Fungal Ecology and Disinfection in Drinking Water Systems

Drinking water is far from a sterile environment and hosts a complex microbial community, including bacteria, eukaryotes, and viruses. Previous research regarding drinking water microbiology has been focused on bacteria. Fungi are commonly found microorganisms in drinking water; however, fungal ecology in drinking water is poorly understood, because of both limited amount of studies and methodological limitations of culture methods. Centralized water treatment processes, which may include coagulation-sedimentation, media filtration, and disinfection, has been suggested as a threshold shaping bacterial community structure in treated drinking water. In addition, a holistic knowledge of microbial ecology within the centralized drinking water treatment process could enable updated water microbiological quality control. On-site addition of secondary disinfectant to premise plumbing has been used to eliminate opportunistic pathogens, primarily Legionella. However, the effect of disinfection on fungal ecology has not been evaluated in detail, hindering the holistic understanding of drinking water microbial ecology.\ud This dissertation is focused on fungal ecology in relation with centralized drinking water treatment process and premise plumbing secondary disinfection; free chlorine and monochloramine disinfection kinetics of waterborne fungi were also evaluated. In the current study, fungal abundance and community structure change along drinking water treatment processes were evaluated using culture-independent methods including qPCR and next generation sequencing (NGS). Fungal abundance and community structure was found to be significantly affected by the media filtration step, but the disinfection step did not demonstrate significant effects on fungal ecology. NGS was also applied to evaluate fungal community structure change in a hospital premise plumbing system treated with on-site monochloramine disinfection. No significant change in the fungal community structure was observed before and after the initiation of on-site disinfection, although the on-site disinfection was previously found to shift bacterial community structure. Fungal community was found to be dominated by phyla Ascomycota, with Penicillium and Aspergillus were the most frequently detected genera. \ud Free chlorine and monochloramine disinfection kinetics of Penicillium and Aspergillus were evaluated. The tested Penicillium and Aspergillus strains were found to be disinfection resistant. The observed inactivation data were fitted to the delayed Chick-Watson model, and the required Ct values (product of disinfectant concentration C × contact time t) for 3-log10 inactivation of the tested fungi ranged 48.99 mg•min/L to 194.7 mg•min/L for free chlorine; and ranged from 90.33 mg•min/L to 531.3 mg•min/L for monochloramine. The 3-log10 inactivation Ct values for fungi are within the similar range for Legionella and Mycobacterium, which are common waterborne, disinfection resistant bacteria. The resistance to disinfection by Penicillium and Aspergillus could facilitate the survival in treated municipal drinking water