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 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 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 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 Handbook of Soil Sciences Two Volume Set written by Pan Ming Huang and published by CRC Press. This book was released on 2018-10-03 with total page 2249 pages. Available in PDF, EPUB and Kindle. Book excerpt: An evolving, living organic/inorganic covering, soil is in dynamic equilibrium with the atmosphere above, the biosphere within, and the geology below. It acts as an anchor for roots, a purveyor of water and nutrients, a residence for a vast community of microorganisms and animals, a sanitizer of the environment, and a source of raw materials for co

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 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 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.

Download or read book Handbook of Surface and Colloid Chemistry written by K. S. Birdi and published by CRC Press. This book was released on 2008-11-20 with total page 772 pages. Available in PDF, EPUB and Kindle. Book excerpt: The third edition of this besteller covers the latest advancements in this rapidly growing field. Focusing on analyses and critical evaluation of the subject, this new edition reviews the most up-to-date research available in the current literature. International contributors offer their perspectives on various topics including micellar systems, mi

Download or read book Modelling of Pollutants in Complex Environmental Systems written by Grady Hanrahan and published by ILM Publications. This book was released on 2010 with total page 489 pages. Available in PDF, EPUB and Kindle. Book excerpt: Environmental modelling has enjoyed a long tradition, but there is a defined need to continually address both the power and the limitations of such models, as well as their quantitative assessment. This book showcases modern environmental modelling methods, the basic theory behind them and their incorporation into complex environmental investigations. It highlights advanced computing technologies and how they have led to unprecedented and adaptive modelling, simulation and decision-support tools to study complex environmental systems, and how they can be applied to current environmental concerns. This volume is essential reading for researchers in academia, industry and government-related bodies who have a vested interest in all aspects of environmental modelling. Features include: A range of modern environmental modelling techniques are described by experts from around the world, including the USA, Canada, Australia, Europe and Thailand; many examples from air, water, soil/sediment and biological matrices are covered in detail throughout the book; key chapters are included on modelling uncertainty and sensitivity analysis; and, a selection of figures are provided in full colour to enable greater comprehension of the topics discussed.

Download or read book Colloidal Transport in Porous Media written by Fritz H. Frimmel and published by Springer Verlag. This book was released on 2007-05-29 with total page 291 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloids are known to be the often neglected phase for the transport of pollutants in aquatic ecosystems. This book covers the basics of abiotic colloid characterization, of biocolloids and biofilms, the resulting transport phenomena and their engineering aspects. The contributors are leading specialists devoted to colloidal sciences. The discussion reflects their broad scope of viewpoint and depth of expertise. Coverage includes theoretical considerations, results from model experiments, and field studies.

Download or read book Colloid Facilitated Transport of Radionuclides Through the Vadose Zone written by John F. McCarthy and published by . This book was released on 2006 with total page 317 pages. Available in PDF, EPUB and Kindle. Book excerpt: The main purpose of this project was to advance the basic scientific understanding of colloid and colloid-facilitated Cs transport of radionuclides in the vadose zone. We focused our research on the hydrological and geochemical conditions beneath the leaking waste tanks at the USDOE Hanford reservation. Specific objectives were (1) to determine the lability and thermodynamic stability of colloidal materials, which form after reacting Hanford sediments with simulated Hanford Tank Waste, (2) to characterize the interactions between colloidal particles and contaminants, i.e., Cs and Eu, (3) to determine the potential of Hanford sediments for \textit{in situ} mobilization of colloids, (4) to evaluate colloid-facilitated radionuclide transport through sediments under unsaturated flow, (5) to implement colloid-facilitated contaminant transport mechanisms into a transport model, and (6) to improve conceptual characterization of colloid-contaminant-soil interactions and colloid-facili\-tated transport for clean-up procedures and long-term risk assessment. We have previously shown that upon contact with simulated waste tank solutions, Hanford sediments change their mineralogical composition. Certain minerals, i.e., quartz, smectite, and kaolinite, are partially dissolved, and new mineral phases, i.e., the feldspathoids cancrinite and sodalite, are formed. We have characterized these mineral transformations and clarified the mineral transformation pathways. The new minerals were mainly in the colloidal size fraction (diameter less than 2 mum), had a negative surface charge, and were microporous, meaning they contained small pores. When Cs was present during the formation of the minerals, contaminants, like Cs, could be trapped inside the mineral structure. Transport experiments under water saturated and unsaturated conditions showed that the colloids were mobile in Hanford sediments. As the water saturation of the sediments decreased, the amount of colloids transported also decreased. The colloids had the ability to enhance the migration of the radionuclide Cs; however, Cs initially sorbed to colloids was desorbed during transport through uncontaminated Hanford sediments. The finding that Cs was stripped off the colloids during the transport through uncontaminated sediments implies that colloids will likely not be an effective carrier for Cs, unless the Cs is incorporated into the mineral structure of the colloids such that the radionuclide cannot desorb from the colloids. Nevertheless, it appears that the amount of Cs that can be transported by mobile colloids beneath Hanford waste tanks is limited. Colloids will not be able to move the bulk mass of Cs through the vadose zone at Hanford. Colloid stability studies indicate that Hanford sediment form stable colloidal suspensions when suspended in Hanford sediment pore waters. Colloid stability was assessed by determination of the critical coagulation concentration, i.e., the chemical electrolyte concentration at which colloidal suspensions flocculate and settle out (become unstable). Although in the stable mode, Hanford colloids will settle out of solution after extended periods of time (months to years). Given the low recharge rates at Hanford range, which from near 0 to more than 100 mm/year, and the long travel times for rainwater to reach the groundwater of more than 40 years, it appears that colloidal transport is unlikely to occur if colloids are initially to be suspended close to the soil surface by infiltrating rainwater. However, if preferential flow or transient flow occurs, then colloidal transport may become more important. The results of this project have also led to improvements of our fundamental understanding of colloid transport and mobilization under unsaturated flow conditions in porous media. We have found that colloid attachment to the liquid-gas interface is not that relevant and that colloids rather attached near the triple phase interface where air, water, and solid phases meet. We have also found that capillary forces are the most dominant forces governing colloid release in unsaturated porous media. These results help to advance our understanding of colloid fate and transport in unsaturated porous media.

Download or read book Saturated Zone Colloid Transport written by H. S. Viswanathan and published by . This book was released on 2003 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt: Colloid retardation is influenced by the attachment and detachment of colloids from immobile surfaces. This analysis demonstrates the development of parameters necessary to estimate attachment and detachment of colloids and, hence, retardation in both fractured tuff and porous alluvium. Field and experimental data specific to fractured tuff are used for the analysis of colloid retardation in fractured tuff. Experimental data specific to colloid transport in alluvial material from Yucca Mountain as well as bacteriophage field studies in alluvial material, which are thought to be good analogs for colloid transport, are used to estimate attachment and detachment of colloids in the alluvial material. There are no alternative scientific approaches or technical methods for calculating these retardation factors.

Download or read book Site Characterization Progress Report written by and published by . This book was released on 1997 with total page 840 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book American Doctoral Dissertations written by and published by . This book was released on 2002 with total page 776 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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.