PRINCIPLES AND APPLICATIONS OF DISSOLVED AIR FLOTATION

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.