Can wet airscrubbers spread Legionella to the environment?

Kunnen natte lucht- en gaswassers aerosolen met legionellabacteriën verspreiden naar de omgeving?


Industrial plants and cattle farms use scrubber units to remove inorganic or organic substances, gasses or odours from air or gas. In theory, certain conditions of temperature and pH can favour the growth of Legionella in some types of wet air and gas scrubbers. If water droplets can leave the scrubber system, there is a possibility that Legionella will be able to spread to the environment. Further research is needed to determine if this can occur in practice. These facts were revealed by a literature survey and interviews performed by the Dutch National Institute for Public Health and the Environment (RIVM) in response to questions from municipal health services and environmental services on possible health risks to people living in the vicinity of wet air or gas scrubber units due to the spread of Legionella bacteria from such units. These scrubbers remove unwanted substances from air or gas by treating it with fine water spray. Certain chemicals or bacteria may be added to the water in some types of scrubbers (e.g. acidic, caustic and bioscrubbers), and the scrubber water is often collected and reused. Legionella can grow in water if it has a neutral pH and a temperature of between 20°C and 50°C, even for relatively short periods. Dust scrubbers, bioscrubbers and biofilters use water at a neutral pH, and the temperature may rise to within the 20-50°C range for example due to heating by nearby equipment or due to high ambient temperature. Legionella are unlikely to grow in acidic air scrubbers with a pH below 4 or caustic air scrubbers with a pH above 9. About 90 per cent of the roughly 1,500 air scrubber units used in Dutch cattle husbandry is of the acidic type, with a pH of 4 or less, which are unlikely to represent a health hazard. The remaining 10 per cent consists of mainly bioscrubbers, which use bacteria to remove undesirable substances. Growth of Legionella in scrubbers of this kind cannot be excluded if their water temperature rises to above 20°C. The bioscrubbers and dust scrubbers used in Dutch industry could also act as sources of Legionella. From the literature survey and interviews it was not possible to determine how many of these types of air scrubbers are used in the various branches of industry. This report serves as guidance for municipal health services and environmental services to answer questions about Legionella risks of air scrubbers.

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