What type of contaminants does the sedimentation process primarily target?

The sedimentation process primarily targets suspended solids, which are particles that are not dissolved in water but are instead held in suspension. During sedimentation, the flow of water is slowed down, allowing these particles, such as silt, clay, and larger debris, to settle out of the water column due to gravity. This is a critical step in water treatment, as the removal of suspended solids helps improve water quality by reducing turbidity, which can harbor other contaminants and microorganisms.

The other options focus on contaminants that are not effectively removed by sedimentation. Gases do not settle out and typically require different treatment processes, such as aeration or chemical treatment. Dissolved substances, such as salts, are also not removed by sedimentation since they are present in a state that keeps them dispersed in the water. Microorganisms can often remain within the suspended solids, but sedimentation is not a definitive method for their removal, as some may still remain in the water even after solids have settled. Therefore, understanding that sedimentation is specifically designed to target suspended solids clarifies why this answer is accurate.