WO2017013200A1

WO2017013200A1 - Filtration apparatus

Info

Publication number: WO2017013200A1
Application number: PCT/EP2016/067384
Authority: WO
Inventors: Christian STAAKS; Jochen PESCHEL; Peter Berg
Original assignee: Basf Se
Priority date: 2015-07-22
Filing date: 2016-07-21
Publication date: 2017-01-26

Abstract

The invention relates to a filtration apparatus (10) for filtering fluids, comprising a top compartment (12) containing a permeate collecting chamber (34), a bottom compartment (16) containing a retentate collecting chamber (46) and a filtration compartment (14) arranged between the top compartment (12) and the bottom compartment (16), wherein the filtration compartment (14) comprises at least one filtration element (18) that contains at least one permeate collecting tube (30), and wherein the permeate connecting tube (30) is in fluid communication with the top compartment (12), such that in filtration operation permeate flows through an effective membrane surface area of the at least one filtration element (18) via the at least one permeate collecting tube (30) into the permeate collecting chamber (34). A permeate pipe (140) is attached to the permeate collecting chamber (34), and a fitting (142) through which pressurized air can be applied is arranged at the permeate pipe (140), such that in backwash operation permeate available in the permeate pipe (140) can be flushed back through the filtration elements (18), whereby a volume of the permeate pipe (140) between the fitting (142) and the permeate collecting chamber (34) is at least 0.1 liter per square meter of the effective membrane surface area. The invention also relates to a method for filtering fluids, whereby in filtration operation a fluid to be filtered is fed to the filtration compartment (14), such that permeate flows via the effective membrane surface area of the at least one filtration element (18) into the permeate pipe (140), and whereby in backwash operation permeate available in the permeate pipe (140) is flushed back through the filtration elements (18), in particular by applying pressurized air to the fitting (142).

Description

Filtration Apparatus

Description The invention relates to a filtration apparatus for filtering fluids, particularly raw water, comprising a top compartment containing a permeate collecting chamber, a bottom compartment containing a retentate collecting chamber and a filtration compartment arranged between the top compartment and the bottom compartment, wherein the filtration compartment comprises at least one filtration element. The invention also relates to a method for filtering fluids using a fil- tration apparatus according to the invention.

Water treatment is one of the most vital applications of filtration processes which thus experience a strong interest not only due to global water scarcity, particularly in draught-prone and environmentally polluted areas, but also due to the continuous need for drinking water supplies and for treatment of municipal or industrial waste water. Typically, water treatment relies on a combination of different methods and technologies, which depend on the intended purpose of the cleaned water as well as on the quality and degree of the contaminated or raw water.

Conventionally, water treatment is based on treatment steps such as flocculation, sedimentation and multi-media filtration. In recent years, however, membrane technologies such as microfiltra- tion, ultrafiltration, nanofiltration and reverse osmosis have emerged, providing more efficient and reliable filtration processes. Membrane-based processes, such as microfiltration or ultrafiltration, remove turbidity caused by suspended solids and microorganisms such as pathogens like bacteria, germs and viruses from raw water. Further, significant advantages of membrane- based processes are that less chemical and no temperature treatment is required.

Common membranes for filtration are either flat-shaped membranes or tubular membranes with one or more capillaries. Typically, such membranes are semi-permeable and mechanically separate permeate or filtrate and the retentate from raw water. Thus, the microfiltration and ultrafil- tration membranes allow permeate, such as water, to pass and hold back suspended particles or microorganisms as retentate. In this context, vital membrane parameters are, amongst others, the selectivity, the resistance to fouling and the mechanical stability. The selectivity is mainly determined by the pore size usually specified in terms of the exclusion limit given by the nominal molecular weight cut-off (NMWC) in Dalton (Da). The NMWC is usually defined as the min- imum molecular weight of a globular molecule retained by the membrane to 90%. For example in ultrafiltration, the nominal pore size lies between 50 nm and 5 nm and the NMWC lies between 5 kDa and 200 kDa. In nanofiltration, the pore size lies between 2 nm and 1 nm and the NMWC lies between 0.1 kDa and 5 kDa. Thus, while ultrafiltration already filters bacteria, viruses and macromolecules, leading to water with drinking quality, nanofiltration leads to partially demineralized water. In reverse osmosis, the nominal pore size shrinks even further, below

1 nm and the NMWC shrinks below 100 Da. Reverse osmosis is thus suitable for filtering even smaller entities, such as salts or small organic molecules. In combining the different filtration technologies, a wide variety of filtration actions can be obtained which may be adapted to a specific intended purpose.

Membranes are usually embedded within a filtration system which allows to feed the raw water and to discharge the permeate as well as the concentrate. For this purpose, filtration systems encompass an inlet as raw feed and outlets to discharge both the permeate and the concentrate. For tubular-shaped membranes, different designs of filtration systems exist.

