Rethinking Dissolved Air Flotation (DAF) Design for Industrial Pretreatment

By Charles C. Ross, P.E., Brandon M. Smith, E.I.T., G.E. Valentine, Jr. Environmental Treatment Systems, Inc.



Dissolved air flotation (DAF) has been used with increasing frequency in recent decades for the treatment of industrial wastewater. Advances in the technology have expanded the range of applications for DAF; however, engineers and designers frequently use outdated and insufficient design data to design and specify DAF systems for industrial pretreatment. Discussions of advances in DAF design are discussed, including recycle pressurization, improved white water systems, enhanced chemical programs, and expansion of manufacturers’ base of experience in industrial applications. The need for treatability testing is also emphasized. A case study illustrating these advances is presented, describing the application of DAF at a poultry rendering facility.




Dissolved air flotation (DAF) has gained widespread usage over the last forty years for the removal of suspended solids (TSS), oils and greases (O&G), and biochemical oxygen demand(BOD) from wastewater and other industrial process streams. DAF systems are frequently used to provide wastewater pretreatment, product recovery, and thickening of biological solids in industries ranging from food processing to pulp and paper to petrochemicals.


Years of experience in specifying DAF systems for industrial applications has shown that many engineers, designers, and end users have come to rely on DAF design information from common reference materials, such as engineering handbooks. Such reference materials base specification of DAF systems on parameters such as recycle rate and pressure, air-solids ratio, hydraulic loading, and surface loading. However, the values provided in common references for these parameters tend to be outdated or inadequate when compared to data from actual operating systems.


In other words, the reliability and performance of DAF systems have improved with increased use of this technology, but there has not been a corresponding change in the standard design criteria for these systems. Moreover, DAF systems have evolved to a point where some of these parameters are not as critical to the design and are frequently not used for design purposes. This paper will address these issues and provide suggestions for improving the design and specification of DAF-based treatment systems for industrial wastewater.



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