Study On Phytoremediation Of Contaminated Agricultural Soil With Heavy Metals

Heavy metals contamination is one of the global environmental concern, currently, for its low-cost, environmentally-friendly and other characteristics, the technology of phytoremediation is becoming a significant method to remove the contaminat of the agricultural soil.Relied on the project called "Core-Technology Research of Ecological Remediation in Contaminated Farmland with Heavy Metals" (Item Number: E-2007-06 and 2007). By the field experiments, this thesis studied on the remediation potential and bioconcentration characteristics of three hyperaccumulators grown in the contaminated agricultural soil with heavy metals, and the remediation effects of seven configuration of hyperaccumulators, then the best configuration also has been screened out; the effect of Superphosphate in different levels on biological activity, as well as on the remediation effects for seven configuration of hyperaccumulators was evaluated. The results indicated as follows:(Ⅰ) A field experiment was carried out to evaluate the phyremediation abilities of three hyperaccumulators, including Tephrosia candida, Solanum nigrum and Pteris nervosa. These experimental fields were contaminated with Pb, Cd and As. The results indicated that Tephrosia candida accumulated 365.071 mg·kg-1Pb, Solanum nigrum accumulated 22.109 mg·kg-1Cd, and Pteris nervosa accumulated 282.698 mg·kg-1As (dry weight) in shoots, with transfer factors (TF) up to 2.569,1.692 and 1.611, respectively. The phytoextraction rates (PER) of Tephrosia candida, Solanum nigrum and Pteris nervosa for Pb, Cd and As were at 1.257%,2.550% and 0.224%, respectively. To control the polluting situation and remediate the contaminated agricultural soil, the remediation years of Tephrosia candida to removal Pb is 2.847 a, Solanum nigrum to removal Cd is 9.953 a, and Pteris nervosa to removal As is 101.023 a, with the assumption that the harvested times each year was two times, three times and three times, respectively. The three tested plants were proved to have the potential value in use of remediation the contaminated field soil.(Ⅱ) The experimental plots were carried out to research the remediation effects of seven configuration of hyperaccumulators. The results indicated that the plots decline in the value of Pb, Cd and As up to 11.492 mg·kg-1,0.177 mg·kg-1 and 3.376 mg·kg-1, with individual planting of Tephrosia candida, Solanum nigrum and Pteris nervosa, respectively, which indicate that the hyperaccumulators have the huge remediation capacity and potential application prospects in contaminated soil. The comprehensive assessment by improved model of AHP results indicated that the best configuration to remediate this contaminated soil, was individual planting of Cd hyperaccumulator Solanum nigrum, and followed by mixed planting of Solanum nigrum and Pteris nervosa.(Ⅲ) The effect of Superphosphate in different levels on biological activity was evaluated. It is indicated that the residual fraction was the main existing fractions of Pb, Cd and As, and the strongest biological activity of three heavy metals was Cd. With increasing in the amount of Superphosphate, the biological activity of Pb, Cd and As, had a significant trend of downward, erratic subtle change and first increase then decrease, respectively, which indicated that the vary effects of Superphosphate on biological activity of heavy metals in different levels do exist.(IV) The effect of Superphosphate in different levels on the remediation effects for seven configuration of hyperaccumulators was studied. The results indicated that the increased rates curve of removal of Pb, Cd and As were showing a significant trend of decline, upward, and decline after first increase, respectively, within 0-600 kg·ha-1 by increasing the amount of Superphosphate. The comprehensive assessment by improved model of AHP results indicated that the best configuration to remediate this contaminated soil, was the amount of 600 kg·ha-1 Superphosphate and individual planting of Cd hyperaccumulator Solanum nigrum.