Field-Scale Bioremediation of Arsenic-Contaminated Groundwater Using Sulfate Reducing Bacteria: Geochemical Monitoring and Hydrological Modeling

Levitt, Eric; Ghandehari, Shahrzad Saffari; Lee, Ming‐Kuo; Miller, Bill R.; Saunders, James A.; Ahmed, Nur; Uddin, Ashraf; Wang, Luxin; Billor, M. Zeki; Redwine, Jim; Marks, Justin

doi:10.1130/abs/2016am-281133

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“…The bioremediation technology employed in this study utilizes these geochemical properties of arsenic, while optimizing the growth of sulfate reducing bacteria and the formation of biogenic pyrite (pyrite formed through the induced changes caused by micro bacteria) in an attempt to reduce arsenic concentrations in the groundwater below the EPA's standard. This study furthers the research of Starnes (2015), Saffari 2015, and Levitt (2016) at an industrial site in Florida where the groundwater is heavily contaminated with herbicide-based arsenic. The main objective of this study is to gain a better understanding of the pyrite-grain formation that takes places during the bioremediation process that has been initiated at this Florida field site.…”

Section: Introductionsupporting

confidence: 73%

Pyrite Biomineralization and Arsenic Sequestration at a Florida Industrial Site: Imaging and Geochemical Analysis

Wilson¹

2017

Geological Society of America Abstracts With Programs

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A yearlong field-scale bioremediation experiment was conducted at a Florida industrial site, where groundwater in an unconfined aquifer was contaminated by an arsenic-based herbicide. The bioremediation technique stimulated the indigenous sulfate reducing bacteria (SRB) with a nutrient-rich slurry solution containing labile organic carbon, ferrous iron, sulfate, and fertilizer. This amendment induced sulfate reducing conditions and caused the coprecipitation and adsorption of the dissolved arsenic in biogenic pyrite. This research characterized the biogenic pyrite formed and assessed the spatial and temporal changes in groundwater chemistry during the project. Pyrite was characterized using multiple techniques including X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and electron microprobe analysis. These analyses confirmed the rapid formation of pyrite one week after the injection. The pyrite formed either as well-defined euhedral nano-crystals or as spherical aggregates (framboids) 1-50 µm in diameter. The electron microprobe analysis determined that the pyrite contained between 0.05-0.4 weight % of sequestered arsenic. The dissolved arsenic concentration in the water decreased from pre-injection levels of 300-500 ppb to below the site regulatory limit of 50 ppb (> 90% removal rate) during the initial six month period. The reactive transport of the injectant plume was investigated using a conservative chloride tracer and biomineralization of pyrite along two flow transects. The results show that the stimulated pyrite biomineralization accounted for more than 80% of overall arsenic removal and dilution caused less than 20% of concentration reduction. Saturation index calculations show that arsenian-pyrite iii quickly became oversaturated in targeted wells one week after injection of the solution and then remained mostly saturated during the one-year monitoring period, suggesting that the arsenic sequestration was effectively maintained by the stability of arsenian-pyrite. This research presents data showing through the amendment of a nutrient-rich solution, indigenous SBR can effectively sequester arsenic into pyrite at levels great enough to bring dissolved arsenic concentrations below the regulatory or perhaps even drinking water standards. Grants obtained from the National Science Foundation were integral to the execution of this research. I would like to thank the following people who generously gave their time, advice, and criticisms: Dr. Ming-Kuo Lee, Dr. James Saunders, Dr. Ashraf Uddin, and the entire faculty at the Auburn Department of Geosciences. A special thanks to the chair of my advising committee, Dr. Lee, who provided me with invaluable guidance and mentorship during my time at Auburn. He always had an open door and was more than willing to help with any problem or question I encountered. A thanks is also owed to Dr. Saunders for his guidance and hand in recruiting me to Auburn University. Another member of the Geosciences Department that was vital to my research was Dr. Bil...

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Section: Introductionsupporting

confidence: 73%