Filter and water treatment device for removing micro- or nano-scale plastic particles from water

Abstract

The present invention relates to a filter (1) for removing micro- or nano-scale plastic particles (6) from water, the filter (1) comprising a filter medium (3; 3a) through which water can flow. Advantageously, the filter medium (3; 3a) comprises spheres (4, 5, 14-17; 4a, 5a, 14a-17a), the spheres (4, 5, 14-17; 4a, 5a, 14a-17a) comprising a layer (7) adapted to receive the plastic particles (6), the spheres (4, 5, 14-17; 4a, 5a, 14a-17a) being in a bidisperse sphere packing arrangement. The bidisperse sphere packing arrangement of the coated layer advantageously allows a very high packing density to be achieved and allows a very high flow through the filter to be set up.

Description

[Technical field]

[0001] The present invention relates to a filter for removing micro- or nano-scale plastic particles from water, the filter comprising a filter medium through which water can flow.The present invention further relates to an apparatus for water treatment, in particular for removing micro- or nano-scale plastic particles from water.

[0002] Nanoscale plastic particles have a particle size between 1 nm and 100 nm, while microscale plastic particles have a particle size between more than 100 nm and less than 35 μm. Such nanoscale or microscale plastic particles, which in particular include polyethylene (PE), polypropylene (PP) or polyethylene terephthalate (PET), can be ingested by living organisms through drinking water and accumulate in the body, especially in the internal organs, as well as in the blood and brain, which can cause serious health damage. For example, inflammation of the blood vessel walls of the human aorta (e.g., https: / / journals.plos.org / plosone / article?id=10.1371 / journal.pone.0260181, last accessed on April 19, 2023) or stretching and rupture of cell membranes (e.g., https: / / www.pnas.org / doi / 10.1073 / pnas.2104610118, last accessed on April 19, 2023).

[0003] For the treatment of drinking water, it is known to use filters, which in particular remove limescale and ions from tap water, and furthermore activated carbon filters are known for purifying water contaminated by bacteria.

[0004] Other filters are known from Chinese Patent Application Publication No. 108926880, US Patent Application Publication No. 2006 / 0260997 and US Pat. No. 6,361,710.

[0005] German Patent Application No. DE 102020132439 A1 discloses a filter with a filter medium that is provided with a hydrophobic layer for adsorbing micro- or nano-scale plastic particles. This publication also discloses a pressurized water treatment device. It is a disadvantage that with nano- or micro-scale plastic particles, high pressures are required or long treatment times must be accepted in order to achieve the required filter performance.

[0006] The problem on which the invention is based is to provide a filter of the type mentioned at the outset, which makes it possible to overcome the disadvantages of prior art filters.

[0007] According to the invention, this problem is solved in that the filter medium comprises spheres, which have a layer configured to receive plastic material particles, the spheres forming a bidisperse sphere packing arrangement.

[0008] The term acceptance refers to both absorption and adsorption, absorption or adsorption, in particular adsorption, ie deposition in a layer which at least partially, in particular completely, covers the sphere surface.

[0009] A sphere within the meaning of the present invention is an object which may deviate from a perfect spherical shape within the scope of technical manufacturing tolerances, for example an ellipsoid is considered to be a sphere within the meaning of the present invention as long as the deviation between its smallest and largest radii does not exceed 4%.

[0010] A bidisperse sphere packing is a sphere packing in which spheres of a first size are intermingled with spheres of a second size. The size of the spheres can be determined in particular by the diameter. A bidisperse sphere packing in the sense of the present invention has only spheres of a first size and spheres of a second size, taking into account manufacturing tolerances. In contrast to a bimodal distribution, in a bidisperse sphere packing in the sense of the present invention, there are no spheres with a size between the size of the first sphere and the size of the second sphere, taking into account manufacturing tolerances. It is considered a disadvantage that such spheres with intermediate sizes occupy intermediate spaces in the filter, which can significantly reduce the flow through the filter. The possible throughput, i.e. the flow performance, can be significantly reduced.

