Calculation of Hydroxyl Radical Concentration Using an Indirect Method-Effect of pH and Carbonate Ion

Abstract

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 reaction with molecular ozone is selective to certain organic and inorganic compounds. But, the hydroxyl radicals can readily react with these compounds through radical-radical reactions, hydrogen abstraction, electron transfer and electrophilic addition which can completely mineralize the pollutant and their intermediates. Quantitative measurement of the hydroxyl radical concentration is rather difficult due to its low concentration. A few computer models have been developed for the prediction of concentration of hydroxyl radicals. An indirect method of the measurement of the concentration of hydroxyl radical is developed which works with a probe compound. Concentration of hydroxyl radicals generated from ozone microbubbles was determined by using this indirect method for pH 3–10. p-Chlorobenzoic acid (PCBA) was used as the probe compound to calculate the concentration of hydroxyl radicals. A constant, R _ct , was defined as the ratio of ∙OH and O₃ exposures, which was employed to estimate the concentration of hydroxyl radicals. It was observed that the O₃ exposure and the depletion of PCBA were higher at acidic pH than at the alkaline pH. The feasibility of the method was calculated by detecting the depletion of phenol. The fractional contribution of hydroxyl radical and molecular ozone was calculated by this method.