JP2006281023A - Water cleaning system and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water cleaning system which prevents degradation of a functional layer of an RO membrane and an NF membrane causing bio-fouling and residual chlorine, can extend a life of a cartridge, and can suppress bacterial contamination from a storage tank at a rear stage to an intake bib cock in the water cleaning system including a silver-deposited activated carbon cartridge, a reverse osmosis membrane cartridge or a nano filtration membrane cartridge for carrying out membrane filtration of water treated by the silver-deposited activated carbon cartridge, and a storage tank for storing water carried out filtration treatment by the reverse osmosis membrane cartridge or the nano filtration membrane cartridge; and a water cleaning method. <P>SOLUTION: The water cleaning system comprises the silver-deposited activated carbon cartridge, the reverse osmosis membrane cartridge or the nano filtration membrane cartridge for carrying out membrane filtration of the water treated by the silver-deposited activated carbon cartridge, and the storage tank for storing the water carried out filtration treatment by the reverse osmosis membrane cartridge or the nano filtration membrane cartridge, wherein a silver zeolite cartridge is immersed and placed in the storage tank. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a water purification system and a water purification method using silver impregnated activated carbon, silver zeolite, and a reverse osmosis membrane or a nanofiltration membrane. More specifically, pretreatment is performed with a silver-impregnated activated carbon cartridge installed in the previous stage of the reverse osmosis membrane cartridge or nanofiltration membrane cartridge, and functional layer deterioration caused by biofouling and residual chlorine of the reverse osmosis membrane or nanofiltration membrane is performed. The present invention relates to a water purification system and a water purification method capable of preventing and extending the life of a cartridge and suppressing bacterial contamination from a storage tank to a water intake faucet by a silver zeolite cartridge immersed in a subsequent storage tank.

  In recent years, various impurities remain in tap water due to deterioration of water source water quality due to environmental pollution, resulting in off-flavor damage such as chalky odor and mold odor. In particular, the carcinogenic trihalomethane produced due to chlorine remains in a small amount, and it is preferable to purify tap water by an appropriate method in order to obtain safer and more delicious beverage / cooking water.

  As one of the methods for purifying tap water, a method using a reverse osmosis membrane (hereinafter referred to as “RO membrane”) or a nanofiltration membrane (hereinafter referred to as “NF membrane”) is a method of using organic matter or inorganic in water. Although it is possible to remove many impurities such as ions, bacteria, viruses, etc., since the amount of membrane filtration treated water per unit pressure per unit membrane area is low compared to microfiltration membranes and ultrafiltration membranes, a given membrane A large membrane area and a booster pump were required to secure the amount of filtered water. Therefore, a method has been used in which filtration is continued while the amount of membrane filtration treated water is small even when the membrane filtration treated water is not used, the membrane filtration treated water is secured in a storage tank, and water is taken from there.

  Moreover, since many of the materials of RO membrane and NF membrane are a polyamide type, there exists a possibility that a functional layer may deteriorate with the residual chlorine in tap water, and membrane filtration processing water quality may deteriorate. Generally, after removing residual chlorine in tap water using activated carbon etc., there is a method of filtering with RO membrane or NF membrane, but because the residual chlorine is removed, the antibacterial property of tap water is lost, Problems that the permeability of RO membranes and NF membranes deteriorates due to the growth of microorganisms on the membrane surface or the adhesion of slime substances (biofilms) occupied by microorganisms and microbial metabolites to the membrane surface, that is, biofouling Occurs.

  In order to solve such a problem, for example, as disclosed in Patent Document 1, when using a method using silver-impregnated activated carbon and sterilizing with silver ions, it is possible to suppress biofouling of RO membrane or NF membrane. Although it is possible, silver ions eluted in tap water are removed by RO membranes and NF membranes, so almost no silver ions remain in membrane filtration treated water, and bacterial contamination in the storage tank can be avoided. There is no problem. In order to solve this problem, it is recommended to periodically wash the storage tank and discard the membrane filtration treated water that stayed in the storage tank for a certain period of time, but it is difficult to implement in practice, The effect is unknown and has not led to a fundamental solution.

