Award Date
12-1-2024
Degree Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Civil and Environmental Engineering and Construction
First Committee Member
Erica Marti
Second Committee Member
Eakalak Khan
Third Committee Member
Daniel Gerrity
Fourth Committee Member
Stephen Lepp
Fifth Committee Member
Jaeyun Moon
Number of Pages
268
Abstract
Water is a critical resource that supports economic growth, ecosystem health, food security, and overall human well-being. However, water scarcity poses significant challenges globally, affecting more than two billion people and causing conflicts, health issues, and economic instability. Water scarcity in the Southwest U.S., particularly in Las Vegas, is worsening due to drought and reliance on diminishing sources like the Colorado River. Alternative water sources, such as stormwater runoff and reclaimed water, are increasingly used but may introduce impurities, including organic matter from urban runoff and wastewater. This organic matter can form disinfection byproducts (DBPs) when treated with chlorine, including harmful regulated compounds like trihalomethanes (THMs) and haloacetic acids, as well as unregulated emerging contaminants like haloacetonitriles (HANs) and nitrosamines. Many of these DBPs are potential carcinogens, highlighting the need for a deeper understanding of their sources and impacts on water quality and public health.
This dissertation addresses three interrelated issues concerning DBP formation and measurement. The first issue examines the effects of unsheltered homelessness, urban runoff, and wastewater effluent on DBP formation potential (FP) in a tributary that feeds Lake Mead. The second issue investigates the kinetics of various quenching agents (QAs) used to halt DBP formation, as well as the impact of QAs on DBP stability. Lastly, the research explores how these QAs and chlorine affect fluorescence excitation-emission matrices (EEMs), providing insights into changes in water quality. Overall, the study aims to enhance understanding of DBP formation and the effectiveness of QAs for accurate water quality assessments.
The first task investigated the impact of unsheltered homelessness, urban runoff, and wastewater effluent on DBP FP in Lake Mead and a tributary. The study found significant correlations between water quality parameters such as UV254 absorbance, total organic carbon (TOC), and chlorine demand with THM and HAN FP, demonstrating their effectiveness as surrogates for DBP formation. Notably, wastewater effluents significantly influenced THM and HAN FP compared to non-wastewater impacted locations. Furthermore, central and northern wash sites, which are affected by unsheltered homelessness but not by wastewater discharge, also showed a substantial presence of THM and HAN precursors. The mass loading calculations for THM and HAN FP revealed the extent of wastewater treatment’s role in reducing contaminant concentrations and improving water quality. These findings highlight the intricate relationship between urban water quality, public health, and the broader implications of homelessness on water management and policy.
Task 2 examined the effectiveness of various QAs in reducing free chlorine and preventing the formation of DBPs during FP tests. QAs tested included ascorbic acid (AA), sodium bisulfite, sodium thiosulfate, sodium arsenite, 1,3,5-trimethoxybenzene (TMB), and ammonium chloride (AC), at chlorine concentrations of 3, 5, and 9 mg/L and molar ratios of 1:1, 1.3:1, 1.5:1, and 1.7:1 for QA:chlorine. At a 1:1 ratio, most QAs reduced chlorine by about 80% within 45 to 60 seconds, except for AC and TMB. Increasing the ratio to 1.7:1 improved quenching times to 10-20 seconds, with most QAs achieving over 80% reduction in 10 seconds. Kinetic analysis showed lower than expected rate constants for AC and TMB, with TMB showing minimal reduction even after five minutes. DBP levels remained stable over 24 hours in quenched samples, suggesting reliable measurements when QAs were used below 1.7:1 molar ratios.
In the final task, the effects of various QAs on the fluorescence peaks of EEMs were examined. Chlorine concentrations of 3, 5, and 9 mg/L were tested, using QA:chlorine molar ratios of 1:1 and 1.7:1 for all QAs. The study assessed the impact of chlorine on major fluorescence peaks (A, M, C, B, and T) in EEMs, revealing that the error percentage increased with higher chlorine concentrations for all peaks. Furthermore, the individual effect of QAs, as well as the combined influence of chlorine and QAs, was evaluated. Results showed statistically significant changes, with error measurements ranging from 30% to 90% across nearly all peaks.
Key findings highlight that increased organic matter from urban pollutants and wastewater significantly raises DBP FP, with implications for water safety. The kinetics of QAs vary, impacting their effectiveness in stopping DBP formation and their influence on fluorescence measurements.
Keywords
Disinfection byproducts; Quenching agents; Reclaimed water; Urban Runoff; Water Quality; Water scarcity
Disciplines
Civil Engineering | Environmental Engineering
File Format
File Size
6800 KB
Degree Grantor
University of Nevada, Las Vegas
Language
English
Repository Citation
Ejjada, Meena, "Assessing Disinfection Byproducts in Diverse Water Sources: Factors Affecting Formation and Accuracy in Direct and Indirect Analysis" (2024). UNLV Theses, Dissertations, Professional Papers, and Capstones. 5169.
http://dx.doi.org/10.34917/38330380
Rights
IN COPYRIGHT. For more information about this rights statement, please visit http://rightsstatements.org/vocab/InC/1.0/
