JP2012086120A - Method for washing immersion type membrane module with chemical - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for washing an immersion type membrane module with chemicals, without extracting the immersion type membrane module to the outside of tanks, while reducing the amount of chemicals to be used, in the method for washing the immersion type membrane module having two or more membrane immersion tanks.SOLUTION: In a water treatment method, a chlorine-based oxidizing agent is added to manganese ion-containing raw water, to be filtrated by two or more immersion type membrane modules while diffusing air from a lower part and/or from a side part. In the water treatment method, after precipitating manganese dioxide in the membrane immersion tanks 3a, 3b, water in the second membrane immersion tank is filtered with the immersion type membrane module 4b to lower a water level in the second membrane immersion tank. The manganese dioxide at a lower part in the first membrane immersion tank is transported into the second membrane immersion tank through a communication part 7 at the lower part of the membrane immersion tank, while keeping the water level in the second film immersion tank lower than the water level in the first membrane immersion tank and then the immersion type membrane module 4a in the first membrane immersion tank is brought into contact with the chemicals.

Description

  The present invention relates to a chemical cleaning method for an immersion type membrane module having a plurality of membrane immersion tanks.

  In recent years, in water treatment applications such as water and sewage and wastewater treatment, membrane filtration methods that separate and remove impurities in raw water and convert them into clear water have become widespread. The substance to be removed varies depending on the type of the membrane, but in the case of a microfiltration membrane or an ultrafiltration membrane, generally suspended materials, bacteria, protozoa, colloidal materials, and the like are included. However, manganese ions contained in a large amount of groundwater and the like have a problem that they cannot be removed with a microfiltration membrane or an ultrafiltration membrane unless they are precipitated as manganese dioxide with a strong oxidizing power. Manganese does not precipitate by adding a normal chlorinated oxidizer, so there is a method of adding a strong oxidizer such as potassium permanganate or ozone. According to this method, it is possible to easily oxidize and precipitate and remove manganese by membrane filtration, but when potassium permanganate is added more than necessary, manganese ions and unreacted permanganate ions pass through the membrane. It had the problem that the manganese concentration of membrane filtration water became high. Further, when ozone is added more than the necessary amount, the oxidized manganese dioxide is further oxidized to become permanganate ions and has a problem that the manganese concentration of the membrane filtrate becomes high by passing through the membrane.

  Therefore, a contact tank is provided in the previous stage of the submerged membrane separation device, and manganese dioxide particles solid-liquid separated by the submerged membrane module are returned to the contact tank, or the suspended manganese dioxide is diffused in the immersion tank. A technique for oxidizing manganese ions in raw water by the autocatalytic action of is known (Patent Document 1).

First, manganese ions are exchanged and adsorbed on manganese dioxide by the reaction shown in the formula (1). Manganese dioxide that has come into contact with manganese ions becomes MnO ₂ .MnO and loses the contact oxidizing power, but is reactivated by the oxidation reaction with the chlorine-based oxidizing agent of formula (2). Therefore, in order to oxidize manganese ions, both manganese dioxide for exchange adsorption and a chlorine-based oxidant for reactivating manganese dioxide are required.

^{_{Mn 2+ + MnO 2 · H 2}} O → MnO 2 · MnO + 2H + (1)
MnO ₂ · MnO + HOCl + 2H ₂ O → 2 (MnO ₂ · H ₂ O) + H ⁺ + Cl ⁻ (2)
On the other hand, when performing filtration operation of microfiltration membranes or ultrafiltration membranes, the attached amount of humic substances, microorganism-derived proteins, iron oxide, manganese oxide, etc. on the membrane surface and pores with the amount of membrane filtration water Increasing, a decrease in the amount of filtered water or an increase in membrane differential pressure becomes a problem.

  Therefore, air is introduced into the raw water side of the membrane, the membranes are shaken, and the membranes are brought into contact with each other, so that the membrane filtration water is removed in the opposite direction to the membrane cleaning method. Alternatively, physical cleaning such as back-pressure cleaning that pushes clear water with pressure to eliminate fouling substances adhering to the membrane surface and membrane pores has been put into practical use.

  Furthermore, if the filtration capacity is reduced even after performing physical cleaning, chemical cleaning has been put into practical use that chemically decomposes and dissolves and removes fouling substances that could not be eliminated by physical cleaning (Patent Document). 2, 3).

  As a chemical cleaning method for a conventional immersion type membrane separation apparatus, the immersion type membrane module is taken out of the membrane immersion tank by using a heavy machine, and the chemical cleaning is performed in another small tank. However, in this method, the cleaning operation is complicated and workability is very poor.

  Also, divide the membrane immersion tank into multiple parts, place each immersion type membrane module in the divided tank, and install the immersion type membrane module in the membrane immersion tank by sequentially switching the membrane immersion tank for chemical cleaning There has also been proposed a method of cleaning chemicals in the state (Patent Document 4). This method is excellent in cleaning operability because it is not necessary to take out the submerged membrane module out of the tank. However, since the membrane immersion tank itself is used as a tank for cleaning, the amount of cleaning chemical used becomes enormous. In addition, as described above, manganese dioxide is required for the oxidation of manganese ions, but since the liquid in the membrane immersion tank is discharged, the manganese dioxide particles are discarded, and after restarting the operation, the manganese dioxide particles take time. There was a problem that had to be generated.

  By filling the inside of the membrane soaking tank with activated sludge, it is possible to biodegrade organic matter such as general municipal sewage, merged septic tanks, and various organic wastewater, and to obtain clarified water without suspended components with the soaking membrane module. Even in the membrane separation activated sludge method (MBR method) that can be performed, when this chemical cleaning method is carried out, the activated sludge is discarded, and there is a problem that the activated sludge must be acclimatized over time.

  Then, the method of transferring a part or all of the liquid in a film | membrane immersion tank to another film | membrane immersion tank is also proposed (patent document 5). Although this method can clean chemicals without discarding manganese dioxide particles or activated sludge, it is necessary to install a pump to transfer to each membrane immersion tank, and further to the membrane immersion of the transfer destination The tank volume had to be overdesigned.

Japanese Patent No. 3467713 JP 2005-193119 A JP 2006-305444 A JP-A-8-131785 Japanese Patent No. 3384281

  The present invention provides a chemical cleaning method for an immersion membrane module having a plurality of membrane immersion tanks, and does not require the immersion membrane module to be taken out of the tank. Activated sludge in the membrane dip tank required for decomposition of manganese or organic matter in raw water can be easily transferred to the other film dip tank using existing equipment for temporary storage, and the amount of chemicals used can be reduced. It is an object to provide a chemical cleaning method for a submerged membrane module.

  In order to solve the above problems, the chemical cleaning method for a submerged membrane module of the present invention has the following characteristics.