In order to solve such a problem, as disclosed in Patent Document 2, for example, when using a method of storing membrane filtration treated water in a storage tank after processing with a cartridge made of silver-impregnated activated carbon or silver zeolite, With impregnated activated carbon, the amount of adsorbed organic matter that can be a nutrient source for microorganisms increases on the activated carbon surface where silver is not impregnated. There was a risk that bacteria would grow on the surface of activated carbon that was not attached. In addition, in silver zeolite, since the sustained release amount of silver ions is generally small, it is difficult to say that sufficient silver ion concentration is obtained only by passing water. As the number of cartridges increases, it is difficult to make the cartridge compact.
JP-A 61-054278 Japanese Patent Laid-Open No. 10-085590

  The present invention solves the above-mentioned problems of the prior art, and pre-treats with a silver-impregnated activated carbon cartridge installed in the previous stage of the RO membrane cartridge or NF membrane cartridge, so that biofouling of RO membrane or NF membrane and It is an object of the present invention to provide a water purification system and a water purification method capable of preventing functional layer deterioration due to residual chlorine, extending the life of a cartridge, and suppressing bacterial contamination from a storage tank at a later stage to a water intake faucet.

  In order to achieve the above object, the present invention adopts the following configuration.

  That is, a silver-impregnated activated carbon cartridge, an RO membrane cartridge or NF membrane cartridge that performs membrane filtration on water treated with the silver-impregnated activated carbon cartridge, and water that has been membrane filtered with the RO membrane cartridge or NF membrane cartridge are stored. A water purification system comprising a storage tank that has a storage tank in which a silver zeolite cartridge is immersed and installed in the storage tank.

  At this time, when turbidity such as iron rust is mixed in the tap water, the flow path on the primary side of the RO membrane cartridge or the NF membrane cartridge is clogged or the cake layer on the membrane surface becomes thick, so that membrane filtration treatment is performed. Since there is a concern that the amount of water may decrease, it is preferable that a filter cartridge having an average pore diameter of 0.5 to 10 μm is installed in the front stage of the RO membrane cartridge or the NF membrane cartridge. In order to reduce the number of cartridges and save the trouble of cartridge replacement, it is preferable that the silver impregnated activated carbon and the filter having an average pore diameter of 0.5 to 10 μm are integrally configured.

  Further, the RO membrane cartridge includes a water level sensor that controls the water level of the storage tank and a supply valve that opens and closes by a signal from the water level sensor, or when the tap water pressure is too low to secure a predetermined amount of membrane filtration water. Alternatively, it is preferable that a pump is provided in front of the NF membrane cartridge, or a constant flow valve for controlling the flow rate of the concentrated water of the RO membrane cartridge or the NF membrane cartridge to be constant in order to control the water recovery rate.

  Further, the present invention uses tap water pressure alone or water pressure increased by a pump to treat tap water with a silver-impregnated activated carbon cartridge, and then membrane-filter with an RO membrane cartridge or an NF membrane cartridge. A water purification method for storing treated water in a storage tank, wherein silver is gradually released from the silver zeolite cartridge immersed in the storage tank to the membrane filtration treated water.

  At this time, before treating the tap water with the silver-impregnated activated carbon cartridge, pre-treat with a filter cartridge having an average pore diameter of 0.5 to 10 μm, or after treating the tap water with the silver-impregnated activated carbon cartridge, Prior to membrane filtration with a reverse osmosis membrane cartridge or the nanofiltration membrane cartridge, it is preferable to pre-treat with a filter cartridge having an average pore size of 0.5 to 10 μm.

