The initial stage involves the removal of larger solid objects from the wastewater through physical processes. This includes:

• Screening: Large debris like branches, leaves, and trash are removed using screens.
• Grit removal: Heavier particles settle at the bottom of a grit chamber due to gravity.
• Sedimentation: Finer suspended particles settle as sludge in a sedimentation tank.

By the end of this stage, approximately 30% of polluting matter is successfully eliminated from the incoming raw wastewater.