[0011] In one example of a bidisperse sphere packing, for example, spheres with a diameter of 3 mm are mixed with spheres with a diameter of 1 mm. The advantage of bidisperse sphere packing is that the packing density that can be achieved is particularly high, at which the intermediate space between the relatively large spheres can be occupied by the relatively small spheres, and at the same time a particularly large specific surface is achieved, to which the plastic particles removed from the water to be treated can adhere. Bidisperse sphere packing advantageously leads to a filter with optimal filter performance.

[0012] It is conceivable that a first size of the bidisperse sphere packing is adapted to remove a first type of plastic particles from the water, while a second size of the bidisperse sphere packing is provided to remove a second type of plastic particles. This is in particular achieved by means of different coating materials. For example, the first size of the spheres can be adapted to remove polypropylene (PP) and the second size of the spheres can be adapted to remove polymethylmethacrylate (PMMA).

[0013] Additionally, the spheres may be arranged in a polydisperse sphere packing, which would require three different sizes of spheres, and a tetradisperse sphere packing which would require four mutually different sizes of spheres.

[0014] Furthermore, the present invention is based on the problem of providing a water treatment device which can be operated in the water pipe network of a building, for example at a kitchen tap of a house, where the usual water pressure in a building is between 2 and 6 bar, which is sufficient to remove plastic particles, and at the same time in the water pipe network of a building with a volume flow rate of between 5 and 15 l / min, which is typical for such a water pipe network.

[0015] This object is achieved by the water treatment device according to the invention.

[0016] The inventors have realised that by appropriately selecting the sphere parameters of the spheres arranged in a bidisperse sphere packing, in particular the sphere diameter, or the volume fraction of the spheres in the filter medium, the filter properties can be tailored, in particular very high packing densities can be achieved whilst simultaneously increasing the flow rate through the filter.

[0017] It is furthermore possible to ensure that a very high filter performance is achieved, i.e. that a very large number of plastic particles are removed, which is achieved in particular by the fact that the specific surface area of ​​the filter medium is particularly large, i.e. that the surface area of ​​all the coated spheres arranged in a bidisperse sphere packing is particularly large and is available for receiving the plastic particles to be removed from the water.

[0018] The sphere may be a hollow sphere or a solid sphere.

[0019] Preferably, the packing density of the spheres is between 55% and 90% by volume, in particular between 65% and 80% by volume, particularly preferably between 71% and 76% by volume. The term vol% refers to the total volume of the filter medium. For example, a percentage of 90% by volume means that 90% of the volume of the filter medium is occupied by the spheres, and 10% by volume is available as space for the water to be treated to flow through. The above-mentioned volume percentages allow a very high flow rate through the filter and a low pressure drop between the inlet and outlet sides.

[0020] In one embodiment of the present invention, the ratio K of the first diameter d2 of the sphere to the second diameter d1 of the sphere is d is between 0.10 and 0.35, preferably between 0.20 and 0.31, particularly preferably 0.3. d is defined as the quotient of the diameter d2 of the second type of sphere and the diameter d1 of the first type of sphere, where d1>d2. d and in a defined first diameter d1, d1 is K d The second diameter d2 can be determined by multiplying it by K d It is understood that σ is not always 1, because otherwise there would be no bidisperse sphere packing.

[0021] The inventors have d It has been recognized that when is less than 0.10, the flow rate that can pass through a filter according to the invention falls below a flow rate value that still allows for utilization, for example, under unpressurized conditions of the filter.

[0022] Ratio K greater than 0.35 d Although the flow rate through the filter does increase, the filter performance decreases because the total spherical surface area is no longer sufficient to accommodate the micro- or nano-scale plastic particles that are to be removed from the water.

[0023] The inventor, K dIt has been found that a ratio of =0.3 results in a very high performance filter with high flow rate and high purification capacity.

[0024] In another embodiment of the invention, the sphere diameter d1 is greater than the sphere diameter d2 and is between 0.95 mm and 1.05 mm, preferably between 0.98 mm and 1.02 mm, particularly preferably 1.0 mm. This diameter of the first type of spheres arranged in a bidisperse sphere packing has been found to be particularly advantageous in order to provide a sufficiently large specific surface area of ​​the filter medium capable of adsorbing almost all plastic particles from the water to be purified.

