JP5245216B2 - Hollow fiber membrane water treatment method and water treatment apparatus - Google Patents

Description

  The present invention relates to a water treatment method and a water treatment apparatus using a hollow fiber membrane module.

  In a water treatment apparatus using a membrane, suspended substances, organic substances, etc. in the water to be treated are gradually deposited on the surface of the membrane over a long period of operation, and membrane fouling occurs. When membrane fouling occurs, an increase in membrane pressure, a decrease in filtration flux, and the like are caused, water purification efficiency is lowered, and the overall operation efficiency of the water treatment device is lowered. Therefore, in the operation cycle of the water treatment apparatus, the membrane is physically washed after the filtration process for a predetermined time.

  The physical cleaning method for the hollow fiber membrane module includes backwashing by passing membrane filtrate from the secondary side of the membrane to the primary side, flushing by passing raw water etc. to the primary side of the membrane and washing, and raw water on the primary side of the membrane Flushing with water and air mixed water to wash, a method of injecting air to the primary side of the hollow fiber to wash the water remaining in the hollow fiber membrane, a sponge ball on the primary side of the hollow fiber membrane during backwashing, etc. Sponge ball method to add, air bubbling method to contain fine bubbles in the cleaning water on the primary side of the membrane, ultrasonic method to attach ultrasonic vibrator to pressure vessel etc. and wash using the vibration etc. are known Yes.

  Patent Document 1 below discloses a membrane module cleaning method characterized by performing an operation of injecting a gas of 0.3 MPa or less from at least one open end of a perforated hollow tube.

Further, in Patent Document 2 below, backwash water is injected with pressure or no pressure from the permeate outlet side of the internal pressure type hollow fiber module, and air is blown from one of the ports of the internal pressure type hollow fiber module. A method for cleaning a hollow fiber membrane module is disclosed in which solid matter is peeled off from the inner wall and the peeled solid matter is discharged from the other port.
JP 2002-79061 A Japanese Patent Laid-Open No. 7-236818

  Although the film cleaning method using air is relatively effective, it has problems such as causing damage to the film.

  Further, even with the cleaning methods disclosed in Patent Documents 1 and 2 above, deposits on the film surface could not be completely removed, and it was difficult to prevent a long-term increase in the film differential pressure. .

  Accordingly, an object of the present invention is to provide a water treatment method and a water treatment apparatus for a hollow fiber membrane that can prevent a long-term increase in membrane differential pressure and hardly cause membrane breakage.

In order to solve the above-mentioned problems, the water treatment method of the present invention includes a membrane filtration treatment step for removing the contaminants in the treated water by passing the treated water through the hollow fiber membrane module, and a washing treatment of the hollow fiber membrane module. In the water treatment method that repeats the steps, as the washing treatment step, backwashing is performed by flowing water from the secondary side that is the outflow side of the filtrate of the hollow fiber membrane module to the primary side that is the inflow side of the water to be treated. After the step (A) and the backwashing step (A), the primary side and the secondary side of the hollow fiber membrane module are pressurized at a predetermined air pressure while staying on the primary side and the secondary side of the hollow fiber membrane module. The retained water extraction step (B) for draining the retained water from the primary side of the hollow fiber membrane module, and the retained water extraction step (B), after supplying water to the primary side of the hollow fiber membrane module , Stay in hollow fiber membrane module That after the physical cleaning including the air vent step (C) for removing air Tsu row, from the secondary side chemical cleaning liquid injection step of injecting chemicals washing liquid to the primary side (D) of the hollow fiber membrane module, this A chemical cleaning liquid retention step (E) for retaining a chemical cleaning liquid in the hollow fiber membrane module, and after supplying cleaning water from the secondary side of the hollow fiber membrane module, the secondary side of the hollow fiber membrane module is set to 0.01 to Pressurize with a pressure of 0.05 MPa to discharge the water to the primary side of the hollow fiber membrane module, then pressurize the primary side of the hollow fiber membrane module with a pressure of 0.01 to 0.05 MPa to supply water. It is characterized by performing chemical cleaning including a rinsing step (F) of drawing out from the primary side of the hollow fiber membrane module and washing the hollow fiber membrane module with water .

According to the water treatment method of the present invention described above, the retained water in the hollow fiber membrane module is drained from the primary side of the hollow fiber membrane module while pressurizing the primary side and secondary side of the hollow fiber membrane module with a predetermined air pressure. Since the stagnant water extraction step is performed, the stagnant water is withdrawn at a high speed, and contaminants accumulated on the film surface or inside can be efficiently peeled off by the shearing force at that time. Further, since the primary side and the secondary side of the film are pressurized simultaneously, the load applied to the film is offset and reduced, and film deformation and film breakage are unlikely to occur.
Moreover, after finishing the physical cleaning including the backwashing step (A), the stagnant water drawing step (B), and the air venting step (C), the chemical cleaning liquid is applied from the secondary side to the primary side of the hollow fiber membrane module. A chemical cleaning liquid injection step (D) for injecting, a chemical cleaning liquid retention step (E) for retaining the chemical cleaning liquid in the hollow fiber membrane module, and water injected from the secondary side to the primary side of the hollow fiber membrane module Since the chemical cleaning including the rinsing step (F) for washing the membrane module with water is performed, it is possible to remove and remove contaminants that are difficult to remove only by a physical backwashing action, and to effectively prevent clogging of the membrane.
In the rinsing step (F), after supplying cleaning water from the secondary side of the hollow fiber membrane module, the secondary side of the hollow fiber membrane module is pressurized with an air pressure of 0.01 to 0.05 MPa to supply this water. Since it is discharged to the primary side of the hollow fiber membrane module, and then the primary side of the hollow fiber membrane module is pressurized with an air pressure of 0.01 to 0.05 MPa to draw water from the primary side of the hollow fiber membrane module, the membrane The chemical cleaning liquid staying in the hollow fiber membrane module can be discharged out of the system without damaging.

