Increasing nitrogen removal efficiency by intermittent aeration in partial areas of laboratory-scale vertical flow constructed wetlands

Intermittent aeration (IA) has been widely used in constructed wetlands (CWs) because it is economical and results in high nitrogen removal efficiency (RE). The aim of this study was to identify whether IA (4 h day(-1); the recommended frequency according to previous studies) in a partial area (PIA) can improve nitrogen RE compared with IA applied throughout the CW (TIA). Three types of laboratory-scale vertical flow CWs were constructed: PIA, TIA and non-aerated (NA). PIA achieved a higher RE of total nitrogen than TIA and NA (mean RE 60.6 v. 45.2 and 37.4% respectively). In the PIA, the ammonia mono-oxygenase subunit A (amoA) gene was abundant in aerated areas, whereas the nitrate reductase gene narG and nitrite reductase genes nirK and nirS were abundant in anaerobic areas. The results of this study suggest that PIA is an effective strategy for nitrogen removal when applying aeration in CWs because it preserves a constant anaerobic area for denitrification.