High Rate Filtration System
A high rate, upflow filtration system is described in which a compressible, fibrous lump filtration media is compressed to adjust the porosity and collector size of the media in the bed and to provide a porosity gradient within the bed proceeding from more porous to less porous in a direction opposite to the flow of fluid so that filtration proceeds in a direction from a more porous to a less porous filter bed. Larger particles are removed by the more porous media and successively smaller particles are removed as the filter bed becomes less porous. The system is capable of reducing the turbidity of influent municipal wastewater from about 8 NTU to about 2 NTU at a wastewater flow rate of from about 820 to 1230 L/m 2 ·min (20 to 30 gal/ft 2 ·min), at a bed compression ration of from about 15 to 40 percent, and at a backwash rate of from about 1 to 6 percent based on the total wastewater passing through the filter.
1 . An activated sludge plant for the biological treatment of waste water, said plant comprising:
a) an activated sludge reactor for digestion by a biological sludge of carbonaceous organic compounds in influent waste water;
b) a clarifier in flow receiving communication with said reactor for receiving a mixture of sludge and waste water from said reactor and separating the sludge from the wastewater; and
c) a filter in flow receiving communication with said clarifier for receiving clarified waste water from said clarifier, said filter comprising:
i) at least one filter housing having an axial flow direction therethrough for waste water;
ii) a first perforated panel fixedly secured in said housing transverse to said flow direction;
iii) a second perforated panel movably secured in said housing transverse to said flow direction and spaced from said first perforated panel;
iv) a single influent liquid conduit located adjacent said fixed first panel, said influent conduit in flow receiving communication with said clarifier;
v) an effluent liquid conduit located adjacent said movable second panel thereby establishing said axial flow direction through said housing;
vi) compressible filtration media located between said first and second panels; and
vii) a piston for moving said second perforated panel toward and away from said fixed first panel to define:
a) a fixed filter bed of said media compressed between said panels during filtration, said filter bed having a porosity gradient across the bed proceeding progressively from more porous to less porous in said axial flow direction; and
b) a cleaning chamber between said panels during washing wherein said second panel is moved away from said first panel to provide said media in an uncompressed condition for washing in said axial flow direction with influent.
2 . An activated sludge plant for the biological treatment of waste water, said plant comprising:
a) an activated sludge reactor for digestion by a biological sludge of carbonaceous organic compounds in influent waste water;
b) a clarifier in flow receiving communication with said reactor for receiving a mixture of sludge and waste water from said reactor and separating the sludge from the wastewater; and
c) at least one up-flow high-rate depth filter for removing suspended solids from clarifier effluent, said filter in flow receiving communication with said clarifier for receiving clarified effluent from said clarifier, said filter comprising:
i) a vertically oriented filter housing having a clarified effluent influent conduit located in a lower portion thereof and separate filtered water and wash water effluent conduits located in an upper portion thereof, said conduits establishing an upward axial flow direction through said housing;
ii) a first perforated panel fixedly secured in said housing above said influent conduit and transverse to said axial flow direction;
iii) a second perforated panel movably secured in said housing transverse to said axial flow direction, above said first panel and spaced therefrom, and below said filtered water and wash water effluent conduits;
iv) substantially spherical and compressible filtration media of individual, fibrous lumps of bundled, crimped fibers located between said first and second panels;
v) a piston for moving said second perforated panel toward and away from said fixed first panel to define:
a) a fixed filter bed of media compressed between said panels at a bed compression ratio of from about 15 to 40 percent during filtration, said fixed filter bed having a porosity gradient across the bed proceeding progressively from more porous to less porous in said axial flow direction, wherein collector size, effective pore size, and depth of said filter bed are adjustable by movement of said second panel as filtration proceeds at a flow rate of about 820 to 2050 L/m2° min (20 to 50 gal/ft2° min), and whereby head loss can be adjusted and filtration efficiency maintained during filtration by mechanically expanding said fixed bed; and
b) a cleaning chamber between said panels during washing wherein said second panel is moved away from said first panel to provide said media in an uncompressed condition for washing at a rate of from about 1 to 6 percent of clarifier effluent based on the total fluid passing through the filter.