WO2016090432A1 - A filtration membrane and its method of production - Google Patents

A filtration membrane and its method of production Download PDF

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Publication number
WO2016090432A1
WO2016090432A1 PCT/AU2015/050780 AU2015050780W WO2016090432A1 WO 2016090432 A1 WO2016090432 A1 WO 2016090432A1 AU 2015050780 W AU2015050780 W AU 2015050780W WO 2016090432 A1 WO2016090432 A1 WO 2016090432A1
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Prior art keywords
mesorhizobium
membrane
layer
eps
filtration membrane
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PCT/AU2015/050780
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French (fr)
Inventor
Carol NICHOLS
Thuy Tran
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Commonwealth Scientific And Industrial Research Organisation
Murdoch University
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Priority claimed from AU2014905015A external-priority patent/AU2014905015A0/en
Application filed by Commonwealth Scientific And Industrial Research Organisation, Murdoch University filed Critical Commonwealth Scientific And Industrial Research Organisation
Publication of WO2016090432A1 publication Critical patent/WO2016090432A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B01D69/1216—Three or more layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/08—Polysaccharides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0081—After-treatment of organic or inorganic membranes
    • B01D67/0093—Chemical modification
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
    • B01D67/0081—After-treatment of organic or inorganic membranes
    • B01D67/0093—Chemical modification
    • B01D67/00933—Chemical modification by addition of a layer chemically bonded to the membrane
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/14—Dynamic membranes
    • B01D69/141—Heterogeneous membranes, e.g. containing dispersed material; Mixed matrix membranes
    • B01D69/142—Heterogeneous membranes, e.g. containing dispersed material; Mixed matrix membranes with "carriers"
    • B01D69/144—Heterogeneous membranes, e.g. containing dispersed material; Mixed matrix membranes with "carriers" containing embedded or bound biomolecules
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/74—Natural macromolecular material or derivatives thereof
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2321/00—Details relating to membrane cleaning, regeneration, sterilization or to the prevention of fouling
    • B01D2321/16—Use of chemical agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/28—Degradation or stability over time
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D65/00—Accessories or auxiliary operations, in general, for separation processes or apparatus using semi-permeable membranes
    • B01D65/08—Prevention of membrane fouling or of concentration polarisation

Definitions

  • the present specification relates to a composite filtration membrane, various uses thereof and its method of production.
  • Membranes are widely used in the separation of mixtures.
  • the membrane separation process allows for the removal of material (for example, salt ions) dissolved in a liquid (for example, water) in a cost effective and efficient manner.
  • Typical membranes used in the membrane separation process include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, forward osmosis (FO) membranes and reverse osmosis (RO) membranes.
  • Reverse osmosis (RO) is a water purification technique commonly used in the desalination of salt water.
  • Other applications of RO include wastewater treatment, food and pharmaceutical processing, minerals processing and pure water production.
  • Central to RO technology is the use of a semipermeable membrane and the application of a pressure greater than the osmotic pressure on the feed water. Under pressure, purified water passes through the membrane whilst salts and other dissolved ions and molecules are retained.
  • CA membranes were made from cellulose acetate (CA) via a phase inversion process.
  • the first developed CA membranes had an asymmetric structure with a dense surface layer which is responsible for the salt rejection property.
  • the rest of the membrane supported the thin surface layer mechanically and has high water permeability (Loeb and Sourirajan (1963) Advances in Chemistry Series, 38, 117; Loeb and Sourirajan (1964) US Patent No. 3,133,132).
  • RO membranes are now mostly composite semipermeable (CS) membranes, such as thin film composite (TFC) membranes, with a gel layer or thin layer (separation functional layer) formed on a microporous support.
  • the thin layer (separation functional layer) is produced by crosslinking a polymer, such as a polyamide, on a microporous support, such as a porous polysulfone support layer (Cadotte (1981) US Patent No. 4,277,344).
  • a composite semipermeable membrane in which a microporous support is coated with a thin layer comprising a crosslinked polyamide is widely applied as a reverse osmosis membrane, as described by Tomaschke (1989), US Patent No.
  • CS membranes are widely used in the water treatment industry, mainly because they can tolerate harsher chemical environment and are operable over wider pH, pressure and temperature ranges with improved flux and salt rejection compared to cellulose acetate membranes.
  • membrane fouling is a major obstacle that prevents efficient operation of RO systems, causing deterioration of both the quantity and quality of the treated water and increasing the pressure requirements to pass water through the membrane resulting in higher treatment cost.
  • membrane fouling occurs when impurities in the feed water deposit onto the surface of the membranes. Biofouling occurs where microorganisms attach to the membrane surface and proliferate to form biofilms.
  • Biofilms are formed by microorganisms in aqueous environments by the production of extracellular polymeric substances (EPS) that are essential for the attachment, survival and growth of microorganisms within the surface- bound biofilm.
  • EPS extracellular polymeric substances
  • the excreted EPS forms a complex matrix of polysaccharides, proteins, nucleic acids and lipids to provide a layer of protection to cells against toxic compounds, other organisms, or physical damage.
  • proliferating microorganisms produce biologic/organic, colloidal and particulate or crystalline matter that degrades the membrane surface.
  • biofouling can become so severe that continued operation is not acceptable and membrane replacement is required.
  • a number of methods have been advanced to mitigate membrane biofouling.
  • One approach involves the application of biocides to kill microorganisms that are attached to the membrane surface.
  • biocides used for this purpose include nanoscale Ti02 particles, which exhibit antimicrobial properties when exposed to ultra-violet (UV) radiation (Kwak et al. (2003) US Patent No. 6,551,536); and silver dispersed in a solution of polyvinyl alcohol (Nishiyama et al. (2010) US Patent No. 2010/0178489).
  • Another anti-fouling approach is to modify the membrane surface. Hydrophilic materials have low fouling potential; therefore, membrane surface hydrophilicity may be increased by coating the surface with a layer of hydrophilic species.
  • Hydrophilic coating substances that have been previously used include polyethylene glycol, polyvinylpyrrolidinone, poly(vinyl alcohol) (Hachisuka and Ikeda (2001) US Patent No. 6,177,011); polyethylene glycol diepoxide (Mickols (2001) US Patent No. 6,280,853); polyfunctional epoxy compounds comprising at least two epoxy groups (Koo et al. (2005) US Patent No. 6,913,694); copolymers of poly(ethylene glycol) methyl ether methacrylate and glycidyl methacrylate or glycidyl methacrylates (Niu (2007) US Patent No.
  • micro-, ultra- and nano- filtration membranes have been used for the pre-treatment of feed water prior to RO filtration.
  • the main purpose of pre- treatment is to reduce the concentration of fouling agents present in the feed water to be subjected to the RO membrane surface and therefore reduce biofouling.
  • pre- treatment using these membranes is not totally effective in the removal of bacteria from the feed water, resulting in persistent formation of biofilms on the RO membrane surface (Ghayeni et al. (1998) Journal of Membrane Science, 138, 29; Ghayeni et al. (1999) Journal of Membrane Science, 153, 71).
  • such pre-treatment membranes are also subject to biofouling by bacteria and the adsorption of dissolved matter such as colloids (Howe and Clark (2002) Environmental Science and Technology, 36(16), 3571).
  • the present specification teaches a composite filtration membrane comprising: a) a membrane;
  • a layer which presents as a coating across a surface of the membrane wherein the layer comprises:
  • the membrane is a semipermeable membrane.
  • the present specification teaches a composite filtration membrane comprising: a) a semipermeable membrane;
  • a layer which presents as a coating across a surface of the membrane wherein the layer comprises:
  • an extracellular polymeric substance produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • EPS extracellular polymeric substance
  • the layer confers biofouling resistance.
  • the present specification teaches a composite filtration membrane comprising: a) a semipermeable membrane;
  • a biofouling resistant layer which presents as a coating across a surface of the membrane, wherein the layer comprises:
  • an extracellular polymeric substance produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism;
  • the microbial cell is selected from the list comprising Mesorhizobium huakuii, Mesorhizobium loti, Mesorhizobium abyssinicae, Mesorhizobium albiziae, Mesorhizobium alhagi, Mesorhizobium amorphae, Mesorhizobium australicum, Mesorhizobium camelthorni, Mesorhizobium caraganae, Mesorhizobium chacoense, Mesorhizobium cicero, Mesorhizobium gobiense, Mesorhizobium hawassense, Mesorhizobium mediterraneum, Mesorhizobium metallidurans, Mesorhizobium muleiense, Mesorhizobium opportunistum, Mesorhizobium plurifarium, Mesorhizobium qingsheng
  • the microbial cell is M. huakuii or M. loti or a microorganism having biochemical, physiological or genetic properties similar to M. huakuii or M. loti.
  • the microbial cell is designated CAM543 which was deposited at the National Measurements Institute on 29 October, 2014 under accession number V14/017216.
  • the composite filtration membrane comprises a membrane and a layer which comprises an isolated polysaccharide derived from EPS produced by the microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • the layer can be formed on the surface of the membrane by any suitable means.
  • the layer is attached to the surface of the membrane via a linker.
  • the layer is attached to the surface of the membrane via an inorganic linker.
  • the layer is attached to the surface of the membrane via a linker derived from any suitable metal alkoxide or alkoxysilane. [0027] In an embodiment, the layer is attached to the surface of the membrane via a titanium alkoxide.
  • the layer is attached to the surface of the membrane via titanium isopropoxide.
  • the composite filtration membrane of the present specification comprises two main components, namely, a membrane and a layer which is formed on the surface of the membrane. Each of these components has specific features and collectively they provide for a composite filtration membrane that exhibits useful properties including removing or concentrating particular solutes or other molecules from a liquid.
  • the combination of the membrane with the layer provides the composite filtration membrane with sound mechanical properties.
  • the composite filtration membrane of the present specification exhibits biofouling resistance in conditions that are comparable to water treatment plant operating conditions.
  • the layer is stable under conditions of high applied transmembrane pressure (Table 6) and high cross- flow velocity for prolonged periods of time ( Figure 11).
  • the composite filtration membrane is useful for concentrating or isolating proteins, including polypeptides in the form of antibodies.
  • the composite filtration membrane is useful for concentrating or isolating proteins from liquid foodstuffs.
  • the composite filtration membrane is useful for purifying and concentrating biologically useful molecules such as peptides, proteins, antibodies and antibiotics.
  • the layer can advantageously be presented on the surface of the membrane in the form of an ultrathin layer (e.g. less than 100 nm). Minimizing the thickness of the layer has been found to improve filtration properties and also reduce the manufacturing cost of the membrane.
  • the present specification also teaches a method for preparing a composite filtration membrane comprising: a) providing a membrane; and
  • a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • the present specification teaches a method for preparing a composite filtration membrane comprising: a) providing a semipermeable membrane; and
  • a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • the present specification teaches a method for preparing a composite filtration membrane having a biofouling resistant layer, the method comprising: a) providing a semipermeable membrane; and
  • biofouling resistant layer comprises:
  • a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; wherein the resulting composite filtration membrane exhibits biofouling resistance.
  • the membrane may be a microfiltration, ultrafiltration, nanofiltration or a reverse osmosis membrane.
  • the membrane may be prepared by any suitable means. The art of making membranes is well documented in the published literature and are commercially available.
  • the membrane is a semipermeable membrane.
  • the membrane is a reverse osmosis membrane. In another embodiment, the membrane is a forward osmosis membrane.
  • the method for preparing a composite filtration membrane comprises forming a layer on a surface of the membrane.
  • the layer is formed on the surface of the membrane by any suitable means.
  • the layer is formed on the surface of the membrane using a linker.
  • the layer is formed on the surface of the membrane using an inorganic linker.
  • the layer is formed on the surface of the membrane using a metal alkoxide.
  • the layer is formed on the surface of the membrane using a titanium metal alkoxide.
  • the layer is formed on the surface of the membrane using titanium isopropoxide.
  • a method for preparing a composite filtration membrane having a layer wherein the layer is formed on a surface of the membrane by treating the membrane with a composition comprising one or more metal alkoxides and the EPS or polysaccharide component thereof.
  • a method for preparing a composite filtration membrane having a biofouling resistant layer wherein the biofouling resistant layer is formed on a surface of a semipermeable membrane by treating the semipermeable membrane with a composition comprising one or more metal alkoxides and the EPS or polysaccharide component thereof.
  • the present specification teaches a process for the treatment of a liquid comprising subjecting the liquid to filtration by contacting the liquid with a composite filtration membrane comprising: a) a membrane; and
  • a layer which presents as a coating across the surface of the membrane wherein the layer comprises:
  • an extracellular polymeric substance produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism.
  • EPS extracellular polymeric substance
  • the present specification teaches a process for the treatment of a liquid comprising subjecting the liquid to filtration by contacting the liquid with a composite filtration membrane comprising: a) a semipermeable membrane; and
  • a layer which presents as a coating across the surface of the membrane wherein the layer comprises:
  • an extracellular polymeric substance produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism.
  • EPS extracellular polymeric substance
  • the present specification teaches a process for the treatment of a liquid comprising subjecting the liquid to filtration by contacting the liquid with a composite filtration membrane comprising: a) a semipermeable membrane; and
  • a biofouling resistant layer which presents as a coating across the surface of the membrane, wherein the layer comprises:
  • an extracellular polymeric substance produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-Xi e, microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism;
  • the composite filtration membrane of the present specification is a reverse osmosis filtration membrane for filtering salt water.
  • the composite filtration membrane of the present specification is a forward osmosis (FO) filtration membrane for filtering salt water.
  • the membrane of the present specification is a microfiltration, ultrafiltration or nanofiltration membrane for pre-treating liquids before reverse osmosis filtration.
  • the membrane of the present specification is a microfiltration, ultrafiltration or nanofiltration membrane for purifying and concentrating proteins.
  • the nanofiltration, microfiltration or ultrafiltration may be used to purify and concentrate antibodies, antibiotics or proteins from liquid foodstuffs.
  • Figure 1 is a graphical representation of a cross section of the filtration membrane which comprises (a) a porous substrate; (b) a separation functional layer; (c) an optional hydrophilic layer; and (d) a biofouling resistant layer.
  • Figure 2 is a schematic representation of coordination modes between carboxylic group (-COOH) groups and titanium.
  • Figure 3 is a schematic representation of the reaction between titanium alkoxide and compounds containing hydroxyl groups (-OH).
  • Figure 4 is a photographic representation of the SEM analysis of the surface of (a) uncoated membrane; and sample series (b) Tl, (c) T2, (d) T3, (e) T4, (f) T5 and (g) T6.
  • Figure 5 is a graphical representation of the ATR-FTIR spectra of sample series T1-T6 after the water flux tests.
  • Figure 6 is a graphical representation of the magnified ATR-FTIR spectra after the water flux tests in the wave number region (a) 2600-3800 cm-1 and (b) 950-1150 cm-1.
  • Figure 7 is a graphical representation of a deconvoluted XPS Cls peak for (a) uncoated membrane; and (b) coated T3 membrane.
  • Figure 8 is a graphical representation of a deconvoluted XPS Ols peak for (a) uncoated membrane; (b) coated T3 membrane; and coated D3 membrane with high cross link density.
  • Figure 9 is a photographic representation of contact angles of a drop of water on the surfaces of (a) uncoated membrane; (b) sample series Tl; and (c) sample series T2- T6.
