Effect of aeration modes and influent COD/N ratios on the nitrogen removal performance of vertical flow constructed wetland

Nitrification and denitrification have been proved to be the main pathways for nitrogen removal in constructed wetlands (CWs), but they usually could not occur in a single wetland unit simultaneously due to conflicting oxygen demand. In this study, we employed two artificial aeration modes including continuous aeration (CA) and intermittent aeration (IA) in lab-scale vertical flow constructed wetlands (VFCWs) to investigate the nitrogen removal performance with different influent COD/N ratios. The artificial aeration significantly enhanced NH4+-N removal, especially for the wetland units with higher COD/N ratios. The variations of aeration modes and COD/N ratios also had a great effect on nitrogen removal. The IA units had a better performance on nitrogen removal compared to CA units when the COD/N ratio ranged from 5 to 10. Plant biomass and nitrogen accumulation by plant were also studied. It was observed that plants in IA and CA had less biomass and nitrogen uptake at lower COD/N ratios, but plants in IA could achieve a better performance with higher COD/N ratios.