Application of potassium permanganate as an oxidant for in situ oxidation of trichloroethylene-contaminated groundwater: A laboratory and kinetics study

The objectives of this bench-scale study were to (1) determine the optimal operational parameters and kinetics when potassium permanganate (KMnO 4) was applied to in situ oxidize and remediate trichloroethylene (TCE)-contaminated groundwater and (2) evaluate the effects of manganese dioxide (MnO 2) on the efficiency of TCE oxidation. The major controlling factors in the TCE oxidation experiments included molar ratios of KMnO 4 to TCE ( P value) and molar ratios of Na 2HPO 4 to Mn 2+ ( D value). Results show that the second-order decay model can be used to describe the oxidation when P value was less than 20, and the observed TCE decay rate was 0.8 M −1 s −1. Results also reveal that (1) higher P value corresponded with higher TCE oxidation rate under the same initial TCE concentration condition and (2) higher TCE concentration corresponded with higher TCE oxidation rate under the same P value condition. Results reveal that significant MnO 2 production and inhibition of TCE oxidation were not observed under acidic (pH 2.1) or slightly acidic conditions (pH 6.3). However, significant reduction of KMnO 4 to MnO 2 would occur under alkaline condition (pH 12.5), and this caused the decrease in TCE oxidation rate. Results from the MnO 2 production experiments show that MnO 2 was produced from three major routes: (1) oxidation of TCE by KMnO 4, (2) further oxidation of Mn 2+, which was produced during the oxidation of TCE by KMnO 4, and (3) reduction of MnO 4 −1 to MnO 2 under alkaline conditions. Up to 81.5% of MnO 2 production can be effectively inhibited with the addition of Na 2HPO 4. Moreover, the addition of Na 2HPO 4 would not decrease the TCE oxidation rate.