Award Date
8-1-2023
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Civil and Environmental Engineering and Construction
First Committee Member
Jacimaria Batista
Second Committee Member
Daniel Gerrity
Third Committee Member
David James
Fourth Committee Member
Erica Marti
Fifth Committee Member
David Hatchett
Number of Pages
377
Abstract
Although heterotrophic reduction of perchlorate using various electron donors has been demonstrated successfully, there have been only a few continuous-flow reactor studies that have addressed perchlorate reduction in the presence of co-contaminant oxyanions with ZVI. This research compares the effectiveness of ZVI alone and ZVI supplemented with emulsified vegetable oil (EVO) to reduce the co-occurring contaminants perchlorate, chlorate, and nitrate. Batch and continuous flow bioreactor testing, employing actual groundwater and soils from a contaminated aquifer, were performed with different ZVI grain sizes and varying ZVI-to-contaminant mass ratios.
The results revealed that significant perchlorate reduction did not occur when using ZVI alone. Nitrate and chlorate removal increased with longer contact times, larger ZVI-tocontaminant ratios, and smaller ZVI grain size. Significant differences (p<0.05) were observed in the nitrate and chlorate reduction at different mass ratios of ZVI to contaminant. A first-order model best described nitrate and chlorate degradation. Despite similar initial concentrations, complete chlorate reduction was faster than nitrate reduction. Addition of soil to the groundwater had a statistically significant p<0.05) impact on nitrate removal. Soil addition caused a 2-day delay in nitrate reduction, but had minimal impact on chlorate reduction. Nitrate and chlorate degradation followed a first-order model, with rate constants from 0.128 d−1 to 0.697 d−1 for nitrate and 0.784 d−1 to 2.20 d−1 for chlorate at 100x and 400x ratios.
The addition EVO promoted perchlorate degradation. In the presence of EVO and ZVI, contaminant degradation follows a first order model with constants ranging from 0.953 to 1.04 d−1 for nitrate, and 1.00 to 2.37 d−1 for chlorate, 0.271 d−1 for perchlorate at 100x and 200x mass ratios. Overall, the investigation showed that nitrate and chlorate were abiotically degraded with nitrate being converted to ammonium in the presence of ZVI alone. Given the low cost of ZVI, implementing bio-ZVI, rather than ZVI alone, can be highly suitable for treating groundwater contaminated with multiple oxyanions at high concentrations.
Keywords
bio-ZVI; biodegradation; nitrate-reducing genes; perchlorate; perchlorate-reducing genese; zero-valent iron
Disciplines
Environmental Engineering
File Format
File Size
4040 KB
Degree Grantor
University of Nevada, Las Vegas
Language
English
Repository Citation
Gonzales, John Michael, "Abiotic and Bio-Enhanced Reduction of Perchlorate and Co-Contaminants with Zero-Valent Iron (ZVI)" (2023). UNLV Theses, Dissertations, Professional Papers, and Capstones. 4830.
http://dx.doi.org/10.34917/36948180
Rights
IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/
Comments
Although heterotrophic reduction of perchlorate using various electron donors has been demonstrated successfully, there have been only a few continuous-flow reactor studies that have addressed perchlorate reduction in the presence of co-contaminant oxyanions with ZVI. This research compares the effectiveness of ZVI alone and ZVI supplemented with emulsified vegetable oil (EVO) to reduce the co-occurring contaminants perchlorate, chlorate, and nitrate. Batch and continuous flow bioreactor testing, employing actual groundwater and soils from a contaminated aquifer, were performed with different ZVI grain sizes and varying ZVI-to-contaminant mass ratios.
The results revealed that significant perchlorate reduction did not occur when using ZVI alone. Nitrate and chlorate removal increased with longer contact times, larger ZVI-tocontaminant ratios, and smaller ZVI grain size. Significant differences (p<0.05) were observed in the nitrate and chlorate reduction at different mass ratios of ZVI to contaminant. A first-order model best described nitrate and chlorate degradation. Despite similar initial concentrations, complete chlorate reduction was faster than nitrate reduction. Addition of soil to the groundwater had a statistically significant p<0.05) impact on nitrate removal. Soil addition caused a 2-day delay in nitrate reduction, but had minimal impact on chlorate reduction. Nitrate and chlorate degradation followed a first-order model, with rate constants from 0.128 d−1 to 0.697 d−1 for nitrate and 0.784 d−1 to 2.20 d−1 for chlorate at 100x and 400x ratios.
The addition EVO promoted perchlorate degradation. In the presence of EVO and ZVI, contaminant degradation follows a first order model with constants ranging from 0.953 to 1.04 d−1 for nitrate, and 1.00 to 2.37 d−1 for chlorate, 0.271 d−1 for perchlorate at 100x and 200x mass ratios. Overall, the investigation showed that nitrate and chlorate were abiotically degraded with nitrate being converted to ammonium in the presence of ZVI alone. Given the low cost of ZVI, implementing bio-ZVI, rather than ZVI alone, can be highly suitable for treating groundwater contaminated with multiple oxyanions at high concentrations.