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1.
Dong Ding 《Hydrogeology Journal》2010,18(3):669-679
A mathematical model based on the advection-dispersion equation, modified to account for growth, decay, attachment, and detachment of microorganisms, was developed to describe the transport and growth of bacteria in aquifers. Column experiments on the transport of a species of sulfate-reducing bacteria through saturated-aquifer sediment were conducted to gain a quantitative knowledge of the attachment and detachment processes. Relevant parameter values such as the attachment-site capacity of the sediment and the attachment and detachment coefficients under different conditions, were obtained by fitting the experimental data with the non-growth condition transport model. The transport model was then refined and improved to incorporate the microbial sulfate reduction mechanism. To evaluate the applicability of this model, bacterial transport in aquifers under both nutrient-rich and oligotrophic environments was modeled by employing the parameters gained from experiments and from available literature; the model results were consistent with observations reported in former studies. In addition, the results revealed that the distribution of bacteria in the aqueous phase and in the sediments is directly related to the attachment-site capacity of the sediment. Thus, the attachment-site capacity of the sediment is a key factor to evaluate the transport and growth of bacteria in aquifers. 相似文献
2.
Serial data from soil–sawdust column experiments were used to develop a mathematical model to describe the biological sulfate
reduction processes in porous media. The mathematical model numerically solves the equation of solute transport in one-dimensional
saturated state. Solute transport is coupled to sulfate reducing bacteria sub model. Bacterial growth is assumed to follow
double Monod kinetic equation. Two bacterial groups (X1 and X2) were described. Bacterial group X1 uses under aerobic conditions
oxygen and under anaerobic conditions nitrate as electron acceptor. Under anaerobic conditions bacterial groups X2, use sulfate
as an electron acceptor. Sulfate rich wastewater is usually deficient in electron donor and requires external addition of
electron donors in order to achieve complete sulfate reduction. The organic carbon as electron donor is one of the most important
factors that affect sulfate reduction bacterial activity. In this study the possible source of organic carbon is the solid
organic carbon supplied to the system in the form of sawdust. The results of this study indicate that sawdust could be employed
as low-cost materials to enhance the biological sulfate reduction processes in porous media. While the availability of organic
carbon as electron donor is one of the most important factors that affect the sulfate reducing bacterial activity in porous
media, this study demonstrates that using sawdust as a carbon source can improve the bacterial activity and increase the column
permeability. 相似文献
3.
Understanding particle transport in porous media is critical in the sustainability of many geotechnical and geoenvironmental infrastructure. To date, the determination of the first-order rate coefficients in the advection–dispersion equation for simulating attachment and detachment of particles in saturated porous media typically has been relied on the result of laboratory-scale experiments. However, to determine attachment and detachment coefficients under varied hydraulic and geochemical variables, this method requires a large experimental matrix because each test provides only one set of attachment and detachment coefficients. The work performed in this study developed a framework to upscale the results obtained in pore-scale modeling to the continuum scale through the use of a pore network model. The developed pore network model incorporated variables of mean particle size, the standard deviation of particle size distribution, and interparticle forces between particles and sand grains. The obtained retention profiles using the pore network model were converted into attachment coefficients in the advection–dispersion equation for long-term and large-scale simulation. Additionally, by tracking individual particles during and after the simulation, the pore network model introduced in this study can also be employed for modeling the clogging phenomenon, as well as fundamental investigation of the impact of particle size distribution on particle retention in the sand medium.
相似文献4.
Transport and retention of microparticles in packed sand columns at low and intermediate ionic strengths: experiments and mathematical modeling 总被引：1，自引：1，他引：0
Functional relationships correlating particle filtration coefficients and porewater ionic strength are herein proposed and
validated, based on deposition experiments of micrometer-sized particles onto siliceous sand. Experiments were conducted using
one-dimensional laboratory columns and stable monodisperse aqueous suspensions of negatively charged latex particles with
a mean size of 1.90 μm. The role of ionic strength was systematically investigated and six different monovalent salt concentrations
(1, 3, 10, 30, 100, 300 mM) were employed by addition of sodium chloride to the aqueous solution. A mathematical advection–dispersion-deposition
transport model was adopted assuming that attachment and detachment of particles in the porous medium are concurrent mechanisms
of particle filtration, and including a Langmuir-type blocking function to account for availability in deposition sites. The
system of equations modeling colloid transport was solved numerically. Attachment rate and detachment rate coefficients were
thereby determined for each employed ionic strength, as well as a blocking coefficient in the form of a maximum particle concentration
in the solid phase. Therefore, functional relationships expressing the dependence of these coefficients on ionic strength
were proposed, based on literature findings and present experimental observations. The existence of a critical salt deposition
concentration (and release concentration) separating a favorable attachment (and detachment) regime from an unfavorable condition
is assumed. In respect to the blocking coefficient, a power–law dependence on ionic strength is hypothesized. The proposed
functional relationships proved adequate to reproduce the coefficient trends extrapolated from data fitting by the transport
model. They may represent a powerful tool to describe and predict microparticle mobility in saturated porous media if embedded
a priori in the related mathematical transport models. 相似文献
5.
