Degradation of surface water quality by excess nutrients in stormwater is a substantial environmental and economic problem in the U.S. Phosphorus (P) is often the limiting nutrient for harmful algal blooms and the best target to prevent degradation. Natural treatment strategies such as constructed wetlands (CW) demonstrate effective and economical P management but obstacles exist to implementation. Biological P removal has large land requirements that limit the use of best management practices (BMP) in high land-value areas. Various BMP also utilize sorption processes (SP) for P removal but variations in performance and finite sorption capacity limit SP as a viable long-term removal strategy. However, by understanding variability and making sorption capacity renewable, SP could provide, with shorter retention times, a space-efficient, long-term removal strategy. This multi-study research program developed the urban wetland filter (UWF), a concept intended to overcome the unique limitations of high land-value areas to natural treatment strategies and provide a low-cost, easily implemented BMP to meet P management goals while harvesting sequestered P for use as a fertilizer. Experimental factors included substrate and influent properties pertinent to understanding performance variation and optimizing microbial iron (Fe) reduction for rejuvenation of sorption capacity. Regarding performance, modeling identified major sources of variability including, by order of importance, magnitude of a solution/substrate concentration gradient, length of the "antecedent dry period" between loadings, and pH. Field-scale results confirmed this multifactor dependence of P-removal while also supporting the inclusion of cast-iron filings in substrate to improve P removal. Regarding rejuvenation, results indicated that microbial Fe reduction is capable of releasing previously sequestered P from substrates. A sufficient carbon source was necessary, but microbial inoculation was not necessary to facilitate Fe reduction, which released most of the previously sequestered P, albeit more slowly than P sequestration. Field-scale results indicated that Fe reduction might occur faster under field conditions, possibly due to humic acids, and that inclusion of cast-iron filings enabled additional P removal after rejuvenation by providing a conservative source of Fe for the creation of new sorption sites; however, cast-iron filings may also limit the release of P during rejuvenation. / Ph. D.

Both crystalline and sedimentary rocks are being considered as potential host rocks for a deep geological repository in Canada. Deep-seated sedimentary rocks in the Michigan Basin, Ontario, Canada contain highly saline ground and pore waters. The relatively high I of these waters may influence speciation and rock matrix sorption properties. To this end, laboratory sorption experiments were conducted to examine sorption of Pd(II) on sodium bentonite, illite and Ordovician age shale as a function of pH and solution I and initial concentration of Pd. Solutions with pH values in the range of 5 to 9, I ranging from 0.1 to 4 M and initial concentration of Pd ranging from 5×10 −8 to 1×10 −6 M were considered. A sorption time of 14 days was used and the separation method was by centrifuge. Experiments were performed under aerobic conditions at 25 ◦ CC, and the Eh value of the solution ranged from 300 to 600 mV. The data from sorption experiments were used to validate surface complexation models developed in PHREEQC with the JAEA TDB. The sorption of Pd on bentonite, shale and illite all showed strong dependence on I and pH. The dependence on initial concentration of Pd was used to plot sorption isotherms. The slope of the isotherms showed that Pd was forming inner- and outer- sphere complexes inside the stern layer for sorption onto bentonite and illite. It also showed however that shale was most likely undergoing cooperative sorption. Strong fit was found between the single layer surface complexation model for montmorillonite (the major constituent clay mineral of sodium bentonite) and experimental data, but not for illite (the major constituent clay mineral of shale). / Thesis / Master of Applied Science (MASc)

No description available.

