Preliminary Treatment is aimed at removing large objects, coarse debris and inorganic material from the wastewater.
Removal of Inorganic Material
Large objects like clothing, soda cans, beer bottles, rags, sticks, feminine hygiene products, diapers, tree roots, large 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 wastewater passes through openings in parallel bars while the debris (called screenings) gets caught on the bars and is removed by means of a mechanically operated rake that pushes the screenings onto a trough.
Compacting and Disposal of Screenings
The screenings generated from the preliminary treatment are pressed to remove excess water and then bagged into a plastic tube. They are then put in a dumpster to be hauled off to a sanitary landfill for burial.
Next, the wastewater is put into a velocity controlled tank called a cyclone dewatering unit. 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.”
Disposal of Grit
The grit is then conveyed up an incline and placed in a dumpster for disposal in the sanitary landfill.
Continuation of the Treatment Process
The lighter organic materials remain in the wastewater and move on to the next stage of treatment. Pumps move the wastewater, now strained of trash, sand, and gravel, on to Primary Treatment.