JP2008279431A - Membrane washing method and membrane washing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane washing method and a membrane washing apparatus capable of stably maintaining a membrane filtration operation without reducing the permeation performance of a membrane. <P>SOLUTION: The membrane washing method for processing a treating water by membrane filtration comprises: a membrane filtration process of filtering the treating water with a membrane; a reverse flow washing process of reversely washing the membrane by reversely flowing a filtrated water in a direction opposite to that of the filtration after the membrane filtration process; and a chemical-added reverse flow washing process of reversely washing the membrane by adding chemicals to the membrane-filtrated water after repeating the membrane filtration process and the reverse flow washing process a predetermined number of times or responding to the clogging of the membrane, wherein the washing of the membrane is performed in the chemical-added reverse flow washing process by an acid-added reverse flow washing process using an acid for a chemical to be added in combination with a reducing agent-added reverse flow washing process using a reducing agent for a chemical to be added. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a membrane cleaning method and membrane cleaning apparatus for subjecting water to be treated to membrane filtration.

  Conventionally, a water treatment apparatus using a membrane has been used in fields such as wastewater treatment and water purification. In the water treatment apparatus using this membrane, fouling occurs due to long-time operation, and the filtration performance deteriorates. Therefore, in the operation cycle, after a filtering process for a predetermined time, physical cleaning is performed to reduce fouling. This physical cleaning includes backwashing (backwashing) that reverses membrane filtered water, flushing with water flow on the primary side of the membrane, and air scrubbing that vibrates the membrane with air, and removes adhered substances by physical action. ing.

However, even if these physical cleanings are performed, fouling gradually progresses, and a membrane whose filtration performance has deteriorated due to fouling is subjected to chemical cleaning.
Chemical cleaning is a cleaning method in which substances that cannot be removed by physical cleaning are decomposed or dissolved by chemicals and removed. As one of chemical cleaning methods, a cleaning method has been devised in which back cleaning is performed with water containing a chemical and a chemical immersion step is provided to improve the cleaning effect of the film.

  Patent Document 1 proposes a method of performing cleaning with a reducing agent after cleaning with an oxidizing agent, and Patent Document 2 proposes a cleaning method in which a reducing agent is added to an inorganic acid solution.

In addition, as a method for cleaning a membrane using raw water containing manganese or iron pretreated with an oxidizing agent as raw water, a method of cleaning the primary side of the membrane with a reducing agent is described (see Patent Document 3). .
JP-A-9-290141 JP 2000-202255 A JP 2006-305444 A

  However, in chemical cleaning, it is necessary to increase the concentration of chemicals or increase the contact time if the selection of chemical types suitable for membrane fouling substances and the order of cleaning are not performed properly. There was a problem that could not be initialized. In addition, the cleaning method in which a chemical solution is mixed has a problem that the types of chemicals to be mixed are limited from the viewpoint of chemical reaction.

  In addition, regular backwashing in membrane filtration of raw water containing manganese and iron may cause clogging due to oxidation of soluble metal permeated through membrane filtration water and precipitation on the secondary membrane surface. . In addition, in chemical cleaning performed by adding chemicals, dissolved chemicals in raw water or membrane filtered water are suspended by the added chemicals, and clogging of the membrane may be accelerated. Thus, clogging of the film may occur not only on the primary film surface but also on the inside of the film or on the secondary film surface of the film by backwashing. Dissolved metal that has been oxidized and adhered to the film cannot be removed by commonly used acid and alkali chemical cleaning, or it took time and high concentration chemicals.

  In Patent Document 3, since only the primary side is washed, clogging substances in the pores of the membrane and the secondary side of the membrane cannot be removed. In the method of chemical cleaning by passing a reducing agent from the primary side to the secondary side, metals such as high-concentration manganese and iron dissolved in the secondary side of the membrane are permeated and the membrane filtrate is contaminated. There was a problem that the film was re-oxidized and deposited on the membrane side of the filtration side (secondary side) or in the piping.

  The present invention has been made in view of the above problems, and provides a membrane cleaning method and a membrane cleaning apparatus that can stably continue the membrane filtration operation without deteriorating the permeation performance of the membrane. Objective.

