Legionella bacteria and Scaling Problems

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I have a problem with scale which has caused the formation of Legionella bacteria in my water cooling towers. 

How can I get rid of the bacteria most efficiently and quickly?

How should I change the temperature, water hardness and pH to prevent scale formation?

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22 Answers

  2. Bonjour 

    On reste là sur l'objectif de pouvoir combattre la Nature avec la technicité.

    Quoi que l'on fasse, la Nature contournera votre dispositif et le reportera sur une autre approche.

    Il n'y a pas plus de formation de bactérie légionella que d'autres bactéries. il y a la formation d'un support spécifique aux dévelopement de certaines bactéries et mieux encore la Légionella. Que dire que toutes tours ayant le même fonctionnement développent à outrance ce genre de bactérie comme d'ailleurs bien d'autres.

    C'est faire preuve d'une méconnaissance totale de cette information: la bactérie est partout sur terre et c'est grâce à elle que nous sommes encore Vivant. Toutes les bactéries de notre planète sont UTILES la Legionella comprise. C'est le support qu'il vous faut combattre. Et là on est sur un autre domaine, une autre approche.

    La bactérie Legionella se trouve partout dans l'atmosphère, dans l'air. En passant par un dispositif qui lui sert convenablement de support elle s'y installe et prospère.

    La problématique contre le tartre est la même: c'est un composant de l'eau. 

    Hello

    There on the goal to fight Nature with the technicality.

    Whatever we do, Nature will bypass your device and see it by another approach.There is no more training than other bacteria legionella bacteria. There is the formation of a support specific to the development of certain bacteria and better still the Legionella. What can I say that all towers have the same functioning develop excessively this kind of bacteria like many others besides

    It is a total lack of knowledge this information: the bacteria is everywhere on Earth and it is thanks to her that we are still alive. All bacteria of our planet are useful including Legionella. It's the support you need to fight. And here we are on a different domain, a different approach.

    The Legionella bacteria everywhere in the atmosphere, in the air. Through a device that serves as a properly support she settled and prosperous. The problem against the Tartar is the same: it's a componant of water.

     

  3. Dear Oliver

    Herewith attached excellent technical guidelines for Legionella control  (WHO, Australia, Irland, and European standards etc..) helping you for setting water safety plan (System assessment, Monitoring, assess hazards and prioritize the risks), prepare Management procedures and finding solutions for each problem regarding Legionella in water cooling tower.

    This procedure will help to prevent the problem to be issued in the future instead of just working on controlling.

  4. You will be given lots of conflicting advice as to how to control issues.  I would advise contacting a reputable specialist who can look at your specific process and how to overcome it.  Scale can occur for several reasons.  The obvious one is supply by a scale-forming water.  In this case, either scale retardents and or pre-softening can help overcome it.  If you have an existing scale then it will impact the process so either descaling using some form of acid (think carefully about handling issues) and passivation afterwards.  

    The use of softening or RO water will mean that a corrosion inhibitor will be required.

    It could also be caused by over-concentration of a cooling system.  In this case control using a conductivity controlled bleed and scale/corrosion inhibitors.

    The third cause of scale is the presence of iron or manganese bacteria.  This could either be from the water source or just by development on the surface of iron or galvenised pipework.  This is harder to control.  Citric acid along with specialised dispersants can help break this down but you will need side-stream filtration to help remove the metal particulates.

    This doesn't appear to answer the question about Legionella in the water.  This is because a cooling system needs a full package including scale or corrosion inhibitors to control conditions.  No single biocide provides a solution but general guide is the use of an oxidising biocide in conjunction with dispersant and/or non-oxidising biocide, which should be Legionella effective at the dose rates given and contact time.  Advise such as high levels of chlorine dioxide are not sustainable and chlorine dioxide becomes de-gassed under high agitation and by the scrubbing action of the air in a cooling tower.  Chlorine becomes less effective as the pH rises from 7-8 and is highly corrosive.  Bromine can extend the pH although it also starts dropping its activity above pH 8.  Ozone kills all but is highly corrosive. UV on its own does not work in re-cycled systems.  Non-oxidising biocides have to be selected carefully based on the pH of the system and its contact time within the system and how quickly it breaks down.  