Retention of surface-modified nanoscale zero-valent iron (NZVI) particles in the porous media near the point of injection has been reported in the recent studies. Retention of excess particles in porous media can alter the media properties. The main objectives of this study are, therefore, to evaluate the effect of particle retention on the porous media properties and its implication on further NZVI particle transport under different flow conditions. To achieve the objectives, a one-dimensional transport model is developed by considering particle deposition, detachment, and straining mechanisms along with the effect of changes in porosity resulting from retention of NZVI particles. Two different flow conditions are considered for simulations. The first is a constant Darcy’s flow rate condition, which assumes a change in porosity, causes a change in pore water velocity and the second, is a constant head condition, which assumes the change in porosity, influence the permeability and hydraulic conductivity (thus Darcy’s flow rate). Overall a rapid decrease in porosity was observed as a result of high particle retention near the injection points resulting in a spatial distribution of deposition rate coefficient. In the case of constant head condition, the spatial distribution of Darcy’s velocities is predicted due to variation in porosity and hydraulic conductivity. The simulation results are compared with the data reported from the field studies; which suggests straining is likely to happen in the real field condition. 相似文献
6.
退化喀斯特植被恢复过程中土壤生态肥力质量评价——以贵州花江喀斯特峡谷地区为例 总被引：2，自引：0，他引：2
应用多元统计分析方法,建立能够揭示退化喀斯特植被恢复对土壤微生态影响效果的生物学指标评价体系.研究结果表明:细菌、真菌、放线菌、微生物总数等微生物活性指标在评价土壤生物学肥力质量时具有十分重要的作用;氨化细菌数量、微生物熵、代谢熵等微生物活性指标在土壤生物学肥力评价中也具有一定的作用,但对土壤肥力质量评价的影响较小.利用土壤综合肥力指标值综合评价结果表明,不同退化喀斯特植被恢复阶段土壤生物学肥力具有明显的垂直变化特征,均表现A层>B层的特点,这说明各恢复阶段的土壤生物学肥力具有随土壤层次加深而下降的变化趋势.同时,从裸地阶段→草本群落阶段→灌木群落阶段一乔木群落阶段,由于土壤物质循环逐渐加快,微生物活性逐渐增强,土壤生物学肥力逐步提高. 相似文献
7.
Microbial enhanced oil recovery (MEOR) utilizes microbes for enhancing the recovery by several mechanisms, among which the most studied are the following: (1) reduction of oil-water interfacial tension (IFT) by the produced biosurfactant and (2) selective plugging by microbes and metabolic products. One of the ways of bacterial survival and propagation under harsh reservoir conditions is formation of spores. A model has been developed that accounts for bacterial growth, substrate consumption, surfactant production, attachment/filtering out, sporulation, and reactivation. Application of spore-forming bacteria is an advantageous novelty of the present approach. The mathematical setup is a set of 1D transport equations involving reactions and attachment. Characteristic sigmoidal curves are used to describe sporulation and reactivation in response to substrate concentrations. The role of surfactant is modification of the relative permeabilities by decreasing the interfacial tension. Attachment of bacteria reduces the pore space available for flow, i.e., the effective porosity and permeability. Clogging of specific areas may occur. An extensive study of the MEOR on the basis of the developed model has resulted in the following conclusions. In order to obtain sufficient local concentrations of surfactant, substantial amounts of substrate should be supplied; however, massive growth of bacteria increases the risk for clogging at the well inlet areas, causing injectivity loss. In such areas, starvation may cause sporulation, reducing the risk of clogging. Substrate released during sporulation can be utilized by attached vegetative bacteria and they will continue growing and producing surfactant, which prolongs the effect of the injected substrate. The simulation scenarios show that application of the spore-forming bacteria gives a higher total production of surfactant and the reduced risk of clogging, leading to an increased period of production and a higher oil recovery. 相似文献
8.
