Microbially Induced Calcite Precipitation for Subsurface Immobilization of Contaminants
Abstract
Subsurface radionuclide and metal contaminants throughout the U.S. Department of Energy (DOE) complex pose one of the greatest challenges for long-term stewardship. One promising stabilization mechanism for divalent trace ions, such as the short-lived radionuclide 90Sr, is co-precipitation in calcite. We have found that calcite precipitation and co-precipitation of Sr can be accelerated by the activity of urea hydrolyzing microorganisms, that higher calcite precipitation rates can result in increased Sr partitioning, and that nutrient additions can stimulate ureolytic activity. To extend our understanding of microbially induced calcite precipitation (MICP) in an aquifer setting a continuous recirculation field experiment evaluating MICP was conducted at the Integrated Field Research Challenge (IFRC) site located at Rifle, CO. In this experiment, groundwater extracted from an onsite well was amended with urea (total mass of 42.5 kg) and molasses (a carbon and electron donor) and re-injected into a well approximately 4 meters up-gradient for a period of 12 days followed by 10 months of groundwater sampling and monitoring. Crosshole radar and electrical tomographic data were collected prior, during, and after the MICP treatment. The urea and molasses treatment resulted in an enhanced population of sediment associated urea hydrolyzing organisms as evidenced by increases in the number of ureC gene copies, increases in 14C urea hydrolysis rates, and long-term observations of ammonium (a urea hydrolysis product) in the injection, extraction and down gradient monitoring wells. Permeability changes and increases in the calcite saturation indexes in the well field suggest that mineral precipitation has occurred; ongoing analysis of field samples seeks to confirm this. Changes in dielectric constant and electrical conductivity were used to interpret the spatiotemporal distribution of the injectate and subsequent calcite precipitation. Modeling activities are underway to define field-scale urea hydrolysis rates.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.H21A1051S
- Keywords:
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- 0412 BIOGEOSCIENCES / Biogeochemical kinetics and reaction modeling;
- 0448 BIOGEOSCIENCES / Geomicrobiology;
- 1831 HYDROLOGY / Groundwater quality