Detection of Legionella pneumophila and Pseudomonas aeruginosa and biofilm experiments in four different cooling towers (construction and biocide treatment) and evaluation of IDEXX most probable number methods in industrial water samples
Detection of Legionella pneumophila and Pseudomonas aeruginosa and biofilm experiments in four different cooling towers (construction and biocide treatment) and evaluation of IDEXX most probable number methods in industrial water samples
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DissertationDate of Exam
27.09.2021Date of Publication
30.11.2021Advisor
Exner, MartinCo-Referee
Deppenmeier, UweMetadata
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Abstract
The responsible maintenance of evaporative cooling systems is an essential element in reducing the risk of the environmental dispersion of legionellae and Legionnaires’ disease outbreaks. In Germany, the 42nd Ordinance Implementing the Federal Immission Control Act (42nd BImSchV) rules in accordance with the German Cooling Tower Code of Practice VDI 2047-2 the cooling tower water monitoring of Legionella spp., heterotrophic plate counts (HPC) and P. aeruginosa by ISO methods. The studies in this thesis aimed to improve microbial cooling tower monitoring and surveillance.
For enhanced surveillance of evaporative cooling systems, reliable prediction tools for microbial concentrations in the cooling system would be very advantageous. A prediction tool was designed using correlation analyses of retrospective microbiological and the process parameter data water temperature or redox potential. The tool requires a cooling tower specific testing for its suitability to promote the early initiation of measures. Thus, an increase in biofilm might be preventable at an early stage. Another simple risk factor calculation tool has been created indicating the microbial status of the cooling system. The risk factor calculation is based on Legionella concentrations or combined Legionella concentrations and HPC of previous sample results. Depending on the level of the cooling tower-specific risk factor, graduated measures to irregularities in the operation mode can be implemented cooling tower specific.
The ISO methods for the detection of microorganisms in cooling water samples apply agar plates and their evaluation is often complicated by the high amount of accompanying microorganisms. Alternative methods for a cooling tower monitoring are provided by the IDEXX most probable number methods Legiolert™/Quanti-Tray® for the detection of L. pneumophila and Pseudalert™/Quanti-Tray® for the detection of P. aeruginosa. Comparative testing of ISO and IDEXX methods in numerous industrial samples demonstrated that the IDEXX methods are easier in handling and reading results and offer a very good suitability for the detection of these parameters in cooling tower water samples.
The detection of HPC by the ISO method is carried out at two incubation temperatures. Due to the high amounts of microorganisms in cooling water, counting the colony forming units is laborious and the production of dilution series is time and material consuming. Therefore, the HPC results of 2,868 industrial samples from the Laboratory for Technical Hygiene were ana-lysed to determine the feasibility of incubation at only one temperature. The analysis showed that the use of one temperature is in principle sufficient to trace biofilm formation in the cooling system without loss of information.
To evaluate the influence of the construction material and biocide on the biofilm formation microbial growth on stainless steel and polyethylene plates and planktonic microorganisms were analysed in four closely located cooling towers sourced by the same make-up water during a ten-month observation period. Results of this study showed that the cooling towers differed in their microbial composition. Statistically significant differences in biofilm formation on the materials of the different plates were not verified. This indicates that the biocide and not the construction material seems to have the major impact on the biofilm formation. The lowest sessile and planktonic microbial concentrations were observed in cooling towers treated with chlorine dioxide and ozone. In accordance with the literature, the initial microbial community persisted over a long period as long as the biocide was able to limit biofilm growth. Increased visually assessed biofilm thickness on the long-term plates was associated with significantly different short- and long-term concentrations of sessile microorganisms.
Seasonal dynamics of Legionella and HPC in the four cooling towers were analysed by using retrospective data. Each cooling tower showed specific dynamics, but always Legionella tended to be highest in late summer/autumn and HPC in midsummer. Within four weeks, heterotrophic microorganisms cultivable under ISO conditions reached concentrations up to 108 cfu/cm2. Planktonic Legionella increased to an objectionable level within six weeks under deactivated biocide treatment in a cooling tower of always low microbial concentrations. Based on both latter facts, the regular four-week inspection interval of the 42nd BImSchV is considered appropriate with regard to the protection of public health.
