Wastewater treatment apparatus and wastewater treatment method

Abstract

To provide a wastewater treatment apparatus 10 that allows long-term and continuous use of a membrane separation apparatus 12.SOLUTION: A wastewater treatment apparatus 10, in which activated sludge performs wastewater treatment, includes a membrane separator 12 for separating treated water and activated sludge after wastewater treatment is performed, an air diffuser 13 for aerating coarse air bubbles of 100 μm or more in diameter to the membrane separator 12, and a micro bubble generator 14 for aerating fine air bubbles of less than 100 μm in diameter to the membrane separator 12. The bubbles that are aerated to the membrane separator 12 are a mixture of coarse bubbles aerated by the diffuser 13 and fine bubbles aerated by the micro bubble generator 14.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a wastewater treatment apparatus and a wastewater treatment method for separating sludge contained in wastewater.

Background Art

[0002] Conventionally, activated sludge, which is organic sludge containing microorganisms, treats wastewater, and a membrane separation activated sludge method is known in which a membrane such as a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane) separates the treated water and the activated sludge (see, for example, Patent Document 1). The wastewater treatment apparatus based on the membrane separation activated sludge method of Patent Document 1 includes an activated sludge tank that treats wastewater with activated sludge, a membrane separation device that is installed in the activated sludge tank and separates the treated water and the activated sludge, and a diffuser device that aerates a large amount of bubbles to the membrane separation device.

[0003] When the diffuser device aerates a large amount of bubbles to the membrane separation device, oxygen dissolves in the wastewater in the activated sludge tank, so the activated sludge performs a nitrification reaction on the wastewater in the activated sludge tank. In addition, since a large amount of bubbles aerated from the diffuser device collide with the surface of the membrane separation device, it is possible to prevent the occurrence of a fouling phenomenon in which activated sludge accumulates on the membrane separation device and deteriorates the filtration performance of the membrane separation device, or to eliminate a slight fouling phenomenon that has already occurred. By the way, a method of periodically cleaning the membrane separation device with chemicals is also known in order to prevent the occurrence of the membrane separation device fouling phenomenon or to eliminate a slight fouling phenomenon that has already occurred (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, even if fouling in the membrane separator is prevented or minor fouling that has already occurred is eliminated by a large amount of bubbles aerated from the diffuser colliding with the surface of the membrane separator, or by periodic chemical cleaning of the membrane separator, serious fouling that cannot be eliminated may occur due to the long-term and continuous use of the membrane separator. In this case, it is necessary to take measures such as replacing the membrane separator, which is time-consuming. Therefore, there was a problem in that the membrane separator could not be used for a long period of time and continuously.

[0006] The object of the present invention is to provide a wastewater treatment apparatus and a wastewater treatment method that allow the membrane separation apparatus to be used continuously over a long period of time. [Means for solving the problem]

[0007] To achieve the above objective, the wastewater treatment apparatus of the present invention is a wastewater treatment apparatus in which activated sludge performs wastewater treatment, wherein treated water and activated sludge are separated after the wastewater treatment has been performed. Membrane separation device having hollow fiber membrane And, as stated above membrane separation equipment against Based on the pore size at the aeration port diameter but A first aeration means for aerating coarse air bubbles of 100 μm or more and 50 mm or less, and the membrane separation equipment against Based on the pore size at the aeration port diameter but The system comprises a second aeration means for aerating fine bubbles of 0.0001 μm or more and less than 100 μm, and the membrane separation equipment The bubbles aerated to the fine bubbles are a mixture of the coarse bubbles and the fine bubbles, and the mixing ratio (volume ratio) of the coarse bubbles to the fine bubbles is 80 / 20 to 20 / 80, and the fine bubbles contain Based on the pore size at the aeration port diameter but This product is characterized by having a mixing ratio (volume ratio) of microbubbles between 1 μm and 100 μm in size of 75% by volume or more.

