METHOD AND APPARATUS FOR REMOVING RADIOACTIVE NUCLIDES FROM WATER

Description

[0001] The present invention relates to a method for removing radioactive nuclides from water, comprising the features of the preamble of claim 1. The invention further relates to a system for removing radioactive nuclides from water, comprising the features of the preamble of claim 12.

[0002] Water is a precious resource in many countries, including numerous African and Arab states, where extensive measures must be taken to meet the demand for drinking and process water. In some countries, significant quantities of water are extracted from deep wells or supplied via seawater desalination plants. However, a problem arises from the fact that water from deep wells very often contains very high levels of radioactive nuclides and heavy metal salts such as iron and manganese salts. In particular, the isotopes 226<Ra and 228<Ra are found in deep well water, as well as 228<Th, which is part of the same decay chain, where Ra represents radium and Th represents thorium. These radioactive nuclides are primarily formed by the decay of naturally occurring uranium.In deep groundwater, radioactive nuclides are generally present both as dissolved ions and bound to very small suspended mineral particles. Water containing radioactive nuclides can therefore be referred to as contaminated water. Product water generated using a process or system of the type mentioned above, from which the radioactive nuclides have been largely removed, can therefore be called decontaminated water. This product water can then be used as drinking water or process water, or further treated to become drinking water or process water.

[0003] Deep groundwater can generally be purified using reverse osmosis, a process that can remove large portions of the contaminants it contains. To prevent excessive strain on the reverse osmosis membranes, several pre-treatment steps are typically performed before the reverse osmosis process. These pre-treatment steps can include filtration, for example, to remove suspended particles, precipitated heavy metal compounds, and the radioactive nuclides bound to them.

[0004] Sand filters, for example, can be used for such filtration tasks. However, these sand filters have several disadvantages. After a few months, such high quantities of radioactive nuclides regularly accumulate in the sand filters that they must be replaced. Regeneration of the filters is not practical. Their disposal is problematic simply because of the extraordinarily large quantities of contaminated sand.

[0005] Furthermore, the radioactive nuclides contained in deep groundwater, such as radium or thorium ions, are not adequately removed by a sand filter alone. Therefore, attempts are made to precipitate the radioactive nuclides chemically before the deep groundwater enters the sand filter. The resulting radioactive precipitates can then be retained in the sand filter. For example, water-soluble barium salts, such as barium chloride, can be used to precipitate radioactive nuclides. However, barium chloride is a relatively toxic and expensive chemical.

[0006] From WO 2013 / 034442 A1, a method and a system for removing radioactive nuclides from water of the type mentioned above are known. In the generic method, an adsorption additive that acts as an absorber for the nuclides is used, and a filter device that is essentially impermeable to the adsorption additive and the nuclides adsorbed to it. Manganese dioxide is primarily used as the adsorption additive in the known method. The known system comprises at least one filtration station containing at least one filter device in a filter basin through which a water flow can pass. Furthermore, the known system comprises at least one dosing device for adding the adsorption additive to the water flow.In the known system, the adsorption additive is added to the water flow within a mixer with a downstream mixing basin in a mixing station located upstream of the filtration station. Within the mixing basin, the water flow has a relatively long residence time, which is necessary for a homogeneous distribution of the adsorption additive. A homogeneous distribution of the adsorption additive within the water flow promotes the adsorption of the radionuclides contained in the water flow. In the known system or process, the removal of the radionuclides from the water thus occurs because the radionuclides bind to the adsorption additive within the mixing basin, i.e., upstream of the respective filter unit. For this purpose, the adsorption additive must be continuously supplied to the water flow in the mixing station. This addition is carried out, for example, at a maximum concentration of 10 ppm.Due to the long residence time in the mixing station, a large proportion of the nuclides contained in the water can be adsorbed by the adsorption additive. In the subsequent filtration station, the adsorption additive, along with the adsorbed nuclides, is then filtered out. During this process, a so-called filter cake ("cake layer") can form on an upstream surface of the respective filter unit. This cake layer grows uniformly and slowly throughout the entire filtration process and consists of deposited impurities, primarily the adsorption additive with adsorbed nuclides, as well as any other particulate impurities that may be present in the water. In the known process, the adsorption of the nuclides onto the adsorption additive thus occurs within the mixing station and therefore upstream of the filtration station.

