The primary stage of sewage treatment is the first step in cleaning wastewater and involves removal of large and suspended solid particles.
Sewage is first passed through screens to remove large objects like sticks, rags, and plastics.
It then enters sedimentation tanks (primary settling tanks), where the heavier organic solids settle down as sludge.
The liquid portion (supernatant) moves to the next stage for further treatment, while the sludge is collected for decomposition or further processing.