Question

A conventional, rectangular flocculation basin is 38 ft. wide, 90 ft. long and 16 ft. deep. The flow through the basin is 24 mgd and the water horsepower input by the reel type paddles is 15 hp. The dynamic viscosity of water is 2.73 E -5 lb/sec/ft2 at 50 degrees Fahrenheit.

The flocculation basin in above is followed by four sedimentation basins which operate in parallel.   Each basin is 30 ft. wide, 240 ft. long and has an effective settling depth of 10 ft. The kinematic viscosity of the water is 1.41 E-5 ft2/sec. The specific gravity of the particles to be settled is 1.60.

a. What is the nominal detention time for sedimentation?

b. What is the overflow rate in gal/day/ft2.

c. What is the settling velocity ( ft/sec) of the smallest discrete particle that will be 100% removed?

d. According to Stokes law what is the diameter ( ft ) of the smallest discrete particle that will be 100% removed?

e. What is the horizontal water velocity ( ft/min) in the sedimentation basin?

Answer 1