吸附和降解耦合对填埋场污染物运移过程的影响

针对压实粘土衬里和有限深度含水层等实际情况，考虑填埋场垃圾生物降解效应及土颗粒对污染物的非线性吸附和一级动力降解效应，建立在压实粘土衬里和含水层中描述填埋场渗滤液运移过程的数学模型。通过数值模拟探讨污染物运移过程中非线性吸附物理化学作用和一级动力降解生物化学作用对污染物运移的影响：通过变动参数比较计算与对比分析发现，非线性吸附和一级动力生物降解对污染物运移过程及机理具有显著的影响；穿透曲线变得尖锐而狭窄，峰值点前移，尾部拖长，最大吸附能力对污染物的运移具有显著影响。压实粘土衬里的渗透性是控制污染物运移的重要因素。     

非饱和土层中污染物运移过程的数值分析

针对填埋场下部为压实粘土衬里、非饱和土层和含水层的三层结构体系,建立了描述填埋场污染物运移的一维控制方程,在控制方程中考虑了压实粘土衬里的平衡非线性吸附方程与非饱和土层的线性吸附方程。采用数值法求解控制方程,通过变动参数探讨了污染物在三层结构体系中运移过程的各种影响因素。     

非线性吸附条件下填埋场污染物运移过程二维数值分析

假设填埋场下部为三层结构体系,且渗流场稳态,建立了污染物二维运移控制方程。在控制方程中分别考虑垃圾降解效应、压实黏土衬里的非线性吸附特性、滞水层与含水层的线性吸附特性及各向异性。采用数值分析方法对某一假想填埋场进行具体计算。通过变动参数计算与分析,计算结果表明:压实黏土衬里和滞水层的垂直弥散系数为污染物二维运移的敏感因素。仅考虑压实黏土衬里的非线性吸附特性下,复合参数Sl,m为污染物运移的敏感因素,当Sl,m取值较大时,污染物的水平向运移能力增强,而对吸附强度Kl,l不敏感。滞水层线性吸附对污染物运移影响显著而含水层吸附性影响较弱。     

关于“污染物运移过程的一维数值分析”的讨论

 《岩土工程学报》2005年第2期发表的“污染物运移过程的一维数值分析”一文(以下简称“原文”)对于垃圾填埋场内污染物质一维的运移作了计算分析,特别针对粘土衬垫下卧含水层的吸附作用对于污染物质运移的抑制作用作了深入的探讨和比较,取得了很好的结果。笔者意欲在下述几点存在的问题向原文作者请教和商讨。(1)关于填埋场内污染物质浓度随时间变化的数学描述。原文将填埋场内污染物质浓度随时间的变化表达成为指数降低关系。实际当中这一关系应当有其使用条件:即这一关系应该在垃圾填埋场闭锁(landfill closure)之后成立[1]。在闭锁之前,随着垃圾的不断堆放和雨水的进入而导致垃圾的淋滤,填埋场内污染物质浓     

粘土环境岩土工程特性对填埋场衬垫防渗标准的影响

采用溶质运移的一维迁移模型,研究了粘土环境岩土工程特性对填埋场衬垫防渗标准的影响,对目前采用的填埋场粘土类衬垫防渗设计标准及其有效性进行了多参数组合的计算分析;此外,还比较了粘土衬垫与复合衬垫对污染物离子的防渗阻隔性能,对土工膜在衬垫中的作用进行分析;研究表明,应针对不同地区的情况(干旱少雨或多雨等)考虑衬垫的形式。与其他因素相比,粘土的渗透系数对衬垫层渗漏影响最大,以水力渗透系数作为填埋场粘土衬垫的设计标准是可行的,但离子扩散系数的影响也不可忽略;而增强粘土的活性,提高粘土吸附离子的性能,则可延长离子通过衬垫的击穿时间;与单纯的粘土衬垫相比,复合衬垫对离子具有更好的阻隔性能,故在南方多雨地区宜采用复合衬垫;而用污染物的渗漏总量作为填埋场衬垫的设计标准比击穿时间更合理。     

