Processing coarse solids reduces their size so they can be removed during downstream treatment operations, such as primary clarification, where both floating and settleable solids are removed.
Comminuting and grinding devices are installed in the waste-water flow channel to grind and shred material up to 6 to 19 mm (0.25 to 0.75 in) in size.
Comminutors consist of a rotating slotted cylinder through which waste- water flow passes. Solids that are too large to pass through the slots are cut by blades as the cylinder rotates, reducing their size until they pass through the slot openings.
Grinders consist of two sets of counter rotating, intermeshing cutters that trap and shear waste-water solids into a consistent particle size, typically 6 mm (0.25 in). The cutters are mounted on two drive shafts with intermediate spacers. The shafts counter rotates at different speeds to clean the cutters.
The chopping action of the grinder reduces the formation of rag ―balls‖ and rag ―ropes‖ (an inherent problem with comminutors). Waste-waters that contain large quantities of rags and solids, such as prison waste- waters, utilize grinders downstream from coarse screens to help prevent frequent jamming and excessive wear.