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, diapers, tree roots - 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. This non-organic material is then packed up into plastic bags for disposal.
Grit Removal
Next, the wastewater is put into a tank that spins it at a speed that lets only the heavier glass, metal, sand and gravel particles, referred to as "grit," settle out. The lighter organic materials remain and move on to the next stage of treatment. The grit is taken to a landfill disposal site.
Influent
Pumps move the wastewater, now strained of trash, sand, and gravel, on to Primary Treatment.