| Heavy metal pollution lasts long, has stong elusiveness and is hard to eliminate, and italso can pose a great threat to human health through the migration and enrichment of the foodchain. It is very difficult to remove heavy metals by conventional secondary treatment. Theconcentration of heavy metals is greatly reduced through absorption and transportation of thesediment, plants and microorganisms in the constructed wetland system. Therefore, it isnecessary to study the migration and accumulation of heavy metal in the wastewater treatmentsystem of the constructed wetland. The test site of this research is located in the fifth groupwetland system of Zao River wetland demonstration project which is a two level surface flowconstructed wetland.This wetland consists of the A and B pools, A pool is the first, B pool isthe second. The main sediment in A pool is sand, and the sediment in B pool is mainly sandand water plant’s aluminum sludge. Plant and plant rhizosphere sediment along at differentdistances from the inlet water,and water at the inlet and outled of the wetland were sampled,including3water sampling points,11reeds and rhizosphere sediment sampling points and6cattails and rhizosphere sediment samples. Cd, Cr, Cu, Ni, Pb, Zn were measured in this studyusing ICP-OES inductively coupled plasma emission spectrometer. The project aims toanalyze the concentration, total accumulation of the heavy metals in all structures and all thewastewater, aquatic plants,sediments in the whole plant, and to analyze the concentrationrelativity between them,and then to get the removal efficiency, space distribution, themigration and accumulation patterns of the heavy metals.1. By analyzing the constructed wetland system on the removal efficiency of the heavymetal in wastewater, we learn that when the concentration of Cd, Cr, Cu, Ni, Pb and Zn theinlet water of wetland system are2.33±0.13ug/l,37.90±27.77ug/l,7.30±1.41ug/l,11.25±0.30ug/l,8.63±3.13ug/l,177.93±81.29ug/l, the removal rates reach92%,94%,38%,50%,44%,38%.2. By analyzing the constructed wetland system on the distribution of the heavy metal inplant rhizosphere sediment, we learn that the concentration of Zn and Cu fall along the ride inA pool, the concentration of Zn and Cu in the reed rhizosphere sediment rise slightly in thelast three sampling points of B pool (aluminum substrate sludge).3. By analyzing the constructed wetland system on the distribution of heavy metals inplants, we learn that the concentration of heavy metals in various parts of reeds decreasealong the former three sampling points of A pool, while increase slightly along latter threesampling points (aluminum sludge sediment) of the B pool, which is the same as the distribution of heavy metals in reed rhizosphere sediment, indicating the concentration ofheavy metal in various parts of reeds is closely related to its concentration of heavy metals inthe sediment itself. The concentration of Cu of cattail roots, Pb, Ni and Zn of cattail leavesdecrease along the way in A pool, while elevate in B pool. Results show that belowgroundorgans aer the primary areas of metal accumulation. In particular, the concentration of Cr inreeds organs and Cd and Cr in cattails organs decrease in the order of root> stem> leaf. Whileheavy metals (Cd, Ni, Pb, Cu, Zn) concentrations in reeds organs and heavy metals (Ni, Pb,Cu, Zn) concentrations in cattails organs decrease in the order of roots> leaves> stems.Periodically harvesting ground parts of the plant can be removed relatively more Cu and Zn,while the significance of the removal of Cd, Cr, Ni and Pb was little.4. By analyzing the constructed wetland system on the enrichment and migration ofheavy metals in plants, we learn that BCF (enrichment factor) of reeds descend in order of Cd(0.63)> Cu (0.17)> Zn (0.15)> Ni (0.08)> Pb (0.05)> Cr (0.02), and BCF (enrichment factor)of cattails descend in order of Zn(0.25)＞Cd(0.18)＞Cu(0.12)＞Ni(0.05)＞Pb(0.04)＞Cr(0.01). TF (transfer coefficient) of heavy metals (Cu, Pb, Cd, Ni, Zn) except Cr in reedsand cattails decrease in the order of leaf> stem. The TF of Zn, Cu, Cr, Pb, Cd and Ni are0.32~1.56、0.61~0.99、0.14~0.62、0.10~0.53、0.11~0.41、0.09~0.40，described the abilityof migration Zn, Cu and Cr in plants are stronger than Cd, Ni and Pb.5. By analyzing the correlation between the concentration of heavy metals in plant rootsand the form of heavy metals in rhizosphere sediment, we learn that the distribution of heavymetals in plant roots are similar to the form distribution of heavy metals in sediment, and theconcentration of heavy metals in plant roots are related to the concentration of different heavymetals forms in the sediment, indicating that distribution of heavy metals in plants is closelyrelated to their form in environment.6. The heavy metal concentration relativity in wastewater, aquatic plants, sediment hasbeen analyzed, and the heavy metal accumulation, the migration pattern of heavy metal hasbeen detected. Cd, Cr, Ni, Pb and Zn in water are easy to accumulate to the sediment, Cd andPb are easy to accumulate in plant roots, but not to migrate in plant, Cu and Zn are are easy toaccumulate in stems, and they are also easy to migrate from stems to leaves. The enrichmentpattern of heavy metal is that: the accumulative percentage (AP) of six heavy metals (Cd, Cr,Pb, Zn, Ni and Cu) in the sediment is86~99%, the AP of plants is1~14%, indicating that thesediment has a much stronger ability than the aquatic plants. The concentration of Cd, Cr, Ni,Pb, Zn was significantly positively correlated to concentration of heavy metals in the water, indicating that the sediment is a key factor in the removal of the heavy metal, which is thesame as many previous conclusions. |
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