In Situ Bioremediation of Uranium with Emulsified Vegetable Oil as the Electron Donor

Abstract

A field test with a one-time emulsified vegetable oil (EVO) injection was conducted to assess the capacity of EVO to sustain uranium bioreduction in a high-permeability gravel layer with groundwater concentrations of (mM) U, 0.0055; Ca, 2.98; NO3(-), 0.11; HCO3(-), 5.07; and SO4(2-), 1.23. Comparison of bromide and EVO migration and distribution indicated that a majority of the injected EVO was retained in the subsurface from the injection wells to 50 m downgradient. Nitrate, uranium, and sulfate were sequentially removed from the groundwater within 1-2 weeks, accompanied by an increase in acetate, Mn, Fe, and methane concentrations. Due to the slow release and degradation of EVO with time, reducing conditions were sustained for approximately one year, and daily U discharge to a creek, located approximately 50 m from the injection wells, decreased by 80% within 100 days. Total U discharge was reduced by 50% over the one-year period. Reduction of U(VI) to U(IV) was confirmed by synchrotron analysis of recovered aquifer solids. Oxidants (e.g., dissolved oxygen, nitrate) flowing in from upgradient appeared to reoxidize and remobilize uranium after the EVO was exhausted as evidenced by a transient increase of U concentration above ambient values. Occasional (e.g., annual) EVO injection into a permeable Ca and bicarbonate-containing aquifer can sustain uranium bioreduction/immobilization and decrease U migration/discharge.

Push-pull tests for estimating effective porosity: expanded analytical solution and in situ application

“…Therefore, the range of hydraulic conductivity reported in this study was notably less (up to two orders of magnitude) than to the value previously reported. It is important to note that Watson et al (2013), and Phillips et al (2008), also reported that the fill material was gravelly, whereas no gravel component is known to exist within the area of this study site. Therefore, the lack of a gravel component in the fill material within the study site may explain the lower values of hydraulic conductivity.…”

“…However, Watson et al (2013) reported that the hydraulic conductivity of the fill material, in Area 2 test wells immediately east of the study site, was approximately Table 3 Effective porosity calculated from the truncated and expanded solutions, (20) and (18), respectively, for tests in this study (FW220-FW225) and for tests from Hall et al (1991) and Istok (2013) …”

Distribution of uranium and thorium in dolomitic gravel fill and shale saprolite

“…Baker). Linear combinations of these three standard spectra accounted for >99% of the measured counts indicating no 8 significant content of other γ-emitting radionuclides in these soils. Results were expressed as mass of each element per unit weight of air-dried soil (i.e., µg g -1 ) to be directly comparable with other analytical methods.…”

“…A large mixed waste plume of contaminated groundwater is preferentially migrating away from the ponds towards nearby Bear Creek [5][6][7][8]. Rates and mechanisms of immobilization and natural attenuation of metals, radionuclides (i.e., U, Th) and co-contaminants like nitrate are being studied at the U.S. DOE Oak Ridge Integrated Field Research Challenge (ORIFRC) field site located near the S-3 ponds [7][8][9][10].…”

Potential aquifer vulnerability in regions down-gradient from uranium in situ recovery (ISR) sites

“…In situ bioremediation processes have been demonstrated in the field for metal(loid)-contaminated groundwater (including uranium) using both iron-reducing bacteria (e.g., Anderson et al, 2003) and sulfate-reducing bacteria (Saunders et al, , 2008Tang et al, 2013;Watson et al, 2013;Wu et al, 2006). Taken together, these approaches are apparently analogous in real time to the important redox geochemical and geomicrobiologic processes that were involved in the formation of roll-front uranium ores.…”