Testing Cooling Tower Water for Total Bacteria and Legionella

Published on by in Academic

Testing Cooling Tower Water for Total Bacteria and Legionella
Is it time to reconsider testing for total bacteria and Legionella in cooling tower water? Two case histories demonstrate how current water-testing methods could be indicating that bacteria control is acceptable and under good control — when the opposite is true.

Attached link

https://www.process-cooling.com/articles/89404-testing-cooling-tower-water-for-total-bacteria-and-legionella

Taxonomy

3 Comments

  1. I should also add, using ATP monitoring such as the Bioscan can provide results after 1 minute.  Testing the ATP before and after dosing bio-dispersant will detect the release of slime because the ATP readings increase.  This is a good technology to use.  Although it does not differentiate between Legionella and other bacteria it does provide a good indication of bacterial levels and any changes.  These can be confirmed by conventional plate counts and Legionella tests.

  2. A good system is to assess the plant for any dead legs, because they are a source for the growth of microbial slimes and Legionella, then get them removed or looped so that circulation takes place.  One site, who said they had no dead-legs had 17 of them.  The second main source is building debris and or sediment getting into the cooling system.  Materials such as china clay dust, coffee grounds and fibres all of which protect bacteria from the biocides in use.  The use of bio-dispersant as part of a program on a weekly basis helps prevent the build up of slimes.  I noted that one of the materials in use was glutaraldehyde.  Glutaraldehyde is volatile so some is lost from the system by evaporation.  It is also mutagenic at low levels and can promote resistant strains from developing.  The choice of non-oxidising biocide and its alternation, even in the presence of bromine, along with the intermittent dosing of biodispersant can prevent and clean up fouled systems in high risk systems.  The use of the stainless steel mesh for monitoring is another tool used to monitor the system but will not prevent Legionella or microbial slimes.

     

  3. It is not completely true that testing methods have not changed for many years.  We have been running bacterial DNA to get a far better and more accurate identification of what is growing in a system. It is extremely difficult to identify some bacteria by way of running cultures. An example is where you have iron or manganese depositing bacteria. Their destructive work is very visible during equipment inspections but finding their existence in a water sample in some cases is zero.  This is also the case with legionella. You may not find viable cells but if you find their DNA, you know you have them. That makes finding where they are a little easier because you know that you must look.