Both low pressure and medium pressure UV systems exploit the power of UV radiation. However, there is a huge difference in their technology and effects they have on the treated water. In this article we aim to explain why UV is not always the same UV and also why it is crucial to distinguish these two technologies. As producers of both technologies, low pressure and medium pressure UVs, we can provide an independent view.
To find out how the UV light works and also for other basic information about UV for water treatment, see our previous article: HOW UV LAMP WORKS? LOW PRESSURE AND MEDIUM PRESSURE UV
Both low pressure and medium pressure UV target the DNA of microorganisms. When the UV gets to the DNA it basically cuts it into pieces and the genetic information is rearranged. As a result, the cell is not able to reproduce and thus, is considered dead (unable to multiply to infectious amount).
The basic difference between low pressure and medium pressure UV is the UV radiation they emit. Simply put, UV radiation has some wavelengths it consists of and the broader the spectrum of wavelengths is, the more effective the UV disinfection. It is because each organism or substance is destroyed and decomposed by a certain wavelength.
Low pressure lamps emit a single wavelength at 254 nm whereas medium pressure UVs emit a broad spectrum of wavelengths all over the germicidal UV areas – from 200 to 600 nm. You can see the wavelength spectrum in the graph below. The blue line represents low pressure UV and the purple line represents medium pressure UV.
In the graph, you can also see the wavelengths at which chloramines are eliminated. Chloramines are an issue in pool and Jacuzzi water. But not all chloramines are bad. Trichloramines, main part of bound chlorine (sometimes called combined chlorine) are what needs to be eliminated. They are the source of the typical chlorine pool smell, asthma, eye redness, allergies, skin iritation or drying. And as the graph suggests, trichloramines can only be eliminated by medium pressure UV systems.
It works similarily with other microorganisms and particles in water. Medium pressure UVs remove what low pressure UV does plus much more.
It is well-known that bacteria and other microorganisms are capable of repairing their DNA after being damaged by ultraviolet (UV) radiation. This phenomenon known as ‘reactivation’ is a natural defense mechanism that has evolved over millions of years. This self-repair ability poses obvious problems when UV disinfection technology is used to treat potable water, swimming pool water, effluent or other liquids.
A study number 1 proved that polychromatic medium pressure UV radiation causes irreparable (permanent) damage to bacteria and microorganisms, whereas monochromatic low pressure UV does not. For any industry where UV is used to disinfect water or effluent, the operator needs to be sure that the water treatment is permanent – that is reason why to use medium pressure UV systems!
LIFETECH produces medium pressure UV systems from 250 W to 18 kW. Other types on request.
Left: LifeUVM ProfiPure (250 W), right: LifeUVM EXCELLENT (up to 18 kW)
In chlorinated pools the content of chloramines, namely bound or combined chlorine, is used as the parameter of water quality. The less of bound chlorine, the better quality the swimming pool or Jacuzzi water has. Exactly this combined chlorine is the particle responsible for the known unpleasant chlorine smell and is drying skin, causing eye redness and respiratory problems.
Furthermore, especially thrichloramine, is a known cause for an eventual increased incidence of asthma for children which are regularly swimming in chlorinated pools. Moreover, the staff of the swimming pool such as lifeguards and instructors can easily get these health problems if the level of bound chlorine is high in the long-run. A last thing not to forget is that thrichloramines are also causing corrosion so its presence in the swimming pool water can lead to damages of the building construction.
Therefore the reduction of chloramines in the pool water protects the health of all and protects the building construction itself resulting in cost savings for dillution water or building repairs.
The last version of German Norm DIN 19643 clearly states:
Only UVM (medium pressure UV) systems can properly disinfect swimming pool water and lower the level of bound (combined) chlorine. Low pressure UV systems are therefore not appropriate to be used for these effects!
One of the main reasons why a lot of main institutions were not using medium pressure UV technology was a short life cycle of the lamps. Now with expected 18 000 hours of UV lamp lifetime, we can forget about this worry.
1) Zimmer, J. L. & Slawson, R. M. (2002). Potential repair of Escherichia coli DNA following exposure to UV radiation from both medium- and low-pressure UV sources used in drinking water treatment. Applied & Environmental Microbiology, Vol. 68, No. 7, 3293-3299.
2) The latest version of the German NORM for pools DIN 19643, November 2012
