Apparatus and method for the purification of water

Abstract

The invention relates to a device and a method for purifying drinking water, and to a method for operating a drinking water purification device. The device according to the invention has an inlet (50) suitable for introducing feed water, an outlet suitable for discharging purified water, and a filter device (30, 54) arranged between the inlet (50) and the outlet. The device comprises a control device for maintaining the flow rate of the water flowing out through the outlet at a constant value during the useful life of the filter device (30, 54). The filter device comprises a pre-filter (52) and a microporous membrane filter (53). The method for purifying drinking water consists in passing water at a constant flow rate through a water purification filter device (54) comprising a pre-filter (52) and a microporous membrane filter (53). The essence of the method for operating the device according to the invention is that the device according to the invention for purifying drinking water is used as a filter device (54);the water is allowed to flow through the filter element at an initial flow rate until the pressure difference between the inlet and outlet of the filter device reaches a predetermined value; during the previous step, the permeability of the device is measured and plotted on a graph as a function of the water flow rate, where the flow rate is the ratio of the flow rate to the total surface area of ​​the filter elements; by changing the flow rate or the surface area of ​​the filter elements, the previous two steps are repeated at different flow rates and the permeability of the device is plotted on a graph as a function of the water flow rate; based on the graph, the desired value of the permeability is selected and the flow rate associated with the desired permeability is determined; finally, the flow rate corresponding to the selected permeability is maintained and a filter surface of the corresponding size is used. à;

