Matching Items (3)
Description
Pathogens can proliferate in the built environment and can cause disease outbreaks if water and wastewater are not properly managed. Understanding pathogens that grow in engineered systems is crucial to protecting public health and preventing disease. Using dynamic computational models can reveal mechanistic insights into these systems to aid in understanding risk drivers and determining risk management strategies. The first research chapter of this thesis investigates tradeoffs for reducing the cost associated with Legionnaire’s Disease, hot water scalding, and energy use using a computational framework for evaluating an optimal water heater temperature set point. The model demonstrated that the optimal temperature set point was highly dependent on assumptions made regarding the dose response parameter for a common configuration of an electric water heater in a hospital setting. The optimal temperature was 55°C or 48°C for subclinical vs. clinical severity dose response, respectively, compared with current recommendations of 60°C to kill bacteria and 49°C to prevent scalding and conserve energy.
The second research chapter models the population dynamics of antibiotic-susceptible Escherichia coli (E. coli) and antibiotic-resistant E. coli with a population ecology-exposure assessment model in surface water to quantify the risk of urinary tract infection from recreational swimming activities. Horizontal gene transfer (HGT) was modeled in the environment and the human gastrointestinal tract for several scenarios. HGT was generally not a dominant driver of exposure estimates compared to other factors such as growth and dilution, however, the rank order of factors was scenario-dependent.
The final research chapter models pathogen transport from wastewater treatment plant (WWTP) exposures and assesses the risk to workers based on several exposure scenarios. Case studies were performed to investigate infection risk drivers across different scenarios, including adjustments for the timing of exposure and personal protective equipment. A web application was developed for use by WWTP risk managers to be used with site-specific data.
The proposed modeling frameworks identified risk drivers across several microbial risk scenarios and provide flexible tools for risk managers to use when making water treatment and use decisions for water management plans used for premise plumbing as well as for wastewater treatment practices.
ContributorsHeida, Ashley (Author) / Hamilton, Kerry (Thesis advisor) / Garcia, Margared (Committee member) / Muenich, Rebecca (Committee member) / Wilson, Amanda (Committee member) / Arizona State University (Publisher)
Created2023
Description
Waterborne opportunistic pathogens, particularly non-tuberculous mycobacteria(NTM), pose significant challenges to public health. This study aims to address critical gaps in understanding mycobacterial succession within premise plumbing systems, focusing on diversity, morphology, and factors influencing persistence. A premise plumbing pipe rack experiment was conducted with various pipe materials under real-world conditions. Water samples were collected and analyzed for NTM presence using culture-based and molecular techniques. During the cultivation of various isolates, two main morphologies were noted, revealing insights into the dynamics of mycobacterial communities within premise plumbing systems. Polymerase chain reaction (PCR) analysis attributed the yellow colonies to M. intracellulare or M. chimaera, while the white colonies represented unidentified mycobacterial species. The temporal dynamics of mycobacterial presence, assessed through PCR analysis over 7 weeks, demonstrated fluctuations influenced by source water conditions and disinfectant levels. Different pipe materials exhibited varying levels of mycobacterial colonization, with PVC pipes showing the highest percent positive. Species-level PCR analysis revealed dominance of M. intracellulare/M. chimaera in copper and PEX pipes, while "other" species were more prevalent in PVC pipes. The dominance of human-relevant species raises concerns for health, particularly among immunocompromised individuals. Future sequencing work is necessary to distinguish between M. intracellulare and M. chimaera, a differentiation that could provide valuable insights into the sources and transmission routes of these pathogens in the environment.
ContributorsCahill, Molly (Author) / Hamilton, Kerry A (Thesis advisor) / Boyer, Treavor (Committee member) / Voth-Gaeddert, Lee (Committee member) / Arizona State University (Publisher)
Created2024
Description
The intent of this dissertation was to advance the knowledge of the impacts of building design and use on the quality of the potable water. Fluctuations in water use by occupants and equipment can cause stagnant conditions that causes water quality decay such as loss of chlorine disinfectant, an increase in microorganism and pathogen growth, an increase in metals concentrations, and an increase in disinfection byproducts. The United States Environmental Protection Agency has drinking water standards for distribution systems, but these standards stop at the meter with exception of the Lead and Copper Rule. There are also building codes to ensure proper plumbing materials are used that come in contact with potable water. However, neither standards nor codes require building water quality monitoring. Therefore, monitoring the building potable water system is an important aspect of building water quality that is not done on a large scale.Chapter 2 investigated how water quality evolved in a “green”, multi-story, institutional building during the first 6 months of building life. The results indicated that Wi-Fi logins could be used to correlate occupancy activity and copper (Cu) concentrations in water. As occupancy activity increased, Cu concentrations decreased. However, chlorine (Cl2) residual (or free chlorine) was only measurable twice at two kitchen sinks via grab sampling during the duration of the 6-month study regardless of occupancy activity.
Chapter 3 provided improved understanding of how to carry out effective building water sampling (e.g., grab samples vs real time) and which water quality parameters were most influenced by the building water system during the first year of occupancy in relation to municipal water quality. The results showed the temperature (T), pH, UVA254, a surrogate for organic matter, cellular adenosine triphosphate (cATP), trihalomethanes (THMs), and Cu were always greater inside the building than at building entry while free Cl2 was always lower inside the building than at the building entry.
Chapter 4 investigated a remedial flushing program for three schools. Overall, the study showed the quality of water does change after a flushing event. Free Cl2 was reestablished, and metals concentrations decreased. However, equipment flushing, such as hot water heaters, may be necessary to fully remediate Legionella. Lastly, one-time flushing is most likely a temporary solution. A more routine approach to building flushing and monitoring may be necessary until normal or sustained occupancy resumes.
ContributorsRichard, Rain (Author) / Boyer, Treavor H (Thesis advisor) / Hamilton, Kerry A (Committee member) / Ross, Heather M (Committee member) / Arizona State University (Publisher)
Created2021