  • Figure 10 is a graphical representation of the ATR-FTIR spectra of coated membrane (a) before and (b) after the water exposure test.
  • Figure 11 is a graphical representation of the ATR-FTIR spectra of coated membrane (a) before and (b) after the cross-flow test.
  • Figure 12 is a photographic representation of SEM images of uncoated and coated membrane samples following exposure to E. coli in culture for 72 h for (a) uncoated membrane; (b) Tl coated membrane; (c) T2 coated membrane; (d) T3 coated membrane; and (e) T4 coated membrane. Images were acquired at 1000X and 5000X magnification.
  • the present specification teaches a composite filtration membrane comprising: a) a membrane;
  • a layer which presents as a coating across a surface of the membrane wherein the layer comprises:
  • an extracellular polymeric substance produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • EPS extracellular polymeric substance
  • microbial cell and “microorganism” may be used interchangeably throughout this specification.
  • Reference to a "Mesorhizobium or Mesorhizobium-li e microorganism” includes a Gram negative bacterium with monotrichous flagella, which grows to a colony diameter of 1 to 4 mm after 7 days on yeast mannitol agar (YMA), exhibits a generation time of 4 to 10 hours in yeast mannitol broth (YMB), tolerates a maximum growth temperature of 36°C to 39°C, exhibits a maximum NaCl tolerance for growth of 1 to >2.5 (% w/v), tolerates a pH range for growth of 4 to 10 and has the ability to grow on melibiose.
  • YMA yeast mannitol agar
  • YMB yeast mannitol broth
  • YMB yeast mannitol broth
  • tolerates a maximum growth temperature of 36°C to 39°C exhibits a maximum NaCl tolerance for growth of
  • membrane includes a semipermeable membrane.
  • the membrane may be a nanofiltration, microfiltration, ultrafiltration, forward osmosis (FO) or reverse osmosis (RO) membrane.
  • the membrane is a semipermeable membrane.
  • the present specification teaches a composite filtration membrane comprising: a) a semipermeable membrane;
  • a layer which presents as a coating across a surface of the membrane wherein the layer comprises:
  • an extracellular polymeric substance produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • EPS extracellular polymeric substance
  • the layer confers biofouling resistance.
  • biofouling resistant or “biofouling resistance” includes a reduction or complete prevention of biofouling on the surface of a filtration membrane as a result of the layer when compared to membranes that do not have the layer.
  • the present specification teaches a composite filtration membrane comprising: a) a semipermeable membrane;
  • biofouling resistant layer which presents as a coating across a surface of the membrane, wherein the biofouling resistant layer comprises:
  • an extracellular polymeric substance produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism;
  • the composite filtration membrane exhibits biofouling resistance.
  • the membranes described in the present specification are well known in the art and are commercially available. The present specification encompasses instances where the membrane is purchased from a commercial vendor or produced de novo by a person skilled in the art.
  • the membrane is a RO membrane with a separation functional layer attached to the surface of a porous substrate.
  • An optional hydrophilic layer may also be attached to the surface of the separation functional layer.
  • the present invention further encompasses any other additional layers which may be reasonably attached to the porous substrate for the purposes of separating aqueous solutions.
  • the membrane is a FO membrane.
  • Figure 1 illustrates a schematic cross-section of the composite filtration membrane comprising (a) a porous substrate; (b) a separation functional layer; and (c) an optional hydrophilic layer; and (d) a layer presenting as a coating across the surface of the membrane.
  • the separation functional layer, optional hydrophilic layer and the layer presenting as a coating across the surface of the membrane are attached to the (e) feed water surface of the membrane.
  • the (f) permeate surface of the membrane does not have any additional layers attached.
  • Reference to a "feed water surface” means the surface of the porous substrate that is exposed to the influent water for treatment.
  • the feed water surface may be exposed to salt water.
  • Reference to the "permeate surface” means the surface of the porous substrate that the filtration permeate is expelled from the membrane.
  • the porous substrate will generally impart mechanical strength to the composite membrane.
  • the porous substrate may therefore also be described as a porous substrate support structure or simply a porous support structure. Provided the porous substrate functions as herein described, there is no particular limitation on the composition from which the substrate is made.
  • the porous substrate is to come into contact with a solvent during application of the separation functional layer, the substrate should not be adversely affected by the solvent (e.g. it should not be soluble in the solvent).
  • porous substrate examples include polymer and inorganic substrates.
  • the porous substrate is inorganic.
  • suitable inorganic substrates include ceramics and metal oxides such as silica and alumina.
  • the porous substrate is a polymer
  • Suitable polymers from which the porous substrate may be made include, but are not limited to, poly(acrylonitrile) (PAN), polysulfone (PSf), polyethylene terephthalate (PET), polyethersulphone, polyaniline, polypropalene, polyimides (PI), cellulose acetate (CA), cellulose diacetate and cellulose triacetate, and co-polymers thereof.
  • PAN poly(acrylonitrile)
  • PSf polysulfone
  • PET polyethylene terephthalate
  • PET polyethersulphone
  • PI polyimides
  • CA cellulose diacetate
  • cellulose triacetate co-polymers thereof.
  • references to "co-polymers thereof” is intended to mean the "general polymer” that comprises one or more difference polymerized monomer residues.
  • a copolymer of PAN is intended to mean polymer comprising polymerized residues of acrylonitrile and one or more other monomers.
  • references to "general polymer”-based polymers is intended to embrace the homo-polymer and co-polymer thereof.
  • poly(acrylonitrile) homo- or copolymers may be referred to simply as "PAN-based" polymers.
  • PAN-based polymers poly(acrylonitrile) homo- or copolymers
  • a homo-polymer consists essentially of polymerized residues of one monomer type.
  • a co-polymer will comprise polymerized residues of at least two monomer types.
  • the polymer is a copolymer
  • that specified polymer will typically comprise less than 50 wt% of a second polymerized monomer residue.
  • the co-polymer will comprise less than 50 wt% of polymerized monomer residues other than polymerized acrylonitrile monomer residues.
  • the co-polymer must of course comprise at least some of the other polymerized monomer residue.
  • the porous substrate is a porous polysulfone homo- or copolymer substrate.
  • the porous substrate can be fabricated into the composite filtration membrane in accordance with the invention there is no particular limitation on the shape or dimensions which it may take. Generally, the porous substrate will have a thickness ranging from about 20 ⁇ to about 100 ⁇ .
  • Reference to "20 ⁇ to about 100 ⁇ " means 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100 ⁇ .
  • porous substrate contains pores that enable solutions to flow through the substrate.
  • the substrate being “porous” or the substrate containing "pores” is meant that the substrate contains voids or holes that are suitably arranged to provide channels within the substrate through which solution can flow.
  • the separation functional layer is a layer substantially having separation performance that is made of polymer film and is located on and attached to the porous support membrane.
  • the separation functional layer is obtained by crosslinking a polymer onto the surface of the porous support.
  • the separation functional layer is a layer obtained by polymerizing one or more monomers onto the surface of the porous support.
  • the separation functional layer forms a continuous coating on the surface of the porous support membrane.
  • Reference to a "polymer film” means that the layer presents a film having a polymer matrix formed by crosslinking one or more monomers.
  • the separation functional layer is covalently coupled to the porous support membrane. In other words, the separation functional layer is not merely adhered to the porous support membrane but rather is coupled to it on a molecular level.
  • the separation functional layer has a suitable degree of selectivity for the target solutes, there is no particular limitation on the composition of the separation functional layer. Those skilled in the art will be able to choose an appropriate separation functional layer for use in a given solvent purification process.
  • the separation functional layer is in the form of a crosslinked polyamide film and the filtration membrane is for separating water from brackish or salt water.
  • the separation functional layer may also be functionalized by the addition of a crosslinked hydrophilic layer.
  • hydrophilic layers include crosslinked polyethylene glycol, polyvinylpyrrolidinone, poly(vinyl alcohol), polyethylene glycol diepoxide; polyfunctional epoxy compounds comprising at least two epoxy groups; copolymers of poly(ethylene glycol) methyl ether methacrylate and glycidyl methacrylate or glycidyl methacrylates; sulfobetaine and other zwitterionic polymers; and polyactams, poly-amino acids and polymers containing tertiary ammonium groups to the membrane surface either directly or via pre-defined spacers (tethers) and linkers.
  • the separation functional layer is a crosslinked polyamide film functionalized by the addition of a crosslinked polyvinyl alcohol hydrophilic layer.
  • the separation functional layer is a crosslinked polyamide film with an additional polyvinyl alcohol hydrophilic layer.
  • the polyvinyl alcohol hydrophilic layer may be applied by way of spin coating, knife coating or dip coating.
  • the separation functional layer can be seen as comprising a continuous coating on the surface of the porous substrate, or alternatively, further comprising an optional hydrophilic layer that is a continuous coating on the surface of the separation functional layer.
  • the separation functional layer is attached to the (e) feed water surface of the porous substrate.
  • the (f) permeate surface is not coated with a separation functional layer.
  • the separation functional layer performs its function of separating water from aqueous solutions there is no particular limitation on the thickness of the layer that can be used.
  • the separation functional layer is provided as an ultrathin polymer layer, which can be produced using conventional techniques.
  • the ultrathin layer will be between 1 to 150 nm.
  • Reference to "between 1 to 150 nm" means 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97,
  • the EPS may comprise one or more types of polysaccharide.
  • Reference to a "polysaccharide” means polymeric carbohydrate molecules comprising repeating units or monomers, such as monosaccharides, disaccharides or oligosaccharides, joined by glycosidic bonds. It is further understood that the terms “polysaccharide” and “glycan” may be used interchangeably.
  • the EPS comprises a single polysaccharide or polysaccharide derivative.
  • the EPS comprises combinations of two or more polysaccharides, or polysaccharide derivatives.
  • the agent may comprise either homogenous (homopolysaccharide) or heterogeneous (heteropolysaccharide) polysaccharide components of the EPS.
  • the polysaccharide in accordance with the present invention is a combination of homopolysaccharides and heteropolysaccharides.
  • the polysaccharides are linear, and may optionally comprise degrees of branching.
  • the polysaccharide is soluble or is a soluble derivative, in particular a water-soluble polysaccharide or a water-soluble derivative of a polysaccharide.
  • the polysaccharide is an exopolysaccharide.
  • An exopolysaccharide may additionally comprise other non-carbohydrate substituents.
  • other non-carbohydrate substituents may include acetate, pyruvate, succinate, sulfate and phosphate substituents.
  • the polysaccharide including an exopolysaccharide is a naturally-occurring polysaccharide.
  • the polysaccharide is a polysaccharide derivative.
  • Derivatives include, for example, modified monosaccharides or monosaccharide derivatives. Examples of monosaccharide derivatives include aminosugars, sulfosugars and sugar alcohols.
  • polysaccharide derivatives may comprise one or more monosaccharides modified by chemical methods known in the art.
  • the biofouling resistant characteristics of the EPS or polysaccharide component thereof is thought to arise from its ability to form a hydrophilic coating with heavily hydrated and randomly oriented polysaccharide chains. Furthermore, the EPS or polysaccharide component thereof is also thought to comprise large molecules with randomly oriented polysaccharide chains which promotes steric hindrance and unfavorable entropy changes associated with adsorption. In addition, the EPS or polysaccharide component thereof of the present specification is essentially non-ionic, which also minimizes the attachment of charged species. Consequently, it is proposed that the EPS or a polysaccharide component thereof can, in an aspect, transform solid substrates to substrates with high biofouling resistance.
  • Reference to a "Mesorhizobium or Mesorhizobium-li e microorganism” includes a microorganism which is Gram negative, comprises a monotrichous flagella, grows to a colony diameter of 1 to 4 mm after 7 days on yeast mannitol agar (YMA), exhibits a generation time of 4 to 10 hours in yeast mannitol broth (YMB), tolerates a maximum growth temperature of 36°C to 39°C, exhibits a maximum NaCl tolerance for growth of 1 to >2.5 (% w/v), tolerates a pH range for growth of 4 to 10 and has the ability to grow on melibiose.
  • YMA yeast mannitol agar
  • YMB yeast mannitol broth
  • tolerates a maximum growth temperature of 36°C to 39°C exhibits a maximum NaCl tolerance for growth of 1 to >2.5 (% w/v)
  • tolerates a pH range for growth of 4 to 10 and has the ability
  • the Mesorhizobium is selected from the list comprising Mesorhizobium abyssinicae, Mesorhizobium albiziae, Mesorhizobium alhagi, Mesorhizobium amorphae, Mesorhizobium australicum, Mesorhizobium camelthorni, Mesorhizobium caraganae, Mesorhizobium chacoense, Mesorhizobium cicero, Mesorhizobium gobiense, Mesorhizobium hawassense, Mesorhizobium huakuii, Mesorhizobium loti, Mesorhizobium mediterraneum, Mesorhizobium metallidurans, Mesorhizobium muleiense, Mesorhizobium opportunistum, Mesorhizobium plurifarium, Mesorhizobium qingshengii, Mesorhizobium robini
  • the Mesorhizobium is M. huakuii or M. loti.
  • the Mesorhizobium or Mesorhizobium-li e microorganism is the microbial cell designated CAM543 deposited at the National Measurements Institute on 29 October, 2014 under accession number V14/017216.
  • the present specification further teaches a composite filtration membrane with a layer comprising an isolated polysaccharide derived from an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • the present specification enables a composite filtration membrane with a layer comprising an isolated polysaccharide derived from an EPS produced by a microbial cell designated CAM543 deposited at the National Measurements Institute on 29 October, 2014 under accession number V14/017216.
  • a layer comprising an EPS or an isolated polysaccharide thereof produced by a genetically modified Mesorhizobium or Mesorhizobium-li e microorganism with introduced traits. Examples of genetic modification include generation of auxotrophic mutants and mutants which have the capacity to metabolize and grow on an expanded spectrum of carbon sources. The mutants may also be useful proprietary markers.
  • the layer is attached to the surface of the membrane by any suitable means.
  • the layer is attached to the surface of the membrane via a linker.
  • the layer is attached to the surface of the membrane via an inorganic linker [0128]
  • the linker may be derived from any suitable metal alkoxide or alkoxysilane.
  • One or more a metal alkoxides or alkoxysilanes within the scope of the present application may react with suitable functional groups on the EPS or a polysaccharide component thereof and the membrane to link the EPS or a polysaccharide component thereof and the membrane.
  • the metal alkoxide or alkoxysilane may link the EPS or a polysaccharide component thereof and the membrane by transesterification or alcoholysis.
  • the suitable functional groups on the EPS or a polysaccharide component thereof and the membrane may include hydroxyl groups, carbonyl groups, carboxyl groups and combinations thereof.
  • the linker may comprise two or more metal alkoxides.
  • Taught herein is a metal which forms part of the metal alkoxide linker which is any suitable metal.
  • suitable metals include, but are not limited to, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and lanlhanides, such as cesium, samarium, gadolinium, dysprosium, erbium and neodymium.
  • the metal of the present specification may further comprise a bivalent, trivalent, tetravalent, pentavalent, or hexavalent metals,
  • the linker may be derived from an alkoxysilane.
  • alkoxy means a group having the formula -OR, where R is an alkyl group.
  • linear alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy, butoxy, pentoxy, and hexoxy.
