METHOD AND DEVICE FOR FILTERING A RAW FLUID CONTAINING CONTAMINATION BY MEANS OF AT LEAST ONE MEMBRANE FILTER UNIT AND A USE THEREFORE

Description

[0001] The invention relates to a method for filtering a raw fluid containing contamination by means of at least one membrane filter unit, according to claim 1.

[0002] The invention also relates to a device for filtering raw water by means of at least one membrane filter unit according to claim 7.

[0003] Last but not least, the invention relates to the use of a powdered activated carbon in raw water in a device and / or a method for filtering raw water by means of at least one membrane filter unit according to claim 9.

[0004] Filtering methods and filtering devices are generally known from the state of the art.

[0005] To filter raw water, e.g. spring water, filter systems with membrane filters are used. In these systems, the raw water is pumped through membrane filter elements using a pump. The membrane filter elements can be tubular membranes made of a wide variety of materials, with wall thicknesses of 0.1 to 1.0 mm or more. As the raw water passes through these thin-walled membranes, suspended matter and dirt particles, as well as viruses and bacteria, which settle on the surface of the membranes are removed. To clean the membranes, the membranes are then backwashed at regular intervals. In conventional filter systems, an additional backwash pump is used to pressurize the membrane elements with clean water in the opposite direction to the direction of filtration. The dirt particles deposited on the membrane elements are thereby detached and can be drained away via a wastewater line.The use of activated carbon in certain filter systems is also known, for example. Furthermore, DE 10 2005 033 314 A1 discloses a method and a filter system for filtering raw water and backwashing membrane filter units. At least two membrane filter units are used to generate pure water from contaminated or polluted raw water during filtering operation. During backwashing operation, the membrane filter elements are cleaned by means of pure water used as rinse water, flowing in the opposite direction to the direction of filtration. Raw water is supplied to at least one membrane filter unit operating in filtering operation via a pump. The pure water generated by at least one membrane filter unit is fed in the backwashing direction into the membrane filter unit to be backwashed and then discharged from the outlet side as rinse wastewater.

[0006] FR 2 737 202 A1 discloses a plant for the biological treatment of water, in which the water is rendered potable. The plant comprises a biological reactor having means for introducing an oxygen-containing gas, at least one separation membrane immersed in the reactor for micro- or ultrafiltration, biomass, at least one suspended, powdered substance serving as a substrate for the biomass, and means for feeding the powdered substance inside the reactor. The substance can be a reactive powder capable of retaining the substrate required by the biomass.

[0007] It is an object of the present invention to provide a method, a device, and a use for improved filtration. In particular, it is an object to provide a method for filtering raw water and for backwashing membrane filter units, in which an improved filtration process and also an improved backwash process are achieved.

[0008] These and other objects are achieved by a method according to claim 1, a device according to claim 7 and a use according to claim 9.

[0009] Advantageous further developments of the invention are specified in the dependent claims or are specified below in connection with the description of the figures.

[0010] The invention includes the technical teaching that in a method for filtering a raw fluid containing contamination by means of at least one membrane filter unit, it is provided that in a filtering operation, the contaminated raw fluid is conveyed from a raw fluid side in a filtering direction through the membrane filter unit to a clean fluid side in order to generate a clean fluid substantially cleansed of contamination on the clean fluid side, and in a backwashing operation, a flushing fluid is conveyed in a backwashing direction through the membrane filter unit in order to clean the membrane filter unit of the filtered contamination, wherein in the filtering operation, an additional filter medium is added to the raw fluid on the raw fluid side in order to improve the filtration and wherein in the backwashing operation, additional shear force-increasing agents, in particular compressed air, are blown into the membrane filter unit,To clean the membrane filter unit of dirt and the additional filter media during backwash operation. The process follows the IN / OUT principle, which is described in more detail below.

[0011] In the first filtration stage, a raw fluid is fed into a membrane filter unit in the filter direction. In addition to unwanted contaminants, the raw fluid also contains an additional filter medium, which thus represents desired contaminants. The raw fluid is thus a combination of a clean fluid, which represents the end product of the filtration process, with unwanted contaminants and desired contaminants—in other words, a clean fluid plus contaminants. To separate the raw fluid from the unwanted contaminants, the desired contaminants are added. The desired contaminants are thus matched to the unwanted contaminants and support the filtration process.

