AWWA WQTC69371

This paper examines significant developments in dissolved air flotation (DAF) that have occurred over the last 40 years. DAF processes are being designed and operated with shorter flocculation detention times than have been used in the past. Fundamental concepts show that flocs of 20-50 µm are optimum in size regarding the collisions and attachment of flocs to air bubbles in the DAF contact zone, and thus link flocculation practice to fundamentals. Floc-bubble aggregates can rise and be removed in the DAF separation zone with one bubble attachment to flocs with sizes < 50 µm. Data are presented showing the effectiveness of DAF for treating low turbidity waters containing total organic carbon (TOC) and for removing algae and Cryptosporidium oocysts. High rate DAF systems are a recent development (over the last 10 years) with hydraulic loadings of 8-16 gpm/sf that yield a small process footprint. These high rate processes have different hydraulic flow through patterns than conventional rate DAF that allow them to produce high quality clarified water. Includes 15 references, figures.