ARRANGEMENTS FOR A FILTRATION SYSTEM AND A SEAFOOD AND METHOD FOR OPERATING THE ARRANGEMENT

Description

[0001] The invention relates to an arrangement comprising a basin and a filtration system for filtering the water in the basin, wherein the basin is designed as a settling basin. The invention further relates to a method for operating the arrangement.

[0002] The invention is particularly applicable to wastewater treatment plants. Increasingly stringent demands are being placed on the treatment performance of wastewater treatment plants. These plants are generally structured in three stages. They typically have a first treatment stage in the form of mechanical treatment / primary clarification, a second treatment stage in the form of an aeration stage and a secondary clarifier, and a third treatment stage in the form of phosphate precipitation.

[0003] Secondary clarifiers are typically designed as settling tanks, in which a clear water zone forms through sedimentation. The water in this clear water zone flows into or is directed to an outlet. Generally, the water entering the outlet is discharged into a receiving water body.

[0004] Due to the relatively high pollution load of the wastewater requiring treatment, particularly high levels of contaminants, existing wastewater treatment plants have insufficient purification capacity. As a result, the water in the clear water zone contains excessively high concentrations of pollutants, such as microplastics, pharmaceutical residues, hormones, X-ray contrast agents, and germs, especially multi-resistant germs. Furthermore, floating and swollen sponges are present. In particular, low-capacity receiving waters must be protected from the discharge of excessive amounts of pollutants.

[0005] To reduce the pollutant load of the wastewater treated in the sewage treatment plant, it is planned that sewage treatment plants will have a further purification stage, a so-called 4th purification stage.

[0006] Retrofitting existing wastewater treatment plants with an additional treatment stage is also advisable or even necessary, particularly if their secondary clarifiers have insufficient depth and / or are hydraulically overloaded during combined sewer overflow. Furthermore, secondary clarifiers can become overloaded if the amount of dry solids in the aeration tank needs to be increased due to the increasing load on the treatment plant.

[0007] The next purification stage can take the form of wastewater filtration or have a filtration of the wastewater.

[0008] The construction of a filtration plant is technically complex, as it requires the construction of appropriate filter systems with storage tanks, pumps, and a balancing basin for backwashing. These systems may need to be protected from the elements by structures. This significantly increases the space required for the wastewater treatment plant. Due to this additional space requirement, retrofitting existing three-stage wastewater treatment plants is problematic.

[0009] Wastewater treatment plants with a filtration device arranged in a basin are known from the prior art. German patent application AT 403 374 B discloses a compact small-scale wastewater treatment plant in which a filter is installed upstream of the outflow channel of a secondary clarifier. Further devices for water purification, which include a filter, are known from German patent applications DE 93 16 554 U1, DE 197 20 983 A1, and DE 2 261 203 A.

[0010] From US 2 878 935 A, an arrangement of a settling tank and a filtration system for filtering the water of the settling tank is known, which has the features of the preamble of claim 1.

[0011] Further state of the art includes US 5 804 062 A, US 4 743 382 A, WO 93 / 23335 A1, US 1 379 095 A, US 3 473 661 A and US 5 227 076 A.

[0012] The object of the present invention is to further develop an arrangement having the features of the preamble of claim 1 in such a way that the arrangement is particularly space-saving and retrofitting existing wastewater treatment plants, especially municipal wastewater treatment plants, with the filtration system is particularly simple and cost-effective, and in particular, continuous operation is ensured. Furthermore, it is an object of the invention to provide a method for operating the arrangement.

[0013] This problem is solved by an arrangement having the features of claim 1. Furthermore, the problem is solved by a method according to claim 13.

[0014] The filtration system is used to filter the water of a settling basin, in particular a settling basin of a wastewater treatment plant.

[0015] In this context, a settling basin is understood to be a virtually flow-free basin in which substances present in the water, particularly solids such as sludge from an upstream aeration basin, are sedimented by gravity, thus enabling the separation of settleable solids from the water. In the upper part of the water in the settling basin, a so-called clear water zone forms as a result of sedimentation; this zone is free or essentially free of settling substances.

[0016] Secondary clarifiers in sewage treatment plants are typically designed as settling tanks.

