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Preliminary Treatment Devices in Waste Water Treatment
Screens and Shredders
Required to measure flow, remove solids > 1”, pump the wastewater, and remove sand and other heavy particulates
Chlorine can be added for odor control
FeCl3 can be added to help settling Coagulation
First unit process – measures flow and is equipped with a data acquisition system
Advantage of flume
Low head loss – why is this good?
Smooth hydraulic flow – benefit?
How do you maintain a constant flow?
Screen and Shredders
Required to remove objects greater than ½- 1” (e.g., paper, twigs, rags, plastics) – WHY?; (BAR RACKS)
Mechanically cleaned to remove objects from screens (debris landfilled) Dewatered prior to hauling
For WW flows w/ greater quantities of papers and plastics, can use screens w/ smaller openings (i.e., 1/8-1/4”)
Design to keep velocity < 3 ft/s
Shredders or grinders – cut material into smaller ¼” pieces (Communitors)
Requires regular maintenance so must design a bypass channel
In the bypass channel would install a hand cleaned screen
Need to remove “grit” to protect pumps, valves, and deposition (30m3-90m3/106m3 of WW) Grit includes sand, seeds, coffee grounds, glass,
etc. Where is there a large source of glass and coffee grounds?
Most commonly employed in WWTP Velocity controlled – Sed. Basin
Aerated – air causes a spiral roll “driving” the grit into a hopper
Since WW does not flow at a constant rate (i.e., varies from hour to hour), you can design an equalization basin to maintain constant flow