Permanently Removing Legionella from the Cooling Tower

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I have a cooling tower and sometimes we have Legionella bacteria and we do not know to remove them permanently. 

What is the best solution for permanent Legionella bacteria removal from a cooling tower?

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24 Answers

  1. If you like to monitor if your treatment of your cooling tower was succefull or not the rapid quantitative microbiology technolgy of www.rqmicro.com tells you the result within 2 hours.

  2. You can hardly completely remove Legionella bacteria,  especially
     with one solution. To reduce  quantity of Legionella bacteria  to a minimum, an integrated approach with effective and environmentally friendly solutions is needed. Such solutions can be selected having, information about the entire system, the chemical composition of water, its microbiologia.  To reduce the growth of microbes after cleaning the system, regular alternation of biocides is recommended..

  5. Check Out this proven disinfection tech. 

    http://www.miox.com/

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    MIOX water treatment technologies combine salt, water and power to generator cost-effective water disinfection chemistries on site, on demand.

  6. I want to add to the answers below that it is nearly impossible to "permanently remove" legionella from the cooling tower water. All natural water contain these bacteria, so any feed water will add them into the cooling system.

    An ongoing maintenance/cleaning process has to be accompanied to the appropriate water treatement (as already described) to keep the legionella (and other problematic bacteria) on a low level.

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  8. As mentioned traditional Ozone is great, but has its downfalls: high energy use and corrosion and chemicals solutions require regular maintenance and sometimes permits. The AOPure/OzoMax technology is used to clean water in cooling towers, pools and water features providing an extreme reduction in “blowdown” discharge in cooling towers. The technology will reduce costs through lower water/sewer charges,  the elimination of added chemicals, lower energy use, less maintenance and cleaning. This patented technology will also control pathogens such as Legionella, C. diff, coliform, and cryptosporidium in water systems, while adding no chlorine or other toxic chemicals to the water. There is little blowdown and you do not have to deal with the costs, hazards or treatment created by blowdown.

    The Ozomax Insitu Advanced Oxidation Process generators produce a mixture of oxidants not from air or gaseous oxygen but directly from the water using a patented electro-catalytic dissociation process. The resulting nascent oxygen in the presence of precious metal catalysts produces a mixture of powerful oxidants including oxygen radicals, ozone, hydrogen peroxide and hydroxyl radicals. These work together to oxidize and eliminate organic and inorganic pollutants and are especially effective at destroying micro-organisms.

    For more information go to the link above or contact me directly.

  9. I was quickly reading all the useful recommendations.

     

    If you like to know within 1-2 hours if the treatment was successful, we can support you with our CellStream Technology.

     

    Our lab-on-a-chip technology is able to automatically isolate Legionella cells from water samples in just one hour. The automated and highly specific method is based on immunomagnetic separation, microfluidics and flow cytometry. The results correlate to the cultivation method with higher sensitivity and minimal standard deviation. For more information, best please consult @ www.rqmicro.com

  10. Ozone can be used but has a disasterous effect on any metal in the system and can cause corrosion of pipework, heat exchangers and cooling towers but will kill Legionella.  The treatment of cooling systems to control Legionella is relatively simple but requires an assessment of risk generation, a management system to ensure that all systems put in place are actually carried out and that routine monitoring is carried out.  

    One of the common sources of Legionella bacteria is areas of poor or low flow.  The number of times I have been assured that there are no dead legs, yet when tracing the pipework I found old pieces of equipment out of use with no circulation, or pipework with caps on the end several meters away from the main circulation.  Is there an area where flow is very slow that deposits fall out of suspension.  It is in these areas where Legionella bacteria can develop.

    Another question should be is there an automatic bleed system.  Does this limit the cycles of concentration?  If the cycles of concentration becomes too high, then sediments start depositing within the system.  If the cycles of concentration are too low, then either chemicals being dosed become too dilute to be effective or the cost of dosing becomes too high and very costly.

    I advise that you employ a professional water treatment company, who look at the whole system not just the cooling tower.  There are questions, which need to be asked, is there ingress of dirt, product or dust getting into the cooling system?  I worked with a cooling system, which was always clear of Legionella until building work caused an ingress of building dust into the environment, the same occurred with powder in the environment.  As air is drawn through the water in a cooling tower, materials are scrubbed from the air and then become part of the water circulating.

    As a result the program of treatment needs to be complete.  It will always need some form of corrosion inhibitor to stop iron from becoming available for Legionella growth.  It will need some form of scale control, because either scale will form causing inefficiency in running the plant, or it will generate suspended solids, which will settle and allow bacteria to grow.  It will need some form of dispersant to keep these suspended solids in suspension until they leave the plant through the bleed system.  Often these components are formulated into a single product.  However, if there is dust ingress additional dispersant may be required.

    Biological control will be required.  If non-oxidising bacteria are being used, they are dosed on an intermittent basis, which allows for bacteria to grow in between doses and if just a single biocide is used, then resistance frequently occurs.  If materials such as oxidising biocides are used, they are dosed on a continuous basis.  They are able to kill bacteria in the water but may not kill bacteria, which generate biofilms.   Chlorine is pH dependant.  As the pH rises above 7.2, its effectiveness starts dropping over the next pH to 8.2 and severely deteriorates above pH 8.  Bromine changes the pH range where effectiveness starts dropping to 8.2 to 9.2.  Because bromine is a bigger molecule than chlorine, it is less volatile and less is lost due to losses through the tower.  Chlorine dioxide is effective but can be totally absent within the cooling tower because it is a gas dissolved in water and it easily de-gasses.

