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UV Light Treatment for Legionella Removal

Since in 1976, this dangerous bacterium leapt to the headlines for the dramatic epidemic episode in the Philadelphia hotel, the history of Legionella has been studded with irrefutable scientific discoveries, but also with many false beliefs.

One of these concerns precisely the possibility of eliminating once and for all the bacterium from the water, its natural habitat of proliferation.

To believe that Legionella is a problem that can be eliminated is a mistaken belief which has as a consequence the underestimation by the directors and managers of hospital and community structures of the adequate measures and of the correct prevention and control protocol. Thus legionella bacteria pose a significant risk to public health, especially when present in water systems.

In this article we will try to clarify the topic of Legionella in water, illustrating which are the most effective methods to prevent and treat this problem, keeping you safe from any possible risk.

UV Light Treatment for Legionella Removal
UV Light Treatment for Legionella Removal



How To Remove Legionella From Water?

Various methods are employed to control and eliminate Legionella, and one such method is UV (ultraviolet) light treatment. UV light has proven to be effective in neutralizing Legionella bacteria, making it a valuable tool in Legionella removal strategies. In this article, we will explore the use of UV light treatment for the removal of Legionella and its advantages in ensuring water system safety.

Controlling and removing Legionella bacteria from water systems is crucial for public health. UV light treatment has emerged as a promising method for Legionella removal, providing an effective and environmentally friendly approach to water system disinfection.

Is it possible to eliminate Legionella from water?

Eliminating Legionella pneumophila from water is nearly impossible. Assuming that it is, is one of the most frequent mistakes in managing Legionella.

Legionella bacteria are naturally occurring microorganisms found in water environments. They thrive in warm water and can proliferate in human-made water systems, including cooling towers, hot tubs, and plumbing systems. Legionella can cause Legionnaires' disease, a severe respiratory illness.

Because it is a water bacterium, which lives naturally in natural and artificial aquatic environments such as, for example:

  • Spring waters and thermal waters;

  • Rivers, lakes, ponds and muds;

  • artificial reservoirs;

  • Water systems and pipes;

  • Hot and cold water tanks;

  • Evaporative or cooling towers;

  • Humidification systems.

If it is therefore not possible to eliminate it completely, it is equally possible to prevent its pathogenic proliferation by keeping the bacterial concentration low (or in any case under control) in what are considered its natural habitats.

What is a safe reference limit of Legionella in water?

We take indicatively 1000 CFU/L as a reference limit for legionella in water levels. With detected contaminations lower than this value, one can reasonably consider oneself in a low risk condition. Higher values, on the other hand, indicate important contaminations and therefore high risk conditions.

This is a very simplified concept and has only the purpose of understanding. In fact, we cannot only consider the microbiological limits of contamination to define a biological risk, much less use a universal one.

In fact, there are many variables that determine the risk of contracting Legionella, sometimes independent of the contamination present, such as:

  • The age and state of health of the exposed persons;

  • The critical points of the plants;

  • Plant malfunctions;

  • The sources of aerosols;

  • The temperature of the water;

  • The type of environment.

The bacterium that lurks in the water is responsible for the associated disease called Legionellosis, which is not transmitted directly and nor is Legionella contracted by drinking water from the tap. In fact, the spread and contagion occur by respiratory route, by inhalation, aspiration or micro-aspiration of nebulised infected water (aerosol).

Risks Associated with Legionella in Water Systems

When Legionella bacteria contaminate water systems, as well as other bacteria such as coliform bacteria, the risk of individuals inhaling the bacteria and developing Legionnaires' disease increases. This poses a significant threat to vulnerable populations, such as the elderly and individuals with compromised immune systems.


UV Light Treatment for Legionella Removal

UV light treatment is a powerful method used to eliminate Legionella bacteria in water systems. It involves exposing the water to UV light of specific wavelengths, which damages the DNA of the bacteria, rendering them unable to reproduce and causing their destruction.

How UV Light Treatment Works

UV light treatment utilizes ultraviolet radiation in the range of 200 to 280 nanometers (nm). This range is known as the germicidal UV-C range, as it possesses the ability to disrupt the DNA structure of microorganisms, including Legionella bacteria. When exposed to UV-C light, the bacteria's genetic material is damaged, preventing their reproduction and rendering them harmless.

UV Light Treatment for Legionella Removal Equipment Design
UV Light Treatment for Legionella Removal Equipment Design

Advantages of UV Light Treatment

UV light treatment offers several advantages for Legionella removal in water systems:

Effectiveness: UV light treatment is highly effective in neutralizing Legionella bacteria, reducing the risk of Legionnaires' disease outbreaks.

Chemical-free: UV light treatment does not involve the use of chemicals, making it an environmentally friendly disinfection method.

Residual-free: Unlike chemical disinfection methods, UV light treatment does not leave behind any harmful residuals in the water, ensuring its safety for various applications.