  In order to solve the above-described problems, the membrane cleaning method of the present invention includes a step of membrane-filtering water to be treated, and a reverse-flow cleaning of the membrane by passing filtered water in a direction opposite to the filtration after the membrane filtration step. And a chemical-added backwashing step for performing backwashing by adding chemicals to the membrane filtration water (periodically) after repeating filtration and backwashing a predetermined number of times (periodically). As the backwashing process, the membrane is washed by combining an acid-added backwashing process in which an acid is used as the additive chemical and a reducing agent-added backflow process in which a reducing agent is used.

  According to this configuration, by adding acid and a reducing agent to the backwash water and passing the medicinal-added membrane filtrate from the secondary side to the primary side, the surface of the membrane (both primary and secondary sides) and The clogging substance due to the metal oxide precipitated in the membrane pores can be dissolved and eliminated. As a result, it is possible to dissolve and remove deposited substances that are deposited on the film surface and cannot be removed by ordinary chemical cleaning, and since the dissolved high-concentration metal oxide is discharged from the primary side, Water quality is maintained. Thereby, the membrane filtration operation can be stably continued without deteriorating the permeation performance of the membrane. Further, by carrying out the step using an acid and a reducing agent as separate steps, it is possible to use a reducing agent that causes a chemical reaction when the acid is mixed. As a result, a chemical suitable for the fouling substance can be selected.

  Further, the frequency of the acid-added backwashing and the reducing agent-added backwashing in the chemical-added backwashing step is set according to the contamination state such as clogging of the film. According to this configuration, when there are many (less) components that can be removed by reductive dissolution, the frequency of the reducing agent-added backwashing is high, and when there are many (small) components that can be removed by acid dissolution, the frequency of acid-added backwashing By raising (lowering) the membrane can be cleaned efficiently and the amount of chemicals used can be reduced.

  In the chemical addition backwashing step, the chemical addition backwashing step using the acid solution is successively performed after the chemical addition backwashing step using the reducing agent. According to this configuration, after the metal oxide in water is reduced and dissolved by the reducing agent, the metal component and the like attached to the film surface can be further dissolved by the acid, and the film can be initialized in one chemical cleaning step. It can be done quickly.

  Further, the present invention provides a secondary oxide of the membrane by dissolving a metal oxide substance that has passed through the membrane and precipitated by oxidation of the soluble metal contained in the membrane filtrate with the reducing agent. It is desirable to pass from the side to the primary side. Further, the present invention provides a metal oxide substance deposited on the primary side or secondary side of the filtration membrane or in the pores of the filtration membrane by oxidizing the soluble metal contained in the water to be treated. It is desirable to dissolve with an agent and back flow to the primary side of the filtration membrane.

  As the chemical-added backwashing step, combined washing of the acid-added backwashing and the reducing agent-added backwashing backwashing, and an oxidizing agent-added backwashing using an oxidizing agent are further performed. According to this configuration, sterilization in the membrane system and removal of organic substances can be performed by using an oxidizing agent.

  As the chemical-added backwashing, the oxidant-added backwashing is performed after the combined cleaning of the acid-added backwashing and the reducing agent-added backwashing. According to this configuration, the oxidant-added backwashing is finally performed, so that it is possible to oxidize the soluble substance remaining in the membrane apparatus by dissolving with an acid or a reducing agent, and to permeate water (treated water). Of soluble substances can be prevented.

  The treated water contains at least one of manganese, iron and aluminum.

  The membrane cleaning apparatus of the present invention includes a membrane module for filtering water to be treated, backflow cleaning means for storing filtered water, passing the membrane filtered water through the membrane module and cleaning the membrane module, A chemical addition means for adding chemicals to the membrane filtrate, wherein the chemical solution addition means includes an acid solution addition means for adding an acid solution to the membrane filtrate as the chemical to be added, and a reducing agent as the chemical to be added. And a reducing agent adding means for adding to the filtered water.

  In addition, the membrane cleaning apparatus of the present invention further includes an oxidant addition unit in which the chemical solution to be added is an oxidant as the chemical solution addition unit.