  Further, the silver-impregnated activated carbon and the filter having an average pore diameter of 0.5 to 10 μm are integrally formed, or silver eluted into water from the silver-impregnated activated carbon constituting the silver-impregnated activated carbon cartridge. The concentration of ions is 10 μg / l or more, and the chlorine concentration in the treated water after treatment with the silver-impregnated activated carbon cartridge is 0.1 mg / l or less, or from the silver zeolite constituting the silver zeolite cartridge When the concentration of silver ions in the stored water in the storage tank that has been gradually released is 10 μg / l or more and 100 μg / l or less, or when the water level of the storage tank reaches a certain water level, the RO membrane cartridge or the NF The membrane filtration process in the membrane cartridge is automatically stopped, the concentration of the RO membrane cartridge or the NF membrane cartridge is It is preferable to control the water flow rate constant.

  The present invention uses tap water pressure alone or water pressure via a pump to treat tap water with a silver-impregnated activated carbon cartridge, and then membrane-filter the RO membrane cartridge or NF membrane cartridge. A method for purifying water stored in a storage tank, wherein pretreatment is performed with a silver-impregnated activated carbon cartridge installed upstream of the RO membrane cartridge or the NF membrane cartridge, thereby biofouling and residual chlorine of the RO membrane or NF membrane. By preventing functional layer deterioration caused by the above, and extending the life of the RO membrane cartridge and the NF membrane cartridge, and gradually releasing silver into the membrane filtration treated water from the silver zeolite cartridge immersed in the storage tank, Bacterial contamination from the storage tank at the rear stage to the intake tap can be suppressed.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the drawings. Note that the present invention is not limited to the following embodiments.

  FIG. 1 is a schematic flow diagram showing an embodiment of a water purification system preferably used in the present invention. For example, as shown in FIG. 1, the water purification system of the present invention is directly connected to a water pipe, removes residual chlorine in tap water, and a filter 2a for removing turbidity such as iron rust in tap water. Membrane filtration treatment is performed on the water treated by the cartridge 2 in which the silver-impregnated activated carbon 2b for eluting silver into tap water and the cartridge 2 in which the silver-impregnated activated carbon and the filter are integrally formed. The RO membrane cartridge or NF membrane cartridge 4, the pump 3 provided in the previous stage of the RO membrane cartridge or NF membrane cartridge 4 when the tap water pressure is too low to secure a predetermined amount of membrane filtration water, and the water recovery rate is controlled. Therefore, a constant flow valve 5 for controlling the flow rate of the concentrated water of the RO membrane cartridge or the NF membrane cartridge 4 to be constant, and a storage tank 6 for storing the water subjected to the membrane filtration treatment, A silver zeolite cartridge 7 filled with silver zeolite pellets 9 for gradual release of silver in the membrane filtration treated water and immersed in the storage tank 6, a water level sensor 8 for controlling the water level of the storage tank, and a water level sensor 8 The supply valve 1 which opens and closes by the signal from and the water intake faucet 10 are provided.

  Here, as the cartridge 2 in which the filter 2a and the silver impregnated activated carbon 2b are integrally formed, for example, as shown in FIG. 2, a cylindrical filter 2a having an average pore diameter of 0.5 to 10 μm at the bottom of the cartridge, The cylindrical container is filled with silver impregnated activated carbon 2b, and the tap water filtered by the filter 2a passes through the silver impregnated activated carbon 2b. However, the order of passage of the filter 2a and the silver impregnated activated carbon 2b is reversed. It doesn't matter. The filter layer shape of the filter to be used is not particularly limited, and may be any of a pleated type and a wind type, and the material is not particularly limited, and may be any of polypropylene, polyester and the like. The silver-impregnated activated carbon to be used is not particularly limited as long as the silver ion concentration in tap water after passing through the silver-impregnated activated carbon is 10 μg / l or more and the chlorine concentration is 0.1 mg / l or less. For example, it is obtained by dissolving silver nitrate and magnesium nitrate in distilled water, spraying it uniformly on activated carbon, and then drying. Further, the shape of the silver-impregnated activated carbon may be any of powder, granule, fiber, etc., but the water inflow portion and the water outflow portion have a mesh structure, a nonwoven fabric filter, etc. so that the silver-impregnated activated carbon does not leak out of the cartridge 2. It is preferable that The raw material of the activated carbon forming the silver-impregnated activated carbon may be coconut shell, wood, coal, petroleum coke or the like.

