DEVICE FOR THE TREATMENT OF WATER TO BE PURIFYED, NAMELY FRESH WATER, SALT WATER OR BROWN WATER, IN PARTICULAR FOR THE DESALIZATION OF WATER TO BE PURIFYED; REVERSE OSMOSIS UNIT FOR THE TREATMENT OF WATER TO BE PURIFYED, NAMELY FRESH WATER, SALT WATER OR BROWN WATER, IN PARTICULAR FOR THE DESALIZATION OF WATER TO BE PURIFYED; METHOD FOR THE TREATMENT OF WATER TO BE PURIFYED, NAMELY FRESH WATER, SALT WATER OR BROWN WATER, IN PARTICULAR FOR THE DESALIZATION OF WATER TO BE PURIFYED

Description

State of the art

[0001] The invention is based on a device for treating water to be purified, namely fresh water, salt water or brackish water, in particular for desalinating water to be purified, according to the preamble of claim 1, and a method for treating water to be purified, namely fresh water, salt water or brackish water, in particular for desalinating water to be purified, according to the preamble of claim 9.

[0002] Filters are used to treat water that is to be purified, as it is necessary to remove coarse particles, suspended matter and flavors, limescale, minerals, pesticides, and nitrate. If the water to be purified, which can be freshwater, saltwater, or brackish water, is to be treated to produce drinking water, the requirements for drinking water quality are very high. Rising water consumption worldwide is leading to water shortages, making clean drinking water rare and thus an extremely precious commodity. Since water covers more than two-thirds of the Earth's surface, efforts have been underway for some time to extract drinking water from seawater (saltwater). To do this, it is essential to desalinate the seawater. Seawater desalination processes for producing drinking water are already state of the art.The disadvantage here is that these are very energy-intensive because they require either very high temperatures or electrical current if the process relies on electrolysis.

[0003] Another option for producing drinking water is reverse osmosis seawater desalination.

[0004] In reverse osmosis, the water to be purified (freshwater, saltwater, or brackish water) is forced under high pressure through a semi-permeable membrane with a pore diameter of 0.5 to 5 nm to overcome the osmotic pressure. This membrane acts like a filter and only allows certain ions and molecules to pass through. This separates the original solution. The membrane filter is particularly effective at removing salts, bacteria, viruses, excess limescale, and toxins such as heavy metals. Osmotic pressure increases with increasing salt concentration, which would eventually bring the process to a halt. Therefore, in reverse osmosis seawater desalination, the water to be purified, for example seawater, is forced under high pressure through an osmosis membrane, the semi-permeable membrane, which only allows the ultrapure water, which then becomes freshwater or drinking water, to pass through.The pressure required for this is very high and is in the range of over 50 bar for currently available devices or osmosis membranes. It can even be as high as 80 to 100 bar. To generate this pressure, for example for reverse osmosis seawater desalination, electrically driven pumps must force the seawater through the reverse osmosis membrane all day long. The disadvantage of this is the high energy consumption. Therefore, utility model DE 20 2018 001 627 U1 proposes using a tall concrete silo, in particular silos up to 100 m high, which is filled with the water to be purified to generate the required pressure. The idea behind this is that in addition to the normal atmospheric pressure (air pressure), which is approximately 1 bar, a change in depth in the water of 10 m causes a pressure change of 1 bar.Therefore, at the bottom of the 100 m high, water-filled silo, the ambient pressure is 11 bar, resulting from the sum of air pressure and water pressure. Drinking water has an osmotic pressure of less than approximately 2 bar; the pressure applied for reverse osmosis of drinking water is approximately 3 to 30 bar, depending on the membrane used and system configuration. Seawater desalination requires a pressure of approximately 50 to 80 bar, as seawater, at approximately 30 bar, has a significantly higher osmotic pressure than drinking water. The disadvantage, therefore, is that the additional pressure required for seawater desalination must still be generated by energy-consuming pumps. Energy is also required to pump the seawater into the 100 m high concrete silos.

