What method is primarily used for the removal of suspended solids from sewage?

The removal of suspended solids from sewage is primarily accomplished through sedimentation. This process involves allowing the sewage to sit undisturbed in a tank, where the solid particles settle to the bottom due to gravity. This settling separates the solids, forming a sludge layer at the bottom and leaving clearer water on top. Sedimentation is highly effective in reducing the concentration of suspended solids before further treatment processes, such as biological treatment or filtration, are applied.

In contrast, aeration is used to promote the growth of bacteria that break down organic matter, washing typically involves removing contaminants from a surface rather than suspensions in liquid, and elutriation pertains to separating particles based on size and density but is not the primary method for dealing with large volumes of sewage.