As waterborne disease originating in potable water plumbing systems (such as Legionnaires' Disease and Nontuberculous Mycobacterial (NTM) infections) continue to increase, it is important to better understand the cause(s), responsible parties and interventions to prevent disease. This dissertation begins with a literature review characterizing the propensity of building (premise) plumbing to enhance or diminish opportunistic pathogen growth, including Legionella.
It then holistically examines the problem at the field, bench and pilot scale by first discovering problems with lead and Legionella in Flint, MI, during an event popularly referred to as the Flint Water Crisis in 2014-2016. Four years were then spent simulating critical factors hypothesized to have triggered the Legionella outbreak in residences and in a large hospital in Flint. In parallel with that work, pilot scale rigs were operated for several years, to examine the important role of water heater system design and operation on energy efficiency, hot water delivery, and Legionella.
The first chapter literature review is entitled "Critical Review of the Propensity of Premise Plumbing Pipe Materials to Enhance or Diminish the Growth of Legionella and Other Opportunistic Pathogens." It examines the complex environments found in premise systems, focusing primarily on the role of pipe materials. The effects of metallic (copper, iron) and plastic pipe materials on opportunistic pathogens and Legionella include their effect on nutrient availability, disinfectant levels, and the composition of the broader microbiome. Design, configuration, and operation are also examined in terms of their potential for influencing opportunistic pathogens. This chapter demonstrates that pipe materials have the potential to stimulate or inhibit pathogen growth, dependent on circumstance and water chemistry. This chapter will be submitted to the journal Pathogens.
The field study in this work first predicted, discovered and then exposed problems with lead and Legionella in Flint, Michigan. A citizen science project that sampled Flint water in August 2015, demonstrated a city-wide problem with water lead exceeding the EPA limit of 15 µg/L after corrosion control was interrupted. Follow-up sampling events between August 2015 and August 2017 demonstrated that the switch back to the original water source and addition of enhanced corrosion control in October 2015, dramatically reduced lead, copper and iron levels flowing into consumer homes. Entitled "Evaluating Water Lead Levels During the Flint Water Crisis," this work was published in Environmental Science and Technology in 2018.
After our Virginia Tech team's work helped expose a Legionnaires' disease outbreak that killed twelve people and sickened nearly one hundred individuals, the started to explore possible links between corrosion control, plumbing materials and disinfection that could help explain the trajectory of disease in Flint and elsewhere. Three separate experiments were performed using bench-scale simulated glass water heaters. Two of the studies attempted to simulate what occurred in Flint homes before, during and after the water crisis in relation to factors that either encouraged or discouraged Legionella growth, while the third examined the more benign Blacksburg tap water and a broader range of influential plumbing conditions.
The first study entitled "Copper Pipe, Lack of Corrosion Control, and Uncontrolled pH Influenced the Trajectory of the Flint Legionnaires' Disease Outbreak," determined that the very low pH levels in summer 2015 and interruption of phosphate corrosion control, could cause explosive growth of Legionella in PEX plumbing held at warm temperature, without disinfectant and with constant mixing. Under the same conditions copper pipe had antimicrobial properties that markedly reduced Legionella in our experiments. This work has been submitted for review to Environmental Science and Technology.
The second companion study conducted at a higher pH, without mixing and with trace chlorine, found 2.5 log10 lower levels of Legionella compared to the worst-case conditions in the aforementioned study, demonstrating the importance of mixing and traces of chlorine. Higher levels of disinfectant and the presence of copper pipe also enhanced control of Legionella. This manuscript is titled "Interactive Effects of Copper Pipe, Stagnation, Corrosion Control, and Disinfectant Residual Influenced Reduction of Legionella pneumophila during Simulations of the Flint Water Crisis," and it has been published in Pathogens.
The third simulated glass water heater study examined the disinfection of opportunistic pathogens in the presence of six different premise plumbing materials or conditions in Blacksburg tap water. Generally speaking, all of the premise plumbing materials reduced disinfection of opportunistic pathogens compared to a control condition with glass surfaces. Chlorine decay was catalyzed by iron pipe, warmer temperature and the presence of organic matter, increasing the persistence of Legionella. Magnesium anodes in particular, encouraged much higher Legionella growth compared to all other materials. This work titled "Chlorine and Chloramine Disinfection of Legionella spp., L. pneumophila, and Acanthamoeba Under Warm Water Premise Plumbing Conditions," has been submitted to Microorganisms.
