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1.
Application of a newly developed column test device to analyze seawater transport in sandy soils 总被引：2，自引：1，他引：1
Xiaoqiang Dong Heesoo Woo Hisoo Park Junboum Park 《Environmental Earth Sciences》2013,70(5):2397-2404
To verify the applicability of the time-continuous electrical conductivity (EC) measurement in analyzing the contaminant movement in the subsurface, a new column test device employing non-destructive four-electrode sensors was developed. Using the seawater to create a simple one-dimensional steady-flow condition, laboratory transport experiments were conducted and the EC breakthrough curves at different distances were obtained. Comparison between the EC breakthrough curves obtained from the EC sensors and those from the effluent solute chemical analysis showed that the estimated resident concentration from the EC breakthrough curves are useful in understanding solute transport in soils. The pore water velocity and longitudinal dispersion coefficient estimated using the computer code, CXTFIT, were found to be slightly underestimated, especially at sensors located at smaller distances from the outlet boundary. Results showed that the developed column test device employing the four-electrode sensors proposed in this study provides a non-destructive, convenient, and inexpensive means of evaluating the seawater transporting in soils. 相似文献
2.
Consolidation of clayey contaminant barriers such as landfill liners has been postulated as a cause of early breakthrough of contaminants. In this paper we theoretically investigate this proposition. For this purpose a sophisticated one‐dimensional, large‐deformation model of coupled mechanical consolidation and solute transport is employed. This new model is a generalization of existing coupled consolidation and solute transport models described in the literature. It takes into account both non‐linearities in geometry as well as constitutive relations. The latter relate the compressibility, hydraulic conductivity and coefficient of effective diffusivity to the deformation of the soil. The model is applied to a case study of a clay liner and geomembrane system. Results obtained from numerical solution of the model equations are compared with those from various simplified models, including a ‘diffusion only’ (i.e. a rigid soil) model traditionally used in contaminant barrier design. For barriers incorporating low compressibility soils (as for many well compacted clays), there is little difference between contaminant transit (i.e. breakthrough) times predicted by the two models. However, for contaminant barriers incorporating more compressible soils, consolidation is shown to significantly accelerate transport. These results indicate the potential importance of accounting for the effects of soil consolidation and highlight the limitations of existing models when modelling solute transport through composite barriers utilizing soft soils. Based on these limited results, we suggest a possible way of taking into account soil consolidation using simplified models. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
3.
1 IntroductionIncorporation of potentially toxic metals ( e.g.Cd, Cu, Cr, Pb, Hg, As, Se, Zn, Ni) into soils ei-ther through sewage-sludge irrigation or some othersources of pollution (e.g. atmospheric deposition, ap-plication of agri-chemicals) has posed… 相似文献
4.
CCL吸附特性及孔隙率降低对污染物运移的影响 总被引：1，自引：0，他引：1
假定孔隙均匀地分布于土体的物质空间内和土骨架对污染物的吸附特性服从平衡线性,对基本体积质量关系进行分析,提出了由于土体对污染物的吸附而引起的孔隙率降低的估算公式。在考虑土体孔隙率变化的条件下,建立了污染物一维运移的控制方程,并考虑垃圾生物降解效应、压实黏土衬里（CCL）防渗层、下覆有限厚度含水层等实际情况,确定了初始条件和边界条件。对所建立的初边值问题进行了数值求解,且对某假想填埋场情况进行了变动参数与对比计算,结果表明,由于土颗粒对污染物的吸附所引起的孔隙率降低,显著地降低了污染物对压实黏土衬里的穿透能力。与常孔隙率情况相比,CCL中污染物的峰值浓度降低近10 %,含水层中污染物浓度降低更显著。当考虑土体孔隙率变化时,弥散对污染物运移具有控制作用,分布系数对污染物的运移具有重要影响。 相似文献
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6.
