Uranium contamination of soils and groundwater at Department of Energy facilities across the United States is a primary environmental concern and the development of effective remediation strategies is a major challenge. Bioremediation, or the use of microbial enzymatic activity to facilitate the remediation of a contaminant, offers a promising in situ approach that may be less invasive than traditional methods, such as pump and treat or excavation. This study demonstrates for the first time the successful biomineralization of uranium phosphate minerals as a result of microbial phosphatase activity at low pH in both aerobic and anaerobic conditions using pure cultures and soils from a contaminated waste site. Pure cultures of microorganisms isolated from soils of a low pH, high uranium- and nitrate-contaminated waste site, expressed constitutive phosphatase activity in response to an organophosphate addition in aerobic and anaerobic incubations. Sufficient phosphate was hydrolyzed to precipitate 73 to 95% total uranium as chernikovite identified by synchrotron X-ray absorption spectroscopy and X-ray diffraction. Highest rates of uranium precipitation and phosphatase activity were observed between pH 5.0 and 7.0. Indigenous microorganisms were also stimulated by organophosphate amendment in soils from a contaminated waste site using flow-through reactors. High phosphate concentrations (0.5 to 3 mmol L-1) in pore water effluents were observed within days of organophosphate addition. Highest rates of phosphatase activity occurred at pH 5.5 in naturally low pH soils in the presence of high uranium and nitrate concentrations. The precipitation of uranium phosphate was identified by a combination of pore water measurements, solid phase extractions, synchrotron-based X-ray spectroscopy, and a reactive transport model. The results of this study demonstrate that uranium is biomineralized to a highly insoluble uranyl phosphate mineral as a result of enzymatic hydrolysis of an organophosphate compound over a wide range of pH, in both aerobic and anaerobic conditions, and in the presence of high uranium and nitrate concentrations. The nonreductive biomineralization of U(VI) provides a promising new approach for in situ uranium bioremediation in low pH, high nitrate, and aerobic conditions that could be complementary to U(VI) bioreduction in high pH, low nitrate, and reducing environments.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on November 6, 2007) Includes bibliographical references.

Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references: leaf 252-266.

Chromium exists largely in two oxidation states, namely hexavalent chromium (Cr(VI)) which is carcinogenic, mutagenic to living organisms including humans and trivalent chromium (Cr(III)) which is known to be 1000 times less toxic than Cr(VI). It is therefore desirable in most cases to reduce Cr(VI) to Cr(III). Various studies have been conducted on the Cr(VI) reduction process either in situ or ex situ. However in situ bioremediation using permeable reactive barrier system appears as a potential and attractive technology compared to other in situ technologies. This study was conducted to evaluate the reduction of Cr(VI) to Cr(III) in the short term and regeneration of the biological reactive barrier to achieve continuous long term operation. It was observed from the study that the chromium hydroxide Cr(OH)3(s) precipitated and thus affected the porosity and hydraulic conductivity of the barrier system. It was therefore proposed to implement a regeneration process involving remobilization of precipitated Cr(OH)3 using a dilute acid (0.1% HCl) and recover Cr(III) by electrokinetics. Lowering the pH in the reactor introduced harsh conditions which necessitated the evaluation of a possible culture shift during the regeneration phase. Microbial culture composition during bioremediation and after soil washing was evaluated using a 16S rRNA finger printing method. The microbial barrier was initially inoculated with indigenous bacterial species from dried sludge. The results presented in the phylogenic tree diagrams confirm that, after microbial barrier system operation, the well-known Cr(VI) reducers Bacillus mycoides, Lysinibacillus fusiformis and Micrococcus lylae were the predominant species in the microbial community of the barrier. The microbial barrier system successfully achieved near complete removal of Cr(VI), whereby approximately 75% Cr(VI) removal was achieved within 63 days of operation. The formation of Cr(OH)3(s) was observed in the second week of operation. After 4 weeks of operating the mesocosm under soil washing with 0.1% HCl and electrokinetics remediation with a DC voltage of 50-150 V an increase in total chromium (73%) was observed suggesting that the trapped chromium species in the mesocosm was effectively remobilized with the assumption that Cr(III) had attached to the cathode forming a white-yellow precipitate layer around the cathode. Additionally more than 95% Cr(VI) was transformed to lower toxicity Cr(III) during electrokinetics and soil washing remediation. However, one of the limitations of electrokinetics is near anode focusing effect whereby a layer of precipitate is formed around the anode that lead to the reduction of efficiency of the technology. / Dissertation (MSc)--University of Pretoria, 2014. / lk2014 / Chemical Engineering / MSc / Unrestricted

Volatile organic compound (VOC) contamination of low permeability geologic deposits due to Dense Non-Aqueous Phase Liquid (DNAPL) penetration through fractures is exceptionally difficult to remediate using in-situ methods as the low permeability of the sediments limits the delivery of reagents proximal to contaminant mass. This thesis examines in detail the extent of organic contaminant treatment away from hydraulically-induced fractures injected with particulate Zero Valent Iron as (1) ZVI and glycol (G-ZVI) and (2) an emulsified ZVI (EZVI) mixture within a contaminated glaciolacustrine clayey deposit. Continuous vertical cores were collected through the treatment zone at 2 and 2.5 years after substrate injections and soil sub-sample spacing was scaled to show the extent of the treatment zone adjacent to the ZVI in the fractures, expecting the treatment would be controlled by diffusion limited transport to the reaction zone. Analytical results show evidence of treatment in both the EZVI and the G-ZVI containing fractures with the presence of degradation by-products and reduced VOC concentrations in the fracture and surrounding clay matrix. / Natural Sciences and Engineering Research Council of Canada, University Consortium for Field-Focused Groundwater Contamination Research

