JP3841735B2 - Filtration membrane cleaning method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a water treatment method for water supply, sewerage, industrial water or wastewater treatment, and more particularly to a water treatment method using membrane filtration treatment and a filtration membrane cleaning method used in a water treatment apparatus.
[0002]
[Prior art]
In the conventional membrane filtration method, if the operation is continued, the membrane surface or the inside of the membrane pores are contaminated by suspended substances and organic substances in the raw water supplied to the membrane filtration treatment as membrane supply water, or the amount of membrane filtration water decreases or An increase in transmembrane pressure is observed.
[0003]
Therefore, regular physical cleaning is usually performed in order to prevent contamination in the membrane surface and membrane pores. Examples of the physical cleaning method include reverse flow cleaning in which membrane filtrate is passed from the membrane filtrate side to the raw water supply side, and air cleaning in which air or air and raw water are passed from the primary side of the filtration membrane. These methods are very effective for clogging caused by deposits and solids in the membrane surface and pores, and have the effect of reducing the increase in transmembrane pressure difference. In recent years, a method of using ozone treatment in combination with this physical cleaning has been proposed, and is described in, for example, JP-A-2002-35552, JP-A-2002-35554, JP-A-2002-79064, and the like. . These methods are methods of cleaning the membrane with ozone-containing water, and decompose and remove deposits on the membrane surface and membrane pores by the oxidizing action of ozone.
[0004]
[Problems to be solved by the invention]
However, the conventional cleaning with ozone-containing water has the following problems.
[0005]
First, the ozone injection amount is excessive and uneconomical when the concentration of ozone in the ozone containing water is constant and the raw water quality is stable, or when the membrane is not contaminated.
[0006]
Secondly, in a state where the contamination of the membrane has progressed to some extent, the ozone-containing water ozone concentration becomes too low and the transmembrane pressure difference increases.
[0007]
Thirdly, under conditions where the load on the membrane is excessive when the raw water quality deteriorates, the ozone-containing water ozone concentration becomes too low and the transmembrane pressure difference increases.
[0008]
Fourth, at a low water temperature, even if ozone concentration within a predetermined range remains in the waste water, ozone does not react and the transmembrane pressure rises.
[0009]
The present invention has been made to solve the above-mentioned problems, and not only can the membrane clogging be greatly reduced even during high flux membrane filtration, but also can prevent clogging in advance. And it aims at providing the washing | cleaning method of the filtration membrane which enables water treatment economically by preventing excessive ozone injection | pouring.
[0010]
[Means for Solving the Problems]
The filtration membrane cleaning method of the present invention includes a membrane filtration step in which raw water is treated by membrane filtration means to obtain membrane filtered water, and an ozone injection step in which ozone is injected into a part of the membrane filtrate to obtain ozone treated water. And a filtration membrane cleaning step of supplying the ozone-treated water from the filtered water side of the membrane filtration means and backwashing the filtration membrane,
The residual ozone concentration in the wastewater that has passed through the filtration membrane by the backflow cleaning is detected, and the amount of ozone necessary to remove the contaminants attached to the filtration membrane is calculated and calculated based on the detected residual ozone concentration. A step of controlling the amount of ozone injected in the ozone injection step based on the amount of ozone;
Detecting the water temperature of the raw water, calculating a reaction time necessary for removing contaminants adhering to the filtration membrane based on the detected water temperature, and backwashing in the filtration membrane cleaning step based on the calculated reaction time Controlling the time;
It comprises.
[0011]
In the filtration membrane cleaning method of the present invention, in the injected ozone amount control step, the injected ozone amount is controlled so that the residual ozone concentration in the backwash waste water is within a range of 0.01 to 10 mg / L. preferable.
[0012]
According to the filtration membrane cleaning method of the present invention, in the injected ozone amount control step, the quality of the raw water is detected instead of the residual ozone concentration in the backwash waste water, and the necessary amount of ozone is calculated by using the detected water quality. It is also possible to ask for it.
[0013]
The present invention will be described in detail below.
