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.

BIOFILMBiofilm 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 TREATMENTLegionella 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/DisadvantagesRemoves biofilm NoEffective against bacteria in biofilm LowEffective against free bacteria MidAffects water taste and smell NoSensitive to pH level NoLife cycle cost HighRisk of user scalding YesLong term effect 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/DisadvantagesRemoves biofilm NoEffective against bacteria in biofilm NoEffective against free bacteria YesAffects water taste and smell NoSensitive to pH level NoLife cycle cost MidRisk of user scalding NoLong term effect No

FILTRATIONUltra-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/DisadvantagesRemoves biofilm NoEffective against bacteria in biofilm NoEffective against free bacteria YesAffects water taste and smell NoSensitive to pH level NoLife cycle cost MidRisk of user scalding NoLong term effect No

CHLORINATIONCommon methods used in water disinfection :-

1. Chlorine gas. 2. Dosing of Sodium Hypochlorite 3. Electrolytic Sodium Hypochlorite generation (using NaOH common salt)

Advantages/DisadvantagesRemoves biofilm NoEffective against bacteria in biofilm MidEffective against free bacteria HighAffects water taste and smell YesSensitive to pH level YesLife cycle cost LowRisk of user scalding NoLong term effect 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 ComponentsA) Chlorine gas storage cylinderB) Vacuum regulatorC) Dosing regulatorD) Injector

Other Items on this DiagramE) Absorption cylinderF) Safety valveG) Changeover deviceH) Water apparatus

SELCOPERMUsing 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 chlorine-

gas-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/DisadvantagesRemoves biofilm NoEffective against bacteria in biofilm NoEffective against free bacteria HighAffects water taste and smell NoSensitive to pH level NoLife cycle cost LowRisk of user scalding NoLong term effect 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/DisadvantagesRemoves biofilm YesEffective against bacteria in biofilm HighEffective against free bacteria HighAffects water taste and smell NoSensitive to pH level NoLife cycle cost LowRisk of user scalding NoLong term effect 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)

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