  (1) While adding a chlorine-based oxidizing agent to raw water containing 0.05 mg / L or more of manganese ions, and diffusing from below and / or from the side of the submerged microfiltration membrane / ultrafiltration membrane module In the water treatment method of filtering with a plurality of submerged membrane modules, the submerged membrane module in the plurality of membrane submerging tanks is sequentially contacted with the chemical by the chemical cleaning method of the raw water and the chlorine-based oxidizing agent After stopping the introduction and aeration of the liquid into the membrane immersion tank and precipitating manganese dioxide in the film immersion tank, the water in the second film immersion tank is filtered through the immersion membrane module, and the second Lowering the water level in the film immersing tank and maintaining the water level in the second film immersing tank lower than the water level in the first film immersing tank. Manganese is immersed in the second film through the communicating part at the bottom of the film immersion tank Transferring within, then chemical cleaning method of the submerged membrane module contacting the submerged membrane module of the first film immersion bath medicines.

  (2) Supplying raw water into a membrane immersion tank in which an immersion membrane module and activated sludge are immersed, and filtering with a plurality of immersion membrane modules while diffusing from below and / or from the side of the immersion membrane module In the water treatment method, the submerged membrane module in a plurality of membrane immersing tanks is in contact with chemicals in order, and the introduction and diffusion of raw water into the membrane immersing tank is stopped. Then, after the activated sludge in the membrane immersion tank is precipitated, the water in the second membrane immersion tank is filtered through the immersion membrane module to lower the water level in the second membrane immersion tank, and the second While maintaining the water level in the membrane dip bath lower than the water level in the first membrane dip bath, the activated sludge in the lower portion of the first membrane dip bath is passed through the communicating portion at the lower portion of the membrane dip bath. Immersion type membrane module transferred into the immersion tank and then in the first membrane immersion tank Chemical cleaning method of the immersion type membrane module is brought into contact with chemicals.

  (3) After the immersion membrane module in the first membrane immersion tank is brought into contact with the chemical, the water level in the first membrane immersion tank is further lowered, and the water level in the first membrane immersion tank is The manganese dioxide or activated sludge in the lower part of the second film dip tank is transferred into the first film dip tank through the communicating part in the lower part of the film dip tank while maintaining the water level lower than the water level in the film dip tank. Then, the chemical cleaning method for the immersion type membrane module according to (1) or (2), wherein the immersion type membrane module in the second membrane immersion tank is then brought into contact with the chemical.

  (4) The immersion membrane module according to any one of (1) to (3), wherein the chemical includes at least one selected from the group consisting of citric acid, oxalic acid, sulfite ion, hydrogen sulfite ion, and thiosulfate ion. Chemical cleaning method.

  (5) Chemical cleaning of the submerged membrane module according to any one of (1) to (4), wherein a flocculant and / or a pH adjuster is added to precipitate manganese dioxide or activated sludge in the membrane soaking tank. Method.

  (6) The chemical cleaning method for a submerged membrane module according to any one of (1) to (5), wherein the submerged membrane module is brought into contact with the chemical by back pressure cleaning with the chemical.

  (7) The chemical cleaning method for a submerged membrane module according to (6), which is left for a certain period of time after being backwashed with a chemical, and further backwashed with clear water.

  According to the chemical cleaning method of the present invention, it is not necessary to take out the submerged membrane module out of the membrane soaking tank, and the manganese dioxide or organic matter in the membrane soaking tank required for oxidation of manganese ions without a new pump is provided. Activated sludge in the membrane immersion tank required for biochemical decomposition can be easily transferred to the other membrane immersion tank using existing equipment for temporary storage, and the volume of the destination film immersion tank is excessive. Therefore, the amount of chemicals used can be reduced.

It is the schematic which shows the state of the normal filtration process before chemical | medical agent washing | cleaning of the immersion type membrane modules 4a and 4b of this invention. It is the schematic which shows the state of the normal back pressure washing | cleaning process before chemical | medical agent washing | cleaning of the immersion type membrane modules 4a and 4b of this invention. It is the schematic which shows the state of the normal drainage process before chemical | medical agent washing | cleaning of the immersion type membrane modules 4a and 4b of this invention. It is the schematic which shows the state which implements a precipitation process (STEP1) in the chemical | medical agent cleaning method of the immersion type membrane modules 4a and 4b of this invention. It is the schematic which shows the state which implements the water level fall process (STEP2) of the 2nd film | membrane immersion tank 3b in the chemical | medical agent cleaning method of the immersion type membrane modules 4a and 4b of this invention. In the chemical cleaning method for the submerged membrane modules 4a and 4b of the present invention, an outline showing a state in which the manganese dioxide / activated sludge transfer step (STEP 3) is performed from the first membrane immersion tank 3a to the second membrane immersion tank 3b. FIG. It is the schematic which shows the state which implements the chemical cleaning process (STEP4) of the immersion type membrane module 4a in the 1st membrane immersion tank 3a in the chemical cleaning method of the immersion type membrane modules 4a and 4b of this invention. It is the schematic which shows the state which implements the rinse process (STEP5) of the immersion type membrane module 4a in the 1st membrane immersion tank 3a in the chemical | medical agent cleaning method of the immersion type membrane modules 4a and 4b of this invention. In the chemical cleaning method for the submerged membrane modules 4a and 4b of the present invention, an outline showing a state in which the manganese dioxide / activated sludge transfer step (STEP 6) from the second membrane soaking tank 3b to the first membrane soaking tank 3a is performed. FIG. It is the schematic which shows the state which implements the chemical cleaning process (STEP7) of the immersion type membrane module 4b in the 2nd membrane immersion tank 3b in the chemical cleaning method of the immersion type membrane module 4a, 4b of this invention. It is the schematic which shows the state which implements the rinse process (STEP8) of the immersion type membrane module 4b in the 2nd membrane immersion tank 3b in the chemical | medical agent cleaning method of the immersion type membrane modules 4a and 4b of this invention. In the chemical cleaning method for the submerged membrane modules 4a and 4b of the present invention, an outline showing a state in which the manganese dioxide / activated sludge transfer step (STEP 9) from the first membrane immersion tank 3a to the second membrane immersion tank 3b is performed. FIG.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the drawings. In addition, this invention is not limited to the following embodiments. FIGS. 1-12 is a schematic flowchart which shows one embodiment of the water treatment apparatus and process which can perform chemical | medical agent washing | cleaning by this invention.

  For example, as shown in FIG. 1, the water treatment apparatus used in the present invention includes raw water supply valves 1a and 1b that are opened when raw water is supplied, and a membrane module selection valve 2a that is opened only for a submerged membrane module for chemical cleaning. 2b, membrane immersion tanks 3a and 3b for storing raw water, immersion type membrane modules 4a and 4b immersed in the film immersion tanks 3a and 3b, and below and / or laterally of the immersion type membrane modules 4a and 4b Diffuser pipes 5a and 5b, drainage valves 6a and 6b which are opened when the water in the membrane immersion tanks 3a and 3b is discharged, and manganese dioxide / activated sludge precipitated on the bottom of the membrane immersion tanks 3a and 3b. A communication valve 7 which is opened when transferring the air, a blower 8 for sending air for aeration, an oxidant pump 9 for injecting a chlorine-based oxidant into the film immersion tanks 3a and 3b, chlorine Oxidant storage for storing oxidants Tank 10, Filtration valve 11 that is opened during the filtration process, Filtration pump 12 that operates during the filtration process, Filtration water storage tank 13 that stores the membrane filtrate of the submerged membrane modules 4a and 4b, and back pressure with chemicals A backwash selection valve 14 that is closed when cleaning, a backwash valve 15 that is opened during the backwash process, a backwash pump 16 that operates during the backwash process, and a chemical reservoir that stores chemicals used in chemical cleaning. A tank 17 and a chemical selection valve 18 that is opened when backwashing with chemicals is provided.

