FIELD OF THE INVENTION

The present invention relates to a method for operating a water filtration module and the module itself. The water filtration module can be used for water treatment, more particularly water filtration and wastewater purification.

BACKGROUND

Filter systems for wastewater treatment may consist of a filtration unit with a boxshaped housing, open at the top and bottom, in which multiple membrane envelopes are arranged, vertically and parallel to one another and spaced apart from adjacent membrane envelopes. The spaces between the individual membrane envelopes form passages that are traversable by a fluid. Such modules are for instance known from WO 2003 037 489 and WO 2006 015 461. Alternative water filtration modules are also disclosed in WO 2012 098 130 and WO 2016 087 638.

During operation, the flow distribution across a single membrane envelope needs to be as uniform as possible, at all moments of operation (both in the active filtration permeate extraction mode and the backwashing mode). Ideally, all local flows are identical at any given coordinate of the membrane envelope. In this ideal situation, the fouling rate and build-up of the membrane envelopes will be uniform across the envelope. In addition, also the removal of the fouling during backwashing will be a uniform process. A uniform flow distribution will result in an overall better operation of a plant, with higher overall flux, less membrane area that needs to be installed and also less energy (for air scouring) that is consumed during the operation of the system.

In reality, however, such uniform flow distribution within the membrane envelope is often not achieved and hence as a consequence a less efficient and less optimal water treatment will occur. This results in higher operating and maintenance costs.

The present invention aims to resolve at least some of the problems and disadvantages mentioned above. The aim of the invention is to provide a method and system which eliminates those disadvantages. SUMMARY OF THE INVENTION

The present invention and embodiments thereof serve to provide a solution to one or more of the above-mentioned disadvantages. To this end, the present invention relates to a method for operating a water filtration module according to claim 1 and a water filtration module according to claim 8. During the operation of the module, an even and optimal flow distribution is obtained. This is due to both the specific operating settings as well as to the characteristics of the module and in particular the membrane envelopes. It was found that this combination of features allows for an optimal flow distribution across the membrane envelope during filtration. Ideally, the flow distribution differs maximally 10% between the highest and lowest local filtration flux observed across the membrane envelope during filtration. In addition, the optimal distribution is observed when the module is set to filter or purify the water and also during the cleaning process, by means of backwashing. This will eventually result in lower operating and maintenance costs.

DESCRIPTION OF FIGURES

Figure 1 shows a top view (Figure 1A) and a side view (Figure IB) of a module according to an embodiment of the current invention. Figure 1C shows a detail of a membrane envelope according to the current invention, comprised of a permeate channel interposed between two membrane layers

Figure 2 shows a representation of a non-ideal flow inside a membrane envelope during filtration (Figure 2A) and a schematic representation of an optimal flow inside a membrane envelope (Figure 2B).

Figure 3 shows a calculation of pressure loss during back-washing in a setting according to an embodiment of the current invention.

Figure 4 shows a graphical representation of the resistance to delamination and permeability of various membrane envelopes. DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns a method for operating a water filtration module. Said method can be used in water treatment, for instance, water filtration and/or purification of water, such as wastewater or chemically contaminated water. The combination of module features and specific process parameters were found to result in an optimal flow distribution across the membrane envelopes during filtration operation.

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, term definitions are included to better appreciate the teaching of the present invention.

As used herein, the following terms have the following meanings:

"A", "an", and "the" as used herein refers to both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a compartment" refers to one or more than one compartment.

"About" as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of +/- 20% or less, preferably +/-10% or less, more preferably +/-5% or less, even more preferably +/-1% or less, and still more preferably +/-0.1% or less of and from the specified value, in so far such variations are appropriate to perform in the disclosed invention. However, it is to be understood that the value to which the modifier "about" refers is itself also specifically disclosed.

"Comprise", "comprising", and "comprises" and "comprised of" as used herein are synonymous with "include", "including", "includes" or "contain", "containing", "contains" and are inclusive or open-ended terms that specify the presence of what follows e.g. component and do not exclude or preclude the presence of additional, non-recited components, features, element, members, steps, known in the art or disclosed therein. Furthermore, the terms first, second, third and the like in the description and the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order, unless specified. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range, as well as the recited endpoints.

The expression "% by weight", "weight percentage", "%wt" or "wt%", here and throughout the description, unless otherwise defined, refers to the relative weight of the respective component based on the overall weight of the formulation.

Whereas the terms "one or more" or "at least one", such as one or more or at least one member(s) of a group of members, is clear per se, by means of further exemplification, the term encompasses inter alia a reference to any one of said members, or any two or more of said members, such as e.g., any >3, >4, >5, >6 or >7 etc. of said members, and up to all said, members.

