Detention time in sedimentation basins must be at least ________ hours to allow floc to settle.

Detention time in sedimentation basins must be at least ________ hours to allow floc to settle.

• A. four
• B. eight
• C. six
• D. ten

Answer: (C)

Detention time is the average time water spends in the sedimentation basin, giving suspended floc time to settle by gravity. To remove the floc effectively, the basin must provide enough time for aggregates to form and for the heavier particles to settle to the bottom. If the water flows through too quickly or the basin isn’t large enough, some floc stays suspended and exits with the treated water, reducing clarity and solids removal. The minimum time commonly specified to ensure adequate settling for typical floc is six hours. Shorter times, like four hours, are usually not sufficient for complete settling, while longer times (eight or ten hours) can be used in plants with higher solids loads but aren’t required as the minimum. Detention time is calculated as basin volume divided by flow rate, so increasing volume or decreasing flow increases the time available for settling.

Detention time is the average time water spends in the sedimentation basin, giving suspended floc time to settle by gravity. To remove the floc effectively, the basin must provide enough time for aggregates to form and for the heavier particles to settle to the bottom. If the water flows through too quickly or the basin isn’t large enough, some floc stays suspended and exits with the treated water, reducing clarity and solids removal. The minimum time commonly specified to ensure adequate settling for typical floc is six hours. Shorter times, like four hours, are usually not sufficient for complete settling, while longer times (eight or ten hours) can be used in plants with higher solids loads but aren’t required as the minimum. Detention time is calculated as basin volume divided by flow rate, so increasing volume or decreasing flow increases the time available for settling.