[0017] The filtration system comprises at least two filtration devices. Each filtration device has an inlet opening for the water from the pool to be filtered. The water entering the filtration device through the inlet opening flows through a filtration medium within the device. The filtration system includes a first collection line to receive the filtered water flowing out of each filtration device and to convey the filtered water to a common outlet. This outlet can then, for example, discharge into a receiving water body. Furthermore, the filtration devices are backwashable.

[0018] The filtration medium of the filtration device retains suspended solids and fine particles, especially floating sludge, as well as pollutants such as microplastics, etc., which are still present in the pool water. This results in particularly good purification of the water fed into the common outlet.

[0019] The filtration system with multiple filtration units has the advantage that the required filtration capacity can be distributed across several units. This simplifies manufacturing, transport, and installation, particularly when retrofitting existing tanks, such as existing settling tanks in wastewater treatment plants, with the filtration system.

[0020] Furthermore, a filtration system with at least two filtration devices has the advantage that the filtration devices can operate independently or at least largely independently of each other.

[0021] It should be noted here that the at least two filtration devices are not "connected in series" but "connected in parallel." "Connected in series" means that the water filtered by the first of the at least two filtration devices is fed to the second of the at least two filtration devices. Therefore, the proper operation of a filtration system with two filtration devices connected in series requires that both devices are operational.

[0022] The at least two filtration devices of the filtration system according to the invention, however, operate independently or at least largely independently of each other and are therefore "connected in parallel". Thus, one or more of the filtration devices of the at least two filtration systems can be taken out of operation, whereby in this state no filtration of the water takes place by the inactive filtration devices, and the remaining filtration devices can continue to operate and thus filter the water.This makes it possible, with sufficient filter capacity of the remaining filtration devices, to take one or more of the at least two filtration devices out of service, for example to repair, maintain, clean, in particular backwash or to replace the filtration medium, without stopping the operation of the filtration system, so that water from the pool can continue to be filtered and wastewater can therefore continue to be supplied to the pool.

[0023] The overall filtration performance of the filtration system can also be regulated by commissioning or decommissioning the filtration devices.

[0024] Because the filtration devices are backwashable, the filtration medium coated with filtered substances can be cleaned particularly easily.

[0025] The backwashing of the filtration device can be carried out, for example, with process or purified wastewater.

[0026] It is quite conceivable that air is blown or sucked into the filtration medium during backwashing, especially to loosen the filtration medium.

[0027] One of the at least two filtration units can be backwashed independently of the other filtration units, and / or several of the at least two filtration units can be backwashed independently of the other filtration units. Thus, while one or more filtration units are being backwashed, the remaining filtration units can remain in operation. The amount of backwash water required is less than with a single, larger filtration unit with the same overall filtration capacity. This has a positive effect on the space requirements of the filtration system, the amount of backwash water needed, and the sizing of the inlet and / or outlet pipes for the backwash water.

[0028] Preferably, each filtration device can be backwashed independently of the other filtration devices. In this embodiment, the multiple filtration devices can thus be backwashed independently of one another, so that each filtration device can be backwashed separately.

[0029] However, it is also quite conceivable that several filtration units can be backwashed together and independently of the other filtration units. For example, in a filtration system with six filtration units, two filtration units can be backwashed together and independently of the other four filtration units.

[0030] With regard to backwashing, it is considered advantageous if the respective filtration device has an inlet opening for rinsing water for the purpose of backwashing the filtration medium.

[0031] It is quite conceivable and preferred that the inlet opening for the rinse water is formed by an outlet opening of the respective filtration device for the filtered water.

[0032] The first collection line gathers the filtered water from at least two filtration units before it is fed into the common outlet. This offers the advantage of a particularly simple way to regulate the flow rate of the entire filtered water, for example, by controlling the flow rate of the water from the first collection line to the common outlet. Because the at least two filtration units are connected via the first collection line, there is no need for complex separate controls for each individual filtration unit.

[0033] Furthermore, the first collection line has the advantage that, even if one filtration device is out of service, water is still supplied to the other filtration devices of the first collection line, thus largely avoiding the drying out of pipes in the filtration system.