Unless otherwise defined, all terms used in disclosing the invention, including technical and scientific terms, have the meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. By means of further guidance, definitions for the terms used in the description are included to better appreciate the teaching of the present invention. The terms or definitions used herein are provided solely to aid in the understanding of the invention.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to a person skilled in the art from this disclosure, in one or more embodiments. Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

The term "filtration membrane envelope" or "membrane envelope" as interchangeably used herein is an IPC membrane comprising a 3D spacer fabric interposed between two membrane layers and forming a permeate channel, wherein said membrane layers are cast respectively on said upper and lower fabric surface of said 3D spacer fabric.

The term "permeability" of a membrane, filter, material, membrane envelope or the like, as used herein, is defined as the ability of said material to allow the molecules of pure water to pass through, caused by a driving force at a set temperature (25°C). The permeability of a membrane can be influenced by a variety of factors, including the pore size and distribution of the membrane and the thickness and structure of the membrane. The water permeability is the volume of water liquid per time unit and per m ² that is able to pass through said membrane, filter, material or the like at 1 bar driving force and 25°C (l/m ² h.bar).

As used herein, the term "filtration flux" is to be understood as the flow rate at which a liquid sample passes through a membrane or membrane envelope per unit area per unit time under the operational pressure and during liquid extraction ("filtration") in a submerged filtration setup under negative pressure. The flux of a fluid through a membrane is typically influenced by the permeability of the membrane, as well as by the pressure difference between the two sides of the membrane, the viscosity of the fluid, the capability of the membrane to retain impurities, contaminants or unwanted substances, the size and charge of the molecules being filtered and the temperature of water. Said liquid is preferably water such as wastewater or process water.

In general, a membrane with high permeability will have a high flux, meaning that it allows a large volume of water to pass through it at a fast rate. A membrane with low permeability, on the other hand, will have a low flux, meaning that it allows a volume of water to pass through it at a slower rate.

However, high flux does not necessarily imply high effectiveness in terms of retaining impurities and contaminants. Similarly, low flux does not necessarily imply low effectiveness. The effectiveness of a membrane in retaining impurities and contaminants depends on the size and charge of the molecules being filtered, the pore size and distribution of the membrane, the structure of the membrane, the temperature and pressure of the water, and the presence of other substances in the water that could potentially interfere with the filtration process.

As used herein, the term "backwash flux" is to be understood as the flow rate at which a liquid sample passes through a membrane or membrane envelope per unit area per unit time under the operational pressure and during backwash through the membrane envelope in a submerged filtration setup under positive pressure.

In a first aspect, the invention relates to a method for operating a water filtration module comprises a plurality of planar filtration membrane envelopes, that are vertical, parallel, and spaced to one another in a rigid holder, wherein each filter membrane envelope comprises a 3D spacer fabric interposed between two membrane layers. In particular, said membrane envelopes have a membrane permeability of between 500 and 1500 l/m ² .h.bar, more preferably of between 600 and 1200 l/m ² .h.bar. In an embodiment, the membrane envelopes have a permeability during operation of between 500 and 1400 l/m ² .h.bar, between 500 and 1300 l/m ² .h.bar, between 500 and 1200 l/m ² .h.bar, between 500 and 1100 l/m ² .h.bar, between 500 and 1000 l/m ² .h.bar, between 500 and 900 l/m ² .h.bar, between 500 and 800 l/m ² .h.bar, between 500 and 700 l/m ² .h.bar, between 500 and 600 l/m ² .h.bar, between 600 and 1500 l/m ² .h.bar, between 700 and 1500 l/m ² .h.bar, between 800 and 1500 l/m ² .h.bar, between 900 and 1500 l/m ² .h.bar, between 1000 and 1500 l/m ² .h.bar, between 1100 and 1500 l/m ² .h.bar, between 1200 and 1500 l/m ² .h.bar, between 1300 and 1500 l/m ² .h.bar or between 1400 and 1500 l/m ² .h.bar. Permeability can be measured as the volume of ultrapure water that passes through a membrane with a membrane surface of 80 cm ² at 25° C at a pressure of 0.3 bar for 5 min. This permeability range was shown to be optimal for the operation of the module. In addition, it was found that the average filtration flux of the wastewater at the membrane, such as at the membrane entrance, is to be set at between 20 and 100 l/m ² .h, more preferably between 20 and 80 l/m ² .h, more preferably between 20 and 70 l/m ² .h to ensure good uniform flow distribution across the complete membrane envelope. During operation, the system may be aerated. By preference, the aeration rate will be between 1 and 40 Nm ³ /h of air for every m ³ of filtered water, more preferably an aeration rate of between 4 and 30 Nm ³ /h of air for every m ³ of filtered water when a membrane module is operated at a flux rate of between 20 and 80 l/m ² .h.

