Efficient Water Management Blog

Legionella Prevention with Secondary Control in Cooling Towers

Most people have read recent news reports of Legionella outbreaks across the country. The increase of news articles can also be attributed to the increased frequency of testing by building operators that are discovering high levels of legionella bacteria due to quarterly or established testing requirements.

Legionella is not a new strain of pathogen, and more than 58 Legionella species have been identified, fewer than 20 Legionella pneumophila strains are attributed to disease in humans. What most have in common are that they require a habitat to establish colonies. Water systems that have algae and biofilm tend to have the highest incidence of pathogens that include Legionella, since they provide protection and a food source.

Chemical programs for primary water treatment are the standard line of defense, though physical water conditioning should also be incorporated into a building operator’s Risk Management for Building Water Systems as a secondary control measure.

Biofilm Protects Bacteria Colonies

Biofilm forms on nearly all wet surfaces on earth such as rocks in streams and oceans, drains, cooling towers, ice machines, and is frequently discovered inside water lines. Biofilms are formed when bacteria adhere to a solid surface and enclose themselves in a sticky coating that functions as a protective layer that encloses a consortium of different bacteria. This layer of biofilm is highly protective for the organisms within it and is difficult to remove once established. Legionella requires this environment to multiply, since they normally depend on protozoa for nutrients.

HydroFLOW physical water conditioning causes biofilm to detach and helps to prevent new biofilm from colonizing in cooling towers

Once a biofilm attaches, a robust colony forms under its protection, and expands laterally over time. A part of the life cycle of a biofilm involves portions breaking loose and are carried by the water flow to where it attaches in a new location and establishes a new colony. Legionella colonies spread in this way, and while mobile their numbers increase in water sample testing results.

When water-borne legionella become transferred into the air by a cooling tower, fountain or humidifier, the water droplets are able to be inhaled, which makes them potentially harmful to humans.

Legionella Grows in Water and then Becomes Airborne

Legionella bacteria can remain viable in airborne water droplets for more than a half-mile, and when inhaled they pose a threat to people’s health if they become established in the lungs. Legionnaire’s disease is not passed from one person to another.

The U.S. CDC, Legionnaires’ disease requires treatment with antibiotics, and most cases of this illness can be treated successfully. Healthy people usually get better after being sick with Legionnaires’ disease, but they often need care in the hospital. About 1 in 10 people who get Legionnaires’ disease will die from the infection.

Legionella are controlled in cooling towers by HydroFLOW physical water conditioning, which causes biofilm to release from piping and equipment.

Preventing Biofilm Reduces the Risk of Legionella

Biofilm and algae are present in cooling towers, hot tubs, pools, hot water systems, and nearly every type of water system that exists. Chemical dosing is effective for water-borne bacteria control but requires high concentrations to oxidize and remove biofilm from piping material and equipment surfaces. Secondary control measures help to make biocides more effective.

The absence of biofilm eliminates a hospitable environment for pathogens like Legionella to colonize. Biofilm protects consortiums of bacteria and pathogens from chemical oxidizers that are depleted before eliminating entire colonies. When under attack the biofilm increases production to replace and strengthen the protective layer, and unless an area is scoured and oxidized to remove all biofilm, a colony will regrow, and pieces will be released to recolonize other areas. The smaller particles have potential to become airborne by the evaporation process of a cooling tower.

Chemicals remain the primary protection for water system operators, but chemical levels vary at different times, and they cannot reach “dead-leg” piping and areas of slow moving water. These areas are where biological activities are highest, and water systems most vulnerable. An effective means of secondary control for biofilm is physical water conditioning, which operates 24/7 and does not need replenishment.

HydroFLOW physical water conditioner controls biofilm and Legionella in Cooling TowersPhysical Water Conditioning is an Effective Secondary Biofilm Control

HydroFLOW physical water conditioning sends a frequency throughout a water system, using the water to carry the signal. The pulsed frequency disturbs biofilm causing it to detach and removed by filtration. The continuous pulsed frequency creates an inhospitable environment for biofilm and bacteria, which will not colonize.

Particles that are released will tend to seek hospitable zones to establish colonies, but the frequency extends throughout the water system so new colonies are prevented. The suspended particles become clustered and removed with side stream filtration.

HydroFLOW improves filtration with a pulsed signal that causes small particles to cluster and more readily removed by filtration, which improves water quality, heat transfer capability is increased, and less biological activity is sustained in the circulating water.

Secondary Prevention While Reducing Operating Costs

HydroFLOW also prevents scale accumulation by causing dissolved calcium to precipitate into suspended particles. Cooling systems without scale perform close to factory specification for heat exchange, which improves and sustains energy conservation.

Accumulated scale provides an anchor location for biofilm establishment, so HydroFLOW improves water system performance while reducing scale and biological activity.

HydroFLOW conserves water, energy and chemistry, while preventing biofilm and scale accumulation that serves as a reliable secondary Legionella control device. 

Learn More About Total Water Management HydroTech Solutions has developed the Total Water Management program for cooling systems that conserves 50% of water use (make-up and blowdown) and pays for itself through cost savings on cooling tower operations.

The HydroFLOW physical water conditioner is solid state and installs in less than 30 minutes on the outside of any type of pipe. No maintenance or troubleshooting, with IoT sensors and real-time data for monitoring performance and cost-savings on a mobile device or computer.

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