Math Problem

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1. You need to calculate the velocity in a grit channel at your plant’s peak flow. Based

on the flow charts, you determine that peak flows are usually about 2.75 MGD. The grit

channel is 3ft wide, and the flow depth is 17in at peak flow. What is the velocity in the

grit channel under these conditions?

2. A chlorinator treats a flow of 2 MGD. The chlorine demand is 9 mg/L and the desired

residual is 1 mg/L. What should be the setting on the chlorinator in pounds of chlorine

per 24 hours?

3. A reaction basin that is 4 meters in diameter and 1.2 meters deep can treat a flow of

0.9 MLD. What is the average detention time in minutes?

required for the water to rise 3 feet in an 8-foot by 6-foot rectangular tank. (Hint:

calculate volume pumped in cu ft, convert cu ft to gal, calculate gpm)

5. What is 90% of 5?

6. What is the maximum volume (in gallons) of water that can be stored in a

cylindrical tank that is 10ft in diameter and 20ft high with an overflow at 18ft from the

base?

7. What is the external surface area for a cylindrical tank 10ft in diameter and 20ft high

(not including the top and bottom)?

8. How many pounds of 68% calcium hypochlorite Ca(ClO)2 are needed to make 200

gal of a 10% Ca(ClO)2 solution?

9. A 15in diameter pipe is flowing full. What is the gpm flow rate in the pipe if the

velocity is 110 ft/min?

10. The influent BOD to an activated sludge plant is 225 mg/L and the effluent BOD is

25 mg/L. What is the BOD removal efficiency of the plant?

11. What is the weight of dry solids in a ton (2,000lbs) of wastewater sludge containing

5% solids and 95% water?

12. If a tank is two-thirds full and it contains 8,000 gallons, what is the tank capacity?

13. A rectangle channel is 3ft wide and contains water 2ft deep, moving at 1.5 ft/sec.

What is the flow rate in cfs?

14. Estimate the pounds of lime needed to neutralize a sour digester if the digester

contains 0.25 mg of sludge with a volatile acid level of 2,400 mg/L as acetic acid.

15. A small chemical feed pump lowered a chemical solution in a 2.5-foot diameter tank

by 2.25 ft during a seven-hour period. Estimate the flow delivered by the pump in gallons

per day.

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