Stormwater filtration apparatus, system and method

1. A filter cartridge for removing pollutants from stormwater, comprising:

a housing having a water inlet and a filtered water outlet;

a filter medium disposed along a flow path between the water inlet and the filtered water outlet;

a drainage space that forms at least part of the flow path and that is disposed between a downstream side of the filter medium and the filtered water outlet;

a solid wall float tube disposed in the drainage space and having an open lower end and open upper end to allow air to pass into, upward through and out of the tube into the drainage space, the solid wall float tube movable between a lowered position that inhibits or substantially restricts filtered water at the bottom of the drainage space from passing to the filtered water outlet and a raised position that permits free flow of filtered water to the filtered water outlet;

a fluid reservoir in fluid communication with the drainage space and disposed within the housing and above the filter medium for collecting filtered water as water level in the housing rises while the solid wall float tube is in the lowered position;

wherein, as the housing fills, water level in the housing rises to cause the solid wall float tube to move to the raised position and a negative pressure can be established in the housing that draws fluid through the filter medium;

wherein, as water level outside the filter cartridge drops, air enters the housing via the water inlet and causes the solid wall float tube to drop to the lowered position, and filtered water in the fluid reservoir backflows through the filter medium and out of the housing through the water inlet while air enters the housing by passing upward through the solid wall float tube so as to enhance rate of backflow while the solid wall float tube is in the lowered position.

2. The filter cartridge of claim 1 wherein the drainage space is centrally located within the housing, the filtered water outlet is at the bottom of the drainage space, and the drainage space is defined at least in part by a tube that surrounds the solid wall float tube and which is perforated along at least a lower section thereof.

3. The filter cartridge of claim 2 wherein an upper portion of the tube is not perforated.

4. The filter cartridge of claim 1 wherein the filter medium comprises one or more of a granular filter media, a pelletized filter media, a filter fabric or a filter mesh.

5. The filter cartridge of claim 1 wherein the fluid reservoir includes an associated check valve for purging air from the fluid reservoir as it fills with filtered water.

6. The filter cartridge of claim 1 wherein at least one upwardly directed air flow passage is provided internal of the cartridge from an upper portion of the fluid reservoir to an upper portion of the drainage space.

7. The filter cartridge of claim 6 wherein a deflecting structure is located below the air flow passage in the drainage space.

8. A stormwater treatment system including a plurality of filter cartridges; each filter cartridge comprising housing having a water inlet and a filtered water outlet; a filter medium disposed along a flow path between the water inlet and the filtered water outlet; a drainage space that forms at least part of the flow path and that is disposed between a downstream side of the filter medium and the filtered water outlet; a solid wall float tube disposed in the drainage space and having an open lower end and open upper end to allow air to pass into, upward through and out of the tube into the drainage space, the solid wall float tube movable between a lowered position that inhibits or substantially restricts filtered water at the bottom of the drainage space from passing to the filtered water outlet and a raised position that permits free flow of filtered water to the filtered water outlet; a fluid reservoir in fluid communication with the drainage space and disposed within the housing and above the filter medium for collecting filtered water as water level in the housing rises while the solid wall float tube is in the lowered position; wherein, as the housing fills, water level in the housing rises to cause the solid wall float tube to move to the raised position and a negative pressure can be established in the housing that draws fluid through the filter medium; wherein, as water level outside the filter cartridge drops, air enters the housing via the water inlet and causes the solid wall float tube to drop to the lowered position, and filtered water in the fluid reservoir backflows through the filter medium and out of the housing through the water inlet while air enters the housing by passing upward through the solid wall float tube so as to enhance rate of backflow while the solid wall float tube is in the lowered position, the system including:

a containment structure including an inlet and at least one drain manifold, each filter cartridge within the containment structure and having its outlet connected to deliver filtered stormwater to the drain manifold.

