Title page for ETD etd-05132009-163159

Type of Document Master's Thesis
Author Methvin, Rachel M
Author's Email Address rmethvin@vt.edu
URN etd-05132009-163159
Title Microbial Ecology of Acanthamoeba polyphaga and Sulfate-Reducing Bacteria in Premise Plumbing
Degree Master of Science
Department Civil Engineering
Advisory Committee
Advisor Name Title
Edwards, Marc A. Committee Chair
Gallagher, Daniel L. Committee Member
Marr, Linsey C. Committee Member
  • SRB
  • A. polyphaga
  • copper
  • nutrients
Date of Defense 2009-05-06
Availability unrestricted
Great advances have been made in the last 100 years in the effort to provide safe and reliable potable water. Unfortunately, organisms surviving the water treatment process still cause illnesses in the population. Acanthamoebae are ubiquitous in the environment and are resistant to commonly used disinfection methods. In addition to being pathogenic on their own, Acanthamoeba spp. are capable of acting as a host to pathogenic bacteria in potable water. The amoebae provide the bacteria with protection from chemical and physical means of disinfection. In this way many pathogens that would otherwise be killed in the water treatment process survive and are capable of infecting water customers.

Most likely due to experimental limitations discussed herein, the concentration of organic carbon in solution was not found to affect the number of Acanthamoeba polyphaga surviving within reactors designed to model residential water tanks. A copper ion concentration of 1.3 mg/L was determined to be an effective disinfectant against A. polyphaga trophozoites, while free chlorine at 10 mg/L and monochloramine at 50 mg/L were deemed effective against trophozoites.

Sulfate-reducing bacteria (SRB) are suspected to be causative agents in copper pitting corrosion. SRB have been found in tubercles covering pits in many homes experiencing pinhole leaks, but the mechanisms of the survival of these organisms in potable water systems are poorly understood. Nutrient studies conducted show that the absence of nitrogen in solution may encourage copper corrosion by SRB. In addition, a medium specifically designed to encourage SRB growth resulted in a large increase in copper corrosion as compared to the control water.

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