The invention relates to a process for cleaning a polymer membrane comprising the steps of (A) filtering an aqueous liquid through the polymer membrane to yield a filtrate; (B) reducing the concentration of metal ions in the filtrate by nanofiltration or ion exchange to yield a purified filtrate; (C) backwashing the polymer membrane with a chemical washing solution made from the purified filtrate; and (D) continuing the filtering of the aqueous liquid through the polymer membrane. Combinations of preferred embodiments with other preferred embodiments are within the scope of the present invention.

Membrane fouling is a very complex process, which is not yet fully understood. Most of the deposits consist of material not belonging to one single chemical“class” but, depending on the feed water conditions such as temperature, time of the year or intensity of rainfall, showing strong variations of its composition. For example, such fouling deposit may contain major components of:

• Mechanical particles such as sand, clay, Si-compounds etc.

• Scaling products from Ca-, Mg-, Ba- sulfate or carbonate

• Iron precipitations

• Bacteria and bacteria films

• Algae and its biofilms

• Polysaccharides, humic acids and other organics

• Metabolism products from bacteria, algae and other microorganisms

In filtration processes, especially on industrial scale, the prevention of irreversible fouling and the maintenance of flux properties is most important. For the regular cleaning of filter units, such membranes thus are often contacted with for example oxidizing solutions; such steps are also recalled as chemical backwash, disinfection or bleaching. However, the known cleaning processes for membranes often do not lead to complete restoration of the permeability.

Object of the present invention was to identify a process for cleaning a polymer membrane which can restore a high permeability of the membrane, which avoids the development of new cleaning agents and works with the established cleaning agents, which is environmentally friendly or cost efficient, or which works on the available filtration systems.

The object was solved by a process for cleaning a polymer membrane comprising the steps of

(A) filtering an aqueous liquid through the polymer membrane to yield a filtrate;

(B) reducing the concentration of metal ions in the filtrate by nanofiltration or ion exchange to yield a purified filtrate; (C) backwashing the polymer membrane with a chemical washing solution made from the purified filtrate; and

(D) continuing the filtering of the aqueous liquid through the polymer membrane.

Typical filtration processes are operated at a constant flux rate. When fouling of the polymer membrane occurs the membrane resistance may increase and result in an increased transmembrane pressure (TMP). Usually, the fouling of the polymer membrane results in a reduced permeability. The permeability may be calculated by flux rate (given e.g. in the unit liter / (m ² x h)) divided by transmembrane pressure (given e.g. in the unit bar).

The cleaning of a polymer membrane typically means that foulants are removed from the polymer membrane. The cleaning of a polymer membrane should inrease its permability.

The process for cleaning according to the invention is often initiated when the permeability of the polymer membrane is below 50%, preferably below 35%, and in particular below 20% of the initial permeability of the clean membrane. In another form the process for cleaning may be initiated after a preset duration of time (e.g. in the range from 4 times per day to once per months), which usually depends on the membrane type and process conditions.

The steps (A) to (D) are usually made in the alphabetic order.

Step (A)

In step (A) an aqueous liquid is filtered through the polymer membrane. The filtration may yield the filtrated, and it may be made by conventional filtration processes and parameters, which are known to experts. Typically, the aqueous liquid is forced through the membrane from the feed side to the filtrate side.

The liquid may contain at least 80 wt%, preferably at least 90 wt%, and in particular at least 95 wt% water.

Usually, the liquid is industrial waste water, sea water, salt water, surface water, ground water, process water, drinking water, liquid food (e.g. a beverage, such as beer, wine, juices, dairy products, or soft drinks). In one form the liquid is sea water. In another form the liquid is ground water or surface water. In another form the liquid is industrial waste water or process water. In another form the liquid is a beverage, such as beer.