The 3D spacer fabric present in the membrane envelopes forms a permeate channel. This permeate channel is the free space for liquid extraction in between the parallel two membrane sheets that from one membrane envelope or "pocket". In a preferred embodiment, said permeate channel has a channel height of between 1 and 4 mm, more preferably between 1.5 and 3 mm, more preferably between 1.8 and 2.8 mm. When the above conditions are present, the pressure drop within the permeate channel is negligible during filtration and/or backwash operation of the module.

In an embodiment, the spacer fabric has an upper and a lower fabric surface, tied together and spaced apart by monofilament threads at a predefined distance. The fabric surfaces and the monofilaments of the 3D spacer fabric are linked by loops in the monofilament threads. Said loops are embedded in said membrane layers. Preferably, the fabric surfaces are of a knitted, woven or non-woven type. In a preferred embodiment, the 3D-spacer fabric has a woven structure.

In an embodiment, the 3D spacer fabric preferably comprises a material selected from the group consisting of polyester, nylon, polyamide, polyphenylene sulfide, polyethylene and polypropylene.

The 3D spacer fabric is interposed between two membrane layers. Said membrane layers preferably comprise a hydrophilic filler material selected from the group consisting of HPC, CMC, PVP, PVPP, PVA, PVAc, PEO TiO2, HfO2, AI2O3, ZrO2, Zr3(PO4)4, Y2O3, SiO2, perovskite oxide materials, SiC; and an organic binder material selected from the group consisting of PVC, C-PVC, PSf, PESU, PPS, PU, PVDF, PI, PAN, and their grafted variants. In an embodiment, the membrane envelope further comprises a sealant at the perimeter of the planar membrane envelope arranged to prevent direct fluid movement from or to the permeate channel without passing through a membrane layer, and an inlet/outlet port connection(s) in fluid connection with the permeate channel, provided at least one edge on the perimeter.

The membrane envelope can be produced by providing a 3D spacer fabric comprising an upper and lower surface fabric spaced apart by monofilament thread at a predefined distance such that the fabric surfaces and the monofilaments of the 3D spacer fabric are limited by loops in the monofilament threads, and by subsequently applying a membrane layer to said upper and said lower surface fabric such that said loops are embedded in said membrane layers. The step of applying the membrane layers preferably comprises a coating step with dope and coagulation of said dope to form a membrane layer linked at a multitude of points with said upper and lower fabric surface. This process is known as "immersion precipitation" wherein a polymer plus solvent (polymer solution) is cast on a supporting layer and then submerged in a coagulation bath containing nonsolvent. Due to the solvent and nonsolvent exchange, precipitation takes place.

In an embodiment, the membrane envelope as disclosed herein is manufactured by means of a process that employs a specific casting step. It is believed that this specific manufacturing step contributes to the advantageous characteristics of the membrane envelope, such as flux and permeability and durability, as discussed above.

During said casting step a polymer solution is applied to the upper and lower side of said 3D spacer fabric, forming the upper and lower surfaces of the membrane envelope. More specifically, said polymer is applied by means of an injection process by means of a casting module comprising a casting head. Prior or during the casting process, the variation in thickness, roughness, and/or tapering of the fabric is measured and the distance between the 3D fabric and the casting head is adjusted based on said measurement.

3D textiles used for filtration membranes fabrication usually lack uniformity of the surface and are generally variable in thickness and roughness. The outcome of the weaving process is often a tapered textile. It was found that real-time measuring of the variability in the thickness of the 3D spacer fabric and adjustment of the casting head accordingly, results in membrane envelopes with uniform cast layers throughout their surface.

By preference, the thickness of the 3D spacer fabric is measured throughout its length before said fabric descends in the casting module. Said measurements are used to adjust the distance between the 3D spacer fabric and the casting head. By adjusting said distance, a uniform cast layer throughout the membrane envelope, which takes into consideration the variation in thickness, roughness and/or tapering of the fabric, is achieved. In an embodiment, said casting process is done on a fabric that is positioned vertically and which during the casting descents in a precipitation bath. The precipitation bath preferably contains water.

Said casting process can be a one-step process or a multiple-step process, wherein a polymer is cast onto the material, and precipitated, after which a second round of casting or coating occurs.

The membrane layer is subjected to densification during the coagulation process. Due to the casting process used, the porosity of the membrane layer will gradually increase in the direction of polymer penetration of the polymer in the 3D fabric. As a result, the membrane layer will comprise of two sections, being a filtration layer with relatively fine or small pore size, and an anchorage section with relatively large pore size. The filtration layer will preferably have pores with a size of between 10 nm and 1 micron, whereas the pore sizes in the anchorage section will have macrovoids.

In an embodiment, the membrane envelope as described herein is obtainable by means of a manufacturing process comprising a casting process as described herein.

