Ultra Violet Disinfection

The ultraviolet spectrum is in the wavelength range of 180 – 390 nm. It has been shown that a wavelength of 254 nm penetrates bacterial cell walls causing alteration in their DNA. Many organisms are destroyed by exposure to this wavelength of light and others are rendered incapable of multiplication. Ultraviolet radiation can, therefore, be used to control bacterial levels in product water. The effectiveness of ultraviolet disinfection depends on the dose of radiant energy applied (microwatt-sec/sq.cm.).

In an ultraviolet device, low-pressure mercury vapour lamps are used, water passing over and around a quartz sleeve fitted over the radiation source. Water is then brought in close proximity to the light source. It should, however, be noted the ultraviolet radiation does not remove endotoxin but actually increases the endotoxin load by bacterial destruction. The mercury vapour lamp needs to be replaced periodically to ensure an adequate radiant dose. Typically, ultraviolet lamps have a one-year life, beyond which there is a decrease in radient output. Periodic cleaning of the quartz sleeve is also necessary to prevent the build up of a coating that reduces the radiation dose.