Evaluating the Potential of Native Ureolytic Microbes To Remediate a ⁹⁰Sr Contaminated Environment

Abstract

This study was a preliminary evaluation of ureolytically driven calcite precipitation and strontium coprecipitation for remediating (90)Sr contamination at the Hanford 100-N Area in Washington; in particular the approach is suitable for treating sorbed (90)Sr that could otherwise be a long-term source for groundwater contamination. Geochemical conditions at the site are compatible with long-term calcite stability, and therefore groundwater and sediment samples were examined to assess the ureolytic capabilities of the native microbiota. Quantitative assays detected up to 2 × 10(4) putative ureC gene copies mL(-1) in water and up to 9 × 10(5) copies g(-1) in sediment. The ureC assays and laboratory-based estimates of ureolytic activity indicated that the distribution of in situ ureolytic potential was very heterogeneous with depth and also that the ureolytic activity was predominantly associated with attached organisms. A mixed kinetic-equilibrium model was developed for the 100-N site to simulate urea treatment and predict strontium removal. Together, the microbial characterization data and modeling suggest that the site has the requisite biogeochemical characteristics for application of the calcite precipitation remediation approach for (90)Sr.

Biomineralization Mediated by Ureolytic Bacteria Applied to Water Treatment: A Review

“…On the other hand, the carbonate ions promote the precipitation of calcium carbonate and coprecipitation of heavy metals in high pH environments [68,69]. Although most of the studies are related to the bioremediation of contaminated soils, they begin with tests on aqueous solutions and the immobilization process may enable metal(loid)s to be transformed in situ into insoluble and chemically inert forms and are applicable to removing metals from aqueous solution.…”

Microbially-induced Carbonate Precipitation for Immobilization of Toxic Metals

“…90 Sr is a significant aquifer and vadose zone contaminant at the INEEL, as well as at a number of DOE facilities across the USA (Riley & Zachara, 1992). Native ureolytic microbes were used to remediate 90 Sr contamination at the Hanford 100-N area in Washington where ureolytic activities of microbes were confirmed by UreC amplification (Fujita et al, 2010). Quantitative assays detected up to 2×10 4 putative ureC gene copies mL -1 in water and up to 9×10 5 copies g -1 in sediment.…”

“…Quantitative assays detected up to 2×10 4 putative ureC gene copies mL -1 in water and up to 9×10 5 copies g -1 in sediment. Further analyses indicated that the Sr was incorporated into calcite ensuring the relative stability of 90 Sr (Fujita et al, 2010).…”

“…The hydrolysis of urea produces bicarbonate and ammonium, where bicarbonate participates directly in calcite precipitation, and ammonium can exchange for sorbed strontium, calcium, and other metals, resulting in their enhanced susceptibility to recapture via carbonate mineral formation (Fujita et al, 2010). Some possible chemical reactions can be summarized as follows (Achal, Pan, & Zhang, 2012) …”

A simple reactive-transport model of calcite precipitation in soils and other porous media

“…If CaCO 3 precipitates in the zone of pH increase, this will curb the pH rise and thereby reduce the losses of NH 3 . There is currently particular interest in exploiting microbiallyenhanced urea hydrolysis in soils and sub-strata to stimulate CaCO 3 precipitation for various applications such as physical stabilisation of soils (Stocks-Fischer et al, 1999;Chu et al, 2012), capture of heavy metals and radionuclides (Mitchell and Ferris., 2005;Fujita et al, 2010;Tobler et al, 2011), sealing of leaks in CO 2 storage reservoirs (Ferris et al, 1996;Cunningham et al, 2009), and carbon sequestration (Dupraz et al, 2009;Mitchell et al, 2010;Renforth et al, 2009;Whitmore et al, 2014).…”