[0012] The raw fluid is preferably a raw liquid, more specifically raw water. Accordingly, the clean fluid is preferably a clean liquid, more specifically pure water. The contaminant—intentional and / or unintentional—is a fluid, but can also be present in the raw fluid in particle form, either soluble or insoluble.

[0013] The raw fluid is fed to the membrane filter unit on the raw fluid side. The raw fluid filtered to the clean fluid is discharged on the clean fluid side of the membrane filter unit. The contaminants remain in the membrane filter unit during filter operation. The contamination of the clean fluid to the raw fluid preferably occurs at different times. Initially, the clean fluid is only contaminated with the unwanted contaminants. This is combined with the desired contaminants at different times. The raw fluid thus produced is fed to the membrane filter unit via a conveying unit, a pump. The pressure at which the raw fluid is fed to the membrane filter unit can be selected as desired.

[0014] The membrane filter unit filters contaminants from the raw fluid. To ensure smooth filtration, the membrane filter unit must be cleaned when contaminated. This is done by backflushing. A (back)flushing fluid is pumped into the membrane filter unit in a flushing direction. The flushing direction is opposite to the filtering direction. The flushing fluid can be any fluid suitable for cleaning the membrane filter unit. The flushing fluid is preferably a clean fluid, preferably in liquid form, in particular pure water.

[0015] To improve the backwash process, a shear force-increasing agent is supplied to the membrane filter unit in addition to the clean fluid. Compressed air is used as the shear force-increasing agent. Therefore, compressed air will be used instead of the shear force-increasing agent in the following. The compressed air is supplied from the raw water side. Thus, during the backwash process, the compressed air acts in the filtering direction, while the flushing fluid acts in the opposite direction, in the flushing direction. For improved backwashing, the pressure of the flushing fluid and the compressed air are coordinated. The ratio of flushing fluid pressure to compressed air pressure is preferably at least approximately 25:75, more preferably approximately 50:50. Due to the additional contamination of the raw fluid with an intended contaminant, the additional filter medium, the pressures must be coordinated.By supplying compressed air, additional shear forces act on the contaminants on and / or in the membrane filter unit. These forces, together with the action of the flushing fluid, result in improved removal of the contaminants from the membrane filter unit. The contaminants removed from the membrane filter unit are removed from the membrane filter unit with the flushing fluid and the compressed air via a corresponding outlet. This removal of the now contaminated flushing fluid takes place on a discharge side. The flushing fluid, once uncontaminated for cleaning, now contains the filtered, both desired and unwanted contaminants.

[0016] With a substantially vertical orientation of the membrane filter unit, the compressed air also causes the contaminants to rise against gravity, allowing them to be easily removed from the upper end of the membrane filter unit. The rest of the membrane filter unit thus remains flushed or surrounded by the uncontaminated or barely contaminated flushing fluid.

[0017] During the backwashing process, the supply of raw fluid is interrupted. After backwashing, the system can then switch back to filtering operation. The filtering process can be carried out in parallel using multiple filter devices. The filtering processes can be carried out at staggered times, so that filtering occurs in one process and backwashing occurs in the parallel process. The processes can be coupled in such a way that clean fluid from one process is diverted during filtering or used to carry out backwashing in the parallel process. By carrying out the process in parallel, especially at staggered times, quasi-continuous filtering operation can be achieved. The process can therefore be carried out discontinuously and (quasi-)continuously.

[0018] Powdered activated carbon is added as an additional filter medium. Activated carbon is particularly suitable for filtering chemical contaminants. The contaminants adhere to the activated carbon and remain in the membrane filter unit. The filter medium is supplied in powder form. In this way, the effective surface of the filter medium is optimized for improved filtration. The addition of powdered activated carbon is therefore particularly preferred. When using a membrane filter unit, the filter medium or the contaminants, or the contaminants and the filter medium, can penetrate the pores of the membrane filter elements used in the membrane filter unit. Nevertheless, a preferred embodiment of the present invention provides that the grain or particle size of the powdered filter medium is such that it can penetrate the pores of the membrane filter elements.A smaller grain size optimizes the effective surface area of ​​the added amount of filter media. Larger grain sizes cause the media to adhere predominantly to the outside of the membrane filter elements. The smaller grain sizes cause at least partial penetration into the membrane pores. This clogging necessitates an improved backwashing process. With conventional backwashing processes, such a small grain size is not possible because the clogging of the membrane pores cannot be sufficiently reversed by backwashing. According to the invention, the shear force-increasing agent, compressed air, is therefore supplied during backwashing. To achieve an optimal flushing effect, the pressure of the flushing fluid and compressed air is coordinated. Furthermore, the grain size and the membrane pore size are coordinated. By adjusting and coordinating the aforementioned parameters, an optimal filtering and backwashing process can be achieved.

