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 X 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 (k(obs) = 30 X 10(-3) s(-1) at MnO4- = 1 mM) as compared to cis-DCE (k(obs) = 0.9 X 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 far 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. (C) 1999 Elsevier Science B.V. All rights reserved.