JP2005313151A - Water treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water treatment method suppressing the deterioration in a filtration performance of a membrane by sterilizing microorganisms existing in water by the elution of silver from an introduced silver based inorganic antibacterial agent, in a water treatment method using a membrane having the average pore diameter of less than 0.1 μm by solving such problems that sodium hypochloride used recently causes chemical deterioration of a membrane with chlorine, especially in a case of using a reverse osmosis membrane for a water separation apparatus, and moreover, it is well known that a water cleaner for domestic use uses silver zeolite for preventing the deterioration of a membrane, however in cases that holes of a membrane are fine or objective water is dirty compared with cleaned drainage, seawater, or the like, it is not confirmed that the same effect can be obtained. <P>SOLUTION: In the water treatment method using the membrane having the average pore diameter of less than 0.1 μm, the silver based inorganic antibacterial agent having excellent safety/versatility/operability is introduced into parts of piping, and the deterioration in various filtration membranes derived from microorganisms is suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a water treatment method characterized by passing a target water through a separation membrane after contacting the target water with a silver-based antibacterial agent.

Membrane separation technology is used in a wide range of fields such as desalination of seawater and brine, medical care, industrial pure water, ultrapure water production, domestic water purification, and industrial wastewater treatment. In these membrane separations, the contamination of the separation device by microorganisms is caused by deterioration of the quality of the permeated water obtained, growth of microorganisms on the membrane surface, adhesion of microorganisms and their metabolites to the membrane surface, separability, etc. Bring about a decline. In order to avoid such an important problem, various sterilization methods for membrane separation apparatuses have been proposed. In general, a method in which a sterilizing agent is added to the supply liquid constantly or intermittently is employed. As a disinfectant, it is most common to add a chlorine-based disinfectant having a proven record and advantageous in terms of price and operation so as to have a concentration of about 0.1 to 50 ppm. However, it has become clear that chlorine-based disinfectants not only cause chemical deterioration of reverse osmosis membranes, but chlorine is not necessarily sufficient to disinfect microorganisms. There is also a theory that by adding chlorine, organic carbon present in the feed liquid is oxidized and converted into a compound that is easily decomposed by microorganisms (Non-Patent Document 1), but it has not been proved. Therefore, a method of sterilizing by adding sodium hydrogen sulfite intermittently at a concentration of usually 500 ppm has been developed and has been generally used. However, this method is also not effective in some cases, and microorganisms are not membranes. It is becoming increasingly clear that it accumulates in Examples of the bactericidal effect of sodium hydrogen sulfite include the ability to remove oxygen in the supply liquid and lowering the pH.
In Patent Documents 1 and 2, it is effective to lower the pH for antibacterial purposes, and it is not necessary to add expensive sodium bisulfite at a high concentration, and it is sufficient to simply lower the pH by adding an inexpensive acid such as sulfuric acid. It was found that it can be sterilized.

    In recent years, in the field of antibacterial technology, inorganic antibacterial agents mainly composed of silver ions as antibacterial components have attracted attention because they are superior in safety, heat resistance and permanence compared to organic antibacterial agents. As a specific form of the antibacterial agent, it is possible to effectively exhibit the antibacterial performance of silver ions, and at the same time it is easy to use, so a structure in which silver ions are held in a porous ceramic is generally used. It has become. Zeolite (Patent Document 3), layered silicate (Patent Document 4), calcium phosphate (Patent Document 5) and the like are used as the porous ceramic as the support.

As a measure for preventing the generation of microorganisms such as bacteria, Patent Document 6 uses silver zeolite (Zeomic made by Sinanen Zeomic or Bacterial made by Kanebo Co., Ltd.) as a silver-based antibacterial agent in front of the hollow fiber membrane used in household water purifiers. It is known to use coated nonwovens.
Japanese Patent Laid-Open No. 10-204873 JP 2000-354744 A JP-A-3-255010 Japanese Patent Laid-Open No. 2-19308 JP-A-4-243908 JP 2002-239539 A AB Hamida, I. Moch Junior, Desalination & Water Reuse, 6/3, 40-45, 1996

However, in the methods of Patent Documents 1 and 2, in order to further enhance the sterilizing effect, it is preferable that the acid addition apparatus can be automatically controlled, and a pump capable of appropriately controlling the injection amount must be provided. In addition, it is equipped with a device that measures the pH of the supply liquid and concentrate, a device that can measure time to control intermittent addition, an automatic control device that can be operated automatically, etc. There must be. In addition, the structural members such as pipes and valves have many problems that lead to enlarging of the apparatus and deterioration of operability, such as having to use materials that are difficult to change under a pH of 2.6 or less.
In the technique described in Patent Document 6, the pore diameter of the hollow fiber membrane of a domestic water purifier is generally about 0.1 μm, and the effect is not shown in the case of a membrane having a pore diameter smaller than that. In addition, water used at home has been purified to some extent at the water treatment plant before arrival, so the number and type of bacteria is considered to be relatively small compared to sewage, wastewater, seawater, etc. It has not been confirmed whether the same antibacterial technology is effective even under severe conditions.