Results of a six-year pilot study titled "Elucidating the Role of Water Heater System Configuration in Energy Efficiency, Consumer Comfort and Legionella Proliferation," examined different types of residential-sized water heater systems with plastic pipes including: a standard tank system with water stagnant between uses, a recirculating tank system with flowing water between uses, and an on-demand system which only heated water and had flow during use. Considering the volume of water in each tank between 38 and 47 ° C as a measure of Legionella growth risk, with a heater setpoint at 48 °C (118 °F) the recirculating system had 90% of its volume at risk daily compared to only 24% of the standard system volume. The on-demand system used a minimum of 10% less energy than the standard tank, and 50% less energy than the recirculating tank, and had one tenth of the volume at risk of growing Legionella than either tank system. In fact, it was only by contriving a system to keep distal lines artificially warmed to above room temperature, that Legionella growth could occur in the on-demand system, whereas it rose to 107 L. pneumophila MPN per liter in a normally operating recirculating system. On the other hand, the on-demand heaters were repeatedly subject to mechanical malfunction during the study, and had difficulty delivering water at the desired temperature and flow rates versus traditional tank systems. This manuscript will be submitted to Water Research. / Doctor of Philosophy / Recent water crises in Flint, Michigan and Legionnaires' Disease outbreaks in Flint, New York City, and Quincy, Illinois have demonstrated the need to better understand the cause(s), responsible parties, and interventions required to prevent waterborne diseases. As waterborne disease originating in building plumbing systems (premise plumbing), such as Legionnaires' Disease and Nontuberculous Mycobacterial infections, continue to increase each year, the burden on healthcare systems and impact on public health also grows. In this dissertation, a literature review, a field study of water in Flint, small-scale laboratory studies, and residential-sized water heater systems were examined to study interactions between water chemistry, premise plumbing, and disease-causing opportunistic pathogens (OPs) with a focus on Legionella, the OP which causes Legionnaires' Disease.
The first chapter literature review is entitled "Critical Review of the Propensity of Premise Plumbing Pipe Materials to Enhance or Diminish the Growth of Legionella and Other Opportunistic Pathogens." It examines the complex environments found in premise systems, and the important role of pipe material selection. The effects of metallic (copper, iron) and plastic pipe materials on opportunistic pathogens and Legionella include their impact on nutrient availability, disinfectant levels, and the composition of the broader microbiome. Design, configuration, and operation of plumbing systems are also examined in terms of their potential for influencing growth of opportunistic pathogens. This chapter demonstrates that pipe materials have the potential to stimulate or inhibit pathogen growth, dependent on circumstance and water chemistry.
The field study in this work exposed problems with lead and Legionella in Flint, Michigan, during an event known in the popular press as the Flint Water Crisis 2014-2016. In August 2015, a citizen science sampling campaign demonstrated a citywide lead in water problem. After a federal emergency was declared, follow-up sampling events between August 2015 and August 2017 demonstrated that the switch back to the original water source, enhanced disinfection, and corrosion control under federal direction had reduced lead levels to half of the EPA limit. Additionally, the pipe material installed between each home and the water main (service lines) affected levels of lead and copper in water, with the lowest lead concentrations measured in homes with copper service lines.
After our teams' work in Flint helped expose a Legionnaires' disease outbreak that killed twelve people and sickened nearly one hundred other individuals, we started to explore possible links between corrosion control, plumbing materials, and disinfection that could affect the trajectory of disease in Flint and elsewhere. Three follow-up studies, using small glass bottles to simulate water heaters, provided more specific comparisons between water conditions in premise plumbing and OP occurrence. Two studies expanded on phosphate corrosion control, chlorine (disinfectant) decay, and pH-related research questions, which arose during the Flint water crisis field study. The first determined that properly treated drinking water and some mixing could inhibit Legionella growth in copper pipes. The second study found that without mixing, copper could be antimicrobial and reduce Legionella growth even if the water chemistry was slightly altered with higher pH. The third simulated water heater study examined the reduction of OPs using a chlorine or chlorine plus ammonia disinfectant to reduce Legionella in the presence of six different plumbing conditions. The reduction of Legionella with chlorine was inhibited when carbon was increased and in the presence of a magnesium anode rod, a necessary water heater component.
A six-year study using a residential-sized water heater system holistically examined three different types of water heater systems with plastic pipes: one using a standard water heater tank with water stagnant between uses, one using a water heater tank connected to a recirculating pump to provide constantly flowing water, and one tankless (on-demand) heater which only heated water and provided flow during use. Using temperature as an indicator of risk for Legionella growth, the recirculating system at a temperature setpoint of 48 °C (118 °F) would be at high risk for Legionella growth (water volume at 38-47 °C or 100-117 °F) in 90% of the tank volume each day, whereas the standard system would only be at high risk in 24% of the tank each day. The on-demand system provided the safest alternative for hot water distribution with virtually undetectable levels of Legionella risk when the pipes were kept at room temperature as per normal operation. The on-demand system also used at least 50% less energy than the recirculating system and 10% less energy than the standard system; however, we were not successful in finding a reliable on-demand system that could also provide hot water at the desired temperature and flow rate.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/109305 |
| Date | 16 September 2020 |
| Creators | Martin, Rebekah Leighann |
| Contributors | Civil and Environmental Engineering, Edwards, Marc A., Pearce, Annie R., Falkinham, Joseph O. III, Pruden, Amy |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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