Chemical Engineering Journal 162 (2010) 142–150 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Removals of PAHs and acute toxicity via sonication in a petrochemical industry wastewater Delia Teresa Sponza * , Rukiye Oztekin Dokuz Eylül University, Engineering Faculty, Department of Environmental Engineering, Tınaztepe Campus, 35160 Buca/ ˙ Izmir, Turkey article info Article history: Received 11 January 2010 Received in revised form 6 May 2010 Accepted 8 May 2010 Keywords: Polycyclic aromatic hydrocarbons Petrochemical industry Sonication PAHs Pyrolysis Pseudo first order kinetic Daphnia manga acute toxicity abstract The effects of ambient conditions (25 ◦ C), increasing sonication time (0–150 min), temperature (30–60 ◦ C), dissolved oxygen (DO, 2–10 mg L -1 ) and hydrogen peroxide (H 2 O 2 , 100–2000 mg L -1 ) concentrations on the removal of polycyclic aromatic hydrocarbon (PAH) and destruction of toxicity in a petrochemical industry wastewater in Izmir (Turkey) were investigated. The maximum PAH removals were 80.2%, 91%, 98.5% and 98% at 25 ◦ C, 60 ◦ C, DO concentration of 6 mg L -1 and H 2 O 2 concentration of 2000 mg L -1 , respectively, after 150 min sonication. Sonication alone provides PAH removals varying between 88% and 92% without DO and H 2 O 2 at 30 ◦ C and 60 ◦ C after 150 min sonication. The Daphnia magna acute toxicity decreased significantly from 342.6 ng mL -1 to 5.4 ng mL -1 , to 0.7 ng mL -1 , and to 0.4 ng mL -1 , respectively, as the temperature, the DO and the H 2 O 2 concentrations were increased. The PAH sonodegradation appeared to be pseudo first order in PAHs naphthalene (NAP), acenaphthylene (ACL), phenanthrene (PHE), pyrene (PY) and benz[b] fluoranthene (BbF) (k = 0.026 min -1 , 0.024 min -1 , 0.017 min -1 , 0.015 min -1 and 0.011 min -1 , respectively). The main mechanism of PAH sonodegradation appears to be pyrolysis. © 2010 Elsevier B.V. All rights reserved. 1. Introduction PAHs are listed as US-EPA and EU priority pollutants, and their concentrations, therefore, need to be controlled in treated wastew- ater effluents [1,2]. Due to their toxic, mutagenic and carcinogenic properties the US-EPA classifies 16 of these PAHs as priority pol- lutants [1,2]. Recent studies have shown that sonication may be a useful tool for degrading the aqueous pollutants [3–6]. The sonica- tion process is capable of effectively degrading target compounds including chlorophenols, chloroaromatics and PAHs present in dilute solutions, typically in the micro and nano ranges. The pro- cess does not require the use of additional chemicals commonly employed in several oxidation processes, thus again reducing costs. David [5] found that naphthalene (NAP), phenanthrene (PHE), anthracene (ANT) and pyrene (PY) removal efficiencies varied between 93% and 95%, after a sonication time of 90 min in a sonica- tor with a power of 400 W and a frequency of 20 kHz. Psillakis et al. [7] reported a 99% removal efficiency for 0.01 gL -1 of acenaph- thalene (ACT), PHE and NAP at a power of 300 W and frequency of 24 kHz. Benabdallah El-Hadj et al. [4] found 57% NAP, 40% PY and 45% total COD removal efficiencies in a sonicator with a power of 70 W and frequency of 20 kHz. Taylor et al. [8] investigated the son- ication of PAHs, namely ANT, PHE and PY. 46%, 20% and 50% removal * Corresponding author. Tel.: +90 232 412 71 19; fax: +90 232 453 11 53. E-mail address: delya.sponza@deu.edu.tr (D.T. Sponza). efficiencies, respectively, were found at a power of 600 W and a frequency of 20 kHz. Laughrey et al. [9] investigated the effects of DO, air on the sonication of PHE, PY and ANT. They found removals of these PAHs as high as 80–90% as the DO concentration, air and N 2 (g) purges were increased from 1 mg L -1 to 5 mg L -1 and from 2, 4 mL min -1 up to 3, 6 mL min -1 . When sonolysis of water occurs, it leads to the formation of the non-specific oxidative species OH • . The ultrasonic degradation of hydrophobic organics such as PAHs can occur when they penetrate to the surrounding of the hot heart of the cavitation bubble being pyrolyzed, burnt and/or ionized in the plasma core [10,11]. The lit- erature data concerning the sonodegradation of PAHs is scarce and the results are contradictory. Two mechanisms have been proposed to account for sonolytic degradation: (i) oxidation by OH • [8,9] and (ii) pyrolytic decomposition [7]. 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 aimed at increasing the degradation of some PAHs (NAP, PHE, ANT, PY and ACT) with sonication have appeared, these have been lim- ited to only a few of those generally present (3–5) [4,7,12,13]. No study was found investigating the effects of operational conditions such as sonication time, temperature, DO and H 2 O 2 on the son- ication of a petrochemical industry wastewater. Furthermore, the effects of the operational conditions on the removal of acute toxicity has not been determined for a petrochemical industry wastew- 1385-8947/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2010.05.014