WO 2006/012920 A1 discloses a filtration system for tubular membranes. The tubular mem- brane includes a number of capillaries which are embedded in a porous substrate. The liquid to be filtered flows from or to at least one long inner channel of the capillaries for transporting the liquids to be filtered or filtered liquid. The tubular membrane is disposed in a tubular housing with an inlet and outlets for discharging permeate and concentrate. In particular, permeate is discharged through an outlet opening located centrally along the long axis of the tubular hous- ing.

EP 0 937 492 A2 discloses a capillary filtration membrane module comprising a filter housing with an inlet, an outlet and a membrane compartment. To discharge the permeate, the membrane compartment further comprises discharge lamellae, which guide the permeate to a cen- trally located discharge compartment.

DE 197 18 028 C1 discloses a filtration system including an apparatus housing with membrane modules connected parallel to each other. The filtration apparatus further comprises a back flush component which allows to back flushing one of the membrane modules while the others remain in filtration mode.

WO 2001/23076 A1 is related to an apparatus for purifying feed water which is fed to bundles of hollow fiber membranes arranged within the apparatus. The feed water is introduced at the top of the apparatus into a perforated tube which leads the feed water into the membranes. Filtrate is collected at the bottom and partially is stored in a diaphragm tank for backwashing.

WO 2003/013706 A1 describes a membrane module assembly with a hollow fiber membrane located in a vessel. The ends of the membranes open into respective collection headers. Feeds are located on the side of the vessel applying feed to the side walls of the membrane fibers and withdrawing permeate through the fiber lumens. Filtrate is removed from the headers and waste is discharged through discharge ports located on the side of the vessel opposite the feed ports.

WO 2006/047814 A1 discloses a membrane module having a plurality of hollow fiber membranes extending between upper and lower headers. The fibers in the upper header open into a permeate collection chamber. The lower header has a plurality of aeration openings for feeding gas and/or liquid into the membrane module. DE 10 2005 032 286 A1 discloses a filtration system including several filtration modules. Each filtration module has an inlet pipe connected to an inlet compartment for the liquid to be filtered and an outlet pipe connected to an outlet compartment for the filtrate. In filtration operation, the liquid, particularly raw water, is fed through the inlet pipe to the inlet compartment. The filtrate permeates a membrane and reaches the outlet compartment, while the retentate remains within the inlet compartment. The retentate is eliminated from the inlet compartment by backwash operation. For backwash operation, filtrate is used.

It is an object of the invention to provide an improved filtration apparatus that has a relatively simple design and that allows backwash operation with filtrate or permeate. A further object of the invention is to provide an improved method for filtering fluids, in particular by using the filtering apparatus according to the invention.

These objects are achieved according to the present invention by a filtration apparatus for filter- ing fluids, comprising a top compartment containing a permeate collecting chamber, a bottom compartment containing a retentate collecting chamber and a filtration compartment arranged between the top compartment and the bottom compartment, wherein the filtration compartment comprises at least one filtration element that contains at least one permeate collecting tube, wherein the permeate connecting tube is in fluid communication with the top compartment, such that in filtration operation permeate flows through an effective membrane surface area of the at least one filtration element via the at least one permeate collecting tube into the permeate collecting chamber.

According to the invention, a permeate pipe is attached to the permeate collecting chamber, and a fitting through which pressurized air can be applied is arranged at the permeate pipe, such that in backwash operation permeate available in the permeate pipe can be flushed back through the filtration elements, whereby a volume of the permeate pipe between the fitting and the permeate collecting chamber is at least 0.1 liter per square meter of the effective membrane surface area.

The filtration apparatus according to the invention has a simple design and allows backwash operation with filtrate or permeate that is stored in the permeate pipe. Therefore, the permeate collecting chamber in the top compartment does not need to store the whole amount of permeate necessary to perform a backwash operation. Hence, the volume of the top compartment can be kept relatively small.

Advantageously, the permeate pipe is connected to a permeate outlet which is connected to the top compartment, and which comprises an aeration opening for deaerating the permeate pipe. The aeration opening is arranged close to the top compartment. Preferably, the bottom compartment is in fluid communication with the filtration elements, such that retentate can be discharged into the retentate collecting chamber.

Also preferably, a drain is attached to the bottom compartment through which retentate can be released into a drainage in filtration operation, and through which fluid can be flushed into the drainage in backwash operation.

According to an improvement of the invention, a recycling system is provided that allows enhanced forward wash operation by pressing fluid in loops through the filtration compartment and through the bottom compartment. The recycling system in particular allows saving cleaning me- dium for cleaning the filtration apparatus.

Preferably, the recycling system comprises a circulation valve and a pump that are arranged between a drain through which retentate can be released into a drainage and a feed through which fluid to be filtered can be fed to the filtration compartment.

