WHAT IS LEGIONELLA BACTERIUM?
Often in systems for sanitary use, stagnant water can promote the proliferation of the legionella bacterium. Legionella is found in springs, including thermal ones, rivers, lakes, vapours, and soils. From these environments, it is conducted to artificial ones such as city conduits and hydraulic systems of buildings, such as tanks, pipes, fountains, and pools. Legionella is a bacterium for which over 40 species have been identified.
The most dangerous one, which has been attributed to nearly 90% of cases of legionnaire’s disease, causes a serious pneumonia. The name derives from the acute epidemic that affected a group of veterans of the American Legion in 1976 who had met up in a Philadelphia hotel, causing 34 deaths out of 221 infected people. The most favourable conditions for proliferation are stagnant waters with temperatures between 25 and 42 °C, acidic and alkaline environments, and the presence of incrustations and sediments.
WHERE IS THE LEGIONELLA BACTERIUM FOUND?
Installations that produce nebulized water, such as air conditioning systems and hot water circulation networks in hydro-sanitary systems are favourable sites for the diffusion of the bacterium.
Critical areas appear in hydro-sanitary systems inside pipes - particularly if they are obsolete and have sediments inside, or even closed sections - storage tanks, boilers, shower heads and distribution terminals; emergency water systems, such as decontamination showers, eye washing stations and fire prevention sprinkler systems can also be places of proliferation.
Legionella has also been found in baths and jacuzzis.
Systems that spray nebulized water at high speed: the bacteria can be released into the air from the bubbles that rise or through a fine aerosol.
Some cases of legionnaire’s disease have been associated with the presence of decorative fountains where water is sprayed into the air or splashes down onto a base.
Fountains that work intermittently have a higher risk of contamination Other systems where the risk of legionella is high are open and closed circuit cooling towers where there are air recovery or suction channels nearby.
Air conditioning systems must also be considered, like humidifiers/wet pack coolers, nebulizers and spray systems
HOW TO COMBACT THE PROLIFERATION OF LEGIONELLA?
Combating the proliferation of legionella first requires careful design and accurate management/maintenance. With regard to water systems, the avoidance of pipelines with dead ends or without circulation is recommended, as is the avoidance of stagnation, excessive lengths of piping, contact between air and water, and accumulation in non-sealed tanks. Provide regular and easy cleaning.
It has been observed that legionella has more difficulty proliferating in the presence of copper pipes and fittings.
Areas of stagnant water must be avoided, acting on the correct dimensioning and circulation in the system and if possible, seeing to treatment stations as presented below. Whenever possible, a heat treatment is recommended, in which the water is maintained at a temperature higher than 60 °C, a condition that inactivates legionella, or a thermal shock in which the water temperature is raised to 60-70 °C for at least 30 minutes a day for three days, up to the taps.
The use of copper (unlike common plastic materials) enables maximum safety in the event of a thermal shock to be used for removing legionella within systems. Other treatments are continuous hyperchlorination: chlorine is added to the system in the form of calcium or sodium hypochlorite, until the residual concentration of the disinfectant is between 1 and 3 mg/L or with chlorine dioxide which enables continuous disinfection, with moderate levels of residual chlorine, leaving the water suitable for drinking, removing the biofilm (natural habitat of legionella), a very prolonged action over time and in terms of the distance from the injection point, recommended levels 0.2-0.4 mg/l, does not produce sub-products (such as THM), is produced on site with special generators with suitable production capacity for the system to be disinfected and with the aforementioned concentrations does not attack the pipes.
With UV rays generated by special lamps, the bacteria are killed, or with copper-silver ionisation, or with hydrogen peroxide and silver, it is possible to reduce the presence of legionella. Finally, we mention ozone and terminal filters: thanks to the properties of ozone, all the macromolecular structures of cells (mould, bacteria, yeast, etc.) are profoundly altered and inactivated and with the use of terminal filters applied directly at the sampling point, a mechanical barrier (0.2_m) to the bacteria is formed (they must be replaced quite regularly).