大变形黏土防渗层中的污染物迁移和转化规律研究 总被引：1，自引：0，他引：1
国内湖泊疏浚污染底泥堆场一般以较厚的黏土层作为主要防渗层,由于在上覆底泥作用下黏土层会发生较大的固结变形,因此,在研究黏土防渗层中的污染物运移和转化规律时,应该考虑土体变形的影响。基于Gibson一维大变形固结理论和饱和多孔介质中的污染物对流扩散方程,建立了二者耦合的可变形多孔介质中污染物的运移和转化模型,其中首次考虑了土体自重和生物降解作用的影响。利用所建立模型的数值解,研究了在可变形黏土防渗层中的污染物运移和转化规律,同时分析了模型中不同项和主要参数的作用和影响。研究结果表明,土体大变形对黏土防渗层中污染物的运移有着较复杂的影响,一方面土体变形会加速污染物的运移;另一方面土体固结带来的渗透性减小会增加污染物的穿透时间,二者的不同作用取决于众多的影响因素,如土层厚度和吸附作用等。研究结果对于评估天然黏土防渗层对污染物的阻隔作用有重要的指导意义。 相似文献
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8.
Experiments were conducted under static batch and dynamic flow conditions to evaluate the sorption of FeII onto three goethites (G1, G2 and G3) having different crystal habits, morphologies and surface properties. Results reveal that G1 exhibited the highest FeII sorption extent and lowest kinetic rate constant, which may result from higher surface site density, surface roughness and edge surface faces. Surface complexation modeling parameters derived from batch experiments were combined with hydrodynamic parameters to simulate breakthrough curves in goethite-coated sand packed columns. The total sorbed amount of FeII at complete breakthrough was in agreement with that expected from the batch experiments, except for G1. Sorption breakthrough predictions that make use of surface complexation parameters accurately predicted FeII mobility in G2 and G3 columns, but poorly in G1 column. Experiments at various flow rates in G1 columns represented different amounts of FeII sorbed at complete breakthrough, thereby underscoring the impact of kinetic sorption. Moreover, Fe dissolution/re-precipitation or FeII-induced transformation of goethite was suspected at the lowest flow rate in the G1 column. The influence of goethite phase specific reactivity on FeII sorption under batch versus advective–dispersive flow is herein demonstrated. These findings have strong implications to assess transport of FeII and environmental contaminants both in natural and engineered systems. 相似文献
9.
为了研究河床粗化破坏与形成过程中推移质的输移特征,基于一套新型的接沙系统,在上游无来沙条件下,进行了3组不同床沙级配的水槽试验,研究了递增梯级流量作用下河床粗化破坏与形成的过程,采集到一套高精度（0.1 g）、高频率（1 Hz）的实时推移质输沙率及分时段输沙级配数据,分析了累积输沙量、输沙率及输沙级配的变化特征。结果表明,粗化过程中累积输沙量随时间基本呈幂函数规律增长,且"粗化破坏再形成"的累积输沙量曲线出现明显转折点;推移质输沙率表现出明显的非恒定性,其粗化形成阶段的耗时要远大于粗化破坏阶段的时间,两者之比范围为3.5~20.5;推移质输沙级配中粗颗粒比例随时间变化趋势与输沙率相似,在输沙率达到峰值附近时,输沙级配与原始床沙级配相同。 相似文献
10.
基于室内土柱穿透实验的优先流定量评价 总被引：4，自引：0，他引：4
土壤优先流对包气带水流和污染物运移的影响已引起广泛关注,但大多数研究还停留在定性描述上,缺乏对优先流定量评价的标准。基于室内土柱实验获取的穿透曲线,分析了饱和条件下土壤溶质优先运移的一般规律,采用解析法模拟软件CX-TFIT拟合了溶质优先运移的参数,同时结合时间矩方法计算了定量评价优先流的指标PFSP。研究结果表明:时间矩方法中的一阶标准矩μ′1、二阶中间矩μ2以及偏态系数S可以定量刻画穿透曲线的特征,从而指示优先流的程度;PFSP能很好地刻画优先流作用的大小。该研究对优先流的定量评价具有重要指导意义。 相似文献
11.
