Reduction of Backwash liquid Waste

• US 20070227973A1
• Filed: 09/07/2005
• Published: 10/04/2007
• Est. Priority Date: 09/07/2004
• Status: Active Grant

• Current Assignee: Evoqua Water Technologies LLC (Xylem, Inc.)
• Original Assignee: Evoqua Water Technologies LLC (Xylem, Inc.)
• Inventors: Zha, Fufang, Cao, Zhiyi
• Granted Patent: US 8,790,515 B2
• Time in Patent Office: Days
• US Class Current: 210/636
• CPC Class Codes: B01D 2315/06 Submerged-type; Immersion type
• CPC Class Codes: B01D 2321/04 Backflushing
• CPC Class Codes: B01D 2321/185 Aeration
• CPC Class Codes: B01D 63/02 Hollow fibre modules
• CPC Class Codes: B01D 65/02 Membrane cleaning or sterilisation ; Membrane regeneration

Abstract

A method of filtering solids from a liquid suspension comprising providing a pressure differential across the walls of permeable, hollow membranes (5) immersed in the liquid suspension contained in a vessel (8), the liquid suspension being applied to the outer surface of the porous hollow membrane (5) to induce and sustain filtration through the membrane walls. Some of the liquid suspension passes through the walls of the membranes (5) to be drawn off as permeate from the hollow membrane lumens, and at least some of the solids are retained on or in the hollow membranes or otherwise as suspended solids within the liquid surrounding the membranes (5). The method includes the steps of suspending the flow of the liquid suspension to the vessel (8); reducing the volume of liquid suspension within the vessel (8); suspending the filtration process; cleaning the membranes (5) by dislodging at least some of the solids retained on or in the membranes (5); and removing the liquid containing dislodged solids from the vessel (8).

Claims

1. A method of filtering solids from a liquid suspension comprising the steps of:

(i) providing a pressure differential across the walls of permeable, hollow membranes immersed in the liquid suspension contained in a vessel, said liquid suspension being applied to the outer surface of the porous hollow membranes to induce and sustain filtration through the membrane walls wherein;

(a) some of the liquid suspension passes through the walls of the membranes to be drawn off as permeate from the hollow membrane lumens, and

(b) at least some of the solids are retained on or in the hollow membranes or otherwise as suspended solids within the liquid surrounding the membranes,

(ii) suspending the flow of the liquid suspension to said vessel;

(iii) reducing the volume of liquid suspension within said vessel;

(iv) suspending the filtration process;

(v) cleaning the membranes by dislodging at least some of the solids retained on or in the membranes; and

(vi) removing the liquid containing dislodged solids from said vessel.

2. A method according to claim 1 wherein the cleaning step includes backwashing the membranes.

3. A method according to claim 1 wherein the cleaning step includes scouring the membrane surfaces with gas bubbles.

4. A method according to claim 1 wherein the volume of liquid suspension within the vessel is reduced by continuing withdrawal of the permeate from the membranes while the flow of liquid suspension to the vessel is suspended.

5. A method according to claim 4 wherein the continuing withdrawal of permeate step includes applying gas pressure to the liquid suspension to assist the provision of said pressure differential across the membrane walls.

6. A method according to claim 5 wherein the gas pressure is applied by feeding aerating or scouring gas bubbles into the liquid suspension.

7. A method according to claim 5 wherein the step of applying gas pressure includes applying a separate source of gas pressure to the liquid suspension.

8. A method according to claim 1 wherein the volume of liquid suspension in the vessel is reduced by reversing the liquid suspension flow into the vessel.

9. A method according to claim 1 wherein the volume of liquid within the vessel is reduced to a predetermined level.

10. A method according to claim 9 wherein the predetermined level is sufficient such that the membranes remain immersed in the liquid suspension during scouring and liquid backwash.

11. A filtration system for removing solids from a liquid feed suspension comprising the steps of:

(i) a vessel for containing said liquid feed suspension;

(ii) means for providing a flow of liquid feed suspension to the vessel;

(iii) a plurality of permeable, hollow membranes within the vessel;

(iv) means for providing a pressure differential across walls of said membranes such that some of the liquid suspension passes through the walls of the membranes to be drawn off as permeate while at least some of the solids are retained on or in the hollow membranes or otherwise as suspended solids within the liquid surrounding the membranes,

(v) means for withdrawing permeate from the membranes;

(vi) means for reducing the volume of liquid suspension in the vessel;

(vii) means for suspending the withdrawal of permeate from the membranes;

(viii) means for cleaning the membranes by dislodging at least some of the retained solids from the membranes;

(ix) means for removing the liquid containing the solids from the vessel.

12. A filtration system according to claim 11 wherein the cleaning means includes means for backwashing the membranes.

13. A filtration system according to claim 11 wherein the cleaning means includes means for scouring the membrane surfaces with gas bubbles.

14. A filtration system according to claim 11 wherein the volume of liquid suspension within the vessel is reduced by continuing withdrawal of the permeate from the membranes while the flow of liquid suspension to the vessel is suspended.

15. A filtration system according to claim 11 wherein the volume of liquid suspension in the vessel is reduced by reversing the liquid suspension flow into the vessel.

16. A filtration system according to claim 11 wherein the volume of liquid within the vessel is reduced to a predetermined level.

17. A filtration system according to claim 11 wherein the predetermined level is sufficient such that the membranes remain immersed in the liquid suspension during scouring and liquid backwash.