Principles of dissolved air flotation (DAF) discussed include: bubble
formation and size, bubble-particle interactions, measures of supplied
air, and modeling of the reaction and clarification zones of the flot
ation tank. Favorable flotation conditions for bubble attachment or ad
hesion to panicles requires a reduction in the charge of particles and
production of hydrophobic particles or hydrophobic spots on particle
surfaces. A conceptual model for the bubble-particle reaction zone bas
ed on the single collector collision efficiency is summarized and disc
ussed. An alternative modeling approach is considered. Clarification o
r separation zone modeling is based on particle-bubble agglomerate ris
e velocities. The application of DAF in drinking water treatment is ad
dressed beginning with summaries of design and operating parameters fo
r several countries. DAF should not be considered as a separate proces
s, but integrated into the design and operation of the overall treatme
nt plant This concept shows that flocculation ahead of DAF has differe
nt requirements regarding flee size and strength compared to sedimenta
tion. The efficiency of DAF in removing particles and reducing particl
e loads to filters needs to be integrated into DAF plant design. The i
mpact on filtration performance is illustrated. Finally, fundamental a
nd applied research needs are addressed.