JP3269496B2 - Sterilization method and fresh water method of membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for disinfecting and desalinating water when separating water using a membrane, particularly a reverse osmosis membrane, and further for desalinating seawater. Things.

[0002]

2. Description of the Related Art Separation techniques using membranes are used in a wide range of fields such as desalination of seawater and canned water, medical treatment, production of industrial pure water and ultrapure water, and industrial wastewater treatment. In these membrane separations, contamination of the separation device by microorganisms causes deterioration of water quality of the obtained permeated water, permeability of the membrane due to growth of microorganisms on the membrane surface or adhesion of microorganisms and metabolites to the membrane surface,
This causes a decrease in separability. In order to avoid such an important problem, various methods of sterilizing a membrane separation device have been proposed. In general, a method of constantly or intermittently adding a sterilizing agent to a feed solution has been adopted. As a disinfectant, a chlorine-based disinfectant that has a proven track record and is advantageous in price and operation is 0.1%
It is most common to add it to a concentration of about 50 ppm. However, a chlorine-based disinfectant causes chemical degradation of the reverse osmosis membrane. Therefore, when the disinfectant is used, it is necessary to reduce free chlorine using a reducing agent before supplying the reverse osmosis membrane. As a reducing agent, sodium bisulfite is generally added in an amount of 1 to 10 times the same amount. This is a concentration considering that the residual germicide is completely eliminated and at the same time the reducing agent also reacts with dissolved oxygen. However, it has become clear that such an operation method is not always sufficient to sterilize microorganisms, since the membrane performance may be reduced even if the operation is continued by this method. There is a theory that the addition of chlorine oxidizes the organic carbon present in the feed and converts it into compounds that are easily degraded by microorganisms (AB Hamida and I. Moch, jr., Des.
alination & Water Reuse, 6/3, 40-45, (1996).)
It has not been demonstrated. Therefore, a method of sterilizing by adding sodium bisulfite intermittently, usually at a concentration of 500 ppm has been developed and has been generally used. However, this method is also not effective in some cases, and microorganisms are not effectively used. It is becoming increasingly clear that they will accumulate on the surface.
Examples of the bactericidal effect of sodium bisulfite include the ability to remove oxygen from the supply liquid and the reduction of pH. However, at the time of operation of the membrane device, sterilization by intermittent addition of sodium bisulfite is not currently effective. The present inventors have investigated the cause, and the anaerobic state for general aerobic bacteria that live in neutral to weak alkaline is not an environment where death is suppressed even if growth is suppressed, but rather a decrease in pH is the most effective for sterilization Was reached. This is a microbiologically consistent conclusion. On the other hand, for a feed solution having a high salt concentration such as seawater, 500
It was found that even when sodium bisulfite at a high concentration of ppm was added, the pH did not drop so much as to kill general bacteria. Therefore, even in a feed solution containing a lower concentration of salt, the disinfecting effect of sodium bisulfite is not due to the anaerobic state, but a decrease in pH is effective,
It has been found that it is not necessary to add expensive sodium bisulfite at a high concentration, and it is possible to sufficiently sterilize by simply adding an inexpensive acid such as sulfuric acid to lower the pH.
No. 04873 was reached. However, it has been recognized that there is a need for a more effective sterilization method, for example, in response to a case where bacteria having resistance to acidic conditions accumulate on the membrane.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and to provide an effective method for sterilizing a membrane and a method for producing fresh water.

[0004]

The object of the present invention is achieved by the following constitution. That is, the present invention provides "an acidic water treatment step A for adjusting the pH of water supplied to a membrane separation device to a range of 2.7 to 4 when separating and purifying water using a membrane separation device having a membrane, A method for sterilizing a membrane for performing an acidic water treatment step B for adjusting the pH to 2.6 or less. "," A method for producing water using the above-described method for sterilizing a membrane ", and" Water using a membrane separation apparatus having a membrane. " In the step of separating and purifying, a step of adjusting the pH of the water supplied to the membrane separation device to a range of more than 2.6 to 4 or less and a step of adjusting the pH to 2.6 or less during the separation and purification. A method for sterilizing a membrane, which is carried out. "

