The Role And Mechanism For Saponin To Remediate Co-contaminated Soils With Heavy Metals And PAHs

The co-contaminated soils by heavy metals and persistent organic pollutants is a widespread environmental problem as the result of numerous industrial activities and rapid urbanization. Based on the review of remediatiaon of co-contaminated soils, This thesis studied the effect of saponin on remediation of PAHs and heavy metal co-contaminated soil, including the effect of environment factors on the solubility of PAHs, the complexation of heavy metals by saponin, the role and mechanism for biosurfactant saponin to enhance the desorption of heavy metals and PAHs from co-contaminated soils and the effect of saponin on the remediation of co-contaminated soils by plant. The main results of this thesis are shown below:(1) Saponin can effectively solubilize PAHs and complex heavy metals due to the complexation of heavy metals with the external carboxyl or hydroxyl groups of saponin micelle, on the other hand, it can incorpoate or partition of PAHs within saponin micelles. The solubilization capabilities of saponin for PAHs decreased with the increase of pH in solution, but increased with the increase of temperature and ionic strength. The conditional stability constants for saponin complexation of heavy metals were followed the order of Pb2+>Cu2+>Zn2+>Cd2+.(2) Saponin can effectively remove PAHs and heavy metals from the co-contaminated soils. The remove rates of PAHs by saponin were about90%, while the remove rates of Cu, Cd, Zn and Pb were58.1%,55.8%,47.8%and22.1%. This behavior was generally attributed to the PAHs had no competition each other, while the heavy metals had the competition with each other.(3) The presence of saponin can significantly enhance plant uptake of Pb and pyrene from the co-contaminated soils. With addition of saponin at2000mg/kg, the concertration of Pb in ryegrass roots and shoots were1.1and11.8times compared with the treatment without addition of saponin, respectively. The residual concentration of pyrene in soil was35.6mg/kg, which was about43.0%lower compared with the control.