生物表面活性剂增效修复疏水性有机物-重金属复合污染土壤机制研究

Hydrophobic organic compounds (HOCs) and heavy metals (HMs) are two of the most important persistent pollutants and usually coexists in soil matrix. They have posed a serious threat to soil eco-environment.Therefore, the research on high-efficient and simultaneous removal of HOCs and HMs is very necessary for enhancing the remediation efficiency and reducing the remediation cost. Rhamnolipid biosurfactant has several characteristics, including good emulsifying activity to HOCs, high chelating capacity with various metal ions, being readily biodegradable and lower-toxic. These distinct perspectives make rhamnolipid biosurfactant valuable as an environmental-friendly remediation agent to remove the HOCs and HMs from the soil matrix simultaneously. In this research, the micelle microstructure and properties of rhamnolipid biosurfactant will be determined.Then, based on the variations of micelle structure, the effects of rhamnolipid biosurfactant on the solubilization of HOCs and complexation of HMs in the interface of soil matrix, as well as the adsorption and desoption of rhamnolipid in the soil matrix, will be also evaluated by combined applying the methods of laboratory simulation experiment, the field experiment and numerical simulation. Meanwhile, this research will focus on the interations and behaviours of rhamnolipid biosurfactant in a complex system containing water, soil, HOCs and HMs. Futhermore, the possible mechanisms and various influencing factors of simultanous removal of HOCs and HMs by rhamnolipid bisurfactant will be discussed. The research results will provide theoretical basis for applications of biosurfactants in remediation for soils jointly contaminated with HOCs and HMs.

疏水性有机物和重金属是土壤中普遍共存的两类持久性污染物,对土壤生态环境构成严重危害。如何高效同时去除两类污染物，对提高修复效率、降低修复成本具有重要意义。鼠李糖脂生物表面活性剂对疏水性有机质具有良好的乳化增溶性能、对金属离子具有较强的络合性能，并具有低毒、易于生物降解等特性，可作为环境友好型淋洗修复剂以同时去除土壤中疏水性有机质和重金属。 本研究在表征和确定鼠李糖脂生物表面活性剂胶束微结构和性质的基础上,综合应用实验室模拟实验、现场实验和数值模拟的方法，考察鼠李糖脂在土壤基质上的吸附-解吸附行为及其对疏水性有机质的胶束增溶作用和对重金属离子的络合作用，重点研究鼠李糖脂在土壤-水-污染物这一复杂体系中的作用过程和行为，深入探讨鼠李糖脂同时去除疏水性有机质和重金属污染物的影响因素及其作用机制，为生物表面活性剂在疏水性有机物-重金属复合污染土壤修复中的应用提供理论基础。

土壤环境中疏水性有机物和重金属形成的复合污染普遍存在。由于两类污染物理化性质差别较大，目前尚缺乏两类污染物同时、高效的去除技术。本项目以鼠李糖脂类生物表面活性剂在疏水性有机物-重金属复合污染淋洗修复中的应用为切入点，以多环芳烃（PAHs）和Cu2+、Pb2+、Zn2+、Cd2+、Cr3+分别为疏水性有机物和重金属的代表，综合应用室内模拟实验、现场实验和数值模拟的方法，在表征鼠李糖脂胶束微结构基础上，研究其对PAHs和重金属的同时去除作用和影响因素。取得的重要研究结果如下：（1）发现鼠李糖脂具有临界胶束浓度（CMC）低、胶束聚集数小、胶束内核尺寸大等特点，对PAHs的增溶能力显著高于化学合成表活剂；溶液pH、离子强度等对鼠李糖脂胶束聚集体有明显影响，进而影响其增溶能力；在pH为5.5-6.0时，胶束尺寸最大，对PAHs强化增溶系数最高。（2）查明鼠李糖脂对重金属离子的络合平衡常数远大于土壤中常量离子，可优先络合重金属离子，适用于重金属污染土壤修复。（3）明确了鼠李糖脂在土壤基质上的吸附行为符合Langmuir等温吸附曲线，最大吸附量受溶液pH和离子强度影响显著；鼠李糖脂与槐糖脂复配后可有效减少其在土壤基质上的吸附损失。（4）阐明了鼠李糖脂作为淋洗剂同时去除土壤基质中两类污染物的作用效果和机制，即不仅通过胶束增溶作用强化PAHs从土壤基质上脱附和洗脱；而且通过羧基等与重金属的络合作用提高重金属的解吸附和迁移，而共存重金属可使得鼠李糖脂胶束缔合为体积更大的胶团，有效降低CMC值，有利于PAHs増洗脱。（5）PAHs和重金属的去除率随土壤有机质含量增大和土壤老化时间增长而减小，淋洗液pH值对两类污染物的去除率有较大影响，适宜两类污染物去除的淋洗液pH值为6.0-7.0。（6）在青岛红星化工厂和天津塘沽某石油化工厂场地现场修复结果表明，鼠李糖脂及其与槐糖脂的复配体系不仅可同时去除PAHs和金属Cr，也可有效去除石油烃和重金属。上述结果表明生物表活剂在疏水性有机物-重金属复合污染土壤修复中具有良好的应用潜力。