Water treatment method and water treatment system

Abstract

To provide a water treatment method and a water treatment system capable of sufficiently sterilizing a semipermeable membrane of a membrane module and suppressing deterioration of the semipermeable membrane due to sterilization.SOLUTION: There is provided a water treatment method including: a water treatment step of using a membrane module having a semipermeable membrane and a first chamber and a second chamber separated by the semipermeable membrane; and a sterilization step of sterilizing the semipermeable membrane, wherein in the sterilization step, a sterilizing liquid containing a chlorine-based sterilant and a phosphate-based buffer having a buffering ability to maintain a pH of 3 to 8 is supplied to at least one of the first chamber and the second chamber of the membrane module, whereby the sterilizing liquid is brought into contact with the semipermeable membrane to sterilize the semipermeable membrane.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a water treatment method and a water treatment system.

Background Art

[0002] In semipermeable membranes used for various water treatments (membrane separation treatments such as forward osmosis treatment and reverse osmosis treatment), contamination (fouling) progresses over time due to the adhesion and deposition of contaminants such as inorganic substances, organic substances, and microorganisms contained in the water to be treated (target liquid). The progress of semipermeable membrane contamination causes problems such as a decrease in the amount of permeated water, deterioration of the quality of the permeated water, an increase in the pressure loss within the membrane module, and a decrease in water treatment efficiency resulting from these.

[0003] Patent Document 1 (Japanese Patent No. 4304573) discloses performing sterilization of a semipermeable membrane with chlorine. By sterilizing the semipermeable membrane, biological fouling by microorganisms and the like can be suppressed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, when sterilizing a semipermeable membrane using a chlorine-based bactericide such as chlorine, there is a possibility that the semipermeable membrane may deteriorate due to the chlorine-based bactericide. Due to the deterioration of the semipermeable membrane, the permeation salt concentration may increase. When the permeation salt concentration of the semipermeable membrane increases, for example, in forward osmosis (FO) treatment, the amount of solute (draw solute) in the draw solution (DS) that leaks (reverse solute diffuses) through the semipermeable membrane to the feed solution (FS) side increases, and there is a problem that the operating cost (additional cost of the draw solute) increases.

[0006] Accordingly, an object of the present invention is to provide a water treatment method and a water treatment system that can sufficiently sterilize the semipermeable membrane of a membrane module and suppress deterioration of the semipermeable membrane due to sterilization. **Means for Solving the Problems**

[0007] (1) A water treatment step using a membrane module having a semipermeable membrane and a first chamber and a second chamber partitioned by the semipermeable membrane, and a sterilization step of sterilizing the semipermeable membrane, the water treatment method including: In the sterilization step, a sterilizing solution containing a chlorine-based sterilizing agent and a phosphoric acid-based buffer having a buffering ability to maintain the pH at 3 to 8 is supplied to at least one of the first chamber and the second chamber of the membrane module, so that the sterilizing solution contacts the semipermeable membrane to sterilize the semipermeable membrane.

[0008] (2) The water treatment method according to (1), wherein in the sterilization step, the sterilizing solution discharged from the membrane module is supplied to the membrane module again.

[0009] (3) In the sterilization step, the concentration of the chlorine-based sterilizing agent in the sterilizing solution is measured, and based on the measured value of the concentration of the chlorine-based sterilizing agent, the chlorine-based sterilizing agent is added to the sterilizing solution so that the concentration of the chlorine-based sterilizing agent is within a predetermined concentration range, thereby adjusting the concentration of the chlorine-based sterilizing agent. The water treatment method according to (2).

[0010] (4) The water treatment method according to (2) or (3), wherein at least one of the addition amount and the addition frequency of the chlorine-based sterilizing agent is adjusted according to at least one of the frequency of implementation of the sterilization step and the sterilization effect.

[0011] (5) The water treatment method according to any one of claims (2) to (4), wherein the flow rate of the sterilizing solution supplied to the membrane module is adjusted.

[0012] (6) The sterilizing liquid discharged from the membrane module is supplied to the membrane module after the suspension contained in the sterilizing liquid is removed by filtration, and is the water treatment method according to any one of (2) to (5).

