Since July 10, the citizens of New York City have been on alert following the discovery of an outbreak of Legionnaires' disease, a bacterial infection that spreads through water systems and can be deadly to smokers and the elderly. Already, ten people have died, 100 have tested positive for the disease, and officials think more people will be diagnosed before the outbreak is contained. For a detailed explanation of Legionnaires' disease, symptoms ands how it is spread, you can read VOX EXPLAINERS HERE.

Legionnaires Disease is a form of pneumonia caused by Legionella bacteria. The majority of the cases are caused by Legionella pneumophila. These bacteria thrive in water temperatures between 77 degrees F and 113 degrees F, which is why cooling towers are a prime source of Legionella. However, it can also be found in many other areas, such as evaporative coolers, nebulizers, humidifiers, whirlpool spas, water heating systems, showers, windshield washers, fountains, room-air humidifiers, ice-making machines, and misting systems typically found in grocery-store produce sections. There is even the possibility of hospital-acquired legionella from which the principal source of infection is the drinking-water distribution system. Mortality from Legionella can approach 30%, so its a horrible, killing disease. However, the purpose of this blog is not to tell you how to treat it, but rather, how to prevent it. That is the course of wisdom. It should be noted that if treatment were always easy, Legionella would have been eradicated by now. The fact of the matter is that Legionella is most deadly to older adults who may be immune compromised or who may have underlying medical conditions. The United States Environmental Protection Agency (USEPA) has published a white paper on treatment for Legionella which is very informative.

There are several control methods available for disinfection of water distribution systems. These include thermal (super heat and flush), hyperchlorination, copper-silver ionization, ultraviolet light sterilization, ozonation, and instantaneous steam heating systems. Because some methods have not always proven completely successful or have not provided permanent protection from recolonization, a combination of these methods may be the most effective way of managing water systems and preventing future outbreaks.

Thermal disinfection, hyperchlorination and copper-silver ionization as well as the use of other biocides are something that we recommend you do or if you are doing these things, we recommend you continue. We believe that it is imperative to maintain a residual in the water supply for continuous killing capability. However, Ozonation and Ultraviolet Disinfection are viable options in the treatment to prevent Legionella.

Ultraviolet light or UV, kills Legionella by disrupting cellular DNA synthesis. A UV light sterilization system can be positioned to disinfect the incoming water, or it can be installed at a specific place in the pipe system that services a designated area. No chemical by-products are produced, and the taste and odor of water from a water distribution system containing a UV sterilizer are not affected. The UV sterilization system requires maintenance in order to prevent scale from coating the UV lamps. The system does not provide residual protection, so continuous disinfection is very important.

Ozone, which is generally created using an ozone generator, can be used to kill L. pneumophila. Ozone instantaneously inactivates Legionella; however, it has a short half-life and decomposes quickly back to oxygen. A second form of disinfection may be required in the distribution system for residual protection. Also, ozonation is more expensive than hyperchlorination, and a large amount of space is required for the air preparation equipment or oxygen tanks and contacting tank.

Conclusion: There is no question that Ultraviolet Disinfection and/or Ozone should be part of any cooling tower treatment regimen it just shouldn't be the only method. There needs to some kind of residual disinfectant and/or biocide to prevent re-contamination downstream.

US Water Systems Ultraviolet Disinfection Systems