Permanganate treatment of DnAPLs in reactive barriers and source zone flooding schemes. 1998 annual progress report
- Ohio State Univ., Columbus, OH (US). Mendenhall Lab.
- Duke Engineering Services, Albuquerque, NM (US)
'The goals of this study are: (1) to elucidate the basic mechanisms by which potassium permanganate oxidizes common chlorinated solvents, various constituents in aqueous solution, and porous-medium solids, and (2) to assess the potential for chemical oxidation by potassium permanganate to serve as a remedial scheme involving either source zone flooding or reactive barriers. The combined theoretical and experimental study is designed to contribute fundamental knowledge about reaction pathways, reaction rates, specific intermediates formed, and controls on reaction processes. The specific objectives of this study are: (1) to describe through batch experiments the kinetics and mechanisms by which potassium permanganate oxidizes dissolved tetrachloroethene (PCE), trichloroethene (TCE), and dichloroethene (DCE), (2) to examine using column studies the nature and kinetics of reactions between potassium permanganate, residual DNAPLs (PCE, TCE, and DCE) and porous medium solids, (3) to represent the process understanding in flow and transport models that demonstrate the potential applicability of the approach, and (4) to apply the resulting computer code in the development of appropriate field tests for assessing the approach. Approaching the end of Year 2 of this 3-Year project, the authors can report significant progress in meeting the objectives of the study. Through a series of batch experiments, it has been shown that permanganate oxidation is effective in degrading various chlorinated ethylenes in aqueous solution. The disappearance of chlorinated ethylenes can be simply characterized by a pseudo-first-order model. Degradation half-lives for TCE, cis-1,2-DCE, trans-1,2-DCE and 1,1-DCE reacting with 1mM MnO{sub 4}{sup -} range from about 24 s to 18 min. Degradation of PCE is much slower with a half-life of about 257 min. Overall, the degradation rate is inversely proportional to the number of chlorines present as substituents on ethylenes. These rates of degradation are impressive given the fact that the experiments were run with MnO{sub 4}{sup -} concentrations only a factor of 10 or so greater than that of the particular chlorinated ethylene. It would be feasible in practice to increase rates of reaction by increasing MnO{sub 4}{sup -} concentrations. The experiments also showed how the efficiency of degradation is reduced due to competition from other organic compounds. Contaminated ground water was synthesized as a mixture of ground water and landfill leachate. Three experiments were run with a fixed TCE concentration of 2 mg/L, a concentration of other organic compounds of 101 mg/L (TOC) and concentrations of MnO{sub 4}{sup -} of 20, 80 and 120 mg/L. As expected, the competition for MnO{sub 4}{sup -} led to a reduction in the reaction rate, as compared to experiments with TCE in Milli-Q water. However, with the largest MnO{sub 4}{sup -} concentration, the competition appeared to be offset by other processes that effectively increased the degradation rate of TCE. The preliminary assessment is that colloidal MnO{sub 2} was catalyzing reactions between MnO{sub 4}{sup -} and TCE. The authors will explore this aspect of the study in the coming year. Early in the study, the authors confirmed previous work that indicated TCE degraded completely to CO{sub 2} in a series of three steps. However, little was known about the overall reaction pathways and intermediates that formed. Preliminary indications were that TCE reacted with MnO{sub 4}{sup -} to produce a cyclic complex, then carboxylic acids, and finally CO{sub 2} , along with Cl{sup -} and MnO{sub 2} . Of particular interest in the work were steps two and three. The authors undertook kinetic experiments with radiolabeled TCE (i.e., 1,2-14 C) to understand these reactions.'
- Research Organization:
- Ohio State Univ., Mendenhall Lab., Columbus, OH (US); Duke Engineering Services, Albuquerque, NM (US)
- Sponsoring Organization:
- USDOE Office of Environmental Management (EM), Office of Science and Risk Policy
- OSTI ID:
- 13521
- Report Number(s):
- EMSP-54585-98; ON: DE00013521
- Country of Publication:
- United States
- Language:
- English
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