[0013] (7) A water treatment system used in the water treatment method according to any one of (1) to (6), A membrane module having a semipermeable membrane and a first chamber and a second chamber partitioned by the semipermeable membrane, A water treatment system comprising a tank for storing the sterilizing liquid.

[0014] (8) The water treatment system according to (7), further comprising a pump for flowing the sterilizing liquid stored in the tank to the membrane module.

[0015] (9) The water treatment system according to (7), further comprising a flow rate adjustment valve for adjusting the flow rate of the sterilizing liquid supplied from the tank to the membrane module.

[0016] (10) The water treatment system according to (7), further comprising a filtration device for filtering the sterilizing liquid stored in the tank in a flow path connecting the tank and the membrane module.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a water treatment method and a water treatment system capable of sufficiently sterilizing the semipermeable membrane of the membrane module and suppressing the deterioration of the semipermeable membrane due to sterilization.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or corresponding parts. Also, dimensional relationships such as length, width, thickness, depth, etc. have been appropriately changed for the sake of clarity and simplification of the drawings, and do not represent actual dimensional relationships.

[0020] <Water treatment method> Referring to FIGS. 2 and 3, the water treatment method of the present embodiment includes a water treatment step using a membrane module 1 having a semipermeable membrane 10 and a first chamber 11 and a second chamber 12 partitioned by the semipermeable membrane 10, and a sterilization step of sterilizing the semipermeable membrane 10.

[0021] (Water treatment step) In the water treatment step, a membrane module 1 having a semipermeable membrane 10 and a first chamber 11 and a second chamber 12 partitioned by the semipermeable membrane 10 is used. The water treatment step of the present embodiment is a step of performing treatment of a liquid (target liquid) by membrane separation treatment such as forward osmosis treatment and reverse osmosis treatment. Concentration of the target liquid, separation of water (solvent) or components (solute) in the target liquid, etc. are performed.

[0022] The water treatment method (water treatment step, water treatment system) shown in FIG. 2 is a method using a membrane module 1 for reverse osmosis (RO). In the water treatment method shown in FIG. 2, the target liquid is flowed into the first chamber 11 at a high pressure, so that the water contained in the FS in the first chamber 11 migrates into the second chamber 12 through the semipermeable membrane 10.

[0023] The water treatment method (water treatment step, water treatment system) shown in FIG. 3 is a method using a membrane module for forward osmosis (FO). In the water treatment method shown in FIG. 3, a feed solution (FS) is flowed into the first chamber 11, and a draw solution (DS) having an osmotic pressure higher than that of the first target solution is flowed into the second chamber 12, so that the water contained in the FS in the first chamber 11 moves through the semipermeable membrane 10 into the DS in the second chamber 12.

[0024] (Membrane module) The material constituting the semipermeable membrane 10 is not particularly limited, and examples thereof include cellulose-based resins, polysulfone-based resins, and polyamide-based resins. The semipermeable membrane is preferably composed of a material containing at least one of a cellulose-based resin and a polysulfone-based resin.

[0025] The cellulose-based resin is preferably a cellulose acetate-based resin. The cellulose acetate-based resin generally has higher resistance to chlorine, which is a bactericide, than polyamide-based resins and the like. By sterilization using a chlorine-based bactericide, the growth of microorganisms can be suppressed. The cellulose acetate-based resin is preferably cellulose acetate, and more preferably cellulose triacetate (CTA) from the viewpoint of durability. However, even in the case of a cellulose acetate-based resin, deterioration over time may occur due to the use of a chlorine-based bactericide, and the permeation salt concentration of the semipermeable membrane may increase. According to the sterilization step of the present embodiment, deterioration of the semipermeable membrane due to sterilization can be suppressed.

[0026] The polysulfone-based resin is preferably a polyethersulfone-based resin. The polyethersulfone-based resin is preferably sulfonated polyethersulfone.