  • branched alkoxy groups include, but are not limited to, isopropoxy, sec-butoxy, tert-butoxy, isopentoxy, and isohexoxy.
  • cycloalkoxy groups include, but are not limited to, cyclopropyloxy, cyclobutyloxy, cyclopentyloxy, and cyclohexyloxy.
  • alkyl includes straight chain and branched alkyl groups having from 1 to about 20 carbon atoms or, in some embodiments, from 1 to 8, 1 to 6, or 1 to 4 carbon atoms.
  • the alkyl group may be a cycloalkyl group.
  • straight chain alkyl groups include those with from 1 to 8 carbon atoms such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl groups.
  • Examples of branched alkyl groups include, but are not limited to, isopropyl, iso-butyl, sec-butyl, tert- butyl, neopentyl, isopentyl, and 2,2-dimethylpropyl groups.
  • Examples of cycloalkyl groups include but are not limited to cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl.
  • the layer is attached to the surface of the membrane via a titanium alkoxide, a zirconium alkoxide, an aluminum alkoxide or an alkoxysilane linker.
  • the layer is attached to the surface of the membrane via an alkoxide linker of the following formula Si(OR) 4 , Ti(OR) 4 , Zr(OR) 4 and Al(OR) 4 .
  • the linker may be titanium isopropoxide.
  • the present specification teaches a method for preparing a composite filtration membrane comprising: a) providing a membrane; and
  • a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • the present specification teaches a method for preparing a composite filtration membrane comprising: a) providing a semipermeable membrane; and
  • a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • the present specification teaches a method for preparing a composite filtration membrane comprising: a) providing a semipermeable membrane; and
  • biofouling resistant layer comprises:
  • a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-Yi e, microorganism.
  • the method for producing a composite filtration membrane comprises providing a membrane and forming a layer on a surface of the membrane comprising the EPS or a polysaccharide component thereof wherein the resulting layer exhibits biofouling resistance.
  • the method for producing a composite filtration membrane comprises providing a membrane that is a reverse osmosis membrane and forming a layer on a surface of the reverse osmosis membrane comprising the EPS or a polysaccharide component thereof wherein the resulting composite filtration membrane exhibits biofouling resistance.
  • the method for producing a composite filtration membrane comprises providing a membrane that is a polyamide thin film composite membrane and forming a layer on a surface of the polyamide thin film composite membrane comprising the EPS or a polysaccharide component thereof wherein the resulting composite filtration membrane exhibits biofouling resistance.
  • the method for producing a composite filtration membrane comprises providing a membrane that is a polyamide thin film composite membrane with a hydrophilic surface layer comprising polyvinyl alcohol and forming a layer on a surface of the hydrophilic surface layer comprising the EPS or a polysaccharide component thereof wherein the resulting composite filtration membrane exhibits biofouling resistance.
  • the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane by any suitable means.
  • the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane using a linker.
  • the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane using an inorganic linker.
  • the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane using any suitable metal alkoxide or alkoxysilane.
  • One or more metal alkoxides or alkoxysilanes within the scope of the present application may react with suitable functional groups on the EPS or a polysaccharide component thereof and the membrane to link the EPS or a polysaccharide component thereof and the membrane.
  • the metal alkoxide or alkoxysilane may link the EPS or a polysaccharide component thereof and the membrane by transesterification or alcoholysis.
  • the suitable functional groups on the EPS or a polysaccharide component thereof and the membrane may include hydroxyl groups, carbonyl groups, carboxyl groups and combinations thereof.
  • the linker may comprise two or more metal alkoxides. [0148] Taught herein is a metal which forms part of the metal alkoxide linker which is any suitable metal.
  • suitable metals include, but are not limited to, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and lanthanides, such as cesium, samarium, gadolinium, dysprosium, erbium and neodymium. Further taught herein is a metal comprising one or more of the metals described above.
  • the metal of the present specification may further comprise a bivalent, trivalenl, tetravalent, pentavalent, or hexavalent metals.
  • the linker may be a crosslinker derived from an alkoxysilane.
  • the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane using a titanium alkoxide, a zirconium alkoxide, an aluminum alkoxide or an alkoxysilane linker.
  • the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane using an alkoxide linker of the following formula Si(OR) 4 , Ti(OR) 4 , Zr(OR) 4 and Al(OR) 4 .
  • the linker may be titanium isopropoxide.
  • the present specification teaches an immobilization strategy that uses specific crosslinking molecules to act as a bridge between the layer and a surface of the membrane.
  • carboxylic groups are present on the surface of the membrane from the hydrolysis of the unreacted acyl chloride groups.
  • the abundance of hydroxyl groups in the EPS or polysaccharide component thereof reacts with the linker to form bonds.
  • titanium alkoxides are known to react with compounds containing hydroxyl groups via the protolytic loss of one or more alkoxide ligands (Figure 2; Uekawa, N., et al. (2006) Journal of the Ceramic Society of Japan, 114(10), 807; Yi, Y., et al. (2010) US Patent No. 2010/0239493; Kariduraganavar, M.Y., et al. (2009) Industrial and Engineering Chemistry Research, 48, 4002.
  • titanium isopropoxide reacts with carboxyl groups to form carboxylate completes through chelating bidentate, bridging bidentate or monobidentate mechanisms (Figure 3; see also Hojjati, B.
  • metal alkoxides for the formation of a layer on a surface of the membrane taught by the present specification does not reduce water flux when compared to the water flux of a membrane without a biofouling resistant layer ( Figures 5 and 6).
  • the use of metal alkoxides for the formation of a layer on a surface of the membrane taught by the present specification requires that the metal alkoxides are dissolved in alcohol prior to being combined with the EPS or polysaccharide component thereof and water.
  • the alcohol is ethanol or 1-propanol.
  • the volume ratio of titanium isopropoxide to alcohol is between 1: 10 and 1:20. Reference to "between 1: 10 and 1:20" means 1: 10, 1: 11, 1: 12, 1: 13, 1: 14, 1: 15, 1: 16, 1:17, 1: 18, 1: 19 or 1:20.
  • the weight/weight (w/w) ratio of the EPS or polysaccharide component thereof and the linker is proposed to be between 0.15 and 1.25.
  • Reference to the w/w ratio of "between 0.15 and 1.5" means 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.0, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45 or 1.50.
  • the layer is formed on a surface of the membrane by treating the membrane with one or more metal alkoxides and the EPS or a polysaccharide component thereof.
  • Application of the layer to the membrane is proposed to be with the range of 1 to 100 ⁇ g/cm 2 .
  • Reference to " 1 to 100 ⁇ g/cm 2" means 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100 ⁇ g/cm 2 .
  • Formation of the layer is proposed to be undertaken at a temperature between 25 and 50°C, including 40°C.
  • Reference to "between 25 and 50°C" means 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 or 50°C.
  • Formation of the layer is proposed to be undertaken for a time between 1.0 h to 5.0 h, including 3.0 h.
  • Reference to "between 1.0 h to 5.0 h” means 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0 h.
  • the present specification teaches a method for modifying existing filtration membranes with surface carboxylic and/or hydroxyl functionalities to have biofouling resistance by forming a layer on a surface of the existing membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • the present specification further teaches a method for modifying existing RO filtration membranes to have biofouling resistance by forming a layer on the surface of the existing RO filtration membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • the present specification also teaches a method for modifying existing FO filtration membranes to have biofouling resistance by forming a layer on the surface of the existing FO filtration membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • the present specification teaches a composite filtration membrane having biofouling resistance by forming a layer on the surface of a filtration membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • the filtration membrane is a RO filtration membrane having biofouling resistance by forming a layer on a surface of a RO filtration membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism.
  • the filtration membrane is a FO filtration membrane having biofouling resistance by forming a layer on the surface of a FO filtration membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
  • the filtration membrane is a polyamide thin film composite membrane having biofouling resistance by forming a layer on a surface of a polyamide thin film composite membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism.
  • the filtration membrane is a polyamide thin film composite membrane comprising a hydrophilic surface layer having biofouling resistance by forming a layer on a surface of a polyamide thin film composite membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism.
  • Taught herein is a process for treating a liquid, comprising subjecting the liquid to filtration with a composite filtration membrane comprising: a) a membrane; and
  • a layer which presents as a coating across the surface of the membrane wherein the layer comprises:
  • an extracellular polymeric substance produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism.
  • EPS extracellular polymeric substance
  • salt water includes brackish, saline and hyper-saline water.
  • salt water may include any water with a salt concentration of about >0.05%.
  • Brackish water has a salt concentration of about 0.05-3%;
  • saline has a salt concentration of about 3-5%;
  • hyper-saline water has a salt concentration of about >5%.
  • brine includes water with a salt concentration of about >3.5% and may be naturally occurring or a product of other water treatment processes.
  • the present specification teaches a process for treating a liquid, comprising subjecting the liquid to filtration with a composite filtration membrane comprising: a) a semipermeable membrane; and
  • a layer which presents as a coating across the surface of the membrane wherein the layer comprises:
  • the present specification also teaches a process for treating a liquid comprising subjecting the liquid to filtration with a composite filtration membrane comprising: a) a semipermeable membrane; and b) a biofouling resistant layer which presents as a coating across the surface of the membrane, wherein the layer comprises:
  • an extracellular polymeric substance produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism;
  • the filtration membrane exhibits biofouling resistance.
  • the present specification teaches a process for the purification of salt water and the decontamination of industrial waste water.
  • the present specification teaches a process for the purification and concentration of biologically useful molecules such as peptides, proteins, antibodies and antibiotics.
  • liquid foodstuffs includes extracts from vegetable and animal products.
  • liquid foodstuffs according to the present invention also encompasses beverages.
  • liquid foodstuffs may include dairy products, yoghurts, ice creams, milk-based soft ice, milk-based garnishes, puddings, cream, whipped cream, chocolate cream, butter cream, creme fraiche, curd, milk, such as skim milk, buttermilk, soured milk, kefir, milkshakes, egg custard, cheese, confectionary, snack products, diet drinks, finished drinks, sports drinks, stamina drinks, spreads, meat products, mayonnaise, dressings, sauces, gravy, soups, shortenings and wine.
  • the present specification teaches a process for the purification and concentration of hydrocarbons.
  • hydrocarbons includes liquid hydrocarbons.
  • hydrocarbons may include fuels, petroleum, mineral oil, oil, crude oil, lube oil, hydraulic oil, wet gases, natural gasoline or condensate.
  • Solutions A and B were diluted to prepare membrane samples T1-T4 and Dl- D3 (thin).
  • Solutions B l and B2 were diluted to prepare membrane samples T5 and T6 (thick).
  • the coating solutions were prepared to obtain a weight/weight ratio of titanium to polysaccharide between 0.187 and 1.251 and the amount of polysaccharide delivered on 2
  • the membrane surface was between 0.37 and 223.97 ⁇ g/cm .
  • the mixture was stirred for 30 min at room temperature before being coated on the membrane surface.
  • the coating solution delivered on membrane surface was 7.14 x 1(T -2 mL/cm 2".
  • the membrane was then placed in an oven at 40-45°C for 3-5 h, until the membrane was nearly dry. Thereafter, the coated membrane was washed and stored in water.
  • Coated membranes were prepared for surface morphology analysis by washing several times in water and immersing in water overnight to remove unreacted or unbound compounds. The surface morphology of the coatings was examined by scanning electron microscopy (SEM).
  • SEM imaging was carried out by sputter coating samples with a very thin layer of iridium before imaging with a Philips XL30 field emission scanning electron microscope operating at 4kV.
  • Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra were recorded on a Thermo Scientific Nicolet 6700 spectrometer equipped with diamond ATR accessories.
  • ATR-FTIR Attenuated total reflectance-Fourier transform infrared
  • the elemental composition of coated surfaces was analyzed by X-ray photoelectron spectroscopy (XPS) using an AXIS-HSi spectrometer (Kratos Analytical Inc., Manchester, U.K.) with a monochromatic Al X-ray source. Spectra were recorded at an emission angle of 0° with respect to the surface normal with corresponding depths of penetration on the order of 5-10 nm. The analysis was performed as three independent experiments with the averaged data described in this specification. Water contact angle analysis
  • Coated membranes were exposed to water at different pH levels to test the durability of the polysaccharide coating.
  • Water of pH 2 and 9 was prepared using NaOH and HC1 and ultrapure (type I) water, such as Milli-Q (trade mark) water (pH 6.998) was used as a control.
  • Coated membranes were exposed to ultrapure (type I) water for 90 d and water of pH 2 and 9 for 15 d. Following water exposure, the coated membranes were dried under ambient conditions for 2 d prior to ATR-FTIR and contact angle analyses to assess the polysaccharide coating.
  • Anti-biofouling analysis of coated membranes [0200] The anti-biofouling effect of the polysaccharide coating was analyzed by exposing membrane samples T1-T6 to bacterial cultures. Uncoated membrane samples were used as controls.
  • ATR-FTIR was used to analyze the surfaces of membrane samples T1-T6 before and after the water flux tests described in Example 1.
  • the coated samples, including samples T1-T3 with thin polysaccharide coatings, have less pronounced peaks in the A and C regions when compared to those of the uncoated membrane (Figure 5). This is consistent with the presence of a surface coating layer which obscured or changed the characteristics of the spectral features in regions A and C of the uncoated membrane.
  • the O/N ratio of the uncoated sample had a value of 1.26, which is close to the theoretical O/N ratio of unity when the polyamide layer is fully cross-linked (i.e., all the O and N atoms are associated with the amide groups to give a 1: 1 ratio).
  • the O/N ratio increased in value with Tl having a value of 6.37 and T3 a value of 14.01.
  • the C/N ratio of the coated samples also had higher values compared to those of the uncoated sample (Table 3).
  • Table 3 also shows the values of titanium/nitrogen (Ti/N) ratio for the uncoated and coated samples.
  • the uncoated sample had a Ti/N ratio of zero, as expected, whereas the Ti/N ratio of the coated samples had values ranging from 0.04 to 0.14, confirming the presence of the cross linker in the coating layer of these samples.
  • Table 3 Elemental analysis of uncoated and coated membrane samples T1-T3
  • XPS In addition to elemental composition analysis, XPS also provides information about the chemical state of different elements by deconvoluting the high resolution XPS spectra of different elements into individual component peaks.
  • Figure 8 shows examples of the deconvolution of the XPS Ols spectra into individual component peaks and the assignments of the peaks, and Table 5 shows the atomic percentage of the component peaks for the uncoated and coated membrane samples.
  • the Ols spectrum and the individual component peaks of sample D3 with high crosslink density are also included in Figure 7 and Table 5 for comparative purposes.
  • the Ols spectrum can be deconvoluted into peaks 01 and 02.
  • the durability of the polysaccharide coatings was also tested in cross-flow environments under conditions of high applied pressures and ionic strengths.
  • the tests were carried out using laboratory-scale cross-flow membrane test units which were either a CF042 or a Sepa CF II cross-flow cell system (Sterlitech).
  • the feed water was either water, or aqueous solutions containing 2000 ppm or 32000 ppm NaCl.
  • the applied trans membrane pressure difference was either 15.5 or 55 bar, and the feed cross-flow velocity was maintained at 40 cm/sec.
  • the membrane test units were operated in a closed loop mode, where the permeate and retentate were circulated back to the feed water reservoir, to maintain a constant salt concentration. The duration of each test was 49 h. Following the cross-flow experiments, the coated membranes were dried under ambient conditions for two days prior to analysis using ATR-FTIR and contact angle measurements.