[0008] To achieve the above objective, the wastewater treatment method of the present invention is a wastewater treatment method in which activated sludge performs wastewater treatment, comprising a separation step of separating treated water and activated sludge after the wastewater treatment has been performed, and separating the treated water and activated sludge Membrane separation device having hollow fiber membrane against Based on the pore size at the aeration port diameter but A first aeration step of aerating coarse air bubbles of 100 μm or more and 50 mm or less, and the membrane separation equipment against The diameter based on the hole size at the aeration port The process includes a second aeration step of aerating fine bubbles of 0.0001 μm or more and less than 100 μm, and the above membrane separation equipment The bubbles aerated to the fine bubbles are a mixture of the coarse bubbles and the fine bubbles, and the mixing ratio (volume ratio) of the coarse bubbles to the fine bubbles is 80 / 20 to 20 / 80, and the fine bubbles contain Based on the pore size at the aeration port diameter but This product is characterized by having a mixing ratio (volume ratio) of microbubbles between 1 μm and 100 μm in size of 75% by volume or more. [Effects of the Invention]

[0009] According to the present invention, the membrane separation device can be used continuously over a long period of time. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing the configuration of a wastewater treatment apparatus according to an embodiment of the present invention. [Figure 2] This flowchart shows the wastewater treatment procedure performed by the wastewater treatment device shown in Figure 1. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described in detail below with reference to the drawings.

[0012] Figure 1 is a schematic diagram showing the configuration of a wastewater treatment apparatus 10 according to an embodiment of the present invention.

[0013] The wastewater treatment apparatus 10 shown in Fig. 1 includes a biological treatment tank 11, a membrane separation device 12 (separation means), an air diffuser 13 (first aeration means), and a microbubble generator 14 (second aeration means). The membrane separation device 12 is connected to a pump P, and the air diffuser 13 is connected to a blower B1. The microbubble generator 14 is connected to a blower B2. The air diffuser 13 and the microbubble generator 14 are arranged between the bottom of the biological treatment tank 11 and the membrane separation device 12. The biological treatment tank 11 stores raw water containing activated sludge, organic matter, and ammonia, and the activated sludge decomposes the organic matter and ammonia in the raw water. When the pump P is driven, the membrane separation device 12 separates the activated sludge from the water in which the organic matter and ammonia have been decomposed (hereinafter referred to as "treated water"). The treated water from which the activated sludge has been separated is discharged outside the tank of the biological treatment tank 11.

[0014] The membrane separation device 12 has a rectangular parallelepiped housing that extends in the vertical direction, and inside the housing, there is installed, for example, a long hollow fiber membrane having a hollow portion surrounded by fibers in which fine pores are formed. The four side surfaces of the housing of the membrane separation device 12 are each composed of a long, dividable plate-like member, and the bottom of the housing is open. When the pump P is driven, the treated water enters the interior of the housing from the bottom of the housing and migrates from the surface of the hollow fiber membrane to the inside of the hollow fiber membrane. The fibers of the hollow fiber membrane are, for example, polytetrafluoroethylene resin (PTFE) or polyvinylidene fluoride (PVDF) resin, and it is preferable to use polytetrafluoroethylene resin, which is excellent in chemical resistance and durability. In the present embodiment, the length of the hollow fiber membrane in the longitudinal direction may be 5 m or less.

[0015] The air diffuser 13 converts the air supplied from the blower B1 into bubbles with a diameter of 100 μm or more (hereinafter referred to as "coarse bubbles") and aerates the membrane separation device 12. There is no particular limitation on the upper limit of the diameter of the coarse bubbles, and it may be 50 mm or less. The coarse bubbles collide with the membrane separation device 12 and peel off the activated sludge adhering to the membrane surface of the membrane separation device 12 from the membrane surface. In addition, a part of the oxygen constituting the coarse bubbles dissolves in the raw water stored in the biological treatment tank 11, and the activated sludge survives based on the oxygen dissolved in the raw water and acts to treat the raw water into treated water. The micro-bubble generator 14 converts the air supplied from the blower B2 into fine bubbles, which are bubbles with a diameter of less than 100 μm, and aerates the membrane separation device 12. There is no particular limitation on the lower limit of the diameter of the fine bubbles, and it may be 0.0001 μm or more. The diameters of the coarse bubbles and the fine bubbles can be set by adjusting the pore diameter of the porous tube or plate installed at the aeration port of the air diffuser 13 and the micro-bubble generator 14 or the pore diameter of the outlet discharge hole of the nozzle.

