JP4066455B2 - Membrane separation activated sludge treatment equipment - Google Patents

Description

  The present invention relates to a membrane separation type activated sludge treatment apparatus, and more particularly to a membrane separation type activated sludge treatment apparatus in which a membrane unit is immersed in a treatment tank.

As this type of membrane-separated activated sludge treatment apparatus, one having a coarse bubble diffusing unit and a fine bubble diffusing unit is known (for example, see Patent Document 1).
FIG. 5 is a system diagram showing the schematic configuration. The activated sludge is maintained at a high concentration in the treatment tank 1 and the treated water 2 is treated aerobically. A membrane unit 3 is immersed in the treatment tank 1. Below the membrane unit 3, a coarse bubble diffusing means 4 is arranged. Further, a fine bubble diffusing unit 5 is disposed further below the coarse bubble diffusing unit 4.

  The to-be-treated water 2 flowing in from the pipe 8 is aerobically biologically treated by microorganisms kept at a high concentration in the treatment tank 1, so-called activated sludge. By this biological treatment, the organic substance in the treated water 2 is oxidized and decomposed, and the treated water 2 is purified. The membrane unit 3 has a structure in which a plurality of vertical flat membranes are arranged in parallel at intervals. The membrane 2 separates the water 2 to be treated. The treated water that has passed through the membrane unit 3 is discharged from the secondary side of the membrane unit 3 to the outside of the apparatus as treated water 7 by the treated water discharge means 6 through the discharge pipe 9.

  The coarse bubbles diffused from the coarse bubble diffuser 4 mainly have three actions. The first effect is a membrane surface cleaning effect on the flat membrane of the membrane unit 3. That is, the coarse bubbles rise in the gap between the flat membranes of the membrane unit 3 due to the buoyancy, rub the membrane surface of the flat membrane in the ascending process, and the suspended separation such as activated sludge adhered to the membrane surface by membrane separation. Is removed from the film surface and washed. The second action is an oxygen supply action for the water to be treated. In the process in which coarse bubbles come into contact with the water to be treated, oxygen in the bubbles is dissolved in the water to be treated. Oxygen dissolved in the water to be treated is used as an oxygen source necessary for biological treatment with activated sludge. The third action is a swirling flow forming action. The upward flow of the water to be treated is generated in the gap between the flat membranes by the air lift action of the diffused coarse bubbles, and a swirling flow in the vertical direction as shown by the arrow F is formed in the treatment tank 1. . By this swirl flow, the water to be treated and the activated sludge are sufficiently mixed and contacted, and the biological treatment with the activated sludge proceeds efficiently.

  Since activated sludge remains in the treatment tank 1 by membrane separation, the activated sludge is maintained at a high concentration in the treatment tank 1. Therefore, this type of membrane-separated activated sludge treatment apparatus can be operated at a high load and has a high oxygen consumption rate. For this reason, only oxygen dissolved in the water to be treated by the coarse bubbles diffused from the coarse bubble diffusing means 4 cannot provide oxygen necessary for biological treatment, and dissolved oxygen in the water to be treated may be insufficient. Coarse bubbles are effective in the above-described film surface cleaning action and swirl flow forming action since the air lift force is large. On the other hand, since the bubble surface area per unit volume is small, there is a drawback that the oxygen dissolution efficiency for the water to be treated is low. On the other hand, the fine bubbles diffused from the fine bubble diffusing means 5 have a large bubble surface area per unit volume, and have high oxygen dissolution efficiency with respect to the water to be treated. For this reason, it is effective to supplement dissolved oxygen in the water to be treated.

  Therefore, in this type of membrane separation type activated sludge treatment apparatus, efficient operation is performed by appropriately distributing the amount of air diffused from the coarse bubble diffuser 4 and the fine bubble diffuser 5. .

