Validation, Design and Operation of UV Systems According to the Uspea UV Disinfection Guidance Manual

Since more than a decade, several countries in Europe started to accept the widespread use of ultraviolet (UV) systems for the disinfection of drinking water. The history in the USA of UV technology for that particular application is still young in comparison: Only over the last 2 - 3 years, the focus of the North-American municipalities and designers shifted towards UV as an additive disinfection possibility ([1] describes North-American and European similarities and differences in detail).The most important precursor of the increased attention was the release of the USEPA UV Disinfection Guidance Manual (“UVDGM”; 1st draft release in 06/2002 and 2nd draft release in 06/2003 [2], also see very useful overview in [3]). With the USEPA officially preparing the ground of giving correctly sized UV systems inactivation credits for Cryptosporidium, Giardia and virus, UV becomes available for US-American utilities as an important disinfection tool with a series of benefits in regards to health and environmental friendliness.The UVDGM also gives guidance to what a .correctly sized. UV system actually is: In order to arrive at a .correctly sized. UV system, it first of all has to undergo a validation process. This is actually the case of every UV reactor model, a UV manufacturer wishes to use in the municipal drinking water market. Secondly, it needs to be operated within the boundaries of the successful validation.A big challenge to all, that wish to use UV in accordance to the UVDGM, is that a multitude of UV dose rates (or better: Reduction Equivalent Doses = REDs) are acceptable, depending on the actual target organism and log inactivation credit (project-specific sizing). Secondly, it does not specify one sole method to arrive at a specific UV dose but allows three possibilities (validation-specific sizing). Finally, there are even two approaches to arrive at a certain inactivation credit (validation/manufacturer-specific sizing).Overall, the possible variations and project-, customer- and manufacturer-specific requirements lead to a very complex design scenario.