Use of dissolved air flotation in potable water treatment in Finland

The basic concepts of treating humic waters with dissolved air flotation are discussed emphasizing the important role of zeta potential in the forming of floc-air-bubble-agglomerates. Then practical experiences from Finnish drinking water treatment plants are presented. When surface water is used as a raw water, it is more or less humic. Thirty-six such plants have dissolved air flotation as a clarification process, the oldest one dating from 1965. They serve about one million people. All of them are working well proving that dissolved air flotation is a suitable method in humic water treatment. Some special cases are discussed in detail. These are cases where sufficient data about design, operation and costs are available and which it is hoped can help other designers. The last plant referred to is an example of an advanced treatment process where dissolved air flotation is an integrated unit process.