  In the water treatment method of the present invention, after the backwashing step (A) is performed, water containing bubbles is supplied to the primary side of the hollow fiber membrane module, and then the retained water drawing step (B). It is preferable to carry out. According to this aspect, the boundary surface where water and air come into contact with each other during the step of withdrawing the accumulated water (B), and a large shearing force due to the difference in surface tension between water and air can be obtained. improves.

  In the water treatment method of the present invention, after the air venting step (C) is performed, the stay water draining step (B) and the air venting step (C) are alternately repeated one more times. Preferably it is done. According to this aspect, the accumulated water is effectively removed from the membrane surface or inside by repeating the stagnant water extraction step (B) and the air extraction step (C) alternately and more once more. Can be removed.

  In the water treatment method of the present invention, the chemical cleaning liquid injection step (D) is performed until the concentration of the chemical cleaning liquid on the primary side of the hollow fiber membrane module reaches 80% or more of the concentration of the supplied chemical cleaning liquid. Is preferred.

  In the water treatment method of the present invention, in the chemical cleaning liquid retention step (E), after stopping the injection of the chemical cleaning liquid into the hollow fiber membrane module, the chemical cleaning liquid is added to the hollow fiber membrane module in 10 to 10 minutes. It is preferable to retain for 120 minutes.

  According to each aspect described above, contaminants accumulated on the surface or inside of the membrane can be effectively peeled and removed, and the filtration capability of the membrane can be restored to an almost initial state.

On the other hand, the water treatment apparatus of the present invention comprises a hollow fiber membrane module for obtaining filtered water by removing pollutants in the treated water, and a treated water for storing the treated water to be supplied to the hollow fiber membrane module. Water to be treated for supplying the water to be treated from the water to be treated to be supplied to the hollow fiber membrane module, provided in a water supply tank and a pipe on the primary side which is the inflow side of the water to be treated of the hollow fiber membrane module. A backflushing water supply pump for supplying water from the secondary side of the hollow fiber membrane module to the primary side, provided on a secondary pipe that is the outflow side of the filtrate of the hollow fiber membrane module; a compressor for supplying compressed air to the piping of the primary piping and the secondary side of the hollow fiber membrane module, possess a valve body provided in each of the connection pipe, and the water to be treated supply pump Connected to the hollow fiber membrane module That the pipe is branched from the middle, and said linked via the treated water supply tank and the valve body.

According to the water treatment device of the present invention, the primary side and the secondary side of the hollow fiber membrane module are pressurized with a predetermined air pressure, and the retained water in the hollow fiber membrane module is drained from the primary side of the hollow fiber membrane module. Since the accumulated water can be drawn out, the contaminants accumulated on the film surface or inside can be efficiently peeled off by the shearing force generated at that time. In addition, since the primary side and the secondary side of the hollow fiber membrane module are simultaneously pressurized, the pressure applied to the membrane surface can be almost offset, and membrane deformation and membrane breakage are unlikely to occur. And since the pipe connecting the treated water supply pump and the hollow fiber membrane module branches from the middle and is connected via the treated water supply tank and the valve body, the supply and stop of the raw water are promptly performed. At the same time, it is possible to prevent pressure fluctuations when starting up the raw water supply pump.

  Further, the water treatment apparatus of the present invention is a filtered water in which a part of the secondary pipe of the hollow fiber membrane module is obtained from the secondary side of the hollow fiber membrane module via the backwash water supply pump. It is preferable that it is connected with the filtrate storage tank which stores water, and it is comprised so that a part of filtrate can be supplied from the secondary side of a hollow fiber membrane module to a primary side. According to this aspect, it is not necessary to provide a dedicated backwash water supply system, and the apparatus can be simply configured.

  Moreover, it is preferable that the water treatment apparatus of this invention has a chemical cleaning liquid injection | pouring means for supplying a chemical cleaning liquid from the secondary side of the said hollow fiber membrane module. According to this aspect, the contaminant accumulated on the surface or inside of the membrane can be dissolved and decomposed by the chemical, so that the filtration ability of the membrane can be restored to almost the initial state.

  According to the present invention, while the primary side and the secondary side of the hollow fiber membrane module are pressurized with a predetermined air pressure, the retained water in the hollow fiber membrane module is drained from the primary side of the hollow fiber membrane module to Since the water is pulled out, the accumulated water is pulled out at a high speed, and the contaminants accumulated on the surface or inside of the membrane can be efficiently peeled off by the shearing force generated at that time. Further, since the primary side and the secondary side of the hollow fiber membrane module are simultaneously pressurized, the pressure applied to the membrane surface can be almost canceled out, and membrane breakage hardly occurs.

  As the water to be treated in the present invention, any water containing insoluble organic substances can be used. Specifically, river water, lake water, sewage, factory waste water, and the like are preferable.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. The schematic block diagram of 1st Embodiment of the water treatment apparatus used for the water treatment method of this invention is shown by FIG.

  First, the water treatment device of FIG. 1 will be described. This water treatment device captures raw water supply tank 10 for storing water to be treated (hereinafter referred to as raw water), and captures pollutants in the raw water. Thus, the hollow fiber membrane module 30 that obtains filtrate and the filtrate storage tank 13 that stores filtrate is mainly configured.

  The raw water supply tank 10 is connected to the primary side 30a which is the inflow side of the raw water of the hollow fiber membrane module 30 via the pipe 1 in which the raw water supply pump 11 and the first raw water supply valve V1 are arranged. . Moreover, the middle of the pipe 1 connecting the first raw water supply valve V1 and the hollow fiber membrane module 30 is bifurcated, and one of the pipes is connected to the pipe 5a where the first discharge valve V5a is arranged. The other is connected to the compressor 14 via a pipe 7a in which a first compressor inlet valve V6 and a first check valve 40 are arranged.

