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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 4th 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
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 Refresher2011 • Legionella Sources • Legionella Control • Planning and Record Keeping
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 • 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 • 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 • 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 • 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 • 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 • 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 • 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/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/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 • 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 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
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.
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
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.
Inspection for visible slime or sludge's Decks Mist eliminators Fill Sumps Corrosion or biofilm coupons Monitoring and Inspection
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
Preventive Action • Use your Biocides in a Prudent Manner And Remember • Sterility Does Not Exist Except in Higher Life Forms