|M.Sc Student||Blanky Marina|
|Subject||Legionella pneumophila in Greywater - Quantification,|
Removal during Treatment and Assessment of Human
Exposure via Aerosols
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Eran Friedler|
|Dr. Malka Halpern|
|Full Thesis text|
Greywater reuse as a "new" unconventional source of water can help alleviate stress on depleted water resources by lowering overall consumption of potable water in the urban sector. Alongside its many potential benefits, there are also potential drawbacks related to greywater reuse, stemming from the fact that it contains various pollutants including microbial pathogens. The presence of these pathogens raises a legitimate concern about the impact on human health. Microbial quality assessment of greywater so far, focused mainly on faecal cross-contamination. Much less research was performed on other opportunistic bacteria such as skin and mucus tissues pathogens, while almost no data can be found on inhalatory pathogens such as Legionella.
Legionella dynamics in potable water and greywater in three stages of treatment and the efficiency of the greywater treatment systems was studied and monitored over the course of four seasons. This was followed by an assessment of the potential risks that may arise from exposure to Legionella-contaminated greywater. A protocol for Legionella detection and enumeration in greywater was developed based on established ISO methods for potable water and a pilot sampling campaign. The presence of feacal coliform, Enterrococcus faecalis and Pseudomonas aeruginosa was quantified along with L. pneumophila in order to assess background greywater quality as well as try to establish possible associations with Legionella. Legionella mean concentrations were 6.4?102 and 5.9?103 (cfu/ l) in cold and hot potable water. The mean concentrations of Legionella in raw-, treated- and treated and chlorinated- greywater were 1.4?104, 7.8?102 and 2.0?102 cfu/l, respectively. Statistically significant reduction in Legionella concentrations was found along the greywater treatment process. No significant difference was found between Legionella concentrations in potable water and the treated and chlorinated greywater.
Legionella in potable water presented a seasonal pattern with relatively low concentrations in autumn, winter and spring and an increase during summer. Legionella in greywater presented an almost inverse pattern of relatively high concentrations in autumn and spring, and a decrease in summer.
In the second part of the research, quantitative microbial risk assessment (QMRA) was performed, based on Legionella monitoring and field measurements aimed at quantifying the exposure to aerosols that may contain Legionella. The QMRA results demonstrated that treated and chlorinated greywater can be safely reused as the added risk resulting from its reuse in irrigation and toilet flushing is expected to be negligible. However, reuse of untreated greywater is not recommended as it poses a significant health risk.