JP2009148667A - Membrane filtration apparatus and membrane washing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane filtration apparatus which is capable of properly conducting the pasteurization and washing while preventing the scale generation due to the injection of an alkaline solution, and to provide a membrane washing method. <P>SOLUTION: In the membrane filtration apparatus 1 which washes a membrane module 6 to filtrate seawater as a raw water by allowing the water filtrate through the membrane module 6 to flow backwards, it can conduct the pasteurization and washing properly while preventing the scale generation due to the injection of the alkaline solution because hydrogen peroxide within a hydrogen peroxide tank 9 in place of the alkaline solution is injected into the water filtrate used for the washing of the membrane module 6 in a stabilized state under acidity as a microbicide and detergent. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a membrane filtration apparatus and a membrane washing method for washing a membrane for filtering seawater or calcium ion-containing water as raw water.

  Seawater is attracting attention as a powerful water resource due to global concerns about water scarcity, and this seawater desalination technology is drawing attention. Among these desalination technologies, membrane treatment technology using reverse osmosis membranes is expected to be introduced in countries around the world due to its low energy consumption. In the seawater desalination method using this reverse osmosis membrane, the pretreatment such as sand filtration is used to reduce the seawater clarity (Silt Density Index: SDI). Fouling is intense and it may be difficult to reduce the clarity of seawater.

  Development of a pretreatment technique using a microfiltration membrane or an ultrafiltration membrane has been carried out on this seawater. In some cases, seawater is used to wash seafood. As a device for removing Vibrio parahaemolyticus and Norovirus from this seawater, a membrane filtration device using a microfiltration membrane or an ultrafiltration membrane is used. However, there are much more microorganisms in seawater than river water, lake water, etc., biofouling of membranes also progresses violently, and because of the promotion effect due to high salt concentration in seawater, There was a problem that fouling also increased dramatically.

  For this reason, for membrane filtration of seawater, for the purpose of sterilization and membrane cleaning, sodium hypochlorite that functions as a sterilizer and cleaning agent is injected into seawater that is raw water or membrane permeated seawater used for backwash cleaning Was.

  Here, the seawater to be treated exhibits a weak alkalinity of about pH 9 and has high calcium and magnesium concentrations. When an alkali solution such as sodium hypochlorite is injected into seawater showing such characteristics to increase the alkalinity, scales such as calcium carbonate and magnesium hydroxide are generated. As a result, the inside of the pipe for injecting an alkaline solution such as sodium hypochlorite may be blocked by the generated scale, resulting in the apparatus being stopped.

  In order to solve such problems, a method of reducing the contact between the alkaline solution and seawater by further installing an air-sealed pipe in the alkaline solution injection pipe (see Patent Document 1), or injecting acid into the alkaline solution injection pipe A method of reducing the generation of calcium carbonate and magnesium hydroxide (see Patent Document 2) has been proposed.

JP 2003-251335 A JP 2007-098321 A

  However, both of the method described in Patent Document 1 and the method described in Patent Document 2 are air-filled piping or acid in addition to piping for injecting an alkaline solution such as atrium hypochlorite that functions as a disinfectant and cleaning agent. Since injection piping is required, there is a problem that the apparatus configuration is complicated. In addition, both of the method described in Patent Document 1 and the method described in Patent Document 2, when fouling is severe, it is necessary to inject high concentration of sodium hypochlorite into seawater. It was difficult to prevent scales completely because there was a limit to the contact with seawater and the amount of acid injection.

  According to the present invention, there is provided a membrane filtration device and a membrane cleaning method that have been made in view of the above and can appropriately perform sterilization and cleaning while preventing scale generation due to alkaline solution injection. With the goal.

  In order to solve the above-described problems and achieve the object, a membrane filtration device according to the present invention includes a membrane for filtering seawater or calcium ion-containing water as raw water, and filtered water or raw water filtered by the membrane. A membrane filtration apparatus comprising a washing means for washing the membrane using the holding means for holding the filtrate or raw water used for washing the membrane under an acidic condition; Hydrogen peroxide injection means for injecting hydrogen peroxide into the filtered water or raw water, and the cleaning means uses the filtered water or raw water into which hydrogen peroxide has been injected by the hydrogen peroxide injection means. It is characterized by washing.