Advantageously, the filtration compartment comprises a connection port for deaerating the filtration compartment that is arranged in an upper area of the filtration compartment. In filtration operation a fluid volume extends until the upper end of the connection port, and an air buffer resides between the fluid volume and the top compartment.

According to another embodiment of the invention, a tubing is attached to a connection port arranged in an upper area of the filtration compartment and to a feed through which fluid to be filtered can be fed to the filtration compartment in filtration operation. Hence, fluid can be flushed into the tubing in extended backwash operation.

Preferably the feed is arranged in a lower area of the filtration compartment. Thus, the tubing is connected to an upper area of the filtration compartment and to a lower area of the filtration compartment. Thus, extended backwash operation is even more effective. Advantageously, an aeration opening for deaerating the tubing and the filtration compartment is arranged close to the connection port. In filtration operation a fluid volume extends until the upper end of the connection port, and an air buffer resides between the fluid volume and the top compartment. The objects of the invention are further achieved by a method for filtering fluids using a filtration apparatus according to the invention, whereby in filtration operation a fluid to be filtered is fed to the filtration compartment, such that permeate flows via the effective membrane surface area of the at least one filtration element into the permeate pipe, and whereby in backwash operation permeate available in the permeate pipe is flushed back through the filtration elements. In par- ticular, the permeate is flushed back through the filtration elements by applying pressurized air to the fitting. Preferably, in filtration operation retentate is released through a drain attached to the bottom compartment into a drainage, and in backwash operation fluid is flushed through the drain into the drainage. According to an improvement of the invention, in filtration operation fluid to be filtered is fed through a feed to the filtration compartment, and in extended backwash operation fluid is flushed into a tubing that is attached to a connection port arranged in an upper area of the filtration compartment and to the feed. Advantageously, in enhanced forward wash operation fluid is pressed by means of a recycling system in loops through the filtration compartment and through the bottom compartment.

Preferably, the filtration compartment is deaerated by means of a connection port or by means of an aeration opening arranged close to the connection port, such that in filtration operation a fluid volume extends until the upper end of the connection port, and an air buffer resides between the fluid volume and the top compartment.

Brief description of the drawings

For a better understanding of the aforementioned embodiments of the invention as well as additional embodiments thereof, reference should be made to the description of embodiments below, in conjunction with the appended drawings showing:

Figure 1 a longitudinal sectional view of a filtration apparatus according to a first embodiment, Figure 2 a perspective view of the top compartment,

Figure 3 a perspective view of the bottom compartment, Figure 4 a perspective view of the filtration compartment, Figure 5 a perspective view of a filtration element,

Figure 6 detailed views of a membrane of Figure 5,

Figure 7 a cross-sectional view of the filtration element attached to a top plate of the top

compartment and a bottom plate of the bottom compartment,

Figure 8 a detailed view of the filtration element attached to a top plate of the top compartment, Figure 9 a detailed view of the filtration element attached to a bottom plate of the bottom compartment and

Figure 10 a longitudinal sectional view of a filtration apparatus according to a second embodi- ment.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The drawings only provide schematic views of the invention. Like reference numerals refer to corresponding parts, elements or components throughout the figures, unless indicated otherwise.

Description of Embodiments

Figure 1 shows a schematic, longitudinal sectional view of a filtration apparatus 10 according to a first embodiment composed of three compartments, namely a top compartment 12, a filtration compartment 14 and a bottom compartment 16.

The filtration compartment 14 of the filtration apparatus 10 is arranged between the top compartment 12 and the bottom compartment 16. The filtration compartment 14 comprises filtration elements 18, which are arranged in parallel inside a compartment housing 20. The filtration compartment 14 further comprises a feed 22, through which a fluid to be filtered, such as raw water, is fed to the filtration elements 18 inside the filtration compartment 14 as indicated by feed arrow 24. The feed 22 is arranged in a lower area of the filtration compartment 14 and is connected to a feed pipe 155.

The filtration elements 18 are arranged such that fluid to be filtered enters the filtration elements 18 from the top of the filtration compartment 14 as indicated by inlet arrow 26. Inside the filtration elements 18 the fluid to be filtered is moving downwards, as indicated by filtration arrow 28, and is separated into filtrate or permeate and retentate or concentrate. Each filtration element 18 has a filtering membrane that lets the permeate pass through and that holds back the retentate. Said filtering membrane of each filtration element 18 has a defined surface area. The whole filtration apparatus 10 has an effective membrane surface area which is the defined as the surface area of one filtration element 18 multiplied with the number of filtration elements 18 arranged in the filtration compartment 14.