[0027] The shape of the semipermeable membrane (and the reverse osmosis membrane described later) is not particularly limited, and examples thereof include a flat membrane, a spiral membrane, and a hollow fiber membrane. In the drawings, the semipermeable membrane 10 is drawn in a simplified manner as a flat membrane, but it is not particularly limited to such a shape. The hollow fiber membrane (hollow fiber type semipermeable membrane) is advantageous in that the membrane area per module can be increased and the permeation efficiency can be enhanced as compared with a spiral type semipermeable membrane and the like.

[0028] The form of the membrane module (and the reverse osmosis module described later) is not particularly limited. When using a hollow fiber membrane, examples include a module with the hollow fiber membrane arranged straight, a cross-wound module with the hollow fiber membrane wound around a core tube, etc. When using a flat membrane, examples include a laminated module with flat membranes stacked, a spiral module with a flat membrane formed into a cylindrical shape and wound around a core tube, etc.

[0029] (Sterilization process) In the sterilization process, a sterilizing solution is supplied to the membrane module 1 (to at least one of the first chamber 11 and the second chamber 12 of the membrane module 1), so that the sterilizing solution contacts the semipermeable membrane 10 to sterilize the semipermeable membrane 10.

[0030] The sterilizing solution contains a chlorine-based disinfectant and a phosphate buffer.

[0031] The chlorine-based disinfectant is a component having a sterilizing action and containing chlorine. Examples of the chlorine-based disinfectant include sodium hypochlorite, calcium hypochlorite, chlorinated isocyanuric acid, hypochlorous acid, chlorine (Cl2) gas, etc.

[0032] The concentration of the chlorine-based disinfectant in the sterilizing solution, as the free chlorine concentration, is preferably 0.01 mg / L to 20 mg / L, and the concentration can be appropriately changed depending on the form of sterilization / washing, such as shock washing or intermittent sterilization.

[0033] The phosphate buffer used in this embodiment is a buffer having a buffering ability to maintain the pH (of the solution to which it is added) at 3 to 8 and contains phosphoric acid. Examples of the phosphate buffer include a phosphate buffer (a mixture of sodium dihydrogen phosphate (NaH2PO4) and disodium hydrogen phosphate (Na2HPO4)), etc. The mixing ratio (molar ratio) of sodium dihydrogen phosphate:disodium hydrogen phosphate in the phosphate buffer is preferably 1:1 to 100:1, more preferably 2:1 to 50:1, still more preferably 4:1 to 6:1, for example, 5:1.

[0034] By adding a phosphate buffer to the sterilizing liquid containing a chlorine-based bactericide, it is possible to sufficiently sterilize the semipermeable membrane of the membrane module and obtain the effect of suppressing the deterioration of the semipermeable membrane due to sterilization. The mechanism by which the deterioration (oxidative deterioration) of the semipermeable membrane is suppressed is not clear. However, for example, suppression of oxidative deterioration of the membrane by coating the membrane with phosphoric acid, masking cobalt with phosphoric acid, electron donation from the buffer solution, or suppression of pH fluctuation (suppression of hydrolysis of cellulose acetate resin, etc.) is conceivable. For example, when the target liquid is seawater, seawater contains cobalt, and it is considered that the chlorine-based bactericide reacts with cobalt to generate a compound that promotes the oxidative deterioration of the semipermeable membrane. Therefore, it can be considered that by adding a phosphate-based buffer, cobalt is masked by phosphoric acid, and the oxidative deterioration of the semipermeable membrane is suppressed.

[0035] In addition, even when citric acid is added instead of the phosphate-based buffer to the sterilizing solution containing the chlorine-based bactericide, it is possible to obtain the effect of sufficiently sterilizing the semipermeable membrane of the membrane module and suppressing the deterioration of the semipermeable membrane due to sterilization, similar to the water treatment method of the present embodiment.

[0036] The concentration of the phosphate-based buffer in the sterilizing liquid is preferably 0.01% by mass or more, more preferably 0.05 - 5% by mass, and may be determined in consideration of the effect and cost.