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a membrane separation device is a device for supplying a liquid to be treated, such as seawater or brine, to a membrane module under pressure for the purpose of water production, concentration, separation, etc. And a device for separating the two. Membrane modules include reverse osmosis membrane modules, ultrafiltration membrane modules, microfiltration membrane modules, etc.Depending on the type of membrane module used there, reverse osmosis membrane devices, ultrafiltration membrane devices, microfiltration Although there are membrane devices and the like, a reverse osmosis membrane device will be described below. The reverse osmosis membrane device is composed of a reverse osmosis membrane module or a high-pressure pump in which a plurality of reverse osmosis membrane elements are connected in series and housed in a pressure-resistant container. The liquid to be separated supplied to this reverse osmosis membrane device is added and coagulated with a chemical such as a bactericide, a coagulant, a reducing agent, a pH adjuster, sedimentation, sand filtration, polishing filtration, activated carbon filtration, microfiltration, ultrafiltration. Pretreatment such as filtration and security filter filtration is performed. For example, in the case of seawater desalination, after taking in seawater, particles and the like are separated in a sedimentation basin, and a sterilizing agent such as chlorine is added here to sterilize. Further, sand filtration is performed by adding a flocculant such as iron chloride or polyaluminum chloride. The filtrate is stored in a storage tank, and after adjusting the pH with sulfuric acid or the like, is sent to a high-pressure pump. A reducing agent such as sodium bisulfite is added to the liquid to remove the germicide, and after passing through a security filter, the pressure is increased by a high-pressure pump and supplied to the reverse osmosis membrane module. However, these pretreatments are appropriately adopted depending on the type of the supply liquid to be used and the application.

[0006] 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 pass through but not other components. Nanofiltration membranes or loose RO membranes are also broadly included in reverse osmosis membranes.
The material is cellulose acetate polymer, polyamide,
Polymer materials such as polyester, polyimide, and 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 having a large pore diameter gradually from the precision layer to the inside or the other side of the membrane, 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 a hollow fiber and a flat membrane. The thickness of hollow fiber and flat membrane is 10μ
m to 1 mm, and the outer diameter of the hollow fiber is preferably 50 μm to 4 mm. In the case of a 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 irrespective of the material, membrane structure and membrane form of the reverse osmosis membrane, and both are effective. Typical reverse osmosis membranes include, for example, a cellulose acetate-based or polyamide-based asymmetric membrane and a composite membrane having a polyamide-based or polyurea-based active layer. Among these, the method of the present invention is effective for cellulose acetate-based asymmetric membranes and polyamide-based composite membranes, and is particularly effective for aromatic polyamide-based composite membranes.

[0007] A reverse osmosis membrane element is formed by actually using the above reverse osmosis membrane. The flat membrane is a spiral, tubular, plate and frame type element, and the hollow fiber is a hollow fiber. Although it can be used after being bundled and assembled in a case, the present invention does not depend on the form of these reverse osmosis membrane elements.

Further, the reverse osmosis membrane element incorporates members such as a feed water channel material and a permeated water channel material in a spiral shape, and any of these members may be used. Effective in elements designed for For example, if a net having rhombuses is used as a feed water channel material, the flow of the feed water is disturbed, so that the thickness of the concentration polarization layer can be reduced, and the feed water containing a high concentration of solute is used. Effective. If a perforated water channel material is made of a polyester fiber taffeta having a groove that constitutes the permeated water flow path, or a nonwoven fabric or the like is laminated on the surface having the groove, the membrane may deform or fall even at high pressure. Performance can be effectively prevented.

The operating pressure of the reverse osmosis membrane device is 0.1 MPa to
It is 15 MPa, and can be appropriately used depending on the kind of the supply liquid, the operation method and the like. A relatively low pressure is used when a solution having a low osmotic pressure such as canned water or ultrapure water is used as a feed liquid, and a relatively high pressure is used for desalination of seawater, wastewater treatment, and recovery of useful substances.

[0010] The operating temperature of the reverse osmosis membrane device is from 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.

The recovery rate of the separation device is 5 to 100%.
Up to the separation operation and the device can be set. The recovery rate of the reverse osmosis membrane device can be appropriately selected from 5 to 98%. However, the properties, concentration,
Pretreatment, operating pressure, must be considered depending on the osmotic pressure. For example, in the case of seawater desalination, usually 10 to 40
%, And in the case of a highly efficient device, the recovery rate is 40 to 70%. 70% or more for desalination and ultrapure water production
It can also operate at 90-95% recovery.

