UV treatment with lamps
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.
Contents
Suitable conditions
| Advantages | Disadvantages |
|---|---|
| - effective for inactivating waterborne pathogens - simple to apply at the household and community levels |
- the need for a source of lamps, which have to be replaced periodically (typically every year or two - the need for a reliable source of electricity to power the lamps |
Construction, operations and maintenance
Costs
Because the energy requirements are relatively low (several tens of watts per unit or about the same as an incandescent lamp), UV disinfection units for water treatment can be powered at relatively low cost using solar panels, wind power generators as well as conventional energy sources. The energy costs of UV disinfection are considerably less than the costs of disinfecting water by boiling it with fuels such as wood or charcoal.
UV units to treat small batches (1 to several liters) or low flows (1 to several liters per minute) of water at the community level are estimated to have costs of 0.02 US$ per 1000 liters of water, including the cost of electricity and consumables and the annualized capital cost of the unit. On this basis, the annual costs of community UV treatment would be less than US$1.00 per household. However, if UV lamp disinfection units were used at the household level, and therefore by far fewer people per unit, annual costs would be considerably higher, probably in the range of $US10-100 per year. Despite the higher costs, UV irradiation with lamps is considered a feasible technology for household water treatment.
