Fe-EDTA Transformation Affecting Factors and the Cost-Optimal Operation Conditions for NO Removal in a Chemical Absorption-Biological Reduction Integrated Reactor

In the novel chemical absorption-biological reduction (CABR) integrated NO_x removal system, Fe(II) ethylenediaminetetraacetic acid (EDTA) is used to overcome the mass-transfer limitation by complex formation. The complexed NO, Fe(II)EDTA-NO, would be biologically reduced to N₂. At the same time, Fe(II)EDTA, oxidized by O₂ in flue gas, could be regenerated in a function of iron-reducing bacteria. Thus, the Fe(II)EDTA concentration is critical for NO_x removal. It has been proved by previous work that the FeEDTA transformation involved iron precipitation and EDTA degradation. The EDTA degradation facilitated the iron precipation. A total of 44.2% iron deposited out of the system in the form of Fe(OH)₃ under typical conditions. In this work, The influences of initial Fe(III)EDTA added into the system ([Fe(III)EDTA]₀), O₂ concentrations (O₂), and the simulated flue gas rate (G) on FeEDTA transformation rate were explored. The transformation rate was the average loss rate during 72 h, while NO load for unit complexant loss (g/mol) was defined as “mass of NO treated (g) / loss amount (mol)” in order to find the cost-optimal conditions. The results shown that transformation rate of iron and EDTA increased with [Fe(III)EDTA]₀, O₂ and G raising, but the changes of NO load for unit complexant loss were different. Moreover, in the view of complexant loss, the the cost-optimal operation conditions were [Fe(III)EDTA]₀=5 mmol·L^-1 and G=2L/min.