Browsing by Subject "Sulfate"

Now showing 1 - 5 of 5
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    Biogeochemical Interactions and Cycling of Sulfur, Iron, and Carbon in Sulfate-Impacted Riparian Wetlands and Wild Rice Waters
    (2018-08) Torgeson, Joshua
    Sulfide accumulation in the porewater of freshwater aquatic systems has been shown to inhibit the growth of many aquatic macrophytes, including wild rice. While interactions between sulfur (S), carbon (C), and iron (Fe) cycles are recognized, secondary “cryptic” S cycles are much less understood; these cycles favor reduction of sulfate over Fe, contrary to traditional thermodynamic expectations; these “cryptic” cycles have been suggested to occur at Second Creek through models by Ng et al. (2017). Using field observations, hydrologic monitoring, and geochemical analyses, we found that changes in hyporheic flux result in changes in porewater SO42- concentrations. Additionally, we have found that intermediate valence S species may act as primary sinks for excess dissolved sulfide. Our comparison study between a SO42--impacted stream and a less-impacted river demonstrates that the accumulation of porewater sulfide may be suppressed through limited TOC, excess sediment Fe, or through generation of S-intermediates.
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    Calcium Sulfate, Mixed Sulfate, and Mixed Oxide Corrosion of FeCrAlY Alloy in Dry Air at 1025 ºC
    (2022-11-28) Chikhalikar, Atharva S; Godbole, Eeshani P; Poerschke, David L; dpoersch@umn.edu; Poerschke, David; Poerschke Research Group
    Backscattered electron micrographs provide information about the thickness of the thermally grown oxide (TGO) thickness and the alloy-TGO interface roughness caused by oxidation of FeCrAlY alloy for 100 h at 1025 ºC in dry air upon exposure to corrosive deposits comprising mixed oxides, mixed sulfates, or calcium sulfate. Micrographs were processed to provide tabulated values for TGO thickness as a function of location across the sample cross section, and changes in the TGO-alloy interface position. The purpose of release is to provide access to detailed data related to alloy hot corrosion process. It is released now to correspond with the publication of the analyzed results in a related paper.
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    Enhanced Microbial Sulfate Removal Through a Novel Electrode-Integrated Bioreactor
    (2018-07) Takaki, Daniel
    In northeast Minnesota, elevated levels of sulfate in freshwater systems is a topic of great interest, due to potential adverse impacts to wild rice ecosystems. Sulfate may contribute to methylmercury production and eutrophication in certain conditions. Increased interest has emerged for developing low cost and efficient technologies to treat high levels of sulfate in mining and industrial waste water. The use of biological sulfate reduction is a promising and economically viable plan for maintaining low levels of sulfate and sulfide, but its performance is highly variable. This project developed a sediment bioelectrochemical batch reactor that used a low electrical potential to enhance and sustain biological sulfate reduction by continuously supplying electron donor substrates (electrolytic hydrogen) to sulfate reducing bacteria. The project aims to understand the effect of a low applied voltage on the efficacy of sulfate reduction and iron sulfide formation. Reactors contained creek sediment (Second Creek, MN) and an artificial mine water with a sulfate concentration of ~1000 ppm. The sulfur chemistry in the pore water of the reactors was assessed to determine sulfate reduction, resulting in over 90% reduction in porewater sulfate at the cathode in batch reactors, where electrolytic hydrogen gas was generated at a rate of 4.14 mmol/day. Simultaneously, ferrous iron was released into the reactor via iron electrodissolution and reacted with reduced sulfide ions to form iron sulfide precipitates. This level of hydrogen generation was sustained over a 14-day period and successfully showed that the application of a low voltage to sediment bioreactors is a promising technology to treat sulfate contaminated waste waters. The microbial community structure and relative abundance of different species associated with sulfate reduction were also examined. It was shown that relative abundance of sulfate reducing bacteria, specifically Desulfovibrio, a genus of deltaproteobacteria positively associated with sulfate reduction, which utilize hydrogen as their preferred electron donor, increased throughout batch reactor operation when operated at 2V. Finally, the sediment bioelectrochemical batch reactor served as a proof of concept for the application of low electrical potential to enhance and sustain biological sulfate reduction. The outcomes of this reactor operation laid the groundwork to develop a prototype flow-through bioelectrochemical reactor designed to handle larger volumes of waste water for an extended period of time. Preliminary results from this flow-through reactor demonstrated the ability to generate a constant supply of electrolytic hydrogen used by sulfate reducing bacteria. Through these experiments, recommendations have been made to improve efficacy of flow-through reactors.
