2,774 bytes added,
01:03, 19 September 2012
Two alternative configurations or physical systems are used for UV disinfection of small or household water supplies, submerged lamps or lamps in air and mounted above a thin layer of the water to be irradiated. In the units with submerged lamps, the lamps are covered with a protective, UV-penetrable as protection from the electrical hazards associated with water. Water can be treated on a batch basis by placing the lamp in a container of water for several minutes or longer, or on a flow-through basis in a housing or channel, with the water flowing parallel or perpendicular to the lamp(s).
In units having the lamps mounted in the air, the UV lamps are in a metal housing with reflective surfaces that direct the UV radiation downward onto a thin layer of water flowing through a channel or tray below the lamps. The advantage of the submerged systems is intimate lamp contact with the water, water-mediated cooling of the lamps, and the use of housing designs that maximize UV exposure of the water.
However, the protective sleeves over the lamps must be mechanically or chemically cleaned on a regular basis to overcome fouling by a physical, chemical or biological film that can forms on the sleeve surface, reducing UV passage into the water. The non-submerged, in-air lamp units have the advantage of no need for lamp cleaning due to lamp fouling, but there is some loss of UV radiation due atmospheric and surface absorption. However, both types of UV disinfection system designs are available for disinfection of household water at point- of-use, point-of-entry or at the community level.
==Suitable conditions==
{| border="1" cellpadding="5" cellspacing="0" align="center"
|-
! width="50%" style="background:#efefef;" | Advantages
! style="background:#ffdead;" | Disadvantages
|-
| valign="top" | - effective for inactivating waterborne pathogens <br>
- simple to apply at the household and community levels<br>
- relatively low cost<br>
- does not use chemicals or create tastes, odors or toxic chemical by-products
| valign="top" | - the need for a source of lamps, which have to be replaced periodically (typically every year or two <br>
- the need for a reliable source of electricity to power the lamps<br>
- the need for periodic cleaning of the lamp sleeve surface to remove deposits and maintain UV transmission<br>
- the uncertainty of the magnitude of UV dose delivered to the water, unless a UV sensor is used to monitor the process<br>
- UV provides no residual chemical disinfectant in the water to protect against post-treatment contamination, and therefore care must be taken to protect UV-disinfected water from post-treatment contamination, including bacterial regrowth or reactivation
|}
==Construction, operations and maintenance==
