The increased acceptance of UV drinking water disinfection is attributed, amongst other reasons, to the better understanding of the process and the higher quality assurance of the UV disinfection devices. Establishment of quality standards on the requirements, including validation testing and certification of commercial UV devices, have provided the basis for the safe application of UV irradiation as primary disinfection for drinking water supply.
So far, the Austrian national standards ÖNORM M 5873-1 (low pressure UV radiation; versions 1996, 2001), ÖNORM M 5873-2 (medium pressure UV radiation; version 2003) and the Work sheet W 294; versions 1997, 2006) by the German Association for Gas and Water (DVGW) have had been established in Europe.
The regulations are based on the following basic prerequisites and principles:
- The knowledge of the UV resistance of pathogens and indicator microorganisms relevant in water hygiene based on exactly controlled UV inactivation laboratory studies
- Standardized UV (duty) radiometers for the surveillance of the irradiation process during practical operation, measurement in W/m². These radiometers need to be annually controlled by means of a reference radiometer traceable to a national calibration office
- A full scale biodosimetric validation test under well-defined operation conditions by variation of water flow, UV-254 nm transmittance of the water and the UV lamp power
- A UV-254 nm calibrated microorganism serving as biodosimeter to measure the Reduction Equivalent Fluence (J/m²) representing the microbicidal effective UV fluence (dose)
After careful consideration and negotiations over several years, a harmonization between the Austrian and German regulations has recently been achieved. This facilitates from now on the tasks of waterworks operators, of the manufacturers of UV devices and of the authorities for the benefit of the drinking water consumers.
The UV devices validated by the ÖNORM/DIN standard offer a guaranteed UV-254 nm fluence of at least 400 J/m² during operation. International studies show that by applying this fluence a 4 to 6 log inactivation of the most relevant water-borne pathogens is achieved. If the risk assessment of the water supply system reveals the necessity of enhanced inactivation conditions, e.g. if the occurrence of adenoviruses must be expected, a multi-barrier disinfection is recommended.
In this case, UV radiation is combined e.g. with a chlorine dioxide treatment. In this way, the respective advantages of each individual technique, the high potential of UV radiation to inactivate protozoa and the high virucidal efficiency of chlorine-based disinfectants, can be perfectly combined. However, it has to be pointed out, that an application of UV irradiation below a REF of 400 J/m² cannot be recommended, since a fluence below 400 J/m² is needed to overcome the photoreactivation of bacteria. Repair of UV damages and regaining infectivity of bacterial pathogens would be the consequences.
References
ÖNORM M 5873-1:2020 / DIN 19294-1:2020:
Devices for the disinfection of water using ultraviolet radiation
Part 1: Devices equipped with UV low pressure lamps - Requirements and testing
ÖNORM M 5873-3:2020 / DIN 19294-3:2020:
Part 3: Reference radiometers for devices equipped with UV low pressure lamps - Requirements and testing