  The membrane filtration device according to the present invention includes a membrane that filters seawater or calcium ion-containing water that is raw water, and a cleaning means that cleans the membrane using the filtered water filtered by the membrane or the raw water. The membrane filtration apparatus further comprises hydrogen peroxide injecting means for injecting hydrogen peroxide held under acidity into the filtered water or raw water used for cleaning the membrane, the cleaning means comprising the hydrogen peroxide The membrane is washed with filtered water or raw water into which hydrogen peroxide has been injected by an injection means.

  Further, in the membrane filtration device according to the present invention, the cleaning means causes the filtered water injected with hydrogen peroxide by the hydrogen peroxide injection means to flow backward from the secondary side of the membrane to the primary side of the membrane. The film is washed.

  The membrane filtration apparatus according to the present invention is characterized in that the cleaning means cleans the primary side of the membrane using filtered water or raw water into which hydrogen peroxide has been injected by the hydrogen peroxide injection means. .

  Moreover, the membrane filtration apparatus according to the present invention is characterized in that the holding means holds the filtered water or raw water used for washing the membrane under an acidic condition using an inorganic acid.

  Moreover, the membrane filtration apparatus according to the present invention is characterized in that the hydrogen peroxide injection means injects the hydrogen peroxide held under acidity by an inorganic acid.

  Moreover, the membrane filtration apparatus according to the present invention is characterized in that the holding means holds filtered water or raw water used for washing the membrane at a pH of less than 3.0.

  The membrane filtration apparatus according to the present invention is characterized in that the hydrogen peroxide injection means injects the hydrogen peroxide maintained at a pH of less than 3.0.

  The membrane cleaning method according to the present invention is a membrane cleaning method for cleaning a membrane that filters seawater or calcium ion-containing water as raw water, and the filtered water or raw water used for cleaning the membrane is kept acidic. Holding step, hydrogen peroxide injection step of injecting hydrogen peroxide into the filtered water or raw water held under acid in the holding step, and filtered water injected with hydrogen peroxide in the hydrogen peroxide injection step or And a cleaning step of cleaning the membrane with raw water.

  Moreover, the membrane cleaning method according to the present invention is a membrane cleaning method for cleaning a membrane for filtering seawater or calcium ion-containing water as raw water. A hydrogen peroxide injection process for injecting the retained hydrogen peroxide; and a cleaning process for cleaning the film using filtered water or raw water into which hydrogen peroxide has been injected in the hydrogen peroxide injection process. Features.

  The present invention relates to a membrane filtration apparatus comprising a membrane for filtering seawater or calcium ion-containing water as raw water, and a cleaning means for washing the membrane using the filtered water filtered by the membrane or the raw water. In order to inject hydrogen peroxide instead of alkaline solution as a sterilizing agent and cleaning agent into the filtered water or raw water used for washing the water, and to keep the filtered water or raw water in an acidic state where the hydrogen peroxide is stable, Sterilization and washing can be appropriately performed while preventing the generation of scale due to the alkaline solution injection.

  Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments. In the description of the drawings, the same parts are denoted by the same reference numerals.

  Drawing 1 is a mimetic diagram showing composition of a membrane filtration device concerning an embodiment. The membrane filtration apparatus 1 shown in FIG. 1 selects hydrogen peroxide instead of an alkaline solution as a sterilizing agent and a cleaning agent to be injected into filtered water or raw water used for membrane cleaning, and this hydrogen peroxide is stabilized. The filtered water or raw water is kept acidic under acidic conditions.