In an embodiment, the dope may comprise: hydrophilic filler material selected from the group consisting of HPC, CMC, PVP, PVPP, PVA, PVAc, PEO, TiO2, HfO2, AI2O3, ZrO2, Zr3 (PO4)4, Y2O3, SiO2, perovskite oxide materials and SiC; an organic binder material selected from the group consisting of PVC, C-PVC, PSf, PESU, PPS, PU, PVDF, PI, PAN and their grafted variants; and a solvent selected from the group consisting of NMP, DMF, DMSO or DMAC or a mixture thereof. A solvent-free process may be considered as well. It will be clear to a skilled person that also other production methods may be known in the art and applied.

In an embodiment, the thickness of the resulting fabric with cast membrane layers is measured again after said fabric is removed from the bath.

In a preferred embodiment, the measuring of the thickness of said 3D fabric prior and/or post-casting occurs by means of laser, preferably confocal laser, one or more sensors, or mechanically. Laser confocal measurement of the thickness and/or roughness of a surface is a non-contact measuring method that does not damage the measured surface. This is very important, especially when measuring the membrane thickness and/or roughness after the cast is applied. The light emitted by a laser is reflected by the fabric, and most of the reflected light passes through the pinhole when the target point is on the focal plane. In the range of the confocal system's Depth of Field (DOF), the reflected light intensity detected by the photodiode forms a Depth Response Curve (DRC). The peak point of the DRC detected by the photodiode indicates the focus plane of the target point on the measured surface. With a high-resolution encoder of the confocal system, the height of the target point on the surface can be measured. Thus through the recording of the heights, the fabric's profile can be obtained and roughness is derived.

Alternatively, the thickness and/or roughness of the fabric is measured by mechanical means. While any mechanical means suited in the art and known to the skilled person are possible, such mechanical means may include using measuring rolls for detecting thickness or a stylus for detecting the thickness and roughness.

In an embodiment, said measurement occurs on distinct locations of said textile, or over the entire length of said textile. As the variability in thickness, roughness and/or tapering of the fabric is caused by the weaving of the fabric and occurs randomly, it can be interesting to sample various locations of the fabric and identify them. Surface roughness measurement methods are any means suited in the art and known to the skilled person and include linear roughness measurement (profile method type), which measures roughness on a single line of the sample surface, and areal roughness measurement (areal method type), which measures roughness over an acquired area of the surface. With linear roughness measurement (profile method type), the degree of roughness in the surface is measured along an arbitrary straight line. Long, continuous dimensions are measured, and a contact stylus is commonly used to perform the roughness measurement. With areal roughness measurements (areal method type), the degree of roughness in the surface is measured over an arbitrary rectangular range. Areal roughness measurement uses a larger sampling area of the surface, providing a more accurate depiction of the state of the surface. A laser scanner is commonly used to perform areal roughness measurements.

The inventors surprisingly observed that the membrane envelopes wherein the deviations of the spacer fabric are taken into account during the casting process have controlled and uniform thickness of the layers of said membrane envelopes. The speed of the casting process, the volume of polymer applied, the positioning of the casting head, the composition of the dope or the level in the water bath can influence the casted membrane properties. The controlled and uniform thickness of the layers, which is directly influenced by the method of casting, imprints specific properties to said membrane envelope like specific permeability and attainable filtration flux. These specific properties of the membrane envelope allow for an ideal operating mode of the water filtration module as disclosed herein.

Due to the nature of the 3D fabric, the permeate channel will comprise open spaces. In order to ensure an optimal flow distribution through the membrane envelopes, the amount of open spaces in said permeate channel is between 80 and 99%, more preferably between 85 and 99% more preferably between 90% and 99%.

The module according to the current invention can be used for various operations that include water filtration and/or purification. Due to the nature of the membrane envelopes, the module is particularly useful to be cleaned by means of backflushing, back pulsing or backwashing. In an embodiment, said filtration module can be backwashed at a pressure of at least 20 mbar, more preferably at least 30 mbar, more preferably at least 40 mbar, more preferably at least 50 mbar, more preferably at least 60 mbar, more preferably at least 70 mbar, more preferably at least 80 mbar, more preferably at least 90 mbar, more preferably at least 100 mbar, more preferably at least 200 mbar, more preferably at least 300 mbar, more preferably at least 400 mbar, at least 500 mbar, at least 1 bar up to 2 bar. This high-pressure back pulse is possible without losing the mechanical cleaning efficiency of the backwashing. During this operation, the membrane envelopes and more specifically the pores present are cleaned from any debris that was filtered out of the water. This may also include chemically enhanced backwash cleaning, wherein the pores are chemically cleaned by means of a volumetric flow of chemicals over the whole membrane envelope. As for any operation, this again requires an optimal and even flow.

