AWWA JAW41509

Although dissolved air flotation (DAF) has been used in Europe for over 20 years, it is a relatively new technology in North America. DAF is considered not only an alternative to sedimentation plants but also a clarification method to improve filtration. Flocculation tanks prior to DAF are typically designed with two stages and a total detention time of 20-30 min. The primary purpose of this research was to investigate the flocculation step prior to DAF, including examining the effects of coagulant type, flocculation time, flocculation stages, flocculation mixers, and flocculation mixing intensity on flotation and filtration performance. Good dissolved air flotation and filtration performance were observed for all pretreatment flocculation conditions studied. The research showed that DAF plants can be designed with flocculation times as low as 5 minutes and that DAF is a robust particle removal process--i.e., it can produce consistently good water quality for a variety of conditions. Includes 8 references, tables, figures.