The structure of a reverse osmosis membrane device is mainly composed of 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 modules can be arranged in one stage, but can be arranged in series or in parallel with the supply water in multiple stages. When arranged in series, a booster pump can be installed between each stage. In the seawater desalination series arrangement, a two-stage arrangement is particularly preferable from the viewpoint of the equipment cost. A booster pump is installed between the modules arranged in series to increase the supply liquid to about 1.0 to 5.0 MPa. It is preferable to supply the module to a subsequent module. When arranged in series with the supply liquid, the time of contact between the membrane module and the supply water is long, and the effect of the method of the present invention is large.

Furthermore, the reverse osmosis membrane modules can be arranged in series with the permeated water. This is a preferable method when the quality of the permeated water is insufficient or when it is desired to recover solute components in the permeated water. If arranged in series with the permeate, install a pump between them and pressurize the permeate again,
Extra pressure can be applied in the first stage to apply back pressure to perform membrane separation. When arranged in series with the permeated water, an acid addition device is provided between the membrane modules to sterilize the rear membrane module.

In the reverse osmosis membrane device, a portion of the feed water that has not passed through the membrane is taken out of the membrane module as concentrated water. The concentrated water can be treated and discarded according to the intended use, or can be further concentrated by another method. Also, part or all of the concentrated water can be circulated to the feed water. The portion that has permeated the membrane can also be discarded according to the application, used as it is, or part or all of it can be circulated to 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 is possible to recover energy using an energy recovery device attached to any part of the high-pressure pump.However, use 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 device is a device having a water volume of 0.5 m ³ to 1,000,000 m ³ per day.

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

In the present invention, the step A for adjusting the pH to 2.7 to 4 is extremely important for providing a high bactericidal effect on the membrane, and the step B for adjusting the pH to 2.6 or less is important for the membrane. It is extremely important in providing a high bactericidal effect on bacteria including acid-resistant bacteria. This effect is particularly remarkable in membrane filtration using seawater as feed water. The pH at which microorganisms die is specific to individual microorganisms. For example, in the case of Escherichia coli, the lower limit of growth is pH 4.6, but killing occurs at pH 3.4 or less. On the other hand, a variety of microorganisms also exist in seawater, and the pH at which they die is different from each other. If seawater containing various viable bacteria is kept at pH 4 or lower for a certain period of time, 5
It is possible to kill 0-100%. Also pH
An acidity of 3.9 or less, and an acidity of pH 3.7 or less are also in the preferable ranges. However, although there are acid-resistant microorganisms in seawater containing various viable bacteria, if the seawater is kept at a pH of 2.6 or less for a certain period of time, 60 to 100 of the acid-resistant bacteria will be removed.
% Can be killed. To bring the pH to a desired state, an acid is usually used. As the acid, either an organic acid or an inorganic acid may be used, but from the viewpoint of economy, it is preferable to use sulfuric acid. The amount of sulfuric acid added is proportional to the salt concentration of the feed solution. For example, a physiological saline (salt concentration: 0.9%) sterilized under pressure (120 ° C., 15 minutes).
%), The addition of 50 ppm of sulfuric acid lowers the pH to 3.2, but in three places of autoclaved seawater (120 ° C., 15 minutes) and commercially available artificial seawater (salt concentration of about 3.5%), 100 ppm of sulfuric acid is added. Even when added, the pH was 5.0 to 5.8. It is considered that this largely varies mainly depending on the M alkalinity of seawater. In order to further adjust the pH to 4 or less, it is preferable to add 120 ppm or more, and to adjust the pH to 2.6 or less, it is preferable to add 250 ppm or more. The maximum amount of addition is 400p
pm, more preferably 300 ppm. The above seawater, the concentration of sulfuric acid added to artificial seawater is further 150 ppm,
Assuming 200 ppm, 250 ppm, and 300 ppm,
PH 3.2 to 3.6, pH 2.8 to 2.9, p
H2.6 and pH 2.4, the pH fluctuation decreases as the added concentration increases. When the pH is always set to 2.6 or less, a high bactericidal effect is exhibited for all bacteria including acid-resistant bacteria, but the ratio of acid-resistant bacteria to the bacteria in seawater is small. It is preferable to sterilize and acidify bacteria at a pH of 2.6 or less from the viewpoint of reducing the cost of a chemical solution for making the supply liquid acidic and affecting facilities such as piping.