Description

The invention relates to an apparatus and a method for purifying drinking water, and to a method for operating a drinking water purification apparatus. The apparatus and method according to the invention are particularly related to making water contaminated by microorganisms suitable for human consumption. Many settlements today do not have a safe and reliable water supply. This may be due to the lack of a water supply network, but it often happens that even if a water supply network is installed, the water supplied is not suitable for human consumption, as it is contaminated - for example by microorganisms. The provision of potable drinking water in such settlements has received serious attention in recent times, and many solutions have been developed to solve the problem. One possible solution is water filtration. In most cases, filters used in water purification equipment operate in a constant pressure mode, i.e. a filter is placed on a constant pressure water source and filters the water until the water purity reaches a predetermined limit. There are systems in which it is necessary to control the flow rate. For example, US-5 503 735 patent describes a liquid purification system in which a filter membrane implementing reverse osmosis is located in a filter cartridge. Only a part of the water flows through the membrane, and the water that does not flow through the membrane passes through a pressure reducing valve, which allows the water pressure to be controlled, and thus the water flow rate in the system. In water circulation systems - for example, in irrigation systems - devices are used that provide a constant flow rate with varying water pressure.The operation of processes for controlling the flow rate of water in water purification devices is also well known to those skilled in the art. A device for water purification is disclosed, for example, in US-5,238,559. Patent specification JP-05185070 mentions that in household water purification devices, the filter module must be replaced when the amount of water flowing through it exceeds the maximum amount of water containing pollutants allowed for the absorbent device in the device. This specification also mentions that water purification devices are known which are equipped with a life measuring device which indicates the expected time for replacing the filter module. However, these devices cannot be considered reliable because they only measure during the time when water flows through them and this does not provide reliable information on the extent of the fluctuation of the water flow rate.Therefore, the said description proposes a domestic water purification device which comprises a valve providing a constant flow rate and a sensor which detects the start and stop of the water flow and generates signals corresponding thereto. The said device also comprises a device which serves to measure the integrated operating time based on the said signals and indicates when the integrated operating time reaches a predetermined value. The description only describes the valves providing a constant flow rate of various structures, but neither the structure nor the states of the filter module are described in the description, nor are the known structures used in the said invention disclosed. US Patent No. 4,784,763 discloses a filtration device comprising an inlet and outlet, a pre-filter, a membrane filter and a microprocessor control device. However, the said specification does not mention a filtration device comprising both a pre-filter and a microporous membrane filter, nor does it mention a control device which would keep the flow rate of water flowing out of the filtration device at a constant value. The membrane used in the device in question is an extremely thin ion separation membrane with pores smaller than 10 angstroms and which is mechanically held by a granular microporous structure. Since its function is to bind ions - and not to filter out particles - it can only operate in a flow-through mode, i.e. water must be passed over the membrane surface in order to prevent the ions from accumulating on the solution side of the membrane.Therefore, a constant pressure difference must be maintained to allow water to flow through the ion separation layer. The regulating device is located on the high-pressure side and regulates the maximum pressure difference between the two sides of the membrane, which depends solely on the nature of the water source and the mechanical specifications of the filter and its housing. Known water purification systems - especially those that not only remove solids but also microorganisms, thereby making the water drinkable - are objectionable in several respects. On the one hand, they generally have a low permeability, which means that the filters have to be replaced frequently, and on the other hand, the filters have to have a large surface area, which means that they are very expensive. Our aim with the invention is to implement a device for purifying drinking water that can eliminate the above-mentioned disadvantages. Our aim with the invention is also to implement a method for purifying drinking water that eliminates the disadvantages of known methods. A further aim of the invention is to implement a method by which the drinking water purification equipment can be operated under optimal conditions. The objectives are achieved by implementing a device having an inlet suitable for introducing feed water, an outlet suitable for discharging purified water, and a filter device arranged between the inlet and the outlet. The essence of the device according to the invention is that it comprises a control device for maintaining the flow rate of the water flowing out through the outlet at a constant value during the useful life of the filter device, and the filter device comprises a pre-filter device and a microporous membrane. A possible variant of the device according to the invention includes a device for measuring the time elapsed since the filter device was put into operation - as a first period of time -, the filter device2 HU 222 893 Bl comprises means for measuring the cumulative sum of the flow periods of water flowing through the filter means - as a second period of time, and means for preventing the flow of water through the filter means if a predetermined threshold value is reached by either of the