Thesis (Ph.D.) -- Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

This thesis deals with a contaminated area in the municipality of Östersund where a gas plant has previously been operating from 1914 to 1951. Operations at the property where the gas plant has been located currently consist of a workshop and commercial premises with associated car parking. In order to be able to build on the gas plant area, the municipality intends to implement post-treatment measures in the area. The substances found in the contaminated area (hotspot area E) are polycyclic aromatic hydrocarbons (PAH), aromatics, arsenic, nickel, lead and benzene. Measurement data indicate that these substances have been found at high levels, above the Swedish Environmental Protection Agency's guideline values for contaminated soil. Many areas today are polluted to the level that they pose great risks to the environment and people, and this thought requires the treatment of contaminated soil. A risk assessment for hotspot area E determined that PAH, aromatics, arsenic, nickel, lead and benzene pose an unacceptable risk, and the area is therefore deemed to need remediation. Based on nearby buildings, in-situ soil remediation is a suitable approach that fits. This study summarizes the progress made in remediation research and shows that soil remediation methods have different advantages and disadvantages, and different strains on human health and the environment. Based on this study, it may be more appropriate to wait for more efficient or cheaper remediation techniques to be developed, but with the idea that these substances are volatile, toxic, and dangerous to us humans and the environment. This means that they pose a potential risk to society and a tendency to spread easily. Conclusions that can be drawn are that all in-situ methods included in this work can be applied in Sweden based on the geological conditions. In order to achieve optimum in-situ soil remediation, site-specific conditions, such as large groundwater flow or heterogeneous soil, control the choice of remediation method.

No description available.

No description available.

Groundwater arsenic contamination is currently a global problem, and also a concern at numerous former industrial sites, agricultural sites, landfill sites and mining operations in the U.S. This dissertation aims to develop improved strategies of remediating these arsenic contaminated aquifers. It focuses on two distinct approaches of remediation: (1) mobilizing arsenic from contaminated aquifer sediments to decrease the quantity of arsenic at the source of contamination; and (2) immobilizing arsenic in situ, to decrease the mobility and bioavailability of this arsenic. Optimal remediation may well involve combinations of these two approaches. Arsenic mobilization using oxalic acid is effective because oxalic acid dissolves arsenic host minerals and competes for sorption sites on those minerals. In this dissertation, oxalic acid treatment was tested using sediments with contrasting iron mineralogies and arsenic contents from the Dover Municipal Landfill and the Vineland Chemical Company Superfund sites. Oxalic acid mobilized arsenic from both sites and the residual sediment arsenic was less vulnerable to microbial reduction than before the treatment. Oxalic acid thus could improve the efficiency of widely used pump-and-treat remediation. Oxalic acid did not remove all of the reactive iron(III) minerals in Vineland sediment samples, and thus released significant quantities of arsenic into solution under reducing conditions than the Dover samples. Therefore, the efficacy of pump-and-treat must consider iron mineralogy when evaluating its overall potential for remediating groundwater arsenic. Arsenic immobilization occurs by changing the chemical state, or speciation, of arsenic and other elements in the system. Arsenic is often assumed to be immobile in sulfidic environments. In this dissertation, sulfate reduction was stimulated in sediments from the Vineland Superfund site and the Coeur d'Alene mining district. Sulfate reduction in the Coeur d'Alene sediments was more effective at removing arsenic from solution than the Vineland sediments. The Vineland sediments initially contained abundant reactive ferrihydrite, and underwent extensive sulfur cycling during incubation. As a result, arsenic in the Vineland sediments could not be effectively converted to immobile arsenic-bearing sulfides, but instead a part of the arsenic was probably converted to soluble thioarsenates. Therefore, coupling between the iron and sulfur redox cycles must be fully understood for arsenic immobilization by sulfate reduction to be successful. Arsenic can also be immobilized by retention on magnetite (Fe3O4). Magnetite is stable under a wide range of aquifer conditions including both oxic and iron(III)-reducing environments. In this dissertation, a series of experiments were performed with sediments from the Dover and Vineland Superfund sites, to examine the potential of magnetite for use in arsenic immobilization. Our data suggest that the formation of magnetite can be achieved by the microbial oxidation of ferrous iron with nitrate. Magnetite can incorporate arsenic into its structure during formation, forming a stable arsenic sink. Magnetite, once formed, can also immobilize arsenic by surface adsorption, and thus serve as a reactive filter when contaminated groundwater migrates through the treatment zone. Reactive transport modeling is used for investigating the magnetite based arsenic immobilization strategy and for scaling laboratory results to field environments. Such modeling suggests that the ratio between iron(II) and nitrate in the injectant regulates the formations of magnetite and ferrihydrite, and thus regulates the long-term evolution of the effectiveness of the strategy. The results from field-scale models favor scenarios that rely on the chromatographic mixing of iron(II) and nitrate after injection. The studies in this dissertation demonstrate that the environmental fate of arsenic depends on the biogeochemical cycling of arsenic, iron, and to a lesser extent, sulfur. The development of effective groundwater arsenic remediation strategies depends on a good understanding of each of the involved processes, and their combinations.