Thermally Activated Persulfate Oxidation of Trichloroethylene: Experimental Investigation of Reaction Orders

Abstract

The kinetics of dissolved trichloroethylene (TCE) oxidation by thermally activated sodium persulfate (Na2S2O8) was investigated in a phosphate-buffered solution at pH 7 and an ionic strength of 0.1 at a temperature of 40 °C. Thermal activation results in the production of a highly reactive sulfate free radical (SO4•-). The method of half-lives was used to determine the reaction order with respect to TCE. This was accomplished by conducting a series of kinetic experiments and keeping in great excess (and therefore essentially constant) the sodium persulfate concentration while varying the TCE initial concentration. Resulting plots of normalized TCE concentration (C/Co) vs time were analyzed by polynomial regression analysis. Half-lives were calculated based on the resulting polynomial equations. To determine the reaction order with respect to persulfate, experiments were designed to examine a range of initial persulfate concentrations while maintaining the same initial TCE concentration. These results were also analyzed using polynomial regression analysis. The results of these studies indicate that the degradation rate of TCE by sodium persulfate could be described by the kinetic rate equation −d[TCE]/dt = (5.59 × 10-4 mM0.2 min-1)[TCE]0[S2O82-]0.8 within the limits of the experimental conditions utilized here (i.e., 40 °C, ionic strength 0.1, pH 7, TCE 0.14−0.52 mM, and S2O82- 13.5−43.7 mM). This equation indicates that the thermally activated persulfate oxidation of TCE appears to be pseudo zero order with respect to TCE (and therefore independent of the initial TCE concentration) and fractional order with respect to persulfate. This result should serve as a starting point for modeling of the TCE/persulfate system.