JP5174548B2 - Operation method of combined filtration equipment - Google Patents

Description

  The present invention relates to a method for operating a combined filtration facility that produces treated water used as drinking water or the like by membrane separation treatment and media filtration using river water, lake water, or the like as raw water (treated water).

  As a water treatment method in a water purification plant using river water, lake water, etc. as raw water (treated water), after adding a flocculant to the raw water, it is passed through a coagulation filtration device and the raw water is turbidized by coagulation filtration Are known. As another treatment method, a media filtration basin (media filtration device) using a particulate filter medium such as sand, anthracite (crushed anthracite and granulated), and granular activated carbon as a filtration layer is known.

  A membrane filtration device that filters raw water using a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) is also often used. Membrane filtration devices are more compact than other water treatment devices such as media filtration ponds, have a small installation space, and can remove pathogenic microorganisms in addition to suspended substances. By selecting the membrane to be used, it can be applied to raw water of various water quality and the construction period for installation is short.

  However, since the membrane filtration apparatus uses a membrane having a small hole diameter as a filtration medium, the membrane module is likely to be clogged unless the chemical solution is periodically cleaned. Moreover, since it is necessary to replace a membrane module regularly, there exists a fault that a running cost is high.

  On the other hand, media filtration devices such as media filtration ponds have a constant filtration rate (the amount of treated water is constant). Therefore, it is necessary to repeat the operation / stop of the media filtration device for fluctuations in the amount of treated water. Is prone to decline. In addition, when the amount of treated water has to be increased, there is also a problem that the filtration process cannot catch up.

  For this reason, the composite filtration apparatus which combined two or more types of processing apparatuses is proposed. For example, Patent Document 1 discloses a composite filtration device in which a submerged membrane separation device is incorporated in a media filtration tank and can be simultaneously filtered by both the media filtration basin and the submerged membrane separation device.

  Further, Patent Document 2 discloses a water treatment apparatus in which raw water to which a flocculant is added in a set addition amount is passed through a coagulation filtration device and subjected to coagulation filtration, and then the treated water of the coagulation filtration device is subjected to membrane separation by a membrane filtration device. It is disclosed.

Incidentally, Patent Document 3 discloses a water treatment method in which an iron-based flocculant is added to aggregate suspended substances and soluble organic substances in raw water, and the aggregates are removed only by a ceramic membrane separator.
JP-A-2005-279408 Japanese Patent Laid-Open No. 10-15307 JP 2002-59173 A

  In the water treatment device disclosed in Patent Document 2, the amount of the flocculant added to the raw water is determined by the rate of increase in the differential pressure when water is passed through the flocculent filtration device. However, since the optimum amount of flocculant added when using the flocculent filtration device alone is not necessarily the optimum amount of flocculant added to the membrane separator, an excessive amount of flocculant is used as the water to be treated in the membrane separator. Sometimes used.

  In the membrane separator and the coagulation filtration device, the pore size of the membrane separator is smaller. For this reason, the size of the solid content (floc) formed by the addition of the flocculant is smaller in the membrane separation device. That is, the amount of the flocculant added to the water to be treated is smaller in the membrane filtration device. However, in the conventional technique disclosed in Patent Document 2, the flocculant is added to the water to be treated (raw water) of the membrane separation device so that the concentration is adjusted to the media filtration device in which the amount of flocculant injected is large. .

  For membrane separators, excessive injection of flocculant into the water to be treated should be suppressed to the minimum amount of flocculant injected to promote clogging of membrane pores due to increase in the concentration of unaggregated flocculant. Is preferred. Further, in order to suppress the processing cost, it is preferable that the amount of the flocculant injected is minimized.

  Patent Document 1 does not disclose what kind of aggregating agent should be added in the composite filtration apparatus.

  Membrane separation is performed by a submerged membrane separator to obtain membrane permeated water, concentrated water of the submerged membrane separator is filtered by a media filtration device to obtain filtered water, and both the permeated water and the filtered water are drinking water. In the case of a filtration facility, the treatment capacity can be maintained by increasing the amount of permeated water of the submerged membrane separator even if the amount of treated water increases. Moreover, since the concentrated water (the remaining water obtained by removing permeate from the raw water) can be filtered and biologically processed by the media filtration device, the raw water is not wasted.

