THE WETTABILITY OF A DNAPL/SURFACTANT SOLUTION ON QUARTZ AND IRON OXIDE SURFACES

DNAPLs in the subsurface may contain surface-active compounds that impact DNAPL migration and distribution. A number of studies to-date have focused on the role surface active compounds play in altering the wettability of quartz sands without examining the implications for other minerals commonly present in the subsurface. This study aims to extend the understanding of DNAPL/surfactant wettability to iron oxide surfaces. Specifically the objective was to compare the changes in the wettability of quartz and iron oxide sands in a tetrachloroethylene/water system containing a representative organic base. Wettability was assessed through: contact angles; Pc-S curves; and a two- dimensional flow cell experiment. It was discovered that quartz and iron oxide surfaces may exhibit different wetting characteristics under similar subsurface conditions. At neutral pH the quartz was strongly NAPL-wetting while the iron oxide remained hydrophilic. This study concludes that the isoelectric point, the pH at which there is a net zero surface charge, plays a major role in governing cationic surfactant sorption

Silver Nanoparticle Transport Through Soil: Illuminating the Governing Pore-Scale Processes

Engineered nanoparticles are widely used and will eventually be released to the subsurface environment and contaminate groundwater resources. However, the transport of engineered nanoparticles through soil is currently not well understood and cannot be modelled in any fundamental manner, placing groundwater resources at risk from nanoparticle contamination. This inability to accurately simulate transport is due to a lack of experimental information on nanoparticle interactions in the pore spaces of real soils. This thesis illuminates the pore-scale processes governing silver nanoparticle transport through soil. In addition, it examines the influence of surface chemistry and grain/pore distributions on those processes. For the first study, a method was developed and validated which employs Synchrotron X-ray Computed Microtomography (SXCMT) to experimentally quantify changing concentrations of silver nanoparticles, both spatially and temporally, within real soil pore spaces during transport. For the second study, the SXCMT imaging method was employed to experimentally investigate the role of pore-scale processes on silver nanoparticle transport through different soils representing different surface chemistries and grain distributions. The experiments found that nanoparticle transport and retention is significantly impacted by small regions of low fluid velocity near grain-grain contacts (termed ‘immobile zones’). For the third study, the experimental SXCMT datasets from the second study were coupled with Computational Fluid Dynamics to estimate the pore-scale nanoparticle mass flux and flow rates. The estimated distributions of mass flux and flow rates suggested that the current approach to modelling nanoparticle retention was incapable of considering mass flow in the centers of soil pores, rendering it unable to accurately predict the rate at which nanoparticles will be retained by soil. Overall, this thesis presents the first experimental datasets of pore-scale nanoparticle concentrations during transport. These previously unobtainable datasets provided the first direct confirmation of ‘immobile zones’ and their contribution to anomalous nanoparticle transport behaviour. In addition, they provided some of the first evidence as to why current modelling approaches are unable to predict nanoparticle retention rates

Electro‐Thermal Subsurface Gas Generation and Transport: Model Validation and Implications

Gas generation and flow in soil is relevant to applications such as the fate of leaking geologically sequestered carbon dioxide, natural releases of methane from peat and marine sediments, and numerous electro‐thermal remediation technologies for contaminated sites, such as electrical resistance heating. While traditional multiphase flow models generally perform poorly in describing unstable gas flow phenomena in soil, Macroscopic Invasion Percolation (MIP) models can reproduce key features of its behavior. When coupled with continuum heat and mass transport models, MIP has the potential to simulate complex subsurface scenarios. However, coupled MIP‐continuum models have not yet been validated against experimental data and lack key mechanisms required for electro‐thermal scenarios. Therefore, the purpose of this study was to (a) incorporate mechanisms required for steam generation and flow into an existing MIP‐continuum model (ET‐MIP), (b) validate ET‐MIP against an experimental lab‐scale electrical resistance heating study, and (c) investigate the sensitivity of water boiling and gas (steam) transport to key parameters. Water boiling plateaus (i.e., latent heat), heat recirculation within steam clusters, and steam collapse (i.e., condensation) mechanisms were added to ET‐MIP. ET‐MIP closely matched observed transient gas saturation distributions, measurements of electrical current, and temperature distributions. Heat recirculation and cluster collapse were identified as the key mechanisms required to describe gas flow dynamics using a MIP algorithm. Sensitivity analysis revealed that gas generation rates and transport distances, particularly through regions of cold water, are sensitive to the presence of dissolved gases

Colloid Transport in Porous Media: A Review of Classical Mechanisms and Emerging Topics