  As shown in FIG. 1, a membrane filtration apparatus 1 according to an embodiment includes a raw water tank 2 that stores seawater or calcium ion-containing water as raw water, and a membrane supply pump 3 that supplies raw water in the raw water tank 2 to a disk filter 4. , A disk filter 4 for removing fine shells and layers in the raw water, a circulation pump 5 for feeding the incoming water to the membrane module 6, a membrane module 6 for filtering the incoming raw water, and introducing air into the membrane module 6 An air bubbling blower 8, a hydrogen peroxide tank 9 holding hydrogen peroxide functioning as a sterilizing agent and a cleaning agent, and a flow path between the membrane permeating water tank 12 and the membrane module 6 for hydrogen peroxide in the hydrogen peroxide tank 9. A hydrogen peroxide injection pump 10 that feeds water into the membrane, and a backwash pump 11 that feeds the filtered water in the membrane permeate tank 12 to the membrane module 6 during backwashing for the membrane module 6. Membrane permeated water tank 12 storing membrane permeated water (filtrated water) that has passed through the module 6, a valve 15 a that regulates inflow of the raw water returned from the membrane module 6 to the circulation pump 5, and a membrane fed from the membrane permeated water tank 12 A valve 15b for adjusting the inflow of the permeated water to the membrane module 6 primary side, a valve 15c for adjusting the inflow of the membrane permeated water sent from the membrane permeated water tank 12 to the secondary side of the membrane module 6, and the hydrogen peroxide tank 9 The hydrochloric acid tank 16 for containing hydrochloric acid injected into the tank, the hydrochloric acid injection pump 17 for injecting hydrochloric acid into the hydrogen peroxide tank 9 from the hydrochloric acid tank 16 and the pH in the hydrogen peroxide tank 9 under the control of the control unit 20 are measured. The membrane filtration mechanism 1 a having a pH meter 18 that outputs the measured pH value to the control unit 20 is provided. The membrane module 6 includes an external pressure type hollow fiber microfiltration membrane.

  Furthermore, the membrane filtration device 1 includes a control unit 20 that controls each component of the membrane filtration device 1, an input unit 22 that inputs information related to the processing operation of the membrane filtration device 1 to the control unit 20, and a processing operation of the membrane filtration device 1. The output part 23 which outputs the information regarding is provided. The control unit 20 determines that the pH value in the hydrogen peroxide tank 9 is at least less than 3.0 based on the pH value measured by the pH meter 18 and the amount of the hydrogen peroxide solution stored in the hydrogen peroxide tank 9. Thus, the hydrochloric acid injection amount and hydrochloric acid injection timing by the hydrochloric acid injection pump 17 are controlled.

  First, each process in the membrane filtration apparatus 1 is demonstrated with reference to FIG. 1 and FIG. FIG. 2 is a flowchart showing a processing procedure of each process performed by the membrane filtration device 1 shown in FIG.

  As shown in FIG. 2, in the membrane filtration device 1, a filtration process for filtering the raw water is performed based on the instruction information such as the input unit 22 (step S <b> 2). In this filtration process, the raw water stored in the raw water tank 2 is sent to the disk filter 4 by the membrane supply pump 3 as shown by the arrow Y11 in FIG. As indicated by Y12, water is sent to the membrane module 6 by the circulation pump 5. A part of the raw water sent to the membrane module 6 is returned to the inlet of the circulation pump 5 as shown by an arrow Y13 in FIG. 1 when the valve 15a is opened under the control of the control unit 20. Then, it is sent again to the membrane module 6 as return water. The membrane permeated water (filtrated water) that has passed through the membrane module 6 is stored in the membrane permeated water tank 12 as indicated by an arrow Y14.

  And the control part 20 judges whether predetermined | prescribed filtration time was reached | attained after starting the filtration process (step S4). When the control unit 20 determines that the predetermined filtration time has not been reached since the filtration process was started (step S4: No), the control unit 20 returns to step S2 to perform the filtration process on each component of the filtration mechanism 1a. Let it continue.

  On the other hand, when the control unit 20 determines that the predetermined filtration time has been reached after the filtration process is started (step S4: Yes), the membrane cleaning for removing the deposit on the membrane surface of the membrane module 6 or the like is performed. The filtration process is stopped for processing.

  Here, in the membrane filtration device 1 according to the embodiment, hydrogen peroxide is selected instead of an alkaline solution as a sterilizing agent and a cleaning agent, and this hydrogen peroxide is injected into filtered water used for membrane cleaning of the membrane module 6. is doing. Furthermore, in the membrane filtration device 1, the hydrogen peroxide injected into the filtered water used for membrane cleaning is kept acidic in the hydrogen peroxide layer 9, thereby stabilizing the hydrogen peroxide and This prevents clogging in the hydrogen peroxide injection pipe due to the generation of bubbles, which becomes a problem when destabilized.

