How Does Ultraviolet (UV) Light Work?

UV light is widely used as a bactericide and to break down and photo-oxidize organic contaminants to polar or ionized species for subsequent removal by ion exchange.

How UV photo-oxidizes organic contaminants and is effective against bacteria

The UV lamps used in laboratory water purification systems are low pressure mercury lamps that produce radiation with a wavelength of 254 nm. This wavelength has the most effective bactericidal action as it damages DNA and RNA polymerase at low doses thereby preventing replication.

Radiation at shorter wavelengths (185 nm) is most effective for oxidizing organics as it breaks large organic molecules into smaller ionized components. They can then be removed by a downstream high purity ion exchange resin bed.

Advantages and Restrictions

Advantages:

  • Oxidation of organic compounds (185nm and 254nm) to reach TOC levels <5ppb
  • Effective bactericide treatment

Restrictions

  • Photo-oxidation of organics is a polishing step that can only decrease the TOC levels by a restricted amount
  • No influence on ions, particles or colloids
  • The water's resistivity is decreased as a result of the CO2 released by photo-oxidation, as it produces H2CO3 (H+, HCO3-)

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