Legionella pneumophila in cooling towers and evaporative condensers. Instituto Superior Técnico, Industrial Safety and Health

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1 Legionella pneumophila in cooling towers and evaporative condensers MARIA JOÃO ALVES Instituto Superior Técnico, Industrial Safety and Health

2 Introduction Legionella is a public and an occupational health issue The World Health Organization (WHO) provides guidance on Legionella risk assessment and management in three principal documents: - Guidelines for Drinking-water Quality (WHO, 2004) - Guidelines for Safe Recreational Water Environments (WHO, 2006) - Guide to Ship Sanitation (WHO, 2007) In most European countries, risks from Legionella are covered by laws, decrees based on Directive 2000/54/EC INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 2

3 Legionella pneumophila Gram- negative; Coccobacillus; Multiple strategies to adapt to stressful environment conditions; Sources : Cooling towers and evaporative condensers Health care facilities Hotels and ships Natural spas, hot tubs and swimming pools Conditions: T < 20 C no proliferation T: C growth T > 60 C Can t survive Fig 1: Legionella pneumophila INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 3

4 Legionella in Portugal: Outbreak in 2014 Duration : 12 October - 4 December Source: cooling tower of a fertilizer company (ADP fertilizantes) Cases: 375 Deaths: 12 Fig 3: Outbreak of Legionella in 2014 in a factory in Vila Franca de Xira INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 4

5 Evaporative Cooling: Cooling Towers and Evaporative Condensers In the system water is stored or re-circulated; Water temperature between C; There are deposits that can support bacterial growth; Fig 4: Configuration of a typical cooling tower Production of water droplets; Right environmental conditions for Legionella growth and spread Develop a strategy to minimize the risks of Legionella proliferation Fig 5: Configuration of a typical evaporative condenser INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 5

6 How to minimize the risks of Legionella proliferation in cooling towers and evaporative condensers? Health Based Targets Public health context and health outcome System Assessment Water Safety Plans Monitoring Management and Communication Surveillance Fig 6: Legionella pneumophila INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 6

7 2. Water Safety Plans System Assessment Water Safety Plans Monitoring Management and Communication Comprehensive risk assessment and risk management approach that encompasses all steps in water supply. Benefits: Systematic and detailed assessment and prioritization of hazards; The operational monitoring of barriers and control measures; INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 7

8 2.1 System Assessment Develop and implement effective strategies for controlling hazards Assemble the team System Assessment Document and describe the system Assess hazards and prioritize risks Assess the system Fig 7: Example of a deadleg in piping Example: Process Step Water Source Heat Exchanger Distribution Cooling Tower Assess hazards and prioritize risks High level of nutrients and microbial load High temperature and level of nutrients in biofilm Stagnant water in dead legs in the pipework Excessive drift loss from the tower exhaust INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 8

9 2.2 Monitoring Identification and monitoring of control measures used to ensure water safety Indentify control measures Monitoring Monitor control measures Validate effectiveness of WSP Fig 8: Total colony count of Legionella INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 9

10 Control measures for Legionella Control Legionella and other microbial activity, corrosion, scale formation and fouling, and include appropriate measures, such as regular physical cleaning and disinfection, to maintain the system s cleanliness. Temperature Control Microbial Control Corrosion Control Scale Control Fouling Control Pre treatment Measures T at the upper or lower limits of the Legionella multiplication range Biocides : oxidizing (chlorine ; bromine) and non oxidizing Corrosion inhibitors Scale inhibitors Dispersant chemicals ; filtration Filtration; Clarification; Biocides; Reverse osmosis; Water softening Drift Control Use drift eliminators Fig 9: Example of a drift eliminator INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 10

11 2.3 Management and Communication To document the system assessment and monitoring, and describe actions to be taken during normal operation and after incidents, including documentation and communication. Develop supporting programmes Management and Communication Prepare management procedures Establish documentation and communication procedures Fig 10: Cooling Towers INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 11

12 Conclusions Well design process and strict control measures are very effective controlling Legionella in cooling towers and evaporative condensers; Nowadays some outbreaks result from lack of maintenance ; The development of new techniques and the discovery of new information will reduce the probability of outbreaks occur; INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 12

13 References Mekkour, M. Tai, J et al. (2013) Legionella pneumophila: An Environmental Organism and Accidental Pathogen. International Journal of Science and Technology Volume 2 No. 2. Bartram, J. Chartier, Y et al. (2017) Legionella and the prevention of legionellosis. World Health Organization. 1-27, 29-38, 39-56, Sas, K. (2011) Legionella and Legionnaires disease: a policy overview. European Agency for Safety and Health at Work - EU-OSHA. Legionnaires disease: Technical guidance. Health and Safety Executive. INSTITUTO SUPERIOR TÉCNICO, INDUSTRIAL SAFETY AND HEALTH 13