TABLE OF CONTENTS A water treatment plant is to treat 25 million gallons per day of water from a large river. Treatment consists of rapid mixing, flocculation, sedimentation, standard rate sand filtration, and chlorination. Alum is added at the rate of 1.5 grains per gallon. Peak daily demand is 220% of average daily flow. Calculate the following:
Design capacity and size of each treatment unit.
The amount of alum and chlorine required on a daily basis.
Flash Mixing
Design for minimum detention period of 30 seconds.
For square tank 10 feet deep, Area = 116 ft 2
Tank Dimensions: 10.5 ft 10.5 ft 10 ft deep
Flocculation
Use horizontal paddle mixer in flocculation basins. Design for 30 minutes detention time (minimum required).
For 15 foot deep basin, Area = 4642 sq. ft.
Choose four basins each 1161 sq. ft.
Assume length: width ratio of 2:1 for rectangular tank.
Tank Dimensions: 15 ft deep 24 ft 48 ft
Sedimentation
Design for four hour detention time, loading rate of 360 ? 540 gpd/sq. ft. surface area.
For 12 foot tank depth,
Total Area = 46,420 ft 2
Surface loading = 538 gpd/ft 2
Use eight basins, each 5803 ft 2.
Assume length: width ratio of 4:1 for rectangular basin.
Tank Dimensions: 12 ft deep 38 ft 152 ft
Filtration
Design for filtration rate of 2 gpm/ft 2.
Assuming each filter unit will treat 2.5 mgd, 10 beds will be required.
Assume 5 filters...