first and second periods. In the device according to the invention, the control device preferably includes a device for applying pressure to the filter device and a device for controlling the flow rate independently of the pressure change. A preferred embodiment of the apparatus according to the invention comprises pre-filter means and microporous membrane means, which are arranged and assembled as described below to form a filter means. However, the filter means themselves are not part of the invention. The apparatus according to the invention is provided with filters of various structures, including a pre-filter and a microporous membrane filter, through which the water to be purified flows. A preferred embodiment of the aforementioned filter device comprises several different filter elements, which are also capable of filtering independently. Such a filter element comprises the following layers: a) an innermost absorbent layer, which is preferably a substantially loosely woven plastic fabric; b) two microporous membrane layers, which are preferably mounted on support layers which are located between the membrane layer and the absorption layer and which bind microorganisms in more than 95%, and the two membrane layers are located symmetrically on the outer sides of the two absorption layers; c) two thick filter or pre-filter layers (the two terms are used interchangeably in the following description), which are preferably made of glass fiber and are symmetrically arranged on the outer sides of the microporous membrane layers; d) the microporous membrane layers and the pre-filter layers are sealed together along their upper edge, which upper edge preferably extends above the absorption layer and any support layers; e) the bottom of the absorption layer and the microporous membrane layers, as well as the bottom of any support layers, extend below the bottom of the pre-filter layers and microporous membrane layers, where the pre-filter layers and microporous membrane layers are sealed to the pre-filter layers at their lower edges; and f) the microporous membrane layers and the pre-filter layers are thicker than the absorption layer and any support layers and are tightly connected to each other along their side edges. The terms "top" and "bottom" refer to the position of the filter elements as they are arranged in the filter device. The said filter device has a bottom plate with a central opening and an upper plate. The filter elements are arranged parallel to each other, perpendicular to the bottom plate, covering the central opening of the bottom plate. The lower edge of the pre-filter layers is flush with the upper plate of the bottom plate. The filter elements are attached to the bottom plate in such a way that the space between them and the inner edge of the central opening of the bottom plate is filled with adhesive. The filter device also includes a hermetically sealed housing in which the filter elements attached to the bottom plate are arranged closely next to each other. In one possible embodiment of the filter device, the microporous membrane layers and the pre-filter layers are sealed together with an adhesive. In another possible embodiment of the filter device, the pre-filter layers are laminates, each of which includes a layer made of a porous thermoplastic material. In addition, both the microporous membrane layers and their support layers are also made of a thermoplastic material. If the melting point of the microporous membrane layer is at least 50 °C, i.e. higher than that of any other thermoplastic layer, then the layers can be sealed together at high pressure and high temperature. The method of this will be described in detail later. A possible embodiment of the filter device according to the invention comprises the following components: pre-filter; membrane filter, which can be designed as a separate unit or integrated with the pre-filter; pressure control device; flow measuring device; time measuring device; an outlet for draining clean water; and valves and pressure gauges if necessary. The objectives are also achieved by implementing a method for purifying drinking water. The essence of the method is that water is passed through a water purification filter device comprising a pre-filter device and a microporous membrane at a constant flow rate. In a possible variant of the method according to the invention, the time elapsed since the filter device was put into operation is measured - as a first period -, the cumulative sum of the flow periods of water flowing through the filter device is taken - as a second period - and the flow of water through the filter device is prevented if the first or second period has reached a predetermined threshold value. The means for conveying water at a uniform flow rate through the device comprises means for providing a suitable water pressure for introducing the water to be purified, and means for regulating the flow rate - for example a known type of restrictor - comprises. The pre-filter means and the microporous membrane means are conveniently arranged and assembled in the filter element to form a filter means in the filter device according to the invention.For the operation of the method according to the invention, a filtering device can also be used that contains filters of different structures, provided that there is a pre-filter and a microporous membrane filter among them. Since the purpose of the method according to the invention is the purification of drinking water, we will only deal with the purification of drinking water in the following. HU 222 893 Bl The term "purification of drinking water" in the remainder of the description means, on the one hand, making water unfit for human consumption drinkable, and on the other hand, increasing the purity of drinking water. The purified water is preferably essentially sterile. The set objectives are further achieved by implementing a method for operating a filter device according to the invention, in which the device for purifying drinking water according to the invention is used as the filter device; the water is allowed to flow through the filter element at an initial flow rate until the pressure difference between the inlet and outlet points of the filter device reaches a predetermined value; the previous step is repeated and the permeability of the device is plotted as a function