The Distribution And Change Of Heavy Metals (Cu, Cd, Pb And Zn) In Constructed Wetlands

Heavy metal pollution in water is one of the most serious environmental problems in the world, because it does not only do harm to ecosystem, but also increases the potential health risk for human. Constructed wetland treatment has been expected as one perfect solution for water pollution problem since it is more efficient, cheaper and has more environmental benefits. However, does not like any other contaminant in ecosystem, heavy metal could not be degraded. The removal of heavy metal is the redistribution and transformation of heavy metal, so it is quite important to focus on the fraction of heavy metal pollutants and their distribution in constructed wetlands which have already been recommended and widespread used.The constructed wetland we investigated in this research is used to treat polluted Yellow River water. This constructed wetland has a dimension of 18m×15m×1m (length×width×height), and covered with 20 cm clean and homogenous soil. The depth and hydraulic retention time of wetland are 0.5 m and 3 d. Additionally, it has been planted with Phragmites australis. The present study includs the following three sections: 1. The removal and distribution of Cu, Cd, Pb, and Zn in wetland water Constructed wetland could removal Cu, Cd, Pb, and Zn efficiently with the lowest removal rate 60%, and almost all four metals in water are inslouble fraction (＞99%). 2. The removal and distribution of Cu, Cd, Pb, and Zn in wetland sediments Except Zn, all other metals have higher concentration in Yellow River sediments; and no matter in which kind of sediments, the percentage of each fraction vary with metals:for Cu and Zn, the mainly forms is residual fraction and in sediments, however, Cd mainly bound to carbonate in sediments, and Pb has lager part of metals which bound to iron and manganese oxides. 3. The removal and distribution of Cu, Cd, Pb, and Zn in wetland plants Wetland plants play an important role in absorption of heavy metals in wetland eco-system and they have unequal transformations in the roots and stems:The order of metal concentration in different tissues of plant is:root> leaf> stem.