Web Release Date: October 7,
Uranium and Technetium Bio-Immobilization in Intermediate-Scale Physical Models of an In Situ Bio-Barrier
and
Department of Civil Engineering, Oregon State University, Corvallis, Oregon 97331, Department of Natural Resources and Environmental Science, University of Illinois, Urbana, Illinois 61801, Environmental Research Division, Argonne National Laboratory, Argonne, Illinois 60439, and William R Wiley Lab, Pacific NW National Laboratory, Richland, Washington 99352
Received for review February 21, 2006
Revised manuscript received August 28, 2006
Accepted August 30, 2006
Abstract:
We investigated the long-term effects of ethanol addition
on U and Tc mobility in groundwater flowing through
intermediate-scale columns packed with uncontaminated
sediments. The columns were operated above-ground at a
contaminated field site to serve as physical models of
an in situ bio-barrier for U and Tc removal from groundwater.
Groundwater containing 4 
M U and 520 pM Tc was
pumped through the columns for 20 months. One column
received additions of ethanol to stimulate activity of indigenous
microorganisms; a second column received no ethanol
and served as a control. U(VI) and Tc(VII) removal was
sustained for 20 months (~189 pore volumes) in the stimulated
column under sulfate- and Fe(III)-reducing conditions.
Less apparent microbial activity and only minor removal
of U(VI) and Tc(VII) were observed in the control. Sequential
sediment extractions and XANES spectra confirmed that
U(IV) was present in the stimulated column, although U(IV)
was also detected in the control; extremely low concentrations precluded detection of Tc(IV) in any sample. These
results provide additional evidence that bio-immobilization
may be effective for removing U and Tc from groundwater.
However, long-term effectiveness of bio-immobilization may
be limited by hydraulic conductivity reductions or depletion
of bioavailable Fe(III).
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