Sludge scraper is a machine that cleans out the sludge from the river or wastewater treatment plant. It is used in municipal wastewater treatment plants, drinking water plant and circular sedimentation tanks with large diameter in industrial wastewater treatment. Reduce sludge and scum from the tank surface. The driving device drives the scraper to rotate around the center of the sedimentation tank. After the war water is precipitated by the sedimentation tank, the supernatant liquid is discharged from the overflow port, the sludge at the bottom of the tank is slowly driven by the scraper to the central collecting tank and is discharge through the drain pipe, At the same time, the scum is concentrated to the area between the scum scraper and the scum baffle and the scum is discharged form discharge tank.