  INDUSTRIAL APPLICABILITY The present invention is suitable for both a submerged membrane separation device and a media filtration device in a combined filtration facility that uses a submerged membrane separation device and a media filtration device at the same time to obtain membrane separation water and media filtration water. Most suitable for both the treated water of the submerged membrane separator (raw water, raw water such as lake water) and the treated water of the media filtration device (concentrated water of the submerged membrane separator) An object of the present invention is to provide an operation method in which a flocculant is dispersed and added so as to be in a concentration range.

  The present inventors obtained raw water (treated water) such as river water and lake water by membrane separation using a submerged membrane separation device to obtain membrane permeated water, and filtered the concentrated water of the submerged membrane separation device using a media filtration device. In the combined filtration equipment that supplies filtered water and supplies both the permeated water and the filtered water as treated water, various investigations were made on the coagulant concentration that is optimal for both the submerged membrane separation device and the media filtering device. As a result, if the raw water is in a certain range of low turbidity, the flocculant is added to the raw water supplied to the submerged membrane separator so as to be in a specific concentration range, and then the submerged type that becomes the treated water of the media filtration device If the flocculant is added to the concentrated water of the membrane separator so as to be in a specific concentration range, the optimum flocculant concentration can be secured for two types of water treatment devices while minimizing the amount of flocculant used. And the present invention is completed. It came to that.

Specifically, the present invention
The water to be treated is membrane-separated by a submerged membrane separator to obtain membrane permeated water, the concentrated water of the submerged membrane separator is filtered by a media filtration device to obtain filtered water, both the permeated water and the filtered water In combined filtration equipment that supplies water as treated water,
Add flocculant to the concentration range of 0.3 mg / L or more and 0.55 mg / L or less to the raw water with turbidity of 1 to 15 degrees supplied to the submerged membrane separator, and supply it to the media filter. A flocculant is further added to the concentrated water so as to have a concentration range of 0.55 mg / L or more and 0.8 mg / L or less.

  When raw water (treated water) such as river water or lake water is placed in series with a submerged membrane separation device and a media filtration device, and the concentrated water of the submerged membrane separation device is treated water of the media filtration device, In the former immersion membrane separator, the concentration of the flocculant added to the raw water (treated water) is as much as possible from the viewpoint of preventing clogging of the MF membrane or UF membrane used as the separation membrane of the immersion membrane separator. Ideally, the concentration should be low. However, in the subsequent media filtration device, it is not preferable that the concentration of the flocculant in the water to be treated is low from the viewpoint of preventing turbidity leakage into the treated water.

  In this way, the membrane is separated by the submerged membrane separator to obtain the membrane permeated water, the concentrated water of the submerged membrane separator is filtered by the media filtration device to obtain the filtered water, both the permeated water and the filtered water. In a combined filtration facility that supplies drinking water or the like, the optimum flocculant concentration differs between the two types of filtration devices. However, in the operation method of the present invention, when the turbidity of the raw water is stable at a low turbidity of 1 degree or more and 15 degrees or less, the flocculant in the raw water supplied as treated water to the preceding immersion membrane separator The concentration range is 0.3 mg / L or more and 0.55 mg / L or less, and the concentration range of 0.55 mg / L or more and 0.8 mg / L or less is used for the concentrated water of the submerged membrane separator, which is the treated water of the media filtration device. By further adding a flocculant so as to become, it is possible to increase the solid content removal efficiency of the entire system while preventing clogging of the MF membrane or UF membrane with respect to the submerged membrane separation apparatus. At the same time, the amount of the flocculant used can be suppressed to the minimum necessary amount.

  Here, the concentrated water of the submerged membrane separator is in a state where all of the flocculant added to the raw water has been consumed. In the present invention, this concentrated water is treated with a media filtration device, but before the treatment, a flocculant is further added so that the concentration range is 0.3 mg / L or more and 0.55 mg / L or less. That is, the flocculant is further added to the concentrated water of the submerged membrane separator so that the concentration range is 0.55 mg / L or more and 0.8 mg / L or less together with the flocculant added to the raw water.

  The separation membrane of the submerged membrane separation device is preferably an MF membrane or a UF membrane.

