Reduction of Nitroaromatic Compounds Coupled to Microbial Iron Reduction in Laboratory Aquifer Columns

Using 10 monosubstituted nitrobenzenes as model compounds, the interdependence between the reduction of organic pollutants and microbial iron reduction in anaerobic aquifers has been studied in laboratory column systems. All nitroaromatic compounds (NACs) investigated were stoichiometrically reduced to the corresponding amino compounds. It is proposed that NAC reduction occurred primarily by a reaction with surface-bound iron species, which served as mediators for the transfer of electrons originating from microbial oxidation of organic material by iron-reducing bacteria. Although the different NACs studied exhibited very different one-electron reduction potentials, they were reduced at very similar rates under all conditions investigated, indicating that the regeneration of reactive sites and not the electron transfer to the NAC was the rate-limiting process. It is also proposed that the presence of reducible organic pollutants such as NACs may significantly enhance the activity of iron-reducing bacteria in aquifers, in that reduction of such compounds continuously regenerates easily available Fe(III) species.