Evaluation of complexed NO reduction mechanism in a chemical absorption-biological reduction integrated NO_x removal system

Biological reduction of nitric oxide (NO) from Fe(II) ethylenediaminetetraacetic acid (EDTA)-NO to dinitrogen (N₂) is a core process for the continual nitrogen oxides (NO_x) removal in the chemical absorption-biological reduction integrated approach. To explore the biological reduction of Fe(II)EDTA-NO, the stoichiometry and mechanism of Fe(II)EDTA-NO reduction with glucose or Fe(II)EDTA as electron donor were investigated. The experimental results indicate that the main product of complexed NO reduction is N₂, as there was no accumulation of nitrous oxide, ammonia, nitrite, or nitrate after the complete depletion of Fe(II)EDTA-NO. A transient accumulation of nitrous oxide (N₂O) suggests reduction of complexed NO proceeds with N₂O as an intermediate. Some quantitative data on the stoichiometry of the reaction are experimental support that reduction of complexed NO to N₂ actually works. In addition, glucose is the preferred and primary electron donor for complexed NO reduction. Fe(II)EDTA served as electron donor for the reduction of Fe(II)EDTA-NO even in the glucose excessive condition. A maximum reduction capacity as measured by NO (0.818 mM h^-1) is obtained at 4 mM of Fe(II)EDTA-NO using 5.6 mM of glucose as primary electron donor. These findings impact on the understanding of the mechanism of bacterial anaerobic Fe(II)EDTA-NO reduction and have implication for improving treatment methods of this integrated approach.