Membrane System Backwash Energy Efficiency

• US 20110139715A1
• Filed: 08/17/2009
• Published: 06/16/2011
• Est. Priority Date: 08/20/2008
• Status: Active Grant

• Current Assignee: Evoqua Water Technologies LLC
• Original Assignee: Siemen Water Technologies Corporation (Siemens AG)
• Inventors: Cao, Zhiyi, Zha, Fufang
• Granted Patent: US 8,652,331 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 2321/18 Use of gases
• CPC Class Codes: B01D 61/22 Controlling or regulating
• CPC Class Codes: B01D 65/02 Membrane cleaning or sterilisation ; Membrane regeneration
• CPC Class Codes: C02F 1/44 by dialysis, osmosis or reverse osmosis general membrane separation processes B01D61/00, membrane modules B01D63/00, electrodialysis C02F1/4693, combination of membrane modules and bioreactors C02F3/1268
• CPC Class Codes: C02F 2303/16 Regeneration of sorbents, filters

Abstract

A method of backwashing a membrane filtration system comprising at least one permeable membrane, preferably a hollow fibre membrane, the method comprising the step of applying a pressurised gas at a variable pressure to permeate remaining present in the system when filtration process is stopped or suspended to provide liquid for backwashing pores of the permeable membrane during a backwashing process. Also provided are methods of filtering solids from a liquid suspension using alternating liquid backwash pressures.

Claims

1. A method of backwashing a membrane filtration system comprising at least one permeable hollow membrane, the method comprising applying a pressurised gas at a variable pressure to permeate remaining present in the system when a filtration process is stopped or suspended to provide liquid for backwashing pores of the permeable hollow membrane during a backwashing process.

2. A method of filtering solids from a liquid suspension comprising:

(i) providing a pressure differential across a wall of a permeable hollow membrane immersed in the liquid suspension, the liquid suspension being applied to an outer surface of the permeable hollow membrane to induce and sustain filtration through the wall of permeable hollow membrane wherein;

(a) at least part of the liquid suspension passes through the wall of the membrane to be drawn off as permeate from a lumen of the permeable hollow membrane; and

(b) at least some of the solids are retained on or in the permeable hollow membrane or otherwise as suspended solids within the liquid surrounding the permeable hollow membrane; and

(ii) periodically backwashing membrane pores using permeate remaining within the permeable hollow membrane lumen and/or a filtrate manifold where present by applying a gas at a variable pressure below bubble point of the permeable hollow membrane to the permeate to displace at least some of the permeate within the lumen and/or filtrate manifold through pores of the permeable hollow membrane resulting in removal of the solids retained on or in the permeable hollow membrane.

3. A method of filtering solids from a liquid suspension in a filtration system comprising:

(i) providing a pressure differential across a wall of a permeable hollow membrane having a liquid suspension applied to a lumen surface of the permeable hollow membrane to induce and sustain filtration through the wall of the permeable hollow membrane wherein;

(a) at least part of the liquid suspension passes through the wall of the permeable hollow membrane to be drawn off as permeate from an outer surface of the permeable hollow membrane; and

(b) at least some solids are retained on or in the permeable hollow membrane or otherwise as suspended solids within the permeable hollow membrane;

(ii) stopping or suspending the filtration process; and

(iii) periodically backwashing pores of the permeable hollow membrane using permeate remaining in the filtration system after the suspension of the filtration process by applying a gas at a variable pressure below bubble point of the permeable hollow membrane to the permeate to displace at least some of the permeate through pores of the permeable hollow membrane resulting in removal of the solids retained on or in the permeable hollow membrane.

4. The method according to claim 3, wherein the gas pressure is varied between a first and a second value, wherein the first value is higher than the second value.

5. The method according to claim 4, wherein the first and the second pressure values are determined using a measurable membrane characteristic.

6. The method according to claim 5, wherein the membrane characteristic is membrane permeability.

7. The method according to claim 5, wherein the membrane characteristic is membrane resistance.

8. The method according to claim 4, wherein the first value gas pressure is used when membrane permeability is at or below a first predetermined value and the second value gas pressure is used when membrane permeability is at or above a second predetermined value.

9. The method according to claim 4, wherein the first value gas pressure is used when membrane resistance is at or above a first predetermined value and the second value gas pressure is used when the membrane resistance is at or below a second predetermined value.

10. The method according to claim 8, wherein the first predetermined value and second predetermined value are different.

11. The method according to claim 8, wherein the first predetermined value and second predetermined value are the same.

12. The method according to claim 4, wherein the gas pressure is continuously varied between the first value gas pressure and the second value gas pressure.

13. The method according to claim 4, wherein the gas pressure is alternated between the first value gas pressure and the second value gas pressure.

14. The method according to claim 4, wherein solids are removed into bulk liquid surrounding the membranes during the backwashing step.

15. The method according to claim 4, including a plurality of membrane modules in the filtration system.

16. The method according to claim 4, including a plurality of hollow fibre membrane modules in the filtration system.

17. The method according to claim 15, wherein the membrane filtration system is a pressurised membrane filtration system.

18. The method according to claim 15, wherein the membrane filtration system is a submerged membrane filtration system.

19. The method according to claim 3, wherein:

the gas pressure is varied between a first and second value, such that the first value is higher than the second value;

the first and the second pressure values are determined using a measurable membrane characteristic, such that the membrane characteristic is membrane permeability or membrane resistance;

the first value gas pressure is used when membrane permeability is at or below a first predetermined value and the second value gas pressure is used when membrane permeability is at or above a second predetermined value, or the first value gas pressure is used when membrane resistance is at or above a first predetermined value and the second value gas pressure is used when the membrane resistance is at or below a second predetermined value; and

solids are removed into bulk liquid surrounding the membranes during backwashing.

20. The method according to claim 4, wherein:

the gas pressure is varied between a first and second value, such that the first value is higher than the second value;

the first and the second pressure values are determined using a measurable membrane characteristic, such that the membrane characteristic is membrane permeability or membrane resistance;

the first value gas pressure is used when membrane permeability is at or below a first predetermined value and the second value gas pressure is used when membrane permeability is at or above a second predetermined value, or the first value gas pressure is used when membrane resistance is at or above a first predetermined value and the second value gas pressure is used when the membrane resistance is at or below a second predetermined value; and

solids are removed into bulk liquid surrounding the membranes during backwashing.