    An object of the present invention is to provide a water treatment method that solves the above-described conventional problems, has high operability and economy, and is effective for various types of target water and filtration membranes.

    The object of the present invention is achieved by the following constitution. That is, the present invention is “a water treatment method characterized by passing a target water to a silver antibacterial agent and then passing through a separation membrane having pores having a pore diameter of less than 0.1 μm”.

    In the water treatment method characterized by using a membrane, the elution of silver from the introduced silver-based inorganic antibacterial agent sterilizes and disinfects microorganisms present in the water, and suppresses the filtration performance deterioration of the membrane.

    The present invention is described in detail below. The water treatment method of the present invention is a water treatment method using a membrane having a pore diameter of less than 0.1 μm, and is introduced into a membrane separation apparatus after contacting the target water with a column filled with a silver-based inorganic antibacterial agent. And

    In the method of the present invention, a membrane having an average pore size of less than 0.1 μm is used as the membrane. There are three types of membranes of 5 μm or less, a microfiltration membrane having an average pore size of 5 μm to 20 nm (0.02 μm) capable of capturing bacteria and yeast, and 20 nm (0. There are ultrafiltration membranes having an average pore size of 02 μm) to 1 nm (0.001 μm), and reverse osmosis membranes having an average pore size of 1 nm (0.001 μm) or less capable of capturing glucose, metal ions and the like.

    Ultrafiltration membranes and reverse osmosis membranes are known to have an average pore size of less than 0.1 μm from the above, but some microfiltration membranes have an average pore size of 0.1 μm or more. In order to evaluate the average pore diameter of the microfiltration membrane, the bubble point method was used. The bubble point method will be described below. A microfiltration membrane is installed on a glass Nutsche, and water is poured from above. Air pressure is applied from the underside of Nutsche to measure the minimum pressure at which bubbles can be confirmed on the membrane surface. This is called a bubble point. The pore diameter can be estimated from the relational expression between the surface tension of the liquid and this pressure.

d = 4γcosθ / ΔP
Where d: pore diameter / m, θ: contact angle between membrane and solvent, γ: surface tension of solvent / N / m, ΔP: bubble point pressure / Pa. Solving the above equation with a pore system of 1.0 × 10 ⁻⁷ , a surface tension of water of 0.072 N / m, and cos θ = 1,
ΔP = 4γcosθ / d = 0.284 × 10 ⁷ = 2.84 MPa
It becomes. Therefore, the film having a bubble point of greater than 2.84 MPa was made a film of less than 0.1 μm.

    In this study, an indicator bacterium having a size of 0.1 μm was used, and those having a retention of 90% or more were evaluated as having a membrane pore of less than 0.1 μm.

    In the present invention, it is important that the target water is brought into contact with the silver-based antibacterial agent prior to contacting with the membrane. As the silver-based antibacterial agent, an inorganic antibacterial agent mainly composed of silver ions as an antibacterial component is preferable because it is excellent in safety, heat resistance and durability. In order to sufficiently exhibit the antibacterial performance of silver, it is preferable to retain silver in a highly reactive ionic state rather than retaining silver in a metal state. However, although silver in a metallic state is inferior to silver ions, a certain sterilizing power is recognized. Although there are no legal regulations regarding silver elution in Japan, the water purifier leaching performance standard of the Japan Water Works Association is 100 ppb or less, which is consistent with the drinking water standard of the US Environmental Protection Agency (EPA). I'm doing it. That is, in the water treatment method using the present invention, there is a high possibility of drinking the treated water, and it is preferable to keep the elution amount of silver at 100 ppb or less.

    As a specific form of the antibacterial agent, it is possible to effectively exhibit the antibacterial performance of silver ions, and at the same time it is an easy-to-use form. ing. At that time, zeolite, layered silicate, calcium phosphate, or the like is used as the porous ceramic as the carrier. Among the porous ceramics used as the support, it is preferable to use zeolite.