[0019] In a further embodiment, during backwash operation, the contaminants, including the additional filter media, are conveyed from the membrane filter unit with the flushing fluid and / or the shear force-enhancing agent or the compressed air into at least one further filter stage and filtered there, so that pure water is again produced. This allows for a multi-stage filtration process in which the activated carbon or filter media present in the flushed, contaminated flushing agent, whose effectiveness is maintained for multiple filtration processes, can be further utilized.

[0020] The contamination, along with the flushing fluid and / or shear force-enhancing agent, is collected and removed by suitable means. A suitable collecting vessel is preferably provided for collection. The shear force-enhancing agent, the compressed air, causes the contamination to rise in the flushing fluid, i.e., move against gravity. Accordingly, the contamination is collected at an upper end of the membrane filter unit to be flushed. In the upper area, for example, at the collecting vessel, a discharge line is attached, which can be closed using appropriate actuators, or more precisely, valves. During backwash operation, the corresponding actuators are opened, and the contamination is removed. The contaminated flushing fluid is discharged to a further filter stage. This further filter stage is constructed analogously to the first filter stage.In the second filter stage, the contaminated flushing fluid is fed via a feed line to one or more membrane filter units, similar to the raw water in the first filter stage, optionally with the addition of activated carbon. In the second filter stage, the supply of activated carbon or another filter medium can be reduced because the additional filter medium is already present in the contaminated flushing fluid. The contaminated flushing fluid is pumped through the membrane filter unit(s), and on the clean fluid side, clean water freed of contaminants is obtained in the filter operation. The second filter stage can also be switched from filter operation to backwash operation. In backwash operation, similar to the first filter stage, a flushing fluid is pumped through the membrane filter unit(s) against the filter direction, i.e. in the backwash direction.The purified water produced in one of the filter stages or a separately supplied or generated flushing fluid can be used as the flushing fluid. Depending on whether additional filter stages with a similar structure are planned, appropriate filtering processes follow.

[0021] Accordingly, one embodiment provides for filtering and backwashing to be carried out in the at least one additional filter stage as in the first filter stage. In this way, any number of filter stages can be arranged in series. The obtained clean fluid and / or flushing fluid can be fluidically connected to flushing fluid and / or clean water from different filter stages via appropriate lines. Likewise, the raw fluid and / or contaminated flushing fluid can be fluidically connected to the raw fluid and / or contaminated flushing fluid from other filter stages via appropriate line systems. The coupling of flushing / clean / raw fluid can be controlled via appropriate actuators such as valves, pumps, and the like.

[0022] In yet another embodiment, the contamination created in a further filter stage, including additional filter media, flushing fluid, and shear-enhancing agent, in particular compressed air, is sedimented in a sedimentation tank to form a sediment sludge. Sedimentation preferably takes place in a final filter stage, but can also be carried out in intermediate filter stages. The contaminated flushing fluid is conveyed into one or more sedimentation tanks. There, the contaminated flushing fluid is calmed or allowed to rest so that the contamination can settle in the sedimentation tank. The settled contamination forms a sediment sludge. The sediment sludge is removed or discharged from the sedimentation tank using suitable means. The discharged sediment sludge can then be reused in a variety of ways.Depending on the filter stage, the sediment sludge can, for example, be added to the raw water of a front filter stage. The activated carbon contained in the sediment sludge, or more generally, the additional filter media contained therein, can then be used in a front filter stage. This is particularly beneficial because the activated carbon has not completely lost its filtering effect in the sediment filter stage, and this effect can therefore continue to be utilized. This allows for an environmentally friendly filter cycle.

[0023] Accordingly, a preferred embodiment provides for the sediment sludge to be added to the raw fluid of a front filter stage. The addition of sediment sludge, raw fluid, flushing fluid, additional filter medium, and / or shear-enhancing agents takes place under predetermined parameters, such as quantity ratios, pressure ratios, and / or temperature conditions. Depending on the filter stage, the addition takes place under predetermined quantities and / or pressure ratios that are coordinated accordingly. Thus, the compressed air or the shear-enhancing agent and the flushing fluid are supplied in a backwash operation at a pressure ratio such that the pressure of the shear-enhancing agent does not exceed the pressure of the flushing fluid by more than 30%, preferably by more than 20%, and most preferably by no more than 10%.This ensures that during backwash operation the contaminated flushing fluid rises into the collection vessel and the contamination can be removed in an optimized manner.

