Flocculation The term flocculation is used to describe
Flocculation
The term flocculation is used to describe the process where the size of particles increases as a result of particle collision due to gentle mixing. The purpose of flocculation is to produce particles that can be removed by sedimentation, this could be achieved by providing particle contact while not creating sufficient turbulence to break up the floc already formed.
• Flocculant being a polymer has the ability to bridge particles by adsorption of the polymer onto the colloids. The resulting structure grows as a single particle several time larger than its constituents.
• The design objective in hydraulic flocculant is to achieve gentle uniform mixing that will not shear the floc. • The mixer typically used in flocculation basins are horizontal shaft paddle wheel flocculator.
• This design helps to : 1. Produce uniform and tough flocs that will settle rapidly. 2. This design helps to minimize short ciruiting efficiently 3. No need to large paddle e wheel
13. 0 Flocculation Tank Design Provide 5 tank Q = 3, 500 m 3/h Flow for each tank, q = 3500 m 3/h 5 = 700 m 3/h
Proposed Contact Time = 25 minutes Volume of tank = 700 m 3/h x 25 = Proposed tank size, depth 291. 7 m 3 = Area 60 3. 5 m = 291. 7 m 3 3. 5 = 83. 34 m 2
Tank Size Ratio Say Width Length = 2 : 1 (Mechanical Flocculator) = B L Lx. B 2 B x B = 83. 34 B = 6. 4 m L = 12. 8 m
6. 4 x x x 8 6. 4 x Effective Volume Retention time = (6. 4 x 3. 5) x 2 = 287 m 3 = 287 m 3 700 m 3/h = 25 minutes
If one tank is not in operation Q 4 = Retention Time = 875 m 3/h 287 m 3 875 m 3/h = 20 minutes (15 < t < 45 min) - OK
If two tanks are not in operation Q 3 = Retention Time = 1, 167 m 3/h 287 m 3 1, 167 m 3/h = 15 minutes (15 < t < 45 min) – Still OK
Flocculators Size G = P P = ( G 2 ) ( Vμ ) Proposed. G = Say P ½ Vμ 25 s-1 P = (25 s-1)2 (6. 4 x 3. 5) (0. 00086 Ns/m 2) P = 77 Watts = 80 Watts
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