Improvement of nitrogen removal by external aeration and intermittent circulation in a subsurface flow constructed wetland of landscape garden ponds

An external aeration and intermittent circulation were used to improve the nitrogen removal performance of subsurface flow constructed wetland (SSF CW) in landscape garden ponds. Nitrification was the main mechanism of ammonium-nitrogen (NH4+N) removal and partial nitrification/anaerobic ammonia oxidation was a minor process. Field measurements yielded a removal rate of NH4+N of 0.266-0.566 g N/d m2 and a corresponding temperature-dependent rate constant of 0.184 d−1 to 0.377 d−1 representing an improvement over nitrogen removal. The nitrate-nitrogen (NO3−N) removal was degraded to the background level of NO3−N concentration in an environment with a high concentration of dissolved oxygen. The NO3−N removal rate ranged from 0.0393 g N/d m2 to 0.0825 g N/d m2 and resulted from aerobic denitrification, indicating that external aeration and intermittent circulation effectively improved oxygen transportation in SSF CW. This could remove NO3−N of the effluent of SSF CW when using in-tank aeration to improve the nitrogen removal performance of SSF CW.