title: Uranium bioreduction rates across scales: biogeochemical hot moments and hot spots during a biostimulation experiment at Rifle, Colorado.
abstract: We aim to understand the scale-dependent evolution of uranium bioreduction during a field experiment at a former uranium mill site near Rifle, Colorado. Acetate was injected to stimulate Fe-reducing bacteria (FeRB) and to immobilize aqueous U(VI) to insoluble U(IV). Bicarbonate was coinjected in half of the domain to mobilize sorbed U(VI). We used reactive transport modeling to integrate hydraulic and geochemical data and to quantify rates at the grid block (0.25 m) and experimental field scale (tens of meters). Although local rates varied by orders of magnitude in conjunction with biostimulation fronts propagating downstream, field-scale rates were dominated by those orders of magnitude higher rates at a few selected hot spots where Fe(III), U(VI), and FeRB were at their maxima in the vicinity of the injection wells. At particular locations, the hot moments with maximum rates negatively corresponded to their distance from the injection wells. Although bicarbonate injection enhanced local rates near the injection wells by a maximum of 39.4%, its effect at the field scale was limited to a maximum of 10.0%. We propose a rate-versus-measurement-length relationship (log R' = -0.63 log L - 2.20, with R' in μmol/mg cell protein/day and L in meters) for orders-of-magnitude estimation of uranium bioreduction rates across scales.
authors: John and Willie Leone Department of Energy and Mineral Engineering, ‡EMS Energy Institute, and §Earth and Environmental Systems Institute (EESI), Pennsylvania State University , University Park, Pennsylvania 16802, United States.
authors: Chen
authors: C
authors: Bao
authors: Hongfei
authors: H
authors: Wu
authors: Li
authors: L
authors: Li
authors: Darrell
authors: D
authors: Newcomer
authors: Philip E
authors: PE
authors: Long
authors: Kenneth H
authors: KH
authors: Williams
mesh_terms: D001419:Bacteria / Q000378:metabolism; D001673:Biodegradation, Environmental; D003120:Colorado; D008962:Models, Theoretical; D013997:Time Factors; D014501:Uranium / Q000302:isolation & purification*; D014867:Water / Q000737:chemistry; D014875:Water Pollutants, Radioactive / Q000302:isolation & purification
chemical_list: D014875:Water Pollutants, Radioactive; D014867:Water; D014501:Uranium