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2.4.3 Ultraviolet Radiation Disinfection

The use of ultraviolet radiation (UV light) also is an effective disinfection technology. Exposing the water to UV radiation of sufficient will result in the destruction of a large number of viruses.

Technology Description

Ultraviolet radiation is produced with low-pressure mercury vapor lamps. Their radiation energy can reach up to 200 watts, with a lifetime of between 2,000-4,000 hours. The radiation wavelengths are between 2,000-3,000, and their effectiveness is best on microbes of about 250 mm. In using this disinfection technology, a very thin sheet of water has to flow very close to the UV lamp, in order to permit the radiation to penetrate suffiently through the water. The water to be treated also must be completely clear, with no traces of turbidity.

Extent of Use

The use of this technology for disinfecting water is relatively limited in the West Asia region, focusing on the local scale and for laboratories. This technology cannot be used to disinfect large networks of potable water. Several rural residences and recreational parks use this technology to disinfect the groundwater that constitutes their primary water supply. The use of this technology for industrial-scale water disinfection is beginning to attract attention.

Operation and Maintenance

In using this technology, the water to be treated has to be clear and without turbidity. It also should not contain significant quantities of iron, organic colloids or planktonic microorganisms that could be deposited on the pipes, thereby reducing the radiation effect. The water has to flow through in the form of a thin film of a thickness of no more than 15-25 cm. In general, a 36-watt UV lamp is capable of disinfecting about three cubic meters of water per hour. The water is passed under pressure through a tube which contains a quartz tube inside of it to generate the UV radiation source. In its passage, the thin water sheet is exposed to the disinfecting UV radiation, thereby destroying the germicidal cells contained in it, or at least stopping them from reproducing or otherwise impacting the water medium. An energy consumption of about 40 watts/hr is needed to effectively disinfect one cubic meter of water.

Level of Involvement

Interest in this technology is relatively limited in the West Asia countries, primarily because of its operational difficulties and the need to frequently replace the lamps. The quantities of water that can be effectively treated within a reasonable time period is also limited. Thus, the technology can best be used to disinfect small quantities of water at a given site for use in laboratories and limited water consumption centers.

Costs

The relative costs of this technology are limited to the price of equipment and its installation. The maintenance costs primarily comprise the price of the radiation generating lamps. The technology does not require any specific maintenance, except for replacing the lamps when they lose their strength, and repairing any malfunctioning equipment.

Effectiveness of the Technology

This technology is considered very effective in killing a large number of viruses, but is limited to relatively small quantities of water.

Suitability

This technology can be used in locations with limited water consumption needs.

Advantages

The advantages of this technology are as follows:

• It is a clean, effective technology, suitable where only limited quantities of disinfected water are needed (e.g., water analysis laboratories of industrial centers);
• It does not have large maintenance requirements.

Disadvantages

The disadvantages of this technology are as follows:

• The disinfection effect is temporary, and does not last for long periods of time;
• Only a limited quantity of water can be efficiently treated;
• There is a continuous need to replace UV lamps, which is costly and requires equipment not readily available on the local level.

Cultural Acceptance

No obstacles exist to prevent the spread and acceptance of this disinfection technology.

Further Development of the Technology

Further development of this technology should focus on making it more applicable to disinfecting potable water networks, similar to the manner in which its industrial development has made it capable of disinfecting treated sewage water.

Information Sources

Contacts

Chemist Ibtesam Nahhas
Laboratory Directorate
Potable Water and Sanitary Drainage Agency
Damascus, Syria
Tel: 2230684
Fax: 2218001

Chemist Saad Allah Al-Shawwaf
Head, Laboratory and Environmental Directorate
Ministry of Irrigation
Damascus, Syria
Tel: 2218251
Fax: 2246888

Fouad Abu Samrah
Arab Center for the Studies of Arid Zones and Dry Lands
P.O. 2440
Damascus, Syria
Tel: 523087
Fax: 5323063

References

Degremont. 1979.Water Treatment Handbook, 5^th Edition. 1186 p.

ACSAD/AFESD (Arab Fund for Economical and Social Development). 1985. Lectures of the water resources technology workshop. Workshop, 2-23 November 1985, Damascus, Syria.

WHO. 1997. Technological manuals of water supply systems in small communities. World Health Organization, Regional Office for the Middle East, Regional Office of Environmental Health. 292 p.

 

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