The liquid may comprise up to 1000 ppm, preferably up to 100 ppm and in particular up to 20 ppm of metal ions, such as of the multivalent cations of iron and manganese. In another form the filtrate may comprise 0.01 to 100 ppm, preferably up to 0.1 ppm to 10 ppm of metal ions, such as of the multivalent cations of iron and/or manganese. In one form the liquid is salt water which may comprise at least one salt selected from the group consisting of an alkaline metal salt, an alkaline earth metal salt and mixtures thereof. For example, the salt water is process water, ground water, river water, brackish water, or sea water, wherein sea water is preferred. Suitable process water is cooling water in industrial plants or in power plants. The salt water usually comprises the salt in a range from 0.001 to 10 % by weight, preferably from 0.005 to 7.5% by weight, particularly preferably from 0.01 to 5% by weight, and in particular from 0.02 to 4% by weight. The salt water may comprise up to 2000 ppm, preferably up to 1000 ppm and in particular up to 400 ppm of calcium. The salt water may comprise up to 3000 ppm, preferably up to 2000 ppm and in particular up to 1200 ppm of magnesium.

Suitable alkaline metal salts are for example sodium sulfate (Na ₂ S0 ₄ ), sodium chloride (NaCI), sodium bromide (NaBr), sodium iodide (Nal), sodium carbonate (Na2COs), potassium chloride (KCI), potassium bromide (KBr) and potassium iodide (Kl). Suitable alkaline earth metal salts are for example calcium fluoride (CaF2), calcium sulfate (CaS0 ₄ ), calcium carbonate (CaCC^), magnesium fluoride (MgF ₂ ), magnesium chloride (MgCh), magnesium bromide (MgBr2), magnesium iodide (Mgl ₂ ), magnesium sulfate (MgS0 ₄ ), magnesium carbonate (MgCOs) and magnesium hydroxide (Mg(OH) ₂ ). The person skilled in the art knows that alkaline metal salts and alkaline earth metal salts generally dissociate in water. For example sodium chloride (NaCI) dissociates in water to give a sodium cation (Na ⁺ ) and a chloride anion (Cl·), sodium

carbonate (Na2CC>3) dissociates in an aqueous medium to form two sodium cations (Na ⁺ ) and a carbonate anion (CO3 ² -) and calcium carbonate (CaCOs) dissociates to give a calcium cation (Ca ²⁺ ) and a carbonate anion (CO3 ² ). A carbonate anion can also form

bicarbonate (HCO3 ) in water. Therefore, alkaline metal salts and alkaline earth metal salts in water are usually present in their ionic form.

Step (B)

Step (B) is reducing the concentration of metal ions in the filtrate by nanofiltration or ion exchange to yield a purified filtrate.

The metal ions preferably multivalent metal cations, such as multivalent cations of iron, manganese, copper, cobalt, titanium, chromium, vanadium, nickel, molybdenum, palladium, platinum, zinc, cadmium, mercury. Specific examples are Fe ²⁺ , Mn ²⁺ , Cu ²⁺ , or Co ²⁺ . Preferably, the metal ions are multivalent cations of iron and manganese.

The concentration of the metal ions in the backwash may be reduced by at least 50 mol%, preferably at least 75 mol%, and in particular at least 95%. In another form the concentration of the metal ions in the backwash may be reduced by at least 50, 60, 70, 80, 90, 97, 98, 99, 99.5, or 99.9 mol%.

The filtrate may comprise up to 1000 ppm, preferably up to 100 ppm and in particular up to 20 ppm of metal ions, such as of the multivalent cations of iron and manganese. In another form the filtrate may comprise 0.01 to 100 ppm, preferably up to 0.1 ppm to 10 ppm of metal ions, such as of the multivalent cations of iron and manganese.

The purified filtrate may comprise less than 100 ppm, preferably less 10 ppm, and in particular less than 1 ppm of the sum of all metal ions, preferably multivalent metal cations, such as multivalent cations of iron and manganese. In another form the purified filtrate may comprise less than 0.5 ppm, preferably less 0.2 ppm, and in particular less than 0.1 ppm of the sum of all metal ions, preferably multivalent metal cations, such as multivalent cations of iron and manganese.

The purified filtrate usually comprises at least 99 wt%, preferably at least 99.5 wt%, and in particular at least 99.9 wt% of water.

