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Legionella pneumophila is the bacterium associated with 90% of all cases of Legionnaire’s disease which is a fatal form of pneumonia. It can affect anyone, but is particularly dangerous for people who suffer from any level of immunosupression such as the very young and the elderly, smokers and people who suffer from respiratory problems. Small quantities of the bacteria do exist naturally in nature such as in the micro flora in rivers, lakes and ground water but in such low concentrations that they pose no real threat.
The disease was first identified in 1977 following an outbreak of pneumonia that occurred among people attending a convention of the American League in Philadelphia in July 1976 when 234 people became ill and 34 died. It was initially difficult to identify the disease as people only became ill after the conference was over and attendees had gone home and initially the causative agent did not show up on routine staining cultures. The source of the outbreak was eventually traced to an air-conditioning ventilator in the hotel lobby.
Today Legionnaires disease may not be in the news as much as it was in the early days after its discovery, however it still poses a real threat with 300-400 cases of Legionnaire’s reported in the UK annually that translate into a 14% fatality rate.
Getting it right
This bacterium generally thrives in hot water systems with a low flow rate and where areas of stagnation can occur. The bacteria breeds and thrives in the slimy layer of biofilm within pipes and tanks in temperatures between 25 and 46°C. Some of the more vulnerable commercial applications are those that offer shower and bathing facilities and where water mist is sprayed into the air such as in cooling towers, air-conditioning systems and even fountains. However even the cold water supplies in larger building applications can frequently heat to temperatures that create the ideal conditions for this bacteria to grow.
There are a range of methods available for combating the bacteria all of which have some practical advantages and disadvantages.
One of the most commonly used methods to combat legionella is thermal pasteurisation. Legionella begins to die above 56°C which makes it possible to get rid of the bacteria by heating the infected system. However a temperature of 70°C must be reached and maintained throughout the entire piping system over a period of around 10 minutes, which is difficult to achieve given that the water cools down as it reaches water outlets.
There are few advantages to this method and many disadvantages that include the risk of an acute scald due to the temperature that needs to be reached and maintained, the fact that the biofilm is left unaffected which means that the germs build up quickly between cycles and that the dead ends in the system are not treated at all.
Another common method used is water disinfection and chlorine is often the disinfection chosen for the task. One of the main advantages of chlorine is that it is a low cost solution; however there are numerous disadvantages that include the fact that the smell and taste post treatment make it unsuitable for drinking. Additionally the pH balance needs to be carefully maintained for the treatment to be effective and the long term effect is limited.
The method of UV Radiation uses ultra violet rays with a wavelength of 254nm. The rays penetrate the cell wall and damage the genetic information of the bacteria and viruses, disrupting their reproductive systems. There are advantages to this system as no chemicals are used so the smell and taste of the water is not affected. However some of the drawbacks are significant including the fact that it is only the free bacteria that are actually exposed to the UV rays that are killed.
Ultra-filtration or membrane filtration is commonly used in domestic water supply to remove free bacteria in water supplies. Although this method is effective against free bacteria this has no impact on the bacteria population and the biofilm is unaffected.
Ozone can also be used as a sanitiser that is produced by passing oxygen through a high intensity electrical field. This alters the oxygen gas to ozone gas which creates a short-lived oxidiser. This method is effective against free floating bacteria and does not affect the smell or taste of the water. However the main disadvantages are that it breaks down rapidly when exposed to oxygen and the method has no impact on the biofilm in the pipe network.
Finally, treatment by Chlorine Dioxide has a very powerful disinfecting action against all kinds of germs and contaminants such as viruses, bacteria, fungi and algae compared to other biocides. 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 timeframe using a concentration of 1.5 ppm. Other benefits include chlorine dioxide leaving no residual taste and that even after periods of very low flow or no flow the system is still protected for up to a week.
The perfect solution
The Grundfos chlorine dioxide system Oxiperm Pro/OCD-162 is the perfect solution for fighting Legionella.
Oxiperm Pro/OCD-162 systems produce chlorine dioxide using diluted solutions of sodium chlorite (NaClO2 7.5%) and hydrochloric acid (HCl 9%). They are available in four capacity levels, producing 5, 10, 30 or 60 g/h of chlorine dioxide. This capacity is sufficient to treat up to 150m³ of drinking water per hour at the maximum admissible concentration of 0.4 mg/l ClO2. Being so compact, the system can be installed in confined areas.
The Oxiperm Pro/OCD-162 can also be connected without interrupting the building's water supply which represents a decisive cost factor when it comes to decontaminating hospitals or nursing homes of Legionella. The newly designed control system makes for straightforward and user-friendly operation.
There are a number of ideal application areas where Oxiperm Pro/OCD-162 will help combat Legionella in building installations such as hospitals and old people's homes, hotels and restaurants, sports facilities, schools and shower installations.
The legal buck stops where?
In the UK today people who contract legionnaire’s disease (or their families) can and do sue. An example of this is after a recent outbreak in Barrow which resulted in a fatality, where the source of the disease was traced to the exit of the cooling system at a council owned arts and leisure facility in the town centre. The senior architect at the council was tried for manslaughter for contravening health and safety.
Within the world of commercial building services today, the remit is becoming wider and wider, we are all doing our best to be all things to all people. Sometimes to deliver the highest standards and most up-to-date solutions means being able to access strategic partners who can bring their expertise to bear in areas of particular complexity.