  ADVANTAGE OF THE INVENTION According to this invention, the membrane washing | cleaning method and membrane washing | cleaning apparatus which can continue a membrane filtration operation stably, without reducing the permeation | transmission performance of a membrane can be provided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, exemplary embodiments of the invention will be described with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram of a water treatment apparatus 100 according to an embodiment of the present invention. As shown in FIG. 1, the water treatment apparatus 100 includes a raw water tank 2, an operation pump 3, a membrane inlet valve 4, a membrane filtration device 5, a membrane outlet valve 6, a backwash tank inlet valve 7, a backwash tank 8, a backwash. Pump 10, backwash valve 11, backwash drain valve 12, reducing agent tank 14, reducing agent injection pump 15, reducing agent injection valve 16, acid tank 17, acid injection pump 18, acid injection valve 19, oxidant tank 20, An oxidant injection pump 21, an oxidant injection valve 22, a chemical injection facility 28, and the like are included.

  This water treatment apparatus 100 produces water by separating a contaminant contained in water with a membrane filtration device 5, and after filtration of water to be treated by the membrane, membrane filtration water in a direction opposite to the filtration. Pass water and perform back-flushing regularly.

  The raw water 1 which is to-be-treated water contains, for example, manganese, iron or aluminum. The raw water tank 2 stores the raw water 1. A raw water supply pipe 31 that supplies raw water 1 from the raw water tank 2 to the membrane filtration device 5 is connected to the membrane filtration device 5. The raw water supply pipe 31 is provided with an operation pump 3 and a membrane inlet valve 4.

  The membrane filtration device 5 has a membrane module 51 made of, for example, an internal pressure type hollow fiber inside, and is configured to inject raw water 1 into a straw-shaped central hole of the hollow fiber membrane and obtain membrane filtered water on the outside. ing. The material of the membrane is preferably polyethersulfone or a mixture of polysulfone and polyvinylpyrrolidone.

  The membrane in the membrane filtration device 5 is subjected to chemical cleaning in which at least a reducing agent and an acid solution are added to the membrane filtration water, and the membrane filtration water to which the chemical is added is passed in the direction opposite to the filtration, The side, the pores and the secondary side (treated water side) are cleaned.

  The backwash water tank 8 is connected to each membrane module 51 in the membrane filtration device 5 to guide the membrane filtrate water to the backwash water tank 8, and the membrane filtrate water in the tank is treated water 9. A treated water pipe 33 to be taken out and a backwash water supply pipe 34 for sending the membrane filtrate in the tank as backwash water to the membrane filtration device 5 are connected. The membrane filtrate supply pipe 32 is provided with a membrane outlet valve 6 and a backwash tank inlet valve 7. The backwash water supply pipe 34 is connected to the middle of the membrane filtrate water supply pipe 32. Further, a backwash drain pipe 35 is connected to the membrane filtration device 5.

  The reducing agent tank 14 stores a reducing agent. Examples of the reducing agent include, but are not limited to, sodium bisulfite, sodium thiosulfate, sodium ascorbate, and sodium erythorbate.

  The acid tank 17 stores an acidic solution. Here, examples of the acidic solution include, but are not limited to, sulfuric acid, nitric acid, hydrochloric acid, and the like. It is desirable that the acidic solution has a pH of 5 or less, particularly pH 2-4.

  The oxidant tank 20 stores an oxidant. Oxidizer facilities will be provided as appropriate according to the quality of the raw water.

  The backwash water supply pipe 34 includes a reducing agent injection pipe 36 led from the reducing agent tank 14, an acid injection pipe 37 led from the acid tank 17, and an oxidant injection pipe 38 led from the oxidant tank 20. And are connected. The reducing agent injection pipe 36 is provided with a reducing agent injection pump 15 and a reducing agent injection valve 16. The acid injection pipe 37 is provided with an acid injection pump 18 and an acid injection valve 19. The oxidant injection pipe 38 is provided with an oxidant injection pump 21 and an oxidant injection valve 22.

  The backwash drain pipe 35 is connected to a chemical waste water treatment pipe 39 led from the chemical waste water treatment tank 24. The chemical waste water treatment pipe 39 is provided with a chemical cleaning drain valve 23.

