JP4742671B2 - Water treatment method and apparatus by membrane filtration - Google Patents

Description

  The present invention relates to a water treatment method and a water treatment apparatus by membrane filtration, in which contaminants contained in raw water such as water supply, sewerage, industrial water, or wastewater treatment water are separated and removed by a filtration membrane and purified.

  In a water treatment apparatus using a filtration membrane, fouling occurs due to long-time operation, and the filtration performance deteriorates. Therefore, in the operation cycle, after a filtering process for a predetermined time, physical cleaning is performed to reduce fouling. Physical cleaning includes backflow cleaning (backwashing) that reverses the treated water after membrane filtration, flushing by water flow on the primary side of the membrane, and air scrubbing that vibrates the membrane with air. Has been removed.

  In the case of backwashing or flushing with water flow, the effect of suppressing fouling can be improved by shortening the physical cleaning interval. However, since these physical cleanings are performed using treated water, the recovery rate (raw material) There is a problem that the ratio of the amount of treated water to the amount of water decreases. From this point of view, in the conventional operation, the operation was performed at a good balance between the physical cleaning interval and the recovery rate.

  One method for improving the recovery rate is a method of reusing backwash wastewater (see Patent Document 1). As is clear from the summary description, Patent Document 1 discloses that “wash wastewater is reused as wash water in a range in which the turbid mass in the wash wastewater does not exceed a predetermined value”. That is, in the case of the invention described in Patent Document 1, the cleaning wastewater reused for cleaning is treated as wastewater when the turbid mass exceeds a predetermined value, and the recovery rate depends on the amount of wastewater. There is a low problem.

  As a method of further improving the recovery rate, a method of obtaining treated water by membrane filtration of backwash wastewater or returning water obtained by membrane filtration of backwash wastewater to the raw water side (membrane filtration after returning and mixing with raw water) To obtain treated water). Further, as described above, the following method has been proposed as a method for membrane filtration of backwash wastewater.

One of them is a method (so-called two-stage filtration method) in which another membrane filtration device is installed separately from the device for membrane filtration of raw water. In this case, there are problems such as an increase in installation space and an increase in maintenance due to the expansion of the apparatus. Another method is a method applied by the inventors of the present invention according to Japanese Patent Application No. 2003-305705, in which backwash wastewater is filtered prior to raw water at the start of a membrane filtration step. This method is an operation method (so-called precoat filtration method) having the merit of not only increasing the recovery rate by membrane filtration of the backwash wastewater but also suppressing membrane clogging by the coagulation flock in the backwash wastewater. However, this method also has the following problems. In other words, water obtained by membrane filtration of backwash wastewater is clear raw water that satisfies the tap water quality standards, but water obtained by filtering backwash wastewater from which foreign matters have been peeled off from the filtration membrane, that is, dirty backwash wastewater. Therefore, for users of treated water, there is a negative image in terms of hygiene and spirit, which has been a factor that hinders its spread.
JP 2002-224542 A

  The present invention has been made in view of the above-described problems, and an object of the present invention is to improve the recovery rate of water treatment by recycling the backwash wastewater by membrane filtration and saving the wastewater. An object of the present invention is to provide a water treatment method and apparatus by membrane filtration that solves problems such as sanitary aspects as treated water in a space.

In order to solve the above-described problems, the present invention includes a membrane module having a filtration membrane, a backwash water tank that communicates with the secondary side of the membrane module and stores backwash water, and a primary side of the membrane module. A main pump for supplying the backwash wastewater recovery tank for storing the drained backwash wastewater, the raw water for storing the raw water or the backwash wastewater for the backwash wastewater recovery tank to the primary side of the membrane module; A backwash pump for supplying backwash water from the backwash water tank to the secondary side of the membrane module; a line for communicating backwash water to the secondary side of the membrane module; A water treatment device comprising a line that communicates with the secondary side of the membrane module and takes out treated water without going through the backwash water tank, and is capable of switching between a line that supplies the backwash water and a line that takes out the treated water Water treatment method The raw water is filtered from the primary side to the secondary side of the filtration membrane to obtain treated water without going through the backwash water tank, and the backwash water is supplied by stopping the line for taking out the treated water. Backwash water stored in the backwash water tank and backwashed from the secondary side of the filtration membrane to the primary side and discharged from the secondary side into the backwash drainage recovery tank. A backwashing step of storing, and a backwashing drainage filtration step of filtering only the backwashing wastewater stored in the backwashing wastewater recovery tank from the primary side to the secondary side of the filtration membrane and storing it in the backwashing water tank. And the process returns to the raw water filtration step after the backwash drainage filtration step (invention of claim 1).