  • the cross-link density of the polysaccharide coating may affect properties including water uptake and water permeability.
  • Samples D1-D3 were prepared with a polysaccharide surface concentration of 3.34 ⁇ g/cm , and variable cross-link densities ranging from 0.374 to 1.251 (w/w; titanium/polysaccharide).
  • the water flux of samples D1-D3 was measured using the same method described in Example 1. The results showed that the relative flux J/Jo of the coated membranes was the same as the flux of corresponding uncoated membranes. These results indicate that the cross linker density does not influence the water uptake and water permeability of the polysaccharide coating layer.
  • Example 8

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  • Separation Using Semi-Permeable Membranes (AREA)

Abstract

The present specification relates to a composite filtration membrane, various uses thereof and its method of production. The composite filtration membrane comprising a layer comprising an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a polysaccharide component of said EPS.

Description

A FILTRATION MEMBRANE AND ITS METHOD OF
PRODUCTION
FILING DATA
[0001] This application is associated with and claims priority from Australian Provisional Patent Application No. 2014905015, filed on 11 December 2014, entitled "A filtration membrane and its method of production", the entire contents of which, are incorporated herein by reference.
BACKGROUND
FIELD
[0002] The present specification relates to a composite filtration membrane, various uses thereof and its method of production.
DESCRIPTION OF RELATED ART
[0003] Bibliographic details of publications referred to by author in this specification are collected alphabetically at the end of the description.
[0004] Reference in this specification to any prior publication (or information derived from it) or to any matter which is known, is not, and should not be taken as, an acknowledgement or admission or any form of suggestion that the prior publication (or information derived from it) or known matter form part of the common general knowledge in the field of endeavor to which this specification relates.
[0005] Membranes are widely used in the separation of mixtures. The membrane separation process allows for the removal of material (for example, salt ions) dissolved in a liquid (for example, water) in a cost effective and efficient manner. Typical membranes used in the membrane separation process include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, forward osmosis (FO) membranes and reverse osmosis (RO) membranes. [0006] Reverse osmosis (RO) is a water purification technique commonly used in the desalination of salt water. Other applications of RO include wastewater treatment, food and pharmaceutical processing, minerals processing and pure water production. Central to RO technology is the use of a semipermeable membrane and the application of a pressure greater than the osmotic pressure on the feed water. Under pressure, purified water passes through the membrane whilst salts and other dissolved ions and molecules are retained.
[0007] Traditionally, RO membranes were made from cellulose acetate (CA) via a phase inversion process. The first developed CA membranes had an asymmetric structure with a dense surface layer which is responsible for the salt rejection property. The rest of the membrane supported the thin surface layer mechanically and has high water permeability (Loeb and Sourirajan (1963) Advances in Chemistry Series, 38, 117; Loeb and Sourirajan (1964) US Patent No. 3,133,132).
[0008] RO membranes are now mostly composite semipermeable (CS) membranes, such as thin film composite (TFC) membranes, with a gel layer or thin layer (separation functional layer) formed on a microporous support. The thin layer (separation functional layer) is produced by crosslinking a polymer, such as a polyamide, on a microporous support, such as a porous polysulfone support layer (Cadotte (1981) US Patent No. 4,277,344). For example, a composite semipermeable membrane in which a microporous support is coated with a thin layer comprising a crosslinked polyamide is widely applied as a reverse osmosis membrane, as described by Tomaschke (1989), US Patent No. 4,872,984; Tran et al. (1989), US Patent No. 4,830,885; Chau (1990), US Patent No. 4,950,404; Chau et al. (1991), US Patent No. 4,983,291; Ikeda et al. (1993), US Patent No. 5,178,766; Hirose and Ikeda (1996), US Patent No. 5,576,057; Hirose et al. (1997), US Patent No. 5,614,099; Koo and Kim (2000), US Patent No. 6,015,495; Koo and Yoon (2000), US Patent No. 6,063,278; and Koo et al. (2001), US Patent No. 6,245,234. Currently, CS membranes are widely used in the water treatment industry, mainly because they can tolerate harsher chemical environment and are operable over wider pH, pressure and temperature ranges with improved flux and salt rejection compared to cellulose acetate membranes. [0009] As with other membrane filtration processes, membrane fouling is a major obstacle that prevents efficient operation of RO systems, causing deterioration of both the quantity and quality of the treated water and increasing the pressure requirements to pass water through the membrane resulting in higher treatment cost. Generally, membrane fouling occurs when impurities in the feed water deposit onto the surface of the membranes. Biofouling occurs where microorganisms attach to the membrane surface and proliferate to form biofilms. Biofilms are formed by microorganisms in aqueous environments by the production of extracellular polymeric substances (EPS) that are essential for the attachment, survival and growth of microorganisms within the surface- bound biofilm. The excreted EPS forms a complex matrix of polysaccharides, proteins, nucleic acids and lipids to provide a layer of protection to cells against toxic compounds, other organisms, or physical damage. Within the matrix of the EPS, proliferating microorganisms produce biologic/organic, colloidal and particulate or crystalline matter that degrades the membrane surface. As a consequence, the formation of biofilms on RO membranes leads to considerable loss of membrane performance and requires higher operating pressures and/or frequent costly cleaning procedures to maintain the output and quality of treated water. In fact, biofouling can become so severe that continued operation is not acceptable and membrane replacement is required.
[0010] A number of methods have been advanced to mitigate membrane biofouling. One approach involves the application of biocides to kill microorganisms that are attached to the membrane surface. Examples of biocides used for this purpose include nanoscale Ti02 particles, which exhibit antimicrobial properties when exposed to ultra-violet (UV) radiation (Kwak et al. (2003) US Patent No. 6,551,536); and silver dispersed in a solution of polyvinyl alcohol (Nishiyama et al. (2010) US Patent No. 2010/0178489). [0011] Another anti-fouling approach is to modify the membrane surface. Hydrophilic materials have low fouling potential; therefore, membrane surface hydrophilicity may be increased by coating the surface with a layer of hydrophilic species. Hydrophilic coating substances that have been previously used include polyethylene glycol, polyvinylpyrrolidinone, poly(vinyl alcohol) (Hachisuka and Ikeda (2001) US Patent No. 6,177,011); polyethylene glycol diepoxide (Mickols (2001) US Patent No. 6,280,853); polyfunctional epoxy compounds comprising at least two epoxy groups (Koo et al. (2005) US Patent No. 6,913,694); copolymers of poly(ethylene glycol) methyl ether methacrylate and glycidyl methacrylate or glycidyl methacrylates (Niu (2007) US Patent No. 2007/0251883); sulfobetaine and other zwitterionic polymers (Constantopoulos et al. (2011) WO Patent No. WO2011/088505); and polyactams, poly-amino acids and polymers containing tertiary ammonium groups to the membrane surface either directly or via predefined spacers (tethers) and linkers (Kasher et al. (2012) WO Patent No. WO2012/172547).
[0012] More recently, micro-, ultra- and nano- filtration membranes have been used for the pre-treatment of feed water prior to RO filtration. The main purpose of pre- treatment is to reduce the concentration of fouling agents present in the feed water to be subjected to the RO membrane surface and therefore reduce biofouling. However, pre- treatment using these membranes is not totally effective in the removal of bacteria from the feed water, resulting in persistent formation of biofilms on the RO membrane surface (Ghayeni et al. (1998) Journal of Membrane Science, 138, 29; Ghayeni et al. (1999) Journal of Membrane Science, 153, 71). Furthermore, such pre-treatment membranes are also subject to biofouling by bacteria and the adsorption of dissolved matter such as colloids (Howe and Clark (2002) Environmental Science and Technology, 36(16), 3571).
[0013] Whilst these methods can lead to a reduction in biofouling, there are nevertheless, some drawbacks including reduction in water flux on a coated membrane, inadequate anti-fouling effects, the frequent need to use complex and expensive coating protocols and difficulties in coating surfaces on a large scale. Thus, there is a need for alternative approach to modifying the surface of filtration membranes not only to mitigate biofouling, but also to facilitate the separation of molecules from a solvent. SUMMARY
[0014] The present specification teaches a composite filtration membrane comprising: a) a membrane; and
b) a layer which presents as a coating across a surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism. [0015] In an embodiment, the membrane is a semipermeable membrane.
[0016] Accordingly, in an embodiment, the present specification teaches a composite filtration membrane comprising: a) a semipermeable membrane; and
b) a layer which presents as a coating across a surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
[0017] In an embodiment, the layer confers biofouling resistance.
[0018] Accordingly, in an embodiment, the present specification teaches a composite filtration membrane comprising: a) a semipermeable membrane; and
b) a biofouling resistant layer which presents as a coating across a surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism;
wherein the composite filtration membrane exhibits biofouling resistance. [0019] In an embodiment, the microbial cell is selected from the list comprising Mesorhizobium huakuii, Mesorhizobium loti, Mesorhizobium abyssinicae, Mesorhizobium albiziae, Mesorhizobium alhagi, Mesorhizobium amorphae, Mesorhizobium australicum, Mesorhizobium camelthorni, Mesorhizobium caraganae, Mesorhizobium chacoense, Mesorhizobium cicero, Mesorhizobium gobiense, Mesorhizobium hawassense, Mesorhizobium mediterraneum, Mesorhizobium metallidurans, Mesorhizobium muleiense, Mesorhizobium opportunistum, Mesorhizobium plurifarium, Mesorhizobium qingshengii, Mesorhizobium robiniae, Mesorhizobium sangaii, Mesorhizobium septentrionale, Mesorhizobium shangrilense, Mesorhizobium shonese, Mesorhizobium silamurunense, Mesorhizobium tamadayense, Mesorhizobium tarimense, Mesorhizobium temperatum, Mesorhizobium thiogangeticum or Mesorhizobium tianshanense.
[0020] In an embodiment, the microbial cell is M. huakuii or M. loti or a microorganism having biochemical, physiological or genetic properties similar to M. huakuii or M. loti.
[0021] In an embodiment, the microbial cell is designated CAM543 which was deposited at the National Measurements Institute on 29 October, 2014 under accession number V14/017216.
[0022] In an embodiment, the composite filtration membrane comprises a membrane and a layer which comprises an isolated polysaccharide derived from EPS produced by the microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism. [0023] The layer can be formed on the surface of the membrane by any suitable means.
[0024] In an embodiment, the layer is attached to the surface of the membrane via a linker. [0025] In an embodiment, the layer is attached to the surface of the membrane via an inorganic linker.
[0026] In an embodiment, the layer is attached to the surface of the membrane via a linker derived from any suitable metal alkoxide or alkoxysilane. [0027] In an embodiment, the layer is attached to the surface of the membrane via a titanium alkoxide.
[0028] In an embodiment, the layer is attached to the surface of the membrane via titanium isopropoxide.
[0029] The composite filtration membrane of the present specification comprises two main components, namely, a membrane and a layer which is formed on the surface of the membrane. Each of these components has specific features and collectively they provide for a composite filtration membrane that exhibits useful properties including removing or concentrating particular solutes or other molecules from a liquid.
[0030] The combination of the membrane with the layer provides the composite filtration membrane with sound mechanical properties. In an embodiment, the composite filtration membrane of the present specification exhibits biofouling resistance in conditions that are comparable to water treatment plant operating conditions. Importantly, the layer is stable under conditions of high applied transmembrane pressure (Table 6) and high cross- flow velocity for prolonged periods of time (Figure 11). In another embodiment, the composite filtration membrane is useful for concentrating or isolating proteins, including polypeptides in the form of antibodies. In another embodiment, the composite filtration membrane is useful for concentrating or isolating proteins from liquid foodstuffs. In another embodiment, the composite filtration membrane is useful for purifying and concentrating biologically useful molecules such as peptides, proteins, antibodies and antibiotics.
[0031] The layer can advantageously be presented on the surface of the membrane in the form of an ultrathin layer (e.g. less than 100 nm). Minimizing the thickness of the layer has been found to improve filtration properties and also reduce the manufacturing cost of the membrane.
[0032] The present specification also teaches a method for preparing a composite filtration membrane comprising: a) providing a membrane; and
b) coating a surface of the membrane with a layer, wherein the layer comprises:
i. an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or
ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
[0033] In an embodiment, the present specification teaches a method for preparing a composite filtration membrane comprising: a) providing a semipermeable membrane; and
b) coating a surface of the semipermeable membrane with a layer comprising:
i. an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or
ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
[0034] In an embodiment, the present specification teaches a method for preparing a composite filtration membrane having a biofouling resistant layer, the method comprising: a) providing a semipermeable membrane; and
b) coating a surface of the semipermeable membrane with a biofouling resistant layer, wherein the biofouling resistant layer comprises:
a. an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e, microorganism; or
b. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; wherein the resulting composite filtration membrane exhibits biofouling resistance.
[0035] The membrane may be a microfiltration, ultrafiltration, nanofiltration or a reverse osmosis membrane. The membrane may be prepared by any suitable means. The art of making membranes is well documented in the published literature and are commercially available.
[0036] In an embodiment, the membrane is a semipermeable membrane.
[0037] In an embodiment, the membrane is a reverse osmosis membrane. In another embodiment, the membrane is a forward osmosis membrane. [0038] The method for preparing a composite filtration membrane comprises forming a layer on a surface of the membrane.
[0039] In an embodiment, the layer is formed on the surface of the membrane by any suitable means.
[0040] In an embodiment, the layer is formed on the surface of the membrane using a linker.
[0041] In an embodiment, the layer is formed on the surface of the membrane using an inorganic linker.
[0042] In an embodiment, the layer is formed on the surface of the membrane using a metal alkoxide. [0043] In an embodiment, the layer is formed on the surface of the membrane using a titanium metal alkoxide.
[0044] In an embodiment, the layer is formed on the surface of the membrane using titanium isopropoxide.
[0045] Enabled herein is a method for preparing a composite filtration membrane having a layer wherein the layer is formed on a surface of the membrane by treating the membrane with a composition comprising one or more metal alkoxides and the EPS or polysaccharide component thereof.
[0046] In an embodiment, enabled herein is a method for preparing a composite filtration membrane having a biofouling resistant layer wherein the biofouling resistant layer is formed on a surface of a semipermeable membrane by treating the semipermeable membrane with a composition comprising one or more metal alkoxides and the EPS or polysaccharide component thereof.
[0047] The present specification teaches a process for the treatment of a liquid comprising subjecting the liquid to filtration by contacting the liquid with a composite filtration membrane comprising: a) a membrane; and
b) a layer which presents as a coating across the surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism.
[0048] In an embodiment, the present specification teaches a process for the treatment of a liquid comprising subjecting the liquid to filtration by contacting the liquid with a composite filtration membrane comprising: a) a semipermeable membrane; and
b) a layer which presents as a coating across the surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism. [0049] In another embodiment, the present specification teaches a process for the treatment of a liquid comprising subjecting the liquid to filtration by contacting the liquid with a composite filtration membrane comprising: a) a semipermeable membrane; and
b) a biofouling resistant layer which presents as a coating across the surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-Xi e, microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism;
wherein the composite filtration membrane exhibits biofouling resistance.
[0050] Further taught herein is a process for creating a difference in pressure across the composite filtration membrane so as to filter water; wherein the water purity is higher in the separated solution when compared with that of the solution that was subject to filtration.
