How long is the desirable retention time of using presettling reservoirs to eliminate heavy turbidity or pollution?

The desirable retention time in presettling reservoirs to effectively eliminate heavy turbidity or pollution is typically around 2 to 3 days. This timeframe allows sufficient time for larger particulate matter, sediments, and other pollutants to settle effectively.

During this retention period, the water undergoes a natural clarification process where denser particles settle at the bottom, reducing turbidity before the water moves on to further treatment processes. Retaining water for 2 to 3 days strikes a balance between allowing adequate settling while also minimizing the risk of stagnation, which can lead to issues such as odor or algal growth.

Longer retention times may not be necessary and could potentially lead to diminished water quality due to stagnation, while shorter times may not allow for adequate sedimentation, thereby not achieving the desired level of turbidity reduction. Thus, a 2 to 3 day retention time represents an effective compromise to manage water quality before further treatment.