Bioremediation of Groundwater Uranium Contamination: Field Experiments and Biogeochemical Modeling

Chen Zhu¹, Qusheng Jin², Zuoping Zheng¹, and Matthew Reeder^1
1Geological Sciences, Indiana University, Bloomington, IN
²Geology, Univ. of Oregon, Eugene, OR

From a field biostimulation experiment conducted at the Department of Energy's Oak Ridge Field Research Center, Tennessee, we took a time series of groundwater samples and have measured major, minor, and trace elements as well as C, N, and S stable isotopes. Data show NO₃-, Mn (IV), Fe (III), U (VI), Tc (VII), and SO_4-2 reduction. A zeroth order rate law generally describes the data well, but the derived in situ rates are effective rates that mask many simultaneous and competing reactions and processes. However, our comprehensive suite of chemicals, stable isotopes, and characterization of the solid matrix in our study provided an opportunity to decipher a network of redox and non-redox reactions through biogeochemical modeling. The model describes the metabolisms of diverse microorganisms in the aquifer as a network of metabolic reactions. It considers various interactions among the pathways, such as inhibition, syntrophism, and competition. To incorporate the close interactions between microorganisms and aquifer environments, the model also considers inorganic geochemical reactions pertinent to microbial metabolisms, including abiotic redox reactions, mineral precipitation and dissolution, surface adsorption, and ion exchange. The new model predicts well the progress of redox transformations observed during the field experiment. The results revealed the key roles of metabolic diversity and energy availability in controlling the kinetics of redox reactions in aquifers.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas