The use of dissolved air flotation in municipal wastewater treatment

Flotation can be used in municipal wastewater treatment plants in different ways. Since the pollutants in wastewater to such a large extent are associated with particles, a very substantial treatment efficiency can be reached at a very small space, by using flotation in a chemical (or enhanced primary) treatment scheme. This is demonstrated in this paper with reference to results from small, prefabricated chemical plants based on flotation, which are frequently used in Norway. If used in connection with biological plants (for instance for nitrogen removal), the combination of biofilm reactors and flotation is especially advantageous because coagulation/flocculation/flotation can be placed directly after the bioreactor. Results from two such plants in Norway are presented. Recommendations with respect to design and operation of flotation plants in wastewater treatment are given.