To celebrate the tenth anniversary of InterPore, we present an interdisciplinary review of colloid transport through porous media. This review aims to explore both classical colloid transport and topics that fall outside that purview and thus offer transformative insights into the physics governing transport behavior. First, we discuss the unique colloid characteristics relative to molecules and larger particles. Then, the classical advection?dispersion?filtration models (both conceptual and mathematical) of colloid transport are introduced as well as anomalous transport behaviors. Next, the forces of interaction between colloids and porous media surfaces are discussed. Fourth, applications that are interested in maximizing the transport of colloids through porous media are considered. Then the concept of motile, active biocolloids is introduced, and finally, colloid swarming as a newly recognized mode of transport is summarized.Fil: Molnar, Ian L.. York University; CanadáFil: Pensini, Erica. School Of Engineering; CanadáFil: Asad, Md Abdullah. York University; CanadáFil: Mitchell, Chven A.. Department Of Physics And Astronomy; Estados UnidosFil: Nitsche, Ludwig C.. College Of Engineering; Estados UnidosFil: Pyrak-Nolte, Laura J.. Department Of Physics And Astronomy; Estados UnidosFil: Miño, Gastón Leonardo. Universidad Nacional de Entre Ríos. Instituto de Investigación y Desarrollo en Bioingeniería y Bioinformática - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigación y Desarrollo en Bioingeniería y Bioinformática; ArgentinaFil: Krol, Magdalena M.. York University; Canad

Quantified Pore-Scale Nanoparticle Transport in Porous Media and the Implications for Colloid Filtration Theory

This study evaluates the pore-scale distribution of silver nanoparticles during transport through a sandy porous medium via quantitative synchrotron X-ray computed microtomography (qSXCMT). The associated distributions of nanoparticle flow velocities and mass flow rates were obtained by coupling these images with computational fluid dynamic (CFD) simulations. This allowed, for the first time, the comparison of nanoparticle mass flow with that assumed by the standard colloid filtration theory (CFT) modeling approach. It was found that (i) 25% of the pore space was further from the grain than assumed by the CFT model; (ii) the average pore velocity agreed well between results of the coupled qSXCMT/CFD approach and the CFT model within the model fluid envelope, although the former were 2 times larger than the latter in the centers of the larger pores and individual velocities were upwards of 20 times those in the CFT model at identical distances from grain surfaces ; and (iii) approximately 30% of all nanoparticle mass and 38% of all nanoparticle mass flow occurred further away from the grain surface than expected by the CFT model. This work suggests that a significantly smaller fraction of nanoparticles than expected will contact a grain surface by diffusion via CFT models, likely contributing to inadequate CFT model nanoparticle transport predictions

Exploring the governing transport mechanisms of corrosive agents in a Canadian deep geological repository

All nuclear energy producing nations face a common challenge associated with the long-term solution for their used nuclear fuel. After decades of research, many nuclear safety agencies worldwide agree that deep geological repositories (DGRs) are appropriate long-term solutions to protect the biosphere. The Canadian DGR is planned in either stable crystalline or sedimentary host rock (depending on the final site location) to house the used nuclear fuel in copper-coated used fuel containers (UFCs) surrounded by highly compacted bentonite. The copper-coating and bentonite provide robust protection against many corrosion processes anticipated in the DGR. However, it is possible that bisulfide (HS−) produced near the host rock-bentonite interface may transport through the bentonite and corrode the UFCs during the DGR design life (i.e., one million years); although container performance assessments typically account for this process, while maintaining container integrity. Because the DGR design life far exceeds those of practical experimentation, there is a need for robust numerical models to forecast HS− transport. In this paper we present the development of a coupled 3D thermal-hydraulic-chemical model to explore the impact of key coupled physics on HS− transport in the proposed Canadian DGR. These simulations reveal that, although saturation delayed and heating accelerated HS− transport over the first 100s and 10,000s of years, respectively, these times of influence were small compared to the long DGR design life. Consequently, the influence from heating only increased total projected HS− corrosion by − corrosion. Therefore, those parameters need to be carefully resolved to reliably forecast the extent of HS− corrosion

Exome sequences and multi-environment field trials elucidate the genetic basis of adaptation in barley

Broadening the genetic base of crops is crucial for developing varieties to respond to global agricultural challenges such as climate change. Here, we analysed a diverse panel of 371 domesticated lines of the model crop of barley to explore the genetics of crop adaptation. We first collected exome sequence data and phenotypes of key life history traits from contrasting multi-environment common garden trials. Then we applied refined statistical methods, including based on exomic haplotype states, for genotype-by-environment (G 7E) modelling. Sub-populations defined from exomic profiles were coincident with barley's biology, geography and history, and explained a high proportion of trial phenotypic variance. Clear G 7E interactions indicated adaptation profiles that varied for landraces and cultivars. Exploration of circadian clock-related genes, associated with the environmentally-adaptive days to heading trait (crucial for the crop's spread from the Fertile Crescent), illustrated complexities in G 7E effect directions, and the importance of latitudinally-based genic context in the expression of large effect alleles. Our analysis supports a gene-level scientific understanding of crop adaption and leads to practical opportunities for crop improvement, allowing the prioritisation of genomic regions and particular sets of lines for breeding efforts seeking to cope with climate change and other stresses