The submerged module according to the current invention can be operated in at least two manners. The first mode is the permeate extraction mode, wherein contaminants are removed from the incoming fluid. The second operation mode is the backflushing mode, which allows the cleaning of the membrane envelope filtration surface and pores from debris. As mentioned already above and when set in permeate extraction mode, the water flow rate will preferably be between 20 and 100 l/m ² .h, more preferably between 20 and 80 l/m ² .h, more preferably between 20 and 70 l/m ² .h.

In an embodiment, and when the water filtration module is set in backflushing mode, the flow rate is between 40 and 320 l/m ² .h, preferably between 40 and 200 l/m ² .h.

During backflush mode, it is advised that the water flow rate is at least two times the flow rate during permeate extraction mode, preferably for a short amount of time such as between 1 second to 40 seconds, more preferably between 10 to 20 seconds. The backflushing can occur in pulses. In an embodiment, the duration of said backflushing is between 1 and 40 seconds, more preferably between 5 and 30 seconds, more preferably between 10 and 20 seconds. It was seen that when the parameters as described above were met, an even pressure distribution within the channel is obtained, with only losing 20 to 30% of the pressure at those points of the membrane envelope that are located at the far edges of said membrane envelope. Again, such even pressure results in a stable and effective cleaning of the system wherein the membrane envelopes are kept in place even when high pressure is exerted during backwashing. The membrane envelope and module integrity is not compromised and the lifespan of the system is significantly extended.

In a second aspect, the current invention also relates to a water filtration module comprising a plurality of planar filtration membrane envelopes that are vertical, parallel, and spaced to one another in a rigid holder, wherein each filter membrane envelope comprises a 3D spacer fabric interposed between two membrane layers, characterized in that the membrane envelopes have a membrane permeability of between 500 and 1500 l/m ² .h.bar, more preferably between 600 and 1200 l/m ² .h.bar. In an embodiment, the membrane envelopes have a permeability between 500 and 1400 l/m ² .h.bar, between 500 and 1300 l/m ² .h.bar, between 500 and 1200 l/m ² .h.bar, between 500 and 1100 l/m ² .h.bar, between 500 and 1000 l/m ² .h.bar, between 500 and 900 l/m ² .h.bar, between 500 and 800 l/m ² .h.bar, between 500 and 700 l/m ² .h.bar, between 500 and 600 l/m ² .h.bar, between 600 and 1500 l/m ² .h.bar, between 700 and 1500 l/m ² .h.bar, between 800 and 1500 l/m ² .h.bar, between 900 and 1500 l/m ² .h.bar, between 1000 and 1500 l/m ² .h.bar, between 1100 and 1500 l/m ² .h.bar, between 1200 and 1500 l/m ² .h.bar, between 1300 and 1500 l/m ² .h.bar or between 1400 and 1500 l/m ² .h.bar, preferably between 600 and 1200 l/m ² .h.bar. Advantageously, the 3D spacer fabric forms a permeate channel, and said permeate channel has a channel width of between 1 and 4 mm, more preferably between 1.5 and 3 mm, more preferably between 1.8 and 2.8 mm. Further features of the module have been described above and are deemed repeated herein in the context of the module.

In a preferred embodiment of the water filtration module as disclosed herein, the membrane envelopes are obtainable by means of a casting process wherein said method comprises a casting step, wherein during said casting step a polymer solution is applied to the outer surfaces of a 3D spacer fabric, wherein said polymer is applied by means of an injection process by means of a casting module comprising a casting head, wherein prior or during the casting process the variation in thickness, roughness and/or tapering of the 3D spacer fabric is measured by means of laser, preferably confocal laser, one or more sensors or mechanically and the distance between the 3D spacer fabric and the casting head is adjusted based on said measurement.

According to a further feature of the invention, the holder is comprised of a rectangular frame that encloses the filtration membrane envelopes or within the interior of which the filtration membrane envelopes are held parallel to one another between opposite sides of that frame. Especially a holder of a synthetic resin is selected, preferably in the form of a cast thermosetting synthetic resin body whereby during the casting process a connection is made to the filtration membrane envelopes. The duroplastic or thermosetting material used can especially be polyester with or without a filler or polyurethane.