  Moreover, it is preferable that the separation membrane of the submerged membrane separation device is a hollow fiber membrane. This is because it is less likely to clog than a flat membrane.

  The filtration medium of the media filtration device is a hollow cylinder, granular or spherical, and in the case of a hollow cylinder, the average inner diameter is 1 mm or more and 10 mm or less, and in the case of granular or spherical, the average diameter is 0.5 mm or more and 1.5 mm or less. (Claim 4).

  According to the operation method of the composite filtration facility of the present invention, if raw water (treated water) such as river water and lake water is within a certain range, the submerged membrane separation device and The optimal filtration state can be maintained for both media filtration devices.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. In addition, this invention is not limited to the following description.

  An example of a combined filtration facility suitable for carrying out the operating method of the present invention is shown in FIG. The composite filtration facility shown in FIG. 1 includes a submerged membrane separation device 11 and a media filtration tower 22 (media filtration device) as a filtration device, to which an external device is connected.

  The submerged membrane separation device 11 is installed in the membrane separation tank 10 and is immersed under the surface of the water to be treated (for example, raw water of fresh water). A raw water tank 1 and a mixing tank 5 are connected to the membrane separation tank 10, and the raw water after adding the flocculant is supplied.

  Next, a water treatment method in this composite filtration facility will be described. Fresh water such as river water and lake water is first stored in the raw water tank 1. The raw water 2 is supplied to the mixing tank 5 through the path 4 by the pump 3. At this time, a turbidity meter is installed in the path 4 to measure the turbidity of the raw water 2. When the turbidity is in the range of 1 to 15, a flocculant is added to the mixing tank 5 so that the concentration range is 0.3 mg / L to 0.55 mg / L. Then, the mixture is stirred by the mixer 6.

  As the flocculant, in addition to aluminum flocculants such as polyaluminum chloride and aluminum sulfate, iron flocculants such as ferric chloride and ferric sulfate, and organic polymer flocculants such as polyacrylamide are used. The type is not particularly limited. It is preferable that the flocculant is stored in a flocculant tank (not shown) as an aqueous solution, and a necessary amount is appropriately supplied to the mixing tank 5.

  The raw water 7 after the addition of the flocculant is supplied to the membrane separation tank 10 via the path 9 by the pump 8. A submerged membrane separator 11 is installed in the membrane separator 10, and the main body of the submerged membrane separator 11 is located below the surface of the water to be treated in the membrane separator 10.

  The submerged membrane separation device 11 performs membrane separation of the water to be treated in the membrane separation tank 11 with an MF membrane or a UF membrane module, and the permeated water passes through the path 12 by the pump 13 to the permeated water tank 14 as the permeated water 15. Water is stored.

  In the membrane separation tank 10, the submerged membrane separation device 11 performs membrane separation of the suspended substances and moves the permeate to the outside, so that the concentration of suspended substances in the water to be treated outside the submerged membrane separation device 11 increases. . The raw water 16 in which the suspended solid concentration is increased is stored in the concentrated water tank 18 via the path 17.

  The concentrated water 19 supplied to the media filtration device 22 has a suspended substance concentration higher than that of the raw water 2. However, the concentration of the flocculant is lower than the concentration in the raw water because a part of the flocculant has already been consumed due to the aggregation of the solid content. Further, the optimum concentration of the flocculant added to the water to be treated of the media filtration device 22 is higher than that of the submerged membrane separation device. For this reason, it is necessary to further add a flocculant to the concentrated water 19 in the concentrated water tank 18. Therefore, a flocculant is added to the concentrated water 19 in the concentrated water tank 18 so that the concentration range is 0.55 mg / L or more and 0.8 mg / L or less. Then, the mixture is stirred by the mixer 34.

  In the present invention, the flocculant in the concentrated water of the submerged membrane separation device 11 that is the water to be treated of the media filtration device 22 is measured, and the flocculant is added again so that the optimum flocculant concentration of the media filtration device 22 is obtained. By doing so, the coagulant | flocculant density | concentration optimal for both the immersion type membrane separator 11 and the media filtration apparatus 22 is maintained. As a result, it is possible to efficiently remove the solid content in the raw water while suppressing the amount of the flocculant used to the minimum necessary.