  According to the above invention, the backwash wastewater is filtered through a filtration membrane and stored in the backwash water tank, and only reused for backwashing and not provided to the user as treated water. As a result, problems such as hygiene can be solved. Further, unlike the two-stage filtration method, the backwash wastewater is filtered by a raw water filtration membrane, so that it is possible to realize improvement in recovery rate and elimination of problems such as hygiene in spite of space saving.

As an embodiment of the invention of claim 1, the inventions of claims 2 to 3 are preferable. That is, in the water treatment method according to claim 1, the raw water is filtered from the primary side to the secondary side of the filtration membrane between the backwash drainage filtration step and the raw water filtration step. The water remaining in the membrane is passed through the backwash water tank, and the residual backwash water draining step is performed (invention of claim 2).

Furthermore, in the water treatment method according to claim 1 or 2, the backwashing step and the backwash drainage filtration step are interchanged (invention of claim 3) .

Moreover, as invention of the water treatment apparatus for enforcing the said water treatment method, invention of the following Claim 4 is preferable. That is, an apparatus for carrying out the water treatment method according to any one of claims 1 to 3 , wherein a raw water tank for storing raw water, a membrane module having a filtration membrane,
A backwash water tank that communicates with the secondary side of the membrane module and stores backwash water, a line that communicates with the secondary side of the membrane module and supplies the backwash water to the backwash water tank, and the membrane module A line for communicating treated water without passing through the backwash water tank, a valve for switching between a line for supplying the backwash water and a line for removing the treated water, and a primary side of the membrane module A backwash wastewater recovery tank for storing backwash wastewater discharged from the main water tank, a main pump for supplying the raw water of the raw water tank or the backwash wastewater of the backwash wastewater recovery tank to the primary side of the membrane module, and the reverse A backwash pump for supplying backwash water from the wash tank to the secondary side of the membrane module;
(Invention of claim 4).

  According to this invention, in the water treatment method and apparatus by membrane filtration, the backwash wastewater is membrane-filtered and reused to improve the recovery rate of water treatment, and as the treated water while saving space It can solve problems such as hygiene.

  An embodiment of the present invention will be described below based on FIG. In addition, this invention is not limited by this Example.

  FIG. 1 is a system diagram of a water treatment apparatus using membrane filtration according to an embodiment of the present invention. In FIG. 1, 1 is raw water, 2 is flocculant PAC, 3 is sulfuric acid, 4 is raw water tank, 5 is raw water supply valve, 6 is backwash drainage supply valve, 7 is main pump, 8 is membrane module, 9 is treatment Water valve 10 is a backwash water valve, 11 is treated water, 12 is a backwash water, 13 is a backwash water tank, 14 is a backwash pump, 15 is a backwash valve, 16 is a backwash drain, 17 is a backwash A waste water recovery tank, 18 is a raw water return line, 19 is a drain valve, and 20 is sludge. In FIG. 1, illustration of a control device that controls opening and closing of the water discharge valve 19 is omitted.

  Next, the flow of the filtration process and backwashing process of the water treatment apparatus by membrane filtration shown in FIG. 1 will be described. First, the filtration process will be described. The water agitated by injecting the flocculant PAC2 and sulfuric acid 3 for pH adjustment into the raw water 1 flowing into the raw water tank 4 is supplied to the filtration membrane by the main pump 7 via the raw water supply valve 5. Water is passed through the membrane module 8. The membrane-filtered water is supplied to the next step as treated water 11 through the treated water valve 9. In the first filtration step, a part of the treated water is stored as backwash water 12 in the backwash water tank 13 via the backwash water valve 10, and this stored water (backwash water) is used. The filtration membrane is backwashed after the predetermined membrane filtration treatment time (first backwashing step).

