Page 268 - Water and wastewater engineering

COAGULATION AND FLOCCULATION 6-45

TABLE 6-7
Design recommendations for a paddle wheel flocculator
Parameter Recommendation
G 50 s 1

Basin
Depth 1 m wheel diameter
Clearance between wheel and walls 0.3–0.7 m
Wheel
Diameter 3–4 m
Spacing between wheels on same shaft 1 m
Spacing between wheel
“rims” on adjacent shafts 1 m
Paddle board
Width 10–15 cm
Length 2–3.5 m
Area of paddles/tank cross section 0.10–0.25
Number per arm 3
Spacing at 1/3 points on arm
Tip speed 0.15–1 m/s
C D L/W 5 1.20
L/W 20 1.50
L/W 20 1.90
Motor
Power 1.5–2 water power
Turn down ratio 1:4
Sources: Kawamura, 2000; MWH, 2005; Peavy et al., 1985

Design recommendations for a paddle wheel flocculator are given in Table 6-7 .
1
The maximum G for paddle flocculators is limited to about 60 s with a recommended
1

maximum value of 50 s to avoid severe wear of the shaft bearings in a very short time. Each
arm should have a minimum of three paddles so that the dead space near the shaft will be mini-
mized (Kawamura, 2000).
Example 6-10. Design a paddle flocculator by determining the basin dimensions, the paddle
configuration, the power requirement, and rotational speeds for the following parameters:
3
3
Design flow rate 50 10 m /d
t 22 min
1
Three flocculator compartments with G 40, 30, 20 s
Water temperature 15 C