地下环境中可移动的胶体能够促进强烈吸附的污染物质的运移,而胶体自身在运移过程中也会伴随发生沉淀、释放。根据高岭石胶体的土柱出流实验,对不同离子强度条件下胶体在饱和多孔介质中的沉淀和释放行为进行分析,并采用不同模型对其过程进行数值模拟。结果表明,离子强度是影响胶体沉淀和释放过程的重要因素,随着离子强度的增加,胶体的出流峰值逐渐降低,即胶体在多孔介质中的沉淀量逐渐增大,且沉淀速率系数K d 与离子强度成正相关;模型拟合的释放系数与NaCl 浓度显著相关,Grolimund 模型可以很好地模拟胶体的沉淀过程（R 2 >0.95）,但不能准确地模拟释放过程;而胶体运移方程耦合溶质运移方程能够模拟不同离子强度影响下胶体的释放过程（R 2 >0.9） 相似文献
9.
The effect of distribution of iron-oxyhydroxide grain coatings on the transport of bacterial cells in porous media 总被引：3，自引：0，他引：3
E. P. Knapp Janet S. Herman George M. Hornberger Aaron L. Mills 《Environmental Geology》1998,33(4):243-248
Among the demonstrated processes influencing the transport of bacteria through aquifers, the deposition of cells on mineral
surfaces is one of the most important. For example, understanding the transport of introduced bacteria through aquifers is
essential to designing some in situ bioremediation schemes. The impact of the presence and distribution of Fe(III)-oxyhydroxide-coated
sand grains on bacterial transport through porous media was evaluated in column experiments in which bacteria (short rods;
1.2 μm length) were eluted through columns of quartz sand (0.5–0.6 mm in diameter) for several conditions of chemical heterogeneity
of mineral substrate. Fe(III)-oxyhydroxide-coated sand was present as 10% of the mass, and it was arranged in three treatments:
(1) homogeneously distributed, and present as a discrete layer (2) at the top and (3) at the bottom of 14-cm-long sand columns.
A pulse input of 108 cells ml–1 was introduced in an artificial groundwater solution flowing at 14 cm h–1 through the column, and eluted cells were counted. Peak breakthrough occurred at 1.0 pore volume. A large proportion of cells
were retained; 14.7–15.8% of the cells were recovered after three pore volumes of solution had eluted through clean quartz
sand, and only 2.1–4.0% were recovered from the Fe(III)-oxyhydroxide-coated sand mixtures. The three physical arrangements
of the chemical heterogeneity resulted in essentially the same breakthrough of cells, indicating that the spatial distribution
of iron coating does not affect the transport of bacteria. The results of the column transport experiments, which mimic hydrogeological
conditions encountered in field problems, are consistent with our mechanistic understanding of bacterial sorption.
Received: 10 April 1996 · Accepted: 17 February 1997 相似文献
10.
Hybrid analytical and finite element numerical modeling of mass and heat transport in fractured rocks with matrix diffusion 总被引：1，自引：0，他引：1
Christopher I. McDermott Robert Walsh Ralph Mettier Georg Kosakowski Olaf Kolditz 《Computational Geosciences》2009,13(3):349-361
Quantification of mass and heat transport in fractured porous rocks is important to areas such as contaminant transport, storage
and release in fractured rock aquifers, the migration and sorption of radioactive nuclides from waste depositories, and the
characterization of engineered heat exchangers in the context of enhanced geothermal systems. The large difference between
flow and transport characteristics in fractures and in the surrounding matrix rock means models of such systems are forced
to make a number of simplifications. Analytical approaches assume a homogeneous system, numerical approaches address the scale
at which a process is operating, but may lose individual important processes due to averaging considerations. Numerical stability
criteria limit the contrasts possible in defining material properties. Here, a hybrid analytical–numerical method for transport
modeling in fractured media is presented. This method combines a numerical model for flow and transport in a heterogeneous
fracture and an analytical solution for matrix diffusion. By linking the two types of model, the advantages of both methods
can be combined. The methodology as well as the mathematical background are developed, verified for simple geometries, and
applied to fractures representing experimental field conditions in the Grimsel rock laboratory. 相似文献
11.
