Page 423 - Water and wastewater engineering

10-40 WATER AND WASTEWATER ENGINEERING

10-7 PROBLEMS

10-1. Calculate the diameter of a discrete particle whose terminal settling velocity is 1.044
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cm/s. The particle density is 2.65 g/cm and the water temperature is 12 C. Assume
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Stokes’ law applies and that the density of water is 1,000 kg/m .
10-2. You have been asked to evaluate the ability of a horizontal flow gravity grit chamber
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to remove particles having a diameter of 1.71 10 m. The depth of the grit cham-
ber is 1.0 m. The detention time of the liquid in the grit chamber is 60 s. The particle
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density is 1.83 g/cm . The water temperature is 12 C. Assume the density of water is
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1,000 kg/m .
10-3. If the settling velocity of a particle is 0.70 cm/s and the overflow rate of a hori-
zontal flow clarifier is 0.80 cm/s, what percent of the particles are retained in the
clarifier?
10-4. If the settling velocity of a particle is 2.80 mm/s and the overflow rate of an up-

flow clarifier is 0.560 cm/s, what percent of the particles are retained in the
clarifier?

10-5. If the settling velocity of a particle is 0.30 cm/s and the overflow rate of a horizon-
tal flow clarifier is 0.25 cm/s, what percent of the particles are retained in the
clarifier?
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10-6. If the flow rate of the original plant in Problem 10-3 is increased from 0.150 m /s to
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0.200 m /s, what percent removal of particles would be expected?
10-7. If the flow rate of the original plant in Problem 10-4 is doubled, what percent re-
moval of particles would be expected?
10-8. If the flow rate of the original plant in Problem 10-5 is doubled, what percent re-
moval of particles would be expected?
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10-9. If a 1.0-m /s flow water treatment plant uses 10 sedimentation basins with an over-
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2
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flow rate of 15 m /d · m , what should be the surface area (m ) of each tank?
10-10. Assuming a conservative value for an overflow rate, determine the surface area
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(in m ) of each of two sedimentation tanks that together must handle a flow of
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0.05162 m /s of lime softening floc.
10-11. Repeat Problem 10-10 for an alum or iron floc.
10-12. Two sedimentation tanks operate in parallel. The combined flow to the two tanks is
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0.1000 m /s. The depth of each tank is 2.00 m and each has a detention time of 4.00 h.
What is the surface area of each tank, and what is the overflow rate of each tank in
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2
m /d · m ?
10-13. Determine the detention time and overflow rate for a settling tank that will reduce the
influent suspended solids concentration from 33.0 mg/L to 15.0 mg/L. The following
batch settling column data are available. The data given are percent removals at the
sample times and depths shown.