共查询到19条相似文献，搜索用时 330 毫秒
1.
2.
土壤中污染物迁移转化规律的数值模拟研究 总被引：2，自引：0，他引：2
考虑到田间土壤的结构性以及运移其中的污染物的化学反应特征,建立了两区双点平衡/动力学吸附溶质运移模型。用拟交替显隐式有限差分格式对模型进行了离散,通过编制的相应程序,对一施药期的水田进行了模拟。研究了土壤中污染物的迁移转化规律,分析了不可动水和非平衡吸附相对浓度分布的影响。结果表明：不可动区水相和非平衡吸附相的浓度具有的滞后现象,在污染前期一定程度上起到了延缓污染作用,而在污染后期又在一定程度上加重了污染。二者的存在均对溶质的迁移转化具有重要的影响,进行数值模拟时应充分考虑二者的存在。模拟及分析结果为土壤环境质量评价提供了定量依据,同时对环境污染的治理与控制具有理论和现实意义。 相似文献
3.
根据含水层中水、表面活性剂和DNAPLs的运移规律和相互作用机理, 建立三维多相流数值模拟模型, 用以模拟表面活性剂强化的DNAPLs污染含水层的修复过程.将所建立的模型应用于一个被PCE污染的非均质含水层中, 并分别对污染物的污染过程以及修复过程进行模拟.研究结果表明: 数值模拟模型给出了表面活性剂强化含水层修复过程中非水相流体迁移转化的数学描述, 能够在短时间内、参数有限的条件下真实地刻画DNAPLs在含水层中的运移规律, 并能有效地模拟表面活性剂的修复过程.此外, 模拟结果显示, 由于表面活性剂对PCE的增溶增流作用, 有效地提高了PCE在水中的溶解性和迁移性, 其修复40 d的去除率达到63.5%, 与抽出处理法(去除率为31.8%)相比修复效果明显增强. 相似文献
4.
在地下水数值模拟中,模型参数的网格尺度一般大于参数的测量尺度,为此涉及到参数的尺度提升。合理的尺度提升方法既能有效提高计算效率,又能保证模拟精度。在概略介绍拉普拉斯-外壳法的基础上,将其引入到地下水典型非水相液体(non-aqueous phase liquids,NAPLs)污染运移数值模拟的非均质渗透系数场尺度提升,并与尺度提升前的小尺度模型及基于算术平均的尺度提升模拟结果进行对比。研究表明:采用UTCHEM建立的典型NAPLs污染物运移模型,无论是单一污染源还是双重污染源,基于拉普拉斯-外壳法提升尺度后的大尺度模型都能较好地刻画污染羽的空间矩(包括零阶矩、一阶矩和二阶距)随时间的变化,其零阶矩的模拟相对误差小于0. 25%,在水流方向上利用拉普拉斯-外壳法建立的模型对质心位置与污染羽范围的估计均优于算术平均尺度提升法所建模型,且随着含水介质非均质性的增大,拉普拉斯-外壳法的优越性越为明显;而且大尺度模型还能大幅减少计算时间,耗时约为小尺度模型的3%,值得推广应用。 相似文献
5.
多孔介质中毛细压力、饱和度和相对渗透率的确定方法 总被引：3，自引：0，他引：3
目前石油溢出或者地下储油罐泄漏等原因引起的土壤和地下水非水相流体（NAPLs）污染问题越来越引起人们的关注，由NAPLs、水和气所组成的两相或三相系统中的多相流问题亦是当前的研究热点。其中毛细压力（h），饱和度（S）和相对渗透率（k）是多孔介质多相流研究中的三个重要参数，在多相流室内试验研究中是主要的物理监测量，而且三者之间基本关系式的确定是多相流模拟时进行流动控制方程求解的前提条件。本文从室内试验和模型关系两个方面综述了土壤中NAPLs、水和气所组成的多相流系统中毛细压力、饱和度和相对渗透率以及它们之间相关关系的确定方法。 相似文献
6.
分析了有机污染物在土壤中的迁移转化机理，建立了非平衡吸附作用下渗滤液中有机污染物在土壤中迁移转化的动力学模型，给出了模型的数值解法，模拟出渗滤液在非平衡吸附作用下的污染过程；同时还探讨了模型参数降雨量p，垃圾土土层的厚度h，含水率θ等对有机污染物运移的影响。结果表明：在总的污染源一定的情况下，降雨量的增大和污染土层厚度的增大会使得下层土壤中有机物的浓度降低，为定量研究有机污染物在土壤-水环境系统中分配与归宿提供理论依据，同时也可为监测、治理和恢复地下水污染提供一定的科学根据。 相似文献
7.
