This labor describes the mechanical processes of waste water treatment, structural parts of which are made, and how they works. The mechanical treatment is the primary purification process. These procedures is made to improve the quality of waste water, and this is done by screening and sedimentation to eliminate large, floating and the fatty particles. This process also reduces the biological oxygen demand (BOD). The processes have a specific sequence, so we are first saperated large, then small particles and floating substances. Then separating the fat and the sand, and at the end mechanical process sepatation of the primary sludge, which is the last mechanical process.. Primary purification procedures protect the other components of the plant from clogging and damage of substances contained in the waste water.