Destruction efficiencies and dynamics of reaction fronts associated with the permanganate oxidation of trichloroethylene

Although potassium permanganate (KMnO4) flushing is commonly used to destroy chlorinated solvents in groundwater, many of the problems associated with this treatment scheme have not been examined in detail. We conducted a KMnO4 flushing experiment in a large sand-filled flow tank (L x W x D = 180 cm x 60 cm x 90 cm) to remove TCE emplaced as a DNAPL in a source zone. The study was specifically designed to investigate cleanup progress and problems of pore plugging associated with the dynamics of the solid-phase reaction front (i.e., MnO2) using chemical and optical monitoring techniques. Ambient flow through the source zone formed a plume of dissolved TCE across the flow tank. The volume and concentration of TCE plume diminished with time because of the in situ oxidation of the DNAPL source. The migration velocity of the MnO2 reaction front decreased with time, suggesting that the kinetics of the DNAPL oxidation process became diffusion-controlled because of the pore plugging. A mass balance calculation indicated that only approximately 18% of the total applied KMnO4 (MnO4- = 1250 mg/ L) participated in the oxidation reaction to destroy approximately 41% of emplaced TCE. Evidently, the efficiency of KMnO4 flushing scheme diminished with time due to pore plugging by MnO2 and likely CO2, particularly in the TCE source zone. In addition, the excess KMnO4 used for flushing may cause secondary aquifer contamination. One needs to be concerned about the efficacy of KMnO4 flushing in the field applications. Development of a new approach that can provide both contaminant destruction and plugging/ MnO4- control is required.