PRELIMINARY WASTEWATER TREATMENT. PRELIMINARY TREATMENT Municipal wastewater treatment can be divided into Preliminary, Primary, Secondary and Tertiary.

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.