The main operational part of rotary screen is a slot tube which is a welded structure with support profiles which are rods in the axial direction of the tube and surface profiles spirally wound around the support profiles. Water is conveyed by a pump or flows with gravity on the slot tube and passes through slots. The solid pollution that exceeds the dimension of the slot, remains on the exterior of the rotating slot tube and it is scrapped and falls down in a container. Treated water, free of solid pollution, flows out from the lower part of the rotary screen. Rotary screen is used especially in different branches of the food-processing industry as are meat-processing factories, slaughterhouses, dairy works, canning factories etc. Generally the rotary screen is inserted before flotation as the first step in pretreatment.