Soil, Water and Environmental Science
Impact of Electron Donor and Other Factors on In-situ Biosequestration of Uranium
Uranium contamination of groundwater is a major issue in the United States where the sources of contamination are both anthropogenic (eg., mining, and nuclear testing), and natural. According to a recent study (Nolan and Weber, 2015), groundwater uranium concentrations in several aquifers in the US are higher than the Maximum Contaminant Level (MCL) that is set by the U.S. EPA (30 µg/L). There are more than 500 abandoned uranium mines in the Navajo Nation, many of which have elevated uranium concentrations in groundwater (EPA, 2016). Ingestion of uranium-contaminated groundwater causes severe risks to human health such as cancer, and kidney and liver damage. We are studying different methods to clean up contaminated groundwater at a former uranium mine in Monument Valley, northern Arizona. One method being tested is called in-situ biosequestration. This process involves injecting an organic compound (electron donor) that provides a food source for microorganisms living in the subsurface. These microorganisms create conditions that alter the subsurface so that uranium can be sequestered, whereby it is removed from groundwater and becomes associated with the sediment as well as reducing sulfate and nitrate concentrations. A pilot-scale test of in-situ biosequestration for uranium in groundwater is in progress at the site. Complementary bench-scale experiments are being conducted to support the analysis of the pilot field test where sediments and groundwater collected from the site are used for this purpose. These experiments showed that of several tested electron donors, ethanol performed best in sequestering uranium in the sediments and stimulating microbial reduction of nitrate and sulfate. The impact of different concentrations of nitrate and sulfate on uranium sequestration is also being examined.
Nolan, J., and Weber, K., A., (2015): Natural Uranium Contamination in Major US Aquifers Linked to Nitrate. Environ. Sci. Technol. Lett., 2, 215−220.
US. Environmental Protection Agency, (2016): https://www.epa.gov/navajo-nation-uranium-cleanup.