  In the first invention, the raw water to be treated is not particularly limited as long as it contains 0.05 mg / L or more of manganese ions, and ground water, river water, lake water, and the like can be used.

  Here, as a method of measuring the concentration of manganese ions, the sample is filtered through a microfiltration membrane or an ultrafiltration membrane having a pore size of 0.45 μm or less, and the filtered water is subjected to flameless-atomic absorption spectroscopy or ICP emission spectrometry. (Measurement wavelength 257.610 nm) and a method of measuring by ICP mass spectrometry.

  In the second invention, the raw water to be treated by the membrane separation activated sludge method (MBR method) may be any material that contains biochemically decomposed organic matter regardless of the presence or absence of manganese ions. It does not restrict | limit in particular, Sewage, various organic wastewaters, etc. are mentioned.

  Here, as the separation membrane constituting the submerged membrane modules 4a and 4b in the present invention, the pore diameter is not particularly limited as long as it is porous, but depending on the desired quality and amount of treated water, a microfiltration membrane may be used, An ultrafiltration membrane is used, or both are used together. For example, if you want to remove turbid components, Escherichia coli, Cryptosporidium, etc., you can use either a microfiltration membrane or an ultrafiltration membrane. Is preferably used.

  Examples of the shape of the separation membrane include a hollow fiber membrane, a flat membrane, and a tubular membrane, and any of them may be used.

  The material of the separation membrane is not particularly limited, but polyethylene, polypropylene, polyacrylonitrile, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, polytetrafluoroethylene, polyvinyl fluoride, tetrafluoroethylene-hexafluoropropylene At least one selected from the group consisting of copolymers, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers and chlorotrifluoroethylene-ethylene copolymers, polyvinylidene fluoride, polysulfone, cellulose acetate, polyvinyl alcohol and polyethersulfone In view of film strength and chemical resistance, polyvinylidene fluoride (PVDF) is more preferable, and hydrophilicity is high and stain resistance is strong. From polyacrylonitrile it is more preferable.

  As the communicating part at the lower part of the membrane immersion tank in the present invention, a communication pipe that can easily control the water flow with the communication valve 7 is preferable, but an open / close gate may be provided below the partition walls of the membrane immersion tank 3a and the membrane immersion tank 3b. Good.

  In the above water treatment apparatus, the chemical cleaning of the present invention is performed as follows.

  FIG. 1 shows a state of a normal filtration step before chemical cleaning of the immersion type membrane modules 4a and 4b of the present invention.

  First, when the raw water supply valves 1a and 1b are opened, the raw water is supplied into the membrane immersion tanks 3a and 3b. Further, the chlorine-based oxidant stored in the oxidant storage tank 10 is supplied into the film immersion tanks 3 a and 3 b by the power of the oxidant pump 9. Further, by operating the blower 8 and feeding air, bubbles are generated from the diffuser tubes 5a and 5b provided below and / or on the side of the submerged membrane modules 4a and 4b, and the air is diffused. Suction filtration of the submerged membrane modules 4a and 4b is performed by operating the filtration pump 12 with the selection valves 2a and 2b and the filtration valve 11 open.

  The chlorine-based oxidizing agent in the first invention may be any one as long as it can reactivate manganese dioxide that has lost contact oxidizing power, such as hypochlorous acid and chlorine dioxide, and ferrous ions and manganese ions in raw water. It is preferable to control the injection amount as appropriate according to the concentration of the liquid. However, in the membrane separation activated sludge method (MBR method), microorganisms in the activated sludge may be killed, and the decomposition ability of organic substances may be reduced. Therefore, in the second invention, it is preferable not to inject a chlorine-based oxidizing agent. .

  In the first invention, the time and the air flow rate of air diffused from the air diffusers 5a and 5b are appropriately determined according to the manganese ion concentration in the raw water, the manganese dioxide concentration in the membrane immersion tanks 3a and 3b, the filtration time, and the like. You only have to set it. Air bubbles may be generated at all times during the filtration step, or may be generated intermittently as long as manganese dioxide particles sufficient for oxidation of manganese ions can be suspended. When bubbles are constantly generated during the filtration process, in order to suppress the abrasion of the membrane as much as possible, air is not diffused from the lower side where the bubbles are in direct contact with the submerged membrane modules 4a and 4b, but is diffused only from the side. You may let them.

  In the second invention, the time and the air flow rate of air diffused from the air diffusers 5a and 5b in the membrane separation activated sludge method (MBR method) can clean the membrane surface of the submerged membrane modules 4a and 4b. It is possible to supply oxygen necessary for the activated sludge treatment in the membrane immersing tanks 3a and 3b, and depending on the concentration of organic matter in the raw water, the activated sludge concentration in the membrane immersing tanks 3a and 3b, the membrane filtration flux, etc. You only have to set it.

  The filtration time of the submerged membrane modules 4a and 4b is preferably set as appropriate according to the raw water quality and the membrane permeation flux. However, the filtration time may be continued until a predetermined membrane filtration differential pressure is reached. In the first invention, the generation of bubbles in the membrane immersion tanks 3a and 3b causes the manganese dioxide particles solid-liquid separated in the immersion membrane modules 4a and 4b to settle to the bottoms of the membrane immersion tanks 3a and 3b. In the second invention, the activated sludge settles at the bottom of the membrane immersion tanks 3a and 3b in the membrane separation activated sludge method (MBR method). The organic matter in the raw water can be decomposed in a floating state.

  The filtration control method of the submerged membrane modules 4a and 4b may be constant flux filtration or constant pressure filtration, but a constant amount of membrane filtration water can be obtained, and the overall control is easy. From the point of view, constant flux filtration is preferred.

  Moreover, as filtration power of the submerged membrane modules 4a and 4b, a siphon using the water level difference between the membrane submerged tanks 3a and 3b and the filtrate storage tank 13 as well as suction filtration with the filtration pump 12 as shown in FIG. The suction filtration may be performed according to the principle described above.

  If the above filtration process is continued, organic substances such as iron and manganese oxides and humic acid adhere to the membrane surfaces and pores of the submerged membrane modules 4a and 4b, resulting in a decrease in the amount of filtered water or between the membranes. In order to cause an increase in the differential pressure, the back pressure washing process is started after the filtration process. FIG. 2 shows a state of a normal back pressure cleaning step before chemical cleaning of the immersion type membrane modules 4a and 4b of the present invention. First, after the blower 8, the oxidant pump 9, and the filtration pump 12 are stopped and the raw water supply valves 1a and 1b and the filtration valve 11 are closed, the backwash selection valve 14 is opened and the chemical selection valve 18 is closed. After confirming this, the backwash valve 15 is opened and the backwash pump 16 is operated to perform back pressure washing using the membrane filtrate of the filtrate storage tank 13. By doing so, iron and manganese oxides and organic substances are peeled off from the membrane surface and inside the membrane pores, so that it is possible to recover the amount of filtered water or suppress the transmembrane pressure difference.