[0007] Using such a conventional system or process, a maximum of 80% of radionuclides can currently be removed from water in a single-stage process. Therefore, further measures are necessary to achieve drinking water quality. In particular, the process can be applied in several stages, i.e., multiple times, to achieve the desired high filtration efficiency. Accordingly, the known processes and systems are comparatively complex to implement.

[0008] Furthermore, established processes and systems assume that the entire water flow receives uniform treatment during a pretreatment phase in which the radionuclides are absorbed using the adsorption additive. This results in only consistent water quality being achieved throughout the entire process. Demand-based partial flow treatment with varying removal rates for specific radionuclides is either impossible or only achievable with significant technical effort using conventional methods or systems.

[0009] For optimal mixing and adsorption of the radionuclides, a residence time of approximately 30 minutes in the respective mixing tank is required. This necessitates that the mixing tank be dimensioned accordingly, depending on the volume flow of the water stream to be purified. Consequently, the effort required to implement such a system also increases.

[0010] From FR 2 624 758 A1, finished ceramic filters as a cartridge with manganese dioxide as an adsorbent are known.

[0011] EP 1 820 565 A1 discloses Fe(OH)3 as a blocking agent in the form of a cover layer on the ceramic-based filter membrane.

[0012] US 4 636 367 A teaches the removal of radium from water using soluble barium salts and quartz sand filtration.

[0013] The present invention addresses the problem of providing an improved embodiment for a method or plant of the type described above, which is characterized in particular by a particularly high degree of separation and / or by simplified implementation.

[0014] This problem is solved by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

[0015] The invention is based on the general concept of carrying out the adsorption of nuclides onto the adsorption additive directly at the respective filter device by creating an adsorption layer on an upstream surface of the respective filter device using the adsorption additive. The adsorption layer can be created in the manner of a filter cake by adding the adsorption additive upstream of the respective filter device to a water flow passing through it. During operation of the respective system or during the execution of the process, the contaminated water first flows through the adsorption layer and then through the filter device. As it flows through the adsorption layer, the entrained nuclides are adsorbed, while the respective filter device retains the adsorption additive with the adsorbed nuclides in the adsorption layer.

[0016] The adsorption layer consists largely of the adsorption additive, at least at the beginning of a filtration phase of a filtration process, i.e., at least 50%, preferably at least 75%, and particularly at least 90%. Other components of the adsorption layer can be formed by suspended particles that may also be present in the water flow. The adsorption additive is a single chemical or a mixture of at least two different chemicals, each chemical acting as an adsorber for a specific nuclide. For example, a mixture of chemicals that act as adsorbers for different nuclides is conceivable. The realization of a multilayer adsorption layer is also particularly advantageous.For example, a first layer could be applied to the upstream surface, consisting of the respective adsorption additive that has an adsorbing effect on the interfering nuclides, while a second layer could then be applied to the first layer, consisting of a different chemical that can adsorb other water constituents, for example, those that can interfere with the adsorption of the nuclides.

[0017] Within this adsorption layer, there is an extremely high concentration of adsorption additive, so that when water contaminated with radioactive nuclides flows through the adsorption layer, efficient adsorption of the nuclides occurs. According to the invention, the adsorption of the nuclides is thus shifted to the area of ​​the respective filter device, namely to the respective adsorption layer. In this respect, the respective filter device acts like an adsorption filter.

[0018] The inventive method and system thus generally do not require a pre-mixing station that provides a relatively long residence time for the water flow in a corresponding mixing basin to achieve sufficient homogenization for the desired adsorption, which takes place within the mixing basin. Accordingly, the invention eliminates the necessary equipment for this purpose. In particular, the inventive system is characterized by the fact that the dosing device feeds the adsorption additive into the water flow within a filter basin, i.e., directly upstream of the respective filter unit. No residence time is required. It is merely advantageous to apply the adsorption layer as uniformly as possible to the entire upstream surface of the respective filter unit.

[0019] Furthermore, it has been shown that significantly higher separation efficiencies can be achieved with the process according to the invention. In tests, separation efficiencies of more than 90% and in some cases even more than 95% were achieved. This is explained by the fact that within the adsorption layer, through which the contaminated water flows, there are extremely short migration paths for the nuclides to the adsorption additive, which are sufficient to adsorb the nuclides carried in the water almost completely.