Permeate is collected in permeate collecting tubes 30, which are closed by seals 32 towards the bottom compartment 16 and open towards the top compartment 12. Permeate is thus channeled into a permeate collecting chamber 34 in the top compartment 12 as indicated by permeate arrow 36. Thus, the permeate collecting chamber 34 fills with permeate and excess perme- ate is released through a permeate outlet 38 towards a permeate pipe 140 as indicated by outlet arrow 40. The permeate pipe 140 that the permeate outlet 38 is connected to, is relatively long and includes a relatively large volume. The permeate pipe 140 is terminated by an outlet valve 41. Thus, the permeate is conducted through the relatively long permeate pipe 140 and through the outlet valve 41 . Close to the outlet valve 41 a fitting 142 is arranged at the permeate pipe 140. Through said fitting 142 pressurized air can be applied into the permeate pipe 140.

The volume of the permeate pipe 140 between the fitting 142 and the permeate collecting chamber 34 is at least 0.1 liter per square meter of the effective membrane surface area of the filtration apparatus 10. In the present case, the volume of the permeate pipe 140 is 0.5 liter per square meter of the effective membrane surface area. The volume of the permeate pipe 140 can also be larger, especially 1 liter per square meter of the effective membrane surface area or 1 .5 liter per square meter of the effective membrane surface area.

In the present case, the volume of the permeate collecting chamber 34 in the top compartment 12 is relatively small, and the volume of the permeate pipe 140 may be larger than the volume of the permeate collecting chamber 34. The volume of the permeate pipe 140 may also be larger than the volume of the filtration compartment 14.

Retentate is released through bottom openings 42 from the filtration elements 18 into a reten- tate collecting chamber 46 in the bottom compartment 16 as indicated by retentate arrow 44. The bottom compartment 16 further comprises a drain 48 through which the retentate is released into a drainage 132 as indicated by drain arrow 50. The drainage is terminated with a drain valve 51 . The filtration apparatus 10 is suitable to realize an enhanced forward wash operation in which the cleaning medium, such as a cleaning liquid including cleaning chemicals, is recycled. For such an enhanced forward wash operation the filtration apparatus 10 comprises a recycling system 130, which includes a circulation valve 134 and a pump 136. Thus, in order to recycle a cleaning liquid in enhanced forward wash operation the drainage 132 includes a branching for the recycling system 130, which may be opened by circulation valve 134. The recycling system 130 is also connected to the feed pipe 155.

In enhanced forward wash operation the drainage 132 is closed by the drain valve 51 and the permeate pipe 140 is closed by the outlet valve 41. Furthermore, the feed pipe 155 is closed. The pump 136 pumps the cleaning medium in loops through the feed 22, through the filtration compartment 14, through the bottom compartment 16 and through the drain 48. Optionally cleaning chemicals known to the person skilled in the art may be added to the recycled cleaning medium via dosage 138, which is located in the branch of the recycling system 130 between circulation valve 134 and pump 136. The filtration compartment 14 further comprises a connection port 55 for deaerating the filtration compartment 14 that is arranged in an upper area of the filtration compartment 14.

When open, the connection port 55 allows air to exit the inside of the filtration compartment 14 as indicated by aeration arrow 57. Hence, in filtration operation, in the filtration compartment 14 a fluid volume 151 extends until the upper end of the connection port 55, and an air buffer 150 resides between the fluid volume 151 and the top compartment 12. The permeate outlet 38 comprises an aeration opening 52 for deaerating the permeate pipe 140. When open, the aeration opening 52 allows air to exit the permeate pipe 140 as indicated by aeration arrow 54. In backwash operation the fluid flow is reversed such that permeate is released under pressure from the permeate pipe 140 in reverse direction through the permeate collecting chamber 34 and through the filtration elements 18. The backwash operation is initiated by applying pressure, for instance air pressure, via the fitting 142 to the permeate pipe 140 as indicated by pressure arrow 144. In backwash operation the permeate pipe 140 is closed by the outlet valve 41 , and the recycling system 130 is closed by the circulation valve 134. Furthermore, the feed pipe 155 is closed.

The pressure level producing such a backwash operation may be at least 1 bar, for example 3 bar. By reversing the fluid flow direction permeate is induced into the permeate collecting tubes 30 and the filtration elements 18 are penetrated by the permeate in reverse direction, thus removing any residues or contamination of the filtration elements 18 which diminish the filtration effect. The fluid coming out the filtration elements 18 is flushed through the drain 48 into the drainage 132. The compartments 12, 14, 16 may be built as separate elements, which are assembled to form the filtration apparatus 10. Thus, the filtration apparatus 10 is composed of separate parts, which are connected together in a fluid tight manner. Furthermore, the built up of the filtration apparatus 10 allows for different wash operations to be carried out, in particular a forward wash operation, an enhanced forward wash operation with recycling system 130 and chemical dos- age 138, a backwash operation and a chemically enhanced backwash operation with a chemical dosing 139 in the permeate pipe 140.

The individual compartments 12, 14, 16 of the filtration apparatus according to the fist embodiment are described in more detail with respect to Figures 2, 3 and 4.

