Cooling Tower Legionella & Microbiology Testing

Are Legionnaires’ Disease Bacteria Lurking in Your Cooling Tower? 

Cooling Tower Legionella & Microbiological TestsAlthough cooling towers range in application and size from building size towers that are used in nuclear power and other industrial applications, the vast majority of cooling towers are much smaller, primarily installed on or near buildings to discharge heat from air conditioning. These Heating Ventilation and Air Conditioning (HVAC) cooling towers mainly use the evaporation of water to remove process heat, and to cool the working fluid near the wet-bulb air temperature using radiators. Cooling towers are also often mistaken to emit smoke or harmful fumes by the general public, when in reality the emissions from those towers do not contribute carbon to the atmosphere and consist of water vapor and varying amounts and sizes of water droplets, referred to as cooling tower drift.

However, cooling tower drift is not without risk.    Amoeba and biofilms can provide an environment for Legionella bacteria to proliferate.  These Legionella bacteria can then be aerosolized as part of the discharged drift, where they can encounter susceptible individuals.   Prevention of Legionnaire’s disease outbreaks can be achieved through a well administered cooling water biocide treatment program.  Evaluation of the efficacy of this plan can be achieved through both verification of biocide administration, as well as, validation of Legionella control by testing with a CDC Elite Legionella laboratory like EST.


Cooling Tower Legionella Testing 

Dr. Richard Miller and the EST Team have been providing the water treatment industry with expert Legionella interpretations and recommendations since 1977.  These valuable tools have allowed our water treatment customers to not only provide safe environment for their customers, but also build their businesses by providing a superior service.  We have the experience and credentials to help you protect cooling towers everywhere from Legionella bacteria. 

Below is some information from The Centers for Disease Control and Prevention (CDC) regarding cooling towers.

Key Points

  • Scale, corrosion, sediment controls, and system cleaning are critical for cooling tower operations and Legionnaires’ disease prevention.
  • Legionella risks are similar for open and closed-circuit cooling tower systems.
  • Disinfectant residual should be monitored and adjusted by an automated system.

What does the CDC recommend for Legionella Control?

Safe operation and regular cooling tower maintenance protect building operators, staff, visitors, and the adjacent community from exposure to Legionella. The necessary frequency of these activities depends on the cooling load, the environmental conditions present in the area where the cooling tower is located, and the cooling tower’s design. Use a water management program to establish, track, and improve operation and maintenance activities.

What do I do in case of an outbreak?

  • Confirm the presence of Legionella before performing remediation.
  • Confirm elimination of Legionella after remediation activities.

Cleaning, disinfecting, and remediating cooling towers involve a hierarchy of protocols. Determine how the following response protocols fit into your water management program. The protocols are listed in order of increasing intensity from routine treatment to offline emergency disinfection. Consult ASHRAE Guideline 12-2020 for instructions for each response. These steps may require customization based on system components, operating conditions, or other factors.

Read the full article on the CDC website.

What can Dr. Legionella and the EST Team do to help?  

Cooling Tower Legionella & Other Microbiology Testing 

  • Analyses that measure Legionella control:

    • Legionella pneumophila serogroup 1– Primary Legionnaires disease pathogen should be None Detected or < 10 cfu/ml (colony forming units per milliliter). EST recommends QUARTERLY testing unless otherwise directed by your Water Management Program.
    • Legionella pneumophila serogroups 2-14 –Important Legionnaires disease pathogen should be < 100 cfu/ml. EST recommends QUARTERLY testing unless otherwise directed by your Water Management Program.
    • Legionella (other species)– Important Legionnaires disease pathogenshould be < 100 cfu/ml. EST recommends QUARTERLY testing unless otherwise directed by your Water Management Program.
  • Analyses that measure disinfection or performance parameters:

    • Heterotrophic Plate Count (HPC) – Aerobic Bacterial Count – provides a measure of the biocide disinfection adequacy in the cooling tower sperate from Legionella. Should be < 10,000 cfu/ml. EST recommends QUARTERLY sampling unless otherwise directed by your Water Management Program.
    • Microbial Induced Corrosion (MIC) – Aggressiveness Index – provides a measure of the disinfection adequacy in the cooling tower or closed loop based on categories of corrosion related bacteria. EST recommends BASELINE and QUARTERLY sampling unless otherwise directed by your Water Management Program.

Overall Cooling Tower System Safety – Interpretations and Recommendations 

Learn more about which testing method would be best for Legionella Control here:

Other Cooling Tower Testing 

Cooling water systems are typically the highest user of energy in facilities. Continuous use without fouling of these systems requires proper chemical treatment Cooling Water Treatment Program and preventive maintenance. The problems normally associated with cooling water systems are scale, corrosion, microbiological fouling, and suspended solids control.

Corrosion costs the United States nearly ~2.8 trillion dollars a year in both direct and indirect costs.  Corrosion can potentially have long-term and costly impacts on your cooling towers.  Efficiency loss and potential repair costs of damaged systems can be avoided by closely monitoring the microbial conditions of the systems in your facility.  Some of the major cost impacts of Microbial Induced Corrosion (MIC) are:

  • Equipment malfunction or failure
  • Increased capital costs to repair or replace failed equipment
  • Operational challenges from loss of services from failed equipment
  • Scale build-up in pipes and on mechanical parts
  • Increased operation cost due to loss of efficiency
  • Accelerated wear and reduced operational life of equipment

Cooling Tower Legionella Testing

Learn more about MIC and how EST can help at the link below:

Microbiological Influenced Corrosion (MIC) Testing

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