    The silver-based inorganic antibacterial agent used in the present invention is preferably silver zeolite. Zeolite is a crystalline microporous material. Crystalline aluminosilicate, crystalline metallosilicate, crystalline metalloaluminosilicate, crystalline aluminophosphate, crystalline metalloaluminophosphate having a uniform pore size of molecular size. It is crystalline silicoaluminophosphate. The metallosilicate and metalloaluminosilicate herein are those in which a part or all of the aluminum of the aluminosilicate is substituted with a metal other than aluminum such as gallium, iron, titanium, boron, cobalt, and chromium. Similarly, metalloaluminophosphate refers to aluminophosphate in which a part of aluminum or phosphorus is substituted with other metal.

In the present invention, the term “zeolite” refers to Atlas of Zeolite Structure types (WM Meier, DH Olson, Ch. Baerlocher, Zeolites, 17 (1/2), 1996) (Ref. 1) means all zeolite structures. A new type of zeolite having a structure not described in the above literature is also included in the zeolite of the present invention. However, L-type zeolite, faujasite-type zeolite, A-type zeolite, MFI-type zeolite, mordenite-type zeolite, β-type zeolite, Ω-type zeolite, AFI-type zeolite, AEL-type zeolite, and ATO-type zeolite are preferably easily available. preferable. In addition, artificial zeolite based on various raw materials such as coal ash, paper sludge incineration ash, activated sludge incineration ash and the like can also be used.

    Various methods have been disclosed so far for the synthesis method of zeolite. For example, various synthesis methods are described in Handbook of Molecular Sieves (R. Szostak, VAN NOSTRAND RAINHOLD, 1992) (Reference 2). The crystallite size of the zeolite varies depending on the composition of the reaction mixture at the time of synthesis, the crystallization temperature, the crystallization time, the stirring speed, the crystal size, the molar ratio of silica and alumina, and the crystallinity. Does not matter.

    In addition, the amount of zeolite used varies depending on the various zeolites, but since the amount of silver retained is 0.1 to 50% by weight, the smaller the amount of zeolite used, the more zeolite that can retain silver, from the viewpoint of production cost. preferable.

    The introduction of silver into the zeolite includes an ion exchange method, an impregnation method, a CVD method, etc., but any method may be used. Preferably, the ion exchange method is good, and the operation of immersing the zeolite in an aqueous solution containing silver ions equimolar to the ion exchange capacity of the zeolite and stirring at room temperature to 80 ° C. replaces all ion exchange points of the zeolite with silver. It is preferable to carry out until

    The silver retained in the zeolite may be reduced to metallic silver, chlorinated to silver chloride, and sulfided to silver sulfide, and the state of silver and its modification method and conditions are not limited. In order to minimize the amount of silver ions eluted from the silver zeolite, modification by sulfurization in which hydrogen sulfide gas is allowed to flow through the silver zeolite under room temperature conditions is preferable. When the pore diameter of the zeolite is small and the retained silver is not completely sulfided, the same sulfurization treatment is performed under a temperature condition of 60 to 200 ° C.

    The surface of the silver zeolite may be modified with an organic silane agent such as tetramethoxysilane or tetraethoxysilane, or another kind of modifier. This is because the effect of suppressing the elution amount of silver ions to the necessary minimum can be obtained by controlling the size of the pore diameter by surface modification of silver zeolite or converting the surface properties into hydrophobicity. Of these, tetramethoxysilane or tetraethoxysilane is preferably used as the modifier.

    Moreover, you may coexist copper and zinc which are other types of metals which have antimicrobial property in a silver type antimicrobial agent. Depending on the target water, silver may not work effectively like silver-resistant bacteria. However, considering safety and antibacterial effect, it is most preferable that the metal contained in the zeolite is only silver.

    The silver antibacterial agent may be mixed with other antibacterial agents such as other types of inorganic antibacterial agents, organic antibacterial agents, and natural antibacterial agents. Examples of silver-based inorganic antibacterial agents include those obtained by holding the above copper and zinc on a carrier such as porous ceramics. Examples of organic antibacterial agents include quasi drugs, bactericidal disinfectants, and pharmaceuticals that are used as wound protection materials such as triclosan, chlorhexidine, sulfadiazine, and zinc pyrithione. Examples of natural antibacterial agents that are superior in terms of safety and environmental protection include chitosan, catechin, hinokitiol, and Miso bamboo.

    Moreover, when making a silver-type antibacterial agent contact with object water, the method is not ask | required. A column filled with a silver antibacterial agent may be installed in front of the membrane separation device, or when the target water is circulating water, it may be circulated with the target water as powder. When the pipe is made of resin or the like, zeolite may be mixed, and when there is a water storage tank, it may be simply immersed in the tank. However, in consideration of operability and recovery after use, a method of packing the column is preferable.

