A method of oxidation or pathogen inactivation in water supplies using the combination
of treatments of chlorine dioxide and ozone in the sequential steps prior to filtration
and distribution. Results indicate that the addition of chlorine dioxide before
prezonation reduces the bromate formation and chlorine dioxide can be substituted
for preoxidation with ozone, while maintaining the enhanced filtration effects
observed from the presence of a preoxidant. A majority of the chlorite formed from
reactions of chlorine dioxide with constituents in raw water are converted to chlorate
by the following ozonation step.