The influence of sulfate on terrestrial and aquatic ecosystems depends on the mobility of the sulfate anion in soils. This mobility is determined by several factors, one being the types and amounts of soil constituents. In this study, several iron oxide/hydroxide minerals were evaluated for sulfate sorption characteristics.Hematite and goethite were synthesized and positively identified using x-ray diffraction, mossbauer spectroscopy and scanning electron microscopy. Mineral surfaces were characterized using surface area and zero point of charge measurements, infrared spectroscopy and thermal analyses. Neutron activation and x-ray fluorescence were used to look for impurities. Samples were compared to a natural hematite sample and a synthetic jarosite. Sorption experiments, conducted on mineral suspensions in KNO3 media at room temperature, considered the variables time, ionic strength, solid:solution ratio, pH and sulfate concentration. Sorption was initiated by a fast reaction, followed by a longer, slower one which reached an apparent equilibrium in 24 hours. Sorption was unaffected by sol id:solution ratio and decreased with ionic strength at pH 5 for goethite only. Sorption increased with increasing sulfate concentration and decreasing pH. A sorption maximum was reached by a I 1 minerals except synthetic hematite. Under optimum pH and [SO4]. approximately half of the mineral surface is covered by su1 fate ions. Sulfate was sorbed irreversibly. Only a fraction of sorbed sulfate can be desorbed, an amount which increases with pH. Thermal analyses indicate sulfate to be strongly bonded. The presence of four infrared bands on sulfate treated surfaces indicate direct coordination of the anion to the iron cation. The above evidence, including irreversibility of sorption, supports inner sphere complexing of sulfate. Sulfate sorption on iron oxide/hydroxide minerals is thus a combination of nonspecific electrostatic attraction and mono - multi ligand exchange (including binuclear bridging) which act under different system conditions to form the basis of sulfate sorption behavior. The present observations are important in model ling of environmental systems, such as in the Direct Delayed Response Program Model, due to the significance of irreversibility of sulfate sorption on model assumptions. / Thesis / Doctor of Philosophy (PhD)

Recent studies have demonstrated that nanoscale crystalline iron oxide minerals are common in natural systems. The discipline of nanoscience suggests that these particles in the size range of approximately 1-50 nm will have properties that deviate from the bulk properties of the same material and that these properties will change as a function of particle size. This study begins to fill the void of corresponding experimental investigations that apply the principles of nanoscience to the geochemical reactivity of nanominerals. The rate of Mn²⁺(aq) oxidation on hematite with average diameters of 7.3 nm and 37 nm was measured in the presence of O₂(aq). In the pH range of 7-8, the surface area normalized rate was one to two orders of magnitude greater on the 7.3 nm average diameter particles. Based on the application of electron transfer theory, it is hypothesized that the particles with diameters less than approximately 10 nm have surface crystal chemical environments which distort the symmetry of the MnMn²⁺ surface complex, reducing the energy required to reorganize the coordinated ligands after oxidation to Mn³⁺. Cu²⁺, an analog for Mn³⁺, was used to probe for the presence and nature of the proposed changes in surface structure. Cu²⁺ and Mn³⁺ show similar electronic structure changes in response to the surrounding crystal field due to their d-electron configurations and Jahn-Teller coordinative distortions. Batch sorption experiments on hematite nanoparticles revealed a shift in the pH-dependent adsorption of Cu²⁺(aq). Specifically, an affinity sequence of 7 nm > 25 nm = 88 nm was determined based on the shift of the 7 nm sorption edge to approximately 0.8 pH units lower than that for the 25 nm and 88 nm samples. These data support the hypothesis that unique binding sites exist on the 7 nm nanoparticles that are not significantly present on the larger particles. The National Nanotechnology Initiative stresses the need to address the broader societal impacts of nanoscale research. This dissertation embraces this viewpoint through the development and inclusion of "Nano2Earth: Introducing Nanotechnology Through Investigations of Groundwater," a curriculum which combines nanoscience with the Earth sciences for high school students. / Ph. D.

Natural steroid estrogens such as 17beta-estradiol in low nanogram per liter concentrations can adversely affect the reproductive health of aquatic organisms. The overall goal of this research was to quantify the sorption of 17beta-estradiol to three soils considered to be agriculturally productive from different physiographic regions in Virginia to aid in modeling the concentration of estrogens available for transport in runoff from agricultural fields. Batch equilibrium experiments were conducted with various concentrations of 17beta-estradiol (E2) in a background solution of 5 mM calcium chloride and 100 mg/L sodium azide added to four separate soil samples representative of productive agricultural soils from three different physiographic regions of Virginia. Groseclose loam, Myatt sandy loam and Cecil loam were supplied by the Crop and Soil Environmental Sciences Department at Virginia Tech. All soils were collected from the plow layer (0 to 15 cm) except for an additional Cecil soil sample from the Bt horizon. The concentration of E2 in the liquid phase was measured by gas chromatography/mass spectrometry (GC/MS) and was used to find the time to reach equilibrium and to develop sorption isotherms for each soil. The time required to reach equilibrium for all soils was less than 24 hours. A linear isotherm provided the best fit to model the sorption of E2 to Cecil and Myatt soils (R2 = 0.94 and 0.96, respectively). For Groseclose soil, the general form of the Freundlich isotherm fit best (R2 = 0.98), although the linear isotherm also provided a good fit (R2 = 0.93). The sorption of E2 to agricultural soil appears to be related to the organic carbon content of each soil (Pearson coefficient, 0.82). Attempts to analyze and create isotherms for conjugated E2 by deconjugating with metholysis were unsuccessful. / Master of Science