[0014]
In the washing of the filtration membrane according to the present invention, it is necessary to control the backwashing time. If the water temperature is lowered unless the backwashing time is controlled, the reaction rate between ozone and contaminants on the membrane surface is reduced, and unreacted residual ozone exceeding a predetermined concentration range is detected in the backwashing waste water. On the other hand, when the water temperature rises, the reaction rate between ozone and contaminants on the membrane surface and the self-decomposition of ozone become faster, and residual ozone within a predetermined concentration range cannot be detected in the backwash waste water. For this reason, the backwashing time is controlled by the water temperature. Here, in the present specification, “backwash waste water” refers to waste water containing pollutants separated from the filter membrane by supplying ozone-treated water to the filter membrane in the opposite direction to the water flow during steady operation. .
[0015]
Therefore, considering that the reaction rate between ozone and the contaminants on the film surface varies depending on the water temperature, it is preferable to change the backwashing time in the range of 15 seconds to 300 seconds depending on the water temperature of the raw water. If the backwashing time is longer than 300 seconds, the time during which the raw water filtration treatment by the membrane filtration device is stopped becomes longer and the operation rate of the device may be lowered. On the other hand, if the backwashing time is shorter than 15 seconds, the backwashing flow rate for one time becomes excessive, and the load on the membrane filtration device may become too high. From the above, the backwashing time is preferably changed in the range of 15 seconds to 300 seconds, more preferably 30 to 120 seconds.
[0016]
The residual ozone concentration in the backwash waste water is preferably 0.01 to 10 mg / L. Considering the amount of ozone consumed during backwashing, if the residual ozone concentration in the backwash wastewater exceeds 10 mg / L, the ozone concentration of the ozone treated water used for backwashing will increase, so the filter membrane will be ozone resistant. Even if a membrane material is used, there is a risk that the membrane will deteriorate due to a reaction with ozone in the long term. For this reason, considering the replacement time of the membrane module, the residual ozone concentration can be allowed up to 10 mg / L. On the other hand, if the residual ozone concentration in the backwash waste water is less than 0.01 mg / L, it may be difficult to sufficiently obtain the effect of ozone for removing contaminants attached to the filtration membrane. From the above, the residual ozone concentration in the backwash waste water is preferably 0.01 to 10 mg / L, more preferably 0.1 to 5 mg / L.
[0017]
When the filtration membrane is backwashed, the backflow flux is preferably 0.2 to 5 times the membrane filtration flux. If it is less than 0.2 times, a sufficient cleaning effect may not be obtained, while if it exceeds 5 times, the film may be damaged. For this reason, the reverse flux is preferably 0.2 to 5 times, more preferably 0.5 to 3 times the membrane filtration flux.
[0018]
It is also possible to detect the water quality of the raw water instead of the residual ozone concentration, calculate the amount of ozone required to remove the contaminants attached to the filter membrane, and control the ozone concentration of the ozone treated water. is there. As used herein, “water quality” refers to a comprehensive concept including turbidity, potassium permanganate consumption, TOC, ultraviolet absorbance, chromaticity, and the like, which are measures of the degree of water contamination.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the cleaning method for the filtration membrane of the present invention will be described in detail with reference to FIG. Note that this embodiment does not limit the present invention.
[0020]
FIG. 1 is a block diagram showing a water treatment apparatus for explaining an embodiment of the present invention. As shown in FIG. 1, a water treatment apparatus in which the filtration membrane cleaning method according to the present invention is used is a circulating water tank (or a membrane supply water tank) 2, a membrane filtration apparatus 4, a membrane filtration water tank 7, an ozone generator 11, A backwash water tank 10 with a built-in trachea 13 is provided.
