Electrokinetic remediation of a nitrate-contaminated soil

The potential for groundwater contamination by inorganic forms of nitrogen from intensive livestock operations has become a major concern for surrounding communities that use groundwater as their water supply. The traditional pump-and-treat method is ineffective in medium to fine textured agricultural soils due to their low hydraulic conductivity. Application of an electrical potential gradient results in the movement of charged particles and water in soil. A diffuse double layer formed around hydrated clay particles is the basis for the electrokinetic phenomena. Three sets of laboratory experiments were conducted to assess the effectiveness of electrokinetic methods in remediating a nitrate contaminated soil i.e. the first set of experiments tested denitrification of nitrates, the second looked at retarding nitrate ion movement, and the third evaluated the complete remediation of a nitrate contaminated soil using electrokinetics.; The first set of laboratory experiments showed that the nitrates in soil can be converted to other forms using electrokinetic treatment. The conversion occurred at the cathode (negative electrode) and in the surrounding soil. After nine days of electrokinetic treatment, compared to control, the nitrate concentration at the inflow end and at a relative distance of 0.2 in electrokinetic columns were significantly (p < 0.05) lower showing successful reduction of nitrates near the cathode end.; The second set of laboratory experiments showed that nitrate ion movement can be retarded by applying an electrical potential gradient. The retardation occurred at the anode (positive electrode). The application of the electrical potential gradient induced a nitrate ion barrier around the anode against a hydraulic gradient of 1.25. Nitrate concentration at a relative distance of 0.2 from the anode was significantly lower (p < 0.05) than that in the hydraulic column even after thirteen days of treatment.; The third set of experiments showed that by changing the polarity of the electrodes after a period of time, the nitrate levels in a contaminated soil can be brought to below 10 mg NO3-N L-1 which is the Maximum Acceptable Concentration (MAC) for nitrate in drinking water in Canada. Six days after switching polarity, the nitrate concentration at a relative distance of 0.2 from the cathode was significantly lower (p < 0.05) than that in the hydraulic column. The nitrate concentrations in the entire treatment columns were brought to <5 mg NO3-N L -1 and significantly lower (p < 0.05) than control by the twelfth day. Electrokinetic treatment retarded nitrate movement against a hydraulic gradient of 1.25, and effectively restored a medium textured soil contaminated with NO3-N. To achieve optimum results in the field, the electrodes have to be located based on contamination location and the direction of the hydraulic gradient.