Methods and systems for reducing biofouling of microfiltration membranes

• US 9,868,660 B2
• Filed: 02/09/2016
• Issued: 01/16/2018
• Est. Priority Date: 04/17/2012
• Status: Active Grant

• Current Assignee: Water Solutions Technology LLC
• Original Assignee: Water Solutions Limited
• Inventors: Allen, Stephen D., Lewis, Edward
• Primary Examiner(s): Drodge, Joseph
• Application Number:
  US15/019,780
• Publication Number:
  US 20160159674A1
• Time in Patent Office: 707 Days
• Field of Search: 210200-203, 210259, 2103216, 21032169, 210513, 210636, 210638, 210639, 210650, 210651, 210710, 210716, 210717, 210722-729, 210732-736, 210764
• CPC Class Codes: B01D 29/56 in series connection
• CPC Class Codes: B01D 65/08 Prevention of membrane fouling or of concentration polarisation
• CPC Class Codes: C02F 1/441 by reverse osmosis
• CPC Class Codes: C02F 1/444 by ultrafiltration or microfiltration
• CPC Class Codes: C02F 1/5236 using inorganic agents
• CPC Class Codes: C02F 1/5245 using basic salts, e.g. of aluminium and iron
• CPC Class Codes: C02F 1/56 Macromolecular compounds
• CPC Class Codes: C02F 1/66 by neutralisation; pH adjustment for degassing C02F1/20; using ion-exchange C02F1/42; for flocculation or precipitation of suspended impurities C02F1/52; for removing dissolved compounds C02F1/58
• CPC Class Codes: C02F 1/725 by catalytic oxidation
• CPC Class Codes: C02F 2101/006 Radioactive compounds
• CPC Class Codes: C02F 2101/103 Arsenic compounds
• CPC Class Codes: C02F 2101/106 Selenium compounds
• CPC Class Codes: C02F 2103/007 Contaminated open waterways, rivers, lakes or ponds
• CPC Class Codes: C02F 2103/10 from quarries or from mining activities
• CPC Class Codes: C02F 2303/20 Prevention of biofouling
• CPC Class Codes: C02F 9/00 Multistage treatment of water, waste water or sewage

Abstract

Systems and methods for reducing biofouling of microfiltration membranes that are biofouled with biological substances are disclosed. The methods include providing impound water containing biomolecule-based exopolymeric substances, reacting with calcium oxide or calcium hydroxide, encapsulating the exopolymeric substance into filterable non-tacky particles by reacting with an inorganic coagulant and a low molecular weight polymer, and microfiltering to remove the filterable non-tacky particles encapsulating the exopolymeric substances. The filterable non-tacky particles encapsulate the exopolymeric substances and prevent the exopolymeric substances from biofouling the microfiltration membranes.

Claims

1. A method for reducing biofouling of microfiltration membranes by a biomolecule-based exopolymeric substance, the method comprising:

providing impound water comprising a biomolecule-based exopolymeric substance;

reacting the impound water with calcium oxide or calcium hydroxide to generate a calcium-treated biomolecule-based exopolymeric substance mixture;

encapsulating the reacted biomolecule-based exopolymeric substance into filterable, non-tacky particles by reacting the calcium-treated biomolecule-based exopolymeric substance mixture with an aluminum-based inorganic coagulant and a cationic polymer having a molecular weight in the range from about 200,000 to about 800,000 Daltons (Da) having a molecular weight in the range from 200,000 to 800,000 Da;

removing a first portion of the encapsulated biomolecule-based exopolymeric substance as bulk solid; and

removing a second portion of the encapsulated biomolecule-based exopolymeric substance by low pressure microfiltration through a microfiltration membrane comprising a pore size of between about 0.7 to 12 microns,

wherein encapsulating the biomolecule-based exopolymeric substance into filterable, non-tacky particles reduces biofouling of the microfiltration membrane.

2. The method of claim 1, wherein the calcium oxide or calcium hydroxide is reacted at a final concentration of between about 100 mg/L to 225 mg/L.

3. The method of claim 1, wherein the inorganic coagulant comprises aluminum chlorohydrate.

4. The method of claim 3, wherein the aluminum chlorohydrate is reacted at a final concentration of about 25 mg/L to 75 mg/L.

5. The method of claim 1, wherein the cationic polymer comprises epi-dma (poly(epichlorhydrin-dimethylamine).

6. The method of claim 1, wherein the inorganic coagulant and cationic polymer are reacted with the calcium-treated biomolecule-based exopolymeric substance mixture at a ratio of coagulant to polymer of about 1:

1 to 10;

1.

7. The method of claim 1, wherein the microfiltration membrane comprises polypropylene, polysulfone, polyethylene, polytetrafluoroethylene, or combinations thereof.

8. The method of claim 1, wherein the microfiltration membrane comprises a pore size between about 1 to 2.5 microns.

9. The method of claim 1, wherein microfiltering further comprises:

microfiltering with a microfilter membrane at a back pressure of less than about 15 pounds per square inch and at a flow rate of at least 650 gallons per square foot of microfilter membrane per day; and

periodically backwashing the microfilter membrane to remove collected filterable non-tacky particles.

10. A method for removing polysaccharide-based exopolymeric substance from an aqueous mixture, the method comprising:

providing an aqueous mixture, the aqueous mixture containing exopolymeric substance and one or more of dissolved solids, suspended solids or heavy metals;

reacting the aqueous mixture with calcium oxide or calcium hydroxide to generate a calcium-treated mixture;

encapsulating the reacted polysaccharide-based exopolymeric substance into filterable, non-tacky particles by reacting the calcium-treated mixture with aluminum chlorohydrate and epi-dma (poly(epichlorhydrin-dimethylamine);

mechanically removing a first portion of the encapsulated polysaccharide-based exopolymeric substance as bulk solid; and

microfiltering to remove a second portion of the encapsulated polysaccharide-based exopolymeric substance.

11. The method of claim 10, wherein microfiltering further comprises:

microfiltering with a microfilter membrane at a back pressure of less than about 15 pounds per square inch and at a flow rate of at least 650 gallons per square foot of microfilter membrane per day; and

periodically backwashing the microfilter membrane to remove collected filterable non-tacky particles.

12. The method of claim 10, further comprising microfiltering with a microfilter membrane comprising polypropylene, polysulfone, polyethylene, polytetrafluoroethylene, or combinations thereof.

13. The method of claim 11, wherein the microfilter membrane comprises a pore size between about 0.7 and about 12 microns.

14. The method of claim 11, wherein the microfilter membrane comprises a pore size between about 1 to 2.5 microns.