can someone please tell me how to remove legionella from a cooling tower? is there an effective technique or process? I use H2O2 (30%) and UV lamps but the legionella problem still persists! thank you.
To deal with the immediate issue, you may need to make sure that the cooling tower and the water within it are clean, and that surfaces are free from biofilm. A pre-clean and post-clean super-chlorination is recommended. You would do this by adjusting the pH to no higher than 7.5 and circulating free chlorine at a concentraiton of 5 ppm for 5 hours.
The best way to routinely control Legionella growth in a cooling tower is to use an oxidising biocide at an effective concentration. Adding sodium hypochlorite to give you a free chlorine concentration of 0.5-1.0 ppm in all parts of the system is effective at a pH of less than 7.5. Where the pH is higher than 7.5, then a bromine-based disinfectant is better. The effective free bromine concentration should be 1-2 ppm.
The added advantage of halogens (i.e. chlorine and bromine), are that they are easy and cheap to measure in situ.
There is some good guiding principles in this HSE technical guidance:
https://www.hse.gov.uk/pubns/priced/hsg274part1.pdf
UV is a focal disinfectant only and it's effectiveness will be deminished if the water has a lot of suspended solids in. Hydrogen peroxide could be consumed quickly if there is a high biological demand.
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