  The chemical injection equipment 28 includes chemical tanks 40 and 41. A chemical supply pipe 42 that supplies chemicals in the chemical tank 40 and a chemical supply pipe 43 that supplies chemicals in the chemical tank 41 are connected to the chemical wastewater treatment tank 24. The medicine supply pipe 42 is provided with a medicine supply pump 44 and a medicine supply valve 45. The chemical supply pipe 43 is provided with a chemical supply pump 46 and a chemical supply valve 47.

  The chemical wastewater treatment tank 24 is agitated by a stirrer 26, and the pH and the oxidation-reduction potential in the chemical wastewater treatment tank 24 are measured by a pH meter / ORP meter 27. The chemical cleaning wastewater discharged from the primary side of the membrane module 51 is supplied to the chemical wastewater treatment tank 24 via the chemical cleaning drainage valve 23, and is subjected to chemical treatment so that the pH and oxidation-reduction potential are within a predetermined range. 25 is discharged.

  Next, the operation method of the water treatment apparatus 100 will be described. The operation of the water treatment device 100 is performed by passing the raw water 1 from the primary side of the membrane module 51 in the membrane filtration device 5 and performing membrane filtration treatment to obtain membrane filtrate, and the membrane secondary after the membrane filtration step. Reverse flow washing process that reverses the membrane by passing the membrane filtered water from the side opposite to the filtration, adding chemicals to the membrane filtered water and passing the water from the secondary side of the membrane to the primary side. It consists of a chemical-added backwashing process that performs backwashing. Each operation condition is decided according to raw water conditions. After the membrane filtration process and the backwashing process are repeated a predetermined number of times, or when the membrane differential pressure reaches a predetermined value in response to clogging of the membrane, a chemical addition backwashing is performed instead of the backwashing process. Is called.

  In the membrane filtration step, the membrane inlet valve 4, the membrane outlet valve 6 and the backwash tank inlet valve 7 are opened, and the raw water 1 in the raw water tank 2 is passed through the membrane inlet valve 4 by the operation pump 3 in the membrane filtration device 5. Water is passed to the primary side (raw water side) of the membrane module 51. Subsequently, the treated water membrane-filtered by the membrane filtration device 5 is stored in the backwash water tank 8 through the membrane outlet valve 6 and the backwash tank inlet valve 7. The membrane filtrate 9 stored in the backwash water tank 8 is sent to the next process as treated water by the treated water pipe 33.

  In the backwashing process, the membrane inlet valve 4 and the backwash tank inlet valve 7 are closed, the membrane outlet valve 6, the backwash valve 11 and the backwash drain valve 12 are opened. A part of the treated water flows from the secondary side of the membrane module 51 in the membrane filtration device 5 to the primary side, and the backwash drainage 13 discharged from the primary side of the membrane module 51 passes through the backwash drainage valve 12. Discharged.

  In the chemical-added backwashing process, a reducing agent-added backwashing process used as a chemical for adding a reducing agent, an acid-added backwashing process used as a chemical for adding an acid, and an oxidizing agent that uses an oxidant as necessary The membrane is cleaned in combination with an additional backwashing step. The oxidant-added backwash process is implemented and installed only when necessary.

  In the reducing agent-added backwashing process, the membrane filtration is carried out by the reducing agent pump 15 and the reducing agent is pumped from the backwash water tank 8 through the reducing agent injection valve 16 so that the inside of the membrane filtration device 5 has a predetermined reducing agent concentration. Pour into water and immerse for 20-30 minutes. In this manner, in the chemical addition backflow cleaning step, the chemicals are introduced into the film and then held for a predetermined time, so that the deposited substance can be sufficiently dissolved and removed. In the above, the concentration of the reducing agent is desirably 1% or less.

  Then, after the immersion, the backwash drain valve 12 and the chemical wash drain valve 23 are opened, and the backwash using the membrane filtrate in the backwash water tank 8 is performed as a rinse of the membrane in the membrane filtration device 5. The reducing agent-containing cleaning wastewater in the membrane in the filtration device 5 is discharged to the wastewater treatment tank 24. The discharged reducing agent-containing waste liquid is neutralized by the chemical waste water treatment equipment 28 and then drained as the waste water 25.