    To quickly remove Legionella firstly chlorinate the water with dispersant to a minimum of 50 ppm free chlorine for at least 1 hour but preferably for at least 5-6 hours, ensuring that all parts of the system including standby  pumps are run for 1 hour.  Neutralise the chlorine then run a de-scaling program based on acid whether it is sulphamic, citric or other.  Drain and flush the system then clean the tower (use a specialist service provider qualified to do this).  Re-fill then re-chlorinate the system.  Then make sure that the scale and corrosion dosing systems are working properly, that the automatic dosing and conductivity control system is operational and that your biocide regime is working properly.

    You need to review your operation to see why you have developed both scale and Legionella growth and implement a full risk assessment for Legionairres Disease and carry out its monitoring program.

    1 Comment

    1. Hi Don, I agree with your advice, especially the need for a full risk assessment and monitoring program. My only added suggestion in the case of removing existing scale that other forms of descalers be trialed rather than acids. I believe there are far safer and less toxic ways of managing scale. If you are interested in learning more about the non-toxic, non-corrosive and bio-degradable descaler my company has developed and manufactures, please email me at andrew@waterandoilsolutions.com.au

  5. We should correctly define the problem. Scale does not "cause the formation of Legionella bacteria." Legionella bacteria are common in natural water courses and widespread in the environment they may contaminate and grow in other water systems such as cooling towers and hot and cold water services. Scale will provide a surface where biofilms can develop and make it difficult for chemical oxidizing products to penetrate the biofilm for effective microbiological control. The EU, and finally the US, have addressed this concern through legislation requiring effective water management programs to minimze the risk of Legionella outbreaks. Here are some good references for a total water management assessment:

  6. Reducing the hardness can reduce the scale, but there can be other scaling as well (e.g. based on Iron).

    So my suggestion would be to get in contact with a water treatment company to analyze the used water quality. They then can suggest a proper treatment for both, the scaling and the biological hazards in your cooling tower. Please beware that e.g. changing the pH of your water can effect other parts of cooling system (like metal heat exchangers, where scaling or corrosion is unwanted, too). Therefore this has to be done with care.

    If you cycle the water within the tower, another parameter, which may influence the scaling it the amount of effluent water you have compared to the evaporative water loss. If you increase the effluent, that may as well help.

    Depending on the severeness of the scaling, after you chosen the right water treatment, you have to clean or exchange the fill inside the tower. Additionally to the biological problem, severe scaling can also cause structural and thermal issues within a cooling tower.

  7. 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

  8. Dear Oliver,

    of course the easiest way and probably the fastest way to get rid of legionella and scale is to use chemiclas as mentioned by Manuel. Easy to control and to handle? Fast reaching all effected corners? Cheap buying permanently chemicals and paying for permanent menpower control? Permanent efficient only by adding permanently chemicals and anticorrosives? 100% effective?

    Have you ever thought of a non chemical, non toxic environmental friendly treatment? A permanent 100% efficient solution?

    Some of our references are: EADS Munic, Ministry of Interieur Vienna, State opera house Vienna, Technical University Vienna and more.

    Our certified and approved technology removes all biofilm, germs, bacteries and legionella, permanent without any chemicals. Scale will be removed over time and as long as you keep your temperatures below 50°C you dont have any new scale formation.

    Your equipment is no longer exposed to corrosive chemicals as chloride, and you dont need to add anticorrosive additives - mostly toxic and difficult to remove when disolved in water.

    As we dont add any chemicals, ph levels will not vary and stay persistently at approx. 7

    In addition malodor formation is stopped, as any amonia-compund creation is eliminated.

    Please request detailed information from:

    APW, Axenic Prim Water GmbH i.G.

