrenediol were as follows: a C-18 reverse phase HPLC column (Ace 5C18 model, Wasington DC, USA) was used with dimensions 25 cm 4.6 mm, 5 µm, the mobile phase consisted of 5/5 (v/v) methanol/organic-free reagent water. The CH 4,CO 2 and H 2 S gas analysis was performed following Standard Methods. 25 Daphnia magna toxicity test To test toxicity 24 h Daphnia magna were used as described in Standard Methods. 25 After preparing the test solution, experimentswerecarriedout using 5or1 daphnids introduced into the test vessels. These vessels had 1 ml effective volume at 7 8 ph, providing a minimum DO concentration of 6 mg L 1 at an ambient temperature of 2 25 C. Young Daphnia magna were used in the test ( 24 h old). A 24 h exposure is generally accepted as standard for a Daphnia acute toxicity test. The results were expressed as mortality percentage of the Daphnids. Immobile animals were reported as dead Daphnids. All experiments were carried out three times and the results given as the means of triplicate samplings. Individual PAH concentrations are given as the mean with standard deviation (SD) values. Statistical analysis Analysis of variance (ANOVA) of experimental data was performed to determine the F and P values, i.e. the ANOVAtestwas used to test Table 1. Wastewater characterization (mean values ± SD) Parameter Level, concentration a Parameter Level, concentration a ph ±.3 Cd ±.27 Sampling temperature ( C) ± 1.4 Cr ±.65 Total PAH b ± 9.2 Mo ±.8 Dissolved oxygen ±.4 Ni ±.8 Total COD ± 9.7 Pb ±.56 soluble COD ± 9.6 Zn ± 9.9 BOD ± 2.78 Fe ± 6. Total N ±.22 Cd ±.17 Total P ±.9 Cr ±.56 Ammonium ± 4.46 Ni ± 2.8 Nitrate ± 1.82 Pb ± 1.76 Nitrite ±.1 Mn ±.1 VSS ± 7.8 Co ±.2 Oil-grease ± 2.25 Mg ± 4.5 TSS ± K ± 9.7 a All concentrations (except ph and temperature) in mg L 1. b Concentration in ng ml J Chem Technol Biotechnol 21; 85: c 21 Society of Chemical Industry

4 DT Sponza, R Oztekin Table 2. Physical and chemical properties of the PAHs studied in this work PAHs CAS-No MF MW T M T B S W (25 C) VP (25 C) H (25 C) log K OA (25 C) log K OW IPC NAP C 1 H E-1 8.5E-2 4.4E E- ACL C 12 H E E E E-2 ACT C 12 H E E E E-2 FLN C 13 H E-2 6.E E E-2 PHE C 14 H E E E E-2 ANT C 14 H E E E E-3 CRB C 12 H E-3 7.5E E E-2 FL C 16 H E E E E-2 PY C 16 H E-3 4.5E E E-2 BaA C 18 H E-5 2.1E-7 1.2E E-4 CHR C 18 H E E E E-4 BbF C 2 H E-5 5.E E E-4 BkF C 2 H E-6 9.7E E E-4 BaP C 2 H E E E E-5 IcdP C 22 H E E E E-4 DahA C 22 H E-6 1.E E E-3 BghiP C 22 H >5 267E-6 1.E E E-1 Naphthalene (NAP), acenaphthylene (ACL), acenaphthene (ACT), flourene (FLN), phenanthrene (PHE), anthracene (ANT), carbozole (CRB), fluoranthene (FL), pyrene (PY), benz[a]anthracene (BaA), chrysene (CHR), benz[b]fluoranthene (BbF), benz[k]fluoranthene (BkF), benz[a]pyrene (BaP), indeno[1,2,3-cd]pyrene (IcdP), dibenzo[a,h]anthracene (DahA), benzo[g,h,i]perylene (BghiP). MF : Molecular formula, MW:Molecularweight(gmol 1 ), T M :Meltingpoint( C), T B : Boiling point ( C), S W : Solubility in water (mg L 1 ), VP: Vapor pressure (mm Hg), H: Henry s law constant (atm m 3 mol 1 ), log K OW : Octanol-water coefficient, log K OA : Octanol-air coefficient; IPC: InitialPAH concentration (mean, ng ml 1 ). 916 the differences between dependent and independent groups. 26 Comparison between the actual variation in experimental data averages and standard deviation was expressed in terms of F ratio. F was equal to found variation of the data averages/expected variation of the data averages. P reports the significance level. Regression analysis was applied to the experimental data to determine the regression coefficient R RESULTS AND DISCUSSION Effect of sonication frequency and power on the degradation of PAHs The effect of ultrasonic frequency in the range 35 to 15 khz on the degradation ratio of PAHs, COD and TOC was also considered. The preliminary studies showed that the best PAH degradation ratios were obtained at a frequency of 35 khz. 28,29 Increasing sonication frequency did not increase the number of free radicals, therefore a low number of free radicals did not escape from the bubbles and did not migrate, as reported by David. 