    In the present invention, the step of passing through a separation membrane is to supply a liquid to be treated, such as seawater or brine, to the membrane module under pressure for separation, permeation and concentration, for the purpose of fresh water, concentration, separation, etc. Process. Examples of membrane modules include reverse osmosis membrane modules, ultrafiltration membrane modules, and microfiltration membrane modules. In this step, it is preferable to use a membrane separation device, and there are a membrane separation device, such as a reverse osmosis membrane device, an ultrafiltration membrane device, a microfiltration membrane device, etc., depending on the type of membrane module used.

The reverse osmosis membrane apparatus preferably used in the membrane separation of the present invention will be described below. The reverse osmosis membrane device is composed of a reverse osmosis membrane module, a high pressure pump, and the like in which a plurality of reverse osmosis membrane elements are connected in series and stored in a pressure vessel. The liquid to be separated supplied to this reverse osmosis membrane device is the addition and aggregation of chemicals such as bactericides, flocculants, reducing agents and pH adjusters, precipitation, sand filtration, polishing filtration, activated carbon filtration, microfiltration, ultrafiltration. Pretreatments such as filtration and safety filter filtration are performed. For example, in the case of seawater desalination, after taking in seawater, particles and the like are separated in a sedimentation basin, and here, a disinfectant such as chlorine is added to perform sterilization. Further, sand filtration is performed by adding a coagulant such as iron chloride or polyaluminum chloride. The filtrate is stored in a storage tank, adjusted to pH with sulfuric acid, etc., and sent to a high pressure pump. A reducing agent such as sodium bisulfite is added to the solution to eliminate the bactericidal agent, and after passing through the safety filter, the pressure is increased by a high-pressure pump and supplied to the reverse osmosis membrane module. However, these pretreatments are appropriately employed depending on the type and use of the supply liquid to be used.
In addition, for example, in a reverse osmosis membrane device used for purification of domestic water, water purification is performed in the order of prefiltration, activated carbon treatment, (filtration), and reverse osmosis membrane treatment, and the obtained purified water is temporarily stored in a water tank. It is stored and further activated charcoal treated before being used.

    Here, the reverse osmosis membrane is a semipermeable membrane that allows some components in the liquid mixture to be separated, for example, a solvent to permeate and does not allow other components to permeate. A nanofiltration membrane or a loose RO membrane is also included in the reverse osmosis membrane in a broad sense. As the material, polymer materials such as cellulose acetate polymer, polyamide, polyester, polyimide, vinyl polymer are often used. In addition, the membrane structure has a dense layer on at least one side of the membrane, an asymmetric membrane having fine pores gradually increasing from the precision layer to the inside of the membrane or the other side, and another layer on the dense layer of the asymmetric membrane. There are composite membranes with a very thin active layer formed of a material. The membrane form includes hollow fiber and flat membrane. The film thickness of the hollow fiber and the flat film is preferably 10 μm to 1 mm, and the outer diameter of the hollow fiber is preferably 50 μm to 4 mm. In the flat membrane, the asymmetric membrane and the composite membrane are preferably supported by a substrate such as a woven fabric, a knitted fabric, or a nonwoven fabric. However, the method of the present invention can be used regardless of the reverse osmosis membrane material, membrane structure and membrane form, and both are effective. Typical reverse osmosis membranes include, for example, cellulose acetate-based and polyamide-based asymmetric membranes and composite membranes having polyamide-based and polyurea-based active layers. Among these, the method of the present invention is effective for cellulose acetate-based asymmetric membranes and polyamide-based composite membranes, and aromatic polyamide composite membranes are more effective.

  The reverse osmosis membrane element is formed to actually use the reverse osmosis membrane. The flat membrane is a spiral, tubular, plate and frame type element, and the hollow fiber is bundled. However, the present invention does not depend on the form of these reverse osmosis membrane elements.

  In addition, the reverse osmosis membrane element incorporates members such as a feed water channel material and a permeate channel material in a spiral shape, and any of these components may be used, but it is especially designed for high concentrations and high pressures. It is effective in the selected element. For example, if a mesh body with a rhombus is used as the feed water flow path material, the flow of the feed water is disturbed, so the thickness of the concentration polarization layer can be reduced, and the feed water containing a high concentration of solute It is effective. In addition, if a polyester fiber taffeta having grooves forming the permeate flow path is used as the permeate flow path material, or a non-woven fabric is laminated on the surface having the grooves, the membrane may be deformed or dropped even at high pressure. It is possible to effectively prevent the performance degradation due to.