[0016] The fine bubbles include micro-bubbles with a diameter of 1 μm or more and less than 100 μm and ultra-fine bubbles with a diameter of less than 1 μm. By the way, when the coarse bubbles collide with the membrane separation device 12, there is activated sludge peeled off from the membrane surface of the membrane separation device 12 and activated sludge not peeled off from the membrane surface of the membrane separation device 12. Since the fine bubbles are small with a diameter of less than 100 μm, they enter between the activated sludge not peeled off from the membrane surface of the membrane separation device 12 and the membrane surface, reducing the contact area between the membrane surface and the activated sludge. As a result, even when the coarse bubbles collide with the membrane separation device 12, the activated sludge that does not peel off from the membrane surface of the membrane separation device 12 peels off from the membrane surface.

[0017] The micro-bubbles contained in the fine bubbles rise in the raw water more slowly than the coarse bubbles. In addition, the micro-bubbles float the minute activated sludge in the raw water toward the water surface of the raw water. The minute activated sludge in the raw water floats toward the water surface without entering the membrane inside of the membrane separation device 12, thereby reducing the risk of the activated sludge adhering to the membrane surface.

[0018] Figure 2 is a flowchart showing the procedure of wastewater treatment (wastewater treatment method) performed by the wastewater treatment device 10 shown in Figure 1.

[0019] In Figure 2, first, when the raw water is stored in the biological treatment tank 11, the aeration device 13 and the microbubble generator 14 are activated (S1). The aeration device 13 aerates coarse bubbles to the membrane separator 12 (first aeration step), and the microbubble generator 14 aerates fine bubbles to the membrane separator 12 (second aeration step). The aeration device 13 and the microbubble generator 14 may operate continuously or intermittently. The bubbles aerated to the membrane separator 12 are a mixture of coarse bubbles aerated by the aeration device 13 and fine bubbles aerated by the microbubble generator 14.

[0020] In this embodiment, mixing of coarse bubbles and fine bubbles means that at least a portion of the coarse bubbles and at least a portion of the fine bubbles come into contact, and that both coarse bubbles and fine bubbles exist without disappearing. To mix coarse bubbles and fine bubbles, at least a portion of the aeration port of the microbubble generator 14, from which fine bubbles are aerated, should be positioned below or above at least a portion of the aeration port of the diffuser 13, from which coarse bubbles are aerated. When the microbubble generator 14 is positioned below the diffuser 13, the fine bubbles aerated from the microbubble generator 14 pass through the diffuser 13, mix with the coarse bubbles, rise together with the coarse bubbles, and come into contact with the hollow fiber membrane inside the membrane separator 12. Furthermore, because the microbubble generator 14 is positioned below the diffuser 13, the aeration port of the diffuser 13 is positioned near the membrane separator 12, so that the coarse bubbles can reliably agitate the hollow fiber membrane of the membrane separator 12, and the membrane separator 12 can be physically cleaned. Considering the effect of removing activated sludge from the surface of the hollow fiber membrane, it is preferable to position the entire microbubble generator 14, which aerates fine bubbles, below the membrane separation device 12 and below the diffuser 13, which aerates coarse bubbles.

[0021] Some of the oxygen constituting the coarse bubbles and fine bubbles dissolves in the raw water, and the activated sludge decomposes organic matter and ammonia in the raw water (S2, biological treatment), producing treated water. Next, the pump P is driven, and the membrane separator 12 separates the treated water and activated sludge (S3, separation step). As a result, only the treated water passes through the membrane separator 12 and is discharged outside the biological treatment tank 11, while the activated sludge remains inside the biological treatment tank 11. After this, the treatment is completed.

