Download or read book Comments on Pore Scale Visulization of Colloid Transport AndRetention in Partly Saturated Porous Media written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The recent study by Crist et al. (2004) attempted to provide pore scale insights into mechanisms responsible for controlling colloid transport in unsaturated porous media. However, because they relied on images obtained along surfaces that were open to the atmosphere, artificial evaporation resulted in 2 more critical artifacts; formation of air-water-solid (AWS) contact lines, and advection/deposition of colloids to AWS contact lines. These evaporation-related artifacts need to be addressed because they account for most of the colloid deposition at AWS contact lines reported in Crist et al. (2004) ... As stated in Crist el al. (2004), '' ... the front panel was removed to avoid light reflections that obscured the view and, thus, exposed one side of the sand column to air''. Although a more recent paper (Crist et al., 2005) also presents results using the same methods and is therefore also affected by evaporation, we will restrict our present comments to Crist et al. (2004). Here, we show that removal of the front panel results in a sequence of three critical artifacts; (1) significant evaporation, (2) drying of thin films and formation of air-water-solid (AWS) contact lines, and (3) advection of colloids to AWS contact lines where they are deposited. As explained below, these artifacts so drastically disturbed their system that the magnitude of their observations are not likely to occur anywhere except within the most superficial few cm of soils. Before explaining these artifacts, we note that although trapping of colloids at AWS contact lines reported in Crist et al. (2004) is largely an artifact of evaporation, colloid filtration within perimeters of pendular rings is in fact a main prediction of the film straining model (Wan and Tokunaga, 1997). In that model, colloid filtration is predicted to be more efficient below a critical water saturation, when capillary connections between pendular rings become separated by adsorbed water films. In that paper we stated that ''Retardation of ideal, nonsorbing colloids can occur at two locations: trapped within individual pendular rings due to exclusion from entry into surrounding thin films and within film ... '' (Wan and Tokunaga, 1997). Thus, while Crist et al. (2004) implied that the film straining model applies only to retardation of colloid transport within thin films, colloid retention within perimeters of pendular rings is a main feature of our model.

Download or read book Three dimensional Pore scale Visualization and Trajectory Analysis of Colloid Transport and Retention in Saturated Porous Media written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The research contained in this thesis investigates the transport and deposition behavior of 1.1 and 3ìm carboxylate-modified microspheres in saturated porous media under unfavorable deposition conditions. Colloid motion and deposition patterns are visualized in three dimensions using a high-speed confocal microscope and micromodels packed with glass beads or sand grains. This study specifically focuses on colloid behavior in the grain-to-grain contact region, which has been suggested in previous studies as an important location for colloid retention under unfavorable conditions. The use of the high resolution confocal microscope allowed the distinction of two types of colloidal retention that can occur in the grain-to-grain contact region and showed that single surface retention was much more abundant than retention on two surfaces (straining). This study also demonstrated that both the extent and rate of straining are enhanced by increasing flow rate. In addition to obtaining qualitative descriptions of colloid deposition patterns, this study is the first to provide quantitative analysis of the motion of individual colloidal particles leading to the construction of three-dimensional colloid trajectory in both the bulk phase and grain-to-grain contact regions. The results demonstrated the dominant effects of hydrodynamics on colloid motions, i.e., most colloids entering the grain-to-grain contact region tend to follow the streamlines to detour the contact point, making straining a transport-limited process. Retention in the secondary energy minimum can significantly retard colloid movement but this association was not strong enough to keep the retained colloid inside the energy well over time. Colloid retention and movement through sand-packed sand micromodels were more complex compared to those packed with glass beads due to the more complex hydrodynamic conditions resulting from the irregular packing geometry and surface roughness of sand. These results suggest that theoretical torque analysis based on the idealized scenarios is not a suitable approach for describing colloid transport and deposition under unfavorable conditions in complex natural porous media.

Download or read book Colloidal Transport in Porous Media written by Fritz H. Frimmel and published by Springer Science & Business Media. This book was released on 2007-05-26 with total page 294 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers the basics of abiotic colloid characterization, of biocolloids and biofilms, the resulting transport phenomena and their engineering aspects. The contributors comprise an international group of leading specialists devoted to colloidal sciences. The contributions include theoretical considerations, results from model experiments, and field studies. The information provided here will benefit students and scientists interested in the analytical, chemical, microbiological, geological and hydrological aspects of material transport in aquatic systems and soils.