  The operating pressure of the reverse osmosis membrane device is 0.1 MPa to 15 MPa, and it is properly used depending on the type of the supply liquid, the operating method, and the like. Relatively low pressure when supplying low osmotic pressure solutions such as brine water desalination, ultrapure water production, and domestic water purification. Used at high pressure.

  The operating temperature of the reverse osmosis membrane device is in the range of 0 ° C. to 100 ° C. If the temperature is lower than 0 ° C., the supply liquid is frozen and cannot be used. If the temperature is higher than 100 ° C., the supply liquid evaporates and cannot be used. .

    Further, the recovery rate of the separation device can be set from 5 to 100% according to the separation operation and the device. The recovery rate of the reverse osmosis membrane device can be appropriately selected between 5 and 98%. However, pretreatment and operating pressure must be taken into account according to the properties, concentration, and osmotic pressure of the supply liquid and concentrate. For example, in the case of seawater desalination, the recovery rate is usually 10 to 40%, and in the case of a highly efficient apparatus, the recovery rate is 40 to 70%. In the case of brine water desalination, ultrapure water production, and domestic water purification, it is possible to operate at a recovery rate of 70% or more and 90 to 95%.

  The configuration of the reverse osmosis membrane device mainly includes a high pressure pump and a reverse osmosis membrane module, and an optimum pump can be selected according to the operating pressure of the device.

  The reverse osmosis membrane module can be arranged in a single stage, but can be arranged in multiple stages in series and in parallel with the feed water. When arranged in series, a booster pump can be installed between each stage. In the serial arrangement of seawater desalination, a two-stage arrangement is particularly preferable from the viewpoint of equipment cost. A booster pump is installed between modules arranged in series to boost the supply liquid by about 1.0 to 5.0 MPa. It is preferable to supply the module to the subsequent stage. When arranged in series with the supply liquid, the effect of the method of the present invention is great because the time for the membrane module to contact with the supply water is long.

  Further, the reverse osmosis membrane module can be arranged in series with respect to the permeated water. This is a preferable method when the quality of the permeated water is insufficient or when it is desired to recover the solute component in the permeated water. When arranging in series with the permeated water, a membrane can be separated by pressurizing the permeated water again or applying extra pressure in the previous stage and applying back pressure. In the case where they are arranged in series with respect to the permeated water, an acid addition device is provided between the membrane modules in order to sterilize the rear membrane module portion.

  In the reverse osmosis membrane apparatus, the portion of the supplied water that has not permeated the membrane is taken out from the membrane module as concentrated water. The concentrated water can be discarded after being treated according to the application, or further concentrated by other methods. Further, part or all of the concentrated water can be circulated to the supply water. Even in the portion that has passed through the membrane, it can be discarded or used as it is, or a part or all of it can be circulated in the supply water.

Generally, the concentrated water of the reverse osmosis membrane device has pressure energy, and it is preferable to recover this energy in order to reduce the operating cost. As an energy recovery method, it can be recovered with an energy recovery device attached to any part of the high-pressure pump, but it must be recovered with a dedicated turbine-type energy recovery pump installed before and after the high-pressure pump or between modules. Is preferred. Further, the processing capacity of the membrane separation apparatus is an apparatus having a water volume of 0.5 m ^{3 to} 1 million m ³ per day.

  In the separation apparatus in which the present invention is used, it is preferable that the apparatus piping has a structure having as few residence portions as possible.

  Furthermore, the sterilization method of the present invention can be used in combination with other sterilization methods such as chlorine.

The membrane sterilization method of the present invention can be applied not only to a membrane separation apparatus but also to a water separation system including the membrane separation apparatus in part. For example, the system has the following configuration.
A. Intake device. This is a device that takes in raw water, and is usually composed of a water intake pump, chemical injection equipment, and the like.
B. A pretreatment device in communication with the water intake device. In this method, water supplied to the separation membrane device is pretreated and purified to a desired level. For example, it can be configured in the following order.
B-1 Coagulation filtration device.
B-2 Polishing filtration device.