[0021]
The circulating water tank (or membrane supply water tank) 2 is communicated with a raw water supply tank (not shown) through a supply line 1. The line 1 is provided with a raw water temperature meter 18 and a raw water turbidity meter 19. The circulating water tank (or membrane supply water tank) 2 is further communicated with the membrane filtration device 4 via a supply line 22 provided with a valve V1. A supply pump 3 is installed in the line 22. The membrane filtration device 4 is provided with a transmembrane differential pressure measuring device 21. The membrane filtration device 4 communicates with a membrane filtration water tank 7 through a membrane filtration water line 6 provided with a valve V2. The membrane filtration water tank 7 is communicated with a water tank (not shown) through a treatment water line 8. Further, the membrane filtration water tank 7 is communicated with a backwash water tank 10 having a diffuser pipe 13 built in via a membrane filtration water line 9. An ozone generator 11 is connected to the backwash water tank 10 through an ozone gas transfer line 12. The backwash water tank 10 is communicated with the membrane filtrate water line 6 through the ozone treated water lines 14 and 23. A backwash pump 15 is provided at a connection portion between the lines 14 and 23, and a valve V <b> 3 is provided in the ozone treated water line 23. A compressor 24 communicates with the downstream side of the valve V1 of the line 22 or the raw water side of the filtration device 4 via the valve V6. The membrane filtration device 4 communicated with the line 6 is communicated with a circulating water tank (or a membrane supply water tank) 2 through a circulation line 5 provided with a valve V5. The line 5 is connected with a backwash drainage line 16 provided with a valve V4. The line 16 is connected to a drain tank (not shown). The line 16 is provided with an ozone detector 17.
[0022]
The supply pump 3, the ozone generator 11, the backwash pump 15, the ozone detector 17, the raw water temperature meter 18, and the raw water turbidity meter 19 are connected to the controller 20.
[0023]
Next, the operation will be described. First, a case where raw water is subjected to membrane filtration will be described.
[0024]
When membrane filtering raw water, valves V1, V2, and V5 are opened. Raw water is supplied from a raw water supply tank (not shown) to a circulating water tank (or membrane supply water tank) 2 through a supply line 1. Subsequently, the supply pump 3 is driven by a signal from the controller 20, and the raw water is pumped from the circulating water tank (or membrane supply water tank) 2 to the membrane filtration device 4 through the supply line 22 to perform membrane filtration. A part of the supplied raw water is sent to the circulating water tank (or membrane supply water tank) 2 through the circulation line 5 and again subjected to membrane filtration. The membrane filtrate is sent from the membrane filtration device 4 to the membrane filtration water tank 7 through the membrane filtration water line 6. A part of the membrane filtered water in the membrane filtered water tank 7 is transferred to the backwash water tank 10 through the membrane filtered water line 9, and the remaining membrane filtered water is transferred to the water tank (not shown) through the processing water line 8. Get as. In this way, the raw water is subjected to membrane filtration. The treatment water is set to a recovery rate within a predetermined range. After performing the membrane filtration process for a predetermined time, the supply pump 3 is stopped by a signal from the controller 20, and the valves V1, V2, and V5 are closed. The membrane filtration treatment may be performed for a certain time, or the turbidity of the raw water may be measured by the turbidimeter 19 and the treatment time may be determined from this result. Further, the transmembrane pressure difference of the filtration membrane may be measured by the transmembrane pressure gauge 21 and processing may be performed until the result reaches a certain value. In this case, the transmembrane pressure gauge 21 is input to the controller 20. It may be connected to the control unit and controlled based on the input signal.
[0025]
Next, a case where the filtration membrane is backwashed will be described.
[0026]
During membrane filtration and cleaning of the filtration membrane, the ozone generator 11 is controlled in real time by a signal from the controller 20 so that the amount of ozone blown into the backwash water tank 10 becomes a predetermined target value. A predetermined amount of ozone gas is sent from the ozone generator 11 to the diffuser pipe 13 of the backwash water tank 10 through the ozone gas transfer line 12 by the basic pressure during steady operation of the ozone generator 11. Ozone gas is blown into the membrane filtrate in the backwash water tank 10 from the air diffuser 13. In this way, the membrane filtered water in the backwash water tank 10 is subjected to ozone treatment to obtain ozone treated water having an ozone concentration within a predetermined range. In addition, in order to obtain the ozone treated water having a predetermined ozone concentration, it may be performed by controlling the ozone gas concentration of the ozone gas sent from the ozone generator 11 to the diffusion tube 13 or by controlling the ozone gas flow rate. May be.
