Studies On Constructed Wetland Aquatic Plants In Removing N,P Nutrients And Heavy Metal Cd

Water pollution is one of the global environmental problems and restricts the development of economy. Constructed wetland has been used for water treatment and has high removing efficiency of N and P with low construction cost. Easy operation of this system makes it to be an attractive way for water treatment.Aquatic plants play an important role in the pollutant removal in constructed wetlands. Understanding of the ability to remove the pollutants from wastewater by aquatic plants would be critical for the selection of aquatic plants to be used in the constructed wetland system. On the basis of preliminary experiment, present study was conducted to study the ability of different aquatic plants to remove N, P and Cd, and the results obtained were summarized as follows:1. A solution culture experiment was conducted to study the ability of nine aquatic plants in absorbing N and P. The results showed that the ability to uptake N and P varied significantly among nine aquatic plants. Lythrum salicaria Linn, and Herba Alternantherae had higher ability in N uptake, and Iris pseudacorus L., Sagittaria trifolia Linn, and Lythrum salicaria Linn, had higher ability in P uptate. So Lythrum salicaria Linn, was more suitable for constructed wetland for the removal of N and P.2. Ion depletion technique was adopted to study root P uptake kinetics of seven aquatic plants. Results showed that there was significant difference in P uptake kinetic parameters among seven aquatic plants. The defination of I_max and K_m implies that K_m was more important than I_max for wasterwater in the condition of low level of P concentration. These results suggested that Lythrum salicaria Linn, was more suitable for constructed wetland for the removal of P.3. A solution culture experiment was carried out to study the ability of Zinania latifolia Turcz. and Alisma plantago-aquatica Linn, to remove Cd. Results showed that the quantity of Cd moval by plants was increased with the increased Cd concentration in the cultural solution. The efficiency of Cd removal was increasedwith the increase of duration time of culture for both aquatic plants. The present study indicated that two processes, both physichemical and biological processes, were involved in Cd uptake by aquatic plants.