[0034] Preferably, the first collecting pipe is arranged in the basin, in particular below the water level of the basin.

[0035] Preferably, the filtration system has at least five filtration devices, more preferably at least twenty filtration devices, and in particular at least fifty filtration devices.

[0036] In a preferred embodiment, the filtration medium comprises or is formed by a filter bed. The bed is, in particular, a sand and / or gravel bed.

[0037] Preferably, the filter bed rests on a perforated filter base of the filtration device.

[0038] The filtration medium can also consist of another suitable material. For example, the filtration medium can be designed as a microfabric, e.g., as a three-dimensional microfabric, or as a membrane.

[0039] In a further advantageous embodiment, the water to be filtered flows through the filtration medium in a vertical or substantially vertical direction. In this context, it is considered particularly advantageous if the inlet opening is located above the filtration medium and / or an outlet opening for the filtered water is located below the filtration medium. Preferably, one opening area of ​​the inlet extends horizontally or substantially horizontally.

[0040] To remove the rinse water, the filtration device is provided with an outlet opening to remove the rinse water flowing through the filtration medium during backwashing.

[0041] Preferably, the supplied rinse water can leave the filtration device exclusively through the outlet opening. This prevents rinse water from escaping the inlet opening and thus avoids disturbing the water in the basin. The contaminated rinse water exiting the outlet opening can then be fed back into the basin or a cleaning stage upstream of the basin, or returned to the cleaning process.

[0042] The outlet opening is preferably formed on one side of the filtration medium opposite the inlet opening, in particular above the filtration medium.

[0043] It is provided that the respective filtration device includes a sealing means for closing the inlet opening.

[0044] It is designed that the sealing agent closes the inlet opening during backwashing of the filtration device under the influence of the backwash water. With this design of the sealing agent, it is considered particularly advantageous that, after backwashing has finished, the sealing agent opens the inlet opening under the influence of the water pressure from the settling tank.

[0045] In an advantageous embodiment, the filtration system includes a control device for regulating the flow rate of the filtered water supplied to the common outlet, wherein the control device is arranged between the first collecting pipe and the common outlet. Preferably, the control device regulates the flow rate of the filtered water such that the water level in the basin remains constant regardless of the inflow rate of water supplied to the basin.

[0046] Preferably, the control device comprises a control shaft, wherein the filtered water is fed into the control shaft, the control shaft having an outlet leading into the drain, and wherein a device for regulating the difference between a water level in the control shaft and a water level in the basin is arranged in the control shaft. Thus, the difference between the water level in the settling basin and the water level in the control shaft can be adjusted such that a flow resistance generated by the filtration devices and, if applicable, other elements of the filtration system is overcome.

[0047] The device for regulating the difference between the water level in the control shaft and the water level in the basin is preferably a mobile weir.

[0048] Preferably, the water level in the control shaft is regulated in such a way that the water level in the basin remains constant regardless of the amount of water supplied to the basin.

[0049] It is quite conceivable that the filtration system, in particular the respective filtration device, includes a conveying device for conveying the filtered water. Preferably, the conveying device is a pump. Preferably, the conveying device is operated in such a way that the water level in the basin remains constant regardless of the amount of water supplied to the basin.

[0050] Preferably, the respective filtration device has a first line for supplying the filtered water to the first collecting line, wherein the first line has a first control valve for regulating a volume flow of the filtered water through the first line, in particular for closing the first line.

[0051] This allows the flow rate of the filtered water to be regulated. Furthermore, during backwashing of the filtration system, it prevents rinse water from entering the collection line by closing the first line using the first control valve.

[0052] It is considered advantageous if the filtration device has a second line for supplying the rinsing water to the filtration device, preferably the second line opening into the inlet opening for the rinsing water, wherein the second line has a second control valve for regulating the volume flow of the rinsing water through the second line, in particular for closing the second line.

[0053] This allows the flow rate of the rinse water to be regulated. Furthermore, when the filter is in operation, the filtration device can be prevented from discharging filtered water through the second line.

[0054] The respective control valve can be designed, for example, as a gate valve, solenoid valve or pinch valve.

