Process Technologies at a Glance
The UV radiation damages the cell's DNA, thus rendering the bacteria incapable of reproduction and the bacteria dies off.
Thermal disinfection
Functional principle:
The complete system including the withdrawal fittings are heated up to > 70 °C for a period of at least 3 minutes.
Advantages:
- Provided the heating capacity is available, this can be done at any time
Disadvantages:
- Risk of scalding
- Increasing scale precipitation
- Scale precipitation generates the medium for legionellae
- Risk of corrosion in the piping system
- High organisational and personnel effort required
Chemical disinfection
Functional principle:
Dosing of high chlorine concentrations, at least 10 mg/l free chlorine. The DVGW work sheet W 291 must be observed.
Advantages:
- Feasible from the technical point of view as long as the facility has been shut down or is in disuse.
Disadvantages:
- High demand regarding personnel and chemicals
- Risk of corrosion in the piping system
- Problematic disposal
- Legionellae located in host organisms are not eliminated completely.
- A minimum concentration of 50 ¿ 100 mg/l of chlorine is required to destroy the host organisms.
Chemical disinfection - Chlorine electrolysis
Functional principle:
Electrolytic generation of hypochlorous acid (free chlorine), distribution of the chlorine by means of existing circulation pipes.
Advantages:
- Operation even at lower temperatures is possible
Disadvantages:
- The electrolytically generated values of max. 0,3 mg/l of free chlorine are not adequate to kill legionellae
- If not enough chloride is contained in the water, additional dosing of chloride is required.
- Due to the electrolytic processes hydrogen is generated which in turn leads to corrosion.
UV irradiation
Functional principle:
Irradiation of the water by means of UV-C light at a wave length of 254 nm
Advantages:
- Immediate destruction of legionellae that are floating free in the water
Disadvantages:
- Legionellae located in protective shelters (amoebae) are not destroyed
Ultrasound/UV treatment
Functional principle:
Combination of ultrasound and UV. The ultrasound is used to break up the amoebae thus setting free the legionellae which will then be killed by means of UV light.
Advantages:
- Unit may be installed in new as well as in existing systems, easy system integration
- Operation even at lower temperatures is possible
- No scale precipitation and corrosion problems
- No dosing of chemicals
- Legionellae located in protective shelters (amoebae) are killed as well
Disadvantages:
- Sizeable space required