BioDeNOx:: novel process for NOx removal from flue gases based on chemically enhanced biological NO and iron reduction

A novel process for NO, removal from flue gases, called BioDeNOx, combines the principles of wet absorption of NO into a aqueous Fe(II)EDTA solution with biological reduction of NO in a bioreactor. This research investigates the core processes of the biological regeneration of Fe(II)EDTA: reduction of NO and EDTA chelated Fe(III). The reduction of NO to N-2 was found to be biologically catalyzed. The NO reduction kinetics follow first order with the NO/nitrosyl concentration. Besides absorbent, Fe(II)EDTA serves as electron donor for NO reduction. This implies that redox cycling of FeEDTA plays an important role in the biological denitrification process. However, continuous reactor experiments demonstrated that not the denitrification capacity, but the iron reduction capacity was the limiting the load of the bioreactor. When treating flue gas containing 3,3% O-2 and 500 ppm NO, approximately 90% of the electron flow was used for Fe(III)EDTA reduction and only 10% for NO reduction. Batch experiments strongly suggest that the reduction of EDTA chelated Fe(III) is not a direct enzymatic conversion, but an indirect nonenzymatic reaction. The redox couple S-0/S(2-)plays an important role in the electron transfer between the bacteria and Fe(III)EDTA. The redox couple sulfide/elemental accelerates the electron transfer between the bacteria and Fe(III)EDTA. Thus, Fe(III)EDTA reduction is most likely a nonenzymatic conversion.