SIMULATION STUDY ON INTERCEPTION EFFECT OF DITCH PLANT TO NITROGEN AND PHOSPHORUS IN LOW-POLLUTION WASTEWATER

Ecological ditch was an important technology for controlling non-point source pollution, such as nitrogen (N), phosphorus (P). The traditional study methods of aquatic plants purification in low-polluted water could not fully reflect the real field ditches environment. In this study, Myriophyllum spicatum ditch (MSD) and Hydrocotyle vulgaris ditch (HVD) were constructed, respectively. Ditch with no aquatic plants was used as control group (CKD). Two nitrogen concentrations of the influent, TN between 5 mol/L and 8 mol/L (LTN), and TN between 10 mol/L and 15 mol/L (HTN) were adjusted to study the interception effects on N and P under the same hydraulic retention time. Results showed that the total nitrogen (TN), ammonia nitrogen (NH4+-N), and total phosphorus (TP) concentrations were lower in effluent from MSD and HVD than from CKD. The TN and NH4+-N concentrations in MSD and HVD both decreased with the distance on a whole at LTN and HTN. The interception rates of NH4+-N in MSD were the highest among all the treatments between 53.2% and 54.4%, which showed the good nitrogen interception ability of M .spicatum. The NO3--N concentrations were relatively higher in MSD and HVD. It might be ascribed to the absent of sediment in cement ditch which limited denitrification to a certain extent. This flow test provided some parameters for plants arrangement and engineering application in ecological ditches. However, long-term experiment was needed in the future to evaluate the stability of these plants further for interception effect on nitrogen and phosphorus in a low-pollution wastewater.