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Water Science & Technology Vol 43 No 8 pp 139–144 © IWA Publishing 2001 Collision efficiency factor of bubble and particle (abp) in DAF: theory and experimental verificationM Han*, W Kim** and S Dockko****
Seoul National University, Seoul, 151-742, Korea
ABSTRACT The collision efficiency factor of bubble and particle (  bp)
in dissolved air flotation (DAF) can be calculated theoretically by
trajectory analysis, which takes into account both hydrodynamics and
inter-particle forces. To determine the theoretically optimum particle
size for any given bubble size, a collision efficiency diagram for DAF
was developed where collision efficiency is contoured on a plane of
particle and bubble sizes for different conditions of particle zeta
potential.
A set of experiments tested the validity of the suggested collision
efficiency diagram, and examined whether pretreatment is important and
why slight coagulant overdosing and shorter flocculation times are
generally preferred in DAF, both current accepted practice. Batch DAF
reactors were used and kaolin samples were prepared from jar tests
using different alum dosages and flocculation times. The particle size
distribution, particle zeta potential, and turbidity removal in each
experiment were measured, as were bubble size and zeta potential.
The results agreed well with the predictions of the collision efficiency
diagram and explained current practices. A collision efficiency diagram
identifies the pretreatment goal, i.e., tailoring of the optimum
characteristics required of particles (zeta potential and size) under
existing operational bubble characteristic.
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