Skimming Tank

Detention period is the time required for a given volume of liquid to pass through a particular unit or process. In the context of wastewater treatment, detention period refers to the time that wastewater spends in a specific treatment unit.

Among the given options, the skimming tank has the minimum detention period.

A skimming tank is a unit used in wastewater treatment to remove floating solids and oils from the wastewater. It is typically designed with a large surface area and a low depth, allowing the lighter solids and oils to rise to the top and be skimmed off.

The skimming tank operates based on the principle of gravity separation. As the wastewater enters the tank, it flows slowly and the floating solids and oils rise to the surface due to their lower density. These floating materials are then skimmed off using a mechanical device or manually.

The detention period in a skimming tank is relatively short because the separation process occurs quickly. The lighter solids and oils float to the surface within a short period of time, allowing for efficient removal. Therefore, the detention period in a skimming tank is minimal compared to other treatment units.

On the other hand, other treatment units mentioned in the options have longer detention periods:

- Sludge digestion tank: Sludge digestion is a biological process used to reduce the volume of sludge and stabilize its organic content. The sludge is typically held in a digestion tank for an extended period, ranging from several days to several weeks, to allow for the digestion process to take place.

- Primary sedimentation: Primary sedimentation is a process where suspended solids settle out from the wastewater by gravity. The wastewater is allowed to flow slowly through a primary sedimentation tank, providing sufficient time for the heavier solids to settle at the bottom. The detention period in a primary sedimentation tank is longer compared to a skimming tank.

- Oxidation pond: An oxidation pond is a natural or artificial shallow body of water used for the treatment of wastewater. It relies on the natural processes of sunlight, algae growth, and bacterial activity to treat the wastewater. The detention period in an oxidation pond can range from several weeks to several months, allowing for the necessary biological and chemical reactions to occur.

In conclusion, the skimming tank has the minimum detention period among the given options due to the quick separation of floating solids and oils.