Sedimentation is the first step of sewage treatment. This process involves the separation of solid particles from the wastewater.

Explanation:
Sewage treatment is a process that aims to remove contaminants from wastewater before it is discharged into the environment. The primary goal of sewage treatment is to protect public health and the environment by treating the wastewater to remove harmful substances and reduce pollution.

The process of sewage treatment involves several steps, one of which is sedimentation. Let's understand this step in detail:

1. Sedimentation:
Sedimentation is the first step in the sewage treatment process. It involves the separation of solid particles from the wastewater. During this step, the wastewater is allowed to sit in a large tank called a sedimentation tank or clarifier. The wastewater enters the tank and is left undisturbed for a certain period.

During this time, the solid particles present in the wastewater, such as sand, grit, organic matter, and other suspended solids, settle down to the bottom of the tank due to gravity. These settling particles form a layer of sludge at the bottom of the tank.

The clarified liquid, also known as effluent, is then removed from the top of the tank and transferred to the next stage of the treatment process. This effluent contains fewer suspended solids and is relatively cleaner than the original wastewater.

The sedimentation process helps in the removal of large solid particles and heavy organic matter that can settle down. It also aids in the removal of floating debris, such as oil and grease, which can be skimmed off the surface of the tank.

Advantages of sedimentation:
- Removes large solid particles and heavy organic matter.
- Reduces the load of suspended solids in the wastewater.
- Improves the efficiency of subsequent treatment processes.
- Helps in the removal of floating debris.

Conclusion:
Sedimentation is the first step of sewage treatment, where solid particles are separated from the wastewater. This process plays a crucial role in reducing the contamination of the wastewater and preparing it for further treatment processes.