Further, the pH of the water supplied to the membrane separation device is adjusted to 2.
The sterilization can be performed by adjusting the pH to a range of more than 6 and 4 or less, and also performing a step of adjusting the pH to 2.6 or less to sterilize the acid-resistant bacteria.

The sterilization of the membrane of the present invention may be performed intermittently during the supply of the water to be treated to the membrane module after the pretreatment, ie, while supplying the treated water. The time and frequency of the process depend on the place of use,
It differs greatly depending on the conditions of use and is appropriately selected. For example, one time of the step A and the time of the step B are each set to 0.
It can be 5 to 2.5 hours. The frequency can be set at intervals of every day, every week, every month, etc.
Once a day, the acid water treatment step B is preferably performed once every two to 180 days. These reduce the amount of water permeated through the membrane,
It fluctuates depending on the number of viable bacteria in the concentrate, the increase in the content of organic carbon, and the increase in the membrane pressure. In the case of non-continuous use, it can be carried out by immersing the membrane in supply water adjusted to a pH within the above range during non-permeation, that is, at rest. When attention is paid to a certain period in which the process A and the process B are performed a plurality of times, the value of (total time of the acidic water treatment process A) / (total time of the acidic water treatment process B) is 1/10.
It is preferable to be in the range of 0 to 100. Further, in the present invention, it is possible to directly move from the state of step A to the operation of step B, and conversely, directly from the state of step B to the operation of step A.
In the present invention, it is preferable to supply a supply liquid whose pH has not been adjusted between the processing step A and the processing step B. In this case, the supply liquid whose pH has not been adjusted is separated by a normal water membrane separation operation, and the permeated liquid or the concentrated liquid can be used for the original purpose. Further, in the above process, for the purpose of protecting the piping of the membrane separation device and the like as much as possible, first, an acidic water treatment process A having a high pH value is performed, and then the acidic water treatment process B is performed as necessary. preferable.

Further, the sterilization method of the present invention can be used in combination with another sterilization method such as chlorine.

The method for sterilizing a membrane of the present invention can be applied not only to a membrane separation device but also to a water separation system partially including the membrane separation device. 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, a chemical injection facility, and the like. B. A pretreatment device connected to the water intake device. In this method, water to be supplied to a separation membrane device is pretreated and purified to a desired degree. For example, they can be configured in the following order. B-1 Aggregation 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 a flocculant, a bactericide, and a pH adjuster. C. An intermediate tank that communicates with the pretreatment device and is installed as needed. This provides functions of water volume control and water quality buffering. D. A filter connected to the intermediate tank when C is installed, or connected to the pretreatment device when C is not installed. This removes solid impurities of the water supplied to the membrane separator. E. FIG. Membrane separation device. 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-processing device that communicates with the outlet of the membrane permeation side of the membrane separation device. The following devices are exemplified. F-1 Deaerator. This has a function of decarboxylation. F-2 Calcium tower. F-3 Chlorine injection. G. FIG. Post-treatment device connected to the raw water side outlet of the membrane separation device. The following devices are exemplified. G-1 An apparatus for processing a supply liquid having a lowered pH. For example, a neutralization device. G-2 Discharge facility. H. In addition, a wastewater treatment device may be appropriately provided.

In such a device, a pump can be provided at an arbitrary position. In order to adjust the pH to 2.7 to 4 or 2.6 or less, a drug or a solution of the drug is added in the water intake device of A, the pretreatment device of B, or before the pretreatment device, or in the case of D. Before the filter,
Alternatively, it is preferably after the filter.

In order to further enhance the effects of the present invention, it is preferable that the acid adding device can be automatically controlled, and it is preferable that a pump capable of appropriately controlling the injection amount is provided. Further, it is preferable that a device for measuring the pH of the supply liquid or the concentrated solution is provided at an appropriate place in the device for control. Further, it is preferable to have a device capable of measuring time in order to control intermittent addition. More preferably, it is preferable to have an automatic control device capable of automatic operation.