Japanese Patent Laid-Open No. 2001-212587

  However, according to the knowledge of the present inventors, it has been found that there is a problem in the installation position of the fine bubble aeration means 5 in the membrane separation activated sludge treatment apparatus. That is, the fine bubble diffusing means 5 is installed below the coarse bubble diffusing means 4. For this reason, the fine bubbles from the fine bubble diffusing means 5 and the coarse bubbles from the coarse bubble diffusing means 4 rise while being mixed in the same direction by the buoyancy. As a result, firstly, some of the fine bubbles are combined into coarse bubbles, and the advantage of the fine bubbles having high oxygen dissolution efficiency is lost. Secondly, since the air lift action of fine bubbles and coarse bubbles is added, the rising speed of these bubbles is increased. For this reason, the contact time between the bubbles and the water to be treated is reduced. Due to these two causes, the membrane separation activated sludge treatment apparatus having the above-described configuration is advantageous for the membrane cleaning action and the forming action of the swirling flow of the water to be treated, but is disadvantageous for the oxygen dissolving action in the water to be treated. . That is, the presence of the fine bubble diffusing means 5 is weakened, and the role of the fine bubble diffusing means 5 is halfway.

  The object of the present invention is to eliminate the above-mentioned problems of the prior art, and the role sharing between the fine bubble diffuser and the coarse bubble diffuser is clear, and the membrane separation type activated sludge treatment is excellent in the action of dissolving oxygen in the water to be treated. To provide an apparatus.

In order to achieve the above object, a membrane separation type activated sludge treatment apparatus according to the present invention includes a treatment tank for aerobically treating water to be treated with activated sludge held in a tank, and a plurality of vertical-shaped treatment sludges. A flat membrane is arranged in parallel with an interval, a membrane unit whose side is immersed in the treatment vessel with a gap from the side of the treatment vessel, and a coarse unit disposed below the membrane unit A bubble diffusing means and a fine bubble diffusing means arranged in the processing tank, and a vertical swirling flow is generated in the processing tank by the air lift action of the coarse bubbles diffused from the coarse bubble diffusing means. in membrane separation type activated sludge treatment apparatus to form, pinched the fine bubble diffuser means on the side wall of the processing tank and the side surface of the membrane unit, and in the region where the downward flow of the swirling flow is present, the processing Deeper than 1/2 of the water depth of the tank, the coarse Characterized by being arranged in a shallow position than 200mm than Awachiki means.

  The fine bubbles are diffused in the downward flow, and the contact time with the water to be treated becomes long. Therefore, it is possible to realize a membrane separation type activated sludge treatment apparatus having an excellent oxygen dissolving action in water to be treated. Moreover, since the division of roles between the coarse bubble diffuser and the fine bubble diffuser is clarified, the amount of diffused air from the coarse bubble diffuser and the fine bubble diffuser can be appropriately distributed, and the operation is efficient. It can be performed.

FIG. 1 is an apparatus system diagram showing an embodiment of a membrane separation type activated sludge treatment apparatus according to the present invention. The activated sludge is maintained at a high concentration in the treatment tank 10 and the treated water 12 is treated aerobically. The membrane unit 14 is immersed in the processing tank 10 so that the side surface is spaced from the side wall of the processing tank 10 . A coarse bubble diffusing means 16 is disposed below the membrane unit 14. Further, the fine bubble diffusing means 18 and 18 are arranged in a region sandwiched between the side surface of the membrane unit 14 and the side wall of the processing tank 10 and in a region where the downward flow of the swirling flow exists . A suction pump 20 is connected to the secondary side of the membrane unit 14 via a conduit 24.

  The to-be-processed water 12 which flowed in from the pipe line 22 is aerobically biologically treated by the activated sludge maintained in the treatment tank 10 at a high concentration. By this biological treatment, the organic substance in the treated water 12 is oxidatively decomposed and the treated water 12 is purified. The membrane unit 14 has a structure in which a plurality of vertical flat membranes are arranged in parallel at intervals. The membrane 12 separates the water 12 to be treated. The treated water that has passed through the membrane unit 14 is discharged from the secondary side of the membrane unit 14 as treated water by the suction pump 20 through the discharge pipe 24 to the outside of the apparatus. The coarse bubbles diffused from the coarse bubble diffusing means 16 mainly have three actions. The first effect is a membrane surface cleaning effect on the flat membrane of the membrane unit 14. Coarse bubbles raise the gap between the flat membranes of the membrane unit 14 by the buoyancy, and rub the membrane surface of the flat membrane in the rising process. As a result, the suspended separation such as activated sludge that has been membrane-separated and adhered to the membrane surface is peeled off from the membrane surface and washed. Further, an upward flow of the water to be treated 12 is generated in the gap between the flat membranes by the air lift action of the coarse bubbles. The membrane surface is also cleaned by the upward flow of the water to be treated. The second action is an oxygen supply action for the treated water 12. In the process in which coarse bubbles come into contact with the water to be treated 12, oxygen in the bubbles is dissolved in the water to be treated 12. Oxygen dissolved in the water to be treated 12 is used as an oxygen source necessary for biological treatment with activated sludge. The third action is a swirling flow forming action. As described above, an upward flow of the water to be treated 12 is generated in the gap between the flat membranes by the air lift action of the coarse bubbles diffused, and the arrow F is generated in the processing tank 10 as the upward flow is generated. A swirling flow in the vertical direction as shown in FIG. By this swirl flow, the water 12 to be treated and the activated sludge are sufficiently mixed and contacted, and biological treatment with the activated sludge proceeds efficiently. Moreover, the to-be-processed water 12 will pass the membrane unit 14 uniformly by a swirl flow, and the stable membrane separation will be performed.