The nanofiltration (NF) is usually achieved with a nanofiltration membrane, which may have a molecular weight cutoff (MWCO) below 2000 g/mol, preferably below 1000 g/mol, and in particular below 500 g/mol. In another form the nanofiltration (NF) is usually achieved with a nanofiltration membrane, which may have a molecular weight cutoff (MWCO) below 5000,

2000, 800, 600, 400, 300, 200, 100, 50, or 20 g/mol. In nanofiltration membrane may have a pore size between 1 and 10 nm, such as up to 8, 6, 4, or 3 nm.

The nanofiltration membranes may be made of any suitable polymers. NF membranes may comprise as the main component at least one polyamide (PA), polyvinylalcohol (PVA), Cellulose Acetate (CA), Cellulose Triacetate (CTA), CA-triacetate blend, Cellulose ester, Cellulose Nitrate, regenerated Cellulose, aromatic , aromatic/aliphatic or aliphatic polyamide, aromatic, aromatic/aliphatic or aliphatic polyimide, polybenzimidazole (PBI), polybenzimidazolone (PBIL), Polyacrylonitrile (PAN), PAN-poly(vinyl chloride) copolymer (PAN-PVC), PAN-methallyl sulfo- nate copolymer, polyetherimide (PEI), Polyetheretherketone (PEEK), sulfonated polyether- etherketone (SPEEK), Poly(dimethylphenylene oxide) (PPO), Polycarbonate, Polyester, Polytetrafluroethylene (PTFE), Poly(vinylidene fluoride) (PVDF), Polypropylene (PP),

Polyelectrolyte complexes, Poly(methyl methacrylate) PMMA, Polydimethylsiloxane (PDMS), aromatic, aromatic/aliphatic or aliphatic polyimide urethanes, aromatic, aromatic/aliphatic or aliphatic polyamidimides, crosslinked polyimides or polyarylene ether, polysulfone, polyphenyl- enesulfone or polyethersulfone, or mixtures thereof. In another embodiment of the invention, NF membranes comprise as the main component at least one polysulfone, polyphenylenesulfone and/or polyethersulfone. In a particularly preferred embodiment, the main components of a NF membrane are positively or negatively charged. In another embodiment, NF membranes comprise as the main component polyamides, poly-imides or polyimide urethanes, Polyether- etherketone (PEEK) or sulfonated polyetheretherketone (SPEEK).

Preferably the nanofiltration membranes are made of polyamide, e.g. polyamide composite membranes, which may be based on polystyrene. Nanofiltration apparatuses are know and commercially available. Nanofiltration membranes are normally used in crossflow filtration processes.

The ion exchange is usually achieved with a ion exchange resin made of polymer matrix which contains functional groups. The matrix often consists of polystyrene or of acrylic polymers, both cross-linked e.g. by means of divinylbenzene (DVB). The functional groups may be acidic (e.g. -SO ₃ H, -COOH) or basic (e.g. -N(CH ₃ ) ₃ 0H), where acidic functional groups are preferred.

The ion exchange is preferably achieved with a cationic exchange resin, which usually has strong (e.g. sulfonic groups) or weak acidic (e.g. carboxylic acid groups) functional groups.

The ion exchange may be made with any known apparatuses, e.g. ion exchange columns.

Step (C)

Step (C) is the backwashing the polymer membrane with a chemical washing solution made from the purified filtrate.

The term backwash or backwashing are also termed BW in the following.

Polymer membranes are often backwashed with water (a“normal" backwash). The water for a normal BW may be permeate, fresh water, feed water or any other clean water source. In a typical backwash operation, a first rinsing (e.g. by opening the retentate path during the active feed flow) step is performed for a short period of time (e.g. 10 to 60 seconds);

the flow rate of permeate during the back wash is much higher as the filtration rate. For dead end filtration it should be higher than the feedflow in filtration, typically more than 80 l/m ^2* h (higher flow rate is advantageous, but the mechanical membrane stability and the system costs have to be considered);

the amount of back wash per m ² is preferably at least 1 I/m ² per BW. The optimum typically depends on the feed water/wastewater quality, and is a compromise between the optimal membrane regeneration and the highest possible permeate yield.

T o complete the back wash, higher pressure in permeate than in the feed should to be established in order to induce a high flow rate in reverse direction. Typically during BW, the feed inlet is closed and the retentate outlet is opened; a permeate buffer tank is advantageous.

In step (C) is the backwashing the polymer membrane is made with a chemical washing solution (also called a chemical enhanced backwash CEB). Usually, the chemical washing solution comprises a cleaning chemical selected from an acid, a base, and/or an oxidant.

Preferably, the chemical washing solution comprising an cleaning chemical selected from alkaline hydroxide, alkaline earth hydroxide, mineral acid, H2O2, ozone, peracid, CIO2, KMn0 ₄ , chlorate perchlorate or hypochlorite. In particular, the cleaning chemical is hypochlorite.

The concentration of the cleaning chemical into chemical washing solution is known to an expert, and can be adapted to the polymer membranes or cleaning purpose. For example the chemical washing solution may comprise up to 40 wt%, preferably up to 20 wt%, and in particular up to 10 wt% of the cleaning chemical.

Often used chemical washing solutiona are:

• Sulfuric acid, typically in a concentration of 0.015 N or higher, so that the pH of the

cleaning liquid ranges between 0.5 and 2.5.

• Other inorganic acid solutions, typically of similar pH range.

• Base solution, mostly NaOH as the cheapest base, typically in a concentration of 0.03 N or higher, so that the pH of cleaning solution ranges between 10.5 and 12.5.

• Oxidizing agents such as NaOCI, typically in a concentration between 3 and 50 ppm in alkaline solution. Other oxidizing chemicals such as H2O2 can also be used.

The chemical washing solution is made from the purified filtrate. Typically, the chemical washing solution is made by mixing the purified filtrate and cleaning chemical. The chemical washing solution may contain at least 50 wt%, preferably at least 80 wt%, and in particular at least 90 wt% of the purified filtrate.

In order to contact the membranes with the chemical washing solution, a separate chemical back wash system is usually applied, especially to avoid permeate contamination and/or to allow separate cleaning of different membrane sections. It may contain:

• Dosing equipment of concentrated chemicals to the back wash permeate, such as dosing pumps, flow meters, pressure transmitters

• Mixing device like for instance Venturi injector, pump injector or static mixer

• pH sensor in feed for pH control of cleaning solution

• pH sensor in outlet to ensure the complete removal of chemicals from the system

• Separate piping system for removal of one chemical before the second one is applied.

In case of CEB, flow through the membrane is not as essential as in case of BW. The main point is that the CEB solution completely fills the modules to ensure optimal conditions for CEB in the whole membrane area.

In a typical CEB cleaning step, once one of the cleaning chemicals is filled into the module, the dosing is stopped and the static washing is started. The optimal washing time depends on the origin and composition of the deposits and the chemicals used, and often varies from about 5 to 60 minutes. For example, a CEB sequence for optimal membrane regeneration may be as follows: a) Rinsing of the modules using feed by opened retentate path (10-30 seconds);

b) NaOH washing with a chemical washing solution comprising NaOH, typically by filling NaOH solution into the module and steeping it for about 30-60 minutes;

c) ejection of NaOH solution, controlled, for instance, by a pH sensor;

d) NaOCI washing (or washing with any other oxidizing agent) with a chemical washing

solution comprising NaOCL, e.g. by filling NaOCI solution into the module and steeping it for about 30-60 minutes (as an alternative, this step d may be combined with aforesaid step b);

e) ejection of the NaOCI solution (or the solution of the oxidizing agent), controlled, for

instance, by a pH or redox sensor (alternatively to be combined with step c);

f) washing with a chemical washing solution comprising an acid, typically sulphuric acid, e.g. by filling H2SO4 solution into the module and steeping it for about 30-60 minutes;

g) ejection of acid solution, controlled, for instance, by a pH sensor;

h) restart of the filtration process.