[0024] The invention includes the technical teaching that in a device for filtering raw fluid by means of at least one membrane filter unit, it is provided that the device has means for carrying out a method described above, in particular a filter stage with at least one membrane filter unit, which is fluidically connected on a raw fluid side to a raw fluid supply and which is designed to convey raw fluid in a filtering direction through the membrane filter unit in a filtering operation in order to generate clean fluid on a clean fluid side, and which is fluidically connected on the clean fluid side to a rinsing fluid supply and which is designed to convey rinsing fluid in a backwashing direction through the membrane filter unit in a backwashing operation in order to clean the membrane filter unit of filtered dirt particles, wherein a supply for supplying shear force-increasing agents, in particular a compressed air supply, is further provided,which is designed to inject shear force-increasing agents during backwash operation, wherein a medium feed is further provided which is designed to add an additional filter medium to the raw fluid during filter operation to improve filtration. The device is designed for filter operation according to the IN / OUT principle.

[0025] The membrane filter unit has at least one membrane filter element with membrane pores through which the raw fluid is conveyed and in whose membrane pores or on whose membrane surfaces dirt particles accumulate.

[0026] On the raw fluid side, raw fluid and an additional filter medium, powdered activated carbon, are added during filter operation to convey them through the membrane filter unit.

[0027] Yet another embodiment provides that several filter stages are provided which are coupled to one another and whose corresponding clean fluid sides and / or raw fluid sides are at least partially coupled or can be coupled to one another.

[0028] Last but not least, the invention includes the technical teaching that a use of a powdered activated carbon in the raw fluid in a device and / or a method for filtering raw fluid by means of at least one membrane filter unit which has at least one membrane element with membrane pores through which the raw fluid is conveyed for filtering, wherein the membrane filter units are cleaned by means of backwashing processes with the supply of shear force-increasing agents, in particular compressed air.

[0029] The shear force-increasing agent is compressed air. The compressed air, at least during injection, has a pressure that preferably ranges from approximately greater than or equal to 0.2 bar to approximately less than or equal to 2.0 bar, for example, approximately 0.5 bar, approximately 1.0 bar, and more preferably approximately 1.5 bar, most preferably less than or equal to 2.5 bar.

[0030] The additional filter medium is powdered activated carbon.

[0031] In particular, the additional filter medium is designed with a grain size such that the powder grains or the activated carbon can penetrate the membrane pores of the membrane filter unit. The additional filter medium is preferably designed as powdered activated carbon.

[0032] In one embodiment, the device, which is designed in particular as a filter system, comprises a membrane filter unit. Preferably, the device has at least two membrane filter units. The membrane filter units can be arranged in one filter stage or in different filter stages. The membrane units can be of identical design. In another embodiment, the membrane filter units are of different design. In particular, membrane filter units are of different design in different filter stages. In filtration mode, raw water is pumped through the membrane filter units as raw fluid, while in backwash mode at least one of the membrane filter units is decoupled from the filtration mode. In one embodiment, a separate supply of flushing fluid is provided.The clean water generated by the other membrane filter unit(s) is fed to this decoupled membrane filter unit as flushing fluid in the backwash direction, so that the dirt particles or contaminants on the membrane filter elements can be detached and drained away via a wastewater line. In this embodiment, no additional backwash pump is required. In other embodiments, backwashing is carried out via a separate backwash pump. With an appropriate design of the filter system, this method can also be used to backwash individual membrane filter units one after the other without interrupting the filtration operation, thus in a quasi-continuous process. It is particularly advantageous to support the detachment of the dirt particles from the individual membrane filter elements during the backwash process by blowing compressed air onto the raw fluid side or the raw water side.Support is particularly beneficial when using an additional filter medium such as powdered activated carbon. To carry out the process, several membrane filter units are preferably used, which are backwashed individually one after the other or several together, while all other membrane filter units operate in normal filter mode. Tests have also shown that blowing in compressed air -- even during filtration -- is very advantageous, as this can prevent the membrane filter elements from becoming dirty too quickly. The shear force-increasing agent, compressed air, is preferably blown in exclusively during backwashing mode. The blown-in compressed air loosens dirt deposits more easily and also detaches them from the membrane filter elements. They can then collect in an upper chamber of the membrane filter elements, from where they can then be discharged via the wastewater line during the backwash process.The filter system according to one embodiment has at least two membrane filter units, which enables filtration and backwashing operation with just a single pump, or in other embodiments with multiple pumps. To backwash one or more membrane filter units, the clean water generated by one or more other membrane filter units is used as rinsing fluid, more precisely as rinsing water, by introducing this rinsing water in the backwash direction into the membrane filter unit to be backwashed. Appropriate shut-off valves are provided for this purpose. The supply lines leading from the pump(s) to the membrane filter units have separate shut-off valves, and the drain lines leading from the membrane filter units to the wastewater line also each have separate shut-off valves.In conjunction with an additional shut-off valve in the outlet-side clean fluid or clean water line, this enables the clean water generated in the filter system to be used to backwash individual membrane filter units. Using an air compressor, compressed air can be blown into the membrane filter units via separately shut-off compressed air lines in the raw water supply area or the raw water side. This very advantageously results in the detachment of dirt particles from the membrane filter elements, at least during backwash operation. The membrane filter elements of the membrane filter units can be tubular or otherwise shaped elements through which flow can flow from the inside to the outside or vice versa during the filtration process. The membrane filter elements can, for example, be installed in cylindrical, vertically aligned pressure vessels that form the membrane filter units of the filter system.Drain lines can be connected to an upper chamber via shut-off valves to a common wastewater line for discharging the backwashed rinse water. This upper chamber, containing the membrane filter units, can be vented via an automatic vent valve.

