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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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Cooling Tower Maintenance Legionella Awareness

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Cooling tower maintenance legionella awareness

Cooling Tower Maintenance Legionella Awareness

4th Installment

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 sources

Legionella Sources

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

Cooling tower maintenance legionella awareness

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

Field study on biofilm growth

Field Study on Biofilm Growth

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

Cooling tower maintenance legionella awareness

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)

Legionella control

Legionella Control

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)

Legionella control with non oxidizing biocides

Legionella Control with Non-Oxidizing Biocides

Cooling tower maintenance legionella awareness

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

Oxidant feedrate

Oxidant Feedrate

Legionella testing requirements

Legionella Testing Requirements

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

Suggested legionella remedial action criteria

Suggested Legionella Remedial Action Criteria

Frequency of cleaning disinfection

Frequency of Cleaning/Disinfection

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.

Planning and record keeping

Planning and Record Keeping

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

Cooling tower maintenance legionella awareness

 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.

Influence risk associated with legionella

Influence Risk Associated With Legionella

Survey of process risk

Survey of Process Risk

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

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