Browsing by Subject "redox"
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Item An Investigation of Linked Physical And Biogeochemical Processes In Heterogeneous Soils In The Vadose Zone(2012-10-19) Hansen, David JosephChemical dynamics in the vadose zone are poorly understood due to the transient nature of chemical and hydrologic conditions, but are nonetheless critical to understanding contaminant fate and transport. This work explored the effects of soil structure (i.e. layers, lenses) on linked geochemical, hydrological, and microbiological processes under changing hydrologic conditions (e.g. rainfall, introduction of groundwater, and fluctuating water table heights). A homogenized medium-grained sand, homogenized organic-rich loam and a sand-over-loam layered column were constructed for the first series of experiments. The second series of experiments employed two soil columns with lenses that were packed identically with sterilized and untreated sediments. Each consisted of two lenses of organic-rich loam in a medium-grained sand matrix. Lenses were located at different vertical depths and were horizontally offset. In-situ collocated probes collected soil hydrologic and chemical data. In the layered column, enhanced biogeochemical cycling was observed over the texturally homogeneous soil columns. Enumerations of Fe(III) and SO42- reducing microorganisms also show 1-2 orders of magnitude greater community numbers in the layered column. The greatest concentrations of aqueous FeS clusters (FeSaq) were observed in close proximity to the soil interface. To our knowledge, this was the first documentation of FeSaq in partially saturated sediments. Mineral and soil aggregate composite layers were also most abundant near the soil layer interface; the presence of which, likely contributed to an order of magnitude decrease of hydraulic conductivity. In the live lens column, Fe-oxide bands formed at the fringes of the lenses that retarded water flow rates by an order of magnitude compared to the sterilized column. Microbial activity also produced insoluble gases and that led to the creation of a separate gas phase that reduced hydraulic conductivity. This limited the interaction between groundwater with soil-pore waters that led to the formation of geochemically distinct water masses in relatively close proximity to one another. No such changes were observed in the sterilized column. When compared to homogenous columns, the presence of soil heterogeneities altered biogeochemical and hydrologic processes considerably which highlights the need to consider soil heterogeneity in contaminant fate and transport models. These findings suggest that quantifying coupled hydrologic-biogeochemical processes occurring at small scale soil interfaces is critical to accurately describing and predicting chemical changes at the larger system scale.Item Paleoenvrironmental Controls on Diagenesis of Organich-Rich Shales in the Eagle Ford Group(2014-08-27) Kruse, KendraCarbonate precipitation can be either promoted or inhibited by microbial processes in different redox zones. It is therefore possible for basin redox evolution to indirectly control early carbonate diagenesis and modify reservoir properties of corresponding shale units. The goals of this study were to analyze geochemical characteristics of the Late Cretaceous Eagle Ford Group in McMullen County, Texas to test the hypotheses that (1) the redox state of the water column controlled carbonate cement abundance and (2) carbonate cement lowered organic matter content by volumetric dilution. An x-ray analytical microscope was used to map elemental compositions of fresh core samples within the Eagle Ford Group. Resultant maps were used to characterize carbonate cements and to estimate the redox state of the overlying water column during deposition, as indicated by the relative abundances of the trace metals Mo, V, and Cr. Results indicate that cementation occurred early relative to compaction. Ti Kal normalized Mo Kal and CaKal fluorescence intensities are positively correlated throughout the unit, suggesting that carbonate cementation was related to the redox state. Total organic carbon is negatively correlated in the upper Lower Eagle Ford with (Ca Kal)/(Ti Kal) fluorescence ratio, consistent with volumetric dilution of organic matter by diagenetic cementation prior to compaction. In contrast, there is no significant correlation between total organic carbon and carbonate content in the more organic-rich Lower Eagle Ford.Item Perchlorate Degradation Using Partially Oxidized Titanium Ions and Ion Exchange Membrane Hybrid System(2011-08-08) Park, Sung HyukPerchlorate has entered human and environmental food chains and has received a great deal of attention because of its toxicity to humans. In this study, chemical degradation of perchlorate was investigated using partially oxidized titanium ions (Ti2+ and Ti3+) in solutions and as part of an ion exchange membrane reactor system. Aqueous titanium ions (Ti2+ and Ti3+) were applied to remove perchlorate ions and its destructive mechanism, reaction kinetics, and the effect of environmental factors were investigated. Titanium ions were able to degrade perchlorate ions very rapidly with half life less than one hour under conditions of high acid concentrations. A new reactor system with an ion exchange membrane was adapted to apply better the reactions of perchlorate destruction to water treatment practice. A novel treatment method was developed by integrating partially oxidized titanium ions with an ion exchange membrane, and it is named the Titanium and Membrane Hybrid System (TMH System). The results shown in this research demonstrate the feasibility of TMH System for perchlorate reduction. The perchlorate ions were rapidly adsorbed onto the ion exchange membrane and diffused through it, but they were reduced by titanium ions in the degradation zone relatively slowly. To enhance the overall rate of reaction, high concentrations of acid and Ti(III) are needed, but transport of hydrogen ions through the anion permeable membrane was observed and would be greater at higher acid concentrations. The proposed mathematical model predicts the performance and behavior of the TMH system for different physical and chemical conditions. It successfully described adsorption, diffusion and reduction of perchlorate in the system. This model could be used as an important tool for process design and optimization.