SEMI-PASSIVE TREATMENT OF DNAPL PLUME USING SLOW-RELEASE PERMANGANATE

The in situ chemical oxidation (ISCO) scheme using KMnO4 is considered attractive as a remedial technology for groundwater because of the rapid destruction of most chlorinated solvents and the ease of field implementation. Although ISCO is now regarded as a developing technology in an industrial sense, it has not been researched extensively. For example, beyond active flushing schemes, there have been relatively limited investigations in how ISCO might be better used. Our recent large-scale flow-tank study showed that destruction efficiencies associated with KMnO4 flushing approaches diminished with time due to plugging of porous media by low-permeability reaction products, i.e., MnO2 and likely CO2. It was thereby suggested that development of a new approach that can provide both contaminant destruction and plugging control is desired.

This paper describes a new semi-passive remediation concept with ISCO. It involves the manufacture of slow-release permanganate solids and understanding how they interact with the flow systems. Properties of our slow-release permanganate were tested using column and flow-tank experiments. In column experiments, permanganate concentration in the outflow ranged between 2 to 4 mg/L with an average release rate of 125mg/day throughout the 37 days of testing period. This result indicated that slow-release permanganate may release permanganate for ~300 days in a controlled fashion. In flow-tank experiments, distribution pattern of permanganate concentrations remained constant throughout the 93 days of testing period and ranged from ~900 ppb nearby the upstream permanganate source to ~100 ppb in the downstream end of the tank.