Cooling Towers: How to Prevent the Growth and Spread of Legionella

A cooling tower is a cost-effective and energy-efficient way to remove heat from an industrial facility. The cooling effect occurs when air and water are brought into direct contact within the tower. Some of the water evaporates, thus reducing the water’s temperature. The heat and evaporated water exit the top of the tower as a cloud-like mist, and the cooled water collects in the basin, where it is pumped back into the facility for reuse. Without proper maintenance and operation, potentially harmful bacteria can flourish within the cooling tower as a result of this process, putting anyone who inhales the contaminated water droplets at risk.

Legionella is one type of bacteria that can thrive inside a cooling tower. Trace amounts of Legionella are commonly found in both naturally occurring bodies of water and man-made water systems. In such small amounts, Legionella is generally harmless, but if the environment is ideal for growth, exposure to Legionella can lead to Legionnaires’ disease, a potentially fatal form of atypical pneumonia.

Legionella flourishes under the following conditions:

-Water temperatures between 68°F and 122°F, with optimum growth between 95°F and 105°F

-Presence of biofilm as a result of stagnant water

-Presence of sediment

-Presence of corrosion, specifically on drift eliminators

-pH levels between 5.0 and 8.5

-Untreated water that can be aerosolized or misted

The risk for Legionella growth cannot be eliminated completely, but it can be greatly reduced by:

-Writing and implementing a detailed water safety plan

-Conducting a visual inspection at least once a month

-Cleaning and disinfecting the cooling tower quarterly

-Treating cooling water with chemical biocides on a continuous basis

-Keeping water temperatures below 68°F or above 122°F

-Minimizing stagnation in order to reduce the buildup of biofilm

-Replacing corroded parts

-Installing a high-efficiency drift eliminator

Safety precautions should always be taken when working in or around a cooling tower. Hard hats, goggles, face masks, gloves, and leather boots should be worn. Regular maintenance and inspection, in addition to proper operation, will not only control Legionella and other bacteria growth, but will promote a long and productive life for the industrial cooling tower.

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