填埋场渗滤液在饱和土壤中运移的数值研究

垃圾填埋场渗滤液是造成地下水污染的一个重要原因。针对农村简易填埋场,本文建立数学模型,土壤被看成各向同性均匀多孔介质,采用Darcy定律描述多孔介质中的渗流,在此基础上,数值模拟了吸附性污染物COD在饱和土壤中的运移过程。分析了降雨量及其他参数对COD运移的影响,为控制地下水污染及填埋场选址提供可靠依据。     

谈垃圾填埋场勘察过程中水文地质试验

在生活垃圾卫生填埋场勘察过程中,往往要辅以水文地质调查与测试工作,主要手段为抽水试验(抽水、提水)、渗水试验、压水试验、地下水流速及流向测定等。以期达到明确查明场地开挖深度范围内目标含水层的渗透性,地下水的运移规律,为设计方提供准确的水文地质参数。对垃圾填埋场后期的使用、污染物的处理及对环境的影响尤为重要。     

某垃圾发电厂地下水污染模拟研究

垃圾焚烧发电是提高城市生活垃圾处理技术的有效举措。本文以芜湖某垃圾发电厂为对象,基于现场水文地质条件和GMS(Groundwater Modeling System)软件分别建立了地质结构模型、地下水流概念模型和数值模型以及溶质运移数值模型,模拟了不同类型污染物的污染路径和污染羽迁移状况,分析了污染对地下水环境可能造成的影响。结论可知:污染物在含水层中会沿地下水流方向呈近似椭圆形状运移,且在水流的反方向亦有运移;同一模拟时段内,COD和氨氮会随时间在局部造成一定程度的污染,但是污染物的垂向迁移距离均未到达细砂含水层,所有污染物在模拟时段内均未抵达长江,故不会影响长江水质。     

迁移机理下污染物场地隔离屏障的设计研究

重点对迁移机理下污染物填埋场地天然粘土隔离屏障的厚度设计展开研究.运用溶质在饱和土中迁移的一维平流-弥散运移模型,根据影响污染物迁移的基本参数(弥散系数、阻滞因子等),对饱和土隔离屏障建立一套估算污染物击穿屏障的时间、对指定的击穿浓度和设计寿命确定屏障厚度的设计分析方法,绘制了一些便于工程应用的设计图表,分析了扩散系数...     

重金属离子和LNAPLs在非饱和土中的运移规律研究

以重金属和轻非水相流体(LNAPLs)为例,介绍了清华大学开展非饱和土中污染物运移规律研究的部分工作成果。利用土工离心机对污染物的运移过程模拟,取样得到污染物的浓度分布特征。同时采用数值分析手段对污染物的长期运移规律和其影响因素进行分析。研究表明:离心模型试验可以有效模拟污染物的运移过程,离心模型试验和数值分析相结合,是研究污染物在非饱和土中运移规律的有效手段。     

Modelling migration of contaminants from waste disposal facility

Waste disposal facility design must involve some form of barrier that separates the waste from the groundwater system located below it. This barrier is intended to minimize the migration of contaminants from the waste facility. Natural clay deposits and compacted clay liners of a certain minimum thickness are often used to prevent leachate from flowing down towards groundwater. The finite difference numerical model developed in this study is validated for two case studies. Subsequently, a study was conducted by taking the finite mass of a leachate at the top of the liner; the variation of the maximum concentration of the pollutant in the liner is then determined. From the concentration profiles generated, the optimum clay barrier thickness required to prevent migration of contaminants to the aquifer located below can also be determined.     