For enhanced surveillance of evaporative cooling systems, reliable prediction tools for microbial concentrations in the cooling system would be very advantageous. A prediction tool was designed using correlation analyses of retrospective microbiological and the process parameter data water temperature or redox potential. The tool requires a cooling tower specific testing for its suitability to promote the early initiation of measures. Thus, an increase in biofilm might be preventable at an early stage. Another simple risk factor calculation tool has been created indicating the microbial status of the cooling system. The risk factor calculation is based on Legionella concentrations or combined Legionella concentrations and HPC of previous sample results. Depending on the level of the cooling tower-specific risk factor, graduated measures to irregularities in the operation mode can be implemented cooling tower specific.
The ISO methods for the detection of microorganisms in cooling water samples apply agar plates and their evaluation is often complicated by the high amount of accompanying microorganisms. Alternative methods for a cooling tower monitoring are provided by the IDEXX most probable number methods Legiolert™/Quanti-Tray® for the detection of L. pneumophila and Pseudalert™/Quanti-Tray® for the detection of P. aeruginosa. Comparative testing of ISO and IDEXX methods in numerous industrial samples demonstrated that the IDEXX methods are easier in handling and reading results and offer a very good suitability for the detection of these parameters in cooling tower water samples.
The detection of HPC by the ISO method is carried out at two incubation temperatures. Due to the high amounts of microorganisms in cooling water, counting the colony forming units is laborious and the production of dilution series is time and material consuming. Therefore, the HPC results of 2,868 industrial samples from the Laboratory for Technical Hygiene were ana-lysed to determine the feasibility of incubation at only one temperature. The analysis showed that the use of one temperature is in principle sufficient to trace biofilm formation in the cooling system without loss of information.
To evaluate the influence of the construction material and biocide on the biofilm formation microbial growth on stainless steel and polyethylene plates and planktonic microorganisms were analysed in four closely located cooling towers sourced by the same make-up water during a ten-month observation period. Results of this study showed that the cooling towers differed in their microbial composition. Statistically significant differences in biofilm formation on the materials of the different plates were not verified. This indicates that the biocide and not the construction material seems to have the major impact on the biofilm formation. The lowest sessile and planktonic microbial concentrations were observed in cooling towers treated with chlorine dioxide and ozone. In accordance with the literature, the initial microbial community persisted over a long period as long as the biocide was able to limit biofilm growth. Increased visually assessed biofilm thickness on the long-term plates was associated with significantly different short- and long-term concentrations of sessile microorganisms.
Seasonal dynamics of Legionella and HPC in the four cooling towers were analysed by using retrospective data. Each cooling tower showed specific dynamics, but always Legionella tended to be highest in late summer/autumn and HPC in midsummer. Within four weeks, heterotrophic microorganisms cultivable under ISO conditions reached concentrations up to 108 cfu/cm2. Planktonic Legionella increased to an objectionable level within six weeks under deactivated biocide treatment in a cooling tower of always low microbial concentrations. Based on both latter facts, the regular four-week inspection interval of the 42nd BImSchV is considered appropriate with regard to the protection of public health.
