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UV-tubes

Author/Compiled by
Raju Shrestha (Environment and Public Health Organization, ENPHO)
Dorothee Spuhler (seecon international gmbh)
Executive Summary

The bactericidal effect of concentrated ultraviolet (UV) light is used in many areas and in many set-ups. For drinking water treatment, simple, commercially available UV tubes can be used to kill pathogenic microorganisms in the drinking water. Such UV tube water disinfection devices are an effective, low-cost and simple mean for a very rapid disinfection. They generally consist of a pipe, through which water slowly flows, and in which an UV light bulb is installed, which can be run on electric or solar power. There are many ways to design UV tubes devices and they can be used at household, community or institutional level. Even though very effective, however, chemical or physical pollution (e.g. salinity, heavy metals turbidity) cannot be treated and in opposition to chlorine, there is no residual disinfection effect.

Advantages
Large quantities of disinfected water can be obtained quickly
Minimum behaviour change required
Can be constructed with locally available material
Highly effective on broad range of pathogens, including E. Coli, Guardia and Cryptosporidium
No risk for DBP formation (e.g. trihalomethanes)
Inactivation independent of pH and temperature
No unpleasant taste or odour (as it can appear for chemical treatments)
No transportation, storage or handling of chemicals
Disadvantages
Higher cost of equipment when compared with chlorine solution
Requires regular power source for operation
Lamp tube needs replacement every 6-12 months
Some investment for installation is required
UV lamp needs to be cleaned regularly and handled with care because of their mercury content
Only effective for microbial pollution
No residual disinfection effect and risk of re-growth or recontamination
In Out

Freshwater

Drinking Water

The bactericidal effect of concentrated ultraviolet (UV) light has been known over many years and is used in many areas and set-ups. The first use of UV light for drinking water disinfection has been reported to be in France in 1910. With the recent development of the UV tube, using locally available components, this technology is now a viable household water treatment method (CAWST 2009). Facing the challenge that disinfection by-products (DBPs) are formed during chlorination of water containing high organic contents, simple physical instead of chemical disinfection methods, such as UV tubes have gained in interest (U.S. EPA 1999).

Different design of a household / community level UV tube disinfection system.

Different design of a household / community level UV tube disinfection system. Sources: http://i.treehugger.com/files/waterfilter_500x375.jpghttp://edge.rit.edu/content/P07402/public/originalDesign2.jpghttp://ct3.pbase.com/v3/49/542549/4/48964881.DSC_0083.jpg; [Accessed: 20.05.2010]

A typical UV system provides a flow path surrounding a UV lamp, structured to provide close proximity of the water flow along the length of the UV lamp all by preventing direct contact.

UV Tube Design Concept from the Fundacion Cantaro Azul. Source: CAWST (2009)

UV Tube Design Concept from the Fundacion Cantaro Azul. Source: CAWST (2009)

UV Radiation Disinfection Mechanism

The UV tube is basically the same as a commercial fluorescent bulb, except that it lacks the phosphor coating and the glass exterior is replaced by fused quartz. This means the bulb emits mostly UV light. UV light is generally defined to be wavelength of electromagnetic radiation shorter than 400 nm and is further divided into UV-A (315-400nm), UV-B (280-315nm) and UV-C (200-280 nm). UVA and UVB are responsible for sun tanning and sunburning. UVB is partly filtered out by the atmosphere and only a few percent reach the earth surface. This is good, because UVB light can be directly absorbed by DNA, where it would induce cellular damage. UVC also penetrates cells and damage the DNA, but it is almost entirely filtered out by the ozone layer. The UV tubes used for disinfection do contain the whole spectrum of UV light, including the UVB and UVC. The light, when it reaches microbial cells leads to damage of the genetic material (DNA), rendering them unable to replicate.
The bulbs are suspended inside a larger tube in a covered channel. Water enters at one end and flows through the outlet at the other end. While the water flows through the tube, the UV light emitted from the bulb inactivates the microorganisms. The inactivation is directly related to continuous UV dose and depends on the intensity of the UV light and the duration of UV exposition. The height of the outlet determines the depth of the water in the tube and thus the hydraulic retention time (HRT, CAWAST 2009). In theory, the hydraulic retention time is equal to the exposure time of the microorganisms and should be designed, depending on the bulb intensity, to achieve a sufficiently long contact time for all microorganisms to be inactivated. For the calculations of the HRT, the intensity of the bulb may be adjusted according to the water depth of the farthest point away from the light source as the UV light is attenuated as it penetrates the water.

Effectiveness

UV tubes are effective in inactivating most pathogens, including bacteria, viruses, and cyst forming protozoa such as cryptosporidium (CAWST 2009). Yet, the effectiveness depends strongly on the UV dose.

