Studies On Selection Of Constructed Wetland Plant Species

This paper provided a brief review on the definition, composition, design, mechanic sm of sewage disposal, presented the efficiency of 13 plants species purification ability such as Canna generalis, Coix aquatica Roxb etc... and selected Coix aquatica Roxb.,Canna generalis,Hymenocallis American and Crinum asiaticum which were suitable to grow in subtropical climate zones, and the application of constructed wetlands. The mechanism of polluted water purification of these 4 plants species was also studied.The results of the investigation were as follows:1,The removal rate of CODcr, TN and TP by the constructed wetland increase with time, the fifth day removal was the largest, NH₄⁺-N showed good performance of removal during the third day.2,The vertical flow constructed wetland of Coix aquatica Roxb.,Canna generalis,Hymenocallis Americana and Crinum asiaticum good had strong removal capacity of pollutants, The quality of outflow is accord withâ…¢(Environmental quality standards for surface water)(GB 3838-2002).3,The Cellulase,Protease,Phosphatase and Urease of the vertical flow constructed wetland of Coix aquatica Roxb.,Canna generalis,Hymenocallis Americana and Crinum asiaticum had high activities. Correlation analysis showed that there was significant correlation between activity of Phosphatase in vertical flow constructed wetland and removal rates of TP in the wastewater; there was a certain correlation between Urease activity and removal rates of NO₃-N and TN , particularly, the removal of NO₃-N showed significant correlation, and the maximum correlation Coefficient was 0.778; Protease activity and the removal rates of TN showed significant correlation.4,After the test, the plants' shoot and root concentrations of nitrogen and phosphorus have increased, Wetlands matrix containing N, P had certain increase too. The nitrogen and phosphorus accumulation in the shoot is higher than their accumulation in root and this contribute to the transfer of nitrogen and phosphorus of the wetland by harvesting the shoot. In this test, the Hymenocallis Americana and Crinum asiaticum showed strong absorption capacity of P, and after the experiment, the concentrations of P increased by 33-57% in Matrix and this is in line with the fact that the physical and chemical reaction of matrix is the primary means of removing of P, which coincides with previous studies.