14 The most effective sonication power applied in the sonication process in this study was found to be 65 W. 29 Ultrasonic irradiation of high output power can facilitate the dispersion of organic pollutants with OH o radicals, resulting in the destruction of PAHs. As the power is increased, the number of collapsing cavities also increases, leading to enhanced removal rates, as reported by Papadaki et al. 4 and Psillakis et al. 6 Effect of increasing sonication time on PAH removal efficiencies in ambient conditions (25 C) Raw PCI ww samples were sonicated at a starting ambient temperature of 25 C and at increasing sonication times (6, 12 and 15 min). In general, PAH removal efficiencies increased PAH removal eff. (%) PAH Removal (%) 25 C Figure 2. Effect of increasing sonication time on PAH removal efficiencies at ambient temperature (25 C). as sonication time was increased (Fig. 2). Although Park et al. 23 reported that lower molecular weight (2-, 3- and 4-ring) PAHs were degraded more rapidly than the heavier (5- and 6-ring) compounds, in this present study high removal efficiencies were found for PAHs with high numbers of benzene rings after a long sonication time (15 min) at 25 C (Tables 2 and 3). As seen in Table 3 the mean maximum removal was 89.95% for BaA, BbF, BkF, DahA and BghıP PAHs with five and six benzene rings after 15 min sonication at 25 C. In this study, no significant difference in PAH yields between PAHs with three (ANT, FL, PY), five (BbF, BkF) and six rings (Daha, BghiP) was observed, although PAHs with more benzene rings became increasingly less soluble in water with increasing number of benzenoid rings and molecular weight, and with decreasing Henry s law constants at short sonication times (R 2 =.96, F = 4.36 P =.1) (Tables 2 and 3). In other words, although DahA and BghıP PAHs were the most hydrophobic types, c 21 Society of Chemical Industry J Chem Technol Biotechnol 21; 85:

5 Sonication enhanced toxicity removals from a petrochemical industry wastewater Table 3. Effect of sonication time on the maximum removal efficiencies of 17 PAHs in the influent and in the effluent of the sonication experiments at ambient conditions (25 C) PAH PAH t= PAH t=15 PAH t=6(%) PAH t=12(%) PAH t=15(%) NAP 1E-± E-± ACL 519E-2± E-± ACT 6682E-3± E-± FLN 5557E-2±6.99 1E-± PHE 1255E-2± E-± ANT 747E-3± E-2± CRB 1419 E-2± E-2± FL 1936E-2±2.1 31E-1± PY 1554 E-2± E-1± BaA 55E-4±.12 5E-2± CHR 268E-3± E-2± BbF 79 E-4±.14 4E-3± BkF 8E-4±.17 8E-3± BaP 73E-4±.6 25E-3± IcdP 193E-3±.27 4E-2± DahA 4578E-3±.22 1E-2± BghıP 513E-4±.26 1E-2± PAH t= : mean influent PAH concentration before sonication (ng ml 1 ) ± SD; PAH t=15 : mean effluent PAH concentration after 15 min sonication(ng ml 1 ) ± SD; PAH t=6(%) : mean PAH removal efficiency after 6 min sonication; PAH t=12(%) : mean PAH removal efficiency after 12 min sonication; PAH t=15(%) : mean PAH removal efficiency after 15 min sonication. Table 4. Maximum removal efficiencies of 17 PAHs measured in the influent and in the effluent of sonication experiments at 6 C PAH PAH t= PAH t=5 PAH t=6(%) PAH t=12(%) PAH t=15(%) NAP 182E-± ± ACL 7E-2± ± ACT 466E-2± ± FLN 5589E-2± ± PHE 1379E-1± ± ANT 363E-3±.49.3 ± CRB 2651E-2± ± FL 1697E-2± ± PY 1449E-2± ± BaA 28E-4±.4.2 ± CHR 232E-3± ± BbF 23E-3±.31.3 ± BkF 47E-4±.64.3 ± BaP 13E-4±.18.1 ± IcdP 217E-3± ± DahA 542E-4± ± BghıP 58E-4±.8.2 ± PAH t= :mean influent PAH concentration before sonication (ng ml 1 ) ± SD; PAH t=15 : mean effluent PAH concentration after 15 min sonication (ng ml 1 ) ± SD; PAH t=6(%) : mean PAH removal efficiency after 6 min sonication; PAH t=12(%) : mean PAH removal efficiency after 12 min sonication; PAH t=15(%) : mean PAH removal efficiency after 15 min sonication. with low Henry s law constants, vapor pressures and solubilities and high octanol-water coefficients, a significant correlation was not observed between the removal percentages of the these PAHs and their physicochemical properties after long sonication times and at low temperatures such as 25 C. Treatment by sonication converts PAHs with multiple benzene rings to much smaller compounds. It is obvious that higher sonication times are needed for complete mineralization: short sonication times did not provide high removal yields for refractory PAHs. Therefore, a decrease in the percentage remaining PAHs was expected at longer sonication times due to high temperature and radical reactions as a rsult of cavitation. Although ANT and PHE contained a similar number of benzene rings (3), PHE PAH have higher removal yields than ANT at long sonication times (Table 3). This could be attributed to the high solubility, water pressure, Henry s law constant and low octanol/water partition coefficient of PHE compared with ANT (Tables 2 and 3). This constrasts with the study performed 917 J Chem Technol Biotechnol 21; 85: c 21 Society of Chemical Industry

