Oxidative degradation and kinetics of chlorinated ethylenes by potassium permanganate

The oxidative treatment of chlorinated ethylenes in ground water using permanganate was investigated in a series of batch kinetic tests. Five chlorinated ethylenes including tetrachloroethylene (PCE), trichloroethylene (TCE), and three isomers of dichloroethylenes (DCEs) were examined. The degradation process was rapid with pseudo-first-order rate constants ranging from 4.5×10−5 to 0.03 s−1 at MnO4−=1 mM. The rate increased with a decreasing number of chlorine substituents on the ethylene. The higher reactivity of trans-DCE (kobs=30×10−3 s−1 at MnO4−=1 mM) as compared to cis-DCE (kobs=0.9×10−3 s−1 at MnO4−=1 mM) is thought to be caused by a significant steric effect due to the formation of a large cyclic activated complex. TCE oxidation as a second-order reaction was confirmed and the rate constant, k=0.67±0.03 M−1 s−1, is independent of pH over the range of 4–8. The activity of both Cl− and hydrogen ions was monitored over time and suggests essentially complete dechlorination, making the degradation products less harmful than the parent compounds. Competition for MnO4− from other organic compounds in ground water or highly contaminated ground water was also evaluated in experiments. A simple and quick approach was demonstrated to estimate permanganate consumption by other organic compounds for field applications and to predict the TCE degradation rate in a system involving multiple contaminants. The modeling results suggest that the effect of autocatalysis by MnO2 on TCE degradation is significant when the system contains high concentration levels of MnO4− and TOC.