Groundwater contaminants such as chlorinated ethenes, chlorinated ethanes and nitroaromatic explosive compounds (e.g. 2,4,6-Trinitrotoluene (TNT)) degrade in the subsurface primarily by microbially catalyzed reductive transformation reactions. From a regulatory point of view, the capability to simulate the kinetics of these reductive transformation reactions coupled with other attenuation processes in the subsurface (e.g., sorption, advection, and dispersion) is required for site-specific solute transport models. A kinetic model based on Michaelis-Menten type equations (Widdowson 2004) has been successfully validated for the linear reductive dechlorination pathway of chlorinated ethenes, and implemented in solute transport codes such as SEAM3D (Waddill and Widdowson 2000). However, TNT degrades through more complex branched pathways, and kinetic models are lacking in the current literature. This research study was undertaken with the objective of extending the kinetic model developed for the linear reductive pathway of chlorinated ethenes to branched pathways. The proposed extended kinetic model was validated with experimental concentration-time data of TNT and its metabolites from two prior published laboratory studies (Daun et al. 2000; Hwang et al. 2000), both in the presence and absence of sorption. The model-predicted concentrations with time of TNT and its degradation intermediates and end-products correlated well with the experimental data. The model is further compatible with and can be easily incorporated into solute transport codes (e.g., SEAM3D), and used to evaluate the fate and transport of TNT and other similar contaminants in the subsurface. / Master of Science

Synthetic polymers are one of the most significant pollutants in the aquatic environment, because of abilities such as buoyancy and extreme persistency. Serious effects are expected from so-called microplastics (particle size <5 mm) that are reported in rivers, lakes as well as the ocean and that accumulate in sediments worldwide. In this thesis the abundance of microplastics in river shore sediments in the Rhine-Main area of Germany was studied. Therefore, a new method was developed that is based on a sodium chloride density separation with subsequent destruction of natural debris, and identification of the plastic particles by microscopy or Fourier transform infrared spectroscopy (FTIR). Using the improved density separation, microplastics were separated from river shore sediments of 12 sites originating from the river Rhine, the river Main, and the stream Schwarzbach. Large amounts of microplastic particles of up to 1 g kg-1 or up to 4000 particles kg-1 were detected in the shore sediments. The identification by FTIR showed that polyethylene, polypropylene, and polystyrene were the most abundant polymer types in the sediments, covering over 75% of all plastics identified. Transport of microplastics from tributaries to main streams was indicated by the detection of identical pellets in the River Rhine and in the Main mouth. Comparable concentrations detected by sampling one site over a period of two years suggest a constant pollution of the river shore sediments with microplastics. For deeper insights into the sorption process of organic contaminants to synthetic polymers in freshwater systems, batch experiments in synthetic freshwater were conducted to determine sorption kinetics and sorption isotherms for four selected glass state polymers (polycarbonate, poly(methyl methacrylate), polystyrene, and polyvinyl chloride) and six different model substances (carbamazepine, hexachlorocyclohexane (β/γ), 17α-ethynilestradiol, chlorpyrifos, and o,p-dichlorodiphenyltrichlorethane). Sorption to the polymer particles was observed for all contaminants increasing with the KOW values of the contaminants. Because of losses of contaminants in control samples, sorption reaction models could be applied to four out of six contaminants, and isotherms were calculated for three contaminants. Furthermore, influences of the different polymer types used were observed in the experiments. Finally, microplastics separated from sediments were extracted and analyzed by GC/MS and LC-MS/MS using target screening methods and non-target approaches. Different pesticides were identified in the polymer particles, suggesting that microplastics can act as a sink for hydrophobic contaminants. Moreover, several plastic additives such as phthalates or chlorinated flame retardants were identified. For this reason, it is very likely that microplastics act as a direct source for these chemicals in aquatic systems. The results of this thesis stress the urgency for the mitigation of the plastic particles in the aquatic environment.