CEB is advantageously started, when the TMP increases above a certain value, or after a predefined operation time, for instance every 8 hrs.

In step (D) the filtering of the aqueous liquid through the polymer membrane is continued. The aqueous liquid may be the same as used in step (A) or it may be a different aqueous liquid. The filtering may be continued immediately after the end of step (C), or the polymer membrane may be stored for any desired time until filtration of the step (D) is continued.

The polymer membrane may be understood to be a thin, semipermeable structure capable of separating two fluids or separating molecular and/or ionic components or particles from a liquid. The membrane acts usually as a selective barrier, allowing some particles, substances or chemicals to pass through, while retaining others.

For example, the polymer membranes can be ultrafiltration (UF) membranes or microfiltration (MF) membranes. These membrane types are generally known in the art and are further described below.

UF membranes are normally suitable for removing suspended solid particles and solutes of high molecular weight, for example above 10000 Da. In particular, UF membranes are normally suitable for removing bacteria and viruses. UF membranes normally have an average pore diameter of 2 nm to 50 nm, preferably 5 to 40 nm, more preferably 5 to 20 nm. In one embodiment, UF membranes comprise as the main component at least one polyamide (PA), polyvinylalcohol (PVA), Cellulose Acetate (CA), Cellulose Triacetate (CTA), CA-triacetate blend, Cellulose ester, Cellulose Nitrate, regenerated Cellulose, aromatic , aromatic/aliphatic or aliphatic Polyamide, aromatic, aromatic/aliphatic or aliphatic Polyimide, Polybenzimidazole (PBI), Polybenzimidazolone (PBIL), Polyacrylonitrile (PAN), PAN-poly(vinyl chloride) copolymer (PAN-PVC), PAN-methallyl sulfonate copolymer, polyetherimide (PEI), Polyetheretherketone (PEEK), sulfonated polyetheretherketone (SPEEK), Poly(dimethylphenylene oxide) (PPO), Polycarbonate, Polyester, Polytetrafluroethylene PTFE, Poly(vinylidene fluoride) (PVDF), Polypropylene (PP), Polyelectrolyte complexes, Poly(methyl methacrylate) PMMA,

Polydimethylsiloxane (PDMS), aromatic, aromatic/aliphatic or aliphatic polyimide urethanes, aromatic, aromatic/aliphatic or aliphatic polyamidimides, crosslinked polyimides or polyarylene ether, polysulfone, polyphenylenesulfone, or polyethersulfone, or mixtures thereof. In another embodiment of the invention, UF membranes comprise as the main component at least one polysulfone, polyphenylenesulfone and/or polyethersulfone.“Polysulfones”,“polyethersulfones” and“polyphenylenesulfones” shall include the respective polymers that comprise sulfonic acid and/or salts of sulfonic acid at some of the aromatic moieties. In one embodiment, UF mem- branes comprise as the main component or as an additive at least one partly sulfonated polysulfone, partly sulfonated polyphenylenesulfone and/or partly sulfonated polyethersulfone.

In one embodiment, UF membranes comprise as the main component or as an additive at least one partly sulfonated polyphenylenesulfone.“Arylene ethers”,“Polysulfones”,“polyether- sulfones” and“polyphenylenesulfones” shall include block polymers that comprise blocks of the respective arylene ethers, Polysulfones, polyethersulfones or polyphenylenesulfones as well as other polymer blocks. In one embodiment, UF membranes comprise further additives like polyvinyl pyrrolidones.

In one embodiment of the invention, UF membranes are present as spiral wound membranes, as pillows or flat sheet membranes. In another embodiment of the invention, UF membranes are present as tubular membranes. In another embodiment of the invention, UF membranes are present as hollow fiber membranes or capillaries. In yet another embodiment of the invention,

UF membranes are present as single bore hollow fiber membranes. In yet another embodiment of the invention, UF membranes are present as multibore hollow fiber membranes.

