In the pre-treatment, , paper, textile waste, plastic, metal such as solid materials and sand materials, oil-grease is applied to the separation process in waste water. If these substances has not been away from at this stage, pumps and sludge removal equipment, valves and pipe damage and can be problems in the treatment. Screens and fine grid are used remove suspended solids.

Coarse grid; they are used the first unit as protective equipment. The most commonly used are coarse grid  are bar grille.

Fine grids and Screens; This type of grills have mechanical cleaning mechanisms and grill from time to time held in solids are automatically cleaned and stored in containers then are put into the appropriate fields.

Fine grids consists of moving and still screens. Stationary or static screens are mounted vertical, inclined or horizontally. These screens are cleaned scratch or teeth. Moving screens are cleaned during the study. 20-25% suspended solids and BOD removal will be provided in both types of screens. In addition, this system also provides oil and dissolved oxygen removal.