Page 266 - Water and wastewater engineering

COAGULATION AND FLOCCULATION 6-43

d. Each basin is divided into three equal volume compartments or tanks

3
120 m 3
V compartment 40 m
3
e. With the recommended water depth range of 3 to 4.5 m, assume water depth of 4.0 m.
The surface area is then
40 m 3
A surface 10 0 . m 2
40 . m
f. With a rectangular plan, the length equals the width and

/
.
)
.
L W (10 0 m 21 2 3 16 m
g. The equivalent diameter exist
/
⎧ () ( . 2 12
410 0 m ) ⎫ ⎪
T ⎨ ⎬ 357 m.
⎩ ⎪ ⎭
h. The required input water power for each compartment can be calculated by using
Equation 6-12 . Using Table A-1 in Appendix A and the temperature of the water, find
3

1.519 10 Pa · s.

s
.
.
P (70 s 12 . 10 3 Pa
)(40 0 m 3 ) 297.7 or 300 W
) (1 519
12 3 3

P ( 50 s ) ( . 1 519 10 Pa s)(440 0. m ) 1519 or 150 W
.

12
3
.
.
0
.
P ( 30 s ) ( 1 519 10 3 Pa
s)( 40 0 m ) 547 or 55 W
Because the efficiency of transfer of motor power to water power is about 80%, the mo-
tor power for each compartment should be
300 W
Motor power 375 W
08 .
150 W
Motor power 187 5 or 190 W
.
.
0 08
55 W
5
.
Motor power 68 75 or 70 W
.
08
i. The impeller is located at B (0.333)(4.0 m) 1.587 or 1.6 m above the bottom of the
tank.
j. Using Table 6-5 , evaluate the different size radial impellers using the geometric ratios.
Below is a comparison of the ratios for the available sizes of radial impellers and the
rapid mix basin dimensions.