[0051] In an embodiment, the composite filtration membrane of the present specification is a reverse osmosis filtration membrane for filtering salt water. In another embodiment, the composite filtration membrane of the present specification is a forward osmosis (FO) filtration membrane for filtering salt water.
[0052] In an embodiment, the membrane of the present specification is a microfiltration, ultrafiltration or nanofiltration membrane for pre-treating liquids before reverse osmosis filtration. In another embodiment, the membrane of the present specification is a microfiltration, ultrafiltration or nanofiltration membrane for purifying and concentrating proteins. For example, the nanofiltration, microfiltration or ultrafiltration may be used to purify and concentrate antibodies, antibiotics or proteins from liquid foodstuffs.
Abbreviations used herein are defined in Table 1. Table 1. Abbreviations
Abbreviation Description
RO Reverse osmosis
FO Forward osmosis
CA Cellulose acetate
TFC Thin film composite
EPS Extracellular polymeric substance
UV Ultra violet
YMA Yeast mannitol agar
YMB Yeast mannitol broth
w/w Weight/weight
w/v Weight/volume
v/v Volume/volume
g, mg, μg, ng Gram, milligram, microgram, nanogram m, cm, mm, μΜ Meter, centimeter, millimeter, micrometer h, min, sec Hour, minute, second
SEM Scanning electron microscopy
ATR-FTIR Attenuated reflectance-Fourier transform infrared
XPS X-ray photoelectron spectroscopy
UF Ultrafiltration
DNA Deoxyribonucleic acid
L, mL, μL· Liter, milliliter, microliter
ATR Attenuated total reflectance
cfu Colony forming units
J Water flux
AFM Atomic force microscopy
ppm Parts per million BRIEF DESCRIPTION OF THE FIGURES
[0053] Figure 1 is a graphical representation of a cross section of the filtration membrane which comprises (a) a porous substrate; (b) a separation functional layer; (c) an optional hydrophilic layer; and (d) a biofouling resistant layer.
[0054] Figure 2 is a schematic representation of coordination modes between carboxylic group (-COOH) groups and titanium.
[0055] Figure 3 is a schematic representation of the reaction between titanium alkoxide and compounds containing hydroxyl groups (-OH). [0056] Figure 4 is a photographic representation of the SEM analysis of the surface of (a) uncoated membrane; and sample series (b) Tl, (c) T2, (d) T3, (e) T4, (f) T5 and (g) T6.
[0057] Figure 5 is a graphical representation of the ATR-FTIR spectra of sample series T1-T6 after the water flux tests.
[0058] Figure 6 is a graphical representation of the magnified ATR-FTIR spectra after the water flux tests in the wave number region (a) 2600-3800 cm-1 and (b) 950-1150 cm-1. Regions A = free N-H stretching; B = hydrogen-bonded N-H stretching; C = aromatic =C- H stretching; E = alipathic C-H stretching; F = C-O-C stretching of polysaccharide.
[0059] Figure 7 is a graphical representation of a deconvoluted XPS Cls peak for (a) uncoated membrane; and (b) coated T3 membrane. [0060] Figure 8 is a graphical representation of a deconvoluted XPS Ols peak for (a) uncoated membrane; (b) coated T3 membrane; and coated D3 membrane with high cross link density.
[0061] Figure 9 is a photographic representation of contact angles of a drop of water on the surfaces of (a) uncoated membrane; (b) sample series Tl; and (c) sample series T2- T6. [0062] Figure 10 is a graphical representation of the ATR-FTIR spectra of coated membrane (a) before and (b) after the water exposure test.
[0063] Figure 11 is a graphical representation of the ATR-FTIR spectra of coated membrane (a) before and (b) after the cross-flow test. [0064] Figure 12 is a photographic representation of SEM images of uncoated and coated membrane samples following exposure to E. coli in culture for 72 h for (a) uncoated membrane; (b) Tl coated membrane; (c) T2 coated membrane; (d) T3 coated membrane; and (e) T4 coated membrane. Images were acquired at 1000X and 5000X magnification.
DETAILED DESCRIPTION
[0065] Throughout this specification and the claims that follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not to the exclusion of any other integer or step or group of integers or steps.
[0066] As used in the subject specification, the singular forms "a", "an" and "the" include plural aspects unless the context clearly dictates otherwise. Thus, for example, reference to "a membrane" includes a single membrane, as well as two or more membranes; reference to "an antibiofouling property" includes a single property, as well as two or more properties; reference to "the disclosure" includes a single and multiple aspects taught by the disclosure; and so forth. Aspects taught and enabled herein are encompassed by the term "invention". All aspects are enabled within the width of the present invention.
[0067] The present specification teaches a composite filtration membrane comprising: a) a membrane; and
b) a layer which presents as a coating across a surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
[0068] The terms "microbial cell" and "microorganism" may be used interchangeably throughout this specification. [0069] Reference to a "Mesorhizobium or Mesorhizobium-li e microorganism" includes a Gram negative bacterium with monotrichous flagella, which grows to a colony diameter of 1 to 4 mm after 7 days on yeast mannitol agar (YMA), exhibits a generation time of 4 to 10 hours in yeast mannitol broth (YMB), tolerates a maximum growth temperature of 36°C to 39°C, exhibits a maximum NaCl tolerance for growth of 1 to >2.5 (% w/v), tolerates a pH range for growth of 4 to 10 and has the ability to grow on melibiose.
[0070] Reference to a "membrane" includes a semipermeable membrane. For example, the membrane may be a nanofiltration, microfiltration, ultrafiltration, forward osmosis (FO) or reverse osmosis (RO) membrane.
[0071] In an embodiment, the membrane is a semipermeable membrane.
[0072] Accordingly, in an embodiment, the present specification teaches a composite filtration membrane comprising: a) a semipermeable membrane; and
b) a layer which presents as a coating across a surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
[0073] In an embodiment, the layer confers biofouling resistance.
[0074] Reference to "biofouling resistant" or "biofouling resistance" includes a reduction or complete prevention of biofouling on the surface of a filtration membrane as a result of the layer when compared to membranes that do not have the layer.
[0075] Accordingly, in an embodiment, the present specification teaches a composite filtration membrane comprising: a) a semipermeable membrane; and
b) a biofouling resistant layer which presents as a coating across a surface of the membrane, wherein the biofouling resistant layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism;
wherein the composite filtration membrane exhibits biofouling resistance. [0076] The membranes described in the present specification are well known in the art and are commercially available. The present specification encompasses instances where the membrane is purchased from a commercial vendor or produced de novo by a person skilled in the art.
[0077] In an embodiment, the membrane is a RO membrane with a separation functional layer attached to the surface of a porous substrate. An optional hydrophilic layer may also be attached to the surface of the separation functional layer. The present invention further encompasses any other additional layers which may be reasonably attached to the porous substrate for the purposes of separating aqueous solutions.
[0078] In a further embodiment, the membrane is a FO membrane. [0079] To assist with describing the nature of the composite filtration membrane according to the present specification, reference is made to Figure 1, which illustrates a schematic cross-section of the composite filtration membrane comprising (a) a porous substrate; (b) a separation functional layer; and (c) an optional hydrophilic layer; and (d) a layer presenting as a coating across the surface of the membrane. The separation functional layer, optional hydrophilic layer and the layer presenting as a coating across the surface of the membrane are attached to the (e) feed water surface of the membrane. The (f) permeate surface of the membrane does not have any additional layers attached.
[0080] Reference to a "feed water surface" means the surface of the porous substrate that is exposed to the influent water for treatment. For example, the feed water surface may be exposed to salt water. Reference to the "permeate surface" means the surface of the porous substrate that the filtration permeate is expelled from the membrane.
[0081] The porous substrate will generally impart mechanical strength to the composite membrane. The porous substrate may therefore also be described as a porous substrate support structure or simply a porous support structure. Provided the porous substrate functions as herein described, there is no particular limitation on the composition from which the substrate is made.
[0082] If the porous substrate is to come into contact with a solvent during application of the separation functional layer, the substrate should not be adversely affected by the solvent (e.g. it should not be soluble in the solvent).
[0083] Examples of suitable materials from which the porous substrate can be made include polymer and inorganic substrates.
[0084] In an embodiment, the porous substrate is inorganic. [0085] Examples of suitable inorganic substrates include ceramics and metal oxides such as silica and alumina.
[0086] In an embodiment, the porous substrate is a polymer.
[0087] Suitable polymers from which the porous substrate may be made include, but are not limited to, poly(acrylonitrile) (PAN), polysulfone (PSf), polyethylene terephthalate (PET), polyethersulphone, polyaniline, polypropalene, polyimides (PI), cellulose acetate (CA), cellulose diacetate and cellulose triacetate, and co-polymers thereof.
[0088] Reference to "co-polymers thereof" is intended to mean the "general polymer" that comprises one or more difference polymerized monomer residues. For example, a copolymer of PAN is intended to mean polymer comprising polymerized residues of acrylonitrile and one or more other monomers.
[0089] Reference to "general polymer"-based polymers, is intended to embrace the homo-polymer and co-polymer thereof. For example, poly(acrylonitrile) homo- or copolymers may be referred to simply as "PAN-based" polymers. Those skilled in the art will appreciate that a homo-polymer consists essentially of polymerized residues of one monomer type. A co-polymer will comprise polymerized residues of at least two monomer types. [0090] Where the polymer is a copolymer, that specified polymer will typically comprise less than 50 wt% of a second polymerized monomer residue. For example, by being a PAN co-polymer is meant that the co-polymer will comprise less than 50 wt% of polymerized monomer residues other than polymerized acrylonitrile monomer residues. The co-polymer must of course comprise at least some of the other polymerized monomer residue.
[0091] In an embodiment, the porous substrate is a porous polysulfone homo- or copolymer substrate.
[0092] Provided the porous substrate can be fabricated into the composite filtration membrane in accordance with the invention there is no particular limitation on the shape or dimensions which it may take. Generally, the porous substrate will have a thickness ranging from about 20 μιη to about 100 μιη. Reference to "20 μιη to about 100 μιη" means 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100 μιη.
[0093] An important feature of the porous substrate is that it contains pores that enable solutions to flow through the substrate. By the substrate being "porous" or the substrate containing "pores" is meant that the substrate contains voids or holes that are suitably arranged to provide channels within the substrate through which solution can flow.
[0094] The separation functional layer is a layer substantially having separation performance that is made of polymer film and is located on and attached to the porous support membrane.
[0095] In an embodiment, the separation functional layer is obtained by crosslinking a polymer onto the surface of the porous support.
[0096] In another embodiment, the separation functional layer is a layer obtained by polymerizing one or more monomers onto the surface of the porous support. [0097] By being in the form of a film, it will be appreciated that the separation functional layer forms a continuous coating on the surface of the porous support membrane.
[0098] Reference to a "polymer film" means that the layer presents a film having a polymer matrix formed by crosslinking one or more monomers. The separation functional layer is covalently coupled to the porous support membrane. In other words, the separation functional layer is not merely adhered to the porous support membrane but rather is coupled to it on a molecular level.
[0099] Provided that the separation functional layer has a suitable degree of selectivity for the target solutes, there is no particular limitation on the composition of the separation functional layer. Those skilled in the art will be able to choose an appropriate separation functional layer for use in a given solvent purification process.
[00100] In an embodiment, the separation functional layer is in the form of a crosslinked polyamide film and the filtration membrane is for separating water from brackish or salt water.
[0101] The separation functional layer may also be functionalized by the addition of a crosslinked hydrophilic layer.
[0102] Examples of suitable hydrophilic layers include crosslinked polyethylene glycol, polyvinylpyrrolidinone, poly(vinyl alcohol), polyethylene glycol diepoxide; polyfunctional epoxy compounds comprising at least two epoxy groups; copolymers of poly(ethylene glycol) methyl ether methacrylate and glycidyl methacrylate or glycidyl methacrylates; sulfobetaine and other zwitterionic polymers; and polyactams, poly-amino acids and polymers containing tertiary ammonium groups to the membrane surface either directly or via pre-defined spacers (tethers) and linkers. [0103] In an embodiment, the separation functional layer is a crosslinked polyamide film functionalized by the addition of a crosslinked polyvinyl alcohol hydrophilic layer. [0104] In an embodiment, the separation functional layer is a crosslinked polyamide film with an additional polyvinyl alcohol hydrophilic layer. For example, the polyvinyl alcohol hydrophilic layer may be applied by way of spin coating, knife coating or dip coating. [0105] To further describe the features of the separation functional layer in accordance with the present specification, reference is again made to Figure 1 where the separation functional layer can be seen as comprising a continuous coating on the surface of the porous substrate, or alternatively, further comprising an optional hydrophilic layer that is a continuous coating on the surface of the separation functional layer. The separation functional layer is attached to the (e) feed water surface of the porous substrate. The (f) permeate surface is not coated with a separation functional layer.
[0106] Conventional techniques and equipment can be used to apply the hydrophilic layer to the separation functional layer.
[0107] Provided that the separation functional layer performs its function of separating water from aqueous solutions there is no particular limitation on the thickness of the layer that can be used.
[0108] In an embodiment, the separation functional layer is provided as an ultrathin polymer layer, which can be produced using conventional techniques. Generally, the ultrathin layer will be between 1 to 150 nm. Reference to "between 1 to 150 nm" means 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 101, 102, 103, 104, 105, 106, 107, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149 or 150 nm. [0109] Reference to an "extracellular polymeric substance" or "EPS" includes high- molecular weight compounds comprising, but not limited to, polysaccharides, proteins, DNA, lipids and acids; which are secreted by microorganisms.
[0110] The EPS may comprise one or more types of polysaccharide. Reference to a "polysaccharide" means polymeric carbohydrate molecules comprising repeating units or monomers, such as monosaccharides, disaccharides or oligosaccharides, joined by glycosidic bonds. It is further understood that the terms "polysaccharide" and "glycan" may be used interchangeably.
[0111] In an aspect, the EPS comprises a single polysaccharide or polysaccharide derivative. In another aspect, the EPS comprises combinations of two or more polysaccharides, or polysaccharide derivatives. Hence, the agent may comprise either homogenous (homopolysaccharide) or heterogeneous (heteropolysaccharide) polysaccharide components of the EPS. In another aspect, the polysaccharide in accordance with the present invention is a combination of homopolysaccharides and heteropolysaccharides.
[0112] In an embodiment, the polysaccharides are linear, and may optionally comprise degrees of branching. In another embodiment, the polysaccharide is soluble or is a soluble derivative, in particular a water-soluble polysaccharide or a water-soluble derivative of a polysaccharide. [0113] In an embodiment, the polysaccharide is an exopolysaccharide. An exopolysaccharide may additionally comprise other non-carbohydrate substituents. For example, other non-carbohydrate substituents may include acetate, pyruvate, succinate, sulfate and phosphate substituents.
[0114] In another aspect, the polysaccharide including an exopolysaccharide is a naturally-occurring polysaccharide. In still another aspect, the polysaccharide is a polysaccharide derivative. Derivatives include, for example, modified monosaccharides or monosaccharide derivatives. Examples of monosaccharide derivatives include aminosugars, sulfosugars and sugar alcohols. Furthermore, polysaccharide derivatives may comprise one or more monosaccharides modified by chemical methods known in the art.