Subjects
Legionella pneumophila, Kühltürme, Biofilm, 42. Bundesimmissionsschutzverordnung, Methodenvergleich, cooling towers, 42nd Ordinance Implementing the Federal Immission Control Act (42nd BImSchV), Methods comparison
Classification (DDC)
570 Biowissenschaften, BiologieSpies, Kirsten: Detection of Legionella pneumophila and Pseudomonas aeruginosa and biofilm experiments in four different cooling towers (construction and biocide treatment) and evaluation of IDEXX most probable number methods in industrial water samples. - Bonn, 2021. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-64682
Online-Ausgabe in bonndoc: https://nbn-resolving.org/urn:nbn:de:hbz:5-64682
@phdthesis{handle:20.500.11811/9433,
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-64682,
author = {{Kirsten Spies}},
title = {Detection of Legionella pneumophila and Pseudomonas aeruginosa and biofilm experiments in four different cooling towers (construction and biocide treatment) and evaluation of IDEXX most probable number methods in industrial water samples},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2021,
month = nov,
note = {The responsible maintenance of evaporative cooling systems is an essential element in reducing the risk of the environmental dispersion of legionellae and Legionnaires’ disease outbreaks. In Germany, the 42nd Ordinance Implementing the Federal Immission Control Act (42nd BImSchV) rules in accordance with the German Cooling Tower Code of Practice VDI 2047-2 the cooling tower water monitoring of Legionella spp., heterotrophic plate counts (HPC) and P. aeruginosa by ISO methods. The studies in this thesis aimed to improve microbial cooling tower monitoring and surveillance.
For enhanced surveillance of evaporative cooling systems, reliable prediction tools for microbial concentrations in the cooling system would be very advantageous. A prediction tool was designed using correlation analyses of retrospective microbiological and the process parameter data water temperature or redox potential. The tool requires a cooling tower specific testing for its suitability to promote the early initiation of measures. Thus, an increase in biofilm might be preventable at an early stage. Another simple risk factor calculation tool has been created indicating the microbial status of the cooling system. The risk factor calculation is based on Legionella concentrations or combined Legionella concentrations and HPC of previous sample results. Depending on the level of the cooling tower-specific risk factor, graduated measures to irregularities in the operation mode can be implemented cooling tower specific.
The ISO methods for the detection of microorganisms in cooling water samples apply agar plates and their evaluation is often complicated by the high amount of accompanying microorganisms. Alternative methods for a cooling tower monitoring are provided by the IDEXX most probable number methods Legiolert™/Quanti-Tray® for the detection of L. pneumophila and Pseudalert™/Quanti-Tray® for the detection of P. aeruginosa. Comparative testing of ISO and IDEXX methods in numerous industrial samples demonstrated that the IDEXX methods are easier in handling and reading results and offer a very good suitability for the detection of these parameters in cooling tower water samples.
The detection of HPC by the ISO method is carried out at two incubation temperatures. Due to the high amounts of microorganisms in cooling water, counting the colony forming units is laborious and the production of dilution series is time and material consuming. Therefore, the HPC results of 2,868 industrial samples from the Laboratory for Technical Hygiene were ana-lysed to determine the feasibility of incubation at only one temperature. The analysis showed that the use of one temperature is in principle sufficient to trace biofilm formation in the cooling system without loss of information.
To evaluate the influence of the construction material and biocide on the biofilm formation microbial growth on stainless steel and polyethylene plates and planktonic microorganisms were analysed in four closely located cooling towers sourced by the same make-up water during a ten-month observation period. Results of this study showed that the cooling towers differed in their microbial composition. Statistically significant differences in biofilm formation on the materials of the different plates were not verified. This indicates that the biocide and not the construction material seems to have the major impact on the biofilm formation. The lowest sessile and planktonic microbial concentrations were observed in cooling towers treated with chlorine dioxide and ozone. In accordance with the literature, the initial microbial community persisted over a long period as long as the biocide was able to limit biofilm growth. Increased visually assessed biofilm thickness on the long-term plates was associated with significantly different short- and long-term concentrations of sessile microorganisms.
