Performance Of Constructed Wetland For Sewage Purification

Two lab-scale wetland systems with and without iron plaque on plant roots (Typha angustifolia) were setup to investigate P removal efficiency with two levels of P in inflow as well as the influence of P uptake by iron plaque on the P content in the plant roots and shoots. A constructed wetlands located in Anji County, Zhejiang Province was monitored to observe the pollutant removal efficiency and enzyme activity during four seasons. The enzyme activity vary with the season and their relationship with pollutant removal efficiency were analyzed. The research offered the theoretical basis for using enzyme activity as evaluation index of purification mechanism. The results obtained were summarized as follows:1. The mean removal efficiencies of TP in the systems with and without iron plaque were 85% and 55%, respectively, with low level of P inflow, 76% and 1.71%, respectively, during the first 12 days of application with normal level of P inflow. The removal efficiency of P in the system with iron plaque was higher than the system without iron plaque. When experiment finished, the amount of P adsorbed on the iron plaque was lower than the amount of the beginning stage. The decrement of P adsorbed on the iron plaque was 51%,55%and 23%,27% in the direction of water flow when the inflow was treated with low and normal level of P separately. Simultaneously, the amount of P cumulated in the plant roots and shoots was more than that of the beginning stage, and increased 31%,16% and 28%,25% likewise, and the level of P in plant roots increased 65%,65% and 73%,73% when treated with low and normal level of P inflow. The amount of P absorbed on the iron plaque accelerated P uptake in the plant roots and shoots. The results suggested that we could use iron plaque on the plant roots to enhance P uptake efficiency by the plants and P removal efficiency in the wastewater.2. To evaluate pollutant removal efficiency and dynamic feature of enzyme activity in a constructed wetland system in Anji County, Zhejiang Province, water samples and soil samples collected from July. 2007 to February. 2008 were analyzed. Urease activity and phosphatase activity decreased, catalase activity did not change with seasons. The mean removal efficiency of CODCr, TP, TN were 68%～92%, 71%～91% and 68%～83%, respectively. The activity of phosphatase and catalase in substrate is positively correlated to the removal rates of TP and CODCr, respectively. It means that we could separately use phosphatase and catalase activity to evaluate the efficiency of constructed wetland.