700 likes | 725 Views
Cooling Tower Maintenance Legionella Awareness. 3 rd Installment. CTM/Ashland Presentations. Legionella Awareness – 2003 Filtration of Cooling Waters – 2005 Legionella Risk Management – 2006 Legionella Proactive Protocol – 2008 Literature References. Legionella Proactive Protocol.
E N D
Cooling Tower Maintenance Legionella Awareness 3rd Installment
CTM/Ashland Presentations • Legionella Awareness – 2003 • Filtration of Cooling Waters – 2005 • Legionella Risk Management – 2006 • Legionella Proactive Protocol – 2008 • Literature References
Legionella Proactive Protocol • Introduction/Refresher • ASHRAE - Systems that may Harbour 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 Proactive Protocol • Implement Risk Management Criteria • Maintenance and Record Keeping • Begin now as Legislation will be forth coming • Allows for a Basis of Estimation • Man • Methods • Materials • Estimates can be Reported to Management. While Focus has been Reduction of Costs they will need Estimates as the Cost of Ownership is Going Up.
Source of Legionella • Pervasive organism • 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 aerosol • Sufficient organisms to causeinfection • Susceptible individual
Total System Approach:Five Areas of Activity and Performance Comprehensivesystem assessment Intensive microbiological treatment program Sterilization and cleaning Monitoring and control Documentation
Preventive Actions • Inspect and Test • Domestic Waters • Fountains • Spas • Air Handling Units • Humidifying/Dehumidifying Equipment/Coils • Cooling Towers
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)
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
Inspection for visible slime or sludge's Decks Mist eliminators Fill Sumps Corrosion or biofilm coupons Monitoring and Inspection
Monitoring and Inspection • Testing • Bulk water dip slides • Prior to non-oxidizing biocide addition • Minimum once per week • Target ≤ 104 CFU/ml • Coupon surfaces - if available • Prior to non-oxidizer and/or biodispersant addition • Every 30 to 60 days, but be consistent • Target ≤105 CFU/cm2
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
Potable Water Supply (AWWA) • New Piping and Additions • High Velocity Flush (HVF) initially at 8-15 ft./sec. if possible • Continuous Flush at 2.5 ft/sec. • ≥ 10 ppm FAC for 24 Hours • ≥ 50 ppm FAC for 3 Hours • Slug and Hold at ≥ 100 ppm FAC for 3 Hours is an alternative
Potable Water Systems • Emergency Water Systems • Stagnant/Idle • Ideal Temperatures – Reach Room Temp • Eye Wash/Showers (Low to no Atomization) • Fire Systems • Periodically Flush
Potable Water Systems • Cold Water – Store at ≤ 20ºC (68ºF) • Hot Water - Store at 50 - 60ºC (124-148ºF) - Operate Return Water ≥ 50ºC (124ºF) • Eradication • Thermal - 66ºC to 70ºC (150ºF) for 8 hours and Flush outlets for 30 minutes • Chemical - ≥ 2 ppm (10 ppm) FAC for 2-24 hours at pH 7-8; Flush for 5 minutes • Copper/Silver Ionization, • 0.2 – 0.8 ppm Copper • 0.02 – 0.08 ppm Silver
SPAS • Hydrotherapy Pools, Whirl Pools, Hot Tubs • pH 7.2 - 7.8; 7.4 - 7.6 Ideal • FAC 3 - 10 ppm; 4 - 5 ppm Ideal • FABr 4 - 10 ppm; 4 - 6 ppm Ideal • Ultra Violet Plus Peroxide • Ozone • Maintenance Once per day for 1 to 4 hours at 10 ppm FAC or 10X FAC in use
Other Water Systems • Treat and Maintain Similar to Cooling Tower Protocols • Fountains and Waterfalls • Filtration • Drain Regularly • Misters/Atomizers, Humidifiers, Air Washers • Coils, Spray Bars, Sumps, Mist Eliminators • Pre/Post Air Filtration • Bleed/Drain • Clean/Disinfect • Sludge Removal • UV – Air Space
Dutch Risk Category • Highest Risk – Cooling Towers < 200 meters from Hospital, Nursing Home or Health Care Facility where Occupants maybe immunologically compromised • Cooling Tower < 200 meters of Retirement Home, Hotel or Building Accommodating a Large Number of People • Cooling Tower in Residential and Industrial Neighbourhoods • Lowest Risk – Cooling Tower in Industrial Area > 600 metres Away from a Residential Area.
Factors Contributing to Legionella Health Risks in Cooling Systems
Precleaning Determination DEPOSIT ANALYSIS COUPONS/SURFACES HIGHLY TUBERCULATED AND SHINY SILVER BASE LOW % IRON ON LINE BIOFILM CLEAN-UP AND STIFLING OF TUBERCLES – PLUG APPARENT POROSITY, MIXED BIO/CORROSION FOULING ON LINE BIOFILM CLEAN-UP, BIOFOULING ONLY
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 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 • 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.
Implications of the Need for Biocide Improvements • Action 3 - 14 Days After Action 2 Completed • Nonoxidizers Review Dosing Schedule and Amount Used vs. Contact Time (Feed/Bleed Issues) • Oxidizer – Semi-Continuous; Frequency and Duration for 1 to 2 ppm FAC Applied. Minimum 0.5 – 1.0 ppm 4hours/24hours • Oxidizer – Continuous; 0.2 to 0.5 ppm FAC go to 0.5 – 1.0 ppm FAC • Retest within 3-5 Days
Implications of the Need for Biocide Improvements • Action Level 4 - 14 Days After Action Level 3 Completed • Non-oxidizer Program May Require Oxidant Use At 1/Week in Summer and ½ Weeks Winter at 1-2 ppm FAC for 1 Hour CT (i.e. 2 Hour Run Time) • Semi-Continuous Oxidizer may require either or both non-oxidizer or Biodispersant Once per Week • Continuous Oxidizer at 1-2 ppm FAC may Require Either or Both Non-Oxidizer or Biodispersant once per Week • Non-Oxidizer or Biodispersant Addition Maybe Required Every System Retention Time (Vol/BD Loss) • May Require On-line Clean Within 30 Days • Retest Within 3-5 Days
Implications of the Need for Biocide Improvement • Action Level 5 – 14 Days After Action Level 4 Completed • On-line Clean within 7 Days of This State • Biodispersant Plus ≥ 5 ppm FAC for OR • Biodispersant Plus ≥ 25 ppm FAC for 2 Hours OR • Biosdispersant Plus ≥ 50 ppm for 1 Hour • Test 3-7 Days Latter – Poor Results Repeat or Go to Off-line Approach
Implications of the Need for Biocide Improvement • Off-line Cleaning • Pre Conditioning with • Blowdown to ½ COC • Biodispersant and Non Oxidizer for 24 Hours • Hyper Chlorination • pH 7.5 – 8.0 • Biodispersant • ≥ 10 ppm FAC for 24 hours • Drain and Flush • Post Conditioning of ≥ 10 ppm FAC for 1 Hour • Test 3-7 Days Latter – Poor Results Repeat or Go to Wisconsin Protocol
Implications of the Need for Biocide Improvement • Special Notes • Action Levels Are a Forward Progression • Upon Attaining Steady State Correction Move Backwards on the Action Levels Assuring No Return to Control State Loss • It is not Unusual to have to Repeat Online or Off-line Cleans as Previous Suppressed Bioflims, Sludge and Muds have now been Conditioned/ Loosened for Release to the Bulk Water