  Since activated sludge remains in the treatment tank 10 by membrane separation, the activated sludge is maintained in the treatment tank 10 at a high concentration. Therefore, high-load operation is possible and the oxygen consumption rate is fast. For this reason, only oxygen dissolved in the water to be treated by the coarse bubbles diffused from the coarse bubble diffusing means 16 cannot provide oxygen necessary for biological treatment, and dissolved oxygen in the water to be treated may be insufficient. That is, the coarse bubble has a diameter of about 10 mm at the outlet and has a large air lift force, so that it is effective for the above-described film surface cleaning action and swirl flow forming action. On the other hand, since the bubble surface area per unit volume is small, there is a disadvantage that the oxygen dissolution efficiency for the water to be treated 12 is low. On the other hand, the fine bubbles diffused from the fine bubble diffusing means 18 have a diameter of about 1 mm at the outlet and a large bubble surface area per unit volume, so that the oxygen dissolution efficiency in the water to be treated is high. For this reason, it is effective to supplement dissolved oxygen in the water to be treated.

  The coarse bubble diffusing unit 16 and the fine bubble diffusing unit 18 are connected to a common blower 30 through pipes 26 and 28, and air pressurized by the blower 30 is supplied to each of the diffusing units. Is done. The pipes 26 and 28 are provided with flow control valves 32 and 34, respectively. The opening degree of these flow control valves 32 and 34 is adjusted, and the amount of air diffused from the coarse bubble diffuser 16 and the fine bubble diffuser 18 is distributed.

By the way, the fine bubble diffusing means 18 is installed on the side of the membrane unit 14 as described above, and this position is located in the downward flow region of the swirling flow formed by the diffusing from the coarse bubble diffusing means 18. is doing. For this reason, the fine bubbles diffused from the fine bubble diffusing means 18 are placed under conditions suitable for improving the oxygen dissolution efficiency with respect to the water to be treated. FIG. 2 is an explanatory diagram modeling the relationship between fine bubbles and downward flow. FIG. 2 (a) shows a case where the diameter of the fine bubbles is relatively large and the theoretical levitation velocity V ₁ is larger than the downward flow velocity V ₂ . In this case, the fine bubbles float up against the downward flow, but the actual ascent speed V ₃ becomes V ₃ = V ₁ −V ₂ , which is sufficiently smaller than the theoretical ascent speed V ₁ . For this reason, the fine bubbles rise slowly in the water to be treated, and the contact time with the water to be treated becomes long. As a result, the efficiency of dissolving oxygen in the water to be treated by the fine bubbles is increased. FIG. 2B shows a case where the diameter of the fine bubbles is relatively small and the theoretical ascent velocity V ₁ is smaller than the downward flow velocity V ₂ . In this case, while the fine bubbles are opposed to the downward flow, at a descending speed V ₄ = V ₂ −V ₁ , the fine bubbles slowly descend along with the water to be treated, and the contact time with the water to be treated becomes long. As a result, in this case as well, the efficiency of dissolving oxygen in the water to be treated by the fine bubbles is increased.

FIG. 3 is an explanatory diagram modeling the relationship between fine bubbles and upward flow. The upward flow velocity V ₅ is added to the theoretical ascent velocity V ₁ in both the upward flow (i) and the fine bubble diameter (b) and the small bubble size (b). The fine bubbles rise rapidly at a substantial ascent speed V ₆ = V ₁ + V ₅ . As a result, the contact time between the fine bubbles and the water to be treated is shortened, and the efficiency of dissolving oxygen in the water to be treated by the fine bubbles is lowered.