Download or read book Pore scale Characterization of Colloid Transport in the Unsaturated Zone written by John T. Crist and published by . This book was released on 2002 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Nuclear Power written by Wael Ahmed and published by BoD – Books on Demand. This book was released on 2012-10-10 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt: The serious challenge facing the world today, in obtaining enough energy for growing population and in controlling the carbon emission caused by fossil fuel use, calls for nuclear energy as an alternative power source. This book presents research work and technical experience from several power plants and research institutions around the world from practical prospective. This book intends to provide useful information for scientists and those in technical fields in several areas in nuclear power plants including: nuclear systems protection, design and modelling of critical parameters in nuclear power plants, thermalhydraulic analysis, nuclear waste management and safety and reliability assessment.

Download or read book Distribution of Colloid Particles Onto Interfaces in Unsaturated Porous Media written by Yuniati Zevi and published by . This book was released on 2004 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Pore scale Investigation on Mechanisms of Colloid Retention in Unsaturated Porous Media written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloid-facilitated transport of contaminants and transport of biocolloids (e.g., viruses and bacteria) in soil porous media are acknowledged environmental issues. Understanding of the mechanisms and parameters controlling colloid transport is important for protection of soil and groundwater resources from bio- and chemical contamination and improvement of remediation practices. For research purposes, unsaturated soil is often represented with idealized porous media, which facilitates conceptual understanding of colloid transport and retention mechanisms. Major colloid retention mechanisms include retention at solid-water interface (SWI), at air-water interface (AWI), and on the contact line. Additional colloid retention occurs as a result of straining in the narrow, compared to colloid size, regions of porous media. Colloid retention at AWI and colloid retention on the contact line are characteristic of unsaturated porous media and are currently associated with substantial uncertainty in colloid transport literature regarding their respective roles and contributions to overall colloid retention. In order to distinguish colloid retention mechanisms, traditional laboratory column experiments often require supplementary pore-scale investigation. The focus of this research was to investigate colloid retention at AWI and contact line at the pore scale. In this work, open capillary channels and microfluidic channels were utilized as models of soil capillaries, and behavior of colloids was visualized directly with confocal microscope. The employed channels have angular cross sections, which is in agreement with a more realistic angular representation of soil capillaries. The open-channel configuration served as a model of free-surface flow in microscopic grooves and corners in soil while the microfluidic channels were used to represent two-phase (air-water) flow in soil such as during drainage and infiltration events. To acquire qualitative and quantitative information, experimental confocal images were recorded and systematically processed with advanced imaging software. Colloid behavior in open channels with square cross section was investigated both in static and dynamic regimes. During flow in the channel, colloid movement occurred along the contact line, which acted as a colloid accumulation site due to reduced velocities in the contact line region. For this channel configuration, flow stagnation at AWI was observed, which promoted colloid retention at AWI. The maximum velocity and therefore maximum colloid transport were observed inside the channel. These observations indicated the importance of hydrodynamic conditions in affecting colloid retention. In the static regime, effects of a number of physicochemical parameters on colloid retention at AWI, including ionic strength, colloid contact angle, and surface tension (addition of surfactant), were investigated. It was shown that retention of colloids at AWI was dependent on electrostatic conditions and colloid contact angle and varied to a lesser extent with addition of non-ionic surfactant. The retention of colloids at AWI in a static system was analyzed with extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and was attributed to a possible secondary energy minimum retention. In microfluidic channels, which have a trapezoid cross section, AWI was observed as a two-phase boundary. In such configuration, both AWI and contact line move in the flow direction. It was shown that colloid retention on the contact line was considerably affected by hydrodynamic conditions. Colloid retention at AWI occurred primarily via involvement of colloids, which were previously deposited on the wall, with the moving contact line. Direct retention of dispersed colloids at AWI was not observed. The moving AWI was realized both as receding (air) and advancing (water) fronts, which allowed examination of the role that AWI played in colloid mobilization under both drainage and infiltration scenarios. Experimental results were considered in view of colloid interaction energies as well as forces acting on colloids at the sites of interest. Both experimental and theoretical findings resulted in improved understanding of colloid retention at AWI and contact line in the considered configurations, i.e., open channel and two-phase flows. The results of this research provide mechanistic understanding of colloid retention and can be applied in interpretation of observations at larger scales and in modeling of colloid transport in unsaturated porous media. This dissertation is accompanied with supplementary material showing representative video images and illustrating the discussed processes. System requirements for viewing the video: Windows Media Player or RealPlayer.

