Combined Microbial-Fe(0) Treatment System to Remove Nitrate from Contaminated Groundwater

Experiments were conducted to delineate the applicability and limitations of biologically active Fe(0) barriers to remove nitrate under various geochemical and hydraulic conditions. Microcosm studies showed that, while no Fe(0) treatment was needed to remove nitrate from a high-carbon soil, adding Fe(0) to a low-carbon soil supplemented the electron donor pool and enhanced nitrate removal. Montmorillonite, an acidic aluminosilicate mineral, enhanced Fe(0) corrosion and nitrate removal (from about 1 to 3 mg/L NO₃-N per day), and reduced the transient accumulation of nitrite. Combining autotrophic denitrifiers (e.g., Paracoccus denitrificans) with Fe(0) significantly reduced the amount of nitrite eluted from aquifer columns, from up to 7 to less than 1 mg/L NO₂∼-N. Bacteria were observed to preferentially colonize the Fe(0) surface, which produces cathodic H₂ when corroded by water. The preferential colonization of Fe(0) suggests that hydrogenotrophic consortia are likely to develop around Fe(0) walls to exploit cathodic depolarization as a metabolic niche.