    The tower pack will need to be removed for cleaning.  The process should involve a pre-chlorination of a very high level of 50 ppm for at least 1 hour and ensuring that all parts of the system are circulated.  The tower will need to be shut down and cleaned removing the pack and cleaning it.  After it is put back and the tower is re-filled, the system will again need to be re-chlorinated to a minimum of 50 ppm for 1 hour and allowed to decline. (Any chlorinated water will need to be neutralised prior to sending it to any waste treatment plant, also if there is hardness scale then acid will need to be used in the cleaning process and this will need to be neutralised).

    If a system is already fouled with slime, then a combination of biocides will be required.  I once took over a plant where dust was scrubbed into the cooling system, and slime had colonised all the internal surfaces.  It took over 6 months of treatment to bring the slime under control.  The biofilm declined over that period and did not become re-established.  But it required heavy dosing of chemical and increased cleaning.  During this period Legionella did appear until it was brought under control.

    Routine monitoring is required, weekly microbial counts, pH, conductivity and chlorine or bromine.  Monthly analyses should be carried out, which consists of more detailed tests.

    If your current water treatment supplier is unable to provide a solution, then look for an alternative, reputable supplier.  The clue will be that the cheapest solution is unlikely to provide the result you want.

  11. I have just read all the answers posted here very quickly. I presume TwinOxide is an oxidizing biocide and I presume that it is chlorine dioxide. Let me first state that chlorine dioxide is not chlorine and the mode of action is by oxidation. 

    Chlorine Dioxide has a very high efficacy of oxidizing the legionella bacterium. 

    Legionella proliferates in water with temperatures between 35 degrees celsius to 55 degrees celsius. Legionella can survive temperatures as high as 80 degrees celsius in some cases. 

    The easiest and cost effective way to treat legionella is by constant dosing of chlorine dioxide into the cooling tower. This can be carried out using an on site chlorine dioxide generator. 

  13. We have a very simple and highly effective answer. Add Solutek to the water, we can provide dosing details once we have a little information. Not only will it take care of your problem it will clear the entire system of slime and growth of bacteria on all internals. Our product is 100% fully organic and bio-degradable.

    Contact us for a quick discussion.

    www.soleco-technology.com

     

    Hugh.

  14. I do concur with most of the Oxygen use items. oxides, ozone, micro and nowadays nano bubbles. All will improve but not complete the task you requested. In order to stop this or any pathogen is to stop inviting them in.  Not a joke. The first rule in all drinking water never use any kind of chlorine. It has a narrow ph range relative to your pathogen. When you kill the beneficial microbes that use the legionella as their food source you allow/invite them to populate your tank. ( You are killing all of your chickens so the wolves will have to find a new food source. You! Rule #2 DNA microbes will reduce organic into less complex form. But only RNA microbes have the genetic code to reduce all organic compounds into their elemental /nutritional state.  Since  the waste/waste water is centralized (huge mistake, just ask Texas, Florida, and Puerto Rico) then your microbial purification systems must be at the central processing. They can then be recycled back into the potable drinking water, agricultural use, or put into rivers to ocean and will continue cleaning the environment until their 12 week active life work span has concluded. They also generate collectable electrons/electricity. Waste not want not! 

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  15. Alemayehu, regular and ongoing effective treatment and maintenance are required to maintain Legionella control in a cooling tower. A highly qualified water treatment company can specify, implement, and measure a program for your tower. In a large study, Richard Miller of the Univ of Louisville found that, although some biocides worked better than others against Legionella, most of them were effective if applied properly and accompanied by good maintenance -- and none of them were effective in the absence of those factors.

  17. all answers provided are great. the whole idea is to remove biofilms (either mechanically by blowing, high pressure water through the water channel or other methods as stated by others) and the disinfect the tower channel, but which method will be cost effective?

  19. The simplest and cheapest way is to first drain the tower and clean out any biofilm then refill and apply continuous chlorine to maintain a residual. Periodically remove biofims if they form.

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  21. The most effective way is to use TwinOxide as the disinfectant, it will be effective between ph 4-11 it will remove All bio film and therefore eliminate the possibility to grow Legionella, besides all this it will also kill active Legionella. All this is done in the most simple way of just dosing 99% pure CLO2 made by Twinoxide 

  22. Most of the resources for removal and control of legionella can be find here  https://www.awt.org/legionella/index.cfm, contains all kind of discussion , guidelines and technologies for removal of legionella. Hope this will help. 

    1 Comment

  23. We have just installed a UV system to remove legionella in a site that already were some people infected and a couple die...let me know if you need our support.

     

    1 Comment

    1. Dear, what you mean infected and die, who?

  24. The easiest way is to install an ozonator circuit and ozonate the cooling water for periods when the bacteria becomes a problem. The effective ozone will kill the bacteria and the ozone is quickly removed from the water which does not require any other action from you as with other chemicals. You obviously need to filter the dead bacteria from the water which might require a bypass filter for this purpose.

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