[0037] The pH of the sterilizing liquid is preferably 3 - 8, more preferably 5 - 7, and even more preferably 5.5 - 6.5. When the pH of the sterilizing liquid is within such a range, it is possible to sufficiently sterilize the semipermeable membrane of the membrane module and obtain the effect of suppressing the deterioration of the semipermeable membrane due to sterilization. For this reason, the phosphate-based buffer has a buffering ability to maintain the pH of the liquid to which it is added preferably at 3 - 8, more preferably at 5 - 7, and even more preferably at 5.5 - 6.5.

[0038] The solvent of the sterilizing liquid is not particularly limited. For example, it may be the target liquid to be treated by water treatment (including the case of reuse), the membrane permeate of the target liquid, or another liquid different from these.

[0039] That is, during the implementation of the water treatment process, a chlorine-based bactericide and a phosphate buffer may be added to the target liquid, and the sterilization process may be carried out by supplying the target liquid containing the chlorine-based bactericide and the phosphate buffer to the membrane module 1 as the sterilizing liquid. That is, the sterilization process may be carried out online. As a method of adding a chlorine-based bactericide and a phosphate buffer to the target liquid during the implementation of the water treatment process, for example, a method of supplying a liquid containing the chlorine-based bactericide and the phosphate additive from another flow path connected to the flow path of the target liquid to the flow path of the target liquid can be mentioned.

[0040] Alternatively, in a state where the water treatment process is stopped (interrupted), the sterilization process may be carried out by supplying a liquid containing a chlorine-based bactericide and a phosphate buffer (a solvent different from the target liquid) to the membrane module 1 as the sterilizing liquid. That is, the sterilization process may be carried out offline. When a membrane separation method using osmotic pressure such as forward osmosis is used in the water treatment process, the sterilization process of the membrane module used for forward osmosis or brine concentration is preferably carried out by supplying a solvent different from the target liquid containing a chlorine-based bactericide and a phosphate buffer to the membrane module 1 as the sterilizing liquid in a state where the water treatment process is stopped (see FIGS. 3 to 5). This is because the addition of a phosphate buffer or the like may change the osmotic pressure of the target liquid and affect the water treatment.

[0041] The sterilization process online or offline may be set to be performed a predetermined number of times at regular intervals (periods), for example, according to the confirmation of the sterilization effect and the operating status of the device. Here, as will be described later, when the sterilizing liquid is reused, the sterilization effect can be confirmed based on the measured value by measuring the concentration of the chlorine-based bactericide in the sterilizing solution.

[0042] (Reuse of the sterilizing liquid) In the sterilization process, it is preferable to supply (reuse) the sterilizing liquid discharged from the membrane module 1 to the membrane module 1 again. That is, it is preferable to supply the sterilizing liquid discharged from at least one of the first chamber 11 and the second chamber 12 of the membrane module 1 to at least one of the first chamber 11 and the second chamber 12 of the membrane module 1 again. In this case, the cost of the chemicals including the chlorine-based disinfectant and the phosphate buffer used in the sterilizing liquid can be reduced. In addition, since the waste liquid of the sterilizing liquid can be reduced, the cost of waste liquid treatment, the environmental load, etc. can be reduced.

[0043] Such reuse of the sterilizing liquid may be repeated. For example, the reuse of the sterilizing liquid may be repeated by circulating the sterilizing liquid in the flow path for the sterilization process indicated by the dotted line in FIG. 2.

[0044] When the sterilizing liquid is reused as described above, in the sterilization process, the concentration of the chlorine-based disinfectant in the sterilizing liquid is measured, and based on the measured value of the concentration of the chlorine-based disinfectant, the concentration of the chlorine-based disinfectant is adjusted by adding the chlorine-based disinfectant to the sterilizing liquid so that it falls within a predetermined concentration range. In the sterilization process, the chlorine-based disinfectant is consumed and the concentration of the chlorine-based disinfectant in the sterilizing liquid decreases. In particular, when the sterilizing liquid is repeatedly reused, the concentration of the chlorine-based disinfectant in the sterilizing liquid gradually decreases. In this case, by adding the chlorine-based disinfectant to the sterilizing liquid as described above, the concentration of the chlorine-based disinfectant can be maintained within a predetermined concentration (for example, a concentration at which an effective sterilizing action can be exerted) range.