Multiple channel membranes, also referred to as multibore membranes, comprise more than one longitudinal channels also referred to simply as“channels”. In a preferred embodiment, the number of channels is typically 2 to 19. In one embodiment, multiple channel membranes comprise two or three channels. In another embodiment, multiple channel membranes comprise 5 to 9 channels. In one preferred embodiment, multiple channel membranes comprise seven channels. In another embodiment the number of channels is 20 to 100. The shape of such channels, also referred to as“bores”, may vary. In one embodiment, such channels have an essentially circular diameter. In another embodiment, such channels have an essentially ellipsoid diameter. In yet another embodiment, channels have an essentially rectangular diameter. In some cases, the actual form of such channels may deviate from the idealized circular, ellipsoid or rectangular form. Normally, such channels have a diameter (for essentially circular diameters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) of 0.05 mm to 3 mm, preferably 0.5 to 2 mm, more preferably 0.9 to 1.5 mm. In another preferred embodiment, such channels have a diameter (for essentially circular diameters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) in the range from 0.2 to 0.9 mm. For channels with an essentially rectangular shape, these channels can be arranged in a row. For channels with an essentially circular shape, these channels are in a preferred embodiment arranged such that a central channel is surrounded by the other channels. In one preferred embodiment, a

membrane comprises one central channel and for example four, six or 18 further channels arranged cyclically around the central channel. The wall thickness in such multiple channel membranes is normally from 0.02 to 1 mm at the thinnest position, preferably 30 to 500 pm, more preferably 100 to 300 pm. Normally, the membranes and carrier membranes have an essentially circular, ellipsoid or rectangular diameter. Preferably, membranes are essentially circular. In one preferred embodiment, membranes according to the invention have a diameter (for essentially circular diameters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) of 2 to 10 mm, preferably 3 to 8 mm, more preferably 4 to 6 mm. In another preferred embodiment, membranes have a diameter (for essentially circular diameters), smaller diameter (for essentially ellipsoid diameters) or smaller feed size (for essentially rectangular diameters) of 2 to 4 mm. In one embodiment the rejection layer is located on the inside of each channel of said multiple channel membrane. In one embodiment, the channels of a multibore membrane may incorporate an active layer with a pore size different to that of the carrier membrane or a coated layer forming the active layer. Suitable materials for the coated layer are polyoxazoline, polyethylene glycol, polystyrene, hydrogels, polyamide, zwitterionic block copolymers, such as sulfobetaine or carboxybetaine. The active layer can have a thickness in the range from 10 to 500 nm, preferably from 50 to 300 nm, more preferably from 70 to 200 nm. In one embodiment multibore membranes are designed with pore sizes between 0.2 and 0.01 pm. In such embodiments the inner diameter of the capillaries can lie between 0.1 and 8 mm, preferably between 0.5 and 4 mm and particularly preferably between 0.9 and 1.5 mm. The outer diameter of the multibore membrane can for example lie between 1 and 26 mm, preferred 2.3 and 14 mm and particularly preferred between 3.6 and 6 mm. Furthermore, the multibore membrane can contain 2 to 94, preferably 3 to 19 and particularly preferred between 3 and 14 channels. Often multibore membranes contain seven channels. The permeability range can for example lie between 100 and 10000 L/m ² hbar, preferably between 300 and 2000 L/m ² hbar.