[0020] In the process according to the invention, contaminated water is supplied to the respective filter unit in the form of a water flow. This water flow passes through the respective filter unit and thus inevitably also through the adsorption layer, whereby the entrained nuclides are largely adsorbed by the adsorption additive. Decontaminated water can then be discharged from the respective filter unit.

[0021] According to an advantageous embodiment, the adsorption layer is generated from an adsorption additive that is essentially free of radionuclides. Additionally or alternatively, it can be provided that the adsorption layer is generated with an adsorption additive that is at least 50%, preferably at least 75%, and particularly at least 90% free of radionuclides. This means that in these cases, the adsorption additive is introduced into the water flow in such a way that there is essentially no time available before it attaches to the respective filter device that would allow for the adsorption of radionuclides that may be carried along in the water flow. Likewise, it is also conceivable, independently of the above, to generate the absorption layer using a water flow consisting of purified water, i.e., water that contains no or essentially no radioactive radionuclides.In this way, a particularly high adsorption effect for the entrained nuclides is generated within the adsorption layer.

[0022] According to another advantageous embodiment, the method can be carried out such that the adsorption of the nuclides during a filtration phase of a filtration process occurs largely or substantially within the adsorption layer. Additionally or alternatively, it can be provided that at least 50%, preferably at least 75%, and particularly at least 90%, of the adsorption of the nuclides during a filtration phase of a filtration process occurs within the adsorption layer. Preferably, the adsorption of the nuclides during the filtration phase occurs only or exclusively within the adsorption layer. This approach largely or completely eliminates the need for adsorption of nuclides within the water flow upstream of the filter device. The largely or completely adsorption occurs during the flow through the adsorption layer.

[0023] According to another advantageous embodiment, the adsorption layer can be generated during a start-up phase of a filtration process, namely by adding the adsorption additive to a water flow passing through the respective filter device. In addition to the start-up phase, the filtration process includes a subsequent filtration phase that is longer than the start-up phase. Preferably, the filtration phase is at least 10 times, and in particular at least 100 times, longer than the start-up phase. During the filtration phase, contaminated water flows through the adsorption layer, and the nuclides are largely adsorbed by the adsorption additive. The water flow to which the adsorption additive is added during the start-up phase to generate the adsorption layer can consist of the contaminated water to be purified, or it can be used to purify water that is free of contaminants.essentially contains no nuclides.

[0024] In an advantageous further development, it can be provided that the adsorption additive is supplied to the water flow largely or essentially only during the start-up phase. Additionally or alternatively, it can be provided that at least 50%, preferably at least 75%, and particularly at least 90% of the total adsorption additive used during a filtration process is contained in the adsorption layer. This means that relatively little to no adsorption additive is supplied to the water flow during the filtration phase.

[0025] If the adsorption additive is added exclusively during the start-up phase to generate the adsorption layer, the process according to the invention is a discontinuous process, meaning the adsorption additive is added only during the start-up phase. In contrast, known, conventional processes that have a mixing station upstream of the filtration station use a continuous addition of the adsorption additive. It has been shown that the process according to the invention requires less adsorption additive overall to purify a predetermined quantity of water, which is added discontinuously during the start-up phase, than a conventional process in which the adsorption additive is supplied continuously throughout the entire filtration process.

[0026] According to another advantageous embodiment, the adsorption additive for generating the adsorption layer can be added to the water flowing through the respective filter device at a concentration of at least 50 ppm, advantageously at least 100 ppm, preferably at least 500 ppm, and particularly at least 1000 ppm. In contrast, in known methods that operate with a continuous addition of the adsorption additive, the adsorption additive is added at a concentration of a maximum of 10 ppm. In other words, to generate the adsorption layer, the adsorption additive is added to the water flow at a dosage that is much higher than that required for adsorption of the nuclides upstream of the filter device. By using this high concentration, the adsorption layer can be built up relatively quickly, so that the start-up phase can be designed to be correspondingly short.The addition of the adsorption additive with the aforementioned high concentration takes place within the start-up phase during a predetermined dosing time, which may be shorter than the start-up phase or be the same length as the start-up phase.

[0027] In a preferred embodiment, at least one ceramic filter membrane can be used in the respective filter device. This embodiment is based on the finding that other filter materials, for example plastic filter membranes or sand filters, are unsuitable for the high concentrations of adsorption additive that can be used in the inventive method for generating the adsorption layer.

