Denitrification in aqueous FeEDTA solutions

The biological reduction of nitric oxide (NO) in aqueous solutions of FeEDTA is an important key reaction within the BioDeNOx process, a combined physico-chemical and biological technique for the removal of NO, from industrial flue gasses. To explore the reduction of nitrogen oxide analogues, this study investigated the full denitrification pathway in aqueous FeEDTA solutions, ie the reduction of NO3-, NO2-, NO via N2O to N-2 in this unusual medium. This was done in batch experiments at 30degreesC with 25 mmol dm(-3) FeEDTA solutions (pH 7.2 +/- 0.2). Also Ca2+ (2 and 10 mmol dm(-3)) and Mg2+ (2 mmol dm(-3)) were added in excess to prevent free, uncomplexed EDTA. Nitrate reduction in aqueous solutions of Fe(III)EDTA is accompanied by the biological reduction of Fe(III) to Fe(II), for which ethanol, methanol and also acetate are suitable electron donors. Fe(II)EDTA can serve as electron donor for the biological reduction of nitrate to nitrite, with the concomitant oxidation of Fe(II)EDTA to Fe(III)EDTA. Moreover, Fe(II)EDTA can also serve as electron donor for the chemical reduction of nitrite to NO, with the concomitant formation of the nitrosyl-complex Fe(II)EDTA-NO. The reduction of NO in Fe(II)EDTA was found to be catalysed biologically and occurred about three times faster at 55 degreesC than NO reduction at 30 degreesC. This study showed that the nitrogen and iron cycles are strongly coupled and that FeEDTA has an electron-mediating role during the subsequent reduction of nitrate, nitrite, nitric oxide and nitrous oxide to dinitrogen gas. (C) 2004 Society of Chemical Industry.