6 DT Sponza, R Oztekin 918 by David 14 which reported that the geometry of the chemical structure of PAHs affected the degradation efficiency of PAH, with a straight structure (ANT) more easily degraded than a branched structured (PHE). Moreover, the choice of solvent affected the degradation of PAHs under sonication, and this ultimately is expected to alter the effectiveness of ultrasonic extractions at long sonication times. 3 High PHE yields compared with ANT could be attributed to the type of solvent used. Cavities are more readily formed when using solvents with low viscosity and low surface tension during long sonication times. 3 Preliminary studies showed that solvents with high surface tension and viscosity generally have a higher threshold for cavitation resulting in fewer cavitation bubbles but harsher conditions once cavitation is established, resulting in higher temperatures and pressures upon bubble collapse. 31 In this study, among the solvents used, acetone and hexane have the highest surface tension and viscosity. Higher cavitation bubbles resulting in fiercer cavitation conditions was a reason for less PHE remaining with acetone after 15 min sonication. The vapor pressure of the solvent is another important factor affecting cavitation. 31 Higher vapor pressure leads to more solvent volatilizing into cavitation bubbles which are able to be dissociated by high temperature after 15 min sonication. Hexane and acetone have the highest vapor pressure among thesolventsused.thus,morehexanemoleculesmigrateinto cavitation bubbles leading to more molecules dissociating to generate radicals. As a result, more radical reactions of PHE occurred resulting in a lower percentage remaining in hexane after 15 min sonication. The results found in this study were stronger in comparison with the study performed by Psillakis et al. 6 They found 74%, 72% and 76% PHE, NAP and ACL removal rates, respectively, at a temperature 4 C, power 45 W and frequency of 28 khz after 98 min sonication. Similarly, in a study performed by Littlee et al ng ml 1 PHE was found to be recalcitrant to sonochemical removal at 22 C at an ultrasound frequency of 3 khz and power 32 W after 135 min sonication. However, increasing the liquid bulk temperature to 4 C led to about 56% removal at the same operational conditions. Effect of increasing temperature on the removal of PAHs with increasing sonication time Raw PCI ww samples were sonicated at 3 Cand6 C for 6, 12 and 15 min. Similar total PAH removal yields were found at 25 C and 6 C(E= approximately 55%) after 6 min sonication time (Fig. 3). In other words, increasing the temperature from 25 Cto 3 Cand6 C did not contribute to PAH removal with 6 min sonication. Total PAH removed decreased slightly at a temperature of 3 C with the same sonication time (Fig. 3). Similarly, total PAH removals at 3 C remained at the same level as at 25 Cafter 12 min sonication. Increasing the temperature to 6 C increased total PAH removal efficiency for 12 and 15 min sonication times (Fig. 3). As seen in Table 4, all removal yields of individual PAHs increased as sonication time was increased from 6 min to 15 min at a temperature of 6 C. The yields of all individual PAHs were above 91% except for BbF PAH (86.21%) after 15 min sonication at 6 C (Table 4); i.e. sonication at high temperature increased the yields of all PAH species. The results of this study show that PAH removal was not dependent on the number of benzene rings for individual PAH species. Therefore, it can be concluded that no correlation was found at 6 C between the removal of PAHs and water solubility, Henry s law constants and vapor pressure, and PAH removal eff. (%) PAH (%) 25 C PAH (%) 3 C PAH (%) 6 C Figure 3. Effect of increasing temperature on PAH removal efficiencies versus sonication time. the difference is not significant (R 2 =.54, F = 56.34, P =.1). It was found that PAH degradation is a function of sonication time (15 min) and temperature (6 C). Strong correlation was found between PAH yields, time and temperature (R 2 =.97). This correlation is also significant (F = 4.93, P =.1). The two experimental conditions employed in this study influenced the important physical parameters related to cavitation bubbles such as the extent of radical production from the bubble, thickness of the liquid shell surrounding the bubble, concentration of PAHs in the interfacial region, and extent of radical scavenging in the medium. 