Immobilization of selenite via two parallel pathways during in situ bioremediation.
It is widely understood that selenite can be biologically reduced to elemental selenium. Limited studies have shown that selenite can also be immobilized through abiotic precipitation with sulfide, a product of biological sulfate reduction. We demonstrate that both pathways significantly contribute to selenite immobilization in a microfluidic flow cell having a transverse mixing zone between propionate and selenite that mimics the reaction zone along the margins of a selenite plume undergoing bioremediation in the presence of background sulfate. The experiment showed that red particles of amorphous elemental selenium precipitate on the selenite-rich side of the mixing zone, while long crystals of selenium sulfides precipitate on the propionate-rich side of the mixing zone. We developed a continuum-scale reactive transport model that includes both pathways. The simulated results are consistent with the experimental results, and indicate that spatial segregation of the two selenium precipitates is due to the segregation of the more thermodynamic favorable selenite reduction and the less thermodynamically favorable sulfate reduction. The improved understanding of selenite immobilization and the improved model can help to better design in situ bioremediation processes for groundwater contaminated by selenite or other contaminants (e.g., uranium(IV)) that can be immobilized via similar pathways.
†Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, Illinois 61801, United States.|∥Department of Civil and Environmental Engineering, FAMU-FSU College of Engineering, Florida State University, 2525 Pottsdamer Street, Tallahassee, Florida 32310, United States.
Youneng
Y
Tang
†Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, Illinois 61801, United States.|‡Department of Civil, Architectural, and Environmental Engineering, University of Texas at Austin, 301 East Dean Keeton Street, Austin, Texas 78712, United States.
Charles J
CJ
Werth
§Department of Geology, University of Illinois at Urbana-Champaign, 1301 West Green Street, Urbana, Illinois 61801, United States.
Robert A
RA
Sanford
†Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, Illinois 61801, United States.
Rajveer
R
Singh
†Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, Illinois 61801, United States.
Kyle
K
Michelson
†Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, Illinois 61801, United States.
Masaru
M
Nobu
†Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, Illinois 61801, United States.
Wen-Tso
WT
Liu
†Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, 205 North Mathews Avenue, Urbana, Illinois 61801, United States.
Albert J
AJ
Valocchi
D001419:Bacteria / Q000378:metabolism*; D001673:Biodegradation, Environmental; D052918:Environmental Restoration and Remediation / Q000379:methods*; D060587:Groundwater / Q000032:analysis*; D008962:Models, Theoretical; D020887:Selenious Acid / Q000378:metabolism*; D012643:Selenium / Q000378:metabolism; D018036:Selenium Compounds / Q000378:metabolism
D018036:Selenium Compounds; D020887:Selenious Acid; D012643:Selenium; C025698:selenium disulfide