  Further, in the backwashing process, when the membrane filtrate passes through the membrane, the soluble metal contained in the membrane filtrate is deposited on the secondary side of the membrane by oxidation. For this reason, the metal-oxidized substance deposited on the secondary side of the membrane by the reducing agent can be dissolved by allowing the membrane filtrate to pass from the secondary side to the primary side of the membrane in the reducing agent-added backwashing step. In addition, the soluble metal contained in the water to be treated is oxidized and deposited on the primary side of the membrane or in the membrane pores. For this reason, the metal oxide deposited on the primary side of the membrane or in the membrane pores in the reducing agent-added back-flow cleaning step is dissolved by the reducing agent and discharged from the primary side of the membrane to the outside of the system. As a result, the dissolved high-concentration metal oxide is discharged from the primary side, so that there is no risk of mixing into the membrane filtered water, so that the water quality is maintained. Therefore, the membrane filtration operation can be continued stably without reducing the permeation performance of the membrane.

  The acid-added backwashing process and the oxidant-added backwashing process are performed in the same procedure. In the acid-added backwashing step, the acid solution is fed from the backwash water tank 8 to the membrane filtered water pumped from the backwash water tank 8 by the acid injection pump 18 through the acid injection valve 19 so that the inside of the membrane filtration device 5 has a predetermined acidic solution concentration. Inject and immerse for 20 to 30 minutes. After soaking, the backwash drain valve 12 and the chemical wash drain valve 23 are opened, and backwashing using the membrane filtrate of the backwash water tank 8 is performed as a membrane rinse in the membrane filtration device 5. 5 is discharged to the waste water treatment tank 24. The discharged acidic solution-containing waste liquid is neutralized by the chemical waste water treatment equipment 28 and then drained as the waste water 25.

  Further, in the oxidant-added backwashing process, the oxidant is pumped by the oxidant injection pump 21 through the oxidant injection valve 22 to sterilize the membrane system and remove organic substances. It inject | pours into the membrane filtration water pumped from the backwash water tank 8 so that it may become a density | concentration, and it immerses in the range for 20 minutes-30 minutes. After soaking, the backwash drain valve 12 and the chemical wash drain valve 23 are opened, and backwashing using the membrane filtrate of the backwash water tank 8 is performed as a membrane rinse in the membrane filtration device 5. 5 is discharged to the waste water treatment tank 24. The discharged oxidant-containing effluent is neutralized by the chemical wastewater treatment facility 28 and then drained as the drainage 25. The oxidizing agent-added backwashing step is performed after combined cleaning of the acid-added backwashing step and the reducing agent-added backwashing step. By performing backwashing with the addition of an oxidizing agent at the end, it is possible to oxidize soluble substances that are dissolved with an acid or a reducing agent and remain in the membrane filtration device 5, thereby preventing the inclusion of soluble substances in the treated water. be able to.

  FIG. 2 shows the membrane differential pressure when the type of chemical used for cleaning is changed using the water treatment apparatus 100 shown in FIG. FIG. 2 shows the effect of the cleaning sequence in the present invention. Table 1 shows the conditions in FIG. Here, sulfuric acid is used as the acidic solution, sodium bisulfite is used as the reducing agent, and sodium hypochlorite is used as the oxidizing agent. Each combination was examined under the conditions shown in Table 1 without changing the concentration and contact time in each chemical addition backwashing step.

The operation process was performed as shown in FIG. The membrane feed water put in the raw water tank 2 is sent to the membrane in the membrane filtration device 5 by the operation pump 3 and the whole amount is filtered for 30 minutes, and the membrane filtrate is fed from the secondary side of the membrane module 51 by the backwash pump 10. Water was sent to the primary side and backwashing was performed. After filtration and backwashing 41 times, chemical addition backwashing was performed. The number of times of filtration and backwashing was set so that the chemical addition backwashing step would be about once a day. Each chemical addition process was performed continuously.

