Methods for cleaning and maintaining membrane surface during filtration

• US 7,531,042 B2
• Filed: 12/18/2003
• Issued: 05/12/2009
• Est. Priority Date: 12/19/2002
• Status: Expired due to Fees

• Current Assignee: Hydranautics (Nitto Denko Corporation)
• Original Assignee: Hydranautics (Nitto Denko Corporation)
• Inventors: Tvaruzek, Pavel, Murkute, Pravin
• Primary Examiner(s): Barr; Michael
• Assistant Examiner(s): Chaudhry; Saeed T
• Application Number:
  US10/740,657
• Publication Number:
  US 20040139992A1
• Time in Patent Office: 1,972 Days
• Field of Search: 134/1, 210/636, 210/644, 210/321.79, 210/321.84, 210/321.88
• US Class Current: 134/1
• CPC Class Codes: B01D 2315/06 Submerged-type; Immersion type
• CPC Class Codes: B01D 2321/04 Backflushing
• CPC Class Codes: B01D 2321/2066 Pulsated flow
• CPC Class Codes: B01D 61/14 Ultrafiltration; Microfiltration
• CPC Class Codes: B01D 63/02 Hollow fibre modules
• CPC Class Codes: B01D 63/04 comprising multiple hollow fibre assemblies
• CPC Class Codes: B01D 65/02 Membrane cleaning or sterilisation ; Membrane regeneration
• CPC Class Codes: B01D 65/08 Prevention of membrane fouling or of concentration polarisation
• CPC Class Codes: C02F 3/12 Activated sludge processes
• CPC Class Codes: Y02W 10/10 Biological treatment of water, waste water, or sewage

Abstract

A method is provided for cleaning a membrane surface or maintaining a clean outside surface of a membrane during a process of outside-in membrane separation to remove suspended solids from a liquid phase. The method involves applying pressurized gas pulses to the membrane surface with individual pulse lengths of about 0.1 to 10 seconds. The pulses may be injected singularly with an interval of about 10 to 1000 seconds between pulses for a total duration of about 0.1 to 1000 hours. Alternatively, the pulses may be injected in clusters of about 2 to 100 pulses with an interval of 50-300% of the pulse length between individual pulses for a total duration of about 10 to 1000 seconds. In a preferred embodiment, both types of pulsation methods are combined in a particular sequence. The expanding gas directed toward the membrane surface in the course of one pulse dissipates energy of up to about 40 kJ/m³. One embodiment of the cleaning method involves backwashing the membrane with a permeate and applying the pressurized gas pulses during the filtration and/or backwashing steps of a filtration cycle.

Claims

1. A method of cleaning a membrane surface or maintaining a clean membrane surface during an outside-in membrane separation process, the method comprising applying pressurized gas pulses having an individual pulse length of about 0.1 to about 5 seconds to an immediate vicinity of the membrane surface to form an aerated volume while simultaneously performing a separation process.

2. The method according to claim 1, wherein the pressurized gas pulses exhibit a pressure of about 10 to 90 psig and a flow rate of about 20 to 300 scfm per square meter of a cross section of the aerated volume.

3. The method according to claim 1, wherein the pressurized gas pulses generate an energy dissipation of up to about 40 kj/m3 of power to the immediate vicinity of the membrane surface.

4. The method according to claim 1, wherein the method comprising applying the pressurized gas pulses comprises at least one operation selected from the group consisting of:

(a) injecting the pressurized gas pulses singularly for a total duration of about 0.1 to about 1000 hours, wherein an interval between the pulses is about 10 to 1000 seconds; and

(b) injecting the pressurized gas pulses in clusters comprising about 2 to 100 individual pulses for a total duration of about 0.1 to about 1000 seconds, wherein an interval between the individual pulses in the clusters is about 50 to 300% of a pulse length.

5. The method according to claim 1, wherein the membrane comprises at least one selected from the group consisting of hollow fiber, flat sheet, tubular, and capillary sheet.

6. The method according to claim 1, wherein the method comprises holding the membrane with its longitudinal axis vertical such that the membrane surface is parallel to a direction of gas flow from the pressurized gas pulses.

7. The method according to claim 1, wherein the method comprises holding the membrane with its longitudinal axis horizontal such that the membrane surface is orthogonal to a direction of gas flow from the pressurized gas pulses.

8. The method according to claim 7, wherein the membrane comprises at least one hollow fiber orthogonal to the direction of gas flow from the pressurized gas pulses.

9. The method according to claim 1, wherein applying the pressurized gas pulses to the membrane surface is carried out by at least one distributor having openings of about 0.2 to 7 mm placed near a lower end of the membrane and oriented at an angle of about 0 to 80°

with respect to a vertical direction, such that a direction of gas flow from the gas pulses is upward.

10. The method according to claim 1, wherein the membrane is inside a closed, pressurized vessel and the membrane separation process is one selected from the group consisting of a dead-end membrane separation, a semi-dead-end membrane separation, and a separation wherein a liquid to be filtered flows tangentially across the surface of the membrane.

11. The method according to claim 10, wherein the liquid to be filtered comprises a multicomponent liquid containing at least one suspended solid.

12. The method according to claim 1, wherein the method is performed in a closed vessel comprising a liquid phase and a gas phase.

13. The method according to claim 1, further comprising contacting the membrane with a cleaning or washing liquid substantially contemporaneously with applying the pressurized gas pulses.

14. The method according to claim 1, wherein the membrane separation process comprises a step of filtering a liquid containing at least one suspended solid to produce a permeate, further comprising a step of backwashing the membrane surface with the permeate.

15. The method according to claim 14, wherein the method comprises applying the pressurized gas pulses substantially simultaneously with at least one of the filtering and backwashing steps.

16. The method according to claim 14, wherein the backwashing step comprises applying a backwash flow of about 12 to 80 gfd and a backwash pressure of about 3 to 40 psig.

17. The method according to claim 14, wherein a duration of the backwashing step is about 0.25 to 5 minutes.

18. The method according to claim 14, wherein the backwashing step is conducted after each filtering step.

19. The method according to claim 14, wherein a duration of the filtering step is about 10 to 1440 minutes.

20. The method according to claim 14, wherein the method comprises injecting the pressurized gas pulses in clusters simultaneously with the backwashing step.

21. The method according to claim 14, wherein the backwashing step comprises applying the permeate as pressure or flow pulses.

22. The method according to claim 14, wherein the backwashing step further comprises adding at least one cleaning chemical to the permeate for backwashing the membrane surface.