Calculation of Hydroxyl Radical Concentration Using an Indirect Method-Effect of pH and Carbonate Ion
The Advanced oxidation process using the hydroxyl radicals is an emerging method in water and wastewater treatment. The oxidative potential of ozone is 2.07, whereas for ozone it is 2.80 V which is higher than the conventional oxidants. However, the react
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1 Introduction The use of hydroxyl radicals in oxidation is known as advanced oxidation process, which is an emerging method in the water and wastewater treatment (Legrini et al. 1993). The oxidation potentials of O3 (molecular ozone) and hydroxyl radical (∙OH) are 2.07 and 2.80 V, respectively (Beltrán 2004). The reaction with molecular ozone is selective to certain organic and inorganic compounds such as the compounds having C=C bonds, and the functional groups containing sulfur, phosphorous, nitrogen and oxygen (Oppenländer 2003). The hydroxyl radicals are able to mineralize many organic and inorganic compounds through various reaction mechanisms such as, radical–radical reactions, hydrogen abstraction, electron transfer and electrophilic addition. This often leads to the complete mineralization of the pollutant compounds (Oppenländer 2003).
S. Khuntia (&) Institute of Engineering and Technology-Ahmedabad University, Commerce Six Roads, Navrangpura, Ahmedabadd, India e-mail: [email protected] M.K. Sinha Marwadi Education Foundation, Rajkot, India e-mail: [email protected] S.K. Majumder P. Ghosh Indian Institute of Technology Guwahati, Guwahati 781039, Assam, India e-mail: [email protected] P. Ghosh e-mail: [email protected] © Springer Science+Business Media Singapore 2016 I. Regupathi et al. (eds.), Recent Advances in Chemical Engineering, DOI 10.1007/978-981-10-1633-2_20
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The hydroxyl radicals concentration [∙OH], generated from ozone is an important parameter to measure the rate constant of the reaction. [∙OH] can be measured by various methods such as, electrochemical, optical, spectrophotometric and colorimetric techniques (Langlais et al. 1999). However, quantitative measurement of [∙OH] is rather difficult due to its low concentration in water. A few computer models have been developed for the prediction of concentration of hydroxyl radicals (Chelkowska et al. 1992). Elovitz and von Gunten (1999) have developed an indirect method to determine the concentration of hydroxyl radicals generated from ozone by using a probe compound (i.e. p-Chlorobenzoic acid). In this work, [∙OH] generated from ozone microbubbles has been determined. The effects of pH and carbonate ions on the generation of hydroxyl radicals has been studied. Oxidation of phenol using O3 and [∙OH] has been investigated at pH 3–10. The contribution of hydroxyl radicals on the degradation of phenol has been calculated.
2 Materials and Methods All the chemicals used in this work are of analytical grade. The details of the experimental setup are given in our earlier work (Khuntia et al. 2013). Oxygen was isolated from air [make: Oz-Air (India), model: HG 03]. An ozonator [make: Oz-Air (India), model: ISM 10 Oxy EC] converted the oxygen to ozone by the corona-discharge method. The ozone generator worked in the range of 0–3 mg s‒1. The flow rate of the oxygen and ozone mixture coming out of the ozonator was measured by a rotameter, which had the range of 8–80 cm3 s‒1. The percentage of ozone in
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