[0005] Therefore, in the published patent application DE 10 2012 213 214 A1, a device and a method for water desalination are proposed, wherein osmosis membranes are used, whereby water can be desalinated or drinking water can be obtained simply, efficiently and reliably, since an osmosis membrane is sunk in a water depth of several hundred meters, preferably at least 500 m or 800 m, and the water pressure is applied on the inlet side of the osmosis membrane and a closed volume is arranged on the other side of the osmosis membrane, wherein essentially atmospheric pressure prevails behind the osmosis membrane, and the desalinated water (ultrapure water) is pumped through a water pipe by means of pumps driven by working animals (e.g. donkeys, horses, camels) to the water surface or onto land.To prevent the osmosis membrane from becoming clogged within a very short time, each osmosis unit must be preceded by a filter unit that filters the water to be purified (e.g. seawater), creating filtered water that can be forced through the osmosis membrane. The disadvantage is that a filter unit becomes clogged over time. On land, this would not be a significant problem, as the filters or filter unit can be replaced and cleaned again at any time and with little effort. Underwater, the situation is entirely different. Here, it is an immense effort to hoist the system to the surface, replace the filters or filter unit, and restart the system.

[0006] US 2017 / 0209834 A1 discloses a reverse osmosis unit and an upstream filter unit that can be controlled in such a way that the filter unit can be flushed with water from the reverse osmosis unit by reversing the flow direction in the filter unit. This requires the water purification process to be interrupted.

[0007] US 2007 / 0181496 A1 also discloses a reverse osmosis unit in which the upstream microfiltration modules can be flushed using purified saline, although the actual reverse osmosis must be interrupted for this process.

[0008] Reverse osmosis systems are known from the documents US 6 139 750 A, US 2015 / 307374 A1 and US 3 456 802 A, which disclose different pre-filter systems, in all of which only one flow direction is provided.

[0009] The object of the invention is therefore to provide a device for treating water to be purified, namely fresh water, salt water or brackish water, in particular for desalinating water to be purified, and a method for treating water to be purified, namely fresh water, salt water or brackish water, in particular for desalinating water to be purified, by which the disadvantages of the prior art are overcome. The invention and its advantages

[0010] The device according to the invention for the treatment of water to be purified, namely fresh water, salt water or brackish water, in particular for the desalination of water to be purified, with the features of claim 1 and the method according to the invention for the treatment of water to be purified, namely fresh water, salt water or brackish water, in particular for the desalination of water to be purified, with the features of claim 9, have the advantage that at least two filter units and one reverse osmosis unit are used to produce filtered water or ultrapure water (e.g. drinking water), wherein the reverse osmosis unit is placed centrally between the two filter units, and the filter units are mounted in mirror image on both sides of the reverse osmosis unit, wherein a first filter unit, which serves to produce filtered water, is flowed through in the flow direction by the water to be purified or water filtered by another filter,wherein the filtered water can be separated into concentrated water and ultrapure water by means of the reverse osmosis unit, wherein the mirror-image second filter unit, which is arranged downstream of the reverse osmosis unit in the flow direction, is flowed through backwards by the concentrated water, and the flow direction in the reverse osmosis unit and in the filter units can be reversed, so that the second filter unit is loaded by filtering the water to be purified and the first filter unit is rinsed free, whereby the service life of the filter units can be extended.

[0011] The device according to the invention can be used on land, on the water surface, and / or underwater. When using a filter unit with a reversible flow direction, clogging of the filter unit is reliably prevented by at least partial cleaning of the filter unit. For at least partial cleaning of the filter unit, by which the filter unit is flushed with liquid, in particular water to be purified, pre-filtered water, ultrapure water, and / or concentrated water, the flow direction within the filter unit is reversed. Thus, cleaning of the filter unit is also possible underwater.

[0012] The structure of a seawater desalination plant according to the invention, in particular a seawater desalination plant according to the invention, should preferably be modular. This allows the capacity of the plant to be dimensioned essentially by the number of similar modules (units), and only the necessary filter modules (e.g., UV light) need to be financed cost-effectively. The essential components of a module are described below.