[0027]
When the filter membrane is backwashed, valves V3 and V4 are opened. The backwash pump 15 is driven by a signal from the controller 20, and the obtained ozone treated water is sent to the membrane filtrate water line 6 through the ozone treated water lines 14 and 23. Subsequently, the ozone-treated water is pumped back from the filtered water side of the membrane filtration device 4 to the raw water supply side through the line 6 as backwash water. Further, the valve V6 can be opened, and air can be pumped from the compressor 24 to the raw water side of the membrane filtration device 4 through the line 22, so that the raw water side of the filtration membrane can be washed with air simultaneously with the backwashing. The backwashing of the filtration membrane is performed by driving the backwash pump 15 every predetermined time. The backwash pump 15 may be driven not only at regular intervals, but also at intervals determined by the turbidity of raw water detected by the turbidimeter 19. Alternatively, it may be performed when the transmembrane pressure difference detected by the transmembrane pressure gauge 21 exceeds a predetermined range.
[0028]
Furthermore, after the backwashing is completed, the valves V3 and V6 are closed, the valve V1 is opened, the supply pump 3 is driven by a signal from the controller 20, and the raw water is supplied to the membrane filtration device to perform flushing. By this flushing with raw water, dirt and clogged substances separated from the filtration membrane by backflow cleaning can be discharged from the membrane filtration device 4. Thereby, the dirt and clogging substances of the film can be effectively removed.
[0029]
The backwash wastewater that has passed through the filtration membrane is discharged to a drainage tank (not shown) or the like through the backwash drainage line 16. At this time, the residual ozone concentration of the backwash waste water in the line 16 is measured by the ozone detector 17. After the backwashing is completed, the valves V3 and V4 are closed, and then the valves V1, V2 and V5 are opened to start the membrane filtration process again.
[0030]
In the water treatment in which the filtration membrane cleaning method of the present invention is used, the membrane filtration and the filtration membrane backwashing as described above are repeatedly performed alternately.
[0031]
At the time of membrane filtration, the raw water temperature is measured by the raw water thermometer 18. This measurement result is sent to the controller 20, and the controller 20 computes the ozone reaction time during backflow cleaning necessary to remove contaminants attached to the filtration membrane. The backwashing time can be controlled by controlling the pump 15 from the processing result. The controller 20 may be a CPU (Central Processing Unit), for example.
[0032]
Furthermore, the residual ozone concentration in the backwash waste water is measured by the ozone detector 17 during backwashing. This measurement result is sent to the controller 20, and the controller 20 computes the ozone consumption necessary for removing the contaminants attached to the filtration membrane. From this processing result, the amount of ozone gas generated from the ozone generator 11 can be feedback controlled to change the ozone concentration in the ozone-treated water. If the measurement result of residual ozone concentration in the backwash wastewater is not yet obtained at the start of membrane filtration, for example, an appropriate ozone gas injection rate is determined in advance according to the preliminary experiment result or the raw water quality test result, for example. be able to.
[0033]
Similarly, it is also possible to calculate the ozone consumption necessary for removing the contaminants adhering to the filtration membrane, and to feedback control the ozone concentration of the ozone treated water and the backwash amount (ozone treated water amount). That is, when the raw water quality is extremely poor or good than normal, the residual ozone concentration in the backwash waste water is within a predetermined concentration range by adjusting the injection amount of ozone gas generated from the ozone generator 11. If not, the amount of ozone treated water (membrane filtered water sent from the membrane filtration water tank 7 to the backwash water tank 10) used for backwashing is within the range where the treatment water can be collected at a predetermined recovery rate. It is also possible to change. This can be performed, for example, by controlling the membrane filtration water tank 7 with a signal from the controller 20.
[0034]
Further, instead of detecting the residual ozone concentration in the backwash waste water, the turbidity of the raw water is measured by the raw water turbidimeter 19, and the amount of ozone necessary for cleaning the filter membrane is calculated by the controller 20 from this measurement result. However, it is possible to control the ozone concentration of the ozone-treated water based on this result.
