Transcript INTRODUCTION GLYNN WILLIAMS

LEGIONELLA
DAVID CONSIDINE
WHAT IS LEGIONELLA
Legionella pneumophila is the bacterium associated with over 90% of all cases of
legionnaires disease. It is a bar shaped bacterium of the Legionellaceae family.
THE EFFECTS OF LEGIONELLA
•
•
Legionella can be transferred to the human respiratory system in any water
aerosol with a droplet size of 3 to 5 μm.
Even a relatively low concentration of bacteria in aerosols is sufficient to affect
a healthy person.
•
Following an incubation period of 2-10 days the legionella pneumophila
generates a form of pneumonia which can also be accompanied by Pontiac
fever.
•
For people with weakened immune systems the subsequent death rate can be
quite high. Estimated at 30% of those who succumb to the disease.
WHERE IS LEGIONELLA FOUND
Small quantities are found naturally in lakes and ground water. These are rarely
sufficient in quantity to create disease.
To proliferate the legionella bacterium to levels that could become dangerous
would require:•
Low flow movement or water stagnation.
•
Elevated water temperatures to between 25 and 46 deg C.
•
Biofilms in the environment which would then provide shelter and a source of
food for the bacterium.
BIOFILM
Biofilm consists mainly of mixed colonies of microorganisms; bacteria, algae,
protozoans that are connected to one another and then attached to a common surface.
They are integrated fully or partially in a polymeric mass (slime) produced by the
organisms.
This creates:•
Food for bacteria.
•
Increased surface friction in pipes.
•
Gas production leading to smells (methane and hydrogen sulphide).
•
Possible “gas locking” of sections of pipework.
•
Possible corrosion of pipes and tanks.
SOURCES OF LEGIONELLA IN COMMERCIAL
BUILDINGS
•
Cold water systems.
•
Hot water systems.
•
Evaporative cooling applications (cooling towers and evaporative condensers).
•
Decorative water fountains.
•
Spa baths.
•
Swimming pools.
•
Misting devices (i.e retail outlets for maintaining fresh food quality).
METHODS OF WATER TREATMENT
•
Thermal Treatment
•
UV radiation
•
Filtration
•
Chlorination
•
Ozone
•
Chlorine dioxide
THERMAL TREATMENT
Legionella begins to die above 56 degrees C which makes it possible to get rid of
the bacteria by heating an infected system. A temperature of 70 deg C must be
maintained throughout the system for a period of around 10 minutes.
Advantages/Disadvantages
Removes biofilm
Effective against bacteria in biofilm
Effective against free bacteria
Affects water taste and smell
Sensitive to pH level
Life cycle cost
Risk of user scalding
Long term effect
No
Low
Mid
No
No
High
Yes
No
HWS CIRCULATION
Generally a HWS circulation loop is designed for the comfort of the user. Without
a “circulation loop” the hot outlets in a commercial building would have to wait far
too long for any hot water to arrive.
Legionella thrives between 25 and 46 deg C so any HWS circulation loop must be
kept well above the 46 deg C in order to control the growth of the bacterium.
Systems with showers require a high level of vigilance i.e.
• Sports Centre
• Hotels
• Motels
• Apartment buildings.
UV RADIATION
The UV rays penetrate the cell wall and damage the genetic information of the
bacteria and viruses, disrupting their reproductive systems. The UV bulb must be
kept clean for effective function; hard water may need separate treatment!
Advantages/Disadvantages
Removes biofilm
Effective against bacteria in biofilm
Effective against free bacteria
Affects water taste and smell
Sensitive to pH level
Life cycle cost
Risk of user scalding
Long term effect
No
No
Yes
No
No
Mid
No
No
FILTRATION
Ultra-filtration or membrane filtration can be used in domestic water supply to
remove free bacteria in water supplies. Filters will require maintenance checks to
ensure correct function and to prevent microbiological growth in the membrane.