有效地管理地下水系统需要论述和预测该系统中污染质的运移和消亡情况,以便能更好地运用数学模型准确地描述系统的物理现象。影响许多有机污染物运移的最明显现象是在固(土壤)和液(地下水)两相之间的分配现象。污染物的分配趋势大体可以用对辛醇的基本性质的测量值进行估计,即取决于污染物的水分配系数和土壤的有机碳含量。这个粗略估计是定性评价的基础,但对系统的定量描述就不行,特别是所考虑的问题是非线性平衡吸附问题,分配取决于动力条件或是不可逆的,或者滞后相的分布现象等。准确地进行溶质运移模拟常常需要结合动力学参数和非线性吸附方法才能正确地确定质量守恒方程中的溶质运移现象。实验的方法可以用来确定重要的吸附因子,有机溶质和土壤系统的动力学性质及平衡分配关系。因此利用这种方法能够更准确地模拟污染质的迁移情况。 相似文献
8.
`土壤-地下水耦合数值模拟是定量刻画水流和溶质运移的主要手段。现有大范围场地尺度的研究受到数据采集难度及模拟计算量的限制,多是将土壤和地下水分成两个系统,这种方式不利于模型之间的计算反馈,易出现计算误差,因此将土壤和地下水作为整体系统研究具有重要意义。为精确刻画实际场地土壤-地下水系统中污染物迁移规律,揭示变饱和反应溶质迁移模型的参数敏感性,以某铬污染场地为研究对象,基于现场试验及前人研究所获数据,采用Galerkin有限元法建立三维土壤-地下水模型,定量描述六价铬在土壤-地下水中的迁移规律。在此基础上,通过改变补给条件,研究潜水面在土壤-地下水系统中的波动。并讨论阻滞系数和反应常数对溶质运移的影响。结果表明:在土壤中,污染物最大水平迁移距离为场地东南侧300 m;地下水中污染晕最大分布面积约为1.632 km2;垂向上土壤中的六价铬仅需15.6 h即可下渗至潜水面,第6天贯穿含水层。当潜水面随着补给量变化而波动时,地下水中六价铬会随水流进入土壤,影响土壤中污染分布。对溶质运移参数的讨论显示,当反应常数由0增大至10?6 s-1时,迁移出场区边界时地下水中污染物浓度约减少2000 mg/L,较难迁移至涟水河。基于FEFLOW的数值模型,能够解决各系统之间交互性差的问题,提供较为精确的模拟结果。 相似文献
9.
中俄原油管道原油泄漏造成的环境污染和环境岩土工程问题是目前迫切需要解决的重要问题。通过淋滤作用下的石油污染物迁移过程室内模拟试验,研究了石油污染物在冻土区的迁移过程和迁移特征,研究发现：石油污染物在迁移过程中,油、水、气三相流体存在一个动态的平衡过程,其三者共同占据土样中的孔隙空间;石油污染物在冻土区迁移主要经历3个过程：吸附、迁移和聚集;石油污染物在迁移过程中,其各个成分和各烃类化合物迁移能力都有所不同,烃类化合物中碳数和烃类结构影响其迁移速度;冻土层对石油污染物的迁移具有明显的阻碍作用,可有效防治土壤深层次污染。研究成果为冻土区石油污染物多相流（油、水、气）水热质迁移动力学模型的建立以及石油污染引起的岩土工程特性变化等研究奠定了重要的基础 相似文献
10.
重金属污染物在黏土固化注浆帷幕中的运移规律 总被引：3，自引：0，他引：3
基于渗透和弥散作用,探讨了黏土固化注浆帷幕对污染物的阻滞机制,通过土柱试验,分析了注浆帷幕对重金属污染物的渗透性能和弥散性能,采用污染物运移过程数值模拟的一维对流-弥散计算模型,研究了重金属污染物在注浆帷幕中的运移规律。试验表明,不同的污染物质在黏土固化注浆帷幕中的渗透性能和弥散性能不同,镉的迁移速度大于铅。数值计算表明,注浆帷幕的厚度及其渗透性、弥散性和水力梯度等重要控制参数对重金属污染物在帷幕中的运移过程具有显著影响。 相似文献
11.
