Vanadium (V) is both a widespread environmental contaminant from fossil fuel combustion and a poorly understood, but commercially important, metal. Although several vanadium reducers have been isolated from the environment, none are from highly contaminated sites or have been implicated in bioremediation. Injection of organic carbon directly into an aquifer to biostimulate contaminated sediments in Rifle, CO has resulted in the removal of up to 68 uM (96%) of contaminant vanadium from groundwater for an extended period of time (months to years). This process occurs concurrent with iron reduction. In order to better evaluate the microbial role in vanadium removal, we used in-well flow-through columns to allow the simultaneous addition of acetate (a carbon source) and additional (5 mM) vanadate - V (V) - to sediments along with the influx of natural groundwater. In these experiments we measured vanadium loss by colorimetric methods, enumerated numbers of V(V) reducers present before and after and stimulation using the most probable number (MPN) method, and isolated vanadium reducers from unstimulated sediments. Currently, community analysis of the sediment is being performed.
Results/Conclusions
Our results demonstrated the in situ removal of V(V) (72-98%) from sediments with an organic carbon amendment, suggesting microbially mediated removal of V(V). In addition, MPNs showed up to a 50-fold increase in cell numbers (1,100,000 vs. 23,000 cells/g of sediment) of organisms able to reduce V(V) in columns after three weeks of acetate addition. From unamended sediment we isolated a strain of Betaproteobacteria (BODI) that grows well at high vanadium concentrations. BODI was able to grow on nitrate and iron Fe(III) and reduces vanadium. Ongoing genome sequencing and physiological experiments will target this organism’s physiology and identify potential vanadium-reducing enzymes, for which there is no information at present. Community analysis of the stimulated sediments will help to determine the importance of strain BODI in vanadium reduction in situ. These results suggest that vanadium reducers exist in contaminated sediments and show that in situ microbial communities can be used to remove vanadium from groundwater.