Sequestration of Radionuclides and Metal Contaminants through Microbially-Induced Carbonate Precipitation

Nasser Hamdan, Edward Kavazanjian, Bruce E. Rittmann

In the proceedings of: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Ground Improvement/Remediation

ABSTRACT: Microbially induced carbonate precipitation (MICP), an emerging technology for soil improvement, also may be used to sequester (biomineralize) radionuclides and metal contaminants (e.g., 90Sr2+, Cd2+) in groundwater, a significant problem at some U.S. Department of Energy sites. Previous work using the bacterium Bacillus pasteurii suggests that in-situ sequestration of these contaminants can be achieved through MICP via hydrolytic ureolysis. However, ureolysis produces harmful byproducts, such as ammonium, and requires aerobic conditions. Biomineralization through bacterial denitrification offers a promising alternative for in-situ remediation in these cases. In contrast to ureolysis, highly ubiquitous denitrifying bacteria, including Pseudomonas denitrificans, are capable of MICP without the production of harmful byproducts. Biomineralization of metal contaminants through the stimulation of native denitrifying bacteria may provide a more sustainable means of remediating groundwater impacted by radionuclides and metal contaminants than hydrolytic ureolysis.

RÉSUMÉ: peut être utilisée pour séquestrer des radionucléides ou contaminants métalliques (99Sr+2, Cd+2) dans les eaux de la bactérie Bacillus pasteurii suggèrent que séquestrer in-situ ces contaminants peut être accomplie par MICP via -aérobique. La biominéralisation par dénitrification bactérienne est dans ce cas une alternative prometteuse pour in-situ. Par contraste avec lomniprésentes (Pseudomonas denitrificans incluses) provoquent la MICP sans sous-produits nuisibles. La biominéralisation par stimulation des bactéries dénitrifiantes natives serait un moyen plus souterraines contaminées par radionucléides et contaminants métalliques. 1. INTRODUCTION 1.1 Background Groundwater has historically been and continues to be an important source of freshwater on earth, as well as an integral component of the hydrologic cycle. Recent estimates place approximately 22% (8,400,000 km3) of , where a large portion of this total figure can be readily accessed via aquifers (Christopherson, 2009). Unfortunately, groundwater is susceptible to contamination through wells, unlined waste storage units, run-off, and surface waterways. The contamination of aquifers has become a growing concern in many areas and, therefore, has been the focus of recent research efforts to develop novel and effective remediation methods. One such novel approach is microbial biomineralization of radionuclides and metal contaminants through in-situ remediation of contaminated aquifers (Mitchell and Ferris, 2005; Colwell et al., 2003; Fujita et al., 2000; Smith et al., 2004). Poor waste-disposal practice has resulted in the release of low-level radioactive waste and metal contaminants (e.g., 90Sr2+, 60Co2+, Cd2+) into the vadose zone and groundwater at many U.S. Department of Energy (DOE) weapons-production sites. These toxic waste products are a legacy of DOE chemical synthesis and nuclear waste facilities in locations such as Hanford, WA (100-N area) and the Idaho Nuclear Technology and Engineering Center

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