Pilot-scale study on the removal of nitrogen and phosphorus in urban rainfall runoff by reconstructed infiltration riparian

A pilot-scale apparatus of reconstructed infiltration riparian was established by using coal cinder, sawdust, zeolite, medical stone and local soil, as well as Cynodon dactylon. Capability of this multiple-composing apparatus in removing the nitrogen and phosphorus in urban rainfall runoff was studied. Results showed that the reconstructed infiltration riparian had high removal efficiencies of ammonia (NH₄⁺-N) and total phosphorus (TP) both in surface and infiltration runoff. The average NH₄⁺-N removal rates were 66.5% in surface and 83.7% in infiltration runoff, respectively, and the removal rates for TP were 42.6% and 96.2%, respectively. The concentrations of NH₄⁺-N and TP in the final effluent were lower than the corresponding values of the type IV and III in Chinese National Environmental Quality Standards for Surface Water (GB3838-2002). The average removal rates of total nitrogen (TN) were much lower than those of NH₄⁺-N and TP, and could reach about 20% when the apparatus became stabilized. The treatment load of NH₄⁺-N, TN and TP were 634.1~1114.5 mg·m^-2·h^-1, 102.2~594.2 mg·m^-2·h^-1 and 20.6~209.0 mg·m^-2·h^-1, respectively. The removal capability of apparatus was generally higher in surface runoff than in infiltration runoff. Mediums of the apparatus could promote the transformation of nitrogen, e.g. sawdust as the carbon source, but they could also reduce the removal efficiency of TN due to the release of nitrogen from added mediums. There was obvious difference in removal rate and treatment load between the concaved section and end section. However, the difference would gradually decrease with the stabilization of the apparatus. The removal capability of the apparatus was significantly positively correlated with the nitrogen and phosphorus concentrations in influent, which indicated that the reconstructed infiltration riparian had a better pollutant loading and certain impact resistance ability.