Process Technologies at a Glance

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