Alteration of Chemical Disinfection to Environmentally Friendly Disinfection by UV-Radiation

In the summer season the waterworks Ponikve distribute daily approximately 7000 m3 of treated lake water "Jezero" through the complex drinking water distribution system of the northern part of the island Krk, Croatia. Until 2000 disinfection was done by chlorine and chlorine dioxide, which may be hazardous to human health by itself or by its by-products. In order to avoid problems with disinfection by-products of both chlorine and chlorine dioxide that were present due to presence of natural organic matter in lake water, the large-scale pilot test of UV irradiation for disinfection of drinking water for the part of distribution system was started in 2000. Four microbial groups, total coliforms, fecal coliform, fecal Streptococcus and total microbial count group have been used as indexes to test disinfection efficiencies. Samples were taken before and after the irradiation and at the point of use from distribution system - approx 2000 m far from the UV-disinfection unit. This paper presents the results of a 9 months investigation period that includes different seasonal qualities of raw water. During the test period intensive bacteriological monitoring showed that microbial water quality standards could be held. Despite the natural organic matter (NOM) content and very high summer temperatures of water (up to 30°C) and quite a complex distribution system, the disinfection process was successfully conducted solely with the UV-radiation. The waterworks Ponikve continues to change chemical disinfection equipment to UV-radiation.