界面水动力和水化学瞬时变化对胶体在包气带中滞留及再运移的影响

The viruses and bacteria (sometimes referred to as microorganisms) from the landfill leachate can migrate through the vadose zone, and further pollute groundwater. The understanding on the fate and transport of colloid in the vadose zone has been proven far more not enough. This study aims to solve two key research questions, one is how the retention and remobilization of colloids depend on the specific physical and hydro-chemical conditions in the vadose zone and their transients, and another one is to establish the mathematical formula of retention and remobilization of colloids interacting with solid-water interface, air-water interface, and air-water-solid contact line individually under transient conditions. To answer the questions, x-ray tomography will be employed to directly observe the behavior of colloids in the soil; meantime we will obtain the colloid concentration breakthrough curves and the distribution of colloids inside the soil through column experiments. Based on the results of the experiments, combing theory, we will modify the mathematical model of colloid transport under transient flow and hydro-chemical conditions. The upcoming results can provide theoretical guidance for the prevention of soil and groundwater contamination as well as the removal of microorganisms from the vadose zone and groundwater.

来自垃圾渗滤液等多种渠道的病毒和细菌等有机胶体，会经过包气带向下迁移，进而污染地下水。但目前对胶体在包气带中迁移的认识还远远不够。本项目拟重点解决两个科学问题，一是阐明水动力和水化学瞬时变化对胶体在包气带中滞留和再运移的影响；二是分别构建水-气界面、水-固界面、以及水-气-固三相接触线与胶体相互作用的数学表达式，完善胶体运移的数学方程。为解决上述问题，拟采用x射线三维高精度扫描仪对胶体在土壤中的滞留和再运移进行实时扫描观察，并借助土柱实验获得胶体浓度穿透曲线及剖分实验获得胶体在土壤内部的空间分布特征，根据三维可视化结果及浓度曲线和剖分数据，结合理论指导，完善胶体在非稳态条件下迁移的数学模型，阐释水动力和水化学瞬时变化条件下，胶体在非饱和多孔介质中的滞留和再运移规律。研究结果可望为预防土壤及地下水受到污染及微生物在包气带和地下水中的去除提供理论指导。

包气带是保护地下水免受污染的第一道屏障。病毒和细菌以及垃圾渗滤液等会通过包气带进而污染地下水。因此，研究胶体颗粒在包气带及地下水中的迁移十分必要。本研究采取室内实验和数值模拟的手段，选取聚苯乙烯微球为目标胶体，对水化学瞬时变化条件下多孔介质中胶体的滞留及再运移进行浓度穿透曲线的测量，并建立数值模型进行模拟，实验同时采取了共轭聚焦显微镜对水化学瞬时改变条件下胶体的迁移进行了可视化。本工作对瞬时水动力条件，即不同水流速度对多孔介质中胶体滞留量的影响，并建立力学模型。研究发现，离子强度、胶体粒径及摩尔比的瞬时变化均可引起多孔介质中胶体的再运移，通过可视化发现，再运移行为主要是由于移动的具有不同表面张力的水气界面和水气固三相交接线引起。水动力条件即水流速度的瞬时增加会减少多孔介质中胶体的滞留量，由于拉力的增加。 研究成果对于掌握胶体在多孔介质中的迁移具有重要的意义，并可为制定水土健康标准 、预防和控制地下水受到病原性微生物的污染提供理论基础和决策依据。