Download or read book Colloid Transport in Porous Media written by Jennifer Smith and published by . This book was released on 2006 with total page 136 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book New Trends in Emerging Environmental Contaminants written by Swatantra P. Singh and published by Springer Nature. This book was released on 2021-12-12 with total page 623 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book is based on recent trends for the research in emerging environmental contaminants in different compartment of the environment. It provides a recent understanding for the fate, transport, and degradation of emerging contaminants in different environmental sectors, including water, air, and soil. The contents discuss the fate and transport of microplastics, PPCPs, along with the method of detection and degradation. It includes removal of variety of pollutants including microplastics, pharmaceuticals, and personal care products from the water using adsorption technique, electrooxidation, membrane technology and other advance oxidation methods. This volume will be of great value to those in academia and industry involved in environmental science and engineering research.

Download or read book Unsaturated zone Modeling written by R.A. Feddes and published by Springer Science & Business Media. This book was released on 2004-10-11 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mankind has manipulated the quantity and quality of soil water for millennia. Food production was massively increased through fertilization, irrigation and drainage. But malpractice also caused degradation of immense areas of once fertile land, rendering it totally unproductive for many generations. In populated areas, the pollutant load ever more often exceeds the soil’s capacity for buffering and retention, and large volumes of potable groundwater have been polluted or are threatened to be polluted in the foreseeable future. In the past decades, the role of soil water in climate patterns has been recognized but not yet fully understood. The soil-science community responded to this diversity of issues by developing numerical models to simulate the behavior of water and solutes in soils. These models helped improve our understanding of unsaturated-zone processes and develop sustainable land-management practices. Aimed at professional soil scientists, soil-water modelers, irrigation engineers etc., this book discusses our progress in soil-water modeling. Top scientists present case studies, overviews and analyses of strengths, weaknesses, opportunities and threats related to soil-water modeling. The contributions cover a wide range of spatial scales, and discuss fundamental aspects of unsaturated-zone modeling as well as issues related to the application of models to real-world problems.

Download or read book Encyclopedia of Agrophysics written by Jan Gliński and published by Springer Science & Business Media. This book was released on 2011-06-07 with total page 1075 pages. Available in PDF, EPUB and Kindle. Book excerpt: This Encyclopedia of Agrophysics will provide up-to-date information on the physical properties and processes affecting the quality of the environment and plant production. It will be a "first-up" volume which will nicely complement the recently published Encyclopedia of Soil Science, (November 2007) which was published in the same series. In a single authoritative volume a collection of about 250 informative articles and ca 400 glossary terms covering all aspects of agrophysics will be presented. The authors will be renowned specialists in various aspects in agrophysics from a wide variety of countries. Agrophysics is important both for research and practical use not only in agriculture, but also in areas like environmental science, land reclamation, food processing etc. Agrophysics is a relatively new interdisciplinary field closely related to Agrochemistry, Agrobiology, Agroclimatology and Agroecology. Nowadays it has been fully accepted as an agricultural and environmental discipline. As such this Encyclopedia volume will be an indispensable working tool for scientists and practitioners from different disciplines, like agriculture, soil science, geosciences, environmental science, geography, and engineering.

Download or read book Computational Fluid Flow and Transport of Colloidal Particles in Soil Pores written by Mehmet Ekrem Cakmak and published by . This book was released on 2011 with total page 144 pages. Available in PDF, EPUB and Kindle. Book excerpt: Transport of colloidal size particulate matter is of special interest of environmental studies because colloids and adsorbed chemicals can be transported over long distances. Colloid facilitated transport can pose potentially high risk for pollution of ground water. Visualizations of colloid transport using bright field and confocal microscopes have discovered interesting phenomena such colloids moving in circles that cannot be described by the traditional Darcy scale models. That is why computational pore scale models are needed to better understand colloid transport and fate in porous media. Transport and fate of colloids depend largely on flow field in the pores and it is, therefore, important to simulate the flow field while taking grain surface properties into account. The aim of this dissertation is hence to determine the flow fields in realistic pores by solving the incompressible Navier-Stokes equation with a powerful commercial available finite element program COMSOL Multiphysics. The dissertation has five chapters. In the first chapter a short introduction is given. In the second chapter the COMSOL Multiphysics program is tested by revisiting the classical colloid filtration theory on colloid retention on a spherical sand grain. Retention of colloids on grains simulated with COMSOL is found to be similar to semi-analytical solutions previously published. Subsequently colloid retention on an air bubble is simulated and greater colloid retention is calculated than on a soil grain due to the slip boundary condition at the Air-Water interface which creates higher velocities and more fluid flow around air bubble resulting in greater amounts of colloids that can diffuse to the interface. In the third chapter the effect of surface roughness on hydrodynamics of colloid transport in a saturated porous media is investigated by simulating the flow fields around perfectly smooth, smoothed, and naturally rough sand grains. The results show that micron scale surface asperities of rough grains create greater vorticity and more stagnant flow regions compared to smooth grains likely resulting in greater colloid retention for the rough grains. In the fourth chapter the dependence of dynamic contact angle between the interface of two immiscible fluids and solid surface on the interface velocity is simulated in an empty capillary channel to provide a new understanding on the formation of unstable wetting fronts in coarse or water repellent soils. The results show an increase in contact angle when the velocity of the front increases, which is consistent with experimental studies in the literature. In the fifth chapter the problems encountered during the research and future directions are briefly explained.

