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 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 that can also descend as water spray or mist.
Potentially everyone is susceptible to Legionella. At greatest risk are small children and people in the age group of 45 years and above. Those with a weakened immune system, people with breathing difficulties and/or kidney problems and 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 ionisation||Chlorination||Flushing and Heating||Chlorine Dioxide||Ultra Violet Light (U.V.)||Membrane filtration|
|Required concentrations||Cu = 0.2 - 0.8 mg/l,|
Ag = 0.02 - 0.08 mg/l
|2 - 4 mg/l||80ºC for 30 minutes||0.5 - mg/l as CLO2||10 - 0,1um|
|Application documented in literature||Yes||Yes||Yes||Yes||Yes||Yes|
|Residual effect||Yes||No||No||More stable than chlorination||No||No|
|Re-colonisation time||6 - 12 weeks||1 - 2 weeks||Varies||No information||Only locally effective (gatekeeper)||Only locally effective (gatekeeper)|
|Temperature effect||No effect||Disintegration||Not applicable||Disintegration||Only locally effective||Only locally effective
|pH effect||Elevated pH (> 8.5) may affect operation||Elevated pH (> 8.5) negatively affect operation||No effect||No effect||No effect||No effect
|By-products||None||Trihalomethanes (THMs)||None||Chlorate and Chlorite||None||None|
|Impact on taste and smell||None||Yes||None||Minimal despite high concentrations||None||None|
|Maintenance||4/year inspection of electrodes, 4/year inspection of concentration||Rules for transport, storage and handling in effect. Routine inspection of concentration, corrosion inspection||Incineration is possible; labour-intensive||Rules for transport, storage and handling in effect. Regular inspection of concentration, corrosion inspection||Regular cleaning otherwise effect wears off quickly||Clean filters regularly or replace|
|Reduction of effectiveness||None||Does not eliminate biofilm. Loses effectiveness at high pH. Disintegrates at high temperatures and over distance||Does not eliminate biofilm and re-colonisation is possible.||Disintegrates at high temperatures and over distance||Only locally effective; only as a water system is in direct contact with UV, otherwise it does not eliminate the biofilm||Only locally effective, does not eliminate biofilm|