With a variety of maintenance and preventative actions, it is possible to minimize or even prevent the risk of Legionella in cooling towers. There are 39 known species of aerobic bacteria which can potentially cause disease, including Legionella pneumophila, which is most commonly associated with the disease legionellosis or Legionnaires' disease. Living spaces, natural aquatic bodies and man-made water systems can all contain Legionella bacteria.
Several factors can increase the likelihood of Legionella developing: stagnant water in tanks, reservoirs, dead legs in piping systems and poor flow areas; temperatures between 20 and 45° Celsius; water pH levels between 5.5 and 8.1; ferrous ions from corrosion, which can be caused by biocide treatments such as chlorine or ozone; the presence of zinc, calcium, scale and magnesium; and biofilm, a layer of microorganisms that forms a slime layer on surfaces in contact with water. Treating these issues can help with preventing Legionella in cooling towers.
Biofilm thrives on rough surfaces and corroded materials. Wall scaling and the presence of other microorganisms such as algae, amoebae and other bacteria can host Legionella. Rubber, silicone and some plastics are also breeding grounds for Legionella. In terms of prevention, it is important to use the correct biocides; for example, chlorine does not perform well against biofilm.
Humans contract Legionella by breathing in contaminated water. This can occur when water droplets smaller than 5 µm are suspended in the air. The groups who are most at risk are smokers, people with chronic lung diseases or suppressed immune systems, organ transplant recipients, people who regularly use corticosteroid medicines, and those over age 55. If your cooling tower is contaminated, employees of your company could be exposed to serious danger when working with contaminated parts. Preventing Legionella in cooling towers is therefore of the utmost importance with regard to public health.
Major sources of Legionella contamination include the water distribution systems in large buildings such as hospitals and hotels; mist machines; humidifiers; whirlpool spas; showers; and, in some cases, cooling towers, although this issue is not as prevalent as once believed. Preventing Legionella in cooling towers ensures public and employee safety around your plant. There are a variety of preventative maintenance options available. Hamon is an excellent source to answer all your questions about preventing Legionella in cooling towers.
Hamon can help you design a system for preventing Legionella in cooling towers. Using the correct biocides and a regular maintenance schedule are both vital steps. Permanent water streaming, temperatures under 20°C and over 50°C, silver and copper ions, and bromine treatments are all factors that can help to prevent the presence of Legionella.
Firstly, you can minimize the spread of Legionella through water quality evaluations; reducing water stagnation; detecting and correcting process leaks into the cooling system that can provide nutrients to the bacteria; maintaining overall system cleanliness; applying scale and corrosion inhibitors; and controlling the overall microbial population. Prevention of the diffusion of bacteria can include the use of high-efficiency drift eliminators at the air inlet to prevent blow-off and at the air outlet to avoid plumes.
Symptoms of Legionnaire’s disease progress over a period of two or three days and can appear from two to ten days after exposure to the bacteria. The first signs of the disease may include headaches, muscle aches, and a fever over 40°C. In the second and third days, other symptoms may arise such as a cough which brings up mucus and/or blood; shortness of breath; chest pain; gastrointestinal maladies such as nausea, vomiting and diarrhea; and confusion or other mental changes. Occasionally, the bacteria can cause infections in wounds and other parts of the body such as the heart.
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