[0055] It is quite conceivable that a section of the first pipe also forms a section of the second pipe, especially if the inlet opening is formed by the outlet opening.

[0056] In an advantageous further development, the filtration system has a second collecting line for receiving the rinse water flowing out of the respective filtration device, in particular from the respective outlet opening.

[0057] Preferably, the second collecting pipe is arranged outside the basin, in particular above the water level of the basin.

[0058] With regard to the sterilization and disinfection of the water, the filtration system in a preferred embodiment includes an irradiation device for irradiating the filtered water with ultraviolet radiation, in particular with radiation in a wavelength range of 200 nm to 280 nm.

[0059] The irradiation device can be located in the area of ​​the manifold and / or in the area of ​​the first line. Preferably, the first manifold or the first line is designed as a pipeline, with a radiation source of the irradiation device arranged inside the pipeline. Preferably, the radiation source is arranged concentrically in the pipeline.

[0060] It is considered particularly advantageous if the respective filtration device includes an irradiation unit. This has the advantage that the amount of water to be irradiated by the irradiation unit is relatively small, since the flow rate of the filtered water through the respective filtration device is lower than the total flow rate of the filtered water discharged to the outlet. This allows the use of less powerful irradiation units. Furthermore, the filtration system can continue to operate even if one or more irradiation units fail, as only the filtration unit corresponding to the failed irradiation unit needs to be taken out of service.

[0061] Preferably, the filtration system includes a device for introducing, in particular for bubbling, ozone into the water, wherein the ozone is supplied to the water to be filtered in the area of ​​the filtration device and / or the ozone is supplied to the filtered water. For example, the introduction of ozone can neutralize pharmaceutical residues.

[0062] Ozone is preferably introduced before the filtration medium.

[0063] Preferably, the filtration system contains activated carbon.

[0064] It is considered particularly advantageous if the activated carbon is located downstream of the device for introducing ozone in the direction of flow of the filtered water, since the substances oxidized by the ozone can typically be separated by means of the activated carbon.

[0065] It is quite conceivable that the filtration medium contains activated carbon.

[0066] However, it is also quite conceivable that the activated carbon is located downstream of the filtration medium.

[0067] Preferably, the respective filtration device has a section containing activated carbon.

[0068] Preferably, the filtration system, and in particular the respective filtration device, includes a flow sensor and / or pressure sensor for measuring the flow rate of the filtered wastewater or for measuring the pressure of the filtered wastewater. The sensor can be used, for example, to detect a malfunction of the filtration device. In particular, the sensor enables the determination of the filter performance of the respective filtration device.

[0069] It is particularly conceivable that if a limit value for the flow rate or volume flow of the water, or for the pressure or pressure difference is undershot, the corresponding filtration device is automatically backwashed.

[0070] In the arrangement of the filtration system and a basin according to the invention, the basin is designed as a settling basin. The inlet opening of the respective filtration device is located in a clear water zone of the settling basin. The arrangement of the inlet in the clear water zone of the settling basin has the advantage that only water from the clear water zone is supplied to the respective filtration device. The water supplied to the respective filtration device is therefore already free or substantially free of impurities from the wastewater supplied to the settling basin, since a large proportion of the impurities have already settled. This has a beneficial effect on the service life, the filter performance, and the maintenance and cleaning intervals of the filtration devices.

[0071] In the arrangement of the filtration system and a basin according to the invention, the filtration devices are arranged within the basin, in particular the filtration devices are arranged below the water level of the basin. Such an embodiment is particularly suitable for retrofitting an existing basin, especially a settling basin, with filtration in a simple and particularly space-saving manner.

[0072] Preferably, the filtration devices are arranged in a peripheral area of ​​the basin. This ensures good accessibility. Furthermore, the clear water zone in the peripheral area of ​​a basin designed as a settling tank typically exhibits the lowest concentration of substances that settle out through sedimentation, which has a beneficial effect on the service life and / or maintenance interval of the filtration medium.

[0073] It is considered advantageous if the filtration devices are arranged evenly distributed in the perimeter area of ​​the basin.

