1. Express a flow rate of 1 cubic feet per second in gallons per minute. (Round to the nearest whole number)

2. Express of flow rate of 1 gallon/minute in gallons/day.

3. If 1 gallon of water weighs 8.34 pounds and 1 cubic foot of water weighs 62.4 pounds, how many gallons are in 1 cubic foot of water?

4. What is the loading, in pounds/day, of wastewater with a strength of 500 mg/L and a flow rate of 0.89 million gallons/day?

5. Find the detention time if the volume is 10,000 gpd and the flow rate is 250 gal/min.

Answers:

1. There is 7.48 gallons per cubic foot. So:
1 cuft/sec X 7.48 gal/cuft = 7.48 gal/sec (notice cu ft cancel each other out but there is nothing to cancel out the seconds so it carries on – keep track of those units), next get from seconds to minutes. There are 60 seconds per minute:
7.48 gal/sec X 60 sec/min = 448.8 gal/min or 449 gpm (notice the seconds cancel each other out leaving gallons per minute) Then the 0.8 is greater than 5 so you round up to 449 with no decimal point.

2. This time you are only working with converting time units and you know there is 60 minutes per hour and 24 hours per day, but there is a shortcut of 1440 minutes per day (60 min/hr X 24 hrs/day = 1440 min/day). So:
1 gal/min X 1440 gal/day = 1440 gal/day

3. This one may work best by looking at what the answer is asking for first = gal/cuft, then from there start working the problem out backwards if you will:
(62.4 pounds/cuft) / (1 gal X 8.34 lbs/gal) = 7.48 gal/cuft

4. Loading formula = Flow, MGD X Conc., mg/L X 8.34 lbs/gal, so fill in the formula and work it
0.89 MGD X 500 mg/L X 8.34 lbs/gal = 3,711.3 lbs/day

5. The formula is: (Volume) / (Flow Rate) So:
(10,000 Gal) / (250 gal/min) = 40 minutes