  Thus, when the fine bubbles are diffused in the downward flow and when the fine bubbles are diffused in the upward flow, the behavior of the fine bubbles is the opposite, and a large difference occurs in the efficiency of dissolving oxygen in the water to be treated. In the present embodiment, as described above, the fine bubble diffusing means 18 is located in the downward flow region of the swirling flow. For this reason, the fine bubbles are diffused in the downward flow, and the oxygen dissolution efficiency in the water to be treated is good. Therefore, according to the present embodiment, it is possible to realize a membrane separation type activated sludge treatment apparatus having an excellent oxygen dissolving action in the water to be treated. In addition, since the role sharing between the coarse bubble diffusing means 16 and the fine bubble diffusing means 18 is clear, the coarse bubble diffusing means 16 and the fine bubbles are adjusted by adjusting the opening degree of the flow rate control valves 32 and 34 appropriately. The amount of air diffused from the air diffuser 18 can be appropriately distributed, and efficient operation can be performed.

In addition, it is preferable that the fine bubble diffusing means 18 is installed at a position deeper than ½ of the water depth of the treatment tank. FIG. 4 is an explanatory diagram showing a preferred positional relationship between the fine bubble diffuser 18 and the coarse bubble diffuser 16. As described with reference to FIG. 2, the fine bubbles diffused from the fine bubble diffusing means 18 are roughly classified into two types. There are a fine bubble B1 having a relatively large diameter that floats against the downward flow R, and a fine bubble B2 having a relatively small diameter that is pushed away by the downward flow R while facing the downward flow R. In the fine bubble diffuser 18 using a normal diffuser tube or diffuser plate, such fine bubbles B1 and fine bubbles B2 are diffused simultaneously. When the fine bubbles B1 having a relatively large diameter are emphasized, the deeper the aeration position, the longer the ascent time (contact time with the water to be treated), and the oxygen dissolution efficiency is improved. From such a viewpoint, it is preferable to install the fine bubble diffusing means 18 at a position deeper than ½ of the water depth of the treatment tank. On the other hand, if importance is attached to the fine bubbles B2 having a relatively small diameter, it takes a long time for the downward flow R to turn upward from the coarse bubble diffusing means 16 by the diffusing air, and during that time, the oxygen dissolved by the fine bubbles B2 is dissolved. It is advantageous to promote. From this point of view, it is advantageous to install the fine bubble diffusing means 18 at a position as shallow as possible. Specifically, it is preferable in actual design that the water depth difference H between the fine bubble diffuser 18 and the coarse bubble diffuser 16 is 200 mm or more.

1 is a system diagram showing an embodiment of a membrane separation activated sludge treatment apparatus according to the present invention. It is explanatory drawing which modeled and showed the relationship between a microbubble and a downward flow. It is explanatory drawing which modeled and showed the relationship between a microbubble and an upward flow. It is explanatory drawing which shows the preferable positional relationship of a fine bubble aeration means and a coarse bubble aeration means. It is an apparatus system diagram which shows schematic structure of the membrane separation type | formula activated sludge processing apparatus concerning a prior art.

Explanation of symbols

10 ......... Treatment tank, 12 ......... Water to be treated, 14 ......... Membrane unit, 16 ......... Coarse air bubble diffuser, 18 ...... Fine bubble diffuser, 20 ...... Suction pump, 30 ......... Blower, 32, 34 ......... Flow control valve.

Claims (1)

A treatment tank that aerobically treats water to be treated with activated sludge held in the tank, and a structure in which a plurality of vertical flat membranes are arranged in parallel at intervals, the side surface of which is the treatment tank A membrane unit immersed in the treatment tank at a distance from the side wall, coarse bubble diffusing means disposed below the membrane unit, and fine bubble diffusing means disposed in the treatment tank. In the membrane-separated activated sludge treatment apparatus configured to form a swirling flow in the vertical direction in the treatment tank by an air lift action of the coarse bubbles diffused from the coarse bubble diffuser, the fine bubble diffuser is In a region sandwiched between the side surface of the membrane unit and the side wall of the treatment tank and where the downward flow of the swirling flow exists, it is deeper than 1/2 of the water depth of the treatment tank and is shallower than the coarse bubble diffusing means by 200 mm or more. film, which is arranged at a position Hanareshiki activated sludge treatment equipment.

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