This document discusses approaches for managing risks from Legionella bacteria in potable water systems and cooling towers. It notes that high levels of organic materials can increase biofilm formation, and stagnant or slow-moving water poses the highest risk for outbreaks. Multiple barriers like disinfection, maintenance plans, and indicator monitoring are recommended. Cooling towers present unique challenges as the same bacteria can be pathogenic in towers but harmless in water. The Quebec law requires documentation and signed maintenance plans, though it is missing some elements like penalties. District cooling systems that circulate non-potable water can eliminate Legionella risk while improving energy efficiency.

1. Potable Water vs Atypical
Pneumonia Risk Management &
Bionebulisation
CWWA, Ottawa
27th of November 2013

2. Transferable Approaches
TOC & Phosphorus :
• High levels increase tendency to form Biofilm.
• Concentration in CTs will be 3 to 6 times
higher

3. Transferable Approaches
Stale or slow moving water:
• Risk №1 demonstrated to cause outbreaks
Disinfectants:
• negative synergies, half life, Minimal Effective
Concentration, Corrosion, Contact
time, Temperature & pH effects.

4. Transferable Approaches
• Cyst control vs Amoeba & Protozoa
• Outbreak much more likely if water source is
from surface water
• Giardia & Crypto reduction may reduce risk
• Potable technologies difficult to transfer to CTs
• Zero risk does not exist.
• Risk = Probability x Consequences

5. Transferable Approaches
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Reservoir hydraulics
Last in, last out reservoirs
Cross connections
Back-flow preventers
IRBs : SRBs & Ferrogineous

6. Transferable Approaches
• Risk management: Critical control
points, Gradated risk management, Audits, Check
lists, Maintenance plan, Documentation & Tests
history, Training.
• Multiple barriers approach
• Use of indicators : fast drop in HOCl, Aerobes
levels, Turbidity
• Algae management-reduction
• Chemical pumps, controllers, sensors, on-site
chemical tests

7. Transferable Approaches
• ≠ Materials = Different tendencies for biofilm.
• Biofilm media: PVC high surface area
• CTs use exactly the same in cooling towers!
Coated to reduce surface tension? No.
Impregnated with silver ions-zeolite? No
• No kidding, no joke.

8. Counterintuitive & Different
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Fecal microorganisms vs water-borne
Oral vs Inhalation
Planktonic Vs Sessile
Indicators in potable water allow validation.
NOT in CTs. There is no definitive validation in
CTs with a test.
• Finished water quality control vs Process QC

9. Counterintuitive & Different
• In CTs same bug (DNA) can be mostly
innocuous or highly pathogenic!
• Potable water can contain 3 logs of Legionella
that are non-cultivable but viable & infectious.
• You do it right nobody gets sick. In CTs we are
never sure.
• You can get away with important deposits &
biofilm. Not in CTs.

10. Counterintuitive & Different
Cleaning:
• Flushing does not work
• High levels of disinfectant do not work

11. Québec 2012: lessons
• Do not disinfect without having clean surfaces.
Remove the deposits 1st.
• Install high efficiency drift eliminators at the
onset : very low implementation
• Validate biocide concentration, contact time &
circulation at time of injection: >75% wrong.
• Involve external pros & a chemist (please)!

12. Québec 2012: lessons
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Have a plan of action. If this then that, etc.
What, Where, How, When, Whom.
Priorities.
Work upstream of Legionella pneumophila.
Do not ASSume.

13. Québec Law : the Excellent
• Mandatory documentation of actions & test
results.
• Schematics of the CT system.

14. Québec Law : the Excellent
• Maintenance plan signed by a professional
with an ethic’s code to be revised after:
1. Over limit Legionella result
2. Change to the equipment or systems
3. Changes vs the Maintenance plan

15. Québec Law : the Excellent
• Maintenance plan covers:
1.
2.
3.
4.
CT layout & start-up
CT operational stops & starts.
Decontamination
Normal operation

16. Québec Law : the Excellent

17. Québec Law : the Excellent

18. Québec Law – Interpretation - Who

19. Québec Law : the Good
• Law: any law is great.
• List of CTs, owners, localisation, tons.
• 40 inspectors actually visiting every CT!!!
– Systematic validation of back-flows, existence of
required signed documentation. Issuance of
‘tickets’ with 7 days to comply! Pictures.
• Technical guide & training sessions.

20. Québec Guide : the Good
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Iron as a virulence & amplification factor.
Relationship between biofilm, amoeba & Lp.
Association between deposits & Lp.
Indicators & Lp analysis w/ action levels.
Personalised planning.
Hydraulic management.

21. Québec Law : the Missing
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ASHRAE 188, 62.1
Penalties & Responsabilisation.
Content of the plans & documentation.
Not specific as to the actors:
Eng, Chemist, Water treat, Mechanics, Control
cie., Chiller & CT maintenance cies.
• Reducing agents as microbiostat –cide
• Risk analysis framework.

22. Québec Guide : the Bad
• False information:
1. Non oxidizing biocides can be measured with test
kits on site or off-site (GC).

23. Consumption Implications

24. Reduced consumption
• When risk is perceived as hard to control then
managers replace CTs with Air-cooled units.
• ~ 2x more energy consumption
• HVAC: 40-60% of the bld energy consumption.
• Buildings = 39% of total energy consumption.
• Island heat effect amplified. In Paris over 3°C.
• Ex. L’Oréal

25. Increased Consumption
• Fastest way to reduce risk is to reduce cycles
of concentration
• Also improves energy efficiency
• Increases water consumption. Usually 2nd
biggest after toilets & urinals.
• Increases proportion of water returned to
drain.
• Reduces water gas thus reducing Island heat.

26. District Cooling – Water2Water
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Ex. Toronto, Morocco.
No potable water or net water use.
Energy & GHG savings.
No island heat effect. Less smog.
Increased floor space & competitiveness.
Less city hollowing.
• NO LEGIONELLA RISK

27. Quantitative Microbiology
Case: 1000 tons CT, 35% in operation, Lp within
guidelines at 3 logs
Drift eliminators at 0.5% vs 0.0005% efficiency
20 000 vs 20 cfu Lp/minute
Material cost of about 300$/CT
CTI’s 1st recommendation is for validation of
drift control. Never followed.

28. Questions, Comments ?