What is ultraviolet radiation?
Ultraviolet, or UV light is invisible electromagnetic radiation covering the wavelengths bordering x-ray and visible light, within the 10-400 nm range. UV has become a widely accepted method of disinfection in various applications and media as it alters the DNA of micro-organisms, effectively eliminating them.
There are four UV categories:
- Vacuum UV – wavelengths between 10-100 nm
- UVC – wavelengths between 100 and 280 nm
- UVB – wavelengths between 280 and 315 nm
- UVA – wavelengths between 315 and 400 nm
UV as a disinfectant
The fact that UV is a powerful disinfectant has been known for centuries and today the technology is commonly used in a wide array of applications. When micro-organisms are exposed to UV within certain ranges inactivation occurs as the absorbed UV terminally damage their DNA inhibiting the reproductive ability.
UV provides an in-situ germicidal effect, only affecting the surface or media with which the rays are in direct contact unlike chemical agents. It does not produce any disinfection-by-products which are commonly formed when using chlorine, chlorine dioxide and some other chemical agents, it has no smell and does not affect the taste or color of liquids. Also, unlike chemical agents UV is not affected by the temperature or pH.
Parameters to consider for the optimization of micro-organism inactivation are primarily dosage and wavelength, (see table 1 for dosage requirements of specific micro-organisms). The absorbance of different wavelengths differs between organisms which is of importance when choosing UV source.
There are multiple types of UV lamps, the most common lamps are divided into two categories: low- and medium pressure lamps.
Low pressure lamps
These lamps emit UV at a set wavelength, 254 nm and are thus monochromatic. In relation to medium pressure lamps they have lower running temperatures, operate more efficiently, and have a longer lifetime. The single wavelength is oftentimes enough for disinfection of surfaces and airborne organisms, and the parameters regulating the dosage can be adjusted to necessary levels.
Medium pressure lamps
These are polychromatic lamps, meaning they emit a range of wavelengths within the 200-400 nm spectra, the actual span varies between lamps. Compared to low pressure lamps the wider span of emitted wavelengths provides more efficient inactivation of micro-organisms whose peak absorbance is not 254 nm. It should however be noted that medium pressure lamps consume more energy, have higher running temperatures and shorter lifetime.
Designing the UV system
Reactor design, such as its geometry, the selection and arrangement of lamps and quartz sleeves within the reactor, volumetric flows, the dimensioning of a ballast as well as auxiliary equipment are all imperative parts of the design in order to deliver a well-working solution.
In order to design a system, parameters such as flow rates, transmittance, micro-organisms to disinfect and to what grade, maintenance need, OPEX and CAPEX, environmental aspects and target media are some of the things that should be taken into consideration.
|Consideration||Low Pressure||Medium pressure|
|Process Flow||Better for intermittent flow||Needs constant flow|
UV and Ozone
Ozone is generated naturally in two major ways: through corona discharges during thunderstorms and continuously through photolysis of the oxygen molecule in the upper atmosphere. Thus, the ozone layer is generated with UV-rays from the sun which are absorbed by oxygen molecules, providing protection against the harmful radiation.
When producing ozone artificially with the use of UV lamps, air or oxygen is exposed to UV radiation with a 185 nm wavelength. Paradoxically, UV can also be used to destroy ozone, this is achieved when ozone is exposed to 254 nm radiation.
Advanced Oxidation Process – UV and Ozone combined
The synergies of a well-designed UV and ozone treatment system renders hydroxyl radicals, an extremely powerful oxidant with more than double the oxidation potential of chlorine. This is the best-known type of Advanced Oxidation Process, AOP – suitable for the most demanding sanitation applications.
This can be done in two ways, either by using bichromatic lamps, producing and destroying ozone simultaneously in the presence of water or by introducing a source of ozone before a UV lamp within the right wavelength range.
Product parameters – radiance, dose, etc.
|Ultraviolet dosage required for 99,99% reduction of organisms in µWs/cm2 at 254 nanometer|
|Bacillus anthracis – Anthrax||8,700|
|Bacillus anthracis spores – Anthrax spores||46,200|
|Bacillus magaterium sp. (spores)||5,200|
|Bacillus magaterium sp. (veg.)||2,500|
|Bacillus subtilis spores||22,000|
|Leptospira canicola – infectious Jaundice||6,000|
|Salmonella paratyphi – Enteric fever||6,100|
|Salmonella typhosa – Typhoid fever||4,100|
|Shigella dysenteriae – Dysentery||4,200|
|Shigella flexneri – Dysentery||3,400|
|Vibrio comma – Cholera||6,500|
|Mucor racemosus A||35,200|
|Mucor racemosus B||35,200|
|Bacteriopfage – E. Coli||6,600|
|Poliovirus – Poliomyelitis||6,600|
|Common yeast cake||13,200|
- Air disinfection
- Water disinfection and wastewater treatment
- Ultrapurification of water
- Surface disinfection
- Equipment disinfection
- Food & beverage disinfection