9. A stormwater filter assembly, comprising:

a housing including an inlet and an outlet;

an inner float tube within the housing and having a lower end associated with the outlet, the float tube movable between a lowered position that inhibits or substantially restricts filtered water from passing to the outlet and a raised position that permits flow of filtered water to the outlet, the inner float tube having an air flow passage therein from its lower end to its upper end to allow air to pass into, upward through and out of the inner float tube;

an outer tube disposed about the inner float tube defining a flow space therebetween for receiving filtered stormwater;

a filter medium disposed between the inlet and the outer tube through which stormwater travels during a filtering operation, the inner float tube extends upward above a height of the filter medium and the outer tube extends upward above the height of the filter medium;

a fluid reservoir located above the filter media for collecting filtered stormwater as water level in the housing rises while the inner float tube is in the lowered position;

wherein during a stormwater filtration event water level in the housing rises to cause the inner float tube to move to the raised position and a negative pressure is established in the housing that draws fluid through the filter medium;

wherein, as water level outside the filter cartridge drops, air enters the housing and disrupts the reduced pressure condition and causes the inner float tube to drop to the lowered position and filtered water in the fluid reservoir backflows through the filter medium and out of the housing while air enters the housing by passing upward through the inner float tube along the air flow passage so as to enhance rate of backflow while the inner float tube is in the lowered position.

10. The filter assembly of claim 9 wherein the inner float tube and outer tube are centrally located within the housing, the filtered water outlet is at the bottom of the housing, the outer tube includes a plurality of openings along at least a lower section thereof.

11. The filter assembly of claim 10 wherein an upper portion of the outer tube is not perforated.

12. The filter assembly of claim 9 wherein the filter medium comprises one or more of a granular filter media, a pelletized filter media, a filter fabric or a filter mesh.

13. The filter assembly of claim 9 wherein the fluid reservoir includes an associated check valve for purging air from the fluid reservoir as it fills with filtered water.

14. The filter assembly of claim 9 wherein at least one upwardly directed air flow passage is provided internal of the cartridge from an upper portion of the fluid reservoir to an upper portion of the flow space.

15. The filter assembly of claim 14 wherein a deflecting structure is located below the air flow passage in the flow space.

16. A stormwater treatment system including a plurality of filter assemblies, each filter assembly comprising: a housing including an inlet and an outlet; an inner float tube within the housing and having a lower end associated with the outlet, the float tube movable between a lowered position that inhibits or substantially restricts filtered water from passing to the outlet and a raised position that permits flow of filtered water to the outlet, the inner float tube having an air flow passage therein from its lower end to its upper end to allow air to pass into, upward, through and out of the inner float tube; an outer tube disposed about the inner float tube defining a flow space therebetween for receiving filtered stormwater; a filter medium disposed between the inlet and the outer tube through which stormwater travels during a filtering operation, the inner float tube extends upward above a height of the filter medium and the outer tube extends upward above the height of the filter medium; a fluid reservoir located above the filter media for collecting filtered stormwater as water level in the housing rises while the inner float tube is in the lowered position; wherein during a stormwater filtration event water level in the housing rises to cause the inner float tube to move to the raised position and a negative pressure is established in the housing that draws fluid through the filter medium; wherein, as water level outside the filter cartridge drops, air enters the housing and disrupts the reduced pressure condition and causes the inner float tube to drop to the lowered position and filtered water in the fluid reservoir backflows through the filter medium and out of the housing while air enters the housing by passing upward through the inner float tube along the flow passage so as to enhance rate of backflow while the inner float tube is in the lowered position, the system including:

a containment structure including an inlet and at least one drain manifold, each filter assembly within the containment structure and having its outlet connected to deliver filtered stormwater to the drain manifold.

17. A method of filtering stormwater to remove contaminants, comprising:

flowing stormwater into a filter unit;

purging air from the filter housing as the filter unit fills with stormwater;

providing a float tube within the unit in a lowered position that inhibits filtered stormwater from exiting through an outlet of the filter unit, the float tube having an air flow passage therein from its lower end to its upper end to allow air to pass upward through the float tube;

filling an upper fluid reservoir of the filter unit with filtered stormwater;

moving the float tube to a raised position that permits filtered stormwater to exit the outlet and creating a reduced pressure condition that draws stormwater through the filter unit;

as water level around the filter housing drops:

air enters the filter unit and disrupts the reduced pressure condition and causes the float tube to drop back to the lowered position; and

filtered water in the fluid reservoir backflows through the filter unit while air enters the filter unit by passing upward through the float tube so as to enhance rate of backflow while the float tube is in the lowered position.

18. The filtration cartridge of claim 1 wherein when the solid wall float tube is in the lowered position the open upper end of the solid wall float tube is located higher than the fluid reservoir.