3 For this reason, most probably, a significant difference was not observed between the lower molecular weight PAHs (e.g. those with two, three or four aromatic rings) and the higher molecular weight, more hydrophobic PAHs, in their individual removals (R 2 =.62, F = 23.67, P =.1) at 6 C. On the other hand, low-frequency ultrasound is expected to induce destructive effects in hydrophobic solutes, since they can easily diffuse near cavitation bubbles and undergo pyrolytic destruction inside the collapsing bubble or hydroxylation and thermal decomposition at its interfacial sheath. 3,31 Given that all PAHs with high molecular weight used in this study are relatively non-volatile (Table 3), their ability to migrate towards the bubble and rapidly decompose at the interface is likely to be dictated by their hydrophobicity. It appears that the more hydrophobic PAHs are all readily susceptible to sonochemical degradation, and nearcomplete removal (98%) is achieved with15 min of irradiation under the conditions considered. Different mechanisms have been proposd to explain the effect of temperature on sonochemical degradation of PAHs since it is a relatively complex issue closely related to the properties and reaction conditions of each specific system. As the temperature is increased the collapse temperature of the cavitation bubble should decrease. 14 However, other studies have shown that following an initial increase in solution temperature the rate of reaction increases leading to a greater fraction of volatile compounds partitioning into the cavity. 3,31 Increased temperatures probably facilitate bubble formation due to an increase in equilibrium vapor pressure. The bubbles contain more vapor and consequently reduce the maximum temperature obtained during bubble collapse.in addition, increased temperatures probably encourage degassing of the liquid phase, thus reducing the number of gas nuclei available for bubble formation. 6 In the study by Laughrey et al. 2 77% PAH removal efficiency was observed for the sonochemical removal of a 5 µgl 1 initial c 21 Society of Chemical Industry J Chem Technol Biotechnol 21; 85:

7 Sonication enhanced toxicity removals from a petrochemical industry wastewater PAHs mixture concentration (NAP, ACL and PHE) in water after a sonication time of 12 min at a temperature 4 C, power 15 W and ultrasound frequency 24 khz. Benabdallah El-Hadj et al. 13 found 33% and 47% PAH removal effiencies in mesophilic (35 C) and thermophilic (55 C) conditions for NAP and PY in a sonicator with a frequency of 2 khz and ultrasonic power 7 W, after 11 min sonication, before anaerobic digestion. The yields obtained in these studies are low in comparison with the removal performances of PAHs found in this study. The removal efficiencies for PAHs with any number of benzene rings were above 9%. The maximum removals for PAHs with one, three, four and five rings were determined as 99%. It was observed that PAHs with more benzene rings were also degradable with high yields, even though some other studies have demonstrated that sonication is not effective for PAHs with a high number of benzene rings. 2 Effectoftitaniumdioxide(TiO 2 )concentrationonpahremoval efficiencieswithincreasingsonicationtimesandtemperatures In order to optimize the addition of an amount of TiO 2 catalyst to obtain the greatest sonocatalytic destruction of PAHs.1 mg L 1,.5 mg L 1,1and2mgL 1 TiO 2 was added to the PCI ww before the sonication experiments. In general, the results of this study showed that as sonication time was increased, total PAH yields also increased at 3 C. All TiO 2 concentrations increased total PAH removals after 6 and 12 min sonication, compared with the control reactor containing no TiO 2 (Fig. 4(a)). The increase of TiO 2 concentration from.1 mg L 1 to 2 mg L 1 increased total PAH removal after 6 and 12 min sonication times at 3 C. Total PAH yields were the same in the control reactor free of TiO 2 and the reactor containing 2 mg L 1 TiO 2 after 15 min sonication at 3 C. Total PAH removals were slightly lower in the reactors containing.1 and.5 mg L 1 TiO 2 concentrations