Past research projects and findings
The ORFRC originally was established by DOE's Natural and Accelerated Bioremediation Research (NABIR) program to encourage hypothesis-based field research and develop process-level understanding of bioremediation of metals and radionuclides. From 2001-2007, NABIR scientists conducted field-scale research on several small field plots and obtained thousands of subsurface samples for laboratory-based studies. Research focused on active interventions to achieve accelerated microbially mediated bioreduction and immobilization of subsurface contaminants.
The Natural and Accelerated Bioremediation Research (NABIR) Program was a multi-year, interdisciplinary, basic research program in the Environmental Remediation Sciences Division (ERSD) in the Office of Biological and Environmental Research (BER) in the Department of Energy's (DOE's) Office of Science. Ending in 2006, the NABIR program sought to provide a fundamental science basis for the development of cost-effective strategies for microbial bioremediation of radionuclides and metals in the subsurface at DOE sites. Research focused on the metals chromium and mercury, and on the radionuclides uranium, technetium and plutonium because these radionuclides and metals are of concern at DOE sites and are tractable to bioremediation.
NABIR research was oriented toward application in areas that have low levels of widespread contamination in the subsurface below the zone of root influence, and includes both the unsaturated (vadose) zone and the saturated (ground water) zone. It encompassed intrinsic bioremediation by naturally occurring microbial communities, as well as accelerated bioremediation through biostimulation (addition of inorganic or organic nutrients) or, if necessary, bioaugmentation (additions of microorganisms). Strategies leading to the immobilization of contaminants in place were of primary interest.
To encourage hypothesis-based field research, process-level understanding, and long-term field studies, the NABIR program established the Oak Ridge Field Research Center (ORFRC). The ORFRC provides a location on a DOE site where scientists can conduct field-scale research and obtain DOE-relevant subsurface samples for laboratory-based studies of bioremediation.
Accomplishments and findings [top]
Overview: Previous research activities at the ORFRC focused on small plot-scale studies where interventions can produce in situ bioreduction and immobilization of subsurface U and Tc contamination. ORFRC researchers have shown that microorganisms found in subsurface environments can be used to transform contaminants, such as U and Tc, into chemical forms that are less mobile in ground water. In addition to investigating naturally occurring microbial communities in the ORFRC's subsurface, researchers tested novel geophysical, hydraulic, and tracer techniques for characterizing and monitoring subsurface processes and ground water flow. For example, they tested new inexpensive surface geophysical techniques in which seismic waves and electrical currents are used to create three-dimensional images of the subsurface geology and of contaminated ground water plumes. As of 2007, over 60 peer-reviewed publications resulted from ORFRC research with numerous others pending. Site-wide conceptual and numerical models were developed. This web site incorporates descriptions of these past research activities, and evolving data as well as experimental and analytical capabilities.
Field research projects: Three major multi-disciplinary field-scale research projects (and numerous smaller ones) were implemented successfully at the ORFRC (more).
Stimulated microbial reduction of U and Tc: Microbially mediated reduction of U, Tc, and nitrate in the subsurface via biostimulation was demonstrated at the ORFRC (Istok et al. 2004). Biological reduction/immobilization of U(VI) using a 3-step process involving ethanol injection lowered ground water U concentrations from as high as ~60 mg/L to <0.030 mg/L. Studies showed that U concentrations could be maintained below 0.030 mg/L for a limited time, even without continuous injection of ethanol (Wu et al. 2006a, 2006b). More studies are needed to determine the long-term applicability of the process.
- Stanford University: A stimulated bioreduction zone protected by inner and outer recirculation loops for uranium biotransformation combined with denitrification.
- Oregon State University: Push-pull tests to determine the kinetics of electron-acceptor and electron-donor use for microbially mediated uranium and technetium reduction and reoxidation.
- Pacific Northwest National Laboratory (PNNL): Stimulation of microbial uranium reduction in hydrologically accessible fractured zones to precipitate uranium oxide and isolate the uranium in low-permeability porous regions.
Inhibition/reoxidation of U and Tc:
Limited, small scale in situ investigations documented the inhibition of U reduction by nitrate, NOx, and Ca and the reoxidation of U by nitrate and NOx (Senko et al. 2005; Brooks et al. 2003). Although the presence of humics can accelerate the reduction of U, humics also can accelerate the reoxidation process (Gu et al. 2005).
