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Cooling Tower Maintenance Legionella Awareness - PowerPoint PPT Presentation

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Cooling Tower Maintenance Legionella Awareness. 4 th Installment. CTM/Ashland Presentations. Legionella Awareness – 2003 Filtration of Cooling Waters – 2005 Legionella Risk Management – 2006 Legionella Proactive Protocol – 2008 Legionella Refresher -- 2011 Literature References.

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Ctm ashland presentations
CTM/Ashland Presentations

  • Legionella Awareness – 2003

  • Filtration of Cooling Waters – 2005

  • Legionella Risk Management – 2006

  • Legionella Proactive Protocol – 2008

  • Legionella Refresher -- 2011

  • Literature References

Legionella proactive protocol 2008
Legionella Proactive Protocol2008

  • Introduction/Refresher

  • Systems that may Harbor Legionella and What to Do

  • Risk Category

  • Legionella Testing Requirements

  • Frequency of Cleaning/Disinfection

  • Action Levels and Associated Response and Cleaning Steps

  • Cooling Tower Design Best Practice

  • Maintenance Considerations

Legionella refresher 2011
Legionella Refresher2011

  • Legionella Sources

  • Legionella Control

  • Planning and Record Keeping

Legionella bacteria

  • Source of Legionella

    • Pervasive organism

    • Soil derived

  • Conditions for growth

    • 68 - 122 F (20 - 50 C)

    • pH 6-8

    • Stagnant waters

    • A nutrient source

      • Biofilms, organics

      • Sediments, deposits

Legionella Bacteria

Factors determining the risk of contracting the disease
Factors Determining the Risk of Contracting the Disease

  • A source of Legionella

  • Favorable growth conditions

  • Aqueous aerosols less than or equal to 5 microns

  • Sufficient organisms to causeinfection

  • Susceptible individual

Systems Promoting Growth

  • Cooling towers

  • Evaporative condensers

  • Hot and cold water systems

  • Taps and showerheads

  • Humidifiers and air washers

  • Spa and whirlpool baths

  • Decorative fountains

Cyclic operation and biofilms
Cyclic Operation and Biofilms

  • AOC supports bofilm growth

  • Flow and AOC supply stopped results in biofilm starvation and detachment

  • - 90% in 24 hours

  • - 80% in 12 hours

  • - 60% in 10 hours

  • - 40% in 8 hours

  • Continuous flow without AOC achieves 90% biofilm detachment in 3 days

Effects of Cooling System Dynamics – cfu/ml Same Day Comparative Samples(Example System Treated with Continuous Oxidant and Slug Feed of Glutaraldehyde Once Per Week)

Microbiological control capability
Microbiological Control Capability

  • Efficacious biocides selection

  • Biodispersant supplement for biofilm

  • Effective application for required concentration and contact time

    • System dynamics (ART, T½) and volume

    • Dedicated automated feed of microbiocides

    • Feedback control Loop (ORP, self verifying feed pumps)

  • Pre-conditioning/sterilization

    • Preseason start-up

    • Idle restarts

    • Sterilization/hyper chlorination at the summer peak

    • End of season shutdown

Microbiological control additives of choice
Microbiological Control Additives of Choice

  • Oxidation

    • Bleach (CSW 20)

    • Sodium Bromide/Bleach (Drewbrom)

    • BCDMH (Biosperse 261T)

    • Chlorine Dioxide

  • Non Oxidants

    • Glutaraldehyde 1º (Biosperse 254/255)

    • Isothiazolin 2º (Biosperse 250)

  • Biodispersants

    • Nonionic Surfactants (Drewsperse 739)

    • Protein cross linking/cationic surfactant blend (Performax 405)

    • Anionic surfactants(Drewsperse 7211)

Continuous Oxidant Feed Protocol

  • Continuous feed for chlorine, bromine, BCDMH or stabilized bromine

    • Dosage:

      • Recommended 0.2 - 0.4 FAH and/or equivalent mV ORP with a minimum requirement of a measurable residual FAH

      • For higher risk systems increase FAH residual as needed to control CFU level and biofilm

  • Feed a supplemental organic biocide*

    • Recommend biocide be glutaraldehyde or an alternate biocide fed with biodispersant

    • Feed once per week or as needed to control biofilm

*Alternative choices of non-oxidizing biocide should be based on Relative Population Density (RPD) lab results

Intermittent oxidant feed protocol
Intermittent Oxidant Feed Protocol

  • Intermittent Oxidant Feed

    • Chlorine, bromine, BCDMH or stabilized bromine

    • Minimum dosage: Hold 0.5 - 1.0 FAH and/or equivalent mV ORP for a minimum of 2 hours each day

  • Feed alternating supplemental organic biocides*

    • Recommend one biocide be glutaraldehyde or an alternate biocide fed with biodispersant

    • Feed an additional compatible organic biocide*

    • Alternate feed once per week

*Alternative choices of non-oxidizing biocide should be based on RPD results

Action levels
Action Levels

  • Immediate response to positive test results

  • On-line treatment requires a minimum of 14 days to produce results

  • Unrealistic a system could be totally Legionella free

Direct testing of legionella
Direct Testing of Legionella

  • Frequency Consideration

    • Prior to peak summer sterilization (i.e. beginning/mid August) for seasonally operated HVAC or after a sterilization.