  The concentrated water 19 to which the flocculant has been added is supplied to the media filtration device 22 (media filtration tower) via the path 21 by the pump 20.

  The media filtration device is filled with sand, anthracite, granular activated carbon, spherical ceramic, hollow polypropylene, or the like as a filtration medium, and the filtration medium may be one type or two or more types. The kind and usage-amount of each filtration medium can be adjusted suitably. In addition, in the media filtration apparatus 22 of FIG. 1, three types of filtration media, the 1st filtration media 23a, the 2nd filtration media 23b, and the 3rd filtration media 23c, are filled.

  The suspended matter in the concentrated water 19 is removed by the media filtration device 22. The filtered water from which suspended substances have been removed is stored in the filtered water tank 26 via the path 25. The permeated water 15 stored in the permeated water tank 14 and the filtered water 27 stored in the filtered water tank 26 may be mixed and sterilized by chlorine disinfection, and then used as drinking water. Is possible.

  In addition, an air diffuser 32 for air scrubbing and cleaning the membrane surface of the submerged membrane separator 11 is installed in the lower part of the membrane separator 10, and a gas (air) is supplied to the air diffuser 32 outside the membrane separator 10. It is preferable to perform scrubbing by installing a blower 28 for supplying the air and the like, and blowing air from the air path 29 during operation of the MF membrane (at the time of membrane separation).

  Further, the filtration media (23a to 23c) of the media filtration device 22 are periodically supplied by supplying the filtered water 27 in the filtrate water tank 26 from the backwash path 31 to the media filtration device 22 by the backwash pump 30. In this case, scrubbing is preferably performed by air sent from a blower 24 installed outside the media filtration device 22 through an air diffuser 33 installed below the media filtration device 22.

[Example]
Raw water (turbidity: minimum 1.0 degrees, maximum 15.0 degrees, average 6.5) using a filtration facility equipped with a submerged membrane separator (using MF membrane) and a media filtration tower (media filtration device / No.1 and No.2) The injection amount of the flocculant (substance name: aluminum sulfate) to be added was changed. Then, the transmembrane pressure difference of the MF membrane of the submerged membrane separator and the turbidity change of the mixed treated water of the permeated water of the submerged membrane separator and the filtered water of the media filtration tower were measured.

Table 1 shows the types of MF membranes, and Table 2 shows the raw water flow rate. The dimensions and the like of media filtration towers No. 1 and No. 2 are as shown in Table 3 and Table 4, respectively. The treated water flow rates of the media filtration towers No. 1 and No. 2 are each 0.31 m ³ / hour.

Here, the amount of drain water shown in Table 2 is the amount of water discharged out of the system without being supplied to the media filtration tower. From the overflow water volume (3.14 m ³ / hour), the media filtration tower No. 1 and No. 2 This is the value obtained by subtracting the amount of water to be treated (0.31 m ³ / hour × 2).

  First, in the submerged membrane separator, the injection amount (addition concentration) of aluminum sulfate into the raw water was changed, and the change in the corrected membrane differential pressure increase rate was examined. The corrected membrane differential pressure increase rate here is a numerical value obtained by correcting the differential pressure increase rate before and after the MF membrane at a certain water temperature to the differential pressure increase rate at a water temperature of 25 ° C.

  Further, the concentrated water of the submerged membrane separation device is supplied to the media filtration tower and subjected to filtration treatment, and the treated water in which the permeated water of the submerged membrane separation device and the filtered water of the media filtration tower are mixed (see the lower diagram of FIG. 2). The vertical axis represents mixed treated water (hereinafter referred to as mixed treated water). The result is shown in FIG. The flocculant injection amount indicated on the horizontal axis represents the concentration of the flocculant in the raw water supplied to the submerged membrane separator.

  In the submerged membrane separator, the corrected membrane differential pressure increase rate was minimized within the concentration range of 0.3 mg / L or more and 0.55 mg / L or less of the injection amount of aluminum sulfate as a flocculant. When the injection amount of aluminum sulfate exceeded 0.55 mg / L, the rate of increase in the corrected membrane differential pressure increased in proportion to the injection amount.