[0035]
The membrane used in the membrane filtration device 4 may be any membrane as long as it can remove turbid components and bacteria. For example, a microfiltration membrane or an ultrafiltration membrane is used. be able to. It is preferable to use a microfiltration membrane having a nominal pore size of 0.01 to 1 μm. It is preferable to use an ultrafiltration membrane having a molecular weight cut off of 1,000 to 1,000,000 daltons. As the shape of the membrane module, for example, a hollow fiber shape, a spiral shape, a tubular shape, a flat membrane shape or the like can be used. It is desirable to use an ozone-resistant material for the membrane material and the module bonding portion in order to come into contact with high-concentration ozone. As the film material, an ozone-resistant organic resin such as vinylidene fluoride polymer resin, an inorganic material such as ceramic, or a combination thereof can be used. Moreover, the filtration method of a membrane module has a total amount filtration method and a crossflow filtration method, and any filtration method may be sufficient. Moreover, any of an external pressure type and an internal pressure type may be used as the water flow method to the filtration membrane.
[0036]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples. The examples do not limit the present invention.
[0037]
Example 1
As Example 1, a water treatment experiment was conducted using the water treatment experiment apparatus (treatment amount: 14 m ³ / day) shown in FIG.
[0038]
River surface water was used as raw water. The membrane filtration device 4 uses a microfiltration membrane made of polyvinylidene fluoride having a nominal pore size of 0.1 μm (a hollow fiber membrane having an effective membrane area of 7 m ² ), and a set membrane filtration flux of 2 m ³ / m ² / The daily constant flow filtration operation was performed. After performing the filtration operation for 30 minutes, backwashing using ozone-treated water 14 was performed, and at the same time, air was supplied from directly below the membrane module to perform air washing. After the washing, in order to remove suspended matter in the membrane module, the raw water was passed from the supply line 22 to the backwash drainage line 16, and flushing with the raw water was performed. Thus, filtration and washing were alternately repeated, and the above operation was performed for 1800 hours.
[0039]
Filtration was performed for 30 minutes each time, and the backwashing time was changed in the range from 30 seconds to 120 seconds depending on the water temperature.
[0040]
At the start of backwashing, the ozone concentration of the ozone-treated water 14 was 5 mg / L. In the subsequent backwashing, the residual ozone concentration in the backwashing waste water 16 is monitored, the ozone gas concentration in which the residual ozone concentration is in the range of 0.2 to 0.5 mg / L is calculated by the controller 20, and the ozone is The injection amount of the ozone gas 12 generated by the generator 11 was feedback controlled.
[0041]
Furthermore, when the raw water quality is extremely poor or good than normal, the residual ozone concentration in the backwash waste water is adjusted to the above range of 0.2 to 0.5 mg / L only by adjusting the injection amount of the ozone gas 12. When it was difficult to do so, in addition to adjusting the injection amount of ozone gas 12, the amount of ozone treated water 14 used for backwashing was also changed. At this time, the amount of the ozone treated water was changed so that the recovery rate of the treated water 8 changed within the range of 85% to 95% and the average value was 90%.
[0042]
Changes in the raw water temperature measured by the raw water thermometer 18 and the turbidity of the raw water measured by the raw water turbidimeter 19 are shown in FIG.
[0043]
Further, FIG. 3 shows the change over time in the ozone concentration of the ozone treated water 14 controlled by feedback control of the injection amount of the ozone gas 12 generated by the ozone generator 11.
[0044]
The time-dependent change in transmembrane pressure difference (converted to 25 ° C.) in the membrane filtration device 4 obtained from the above processing experiment was measured by the transmembrane pressure gauge 21 and the results are shown in FIG.
[0045]
As shown in FIG. 4, the transmembrane pressure difference does not increase over 3 months including the time of high turbidity and low water temperature as shown in FIG. 2 under the condition of membrane filtration flux of 2 m ³ / m ² / day. The water flow was stable. Further, as is clear from FIGS. 3 and 4, it was confirmed that the backwashing time, the ozone treated water ozone concentration, and the amount of the ozone washing water were all appropriately controlled and the optimum washing was performed.
