INTRODUCTION
One of the problems with using surface water as a
water source in northern climates is often the pre-
sence of humic substances.This gives the water a
high colour and total organic carbon (TOC) levels.
Removal of humic substances is required since
coloured water is unattractive to consumers, results
in colouring of clothes during washing, and can
cause odour and taste. Humic substances also lead
to the formation of disinfection by-products when
water is chlorinated. Carcinogenic, halogenated
compounds resulting from the chlorination of
drinking water has been a major concern since their
discovery in the early 1970s (Rook, 1974). Since
then, a considerable amount of research has been
carried out in order to minimise their formation in
drinking water. One possibility is to replace chlori-
nation for main disinfection by ozonation. Ozona-
tion is also an ecient treatment process for