Abiotic degradation of nitrates using zero-valent iron and electrokinetic processes

Nitrate transformation in artificial saturated soils made from sand and/or clay mixed with nitrate-contaminated water was investigated using (1) zero-valent iron treatment, (2) electrokinetics treatment alone, and (3) electrokinetics coupled with an iron treatment wall placed near the cathode or anode. Approximately 75-98% of the nitrates were transformed using zero- valent iron to treat the artificial soils. The major products in the zero- valent-assisted transformation were nitrogen gases (75-81%) and ammonia- nitrogen (2-18%). Nitrite-nitrogen was less than 1% in all these experiments. With electrokinetics alone, some nitrates were transformed (about 30%). Nitrate transformation was about 60% with the iron wall placed near the cathode, and was about 95% with the iron wall placed near the anode. The major products were nitrogen gases and ammonia. Nitrite-nitrogen was less than 1% in these runs. Electroosmotic permeability (Ke) variation appeared to be dependent on the voltage in the reactor. The pH variations over time in electrokinetics (control and iron wall near cathode) indicated the movement of a small acid front. However, the presence of an iron wall near the anode tended to increase the pH slightly. The pH variations over time in the electrokinetics coupled with an iron wall depend on the location of the iron wall. This study demonstrates that electrokinetics coupled with an iron wall near the anode is capable of remediating nitrate contamination in low permeability soils.