Low pressure filtration

• US 20070131614A1
• Filed: 07/07/2006
• Published: 06/14/2007
• Est. Priority Date: 01/09/2004
• Status: Active Grant

• Current Assignee: Mann+Hummel Water & Fluid Solutions GmbH
• Original Assignee: Trisep Corporation (Hummel Familien-Beteiligungsgesellschaft mbH + Co. KG)
• Inventors: Knappe, Peter, Snodgrass, Michael
• Granted Patent: US 7,585,411 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 2317/04 Elements in parallel
• CPC Class Codes: B01D 2321/04 Backflushing
• CPC Class Codes: B01D 2321/185 Aeration
• CPC Class Codes: B01D 61/14 Ultrafiltration; Microfiltration
• CPC Class Codes: B01D 61/18 Apparatus therefor
• CPC Class Codes: B01D 63/10 Spiral-wound membrane modules
• CPC Class Codes: B01D 63/101 Spiral winding
• CPC Class Codes: B01D 63/12 comprising multiple spiral-wound 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 1/444 by ultrafiltration or microfiltration

Abstract

High flow, low-pressure ultrafiltration or microfiltration spiral wound membrane cartridges are used in filtration of liquid feedstocks having high suspended solids. Applications may utilize either vacuum or pumping for transmembrane drive pressure (TMP), and gas may optionally be bubbled up through the cartridges with certain feedstocks. Water permeate flux rates as high as 90 gallons per square foot per day (gfd) can be obtained at TMPs below 5 pounds per square inch. By locating each spiral wound cartridge in its own casing and supplying liquid feedstock to an open lower end of the casing, as opposed to submerging such cartridges in a tank filled with feedstock, overall low pressure performance is greatly improved. High permeate flow can be maintained for long periods of time between shutdowns for intensive cleaning. TMP is gradually increased to maintain a substantially constant rate of permeate discharge until a target is reached, indicative of solids accumulation on the membrane surface to an undesirable extent; then backflushing is effected for a short time. Discarding the hold-up volume of feedstock in the cartridge, the backflushing fluid and dislodged solids, allows production to be promptly resumed with fresh feedstock at performance at near original levels.

Claims

1. A method for the filtration of a liquid feedstock high in suspended solids for the purpose of economically producing permeate lean in suspended solids, which method comprises:

a) providing a spiral wound membrane filtration cartridge which includes membrane filter sheet material, feed spacer sheet material and permeate carrier sheet material spirally wound about a perforated permeate collection tube and confined within an open-ended tubular casing in a generally cylindrical, liquid-tight configuration,

b) supporting said cartridge in a substantially vertical orientation,

c) supplying a liquid feedstock to an open end of said cartridge,

d) withdrawing liquid from said cartridge which permeates through said membrane sheet material and enters said permeate collection tube by establishing an initial transmembrane pressure (TMP) across said membrane of at least about 0.5 psi,

e) increasing said TMP over time so as to maintain a permeate flow from said cartridge at about a constant rate, and

f) periodically applying pressurized back-flush fluid to said permeate carrier fabric sheet to back-flush said cartridge by creating flow from within said permeate carrier sheet through said membrane sheet and into said feed spacer each time a predetermined target value is reached, and

g) discarding the feedstock within said feed spacer material in said cartridge along with the back-flush fluid and dislodged solids after said periodic back-flushing and then resupplying said liquid feedstock.

2. The method of claim 1 wherein said periodic back-flushing is carried out to an extent such that said permeate flow rate through said cartridge upon said resupplying of said feedstock is at least about 90% of the flow rate at the initial TMP.

3. The method of claim 1 wherein cartridge is operated in a dead end mode during filtration by maintaining liquid feedstock level in said casing at about the upper end of said cartridge.

4. The method of claim 1 which includes flowing a stream of gas bubbles upward through the lower end of said cartridge, which bubbles travel through said feed spacer material and exit an open upper end of said cartridge.

5. The method of claim 4 which includes collecting said gas from said gas bubbles which exit the upper end of said cartridge and recirculating said gas.

6. The method of claim 5 wherein a cleaning solution is pumped through said cartridge and out the upper end of said casing to aid in removal of accumulated solids and potential contamination at intervals of greater than one month.

7. The method of claim 1 wherein said cartridge is operated in cross flow mode with a rate of feed to said cartridge at least about 5% greater than said rate of permeate flow from said cartridge.

8. The method of claim 1 wherein said membrane material of said cartridge has a permeability to water of at least about 50 gfd/psi and is of a microfiltration or ultrafiltration type made from polysulfone, polyethersulfone, polyvinylidene fluoride or polyacrylonitrile, and wherein a permeation flux through said spiral wound cartridge averaging at least about 5 gfd per psi of average TMP is obtained for operation over an extended period of time of one month or more.