Taicheng An Hui Chen Huiying Zhan Kun Zhu Ronny Berndtsson 《Environmental Geology》2005,47(4):467-474
A laboratory study was executed to investigate the effect of surfactants to enhance sorption of polycyclic aromatic hydrocarbon (PAH) contaminants in loess soil. Phenanthrene and naphthalene were chosen as organic contaminant indicators in loess soil modified by the cation surfactant hexadecyltrimethylammonium (HDTMA) bromide. The kinetic behavior of sorption during transport in natural and modified loess soil was studied. The results indicated that sorption rate in the cation surfactant modified loess soils was at least 3 times faster than that of the natural soil. A first-order kinetics model fitted the sorption data well for both soils. The sorption rates of the two organic compounds were related to their primary residual quantity on the soils. The experiments showed that sorption amounts approached constant values approximately within 30 and 90 min for naphthalene and phenanthrene at 298–318 K, respectively. The rate constants, however, displayed negative correlation with increasing temperature. With changing temperature, the activation energy was calculated at –6.196–1.172 kJ/mol for naphthalene and –28.86–15.70 kJ/mol for phenanthrene at 298–318 K. The results can be used to predict the sorption kinetics of phenanthrene and naphthalene in loess soils, and in a wider perspective, be used to better understand the transport of petroleum contaminants in the soil environment. 相似文献
12.
考虑土体固结变形的污染物运移模型 总被引：4，自引：1，他引：3
土体的固结压缩变形对污染物的运移具有重要的影响,而目前国内关于污染物在变形多孔介质中运移规律的研究尚处于空白,在国外也是近几年才有人开始这方面的研究工作。在Biot固结理论和污染物运移理论相结合的基础上,提出了污染物在黏土防渗层中迁移转化的一维数学模型,该模型的最大特点是考虑了土体受力变形对污染物运移的影响,在合理简化的基础上给出了模型的解析解,并将计算结果与太湖疏浚污染底泥堆场的实测结果进行了比较分析,模拟计算的结果在一定程度上能够反映实际土层中污染物的运移情况。 相似文献
13.
Jing Liu Xi Huang Juan Liu Weiqing Wang Wei Zhang Faqin Dong 《Environmental Earth Sciences》2014,72(6):2081-2090
Bone char has been used as a low-cost adsorbent for the removal of As(V) from waste water. The batch experiments show that the Langmuir isotherm describes well the adsorption behavior. The adsorption process follows a pseudo-second-order kinetic model. The column experiments were conducted at pH = 4 and 10 mg/L an initial concentration of As(V). The breakthrough curves were investigated for various conditions, such as different flow rates, column bed heights, adsorption cycles, coexisting cations and anions such as Mn2+, Al3+, PO4 3?, SO4 2? and SiO3 2?. The convection–diffusion equation was used to model the experimental transport data of As(V) for these conditions. It has been found that the coexisting cations can enhance As(V) immobilization and increase retardation factor (R f), and coexisting anions significantly decrease the diffusion coefficient (D L) of As(V). The secondary adsorption phenomena were observed in the breakthrough curves of column studies of As(V) with cations, especially Mn2+. The regeneration experiments using distilled water and 0.1 mol/L NaOH solution were done to evaluate the desorption degree. The total desorbed amounts from whole column for three experiments decreased from 8.98 to 7.67 mg and the desorption degrees increased from 0.51 to 0.71 unexpectedly, which indicates that the regeneration operation is feasible. Finally, the chemical analysis of column effluents and infrared spectroscopic analysis of absorbent both revealed that the ligand exchange and electrostatic interaction are the main removal mechanisms. 相似文献
14.