Figure 2 shows a perspective view of the top compartment 12.

The top compartment 12 comprises a cover shell 56 which forms the permeate collecting chamber 34 and a top plate 58, which separates the permeate collecting chamber 34 from the filtration compartment 14. The cover shell 56 and the top plate 58 may be connected to each other via fix or releasable connection means. In this representation, the permeate outlet 38 is not visible. The top plate 58 has through-holes 60 for connecting the permeate collecting tubes 30 allowing for permeate flow between the filtration compartment 14 and the permeate collecting chamber 34. Furthermore, the top plate 58 and the cover shell 56 have connection means 62 and sealing means 64 for a tight connection between the two parts. In the embodiment of figure 2 the connection means 62 are formed by holes which allow for connection via screws. However, the connection means 62 can be formed by any connection means 62 known to the person skilled in the art, which allow for tight connection. The sealing means 64 may be formed by e.g. an O-ring, a gasket or other suitable seals. Figure 3 shows a perspective view of the bottom compartment 16.

The bottom compartment 16 comprises a bottom shell 66 which forms the retentate collecting chamber 46 and a bottom plate 68, which separates the retentate collecting chamber 46 from the filtration compartment 14. The bottom shell 66 and the bottom plate 68 may be connected to each other via fix or releasable connection means. The bottom shell 66 is formed by a round head or semi -circular shell with the drain 48 in the bottom position. The bottom plate 68 has through-holes 70 for connecting the filtration elements 18 allowing retentate to flow from the filtration compartment 14 into the retentate collecting chamber 46. Furthermore, the bottom plate 68 and the bottom shell 66 have connection means 72 and sealing means 74 for a tight connection between the two parts. In the embodiment of figure 3 the connection means 72 are formed by holes which allow for connection via screws. However, the connection means 72 can be formed by any connection means 72 known to the person skilled in the art, which allow for tight connection. The sealing means 74 may be formed by e.g. an O-ring, a gasket or other suitable seals. The bottom compartment 16 is supported by a stand 76 for keeping the filtration apparatus 10 in the upright position.

Figure 4 shows a perspective view of the filtration compartment 14.

The filtration compartment 14 comprises several filtration elements 18, which are arranged in parallel inside the compartment housing 20. The compartment housing 20 has cylindrical form and is open at the top and bottom end such that a fluid communication with the top compartment 12 and the bottom compartment 16 can be established. For connection to the bottom compartment 16 and the top compartment 12 the filtration compartment 14 further comprises connection means 78, 80 on either side of the compartment housing 20. The feed 22 is ar- ranged in a bottom area of the filtration compartment 14. The connection port 55 is arranged in a top area of the filtration compartment 14.

Figure 5 shows a perspective view of a filtration element 18. In operation, the filtration element 18 shown in Figure 5 is oriented vertically, i.e. the longitudinal axis of the filtration element 18 or the permeate collecting tube 30 is arranged parallel to the longitudinal axis of the filtration compartment 14 as shown in figures 1 and 4. The filtration element 18 comprises an element housing 90, a membrane arrangement 92 particularly suitable for microfiltration, ultrafiltration or nanofiltration. The membrane arrangement 92 comprises several but at least one membrane 93 explained in more detail with reference to figure 6. The membrane 93 includes several capillaries 94, which act as filter medium and extend along the longitudinal axes of the filtration element 18. The element housing 90, the permeate collecting tube 30 and the membrane arrangement 92 are fixed at each end in membrane holders 96 comprising a resin preferably consisting of epoxy, in which the element housing 90, the permeate collecting tube 30 and the membrane arrangement 92 are embedded.

In the configuration shown in figure 5 fluid to be filtered, such as raw water, is fed to the filtration element 18 from the left as indicated by arrow 86. The fluid to be filtered is at least partly filtered through the filtration element 18 and permeate is collected in the permeate collecting tube 30. Retentate, which is not filtered through the filtration element 18, is - in the configuration shown in figure 5 - discharged to the right as indicated by arrow 88.

Further with reference to figure 5, the membrane arrangement 92 comprises a permeate collecting tube 30, which is arranged within the filtration element 18. In particular, the permeate collecting tube 30 is arranged at the center or in a central part of the filtration element 18 and com- prises a tube including openings (not shown), which allow permeate to flow into the permeate collecting tube 30 conducting the permeate out of the filtration element 18. This location allows for easy assembly and construction of the filtration apparatus 10 and the filtration elements 18 to be easily remounted. The filtration element 18 as depicted in the embodiment of figure 5 further comprises a perforated tube 108 enclosing the membrane arrangement 92. The perforated tube 108 encloses the permeate collecting tube 30. The perforation of the tube 108 can be of any kind. In the example of figure 5 the perforation comprises holes 1 10 in the tube 108, which allow for liquid flow. With the perforated tube 108 enclosing the membrane arrangement 92 an annular gap 1 12 is formed between the element housing 90 and the perforated tube 108. In operation, i.e. in filtration or backwash operation, this allows for an even distribution of water within the filtration element 18. In particular an even pressure distribution is also reached in axial flow direction.