 

Very effective for:

Not effective for

Bacteria

Viruses

Protozoa

Helminth eggs

Turbidity

Chemicals

Taste, odour, colour

Potential treatment capacity of UV tubes. Source: CAWST (2009)

 

UV tubes are not effective for all pollution other than microbial (chemical and physical pollution) and there is now residual disinfection effect during storage of the treated water. The efficiency of UV light for bacterial inactivation is lowered by the presence of organic matter, iron, sulphites, and nitrites. Turbidity can also interfere with UV radiation, protect microorganisms from inactivation and serve as a food source for re-growth after the disinfection step. Therefore, it is common for UV tubes to incorporate a pre-filtration step, such as a settling unit.

Operation and Maintenance

Operation and maintenance of UV tubes is generally low, provided that there is a more or less continuous source of electricity to run the bulb. Once the system is installed, the user needs to make sure that the theoretical flow rate of the water and the corresponding HRT are respected and that the bulb is working correctly. If the bulb becomes dirty, it needs to be taken out and cleaned to maintain the light emission intensity. The systems have generally a long life spam, but bulbs should be replaced at least once every 12 months (CAWST 2009). During any maintenance activity, however it is important that operators or users protect their skin and eyes from the UV radiation as it is also damaging for human cells.



 

Applicability

Ultraviolet is being widely used in the water supply systems for disinfection and has a potential to kill most bacteria, viruses, protozoa or helminths. Though, a more or less continuous energy supply is required and the system is not suitable for removing chemical contaminants or turbidity. There is also possibility of re-contamination during distribution or storage of the treated water as there is no residual disinfection effect. However, as it is only a physical treatment, there is low risk for the formation of toxic disinfection by-products (DBP).
The UV tubes can be produced with locally available material and be installed at household, community or institutional level, as long as electricity is provided.
 

Library references
Further Readings

Disinfection of water by Ultraviolet light

This document shares information on UV introduction, mechanics of disinfection, Ultraviolet dose calculation, estimated lethal dose for microorganisms etc.

INTERNATIONAL WATERGUARD (n.y): Burnaby: International Waterguard

Smart Water Solutions

This booklet on water gives examples of innovations such as the use of sunlight to purify water, effective low-cost water filters, low-cost drip irrigation and locally produced hand pumps that are five times cheaper than imported pumps.

NWP (2006): Examples of innovative, low-cost technologies for wells, pumps, storage, irrigation and water treatment. (= Smart water solutions ). Amsterdam: Netherlands Water Partnership (NWP) URL [Accessed: 06.09.2011]

Smart Disinfection Solutions

This booklet, part of the Smart Water Solutions series provides a wide range of methods and products for home water treatment in rural areas.

NWP (2010): Examples of small-scale disinfection products for safe drinking water. (= Smart water solutions ). Amsterdam: KIT Publishers URL [Accessed: 07.07.2010]

Ultraviolet Water Disinfection

Factsheet summarizing the process, advantages, limitation, monitoring, and operation of UV disinfection.

TECH BRIEF (2000): (= Tech Brief, A National Drinking Water Clearinghouse Fact Sheet, 15 ). URL [Accessed: 19.05.2010]

Conservation et Traitement de l Eau a Domicile

This practical guide provides a review of different processing techniques and adequate water conservation at home and is structured around 10 key questions that should be posed before choosing a suitable solution.

DESILLE, D. ; (2013): Paris: Programme Solidarite Eau (PSeau) URL [Accessed: 06.06.2013]
Case Studies

UV tube as an appropriate water disinfection technology

This master thesis researches UV tube performance, effectiveness and optimization of design at Laboratory (Renewable and Appropriate Energy Laboratory at UC Berkeley) and in the field (near Patzcuaro, Mexico).

COHN, A. ; (2002): Master Thesis. Berkeley: University of California URL [Accessed: 06.07.2010]

Field testing UV Disinfection of Drinking Water

GADGIL, A. ; DREASCHER, A. ; GREENE, D. ; MILLER, P. ; MOTAU, C. ; STEVENS, F. (1997) In: Proceedings of the 23rd WEDC Conference "Water and Sanitation for All," Durban South Africa, September 1-5, 1997. . URL [Accessed: 19.05.2010]
Training Material

UV tube Project Design

Presentation on different designs of UV tubes with field experiences in different countries of the world.

PELETZ, R. ; Berkeley: Engineers for a Sustainable World Engineers World URL [Accessed: 19.05.2010]
Awareness Raising Material

Water Disinfection Systems- Ultra Violet Light

A paper containing frequently Asked Questions on UV light water disinfection.

Government of Western Australia ; Department of Health (DH) (2009): Government of Western Australia, Department of Health (DH)

Alternative Versions to

No Structure Described.