[0046]
(Example 2)
Using the same apparatus as in Example 1, membrane filtration of river surface water as raw water and backwashing of the filtration membrane were performed.
[0047]
The backwashing time was changed in the range from 30 seconds to 120 seconds depending on the water temperature. Further, during backwashing, the raw water turbidity is monitored by the turbidimeter 19, and the required ozone amount corresponding to the turbidity of 5 to 20 degrees is calculated, so that the ozone concentration of the ozone-treated water becomes 3 to 10 mg / L. Thus, the concentration of the ozone treated water 14 was adjusted by controlling the injection amount of the ozone gas 12 generated by the ozone generator 11. The time-dependent change of the ozone concentration of the ozone treated water 14 at this time is also shown in FIG.
[0048]
Furthermore, when the raw water turbidity is less than 5 degrees or when the water quality is worse than 20 degrees, the adjustment of the injection amount of the ozone gas 12 generated by the ozone generator 11 only makes the required ozone amount according to the turbidity. When the ozone concentration of the ozone treated water 14 based on the ozone concentration is excessive or insufficient, the amount of the ozone treated water 14 used for the backflow cleaning is changed in addition to the adjustment of the injection amount of the ozone gas 12. At this time, the amount of the ozone treated water 14 was changed so that the recovery rate of the treated water 8 varied within the range of 85% to 95% and the average value was 90%.
[0049]
Except for the treatment conditions described above, filtration and washing were performed in the same manner as in Example 1.
[0050]
The time-dependent change of the transmembrane pressure difference (converted at 25 ° C.) in the membrane filtration device 4 obtained by the above processing experiment is also shown in FIG.
[0051]
As shown in FIG. 4, the transmembrane pressure difference does not increase over 3 months including the time of high turbidity and low water temperature as shown in FIG. 2 under the condition of membrane filtration flux of 2 m ³ / m ² / day. The water flow was stable. Further, as is clear from FIGS. 3 and 4, all of the backwashing time, the ozone treatment water ozone concentration and the ozone washing water amount are appropriately controlled according to the raw water quality and the water temperature, and the optimum washing is performed. confirmed.
[0052]
(Comparative Example 1)
Using the same raw water as in Example 1, a constant flow filtration operation was performed with a set membrane filtration flux of 2 m ³ / m ² / day by cross flow filtration. After performing the filtration operation for 30 minutes, back-flow cleaning using ozone-treated water 14 having an ozone concentration of 7 mg / L was performed for 60 seconds, and at the same time, air was supplied from directly below the membrane module to perform air cleaning. At the end of washing, flushing with raw water was performed to remove suspended matter in the membrane module. Control of the backwashing time by the raw water temperature and control of the ozone concentration of the ozone treated water 14 by the residual ozone concentration in the backwash wastewater or the quality of the raw water were not performed. The time-dependent change of the ozone concentration of the ozone treated water 14 at this time is also shown in FIG. The operation was performed such that the recovery rate of the water for treatment 8 was 88%. Except for this, a membrane filtration treatment experiment was conducted in the same manner as in Example 1.
[0053]
FIG. 4 also shows the change over time in the transmembrane pressure difference (converted to 25 ° C.) in the membrane filtration device 4 obtained from the above treatment experiment.
[0054]
As can be seen from FIGS. 2 and 4, in Comparative Example 1, in the low water temperature period in the initial stage of membrane filtration, the transmembrane differential pressure is equal or slightly increased in spite of the higher ozone concentration in the ozone treated water than in Example 1. There was a trend. This is because the reaction between ozone and the contaminants on the film surface did not sufficiently proceed because the backwashing time was fixed at 60 seconds in the low water temperature period. In addition, when the raw water turbidity increased, the transmembrane pressure difference increased rapidly and exceeded the transmembrane pressure limit. For this reason, a sufficient decrease in the transmembrane pressure difference cannot be obtained only by cleaning with ozone-treated water, and it has been necessary to use chemicals for cleaning the filtration membrane. This is because the ozone concentration in the ozone-treated water is not controlled by the residual ozone concentration in the backwashing wastewater and is kept constant as shown in FIG. 3, so the residual ozone concentration in the backwashing wastewater cannot be kept within a predetermined range. This is because the.