[0022] According to the wastewater treatment shown in Figure 2, the diffuser 13 aerates coarse bubbles to the membrane separator 12, and the microbubble generator 14 aerates fine bubbles to the membrane separator 12 (S1). The bubbles aerated to the membrane separator 12 are a mixture of coarse bubbles aerated by the diffuser 13 and fine bubbles aerated by the microbubble generator 14. As a result, the fine bubbles enter between the activated sludge adhering to the membrane surface of the membrane separator 12 and the membrane surface, reducing the contact area between the membrane surface and the activated sludge. Therefore, when coarse bubbles collide with the membrane separator 12, the activated sludge easily peels off from the membrane surface of the membrane separator 12. In addition, the microbubbles contained in the fine bubbles cause minute activated sludge in the raw water to float towards the water surface. This reduces the amount of activated sludge adhering to the membrane surface and reduces the risk of fouling occurring in the membrane separator 12. As a result, the membrane separator 12 can be used for a long period of time and continuously. [Examples]

[0023] Next, embodiments of the present invention will be described.

[0024] Using the wastewater treatment device 10 shown in Figure 1, raw wastewater was treated, and then treated water and activated sludge were separated by the membrane separator 12. The aeration device 13 converted the air supplied from blower B1 into coarse bubbles with a diameter of 100 μm to 50 mm and aerated it to the membrane separator 12. The microbubble generator 14 converted the air supplied from blower B2 into fine bubbles with a diameter of 0.0001 to 100 μm and aerated it to the membrane separator 12. The higher the mixing ratio (volume ratio) of microbubbles contained in the fine bubbles, the longer and more continuously the membrane separator 12 can be used. For example, a ratio of 30 vol% or more is sufficient, 50 vol% or more is more preferable, and 75 vol% or more is even more preferable. In this embodiment, it is assumed that the bubbles aerated to the membrane separation device 12 are a mixture of coarse bubbles and fine bubbles, and the optimal mixing ratio was investigated. Table 1 shows the power required to aerate bubbles to the membrane separation device 12 and the cleaning effect of the membrane separation device 12 for each mixing ratio (volume ratio) of coarse bubbles and fine bubbles. The mixing ratio (volume ratio) of coarse bubbles to fine bubbles is the amount of air (m³) supplied from blower B1 to diffuser 13. 3 (m³ / min) and the amount of air supplied from blower B2 to the microbubble generator 14 3 It was determined from the volume ratio with ( / min).

[0025] [Table 1]

[0026] First, the change in the permeation flux per unit time and unit area of ​​the membrane separator 12 (hereinafter referred to as "membrane flux") was confirmed when coarse bubbles and fine bubbles of various mixing ratios were aerated into the membrane separator 12. As a result, the membrane flux decreased in the order of aerating bubbles with a coarse bubble to fine bubble mixing ratio of 0 / 100, and aerating bubbles with a coarse bubble to fine bubble mixing ratio of 100 / 0. Next, the membrane flux decreased when bubbles with a coarse bubble to fine bubble mixing ratios of 90 / 10 and 10 / 90 were aerated. On the other hand, no decrease in membrane flux was observed when bubbles with a coarse bubble to fine bubble mixing ratios of 80 / 20, 50 / 50, and 20 / 80 were aerated. When the membrane flux decreases little, the activated sludge is removed from the membrane surface of the membrane separator 12 by aeration with coarse bubbles and fine bubbles, and the adhesion of activated sludge to the membrane surface is reduced, which is considered to result in a high cleaning effect of the membrane separator 12.