[0025] In one embodiment of the present invention, the ratio K of the volume fraction p2 of the spheres in the total sphere volume of the filter medium to the volume fraction p1 of the spheres in the total sphere volume of the filter medium is P is between 0.4 and 0.9, preferably between 0.45 and 0.70, particularly preferably between 0.49 and 0.61. P is defined as the quotient of the volume fraction p2 of the second type of spheres (having a diameter d2) and the volume fraction p1 of the first type of spheres (having a diameter d1), where p1+p2=1. The volume fractions represent the fraction of spheres with diameter d1 and the fraction of spheres with diameter d2 based on the total volume of spheres in the filter media. For example, the ratio K p A ratio of 0.5 means that the volume fraction p1 of spheres having a diameter d1 is twice as large as the volume fraction p2 of spheres having a diameter d2. This means that two-thirds of the total sphere volume in the filter medium is classified as spheres having a diameter d1. The inventors have found that the above range results in a filter that is particularly economical to manufacture.

[0026] Advantageously, the filter medium has a length in the flow direction of the filter between 3 cm and 12 cm, preferably between 4 cm and 10 cm, particularly preferably 8 cm or 9 cm. Experiments and flow simulations have shown that filter media with such lengths have particularly good purification performance. If the filter medium has a length of 9 cm, it is possible to remove almost all plastic particles having a size between 1 nm and 10 μm from the water. On the other hand, with a length of 8 cm, it is possible to remove almost all plastic particles having a size between 10 μm and 30 μm from the water. Depending on the length of the filter medium, the purification performance can be tailored. Advantageously, the filter according to the invention can be used in many ways.

[0027] In another embodiment of the invention, the volume flow rate at which water can flow through the filter is between 4 l / min and 15 l / min, preferably between 7 l / min and 12 l / min. Advantageously, it can be used in daily life without additional pressurization, in particular in daily life at home for additional drinking water purification.

[0028] In another embodiment of the invention, the spheres contain a material with an activatable surface, preferably silicon dioxide. Besides silicon dioxide (SiO2), the use of technical ceramics, in particular zirconium dioxide (ZrO2) or aluminum oxide (Al2O3), is conceivable. However, the spheres preferably consist of SiO2. By activation of the surface, silanol and / or hydroxide groups, depending on the material, are formed, which bond very strongly with the coating material. Advantageously, it is ensured that the coating material, in particular the coating material formed from plastic, does not peel off. Activation of the surface is carried out, for example, with the so-called piranha solution (peroxomonosulfuric acid; 3 parts concentrated sulfuric acid and 1 part 30% by weight hydrogen peroxide solution) or by plasma, for example the so-called plasma etching.

[0029] Preferably, the layer is made of a hydrophobic or hydrophilic material, in particular a hydrophobic or hydrophilic material selected from the group consisting of trichlorosilane, cellulose, polyamide and polyethylene glycol, or the layer is made of a material having an electric dipole moment and selected from the group consisting of polytetrahydrofuran, polymethylmethacrylate and zeolite.

[0030] The trichlorosilane is preferably octadecyltrichlorosilane. The layer with trichlorosilane, especially octadecyltrichlorosilane (OTS), is hydrophobic and suitable for receiving nano- or micro-scale plastic particles. The layer with cellulose, polyamide and / or polyethylene glycol (PEG) is hydrophilic. Hydrogen bonds can be formed between the layer and the plastic particles to absorb them. The hydrophilic layer can remove especially polyurethane (PU), polycarbonate (PC), polyamide (PA), polyvinyl chloride (PVC), phenolic resin, polymethylmethacrylate (PMMA) and polypropylene (PP) from drinking water.

[0031] It is also conceivable that the layer is formed from a material with a permanent electric dipole moment, preferably tetrahydrofuran and / or natural zeolite. It is further conceivable that the layer is formed from a carbon molecular sieve. The zeolite can be natural or synthetic. If the layer comprises a material with a permanent electric dipole moment, then polyurethane (PU), polycarbonate (PC), polyamide (PA) in particular can be removed particularly well from drinking water.

[0032] In one embodiment of the invention, the layer is made of a material with a permanent dipole and is configured to induce a dipole in non-polar plastic particles, preferably acetone and / or polymethylmethacrylate (PMMA). When the layer comprises a material with a permanent dipole, in particular polymethylmethacrylate (PMMA), polyamide (PA) and polypropylene (PP) can be particularly well removed from drinking water.