  Therefore, under the control of the control unit 20, the backwash pump 11 sends the filtered water in the membrane permeate tank 12 to the membrane module 6 as shown by an arrow Y20 in FIG. The hydrogen peroxide injection pump 10 performs a hydrogen peroxide injection process for injecting the hydrogen peroxide held under acidity in the hydrogen peroxide tank 9 into the filtered water used for membrane cleaning, as indicated by an arrow Y21. Perform (step S6).

  Next, the membrane filtration device 1 opens the valve 15b and continues as shown by an arrow Y22 while keeping the filtered water supplied by the backflow cleaning pump 11 and the hydrogen peroxide injection by the hydrogen peroxide injection pump 10 continued. In addition, the filtered water injected with hydrogen peroxide is sent to the primary side of the membrane module 6 to flush the primary side of the membrane module 6, and after the flushing is completed, the valve 15b is closed and the valve 15c is opened. As shown by an arrow Y23, a membrane cleaning process is performed in which the filtered water into which hydrogen peroxide has been injected flows back from the secondary side of the membrane module 6 to the primary side of the membrane module 6 to perform back-flow cleaning (step S8). In the filtration treatment, microorganisms in the seawater are trapped on the membrane surface of the membrane module 6 (biofouling), and organic matter is adsorbed on the membrane surface (organic matter fouling), so that the membrane differential pressure increases. When this membrane differential pressure increases rapidly, the membrane filtration device 1 cannot be filtered and stops. In order to prevent this bio-fouling and organic matter fouling, flushing washing and back-flow washing are performed with filtered water into which hydrogen peroxide has been injected. The flushing waste water and the backwash waste water are discharged from the upper part of the membrane module 6 as indicated by an arrow Y24.

  The membrane filtration device 1 stops the total waste treatment of the backflow washing pump 11 and the hydrogen peroxide injection pump 10 and ends the membrane washing treatment, and then, as shown by an arrow Y25 in FIG. 6. Air bubbling is performed to introduce air from the bottom to the secondary side of the film (step S10). In addition, the air washing waste water is discharged from the upper part of the membrane module 6 as indicated by an arrow Y24, similarly to the flushing waste water and the backflow washing waste water. After the air bubbling process is completed, the backwash water remaining on the primary side of the membrane module 6 is discharged from the drain 14 as indicated by an arrow Y26.

  Next, the control unit 20 determines whether or not to continue the filtering process based on the instruction information input by the input unit 22 (step S12). Step S12: Yes), the process returns to step S2 to start the filtration process, and when it is determined that the filtration process is not continued (step S12: No), each processing operation such as the filtration process is terminated as it is.

  Thus, in the membrane filtration apparatus 1 according to the embodiment, calcium carbonate, water is used to inject hydrogen peroxide, not an alkaline solution, into the filtered water used for membrane cleaning as a bactericidal agent and a cleaning agent. Scale itself such as magnesium oxide does not occur. Therefore, according to the membrane filtration apparatus 1, sterilization and washing can be appropriately performed while preventing the generation of scale due to the alkaline solution injection.

  Further, in the membrane filtration device 1, since hydrogen peroxide injected into the filtered water used for membrane cleaning is stabilized in the hydrogen peroxide layer 9 under acidic conditions, the hydrogen peroxide is stabilized. This prevents the clogging in the hydrogen peroxide injection pipe due to the generation of bubbles, which becomes a problem when destabilization occurs.

  The reason why the hydrogen peroxide is kept acidic will be described. For example, a hydrogen peroxide solution with a hydrogen peroxide concentration of 35% shows weak acidity of about pH 4.5 to 4.7, and even if this hydrogen peroxide solution is injected into seawater, it does not increase the alkalinity of seawater. No scale occurs.

