The sewage water treatment process must be divided into different stages to ensure good water and sanitation quality. The preliminary stage of the treatment process uses large filtering screens that remove large solid inorganic material such as paper, plastic, and metal. This is followed by the removal of the grit and slit which are abrasive to plant equipment. In the primary stage, wastewater is passed through a primary sedimentation tank where solid particles of organic material are removed by gravity settling at the bottom of the tank. The resultant primary sludge is then raked to the center of the tank where it is concentrated and pumped away for further treatment.