UV Disinfection of Water

In the US, water disinfection with ultraviolet rays is a well known technology to minimize the microbiological pollution of treated waste water effluents. In drinking water the method is not applied. In contrast, the situation in Europe is different: Whereas waste water disinfection is “new”, drinking water disinfection with ultraviolet rays is looking back on a 100 year old tradition. The following overview summarizes the European experiences UV disinfection of drinking water and gives an outlook on possible solutions for the US with special reference to recent trends in drinking water disinfection.

Historical Background
The first technical UV installation was made in Marseille, France 1910. Nevertheless a couple of years later the water works replaced it by chlorine which was available without costs. In the fifties UV disinfection came up again as an alternative to chemical disinfectants for special drinking water applications (remote areas), such as disinfection of water in mountain areas. The oldest UV installation worldwide which is still on duty is one of these (Küssnacht am Rigi, Switzerland). Later on the UV share of the disinfection market increased due to better technical solutions, reliability of UV lamps and constantly growing experiences. In the seventies the market for UV was going to explode with respect to recent drinking water research at that time. Since Rook came out with the first results of his research on chlorine disinfectionby- products everyone was interested to find possible alternatives. UV was the new subject of interest. UV installation became bigger in comparison to the old times. Mid sized water works (up to 100.000 people supplies) were using UV more often. In recent times UV is accepted as a fully reliable and safe disinfection method. The biggest installation worldwide supplies 82 MGD (Helsinki, Finnland).

Disinfection Mechanism of Ultraviolet Rays
UV rays in the UVC region (200-280 nm) are targeting bacterial and viral DNA. The main absorption of DNA is 260 nm. As every disinfection method the effect relies on a CT product which must be transferred into intensity times time in case of UV. This leads to: Intensity (W/m2) x time (s) = J/m2 = 0,1 mJ/cm2 = 1000 mWs/cm2

UV Lamps

  • There are 3 lamp sources available on the market:
  • Low pressure Low intensity (LowLow)
  • Low pressure High intensity (LowHigh)
  • Medium pressure (MedHigh)

UV lamps are generating UV rays due to the formation of a mercury plasma which is induced from electrical energy. The main parameter to compare UV lamps is generally the efficiency in terms of the percentage of the electrical energy which is transferred into UV emission.The total output has to be related to the lamp length (discharge length).