Seasonal dynamics of Legionella and HPC in the four cooling towers were analysed by using retrospective data. Each cooling tower showed specific dynamics, but always Legionella tended to be highest in late summer/autumn and HPC in midsummer. Within four weeks, heterotrophic microorganisms cultivable under ISO conditions reached concentrations up to 108 cfu/cm2. Planktonic Legionella increased to an objectionable level within six weeks under deactivated biocide treatment in a cooling tower of always low microbial concentrations. Based on both latter facts, the regular four-week inspection interval of the 42nd BImSchV is considered appropriate with regard to the protection of public health.},
url = {https://hdl.handle.net/20.500.11811/9433}
}
urn: https://nbn-resolving.org/urn:nbn:de:hbz:5-64682,
author = {{Kirsten Spies}},
title = {Detection of Legionella pneumophila and Pseudomonas aeruginosa and biofilm experiments in four different cooling towers (construction and biocide treatment) and evaluation of IDEXX most probable number methods in industrial water samples},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2021,
month = nov,
note = {The responsible maintenance of evaporative cooling systems is an essential element in reducing the risk of the environmental dispersion of legionellae and Legionnaires’ disease outbreaks. In Germany, the 42nd Ordinance Implementing the Federal Immission Control Act (42nd BImSchV) rules in accordance with the German Cooling Tower Code of Practice VDI 2047-2 the cooling tower water monitoring of Legionella spp., heterotrophic plate counts (HPC) and P. aeruginosa by ISO methods. The studies in this thesis aimed to improve microbial cooling tower monitoring and surveillance.
For enhanced surveillance of evaporative cooling systems, reliable prediction tools for microbial concentrations in the cooling system would be very advantageous. A prediction tool was designed using correlation analyses of retrospective microbiological and the process parameter data water temperature or redox potential. The tool requires a cooling tower specific testing for its suitability to promote the early initiation of measures. Thus, an increase in biofilm might be preventable at an early stage. Another simple risk factor calculation tool has been created indicating the microbial status of the cooling system. The risk factor calculation is based on Legionella concentrations or combined Legionella concentrations and HPC of previous sample results. Depending on the level of the cooling tower-specific risk factor, graduated measures to irregularities in the operation mode can be implemented cooling tower specific.
The ISO methods for the detection of microorganisms in cooling water samples apply agar plates and their evaluation is often complicated by the high amount of accompanying microorganisms. Alternative methods for a cooling tower monitoring are provided by the IDEXX most probable number methods Legiolert™/Quanti-Tray® for the detection of L. pneumophila and Pseudalert™/Quanti-Tray® for the detection of P. aeruginosa. Comparative testing of ISO and IDEXX methods in numerous industrial samples demonstrated that the IDEXX methods are easier in handling and reading results and offer a very good suitability for the detection of these parameters in cooling tower water samples.
The detection of HPC by the ISO method is carried out at two incubation temperatures. Due to the high amounts of microorganisms in cooling water, counting the colony forming units is laborious and the production of dilution series is time and material consuming. Therefore, the HPC results of 2,868 industrial samples from the Laboratory for Technical Hygiene were ana-lysed to determine the feasibility of incubation at only one temperature. The analysis showed that the use of one temperature is in principle sufficient to trace biofilm formation in the cooling system without loss of information.
To evaluate the influence of the construction material and biocide on the biofilm formation microbial growth on stainless steel and polyethylene plates and planktonic microorganisms were analysed in four closely located cooling towers sourced by the same make-up water during a ten-month observation period. Results of this study showed that the cooling towers differed in their microbial composition. Statistically significant differences in biofilm formation on the materials of the different plates were not verified. This indicates that the biocide and not the construction material seems to have the major impact on the biofilm formation. The lowest sessile and planktonic microbial concentrations were observed in cooling towers treated with chlorine dioxide and ozone. In accordance with the literature, the initial microbial community persisted over a long period as long as the biocide was able to limit biofilm growth. Increased visually assessed biofilm thickness on the long-term plates was associated with significantly different short- and long-term concentrations of sessile microorganisms.
Seasonal dynamics of Legionella and HPC in the four cooling towers were analysed by using retrospective data. Each cooling tower showed specific dynamics, but always Legionella tended to be highest in late summer/autumn and HPC in midsummer. Within four weeks, heterotrophic microorganisms cultivable under ISO conditions reached concentrations up to 108 cfu/cm2. Planktonic Legionella increased to an objectionable level within six weeks under deactivated biocide treatment in a cooling tower of always low microbial concentrations. Based on both latter facts, the regular four-week inspection interval of the 42nd BImSchV is considered appropriate with regard to the protection of public health.},
url = {https://hdl.handle.net/20.500.11811/9433}
}
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