[0074] If the filtration units are arranged in the perimeter of the basin, particularly radially on the outside or on one side of a basin that is rectangular in the area of ​​the water surface, the filtration units generate a directed flow within the basin – radially or longitudinally. This ensures a substantially uniform supply to the filtration units and thus uniform treatment of the water, even when wind is acting on the water surface in the basin. In particular, each filtration unit experiences a substantially equal hydraulic load, resulting in a substantially uniform discharge of water and thus preventing short-circuiting of the water flow.

[0075] In particular, a decentralized arrangement and thus the distribution of the water outflow creates a uniform hydraulic load on the filtration equipment and thus a uniform flow in the basin.

[0076] It is considered advantageous if water can only flow out of the basin through the filtration devices. This ensures that only filtered water enters the common drain and, if necessary, from there into the receiving water body.

[0077] Preferably, the first collecting pipe is arranged in the basin, in particular below the water level of the basin.

[0078] Preferably, the second collecting pipe is arranged outside the basin, in particular above the water level of the basin.

[0079] The inventive method for operating the filtration system with at least two filtration devices is carried out such that during the backwashing of one or more filtration devices, at least one of the other filtration devices is in operation.

[0080] The term "in operation" means that the filtration device is in a state in which water flows into the filtration device via the inlet opening and the incoming water is filtered through the filtration medium.

[0081] It is entirely conceivable that the filtration units are backwashed individually. It is also entirely conceivable that several filtration units are backwashed together while the other filtration units are in operation. It is also entirely conceivable that the filtration units are backwashed in groups, for example, in pairs.

[0082] According to the invention, during backwashing of the filtration device, the inlet opening is closed by means of the sealing device. This prevents the backwash water from escaping from the inlet opening and flowing into the settling tank, which would lead to significant disturbance of the water in the settling tank, which in turn would negatively affect the sedimentation of the substances contained in the water.

[0083] According to the invention, during backwashing of the filtration device, the rinse water acts on the sealing element in such a way that it closes the inlet opening. Thus, the sealing element and the inlet opening form a type of check valve. Preferably, after the rinsing process is complete, the water pressure from the basin acts on the sealing element in such a way that it releases the inlet opening. This eliminates the need for active control of the sealing element.

[0084] Preferably, the backwashing of the respective filtration device is carried out in a time-dependent manner, particularly at fixed time intervals. Specifically, the filtration devices are backwashed at staggered intervals.

[0085] It is quite conceivable that the backwashing of the respective filtration device is triggered depending on a flow rate or volume flow of the filtered water flowing out of the respective filtration device and / or the water pressure of the filtered water.

[0086] It is considered particularly advantageous if the first collecting pipe and / or the second collecting pipe and / or the first pipe and / or the second pipe is designed as a pipeline.

[0087] The figures illustrate the invention using a preferred embodiment, but are not limited to this embodiment. They show: Fig. 1 Settling tank with an embodiment of the filtration system in a top view, Fig. 2 A filtration device of the filtration system according to Figure 1 in a state where water is filtered by means of the filtration device, in a sectional view, Fig. 3. The filtration device according to Figure 2 in a sectional view in a state where the filtration device is being backwashed, in a sectional view.

[0088] The one in Fig. 1The depicted filtration system serves to filter the water of a basin 1. Basin 1 is designed as a settling basin. Basin 1 has a circular cross-section. The wastewater to be treated flows into basin 1 from a central shaft 2 and radially outwards. Basin 1 has a diameter of approximately 20 m. The filtration system comprises several, namely thirty-two, filtration devices 3. These are evenly spaced around the perimeter of basin 1 and attached to a wall of basin 1.

[0089] The respective filtration device 3 is arranged below the water level of the basin 1.

[0090] How to Fig. 2 and 3 As can be seen, the respective filtration device 3 has an inlet opening for water to be filtered from the basin 1, wherein the inlet opening is located in the area of ​​a clear water zone of the basin 1.

[0091] The Fig. 2shows the filtration device 3 in a state in which the water is filtered by means of the filtration device 3.

[0092] The filtration device 3 has an inlet opening for the water to be filtered, the inlet opening being closable by means of a closure device 4. In the Fig. 2 In the depicted state, the inlet opening is open. The water to be filtered enters the respective filtration device 3 through the open inlet opening and flows through a filtration medium 5 of the filtration device 3. In this case, the water to be filtered flows vertically from top to bottom through the filtration medium 5, thus in the direction of arrow 16.

