| 摘要 |
A method of and apparatus for filtering, including a plurality of separate filter media beds progressively decreasing in granular media size in the direction of filtration flow. One embodiment of the invention includes two separate media beds comprised of two intimately contacting granular layers of different granular size. A second embodiment of the invention includes three separated media beds. In this embodiment the first bed consists of a single media layer and the second and third beds are comprised of two intimately contacting media layers of different granular size. In both embodiments, the filtration flow rate through each successive separate bed is less than that in the immediately preceeding bed. The overall arrangement of the present invention reduces accumulation of contaminants at the surface of each filter bed and at the interface between media layers, is capable of accommodating contaminant overload conditions, and eliminates the reverse stratification problem normally encountered during and after backwash procedures.
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