Kananizadeh Negin, Chokejaroenrat Chanat, Li Yusong, Comfort Steven
Department of Civil Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0856, USA.
Department of Civil Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0856, USA; School of Environmental Engineering, Institute of Engineering, Suranaree University of Technology, Nakhon Ratchasima, 30000, Thailand.
J Contam Hydrol. 2015 Feb;173:25-37. doi: 10.1016/j.jconhyd.2014.11.009. Epub 2014 Dec 6.
A major challenge to successfully using in situ chemical oxidation (ISCO) for groundwater treatment is achieving uniform contact between the oxidant and contaminants in a heterogeneous aquifer. Viscosity modification technology, where a water-soluble polymer is mixed with remedial fluids, has been introduced in recent years to improve oxidant coverage of the target zone (i.e., sweep efficiency) and thus, treatment efficacy. In this work, we developed a numerical model to simulate the remedial fluid coverage from an ISCO injection with viscosity modification. Specifically, solution mixtures of xanthan and NaMnO4 were injected into a two-dimensional (2D) transport flow box that contained heterogeneous layers. Xanthan solutions were simulated as shear-thinning non-Newtonian fluids, where viscosity is a function of shear rate, polymer and NaMnO4 concentrations. Reactive transport of the polymer, NaMnO4, TCE, and reaction products were simultaneously modeled using advection dispersion reaction (ADR) equations coupled with the simulated flow field. The numerical model was validated using experimental data from the 2D cell experiments. Sensitivity analysis was conducted to investigate the relative contributions of system variables, such as polymer and permanganate concentrations, flow rate, permeability contrast, and different geometry settings. Results showed that higher concentration of permanganate and slower flow rate of the shear-thinning non-Newtonian fluids improved the oxidants ability to enter low permeable zones and react with the TCE. Higher permeability contrast decreased the velocity of the xanthan-MnO4(-) mixture inside the low permeable zone (LPZ), which increased TCE oxidation and product recovery. Changing the architecture of the LPZ from one zone to two smaller zones separated by a transmissive zone increased the overall product recovery. Thus, viscosity modification can improve both the sweeping efficiencies and TCE removal.
成功运用原位化学氧化法（ISCO）处理地下水面临的一个主要挑战是，要在非均质含水层中使氧化剂与污染物充分均匀接触。近年来，引入了粘度改性技术，即将水溶性聚合物与修复液混合，以提高目标区域的氧化剂覆盖范围（即波及效率），进而提升处理效果。在本研究中，我们开发了一个数值模型，用于模拟采用粘度改性的ISCO注入时修复液的覆盖情况。具体而言，将黄原胶和高锰酸钠的混合溶液注入一个包含非均质层的二维（2D）输运流箱中。黄原胶溶液被模拟为剪切变稀的非牛顿流体，其粘度是剪切速率、聚合物和高锰酸钠浓度的函数。利用对流弥散反应（ADR）方程结合模拟流场，同时对聚合物、高锰酸钠、三氯乙烯（TCE）及反应产物的反应输运过程进行建模。该数值模型通过二维单元实验的实验数据进行了验证。开展了敏感性分析，以研究系统变量的相对贡献，如聚合物和高锰酸盐浓度、流速、渗透率对比度以及不同的几何设置。结果表明，较高浓度的高锰酸盐和剪切变稀非牛顿流体的较慢流速，提高了氧化剂进入低渗透区域并与TCE反应的能力。较高的渗透率对比度降低了低渗透区域（LPZ）内黄原胶 - 高锰酸根（-）混合物的流速，这增加了TCE氧化和产物回收率。将LPZ的结构从一个区域改变为被一个透水区域隔开的两个较小区域，提高了总体产物回收率。因此，粘度改性既能提高波及效率，又能提高TCE去除率。