[0045] Specifically, for example, the concentration of the chlorine-based disinfectant is measured (monitored) at the outlet of the tank 2 or the inlet of the membrane module 1 and at the inlet of the tank 2 or the outlet of the membrane module 1. From the concentration difference between the two, the consumption amount of the chlorine-based disinfectant in the membrane module 1 is obtained, and the concentration of the chlorine-based disinfectant can be adjusted by adding the chlorine-based disinfectant to the sterilizing liquid according to the consumption amount.

[0046] For example, a tank 2 may be provided in the flow path for the sterilization process (the flow path indicated by a dotted line in the figure). The concentration of the chlorine-based disinfectant may be adjusted by adding a chlorine-based disinfectant (or a liquid containing a chlorine-based disinfectant) to the liquid in the tank 2.

[0047] Further, it is preferable to adjust at least one of the addition amount and the addition frequency of the chlorine-based disinfectant according to at least one of the frequency of the sterilization process and the sterilization effect. Also, it is preferable to adjust the flow rate of the liquid for sterilization supplied to the membrane module 1. By such adjustment, the concentration of the chlorine-based disinfectant in the liquid for sterilization can be adjusted more precisely, and the sterilization effect can be achieved more reliably.

[0048] The liquid for sterilization discharged from the membrane module 1 is preferably supplied to the membrane module 1 (at least one of the first chamber 11 and the second chamber 12) after the suspension contained in the liquid for sterilization is removed by filtration. In this case, the suspension contained in the reused liquid for sterilization (including iron chloride generated by the chlorine-based disinfectant) can be removed, and the contamination of the semipermeable membrane by the suspension can be suppressed.

[0049] In the drawing, the liquid for sterilization is flowing through one of the first chamber 11 and the second chamber 12, but the liquid for sterilization may flow through both the first chamber 11 and the second chamber 12. In this case, both sides of the semipermeable membrane 10 can be washed with the chemical solution, and both sides of the semipermeable membrane 10 can be sufficiently sterilized.

[0050] (Washing process) Before the sterilization process or in parallel with the sterilization process, a washing process for washing the dirt attached to the semipermeable membrane may be performed. The washing process may be performed, for example, by chemical solution washing in which a chemical solution for washing is flowed through the membrane module 1 in the same manner as the sterilization process.

[0051] The chemical solution for washing is not particularly limited as long as it can wash the dirt on the semipermeable membrane. As agents used in the chemical solution for cleaning, for example, agents capable of removing scale (such as calcium sulfate, magnesium sulfate, calcium carbonate, silicate, etc.) adhering to the semipermeable membrane and removing organic substances that are generated by organisms and cause biofouling are used. Examples of such agents include surfactants, acids (inorganic acids such as hydrochloric acid, organic acids such as carboxylic acids, etc.), and alkaline agents. For example, citric acid is suitably used for dirt caused by inorganic substances. In addition, chlorine-based bactericides such as sodium hypochlorite used in the sterilization process also have a cleaning effect on dirt caused by organic substances, and thus can be suitably used as agents for cleaning. Thus, the sterilization process may also serve as the cleaning process.

[0052] In the cleaning process, cleaning called "backwashing" may be performed. Backwashing is a cleaning method in which the liquids flowing on both sides of the semipermeable membrane during the membrane separation process are reversely exchanged, and the direction of water permeating through the semipermeable membrane is made opposite to that during the membrane separation process, thereby physically removing the dirt adhering to the semipermeable membrane. In addition, cleaning called "flushing" may be performed. Flushing is a cleaning method in which the dirt adhering to the surface of the semipermeable membrane is washed away with a cleaning liquid at a low pressure and a high flow rate.

[0053] <Water treatment system> The water treatment system of this embodiment is a water treatment system used in the above water treatment method. Referring to FIG. 2, FIG. 3, etc., the water treatment system includes a membrane module 1 having a semipermeable membrane 10 and a first chamber 11 and a second chamber 12 partitioned by the semipermeable membrane 10.

[0054] The water treatment system may include a tank 2 for storing the liquid for sterilization.

