Oliver, Another tactic is ...

Oliver,

Another tactic is to use ultrasound to reduce the Legionella count.  Legionella reproduce by being first being ingested into a larger organism where it will be expelled after reproduction.  The larger organisms are being supported in the biofilm layer where first anaerobic bacteria attach to the walls with polysaccharide glue.  Once the anerobic layer has reached a sufficient population, they emit a chemical that attracts aerobic bacteria that coat over them and act as an oxygen shield as well as a chemical shield making the difficult to remove.  The layers are approximately 20% anerobic and 80% aerobic.  This biofilm acts as a host to the larger organisms that support the reproduction of the Legionella.  Ultrasound helps by causing a sensation of water turbulence to the anaerobic bacteria, a condition that they are genetically disposed to avoid.  This begins to reduce the biofilm growth generally seen working at the edges where your biocides have greatest access to the anerobes.  As the biofilm shrinks, the population of organisms that support the Legionella also shrinks and so does their count.  The ultrasound does not kill the Legionella, but by reducing the number of available hosts, this acts to reduce their propensity to reproduce and will reduce your chemical and biocide treatment costs.  george@algaecontrol.us