Nitrogen removal from polluted river water in a novel ditch–wetland–pond system

Abstract

To remove nitrogen from polluted river water in situ, a ditch–wetland–pond system (DWPS) with a length of 25m was designed and built near the Liu River, Tianjin, China. Average ammonia (NH4+-N), total nitrate (NO3−-N) and nitrogen (TN) removal efficiencies of 76.90%, 54.24% and 58.71%, respectively, were attained by the DWPS under optimum operating conditions. A DWPS application project with a length of 500m was then constructed near Qilihai Wetland, Tianjin to treat polluted river water from the Chaobaixin River, and average NH4+-N, NO3−-N and TN removal percentages of 52.04%, 33.33% and 38.66%, respectively, were observed during monitoring. Moreover, denitrification and nitrification were found to be the most important processes associated with nitrogen removal. The DWPS, which was designed to be elongated and including duplicate units, was found to be technologically feasible and applicable to treat polluted water from rivers or ditches in situ; therefore, its use will be expanded locally and to similar areas.