  Any membrane can be used for the hollow fiber membrane module 30 as long as it is a general filtration membrane, and examples include a microfiltration membrane (MF membrane), an ultrafiltration membrane (UF membrane), and a nanofiltration membrane (NF membrane). . Examples of the form of the hollow fiber membrane module 30 include, but are not limited to, an internal pressure type hollow fiber membrane, an external pressure type hollow fiber membrane, a vertical hollow fiber membrane module, and a horizontal hollow fiber membrane module.

  A part of the pipe 1 connecting the raw water supply pump 11 and the first raw water supply valve V1 is branched, and the hollow fiber membrane module 30 is connected via the pipe 2 provided with the second raw water supply valve V2. It is connected to the primary side 30a. Moreover, the middle of the pipe 2 connecting the second raw water supply valve V2 and the hollow fiber membrane module 30 is bifurcated, and one of the pipes is connected to the pipe 5b where the second discharge valve V5b is arranged. The other is connected to the pipe 7c through the pipe 7b in which the second check valve 41 is arranged. The pipe 7c is connected to the pipe 7a via the second compressor inlet valve V7.

  The secondary side 30b which is the filtrate water outflow side of the hollow fiber membrane module 30 is connected to the filtrate storage tank 13 via a pipe 6 in which a membrane outlet valve V3 and a filtrate storage tank inlet valve V4 are arranged. It is connected. The middle of the pipe 3 connecting the hollow fiber membrane module 30 and the membrane outlet valve V3 is bifurcated. One is connected to the pipe 6 where the air vent valve V8 is arranged, and the other is the third. The first compressor inlet valve V6 and the first check valve 40 are connected to a pipe 7a through a pipe 7c on which the check valve 42 is disposed.

  A pipe 4 provided with a backwash water supply pump 12 extends from the lower part of the filtrate storage tank 13, and is connected to a pipe 6 that connects the membrane outlet valve V3 and the filtrate storage tank inlet valve V4. ing.

  Next, the water treatment method of the present invention using the water treatment apparatus will be described with reference to FIGS. In the figure, the open valve and the operating pump and compressor are shown in white, and the closed valve and the stopped pump and compressor are shown in black. Moreover, the broken line part in a figure means distribution | circulation of raw | natural water, filtered water, and air, and a continuous line part means the stop of raw | natural water, filtered water, and air.

  First, a flocculant and / or a pH adjuster are stirred into the raw water that has flowed into the raw water supply tank 10 as necessary, and processing such as aggregation of solids in the raw water and pH adjustment are performed. Thereafter, as shown in FIG. 2, the first raw water supply valve V1, the second raw water supply valve V2, the membrane outlet valve V3, and the filtrate storage tank inlet valve V4 are opened, and the other valves are closed. Then, the raw water supply pump 11 is operated and water is passed through the primary side 30a of the hollow fiber membrane module 30 to perform filtration, and a membrane filtration treatment step is performed to obtain filtrate. The filtrate passes through the membrane outlet valve V3 and the filtrate storage tank inlet valve V4 and is supplied to the filtrate storage tank 13. After the filtrate filtered by the hollow fiber membrane module 30 is stored in the filtrate storage tank 13, most of the filtrate is extracted from the pipe 50 and passed to the next process, and the stored filtrate is stored. A part is used as backwash water for cleaning the hollow fiber membrane module 30.

  After performing the membrane filtration process for a predetermined time, the operation of the raw water supply pump 11 is stopped, the membrane outlet valve V3 and the first discharge valve V5a are opened, and the other valves are closed as shown in FIG. Then, the backwash water supply pump 12 is operated to pass the filtrate stored in the filtrate storage tank 13 from the secondary side 30b of the hollow fiber membrane module 30 to the primary side 30a, and to the primary side 30a. The backwashing process (A-1) which drains the backwashed wastewater drained out of the system from the pipe 5a is performed.

  After performing the backwashing step (A-1) for a predetermined time, as shown in FIG. 4, the second discharge valve V5b is opened, the first drain valve V5a is closed, and the membrane outlet valve V3 is opened. The filtered water stored in the filtrate storage tank 13 was passed from the secondary side 30b of the hollow fiber membrane module 30 to the primary side 30a by the backwash water supply pump 12, and then passed to the primary side 30a. A backwash process (A-2) for draining the backwash drainage from the pipe 5b to the outside of the system is performed.

  The time required for the backwashing step (A) can be appropriately set depending on the quality of the raw water such as raw water turbidity, and from the viewpoint of saving the produced filtrate, a short time with a low flux (low pressure) is good. The backwash flux is preferably 2 to 8 m / d, and 10 to 60 seconds in total. Only one of the backwashing step (A-1) and backwashing step (A-2) may be performed, but the backwashing step (A-1) and the backwashing step (A-2) Can be used to remove large solid matter deposited on the primary side 30a of the hollow fiber membrane module 30, so that damage to the hollow fiber membrane can be prevented in the retained water extraction step (B) described below (hereinafter, The backwashing step (A-1) and the backwashing step (A-2) are collectively referred to as the backwashing step (A)).

  And in this invention, after performing the said backwashing process (A), it retains in the hollow fiber membrane module 30, pressurizing the primary side 30a and the secondary side 30b of the hollow fiber membrane module 30 with predetermined air pressure. A stagnant water extraction step (B) for draining water from the primary side 30 a of the hollow fiber membrane module 30 is performed.

  That is, as shown in FIG. 5, the first discharge valve V5a and the second compressor inlet valve V7 are opened, the other valves are closed, the compressor 14 is operated, and the hollow fiber membrane is obtained by the backwashing step (A). A stagnant water extraction step (B) for draining the stagnant water in the module 30, that is, backwash water and / or backwash wastewater, is performed.

