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Photochemical Disinfection of Escherichia coli in the Presence of Natural Aquatic Sensitizers: Influence of Solution Chemistry and Extracellular Polymeric Substances

  • Author(s): Gong, Amy Shin Hwei
  • Advisor(s): Walker, Sharon L
  • et al.
Abstract

The objective of this dissertation study was to elucidate how the level and composition of bacterial surface extracellular polymeric substances (EPS) contribute to indirect photochemical disinfection processes. This study was developed to generate mechanistic information on EPS function in bacterial die-off under natural occurring sensitizing environments to inform future process design. Specifically, this research

focused on whether EPS promotes or prohibits disinfection, or be able to facilitate association with sensitizing surfaces.

To accomplish this, the influence of bacterial EPS has been studied in batch (solar simulator and reactor) and flowing (parallel plate) systems simulating groundwater and agriculturally impacted surface water. Model strains of E. coli and Salmonella were utilized. In the initial work, the model Salmonella was incubated in different solution chemistries for varying times. Three EPS extraction methods (lyophilization, ethanol, and sonication) were applied and compared over the range of conditions for the sensitivity and extent of cell lysis after the extraction processes. The sonication method was deemed the best method for further use in subsequent disinfection kinetic studies in

the solar simulator with E. coli. This work was followed by E. coli transport and deposition experiments in the flow chamber. Throughout the research, a series of physical-chemical-biological characterization techniques have been applied on the

bacterial strains including EPS compositional analysis, cell lysis testing, and the measurement of bacterial hydrophobicity, zeta potential, surface charge density, and size.

The findings from this doctoral study provide the following fundamental insights. First, the composition and levels of EPS depends on the extraction protocol utilized, where no single method has the ability to separate all EPS from the cell surface without disturbing cell structure. Next, the presence of nitrate in photochemical disinfection was not sensitive to EPS level. Additionally, EPS did not hinder the disinfection by acting as a physical barrier or chemical quencher. Finally, this study has shown the ability of EPS to facilitate interactions between bacteria and sensitizers in photochemical disinfection processes.

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