Methods for testing the efficacy of ultraviolet light disinfection devices for drinking water

Ultraviolet (UV) light devices have been used in the disinfection of raw drinking water at the point of use, but the need for reliable fail-safe devices has been demonstrated. A study was performed to establish test protocols that could be used to ensure adequate disinfection under adverse conditions, particularly in the presence of turbidity and color in the water. A test protocol was devised for fail-safe light sensors by using a color or turbidity agent in the feed solution to reduce the UV dosage to the established minimum limit, 16 000 PW-s-cm-z, in order to determine whether the fail-safe device was properly calibrated and functional. Three commercial UV devices were tested with this method; one device was satisfactory, the second unit was set too low by a factor of 1.6, and the third unit was set too low by a factor greater than 2.