  As a separation membrane used for the RO membrane cartridge or NF membrane cartridge 4 of the present invention, a RO membrane having a desalination rate of 93% or more (evaluation conditions NaCl concentration: 500 mg / l, operating pressure: 0.5 MPa), An NF membrane having a salt ratio of 5% or more and less than 93% (evaluation conditions NaCl concentration: 500 mg / l, operating pressure: 0.5 MPa) can be selected and used.

  As the material of the separation membrane having such performance, in the case of RO membrane, polymer materials such as cellulose acetate, cellulose-based polymer, polyamide, and vinyl polymer can be used. In the case of NF membrane, polyamide-based, polypiperazine An amide type, a polyester amide type, or a crosslinked water-soluble vinyl polymer can be used. Typical RO membranes include cellulose acetate-based or polyamide-based asymmetric membranes and composite membranes having a polyamide-based active layer. Among them, polyvinyl alcohol is used as the surface layer of the polyamide-based active layer. The coated composite membrane is preferable because it has high exclusion performance, high water permeability, and high stain resistance.

  As the shape of the separation membrane, it is preferable that both the RO membrane and the NF membrane are flat membranes or hollow fiber membranes. For example, the thickness of the separation membrane is in the range of 10 μm to 1 mm, and in the case of hollow fiber membranes, the outer diameter is 50 μm to 4 mm. It is preferable to be in the range.

  The RO membrane cartridge or NF membrane cartridge 4 has a spiral type, a pleated type, a plate-and-frame type, and a disc type in which disc-like discs are stacked when the separation membrane is a flat membrane. In this case, there is a cylindrical type in which hollow fiber membranes are bundled in a U shape or I shape and stored in a container, but the present invention is not affected by the shape of these cartridges. These cartridges are preferably capable of being operated at a low pressure from the viewpoint of reducing running costs.

  The silver zeolite forming the silver zeolite pellets 9 used in the present invention is one in which silver ions are incorporated into the structure of the aluminosilicate using the cation exchange ability of the aluminosilicate having a three-dimensional network structure, that is, At least a part of the cation (sodium ion, potassium ion, etc.) constituting the aluminosilicate with high ion exchangeability is replaced with silver ion, and the supported amount of silver ion is 0.1 to several wt%. Degree. Examples of the method for producing the silver zeolite pellets 9 include powdered silver zeolite kneaded into a resin such as polypropylene, polyethylene, ABS, and the like. The content of the kneaded silver zeolite is silver zeolite. It is appropriately selected depending on the silver ion sustained release performance. The silver zeolite exposed on the outer surface of the silver zeolite pellet 9 releases silver ions slowly, but the silver zeolite embedded in the silver zeolite pellets 9 does not release silver ions, so that the silver ions are released slowly. In order to improve the performance, it is necessary to reduce the particle diameter of the silver zeolite pellet 9 so that the outer surface area of the silver zeolite pellet 9 increases.

  The silver zeolite pellet 9 is mainly composed of slurry-like silver zeolite dispersed in water and acrylic resin, polyvinyl acetate, polyvinyl alcohol, etc., in addition to the powdered silver zeolite kneaded into a resin and granulated. And a binder, such as polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyester, etc., and those adhered to the surface of fibers or nonwoven fabrics, polyethylene, polyvinyl chloride, as in Japanese Patent No. 3087863, A powdery silver zeolite may be adhered in a state where the surface of a granular material of a thermoplastic resin such as polystyrene or polyamide is melted, or the silver zeolite itself may be a granular material. However, it is preferable that the water inflow portion and the water outflow portion have a mesh structure, a nonwoven fabric filter or the like so that the silver zeolite pellet 9 does not leak out of the silver zeolite cartridge 7. The container portion immersed in the storage tank of the silver zeolite cartridge 7 has, for example, a mesh structure and a non-woven fabric so that the silver ions released from the silver zeolite pellets 9 are easily diffused throughout the storage tank as shown in FIG. A filter or the like is preferable.

