In the last decades UV irradiation as a tool for drinking water disinfection has gained remarkable popularity especially in Europe but also throughout the world. Besides many advantages of this technology it became evident that the microbicidal efficacy of UV plants for water disinfection
neither can be measured directly nor can it be calculated. The reason for this facts is that during UV irradiation in flow through systems several factors act in complex combination, as there are: the intensity of the UV lamps, the water flow, the transmittance (253.7 nm) of the water being
irradiated and the hydraulic properties of the UV device. From inhomogeneous irradiation geometries and individual, unpredictable hydraulic behaviors dose distributions result. Additionally it has to be pointed out that a control of disinfected water by the means of measuring the routinely
used bacterial parameters (E. coli and enterococci) has to be regarded as insufficient due to the extremely high sensitivity of these bacteria to disinfectants. Therefore besides microbiological investigations technical conditions have to be defined to ensure safe drinking water disinfection. For
public health reasons three prerequisite for the safe and reliable application of UV disinfection have to be fulfilled: The knowledge of the UV resistance of health related microorganisms transmittable by water: Based on these data a minimum
UV fluence required for safe drinking water disinfection has to be established. A standardized procedure for the testing and surveillance of UV drinking water disinfection plants, by which alarmpoints and an approved range of application (maximum flow,
minimum reference irradiance and minimum UV transmittance of the water are fixed. Determination of an admissible range of operation and alarm points for each type of commercial UV plant and control of these parameters during the practical operation of
a UV plant in the water work: For measuring the reference irradiance commercial UV plants have to be equipped with a calibrated UV sensor fixed at a standardized measuring window on a reference position in the irradiation chamber (sensor reading in W/m2). The sensor has to be
removable during operation of the UV plant to enable the check against official specifications. We introduce the Austrian National Standard ÖNORM M5873-1 (2001) in which these aspects have been successfully included (2).
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