Oxidation kinetics and mechanisms of trihalomethanes by Fentonʹs reagent

Oxidation kinetics and mechanisms of four trihalomethanes (THMs) commonly found in chlorinated drinking water by Fentonʹs reagent were investigated. All the experiments were carried out in air-tight and well-mixed batch reactors in which no headspace was allowed in order to minimize volatilization of any THM during reaction. The optimum dosages of H2O2 and Fe2+ in the oxidation of bromoform was 3.7-1.9 m for all the initial concentrations at pH 3.5. The maximum bromoform degradations of 85, 78 and 65% at 3 min were achieved for bromoform concentrations of 295, 98.3 and 49.2 μg/l, respectively. The pseudo-first-order oxidation constants of THMs increase with the increasing number of bromine atoms present in a THM molecule, with bromoform being oxidized the fastest and bromodichloromethane being oxidized the slowest. No oxidative degradation of chloroform was oberved, because the losses in chloroform concentration during the oxidation experiments are the same as what was observed in control experiments. Experiments conducted on the THM mixtures gave similar results in terms of extent of observed oxidative degradation, the amount of THM oxidized increased with increasing initial organic concentrations. The oxidation rate constants for each THM in the mixture also increased as the number of bromine atoms present in a THM molecule increased, with bromoform exhibiting the fastest kinetic rates and bromodichloromethane exhibiting the slowest kinetic rates.