Calculate detention time of the tank whose breadth is 2 m, length is 4 m and depth is 2.5 m. The rate of flow is 4 × 103 liters per hour.

Concept:The detention time (t) of a settling tank may be defined as the average theoretical time required for the water to flow through the tank. It is thus the time that WOULD be required for the flow of water to fill the tank, if there was no outflow. In other words, it is the average time for which the water is detained in the tank. Hence it is the ratio of the volume of the basin to the rate of flow through the basin.Detention Time (DT)Average theoritical time taken by water to travel from inlet to outlet of settling tank is known as detention time. Detention time should be greater than settling time of particle to capture the particle in the settling tank.\({\RM{DT}} = \frac{{{\rm{Volume\;of\;settling\;tank}}}}{{{\rm{Discharge}}}} = \frac{{\rm{V}}}{{\rm{Q}}}\)It is expressed in hoursCalculation:Breadth = 2 m, length = 4 m and depth = 2.5 m.The rate of flow (Q) = 4 ×103 liters per HOUR =4 M3/hrVolume of the tank = 20 m3 \({\rm{DT}} = \frac{{{\rm{Volume\;of\;settling\;tank}}}}{{{\rm{Discharge}}}} = \frac{{\rm{20}}}{{\rm{4}}}=5\)Detention time = 5 hours