However, an ultrafiltration device or a microfiltration device may be used instead of B-1 and B-2.
B-3 Chemical injection equipment such as flocculants, bactericides, and pH adjusters.
C. An intermediate tank that communicates with the pretreatment equipment and is installed as needed. This provides water volume control and water quality buffering functions.
D. When C is installed, the filter communicates with the intermediate tank, or when C is not installed, the filter communicates with the pretreatment device. This removes solid impurities from the water supplied to the membrane separator.
E. Membrane separator. It consists of a high-pressure pump and a separation membrane module. A plurality of membrane separation devices may be installed, and these may be installed in parallel or in series. In the case of setting in series, a pump for increasing the water pressure supplied to the subsequent separation membrane device can be provided between the membrane separation devices.
F. A post-treatment device connected to the membrane permeation side outlet of the membrane separator. The following devices are exemplified.
F-1 Deaerator. This has a decarboxylation function.
F-2 Calcium tower.
F-3 Chlorine injection.
G. An aftertreatment device connected to the raw water side outlet of the membrane separator. The following devices are exemplified.
G-1 A device for processing a feed solution whose pH is lowered. For example, neutralization equipment.
G-2 Discharge facilities.
H. In addition, a wastewater treatment apparatus may be provided as appropriate.

  In such an apparatus, a pump can be provided at an arbitrary place. Further, it is preferable that the silver-based inorganic antibacterial agent is introduced to elute the silver ions after the pretreatment device, before and after the D filter, or before the E high pressure pump.

  The method of the present invention can be suitably used for separation using a membrane, but is particularly effective for separation of an aqueous solution and can provide a highly efficient water production method. Furthermore, separation applications include separation and concentration of liquids and solids using microfiltration membranes, separation and concentration of turbid components using ultrafiltration membranes, and separation and concentration of dissolved components using reverse osmosis membranes. effective. In particular, seawater desalination, brine water desalination, industrial water production, ultrapure water, pure water production, pharmaceutical water production, food concentration, decontamination of tap water, advanced treatment in tap water, domestic water Effective in purification. Even when separating and concentrating organic substances that can be easily separated by a conventional oxidizing disinfectant, it can be concentrated and recovered without being decomposed by disinfection, and the effect of the method of the present invention is great. In the case of drinking water production, there is an effect of preventing generation of trihalomethane by chlorine sterilization.

  Hereinafter, the present invention will be described by way of examples.

Reference Example 1 Production of Zeolite Silver zeolite prepared as follows was used as a silver-based antibacterial agent.

Solid caustic soda (NaOH content 96.0 wt%, H ₂ O content 4.0 wt%, Katayama Chemical Co., Ltd.) 7.3 g, tartaric acid powder (tartaric acid content 99.7 wt%, H ₂ O content 0.3 wt%, Katayama Chemical Co., Ltd.) 10.2 g Dissolved in 583.8 g of water. To this solution was added 35.4 g of sodium aluminate solution (Al ₂ O ₃ content 18.5 wt%, NaOH content 26.1 wt%, H ₂ O content 55.4 wt%, manufactured by Sumitomo Chemical Co., Ltd.) to obtain a uniform solution. 111.5 g of silicic acid powder (SiO ₂ content 91.6 wt%, Al ₂ O ₃ content 0.33 wt%, NaOH content 0.27 wt%, Nipseal VN-3, manufactured by Nippon Silica Co., Ltd.) was gradually added to this mixture while stirring. A slurry aqueous reaction mixture was prepared. The composition ratio (molar ratio) of this reaction mixture was as follows.

SiO ₂ / Al ₂ O ₃ 25
H ₂ O / SiO ₂ 20
OH− / SiO ₂ 0.164
A / Al ₂ O ₃ 1.0 A: Tartrate The reaction mixture was sealed in a 1000 ml autoclave and then reacted at 160 ° C. for 72 hours with stirring at 250 rpm.

    After completion of the reaction, washing with distilled water 5 times and filtration were repeated, followed by drying at about 120 ° C. overnight. The obtained product was a pentasil-type zeolite having a 10-membered oxygen ring at the main cavity entrance, and the silica / alumina molar ratio was 21.9 as a result of composition analysis. The maximum secondary particle diameter of the zeolite was 40 μm.

15 g of alumina sol (Al ₂ O ₃ content: 10 wt%, manufactured by Sanyo Chemical Co., Ltd.) was added to 10 g of this zeolite powder (absolutely dry basis) and kneaded for about 2 hours. When kneading, an appropriate amount of distilled water was added to see the kneaded state to obtain a paste-like mixture. This was formed into a noodle-like shaped body through a screen having a 0.8 mmφ hole. After drying at 120 ° C. overnight, baking was performed at 500 ° C. for 1 hour. The fired molded body was passed through a 12-24 mesh sieve, and the size of the particles was made uniform.