[0055] The water treatment system may include a pump 4 for flowing the liquid for sterilization stored in the tank 2 to the membrane module 1.

[0056] The water treatment system may further include a flow rate adjustment valve 53 for adjusting the flow rate of the sterilizing liquid supplied from the tank 2 to the membrane module 1.

[0057] A filtration device 3 for filtering the sterilizing liquid stored in the tank 2 may be further provided in the flow path (upstream of the membrane module 1) connecting the tank 2 and the membrane module 1.

[0058] For example, by opening and closing each flow path with valves 51, 52, 54, 55, switching between the water treatment process and the sterilization process may be performed.

[0059] In the water treatment system using the membrane module 1 for forward osmosis as shown in FIG. 3, the number of membrane modules 1 may be plural. For example, as shown in FIG. 4, a plurality of membrane modules 1a, 1b may be connected in series, or may be connected in parallel. Also, for example, as shown in FIG. 5, a plurality of membrane modules 1a, 1b, 1c may be connected in series and in parallel.

Example

[0060] (Measurement of the change ratio of the salt permeation performance of the semipermeable membrane by sterilization) When the semipermeable membrane was immersed in various test liquids (simulated sterilizing liquids), the change ratio (degree of deterioration) of the salt permeation performance of the semipermeable membrane was measured. Specifically, in a sealed container with a maximum volume of 10 L, a test liquid (simulated sterilizing liquid) and a semipermeable membrane sample (a hollow fiber membrane bundle sample made of CTA) were enclosed, and the hollow fiber membrane bundle sample was immersed in the test liquid. The composition of the test liquid is as follows.

[0061] (Test liquid) Free chlorine concentration (average) = 100 mg / L (concentration adjustment by adding sodium hypochlorite solution) Temperature (average): 40°C pH (average): 6.5 Cobalt (Co) concentration: 0.1 ppb Copper (Cu) concentration: 0.5 ppb Phosphate buffer: None, 0.01% by mass, 0.2% by mass, 2% by mass

[0062] As the phosphate buffer, a phosphate buffer (a mixture of sodium dihydrogen phosphate and disodium hydrogen phosphate) was used. The mixing ratio (molar ratio) of sodium dihydrogen phosphate to disodium hydrogen phosphate in the phosphate buffer was 5:1. Four types of test solutions were prepared, a solution without the addition of a phosphate buffer for comparison, and three test solutions containing 0.01% by mass, 0.2% by mass, or 2% by mass of the phosphate buffer.

[0063] During the test, the test solution was stirred and convection of the test solution was imparted by operating the sealed container at 75 r / min using a shaker. Also, during the test, the free chlorine concentration (average) in the test solution was adjusted by adding an aqueous NaOCl solution to the test solution, and the pH (average) of the test solution was adjusted by adding 10% sulfuric acid or a 0.1 mol / L sodium hydroxide solution to the test solution. The free chlorine concentration was measured by the colorimetric DPD method using a residual chlorine meter.

[0064] After immersion for a predetermined time between 50 and 200 hours, a hollow fiber membrane bundle sample was collected, and the permeate salt concentration was measured by evaluating the reverse osmosis membrane performance of the hollow fiber membrane bundle sample (performance evaluation conditions: feed solution concentration: 3.5% - NaCl concentration brine, feed pressure = 5.39 MPa, feed temperature = 25°C). Then, the ratio of the permeate salt concentration of the hollow fiber membrane sample after immersion to the permeate salt concentration of the hollow fiber membrane bundle sample before immersion (the value of [permeate salt concentration of the membrane after the immersion test (after deterioration)] ÷ [permeate salt concentration of the membrane before immersion (new product)]) that had been measured in advance was determined. The "change ratio of salt permeation performance" on the vertical axis of the graph in Figure 1 is this ratio. The relationship between this salt permeation performance change ratio (change ratio of permeate salt concentration) and the immersion time is shown in the graph of Figure 1.

[0065] From the results shown in Fig. 1, in the case of the test solution containing the phosphate buffer, compared with the case of the test solution not containing the phosphate buffer, the variation in the ratio of the change in the permeated salt concentration is less, indicating that the oxidative degradation of the semipermeable membrane is suppressed.

