PHENOL OXIDATION UNDER PULSED MODE OF ULTRASONIC IRRADIATION † Robina Farooq* , Fahad Mateen*, Maria Siddique**, Asad U. Khan*, Zaki Ahmad*, M. Ashraf Shaheen*** * Deptt. of Chemical Engg, COMSATS Institute of Information Technology (CIIT), Lahore, Pakistan. Email: drrobinafarooq@ciitlahore.edu.pk ** Deptt. of Environmental Sciences, CIIT, Abbottabad Pakistan. *** Deptt. of Chemistry, University of Sargodha, Sargodha, Pakistan. † 17 ABSTRACT This study demonstrates ultrasound assisted Fenton oxidation of phenol present in waste water produced as a result of synthetic processes. The degradation of phenol was investigated at isothermal conditions under 20 kHz ultrasonic frequency, under pulsed and continuous mode of irradiations. The ultrasonic system was calibrated by calorimetric measurements. Various experimental conditions of H O , FeSO .7H O, 2 4 aeration, initial pH and acoustic intensity have shown that phenol oxidation was enhanced using ultrasound at pulsed mode instead of continuous mode. It was found that optimum oxidation of phenol was achieved at 80 mM H O , 8.9x10 mM FeSO .7H O, pH of 3 and 2 2 4 2 -2 20 Wcm of ultrasonic acoustic intensity. Pseudo first order rate kinetics were observed at different phenol concentrations of 2 mM, 4 mM and 5 mM. A fitted regression model by R software confidently provided a tool for quantifying the main factors involved in oxidation. Multiple linear regression analyses showed that phenol oxidation is enhanced by increasing concentrations of H O and FeSO and reducing pH of 2 2 4 solution. Keywords: Ultrasonic irradiation, fenton oxidation, sonofenton kinetics, half-life studies, regression model, phenol oxidation 1. INTRODUCTION The waste stream discharged by leather, textile, dyes, oil refineries, and paint industries contains substantial amount of phenol. These waste streams when exposed to ambient environment can cause severe tribulations and even minute concentrations of phenol -2 (<3.3x10 mM) are intolerable in water. Higher concentrations of phenol in water not only kill fish, but also completely act as biogenic compound (Saha, et al., 1999; Jain, et al., 2011). The presence of phenol in water bodies contributes to severe pollution and causes carcinogenic and mutagenic effects to human and aquatic life. Hence, prior treatment of phenol containing waste stream is requisite before it is discharged to environment. Previous investigations introduced various methods for the treatment of hazardous organic pollutants from the wastewater (Berlan, et al., 1994; Pera-Titus, et al., 2004; Bremner, et al., 2009; and Babuponnusami and Muthukumar, 2011). However, biological, chemical and physical treatment processes suffer from either 2 2 -4 inefficiency, phase transfer of pollutants, or toxic end- products (Kušiã, et al., 2006). Recently, advanced oxidation processes are gaining momentum for oxidation of phenol as its oxidation is inhibited by conventional chemical and biological methods. Advanced Oxidation: Process (AOP) has shown potential to mineralize organic pollutants, including phenols. However, AOP requires transition metals, e.g., Fe, Cu, etc. along with a large amount of H O , 2 2 which themselves contribute towards pollution (Siddique, et al., 2014). The decomposition of organic pollutants occurs by its OH• radicals that are generated by H O in the presence of ultraviolet light, 2 2 ultrasound radiations or microwaves (Barros, et al., 2013). The use of ultrasound leads to the formation of acoustic cavitation by pressure fluctuation in a liquid and the collapse of these cavitation bubbles develop hotspots with extremely high local conditions of temperature and pressure, which allow the formation of reactive radicals, such as H•, OH•, O•. Ultrasonic oxidation of organic compounds can be enhanced by using oxidizing agents. Particularly, the Fenton's reagent (FeSO .7H O, H O ), along with the 4 2 2 2 ultrasound irradiation leads to much higher oxidation efficiency in very short span (Segura, et al., 2009; Bach, et al., 2010; Luis, et al., 2009; APHA, 1998). Hence the hydroxyl radicals (2.33 V oxidation potential) formed by cavitations quickly remove hydrogen from the aromatic ring of phenol, resulting in a series of oxidation reactions to mineralization and non-toxic end-products (Bhargava, et al., 2006). Studies on sonofenton oxidation of phenol have been restricted to continuous mode of ultrasonic irradiation. However, little attention is paid to investigate sonofenton oxidation of phenol using pulsed mode of ultrasonic irradiation. During pulsed mode of ultrasonic irradiation, it was observed that the specific energy consumption is lower in the case of concentrated aqueous effluents. This trend indicates that the process is more efficient in terms of energy consumption for more polluted streams (Cailean, et al., 2014). Therefore, the present study was performed to determine sonofenoton oxidation of phenol under various experimental conditions using pulsed and continuous mode of ultrasonic irradiation and to A scientific journal of COMSATS – SCIENCE VISION Vol. 21 No. 1&2 (January to December 2015)