The components of the apparatus of the present invention, such as pipes and valves, are those which are hardly changed under the condition of pH 2.6 or less.

Further, by setting the pH to 2.7 to 4, a high sterilizing effect can be obtained, and at the same time, an effect that scale in the pipe can be removed can be obtained. Also pH
Is set to 2.6 or less, microorganisms having resistance to acidic conditions can be sterilized. In addition, sodium bisulfite is usually added to a certain amount or more in order to prevent film deterioration due to oxides such as chlorine. However, microorganisms (such as sulfur bacteria) that adhere to the film surface and metal salts are added. In the case where the amount of consumption increases due to the influence of the above, the effect of remarkably reducing the amount of addition can be obtained by the acidic water treatment of the present invention.

The method of the present invention can be suitably used for separation using a membrane, but is particularly effective for separating an aqueous solution, and can provide a highly efficient water-making method. Separation and concentration of liquids and solids using microfiltration membranes, separation and concentration of suspended matter using ultrafiltration membranes, and separation and concentration of dissolved components using reverse osmosis membranes effective. In particular, desalination of seawater, desalination of can water, production of industrial water, production of ultrapure water, pure water, production of pharmaceutical water, concentration of food, turbidity of tap water,
Great effect in advanced treatment in water supply. When separating and concentrating organic substances that are easy to separate with conventional oxidizing germicides, they can be concentrated and recovered without decomposition by sterilization.
The effect of the method of the present invention is great. In addition, in the case of producing drinking water, there is an effect that the generation of trihalomethane due to chlorine sterilization can be prevented.

[0029]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. (Reference Example 1) 1% of seawater was added to commercially available 3.5% artificial seawater that had been autoclaved (120 ° C, 15 minutes) and the pH was measured to be 8.5. After keeping at 20 ° C. for 2 hours, 100 μl was added to an agar medium for marine bacteria adjusted to pH 7.
1 was applied and kept at 20 ° C. After culturing for several days, 200 colonies appeared on the agar medium. Reference Example 2 Sulfuric acid was added after autoclaving (120 ° C, 15 minutes).
1% of seawater was added to commercially available 3.5% artificial seawater whose pH was adjusted by adding it to 00 ppm, and the pH was adjusted to 2.8. After keeping at 20 ° C. for 2 hours, 100 μl was added to an agar medium for marine bacteria adjusted to pH 7.
1 was applied and kept at 20 ° C. After culturing for several days, three colonies appeared on the agar medium. The results are shown in Table 1 together with Reference Example 1. These bacteria are acid-resistant bacteria that cannot be sterilized at pH 2.8, and it is considered that 1.5% of the bacteria were present in seawater.

[0030]

[Table 1]

(Reference Example 3) Pressure sterilization (120 ° C., 15
Min) Then, to the commercially available 3.5% artificial seawater whose pH has been adjusted by adding sulfuric acid, three unidentified acid-resistant bacteria strains obtained in Reference Example 2 were added in fixed amounts at a time, and kept at 20 ° C. for a certain time. The results in Table 2 were obtained by determining the survival rate. From Table 2, it can be understood that extremely high bactericidal effect is provided by maintaining the pH at 2.6 or less for 0.5 hours or more.

[0032]

[Table 2]

