Long-term Experience of Ozone and UV in Large Waterworks: Case Helsinki Water

摘要

Treating the low quality raw water in Helsinki at 1970s demanded high chlorine doses resulting in the formation of chlorinated by-products. The new raw water contained organics from pulp mill effluents. The aim of organics removal studies was to find effective and best available treatment technique to improve the quality of water. Ozonation proved to be efficient and was introduced in 1979. Raw water coming from Lake P?ij?nne was taken into use in 1982. In ozonation a part of NOM decomposes causing biofilm formation in the network. As the result of intensive organics removal studies GAC-filtration was introduced in 1988 and also UV-disinfection to inactivate microbes originating from carbon. After 27 years of operation the old air-fed ozonators needed ur- gent repair. The cost evaluation showed that replacing them by two new oxygen ozonators was 20 % cheaper.