  Since the compressed air flows from the pipe 7b to the primary side 30a of the hollow fiber membrane module 30 by the operation of the compressor 14, the accumulated water in the hollow fiber membrane module 30 is drained out of the system from the pipe 5a. . At this time, since compressed air flows into the primary side 30a and at the same time compressed air also flows into the secondary side 30b from the pipe 7c, the primary side 30a and the secondary side 30b of the hollow fiber membrane module 30 are pressurized simultaneously. Thus, it is possible to draw out the accumulated water in the hollow fiber membrane module 30 while preventing the washing water from flowing from the primary side 30a to the secondary side 30b and the high-pressure load on the hollow fiber membrane.

  The air pressure for pressurizing the primary side 30a and the secondary side 30b of the hollow fiber membrane module 30 is preferably set to be almost the same pressure from the viewpoint of suppressing the load on the membrane. The air pressure is preferably 0.05 to 3 MPa, and more preferably 0.1 to 1 MPa. If the pressure is less than 0.05 MPa, a sufficient cleaning effect cannot be obtained, and if it exceeds 3 MPa, film breakage may occur.

  For example, the primary side 30a and the secondary side 30b of the hollow fiber membrane module 30 are each pressurized at 0.2 MPa, whereby the accumulated water is drawn out from the primary side 30a of the hollow fiber membrane module 30 at a linear velocity of 2 to 3 m / sec. be able to.

  The time required for the retained water extraction step (B), that is, the opening time of the second compressor inlet valve V7 may be appropriately adjusted according to the length of the hollow fiber membrane, and is not particularly limited. For example, when the length of the hollow fiber membrane is about 1 m, 0.5 to 3 seconds is preferable. If it is less than 0.5 seconds, the staying water may not be completely discharged, and if it exceeds 3 seconds, the cleaning effect is not improved, and only the air consumption increases.

  In the present invention, the first raw water supply valve V1 and the second discharge as shown in FIG. 6 are performed before performing the above-described staying water extraction step (B), that is, immediately after the backwashing step (A). The valve V5b and the first compressor inlet valve V6 are opened, and the raw water supply pump 11 and the compressor 14 are operated to supply water containing air to the primary side 30a of the hollow fiber membrane module 30. An air flushing step of washing the membrane surface of the side 30a with air-containing water may be performed.

  At this time, the water supplied to the primary side 30a of the hollow fiber membrane module 30 includes filtered water or raw water. Moreover, when using raw | natural water, it is preferable to install the filter of about 100 mesh in the raw | natural water supply tank 10, and to remove big solid content. Further, the supply amount of air from the compressor 14 is preferably 1.2 to 2 times the supply amount of water. The water supply rate is preferably 0.3 to 1.0 m / sec.

  Thus, air can be made to remain in the staying water in the hollow fiber membrane module 30 by performing the air flushing step before the staying water extraction step (B). For this reason, in the staying water extraction step (B), the boundary surface where water and air come into contact increases, and a large shearing force due to the difference in surface tension between water and air is obtained, so that the membrane cleaning effect is improved.

  In addition, you may perform the said air flushing process, after finishing a stagnant water extraction process (B), ie, just before an air extraction process (C).

  Then, after the above-mentioned retained water extraction step (B) is completed, as shown in FIG. 7, the first raw water supply valve V1 and the second discharge valve V5b are opened, the other automatic valves are closed, and the raw water supply pump 11 is operated, water is passed through the primary side 30a of the hollow fiber membrane module 30, and a so-called air venting process (C) is performed for draining from the pipe 5b.

  The time for performing the air venting step (C) is preferably 10 seconds to 60 seconds, and more preferably 10 to 30 seconds. In the air venting step (C), examples of water supplied to the hollow fiber membrane module 30 include filtered water and raw water. Moreover, when using raw | natural water, it is preferable to install the filter of about 100 mesh in the raw | natural water supply tank 10, and to remove big solid content. In the case where the state of contamination of the film is severe and the cleaning is insufficient, it is preferable to repeat the cleaning cycle again after finishing the air venting step (C). At this time, even if the backwashing step (A) is repeated, there may be a case where a remarkable cleaning effect may not be obtained. Therefore, the backwashing step (A) is not carried out, the stagnant water drawing step (B), and the air removal. It is preferable to repeat the step (C) alternately one or more times.

  Further, the air flushing step may be further performed after the staying water extraction step (B), that is, immediately before the air extraction step (C). By further performing the air flushing step, contaminants attached to the film can be more effectively removed.

  According to the water treatment method of the present invention, after the backwashing step (A) is finished, the retained water in the hollow fiber membrane module 30 is drawn out while simultaneously pressurizing the primary side 30a and the secondary side 30b. Is pulled out at a high speed, and contaminants accumulated on the surface or inside of the film can be efficiently peeled off by the shearing force at that time. Further, since the primary side 30a and the secondary side 30b are pressurized simultaneously, the washing water is prevented from flowing out from the primary side 30a to the secondary side 30b, and the load applied to the membrane is offset and reduced. And film breakage hardly occurs.

  FIG. 8 shows a second embodiment of a water treatment apparatus that can be used in the water treatment method of the present invention. Note that parts that are substantially the same as those of the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The main change from the first embodiment shown in FIG. 1 is that <1> the middle of the pipe 1 connecting the raw water supply pump 11 and the first raw water supply valve V1 is bifurcated into the raw water inlet. It is the point connected to the raw | natural water supply tank 10 through the piping 9 which has arrange | positioned valve | bulb V9.

  Next, a water treatment method using this water treatment apparatus will be described. The basic steps are the same as in the above embodiment, and different points will be described in detail.

  In this embodiment, the backwashing step (A), the stagnant water extraction step (B), and the air extraction step (C) are the same as those in the first embodiment, and thus detailed description thereof is omitted.

  After the backwashing step (A) is finished, the raw water inlet valve V9 is opened, the raw water supply pump 11 is operated, and the raw water is circulated through the pipe 9 during the staying water extraction step (B).