The membrane envelopes of the filtration module have a width between 630 and 690 mm and a length between 1000 and 1060 mm on both sides and the surface of a membrane envelope is between 1.26 and 1.46 m ² . In a preferred embodiment, the membrane envelopes have a width on both sides between 630 and 690 mm, between 630 and 680 mm, between 630 and 670 mm, between 630 and 660 mm, between 630 and 650 mm, between 630 and 640 mm, between 640 and 690 mm, between 650 and 690 mm, between 660 and 690 mm, between 670 and 690 mm or between 680 and 690 mm, preferably about 660 mm. In a further and preferred embodiment, the membrane envelopes have a length between 1000 and 1060 mm, between 1000 and 1050 mm, between 1000 and 1040 mm, between 1000 and 1030 mm, between 1000 and 1020 mm, between 1000 and 1010 mm, between 1010 and 1060 mm, between 1020 and 1060 mm, between 1030 and 1060 mm, between 1040 and 1060mm or between 1050 and 1060, preferably about 1030 mm. In a further and preferred embodiment, the surface of a membrane envelope is between 1.26 and 1.46 m ² , preferably about 1.36 m ² .

In an embodiment, the membrane envelopes of the filtration module have a width between 630 and 690 mm and a length between 400 and 600 mm, and the surface of a membrane envelope is between 0.5 and 0.83 m ² . In a preferred embodiment, the membrane envelopes have a width on both sides between 630 and 690 mm, between 630 and 680 mm, between 630 and 670 mm, between 630 and 660 mm, between 630 and 650 mm, between 630 and 640 mm, between 640 and 690 mm, between 650 and 690 mm, between 660 and 690 mm, between 670 and 690 mm or between 680 and 690 mm, preferably about 660 mm. In a further and preferred embodiment the membrane envelopes have a length between 400 and 600 mm, between 400 and 590 mm, between 400 and 580 mm, between 400 and 570 mm, between 400 and 560 mm, between 400 and 550 mm, between 400 and 540 mm, between 400 and 530 mm, between 400 and 520 mm, between 400 and 510 mm, between 400 and 500 mm, between 400 and 490 mm, between 400 and 480 mm, between 400 and 470 mm, between 400 and 460 mm, between 400 and 450 mm, between 400 and 440 mm, between 400 and 430 mm, between 400 and 420 mm, between 400 and 410 mm, between 410 and 600 mm, between 420 and 600 mm, between 430 and 600 mm, between 440 and 600 mm, between 450 and 600 mm, between 460 and 600 mm, between 470 and 600 mm, between 480 and 600 mm, between 490 and 600 mm, between 500 and 600 mm, between 510 and 600 mm, between 520 and 600 mm, between 530 and 600 mm, between 540 and 600 mm, between 550 and 600 mm, between 560 and 600 mm, between 570 and 600 mm, between 580 and 600 mm, between 590 and 600 mm, between 500 and 560 mm, between 510 and 560 mm, between 520 and 560 mm, between 530 and 560 mm, between 540 and 560 mm, between 550 and 560 mm, preferably about 520 mm. In a further and preferred embodiment, the total membrane envelope surface in a filtration module is between 0.5 and 0.83 m ² or between 0.60 and 0.77 m ² , preferably about 0.69 m ² . In an embodiment, the module comprises between 50 and 120 filter membrane envelopes. In a further embodiment, the module comprises between 50 and 110 filter membrane envelopes, between 50 and 100 membrane envelopes, between 50 and 90 membrane envelopes, between 50 and 80 membrane envelopes, between 50 and 70 membrane envelopes, between 50 and 60 membrane envelopes, between 50 and 110 membrane envelopes, between 50 and 100 membrane envelopes, between 50 and 90 membrane envelopes, between 50 and 80 membrane envelopes or between 50 and 70 membrane envelopes, preferably between 66 and 107 membrane envelopes.

The filtration module according to any of the above embodiments, has an outer width between 686 and 746 mm and an outer length between 706 and 766. In a preferred embodiment, the outer width of the filtration module is between 686 and 746 mm, between 686 and 736 mm, between 686 and 726 mm, between 686 and 716 mm, between 696 and 746 mm, between 706 and 746 mm, or between 716 and 746 mm, more preferably about 716 mm. In a further preferred embodiment, the outer length of the filtration module is between 706 and 766 mm, between 706 and 756 mm, between 706 and 746 mm, between 706 and 736 mm, between 716 and 766 mm, between 726 and 766 mm or between 736 and 766 mm, preferably about 736 mm. In a further and preferred embodiment, the footprint of the module is between 0.48 and 0.57 m ² , preferably about 0.53 m ² .