[0115] Without wishing to be bound by any specific theory, the biofouling resistant characteristics of the EPS or polysaccharide component thereof is thought to arise from its ability to form a hydrophilic coating with heavily hydrated and randomly oriented polysaccharide chains. Furthermore, the EPS or polysaccharide component thereof is also thought to comprise large molecules with randomly oriented polysaccharide chains which promotes steric hindrance and unfavorable entropy changes associated with adsorption. In addition, the EPS or polysaccharide component thereof of the present specification is essentially non-ionic, which also minimizes the attachment of charged species. Consequently, it is proposed that the EPS or a polysaccharide component thereof can, in an aspect, transform solid substrates to substrates with high biofouling resistance.
[0116] Reference to a "Mesorhizobium or Mesorhizobium-li e microorganism" includes a microorganism which is Gram negative, comprises a monotrichous flagella, grows to a colony diameter of 1 to 4 mm after 7 days on yeast mannitol agar (YMA), exhibits a generation time of 4 to 10 hours in yeast mannitol broth (YMB), tolerates a maximum growth temperature of 36°C to 39°C, exhibits a maximum NaCl tolerance for growth of 1 to >2.5 (% w/v), tolerates a pH range for growth of 4 to 10 and has the ability to grow on melibiose. [0117] In an embodiment, the Mesorhizobium is selected from the list comprising Mesorhizobium abyssinicae, Mesorhizobium albiziae, Mesorhizobium alhagi, Mesorhizobium amorphae, Mesorhizobium australicum, Mesorhizobium camelthorni, Mesorhizobium caraganae, Mesorhizobium chacoense, Mesorhizobium cicero, Mesorhizobium gobiense, Mesorhizobium hawassense, Mesorhizobium huakuii, Mesorhizobium loti, Mesorhizobium mediterraneum, Mesorhizobium metallidurans, Mesorhizobium muleiense, Mesorhizobium opportunistum, Mesorhizobium plurifarium, Mesorhizobium qingshengii, Mesorhizobium robiniae, Mesorhizobium sangaii, Mesorhizobium septentrionale, Mesorhizobium shangrilense, Mesorhizobium shonese, Mesorhizobium silamurunense, Mesorhizobium tamadayense, Mesorhizobium tarimense, Mesorhizobium temperatum, Mesorhizobium thiogangeticum or Mesorhizobium tianshanense.
[0118] In an embodiment, the Mesorhizobium is M. huakuii or M. loti.
[0119] In an embodiment, the Mesorhizobium or Mesorhizobium-li e microorganism is the microbial cell designated CAM543 deposited at the National Measurements Institute on 29 October, 2014 under accession number V14/017216.
[0120] The present specification further teaches a composite filtration membrane with a layer comprising an isolated polysaccharide derived from an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism. [0121] Enabled herein is a composite filtration membrane with a layer comprising an isolated polysaccharide derived from an EPS produced by a microbial cell selected from the list comprising M. huakuii, M. loti, M. abyssinicae, M. albiziae, M. alhagi, M. amorphae, M. australicum, M. camelthorni, M. caraganae, M. chacoense, M. cicero, M. gobiense, M. hawassense, M. mediterraneum, M. metallidurans, M. muleiense, M. opportunistum, M. plurifarium, M. qingshengii, M. robiniae, M. sangaii, M. septentrionale, M. shangrilense, M. shonese, M. silamurunense, M. tamadayense, M. tarimense, M. temperatum, M. thiogangeticum or M. tianshanense.
[0122] Further taught herein is a composite filtration membrane with a layer comprising an isolated polysaccharide derived from an EPS produced by a microbial cell selected from M. huakuii and M. loti.
[0123] In a particular embodiment, the present specification enables a composite filtration membrane with a layer comprising an isolated polysaccharide derived from an EPS produced by a microbial cell designated CAM543 deposited at the National Measurements Institute on 29 October, 2014 under accession number V14/017216. [0124] Further contemplated herein is a layer comprising an EPS or an isolated polysaccharide thereof produced by a genetically modified Mesorhizobium or Mesorhizobium-li e microorganism with introduced traits. Examples of genetic modification include generation of auxotrophic mutants and mutants which have the capacity to metabolize and grow on an expanded spectrum of carbon sources. The mutants may also be useful proprietary markers.
[0125] In an embodiment, the layer is attached to the surface of the membrane by any suitable means.
[0126] In an embodiment, the layer is attached to the surface of the membrane via a linker.
[0127] In an embodiment, the layer is attached to the surface of the membrane via an inorganic linker [0128] In an embodiment, the linker may be derived from any suitable metal alkoxide or alkoxysilane.
[0129] One or more a metal alkoxides or alkoxysilanes within the scope of the present application may react with suitable functional groups on the EPS or a polysaccharide component thereof and the membrane to link the EPS or a polysaccharide component thereof and the membrane. In particular, the metal alkoxide or alkoxysilane may link the EPS or a polysaccharide component thereof and the membrane by transesterification or alcoholysis. In an embodiment, the suitable functional groups on the EPS or a polysaccharide component thereof and the membrane may include hydroxyl groups, carbonyl groups, carboxyl groups and combinations thereof. In another embodiment, the linker may comprise two or more metal alkoxides.
[0130] Taught herein is a metal which forms part of the metal alkoxide linker which is any suitable metal. Examples of suitable metals include, but are not limited to, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and lanlhanides, such as cesium, samarium, gadolinium, dysprosium, erbium and neodymium. Further taught herein is a metal comprising one or more of the metals described above. The metal of the present specification may further comprise a bivalent, trivalent, tetravalent, pentavalent, or hexavalent metals, In an embodiment, the linker may be derived from an alkoxysilane.
[0131] Reference to an "alkoxy" means a group having the formula -OR, where R is an alkyl group. Examples of linear alkoxy groups include, but are not limited to, methoxy, ethoxy, propoxy, butoxy, pentoxy, and hexoxy. Examples of branched alkoxy groups include, but are not limited to, isopropoxy, sec-butoxy, tert-butoxy, isopentoxy, and isohexoxy. Examples of cycloalkoxy groups include, but are not limited to, cyclopropyloxy, cyclobutyloxy, cyclopentyloxy, and cyclohexyloxy.
[0132] Reference to an "alkyl" includes straight chain and branched alkyl groups having from 1 to about 20 carbon atoms or, in some embodiments, from 1 to 8, 1 to 6, or 1 to 4 carbon atoms. In an embodiment, the alkyl group may be a cycloalkyl group.
Examples of straight chain alkyl groups include those with from 1 to 8 carbon atoms such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, and n-octyl groups.
Examples of branched alkyl groups include, but are not limited to, isopropyl, iso-butyl, sec-butyl, tert- butyl, neopentyl, isopentyl, and 2,2-dimethylpropyl groups. Examples of cycloalkyl groups include but are not limited to cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl.
[0133] In an embodiment, the layer is attached to the surface of the membrane via a titanium alkoxide, a zirconium alkoxide, an aluminum alkoxide or an alkoxysilane linker. [0134] In another embodiment, the layer is attached to the surface of the membrane via an alkoxide linker of the following formula Si(OR)4, Ti(OR)4, Zr(OR)4 and Al(OR)4. In an embodiment, the linker may be titanium isopropoxide.
[0135] It will be appreciated from the discussion above that in the composite filtration membrane according to the present specification, the membrane and layer are positioned such that a solvent passing through the membrane must pass through each of the membrane and the layer.
[0136] The present specification teaches a method for preparing a composite filtration membrane comprising: a) providing a membrane; and
b) coating a surface of the membrane with a layer, wherein the layer comprises:
i. an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or
ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
[0137] In an embodiment, the present specification teaches a method for preparing a composite filtration membrane comprising: a) providing a semipermeable membrane; and
b) coating a surface of the membrane with a layer, wherein the layer comprises:
i. an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or
ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
[0138] In another embodiment, the present specification teaches a method for preparing a composite filtration membrane comprising: a) providing a semipermeable membrane; and
b) coating a surface of the membrane with a biofouling resistant layer, wherein the biofouling resistant layer comprises:
i. an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or
ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-Yi e, microorganism.
wherein the composite filtration membrane exhibits biofouling resistance.
[0139] In an embodiment, the method for producing a composite filtration membrane comprises providing a membrane and forming a layer on a surface of the membrane comprising the EPS or a polysaccharide component thereof wherein the resulting layer exhibits biofouling resistance.
[0140] In an embodiment, the method for producing a composite filtration membrane comprises providing a membrane that is a reverse osmosis membrane and forming a layer on a surface of the reverse osmosis membrane comprising the EPS or a polysaccharide component thereof wherein the resulting composite filtration membrane exhibits biofouling resistance.
[0141] In an embodiment, the method for producing a composite filtration membrane comprises providing a membrane that is a polyamide thin film composite membrane and forming a layer on a surface of the polyamide thin film composite membrane comprising the EPS or a polysaccharide component thereof wherein the resulting composite filtration membrane exhibits biofouling resistance.
[0142] In an embodiment, the method for producing a composite filtration membrane comprises providing a membrane that is a polyamide thin film composite membrane with a hydrophilic surface layer comprising polyvinyl alcohol and forming a layer on a surface of the hydrophilic surface layer comprising the EPS or a polysaccharide component thereof wherein the resulting composite filtration membrane exhibits biofouling resistance.
[0143] In an embodiment, the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane by any suitable means. [0144] In an embodiment, the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane using a linker.
[0145] In an embodiment, the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane using an inorganic linker.
[0146] In an embodiment, the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane using any suitable metal alkoxide or alkoxysilane. [0147] One or more metal alkoxides or alkoxysilanes within the scope of the present application may react with suitable functional groups on the EPS or a polysaccharide component thereof and the membrane to link the EPS or a polysaccharide component thereof and the membrane. In particular, the metal alkoxide or alkoxysilane may link the EPS or a polysaccharide component thereof and the membrane by transesterification or alcoholysis. In an embodiment, the suitable functional groups on the EPS or a polysaccharide component thereof and the membrane may include hydroxyl groups, carbonyl groups, carboxyl groups and combinations thereof. In another embodiment, the linker may comprise two or more metal alkoxides. [0148] Taught herein is a metal which forms part of the metal alkoxide linker which is any suitable metal. Examples of suitable metals include, but are not limited to, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, silver, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and lanthanides, such as cesium, samarium, gadolinium, dysprosium, erbium and neodymium. Further taught herein is a metal comprising one or more of the metals described above. The metal of the present specification may further comprise a bivalent, trivalenl, tetravalent, pentavalent, or hexavalent metals. In an embodiment, the linker may be a crosslinker derived from an alkoxysilane. [0149] In an embodiment, the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane using a titanium alkoxide, a zirconium alkoxide, an aluminum alkoxide or an alkoxysilane linker.
[0150] In another embodiment, the method for producing a composite filtration membrane comprises forming a layer on a surface of the membrane using an alkoxide linker of the following formula Si(OR)4, Ti(OR)4, Zr(OR)4 and Al(OR)4. In an embodiment, the linker may be titanium isopropoxide.
[0151] Hence, the present specification teaches an immobilization strategy that uses specific crosslinking molecules to act as a bridge between the layer and a surface of the membrane. In an aspect, the carboxyl (-COOH) and hydroxyl (-OH) functional groups on the surface of the membrane and the hydroxyl (-OH), carbonyl (-C=0) and carboxyl (- COOH) functional groups on the EPS or a polysaccharide component thereof, are reacted with the metal alkoxide to allow chemical bonding to occur. For example, where the surface of the membrane is a film of crosslinked polyamides, carboxylic groups are present on the surface of the membrane from the hydrolysis of the unreacted acyl chloride groups. The abundance of hydroxyl groups in the EPS or polysaccharide component thereof reacts with the linker to form bonds.
[0152] In another aspect, titanium alkoxides are known to react with compounds containing hydroxyl groups via the protolytic loss of one or more alkoxide ligands (Figure 2; Uekawa, N., et al. (2006) Journal of the Ceramic Society of Japan, 114(10), 807; Yi, Y., et al. (2010) US Patent No. 2010/0239493; Kariduraganavar, M.Y., et al. (2009) Industrial and Engineering Chemistry Research, 48, 4002. In particular, titanium isopropoxide reacts with carboxyl groups to form carboxylate completes through chelating bidentate, bridging bidentate or monobidentate mechanisms (Figure 3; see also Hojjati, B. and Charpentier, P. A. (2001) Journal of Polymer Science Part A: Polymer Chemistry, 46, 3926; Nakamoto, K. (1997) Infrared and Raman Spectra of Inorganic and Coordination Compounds. Wiley- Interscience: New York, 59; Deacon J.B. and Phillips, R.J. (1980) Coordination Chemistry Reviews, 33, 227).
[0153] Those skilled in the art will appreciate that the formation of a layer on the surface of membranes may adversely impact membrane performance, for example, by reducing water flux. The use of metal alkoxides for the formation of a layer on a surface of the membrane taught by the present specification does not reduce water flux when compared to the water flux of a membrane without a biofouling resistant layer (Figures 5 and 6). [0154] The use of metal alkoxides for the formation of a layer on a surface of the membrane taught by the present specification requires that the metal alkoxides are dissolved in alcohol prior to being combined with the EPS or polysaccharide component thereof and water.
[0155] In an embodiment, the alcohol is ethanol or 1-propanol. [0156] In a further embodiment, the volume ratio of titanium isopropoxide to alcohol is between 1: 10 and 1:20. Reference to "between 1: 10 and 1:20" means 1: 10, 1: 11, 1: 12, 1: 13, 1: 14, 1: 15, 1: 16, 1:17, 1: 18, 1: 19 or 1:20.
[0157] The weight/weight (w/w) ratio of the EPS or polysaccharide component thereof and the linker is proposed to be between 0.15 and 1.25. Reference to the w/w ratio of "between 0.15 and 1.5" means 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.0, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45 or 1.50.
[0158] In an embodiment, the layer is formed on a surface of the membrane by treating the membrane with one or more metal alkoxides and the EPS or a polysaccharide component thereof.
[0159] Application of the layer to the membrane is proposed to be with the range of 1 to 100 μg/cm2. Reference to " 1 to 100 μg/cm2" means 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 or 100 μg/cm2.
[0160] Formation of the layer is proposed to be undertaken at a temperature between 25 and 50°C, including 40°C. Reference to "between 25 and 50°C" means 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49 or 50°C.
[0161] Formation of the layer is proposed to be undertaken for a time between 1.0 h to 5.0 h, including 3.0 h. Reference to "between 1.0 h to 5.0 h" means 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0 h.
[0162] Further enabled herein is a method for modifying existing filtration membranes to have biofouling resistance by forming a layer on a surface of the existing filtration membrane in accordance with the present specification. [0163] In an embodiment, the present specification teaches a method for modifying existing filtration membranes with surface carboxylic and/or hydroxyl functionalities to have biofouling resistance by forming a layer on a surface of the existing membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
[0164] In an embodiment, the present specification further teaches a method for modifying existing RO filtration membranes to have biofouling resistance by forming a layer on the surface of the existing RO filtration membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
[0165] In another embodiment, the present specification also teaches a method for modifying existing FO filtration membranes to have biofouling resistance by forming a layer on the surface of the existing FO filtration membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism. [0166] Hence, the present specification teaches a composite filtration membrane having biofouling resistance by forming a layer on the surface of a filtration membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
[0167] In an embodiment, the filtration membrane is a RO filtration membrane having biofouling resistance by forming a layer on a surface of a RO filtration membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism.
