Remediation Of Chlordane And Mirex Contaminated Site Soil By Enhanced Soil Washing

With the forbidden use of synthetic persistent organochlorine pesticides (OCPs), like, chlordane and mirex, a great number of pesticide plants have been decommissioned and environmental problem associated with soil contamination has been increasingly serious. Investigation of rapid and efficient soil remediation technologies are furthermore very urgent and necessary. In the present study, batch soil washing experiments and zero-valent iron reductive dechlorination experiments were tested to remediate a chlordane and mirex contaminated soil, and various influencing factors of removal were studied. Main conclusions are summed as follows:(1)Firstly, the effects of deionized water, Tween80, TritonX-100and SDS on the desorption of OCPs were investigated. Results showed that Tween80, Triton X-100and SDS had certain effect on OCPs elution. Desorption capability of the surfactants on OCPs follows the order of Tween80>TritonX-100>SDS for chlordane and endosulfan and TritonX-100>Tween80>SDS for mirex, Tween80≈TritonX-100>SDS for heptachlor. Removal efficiency of the surfactants on OCPs from the soil increased gradually with increase surfactant concentrations. Soil treatment by Tween80and TritonX-100at10000mg·L-1, and SDS at8500mg-L-1, resulted in total OCPs removal percentages of32.8%,59.7%and60.1%, respectively. Removal percentages of chlordane, endosulfan and heptachlor were higher than mirex by all the three surfactants. Furthermore, removal percentage of mirex by Trinton X-100was si②ificant higher than SDS and Tween80. We suggested that TritonX-100is suitable for chlordane, mirex, heptachlor and endosulfan multi-contaminated soil; while SDS is not so effective to remove mirex from the soil, thus is more suitable for chlordane, heptachlor and endosulfan contaminated site soil.(2)Secondly, desorption capability of Triton X-100, SDS and mixed surfactants on OCPs from soil at50℃was investigated, respectively. The consideration was that OCPs removal by a single surfactant and at room temperature was limited. Results showed that Results showed that three surfactants had certain effect on OCPs elution at50℃. Removal of OCPs by TritonX-100at50℃was significantly higher than that at room temperature. The maximum decontamination efficiency of the total OCPs from soil was80.1%,39.5%and65.5%by10000mg-L-1Triton X-100,4250mg·L-1SDS and mixed surfactant, respectively.Soil treatment by Triton X-100of1OOOOmg·L-1resulted in a maximal total removal percentages of81.7%after5min at50℃, and5000mg·L-1of Ttriton X-100resulted in a maximal total OCPs of72.4%after15min at50℃, both of which were higher than those at room temperature. With the concentration increased, the adsorption amount of TritonX-100was gradually increased. The adsorption amount of TritonX-100to soil reached a plateau at5000mg·L-1, and the adsorption percentage of Triton X-100to soil could be described by a power function decay curve. According to the Triton X-100elution test, the concentration of10000mg·L-1, shaking time of5min, and liquid/soil of20was the best condition.(3) Finally, dechlorination degradation of chlordane and mirex in contaminated soil by①iron powder and②iron powder was stduied. Results showed that dechlorination degradation rates of chlordane and mirex by①iron powder were significantly higher than those by②iron powder. After30day, degradation rate of y-chlordane, a-chlordane, heptachlor and mirex from soil by5%①iron powder were85.2%、83.7%、100%and96.9%, respectively. The total OCPs degradation rate reached88.7%, while1%①iron powder exhibited a little effect but heptachlor degradation. Except for heptachlor,②reduced iron powder had little effect on the degradation rate of chlordane and mirex. After30day, degradation rate of γ-chlordane, a-chlordane, heptachlor and mirex from soil by5%②iron powder were18.9%、18.6%、89.3%and21.7%respectively, the total OCPs degradation rate reached33.8%.5%①iron powder was more efficient to remediate such kind of contaminated site...