Advantages/Disadvantages
Removes biofilm
Effective against bacteria in biofilm
Effective against free bacteria
Affects water taste and smell
Sensitive to pH level
Life cycle cost
Risk of user scalding
Long term effect
No
No
Yes
No
No
Mid
No
No
CHLORINATION
Common methods used in water disinfection :1. Chlorine gas.
2. Dosing of Sodium Hypochlorite
3. Electrolytic Sodium Hypochlorite generation (using NaOH common salt)
Advantages/Disadvantages
Removes biofilm
Effective against bacteria in biofilm
Effective against free bacteria
Affects water taste and smell
Sensitive to pH level
Life cycle cost
Risk of user scalding
Long term effect
No
Mid
High
Yes
Yes
Low
No
Mid
VACCUPERM CHLORINE GAS DISTRIBUTION
This method reduces the pressure of the chlorine gas to a vacuum which reduces
the risk of chlorine gas leakage.
Key Components
A) Chlorine gas storage cylinder
B) Vacuum regulator
C) Dosing regulator
D) Injector
Other Items on this Diagram
E) Absorption cylinder
F) Safety valve
G) Changeover device
H) Water apparatus
SELCOPERM
Using electrolysis, chlorine is produced directly from a solution of common salt using
electricity, without creating any notable by-products.
The following reactions take place in the electrolytic cell:
2 NaCl + 2 H2O = 2 NaOH + Cl2 + H2
The chlorine produced reacts immediately with the caustic soda solution also formed,
resulting in a sodium hypochlorite solution:
Cl2 + 2 NaOH = NaCl + NaClO + H2O
The solution generated has a pH value between 8.5 and 9.5, and a maximum equivalent
chlorine concentration in the range of 6-7 g/l. It has a very long half-life which makes it ideal
for storage in a buffer tank.
The sodium hypochlorite solution reacts in a balance reaction, resulting in hypochlorous
acid, the efficient disinfectant:
NaClO + H2O = NaOH + HClO
Benefits
• Common salt is the base material – it is nontoxic and easy to store.
• Only water, common salt and electricity is needed for the electrolysis – low operating
costs, world-wide use.
• Fresh hypochlorite is always on hand – the disinfectant solution does not dissociate like
commercial hypochlorite solutions.
• Approved disinfection method – an alternative with less safety requirements to chlorinegas-based systems.
OZONE
Ozone is a sanitizer that is produced by passing oxygen through a high intensity
electrical field (ozone generator). This alters the oxygen gas to become ozone gas
which creates a short-lived oxidiser, it breaks down rapidly and only has about a
one hour half life. It will also react with all materials which can be oxidized. Metals,
polymers, natural rubbers, even glass.
Advantages/Disadvantages
Removes biofilm
Effective against bacteria in biofilm
Effective against free bacteria
Affects water taste and smell
Sensitive to pH level
Life cycle cost
Risk of user scalding
Long term effect
No
No
High
No
No
Low
No
No
CHLORINE DIOXIDE (CIO2)
Powerful disinfecting action against viruses, bacteria, fungi and algae. The
significant advantage of chlorine dioxide in relation to chlorine or hypochlorite is
the gradual effect it has on degrading biofilm at low doses. A chlorine dioxide
concentration of 1 ppm will kill virtually all Legionella in the biofilm within 18
hours. A significant reduction in biofilm can be achieved in the same time frame
using a concentration of 1.5 ppm. Chlorine dioxide leaves no residual taste and
that even after periods of very flow or no flow the system is still protected.
Advantages/Disadvantages
Removes biofilm
Effective against bacteria in biofilm
Effective against free bacteria
Affects water taste and smell
Sensitive to pH level
Life cycle cost
Risk of user scalding
Long term effect
Yes
High
High
No
No
Low
No
High
PRODUCTION OF CIO2
Chlorine Dioxide Generation
• Sodium chlorite and Hydrochloric acid method
• 5 parts NaClO2 + 4 parts HCl = 4 ClO2 + 5 NaCl + 2 H2O
Chlorine Dioxide Properties
• Yellow-orange gas
• Must be produced on-site
• Good water solubility (30 g/l)
DISCUSSION?