[[Image:UV lamp icon.png|right|80px]][[Image:UV lamps.jpg|thumb|right|300px200px|In Bhupalpur, India, Ashok Gadgil's ultraviolet-light water purification system treats water from a public well. Photo: [http://web.mit.edu/invent/www/ima/gadgil_bio.html Ashok Gadgil.]]]__NOTOC__ <small-title />UV irradiation (using lamps in particular) provides a quick and effective way of disinfecting water supply from harmful bacteria without leaving a chemical residue, like the one chlorine leaves. Usually it is used as one step in the process of making water safe to drink. Other steps include filtration and/or reverse osmosis. But in general, UV light (whether by sun of lamps) has demonstrated efficacy against pathogenic organisms, including those responsible for cholera, polio, typhoid, hepatitis and other bacterial, viral and parasitic diseases.<ref> Trojan UV: [http://trojanuv.com/uv-disinfection Introduction to UV Disinfection]</ref> Special low-pressure mercury vapor lamps produce UV radiation at 253.7nm, the optimal wavelength for disinfection.<ref>[http://www.hitechultraviolet.com/ultraviolet.html HiTech Ultraviolet Pvt. Ltd.]</ref>
UV irradiation (using lamps in particular) provides a quick and effective way of disinfecting water supply from harmful bacteria without leaving a chemical residue, like the one chlorine leaves. Usually it is used as one step in the process of making water safe to drink. Other steps include filtration and/or reverse osmosis. But in general, UV light (whether by sun of lamps) has demonstrated efficacy against pathogenic organisms, including those responsible for cholera, polio, typhoid, hepatitis and other bacterial, viral and parasitic diseases.<ref> Trojan UV: [http://trojanuv.com/uv-disinfection Introduction to UV Disinfection] </ref> Two alternative configurations or physical systems are used The set up for UV disinfection of small or household water supplies, consists of submerged lamps or lamps in the 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.
'''Low maintenance'''<br>
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:#ffdeadf0f8ff;" | Disadvantages
|-
| valign="top" | - effective for inactivating waterborne pathogens <br>
- simple to apply at the household and community levels<br>
- relatively low cost, depending on scale of use and UV lamp system used<br>
- does not use chemicals or create tastes, odors or toxic chemical by-products<br>- UV is simple to install and requires little supervision, maintenance, or space<br>- UV effectiveness is relatively insensitive to temperature and pH differences. In addition, researchers found that UV application does not convert nitrates to nitrites, or bromide to bromines or bromates.<ref>[http://www.nesc.wvu.edu/ndwc/pdf/ot/tb/ot_tb_f00.pdf Tech Brief: Ultraviolet Disinfection] National Drinking Water Clearinghouse (NDWC) newsletter. Sept. 15, 2000.</ref><br>- UV provides protection against cryptosporidium, unlike chlorine
| 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>
|}
===Construction, operations and maintenance===[[Image:UV WaterBox.jpg|thumb|right|200px|The UV WaterBox by Aqua Aero.]] There are not many known homemade UV lamp systems, most are small units that are commericially commercially available. However, an alternative to a lamp UV is to use direct sunlight, and there are several methods on how to build your own [[UV treatment / Solar disinfection (SODIS)]] system. Otherwise commercial units can be bought, for instance, the [[Naiade water purification unit]] or the UV WaterBox. Technical aspects of the [http://www.aaws.nl/uv-waterbox-2/ UV WaterBox] by Aqua Aero.
===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 $US10-100 per year. Despite the higher costs, UV irradiation with lamps is considered a feasible technology for household water treatment.
===Field experiences===
'''The Power of UV Light'''<br>
UV Waterworks systems have been used in India, South Africa, the Philippines, Honduras, and other countries. Since 1998, the Mexican government has installed about 100 in Guererro, a state on the Pacific in southwestern Mexico. The results have been very positive. In the summer of 2000, Gadgil reports, people from Water Health International returned with stories and data showing a dramatic decline in the incidence of diarrhea among children and adults. And preventing deaths and illness are just the most visible effects of purifying water—it also protects children from stunted physical and mental growth. "This is the kind of story that really makes my day, really makes me happy," Gadgil continues. "It makes me feel good when I get up in the morning."
===Manuals, videos, and links===[[Image:UV lamp unit.jpg|thumb|right|250200|UV Waterworks commercial unit. Photo: [http://eetd.lbl.gov/l2m2/waterworks.html UV Waterworks.]]]
* [http://youtu.be/-ksYv-EX9EQ Sharon Davis Design and UV Water Filtration in Rwanda.]
* Commercial UV units: [http://www.purestfilters.com/ultraviolet.htm Ultraviolet Water Purification Systems Available from Purest Filters.com.] Prices start at USD$ 365.
* Commercial UV unit: [http://eetd.lbl.gov/newsletter/cbs_nl/nl09/cbs-nl9-waterworks.html UV Waterworks: Reliable, Inexpensive Water Disinfection for the World.]
* [http://energy.lbl.gov/iep/archive/uv/pdf/LoV-final-results.pdf Low Cost UV Disinfection System for Developing Countries: Field Tests in South Africa.] Ashok Gadgil, Peter Miller, Ndirangu Kibata.
* [http://www.ultraviolet.com/microorgan.htm What microorganisms are deactivated by germicidal ultraviolet light?] Ultraviolet.com.
===References===
<references/>
===Acknowledgements===* [http://wwwdocs.whowatsan.intnet/water_sanitation_healthDownloaded_Files/dwqPDF/wsh0207/en/index4Sobsey-2002-Managing.html pdf Managing Water in the Home: Accelerated Health Gains from Improved Water Supply. Heat and UV Radiation]or ([http://www.who.int/water_sanitation_health/dwq/wsh0207/en/index4.html alternative link]). World Health Organization (WHO, ) 2002.
* [http://web.mit.edu/invent/www/ima/gadgil_bio.html Courage: Ashok Gadgil.] From the book: Inventing Modern America: From the Microwave to the Mouse. David E. Brown. MIT Press.