In other embodiments the permeate collecting tube 30 can be arranged at an outer circumfer- ences of the filtration element 18. This location of the permeate collecting tube 30 in combination with the perforated tube 108 provides for an even pressure distribution within the membrane arrangement 92. In particular, the cross-section of the membrane arrangement 92, through which the permeate flow flows through, is not reduced and thus, the flow velocity remains even across the whole cross-section of the membrane arrangement 92. In contrast, when placing the permeate collecting tube 30 in the center of the membrane arrangement 92 the cross-section reduces towards the central tube and the flow velocity increases, which results in a higher pressure applied to the capillaries 94 close to the central tube. Thus, the disadvantages resulting from the central location of the permeate collecting tube 30 are abandoned and an even pressure distribution in radial direction can be achieved. Figure 6 shows a detailed view of a single membrane 93 as indicated by the circle 98 in figure 6 and a further detailed view of one capillary 94 of the membrane 22 as indicated by circle 100 in figure 2.

The capillaries 94 include a porous substrate 102 forming channels 104, which extend longitu- dinally along the length of the membrane 93. Inside the channels 104 an active layer 106 is arranged as filtration layer, which can either be incorporated into a substrate 102 with a different pore size or which can be formed by a coating. The capillaries 94 are thus embedded in the porous substrate 102, which aids stability and avoids capillary rupture. The porous substrate 108 of the membrane 93 is formed by a polymer, such as polysulphone type polymers, cellulose acetate, polyacrylonitrile, polyvinylidene. For example polyethersulfon or polysulfon are used to form the porous substrate 108 by extrusion, in particular by wet spinning. In wet spinning a suitable polymer is dissolved in a solvent, optionally adding additives and extruded through a spinneret for forming the membrane 93. After extrusion the membrane is coagulated and dissolvable components are removed. Such membranes 93 having an outer diameter of for instance 4 mm include for instance seven capillaries 94 with an inner diameter of 0.9 mm, and a pore size of 0.02 μηη. Other membranes 93 having an outer diameter of for instance 6 mm and allowing for higher sediment concentrations for instance include seven capillaries 94 with an inner diameter of 1.5 mm, and a pore size of 0.02 μηη.

Figure 7 shows a longitudinal-sectional view of the filtration element 18 attached to the top plate 58 of the top compartment 12 and the bottom plate 68 of the bottom compartment 16.

The filtration element 18 separates the fluid to be filtered into permeate and retentate, wherein the fluid to be filtered is fed to the capillaries 94 of the membrane arrangement 92, permeate is collected in the permeate collecting tube 30 and retentate is kept in the capillaries 94. In order to discharge the permeate into the top compartment 12 the permeate collecting tube 30 is connected to through-holes 60 in the top plate 58 allowing permeate to flow from the filtration compartment 14 into the permeate collecting chamber 34. The connection is established via adapter pieces 1 14, which are described in more detail with respect to figure 8.

Figure 8 shows a detailed view of the filtration element 18 attached to a top plate 58 of the top compartment 12 via adapter pieces 1 14. The adapter pieces 1 14 include sealing regions 120 and a stopper region 122. The sealing regions 120 are arranged on each side of the stopper region 122. Furthermore the sealing regions 120 are in contact with the through-hole 60 in the top plate 58 on one side and with the permeate collecting tube 30 of the filtration element 18 on the other side. The sealing regions 120 further comprise sealing means 121 such as O-rings, gaskets or the like to establish a fluid tight connection. The stopper region 122 includes a thickening forming notches which the filtration element 18 and the top plate 58 rest upon. In the center of the adapter piece 1 14 a channel 124 is arranged, which allows for fluid communication and hence permeate flow between the permeate collecting tube 30 and the permeate collecting chamber 34.

Further with reference to figure 7, in order to discharge the retentate from the filtration com- partment 14 into the bottom compartment 16 the capillaries 94 of the membrane arrangement 92 are connected to through-holes 70 forming bottom openings 42 in the bottom plate 68 for retentate to flow from the filtration compartment 14 into the retentate collecting chamber 46 and the drain 48. Details regarding the bottom connection of the filtration element 18 are described in more detail with respect to figure 9.

Figure 9 shows a detailed view of the filtration element 18 attached to the bottom plate 68 of the bottom compartment 16.

The bottom plate 68 comprises a notch 126 with sealing means 128 such as an O-ring, a gasket or other suitable sealing means. The through-hole 70 and the notch 126 are arranged such that the filtration element 18 tightly fits into the notch 126 thus being supported by the notch 126. The permeate collecting tube 30 has a seal 32 at the bottom end in order to preclude permeate to mix with the retentate flow. Thus, it is only the membrane arrangement 92 with its capillaries 94 that is in fluid communication with the bottom part through bottom openings 42.

