University of Illinois Urbana-Champaign

Effects of corrosion inhibitors on biofilm physical characteristics and associated infection risk of legionella pneumophila

Huang, Conghui

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HUANG-DISSERTATION-2022.pdf

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https://hdl.handle.net/2142/115657

Description

Title
Effects of corrosion inhibitors on biofilm physical characteristics and associated infection risk of legionella pneumophila
Author(s)
Huang, Conghui
Issue Date
2022-02-22
Director of Research (if dissertation) or Advisor (if thesis)
Nguyen, Thanh H.
Doctoral Committee Chair(s)
Nguyen, Thanh H.
Committee Member(s)
  • Espinosa Marzal, Rosa M.
  • Elbanna, Ahmed E.
  • Ginn, Tim R.
Department of Study
Civil & Environmental Eng
Discipline
Environ Engr in Civil Engr
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
  • Drinking water biofilms
  • corrosion inhibitors
  • mechanical properties
  • L. pneumophila
Abstract
Biofilms, a porous matrix developed by microorganisms accumulating on a surface, are ubiquitous in drinking water distribution systems (DWDS). Corrosion inhibitors were added to control soluble metal level, such as lead and copper, in drinking water. However, corrosion inhibitors, commonly containing phosphate, can provide nutrients to microbial organisms in the distribution systems. Biofilms can also play an important role in opportunistic pathogen survival and propagation in both large-scale DWDS and small-scale premise plumbing systems. Legionella pneumophila is a causative agent for Legionnaires' disease, which occurs at increasing frequency in the United States. Understanding the effects of biofilm structural and mechanical properties, which can influence biofilm cohesiveness and detachment under physical stress, is critical for biofilm and biofilm-associated pathogen control. In this study, we 1) determined the role of corrosion inhibitors on biofilm physical characteristics, such as thickness, pore structure, and stiffness; 2) determined the role of corrosion inhibitors on two common disinfectants (free chlorine and monochloramine) consumption; 3) determined the infection risks of L. pneumophila associated with biofilms developed under the influence of corrosion inhibitors. First, this research identified the important factors controlling the infection risks of L. pneumophila under the interactive effects of stagnation, residual chlorine, and biofilm growth in the premise plumbing. The L. pneumophila concentration in the drinking water, residual chlorine, and release kinetics of L. pneumophila from biofilms were identified as the three important factors in the quantitative microbial risk assessment (QMRA). Next, the porous biofilm structure developed under the influence of silicate was found to be softer compared to those developed in groundwater with or without tin additives. The larger connecting throats in the silicate biofilms may contribute to the lower stiffness compared to other biofilms. Third, phosphate and phosphate blends with polyphosphate corrosion inhibitors led to a more porous biofilm with more connecting throats compared to that developed with silicate additives or no additives. This porous structure and connecting throats in phosphate and phosphate blends biofilms led to a softer and more viscoelastic response compared to those in silicate and groundwater biofilms. This stiffer silicate biofilm allowed the less L. pneumophila adhesion and release over flush compared to other biofilms. Thus, the infection risk of L. pneumophila released from the silicate biofilms was the lowest among the four biofilms. Finally, the porous structure in phosphate and phosphate blends biofilms can lead to more monochloramine consumption compared to other biofilms, while the reaction rate of monochloramine was independent of the biomass type. A similar trend in free chlorine reaction rate between biofilm and disrupted biomass showed that free chlorine consumption with these four biofilms was reaction-driven. The results of this research can facilitate decision-making to reduce the premise plumbing infection risk from L. pneumophila.
Graduation Semester
2022-05
Type of Resource
Thesis
Handle URL
https://hdl.handle.net/2142/115657
Copyright and License Information
Copyright 2022 Conghui Huang

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Graduate Theses and Dissertations at Illinois