Cooling Tower Maintenance
Legionella Awareness
4th Installment
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CTM/Ashland Presentations
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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 Protocol
2008

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 Refresher
2011
 Legionella
Sources
 Legionella
Control
 Planning
®
and Record Keeping
Legionella Sources
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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
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
Biofilms, organics

Sediments, deposits
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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Systems Promoting Growth

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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
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Field 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 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)
Flowing Bulk Water
Basin Chip Scale
Basin Sludge
Dead Head (off)
Plate/Frame XER
Slip Stream
By-pass (10%)
Plate/Frame
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Aerobic
Bacteria
Fungi
Anaerobic
Bacteria
Higher
Life Forms
<10
1600
<10
10
<10
1,000,000
No
Yes
3,500,000
20
1,000,000
Yes
400
<10
10,000
Yes
<10
<10
<10
No
Legionella Control
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Microbiological Control Capability

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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 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 Biocides
Chemical Compound
Glutaraldehyde
Isothiazolin
2 Bromo-2-Nitro Propane-1,3, diol
(BNPD)
Dithiocarbamates
Di-bromo-nitrilo-propionamide (DBNPA)
Active Concentration mg/ℓ
Contact Time
25 - 54
1 Hour
2.25 - 2.6
6 Hours
25
400
24 Hours
60 Minutes
40.0 - 60.0
6 Hours
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 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
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 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 Feedrate
Oxidant Feedrate
5
4.5
4
3.5
3
2.5
2
1.5
Ff 1
0.5
0
Fi
system biofilm demand
0.5 ppm oxidant residual
raw water demand
1
2
3
4
5
6
7
8 9
Time
Time to satisfy System Demand
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10 11 12 13 14 15
tBreakthrough
Legionella Testing
Requirements
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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
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Direct Testing of Legionella
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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
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Suggested 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.
Frequency of
Cleaning/Disinfection
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Frequency of
Cleaning/Disinfection

Immediately prior to new system being
commissioned

If the system has been out of use for one month or
longer
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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
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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 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
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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 Assessment

System survey
– In-depth survey of system mechanical layout and
operating conditions
– Utilizes established protocol, ex BSRIABuilding 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
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Documentation

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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Documentation

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 makeup 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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Documentation

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 Legionella
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Survey of Process Risk
HIGH
Humididifer/Fogger
Aerosol Producing Process
Misters, Atomizers
Air Washers
Decorative Fountains and
Waterfalls
Whirl Pools
Hot Tubs
Shower Heads
Sludge/Settled Solids
>⅛″ - ¼″
LOW
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
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
Monitoring and Inspection

Inspection for visible slime or sludge's
– Decks
– Mist eliminators
– Fill
– Sumps
– Corrosion or biofilm coupons
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Biofilms

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 Action

Use your Biocides in a Prudent Manner
And Remember

Sterility Does Not Exist Except in Higher
Life Forms
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