  The normal back pressure cleaning time is not particularly limited, but is preferably in the range of 5 seconds to 120 seconds. If the back pressure cleaning time for one time is less than 5 seconds, a sufficient cleaning effect cannot be obtained, and if it exceeds 120 seconds, the operation efficiency of the submerged membrane modules 4a and 4b is lowered and the water recovery rate is lowered. .

  The normal backwashing flux is not particularly limited, but is preferably 0.5 times or more and 2 times or less the filtration flux. If the backwashing flux is less than 0.5 times the filtration flux, it is difficult to sufficiently remove the fouling material adhering to and depositing on the membrane surface. A higher back-pressure cleaning flux is preferable because the membrane cleaning effect is higher, but if it is too high, the water recovery rate will decrease, and there will be problems such as damage to the submerged membrane module container and membrane cracking. Therefore, it is set appropriately within the range where this is not the case.

  The frequency of normal back pressure washing may be appropriately set according to the filtration flux, filtration time, and raw water quality, and is not particularly limited, but is preferably about several tens of minutes to once every few hours. .

  In addition, the water used for normal back pressure washing | cleaning may be anything if it is clarified water, and is not limited to membrane filtration water. In the first aspect of the invention, it is more effective to add an oxidizing agent such as sodium hypochlorite, chlorine dioxide, hydrogen peroxide, ozone or the like to the water used for normal back pressure cleaning in the back pressure cleaning pipe. It is preferable because organic substances adhering to can be decomposed and cleaning effect is enhanced. For example, an oxidant is introduced into the chemical reservoir 17 and the chemical selection valve 18 is opened. However, it is preferable to appropriately control the concentration so that the oxidizing agent in the film immersion tanks 3a and 3b does not remain at a high concentration and the film does not deteriorate. When the concentration of the oxidant is high, the oxidant remaining in the secondary pipe at the time of resumption of filtration flows into the filtrate storage tank 13, so it is also preferable to stop the addition of the oxidant before the end of the backwashing. . On the other hand, in the second invention, in the membrane separation activated sludge method (MBR method), microorganisms in the activated sludge may be killed by the oxidizing agent, and the decomposition ability of organic substances may be reduced. It is preferable not to inject an oxidizing agent.

  Furthermore, by operating the blower 8 and feeding air, bubbles are generated from the diffuser tubes 5a and 5b provided below and / or on the side of the submerged membrane modules 4a and 4b, and the submerged membrane modules 4a and 4b It is also preferable to perform air cleaning that vibrates the membrane surface during at least a part of the above-described normal back-pressure cleaning and before and after the execution. The fouling material accumulated on the membrane surface and membrane pores is peeled off by the combined use of back pressure washing and air washing. The supply time and air flow rate of the bubbles from the diffuser tubes 5a and 5b may be set as appropriate according to the shape of the submerged membrane modules 4a and 4b, the performance of the membrane, and the contamination status. The time is preferably as short as possible, and is preferably set within 60 seconds.

  The drainage process is started after the normal back pressure washing process is completed. FIG. 3 shows a state of a normal drainage process before chemical cleaning of the submerged membrane modules 4a and 4b of the present invention. After the backwash pump 16 is stopped and the backwash valve 15 is closed, the drainage valves 6a and 6b are opened to peel off the membrane surface and membrane pores and float in the membrane immersion tanks 3a and 3b. The fouling substances that are being discharged are discharged out of the system. As described above, in the first invention, it is necessary to float manganese dioxide in the film immersion tanks 3a and 3b in order to oxidize manganese ions. When all the water in the membrane immersion tanks 3a, 3b is drained in the drainage process, it is necessary to generate manganese dioxide particles again over time, so that part of the water is drained to the extent that it does not hinder the oxidation of manganese ions. Is preferable. In the case of the membrane separation activated sludge method (MBR method) according to the second aspect of the invention, when all the water in the membrane immersion tanks 3a and 3b is drained in the drainage process, the activated sludge is acclimatized over time. Therefore, it is preferable to drain part of the organic matter so as not to hinder the decomposition of the organic matter. The draining process may be performed before back pressure cleaning or during back pressure cleaning. When back pressure cleaning is performed after draining and exposing the primary side of the membrane to air, there is an advantage that the fouling substance is easily peeled off from the membrane surface because no water pressure is applied to the primary side of the membrane.

  After the drainage process is completed by closing the drainage valves 6a and 6b, the raw water supply valves 1a and 1b are opened, the oxidant pump 9 is operated, the water supply process is performed, and the submerged membrane modules 4a and 4b are connected. After being immersed in water, the filtration valve 11 is opened and the filtration pump 12 and the blower 8 are operated to return to the filtration step and repeat the above steps. Since the substance cannot be completely removed, the membrane filtration suction pressure will eventually reach the limit of reaching the total suction head of the filtration pump 12 or causing cavitation. In this case, chemical cleaning (STEP 1 to STEP 9) of the immersion type membrane modules 4a and 4b of the present invention is performed.

  In addition, this invention makes it essential requirements to perform STEP1-STEP5, and it does not necessarily need to implement STEP6 and after. However, from the viewpoint of improving the efficiency of chemical cleaning, STEP 1 to STEP 9 are preferably performed as a series of steps, and chemical cleaning is performed on one submerged membrane module or on two or more submerged membrane modules. Is appropriately set according to the degree of fouling of each submerged membrane module, the concentration of manganese ions and organic matter in the raw water, the concentration of manganese dioxide and activated sludge in the membrane immersion tanks 3a and 3b, the filtration time, etc. be able to. Further, STEP 9 does not constitute the present invention, but can be preferably performed when the membrane filtration operation is carried out after the chemical cleaning method for the submerged membrane module of the present invention. That is, in this invention, after performing STEP1-STEP5, STEP9 may be implemented and a membrane filtration operation may be continued, or STEP1-STEP9 may be performed as a series of processes, and a membrane filtration operation may be continued.

