UV water purification systems are also used for sterilizing water in air-conditioning systems and preventing infection due to microorganisms in air humidifying systems. UV is used for control of Legionella with applications in hospitals, office buildings and large residential buildings.
Legionellosis, commonly referred to as Legionnaires' disease is a severe form of pneumonia caused by legionnella and can be lethal, particularly with the elderly and with people whose immune system is impaired. It is transmitted by inhaling the legionella existing in droplets of water. Legionella reproduce particularly well in the luke-warm water (30-45°C) of stale circulation pipes of hotels, public swimming pools, schools or residential buildings or in humidifiers of air-conditioners.
If these water reserves are not used or exchanged on a daily basis this strongly encourages reproduction of the bacteria. When water is extracted, e.g. during a shower, use of a humidifier, the legionella reach the human respiratory tract via inhaled aerosols. In the lungs the bacteria then reproduce in the monocytes.
However, acute disease only manifests if a larger number of pathogens is inhaled or if the host has an impaired immune system. There are no statutory limits for contamination with legionella, however, a load of 20 CFU/ml, i.e. 20 colony-forming units per milliliter is considered to be critical. From 100 CFU/ml, for example, public baths are closed down. With regard to the hygienically permitted dose, legionella are to a large extent also immune against chemical disinfectants, e.g. chlorine.
A warm water UV disinfection system is installed directly behind the boiler which continuously disinfects the water in the circulation pipes, thus providing guaranteed protection from re-infestation with pathogens.
UV reactors can be integrated in all water pipes and therefore represent effective protection against re-infestation of a system.
Air-conditioners which work with spray evaporators to humidify the air also represent an excellent breeding ground for legionella. For these systems as well, physical UV disinfection of the stored water offers safe protection from re-infestation even outside of operating times.
