Chain scrapers are used in rectangular settling tank. Stepping pallets are located between two separate chains mounted between the shaft and gears placed on both sides of the pool. Thus, the chain starts infinite rotation and directs the sludge accumulated in the base to the collection pit with the rotation of the shaft where the drive group moves. At the same time, foam and oil accumulated on the surface of the tank directed towards oil and foam collecting chambers through the scraper pallet during the rotation of chain. Depending on the operation requirement, there are also chain scrapers that clean the pool floor or surface with two independent scrapers.