Prediction of colloid release and transport as affected by reactive species remains a significant challenge for field applications. In this paper, we report experimental and modeling results of ferrihydrite colloid release under the influence of citrate species. Using a 3-plane surface complexation model, equilibrium constants were obtained for the three proposed inner-sphere complexes by fitting a citrate adsorption isotherm on ferrihydrite at pH 4, and a pH adsorption envelop with 0.64 mM citrate. The constants were used in a reactive transport model for simulating reaction fronts of dissolved species during injection of citrate in ferrihydrite-coated quartz columns. Simulation results show that sorption alone may not adequately describe the breakthrough curves. Inclusions of ferrihydrite dissolution and re-adsorption of Fe(III) improve the prediction of dissolved species transport. Additionally, matrix diffusion may be needed for improved prediction. For the release of colloidal iron oxides it was shown that both oxide dissolution and interfacial repulsion controlled the process during complete breakthrough. However, the peak release of colloids, which occurred during the actual breakthrough of dissolved species, was mainly brought about by electric double layer forces. These particles underwent detachment-deposition-detachment cycles along the flow path, and emerged in the effluent with the major reaction front. To quantitatively predict colloid release, a semi-empirical linear correlation was established, linking the calculated electric potential to experimental colloid release rates. The model may be applied to the prediction and scaling of aquifer remediation studies involved in the injection of organic ligands to mobilize particle bound contaminants. 相似文献
15.
Assessment of the role of facies heterogeneity at the fine scale by numerical transport experiments and connectivity indicators 总被引：2，自引：1，他引：1
The heterogeneity of facies at the scale of individual lithological levels controls, at a macroscopic scale, water flow and contaminant transport in porous sediments. In particular the presence of organized features such as permeable connected levels, has a significant effect on travel times and dispersion. Here, the effects of facies heterogeneity on flow and transport are studied for three blocks, whose volume is of the order of a cubic meter, dug from alluvial sediments from the Ticino valley (Italy). Using the results of numerical tracer experiments on these domains, the longitudinal dispersion coefficient is computed with an Eulerian approach based on the fit of the breakthrough curves with the analytical solution of the convective-dispersive transport equation. Moreover, the dispersion tensor is computed with a Lagrangian approach from the second order moments of particle distributions. Three types of connectivity indicators are tested: (1) connectivity function; (2) flow, transport and statistical connectivity; (3) original (intrinsic, normal and total) indicators of facies connectivity. The connectivity function provides the most complete information. Some of the transport and statistical connectivity indicators are correlated with dispersivity. The simultaneous analysis of the three indicators of facies connectivity emphasizes the fundamental geometrical features that control transport. 相似文献
16.
Drinking water supply wells were constructed in the Sabarmati river bed aquifer of Ahmedabad city using radial pipes and
are known as French Collector wells. Contamination of groundwater from one of the French wells near Sabarmati railway bridge
was noticed in 1992. The suspected pollution sources are Duff-nala of Shahibaug and two other sources from slum dwellings
on either side of Sabarmati river. A combined groundwater flow, pathlines and a mass transport model was constructed covering
an area of 9 km2 to analyse the capture zone of the French well under two different scenarios. Aquifer parameters of the river bed aquifer
were available. Dry river bed condition was simulated under scenario I and controlled flow in the river bed was simulated
under scenario II. The groundwater velocity and migration of contaminant particles from sources was analysed in the pathline
model. Total dissolved solids (TDS) concentration contours originating from sources in the mass transport model (MT3D) were
computed by solving an advection-dispersion equation. The computed pathlines and TDS concentration contours indicate likely
migration of contaminant plume from pollutant sources to the French well during 365 days under two scenarios. The model results
confirm the tracer injection studies carried out to know the likely migration of contaminants towards the French well. The
modelling study emphasised the necessity of controlled release of surface water in Sabarmati river bed from Dharoi reservoir
throughout the year.
Received: 28 October 1998 · Accepted: 17 June 1999 相似文献
17.
