• DOI:10.1021/ES051960U
• Corpus ID: 19762292

Pilot-scale in situ bioremedation of uranium in a highly contaminated aquifer. 2. Reduction of u(VI) and geochemical control of u(VI) bioavailability.

@article{Wu2006PilotscaleIS,
  title={Pilot-scale in situ bioremedation of uranium in a highly contaminated aquifer. 2. Reduction of u(VI) and geochemical control of u(VI) bioavailability.},
  author={Wei-Min Wu and Jack Carley and Terry J Gentry and Matthew Ginder‐Vogel and Michael N. Fienen and Tonia L. Mehlhorn and Hui-Jun Yan and Sue Caroll and Molly N Pace and Jennifer L. Nyman and Jian Luo and Margaret E Gentile and Matthew W. Fields and Robert F. Hickey and Baohua Gu and David B. Watson and Olaf Arie Cirpka and Jizhong Zhou and Scott Fendorf and Peter K. Kitanidis and Philip M. Jardine and Craig S. Criddle},
  journal={Environmental science \& technology},
  year={2006},
  volume={40 12},
  pages={
          3986-95
        }
}

• Wei-Min Wu, J. Carley, +19 authors C. Criddle
• Published 13 May 2006
• Environmental Science
• Environmental science & technology

In situ microbial reduction of soluble U(VI) to sparingly soluble U(IV) was evaluated at the site of the former S-3 Ponds in Area 3 of the U.S. Department of Energy Natural and Accelerated Bioremediation Research Field Research Center, Oak Ridge, TN. After establishing conditions favorable for bioremediation (Wu, et al. Environ. Sci. Technol. 2006, 40, 3988-3995), intermittent additions of ethanol were initiated within the conditioned inner loop of a nested well recirculation system. These additions initially stimulated denitrification of matrix-entrapped nitrate, but after 2 months, aqueous U levels fell from 5 to approximately 1 microM and sulfate reduction ensued. Continued additions sustained U(VI) reduction over 13 months. X-ray near-edge absorption spectroscopy (XANES) confirmed U(VI) reduction to U(IV) within the inner loop wells, with up to 51%, 35%, and 28% solid-phase U(IV) in sediment samples from the injection well, a monitoring well, and the extraction well, respectively. Microbial analyses confirmed the presence of denitrifying, sulfate-reducing, and iron-reducing bacteria in groundwater and sediments. System pH was generally maintained at less than 6.2 with low bicarbonate level (0.75-1.5 mM) and residual sulfate to suppress methanogenesis and minimize uranium mobilization. The bioavailability of sorbed U(VI) was manipulated by addition of low-level carbonate (< 5 mM) followed by ethanol (1-1.5 mM). Addition of low levels of carbonate increased the concentration of aqueous U, indicating an increased rate of U desorption due to formation of uranyl carbonate complexes. Upon ethanol addition, aqueous U(VI) levels fell, indicating that the rate of microbial reduction exceeded the rate of desorption. Sulfate levels simultaneously decreased, with a corresponding increase in sulfide. When ethanol addition ended but carbonate addition continued, soluble U levels increased, indicating faster desorption than reduction. When bicarbonate addition stopped, aqueous U levels decreased, indicating adsorption to sediments. Changes in the sequence of carbonate and ethanol addition confirmed that carbonate-controlled desorption increased bioavailability of U(VI) for reduction.