Abstract
A novel chemical absorption-biological reduction (CABR) integrated process, employing ferrous ethylenediaminetetraacetate (Fe(II)EDTA) as a solvent, is deemed as a potential option for NOx removal from the flue gas. Previous work showed that the Fe(II)EDTA concentration was critical for the NOx removal in the CABR process. In this work, the pathway of FeEDTA (Fe(III)/Fe(II)-EDTA) transformation was investigated to assess its impact on the NOx removal in a biofilter. Experimental results revealed that the FeEDTA transformation involved iron precipitation and EDTA degradation. X-ray photoelectron spectroscopy analysis confirmed the iron was precipitated in the form of Fe(OH)3. The iron mass balance analysis showed 44.2% of the added iron was precipitated. The EDTA degradation facilitated the iron precipitation. Besides chemical oxidation, EDTA biodegradation occurred in the biofilter. The addition of extra EDTA helped recover the iron from the precipitation. The transformation of FeEDTA did not retard the NO removal. In addition, EDTA rather than the iron concentration determined the NO removal efficiency.
Highlights
Only half of that of the bound NO15
They confirmed that the degradation of EDTA was due to the chemical oxidation by the oxygen in the scrubber rather than in the bioreactor since the dissolved oxygen could only be expected at the gas-liquid interface in the scrubber[17]
In the absence of oxygen, the maximum iron reducing rate in this biofilter was about 1.87 mM h−1 (Figure S1), which was almost twice of that reported in our previous study[18], indicating the high activity of microbes applied in this work
Summary
Only half of that of the bound NO15. Zhang et al.[16] reported that during the operation of the CABR process, the total iron concentration in the recirculated solution dropped gradually in a biofilter. Van der Maas et al.[17] showed that 2 mM d−1 of EDTA degradation occurred during the long-term operation of NO removal in presence of 3.5–3.9% (v/v) oxygen. They confirmed that the degradation of EDTA was due to the chemical oxidation by the oxygen in the scrubber rather than in the bioreactor since the dissolved oxygen could only be expected at the gas-liquid interface in the scrubber[17]. The iron transformation (loss) pathway and EDTA degradation mechanism, which can provide some insight to prevent the FeEDTA (Fe(III)/Fe(II)-EDTA) loss and reduce the CABR operation cost, remain unknown. Iron transformation and EDTA degradation were determined to identify the fate of FeEDTA in the CABR system with a long-term operation. This work may provide some insight on how to maintain the Fe(II) EDTA at a certain level and sustain the continuous NOx removal as well reduce the operation cost for the practical application
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