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Legionella Prevention

The problem of water circulations contaminated with Legionella is of great importance, because the increasing number of deaths caused by Legionaires’ Disease are focusing public interest on the Legionella issue. Instead of combating isolated symptoms, ProMinent offers integrated solutions for solving the Legionella problem at its source.

Legionaires’ Disease

Legionaires’ disease is a dangerous, potentially fatal form of pneumonia. Certain groups, such as old or sick people, are known to be at higher risk of contracting Legionaires’ disease. Men appear more susceptible than woman, as do those over 45 years of age, smokers, alcolholics and diabetics. Infection by Legionella is also responsible for a feverish form of illness known as Pontiac fever. We don’t know how many deaths are caused by Legionella infection because pneumonia is very often accepted without further inquest as a “natural” cause of death in older persons. For the USA 15.000 deaths/year are estimated!

The Cause

Main determined pathogen is the Legionella bacterium "Legionella pneumophila". Not only the best known sero-group 1, but all 40 sero-groups as well as other Legionella types are pathogenous. Legionella have optimal growth conditions between 30 and 37 °C, they stagnate between 40 and 45 °C and will die above 70 °C. Characteristic to Legionella is that they live and proliferate in other microorganism such as amoebae. Biofilm which is present in every water pipe and tank provides optimal living conditions for Legionella at appropriate temperatures.

Risk Areas

Legionella bacteria are common and can be found in every natural lake, in slop and in wet soil, without becoming dangerous for humans. Infection by Legionella will appear after inhalation of tiny droplets of water (aerosols) contaminated with Legionella. For that reason, the following risky areas can be specified:

  • showers in hotels, hospitals, nursing homes, swimming-pools and other sport facilities
  • spa baths and swimming pools with other sparkling water attractions
  • ventilation plants with wet gas scrubbers
  • cooling towers
  • areas, where water is sprayed for cooling and moistening purposes (e.g. coolants/lubricants in metal-cutting manufacturing, wetting of carbon powder with river water)

Effective Legionella prevention

The following measures and methodologies have proven effective and especially cost efficient for Legionella prevention and destruction.

Appropriate Design of Piping and Fittings

  • correct selection of material
  • correct hydraulics (high flow velocity, no „dead“ corners)
  • avoidance of risky areas
  • no parallel connection of boilers
  • no heat recovery via pre-heaters

Maintenance and Control

  • regular maintenance with checkup and cleaning of the boilers
  • regular inspection regarding Legionella infestation

Treatment with Chlorine Dioxide

  • high disinfectant effect independent of the pH value
  • decomposition of the biofilm in the piping system, thus protection against re-infection by Legionella
  • deposit action longer than with chlorine
  • less danger of corrosion than with chlorine

Treatment with Ozone

  • strong disinfectant, reliably removes biofilm
  • reacts without resulting residuals in oxygen
  • in water, short half life period, for that reason no deposit effect
  • good application in cooling towers and air scrubbers

Other Measures for the Legionella prevention

Beside these really effective and cost-efficient measures, there are some more measures used for Legionella prevention, which are however afflicted with more or less considerable disadvantages.

High Temperature Water (> 70 °C)

  • high energy consumption
  • danger of scalding at the taps
  • hardly practical with long pipelines
  • Boiler temperature of > 55 °C avoids proliferation of Legionella only in the boiler, not in the system


  • high radiation dose necessary in case of infestation with amoebae
  • no deposit effect
  • no protection against re-infection of biofilm by Legionella

UV-Radiation + Ultrasonic

  • Legionella are released when treating amoebae and pieces of biofilm with ultrasonic
  • no deposit effect
  • no protection against re-infection of biofilm by Legionella
  • high investment costs, large space required


  • no deposit effect
  • no decomposition of the biofilm, thus no protection against re-infection by Legionella

Chlorination (bleach, electrolyses)

  • no sufficient disinfectant effect without simultaneous adjustment of the pH value
  • no decomposition of the biofilm, thus no protection against re-infection by Legionella
  • chlorine odour due to oxidation byproducts such as chloramine is possible
Process Overview Legionella Prevention
Process Overview Legionelle Prevention

Chlorine dioxide and ozone are the most successful and economical disinfectants for controlling Legionella infestations in water systems, as they break biofilms down efficiently and prevent them re-forming.

ProMinent Processes for Legionella Prevention
Chlorine Dioxide for Legionella Prevention in Potable Water

Chlorine dioxide is the most reliable disinfectant for legionella prevention in potable water because it not only eliminates the pathogenic bacteria but also biofilm as a cause of disease.

Chlorine Dioxide for Cooling Water Disinfection

Very good depot action and strongly reduced AOX-values in the waste water: Just two out of many advantages.

Ozone for Cooling Water Disinfection

The strongest disinfectant in water treatment: Ozone shows excellent efficacy even at low concentrations, at any pH value - at very low operating costs.

Product Overview Legionella Prevention
Chlorine Dioxide Plants Bello Zon® CDKc

Capacity range: 170 to 7.500 g/h
This plant produces chlorine dioxide for large water quantities. The continuous water treatment is particularly economic thanks to the use of concentrated chemicals.

Chlorine Dioxide Plants Bello Zon® CDVc

Capacity range: 20 to 2.000 g/h
The ideal system for medium to large water quantities. The continuous treatment is safe and simple thanks to the use of diluted chemicals.

Chlorine Dioxide Plants Legio Zon®

Up to 5 g/h of chlorine dioxide, especially for the combat of legionella in smaller and mid-sized public buildings, such as hospitals, hotels or sports complexes.

Chlorine Dioxide Measurement

As an alternative to Chlorine compounds (drinking water treatment) or to peracetic acid (food and beverage industries) for the oxidation and disinfection of waters more and more often Chlorine dioxide is used. In this context, the measurement of this parameter gains equally of importance.

Bono Zon® Ozone Plant

Capacity range 80 – 720 g/h (larger plants on request)
A range of compact ozone plants with integrated gas conditioning application. Bono Zon® plants work using positive suction pressure and are therefore particularly reliable.

OZONFILT® OZVa Ozone Plant

Capacity range 5 to -90 g/h
Range of universal compact ozone plants. Air or oxygen is used as the operating gas.

Ozone Measurement

Ozone is the strongest oxidant used for water treatment to a great extent and has the strongest near-term disinfection efficiency.

Biofilms - breeding ground for legionella

Biofilms are slimy deposits of microorganisms and extracellular substances in piping systems and tanks. These deposits are the breeding ground for many pathogenic germs such as E. coli or legionella and also protect them from chemical and physical influences. Microorganisms that occur in biofilms are extremely resistant to disinfectants.

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