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随着工农业生产的快速发展,各种污染物质通过多种途径进入土壤环境并共存,造成了严重的土壤污染,其中多环芳烃是主要的污染物之一。近年来,多环芳烃在自然界中有不断累积的趋势,美国环境保护局已将其列为优先控制污染物,因此,开展对其污染土壤的修复治理研究具有重要意义。目前,关于土壤多环芳烃的修复技术主要有热力学、热解吸、焚烧、土地填埋、电动力学、化学淋洗、植物修复以及生物修复等[1]。其中,电动力学修复(electrokinetic repair, EKR)是通过施加一定的电压梯度,利用一系列电动运输现象(电渗透、电迁移、电泳)以及在土壤中发生的热和水力现象来将污染物迁移到受控提取点的土壤修复技术[2]。许多研究人员[3-5]对电场修复PAHs污染的土壤进行了初步的探究,也证明了其修复效果,关于EKR技术的修复PAHs迁移机制,却鲜少报道。
在过去的25年中,关于EKR的数学模型的研究一直在展开。KIM等[6]和WANG等[7]开发了关于化学平衡的一维数学模型,在此模型中考虑了孔隙水中的物质,电化学反应,扩散和电渗透输送以及离子的电迁移等因素。JACOBS等[8]通过添加偶联络合反应、吸附和沉淀/溶解过程来改进该模型,并将模型从一维域扩展到二维域。LÓPEZ-VIZCAÍNO等[9]提出了一个用于估计电动过程中pH分布的一维模型。MASI等[10]提出了一种基于Poisson-Nernst-Planck系统的运输模型,用于计算电渗平流和水化学平衡。PAZ-GARCIA等[11]提出了一种类似的去除镉的模型并由OTTOSEN等[12]推广,这种模型适用于受多种金属污染的土壤。RIBEIRO等[13]开发了一个适用于去除有机污染物阿特拉津的的模型实例,并开发了一个用于模拟在不饱和条件下土壤中离子的电动传输(假设在施加电梯度期间土壤中的电流类似于水流)的三维模型。
尽管关于EKR技术处理重金属和农药类污染物的数学模型已经有了大量的研究和比较成熟的应用,但关于多环芳烃类的数学模型却鲜少报道。因此,对基于实验和建模方法的EKR技术方案的实现是当务之急。本研究构建了电动体系中土壤菲的迁移模型,并探讨了相关因素对修复效果的影响以及土壤菲修复的主要机制,评估了新模型用于土壤中菲的去除可行性,为电动力学修复土壤有机污染物提供参考。
土壤电动修复中菲迁移的数值模拟
Simulation on phenanthrene migration in electrokinetic remediation of soil
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摘要: 针对菲污染土壤修复建模的问题,通过对电动力学作用下菲污染土壤的迁移现象的室内模拟实验,确定了影响菲迁移的电渗流、电迁移、对流和弥散4个主要过程,建立了电动力学作用下菲在污染土壤中的迁移模型;运用COMSOL Multiphysics 5.3软件结合迁移模型的各项方程和选取的参数对菲的迁移过程进行了模拟计算。结果表明:当孔隙率分别为0.33、0.38、0.43和0.48时,菲的最大迁移率分别为31.89%、34.78%、37.97%和41.74%;当电压从0.5 V·cm−1增加至2 V·cm−1的过程中,电渗流通量增大,最大迁移率可达到44.35%;修复区域的浓度均呈“碗状”分布,模拟计算得到在中间靠近阳极区域的菲的浓度达到最小值2.14 mol·m−3,迁移率最大为38%。模拟计算的菲迁移分布结果与实验所得结果相吻合,证明该模型用于电动修复多环芳烃污染土壤的适用性。Abstract: In order to address the problem of repairing phenanthrene-contaminated soil, both laboratory simulation and experiments were conducted to study the phenanthrene migration in soil under electrodynamics. Electroosmotic flow, electromigration, convection, and dispersion were determined to be the four main processes to affect phenanthrene migration. A phenanthrene migration model in contaminated soil under electrodynamics was established. The phenanthrene migration process was simulated using COMSOL Multiphysics 5.3 software, the migration equations and the selected parameters. Results showed that at the porosities of 0.330, 0.380, 0.430, and 0.480, the maximum mobility of phenanthrene were 31.9%, 34.8%, 38.0% and 41.7%, respectively. As the voltage increased from 0.500 V·cm−1 to 2.00 V·cm−1, the electroosmotic flux increased accordingly, resulting in a maximum mobility of 44.4%. In the remediation area, a bowl-shaped distribution occurred for the phenanthrene concentration. The simulation calculation determined that phenanthrene concentration reached a minimum value of 2.14 mol·m−3 in the middle region close to the anode, and the maximum mobility was 38.0% accordingly. The simulated results for phenanthrene migration and distribution were in a good agreement with the experimental results, which verified that the applicability of the developed model in the electrokinetic remediation of soil contaminated by polycyclic aromatic hydrocarbon.
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Key words:
- phenanthrene /
- soil electrokinetic remediation /
- migration model /
- numerical simulation
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表 1 实验及模拟浓度
Table 1. Experimental and simulated concentrations
mol·m−3 数据来源 S1 S2 S3 S4 S5 S6 初始浓度 实验 3.45 2.37 2.29 2.71 2.93 3.25 3.47 模拟 3.45 2.21 2.27 2.74 3.15 3.35 3.45 -
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