  First, a precipitation step (STEP 1) is performed. FIG. 4 is a schematic view showing a state in which the precipitation step (STEP 1) is performed in the chemical cleaning method for the submerged membrane modules 4a and 4b of the present invention. When the blower 8, the oxidant pump 9, and the filtration pump 12 are stopped from the state of the filtration process and the raw water supply valves 1a and 1b and the filtration valve 11 are closed, the manganese dioxide floating in the membrane immersion tanks 3a and 3b Particles / activated sludge settles to the bottom of the tank. When the particle diameter of manganese dioxide is small and the sedimentation rate is slow, it is preferable to increase the sedimentation rate by adding a flocculant and / or a pH adjuster into the film immersion tanks 3a and 3b. Also in the membrane separation activated sludge method (MBR method), it is preferable to add a flocculant and / or a pH adjuster when the sedimentation rate of activated sludge is slow. As the flocculant to be used, any of iron-based and aluminum-based inorganic flocculants, dimethylamine-based and polyacrylamide-based cationic polymer flocculants may be used. As the pH adjuster to be used, inorganic adjusters such as sulfuric acid, hydrochloric acid, sodium hydroxide, sodium carbonate and the like are preferable. The applied pH is preferably from 6.5 to 8.5, where aggregated flocs are easily formed. In the case of adding a flocculant or a pH adjuster, it is preferable that the blower 8 is operated and diffused for a certain period of time because there is an effect of forming a floc floc by stirring. In addition, when the water level lowering step (STEP 2) of the second membrane immersion tank 3b described below is performed without performing the precipitation step (STEP 1), manganese dioxide particles / activated sludge is formed on the membrane surface of the immersion membrane module 4b. This is an important process because it attaches a lot and reduces the chemical cleaning effect.

  After the manganese dioxide particles / activated sludge is precipitated at the bottom of the tank in the precipitation step (STEP 1), the water level lowering step (STEP 2) of the second membrane immersion tank 3b is performed. FIG. 5 is a schematic view showing a state in which the water level lowering step (STEP 2) of the right membrane immersion tank 3b is performed in the chemical cleaning method for the immersion type membrane modules 4a and 4b of the present invention. When the membrane module selection valve 2a is closed, the filtration valve 11 is opened, and the filtration pump 12 is operated, only the submerged membrane module 4b performs suction filtration, and only the water level of the membrane immersion tank 3b decreases.

  After the water level of the second membrane immersion tank 3b is lowered, a manganese dioxide / activated sludge transfer step (STEP 3) from the first membrane immersion tank 3a to the second membrane immersion tank 3b is performed. FIG. 6 shows a state in which a manganese dioxide / activated sludge transfer step (STEP 3) from the first membrane immersion tank 3a to the second membrane immersion tank 3b is performed in the chemical cleaning method for the immersion type membrane modules 4a and 4b of the present invention. FIG. When the membrane module selection valve 2b, the filtration valve 11 and the backwash selection valve 14 are closed, the filtration pump 12 is stopped, and the communication valve 7 is opened, the difference in the water level is utilized for the first membrane immersion tank 3a. Manganese dioxide particles / activated sludge precipitated at the bottom is transferred to the second membrane immersion tank 3b. During this time, the transfer of manganese dioxide particles / activated sludge is performed while maintaining the water level of the second membrane immersion tank 3b to be lower than the water level of the first film immersion tank 3a. As the water level difference gradually disappears, the flow of water passing through the communication valve 7 decreases and the transfer effect of manganese dioxide particles / activated sludge decreases, so the raw water supply valve 1a is opened and the raw water is immersed in the first membrane. Supplying into the tank 3a is preferable because a difference in water level can be secured.

  After transferring the manganese dioxide particles / activated sludge precipitated at the bottom of the first membrane immersion tank 3a to the second membrane immersion tank 3b, the chemicals of the immersion membrane module 4a in the first membrane immersion tank 3a A cleaning step (STEP 4) is performed. FIG. 7 is a schematic view showing a state in which the chemical cleaning step (STEP 4) of the immersion membrane module 4a in the first membrane immersion tank 3a is performed in the chemical cleaning method for the immersion membrane modules 4a and 4b of the present invention. . When the raw water supply valve 1a and the communication valve 7 are closed, the membrane module selection valve 2a, the backwash valve 15 and the chemical selection valve 18 are opened, and the backwash pump 16 is operated, the chemical in the chemical reservoir 17 is immersed in the membrane. Back pressure washing of the module 4a is performed.

  The chemical for cleaning the chemical can be selected after setting the concentration and holding time to such an extent that the membrane does not deteriorate, but it can be selected from citric acid, oxalic acid, sulfite ion, bisulfite ion, and thiosulfate ion. It is preferable to contain at least one selected from the group because the cleaning effect on iron and manganese oxides is increased. If the water permeability of the membrane does not recover with the above chemicals, organic fouling substances may adhere to the membrane surface or pores, so sodium hypochlorite, chlorine dioxide, peroxidation Washing with a chemical containing at least one selected from the group consisting of hydrogen, ozone and the like is preferable because the cleaning effect on the organic matter is enhanced.

  Also, if backwashing with chemicals is continued, the amount of chemicals used increases, so the backwash pump 16 is stopped so that fouling substances can be efficiently dissolved and decomposed with the minimum necessary chemicals. It is preferable to hold the secondary side of the submerged membrane module 4a with a chemical for a predetermined time. The time for holding the secondary side of the submerged membrane module 4a with the chemical is preferably 5 minutes or longer so that the fouling substance adhering to the membrane surface and the membrane pores can be sufficiently dissolved.

  After the chemical cleaning of the immersion type membrane module 4a in the first membrane immersion tank 3a is performed, the rinsing process of the immersion type membrane module 4a in the first film immersion tank 3a is subsequently performed. FIG. 8 is a schematic view showing a state in which the rinsing step (STEP 5) of the immersion membrane module 4a in the first membrane immersion tank 3a is performed in the chemical cleaning method for the immersion membrane modules 4a and 4b of the present invention. When the chemical selection valve 18 is closed, the backwash selection valve 14 and the drain valve 6a are opened, and the backwash pump 16 is operated, the reverse pressure of the submerged membrane module 4a using the membrane filtrate in the filtrate storage tank 13 Perform cleaning. As a result, the chemicals remaining on the secondary side, the membrane surface, and the membrane pores of the submerged membrane module 4a are washed away and discharged out of the system.

  The water used for the back pressure washing in the rinsing step (STEP 5) may be any clarified water, and is not limited to membrane filtered water. The time for the back pressure washing in the rinsing step (STEP 5) is not particularly limited, but it is preferably carried out until the pH of the waste water discharged from the drain valve 6a becomes neutral. The flux of the back pressure washing in the rinsing step (STEP 5) is not particularly limited, but is preferably 0.5 to 2 times the filtration flux. When the back pressure washing flux is less than 0.5 times the filtration flux, it is difficult to sufficiently wash away the chemical remaining on the membrane surface and membrane pores. A higher back-pressure cleaning flux is preferable because the membrane cleaning effect is higher, but if it is too high, membrane filtration water is wasted, damage to submerged membrane module containers, membrane cracks, etc. Since problems that occur will occur, it is set as appropriate within the range that does not.