  As shown in Fig. 2, the membrane differential pressure gradually rises while repeating filtration and backwashing under any operating conditions (marked with "Black" in the figure). The pressure difference across the membrane recovered to some extent (“◇” in the figure). However, as shown in Fig. 2 and operation (1) and (2) in Table 1, the membrane differential pressure is recovered to some extent by chemical cleaning in the combination of sulfuric acid and sodium hypochlorite, sodium bisulfite and sodium hypochlorite. However, the membrane differential pressure gradually increased, and the membrane differential pressure could not be completely initialized. On the other hand, in the operation (3), the membrane differential pressure did not increase and the membrane could be initialized with the same contact time as in the operations (1) and (2). Furthermore, as shown in operation (4), when sodium hypochlorite was washed with sodium bisulfite and sulfuric acid, the membrane differential pressure was stable as in operation (3), and the membrane differential pressure was The level of has declined. This is considered to be because the film clogging derived from organic substances was removed by sodium hypochlorite.

  When sodium bisulfite is used as a reducing agent, mixing sodium bisulfite and an acid is not usually possible because of the risk of generating sulfurous acid gas. For this reason, by carrying out the step using an acid and a reducing agent in separate steps, it is possible to use a reducing agent that causes a chemical reaction when the acid is mixed. As a result, a chemical suitable for the fouling substance can be selected.

Table 2 shows the results of analysis of the main components in the cleaning waste water of chemical cleaning with sodium bisulfite and sulfuric acid.

  Manganese was dissolved by the reducing agent, but iron, aluminum and organic components were not dissolved. On the other hand, in the acid cleaning, manganese is hardly dissolved, but inorganic metals such as iron and aluminum are dissolved, and organic components represented by TOC (total organic carbon of water to be treated) are also dissolved. As shown in the results of Table 2, it was confirmed that some metal oxides in water could not be dissolved by acid and could not be dissolved by reducing agent with limited contact time and concentration. When raw water containing such a metal oxide is subjected to membrane filtration, the membrane can be efficiently washed by combining an acid and a reducing agent.

  In the chemical addition backflow cleaning step, it is desirable to inject the reducing agent and the acid in this order. The reason is based on the result shown in FIG. FIG. 4 shows that in chemical-added backwashing, only washing with sodium hypochlorite was repeated for 10 days, and after increasing the membrane differential pressure after chemical washing (Δ in the figure), sodium bisulfite and sulfuric acid were used. It is a result of having carried out washing. In the figure, the “black circle” mark is a result of washing with sulfuric acid followed by washing with sodium bisulfite. In the figure, the “black square” mark is a result of washing with sodium bisulfite followed by sulfuric acid washing. From this result, it is understood that the membrane in the membrane filtration device 5 can be initialized by repeating washing with sodium bisulfite and sulfuric acid.

  However, it can be seen that it is possible to initialize in a short period of time after washing with sodium bisulfite before washing with sulfuric acid (black square in the figure). As a result, it is understood that it is preferable to perform the sulfuric acid cleaning subsequent to the cleaning with sodium bisulfite, but the present invention is not limited to this. In this way, in the chemical-added backwashing process, the acid-added backwashing process is performed after the reducing agent-added backwashing process, so that the metal oxide in water is reduced and dissolved by the reducing agent, and then the film surface is further added by the acid. An attached metal component or the like can be dissolved in an acid, and the film can be quickly initialized in one chemical cleaning step.

  FIG. 5 is a flowchart when the frequency of acid-added chemical cleaning and reducing agent-added chemical cleaning is changed in chemical-added backflow cleaning. FIG. 6 shows the membrane differential pressure when operating based on FIG. In operation A, after repeating filtration and backwashing a predetermined number of times (41 times), reducing agent addition backwashing and acid addition backwashing were performed once a day as chemical backwashing. Operations B and C are performed by changing the frequency of reducing agent-added backwashing and acid-added backwashing, and operation B usually performs acid-added backwashing and reduces the chemical cleaning once in 5 times. In the operation C, the reducing agent-added back-flow cleaning is usually performed, and the acid-added back-flow cleaning is performed once every five chemical cleanings.

