The resistance of Legionella to disinfection explained byexperiments on a hot water distribution system

摘要

Efficiency of various treatments of disinfection against Legionella were tested on a Hot Water Distribution System (HWDS) pilot unit. The results demonstrated clearly that a large majority of Legionella in the networks were fixed in the biofilm at the surface of the pipe (more thanrn98% for each loop). Chemicals treatments (continuous chlorination, hyperchlorination, hydrogen peroxide and peracetic acid mixing) commonly used for the eradication of Legionella in hot water distribution networks, appeared to be inadequate for eradicating thernbacteria in the biofilm. Unfortunately, the biofilm contained a large majority of the pathogensrnin an HWDS whereas legislation is only restricted to the Legionella concentration in the waterrnphase. Thermal treatment appeared to be efficient to disinfect the majority of the biofilm butrnseemed to promote the biofilm re-growth as well. It was then concluded that the best solutionrnto prevent Legionella contamination in hot water distribution system would be to have arnperfect control of the temperature in the networks (temperature > 55℃ at all points).rnNevertheless, in many cases it is difficult to have such a control, so during the time necessary to do the networks modifications, the best solution to control the Legionella proliferation appeared to be to apply a treatment shock (thermal or chlorination in function of pipes characteristics). These treatments must be followed by a continuous chlorination totally controlled and equipped with alarm systems. This study demonstrated that biofilm sampling devices must be installed in hot water distribution systems to anticipate Legionella contamination and correctly determine the efficiency of the treatments.