MF membranes are normally suitable for removing particles with a particle size of 0.1 pm and above. MF membranes normally have an average pore diameter of 0.05 pm to 10 pm, preferably 1.0 pm to 5 pm. Microfiltration can use a pressurized system but it does not need to include pressure. MF membranes can be capillaries, hollow fibers, flat sheet, tubular, spiral wound, pillows, hollow fine fiber or track etched. They are porous and allow water, monovalent species (Na+, CI-), dissolved organic matter, small colloids and viruses through but retain particles, sediment, algae or large bacteria. M Microfiltration systems are designed to remove suspended solids down to 0.1 micrometers in size, in a feed solution with up to 2-3% in concentration. In one embodiment, MF membranes comprise as the main component at least polyamide (PA), polyvinylalcohol (PVA), Cellulose Acetate (CA), Cellulose Triacetate (CTA), CA-triacetate blend, Cellulose ester, Cellulose Nitrate, regenerated Cellulose, aromatic, aromatic/aliphatic or aliphatic Polyamide, aromatic, aromatic/aliphatic or aliphatic Polyimide, Polybenzimidazole (PBI), Polybenzimidazolone (PBIL), Polyacrylonitrile (PAN), PAN-poly(vinyl chloride) copolymer (PAN-PVC), PAN-methallyl sulfonate copolymer, polyetherimide (PEI), Polyetheretherketone (PEEK), sulfonated polyetheretherketone (SPEEK), Poly(dimethyl- phenylene oxide) (PPO), Polycarbonate, Polyester, Polytetrafluroethylene PTFE, Poly(vinyl- idene fluoride) (PVDF), Polypropylene (PP), Polyelectrolyte complexes, Poly(methyl meth- acrylate) PMMA, Polydimethylsiloxane (PDMS), aromatic, aromatic/aliphatic or aliphatic polyimide urethanes, aromatic, aromatic/aliphatic or aliphatic polyamidimides, crosslinked polyimides or polyarylene ether, polysulfone, polyphenylenesulfone or polyethersulfone, or mixtures thereof. In another embodiment of the invention, MF membranes comprise as the main component or as an additive at least one polysulfone, polyphenylenesulfone and/or polyether- sulfone. In one embodiment, MF membranes comprise as the main component or as an additive at least one partly sulfonated polysulfone, partly sulfonated polyphenylenesulfone and/or partly sulfonated polyethersulfone. In one embodiment, UF membranes comprise as the main component or as an additive at least one partly sulfonated polyphenylenesulfone.

The polymer membranes may be based on at least one polymer selected from polyamide (PA), polyvinylalcohol (PVA), Cellulose Acetate (CA), Cellulose Triacetate (CTA), CA-triacetate blend, Cellulose ester, Cellulose Nitrate, regenerated Cellulose, aromatic, aromatic/aliphatic or aliphatic Polyamide, aromatic, aromatic/aliphatic or aliphatic Polyimide, Polybenzimidazole (PBI), Polybenzimidazolone (PBIL), Polyacrylonitrile (PAN), PAN-poly(vinyl chloride) copolymer (PAN-PVC), PAN-methallyl sulfonate copolymer, polyetherimide (PEI), Polyetheretherketone (PEEK), sulfonated polyetheretherketone (SPEEK), Poly(dimethylphenylene oxide) (PPO), Polycarbonate, Polyester, Polytetrafluroethylene (PTFE), Poly(vinylidene fluoride) (PVDF), Polypropylene (PP), Polyelectrolyte complexes, Poly(methyl methacrylate) PMMA, Polydi methylsiloxane (PDMS), aromatic, aromatic/aliphatic or aliphatic polyimide urethanes, aromatic, aromatic/aliphatic or aliphatic polyamidimides, crosslinked polyimides or polyarylene ether, polysulfone (PSU), polyphenylenesulfone (PPSU) or polyethersulfone (PESU), or mixtures thereof. Preferably, polymer is selected from poly(vinylidene fluoride) (PVDF), polyarylene ether, polysulfone (PSU), polyphenylenesulfone (PPSU) or polyethersulfone (PESU). In one especially preferred embodiment, polymer is polyethersulfone.

In another preferred for the polymer membrane is based on polyvinyl pyrolidone, polyvinyl acetates, polyurethanes, cellulose acetates, polyacrylonitriles, polyamides, polyolefines, polyesters, polysulfones, polyethersulfones, polycarbonates, polyether ketones, sulfonated polyether ketones, polyamide sulfones, polyvinylidene fluorides, polyvinylchlorides, polystyrenes and polytetrafluorethylenes, copolymers thereof, and mixtures thereof, which polymer or mixture thereof preferably makes up 80 percent or more of the membrane weight. In an especially preferred form the polymer membrane is based on polysulfones, polyethersulfones, copolymers thereof, and mixtures thereof, which polymer or mixture thereof preferably makes up 80 percent or more of the membrane weight.