http://dspace.nitrkl.ac.in:8080/dspace/bitstream/2080/134/1/tksen5.pdf

Review on subsurface colloids and colloid-associated contaminant transport in saturated porous media.

The hazards associated with pathogens in land-applied animal and human wastes have long been recognized. Management of these risks requires an understanding of sources, concentrations, and removal by processes that may be used to treat the wastes; survival in the environment; and exposure to sensitive populations. The major sources are animal feeding operations, municipal wastewater treatment plant effluents, biosolids, and on-site treatment systems. More than 150 known enteric pathogens may be present in the untreated wastes, and one new enteric pathogen has been discovered every year over the past decade. There has been increasing demand that risks associated with the land treatment and application be better defined. For risks to be quantified, more data are needed on the concentrations of pathogens in wastes, the effectiveness of treatment processes, standardization of detection methodology, and better quantification of exposure.

/pdf/sources-of-pathogenic-microorganisms-and-their-fate-during-f8n8lsujzr.pdf

Sources of pathogenic microorganisms and their fate during land application of wastes.

Our ability to accurately simulate the transport and retention of colloids in the vadose zone is currently limited by our lack of basic understanding of colloid retention processes that occur at the pore scale. This review discusses our current knowledge of physical and chemical mechanisms, factors, and models of colloid transport and retention at the interface, collector, and pore scales. The interface scale is well suited for studying the interaction energy and hydrodynamic forces and torques that act on colloids near interfaces. Solid surface roughness is reported to have a significant influence on both adhesive and applied hydrodynamic forces and torques, whereas non-Derjaguin–Landau–Verwey–Overbeek (DLVO) forces such as hydrophobic and capillary forces are likely to play a significant role in colloid interactions with the air–water interface. The flow field can be solved and mass transfer processes can be quantified at the collector scale. Here the potential for colloid attachment in the presence of hydrodynamic forces is determined from a balance of applied and adhesive torques. The fraction of the collector surface that contributes to attachment has been demonstrated to depend on both physical and chemical conditions. Processes of colloid mass transfer and retention can also be calculated at the pore scale. Differences in collector- and pore-scale studies occur as a result of the presence of small pore spaces that are associated with multiple interfaces and zones of relative flow stagnation. Here a variety of straining processes may occur in saturated and unsaturated systems, as well as colloid size exclusion. Our current knowledge of straining processes is still incomplete, but recent research indicates a strong coupling of hydrodynamics, solution chemistry, and colloid concentration on these processes, as well as a dependency on the size of the colloid, the solid grain, and the water content.

/pdf/colloid-transport-and-retention-in-unsaturated-porous-media-50pnbjap46.pdf

Colloid Transport and Retention in Unsaturated Porous Media: A Review of Interface-, Collector-, and Pore-Scale Processes and Models

Modeling microbial transport in porous media: Traditional approaches and recent developments

This review quantitatively examines a number of published studies that evaluated survival and inactivation of public-health-related microorganisms in groundwater. Information from reviewed literature is used to express microbial inactivation in terms of log10 decline per day for comparison to other studies and organisms. The geometric mean value for inactivation rates for coliphage, poliovirus, echovirus, coliform bacteria, enterococci, and Salmonella spp. were similar at approximately 0.07−0.1 log10 day-1, while geometric mean inactivation rates for hepatitis A virus, coxsackievirus, and phage PRD-1 were somewhat less at 0.02−0.04 log10 day-1. Viruses show a temperature dependency with greater inactivation at greater temperatures; however this occurs largely at temperatures greater than 20 °C. Coliform bacteria dieoff in groundwater does not show the temperature dependency that viruses show, likely indicating a complex interplay of inactivation and reproduction subject to influences from native groundwat...

/pdf/review-of-factors-affecting-microbial-survival-in-emqkmjoi5c.pdf

Review of factors affecting microbial survival in groundwater.

