The theoretical time taken by a particle of water to pass between entry and exit of a settling tank is known as
- AWeir loading
- BDetention periodCorrect
- CVelocity of flow
- DOverflow rate
Solution
Concept
Detention period is the theoretical time water stays in a tank, from entry to exit.
Formula
td = V / Q
Step-by-step solution
1. A settling tank holds water for some time so that particles can settle. 2. The theoretical time a water particle takes to move from inlet to outlet is called the detention period. 3. It is found as tank volume divided by flow rate (td = V/Q). 4. So the answer is (B) Detention period.
Explanation
Detention period is the theoretical time water stays in the tank. It equals tank volume divided by discharge. For plain sedimentation tanks it is usually about 2 to 4 hours.
Why the other options are wrong
A: Weir loading is flow per unit length of outlet weir (m³/m/day), not time. C: Velocity of flow is the speed of water through the tank (m/s), not time. D: Overflow rate (surface loading) is flow per unit surface area (m³/m²/day), not time.
Shortcut
Time in the tank = Detention period = Volume / Flow.
Common mistake
Confusing detention period with overflow rate. Overflow rate has units m³/m²/day, not time.
Correct answer: B) Detention period