Water & Wastewater Treatment

www.wwtonline.co.uk | WWT | NOVEMBER 2015 | 39 L egionella is always at the forefront of our minds in the water treatment industry, with the risks well publicised. While legionella bacteria – which can cause serious health conditions including the pneumonia-like Legionnaire's Disease – can be readily found in natural water systems such as rivers, conditions are rarely right for people to catch the disease from these sources. It is when legionella multiply in man-made water systems where the temperature is warm enough to encourage growth that it becomes a health risk. What conditions can result in legionella growth? As a rule of thumb, in the environment, legionella will survive at temperatures below 20 0 C, but is unlikely to multiply. As temperatures rise above 50 0 C, legionella is less likely to survive, and at 60 0 C, the majority would be killed in minutes. Therefore maintaining water temperature at below 20 0 C or above 50 0 C is the main method in controlling Legionella in domestic and commercial water systems. Where calorifiers with recirculating hot water distribution systems are used, the recommended temperature is 60C. It is, however, worth noting that water entering the system as a feed as cold water could drop the temperature to a level where the growth of legionella is possible. For this reason, calorifiers are now fitted with anti-stagnation pumps which recirculate hot water from the higher levels of the calorifier to the bottom colder water, reducing the temperature difference and ensuring a warm, dangerous stagnant water is not promoted. What is the best way to keep water systems clean? Along with careful monitoring and temperature control, it is prudent to use a safe disinfectant as an adjunct in arresting possible bacteria, biofilm and other microbiological contamination. Water hygiene and safety is the key, and it cannot be stressed too strongly that monitoring of temperatures of water systems with a regime of cleaning and disinfection will ensure responsible operational use of that system. It is important that all parts of the system are disinfected, not just those which are accessible. If out of sight means out of mind, this could result in an expensive or dangerous failure. Bill ABBott MaNagiNg DiREcTOR HyDROcHEM Danger in the water With many types of water systems vulnerable to legionella, owners and operators should be aware of the risk factors and how to reduce them In the know Getting to grips with… legionella

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