[0168] In an embodiment, the filtration membrane is a FO filtration membrane having biofouling resistance by forming a layer on the surface of a FO filtration membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
[0169] In an embodiment, the filtration membrane is a polyamide thin film composite membrane having biofouling resistance by forming a layer on a surface of a polyamide thin film composite membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism. [0170] In an embodiment, the filtration membrane is a polyamide thin film composite membrane comprising a hydrophilic surface layer having biofouling resistance by forming a layer on a surface of a polyamide thin film composite membrane comprising: (a) an EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or (b) a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism.
[0171] Taught herein is a process for treating a liquid, comprising subjecting the liquid to filtration with a composite filtration membrane comprising: a) a membrane; and
b) a layer which presents as a coating across the surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism.
[0172] A person skilled in the art would recognize that a variety of different liquids, either alone or in combination, could be used in conjunction with the disclosed composite filtration membrane. For example, aqueous solutions, biological fluids, liquid foodstuffs, hydrocarbons and salt water are all comprehended by the present specification.
[0173] Reference to "salt water" includes brackish, saline and hyper-saline water. For example, salt water may include any water with a salt concentration of about >0.05%. Brackish water has a salt concentration of about 0.05-3%; saline has a salt concentration of about 3-5%; hyper-saline water has a salt concentration of about >5%.
[0174] Reference to "brine" includes "brine water", "brine waste" and "brine stream". For example, brine may include water with a salt concentration of about >3.5% and may be naturally occurring or a product of other water treatment processes.
[0175] In an embodiment, the present specification teaches a process for treating a liquid, comprising subjecting the liquid to filtration with a composite filtration membrane comprising: a) a semipermeable membrane; and
b) a layer which presents as a coating across the surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism. [0176] In another embodiment, the present specification also teaches a process for treating a liquid comprising subjecting the liquid to filtration with a composite filtration membrane comprising: a) a semipermeable membrane; and b) a biofouling resistant layer which presents as a coating across the surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism;
wherein the filtration membrane exhibits biofouling resistance.
[0177] Further taught herein is a process to create a difference in pressure across the filtration membrane so as to separate solvents, including, but not limited to, salts and other dissolved ions and molecules from a liquid; wherein the solute concentration in the filtrate is lower compared with that of the liquid that was subjected to purification.
[0178] In an embodiment, the present specification teaches a process for the purification of salt water and the decontamination of industrial waste water. [0179] In another embodiment, the present specification teaches a process for the purification and concentration of biologically useful molecules such as peptides, proteins, antibodies and antibiotics.
[0180] In another embodiment, the present specification teaches a process for the purification and concentration of liquid foodstuffs. [0181] Reference to "liquid foodstuffs" includes extracts from vegetable and animal products. The term "liquid foodstuffs" according to the present invention also encompasses beverages. For example, liquid foodstuffs may include dairy products, yoghurts, ice creams, milk-based soft ice, milk-based garnishes, puddings, cream, whipped cream, chocolate cream, butter cream, creme fraiche, curd, milk, such as skim milk, buttermilk, soured milk, kefir, milkshakes, egg custard, cheese, confectionary, snack products, diet drinks, finished drinks, sports drinks, stamina drinks, spreads, meat products, mayonnaise, dressings, sauces, gravy, soups, shortenings and wine. [0182] In another embodiment, the present specification teaches a process for the purification and concentration of hydrocarbons.
[0183] Reference to "hydrocarbons" includes liquid hydrocarbons. For example, hydrocarbons may include fuels, petroleum, mineral oil, oil, crude oil, lube oil, hydraulic oil, wet gases, natural gasoline or condensate.
EXAMPLES
[0184] Aspects of certain embodiments of the present invention are further described by reference to the following non-limiting Examples. Protocols Chemicals
[0185] Unless otherwise specified, all chemicals and reagents were analytical grade with purity of over 99%. Ultrapure (type I) water, such as Milli-Q (trade mark) was used throughout the present specification. Preparation of coating solution
Solution A
[0186] 1.250 mL of titanium isopropoxide was slowly added to 25 mL absolute ethanol and mixed to obtain a clear solution. The resulting solution was added drop wise to 250 mL of water (pH 1.5) at a constant temperature of 4-7°C that was being vigorously stirred. Thereafter, the solution was stirred for 2-3 h before being stored at 4°C.
Solutions B, Bl and B2
[0187] A measured amount of polysaccharide was dissolved in water (pH 1.5) to obtain solutions with polysaccharide concentrations of 2.34 mg/mL (solution B); 4.68 mg/mL (solution B l) or 15.68 mg/mL (solution B2). Coating polysaccharide on membrane surface
[0188] Solutions A and B were diluted to prepare membrane samples T1-T4 and Dl- D3 (thin). Solutions B l and B2 were diluted to prepare membrane samples T5 and T6 (thick).
[0189] The coating solutions were prepared to obtain a weight/weight ratio of titanium to polysaccharide between 0.187 and 1.251 and the amount of polysaccharide delivered on 2
the membrane surface was between 0.37 and 223.97 μg/cm . The mixture was stirred for 30 min at room temperature before being coated on the membrane surface.
[0190] The coating solution delivered on membrane surface was 7.14 x 1(T -2 mL/cm 2". The membrane was then placed in an oven at 40-45°C for 3-5 h, until the membrane was nearly dry. Thereafter, the coated membrane was washed and stored in water.
[0191] The coating composition of the different membrane samples are summarized in Table 1.
Table 1. Coating composition of membrane samples T1-T6 and D1-D3
Figure imgf000039_0001
Characterization of membrane surfaces
Water flux analysis
[0192] Measurements of the water flux of membrane surfaces were performed in cross-flow environments using the laboratory-scale CF042 cross-flow system (Sterlitech). The feed water was ultrapure (type I) water, such as Milli-Q (trade mark) water, with an applied trans membrane pressure difference of 15.5 bar and feed cross-flow rate of 60 L/h. Each membrane sample was tested in the cross-flow environment for at least 6 h. The membrane test unit was operated in an open-loop mode, where the permeate was directed to a balance, the weight data recorded every 30 sec and the flux values calculated thereafter.
Surface morphology analysis [0193] Coated membranes were prepared for surface morphology analysis by washing several times in water and immersing in water overnight to remove unreacted or unbound compounds. The surface morphology of the coatings was examined by scanning electron microscopy (SEM).
[0194] SEM imaging was carried out by sputter coating samples with a very thin layer of iridium before imaging with a Philips XL30 field emission scanning electron microscope operating at 4kV.
ATR-FTIR analysis of surfaces
[0195] Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra were recorded on a Thermo Scientific Nicolet 6700 spectrometer equipped with diamond ATR accessories. For diamond ATR crystal, the depth of penetration is approximately 1.7 μιη οΓ less (depending on the wavenumber of the vibration band). Thirty-two scans were accumulated with a resolution of 4 cm"1 for each spectrum.
Elemental analysis of surfaces
[0196] The elemental composition of coated surfaces was analyzed by X-ray photoelectron spectroscopy (XPS) using an AXIS-HSi spectrometer (Kratos Analytical Inc., Manchester, U.K.) with a monochromatic Al X-ray source. Spectra were recorded at an emission angle of 0° with respect to the surface normal with corresponding depths of penetration on the order of 5-10 nm. The analysis was performed as three independent experiments with the averaged data described in this specification. Water contact angle analysis
[0197] The water contact angles of the membranes were measured at 20°C using a KSV CAM200 Contact Angle Goniometer. The analysis was performed as three independent experiments with the averaged data described in this specification. Water exposure analysis
[0198] Coated membranes were exposed to water at different pH levels to test the durability of the polysaccharide coating. Water of pH 2 and 9 was prepared using NaOH and HC1 and ultrapure (type I) water, such as Milli-Q (trade mark) water (pH 6.998) was used as a control. [0199] Coated membranes were exposed to ultrapure (type I) water for 90 d and water of pH 2 and 9 for 15 d. Following water exposure, the coated membranes were dried under ambient conditions for 2 d prior to ATR-FTIR and contact angle analyses to assess the polysaccharide coating.
Anti-biofouling analysis of coated membranes [0200] The anti-biofouling effect of the polysaccharide coating was analyzed by exposing membrane samples T1-T6 to bacterial cultures. Uncoated membrane samples were used as controls.
[0201] Membrane samples were exposed to a suspension of Escherichia coli (E. coli) strain K12, at a concentration of 1.0 x 109 colony forming units per milliliter (cfu/mL). After an exposure time of 24 and 72 h, the membrane samples were washed thoroughly in water for 15 min. The samples were then treated with UV radiation (270 nm) for 30 min to inactivate the E. coli. After drying, the samples were prepared for SEM analysis as described above. Example 1
Water flux analysis of coated samples
[0202] The water flux of each individual uncoated membrane (Jo) was determined prior to the polysaccharide coating. The water flux of the membrane after the polysaccharide coating (J) was then obtained and the relative flux of the coated membrane calculated (J/Jo). Values of the relative flux of membrane samples T1-T6 are presented in Table 2.
Table 2. Relative flux (J/Jo) of membrane samples T1-T6
Figure imgf000042_0001
[0203] There was no difference in the water flux of membrane samples T1-T4 compared to the corresponding uncoated membranes. The increased polysaccharide surface concentration and cross linker of membrane samples T5 and T6, resulted in a decrease in water flux when compared to the corresponding uncoated membranes. Example 2
Surface morphology analysis of coated samples
[0204] The SEM images of membrane samples T1-T3 indicated that the polysaccharide coating was quite thin, as demonstrated by the retention of the typical peak- and-valley structures of underlying polyamide membrane (Figure 4). There was no difference in the surfaces of the uncoated membrane and Tl. However, the coating appeared to cover parts, or most of the fine structures of the polyamide membrane in samples T2 and T3. Previous studies using atomic force microscopy (AFM) have shown that the surface roughness of the uncoated membrane used in this analysis is about 0.1 μιη for a scan area of 1 μιη x 1 μιη (Dach (2008) PhD Thesis, Universite d'Angers). As the peak-and-valley structures of the polyamide membrane were still visible for samples Tl- T3, we predict that the coating thickness of these samples was less than about 0.1 μιη.
[0205] By contrast, the surfaces of T4-T6 demonstrated that the peak-and-valley structures of the underlying polyamide membrane were completely covered by the coating layer (Figure 4).
Example 3
ATR-FTIR analysis of coated samples
[0206] ATR-FTIR was used to analyze the surfaces of membrane samples T1-T6 before and after the water flux tests described in Example 1. [0207] The uncoated membrane surface is characterized by broad peaks in regions A, B and C (Figure 5). Peaks in regions A and B are due to the free and hydrogen-bonded N- H stretching, respectively, whereas peaks in region C are due to aromatic =C-H stretching. The coated samples, including samples T1-T3 with thin polysaccharide coatings, have less pronounced peaks in the A and C regions when compared to those of the uncoated membrane (Figure 5). This is consistent with the presence of a surface coating layer which obscured or changed the characteristics of the spectral features in regions A and C of the uncoated membrane.
[0208] Peaks in region B of the coated samples became more prominent as the coating thickness increased (Figure 5). This is presumably due to an abundance of hydroxyl groups and consistent with the presence of polysaccharide in the coating layer. There were also pronounced changes in the peaks in region E (Figure 5), which are due to aliphatic C-H stretching, where the peaks exhibited characteristics similar to those of polysaccharide as the coating thickness increased. [0209] The spectral peaks in region F are due to the C-O-C stretching of polysaccharide. For samples T4-T6, the peaks in this region were quite prominent, indicating the presence of polysaccharide in the coating layer (Figure 5). For samples TITS, the peaks in region F were less obvious (Figure 5). This is likely due to the deep penetration of IR radiation in this wave number region which greatly exceeded the thin coatings on these samples.
Example 4
Elemental analysis of coated samples
[0210] Elemental analysis of samples T1-T3 was performed after the water flux analysis described in Example 1. The uncoated membrane sample was also included in this analysis as a control.
[0211] The O/N ratio of the uncoated sample had a value of 1.26, which is close to the theoretical O/N ratio of unity when the polyamide layer is fully cross-linked (i.e., all the O and N atoms are associated with the amide groups to give a 1: 1 ratio). For the coated samples, the O/N ratio increased in value with Tl having a value of 6.37 and T3 a value of 14.01. Likewise, the C/N ratio of the coated samples also had higher values compared to those of the uncoated sample (Table 3).
[0212] The increase in values of the O/N and C/N ratios indicates the existence of a coating layer which is rich in oxygen and carbon on the top surface of samples T1-T3 (Table 3). These characteristics are consistent with the presence of polysaccharide in the coating layer.
[0213] Table 3 also shows the values of titanium/nitrogen (Ti/N) ratio for the uncoated and coated samples. In particular, the uncoated sample had a Ti/N ratio of zero, as expected, whereas the Ti/N ratio of the coated samples had values ranging from 0.04 to 0.14, confirming the presence of the cross linker in the coating layer of these samples. Table 3. Elemental analysis of uncoated and coated membrane samples T1-T3
Figure imgf000045_0001
[0214] In addition to elemental composition analysis, XPS also provides information about the chemical state of different elements by deconvoluting the high resolution XPS spectra of different elements into individual component peaks.
[0215] Generally, the relative intensity of peaks C3 and C5 of the coated samples were higher compared to those of the uncoated sample, which is likely due to increase in surface concentrations C-O-C / C-0 and 0-C=0 species, respectively. Such an increase is consistent with the presence of the polysaccharide in the coating layer. There is also a decrease in the concentrations of C4 and C6 on the coated samples compared to those on the uncoated sample, which is presumably due to the presence of a coating layer masking the N-C=0 and aromatic ring species, respectively.
Table 4. Atomic composition of Cls spectra peaks of the uncoated and coated membrane samples T1-T3
CI ( ) C2 ( ) C3 % C4 ( ) C5 ( ) C6 ( )
Uncoated Avera^ ?e 36.73 28.32 18.49 12.86 0.37 3.23
STD 4.30 2.25 2.35 0.28 0.32 0.13
Tl Avera^ ?e 50.93 4.07 35.85 7.70 1.02 0.43
STD 2.77 3.32 2.07 0.42 0.75 0.09
T2 Avera^ ?e 50.91 1.73 35.89 9.34 1.67 0.46
STD 2.32 2.30 2.14 7.58 0.23 0.73
T3 Avera^ 43.66 3.62 45.53 5.61 1.28 0.29
STD 2.93 3.04 7.53 1.31 0.34 0.24 [0216] Figure 8 shows examples of the deconvolution of the XPS Ols spectra into individual component peaks and the assignments of the peaks, and Table 5 shows the atomic percentage of the component peaks for the uncoated and coated membrane samples. The Ols spectrum and the individual component peaks of sample D3 with high crosslink density are also included in Figure 7 and Table 5 for comparative purposes.