For the safety assessment of high-level nuclear waste repositories, it is mandatory to know the transportation paths of contaminants, e.g. actinyl ions, in the geological barrier. The most attention needs to be focused on the transport in aquifers, because water contamination, depending on retention and migration processes of radionuclides in the geosphere, is of primary environmental concern. The migration behavior of actinides in ground water is mainly controlled by aquatic speciations and sorption processes at water-mineral interfaces. Hence, the investigation of complexspecies in aqueous solutions and at mineral surfaces becomes essential for the safety assessment in the near and far field of nuclear repositories. For deep ground repositories, clay and clay minerals are considered as possible host rocks, because they show a low permeability and are expected to have a high retention capacity towards actinyl ions. But the complexity of naturally occurring minerals in particular their surface often hampers the unequivocal interpretation of results obtained from sorption experiments. The use of model phases only showing one particular functional group at the surfaces with a well defined surface topology is an appropriate approach for the understanding of the basic sorption processes. Aluminum oxide and hydroxides are of special interest because they represent main components in clays and clay minerals. In particular, gibbsite is widely used as a model system because it represents not only the most common crystalline aluminum hydroxide but also a ubiquitous weathering product of alumosilicates. Furthermore, the elemental structural unit of gibbsite, that is the Al(OH)6 octahedron, occurs ubiquitously as part of the structure of common clay minerals like kaolinite. In the present study, the sorption processes of U(VI) and Np(V) on gibbsite were studied under consideration of the aqueous speciation.