    • After cleaning of a confirmed cooling tower sourced outbreak

    • If a confirmed outbreak has occurred in the area (≤3 km minimum)

    • Three times per year of 24/7 Industrial process cooling systems of higher risk noted earlier

Frequency of cleaning disinfection1
Frequency of Cleaning/Disinfection

  • Immediately prior to new system being commissioned

  • If the system has been out of use for one month or longer

  • If the system has been modified, entered or disturbed in such a way to lead to contamination

  • If the cleanliness of the system is in any doubt

  • If microbiological monitoring indicates there is a problem

  • At least twice a year

Frequency of cleaning disinfection2
Frequency of Cleaning/Disinfection

  • Preconditioning/Disinfection

    • End of Operating Season

    • 2 per Year Minimum for 24/7 Systems (4)

  • Disinfection Only

    • At Peak Seasonal Demand

    • Occurrence of Outbreaks in the Area

    • Upon System Restarts of ≤ 4 weeks Idleness (≥ 3 Days?)’

  • Idle System of 1 Month or More to be Drained

Sterilization only
Sterilization Only

  • Frequency

    • During restart of idle/stagnant towers, condensers, heat exchangers

    • Seasonal restart of HVAC system, which was preconditioned and sterilized the end of the previous season

    • Peak of summer cooling demand

      (i.e. beginning of August).

    • Known outbreaks in the area

    • Biological dip slide counts exceed 105 – 106 CFU/ml. Visible slime (i.e. biofilm) present.

Total system approach five areas of activity and performance
Total System Approach:Five Areas of Activity and Performance

Comprehensivesystem assessment

 Intensive microbiological treatment program

 Sterilization and cleaning

 Monitoring and control

  • Documentation

  • All Information is Available in Previous Presentations 03, 06, 08

System Assessment

  • System survey

    • In-depth survey of system mechanical layout and operating conditions

    • Utilizes established protocol, ex BSRIA-Building Services Research Institute Assoc. (UK)

  • Identify, evaluate and rank specific factors associated with potential for microbiological growth and Legionella

    • Mechanical and chemical

  • Determine risk minimization action plans


  • Why Document?

    • When a pneumonia outbreak occurs in a facility it allows for:

      • Speed in identifying the source for eradication purposes, removing a potential and continual threat. After all it may not be cooling system derived.

      • Clinical micro biologists and physicians to select appropriate antibiotics, dosages and monitor the progress without the presence of further stressors.


  • To name a few:

    • Simplified line drawing of the cooling system and all equipment, dead legs cross over lines, chemical feed points/lines/control, system volume, recirculation make-up and blowdown rates

    • Key water test results/date

      • Chlorides or conductivity for cycles of concentration assessment

      • Make-up, blowdown water meter readings

      • FAH and/or ORP for Halogen concentration

      • Biological Tests – CFU/ml; CFU/cm2

      • Start, end and expiry dates of dip slide lots for bio testing


  • To name a few:

    • Chemical pump and timer settings

    • Biocide usage

    • Start-up/shutdown and other application logs of preconditioning/sterilization and sterilization only

    • Inspection/observations for slimes, muds, algae in cooling tower and on coupons and what was done to improve

    • Contingency plans procedures, and results/check offs when performed.

Monitoring and inspection

Inspection for visible slime or sludge's


Mist eliminators



Corrosion or biofilm coupons

Monitoring and Inspection


  • Biofilms Don’t Just Harbour Legionella, They:

    • Restrict Air Flow

    • Restrict Water Flow

    • Reduce Heat Transfer

    • Reduce Heat Rejection

    • Induce Localized Corrosion

  • Biological Control

    • Higher Life Forms – None

    • Bacteria CFU/ml <104, > 105 Do something

    • Bacteria CFU/cm2 <105, >106 Do something

Preventive action
Preventive Action

  • Use your Biocides in a Prudent Manner

    And Remember

  • Sterility Does Not Exist Except in Higher Life Forms