Figure 10 shows a schematic, longitudinal sectional view of a filtration apparatus 10 according to a second embodiment. The filtration apparatus 10 according to the second embodiment also contains three compartments, namely a top compartment 12, a filtration compartment 14 and a bottom compartment 16 that are set up just like in the filtration apparatus 10 according to the first embodiment shown in figure 1 .

Deviating from the filtration apparatus 10 according to the first embodiment, the filtration apparatus 10 according to the second embodiment comprises a tubing 210 that is attached to the connection port 55 and to the feed 22.

An aeration opening 152 for deaerating the tubing 210 and the filtration compartment 14 is arranged close to the connection port 55. When open, the aeration opening 152 allows air to exit the tubing 210 and the filtration compartment 14 as indicated by aeration arrow 57 and by aeration arrow 157. Hence, in filtration operation, in the filtration compartment 14 a fluid volume 151 extends until the upper end of the connection port 55, and an air buffer 150 resides between the fluid volume 151 and the top compartment 12. The fluid volume 151 also extends into the tubing 210.

A first tubing valve 201 is arranged in a sector of the tubing 210 that is attached to the connec- tion port 55. A second tubing valve 202 is arranged in a sector of the tubing 210 that is attached to the feed 22 and to a sector of the recycling system 130 downstream of the pump 136. A third tubing valve 203 is arranged in a sector of the tubing 210 that is attached to a sector of the drainage 132 downstream of the drain valve 51. The tubing 210 is also connected to an inlet valve 204 through which the fluid to be filtered, such as raw water, can be fed to the tubing 210.

In filtration operation the first tubing valve 201 and the third tubing valve 203 are closed. The second tubing valve 202 and the inlet valve 204 are open. The fluid to be filtered is fed through the inlet valve 204 and the second tubing valve 202 to the feed 22 and into the filtration compartment 14.

In extended backwash operation the fluid flow is reversed such that permeate is released under pressure from the permeate pipe 140 in reverse direction through the permeate collecting chamber 34 and through the filtration elements 18. The extended backwash operation is initiated by applying pressure, for instance air pressure, via the fitting 142 to the permeate pipe 140 as indicated by pressure arrow 144. In extended backwash operation the permeate pipe 140 is closed by the outlet valve 41 , and the recycling system 130 is closed by the circulation valve 134. Furthermore, the drain valve 51 and the inlet valve 204 are closed. The first tubing valve 201 and the second tubing valve 202 are open. When the third tubing valve 203 is opened, the fluid coming out the filtration elements 18 is flushed into the tubing 210 and through the first tubing valve 201 , the second tubing valve 202 and the third tubing valve 203 into the drainage 132.

The foregoing description, for purpose of explanation, has been described with reference to specific embodiments. However, the illustrative discussions above are not intended to be ex- haustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings and those encompassed by the attached claims. The embodiments were chosen and described in order to explain the principles of the invention and its practical applications, to thereby enable others skilled in the art to utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. List of Reference Numerals

10 filtration apparatus

12 top compartment

14 filtration compartment

16 bottom compartment

18 filtration elements

20 compartment housing

22 feed

24 feed arrow

26 inlet arrow

28 filtration arrow

30 permeate collecting tube

32 seal

34 permeate collecting chamber

36 permeate arrow

38 permeate outlet

40 outlet arrow

41 outlet valve

42 bottom opening

44 retentate arrow

46 retentate collecting chamber

48 drain

50 drain arrow

51 drain valve

52 aeration opening

54 aeration arrow

55 connection port

56 cover shell

57 aeration arrow

58 top plate

60 through-holes

62 connection means

64 sealing means

66 bottom shell

68 bottom plate

70 through-holes

72 connection means

74 sealing means

76 stand

78 connection means

80 connection means 86 flow arrow

88 flow arrow

90 element housing

92 membrane arrangement 93 membrane

94 capillaries

96 membrane holders

98 indication circle

100 indication circle

102 substrate

104 channels

106 active layer

108 perforated tube

1 10 holes

1 12 annular gap

114 adapter piece

1 16 indication circle

1 18 indication circle

120 sealing regions

122 stopper region

124 channel

126 notch

128 sealing means

130 recycling system 132 drainage

134 circulation valve

136 pump

138 dosage

139 dosing

140 permeate pipe

142 fitting

144 pressure arrow

150 air buffer

151 fluid volume

155 feed pipe

157 aeration arrow

201 first tubing valve

202 second tubing valve

203 third tubing valve 204 inlet valve

210 tubing

Claims

1 . Filtration apparatus (10) for filtering fluids, comprising

a top compartment (12) containing a permeate collecting chamber (34),

a bottom compartment (16) containing a retentate collecting chamber (46) and

a filtration compartment (14) arranged between the top compartment (12) and the bottom compartment (16), wherein

the filtration compartment (14) comprises at least one filtration element (18)

that contains at least one permeate collecting tube (30), and wherein

the permeate connecting tube (30) is in fluid communication with the top compartment