  After the retained water extraction step (B) is finished, the first raw water supply valve V1 and the second discharge valve V5b are opened, the other automatic valves are closed, and water is supplied to the primary side 30a of the hollow fiber membrane module 30. A so-called air venting step (C) is performed in which water is passed and drained from the pipe 5b.

  Thus, according to this embodiment, it is not necessary to stop the operation of the raw water supply pump 11 when switching between the backwashing step (A) and the retained water extraction step (B). It is possible to reduce the work at the start of operation and the initial starting force. The opening and closing of the first raw water supply valve V1 and the second raw water supply valve V2 makes it possible to quickly supply and stop the raw water, shorten the time required for the membrane cleaning process, Processing can be carried out efficiently.

  FIG. 9 shows a third embodiment of a water treatment apparatus that can be used in the water treatment method of the present invention. Note that parts that are substantially the same as those of the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.

Changes from the processing apparatus according to the embodiment are as follows.
<1> The pipe 3 that connects the secondary side 30b of the hollow fiber membrane module 30 and the membrane outlet valve V3 is bifurcated, and the pipe 51 is provided with the chemical tank inlet valve V10 and the chemical solution injection pump 15. The point connected to the chemical tank 16
<2> The pipe 52 connecting the primary side 30a of the hollow fiber membrane module 30 and the first raw water supply valve V1 is bifurcated, and the pipe 52 provided with the reduction neutralization tank inlet valve V11 is being reduced. The point connected to the Japanese tank 17
<3> The chemical solution drain valve V12 is arranged in the middle of the pipe 7b connecting the second check valve 41 and the pipe 7c.

  Next, a water treatment method using this water treatment apparatus will be described. The basic steps are the same as in the above embodiment, and different points will be described in detail.

  In this embodiment, the backwashing step (A), the stagnant water extraction step (B), and the air extraction step (C) are the same as those in the first embodiment, and the description thereof is omitted. However, in each of the above steps, the chemical solution drain valve V12 is always open, and the chemical tank inlet valve V10 and the reduction neutralization tank inlet valve V11 are always closed.

  After completing the air venting step (C), the chemical tank inlet valve V10 and the reduction neutralization tank inlet valve V11 are opened, the other valves are closed, the chemical solution injection pump 15 is operated, and the hollow fiber membrane module 30 A chemical cleaning liquid injection step (D) for supplying chemical to the secondary side 30b is performed.

  Examples of chemicals to be injected into the hollow fiber membrane module 30 include inorganic acids such as hypochlorous acid, nitric acid, hydrochloric acid and sulfuric acid, organic acids such as citric acid and oxalic acid, oxidizing agents such as sodium hypochlorite, hydrogen peroxide And a reducing agent such as sodium hydroxide and an alkali agent such as sodium hydroxide can be used alone or in combination. Of these, sulfuric acid and sodium hypochlorite are preferred because they are generally used in water purification plants. When two or more kinds of chemicals are used in combination, for example, a combination of using sodium hypochlorite once a day and using sulfuric acid once every seven days may be mentioned.

  The concentration of the chemical to be injected is preferably 1 to 500 mg / l, more preferably 10 to 100 mg / l for sodium hypochlorite. When it is less than 1 mg / l, the cleaning effect is deteriorated, and when it exceeds 500 mg / l, the film is deteriorated.

  The chemical cleaning liquid injection step (D) is preferably performed until the concentration of the chemical cleaning liquid flowing into the primary side 30a reaches 80% or more of the concentration of the set chemical cleaning liquid.

  After the concentration of the chemical flowing into the primary side 30a exceeds a predetermined concentration, the chemical injection pump 15 is stopped and all the valves are closed, so that the film clogging substance and the blocked solid content due to the chemical are dissolved or decomposed. A chemical cleaning liquid retention step (E) is performed.

  The retention time of the chemical cleaning liquid in the chemical cleaning liquid retention step (E) is preferably 10 to 120 minutes, and more preferably 10 to 20 minutes. If the residence time of the chemical cleaning liquid is less than 10 minutes, there may be a case where the film clogging substance or the clogging solid content cannot be completely removed. Moreover, even if it is 120 minutes or more, since an effect does not improve so much, it exists in the tendency for water treatment efficiency to fall.

  After the chemical cleaning liquid retention step (E) is completed, a rinsing step (F) is performed. The rinsing step (F) preferably includes a chemical cleaning solution dilution step (F-1) for reducing the concentration of the chemical staying in the hollow fiber membrane module 30 and a chemical cleaning solution discharge step (F-2). According to this, the usage-amount of the water which a rinse process (F) requires can be reduced, and it can reduce to about 1 / 2-1 / 3 compared with the past.

  First, the membrane outlet valve V3 and the reduction neutralization tank inlet valve V11 are opened, the other valves are closed, the backwash water supply pump 12 is operated, and the chemical washing liquid staying in the hollow fiber membrane module 30 is retained. A chemical cleaning liquid dilution step (F-1) is performed to dilute the liquid. The chemical cleaning liquid discharged from the primary side 30a is sent to the reduction neutralization tank 17, where it is neutralized.

  And after finishing the said chemical cleaning liquid dilution process (F-1), the 2nd compressor inlet valve V7 and the reduction | restoration neutralization tank inlet valve V11 are opened, another valve is closed, the compressor 14 is operated, A compressed air pressure of 0.01 to 0.05 MPa is supplied to the secondary side 30b of the membrane, and the chemical cleaning liquid staying on the secondary side 30b is drained to the primary side 30a. Thereafter, the second compressor inlet valve V7, the reduction neutralization tank inlet valve V11, and the chemical solution drain valve V12 are opened, the other valves are closed, the compressor 14 is operated, and 0.01 to 0.05 MPa. The compressed air pressure is supplied to the primary side 30 a and the chemical cleaning liquid staying on the primary side 30 a is transferred to the reduction neutralization tank 17.

