Aqueous degradation of VOCs in the ozone combined with hydrogen peroxide or UV radiation processes1. Experimental results

Abstract

Trichloroethane, TCA, and trichloroethylene, TCE, have been taken as model compounds to study the elimination of volatile organochlorine compounds present in surface waters with ozone combined with hydrogen peroxide or UV radiation. The effect of gas flow rate, water type (surface and ultrapure water), hydrogen peroxide concentration and oxidation type (ozonation alone, UV radiation alone and combined ozonation with hydrogen peroxide or UV radiation) have been observed on the elimination of VOCs. Reactions of ozone in this system develop in the slow kinetic regime of absorption except when a concentration of hydrogen peroxide higher than 10‐3 M is applied. Rates of VOC elimination follow pseudo first order kinetics and can be represented by the contribution of four terms due to volatility, hydroxyl radical oxidation, direct reaction with ozone and direct photolysis, the latter two in the case of TCE. Because of the elevated vapor pressure, volatility is the only way of elimination of TCA when treated at 20 Lh‘1 in spite of the presence of ozone and hydrogen peroxide. At low gas flow rate, 2.5 Lh‐1, volatility of TCA still represents 85% of elimination rate. For TCE, hydroxyl radical oxidation can be, in some cases, the main pathway of oxidation followed by volatility. In all cases, hydroxyl radical oxidation contribution is increased when the oxidation is carried out in ultrapure water. Combination of ozone with hydrogen peroxide or UV radiation leads to oxidation rates two to three times those due to volatility, depending on the gas flow rate applied and type of VOC.