[0033] Advantageously, the layer comprises a material having a π-conjugated system and preferably selected from the group consisting of activated carbon, graphene, organic zeolites and polycyclic aromatic hydrocarbons. The polycyclic aromatic hydrocarbons are in particular selected from the group consisting of naphthalene, anthracene, benzopyrene, acenaphthylene, acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, benzanthracene, coronene, ovalene, tetracene, pentacene, chrysene, perylene, benzo[a]fluoranthene, benzo[j]fluoranthene, pentaphene, hexacene, heptaphene, heptacene, trinaphthylene and superphenalene. The use of mesitylene and xylene is also conceivable.

[0034] Layers having a π-conjugated system make it possible, in particular, to remove polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) or polystyrene (PS) from water.

[0035] In one embodiment of the present invention, the layer is formed from a hydrophobic or hydrophilic material selected from the group consisting of cellulose, polyamide and polyethylene glycol, or the layer is formed from a material having an electric dipole moment and selected from the group consisting of polytetrahydrofuran, polymethylmethacrylate and zeolite, and / or the layer comprises a material having a π-conjugated system.

[0036] The inventors have realized that the hydrophobic layer with trichlorosilane is indeed suitable for accepting nano- or micro-scale plastic particles, however, a coating other than the aforementioned coating provides a better acceptance of the nano- or micro-scale plastic particles. Advantageously, when a coating material other than the coating material with trichlorosilane is used, a filter with a 3% to 10% higher filter performance can be obtained.

[0037] In one embodiment of the invention, the filter medium has a number of regions arranged one behind the other in the flow direction of the filter, each region adapted to remove specific plastic particles from the water. Advantageously, a single filter can be used universally to remove different plastic particles from drinking water. This is particularly important for filters intended for home use.

[0038] It is conceivable that adjacent regions are identically formed with respect to the size of the spheres, i.e., with respect to the bidisperse sphere packing, and thus have the same hydrodynamic properties, and the spheres of the individual regions are only differentiated from one another by a coating. It is further conceivable that the regions have mutually different hydrodynamic properties. For example, a first region may contain a bidisperse sphere packing having a lower packing density than an adjacent second region. Also, the diameter d of the spheres of the first region may be different from that of the first region. 1,1 and d 2,1 is the diameter d of the sphere in the adjacent second region 1,2 and d 2,2 The same applies to the sphere volume fraction p 1,1 , p 1,2 and p 2,1 , p 2,2 Ratio of K p , and the ball diameter d 1,1 , d 1,2 and d 2,1 , d 2,2 Ratio of K d This can also be considered.

[0039] For example, a first region may be provided for removing polyethylene (PE) particles and a second region may be provided for removing polymethylmethacrylate (PMMA) particles.

[0040] It is further conceivable that each zone has two different types of spheres, which, besides their size, also differ in coating material. For example, a first type of sphere of the bidisperse sphere packing can be configured to remove a first type of plastic particles, while a second type of sphere of the bidisperse sphere packing in the respective zone can be configured to remove a second type of plastic particles. Advantageously, the filter according to the invention as well as the water treatment device according to the invention can be tailored to a specific application.

[0041] Advantageously, the filter material is rotationally symmetric, preferably cylindrical, and is axially flowable. Boundary layer effects, which reduce filter performance, are advantageously minimized or prevented.

[0042] In another embodiment of the invention, the spheres of adjacent regions have different layers. The spheres of each region have a bidisperse sphere packing and are covered by a layer configured to receive a specific type of plastic particles. For example, the spheres of a first region can have a layer comprising a coating material with an electric dipole moment, while the spheres of a second region can have a layer comprising a hydrophobic material and the spheres of a third region can have a layer comprising a hydrophilic material. Advantageously, a universally usable filter with high filter performance is provided. Advantageously, an apparatus for water treatment, in particular an apparatus for removing micro- or nano-scale plastic particles from water, comprises a filter according to any one of claims 1 to 12.

[0043] In one embodiment of the water treatment device according to the invention, the water treatment device can be operated by hydrostatic pressure or by the pipe pressure of the building's water mains, which means that the water from which the plastic particles are to be purified can flow through the filter medium under the force of gravity in the water column located above the filter.

