In-situ remediation of nitrate-contaminated ground water by electrokinetics/iron wall processes

The feasibility of using electrokinetics coupled with a zero valent iron (Fe⁰) treatment wall to abiotically remediate nitrate-contaminated soils was investigated. Upon completion of each test run, the contaminated soil specimen was sliced into five parts and analyzed for nitrate-nitrogen, ammonia-nitrogen and nitrite-nitrogen. Nitrogen mass balance was used to determine the major transformation products. In control experiments where only electrokinetics was used at various constant voltages, 25 to 37% of the nitrate-nitrogen was transformed. The amount of nitrate-nitrogen transformed improved when a Fe⁰ wall (20 g or about 8-10% by weight) was placed near the anode. For test runs at various constant voltages, the amount of nitrate-nitrogen transformed ranged from 54 to 87%. By switching to constant currents, the amount of nitrate-nitrogen - transformed was about 84 to 88%. The major transformation products were ammonia-nitrogen and nitrogen gases. Nitrite-nitrogen was less than 1% in all experimental runs. Two localized pH conditions exist in the system, a low pH region near the anode and a high pH region near the cathode. Placing of an iron wall near the anode increases the pH in that area as time increases. Movement of the acid front did not flush across the cathode. This research has demonstrated that the electrokinetics/iron wall process can be used to remediate nitrate-contaminated groundwater.