Nitrogen removal performance and functional genes distribution patterns in solid-phase denitrification sub-surface constructed wetland with micro aeration

An up-flow vertical flow constructed wetland (AC-VFCW) filled with ceramsite and 5% external carbon source poly(3-hydroxybutyrate-hydroxyvalerate) (PHBV) as substrate was set for nitrogen removal with micro aeration. Simultaneous nitrification and denitrification process was observed with 90.4% NH4+-N and 92.1% TN removal efficiencies. Nitrification and denitrification genes were both preferentially enriched on the surface of PHBV. Nitrogen transformation along the flow direction showed that NH4+-N was oxidized to NO3−-N at the lowermost 10 cm of the substrate and NO3−-N gradually degraded over the depth. AmoA gene was more enriched at −10 and −50 cm layers. NirS gene was the dominant functional gene at the bottom layer with the abundance of 2.05 × 107 copies g−1 substrate while nosZ gene was predominantly abundant with 7.51 × 106 and 2.64 × 106 copies g−1 substrate at the middle and top layer, respectively, indicating that functional division of dominant nitrogen functional genes forms along the flow direction in AC-VFCW.