of the water flow rate, where the flow rate is the ratio of the flow rate to the total surface area of ​​the filter elements; Repeat the previous two steps at different flow rates by changing the flow rate or the surface area of ​​the filter elements and plot the throughput of the device as a function of the water flow rate on a graph; Based on the graph, we select the desired value of the permeability and determine the flow rate corresponding to the desired permeability; finally, we maintain a flow rate corresponding to the selected permeability and use a filter surface of the appropriate size. The objectives are finally achieved by implementing a method for filtering liquids, in which the optimal flow rate of the liquid flowing through a filter device having a filter surface and at least one pre-filter placed near a microporous membrane is determined by operating identical filter devices at different constant flow rates until the total pressure drop in each of the filter devices reaches a given value; the throughput associated with each filter device is recorded for a given period of time; and then, based on the throughputs associated with the different constant flow rates, the relationship between the flow rate and throughput associated with the filter device is determined, where the flow rate is the ratio of a given flow rate to the filter surface of the filter device.Finally, the filter device is operated by maintaining a constant flow rate corresponding to the desired throughput. Preferably, a filter device is used which has a variable filter surface area, the size of the filter surface being selected according to the flow rate corresponding to the desired throughput. The invention will be described in detail below with reference to the drawing, where the Figure 1 is a cross-section of a possible embodiment of a filter element used in the device according to the invention; Figure 2 is a front view of the filter element shown in Figure 1; Figure 3 is a perspective view of a possible embodiment of the filter element used in the device according to the invention in an intermediate manufacturing step; Figure 4 is a cross-section of a possible embodiment of the filter device according to the invention, taken along the center line of the filter elements; Figure 5 is a cross-section of the filter device shown in Figure 4 taken in a plane parallel to the filter elements; Figure 6 is a cross-section of another possible embodiment of the filter element used in the filter device according to the invention; Figure 7 is a graph of the total throughput of the filtration device according to the invention as a function of flow rate; and Figure 8 is a block diagram of a possible embodiment of the device according to the invention. As shown in Figure 8, the device according to the invention has an inlet 50, which conveniently includes a pressure gauge and a pressure regulator of a known type. The pressure required for the flow of water through the device can be provided by the water source itself, for example a water tap or a water pressure pipe, or in their absence - or if they provide insufficient pressure - by any pump 51. The device according to the invention also includes a pre-filter 52 and a membrane filter 53, which can also be incorporated into a single filter device 54, indicated by a dashed line in Figure 8. At the other end of the filter device 54 is an outlet, which conveniently includes a pressure gauge 55 and a pressure regulator 56 providing a constant pressure. A needle valve 57 may be located after the pressure regulator 56. Through the needle valve 57, the water flows into a composite unit 58, which conveniently includes a flow measuring device, a time measuring device, a shut-off valve and an outlet. Figures 1-5 illustrate a preferred embodiment of a filter device used in a filter apparatus according to the invention. As previously mentioned, the filter device is not part of the present invention but is the subject of other pending applications. The filter element 10 shown in Figures 1-5 comprises two outer layers, preferably made of glass fiber, pre-filter layers 11 and 11'. Between the pre-filter layers 11 and 11' are microporous membrane layers 12 and 12', which have a microorganism-binding capacity of preferably at least 95%. The microporous membrane layers 12 and 12' are supported by support layers 13 and 13'. All of the aforementioned layers are arranged symmetrically around a substantially loosely woven plastic mesh, which forms an absorption layer 14, which conducts liquid through the layers 11, 1Γ, 12, 12' and the support layers 13 and 13'. The layers 11 and 11' and 12 and 12' are congruent and are sealed together by adhesive, preferably thermoplastic adhesive, or by welding. The pre-filter layers 11 and 11' and the microporous membrane layers 12, 12' are also sealed together along their edges 22. The absorption layer 14 and the support layers 13, 13' do not extend beyond the top of the filter element, i.e. HU 222 893 Bl do not extend beyond the seal 15, although in the embodiment of the invention in which welding is used, the support layers 13 and 13' may reach the sealed edge and be thermoplastically bonded together. As shown in Figures 1 and 2, none of the pre-filter layers 11, 11' reach the bottom of the filter element, while the microporous membrane layers 12, 12', the support layers 13, 13' and the absorption layer 14 extend beyond the bottom of the pre-filter layers 11, 1Γ. The pre-filter layers 11 and 11' are sealed to the microporous membrane layers 12, 12' along their edges 20 and 20'. The support layers 13 and 13' and the absorption layer 14 are narrower than the other layers and do not contact the seals 22. As shown in Figures 4 and 5, a plurality of filter elements 10 are connected to each other in the filter device. Figure 3 shows a perspective view of the filter device used in the filter device according to the invention during an intermediate manufacturing step. The filter device 30 has a bottom plate having a central opening 32. The opening 32 has a rim 33. The filter elements 10 are pulled through the central opening 32 and are positioned therein such that their upper edges 20 are flush with the upper surface of the bottom plate 31. As shown in Figure 3, the central opening 32 is not filled with the filter elements 10, but a space of suitable size is left