热解吸修复污染土壤过程中DDTs的去除动力学

采用热解吸修复技术对北京某农药厂旧址的DDTs(滴滴涕)污染土壤进行修复试验,优化了土壤中DDTs的热解吸温度,对DDTs热解吸动力学过程以及土壤水分对热解吸修复效果的影响进行了研究. 结果表明,热解吸修复技术可有效去除土壤中DDTs,在340℃时土壤中∑DDTs的去除率达到99%,此时土壤中的w(∑DDTs)为0.598mg/kg,低于HJ 350—2007《展览会用地土壤环境质量评价标准(暂行)》(1.0mg/kg),但继续升温∑DDTs去除率的变化不明显. 土壤中∑DDTs的热解吸动力学符合二级动力学方程(R2为0.9914),热解吸过程受土壤中w(∑DDTs)的影响较大,即随时间的增加,w(∑DDTs)下降,热解吸速率会迅速降低. 土壤含水率对热解吸效果有一定的影响,特别是当土壤含水率超过16%时p,p-DDE的去除率明显降低,而土壤含水率对其他组分的影响较小. 

Desorption Kinetics of DDTs from Contaminated Soil during Processes of Thermal Desorption

Soil samples collected from a pesticide-contaminated site in Beijing were treated with thermal desorption to determine the optimum temperature to remove DDTs and investigate the thermal desorption kinetics of DDTs from soil. Meanwhile, the effect of soil moisture on removal efficiency was investigated. Results indicated that thermal desorption could effectively remove DDTs from the soil. The removal efficiency reached 99%, when thermal desorption temperature was 340℃. The residue of concentration ∑DDTs in the soil was 0.598mg/kg, which meets the standard of soil quality assessment for exhibition sites in China (1.0mg/kg). The removal efficiency did not change much when the temperature gradually increased. The thermal desorption kinetics of ∑DDTs in the soil was well interpreted with the second-grade rate equation, which suggested that desorption rate was much impacted by the residue concentration of ∑DDTs. In another word, the thermal desorption rate would greatly decreased during this process. The removal efficiency of ∑DDTs was slightly affected by the moisture in soil. When the proportion of water in the soil was over than 16%, the removal efficiency of p,p-DDE obviously decreased, while those of other components changed not significantly.