9. The method of claim 8 wherein said discarding step is carried out following at least every other of said back-flush steps.

10. The method of claim 8 wherein discarding step is carried out following substantially every said back-flush step and is carried out to an extent such that said permeate flow rate through said cartridge upon said resupplying of said feedstock is at least about 90% of the flow rate at the initial TMP.

11. A system for the filtration of a liquid feedstock high in suspended solids for the purpose of economically producing permeate lean in suspended solids, which system comprises:

a) a spiral wound membrane filtration cartridge which includes membrane filter sheet material, feed spacer sheet material and permeate carrier sheet material spirally wound about a perforated permeate collection tube and confined within an open-ended tubular casing in a generally cylindrical, liquid-tight configuration,

b) a base for supporting said cartridge in a substantially vertical orientation,

c) means for supplying a liquid feedstock to said base and to an open end of said cartridge,

d) means for creating a liquid-tight seal between said base and said cartridge so that liquid feedstock being supplied flows through said feed spacer material,

e) means for withdrawing liquid from said cartridge which permeates through said membrane sheet material and enters said permeate collection tube as a result of transmembrane pressure (TMP),

f) means for applying pressurized back-flush fluid to said permeate carrier fabric sheet to back-flush said cartridge by creating flow from within said permeate carrier sheet through said membrane sheet and into said feed spacer material,

g) means for periodically initiating such back-flush flow when permeate flow from said cartridge is indicative of an undesirable extent of solids accumulation on said membrane surface, and

h) means for discarding the volume of liquid in said feed spacer sheet material including said back-flush fluid and solids dislodged by said back-flush fluid following completion of said back-flush flow and then resupplying said liquid feedstock to said cartridge.

12. The system of claim 11 wherein there is included means in said base for creating an upwardly flowing stream of gas bubbles in the liquid feedstock below said cartridge, which stream will enter said open end at the bottom of said cartridge and exit an open upper end of said tubular casing.

13. The system of claim 12 wherein said feed spacer sheet material has a thickness of at least about 0.05 inch (about 1.3 mm) and an open pattern such as to allow an upwardly flowing stream of bubbles to rise in the axially extending spiral passageways provided by said feed spacer sheet material in a manner such that bubbles reach and scour active surfaces of said membrane sheet material flanking said feed spacer sheet material, whereby the provision of a net driving pressure of at least about 0.5 psi (about 26 mm of Hg) across said membrane sheet material causes permeation of water lean in solids and low in turbidity into said permeate carrier sheet material at a flux of at least about 5 gfd per psi of average net driving pressure over an extended period of time.

14. The system of claim 11 wherein a cap is connected to the tubular casing at its top and means is provided for collection of gas or liquid that exits the upper end of said casing.

15. The system of claim 14 wherein a plurality of said cartridges and bases are provided and wherein said caps are mechanically interconnected for liquid flow therebetween.

16. The system of claim 15 wherein said bases are interconnected in series to other adjacent bases from which cartridges extend upward.

17. The system of claim 16 wherein means is provided for feeding a cleaning solution into said bases for flow upward through said cartridges and out the top of said casings to effect cleaning and removal of accumulated solids and potential contamination.

18. The system of claim 11 wherein said membrane has a permeability to water of at least about 50 gfd/psi and is of a microfiltration or ultrafiltration type made from polysulfone, polyethersulfone, polyvinylidene fluoride or polyacrylonitrile, and wherein feed spacer material is between 0.05″

to 0.15″

in thickness.

19. The system of claim 18 wherein feed spacer material is made from two sets of polymeric strands, with the strands of each set being aligned in generally parallel relationship, and with a strand count for each set of between two and to six strands per inch, said two sets being aligned generally perpendicular to each other and each being oriented at an angle of about 45°

to the axis of said cartridge.

20. A system for the filtration of a liquid feedstock high in suspended solids for the purpose of economically producing permeate lean in suspended solids, which system comprises:

a) a spiral wound membrane filtration cartridge which includes membrane filter sheet material, feed spacer sheet material and permeate carrier sheet material spirally wound about a perforated permeate collection tube and confined within an open-ended tubular casing in a generally cylindrical, liquid-tight configuration,

b) a base for supporting said cartridge in a substantially vertical orientation,

c) means for supplying a liquid feedstock to said base and to an open end of said cartridge,

d) means for creating a liquid-tight seal between said base and said cartridge so that liquid feedstock being supplied flows through said feed spacer material,

e) means for withdrawing liquid from said cartridge which permeates through said membrane sheet material and enters said permeate collection tube as a result of transmembrane pressure (TMP), and

f) means for applying pressurized back-flush fluid to said permeate carrier fabric sheet to back-flush said cartridge by creating flow from within said permeate carrier sheet through said membrane sheet and into said feed spacer material, whereby wastewater treatment can be effectively carried out without submergence of such cartridges in a tank.