free in front of and behind the filter elements 10. Figures 4 and 5 show a filter device which already contains a finished filter device. Filter elements 10 are arranged in the central opening 32 of the filter device. The filter elements 10 are here already in place and are fixed to the bottom plate in such a way that the inner edge 33 of the opening 32 and the space between the filter elements 10 are filled with a suitable adhesive, thereby preventing the flow of liquid between the filter elements 10 and the bottom plate 31. The bottom plate 31 is then mechanically fixed in a suitable housing 35. The housing 35 has an open top which serves as an inlet 36 for the water to be filtered. The water flows through successive layers of filter elements 10, entering the outer pre-filter layers 11, 11' and exiting the absorption layer 14, and the filtered water then leaves the filter device through the outlet opening 37 of the housing 35. In the embodiment of the filter element used in the filter device according to the invention shown in Figure 6, the pre-filter layers can be replaced by laminated filter layers 40, 40' made of glass fiber and porous support layers 41, 41' made of a synthetic material with a melting point of TPA. The filter element comprises microporous membrane layers 42, 42' made of a thermoplastic material with a melting point of T2, and further comprises porous support layers 43, 43' made of a synthetic material with a melting point of T3, which are coincident with the previous layers and - as shown in Figure 2 - are connected to them along their edges 15 and 22, respectively. If the temperature T2 is at least 50°C and is greater than the temperature Tj or T3, the seals of the filter elements 15 and 22 can be formed in a single step by welding said layers together with a hot press tool at a temperature higher than the temperatures Tj and T3. The device according to the invention purifies drinking water by passing it through one or more filter elements at a constant flow rate. If a pre-filter and a microporous membrane are used for filtration, it is advisable to maintain a constant flow rate and a constant water pressure during filtration, since a filter device operating at a constant flow rate requires a much smaller - even a tenth - membrane surface area to achieve the same permeability as a filter device operating at a constant water pressure. The filter device in the device according to the invention has a filter surface area of ​​0.05 m2, which is capable of filtering 3 m3 of tap water at a constant flow rate of 0.002 m3 / min, so that the average filtration factor is 10. In the case of the aforementioned parameters, it is sufficient to replace the filter elements once every three months. At constant water pressure, the following phenomenon occurs in a filter device consisting of a pre-filter and a microporous membrane filter. At the beginning of the process, the hydraulic resistance of the filter is minimal, the flow rate is maximal, and the efficiency of the pre-filter is low, since the efficiency of the pre-filter is inversely proportional to the speed of the particles in the flowing material. After that, the particles flow through the pre-filter and bind on the surface of the microporous membrane, thereby blocking the pores, resulting in a decrease in the flow rate. During filtration, the velocity of the liquid decreases continuously, and finally the binding efficiency of the pre-filter begins to improve. The resistance of the pre-filter and the membrane increases until their combined resistance becomes so great that the filter can no longer provide the required flow rate.In constant flow operation, it is possible to adjust the fluid velocity so that the number of particles captured by the pre-filter is maximized from the beginning of the filtration process. This significantly increases the filter throughput. Optimal operation of the device according to the invention, i.e. the filter device comprising a pre-filter and a microporous membrane filter as described above, can be achieved by performing the following steps: 1. The filter element is first operated at a favorable, constant flow rate until the pressure difference between the filter inlet and outlet reaches a predetermined value. 2. The flow rate resulting from the previous step is recorded on the graph shown in Figure 7, which plots the permeability as a function of the flow rate of the liquid, where the flow rate is the ratio of the flow rate to the surface area of ​​the filter elements. 3. The procedure is continued at other constant flow rates or using filter elements with different total areas until the complete graph shown in Figure 7 is obtained. 4. We determine a desired permeability, then based on this we read the appropriate flow rate from the graph, from which we calculate the flow rate and the total surface area of ​​the filter elements. HU 222 893 Bl 5. The filter device is continued to operate at the constant flow rate determined in the previous step. Figure 7 shows the variation of the permeability of the filter device as a function of the water flow rate, when the predetermined pressure difference between the two sides of the filter is 253.312 kPa. The filter device uses a flat membrane filter element that contains a glass fiber pre-filter and a microporous membrane with a nominal pore size of 0.2 micrometers. It is obvious from the graph in Figure 7 that at a constant flow rate, the permeability of the membrane filter can be increased several times below a critical flow rate. The pre-filter layer may conveniently be made of any known suitable material, including fibrous or particulate, inorganic or organic materials, such as glass fibers, carbon fibers, cellulose, polyolefins or other synthetic polymeric materials. The pre-filter may also be made of a material comprising compacted, porous fibers, such as microscopic fibers or particles having a pore diameter at least five times the pore diameter of the membrane. The pre-filter may also be made of woven or non-woven fibrous materials well known in the art. A non-woven glass fiber material, which does not contain a binder, is particularly suitable for filtering tap water, and has a thickness of about 0.45 mm and a nominal diameter of the particles it binds of 1 pm. The microporous membrane layer is preferably a microporous filter having pores of 0.05-0.45 