  After performing the rinse process of the immersion type membrane module 4a in the 1st membrane immersion tank 3a, when performing chemical | medical cleaning of the immersion type membrane module 4b continuously, it is 1st film immersion from the 2nd film immersion tank 3b. A manganese dioxide / activated sludge transfer step (STEP 6) to the tank 3a is performed. FIG. 9 shows a state in which a manganese dioxide / activated sludge transfer step (STEP 6) is performed from the second membrane immersion tank 3b to the first membrane immersion tank 3a in the chemical cleaning method for the immersion type membrane modules 4a and 4b of the present invention. FIG. When the filtration selection valve 2a, the drain valve 6a, the backwash selection valve 14, and the backwash valve 15 are closed, the backwash pump 16 is stopped, and the communication valve 7 is opened, the second membrane is utilized by utilizing the water level difference. Manganese dioxide particles / activated sludge that has settled at the bottom of the immersion tank 3b is transferred to the first membrane immersion tank 3a. During this time, the transfer of manganese dioxide particles / activated sludge is performed while maintaining the water level of the first membrane immersion tank 3a to be lower than the water level of the second film immersion tank 3b. As the water level difference gradually disappears, the flow of water passing through the communication valve 7 falls and the transfer effect of manganese dioxide particles / activated sludge also falls, so the raw water supply valve 1b is opened and the raw water is fed into the second membrane immersion tank 3b. It is preferable to supply the inside because a difference in water level can be secured.

  After the manganese dioxide particles / activated sludge precipitated at the bottom of the second membrane immersion tank 3b are transferred to the first membrane immersion tank 3a, the chemicals of the immersion membrane module 4b in the second membrane immersion tank 3b A cleaning step (STEP 7) is performed. FIG. 10 is a schematic view showing a state in which the chemical cleaning step (STEP 7) of the immersion type membrane module 4b in the second membrane immersion tank 3b is performed in the chemical cleaning method for the immersion type membrane modules 4a and 4b of the present invention. . When the raw water supply valve 1b and the communication valve 7 are closed, the membrane module selection valve 2b, the backwash valve 15 and the chemical selection valve 18 are opened, and the backwash pump 16 is operated, the chemical in the chemical reservoir 17 is immersed in the membrane. Back pressure cleaning of the module 4b is performed. The conditions of the chemical cleaning step (STEP 7) of the immersion type membrane module 4b in the second membrane immersion tank 3b may be the same as the chemical cleaning step (STEP 4) of the immersion type membrane module 4a in the first membrane immersion tank 3a. .

  After the chemical cleaning of the immersion type membrane module 4b in the second membrane immersion tank 3b is performed, the rinsing process of the immersion type membrane module 4b in the second film immersion tank 3b is subsequently performed. FIG. 11 is a schematic view showing a state in which the rinsing step (STEP 8) of the immersion type membrane module 4b in the second membrane immersion tank 3b is performed in the chemical cleaning method for the immersion type membrane modules 4a and 4b of the present invention. When the chemical selection valve 18 is closed, the backwash selection valve 14 and the drain valve 6b are opened, and the backwash pump 16 is operated, the back pressure of the submerged membrane module 4b using the membrane filtrate in the filtrate storage tank 13 is increased. Perform cleaning. As a result, the chemicals remaining on the secondary side, the membrane surface, and the membrane pores of the submerged membrane module 4b are washed away and discharged out of the system. The condition of the rinsing step (STEP 8) of the immersion type membrane module 4b in the second membrane immersion tank 3b may be the same as the chemical cleaning step (STEP 5) of the immersion type membrane module 4a in the first membrane immersion tank 3a.

  After carrying out the rinsing step of the submerged membrane module 4b in the second membrane dip bath 3b, the manganese dioxide / activated sludge transfer step (STEP 9) from the first membrane dip bath 3a to the second membrane dip bath 3b carry out. FIG. 12 shows a state in which the manganese dioxide / activated sludge transfer step (STEP 9) is performed from the first membrane immersion tank 3a to the second membrane immersion tank 3b in the chemical cleaning method for the immersion type membrane modules 4a and 4b of the present invention. FIG. When the drain valve 6b and the backwash valve 15 were closed and the backwash pump 16 was stopped, and the communication valve 7 was opened, it was precipitated at the bottom of the first membrane immersion tank 3a using the water level difference. Manganese dioxide particles / activated sludge is transferred to the second membrane immersion tank 3b. When the water level difference disappears, the communication valve 7 is closed and the process ends.

  Then, raw | natural water is supplied in the film | membrane immersion tanks 3a and 3b through the raw | natural water supply valves 1a and 1b of an open state. Further, the chlorine-based oxidant stored in the oxidant storage tank 10 is supplied into the film immersion tanks 3 a and 3 b by the power of the oxidant pump 9. Further, by operating the blower 8 and feeding air, bubbles are generated from the diffuser tubes 5a and 5b provided below and / or on the side of the submerged membrane modules 4a and 4b, and the membrane module selection valves 2a and 2b. The suction filtration of the submerged membrane modules 4a and 4b is resumed by operating the filtration pump 12 with the filtration valve 11 open.

Example 1
As shown in FIG. 1, the immersion membrane modules 4a and 4b include one immersion membrane module made of polyvinylidene fluoride hollow fiber UF membrane having a molecular weight cut off of 150,000 Da made by Toray Industries, Inc. and having a membrane area of 25 m ^2. , The raw water supply valves 1a and 1b, the membrane module selection valves 2a and 2b and the filtration valve 11 are opened, the blower 8, the oxidant pump 9 and the filtration pump 12 are operated, and the submerged membrane modules 4a and 4b are operated. From below, groundwater with a turbidity of 0.3 degrees, TOC of 1 mg / l, manganese ion concentration of 0.13 mg / l was determined at a membrane filtration flux of 1.5 m ³ / m ² / d while aeration at an air flow rate of 20 L / min. The flow rate was filtered. As the oxidizing agent, sodium hypochlorite was used and injected so that the chlorine concentration in the film immersion tanks 3a and 3b was 0.5 mg / l.

After the immersion type membrane modules 4a and 4b are filtered for 30 minutes, the oxidant pump 9 and the filtration pump 12 are stopped, the raw water supply valves 1a and 1b and the filtration valve 11 are closed, and the backwash selection valve 14 is opened. After confirming that the medicine selection valve 18 is closed, the backwash valve 15 is opened and the backwash pump 16 is operated, so that the back pressure washing with a flux of 1.5 m ³ / m ² / d and the immersion type are performed. Air cleaning at an air flow rate of 60 L / min was simultaneously performed for 1 min from below the membrane modules 4a and 4b. After the blower 8 and the backwash pump 16 were stopped and the backwash valve 15 was closed, the drainage valves 6a and 6b were opened, and the drainage process was performed. The amount of drainage was 52 L, twice the amount of backwash water.

  After the drainage process is completed by closing the drainage valves 6a and 6b, the raw water supply valves 1a and 1b are opened, the oxidant pump 9 is operated, the water supply process is performed, and the submerged membrane modules 4a and 4b are connected. After being immersed in water, the filtration valve 11 was opened, and the filtration pump 12 and the blower 8 were operated to return to the filtration step, and the above steps were repeated. Although the membrane filtration differential pressure at the start of operation was 20 kPa, it reached 65 kPa after 3 months, so chemical cleaning of STEP 1 to 9 was performed.

  In STEP1, the oxidant pump 9 and the filtration pump 12 were stopped from the filtration step, and the raw water supply valves 1a and 1b and the filtration valve 11 were closed. Thereafter, 1 mg-Fe / l of a coagulant ferric chloride is injected into the film immersion tanks 3a and 3b, sodium hydroxide is injected so that the pH in the film immersion tanks 3a and 3b is 8, and the blower 8 Was operated, and aeration and stirring with an air amount of 60 L were performed for 2 min from below the submerged membrane modules 4a and 4b. Thereafter, the blower 8 was stopped and left for 5 minutes.