Dans le contexte des futurs stockages des matières nucléaires en couches géologiques profondes, le transfert de sélénium 79 des eaux de nappes vers la biosphère, par le biais de l’irrigation, est un des scenarii envisagés par l’ANDRA. Le sol servirait alors d’interface entre la géosphère et la biosphère. Le modèle actuellement utilisé pour évaluer la mobilité de nombreux éléments dans le sol repose sur une représentation simple de leur distribution entre la quantité adsorbée sur le sol et la quantité restante en solution (modèle Kd), considérée comme instantanée, réversible et linéaire avec la concentration de contamination. Ce modèle présente des lacunes vis-à-vis du sélénium puisque ce dernier peut être présent sous différents états redox qui contrôlent sa mobilité et dont les cinétiques de transformation entre ces états sont peu connues (Se(-II), Se(0),Se(IV) et Se(VI)).Dans le but d’améliorer les prédictions faites sur la mobilité du sélénium dans un sol, le séléniate (Se(VI)), qui est la forme la plus mobile, a été utilisé pour étudier ses interactions vis-à-vis de deux sols différents (sol B et sol R).Un modèle cinétique, alternatif au modèle Kd, a été développé pour décrire l’évolution des stocks de Se(VI) en solution, en considérant une fraction de sélénium associée au sol de façon réversible (potentiellement mobile) et une fraction stabilisée sur le sol (fixée pseudo-irréversiblement). Ce modèle intègre des cinétiques de stabilisation biotique et abiotique sur le sol, et une cinétique de réduction en solution. Afin d’acquérir les paramètres des modèles, des expériences en batchs et en réacteurs à flux ouvert avec l’utilisation de sacs à dialyse ont été réalisées. L’acquisition des paramètres a permis de confronter les modèles cinétiques et Kd dans différents scenarii réalistes de contamination (chronique ou séquentielle) d’un sol de surface par du 79Se(VI).De plus, les mécanismes de sorption du Se(VI) au sein des deux sols ont été évalués en batch avec l’ajout de compétiteurs spécifiques vis-à-vis de certains sites pouvant sorber ce dernier (acides humiques et carbonates de calcium). Ceci a été complété avec l’étude de la sorption du Se(VI) sur des phases pures commerciales (silice, hydroxyde d’aluminium, goethite, bentonite, carbonate de calcium et acides humiques) ou extraites d’un sol (substances humiques), pour différentes concentrations en Se(VI) (10-8, 10-6 et/ou 10-3 mol/L), de l’impact de l’ajout de phases pures réactives, dans les sols, sur la sorption du Se(VI).Il a été montré que le Se(VI) était sorbé sous la forme de complexes de sphères externes (CSE) au sein du sol R pour des concentrations inférieures à 10-6 mol/L, tandis que dans le sol B, la majorité était sorbée sous la forme de complexes de sphère internes (CSI). La formation de CSE étant réversible et instantanée, l’utilisation du modèle Kd était donc suffisante pour décrire la sorption du Se(VI) au sein du sol R, dans les expériences en réacteurs à flux ouvert. A contrario, pour le sol B, il a été montré que le modèle Kd, contrairement au modèle cinétique, présentait des lacunes pour décrire la sorption pseudo-irréversible du Se(VI), engendrée par la formation de CSI. Il a été montré que les mécanismes biotiques étaient majoritaires au sein du sol B, en raison de l’apport de nutriments pour les microorganismes, par l’utilisation de sacs à dialyse en cellulose régénérée. Cependant les mécanismes abiotiques ont aussi eu lieux au sein du sol B.14/256. Les études sur les phases pures ont montré que seuls l’hydroxyde d’aluminium (pH 5,2 et 8) et la goethite (pH 5,2) pouvaient sorber le Se(VI) respectivement de manière pseudo-irréversible et réversible (pour [Se(VI)] < 10-6mol/L). Enfin, il a été montré que l’ajout de certaines phases pures (goethite et hydroxyde d’aluminium) au sein des deux sols, pouvait entrainer une augmentation ou une diminution de la sorption du Se(VI) par rapport à celle attendue (additivité réactionnelle). / In the context of future storage of nuclear material in deep geological layers, the transfer of selenium-79 from groundwater to biosphere through irrigation is one of the scenarios considered by the ANDRA (National Agency for Radioactive Waste Management). So, the soil would act as an interface between the geosphere and biosphere. Actually the model adopted to evaluate the element mobility in soil is based on a simple representation of its distribution between the quantity adsorbed on the soil and the amount remaining in the solution (KD model). Such distribution is considered as instantaneous, reversible and linear with the concentration of contamination. This model has some inadequacies with respect to selenium because this latter can be present in different redox states that control its mobility and whose transformation kinetics among states are poorly known (Se(-II), Se(0), Se(IV)and Se(VI)). In order to improve predictions on the mobility of selenium in soil, selenate (Se(VI)) - which is the most mobile form - has been used to study its interactions with respect to two different soils (soil B and soil R). Akinetic model, alternative to the Kd model, has been developed to describe the evolution of stocks of Se(VI) in solution. This model considers that a fraction of selenium is associated with soil in a reversibly way (potentially mobile) and a portion of it is stabilized in soil (pseudo-irreversibly fixed). This model integrates on one hand, in the soil, kinetics of biotic and abiotic stabilization and on the other hand, in solution, a reduction kinetic. With the goal of acquiring the parameters of the models, various experiments using dialysis bags have been effectuated, both in batch and with open-flow reactors. The parameter acquisition has allowed kinetic and Kd models to be compared in different realistic scenarios of contamination (chronic or sequential) of a surface soil with 79Se(VI). In addition, the sorption mechanisms of Se(VI) have been evaluated in the two soils in batch adding specific competitors (humic acid and calcium carbonates) that can sorb on solid sites such as selenate. This study has been completed with the analysis of the sorption of Se(VI) on pure phases available on the market (silica, aluminum hydroxide, goethite, bentonite, calcium carbonate and humic acids) or extracted from a soil (humic substances).This investigation has been carried out at different concentrations of Se(VI) (10-8, 10-6 et/ou 10-3 mol/L). In addition, some pure reactive phases have been added to the soil in order to study the solid-solid interaction having a role on the sorption of Se(VI).This study has underlined that in the R-soil Se(VI) was sorbed in the form of outer sphere complexes (OSC) at concentration slower than 10-6 mol/L, whereas in B-soil, the majority were sorbed as inner sphere complexes (ISC). As the formation of OSC is reversible and instantaneous, in experiments with open-flow reactors, the use of Kd model was sufficient to describe the sorption of Se(VI) in R-soil. On the contrary, for soil B, the study has shown that the Kd model, unlike the kinetic model, was inadequate to describe the pseudo-irreversible sorption of Se(VI), caused by the formation of ISC. Due to the supply of nutrients for microorganisms, it has been shown that biotic mechanisms predominated in soil B, due to the utilization of cellulose dialysis bags. However, abiotic mechanisms took places in soil B, too. The studies on pure phases have shown that only aluminum hydroxide (pH 5.2 and 8) and goethite (pH 5.2) could sorb Se(VI), respectively in a pseudo-irreversible and reversible way (for [Se(VI)] < 10-6 mol/L).Moreover, it has been shown that, in both soils, the addition of some pure phases (goethite and aluminum hydroxide),could cause an increase or a decrease of the sorption of Se(VI) with respect to the one expected (additivity reaction).