Three constructed wetland systems were established to treat saline sewage via high-porosity ceramsite, activated carbon, and low-porosity sand: A (ceramsite + activated carbon + sand), B (sand + activated carbon + ceramsite), and C (sand). The distribution of dissolved oxygen in these systems varied with different filling methods with the best removal efficiency of ammonium nitrogen and total nitrogen observed in system B (97.4 and 96.2%, respectively). The 16S rDNA amplicon sequencing results showed that all the systems had a high abundance of salt-tolerant denitrifiers, and the filling method significantly impacted denitrifying bacteria (e.g., Vibrio and Planctomyces) in the substrate. System B had more diverse dissolved oxygen conditions than system A and showcased aerobic nitrification-denitrification and anaerobic ammonium oxidation pathways. Therefore, the use of substrates with different porosities can improve the dissolved oxygen supply and enhance nitrogen removal efficiency in constructed wetlands.
Keywords: Constructed wetland; Denitrification pathway; Dissolved oxygen; Microbial community structure; Porous substrate.
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