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Cooling Tower Maintenance Legionella Awareness

Cooling Tower Maintenance Legionella Awareness

4th Installment

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CTM/Ashland PresentationsCTM/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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Legionella Proactive Protocol2008

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

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Legionella Refresher2011

Legionella Refresher2011

Legionella Sources

Legionella Control

Planning and Record Keeping

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Legionella SourcesLegionella Sources

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Legionella BacteriaLegionella 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

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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 cause

infection

Susceptible individual

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Cooling towers Evaporative condensers Hot and cold water systems Taps and showerheads Humidifiers and air washers Spa and whirlpool baths Decorative fountains

Systems Promoting GrowthSystems Promoting Growth

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Field Study on Biofilm GrowthField Study on Biofilm Growth

Phase Time

Colonization 15 Minutes

Growth Detection 2 Days

Biofilm Formation

(Exopolymer/ Minimum Biofouling)

5 Days

Maximum Biofilm Growth

(8 – 10 Cells Thick)

14 Days

Fully Mature Biofilm Matrix 31 – 40 Days

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Cyclic Operation and BiofilmsCyclic 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

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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)

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)

Aerobic Bacteria Fungi

Anaerobic Bacteria

Higher

Life Forms

Flowing Bulk Water Basin Chip Scale

<10

1600

<10

10

<10

1,000,000

No

Yes

Basin Sludge 3,500,000 20 1,000,000 Yes

Dead Head (off) Plate/Frame XER

400 <10 10,000 Yes

Slip Stream By-pass (10%) Plate/Frame

<10 <10 <10 No

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Legionella ControlLegionella Control

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Microbiological Control CapabilityMicrobiological 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

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Microbiological Control Additives of ChoiceMicrobiological 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)

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Legionella Control with Non-Oxidizing BiocidesLegionella Control with Non-Oxidizing Biocides

Chemical Compound Active Concentration mg/ℓ Contact Time

Glutaraldehyde 25 - 54 1 Hour

Isothiazolin 2.25 - 2.6 6 Hours

2 Bromo-2-Nitro Propane-1,3, diol (BNPD)

25400

24 Hours60 Minutes

Dithiocarbamates 40.0 - 60.0 6 Hours

Di-bromo-nitrilo-propionamide (DBNPA) 4 - 8 2 Hours

Note: System potential contaminants and operational pH must be checked for compatibility with the non-oxidizing biocide

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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

Continuous Oxidant Feed Protocol

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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

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Oxidant FeedrateOxidant Feedrate

00.5

11.5

22.5

33.5

44.5

5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Time to satisfy System Demand

Ff

tBreakthrough

system biofilm demand

Oxidant Feedrate

Time

raw water demand0.5 ppm oxidant residual

Fi

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Legionella Testing Requirements

Legionella Testing Requirements

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Action LevelsAction 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

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Direct Testing of LegionellaDirect 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 CriteriaSuggested Legionella Remedial Action Criteria

Legionalla

(CFU/ml)

Cooling/Tower

Evaporative Condenser

Potable Water Humidifier/Fogger

Detectable;<1 1 2 3

1-9 2 3 4

10-99 3 4 5

100-999 4 5 5

>1000 5 5 5

Actions –

1. Review Maintenance

2. Follow-up Analysis and Implement Action 1

3. Implement Action 2, Conduct review of Direct and Indirect Bio aerosol Contact of Occupants and Health Risk Status of Occupants May Lead to Increased Biocide Applications or Online Clean

4. Implement Action 3, Cleaning/Biocide Improvement is Indicated

5. Immediate Biocide Improvement and Cleaning is Indicated Levels have a Potential for Outbreak

© 1998, PathCon Laboratories, Pathogen Control Associates Inc.

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Frequency of Cleaning/Disinfection

Frequency of Cleaning/Disinfection

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Frequency of Cleaning/Disinfection

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

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Frequency of Cleaning/Disinfection

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

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Sterilization OnlySterilization 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.

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Planning and Record Keeping

Planning and Record Keeping

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Total System Approach:Five Areas of Activity and Performance

Total System Approach:Five Areas of Activity and Performance

Comprehensive system assessment

Intensive microbiological treatment program

Sterilization and cleaning

Monitoring and control Documentation All Information is Available in

Previous Presentations 03, 06, 08

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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

System Assessment System Assessment

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DocumentationDocumentation

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.

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DocumentationDocumentation

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

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DocumentationDocumentation

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.

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Influence Risk Associated With LegionellaInfluence Risk Associated With Legionella

Survey of Process RiskSurvey of Process Risk

HIGH LOW

Humididifer/Fogger

Aerosol Producing Process

Misters, Atomizers

Air Washers

Decorative Fountains and Waterfalls

Whirl Pools

Hot Tubs

Shower Heads

Potable Water Hot/cold

Shower Heads

Cooling Towers/ Evaporative Condensers Risk increases with Location (i.e. Grounds Levels, Near Air Intakes/Windows), Local Ground Cover, Air Contamination/ Proximity to Exhaust See C.T.I. Design and Maintenance Consideration

Sludge/Settled Solids

>⅛″ - ¼″

Non-Visible

Temperature

35ºC (95ºF)

To 46ºC (115ºF)

<20ºC (68ºF)

>50ºC (124ºF)

Biological Activity

>104 CFU/ml

>105 CFU/cm2

Presence of Higher life forms (OMEBA, PROTOZOA, ALGAE, MOLD, FUNGUS).

≤103 CFU/ml

≤104 CFU/cm2

No Higher Life Forms

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Monitoring and InspectionMonitoring and Inspection

Inspection for visible slime or sludge's

– Decks

– Mist eliminators

– Fill

– Sumps

– Corrosion or biofilm coupons

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BiofilmsBiofilms

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

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Preventive ActionPreventive Action

Use your Biocides in a Prudent Manner

And Remember

Sterility Does Not Exist Except in Higher Life Forms