Screened decanter assembly for a settling tank

1. A decanter assembly for use in a primary treatment system for wastewater, comprising:

a) a longitudinal decanter and hood disposable in said wastewater and having a longitudinal trough with a bottom and a horizontal entrance weir; and

b) a screen having a cross-sectional profile selected from the group consisting of polygonal and arcuate, said screen being attached to said decanter and said hood on a manner to seal all the edges of said screen potentially below the level of said wastewater and having screen surfaces disposable above and below the surface of said wastewater outside of said trough and below said entrance weir and being off-spaced from said weir to form in use a closed pool of already screened wastewater resident between said screen and said weir.

2. A decanter assembly in accordance with claim 1 wherein said polygonal screen comprises a plurality of screen surfaces disposable below the surface of said wastewater.

3. A decanter assembly in accordance with claim 1 wherein the opening size in said screen is graded.

4. A decanter assembly in accordance with claim 1 wherein a first side of said screen is attached to said decanter at a point normally above the surface of said wastewater, and a second side of said screen is attached to the underside of said decanter.

5. A decanter assembly in accordance with claim 1 wherein said screen is detachable from said decanter.

6. A decanter assembly in accordance with claim 1 wherein said screen extending below said entrance weir of said longitudinal decanter is configured in such a way that raising said decanter assembly above the surface of said wastewater allows said already screened wastewater resident between said screen and said weir to flow back through said screen under gravity.

7. A decanter assembly in accordance with claim 1 , further comprising a floating baffle pivotably mounted to said decanter and disposable in said wastewater outside of said screen.

8. A primary treatment system, for wastewater, comprising:

a) a settling tank; and

b) a decanter assembly disposed in said settling tank, including,

a longitudinal decanter disposable in said wastewater and having a longitudinal trough and a horizontal entrance weir,

a screen having a cross-sectional profile selected from the group consisting of polygonal and arcuate, said screen being attached to said decanter along all screen edges potentially below the level of said wastewater and having screen surfaces disposable above and below the surface of said wastewater outside of said trough.

9. A primary treatment system for wastewater in accordance with claim 8 , wherein said decanter assembly further comprises a floating baffle pivotably mounted to said decanter and disposable in said wastewater outside of said screen.

10. A method for backflushing a decanter screen in a decanter assembly disposed in a primary treatment system for wastewater, wherein said screen, being attached to a decanter and hood of said decanter assembly at all edges of said screen potentially below the level of said wastewater, functions to remove solids from solids-laden wastewater by allowing wastewater liquid through said screen in a first direction to create a closed pool of screened wastewater between said screen and a weir of said decanter and stopping said solids on a first surface of said screen, the method comprising the steps of:

a) raising said decanter assembly above the surface of said wastewater; and

b) allowing said pool of screened wastewater to flow by gravity through said screen in a second direction opposite to said first direction to dislodge said solids from said first surface.