after 15 min sonication, compared with the control (Fig. 4(a)). When sonication time was increased from 6 min to 15 min at 6 C, total PAH removal increased in all reactors containing TiO 2 and in the control reactor free of TiO 2 (Fig. 4(b)). No significant increase in total PAH yield was obtained by increasing TiO 2 concentration from.1 mg L 1 to 2 mg L 1 at 6 C: the increase in TiO 2 catalyst did not further decompose the PAHs in aqueous solution. Excessive TiO 2 particles sometimes result in mutual screens among TiO 2 particles, which not only protect the PAH molecules, but also reduce the sonocatalytic activity of TiO 2 powder. This affect, at frequency and power of 32 khz and 48 W after 15 min at 6 C, was reported by Wen et al. 3 In this study it was found that high temperature decreased the sonodegradation of total PAHs assisted by TiO 2, as reported by Wang et al. 2 Both sonocatalytic and ultrasonic destruction in the presence of TiO 2 decreased gradually along with the increased temperature. 32 In general, for most chemical reactions, the higher the temperature in the reaction system, the quicker the reaction rate, although it is known that radical reactions do not depend strongly on the system temperature. However, acoustic cavitation, which produces holes on the surface of TiO 2 particles or OH o radicals in aqueous solution, depends on the change of system temperature. Itis well known thatboth sonocatalytic and ultrasonic degradation of organic pollutants are related to the acoustic cavitation. The acoustic cavitation can give rise to holes with strong oxidability on the surface of TiO 2 particles, which either can directly decompose the organic pollutants adsorbed on the surface of TiO 2 particles or indirectly remove the organic pollutants in the aqueous solution through the OH o radicals resulting from hole oxidation of H 2 O molecules. When the temperature in the (a) PAH removal eff. (%) (b) PAH removal eff. (%) PAH (%) 3 C TiO2 =.1 mg L-1, 3 C, PAH (%) TiO2 =.5 mg L-1, 3 C, PAH (%) TiO2 = 1 mg L-1, 3 C, PAH (%) TiO2 = 2 mg L-1, 3 C, PAH (%) PAH (%) 6 C TiO2 =.1 mg L-1,6 C, PAH (%) TiO2 =.5 mg L-1, 6 C, PAH (%) TiO2 = 1 mg L-1, 6 C, PAH (%) TiO2 = 2 mg L-1, 6 C, PAH (%) Figure 4. Total PAH removal efficiencies from petrochemical industry wastewaters for TiO 2 =.1, TiO 2 =.5, TiO 2 = 1 and TiO 2 = 2 mg L 1 at (a) 3 C and (b) 6 C. aqueous solution becomes high, the vapor or gas bubbles escape rapidly from the reaction system and thus do not grow or collapse, which badly weakens the acoustic cavitation. Sometimes high temperatures act against ultrasonic degradation. Similarly, high temperatures also act against sonocatalytic degradation because the holes on the surface or inside the TiO 2 particles result from acoustic cavitation. In addition, sonocatalytic degradation relates to the adsorbability of TiO 2 particles. In general, appropriate adsorbability is likely to encourage sonocatalytic removal. Suitable quantities of organic pollutants adsorbed on the surface of TiO 2 particles can be directly decomposed by the holes. However, high temperatures generally weaken the adsorbability of TiO 2 particles, permitting large numbers of organic pollutants to freely and rapidly move in the solution and thus avoid degradation. As seen in Table 5 removal of all individual PAHs increased significantly as sonication time was increased from 6 to 15 min at 6 C. The PAHs with four and five benzene rings (namely, BkF, BaP, IcdP, DahA and BghıP) were removed with high efficiencies (>92%) at 2 mg L 1 TiO 2 concentration after 15 min sonication time at 6 C, although these PAHs had less solubility in water, low vapor pressure, and low Henry s law constant, and high octanolwater coefficient (Tables 2 and 5). This could be attributed to the hydrophobic PAHs which can easily diffuse near cavitation bubbles and their destruction inside the collapsing bubble and thermal decomposition at its interfacial sheath at 6 C, as reported by Dehghani et al.anddavydovet al. 33,34 The results of this study show that PAH removals were not dependent on the physicochemical properties of the PAHs during sonication enhanced by 2 mg L 1 TiO 2 (R 2 =.45, P = 24.67, P =.1). High PAH removals were also valid for the individual 919 J Chem Technol Biotechnol 21; 85: c 21 Society of Chemical Industry

