Biological Reduction of Nitric Oxide in Aqueous Fe(II)EDTA Solutions

Abstract

The reduction of nitric oxide (NO) in aqueous solutions of Fe(II)EDTA is one of the core processes in BioDeNOx, an integrated physicochemical and biological technique for NO(x)() removal from industrial flue gases. NO reduction in aqueous solutions of Fe(II)EDTA (20-25 mM, pH 7.2 +/- 0.2) was investigated in batch experiments at 55 degrees C. Reduction of NO to N(2) was found to be biologically catalyzed with nitrous oxide (N(2)O) as an intermediate. Various sludges from full-scale denitrifying and anaerobic reactors were capable to catalyze NO reduction under thermophilic conditions. The NO reduction rate was not affected by the presence of ethanol or acetate. EDTA-chelated Fe(II) was found to be a suitable electron donor for the biological reduction of nitric oxide to N(2), with the concomitant formation of Fe(III)EDTA. In the presence of ethanol, EDTA-chelated Fe(III) was reduced to Fe(II)EDTA. This study strongly indicates that redox cycling of FeEDTA plays an important role in the biological denitrification process within the BioDeNOx concept.

Regeneration of spent NOx scrubber liquor using a dual-chamber microbial fuel cell

“…On the other hand, microorganism‐mediated bioelectrochemical reaction could also lead to Fe(III)EDTA reduction and this pathway might be predominant in this system for Fe(III)EDTA reduction, evidenced by the detection of abundant potential iron‐reducing bacteria (Fig. S2) and relatively low oxidability of Fe(III)EDTA at neutral pH . The role of hydrogen in the MFC for the reduction of Fe(III)EDTA or even Fe(II)EDTA‐NO can be excluded because there was no hydrogen produced in this system .…”

“…The reactor cannot be strictly gas‐tight and thus a little oxygen might lead to the oxidation of Fe(II)EDTA‐NO. But the most important reason for the slight decrease of Fe(II)EDTA‐NO is the Fe(II)EDTA‐NO reduction coupled with Fe(II) oxidation via Equations (8) and (9) spontaneously or mediated by the biological action . Another batch test (Test 5) was performed to further confirm electron donor for Fe(II)EDTA‐NO reduction, in which both Fe(II)EDTA‐NO and Fe(II)EDTA were injected into the cathode compartment at open circuit.…”

“…Although higher removal efficiencies can be achieved via the addition of Fe(II)EDTA, this process is not appealing in terms of consistent NO removal. More specifically, Fe(II)EDTA‐NO, the absorption products (Equation (2)), and Fe(III)EDTA, formed via Fe(II)EDTA oxidation by oxygen in the flue gas (Equation (3)), cannot further bind NO, which is neither economic nor environmentally sustainable . Consequently, a means of regenerating Fe(II)EDTA‐NO and Fe(III)EDTA to produce Fe(II)EDTA is urgently required.…”

“…It should also be noted that direct cathodic reduction of ferric iron to ferrous iron has been evidenced at low pH in accordance with the high standard redox potential of Fe 3+ /Fe 2+ . Although the situation might be different due to different Fe sources and pH, at least it gives some hints that direct reduction of Fe(III)EDTA may occur through obtaining electrons from the cathode at pH = 7 because Fe(III)EDTA/Fe(II)EDTA also shows a positive redox potential of 96 mV . Considering the redox reaction shown in Equation (5), it is no surprise that a biocathode for Fe(III)EDTA reduction has been developed.…”

Simultaneous Biological and Chemical Removal of Sulfate and Fe(II)EDTA-NO in Anaerobic Conditions and Regulation of Sulfate Reduction Products

“…Therefore, the final product of NO denitrification was mainly N 2 . In the BioDeNOx process, the reduction of NO to N 2 was found to be biologically catalyzed with nitrous oxide (N 2 O) as an intermediate [43]. They found that the NO (aq) and Fe(II)EDTA concentration had an effect on the accumulation rate of N 2 O [44].…”