[0013] According to an advantageous embodiment of the device according to the invention, the at least one reverse osmosis unit has at least one osmosis membrane, wherein the water filtered by the filter unit is pushed and / or sucked through the osmosis membrane(s) by means of at least one pump at high pressure, so that the filtered water can be separated into ultrapure water and concentrated water. The core component can be the reverse osmosis unit. It consists of membrane foils arranged in a cylindrical or stacked manner, onto which water to be purified (fresh water) or already enriched brine flows on the outside. The separated ultrapure water (fresh water) exits on the inside and is fed for further use, for example, to the consumer at the water surface. The necessary pressure on the outside of the osmosis membrane is provided by the hydrostatic ambient pressure at a water depth of 550 to 800 meters.If sufficient water depth is not available, the prevailing hydrostatic ambient pressure can be increased to the required 55 to 80 bar using an additional pump. Each of these modules contains a low-pressure pump that ensures turbulent flow over the film surfaces. Two valves, which allow targeted control of the flow rate, regulate the inflow of purified fresh water (ultrapure water) and the outflow of enriched brine (concentrated water). The separated fresh water is not fluidically connected to the osmosis circuit and therefore does not require flow control.

[0014] According to an additional advantageous embodiment of the device according to the invention, the liquid used for at least partially cleaning the filter unit is, in addition to the concentrated water, water to be cleaned, filtered water and / or ultrapure water.

[0015] According to an additional advantageous embodiment of the device according to the invention, the mirror-inverted second filter unit, which is arranged downstream of the reverse osmosis unit in the flow direction, is flowed through backwards with water to be purified, filtered water and / or ultrapure water in addition to the concentrated water.

[0016] According to an additional advantageous embodiment of the device according to the invention, the at least one osmosis membrane is surrounded by a pressure tank.

[0017] According to an additional advantageous embodiment of the device according to the invention, the at least one reverse osmosis unit has at least one osmosis membrane and at least one reverse osmosis unit has a pump (e.g. low-pressure pump) to generate a turbulent flow on the osmosis membrane.

[0018] At a constant channel width, low viscosity requires a higher flow velocity, and at a constant flow velocity, lower viscosity requires a smaller gap width to ensure turbulent flow. The Raynolds number itself is determined empirically for various flow geometries and allows an assessment of the presence of turbulent flow. The core of the patented idea is therefore: The osmosis membrane is constructed either in a cylindrical configuration with long channels or in a stack of round membrane plates. The pressure on the outside of the membranes is provided by the hydrostatic ambient pressure in the ocean depths. A pump (low-pressure pump) ensures a circular flow with such a high flow velocity that turbulent flow is guaranteed between adjacent membrane surfaces. Once the brine can be enriched to a salt content of approximately 10%, approximately half of the fresh water can be separated as fresh water.At the separation rate estimated above and a throughput of approximately 1.25%, this requires approximately 30 to 50 overflow processes. This means that the entire fresh water must flow past the membrane surface approximately 30 to 50 times to achieve the desired brine enrichment level of approximately 10%.

[0019] According to an additional advantageous embodiment of the device according to the invention, the at least one reverse osmosis unit has at least one osmosis membrane and water to be purified and / or water filtered through at least one filter is applied to at least one osmosis membrane at a pressure of more than 50 bar, in particular more than 80 bar.

[0020] According to an advantageous embodiment of the device according to the invention, the water to be purified and / or water filtered through at least one filter is supplied by a pump (e.g., a high-pressure pump) at the required pressure. The pressure is composed of hydrostatic ambient pressure plus additional pump pressure. This allows the inventive design to be implemented at any desired water depth. The limits are set by onshore operation with a pump pressure of up to 80 bar and submarine operation at, for example, 800 m water depth with a theoretical pressure of 0 bar.

[0021] According to an additional advantageous embodiment of the device according to the invention, a filter and / or a filter unit, depending on the arrangement, consist of a coarse and / or fine filter and / or an absolute filter and / or an activated carbon filter. Each osmosis unit must be supplied with pre-filtered water (very pure fresh water, purified, saline seawater). Therefore, a filter unit is preferably placed upstream of each osmosis unit. This essentially consists of a coarse filter for removing coarse contaminants, a fine filter for removing contaminants up to a diameter of approximately 50 micrometers, and an absolute filter with a pore size of approximately 0.2 micrometers.