Reference Example 2 Production of Silver Zeolite 10 g of a compact was added to a 4.5 wt% aqueous solution of silver nitrate (manufactured by Aldrich Japan) and subjected to ion exchange treatment at 70 to 80 ° C. for 2 hours. This ion exchange treatment was repeated twice and then washed five times with distilled water. It dried at 120 degreeC overnight and was set as the silver ion exchange type.

    This molded product was introduced into a 25 mmφ Pyrex (registered trademark) glass tube laid with quartz wool, and hydrogen sulfide gas was allowed to flow at room temperature under a condition of 20 ml / min for 1 hour to obtain a silver sulfide zeolite.

Example 1
The performance deterioration test by the adhesion and propagation of microorganisms on the membrane was performed using the apparatus of FIG. As the target water, seawater near Nagoya was stored in a 1000 L tank. In order to remove inorganic and organic impurities contained in seawater, a prefilter (Nippon Millipore) having pores with a pore diameter of 1 to 5 μm was installed after the tank. Water was passed through the system with a liquid feed pump (variable pump manufactured by Yamato Kagaku Co., Ltd.) for 1 month under conditions of a flow rate of 0.1 to 5 L / hr and a water pressure of 5 atm or less. The filtration membrane has an effective membrane area of 0.1 to 0.3 m ³ and a polyethersulfone ultrafiltration membrane (Pericon 2 cassette manufactured by Nihon Millipore) sandwiched between a dedicated holder and having pores with a pore diameter of less than 0.1 μm. used. All the pipes were connected to each device using a silicon tube having an inner diameter of 6.4 mm. The deterioration of the filtration membrane was judged from the change over time of the diaphragm pressure gauge (Nihon Millipore) and the liquid flow meter (As One) equipped before and after the filtration membrane. The results are shown in Table 1.

(Comparative Example 1)
About the above apparatus, let seawater pass through the ultrafiltration membrane without contacting the column filled with silver sulfide zeolite, and use the pressure gauge and the liquid flow meter equipped before and after the filtration membrane in the same way as above to degrade the filtration membrane. Evaluated. The results are shown in Table 1.

    Table 1 shows the measurement results of filter membrane deterioration depending on the presence or absence of an antibacterial agent. It can be seen that the introduction of the antibacterial agent improved both the water treatment flow rate and the pressure loss of the membrane. This suggests that a small amount of silver contained in the antibacterial agent has dissolved and the microorganisms adhering to the system or on the membrane have been antibacterial or sterilized.

(Reference Example 3) Production of zeolite Solid caustic soda (NaOH content 96.0 wt%, H ₂ O content 4.0 wt%, manufactured by Katayama Chemical Co., Ltd.) 1.02 g, cesium hydroxide (ICN Biomedicals Co., Ltd.) 1.37 g in water 10.49 g Dissolved in. 1.30 g of sodium aluminate (Al ₂ O ₃ content 53.38 wt%, Na ₂ O content 43.16 wt%, H ₂ O content 3.46 wt%, manufactured by Katayama Chemical Co., Ltd.) was added to this solution and stirred until a clear solution was obtained. . To this mixture, 9.8 g of colloidal silica (SiO ₂ content 40 wt%, H ₂ O content 60 wt%, Ludox-40, manufactured by DuPont) was gradually added with stirring. The composition ratio (molar ratio) of this reaction mixture was as follows.

Na ₂ O: Cs ₂ O: Al ₂ O ₃ : SiO ₂ : H ₂ O = 2.4: 0.7: 1.0: 10.0: 140.0
The reaction mixture was stirred at room temperature for 30 hours, sealed in a 25 ml autoclave, and reacted at 110 ° C. for 10 days.

  After completion of the reaction, washing with distilled water 5 times and filtration were repeated, followed by drying at about 120 ° C. overnight. The product thus obtained was an analcyme-type zeolite having an 8-membered oxygen ring at the entrance of the main cavity, and the silica / alumina molar ratio was 5.2 as a result of composition analysis. The secondary particle diameter of zeolite was 30 to 100 nm.

15 g of alumina sol (Al ₂ O ₃ content: 10 wt%, manufactured by Sanyo Chemical Co., Ltd.) was added to 10 g of this zeolite powder (absolutely dry basis) and kneaded for about 2 hours. When kneading, an appropriate amount of distilled water was added to see the kneaded state to obtain a paste-like mixture. After baking at 500 ° C. for 1 hour, the powder was ground in a mortar to obtain a particle size on the order of microns.