8 DT Sponza, R Oztekin Table 5. Maximum removal efficiencies of 17 PAHs measured in the influent and in the effluent of the sonication experiments at 2 mg L 1 TiO 2 concentrations PAH PAH t= PAH t=15 PAH t=6(%) PAH t=12(%) PAH t=15(%) NAP 991E-± ± ACL 538E-1± ± ACT 93E-1± ± FLN 429E-1± ± PHE 15E-± ± ANT 894E-2± ± CRB 23E-1± ± FL 134E-1± ± PY 111E-1± ± BaA 68E-3±.91.3 ± CHR 289E-2± ± BbF 116E-2±.16.4 ± BkF 69E-3±.93.5 ± BaP 1E-3±.13. ± IcdP 167E-2±.23.7 ± DahA 417E-2± ± BghıP 46E-3±.6.3 ± PAH t= : mean influent PAH concentration before sonication (ng ml 1 ) ± SD; PAH t=15 : mean effluent PAH concentration after 15 min sonication(ng ml 1 ) ± SD; PAH t=6(%) : mean PAH removal efficiency after 6 min sonication; PAH t=12(%) : mean PAH removal efficiency after 12 min sonication; PAH t=15(%) : mean PAH removal efficiency after 15 min sonication. 92 PAH concentrations measured in a control containing no TiO 2 after 15 min sonication (data not shown). As a result, the removal of seventeen PAHs obtained was nearly the same with 2 mg L 1 TiO 2 and without TiO 2 at 6 C after 15 min sonication. It can be concluded that if petrochemical industry wastewater containing PAHs is sonicated for 15 min at 6 C, it could be removed efficiently without TiO 2. Effect of Ferrous (Fe +2 ) ions concentration on the removal of PAH at increasing sonication time and temperature 2, 8 and 2 mg L 1 Fe +2 ions (from FeCl 2.4H 2 O) were added to the PCI ww before the sonication experiments. As sonication time was increased from 6 to 12 min at 3 C PAH removal increased in the control reactor containing no Fe +2 ions (Fig. 5(a)). As the Fe +2 ions concentration was increased from 2 to 2 mg L 1 the total PAH yields also increased after 6 and and 12 min sonication times at 3 C (Fig. 5(a)). Maximum 92% total PAH removal efficiencies were observed for 2 mg L 1 Fe +2 at 3 C after 15 min sonication. It was found that petrochemical industry wastewater containing PAHs could be treated, with total PAH removal efficiencies of 89% after 12 min sonication without the addition of Fe +2 ions at 3 C. No significant increase in PAH removal was obtained after 15 min sonication at 3 C by increasing the Fe +2 ions concentration from 8to2mgL 1. No significant increase in total PAH yield was obtained with increased Fe +2 concentrations compared with the control after 12 and 15 min sonication at 6 C (Fig. 5(b)). The mean total PAH yields in the control reactor without Fe +2 and in the reactor containing 2 mg L 1 Fe +2 were 68% and 73%, respectively, at 6 C after 6 and 12 min sonication (Fig. 5(b)). The total PAH yields increased at a Fe +2 concentration of 2 mg L 1 after 15 min sonication time, compared with the control. The individual PAH removals for the 17 PAHs are given in Table 6 for 2 mg L 1 Fe +2 ions concentration at 6 C. The removal efficiencies of all 17 PAHs were above 9% after 15 min sonication. The PAHs (a) PAH removal eff. (%) (b) PAH removal eff. (%) PAH (%) 3 C Fe+2 = 2 mg L-1, 3 C, PAH (%) Fe+2 = 8mg L-1, 3 C, PAH (%) Fe+2 = 2 mg L-1, 3 C, PAH (%) PAH (%) 6 C Fe+2 = 2 mg L-1, 6 C, PAH (%) Fe+2 = 8mg L-1, 6 C, PAH (%) Fe+2 = 2 mg L-1, 6 C, PAH (%) Figure 5. Total PAH removal efficiencies from petrochemical industry wastewaters for Fe +2 = 2, Fe +2 = 8andFe +2 = 2 mg L 1 at (a) 3 C and (b) 6 C. containing four (CHr, BaA), five (BkF, BaP) and six benzene (DahA, BGHIp) rings were removed with high efficiencies at 6 Cafter 15 min sonication (Table 6). These high removals of PAHs with high molecular weights could be attributed to effective sonication c 21 Society of Chemical Industry J Chem Technol Biotechnol 21; 85:

9 Sonication enhanced toxicity removals from a petrochemical industry wastewater Table 6. Maximum removal efficiencies of 17 PAHs measured in the influent and in the effluent of sonication experiments at 2 mg L 1 Fe +2 concentrations PAH PAH t= PAH t=15 PAH t=6(%) PAH t=12(%) PAH t=15(%) NAP 177E-± ± ACL 3595E-2± ± ACT 2364E-2± ± FLN 2869E-2± ± PHE 78E-2± ± ANT 186E-3±.25.1 ± CRB 1361E-2± ± FL 871E-3± ± PY 744E-3± ± BaA 14E-4±.2.6 ± CHR 19E-3±.16.4 ± BbF 12E-4±.1.1 ± BkF 24E-4±.3.1 ± BaP 29E-4±.9.1 ± IcdP 112E-3± ± DahA 278E-3± ± BghıP 29E-4±.4.1 ± PAH t= : mean influent PAH concentration before sonication (ng ml 1 ) ± SD; PAH t=15 : mean effluent PAH concentration after 15 min sonication(ng ml 1 ) ± SD; PAH t=6(%) : mean PAH removal efficiency after 6 min sonication; PAH t=12(%) : mean PAH removal efficiency after 12 