[0028] It is advantageous for the adsorption additive to be a solid with a granular or flake-like structure, or to consist largely of such a solid. The solid used can be solid or porous. The use of such a particulate solid as an adsorption additive has the advantage that the adsorption layer itself acquires a porous structure, allowing for easy flow through it. This also results in an extremely large available adsorption surface area, which promotes rapid adsorption. The average pore size within the adsorption layer is advantageously larger than the average inlet-side pore size of the filter material used, such as a ceramic filter membrane, in the respective filter system.

[0029] In a system according to the invention, the respective dosing device adds the adsorption additive to the water flow within the respective filter basin or directly upstream of it during operation of the system, particularly during the start-up phase, i.e., directly upstream of the respective filter unit, so that the desired adsorption layer can form on the upstream side of the filter unit. The adsorption additive can also be added, for example, to a supply line that carries the contaminated water to the respective filter basin. During operation of the system, contaminated water is supplied to the respective filtration station or filter basin, and decontaminated water is discharged from the respective filtration station or filter unit.The system presented here therefore does not require a mixing station for the addition of the adsorption additive, which is located upstream of the respective filtration station and includes a mixer and a mixing basin.

[0030] According to the invention, a control device for operating the system is provided, which is at least coupled to the respective dosing device and which is designed or programmed in such a way that it can carry out the above-described method according to the invention during operation of the system.

[0031] In a further advantageous development of the system, at least two filtration stations can be provided: at least one main-flow filtration station and at least one bypass filtration station. The dosing device can be advantageously designed to add the adsorption additive to the water flow within the respective filter basin of each of the two filtration stations at individual dosages, such that a different filtration rate is generated in the main-flow filtration station than in the respective bypass filtration station. The main flow is characterized by a different, usually larger, volume flow rate than the bypass. For example, it is conceivable to achieve a lower removal rate in the main flow than in the bypass, whereby the bypass can then be blended with the main flow to generate a desired target removal rate in the mixed flow, a process known as "blending."By adjusting the separation between the main and side streams, the same high target filtration rate can always be achieved in the product water (i.e., the decontaminated water), even if the raw water (i.e., the contaminated water) has a varying degree of contamination. Different uses for the main and side streams are also conceivable.

[0032] The inventive method is based on the direct combination of nuclide adsorption with filtration. For this purpose, the absorption layer is generated entirely on the upstream surface of the respective filter device at the beginning of the filtration process, i.e., during a start-up phase. The dosing or addition of the respective adsorption additive, which is preferably a particulate adsorption chemical formed by solid particles (granules), takes place within a comparatively short time, which can be several minutes. Uniform, continuous dosing during the entire filtration process is preferably not required. The desired adsorption layer can form within a short time. The absolute amount of adsorption additive required is comparable to, and preferably even lower than, that required for conventional, continuous dosing.The adsorption additive is introduced in such a way that it cannot disperse in the water flow to be treated beforehand, so that the adsorption surface of the additive is still unoccupied—that is, free of nuclides and contaminants—when the adsorption layer forms on the upstream surface of the respective filter element. In this way, interference processes caused by unwanted adsorption of competing substances can be minimized. The contaminated water to be filtered must pass through the pores of the adsorption layer before reaching the upstream surface of the respective filter device. The pores of the adsorption layer can be larger than the corresponding pores of the respective filter device. For example, the pores of the adsorption layer measure a few micrometers, while the pores of the filter device are in the range of 10 nm to 600 nm, preferably around 200 nm.The thickness of the adsorption layer can range from 0.1 mm to a few millimeters, preferably less than 10 mm.

[0033] A central dosing unit can be used to add the adsorption additive, enabling individual dosing for each filtration stream, i.e., for each filtration station. This allows for different removal rates to be achieved in the water treatment plant, even with a single-stage process. This has the significant advantage that defined partial streams can be used directly as partial product streams without further treatment. For example, a blended stream with high removal rates is conceivable. Other partial streams, intended for further treatment and removal of other pollutants or contaminants, such as by a downstream reverse osmosis unit, can be operated with a lower dosage of the adsorption additive in the respective filtration tank.As a result, savings in operating costs can be achieved, since less adsorption additive is consumed overall.

