Without a comprehensive understanding of the cellular inactivation processes, it is impossible to design effective and efficient processes for any downstream applications, notably potable water reuse. The aim of this thesis was to shed a new light to the fields of antibiotic resistance and water disinfection by utilizing modern tools of molecular biology. The study consists of five parts: literature review, selection, and characterization of the target strains, and investigation of efficacy and inactivation mechanisms of three novel disinfection processes (UV-LEDs, electrochlorination and chloramine/UV advance oxidation process). Antibiotic resistance is a multi -dimensional problem that connects water professionals with scientists from many different professions. Literature review prov...[ Read more ]

Without a comprehensive understanding of the cellular inactivation processes, it is impossible to design effective and efficient processes for any downstream applications, notably potable water reuse. The aim of this thesis was to shed a new light to the fields of antibiotic resistance and water disinfection by utilizing modern tools of molecular biology. The study consists of five parts: literature review, selection, and characterization of the target strains, and investigation of efficacy and inactivation mechanisms of three novel disinfection processes (UV-LEDs, electrochlorination and chloramine/UV advance oxidation process). Antibiotic resistance is a multi -dimensional problem that connects water professionals with scientists from many different professions. Literature review provides the much-needed big picture with respect to wastewater treatment and water safety, while focusing on two aspects: antibiotics and antibiotic resistance and how are they intertwined. Obtained knowledge was used to establish two well-defined microbiological systems, each consisting of a strain of characterized extended spectrum beta lactamase producing E. coli. The system was used to uncover mechanisms of UV wavelength dependent inactivation of antibiotic resistant bacteria by mRNA sequencing. Our findings underline the importance of mimicking and studying actual conditions that are occurring in engineering systems. The electrochlorination process was used as a testing ground for the novel methodology, a flow cytometry-based method for accurate detection of membrane permeability, metabolic activity and intracellular production of reactive oxygens species within a single bacterial cell. Using this method in the chloramine/UV advance oxidation process, we identified at least seven different cell states, aside from perfectly healthy (live) and apoptotic cells (dead). Our current understanding of inactivation processes is vastly oversimplified. Stages of bacterial inactivation are complex and measuring a single parameter does not accurately depict whole story.

This research demonstrates the necessity to look deeper into the inactivation mechanisms of commonly employed disinfection processes. Most of the microbiological knowledge was obtained from ideal, cell-optimized systems that rarely resemble conditions met in real engineering systems. Given that public health depends on microbial safety of the drinking water, thorough understanding of microbial inactivation beyond “is it live or dead” is a necessity.