min sonication; PAH t=15(%) : mean PAH removal efficiency after 15 min sonication. at 35 khz with 2 mg L 1 Fe +2 ions. The findings of the study demonstrate that sonication enhanced with 2 mg L 1 Fe +2 can be used to improve the mass transport of poorly soluble PAHs in petrochemical wastewaters and to alleviate limiting steps of removal of hydrophobic refractory PAHs after 15 min sonication at 6 C. Furthermore, the reaction of Fe +2 with H 2 O 2 forms HO o. This leads to the destruction of benzene rings of hydrophobic and hydrophilic PAHs. Some recent studies showed that there is a highly significant relationship between the average removal percentages and the hydrophobicity of PAHs, indicated by the octanol water partition coefficient. 36,37 It is evident that greater hydrophobicity resulted in reduced removal of PAHs. However, in this study, the 4-, 5- and 6-ring PAHs, in contrast to the relationship mentioned above, exhibited higher removals than expected from their log K ow at 6 C after 15 min sonication time. No significant correlation was observed between PAH yields, water solubility, vapor pressure, number of benzene rings, and Henry s law constant, through sonication assisted 2 mg L 1 Fe +2 at 6 C after 15 min sonication (R 2 =.43, F = 23.56, P =.1). On the other hand, it was found that the coefficient of the correlation between PAH yield and the residual concentrations was strong and significant (R 2 =.83, F = 3.16, P <.1) at 6 Cafter 15 min sonication (Fig. 6). Similar PAH removal in PAHs with low and high numbers of benzene rings could be attributed to the remaining PAH percentages varying between.4% and 1% after 15 min sonication since hydrophobic PAHs can easily diffuse near cavitation bubbles under pyrolytic destruction (Fig. 6). As reported by Lindsey and Tarr 24 a possible explanation for the postive effect of Fe +2 on the sonication of PAHs could be the reaction of Fe +2 with H 2 O 2 to form HO o at 34 khz and 45 W after 125 min sonication at 6 C. As this reaction proceeds, the concentration of Fe +2 declines, and consequently the rate of H 2 O 2 consumption and HO o formation decline. The loss of Fe +2 is eventually balanced by the formation of Fe +2 through reduction of Fe +3 by reaction with peroxide or hydroperoxyl radical, and a Remaining PAH (%) Remaining FLN % Remaining FL % Remaining CHR % Remaining BbF % Remaining IcdP % Remaining DahA % Remaining BghiP % Figure 6. PAH percentages remaining untreated versus sonication time in pseudo-first-order reaction kinetic. steady state Fe +2 concentration is reached. At this point (>6 s), pseudo-first-order loss of H 2 O 2 is observed. This explanation is also supported by evidence that the HO o formation rate is significantly higher in the first 6 s. Psillakis et al. 6 studied the sonoremoval of 15 µgl 1 total initial concentration PAHs mixture (NAP, ACT, PHE) in an aqueous solution: 92.2% of NAP, 96% of ACT and 89.8% of PHE removals were found with Fe +2 = 14 mg L 1 concentration in a 15 W sonicator, at a frequency 8 khz and sonication temperature 2 C, after 15 min irradiation. In our study the removal efficiencies for the aforementioned PAHs were found to be higher (E, NAP = 99%,E,ACT= 98% and E, PHE = 98%) at 35 C for the same sonication time. Beckett and Hua 35 also found that the addition of.2 1 ng L 1 Fe +2 concentrations improved the 1,4-dioxane decomposition rate and mineralization efficiency at 3 khz, 59 W after 115 min sonication. 921 J Chem Technol Biotechnol 21; 85: c 21 Society of Chemical Industry

10 DT Sponza, R Oztekin [ln (PAH) t / (PAH) o ] ln([ PAH]t / [ PAH]o) - FLN ln([ PAH]t / [ PAH]o) - CHR ln([ PAH]t / [ PAH]o) - IcdP ln([ PAH]t / [ PAH]o) - BghiP ln([ PAH] t / [ PAH]o) - FL ln([ PAH] t / [ PAH]o) - BbF ln([ PAH] t / [ PAH]o) - DahA Figure 7. Effects of sonication time on the removal kinetic of seven PAHs according to the pseudo-first-order reaction. During aqueous ultrasonic irradiation, OH o radicals formed during the thermolytic reactions of water recombine to form H 2 O 2 that tends to accumulate in the solution and does not usually play an important role in oxidizing organic species. However, the reaction between H 2 O 2 and ferrous iron Fe +2 is known to produce OH o radicals and is commonly referred to as the Fenton process. 