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    The MnDRIVE Transdisciplinary Project Implementation of Smart Bioremediation Technology to Reduce Sulfate Concentrations in NE Minnesota Watersheds
    (University of Minnesota Duluth, 2017-07-14) Hudak, George J; Estepp, Lisa; Schoff, Patrick K
    This report opens with an Executive Summary, which briefly describes the project’s major accomplishments to date. The body of the report is constructed in sections focused on five related project efforts: 1) Bioreactor Design, Operation, and Performance, 2) Power Management, 3) Microbiology, 4) Chemical Treatments, and 5) Economic Aspects of Sulfate Reduction. Each of these sections, in turn, starts with a brief summary, which is followed by a detailed report. Additional materials concerning bioreactor design, construction, and operation, as well as experimental design, rationale, methods, and data are included in appendices. In addition, the MnDRIVE Project Accountability metrics, which contain a breakdown of particular project tasks, are included as appendices.
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    Temperature dependent sulfate transport in aquatic sediments
    (2014-11) DeRocher, Will D.
    Sulfate, released to overlying waters from natural sources and human activity, has the potential to be reduced to sulfide within the anoxic environments of aquatic sediments and negatively impact the growth of aquatic vegetation. Wild Rice is of particular concern within Minnesota as it is both an economic and cultural resource within the state. This study was conducted to characterize the temperature dependence of sulfate transport, via diffusion, between overlying waters and sediment porewaters through the use of laboratory experimentation and mathematical analysis to study the transient response to changes in the overlying water concentration. Two riverine sediments with contrasting organic carbon content from the St. Louis River watershed in northern Minnesota were characterized for their bulk geochemistry and incubated under laboratory conditions to observe the temperature dependence of ion transport between overlying water and sediment porewaters. Two identical sets of laboratory microcosms, incubated under warm and cold conditions, were subjected to a sulfate loading phase in which the overlying water was spiked with sodium sulfate to induce a concentration gradient between the sediment porewaters and overlying water. At the end of the sulfate loading phase, the sulfate gradient was reversed by replacing the overlying water with fresh water, causing sulfate to diffuse out of the sediment, back into the overlying water. During the sulfate recovery phase, sodium bromide was spiked into the overlying water. Bromide, acting as an inert chemical tracer, provided a diffusion-only baseline with which to compare to reactive sulfate. The anion concentrations in the overlying waters were closely monitored to quantify changes in the concentration through the sulfate loading and recovery phases. Non-destructive porewater samples were collected using Rhizon® soil moisture samplers to measure concentrations of sulfate, bromide, ferrous iron, pH, and sulfide at discrete depths in the sediment during key times after changes in surface boundary conditions.Averaged results from both the high and low organic sediments showed sulfate transport occurred 49% faster out of the overlying waters into the sediments at 23°C when compared to 4.5°C. Estimated rates of sulfate reduction at 4.5°C were on average, 40% of those estimated at 23° C. After seven weeks of recovery from the sulfate loading, porewater sulfate concentrations in the warm microcosms had dropped back to ambient levels while slightly elevated sulfate levels were still noticed within the cold microcosm porewater. Even though more sulfate diffused into the warm sediments, the cold sediments retained the sulfate for a significantly longer period of time after the change in boundary layer conditions due to the retarded rates of diffusion and reaction. The longer the sediment is exposed to elevated sulfate levels a greater potential exists for the wild rice seed within the sediment to be exposed to sulfide.