The most popular chemical used for water disinfection is chlorine which, is largely effective except that there are some microbial pathogens, such as Cryptosporidium and Giardia, that are resistant to chlorine disinfectant, also chlorine when added to our water, combines with other natural compounds to form Trihalomethanes (chlorination byproducts), or THMs. These chlorine byproducts trigger the production of free radicals in the body, causing cell damage, and are said to be carcinogenic.

Due to these reasons world over Water treatment operators, both large and small, are turning to ultraviolet radiation (UV) as an alternative to reduce or eliminate the use of chlorine for disinfection since Ultraviolet (UV) water treatment systems compared to traditional water treatment methods, are reliable, effective, completely chemical-free, environmental-friendly, and create no harmful by-products.

UV light is the invisible radiation within a range of the Electro-magnetic spectrum.

It is measured in millionths of a millimeter i.e. Angstrom units (A) or nanometers (nm). 1nm = 10A

The UV spectrum is from 100 nm to 400 nm or 1000 A to 4000 A and lies in between the X-rays and visible light spectrum.

The UV-C band contains the wavelengths (250-270nm) which are very effective in destroying many microorganisms (optimum wavelength is 254nm). This range is also called the germicidal range.

The three types of UV radiation are classified according to their wavelength. They differ in their biological activity and the extent to which they can penetrate the skin. The shorter the wavelength, the more harmful the UV radiation. However, shorter wavelength UV radiation is less able to penetrate the skin.

The UV radiation spectrum is invisible & divided into three regions called UVA, UVB and UVC. UV-A 320 to 400 nm, UV-B 280 to 320 nm, UV-C 100 to 280 nm.

The UV-C band contains the wavelengths (250-270nm) which are effective in destroying many microorganisms (optimum wavelength is 254nm). This range is also called the germicidal range and primarily has a surface effect.

As sunlight passes through the atmosphere, all UVC and most UVB is absorbed by ozone, water vapour, oxygen and carbon dioxide. UVA is not filtered as significantly by the atmosphere.

Short-wavelength UVC is the most damaging type of UV radiation. However, it is completely filtered by the atmosphere and does not reach the earth’s surface.

Medium-wavelength UVB is very biologically active but cannot penetrate beyond the superficial skin layers. It is responsible for delayed tanning and burning; in addition to these short-term effects, it leads to skin ageing and significantly promotes the development of skin cancer. Most solar UVB is filtered by the atmosphere.

The relatively long-wavelength UVA accounts for approximately 95 percent of the UV radiation reaching the Earth’s surface. It can penetrate into the deeper layers of the skin and is responsible for the immediate tanning effect. Furthermore, it also contributes to skin ageing and wrinkling. For a long time, it was thought that UVA could not cause any lasting damage. Recent studies strongly suggest that it may also enhance the development of skin cancers

Yes, it can. Germicidal UVC lamps kill up to 99.9% of most viruses, airborne bacteria and mold spores.

If not designed, used, or implemented properly, direct exposure to germicidal ultraviolet equipment can have damaging effects on both materials and people. Overexposure to UV-C lighting can harm humans in a variety of ways, such as eye and skin damage. It can also cause damage to materials, such as the erosion of rubber gaskets or plastics.

However, when designed well, keeping in mind safety considerations UV disinfection is very safe, as no radiative properties remain in treated air/water and there is no fear of overdose.

UV as a disinfection principle is effective against all microorganisms, provided the correct dosage is applied. If the proper UV dose is not used, then the microorganism will not be killed and instead, be put only into a dormant state.

• • UV Dose = UV Intensity x Residence Time x Area (The Unit is microwatt seconds/cm2 (uws/cm2)).
  • UV Intensity is dependent on Lamp type, Lamp power, Reactor geometry, Water quality wrt to transmission & total suspended solids.
  • Residence time is dependent on the Flow rate, Baffle design and Reactor design.
  • The UV reactor design is critical to obtaining proper UV dosage in the system.

Ozone is a particularly effective absorber of UV radiation. As the ozone layer gets thinner, the protective filter activity of the atmosphere is progressively reduced. Consequently, the people and the environment are exposed to higher levels of UV radiation, especially UVB.

Ozone depletion is caused by human-made chemicals released into the atmosphere and will continue until the use of chlorine and bromine compounds is drastically reduced.

International agreements, in particular the Montreal Protocol, are gradually succeeding in phasing out the production of ozone-depleting substances. However, the long life-span of the chemicals already released will cause ozone depletion problems to persist for many years to come. A full recovery of the ozone level is not expected until 2050.

Ultra-violet radiation (or UV) is a proven, effective process for disinfecting water, air or solid surfaces that are microbiologically contaminated.

The effects of UV as a disinfection agent have been well-documented by the scientific community.

The U.S. Environmental Protection Agency recognizes the use of ultra-violet as a proven, viable technology;

“Ultraviolet (UV) radiation has been found to be an effective disinfectant…. The simplicity of installation, ease of operation and maintenance, and low costs relative to chemical disinfection make UV a useful disinfection technology option.”

Ultraviolet is preferred compared to other methods of disinfection due to the following reasons;

• UV as a disinfection principle is effective against all microorganisms (bacteria, virus and cysts.)
• UV provides disinfection on contact (it is instantaneous); it does not have any residual disinfection properties left in treated Air/Water at all.
• UV disinfection is very safe, as no radiative properties remain in treated Air/Water and there is no fear of overdose. There are no dangerous chemicals to handle or monitor.
• UV has an economical system cost and a very low cost of operation.
• UV is environmentally friendly. There are no byproducts from the UV process and nothing is discharged into the environment.
• UV causes no change to the taste or odour of the water disinfected.
• UV does not remove any minerals, which is a health benefit and provide water with its good taste.
• UV systems are very easy to install and maintain.

No! Germicidal UVC sterilizes only what it comes in contact with. It cannot penetrate through substances, which means it has only a surface effect.