(Example 1) Reverse osmosis filtration to fresh water is performed by operating a pretreatment device for performing a pretreatment step and a membrane separation device having a module having a reverse osmosis membrane made of polyamide using seawater as feed water. Was. In the pretreatment step, chlorine was continuously added to the supplied seawater so that the residual concentration became 10 ppm, and sodium bisulfite was added before the reverse osmosis membrane module. The concentration of sodium bisulfite added was adjusted so that the residual concentration in the brine discharged from the reverse osmosis membrane module was 1 ppm or more. After the start of operation, the consumption of sodium bisulfite increased, and reached 21 ppm after 10 days of operation. Then, sulfuric acid is added and p
The feed water whose H was adjusted to 2.5 was passed for 30 minutes on the first day, the second day, and the tenth day, and the feed water whose pH was similarly adjusted to 3 was fed for 30 minutes on the 14th and 27th days. After passing water for a minute, the consumption of sodium sulfite was reduced to 10 ppm. (Example 2) Two membrane separation devices (devices A and B) having a pretreatment device for performing a pretreatment process and a module having a reverse osmosis membrane made of polyamide using seawater as feedwater and seawater as feedwater Were operated in parallel to perform reverse osmosis filtration to fresh water. The culture solution of the acid-resistant bacterium obtained in Reference Example 2 was added to seawater after the pretreatment, and water was passed through. In both cases, when the feed water whose pH was adjusted to 3.5 to 4.0 was passed for 30 minutes a day and operated continuously for 30 days, an increase in the membrane pressure was observed.
Thereafter, the membrane separator A passed the feed water whose pH was adjusted to 2.6 for 30 minutes a day, and the membrane separator B passed the feed water whose pH was adjusted to 3.5 to 4.0 for 30 minutes a day. Further, once every 5 days, the pH of the feed water was adjusted to 2.6, and water was supplied for 30 minutes a day. As a result of continuous operation for 30 days, there was no change in the differential pressure in either of the membrane separation devices. When the viable cell count of the filtered concentrated water was measured during normal operation, both membrane separation devices showed p
H was reduced to 1/100 or less as compared with the case where only supply water in which H was adjusted to 3.5 to 4.0 was passed. The results are summarized in Table 3. From Table 3, it was found that the sterilization effect was insufficient with the supply water adjusted to pH 3.5 to 4.0,
It can be understood that the supply water adjusted to 2.6 has a sufficient bactericidal effect, and that the bactericidal effect was sufficient only by lowering the pH to 2.6 once every five times.

[0034]

[Table 3]

[0035]

According to the present invention, when water is purified using a membrane separation device,
As a method for disinfecting microorganisms containing acid-resistant bacteria present on the membrane surface or in the vicinity of the membrane, reliable disinfection is possible according to the method of the present invention, as compared to the conventionally used intermittent addition of high-concentration sodium bisulfite. .

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-11-9973 (JP, A) JP-A-9-29075 (JP, A) Haruhiko Oya, Handbook of Membrane Utilization Technology, Japan, Koshobo Co., Ltd., 1978 June 30, 1st edition, p. 23, 29-30 (58) Field surveyed (Int. Cl. ⁷ , DB name) B01D 61/00-65/10 C02F 1/44

Claims (9)

(57) [Claims] When separating and purifying water using a membrane separation device having a membrane, the pH of water supplied to the membrane separation device is adjusted to 2.
A method for sterilizing a membrane, comprising performing an acidic water treatment step A in which the pH is adjusted to fall within a range of 7 to 4, and an acidic water treatment step B in which the pH is adjusted to 2.6 or less. 2. The method for sterilizing a membrane according to claim 1, wherein after performing the acidic water treatment step A, the acidic water treatment step B is performed. 3. The time of each of the acidic water treatment step A and the acidic water treatment step B is in the range of 0.5 to 2.5 hours, and the time between the acidic water treatment step A and the acidic water treatment step B is The method for sterilizing a membrane according to claim 1 or 2, wherein a step of supplying supply water whose pH has not been adjusted is performed. 4. The acidic water treatment step A is carried out once every 1 to 30 days, and the acidic water treatment step B is carried out every 2 to 180 days.
Each of the acidic water treatments is carried out once a day so that the value of (total time of the acidic water treatment step A) / (total time of the acidic water treatment step B) falls within the range of 1/100 to 100. The method for sterilizing a membrane according to any one of claims 1 to 3, wherein a treatment step is performed. 5. The method according to claim 1, wherein a reverse osmosis membrane is used as the membrane.
5. The method for sterilizing a membrane according to any one of 4. 6. The pH of the feed water by adding sulfuric acid.
The method for sterilizing a membrane according to any one of claims 1 to 5, wherein the pH is adjusted to 2.6 or less. 7. A fresh water producing method, comprising using the method for sterilizing a membrane according to claim 1. 8. use seawater as feed water, fresh water generating method according to 請 Motomeko 7. 9. When separating and purifying water using a membrane separation device having a membrane, the pH of the water supplied to the membrane separation device is adjusted to be within a range of more than 2.6 and 4 or less during the separation and purification. A method for sterilizing a membrane, comprising performing a step and a step of adjusting the pH to 2.6 or less.