  In the first backwashing process, the secondary side of the membrane module 8 (from the treated water side) to the primary side by the backwashing pump 14 from the backwashing water tank 13 through the backwashing valve 15 as in the conventional backwashing. The backwash water is passed through (raw water side), and the backwash drainage 16 from the membrane module 8 is stored in the backwash drainage recovery tank 17. After the back washing step, the filtration step is performed again.

  Next, the backwash process for the second and subsequent times, that is, the backwash process for reusing the backwash waste water will be described.

  When a predetermined filtration time, for example, 20 to 120 minutes, has passed, the raw water supply valve 5 is closed and the backwash drainage supply valve 6 is opened, and the backwash drainage 16 in the backwash drainage recovery tank 17 is supplied to the main pump. 7, the process is switched to the step of passing water to the membrane module 8. At this time, the treated water valve 9 is closed. The membrane-filtered water is stored in the backwash water tank 13 as backwash water 12 through the backwash water valve 10.

Here, in order to reuse the backwash wastewater, the backwash wastewater 16 in the backwash wastewater recovery tank 17 is filtered through the membrane module 8 and stored as backwash water 12 in the backwash water tank 13. About the time to perform, what is necessary is just to have implemented before the start of the backwashing process, but as a particularly preferable form, as in the example described above, the backwash drainage is performed at the timing as in the invention of claim 3. The backwash waste water 16 in the recovery tank 17 may be filtered and stored in the backwash water tank 13 as backwash water 12.

  In addition, when filtering the backwash wastewater 16 in the backwash wastewater collection tank 17, it is preferable to stir the backwash wastewater collection tank 17 and supply the backwash wastewater 16.

  When the backwash wastewater 16 is subjected to membrane filtration for a predetermined time, the filtration process for reusing the backwash wastewater is stopped. The time for membrane filtration of backwash wastewater is the time to filter the amount of water used for backwashing, and therefore depends on the membrane filtration flux, and the time is usually between 1 and 10 minutes.

  Following the filtration process for reusing the backwash wastewater, a backwash process for reusing the backwash wastewater is performed. Water in the backwash water tank 13 is passed from the secondary side of the membrane module 8 to the primary side through the backwash valve 15 using the backwash pump 14. The backwash wastewater 16 discharged from the primary side is stored again in the backwash wastewater recovery tank 17 and is put on standby because it is membrane filtered before the next backwash process. The operation becomes easier when the amount of water used for backwashing and the amount of recovered filtered water of backwash wastewater are made as equal as possible.

  By the way, in the backwash wastewater, in addition to the turbid mass in the backwash wastewater to be recovered and membrane filtered, the turbid component captured by the membrane during raw water filtration increases, so it is necessary to suppress the increase in concentration. Therefore, the sludge in the backwash drainage is concentrated 5 to 20 times by gravity sedimentation (depending on the raw water condition and the gravity sedimentation time), and the concentrated sludge of the backwash wastewater 16 is periodically fed from the lower part of the backwash wastewater recovery tank 17. 20 is pulled out from the water discharge valve 19 and used for sludge treatment or the like. In addition, opening / closing control of the water discharge valve 19 is performed by a control device (not shown). When the water quality of the raw water is relatively stable, the open / close control can be an open / close control with a predetermined time interval determined experimentally in advance, but when the water quality varies relatively, for example, It is also possible to provide a turbidity meter in the backwash waste water recovery tank so as to control opening and closing when the turbidity reaches a predetermined value.

  Also, considering the concentration of backwash wastewater by gravity sedimentation and the amount of extracted sludge at high turbidity, the capacity of the backwash wastewater recovery tank 17 is at least twice the amount of water used for backwashing. It is preferable to use a large tank within an allowable range. A plurality of backwash drainage tanks 17 may be installed.

After backwashing process is completed to recycle the backwash waste water, the process proceeds back to raw water filtration process, but since it is in the membrane module remaining water used for backwash of claim 2 As in the invention, the water immediately after the start of filtration is preferably passed through the backwash water valve 10 to the backwash water tank 13. As another method, after the backwashing step for reusing the backwash wastewater, the backwash wastewater 16 in the backwash wastewater recovery tank 17 is first filtered through the membrane module 8 to obtain backwash water 12. When the process of storing in the water tank 13 is carried out and then the process proceeds to the raw water filtration process again, the water immediately after the start of filtration is supplied from the backwash water valve 10 to the backwash water tank as in the invention of claim 3. After passing through the water 13, the raw water filtering step for obtaining treated water can be carried out.

