WWTP Tour - Primary Treatment
Grit Chambers

Grit removal completes the preliminary treatment of the wastewater. In conjunction with screening, it provides protection to plant equipment, pipes and channels, and it enhances the efficiency of downstream wastewater treatment and sludge handling processes and operations.

The grit chamber is designed to remove sand, gravel, cinders, and other suspended inorganic materials having specific gravities substantially greater than those of the organic solids in wastewater. Grit chambers provide for the early removal of this material, thus protecting the mechanical equipment from abrasive action; reducing the formation of deposits in pipelines, channels and conduits; and reducing the amount of inorganics entering biological process units and sludge handling facilities.

The grit chamber is a square sedimentation tank where the horizontal flow velocity is slowed down just enough to allow the heavy inorganic material to settle out while maintaining the lighter organic material in suspension. The settled solids are continuously raked by a rotating mechanism to a sump on the side of the tank. From this sump the collected solids are pumped through a hydraulic cyclone where the true inorganic grit is separated from the water and organic material unintentionally captured in the grit chamber sump. The grit is discharged into a rake classifier, where it is washed by water sprays and dumped into a container to await ultimate land disposal. The overflow from the cyclone and the classifier, ladden with the organic material separated from the grit, flows back by gravity to the grit chamber influent channel. The grit chambers are covered and their atmospheres continuously scrubbed for odor control.

From the grit chamber the wastewater flows by gravity to the Influent Pump Station.