Page 360 - Fundamentals of Water Treatment Unit Processes : Physical, Chemical, and Biological

Flocculation 315

250 1000
G(22°C) = –26.9 + 12.74 rpm Data obtained 12/21/94 and 11/28/95
•
G =0.00021 R 1.13
•
200
T =22°C
150
G (s –1 ) G (s –1 ) 100

100 T =10°C

Range of practice Range of practice
50

0 10
0 5 10 15 20 25 10 4 10 5 10 6
(a) rpm (b) R

100 50
Data obtained 12/21/94 and 11/28/95
2
If R ≤ 8.0 10 4 log P=–1.22 log R+ 6.63 P=0.372 rpm 2.262 , R =0.991
•
•
40
Power (watts)

P 10 30
P=4.1 20

Range of practice 10
Range of practice
1 0
10 4 10 5 10 6 0 5 10 15 20 25
(c) R (d) rpm reading
FIGURE 11.15 Plots generated from first compartment of flocculation basin of 76 L=min (20 gpm) located at Engineering Research Center,
Colorado State University, Fort Collins, CO. The range of practice, shown as shaded area, is assumed 10 G 100. (a) G versus n,
(b) G versus R, (c) P versus R, and (d) P versus n.

11.5.4 OTHER TECHNOLOGIES decisions, and at the same time, they are simple. For these
reasons they remain favored in many kinds of contexts, e.g.,
Turbines, baffles, sludge-blanket clarifiers, and contact floc-
rural areas and developing countries (Bhargava and Ojha,
culation are among the other technologies that have evolved
1993, p. 465).
as flocculation technologies. The design procedures are
The design approach for a baffled basin is the same, in
empirical and are reviewed in this section.
principle, as for use of a baffled basin for rapid mix (see, for
example Hendricks, 2006, Section 10.4.3.3). The headloss
11.5.4.1 Turbines
dissipated is, as for any form drag (Bhargava and Ojha, 1993,
Turbine flocculators utilize a mixing impeller, e.g., the p. 466; Swamee, 1996, p. 1046; Haarhoff, 1998, p. 145),
Rushton type. Usually, their diameter is large and the rota-
tional velocity is low. The criterion, G, is the basis for design, v(slot) 2
1
e.g., 20 < G < 90 s , in which G is the average for the basin. h L (slot) ¼ K (11:28)
2g
The ‘‘con’’ side of a turbine flocculator is that the G at the tip
of the impeller is several times the average G. where
h L (slot) is the headloss due to turbulence induced by
11.5.4.2 Baffles slot (m)
Baffled basins, as noted, were among the first technologies K is the loss coefficient for slot (dimensionless)
for flocculation. They remain an important option because of v(slot) is the velocity between baffle edge and wall of
their passive character, i.e., no moving parts and no operator basin (m)