36 Removal kinetic of seven PAHs The sonic removal of 17 PAHs in raw PCI ww was found to be pseudo-first-order with respect to PAH concentrations at a frequency of 35 khz and at temperature 6 C after 15 min sonication. In this study, the rate constants of sono-destruction have been given for only seven PAHs representing PAHs with three benzene rings (FLN), with four benzene rings (FL and CHR) with five benzene rings (BbF) and with six benzene rings (IcdP, DahA and BghıP) (Fig. 7). These rate constants are displayed in Table 7. It was found that the pseudo-first-order rate constants decreased in the order PAHs with three benzene rings to PAHs with five and with seven rings at all sonication times. The kinetic rate constants obtained in this study agree with literature data for low frequencies (2 and 32 khz) for powers varying between 39 and 64 W after min sonication and at temperatures 4 65 C. 13,14,17,18 Although the PAH removal yields showed similar ranges (9 99%) in PAHs with low and high numbers of benzene rings after 15 min sonication at 6 C, the removal rate constants decreased in the order from low to high molecular weight PAHs. The reaction kinetic constants of PAHs depend on their properties, such as the number of benzene rings, the vapor pressure, the water solubility and Henry s law constant, as reported by David. 14 The removal rate constants of PAHs increased as vapor pressure, water solubility and Henry s law constants increased and as the number of benzene rings decreased. In this study, it was found that the most hydrophobic PAHs, with five and six benzene rings (BbF, IcdP, DahA and BghıP) (which have low water solubiliy and Henry s law constant) have the lowest reacton rate constants compared with two, three and four ring PAHs (FLN, FL, CHR) (which have high water solubility and Henry s law constant)(tables 2 and 7). In other words, the lower molecular weight PAHs tend to be more volatile (i.e. have higher vapor pressure) and more readily partition into the air from pure water (i.e. have a higher Henry s law constant), and have high reaction kinetic constants throughout sonication. Although the high molecular weight PAHs tend to be less volatile (i.e. have a low vapor pressure) and low partition rate into air from pure water (i.e. have a low Henry s law constant), the untreated percentages of PAHs with five, six and seven rings at a sonication time of 15 min were the same as for PAHs which had low ring numbers after 15 min sonication at 6 C (Table 2 and Fig. 6). As seen in Fig. 6 the percentages remaining in PAHs with low numbers benzene rings (FLN and FL) were low (2% and 35%) after 6 min sonication while the untreated PAH percentages were high (9%, 8%and67%)inPAHswithalargenumberofbenzenerings(BghıP, DahA and IcdP) for the same sonication time. A similar result was obtained after 3 and 12 min sonication. However, similar PAH percentages remaining were obtained (.4 1%) after 15 min sonication since the hydrophobic PAHs were removed under pyrolytic destruction. The results of this study show that although a strict correlation between the percentage of PAHs remaining and physicochemical properties was observed after 3, 6 and 12 min sonication (R 2 =.89, P = 4.89, P =.1), a significant correlation was not observed between the percentages of PAHs remaining and their properties after 15 min sonication (R 2 =.45, P = 16.56, P =.1), and above 9% removal rates were achieved for all PAHs. Furthermore, it is evident that greater hydrophobicity resulted in lower reaction kinetic constants for the PAHs. Low initial PAH concentrations led to low reaction rates and also to smaller residual concentrations. The coefficient of correlation between residual concentration and total initial concentration of single Table 7. Calculated steady-state [HO o ] ss concentrations of six PAHs, comparison of PAH oxidation rates of OH o and experimental PAH removal rates after 15 min sonication at 35 khz and 6 C PAHs Ring number k PAH/HO oa k pf b [HO o ] ss c V PAH/HO od V PAH/US e f FLN , FL , CHR , BbF , IcdP , DahA BghıP a (PAH oxidation rate, ng ml 1 s 1 ); b (experimental pseudo - first - order reaction of PAH, min 1 ); c (steady - state [HO o ] concentrations, ng ml 1 ); d (PAH oxidation rate, ng ml 1 min 1 ); e (experimental rate of PAH sonodegradation, ng ml 1 min 1 ); f the percentage of PAH oxidation with HO o ratio to conventional sonodegradation (V PAH/HO /V PAH/US ). c 21 Society of Chemical Industry J Chem Technol Biotechnol 21; 85: