Application of Sono–photo-Fenton process for degradation of phenol derivatives in petrochemical wastewater using full factorial design of experiment

International Journal of Industrial Chemistry https://doi.org/10.1007/s40090-018-0159-y RESEARCH Application of Sono–photo‑Fenton process for degradation of phenol derivatives in petrochemical wastewater using full factorial design of experiment Aref Shokri1 Received: 24 January 2018 / Accepted: 11 October 2018 © The Author(s) 2018 Abstract In this study, the degradation and mineralization of petrochemical wastewater containing phenol and nitrophenol with chemical oxygen demand (COD) at 260 mg/L and total organic carbon (TOC) at 100 mg/L, were investigated by Sono–photo-Fenton process. The full factorial design of experiment was used to explore the influence of operational variables such as pH, initial concentration of hydrogen peroxide and Ferrous ions on the removal of COD. The analysis of variance (ANOVA) showed a high determination coefficient value (R2 = 0.9884, R2pred = 0.9713, R2adj = 0.9822) for removal of COD and satisfactory prediction second-order regression model. The graphical response surface plots were employed to determine the optimum conditions. The operational variables were optimized by the model as follows: the [Fe2+] = 24 mg/L, pH at 3, and [H2O2] = 500 mg/L. The results showed that at the predicted optimum conditions and after 60 min of reaction, the degradation (removal of COD) and mineralization (removal of TOC) were 76.1 and 68.7%, respectively. Keywords Sono-Fenton process · Photo-Fenton process · Degradation · Mineralization · Response surface plots · Phenolic compounds Introduction The wastewater produced from Karoon petrochemical plant in Iran contains ortho-toluidine, nitrobenzene, nitrocresol, phenol derivatives and other aromatic compounds. Definite amounts of aromatic components are lost during a process which holds a wide range of non-biodegradable chemicals that cause environmental pollution. The phenol derivatives are toxic and bio-refractory pollutant in petrochemical wastewater which can be a source of major harm to the environment and human health [1]. Based on the environmental protection agency, the permissible limit of nitrophenols in aqueous solution is 1 mg/L. The remediation of wastewaters polluted with nitrophenols by traditional methods is really difficult, has high operational costs, secondary contamination and a long reaction time; subsequently, phenol derivatives are resistant according to their high solubility and * Aref Shokri 1 Young Researchers and Elite Club, Arak Branch, Islamic Azad University, Arak, Iran stability in water [2]. Therefore, employing new methods for the treatment of the wastewater containing these pollutants without these problems is essential. Advanced oxidation processes (AOPs) are effective and environmentally friendly methods that can degrade organic pollutants that are resistant to the conventional treatment methods into simple byproducts and finally mineralize them into carbon dioxide and water [3]. The reactive and nonspecific oxidant, hydroxyl radicals, with high electrochemical oxidation potential were produced by AOPs [4]. An aqueous solution containing benzoic acid was treated by electrocoagulation (EC) and electrochemical Fenton (EF) processes by Sandhwar and Prasad [5]. In the previous work, the treatment of spent caustic in the wastewater of petrochemical industries was investigated by ozonation in alkaline media followed by electrocoagulation process [6]. High-Performance Nanocatalyst for Adsorptive and Photoassisted Fenton-Like Degradation of Phenol was studied by Gazi et al. [7]. Several studies have been done on combined AOPs that can increase the production of more hydroxyl radicals for degradation of resistant organic contaminants [8, 9]. The 13 Vol.:(0123456789) International Journal of Industrial Chemistry ultrasonic and Fenton processes are AOPs that can be suitable treatment methods which have been employed for the removal of various pollutants in the wastewater [10, 11]. The addition of ultrasonic irradiation to the Fenton and photoFenton process can be a good choice to overcome the restrictions of mentioned processes. The Sonochemistry includes the chemical effects of producing ultrasound when a sound wave is passed through an aqueous medium. Frequently, as a moment of the hemolytic cleavage of water in the cavitation bubbles, the reactive radical species such as hydroxyl radicals and hydrogen atoms were formed to promote the degradation of pollutant [12]. The use of ultrasonic irradiation can produce vibrational wave energy and shear stresses at the cavitation interface and produce locals with high pressure and temperature; this feature can lead to the improvement of Fenton and photo-Fenton reactions [13]. Thus, the combination of ultrasonic with photo-Fenton process has been employed to increase the efficiency of the mentioned process [14]. In this project, full factorial design(FFD)was used in planning experiments as a statistical technique where several factors are controlled and their effects on each other are explored at three levels [15]. The ability of general full factorial design in the modeling of complex systems makes it a more practical technique than other traditional methods for modeling a multi-variable system [16]. In this work, the effect of operational variables such as pH, initial concentration of ferrous ions and hydrogen peroxide was investigated on the degradation of phenol derivatives by Sono–photo-Fenton process. The important variable and interaction effects between them have been studied by FFD method. The removal of COD (%) was the optimized response and the correlation between the response and significant factors was determined. Experimental Material The diluted wastewater was the effluent of an Iranian petrochemical Company, which was sampled on Mars 2017 with the following properties (Table 1). The features of the real wastewater were not similar in different times and the amounts of factors were not completely fixed. The composition of the real wastewater is highly variable and depends on the process condition. All studied samples were taken at one time and one point and the feedstock samples were kept in the laboratory in a cool place, which were then homogenized and tested; therefore, the amounts of factors in Table 1 were reported fixed. The ferrous sulfate heptahydrate (FeSO4·7H2O) as the source of Fe(II), hydrogen peroxide solution (30% w/w), 13 Table 1  Characteristic of diluted petrochemical wastewater Factors Amounts TDS (mg/L) TOC (mg/L) BOD (mg/L) COD (mg/L) phenol (mg/L) nitrophenol (mg/L) pH 200 100 120 260 50 100 6 H2SO4 and NaOH are all provided by Merck Company of Germany. General procedure The experiments were performed in a glass cylindrical reactor with 1 L of capacity. The light source was a mercury lamp, Philips 15 W (UV-C) at 254 nm, which was positioned horizontally above the reactor. The ultrasonic irradiation was coupled with a transducer in the reactor at a frequency of 20 kHz and equipped with (...truncated)