  In addition, when the capacity | capacitance of the backwash water tank 13 is comparatively small, and the water in the backwash water tank 13 overflows, you may return to a raw | natural water tank from the raw | natural water return line 18. FIG. The water staying on the secondary side of the filter membrane is the water from which the backwash wastewater is filtered. However, when this is returned to the raw water tank and filtered again, a mental negative image problem arises. It is not considered.

The system system | strain diagram of the water treatment apparatus by the membrane filtration which concerns on embodiment of this invention.

Explanation of symbols

1: Raw water, 4: Raw water tank, 5: Raw water supply valve, 6: Backwash drainage supply valve, 7: Main pump, 8: Membrane module, 9: Treated water valve, 10: Backwash water valve, 11: Treated water , 12: Backwash water, 13: Backwash water tank, 14: Backwash pump, 15: Backwash valve, 16: Backwash drainage, 17: Backwash drainage recovery tank, 18: Raw water return line, 19: Waste water Valve, 20: Sludge

Claims (4)

A membrane module having a filtration membrane;
A backwash water tank that communicates with the secondary side of the membrane module and stores backwash water;
A backwash drainage recovery tank for storing backwash drainage discharged from the primary side of the membrane module;
A main pump for supplying raw water from a raw water tank for storing raw water or backwash wastewater from the backwash wastewater recovery tank to the primary side of the membrane module;
A backwash pump for supplying backwash water from the backwash water tank to the secondary side of the membrane module;
A line that communicates with the secondary side of the membrane module and supplies backwash water to the backwash water tank;
A water treatment device comprising a line that communicates with the secondary side of the membrane module and takes out treated water without going through the backwash water tank, and is capable of switching between a line that supplies the backwash water and a line that takes out the treated water In the water treatment method of
A raw water filtration step of filtering raw water from the primary side of the filtration membrane to the secondary side to obtain treated water without going through the backwash water tank;
Stop the line for taking out the treated water, open the line for supplying backwash water, backwash from the secondary side of the filtration membrane to the primary side with the backwash water stored in the backwash water tank, and the secondary side A backwash process for storing backwash wastewater discharged from the backwash wastewater recovery tank;
Only the backwash drainage stored in the backwash drainage recovery tank is filtered from the primary side to the secondary side of the filtration membrane and stored in the backwash water tank, and the backwash drainage filtration step is sequentially performed.
A water treatment method by membrane filtration, wherein the process returns to the raw water filtration step after the backwash drainage filtration step. The water treatment method according to claim 1,
Between the backwash drainage filtration step and the raw water filtration step, the raw water is filtered from the primary side to the secondary side of the filtration membrane, and the water remaining on the filtration membrane is transferred to the backwash water tank. A water treatment method by membrane filtration, characterized by passing water and performing a residual backwash water drainage step. The water treatment method according to claim 1 or 2,
A water treatment method by membrane filtration, wherein the backwashing step and the backwashing drainage filtration step are interchanged. An apparatus for carrying out the water treatment method according to any one of claims 1 to 3,
A raw water tank for storing raw water;
A membrane module having a filtration membrane;
A backwash water tank that communicates with the secondary side of the membrane module and stores backwash water;
A line that communicates with the secondary side of the membrane module and supplies backwash water to the backwash water tank;
A line that communicates with the secondary side of the membrane module and removes treated water without going through the backwash water tank;
A valve for switching a line for supplying the backwash water and a line for taking out the treated water;
A backwash drainage recovery tank for storing backwash drainage discharged from the primary side of the membrane module;
A main pump for supplying raw water in the raw water tank or backwash wastewater in the backwash wastewater recovery tank to the primary side of the membrane module;
A backwash pump for supplying backwash water from the backwash water tank to the secondary side of the membrane module;
A water treatment apparatus using membrane filtration, comprising:

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