NO removal in continuous BioDeNOx reactors: Fe(II)EDTA²⁻ regeneration, biomass growth, and EDTA degradation

Abstract

BioDeNOx is a novel technique for NOx removal from industrial flue gases. In principle, BioDeNOx is based on NO absorption into an aqueous Fe(II)EDTA2- solution combined with biological regeneration of that scrubber liquor in a bioreactor. The technical and economical feasibility of the BioDeNOx concept is strongly determined by high rate biological regeneration of the aqueous Fe(II)EDTA2- scrubber liquor and by EDTA degradation. This investigation deals with the Fe(II)EDTA2- regeneration capacity and EDTA degradation in a lab-scale BioDeNOx reactor (10-20 mM Fe(II)EDTA2-, pH 7.2 +/- 0.2, 55 degrees C), treating an artificial flue gas (1.5 m3/h) containing 60-155 ppm NO and 3.5-3.9% O2. The results obtained show a contradiction between the optimal redox state of the aqueous FeEDTA solution for NO absorption and the biological regeneration. A low redox potential (below -150 mV vs. Ag/AgCl) is needed to obtain a maximal NO removal efficiency from the gas phase via Fe(II)EDTA2- absorption. Fe(III)EDTA- reduction was found to be too slow to keep all FeEDTA in the reduced state. Stimulation of Fe(III)EDTA- reduction via periodical sulfide additions (2 mM spikes twice a week for the conditions applied in this study) was found to be necessary to regenerate the Fe(II)EDTA2- scrubber liquor and to achieve stable operation at redox potentials below -150 mV (pH 7.2 +/- 0.2). However, redox potentials of below -200 mV should be avoided since sulfide accumulation is unwanted because it is toxic for NO reduction. Very low values for biomass growth rate and yield, respectively, 0.043/d and 0.009 mg protein per mg ethanol, were observed. This might be due to substrate limitations, that is the electron acceptors NO and presumably polysulfide, or to physiological stress conditions induced by the EDTA rich medium or by radicals formed in the scrubber upon the oxidation of Fe(II)EDTA2- by oxygen present in the flue gas. Radicals possibly also induce EDTA degradation, which occurs at a substantial rate: 2.1 (+/-0.1) mM/d under the conditions investigated.

Reduction of Fe(II)EDTA‐NO using Paracoccus denitrificans and changes of Fe(II)EDTA in the system

“…11 In this present study, the color of the solution changed from black-brown Fe(II)EDTA-NO to orange-brown Fe(III)EDTA and colorless Fe(II)EDTA finally, which was consistent with the Zhang et al 9 results (Fig. Subsequently, Fe(II)EDTA-NO was reduced continuously for 6-10 h. Based on the sudden decrease in Fe(II)EDTA concentration and the increase in pH value, Equation (5) was dominant at this stage. Figure 3 showed that the reduction rate of Fe(II)EDTA-NO by P. denitrificans in this system was more rapid during the initial 6 h. Based on the increase of Fe(II)EDTA concentration and the decrease of pH value, Equation (4) was followed in this period and glucose was used as the primary electron donor.…”

“…However, the two technologies have many disadvantages, such as high operating costs, failure-prone catalyst and NH 3 leakage. 5,6 Fe(II)EDTA is the most common absorbent because it has the ability to form stable complexes with NO. Due to the low solubility in aqueous solution, the NO removal efficiency of the biological method is limited.…”

Nitric oxide enhanced reduction in a rotating drum biofilter coupled with absorption by FeII(EDTA)

“…Poor NO solubility in water limits NO mass transfer in a bioreactor, resulting in the limitation of biological treatment. One promising technique for NO removal from industrial flue gasses is an integrated physico‐chemical and biological process . Aqueous solutions of ferrous chelates such as Fe II (EDTA) can be applied as scrubber liquor , .…”

“…One promising technique for NO removal from industrial flue gasses is an integrated physico‐chemical and biological process . Aqueous solutions of ferrous chelates such as Fe II (EDTA) can be applied as scrubber liquor , . In the integrated system, Fe II (EDTA) can chelate NO into the solution to form Fe II (EDTA)‐NO.…”

Selective Catalytic Reduction of NO with NH3 over Wire-Mesh Honeycomb Supported V2O5 -MoO3/TiO2/Al2O3 Catalyst

“…Therefore, the removal of nitrogen oxides from waste gases has already become one of the most important tasks of environmental pollution treatment in the 21st century. Different catalytic removal technologies have been made by some researchers in recent years to limit the air pollutants emissions [3]- [6].…”