非平衡-非线性吸附情况下填埋场污染物运移分析 总被引：10，自引：0，他引：10
采用Langmuir等温吸附线方程描述非线性吸附性能, 基于改进的混合元方法，通过数值计算与分析，探讨了非平衡吸附条件下污染物运移过程及其机理。计算结果表明: 当考虑非平衡、非线性吸附性能时, 污染物穿透曲线即浓度的时程变化曲线尖锐而狭窄、峰值点前移, “拖长尾”现象不明显, 由此说明，土颗粒对污染物的非平衡、非线性吸附使得污染物的穿透能力增强, 滞留能力下降。进一步的变动参数比较分析表明：Langmuir等温线方程中的参数B、压实粘土衬里的渗透性及地下水渗流速度对污染物运移过程具有显著的影响。 相似文献
18.
Solute transport experiments were conducted in a one-dimensional saturated column using dissolved methoxy-nonafluorobutane (HFE-7100), a Novec engineered fluid developed by the 3M Corporation, as the solute. Novec engineered fluids are considered dense non-aqueous phase liquids (DNAPLs) because they are immiscible with water and have a specific gravity greater than one. The HFE-7100 fluid is safer and environmentally friendlier than common DNAPL contaminants such as tetrachloroethylene (PCE) or trichloroethylene (TCE); thus, it is an ideal substitute DNAPL for laboratory groundwater contamination research. Three sets of solute transport experiments were conducted. The first set of experiments was conducted in a glass-bead-packed column using dissolved HFE-7100 as the solute. The second set of experiments was conducted in a sand-packed column using dissolved HFE-7100 as the solute. The third set of experiments was conducted in a sand-packed column using dissolved PCE as the solute. The dissolved HFE-7100 column breakthrough concentrations were compared with dissolved PCE breakthrough concentrations. Results show that the one-dimensional solute transport equation was successful in describing the transport behavior of dissolved HFE-7100. This study demonstrates that the HFE-7100 fluid can be used as a safer substitute DNAPL for groundwater contaminant dissolution and transport research. 相似文献
19.
由于废弃物的堆积以及填埋场上覆盖层的重量,衬垫因此承受一定的压力,发生力学固结;由于黏土本身的结构特性,当污染物通过黏土垫层时可能会发生化学固结,而固结作用可直接对污染物的对流输运产生影响,也会引起土层体积和结构的变化,从而改变其固有的输运性质。从混合物理论出发,建立了水力-化学-力学作用下的溶质输运理论框架,统一地描述了水力-化学-力学作用下变形、水的吸附或解吸附、对流和扩散现象。将输运系数考虑为有效孔隙率的函数,由此反映固结对输运参数的影响。对所建立的数学模型进行无量纲化处理,并使用有限元软件COMSOL Multiphysics进行求解,最后进行了参数分析。研究结果表明,垫层土体中吸附水和自由水之间的化学势差异越大,层间吸附水的解吸附量越大;当土体的软硬性质不同时,当层间吸附水解吸附后,土体固结程度不同,从而对污染物输运过程的影响不同。而当垫层上覆荷载增大时,土体宏观孔隙的扩张的限制作用增强,从而对土体产生一种修复作用,抑制污染物在土体中的输运。 相似文献
20.
A two-dimensional boundary integral method to analyse the flow of contaminant in fractured media having a two- or three-dimensional orthogonal fracture network is presented. The method assumes that the fractures provide the paths of least resistance for transport of contaminants while the matrix, because of its low permeability, acts as ‘storage blocks’ into which the contaminant diffuses. Laplace transform is used to eliminate the time variable in the governing equation in order to facilitate the formulation of a boundary integral equation in the Laplace transform space. Conventional boundary element techniques are applied to solve for the contaminant concentrations at specified locations in the spatial domain. The concentration in the time domain is then obtained by using an efficient inversion technique developed by Talbot. The method is able to analyse the behaviour of waste repositories which have diminishing concentration due to the mass transport of the contaminant into the surrounding fractured media. 相似文献