Applicazione del trattamento con monoclorammina alle acque calde sanitarie per il controllo del rischio idrico: valutazione di efficacia microbiologica e impatto sulle caratteristiche chimico-fisiche delle acque trattate

[Autom. eng. transl.] The management of the production process of sanitary hot water evolves with the new scientific evidences, which allow to improve the practices to be applied to the evaluation and control of the water risk. This work reports the preliminary results of environmental surveillance implemented in the new pavilion of the Emergency Acceptance Department of the Pisana Hospital, to assess the effectiveness of the experimental disinfection of domestic hot water with mono chloramine (MCL). From November 2010 to April 2011, a total of 32 ACS samples were taken, of which 6 before the MCL generator was installed and 26, taken monthly, after the disinfection system was put into operation. The samples were analyzed for Legionella spp. according to ISO 11731-2: 2004 and the quantitative research of Mycobacterium spp. through the parallel use of cultivation and molecular methods; positive samples were confirmed with hsp65 gene sequencing. Furthermore, the physical-chemical analysis of the water was performed in order to identify factors favoring microbial colonization. Before the introduction of MCLs, all the samples examined were positive for Legionella pneumophila serogroup 1 with an average charge of 7183 CFU / L. In the samplings following the commissioning of the disinfection system, no sample showed the presence of Legionella. The research of Mycobacterium spp. gave positive results in the samples taken before the introduction of the MCLs in three sites, with an average bacterial load of 39 CFU / L. Subsequently an increase in the charge was observed up to values of 524 CFU / L at four sites out of six. The increase was also confirmed by the analysis in Q-PCR, with average values of the initial Genomic Units (UG) equal to 1692 UG / L before the MCLs, up to 53058 UG / L in the following months. The analysis by sequencing showed that the predominant species is M. gordonae. Physico-chemical analyzes showed high concentrations of Zinc ion in the sites where the presence of mycobacteria was found, despite the low content of nitrogen compounds and phosphate ion. These preliminary results indicate that the monochloramines can be an efficient method for the control of the colonization of the water network by Legionella spp .; the treatment can however favor the selection of other microbial genera endowed with intracellular parasitism in water protozoa, probably favored by the reduced vital competition and the availability of important chemical elements. It is however necessary to evaluate the effect of the disinfection system on the microbial ecosystem for a correct risk assessment in the long term. Research conducted within the PRIN 2008 Project