  The reason why the compressed air is separately supplied to the primary side 30a and the secondary side 30b is that the low-pressure air hardly passes through the hollow fiber membrane. Therefore, when the compressed air is pressurized only on the secondary side 30b, the hollow fiber on the primary side This is because the diluted chemical cleaning liquid in the film is hardly discharged. In addition, when the air pressure of the compressed air supplied to the primary side 30a and the secondary side 30b exceeds 0.05 MPa, there is a possibility that the film breaks.

  Thus, according to this embodiment, by performing the chemical cleaning step, the solid content that could not be peeled only by the back washing step (A) is peeled and removed, so that the filtration ability of the membrane is restored to almost the initial state. be able to.

  Hereinafter, the present invention will be described in more detail by way of examples. In addition, this invention is not limited to a following example.

[Test Example 1]
( Reference Example 1)
Water treatment was performed using the water treatment apparatus shown in FIG. The hollow fiber membrane module 30 used a hollow fiber hole diameter of 0.03 μm, a hollow fiber diameter of 0.8 mm, a length of about 1.4 m, the number of hollow fibers of 10,000, and a hollow fiber membrane area of 35 m ² . As raw water, artificial raw water (TOC 0.6 mg / L, turbidity level 1 degree, dissolved iron 0.05 mg / L) was used.

  The operating conditions were a filtration flux of 4 m / d and a filtration process time of 30 minutes. After the filtration step, first, the backwashing step (A-1) was carried out at a linear velocity of about 0.48 m / sec (flux 6 m / d) for 7 seconds, and the backwashing step (A-2) was carried out for 13 seconds. Subsequently, the primary side 30a and the secondary side 30b of the hollow fiber membrane module 30 were pressurized at 0.2 Mpa for 1.5 seconds, and the retained water was drawn out (B). Next, raw water is supplied to the hollow fiber membrane module 30 at a speed of 6 m / d for 20 seconds, and after performing the air venting step (C), the stagnant water drawing step (B) and the air venting step (C ) And again, the filtration process was restarted and water treatment was performed.

( Reference Example 2)
In Reference Example 1, immediately before the air venting step (C), the feed rate of the raw water is set to about 0.4 m / sec in linear velocity (5 m / d as the flux), and the flow rate of air is set to 1.5% of the flow rate of the raw water. The water treatment was performed in the same manner as in Example 1 except that the air flushing process was performed for 15 seconds.

( Reference Example 3)
Water treatment was performed using the water treatment apparatus shown in FIG. The hollow fiber membrane module 30 uses a microfiltration membrane (MF membrane) and has a hollow fiber hole diameter of 0.02 μm, an MF membrane hollow fiber diameter of 0.8 mm, a length of about 1.4 m, a number of hollow fibers of 10,000, and a hollow fiber membrane. An area of 35 m ² was used. The same raw water as in Example 1 was used.

  The operating conditions were a filtration flux of 4 m / d and a filtration process time of 30 minutes. After the filtration step, first, the backwashing step (A-1) was carried out at a linear velocity of about 0.48 m / sec (flux 6 m / d) for 7 seconds, and the backwashing step (A-2) was carried out for 13 seconds. Next, raw water was supplied at a flux of 5 m / d, and air was supplied at a flux of 7.5 m / d for 7 seconds, and the retained water was drawn out (B). Next, an air flushing process was performed for 7 seconds at a flux of 5 m / d. Next, an air layer is included in the retained water of the hollow fiber, 0.2 Mpa of compressed air is supplied to the primary side and the secondary side of the membrane for 1.5 seconds, and the second stagnant water extraction step (B) is performed. did. Next, raw water was supplied at a flux of 5 m / d, and the air venting step (C) was performed. Thereafter, the third stagnant water drawing step (B), the second air venting step (C), air removal in the middle of the raw water piping was performed, the filtration step was restarted, and water treatment was performed.

( Reference Example 4)
Water treatment was performed using the water treatment apparatus shown in FIG. As the hollow fiber membrane module 30 and raw water, the same ones as in Reference Example 1 were used.

  The operating conditions were a filtration flux of 6 m / d and a filtration time of 20 minutes. After the filtration step, first, the backwashing step (A-1) was carried out at a linear velocity of about 0.4 m / sec (flux 5 m / d) for 7 seconds, and the backwashing step (A-2) was carried out for 13 seconds.

  Next, 0.2 Mpa of compressed air was supplied to the primary side and the secondary side of the hollow fiber membrane for 1.5 seconds, and the retained water extraction step (B) was performed. Subsequently, the said air bleeding process (C) was implemented for 10 seconds.

  After the air venting step (C) was completed, the staying water drawing step (B) and the air venting step (C) were alternately repeated, and the staying water drawing step (B) and the air venting step (C) were performed three times in total.

  Finally, after removing the air in the pipe, the filtration process was resumed.

(Comparative Example 1)
Water treatment was performed using the water treatment apparatus shown in FIG. The same thing as Example 1 was used for the hollow fiber membrane module 30 and raw | natural water.

  The operating conditions were that the filtration step was performed for 30 minutes at a filtration flux of 4 m / d, and then the backwashing step (A-1) was performed for 20 seconds at a backwashing flux of 6 m / d.

(Comparative Example 2)
In Comparative Example 1, the backwashing process (A-1) was performed for 20 seconds, and then the air flushing process was performed for 10 seconds under the conditions of the raw water flow rate of 5 m / d and the air flow rate of 7 m / d. The water treatment was carried out.

(Comparative Example 3)
In Comparative Example 1, the backwashing step (A-1) was performed for 20 seconds, and then the air flushing step was performed for 10 seconds under the conditions of the raw water flow rate of 4 m / d and the air flow rate of 6 m / d. The water treatment was performed.

