Proof of concept was obtained that Fe(0) can stoichio metrically reduce nitrate to ammonium and that cathodic hydrogen [produced during anaerobic Fe(0) corrosion by water] can sustain microbial denitrification to reduce nitrate to more innocuous products (i.e., N2O and N2). Autotrophic, denitrifying growth on Fe(0) was proven through the use of a dual-flask apparatus. Cathodic H2 from a flask containing Fe(0) was allowed to diffuse to another (anoxic) flask containing a pure culture of Paracoccus denitrificans, where denitrification and microbial growth were observed. Nitrate reduction and end product distribution were studied in batch reactors amended with either steel wool or Fe(0) powder. Steel wool, with a smaller specific surface area, was less reactive, and its corrosion did not significantly increase the pH of the solution. This allowed for a greater participation of denitrifiers in the nitrate removal process, which increased nitrate removal rates and transformed a greater portion of the added nitrate to innocuous gases rather than to ammonium. Combining denitrifiers with the more reactive Fe(0) powder did not increase removal rates or decrease the proportion of nitrate reduced to ammonium. This was attributed to a corrosion-induced increase in pH above the tolerance range of the bacteria (pH > 10). Nitrate removal was sustained over 4 months in flow-through columns packed with steel wool and seeded with autotrophic denitrifiers. Increasing the hydraulic retention time from 0.67 to 2.33 days increased the nitrate removal efficiency and decreased the fraction of nitrate reduced to ammonium. The finding that Fe(0) can sustain autotrophic denitrification may have practical applications to treat nitrate-contaminated waters in ex-situ or in-situ reactive filters.

Currently there is considerable interest in using elemental iron (Fe 0 ) for treatment of highly chlorinated organic compounds. Early studies found little microbiological contribution to degradation in laboratory and field tests. Most work since then has focused on abiotic processes. In studies conducted with a mixed, methanogenic culture, however, pseudo-first-order rate coefficients for chloroform degradation were at least 3.6 times greater in serum bottle incubations containing 40 mesh iron filings and live cells as compared to incubations containing Fe 0 and killed cells, Fe 0 and cell-free mineral medium, or Fe 0 -free incubations with live cells. CF cometabolism and methanogenesis was apparently supported using cathodic hydrogen produced by anaerobic corrosion of the added Fe 0 . The use of selective microbial inhibitors showed that H 2 -consuming methanogens and not homoacetogens were responsible for CF degradation. The sustainability of the process was established in a 60-day column study using steel wool as support for microbial growth. The observation that cathodically produced H 2 can support reductive dechlorination by anaerobic bacteria may have significant practical implications.

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