[0022] According to an advantageous embodiment of the method according to the invention for the treatment of water to be purified, namely fresh water, salt water or brackish water, in particular for the desalination of water to be purified, with at least two filter units and a reverse osmosis unit, wherein the reverse osmosis unit is placed centrally between the two filter units, and the filter units are mounted in a mirror image on both sides of the reverse osmosis unit, wherein a first filter unit, which serves to produce filtered water, is flowed through in the flow direction by the water to be purified or water filtered by another filter, wherein the filtered water can be separated into concentrated water and ultrapure water by means of the reverse osmosis unit, wherein the mirror image arranged second filter unit, which is arranged downstream of the reverse osmosis unit in the flow direction, is flowed through backwards by the concentrated water,and the flow direction in the reverse osmosis unit and in the filter units is reversed, so that the second filter unit is loaded by filtering the water to be purified and the first filter unit is rinsed free, and at least one reverse osmosis unit has at least one osmosis membrane, wherein the water filtered by the filter unit is pressed and / or sucked through the osmosis membrane(s) by means of at least one pump at high pressure, so that the filtered water is separated into ultrapure water and concentrated water.

[0023] According to an additional advantageous embodiment of the method according to the invention, the mirror-image arranged second filter unit, which is arranged downstream of the reverse osmosis unit in the flow direction, is flowed through backwards in addition to the concentrated water with water to be purified, filtered water and / or ultrapure water.

[0024] According to an additional advantageous embodiment of the method according to the invention, the at least one reverse osmosis unit has at least one osmosis membrane and a turbulent flow is generated on the osmosis membrane of at least one reverse osmosis unit by means of a pump (e.g. low-pressure pump).

[0025] According to an additional advantageous embodiment of the method according to the invention, the at least one reverse osmosis unit has at least one osmosis membrane and the water to be purified and / or water filtered through another filter is applied to an osmosis membrane at a pressure of more than 50 bar, in particular more than 80 bar.

[0026] According to an advantageous embodiment of the method according to the invention, the water to be purified and / or water filtered by another filter is supplied with the required pressure by means of a pump (e.g. high-pressure pump) or the at least one reverse osmosis unit has at least one osmosis membrane and the osmosis membrane is arranged so deep in the water or in the sea that the water pressure present there is sufficient to pass through.

[0027] According to an additional advantageous embodiment of the method according to the invention, a filter and / or a filter unit are used, which consist of at least one coarse filter, at least one fine filter, at least one absolute filter, and / or at least one activated carbon filter. It is conceivable that at least one filter and / or at least one filter unit is arranged upstream and / or downstream of a gas bead filtration tank.

[0028] Further advantages and advantageous embodiments of the invention can be found in the following description, the claims and the drawings. Drawings

[0029] Preferred embodiments of the subject matter according to the invention are illustrated in the drawings and are explained in more detail below. Fig. 1 a sketchy basic structure of a reverse osmosis unit, Fig. 2 a sketchy filter unit, Fig. 3 a sketchy representation of the overflow in the reverse osmosis unit. Description of the embodiments

[0030] Fig.1 shows a sketchy basic structure of a reverse osmosis unit 1, which can preferably be used under water, where Fig. 1is reduced to functional blocks, which are described in more detail below. The reverse osmosis unit 1, which may be dispensed with when treating freshwater, is positioned centrally between two filter units 2 (filter modules), which are flanged to both sides of the reverse osmosis unit 1 in a mirror image.

