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

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Environ Engr in Civil Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Huang, Conghui

Contributors dc:contributor

• Nguyen, Thanh H.
• Espinosa Marzal, Rosa M.
• Elbanna, Ahmed E.
• Ginn, Tim R.

• Drinking water biofilms
• corrosion inhibitors
• mechanical properties
• L. pneumophila

Statement dc:rights

• Copyright 2022 Conghui Huang

Language dc:language

en, eng

Handle dc:identifier

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

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F115657