Geophysical characterization and monitoring methods:
Geophysical methods, including radar, seismic, and complex electrical crosshole and surface electrical and seismic methods, were used on a limited basis for characterization and monitoring at the ORFRC (Watson et al. 2005). There are many examples of different geophysical characterization and monitoring approaches that were tested at the ORFRC. These examples suggest that integration of hydrological and geophysical data can improve quantitative estimates of flow and transport parameters at locations not sampled by conventional borehole measurements (e.g., Chen et al. 2006). These and other new methods that are under development suggest that geophysical approaches could be extremely useful for guiding sampling and for evaluating long-term natural attenuation and remediation efficacy (more).
Microbiology of subsurface materials:
Many microbial studies were conducted on ORFRC sediment and ground water samples collected during manipulations and site characterization activities (e.g., Fields et al. 2005a, 2005b; Petrie et al. 2003; North et al. 2004; Hwang et al. 2006; Zhou et al. 2004; Kostka et al. 2006). Several thousand genetic sequences from ORFRC ground water and sediment samples were retrieved by numerous investigators and compiled and annotated by one of the PIs (Kostka) into the only sequence database of its kind for DOE sites (more). This database will continue to be updated through the IFRC project. Using this robust sequence database indicates that the ORFRC may support a large diversity and abundance of metal- and nitrate-reducing prokaryotes. Further field studies showed that, in concert with the prevailing physicochemical conditions, contaminant concentrations directly affect the diversity and activity of subsurface microbial communities. From samples taken over a 7 km transect across the shale and carbonate pathways of the ORFRC, clone libraries were constructed from 16S ribosomal RNA gene targets and the metabolically active microorganisms were profiled using terminal restriction fragment length polymorphisms (TRFLP) of reverse-transcribed RNA targets.
Application of functional gene arrays (FGAs):
Construction of the most comprehensive FGAs available for environmental studies (Schadt et al. 2005) allowed investigation of microbial communities in ground water contaminated with U and other metals with unprecedented resolution. Use of these arrays at the ORFRC showed that contaminants and geochemistry have strong influences on existing microbial communities (Wu et al. 2006c). Microarray analysis indicated that in situ U reduction activity correlated with the abundance of multiheme C-type cytochome genes (R=0.6), dissimilatory sulfite reductase genes (dsrAB) (R=0.8) similar to those from Desulfovibrio-like and Geobacter-like species. These results are consistent with findings from 16S rRNA gene-based library studies.
A 3-D flow and transport model coupled with a nitrate nonreactive transport model was implemented in a site-wide effort to predict hydraulics and contaminant concentrations during remediation efforts. A higher resolution plot-scale numerical model (more) was developed to aid experimental design and interpretation of results. Models that include U reduction reactions and immobilization were used to determine reaction rate coefficients and the scale dependence of those coefficients. The models integrated the interpretations of various field and laboratory experiments. NABIR ORFRC research also documented discrepancies between laboratory and observed field rates of microbial reduction (1,000 to 100,000 times slower in the field) and compiled rate data in tables and reports. Those data were incorporated into numerical modeling of ORFRC site characteristics and processes. Advanced data analysis techniques, including neural networks, have also were developed and applied to characterize the relationships between geochemistry and microbial populations (Palumbo et al. 2004).
Development of characterization and monitoring tools:
NABIR ORFRC researchers developed numerous novel and important characterization and monitoring tools including coupons or microbe ("bug") traps for assessing in situ microbial contamination (Peacock et al. 2004; Reardon et al. 2004), portable immunoassay biosensor for U (Blake et al. 2001), solid-phase characterization techniques for sediment samples, flowmeter testing (Fienen et al. 2004), geophysical techniques for site characterization and monitoring of subsurface processes (see above), and novel hydraulic and tracer testing of subsurface ground water flow (Luo et al. 2005a, 2006).
Field research projects [top]
Three major multi-disciplinary field-scale research projects (and numerous smaller ones) were implemented successfully at the ORFRC (more).
- Stanford University: A stimulated bioreduction zone protected by inner and outer recirculation loops for uranium biotransformation combined with denitrification (more).
- Oregon State University: Push-pull tests to determine the kinetics of electron-acceptor and electron-donor use for microbially mediated uranium and technetium reduction and reoxidation (more).
- Pacific Northwest National Laboratory (PNNL): Stimulation of microbial uranium reduction in hydrologically accessible fractured zones to precipitate uranium oxide and isolate the uranium in low-permeability porous regions (more).