[0044] The inventors have provided a filter with a bidisperse sphere packing of coated spheres that allows almost complete removal of nano- or micro-scale plastic particles from drinking water despite their small size without high pressure, so that the water treatment device according to the invention can advantageously be operated with the mains pressure of a building's water mains. A filter cartridge provided with a filter according to the invention can be installed in, for example, a kitchen tap and used to treat tap water.

[0045] In the following, the invention will be explained in more detail on the basis of examples and the accompanying drawings which refer to these examples. [Brief description of the drawings]

[0046] [Figure 1] FIG. 1 illustrates a water treatment device according to the present invention including multiple embodiments of a filter according to the present invention. [Diagram 2] FIG. 2 shows details of a filter according to the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] In Fig. 1a, a filter 1 of a water treatment device 2 is shown diagrammatically in a longitudinal section and comprises a cylindrical filter medium 3. The water treatment device 2 is intended for installation in a tap, not shown in Fig. 1. The filter medium 3 is formed from SiO2 spheres 4, 5, which are arranged in a bidisperse sphere-packed arrangement and are covered by a layer 7 for receiving plastic particles 6, as shown in detail in Fig. 1c. For the sake of clarity, only some of the spheres 4, 5 of the filter medium 3 are shown in Fig. 1a and not all of them are numbered. The sphere 4 has a diameter d1, whereas the sphere 5 has a diameter d2.

[0048] Water can enter the filter 1 through an inlet tube 9 extending coaxially with the cylinder axis 8 and, after passing through the filter medium, can exit the filter 1 through an outlet tube 10 extending coaxially with the cylinder axis. The filter medium 3 has a length of 9 cm in the flow direction.

[0049] In Fig. 1b, the filter 1, which is shown diagrammatically in a longitudinal section, differs from the filter shown in Fig. 1a in that the filter medium 3 has three regions 11, 12, 13, in which the coated SiO2 spheres 4, 5, 14, 15, 16, 17 are arranged in a bidisperse sphere packing arrangement. Here, the spheres 4, 5 have a layer which comprises a material different from that of the layer of the spheres 14, 15, which also have a material different from that of the layer coating the spheres 16, 17. All the regions 11, 12, 13 are accommodated in a single filter housing, which is not given a reference number. With the filter 1 according to Fig. 1b, the removal of different kinds of micro- or nano-scale plastic particles is advantageously achieved.

[0050] In the embodiment according to Fig. 1b, the SiO2 spheres 4, 5 in the region 11 are covered by a layer containing polyamide, while the SiO2 spheres 14, 15 in the region 12 are covered by a layer comprising polyethylene glycol (PEG). The SiO2 spheres 16, 17 in the region 13 are covered by a layer comprising polymethylmethacrylate (PMMA). A water treatment device 2 with a filter 1 is provided, which is particularly suitable for removing polyurethane (PU), polypropylene (PP) as well as polymethylmethacrylate (PMMA) from drinking water.

[0051] It is also conceivable that region 13 comprises SiO2 spheres coated with activated carbon. In this embodiment, spheres 4, 14, 16 are of the same size, and spheres 5, 15, 17 are of the same size, although this is not essential.

[0052] Furthermore, the spheres 4 and 5 in the region 11 have two diameters d 11,1 and d 11,2 and the diameter of these two is d 11,1 and d 11,2 is the diameter d of the spheres 14 and 15 in the region 12. 12,1 and d 12,2 Unlike their diameter d 12,1 and d 12,2 Also, the diameter d of the spheres 16 and 17 in the region 13 13,1 and d 13,2 It is possible that the actual results are different.

[0053] It is further conceivable that the SiO2 spheres 4, 5 in the region 11 are covered by different layers from each other. The same is conceivable for the SiO2 spheres 14, 15 in the region 12 as well as the SiO2 spheres 15, 17 in the region 13. For ease of illustration, only some of the spheres 4, 5, 14-17 of the filter medium 3 are shown in the regions 11-13.

[0054] To produce a filter 1 with a filter medium 3 according to FIG. 1b, in a housing of the filter 1, which is not numbered in FIG. 1, the regions 11-13 are filled in succession with the corresponding bidisperse sphere mixtures.

