Can Heat Shock Treatment eradicate legionella in hot water systems – pilot-scale study
A pilot-scale unit simulating a hot water system was built and designed by the Scientific and Technical Building Centre (Farhat M et al1, Centre Scientifique et Technique du Batiment, CSTB, France) to develop an analytical tool in order to evaluate the effectiveness of anti-Legionella treatment in biofilm and to study the fate of Legionella populations in water and biofilm after applying a heat shock treatment.
Two heat shock treatments (70 degrees C for 30 min) were applied to water in the pilot-scale unit containing a stable cultivable legionella species concentration of 5 x 105cfu/l.
The results showed that the first treatment had a transitional effect on the abatement of Legionella concentrations, while the second treatment had no detectable effect on Legionella populations in water and biofilm.
The legionella counts measured in the dead leg water and the circulating water revealed that there was rapid recolonisation as well as the incomplete destruction of the biofilm.
In addition, a resistance test was conducted and showed that Legionella in the second heat shock treatment was not thermo-resistant but thermo-acclimatised.
Their conclusion1 was that thermal disinfection does not seem to be “efficient enough to eliminate Legionella when it is used as a curative treatment”.
J Appl Microbiol. 2010 Mar;108(3):1073-82. Epub 2009 Aug 28