REDUCTION OF NITROAROMATIC - COMPOUNDS COUPLED TO MICROBIAL IRON REDUCTION IN LABORATORY AQUIFER COLUMNS

Using 10 monosubstituted nitrobenzenes as model compounds, the interde pendence between the reduction of organic pollutants and microbial iro n reduction in anaerobic aquifers has been studied in laboratory colum n systems. All nitroaromatic compounds (NACs) investigated were stoich iometrically reduced to the corresponding amino compounds. It is propo sed that NAC reduction occurred primarily by a reaction with surface-b ound iron species, which served as mediators for the transfer of elect rons 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 NA C was the rate-limiting process. It is also proposed that the presence of reducible organic pollutants such as NACs may significantly enhanc e the activity of iron-reducing bacteria in aquifers, in that reductio n of such compounds continuously regenerates easily available Fe(III) species.