Detention time is calculated as Volume divided by Flow; the resulting unit is hours when volume and flow are in compatible units.

Detention time is calculated as Volume divided by Flow; the resulting unit is hours when volume and flow are in compatible units.

• A. True
• B. False
• C. Not enough information
• D. Only for large plants

Answer: (A)

Detention time tells you how long water stays in a basin. You find it by dividing the basin’s volume by the throughflow rate. Since flow is volume per time, V divided by Q gives a time. If you keep the units consistent, the result will be in hours (for example, 1000 gallons divided by 200 gallons per hour equals 5 hours). If you used different but compatible units, you’d get minutes or hours accordingly, but you still get a time value. So the statement that detention time is Volume divided by Flow and that the unit is hours when the units are compatible is correct. It isn’t limited to large plants, and you have enough information as long as you know the volume and the flow rate.

Detention time tells you how long water stays in a basin. You find it by dividing the basin’s volume by the throughflow rate. Since flow is volume per time, V divided by Q gives a time. If you keep the units consistent, the result will be in hours (for example, 1000 gallons divided by 200 gallons per hour equals 5 hours). If you used different but compatible units, you’d get minutes or hours accordingly, but you still get a time value. So the statement that detention time is Volume divided by Flow and that the unit is hours when the units are compatible is correct. It isn’t limited to large plants, and you have enough information as long as you know the volume and the flow rate.