[0031] The water to be purified 3 (salt water, fresh water, brackish water) or water already filtered (pre-purified) by another filter flows through a filter unit 2 in the flow direction and serves to produce filtered water, which is pressed and / or sucked through the osmosis membrane(s) by means of at least one pump (e.g. high-pressure pump) at high pressure, so that the filtered water can be separated into concentrated water 4 and ultrapure water 5. In this flow direction, the filter unit 2 thus purifies the water to be purified 3 or the water already filtered (pre-purified) by another filter, preferably in several stages, to a degree of purity that enables reverse osmosis.The mirror-image filter unit 2, which is arranged downstream of the reverse osmosis unit 1 in the flow direction, is flowed through by the water to be purified 3, filtered water, ultrapure water 5 and / or concentrated water 4 backwards, i.e. preferably from the finest to the coarsest filter of a filter unit 2, and is thus cleaned. In this arrangement, the reversal of flow causes one filter unit 2 to be loaded by filtering the water to be purified 3 and one filter unit 2 to be rinsed clean. This should significantly increase the filter service life between two maintenance intervals compared to operation with a single filter unit 2. The geometric arrangement or the capacity of the three units in a functioning device is not specified by the schematic diagram. The capacity of a system was determined by the parallel operation of similar modules.

[0032] The symmetrical design of the filter units 2 is thus an alternative to the prior art, as it allows the flow direction in the reverse osmosis unit 1 to be reversed. This makes it possible to symmetrically flange a filter unit 2 to both ends of the reverse osmosis unit 1. During operation, a filter unit 2 will then clean the seawater and feed it in its purified state to the reverse osmosis unit 1. The symmetrically arranged filter unit 2 is reversely flowed through, for example, by the enriched brine from the reverse osmosis unit 1, and rinses the filters again. This should drastically increase the service life of the filter units 2.

[0033] Swapping the reference numbers 3 and 4 indicates the flow reversal.

[0034] Fig. 2shows a schematic of a filter unit 2. The filter unit 2 is preferably composed of at least three filter modules in the direction of flow. The coarse filter 6 could, for example, be a sand filter (e.g., a sediment filter) that removes macroscopic impurities or coarse particles from the water 3 to be purified. The second module, the fine filter 7, removes particles with diameters up to approximately 50 micrometers. Finally, the absolute filter 8 consists of inert glass spheres made of, for example, ruby ​​and / or quartz with a specific diameter (e.g., 127 µm) and can reliably filter out dirt particles up to a diameter of approximately 0.2 micrometers.

[0035] The water 10 filtered through the filter modules is pumped to the reverse osmosis unit by means of a pump 11 with variable pressure to adjust the hydrostatic ambient pressure to the required pressure in order to flow around the osmosis membrane there.

[0036] By reversing the flow direction within the filter modules in flow direction 12, the filter modules loaded with filtered-out material can be cleaned by flushing.

[0037] An osmosis membrane could preferably be based on graphene, i.e. carbon layers which, despite being only one atom thick, are extremely hard and have excellent conductivity. Graphene oxide, a chemical derivative which can be produced by oxidation, could be used for the cost-effective and simple production of the osmosis membrane. Graphene oxide is applied, for example, as a solution to a substrate or porous material, creating a thin membrane. The hard layer of graphene has holes which are so small (pore diameter, for example, 1 nanometer) that only water but not salt can pass through. To prevent the graphene oxide membrane from swelling upon contact with water, which could allow smaller salts to pass through the pores, it is conceivable that extremely thin walls made of, for example, epoxy resin could be placed on both sides of the membrane to prevent this swelling.

[0038] Fig. 3shows a sketch of the overflow in the reverse osmosis unit 1. Reverse osmosis takes place on membranes whose outer surface is exposed to the filtered water 10. The inner surface, in contrast, is essentially almost hermetically sealed. But only almost, since the outer and inner surfaces are connected by extremely fine channels that allow water molecules to pass through but retain salt ions, for example.

[0039] This diffusion of water molecules from the outside to the inside requires a significant pressure difference in the range of 55 to 80 bar. The reverse osmosis process can only occur if the outside of the membrane is subjected to turbulent flow. Otherwise, the pores that enable reverse osmosis become instantly clogged. Since the separation rate of ultrapure water 5 (fresh water) is low compared to the overflowing mass flow, a low-pressure circulation pump 13 (low-pressure pump) is additionally used, which serves to create turbulent flow over the outer surface of the reverse osmosis membrane 6. The mass flow overflowing the reverse osmosis membrane 14 is many times greater, estimated at a factor of 30 to 50, than the supplied, purified ultrapure water 5. The separated ultrapure water 5 (fresh water) is withdrawn via a high-pressure pump 15 (pressure requirement up to 80 bar) and pumped to the surface.The concentrated water 4 leaves the reverse osmosis unit 1 and is released into the environment, e.g. the sea.

