In Situ Immobilization of Uranium in Structured Porous Media via Biomineralization at the Fracture/Matrix Interface – Subproject to Co-PI Eric E. Roden

[摘要] Although the biogeochemical processes underlying in situ bioremediation technologies are increasingly well understood, field-scale heterogeneity (both physical and biogeochemical) remains a major obstacle to successful field-scale implementation. In particular, slow release of contamination from low-permeability regions (primarily by diffusive/dispersive mass transfer) can hinder the effectiveness of remediation. The research described in this report was conducted in conjunction with a project entitled “In Situ Immobilization of Uranium in Structured Porous Media via Biomineralization at the Fracture/Matrix Interface”, which was funded through the Field Research element of the former NABIR Program (now the Environmental Remediation Sciences Program) within the Office of Biological and Environmental Research. Dr. Timothy Scheibe (Pacific Northwest National Laboratory) was the overall PI/PD for the project, which included Scott Brooks (Oak Ridge National Laboratory) and Eric Roden (formerly at The University of Alabama, now at the University of Wisconsin) as separately-funded co-PIs. The overall goal of the project was to evaluate strategies that target bioremediation at interfaces between high- and low-permeability regions of an aquifer in order to minimize the rate of contaminant transfer into high-permeability/high fluid flow zones. The research was conducted at the Area 2 site of the Field Research Center (FRC) at Oak Ridge National Laboratory (ORNL). Area 2 is a shallow pathway for migration of contaminated groundwater to seeps in the upper reach of Bear Creek at ORNL, mainly through a ca. 1 m thick layer of gravel located 4-5 m below the ground surface. Hydrological tracer studies indicate that the gravel layer receives input of uranium from both upstream sources and from diffusive mass transfer out of highly contaminated fill and saprolite materials above and below the gravel layer. We sought to test the hypothesis that injection of electron donor into this layer would induce formation of a redox barrier in the less conductive materials above and below the gravel, resulting in decreased mass transfer of uranium out these materials and attendant declines in groundwater U(VI) concentration. Details regarding the planning, execution, and results of the in situ biostimulation experiment will be provided in separate peer-reviewed publications by the project PIs and colleagues. This report summarizes research activities conducted at The University of Alabama (2002-2005) and the University of Wisconsin (2005-2007) in support of the field experiment, which included (1) chemical and microbiological characterization of sediment cores from Area 2; (2) sediment slurry experiments with Area 2 materials which evaluated the biogeochemical response to ethanol amendment and the potential for U(VI) reduction; (3) analysis of the response of groundwater microbial communities to in situ biostimulation. In addition, biogeochemical reaction models of microbial metabolism in ethanol-stimulated sediments, developed based on sediment slurry experiments, are described.

[发布日期] 2007-11-02

[学科分类] 核能源与工程

[关键词] AQUIFERS;BINDING ENERGY;BIOREMEDIATION;COMMUNITIES;CONTAMINATION;ELECTRONS;ETHANOL;FLUID FLOW;HYPOTHESIS;IMPLEMENTATION;MASS TRANSFER;METABOLISM;ORNL;PLANNING;S