Assessment of consolidation-induced VOC transport for a GML/GCL/CCL composite liner system

In municipal solid waste landfills, a triple-layer composite liner consisting of a geomembrane liner (GML), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) is commonly used at the landfill bottom to isolate the leachates from surrounding environment. This paper presents a numerical investigation of the effect of liner consolidation on the transport of a volatile organic compound (VOC), trichloroethylene (TCE), through the GML/GCL/CCL composite liner system. The numerical simulations were performed using the model CST3, which is a piecewise linear numerical model for coupled consolidation and solute transport in multi-layered soil media and has been extensively validated using analytical solutions, numerical solutions and experimental results. The performed numerical simulations considered coupled consolidation and contaminant transport with representative geometry, material properties, and applied stress conditions for a GML/GCL/CCL liner system. The simulation results indicate that, depending on conditions, consolidation of the GCL and CCL can have significant impact on the transport results of TCE (i.e., TCE mass flux, cumulative TCE mass outflow, and distribution of TCE concentration within the GCL and CCL), both during the consolidation process and long after the completion of consolidation. The traditional approach for the assessment of liner performance neglects consolidation of the GCL and CCL and fails to consider the consolidation-induced transient advection and concurrent changes in material properties and, therefore, can lead to significantly different results. These differences for with and without the consolidation effects can range over several orders of magnitude. The process of consolidation-induced contaminant transport is complex and involves many variables, and therefore case-specific analysis is necessary to assess the significance of liner consolidation on VOC transport through a GML/GCL/CCL composite liner system.     

Seismic performance and numerical simulation of earth-fill dam with geosynthetic clay liner in shaking table test

In this paper, shaking table tests were carried out on both a small-scale and a full-scale earth-fill dams with geosynthetic clay liners to examine their seismic performance. The behavior of these fully instrumented earth-fill dams when subjected to seismic loading was also simulated by numerical analysis. Firstly, in the small-scale shaking table test, no failure was observed along the geosynthetic clay liner when the earth-fill dam was subjected to seismic motion. Numerical analysis confirmed that the behavior of the model earth-fill dam was unaffected by the geosynthetic clay liner. Secondly, a comparative shaking table test was carried out on full-scale earth-fill dams, one with a sloping core zone and another with a geosynthetic clay liner. Both model dams showed similar acceleration response and deformation behavior. It should be mentioned that the acceleration response increased gradually toward the top of the dam, and the deformation, after shaking, was relatively large near the foot of the slope. These observations were successfully simulated by the numerical analysis.     

地下水位变化的数值模拟新方法

 尽管地下水数值计算技术和计算方法发展很快,地下水数值模拟仍然存在着大量的理论问题和实际问题需要研究解决,仍有很多局限性,由此可知,地下水模拟过程中充满了各种各样的不确定因素。如何利用和改进现有技术,减少模型的不确定性,提高数值模拟过程的有效性和预测结果的可靠性,是该研究领域具有挑战性的问题之一。在传统地下水数值模拟的基础上,提出一种预测地下水位变化的新的方法。该方法可以在拥有较少现场资料的情况下,对地下水水位的变化直接进行的预测。本研究的创新点在于减少模拟过程及模型校正过程中对输入数据的需求,简化边界条件;同时引入反复迭代方法求解控制方程,减少计算误差。该研究成果应用到实践中去,可以大大提高对地下水位的预测能力,此项研究及其成果将对水资源管理产生重大影响,对岩土工程设计及施工提供指导。     

Analytical model for coupled consolidation and diffusion of organic contaminant transport in triple landfill liners

A triple-layer composite liner consisting of a geomembrane liner (GMB), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) is commonly used at the landfill bottom liner system to isolate the contaminated leachates. In this paper, one-dimensional quasi-steady-state small deformation model (SDSS) was developed to investigate the behavior of organic chemicals transport in landfill composite liner system considering coupled effect of consolidation, diffusion and degradation. The first and second type bottom boundary conditions are used to derive the analytical solutions. The generalized integral transform technique (GITT) is adopted to derive the analytical solutions. The effect of consolidation on the performance of GMB/GCL/CCL with intact or leaking GMB is investigated. The triple liner under double drainage boundary condition (DDBC) has better performance compared to the case under single drainage boundary condition (SDBC). This is because the velocity induced by consolidation under DDBC is lower than that under SDBC. The effect of GCL consolidation shows an opposite trend compared to CCL consolidation. Considering GCL consolidation can increase the breakthrough time. The effective diffusion coefficient of GCL can be two magnitude orders smaller after consolidation, which provides a better diffusion barrier for the chemical transport. The effects of adsorption and degradation have been analyzed as well. Increasing the adsorption capacity of a deforming composite liner can increase the steady-state bottom flux, which shows the opposite tendency compared to the case without considering consolidation. This is due to the fact that for the case of a deforming composite liner, the advection induced by consolidation includes a new term due to the solid velocity. This velocity will result in the increase the mass of chemical migration through the composite liner.     

