Efficacy of controlled-release KMnO₄ (CRP) for controlling dissolved TCE plume in groundwater: A large flow-tank study

A well-based, reactive barrier system using controlled-release potassium permanganate (CRP system) was recently developed as a long-term treatment option for dilute plumes of chlorinated solvents in groundwater. In this study, we performed large-scale (L × W × D = 8 m × 4 m × 2 m) flow-tank experiments to examine remedial efficacy of the CRP system. A total of 110 CRP rods (OD × L = 5 cm × 150 cm) were used to construct a well-based CRP system (L × W × D = 3 m × 4 m × 1.5 m) comprising three discrete barriers installed at 1-m interval downstream. Natural sands having oxidant demand of 3.7 g MnO₄^- kg^-1 for 500 mg L^-1MnO₄^- were used as porous media. After MnO₄^- concentrations were somewhat stabilized (0.5-6.0 mg L^-1), trichloroethylene (TCE) plume was flowed through the flow-tank for 53 d by supplying 1.19 m³ d^-1 of TCE solution. Mean initial TCE concentrations were 87 μg L^-1 for first 20 d and 172 μg L^-1 for the next 33 d. During TCE treatment, flow velocity (0.60 m d^-1), pH (7.0-8.2), and concentrations of dissolved metals ([Al] = 0.7 mg L^-1, [Fe] = 0.01 mg L^-1) showed little variations. The MnO₂(s) contents in the sandy media measured after the TCE treatment ranged from 21 to 26 mg kg^-1, slightly increased from mean baseline value of 17 mg kg^-1. Strengths of the TCE plume considerably diminished by the CRP system. For the 87 μg L^-1 plume, TCE concentrations decreased by 38% (53), 67% (29), and 74% (23 μg L^-1) after 1st, 2nd, and 3rd barriers, respectively. For the 172 μg L^-1 plume, TCE concentrations decreased by 27% (125), 46% (93), and 65% (61 μg L^-1) after 1st, 2nd, and 3rd barriers, respectively. Incomplete destruction of TCE plume was attributed to the lack of lateral dispersion in the unpumped well-based barrier system. Development of delivery systems that can facilitate lateral spreading and mixing of permanganate with contaminant plume is warranted.