[0033] The filtration process follows the IN / OUT principle, with filtration occurring from the inside out. Accordingly, powdered activated carbon is added to the raw water or raw fluid upstream of a raw water pump, feed pump, or feed pump. Shortly thereafter, the mixed medium—i.e., raw water plus activated carbon—hence hits the membrane of the membrane filter unit, i.e., the filter unit of the first filter stage. During the filtration process, compressed air or any other shear-increasing agent is preferably not added. During backwashing, the previously treated water (filtrate, pure water, or pure fluid in general) is used as rinsing fluid or rinse water for backwashing. Using the pure water produced has the advantage that pure water that once passed through the membrane filter unit in the filter direction can easily pass back through the membrane filter unit in the opposite direction, i.e., in the backwash direction.To intensify backwashing, air, or more precisely compressed air, is blown into a lower area of ​​the membrane filter unit, more precisely into the bottom of the membrane in the module base, as a shear force increasing agent. The rinse or clean water (filtrate) is pressed into the membrane unit from the outside to the inside (OUT / IN). The compressed air creates a shearing effect in the area of ​​the contaminants on the membrane elements, thereby more easily removing the contaminants from the membrane filter unit. The contaminants removed by the air and the backwash water rise together, thus against gravity, into a module head. From there, the contaminated rinse fluid is discharged, preferably laterally. Air is preferably only used for backwashing and is blown into the bottom of the membrane, more precisely into its module base.

[0034] Accordingly, the filtering device is designed for filtration according to the IN / OUT method, i.e. from the inside out, and for backwashing according to the OUT / IN method, i.e. from the outside in. During filtration, the raw fluid is filtered from the inside out. For this purpose, the device has a module base. This is designed, among other things, to introduce purge air and raw water. A module housing is provided in fluid communication with the module base. This is designed approximately as a hollow cylinder. The membrane filter unit with the membrane filter elements is arranged in its interior. The membrane filter elements are arranged in such a way that raw water or raw fluid is introduced from the module base into the membrane filter elements. The membrane filter elements are approximately tubular. During filtration, the raw fluid is introduced from the module base exclusively into the membrane filter elements. From there, the raw fluid pushes outwards through the pores.The contaminants adhere to the inside of the membrane filter elements and / or the inside of the pores. The purified raw fluid pushes out through the pores. When a filter medium such as activated carbon is added, this is also moved through the module base into the filter elements with the raw fluid. As it passes through the pores, the filter medium adheres to the inside of the membrane filter elements and / or the inside of the pores, as does the contaminants. The module base has a raw water inlet and a purge air inlet. Both flow into a common chamber in the module base. From this chamber, the raw fluid, for example, flows through a perforated partition wall to the filter elements. The partition wall is perforated in such a way that the passage created by the perforation leads into the filter elements, or more precisely, into the cavity of the filter elements. Since the chamber is suitable for both the raw fluid and purge air, the same applies to the purge air.The partition wall fluidically connects the chamber with the interior of the filter elements or membrane filter elements. After passing through the pores of the membrane filter elements, the purified raw fluid enters the interior of the hollow cylindrical module housing, which also houses the membrane filter unit. The purified fluid exits the interior via a clean water drain. The rinse wastewater is drained from the membrane filter elements via corresponding rinse wastewater lines. For this purpose, the membrane filter units are fluidly connected to a module head. This head has passages to the cavity of the membrane filter elements, allowing the rinse wastewater to flow through the passages from the cavity to the rinse wastewater line. The membrane filter elements are preferably designed as capillaries. Due to capillary action, the raw fluid pushes through the pores. More precisely, the capillaries are designed as capillaries cast with synthetic resin.The capillaries are sealed with synthetic resin at their ends. In this area, the raw fluid cannot escape through the pores. Due to the hollow cylindrical shape of the filter elements, there is only a small surface area available on the inside for the deposition of the raw fluid contaminants. Thus, the pores clog more quickly in an IN / OUT filtration process than, for example, in an OUT / IN filtration process. Therefore, in conventional solutions, an OUT / IN process is only operated with additional filter media, as this provides a larger membrane surface on which the contaminants and the filter media can settle.

