Award Date

August 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-to-contaminant 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

Degree Grantor

University of Nevada, Las Vegas

Language

English

Rights

IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/

Available for download on Sunday, December 15, 2024


Share

COinS