In an embodiment, the packing density of the filtration module is between 120 and 290 nr ¹ membrane. In a preferred embodiment, said packing density is between 110 and 311 nr ¹ membrane, between 110 and 290 nr ¹ membrane, between 110 and 270 nr ¹ membrane, between 110 and 250 nr ¹ membrane, between 110 and 230 nr ¹ membrane, between 110 and 210 nr ¹ membrane, between 110 and 190 nr ¹ membrane, between 110 and 170 nr ¹ membrane, between 110 and 150 nr ¹ membrane, between 110 and 130 nr ¹ membrane, between 130 and 311 nr ¹ membrane, between 150 and 311 nr ¹ membrane, between 170 and 311 nr ¹ membrane, between 190 and 311 nr ¹ membrane, between 210 and 311 nr ¹ membrane, between 230 and 311 nr ¹ membrane, between 250 and 311 nr ¹ membrane, between 270 and 311 nr ¹ membrane, between 290 and 311 nr ¹ membrane, between 120 and 280 nr ¹ membrane, between 120 and 270 nr ¹ membrane, between 120 and 260 nr ¹ membrane, between 120 and 250 nr ¹ membrane, between 120 and 240 nr ¹ membrane, between 120 and 230 nr ¹ membrane, between 120 and 220 nr ¹ membrane, between 120 and 210 nr ¹ membrane, between 120 and 200 nr ¹ membrane, between 120 and 190 nr ¹ membrane, between 120 and 180 nr ¹ membrane, between 120 and 170 nr ¹ membrane, between 120 and 160 nr ¹ membrane, between 120 and 150 nr ¹ membrane, between 120 and 140 nr ¹ membrane, between 120 and 130 nr ¹ membrane, between 130 and 290 nr ¹ membrane, between 140 and 290 nr ¹ membrane, between 150 and 290 nr ¹ membrane, between 160 and 290 m membrane, between 170 and 290 nr ¹ membrane, between 180 and 290 m membrane, between 190 and 290 nr ¹ membrane, between 200 and 290 m membrane, between 210 and 290 nr ¹ membrane, between 220 and 290 m membrane, between 230 and 290 nr ¹ membrane, between 240 and 290 m membrane, between 250 and 290 nr ¹ membrane, between 260 and 290 m membrane, between 270 and 290 nr ¹ membrane or between 280 and 290 m membrane, preferably between 120 and 290 nr ¹ membrane. In an embodiment, multiple modules of the same size are stacked forming double, triple, quadruple, or quintuple deck systems. Furthermore, multiple modules with different sizes are stacked forming, one and a half, two and a half, three and a half or four and a half deck systems. The present invention will be now described in more detail, referring to examples that are not limitative.

DESCRIPTION OF FIGURES

Figure 1 shows a top view (Figure 1A) and a side view (Figure IB) of a module 1 according to an embodiment of the current invention. The module 1 comprises a rectangular rigid holder 2 equipped with several planar membrane envelopes 3 in the holder 2, and placed side by side and spaced apart. Caps 4 may be provided on the top and bottom part of the membrane envelopes 3 to ensure membrane rigidity and positioning. As an example, the module may comprise between 65 to 107 membrane envelopes. Each membrane envelope has a permeability of between 500 and 1500 l/m ² .h.bar. The module 1 is provided with manifolds 5, 6 regulating the water in- and outlet. The envelopes are comprised of a 3D spacer fabric forming a permeate channel. The 3D spacer fabric is lined by membrane layers 8 that cover the 3D spacer fabric at both sides. A schematic drawing of a section of a membrane envelope 3 is shown in Figure 1C. The permeate channel formed by the 3D spacer fabric 7 has between 80 and 99% of open space, that are formed by the nature of the 3D spacer fabric. Advantageously, the width or thickness of the spacer fabric part of the membrane envelopes is between 1.5 and 3 mm.

Figure 2 shows a representation of a non-ideal flow inside a membrane envelope during filtration (Figure 2A) and a schematic representation of an optimal flow inside a membrane envelope (Figure 2B). The optimal flow conditions inside the membrane envelopes are achieved or closely achieved by the process conditions and the membrane envelope features as described herein. Dotted lines show the direction of the fluid travelling through the membrane envelope, from the outside through the membrane layers and into the permeate channel. The dashed line shows fluid traveling through the permeate channel (permeate flow).

Figure 3 shows a calculation of pressure loss during back-washing. The membrane envelopes having a membrane permeability of 1000 l/m ² .h.bar were back-washed with a flow of 120 l/m ² .h. Figure 3A shows the pressure gradient in the membrane envelope on various simulation spots, whereas Figure 3B shows the pressure pulse on various simulated spots across the membrane envelope. From the latter, it can be understood that a very even pressure distribution is obtained. This allows high- pressure backwashing without losing the cleaning efficiency of the backwash. In addition, the pore-cleaning mechanism is very efficient over the whole membrane envelope. This is particularly important when chemically enhanced backwash (CEB) cleaning is employed, wherein the membrane pores are chemically cleaned with a volumetric flow of cleaning chemicals over the whole membrane envelope. The even pressure distribution also has a positive impact on the overall module, as the stable and effective mechanical and chemical cleaning allows the use of a significant backwash pressure (up to 1 to 2 bar) and allows using chemical cleaning without compromising the membrane envelope and module integrity and lifespan. The even pressure distribution is influenced by a combination of multiple factors, such as the water flow in the module, the geometry of the membrane envelopes, and the size of the permeate channel.