Influence of Geogrid Layer on the Integrity of Compacted Clay Liners of Landfills

The objective of this paper is to examine the influence of geogrid layer on the integrity of clay liners of landfills. A series of centrifuge model tests were performed on model clay liners subjected to non-uniform settlements with and without a geogrid layer embedded within the top one-third portion of the clay liner moist-compacted on the wet side of its optimum moisture content at 40 g. The model clay liner material has been selected in such a way that it envelopes the material characteristics of the clay liners, which are used for constructing an impermeable barrier in a lining system. By maintaining type and location of the geogrid within the clay liner as constant, the thickness of clay liner is varied to check the possibility of reducing the thickness of a geogrid reinforced clay liner. Digital image analysis technique was employed to ascertain the initiation of cracking and to compute strains both on the surface and along the cross-section of the clay liner with and without any geogrid layer. It was observed that clay liners compacted at moulding water content towards wet side of their OMC found to experience multiple cracking at the onset of non-uniform settlements. Contrary to this, geogrid reinforced clay liner was observed to sustain large distortions and experience only tiny cracks limited up to a location of a geogrid. With an increase in thickness of the clay liner reinforced with a geogrid, geogrid reinforced compacted clay liner was observed to retain its integrity and restrains cracking completely.     

A multi-component statistic analysis for the influence of sediment/soil composition on the sorption of a nonionic surfactant (Triton X-100) onto natural sediments/soils

The contents of soil/sediment organic carbon and clay minerals (i.e. montmorillonite, kaolinite, illite, gibbsite and 1.4 nm minerals) for 21 natural soil/sediment samples and the sorption of Triton X-100 on these samples were determined. A multi-component statistic analysis was employed to investigate the importance of soil/sediment organic matters and clay minerals on their sorption of Triton X-100. The sorption power of soil/sediment composition for Triton X-100 conforms to an order of montmorillonite>organic carbon>illite>1.4 nm minerals (vermiculite+chlorite+1.4 nm intergrade mineral)>kaolinite. The sorption of Triton X-100 on a montmorillonite, a kaolinite and a humic acid were also investigated and consistent with the result of multi-component statistic analysis. It is clear that the sorption of Triton X-100 on soils or sediments is the combined contribution of soil/sediment organic matters and clay minerals, which depended on both the contents of soil/sediment organic matters and the types and contents of clay minerals. The important influence of illite on the sorption of nonionic surfactants onto soils/sediments is suggested and demonstrated in this paper. Surfactants for aquifer remediation application may be more efficient for the contaminated soils/sediments that contain little clay minerals with 2:1 structure because of the less sorption of nonionic surfactants on these soils/sediments.     

A comparative assessment of volatile organic compound (VOC) sorption to various types of potential GCL bentonites

The potential improvement in the sorption of volatile organic compounds (VOCs) to bentonite used in Geosynthetic Clay Liners (GCLs) is examined for mixtures of bentonite and several organoclays or activated carbon. Results of batch tests performed with dichloromethane (DCM), 1,2-dichloroethane (1,2-DCA), trichloroethylene (TCE), benzene and toluene are reported. It is shown that all organoclays could potentially increase VOC sorption to GCLs by several orders of magnitude but activated carbon generally appears to provide the most improvement for the samples tested. The engineering relevance of this potential improvement is assessed with respect to design of municipal solid waste landfill liner systems by performing contaminant transport modeling. It is shown that only slight changes in contaminant migration will occur, despite the large potential increases in GCL sorption. This suggests that increased costs associated with modifying GCLs may outweigh the benefit of such additives to GCLs for municipal solid waste landfill applications for the conditions examined herein.