[0217] For the uncoated membrane, the Ols spectrum can be deconvoluted into peaks 01 and 02. Peak 01 is assigned to 0=C-N and 0-C=0* species, whereas peak 02 is associated with H— 0=C-N and 0-C=0 species. For the coated samples, the Ols peak can be deconvoluted into four peaks 01— > 04. Since the 0=C-N species on the uncoated membrane surface are presumably masked by the coating layer and 0-C=0 species already reacted with the cross linker, peak 01 of the coated samples may be partly attributed to Ti-O-C bonds. Likewise, peak 02 is assigned C-O, C-O-C and C=0 groups, which are prevalent in polysaccharide. There are two new peaks 03 and 04. Peak 03 is assigned to Ti-O-Ti bonds in the coating layer, whereas peak 04 is likely associated with absorbed water.
[0218] The presence of Ti-O-C and Ti-O-Ti bonds in the coating layer is further confirmed by the relatively high intensity of peaks 01 and 03 of sample D3, respectively. Sample D3 had high crosslink density, thus was expected to give rise to higher concentrations of Ti-O-C and Ti-O-Ti species in the coating layer.
Table 5. Atomic composition Ols spectra peaks of the uncoated and coated samples T1-T3 and D3
Ol ( ) 02 ( ) 03 ( ) 04 ( )
Uncoated Average 48.92 51.08 0.00 0.00
STD 1.79 1.79 0.00 0.00
Tl Average 7.78 81.34 1.56 9.31
STD 3.31 8.51 0.49 5.68
T2 Average 0.36 80.08 2.08 17.48
STD 0.27 4.95 0.05 5.23
T3 Average 4.61 87.89 4.04 3.45 STD 2.80 4.31 2.35 0.52
D3 Average 14.08 60.07 25.85 0.00
STD 1.69 1.60 1.44 0.00
[0219] The XPS data collected is consistent with the presence of polysaccharide and cross linker on the surface of samples T1-T3 and the formation of Ti-O-C and Ti-O-Ti bonds in the coating layer. Example 5
Water contact angle analysis of coated samples
[0220] Water contact angle measurements were carried out for the uncoated and coated membrane surfaces to investigate the change in membrane surface hydrophilicity as a result of polysaccharide coating. [0221] Water contact angle decreased from 70-75° for the uncoated membrane to 37- 42° for membrane sample Tl and 20-25° for membrane samples T2-T6. The decrease in the contact angles of the coated surfaces indicates that the presence of the polysaccharide coating layer significantly increased the membrane surface hydrophilicity. Without wishing to be bound by any specific theory, the relatively higher contact angle of Tl, compared to those of T2-T6, may be due to the relatively low levels of polysaccharide and cross linker deposited on the membrane surface, leading to incomplete surface coverage of the coating.
Example 6
Water exposure analysis of coated samples [0222] Water exposure analysis was performed to assess the durability of coated membranes under water treatment operating conditions. Membrane sample T6 was assessed for durability.
[0223] The ATR-FTIR spectra of the coated membrane samples following the exposure to water at different pH levels were similar to those before the exposure and had features that are specific to the polysaccharide (Figure 10). The similarity between the spectra of the coating and the polysaccharide is evident, particularly in regions A, B and C, where there is minimal contribution from the underlying membrane to the spectral bands. These spectra indicate that the polysaccharide was still present on the membrane surface following prolonged exposure to water.
[0224] Water contact angle measurements for all coated samples following water exposure showed low contact angles in the range 20-25°, which are similar to the contact angles obtained for the coatings prior to water exposure. These results indicate that the polysaccharide coatings are durable and remain bound to the membrane surface after prolonged exposure to water.
[0225] The durability of the polysaccharide coatings was also tested in cross-flow environments under conditions of high applied pressures and ionic strengths. The tests were carried out using laboratory-scale cross-flow membrane test units which were either a CF042 or a Sepa CF II cross-flow cell system (Sterlitech). The feed water was either water, or aqueous solutions containing 2000 ppm or 32000 ppm NaCl. The applied trans membrane pressure difference was either 15.5 or 55 bar, and the feed cross-flow velocity was maintained at 40 cm/sec. The membrane test units were operated in a closed loop mode, where the permeate and retentate were circulated back to the feed water reservoir, to maintain a constant salt concentration. The duration of each test was 49 h. Following the cross-flow experiments, the coated membranes were dried under ambient conditions for two days prior to analysis using ATR-FTIR and contact angle measurements.
[0226] The polysaccharide coatings remained on the membrane surface following exposure to all conditions. The contact angles of these samples also had low values in the range 20-25°, which are similar to those of the coatings before the cross-flow experiments (Table 6). No difference in the ATR-FTIR spectra was observed in the coated and uncoated membrane before and after the cross-flow tests (Figure 11). Table 6. Durability of polysaccharide coating following exposure to cross-flow environments
Figure imgf000049_0001
Example 7 Effect of cross-link density on the water flux of coated samples
[0227] The cross-link density of the polysaccharide coating may affect properties including water uptake and water permeability. Samples D1-D3 were prepared with a polysaccharide surface concentration of 3.34 μg/cm , and variable cross-link densities ranging from 0.374 to 1.251 (w/w; titanium/polysaccharide). [0228] The water flux of samples D1-D3 was measured using the same method described in Example 1. The results showed that the relative flux J/Jo of the coated membranes was the same as the flux of corresponding uncoated membranes. These results indicate that the cross linker density does not influence the water uptake and water permeability of the polysaccharide coating layer. Example 8
Anti-biofouling effect of coated samples
[0229] The SEM images of the uncoated membrane surface following exposure to E. coli cells indicated that the majority of the surface was covered by E. coli. Furthermore, the cells were covered by what appeared to be capsular EPS, which together form colonies which covered most of the surface (Figure 12). Similar attachment of E. coli was also observed on sample Tl, although the extent of surface coverage of E. coli cells was less than the uncoated sample (Figure 12).
[0230] By contrast, membrane samples T2 and T3 coating of polysaccharide were observed to have a substantially reduced number of attached E.coli cells to the surface of the membrane, with nearly no cells, EPS or cell aggregates visible on the surface (Figure 12). For samples T4-T6, no observable E. coli cells were attached to the membrane surface, demonstrating the high anti-fouling resistance of the polysaccharide coating (Figure 12).
[0231] Without wishing to be bound by any specific theory, it is suggested that the relatively greater extent of E. coli cell attachment on sample Tl, compared to those of T2- T6, may be due primarily to the relatively low levels of polysaccharide and cross-linker deposited on the surface of Tl, leading to incomplete surface coverage of the coating.
[0232] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modification other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within the spirit and scope. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.
BIBLIOGRAPHY
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Claims

CLAIMS:
1. A composite filtration membrane comprising:
a) a membrane; and
b) a layer which presents as a coating across a surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-like microorganism; or
ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
2. The composite filtration membrane of Claim 1 wherein the layer comprises an EPS or polysaccharide component thereof produced by a microbial cell selected from the list comprising Mesorhizobium huakuii; Mesorhizobium loti; Mesorhizobium abyssinicae; Mesorhizobium albiziae; Mesorhizobium alhagi; Mesorhizobium amorphae; Mesorhizobium australicum; Mesorhizobium camelthorni; Mesorhizobium caraganae; Mesorhizobium chacoense; Mesorhizobium cicero; Mesorhizobium gobiense; Mesorhizobium hawassense; Mesorhizobium mediterraneum; Mesorhizobium metallidurans; Mesorhizobium muleiense; Mesorhizobium opportunistum; Mesorhizobium plurifarium; Mesorhizobium qingshengii; Mesorhizobium robiniae; Mesorhizobium sangaii; Mesorhizobium septentrionale; Mesorhizobium shangrilense; Mesorhizobium shonese; Mesorhizobium silamurunense; Mesorhizobium tamadayense; Mesorhizobium tarimense; Mesorhizobium temperatum; Mesorhizobium thiogangeticum; and Mesorhizobium tianshanense.
3. The composite filtration membrane of Claim 2 wherein the layer comprises an EPS or polysaccharide component thereof produced by a microbial cell selected from Mesorhizobium huakuii or Mesorhizobium loti.
4. The composite filtration membrane of Claim 1 wherein the layer comprises an EPS or polysaccharide component thereof produced by a microbial cell designated CAM543 and deposited at the National Measurements Institute on 29 October, 2014 under accession number V14/017216.
5. The composite filtration membrane of Claim 1 wherein the layer comprises an isolated polysaccharide derived from the EPS.
6. The composite filtration membrane of Claim 1 wherein the layer can be formed on a surface of the membrane by any suitable means.
7. The composite filtration membrane of Claim 1 wherein the layer is attached to a surface of the membrane via a linker.
8. The composite filtration membrane of Claim 7 wherein the layer is attached to a surface of the membrane via an inorganic linker.
9. The composite filtration membrane of Claim 8 wherein the layer is attached to a surface of the membrane via a linker derived from any suitable metal alkoxide or alkoxysilane.
10. The composite filtration membrane of Claim 9 wherein the layer is attached to a surface of the membrane via a titanium alkoxide, a zirconium alkoxide, an aluminum alkoxide or an alkoxysilane.
11. The composite filtration membrane of Claim 10 wherein the layer is attached to a surface of the membrane via an alkoxide of the following formula: Si(OR)4, Ti(OR)4, Zr(OR)4 and Al(OR)4.
12. The composite filtration membrane of Claim 11 wherein the layer is attached to a surface of the membrane via titanium isopropoxide.
13. The composite filtration membrane of Claim 1 wherein the membrane is a semipermeable membrane.
14. The composite filtration membrane of Claim 1 wherein the layer confers biofouling resistance.
15. A method for preparing a composite filtration membrane comprising:
a) providing a membrane; and
b) coating a surface of the membrane with a layer, wherein the layer comprises: i. an EPS produced by a microbial cell of the genus Mesorhizobium or a
Mesorhizobium-li e microorganism; or
ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
16. The method of Claim 15 wherein the layer is formed on a surface of the membrane by any suitable means.
17. The method of Claim 16 wherein the layer is formed on a surface of the membrane using a linker.
18. The method of Claim 17 wherein the layer is formed on a surface of the membrane using an inorganic linker.
19. The method of Claim 18 wherein the layer is formed on a surface of the membrane using a linker derived from any suitable metal alkoxide or alkoxysilane.
20. The method of Claim 19 wherein the layer is formed on a surface of the membrane using a titanium alkoxide, a zirconium alkoxide, an aluminum alkoxide or an alkoxysilane.
21. The method of Claim 20 wherein the layer is formed on a surface of the membrane using an alkoxide of the following formula: Si(OR)4, Ti(OR)4, Zr(OR)4 and Al(OR)4.
22. The method of Claim 21 wherein the layer is formed on a surface of the membrane using titanium isopropoxide.
23. The method of Claim 15 wherein the layer is formed on a surface of the membrane by treating the composite semipermeable membrane with a composition comprising one or more metal alkoxides and the EPS or polysaccharide component thereof.
24. The method of Claim 15 wherein the membrane is a semipermeable membrane.
25. The method of Claim 15 wherein the resulting composite filtration membrane exhibits biofouling resistance.
26. A composite filtration membrane obtained by the method of any one of Claims 15 to 25.
27. A process for treating a liquid comprising subjecting the liquid to filtration with a composite filtration membrane comprising:
a) a membrane; and
b) a layer which presents as a coating across the surface of the membrane, wherein the layer comprises:
i. an extracellular polymeric substance (EPS) produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism; or ii. a polysaccharide component of the EPS produced by a microbial cell of the genus Mesorhizobium or a Mesorhizobium-li e microorganism.
28. The process of Claim 27 wherein the process creates a difference in pressure across the composite filtration membrane so as to separate solutes from a liquid, including, but not limited to, dissolved ions and molecules from the liquid; wherein the solute concentration in the permeate is lower compared with that of the liquid that was subjected to filtration.
29. The process of Claim 27 wherein the layer comprises an EPS or polysaccharide component thereof produced by a microbial cell selected from the list comprising Mesorhizobium huakuii; Mesorhizobium loti; Mesorhizobium abyssinicae; Mesorhizobium albiziae; Mesorhizobium alhagi; Mesorhizobium amorphae; Mesorhizobium australicum; Mesorhizobium camelthorni; Mesorhizobium caraganae; Mesorhizobium chacoense; Mesorhizobium cicero; Mesorhizobium gobiense; Mesorhizobium hawassense; Mesorhizobium mediterraneum; Mesorhizobium metallidurans; Mesorhizobium muleiense; Mesorhizobium opportunistum; Mesorhizobium plurifarium; Mesorhizobium qingshengii; Mesorhizobium robiniae; Mesorhizobium sangaii; Mesorhizobium septentrionale; Mesorhizobium shangrilense; Mesorhizobium shonese; Mesorhizobium silamurunense; Mesorhizobium tamadayense; Mesorhizobium tarimense; Mesorhizobium temperatum; Mesorhizobium thiogangeticum; and Mesorhizobium tianshanense.
30. The process of Claim 27 wherein the layer comprises an EPS or polysaccharide component thereof produced by a microbial cell selected from Mesorhizobium huakuii or Mesorhizobium loti.
31. The process of Claim 27 wherein the layer comprises an EPS or polysaccharide component thereof produced by a microbial cell designated CAM543 and deposited at the National Measurements Institute on 29 October, 2014 under accession number V14/017216.
32. The process of Claim 27 wherein the composite filtration membrane is a reverse osmosis filtration membrane for filtering salt water.
33. The process of Claim 27 wherein the composite filtration membrane is a forward osmosis filtration membrane for filtering salt water.
34. The process of Claim 27 wherein the composite filtration membrane is a nanofiltration, microfiltration or ultrafiltration membrane for pre-treating liquids before reverse osmosis filtration.
35. The process of Claims 27 wherein the composite filtration membrane is a nanofiltration, microfiltration or ultrafiltration membrane for purifying and concentrating proteins.
The process of Claim 35 wherein the composite filtration membrane is a nanofiltration, microfiltration or ultrafiltration membrane for purifying and concentrating biologically useful molecules such as peptides, proteins, antibodies and antibiotics.
37. The process of Claim 35 wherein the composite filtration membrane is a nanofiltration, microfiltration or ultrafiltration membrane for purifying and concentrating liquid foodstuffs.
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CN109012232A (en) * 2018-09-02 2018-12-18 郑州成济堂生物科技有限公司 A kind of preparation method of anti-shrink polytetrafluoroethylene (PTFE) composite nanometer filtering film
CN110592175A (en) * 2019-09-26 2019-12-20 清华大学 Method for screening pollution and blockage inhibiting bacteria of RO (reverse osmosis) system and method for controlling biological pollution and blockage
CN112646751A (en) * 2021-01-20 2021-04-13 广东省农业科学院动物科学研究所 Application of mesorhizobium Z1-4 in preparation of bacterial exopolysaccharide

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Publication number Priority date Publication date Assignee Title
CN109012232A (en) * 2018-09-02 2018-12-18 郑州成济堂生物科技有限公司 A kind of preparation method of anti-shrink polytetrafluoroethylene (PTFE) composite nanometer filtering film
CN110592175A (en) * 2019-09-26 2019-12-20 清华大学 Method for screening pollution and blockage inhibiting bacteria of RO (reverse osmosis) system and method for controlling biological pollution and blockage
CN110592175B (en) * 2019-09-26 2021-03-05 清华大学 Method for screening pollution and blockage inhibiting bacteria of RO (reverse osmosis) system and method for controlling biological pollution and blockage
CN112646751A (en) * 2021-01-20 2021-04-13 广东省农业科学院动物科学研究所 Application of mesorhizobium Z1-4 in preparation of bacterial exopolysaccharide

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