[0093] In the Fig. 2In the depicted state, the filtered water flows into a first line 7 for discharge, the first line 7 of the filtration device 3 opening into a first collecting line 9. The remaining filtration devices 3 are identically designed, with the first line 7 of the remaining filtration devices 3 also opening into the collecting line 9.

[0094] The first collecting pipe 9 is located below the water level of basin 1. Collecting pipe 9 is designed concentrically with basin 1.

[0095] The filtered water is fed to a common outlet via the first collecting pipe 9. The filtration system includes a control chamber 14, which is located between the first collecting pipe 9 and the outlet 15. The first collecting pipe 9 feeds the filtered water to the control chamber 14, which has an outlet opening into the outlet 15. A device, in particular a mobile weir, is located in the control chamber 14 to regulate the difference between the water level in the control chamber 14 and the water level in the basin 1.

[0096] The filtration device 3 has a second line 10, wherein the second line 10 opens into the first line 7. Thus, a section of the first line 7 formed between the junction and the filtration device 3 also forms a section of the second line 10.

[0097] In a section of the first line 7, which is formed between the junction of the second line 10 into the first line 7 and the first collecting line 9, the first line 7 has a first control valve 8 for regulating the flow rate, in particular for closing the first line 7.

[0098] The second line 10 has a second control valve 11 for regulating the flow rate, in particular for closing the first second line 10.

[0099] Rinsing water can be introduced into the filtration device 3 via the second line 10 for the purpose of backwashing the filtration medium 5.

[0100] In the Fig. 2In the depicted state, the second control valve 11 is closed and the first control valve 8 is open. Thus, the water to be filtered flows through the open inlet opening into the filtration device 3, and the filtered water flows via the first line 7 into the first collecting line 9.

[0101] The Fig. 3 shows the filtration device 3 in a state where the filtration device 3 is being backwashed.

[0102] In the Fig. 3In the depicted state, the second control valve 11 is open and the first control valve 8 is closed. The rinse water, which may be, for example, process water or treated wastewater, flows through the second line 10 into the first line 7 and from there into the filtration device 3. The introduced rinse water flows through the filtration medium 5 in the opposite direction to the flow direction of the water during filtration, in this case vertically from bottom to top, thus in the direction of arrow 17. This causes accumulated dirt and impurities to be dissolved from the filtration medium 5 and carried away by the rinse water.

[0103] Under the influence of the rinsing water flowing towards the sealing device 4 and / or the pressure of the rinsing water, the sealing device 4 closes the inlet opening. The sealing device 4 and the inlet opening thus form a kind of check valve. This prevents the rinsing water and any substances carried with it from escaping from the inlet opening and flowing into basin 1, which would, among other things, lead to significant disturbance of the water in basin 1, which in turn would negatively affect the sedimentation of the substances.

[0104] The filtration device 3 has an outlet opening 18 for discharging the backwash water flowing through the filtration medium 5 during backwashing. The outlet opening 18 of the respective filtration device 3 is connected by means of a third line 12 to a second collecting line 13, which serves to receive and discharging the backwash water. This second collecting line 13 is attached to the wall of the basin 1 and is arranged above the water level of the basin 1 to prevent water from the basin 1 from flowing into the second collecting line 13.

[0105] The rinse water can be directed via the second collecting pipe 13 into the inlet of an upstream cleaning stage and / or basin 1.

[0106] After successful backwashing of the filtration device, the first control valve 8 opens and the second control valve 11 closes. The water pressure from the water in basin 1, acting on the sealing element 4, reopens the sealing element 4, and the water to be filtered can flow into the filtration device 3 through the inlet opening.