    Dipl, Ing. Gerhard Mangold

    g.mangold@axenic-prim.de

     

  9. Dear Oliver,

    Microbiological fouling in cooling systems is the result of abundant growth of bacteria on surfaces. Once-through and open or closed recirculating water systems may support microbial growth, A wide variety of bacteria can colonize cooling systems. Spherical, rod-shaped, spiral, and filamentous forms are common. Some produce spores to survive adverse environmental conditions such as dry periods or high temperatures. Both aerobic bacteria (which thrive in oxygenated waters) and anaerobic bacteria (which are inhibited or killed by oxygen) can be found in cooling systems.These bacteria are so strong and down the PH up to 6.0 and causing corrosion in piping system.These bacteria can choke the heat exchangers Tube.

    Treatment of legionella bacteria

    Biocide

    At least two (2) types of biocides shall be used alternately on a weekly basis to prevent emergence of resistant strains of microorganisms.Chlorination is the best way to control bacteria.

    Before setting up a biocidal water treatment programme, it shall be ensured that the system is clean.

    1.  The ‘shot/slug dose’ method shall be implemented to prevent microbiological acclimatization. This involves the addition of the biocides, alternating them at suitable intervals, directly into the cooling tower basin using an automatic control system.

    2. The biocide used to eliminate and control the growth of legionella bacteria shall comply with the following:

     (a) It shall not be a prohibited chemical in the Poisons Act for trade effluent discharge to a public sewer;

    (b) It shall be effective against a wide range of micro-organisms (including all legionella bacteria) at the recommended dilutions, and its effectiveness supported by official independent reports.

    (c.)It shall be proven to be effective when dosed in accordance to the manufacturer’s recommendations (frequency, dose strength, preparation);

    (d) It shall have documentation available covering the safety and effectiveness of the product in recirculating systems;

    (e) It shall not interfere with the method used for identification of legionella bacteria;

    (f) It shall be chemically and physically compatible with processed water and neutral to piping materials.

    The chemicals used and the subsequent end-products of the treatment programme shall be degradable with minimal hazards to the environment in the event of accidental spillage or through draining into effluent treatment plants.

    Water sampling and bacteriological monitoring.

    A regular testing programme for legionella bacteria (including total bacteria count) shall be carried out to check the efficacy of the water treatment regime at the following intervals:

    Standard plate count - At least once a month.

    Legionella bacteria count - At least once in every three months.

    The water sample shall be taken before the dosing of biocide. If disinfection is carried out, the water sample shall be taken no less than 3 days after disinfection to ensure effectiveness of the treatment.

     

  12. Hi Oliver,

    first of all you have to remove the scale from your cooling system than you have to clean up with a disinfection with bio dispersant and chlorine (the cheapest way).

    the first step: Depend on how much is havy the problem, but normally I suggest to use sulphamic or formic acid (with corrosion inhibitor), you could use a blending ready to use (2-5% of concentration should be enough)....keep the system under treatment controlling the pH value ...

    second step: you must use chloride (keep 1 ppm of free chlorine inside the system for 5-8 hours) with 50 ppm of bio dispersant ( if you don't use it, you won't be able to remove biofilm) ....than you have to discharge the cleaning solution 

    I can send you the procedure ...write me on m.testoni@ncr-biochemical.it

  14. Let's look at the issue in two parts: 

    1. The formation of scale in pipework and cooling towers.

    2. The growth of Legionella bacteria on the scale substrate.

    The removal of scale can be solved chemically, my company has developed and manufactures a green-rated, non-toxic and cost effective pipe scale remover called 'Clean Pipe Extra.' This is a safe and non-acidic approach which will not damage the seals, fittings, pipework and other equipment in the cooling system. The control of future formation can be managed through control of pH through the use of water softeners. We have experience in developing ongoing scale and corrosion control strategies for cooling towers and water distribution networks for HVAC and potable water supply. 