Virus removal and transport in saturated and unsaturated sand columns

Previous studies suggest that sorption of colloidal particles onto the air-water interface is an important mechanism for enhanced retention and retardation during transport in unsaturated systems. In this study, bacteriophages fX174 and MS-2 and Br 2 tracer were introduced into sand columns of various water contents as a step function under constant flow rates. The results showed that when a "reactive" (water washed) sand was used, the retention of both fX174 and MS-2 increased significantly at low water saturation levels. However, when an "inert" (metals and metal oxides removed) sand was used, the effect of water content was minimal, although observable. These results suggest that in the presence of reactive solid surfaces, increased reactions at the solid-water interface rather than at the air-water interface dominates in virus removal and transport under unsaturated conditions. A model that incorporated reactions at both the solid-water and air-water interfaces was developed and successfully applied to the data.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2000WR900308

Mechanisms of virus removal during transport in unsaturated porous media

Viruses from contaminant sources can be transported through porous media to drinking water wells. The objective of this study was to investigate inactivation and sorption of viruses during saturated and unsaturated transport in different soils. Bacteriophages phiX174 and MS-2, and Br- tracer in a phosphate-buffered saline solution were introduced into saturated and unsaturated soil columns as a step function under constant flow rate and hydraulic conditions. Results showed that significantly greater virus removal occurred in the unsaturated columns than in the saturated columns in the two soils containing high metal oxides content. However, the increase in virus retention under unsaturated conditions was not significant in two other soils having high phosphorus and calcium contents and high pH, and in another soil with high organic matter content. The results imply that the extent of water content effect on inactivation and sorption of viruses can range from significant to minimal depending on the properties of the transport medium. We found that the presence of in situ metal oxides was a significant factor responsible for virus sorption and inactivation. Therefore, soils with high metal oxides content may have the potential to be used as hydrological barriers in preventing microbial contamination in the subsurface environments. We also found that the water content effect on virus removal and inactivation strongly depended on solid properties of the testing medium.

Effect of soil properties on saturated and unsaturated virus transport through columns.

To accurately examine the mechanisms that control virus retention and transport in porous media, it is essential to perform experiments under environmentally relevant conditions. Laboratory studies of virus transport are generally conducted using buffered solutions. However, there are no standards for the concentration and composition of the solution, making comparisons between different studies difficult. Our objective was to systematically investigate the effects of the ionic strength and composition of buffer solutions on adsorption of viruses during transport through saturated sand columns. Two phosphate buffered saline solutions (PBS and PBS2) and one artificial ground water (AGW) were used and experiments were conducted under saturated, steady state flow conditions. Bromide tracer and bacteriophages ΦX174 and MS-2 were introduced into saturated sand columns as step inputs and their concentrations in the outflow samples were determined. Change in ionic strength did not affect the behavior of ΦX174, whereas MS-2 was largely removed in the high ionic strength PBS buffer (0.16 M ) but moved through the columns in the low ionic strength PBS2 and AGW buffers (0.002 M ). An additional experiment conducted under an ionic strength gradient (from 0.002 to 0.2 M) using PBS indicated that the outflow concentration of MS-2 decreased slowly from an ionic strength of ∼0.03 M, reached a minimum at an apparent critical value of ∼0.1 M, and then increased gradually. This study also suggests that metals or metal oxides on sand surfaces can cause significant virus removal under high ionic strength conditions.

Virus transport through saturated sand columns as affected by different buffer solutions

Self–emulsification can be accomplished by enhanced oil recovery (EOR), the realization of the exploration of natural emulsifiers, which is a crucial task to understand the mechanism of crude oil self–emulsification, albeit it is, of course, accompanied by difficulties, during the development of shale crude oil. In this study, we separated the active components of crude oil, and with the help of modern characterization and laboratory tests, coupled with nuclear magnetic resonance of core flooding method, we fully explored the independent and synergistic effects of crude oil active components, and deepened the understanding of the mechanism of crude oil self–emulsification. Among the active components of crude oil, asphaltene and resin have vital effects on its self–emulsification, which is shown in the amphiphilic structure of asphaltene and the effect of resin solvent. Asphaltene can reduce oil–water interfacial tension to 19 mN/m, and the resin significantly increase the viscosity of emulsion. Meanwhile, resin and asphaltene stabilize the viscoelasticity of oil–water interface films and affect the phase transition of emulsions in different water oil ratio environment. As a result, the active components of crude oil are closely related to formation and stabilization of the emulsion, which together endue the inherent conditions of its self–emulsification. Core flooding test confirmed that some emulsions in nanoscale size are produced in shale porous media, and the average emulsion diameter size is 181 nm. This study explored the effects of natural emulsifiers on the self–emulsification of crude oil, thereby promising new potential opportunities for EOR of shale oil. 

Yanjie Chu

Papers

Virus removal and transport in saturated and unsaturated sand columns

Mechanisms of virus removal during transport in unsaturated porous media

Effect of soil properties on saturated and unsaturated virus transport through columns.

Virus transport through saturated sand columns as affected by different buffer solutions

Experimental study on self–emulsification of shale crude oil by natural emulsifiers