Solubilization And Washing Of DDTs From Contaminated Site Soil With Surfactant

In recent years, soil pollution issue has become a major problem of contaminated sites, particularly in the restoration and management of contaminated sites Soil media have become global environmental problems.This study select the surfactant as solubilization reagent, use the DDTs contaminated soil from a pesticide factory as an experimental material, remediation of DDTs contaminated soils by surfactants was studied in the thesis. Effects of surfactant type, concentration, soil adsorption capacity, liquid-soil ratio, elution time on water solubilities of DDTs in the presence of surfactants were also investigated. Meanwhile, to conduct exploratory research on distribution characteristics of DDTs and elution effect of DDTs by surfactant in different grain size soil. These results can provide scientific basis for the remediation of organochlorine pesticide-contaminated soil.This research mainly includes three parts; the main results were as follows:(1)In the study of the selection of solubilization reagent and determine the optimal experimental conditions. Because the non-ionic surfactant with a high solubilization capacity, low biological toxicity, etc., so this paper use Tween20, Tween40, Tween60, Tween80, and Tween85as solubilizing agent. The Solubilization results showed that non-ionic surfactant enhanced desorption and solubilization of DDTs from the soil remarkablely. The apparent solubility of DDTs in surfactant extracts was4～556times higher than that of in Deionized water solution, the solubilization capacity of surfactants follow the order:Tween80> Tween60> Tween40> Tween20> Tween85.Desorption and solubilization of DDTs from soil at different concentrations of Tween80can be described by exponential decay function, and the suitable range of concentrations was8000～10OOOmg·L-1. The elution time and the ratio of the liquid/soil have big influences on the elution amount of the DDTs. The experiment results show that the elution amount of the DDTs increased with the elution time and the liquid-soil ratio, and shows an exponential attenuation function.12hours is the proper concussion time, and the proper ratio of solution to soil was40:1, when adopting the extractant surfactant.(2) The systematic study of elution removal of DDTs from contaminated soils by Tween80 has been researched. The results show that, Tween80removed significant amount of DDTs from the soil. About72%DDTs were removed by Tween80at solution concentration of10000mg·L-1, which led to a decrease in DDTs concentration in the soil from2780mg·kg-1to778mg·kg-1. Most of the Tween80(up to72%for8000mg·L-1treatment) left in the soil can be removed by deionized water, which indicates less environmental and ecological risk associated with Tween80in the soil.(3) Four different soil particle-size fractions that are clay, silt, fine sand and coarse sand from the topsoils in an organochlorine pesticide (OCPs) field were separated by physical method to characterize the OCPs distribution and the solubilization of DDTs by Tween80. Mean while, to study the effect of organic matter and mineral composition in different separates on pollutants distribution. The results show that the content of DDTs is uneven, the content of DDTs follows the order:coarse sand> fine sand> clay> silt. Solubilizations of DDTs from different soil particle were also different, elution efficiency follow the order:clay>silt>fine sand. The content of DDTs and organic matter from different size of soil particle show a good liner relationship.There are some difference with different particle-size fractions in the content and composition of the clay minerals in soil, which affe the adsorption capacity of DDTs in soil to some extents.