  However, when a weakly acidic hydrogen peroxide solution is injected in the presence of a trace amount of metal compound, hydrogen peroxide decomposes violently while generating oxygen. Here, seawater has a high salt concentration, the metal around the seawater is easily oxidized and corroded, and there is a high possibility that trace amounts of metals and metal oxides are mixed in the seawater. In addition, a trace amount of metal and metal oxide may be mixed in the hydrogen peroxide tank storing the hydrogen peroxide solution. In this way, when a weakly acidic hydrogen peroxide solution is injected in a state where metal and metal oxide are mixed, or when a metal and metal oxide are mixed into a weakly acidic hydrogen peroxide solution, oxygen A large amount of bubbles are generated by vigorous decomposition of hydrogen peroxide accompanied by the generation of. As a result, air bubbles are clogged in each injection pump and hydrogen peroxide injection pipe, and hydrogen peroxide cannot be injected into the filtered water while being correctly controlled.

  On the other hand, hydrogen peroxide can exist very stably when held under strong acidity with a pH value of less than 3.0. Even when a metal and a metal oxide are mixed in, oxygen is not decomposed vigorously while generating oxygen. In the membrane filtration device 1 according to the present embodiment, since hydrogen peroxide is held under an acidity where the pH value is at least less than 3.0, bubbles themselves that cause clogging of each injection pump and hydrogen peroxide injection pipe Does not occur. Therefore, according to the membrane filtration device 1 according to the present embodiment, the inside of each injection pump and the hydrogen peroxide injection pipe is not clogged. It can be injected with high precision into the filtered water used, and sterilization and washing can be performed appropriately.

Actually, cross flow of seawater was performed based on the flow of FIG. 1 and FIG. Specifically, membrane filtration of seawater is performed using three external pressure hollow fiber microfiltration membranes (manufactured by Asahi Kasei Co., Ltd.) having a PVDF pore size of 0.1 μm and a membrane area of 7 m ² . In this case, seawater was passed through the 80-mesh (200 μm) disk filter 4, and then supplied to the membrane module 6 by the circulation pump 5 together with the return water of the membrane module 6 at a membrane supply flow rate of 2.52 m ³ / h. And the membrane filtration apparatus 1 performed the constant flow filtration of the filtration flux 1.0m < ³ > / (m < ² > * d) by the crossflow system as a filtration process. The membrane filtration device 1 stops the filtration process after 20 minutes of the filtration process.

Thereafter, the hydrogen peroxide injection pump 10 is a hydrochloric acid acidic solution in which hydrogen peroxide having a concentration of 35% is added to the filtered water sent by the backwashing pump 11 to a pH <2.0 by adding hydrochloric acid. Hydrogen peroxide is injected from the hydrogen peroxide tank 9 so that the concentration of hydrogen peroxide is 20 mg / L. And the membrane filtration apparatus 1 sent the filtered water of the membrane permeation | transmission water tank 12 to the primary side of the membrane with the flow volume of 2.16 m < ³ > / h by the backflow washing pump 11 as flushing washing | cleaning, and washed for 25 seconds. Next, the membrane filtration device 1 performs the backwashing from the secondary side to the primary side of the membrane for 30 seconds after the valve 15b is closed and the valve 15c is opened, and then the backwashing pump 11 is stopped. . The membrane filtration apparatus 1 drains the backwash waste water and finishes the backwash, and then introduces air into the primary side of the membrane module 6 from the air bubbling blower 8 at an air flow rate of 6 m ³ / h and performs air bubbling treatment for 10 seconds. Do. After the air bubbling process is completed, the membrane filtration device 1 discharges the backwash waste water remaining on the primary side of the membrane module 6, fills the primary side of the membrane with raw water, and starts the filtration process.

  FIG. 3 shows the results of operation by repeating the above processing steps for one month. FIG. 3 is a diagram showing the time dependency of the membrane differential pressure when the membrane filtration device 1 performs the filtration treatment and the membrane cleaning treatment for one month. As shown in FIG. 3, even when the filtration treatment and the membrane cleaning treatment under the above-described conditions were performed for one month, the membrane differential pressure was maintained at about 70 kPa at which stable operation was possible. This is caused by injecting hydrogen peroxide held under strong acid into seawater as a sterilizing agent and a cleaning agent, so that neither piping nor scale clogging occurred.