Download or read book Transport and Retention of Colloidal Particles in Partially Saturated Pores written by Yuniati Zevi and published by . This book was released on 2008 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Grain Surface roughness Effects on Colloidal Retention in the Vadose Zone written by Veronica L. Morales and published by . This book was released on 2008 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Treatise on Water Science written by and published by Newnes. This book was released on 2010-09-01 with total page 2131 pages. Available in PDF, EPUB and Kindle. Book excerpt: Water quality and management are of great significance globally, as the demand for clean, potable water far exceeds the availability. Water science research brings together the natural and applied sciences, engineering, chemistry, law and policy, and economics, and the Treatise on Water Science seeks to unite these areas through contributions from a global team of author-experts. The 4-volume set examines topics in depth, with an emphasis on innovative research and technologies for those working in applied areas. Published in partnership with and endorsed by the International Water Association (IWA), demonstrating the authority of the content Editor-in-Chief Peter Wilderer, a Stockholm Water Prize recipient, has assembled a world-class team of volume editors and contributing authors Topics related to water resource management, water quality and supply, and handling of wastewater are treated in depth

Download or read book Australian Journal of Soil Research written by and published by . This book was released on 2005 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Bio colloidal Transfer in Saturated and Unsaturated Porous Media written by Hongjuan Bai and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The investigation of the transport and retention of bacteria in porous media has a great practical importance in environmental applications, such as protection of the surface and groundwater supplies from contamination, risk assessment from microorganisms in groundwater, and soil bioremediation. The aim of this study is to gain a fundamental understanding of the mechanisms that control bacteria transport and deposition in saturated and unsaturated porous media. Laboratory tracer and bacteria transport experiments at Darcy scale were performed in three porous media with distinct pore size distribution in order to investigate and quantify water and bacteria transport process under steady state flow conditions. A conservative solute was used as water tracer to characterize water flow pathways through porous media. A gram negative, motile Escherichia coli, a gram negative, non-motile Klebsiella sp. and a gram positive, non-motile R. rhodochrous were selected for the transport experiments. Characterization of cell properties (such as cell size and shape, zeta potential, motility and hydrophobicity) was performed for each strain. Numerical simulations with HYDRUS-1D code were performed to characterize water flow and to estimate bacteria transport and deposition parameters. The later were explored to identify bacteria flow patterns and physicochemical or physical mechanisms involved in bacteria deposition. To provide a better understanding of the mechanisms involved on bacteria transport and deposition, pore scale experiments were carried out by using microfluidic devices, designed for this purpose. The information obtained from laboratory experiments and numerical modeling was improved by theoretical calculation of different interactions between bacteria and porous media at air/water/solid interfaces. DLVO and non-DLVO interactions such as hydrophobic, steric, capillary and hydrodynamic forces involved in bacteria deposition were considered to describe bacteria-interface interactions in order to identify their relative impact on physicochemical and physical deposition of bacteria. Results obtained through both laboratory experiments and numerical simulationsoutlined non-uniform flow pathways, which were dependent on both grain/pore size as well as pore size distribution of the porous media. For a given porous medium, water flow patterns became more non-uniform and dispersive with decreasing water saturation due to the presence of air phase, which lead to an increase of the tortuosity of the flow pathways under unsaturated conditions. Bacteria transport pathways were different from the tracer transport, due to size exclusion of bacteria from smaller pore spaces and bacteria motility. Bacteria deposition was greatly influenced by pore network geometry, cell properties and water saturation degree. Both physical straining and physicochemical attachment should be taken into account to well describe bacteria deposition, but their importance on bacteria deposition is closely linked to porous media and cell properties. The results obtained in this work highlighted the simultaneous role of cell properties, pore size distribution and hydrodynamics of the porous media on bacteria transport and deposition mechanisms. The calculation of DLVO and non-DLVO interactions showed that bacteria deposition in saturated and unsaturated porous media was influenced by both kinds of interactions.