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theses

Legionella bacteria are an emerging pathogen found in natural and engineered water systems. Infection occurs when infected water becomes aerosolized and is breathed into the lungs. Reclaimed water is commonly used in scenarios where the water becomes aerosolized, such as for spray irrigation and in industrial cooling towers. It is important to measure the risk of Legionella infection from these waters but, their prevalence in reclaimed water distribution systems has not been adequately documented. To determine the occurrence and concentration of Legionella in reclaimed water, a monitoring study was conducted at six water utilities. The systems, located in California, Florida, Texas and Arizona, represented different treatment processes, storage conditions and distribution system sizes. The treatment systems produced water varying in organic carbon and other nutrients, which allowed the examination of each water quality parameter in relation to the occurrence of Legionella and their associated protozoa hosts. From each water utility, samples were taken from the plant effluent, storage reservoir and three points within the distribution system. Legionella was found frequently throughout the storage and distribution systems, though their concentrations were generally low. Sixteen species of Legionella were identified using culture plating and molecular methods, with L. pneumophila being the species most frequently detected and the only species found in all six reclaimed water utilities. Disinfectants were effective at controlling Legionella growth when present, but were rapidly consumed in the distribution systems. Chlorine residuals of at least 1 mg/L (total chlorine) and 0.2 mg/L (free chlorine) reduced Legionella concentrations over 80%. High levels of assimilable organic carbon (AOC), total organic carbon (TOC) and ammonia had a clear impact on the occurrence of Legionella. Over 70% more Legionella were detected in locations where AOC was above 1000 µg/L and/or TOC was above 10 mg/L. In samples where ammonia was less than 2 mg/L, the concentration of viable Legionella was 90% lower than in samples where ammonia was above 2 mg/L. The reclaimed system with the lowest occurrence of Legionella also had the lowest average concentrations of AOC, TOC and ammonia. The two systems with the most Legionella also had the highest average concentrations of AOC, TOC and ammonia. Mesophilic and thermophilic protozoa were regularly detected throughout the reclaimed water systems and their numbers increased as the water aged in the distribution system.

ETD_6959

doi:10.7282/T3DB83XN

M.S.

Includes bibliographical references

by William Joseph Johnson

Subsequently published in Journal - American Water Works Association 110(3) https://doi.org/10.5942/jawwa.2018.110.0021

ETD graduate

The author owns the copyright to this work.