Abstract
The contamination of industrial cooling towers has been identified as one cause of legionellosis, but the real risk has been underestimated. Two different disinfection treatments were tested on Legionella colonization in an industrial Cooling Tower System (CTS). Environmental monitoring of Legionella, P. aeruginosa, and a heterotrophic plate count (HPC) at 36 °C was performed from June to October 2016. The disinfection procedures adopted were based on hydrogen peroxide (H2O2) and silver salts (Ag+), in addition to an anti-algal treatment, then using hyperclorination as a shock, and then continuous treatment by sodium hypochlorite (NaClO). L. pneumophila serogroup 8 was found at a concentration of 5.06 Log cfu/L after the CTS filling; a shock treatment performed by H2O2/Ag+ produced a rapid increase in contamination up to 6.14 Log cfu/L. The CTS activity was stopped and two subsequent shock treatments were performed using NaClO, followed by continuous hyperclorination. These procedures showed a significant decrease (p < 0.05) in Legionella concentration (1.77 Log cfu/L). The same trend was observed for P. aeruginosa (0.55 Log cfu/100 mL) and HPC (1.95 Log cfu/mL) at 36 °C. Environmental monitoring and the adoption of maintenance procedures, including anti-scale treatment, and physical, chemical, and microbiological control, ensure the good performance of a CTS, reducing the Legionella risk for public health.
Highlights
Cooling towers are used in most large commercial and residential buildings, industrial power generation units, and in chemical, petrochemical, and petroleum industries to disseminate waste heat into the environment
The levels of Legionella, P. aeruginosa, and heterotrophic plate count (HPC) at 36 ◦ C in the Cooling Tower System (CTS) were monitored during its operation at six different time points: T0, T1, T2, T3, T4, and T5
L. pneumophila serogroups 8 (SG8) had a concentration of 2.75 ± 0.21 Log cfu/L (∆Log 3.39) with p
Summary
Cooling towers are used in most large commercial and residential buildings, industrial power generation units, and in chemical, petrochemical, and petroleum industries to disseminate waste heat into the environment. These water systems provide an environment highly favorable to microbial growth [1,2] and have been determined to be a source for dissemination of human pathogens, especially. Legionella spp., as well as other pathogenic bacteria, protozoa, and viruses [3,4]. The genus Legionella is a set of Gram negative bacteria which includes approximately 61 species with at least 79 serogroups. The most dangerous species, in 90% of cases that causes legionellosis, is the L. pneumophila serogroup 1 [5,6,7,8]
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