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Legionella bacteria are naturally present in cold water. They are also present in hot water networks at temperatures between 25 and 45°C in conditions that are favourable to their development (nutrients, biofilms). They can cause a serious illness: Legionnaire’s Disease; one which has become a major challenge in terms of public health issues. The treatments traditionally used against Legionella bacteria are of the chemical biocide variety. There are several disadvantages to these treatments:
- The different parameters for optimal efficiency (dosage, pH, resistance phenomena…) are complex
- The use of continuous injection, which requires high levels of input, may be required, thus raising operating costs
- They generate by products that are rejected into the environment during de-concentration phases
- Chemical biocide injection alone does not always enable full control of the level of Legionella bacteria
Shutting down a system for curative or preventive action against Legionella bacteria is expensive.
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Biocide injection is no longer the ultimate weapon for destroying Legionella bacteria in water distribution circuits.
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TREATMENT OF COLD WATER AT THE INLET |
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The source of contamination of Legionella bacteria in hot water networks is the cold water inlet (bore holes or other local resources…). Legionella is a bacteria that is naturally present in water. It is also present in drinking water. Culture analyses (NFT 90-431) highlight some of the germs present, the bacteria that are ‘cultivatable’. PCR analyses show all bacteria, notably the non-cultivatable and cultivatable viable bacteria. Example of analyses carried out on a water network:
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Water source
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NFT 90-431 analysis
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PCR analysis
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Drinking water
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Non identifiable
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13 000 UG/litre
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It is clear that the risk of contamination via cold water is very high. |
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Erect an initial bacteriological barrier to avoid contamination by new bacteria
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A BIO-UV steriliser enables continuous treatment of cold water thus avoiding contamination of water networks. Example of results obtained:
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Water source
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PCR result before UV
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PCR result after UV
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Drinking water
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13 000 UG/litre
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Non identifiable
< 250 UG/litre
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This solution is very easy to apply and has a low investment and maintenance cost. Analyses carried out by Laboratoire Bouisson Bertrand in Montpellier, an accredited independent laboratory. |
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TREATMENT OF HOT WATER CIRCUITS |
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Water in domestic hot water networks is contaminated by Legionella bacteria because:
- The water network design is not always ideal in terms of germ prevention,
- Certain biocide products have operational limits due to phenomena of developed tolerance, concentration dosage management, global water quality parameters (pH, …),
- The biofilm that always forms in the circuit releases Legionella by detachment or abrasion.
Contamination by release from the biofilm must be treated.
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Erect a second bacteriological barrier to treat, on a constant basis, the Legionella released by the biofilm.
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A BIO-UV steriliser enables continuous treatment of water in a circuit. A significant level of efficiency that enables, during circulation through a closed network, continuous destruction of the legionella released by the biofilms. BIO-UV sterilisers in the IBP/AM series have been designed specifically for the treatment of hot water at between 35 and 75°C. Unlike standard UV lamps, which are not as efficient beyond temperatures of 40°C, the BIO-UV sterilisers are equipped with dedicated high performance lamps which guarantee performance up to 75°C.
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UV TREATMENT OF COLD WATER FROM THE WATER METER INLET