(Comparative Example 4)
After performing the filtration step for 30 minutes with a filtration flux of 4 m / d, the backwashing step (A-1) was performed for 20 seconds with a backwashing flux of 6 m / d. And it pressurized to the primary side of the hollow fiber membrane module with the air pressure of 0.3 Mpa once a day.

Water treatment is carried out continuously for 7 days under the operating conditions of each of the above Reference Examples 1 to 4 and Comparative Examples 1 to 4, and the amount of backwash water used, the amount of air used, the amount of raw water used for washing, the rate of increase in membrane differential pressure, the operation The rate was determined. In addition, an operation rate means the ratio of the filtration process time with respect to the whole operation time.

From the above results, it can be seen that Reference Examples 1 to 4 have a small increase in membrane differential pressure per day compared to Comparative Examples 1 to 4, and the amount of backwash water used is small and the filtrate recovery rate is high. .

  This is probably because part of the solid content adhering to the primary side of the hollow fiber membrane was peeled off by backwashing, and at the same time, the remaining solid content was also reduced in adhesion. Another reason is that the compressed air is sent from the same compressed air supply source, the primary side and the secondary side of the hollow fiber membrane are pressurized at the same time, and the retained water in the hollow fiber membrane is pulled out at a high speed. It is considered that the solid content on the primary side of the hollow fiber membrane was completely removed. In addition, even when a sufficient shear force is applied as in Comparative Example 3, if a large film differential pressure is generated on the primary side and the secondary side of the film, a part of the solid content is applied to the film. Since it is easy to re-adhere, the effect of removing solids is high, but the effect of preventing the increase in membrane differential pressure was small.

Further, it is estimated that the reason why the reference example 2 has a higher effect of increasing the film differential pressure than the reference example 1 is the effect of the air flushing process. In addition, compared with Reference Examples 1 and 2, Reference Examples 3 and 4 have a small increase in membrane differential pressure because air is mixed in the accumulated water, and the boundary surface between the water and the air is increased, resulting in shearing. It is estimated that this is because the power has improved.

[Test Example 2]
(Example 1 )
Water treatment was performed using the water treatment apparatus shown in FIG. The hollow fiber membrane module 30 has a hollow fiber hole diameter of 0.03 μm, a hollow fiber diameter of 0.8 mm, a length of about 1.4 m, a number of hollow fibers of 10,000, a hollow fiber membrane area of 35 m ² , and a volume of a vertical hollow fiber membrane module. About 44 L was used. As the raw water, artificial raw water (TOC 0.6 mg / L, turbidity 1 degree level, dissolved iron 0.05 mg / L) was used.

  The operating conditions were a filtration flux of 3 m / d and a filtration process time of 30 minutes. After the filtration step, first, the backwashing step (A-1) was carried out at a linear velocity of about 0.5 m / sec (flux 6 m / d) for 7 seconds, and the backwashing step (A-2) was carried out for 13 seconds. Next, an air flushing process was performed at a water flux of 6 m / d, an air flux of 9 m / d, and a time of 15 seconds. Subsequently, the primary side 30a and the secondary side 30b of the hollow fiber membrane module 30 are pressurized at 0.2 Mpa for 1.5 seconds, and the retained water is drawn out (B), and the flow rate is 6 m / d for 15 seconds. The air venting step (C) was carried out. After the air venting step (C) was completed, the staying water pulling step (B) and the air venting step (C) were alternately repeated, and the staying water pulling step (B) and the air venting step (C) were performed twice in total.

  Next, chemical cleaning liquid injection for injecting 12% sodium hypochlorite into the membrane filtration water pipe so that the hypochlorous acid concentration of sodium hypochlorite in the hollow fiber membrane module is 50 mg / L Step (D) was performed. Next, a chemical cleaning liquid retention step (E) for retaining the chemical cleaning liquid in the hollow fiber membrane module for 20 to 30 minutes was performed. Next, after carrying out the chemical cleaning liquid retention step (E), as a rinsing step (F), the chemical cleaning liquid dilution step (F-1) for reducing the chemical concentration is performed at a flow rate of 6 m / d for 20 seconds. 48 L of filtered water was injected. Next, as a rinsing step (F), a chemical cleaning solution discharging step (F-2) was performed in which a compressed air pressure of 0.05 MPa was supplied for 10 seconds and the diluted chemical cleaning solution on the secondary side of the membrane was drained from the primary side of the membrane. . After the chemical cleaning solution discharging step (F-2), 0.05 MPa compressed air was supplied to the primary side of the membrane for 3 seconds, the diluted chemical cleaning solution on the primary side of the membrane was drained, and the drainage was transferred to a reduction neutralization tank. .

  After the chemical cleaning solution discharge step (F-2) is completed, the chemical cleaning solution dilution step (F-1) and the chemical cleaning solution discharge step (F-2) are alternately repeated, and the chemical cleaning solution dilution step (F-1) and the chemical cleaning solution are repeated. The discharging step (F-2) was performed twice in total.

  These retained water extraction step (B), air removal step (C), chemical cleaning solution injection step (D), chemical cleaning solution retention step (E), and rinsing step (F) were performed about every 23 hours.

(Comparative Example 5)
In Example 1 , the implementation conditions and steps were the same as in Example 1 except that the primary water staying water drawing step (B) on the primary side of the hollow fiber membrane was omitted.

(Comparative Example 6)
In Comparative Example 5, at the time of chemical cleaning liquid injection step (D), except that 12% sodium hypochlorite was injected so that the concentration of sodium hypochlorite in the hollow fiber membrane module was 150 mg / L, Water treatment was performed in the same manner as in Comparative Example 5.

The water treatment of Example 1 and Comparative Examples 5 and 6 was performed for 15 days, and the rate of increase in membrane pressure difference, the amount of rinse water used, and the concentration of hypochlorite in the final rinse water were determined. The hypochlorite concentration in the final rinse water at the rinse drain outlet of the hollow fiber membrane module was measured by a colorimetric method.

