Dissolved air flotation (DAF) plays an important role in processing wastewater streams containing heavy loads of fats, oils, greases, and organic and inorganic particles. The critical mechanisms to maintain within the DAF include: a contact zone with high densities of small bubbles (~40-80 micron bubble diameters), conditions within that zone which promote connection of neutralized particles to those bubbles, floating the particle/bubble groups to the surface, and removal of those solid groups in the DAF float. Pretreatment to the DAF system can result in higher DAF treatment capacity, excellent chemical savings, reduced maintenance costs and improved effluent quality. It can also reduce water content in the final solid waste which can potentially lead to significant reductions in sludge disposal costs.
A large body of research regarding DAF theory, operation and efficiency has been published since the 1970s. Key findings with respect to optimum DAF operational conditions have been published by prominent DAF experts And are well summarized by Edzwald.1 The author describes several points, two of which are of particular interest when evaluating the use of a prefilter in front of a DAF.