[0066] (Verification of bactericidal effect) The bactericidal property against bacteria in seawater was verified. Specifically, the test was conducted according to the following procedure. The test was carried out at a temperature of 27°C. The test results are shown in Table 1.

[0067] (1) Add a phosphate buffer to 200 mL of the collected seawater. (The phosphate buffer is the same as that used in the measurement of the change ratio of the salt permeation performance described above.) (2) Add an appropriate amount of sodium hypochlorite and adjust the pH (adjust to 6.5). (3) Let it stand at room temperature for 4 hours. (4) After 4 hours, measure the change in the free chlorine concentration and pH. Note that the values of the free chlorine concentration and pH in the table are the average values of the measured values before and after the test. (5) Measure the viable count in the sample. Note that the measurement of the viable count was carried out using a water sampler (HPC total count sampler, MHPC10025, Millipore). Saline (3.5 wt%) was used for the preparation of the sample for viable count measurement.

[0068]

Table 1

[0069] From the results shown in Table 1, regardless of the presence or absence of the phosphate buffer, the bactericidal effect by chlorine (a significant decrease in the viable count) was confirmed. Therefore, it is considered that adding a phosphate buffer to the bactericidal solution containing a chlorine-based bactericide has almost no effect on the bactericidal effect.

Explanation of symbols

[0070] 1, 1a, 1b, 1c membrane module, 10 semipermeable membrane, 11 first chamber, 12 second chamber, 2 tank, 3 filtration device, 4 pump, 51, 52, 54, 55 valves, 53 flow rate adjustment valve.

Claims

1. A water treatment process using a membrane module having a semipermeable membrane and a first chamber and a second chamber partitioned by the semipermeable membrane, and a sterilization process for sterilizing the semipermeable membrane, the water treatment method comprising: In the sterilization process, a sterilizing solution containing a chlorine-based sterilizing agent and a phosphate-based buffering agent having a buffering ability to maintain a pH of 3 to 8 is supplied to at least one of the first chamber and the second chamber of the membrane module, whereby the sterilizing solution is brought into contact with the semipermeable membrane to sterilize the semipermeable membrane. A water treatment method.

2. The water treatment method according to claim 1, wherein in the sterilization process, the sterilizing solution discharged from the membrane module is supplied to the membrane module again.

3. In the sterilization process, the concentration of the chlorine-based sterilizing agent in the sterilizing solution is measured, and based on the measured value of the concentration of the chlorine-based sterilizing agent, the chlorine-based sterilizing agent is adjusted so that the concentration of the chlorine-based sterilizing agent is within a predetermined concentration range. The water treatment method according to claim 2, wherein the concentration of the chlorine-based sterilizing agent is adjusted by adding the chlorine-based sterilizing agent to the sterilizing solution.

4. The water treatment method according to claim 2, wherein at least one of the addition amount and the addition frequency of the chlorine-based sterilizing agent is adjusted according to at least one of the frequency of implementation of the sterilization process and the sterilization effect.

5. The water treatment method according to claim 2, wherein the flow rate of the sterilizing solution supplied to the membrane module is adjusted.

6. The water treatment method according to claim 2, wherein the sterilizing solution discharged from the membrane module is supplied to the membrane module after the suspension contained in the sterilizing solution is removed by filtration.

7. A water treatment system used in the water treatment method according to any one of claims 1 to 6, a membrane module having the semipermeable membrane and a first chamber and a second chamber partitioned by the semipermeable membrane, and a tank for storing the sterilizing solution. A water treatment system.

8. The water treatment system according to claim 7, further comprising a pump for flowing the sterilizing solution stored in the tank to the membrane module.

9. The water treatment system according to claim 7, further comprising a flow rate adjustment valve for adjusting the flow rate of the sterilizing solution supplied from the tank to the membrane module.

10. The water treatment system according to claim 7, further comprising a filtration device for filtering the sterilizing solution stored in the tank in a flow path connecting the tank and the membrane module.

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