(12), such that

in filtration operation permeate flows through an effective membrane surface area of the at least one filtration element (18) via the at least one permeate collecting tube (30) into the permeate collecting chamber (34),

characterized in that

a permeate pipe (140) is attached to the permeate collecting chamber (34), and a fitting (142) through which pressurized air can be applied is arranged at the permeate pipe (140), such that

in backwash operation permeate available in the permeate pipe (140) can be flushed back through the filtration elements (18), whereby

a volume of the permeate pipe (140) between the fitting (142) and the permeate collecting chamber (34) is at least 0.1 liter per square meter of the effective membrane surface area.

2. Filtration apparatus (10) according to claim 1 , characterized in that

the permeate pipe (140) is connected to a permeate outlet (38) which is connected to the top compartment (12), and which comprises an aeration opening (52) for deaerating that is arranged close to the top compartment (12).

3. Filtration apparatus (10) according to one of the preceding claims, characterized in that the bottom compartment (16) is in fluid communication with the filtration elements (18), such that retentate can be discharged into the retentate collecting chamber (46).

4. Filtration apparatus (10) according to one of the preceding claims, characterized in that a drain (48) is attached to the bottom compartment (16) through which retentate can be released into a drainage (132) in filtration operation, and through which fluid can be flushed into the drainage (132) in backwash operation.

5. Filtration apparatus (10) according to one of the preceding claims, characterized in that a recycling system (130) is provided that allows enhanced forward wash operation by pressing fluid in loops through the filtration compartment (14) and through the bottom compartment (16). Filtration apparatus (10) according to claim 5, characterized in that

the recycling system (130) comprises a circulation valve (134) and a pump (136) that are arranged between a drain (48) through which retentate can be released into a drainage (132) and a feed (22) through which fluid to be filtered can be fed to the filtration compartment (14).

Filtration apparatus (10) according to one of the preceding claims, characterized in that the filtration compartment (14) comprises a connection port (55) for deaerating arranged in an upper area of the filtration compartment (14), and that in filtration operation a fluid volume (151 ) extends until the upper end of the connection port (55), and an air buffer (150) resides between the fluid volume (151 ) and the top compartment (12).

Filtration apparatus (10) according to one of the preceding claims, characterized in that a tubing (210) is attached to a connection port (55) arranged in an upper area of the filtration compartment (14) and to a feed (22) through which fluid to be filtered can be fed to the filtration compartment (14) in filtration operation, such that fluid can be flushed into the tubing (210) in extended backwash operation.

Filtration apparatus (10) according to claim 8, characterized in that

the feed (22) is arranged in a lower area of the filtration compartment (14).

0. Filtration apparatus (10) according to one of claims 8 or 9, characterized in that

an aeration opening (152) for deaerating is arranged close to the connection port (55), and that in filtration operation a fluid volume (151 ) extends until the upper end of the connection port (55), and an air buffer (150) resides between the fluid volume (151 ) and the top compartment (12).

1 . Method for filtering fluids using the filtration apparatus (10) according to one of the preceding claims, whereby

in filtration operation a fluid to be filtered is fed to the filtration compartment (14), such that permeate flows via the effective membrane surface area of the at least one filtration element (18) into the permeate pipe (140), and whereby

in backwash operation permeate available in the permeate pipe (140) is flushed back through the filtration elements (18),

in particular by applying pressurized air to the fitting (142).

2. Method according to claim 1 1 , whereby

in filtration operation retentate is released through a drain (48) attached to the bottom compartment (16) into a drainage (132), and whereby

in backwash operation fluid is flushed through the drain (48) into the drainage (132). Method according to claim 1 1 , whereby

in filtration operation fluid to be filtered is fed through a feed (22) to the filtration compartment (14), and whereby

in extended backwash operation fluid is flushed into a tubing (210) that is attached to a connection port (55) arranged in an upper area of the filtration compartment (14) and to the feed (22).

Method according to one of claims 1 1 to 13, whereby

in enhanced forward wash operation fluid is pressed by means of a recycling system (130) in loops through the filtration compartment (14) and through the bottom compartment (16).

Method according to one of claims 1 1 to 14, whereby

the filtration compartment (14) is deaerated by means of a connection port (55) or by means of an aeration opening (152) arranged close to the connection port (55), such that in filtration operation a fluid volume (151 ) extends until the upper end of the connection port (55), and an air buffer (150) resides between the fluid volume (151 ) and the top compartment (12).