Kinetics of NDMA (N-nitrosodimethylamine) oxidation by permanganate under a range of pH and temperature conditions

N-Nitrosodimethylamine (NDMA; C2H6N2O) is a highly toxic contaminant that has been found in the groundwater at sites in Colorado, California, and other locations. NDMA is an impurity and breakdown product of hydrazine-based rocket fuels, and also forms during chlorination of water and wastewater. There is no remediation technology that has been demonstrated to reliably destroy NDMA in situ. Permanganate is a popular oxidant that is widely used for in situ oxidation of a range of organic contaminants. This study quantified the rates of NDMA oxidation by permanganate in laboratory batch studies conducted under a range of pH and temperature conditions. Aqueous solutions under these different conditions were set up in triplicate amber vials and incubated at the temperature of interest. Controls without oxidant and controls without NDMA were run. The vials were sacrificed at selected time points. The residual NDMA concentration was determined by liquid:liquid extraction into dichloromethane followed by GC/MS analysis in select ion monitoring mode (SIM). The residual permanganate concentration was determined by spectrophotometric analysis and pH was also measured. It was determined that the optimal permanganate dose was 350 mg/L; at higher permanganate concentrations the NDMA oxidation rate did not increase. The oxidation kinetics were second-order overall, with 1st order dependence on permanganate concentrations from 1 to 350 mg/L and 1st order dependence on NDMA concentrations from 2 to 200mug/L. The overall second order rate is 6*10-5 mol/s. The NDMA oxidation rates increased slightly with higher pH from 5 to 9 (first order coefficients ranging from 0.50 d-1 to 0.54 d-1) and slightly decreased at lower temperatures (5, 10, 15 and 20°C). NDMA oxidation rates are much slower than the rates that permanganate oxidizes organic compounds such as trichloroethylene but similar to benzene oxidation rates. The results indicate that in situ oxidation of NDMA may be feasible if permanganate is retained at sufficiently high concentrations in the groundwater over long time periods.