pm in diameter and is generally made of high temperature thermoplastic polymers such as polysulfone, nylon, polyvinylidene fluoride, or inorganic materials such as ceramics or metals. The microporous membrane layer preferably has a water permeability of about 0.49-29 cm3 / cm2 / s / MPa. Such materials are well known in the art and can be found, among others, in Theodore H. Melzer, (Marcel Dekker Inc., NY): "Filtration in the Pharmaceutical Industry" (1987, ISBN 0.8247-7519-8). The support layers supporting the membrane layer are preferably made of a woven or nonwoven synthetic material that does not swell or deform in water. A nonwoven material made of polyolefins is particularly preferred for this purpose, since its melting point is much lower than the melting point of the polymers used in the membrane layer. Ideally, this layer has maximum permeability, but its permeability should in no case be less than one tenth of the permeability of the membrane layer. The plastic mesh, which is intended to separate the filter layers to ensure fluid flow, can be made of various thermoplastic materials, which are produced by extrusion or other processes, such as continuous weaving of plastic fibers in a known manner. One such material is polypropylene mesh under the brand name Naltex, manufactured by Nalle Plastics (Austin, Texas, USA). The operation of a preferred embodiment of the device according to the invention will be described below. The membrane filter element with an effective filter area of ​​approximately 24 cm2 comprises the following filter layers: a pre-filter layer made of A / E glass fiber material (Gelman Sciences, Ann Arbor, Mi, USA); a membrane layer made of Super 200 microporous material (Gelman Sciences, Ann Arbor, Mi, USA); a support layer made of nonwoven polypropylene material; and an absorption layer made of polypropylene mesh (Nalle Plastics, Texas, USA). An epoxy resin-based adhesive is used as the adhesive. The filter elements are attached to a 4 mm thick plastic base plate with an epoxy resin-based adhesive, thereby creating a filter device with an effective filter area of ​​50-500 cm2. Thermoplastic adhesives that are approved for direct contact with liquid food are commercially available, for example from Bostik, Η. B. Fuller and Collano. The individual filter elements are placed in a suitable housing and a leak test is carried out on them using the well-known bubble point method. The essence of this is that after a short water rinse, a gas line is connected to the housing inlet and the outlet pipe for the filtered water from the housing is led into a water bath. The gas pressure is gradually increased until a constant bubble flow is established in the housing outlet pipe. This pressure, the so-called bubble point pressure, has a value of 324.240 kPa (3.2 atm). This pressure is within ±10.133 kPa (0.1 atm) of the pressure value specified by the manufacturer for the Supor 200 membrane, which proves that the housing and the filter device have been assembled correctly and that the membrane has the required nominal pore size. Another possible embodiment of the water purification device according to the invention, also including the above-mentioned filter device, was tested at a constant flow rate of 2 1 / min. The pressure difference was continuously measured with pressure gauges located before and after the filter, and when the pressure difference (i.e. the pressure drop) exceeded 263.705 kPa (2.6 bar), the test was terminated. The amount of water flowed through was measured with a built-in water meter. The results of the test resulted in a graph similar to that shown in Figure 7. The water quality was regularly tested by measuring the sludge density or the filtration factor, and it was found that the filtration factor value varied between 8 and 15 during one day of observation, with its daily average value ranging between 10 and 12. Based on Figure 7, a filtration system can be designed in which the maximum number of pre-filters and membrane filters must be used to achieve a predetermined filtration throughput and flow rate. For example, based on the graph, a filtration system can be implemented that is capable of filtering 10 m3 of water at a maximum pressure drop of 253.313 kPa and a flow rate of 2 1 / min. As shown in Figure 7, the maximum water flow rate at the mentioned permeability cannot exceed 8 cm / min. Since the desired flow rate is 2000 cm3 / min, the required filter area is large6 HU 222 893 ΒΙ the surface area - i.e. the sum of the surface area of ​​the pre-filter and the membrane filter - is given as the ratio of the flow rate to the flow rate, i.e. 250 cm2. Of course, it is possible to design a larger filter surface in order to ensure adequate filtration performance and to prepare for possible changes in water quality. In the case characterized by the graph shown in Figure 7, the water quality was essentially constant. A block diagram of a possible embodiment of the device according to the invention is shown in Figure 8. In this embodiment, a conventional centrifugal pump operating at a maximum pressure of 1.0133 MPa and providing a flow rate of 10-20 1 / min is connected to a 50 liter tank, which is continuously filled through a water tap. A standard water pressure regulator with a pressure gauge operating in the range of 0-0.6 MPa and set to 0.4 MPa is connected to the outlet of the pump, which sets the pressure of the water entering the tank. The water pressure regulator is connected to the filter housing, which contains the filter elements described above. The water pressure gauge at the outlet is connected to a second water pressure regulator, which reduces the water pressure to 0.05 MPa. This is the lowest possible pressure at which the water pressure regulator still operates effectively. The water pressure regulator is equipped with a water meter (Arad Ltd., Israel), and is connected to a ball flow meter with a built-in needle valve (Fisher Porter, USA). A separate electronic control unit controls the operation of a standard solenoid valve that ensures timely shut-off. The embodiments of the device according to the invention presented in the description serve only as examples, and it is obvious to those skilled in the art that the solutions presented in the description can be arbitrarily modified and combined within the claimed scope of protection.

