1 Treatment of petroleum wastewater using combination of solar 2 photo-two catalyst TiO 2 and photo-Fenton process 3 Dheeaa al deen Atallah Aljuboury a, * Q1 , Puganeshwary Palaniandy a , 4 Hamidi Bin Abdul Aziz a , Shaik Feroz b 5 a School of Civil Engineering, Universiti Sains Malaysia, Malaysia 6 b Caledonian College of Engineering, Oman A R T I C L E I N F O Article history: Received 8 March 2015 Accepted 14 April 2015 Keywords: Petroleum wastewater Photo-catalyst of TiO 2 Advanced oxidation process (AOP) Response surface methodology (RSM) A B S T R A C T The objective of this study is to investigate the performance of employing Fenton’s reagent in the solar photo-catalyst of TiO 2 to treat petroleum wastewater from Sohar oil Refinery, Oman. A central composite design (CCD) with response surface methodology (RSM) is applied to evaluate the relationships between operating variables, such as TiO 2 and Fenton dosage, pH, and reaction time, to identify the optimum operating conditions. Quadratic models for the following three responses prove to be significant with very low probabilities (<0.0001): chemical oxygen demand (COD), total organic carbon (TOC) and residual iron (Fe). The obtained optimum conditions include a reaction time of 90 min, 0.66 g/L TiO 2 , 0.5 g/L H 2 O 2 , 0.01 g/L Fe 2+ , and pH 4.18. TOC and COD removal rates are 62% and 50%, respectively, and 0.8 ppm residual iron is obtained. The predictions correspond well with experimental results (TOC and COD removal rates of 64%, and 48%, respectively, and 0.5 ppm residual iron). The solar photo-Fenton process has well efficient for petroleum wastewater treatment in acidic conditions pH < 7 and more economic by free energy. ã 2015 Published by Elsevier Ltd. 7 Introduction 8 Large amounts of water are used in the petroleum refinery 9 activity and, consequently, significant volumes of petroleum waste 10 water are generated. Recently, one of the major problems facing 11 industrialized nations is contamination of the environment by 12 hazardous chemicals. A wide range of pollutants compounds are 13 detected in petroleum waste water in Sohar oil refinery, so, the 14 elimination of these chemicals from petroleum wastewater is 15 presently one of the most important aspects of pollution control in 16 Oman. Q2 17 Advanced oxidation processes (AOPs) have capability of rapid 18 degradation of recalcitrant pollutants in the aquatic environment. 19 Remediation of hazardous substances is attributed to hydroxyl 20 radical (  OH). Kim et al. showed that  OH exhibits reactivity toward 21 organic compounds [4]. AOPs may be used in petroleum 22 wastewater treatment for overall organic content reduction 23 (COD), specific pollutant destruction, sludge treatment, increasing 24 bioavailability of recalcitrant organics and color and odor 25 reduction [3]. 26 Many technical enhanced the production rate of hydroxyl 27 radical by chemical additives (H 2 O 2 ), external energy (UV, 28 sunlight), catalysts (TiO 2 ) and the integration of two or more 29 AOPs such as (TiO 2 /Fenton/sunlight), TiO 2 photo-catalysis/ozona- 30 tion and TiO 2 photo-catalysis (UV)/Fenton [4]. 31 Several previous studies have reported the enhanced oxidation 32 of contaminants by the photo-catalyst of TiO 2 system in the 33 presence of Fenton. Kim et al. [4] reported that the combination of 34 TiO 2 photo-catalysis and the Fenton-like reaction (the UV/TiO 2 / 35 Fe +3 /H 2 O 2 system) synergistically increased degradation of organic 36 compounds at circum-neutral pH (6.5–7.5) by increased produc- 37 tion of reactive oxidants and improved the reactivity of the oxidant 38 [4]. However, it has not been clearly addressed whether the 39 integration of the UV/TiO 2 and Fe 3+ /H 2 O 2 systems exhibits 40 synergistic results with respect to the degradation of the 41 contaminant. Little data are available on the role of iron in the 42 UV/TiO2 system under neutral pH conditions, where the Fe 3+ /H 2 O 2 43 or UV/ Fe 3+ /H 2 O 2 system alone is not effective for oxidant 44 production and pollutant oxidation due to the low aqueous iron 45 solubility H 2 O 2 decomposition via a non-radical mechanism (not 46 leading to  OH generation) [4,9,11]. Zarei et al. [6] showed that 47 removal efficiency of phenol was 69.36% at 150 min using photo * Corresponding author at: School of Civil Engineering, Universiti Sains Malaysia, Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, 14300, Malaysia. Tel.: +60 968 95358288. E-mail address: msc.dheeaa@yahoo.com (D.a.d.A. Aljuboury). http://dx.doi.org/10.1016/j.jece.2015.04.012 2213-3437/ ã 2015 Published by Elsevier Ltd. Journal of Environmental Chemical Engineering xxx (2015) xxx–xxx G Model JECE 625 1–8 Please cite this article in press as: D.A. Aljuboury, et al., Treatment of petroleum wastewater using combination of solar photo-two catalyst TiO 2 and photo-Fenton process, J. Environ. Chem. Eng. (2015), http://dx.doi.org/10.1016/j.jece.2015.04.012 Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.else vie r.com/locat e/jece