[0034] Manganese oxide and / or manganese dioxide can be used as an adsorption additive, or a chemical that generates manganese oxide and / or manganese dioxide in situ in water. Iron oxide can also be used, either additionally or alternatively. The preferred adsorption additive, i.e., manganese oxide and / or manganese dioxide and / or iron oxide, can be added directly to the contaminated water. A particularly suitable formulation is one in which the respective adsorption additive is present as a porous precipitate with a particularly large internal surface area. For example, a specific surface area greater than 350 m² / g, determined according to PET, can be achieved. Since manganese dioxide ages and loses porosity in the process, it should ideally be produced immediately before its addition.

[0035] Preferably, the manganese oxide and / or manganese dioxide used is obtained by oxidation of an aqueous manganese salt solution adjusted to a pH between 4.5 and 9, particularly between 7 and 9. A suitable manganese salt is, for example, manganese sulfate. A suitable oxidizing agent is, for example, potassium permanganate or sodium hypochlorite. It is also possible to make the potassium permanganate basic, for example with NaOH, and to add the basic potassium permanganate to a slightly acidic manganese sulfate solution. This allows for better control of the stoichiometry of the reaction.

[0036] In another embodiment, the contaminated water can undergo chemical pretreatment, for example, by adding barium salt. Barium salt can promote the precipitation of radium. The barium salt can be added upstream of the filter device in the water flow. It is also conceivable to add barium salt during the formation of the adsorption layer, so that it is present in the adsorption layer in a corresponding proportion.

[0037] Furthermore, the addition of additional chemicals, such as ozone, or atmospheric oxygen is also conceivable, for example to oxidize other metals and metal ions contained in the water, for example to separate iron by oxidation.

[0038] A ceramic filter membrane, preferably used in the respective filter device, can in particular be designed as a microporous filter membrane. The respective ceramic filter membrane is advantageously a flat membrane plate with internal filtrate discharge channels and an external porous separating layer, which forms the upstream surface. Such membranes are described in detail in DE 10 2006 008 453 A1. It is preferred that ceramic filter membranes be used for the present process in which the pores, at least on the upstream surface, in particular in the aforementioned separating layer, have a mean diameter between 80 nm and 800 nm, and in particular between 100 nm and 300 nm.

[0039] Particularly advantageous are plate-shaped filter membranes which can be combined into filter units, as described, for example, in WO 2010 / 015374 A1.

[0040] Ceramic filter membranes can preferably be operated at a negative pressure of 100 mbar to 600 mbar, so that the decontaminated product water is drawn through the respective filter membrane. However, it is also conceivable to use the ceramic filter membranes at a positive pressure, so that the contaminated water is forced through the filter membranes.

[0041] Furthermore, the use of an adsorption additive that itself exists in the form of a particulate solid is particularly advantageous. This applies especially to the aforementioned manganese oxide and / or manganese dioxide and / or iron oxide. Accordingly, the adsorption layer on the upstream surface of the respective filter device is itself porous, and the adsorption of the nuclides cannot cause significant clogging of this porosity. Consequently, the precisely applied adsorption layer does not lead to clogging of the respective filter device. Rather, a consistently high flux can be achieved without clogging of the filter device by the adsorption layer.

[0042] Further important features and advantages of the invention will become apparent from the dependent claims, the drawings and the associated description of the figures based on the drawings.

[0043] It is understood that the features mentioned above and those to be explained below can be used not only in the combinations specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0044] Preferred embodiments of the invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components.

[0045] They show, schematically, Fig. 1 a highly simplified, circuit diagram-like schematic representation of a system for removing radioactive nuclides from water, Fig. 2 a highly simplified sectional view of a filter device in the area of ​​an adsorption layer.

[0046] Accordingly Fig. 1 The system comprises a plant 1, which can be used to remove radioactive nuclides, such as radium isotopes, from water, for example to produce drinking water or process water, at least one filtration station 2, 3 and at least one dosing device 4. In the example of the Fig. 1 The following are purely exemplary: two such filtration stations 2, 3, to which a common dosing unit 4 is assigned. Another system 1 may also manage with only a single filtration station 2, 3 or have more than two filtration stations 2, 3. Likewise, several dosing units 4 may be provided.

