Abstract
In order to prevent Legionella contamination, several methods have been developed with which the bacteria can be killed in (tap) water. The most common method is thermal disinfection, with which the bacteria are killed through heating. Other methods use different techniques to kill Legionella, such as the use of UV-light,
... read more
copper-silver ionisation or oxidizing substances. In this literature study, the specific biological mechanisms behind several methods of Legionella control were studied. Each method has its advantages and disadvantages in effectiveness. Of course, all methods also have advantages and disadvantages in terms of cost, utility, safety and so on, but these are only marginally referred to in this research.
UV-light only has an effect on the DNA of the micro-organism: the DNA is damaged and becomes dysfunctional, due to which the Legionella bacteria die. When using UV-light, it is of importance that the dosage and duration of the radiation is sufficient. With a short exposure, a high intensity is needed to provide enough energy. The dosage emitted by the UV-lamp can moreover damage only a limited amount of DNA. If the Legionella are located in protozoa that have a large amount of DNA (in the nucleus as well as the mitochondria), possibly less damage is done to the DNA of the Legionella bacteria.
Copper-silver ionisation is a cheap method and an effective way of killing Legionella. However, as with UV-light, the Legionella bacteria can be protected by the protozoa and/or a biofilm. Another disadvantage is that the use of heavy metals in waterworks brings with it risks for public health.
Besides above mentioned methods, there are oxidizing substances that can kill off Legionella. Of these, chlorine is especially suitable in preventing the spread of Legionella, as a supplement to other methods. Disinfection with ozone is more effective, but has the disadvantage that ozone is quickly deactivated in water.
Peroxides are also used extensively in waterworks disinfection. Similar to UV-light and copper-silver ionisation, the oxidizing substances must penetrate the protozoa that harbour the Legionella for a proper disinfection. Whether these methods of disinfection have a sufficiently lethal effect on Legionella is not yet known.
With thermal disinfection, Legionella bacteria that have infected the protozoa are also reached, as well as the Legionella bacteria located in a biofilm. The temperature increases without as well as within the protozoa, and leads to damage to the Legionella bacteria present. A second point that supports thermal disinfection methods is that, through heating, multiple parts of the cell are destroyed. The chance that Legionella survives this combination of factors is in this way reduced to a minimum.
show less
