Legionella bacteria encounter optimum growing conditions in hot water systems and cooling towers. A pilot-scale 1 unit was built in order to study the biofilm disinfection. It consisted of two identical loops, one used as a control and the other as a ‘Test Loop’. A combination of a bio-detergent and a biocide (hydrogen peroxide + peracetic acid) was applied in the Test Loop three times under the same conditions at 100 and 1,000 mg/L with a contact time of 24 and 3–6 hours, respectively. Each treatment test was preceded by a three week period of biofilm re-colonization. Initial concentrations of culturable Legionella into biofilm were close to 103 CFU/cm2. Results showed that culturable Legionella spp. in biofilm were no longer detectable three days following each treatment. Nevertheless, initial Legionella spp. concentrations were recovered 7 days after the treatments (in two cases). Before the tests, Legionella spp. and L. pneumophila PCR counts were both about 104 GU/cm2 in biofilm and they both decreased by 1 to 2 log units 72 hours after each treatment. The three tests had a good but transient efficiency on Legionella disinfection in biofilm.
Chemical disinfection of Legionella in hot water systems biofilm: a pilot-scale 1 study
Maha Farhat, Marie-Cécile Trouilhé, Christophe Forêt, Wolfgang Hater, Marina Moletta-Denat, Enric Robine, Jacques Frère; Chemical disinfection of Legionella in hot water systems biofilm: a pilot-scale 1 study. Water Sci Technol 1 August 2011; 64 (3): 708–714. doi: https://doi.org/10.2166/wst.2011.696
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