The average time required by water to pass through the settling tank is called ______

Explanation :

In actual practice, a certain amount of short-circuiting always exists, and therefore the actual average time that a batch of water takes in passing through a settling tank called the flowing through the period is always less than the detention period which is the corresponding theoretical time.

Detention Period :

• The detention period is defined as the time for which the water was in the tank and the overflow rate is the velocity with which the tank fills.
• In a rectangular sedimentation tank,

The velocity of flow, V_f = Q/(B x H)
Detention time, t_a = L/V = Volume of tank/Discharge = (L x B x H)/Q
Surface overflow rate, V_s = Q/(B x L)

 Important PointsSome design Parameters for Plain sedimentation tanks are:
1. Detention period: In a water sedimentation tank using coagulated raw supplies is 2 to 4 hours.  In the case of plain sedimentation, detention time is 4 to 8 hours.
2. Horizontal flow velocity: Not greater than 30 cm/min
3. Length: Breadth ratio: (3 to 5): 1
4. Surface overflow rate: 12000 to 18000 L/m²/day or 500 to 750 liters/hour/m²
5. Depth: 2.5 to 3.5 m