The grit chambers remove any grit that may be contained in the raw wastewater. The grit moving across the bottom of the chamber is hydraulically scoured as the propeller blade of the Pista unit moves over the grit. This causes the hydraulic currents to lift up the organic material which continues through the treatment process. The remaining inorganic material or grit passes from the removal chamber through an opening in the transition plate and drops into a grit storage hopper until it is pumped to the Pista grit concentrator. From there the grit goes by a grit screw conveyor to a dumpster for removal to the central landfill.
Excess water is removed in the grit screw conveyor.
All processed flows returning to the head of the plant re-enter the influent vault. The raw wastewater goes through a second set of grit chambers and manually cleaned bar screens. The wastewater continues through a set of comminutors. A comminutor is essential a circular bar screen placed in the influent channel. It is traversed by a rotating rake that serves as a cutter to engage and shred the accumulated debris, thus, screening and shredding are accomplished in one operation.