[0047] Each filtration station 2, 3 has a filter basin 5 or 6, in which at least one filter unit 7 or 8 is arranged. Each filter unit 7, 8 is permeable to a water flow 9 or 10, indicated by arrows. The water flows 9 and 10 are supplied via a common inlet 11, which branches at 12 to supply contaminated water, i.e., water containing radioactive nuclides, to the filter basins 5 and 6 in parallel. The purified water, i.e., the decontaminated water or product water, is discharged from the filter units 7 and 8 via separate outlet lines 13 and 14.

[0048] The dosing device 4 is designed to supply an absorption additive 15 to the water flows 9, 10 upstream of the filter devices 7, 8, which is in Fig. 2 As indicated, the dosing device 4 can supply the adsorption additive 15 to the respective water flow 9, 10 within the respective filter basin 5, 6. Accordingly, a dosing line 16 of the dosing device 4 is directly connected to the respective filter basin 5, 6. The respective filter device 7, 8 is adjusted with regard to its filtration efficiency or pore size such that it is permeable to water and essentially impermeable to the adsorption additive 15 as well as to the adsorption additive 15 with adsorbed nuclides.

[0049] Provided as in Fig. 1 Since at least two filtration stations 2, 3 are provided, one filtration station 2 can serve as the main-flow filtration station 2, while the other filtration station 3 serves as the side-flow filtration station 3. The dosing device 4 can supply the required amount of adsorption additive 15 separately to the respective filtration stations 2, 3 or introduce it into the respective filter basin 5, 6. Advantageously, the dosing of the adsorption additive 15 to the two filter basins 5, 6 can be carried out individually so that different filtration rates are achieved at the two filtration stations 2, 3.

[0050] To operate the plant 1, it is expediently equipped with a control unit 17, which is coupled to the dosing unit 4, for example, via a control line 18. The control unit 17 is expediently designed and programmed so that it can carry out the procedure for removing radioactive nuclides from water, which has been explained in detail above and is summarized below, when the plant 1 is in operation.

[0051] To remove the nuclides from the contaminated water, for example to produce product water that can be used as drinking water or process water, or is to be treated for such purposes, the adsorption additive 15 is introduced into the filter basins 5, 6 in such a way that, according to Fig. 2 An adsorption layer 20 forms on an upstream surface 19 of the respective filter device 7, 8 from the adsorption additive 15. The adsorption layer 20 is produced from adsorption additive 15, which is essentially still free of nuclides, so that the absorption of the nuclides during a filtration phase of a filtration process occurs essentially only, preferably exclusively, within the adsorption layer 20.

[0052] Such an adsorption layer 20 can be created, for example, by adding the adsorption additive 15 to the respective water flow 9, 10 passing through the filter device 7, 8 during a start-up phase of the filtration process. During the start-up phase, the respective water flow 9, 10 can consist of uncontaminated or already purified water. However, contaminated raw water can also be used during the start-up phase to form the adsorption layer. By adding the adsorption additive 15 to the water flow 9, 10 passing through the respective filter device 7, 8, the adsorption layer 20 forms automatically on the upstream surface 19 of the respective filter device 7, 8, similar to a filter cake. The addition of the adsorption additive 15 to the respective water flow 9, 10 or...The addition of the adsorption additive 15 to the respective filter basin 5, 6 is expediently carried out in such a way that the entire upstream surface 19 of the respective filter unit 7, 8 is loaded as uniformly as possible. The start-up phase can last several minutes. In any case, the start-up phase is significantly shorter than the subsequent filtration phase, in which the nuclides can then be removed from the contaminated water with the help of the adsorption layer 20.

[0053] Advantageously, the adsorption additive is added to the water flow 9, 10 exclusively during the aforementioned start-up phase, so that no adsorption additives 15 are added, particularly during the significantly longer filtration phase. The respective adsorption additive 15 is added during the start-up phase, or during a dosing period within the start-up phase, at a relatively high concentration, which can be, for example, at least 50 ppm or at least 100 ppm, preferably at least 500 ppm, and particularly at least 1000 ppm. The absolute amount of adsorption additive depends on the contamination of the raw water, the volumetric flow rate of the raw water, and the absolute quantity of raw water to be purified during the filtration process. At the end of the filtration process, the adsorption layer 20 is ideally almost saturated with the adsorbed nuclides.For a new filtration process, the respective filter unit 7, 8 can be regenerated, for example by means of a backwash in which the exhausted or consumed adsorption layer 20 is rinsed off the upstream surface of the filter unit 7, 8. Subsequently, a new, unconsumed adsorption layer 20 can be applied again with a new start-up phase.

