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Title: Evaluation of Gaseous Substrates for Microbial Immobilization of Contaminant Mixtures in Unsaturated Subsurface Sediments

Abstract

Extensive vadose zone metals and organic contamination remains at many former industrial and defense manufacturing sites, and effective remedial solutions are needed to slow or prevent its migration to groundwater. In this study, the application of gaseous substrates to stimulate microbial respiratory reduction of comingled radioisotopes and nitrate under unsaturated conditions was examined for possible application at the Hanford Site, a former nuclear production facility in southeastern WA, USA. First, screening studies were performed to qualitatively measure the sediment respiratory response to 14 gaseous or volatile organic substrates at two moisture contents, 4% and 8%. Volatile substrates produced the strongest respiratory response, among them were butyrate, pentane, butyl acetate. Ethane and butane were the most effective gaseous substrates but only at 8% water content. Hanford sediment from two waste sites with distinctive chemistries were wetted to 7% moisture content, packed into columns, and treated with ethane or butane. After 4 weeks, columns were then leached to quantify retardation in the mobility of aqueous contaminant concentrations compared to no gas control columns. Treatment with both gases resulted in >80% removal of Cr from the aqueous phase. However, NO3 concentration and a waste sites exposure history to NO3 had a major effectmore » on U and Tc reduction. Incomplete nitrate reduction outcompeted U and Tc in waste site sediments having limited prior exposure to NO3. Conversely, waste site sediments co-contaminated with NO3 were able to achieve highly reduced conditions resulting in complete denitrification of NO3, and delayed leaching of U and Tc. This implied effective reduction of both contaminants to less mobile species. This study demonstrates that unsaturated vadose sediments at Hanford waste sites have the capacity for a sustained respiratory response to gaseous substrate injection, which could potentially be deployed as part of an overall strategy to reduce the flux of long-lived radionuclides to groundwater at Hanford and other legacy waste sites.« less

Authors:
 [1];  [1];  [1]; ORCiD logo [1]
  1. BATTELLE (PACIFIC NW LAB)
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1599119
Report Number(s):
PNNL-SA-147782
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Journal of Environmental Radioactivity
Additional Journal Information:
Journal Volume: 214-215
Country of Publication:
United States
Language:
English

Citation Formats

Bagwell, Christopher E., Gillispie, Elizabeth C., Lawter, Amanda R., and Qafoku, Nikolla. Evaluation of Gaseous Substrates for Microbial Immobilization of Contaminant Mixtures in Unsaturated Subsurface Sediments. United States: N. p., 2020. Web. doi:10.1016/j.jenvrad.2020.106183.
Bagwell, Christopher E., Gillispie, Elizabeth C., Lawter, Amanda R., & Qafoku, Nikolla. Evaluation of Gaseous Substrates for Microbial Immobilization of Contaminant Mixtures in Unsaturated Subsurface Sediments. United States. doi:10.1016/j.jenvrad.2020.106183.
Bagwell, Christopher E., Gillispie, Elizabeth C., Lawter, Amanda R., and Qafoku, Nikolla. Wed . "Evaluation of Gaseous Substrates for Microbial Immobilization of Contaminant Mixtures in Unsaturated Subsurface Sediments". United States. doi:10.1016/j.jenvrad.2020.106183.
@article{osti_1599119,
title = {Evaluation of Gaseous Substrates for Microbial Immobilization of Contaminant Mixtures in Unsaturated Subsurface Sediments},
author = {Bagwell, Christopher E. and Gillispie, Elizabeth C. and Lawter, Amanda R. and Qafoku, Nikolla},
abstractNote = {Extensive vadose zone metals and organic contamination remains at many former industrial and defense manufacturing sites, and effective remedial solutions are needed to slow or prevent its migration to groundwater. In this study, the application of gaseous substrates to stimulate microbial respiratory reduction of comingled radioisotopes and nitrate under unsaturated conditions was examined for possible application at the Hanford Site, a former nuclear production facility in southeastern WA, USA. First, screening studies were performed to qualitatively measure the sediment respiratory response to 14 gaseous or volatile organic substrates at two moisture contents, 4% and 8%. Volatile substrates produced the strongest respiratory response, among them were butyrate, pentane, butyl acetate. Ethane and butane were the most effective gaseous substrates but only at 8% water content. Hanford sediment from two waste sites with distinctive chemistries were wetted to 7% moisture content, packed into columns, and treated with ethane or butane. After 4 weeks, columns were then leached to quantify retardation in the mobility of aqueous contaminant concentrations compared to no gas control columns. Treatment with both gases resulted in >80% removal of Cr from the aqueous phase. However, NO3 concentration and a waste sites exposure history to NO3 had a major effect on U and Tc reduction. Incomplete nitrate reduction outcompeted U and Tc in waste site sediments having limited prior exposure to NO3. Conversely, waste site sediments co-contaminated with NO3 were able to achieve highly reduced conditions resulting in complete denitrification of NO3, and delayed leaching of U and Tc. This implied effective reduction of both contaminants to less mobile species. This study demonstrates that unsaturated vadose sediments at Hanford waste sites have the capacity for a sustained respiratory response to gaseous substrate injection, which could potentially be deployed as part of an overall strategy to reduce the flux of long-lived radionuclides to groundwater at Hanford and other legacy waste sites.},
doi = {10.1016/j.jenvrad.2020.106183},
journal = {Journal of Environmental Radioactivity},
number = ,
volume = 214-215,
place = {United States},
year = {2020},
month = {4}
}