Aqueous degradation of VOCs in the ozone combined with hydrogen peroxide or UV radiation processes - 1. Experimental results

Trichloroethane, TCA, and trichloroethylene, TCE, have been taken as model compounds to study the elimination of volatile organochlorine compounds pre sent in surface waters with ozone combined with hydrogen peroxide or UV rad iation. The effect of gas flow rate, water type (surface and ultrapure wate r), hydrogen peroxide concentration and oxidation type (ozonation alone, UV radiation alone and combined ozonation with hydrogen peroxide or UV radiat ion) have been observed on the elimination of VOCs. Reactions of ozone in t his system develop in the slow kinetic regime of absorption except when a c oncentration 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 oxida tion, direct reaction with ozone and direct photolysis, the latter two in t he case of TCE. Because of the elevated vapor pressure, volatility is the o nly way of elimination of TCA when treated at 20 Lh(-1) in spite of the pre sence of ozone and hydrogen peroxide. At low gas flow rate, 2.5 Lh(-1), vol atility of TCA still represents 85% of elimination rate. For TCE, hydroxyl radical oxidation can be, in some cases, the main pathway of oxidation foll owed by volatility. In all cases, hydroxyl radical oxidation contribution i s increased when the oxidation is carried out in ultrapure water. Combinati on 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.