[0055] For example, known filter materials, in particular activated carbon, are used, it being understood that further regions can be provided in which they are especially of spherical construction and are present as a bidisperse sphere packing.

[0056] Reference is now made to Figure 2. In Figure 2, parts that are identical or act similarly are given the same reference numbers as in Figure 1, but the corresponding reference numbers are each suffixed with the letter a.

[0057] Table 1 shows, by way of example, three suitable filter media 31, 32 and 33 with bidisperse sphere packing and their flow characteristics and the relationship to sphere parameters. Details of filter media 32 and 33 are shown in Figures 2a and 2b.

[0058] [Table 1]

[0059] The sphere parameters mean: d1: Diameter of the relatively large spheres (4, 14, and 16 in Figure 1) d2: Diameter of the relatively small spheres (5, 15, and 17 in Figure 1) p1: The volume ratio of the relatively large sphere to the total sphere volume p2: The volume ratio of the relatively small spheres to the total sphere volume K d :Ratio of d2 to d1 K p :Ratio of p2 to p1 Packing density: The volume fraction of spheres in the total volume of the filter medium. Specific surface area: the total surface area of ​​spheres 4, 5, 14-17 in the filter medium Volumetric flow: The volumetric flow through a filter medium during water treatment

[0060] A portion of filter media 3a, shown in perspective view in FIG. 2a, is formed in accordance with configuration 2 of Table 1, ie, filter media 32.

[0061] A portion of filter media 3a, shown in perspective view in FIG. 2b, is formed in accordance with configuration 3 of Table 1, ie, filter media 33.

[0062] The hatched surfaces in Figures 2a and 2b are cross-sections of some of the individual spheres shown, some of which do not pass through the sphere centres of the respective spheres, which gives a poor visual impression and accordingly there exists a sphere packing which differs from the bidisperse sphere packing.

[0063] Table 2 shows three particularly suitable filter media with bidisperse sphere loading. 1’ , 3 2’ and 3 3’ is shown as an example.

[0064] [Table 2]

[0065] Configuration 3 1’ For example, when the length of the filter medium, i.e. the size in the flow direction, is 8.0 cm, a filter efficiency of more than 99.0% is achieved, i.e. more than 99.0% of plastic particles (here, polyethylene) having a size between 250 nm and 10 μm are removed from the water flowing through a filter with this filter medium. Here, a flow velocity of 0.02 m / s is achieved at a volume flow of 6.5 l / min. The filter medium is cylindrical with a diameter of 9 cm.

[0066] In the following, various possibilities for coating the SiO2 spheres are explained by way of example:

[0067] Example 1: To produce a filter medium from spheres in a bidisperse sphere packing arrangement, SiO2 spheres with a diameter of 1.00 mm and SiO2 spheres with a diameter of 0.30 mm are placed in a so-called piranha solution (3 parts concentrated sulfuric acid and 1 part 30% by weight hydrogen peroxide) for 60 minutes and then rinsed with distilled water, followed by acetone and ethanol. Drying is carried out at 130°C for 60 minutes. To coat the spheres with a layer with polyethylene glycol (PEG), the dried spheres are placed in a solution prepared by mixing 3.54 g of polyethylene glycol in 1.0 liter of toluene with 0.9 g of triethylamine (TEA) acting as a catalyst and treated with ultrasound for 5 minutes. After being removed from the ultrasound bath, the spheres are rinsed with distilled water and dried at 130°C for 60 minutes. Such a coating is hydrophilic and is suitable for removing, for example, polycarbonate (PC) or polyamide (PA) particles from water.

[0068] Example 2: To produce a filter medium from spheres in a bidisperse spherical packing arrangement, SiO2 spheres with a diameter of 1.0 mm and SiO2 spheres with a diameter of 0.225 mm are rinsed with ethanol, dichloromethane and deionized water for cleaning. Polytetrahydrofuran (THF) is then mixed with dichloromethane in a 1:1 ratio and stirred using a so-called vortex mixer. This mixture is then mixed with 7 Vol% (based on the volume of the mixture) of trifluoroacetic acid and the cleaned spheres are immersed in it for 10 minutes for coating. After cleaning with ethanol, the coated spheres are dried at 130°C for 30 minutes. Such a coating has an electric dipole moment and is suitable for removing, for example, polycarbonate (PC) and polyamide (PA).

