Remediation of TCE-contaminated groundwater using KMnO oxidation: laboratory and field-scale studies.

The objectives of this study were to (1) conduct laboratory bench and column experiments to determine the oxidation kinetics and optimal operational parameters for trichloroethene (TCE)-contaminated groundwater remediation using potassium permanganate (KMnO) as oxidant and (2) to conduct a pilot-scale study to assess the efficiency of TCE remediation by KMnO oxidation. The controlling factors in laboratory studies included soil oxidant demand (SOD), molar ratios of KMnO to TCE, KMnO decay rate, and molar ratios of NaHPO to KMnO for manganese dioxide (MnO) production control. Results show that a significant amount of KMnO was depleted when it was added in a soil/water system due to the existence of natural soil organic matters. The presence of natural organic material in soils can exert a significant oxidant demand thereby reducing the amount of KMnO available for the destruction of TCE as well as the overall oxidation rate of TCE. Supplement of higher concentrations of KMnO is required in the soil systems with high SOD values. Higher KMnO application resulted in more significant H and subsequent pH drop. The addition of NaHPO could minimize the amount of produced MnO particles and prevent the clogging of soil pores, and TCE oxidation efficiency would not be affected by NaHPO. To obtain a complete TCE removal, the amount of KMnO used to oxidize TCE needs to be higher than the theoretical molar ratio of KMnO to TCE based on the stoichiometry equation. Relatively lower oxidation rates are obtained with lower initial TCE concentrations. The half-life of TCE decreased with increased KMnO concentrations. Results from the pilot-scale study indicate that a significant KMnO decay occurs after the injection due to the reaction of KMnO with soil organic matters, and thus, the amount of KMnO, which could be transported from the injection point to the downgradient area, would be low. The effective influence zone of the KMnO oxidation was limited to the KMnO injection area (within a 3-m radius zone). Migration of KMnO to farther downgradient area was limited due to the reaction of KMnO to natural organic matters. To retain a higher TCE removal efficiency, continuous supplement of high concentrations of KMnO is required. The findings would be useful in designing an in situ field-scale ISCO system for TCE-contaminated groundwater remediation using KMnO as the oxidant.