Reference Example 4 Production of Silver Zeolite 10 g of zeolite powder was added to a 4.5 wt% aqueous solution of silver nitrate (manufactured by Aldrich Japan), and ion exchange treatment was performed at 70 to 80 ° C. for 2 hours. This ion exchange treatment was repeated twice and then washed five times with distilled water. It dried at 120 degreeC overnight and was set as the silver ion exchange type.

  This molded product was introduced into a 25 mmφ Pyrex (registered trademark) glass tube laid with quartz wool (Tosoh), and hydrogen sulfide gas was allowed to flow for 1 hour under conditions of 60 ° C. and 20 ml / min. .

(Example 2)
Using the apparatus of FIG. 1, a performance deterioration test was performed by the adhesion and propagation of microorganisms on the membrane. Seawater was fed into the system for 3 months under the conditions of a flow rate of 200 ml / hr and a water pressure of 5 atm or less using 1 g of silver sulfide analthime of Reference Example 4. The deterioration of the filtration membrane was judged from the change with time of the flow rate after the filtration membrane. The results are shown in Table 2. Further, the silver elution concentration in the solution before the filtration membrane was quantified with a graphite furnace heated atomic absorption spectrometer (Z-5700, Hitachi). Furthermore, the state of the filtration membrane surface was confirmed visually.

(Comparative Example 2)
The test was conducted in the same manner as in Example 2 except that water was passed through without contacting the column filled with silver sulfide analthime. The results are shown in Table 2.
From the results in Table 2, it can be seen that the introduction of the antibacterial agent has improved the reduction in water treatment flow rate. This suggests that a small amount of silver contained in the antibacterial agent has dissolved, and the microorganisms adhering in the system or on the film have been antibacterial or sterilized.

Example 3
Using a device equipped with a reverse osmosis membrane (reverse osmosis membrane manufactured by Nitto Denko Corporation (NTR-759HR-S2C, membrane area: about 0.8 m ² )) instead of the ultrafiltration membrane in FIG. The performance degradation test by adhesion and propagation of microorganisms was conducted. Seawater was fed into the system for 3 months under conditions of a flow rate of 20 L / hr and a water pressure of 5 atm or less using 10 g of the silver sulfide analthime of Reference Example 4. The deterioration of the filtration membrane was judged from the change over time in the recovery rate ((permeate flow rate / pressurized raw water flow rate) × 100%). The results are shown in Table 3. Further, the silver elution concentration in the solution before the filtration membrane was quantified with a graphite furnace heated atomic absorption spectrometer (Z-5700, Hitachi). Furthermore, the state of the filtration membrane surface was confirmed visually.

(Comparative Example 3)
The test was conducted in the same manner as in Example 3 except that water was passed through the reverse osmosis membrane without being brought into contact with the column filled with silver sulfide analthime. The results are shown in Table 3.

Example 4
The test was performed in the same manner as in Example 3 except that the target water was Nagoya city tap water. The results are shown in Table 3.

(Comparative Example 4)
The test was conducted in the same manner as in Example 4 except that water was passed through the reverse osmosis membrane without being brought into contact with the column filled with silver sulfide analthime. The results are shown in Table 3.
From the results in Table 3, it can be seen that the reduction in the recovery rate was improved by the introduction of the antibacterial agent. This suggests that a small amount of silver contained in the antibacterial agent has dissolved, and the microorganisms adhering in the system or on the film have been antibacterial or sterilized.

    Elution of silver from the introduced silver-based inorganic antibacterial agent in a water treatment method characterized in that a pretreatment device is installed in front of the membrane separation device and chlorine is intermittently supplied to the pretreatment device. This sterilizes and antibacterials the microorganisms present in the water and suppresses the filtration performance deterioration of the membrane.

1 is a schematic diagram of an experimental apparatus used in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water storage tank 2 Pre filter 3 Liquid feed pump 4 Antibacterial agent filling column 5 Liquid flow meter 6 Diaphragm type pressure gauge 7 Ultrafiltration membrane

Claims (6)

A method for treating water, comprising bringing a target water into contact with a silver-based antibacterial agent and then passing it through a separation membrane having pores having a pore diameter of less than 0.1 μm. The water treatment method according to claim 1, wherein the membrane is a microfiltration membrane, an ultrafiltration membrane, or a reverse osmosis membrane. The water treatment method according to claim 1 or 2, wherein the target water is at least one selected from tap water, sewage, drainage, seawater and brine. The water treatment method according to claim 1, wherein the silver antibacterial agent is a silver inorganic antibacterial agent. The water treatment method according to claim 1, wherein the silver-based inorganic antibacterial agent is silver zeolite. The water treatment method according to claim 1, wherein the column is filled with a silver antibacterial agent.

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