The effective UV-dose in a UV-reactor depends on the transmission and the flow rate of the water being irradiated as well as on the design of the plant and the hydraulic behavior. Since there is no possibility for a direct and simple dose measurement in such a system, it is necessary to develop a testing procedure which estimates the hygienic safety of such a plant. B. subtilis (ATCC 6633) spores were suspended in potable water and irradiated in a commercially available drinking water UV plant with varying flows (0.5 to 7.5 m3/h) and transmission (3 to 80 %; thickness 10 cm).
Sodium thiosulfate and adenosine were used as transmission reducing substances. Because of the known UV sensitivity of the spores it was possible to calculate the effective dose in the reactor as space radiant exposure for each test. The data resulted in an individual diagram of efficiency. It was shown that this testing procedure is suitable for the evaluation of the disinfection capacity of UV plants and the estimation of the field of application depending upon transmission and flow rate of the water being irradiated.