[0035] According to the invention, however, the process is operated using the IN / OUT filtration method, or the device is designed for an IN / OUT method. During the backwashing process, the principle is reversed. This is carried out according to the invention using the OUT / IN method. Here, flushing fluid is flushed from the outside through the pores into the inside of the hollow membrane filter elements. This flushing fluid is fed via the module head into the interior of the module housing. From there, it passes through the pores into the cavity of the membrane filter elements. In addition, flushing air is supplied via the module base (from below). The flushing air passes from the chamber of the module base through the perforation of the partition wall into the cavity of the membrane filter elements. The flushing water, which absorbs the adhering contaminants including the filter media (activated carbon), is discharged via the module head.The module head is designed similarly to the module base, with the difference that the module head has a fluidic connection to the interior of the module housing that is separate from the rinse water drain. The module base only has passages into the cavity of the filter elements. The module head has both a passage to the interior of the module housing and a separate or separable rinse water drain. The rinse water drain comprises a chamber in the module head that is fluidically connected to the respective cavity of the membrane filter elements via a partition wall. In this way, the rinse water and / or the rinse air pass through the cavity to the rinse water drain. The clean water passes out of the interior separately via the fluidic connection between the interior and the clean water drain. The clean water drain also serves as the rinse water inlet.The flow direction from the membrane filter elements to the rinse water outlet is thus the same during filtration and backwashing, while the flow direction in the clean water outlet is reversed during filtration compared to the rinse water inlet. The flow direction in the module base is always the same during filtration and rinsing and leads into the membrane filter units, or more precisely, their cavity. The flow direction in the pores is reversed or different during filtration and rinsing.

[0036] To improve the filtering process, at least one further filter stage is provided in addition to the first filter stage described above. The further filter stage is coupled to the previous filter stage. In the further filter stage, the contaminated backwash water from the previous filter stage, i.e. the mixture of everything that was filtered out in the previous filter stage including the powdered activated carbon, is reprocessed after a predetermined time. The filtrate (pure water, pure fluid or drinking water) from the further filter stage is added back to the raw water or raw fluid of the previous filter stage. The contaminated rinse water is discharged in the same way as in the first or previous filter stage. One filter stage can be designed as a sedimentation filter stage, preferably the last filter stage. Here, the contaminated rinse water is added to a sedimentation tank. The sludge produced in the sedimentation tank, i.e.The mixture from the previous rinsing processes can now be added to the raw water of a previous filter stage, preferably the first filter stage, so that the absorption power of the powdered activated carbon can be further utilized. This creates a coherent cycle.

[0037] Further measures improving the invention are specified in the subclaims or emerge from the following description of at least one exemplary embodiment of the invention, which is schematically illustrated in the figure. In the figures, identical or similar components are designated by identical or similar reference numerals.

[0038] It shows: Fig. schematically an embodiment of a filter device for carrying out the filter method according to the invention

[0039] The figure shows schematically an embodiment of a filter device 100 for carrying out the filter method according to the invention.

