Preventing Legionnaires Disease in Cooling Towers


What is legionnaire's disease & legionella?Cooling Tower Legionella Control is Critical

Most cooling towers are likely to become contaminated with legionella, the bacteria that can cause Legionnaires’ disease, at some point in their serviceable life. It is unrealistic to try to prevent entry of the organism into a cooling tower system or to create an environment that entirely precludes its growth and multiplication. However, an effective water treatment program for cooling tower legionella can help reduce the risk of Legionnaires' disease. To learn more, contact Delta today. Click Here!

How to Prevent Legionnaires’ Disease in Cooling Towers

Preventing Legionella in cooling towers is an ongoing challenge. While good maintenance of cooling towers is necessary to keep cooling tower legionella at bay, no water treatment and maintenance system is guaranteed to fully and permanently eliminate the organism. However, the benefits of proper maintenance, using cooling tower microbial control, allow the cooler tower system to operate more efficiently and have a longer lifecycle. Make Delta your cooling tower manufacturer of choice today!

Cooling Towers Are Susceptible to Legionnaires’ Disease

Cooling tower systems are a concern because they contain pools of warm water that are open to the atmosphere and present perfect breeding grounds for legionella bacteria, if they are not properly cleaned, disinfected, and maintained. Therefore, the responsibility of cooling tower legionella risk assessment belongs to the facility owners or manager. There are many risk factors that can lead to hazards and the presence of legionella bacteria. Below, we list our top six and identify the measures required for prevention.

Top 6 Legionnaires’ Disease Risk Factors

  1. Source Water Quality

    Risk: Make-up water usually comes from a municipal or well supply but can sometimes come from a holding tank, which can contain sludge, rust, and sediment. Less commonly used, surface water that comes from lakes, rivers, or reservoirs could be full of microorganisms and nutrients from the environment.

    Prevention: Twice a year, the cooling tower system should be cleaned and disinfected focusing on the entire tower and any holding tank by removing any rust, sludge, and sediment. If the water is coming from a lake, river, or reservoir, antimicrobial treatments should be used before the water enters the cooling system to prevent fouling.

  2. Water Treatment

    Risk: The temperature, environmental factors, and flow velocities of cooling tower water vary as well as other parameters affecting water treatment.

    Prevention: The industrial or HVAC system design allows for water to circulate throughout the system whenever it is operating. System operation should be coordinated with a full chemical treatment of the water. Also, keep the system clean by removing all dirt and debris. If the cooling tower needs to be shut down for more than three days, the entire system should be drained. For metal cooling tower systems, use extra caution to ensure the free flow of water to prevent the proliferation of microorganisms responsible for corrosion and degradation. This is one reason to consider HPDE engineered plastic cooling towers from Delta Cooling Towers, which come with a 50-year life expectancy and a 20-year warranty. So, you don’t need to worry about replacements.

  3. Disinfection

    Because cooling towers are open to the environment, the system can rapidly become recolonized with microorganisms, like cooling tower legionella, even after chemicals or other agents were added to achieve sterilization.

    Prevention: Vary the antimicrobial stresses applied in the cooling tower microbial control program by alternating between two non-oxidizing biocides as a single dose or alternate an oxidizing antimicrobial with a non-oxidizing antimicrobial.

  4. Biofilms

    Risk:  Dirt, dust, and other particles enter the cooling tower water during the cooling tower process. Depending on where the cooling tower is located, the amount of material can be extensive. The presence of biofilms is important for cooling tower legionella survival and growth-providing nutrients in water systems.

    Prevention: It is strongly advised to use a compatible and environmentally acceptable dispersant and/or detergent to penetrate biofilm and sediments. Make sure to follow proper cleaning and maintenance for your cooling tower system to ensure top performance and to minimize the risk of Legionnaires’ disease.

  5. Design & Material Used

    Risk: Areas of stagnant water prevent proper chemical treatment of the towers and allow legionella and their hosts to flourish.

    Prevention:  Your cooling tower system should be designed for easy cleaning and maintenance to avoid buildup of sludge and deposits. While cooling tower conditions are often dependent on the water treatment chemicals being used, poor piping designs can create an environment where pathogens, like legionella, can thrive. On the plus side, Delta Cooling Towers’ antimicrobial technology is designed to minimize the risk of cooling tower legionella.

  6. Spray Drifts

    Risk: Even under normal operation, water droplets can leave the drift eliminator.

    Prevention: It is for this reason that cooling tower systems should never be installed next to air intakes or windows that may be opened. Also, every six months or so, inspect the conditions of the drift eliminators making sure there are no gaps to allow free flow of dirt. For best results, install the best drift eliminators available with drift rates as low as 0.0005% of the circulating water flow.

    There are many innovative technologies available that can help prevent the growth of cooling tower legionella. One of the most effective is an anti-microbial cooling tower from Delta Cooling Towers.  It contains an anti-microbial resin that’s compounded into the plastic material, so it will not fade or wash away. Furthermore, this product has the only lab-tested anti-microbial efficacy against legionella bacteria out of all the common cooling tower materials.

    To learn more about Delta’s Cooling Tower products or get a quote, click here or call 800-289-3358.

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