Enhanced NOx removal performance and microbial community shifts in an oxygen-resistance chemical absorption–biological reduction integrated system

• An enhanced CABR system with the inoculation of the enriched culture was developed.
• The enhanced system features a shorter start-up period and a higher NO removal rate.
• The enhanced system showed more robust resistance to the oxygen influence.
• The denitrifier was dominant in the biofilter despite of oxygen concentration.
• Oxygen shifted the dominant denitrifier from facultative anaerobic to aerobic one.

The chemical absorption–biological reduction (CABR) integrated process, which employed ferrous ethylenediaminetetraacetate as a solvent, is promising for NOx removal. However, oxygen in the flue gas has a great potential to retard the NOx removal. In this work, an oxygen-resistance CABR system inoculated with enriched culture was established. It features a shorter start-up period and a better performance of NOx removal compared with the conventional CABR system. The microbial community shifts in taxa and diversity in response to oxygen were also investigated. High-throughput sequencing analysis showed that Enterococcus, Clostridium sensu stricto, Chelatococcus, Petrimonas, Escherichia/Shigella, Cupriavidus were the major groups of bacteria, and denitrifying bacteria (Petrimonas, Cupriavidus, Chelatococcus, Enterococcus), accounting for 63.29% of the total bacteria, were dominant in the absence of oxygen. Variation in oxygen concentration resulted in the change of the dominant bacteria. For example, Enterococcus, Petrimonas, and Cupriavidus were dominant in the presence of 0 vol%, 6 vol%, and 10 vol% oxygen, respectively. The diversity of the microbial community also varied along the gas flow path at the different levels of oxygen. Although the increase in oxygen concentration significantly impacted the taxa and distribution of the microbial community, the NOx removal efficiency of the enhanced CABR system was not noticeably changed because of the high species richness under the high oxygen concentration case.

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