[0107] Preferably, the filtration devices 3 are backwashed individually and at staggered intervals. Reference symbol list

[0108] 1 Basin 2 Basin center shaft 3 Filtration device 4 Sealing agent 5 Filtration medium 6 Filter base 7 First line 8 First control valve 9 First manifold 10 Second line 11 Second control valve 12 Third line 13 Second manifold 14 Control shaft 15 Drain 16 Arrow 17 Arrow 18 Outlet opening

Claims

1. Arrangement comprising a tank (1) and a filtration system for filtering the water in the tank (1), wherein: the tank (1) is in the form of a settling tank; the filtration system has at least two filtration units (3) connected in parallel; each filtration unit (3) has an inflow opening for water in the basin (1) that is to be filtered; each inflow opening is located in the region of a clear water zone of the settling tank (1); the water that is to be filtered entering each filtration unit (3) through the inflow opening flows through a filtration medium (5) in the filtration unit (3); the filtration units (3) are back-flushable; one filtration unit (3) of the at least two filtration units (3) can be back-flushed independently of the rest of the filtration units (3) and / or multiple filtration units (3) of the at least two filtration units (3) can be back-flushed jointly and independently of the rest of the filtration units (3); the filtration units (3) are located inside the tank (1); the filtration system has a first header line (9) for receiving the filtered water flowing out of each filtration unit (3) and for feeding the filtered water to a common outflow (15); each filtration unit (3) has an outlet opening (18) for discharging the flushing water flowing through the filtration medium (5) during the back-flushing operation; and each filtration unit (3) has a closure means (4) for closing the inflow opening, characterized in that the closure means (4) closes the inflow opening under the action of the flushing water when the filtration unit (3) is being back-flushed.

2. Arrangement according to Claim 1, wherein each filtration unit (3) can be back-flushed independently of the rest of the filtration units (3).

3. Arrangement according to one of Claims 1 to 2, wherein, after the back-flushing has ended, the closure means (4) opens the inflow opening under the action of the water pressure in the settling tank (1).

4. Arrangement according to one of Claims 1 to 3, wherein the filtration system has a control device for controlling a volume flow of the filtered water fed to the common outflow (15), the control device being located between the first header line (9) and the common outflow (15), in particular the control device having a control hopper (14) for receiving the filtered water, the control hopper (14) having an outlet emerging into the common outflow (15), a device for controlling the difference between a water level in the control hopper (14) and a water level in the tank (1) being located in the control hopper (14).

5. Arrangement according to one of Claims 1 to 4, wherein each filtration unit (3) has a first line (7) for feeding the filtered water to the first header line (9), the first line (7) having a first control valve (8) for controlling a volume flow of the filtered water through the first line (7), in particular for closing the first line (7).

6. Arrangement according to one of Claims 1 to 5, wherein the filtration unit (3) has a second line (10) for feeding the flushing water to the filtration unit (3), the first line (10) having a second control valve (11) for controlling the volume flow of the flushing water through the second line (10), in particular for closing the second line (10).

7. Arrangement according to one of Claims 1 to 6, wherein the filtration system has a second header line (13) for receiving the flushing water flowing out of each filtration unit (3), in particular out of each outlet opening (18).

8. Arrangement according to one of Claims 1 to 7, wherein the filtration system, preferably each filtration unit (3), has an irradiation device for irradiating the filtered water with ultraviolet radiation, in particular with a radiation in a wavelength range of 200 nm to 280 nm.

9. Arrangement according to one of Claims 1 to 8, wherein the filtration system has a unit for introducing, in particular for bubbling, ozone into the water, the ozone being fed to the water to be filtered in the region of each filtration unit (3) and / or the ozone being fed to the filtered water.

10. Arrangement according to one of Claims 1 to 9, wherein the filtration system, preferably the filtration medium (5) in each filtration device (3), comprises activated carbon, in particular the activated carbon is downstream of the ozone introducing unit in the direction of flow of the filtered water.

11. Arrangement according to one of Claims 1 to 10, wherein the first header line (9) is located inside the tank (1), in particular the first header line (9) is located below a water level in the tank (1).

12. Arrangement according to one of Claims 1 to 11, wherein the first header line (9) and / or the second header line (13) and / or the first line (7) and / or the second line (10) is in the form of a pipeline.

13. Method for operating the arrangement according to one of Claims 1 to 12, wherein, during the back-flushing of one or more filtration units (3), at least one of the rest of the filtration units (3) is in operation, preferably the filtration units (3) are back-flushed individually and at different times.