Studies on Nitrogen and Phosphorous Removal Efficiency and Spatial Distribution in Constructed Wetland Systems

Two lab-scale constructed wetland systems using sands as their substrates,with and without plants(Lythrum salicaria Linn),were used to investigate nitrogen and phosphorous removal efficiency and their distribution in the sys-tems.The mean removal efficiency of NH+4-N,TN,TP in the planted system were 55.02%,45.44%,98.52%,respectively,and 38.08%,33.63%,91.37% in the unplanted system,respectively;the removal efficiency of nitrogen and phosphorus in the planted system were higher than that in the unplanted system.Biomass and accumulation of nitrogen and phosphorus in plants decreased along the transect from the inlet to the outlet in the subsurface of the constructed wetland,the concentration of TP in substrates showed the similar pattern as nitrogen and phosphorus distribution in plants;the results suggested that proper combination of different plant species was helpful for the enhancement of nitrogen and phosphorus removal efficiency.Analysis of nitrogen and phosphorus removal pathway showed that nitrogen was mainly removed through nitrification/denitrification process and phosphorous through adsorption and sedimentation by substrates;plant uptake amounted for 9.38% and 12.77%,respectively,of the amount of nitrogen and phosphorus loaded into the wetland,plant uptake was also an important pathway for nitrogen and phosphorus removal.