What is the usual detention period of sewage in a sedimentation tank?

The usual detention period of sewage in a sedimentation tank is typically between 45 minutes to 2 hours. This time frame is designed to allow sufficient settling of solids from the liquid waste. During this period, denser particles and suspended solids naturally settle to the bottom of the tank due to gravity, thus facilitating the separation of solids from liquids.

A detention time of 45 minutes to 2 hours strikes a balance between ensuring adequate sedimentation while also maintaining the flow rate of sewage through the treatment system. If the detention time is too short, not all solids will have the opportunity to settle out, which can lead to increased turbidity in the effluent and potential plant inefficiencies. Conversely, excessively long detention periods may result in additional processes becoming inactive or hindered, and can lead to increased costs and operational challenges.

In contrast, shorter detention times, like those less than 45 minutes, would not allow for effective sedimentation, while longer times, such as those extending beyond 2 hours, could be unnecessary for many municipal wastewater treatment facilities, depending on the specific design goals and characteristics of the incoming wastewater. Hence, the chosen range effectively balances treatment efficiency and operational practicality.