Multi-component mineral precipitation in porous, subsurface environments is challenging to simulate or engineer when in situ reactant mixing is controlled by diffusion. In contrast to well-mixed systems, the conditions that favor mineral precipitation in porous media are distributed along chemical gradients, which evolve spatially due to concurrent mineral precipitation and modification of solute transport in the media. The resulting physical and chemical characteristics of a mixing/precipitation zone are a consequence of coupling between transport and chemical processes, and the distinctive properties of individual chemical systems. We examined the spatial distribution of precipitates formed in “double diffusion” columns for two chemical systems, calcium carbonate and calcium phosphate. Polyacrylamide hydrogel was used as a low permeability, high porosity medium to maximize diffusive mixing and minimize pressure- and density-driven flow between reactant solutions. In the calcium phosphate system, multiple, visually dense and narrow bands of precipitates were observed that were reminiscent of previously reported Liesegang patterns. In the calcium carbonate system, wider precipitation zones characterized by more sparse distributions of precipitates and a more open channel structure were observed. In both cases, formation of precipitates inhibited, but did not necessarily eliminate, continued transport and mixing of the reactants. A reactive transport model with fully implicit coupling between diffusion, chemical speciation and precipitation kinetics, but where explicit details of nucleation processes were neglected, was able to qualitatively simulate properties of the precipitation zones. The results help to illustrate how changes in the physical properties of a precipitation zone depend on coupling between diffusion-controlled reactant mixing and chemistry-specific details of precipitation kinetics. 相似文献
12.
A FEM model for analysis of fully coupled multiphase flow, thermal transport and stress/deformation in geological porous media was developed based on the momentum, mass and energy conservation laws of the continuum mechanics and the averaging approach of the mixture theory over a three phase (solid–liquid–gas) system. Six processes (i.e. stress–strain, water flow, gas flow, vapor flow, heat transport and porosity evolution processes) and their coupling effects are considered, which not only makes the problem well-defined, but renders the governing PDEs closed, complete, compact and compatible. Displacements, pore water pressure, pore gas pressure, pore vapor pressure, temperature and porosity are selected as basic unknowns. The physical phenomena such as phase transition, gas solubility in liquid, thermo-osmosis, moisture transfer and moisture swelling are modeled. As a result, the relative humidity and other related variables in porous media can be evaluated on a sounder physical basis. A three dimensional computer code, THYME3D, was developed, with eight degrees of freedom at each node. The laboratory CEA Mock-up test and the field scale FEBEX benchmark test on bentonite performance assessment for underground nuclear waste repositories were used to validate the numerical model and the software. The coupled THM behaviors of the bentonite barriers were satisfactorily simulated, and the effects and impacts of the governing equations, constitutive relations and property parameters on the coupled THM processes were understood in terms of more straightforward interpretation of physical processes at microscopic scale of the porous media. The work developed enables further in-depth research on fully coupled THM or THMC processes in porous media. 相似文献
13.
多孔介质渗透系数的空间尺度效应研究进展 总被引：6，自引：1，他引：5
多孔介质渗透系数的空间尺度问题是一个与地下流体运动和溶质运移的数值模拟密切相关的应用性课题,广泛的应用需求和新的计算方法使其成为近年的热门课题之一。它涉及到相互联系的两个方面：①非均质介质场渗透系数空间尺度行为的分析与模拟;②将局部测量尺度下的试验参数转化为数值模拟网格尺度下的参数输入值的升尺度（ｕｐｓｃａｌｉｎｇ）方法和计算模型。首先介绍了该课题在概念上的拓展及其物理含义,进而以方法为主线,对这一领域具有代表性的研究成果进行了分类和评述,讨论了该课题的研究对地下水流和溶质运移的模拟分析乃至整个多孔介质流体运动研究的意义。 相似文献
14.
The use of laboratory experiments for the study of conservative solute transport in heterogeneous porous media 总被引：4，自引：1，他引：3
Laboratory experiments on heterogeneous porous media (otherwise known as intermediate scale experiments, or ISEs) have been
increasingly relied upon by hydrogeologists for the study of saturated and unsaturated groundwater systems. Among the many
ongoing applications of ISEs is the study of fluid flow and the transport of conservative solutes in correlated permeability
fields. Recent advances in ISE design have provided the capability of creating correlated permeability fields in the laboratory.
This capability is important in the application of ISEs for the assessment of recent stochastic theories. In addition, pressure-transducer
technology and visualization methods have provided the potential for ISEs to be used in characterizing the spatial distributions
of both hydraulic head and local water velocity within correlated permeability fields. Finally, various methods are available
for characterizing temporal variations in the spatial distribution (and, thereby, the spatial moments) of solute concentrations
within ISEs. It is concluded, therefore, that recent developments in experimental techniques have provided an opportunity
to use ISEs as important tools in the continuing study of fluid flow and the transport of conservative solutes in heterogeneous,
saturated porous media.
