| At present, the constructed wetland system is widely applied for the wastewater treatment of small towns in China. The research focuses on the removal and mechanism of organics and nutrients. Little attention is paid on heavy metal, and most of the affluent is directly discharged into natural water body or is recycled. Heavy metal pollution lasts long, has strong elusiveness and is hard to eliminate, and it also can pose a great threat to human health through the migration and enrichment of the food chain. Therefore, it is necessary to study the heavy metal in the wastewater treatment system of the constructed wetland. The test site for this project is located in the constructed wetland wastewater treatment plant, Huahuiyuan, Baishiyi town, Jiulongpo District, Chongqing. This plant mainly collects domestic wastewater and wastewater sourced from travelling industry. The project aims to analyze the concentration, total accumulation of the heavy metal in all structures and all the wastewater, aquatic plants, sediments in the whole plant, and to analyze the concentration relativity between them, and then to get the removal efficiency, space distribution and the migration and accumulation patterns of the heavy metal.By analyzing the constructed wetland system on the removal efficiency of the heavy metal in wastewater, we learns that during the experiment period, because the heavy metal concentration in the influent is low and the acidification and corruption of the sediment emerge, which lowers the PH value of the wastewater. The constructed wetland system has low or no influence on the removal of the heavy metal, and in the wetland, there even appears the phenomena of heavy metal release.By analyzing the patterns of the heavy metal migration in the aquatic plants, the results are as follows. The migration abilities of the Cyperus alternifolius and the Eichhornia crassipes in the wastewater treatment plant goes like that: the migration ability of leaf is stronger than that of stem. As for the migration ability of Cd, a Cyperus alternifolius leaf is stronger than Eichhornia crassipes leaf, and the migration ability of stems has nothing to do with the plant species. As for the migration ability of Zn, Eichhornia crassipes stem is stronger than Cyperus alternifolius stem, and the migration ability of leaves has nothing to do with the plant species. As for the migration of Cu, Pb, and Cr, it has nothing to do with the plant species.This paper analyzes space distribution patterns of the heavy metal concentration in the sediment, and the result shows that the concentrations of Cu, Pb, Cr, Cd and Zn in the sediment sequentially reduce in logarithm along the flow direction in the structures of the wastewater treatment plant.By analyzing the heavy metal concentration relativity in wastewater, aquatic plants, sediment, and the heavy metal accumulation, the migration pattern of heavy metal has been detected. Cu is easy to migrate to the sediment, but not to accumulate in plant roots, or to migrate in the plant; Pb is difficult to accumulate in roots and to migrate in the leaves, but it is easy to migrate from roots to stems; Cr is difficult to accumulate in roots and to migrate from roots to the aerial portion, but it is easy to migrate from stems to leaves. Zn is easy to migrate to the sediment, Cd and Zn are easy to migrate within the plant but difficult to accumulate in roots. The enrichment pattern of heavy metal is that: as for the accumulation of Cu, Pb, Cr, Cd and Zn, the sediment has a much stronger ability than the aquatic plants, and the sediment is a key factor in the removal of the heavy metal. The heavy metal accumulation in the sediment is affected by the location of structures, hydraulic surface loading and the volumn for fillers. Within structures, the heavy metal accumulation in plants is decided by the coverage area of plants and the plant species. In this project, Cyperus alternifolius has stronger heavy metal accumulation ability than Eichhornia crassipes...
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