In this study, the presence of nonaqueous phase liquids (NAPL) in sandy soils are detected using a TDR probe system and the eigendecomposition method of analysis. As a demonstration, five NAPLs with different physicochemical properties (acetone, benzene, heptane, trichloroethylene, and xylene; Table 1) were used. Samples were prepared in such a way that the soil pore fluid has different contents of deionized water and NAPLs. For each experiment, a pulse signal with known characteristics was used and reflected signals were captured by an oscilloscope and analyzed using the eigendecomposition method. Autoregressive modeling and singular value decomposition were used to calculate the eigenvalues. The most significant eigenvalues were identified based on their power spectrum. The relative eigenvalue of the first mode (Eow), which is a measure of the power carried by the signal, was calculated and correlated to NAPL type and content, and octanol water partition coefficient (log Kow). The results indicated that for the same NAPL content, as log Kow increases, Eow decreases due to increase of hydrophobicity. For the same log Kow, as the organic content in soil pore fluid increases, Eow increases due to decrease of dielectric properties of the pore fluids. 相似文献
12.
Analytical closed-form solutions for assessing pumping cycles,times, and costs required for NAPL remediation 总被引：2，自引：0，他引：2
R. Chesnaux 《Environmental Geology》2008,55(7):1381-1388
An analytical solution is given to evaluate the number and duration of pumping cycles required for the remediation by pumping
of contaminants, both single component and multi-component non-aqueous phase liquids (NAPLs), when no free product is present
in the system. The method can be applied in a homogenous medium if the contamination zones have been delineated and residual
total NAPL concentrations assessed. Based on the principle of the NAPL partitioning in unsaturated or saturated porous media,
analytical closed-form solutions are provided for both cases of remediation by pumping in saturated and unsaturated conditions:
“pump-and-treat” and “soil vapor extraction”. In each case we determine the number of pumping cycles required to reach the
residual required concentration of NAPL (for example, according to health-based standards), considering one or more chemicals
simultaneously present in an aquifer. The method requires information on the aquifer saturation state and the properties of
the chemicals of interest. Calculations are based on the assumption of equilibrium partitioning of chemicals between the pore
water, the soil solids, and the soil gas (in the case of unsaturated conditions), and no presence of a NAPL phase. 相似文献
13.
A three-dimensional, three-phase numerical model is presented for simulating the movement of immiscible fluids, including
nonaqueous-phase liquids (NAPLs), through porous media. The model is designed to simulate soil flume experiments and for practical
application to a wide variety of contamination scenarios involving light or dense NAPLs in heterogeneous subsurface systems.
The model is derived for the three-phase flow of water, NAPL, and air in porous media. The basic governing equations are based
upon the mass conservation of the constitutents within the phases. The descretization chosen to transform the governing equations
into the approximating equations, although logically regular, is very general. The approximating equations are a set of simultaneous
coupled nonlinear equations which are solved by the Newton-Raphson method. The linear system solutions needed for the Newton-Raphson
method are obtained using a matrix of preconditioner/accelerator iterative methods.
Because of the special way the governing equations are implemented, the model is capable of simulating many of the phenomena
considered necessary for the sucessful simulation of field problems including entry pressure phenomena, entrapment, and preferential
flow paths. The model is verified by comparing it with several exact analytic test solutions and three soil flume experiments
involving the introduction and movement of light nonaqueous-phase liquid (LNAPL) or dense nonaqueous-phase liquid (DNAPL)
in heterogeneous sand containing a watertable.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
It occurs worldwide that the organic components of non-aqueous phase liquid (NAPL) enter the porous medium and become the source of contaminants in the subsurface. The transport of the organic components through NAPL interphase into the aqueous phase and the subsurface determines the extent of contamination, the persistence of residual NAPL phases and the techniques of remediation. During the transport process the NAPL interphase may experience "aging", a physical and chemical change when NAPL is exposed to aqueous and or gaseous phases. This aging process alters vice versa the mass transfer behaviour of the organic contaminants in the porous medium. 相似文献
15.