  In the water purification system of the present invention described above, water purification is performed as follows.

  First, when the water level sensor 8 in the storage tank 6 detects the water level L or lower, a signal is sent, the supply valve 1 is automatically opened, and the tap water is integrated with the filter 2a and the silver impregnated activated carbon 2b. The supplied cartridge 2 is supplied. By passing the tap water through the filter 2a, turbidity such as iron rust in the tap water is removed, and by passing through the silver impregnated activated carbon 2b, residual chlorine in the tap water is removed and silver is eluted in the tap water. . Next, the water treated by the cartridge 2 in which the filter 2 a and the silver impregnated activated carbon 2 b are integrally formed is supplied to the RO membrane cartridge or the NF membrane cartridge 4. Since residual chlorine is removed, the functional layer of the RO membrane or NF membrane does not deteriorate, and there is no possibility that the water quality of the membrane filtration treatment water will deteriorate.

  Further, since silver is eluted at 10 μg / l or more, the growth of general bacteria is suppressed and biofouling does not occur. However, since silver ions are almost removed by the RO membrane or NF membrane, almost no silver ions remain in the water filtered by the RO membrane or NF membrane. Therefore, the water filtered through the RO membrane or NF membrane flows into the silver zeolite cartridge 7, contacts with the silver zeolite pellet 9, and then stored in the storage tank 6, and the water not filtered through the RO membrane or NF membrane is constant. It is discharged out of the system as concentrated water through the flow valve 5.

  When the silver zeolite cartridge 7 comes into contact with water filtered through the RO membrane or NF membrane to release silver ions slowly, but the water filtered through the RO membrane or NF membrane does not flow into the silver zeolite cartridge 7 However, if it is immersed in water stored in the storage tank 6, silver ions diffuse into the storage tank 6.

  After the supply valve 1 is opened, when the water level of the storage tank 6 gradually rises and the water level sensor 8 in the storage tank 6 detects the water level H or higher, a signal is sent and the supply valve 1 is automatically turned on. Closed and clean water automatically stops. When the tap water pressure is too low to secure a predetermined amount of membrane filtration water, it is preferable to provide the pump 3 in front of the RO membrane cartridge or the NF membrane cartridge 4. At this time, it is preferable that the pump 3 is interlocked with the supply valve 1 so that the pump 3 operates when the supply valve 1 is open and stops when the supply valve 1 is closed.

  The concentration of silver ions that are gradually released from the silver zeolite pellets 9 in the silver zeolite cartridge 7 varies depending on the temperature, pH, and dissolved ion concentration (Na, Ca, Mg, etc.) of the water in the storage tank 6. Therefore, the silver ion concentration is such that the silver ion concentration in water with low temperature and low electrical conductivity (0 ° C., 10 μS / cm), which is the condition under which silver ions are most difficult to release slowly, is 10 μg / l or more. It is preferable to control so that the silver ion concentration in water with high temperature and high electrical conductivity (35 ° C., 1000 μS / cm), which is the condition under which ions are most easily released, is 100 μg / l or less.

  Here, as a specific means for controlling the concentration of silver ions to 10 μg / l or more and 100 μg / l or less, for example, a beaker containing 1 L of water having a low temperature and low electrical conductivity (0 ° C., 10 μS / cm). The silver zeolite pellets were added in 1 g unit to obtain the weight αg of the silver zeolite pellets when the silver ion concentration reached 10 μg / l, and then the high temperature, high electrical conductivity (35 ° C., 1000 μS / cm) The silver zeolite pellets are charged in units of 1 g into a beaker containing 1 L of water, and the weight of the silver zeolite pellets βg when the silver ion concentration reaches 100 μg / l is determined. Then, when the volume of the storage tank 6 is γL, the filling amount of the silver zeolite pellets 9 in the silver zeolite cartridge 7 is set to a range of αγg or more and βγg or less. This is because when the silver ion concentration is 10 μg / l or more, growth of general bacteria can be suppressed, and the reason why the concentration is 100 μg / l or less is the safety prescribed by the USEPA (US Environmental Protection Agency). It is based on the water quality standard of the drinking water law. In addition, the silver ion concentration prescribed | regulated by this invention is taken as the numerical value measured with the ICP emission-spectral-analysis apparatus.