  In STEP2, the membrane module selection valve 2a is closed, the filtration valve 11 is opened, the filtration pump 12 is operated, and suction filtration is performed with the immersion type membrane module 4b until the water level difference between the membrane immersion tanks 3a and 3b becomes 1 m. did.

  In STEP 3, the membrane module selection valve 2b, the filtration valve 11, and the backwash selection valve 14 were closed, the filtration pump 12 was stopped, and the communication valve 7 was opened. Moreover, the raw water supply valve 1a was opened, the water level of the membrane immersion tank 3a was maintained, and the communication valve 7 was closed when the water level difference became 0.3 m.

In STEP 4, the raw water supply valve 1 a is closed, the membrane module selection valve 2 a, the backwash valve 15, and the chemical selection valve 18 are opened, the backwash pump 16 is operated, and the submerged membrane module is operated with the chemical in the chemical reservoir 17. The back pressure washing of 4a was performed at a flux of 1.5 m ³ / m ² / d for 2 min. As the chemical in the chemical storage tank 17, 1% citric acid was used. Thereafter, the backwash pump 16 was stopped and left for 10 minutes.

In STEP5, the chemical selection valve 18 is closed, the backwash selection valve 14 and the drain valve 6a are opened, the backwash pump 16 is operated, and the submerged membrane module 4a using the membrane filtrate in the filtrate storage tank 13 is used. Was carried out at a flux of 1.5 m ³ / m ² / d for 10 min.

  In STEP 6, the filtration selection valve 2a, the drain valve 6a, the backwash selection valve 14, and the backwash valve 15 were closed, the backwash pump 16 was stopped, and the communication valve 7 was opened. Further, the raw water supply valve 1b was opened to maintain the water level in the membrane immersion tank 3a, and the communication valve 7 was closed when the water level difference became 0.3 m.

In STEP 7, the raw water supply valve 1 b is closed, the membrane module selection valve 2 b, the backwash valve 15, and the chemical selection valve 18 are opened, the backwash pump 16 is operated, and the submerged membrane module is operated with the chemical in the chemical reservoir 17. The back pressure washing of 4a was performed at a flux of 1.5 m ³ / m ² / d for 2 min. As the chemical in the chemical storage tank 17, 1% citric acid was used. Thereafter, the backwash pump 16 was stopped and left for 10 minutes.

In STEP8, the chemical selection valve 18 is closed, the backwash selection valve 14 and the drain valve 6b are opened, the backwash pump 16 is operated, and the submerged membrane module 4b using the membrane filtrate in the filtrate storage tank 13 is used. Was carried out at a flux of 1.5 m ³ / m ² / d for 10 min.

  In STEP 9, the drain valve 6b and the backwash valve 15 were closed, the backwash pump 16 was stopped, and then the communication valve 7 was opened. Thereafter, when the water level difference disappeared, the communication valve 7 was closed and the process was terminated.

Thereafter, the raw water is supplied into the membrane immersion tanks 3 a and 3 b through the raw water supply valves 1 a and 1 b in the open state, and the chlorine-based oxidant stored in the oxidant storage tank 10 is used as the power of the oxidant pump 9. In the membrane immersion tanks 3a and 3b, the blower 8 is further operated to diffuse air at a flow rate of 20 L / min from below the immersion membrane modules 4a and 4b, and the membrane module selection valves 2a, 2b, By operating the filtration pump 12 with the filtration valve 11 open, the constant flow filtration of the membrane filtration flux 1.5 m ³ / m ² / d was resumed.

  As a result, the membrane filtration differential pressure of the submerged membrane modules 4a and 4b recovered from 65 kPa before chemical cleaning to 22 kPa. Further, the manganese concentration of the membrane filtrate in the subsequent filtration step was 0.02 mg / l, which satisfied the tap water quality standard.

(Example 2)
As shown in FIG. 1, the immersion membrane modules 4a and 4b include 200 immersion flat membrane modules made of polyvinylidene fluoride having a nominal pore size of 0.08 μm and a membrane area of 1.4 m ² made by Toray Industries, Inc. , The raw water supply valves 1a, 1b, the membrane module selection valves 2a, 2b, and the filtration valve 11 are opened, the blower 8 is operated, and an air flow rate of 3 m ³ / min from below the submerged membrane modules 4a, 4b. The sewage of 230 mg / l BOD was filtered at a constant flow rate with a membrane filtration flux of 0.6 m ³ / m ² / d with aeration. As filtration power, the filtration pump 12 as in Example 1 was not used, and suction filtration was performed based on the siphon principle using the water level difference between the membrane immersion tanks 3a and 3b and the filtrate storage tank 13. The oxidant was not injected by the oxidant pump 9.

  The filtration process was periodically stopped as in Example 1 and back-pressure washing was not performed, and filtration was continued. In addition, the drain valves 6a and 6b are periodically opened during the filtration process so that the MLSS concentration in the membrane immersion tanks 3a and 3b is constantly maintained at 8,000 to 12,000 mg / l, and some activated sludge is used as a system. Discharged outside.

  Although the membrane filtration differential pressure at the start of operation was 5 kPa, only the submerged membrane module 4a reached 20 kPa, which is the upper limit of the differential pressure after one year.

  In STEP1, the raw water supply valves 1a and 1b and the filtration valve 11 were closed from the filtration step. Thereafter, flocculant MBR sludge modifier MPE-50 (Nalco's cationic flocculant) is injected into the membrane immersing tanks 3a and 3b to a concentration of 2.0% by weight per MLSS unit. The blower 8 was operated, and aeration and stirring with an air amount of 60 L were performed for 2 min from below the submerged membrane modules 4a and 4b. Thereafter, the blower 8 was stopped and left for 10 minutes.

  In STEP 2, the membrane module selection valve 2a was closed, the filtration valve 11 was opened, and suction filtration was performed with the submerged membrane module 4b until the water level difference between the membrane immersion tanks 3a and 3b became 0.6 m.

  In STEP 3, the membrane module selection valve 2b, the filtration valve 11, and the backwash selection valve 14 are closed, and the communication valve 7 is opened. Moreover, the raw water supply valve 1a was opened, the water level of the membrane immersion tank 3a was maintained, and the communication valve 7 was closed when the water level difference became 0.3 m.

In STEP 4, the raw water supply valve 1 a is closed, the membrane module selection valve 2 a, the backwash valve 15, and the chemical selection valve 18 are opened, the backwash pump 16 is operated, and the submerged membrane module is operated with the chemical in the chemical reservoir 17. The back pressure washing of 4a was performed at a flux of 0.3 m ³ / m ² / d for 10 min. Sodium hypochlorite 5,000 mg / l was used as the chemical in the chemical reservoir 17. Thereafter, the backwash pump 16 was stopped and left for 30 minutes.

