![[logo] US EPA](https://webarchive.library.unt.edu/web/20081105232600im_/http://www.epa.gov/epafiles/images/logo_epaseal.gif){kind=logo}
Microbial Reduction of Uranium in Mine Leachate by Fermentative and Iron-Reducing Bacteria
EPA Grant Number: R829515C008Subproject: this is subproject number 008 , established and managed by the Center Director under grant R829515
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: HSRC - Rocky Mountain Regional Hazardous Substance Research Center for Remediation of Mine Waste Sites
Center Director: Shackelford, Charles D.
Title: Microbial Reduction of Uranium in Mine Leachate by Fermentative and Iron-Reducing Bacteria
Investigators: Honeyman, Bruce D. , Spear, John R.
Institution: Colorado School of Mines
EPA Project Officer: Lasat, Mitch
Project Period: November 1, 2002 through October 31, 2004
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (2001)
Research Category: Hazardous Waste/Remediation
Description:
Objective:The goal of this project is to examine the use of microorganisms to remove uranium from mine waste leachates by reductive precipitation in a permeable reactive barrier (PRB). A variety of anaerobic microbial processes, including iron reduction, fermentation and sulfate reduction, can transform uranium (U) from the mobile U(VI) species to the immobile U(IV) species. Sulfate reducing bacteria (SRB) have been studied extensively for their ability to attenuate metal mobility in mine waste plumes; however, these organisms require abundant sulfate, strict circumneutral pH values, cannot directly metabolize complex organic substrates and produce toxic H2S gas. Fermentative organisms are able to directly metabolize high molecular weight organics (substrates ideal for PRBs) producing H2, CO2, and low-molecular weight organic compounds (acetate, lactate); they can tolerate low pH and can reduce U(VI) via indirect and direct (enzymatic) mechanisms. Iron reducers can oxidize H2 and low molecular weight organic compounds while directly reducing U(VI). Biosorption of U(VI) can also result in immobilized U species. This project will explore the hypothesis that fermentative- and iron-reducing microbial activity in a permeable reactive barrier (PRB) intercepting U(VI)-laden leachate will result in a U(IV) precipitate.
This project will examine the use of iron-reducing and fermentative bacteria in a treatment strategy to remove uranium(VI) from impacted groundwater by bioreduction. Batch experiments will be used to optimize reductive processes and promote synergistic reduction of U by fermentative and iron-reductive microbial processes with efficient utilization of carbon substrate. Optimum conditions will be reproduced in column experiments to examine U reduction by a microbial consortium under dynamic flow conditions. Ultimately, this uranium removal and recovery process can be implemented as a permeable reactive barrier (PRB). The efficacy of a citrate extraction process to recover uranium without excavation or serious perturbation of the microbial populations in the PRB will be tested in an initial study for further development.
Approach:The initial approach will be to use a batch culture method in order to maximize efficiency and minimize cost (v. column experiments) in testing the many process variables. Samples will be prepared in 160 ml glass serum bottles in a strictly anaerobic (N2) gloved box and pure microbial cultures will be added to the bottles. The goal of selected treatments will be to stimulate synergistic U(VI)-reduction with efficient utilization of carbon substrate by fermenters and iron-reducers. Carbon sources will be varied, ranging from simple (glucose) to complex (solid hemicellulose substrate) and U species will be varied (U-nitrate, U-carbonate, U-fulvate) as will the addition of iron (species and concentration). The pH range evaluated will be 4 to 8 and the temperature varied from 4 to 30°C. The batch systems will be characterized for: i) microbial growth, and identification of dominant microbial process (by direct counting, pH measurement, and high-performance liquid chromatography (HPLC) to identify soluble metabolites); ii) soluble U(VI) by liquid scintillation counting (LSC) using a 233U(VI) yield tracer; iii) U oxidation state by wet chemistry; and iv) solid phase U by x-ray absorption spectroscopy (XAS) (via our collaborators at Brookhaven National Laboratory: A.J. Francis and Jeffery B. Gillow).
Expected Results:This study will provide an assessment of the efficacy of using fermentative and iron-reducing bacteria to immobilize uranium in an in situ PRB system.
Supplemental Keywords:Ecosystem Protection/Environmental Exposure & Risk, Industry Sectors, TREATMENT/CONTROL, Scientific Discipline, Waste, RFA, Remediation, Geology, Restoration, Waste Treatment, Ecological Risk Assessment, Hazardous Waste, Environmental Engineering, Ecological Effects - Environmental Exposure & Risk, Ecosystem Protection, Groundwater remediation, Hazardous, Mining - NAIC 21, Ecology and Ecosystems, Environmental Monitoring, Bioremediation, bioavailability, heavy metals, risk assessment, treatment, water quality, aquatic ecosystem, ecological impact, environmental rehabilitation, biodegradation, geochemistry, microbial degradation, extraction of metals, anaerobic biodegradation, contaminated waste sites, mining, mining wastes, groundwater hydrology models, acid mine runoff, aquatic toxicology, permeable reactive barrier, uranium, acid mine drainage, groundwater, monitoring, ecological recovery, contaminated aquifers, groundwater pollution, remediation technologies, mining waste, bacterial degradation, contaminant transport, ecological indicators, leaching of toxic metals, aquatic ecosystems, anaerobic degradation, fermentative bacteria, contaminated groundwater, hydrogeology, hydrology, restoration strategies, contaminated sites
Progress and Final Reports:
2003 Progress Report
2004 Progress Report
Main Center Abstract and Reports:
R829515 HSRC - Rocky Mountain Regional Hazardous Substance Research Center for Remediation of Mine Waste Sites