Sanitation Systems: Pros and Cons

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
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