[0055]
【The invention's effect】
As described above, according to the present invention, when the membrane is backwashed with ozone-treated water obtained by injecting ozone into a part of the membrane filtrate after membrane filtration, backwashing is performed according to the water temperature. The time can be determined, and the ozone concentration can be controlled to the optimum according to the residual ozone concentration in the backwash waste water or the quality of the raw water. As a result, clogging of the membrane can be greatly reduced even at high membrane permeation flux, and the labor required for chemical cleaning to cope with clogging of the membrane and the cost of cleaning chemicals can be reduced.
[0056]
In addition, by controlling the optimal ozone concentration and backwash time according to the water temperature and residual ozone concentration in the backwash water or the quality of raw water, excessive ozone generation is prevented, energy consumption is reduced, and The recovery rate of water for treatment can be improved by washing, which is economical.
[0057]
Thus, according to the present invention, not only can membrane clogging be greatly reduced even during high flux membrane filtration, it is possible to prevent clogging in advance and prevent excessive ozone injection. By doing so, it is possible to provide a filtration membrane cleaning method that enables economical water treatment.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a water treatment apparatus according to an embodiment of the present invention.
FIG. 2 is a characteristic diagram showing changes over time in turbidity and water temperature of raw water.
FIG. 3 is a characteristic diagram showing the change over time in the ozone concentration of ozone-treated water.
FIG. 4 is a characteristic diagram showing a change with time in transmembrane pressure difference.
[Explanation of symbols]
1, 22 ... Supply line 2 ... Circulating water tank (membrane supply water tank)
DESCRIPTION OF SYMBOLS 3 ... Supply pump 4 ... Membrane filtration apparatus 5 ... Circulation line 6, 9 ... Membrane filtration water line 7 ... Membrane filtration water tank 8 ... Treatment water line 10 ... Backwash water tank 11 ... Ozone generator 12 ... Ozone gas transfer line 13 ... Aeration pipe DESCRIPTION OF SYMBOLS 14,23 ... Ozone treated water line 15 ... Backwash pump 16 ... Backflow washing drainage line 17 ... Ozone detector 18 ... Raw water thermometer 19 ... Raw water turbidity meter 20 ... Controller 21 ... Transmembrane pressure gauge 24 ... Compressors V1, V2 , V5 ... Membrane filtration valve V3, V4 ... Backflow cleaning valve V6 ... Air valve

Claims (3)

A membrane filtration step of treating raw water with membrane filtration means to obtain membrane filtered water, an ozone injection step of injecting ozone into a part of the membrane filtered water to obtain ozone treated water, and the membrane filtration of the ozone treated water In the filtration membrane cleaning method comprising a filtration membrane cleaning step of supplying the filtration water from the filtered water side of the means and backwashing the filtration membrane,
The residual ozone concentration in the wastewater that has passed through the filtration membrane by the backflow cleaning is detected, and the amount of ozone necessary to remove the contaminants attached to the filtration membrane is calculated and calculated based on the detected residual ozone concentration. A step of controlling the amount of ozone injected in the ozone injection step based on the amount of ozone;
Detecting the water temperature of the raw water, calculating a reaction time necessary for removing contaminants adhering to the filtration membrane based on the detected water temperature, and backwashing in the filtration membrane cleaning step based on the calculated reaction time Controlling the time;
A filtration membrane cleaning method comprising: 2. The method according to claim 1, wherein in the injected ozone amount control step, the injected ozone amount is controlled so that a residual ozone concentration in the backwash waste water is within a range of 0.01 to 10 mg / L. 2. The injection ozone amount control step detects the quality of the raw water instead of the residual ozone concentration in the backwash waste water, and calculates a necessary ozone amount by calculation using the detected water quality. the method of.

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