Complete the following problems dealing with gravity sedimentation: 1a. Design a drinking water treatment clarifier where ferrous sulfate is used as a coagulant and lime is added for supplemental alkalinity. The specific gravity of the floc particles is 1.005 and the water temperature is 10° C. Determine; a. Clarifier overflow rate (gpd/ft2 ) if the volumetric flow rate is 7.0 MGD, and the planar dimensions are 60 ft by 120 ft. 1b. Convert the overflow rate of Part (a.) to the limiting design value of the particle settling velocity (cm/sec). 1c. Using Stokes’ Law for laminar flow, find the diameter (mm) of the smallest spherical floc particle that will be 100 percent removed.

Complete the following problems dealing with gravity sedimentation:
1a. Design a drinking water treatment clarifier where ferrous sulfate is used as a coagulant
and lime is added for supplemental alkalinity. The specific gravity of the floc particles is
1.005 and the water temperature is 10° C. Determine;
a. Clarifier overflow rate (gpd/ft2
) if the volumetric flow rate is 7.0 MGD, and the
planar dimensions are 60 ft by 120 ft.
1b. Convert the overflow rate of Part (a.) to the limiting design value of the particle
settling velocity (cm/sec).
1c. Using Stokes’ Law for laminar flow, find the diameter (mm) of the smallest
spherical floc particle that will be 100 percent removed.
1d. Design a wastewater treatment primary clarifier for an average flow rate of 1.10 MGD,
and a peak hourly flow rate that is 3.1 times the average flow rate. Pertinent parameter
values selected for design include a peak hourly overflow rate of 1800 gpd/ft2
, maximum
hourly weir loading rate of 30,000 gpd/ft, minimum tank depth of 7.0 ft. Determine;
1e. Minimum clarifier diameter (ft).
1f. Clarifier diameter (ft) if collector mechanisms are available only in 5.0 ft
increments of diameter.
1g. An appropriate side water depth (ft), i.e., the tank depth excluding the coneshaped bottom.
1h. If the peak hourly weir loading rate is acceptable when using a peripheral weir.
1i. An existing rectangular clarifier at a drinking water treatment plant is 18 ft wide and 72 ft
long. It was originally designed for an overflow rate of 600 gpd/ft2 and it is currently
operating at its design capacity. Inclined-tube settling bundles are to be added and will
occupy 80 percent of the plan area, inlet flow distribution systems for the retrofitted tube
bundles excludes flow through the remaining 20 percent of the surface area. Tube
bundles will have a design overflow rate of 5,000 gpd/ft2
. Complete an analysis to
determine the present capacity in gal/day, and the increased capacity in gal/day after the
tube bundles are installed.