Page 275 - Water and wastewater engineering

6-52 WATER AND WASTEWATER ENGINEERING

Mississippi River, Baton Rouge, Louisiana (continued)
Constituent Expressed as Milligrams per liter

Chloride Cl 32.0
Phosphate (total) PO4 3.0
Silica SiO2 10.0
Suspended solids 29.9
a
Turbidity NTU 12.0
a
pH 7.6
a
Not in mg/L.
6-8. Determine the size (liters/hour) of a proportioning pump to feed ferric chloride for
3
a 0.438 m /s water treatment plant. The optimum dose selected is 50 mg/L. Ferric
chloride may be obtained in a liquid form that is 42% pure. The density of this solu-
tion is 1.797 kg/L.

6-9. Using Table 6-4 , select an in-line blender to mix alum with a design flow rate of
3
485 m /h. The design water temperature is 10 C. Verify that the detention time
and velocity gradient meet the design criteria for adsorption/destabilization. As-
sume that the water power is 80% of the motor power, that the mixing time must
be between 0.3 and 0.8 s, and that there will be a stand-by mixer for redundancy.
Because this problem will require some iteration, a spreadsheet solution is highly
recommended.
6-10. Using Table 6-4 , select a combination of in-line blenders to mix ferric chloride with
3
a design flow rate that varies from a minimum of 8,200 m /d in winter to a maximum
3
of 49,200 m /d in summer. The design water temperatures are 4 C in the winter and
15 C in the summer. The plant will operate 8 hours per day for seven days per week
in the winter and 24 hours per day for seven days per week in the summer. Assume
that the water power is 80% of the motor power and that the mixing time must be
between 0.3 and 0.8 s. Because this problem will require some iteration, a spread-
sheet solution is highly recommended.

6-11. Rework Example 6-6 to find an appropriate static mixer from those shown in Figure 6-16
that conforms to the design criteria. Because this problem will require some iteration,
a spreadsheet solution is highly recommended. The variables that may be adjusted
include the number of mixing elements and the mixer diameter.
6-12. Design a static mixer for the following conditions:

3
Design flow rate 350 m /h
Minimum water temperature 12 C
Mixer aspect ratio 1.0
To complete this design, specify the following: number of static mixers, number of
mixing elements, and mixer diameter.
6 -13. As a junior field engineer, you have been asked to assist the contractor on your
job in resolving the following problem. A 4.9 kW motor and gear drive rated