[0040] At 10, a supply of raw water is provided. This is fed to the device 200 via a corresponding supply device. At 20, the supply of additional filter media takes place via a suitable supply device. In this case, the additional filter media is in the form of powdered activated carbon. The powdered activated carbon is fed to the raw water. In order to convey the raw water together with the powdered activated carbon to a membrane filter unit 40, a conveying device 30 in the form of a pump 31 is provided. The membrane filter unit 40 has a plurality of membrane filter elements 41 through or into which the raw water is conveyed from a raw water side 11 in the filter direction 12 to a pure water side 45. The membrane filter unit 40, with the corresponding connections and supply and discharge devices, forms a first filter stage 50. The pure water obtained on the pure water side 45 is discharged from the membrane filter unit 40 via the discharge 60 for further use.To clean the membrane filter unit 40, the system switches from the previously described filter operation to backwash operation. In backwash operation, the purified water obtained is pumped at 65 in the flushing direction, i.e., opposite to the filter direction 12, into the membrane filter unit 40 via a conveying device, which is designed as a pump 32 in the figure. This flushing process removes contaminants adhering to and / or in the membrane filter elements 41—intentional or unintentional—such as powdered activated carbon and / or dirt particles. This flushing process is supported by the supply of shear force-increasing agents, schematically indicated here at 70, which are supplied as compressed air via the pump 31 to the membrane filter unit 40. The compressed air assists in improving the cleaning of the membrane filter elements 41. The flushing fluid is contaminated with the contaminants adhering to the membrane filter elements 41.The injected compressed air causes the contaminated flushing fluid to float against gravity. At a flushing fluid outlet indicated at 80, the contaminated flushing fluid, which in this case is sludge-containing water, is guided to a second filter stage 100. In the second filter stage 100, the contaminated fluid is first directed into a sedimentation tank 110. There, the sludge 101 is at least partially separated from the water by sedimentation. The sludge 101, which settles in the sedimentation tank 110, is discharged for further use at 120. The water is also discharged at 130. A pump 140 is provided for this purpose. The pump 140 pumps the water from the sedimentation tank 110 into another membrane filter unit 150. Here, the filtration process takes place analogously to the first filter stage 50.The pure water or filtrate obtained in the second filter stage 100 is discharged from the membrane filter unit 150 at 160 during filter operation in the filter direction. To create an effective circuit, the pure water obtained in the second filter stage 100 is fed to the raw water at 170 to the first filter stage 50. A circuit is thus closed. During filter operation, the contaminated rinsing fluid obtained in the second filter stage 100 is discharged at 180 according to the same principle as in the first filter stage 50 and added to the contaminated rinsing fluid removed from the first filter stage 50 at 190 for further supply to the second filter stage 100. In this way, a second circuit is closed.According to the present figure, flushing fluid or flushing water is added to the line at 160, i.e., where the clean fluid obtained in the second filter stage 100 is discharged to the raw water of the first filter stage 50, at 65 (supply) via a further conveying device, which is designed here as a pump 141. In this way, the second filter stage can also be operated in filter and backwash mode. List of reference symbols

[0041] 10 Supply (raw water, first filter stage) 11 Raw water side, raw fluid side 12 Filter direction 20 Feed device (powdered activated carbon, first filter stage) 30 Conveying device 31 Pump (1, raw water / fluid) 32 Pump (2, rinsing water / fluid) 40 Membrane filter unit 41 Membrane filter elements 45 Clean water side 50 Filter stage (first) 60 Discharge (rinsing fluid) 65 Supply (rinsing fluid) 70 Supply (shear force increasing agent, compressed air) 80 Rinsing fluid discharge 100 Filter stage (second) 101 Sludge 110 Sedimentation tank 120 Discharge (sludge, sedimentation tank) 130 Discharge (water, sedimentation tank) 140 Pump (2, second filter stage, Raw water / fluid) 141Pump (2, second filter stage, rinsing water / fluid) 150Membrane filter unit (second filter stage) 160Discharge (second filter stage, filtrate) 170Supply (second filter stage to first filter stage) 180Discharge (second filter stage, contaminated rinsing fluid) 190Supply (second filter stage, contaminated rinsing fluid) 200Device

