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Impeller-powered Flocculation Basin

8.7 Step-wise solution to a numerical problem related to a flocculation-based water treatment plant having a flow of 25 MGD. The plant is to employ alum coagulation, and pertinent data for the flocculation basin are as follows: detention time = 20 min, G = 35 sec^-1 (at 50 degrees Fahrenheit), GT = 10,000 to 100,000, width = 1.25 times depth, length = twice width, no baffling, number of impellers = 2, number of blades per impeller = 6 pitched at 45 degrees, impeller diameter = 30 % of basin width, K_L = 70.0, and K_T = 1.65.

Determine:
(a) Basin dimensions if 1-in. increments are used.
(b) Impeller diameter
(c) Speed of impellers in rpm.

8.9 A lime-soda softening plant treats a flow of 150 MGD, and the water has 86 mg/l CO2. The commercial grade of quicklime has a purity of 85% and the soda ash has a purity of 95%. Determine:
(a) The pounds of quicklime and soda ash required per million gallons.
(b) The tons of quicklime and soda ash required per month if a month is considered to be 30 days.

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The solution involves step by step calculations about an impeller-powered flocculation basin.

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