  In contrast, when sodium hypochlorite is injected into the backwash water so that the effective chlorine concentration is 5 mg / L instead of hydrogen peroxide held under strong acidity, the same operation is performed. As shown in FIG. 4, unlike the membrane filtration device 1 according to the present embodiment, the membrane differential pressure that was about 15 kPa at the beginning of operation suddenly rose to 100 kPa or more after only about 6 days of operation. Driving became impossible in a week. And when the injection port of sodium hypochlorite was inspected, calcium carbonate crystals were deposited on the check valve of the injection port and the piping was blocked.

  As described above, in comparison with the conventional membrane filtration device using sodium hypochlorite, in the membrane filtration device 1 according to the present embodiment, it is possible to actually prevent the generation of scale and to continue the stable filtration treatment. It is understood that is possible.

  In order to prevent decomposition of hydrogen peroxide in the hydrogen peroxide tank, the acid added to hydrogen peroxide needs to be an inorganic acid in order to avoid reaction with hydrogen peroxide. The inorganic acid added to hydrogen peroxide may be a strong acid. In addition to hydrochloric acid, sulfuric acid or nitric acid may be used, but sulfuric acid may react with calcium in seawater to produce insoluble calcium sulfate, and nitric acid may cause nitrogen contamination in the backwash waste water. Because of concern, hydrochloric acid is the most desirable inorganic acid to use.

  In addition, it is known that acidification conditions for hydrogen peroxide may be a pH value of less than 3.0, but hydrogen peroxide is further stabilized by making the pH value less than 2.0. Therefore, it is further desirable that the pH value is less than 2.0.

  Moreover, it is desirable to inject | pour so that it may become the density | concentration of 10-100 mg / L by the density | concentration of 5 mg / L-500 mg / L as the injection quantity of the hydrogen peroxide to the filtration water used for membrane washing | cleaning. When hydrogen peroxide was injected under this condition, it was confirmed that there was no rapid decomposition caused by metal compounds in seawater. Effective membrane sterilization and cleaning can be performed.

  Moreover, although the external pressure type hollow fiber microfiltration membrane is used as the membrane module 6, it may be an external pressure type or an internal pressure type. Further, the type of membrane may be a microfiltration membrane or an ultrafiltration membrane. However, an ultrafiltration membrane is desirable when used for removal of norovirus in seawater. Moreover, as a membrane filtration system, whole volume filtration or crossflow filtration may be used. The membrane material used for the membrane module 6 is not particularly limited as long as it is a porous membrane. Polyethylene, polypropylene, polyacrylonitrile, polyvinylidene fluoride (PVDF), polysulfone, cellulose acetate, polyethersulfone, ceramic, etc. Selected from inorganic materials.

  In addition, in the embodiment, in addition to injecting hydrogen peroxide held under acidity into filtered water used for membrane cleaning, inject hydrogen peroxide after holding the filtrate water used for membrane cleaning acidic. May be. In this case, the hydrochloric acid in the hydrochloric acid tank 16 can be injected into the filtered water in the flow path between the membrane permeation tank 12 and the hydrogen peroxide injection position, like the filtration mechanism 201a in the membrane filtration apparatus 201 of FIG. A hydrochloric acid injection pump 17 and a hydrochloric acid injection pipe are provided. Then, a pH meter 18 is installed between the hydrochloric acid injection position and the hydrogen peroxide injection position so that the pH of the filtered water after the hydrochloric acid is injected can be measured. The hydrochloric acid tank 16, the hydrochloric acid injection pump 17, and the hydrochloric acid injection pipe function as holding means for holding the filtered water used for cleaning the membrane under the acidic condition described in the claims.

  In the membrane filtration apparatus 201 shown in FIG. 5, as shown in FIG. 6, the filtration process (step S22) and the filtration time arrival judgment process (step S24) are performed in the same manner as in steps S2 and S4 of FIG. Thereafter, under the control of the control unit 220, the backwash pump 11 feeds the filtrate in the membrane permeate tank 12 to the membrane module 6 as indicated by an arrow Y20 in FIG. As described above, hydrochloric acid injection treatment is performed to inject hydrochloric acid in the hydrochloric acid tank 16 into the filtered water used for membrane cleaning (step S25). While the hydrochloric acid injection process is continued, the pH meter 18 measures the pH of the filtered water after the hydrochloric acid is injected, and outputs the measured pH value to the control unit 220. When the controller 220 determines that the pH of the filtered water is at least less than 3.0, the control unit 220 supplies the hydrogen peroxide in the hydrogen peroxide tank 9 to the hydrogen peroxide injection pump 10 as indicated by an arrow Y21. Then, a hydrogen peroxide injection process for injecting the filtrate into the filtered water kept under acidic conditions is performed (step S26). Next, the membrane filtration apparatus 201 performs a membrane cleaning process (step S28), an air bubbling process (step S30), and a filtration process continuation determination process (step S32), similarly to steps S8 to S12 shown in FIG.