[0040] The osmosis membrane 14 of the reverse osmosis unit 1 is surrounded by a pressure tank, inside which a pressure of 80 bar prevails, depending on the water pressure surrounding the pressure tank or the pump 11. If the water depth is sufficient, the pump 11 is not necessary. Thus, the pump 11 is used if the water pressure is less than 80 bar, in order to compensate for the missing difference. The pump 11 is absolutely necessary if the pressure tank is to be operated on land or on the water. The concentrated water 4 leaves the reverse osmosis unit 1 through a valve (pressure relief valve), which opens, for example, at a pressure of 77 bar. The ultrapure water 5 has a very low pressure when leaving the reverse osmosis unit 1, which may be 0 bar.To control the fresh water outflow from the reverse osmosis unit 1, the electrical conductivity of the ultrapure water 5 is preferably used, since the electrical conductivity is an indicator of the purity of the water, so that a low electrical conductivity signals a high degree of purity and a higher electrical conductivity signals a lower degree of purity.

[0041] Depending on the degree of contamination and salt content of the water to be purified, reverse osmosis unit 1, which can be operated on land, on water or underwater, may be dispensed with, so that ultrapure water 5 can be provided by treatment using gas bead filtration and / or using filter unit 2, which may also have a UV light module and / or a microplastic module and / or a centrifuge for purifying the water. Reference number list

[0042] 1Reverse osmosis unit 2Filter unit 3Water to be purified 4Concentrated water 5Ultrapure water 6Coarse filter 7Fine filter 8Absolute filter 9Layer filter 10Filtered water 11Pump 12Flow direction 13Low-pressure pump 14Osmosis membrane, reverse osmosis membrane 15High-pressure pump

Claims

1. A device for treating water (3) to be purified, more specifically fresh water, salt water, or brackish water, in particular for the purpose of desalinating water (3) to be purified, said device having at least two filtering units (2) and a reverse osmosis unit (1), wherein the reverse osmosis unit (1) is placed centrally between the two filtering units (2) and the filtering units are flange-mounted on either side of the reverse osmosis unit (1) in a mirror-inverted manner, wherein the water (3) to be purified or the water (10) that has been filtered by another filter passes, in the flow direction, through a first filtering unit (2) which serves for producing filtered water (10), wherein the filtered water may be separated into concentrated water (4) and ultrapure water (5) by means of the reverse osmosis unit (1), characterised in that the concentrated water (4) passes, in a backward direction, through the mirror-symmetrically disposed second filtering unit (2) which is arranged downstream of the reverse osmosis unit (1) when considered in the flow direction, and in that the flow direction in the reverse osmosis unit (1) and in the filtering units may be inverted, such that the second filtering unit (2') is charged by a filtering of the water (3) to be purified and the first filtering unit (2) is flushed clear.

2. The device as claimed in claim 1, characterised in that the at least one reverse osmosis unit (1) has at least one osmosis membrane (14), wherein the filtered water (10) that has been filtered by the filtering unit (2) is pressed and / or sucked through the osmosis membrane (14), or through the osmosis membranes (14), at a high pressure by means of at least one pump (11), such that the filtered water (10) may be separated into ultrapure water (5) and concentrated water (4).

3. The device as claimed in claim 1 or claim 2, characterised in that in addition to the concentrated water (4), also water (3) to be purified, filtered water (10) and / or ultrapure water (5) pass, in a backward direction, through the mirror-symmetrically disposed second filtering unit (2), which is arranged downstream of the reverse osmosis unit (1) when considered in the flow direction.

4. The device as claimed in any of the preceding claims, characterised in that the at least one reverse osmosis unit (1) has at least one osmosis membrane (14) and said at least one osmosis membrane (14) is surrounded by a pressure tank (24).

