First edition of Guide for Legionella Prevention in biological wastewater treatment plants is made public

Over 2016-2018 several people became ill in the Netherlands after being exposed to Legionella pneumophila bacteria originating in industrial biological water treatment. The bacteria are spread into the environment via aerosols that form during the aeration of the process water. The inhalation of these aerosols caused a number of people to become ill with legionella pneumonia (legionellosis). It has since been shown that L. pneumophila can multiply very rapidly to extremely high levels, particularly in biological water treatment in which nutrient-rich process water is treated at relatively high temperatures (30-38 °C). This is also the case in the warm side streams of sewage treatment plants with sludge digestion. For this reason, the provinces and municipalities began in 2019 to call on companies to analyse the risks presented by their in-house treatment processes. The competent authorities and the market require a guide with information and an assessment framework with which to evaluate the environmental health hazards presented by Legionella originating from such wastewater treatment.

Plant assessment

On a commission from the Ministry of Infrastructure and Water Management, KWR and Royal HaskoningDHV have produced a first edition of the Guide for Legionella Prevention in biological wastewater treatment plants. The guide can – despite all of the remaining uncertainties – assist water treatment operators assess their plant, and support public authorities in their licensing and regulation of these installations. This guide can also be used in the building design and execution of new installations, with a view to minimising the possible presence and spread of Legionella. The guide is directly connected to a Kennisdocument van Hydroscope (Hydroscope Expert Document), which describes many technical and legal aspects of Legionella prevention in WWTPs.

Knowledge gaps

WWTPs were for a long time not recognised as a contamination source for the Guide for Legionella Prevention in wastewater treatment. There is consequently a significant lack of knowledge, for instance, about the growth of Legionella bacteria in these systems, the extent of aerosol formation in WWTPs, but also about the effectiveness of measures. These knowledge gaps are clearly highlighted and described in the guide’s text, and are also summarized in the appendix as a Knowledge Agenda. The guide should therefore be seen as a living document. In other words, the intention is that the guide be periodically updated, for instance, to reflect modifications to the prevailing regulations, new scientific insights and developments in the operational field. At the same time, as a second step, its elements will be incorporated into national regulations as soon as possible. This involves the inclusion of general regulations concerning Legionella prevention in the Environmental Management Activities Decree and in the Environmental Activities Decree, within the context of the implementation of the Environment and Planning Act of the Netherlands.