From the above results, the water treatment method of Example 1 in which the stagnant water extraction step (B) was performed has a remarkable increase in membrane differential pressure per day as compared with Comparative Example 5 in which the stagnant water extraction step (B) was not performed. It became less.

Moreover, compared with the comparative example 6, Example 1 has the usage-amount of rinse water as small as 1/2, and can reduce the usage-amount of chemical | drug | medicine, the time required for a rinse, and the amount of rinse water.

It is a schematic block diagram of 1st Embodiment of the water treatment apparatus used for the water treatment method of this invention. It is a schematic block diagram for demonstrating the filtration process of this invention. It is a schematic block diagram for demonstrating the backwashing process (A-1) of this invention. It is a schematic block diagram for demonstrating the backwashing process (A-2) of this invention. It is a schematic block diagram for demonstrating the stay water extraction process (B) of this invention. It is a schematic block diagram for demonstrating an air flushing process. It is a schematic block diagram for demonstrating the air bleeding process (C) of this invention. It is a schematic block diagram of other embodiment of the water treatment apparatus which can be used for the water treatment method of this invention. It is a schematic block diagram of other embodiment of the water treatment apparatus which can be used for the water treatment method of this invention.

Explanation of symbols

1-9, 50-52: Pipe 10 Raw water supply tank 11 Raw water supply pump 12 Backwash water supply pump 13 Filtrated water storage tank 14 Compressor 15 Chemical liquid injection pump 16 Chemical liquid tank 17 Reduction neutralization tank 30 Hollow fiber membrane module V1 1st Raw water supply valve V2 second raw water supply valve V3 membrane outlet valve V4 filtered water storage tank inlet valve V5a first discharge valve V5b second discharge valve V6 first compressor inlet valve V7 second compressor inlet valve V8 air Drain valve V9 Raw water inlet valve V10 Chemical tank inlet valve V11 Reduction neutralization tank inlet valve V12 Chemical liquid drain valve

Claims (8)

In a water treatment method in which water to be treated is passed through a hollow fiber membrane module to remove contaminants in the water to be treated, and a water treatment method in which a washing treatment step for the hollow fiber membrane module is repeated.
As the washing treatment step, a backwashing step (A) for flowing water from the secondary side which is the outflow side of the filtrate of the hollow fiber membrane module to the primary side which is the inflow side of the water to be treated, and the backwashing step ( A) After that, while the primary side and the secondary side of the hollow fiber membrane module are pressurized with a predetermined air pressure, the retained water staying on the primary side and the secondary side of the hollow fiber membrane module is removed from the hollow fiber membrane module. After the stagnant water extraction step (B) for draining from the primary side of the water and the stagnant water extraction step (B) , water is supplied to the primary side of the hollow fiber membrane module to remove the air remaining in the hollow fiber membrane module after Tsu line physical cleaning including the air vent step (C),
A chemical cleaning solution injection step (D) for injecting a chemical cleaning solution from the secondary side to the primary side of the hollow fiber membrane module; a chemical cleaning solution retention step (E) for retaining the chemical cleaning solution in the hollow fiber membrane module; Is supplied from the secondary side of the hollow fiber membrane module, the secondary side of the hollow fiber membrane module is pressurized with an air pressure of 0.01 to 0.05 MPa, and the water is discharged to the primary side of the hollow fiber membrane module. Next, a rinsing step (F) in which the primary side of the hollow fiber membrane module is pressurized with an air pressure of 0.01 to 0.05 MPa to draw water from the primary side of the hollow fiber membrane module and wash the hollow fiber membrane module with water (F A water treatment method characterized by performing chemical cleaning .   The water according to claim 1, wherein after the backwashing step (A) is performed, water containing bubbles is supplied to a primary side of the hollow fiber membrane module, and then the retained water drawing step (B) is performed. Processing method.   3. The method according to claim 1, wherein after the air venting step (C) is performed, the stagnant water extraction step (B) and the air venting step (C) are alternately and repeatedly performed one or more times. Water treatment method. The chemical cleaning solution injection step (D) is performed until the concentration of the chemicals the cleaning liquid of the primary side of the hollow fiber membrane module has reached more than 80% of the concentration of the supplied chemicals wash any one of claims 1 to 3 The water treatment method as described in any one of. The chemical cleaning solution retaining step (E), after stopping the injection of the chemicals cleaning fluid into the hollow fiber membrane module, the cause chemical washes retained 10-120 minutes in the hollow fiber membrane module, according to claim 1 to 4 The water treatment method as described in any one of these . A hollow fiber membrane module for obtaining filtered water by removing pollutants in the water to be treated;
A treated water supply tank for storing treated water to be supplied to the hollow fiber membrane module;
A treated water supply pump for supplying treated water from the treated water supply tank to the hollow fiber membrane module provided in a primary side pipe that is an inflow side of treated water of the hollow fiber membrane module;
A backwash water supply pump for supplying water from the secondary side of the hollow fiber membrane module to the primary side, provided on the secondary side piping that is the outflow side of the filtrate of the hollow fiber membrane module;
A compressor for supplying compressed air to a primary side pipe and a secondary side pipe of the hollow fiber membrane module;
Possess a valve body provided in each of the connection pipe,
A water treatment apparatus , wherein a pipe connecting the treated water supply pump and the hollow fiber membrane module branches from the middle and is connected to the treated water supply tank via a valve body . A part of the secondary pipe of the hollow fiber membrane module is connected to a filtrate storage tank for storing filtrate obtained from the secondary side of the hollow fiber membrane module via the backwash water supply pump. The water treatment device according to claim 6 , wherein a part of the filtered water can be supplied from the secondary side to the primary side of the hollow fiber membrane module. The water treatment apparatus according to claim 6 or 7 , further comprising a chemical cleaning liquid injection means for supplying a chemical cleaning liquid from a secondary side of the hollow fiber membrane module.