The first process usually associated with municipal wastewater treatment to remove inorganic solids
Screening: Use of screens to remove coarse floating and suspended solids from sewage. Usually 6 mm screens are used.
Primary Settlement: Settling is a separation technique most often used for suspended solids and colloids (collected in the form of floc after the coagulation-flocculation stage) from the water. This occurs when the substance does not dissolve in water and its density is larger than that of water. Flocculating chemicals could be added to enhance sedimentation.
Flotation: A solids-liquid or liquid-liquid separation procedure. This is applied to particles of which the density is lower than that of the liquid they are in, this is natural flotation. Flotation can be induced by artificial fixation of air / gas bubbles to the particules that need to be removed, so that their density becomes lower than water density.
Grit and Grease treatment: Grit: remove the particles with a diameter > 200 ?m and a density close to sand to avoid abrasion and deposit downstream. Grease: remove the Fat, Oil and Grease to prevent clogging on downstream process