5. The device as claimed in any of the preceding claims, characterised in that the at least one reverse osmosis unit (1) has at least one osmosis membrane (14) and at least one reverse osmosis unit (1) has a pump (13) for the purpose of creating a turbulent flow at the osmosis membrane (14).

6. The device as claimed in any of the preceding claims, characterised in that the at least one reverse osmosis unit (1) has at least one osmosis membrane (14) and in that water (3) to be purified and / or water (10) that has been filtered by at least one filter is applied against at least one osmosis membrane (14) with a pressure of more than 50 bar, in particular of more than 80 bar.

7. The device as claimed in claim 6, characterised in that the water (3) to be purified and / or the water (10) filtered by at least one filter is applied with the required pressure by means of a pump (11).

8. The device as claimed in any of the preceding claims, characterised in that a filtering unit (2) consists of at least one coarse filter (6), at least one fine filter (7), at least one absolute filter (8), and / or at least one activated carbon filter (20).

9. A method of treating water (3) to be purified, more specifically fresh water, salt water, or brackish water, in particular for the purpose of desalinating water (3) to be purified, said method involving at least two filtering units (2) and a reverse osmosis unit (1), wherein the reverse osmosis unit (1) is placed centrally between the two filtering units (2) and the filtering units are flange-mounted on either side of the reverse osmosis unit (1) in a mirror-inverted manner, wherein the water (3) to be purified or the water (10) that has been filtered by another filter passing, in the flow direction, through a first filtering unit (2) which serves for producing filtered water (10), wherein the filtered water may be separated into concentrated water and ultrapure water (5) by means of the reverse osmosis unit (1), characterised in that the concentrated water (4) passes, in a backward direction, through the mirror-symmetrically disposed second filtering unit (2), which is arranged downstream of the reverse osmosis unit (1) when considered in the flow direction, and in that the flow direction in the reverse osmosis unit (1) and in the filtering units is inverted, such that the second filtering unit (2') is charged by a filtering of the water (3) to be purified and the first filtering unit (2) is flushed clear.

10. The method as claimed in claim 9, characterised in that in at least one reverse osmosis unit (1) which has at least one osmosis membrane (14), the filtered water (10) that has been filtered by the filtering unit (2) is pressed and / or sucked through the osmosis membrane (14), or through the osmosis membranes (14), at a high pressure by means of at least one pump (11), such that the filtered water (10) is separated into ultrapure water (5) and concentrated water (4).

11. The method as claimed in claim 9 or claim 10, characterised in that in addition to the concentrated water (4), also water (3) to be purified, filtered water (10) and / or ultrapure water (5) pass, in a backward direction, through the mirror-symmetrically disposed second filtering unit (2), which is arranged downstream of the reverse osmosis unit (1) when considered in the flow direction.

12. The method as claimed in any one of claims 9 to 11, characterised in that the at least one reverse osmosis unit (1) has at least one osmosis membrane (14) and a turbulent flow is created at the osmosis membrane (14) of at least one reverse osmosis unit (1) by means of a pump (13).

13. The method as claimed in any one of claims 9 to 12, characterised in that the at least one reverse osmosis unit (1) has at least one osmosis membrane (14) and the water (3) to be purified and / or the water (10) that has been filtered by another filter is applied against an osmosis membrane (14) with a pressure of more than 50 bar, in particular of more than 80 bar.

14. The method as claimed in claim 13, characterised in that the water (3) to be purified and / or the water (10) that has been filtered by another filter is applied with the required pressure by means of a pump (11) or in that the at least one reverse osmosis unit (1) has at least one osmosis membrane (14) and said osmosis membrane (14) is disposed sufficiently deep in the water or in the sea such that the water pressure reigning at this depth is sufficient for the water to pass therethrough.

15. The method as claimed in any one of claims 9 to 14, characterised in that a filtering unit (2) is used that consists of at least one coarse filter (6), at least one fine filter (7), at least one absolute filter (8), and / or at least one activated carbon filter (20).