Getting the Grit Out
Preliminary Treatment is aimed at removing large objects, coarse debris and inorganic material from the wastewater.
Barscreens
Large objects like clothing, soda cans, beer bottles, rags, sticks, feminine hygiene products, diapers, tree roots, cigarette butts, clumps of grease - all the things not meant to be flushed in the first place - are taken out of the wastewater by passing it through openings in parallel bars in machines called "bar screens."
The debris (called "screenings") gets caught on the bars. A mechanical rake pushes the screenings onto a trough.
The screenings generated from the preliminary treatment are pressed to remove excess water and then bagged in a plastic tube in a dumpster and hauled off to a sanitary landfill for burial.
Grit Removal
Next, the wastewater is put into a velocity controlled tank. A vortex mixer controls the velocity in the tank so that only the heavier particles settle out, removing glass, metal, sand and gravel particles, referred to as "grit.
The grit from the preliminary treatment process is pumped through a cyclone dewatering unit and then conveyed up an incline and placed in a dumpster for disposal in the sanitary landfill also.
The lighter organic materials remain in the wastewater and move on to the next stage of treatment.
Influent
Pumps move the wastewater, now strained of trash, sand, and gravel, on to Primary Treatment.