Claims

1. A filter (1) for removing micro- or nano-scale plastic particles (6) from water, comprising: The filter medium (3; 3a) has a filter through which the water can pass, The filter (1), characterized in that the filter medium (3; 3a) comprises spheres (4, 5, 14-17; 4a, 5a, 14a-17a), the spheres (4, 5, 14-17; 4a, 5a, 14a-17a) having a layer (7) adapted to receive the plastic particles (6), the spheres (4, 5, 14-17; 4a, 5a, 14a-17a) forming a bidisperse sphere packing arrangement.

2. 2. The filter according to claim 1, characterized in that the packing density of the spheres (4, 5, 14-17; 4a, 5a, 14a-17a) is between 55 vol.% and 90 vol.%, preferably between 65 vol.% and 80 vol.%, particularly preferably between 71 vol.% and 76 vol.%.

3. A first diameter d of said sphere (5, 15, 17; 5a, 15a, 17a) ２ and a second diameter d of the sphere (4, 14, 16; 4a, 14a, 16a). １ Relative to K ｄ 3. The filter according to claim 1, wherein the .lambda. is between 0.10 and 0.35, preferably between 0.20 and 0.31, particularly preferably 0.

3.

4. The diameter d of said spheres (4, 14, 16; 4a, 14a, 16a) １ The diameter d of the sphere (5, 15, 17; 5a, 15a, 17a) ２ 4. The filter according to claim 1, wherein the thickness of the filter is greater than 1.0 mm and is between 0.95 mm and 1.05 mm, preferably between 0.98 mm and 1.02 mm, particularly preferably 1.0 mm.

5. The volume fraction p of the spheres (4, 14, 16; 4a, 14a, 16a) in the total sphere volume in the filter medium (3; 3a) １ The volume fraction p of the spheres (5, 15, 17; 5a, 15a, 17a) in the total sphere volume in the filter medium (3; 3a) ２ The ratio of K ｐ 5. The filter according to claim 1, wherein the θ is between 0.4 and 0.9, preferably between 0.45 and 0.70, particularly preferably between 0.49 and 0.

61.

6. 6. The filter according to claim 1, wherein the filter medium (3; 3a) has a length in the flow direction of the filter (1) of between 3 cm and 12 cm, preferably between 4 cm and 10 cm, particularly preferably 8 cm or 9 cm.

7. 7. A filter according to any one of claims 1 to 6, characterized in that the volume flow rate at which water can flow through the filter (1) is between 4 l / min and 15 l / min, preferably between 7 l / min and 12 l / min.

8. Filter according to any one of claims 1 to 7, characterised in that the spheres (4, 5, 14-17; 4a, 5a, 14a-17a) comprise a material with an activatable surface, preferably silicon dioxide.

9. 9. The filter according to claim 1, wherein the layer (7) is made of a hydrophobic or hydrophilic material, in particular a hydrophobic or hydrophilic material selected from the group consisting of trichlorosilane, cellulose, polyamide and polyethylene glycol, or the layer is made of a material having an electric dipole moment and selected from the group consisting of polytetrahydrofuran, polymethylmethacrylate and zeolites.

10. 10. The filter according to any one of claims 1 to 9, characterized in that the layer (7) comprises a material having a π-conjugated system and selected in particular from the group consisting of activated carbon, graphene, organic zeolites and polycyclic aromatic hydrocarbons.

11. 11. The filter according to claim 1, wherein the filter medium (3; 3a) has a plurality of regions (11-13) arranged one behind the other in the direction of flow through the filter (1), each region (11-13) being adapted to remove specific plastic particles (6) from the water.

12. 12. The filter according to claim 11, characterized in that the spheres (4, 5, 14-17; 4a, 5a, 14a-17a) of adjacent regions (11-13) have mutually different layers (7).

13. 13. An apparatus (2) for water treatment, in particular for removing micro- or nano-scale plastic particles (6) from water, comprising a filter (1) according to any one of claims 1 to 12.

14. 14. The water treatment device according to claim 13, characterized in that the device (2) can be operated by hydrostatic pressure or by the pipe pressure of the building's water mains.

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