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PRELIMINARY WASTEWATERTREATMENT
PRELIMINARY TREATMENT
Municipal wastewater treatment can be divided into Preliminary, Primary, Secondary and Tertiary Treatment as well as sludge disposal
Preliminary treatment incorporates pumping, screening, comminuting and grit removal
Examples of Screen Types
PROFILE BAR
LOOPED WIRE
RESISTANCE WELDED
Curved Bar Screens
Inclined Bar Screens
Wedge Wire Screens
The screens are also non-plugging, self-cleaning and abrasion-resistant.
Sieve Bends
Drum Screens from Wedge Wire
Special Application Retaining Screens
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02/11/2002
Halvor Nilsen 17
PRINCIPLES inlet fluids enter the hydrocyclone tangentially causing a spiraling centrifugal motion
centrifugal forces cause the heavier fluid phase to be directed outwardly toward the outer diameter of the hydrocyclone tube body
lighter phase fluids are sent inward toward the centreof the hydrocyclone tube body
the lighter phase fluids are discharged from the hydrocyclone by a “reverse flow” action and are discharged at the inlet end of the hydrocyclone
the denser phase fluids are discharged from the hydro cyclone tube body at the end opposite the inlet
Hydrocyclones
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Inlet feed
Lighter Lighter phase outletphase outlet
Denser phase outlet
http://www.krebs.com/tech_pdf/sizing_sel.pdf
Design of hydrocyclones
Final Remarks on Preliminary Treatment
Preliminary treatment removes solids from wastewater – primarily those which would not be effectively removed or degraded
A solid waste is generated which needs to be disposed of. Needs to be handled with care and regarded as infectious. Most commonly disposed of by land filling or combustion
Water Treatment Intake Screens
Protection of Equipment
These underwater photos compare screens over adjacent under-water intakes at a Consumers Power Company station in West Olive, Michigan. The stainless steel screen (left) is completely clogged with zebra mussels. The biostatic copper alloy screen (right) is almost completely free of mussels. It was fabricated by Wheelabrator.