Award Date

December 2016

Degree Type

Thesis

Degree Name

Master of Science in Engineering (MSE)

Department

Civil and Environmental Engineering and Construction

First Committee Member

Daniel Gerrity

Second Committee Member

Jacimaria R. Batista

Third Committee Member

Haroon Stephen

Fourth Committee Member

Jaeyun Moon

Number of Pages

124

Abstract

In the United States, perchlorate contamination has been widely reported, including in Las Vegas, Nevada, where perchlorate has been detected at concentrations of 34.7 mg/kg in vadose zone soil and 0.18-3.7 g/L in groundwater. Once this groundwater reaches the Las Vegas Wash, there is potential for widespread contamination of drinking water sources throughout the Southwest, including in Nevada, Arizona, and California. This issue is becoming increasingly important because even at low perchlorate concentrations, sensitive populations such as infants and pregnant women can be potentially impacted due to perchlorate’s ability to hinder iodine uptake into the thyroid glands, which leads to inhibition of hormone production. Biodegradation is generally recognized as the most cost effective treatment strategy for perchlorate mitigation.

The use of in situ bioremediation is common in vadose zone soils, while ex situ bioremediation has been employed in groundwater and saturated soil applications. For remediation of vadose zone soils, organic or inorganic electron donors can be added to stimulate the native microbial community, specifically perchlorate reducing bacteria, to reduce perchlorate to chloride through a series of redox reactions. However, co-occurring electron acceptors, particularly nitrate, may compete with perchlorate and hinder the bioremediation process. This study evaluated the efficacy of four electron donors, specifically two emulsified soybean oils (EOS-100 and EOS-Pro), glycerol, and a compost/mulch extract, for biological reduction of nitrate and perchlorate using batch microcosm testing. These electron donors were evaluated in two different test matrices: (1) vadose zone soil mixed with surface water from Lake Mead and (2) saturated soil mixed with groundwater. Samples were analyzed to evaluate nitrate and perchlorate removal kinetics, the effects of phosphate addition, and the effects of varying soil to water ratios. Results indicated that EOS-100 and glycerol achieved similar overall reduction of nitrate and perchlorate in the vadose zone soil application, although EOS-100 exhibited faster kinetics. In the saturated soil experiments, EOS-Pro was superior to EOS-100.

The evaluation of soil to water ratios demonstrated that the most significant variable limiting nitrate and perchlorate reduction was the availability of electron donor rather than water volume. Finally, phosphate addition indirectly improved perchlorate reduction by increasing the rate of nitrate biodegradation, particularly for samples with a mass-based nitrogen to phosphorus ratios higher than 0.22:1. The results from this study can be used to better inform bioremediation efforts at perchlorate-contaminated sites, thereby improving treatment efficacy and decreasing risks to downstream drinking water sources

Keywords

Biodegradation; Groundwater; Nitrate; Perchlorate

Disciplines

Environmental Engineering

Language

English


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