  In operation A, the reducing agent and acid-added back-flow cleaning is performed each time chemical cleaning is performed without causing an increase in membrane differential pressure. On the other hand, in operation B, while the acid-added backwashing is continued (b = 1 to 4), the membrane differential pressure gradually increases, but the reducing agent-added backwashing is performed once every five times. The amount of chemicals used can be reduced from operation A. In operation C, it was found that the membrane differential pressure could not be initialized by sulfuric acid cleaning once every five times, and in this raw water, as in operation B, it was necessary to prioritize acid cleaning. As described above, depending on the quality of the raw water, it is not necessary to continuously perform cleaning with an acid and a reducing agent every time chemical cleaning is performed, and the membrane can be initialized by performing cleaning with an acid or a reducing agent at appropriate intervals.

  Therefore, it is desirable to set the frequency of the acid-added backwashing step and the reducing agent-added backwashing step in accordance with the state of contamination such as clogging of the membrane. For example, when many components can be removed by reductive dissolution, the frequency of reducing agent-added backwashing is increased, and when many components can be removed by acid dissolution, the frequency of acid-added backwashing is increased. On the contrary, when the amount of components that can be removed by reductive dissolution is small, the frequency of reducing agent-added backwashing is decreased, and when the amount of components that can be removed by acid dissolution is small, the frequency of acid-added backwashing is decreased. As a result, the membrane can be efficiently cleaned and the amount of chemicals used can be reduced.

  The water treatment apparatus 100 corresponds to the membrane cleaning apparatus of the present invention. Further, the membrane outlet valve 6, the backwash tank inlet valve 7, the backwash water tank 8, the backwash pump 10, the membrane filtrate water supply pipe 32, and the backwash water supply pipe 34 function as backwash cleaning means, and a reducing agent tank. 14, the reducing agent injection pump 15, the reducing agent injection valve 16, and the reducing agent injection pipe 36 function as reducing agent addition means for adding the reducing agent to the membrane filtrate, and the acid tank 17, the acid injection pump 18, and the acid injection valve 19. The acid injection pipe 37 functions as an acid solution addition means for adding the acid solution to the membrane filtrate, and the oxidant tank 20, the oxidant injection pump 21, the oxidant injection valve 22, and the oxidant injection pipe 38 are oxidant addition means. Function as.

  According to the above embodiment, in the cleaning of a membrane filtration device for filtering water containing a metal component in raw water, by using a reducing agent and an acid solution for chemical cleaning, reducing dissolution with a reducing agent and acid dissolution with an acid. The metal oxide that adheres firmly to the film surface can be removed. In the chemical addition backflow washing process, the chemical is added to the membrane filtration water, and the membrane filtration water to which the chemical is added is passed from the secondary side in the reverse direction to the filtration to the temporary side, in the membrane filtration device 5. Wash the membrane. As a result, metal components such as manganese oxide, iron oxide, and aluminum deposited on the temporary and secondary membrane surfaces and membrane pores of the membrane can be efficiently dissolved. As a result, it is possible to dissolve and remove deposited substances that are deposited on the surface of the membrane in the membrane filtration device 5 and cannot be removed by ordinary chemical cleaning, and the high-concentration metal components dissolved by the chemical cleaning are removed from the membrane filtration water. There is no risk of contamination. This makes it possible to perform a stable membrane filtration operation over a long period of time without degrading the permeation performance of the membrane, and the membrane can be operated efficiently.

  The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above-described embodiments, and various modifications may be made within the scope of the gist of the present invention described in the claims. It can be changed. In the above embodiment, a reducing agent and an acidic solution are used as chemical cleaning chemicals, but in addition to cleaning with a reducing agent and an acidic solution, cleaning using an alkaline solution or an oxidizing agent may be used in combination.