  Here, the flocculant injected into the water to be treated (raw water) of the submerged membrane separator reacts with the turbid matter to become a solid (floc), and does not pass through the MF membrane of the submerged membrane separator. It moves to the concentrated water supplied to the media filtration device. For this reason, a flocculant is further added to the water to be treated (concentrated water) of the media filtration device so that the concentration of the flocculant in the water to be treated (raw water) of the submerged membrane separator is equal to or higher.

  From the lower diagram of FIG. 2, it was found that when the concentration of the flocculant in the water to be treated of the media filtration device is less than 0.4 mg / L, the turbidity of the mixed treated water is hardly reduced even when the flocculant is added. It has also been found that the flocculant concentration needs to be 0.55 mg / L or more in order to obtain a turbidity of less than 5 degrees, which is preferable for drinking water.

  On the other hand, when the concentration of the flocculant exceeded 0.8 mg / L, the effect of reducing the turbidity of the mixed treated water was reduced. For this reason, it turned out that it is preferable to further add a flocculant to the to-be-processed water of a media filtration apparatus so that it may become a density | concentration range of 0.55 mg / L or more and 0.8 mg / L or less.

  In the above embodiment, the case where the submerged membrane separation device 11 is installed in the membrane separation tank 10 different from the media filtration device 22 has been described. However, the present invention is not limited thereto, and the submerged membrane separation device is not limited thereto. The apparatus 11 is installed in the media filtration device 22 so as to filter the water to be treated before the filtration medium (for example, in the case of a downflow media filtration device, the immersion membrane separation device 11 is disposed above the filtration medium. It is also possible to install).

  The operation method of the composite filtration equipment of the present invention is useful in the water treatment such as drinking water production and the public health field as the operation method of the composite filtration equipment including membrane separation treatment and media filtration.

It is a conceptual diagram showing an example of the composite filtration equipment suitable for implementing the operating method of this invention. The upper diagram is a graph showing the relationship between the flocculant injection amount with respect to the raw water and the corrected membrane differential pressure increase rate, and the lower graph is the graph showing the relationship between the flocculant injection amount with respect to the raw water and the turbidity of the mixed treated water.

Explanation of symbols

1: Raw water tank 2: Raw water (river water, lake water, etc.)
3: Raw water pump 4: Path 5: Mixing tank 6: Stirrer 7: Raw water after addition of flocculant 8: Pump 9: Path 10: Membrane separation tank 11: Submerged membrane separator 12: Path 13: Pump 14: Permeate Tank 15: Permeated water 16: Raw water with increased suspended solids concentration 17: Route 18: Concentrated water tank 19: Concentrated water 20: Pump 21: Route 22: Media filtration tower (media filtration device)
23a: First filtration medium 23b: Second filtration medium 23c: Third filtration medium 24: Blower 25: Path 26: Filtration water tank 27: Filtration water 28: Blower 29: Air path 30: Backwash pump 31: Backwash path 32, 33: Air diffuser

Claims (4)

The water to be treated is membrane-separated by a submerged membrane separator to obtain membrane permeated water, the concentrated water of the submerged membrane separator is filtered by a media filtration device to obtain filtered water, both the permeated water and the filtered water In combined filtration equipment that supplies water as treated water,
Add flocculant to the concentration range of 0.3 mg / L or more and 0.55 mg / L or less to the raw water with turbidity of 1 to 15 degrees supplied to the submerged membrane separator, and supply it to the media filter. A method for operating a combined filtration facility, wherein a flocculant is further added to the concentrated water so as to have a concentration range of 0.55 mg / L to 0.8 mg / L.   The operation method of the composite filtration equipment according to claim 1, wherein the separation membrane of the submerged membrane separation device is a microfiltration membrane or an ultrafiltration membrane.   The operation method of the composite filtration equipment according to claim 2, wherein the separation membrane of the submerged membrane separation device is a hollow fiber membrane.   The filtration media of the media filtration device is a hollow cylinder, granular or spherical, and in the case of a hollow cylinder, the average inner diameter is 1 mm or more and 10 mm or less, and in the case of granular or spherical, the average diameter is 0.5 mm or more and 1.5 mm or less. The operation method of the composite filtration equipment according to any one of Items 1 to 3.

Images