AWWA JAW17284

Dissolved-air flotation as a primary clarification stage for the production of potable water is particularly effective for the treatment of algae-laden waters and low-turbidity, highly colored waters. Flotation has several process advantages over sedimentation it can produce better water quality; it can be operated at high surface loadings, resulting in relatively small and shallow plants; and it can be started up quickly, with a steady water quality being achieved within forty-five minutes. Also, the solids concentration of the sludge produced is significantly higher than that of sludge produced by sedimentation. This article discusses the design parameters for dissolved-air flotation plants and gives detailed information of the design of flocculation and flotation tanks, the air saturation system, the production of microbubbles, and the different sludge removal systems that can be used. Performance data are given for flotation plants used for the clarification of several raw waters, with special emphasis on the treatment of algae-laden waters and low-turbidity, highly colored waters. A cost comparison between flotation and sedimentation is also presented, taking into account both capital and operating costs. The overall costs of the two processes are similar. The final process selection will depend on the additional advantages offered by both processes. Includes 13 references, tables, figures.