Claims

1. Method for filtering a raw fluid containing a contamination by means of at least one membrane filter unit (40), wherein the membrane filter unit (40) comprises at least one membrane filter element having membrane pores through which the raw fluid is conveyed and in the membrane pores of which or on the membrane surfaces of which dirt particles accumulate, wherein in a filtering operation the contaminated raw fluid is conveyed from a raw fluid side (11) in a filtering direction (12) through the membrane filter unit (40) to a clean fluid side, wherein the raw fluid is supplied to the membrane filter unit (40) via a pump, wherein the pressure with which the raw fluid is supplied to the membrane filter unit (40) can be selected as desired, and the filtering operation is carried out with an IN / OUT principle, wherein the raw fluid passes through the at least one membrane filter element of the membrane filter unit (40) from the inside to the outside in order to generate a clean fluid on the clean fluid side that is substantially cleaned of contaminants, and in a backflushing operation a flushing fluid is conveyed through the membrane filter unit (40) in a backflushing direction, and the backflushing operation is carried out with a OUT / IN principle, wherein the flushing fluid is forced into the at least one membrane filter element of the membrane filter unit (40) from the outside to the inside in order to clean the membrane filter unit (40) of the filtered contamination, wherein in the filtering operation an additional filter medium is added to the raw fluid on the raw fluid side (11) in order to improve the filtering, and wherein in the backflushing operation an additional shear-force-increasing agent, compressed air, is blown into the membrane filter unit (40) in order to clean the membrane filter unit (40) of the contamination and the additional filter medium in the backflushing operation, wherein powdered activated carbon is added as the additional filter medium, wherein the pressure of the flushing fluid and of the compressed air are coordinated with one another for improved backflushing, wherein the compressed air or the shear-force-increasing agent and the flushing fluid are supplied in the backflushing operation in a pressure ratio to one another in which the pressure of the shear-force-increasing agent does not exceed the pressure of the flushing fluid by more than 30%, wherein the compressed air is supplied from the raw water side.

2. Method according to claim 1, characterized in that in the backflushing operation, the contamination together with the additional filter medium is conveyed with the flushing fluid and / or the shear-force-increasing agent or the compressed air from the membrane filter unit (40) into at least one further filter stage (100) and filtered there, so that pure water is produced there again.

3. Method according to either of the preceding claims 1 and 2, characterized in that the filtering and backflushing are carried out in the at least one further filter stage (100) as in the first filter stage (50).

4. Method according to any of the preceding claims 1 to 3, characterized in that the clean fluid obtained in the further filter stage (100) is added to the clean fluid from the first filter stage (50).

5. Method according to any of the preceding claims 1 to 4, characterized in that the contamination produced in a further filter stage (100), including additional filter medium together with flushing fluid and shear-force-increasing agent, in particular compressed air, is sedimented in a sedimentation tank (110), so that a sediment sludge is formed.

6. Method according to any of the preceding claims 1 to 5, characterized in that the sediment sludge is supplied to the raw fluid of a front filter stage (50).

7. Device (200) for filtering raw fluid by means of at least one membrane filter unit (40), wherein the membrane filter unit (40) comprises at least one membrane filter element having membrane pores through which the raw fluid is conveyed and in the membrane pores of which or on the membrane surfaces of which dirt particles accumulate, wherein the device comprises the following means for carrying out a method according to any of the preceding claims 1 to 6: a filter stage (50) having at least one membrane filter unit (40), which is fluidically connected on a raw fluid side (11) to a raw fluid supply line and which is designed, in a filtering operation, to convey raw fluid in the filtering direction (12) through the membrane filter unit (40) in order to generate clean fluid on a clean fluid side, and which is fluidically connected on the clean fluid side to a flushing fluid supply line and which is designed, in a backflushing operation, to convey flushing fluid in a backflushing direction through the membrane filter unit (40) in order to clean the membrane filter unit (40) of filtered dirt particles, wherein further a supply line (70) for supplying shear-force-increasing agents, a compressed-air supply line, is provided, which is designed to blow in shear-force-increasing agents in the backflushing operation, wherein further a means supply line (20) is provided, which is designed to add an additional filter medium to the raw fluid in the filtering operation in order to improve filtering, wherein a pump is provided, which supplies the raw fluid to the membrane filter unit (40), via which pump the pressure with which the raw fluid is supplied to the membrane filter unit (40) can be selected as desired.

8. Device (200) according to claim 7, characterized in that a plurality of filter stages (50, 100) coupled to one another are provided, the corresponding clean fluid sides and / or raw fluid sides of which are or can be coupled to one another at least in part.

9. Use of a powdered activated carbon in the raw fluid in a device (200) according to any of claims 7 to 8 and / or in a method according to any of claims 1 to 6.