cooling tower maintenance legionella awareness
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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. - PowerPoint PPT PresentationTRANSCRIPT
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Cooling Tower Maintenance Legionella Awareness
4th Installment
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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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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 Sources
Legionella Control
Planning and Record Keeping
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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
Biofilms, organics Sediments, deposits
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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 Growth
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Field Study on Biofilm GrowthPhase 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)
Aerobic Bacteria Fungi
Anaerobic Bacteria
Higher Life Forms
Flowing Bulk Water Basin Chip Scale
<101600
<1010
<101,000,000
NoYes
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 Control
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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
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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 Active Concentration mg/ℓ Contact TimeGlutaraldehyde 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 HoursDi-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 – 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
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
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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 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 CriteriaLegionalla(CFU/ml)
Cooling/TowerEvaporative 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 Maintenance2. Follow-up Analysis and Implement Action 13. 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 Indicated5. 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
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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 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
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 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
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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 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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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
Survey of Process RiskHIGH LOW
Humididifer/Fogger Aerosol Producing ProcessMisters, AtomizersAir WashersDecorative Fountains and WaterfallsWhirl 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 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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