State Water Resources Research Institute Program


Project Id: 2010AZ395B
Title: Bioremediation of Uranium Plumes with Nano-Scale Zero Valent Iron
Project Type: Research
Start Date: 3/01/2010
End Date: 2/28/2011
Congressional District: 07
Focus Categories: Toxic Substances, Groundwater, Treatment
Keywords: Uranium, Groundwater, Bioremediation, Microbial Reduction, Nano Zero-Valent Iron
Principal Investigators: Field, James; Sierra, Reyes
Federal Funds: $ 10,000
Non-Federal Matching Funds: $ 20,031
Abstract: Uranium is an important environmental contaminant impacting groundwater supplies in Arizona. The main sources are from uranium mine tailings, former uranium processing plants, and high natural background levels in areas of granite bedrock. In the environment, uranium generally occurs as hexavalent uranium (U6+) or tetravalent uranium (U4+, often present as the mineral uraninite, UO2). While U6+ is soluble and mobile, U4+ is highly insoluble and immobile. Therefore, reductive precipitation is an attractive approach to remove soluble uranium and remediate contaminated groundwater. Reduction of soluble U6+ can be catalyzed by chemical and by microbial processes involving anaerobic bacteria. Typically organic substrates (e.g. ethanol, lactate, acetate) are utilized as the electron donors to drive biological uranium reduction.

Preliminary work by our research group has led to the enrichment of a novel uranium-reducing bacterial culture that is capable of utilizing Fe0 (zero-valent iron or ZVI) as an electron donor. The microbial culture greatly accelerates uranium reduction rates with ZVI by more than 20-fold in a sustained fashion. ZVI has some important advantages over alternative bioremediation strategies relying on organic electron donors. The ZVI could provide a long-term reservoir of slow-release electron equivalents as well as buffer against uranium re-oxidation. The objective of this study is to investigate the use of nano-sized ZVI (nZVI) as an electron donor for uranium-reducing microorganisms. Stabilized dispersions of nZVI can be transported through porous media to facilitate in situ bioremediation of uranium-contaminated groundwater. This project is expected to lead to the development of a low-cost and low-maintenance method for the in situ bioremediation of groundwater contaminated by uranium, which generates insoluble uranium minerals that are stable against re-oxidation over prolonged time periods. Application of this technique could be expanded to the treatment of other toxic contaminants amenable to microbial reductive processes (e.g. perchlorate, arsenate, oxidized radionuclides).

Progress/Completion Report, 2010, PDF

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