[0054] A particularly advantageous embodiment is one in which the filter device 7, 8 is equipped with at least one ceramic filter membrane 21, which has at least a part of the upstream surface 19 of the respective filter device 7, 8. According to Fig. 2The filter membrane 21 has at least one channel 22 inside, into which the purified water flow 9, 10 enters and from which the purified water flow 9, 10 can be discharged from the respective filter device 7, 8. The filter membrane 21 advantageously has a pore size in the two-digit or three-digit nanometer range.

[0055] A solid material, preferably in granular or flake form (i.e., in particle form), is advantageously used as the absorption additive 15. The solid material can be solid or porous. This results in a porous structure for the adsorption layer 20. The porosity of the absorption layer 20 is preferably in the single-digit or double-digit micrometer range. In principle, the porosity of the adsorption layer 20 can also be lower than that of the filter membrane 21.

[0056] The purification or decontamination of the water is achieved by the adsorption of the nuclides onto the adsorption additive 15 during the flow through the adsorption layer 20 with such efficiency that an adsorption rate of at least 90% to 95% can be achieved.

Claims

1. Method for removing radioactive nuclides from water, - in which at least one absorption additive (15), which has an absorbing effect on the nuclides, is used, - in which at least one filter device (7, 8) which is impermeable to the respective adsorption additive (15) is used, characterized by that an adsorption layer (20) is produced with the adsorption additive (15) on an upstream surface (19) of the respective filter device (7, 8).

2. Method according to claim 1, characterized by that the adsorption layer (20) is produced with adsorption additive (15) which is essentially free of nuclides.

3. Method according to claim 1 or 2, characterized by that the adsorption layer (20) is produced with adsorption additive (15) which is at least 50 % free of nuclides.

4. Method according to any one of claims 1 to 3, characterized by that the adsorption of the nuclides during a filtration phase of a filtration process largely or essentially takes place within the adsorption layer (20).

5. Method according to any one of claims 1 to 4, characterized by that at least 50 % of the adsorption of the nuclides takes place during a filtration phase of a filtration process within the adsorption layer (20).

6. Method according to any one of claims 1 to 5, characterized by that the adsorption layer (20) is formed during a start phase of a filtration process by adding the adsorption additive (15) to a water flow (9, 10) flowing though the respective filter device (7, 8).

7. Method according to claim 6, characterized by that the adsorption additive (15) is added to the water flow (9, 10) largely or essentially only during the starting phase.

8. Method according to any one of claims 1 to 7, characterized by that at least 50% of the total adsorption additive (15) used during a filtration process is contained in the adsorption layer (20).

9. Method according to any one of claims 1 to 8, characterized by that the adsorption additive (15) for producing the adsorption layer (20) is supplied to a water flow (9, 10) flowing through the respective filter device (7, 8) at a concentration of at least 50 ppm.

10. Method according to any one of claims 1 to 9, characterized by that at least one ceramic filter membrane (21) is used in the respective filter device (7, 8).

11. Method according to any one of claims 1 to 10, characterized by that the adsorption additive (15) is a particulate solid.

12. System for the removal of radioactive nuclides from water, - with at least one filtering station (2, 3), which in a filter basin (5, 6) contains at least one filter device (7, 8) through which a flow of water (9, 10) can pass, - with at least one dosing device (4) for adding an adsorption additive (15) to the water flow (9, 10), which is arranged and / or configured in such a way that it can add the adsorption additive (15) to the water flow (9, 10) within the respective filter basin (5, 6) or directly upstream thereof, characterized by a control device (17) for operating the system (1), which is coupled to the respective dosing device (4) and which is configured and / or programmed to carry out the method according to one of claims 1 to 11 during operation of the system (1).

13. System according to claim 12, characterized by - that at least two filtering stations (2, 3) are provided, namely at least one main stream filtering station (2) and at least one bypass filtering station (3), - in that the dosing device (4) is configured to add the adsorption additive (15) to the water flow (9, 10) within the respective filter basin (5, 6) of the at least two filtering stations (2, 3) in such a way that a different filtration rate is generated in the respective main flow filtering station (2) than in the respective bypass filtering station (3).