It is a block diagram of the water treatment apparatus which concerns on embodiment of this invention. FIG. 2 shows a film differential pressure after chemical cleaning when the type of chemical used for cleaning is changed using the water treatment apparatus shown in FIG. 1. FIG. It is a figure which shows the process of the driving | operation shown in FIG. This is a result of washing with sodium bisulfite and sulfuric acid after washing with sodium hypochlorite for a predetermined number of days. It is the flowchart which showed the operating method at the time of changing the frequency of reducing agent (sodium bisulfite) addition chemical | medical-agent backwashing, and the acid (sulfuric acid) addition chemical | medical-agent backwashing. It is the figure which showed the film | membrane differential pressure at the time of changing the frequency of reducing agent (sodium bisulfite) addition chemical | medical-agent backwashing, and the acid (sulfuric acid) addition chemical | medical-agent backwashing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Raw water 2 ... Raw water tank 3 ... Operation pump 4 ... Membrane inlet valve 5 ... Membrane filtration device 6 ... Membrane outlet valve 7 ... Backwash tank inlet valve 8 ...・ Membrane filtered water, backwash water tank 9 ... treated water 10 ... backwash pump 11 ... backwash valve 12 ... backwash drain valve 13 ... backwash drain 14 ... reducing agent Tank 15 ... reducing agent injection pump 16 ... reducing agent injection valve 17 ... acid tank 18 ... acid injection pump 19 ... acid injection valve 20 ... oxidant tank 21 ... oxidant Injection pump 22 ... Oxidizing agent injection valve 23 ... Chemical cleaning drain valve 24 ... Chemical waste water treatment tank 25 ... Waste water 26 ... Stirrer 27 ... pH, ORP meter 28 ... Chemical waste water Chemical injection equipment 100 for water treatment ... Water treatment equipment

Claims (10)

In the membrane cleaning method of membrane treatment of water to be treated,
A membrane filtration step of membrane-treating the water to be treated;
A backwashing step for backwashing the membrane by passing filtered water in a direction opposite to the filtration after the membrane filtration step;
A chemical-added back-flow cleaning step for performing back-flow cleaning of the membrane by adding a chemical to the membrane-filtered water after repeating the membrane filtration step and the back-flow cleaning step a predetermined number of times or according to clogging of the membrane; Have
The chemical-added backflow cleaning step combines the acid-added backflow cleaning step using an acid as a chemical to be added with the reducing agent-added backwashing step using a reducing agent as a chemical to be added, to clean the membrane. A method for cleaning a film characterized by the following. The frequency of executing the acid addition backflow cleaning step and the reducing agent addition backflow cleaning step in the chemical addition backflow cleaning step is set according to clogging of the film, respectively. Method for cleaning the membrane. 3. The film cleaning method according to claim 1, wherein in the chemical addition backflow cleaning step, the acid addition backflow cleaning step is performed after the reducing agent addition backflow cleaning step. 4. The soluble metal contained in the membrane filtrate passing through the membrane is deposited on the secondary side of the membrane by oxidation, and is dissolved by the reducing agent in the reducing agent-added backwashing step, The method for cleaning a film according to any one of claims 1 to 3, wherein the film is passed from the secondary side to the primary side of the film. As the soluble metal contained in the water to be treated is oxidized, the metal oxide substance deposited on the primary side of the membrane or in the pores of the membrane is dissolved by the reducing agent in the reducing agent-added backwashing step. The method for cleaning a film according to claim 1, wherein the film is discharged from the primary side of the film to the outside of the system. 2. The chemical-added backwashing step further comprises a combination cleaning of the acid-added backwashing step and the reducing agent-added backwashing step with an oxidizing agent-added backwashing step using an oxidant. The method for cleaning a film according to claim 5. 7. The membrane according to claim 6, wherein the chemical-added backwashing step performs the oxidant-added backwashing step after the combined cleaning of the acid-added backwashing step and the reducing agent-added backwashing step. Cleaning method. The method for cleaning a film according to claim 1, wherein the water to be treated contains at least one of manganese, iron, and aluminum. A membrane module for filtering the water to be treated;
Backflow cleaning means for storing filtered water and washing the membrane module by passing the membrane filtered water through the membrane module;
A chemical addition means for adding a chemical to the filtered water,
The chemical solution adding means includes an acid solution adding means for adding an acid solution as the chemical to be added to the membrane filtrate,
A membrane cleaning apparatus comprising: a reducing agent addition means for adding a reducing agent to the membrane filtrate as the chemical to be added. 10. The membrane cleaning apparatus according to claim 9, wherein the chemical addition means further includes an oxidant addition means for adding an oxidant to the membrane filtrate as the chemical to be added.

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