Knowledge Base

What is Legionella?

Legionella is a bacteria. A micro-organism such as Norovirus, E-coli, Hepatitis A, Cryptosporidium, and Pseudomonas. A potential contamination risk for water and responsible for the deaths of millions of victims world-wide. Legionella pneumophila causes the Legionnaire’s disease, a possibly fatal form of pneumonia. These Legionella bacteria find their way into the human body through the respiratory system by inhalation of small contaminated water droplets and/or water mist.

Potentially everyone is susceptible to Legionella. However, at greatest risk are: small children, the age group of 45 years and above, those with a weakened immune system, people with breathing difficulties and/or kidney problems, the group smokers and drinkers.

How is Legionella caused?

The problem of Legionella is caused by contamination of water installations in which biofilm functions as a breeding ground for other bacteria. Such contamination can in particular be caused by stagnant water and the heating up of cold water. In these situations, all other techniques or interventions are inadequate. Even the Ministry of Infrastructure and Environment has labelled the technique of copper- silver ionisation (CSI) as the ultimate solution.

As soon as bacteria multiply, they deposit polysaccharides which function as a sort of glue and this aids the bacteria to collect on the water pipe wall or on another surface –in the case of a cooling tower. Biofilm is a layer of built up bacteria that usually easily forms on the insides of a water pipe or on another surface. Biofilm is the ideal breeding ground for the Legionella bacterium.

The Legionella bacterium can survive in waters with temperatures between 0°C and 63°C, but mostly multiplies between 20 – 45°C. The growth rate is at its maximum at temperatures of 30 – 40°C (body temperature!).

Technique Comparison Table

An objective overview and comparison of alternative techniques for the treatment of potable water:

 Copper and silver ionisationChlorinationFlushing and HeatingChlorine DioxideUltra Violet Light (U.V.)Membrane filtration
Required concentrationsCu = 0.2 - 0.8 mg/l,
Ag = 0.02 - 0.08 mg/l
2 - 4 mg/l80ºC for 30 minutes
0.5 - mg/l as CLO210 - 0,1um
Application documented in literatureYesYesYesYesYesYes
Residual effectYesNoNoMore stable than chlorinationNoNo
Re-colonisation time6 - 12 weeks1 - 2 weeksVariesNo informationOnly locally effective (gatekeeper)Only locally effective (gatekeeper)
Temperature effectNo effectDisintegrationNot applicableDisintegrationOnly locally effective
Only locally effective
pH effectElevated pH (> 8.5) may affect operationElevated pH (> 8.5) negatively affect operation
No effect
No effect
No effect
No effect
By-productsNoneTrihalomethanes (THMs)NoneChlorate and ChloriteNoneNone
Impact on taste and smellNoneYesNoneMinimal despite high concentrationsNoneNone
CorrosionNoneVery corrosiveCorrosiveCorrosiveNoneNone
Maintenance4/year inspection of electrodes, 4/year inspection of concentrationRules for transport, storage and handling in effect. Routine inspection of concentration, corrosion inspectionIncineration is possible; labour-intensiveRules for transport, storage and handling in effect. Regular inspection of concentration, corrosion inspectionRegular cleaning otherwise effect wears off quicklyClean filters regularly or replace
Reduction of effectivenessNoneDoes not eliminate biofilm. Loses effectiveness at high pH. Disintegrates at high temperatures and over distanceDoes not eliminate biofilm and re-colonisation is possible. Disintegrates at high temperatures and over distanceOnly locally effective; only as a water system is in direct contact with UV, otherwise it does not eliminate the biofilmOnly locally effective, does not eliminate biofilm