Water/Wastewater Laboratory Calculations - Basic Mathematics for Water and Wastewater Operators - page 250

■ Example 16.24
Problem: A total chlorine dosage of 10 mg/L is required to treat a particular waste-
water. If the flow is 1.4 MGD and the hypochlorite has 65% available chlorine, how
many lb/day of hypochlorite will be required?

Solution: First calculate the lb/day chlorine required using the mg/L to lb/day
equation:

Chlorine (lb/day) = Chlorine (mg/L) × Flow (MGD) × 8.34 lb/gal

Chlorine (lb/day) = 10 mg/L × 1.4 MGD × 8.34 lb/gal = 117 lb/day

Then calculate the lb/day hypochlorite required. Because only 65% of the hypochlo-
rite is chlorine, more than 117 lb/day will be required:

117 lb/day
65% Availablechlorine

×= 100 180 lb /day hypochlorite

■ Example 16.25
Problem: A tank is 40 ft in diameter and 20 ft high and is dosed with 50 ppm of
chlorine. How many pounds of 70% HTH are needed?

Solution: Find the volume of the tank in cubic feet:

3.14 × 20 ft × 20 ft × 20 ft = 25,133 ft 3

Change cubic feet to gallons:

25,133 ft 3 × 7.48 gal/ ft 3 = 187,993 gal

Change gallons to million gallons per day:

187,993 gal = 0.188 MGD

Find the pounds of chlorine:

50 ppm × 0.188 mg × 8.34 lb/gal = 78.4 lb

Change percent available to a decimal equivalent:

70% = 0.70

Find pounds of HTH:

78.4 lb ÷ 0.70 = 112 lb