Total Oxidizable Carbons (TOC) is undesirable in high purity water systems in a.o. pharmaceutical and electronics industry because it serves as a food source to support bacterial growth and may interfere with downstream processes.
Although the exact structure of the TOCs is difficult to exactly identify and depends on the original water source, it is known that there are several organic types present:
- 10% to 20% are colloidal organics
- 70% to 80% are dissolved organic acids
- 5% to 10% are “neutral” organics
It is these last remaining “neutral” organics present in extensively treated water (UPW), where ultraviolet (UV) can play an important role and is effective. UV light is able to convert these “neutral organics” into removable components.
UV light acts in two ways:
- indirect: oxidation of TOCs by hydroxyl (OH) radicals, created by short wavelength of 185nm
- direct: photolysis of TOCs by photons, created by wavelengths 185(254) – 400nm
The effect of UV treatment is either total mineralization or dissociation of the TOCs making them removable by polishing filters.
A side effect of TOC reduction by UV light is the disinfection of the treated water. As the applied TOC UV dose is approximately 10 times greater than the regular UV dose for disinfection, the water is additionally well disinfected after TOC treatment.
UV systems for TOC reduction are typically placed in the make-up or recirculation loops of high purity water treatment systems.
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