Quantifying Technetium and Strontium Bioremediation Potential in Flowing Sediment Columns

5 years ago

Quantifying Technetium and Strontium Bioremediation Potential in Flowing Sediment Columns

managing.editor@est.acs.org (American Chemical Society)

The high-yield fission products ⁹⁹Tc and ⁹⁰Sr are found as problematic radioactive contaminants in groundwater at nuclear sites. Treatment options for radioactively contaminated land include bioreduction approaches, and this paper explores ^99mTc and ⁹⁰Sr behavior and stability under a range of biogeochemical conditions stimulated by electron donor addition methods. Dynamic column experiments with sediment from the Sellafield nuclear facility, completed at site relevant flow conditions, demonstrated that Fe(III)-reducing conditions had developed by 60 days. Sediment reactivity toward ⁹⁹Tc was then probed using a ^99mTc(VII) tracer at <10^–10 mol L^–1 and γ camera imaging showed full retention of ^99mTc in acetate amended systems. Sediment columns were then exposed to selected treatments to examine the effects of different acetate amendment regimes and reoxidation scenarios over 55 days when they were again imaged with ^99mTc. Here, partially oxidized sediments with no further electron donor additions remained reactive toward ^99mTc under relevant groundwater O₂ and NO₃^– concentrations over 55 days. Immobilization of ^99mTc was highest where continuous acetate amendment had resulted in sulfate-reducing conditions. Interestingly, the sulfate reducing system showed enhanced Sr retention when stable Sr²⁺ was added continuously as a proxy for ⁹⁰Sr. Overall, sediment reactivity was nondestructively imaged over an extended period to provide new information about dynamic iron and radionuclide biogeochemistry throughout realistic sediment redox cycling regimes.

Publisher URL: http://dx.doi.org/10.1021/acs.est.7b02652

DOI: 10.1021/acs.est.7b02652