  The invention is explained in more detail using the following examples. In the examples and comparative examples, each measurement result was performed according to the following method.

[Chromaticity of tap water (degrees)]
Colorimetric method Japan Water Works Association edited by “Water Supply Test Method”, p99 (2001).

[Electric conductivity of tap water (μg / l)]
Electrode method Measurement was performed according to the method described in “Water Supply Test Method”, p115 (2001), edited by Japan Water Works Association.

[Silver ion concentration (mg / l)]
ICP emission spectroscopic analysis was conducted according to the method described in “Water Supply Test Method”, p370 (2001), edited by Japan Water Works Association.

[General bacteria (cfu / ml)]
Standard agar medium method The measurement was performed according to the method described in Japan Water Works Association, “Water Supply Test Method”, p605 (2001).

Example 1
Using the water purification system shown in FIG. 1, tap water having a tap water pressure of 300 kPa, chromaticity of 4 degrees, electrical conductivity of 400 μg / l, and residual chlorine of 0.7 mg / l was purified daily by 5 L and discharged out of the system. Wind filter (ADVANTEC, TCW-1N-PPS) having an average pore diameter of 1 μm was used for filter 2a, and 250 g of granular activated carbon (Kuraray Chemical, Kuraray Coal T-SB 10/32 mesh) was used for silver-impregnated activated carbon 2b. For the RO membrane cartridge or NF membrane cartridge 4, 0.5 m ² of NF membrane (Toray, UTC-60) was used.

  As the pump 3, a pump having a discharge pressure of 700 kPa and a discharge amount of 26 L / h was used. As the silver zeolite pellets 9 in the silver zeolite cartridge 7, 200 g of 80 g of silver zeolite (Sinanen Zeomic, AJ10D) kneaded in 120 g of polyethylene resin (average particle size 1.5 mm) was used. The storage tank 6 has a volume of 6 L and is made of ABS resin. A constant flow valve 5 having a flow rate of 420 ml / min (Danamark, FLOW420) was used.

  As a result, the silver ion concentration of the water sampled from the water intake tap 10 was 12 to 95 μg / l for 3 months from the start of operation, and the general bacteria at that time were always 10 cfu / ml or less.

(Comparative Example 1)
Except for not using the silver zeolite cartridge 7, it was exactly the same as Example 1. As a result, the silver ion concentration of water collected from the water intake tap 10 was 1 to 3 μg / l for 3 months from the start of operation, and the general bacteria at that time were always 100 cfu / ml or more.

(Comparative Example 2)
Except for filling the silver zeolite cartridge 7 with silver zeolite pellets, the same procedure as in Example 1 was performed except that 30 g of granular activated carbon (Kuraray Chemical, Kuraray Coal T-SB 10/32 mesh) was filled. As a result, the silver ion concentration of water collected from the water intake tap 10 was 25 to 90 μg / l for 5 days from the start of operation, and the general bacteria at that time were always 10 cfu / ml or less. Although the ion concentration was 10 μg / l or more, general bacteria were always 100 cfu / ml or more.

(Comparative Example 3)
The same procedure as in Example 1 was performed, except that the silver zeolite cartridge 7 was not immersed in the tank and the NF membrane filtrate after passing through the silver zeolite cartridge 7 was allowed to flow into the storage tank 6. As a result, the silver ion concentration of water collected from the water intake tap 10 was 10 to 25 μg / l for one month from the start of operation, and the general bacteria at that time were always 10 cfu / ml or less. The silver ion concentration was less than 10 μg / l, and general bacteria were always 100 cfu / ml or more.

