Assessment of biostimulation processes offers a new look at uranium reduction
By analyzing soil and aqueous samples from a laboratory column study, scientists from several universities and Pacific Northwest National Laboratory (PNNL) assessed how the addition of small amounts of nanoparticulate goethite to sediment affects biostimulation processes. The study focused on microbial composition and dynamics involved in uranium remediation, especially as related to the bioavailability of Fe(III) phases and in the presence of sulfate-containing groundwater. The sediment was obtained from a uranium-contaminated former Uranium Mill Tailings Remediation Action (UMTRA) site located at Rifle, Colorado. Field studies and laboratory research were conducted to determine the underlying biogeochemical process involved in attenuation of soluble uranium from the aquifer upon biostimulation of metal-reducing bacteria. Biostimulation was achieved by injecting acetate, an electron donor, into the Rifle aquifer.
For these experiments, the nanoparticulate goethite was synthesized using 95 percent enriched 57Fe metal—a stable iron isotope that facilitated 57Fe-Mössbauer spectroscopy measurements allowing researchers to monitor the 57Fe-goethite (bio)transformation under varying aquifer reducing conditions. Mössbauer spectroscopy and scanning electron microscopy capabilities, housed within the Department of Energy's (DOE) EMSL, were used to track the transformations. Small amounts of goethite suppressed the degree of sulfate reduction and affected the overall electron flux to the electron donors and microbial community structure with no noticeable effect on uranium reduction. The study also showed Geobacter-like species (dissimilatory iron reducer) were active during the dominant sulfate reduction phase, and the relative importance of the iron and sulfate reduction is related to the bioavailability of Fe(III) phases. These results suggest it may be possible to manipulate microbial structure and activity by nanoparticulate Fe-oxide amendment.
Scientific impact: By tracking (bio)transformation of iron oxides on uranium reduction—U(VI) to U(IV)—under varied biostimulated conditions, scientists have gained an additional understanding of how various Fe-oxides affect iron–sulfate precipitation and how these conditions can impact and potentially improve processes used for uranium reduction and removal. It also will assist in developing accurate predictive biogeochemical contaminant transport models.
Societal impact: Understanding these biostimulated processes may enhance applications used in uranium and other bioremediation efforts to resuscitate and revitalize contaminated sites, including 15 UMTRA sites under DOE purview.
Reference: Moon HS, L McGuinness, RK Kukkadapu, AD Peacock, J Komlos, LJ Kerkhof, PE Long, and PR Jaffé. 2010. "Microbial Reduction of Uranium Under Iron- and Sulfate-reducing Conditions: Effect of Amended Goethite on Microbial Community Composition and Dynamics." Water Research 44(14):4015-4028. DOI: 10.1016/j.watres.2010.05.003.
Acknowledgment: This research was funded by DOE's Office of Biological and Environmental Research Environmental Remediation Sciences Program and the Rifle, Colorado, Integrated Field Research Challenge Site project.
User Proposals: 34002 and 30465
Released: July 20, 2010