Claims

PATENT CLAIMS 1. A device for purifying drinking water, having an inlet opening (50) suitable for introducing feed water, an outlet opening suitable for discharging purified water, and a filter device (30, 54) arranged between the inlet opening (50) and the outlet opening, characterized in that it comprises a control device for maintaining the flow rate of the water flowing out through the outlet opening at a constant value during the useful life of the filter device (30, 54), and the filter device comprises a pre-filter (52) and a microporous membrane filter (53).

2. The apparatus of claim 1, characterized in that it comprises means for measuring the time elapsed since the filter means (30, 54) was put into operation - as a first time period -, means for measuring the cumulative sum of the flow periods of water flowing through the filter means (30, 54) - as a second time period - and means for preventing the flow of water through the filter means (30, 54) if a predetermined threshold value is reached by either of the first and second time periods.

3. The apparatus of claim 1, characterized in that the control means for ensuring a constant flow rate of water comprises means for applying pressure to the filter means (30, 54) and means for controlling the flow rate independently of pressure changes.

4. The device according to claim 1, characterized in that the control device comprises a flow restrictor.

5. The apparatus of claim 1, wherein the filter means (30, 54) has at least one filter element (10) comprising an innermost absorption layer (14); two microporous membrane layers (12, 12') symmetrically arranged near the two sides of the innermost absorption layer (14); and two pre-filter layers (11, 11') symmetrically arranged near the outer sides of the microporous membrane layers; wherein the microporous membrane layers (12, 12') and pre-filter layers (11, 11') are sealed together along their upper edges, the absorption layer (14) and the microporous membrane layers (12, 12') are sealed together with the pre-filter layer (11, 11') along the lower edge (20) of the pre-filter layer (11, 11'), the microporous membrane layers (12, 12') and the pre-filter layers (11, 11') are wider than the absorption layer (14), and the microporous membrane layers (12, 12') and the pre-filter layers (11, 11') are sealed together with the side edges (22);further, the filter device (30, 54) comprises one or more filter elements (10) arranged perpendicularly to the bottom plate (31) having a central opening (32) and a top plate, parallel to each other and crossing the central opening (32) directly above the top plate of the bottom plate (31) with the lower edge (20) of the pre-filter layers (11, 11'), said filter elements (10) being sealed to the bottom plate (31) by means of an adhesive filled in the space between the inner rim (33) of the central opening (32) of the bottom plate (31) and the filter elements (10), and further, the filter elements (10) and the bottom plate (31) are fixed in a housing (35) capable of withstanding liquid overpressure in such a way that water flowing into the housing (35) without being harvested is forced to flow through the filter elements (10), and thereby the water is flows out of the housing (35) in a filtered state; 6. A method for purifying drinking water, characterized in that water is passed through a water purification filter device (30, 54) comprising a pre-filter (52) and a microporous membrane filter (53) at a constant flow rate.

7. The method of claim 6, characterized in that the time elapsed since the filter device (30, 54) was put into operation is measured as a first time period, the cumulative sum of the flow periods of water flowing through the filter device (30, 54) is measured as a second time period, and the flow of water through the filter device (30, 54) is prevented if the first or second time period has reached a predetermined threshold.

8. Method for adjusting the device according to claim 5, characterized in that HU 222 893 Bl the water is made to flow at an initial flow rate in the filter element (10) until the pressure difference between the inlet and outlet points of the filter device (30, 54) reaches a predetermined value; the permeability of the device is measured and plotted as a function of the water flow rate, where the flow rate is the ratio of the flow rate to the total surface area of ​​the filter elements (10); the previous two steps are repeated at different flow rates by modifying the constant flow rate or by changing the size of the filter surfaces, and the permeability of the device is plotted on a graph as a function of the water flow rate; the desired value of the permeability is selected based on the graph, and the flow rate corresponding to the desired permeability is determined;finally, we maintain a flow rate corresponding to the selected permeability and use a filter surface of the appropriate size; 9. A method for filtering a liquid, characterized in that the optimum flow rate of the liquid flowing through a filter device having a filter surface and at least one pre-filter placed near a microporous membrane is determined by operating identical filter devices at different constant flow rates until the total pressure drop in each of the filter devices reaches a given value; the throughput associated with each filter device for a given period of time is recorded; then, based on the throughputs associated with the different constant flow rates, the relationship between the flow rate and the throughput associated with the filter device is determined, where the flow rate is the ratio of a given flow rate to the filter surface area of ​​the filter device; and the filter device is operated while maintaining a constant flow rate corresponding to the desired throughput.

10. The method according to claim 9, characterized in that a filter device is used which has a filter surface of variable size, and the size of the filter surface is selected according to the flow rate corresponding to the desired throughput.