It is a schematic flowchart which shows one embodiment of the water purification system preferably used for this invention. It is a figure which shows one implementation structure of the cartridge by which the filter and silver impregnated activated carbon which are preferably used for this invention are comprised integrally. It is a figure which shows one implementation structure of the silver zeolite cartridge preferably used for this invention.

Explanation of symbols

1: Supply valve 2: Cartridge in which a filter and silver impregnated activated carbon are integrally formed 2a: Filter 2b: Silver impregnated activated carbon 3: Pump 4: Reverse osmosis membrane cartridge / nanofiltration membrane cartridge 5: Constant flow valve 6: Storage Tank 7: Silver zeolite cartridge 8: Water level sensor 9: Silver zeolite pellet 10: Water intake faucet

Claims (14)

Silver impregnated activated carbon cartridge, reverse osmosis membrane cartridge or nanofiltration membrane cartridge for membrane filtration of water treated with silver impregnated activated carbon cartridge, and water subjected to membrane filtration treatment with reverse osmosis membrane cartridge or nanofiltration membrane cartridge A water purification system comprising a storage tank for storing water, wherein a silver zeolite cartridge is immersed in the storage tank. 2. The water purification system according to claim 1, wherein a filter cartridge having an average pore diameter of 0.5 to 10 μm is installed upstream of the reverse osmosis membrane cartridge or the nanofiltration membrane cartridge. The water purification system according to claim 2, wherein the silver-impregnated activated carbon cartridge and the filter cartridge are integrally configured cartridges. The water purification system according to any one of claims 1 to 3, further comprising: a water level sensor that controls a water level of the storage tank; and a supply valve that is opened and closed by a signal from the water level sensor. The water purification system according to any one of claims 1 to 4, wherein a pump is provided in front of the reverse osmosis membrane cartridge or the nanofiltration membrane cartridge. The water purification system according to any one of claims 1 to 5, further comprising a constant flow valve for controlling the flow rate of the concentrated water of the reverse osmosis membrane cartridge or the nanofiltration membrane cartridge to be constant. Tap water is treated with a silver-impregnated activated carbon cartridge using tap water pressure alone or with water pressure increased by a pump, and then membrane filtration is performed with a reverse osmosis membrane cartridge or nanofiltration membrane cartridge, and then the membrane filtration treated water is stored. A water purification method for storing in a tank, wherein silver is gradually released from the silver zeolite cartridge immersed in the storage tank into the membrane filtration treated water. The water purification method according to claim 7, wherein the tap water is treated in advance with a filter cartridge having an average pore diameter of 0.5 to 10 μm before the tap water is treated with the silver-impregnated activated carbon cartridge. After treating tap water with the silver-impregnated activated carbon cartridge and before membrane filtration with the reverse osmosis membrane cartridge or the nanofiltration membrane cartridge, it is pretreated with a filter cartridge having an average pore size of 0.5 to 10 μm. The water purification method according to claim 7, wherein the water purification method is characterized. The water purification method according to claim 8 or 9, wherein the silver-impregnated activated carbon cartridge and the filter cartridge are cartridges configured integrally. The concentration of silver ions eluted into the water from the silver-impregnated activated carbon constituting the silver-impregnated activated carbon cartridge is 10 μg / l or more, and the chlorine concentration in the treated water after treatment with the silver-impregnated activated carbon cartridge is 0.1 mg. The water purification method according to any one of claims 7 to 10, wherein the water purification method is 1 or less. The concentration of silver ions in the storage water in the storage tank, which is gradually released from the silver zeolite constituting the silver zeolite cartridge, is 10 μg / l or more and 100 μg / l or less. The water purification method as described in. The water purification method according to any one of claims 7 to 12, wherein when the water level of the storage tank reaches a certain water level, the membrane filtration process in the reverse osmosis membrane cartridge or the nanofiltration membrane cartridge is automatically stopped. . The water purification method according to any one of claims 7 to 13, wherein a concentrated water flow rate of the reverse osmosis membrane cartridge or the nanofiltration membrane cartridge is controlled to be constant.