[0027] In response to this, the cleaning effect of the membrane separation device 12 was defined as "Not good" when bubbles with a mixing ratio of 0 / 100 fine bubbles to coarse bubbles were aerated, "Normal" when bubbles with a mixing ratio of 100 / 0 fine bubbles to coarse bubbles were aerated, "Good" when bubbles with a mixing ratio of 90 / 10 or 10 / 90 fine bubbles to coarse bubbles were aerated, and "Excellent" when bubbles with a mixing ratio of 80 / 20, 50 / 50 or 20 / 80 fine bubbles were aerated.

[0028] Furthermore, it was found that the power required to aerate the membrane separation device 12 with both coarse bubbles and fine bubbles was less than the power required to aerate with coarse bubbles alone. In particular, the power required to aerate bubbles with a mixing ratio of 20 / 80 coarse bubbles to fine bubbles, which was evaluated as having an excellent cleaning effect, was reduced by 38% compared to the power required to aerate bubbles with a mixing ratio of 100 / 0 coarse bubbles to fine bubbles. The power required to aerate bubbles with a mixing ratio of 10 / 90 coarse bubbles to fine bubbles, which was evaluated as having a good cleaning effect, was reduced by 44% compared to the power required to aerate bubbles with a mixing ratio of 100 / 0 coarse bubbles to fine bubbles.

[0029] Based on the above, it is preferable that bubbles with a mixing ratio (volume ratio) of 90 / 10 to 10 / 90 of fine bubbles are aerated to the membrane separation device 12, and it is even preferable that bubbles with a mixing ratio (volume ratio) of 80 / 20 to 20 / 80 of fine bubbles are aerated to the membrane separation device 12.

[0030] Although embodiments of the present invention have been described above, the present invention is not limited in any way to these embodiments. [Explanation of Symbols]

[0031] P Pump B1, B2 Blower 10. Wastewater treatment equipment 11. Biological treatment tank 12 Membrane separation equipment 13 Air diffuser 14. Microbubble Generator

Claims

1. In a wastewater treatment system in which activated sludge performs wastewater treatment, A membrane separation device having a hollow fiber membrane for separating treated water and activated sludge after the wastewater treatment has been performed, A first aeration means for aerating the membrane separation apparatus with coarse air bubbles having a diameter of 100 μm or more and 50 mm or less based on the pore size at the aeration port, The membrane separation apparatus comprises a second aeration means for aerating fine bubbles with a diameter of 0.0001 μm or more and less than 100 μm based on the pore size at the aeration port, The bubbles aerated to the membrane separation device are a mixture of the coarse bubbles and the fine bubbles. The mixing ratio (volume ratio) of the coarse bubbles to the fine bubbles is 80 / 20 to 20 / 80. A wastewater treatment apparatus characterized in that the mixing ratio (volume ratio) of microbubbles contained in the fine bubbles, having a diameter of 1 μm or more and less than 100 μm based on the pore size at the aeration port, is 75 volume% or more.

2. The wastewater treatment apparatus according to claim 1, characterized in that the second aeration means is located below the first aeration means.

3. In a wastewater treatment method in which activated sludge performs wastewater treatment, A separation step is performed to separate the treated water and the activated sludge after the wastewater treatment has been carried out. A first aeration step involves aerating a membrane separation apparatus having a hollow fiber membrane for separating the treated water and the activated sludge with coarse air bubbles having a diameter of 100 μm or more and 50 mm or less based on the pore size at the aeration port, The membrane separation apparatus comprises a second aeration step of aerating fine bubbles with a diameter of 0.0001 μm or more and less than 100 μm based on the pore size at the aeration port, The bubbles aerated to the membrane separation device are a mixture of the coarse bubbles and the fine bubbles. The mixing ratio (volume ratio) of the coarse bubbles to the fine bubbles is 80 / 20 to 20 / 80. A wastewater treatment method characterized in that the mixing ratio (volume ratio) of microbubbles contained in the fine bubbles, having a diameter of 1 μm or more and less than 100 μm based on the pore size at the aeration port, is 75 volume% or more.

4. The wastewater treatment method according to claim 3, characterized in that the fine bubbles are aerated from below the coarse bubbles.

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