Phytoremediation Of Heavy Metal-Organic Complex In Dredged Sewage River Sediment

Phytoremediation is a new technique to clean up heavy metal-organic contaminated sediments or soils with some accumulators or hyperaccumulators which can take up heavy metal, transport and accumulate them in their above ground shoots. These plants also can decompose organic contaminants at the same time. While the mechanisms of phytoremediation for complex contaminated soils are not fully understood and the technology is not established yet. In order to solve the problem of ubiquitous polluted sewage rivers, pot experiment was conducted to study phytoremediation efficiency and mechanism of maize, Indian mustard, oilseed rape, Medicogo sativa L., Lolium multiflorum L., Amaranthus tricolor L., and Chinese cabbage in cleaning heavy metal-organic contaminated dredged sediments of Dagu sewage river. At the same time, the plant species were investigated in order to screen out native hyperaccumulators. The main results obtained were summarized as follows:Maize, Indian mustard, Medicogo sativa L., and Lolium multiflorum L. were screened out as feasible restoration species. Maize-indian mustard rotation system had the highest accumulation amounts to heavy metals and the best removal efficiency to organic contaminations (especially to chlorobenzene) among coatinuous stubbles Lolium multiflorum L., maize and Lolium multiflorum L. co-cropping, Indian mustard and Lolium multiflorum L. co-cropping and maize-indian mustard rotation system. One of the detoxification mechanisms was confirmed in the theory that multinuclear heavy metals chelated on ligand, and heavy metal accumulation in plant existed in the metal-organic clusters through the bridging of ligand and heavy metals for the first time.Citric acid and EDTA is suitable chaletor to improve phytoremediation effect. By adding EDTA in several times, it not only can accelerate phytoremediation effect, but also can abate side effect to sediment and environment because it can lighten the decomposing problem of EDTA and the eluviation risk of EDTA-heavy metals chelator to environment. The results were finded for the first time that by adding EDTA three times to sediment, the average particle size of sediment increased, while specific surface area and crystal lattice intensity decreased, which were contributed to the desorption of heavy metal from sediment particle.A model of heavy metal absorption, translocation and accumulation by plant was established to simulate the heavy metals accumulation process with growth time.Corresponding to the accumulation correlativity of heavy metals, using ODE45 solver of MATLAB simulated the accumulation process of maize to Zn, Pb, Cu, Ni, Cd. The model and simulation result provide scientific gist to know heavy metal absorption, translocation and accumulation mechanism of plants, to forecast heavy metals accumulation amount and to decide the optimal time of harvest and soil remediation.New Zn hyperaccumulator species were fined though investigation along the river which were Polygonum orietale L., S. aizoon L.., and Humulus scandens. The accumulation amount of Zn in the shoots was larger than in the roots among the three species. The highest accumulation amount was in the shoots of Humulus scandens, which attained 4614.11 mg/kg. The Cd accumulation amount in shoots of C. segetum Bge and Taraxacum mongolicum was higher than in roots. The hyperaccumulation coefficient was exceeded one in the two plants, which indicated that the two plants possessed the basic characteristic of hyperaccumulator and the value for further research. The discovery of this species provided the native plant to integratively phytoremediate the sewage river sediment and the vegetation category to cover the sediment fill plant.Horticultural application of dredged sediment can promote the growth of plant, which not only reduced the risk of contaminant entering food chain, but also fertilized the bareen gardens soil. This was a good way to turn dredged sewage river sediment into resource. The potential risk of heavy metal and organic contaminant to groundwater and environment was greatly reduced by application of phytoremediated sediment than unphytoremediated dredged sediment to farmland.