    It is worthy to note that the removal of scale will not necessarily solve your Legionella issue. The reason being is that the 'biofilm' colonies which house and protect the Legionella bacteria from disinfectants can form and grow on any surface within the network, even on the smoothest of surfaces. To effectively control Legionella, you will need a multi-barrier approach which combines preventative technologies, efficient chemical dosing and routine monitoring.

    Research has shown Legionella to be resistant to thermal shock, high chlorine or biocide dosing, and UV irradiation because of their ability to survive inside amoeba and be protected by the biofilm colony that is formed. That is why Legionella outbreaks still exist in cooling towers of buildings in 1st world countries, even with routine monitoring and chemical control. New methods of prevention need to be considered in these situations. We have found in research that mechanical disinfection through hydrodynamic cavitation is the most effective way in breaking apart the biofilm layer, amoeba and Legionella bacteria cell wall. If the Legionella is not instantly killed, it will be killed with a minimal amount of residual chlorine or free radicals generated in the water. My company has developed an effective strategy currently used in Europe, Asia and Australia to prevent and control the growth of Legionella in cooling towers using this method of disinfection without costly chemicals combined with the efficient removal of organic microparticles and dissolved metal nutrients that feed bacteria.

    If you are interested, please send me an email at andrew@waterandoilsolutions.com.au and I will be happy to send you any information you need and set up a time to speak over the phone or on Skype.

  15. Water softners and lime softening are good for issues of hardness and pH. Scale inhibitors can be used.

    Flushing with 5 t 8 percent dilute HCl acids a good option for common calcium carbonates.Mn perhaps a greater problem in PVCpipes.Flushing with white vinegar or EDTA for calcium sulphate.

    High pressure steamers and jet flushers work well in scaling situations.

    Industrial cleaners like Barium nitrate,phosphoric acid and sulfuric acids usually used,appropriately.

    High chlorine dose best for biofilm bacterial inhibition.

    Interestingly residual chlorine,MAPs and organic carbon combo can contribute to faster biofilm build up

  16. Do you have PVC film type fills in your tower? You should first check the scale constituents based on cleaning methodology can be worked out. Is the scale only on fills or on your heat exchangers also? You can use some surfactant in combination with chlorine dioxide/hydrogen peroxide to clean the fills. Then adopt cooling water treatment program with suitable biocide/surfactant. Those require detailed assessment with water quality, system metallurgy, etc

    1. Go to http://GMXINTERNATIONAL.comGMXINTERNATIONAL.COM They use powerful magnets to dissolve the scale and PERMANENTLY stop it from reoccurring. No chemicals, lost employee time to carry chemicals to the site from a storage facility.

  19. Instead of making adjustments only to solve the immediate problem, implement a program for ongoing control of both Legionella and scale. The companies listed at http://hcinfo.com/partners/water-management-plans/partner-list/ have significant experience in cooling water treatment as well as developing comprehensive water management plans for Legionella control. 

  20. If your water temp is above 34 F, and ph. is between 5.5 to 10.0 then the Archaea species is your best bet. It has the genetic code to break down all compounds and change them into nutrients. No pathogens have ever survived in the Archaea matrix since testing began in 1998.  The Archaea will assist in altering the ph.  This water can be potable for drinking, washing , irrigation, or just releasing into nature to continue its cleansing function.

  21. Oliver pretreatment with a water softener or reverse osmosis filtration would be an option for the scale. A good chemical water treatment program would be the other and solve both issues. Please call me to discuss at 708-539-2117. Eric Wallace

  22. Lets first deal with removing the scale formation issue that is due to presence of calcium and magnesium salts in the water. A very effective technology using the template assisted crystallization tank system will bring the calcium and magnesium salts to the surface of the water, thus the salts will not adhere to the packing and scale formation will not occour.

    As far as Legionella is concerned, you need to go to a shock dose of 100-200 ppm of chlorine dioxide. Once the tower is cleaned up, you need to go to constant dosing of chlorine dioxide at 1-3 ppm per day. The actual demand for chlorine dioxide needs to be established.