Non-disruptive: UV light treatment can be integrated into existing water systems without significant modifications or disruptions to their operation.

Continuous disinfection: UV light treatment provides continuous disinfection as water passes through the UV system, ensuring ongoing protection against Legionella bacteria.

UV Light Treatment for Legionella Removal Industrial Equipment
UV Light Treatment for Legionella Removal Industrial Equipment

Get in touch with our team for a free quote for UV light treatment equipment.

Factors Affecting UV Light Treatment Effectiveness

Several factors can influence the effectiveness of UV light treatment for Legionella removal:

UV light strength & capacity: The intensity and duration of UV exposure, often referred to as UV dose, are critical factors in achieving effective disinfection. Proper design and sizing of UV systems ensure adequate UV doses are delivered.

Water quality: The quality of the water being treated can impact UV light treatment effectiveness. High levels of turbidity, suspended solids, or certain organic compounds can reduce the UV transmittance and hinder the disinfection process.

System maintenance: Regular maintenance of UV systems, including lamp replacement and cleaning, is essential to ensure optimal performance and sustained effectiveness.

UV Light Treatment Implementation

Implementing UV light treatment for Legionella removal involves the following steps:

  1. System assessment: Conduct a comprehensive assessment of the water system to determine the appropriate UV system size and configuration.

  2. UV system installation: Install the UV system in the water system, considering factors such as flow rate, water quality, and system design.

  3. Validation and monitoring: Validate the effectiveness of the UV system through testing and monitoring. Regularly monitor UV intensity and perform microbial testing to ensure proper disinfection.

UV Light Treatment Considerations and Maintenance

To maximize the effectiveness of UV light treatment for Legionella removal, certain considerations and maintenance practices should be followed:

Proper system design: Ensure the UV system is correctly sized and configured for the water system's flow rate and intended application.

Regular monitoring: Monitor the UV system's performance by regularly measuring UV intensity and conducting microbial testing.

Lamp replacement: Replace UV lamps according to the manufacturer's recommendations to maintain optimal UV output.

System cleaning: Clean quartz sleeves and other components as needed to prevent fouling and ensure maximum UV transmittance.

You can purchase a UV water disinfection directly on our online store.

What Are The Ideal Conditions For Legionella To Thrive In Water? How UV Can Help Us To Remove It?

Legionella is a bacterium that proliferates above all in stagnant fresh water and, in general, in heated aquatic environments (with temperatures between 35° and 37°C) and where there is the presence of oxygen and nutrients.

The optimal conditions that favor the proliferation of Legionella bacterial colonies in the water up to infectious concentrations concern both the characteristics of the water and those of the system itself and are:

  • Water temperature between 20°C and 45°C;

  • Phenomena of water stagnation in tanks which favor sedimentation and biofilm formation;

  • Limescale and rust encrustations in pipes and water diffusion terminals;

  • Little used pipes or with little or no water flow;

  • Dead branches and/or conditions of obstruction in the water systems;

  • Poor maintenance, cleaning and disinfection of systems and dispensing terminals;

  • Age, degradation and complexity of the system;

  • Seasonal or discontinuous use of a plant or a part thereof;

The presence of algae and amoebas which provide nourishment to Legionella, as well as the formation of biofilm which also protects the bacterium from normal cleaning actions.

Potentially all living and working environments are considered at Legionella risk, since contamination occurs by breathing infected nebulized water produced by water distribution systems and heating systems.

Since the person-to-person transmission of the disease has never been scientifically proven, the only source of contagion is represented by the aerosol flows of contaminated water which, through the mucous membranes of the upper respiratory tract, reach the lungs causing the bacterial infection.



1. Is UV light treatment effective against other microorganisms besides Legionella?

Yes, UV light treatment is effective against a wide range of microorganisms, including bacteria, viruses, and protozoa. It provides comprehensive disinfection for various waterborne pathogens.

2. Does UV light treatment require any additional disinfectants?

UV light treatment does not require the addition of chemicals or disinfectants. However, in certain cases, complementary disinfection methods may be used alongside UV treatment for enhanced water system protection.

3. Can UV light treatment be retrofitted into existing water systems?

Yes, UV light treatment systems can be retrofitted into existing water systems without significant modifications. Proper consideration should be given to system design and installation to ensure optimal performance.

4. How long does UV light treatment take to eliminate Legionella?

The time required for UV light treatment to eliminate Legionella bacteria depends on factors such as water flow rate, UV system capacity, and the initial concentration of Legionella. Proper sizing and UV dose calculations ensure effective disinfection within a specific time frame.

5. Is UV light treatment safe for human exposure?

The UV-C light used in UV light treatment is harmful to microorganisms but can also cause harm to human skin and eyes. UV systems are designed with safety measures, such as protective shields and sensors, to prevent human exposure to UV light during operation.

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