  Even when hydrogen peroxide is injected as a sterilizing agent and a cleaning agent after the filtered water used for cleaning the membrane is kept acidic, as in this membrane filtration device 201, the scale is generated due to the injection of the alkaline solution. Therefore, sterilization and cleaning can be performed appropriately.

  Moreover, although the case where the membrane of the membrane module 6 was wash | cleaned using the filtered water which permeate | transmitted the membrane module 6 was demonstrated to an example, of course, not only this but the primary side of the membrane of the membrane module 6 is wash | cleaned using raw water. May be. In this case, as shown in the filtration mechanism 301a of the membrane filtration device 301 in FIG. 7, the hydrogen peroxide held under acidity in the raw water in the flow path between the circulation pump 5 and the primary side of the membrane module 6 is used. Is provided with a hydrogen peroxide tank 9, a hydrogen peroxide injection pump 10, a hydrochloric acid tank 16, a hydrochloric acid injection pump 17, and a pH meter 18. As shown in the arrow Y320 in FIG. 7, the hydrogen peroxide injection pump 10 in the raw water used for membrane cleaning is controlled under the control of the control unit 320, as indicated by an arrow Y320 in FIG. Inject hydrogen peroxide maintained under acidity. Thereafter, the membrane filtration device 301 performs a membrane cleaning process and an air bubbling process for cleaning the primary side of the membrane of the membrane module 6. As in the case of the membrane filtration device 301, when hydrogen peroxide maintained under acidity is injected into the raw water used for membrane cleaning, scale generation due to the injection of the alkaline solution can be prevented. And cleaning can be performed appropriately.

  Moreover, as shown in the filtration mechanism 401a of the membrane filtration apparatus 401 of FIG. 8, hydrogen peroxide may be injected after the raw water used for membrane cleaning is kept acidic. In this case, a hydrochloric acid injection pump 17 and a hydrochloric acid injection pipe are provided so that hydrochloric acid in the hydrochloric acid tank 16 can be injected into the raw water in the flow path between the circulation pump 5 and the hydrogen peroxide injection position. Then, a pH meter 18 is installed between the hydrochloric acid injection position and the hydrogen peroxide injection position so that the pH of the raw water after the hydrochloric acid is injected can be measured. As the hydrochloric acid injection process, the controller 420 causes the hydrochloric acid injection pump 17 to inject hydrochloric acid in the hydrochloric acid tank 16 into the raw water as indicated by an arrow Y420. When the control unit 420 determines that the pH of the raw water is at least less than 3.0, as a peroxide injection process, the control unit 420 performs a hydrogen peroxide tank for the hydrogen peroxide injection pump 10 as indicated by an arrow Y320. Hydrogen peroxide injection treatment is performed in which the hydrogen peroxide in 9 is injected into the raw water kept under acidity. Thereafter, the membrane filtration device 401 performs a membrane cleaning process and an air bubbling process for cleaning the primary side of the membrane of the membrane module 6. As in this membrane filtration device 401, when hydrogen peroxide is injected after the raw water used for cleaning the membrane is kept acidic, scale generation due to the injection of the alkaline solution can be prevented. Sterilization and washing can be performed appropriately.

