Detention period in a fill and draw type sedimentation tank is the amount of time that the water remains in the tank for settling of suspended solids to occur. It is an important parameter in the design and operation of sedimentation tanks as it determines the efficiency of the sedimentation process.

The correct answer to the given question is option D, which states that a detention period of 24 hours is provided in a fill and draw type sedimentation tank.

Explanation:

1. Fill and Draw Type Sedimentation Tank:
- A fill and draw type sedimentation tank is a type of sedimentation tank where water is filled into the tank, allowed to settle, and then drained out.
- It consists of two main compartments: the settling compartment where sedimentation occurs and the clear water compartment where the settled water is collected.

2. Purpose of Detention Period:
- The detention period is provided to allow sufficient time for the settling of suspended solids in the water.
- During this period, the settling particles (suspended solids) in the water settle down under the influence of gravity.
- The longer the detention period, the more time the particles have to settle, resulting in better separation of solids from the water.

3. Factors Affecting Detention Period:
- The detention period in a fill and draw type sedimentation tank is influenced by several factors, including the nature of suspended solids, particle size distribution, and tank design.
- Generally, a longer detention period is required for tanks with a higher concentration of suspended solids or for tanks with smaller particle sizes.

4. Importance of 24-Hour Detention Period:
- A detention period of 24 hours is commonly provided in fill and draw type sedimentation tanks for efficient settling of suspended solids.
- This duration allows sufficient time for the particles to settle and ensures effective removal of solids from the water.
- A longer detention period helps in achieving a higher removal efficiency and producing clearer and cleaner water.

In conclusion, a detention period of 24 hours is provided in a fill and draw type sedimentation tank to allow sufficient time for the settling of suspended solids. This longer duration ensures better separation of solids from the water and improves the efficiency of the sedimentation process.