Influent flow passes through screens which are intended to remove large material before they enter the treatment plant; this includes rags, branches, Styrofoam, tennis balls, plastic articles, and miscellaneous debris. The material is removed to protect downstream equipment from being plugged or damaged. The turbulence in the collection sewer breaks up fecal matter and other biodegradable organics (wastewater solids) sufficiently that they are not retained on the screens. Screened material is dewatered before being stored in waste containers for offsite hauling.
The grit removal system is then provided to remove inorganic material such as sand and gravel from the wastewater, to protect the downstream equipment from accumulating sediment and to reduce damage that can be caused by the abrasive action of the inorganic material. Fecal matter and other biodegradable organics (wastewater solids) are not intended to be removed in the grit removal process. If excess organics are removed, the grit waste containers will be contaminated with this material and become odorous.
