1. If the chlorine chemical dose is 3 mg/L and the feed in lbs/day is 280, what is the flow in MGD?
2. A rectangular basin 12 feet long and 9 feet wide is 6 feet deep. It treats a flow of 90,000 gallons per day. Determine the detention time in hours.
3. Determine the required flow in gal/day for a settling tank that is 30 ft diameter, and 12 ft deep with a detention time of 3 hours.
4. How many feet in 30 inches?
5. How many cubic feet in one cubic yard?
1. If you know how to work the Davidson Pie Chart you have this one, if not the formula is:
Flow, MGD = (Chemical feed, lbs/day) / (Dose, mg/L X 8.34 lbs/gal)
= (280 lbs/day) / (3 mg/L X 8.34 lbs/gal)
= 11.2 MGD
2. The formula for detention time is (Tank Vol, gal X 24 hrs/day) / (Flow, gal/day)
First thing is we need to figure the Volume of the tank and volume is always in cuft or ft3 which means multiply 3 numbers together = 12 ft X 9 ft X 6 ft = 648 cuft
From cuft we can determine the gallons because there are 7.48 gal/cuft and since we are going from cuft to gallons we multiply = 648 cuft X 7.48 gal/cuft = 4,847 gallons Now we just need to fill out, the formula and work it:
(4847 gal X 24 hrs/day) / (90,000 gal/day) = 1.29 hrs
3. The formula for detention time is (Tank Vol, gal X 24 hrs/day) / (Flow, gal/day)
First thing is we need to find the Volume of a circular tank and volume is always in cuft or ft3 which means multiply 3 numbers together = 3.14 X R, ft X R, ft X depth, ft
R or Radius, ft is 1/2 the diameter = (30 ft) / (2) = 15 ft
3.14 X 15 ft X 15 ft X 12 ft = 8,478 cuft OR using Diameter is:
0.785 X 30 ft X 30 ft X 12 ft = 8,478 cuft
Now convert cuft or ft3 to gallons by multiplying by 7.48 gal/cuft
8,478 cuft X 7.48 gal/cuft = 63,415.4 gal
Okay – now comes the rub – you are asked to find the flow in gal/day when you are given the Detention time in hours. If you know how to work the Davidson Pie chart you have this, if not:
(Tank Vol, gal X 24 hrs/day) / (Detention time, hr)
(63,415.4 gal X 24 hrs/day) / (3 hours) = 507,323.5 gal/day
4. There are 12 inches per foot. So:
(30 inches) / (12 inches/foot) = 2.5 feet
5. There is 3 ft in one yard, but remember it is 3 yards not just one. So:
1 cuft X 3 ft/yd X 3 ft/yd X 3 ft/yd = 27 ft3