Thermal water treatment

One of the most commonly used methods of combating legionella is thermal pasteurization. The efficiency of this method is limited.

Legionella begin to die off at temperatures above 46 °C, which makes it possible to combat the bacteria by heating up the infected water system. This is often done as a daily or weekly procedure.

The hot water is heated up to 70 °C and circulated in the system until is regarded that the bacteria in the system have died. In large water systems the pipe system have to divided into smaller and manageable zones. The zones are flushed one by one with the help of opening motorised valves placed in the system. The pasteurisation process lasts from 10 min and up to several hours.       

Advantages:

- Does not affect smell and taste of the water

- Not sensitive to pH-value of the water

- Well known and understandable principle

- No addition of biocides to the water


Disadvantages:

- Acute risk of scalding if the water outlets are opened during pasteurisation.

- There is no long term effect after the pasteurisation

- Biofilm is left unaffected, with the result that germs quickly grow up again between treatment cycles

- Dead-ends are not treated at all

- Advanced tap-opening process must be implemented

- High energy consumption for the process 

- The desired temperature is seldom achieved in the whole system, because the water cools down before it reaches the water taps.

- Heating increased calcification which damages systems.

- Thermal expansion can cause irreparable damage and leakages in older installations.





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