Princeton Indiana Wastewater Treatment Plant Headworks Solids Removal

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Plant brochure designed by Charles L. Woodruff 1999 and revised in June 2004.

The headwork’s provides pre-treatment of the wastewater through the removal of rags and other large debris via the automatic Lakeside Raptor Fine Screen and removal of sand and grit via the Wemco-Hydrogritter separator.

Lakeside Raptor Fine Screen

The Lakeside Fine Screen removes fine solids from the waste flow. The Bar Section Screen successfully combines three processes in one unit--screening, compaction and dewatering. The Bar Section Screen features simple design and operation to provide a superior screening solution. The Raptor Fine Screen's bar spacing ranges from 1/4 to 1/2 inches (6 to 12 mm) to remove solids that normally pass through conventional screens. Debris is removed from the screening area by a rotating rake that passes through the full depth of the bars.

Not only does the Bar Screen combine screening, compaction, and dewatering into one process, it minimizes maintenance costs due to its stainless steel construction, simple mechanical design, and single moving part.

Positive screenings removal is accomplished by the heavy-duty rake design. Grease, rags and hair will not plug the Raptor Fine Screen.
Tests with a wastewater solids content of 64 cubic feet per million gallons showed that approximately 62 cubic feet of screenings per million gallons were removed by the Raptor Fine Screen. The removal efficiency of the screen was over 96 percent.


Lakeside Raptor Fine Screen	Lakeside Raptor Illustration

Fine Screen
Model # 55FS-.0.25
Size 55”
Bar spacing ¼”
Design capacity 9.5 MGD
The fine screen is mechanical device that automatically removes larger solids from the influent flow stream by directing the wastewater flow through the screening basket. The space between the bars is sized to remove particles larger than ¼”. The solids collected on the drum are periodically remove by a rake and deposited in a shaft. A screw in this shaft draws the solids to the of the unit. The blades of the screw slowly increase in pitch to squeeze water from the solids so that the final solids are relatively dry. These solids are discharged to a dumpster for disposal in the landfill.


Bar Screen & Screw Conveyor	Bar Screen With Rake Arm Illustration

As liquid flows through the screening basket, solids are trapped by the screen bars that form the circular basket.

When the liquid rises to a predetermined level, the rake begins to rotate to clean the screen bars. The rake's teeth pass between the bars of the screen to remove the screened material.

When the rake reaches the top of the screen, the captured material drops into the central screw conveyor. For complete cleaning, the rake reverses direction and passes through a comb.

The central screw conveyor then transports the screened material to the discharge chute. While this material is being transported, it is washed, compacted and dewatered. Dewatered screenings have a solids content exceeding 40 percent when discharged.

Screenings are initially washed as they are deposited in the collection trough.
The screenings are washed a second time at the upper section of the transport tube.
The macerating action of the screw breaks down large organic particles which are then washed back into the flow stream. A spray wash system in the dewatering chamber removes any collected material to ensure free drainage of water that is removed in the compaction process.

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