It is a schematic diagram which shows the structure of the membrane filtration apparatus concerning embodiment. It is a flowchart which shows the process sequence of each process which the membrane filtration apparatus 1 shown in FIG. 1 performs. It is a figure which shows the time dependence of the membrane differential pressure at the time of performing a filtration process and a membrane washing process for 1 month in the membrane filtration apparatus shown in FIG. It is a figure which shows the time dependence of the membrane differential pressure at the time of performing the filtration process and the membrane washing process in the membrane filtration apparatus concerning a prior art. It is a schematic diagram which shows the other structure of the membrane filtration apparatus concerning embodiment. It is a flowchart which shows the process sequence of each process which the membrane filtration apparatus 1 shown in FIG. 5 performs. It is a schematic diagram which shows the other structure of the membrane filtration apparatus concerning embodiment. It is a schematic diagram which shows the other structure of the membrane filtration apparatus concerning embodiment.

Explanation of symbols

1, 201, 301, 401 Membrane filtration device 1a, 201a, 301a, 401a Filtration mechanism 2 Raw water tank 3 Membrane supply pump 4 Disc filter 5 Circulation pump 6 Membrane module 8 Air bubbling blower 9 Hydrogen peroxide tank 10 Hydrogen peroxide injection Pump 11 Backflow cleaning pump 12 Membrane permeate tank 14 Drain 15a to 15c Valve 16 Hydrochloric acid tank 17 Hydrochloric acid injection pump 18 pH meter 20 Control unit 22 Input unit 23 Output unit

Claims (10)

In a membrane filtration apparatus comprising a membrane for filtering seawater or calcium ion-containing water as raw water, and a washing means for washing the membrane using the filtered water filtered by the membrane or the raw water,
Holding means for holding the filtered water or raw water used for washing the membrane under acidic conditions;
Hydrogen peroxide injection means for injecting hydrogen peroxide into filtered water or raw water held under acidity by the holding means,
And the cleaning means cleans the membrane using filtered water or raw water into which hydrogen peroxide has been injected by the hydrogen peroxide injection means. In a membrane filtration apparatus comprising a membrane for filtering seawater or calcium ion-containing water as raw water, and a washing means for washing the membrane using the filtered water filtered by the membrane or the raw water,
Hydrogen peroxide injecting means for injecting hydrogen peroxide maintained under acidity into filtered water or raw water used for cleaning the membrane,
The membrane filtration apparatus, wherein the cleaning means cleans the membrane using filtered water or raw water into which hydrogen peroxide has been injected by the hydrogen peroxide injection means.   The cleaning means cleans the membrane by causing the filtered water injected with hydrogen peroxide by the hydrogen peroxide injection means to flow backward from the secondary side of the membrane to the primary side of the membrane. The membrane filtration apparatus according to 1 or 2.   3. The membrane filtration device according to claim 1, wherein the cleaning unit cleans the primary side of the membrane using filtered water or raw water into which hydrogen peroxide has been injected by the hydrogen peroxide injection unit. .   5. The membrane filtration device according to claim 1, 3 or 4, wherein the holding unit holds the filtered water or raw water used for washing the membrane under an acidic condition using an inorganic acid.   The membrane filtration device according to any one of claims 2 to 4, wherein the hydrogen peroxide injection means injects the hydrogen peroxide held under acidity by an inorganic acid.   5. The membrane filtration device according to claim 1, wherein the holding unit holds filtered water or raw water used for cleaning the membrane at a pH of less than 3.0.   The membrane filtration device according to any one of claims 2 to 4, wherein the hydrogen peroxide injection means injects the hydrogen peroxide maintained at a pH of less than 3.0. In a membrane cleaning method for cleaning a membrane that filters raw water seawater or calcium ion-containing water,
A holding step of keeping the filtered water or raw water used for washing the membrane under acidic conditions;
A hydrogen peroxide injection step of injecting hydrogen peroxide into filtered water or raw water held under acidity in the holding step;
A cleaning step of cleaning the membrane using filtered water or raw water into which hydrogen peroxide has been injected in the hydrogen peroxide injection step;
A film cleaning method comprising: In a membrane cleaning method for cleaning a membrane that filters raw water seawater or calcium ion-containing water,
A hydrogen peroxide injection step of injecting hydrogen peroxide maintained under acidity into filtered water or raw water used for cleaning the membrane;
A cleaning step of cleaning the membrane using filtered water or raw water into which hydrogen peroxide has been injected in the hydrogen peroxide injection step;
A film cleaning method comprising:

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