Page 278 - Water and wastewater engineering

COAGULATION AND FLOCCULATION 6-55

4. Compartment length width depth
5. Impeller type: axial-flow impeller, three blades, N p 0.31

6. Available impeller diameters: 1.0, 1.5, and 2.0 m
7. Assume B (1/3) H

6-20. Continuing the preparation of the proposal for the Waffle treatment plant ( Problem 6-15 ),
design the flocculation tank by providing the following for the first two compart-
ments only:
1. Water power input in kW
2. Tank dimensions in m

3. Diameter of the impeller in m
4. Rotational speed of impeller in rpm
Use the following assumptions:

1. Number of tanks 1 (with 1 backup)
1
2. Tapered G in three compartments: 60, 50, and 20 s

3. Detention time 30 min
4. Depth 3.5 m
5. Impeller type: axial-flow impeller, three blades, N p 0.43
6. Available impeller diameters: 1.0, 1.5, and 2.0 m

7. Assume B (1/3) H
6-21. Determine the required width of the paddle blade and recommend a motor power (in
watts) and rotational speed (in rpm) for the horizontal shaft a cross-flow paddle floc-
culator for the first compartment of a three compartment flocculation basin shown in
Figure P-6-23. ( Note: there are three paddle wheels on one shaft.) Figure P-6-23 and
the following assumptions are to be used in the design:
3
Liquid volume 257.2 m
1
Velocity gradient 40 s
Motor efficiency 80%
Paddle velocity 0.5 m/s
Water temperature 15 C
Drag coefficient 1.8
No stators are present *

* A stator is a vertical baffle.