FE(0)-SUPPORTED AUTOTROPHIC DENITRIFICATION

Proof of concept was obtained that Fe(O) can stoichiometrically reduce nitrate to ammonium and that cathodic hydrogen [produced during anaer obic Fe(O) corrosion by water] can sustain microbial denitrification t o reduce nitrate to more innocuous products (i.e., N2O and N-2). Autot rophic, denitrifying growth on Fe(O) was proven through the use of a d ual-flask apparatus. Cathodic H-2 from a flask containing Fe(O) was al lowed to diffuse to another (anoxic) flask containing a pure culture o f Paracoccus denitrificans, where denitrification and microbial growth were observed. Nitrate reduction and end product distribution were st udied in batch reactors amended with either steel wool or Fe(O) powder . Steel wool, with a smaller specific surface area, was less reactive, and its corrosion did not significantly increase the pH of the soluti on. This allowed for a greater participation of denitrifiers in the ni trate removal process, which increased nitrate removal rates and trans formed a greater portion of the added nitrate to innocuous gases rathe r than to ammonium. Combining denitrifiers with the more reactive Fe(O ) powder did not increase removal rates or decrease the proportion of nitrate reduced to ammonium. This was attributed to a corrosion-induce d increase in pH above the tolerance range of the bacteria (pH > 10). Nitrate removal was sustained over 4 months in flow-through columns pa cked with steel wool and seeded with autotrophic denitrifiers. Increas ing the hydraulic retention time from 0.67 to 2.33 days increased the nitrate removal efficiency and decreased the fraction of nitrate reduc ed to ammonium. The finding that Fe(O) can sustain autotrophic denitri fication may have practical applications to treat nitrate-contaminated waters in exsitu or in-situ reactive filters.