Contribution of free radical oxidation to eliminate volatile organochlorine compounds in water by ultraviolet radiation and hydrogen peroxide

The UV/H2O2 oxidation of trichloroethylene, TCE, and 1,1,1 trichloroethane, TCA, in water was studied. Oxidation rates depend on the initial hydrogen peroxide concentration with maximum values in the presence of concentrations of 10−2 M which represents rates of about 5 and 250 times higher than those obtained from volatilization alone for TCA and TCE, respectively. In the case of TCE, contribution of direct photolysis is negligible. In natural waters, oxidation rates of TCA and TCE slightly decreases compared to those in laboratory prepared waters. When concentrations of hydrogen peroxide applied are higher than 10−2 M, TCA is mainly removed by volatilization since hydrogen peroxide consumes most of radicals generated. On the contrary, free radical oxidation continues to be the principal step of removal in the case of TCE since the rate constant of its reaction with hydroxyl radicals is approx. 65 times higher than that of the reaction OH-TCA. Experiments with high concentration of hydrogen peroxide (>10−2 M) allow to determine the rate constants of TCE-OH and TCA-OH reactions that were found to be 1.8×109 and 2.0×107 M−1s−1, respectively.