The Drinking Water Book by Colin Ingram

Author:Colin Ingram [Ingram, Colin]
Language: eng
Format: epub
ISBN: 978-0-307-79133-7
Publisher: Random House Inc.
Published: 2011-06-07T21:00:00+00:00

How Ultraviolet Units Work

Ultraviolet (UV) radiation is higher in the electromagnetic spectrum than visible light. It is known to be effective in killing bacteria and other pathogens. The only types of pathogens that cannot be killed by ultraviolet are those with hard coverings, such as giardia cysts. Ultraviolet purifiers are made for the specific purpose of disinfecting water and are not effective in removing other pollutants.

Most materials, including common glass, do not transmit ultraviolet radiation efficiently. One of the best transmitters of UV radiation is quartz glass, so it is used for most UV lamps. In order for a UV unit to disinfect water effectively, three conditions must be met: (1) the UV lamp must produce radiation above a critical intensity; (2) the water must be subject to this radiation for a minimum period of time; and (3) both the input water and the UV unit itself must be clean. UV units employ many different designs to meet the first two conditions. The following illustration shows two simple designs: one with water flowing straight through a quartz cylinder past a long tubular UV lamp and the other with the water conduit wound in a spiral to increase the amount of time the water is exposed to the UV lamp. In the latter design, the spiral tubing must also be of quartz glass in order to transmit UV energy efficiently.

To meet the third condition, clean water, prefilters must always be used. If the water contains particles, some bacteria and other pathogens will be shielded from the UV radiation and will pass through the unit unscathed. Because water cleanliness is so critical to UV operation, all UV units for home use need to be designed to allow easy access for cleaning.

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