Oxidation of chlorinated ethenes by heat-activated persulfate: Kinetics and products

In situ chemical oxidation (ISCO) and in situ thermal remediation (ISTR) are applicable to treatment of groundwater contaminated with chlorinated ethenes. ISCO with persulfate (S₂O₈^2-) requires activation, and this can be achieved with the heatfrom ISTR, so there may be advantages to combining these technologies. To explore this possibility, we determined the kinetics and products of chlorinated ethene oxidation with heat-activated persulfate and compared them to the temperature dependence of other degradation pathways. The kinetics of chlorinated ethene disappearance were pseudo-first-order for 1-2 half-lives, and the resulting rate constants-measured from 30 to 70°C - fit the Arrhenius equation, yielding apparent activation energies of 101 ± 4 kJ mol^-1 for tetrachloroethene (PCE), 108 ± 3 kJ mol^-1 for trichloroethene (TCE), 144 ± 5 kJ mol^-1 for cis-1,2-dichloroethene (cis-DCE), and 141 ± 2 kJ mol^-1 for trans-1,2-dichloroethene (trans-DCE). Chlorinated byproducts were observed, but most of the parent material was completely dechlorinated. Arrhenius parameters for hydrolysis and oxidation by persulfate or permanganate were used to calculate rates of chlorinated ethene degradation by these processes over the range of temperatures relevant to ISTR and the range of oxidant concentrations and pH relevant to ISCO.