• Identifying Optimal Electron Donors to Promote Biosequestration of Uranium for an UMTRCA Title 1 Site

      Brusseau, Mark L.; Abel, Erin Jessica; Artiola, Janick F.; Zhong, Hua (The University of Arizona., 2016)
      Biostimulation is the use of in-situ microorganisms and added reagents in order to biosequester, precipitate, or absorb contaminants from contaminated groundwater and sediment. To test the effectiveness of this remediation approach at a particular site, small scale experiments, such as miscible-displacement, batch, or microcosm experiments, should be performed before a large-scale in-situ biosequestration electron donor injection. In this study, electron donor solutions containing contaminated groundwater and ethanol, acetate, benzoate, or glucose were injected into aquifer sediments collected from a UMTRCA Title 1 Site in Monument Valley, AZ. These experiments showed that ethanol, acetate, and glucose were effective electron donors for the stimulation of microbial activity in order to sequester uranium and reduce nitrate and sulfate concentrations. Conversely, benzoate was not effective at sequestering or reducing the contaminants. After electron-donor deficient groundwater was injected into the columns, a rebound of nitrate, sulfate, and uranium concentrations was observed. Due to this rebound, it was inferred that the mechanism of sequestration of uranium and hence reduction of nitrate and sulfate was due to the creation of reducing conditions via microbial activity. The insoluble reduced uranium was hypothesized to have precipitated or adsorbed to surrounding sediments. Incoming groundwater contained dissolved oxygen and therefore oxidized the reduced contaminants, consequently returning them into solution. It was hypothesized that a similar rebound would occur if ethanol, acetate, or glucose were to be injected in-situ due to sustained groundwater flow through the aquifer sediments on site.