Evaluation of the effectiveness of some disinfectants against microbiological contamination and biofilm in hospital water systems

Water quality has a direct link to human-health protection. Safeguarding the quality of drinking water is absolutely essential, especially in particularly critical situations, such as hospitals and other healthcare facilities that represent very vulnerable environments. In these facilities, a contamination of the water may represent a health hazard and a potential risk for exposed people, often characterized by immunosuppression. A water network that is not protected from possible microbiological contaminations, either because not subjected to appropriate disinfection and maintenance operations or because of its structural characteristics, may be responsible for the exposure to water without the necessary quality requirements. In order to prevent water-related microbiological risks, a number of disinfectants has currently been used in these structures; among them monochloramine (NH2Cl) and hydrogen peroxide/silver ion (H2O2-Ag+) have recently acquired more and more importance in the strategy applied to the management of water networks, , especially in the control of Legionella proliferation. A parametric value for this microorganisms has recently been introduced in the recast of the EU Drinking Water Directive taking into account the recommendation published by the WHO in the Guidelines for drinking-water quality. In spite of their potentialities, the use of the two disinfectants is still affected by the lack of detailed information on the optimal conditions to be applied to guarantee the maximum biocidal effect without compromising the chemical quality of the distributed water. With the present doctoral thesis, killing activities of the two disinfectants towards Legionella pneumophila were investigated thouroughly in controlled laboratory conditions taking into account their decomposition kinetics. First-order differential equations were applied to model and compare their biocidal behaviours as initial concentration of the disinfectant, water temperature and contact time varied in the application ranges. Moreover, microbial growth on pipe materials has been examined to understand their role on Legionella proliferation in drinking-water distribution systems. Findings of the batch studies have been used to interprete the results of a monitoring activity made in two different hospitals where hot water treatment with the two disinfectants had been implemented in different periods of time. Corrosion effects of the two chemicals as well as microbiome characterization have been performed by examining coupons exposed to disinfected hot water for different contact times.