Denitrification in aqueous FeEDTA solutions

Journal of Chemical Technology & Biotechnology (Impact Factor: 2.5). 06/2004; 79(8):835 - 841. DOI: 10.1002/jctb.1057

ABSTRACT 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 NOx 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 N2 in this unusual medium. This was done in batch experiments at 30 °C 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 °C than NO reduction at 30 °C. 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. Copyright © 2004 Society of Chemical Industry

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    ABSTRACT: NO pollutant causes acid rain and urban smog. The removal of NO from exhausted gas streams is necessary to meet stringent effluent discharge limits. NO can be removed from exhausted gas streams by putting soluble cobalt salts and ethylenediamine (H2NCH2CH2NH2) into basic solutions. The Co(en)33+ (en stands for ethylenediamine) ion produced by ethylenediamine binding cobalt acts as a homogeneous catalyst to oxidize NO into soluble NO2 and realize the oxidation and absorption of nitric oxide in the same reactor. The dissolved oxygen in equilibrium with the residual oxygen in the exhausted gas stream acts as the oxidant. The experiments manifest that this process is superior to the methods using Fe(II)–ethylenediaminetetraacetate (EDTA) solution and H2O2 solution as absorbents in removing NO from the exhausted gas stream. NO removal efficiency decreases with the increase of the gas flow rate. NO removal efficiency increases with the Co(en)33+ concentration. pH of the solution affects the NO removal efficiencies obviously. Under anaerobic condition, the NO removal efficiency decreases with pH when pH is over 7.73. Under aerobic condition, there is an optimal pH for NO absorption into the Co(en)33+ concentration. More than 90% of NO in the feed gas can be removed by the Co(en)33+ solution.
    Separation and Purification Technology - SEP PURIF TECHNOL. 01/2007; 55(2):226-231.
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    ABSTRACT: BACKGROUND The integrated approach of using metal chelate (e.g. Fe(II)EDTA) absorption combined with microbial reduction for nitric oxide (NO) removal has been a frequent topic of much recent study. The present study was undertaken to evaluate simultaneous Fe(II)EDTA-NO and Fe(III)EDTA with Paracoccus denitrificans as a model microorganism. RESULTSThe experimental results suggested that Fe(III)EDTA reduction was severely inhibited by Fe(II)EDTA-NO while the addition of Fe(III)EDTA could have a positive effect on the reduction of Fe(II)EDTA-NO. Riboflavin, AQDS and vitamin B12 at 0.1 mmol L−1 did not have significant effects on simultaneous reduction of Fe(II)EDTA-NO and Fe(III)EDTA. Addition of sulfide not only could directly react with Fe(II)EDTA-NO and Fe(III)EDTA but also might play multiple roles in biological Fe(II)EDTA-NO reduction and Fe(III)EDTA reduction. The respiratory inhibitor CuCl2 inhibited Fe(II)EDTA-NO reduction as well as Fe(III)EDTA reduction while NaN3 and rotenone showed no measurable effects. CONCLUSIONS The present study showed that Fe(II)EDTA-NO reduction and Fe(III)EDTA reduction reacted upon each other. The roles of sulfide were divided in terms of biological and chemical interactions during the simultaneous reduction. CuCl2 could inhibit the simultaneous reduction rates. © 2013 Society of Chemical Industry
    Journal of Chemical Technology & Biotechnology 01/2014; 89(1). · 2.50 Impact Factor