Combined microbial-Fe(0) system to treat nitrate-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 high-carbon soils, adding Fe(0) to low-carbon soil can supplement the electron donor pool and enhance nitrate removal. Montmorillonite, an acidic aluminosilicate mineral, enhanced Fe(0) corrosion and nitrate removal, 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. Bacteria were observed to preferentially colonize the Fe(0) surface, which produces cathodic H-2, when corroded by water. The preferential colonization of Fe(0) suggest that hydrogenotrophic consortia are likely to develop around Fe(0) walls to exploit cathodic depolarization as a metabolic niche.