Received, December 1996 · Revised, July 1997 · Accepted, August 1997 相似文献
15.
Pore-scale models are becoming increasingly useful as predictive tools for modeling flow and transport in porous media. These
models can accurately represent the 3D pore-structure of real media. Currently first-principles modeling methods are being
employed for obtaining qualitative and quantitative behavior. Generally, artificial, simple boundary conditions are imposed
on a model that is used as a stand-alone tool for extracting macroscopic parameters. However, realistic boundary conditions,
reflecting flow and transport in surrounding media, may be necessary for behavior that occurs over larger length scales or
including pore-scale models in a multiscale setting. Here, pore-scale network models are coupled to adjacent media (additional
pore-scale or continuum-scale models) using mortars. Mortars are 2D finite-element spaces employed to couple independent subdomains
by enforcing continuity of pressure and flux at shared boundary interfaces. While mortars have been used in the past to couple
subdomains of different models, physics, and meshes, they are extended here for the first time to pore-scale models. The approach
is demonstrated by modeling single-phase flow in coupled pore-scale models, but the methodology can be utilized to model dynamic
processes and perform multiscale modeling in 3D continuum simulators for flow and transport. 相似文献
16.
为了研究孔隙结构和水动力对悬浮颗粒在饱和多孔介质中沉积和迁移特性的影响,对天然硅粉（悬浮颗粒）和荧光素钠（示踪剂）在饱和多孔介质中的渗流迁移特性进行土柱试验,分别得到了5种不同渗流速度（0.033、0.066、0.132、0.199、0.265 cm/s）、两种不同多孔介质（石英砂和玻璃球）的悬浮颗粒和示踪剂全组合下的20条穿透曲线。根据试验结果,研究孔隙结构、渗流速度对饱和多孔介质中颗粒迁移和沉积过程中水动力作用机制、弥散效应、加速效应的影响。研究表明,悬浮颗粒的穿透曲线可以用一阶沉积动力学对流弥散方程的解析解来描述。随着渗流速度的增大,水动力学作用对颗粒出流浓度的影响越来越大,而孔隙结构的影响则相对减弱。同时,存在一个临界渗流速度值。当渗流速度超出该值时,悬浮颗粒迁移要快于示踪剂,而且临界渗流速度对于玻璃球和石英砂两种多孔介质是不同的;其次,在两种介质中,随渗流速度增大,弥散度增加,回收率和回收悬浮颗粒粒径增大,沉积系数先增大后减小。此外,在孔隙比相近的情况下,悬浮颗粒在玻璃球介质中的回收率要大于其在石英砂中的。可见,孔隙结构和渗流速度是影响饱和多孔介质中颗粒输运的重要因素,渗流速度越大,孔隙结构的作用越明显。 相似文献
17.
Steven L. Bryant 《Computational Geosciences》2001,5(3):203-223
We present an overview of several applications of reactive flow and transport in which interesting mathematical issues and computational challenges arise. The topics include front propagation through porous media in the presence of dispersion; numerical simulation of large-scale reactive transport problems; the reliability of processes that involve in-situ generation of viscosifying agents; methods for describing pore-scale geometry in granular media; and the information content of reactive tracer experiments. The intent of this survey is to heighten awareness of underlying mathmetical aspects and, it is hoped, to stimulate new contributions in these areas. 相似文献
18.
19.
High groundwater demand in the Great Metropolitan Area (GMA) of Costa Rica, combined with the presence of many septic systems, imposes the necessity to define adequate dimensions for setback distances or protection zones around wellheads to prevent contamination of aquifers by pathogenic organisms. Numerical 3-D simulations of transport of viruses under natural hydrogeological conditions of the northwest section of GMA were performed, considering both porous and fractured porous media with variable saturation. Based on the sensitivity analysis, principal transport parameters for the conditions in the study area are injection concentration, hydraulic conductivity, inactivation rate and attachment rate. Furthermore, a comparative analysis of the arrival of viruses to the water table and the modeling domain’s boundary was carried out using two approaches: maximum permissible concentration criteria and travel time criteria (TT) of 100 days frequently applied in Costa Rica for fractured rocks aquifers. The analysis indicates that under conditions of low mobility and high removal rates (typical for soils of volcanic origin), the TT approach overestimates the dimension of the protection zone. On the other hand, when conditions of high mobility and low removal rate are considered, the TT approach usually underestimates that dimension. It is recommended to perform more field and laboratory studies to obtain better representative parameters for soils of volcanic origin. 相似文献