Page 280 - Water and wastewater engineering

COAGULATION AND FLOCCULATION 6-57

For each compartment L W
Water temperature 10 C

Assume the design recommendations in Table 6-7 apply

To complete the design, provide a dimensioned sketch of the basin and wheels.
Hint: for a first trial assume a wheel diameter of 3.5 m.
6-23. Design the first compartment of a cross-flow paddle flocculator for the city of Some-
such by determining the basin dimensions, the paddle configuration, the power re-
quirement, motor power, and rotational speeds for the following parameters:
3
3
Design flow rate 28.8 10 m /d
t 25 min
1
Three flocculator compartments with G 50, 40, 20 s
For each compartment L W
Water temperature 5 C
Assume the design recommendations in Table 6-7 apply

To complete the design, provide a dimensioned sketch of the basin and wheels.
Hint: for a first trial assume a wheel diameter of 3.0 m.

6-11 DISCUSSION QUESTIONS

6-1. The zeta potential of colloids measured in water from Lake Michigan would be
greater than, less than, or the same as the zeta potential for the same colloidal

dispersion measured in a water from the Atlantic ocean. Select the correct
phrase.
6-2. In Jar Test II in Example 6-3 the pH was held constant while the alum dose was
varied. Explain why the settled turbidity varies from a high of 14 to a low of 4.5 and
then rises again to 13.

6-3. Which type of rapid mix (in-line blender or back mix reactor) would be selected for
the jar test data shown below.

Jar No 1 2 3 4 5
Coagulant dose, mg/L 0 5 20 50 250
Final turbidity, (NTU) 8.35 8.26 7.92 7.51 6.49

Coagulant was Ferric Chloride