Figure 4 shows a graphical representation of the membrane envelope permeability and delamination of membrane envelopes obtained by casting with various adjustments of the distance of the casting head. 5 membrane envelope types were evaluated and the data indicate that the membrane envelopes that used an adjustment of the casting head according to the deviations of the 3D spacer fabric had an increase in permeability and resistance to delamination.

The present invention is in no way limited to the embodiments described in and/or shown in the figures. On the contrary, methods according to the present invention may be realized in many different ways without departing from the scope of the invention.

Figure numbers

1 : module

2: holder

3: membrane envelope

4: cap

5,6: manifold

7: spacer fabric

8: membrane layer Examples

Example 1 Method of determining the permeability of a membrane envelopes

The membrane envelopes were analyzed on a lightbox for identifying eventual damage or air bubbles. Membrane envelope samples were cut from the damage- and air-bubble-free portions, using a 47 mm mould. The cutting was performed with a sharp knife or scissors to keep the edges as intact as possible. For the membrane envelopes made of brittle material, the membrane layer was cut with a knife and the carrier was cut with a scissor to prevent cracks in the membrane envelope.

After cutting, the samples were split into two halves using a sharp Stanley knife.

Each half was placed in 10% ethanol overnight for moistening. The membrane envelope samples were kept wet all the time.

Before measuring permeability, the samples were placed for 5 minutes in reverse osmosis water to remove the ethanol.

Measuring of the permeability is done with a filtration device equipped with: a closing valve an air supply valve a vent valve

- a pressure control valve pressure gauges a water tank measuring cells

The water tank of the filtration device was filled with ultra-pure water (Thermo Fisher Smart2Pure 3UV). The wet membrane envelope samples were then placed in measuring cells and sealed. The desired pressure was set up using the pressure control valve and the air supply valve was opened while the vent valve was closed. Water passed through the membrane envelope samples and was collected into a collection jar placed on a balance. The water temperature in the collection jar and the duration were measured. The permeability was calculated based on the volume of water collected into the collection jar, the surface area of the tested membrane envelope, the duration of the measurement, and the pressure and temperature applied (l/m ² h.bar).

Example 2 Influence of casting process on membrane envelope permeability

Membrane envelopes were cast using the vertical casting method, where the casting head is adjustable in function to the deviations of the 3D spacer fabric.

Five membrane envelopes were constructed, all having the same 3D spacer fabric with a DI thickness. Each membrane envelope was cast with a different die opening as described in Table 1.

Table 1. Membranes envelopes cast with different casting head openings

The permeability and delamination of the membrane envelopes were measured. The results are depicted in Figure 4.

The delamination resistance and permeability of the membrane envelopes increased proportionally with decreasing the casting head openings, with membrane envelope 5, displaying the best performance. It was surprisingly found that adjusting the casting head only in function to the 3D spacer fabric thickness, increased the permeability of the membrane envelopes.

Example 3 Method of determining the water flux of a membrane envelope

Measuring of the water flux was performed with a filtration device eguipped with: a water feed tank containing wastewater an IPC membrane module eguipped with 59 membrane envelopes having a total membrane surface area of 76 m ² - a suction pump to supply suction pressure as a driving force to move the water through the membranes

- a vent valve to de-aerate the system mounted on the permeate extraction pipe.

- a recirculation pipe that brings the extracted permeate or filtrate back into the water feed tank.

- a sampling valve on the pressure side of the pump, on the recirculation pipe.

- a pressure control valve pressure gauges

- a flow meter, mounted on the permeate extraction pipe that connects the membrane module with the extraction pump.

The water feed tank was filled with wastewater and an IPC membrane module was submerged into the tank. The IPC membrane module was connected to the suction pump with the permeate extraction pipe. On this pipe, a vent valve was mounted at the highest point. Once the membrane was filled with water, the suction pump was operated at low speed. The filtrate water passed through the permeate extraction pipe, through the pump and the flow meter and by the recirculation pipe back into the feedwater tank.

While in operation, the system was de-aerated by opening the de-aeration valve. This valve was closed after 10 minutes and the pressure control valve was set at - 100 mbar as a suction pressure to be delivered by the pump.

The system was run in a closed circuit for 5 minutes after which the flux was recorded in two potential ways: read out the water flow on the permeate extraction pipe or open the sampling point and collect the water for 20 seconds. The weight and corresponding permeate water was determined either by weight or by volume.

The water flux (or permeate water flux) was calculated by measuring the water volume in litres x 3600sec/h I 20 sec= x 180 times. The volume in L/h was divided by the total membrane area of the IPC membrane module (76m ² ). This calculation gives the water flux in L/m ² h