基于孔隙网络模型的非水溶相液体运移实验研究进展 总被引：1，自引：0，他引：1
进行多孔介质中非水溶相液体（Non Aqueous Phase Liquids，NAPLs）运移的微观机理研究，微观孔隙网络模型实验是目前应用比较广泛且行之有效的方法。通过网络模型实验，获得对NAPLs在多孔介质中运移更深入的认识。从多孔介质孔隙结构测量、孔隙网络模型制作、NAPLs运移网络模型实验和数值模拟4个方面评述了该方向的研究进展，结果显示测量孔隙结构方法、图像刻蚀技术、可视化测量实验数据方法等有力地促进了本实验研究的发展。分析了孔隙网络模型实验存在的问题以及未来的发展趋势，对开展孔隙网络模型实验研究有一定的启发作用。 相似文献
16.
Subcooled liquid solubility is the water solubility for a hypothetical state of liquid.It is an important parameter for multicomponent nonaqueous phase liquids(NAPLs) containing polycyclic aromatic hydrocarbons(PAHs),which can exist as liquids even though most of the solutes are solid in their pure form at ambient temperature.So far,subcooled liquid solubilities were estimated from the solid water solubility and fugacity ratio of the solid and(subcooled) liquid phase,but rarely derived from experimental data.In our study,partitioning batch experiments were performed to determine the subcooled liquid solubility of PAHs in NAPL-water system.For selected PAH,a series of batch experiments were carried out at increased mole fractions of the target component in the NAPL and at a constant NAPL/ water volume ratio.The equilibrium aqueous PAH concentrations were measured with HPLC and/or GCMS. The subcooled liquid solubility was derived by extrapolation of the experimental equilibrium aqueous concentration to a mole fraction of unity.With the derived subcooled liquid solubility,the fugacity ratio and enthalpy of fusion of the solute were also estimated.Our results show a good agreement between the experimentally determined and published data. 相似文献
17.
离心实验模拟以其可以获得与原型一致的应力水平并且能够大大缩短原型历时而被应用于污染物迁移实验研究。在离心相似理论及离心实验模拟的相似基础上,重点回顾了离心机在饱和带水分、非饱和带水分、保守性溶质、NAPLs、重金属、核素迁移以及污染场地修复方面的实验应用。最后讨论了离心模拟中土壤预制和加速度选择的问题,并简单介绍了离心监测方法。可以得出结论:离心机能够成功用于各类物质迁移的实验研究中,离心实验模拟能够为理论和数值等分析方法快速提供真实可靠的参数依据,但离心实验的理论基础和监测方法需要进一步完善,此外也应积极开展更接近实际情况下的离心实验模拟研究。 相似文献
18.
Screening methodologies aim at improving knowledge about subsurface contamination processes before expensive intrusive operations, i.e. drilling and core-sampling, well installation and development, sampling of groundwater and free-phase product, are implemented. Blind field tests carried out at a hydrocarbon storage and distribution center in NE Spain suggest that Rn monitoring can be effectively used to locate the boundaries of subsurface accumulations of NAPLs. Sixty seven measurements of Rn in soil air were performed with a SARAD RTM 2100 current-ionization alpha-particle spectrometer following a 10 m square grid. Reductions of 222Rn concentration above a pool of LNAPL due to the preferential partition of Rn into the organic phase were spatially analyzed and resolved to yield the surface contour of the NAPL source zone. This surface trace of the source zone agreed well with the extent and situation inferred from measurements of free-phase thickness taken at eight monitoring wells at the site. Moreover, the good repeatability (as measured by replicate measurements at the same sampling point) and spatial resolution of the technique suggest that the boundaries of the plume can be delineated at the sub-decametre level. 相似文献
19.
Dirk Schaefer 《Environmental Earth Sciences》2012,67(8):2459-2467
Organic contaminants in aquifers are often present as non-aqueous phase liquids (NAPL), which are long-lasting sources for groundwater contamination. The existing NAPL mass is an important parameter for the persistence of the source, but its determination is difficult. One possible detection method is based on the ideal multicomponent dissolution theory, using aqueous concentrations downstream of a fully mixed NAPL source to calculate its mass. In this publication, the applicability of this method is tested for a source size of about 5 m, using numerical methods. In contrast to fully mixed source zones, on this scale the NAPL sources are not in contact with each other, do not mix and develop independently over time. Highly soluble NAPL components can be depleted or the NAPL phase can be completely exhausted locally, while in other portions of the source zone NAPL is still present with all its components. Hence, the interpretation of the resulting aqueous concentrations downstream using the ideal dissolution theory leads to erroneous NAPL masses of several orders of magnitude in the investigated scenarios. 相似文献