What factor is crucial in determining the effectiveness of sedimentation basins?

• A. Volume of the basin
• B. Type of coagulant used
• C. Retention time
• D. Inlet water temperature

Answer: (C)

Retention time is a crucial factor in determining the effectiveness of sedimentation basins because it directly affects how long water is held in the basin for particles to settle out. The longer the retention time, the greater the opportunity for suspended solids to settle due to gravity. This settling process is essential for clarifying the water, as it allows denser particles to descend to the bottom of the basin, forming a sludge layer that can be removed.

While other factors may influence the overall performance of sedimentation basins, such as the volume of the basin and the type of coagulant used, they do not impact the basic principle of how sedimentation works as fundamentally as retention time does. Similarly, inlet water temperature, while relevant to the chemical reactions within the basin, does not have the same direct effect on the physical process of sedimentation itself. Therefore, retention time is the key factor that ensures effective sediment removal and overall operation of the sedimentation basin.