Microbial Reduction of Uranium in Mine Leachate by Fermentative and Iron-Reducing Bacteria

EPA Grant Number: R829515C008
Subproject: 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) Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management


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.


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:

RFA, Industry Sectors, Scientific Discipline, Waste, TREATMENT/CONTROL, Ecosystem Protection/Environmental Exposure & Risk, Waste Treatment, Remediation, Ecosystem Protection, Restoration, Mining - NAIC 21, Ecological Effects - Environmental Exposure & Risk, Hazardous Waste, Environmental Monitoring, Bioremediation, Ecological Risk Assessment, Ecology and Ecosystems, Geology, Groundwater remediation, Hazardous, Environmental Engineering, hydrogeology, monitoring, risk assessment, aquatic ecosystem, contaminant transport, contaminated waste sites, microbial degradation, contaminated sites, permeable reactive barrier, acid mine drainage, bioavailability, biodegradation, remediation technologies, groundwater hydrology models, restoration strategies, anaerobic biodegradation, uranium, geochemistry, hydrology, mining, treatment, ecological recovery, in situ bioremediation, leaching of toxic metals, aquatic ecosystems, contaminated groundwater, water quality, environmental rehabilitation, ecological indicators, contaminated aquifers, ecological impact, extraction of metals, anaerobic degradation, aquatic toxicology, mining waste, bacterial degradation, groundwater, heavy metals, mining wastes, groundwater pollution, acid mine runoff

Progress and Final Reports:

  • 2003 Progress Report
  • Final

  • Main Center Abstract and Reports:

    R829515    HSRC - Rocky Mountain Regional Hazardous Substance Research Center for Remediation of Mine Waste Sites

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R829515C001 Redox Transformations, Complexation and Soil/Sediment Interactions of Inorganic Forms of As and Se in Aquatic Environments: Effects of Natural Organic Matter
    R829515C002 Fate and Transport of Metals and Sediment in Surface Water
    R829515C003 Metal Removal Capabilities of Passive Bioreactor Systems: Effects of Organic Matter and Microbial Population Dynamics
    R829515C004 Evaluating Recovery of Stream Ecosystems from Mining Pollution: Integrating Biochemical, Population, Community and Ecosystem Indicators
    R829515C005 Rocky Mountain Regional Hazardous Substance Research Center Training and Technology Transfer Program
    R829515C006 Technical Outreach Services for Communities and Technical Assistance to Brownfields
    R829515C007 Evaluation of Hydrologic Models for Alternative Covers at Mine Waste Sites
    R829515C008 Microbial Reduction of Uranium in Mine Leachate by Fermentative and Iron-Reducing Bacteria
    R829515C009 Development and Characterization of Microbial Inocula for High-Performance Passive Treatment of Acid Mine Drainage
    R829515C010 Reactive Transport Modeling of Metal Removal From Anaerobic Biozones
    R829515C011 Assessment of Electrokinetic Injection of Amendments for Remediation of Acid Mine Drainage
    R829515C012 Metal Toxicity Thresholds for Important Reclamation Plant Species of the Rocky Mountains
    R829515C013 An Improved Method for Establishing Water Quality Criteria for Mining Impacted Streams