In STEP5, the chemical selection valve 18 is closed, the backwash selection valve 14 and the drain valve 6a are opened, the backwash pump 16 is operated, and the submerged membrane module 4a using the membrane filtrate in the filtrate storage tank 13 is used. Was carried out at a flux of 0.3 m ³ / m ² / d for 10 min.

  Then, after closing the drain valve 6a and the backwash valve 15 and stopping the backwash pump 16, the blower 8 is operated and diffused, and the activated sludge in the membrane immersion tank 3b is stirred so as to have a uniform concentration. The communication valve 7 was opened. When the water level difference disappeared, the communication valve 7 was closed.

Further, the raw water is supplied into the membrane immersion tanks 3a and 3b through the raw water supply valves 1a and 1b in the open state, and the blower 8 is operated, and the air flow rate is 3 m ³ / from below the immersion type membrane modules 4a and 4b. A constant flow rate filtration with a membrane filtration flux of 0.6 m ³ / m ² / d was resumed by aeration of min and opening the membrane module selection valves 2 a and 2 b and the filtration valve 11.

  As a result, the membrane filtration differential pressure of the submerged membrane module 4a recovered from 20 kPa before chemical cleaning to 5 kPa. In addition, the BOD of the membrane filtrate in the subsequent filtration step was 5 mg / l, which met the sewer water quality standard.

(Comparative Example 1)
Except for not carrying out STEP 1 in chemical cleaning, it was exactly the same as Example 1.

  As a result, the membrane filtration differential pressure of the submerged membrane module 4a recovered from 65 kPa before chemical cleaning to 22 kPa, but the membrane filtration differential pressure of the submerged membrane module 4b recovered only from 65 kPa before chemical cleaning to about 48 kPa. It was. The manganese concentration of the membrane filtrate in the subsequent filtration step was 0.04 mg / l, which satisfied the tap water quality standard.

(Comparative Example 2)
In chemical cleaning, the communication valve was always closed, and STEP 1, STEP 2, STEP 3, STEP 6, and STEP 9 were not carried out.

  As a result, although the membrane filtration differential pressure of the submerged membrane modules 4a and 4b recovered from 65 kPa before chemical cleaning to 35 kPa, the manganese concentration of membrane filtration water in the subsequent filtration step was 0.09 mg / l, which is the standard for tap water quality Could not meet.

(Comparative Example 3)
Except that STEP 1 was not performed in chemical cleaning, it was exactly the same as Example 2.

  As a result, the membrane filtration differential pressure of the submerged membrane module 4a recovered from 20 kPa before chemical cleaning to 6 kPa, but the membrane filtration differential pressure of the submerged membrane module 4b increased from 15 kPa before chemical cleaning to 22 kPa. I had to wash the chemicals immediately. The BOD of membrane filtrate in the subsequent filtration step was 5 mg / l, which met the sewer water quality standard.

(Comparative Example 4)
In the chemical cleaning, the communication valve was always closed and STEP1, STEP2, and STEP3 were not performed, and the procedure was exactly the same as in Example 2.

As a result, although the membrane filtration differential pressure of the submerged membrane module 4a recovered from 20 kPa before chemical cleaning to 6 kPa, the BOD of membrane filtration water in the subsequent filtration step was 120 mg / l, which cannot meet the sewer water quality standard. There wasn't.

1a, 1b: Raw water supply valve 2a, 2b: Membrane module selection valve 3a, 3b: Membrane immersion tank 4a, 4b: Immersion membrane module 5a, 5b: Air diffuser 6a, 6b: Drain valve 7: Communication valve 8: Blower 9 : Oxidant pump 10: Oxidant reservoir 11: Filtration valve 12: Filtration pump 13: Filtrated water reservoir 14: Backwash selection valve 15: Backwash valve 16: Backwash pump 17: Chemical reservoir 18: Chemical selection valve

Claims (7)

  Water filtered through a plurality of submerged membrane modules while adding a chlorinated oxidant to raw water containing 0.05 mg / L or more manganese ions and diffusing from below and / or from the side of the submerged membrane module In the treatment method, the submerged membrane module in a plurality of submerged baths is sequentially contacted with the chemical by a chemical cleaning method, wherein raw water and a chlorine-based oxidizing agent are introduced into the membrane submerged bath and diffused. , And after precipitating manganese dioxide in the membrane immersion tank, the water in the second membrane immersion tank is filtered through an immersion membrane module to reduce the water level in the second membrane immersion tank, Further, while maintaining the water level in the second film immersion tank to be lower than the water level in the first film immersion tank, the manganese dioxide in the lower part of the first film immersion tank is passed through the communicating part at the lower part of the film immersion tank. 2 is transferred into the film immersion tank, and then the first film Chemical cleaning method of the submerged membrane module contacting the submerged membrane module in 漬槽 medicals.   Water treatment in which raw water is supplied into a membrane immersion tank in which an immersion membrane module and activated sludge are immersed, and filtered through a plurality of immersion membrane modules while being diffused from below and / or from the side of the immersion membrane module In the method, the submerged membrane module in the plurality of membrane immersing tanks is sequentially contacted with the chemical by the chemical cleaning method of the submerged membrane module, and the introduction and diffusion of the raw water into the membrane immersing tank is stopped and the membrane is stopped. After precipitating the activated sludge in the immersion tank, the water in the second membrane immersion tank is filtered through an immersion membrane module to lower the water level in the second membrane immersion tank, and the second membrane immersion While maintaining the water level in the tank to be lower than the water level in the first membrane immersion tank, the activated sludge in the lower part of the first film immersion tank is passed through the communicating part in the lower part of the film immersion tank and in the second film immersion tank. And then the immersion membrane module in the first membrane immersion tank Chemical cleaning method of the immersion type membrane module of contacting.   After the immersion membrane module in the first membrane immersion tank is brought into contact with the chemical, the water level in the first membrane immersion tank is further lowered, and the water level in the first membrane immersion tank is further reduced to the second membrane. The manganese dioxide or activated sludge in the lower part of the second membrane soaking tank is transferred to the first membrane soaking tank through the communicating part at the lower part of the membrane soaking tank while maintaining the water level lower than the water level in the soaking tank. The chemical | medical agent washing | cleaning method of the immersion type membrane module of Claim 1 or 2 which makes a chemical | medical agent contact the immersion type membrane module in 2 membrane immersion tanks.   The chemical cleaning method for a submerged membrane module according to any one of claims 1 to 3, wherein the chemical includes at least one selected from the group consisting of citric acid, oxalic acid, sulfite ions, hydrogen sulfite ions, and thiosulfate ions.   The chemical cleaning method for an immersion type membrane module according to any one of claims 1 to 4, wherein a flocculant and / or a pH adjusting agent is added to precipitate manganese dioxide or activated sludge in the membrane immersion tank.   The chemical cleaning method for a submerged membrane module according to any one of claims 1 to 5, wherein the submerged membrane module is brought into contact with the chemical by reverse pressure cleaning with the chemical.   The method for cleaning a submerged membrane module according to claim 6, wherein the submerged membrane module is left to stand for a certain period of time after backwashing with a chemical, and further backwashed with clear water.

Images